Zhongtiaoshan District - Tongkuangyu, Bizigou, Qinjiagou, Tongmugou, Laobaotan, Hujiayu
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The Zhongtiaoshan District in southern-most Shanxi Province of north-central China contains more than 30 Palaeoproterozoic copper deposits that include some interpreted to be of porphyry style. e.g., Tongkuangyu, and those considered to be metamorphosed sediment hosted stratabound occurrences, e.g., from north to south over a 12 km, NNE aligned, interval: Bizigou, Qinjiagou, Tongmugou, Laobaotan, and Hujiayu. Tongkuangyu is 15 km NE of Bizigou (#Location: Tongkuangyu - 35° 21' 47"N, 111° 40' 29"E).
The Zhongtiaoshan District is located in the southern part of the Palaeoproterozoic Trans-North China Orogen which divides the North China Craton into an eastern and western block (Liu et al., 2012; Zhao et al., 2001).
The North China Craton covers a triangular area of ~1 500 000 km2, bounded by faults and younger orogenic belts. The Archaean crystalline basement was affected by two Palaeoproterozoic tectonic events i). a 1.95 to1.92 Ga collision between the Yinshan and Ordos terranes in the north and south to form the Western Block, and ii). a ~1.85 Ga amalgamation of the Western and the Eastern Blocks along the north-south Trans-North China Orogen (or Central Orogenic Belt; Zhao, 2001; Zhao et al., 2005, 2011; Zhao et al., 2010).
The stratigraphy in the district comprises:
• Sushui Complex - the oldest complex in the Zhongtiaoshan district, consisting mainly of Neoarchaean (2.8 to 2.5 Ga) tonalite-trondhjemite-granodiorite (TTG) gneiss;
• Jiangxian and Zhongtiao groups - primarily composed of terrigenous and volcanosedimentary rocks deposited between 2.5 and 1.9 Ga in a rift setting (Bai, 1997; Sun et al., 1990). This corresponded to a period of extension within the Trans-North China Orogen between 2.2 and 2.1 Ga (Zhai and Santosh, 2011, 2013; Zhai et al., 2010), when abundant extension-related magmatic rocks were emplaced (Du et al., 2010, 2012). In the Zhongtiaoshan district, this Paleoproterozoic magmatism is divided between the Jiangxian (2.166 to 2.115 Ga) and Zhongtiao (2.090 to 2.060 Ga) groups (Sun and Hu, 1993).
The Jiangxian Group is dominantly found in the northern part of the Zhongtiao Mountains. It is composed of a basal meta-conglomerate and quartzite sequence, a middle meta-pelitic schist layer, and an upper sequence of potassic mafic volcanic rocks, quartz porphyries, potassic rhyolites and quartz crystal tuffs, erupted between ~2273 and 2161 Ma (Sun et al., 1990, 1992; Zhao, 2006; Zhang, 2012; Liu et al., 2016). Volcanic activity was most intense in the Jiangxian Group. This sequence is characteristic of a continental rift setting (Zhai and Santosh, 2013). The porphyry Cu mineralisation in the district appears to be genetically linked to porphyry emplacement in a continental extensional setting during the ~2.1 Ga magmatism of the Jiangxian Group.
The metapelites within the Jiangxian Group have subsequently been metamorphosed to rocks with mineral assemblages characterised by staurolite, garnet and biotite, recording peak metamorphic temperature and pressure of 600 to 550°C and 7 to 5 kbar (Mei, 1994).
The Zhongtiao Group is mainly found in the central part of the Zhongtiaoshan district, forming a near NNE trending, ~80 x 8 to 15 km wide belt of rocks unconformably overlying both the Archaean basement and the Jiangxian Group rocks. It represents the intermediate stage of the rift from ~ 2.1 Ga, with sedimentation that was primarily a terrigenous clastic, volcanic and marine carbonate succession (Sun and Ge, 1990; Sun and Hu, 1993), comprising a sequence of calc-silicates and minor pelitic schist, marble, meta-conglomerate, quartzite, meta-sandstones and minor meta-volcanic rocks and meta-tuffs. The sedimentary clastic-pelitic-carbonate sequences were deposited in a transgressive event along the continent margin. The strata-bound sediment hosted copper deposits are hosted in graphite schists and carbonates of the Zhongtiao Group. Three youngest detrital zircons from the basal part of the Zhongtiao Group had a weighted mean age of 2168 5Ma, whilst meta-tuffs at the top of the group were erupted at ~2059 Ma (single zircon evaporation; Sun et al., 1992). An intercalated amphibolite has been dated at ~2086 Ma (SHRIMP zircon U/Pb; Liu et al., 2015). These suggest deposition of the Zhongtiao Group between ~2168 and ~2059 Ma.
