Zircon U–Pb dating, geochemistry, and Sr–Nd–Pb–Hf isotopes of the subvolcanic intrusion from Beina Pb–Zn–(Ag) deposit in the southern Lhasa terrane, Tibet: Implications for petrogenesis and mineralization. (24th July 2018)

• Record Type: Journal Article
• Authors: Liu, Jun; Zheng, Youye; Gao, Shunbao; Jiang, Junsheng; Cao, Huawen
• Editors: Yang, Q.
• Is Part Of: Geological journal. Volume 54:Number 4(2019)
• Page Start: 2064
• Page End: 2083
• Publication Date: 2018-07-24
• Subjects: Pb–Zn–(Ag) deposit -- rhyolite porphyry -- Sr–Nd–Pb–Hf isotopes -- Beina -- southern Lhasa terrane; Geology -- Periodicals; 551
• DOI: 10.1002/gj.3284
• Languages: English
• ISSNs: 0072-1050

Abstract

Abstract : The Beina Pb–Zn–(Ag) deposit is a newly discovered deposit situated in the southern Lhasa terrane, Tibet. LA‐ICP‐MS U–Pb dating for the ore‐bearing rhyolite porphyry indicates that it was emplaced at 64.6 Ma. The Beina rhyolite porphyry displays high SiO2 (74.31–76.52 wt%), K2 O + Na2 O (6.99–8.05 wt%), and A/CNK (0.97–1.33), similar to the peraluminous S‐type granites related to Pb–Zn–(Ag) mineralization in the central Lhasa terrane. The Beina rhyolite porphyry is strongly depleted in Nb, Ta, Ti, P, Sr, and Ba, enriched in Rb, K, Th, U, and Pb, enriched in light rare earth elements (LREEs), slightly depleted in heavy rare earth elements (HREEs) (LaN /YbN = 6.52–9.28), and has moderate negative Eu anomalies (δEu = 0.38–0.48), showing an arc affinity. It also shows high CaO/Na2 O ratios (0.21–0.73), low Rb/Ba (0.30–0.46), and Rb/Sr ratios (1.17–4.01), indicating that it was mainly derived from partial melting of a clay‐poor, plagioclase‐rich metapsammitic source. The samples have relatively high 87 Sr/ 86 Sr(i) (0.7084–0.7092) and Pb isotopes ( 206 Pb/ 204 Pb = 18.61–18.74, 207 Pb/ 204 Pb = 15.65–15.68, 208 Pb/ 204 Pb = 38.99–39.14) and low εNd(t) (−8.6 to −7.2) and εHf(t) (−8.6 to −4.8) values, yielding ancient two‐stage Nd model ages (1, 459–1, 569 Ma) and two‐stage Hf model ages (1, 433–1, 684 Ma), respectively. The Beina rhyolite porphyry was formed at relatively high temperatures (average 817°C) according to zircon saturation thermometer. These results reveal that Beina rhyolite porphyry was generated by partial melting of ancient crustal materials (dominated by metapsammite) heated by mantle‐derived magma during rollback of the Neo‐Tethyan oceanic slab. In addition, our research suggests that both I‐ and S‐type granites related to Pb–Zn mineralization are believed to exist in the Lhasa terrane. Similar to the central Lhasa terrane, the middle segment of the southern Lhasa terrane (83°E–87°E) is also an ancient block, large‐scaled silicic volcanic rocks of the Linzizong Group, and coeval plutons are widely exposed and several Pb–Zn deposits have recently been discovered in the Nuocang–Chazi area. All these facts indicate that there is a great potential for prospecting of intrusions‐related Pb–Zn deposits in the middle segment of the southern Lhasa terrane.