Late neoproterozoic epithermal-style Au mineralization of the Burin Peninsula, Newfoundland: U-Pb geochronology and deposit characteristics

Ferguson, Sarah Anne (2017) Late neoproterozoic epithermal-style Au mineralization of the Burin Peninsula, Newfoundland: U-Pb geochronology and deposit characteristics. Masters thesis, Memorial University of Newfoundland.

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The Burin Peninsula lies within the western portion of the Avalon Zone in Newfoundland. The Avalon Zone constitutes the eastern extent of the northern Appalachian orogen and includes extensive late Neoproterozoic magmatic arc-related volcanic, plutonic and epiclastic sedimentary rocks. The stratigraphy of the Burin Peninsula region is primarily composed of the Marystown, Musgravetown and Long Harbour Groups, all of which are host to high- and/or low-sulphidation epithermal precious metal mineralization, including the Hickey’s Pond, Tower, Stewart (and Forty Creek), Heritage, Big Easy and Long Harbour prospects. A 580-573 Ma plutonic suite, now recognized as the source to extensive hydrothermal activity in the region, runs along the length of the peninsula, intruding roughly coeval volcaniclastic rocks of the Marystown Group. New U-Pb (CA-TIMS) ages for volcanic host rocks within the Marystown Group constrain the timing of high-sulphidation mineralization to a maximum age of 584 ± 3 Ma at Hickey’s Pond and 576.7 ± 2.5 Ma (‘Caribou Tuff’) at Stewart. A previous host rock age of 572.5 ± 1.5 Ma at Hickey’s Pond is re-interpreted as a hydrothermal zircon age, which provides a more explicit age for the high-sulphidation mineralization at the prospect. New U/Pb zircon ages for the Marystown Group stratigraphy of the Stewart prospect also include 575.2 ± 2.1 Ma (‘Stewart Tuff’), 575.9 ± 2 Ma and 575.6 ± 1.7 Ma for other volcanic rocks, and 576.0 ± 2.7 Ma for the ‘Bat Zone’ granite (part of the ‘Burin Knee Intrusive Suite’). In conjunction with field observations, these ages confirm a northwest younging direction within the local Marystown Group stratigraphy at Stewart. The tightly overlapping ages also further link the 580-573 Ma regional plutonism to the volcaniclastic stratigraphy and to the regional high-sulphidation mineralization. A new age of 573.3 ± 2.7 Ma for rhyolite from the Musgravetown Group, proximal to the lowsulphidation Big Easy prospect, demonstrates contemporaneity with the Marystown Group. The Musgravetown Group and Marystown Group are also of similar lithogeochemical affinity, and are presumed to represent different facies within a single, contemporaneous volcanic arc environment, undergoing active subduction between 585 and 570 Ma. The Long Harbour Group is younger than, and compositionally distinct from the Marystown and Musgravetown Groups. A new age for the flow-banded rhyolite of the Belle Bay Formation, host to low-sulphidation epithermal mineralization at the Long Harbour prospect, constrains the timing of the mineralization to a maximum age of 566.5 ± 1.9 Ma. The stratigraphy of the Long Harbour Group is characteristically alkaline and associated with late arc-extension. Thus, the low-sulphidation deposits in the Burin Peninsula region are related to at least two discrete volcano-plutonic sequences. A sample of epiclastic sediment from the Grandy’s Pond Arenite Belt yielded a preliminary youngest detrital zircon age of 566.2 ± 4.4 Ma, which corresponds to the age of Long Harbour volcanism. The belt is predominantly derived from the erosion of volcanic rocks of the Marystown Group based on their similar geochemical signatures, but also contains additional detritus from the younger Long Harbour Group, possibly in the form of ash during active volcanism. SEM-EDX analysis was used to assess the deportment of precious metal mineralization in both high- and low-sulphidation epithermal prospects. At Hickey’s Pond, the most auriferous high-sulphidation prospect, gold occurs as part of the hypogene assemblage as native gold and calaverite (AuTe2), and in the late supergene/weathering assemblage as fischesserite (Ag3AuSe2). At the low-sulphidation Long Harbour prospect, gold occurs as native gold and electrum, and silver occurs in the form of various Agtellurides. Forty Creek, of possible intermediate-sulphidation origin and located proximal to the regionally-developed high-sulphidation epithermal systems, contains gold and silver in the form of various precious-metal tellurides including petzite (Ag3AuTe2) and sylvanite ((Ag,Au)Te2). Sulphur isotope microanalyses of pyrite, chalcopyrite and galena from the highsulphidation Hickey’s Pond, Tower, and Stewart prospects, together yield a single population displaying a normal distribution, and δ34S values ranging from -6.8 to +5.9‰ with an average of -0.6‰, consistent with a magmatic sulphur source for these deposits. Sulphur isotope measurements at Forty Creek have an average δ34S of -7.8‰, significantly lighter than the high-sulphidation deposits, and indicative of a sulphur source perhaps influenced by biogenically derived sulphur from metasediments, and not purely the result of magmatic input.

Item Type: Thesis (Masters)
Item ID: 12913
Additional Information: Includes bibliographical references (pages 307-323).
Keywords: epithermal gold, U-Pb geochronology, geochemistry, Neoproterozoic, Burin Peninsula, Newfoundland, Avalon Zone, Avalonia, high-sulphidation, low-sulphidation, Au-Ag, mineralization, sulphur isotopes
Department(s): Science, Faculty of > Earth Sciences
Date: October 2017
Date Type: Submission
Library of Congress Subject Heading: Mines and mineral resources -- Newfoundland and Labrador -- Burin Peninsula (N.L.); Geology -- Newfoundland and Labrador -- Burin Peninsula (N.L.); Mineralogical chemistry -- Newfoundland and Labrador -- Burin Peninsula (N.L.)

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