Geology and Isotope Geochemistry of the Dongzhongla Pb–Zn Deposit in Tibet: Implications for the Origin of the Ore‐Forming Fluids and Storage Condition of Certain Metals. Issue 3 (23rd February 2018)

• Record Type: Journal Article
• Authors: Fei, Guang Chun; Zhou, Yu; Deng, Yun; Chen, Xu; Wen, Chun Qi; Yu, Qinglin; Ding, Feng; Zhou, Xiong; Huo, Yan
• Is Part Of: Resource geology. Volume 68:Issue 3(2018:Jul.)
• Page Start: 227
• Page End: 243
• Publication Date: 2018-02-23
• Subjects: Dongzhongla Pb–Zn deposit -- isotope geochemistry -- skarn type -- sources of ore‐forming hydrothermal solutions -- Tibet; Mining geology -- Periodicals; Mining geology -- Pacific Area -- Periodicals; Mining geology -- Asia -- Periodicals; Geochemistry -- Periodicals; Environmental geology -- Periodicals; 553
• DOI: 10.1111/rge.12158
• Languages: English
• ISSNs: 1344-1698

Abstract

Abstract : As a newly discovered medium‐sized deposit, the Dongzhongla skarn Pb–Zn deposit is located in the northern margin of the eastern Gangdese, central Lhasa block. Based on the ore‐forming geological conditions in this deposit, H, O, C, S, Pb, Sr, He, Ne, and Ar isotopic compositions were analyzed. According to basic skarn mineralogy, the economic metals, and the origin of the ore‐forming fluids, the Dongzhongla deposit was classified as a skarn‐type Pb–Zn deposit. Abstract: As a newly discovered medium‐sized deposit (proven Pb + Zn resources of 0.23 Mt, 9.43% Pb and 8.73% Zn), the Dongzhongla skarn Pb–Zn deposit is located in the northern margin of the eastern Gangdese, central Lhasa block. Based on the geological conditions in this deposit of ore‐forming fluids, H, O, C, S, Pb, Sr, and noble gas isotopic compositions were analyzed. Results show that δ 18 OSMOW of quartz and calcite ranged from −9.85 to 4.17‰, and δDSMOW ranged from −124.7 to −99.6‰ (where SMOW is the standard mean ocean water), indicating magma fluids mixed with meteoric water in ore‐forming fluids. The δ 13 CPDB and δ 18 OSMOW values of calcite range from −1.4 to −1.1‰ and from 5.3 to 15.90‰, respectively, show compositions consistent with the carbonate limestone in the surrounding rocks, implying that the carbon was primarily sourced from the dissolution of carbonate strata in the Luobadui Formation. The ore δ 34 S composition varied in a narrow range of 2.8 to 5.7‰, mostly between 4‰ and 5‰. The total sulfur isotopic value δ 34 S was 4.7‰ with characteristics of magmatic sulfur. The 3 He/ 4 He values of pyrite and galena ranged from 0.101 to 5.7 Ra, lower than those of mantle‐derived fluids (6 ± 1 Ra), but higher than those of the crust (0.01–0.05 Ra), and therefore classified as a crust–mantle mixed source. The Pb isotopic composition for 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb values of the ores were in the ranges of 18.628–18.746, 15.698–15.802, and 39.077–39.430, respectively, consistent with the Pb isotopic composition of magmatic rocks in the deposit, classified as upper‐crust lead. The ore lead was likely sourced partially from the crustal basement of the Lhasa Terrane. The initial ( 87 Sr/ 86 Sr)i value from five sulfide samples ranged from 0.71732 to 0.72767, and associated ore‐forming fluids were mainly sourced from the partial melting of the upper‐crust materials. Pb isotopic compositions of ore sulfides from the Dongzhongla deposit are similar to that of the Yuiguila and Mengya'a deposit, indicating that they have similar sources of metal‐rich ore‐forming solution. According to basic skarn mineralogy, the economic metals, and the origin of the ore‐forming fluids, the Dongzhongla deposit was classified as a skarn‐type Pb–Zn deposit.