LAUSR

Abstract We provide the first Cu-isotope data for chalcopyrite in Paleozoic carbonate-hosted Mississippi Valley-type (MVT) mineralization, along with corresponding sulfur isotopes, for eastern Wisconsin, USA. Chalcopyrite in this region occurs mainly as disseminated crystals and is associated with regionally extensive dolomite-hosted subeconomic MVT mineralization on the western edge of the ancestral Michigan Basin. A narrow range in δ65Cu values (0 ± 0.5‰) for chalcopyrite is observed along a large region (125 km) of the western margin of the basin that is consistent with a homogeneous Cu-source in the crust with a δ65Cu composition near 0‰, along with limited redox modification during regional flow or hydrothermal precipitation processes. Cu and S-isotope values, in conjunction with existing lead, strontium, and sulfur isotope data from other sulfide minerals in the region, are consistent with a Precambrian source similar to parts of the Midcontinent Rift System, but distinct from some other Precambrian deposits in the region.