The character and setting of gold mineralization associated with the Betts Cove complex

Al, Thomas Anthony (1990) The character and setting of gold mineralization associated with the Betts Cove complex. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Ordovician Betts Cove ophiolite is located in northeast Newfoundland on the southeast side of the Baie Verte peninsula, between the communities of Tilt Cove and Nippers Harbour. Ultramafic rocks occur at the base of the ophiolite in fault contact with the upper ophiolite stratigraphy (mainly pillow lava) to the south. North of the ophiolite, intermediate and felsic volcanic and sedimentary rocks of the Silurian Cape St. John Group, and the Cape Brule Quartz-Feldspar Porphyry are in fault contact with the ultramafic rocks. Locally the Cape St. John Group unconformably overlies the ophiolite. -- Fresh, cumulate ultramafic rocks are altered to carbonate-bearing assemblages. The onset of carbonate alteration is marked by a serpentine-magnesite assemblage which appears where fresh ultramafic rocks are cross cut by shear zones. Serpentine-magnesite reacts to form talc-magnesite with progressive shearing. Talc-magnesite is the most abundant ultramafic rock type present in the area. Localized quartz-hematite-dolomite alteration assemblages with minor fuchsite are present. -- Two types of gold mineralization are described. The first type occurs in a talc-magnesite host and consists of a simple quartz, magnesite, Cu-sulphide mineralogy. The second type is hosted by the quartz-hematite-dolomite altered ultramafic rocks and shear zones within the Silurian Cape St. John Group. These Au-mineralized veins consist of quartz, ankerite, fuchsite, and specularite plus or minus magnetite and Cu-Fe sulphides. -- Gold enrichment in the ultramafic rocks is associated with regional scale carbonate alteration. This link is important for defining exploration targets. Rare earth element and Sr isotope evidence implicate an ultramafic source rock and a fluid derived from hydrated ultramafic rocks (Ordovician seawater). -- Mineralization probably occurred as a result of metamorphic dehydration of serpentinized ultramafic rocks during Acadian Orogenesis. Faults on the margin of a caldera complex to the north, and older structures related to obduction of ophiolitic rocks during the Middle Ordovician, probably acted as fluid conduits.

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