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Geophysical investigation of chromite-bearing ultrabasic rocks in the Baltasound-Hagdale area, Unst, Shetland Islands

By C.E. Johnson, C.G. Smith and N.J. Fortey


Economic deposits of chromite were discovered in Unst, Shetland\ud Islands in the early part of the nineteenth century and extraction\ud continuedi ntermittentlyu ntil exhaustiono f the known near-surface\ud deposits in 1945. Since it is likely that further comparable deposits\ud exist at shallow depth, detailed geophysical smeys employing\ud 2\ud magnetic and electrical methods were carried out over ? km of the area\ud of known mineralisationt o test the feasabilityo f detectinga nd\ud delineatingt hem. Seven of 16 small positive gravity\ud tested by shallow boreholes but only two were attributed to chromite\ud concentrations.T he gravity anomaliesa t the other borehole sites\ud remain unexplained; they may be due to unidentified variations in bedrock\ud density at depth; they may be\ud of weathering and the thickness of\ud in overburden thickness

Topics: Earth Sciences
Publisher: Institute of Geological Sciences
Year: 1980
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