Sedimentology and Geochemistry of the REE-bearing placer

deposits in the Kualakurun area, Central Kalimantan

Billy G. Adhiperdana, ST., M.Si. NIP: 197111301999031002

Faculty of Geology UNIVERSITAS PADJADJARAN

November 2018

Summary

This report contains an outline of preliminary exploration results on mineral-bearing alluvial in Kualakurun area, Central Kalimantan, Indonesia. The results from core drilling, geological fieldwork and geochemical-laboratory examination will be describe in this report. Local mining and abandoned tailing became an important issue in this exploration activity. Distribution of local mining has been roughly delineated during alluvial and bedrock mapping. From total IUP area (18.127 km2), 23% of them are local mining areas (± 4.165 km2). The other 44% (±8.12 km2) in the western portion are covered by bedrocks and weathered bedrocks (Appendix E). Samples were analyzed to standard laboratory procedures at the PT Intertek Laboratory in Jakarta. Sample testing in the laboratory to include several methods of inductive-coupled plasma analysis (ICP-MS, ICP-OES), and fire assay technique. On average, the borehole reached measured total depth of 5.1 m on average. The alluvial-terrace deposits can be divided into two major facies associations, from the bottom to top: 1) Facies B, gravel and coarsed-sand deposits; and 2) Facies A, fine-grained-sand/sand-dominated deposits. In this investigation, Au (ppm) is a proxy for gold, Zr (ppm) is a proxy for zircon mineral, whereas the abundance of REE (REE) is a proxy for REE-bearing minerals such as monazite and xenotime. Detrital composition of the alluvial consists largely of various types of quartz grains, fine-grained feldspar in very small quantity, and heavy minerals. Rutile, ilmenite, zircon, garnet, iron-oxide (hematite), and opaque minerals were evidently observed by using a hand lens. A total of 61 elements were obtained from the laboratory test. These elements can be grouped into seven groups, arranged in decreasing order: 1) Transition metal, 2) Rare-earth elements/REE, 3) Alkaline-earth metal, 4) Alkali metal, 5) Metaloid/semi metal s, 6) Non-metal, and 7) Actinide-transition metal. Test result from laboratory indicate that Au (ppm) in the sample was found in very small quantities (maximum Au 0.305 ppm, g/ton). In total, concentration of Au (ppm) which was obtained from seven drill-core locations is varied in the range between 0.015–0.225 ppm (g/ton). The verage concentration of Au (ppm) is 0.042 ppm (g/ton). It can be concluded that the gold in the exploration area has low economic potential to be developed. The maximum concentration of Zr which was obtained from the Kualakurun samples is less than 100 ppm (g/ton). It can be concluded the Zr concentration in the alluvial deposits of Kualakurun has low economic potential to be developed. The REE concentration found in the samples taken at the Kualakurun are lower than the values determined for the known high-grade REE deposits, thus are considered to be low potential REE deposit. In conclusion, the grade of gold (Au), zircon (Zr) and REE in alluvial placer of the Kualakurun area are too small and low to be developed in today's economic condition. So it is not recommended for further investigation at this time.

i

Table of Contents

Page

Amendment

Summary

Table of contents ......................................................................................................... i

Introduction ................................................................................................................. 1

Methods ........................................................................................................................ 2

Geological setting ........................................................................................................ 3

Alluvial-terrace deposits ............................................................................................. 4

Elemental variation (test result) ................................................................................. 5

Gold (Au) deposit ........................................................................................................ 5

Zircon (Zr) deposit ...................................................................................................... 7

Rare earth (REE) deposit ........................................................................................... 7

Conclusions and recommendations ........................................................................... 8

References .................................................................................................................... 28

Figures

Figure 1. Simplified geographical map shows the exploration area. .......................... 10

Figure 2. Physiographic outline of the Kalimantan. ................................................... 11

Figure 3. Simplified geological map, modified after several authors. ....................... 12

Figure 4. Deposits analogue for Quaternary-alluvial exploration. ............................. 13

Figure 5. Variation diagram of the seven elemental groupes. .................................... 15

Figure 6. Variation plot of the gold signature elements. ............................................ 16

Figure 7. Bivariate plot of indicator elements for gold Au vs. Cu. ............................ 17

Figure 8. Zr/Hf plot and Plot of Th/Sc vs. Zr/Sc (McLennan, 1993). ........................ 18

Figure 9. Zr and associative elements plot in the variation diagram. ......................... 19

Figure 10. The REE concentration of the Kualakurun alluvial. ................................... 22

Figure 11. REE chondrite-normalized plot (Floyd, 1991). .......................................... 23

Figure 12. Facies-based REE chondrite-normalized plot (Floyd, 1991). ..................... 24

Figure 13. REE (ppm) comparison diagram from the Kualakurun. ............................. 25

ii

Figure 14. REE (UCC-normalized) comparison diagram (McLennan, 2001). ............ 26

Figure 15. La/Th vs. Th/Yb plot for igneous discrimination. ...................................... 27

Tables

Table 1. Summarized elemental concentration. ........................................................ 14

Table 2. REE (ppm) comparison diagram from the Kualakurun. ............................. 20

Table 3. Summarized grades of gold (Au), zircon (Zr) and total REE. .................... 21

Appendices (Enclosure)

Appendix A. Geographic-accessibility map of the exploration area.

