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Yinshan |
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Jiangxi, China |
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Cu Au Zn Pb Ag
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Super Porphyry Cu and Au
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The Yinshan epithermal-porphyry Cu-Au-Pb-Zn-Ag deposit is located ~25 km southwest of the Dexing porphyry copper deposit in Jiangxi, south eastern China.
The composite Yinshan deposit is part of the larger Dexing copper-gold polymetallic district which is made up of the ~170 Ma Middle Jurassic Yinshan Cu-Au-Pb-Zn-Ag deposit that contained 0.95 Mt of copper and 107 t of gold in 1996; the Yinshan Pb-Zn Mine; the ~170 Ma Dexing porphyry Cu-Au-Mo deposits with 6 Mt of copper and 138 t of gold (Wang et al., 2006; Zhu et al., 1983), and the ~866 Ma Neoproterozoic Jinshan Au deposit which contained 180 t of gold (Li et al., 2010; Wei, 1996). Mining in the Yinshan district dates back to the sixth century CE, during the Sui Dynasty. The modern Yinshan mine commenced operations in 1958, and by the end of 1990, the remaining proved mineral reserves were 0.67 Mt of copper, 82 tonnes of gold, 0.43 Mt of lead, 0.52 Mt of zinc, and 3112 t of silver, at grades of 0.52% Cu, 0.61 g/t Au, 1.25% Pb, 1.02% Zn and 11.5 g/t Ag (Yinshan Lead-Zinc Mine, 1993). Subsequent deep drilling added proved ore reserves of 0.28 Mt of copper, 25 t of gold, 0.12 Mt of lead-zinc, and 333 t Ag, with grades of 0.6% Cu, 0.57 Au g/t, 4.5% Pb-Zn and 7.6 g/t Ag (Xu et al., 2007).
Regional Setting
The deposits of the Dexing copper-gold polymetallic district lie within the eastern section of the the Neoproterozoic Jiangnan Orogen. This orogen falls within the South China Block, and separates it's two main components, the Archaean Yangtze Craton to the NW and the Proterozoic Cathaysia Block to the SE. The orogen is bounded to the NW by the Yangtze Craton and to the SE by the SW-NE trending Jiangshan-Shaoxing Fault, which is considered represent the suture zone between these two main tectonic blocks.
A second significant regional tectonic boundary influences the architecture of the orogen. This is the Northeast Jiangxi Fault which trends NNE-SSW, extending from the southern margin of the Yangtze Craton in the north, across the orogen to converge in the west with the Jiangshan-Shaoxing Fault on its southern margin. This structure divides the orogen into the juxtaposed, wedge shaped, Jiuling and Huaiyu terranes to the SW and NE respectively.
The Jiuling Terrane has been strongly deformed and is primarily composed of weakly metamorphosed volcano-sedimentary sequences, which include slate, tuff, phyllite and local metabasalt. This sequence, which was deposited at ~880 Ma in the Neoproterozoic, is known the Shuangqiaoshan Group in Jiangxi Province and Shangxi Group in Anhui Province (Wang et al., 2008). Locally, these older rocks are unconformably overlain/intruded by undeformed Upper Palaeozoic and Late Jurassic rocks as detailed below. The Shuangqiaoshan Group, which forms the main wallrocks to the Yinshan deposit, locally comprises lower greenschist facies sandstone and volcaniclastic rocks, intercalated with basaltic lavas.
The Huaiyu Terrane comprises the Shuangxiwu Group in northwestern Zhejiang and the Qigong Group in northeastern Jiangxi. Both groups represent the remnants of a Neoproterozoic continental arc (Charvet et al., 1996; Guo et al., 1996). The Shuangxiwu Group is predominantly made up of volcanic and pyroclastic rocks, intercalated with felsic tuff, tuffaceous sandstones and siltstones, that have been subjected to strong deformation and greenschist-facies metamorphism. Exposures of the Qigong Group is found along the southeastern side of the Northeast Jiangxi Fault and comprise a strongly disrupted sequence of turbidities and volcaniclastic rocks (Liu et al. 2012).
