AUTHORS: Loukola-Ruskeeniemi, K., Airo, M.-L.
ABSTRACT: The Talvivaara Ni-Cu-Zn deposit is hosted by metamorphosed black shale and contains 338 Mt of low-grade ore averaging 0.27% Ni, 0.14% Cu, and 0.55% Zn. The geochemistry was comprehensively studied with 1,960 samples. The high graphitic C contents (average 7-8%) and average thickness of 120m in drill cores in rift-related 1.9-2.1 Ga black shale formations in eastern and northern Finland point to vigorous organic productivity and preservation of organic material in anoxic conditions. Black shale formations are more abundant also in other parts of the world during 2.1-1.9 Ga than during other time periods which may record the breakup of supercontinents resulting in closed marine basins and increased hydrothermal activity in ocean ridges. Black shale of this age is potential in exploration for massive sulphide ores. Black shale is easily located with the aid of geophysical measurements also in sparsely outcropped or deeply weathered terrains. Preliminary characterization of ore-potential black shale is even possible with interpretation of airborne magnetic and gamma-ray responses.
KEYWORDS: black shale, sulphide deposits, nickel, Precambrian, Talvivaara, Finland
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