The geology, geochemistry and U-Pb geochronology of the Stog'er Tight gold prospect, Baie Verte Peninsula, Newfoundland

Ramezani, Jahandar (1992) The geology, geochemistry and U-Pb geochronology of the Stog'er Tight gold prospect, Baie Verte Peninsula, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Baie Verte Peninsula in Newfoundland is the locus of numerous gold occurrences and showings. The great majority of these epigenetic gold prospects are located in the vicinity of the Baie Verte Line, the major structural feature of the Peninsula, and its second (and higher) order splays. The Stog'er Tight prospect, the subject of this study, is a mesothermal, shear-hosted, gold occurrence which is located within the Point Rousse Ophiolite Complex, north of the Scrape Thrust, and to the east of the Baie Verte Line. -- Gold mineralization in the Stog'er Tight prospect is hosted by a variety of subextrusive, gabbroic sills which have intruded a volcanic (and pyroclastic) sequence. The crystallization age of the Stog'er Tight gabbro is constrained by U-Pb zircon geochronology to be 483 + 3/-2 Ma. The chemical composition of the Stog'er Tight gabbro and associated early volcanic lithologies reflects a progressive transition from island-arc to MORB and OIB-dominated magmatism, analogous to that in modern oceanic back-arc basins. The mineralization is structurally controlled and is characterized by pervasive and systematically zoned hydrothermal alteration. Four distinct alteration zones are identified based on dominant mineral assemblages. These include the chlorite-calcite zone, ankerite-sericite zone, chlorite-magnetite zone and the red albite-pyrite (+ gold) zone. The latter, which represents the highest intensity of alteration and gold mineralization, formed between an early episode of ductile deformation (DE) and a subsequent brittle-ductile (DL) phase, within the D₁ shear zones of the area. -- Gold was precipitated as a result of shear zone-induced infiltration of fluids which reacted with the Fe-rich phases of gabbro to destabilize the gold-bearing complexes. Hydrothermal alteration involved progressive CO₂, S and K metasomatism as well as significant LILE, REE, HFSE and Th enrichments. These enrichments imply that the mineralizing fluids were in equilibrium with (or derived from) enriched continental crustal sources, as opposed to the commonly depleted oceanic rocks. -- The hydrothermal alteration in the Stog'er Tight prospect has a U-Pb zircon age of 420 ±5 Ma. The mid-Silurian age of this hydrothermal zircon implies that gold mineralization in the Stog'er Tight prospect occurred at a final stage of Early Silurian orogenic activity in the Baie Verte Peninsula.

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