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Source of ore-forming fluids of the Yangshan gold field, western Qinling orogen, China: Evidence from microthermometry, noble gas isotopes and in situ sulfur isotopes of Au-carrying pyrite
Liang, Jinlong1; Li, Jie2; Sun, Weidong3,4,5; Zhao, Jing1; Zhai, Wei6; Huang, Yi1; Song, Mingchun7; Ni, Shijun1; Xiang, Qirong1; Zhang, Jianchao8; Hao, Jialong8; Nan, Zhenglu9; Li, Jianzhong9
AbstractThe Yangshan gold ore belt contains a series of sediment-hosted disseminated gold deposits in the southern subzone of the western Qinling orogen. The ore deposits formed in the Middle Devonian carbonaceous clastic-carbonate sequences that underwent strong deformation and low greenschist fades regional metamorphism. The shapes and distribution of the ore bodies are strictly confined by the E-W-trending Anchanghe-Guanyinba thrust fault zone. Pyrite and arsenopyrite are the major Au-carrying minerals. Microthermometric results show that the ore-forming fluids are CO2-rich aqueous solutions. The homogenization temperatures range from 221 to 303.5 degrees C, and salinities range from 2.0 to 7.2 wt% NaCl equiv. These characteristics are consistent with orogenic gold deposit. Noble gas isotopic measurement shows that He-3/He-4 ratios of pyrite and quartz grains inherited from the mineralized carbonaceous phyllite, ranging from 0.033 to 0.081 Ra, implying that the origins of ore fluids are restricted within the crustal regime. The Ar-40/Ar-36 ratios range from 434 to 863, indicating 34 to 68% crust-derived radiogenic Ar-40* in the ore fluids. Based on the backscattered electron (BSE) maps of pyrite, three generations (i.e. core, mantle, rim) are distinguished: pre-ore pyrite including framboidal pyrites and the cores of zoned pyrites both in the phyllite and plagiogranite dikes; ore stage pyrites including the middle zones of the three-zoned pyrites in the granitic dikes and the outer zones of the zoned pyrites in the phyllite; post-ore pyrites, i.e. the outermost rims of the zoned pyrites in the dikes. The arsenopyrite in the phyllite has similar texture to the pyrite, and is regarded as the peak of the mineralization due to its highest Au concentrations. High spatial resolution NanoSIMS multi-elemental maps of the pyrites reveal that (i) gold is distributed heterogeneously as lattice-bounded Au in the zoned pyrites with higher Au (As) in the middle zones and lower Au (As) in the inner and outermost zones. No nano-particles of native gold was identified in pyrite; (ii) gold mineralization occurred in a single event instead of multistage ore formation; (iii) gold precipitation event is followed by an overgrown zone with low Au and As concentrations. In situ sulfur isotopes of Au-bearing pyrite identified two types of sulfur sources: one is framboidal pyrite and the barren core of pyrite in the carbonaceous phyllite, which have very negative delta S-34 values (< -20%); the other is the Au-bearing overgrowth zone of pyrite both from the granitic dike and phyllite, which have higher delta S-34 values ranging from -7.3 to 1.3%. This result indicates that the barren pyrites have the sulfur isotopic feature of reduction of seawater sulfate, whereas the As-, Au-bearing pyrites are likely derived from a magmatic sulfur contaminated by a sedimentary sulfur. Combining Au concentrations with the corresponding delta S-34 values in the pyrites reveals that the zones with high Au have lower delta S-34 values (and vice versa). This coupling relation between Au and S isotope has been also identified in other orogenic and Carlin-type gold deposits. The oxidation of ore fluid is taken as the key for gold precipitation during formation of orogenic gold deposit. However, the oxidation of ore fluids accompanied by the escape of reduced gas (e.g. H2S) should result in high Au coupled with high delta S-34. Therefore, we propose that the Yangshan gold deposit forms through partitioning aqueous vapor with high Au, As, and lower delta S-34 from a deep magma chamber under the ore field, which leads to overgrowth of the pre-existing pyrites. Based on the geological features, texture of pyrite, and sulfur isotopic characteristics, we suggested that the Yangshan gold deposits have the characteristics between Carlin-type and orogenic gold deposits. They are the product of the western Qinling orogeny during the Late Triassic.
KeywordYangshan gold ore belt Noble gas isotopes NanoSIMS elemental mapping Sulfur isotopes Western Qinling orogen
Indexed BySCI
Funding ProjectTaishan Scholar Special Project Funds[ts201511076] ; Key Research and Development Project of Shandong Province[2017CXGC1604]
WOS Research AreaGeology ; Mineralogy ; Mining & Mineral Processing
WOS SubjectGeology ; Mineralogy ; Mining & Mineral Processing
WOS IDWOS:000459949300025
Citation statistics
Cited Times:2[WOS]   [WOS Record]     [Related Records in WOS]
Document Type期刊论文
Corresponding AuthorLi, Jie; Zhai, Wei
Affiliation1.Chengdu Univ Technol, Dept Geochem, Chengdu 610059, Sichuan, Peoples R China
2.Hebei GEO Univ, Sch Resources, Shijiazhuang 050031, Hebei, Peoples R China
3.Chinese Acad Sci, Inst Oceanog, Ctr Deep Sea Res, Qingdao 266071, Peoples R China
4.Qingdao Natl Lab Marine Sci & Technol, Lab Marine Mineral Resources, Qingdao 266237, Peoples R China
5.Chinese Acad Sci, Ctr Excellence Tibetan Plateau Earth Sci, Beijing 100101, Peoples R China
6.Sun Yat Sen Univ, Sch Marine Sci, Guangzhou 510006, Guangdong, Peoples R China
7.Shandong Prov Bur Geol & Mineral Resources, Jinan 250013, Shandong, Peoples R China
8.Chinese Acad Sci, Inst Geol & Geophys, Key Lab Earth & Planetary Phys, Beijing 100029, Peoples R China
9.12th Branch Chinese Gold Armed Police Army, Chengdu 610036, Sichuan, Peoples R China
Recommended Citation
GB/T 7714
Liang, Jinlong,Li, Jie,Sun, Weidong,et al. Source of ore-forming fluids of the Yangshan gold field, western Qinling orogen, China: Evidence from microthermometry, noble gas isotopes and in situ sulfur isotopes of Au-carrying pyrite[J]. ORE GEOLOGY REVIEWS,2019,105:404-422.
APA Liang, Jinlong.,Li, Jie.,Sun, Weidong.,Zhao, Jing.,Zhai, Wei.,...&Li, Jianzhong.(2019).Source of ore-forming fluids of the Yangshan gold field, western Qinling orogen, China: Evidence from microthermometry, noble gas isotopes and in situ sulfur isotopes of Au-carrying pyrite.ORE GEOLOGY REVIEWS,105,404-422.
MLA Liang, Jinlong,et al."Source of ore-forming fluids of the Yangshan gold field, western Qinling orogen, China: Evidence from microthermometry, noble gas isotopes and in situ sulfur isotopes of Au-carrying pyrite".ORE GEOLOGY REVIEWS 105(2019):404-422.
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