Date of Award
Master of Science
Geological and Environmental Sciences
Dr. Joyashish Thakurta
Dr. Robb Gillespie
Dr. Peter Voice
Sulfur, volcanogenic, Paleoproterozoic, isotope, penokean
Masters Thesis-Open Access
The Penokean Volcanic Belt (PVB), located in northern Wisconsin and Upper Peninsula, Michigan hosts several volcanogenic massive sulfide deposits (VMS) including the well-known deposits of Flambeau and Crandon. The host rocks of the VMS deposits are Paleoproterozoic in age overlying Archean age basement rocks. This study provides δ34S (VCDT) values for the following deposits within the PVB; (1) Eisenbrey, (2) Schoolhouse, (3) Bend, (4) Flambeau, (5) Reef, (6) Horseshoe, and (7) Back Forty, and explains the distribution of δ34S values in the region.
The study reveals tight ranges of δ34S values for each deposit independent of host rocks, sampling depth, or sulfide type. The median δ34S values for Eisenbrey (-0.4 ‰), Schoolhouse (-1.2 ‰), Bend (-0.2 ‰), Reef (-0.5 ‰), Crandon (0.9 ‰), Flambeau (-0.8 ‰), and Horseshoe (0.6 ‰) fall within the known range of 0 ± 2‰ for mantle derived sulfur. The δ34S values for Back Forty (2.5 ‰) and Lynne (2.4 ‰), are higher and indicate the possible mixing of a secondary source of sulfur with much higher δ34S value. One possible way to explain the higher δ34S values is that Back Forty and Lynne formed closer to the continental margin of the Superior Craton and received an influx of terrestrial sulfur with a high δ34S value.
Moleski, Nicholas M., "Regional Sulfur Isotope Study of the VMS Deposits in the Penokean Volcanic Belt" (2018). Master's Theses. 3799.