Geo-Note 2002-19

Author(s) Date 2003-06-30


Year one (2001-2002) of the two-year (2001-2003) carbonate-hosted Pb-Zn (MVT) project conducted by the Alberta Geological Survey consisted of both office and field investigation of Middle and Upper Devonian carbonate sequences in northern Alberta (north of 56� 30'). This work consisted of evaluation of subsurface fluid flow as well as sedimentological, structural and metallogenic investigations.

Multi-beam RADARSAT-1 satellite imagery was acquired for northern Alberta and was used to search for regional structural lineaments known to control MVT deposit clusters elsewhere in the world as well as to locate karst features indicating near-surface carbonate rocks.

The combined results of office and field data suggest two areas in northern Alberta have increased the prospect of MVT Pb-Zn mineralization.

A coincidence of subsurface fluid flow, structural, sedimentological and past exploration data suggests one area with increased prospectivity is located at Vermilion Chutes on the Peace River. In this region, Gulf Minerals, in 1975 returned 0.1% zinc from the Upper Devonian Grosmont Formation and recommended additional work, which as far as can be determined, was never done. Digital elevation maps of key hydrostratigraphic units indicate a Precambrian basement high exists in the region of Vermilion Chutes. These highs are known to be important factors in directing metal bearing fluids up into overlying porous and reducing carbonate units. Sedimentological data at Vermilion Chutes indicate that the Upper Devonian uppermost Mikkwa Formation and overlying Grosmont Formation are porous, bitumen stained and contain late calcite and dolomite cements in jugs, all characteristic by-products of MVT mineralization. Structural data from the Upper Mikkwa Formation is also supportive. Prominent west-southwest joint surfaces contain steps suggesting incremental, small, oblique slip movements. This joint surface trend is on strike with the Hudsonian Warren-Leland Lakes Shear Zone of the Precambrian Shield to the northeast and could indicate a basement-derived structural trend in the Devonian cover sequence, which might provide access for deep sourced metalliferous fluids.

A coincidence of subsurface fluid flow, sedimentological and structural data also suggests another region of increased MVT Pb-Zn potential is the Whitemud falls area on the Clearwater River east of Fort McMurray. The Middle Devonian Methy Formation is exposed in this area and a minor galena occurrence was previously reported. Digital elevation maps indicate two highs in the Keg River Formation (Methy Formation equivalent) in the Fort McMurray study area. As was the case for the basement high in the Vermilion Chutes study area, these structural features serve as driving forces for subsurface, potentially metalliferous, fluid flow. Sedimentological work has identified a minor occurrence of saddle dolomite cement in these outcrops. Saddle dolomite is known to be associated with MVT Pb-Zn mineralization at the past producing Pine Point mining district in the N.W.T. The Methy Formation here is also locally oxide-altered and faulted with both roughly north-south and west-southwest fault trends

The data gathered at Vermilion Chutes in the Vermilion Chutes study area and at Whitemud Falls in the Ft. McMurray study area are not considered to be strong evidence of undiscovered carbonate-hosted Pb-Zn (MVT) mineralization. However, they are considered to be supportive of some potential for this mineralization to exist. Consequently, a more rigorous sampling program is recommended for both areas.

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Rice, R.J. (2003): The carbonate-hosted Pb-Zn (MVT) project for northern Alberta - background and year one summary: a contribution to the carbonate-hosted Pb-Zn (MVT) targeted geoscience initiative; Alberta Energy and Utilities Board, EUB/AGS Geo-Note 2002-19, 13 p.