A geological, geochemical and structural analysis of the Lower Ordovician Tulks Hill Cu-Zn-(Pb) volcanogenic massive sulphide deposit, central Newfoundland, Canada

Moreton, Christopher (1984) A geological, geochemical and structural analysis of the Lower Ordovician Tulks Hill Cu-Zn-(Pb) volcanogenic massive sulphide deposit, central Newfoundland, Canada. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Tulks Hill Cu-Zn-(Pb) prospect is a volcanogenic massive sulphide deposit located in central Newfoundland. Four sulphide lenses, with a total tonnage of less than 1 million tons, are hosted by felsic pyroclastic and volcanic rocks of the pre-Caradoc Victoria Lake Group. A relative abundance of both felsic rocks and Zn and Pb, distinguishes this deposit from the stratigraphically equivalent ones of Notre Dame Bay. -- Hydrothermally altered rhyolitic-dacitic pyroclastic and volcanic rocks outcrop in the footwall, whereas a tuffaceous chert and iron formation occur in the hangingwall. Chequerboard albite, Fe/Mg- chlorite, sericite and quartz overgrowths on primary quartz phenocrysts, are characteristic alteration features in the footwall. The immediate stratigraphic base of the deposit has K- and Mg(Fe)-rich zones; these zones are thought to have formed at the locus of hydrothermal fluid exhalation. A subvolcanic intrusion, called the Raven rhyolite, is comagmatic with the footwall rocks. It contains secondary microcline (K-enrichment) and sulphide-rich veinlets, suggesting that it played a part in the mineralising process. -- Banded sphalerite-chalcopyrite-galena mineralisation generally overlies massive pyritite; the former two minerals are also common in the siliceous stockwork. Galena and tennantite become more common towards the hangingwall, apparently at the expense of chalcopyrite, while arsenopyrite is sporadically distributed. Covellite, bornite, digenite, electrum, magnetite, ilmenite and marcasite are minor components. -- Dolomite - sericite and siderite - Fe-chlorite are characteristic mineral assemblages of the tuffaceous chert and the iron formation, respectively. Pyrite is the dominant sulphide in these chert-rich chemical sediments. -- Tight to isoclinal folding, with faulting parallel to the axial planes, is the best developed phase (D1) of the three documented deformation episodes. Recumbent folding is inferred to pre-date D1 since the stratigraphy is inverted. Mobilisation of the more plastically deformed sulphides accompanied the development of the SI schistosity. D1 is thought to have occurred in a brittle-ductile regime since annealed pyrite, with distinct pressure shadows, both oriented subparallel to S1, typically lie adjacent to zones of granulated pyrite (fault zones?).

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