Remobilization of the massive sulfide ore of the Black Angel Mine, central West Greenland

Abstract

The stratabound massive Fe-Zn-Pb-sulfide orebodies of the Black Angel mine, central West Greenland, occur in evaporite-bearing marbles in the upper part of the lower Proterozoic Marmorilik Formation.A study of the structural setting of the Angel zone orebody has shown that this sulfide layer has been deformed in three phases at temperatures of 450 degrees to 500 degrees C under low confining presssure. An early period with isoclinal folding was succeeded by thrusting subparallel to the layering of the metasediments, while a late deformational episode resulted in the formation of open to tight folds in the orebody. The deformation resulted in a characteristic relationship between mesoscopic structures, ore tectonites, and major element geochemistry, reflecting the varying intensity of the three deformational episodes in different parts of the orebody.Extensive differential mobilization and remobilization of quartz and ductile sulfides (galena, tennantite, sphalerite, chalcopyrite) took place in the orebody during the late fold episode in response to the mechanical and chemical disequilibria established as a result of nonhydrostatic stresses set up during the folding. This gave rise to a characteristic zoning of the mobilized sulfides in relation to mesoscopic structures; a distinct geochemical distribution pattern of the major elements was developed in the orebody. The mechanisms for the mobilization of the sulfides is discussed and it is concluded that the transfer of matter took place mainly by a combination of solid state diffusion and fluid state remobilization.