technical report on geological and geo-technical

EU EDF 8 – SOPAC Project Report 42: Reducing Vulnerability of Pacific ACP States

TECHNICAL REPORT ON GEOLOGICAL AND GEO-TECHNICAL INVESTIGATIONS OF THE SEMO QUARRY AND SELECTED

AGGREGATE SOURCES IN SOUTH AND WESTERN VITI LEVU, FIJI

January 2005

Semo Quarry in Southwestern Viti Levu, Fiji.

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Author:

Akuila K. Tawake SOPAC Secretariat

January 2005

SOUTH PACIFIC APPLIED GEOSCIENCE COMMISSION c/o SOPAC Secretariat

Private Mail Bag GPO, Suva

FIJI ISLANDS http://www.sopac.org

Phone: +679 338 1377 Fax: +679 337 0040

www.sopac.org [email protected]

Important Notice

This report has been produced with the financial assistance of the European Community; however, the views expressed herein must never be taken to reflect the official opinion of the European Community.

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CONTENTS

EXECUTIVE SUMMARY ………………………………………………………………………...............................5

ACKNOWLEDGEMENT.………………………………………………………………………................................6

PART I – GEOLOGICAL & ECONOMIC ASSESSMENT OF POTENTIAL HARD-ROCK AGGREGATE SOURCES IN SOUTH AND WESTERN VITI LEVU

1. INTRODUCTION ………………………………………………………………………………............................7 1.1 Objectives ……………….………………………………………………………………… ........................7 1.2 Location …………………………………………………………………………………….........................9 1.3 Land Use and Tenure …………………………………………………………………… .........................9 1.4 Previous Study …………………………………………………………………………… .........................9

2. GEOLOGICAL SETTING 2.1 Regional Geology ………………………………………………………………………… ......................10 2.2 Limestone of the Wainimala Group ……………………………………………………. .......................10 2.3 Colo Plutonics …………………………………………………………………………… ........................11 2.4 Shoshonitic Volcanism…………………………………………………………………….......................11 2.5 Koroyanitu Volcano ……………………………………………………………………… .......................14 2.6 Geophysical Survey ……………………………………………………………………….......................14

3. LOCAL GEOLOGY …………………………………………………………………………….. ........................14 3.1 Wainimala Group ………………………………………………………………………… .......................15 3.2 Semo Gabbro …………………………………………………………………………….. .......................15

4. STRUCTURE ……………………………………………………………………………………. .......................16

5. PROPOSED DRILLING PROGRAMME 5.1 Introduction ..……………………………………………………………………………….......................16 5.2 Drilling ………………………………………………………………………………………......................16 5.3 Drilling Cost ..………………………………………………………………………………. .....................19

6. ECONOMIC DEVELOPMENT OF SEMO QUARRY ...……………………………………… ......................20 6.1 Impact Assessment .……………………………………………………………………… ......................21

PART II – GEO-TECHNICAL ASSESSMENT OF POTENTIAL HARD-ROCK AGGREGATE SOURCES IN SOUTH AND WESTERN VITI LEVU

7. INTRODUCTION ………………………………………………………………………………..........................22

8. MECHANICAL TESTS 8.1 Rock Classification Hammer ..……………………………………………………………......................22 8.2 Point Load Tester ………………………………………………………………………….......................22 8.3 Aggregate Durability .…………………………………………………………………….........................23 8.4 Alkali-Silica Reaction ..…………………………………………………………………….......................24 8.5 Alkali-Carbonate Reaction .……………………………………………………………….......................24

9. PHYSICAL TESTS 9.1 Water Absorption .………………………………………………………………………… ......................25 9.2 Density ..…………………………………………………………………………………….......................25 9.3 Petrography ..……………………………………………………………………………… ......................25 9.4 Site Inspection of Aggregate Sources ..…………………………………………………......................26

10. METHODS 10.1 Tested Samples .…………………………………………………………………………......................26 10.2 Schmidt Hammer Test ..…………………………………………………………………......................29 10.3 Point Load Test ..…………………………………………………………………………......................30 10.4 Petrography .……………………………………………………………………………… .....................31

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11. RESULTS 11.1 Schmidt Hammer Test ..…………………………………………………………………......................31 11.2 Density .……………………………………………………………………………………......................33 11.3 Water Content …………………………………………………………………………… ......................34 11.4 Point Load Test ..…………………………………………………………………………......................35 11.5 Petrography ……………………………………………………………………………… ......................36

12. DISCUSSION 12.1 Geo-technical Properties ..………………………………………………………………......................37 12.2 Sabeto Volcanics ………………………………………………………………………… .....................37 12.3 Semo Volcanics ..………………………………………………………………………… .....................37 12.4 Raraikoro Limestone ..…………………………………………………………………….....................38 12.5 Tau Limestone .…………………………………………………………………………….....................38 12.6 Korovisilou Diorite …..……………………………………………………………………......................38 12.7 Vuda Shoshonite …………………………………………………………………………......................39 12.8 Semo Gabbro .……………………………………………………………………………......................39 12.9 Semo Volcanics .………………………………………………………………………… ......................40 12.10 Vuda Agglomeratic Breccia ……………………………………………………………......................40 12.11 Nawainiu Monzonite ……………………………………………………………………......................40 12.12 Korovisilou Basalt Dyke ..………………………………………………………………......................41 12.13 Saru Shoshonite ………………………………………………………………………… ....................41

13. CONCLUSION …………………………………………………………………………………........................42

14. RECOMMENDATIONS …..…………………………………………………………………….......................43

15. REFERENCES ..……………………………………………………………………………….........................45

List of Figures Figure 1 Location Map of visited sites and Semo Quarry .......................................................................8 Figure 2a Geology map of the Semo Quarry Area .................................................................................12 Figure 2b A schematic cross section along line A-B...............................................................................13 Figure 3 The Southwestern rock-face of the Semo Quarry ..................................................................15 Figure 4 Proposed drill-hole location to the west of the quarry site ......................................................17 Figure 5 Measurement of rock face height............................................................................................20 Figure 6 Point Load Testing Apparatus.................................................................................................23 Figure 7 Korovisilou sample Locality Map.............................................................................................27 Figure 8 Sigatoka-Lautoka corridor sample locality map......................................................................28 Figure 9 Rock strength test using a L-Type Schmidt Rock Classification Hammer .............................29 Figure 10 Cube Compressive Strength Diagram ....................................................................................30 Figure 11 Graph of rock strength using a Schmidt Hammer...................................................................33 Figure 12 Graph of rock strength using a Point Load Tester ..................................................................34 Figure 13 Graph of rock densities ...........................................................................................................35 List of Tables Table 1 Proposed drill-hole specification .............................................................................................18 Table 2 Comparison of Radial and UDP drilling cost...........................................................................19 Table 3 South and Western Viti Levu Sample Locality Table..............................................................26 Table 4 Schmidt Hammer Strength test results ...................................................................................32 Table 5 Rock densities.........................................................................................................................33 Table 6 Rock Percentage Water Content ............................................................................................34 Table 7 Point Load Strength Test Results ...........................................................................................35 Table 8 Brief petrographic description of the samples examined........................................................36 List of Appendices Appendix 1 Results of strength tests using a Schmidt Rock Classification Hammer ................................47 Appendix 2 Water Content of each cube sample ......................................................................................49 Appendix 3 Rock Densities before drying, after drying and after soaking in water ...................................50 Appendix 4 Rock Strength Test Results using a Point Load Tester ..........................................................51 Appendix 5 Nomogram for computing point load strength and strength designation................................52 Appendix 6 Petrographic Description of Selected Rock Samples .............................................................53

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EXECUTIVE SUMMARY

This report presents the outcome of an aggregates survey conducted in South and Western Viti Levu, Fiji, in January 2004. The survey was a follow up to the aggregates assessment activities identified during the first three SOPAC-EU Project stakeholder consultation meetings for Fiji in 2003. The assessment involved, site visits to known aggregates extraction sites and potential sites, geological mapping and sample collection. These samples were subjected to appropriate testing methods in order to understand their geo-technical behaviour and performance. The Semo gabbro stock, due to its excellent geo-technical properties, was first used in the construction industry during the tarsealing of the Sigatoka-Nadi Highway in the early 1980s. Three separate studies have been carried out in the last three years in an effort to assess the potential of the quarry in supporting a larger-scale operation, in anticipation of the increased demand for aggregates, especially for hotel construction, in the Sigatoka-Nadi corridor. The survey carried out at the Semo Quarry was specifically requested by Standard Concrete Industries Limited (SCIL), who is the current developer of the quarry. It has been instigated to gain a better understanding of the geology of the Semo area and the potential of the Gabbro Stock (referred to hereafter as Semo Gabbro) as a hard-rock aggregate source. The Semo Gabbro is part of the Colo Plutonic Suite. Since the reconnaissance survey by Houtz (1959), there has been no further attempt to improve the local geology map of the Semo area. Consequently, field investigations carried out during this survey were concentrated on improving the understanding of the local geology of the area where the gabbro crops out. The new geology map produced was intended to supplement the existing geological data of the quarry and would also aid the developer in any future detailed assessment of the quarry as proposed in this report. In order to delineate and quantify the aggregates resource of the quarry, a drilling programme has been proposed. The location of each drill hole has been carefully selected to yield the best possible results. This twelve drill-hole drilling programme would also reveal the stratigraphic sequence of the area as interpreted in the geology map, the depth of overburden in the quarry and the water table depth. Additional factors such as the accessibility of the resource, distance to point of sale, socio-economic development and environmental management that will determine the feasibility of a potentially larger quarry operation at Semo are discussed in the report. Geo-technical investigations are vital in gauging the engineering behaviour and performance of any aggregate source. Having this in mind, rock samples that were collected from 12 different sources in south and western Viti Levu have been used to test some of the geo-technical parameters such as rock density, porosity, strength and petrographic analysis. Strength tests were carried out on the 12 different rock samples using a Schmidt Rock Classification Hammer and a Point Load Tester. There was a lot of variations in the results obtained among different samples that were collected from different locations. However, both strength tests have indicated consistent and comparable results for each individual sample. Some of the results obtained have been affected by pre-existing fracture planes which tend to lower the rebound values and the point load strength of the rock. This scenario has been appropriately discussed in this report. Rock density and water-absorbing capacity of any rock are influenced by its hardness, compactness, size and proportion of the pores, minerals present and mode of occurrence, grain size, degree of weathering and alteration of the rock, and in some cases the existence of microfractures within the rock. In addition, variation in dry and wet densities of the sample is principally determined by the amount of water held within the rock. Generally, the test results obtained have revealed an emerging trend where the density is inversely proportional to the water content of the rock. Fresh, compact, hard and crystalline rocks are bound to contain lesser water and have higher densities.

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Rock petrography is important in determining the physical and chemical characteristics of the material that have a bearing on the performance of the material in its intended use. Thin sections were only prepared for rock samples obtained from aggregate sources that can potentially be developed into quarries and a petrographic microscope was used to examine them. Rock features like minerals present and their mode of occurrence, grain size, approximate percentage composition of each mineral and texture have been highlighted. The interaction of various minerals and alkali hydroxides in a concrete mix has also been discussed. The presence of silica-bearing and carbonate-bearing minerals in some of these samples were highlighted, due to the possibility of long-term reaction within the concrete if they are used as sources of aggregates for construction. These two groups of minerals, if present in certain proportion in a concrete mix, can cause swelling and cracking of the concrete. The expansion causes misalignment of structures and can threaten structural integrity. Cracking can lead to reinforcement corrosion and other durability problems.

ACKNOWLEDGEMENT

This Project was supported by the European Union, under the EDF8 funding. The South Pacific Geoscience Commission (SOPAC), as the implementing agency, provided much needed support prior to and during the survey and sample preparations. Logistic support from the Mineral Resource Department (MRD) prior to the commencement of the survey and during the geo-technical analysis of rock samples is gratefully acknowledged.

The survey was conducted with assistance of personnel from the Standard Concrete Industry Limited (SCIL), who also provided a 4-wheel drive vehicle for the fieldwork. As the current developer of the Semo Quarry, SCIL permission was sought for the aggregate assessment to be carried out at Semo.

Permission was sought, when necessary, from some individual landowning unit prior to conducting reconnaissance survey on their land.

I thank Ilai Waqa (MRD) and Russell Maharaj (SOPAC) for valuable comments and discussion during the geo-technical tests, and Sekove Motuiwaca (SOPAC) for the sample and thin section preparations. The author is also indebted to the Earth Science Department at USP for allowing the use of their petrography microscope for thin section examinations.

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PART I – GEOLOGICAL & ECONOMIC ASSESSMENT OF POTENTIAL HARD-ROCK AGGREGATE SOURCES IN SOUTH AND WESTERN VITI LEVU

1. INTRODUCTION The need to locate and develop on-land aggregate resources in some parts of Viti Levu was raised in the first three stakeholder meetings for Fiji in 2003 (Project Task No: FJ 1.2.1). With the boom in the construction industry in Fiji, suppliers are currently experiencing a high demand for sand and gravel. This has necessitated increasing production in the current quarry sites and sourcing new sites for assessment and development in the near future. Some potential quarry sites have been identified in the Sigatoka-Lautoka corridor and in the southeastern part of Viti Levu but lack proper assessments in terms of geophysical survey, detailed geological mapping and resource estimation. As raised during the multi-stakeholder consultation meetings prior to the fieldwork, identification of potential terrestrial aggregate source, and aggregate resource assessment are the two most pressing issues in major urban centres around Viti Levu. Preliminary assessment of potential aggregate quarry sites is essential in order to identify hard rock sources with excellent geo-technical properties. Economic factors such as location, accessibility of the source and distance from source to the market will determine the order of assessment priority.

Some potential areas are presently used either for cane farming or covered with dense pine forest and are hence difficult to access. The first week of the fieldwork in January 2004, was dedicated to visiting and identifying potential quarry sites in the Sigatoka-Lautoka corridor, and also in the Korovisilou-Korovou area in Serua (Fig. 1). Geological mapping and sampling were carried out during the second and third weeks in the Semo Quarry area with assistance from SCIL personnel. This project is part of the European Union-funded EDF8 Project, entitled “Reducing Vulnerability in the Pacific ACP States”.

