Preliminary Observations of Clinker Deposits in Southern Saskatchewan 1

P. Guliov

Guliov, P. (1995): Preliminary observations of clinker deposits in southern Saskatchewan; in Summary of Investigations 1995, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 95-4.

Naturally baked or fired sediments, sometimes referred to as 'Scoria' or 'clinker', are formed in the coal-bearing Ravenscrag Formation and sometimes in overlying Qua­ternary sediments in southern Saskatchewan as a re­sult of coal seam combustion. Depending on the temperatures achieved during seam combustion and on the nature of the materials in beds overlying and under­lying such coal beds, the intensity of firing varies from a very low level up to and including complete fusion. The richly coloured, indurated material resulting from this natural firing process may be quarried, prepared and marketed as decorative aggregates, landscaping materi­als and a number of other products.

The Glossary of Geology (Bates and Jackson, 1980) considers the terms "Scoria [coal] and "Clinker (coal] as synonymous and defines the terms as "masses of coal ash that are a byproduct of combustion". The current pa­per extends the definition to include sediments lying be­neath and above a burned out coal seam which have been indurated by natural baking or firing as a result of in situ coal combustion. However, the terms have limita­tions in that materials lying more distant from a burning coal seam would be progressively less fired and less in­durated until there is only minimal evidence of firing.

For practical purposes, the terms are herein applied to materials which have been substantially thermally indu­rated by in situ coal seam combustion to a degree up to and including fusion. Any other sediments which have suffered the effects of such heat without any significant induration are referred to as thermally altered. In some cases parent materials may have been well indurated to begin with, such as silicified beds, and may have suf­fered thermal alteration only of some constituent miner­als with possible colour changes. In such cases, without conducting thin section analyses, the materials should also be included with the term scoria [coal] or clinker [coal]. The gradational nature of thermal influence on adjacent sediments, whether it results from variations in the intensity of heat or from variations in the firing prop­erties of the sediment or both, presents some difficulty in defining a boundary between what is considered to be clinker and what is not. The degree of induration as it affects the strength and durability of the material seems to be an acceptable, although less than precise, practical field approach for making the distinction. These properties can be assessed to some degree by simple field observations of the hardness and other physical properties of the material.

o Reg ina

0 Swift Current

; Moo~e Jaw

50"r--------+-------_J ________ _J~---------i-----1 so·

''C, '

CYPRESS BASIN

c:::::> Ravensc rag Formation

WOOD MOUN'fAIN WILLOW BUNCH BASIN BASIN

0 20 4 0 60 80 1 00

Kilome, re $

-ESTEVAN BASIN

~ Li gnite Resource Area

Figure 1 • Ravenscrag coalfields of southern Saskatchewan (Guliov, 1994).

(1) Saskatchewan Project G.202 is a continuation of Project A.242 initiated under the Canada-Saskatchewan Partnership Agreement on Mineral Development 1990-95; funding in 1995 was under the Saskatchewan Energy and Mines Geoscience Program.

Saskatchewan Geological Survey

49•

97

1. Geology The Paleocene Ravenscrag Formation covers about 26 000 km2 in southern Saskatchewan. It is largely con­tinuous in an east-west corridor about 70 km wide adja­cent to the US border and extending from near the Manitoba border westward to longitude 107° west (Fig­ure 1 ). It represents the northern extension of the coal­bearing Ludlow and Tonge River formations of the Fort Union Group occurring extensively in North Dakota and the Tullock, Lebo, Tongue River, and Sentinel Butte for­mations in Montana (Figure 2). From 107° westward to the Cypress Hills area it occurs as erosional outliers.

The Ravenscrag is a sequence of fluvial and lacustrine elastic sediments (silts, sandstones, and clays) interbed­ded with coal seams. In southeastern Saskatchewan, the oldest parts of the formation may be marine in ori­gin representing the northernmost extension of the early Tertiary Cannonball sea which is well recognized and documented in North Dakota.

