Piaohechuan, (Piaohezhen), Hongqiling

Jilin, China

Main commodities: Ni Cu PGE PGM Pt
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The Piaohechuan or Piaohezhen and Hongqiling Cu-Ni-PGE deposits, which are ~85 km apart are located in Jilin Province in northeastern China (#Location: Piaohechuan - 43° 15' 41"N, 127° 22' 26"E; Hongqiling - 42° 54' 3"N, 126° 25' 21"E).

These deposits lie within the 150 km long, ENE-WSW elongated, Hongqiling-Piaohechuan region which contains nearly 200 mafic-ultramafic intrusions in the easternmost part of the Central Asian Orogenic Belt. This region has been one of the more important in China for economic Ni-Cu-(PGE) sulphide mineralisation.
  The final closure in the Late Permian (~250 Ma) of the Tethyan ocean between the Siberian craton and its accreted terranes to the north, and the North China-Tarim cratons to the south, formed the Solonker-Xra Moron-Changchun suture zone in northern China, marking the termination of the Central Asian Orogenic Belt (Wu et al., 2007). This was followed during the Triassic, by post-collisional extension, resulting in extensive emplacement of mafic-ultramafic intrusions and A-type granitoid plutons between 216±5 and 239±3 Ma (SHRIMP zircon U-Pb; Wu et al., 2004; Hao et al., 2013).
  These intrusions were emplaced on the northern margin of the main Solonker-Xra Moron-Changchun suture zone into Palaeozoic gneiss, schist and marble of the Hulan Formation. Only eight of the known intrusions have been found to contain economic Ni-Cu-(PGE) sulphide deposits (Lü et al., 2007). The largest is the Hongqiling no. 7 intrusion, which contained 204 400 tonnes (t) Ni and 39 000 t Cu (Lü et al., 2011). This intrusion is mainly composed of orthopyroxenite and almost the entire intrusion is mineralised. The sulphide ores have an average grade of 2.31 wt.% Ni, and the bulk sulphide ores (recalculated to 100% sulphide) have average PGE concentrations of 5.6 ppb Os, 3.1 ppb Ir, 4.7 ppb Ru, 2.2 ppb Rh, 31 ppb Pt, and 11 ppb Pd on average (Wei et al., 2013). This would equate to 8.85 Mt of ore.
  The Piaohechuan no. 4 intrusion contains 10 000 t of Ni and 4 000 t of Cu, in sulphide ore that averages 0.83 wt.% Ni (Lü et al., 2007). The intrusion has a surface exposure of ~0.07 km2, trending 310° and dipping to the southwest. In plan view, the intrusion is a lenticular body that is ~630 m long and 40 to 250 m wide, that is composed of hornblende-olivine gabbro (53 vol.%) overlain by hornblende gabbro (47 vol.%), and varies from 50 to 150 m in thickness. Sulphide mineralisation mainly occurs in the hornblende-olivine gabbro, whilst the hornblende gabbro is generally barren of sulphides (Jinline Bureau of Geology and Mineral Resources, 1980). The main orebody is exposed in the southeastern part of the intrusion, at the base of the hornblende-olivine gabbro, where it is ~430 m long, 40 to 165 m wide and 4 to 32 m thick. The thickest section is 32 m wide, and becomes progressively thinner to the northwest and southeast. Locally the ore penetrates into the footwall gneiss as veins (Wei et al., 2015).
  The sulphide ores can be divided into:
• Globular ores, comprising mm- to cm-sized spherical to irregular patches or globules containing almost 100% sulphide, within a gabbroic matrix otherwise almost devoid of of sulphide. The sulphides are mainly (80 to 88 vol.%) pyrrhotite and 10 to 11 vol.% pentlandite, with 5 to 7 vol.% anhedral grains or intergrowths of chalcopyrite (Wei et al., 2015).
