Mineralogical and Geochemical Characterization of Hydrothermal Alteration at Lynne Zn-Cu-Pb Deposit, Oneida Co. Wi.

Abstract

The purpose of this project is to determine the specific style of hydrothermal alteration that occurs within the volcanic strata at Lynne Zn-Cu-Pb deposit. The Lynne deposit is a volcanogenic massive sulfide deposit (VMS) that forms from metallic-rich fluid exhaling on the ocean floor, typically during extensional submarine volcanism. These deposits form as a type of mounded or tabular body of sulfide minerals. Wisconsin is host to a chain of VMS deposits within a 1.9-1.8 Ga accreted volcanic arc called the Pembine-Wausau terrane. Noranda Exploration discovered the Lynne deposit in 1990 but the deposit was never mined. For this project, core from the initial exploration was re-logged and sampled throughout the hydrothermally altered strata hosting the deposit. Examination of the core reveals two main alteration types: talc carbonate and calc-silicate. Samples were made into thin sections and were processed to obtain geochemical data. This research quantifies alteration through mass balance geochemical analysis of the altered rocks, showing which elements were mobilized by hydrothermal fluids. Understanding the element mobility during ore formation will allow for comparisons to be made between other deposits elsewhere in Wisconsin.