Geochemical Characteristics Of Copper-polymetallic Deposit In Jameson Land Basin And Discussion On Its Cause Of Formation Within East Greenland

Greenland is one of the important huge polymetallic metallogenic belts in the world, and Jameson Land Basin belongs to its eastern ore-forming zone. Located at the margin of the volcanic rift of eastern Greenland Island, Jameson Land Basin is an extensional and graben basin resulted from Caledonian orogeny, whose basement is metamorphic rock of Precambrian period and overlying cap initiates from middle Devonian epoch, and in which various sediments pile up to 17 km thick.After some researches, it is found out that mineralization on the earth's surface of metals such as copper, lead, zinc etc. is obvious in the area, with high mineralizing intensity, broad distribution extent and large thickness, and ore bodies are stratiform and quasi layered, and mineralization is mainly controlled by the stratigraphic position, which has the conditions for generating large, even giant sediment-hosted stratiform copper mineral deposits and tremendous ore-prospecting potentials. However, scientific study on this area is almost blank currently,so it is necessary to furthermore carry out metallogenetic geological and geochemical researching works about the deposit systematically, thus analyzing a few scientific problems concerning genetic mechanisms of deposit such as minerogenic materials sourcing and metallogenic fluids evolution features and so on. Metallogenic geological setting of Copper-polymetallic ore-forming region including Jameson Land Basin is analyzed in this paper, combined with field geologic survey work, as well as some geochemistry analyses and studies, i.e. fluid inclusions, carbon-oxide and sulphur isotope etc., several preliminary cognitions have been obtained:It is discovered through microscopic study on the ore minerals in the study area that modes of occurrence of metal sulfides are multiple, which shows characteristics both syngenetic deposit and later reformation. Consequently,it is believed that Copper-polymetallic deposit within the area is marked by syngenetic deposit–diagenesis– later hydrothermal reformation.Temperature measuring of fluid inclusions of rocky minerals(quartz and barite) occurred with ore minerals has reached that homogenization temperature ranges from 113? to 387? with a mean value of 185?, and mainly focused on 120~220?, showing metallogenic fluid is middle-low; Salinity alters between 0.4 wt%~13.4 wt% with a mean value of 7.9 wt%, and peak value is within 6.0 wt%~13.0 wt%, suggesting metallogenetic fluid is of middle-low salinity; Fluid density changes between 0.73~0.98 g/cm3 with an average value of 0.94 g/cm3. It can be seen from the homogeneous temperature-salinity typical hydrothermal fluid type diagram that ore-forming fluid is melange of atmospheric precipitation and sea water.?13CVPDB of calcite is-4.7‰~0.5‰ with a mean value of-2.5‰,?18OVPDB ranges between-26.0~-14.0‰ with a mean value of-15.2‰. Carbon-oxide isotope diagram indicates that carbon is derived from the dissolution of marine carbonatites(i.e. wallrocks), and also illustrates that fluids and wallrocks have had water-rock reaction. ?34S of metal sulfides is between-11.0~3.8‰ with a mean value of-3.9‰, and ?34S of barite between 13.4~15.2‰ with a mean value of 14.0‰.Sulfur is sourced from disoxidation of Triassic evaporites and organic matters. Metallogenic metal materials stem from shale of Ravnefjeld Formation and its underlying molasse formation of middle Devonian epoch as well as wallrocks.In summary, it is acquired that Copper-polymetallic deposit in Jameson Land Basin is a characteristic sedimentary-reformed mineral deposit.