The Dexing copper-gold polymetallic district, including the Yinshan deposit, also lies within the broad, and voluminous NE-SW elongated 1400 x 800 km Mesozoic granitoid-volcanic belt, or large igneous province, which overlies and intrudes the Cathaysia Block, the Jiangnan Orogen and the southeastern margin of the Yangtze Craton. This magmatic belt coincides with the development of large-scale W, Sn, Cu, Au, U, Nb, Ta, REE, Pb, Zn and Ag mineralisation related to the granitoids (e.g., Cao et al., 2023; Liu et al., 2013). Magmatic activity persisted from the Triassic to Cretaceous, with two more intense pulses during the Jurassic and Cretaceous. Jurassic granitoids are the most significant in both spatial distribution and economic potential. Middle Jurassic I-type granitoids were responsible for the Cu-Au mineralisation at the Dexing porphyry Cu deposit and the Yinshan epithermal-porphyry polymetallic deposits (Liu et al., 2012). At Yinshan, this mineralisation was related to sub-volcanic to extrusive quartz porphyry and dacitic porphyry, that have been dated at ~172 Ma (see below for more detail) in the Middle Jurassic (Liu et al. 2013). Geochemical data suggest these I-type intrusives were derived from partial melting of Neoproterozoic arc-related mafic to ultra-mafic residues (or mafic underplates) in the lower crust. The same data also provide evidence of crustal contamination from the Neoproterozoic Shuangqiaoshan Group rocks (Liu et al. 2013). These mineralised porphyries, which were coeval with the nearby Dexing granodioritic porphyries, were emplaced into an extensional tectonic regime within a continental setting, resulting from the influences of the temporally overlapping transition, and ~90° rotation of stress fields, from those of the palaeo-Tethyan to that of the palaeo-Pacific subduction systems (Liu et al. 2013). This Middle Jurassic Cu-Au stage was followed by the more intense Late Jurassic 160 to 150 Ma A-type granitoid magmatism which was associated with the regional W-Sn mineralisation in particular (e.g., Liu et al., 2013). The same authors suggest this stage of magmatism was the result of the continued development of an extensional tectonic regime, accompanied by basaltic underplating, and larger scale lower crustal melting, to produce the Jurassic A-type magmatism (Peng et al., 2007; Jiang et al., 2008; Mao et al., 2008; Zhu et al., 2008).
Deposit Geology, Structure and Mineralisation
The wall rocks to mineralisation at Yinshan are principally the:
• The low-grade metamorphic rocks of the Neoproterozoic Shuangqiaoshan Group, which, in the deposit area, comprises up to 2500 m of phyllite and tuffaceous phyllite, occupying the core of the NE-trending Yinshan anticline; and the
• Middle Jurassic Ehuling Formation volcanic to subvolcanic rocks, which, in the Yinshan deposit area, are divided into three cycles:
i). the first of which is characterised by eruptions of rhyolitic lava distributed over an area of 0.8 km2 and thickness of ~450 m in the Xishan segment in the NW part of the deposit area, with coeval rhyolitic quartz porphyry intrusive stocks covering an area of 0.02 to 0.04 km2 in the Jiuqu and Beishan segments in the centre of the mineralised complex and to the NE respectively. Cessation of eruption was accompanpied by the formation of a crater.
ii). the second cycle involved an ~700 m stratigraphic thickness of dacitic volcanic rocks in the Xishan segment, and near east-west trending dacite porphyries over an area of 0.09 km2 in the Jiuqu segment.
iii). the third cycle corresponds to the emplacement of a small, <0.01 km2 intrusive stocks of andesitic to quartz-diorite porphyry within the previous two cycles of volcanic rocks in the Xishan segment.
Liu et al. 2013 dated (U-Pb zircon) the sub-volcanic to extrusive quartz porphyry and dacitic porphyry of cycles 1 and 2, followed by a barren cycle 3 quartz diorite porphyry, to obtain Middle Jurassic dates of 172.2 ±0.4 Ma, 171.7 ±0.5 Ma and 170.9 ±0.3 Ma, respectively. Previous determinations from this suite had returned ages in the range 175 to 170 Ma, (U-Pb zircon; Wang et al., 2012), consistent with muscovite alteration ages of ~175 Ma (40Ar-39Ar; Li et al., 2007), taken to further suggest mineralisation was coeval with these volcanic-subvolcanic events. The quartz and dacitic porphyries occur as dykes that are 700 to 800 m long and 5 to 40 m thick, with maximum vertical extensions of >500 m.
