Textural,mineralogical and stable isotope studies of hydrothermal alteration in the main sulfide zone of the Great Dyke,Zimbabwe and the precious metals zone of the Sonju Lake Intrusion,Minnesota, USA |
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| Authors: | Chusi Li Edward M Ripley Thomas Oberthür Jr" target="_blank">James D MillerJr Gregory D Joslin |
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| Institution: | (1) Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA;(2) China University of Geosciences, Beijing, 100083, China;(3) Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, 30655 Hannover, Germany;(4) Minnesota Geological Survey, St. Paul, MN 55114, USA;(5) Department of Geological Sciences, University of Minnesota, Duluth, MN 55812, USA |
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| Abstract: | Stratigraphic offsets in the peak concentrations of platinum-group elements (PGE) and base-metal sulfides in the main sulfide
zone of the Great Dyke and the precious metals zone of the Sonju Lake Intrusion have, in part, been attributed to the interaction
between magmatic PGE-bearing base-metal sulfide assemblages and hydrothermal fluids. In this paper, we provide mineralogical
and textural evidence that indicates alteration of base-metal sulfides and mobilization of metals and S during hydrothermal
alteration in both mineralized intrusions. Stable isotopic data suggest that the fluids involved in the alteration were of
magmatic origin in the Great Dyke but that a meteoric water component was involved in the alteration of the Sonju Lake Intrusion.
The strong spatial association of platinum-group minerals, principally Pt and Pd sulfides, arsenides, and tellurides, with
base-metal sulfide assemblages in the main sulfide zone of the Great Dyke is consistent with residual enrichment of Pt and
Pd during hydrothermal alteration. However, such an interpretation is more tenuous for the precious metals zone of the Sonju
Lake Intrusion where important Pt and Pd arsenides and antimonides occur as inclusions within individual plagioclase crystals
and within alteration assemblages that are free of base-metal sulfides. Our observations suggest that Pt and Pd tellurides,
antimonides, and arsenides may form during both magmatic crystallization and subsolidus hydrothermal alteration. Experimental
studies of magmatic crystallization and hydrothermal transport/deposition in systems involving arsenides, tellurides, antimonides,
and base metal sulfides are needed to better understand the relative importance of magmatic and hydrothermal processes in
controlling the distribution of PGE in mineralized layered intrusions of this type. |
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| Keywords: | Platinum-group minerals Sulfide Alteration Stable isotopes Great Dyke Sonju Lake Intrusion Zimbabwe USA |
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