Deposition of the Ravenscrag in southeastern Saskatch­ewan was largely controlled by subsidence or cratonic downwarping in the extensive Williston Basin centered in northern North Dakota. It is in this region that these sediments achieved their maximum development with thicknesses up to 305 m. In south-central and south­western areas, salt solution tectonics appear to have in­fluenced Ravenscrag deposition and coal seam formation. Maximum thicknesses attained in south-

EPOCH

,-.: . < ' PLEISTOCENE

·1 PLIOCENE

MIOCENE

i iL ~=~ ~ ~ E~CE-NE

I

PALEOCENE

SOUTHERN ALBERTA NORTHEASTERN

MONTANA

central and southwestern regions are about 200 m and 76 m respectively (Broughton, 1988).

a) Ravenscrag Formation Coal Zones

Coal seams in the Ravenscrag are discontinuous and can be traced with reasonable certainty only over short distances. Individual seams may thicken, thin, split into several thinner units, recombine or pinch out. Correla­tion throughout the coal basins must, therefore, be ac­complished on the basis of groups of related seams (coal zones) which may (by the use of marker beds) be traced over greater distances than individual seams. Three major regions of lignite coal accumulations are recognized in the Ravenscrag of southern Saskatche­wan: Estevan, Willow Bunch-Wood Mountain, and Cypress (Shaunavon). Coal zones associated with these and their average thicknesses, seam designa­tions and seam splits are listed in Table 1.

Outcroppings of the coal seams are controlled by topog­raphy which is, to a large degree, controlled by erosion of the Ravenscrag Formation. It is, therefore, along val­ley walls where Ravenscrag sediments have been ex­posed by erosion, that coal seams outcrop most commonly. The uppermost seams may also be visible along the perimeters of upland areas where Raven­scrag is exposed. Where glaciation has occurred, till may be found lying directly on or in close proximity to coal seams. Figures 3, 4, and 5 are computer­generated maps indicating the interpreted areas of coal zone outcrops in the three coalfields of southern Sas-

SOUTHERN SASKATCHEWAN

NORTHWESTERN NORTH D AKOTA

0: 1::TINEL-:m

" ' i 1--;~NGUE--:~R

SOUTHWESTERN MANITOBA

I: PORCUPINE HILLS '

--- ~,="'"I LEBO RAIIENSCRA() I ~ !LUDLOW / ----,,------ ·

_TULLOCK .. ~--· --- •. r l .J;_,•J-l:-~N8.~t-- TURTLE MOUNTAIN

"' u ::,

6 0

"' UPPER N u 0 .. "' ,-. CRETACEOUS

"' "' ::. a: ,u

I

BAT-T-LE KNEEH'.'.:_L~ ::-. ~ ·

ST. MARY RIVER

· ··--- . BLOOD RESER_IIE _

BEAR PAW --- ·--

JUOITH RI\IER

{BELLY RIVER)

CLAGGETT (PAKOWKI)

HELL CREEK } FRENCHMAN HELL CREEK

< C.Q!.GATE ' , -- ~tmEMV0--5 c:J;.OLGATE ";; BATTLE=:) --1 - - -- BOISSEVAIN

FOX HILLS EASTEND FOX HILLS ,,.~·· l-~.,,.. T ! 1 · .. .

JUDITH RIVER JUDITH RI\IER ~ I PIERRE RIDING MOUNTAIN

CLAGGETT LEA PARK '.i 1'i a:

Figure 2 - Correlation chart of uppermost Cretaceous and Tertiary formations in southern Saskatchewan and adjacent areas (modified after Irvine et al., 1978).

98 Summary of Investigations 1995

Table 1 - Coal zones, seams, thicknesses, and seam splits.

