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Yangshan

Gansu, China

Main commodities: Au
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The Yangshan gold deposit is located ~375 km WSW of Xi'an in Wenxian County, Gansu province, near the borders of Sichuan and Shanxi provinces and is the representative gold deposit in the Shanxi-Gansu-Sichuan "gold triangle" group of Carlin-like gold deposit in the Western Qinling Mountains (Chen et al., 2004

The deposit lies within the Qinling Gold Province of the Qinling Orogen in the convergent collision zone between the Yangtze and North China plates The district belongs to the southern domain of the South Qinling Terrane of the western Qinling Orogenic Belt, which lies in the north of the Mianlue Suture (Lai et al., 2003)

For details of the setting and tectonic framework, see the Qinling Gold Province record.

The crystalline basement comprises the Proterozoic Bikou Group, which is mainly composed of argillaceous and clastic rocks, with minor turbidites and some volcanic and pyroclastic interbeds, all of which have been metamorphosed to schists of a low grade metamorphic volcano-sedimentary package. The overlying succession includes Devonian, Carboniferous, Permian and Triassic sequences, and local Jurassic and Cretaceous units.

The Devonian Sanhekou Group comprises a shallow marine clastic, argillaceous, carbonate sedimentary sequence of phyllite, sandstone, siliceous rocks, carbonate, carbonaceous slate and greenschist. The Carboniferous and Permian are composed of marine facies carbonates to clastic sequences, consisting of limestone, dolostone, sandstone and slate. Triassic sequences are mainly of clastic rocks and carbonates with occasional gypsum interbeds that were deposited in closed and semi-closed marine basins. The Jurassic and Cretaceous are mainly composed of terrestrial facies clastic rocks.

The hosts to gold mineralisation are mainly the Devonian and Triassic of the Western Qinling district and Wenxian arc structural belt (Chen et al., 2004). Magmatic rocks are diverse and were emplaced in multiple stages, and include local stocks and dykes, mainly of plagioclase-granitic porphyry dykes, and minor biotite-granitic porphyry. Intermediate and felsic stocks and dykes are mainly distributed within the North Qinling Domain.

The Devonian Sanhekou Group is the principal host to the Yangshan gold deposit, mainly composed of phyllite, sandstone and limestone. Phyllites are the major host rocks containing the bulk of the framboidal and colloform pyrites. Gold mineralisation occurs along the east-west to ENE trending Anchanghe-Guanyingba fault zone which is >60 km long and 0.5 to 3 km wide. The limestones, phyllites and porphyry dykes adjacent to the fault zone have been variably mineralised. Plagioclase granite porphyry dykes are distributed along the Anchanghe-Guanyingba fault, which is the primary ore control and host structure. The dykes are mostly emplaced along this structure, but also occur as sills following stratigraphic layers. They are commonly 50 to 300 m in length and 1 to 20 m in width, with blastoporphyritic texture and blocky structure. Magmatic rocks have close spatial relationship with the orebodies, some of which lie within granite-porphyry dykes along on the inner and outer contact zones.

The Yangshan gold deposit comprises 98 gold veins distributed over an length of 60 km of the Anchanghe-Guanyingba fault zone and width of 3 to 5 km, grouped into the Nishan, Getiaowan, Anba, Gaoloushan, Yangshan, Zhangjiashan and Beijinshan ore segments.

The Anba segment includes 31 veins, which are clustered into the No. 305 and No. 311 vein groups, which respectively contain 14 and 17 individual veins. The individual veins have slightly undulating plane surfaces, and are generally subparallel and 100 to 140 m apart, dipping at 50 to 70° to the north.

