Genetic deposit model for orogenic Au-Cu-Co-(Ni-Sb-U-REE) deposits: examples from Paleoproterozoic Finland

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Paleoproterozoic terranes in Finland host hydrothermal, orogenic gold-only deposits and Au-Cu-Co-(Ni-Sb-U-REE) deposits. Both deposit types are closely spatially associated, occur in the same host rocks and in the same structures. Paleoproterozoic orogenic gold-only deposits are well-known form Finland and elsewhere. A genetic model for the formation of these deposits is well-developed, although the question on the source of fluids and gold remains open. The co-occurrence of orogenic gold-only deposits and Au-Cu-Co-(Ni-Sb-U-REE) deposits raises the question on how the different metal endowment of the deposits can be explained and how the latter deposit types has formed. We want to investigate selected deposits of both types in central Finland using structural, petrological, geochemical and geochronological methods. We will establish mineral assemblages and relate them to the different metal content. A scheme of relative timing of mineral formation and structures, i.e. auriferous veins, will be developed. Geochronology will yield an absolute time frame for the mineralization process. Detailed trace element, halogen and stable isotope geochemistry will be used as proxies for fluid and metal source as well as precipitation mechanisms in the deposit. The latter will be aided by petrographical observation and structural analysis. All data will be integrated in order to formulate a genetic model for the Au-Cu-Co-(Ni-Sb-U-REE) deposits on the basis of the genetic model for gold-only deposits. We expect important new information on the genesis of hydrothermal ore deposits in metamorphic terranes as a whole, which can be used in future targeted mineral exploration.