The Arthur W. White Mine, Red Lake area, Ontario: Detailed structural interpretation the key to successful grade control and exploration

CIM Bulletin, Vol. 85, No. 957, 1992

J.A. Rogers, Dickenson Mines Limited

The Arthur W. White Mine (formerly Dickenson Mine) is a structurally controlled, hydrothermal gold deposit. A gold producer since 1948, it has, to December 31, 1990, processed 6.9 million (m) tons (T) of ore grading 0.45 ounces per ton gold (oz/T Au). As of December 31, 1991, Proven and Probable Ore Reserves were 3.2 m. T. at 0.32 oz/T Au. The mine is located just east of Placer Dome Inc. 's Campbell Mine, within the Cochenour-Gullrock Lake deformation zone. It is situated on the hanging-wall side of a southeast-plunging anticline in a sequence of metamorphosed Archean volcanic, sedimentary andplutonic rocks of the Red Lake greenstone belt. Ore-bearing structures, found mainly within basaltic rocks, are brittle within greenschist-facies rocks to the northwest, but become more ductile toward the southeast, in amphibolite-facies rocks. Within and proximal to these structures, carbonate and arsenopyrite alteration decreases, whereas biotite, actinolite, pyrite and pyrrhotite all increase to the southeast. Ore and shear structures occur symmetrically about the northwest-trending, steeply southwest-dipping, flattening foliation. The three most common ore trends are on average: (A) northwest-trending with a 55 degree to 85 degree dip to the southwest; (B) north-trending with a 40 degree to 50 degree dip to the west; and (C) due east-west-trending with a vertical dip. In general, the dominant direction of economic gold concentrations are explained and thus predicted by considering deformation style (brittle or ductile), rock anisotropies such as bedding and lithological contacts, and direction/magnitude of relative block movement. Direction "A " can be found adjacent to both right- and left-handed faults. Direction "B" occurs with dominantly right-handed systems and direction "C" is found with predominantly left-handed movement. Major faults active prior to, during, and after ore formation can have offsets in the order of 2500 feet. Movements along these faults were transpressive while their conjugate breaks were dilatant, thus creating zones for alteration and ore solution emplacement. A series of faults, each with offsets up to 30 feet were established under lower temperature brittle conditions during late- to post-ore formation. In more complex zones, formed during more ductile deformation, these faults controlled the localized geometry and, thereby, the depletion and enrichment of ore shoots, causing a high nugget effect. Although an important aspect of production planning and monitoring, grade control is also very important within a complex ore zone so that the nuggets are not missed. Detailed observation of structure at the hand-sample scale and detailed mapping at the slope scale give valuable clues to interpreting the structures on a mine-wide scale. Determining the relative movement along fault structures is very important so that using an action-reaction- type logic, potential dilatant areas can be predicted and targeted for development and diamond drilling.
Mots Clés: Exploration, Arthur W. White mine, Red Lake, Dickenson Mines Ltd.