A Re-Os isotope study of sedimentary rocks and copper-gold ores from the Ertsberg District, West Papua, Indonesia

Re-Os data from pyrite, chalcopyrite, magnetite, gold, and the surrounding sedimentary rocks from the district define a mixing relationship between samples from the initial stockwork mineralization and peripheral ores of each intrusion center. Sulfide and oxide minerals from primary stockwork mineralization are isotopically homogeneous and define trends on isochron diagrams with distinct Os initial ratios, whereas sulfides and oxides taken from peripheral ores are isotopically heterogeneous and define trends on mixing diagrams. One possible end member for the mixing is sedimentary rock surrounding the porphyries. The measured Os ratios of the sedimentary rocks range from 0.52 to 2.21, and overlap the Os initial ratios of the sulfides and oxides sampled from both stockwork and contact mineralization. The data suggest a model in which the continental crust supplied some of the Os (and by inference other metals) during magma genesis in the lower crust and the remainder came from sedimentary rocks near the intrusion centers.