Compression commenced at ~1.95 Ga (Sun and Hu, 1993; Zhang, 2012), and by ∼1.85 Ga inversion was complete to form the Trans-North China Orogen (Liu et al., 2012).
• Danshanshi Group - found in the eastern foothills of the Zhongtiao Mountains over an interval of ~ 40 x ~2 km. It is a molasse sequence composed of post 1.95 Ga (youngest detrital zircon 1848 Ma; U/Pb; Liu et al., 2012) conglomerate and quartzite that accompanied a series of tectonic events, including crustal uplift, exhumation, granite intrusion and regional metamorphism, representing inversion of the Trans-North China Orogen rift zone. This sequence and series of events may indicate the end of cratonisation of the North China Craton (Sun et al., 1991; Zhai and Santosh, 2013).
• Xiyanghe or Xiong'er Group - a Late Paleoproterozoic sequence of mainly unmetamorphosed basaltic andesite volcanic rocks, deposited between 1800 and 1750 Ma (Zhaoet al., 2004).
Sequences in the Zhongtiaoshan district are intensively faulted, with NW- or NE-trending basement structures controlling the emplacement of granite intrusions and the Cu deposits (Sun and Hu, 1993).
Tongkuangyu Porphyry Deposit
The Tongkuangyu porphyry Cu deposit is located in the northern part of the Zhongtiaoshan District, hosted by Palaeoproterozoic quartz-monzonite porphyry and the surrounding Tongkuangyu Formation of the Palaeoproterozoic Jiangxian Group. The deposit and its hosts have been intensely deformed. The Tongkuangyu Formation is strongly sheared and in the deposit area has been folded into an overturned anticline. The rocks exposed in the deposit area include quartz monzonite porphyry, sericite-quartz rock, meta-potassic mafic volcanic rocks, sericite-schists and mafic intrusions. In addition to the shearing and folding, the near north-south trending Dabaogou-Tongkuangyu normal strike slip fault offsets mineralisation, and like many of the faults in the deposit area is post-mineralisation.
The Tongkuangyu Cu deposit is composed of seven mineralised bodies, of which Nos. 4 and 5 are economically viable. No. 5 ore body is an 1100 x 185 m lens, predominantly hosted by metamorphosed quartz monzonite porphyries and quartz crystal tuff country rocks.
There is a general outward and upward zoning of alteration minerals from a core of quartz-K feldspar, to quartz-sericite and carbonate alteration, although the precise alteration and mineral zonation is complicated by the overprinting intense regional metamorphism (Chen and Li, 1998; Sillitoe, 2010; Zhang, 2012).
Mineralisation at the Tongkuangyu porphyry Cu deposit has been interpreted to have taken place in three stages:
i). Early mineralisation, characterized by quartz-K feldspar alteration with minor disseminated chalcopyrite and pyrite. Quartz veinlets carry sparsely disseminated sulphides, are locally developed. Minerals in the quartz-K feldspar assemblage include K feldspar, biotite, quartz, magnetite, scapolite and tourmaline.
ii). Main stage, which is associated with quartz-sericite (phyllic) alteration, is characterised by dissemination and 0.2 to 3 cm veinlets containing quartz and chalcopyrite with minor molybdenite, pyrite, magnetite, hematite, bornite and chalcocite. Chalcopyrite-pyrite-molybdenite is the main ore mineral assemblage. Three sulphide assemblages are recognised as part of this stage, namely (from the deepest to shallowest occurrences) a). pyrite-chalcopyrite; b). molybdenite-chalcopyrite; and c). bornite zones. The phyllic alteration suite includes sericite, quartz, magnetite, hematite, carbonate, chlorite and scapolite. Ore bodies in this zone are mostly located proximal to quartz-potassium feldspar alteration zones. The main stage mineralisation apparently occurred at 450 to 233°C (Jiang et al., 2014).
iii). Late mineralisation, characterised by veining, which includes 3 to 10 cm quartz-calcite veins, which are thicker than those in the main mineralisation stage, and consist of chalcopyrite, pyrite, molybdenite, magnetite and specularite, with a gangue of quartz and calcite. Carbonate alteration also accompanies late stage mineralisation. This mineralisation was emplaced at 245 to 186°C (Jiang et al., 2014).
