| Popis: |
In the ca. 3.8 b.y.-old Isua supracrustal belt, West Greenland, pyrrhotite and chalcopyrite occur as strata-bound mineralizations in layered tuffaceous amphibolites and in an iron-formation. Mineralizations with more complex mineral assemblages comprising galena and sulphides of Ni, Sb, Cd, and Ag are of limited extent only. Field relationships, rare-earth elements and isotopic data indicate that the sulphides are partly of submarine exhalative origin, and partly derived through leaching of basaltic rocks. The sulphides were precipitated on the sea-floor without influence of sulphur bacteria. The mineral zonation was governed by differences in Eh and pH in the depositional environment. |
