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Tongshankou

Hubei, China

Main commodities: Cu Mo
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The Tongshankou porphyry / skarn copper - molybdenum deposit is located in the westernmost Daye district of Hubei Province, ~20 km south-west of the town of Daye and 75 km south-east of the city of Wuhan in eastern China (#Location: 30° 0' 3"N, 114° 50' 11"E).

This deposit lies within the Edong Mining District of Middle to Lower Yangtze River Valley Metallogenic Belt on the northern margin of the Yangtze craton, within a Late Mesozoic metallogenic belt along the middle to lower reaches of the Yangtze River, and is hosted within the 140.6±2.4 Ma Tongshankou granodiorite and at its contact with Lower Triassic marine carbonates. For more detail on the regional setting see the Yangtze River Belt record..

The Yangtze craton is separated from the North China cratons to the north-east by the Triassic Dabie ultra-high pressure metamorphic belt, and from the Cathaysian block to the south-east by a late Mesoproterozoic suture.

The Yangtze craton comprises Archaean to Mesoproterozoic basement consolidated during the late Mesoproterozoic, when the Cathaysian block was accreted to the Yangtze craton, and subsequently overlain by a 10 to 20 000 m thick cover sequence of late Neoproterozoic to early Mesozoic rocks.

The oldest basement within the Yangtze craton comprises the upper amphibolite to granulite facies tonalitic-trondhjemitic-granitic gneisses of the 2.95 to 2.90 Ga Kongling complex exposed as a 360 sq. km dome within the northern Yangtze craton. Archaean rocks are rarely exposed within the eastern Yangtze craton. The Paleoproterozoic felsic gneisses and muscovite-quartz-schists with intercalated amphibolite of the Dongling Group outcrop over a limited area approximately 200 km east of Daye, while greenschist facies Meso- and Neoproterozoic calc-alkaline basalts, rhyolites and shallow marine sedimentary rocks occur widely along the south-eastern margin of the Yangtze craton. Extensive Palaeozoic and Early Triassic sequences, typically marine carbonates, shales and sandstones cover a large area of the craton. Post-Late Triassic sedimentary rocks are continental and highly variable in both composition and thickness.

The Daye Cu-Fe-Au-Mo district is framed on three sides by major faults, namely the: i). WNW trending Xaingfan-Guangji to the north-east marking the south-western margin of the Dabie ultra-high pressure metamorphic belt; ii). NE trending Tan-Lu to the south-east; and iii). NE trending Ma-Tuan to the north-west.

The stratigraphy and structural events affecting the Daye district may be summarised as follows, from the base:
Ordovician and Silurian siliceous and argillaceous limestones, calcareous mudstones, and siltstones that are up to 1000 m thick;
• A Devonian sequence dominated by lower conglomerate and upper quartz sandstones and minor amounts of siltstones, conformably overlain by;
Carboniferous limestones, locally intercalated with dolomites, overlain in turn by;
Permian shales, cherts, coal beds and limestones that are ~600 m thick;
Lower Triassic Daye Formation, composed of 1000 to 1200 m of marine limestones and dolomites which hosts the skarn mineralisation throughout the district;
• Intense Late Triassic folding of the preceding Palaeozoic sequences during continental collision between the Yangtze and North China cratons;
Jurassic continental coal-bearing shales;
• Extensive Early Cretaceous volcanism that resulted in a >2000 m succession of volcanic rocks, divided into the
  - Majiashan formation, mainly pyroclastic and massive to perlitic rhyolites;
  - Lingxiang formation, which consists of a lower section of conglomerates and sandstones, overlain by andesitic-basalts and basalts, and
  - Dasi formation, which outcrops over area of more than 160 sq. km, and comprises andesites, dacites, basalts and rhyolites. Dacites in the middle of this formation have been dated at 128±1 Ma.

The pre-Jurassic strata have been intruded by six intrusives, ranging in composition from diorite to quartz diorite and granite, specifically the Lingxiang and Jinshandian diorites, the Yinzu and Yangxin quartz diorite, the Tieshan complex consisting of diorite and quartz diorite, and the E-Cheng complex comprising diorite, quartz diorite, and granite.  In addition, there are more than 30 small quartz diorite and granodiorite stocks (of generally <1.5 sq. km) - including the Tongshankou granodiorite, and a number of usually <1 to 3 m wide dykes of diorite, monzonite and syenite, which surround or cut the major intrusions. Recent dating (2007) suggests the main intrusions were emplaced between 151 and 132 Ma, peaking between 141 and136 Ma, followed by dyke emplacement between 127 and 121 Ma.

In the Tongshankou deposit area, two stocks of the 140.6±2.4 Ma Tongshankou granodiorite - the Shizishan in the west and the Tongshankou stock in the east, with a total outcrop area of 0.4 sq. km - intrude the Lower Triassic Daye Formation which comprises a 1100 m thick succession of limestones and dolomites. Both stocks have a porphyritic texture and are rich in phenocrysts consisting of white plagioclase (An25-40, 25 to 30 vol.%), orthoclase (5 vol.%), quartz (10 to15 vol.%), biotite (6 to 8 vol.%), and hornblende (3 vol.%), set in a fine-grained matrix of the same minerals. These rocks contain abundant accessory minerals, mainly magnetite (~1 wt.%), apatite (>800 g/t), zircon (700 to 800 g/t) and titanite (approx. 3000 g/t), which occur as both phenocrysts and in the matrix. Barren dioritic stock and dykes are found immediately to the north-west and south-east of the deposit. The structure of the area is marked by several east-northeast- and north-west-striking faults.

