Qinling Gold Province - Yangshan, Liba, Maanqiao, Shuangwang, Baguamiao, Pangjiahe
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The Qinling Gold Province in the Qinling Mountains is located to the west of the Xiaoqinling gold province in Shaanxi and Gasnsu Provinces, central China. The province includes over 50 gold deposits (excluding placer accumulations) varying from the large Yangshan with a resource of 308 t Au, to small ones with resources of <1 t Au (Chen et al., 2004). It also inludes the Baguamiao, Maanqiao, Shuangwang, Pangjiahe and Liba orogenic deposits and goldfields which together contain >500 t of Au (Zeng et al., 2012).
The ores of the gold province are confined to an ENE trending belt of highly-deformed and regionally metamorphosed Devonian and Carboniferous flysch separating the North China and Yangtze (South China) cratons. This belt of gold deposits extends from near Lixian in Gansu Province to Zhenan in Shaanxi Province, over a length of 600 km x ~200 km wide.
The Qinling Orogen can be divided by three major northerly dipping tectonic zones that are subparallel to the trend of the orogen. These tectonic zones are:
i). Palaeozoic Shangdan Suture to the north that separates the North Qinling Terrane from the South Terrane (Gao et al., 1996). The North Qinling Terrane, which consists of an early Palaeozoic arc that was accreted to the North China Craton at ~450 Ma along the Shangdan Suture (Zhang et al., 2000), hosts minor gold mineralisation (Mao et al., 2002).
ii). the Zhenan-Fengxian (Lixian-Shanyang, Mao et al., 2002) Thrust Zone, which divides the South Qinling Terrane into the central and southern domains. The central domain, which is included by Mei et al., (1999) in the northern zone of the South Qinling Terrane, is dominated by flysch and other clastic rocks that accumulated in a late Palaeozoic basin between the converging cratonic blocks. The southern domain is covered by Palaeozoic strata in the east and characterised by the easternmost exposure of Triassic turbiditic deposits in the west that are partly calcareous and form part of the immense Songpan-Ganzi Basin (Mao et al., 2002). Geographically, the South Qinling Terrane is arbitrarily subdivided into East and West Qinling Domains on either side of the Baoji-Chengdu railway (Zheng et al., 2010).; and
iii). the Mianlue Suture to the south, that forms the margin with the South China/Yangtze craton to the south and the main bulk of the Songpan-Ganzi Basin.
Plutons in the Qinling Orogen, range in age from Palaeozoic to Yanshanian (late Mesozoic) and include monzogranite, granodiorite and quartz diorite. Zhang et al. (2006) recognized two major distinct tectono-magmatic events in the orogen, which are late Ordovician (~450 Ma) and late Triassic (~220 Ma) in age. The late Ordovician granites are spatially constrained to the North Qinling Terrane (Zhang et al., 2000; Lu 2000; Zhang et al., 2002), and the late Triassic granites were emplaced into both the North Qinling Terrane (Wang et al., 2008) and the South Qinling Terrane (Sun et al., 2002). Early Triassic magmatism is also reported just south of the Shangdan Suture (e.g., the Xiahedong pluton, Jin et al., 2005, and Xianggou pluton, Zhu et al., 2009).
The late Ordovician tectono-magmatic event is interpreted to relate to the partial melting of thickened island-arc crust. This took place during the northward subduction of the palaeo-Qinling oceanic plate along the Shangdan Suture between the North Qinling and the South Qinling tectonic units. The late Triassic tectono-magmatic event is interpreted to relate to the break-off of a subducted oceanic plate during the continental collision between the North China and South China cratons (Sun et al., 2002). It is uncertain whether the second event was a post-collisional setting or volcanic arc setting (e.g., Chen et al. 2009).