This report is divided into two parts: the geological assessment of the Semo Quarry, and the geological and geo-technical investigation of rock samples collected from potential hard-rock sources in south and western Viti Levu.

1.1 Objectives The principal objectives of the fieldwork are to: • identify and evaluate potential hard rock aggregate sources and rank them in order of

potential, accessibility and distance from source to market, • undertake geological mapping and sampling of priority areas, • produce geological map and cross section of the Semo area, • design drilling programme to delineate and upgrade resource, • carry out geo-technical testings of the samples collected, • present data and interpret results obtained for the survey and the testings, • offer advice and recommendations based on the outcome of this assessment. Based on the geological mapping exercise, resource definition drilling programme can then be initiated not only to delineate the resource but also to upgrade to reserve category.

[EU-SOPAC Project Report 42 – 8]

Figure 1. The locality map of visited areas in South and Western Viti Levu.


1.2 Location

The Semo Quarry occurs between Sigatoka and Nadi in Southwestern Viti Levu. It is located about 15 km to the northwest of Sigatoka (Fig. 1) and is a member of the Colo Plutonic Suite. The stock is partly exposed on the roadside of the Queens Highway near Semo Village. The quarry, which is about 100 m to the southwest off the main road, can be accessed by a vehicle or on foot through a gravel road.

The area surrounding the Semo Quarry, is largely made up of rolling hills, which are steeper in places adjacent to nearby creeks. Creeks and adjacent areas are generally thickly vegetated while the spurs and ridges are dominated by open grassland.

1.3 Land Use and Tenure

The Semo Quarry area is classified as native land belonging to the Tuva and Malomalo Districts in the province of Nadroga. Subsistence and cane farming are common in the area with the closest farm being about 300 metres to the south of the quarry. Part of the area was previously used for pine planting and remnant pine trees still exist.

1.4 Previous Studies at Semo Quarry

A one-day geophysical investigation was carried out at Semo Quarry in June 2001, following a request made to the MRD by SCIL. The survey methods consisted of geological mapping of the quarry site and three 60 m seismic refraction lines on the western side of the quarry (Rahiman, 2001). Apart from the seismic data interpretation, no geological map was produced. Sinclair Knight Merz (SKM) conducted an aggregates resource estimation in 2003 to determine the total volume of rock available and the thickness of overburden and weathered gabbro (Sinclair Knight Merz, 2003). The area bounded by interpreted outcrop limits is taken from a MRD report and section lines together with cross sections were produced by SKM. The SKM Semo Quarry volume calculations are tabulated below:

Volume (m3) Percentage

Volume of overburden 8017 9

Volume of poor rock 41640 48

Volume of sound rock 36817 43 Total volume above present quarry floor 86474

Ilai Waqa, a geologist at MRD, carried out a preliminary investigation of Semo Quarry in May, 2003. The fieldwork was part of his M.Sc. research project, which included quarry face logging and sample collection for geo-technical testing. The results of this study are now available in Waqa (2004).


2. GEOLOGICAL SETTING 2.1 Regional Geology

The oldest rocks in Fiji occur in western Viti Levu, and belong to the Late Eocene to Early Oligocene Yavuna Group (Hathway, 1993). The Wainimala Group dominates the southern half of the island and unconformably overlies the Yavuna Group rocks. All volcanic and sedimentary rocks of the Fiji platform known to have formed from the Late Oligocene to late in the middle Miocene belong to the Wainimala Group (Rodda, 1993).

The Wainimala Group rocks, has been intruded by tonalite and gabbro stocks of the Colo Plutonic Suite between 12.5 and 7 Ma (Hathway, 1994). These plutonic rocks occur in an elongate belt from southwestern Viti Levu through the southern centre of the island to the east (Rodda, 1993; Begg, 1996).

A disconformity marks the period of intrusion of the Colo stock, and separates turbidites sandstones and conglomerates of the Late Miocene Tuva Sedimentary Group from the underlying Wainimala Group. Extensive folding and faulting followed the Tuva deposition (Hathway, 1993; Begg, 1996). Late Miocene post Tuva group sediments are widespread in Viti Levu and are assigned to the Navosa, Nadi, Ra and Medraucusu Sedimentary Groups (Rodda, 1993; Begg, 1996) (Fig. 2).

Calc-alkaline rocks belonging to the Ba Volcanic Group were erupted in the north of the island in the Early Pliocene. At least five volcanic centres occur, mainly along an axis parallel to, and north of a contemporary shoshonitic axis (Rodda, 1993; Begg, 1996).

The Late Miocene to Early Pliocene shoshonitic rocks occur in northwestern Viti Levu, and are assigned to the Koroimavua and the Ba Groups. Predominantly felsic rocks were erupted from the Koroyanitu volcano and other small volcanoes are interpreted to be the sources of the Koroimavua Group. Mafic shoshonitic rocks on the island belong to the Ba Group (Rodda, 1993). Rocks of the Ba Group conformably overlie those of the Koroimavua Group where they are locally in contact (Gill and McDougall, 1973). No volcanic rocks younger than the Ba Volcanic Group are preserved on Viti Levu (McPhie, 1995).

2.2 Limestone of the Wainimala Group

The Early to Middle Miocene Tari Formation of southwestern Viti Levu (including the Malolo and Mamanuca Groups) consists largely of volcanoclastic rudites of basic to acidic andesites, with some dacitic volcanoclastics; massive limestone bodies also occur and contain larger foraminifera (Rodda, 1993).

Massive shallow-water but mainly non-reefal limestones in the Sigatoka Valley and nearby appear to be the youngest rocks of the Wainimala Group in the area, lying conformably on older formations. These limestones belong to the Qalimare Limestone. Other, smaller limestones bodies within other formations of the group in southwestern Viti Levu, mainly the Tari Formation, are considered to be parts of these formations (Rodda,1993). The apparent massiveness of the limestone outcrops is due to re-cementation of broken fragments by precipitating lime derived from solution of the outcrop (Houtz, 1959).

The Tau Limestone and most probably the Raraikoro Limestone, are part of the same limestone formation.


2.3 Colo Plutonics

The Colo Plutonic suite is found within a broad zone trending east-north-east across the southern half of Viti Levu. The largest exposed bodies are in the centre of the island where erosions have proceeded to deeper levels than to the east and west (Rodda, 1993). This Middle to Late Miocene formation is largely composed of two distinct phases of plutonic activity, namely the diorite-tonalite and gabbro stocks. The gabbros occur as isolated stocks and also as large masses within composite intrusions, whereas the diorite-tonalite suite is inferred to have arisen by differentiation from an intermediate magma and there is a clear gradation from early quartz diorite through tonalite to trondhjemite (Band, 1968).

In southwestern Viti Levu, the contact rocks are not recognisable as one of the Wainimala types, which often grade from unaltered country rock through variable metamorphosed rocks to intrusives. They are either siliceous, locally strong in epidote and amphibole, or fine-grained granitoid textured, basic to acid igneous types. The contact aureoles are not homogeneous and contain patches of unaltered materials as well as islands of plutonic rocks (Houtz, 1959).

Microphanerites and porphyries are extensively exposed in some areas as basic flow rocks, small gabbroic lenses, andesitic dykes and microdiorites. They are associated with basic flows that have been intruded and reconstituted (Houtz, 1959).

The Colo Plutonics intrude the Early Miocene Wainimala Series, comprising basic volcanics, grits and breccias, sediments and limestone. Gabbros, diorites and quartz diorite have been identified in southwestern Viti Levu with variable sizes of outcrops. The gabbroic bodies are usually small and boss-like with sharp contact whereas the hornblende-rich diorites occur as massive facies and are usually associated with acidic plutonics (Houtz, 1959).

The plutonic rocks of the Korovisilou area are from the youngest phase of the Colo Plutonic Suite. A radiometric dating of the Korovisilou Stock revealed active magmatic activity at about 5.9 Ma (Wedekind, 1984).

2.4 Shoshonitic Volcanism

Eruption of shoshonitic volcanism occurred between 5.6 and 3 Ma along the Viti Levu Lineament in the northwestern part of the island. This shoshonitic volcanic belt began with the eruption of the Koroyanitu volcano and other small volcanoes in the southwestern end of the lineament. Eruptive centres of Koroimavua volcanism have been exposed by post-Ba erosion in the east-west belt on the Conua-Koroyanitu range (Dickinson, 1968) (Fig. 3). The centres are steep-walled composite stocks, which are 1-10 km2 in area (Dickinson et al., 1968) with composition ranging from monzonite through diorite to gabbro, with augite the dominant mafic mineral. Known volcanic centres are (1) Vuda alteration zone, (2) Nawainiu stock, (3) Navilawa stock, and (4) Nadrou stock (Dickinson, 1968) (Fig. 3).

The Koroyanitu volcano is predominantly felsic in composition (Rodda, 1993) as observed in both the plutonic and volcanic rocks. Biotite- and augite-bearing shoshonitic flows and breccias of the Koroimavua Volcanic Group are extensively exposed around the location of the source volcanoes (Colley and Flint, 1995).


Figure 2a. Geology map of the Semo Quarry Area.


Figure 2b. A schematic cross section along line A-B.


The northern part of Viti Levu is dominated by the Ba Volcanic Group, which conformably overlies the Vatukoro Greywacke (Setterfield et al 1991; Begg, 1996). Mafic rocks were erupted from the Tavua volcano in the middle of the Viti Levu Lineament at about 5.2 Ma (Rodda, 1993). The rocks of the Tavua volcano were derived from a potassium-rich magma of shoshonitic association with relatively simple evolution from an absarokite parent magma to shoshonite, banakite and monzonite derivatives (Colley and Flint, 1995). Shoshonitic volcanism appears to have ceased around 3 Ma (Rodda, 1993).

2.5 Koroyanitu Volcano

The Koroyanitu Volcano is located about 20 km northeast of Nadi town (Fig. 2). Based on radiometric dating, the volcano was active between 5.5 to 4.8 Ma, making it the oldest shoshonitic volcanism in Fiji. It is composed of two major igneous components, namely, the Sabeto Volcanics, a member of the Koroimavua Volcanic Group and the Navilawa monzonite (A-Izzeddin, 2000). The monzonite stock represents the volcanic centre (Rodda, 1993) which covers an approximate area of 5.0 x 2.5 km. This stock has been dated as being 4.85 Ma and is interpreted to be co-magmatic with the Sabeto Volcanics (A-Izzeddin, 2000).

The Sabeto Volcanics occur mainly on topographic highs, unconformably overlying the basal Wainimala Group, and surrounding the monzonite stock to the north, east and south (Fig. 4). This unit comprise a series of interbedded andesitic, volcaniclastics and flows, which are believed to be mantle-derived (A-Izzeddin, 2000).

The volcano was formed along the northeast trending Viti Levu Lineament (A-Izzeddin, 2000) as indicated by the northeast alignment of the stock (Fig. 4).

2.6 Geophysical Survey A major on-land and offshore aerial magnetic survey was conducted over the Fiji Group in 1997. Kevron Geophysics carried out the survey, under close supervision by the Australian Geological Survey Organisation (AGSO). Survey imagery available at the Mineral Resources Department is a representation of the total magnetic response and exhibits an overview of the magnetic characteristics of areas in the Fiji Group.

The magnetic signatures over the Semo Quarry and the gabbro stock location are of high values, trending in a more or less east-west fashion. This generally indicates that the gabbro stock has high magnetic anomaly compared to the host rock. However, the magnetic anomaly cannot be used to predict (to any degree of certainty) the depth of overburden and weathering nor the nature of intrusion.

3. LOCAL GEOLOGY

The geology of the Semo quarry and the immediate surrounding areas are composed of the Wainimala Group rocks, including grits, breccias and sediments, which have been intruded by the gabbro stock a member of the Middle to Late Miocene Colo Plutonic Suite. In addition, fine-grained basaltic dykes occur to the south of the quarry.


3.1 Wainimala Group

The Wainimala Group in the quarry area comprises sediments, volcanic grits and breccias with minor agglomerates. The sedimentary unit appears to represent the upper unit of the Wainimala Group and mainly occurs to the south and western side of the quarry (Fig 2.). Sediments largely consist of inter-bedded sandstones and siltstones with occasional basaltic / andesitic cobbles and pebbles incorporated in the groundmass. The orientation of bedding is variable but generally dipping at 10 to 70 degrees to the northwest.

The volcanic breccia unit occurs extensively around the quarry as observed in creek, road-cut and ridge exposures. It underlies the sedimentary unit and is composed of volcanic grits and breccias, with minor sediments and agglomerates. Rock fragments are rounded to sub-angular and consist of basalt and andesite. Larger boulders being incorporated into the breccia unit is more prominent in creek outcrops and far more infrequent in road cuts along the ridges. This is indicative of the agglomeratic breccia being part of the basal unit of the Wainimala Group. Highly weathered outcrops in road cuts are quite difficult to identify but this unit has a distinguishable pale brown to grey weathering pattern.

3.2 Semo Gabbro

The gabbro stock at the quarry site is a member of the Colo Plutonic Suite and is referred to herein as the “Semo Gabbro”. It intrudes the volcanically-derived polymict breccia of the Wainimala Group, resulting in the invariably metamorphosed rocks around the contact. The contact, as exposed at the quarry, dips at 40 – 600 and rocks closer to the intrusion are relatively hard and siliceous.

Figure 3. The Southwestern rock-face of the Semo Quarry, revealing the typical fracturing pattern of the rock source.


Gabbro outcrops are mostly observed in moderately to highly weathered brown sandy form in the hills and road-cuts. Fresh exposures occur in adjacent creeks and at the quarry site. This unit, as exposed in the quarry, is massive, medium-grained and contains euhedral hornblende and augite crystals with rare fine-grained biotite in groundmass.

On visual analysis, plagioclase feldspar crystals dominate compared to minor amounts of these mafic minerals. It is important to carry out a petrographic analysis of the samples to correctly determine the identity of the minerals and their nature of emplacement.

