Mineralogy and genesis of critical-metal bearing mineralization in the Betts Cove and Tilt Cove volcanogenic massive sulfide (vms) deposits, Baie Verte, Newfoundland Appalachians

Kennedy, Kyra (2024) Mineralogy and genesis of critical-metal bearing mineralization in the Betts Cove and Tilt Cove volcanogenic massive sulfide (vms) deposits, Baie Verte, Newfoundland Appalachians. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Betts Cove and Tilt Cove deposits are two Cu-Co-Ni-Zn-Te-bearing mafic-(Cyprus)-type VMS deposits hosted in the Betts Cove ophiolite, Baie Verte Peninsula, Newfoundland Appalachians. The mineralogy consists of dominantly pyrite, chalcopyrite, pyrrhotite, and sphalerite, and magnetite at Tilt Cove. Accessory minerals include cobaltite and pentlandite and trace phases include acanthite, arsenopyrite, bornite, chromite, clausthalite, electrum, galena, and hessite. These minerals contain base and precious metals (e.g., Au, Ag, Cu, Zn, Ni, Co) and other trace metals (e.g., As, Bi, Co, Hg, Sb, Se, and Te). Mineral textures, relationships, chemistry, and paragenesis show that the deposits evolved from an early, low temperature (< 300⁰C), near neutral pH, and reducing fluid, that deposited sphalerite and pyrite, to a later, high temperature (> 300⁰C), acidic, and reducing fluid, that deposited chalcopyrite and pyrrhotite (+/- pyrite, cobaltite, and pentlandite). The presence of late magnetite and bornite at Tilt Cove reflects the overall cooling of the hydrothermal system and a switch to more oxidizing and sulfur poor fluid conditions. Sulfur isotope compositions range from +2.82 to +23.57‰ and indicate that reduced sulfur in the sulfides was derived from seawater sulfate mixing with leached footwall igneous sulfur; some highly positive values are best explained by the replacement of sulfate minerals by sulfide minerals. The leaching of ophiolitic, Cu-, Co-, Ni-, As-, Au-, and Sb-bearing footwall rocks with minor potential contributions from episodic, short-lived magmatic pulses were most likely responsible for the metals found in the Betts Cove and Tilt Cove deposits.

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