GEOCHEMISTRY AND VMS DEPOSIT FORMATION PROCESSES: COMPARISON BETWEEN RED LEDGE AND LYNNE DEPOSITS

Understanding how sulfide-bearing hydrothermal fluids may react with host rocks to ultimately form volcanogenic massive sulfide (VMS) deposits is important for mineral exploration purposes. In our project we are comparing the geochemical effects of sulfide bearing hydrothermal fluids in Wisconsin at Lynne and Flambeau deposits to see whether we can relate the types and extents of chemical alterations to the amounts and types of sulfide minerals found in those deposits. Both Lynne and Flambeau deposits are VMS deposits, belonging to the Ladysmith-Rhinelander Metavolcanic Complex within the Wisconsin Magmatic Terrane. Lynne is a zinc rich deposit located within the Somo District, while Flambeau is a copper rich deposit located in the Ladysmith district. Both deposits contain stratabound and stratiform sulfide ore minerals near felsic volcanic centers. The host rocks being intruded by sulfide-bearing hydrothermal fluids at Flambeau deposit are mostly sericite rich metavolcanics, whereas those at Lynne deposit are mostly chert and/or carbonate-rich sediments. Though both deposits have been extensively studied for their economic potential, very few detailed studies have been conducted on the geochemical effects of the ore-bearing hydrothermal fluids on the host rocks in either location.

For this project we are conducting detailed chemical analyses on representative core samples from both deposits using a Bruker Handheld X-Ray Fluorescence (XRF) Analyzer and an Inductively Coupled Plasma Optical Emissions Spectrophotometer (ICP-OES) at UW Whitewater campus. Preliminary XRF data indicate the concentrations of Zinc and lead are higher within the sulfide layers of the Lynne Deposit while copper concentrations are higher within the Flambeau Deposit. ICP-OES data confirms the XRF data, while also adding a significant amount of silver within the Lynne Deposit. Future work will help confirm if the silver is in a native or sulfide state.

Here we present the results of our chemical analyses, and discuss the possible implications of the observed distribution patterns of selected elements in terms of exploring for similarly formed VMS deposits in other locations around the world such as the Red Ledge Deposit in the Rocky Mountain Region.