4. STRUCTURE

No major structure was identified at the quarry and surrounding areas except minor cross-cutting shears and thin basalt dykes. Two relatively strong NW-trending shears have been mapped cutting through the gabbro stock (Fig. 3) without any visible displacement. The 5 - 15 cm wide shear that occurs in the quarry is composed of cabonate-sericite-illite-chlorite with minor disseminated fine pyrite. This clay-rich structure will have negligible adverse effects on the geo-technical application of the aggregates, considering it makes up less than 1 % of the total rock mass.

Occasional basalt dykes have been observed to the south of the quarry and closer to the intrusive contact but are absent away from the stock. These moderately weathered dykes are either trending NW or NE and are predominantly less than a metre wide. These dykes intrude the volcanics and sediments but not the gabbro. As such it is likely that both the dykes and the gabbro stock derive from the same magma. Sub-parallel north to northeast trending fractures are quite prominent in the quarry face as shown in Figure 3. This is indicative of a late stage tectonic activity, which resulted in the reactivation of existing faults and the subsequent development of these sympathetic structures. 5. PROPOSED DRILLING PROGRAMME 5.1 Introduction The Semo Gabbro stock has been identified for further assessment due to its close proximity to the main road, has the potential to be developed into a major aggregate source, and its location in relation to major hotel and residential development in the Nadi-Sigatoka corridor. In addition, it possesses excellent geo-technical properties, which make it suitable for any engineering application. In order to ascertain the surface or near-surface extent of the stock, it is necessary to design and carry out an appropriate drilling programme. In addition, this is the most reliable way of testing the integrity of the geological map, especially where outcrops are absent. This will also play a major role in determining the resource volume, upgrading of resource to reserve and the subsequent construction of a 3-D resource model.

5.2 Drilling In order to carry out any proper resource estimation and to upgrade the resource to reserve, drilling has to be carried out to confirm: i) depth of overburden and weathering; ii) continuity of the source rock;


Figure 4. Proposed drill-hole location to the west of the quarry site.


iii) nature of intrusion of the source rock; iv) variation in lithology and mineralogy of the source rock; and v) also provide samples for geo-technical testing. As shown in Figure 4, the drilling programme is designed to test the western extension of the stock where the resource can possibly be developed in the future. The eastern exposure has been constrained by the close proximity of the Queens Highway and the relatively low topographical elevation. The proposed drill-hole collars are located on the periphery of the inferred intrusive contact (Fig. 4); within the gabbro stock, on the intrusive margin and immediately outside the contact. The drill grid is about 50 – 60 m and if the need arises, each collar location should be revised during the course of the drilling programme. The proposed 12 drill-holes are all 30 m vertical holes (Table 1) and drill-hole numbers 1 – 4 (DH #: 1 – 4) must be drilled. The rest of the drill-holes will be considered one at a time depending on the progressive results and the programme can be terminated at any stage if the desired results are not achieved. The 30 m depth is chosen based on the overlying waste material at the quarry in which the combined average overburden and weathered depth is about 20 m before hitting the fresh rocks.

Drilling can also reveal the depth of the watertable from the surface. At least 3 drill-holes, with known watertable depths, are required in order to calculate the groundwater gradient. This gradient can be extrapolated to show the watertable outline at the quarry site, which will in turn help in the quarry design.

It is recommended that drilling should follow the number sequence shown in Figure 4. The specification for each drill-hole is given in Table 1. Table 1. The proposed drill-hole specifications.

DH # Northing (mN) Easting (mE) Azimuth Declination Depth (m)

1 3878872 1855029 – 900 30

2 3878882 1854974 – 900 30

3 3878872 1854916 – 900 30

4 3878933 1854971 – 900 30

5 3878870 1854858 – 900 30

6 3878932 1854916 – 900 30

7 3878873 1854801 – 900 30

8 3878818 1854855 – 900 30

9 3878823 1854795 – 900 30

10 3878989 1854973 – 900 30

11 3878987 1854915 – 900 30

12 3879046 1854911 – 900 30


In hard-rock assessment, the choice of drilling method to be used, hinges on the desired data quality and the cost of drilling. The use of diamond drilling is ideal for the provision of core samples, which will in turn be used for the above-mentioned analysis and testing. However, the cost of diamond drilling (current average rate of F$120.00/m) may be a limiting factor, i.e. the choice of drilling method depends on the allocated budget.

Alternatively, percussion drilling (Reverse Circulation drilling) can be used where rock chips are obtained at a cheaper rate (F$40.00/m). Rock type, overburden and weathering depths can be ascertained in RC drilling but it will be impossible to determine the structural and lithological contact orientation. In addition, rock chip samples cannot be used for geo-technical testing.

5.3 Drilling Cost

The cost of drilling does not entirely depend on the cost per metre ($$/m) negotiated by the two parties (company and drilling contractor). Other factors that influence the total cost of drilling are duration of the drilling programme, drill depth, the core size (in the case of diamond drilling), drill location in relation to water source, accessibility of drill site, rate of production, equipment mobilisation and demobilisation costs. Added costs due to some of these factors are subjected to negotiation and agreement between the two parties.

Two drilling companies are currently operating in Fiji, namely United Pacific Drilling (UPD) and Radial Drilling. A comparison of their operation costs (Table 2) is necessary to facilitate the process of choosing which drilling contractor is preferred. Table 2. Comparison of Radial and UDP drilling cost.

Typical Rates (Based on verbal quotations obtained in April, 2004)

Radial Drilling UPD Reverse Circulation $40.00/m $150.00/m

Diamond Drilling (PQ) $105.00/m $160.00/m

“ (HQ) $85.00/m $150.00/m

“ (NQ) $75.00/m $130.00/m Active Rate (reaming/cementation/casing/rig shift, etc)

$75.00/hr Negotiable

Standby $65.00/hr Negotiable

Mobilisation/Demobilisation Kilometre-rate Negotiable Consumables (sample bags, core trays, drill mud, water polypipe, core blocks, etc)

Provided by, or charged to client Provided by, or charged to client

UPD may charge at either a metre-rate, an hourly-rate or offer package where the terms and conditions are negotiated and agreed between the two parties, whereas Radial operates on a metre-rate alone. Fuel supply should be clarified, whether it’s the responsibility of the drill contractor or should be supplied by the client.


The water source for drilling at Semo will be a problem. The creek to the North of the quarry has limited water supply and will certainly run dry in the dry season. Consequently, the water might have to be carted or pumped from the main Tuva River, which is about 1 km to the west of the quarry. This will be done at an additional cost to the client. In addition, production must be emphasised to meet weekly drill targets and to complete the drilling programme at any given period regardless of whoever will be awarded the contract.

6. ECONOMIC DEVELOPMENT OF SEMO QUARRY

The rock exposures at the quarry (Fig. 3) reveal the most reliable information about the nature of intrusion, the associated structures and the level of overburden and weathering. The clinometer was used with a measuring tape to measure and calculate the height of the Southwestern rock wall as illustrated in Figure 5.

Figure 5. Demonstration on how the clinometer and measuring tape were used to calculate the height of the rock face.

Geological mapping of the quarry site reveals the following sequence: Overlying top-soil and sediments 3 m Weathered Gabbro 12 m Base of weathering to base of oxidation 5 m Fresh gabbro 33 m

Weathered gabbro can be as thick as 16 m on the left hand side of the NW quarry face (Fig. 3). Out of the 53 m maximum rock-face height, the top 20 m is considered waste and the 33 m of fresh rock is referred to as aggregates. The slightly weathered rocks (from base of weathering to base of oxidation) can be utilised for other aggregate applications such as base course for road construction and for landfill.

Sin 42o = X/80 m X = 53 m


Based on the current quarry floor and the rock-face, the ratio of fresh rocks to overburden and weathered rock is about 3 : 2. The fresh gabbro constitutes 62 % while the overburden and the weathered rocks make up the remaining 38 %. The overburden and highly-moderately weathered gabbro constitute 28 % of the rock and have to be removed first in order to develop the resource. A feasibility study needs to be carried out to ascertain the cost of waste removal against the development of the actual resource.

In order to boost production and the viability of the quarry, it is suggested that, if groundwater conditions allow, the present quarry floor could be further developed down to the same elevation as the Queens Highway. The quarry floor is about 28 m above the highway. This option, provided stable engineering conditions can be achieved, will raise the maximum height of the fresh rocks in the southwestern rock-face from 33 to 61 m that will subsequently increase the ratio of aggregates to waste from 3 : 2 to 3 : 1. This means, every cubic metre of waste removed will yield 3 m3 of aggregates.

6.1 Impact Assessment

Social and environmental impact assessments need to be carried out if a bigger quarry operation is envisaged at Semo. The developer should be mindful of the social impacts in terms of land ownership, potential employment and businesses for resource owners. It is imperative to establish and maintain a cordial relationship with landowners and nearby villages. In view of this, it is suggested that someone from SCI should be dedicated on community liaison and land negotiations. This should be done in a consultative process where the involvement of the Native Land Trust Board (NLTB) and the MRD should be sought when necessary.

An Environmental Impact Assessment (EIA) is necessary to establish the impact of an expanded operation on the surrounding environment. The EIA has to be carried out before any quarry development, followed by ongoing environmental monitoring during and after the quarry operation to ascertain the intensity of impact on vegetation, surface and groundwater resources, and living organisms in adjacent creeks. It is recommended that an environment consultant be engaged to do this with supplementary preliminary assessment by the developer’s environment officer.


PART II – GEOLOGICAL AND GEO-TECHNICAL ASSESSMENT OF POTENTIAL HARD-ROCK AGGREGATE SOURCES IN SOUTH AND WESTERN VITI LEVU

7. INTRODUCTION

Due to rapid infrastructure development in the Sigatoka – Lautoka corridor, it was necessary to identify in-situ hard-rock sources that could potentially be developed into quarries in the future. Apart from small-scale active quarries, construction aggregates are mostly sourced from the river in this area. A number of in-situ hard-rock samples were collected from potential sites during the field investigation in January 2004. These rocks were used for density, water content, mechanical testings and petrographic examinations.

Knowledge of physical, chemical and mechanical properties of any rock is very important in determining what sort of application it can be used for. The strength and durability of a rock can be determined by the use of appropriate testing equipment whereas the mineralogical analysis is carried out by examining a rock thin-section using a petrographic microscope.

The second part of this report describes how rock: strength tests were conducted, densities and water content measured and petrographic description of rock specimen. The report will present the results, data interpretation and the recommendations based on these geological and geo-technical investigations.

8. MECHANICAL TESTS

8.1 Rock Classification Hammer

The Rock Classification Hammer is an instrument, which is easy to use, for quick and approximate measurement of the resistance to pressure of rocks and manufactured concrete products. The principle on which it works are based on the rebound impact of a hammer on a piston which rests against the surface of the rock or concrete sample: the greater the resistance of the sample, the greater the rebound impact.

A rebound value does not have any unit. However, by reading this rebound impact on a scale and relating it to curves on graphs supplied with the instrument, the resistance to compression in MPa or PSI can be found.

The test makes it possible to learn the strength of impact, which depends on the resistance of the agglomerate in the absence of large inert or clusters of sand or gravel. From the force of the impact the resistance of the agglomerate surface can be deduced and subsequently the resistance of the rock or concrete.

With the aid of the test hammer the quality of the concrete or of the rock can quickly be determined.

8.2 Point Load Tester

A portable point load tester consists of a small hydraulic pump and ram, with an adjustable loading frame to test rock samples of different sizes (Fig. 6). The sample can be a drill core, a rock block with known dimension or an irregular rock lump. The two parameters measured by this test are the distance (D) between platens contact points that is read from a graduated scale incorporated in the lower frame, and the force (P) required to break the specimen, (this is read from a calibrated gauge in the hydraulic circuit). The point load strength index (Is) is the ratio P/D2.


Figure 6. Point Load Testing Apparatus, used for the strength test of hard-rock specimen.

The point load test gives a measure of the tensile strength of the rock, as does the geological hammer. It gives several important advantages:

1. The specimen fails at much lower loads than in compression, needing a machine load capacity less than one-tenth of that usually required for compression;

2. The core can be tested from the core box without previous machining – even weak or broken rock can thus be tested;

3. Fracture initiates in the specimen interior, platen conditions are of little importance.

8.3 Aggregate Durability

The durability of aggregates may be defined as the ability of individual particles to retain their integrity and not to suffer physical, mechanical or chemical changes to an extent which could adversely affect the properties or performance of concrete (Smith and Collis, 1993). Soundness and the resistance to abrasion, apart from alkali reactivity, are probably the most common properties of rock that need to be addressed in order to maintain the integrity of the concrete mix.


Unsound aggregates are those that show significant volume changes that result in deterioration of concrete when subjected to different environmental conditions (Waqa, 2004). On the other hand, to be able to resist abrasion, an aggregate has to be hard, dense, strong and free from soft particles. The abrasion resistance of an aggregate can be tested using the Los Angeles Abrasion machine where the aggregates are rotated with steel balls in a drum and the mass loss is measured after a given time (Waqa, 2004).

Due to the unavailability of testing equipment, durability tests were not carried out on any of the rock samples.

8.4 Alkali-Silica Reaction

It is imperative to highlight the inevitable reaction that happens in concrete between certain aggregates and alkali hydroxides derived from the cement used in concrete mixes. Mafic minerals such as pyroxene and hornblende contain certain amount of silica, making them susceptible to this reaction if a critical amount of reactive silica is present.

The alkali-silica reaction is the most common of alkali-aggregate reaction. It involves a reaction between alkali hydroxides in the pore solution of the concrete and certain forms of silica in the aggregate, producing an alkali silicate gel. This gel may imbibe water and swell, sometimes causing disruptions of the concrete.

The principal effects of alkali-aggregates reactivity are that affected concrete suffers expansion and cracking. The expansion causes misalignment of structures and can threaten structural integrity. Cracking can lead to reinforcement corrosion and other durability problems (Smith and Collis, 1993).

