Mineralogy, metal zoning, and genesis of the Cambrian Zn-Pb-Cu-Ag-Au Lemarchant volcanogenic massive sulfide (VMS) deposit

Gill, Shannon (2015) Mineralogy, metal zoning, and genesis of the Cambrian Zn-Pb-Cu-Ag-Au Lemarchant volcanogenic massive sulfide (VMS) deposit. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Lemarchant deposit is a Cambrian bimodal felsic Zn-Pb-Cu-Ag-Au volcanogenic massive sulfide (VMS) deposit that is hosted in the Newfoundland Appalachians. The mineralogy consists of barite and normal VMS sulfides (e.g., sphalerite, galena, pyrite, chalcopyrite), as well as minerals common to epithermal deposits (e.g., tetrahedrite, bornite, electrum) and enrichments in epithermal suite elements. Sulfur isotope analyses of sulfides range from δ³⁴S -6.4 to +15.1‰ and indicate sulfur was derived from thermochemically reduced seawater sulfate, igneous leaching and magmatic SO₂ . Lead isotope data are restricted, and indicate Pb-sourcing from Neoproterozoic basement rocks and more juvenile sources. The occurrence of epithermal suite minerals and element enrichments with bladed suggest that precious metals were derived from magmatic fluid additions to the VMS hydrothermal system. Precious metal enrichment of the Lemarchant deposit was caused by low temperature, oxidized, near neutral fluids that boiled upon seafloor discharge in a shallow water (<1500 mbsl) setting.

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