The principal structures in the deposit area are the Yinshan anticline and associated faults. The Yinshan Anticline axis is NE-SW oriented at 45 to 50°, and plunges to the NE. Both limbs of this fold are occupied by low-grade metamorphic rocks of the Shuangqiaoshan Group. The volcanic rocks of the unconformably overlying Jurassic Ehuling Formation are not folded, suggesting deformation was pre-Middle Jurassic, possibly during the Neoproterozoic (Li et al., 2010; Liu, 2005). A series of major NE-oriented faults were generated along the axial plane of the Yinshan anticline, coeval with folding, whilst second-order east-west and NNW-oriented faults were formed in the two limbs. Re-activation of these pre-existing faults is implied at both Yinshan and Dexing during the Middle Jurassic, with sub-volcanic rocks associated with mineralisation emplaced at the intersections of the major NE-trending fault and the second-order cross-faults (Wang et al., 2012, 2006). Polymetallic mineralisation was also primarily deposited along these second-order east-west and NNW-trending faults (Mao et al., 2011; Ye, 1983).
The mineralised system at Yinshan has been subdivided into six segments over an interval of 3.5 km, which are, from south to north, straddling the Yinshan Anticline axis: i). Nanshan and ii). Yinshan East, both to the SW of the fold axis, iii). Yinshan West (or Xishan), is to the NW of the same axis, whilst iv). Jiuqu, and v). Jiulongshangtian (or Jiulong) cross the axis, and vi). Beishan, furthest to the NE, is found to the west of the axis (Wang et al., 2013).
The central cluster of the Jiuqu, Yinshan West and Yinshan East segments contain Cu-Au orebodies, whilst the more peripheral Beishan, Jiulong, Nanshan and Yinshan East segments contain Pb-Zn-Ag mineralisation. Within the segments to the NW of the fold axis, mineralisation trends east-west, whilst those to the SE strike NNW. Most dip steeply and persist vertically for >1000 m, with strike lengths of between 300 and 600 m, and thicknesses of 1 to 15 m (Wang et al., 2013).
The Pb-Zn-Ag mineralisation has been shown to be associated with the first cycle rhyolitic quartz porphyries, whilst the Cu-Au mineralisation is related to the second cycle of dacite porphyries, as described above (Hua, 1987; Li et al., 2005; Zhang et al., 1997).
The quartz-sulphide veins of the Pb-Zn-Ag mineralisation contain galena, sphalerite, pyrite, native silver and Pb-Ag-Sb sulphosalts, with a gangue assemblage that includes quartz, calcite, sericite and chlorite. The quartz-sulphide veins of the Cu-Au mineralisation are predominantly composed of chalcopyrite, pyrite, tetrahedrite and native gold in a gangue that includes sericite, quartz, chlorite and minor calcite. However, the ore minerals in the Cu-Au vein assemblage varies with depth, with abundant tetrahedrite-tennatite at shallow depths, grading to a chalcopyrite-pyrite assemblage with greater depth.
The Pb-Zn-Ag mineralisation has associated sericite and carbonate alteration in wall rock to the veins, whilst Cu-Au is characterised by a phyllic assemblage, and on a broader scale, all lie within a propylitic envelope.
Mineral Resources
In addition to the production and resources detailed in the second paragraph of this record, the deposit is said to have totalled (Li et al., 2007).
83 Mt @ 0.5% Cu, 0.8 g/t Au, 1.3% Pb, 1.0% Zn, 33.3 g/t Ag.
The most recent source geological information used to prepare this decription was dated: 2013.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Liu, X., Fan, H.-R., Santosh, M., Hu, F.-F., Yang, K.-F., Wen, B.J., Yang, Y.H. and Liu, Y., 2013 - Origin of the Yinshan epithermal-porphyry Cu-Au-Pb-Zn-Ag deposit, southeastern China: insights from geochemistry, Sr-Nd and zircon U-Pb-Hf-O isotopes: in International Geology Review v.55, pp. 1835-1864. /dx.doi.org/10.1080/00206814.2013.799256.
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Wang, G.-G., Ni, P., Wang, R.-C., Zhao, K.-D., Chen, H., Ding, J.-Y.,Zhao, C. and Cai, Y.-T., 2013 - Geological, fluid inclusion and isotopic studies of the Yinshan Cu-Au-Pb-Zn-Ag deposit, South China: Implications for ore genesis and exploration: in J. of Asian Earth Sciences v.74, pp. 343-360. dx.doi.org/10.1016/j.jseaes.2012.11.038.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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