OPTICAL CHARACTERISTICS OF HEAT-AFFECTED BITUMENS FROM THE NANISIVIK MINE, NW BAFFIN-ISLAND, ARCTIC CANADA

The optical characteristics of bitumens present in sulfide deposits of the Nanisivik mine, Baffin Island, Arctic Canada, were studied using optical microscopy. Two different types of bitumen were identified, ba sed on their optical texture and morphology. The first type consists o f bitumen that is present in disseminated form in the country rocks (% Ro = 0.40-0.66). This bitumen has not been affected by a dyke that has intruded the strata and represents the thermal maturity of country ro cks in the area. The second type of bitumen has been altered due to mi neralization and has developed mesophase spheres that have occasionall y coalesced to form a fine-grained granular mosaic texture. Reflectanc e of mesophase is of the order of 5.0% Ro(max) with an average birefle ctance of 4.8%. This bitumen is also characterized by rare medium- to coarse-grained mosaic ranges from 3.4 to 4.3% Ro(max). The bitumen mos t likely was either emplaced before the mineralization but was not gre atly affected by it or was emplaced between the mineralization and the diabase infusion. The presence of pyrolytic carbon coating the bitume n fragments indicates that temperatures during the diabase emplacement were > 500-degrees-C and may have reached much higher temperatures (/- 1000-degrees-C) at the dyke-country rock contact.