The timing of gold mineralisation in the Qinling Orogen is loosely constrained between 338 and 234 Ma in age at the Pingding deposit (Liu et al., 1994). Mao et al. (2002) suggested that gold mineralisation took place between about 210 to 170 Ma. Chen et al. (2004) proposed a 220 to 100 Ma age with a peak at ~170 Ma. Zhang et al. (2002, 2004) argued the correlation of gold metallogeny with the oblique collision between the North China and South China Cratons during the Jurassic to Early Cretaceous. The large age ranges may be due to multiple events or the dating methods were not conducted precisely or accurately (Zeng et al., 2012).
The larger orebodies are located in the West and East Qinling Domains and the Southern Domain, localised by the intersection of NE and NW structures with the regional east-west to WNW striking fold and shear zones, mostly dipping 50 to 70°W.
Gold occurs in: i). small quartz stockworks and veinlets along major ductile shear zones (eg., Baguamiao); ii). disseminated in wall rocks along brittle fractures in hornfels zones (eg., Liba), iii). in large breccia zones (eg., Shuangwang), iv). in carbonaceous carbonaye rocks (e.g., Yangshan).
The Yangshan gold deposit, Wenxian county, Gansu province, contains 308 t Au with average grade of 4.74 g/t Au. It is a syn-collisionally Carlin-like gold deposit, with orebodies controlled by an east-trending shear-zone and hosted in Devonian carbonaceous carbonate-phyllite-slate sequence or granite-porphyry dykes intruding into the Devonian strata. Isotopic ratios from fluid inclusions within quartz separates, suggest that the ore-fluids have been mainly sourced, through metamorphism and/or reworking, from the Devonian strata or/and similar lithologies which comprise carbonaceous phyllite, slate, chert and carbonate, with a significant input of meteoric water. In general, the ore-forming fluid-system varies from early, deep, metamorphic fluid to late, shallow, meteoric water (Chen et al., 2008). For more detail see the separate Yangshan record.
Baguamiao, which contains >80 t Au @ 3.5 to 6 g/t Au, is one of the largest orogenic gold deposit in the Qinling Gold Province occurring as a main ore zone of about 1.7 km along strike, 50 to 160 m wide, and a 500 m down dip extent. The major ore minerals, comprising about 5% of the hydrothermal phases, are pyrrhotite, pyrite and secondary marcasite with lesser sphalerite, galena, tellurobismuth and gold. Alteration halos surround the orebodies are characterised by a broad bleaching zone of white mica and ankerite, and a proximal zone of silicification with abundant sulphide minerals. Biotite, albite, and tourmaline are locally developed.
The Liba goldfield in Gansu province, contains a gold resource of 87 tonnes (2.8 Moz), and is located to the NE of the Zhongchuan Granite of the West Qinling Orogen. The structurally controlled gold mineralisation is located ~2 km NE of the Zhongchuan Granite, and is hosted by Devonian metasedimentary rocks, comprising metamorphosed siltstone, sandstone, mudstone and shale, assigned to the Shujiaba Formation, which have been intensely deformed to phyllitic rocks that commonly trend ESE (Cheng and Zhang 2001). Others deposits in the region include the Jinshan and Maquan gold deposits that are located 2 to 5 km south of the 30 km diameter Zhongchuan Granite, and are hosted by the Devonian Xihanshui and Carboniferous Xiajialing groups respectively. The Shujiaba Group, referred to as the Liba Group by Li (1999), comprise a ~5000 m thick succession of clastic-dominant flysch deposits, including siltstone, slate, micrite, sandstone and quartzite (Zhang et al., 2004). By contrast, the Xihanshui Group, regarded as a lateral equivalent of the Liba Group, is a 5800 m thick succession of carbonate with interbedded clastic units, interpreted as a shallow continental shelf deposit (Jin and Li 1996).