Coalfield Coal Zone

Estevan Short Creek Roche Percee Souris Estevan Boundary

Willow Bunch-Wood Mountain Quan tock Willow Bunch Poplar River Fremington Coronach Hart

Fife Lake Landscape

Cypress (Shaunavon) Anxiety Butte Ferris D-1 Ferris J-M

Mappable Seams

5 (C-G) 4 (C-F) 3 (C-E) 5 (C-G) 7 (C-1)

3 (C-E) 5 (C-G) 3 (C-E) 3 (C-E) 3 (C-E) 5 (C-G)

3 (C-E) 6 (C-H)

4 (D-G) 6 (D-1) 4 (J-M)

Av.Zone Thickness (m)

9.6 4.7 1.67 4.5 8.46

0.60 3.98 3.42 2.44 2.82 5.03

2.82 15.11

2.96 6.54 4.3

Seam Splits

F,G

C+D E+F

G,H, a-f

Notes: Zone thicknesses include partings which would be mined Coal Zones are shown in stratigraphic order Coal Seams are lettered in descending order Seam Splits:

-upper case letters indicate greater degree of splitting -lower case letters indicate lesser degree of splitting -plus sign indicates seam combinations

katchewan. It is in these areas that spontaneous com­bustion of coal is most likely to have occurred and pro­duced the naturally fired, colourful shales known as clinker. Hudson (1963) reported well-known occur­rences along the west side of Eastend Coulee north­east of Eastend (particularly at Anxiety Butte), along Mule Creek southeast of Shaunavon, and along Big Muddy Valley south of Harptree. Farther east, toward the Souris Valley, Hudson (1963) indicates that the lig­nite-bearing sediments are more limy and produce buff and salmon coloured clinker. In certain circumstances where the limy sediments were fired to exceptionally high temperatures, as they were at the old Jenish mine south of Estevan on N1/2 Sec. 1, Tp. 2, Rge. 8W2, the resulting material is yellow to yellowish green and dense.

2. Development of Clinker

In-situ firing of sediments by coal combustion and the development of commercial clinker deposits depend on several important conditions for initial ignition of the coal and progressive combustion for a prolonged period of time:

1) the coal must be in a state which promotes natural oxidation, an exothermic reaction;

2) a sufficient supply of air must be available to main­tain combustion;

Saskatchewan Geological Survey

3) moisture levels must not be too great so that com­bustion can initiate and continue; and

4) ignition is commonly initiated by spontaneous com­bustion, but may also result from lightning strikes or prairie fires.

Formation of commercial clinker deposits requires that:

1) the coal seam must extend over a sufficiently large area to provide commercial tonnages of ore;

2) the sediments covering the coal seam must be suffi­ciently thick to have the potential for yielding large tonnages of ore, but not so thick that combustion air would be occluded and the combustion snuffed out at an early stage by collapsing sediments;

3) the overlying and underlying sediments must not be too refractory to permit the development of a strong, durable clinker. Naturally fluxed sediments with a relatively high alkali/alumina ratio (potassium or so­dium) mature and/or fuse at considerably lower tem­peratures than do high-alumina clays such as kao­lin; and

4) the coal seam must be sufficiently thick to produce a prolonged firing of the overlying and underlying materials at sufficiently elevated temperatures.

99

"'\ . .. ,~~~~-~ ... .

· 1 • ,.~ T2 " "'"";· •. " j · .. ~ . 4 - . ~ - ··'( ., •.

- I' - _. -• ,• ...... '

. ;J . . : T1 "' . :

"' .. .

•

R9 RB R7 R6 R5W2 Figure 3 • Ravenscrag coal outcrop areas; Estevan coalfield. This map (and Figures 4 and 5) was generated from the National Coal Inventory database by W.J. McDougall and J.D. Hughes of the Energy and Environmental Subdivision of the Geological Survey of Canada, Calgary. Geomodel was the software used for this purpose and was developed by the GSC. Note: Due to the scale of Figures 3 to 5, many small outcrop areas are not shown. For further information or more detail, the author should be contacted.

3. Spontaneous Combustion of Coal

Scully (1931) presented several requirements for the in­ducement of spontaneous combustion of coal. He stated that any coal will fire spontaneously, but not all will do so with the same degree of readiness. Some of the principal criteria he presented are:

1) The coal must be sufficiently finely divided to pro­vide a large surface area to promote rapid oxidation.

