Fluid Inclusions and S–Pb Isotopes of the Reshui Porphyry Mo Deposit in East Kunlun, Qinghai Province, China

Abstract

The Reshui porphyry Mo deposit is located in the East Kunlun orogenic belt (EKOB). Molybdenum mineralization is distributed in monzogranite and porphyritic monzogranite rocks, mainly presenting as various types of hydrothermal veinlets in altered wall rocks, and the orebodies are controlled by three groups of fractures. In this paper, we present the results of fluid-inclusion and isotopic (S and Pb) investigations of the Reshui Mo deposit. The ore-forming process of the deposit can be divided into three stages: an early disseminated molybdenite stage (stage 1), a middle quartz–molybdenite stage (stage 2) and a late quartz–polymetallic sulfide stage (stage 3). The alteration was mainly potassic and silicic in stage 1, silicic in stage 2, and sericitic and silicic in stage 3. Five types of fluid inclusions (FIs) can be distinguished in quartz phenocrysts and quartz veins, namely W, PL (pure liquid inclusions), PV (pure gas inclusions), C (CO2 three-phase inclusions), and S (daughter mineral-bearing inclusions). The homogenization temperatures of fluid inclusions belonging to stages 1 to 3 are 282.3–378 °C, 238.7–312.6 °C and 198.3–228 °C, respectively. The fluid salinities at stages 1 to 3 are 4.65–8.14% NaCl eq., 4.34–42.64% NaCl eq., and 3.55–4.65% NaCl eq., respectively. The fluids of this deposit were generally moderate–high temperature and moderate–low salinity and belong to the H2O–NaCl–CO2 ± CH4 system. The temperature and pressure changed considerably between stage 2 (high–medium-temperature) and stage 3 (low-temperature). The evidence for ore-forming fluids containing different types of coexisting inclusions in stage 2 and a decrease in the fluid temperature from stage 2 to stage 3 indicate that fluid boiling and fluid mixing were the main mechanisms of ore precipitation. The sulfide 34SV-CDT values range from 4.90‰ to 5.80‰, which is characteristic of magmatic sulfur. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of the ore minerals are 18.210–18.786, 15.589–15.723, and 38.298–39.126, respectively. These lead isotopic compositions suggest that the ores were mainly sourced from crustally derived magmas, with minor input from the mantle. The fluid inclusions and S–Pb isotopes provide important information on the genesis of the Reshui porphyry Mo deposit and indicate that the Triassic has high metallogenic porphyry potential in the EKOB.

Syn‐mineralization Uplifting and Exhumation of Porphyry Systems in China: Evidence from Fluid Inclusion Data

“…The regional faults and tectonic boundaries are after Pan et al (2009). Notes: 1-Yuchiling (Li et al, 2012); 2-Yaochong (Wang et al, 2014); 3-Donggou (Yang et al, 2015); 4-Nannihu (Yang et al, 2012); 5-Xiaofan (Tang X W et al, 2017); 6-Jinduicheng (Yang Y F, 2009); 7-Qiane'chong (Yang et al, 2013); 8-Reshui (Guo et al, 2019); 9-Yandong (Wang et al, 2017(Wang et al, , 2018; 10-Donggebi (Wu et al, 2014); 11-Baogutu (Shen et al, 2010); 12-Shiwu (Li et al, 2017); 13-Gaogangshan (Zhao, 2019); 14-Huzhagaitu (Liu et al, 2019); 15-Duobaoshan (Wei et al, 2011); 16-Baituyingzi (Sun et al, 2017); 17-Daheishan (Zhou et al, 2015); 18-Yaojiagou (He et al, 2017); 19-Laojiagou (Liu et al, 2012); 20-Changfagou (Peng et al, 2018); 21-Hamaling (Bian, 2018); 22-Wuziqilong (Chen et al, 2011); 23-Luoboling (Zhong et al, 2014); 24-Dabaoshan (Mao et al, 2017); 25-Tongchang (Liu et al, 2016); 26-Fujiawu (Li L et al, 2015); 27-Zhushahong (Zhang et al, 2012); 28-Duobuza (Li et al, 2007); 29-Jiama (Zhou et al, 2011); 30-Zhunuo (Li M et al, 2015); 31-Bangpu (Luo et al, 2012(Luo et al, , 2015; 32-Jiudingshan (Lu et al, 2016).…”

“…The decrease of the mineralization depth of porphyry deposits from early to late vein stages have been proposed by researchers. Yang et al (2012) got an early vein (EQ) mineralization depth of ~7 km and late vein mineralization depth of ~3 km from the Early Cretaceous Nannihu porphyry Mo-W deposit in the East Qinling Mo belt on the basis of the minimum trapping pressure of boiling fluid inclusions; Guo et al (2019) acquired mineralization depths of 8.8-13 km, 6.4-10.4 km and 5.8-6.9 km (under hydrostatic pressure) for EQ, QM and QP veins, respectively, in Triassic Reshui porphyry Mo deposits in the East Kunlun orogenic belt; Wu et al (2014) obtained mineralization depths of 8.4 km, 7.9 km and 5.6 km for the first, second and third-stage veins (under lithostatic pressure) at Triassic Donggebi porphyry Mo deposit in eastern Tianshan metallogenic belt through measuring boiling fluid inclusions; Zhou et al (2011) acquired magmatic-hydrothermal transition depth of 2.2 km and early hydrothermal quartz vein (EQ) mineralization depth of 1.2 km at Miocene Jiama porphyry-skarn type Cu-Au deposit in the Gangdese metallogenic belt by studying fluid trapping pressure of melt inclusions in quartz phenocryst and boiling fluid inclusions in hydrothermal vein respectively. In addition, the mineralization depth reduction from early to late vein stages are also found in porphyry deposits such as Yaochong, Baogutu, Duobaoshan, Changfagou, Luoboling, Dabaoshan, Duobuza, Bangpu and Zhunuo (see references in Appendix 1).…”

Tectonomagmatic Setting and Cu-Ni Mineralization Potential of the Gayahedonggou Complex, Northern Qinghai–Tibetan Plateau, China

“…The evolution of the Neo-Tethys had little influence on the EKOB, and only a few magmatic rocks developed during this period. The north, middle, and south Kunlun faults divide the East Kunlun into the North East Kunlun orogenic belt, the Middle East Kunlun orogenic belt, and the South East Kunlun orogenic belt [26][27][28][29]; the secondary faults in the region generally develop towards the northeast (Figure 1). Regional stratigraphic outcropping is relatively complete The Gayahedonggou Cu-Ni deposit was discovered by the Sichuan Nuclear Industry Geology Bureau in 2018.…”

“…The evolution of the Neo-Tethys had little influence on the EKOB, and only a few magmatic rocks developed during this period. The north, middle, and south Kunlun faults divide the East Kunlun into the North East Kunlun orogenic belt, the Middle East Kunlun orogenic belt, and the South East Kunlun orogenic belt [26][27][28][29]; the secondary faults in the region generally develop towards the northeast (Figure 1). Regional stratigraphic outcropping is relatively complete and includes the Paleoproterozoic Jinshuikou Group, the Mesoproterozoic Wanbaogou Group, the Cambrian-Ordovician Nachitai Group, the Qimantage Group, the Upper Devonian Maoniushan Formation, the Carboniferous Dagangou Formation, the Siyangjiao Formation, and the Upper Triassic Elashan Formation [30].…”