Geological setting of the Kemess South copper-gold porphyry deposit, British Columbia.

摘要

The geological setting of the Kemess South copper-gold porphyry was investigated principally by field mapping at a scale of 1:10,000. Methods used in the analysis of specimens collected in the field included: transmitted and reflected light microscopy, scanning electron microscope and electron microprobe analysis, x-ray diffractometry. The combination of field mapping and these analytical methods permitted the recognition of three distinct lithostratigraphic units, which can be correlated with major rock units that have been mapped regionally by Diakow and Metcalfe (1997) and Diakow and Rogers (1998). These major stratigraphic divisions are: (1) the mid-Pennsylvanian to Lower Permian Asitka Group; (2) the Upper Triassic Takla Group; and (3) the lower Jurassic Hazelton Group, specifically the Toodoggone Formation. Two previously unmapped units are exposed as a consequence of the development of the open-pit at Kemess South. The lower unit, which rests directly on supergene ore, has been identified as part of the Saunders Member of the Toodoggone Formation. The uppermost unit is a distinctive, pyroxene-basalt flow that directly overlies and interdigitates the tuff-epiclastic unit. The supergene zone formed as a result of the weathering and oxidation of hypogene zone mineralization (disseminated chalcopyrite + pyrite), located in the upper part of the Maple Leaf pluton, which intrudes Takla Group, Savage Mountain Formation basalts. Supergene copper mineralization is distinguished from hypogene ore, and characterized by, the mineral assemblage: native copper ± chalcocite ± bornite ± covellite. The supergene copper mineralization is set in highly altered, clay- and hematite-rich rocks that preserve some original igneous and hypogene zone textures.