2) Air currents must be small enough that they will not carry the heat of oxidation away.

3) Moisture content increases the rate of oxidation and, up to a point, the natural tendency to heat will increase. In excessively moist coals much of the

heat of oxidation is lost in heating and vaporizing the moisture. Once sufficient water is driven off the temperature rises.

4) Freshly exposed coal surfaces will oxidize readily and absorb larger quantities of oxygen. An ade· quate insulating cover can result in an increasing rate of oxidation and a self accelerating temperature rise which culminates in combustion.

5) Coals with high oxygen content absorb oxygen most readily and such coals are therefore most prone to heating spontaneously.

6) Pyrite and marcasite are common in many coals. The oxidation of these minerals is exothermic but not sufficiently to cause combustion directly. The

E --4-+ ---+---+- UT~ )~~ --~~-_ _.__,___r ___,_,__r -'----"---------'-,-----'-r_......,

-,+i'.' ::I ; - _'' .~_·r~ .~· ... · ·------1---

T7

T6

,., !---·- +-- - 1 - ." ,,.~~::-~ .. ' ·" I .. M •

i~ L_~-- __ i:~L~tt '.~~ x·f~· f:.E Tl

T2

T1

R7 R6 R5 R4 R3 R2 R1 W3 R30 R29 R28 R27 R26 R25 R24 R23 R22 R21 R20 R19 W2

Figure 4 · Ravenscrag coal outcrop areas; Wl1/ow Bunch-Wood Mountain coalfield.

100 Summary of Investigations 1995

I

I T9

. ··--- ---+----- -+-------f--------+---------j

·'

·- TB

----------·----~11-·/. __ · --~t-~_

.. ~

~~----~-----~·-·

R21 R20

... ' '\ I

R19

T7

T6

TS

R18 R17 R16W3

Figure 5 · Ravenscrag coal outcrop areas; Cypress (Shaunavon) coalfield.

process tends to break down the coal and assist in accelerating the rate of coal oxidation.

7) Erosional periods during which the Ravenscrag coal seams have been exposed present the best opportu­nities for coal seam combustion. Lignite exposed to air tends to slake and become finely divided. The re­sulting increase in surface area accelerates oxida­tion and temperature rise. In Saskatchewan the bet­ter part of post-Paleocene time was erosional.

8) Coal occurring along fault zones is generally in a crushed state and has a greater surface area which promotes more rapid oxidation and heat generation.

Bustin et al. (1983) summarized the subject of natural combustion by stating, "Spontaneous combustion thus appears to be more likely with fine, wet, vitrinite-rich coal in which finely dispersed pyrite is present." Vitrinite, together with huminite (in lower rank coals), representing a group of macerals (coal-forming compo­nents) and derived from woody tissues and bark of trees, is the most abundant constituent of coals.

Saskatchewan Geological Survey

4. Guide to Prospecting

Clinker deposits may develop at almost any time follow­ing coal deposition. Saskatchewan deposits associated with the Ravenscrag Formation therefore could have formed during the interval from a short time after coal seam deposition during Paleocene time to the recent past. In fact, coal seam combustion has been reported as recently as the 1980s in the Bengough area. In North Dakota, the process has been going on for the better part of the century with the most recent fire still burning in 1988 in the South Unit of Roosevelt National Park (Bluemle, 1988). Coal seam combustion is cur­rently in progress on a small scale in the Drumheller area of Alberta.

A number of points are provided in the following section as a guide for clinker prospecting:

1) Since the formation of clinker deposits is intimately related to the presence of coal seams it is important to understand the occurrence, distribution, eleva­tions, and structure of the coal seams and zones in

101

the area. If the coal seams are flat or nearly flat­lying, as they are in Saskatchewan, and if erosion has exposed them, then the present topography in areas where glacial drift is thin or absent can pro­vide a useful tool in locating clinker deposits. Geo· logic maps of coal seam distribution and cross­sections of coalfields will also assist. Topographic maps at a scale of 1 :50 000 are necessary for plot­ting estimated coal seam outcrop locations and for recording field observations. Air photos of the pros­pecting areas may reveal features consistent with coal seam combustion, particularly collapse features in the case of more recent clinker deposits and sur­face expressions of fault zones.

