Re-Os Molybdenite, Pyrite, and Chalcopyrite Geochronology, Lupa Goldfield, Southwestern Tanzania: Tracing Metallogenic Time Scales at Midcrustal Shear Zones Hosting Orogenic Au Deposits

摘要

A detailed Re-Os molybdenite, pyrite, and chalcopyrite geochronology at five shear-hosted Au occurrences (Kenge, Mbenge, Porcupine, Konokono, and Dubwana) in the Lupa goldfield, southwestern Tanzania, is reported in this paper. Au occurrences within the Lupa goldfield share many geologic similarities with the orogenic Au deposit type and are situated within a Paleoproterozoic magmatic arc that intruded the Archean Tanzanian cratonic margin. Pyrite ± chalcopyrite ± molybdenite-bearing fault-fill veins and mylonitic shear zones crosscut granitic host rocks and are associated with the highest Au grades. Re-Os sulfide ages are deemed a suitable proxy to constrain the timing of Au based on the occurrence of Au-bearing minerals as inclusions within pyrite and chalcopyrite, whereas Au-bearing minerals filling pyrite fractures may represent a younger and undated metallogenic event.