LA-ICPMS trace elements and C-O isotopes constrain the origin of the Danaopo Cd-Ge-bearing Zn-Pb deposit, western Hunan, China

Abstract

The Danaopo Zn-Pb deposit, hosted in algal limestone, is the second largest Zn-Pb deposit (150 Mt ores at an average grade of 3.06% Zn + Pb) in the western Hunan-eastern Guizhou metallogenic belt (WHEGMB). Here we investigate the trace elements of sphalerite and C-O isotopes and rare earth elements (REEs) of calcite in the Danaopo deposit, aiming to present insights into the mineralization potentiality of critical metals and origin of Zn-Pb deposits in the WHEGMB. In-situ trace element reveals the inhomogeneous distribution of critical metals within sphalerite, including Cd (1520 to 11570 ppm), Ge (0.73 to 236 ppm), Ga (0.04 to 26.90 ppm), and Tl (0.01 to 3.62 ppm). Cd and Ge exceed the Chinese comprehensive utilization standard. The LA-ICPMS elemental map and inter-element correlations suggest that Cd and Ge enter sphalerite lattice via the substitution of Zn2+ ↔ Cd2+ and 4Zn2+ ↔ Ge4+ + 2Fe2+ + □ (vacancy), respectively. The δ13CPDB (-3.93 to −0.12‰) values of the ore-stage calcite indicate that the carbon in hydrothermal fluids primarily originates from the dissolution of Cambrian algal limestone. Calculated δ18Ofluid (+5.23 to + 9.95‰) values on calcites lies between the oxygen isotopic compositions of the algal limestone (+18.76 to + 23.87‰) and the basinal hot brine (+4 to + 10‰), implying that the oxygen was sourced from a binary mixing of ore-host rocks and basin brine. Besides, the REE distribution pattern of Cal-Ⅰ falls within the field of ore-host rocks. In contrast, Cal-Ⅱ is plotted between the Cambrian ore-host and Proterozoic Banxi Group to Cambrian Niutitang Formation footwall. These findings suggest that REE of Cal-Ⅰ was mainly sourced from country carbonate rocks, while Cal-Ⅱ has mixed REE origins from ore-host rocks and footwall sedimentary and metamorphic basement rocks. Overall, based on detailed deposit geology, sphalerite trace elements, and calcite C-O and REE evidences, this study concludes that the Danaopo is a classic Mississippi Valley-type (MVT) Zn-Pb deposit with a low-temperature and low fO2 reductive ore-forming fluid.