2) In areas with poor access, the use of an aircraft for spotting potential clinker deposits by observing dis­coloured soils could provide a basis for ground in­vestigations (Plate 1 a). Reconnaissance traversing along valley walls where the Ravenscrag Formation and its coal seams are likely to outcrop should be one of the first field investigations to be made. The presence of red, brown or buff hard burned shales will soon become evident unless they are well cov­ered by talus from the valley walls. Clinker is more resistant to erosion than the surrounding unbaked sediments and tends to form a more prominent cap rock in eroded areas. Areas which are obscured by talus and which may be grown over by vegetation can still offer clues to the presence of clinker depos­its by observing the materials around gopher and badger holes and fox dens. Because these materi­als indicate the nature of the material beneath the surface any positive indications should be followed up by traversing and periodic excavation up the slope of the valley wall. Fine, loose sediments of similar fired colours are also significant as they may represent thermal alteration and oxidation of sedi­ments too far above the burning coal seam for hard firing. In this case, excavation to greater depths may reveal clinker deposits beneath these indicator mate­rials.

3) Coal seam combustion and collapse of the overlying sediments often produce surface depressions which may still be observable in the field and on air pho· tos. These collapse features tend to be more pro­nounced in areas of thick coal seam development. In cases where the clinker deposits were formed in preglacial times, the collapse features would likely be buried or disturbed and their surface expression would be obliterated. In such cases their discovery is more a matter of chance. A knowledge of the preglacial drainage system in coal-bearing regions and its relationship to the present topography could assist in prospecting. Groundwater and Geology maps published by the Saskatchewan Research Council are useful in this respect as they present in­terpretations of preglacial drainage and bedrock to­pography.

4) In very recent deposits, the surface collapse fea­tures are often associated with visible surface frac­turing of the sediments.

102

5) Sustained coal seam combustion over a large area is necessary for the development of large clinker re­serves. As the combustion front progresses into ar­eas of thick overburden, the collapsing materials are more likely to cut off the air supply and extinguish the fires. In this way lateral extent or reserves are also partly related to thickness of overburden during the time of coal seam combustion. Regardless of this natural controlling mechanism, once the proc­ess progresses into areas of thick overburden, the clinker deposits would likely be beyond the eco· nomic depth and therefore of little interest. It is likely, however, that the combustion front may have been propagated laterally parallel to the valley edges where the overburden thickness is reason­ably low.

6) During the natural firing and/or the subsequent cool­ing process, the temperature of the sediments may reach the Curie point, at which time magnetic materi­als such as iron become aligned and achieve a fer­romagnetic state. On cooling, the fired mass may then become magnetically polarized. This condition, if sufficient volumes of ferromagnetics are present, can sometimes be detected in aeromagnetic or ground magnetic surveys as weak magnetic anoma­lies. Magnetic survey maps then may have an appl i­cation as a prospecting tool for clinker deposits. Such magnetic anomalies are noticeable over some clinker deposits in south-central Saskatchewan.

7) Vegetation of a type preferring dry, well-drained con­ditions, such as cactus and creeping cedar, appear to flourish in areas underlain by clinker at shallow depth.

8) In more recently developed clinker deposits, where little erosion is likely to have taken place since clinker development, it has been noted that fusion of the sediments tends to be more common in loca­tions of the hottest fires due likely to an abundant supply of combustion air. Such materials appear to be most common on valley spurs where air might gain access from two sides. This is a significant ob­servation in evaluating an area for larger block sizes.

5. The Nature of Clinker

The development and nature of clinker deposits result­ing from coal seam combustion are complicated by nu­merous variables.

