Abstract
The Buzhu gold deposit is a newly discovered and representative gold deposit in the Indus-Yarlung Zangbo suture zone. At Buzhu, auriferous quartz veins with paragenetic sequences of quartz-pyrite-sericite hosted by Early Jurassic greenschist facies rocks, and gold occurs mainly as invisible lattice gold in pyrite as well as minor as visible micrograins inside (arseno)pyrite fractures. We have recognized two auriferous pyrite generations formed in the syn-ore stage (Py2a and Py2b). Py2a is euhedral-subhedral granular with cavities, whilst Py2b mainly grew colloidally around Py2a, indicating that pre-existing pyrite may have been dissolved to form the porous Py2a and Py2b rim. Py2a and Py2b have similar δ34SV-CDT values of 6.98‰ to 7.54‰ and 6.18‰ to 6.85‰, respectively, which are also similar to those of the ore-hosting sediments (6.08‰ to 7.08‰). In-situ trace element analysis shows that Py2b (avg. 1.63% Au) contains more gold than Py2a (avg. 0.42% Au). Combined with petrological and geochemical data, we hypothesized that the gold was derived from the metamorphic devolatilization of the sedimentary wallrocks, and pyrite dissolution-reprecipitation has driven the gold enrichment from Py2a to Py2b. The sericite Ar-Ar date of 19.60 ± 0.66 Ma likely represents the gold mineralization age, as the dated sericite coexists with the auriferous pyrite. This age is much younger than most orogenic gold mineralization (ca. 60–41 Ma) in southern Tibet and indicates an orogenic gold mineralization event (ca. 20–15 Ma) related to extensional tectonics during the late-stage India-Asia continental collision.
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