Abstract

Gold lode deposits, hosted within shear zones of Archean metavolcanic belts, have produced some of the world's largest gold mines. Consequently, exploration has focussed on regional lineaments within these belts. However, commonly associated metaturbidite terrains may also become good exploration targets once previously unrecognized structural and lithological ore controls are determined and their genesis better understood. Mapping of lower-greenschist-grade metaturbidites of the Burwash Formation at Gordon Lake (62°54′N, 113°15′W) has identified gold-bearing, quartz-breccia zones that are confined to the central area of a south-closing regional refold of earlier, vertically plunging isoclinal (F1) folds. The refold is partly transected by a "regional" cleavage (S3) and has a crenulation cleavage (S4) restricted to its hinge region. Of five breccia types recognized, the strata-bound, gold-bearing, and sulphide-rich breccias found at Knight Bay are economically the most important. These breccias are restricted to the crenulated domains within the central part of the refold and are hosted preferentially in the black, carbon-rich siltstones. Our data are compatible with a model whereby metamorphic fluids, carrying gold extracted from the metaturbidite pile, were focussed into fractures within the central domain of the refold during (anticlockwise) rotation of the refold's east limb. The limb rotation induced dextral bedding-parallel slip in the central domain of the refold and resulted in the formation of a crenulation cleavage and hydraulic fracturing within overpressured siltstone beds. Decompression during the episodic hydraulic fracturing led to precipitation of grey quartz, gold, sulphides, and minor carbonates. The organic matter within the black siltstone host may have physically enhanced bedding-parallel slip and, if the mineralizing solutions were oxidizing, led to chemical reduction at the site of ore concentration.

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