Plate 1

a) Evidence of clinker deposits in the distant hills in south· central Saskatchewan.

b) Quarry face including Ravenscrag sediments and glacial tiff with evidence of ice-push structure and variable firing charac­teristics and fragmentation due to post-firing collapse.

c) Naturally calcined carbonate clasts (lime) in fired till.

d) Quarry face with coal ash bed {white). Clinker bed above the ash shows a greater degree of firing than the material below.

Summary of Investigations 1995

Saskatchewan Geological Survey 103

104 Summary of Investigations 1995

a) Thickness, Quality, and Moisture Content of the Coal

Thick coal seams, given a sustained and consistent air supply, will tend to burn longer and evolve more heat. With sufficient insulating cover, higher temperatures are likely to be attained. Temperatures as high as 1700°C were indicated by Bluemle (1988). This is only about 111 °C below the fusion temperature of kaolin. The de­gree of firing of clay materials is not only temperature­dependent; it also appears to be, to some extent, time-dependent. A prolonged firing is likely to alter some clay minerals to a greater degree. Temperature and duration are also significant factors in firing of wet clays since a portion of the heat is consumed over time in dehydrating the sediment prior to alteration.

Coal with a high mineral ash content produces a lower heat of combustion than low ash coals. Moisture con­tent of the coal also has a modifying effect on the tem­perature. In a very moist coal, much of the heat of combustion is carried off in the formation of steam and is not available for firing the adjacent sediments. It should be noted that the nature of the coal seams is also subject to vertical and lateral variations and these will have a corresponding effect on the temperature of combustion and, consequently, on the nature of the clinker. The stratigraphic position of sediments relative to a burning coal seam can affect the quality of the product. Plate 1 d illustrates the difference in the degree of firing and appearance of materials above and below a burned out coal seam.

Rose (1916) had recognized "red beds" and "clinker" in the Fort Union (Ravenscrag) of southern Saskatchewan particularly in badland and semi-badland regions where they are most conspicuous. He states that "In places considerable slag having the appearance of lava or sco­riae has been produced by the fusion of the overlying beds." He reported an occurrence "Along Big Muddy val­ley south of Harptree where a seam of coal has burned and left a layer of clinker, the overlying clay was melted and ran down the slopes and is now to be found in the bottom of the neighbouring coulees or strewn over the coulee sides. The same seam is represented less than one mile away by an 18-foot seam of lignite."

b) Mineralogical Variations in the Original Sediments

Ravenscrag sediments are highly variable both laterally and vertically and range from clays and silts of various compositions to sands which range from quartzose to feldspathic and may contain a variety of clays. Such variations are very significant factors in determining the nature of the product of coal seam combustion. For ex-

Plate 1 (con't)

e) Stock piles of crushed clinker product.

f) Bagged clinker product.

g) Landscaping clinker boulder product.

h) Landscaping clinker boulders palletized for shipping.

Saskatchewan Geological Survey

ample, clays of a high kaolin content are more alumi­nous and therefore more refractory than the illitic or ben­tonitic clays in till and tend to produce softer, underfired clinker and altered sediment given similar temperatures. On the other hand, kaolinitic clays from which the origi­nal feldspar alkalis (potassium or sodium) have not been fully leached out are likely to be more highly fluxed. In such a case, the sediments are likely to be more fully fired at a given temperature and produce a strong and durable product. The same material at higher levels above the burning coal where tempera­tures are lower would not be burned fully. In some ar­eas glacial till forms part of the overburden in proximity to the coal seam as it does locally along parts of the Big Muddy valley. In such locations the clinker is a mix­ture of Precambrian pebbles, sand, and partially cal­cined carbonate clasts embedded in a matrix of highly fused clay (Plates 1 band 1 c). In fact, locally, there is clear evidence that the till matrix had reached the mol­ten stage (Rose, 1916).

