Host rock alteration and its application as an ore guide at the Midwest Lake uranium deposit, northern Saskatchewan

Abstract In the unconformity-type uranium deposit at Midwest Lake, mineralization is associated with extensive host rock alteration, which affects the metamorphic basement as well as the overlying Athabasca Group sandstones. Host rock alteration is manifested by (1) transformation of clay minerals [kaolinite into illite andchlorite (sudoite)}; (2) bleaching due to removal of hematite from the latentic paleoweathering profile and the overlying red bed, Athabasca Group sandstones; (3) loss of coherence of the sandstone resulting from corrosion of quartz cement; and (4) in the immediate vicinity of high-grade ore, development of a clay envelope due to residual enrichment of clay minerals caused by massive dissolution of quartz.
Clay mineral transformation and bleaching are the most prominent and the most widespread alteration effects, forming haloes that extend for several kilometres along the strike of the mineralized structure and also constitute distinct alteration pipes that rise for several hundred metres above the unconformity to be truncated at the present top of the bedrock.
Although the two haloes are largely congruent features, cross-cutting relationships indicate that clay mineral alteration represents an earlier phase in the history of the deposit than the large-scale bleaching that gave rise to the superimposed bleaching halo.
Because clay mineral alteration and bleaching are intimately tied to the mineralization and extend well beyond the limits of the actual orebodies, host rock alteration may be used as an ore guide in exploration and drill-hole evaluation. In this application a third hydrothermal discharge centre was identified, as yet untested for ore, which is located between the hydro-thermal centres associated with the two known orebodies of the deposit.
It is estimated that host rock alteration may enlarge a potential drill-target by a factor 10 - 20X. Information on the configuration of bleaching haloes can be obtained from systematic core logging, whereas diagnostic clay mineral alteration is readily identified by means of automated, quantitative XRD techniques.
Keywords: Economic geology, Host rock alteration, Uranium deposits, Mineralization, Athabasca Group, Midwest Lake.
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Summary: In certain instances, rocks around underground excavations behave as a plastic mass. This paper offers several solutions to predicting the mode of plastic flow around cavities and designing mining pillars where plastic conditions exist.
Publication: CIM Bulletin
Author(s): D. MRAZ
Keywords: Rock mechanics, Strata control, Pillar design, Plastic rocks, Pillars, Salt rocks
Issue: 868
Volume: 77
Year: 1984
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Summary: Falconbridge Mine has a history of significant microseismic activity dating back to 1955. Since mid-1981, a microseismic monitoring system has been operating in the area around the No. 9 Shaft hoist room located 25 m from the ore zone at a depth of 1200 m. Several mine wide faults dissect this area and have been shown to be microseismic-active due to mining. The microseismic monitor has been interfaced with a small dedicated personal computer and a communications device to perform routine...
Publication: CIM Bulletin
Author(s): G.R. DAVIDGE
Keywords: Rock mechanics, Strata control, Microseismic monitoring, Computers, Falconbridge Mine, Mine faults, Data evaluation, Structural geology
Issue: 868
Volume: 77
Year: 1984
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Summary: The results of a series of model slope pours designed to investigate working pressures on bulkheads during hydraulic pouring of classified tailings backfill are reported. Total bulkhead pressures and fill water pressures were monitored under the condition of a fully saturated backfill. Similitude of the model testing is discussed and equations are developed to estimate bulkhead pressures under prototype conditions. The model results show that good base drainage, combined with a bulkhead...
Publication: CIM Bulletin
Author(s): ROBERT J. MITCHELL, JAMES J. ROETTGER
Keywords: Rock mechanics, Strata control, Bulkhead pressures, Backfill, Underground mining, Drainage, Sloping
Issue: 868
Volume: 77
Year: 1984
Text
Summary: Microbiological activities affecting the performance of materials have been encountered in diverse situations within Ontario Hydro. Case histories of bacterial problems which are presented include ground rod corrosion at transformer stations, corrosion of a bare steel cooling water intake structure in Lake Huron and corrosion of steel components in a nuclear generation station vacuum building. Possible microbiological activities which may affect the corrosion behaviour of containers for the...
Publication: CIM Bulletin
Author(s): K.W. LAM, A.C. HEADON, D.P. DAUTOVICH
Keywords: Corrosion, Bacterial corrosion, Bacteria, Ontario Hydro
Issue: 868
Volume: 77
Year: 1984
Text
Summary: A computer program is described which will analyze the stability of coal pillars. The extent of the peripheral failed zone and the central elastic core of the pillar, the stress distribution across the pillar and its strength can be determined by a "slice-by-slice" analysis technique. The program incorporates a brittle/pseudo-ductile transition point so that a pillar may fail by brittle fracture or pseudo-ductile yield. It is shown that:
 (i) There is a minimum pillar stress...
Publication: CIM Bulletin
Author(s): K. BARRON
Keywords: Rock mechanics, Strata control, Pillar, Strength, Fracture, Yield, Coal, Stability, Critical widths
Issue: 868
Volume: 77
Year: 1984
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