Appendix B. Topographic map of the exploration area, generated from Digital Grid

Elevation map.

Appendix C. Regional geology of the exploration area, adapted after the Indonesian

GRDC map of 1;250,000.

Appendix D. Proposed and actual drill hole location, and channel sampling location.

Appendix E. Thickness distribution of the alluvial deposits in the Kualakurun area.

Appendix F. Lithologic log of the drill core and channel samples.

Appendix G. Intertek's Laboratory-test result.

Appendix H. Photographs of exploration activities, outcrops, and abandoned local

mines.

Appendix I. Photographs of drilling equipments.

1

Preliminary Exploration Results for Gold, Zircon and REE-Bearing Placer at the Kualakurun Area,

Central Kalimantan Indonesia

Introduction

This report contains an outline of preliminary exploration results on mineral-bearing

alluvial in Kualakurun area, Central Kalimantan, Indonesia. The results from core

drilling, geological fieldwork and geochemical-laboratory examination will be describe

in this report (see Appendix A–I). Data analysis which have relevance to the potential of

mineral deposits in the alluvial sediments which have been investigated will be

summarized as well.

This preliminary exploration in the Kualakurun IUP area is intended to: 1) describe the

mineral-bearing placer, alluvial-terrace deposits at the Kualakurun, Kahayan sub-basin,

2) summarize the provenance and stratigraphy of these deposits, and 3) summarize the

economic mineral potential (gold, zircon and REE) of the Kualakurun area (IUP

exploration area).

Some parts of the Kalimantan areas, for example, Barito basin, Kahayan basin,

Mahakam dan Kapuas basins have been known for a long time as regions of the

Quaternary-alluvial pacers which produce important economic mineral resources, gold,

diamond and rare-earth minerals (e.g. Watters et al., 1991; de Keyser and Noya-Sinay,

1992; Seeley and Sendedn, 1994; Abidin, 1998; Herman, 2007; Lolon and Rahman,

2015).

The Kualakurun areas which is situated in western portion of the Kahayan basin (Figure

1 and 3), thus is likely has the same potential for gold and other economic minerals

which are associated with the Quaternary-alluvial placer.

The exploration area at Kualakurun area is classified into lowland-morphologic setting

under the perhumid climatic condition in equator which is also occupied by the tropical-

lowland rain-forest area (Thorp et al., 1990; Thorp and Thomas, 1992). This climate

condition provide important effects on rock weathering in these regions. Topographic

2

elevation in the exploration area ranges between 34–112 m above mean sea level

(Appendix B).

Local mining, excavation and abandoned tailing materials became an important issue in

this exploration activity (Appendix E and H). Illegal mining are common and obvious in

the Kualakurun. Abandoned and active local mining are very extensive within the IUP

exploration area. This illegal mining have been operated by local people or locals who

cooperate with domestic investors since early 1990's (anonymous, pers. comm.).

Distribution of local mining has been roughly delineated during alluvial and bedrock

mapping. From total IUP area (18.127 km2), 23% of them are local mining areas (±

4.165 km2). The other 44% (±8.12 km2) in the western portion are covered by bedrocks

and weathered bedrocks (Appendix E).

Methods

Samples were collected from channel sampling at the surface and from drill cores

(Appendix F and H). Cores and channel samples were prepared and analyzed to

standard laboratory procedures at the PT Intertek Laboratory in Jakarta. Examination

methods and limitations were enclosed in this report on appendix (Appendix G). Sample

testing in the laboratory to include several methods of inductive-coupled plasma

analysis (ICP-MS, ICP-OES), and fire assay technique.

The total number of drilled boreholes are 18 drill holes. On average, the borehole

reached measured total depth of 5.1 m on average (below the surface). In most cases,

the drill pipes were stuck in more than 5 m depths, and it took a long time to remove the

pipes. The drilling machine (Appendix I) might not be suitable for full-core drilling in

loose and unlithified sediments.

Technical-drilling problems were some times encountered during core drilling in loose

and unconsolidated alluvial deposits, it was almost impossible to obtain 100% core

recovery (Appendix F and H). The average core percentage recovery is 54%. One bore

hole (DH-GMO-005) experienced a total loss (CR = 0%). For this reason, it was

decided to conduct channel sampling (e.g. Halloran, 2013; Haldar, 2013) to complement

borehole which have poor core recovery. In such case, a borehole was located above the

preserved alluvial behind the face of open cut exposure (Appendix H).

