Abstract:

Narigongma deposit, located in the northern section of the Sanjiang polymetallic ore belt, southern Qinghai Province, is a large reserve porphyry molybdenitecopper deposit. This study provides highly precise dating of the mineralization in Narigongma deposit. According to the results of LA-ICP-MS zircon U-Pb isotopic data, the ²⁰⁶Pb/²³⁸U weighted mean age of 33 analytical data from ZK004 is (43.4±0.4) Ma, with MSWD being 1.9, and the ²⁰⁶Pb/²³⁸U weighted mean age of 24 analytical data from ZK805 is (42.9±0.3) Ma, with MSWD being 0.6. These zircons have characteristics of magmatic origin, thus the zircon U-Pb isotopic dating can represent the orebearing rocks forming age. One piece of molybdenite sample from Narigongma deposit determined by ICP-MS shows that the ReOs model age is (40.8±0.4) Ma. It can indicate that the mineralization was developed 2.6 Ma later than the intrusion of the porphyries. Strikeslip fault systems control the distribution of Sanjiang porphyry deposits，and the northern section of Sanjiang porphyries belt have great prospecting potential.
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Key words:  LA-ICP-MS U-Pb dating, biotite granitic porphyry, porphyry deposit, Narigongma, southern Qinghai Province