For damaging alkali-silica reaction to occur there must be all three of the following:

1. A critical amount of reactive silica in the aggregate;

2. A sufficient alkaline pore solution in the concrete;

3. A sufficient supply of moisture.

The reactivity of silica minerals depends principally on the amount of order in the crystal structure. Opal has a high disordered structure and is the most reactive form of silica. At the other end of the scale, well ordered unstrained quartz is normally unreactive. Other varieties of quartz may exhibit immediate reactivity (Smith and Collis, 1993). 8.5 Alkali-Carbonate Reaction

The alkali-carbonate reaction occurs between alkalis from cement and carbonate rocks containing clay minerals. Alkalis react with dolomite breaking it down into brucite and calcite, as represented by the following chemical equation (Waqa, 2004):

CaMg(CO3)2 + 2NaOH → Mg(OH)2 + CaCO3 + Na2CO3

Dolomite Alkali Brucite Calcite

This reaction opens up the aggregates so that water can enter and cause expansion of clay. This will eventually lead to swelling (Smith and Collis, 1993) and cracking of concrete (Waqa, 2004).


9. PHYSICAL TESTS

9.1 Water Absorption

Water absorption is an indirect measure of the permeability of an aggregate, which, in turn can relate to other physical characteristics such as mechanical strength, shrinkage and to its general durability potential. The water-absorbing capacity of any rock is influenced by its compaction, size and proportion of the pores, minerals present and their mode of occurrence, degree of weathering and alteration of the rock, and in some cases the existence of microfractures within the rock.

In general, less absorptive aggregates often tend to be more resistant to mechanical forces and to weathering. A low absorption value might reasonably be considered as less than 1 % (Smith and Collis, 1993). Light weight aggregates generally have high water absorption values of more than 5 %.

It is imperative to clarify that water absorption limits should not be imposed unless it has been established, for a particular material, that it relates closely to some other undesirable property. Although an aggregate may satisfy a water absorption limit, there is no guarantee that problems with concrete will not occur (Smith and Collis, 1993).

9.2 Density

Information on the density of aggregates is required in concrete mixes so that relationships between weight and volume can be worked out. The bulk density of an aggregate also takes into account the effects of voids present in the aggregate at a given degree of compaction (Waqa, 2004).

The density of any rock sample is influenced by many factors including rock type, hardness, compaction, composition, texture, size and proportion of the pores, density of minerals in groundmass, grain size, and degree of alteration and weathering.

9.3 Petrography

The petrographic characteristics and the mineralogy of rock types are important attributes, which influence rock durability, strength and engineering behaviour and performance (Maharaj, 1999). Petrographic examinations are made to determine the following (ASTM C 295-98):

1. The physical and chemical characteristics of the material that have a bearing on the performance of the material in its intended use;

2. The classification of the constituents of the sample;

3. The relative amounts of the constituents of the sample that are essential for proper evaluation of the sample when the constituents differ significantly in properties that have a bearing on the performance of the material in its intended use;

4. For comparison purposes – aggregates from one source with samples from one or more sources, for which test data or performance records are available.


9.4 Site Inspection of Aggregates Sources

A single sample of aggregate submitted for a laboratory petrographic examination, or any other tests, cannot be expected to represent the full character and variability of the rock source. Even regular sampling of the aggregate production could fail to detect a localised feature within the quarry, which might have a significant effect on the quality and durability of the aggregate (Smith and Collis, 1993). For instance, certain types of reactive silica may occur in localised structures such as veins and faults in a quarry or in any other potential hard-rock source.

These problems highlight the importance of geological investigation during the initial assessment of the rock source to ensure that field descriptions of the geology of the area are considered before any decision to develop. During aggregates development, routine assessment of aggregates quality should be carried out. A suitably qualified geologist should be made responsible for this quality control work, which would include sampling, testing, analysis and data interpretation.

Reconnaissance site surveys were conducted in some of the hard-rock sources visited during the January 2004 field expedition as described in Tawake (2004).

10. METHODS 10.1 Tested Samples Samples, which were collected from 12 different hard-rock sources in South and Western Viti Levu during the field expedition in January 2004, were subjected to a number of geo-technical testing methods. Table 3. South and Western Viti Levu Sample Locality Table.

Rock ID Sample Location Comments

Sabeto Volcanics S 17° 42’ 24.12” E 177° 26’ 33.42”

Location is indicated in Figure 8. The sample was taken from the rock face behind the PWD Quarry in Lomolomo. Rock is part of the Sabeto Volcanics.

Semo Volcanics (Ridge)

S 18° 05’ 13.62” E 177° 22’ 37.38”

About 400 m southwest of Semo Quarry. Sample was taken from a pile of float on the ridge. The rock is part of the Wainimala Volcanics.

* Raraikoro Limestone S 17° 42’ 23.34” E 177° 32’ 34.08”

Location is indicated in Figure 8. The outcrop is located about 1.4 km northeast of the Nawainiu Monzonite sample location.

Tau Limestone S 17° 58’ 32.16” E 177° 17’ 09.06”

Location is indicated in Figure 8. Sample was collected from the face of the old quarry. The rock is part of the Wainimala Group.

Korovisilou Diorite S 18° 14’44.66” E 177° 53” 38.22”

Location is indicated in Figure 7. Sample was collected on fresh road cut exposures. The rock is part of the Colo Basic Plutonics.

Vuda Shoshonite S 17° 40’ 32.34” E 177° 26’ 02.94”

Location is indicated in Figure 8. Sample was collected from the eastern end of the Vuda Shoshonite outcrop. The rock is part of the Ba Volcanics.

Semo Gabbro S 18° 05’ 25.40” E 177° 23’ 04.74”

Location is indicated in Figure 8. Sample was taken from the South-western Semo Quarry Face. The rock is part of the Colo Basic Plutonics.

Semo Volcanics (Creek)

S 18° 05’ 13.62” E 177° 22’ 58.86”

About 300 m northeast of Semo Quarry. Sample was taken from a fresh, in-situ creek exposure. The rock is part of the Wainimala Volcanics

Vuda Agglomeratic Breccia

S 17° 40’ 09.84” E 177° 26’ 05.01”

Location is indicated in Figure 8. Sample collected was not a good representation of the different lithologies present. The rock is part of the Koroimavua Volcanic Group.

Nawainiu Monzonite S 17° 42’ 56.70” E 177° 31’ 41.46”

Location is indicated in Figure 8. Fresh outcrop was taken from the eastern ridge. The rock is part of the Nawainiu Monzonite.


Korovisilou Basalt Dyke S 18° 14’ 45.02” E 177° 53’ 37.86”

Location is indicated in Figure 7. Sample was collected at the same place as the Korovisilou Gabbro. Dykes are intruding the gabbro.

Saru Shoshonite S 17° 39’ 50.16” E 177° 28’ 42.36”

Location is indicated in Figure 8. No fresh outcrop was found hence a float sample was collected from the ridge top. The rock is part of the Ba Volcanics.

* This Limestone unit has not been discovered before, hence it is not being identified with any existing limestone formation. However, the Raraikoro Limestone is hosted in the Nadele Breccia, a volcanic formation of the Wainimala Group, so, it is most likely to be part of the Early Miocene Wainimala Limestone. A total of 12 hard-rock cube samples, one from each source, were tested using the L-Type Rock Classification Hammer (a non-destructive strength test method). In addition, the Point Load Tester was used to test at least two samples from each of the 12 locations. The same 12 cubic samples that were used for the non-destructive test were also used to determine the water content and the dry and wet densities of the rock. The samples collection sites are shown in Figures 7 and 8 and their coordinates are given in Table 3. A hand-held GPS was used to locate the sampling sites. This is vital to ensure that the sample locations are easily identified in future, especially the locations that were difficult to locate on the topographic and geologic maps.

Figure 7. Korovisilou sample locality map.


Figure 8. Sigatoka-Lautoka corridor sample locality map.


10.2 Schmidt Hammer Test

Each rock sample was cut to a 3 by 3 by 3-inch dimension cube. The Schmidt Rock Classification Hammer was used for the strength test. Three sets of tests were carried out; one before the sample was dried, the second after it was subjected to a temperature of 1100C for 48 hours and another test was done after soaking in water for 72 hours. To determine the water content, each sample was weighed prior to and after drying, as well as after soaking.

The first set of tests was carried out on each sample prior to drying and soaking. The test was conducted by placing the rock cube on a flat, smooth concrete floor and the rock hammer piston was placed in the middle, perpendicular to the surface of the upper face of the rock cube (Fig. 9). In order to get a reading, a constant pressure was applied against the rock by pushing the piston against the sample until the mass impact was released.

Figure 9. Rock strength test using a L-Type Schmidt Rock Classification Hammer.

The device was kept firmly pressed against the surface being tested whilst the side button was pressed in. The device was removed in order to read the rebound reading (H) on the scale. The piston remained inside the device when it was removed from the surface being tested. In order to prepare the hammer for another test, the piston was released by the method indicated in Paragraph 2. The same procedure was undertaken three times for each sample and the average of the three readings was taken as the rebound impact reading of the rock.

After the first set of tests, the samples were then oven dried at 1100C for 48 hours and each sample was weighted and tested after cooling at room temperature for at least 2 hours. The same testing procedure outlined above was carried out for each sample. In order to determine the water absorption capacity of each sample, all samples were soaked in tap water for 72 hours before being weighed again. Each sample volume was determined by

3 by 3 by 3 inchrock cube sample

Schmidt Rock Classification Hammer


direct displacement of water using a volumetric cylinder. The rebound impact of each rock sample was again tested using the hammer. The H values of rebound have been defined in such a way that they can be converted, by means of diagrams which are provided with the device, into terms of resistance to compression for tests carried out on the cylinder or on the cube. On each diagram, 5 different curves have been reproduced (Fig. 10), which take into account the angle on the instrument. The + 90° (α = 90°) curve was used to determine the compressive strength of each rock sample.

Figure 10. Cube Compressive Strength Diagram, used to determine the resistance to compression of a cube sample (from User Guide, 2001).

10.3 Point Load Test At least two sample blocks were cut using a diamond saw and the dimension of each sample is given in Appendix 4. The height of a block sample was taken as equivalent to the diameter (D) of a drill core sample. After all the setting up of the apparatus, as specified in the Operating Instruction Manual, it was ready for use. Each rock sample, with known dimensions, was placed between the platen points. The pump was used to raise the lower platen point into firm contact with the specimen (Fig. 6) and the diameter of the specimen was taken from the graduated diameter scale incorporated on the side of the load frame. In order to get a load reading (P), a force was steadily applied until the specimen failed. The maximum load achieved, as given in the calibrated gauge, was recorded. Before the apparatus was used for the next test, the pressure release valve was opened and the lower platen was manually lowered.


Samples with obvious pre-existing fractures or possess certain degrees of weathering and alteration often produce erroneous and erratic results. Test results that show low point load strength due to at least one of these factors are normally disregarded. Any rock sample (e.g. Semo Gabbro) that falls in this category is often tested more than twice in order to yield more realistic values. The two readings that were used to calculate the average failure load (P), which was then used to determine the average point load strength (Is) of each sample are given in Appendix 4. Once used for the point load test, a sample can never be used again due to the fragmentation of the sample that normally happens when the rock fails. 10.4 Petrography Thin sections were only prepared for rock samples obtained from aggregate sources that can potentially be developed into quarries. A thin section was prepared for each of the following rocks: Semo Gabbro, Vuda Shoshonite, Saru Shoshonite, Nawainiu Monzonite, Korovisilou Diorite, Korovisilou Basalt Dyke, Raraikoro Limestone and Tau Limestone. All thin sections were examined under a petrographic microscope, where most minerals were identified based on their characteristic optical properties. On some occasions, it was quite difficult to distinguish minerals of the same group. For instance, distinguishing different members of the plagioclase and alkali feldspars can be tedious. For some others, it would require chemical analysis to correctly determine their identity. 11. RESULTS 11.1 Schmidt Hammer Test Table 4 is a summary table showing the average rebound reading for each set of tests with subsequent resistance to compression readings (a measure of strength) taken from the diagram in Figure 10. Full test results can be found in Appendix 1.


Table 4. The diagram in Figure 10 revealed the strength of each rock sample prior to drying, after drying and after soaking in tap water.

Before Drying After Drying After Soaking Rock ID Rebound

Reading Strength

(MPa) Rebound Reading

Strength (MPa)

Rebound Reading

Strength (MPa)

Sabeto Volcanics 33.73 35.40 32.20 32.10 25.77 22.0

Semo Volcanics (Ridge) 63.07 –* 66.00 – 65.33 –

Raraikoro Limestone 53.60 73.50 55.27 – 54.80 76.00

Tau Limestone 42.83 57.90 43.73 52.20 48.53 61.30

Korovisilou Diorite 56.50 – 61.87 – 64.07 –

Vuda Shoshonite 63.33 – 61.67 – 63.27 –

Semo Gabbro 64.33 – 65.33 – 64.33 –

Semo Volcanics (Creek) 58.33 – 57.67 – 58.00 –

Vuda Agglomeratic Breccia 48.67 61.80 49.53 63.60 49.27 62.40

Nawainiu Monzonite 57.37 - 58.07 - 55.00 -

Korovisilou Basalt Dyke 49.53 63.70 48.27 60.50 50.13 64.80

Saru Shoshonite 44.60 50.10 44.33 53.30 43.47 51.90

*– The rebound reading and the subsequent compression resistance value exceeds the limit of the diagram shown in Figure 10.


Rock Strength Test Results Using a Schmidt Hammer

20.00

25.00

30.00

35.00

40.00

45.00

50.00

55.00

60.00

65.00

70.00

Sabeto

Volcan

ics

Semo V

olcan

ics (R

idge)

Raraiko

ro Lim

eston

e

Tau Li

meston

e

Korovis

ilou D

iorite

Vuda S

hosh

onite

Semo G

abbro

Semo V

olcan

ics (C

reek)

Vuda A

gglom

eratic

Breccia

Nawain

iu Mon

zonit

e

Korovis

ilou B

asalt

Dyk

e

Saru Sho

shon

ite

Rock ID

Reb

ound

Val

ues

Before Drying After Drying After Soaking

Figure 11. Histogram showing comparison of rock strengths of individual samples before drying, after drying and after soaking using a Schmidt Hammer. 11.2 Density The specific gravity of each sample is tabulated below (Table 5), before and after drying (dry density) and after soaking (wet density). Table 5. Rock sample densities, showing the density of each sample at normal temperature and pressure plus the dry and wet densities.