3

In addition to drilling, surface mapping was also conducted to delineate the distribution

of alluvial-terrace deposits. On the regional-scale geological map (Sumartadipura and

Margono, 1996) of Tewah (Kualakurun) which has been published by the GRDC, 90%

of the exploration area are covered by bedrock of the Mid-Miocene Warukin Formation.

More detail delineation of bedrock exposure and alluvial terrace were needed to get the

actual distribution of bedrock and surficial deposits in the exploration area (Appendix

E).

In general, potential of the economic-sand minerals are reported in percentage and

estimated based on the proportion of detrital compositon (Haldar, 2013; McLemore et

al., 2016). In this investigation, the laboratory examination of mineral concentration

were not based on the detrital analysis of mineral species, but based on chemical

(elemental) analysis of bulk-sediment samples. In this investigation, Au (ppm) is a

proxy for gold, Zr (ppm) is a proxy for zircon mineral, whereas the abundance of REE

(REE) is a proxy for REE-bearing minerals such as monazite and xenotime.

Since ppm means parts per million (1/106), and ton (metric) equal to 106 grams, then 1

ppm equal to 1 g/ton. Therefore, grade unit g/ton is put together beside the ppm unit

when it is needed in the report.

Geological setting

According to the regional stratigraphic framework, the Kualakurun area is characterized

by the presence of the two bedrock units and widely distributed surficial deposits of

alluvial origin (Sumartadipura and Margono, 1996). The bedrock units are classified

into the Mid-Miocene Warukin Formation and the Miocene─Pliocene Dahor Formation.

In some locations, an outcrop of the Mid-Miocene Warukin Formation have been found.

These bedrock exposures were outcropped at in the roadcut at the western part of the

exploration area (photographs on Appendix H). Bedrocks of the Warukin and Dahor

Formation were also exposed as outcrop windows in several shallow local mining's

excavation. Most of the western part of the exploration area are covered by the

podzolized deposits, which are the product of extensive bedrock weathering. Alluvial

terrace deposits are commonly absent in these area. Podzols from weathered bedrock

are mainly consist of angular-quartz sands, fine to medium sized-sand with typical

4

thick-oxidized whitish-yellow and brownish–reddish clay covers. Extensive

podzolisation are very common in the perhumid climate such in Kalimantan which is

situated in equator under the tropical-climate condition (Thorp et al., 1990; Thorp and

Thomas, 1992).

Sedimentary-alluvial terraces have been widely identified in the areas of Kalimantan.

Many previous workes have divided this terraces into Old and Young Alluvium. Many

economic-mineral deposits were commonly associated with these various facies types of

the Young-alluvium deposits (Figure 4). These sediments were deposited during low sea

level in response to the last major glacial period (Thorp et al., 1990; Thorp and Thomas,

1992, Seeley and Senden, 1994).

In the regional physiographic setting (Figure 2–3), the exploration area is situated in

transitional area between southern boundaries of the Mueler mountains and northern

boundaries of the foothills and lowland of South Kalimantan (Darman, 2014). This

transition represent the proximal alluvial setting in terms of sedimentary provenance.

Alluvial-terrace deposits

The alluvial-terrace deposits can be divided into two major facies associations (Figure

4; Appendix F and H), from the bottom to top: 1) Facies B (gravel and coarsed-sand

deposits), and 2) Facies A (fine-grained-sand/sand-dominated deposits).

Facies B consists mainly of interbed gravel and very-coarsed sands with common

humicrete intercalation, plant remains, lenticular-thin clay and organic clay layers.

Facies B is unconformably underlain by bedrocks and/or residual weathering of

bedrocks. This basal gravels commonly pass upwards into sands with occasional silty

and clay lenses of the Facies A. Cut and fill-erosional structures were evidently

observed.

Facies A consists mainly of sand-dominated deposits, fine–medium sized sand grains,

gravels, organic clay and plant remains are observed locally. This facies is characterized

by gradual basal interval. However, sharp extensive humicrete were also found overlain

the Facies B.

Detrital composition of the Kualakurun-alluvials consists largely of various types of

quartz grains, range between sand to cobble, rock fragments, fine-grained feldspar in

5

very small quantity, and heavy minerals. Rutile, ilmenite, zircon, garnet, Iron-oxide

(hematite), and opaque minerals were evidently observed by using a hand lens.

Elemental variation (test result)

A total of 61 elements were obtained from the laboratory test (see Table 1; Figure 5;

Appendix G.). These elements can be grouped into seven groups, arranged in decreasing

order: 1) Transition metal, such as Au, Ti, Sn, and Zr (27 elements), 2) Rare-earth

elements/REE (14 elements, divided into LREE, and HREE; 5 and 9 elements

respectively), 3) Alkaline-earth metal such as Ba, Be and Sr (5 elements), 4) Alkali

metal such as K and Na (5 elements), 5) Metaloid/semi metal such as Ge and Sb (4

elements), 6) Non-metal (P, S and Se), 7) Actinide-transition metal (Th and U).