Mineralisation and mineralised porphyries of the Tongkuangyu porphyry Cu deposit have been dated at 2108±32 Ma (molybdenite Re-Os isotopic isochron) and 2122±10 Ma (U-Pb; zircon), respectively (Chen and Li, 1998; Li et al., 2013), demonstrating that Cu mineralisation may be genetically linked to the porphyry emplacement. These porphyries were emplaced in a continental extensional setting during deposition of the Jiangxian Group.
Reserves in No 4 and 5 Orebody at Tongkuangyu - ~410 Mt of ore @ 0.68% Cu for 2.8 Mt of contained Cu (Xu, 2010; quoted by Jiang et al., 2014).
These two bodies account for >90% of the known resource.
Hujiayu Sediment Hosted Deposit
The sediment hosted copper deposits of the Zhongtiaoshan district, known as the 'Hu-Bi' (Hujiayu-Bizigou) type, are largely hosted by a sequence in the Zhongtiao Group that includes, from oldest to youngest, the:
• Jiepailiang Formation - predominantly quartzite;
• Lonhyu Formation - sandy slate;
• Yuyuanxia Formation - predominantly composed of stromatolite-bearing dolomitic marble;
• Bizigou Formation - which is the main host to stratabound copper mineralisation. It comprises, from deepest to shallowest, i). amphibolite; ii). scapolite-biotite schist; iii). red dolomitic marble and sandstone; iv). grey dolomitic marble; v). siliceous albitite; and vi). carbonaceous shales to graphitic schists.
• Yujiashan Formation - a thick succession of dolomitic marbles and thin units of stromatolitic dolostones.
Sediment-hosted stratabound Cu mineralisation is widespread in the Zhongtiao Group of the Zhongtiaoshan district. The largest four deposits are distributed over a 12 km, north-south elongated belt parallel to, and a few hundred metres to a kilometre east of a similarly aligned 15 x 3 km anticlinal core of Jiangxian Group bimodal volcanic rocks.
The basal sedimentary section of the host Bizigou Formation contains discontinuously developed red beds, comprising red dolomitic marble and sandstone with a total thickness of up to 100 m (Wei et al., 1984), although individual red beds ranges from 6 to 20 m thick.
The orebodies are mainly hosted within the overlying siliceous albitite, grey dolomitic marble and graphitic schists in the upper sections of the Bizigou Formation, but locally extend further into the uraninite and pyrite bearing carbonaceous shales at the base of the Yujiashan Formation. The siliceous albitite is spatially associated with dolomitic marble and carbonaceous shales, and is characterised by very fine stratification composed of albite and quartz. Strongly limonitic dolomitic marble can also be observed in some parts of the exposed Bizigou Formation (Qiu et al., 2016; Jiang et al., 2014).
Hydrothermal alteration products that are observed at the Hujiayu Cu deposit include albite, carbonate, biotite and silica, although alteration associated with mineralisation is difficult to distinguish as it is masked by the overprinting post-mineralisation regional metamorphism (Sun and Ge, 1990).
Mineralisation at the Hujiayu Cu deposit can be divided into (Qiu et al., 2016; Jiang et al., 2014):
i). Early diagenetic, which is the major ore-forming stage. This mineralisation is characterised by disseminated to veinlet (<5 mm thick) sulphides in siliceous albitite, dolomitic marble and graphitic schists which parallel the foliation of the host rock. The graphitic schists are composed of quartz, albite, muscovite, dolomite, chlorite, rutile, tourmaline and abundant graphite. Ore minerals are predominantly chalcopyrite, pyrite and pyrrhotite with accessory chalcocite, bornite, molybdenite, cobaltite and lesser linneite. The gangue mineralogy is mainly dolomite, quartz and albite. Bedding wraps around diagenetic sulphide nodules due to differential compaction, suggesting the nodules were emplaced during early diagenesis. The veinlets are thin and discontinuous with irregular boundaries with enclosing rocks. Virtually all the nodules and veinlets are aligned parallel to the stratification of siliceous albitite and dolomitic marble (Qiu et al., 2016).