Rock ID Density before drying (g/cm3) Dry Density (g/cm3) Wet Density (g/cm3)

Sabeto Volcanics 2.04 2.01 2.11 Semo Volcanics (Ridge) 2.44 2.44 2.44 Raraikoro Limestone 2.50 2.50 2.52 Tau Limestone 2.23 2.23 2.28 Korovisilou Diorite 2.75 2.74 2.75 Vuda Shoshonite 2.72 2.72 2.72 Semo Gabbro 2.72 2.72 2.73 Semo Volcanics (Creek) 2.66 2.66 2.66 Vuda Agglomeratic Breccia 2.40 2.39 2.43 Nawainiu Monzonite 2.44 2.43 2.45 Korovisilou Basalt Dyke 2.40 2.39 2.43 Saru Shoshonite 2.56 2.55 2.56


Rock Densities

0

0.5

1

1.5

2

2.5

3

Sabeto

Volcan

ics

Semo V

olcan

ics (R

idge)

Raraiko

ro Lim

eston

e

Tau Li

meston

e

Korovis

ilou D

iorite

Vuda S

hosh

onite

Semo G

abbro

Semo V

olcan

ics (C

reek)

Vuda A

gglom

eratic

Breccia

Nawain

iu Mon

zonit

e

Korovis

ilou B

asalt

Dyk

e

Saru Sho

shon

ite

Rock ID

Den

sity

(g/c

m3)

Density Before Drying Dry Density Wet Density

Figure 12. Histogram of rock densities, showing the variation in densities before drying, after drying, and after soaking for each sample. 11.3 Water Content Table 6 presents the percentage water content in each sample. This is calculated by dividing the weight of the sample after drying with the weight of the sample after soaking, and then multiplied by 100. For more details see Appendix 2. Table 6. Percentage water content of each rock sample.

Rock ID % Water Content Sabeto Volcanics 5.33 Semo Volcanics (Ridge) 0.07 Raraikoro Limestone 0.56 Tau Limestone 2.64 Korovisilou Diorite 0.11 Vuda Shoshonite 0.06 Semo Gabbro 0.17 Semo Volcanics (Creek) 0.28 Vuda Agglomeratic Breccia 1.48 Nawainiu Monzonite 0.80 Korovisilou Basalt Dyke 1.48 Saru Shoshonite 0.45


11.4 Point Load Test The point load strength index (Is) is calculated using this formula: Is = P/D2. Table 7. Point load strength and rock designation of each sample.

Rock ID Ave P(MN) Ave D (m) Is (MN/m2) Strength Designation Sabeto Volcanics 0.0106 0.0418 6.02 Very High Semo Volcanics (Ridge) 0.0215 0.0359 16.68 Extremely High Raraikoro Limestone 0.0112 0.0356 8.82 Very High Tau Limestone 0.0077 0.0374 5.48 Very High Korovisilou Diorite 0.0302 0.0285 34.36 Extremely High Vuda Shoshonite 0.0375 0.0368 27.76 Extremely High Semo Gabbro 0.0360 0.0376 25.09 Extremely High Semo Volcanics (Creeks) 0.0147 0.0360 11.33 Extremely High Vuda Agglomeratic Breccia 0.0231 0.0361 17.73 Extremely High Nawainiu Monzonite 0.0289 0.0363 21.87 Extremely High Korovisilou Basalt Dyke 0.0238 0.0355 18.68 Extremely High Saru Shoshonite 0.0277 0.0328 25.78 Extremely High

Rock Strength Test Results Using a Point Load Tester

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Point Load Strength (Is)

Figure 13. Histogram of average point load strength of individual samples using a point load tester.


The variations displayed on the above histogram indicate differing strengths of each sample that reflect the most likely strength of the rocks at source. The point load strength is used to compute the strength designation of each sample using the nomogram shown in Appendix 5. 11.5 Petrography Full petrographic descriptions of all the thin sections examined are given in Appendix 6. Table 8 presents brief descriptions of each thin section examined. Table 8. Brief petrographic description of the samples examined.

Rock ID Description Raraikoro Limestone The petrographic examination of the rock revealed that the rock is

composed entirely of Calcium Carbonate. Aragonite must have been converted to calcite during the diagenetic process. Fossilised shells and marine organisms are common.

Tau Limestone Similar to the Raraikoro Limestone, the Tau Limestone is composed predominantly of Calcium Carbonate. Lesser amount of dolomite is also present. Fossilised shells and marine organisms are common.

Korovisilou Diorite Subhedral to anhedral plagioclase and hornblende crystals occur in an interlocking fashion. Plagioclase is the major constituent and hornblende makes up about 24 % of the minerals present.

Vuda Shoshonite The combined percentage composition of olivine and clinopyroxene comes to 45 %. An equal amount of plagioclase is also present in the groundmass.

Semo Gabbro The rock specimen examined is generally dominated by plagioclase, whereas the clinopyroxene represents a minor component. Olivine occurs in lesser amount and finer-grained.

Nawainiu Monzonite This unit is composed mainly of feldspars with lesser amounts of hornblende and biotite, which occur fine- to medium-grained in the groundmass. Quartz is also present but in very small amount. Field investigations have confirmed the occurrence of pegmatitic monzonite that contains coarse hornblende crystals, which can be as long as 4 cm

Korovisilou Basalt Dyke Major mineral constituents are plagioclase and hornblende and they occur as phenocrysts in a finer groundmass. Fair amount of fine, disseminated opaque minerals are observed.

Saru Shoshonite The Saru Shoshonite sample is similar to the Vuda Shoshonite. The olivine and pyroxene occur in slightly lesser amount, which has been subsequently substituted by an increase in plagioclase in the groundmass.


12. DISCUSSION 12.1 Geo-technical Properties With the exception of the Sabeto Volcanics and the Tau Limestone samples, all the other rock samples exhibit good to excellent geo-technical properties. Site visits and inspections of these rock sources have revealed that some are characterized by strong fracturing patterns. Two classic examples of this are the Semo Gabbro and the Vuda Shoshonite outcrops, both are active aggregates extraction sites. The Korovisilou Diorite, the Vuda Shoshonite and the Semo Gabbro are the heaviest of the lot and their insignificant dry and wet density changes (vary between 2.72 and 2.75 g/cm3) could be attributed to their hardness and compaction, which indicate the presence of strong, impermeable minerals in large quantities in the groundmass. Generally, rocks with higher densities and compaction values normally have very low water content, as they do not allow water to percolate through them. However, this may not be the case if the rock is fractured and it would record invalid mechanical strength, which is usually lower than its normal value. In addition, it allows water to permeate through the fracture plane hence facilitating the process of oxidation over time. The discussion on each sample below is largely based on the geological and geo-technical tests/analyses results summarized in tables and graphs above. These include Figures 11, 12 and 13, Tables 4, 5, 6, 7 and 8, and Appendices 5 and 6. 12.2 Sabeto Volcanics Based on the strength test results, the Sabeto Volcanics can be considered an unsuitable source of construction aggregates. Some of the tested samples, upon visual inspection, were found to be slightly weathered and partially fractured. This could certainly have contributed to the low rebound value obtained hence it may not be a true representative strength for the Sabeto Volcanics. The point load strength of the rock is classified as “very high” under the Strength Designation, but it recorded the second lowest value compared to the other rocks. There is a significant difference in dry and wet densities of the rock due to relatively large amount of water absorbed into the existing fractures and partially weathered groundmass. This has been supported by the water content, which makes up 5.33 % of the rock weight. Water content of the Sabeto Volcanics recorded 5.33 %, the largest out of the whole rock suite. Interestingly, a report by Bartholomew (1960) revealed a small quarry was once worked by the Public Works Department at Lomolomo – the western extremity of the Sabeto Range (where the sample was collected in January 2004). The rock was described as weathered, brecciated andesite of low crushing strength. The sample sent overseas failed the Los Angeles Abrasion Test by 3 % above the allowable limit of 20 %. 12.3 Semo Volcanics (Ridge) The Semo Volcanics (Ridge) is one of the samples that show consistently high rebound values. In comparison with other mechanically sound rocks, it can be classified as a suitable source of aggregates. This was confirmed by its high point load strength of 16.68 MN/m2.


After soaking in water, the sample weight increased by a mere 0.8 grams, representing an insignificant 0.07 % of the rock mass. Its specific gravity remains at 2.44 g/cm3 after drying and soaking in water, and is indicative of a high degree of compaction and strength. 12.4 Raraikoro Limestone The exposed pinnacles of the Raraikoro Limestone Unit cover an approximate area of 40 by 60 metres, to the northeast of the Nawainiu Monzonite Stock. This re-crystallised rock is hard and compact with average rebound values between 53.6 and 55.3. When comparing these results with the outcome of the point load test, where the sample failed at 8.82 MN/m2, it confirms the high strength of the rock. However, the brittle nature of the sample may affect its durability if it has to undergo a durability test. The high densities of the rock can be attributed to its compaction as revealed by the insignificant amount of water contained in the cube after soaking (0.56 %). This is significantly lower compared with that of the Tau Limestone. The absence of silica-minerals and dolomite in the groundmass combined with its good mechanical properties would make the rock a good aggregate source. 12.5 Tau Limestome The physical appearance of the Tau Limestone can be described as a massive and powdery white rock that has variable and significant amount of porosity in variable sizes and proportions. The rebound values vary a lot, ranging from 42.8 to 48.5 and yielding a compression resistance range between 57 and 61. Samples that were subjected to the point load test exhibit relatively poor point load strengths, recording the lowest average failure load of 5.48 MN/m2. The weak powdery content, together with the significant amount of vesicles are responsible for this moderate strength of the rock. The wet density of the rock, which is 0.5 g/cm3 greater than the dry density, signifies the amount of vesicles in the rock that have been filled with water during soaking. The total water content represents 2.56 % of the rock mass, a relatively large figure compared to the other samples. It is worth mentioning that the Tau Limestone is currently being extensively extracted for landscaping and fill at the site of the Momi Bay Resort, which is located about 5 km northwest of the quarry. However, considering the quality of other accessible rock sources around the area, the Tau Limestone is not a recommended source of sand and gravel for construction. 12.6 Korovisilou Diorite The Korovisilou Diorite, like the Semo Gabbro, is part of the Middle to Late Miocene Colo Plutonic Suite. The variation in the rebound values could be attributed to the fractures in the sample hence the true resistance to compression is not known. Except for the test carried out after soaking, which is consistent with results of the Semo Gabbro sample, the other two are relatively lower. Five samples were tested using the point load tester, in which three failed prematurely along fracture planes. The two samples that have been used to calculate the average point load strength in Table 7, recorded excellent strength, the highest out of all the samples tested. This is a true indication that the Korovisilou Diorite possesses excellent strength.


The specific gravity of the rock is consistent with its strength, as it is the densest of all the samples. There is a slight increase in the wet density, mainly due to the small amount of water absorbed during soaking. The water content represents 0.11 % of the rock weight, which is significantly low and comparable with that of the Semo Gabbro. The significant presence of hornblende may have long-term adverse effect on the concrete if the rock is used for construction. The alkali-silica reaction is likely to occur if significant amount of reactive silica is present. 12.7 Vuda Shoshonite The Vuda Shoshonite is part of the Saru Shoshonite and predominantly composed of augite-olivine shoshonitic flow. Euhedral augite and olivine crystals are common and recognizable to the naked eye. The Schmidt Hammer test revealed that this rock is one of the best, yielding rebound values between 61.6 and 63.3. These excellent results are confirmed by the point load strength, exhibiting an average value of 27.76 MN/m2. There is no change in the dry and wet densities, both recording 2.72 g/cm3. The consistently higher densities and insignificant water content have indicated that the rock is compact, hard and consists of denser minerals. This was confirmed by the thin section examination and the strength test results. The significant presence of some silica-bearing mafic minerals (olivine and clinopyroxene) could affect the use of this rock in concrete mix. Olivine in particular, with a huge quantity in the groundmass coupled with its coarse-grained nature, is likely to trigger the alkali-silica reaction in a concrete mix, thus increasing the rock susceptibility when used for construction. 12.8 Semo Gabbro The rock can be described as compact, strong, medium-grained and crystalline. However, the current quarry faces exhibit multiple fracturing that has the tendency to impact on the strength and the durability of the sample. This fracturing nature can be enhanced by the existence of micro-fractures within the material, which will in turn lower the strength of the rock. The Semo Gabbro sample recorded one of the highest Schmidt Hammer rebound values as indicated by the reading of 64.33 at normal temperature and pressure. The point load test also recorded an extremely high strength of 25.09 MN/m2. The given strength test results of the Semo Gabbro sample have shown that the rock has excellent mechanical potential as an aggregates source. However, the quantification of the resource and the subsequent feasibility study are the two pressing issues that need immediate attention. This survey was part of the investigation to address this, together with the recommended drilling programme, which will result in proper aggregates resource estimation. The specific gravity of the sample (2.72 g/cm3), together with the Vuda Shoshonite, recorded the second highest. Its water content amounts to 0.17 % of the rock mass. These results have been confirmed by the strength tests and suggested that the rock is very strong, compact and crystalline. Both clinopyroxene and olivine occur as fine-grained crystals and minor constituents in the groundmass, hence they are less likely to stimulate any alkali-silica reaction in the concrete.