Relative elemental variation and abundances can be seen in the table and variation

diagram (Table 1 and Figure 5). This diagram indicates that transition metal is the group

with the highest concentration in the Kualakurun alluvial deposits (1–10%). Alkali

metal and Alkaline-earth metal are the group with the second highest concentration. The

most important elements in transition metal are Al, Ti, Fe, Mn and Zr (1–10%). The

most important REE are Ce, La and Nd (<0.01%), all of which are Light REE.

This diagram does not show particular concentration trend or association of elemental

groups with particular samples. They show an overall similar patterns with some

overlapping patterns.

Gold (Au) deposit

Although now, local people operates small-scale mining and excavation for gold in the

southern and eastern part of the Kualakurun IUP areas (Appendix H), but they get only

very small and erratic gold placer. The excavation and small-scale mining in search of

gold and zircon which were operated by local people have existed in Kualakurun area,

particularly around the river valley of Kahayan since the late eighties (local residents,

pers. comm.). At that time, such traditional mining were able to collect about 5–20 g of

fine gold for several days work in one location. According to them, gold has been more

difficult to discover in recent years, and its existence is very irregular.

6

Panning tryout for gold on preserved sediments which were taken from abandoned

opencut near drilling locations, was only produced concentrate of heavy minerals

without showing any indications of gold. The panning results only medium-sand

concentrate containing heavy minerals such as rutile, ilmenite, zircon, garnet and

tourmaline medium sized sand.

Test result from laboratory (fire assay method) indicate that Au (ppm) in the sample is

found in very small quantities (maximum Au 0.305 ppm, recovered in the second run

fire assay). In total, concentration of Au (ppm) which was obtained from seven drill-

core locations is varied in the range between 0.015–0.225 ppm (g/ton). The verage

concentration of Au (ppm) which was obtained from seven drill cores is 0.042 ppm

(g/ton) (Table 3; Appendix G).

Bivariate plot (Figure 7) of indicator elements for gold between Au (ppm) and Cu (ppm)

does not show a distinct positive correlation (Kravtsova et al., 2016). The correlation

coefficient between Au (ppm) and Cu (ppm) only gives the small value (r = 0.47), this

represent a weak association. The existence of Au (ppm) is generally associated with

gravel and coarsed-grain sediments of Facies B.

Together with the Au-Cu plot, another interpretation of the gold signature elements

(Figure 6) were also conducted with other associative elements such as Ag, Fe, Mn, S,

As, Pb, Ni, Zn, and Bi (Kravtsova et al., 2016). The element data was normalized to the

average upper-continental crust concentration (McLennan, 2001). The results do not

show any anomalous patterns of the samples that should be higher when there are

anomalies. Gold (Au) value indicates 64 times higher than the average crust

concentration. However, this concentration is not indication of an anomalous

concentration since the average gold concentration in the upper continental crust-value

of about 0.0018 ppm (g/ton) (McLennan, 2001). Moreover, the value of other elements

associated with Au do not indicate any anomalies, and most of them are much smaller

than the average concentration of upper-continental crust (UCC). It can be concluded

based on the Au concentration and the above associated-element analysis, that the gold

in the exploration area has low economic potential to be developed.

7

Zircon (Zr) deposit

Zr (ppm) is a proxy for zircon mineral, because Zr is mostly concentrated in zircon

mineral. Occurrence of zircon in the studied sediments is confirmed by Zr from

laboratory test and also was suggested by the Zr/Hf plot (Figure 8A) which indicates

linear positive correlation (r=0.97). Positively correlated Zr and Hf concentrations are

due to the presence of heavy minerals in the sediments, such as zircon (ZrSiO4),

ilmenite (TiO2, FeO, Fe2O3), or rutile (TiO2).

Zircon is generally occurred as small crystals, commonly associated with the later-

formed minerals, granite and in syenite (Belousova et al., 2002). For this reason, to see

the relative importance of zircon in the samples, thus Zr was plotted in the variation

diagram (UCC-normalized samples) together with its associated trace elements such as

Ti, Nb and Y which are commonly important in granite and syenite (Figure 9). This

diagram indicates there is no Zr anomaly in the samples, that the concentration of Zr is

much lower than the average upper-continental crust (<1 UCC normalized samples). It

may suggests that the provenance of the alluvial deposits in Kualakurun were not

exclusively derived from typical felsic-igneous rocks that rich in zircon (Figure 15). A

typical first-cycle sediment which are derived from granitoid provenance that contain

zircon will have concentration of Zr greater than 500 ppm (Belousova et al., 2002). The

maximum concentration of Zr which was obtained from the Kualakurun samples is less

than 100 ppm (g/ton). It can be concluded based on the Zr concentration in the alluvial

deposits of Kualakurun, that the detrital zircon in the exploration area has low economic

potential to be developed (Table 3).

