19 Fluids, Melts, and Metals in the Crust

Friday, 2 April 2021
1:30 PM - 5:30 PM
Vulcan Materials Company Room

GEOCHEMICAL INFLUENCES ON THE PERIODICITY OF GALENA AND SPHALERITE FORMATION WITHIN MVT DEPOSITS

Paper number: 19-7
Program: Theme Sessions
Time: 3:05 PM – 3:25 PM

Authors

Abstract

Mississippi Valley Type (MVT) lead and zinc deposits provide a significant amount of sedimentary galena (PbS) and sphalerite (ZnS) ores, but geochemical genesis of deposition including the source and production of hydrogen sulfide (H2S) required for galena and sphalerite ore formation and the reasoning behind the quick bursts of mineralization has remained uncertain. By simulating the geochemistry of regional MVT brines (Sangster, 1996), we will identify the optimal and probable conditions for these ore formations. Experiments using autoclaves and brine compositions from North American MVT fluid inclusions were conducted over 2-week periods. Controlled variables during the experiments include temperatures, CO2, lead and zinc, hydrogen sulfide, and overall brine concentrations; lead, zinc and sulfur concentrations were analyzed following removal from the autoclaves. The absence of sulfide minerals in preliminary SEM imaging indicated that at low temperatures (70-80 oC) sulfate does not reduce to hydrogen sulfide within 2 weeks. This may indicate the occurrence of biologic sulfate reduction in low-temperature MVT deposits. SEM has also shown that the regional brine compositions produced primarily galena, confirmed by ICP-OES data in which 84.1% of starting lead precipitated out of solution compared to 35.4% of starting zinc. The chemical implications being the possibility of fluid mixing and episodic bursts of MVT sulfide mineral formation. Ongoing experiments will help to further characterize the geochemical genesis of low-temperature MVT sphalerite and galena by determining the chemical cause for galena and sphalerite exclusivity during precipitation as well as the probability of biological sulfate reduction in low temperature settings.

Sangster, D.F., 1996, Mississippi Valley-Type lead-zinc; in Geology of Canadian

Mineral Deposit Types, (ed.) O.R Eckstrand, W.D. Sinclair, and R.I. Thorpe; Geological Survey of Canada, Geology of Canada, no. 8, pp. 253-261.

Geological Society of America Abstracts with Programs. Vol. 53, No. 2

doi: 10.1130/abs/2021SE-362377

© Copyright 2021 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.