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Procedia Earth and Planetary Science 7 ( 2013 ) 508 – 512

Water Rock Interaction [WRI 14] Study of metallogenetic fluids and metallogenic mechanisms of Xingyuanchong copper deposit, Province,

Ting Liua, Chengdong Liua*, Zhaobin Yana, Yiping Chena, Xuling Wub, Xiujun Fanb

aState Key Laboratory Breeding Base of Nuclear Resources and Environment, East China Institute of Technology, , JX330013, China bJiangxi Provincial Institute of Geology Survey, Nanchang, JX330030 China

Abstract

Xingyuanchong copper deposit at Wanzai, Jiangxi, is located in the west section of Yifeng- deep faults- Huangmao area. By studying the fluid inclusions, and integrating the metallogenic features and sulfur isotope compositions of the ore deposit, the source of metallogenic fluids and metallogenic mechanisms can be studied. The study of fluid inclusions indicates that the deposit was controlled by fluids from at least two different sources: δ34S data indicates sulfur was characterized by submarine exhalation sedimentation and late-stage hydrothermal superimposition. Thus, combining the above geochemical characteristics and the geological setting, it is proposed that the metallogenic fluids of the deposit were extrusive gas-hydrothermal fluids, seawater, and later magmatic hydrothermal fluids. The mineralizing processes can be divided into two stages: first, submarine volcanic sediments or a proto-ore layer formed in the Mesoproterozoic; second, the pre-existing proto-ore was diplogenetically altered by the hydrothermal fluids and dynamic metamorphism mainly derived from the Jinning orogenic period in Late Proterozoic.

© 20132012 The The Authors. Authors. Published Publis byhed Elsevier by Elsevier B.V. B.V. Selection and/or and/or peer-review peer-review under under responsibility responsibility of the Organizing of Organizing and Scientific and Scientific Committee Committee of WRI 14 of – 2013WRI 14 – 2013.

Keywords: fluid inclusion; sulfur isotopic geochemistry; metallogenic fluid; metallogenic mechanism; Xingyuanchong copper deposit.

* Corresponding author. Tel.: +086-0791-3897617; Fax: +086-0791-83897801. E-mail address: [email protected]

1878-5220 © 2013 The Authors. Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Organizing and Scientific Committee of WRI 14 – 2013 doi: 10.1016/j.proeps.2013.03.142 Ting Liu et al. / Procedia Earth and Planetary Science 7 ( 2013 ) 508 – 512 509

1. Introduction

Xingyuanchong copper deposit at Wanzai, Jiangxi, is located in the west section of Yifeng- Jingdezhen deep faults in the north side of Qinhang metallogenic belt. This belt, according to Mao et al. [1] and Lou et al. [2], is a rare in-plate polymetallic metallogenic belt, and along which develops a series of copper, tungsten and tin polymetallic mineral resources. Thus, a systematic study of Xingyuanchong deposit will definitely help us to understand the genesis mechanisms and regional metallogenic regularities of this kind of deposits. In this article, temperature measurement of fluid inclusions in gangue minerals and sulfur isotopic study of the ore have been carried out, so as to discuss the sources of metallogenic fluids, and by combining the metallogenic characteristics, metallogenic mechanisms of the deposit are further explored.

2. Metallogenic geological background

The outcropping strata of Xingyuanchong deposit are mainly Yifengyan Formation in Jixianian, Mesoproterozoic, which are ore-bearing strata of gold, silver, copper, lead and tin polymetallic deposit. The main structure in studied area is a NEE composite nappe (slip) structure, curved in “S”, and NEE ductile-brittle silicified schistosity zones are the most developed, which help ore-bearing metamorphic hydrothermal fluids to transport and concentrate [2]. Large-scale bimodal volcanic activities happened in Early Jinning were mainly manifested as the interlayer of meta-quartz ceratophyre, meta-basalts and epidiabase in Yifengyan Formation; and the large-scale intermediate-acidic magmatic intrusion in Late Jining formed large Jiuling complex biotite granodiorite batholith, which exposed in a large area northeast of the studied district.

3. Fluid inclusion study

Samples for fluid inclusion study are mainly from quartz and calcite veins in different ore bodies in Yemaochong ore section. The types of fluid inclusions are mainly Liquid+Vapour ones with V-L ratios of 5~25%, with a size range of generally 620μm, various shaped, and occasionally banded distributed, but with no regularities (Fig.1). 510 Ting Liu et al. / Procedia Earth and Planetary Science 7 ( 2013 ) 508 – 512

Fig.1 Petrographic characteristics of fluid inclusions in quartz grains from Xingyuanchong copper deposit. A, B, C, D-LH2O+ VH2O inclusions of different shapes, with vapor-liquid ratio of 5%~25%, being isolated or in swarms; A- some inclusions distributed in specific zones; B- LH2O inclusions in irregular shapes; C- Twin inclusions with vapor-liquid ratio of about 20%, and some inclusions distributed in specific zones.