The Tongshankou Cu-Mo deposit is composed of six ore bodies, each of which comprises variable proportions of porphyry, skarn and distal strata-bound carbonate wallrock replacement ore, interpreted to all be part of the same hydrothermal system. Details of individual deposits include:
The No. III orebody is hosted within the Tongshankou stock and predominantly porphyry Mo and Cu-Mo style mineralisation with an ore grade of 0.4 to 0.6% Cu, 0.02 to 0.07% Mo, as stockwork veins, veinlets and sparse to abundant disseminated sulphides. The primary ore minerals are chalcopyrite and molybdenite, with minor bornite and tetrahedrite.
The No. IV orebody has an average ore grade of 1.2% Cu and is mainly developed as skarn along the contact zone between the Shizishan stock and the Triassic carbonates, with lesser ore within the stock. The orebody is 500 m long, by10 to 60 m thick, and persists for more than 140 m down dip.
The No. I orebody, is the largest of the six, accounting for 60% of the total reserve and is located along the contact between the Tongshankou stock and the Lower Triassic carbonates. It is 2100 m long at the surface by 10 to 80 m thick and persists down dip for 300 to 600 m, with an average grade of 0.94% Cu. The ore grade is highest (up to 3.1% Cu) at the contact and decreases inward into the granodiorite and outwards into the carbonate. Chalcopyrite is the dominant ore mineral, accompanied by minor pyrite, magnetite, hematite, bornite, sphalerite, tetrahedrite and molybdenite.
The No. II orebody swarm comprises a number of small stratabound ore bodies which are individually 80 to 300 m long by 5 to 16 m thick, with grades of 0.6 to 1.2% Cu, and occur in interlayered fracture zones within the carbonates, mainly east of the deposit. The sulphide minerals within the strata-bound ores are principally chalcopyrite with subordinate pyrite, marcasite, sphalerite, chalcocite and tetrahedrite, accompanied by gangue calcite, chlorite, serpentine and quartz. Wall-rock alteration related to the strata-bound ores is weak and comprises carbonates, silica, chlorite and serpentinite.

Alteration related to the porphyry and skarn style mineralisation is more extensive and intensive than that associated with the stratabound ores. Potassic and phyllic styles are characteristic of the porphyry mineralisation.

Potassic alteration is found mostly in the central part of the host granodiorite, comprising K feldspar (orthoclase), biotite, quartz and magnetite, typically occurring as mm- to cm-scale K feldspar veins, K feldspar envelopes around stockwork quartz veins, and sparse disseminations of biotite. Sulfide minerals are rare, with minor disseminated pyrite.

Phyllic alteration is more extensive, occurring as veins and abundant disseminations of quartz and sulphides and pervasive replacement of precursor igneous feldspar by sericite and quartz, with a diagnostic mineralogy of sericite, quartz, pyrite, molybdenite, chalcopyrite and tetrahedrite.

Argillic alteration is locally developed in the upper levels of the deposit and comprises sericite, quartz and calcite. Propylitic alteration is rarely recognized.

Skarn alteration occurs as both calcic and magnesian assemblages, dependent upon the wall-rock lithology.

Calcic skarns are mainly found along the south-western contacts of the Tongshankou stock and the western margin of the Shizishan stock within the Triassic limestones and comprises garnet and lesser amounts of scapolite and epidote. Two stages of garnet formation have been recognized, namely: i). an early stage, And70 to 90, mainly developed within the contact zone, occurring as massive, fine grained, and poorly crystallised but extensively mineralised. ii). a late-stage, which is generally confined to the limestones away from the contact, is well crystallised and veined but weakly mineralised.

Magnesian skarns are mostly in the northern and eastern flank of the deposit, where the carbonates are predominantly dolomites. The mineralogy of the magnesian skarns consists of diopside, phlogopite, salite, actinolite, humite, tremolite and serpentine. Two generations of phlogopite, one of the most abundant minerals in this assemblage, are recognised, based on distinct differences in texture and extent of mineralisation: i). an early stage characterised by fine-grained aggregates and mm- to cm-scale veins, which are closely related to magnetite, hematite and chalcopyrite mineralisation. ii). a late-stage which is massive and coarse grained, and apparently devoid of sulphide mineralisation.

The deposit is estimated to contain 0.5 Mt of copper and 2000 t Mo, which at grades of 0.5 to 1% Cu would equate to approximately 50 to 100 Mt of ore. The deposit was discovered in the 1960's, with mining commencing in 1984. Current mining (2007) is by open pit, limited to the skarn ores with an average grade of 0.9 to 1.0% Cu.

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.


Tongshankou

  References & Additional Information
   Selected References:
Li, J.-W., Zhao, X.-F., Zhou, M.-F., Vasconcelos, P., Ma, C.-Q., Deng, X.-Dong., de Souza, Z.S., Zhao, Y.-X. and Wu, G.,  2008 - Origin of the Tongshankou porphyry-skarn Cu-Mo deposit, eastern Yangtze craton, Eastern China: geochronological, geochemical, and Sr-Nd-Hf isotopic constraints: in    Mineralium Deposita   v.43, pp. 315-336.
Zhong, J., Chen, Y.-J. and Pirajno, F.,  2017 - Geology, geochemistry and tectonic settings of the molybdenum deposits in South China: A review: in    Ore Geology Reviews   v.81, pp. 829-855


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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