Chang Shan Hao, 217

Inner Mongolia, China

Main commodities: Au Ag
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The Chang Shan Hao (217) gold-silver deposit is located on the northern margin of the North China Craton in Inner Mongolia (Nei Mongol) Province, approximately 650 km north-west of Beijing and 126 km north-west of the city of Baotou in northern China (#Location: 41° 40'N, 109° 14'E).

The deposits on the northern margin of the North China Craton are within the eastern segment of the Altaid Tectonic Collage which extends across Eurasia from the Caspian Sea to the Pacific Ocean and embraces a diffuse, 1000 km long belt of gold deposits, which includes the Tien Shan Belt in central Asia to the west.

The northern margin of the North China Craton extends from North Korea to central Inner Mongolia and comprises a basement of Archaean to Paleoproterozoic gneisses, schists, amphibolites and banded iron formations. These rocks were deformed and metamorphosed by the 1.8 Ga Zhongtiao Orogeny. They are overlain by an accretionary complex of low grade metamorphosed Proterozoic quartzite, shales and limestones and un-metamorphosed Palaeozoic sequences, extending northwards into Mongolia to become part of the more extensive Mongolian-Great Hinggan Fold Belt that separates the North China and Siberian cratons. These are in turn unconformably overlain by Permian to Cretaceous continental basinal, commonly coal bearing, sediments and sub-aerial volcanic rocks.

Magmatic activity is represented by 1.7 to 1.4 Ga alkalic intrusions to the north of Baotou, including syenite and carbonatite sills. Widespread calc-alkaline to alkalic granitoid plutons were regionally emplaced in multiple episodes from the Caledonian to the Hercynian to the Yanshanian.

The Chang Shan Hao deposit is hosted by Meso- to Neoproterozoic sediments of the Byan Obo Group which is dominated by clastic sediments (sandstones, greywackes and slates) intercalated with carbonate rich rocks (dolomite and limestone).

In the mine area only the central section of the Byan Obo Group is recognised, represented by, from oldest to youngest:
Jianshan Formation - black carbonaceous slate, silty slate, andalusite hornfels, phyllitic schist, meta-siltstone and quartzwacke. This unit outcrops in the western, northern and southern sections of the Chang Shan Hao area and has a gradational contact with the overlying unit;
Halahougete Formation - thin to medium bedded dolomitic limestone intercalated with cherty slate and calcareous sandstone, siltstone and slate;
Bilute Formation - can be divided, from base to top, into:
  Unit b1 - carbonaceous meta-siltstone,
  Unit b2 - carbonaceous phyllite and andalusite-garnet schist with minor meta-siltstone and meta-greywacke,
  Unit b3 - meta-siltstone, meta-sandstone and sedimentary breccia,
  Unit b4 - calcareous and carbonatised phyllite and schist.

All of the significant gold mineralisation at Chang Shan Hao is hosted within Unit b2 of the Bilute Formation, with a consistent footwall band of andalusite-garnet schist. The host unit dips at 82±10°N in the North-west Zone, is near vertical in the Central Zone, but is overturned to 85 to 88°S in the South-west Zone where the bedding has been deformed in the vicinity of a major fault zone.

Intrusive rocks which are found both to the north and south of the deposit area were emplaced during the Late Caledonian, Hercynian and Indosinian orogenies between 413 and 205 Ma and comprise composite granitoid batholiths. Within the deposit numerous igneous bodies include dykes of dolerite, lamprophyre, diorite, aplite and pegmatite, all of which are barren.

The meso-thermal quartz vein mineralisation lies within a broad, south-westerly trending ductile shear zone cutting at about 10° the bedding of the Proterozoic phyllites and andalusite schists on the southern limb of an east plunging syncline. The shear zone is parallel to the regional metamorphic foliation. The immediate host rocks are predominantly carbonaceous phyllite, schist and slate. The main ore zones occurs as the North-east and South-west Zones, both around 1 km in length separated by the low grade 1.5 km long Central Zone over total 4.6 km continuous strike length. The main mineralised zone has true widths of up to 44 m, with a maximum horizontal width of 150 m in the eastern part of the deposit. The vertical extent is at least 260 m.

The gold mineralisation occurs as thin (1 to 10 mm) sulphide and quartz sulphide veins, stringers and boudinaged lenses, concordant with the bedding and foliation and trend along the shear zone. The quartz-sulphide veining was boudinaged by the foliation and are part of the shear deformation. Only weak hydrothermal alteration is evident in the wall-rocks characterised by chlorite and silica. Abundant sericite and andalusite occur in the footwall schists, possibly a reflection of an aluminous protolith.

In the upper third of the host unit, the mineralisation is dominantly quartz-rich, with only minor sulphide seams, while in the lower third it is primarily associated with sulphide veins with only rare scattered quartz material. In the middle of the sequence, there is an even mixture of the two styles.

Mineralisation is principally native gold occurring directly with sulphides in the seams and in association with the quartz vein material. The native gold is visible and occurs as fine locked grains or attachments to arsenopyrite. It is also seen as attachments and inclusions within and on pyrrhotite and as liberated particles. The gold ore has minor accompanying silver, copper, lead and zinc, such that the dore product is approximately 70% Au, 30% Ag.

In the oxide zone gold occurs as liberated particles, with a transition to the sulphide zone at a depth of 40 to 70 m.

The total Proven + Probable open-pit Reserves in the Northeast Zone are estimated at a cut-off of 0.26 g/t Au to be 66.7 Mt @ 0.75 g/t Au, containing approximately 50 t (1.2 Moz) of recovered gold. Additional resources are contained within the South-west and Central Zones (Jinshan Mines, 2007).

Total Measured + Indicated Resources at 0.3 g/t Au cut-off are estimated to be 128.4 Mt @ 0.77 g/t Au for 99 t (3.16 Moz) of contained gold. In addition, the Inferred resource at the same cut-off is quoted at 24.2 Mt @ 0.68 g/t Au for a further 16.5 t (0.53 Moz) of gold (Jinshan Mines, 2007).

Much of this summary is drawn from a report to Jinshan Gold Mines Inc., by Keane (2005).

The most recent source geological information used to prepare this summary was dated: 2005.    
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

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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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