Rare earth (REE) deposit

In general, the REE-bearing placers which have economic potential are characterized by

a large concentration of REE. Its element anomalies can be several times larger than the

average upper-continental crust (Castor and Hedrick, 2006; Atwood, 2012; Hellman and

Duncan, 2014; McLemore et al., 2016). For example, REE data from the Kualakurun

were compared (Table 2; Figure 10–11) with some known high-grade REE-bearing

placer deposits (e.g. JICA, 1993; Zech et al., 1994; Orris and Grauch, 2002; Shuterland

et al., 2013; Budiharyanto et al., 2015; McLemore et al., 2016), such as Bangka Island,

8

Mesaverde-USA, Bald Mountain-USA and alluvial-placer deposits in Thailand (Khlong

Nam Khao).

Compared to the fine samples of clay and silt which were originated from bedrock

weathering, the coarser sand and gravels of Facies A and Facies B (Figure 12–13) have

slightly lower REE concentrations (in both normalized to chondrite and to upper

continental crust/UCC). However, in chondrite-normalized plot (Floyd, 1991), the REE

concentrations shows an overall similar patterns with some overlapping patterns. This

may be due to the secondary accumulation processes during weathering and surface

processes. REEs are commonly in the form of positive hydrated ions, adsorbed on the

surface of clay minerals like kaolinite, halloysite and illite (e.g. Castor and Hedrick,

2006; Atwood, 2012).

REE values which are largely derived from felsic rocks are typically represented by

highly elevated LREE together with distinct negative Eu anomaly (e.g. Floyd, 1991;

McLennan et al., 1993). In contrast, chondrite-normalized REE from the Kualakurun

shows only slightly elevated LREE together with indistinct negative Eu anomaly. It may

suggests that the provenance of the alluvial deposits in Kualakurun were not exclusively

derived from typical felsic-igneous rocks (Figure 12).

The REE concentration found in the samples taken at the Kualakurun are lower than the

values determined for the known high-grade REE deposits (e.g. JICA, 1993; Zech et al.,

1994; Orris and Grauch, 2002; Shuterland et al., 2013; McLemore et al., 2016), thus are

considered to be low potential REE deposit (Table 2–3; Figure 10–11).

Conclusions and recommendations

Test result from laboratory (fire assay method) indicate that Au (ppm) in the sample is

found in very small quantities (maximum Au 0.305 ppm, recovered in the second run

fire assay). In total, concentration of Au (ppm) which was obtained from seven drill-

core locations is varied in the range between 0.015–0.225 ppm (g/ton). The verage

concentration of Au (ppm) which was obtained from seven drill cores is 0.042 ppm

(g/ton). It can be concluded based on the Au concentration and the above associated-

element analysis, that the gold in the exploration area has low economic potential to be

developed.

9

A typical first-cycle sediment which are derived from granitoid provenance that contain

zircon will have concentration of Zr greater than 500 ppm (Belousova et al., 2002). The

maximum concentration of Zr which was obtained from the Kualakurun samples is less

than 100 ppm. It can be concluded based on the Zr concentration in the alluvial deposits

of Kualakurun, that the detrital zircon in the exploration area has low economic

potential to be developed.

The REE concentration found in the samples taken at the Kualakurun are lower than the

values determined for the known high-grade REE deposits (e.g. JICA, 1993; Zech et al.,

1994; Orris and Grauch, 2002; Shuterland et al., 2013; McLemore et al., 2016), thus are

considered to be low potential REE deposit.

Estimated abundance (grade in ppm) of gold (Au in ppm), zircon (Zr in ppm) and REE

from the samples of the Kualakurun give a values much lower than in the other places

that have been known to have potential for economic minerals, gold and REE, such as

Australia, USA and Thailand (e.g. JICA, 1993; Zech et al., 1994; Shuterland et al.,

2013; McLemore et al., 2016). In conclusion, the grade of gold (Au), zircon (Zr) and

REE in alluvial placer of the Kualakurun area are too small and low to be developed in

today's economic condition (Table 3). So it is not recommended for further investigation

at this time.

The following is a tentative interpretation to explain why the alluvial-terrace deposits in

the exploration area has low potential in economic mineral accumulations. From the

provenance point of view, the transitional situation in the proximal alluvial between

source area and alluvial entry point, can be disadvantage for economic placer

accumulation. This particular area is interpreted as bypassing zone during extensive last

glacial period when progressive alluvial terrace were developed. Thus, the economic

mineral accumulation might be concentrated at the more medial–distal part of the

alluvial system to the south and southeast. In addition, the geochemical signatures and

data interpretation indicates that the source rock of detritus for the Kualakurun alluvial

have compositional diversity (Figure 15). This means that they were not entirely derived

from the felsic-igneous rock which were enriched in economic mineral concentrations.