12.9 Semo Volcanics (Creek) All three rebound readings shown in Table 4 are consistent, ranging between 57.6 and 58.3 and they indicate excellent rock strength. The load strength (11.33 MN/m2) was just above the higher boundary of the “very high strength designation” in Appendix 5. This sample has an average density of 2.66 g/cm3. It has water content of 0.28 % of the total rock weight, which indicates that the rock may have micro-pores and some water-bearing clay minerals. When comparing these results with that of the Semo Volcanics (Ridge), the trend shows that the creek sample has lesser rebound values and point load strength but it is denser than the ridge sample. This scenario shows that denser materials do not necessarily become the stronger rock. The results indicate that this rock is a relatively good source of aggregates, a point that needs to be considered and periodically revised during the progressive development of the Semo Quarry. 12.10 Vuda Agglomeratic Breccia This agglomeratic breccia consists of relatively fresh polymict volcanic rock fragments and slightly to moderately weathered volcanically-derived sediment matrices. The percentage clast-matrix abundance is about 70 : 30 %. The friable sedimentary matrices would most likely turn into dust and sand during crushing. The compression resistance of between 61.8 and 63.6 MPa of this unit are good but well below the strength of other samples tested. Furthermore, the point load strength of 17.73 MN/m2 is classified as extremely high. It is worth mentioning that the rock samples used for these tests are biased in favour of the hard, relatively fresh volcanic clasts. The weak, weathered and friable sedimentary matrix is poorly represented in each sample. Due to the friable nature of the matrix, it was quite difficult to obtain an unbiased sample during sample preparation. The dry and wet densities show a slight difference and the water content revealed a 1.48 % of the rock weight. These results, coupled with visual inspection of the hand specimen, indicate that the sample is relatively porous, a common feature of breccias. Based on the above testing results and field descriptions of the rock, the Vuda Agglomeratic Breccia may not be the best source of aggregates. If crushed, the products are likely to be screened in order to remove the significant dust component. 12.11 Nawainiu Monzonite The rock can be described as medium to coarse-grained, compact, crystalline biotite-hornblende monzonite. Occasionally, outcrops exhibit pegmatitic texture due to the coarse nature of the hornblende crystals in the rock that can be as long as 4 cm. Based on the Schmidt Hammer test results, the Nawainiu Monzonite displays high rebound values between 55 and 58. These high values have been supported by the average point load strength of 17.73 MN/m2 of the rock, earning the extremely high strength designation. There was little difference between the dry and the wet densities and the water content only represents 0.8 % of the total rock weight. The possible occurrence of micro-fractures within the sample and the water-bearing white clay minerals in the groundmass could be responsible for the water contained within the rock.


With the exception of pegmatitic monzonite, the rock can be used for any aggregate application. The pegmatitic monzonite, as observed during the field survey, may not be suitable for construction use due to the presence of large hornblende crystals, which may stimulate alkali-silica reaction within the concrete mix. The petrographic characteristics of the specimen are supportive of the rock being suitable for any aggregates application. 12.12 Korovisilou Basalt Dyke The fine-grained Korovisilou Basalt Dyke occurs with the Korovisilou Diorite. The former is commonly found intruding the latter along road-cuts to the east of Korovisilou Village. A resistance range between 60 and 64 MPa have been achieved for this material. The extremely high strength designation has been assigned to the rock with point load strength of 18.68 MN/m2. The water content of 1.48 % is significantly high compared to the other samples. Comparing these results with that of the Korovisilou Diorite, the strength values together with the wet and dry densities of the dyke are lower than that of the diorite. This can be attributed to the huge presence of plagioclase in the groundmass, constituting about 70 % of the total mineral composition. The porphyritic nature of the dyke is also a contributing factor where vesicles are being filled mainly with plagioclase and carbonates that normally alter to water-bearing clays such as sericite and smectite. This may explain the 1.48 % water content in the rock. The absence of dense, medium- to coarse-grained mafic phenocrysts in the groundmass is believed to be responsible for the dyke’s lower densities compared with the Korovisilou Diorite. Petrographic characterization of the rock has reconfirmed the presence of fine-grained minerals, mainly plagioclase and hornblende, in a finer groundmass, a phenomenon that is less likely to induce alkali-silica reaction. Based on these results, the basalt dyke can be taken together with the gabbro as sources of aggregates if any future prospect of quarry development is raised. 12.13 Saru Shoshonite The Saru Shoshonite is physically and chemically the same rock as the Vuda Shoshonite and thus their geo-technical behaviour are expected to be similar. The Schmidt Hammer test results revealed that the Saru Shoshonite is about 20 rebound values less than what was recorded for the Vuda Shoshonite. The dry and wet densities also suggested that the Saru Shoshonite is lighter. This disparity could be attributed to the visible fractures on the tested sample with associated weathering along the fracture plane. Much of the 0.45 % water content could have been absorbed within the fracture zone. In contrast, the samples used for the point load tests are without flaw, which in turn yielded good strength averaging 25.78 MN/m2. This value is comparable with that of the Vuda Shoshonite and confirming the geo-technical excellence of the rock. As for the Vuda Shoshonite, the significant presence of olivine and clinopyroxene in the Saru Shoshonitie, as revealed in the petrographic analysis, may stimulate alkali-silica reaction if the rock is used to make concrete.


13. CONCLUSION The results of these rock sample strength tests reveal a general trend where the rebound value and the point load strength are directly proportional to the density of the rock being tested. In contrast, both the strength and the density of the rock are inversely proportional to the water content. However, there may be exceptional cases when comparing test results like the Semo Volcanics ridge and creek samples. Rock samples that exhibit exceptionally good strength are: Semo Volcanics (both ridge and creek samples), Korovisilou Diorite, Vuda Shoshonite, Semo Gabbro, and the Nawainiu Monzonite. As expected all these rocks are relatively denser with insignificant water content. All the Semo rocks can be used for any application. The Korovisilou Diorite and the Nawainiu Monzonite are suitable aggregate sources but the high percentage and the occasional presence of coarser grained silica-bearing mafic minerals may cause some problems in concrete mix. Otherwise they can be utilized for any application. The Schmidt Hammer results obtained for the Saru Shoshonite are erroneous due to the presence of fractures and weathering within the sample. However, the outcome of the point load strength tests has restored the integrity of the rock as an excellent aggregate source. Due to the significant presence of coarser-grained silica-bearing mafic minerals in the Vuda and Saru Shoshonites, they may not be suitable for construction as these minerals could stimulate alkali-silica reaction within the concrete. The minor pegmatitic-monzonite within the Nawainiu Monzonite may also fall in this category. The Raraikoro Limestone and the Korovisilou Basalt Dyke exhibit reasonably good strengths and high densities. Out of the two limestone units tested, the Raraikoro Limestone is the preferred source due to its excellent mechanical properties. However, the isolation of the source coupled with access problems would discourage any potential developer. The powdery and vesicular nature of the Tau Limestone, with its average mechanical strength and 2.64 % water content, make it unsuitable for road sealing and building construction. Apart from the relatively low strength of the rock, the presence of dolomite might be the catalyst for the carbonate-alkali reaction in concrete. The rock is most suitable for landfill and reclamation, as it is currently being used for the development of the Momi Bay Resort. The Vuda Agglomeratic Breccia, with 30 % being weak, friable sedimentary matrix, is not suitable for building constructions and for road sealing chips. However it can be used for other applications such as landfill and road sub-base. Due to only limited surface exposures and the availability of relatively good aggregate sources in the Nadi-Lautoka corridor, it is not considered a feasible commodity.


14. RECOMMENDATIONS

• SCIL should enquire with the two drill contractors available (UPD and Radial Drilling) the services offered and the cost per metre of drilling, before making any commitment. Additional cost, apart from the standard drilling rate, should be clarified before a contract is signed.

• The sequence of drilling should follow the numbered sequence proposed in the drill plan (Fig. 4). This resource definition drilling should start closer to the quarry and then move towards the west, as indicated.

• The first four proposed drill-holes must be drilled and the rest should be considered one at a time depending on the progressive results. The programme can be terminated at any stage if the desired results are not achieved.

• Production should be emphasised to whoever is being awarded with the drilling contract, to ensure the rig can produce the weekly drill target and complete the drilling programme in a given timeframe.

• Dependent on engineering stability and groundwater conditions, it may prove possible to develop the present quarry floor to the same elevation as the Queens Highway in order to create additional benches, thus increasing the economic viability of the operation.

• If at any stage, the quarry operation at Semo is to be expanded, then social and environmental issues will have to be considered and subsequent mitigating measures may need to be implemented.

• The impact of infrastructure development on any of these sites, in case of future quarry operation, must be considered and appropriately mitigated. These include the safety aspect (rock blasting, and traffic control), road maintenance, excessive noise and geo-technical site investigation for building construction.

• Resource estimation and modelling at Semo should be carried out after the completion of the drilling programme to assess what the updated resource volume is, and also to determine the spatial distribution of the gabbro stock. This will help in the quarrying plan and the assessment of the scale of operation.

• Due to its excellent mechanical properties, the source of the Saru Shoshonite should be further investigated on the possibility of finding a massive surface outcrop, which has the potential to be developed into an aggregate source for the Nadi-Lautoka area.

• Environmental impacts should be considered if further extraction is planned for the Vuda Shoshonite. Reconnaissance survey revealed limited surface exposures of the rock hence the long-term viability of the quarry should be assessed.

• Advanced assessment is required for the Nawainiu Monzonite stock in order to quantify the resource and evaluate the viability of a quarry operation. This may involve detailed geological mapping, drilling and additional geo-technical investigations.

• The quantification of the Korovisilou Diorite needs to be carried out in any future assessment on the potential of the source rock. As a partly exposed plutonic rock, the overburden thickness has to be quantified as well, as a lot of stripping will be required in order to expose the fresh material.


• Due to the significant presence of silica-bearing minerals in most of these rock samples, it is suggested that proper chemical analysis should be carried out to clarify the amount of reactive silica in them. The same method is recommended for the carbonate rocks in order to ascertain the amount of reactive clays present.

• The decision to develop or not to develop any of these rock sources must not be based solely on the geological and geo-technical data presented in this report. These data should be used as a guide for potential hard-rock aggregate developers in their quest to identify quality sources in these areas and to assist them in future detailed surveys.

• Reconnaissance and detailed geological surveys, together with additional representative geo-technical investigations should be carried out prior to any decision to develop the resource in any of the aggregates sources identified in this report.

• Prior to any aggregate extraction, the developer should initiate consultations with the Mineral Resources Department (MRD), the Department of Environment (DOE) and the Native Lands Trust Board (NLTB) with regards to EIA. Based on the outcome of these discussions, a preliminary or a full EIA study should be carried out.

• Any developer or sub-contractor personnel should observe traditional protocol during the exploration stage and within the duration of the quarry operation, especially when visiting villages. This would ensure that a cordial relationship with resource owners is maintained at all times.


15. REFERENCES A-IZZEDDIN, D. 2000. The Geology of the Tuvatu Gold Project. Emperor Gold Mining Co. Ltd

Internal Report (unpubl.).

ASTM C 295-98. 1998. Standard Guide for Petrographic Examination of Aggregates for Concrete. Reprinted from the Annual Book of ASTM Standards.

BAND, R.B. 1968. The Geology of Southern Viti Levu and Mbengga (An Explanation of Viti Levu Sheets 17, 18, 19 and 20). Department of Geological Survey, Ministry of Natural Resources, Fiji. Bulletin No. 15.

BARTHOLOMEW, R.W. 1960. Geology of the Nandi Area, Western Viti Levu. Geological Survey Department, Suva, Fiji. Bulletin 7.

BEGG, G.C. 1996. Genesis of the Emperor Gold Deposit, Fiji: PhD thesis, Monash University (unpubl.).

COLLEY, H. and FLINT, D.J. 1995. Metallic Mineral Deposits of Fiji. Fiji Mineral Resources Division Memoir 4.

DEER, W.A, HOWIE, R.A, and ZUSSMAN, J. 1982. An Introduction to the Rock-Forming Minerals. Longman Group Limited. England.

DICKINSON, W.R. 1968. Sedimentation of Volcaniclastic Strata on the Pliocene Koroimavua Group in Northwest Viti Levu, Fiji. American Journal of Science 266, 440-453.

DICKINSON, W.R., RICKARD, M.J., COULSON, F.I., SMITH, J.G. and LAWRENCE, R.L. 1968. Late Caenozoic Shoshonitic Lavas in North-western Viti Levu, Fiji. Nature 219, 148.

ELE INTERNATIONAL. 2003. Point Load Test Apparatus 77-0110. Operating Instructions.

GILL, J.B. and MCDOUGALL I. 1973. Biostratigraphic and Geological Significance of Miocene-Pliocene Volcanism in Fiji. Nature 241, 176-180.

HATHWAY, B. 1993. The Nadi Basin: Neocene strike-slip faulting and sedimentation in a fragmented arc, western Viti Levu, Fiji. Journal of the Geological Society of London 150, 563-581.

HATHWAY, B. 1994. Sedimentation and Volcanism in an Oligocene-Miocene intra oceanic arc and fore-arc, southwestern Viti Levu, Fiji. Journal of the Geological Society of London 151, 499-514.

HOUTZ, R.E. 1959. Regional Geology of Lomawai-Momi, Nadroga, Viti Levu. Geological Survey Department, Suva, Fiji. Bulletin 3.

KERR, P.F. 1977. Optical Mineralogy (4th Edition). The Southeast Book Company and McGraw-Hill International Book Company. Taiwan.

MAHARAJ, R.J. 1999. Engineering Geological Assessment of Onshore Aggregate Potential, Pohnpei Island, Federated States of Micronesia (FSM). SOPAC Technical Report 301.

MCPHIE, J. 1995. A Pliocene shoaling basaltic seamount: Ba Volcanic Group at Rakiraki, Fiji. Journal of Volcanology and Geothermal Research 64, 193-210.

RAHIMAN, T. 2001. Semo Quarry Site Investigation. Mineral Resources Department Note BP79/14 (unpubl.).


RODDA, P. 1993. Geology of Fiji. In Stevenson A. J., Herzer R. H. and Ballance P. F. eds. Contributions to the Marine and On-land Geology and Resource Assessment of the Tonga-Lau-Fiji Region. SOPAC Technical Bulletin 8.

SETTERFIELD, T.N., EATON, P.C., ROSE, W.J. and SPARKS, R.S.J. 1991. The Tavua Caldera, Fiji: a complex shoshonitic caldera formed by concurrent faulting and downsagging. Journal of the Geochemical Society of London 148, 115-127.

