Sulfur Isotope Ratios from VMS Deposits in the Penokean Volcanic Belt, Great Lakes Region, USA: Constraints on the Source of Sulfur in a Paleoproterozoic Intra-Arc Rift

Abstract

The Paleoproterozoic (~1.8 Ga) Penokean Volcanic Belt (PVB) in the Great Lakes Region of North America hosts several polymetallic volcanogenic massive sulfide (VMS) deposits. These deposits were formed by back-arc extensional volcanism during the accretion of island-arc terranes along the southern margin of the Archean Superior Craton. This study reports δ34S values obtained from sulfide minerals collected from eight VMS deposits in the PVB: Back Forty, Bend, Eisenbrey, Flambeau, Horseshoe, Lynne, Reef, and Schoolhouse. The average δ34S values from most of these deposits lie within the mantle-range between −2 and 2‰, relative to Vienna Canyon Diablo Troilite (V-CDT). Average δ34S values from Back Forty and Lynne deposits are slightly higher, at 2.5 and 2.4‰, respectively. No systematic variation in δ34S was observed based on factors such as the kind of sulfide mineral, ore-texture, type of host rock, or the nature of host-rock alteration. The narrow observed range from the PVB offers a clear indication that sulfur in the mineralizing fluid, originated predominantly from a magmatic source. If there was a significant contribution of sulfur from seawater, the δ34S of seawater sulfur must also have been close to the mantle range. Slightly higher values from Back Forty and Lynne indicate minor involvement of oxidized sulfur at shallow water levels, possibly derived from the continental margin.

The genesis of metamorphosed Paleoproterozoic massive sulphide occurrences in central Colorado: geological, mineralogical and sulphur isotope constraints

“…In the United States, Paleoproterozoic massive sulphide deposits include VMS deposits in the ∼1.81 Ga Penokean Volcanic Belt, Wisconsin (e.g. Moleski et al 2019), the largest of which is Crandon (42.9 Mt @ 0.6% Cu, 8.4% Zn, 51 g/t Ag and 1.4 g/t Au), as well as those in the ∼1.74 Ga Jerome VMS district (>100 Mt of Cu-Zn-Pb-Au-Ag), Arizona, and the ∼1.8 to 1.7 Ga massive sulphide belt in south-central Colorado. Massive sulphide deposits in Arizona and Colorado occur in the regional Yavapai tectonic terrane, or the transitional Yavapai–Mazatzal tectonic terrane, that extends from Nevada through to Colorado.…”