10

Figure 1. Simplified geographical map shows the exploration area, represented by black-empty square, to the north of Palangkaraya, the capital city of Central Kalimantan. The north–south oriented stream is the Kahayan River.

11

Figure 2. Physiographic outline of the Kalimantan, modified after Darman (2014). Exploration area indicated by filled-black square, which is approximately situated in the transition area between arcuate mountains to the north and the flank of South–Southeast Kalimantan alluvial plains.

12

Figure 3. Simplified geological map, modified after several authors. Exploration area indicated by small white square. This map illustrates basinal setting for mineral-bearing Quaternary alluvial. Wide range of felsic, mafic, volcanics and metamorphic rocks characterizing the source area to the north.

13

Figure 4. Deposits analogue for Quaternary-alluvial exploration. This stratigraphic scheme for gold and heavy mineral-bearing alluvial in the Ampalit river, is situated approximately 100 Km southwest of Kualakurun. Modified after Seeley and Senden (1994).

14

Tab

le 1

. Sum

mar

ized

ele

men

tal c

once

ntra

tion

obt

aine

d fr

om th

e la

bora

tory

test

.

15

Figure 5. Variation diagram of the seven elemental groupes which were obtained from the Kualakurun alluvial samples. This diagram shows Transition metal elements as the most important elements from the Kualakurun alluvial. Al, Ti, Fe, Mn and Zr are the highest concentrated elements (1–10%) among the transition metal group.

16

Fig

ure

6. V

aria

tion

plo

t of

the

gol

d si

gnat

ure

elem

ents

suc

h as

Ag,

Fe,

Mn,

S,

As,

Pb,

Ni,

Zn,

and

Bi

(Kra

vtso

va

et

al.,

2016

).

The

el

emen

t da

ta

was

no

rmal

ized

to

th

e av

erag

e up

per-

cont

inen

tal

crus

t co

ncen

trat

ion

(McL

enna

n, 2

001)

.

17

Figure 7. Bivariate plot of indicator elements for gold between Au (ppm) and Cu (ppm) does not show a distinct positive correlation (Kravtsova et al., 2016). The correlation coefficient between Au (ppm) and Cu (ppm) only gives the small value (r = 0.47), this represent a weak association.

18

Figure 8. A) Zr/Hf plot which indicates linear positive correlation (r=0.97). Positively correlated Zr and Hf concentrations are due to the presence of heavy minerals in the sediments, such as zircon (ZrSiO4), ilmenite (TiO2, FeO, Fe2O3), or rutile (TiO2). B) Plot of Th/Sc vs. Zr/Sc (McLennan, 1993) from various facies shows the high Zr/Sc ratio in sand-dominated facies resulting from sedimentary sorting and recycling. Other facies, were less affected by this sedimentary process, may be due to compositional variations of the provenance.

19

Fig

ure

9. Z

r w

as p

lott

ed i

n th

e va

riat

ion

diag

ram

(U

CC

-nor

mal

ized

sam

ples

) to

geth

er w

ith

its

asso

ciat

ed t

race

el

emen

ts s

uch

as T

i, N

b an

d Y

whi

ch a

re c

omm

only

im

port

ant

in g

rani

te a

nd s

yeni

te. T

his

diag

ram

ind

icat

es t

here

is

no

Zr

anom

aly

in t

he s

ampl

es,

that

the

con

cent

rati

on o

f Z

r is

muc

h lo

wer

tha

n th

e av

erag

e up

per-

cont

inen

tal

crus

t.

20

Tab

le 2

. R

EE

dat

a fr

om t

he K

uala

kuru

n w

ere

com

pare

d w

ith

som

e kn

own

high

-gra

de R

EE

-bea

ring

pla

cer

depo

sits

(e.

g.

JIC

A,

1993

; Z

ech

et a

l., 1

994;

Orr

is a

nd G

rauc

h, 2

002;

Shu

terl

and

et a

l., 2

013;

Bud

ihar

yant

o et

al.,

201

5; M

cLem

ore

et

al.,

2016

), s

uch

as B

angk

a Is

land

, Mes

aver

de-U

SA

, Bal

d M

ount

ain-

US

A a

nd a

lluv

ial-

plac

er d

epos

its

in T

hail

and

(Khl

ong

Nam

Kha

o).

21

Table 3. Summarized grades of gold (Au), zircon (Zr) and total REE for the Kualakurun alluvial deposits.

22

Fig

ure

10.