SINCLAIR KNIGHT MERZ. 2003. Semo Quarry Quantities – Topo Survey. Preliminary Report issued for Information (unpubl.).

SMITH, M.R. AND COLLIS, L. 1993. Aggregates. Sand, gravel and crushed rock aggregates for construction purposes (2nd Edition). Geological Society Engineering Geology Special Publication No. 9. Imperial College of Science, Technology and Medicine, London.

TAWAKE, A. 2004. Fiji – Country Mission Report, 14th – 30th January 2004. SOPAC-EU Project Report No. ER0025.

USER GUIDE. 2001. Mechanical Concrete Test Hammer. ASTM C 805.

WAQA, I.R. 2004. Geological and Geo-technical Characterisation of Aggregate Source Rocks from Selected Sites in Viti Levu Fiji. M.Sc. thesis, University of Canterbury (unpubl.).

WEDEKIND, M.R. 1984. The Korovisilou and Wainirevo Stocks, Southern Viti Levu, Fiji. B.Sc (Hon) thesis, Victoria University of Wellington (unpubl.).


APPENDIX 1

ROCK STRENGTH TEST RESULTS USING A SCHMIDT ROCK CLASSIFICATION HAMMER

A) Strength test at normal temperature and pressure

Rebound Reading Rock ID 1st 2nd 3rd Ave Rock Description

Sabeto Volcanics 32 34 35.2 33.73 Slightly weathered and partially fracturagglomeratic breccia

Semo Volcanics (Ridge) 62 63.2 64 63.07 Fresh basaltic flow with minor volcanic fragmenin groundmass

Raraikoro Limestone 55.5 55.3 50 53.60 Compact, recrystalised limestone (low-gramarble)

Tau Limestone 40.8 43.7 44 42.83 Porous, powdery limestone Korovisilou Gabbro 55.7 56 57.8 56.50 Fresh, crystalline rock. Partially fractured

Vuda Shoshonite 62.6 63.4 64 63.33 Fresh rock with euhedral olivine-augite crystalsground mass

Semo Gabbro 64 65 64 64.33 Medium-grained, holocrystalline rock Semo Volcanics (Creek) 58 58 59 58.33 Volcanic breccia unit with minor grits

Vuda Agglomeratic Breccia 48 50.2 47.8 48.67 Predominantly basaltic breccia with minor largfragments

Nawainiu Monzonite 56 57.8 58.3 57.37 Fresh, greyish holocrystalline rock Korovisilou Basaltic Dyke 50 52 46.6 49.53 Fine-grained porphritic basalt

Saru Shoshonite 45.7 38.3 49.8 44.60 Partially fractured with euhedral olivine-augcrystals

B) Strength Test after drying at 110°C for 48 hours

Rebound Reading Rock ID 1st 2nd 3rd Ave

Sabeto Volcanics 29.2 31.4 36 32.20 Semo Volcanics (Ridge) 65.8 66.2 66 66.00 Raraikoro Limestone 55.2 56 54.6 55.27 Tau Limestone 42.4 46.8 42 43.73 Korovisilou Gabbro 62 62 61.6 61.87 Vuda Shoshonite 62.2 62.4 60.4 61.67 Semo Gabbro 64.8 65 66.2 65.33 Semo Volcanics (Creek) 57.8 57.6 57.6 57.67 Vuda Agglomeratic Breccia 49.6 51.2 47.8 49.53 Nawainiu Monzonite 58.8 57 58.4 58.07 Korovisilou Basaltic Dyke 46 47.6 51.2 48.27 Saru Shoshonite 40 45.6 47.4 44.33


C) Strength test after soaking in water for 72 hours

Rebound Reading Rock ID 1st 2nd 3rd Ave

Sabeto Volcanics 28.8 22 26.5 25.77 Semo Volcanics (Ridge) 65.8 65.6 64.6 65.33 Raraikoro Limestone 54.2 54.4 55.8 54.80 Tau Limestone 49.2 49.6 46.8 48.53 Korovisilou Gabbro 63.6 63.8 64.8 64.07 Vuda Shoshonite 64 62 63.8 63.27 Semo Gabbro 64.6 64.2 64.2 64.33 Semo Volcanics (Creek) 57.6 57.4 59 58.00 Vuda Agglomeratic Breccia 52 46.6 49.2 49.27 Nawainiu Monzonite 55 55.8 54.2 55.00 Korovisilou Basaltic Dyke 54 49.6 46.8 50.13 Saru Shoshonite 40.4 45.8 44.2 43.47


APPENDIX 2

WATER CONTENT OF EACH ROCK SAMPLE

Rock ID Weight before drying (g)

Weight after drying (g)

Weight after soaking (g)

Water Content (g)

% Water Content

Sabeto Volcanics 692.00 681.90 718.8 36.90 5.33 Semo Volcanics (Ridge) 1219.90 1218.50 1219.3 0.80 0.07 Raraikoro Limestone 1152.10 1150.80 1157.2 6.40 0.56 Tau Limestone 1202.90 1201.70 1233.4 31.70 2.64 Korovisilou Gabbro 1455.30 1453.80 1455.4 1.60 0.11 Vuda Shoshonite 1250.30 1248.90 1249.7 0.80 0.06 Semo Gabbro 1362.40 1360.50 1362.8 2.30 0.17 Semo Volcanics (Creek) 1265.30 1261.50 1265.1 3.60 0.28 Vuda Agglomeratic Breccia 1286.00 1280.10 1299.1 19.00 1.48 Nawainiu Monzonite 1319.10 1314.40 1324.9 10.50 0.80 Korovisilou Basaltic Dyke 816.20 812.50 824.6 12.10 1.48 Saru Shoshonite 1354.20 1349.00 1355.1 6.10 0.45


APPENDIX 3

ROCK DENSITIES BEFORE DRYING, AFTER DRYING AND AFTER SOAKING IN WATER

A. Density before drying

Rock ID Weight (g) Volume (cm3) Density (g/cm3) Sabeto Volcanics 692.00 340.00 2.04 Semo Volcanics (Ridge) 1219.90 500.00 2.44 Raraikoro Limestone 1152.10 460.00 2.50 Tau Limestone 1202.90 540.00 2.23 Korovisilou Gabbro 1455.30 530.00 2.75 Vuda Shoshonite 1250.30 460.00 2.72 Semo Gabbro 1362.40 500.00 2.72 Semo Volcanics (Creek) 1265.30 475.00 2.66 Vuda Agglomeratic Breccia 1286.00 535.00 2.40 Nawainiu Monzonite 1319.10 540.00 2.44 Korovisilou Basaltic Dyke 816.20 340.00 2.40 Saru Shoshonite 1354.20 530.00 2.56

B. Density after drying Rock ID Weight (g) Density (g/cm3)

Sabeto Volcanics 681.90 2.01 Semo Volcanics (Ridge) 1218.50 2.44 Raraikoro Limestone 1150.80 2.50 Tau Limestone 1201.70 2.23 Korovisilou Gabbro 1453.80 2.74 Vuda Shoshonite 1248.90 2.72 Semo Gabbro 1360.50 2.72 Semo Volcanics (Creek) 1261.50 2.66 Vuda Agglomeratic Breccia 1280.10 2.39 Nawainiu Monzonite 1314.40 2.43 Korovisilou Basaltic Dyke 812.50 2.39 Saru Shoshonite 1349.00 2.55

C. Density after soaking Rock ID Weight (g) Density (g/cm3)

Sabeto Volcanics 718.8 2.11 Semo Volcanics (Ridge) 1219.3 2.44 Raraikoro Limestone 1157.2 2.52 Tau Limestone 1233.4 2.28 Korovisilou Gabbro 1455.4 2.75 Vuda Shoshonite 1249.7 2.72 Semo Gabbro 1362.8 2.73 Semo Volcanics (Creek) 1265.1 2.66 Vuda Agglomeratic Breccia 1299.1 2.43 Nawainiu Monzonite 1324.9 2.45 Korovisilou Basaltic Dyke 824.6 2.43 Saru Shoshonite 1355.1 2.56


APPENDIX 4

SAMPLE DIMENSION AND STRENGTH TEST RESULTS USING A POINT LOAD TESTER

Rock ID Sample No. D (mm) W (mm) L (mm) P (kN) D2 (m2) P (MN) Is (MN/m2) Sabeto Volcanics 1 39.40 52.20 76.00 12.30 0.001552 0.0123 7.92

" 2 44.20 57.80 59.80 8.80 0.001954 0.0088 4.50 Semo Volcanics (Ridge) 1 35.20 74.80 76.20 23.40 0.001239 0.0234 18.89

" 2 36.50 72.80 77.50 19.50 0.001332 0.0195 14.64 Raraikoro Limestone 1 35.00 65.50 75.80 11.60 0.001225 0.0116 9.47

" 2 36.10 65.20 75.80 10.70 0.001303 0.0107 8.21 Tau Limestone 1 37.40 70.60 77.10 8.40 0.001399 0.0084 6.01

" 2 37.30 77.60 77.00 6.90 0.001391 0.0069 4.96 Korovisilou Gabbro 1 36.70 76.30 80.20 40.10 0.001347 0.0401 29.77

" 2 20.20 70.80 80.60 20.20 0.000408 0.0202 49.50 Vuda Shoshonite 1 37.10 75.30 75.80 38.60 0.001376 0.0386 28.04

" 2 36.40 74.00 74.50 36.40 0.001325 0.0364 27.47 Semo Gabbro 1 33.20 67.20 75.30 34.20 0.001102 0.0342 31.03

" 2 42.00 39.50 75.00 37.70 0.001764 0.0377 21.37 Semo Volcanics (Creeks) 1 37.00 59.60 67.00 13.70 0.001369 0.0137 10.01

" 2 34.90 59.10 66.80 15.60 0.001218 0.0156 12.81 Vuda Agglomeratic Breccia 1 35.60 71.20 76.20 22.40 0.001267 0.0224 17.67

" 2 36.50 71.50 76.30 23.70 0.001332 0.0237 17.79 Nawainiu Monzonite 1 38.30 67.20 75.00 31.20 0.001467 0.0312 21.27

" 2 34.30 66.10 73.50 26.60 0.001176 0.0266 22.61 Korovisilou Basalt Dyke 1 38.80 54.00 63.40 26.60 0.001505 0.0266 17.67

" 2 32.20 62.50 64.30 20.90 0.001037 0.0209 20.16 Saru Shoshonite 1 34.20 72.40 75.90 28.30 0.001170 0.0283 24.20

" 2 31.30 76.60 73.30 27.10 0.000980 0.0271 27.66


APPENDIX 5

NOMOGRAM FOR COMPUTING POINT LOAD STRENGTH AND STRENGTH DESIGNATION (FROM ELE INTERNATIONAL, 2003)


APPENDIX 6

PETROGRAPHIC DESCRIPTION OF SELECTED AGGREGATE SOURCE IN SOUTH AND WESTERN VITI LEVU

1. PETROGRAPHIC DESCRIPTION – Raraikoro Limestone

PROJECT. SOPAC-EU EDF8 FJ0104

THIN SECTION NO. 3 COUNTRY. Fiji

FIELD NAME. Limestone LOCALITY. Western Viti Levu

OCCURRENCE. Recrystallised Raised Coral Reef LATITUDE. S 17° 42’ 23.34”

FIELD RELATIONS. Part of the Early Miocene LONGITUDE. E 177° 32’ 34.08” raised limestone (a member of the Wainimala Group)

ROCK NAME. Raraikoro Limestone

HAND SPECIMEN. White, very fine grained, hard and compact recrystallised limestone.

GENERAL DESCRIPTION. Appears pale white, grey to green under both plane and cross-polarised light.

Fine grained green, grey patches occupy about 90 % of the groundmass. Fossilised shells and marine micro-organisms are common in the groundmass.

DETAILED DESCRIPTION. Calcite: occurs as pale white, grey, green groundmass. Appears like subrounded

breccia clasts of variable sizes in some places. The entire groundmass is non-pleochroic, confirming the presence of Calcium Carbonate. Calcite is the only major constituent in this re-crystallised limestone.

Opaque: No opaque mineral is present in the groundmass.

APPROXIMATE COMPOSITION

Calcite Aragonite Dolomite Qtz Plag Alk. Fsp Opaq Total % 100 100 Size (mm) Alteration

TEXTURE. Bioclastic

GROUNDMASS. Plane white, pale yellow-green, green, very fine grained.

ACCESSORIES. None

ALTERATION. None

REMARKS. In the process of limestone re-crystallisation, aragonite must have been converted to calcite. At normal temperature and pressure aragonite is metastable and inverts to calcite fairly quickly (Deer et al. 1982).

Calcite is uniaxial and optically negative (Deer et al. 1982).

CHEMICAL ANALYSIS. AGE. Early Miocene??

PETROLOGIST. A. Tawake DATE. 24/11/04


2. PETROGRAPHIC DESCRIPTION – Tau Limestone



FIELD NAME. Limestone LOCALITY. South western Viti Levu

OCCURRENCE. Recrystallised Raised Coral Reef LATITUDE. S 17° 58’ 32.16”

FIELD RELATIONS. Part of the Early Miocene LONGITUDE. E 177° 17’ 09.06” raised limestone (a member of the Wainimala Group)

ROCK NAME. Tau Limestone

HAND SPECIMEN. White, porous powdery recrystallised limestone. Moderately strong.

GENERAL DESCRIPTION. Appeared as pale white, grey to pale green and fine grained under both plane

and cross-polarised light. Shells and marine micro-organism fossils are common in the groundmass.

DETAILED DESCRIPTION. Calcite: occurs as fine-grained pale white, grey, green in the groundmass.

Generally anhedral and non-pleochroic. Breccia-like structures are observed in some places. Calcium carbonate is the only major constituent in re-crystallised limestone.

Dolomite: occurs with calcite but rarely observed in the groundmass. Showing the characteristic green, pale green, yellow, brown pleochroism with the non-pleochroic calcite background. The presence of yellow, brown colour indicates the presence of iron in small amount.


