Geochronology and Geochemistry of the Granite Xenolith within the Lamprophyre at the Zhenyuan Gold Deposit (Yunnan Province, SW China)

Abstract

The xenoliths in host rocks of hydrothermal gold deposits can generally provide much geochemical information of the deep rocks, which may have an implication for the sources of ore‐forming materials. Geochronology and geochemical characteristics are reported for a granite xenolith, which is enclosed by the lamprophyre in the Zhenyuan gold deposit (Yunnan Province, SW China). This granite xenolith mainly consists of K‐feldspar, quartz, and plagioclase with trace amounts of magnetite, titanite, apatite, zircon, and sulfides. Zircons from the granite xenolith yield a weighted average U‐Pb age of 281.1 ± 1.3 Ma (MSWD = 2.1), which could represent the crystallization age of this granite xenolith. The Ti‐in‐zircon geothermometer and the Mn concentration in apatite calculate that this granite xenolith formed at 685 ± 43°C with the logfO2 values ranging from NNO + 3.7 to NNO + 6.4. The zircons in the granite xenolith have a restricted range of positive ∊Hf(t) values ranging from +9.4 to +10.8, and the corresponding Hf TDM2 model ages range from 588 to 678 Ma. The zircon U‐Pb age and the Hf isotopic compositions indicate this granite xenolith within the lamprophyre is mainly derived from partial melting of juvenile crustal rocks before the completed closure of the Ailaoshan Ocean. The pyrites in the granite xenolith have higher Bi concentrations, and lower As, Sb, and Tl concentrations than the gold‐bearing pyrites of the ores in the Zhenyuan gold deposit. The low Au concentrations of the pyrites together with the ore‐forming age of the Zhenyuan gold deposit (Oligocene) indicate the granite xenolith may have limited contribution to the gold mineralization of the Zhenyuan gold deposit.

Geology and Geochemistry of K‐feldspar Veins in Lamprophyre at the Zhenyuan Gold Deposit, Yunnan, Southwest China: Implications for Gold Mineralization

“…The Late Permian quartz porphyry, Early Triassic granite porphyry, and Oligocene lamprophyre dikes intruded aforementioned strata (Wang et al, 2001;Li et al, 2013). Recently, garnet-bearing granite xenoliths with the age of 281.1 ± 1.3 Ma were identified in the Zhenyuan deposit (Zhang et al, 2022).…”

“…Lamprophyres, a type of volatile-rich mafic-ultramafic rocks, are generally considered to be generated by small degrees of melting of mantle sources (Deng et al, 2017;Pandey et al, 2019). Lamprophyres are widely distributed as dikes in hydrothermal gold deposits (Zheng et al, 2022), and a close spatial relationship between lamprophyres and gold deposits has been widely reported (Müller et al, 1992;Taylor et al, 1994;Deng et al, 2015a;Yu et al, 2020;Zhang et al, 2022). Although lamprophyres and the related mafic intrusions have similar ages to gold deposits (Vielreicher et al, 2010;Chen et al, 2014), Groves et al (2020) suggested that the volumes of these intrusions were insufficient to provide abundant oreforming materials for the formation of gold deposits.…”

Enhancing Geological Understanding and Identifying Gold Anomalies in the Ailaoshan Orogen

“…The ALS is situated between the Yangtze and Simao blocks; it is a triangular area, NW-SE striking, ~500 km long, and 10-50 km wide, which narrows to the NW and widens to the SE (Sun et al, 2009;Faure et al, 2016;Zhang et al, 2022;Fig. 1).…”

In Situ Rb‐Sr Dates of Muscovite and Sulfur Isotope of Pyrite from the Yangshan Gold Deposit in Western Qinling, China

“…However, issues such as the mineralizing time, and the source of the ore-forming materials of the West Qinling gold belt still remain contentious (Goldfarb et al, 2019). Timing constraints of the gold deposits increase understanding of ore-forming mechanisms and enable discrimination of mineralization generations (Huang et al, 2021;Zhang et al, 2022). One of them, the Rb-Sr decay system has frequently been used in a wide variety of geological environments; it requires chemical homogeneity within and amongst large sample volumes (Tillerg et al, 2017).…”