Genetic link between orogenic Au and porphyry Cu ([sbnd]Au) mineralization in the Dananhu Arc, NW China: Evidence from geochronology, geochemistry, and Sr–Nd–Hf isotopes of the Tudunbei Au deposit

Abstract

The late Paleozoic Chinese Tianshan is characterized by large volumes of arc-related magmatic rocks, and numerous associated orogenic Au and porphyry Cu (Au) deposits. The link between these two deposit styles, however, is ambiguous. Here, we present zircon U–Pb–Hf isotopes, bulk-rock geochemistry, and sericite 40Ar/39Ar geochronology from the newly discovered Tudunbei Au deposit located east of the Tuwu–Yandong porphyry Cu (Au) ore district in the Dananhu Arc, Chinese North Tianshan, and combine this with previously published geochronological and geochemical data to characterize the genetic relationship between orogenic Au and porphyry Cu (Au) mineralization. Our new UPb zircon ages indicate that the wall rocks of the Tudunbei Au deposit formed during the Carboniferous between 337 and 314 Ma (K-feldspar granite: 334.8 ± 1.9 Ma, basaltic tuff: 336.6 ± 4.0 Ma, quartz diorite: 316.0 ± 1.8 Ma, gabbroic diorite: 318.3 ± 1.8 Ma, and gabbro: 314.3 ± 1.8 Ma). These wall rocks are enriched in light rare earth elements and large ion lithophile elements (e.g., Ba, U, and Pb), and depleted in high field strength elements (e.g., Nb, Ta, and Ti). Given the absence of Precambrian basement rocks in the Chinese North Tianshan, and the depleted NdHf isotope compositions (εHf(t) = 12.12–14.98; εNd(t) = 5.77–7.06) of the wall rocks, their young Hf model ages (350–510 Ma), the lack of inherited zircons, and their enrichment in Na2O (2.84–4.73 wt%) relative to K2O (0.43–2.40 wt%), it is suggested that they formed in an oceanic arc environment. One sericite sample selected from an auriferous quartz vein yielded 40Ar/39Ar plateau ages of 260.6 ± 1.1 Ma, which is representative of the gold mineralization age. Given the abundance of gold in the Carboniferous wall rocks of the Tuwu–Yandong porphyry Cu (Au) ore district, the similarity in the timing of its magmatism with Tudunbei, and the geochemical–isotopic (Sr–Nd–Hf) similarity of their wall rocks, it is inferred that the gold in the Tudunbei deposit was remobilized from pre-existing gold in the Carboniferous wall rocks during regional metamorphism and deformation.