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
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--- ~,="'"I LEBO RAIIENSCRA() I ~ !LUDLOW / ----,,------ ·
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· ··--- . BLOOD RESER_IIE _
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JUOITH RI\IER
{BELLY RIVER)
CLAGGETT (PAKOWKI)
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< 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
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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
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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
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----------·----~11-·/. __ · --~t-~_
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R19
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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
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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.
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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.
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