Bitumen occurs closely associated with sulphides in carbonate-hosted vein mineralization at Navarana Fjord, northeastern Freuchen Land, central North Greenland.The bitumen in the vein is strongly degraded (carbonized) and occurs typically as small fragments associated with sphalerite (±galena and pyrite). The bitumen has a very low sulphur content and seems to have lost sulphur compared to any other bitumen from the source rocks in the region. The isotopic compositions of sulphur in bitumen and sulphides from the vein are similar with δ34S values of about +14‰.The presence of bitumen in the vein was essential for the sulphide precipitation mechanism. It is suggested that in situ thermal cracking of sulphur-rich organic material added H2S to a metal-bearing fluid, resulting in the precipitation of sulphides. Such a process would probably cause a rapid precipitation of sulphides, thus incorporating bitumen. Furthermore, such a process would not cause any isotopic fractionation of the H2S produced although the bitumen itself would lose sulphur. The thermal cracking and carbonization of the organic material was caused by mixing of hydrocarbons with a hot hydrothermal (200°C) metal-bearing fluid, probably in the vein zone itself or just below in a sandstone succession.The bitumen in the vein has not been correlated with any of the two known source rocks in the area but the S isotopic data suggest that the vein bitumen is similar to a long-distance migrated bitumen from an unknown source rock.
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- Bitumen Associated with Precipitation of Sulphides in Carbonate-Hosted Vein Mineralization, North Greenland
U. H. Jakobsen
- Springer Berlin Heidelberg