Hydrothermal characterization of the West Gore Sb-Au deposit, Meguma Terrane, Nova Scotia, Canada

Autor: Daniel J. Kontak, Richard J. Horne, Paul K. Smith
Rok vydání: 1996
Předmět:
Zdroj: Economic Geology. 91:1239-1262
ISSN: 1554-0774
0361-0128
Popis: The West Gore Sb-Au deposit is anomalous in the Megurea terrane of Nova Scotia because of its enrichment in Sb, a metal that is essentially absent from other Megurea gold deposits. The deposit is hosted by graphitic and sulfide-bearing slates of the lower Paleozoic Halifax Formation that were deformed into a northeast-trending, upright, closed syncline and metamorphosed to the greenschist facies during the regional Acadian orogeny (ca. 400 Ma). Mineralized veins at the deposit define a single structure trending 110 degrees that probably formed the dextral component of a conjugate shear system as part of regional, northwest-directed compression. The veins crosscut a penetrative regional schistosity (S 1 ) in the host slates and vein formation is constrained by (1) the presence of cleaved wall-rock slates in the veins, (2) vein-related sulfides overgrowing the S 1 fabric in wall-rock fragments, and (3) a 370 Ma 40 Ar/ 39 Ar plateau age for hydrothermal muscovite. Mineralization occurs as stibnite, native antimony, aurostibnite, Au-Sb alloys, and Au-Sb-O phases in vein quartz with associated Fe, As, Pb, Zn, Cu sulfides and chlorite-carbonate gangue; wall-rock alteration is variably developed as narrmv zones peripheral to veins enriched in sericite, calcite, sulfides, tourmaline, and chlorite. Early stages of mineralization are constrained to maximum temperatures of 495 degrees C from arsenopyrite geothermometry, but lower temperatures are recorded by chlorite geothermometry (350 degrees -390 degrees C). Textures of vein quartz include comb and plumose varieties with a bimodal grain size and also a coarser, anhedral quartz. Fluid inclusion studies indicate that the fluid was a mixed H 2 O-NaCl-CaCl 2 -CO 2 -CH 4 type and that fluid unmixing occurred, albeit in minor amounts. Thermometric measurements reveal maximum T h of 375 degrees C and a range of salinities (0.4-28.1 wt % NaCl equiv). The volumetric properties of fluid inclusions reflect cycling of fluid pressures with supralithostatic pressures (to 4-5 kbars P fluid ) recorded by the presence of H 2 O-CO 2 inclusions (to 20 mole % CO 2 ) which are interpreted to have resulted from fluid-rock interaction. Subsequent reduction in fluid pressures (to ca. 2 kbars) resulted in decreasing amounts of CO 2 (
Databáze: OpenAIRE
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