Big easy prospect: a well-preserved low-sulfidation epithermal Au-Ag system in the late neoproterozoic, Newfoundland, Canada

• Main Author: Junco Rojas, Andrés Eduardo
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2022
• Subjects: Canada; Long Harbour; Newfoundland
• Online Access: https://research.library.mun.ca/15899/; https://research.library.mun.ca/15899/1/converted.pdf

The Big Easy prospect is a low-sulfidation epithermal gold occurrence of Neoproterozoic age in the Burin-Bonavista region of Newfoundland, Canada. Mineralization is predominantly hosted in epiclastic rocks of the Musgravetown Group. This well-preserved system lies within the tectonostratigraphic Avalon Zone and is dated as Late Neoproterozoic (ca. 573 Ma). Previous work suggests that the most prospective period for epithermal deposits within the Neoproterozoic Avalon Zone is from ca. 620 Ma until the nominal end of the Neoproterozoic at 541 Ma. This period encompassed three episodes of arc magmatism, as recognized in the Burin Peninsula region: ca. 620 Ma (e.g., Broad Island Group), ca. 585 – 570 Ma (Marystown and Musgravetown Groups), and ca. 565 Ma (Long Harbour Group). Big Easy appears to have been associated with the 585 – 570 Ma episode, as were a number of volcanic/volcaniclastic-hosted occurrences in this region. The mineralization at Big Easy is subdivided here into four different styles of discrete Au- and Ag-bearing veins, containing characteristic ore mineral assemblages: Type I) Electrum dominant (High Au) – (pyrite + electrum ± sphalerite); Type II) High Au:Ag – (pyrite + electrum + native silver + naumannite + acanthite ± aguilarite ± chalcopyrite ± uytenbogaardtite); Type III) Ginguro (High Ag:Au) – (native silver + acanthite + electrum ± pyrite ± aguilarite ± chalcopyrite ± freibergite-tetrahedrite,); and Type IV) Molybdenite-rich (molybdenite + native silver + acanthite ± pyrite ± chalcopyrite ± sphalerite). Gold is mainly deported in type I and II veins as electrum observable in grains attached to, or enclosed by, pyrite crystals, or as rare uytenbogaardtite (Ag3AuS2). Geological and numerical models using existing drill hole data exhibit a strong spatial correlation between gold, silver, molybdenum, and arsenic distributions, and illustrate the predominant ambient hydrothermal alteration zone present in the preserved epithermal system. Strong correlations from PCA analysis, Pearson correlation ...