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Robb Lake

British Columbia, Canada

Main commodities: Pb Zn
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Robb Lake is the largest of a number of carbonate hosted "Mississippi Valley" type deposits found in the Canadian Cordillera in north-eastern British Columbia. &nbp; These deposits are hosted by Silurian to Mid Devonian carbonates in the shelf-basin facies transition of the Western Canadian Basin where it has been thrust-telescoped, uplifted and exposed by the Cordilleran Orogen.   This line of deposits parallels the belt of late Devonian shale hosted lead-zinc deposits in the Kechica Trough some 50 to 100 km to the west (the best known of which are the Cirque and other deposits of the Gataga District).

The stratigraphy near Robb Lake represents two distinct sequences separated by two major thrust faults.   To the NE, in the footwall of the upper of these thrust faults there is a platformal sequence of Siluro-Devonian dolostones of the Nonda, Muncho-McConnell, Stone, and Dunedin Formations and shales of the Upper Devonian Besa River Formation.   The hangingwall strata to this thrust comprise basinal units (composed of dark argillites as well as calcareous shales and carbonates) that belong to the Kechika Trough, including the Shoki and Road River Groups, Silurian-Devonian quartzite-dolomite, and Silurian dolostone breccia.   Below the lower thrust is more Upper Devonian which is present as a western facies with dark shales/argillites, compared to the eastern facies of pale laminated calcareous mudstone/siltstone above the lower thrust, but in the footwall of the upper thrust.   All of this thrust package has been folded into an open north-south trending antiform, the Robb Anticline.

The Robb Lake mineralisation is exposed over an area of 8 sq. km.   It comprises a series of interconnected bedding-parallel and crosscutting breccia bodies with matrices of sparry dolomite, sphalerite, galena, pyrite, quartz, calcite and pyrobitumen, and peripheral veins and stockworks.

The Robb Lake breccias have a number of textures, namely:  1). sparry dolomite-cemented crackle,  2). mosaic  3). rubble and  4). rock-matrix or "trash" breccias.

In the crackle and mosaic breccias the fragments are highly angular, little displaced and composed of dolostone host rock in a coarse grained sparry white dolomite cement.   The mosaic breccias grade through crackle to un-fractured dolomite.   In contrast the polymictic rubble and rock-matrix (trash) breccias have completely displaced fragments that include host dolostone as well as sulphide shards and thin curviplanar segments of white sparry dolomite vein selvages with sulphides in the matrix and as fracture fill.   The relationships between these breccia types indicate multiple and repeated brecciation.

Pb-Zn mineralisation is apparently of Late Devonian (362±9 Ma) age.

The geologic resource at Robb Lake is: 6.5 Mt @ 7.11% Pb+Zn using a cutoff of 2.4 m mining width and 5% Pb+Zn.

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2002.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


  References & Additional Information
   Selected References:
Nelson J, Paradis S, Christensen J, Gabites J  2002 - Canadian Cordilleran Mississippi Valley-type deposits: a case for Devonian-Mississippian back-arc hydrothermal origin: in    Econ. Geol.   v97 pp 1013-1036


Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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