STRUCTURAL EVOLUTION OF AURIFEROUS DEFORMATION ZONES AT THE CAMPBELL MINE, RED LAKE GREENSTONE-BELT, SUPERIOR PROVINCE OF CANADA

The Campbell mine, the largest gold mine in the Red Lake camp, lies wi thin the regional (first-order) NW-trending foliation-parallel Cocheno ur-Gullrock Lake deformation zone. The auriferous veins at the mine ar e hosted by subvertical second-order deformation zones within the Coch enour-Gullrock Lake deformation zone. These second-order deformation z ones strike NW, NNW and E-W. Across the foliation-parallel NW-trending ore zones (A, F, F2 and NL ore zones), the rock and magnetic foliatio ns show progressive increase in strain intensity, but their orientatio ns do not change. This, together with the absence of other shear-sense indicators within the foliated rocks, strongly suggests that the foli ation parallel NW-trending ore zones were developed during NE-SW subho rizontal shortening. Foliation-oblique ore zones strike NNW (G and P z ones) and E-W (part of A and L zones). They display shear-sense indica tors such as asymmetrical folding of thin gold-bearing quartz-carbonat e veins and progressive rotation of petro and magnetic fabrics. These shear-sense indicators indicate that NNW- and E-W-trending ore zones a re dextral and sinistral strike-slip shear zones, respectively. The in tersection of these second-order shear zones is approximately parallel to the subvertical boudin axis of foliation-parallel veins in the NW- trending deformation zones, and the NW-trending deformation zones bise ct the NNW- and E-W-trending shear zones. These suggest that the NNW- and E-W-trending shear zones are conjugate shear zones developed in as sociation with the NE-SW subhorizontal shortening, which is normal to the NW-trending deformation zones. Cross-cutting relationships, the de formation recorded in post-ore lamprophyre dykes, and stress tensors i nverted from the fault-slip data suggest that the NE-SW compression de formation spanned a prolonged period. Auriferous veining under the com pression regime is followed by lamprophyre dyke intrusion, then by bri ttle-ductile faulting under NE-SW compression. The mode of deformation may characterize other parts of Cochenour-Gullrock Lake deformation z one and is of significant importance in gold exploration in the easter n part of the Red Lake greenstone belt. Field data from the Cochenour- Gullrock Lake deformation zone and the margin of the Trout Lake bathol ith suggest that the NE-SW shortening is likely related to the batholi th emplacement and that the Cochenour-Gullrock Lake deformation zone c orresponds to a highly attenuated limb of a NW-trending regional fold which overprints earlier NE-trending folds in the area. (C) 1997 Elsev ier Science B.V.