Optical Characteristics of Heat-Affected Bitumens from the Nanisivik Mine, N.W. Baffin Island, Arctic Canada

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Abstract
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, based on their optical texture and morphology. The first type consists of 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 rocks in the area. The second type of bitumen has been altered due to mineralization and has developed mesophase spheres that have occasionally coalesced to form a fine-grained granular mosaic texture. Reflectance of mesophase is of the order of 5.0% Romax with an average bireflectance of 4.8%. This bitumen is also characterized by rare medium- to coarse-grain mosaic texture and layers of pyrolytic carbon. Reflectance of fine- to coarse-grained mosaic ranges from 3.4 to 4.3% Romax. The bitumen most likely was either emplaced before the mineralization but was not greatly affected by it or was emplaced between the mineralization and the diabase intrusion. The presence of pyrolytic carbon coating the bitumen fragments indicates that temperatures during the diabase emplacement were >500°C and may have reached much higher temperatures (± 1000°C) at the dyke-country rock contact.