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  • 1
    Publication Date: 2011-04-01
    Description: Normalized rare earth element patterns of rock and mineral samples from evolved granitic systems and associated hydrothermal tin deposits frequently show an unusual split into four consecutive curved segments, referred to as tetrads. In the present contribution, the simultaneous occurrence of complementary convex and concave tetrads is described for the first time for vein fluorite, suggesting that this unusual trace-element signature may develop during a single evolutionary stage within the hydrothermal environment. Based on geochemical analysis of vein fluorite, fluid inclusion studies, and thermodynamic modeling, it is shown that fractionation of the rare earth elements can be linked to fluid immiscibility and preferential partitioning of these elements between vapor and coexisting liquid. The findings provide the first direct evidence constraining the geological conditions responsible for the occurrence of the tetrad effect in tin-bearing magmatic-hydrothermal systems and require a reassessment of the current understanding of the origin of tin deposits.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 2
    Publication Date: 2011-12-01
    Description: The possibility of mining seafloor massive sulfide deposits has stirred debate about the sustainable use of this new resource and whether commercial development is worth the risk. Among the outstanding questions is how many deposits might be accessible to deep-sea mining. More than 300 sites of high-temperature hydrothermal venting have been identified since the discovery of black smokers, but significant massive sulfide accumulation has been found at only 165 of these sites. Estimates of the total number of vent fields and associated mineral deposits, based on plume studies and deposit occurrence models, range from 500 to 5000. We have used new deposit occurrence data from 10,000 km of ridge, arc, and backarc spreading centers to estimate the amount of massive sulfide in the easily accessible neovolcanic zones of the global oceans. The total accumulation in these areas is estimated to be on the order of 6 x 108 tonnes, containing [~]3 x 107 tonnes of copper and zinc. This is similar to the total discovered copper and zinc in Cenozoic massive sulfide deposits mined on land but is insufficient to satisfy a growing global demand for these metals.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Location Call Number Limitation Availability
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