Calcite Aragonite Dolomite Plag Alk. Fsp Opaq Chlorite Total % 95 4 1 100 Size (mm) Alteration

TEXTURE. Bioclastic

GROUNDMASS. Plane white, grey, green, very fine grained.

ACCESSORIES. Chlorite

Limonite

ALTERATION. none

REMARKS. Calcite is uniaxial and optically negative. Most minerals in the calcite group has no distinct optical properties of their own.

CHEMICAL ANALYSIS. AGE. Early Miocene



3. PETROGRAPHIC DESCRIPTION – Korovisilou Diorite



FIELD NAME. Wainirevo Stock LOCALITY. Mid-Southern Viti Levu

OCCURRENCE. Diorite Intrusion LATITUDE. S 18° 14’44.66”

FIELD RELATIONS. Belongs to the Colo Plutonic Suite, LONGITUDE. E 177° 53” 38.22” intruding Nubuonaboto Volcanic

Conglomerate (a member of the Wainimala Group).

ROCK NAME. Korovisilou Diorite

HAND SPECIMEN. Fresh, medium grained and crystalline rock. Partially fractured.

GENERAL DESCRIPTION. Interlocking crystal structures with clots of mafic and felsic minerals in

groundmass. Plagioclase-rich. Crystals are generally subhedral to anhedral.

DETAILED DESCRIPTION. Plagioclase: occurs mainly as interlocking laths in groundmass. Pale white to pale

green in colour. Generally subhedral to anhedral with rare sericitisation. Crystal sizes range between 0.5 – 2 mm. Simple and multiple twins are common and mostly observed in subhedral crystals.

Hornblende: occurs as interlocking subhedral to anhedral crystals. Crystal sizes are mostly between 1 – 3 mm. Some rounded inclusions of plagioclase and opaques are included within the hornblende. Contains occasional interstitial quartz.

Augite: represents a minor component in the groundmass. Occurs as laths interlocking with other crystal grains. Generally subhedral to anhedral.

Alkali Feldspar: occurs as 0.5 – 2 mm laths in groundmass, generally subhedral to anhedral. Simple and multiple twins are visible. Represents an insignificant component of the rock.

Opaques: occurs predominantly as fill between crystal grains and in anhedral form. Irregular crystals according to the shape of the space, which they occupy.


O/Pyrox C/Pyrox Horn. Plag Qtz Alk. Fsp Opaq Apat Calc Total

% 10 24 54 3 2 6 1 100 Size (mm) 0.5 - 1 1 - 3 0.5 - 2 0.3 - 1 0.5 - 2 Alteration sericite

TEXTURE. Holo-crystalline

GROUNDMASS. medium grained, crystalline

ACCESSORIES. feldspar, calcite.

ALTERATION. plagioclase – slightly sericitised

REMARKS. Mineral composition is similar to the one given in Wedekind (1984).

CHEMICAL ANALYSIS. AGE. Late Miocene PETROLOGIST. A. Tawake DATE. 2/12/04


4. PETROGRAPHIC DESCRIPTION – Vuda Shoshonite



FIELD NAME. Saru Shoshonite LOCALITY. Western Viti Levu

OCCURRENCE. Shoshonite Lava Flow LATITUDE. S 17° 40’ 32.34”

FIELD RELATIONS. Belongs to the Ba Volcanic Group, LONGITUDE. E 177° 26’ 02.94” hosted in sediments and breccias

(part of the Koroimavua Volcanic Group).

ROCK NAME. Vuda Shoshonite

HAND SPECIMEN. Fresh, compact, fine grained groundmass with significant amount of medium to

large crystals of olivine and augite.

GENERAL DESCRIPTION. Fine grained groundmass with large phenocrysts of olivine and augite. Euhedral plagioclase crystals are also common.

DETAILED DESCRIPTION. Plagioclase: occurs mainly as phenocrysts with well developed twinning.

Generally euhedral to subhedral with size between 0.3 and 2 mm. Weak sericite alteration is obvious around the edges.

Olivine: Large phenocrysts are common with size ranging from 1 to 4 mm. Hexagonal crystal shape is well preserved in most crystals. Phenocrysts in the groundmass are predominantly euhedral with iron staining observed along cleavage planes.

Augite: occurs as phenocrysts, which are 0.5 – 2 mm in dimension. Generally euhedral to subhedral. Moderately chloritised around the edges and cleavage planes.

Opaques: predominantly occurs as 0.3 – 1 mm subrounded to rounded phenocrysts in groundmass and as inclusions in olivine crystals.


Oliv O/Pyrox C/Pyrox Horn Plag Opaq Chlor Calc Total

% 30 15 46 6 2 1 100 Size (mm) 1-4 0.5 - 1 0.2 - 2 Alteration chlorite sericite

TEXTURE. Glomeroporphyritic

GROUNDMASS. Fine grained

ACCESSORIES. chlorite, calcite

ALTERATION. plagioclase – partially sericitised

Augite - chloritised

REMARKS. Oxidation has occurred in iron-bearing minerals

CHEMICAL ANALYSIS. AGE. Early Pliocene



5. PETROGRAPHIC DESCRIPTION – Semo Gabbro



FIELD NAME. Semo Gabbro LOCALITY. South western Viti Levu

OCCURRENCE. Gabbro Intrusion LATITUDE. S 18° 05’ 25.40”

FIELD RELATIONS. Belongs to the Colo Plutonic LONGITUDE. E 177° 23’ 04.74” Suite, intruding Sediments and

Volcanic Breccia (part of the Wainimala Group).

ROCK NAME. Semo Gabbro

HAND SPECIMEN. Fresh, medium grained Augite Gabbro with some calcite veinlets.

GENERAL DESCRIPTION. Plagioclase-rich rock with lesser amount of augite and olivine in groundmass.

Equigranular with crystals being generally euhedral to subhedral.

DETAILED DESCRIPTION. Plagioclase: occurs predominantly as phenocrysts with minor lathlike components. Pale white to green in colour. Generally subhedral to euhedral with minor occurrence of sericite along the edges and cleavage planes. Crystal sizes range between 0.5 – 2 mm. Twins rarely occur in this specimen.

Augite: occurs mainly as phenocrysts with 0.5 – 1 mm in dimension. Commonly displaying simple and multiple twinning. Generally subhedral to anhedral with weakly to moderately chloritised crystal edges.

Olivine: represents a minor component. Phenocrysts in the groundmass are predominantly euhedral to subhedral.

Opaques: occurs as phenocrysts in groundmass. Euhedral to subhedral with size range between about 0.2 and 1mm.


Oliv O/Pyrox C/Pyrox Horn Plag Opaq Chlor Apat Calc Total

% 5 20 58 8 5 2 2 100 Size (mm) 0.5 -1 0.5 - 1 0.5 - 2 Alteration chlorite sericite


GROUNDMASS. medium grained, crystalline, equigranular

ACCESSORIES. chlorite Apatite Calcite

ALTERATION. plagioclase – partially sericitised Augite - chloritised

REMARKS.

CHEMICAL ANALYSIS. AGE. Mid-Miocene



6. PETROGRAPHIC DESCRIPTION – Nawainiu Monzonite



FIELD NAME. Monzonite LOCALITY. Western Viti Levu

OCCURRENCE. Monzonite Intrusion LATITUDE. S 17° 42’ 56.70”

FIELD RELATIONS. Belongs to the Nawainiu Monzonite LONGITUDE. E 177° 31’ 41.46” Stock, intruding the Nadele Breccia

(a member of the Wainimala Group) and the Nadi Sedimentary Group.

ROCK NAME. Nawainiu Monzonite

HAND SPECIMEN. Fresh, compact, medium grained crystalline rock. Large, euhedral hornblende

crystals can be identified with the naked eye.

GENERAL DESCRIPTION. Predominantly medium grained with variable amounts of felsic and mafic minerals in groundmass. Feldspars dominate over hornblende and biotite.

DETAILED DESCRIPTION. Plagioclase: occurs as phenocrysts and laths in groundmass, commonly in 0.5 –

2 mm. Generally euhedral to subhedral with well developed twinning and zoning. Zoning are common in subhedral crystals with combinations of discontinuous and oscillatory zoning. Sericite occurs along edges and cleavage planes.

Alkali Feldspar: occurs as phenocrysts and laths in groundmass, commonly in 0.5 – 2 mm. Generally euhedral to subhedral with well developed twinning and zoning. Weak sericitisation on the edges.

Hornblende: Elongated phenocrysts and laths occur in groundmass with size ranging from 0.5 to 2 mm. Generally euhedral to subhedral with well-developed simple and multiple twinning. Parallel striations are observed in the direction of elongation.

Biotite: occurs as a minor component in groundmass, exhibiting its typical Fe-rich brown colour. Fine grained, generally euhedral to subhedral with maximum size of 1 mm.

Opaques: occurs in various shapes and sizes, commonly less than 1 mm. Some have well-developed twins.


C/Pyrox Horn Biot Plag Alk. Fsp Opaq Qtz Apat Calc Total

% 18 8 40 20 9 2 2 1 100 Size (mm) 0.5 – 2 <1 0.3 - 2 0.3 - 2 Alteration sericite sericite


GROUNDMASS. Medium grained, crystalline, equigranular

ACCESSORIES. Quartz, apatite, calcite

ALTERATION. Plagioclase and alkali feldspar – partially sericitised

REMARKS. Field survey has revealed three different monzonite in this area: an inner fine grained

augite-biotite micro-monzonite; a medium- to coarse-grained biotite-hornblende monzonite and a pegmatitic hornblende monzonite.

CHEMICAL ANALYSIS. AGE. Early Pliocene PETROLOGIST. A. Tawake DATE. 24/11/04


7. PETROGRAPHIC DESCRIPTION – Korovisilou Basalt Dyke



FIELD NAME. Basalt Dyke LOCALITY. Mid-Southern Viti Levu

OCCURRENCE. Dyke intruding diorite LATITUDE. S 18° 14’ 45.02”

FIELD RELATIONS. Belongs to the late stage dyke LONGITUDE. E 177° 53’ 37.86” swarm that intrudes the Gabbro

and Diorite (both are members of the Colo Plutonic Suite).

ROCK NAME. Korovisilou Basalt Dyke

HAND SPECIMEN. Fresh, fine-grained porphyritic rock.

GENERAL DESCRIPTION. Crystalline, fine-grained groundmass. Crystals generally occur in anhedral form.

DETAILED DESCRIPTION. Plagioclase: occurs mainly as laths in groundmass in pale white to pale green

colour. Generally subhedral to anhedral with grain sizes range between 1 and <1 mm. Cleavages are parallel to elongation. Oscillatory zoning is rare. Slightly sericitised and chloritised around the edges.

Hornblende: mainly occurs as phenocrysts in groundmass. Generally anhedral with less than 1 mm in length. Characteristic green, greenish-blue, brown, yellowish-green colour were alternately displayed on rotation under cross-polarised light.

Biotite: Rare, poorly developed 6-sided biotite phenocrysts in groundmass. 0.5 mm in diameter.

Calcite: occurs as phenocrysts. General anhedral with grain size not exceeding 1.5 mm. Crystals showing perfect rhombohedral cleavage. Appears to be filling amygdales in some places. Weak chlorite alteration around the edges.

Opaques: scattered all over the groundmass. Generally subhedral to anhedral, which are less than 0.5 mm in size.


C/Pyrox Horn. Plag Qtz Biot. Opaq Chlor Calc Total

% 30 43 5 13 1 8 100 Size (mm) <1 1 - <1 0.5 1.5 – 0.5 Alteration sericite chlorite

TEXTURE. Porphyritic

GROUNDMASS. Fine-grained, equigranular

ACCESSORIES. Chlorite, calcite.

ALTERATION. Plagioclase – slightly sericitised and chloritised

Calcite – weak chlorite alteration

REMARKS. This dyke description is closest to the Plagioclase Porphyrite Dyke in Wedekind (1984).

CHEMICAL ANALYSIS. AGE. Late Miocene



8. PETROGRAPHIC DESCRIPTION – Saru Shoshonite



FIELD NAME. Saru Shoshonite LOCALITY. Western Viti Levu

OCCURRENCE. Shoshonitic Lava Flow LATITUDE. S 17° 39’ 50.16”

FIELD RELATIONS. Belongs to the Ba Volcanic Group, LONGITUDE. E 177° 28’ 42.36” hosted in sediments and breccias

(part of the Koroimavua Volcanic Group).

ROCK NAME. Saru Shoshonite

HAND SPECIMEN. Partially fractured and slightly weathered along fracture plane. Compact, fine

grained groundmass with significant amount of medium to large crystals of olivine and augite.

GENERAL DESCRIPTION. Fine grained groundmass with large phenocrysts of olivine and augite. Euhedral

plagioclase crystals are also common.

DETAILED DESCRIPTION. Plagioclase: occurs as phenocrysts and laths in groundmass. Generally euhedral to subhedral, and well developed twins are common. Crystals are between 0.3 and 2 mm. Some crystals occur in two orientation at 90˚ to one another with weak sericite alteration.

Olivine: Large phenocrysts are common with size ranging from 1 to 3 mm. Hexagonal crystal shape is well preserved in most crystals. Crystals in the groundmass are predominantly euhedral with iron staining observed along cleavage planes.

Augite: occurs as a minor component in groundmass, which are 0.5 – 1 mm in dimension. Generally euhedral to subhedral. Weak to moderately chloritised crystal edges and cleavage planes.

Opaques: predominantly occurs as 0.3 – 1 mm subrounded to rounded phenocrysts in groundmass and as inclusions in olivine crystals.


Oliv O/Pyrox C/Pyrox Horn Plag Opaq Chlor Calc Total

% 28 12 48 10 2 Size (mm) 1 - 4 0.5 - 1 0.3 - 2 Alteration chlorite sericite

TEXTURE. Glomeroporphyritic

GROUNDMASS. fine grained

ACCESSORIES. chlorite

ALTERATION. plagioclase – partially sericitised

Augite – weakly chloritised

REMARKS. Oxidation has occurred in iron-bearing minerals

CHEMICAL ANALYSIS. AGE. Early Pliocene


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