The formation of colour in clinkers is, as in brick produc­tion, very complex and dependent on many variables, the most important of which are: mineralogy, oxida­tion/reduction conditions, temperature, and to some ex­tent the duration of the elevated temperatures. In general, however, iron minerals provide most of the col­ouration. The commonest are hematite, goethite, limo­nite, magnetite, pyrite, and siderite. Under oxidation conditions all of these convert to hematite, the most im­portant constituent in colouration. In brick production hematite (on heating above 1000°C) shows increasing crystal lattice disorder and becomes increasingly darker red (Prentice, 1990). If the air supply is sufficiently low, reducing conditions ensue and the iron combines with the silicates in the clay to form ferrous silicates which liquify at kiln temperatures (up to about 1150°C) produc­ing a dark blue skin on cooling. This effect is called flashing in brick making and has been observed locally in clinker deposits.

Calcium in the form of the mineral calcite plays a signifi­cant role in colouration. In general, high levels of calcite in normally red-firing clays produce yellow or buff col­ours (Prentice, 1990). Some of the iron likely becomes incorporated into complex carbonates such as ankerite, (Ca·Mg·Fe)C03, which do not have the strong coloura­tion of hematite.

c) Oxidation/Reduction Conditions

The supply of air not only affects the rate and tempera­ture of combustion, but the oxidation/reduction condi­tions. With abundant air, the iron content of the sediments will be more completely oxidized and the fired product will tend to be red. With oxygen starvation the iron tends to be reduced and produce darker col­ours such as browns and deep reds. The presence of other minerals may have a modifying effect on colour.

d) Topography and Overburden

Topographic and overburden conditions, during the time of coal seam combustion, will influence the nature of the final product. In areas where the topography allows

105

an increased air supply to the combustion front, such as around the noses of valley spurs where exposure is greatest, the temperatures will be greater and the firing more complete. A harder, more durable and less po­rous clinker is likely to form. This would also be the ten­dency where overburden is relatively thin, allowing a greater supply of combustion air through surface fractur­ing resulting in the generation of a hotter fire. Areas, in which firing is more complete and approaches the fu­sion point of the sediments, would tend to yield larger sizes of clinker blocks, some of which are of large boul­der size. Underfired materials are very porous, incompe­tent, and of little commercial use.

6. Uses and Specifications

Clinker materials are generally used as a source of decorative, coloured aggregates (Plates 1e to 1h), but have recently found a market in innovative landscaping and other applications. In some parts of North Dakota and Montana clinker is also used locally as road mate­rial.

a) Decorative Coloured Aggregate

Clinker is crushed and sized for use as decorative col­oured aggregates. These may be applied as a ground­cover in and around flower beds and around trees, shrubs, and border areas. Some deposits are amenable to a degree of segregation by colour types which adds a desirable element of choice in applications.

Crushed products are sized for various applications and range from "dust" size to large cobbles. Material of boul­der sizes also has special applications.

Clinker is very porous and capable of absorbing consid­erable water. Absorption rates vary according to the in­tensity of the firing and the nature of the original material.

b) Road Materials

The hard-fired clinkers are more durable and less po­rous and are sometimes locally applied as aggregates to roads, lanes, and driveways.

c) Landscaping Blocks

Large sized blocks (Plates 1g and 1h) may be used for the construction of rock gardens and decorative borders in flower gardens and lawns. Their rich red, brown, and buff colours, as well as the textures, provide an attrac­tive and unique appearance. Large flat shapes may be applied as flagging for walkways. This application is gaining a substantial market in western Canada.

d) Mud Control

Fine-grained clinker materials known as crusher dust are used in controlling mud in areas such as golf course pathways and the in-field areas of baseball dia­monds.