The veining of this stage is preserved as quartz and albite concentrated in remobilised syn-metamorphic veinlets or segregations with minor dolomite and muscovite, while sulphides are also distributed in these veinlets. Pyrite is the dominant sulphide (Py I), occurring as scatted subhedral to anhedral grains in quartz-albite-dolomite veinlets. Chalcopyrite, which is less extensive, coexists with pyrite in veinlets. Graphite, derived from organic matter during the prograde metamorphism, is concentrated in narrow zones parallel to metamorphic segregation veinlets (Qiu et al., 2016).
ii). Late metamorphic mineralisation hosted within 3 to 20 cm thick, composite quartz-dolomite veins that are more continuous and thicker than those of the early stage. This thick-vein type hydrothermal mineralisation is subdivided into a first hydrothermal dolomitic alteration phase (phase IIa) and a second siliceous-copper mineralisation (phase IIb). The first phase is dominated by dolomite and minor pyrite (Py II). The main copper mineralisation in the late metamorphic stage in this deposit is intimately associated with the second phase IIb siliceous alteration. Ore minerals include chalcopyrite, pyrite (Py III) and pyrrhotite with minor sphalerite, siegenite and clausthalite. Gangue minerals are dominantly quartz with lesser dolomite. Fluid inclusions in these thick veins showed that the ore forming fluid belongs to a NaCl-H2O-CO2-CH4 system, possibly derived from metamorphic fluids (Qiu et al., 2015). These ore veins are controlled by tectonic fractures, often cross-cutting host rock stratigraphy, foliation and the early stage sulphide veinlets. The grain size of sulphides and gangue minerals is much coarser in the late stage veins.
The mineralisation at Hujiayu is controlled by a NNE-trending fold and occurs as moderately to steeply dipping lenticular and stratabound layers conformable with the host rocks in both limbs of the fold. Mineralised bands appear to vary from a few, up several tens of metres in thickness. The Hujiayu deposit comprises of 167 ore lenses/orebodies. Number 3, which is the largest, is 650 m long x 24 m thick (Sun et al., 1995). At locations observed within the deposit, mineralisation is controlled by interlayer fault zones and thickens in the core of the fold (Qiu et al., 2016).
Bizigou - ~26.4 Mt of ore @ 1.492% Cu, and 7.7 Mt of ore @ 0.024% Co for 0.394 Mt of contained Cu and 1844 t Co (Jiang, et al., 2014).
Hujiayu - ~30 Mt of ore @ 1.07% Cu, and 6.4 Mt of ore @ 0.027% Co for 0.320 Mt of contained Cu and 1700 t Co (Jiang, et al., 2014).
Total reserve at Bizigou, Qinjiagou, Tongmugou, Laobaotan and Hujiayu - ~65 Mt of ore @ 1.21% Cu for 0.79 Mt of contained Cu (Qiu, et al., 2016).
For detail see the reference(s) listed below.
The most recent source geological information used to prepare this summary was dated: 2016.
Record last updated: 31/1/2019
This description is a summary from published sources, the chief of which are listed below.
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Fan, P.-F., 1984 - Geologic setting of selected Copper deposits of China: in Econ. Geol. v.79, pp. 1785-1795.|
Jiang, Y., Niu, H., Bao, Z., Li, N., Shan, Q. and Yang, W., 2014 - Fluid evolution of the Tongkuangyu porphyry copper deposit in the Zhongtiaoshan region: Evidence from fluid inclusions: in Ore Geology Reviews v.63, pp. 498-509.|
Jiang, Y., Niu, H., Bao, Z., Li, N., Shan, Q.,Yang, W. and Yan, S., 2014 - Fluid evolution of the Paleoproterozoic Hujiayu copper deposit in the Zhongtiaoshan region: Evidence from fluid inclusions and carbon-oxygen isotopes: in Precambrian Research v.255, Part 2, pp. 735-747.|
Meng, X., Richards, J., Mao, J., Ye, H., DuFrane, A., Creaser, R., Marsh, J. and Petrus, J., 2020 - The Tongkuangyu Cu Deposit, Trans-North China Orogen: A Metamorphosed Paleoproterozoic Porphyry Cu Deposit: in Econ. Geol. v.115, pp. 51-77.|
Qiu, Z.-J., Fan, H.-R., Liu, X., Yang, K.F., Hu, F.-F., Xu, W.-G. and Wen, B.-J., 2016 - Mineralogy, chalcopyrite Re-Os geochronology and sulfur isotope of the Hujiayu Cu deposit in the Zhongtiao Mountains, North China Craton: Implications for a Paleoproterozoic metamorphogenic copper mineralization: in Ore Geology Reviews v.78, pp. 252-267.|
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