Sie befinden Sich nicht im Netzwerk der Universität Paderborn. Der Zugriff auf elektronische Ressourcen ist gegebenenfalls nur via VPN oder Shibboleth (DFN-AAI) möglich. mehr Informationen...
Mineralogy, textures, and whole-rock geochemistry of advanced argillic alteration: Hugo Dummett porphyry Cu–Au deposit, Oyu Tolgoi mineral district, Mongolia
Advanced argillic (AA) alteration is developed over a vertical interval of 500 m, above (and enclosing) Late Devonian quartz monzodiorite intrusions that accompany porphyry-style Cu–Au mineralization at the Hugo Dummett deposit. The AA alteration is mainly in basaltic rocks and locally extends into the overlying dacitic ash-flow tuff for about 100 m. The AA zone overprints porphyry-style quartz veins associated with quartz monzodiorite intrusions, but at least partly precedes high-grade porphyry-style bornite mineralization. Mineralogically, it consists of andalusite, corundum, residual quartz, titanium oxides, diaspore, alunite, aluminum phosphate-sulfate (APS) minerals, zunyite, pyrophyllite, topaz, kaolinite, and dickite, as well as anhydrite and gypsum, but is dominated by residual quartz and pyrophyllite. Alteration zonation is not apparent, except for an alunite-bearing zone that occurs approximately at the limit of strong quartz veining. Whole-rock geochemistry shows that the AA alteration removes most major elements except Si, Al, Ti, and P, and removes the trace elements Sc, Cs, and Rb. V, Zr, Hf, Nb, Ta, U, and Th are relatively immobile, whilst light REEs (La to Nd), Sr, Ba, and Ga can be enriched. Middle REEs (Sm to Gd) are moderately depleted; Y and heavy REEs (Tb to Lu) are strongly depleted except in two unusual samples where middle to heavy REEs are enriched.