The Devonian rocks are overlain by metamorphosed Carboniferous shale and siltstone to the NW and SE of the Zhongchuan Granite, and metamorphosed Cretaceous sandstone and conglomerate to the NE, SE and SW of the granite. The Jurassic and Carboniferous rocks in the SE are in fault contact. The Cenozoic successions form isolated outcrops in the east and SW where they comprise reddish terrigenous clastic units that total 2000 m in thickness. Up to 50 m thick Quaternary eluvial and alluvial sediments contain small placer gold deposits locally. Sedimentary rocks in the region have been regionally metamorphosed to greenschist-facies.
Mineralisation in the Liba Goldfiled is associated with silica-sericite-chlorite-carbonate alteration, which have also affected most of the dykes, suggesting that most of the dykes are pre- to syn-mineralization.
Individual deposits include the: Zhaogou orebody is the northernmost ore zone delineated in the Liba goldfield. 50 t of gold has been delineated at grade of 1.5 g/t Au (Dragon Mountain Gold, ASX Announcement 2009); Wawugou orebody located in the Wawugou Fault, enveloped by breccia. WWG-1 has a northwest-trending lenticular shape that is over 900 m long and dips ~60°SW, with a thickness of 1 to 12 m, and average grade of 3.78 g/t Au (Zhang 2003). WWG-II is subparallel to WWG-I and located 60 m to the NE. The mineralised zone is steeply dipping, strikes 290°, and is over 400 m long and ~1 m wide; At the Magou orebody, 36 t of contained gold has been delineated at 1.8 g/t Au (Dragon Mountain Gold ASX Announcement, 2009) in two zones, the largest of which is >930 m long, averaging 5.78 g/t Au with an average thickness of 8 m (Shi 2001).
Two main styles of mineralisation are known on the goldfield: i). disseminated sediment-hosted and ii). quartz vein hosted types. Pyrite, arsenopyrite and arsenian pyrite are major gold carriers, while native gold grains and electrum are spatially associated with the sulphides. Numerous felsic/intermediate dykes have a similar structural distribution as the mineralisation, and their contacts with host rocks are considered to be favourable zones for mineralisation.
Three phases of deformation have been recognised in the area. The first deformation (D1) event had a broadly north-south orientation and was compressional. The D2 event was also compressional and orientated in a NE-SW direction, while D3 was post-mineralisation, associated with the emplacement of barren calcite and anhydrite veins. Compression related to D2 controlled the distribution of igneous dykes and gold mineralisation in the Liba goldfield. Both igneous and hydrothermal fluids preferentially focused along dilational jogs under local transtension, which took place during the late stage of D2. Precise dating with high-resolution ion microprobe (SHRIMP) U-Pb on zircon and 40Ar/39Ar on muscovite, biotite, hornblende and plagioclase of crosscutting pre-mineralisation granitic porphyry and diorite dykes have constrained the mineralisation age to after ~227 Ma. 40Ar/39Ar analysis of minerals formed in hydrothermal alteration zones associated with gold mineralisation indicates that there was a widespread ~216 Ma hydrothermal event that affected almost all lithologies in the area (Zhou et al., 2012).
The resources contained within other deposits in the Qinling Gold Province (Zeng et al., 2012) were: ; Yangshan (>300 t Au @ 4.74 g/t Au); Ma'anqiao (20 t Au @ 5 g/t Au); Shuangwang (60 t Au @ 3 g/t Au); Pangjiahe (>40 t Au @ 6 g/t Au).
The most recent source geological information used to prepare this summary was dated: 2012.
Record last updated: 28/11/2012
This description is a summary from published sources, the chief of which are listed below.
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References to this deposit in the PGC Literature Collection:
Zeng Q, McCuaig T C, Hart C J R, Jourdan F, Muhling J and Bagas L, 2012 - Structural and geochronological studies on the Liba goldfield of the West Qinling Orogen, Central China: in Mineralium Deposita v.47 pp. 799-819|
Zhou T, Goldfarb R J and Phillips G N 2002 - Tectonics and distribution of gold deposits in China - an overview: in Mineralium Deposita v37 pp 249-282|
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