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Abstract

Certain aspects of the genesis of Archean epigenetic gold deposits remain controversial, in particular the source of the auriferous fluids, which are arguably magmatic, metamorphic, or mantle derived. In an attempt to constrain the fluid source, it is essential to consider Archean gold mineralization in terms of the tectonic, magmatic, and metamorphic history of greenstone terranes. Asymmetries in the distribution of volcanic, sedimentary, and plutonic rock types, the pattern of deformation, and the rapid evolution of the greenstone sequences within the Norseman-Wiluna belt in the eastern Yilgarn block are akin to those of younger orogenic belts at obliquely convergent continental plate boundaries. Archean gold deposits show many similarities to younger, cordilleran-style gold deposits (e.g., the Mother Lode) which occur in a similar tectonic setting, particularly in terms of their strong dependence on structural controls and the composition of the ore fluids. In the eastern Yilgarn block there is a coincidence of lode gold mineralization, calc-alkaline porphyry, and lamprophyre dike swarms and craton-scale oblique-slip faults with their attendent mantle-derived carbonation. With no compelling evidence for direct derivation of ore fluids from felsic magmas, gold mineralization is best viewed as the upper crustal expression of a deep-seated tectono-thermal event with mantle-crustal outgassing, occurring in response to a deep mantle heat source, related to convergent tectonics. In all probability the ore fluid contained magmatic, metamorphic, and mantle components, but it is impossible at this stage to determine with which component the gold was predominantly associated.

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