Magmatic-hydrothermal evolution of the Cretaceous Duolong gold-rich porphyry copper deposit in the Bangongco metallogenic belt, Tibet: Evidence from U-Pb and 40Ar/39Ar geochronology

The Duolong gold-rich porphyry copper deposit was recently discovered and represents a giant prospect (inferred resources of 4-5 Mt fine-Cu with a grade of 0.72% Cu; 30-50 t fine-gold with a grade of 0.23 g/t Au) in the Bangongco metallogenic belt, Tibet. Zircon SHRIMP and LA-ICP-MS U-Pb geochronology shows that the multiple porphyritic intrusions were emplaced during two episodes, the first at about 121 Ma (Bolong mineralized granodiorite porphyry (BMGP) and barren granodiorite porphyry (BGP)) and the second about 116 Ma (Duobuza mineralized granodiorite porphyry (DMGP)). Moreover, the basaltic andesites also have two episodes at about 118 Ma and 106 Ma, respectively. One andesite yields an U-Pb zircon age of 111.9 +/- 1.9 Ma, indicating it formed after the multiple granodiorite porphyries. By contrast, the 40Ar/39Ar age of 115.2 +/- 1.1 Ma (hydrothermal K-feldspar vein hosted in DMGP) reveals the close temporal relationship of ore-bearing potassic alteration to the emplacement of the DMGP. The sericite from quartz-sericite vein (hosted in DMGP) yields a 40Ar/39Ar age of 115.2 +/- 1.2 Ma. Therefore, the ore-forming magmatic-hydrothermal evolution probably persisted for 6 my. Additionally, the zircon U-Pb ages (106121 Ma) of the volcanic rocks and the porphyries suggest that the Neo-Tethys Ocean was still subducting northward during the Early Cretaceous. (C) 2011 Elsevier Ltd. All rights reserved.