106

e) Fossils

Exceptionally well preserved complete fossil leaves are present in some larger blocks of clinker. Firing appears to have enhanced the visibility of detail and rendered the material much more durable. In addition to their aes­thetic and collector's value they provide useful scientific information about an epoch dating back 57 to 66 million years ago.

f) Quality Control

Clinker as a natural substance is subject to numerous variations in the conditions of formation. These vari­ations are reflected in the variable technical and visual qualities of the end products. Underfired materials tend to be very porous and soft. Such materials tend to break down much more rapidly in areas where they are subjected to stress. They are also subject to decrepita­lion on weathering, particularly in freeze-thaw condi­tions. It is important therefore, to recognize and distinguish the various types and qualities of materials and to segregate these during the quarrying and proc­essing operation as much as possible. Only general guidelines can be provided for such distinctions at this time. Some of the obvious ones are:

1) The degree to which sediments have been naturally fired can be recognized to some extent by the "ring" (as with bricks or biscuit pottery wares). A soft, un­derfired and incompetent material will have a dull sound when the materials are handled and impact against each other. A hard and durable material will have a higher-pitched ring or clinking sound. Pre­sumabty there is a range of variations between the two extremes which the producer could learn to rec­ognize. It would not be difficult to conduct some em­pirical freeze-thaw and hardness tests on various types to establish a correlation between durability and "ring".

2) Absorptive capacity of clinker materials is, to some degree, dependent on the intensity of firing. The hard-fired materials, particularly those that have been fused or partially fused would tend to be less porous than underfired materials. Some guidelines might be established by making simple field tests on the rate of absorption of a drop of water by dry ma­terials. More accurately the materials should be dried at 105°F for 24 hours and weighed, then soaked and boiled for several hours. A second weighing immediately after soaking will provide the final parameters for calculating porosity. The result can be related to the "ring" and appearance of the materials to gain the necessary judgmental experi­ence.

3) The appearance and feel of clinker can sometimes offer clues as to its quality or potential application. Fusion of the sediments, for example, is easily rec­ognized by the glassy or stone-like appearance. On the other hand a dull material which is friable can be discounted for applications requiring durability.

Summary of Investigations 1995

7. Acknowledgments

The author is indebted to Mr. Gilles Therrien, owner of Coloured Shale Products tnc. of Moose Jaw who so generously provided tours of his field operations, infor­mation, critical comments, and much stimulating discus­sion. Many thanks are due J.D. Hughes and W.J. McDougall of the Energy and Environmental Subdivision of the Geological Survey of Canada, Calgary tor providing computerized Ravenscrag coal outcrop maps based on the National Coal Inventory da­tabase. The author is also grateful to SEM staff includ­ing Malcolm Gent for his valuable assistance and discussions, and Pat Kydd and Lyndon Penner for pre­paring the figures and plates.

8. References Bates, R.L. and Jackson, J.A. (1980): Glossary of Geology;

Amer. Geol. Inst., 751p.

Bluemle, J. (1988): North Dakota Clinker; N. Dak. Geol. Surv., Newsletter article, p29-34.

Broughton, P.L. (1988): Formation of Tertiary coal basins in southern Saskatchewan; Sask. Energy Mines, Open File Rep. 88-1, 53p.

Saskatchewan Geological Survey

Bustin, R.M., Cameron, A.A., Grieve, D.A., and Kalkreuth, W.D. (1983): Coal petrology its principles, methods, and applications; Geol. Assoc. Can., short course notes, v3, 230p.

Guliov, P. (1994): Saskatchewan; in 1994 Keystone coal indus­try manual, Maclean Hunter Publishing Co., pS-223-S-228.

Hudson, J.H. (1963): On coloured aggregates; Sask. Res. Counc., Rep. E63-10, 7p.

Irvine, J.A., Whitaker, S.H., and Broughton, P.L. (1978): Coal resources of southern Saskatchewan: A model for evalu­ation methodology; Sask. Energy Mines, Rep. 209, 156p plus atlas volume.

Prentice, J.E. (1990): Geology of Construction Materials; Top­ics in the Earch Sciences 4, Chapman and Hall, London, 202p.

Rose, B. (1916): Wood Mountain-Willow Bunch coal area, Saskatchewan; Can. Dep. Mines, Geol. Surv., Mem. 89, 103p.

Scully, T. (1931): Spontaneous combustion of coal; in Annual Meeting, Min. Soc. Nova Scotia, p808-815.

107