Olivine Geochemistry and Stable Isotope Studies of the Giant Jinchuan Ni-Cu Sulfide Deposit, Western China: Investigation of Ore Genesis in a Magma Conduit

Indiana University, Bloomington IN

Investigators

Abstract

Li&Ripley EAR-0104580 The formation of large Ni-Cu sulfide deposits in mafic magmatic systems appears to require: 1) attainment of sulfide saturation through country rock contamination, 2) concentration of immiscible sulfide liquid in fluid dynamically favored areas within magma conduits, and 3) enrichment of the metal content of the coalesced sulfide by reaction with continued flow of magma through the conduit. The Jinchuan deposit in north-central China is the largest conduit-related occurrence in the world. Major reserves of Ni- and Cu-sulfides are located within ultramafic rocks that intrude a Proterozoic metasedimentary sequence. To date the deposit has not been investigated with respect to the potential role of country rock contamination in ore genesis, nor have the physicochemical dynamics of metal upgrading of sulfide by fresh magma been evaluated. We propose a detailed study of olivine chemical variations and stable isotopic distributions within the rock types present in the Jinchuan intrusion. Olivine chemistry, in conjunction with whole rock major and trace element data, will be used to determine if multiple magmas have been involved in building the Jinchuan intrusion, and if so, to what extent they have interacted with sulfide to produce enriched Ni and Cu contents. Sulfur and oxygen isotopic data will be collected from country rocks and both mineralized and non-mineralized intrusive rocks. These data will be used to evaluate the extent of country rock assimilation recorded in the ore-bearing intrusive rocks, and to construct mixing models that will be utilized in simulating the history of sulfide saturation and concentration in the magmatic system. Findings from the proposed research will not only improve our understanding of the formation of the Jinchuan deposit and other deposits of similar type around the world, but will also improve our knowledge of dynamic petrological processes in mafic magmatic conduit systems.