Geological and geochemical studies of a metaturbidite-hosted lode gold deposit; the Beaver Dam Deposit, Nova Scotia; II, Isotopic studies
| Autor: | Daniel J. Kontak, Robert Kerrich |
|---|---|
| Rok vydání: | 1995 |
| Předmět: | |
| Zdroj: | Economic Geology. 90:885-901 |
| ISSN: | 1554-0774 0361-0128 |
| Popis: | The Beaver Dam gold deposit is located within metaturbidites of the lower Paleozoic Megurea Group of southern Nova Scotia, part of the Meguma terrane of the Canadian Appalachians which records a mid-Devonian metamorphic and deformational history. The deposit, one of several hosted by the Meguma Group, is dominated by bedding-concordant veins, with lesser discordant or fissure veins, that record a two-stage paragenesis: stage 1--quartz-calcic plagioclase-biotite [Mg/(Mg + Fe (super 2+) ) or Mg. no. = 0.50]-tourmaline + or - amphibole (Mg. no. = 0.54) + or - garnet + or - epidote + or - apatite + or - ilmenite; and stage 2--quartz-calcite-chlorite (Mg. no. = 0.50)-albite-scheelite. Muscovite and sulfides (Cu, Fe, Zn, Pb) transcend the two stages and gold is late parDgenetically. Mineralization formed from a low-salinity, H 2 O-CO 2 (X (sub CO 2 ) = 0.15) fluid and vein formationis constrained geochronologically at 370 Ma from 40 Ar/ 39 Ar dating of hydrothermal amphibole, muscovite, and biotite.Isotopic studies (O, C, H, Sr) of mineral phases (quartz, amphibole, feldspar, mica, carbonate, tourmaline) indicate the following:1. The veins were emplaced over a temperature interval of ca. 500 degrees to 300 degrees C based on oxygen isotope geothermometry of silicate phases. This range is comparable to temperatures inferred from silicate-sulfide geothermometry (Kontak and Smith, 1993).2. The stable isotope composition of the parental fluid is delta D = -40 + or - 6 and delta 18 O = 6 to 12 per mil based on mean values of analyzed phases and inferred temperatures of formation. The delta D water values calculated from mica phases concur with extracts from vein quartz samples dominated by a single generation of primary fluid inclusions. These results demonstrate that a delta D signature of the primary fluid can be obtained via crushing of bulk samples where the potential influence of secondary inclusions has been eliminated.3. Interaction of the ore-forming fluid with wall-rock lithologies (i.e., Meguma Group) at the site of deposition has ;reatly influenced the S and C isotope signatures of the carbonates (delta 13 C = -21.1 + or - 1.1ppm) and sulfides (delta 34 S = 10 + or - 1ppm; Kontak and Smith, 1989).4. 87 Sr/ 86 Sr measured ratios of calcite (0.70787-0.71358, n = 8) and tourmaline (0.713055) indicate modification of the primary signature of the fluid (ca. < or = |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|