Examples of significant veins from the Anba and adjacent segment vein groups include:
  No. 305 group - 2100 m long x 515 m down dip, averaging thickness 4.83 m (max. 18.83 m), averaging 6.07 g/t Au, for 51 tonnes of Au.
  No. 311 group - 3500 m long x 700 m down dip, average thickness of 3.39 m, averaging 4.96 g/t Au, for 65.50 t of Au.
  No. 314 group - 2100 m long x 500 m down dip, average thickness of 6.14 m (max. 21.80 m), averaging 5.16 g/t Au, for 39.34 t of Au.
  No. 360 group - 2200 m long x 700 m down dip, average thickness of 4.17 m (max. 15.60 m), averaging 4.05 g/t Au, for 45.38 t of Au.

Ore host protoliths include altered sandstone, phyllite, limestone and porphyry dykes. The veins of the Anaba segment are principally hosted by pyritised phyllite and pyritic altered plagiogranite porphyry, and the metallic minerals are mainly native gold, electrum, arsenopyrite, pyrite, stibnite, ilmenite, vanadiferous titanomagnetite, magnetite, pyrrhotite, sphalerite, galena, marcasite, boulangerite, pyrolusite, psilomelane and secondary limonite where weathered. Granular pyrite and arsenopyrite (<2 mm) are the major sulphide minerals, with arsenopyrite > pyrite. Primary gangue minerals are quartz, sericite, calcite, dolomite and feldspar, with lesser kaolin, chlorite, pyrophyllite, epidote, barite, realgar and garnet, and minor zircon, tourmaline, diopside, scorodite and fluorite.

The principal economic minerals are native gold, with lesser electrum, which occur in arsenopyrite and stibnite in the primary zone and in limonite and clay minerals in the oxide zone. Approximately ~75% of the gold is present as inclusions in arsenopyrite, or in its weathered products of limonite and clay minerals, while ~12% is fissure gold in micro-fractures in pyrite (or limonite), while the remaining ~12% is as intergranular gold in clay minerals. Superfine 2 to 3 µm gold occurs within the pyrite and arsenopyrite. Much of the gold is disseminated, although visible 2 to 3 mm gold is evident in quartz vein ores.

The alteration mainly takes the form of de-carbonatisation and the addition of silica, pyrite and arsenopyrite,as well as oxidation to limonite and associated kaolin and carbonate veining.

The mineralisation has been divided into four main stages: i). barren quartz; ii). quartz-pyrite; iii). quartz-pyrite-arsenopyrite; iv). quartz-carbonate. Stages ii).and iii). represent the major mineralisation events (Yang et al., 2006; Li et al., 2007).

Qi et al. (2005, 2006) obtained a K-Ar isotopic age of altered plagioclase granitic porphyry (209 to 171 Ma), with the average of 5 samples being 189±7.2 Ma, and an isochron age of 190±2.4 Ma. Zircon SHRIMP U-Pb dating gives three ages of 200.9 to 195.4 Ma; 137.9 to 121.4 Ma and 55.3 to 48.1 Ma. Yang Rongsheng et al. (2006) selected monazite from in and around pyrite within the altered plagioclase porphyry and undertook a Th-U-Pb electron microprobe dating to obtain three groups of ages, 297 to 251 Ma with an isochron age of 268±4 Ma; 237 to 207 Ma with an isochron age of 220±3 Ma and 200 to 179 Ma with an isochron age of 190±3 Ma.

This summary closely follows the deposit description in Yan and Li (2008).

The most recent source geological information used to prepare this summary was dated: 2008.    
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.


  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Li Nan, Deng Jun, Yang Li-Qiang, Goldfarb R J, Zhang Chuang, Marsh E, Lei Shi-Bin, Koenig A and Lowers H  2014 - Paragenesis and geochemistry of ore minerals in the epizonal gold deposits of the Yangshan gold belt, West Qinling, China: in    Mineralium Deposita   v.49 pp. 427-449
Yan Fengzeng and Li Qiangzh,  2008 - Yangshan Gold Deposit:The Largest Carlin and Carlin-like Type Gold Deposit in China: in    Acta Geologica Sinica   v.82 pp. 804-810
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


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