The

RE

E c

once

ntra

tion

fou

nd i

n th

e sa

mpl

es t

aken

at

the

Kua

laku

run

allu

vial

are

low

er t

han

the

aver

age

valu

es o

f th

e up

per-

cont

inen

tal c

rust

(M

cLen

nan,

200

1).

23

Figure 11. REE chondrite-normalized plot (Floyd, 1991), shows an overall similar patterns with some overlapping patterns. REE values which are largely derived from felsic rocks are typically represented by highly elevated LREE together with distinct negative Eu anomaly (e.g. Floyd, 1991; McLennan et al., 1993). In contrast, chondrite-normalized REE from the Kualakurun shows only slightly elevated LREE together with indistinct negative Eu anomaly.

24

Figure 12. Compared to the fine samples of clay and silt which were originated from bedrock weathering, the coarser sand and gravels of Facies A and Facies B have slightly lower REE concentrations (in both normalized to chondrite). However, the REE concentrations shows an overall similar patterns with some overlapping patterns. REEs are commonly in the form of positive hydrated ions, adsorbed on the surface of clay minerals like kaolinite, halloysite and illite (e.g. Castor and Hedrick, 2006; Atwood, 2012).

25

Fig

ure

13. R

EE

con

cent

rati

on (

ppm

) fr

om th

e K

uala

kuru

n w

ere

com

pare

d w

ith

som

e kn

own

high

-gra

de R

EE

-bea

ring

pla

cer

depo

sits

(e.

g. J

ICA

, 19

93;

Zec

h et

al.,

199

4; O

rris

and

Gra

uch,

200

2; S

hute

rlan

d et

al.,

201

3; B

udih

arya

nto

et a

l., 2

015;

M

cLem

ore

et a

l., 2

016)

, su

ch a

s B

angk

a Is

land

, M

esav

erde

-US

A,

Bal

d M

ount

ain-

US

A a

nd a

lluv

ial-

plac

er d

epos

its

in

Tha

ilan

d (K

hlon

g N

am K

hao)

.

26

Fig

ure

14. R

EE

con

cent

rati

on (

UC

C n

orm

aliz

ed d

ata)

fro

m th

e K

uala

kuru

n w

ere

com

pare

d w

ith

som

e kn

own

high

-gra

de

RE

E-b

eari

ng p

lace

r de

posi

ts (

e.g.

JIC

A,

1993

; Z

ech

et a

l., 1

994;

Orr

is a

nd G

rauc

h, 2

002;

Shu

terl

and

et a

l., 2

013;

B

udih

arya

nto

et a

l., 2

015;

McL

emor

e et

al.,

201

6),

such

as

Ban

gka

Isla

nd,

Mes

aver

de-U

SA

, B

ald

Mou

ntai

n-U

SA

and

al

luvi

al-p

lace

r de

posi

ts in

Tha

ilan

d (K

hlon

g N

am K

hao)

.

27

Figure 15. A) La/Th vs. Th/Yb plot showing felsic versus mafic character after McLennan et al. (1990). B) Th vs. Cr/Th for the samples. The samples indicate mixing of a continental source enriched in incompatible elements (Th) and a more mafic source enriched in compatible elements (Cr). Curves are mixing lines generated from the data points with the lowest and highest Th concentrations.

28

References

Abidin, H. Z., 1998, The tectonic history and mineral deposits of the East–Central Kalimantan volcanic belt, Indonesia: a comparative study of the Kelian, Muyup and Masuparia gold deposits, Ph.D. thesis, The University of Adelaide.

Atwood, D. A., 2012, The rare earth elements: fundamentals and applications, John Wiley & Sons, West Sussex, 606 p.

Belousova, E. A., Griffin, W. L., O'Reilly, S. Y., and Fisher, N. I., 2002, Igneous zircon: trace element composition as an indicator of source rock type, Contribution to Mineralogy and Petrology, v. 143, 602–622.

Budiharyanto, K., Moe'tamar, Mulyana, T., 2015, Investigation on REE and associated minerals in the WPR proposed area Bangka Island, Unpublished report (in Indonesia).

Castor, S. B., and Hedrick, J. B., 2006, Rare Earth Elements, In: Kogel, J. E., Trivedi, N. C., Barker, J. M., and Krukowski S. T., (eds.), Industrial Minerals and Rocks: Commodities, Markets, and Uses, 7th edition. SME. p.769–792.

Darman, H., 2014, Physiographic units of Borneo, http://phsyiography-indonesia.blogspot.co.id/2014/08/sundaland.html.

de Keyser, F., and Noya-Sinay, J., 1992, History of geoscientific investigations in West Kalimantan Indonesia, BMR Jour. of Australian Geology and Geophysics, v. 13, p. 251–273.

