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

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