Economic geology of the eastern margin of the Continental copper-molybdenum porphyry Deposit

The goal of this thesis project was to determine the vein relationships and overall economic geology observed along the eastern margin of the Continental Deposit located within the mining district of Butte, Montana. An emphasis was placed on determining the origins of the abundant quartz-pyrite veins observed along the eastern margin of the Continental Deposit. Montana Resources LLP is currently undertaking an aggressive exploration program to determine future reserves for their mining efforts within the Continental Pit. Core samples were collected from this diamond drill core and used for petrographic analysis, fluid inclusion analysis, and sulfur isotope analysis.;A set of 36 samples was used for petrographic study to determine vein paragenetic relationships. Vein types observed were separated into categories based on mineralogy, alteration, and cross-cutting relationships. The categories used for this project include: quartz-molybdenite/barren-quartz veins, pale-green sericite (PGS) +/- magnetite/chalcopyrite/pyrite veins, quartz-pyrite veins, and Main Stage (MS) veins: no early dark micaceous (EDM) veins were examined in this study. Quartz-molybdenite veins show weak K-feldspar alteration; PGS veins typically have sericitic alteration with abundant chlorite; both quartz-pyrite veins and MS veins have sericitic alteration. Many samples contained calcite as both disseminations within altered wall rock and as gangue in cross-cutting veins. The majority of this calcite is late and cross-cuts all vein types, however some calcite is also present in early quartz-pyrite veins. The latter occurrence of calcite may indicate MS veins quartz-pyrite veins.;Fluid inclusion data were collected from quartz-pyrite veins, barren-quartz veins, quartz-molybdenite veins, and PGS veins. Fluid inclusion samples were separated based on vapor bubble size as B20, B35, and B60. The most abundant type of fluid inclusion observed was B35 which also had the highest occurrence of chalcopyrite daughter minerals. Temperatures of homogenization for fluid inclusions from different vein types overlapped, with averages of 354°C for barren-quartz veins, 348°C for quartz-molybdenite veins, 348°C for dark green sericite veins, and 319°C for quartz-pyrite veins. Salinities estimated from ice-melting temperatures also overlapped for the various vein stages, and varied between a range of 0 to 10.5 wt % NaCleq, with an overall average of 4.6 wt % NaCleq. The results obtained in this thesis are in agreement with previous fluid inclusion work (Rusk et al., 2008) from Butte pre-Main Stage mineralization.;Sulfur isotope analysis of pyrite from both pre-Main Stage and Main Stage mineralization is in agreement with previous studies of the Butte ore body (summarized in Field et al., 2005). Pre-Main Stage pyrite had delta 34S in the range of 2.5% to 5.1%. Coexisting pyrite and sphalerite from two Main Stage veins gave delta34Spyr/ 34Ssph of 4.2%/1.9%, and 3.2%/2.2%, respectively. Overall, the S-isotopes from sulfide minerals in the eastern portion of the Continental deposit are slightly enriched compared to the central portion of the Butte ore body.