3.1. Homogenization temperature and salinity

Microthermometric measurements in fluid inclusions of quartz veins from diverse generations indicate homogenization temperatures varying from 437°C to 75°C. From the histogram, homogenization temperatures can be divided into two main distribution ranges (Fig. 2), indicating the deposit was controlled by at least two stages of metallogenic fluids and the metallogenic fluid system evolved gradually. Approximate salinity of fluid inclusions varies from 1.74wt% to 22.58wt%, positively related with homogenization temperature (Fig.3).

Fig.2 Histogram of homogenization temperature. FIig.3 Diagram of homogenization temperature-salinity. Ting Liu et al. / Procedia Earth and Planetary Science 7 ( 2013 ) 508 – 512 511

3.2. Density

Bodna r[3] discovered that according to homogenization temperature, salinity and density in NaCl- H2O system, density of the fluids can be acquired [4]. Density of fluid inclusions is 0.74wt% ~1.08wt%, negatively related with homogenization temperature (Fig.4). When temperatures are between 130°C and 200°C, density changes with salinity; while between 220°C and 300°C, density is lower, remaining in 0.85wt% ~ 0.95wt%; and density of those over 350°C is rather low, ranging from 0.74wt% to 0.75 wt%.

4. Source of metallogenic fluids

The fluid inclusions study shows that metallogenic fluids of Xingyuanchong copper deposit are characterized by multi-stage activities, and the deposit is controlled by at least two stages of metallogenic fluids: one stage is the fluids with higher temperature and salinity, but lower density; another stage is the fluids with lower temperature and salinity, but higher density. δ34S compositions of the ore deposit range from 1.0‰ to 6.2‰, quite similar with mantle-derived sulfur (0‰~3‰)(Fig.5). δ34S of Xingyuanchong deposit are closest to δ34S of VHMS deposits (-0.5‰ ~6.1‰)[5], and are also similar with deposits in Qinhang metallogenic belt as Mao et al.[1] have studied, which are deposits formed after early submarine exhalation sedimentation and later hydrothermal superimposition, thus inferring that sulphur in this ore might be the same with that of the former ones. Thus, according to the above discussion of fluid inclusions and sulphur isotopic compositions, we can infer that metallogenic fluids should be the mixture of extrusive gas-hydrothermal fluids, seawater and later magmatic hydrothermal fluids.

Fig.4 T-W-ρ phase diagram of NaCl-H2O system. Fig.5 Sulfur isotopic histogram of the deposit.

5. Metallogenic mechanisms discussion

During Jinning tectonic stage, Xingyuanchong copper deposit was located in the contiguous area of ancient Ghiangnania and South China trough, where submarine volcanoes erupt. Heavy metals are leached from shallow crustal rocks and carried to the sea floor to precipitate into proto-ore layer when encountering cold water. During Late Jinning tectonic stage, there was a subduction and collision between Upper Yangtze ancient platform and Lower Yangtze micro-platform, forming deep faults and intense congruous folds. These deep faults and folds provided advantageous channel for transporting metamorphic fluids, which diplogenetically altered the pre-existing proto-ore, making them into rich ore bodies. The results of fluid inclusions and sulphur isotope study coincide with the magmatic tectonic events in Jinning, thus, integrating the metallogenic geological features, we can conclude that metallogenic processes of the deposit mainly underwent two stages: submarine volcanic sediments or proto-ore layer 512 Ting Liu et al. / Procedia Earth and Planetary Science 7 ( 2013 ) 508 – 512

formed in Mesoproterozoic; and hydrothermal fluids and dynamic metamorphism mainly from Jinning orogenic period in Late Proterozoic.

6. Conclusions

Integrating the above geochemical characteristics with metallogenic features, we can conclude that the metallogenic fluids are mainly extrusive gas-hydrothermal fluids, seawater and later magmatic hydrothermal fluids. And the metallogenic process of the deposit could be divided into two stages: submarine volcanic sediments formed in the Mesoproterozoic; hydrothermal fluids and dynamic metamorphism mainly from the Jinning orogenic period in Late Proterozoic.

References

[1] Mao JW, Chen MH, Yuan SD, Guo CL. Geological characteristics of Qinghang(or Shihang) metallogenic belt in South China and spatial-temporal distribution regularity of mineral deposits. Acta Geologica Sinica 2011; 85(5):636-658(Chinese with English abstract). [2] Lou FS, Wu XL, Fan XJ, Liu CD, Yan ZB, Chen YP, Xu L. Geological Features and Genesis of the Xingyuanchong Copper Deposit in Wanzai County, Jiangxi Province. Geology and Exploration, 2012; 48(4): 704-712(Chinese with English abstract). [3] Bodnar RJ. A method of calculating fluid inclusion volumes based on vapor bubble diameters and PVTX properties of inclusion fluids. Econ Geol 1983; 78:535-542. [4] Lu HZ, Fan HR, Ni P, OU GX, Shen K, Zhang WH. Fluid Inclusions. 1st ed. Beijing: Science Press, 2004 (in Chinese). [5] Robinson DJ, Hutchison RW. Evidence for a volcanogenic-exhalative origin of a massive nickel sulphide deposit at Redstone, Timmins, Ontario. Geol Assoc Canada Spec 1982; 25: 211-254.