Geology and geochemistry of porphyry-related, carbonate-hosted, massive replacement Cu-Au deposits: A case study of the Superior district, Arizona

arbonate-hosted Cu-Au replacement ores represent the products of one of the most striking examples known of metal concentration in the earth's crust. An understanding of the geochemical processes involved in their formation will help us to understand the factors affecting the mobility of metals and fluids at shallow levels of the earth's crust.;Geochemical constraints on the composition of fluids that form carbonate-hosted Cu-Au replacement deposits, including the occurrence of bornite-pyrite, presence of enargite, local occurrence of large volumes of hypogene iron oxides, and kaolinite-zunyite ;In the Superior district (Arizona), individual orebodies are zoned outward from (1) central bornite-pyrite ;Irreversible thermodynamic reaction path modeling demonstrates how variations in the oxidation state and total aqueous sulfur concentrations of ore fluids in the source region may explain mineralogical variations among deposits. Oxidized, sulfide-poor fluids form deposits characterized by abundant hypogene iron oxides and absence of sphalerite, enargite and tennantite. Fluids with moderately high sulfur concentrations form enargite-bearing massive sulfide ores with minor zinc ores and no iron oxides, and sulfur-rich fluids form covellite- and bornite-bearing ores with abundant sphalerite but no iron oxides. Fluid interaction with sulfur-fixing basement rocks prior to reaction with carbonates can effectively reduce sulfur concentrations and so alter the reaction path.;Low...