Lesley Dinnett

Kempt Snare Lake Pb-Zn mineral prospect is hosted within a small greisenised granite cupola that intrudes metasediments of the Goldenville Formation. Major oxide, trace element, REE, and stable isotopes studies (O, H, C, and S) reveal the fluid sources, sequential alteration, greisenising, graphite precipitation, and mineralisation stages. Trace element and REE analyses show all the Kempt Snare Lake lithologies are related through magmatic differentiation. The greisenised units have increased åREE, reflecting REE complexing in the alteration fluids. Alteration has affected all the units and resulted in high K, Na, and Fe contents, albitic plagioclase, phengitic muscovite, and secondary K-feldspar. Stable isotope signatures for silicate minerals from all lithological units (least altered leucomonzogranite to highly altered greisen), and vein silicate minerals have similar isotopic compositions with quartz (d18O = 9.9-11.1‰), and muscovite (d18O = 6.7-8.0‰. Hydrogen isotopes from granitoid and vein muscovite have dD = -39.80 to -58.8‰. Geothermometry carried out on these samples suggests temperatures of equlibration ~500oC with a fluid of mixed igneous/metamorphic origin responsible for these isotopic compositions. K-feldspar signatures from the host units have values out of equilibrium with the other minerals, and reflect continued reequilibration with the alteration fluids to lower temperatures. Carbon values from graphite from lithological units vary in composition from d13C = -17 to -27‰ with carbon probably entering the cupola from the carbonate-bearing Goldenville Formation and from the hydrocarbon-bearing Halifax Formation. Mixing of the CO2 fluid with the CH4 fluid resulted in the formation of graphite with variable isotopic signatures. Brittle deformation followed graphite precipitation and ƒO2 increased, resulting in the oxidation of wall-rock graphite and fluid CH4, forming vein siderites (d13C = -15 to - 18‰; d18O = ~9.5‰). Sulphides from the veins show a narrow range (d34S = 6.9-10.5‰) consistent with H2S being the dominant sulphide species and the sulphur originating within the Meguma Group metasediments. A later, restricted influx of meteoric water reequilibrated some of this siderite to low-temperature oxygen isotopic composition (d18O = 27‰).

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Pages: 220
Supervisor:   D. Barrie Clarke