Genesis of the Aobaotu Pb–Zn deposit in the southern Great Xing'an Range, NE China: Constraints from geochronology and C–H–O–S–Pb isotopic and fluid inclusion studies

Abstract

Xing'an Range, northeastern China, is hosted by the Late Jurassic volcanic tuff and structurally controlled by a near-east-west-trending fault. Three stages of mineralization were identified, namely, stage I of quartz ± pyrite veins, stage II of quartzpolymetallic sulphide veins, and stage III of late quartz-calcite veins. The quartz and calcite that formed in the three stages were selected for fluid inclusion and C-H-O isotope analyses. The results show that the ore-forming fluid of the deposit belongs to the H 2 O-CO 2 -NaCl system at a medium temperature (concentrated at 220-300 C) and in low salinity (0.7-12.1 wt% NaCl equiv). The δ 13 C values of the calcite and ankerite are in the range of À8.4 to À4.8‰, indicating that as a source of deep magma. The δD V-SMOW and δ 18 O H 2 O values of quartz range from À108 to À88‰ and 4.55 to 5.85‰, respectively, indicating that the initial fluid of the Aobaotu deposit was a mixture of residual magmatic and meteoric water. Sulphur isotope analysis of the sulphide minerals, that is, sphalerite, galena, pyrite, and chalcopyrite, yield δ 34 S value in a range of 1.44-4.94‰, indicating that sulphur is mainly derived from magma. In addition, the Pb isotopic composition of the sulphides indicates that the ore-forming material has a mixed crust-mantle source. Zircon U-Pb dating suggests that the formation of the Aobaotu deposit is genetically related to the granodiorite porphyry (130.3 ± 0.9 Ma). The combined geochronology and isotopic evidence suggest that the Aobaotu deposit is a magmatic-hydrothermal vein-type Pb-Zn deposit, opposite to a volcanic Pb-Zn deposit as suggested before. The Aobaotu deposit formed in an extensional tectonic setting caused by the rollback of the Palaeo-Pacific Plate.

Geology, Fluid Inclusions, and C–H–O–S–Pb Isotope Geochemistry of Pb–Zn Deposits within the Tuotuohe Region of the Tibetan Plateau: Implications for Ore Genesis

“…[37] obtained Qibaoshan polymetallic ore field S for 0.5~4.3, and ref. [51] obtained 1.4~2.7 in the Aobaotu Pb-Zn deposit, which is relatively consistent with the QMC results in this paper; both of which are considered to be primarily derived from rocks. The δ 34 S V-CDT values of samples from the CDQ deposit are consistent with the δ 34 S V-CDT measured in galena and sphalerite by [34] and with the results obtained in Dashishan Sn-Pb-Zn deposits [38].…”

“…The 207 Pb/ 204 Pb vs. 206 Pb/ 204 Pb diagram shown in Figure 14a indicates that the majority of samples lie within the upper crust and orogenic belt fields of [49], whereas the same samples plot within the lower crust and orogenic fields in a 208 Pb/ 204 Pb vs. 206 Pb/ 204 Pb diagram (Figure 14b). These Pb isotope values are indicative of sourcing from the lower and upper crusts and orogenic zones, suggesting that the Pb within the Pb-Zn deposits in the study area was derived from both the mantle and crust [50,51], with the upper crust being the main source of lead for these deposits. These lead isotope discrimination diagrams indicate that the Pb-Zn deposits of the Tuotuohe region formed in an orogenic environment, with the majority of metal originating from the crust.…”