GEOLOGICAL CONTROLS ON MAJOR AND TRACE-ELEMENT CHARACTERISTICS CRETACEOUS COALS OF VANCOUVER ISLAND, CANADA
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| Authors: | VANDERFLIERKELLER, E; GOODARZI, F |
| Year: | 1991 |
| Journal: | Bull. Soc. Geol. Fr. 162: 255-265 |
| Title: | GEOLOGICAL CONTROLS ON MAJOR AND TRACE-ELEMENT CHARACTERISTICS CRETACEOUS COALS OF VANCOUVER ISLAND, CANADA |
| Abstract: | Coal-bearing Cretaceous strata on Vancouver Island, western Canada, occur in three major sub-basins; Nanaimo, Comox and Suquash. The coals were deposited under coastal plain conditions on the eastern margin of the Insular Belt, in a foreland basin setting. The sub-basins have distinct patterns for certain elements including anomalous As and Sb values in the Comox coals; Ba in the Nanaimo coals and Au, B, Cl and REE in addition to the majority of inorganically associated elements in the Suquash coals. These patterns appear primarily to reflect differences in depositional environment, source rocks and ash or mineral contents of the coal. For example B values in each sub-basin are quite distinct reflecting most brackish conditions associated with deposition of the Suquash coals. Although dominated by basic igneous rocks, the higher proportion of acidic igneous source lithologies in a northerly direction appear to contribute to an increase in levels of Au, Sb, Zr and HEE in the Comox and Suquash coals and a corresponding decrease in elements such as Cr, Ni, Rb, and Ta. The abundance of inorganically associated elements is controlled largely by the detrital and clay mineral content of the coals, in addition, mineral phases such as pyrite and dolomite control distributions of Zn, Co, Ni, Sc and S, and MgO respectively. Within basin elemental variations are controlled by a variety of factors including structure (Au is enriched on average by a factor of 5 in deformed Wellington Seam coal in the Nanaimo sub-basin compared to equivalent undeformed coal) and depositional environment. |
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