Geology and geochronology of the Jinmuguo Mo polymetallic deposit: Implications for the metallogeny of the Bangongco- Nujiang belt of Tibet
Graphical abstract
Introduction
The Bangongco-Nujiang metallogenic belt (BNMB) is one of the most important metallogenic belts in the Qinghai-Tibet Plateau (Deng et al., 2020a, Lin et al., 2017, Song et al., 2014, Tang et al., 2016, Wang et al., 2020a, Yang and Cooke, 2019, Wang et al., 2020b). The belt extends from Bangongco in the west, to Gêrzê, Nyima, and Basu in the east, and further southeast along the Nujiang River into western Yunnan (Fig. 1a). It hosts multiple ore deposits associated with magmatic suites that occur along the Bangongco-Nujiang suture zone (Song et al., 2014, Tang, 2019.
Intense exploration at the beginning of the century identified several very large ore deposits in the western BNMB, including the Duolong Cu (Au) ore district (Li et al., 2011, Li et al., 2013b, Li et al., 2015a, Li et al., 2015b, Lin et al., 2016, Lin et al., 2019b, Tang et al., 2014), the Ga’erqiong-Galale Cu (Au) ore district (Wang et al., 2019a, Zhang et al., 2015), and the Fuye and Caima Fe deposits (Feng et al., 2006, Feng et al., 2007). Small and moderately-sized Au or Cu deposits have been discovered in the central belt, for example, the Shangxu, Shesuo, Xiongmei, Kuga, and Sangri deposits (Fang et al., 2020, Lin et al., 2018, Lin et al., 2020, Wang et al., 2019b). The eastern BNMB contains several Cu (Mo) deposits, including the Baomai, Yulong, Mangzong, and Malasongduo deposits (Fig. 1b).
The genesis of deposits in the central and western BNMB has been linked to the subduction of the Bangongco-Nujiang Ocean, and the collision of the Qiangtang and Lhasa terranes (Lin et al., 2017, Wang et al., 2019b), as well as Mesozoic magmatism (Fig. 1b) (Lin et al., 2018). However, eastern magmatism and mineralization is thought to have resulted from the Eocene collision of the Indian and Eurasian plates (Hou et al., 2003). It is also unclear whether there is Mesozoic mineralization in the eastern BNMB (Changdu-Mangkang).
The recently discovered Jinmuguo deposit in the eastern BNMB is entirely hosted in hornfels with no evidence of a causative intrusive body, either at the surface or from drilling. The deposit contains base and precious metal (Pb-Zn, Au, Ag) orebodies, which are controlled by large faults. Borehole drilling in the deposit has also revealed molybdenum orebodies, as well as chalcopyrite veinlets within hornfels and skarns. However, further exploration has been hindered by a lack of detailed characterization of the ore minerals, timing of ore formation, and genesis of the Jinmuguo deposit. Therefore, in this study we investigate the geological, geochronological, and isotope geochemical characteristics of the Jinmuguo molybdenum polymetallic deposit to better understand its genesis. The findings presented here provide new insights into the nature and origin of mineralization in the eastern BNMB and provide a better understanding of the mineralization potential of the eastern BNMB and metallogeny in the BNMB as a whole.
Section snippets
Regional geology
The Jinmuguo deposit is located in the eastern BNMB on the southern margin of the Qiangtang terrane, and lies adjacent to the Bangongco-Nujiang suture zone (Fig. 1b(Zhu et al., 2016)). The regional strata are part of the Bangongco-Nujiang sequence, and the major rock types are from the Xijika and Xiarongqu formations of the Late Paleozoic Jiayuqiao Group, the Jurassic Mali Formation, and the Eocene Zongbai Group (Fig. 2a). The Xijika Formation (Pz2xj) is mainly composed of muscovite-quartz
Sampling and analysis
Geochronology and isotopic analyses were performed to investigate the timing of magmatism, mineralization, and alteration in the Jinmuguo deposit, and to explore the source of the ore-forming materials. Zircon U-Pb isotopic dating was performed on granite porphyry from drill core 11,201 (249.9 m depth) and Re-Os dating was performed on molybdenite from several quartz-molybdenite veinlets from the southeastern region of the mining area. Sulfur and lead isotopes of sulfide minerals, and the
Zircon U-Pb geochronology
Zircon grains from the granite porphyry (drill hole 11201, 249.9 m depth) were euhedral, exhibited typical oscillatory zoning, and were 80–270 μm in length (Fig. 5). Most of the Th/U ratios of zircons were greater than 0.4, indicative of magmatic zircons (Table 2) (Belousova et al., 2002). Of the 27 analyses, the twenty youngest ages ranged from 118.2 to 119.7 Ma, and yielded a weighted mean age of 118.6 ± 0.7 Ma (MSWD = 0.04, n = 20) (Table 2, Fig. 6a). This age was interpreted to be the
Geochronology
As a newly discovered deposit in the eastern BNMB, the timing of magmatism and mineralization, as well as the genesis of the Jinmuguo deposit, are important in understanding the regional metallogenic history. Zircon U-Pb geochronology yielded a crystallization age for the granite porphyry in the study area of 118.6 ± 0.7 Ma. According to the available geological information, the scale of the granite porphyry is small, however disseminated pyrite, sericite alteration, quartz-sulfide veinlets,
Conclusions
- 1)
The Jinmuguo deposit is a recently discovered Mo polymetallic deposit in the eastern BNMB. The Early Cretaceous ages suggest that the magmatism and metallogeny were coeval.
- 2)
The sulfur and lead isotopic compositions of sulfides, and the hydrogen and oxygen isotopic compositions of quartz-sulfide veins revealed that the ore-forming fluid was related to magmatic hydrothermal activity. The Jinmuguo mineralization can therefore be considered a porphyry deposit.
- 3)
Based on the spatial distribution and
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by the Science and Technology Plan Project of Tibet Autonomous Region (No. XZ201901-GB-24); the Basic Research Fund of Institute of mineral Resource, Chinese Academy of Geological Sciences (No. KK2017, KJ2001); the National Key R&D Program of China (No. 2018YFC0604101), the National Natural Science Foundation of China (No.41902097), China Scholarship Council project and the Geological Survey project (grant no. DD20190167). The authors would like to thank two anonymous
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