Floyd, P. A., (ed.), 1991, Oceanic basalts, Springer Sci. + Business Media, LLC, 456 p. Haldar, S. K., 2013, Mineral exploration principles and applications, Elsevier, Tokyo,

334 p. Halloran, J., 2013, Placer channel sampling, Propecting and Mining Jour., v. 82, n. 11. Hellman, P. L., and Duncan, R. K., 2014, Evaluation of rare earth element deposits,

Applied Earth Science, 123:2, 107–117. Herman, D. Z., 2007, The potential of zircon distribution in placer deposits of the

Kalimantan Island, Indonesian Jour. of Geology, v. 2, n. 2, 87–96 (in Indonesia). JICA, 1993, Report on the cooperative mineral exploration in the Kra Buri area the

Kingdom of Thailand phase II, No. 34, Japan Int. Coop. Agency, Metal Mining Agency of Japan.

Kravtsova, R. G., Tarasova, Yu. I., Makshakov, A. S., and Pavlova, L. A., 2016, Distribution and modes of occurrence of Au, Ag, and associated elements in the sediment streams of Au–Ag zones at the Dukat deposit (northeastern Russia), Russian Geology and Geophysics, v. 57, p. 529–548.

Lolon, S., and Rahman, F., 2014, Overview of rare earth elements in Indonesia, Coal Asia, April 21–May 21, p. 146–152. www.academia.edu/24214043/Overview of Rare Earth Elements in Indonesia.

McLemore, V. T., Asafo-Akowuah, J., Robison, A., 2016, Mineral resource assessment of heavy mineral, beach-placer sandstone deposits at Apache Mesa, Jicarilla Apache reservation, Rio Aribba county, New Mexico, New Mexico Bureau of Geology and Mineral Resources Open-file report 587.

McLennan, S. M., Hemming, s., McDaniel, D. K., and Hanson, G. N., 1993, Geochemical approaches to sedimentation, provenance and tectonics, Geol. Soc. of America Spec. Paper 284, p. 21–40.

29

McLennan, S. M., 2001, Relationships between the trace element composition of sedimentary rocks and upper continental crust, Geochemistry Geophysics Geosystems, v. 2, paper number 2000GC000109.

Orris, G. J., and Grauch, R. I., 2002, Rare earth elements mines, deposits and occurrences, USGS Open-File Report 02-189.

Seeley, J. B., and Senden, T. J., 1994, Alluvial gold in Kalimantan, Indonesia: a colloidal origin? Jour. of Geochemical Exploration, v. 50, p. 457–478.

Sumartadipura, A. S., and Margono, U., 1996, Geological map of Tewah (Kualakurun) quadrangle Kalimantan, 1:250,000, Bandung GRDC.

Thorp, M., and Thomas, M., 1992, The timing of alluvial sedimentation and floodplain formation in the lowland humid tropics of Ghana, Sierra Leone and western Kalimantan (Indonesia Borneo), Geomorphology, v. 4, p. 409–422.

Thorp, M. B., Thomas, M. F., Martin, T., and Whalley, W. B., 1990, Late Plaeistocene sedimentation and landform development in western Kalimantan (Indonesia Borneo), Geologie en Mijnbouw, v. 69, p. 133–150.

Watters, R. A., Tucker, G. B. H., and Soesila, B., 1991, Reconnaisance and follow-up exploration for gold in Central Kalimantan Indonesia, Jour. of Geochemical Exploration, v. 41, p. 103–123.

Zech, R. S., Reynolds, R. L., Rosenbaum, J. G., and Brownfield, I. K., 1994, Heavy-mineral placer deposits of the Ute Mountain Ute Indian reservation southwestern Colorado and northwestern New Mexico, U.S. Geol. Survey Bull 2061-B.

TailingsTailings

Tailings

Preserved terrace deposits

Outcrop face of the Alluvial terrace deposits, exposed close to the DH-19 in local mining excavation. The succession is generally divided into two lithological associations: 1) interbedded gravel, gravelly-sand, coarse sand, humicrete and plant remains in the lowermost interval, and 2) interbedded sandy-clay, sand, clay, and organic clay in the uppermost interval.

Tailings

Preserved terrace deposits

Outcrop face of the Alluvial terrace deposits, exposed near DH-40 in local mining excavation. The succession is generally divided into two lithological associations: 1) interbedded gravel, gravelly-sand, coarse sand, humicrete and plant remains in the lowermost interval, and 2) interbedded sandy-clay, sand, clay, and organic clay in the uppermost interval.

Facies B

Facies A

A concentrated accumulation of mineral grains (zircon, ilmenite, etc.) in few cm’s impersistent layer which is typically associated with the lower-gravelly-terraces deposits. This example is taken at the outcrop face in front of DH-09

Gravel-bed as coarse lag deposits, heavy mineral accummulation are normally found in such deposits.

Facies B

Facies A

Perform additional channel sampling near the drilling site which has poor core-drilling recovery. (Ref. Halloran, 2013, Prospecting & Mining Journal, vol. 82, n. 11)