• Network ores, which superficially resembles the 'net-textured' ore of other deposits, with similar relative proportions of sulphide and silicate minerals. However, in this deposit, the sulphide of the network ore forms what appears to be irregular tube-like channels with cuspate margins at contacts with the silicate minerals of the host gabbro. These channels are 1 to 2 mm wide and they can be followed discontinuously in thin section for tens of mms. The channels pinch and swell to produce bulbous nodes that are connected by narrower, more rectilinear segments. The sulphides are 83 to 91 vol.% pyrrhotite, 8 to 11 vol.% pentlandite and 1 to 7 vol.% chalcopyrite. Locally the sulphide is rich in Cu, with 80 vol.% pyrrhotite, 13 vol.% chalcopyrite and 7 vol.% pentlandite, with chalcopyrite commonly forming networks of tiny veins filling cracks in silicate minerals. The contacts between sulphide and the fresh gabbro silicate minerals are sharp but smoothly rounded. Where the host rock is altered to secondary minerals, including tremolite, talc and chlorite, the contacts, and the overall form of the networks, are irregular. Locally the host rock is highly fractured, with fine veins of sulphide filling fractures, and small angular fragments of silicate minerals (hornblende or plagioclase) enclosed in a sulphide matrix (Wei et al., 2015).
• Breccia ores, in which cm- to µm-sized fragments of gabbro or broken crystals from the gabbro are enclosed in a sulphide matrix. The proportion of fragments varies from about 10 to 50%, at which point it grades into network ore. This ore type occurs in the lower part of the main orebody near the base of the intrusion. The matrix is composed of 85 to 90 vol.% pyrrhotite, 8 to 11 vol.% pentlandite and <3 vol.%chalcopyrite. The fragments comprise broken pieces of rock, or individual medium- to coarse-grained crystals, from the host intrusion, consisting of olivine, orthopyroxene (altered into talc and chlorite), plagioclase and hornblende. Some fragments are single grains, mainly of hornblende and plagioclase and in some cases fresh clinopyroxene or olivine. Their angular form and contacts with the sulphide matrix cut across twinning and other crystallographic features. The rock fragments have a diversity of textures. Most are coarse-grained gabbro, but some are much smaller, with a doleritic texture, resembling the marginal phases of the intrusion. When the rock in the fragments is altered, the fragments are less compact and far less regular in form and size (Wei et al., 2015).
  Like most rocks in the intrusion, the silicates in these three types of ore are almost totally altered, with only a few fresh fragments occurring enclosed within the sulphide matrix of the breccia ores. Pyrrhotite and pentlandite are the dominant sulphides in the ores, with chalcopyrite being largely confined to finer fractures and patches in the silicate rocks. The Cu-rich ores are sparsely distributed in the orebody and are richer in Pt and Pd than other ores, which is consistent with fractionation of Cu and PGE during crystallisation of sulphide liquid. Breccia and network ores have Pt ranging from 1.72 to 205 ppb. The high Pt concentrations of some ores are related to the sporadic occurrence of sperrylite (Wei et al., 2015).
  Wei et al. (2015) note that nickel in olivine decreases rapidly (from 2258 to 393 ppm) with decreasing Fo (86–72), with s Small sulphide droplets enclosed in olivine, indicating olivine crystallisation from sulphide-saturated magma. They also record that rocks of the intrusion have restricted εNd
total of 4.4 to 4.6, and variable γOs total values of 39 to 67, consistent with the assimilation of external crustal sulphide in a shallow magma chamber. They conclude that early segregated sulphide liquid settled toward the base of this magma chamber, and then were expelled and migrated through partially molten silicates, along small channelways (Wei et al., 2015).

The most recent source geological information used to prepare this summary was dated: 2015.    
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:
Wei, B., Wang, C.Y., Arndt, N.T., Prichard, H.M. and Fisher, P.C.,  2015 - Textural Relationship of Sulfide Ores, PGE, and Sr-Nd-Os Isotope Compositions of the Triassic Piaohechuan Ni-Cu Sulfide Deposit in NE China : in    Econ. Geol.   v.110, pp. 2041-2062

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