Gold mineralization at the Campbell Mine, Red Lake greenstone belt, Uchi subprovince, Ontario.

摘要

The Campbell mine is located in the eastern part of the Red Lake greenstone belt, Uchi Subprovince.; Auriferous veins are parallel to S₂, and are termed foliation parallel auriferous veins (NW striking, SW dipping). Auriferous veins also occur in shear zones which are oblique to the regional NW trending foliation (foliation-oblique deformation zones). These auriferous veins occur proximal to the F₂ fold hinges. The deformation zones are typically meters to 10's of meters wide, and are characterized by more intense foliation development, and abundant carbonate veins and veinlets. Progressive D₂ shortening resulted in a late D₂ decollement along the southwestern limb of the Balmer synform, cutting and offsetting auriferous mineralization.; Several stages of hydrothermal activity are recognized in the Campbell mine area. Subsequent Au mineralization occurs in quartz veins and quartz + arsenopyrite hydrothermal breccias within quartz + carbonate veins; thus most of the Au mineralization overprints pre-existing quartz + carbonates within the D₂ shear zones.; Native gold from amphibolite facies domains contains significant Ag, precluding that it formed by the thermal decomposition of aurostibite. Therefore, the spatial variations in occurrence of Au phases reflect the deposition of Au during the peak metamorphism.; Higher metamorphic grade rocks are extended westward along the auriferous shear zones, suggesting heat transfer along shear zones by hydrothermal fluids. This suggests a magmatic heat source to the east for auriferous hydrothermal activity. Hence, Au mineralization likely took place during the emplacement of the marginal phase of the Trout Lake batholith.; The lack of Type II inclusions in high Au grade breccias is interpreted as a result of the selective loss of H₂O following phase separation.; Phase separation is probably the most important mechanism for the mineralization of high Au grades (>500 g/t Au) at the mine.; The gold-related wallrock alteration at the Campbell Mine is similar to that in other Archean Au deposits hosted by lower amphibolite facies mafic rocks, such as the Coolgardie goldfields (Knight et al., 2000) and the Norseman district deposits (Mueller, 1992). The P-T conditions for the auriferous hydrothermal activity at many Archean lode-type deposits define a low P and high T path. The path indicates much higher temperatures than the Archean geotherm, suggesting either a contribution of heat from contemporaneous magmas to auriferous fluids, or rapid transfer of heat from deep levels. For syn-metamorphic Au deposits, the data support a magmatic heat source. This is in accord with the low P/high T conditions of the metamorphism accompanying the Au deposits. For post-peak metamorphic deposits, the data suggest transport of heat from a source external to the greenstone sequence. (Abstract shortened by UMI.)