地球表層圏における鉱床元素の循環;地球表層圏における鉱床元素の循環;Exogenic Geochemical Cycling of Ore-forming Elements on the Earth.

Determining the source of mineral-forming elements in an ore deposit has proved difficult, since there are no unequivocal criteria for distinguishing “exogenic” ore minerals which are derived from the surficial reservoir where biogeochemical processes prevail from “endogenic” ones which are originated from the deep-seated reservoir (i.e. man-tle) through magmatic processes. The most commonly used criteria, those based on sulfur isotope data, have been often ambiguous: similar isotopic patterns can be generated by biological reactions and high temperature exchange reactions between sulfide and sulfate. Some insight into environmental controls on mineralization and processes of ore formation can be gained by studies of modern sedimentary environments. In this paper, I briefly review the known present-day sources of ore-forming elements, and attempt to assess the potential contribution of biologically-controlled sources to ore genesis, in the light of information obtained from some recent geochemical examinations of marine sediments and stratabound-type mineralizations.