The Odds and the reasons for the odds. I have bolded factors I believe applies to GXS.
It would appear that Mannville coal is often locally thickened in basins of lakes and embayments (troughs). This appears to be what we are finding.
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Model Number 5 SASKATCHEWAN COAL
CONCISE DESCRIPTION: Beds and seams of lignite and sub-bituminous coal within clastic sedimentary sequences.
GEOLOGICAL ENVIRONMENT
Host Rock Types: There are three significant coal-bearing formations:
1) Paleocene Ravenscrag Formation: lignite-bearing, fine-grained, clastic sedimentary rocks. Coal is widely but discontinuously distributed over about 26,000 km2 in southern Saskatchewan. Generally occurs at shallow depths. Four areas of significant coal accumulations: Estevan, Willow Bunch, Wood Mountain, and Cypress-Shaunavon. Ravenscrag Fm. ranges from 76 to 305 m in thickness;
2) Upper Cretaceous Belly River Formation: sub-bituminous (A to C rank) coals together with shales and sandstones. Coal mainly occurs in the upper portion of the formation. Main Belly River coal basin is in the far southwest corner of the province. Deepest coal occurrence is at 550 m. Number of coal seams decrease eastward. Up to 20 seams that range from 0.1 to 3.3 m with a net coal thickness of up to 12 m but commonly 5 to 9 m; and
3) Lower Cretaceous Mannville Group: sub-bituminous (A to C rank) coals together with shales and sandstones. Coal occurs at the base. Individual seams can be > 5 m thick. There are five general areas that have been identified with laterally extensive coal. Bow River coal field (south of La Ronge) with 1 to 3 seams with an average thickness of 1.8 m that occurs at or near to the surface. Four areas in west-central Saskatchewan with coal at depths of about 830 m: Winter-Senlac, Kerrobert Paleovalley, Rosetown, and Empress Basin.
Rock Textures: Thin- to thick-bedded, laterally-extensive coal seams in a clastic sedimentary sequence.
Ages of Host Rocks and Mineralization: Ravenscrag Formation: Paleocene; Belly River Formation: Upper Cretaceous; and Mannville Group: Lower Cretaceous.
Depositional Environment: An area of slow sedimentation in a fresh water fluvial and/or lacustrine environment with few or no marine incursions; and marginal marine swamp shoreline (paralic) settings. Lake, delta, swamps, shoreline and vegetation mats.
Tectonic Setting:
1) Ravenscrag Coal: in southeast Saskatchewan, east of longitude 104o W the coal basins conform to areas of cratonic downwarp; and basins west of 104o W are controlled and modified by structural lows and highs resulting from salt-solution tectonics;
2) Belly River Coal: little is known but presumably the main basin was controlled by an area of tectonic downwarp or subsidence; and
3) Mannville Coal: thin, widespread, marginal marine (paralic) coals generally < 2 m thick; and thicker basinal coal bodies, mainly lacustrine in origin, deposited in paleovalleys and embayments with some that may be associated with subsidence related to dissolution of underlying salt beds.
Associated Deposit Types: Coal-bed methane; leonardite; and clinker.
DEPOSIT DESCRIPTION
Mineralogy: Coal; Ravenscrag Fm.: lignite; Belly River Fm. and Mannville Gp.: sub-bituminous A to C rank. These range from carbonaceous shale to dull- to bright-banded, well-laminated coal, with variable intermixed, fine-grained clastic sediment. Minor pyrite is common.
Textures and Styles of Mineralization: Stratabound, laterally-extensive, thin- to thick-bedded, coal beds and seams. Individual seams may thicken, thin, split into several units or pinch out. Stratigraphic stacking of coal beds which are separated by generally fine-grained clastic sedimentary beds. Tectonic or near-surface processes my cause thickening or disruption of the coal.
Alteration: None related to deposition. Weathering processes generally decrease the coal quality.
Geological Ore Controls:
1) primary deposition of plant material in fresh water to marginal marine environments characterized by slow sedimentation rates;
2) thicker coal basins developed in paleovalleys 1 related to tectonic processes and/or dissolution of underlying salt beds; and
3) later deformation may be locally important in modifying the deposits.
Geochemical Signature: Not significant.
Geophysical Signature: Surface seismic, resistivity, and gravity surveys. Borehole logging includes gamma, neutron, sonic, density, resistivity, and calliper.
EXAMPLES (with grades and tonnages):
The only current production is from the Ravenscrag Formation. Two mines, Bienfait and Boundary Dam, in southeast Saskatchewan produce respectively, 2 million tonnes and 6.5 million tonnes per year.
The Poplar River Mine near Coronach produces 4 million tonnes per year. Resources of immediate interest for the Ravenscrag coals are 6.569 billion tonnes.
There are no resource estimates for the Belly River coal field.
Luscar Ltd. (AF 72N-0001) examined four Mannville coal fields in the Kerrobert paleovalley and estimated a resource of 1.715 billion tonnes. The Bow River coal field has an estimated resource of 60 million tonnes (SMDI 0668-0669).
SELECTED REFERENCES
Frank, M.C. (2005): Coal distribution in the Belly River Group (Upper Cretaceous) of southwest Saskatchewan; in Saskatchewan Geological Society Core Workshop, April 2005, Spec. Publ. No. 17, p.89-106.
Irvine, J.A., Whitaker, S.H. and Broughton, P.L. (1978): Coal resources of southern Saskatchewan: a model for evaluation methodology; Sask. Department Mineral Resources, Report 209, Part I (156p.) and II (56 plates).
Saskatchewan Geological Survey (2003): Geology, and mineral and petroleum resources of Saskatchewan; Saskatchewan Industry and Resources, Miscellaneous Report 2003-7, p.66-72.
Reviewed by: Charles Harper (SGS) November, 2007
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