Lithogeochemistry and hydrothermal alteration of the Pine Cove orogenic gold deposit, Baie Verte Peninsula, Newfoundland, Canada

• Main Author: Ybarra, Samuel
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2020
• Subjects: Baie Verte; Baie Verte Peninsula; Bobby Cove; Canada; Pine Cove; Snooks Arm; Verte; Newfoundland
• Online Access: https://research.library.mun.ca/14422/; https://research.library.mun.ca/14422/1/thesis.pdf

The Pine Cove gold mine is hosted within Ordovician gabbro sills and volcano-sedimentary rocks of the Venam’s Bight and Bobby Cove formations, Snooks Arm Group, Baie Verte Peninsula, Newfoundland Appalachians, Canada. The deposit is located approximately 50 to 200 m above the Scrape thrust fault, a brittle-ductile structure associated with Silurian transpression. Gold mineralization occurs as microscopic native Au inclusions in pyrite disseminated in the selvages of quartz-calcite-chlorite±albite breccia-veins. Multiple generations of overlapping veins are enveloped by sericite-rutile-calcite-pyrite alteration selvages. Mineralized quartz breccia veins are most abundant at the contacts of gabbro sills and volcano-sedimentary strata. Ore-grade mineralization predominantly occurs within Fe-rich gabbros and basalts of the Venam’s Bight Formation. These relationships suggest that there were two fundamental controls on mineralization: 1) hydrofracturing assisted by anisotropic deformation of rigid gabbro sills within more ductile country rocks; and 2) sulfidation of the Fe-rich gabbros and basalts. Comparatively, the volcaniclastic rocks of the Bobby Cove Formation lack abundant gabbro intrusions and are relatively Fe-poor, and were thus a less receptive host rock to gold mineralization at Pine Cove. Three distinct alteration assemblages are identified at Pine Cove: proximal sericite-rutile-chlorite-calcite, intermediate carbonate-chlorite, and distal epidote-titanite-chlorite-calcite. Mass balance calculations for altered wall rock show enrichments in CO₂, K₂O, S, Rb, W, In, Pb, Bi, Te, Se, Cs, and Ba, and depletions in As, Sb, and Na₂O. REE, HFSE, Al₂O₃, and most transition metals were generally immobile during alteration. There are distal to proximal elemental variations in relation to gold mineralization, and the generalized sequence of geochemical variation includes (from distal to proximal - 50m to 1m): CO₂ enrichment + As-Sb depletion Æ K-Rb enrichment Æ Na depletion Æ W±Pb±Ba enrichment Æ Au. The ...