Tonglushan Mine, Edong Mining District, Daye Co., Huangshi, Hubei, Chinai

Regional Level Types
Tonglushan Mine	Open-Cast Mine (Active)
Edong Mining District	Mining District
Daye Co.	County
Huangshi	Prefecture
Hubei	Province
China	Country

Skarn-type Cu-Fe deposit, occurring in the northern end of the Majiao-Tonglüshan anticline. The deposit includes 12 ore bodies, associated with an Early Yanshanian hornblende quartz monzodiorite intrusion that forms the northwestern part of the Yangxin batholith. Mineralization is associated with shallow intrusive rocks where contact metamorphism and alteration are extensive. At greater depths, gold-bearing cryptoexplosive breccias were discovered recently. Magnesian and calcic-magnesian skarns, which are particularly well developed at contacts with dolomitic marbles, are the main host rocks of the Cu-Fe mineralization, whereas calcic skarns related to marbles are poorly mineralized.

It is centred on the Tonglushan quartz monzodiorite intrusive which was mainly emplaced into the Lower Triassic Daye Formation. The latter, which is mainly composed of thinly- to thickly-bedded (dolomitic) limestones with minor gypsum and/or anhydrite and occasional halite pseudocrysts, is the principal host of the exoskarn-type Cu-Fe deposit. The main structures in the area of the Tonglushan quartz monzodiorite porphyry system are Yanshanian NE-striking faults and folds which have overprinted older Indosinian NW-striking faults and folds. The intersection of these has provided the locus for emplacement of the quartz monzodiorite porphyry stock as well as for associated fluid flow and mineralization. Hydrothermal breccias, which are locally developed within carbonate xenoliths and wall rocks, generally trend NE-SW.
The Tonglushan Cu-Fe deposit consists of 13 main ore bodies which mainly strike NNE, mostly parallel to the axis of the anticline, over an area of approximately 2000 by 600 m. Individual ore bodies are generally lenticular in shape, 200–500 m long and 30–110 m thick, with a vertical extent of 100–500 m, and occur along or close to the contacts between the quartz monzodiorite porphyry and carbonate xenoliths and wall rocks. Orebodies II, IV, V, and VI contain 77% of the Cu and 85% of the Fe reserves of the deposit. In addition to this, on the basis of recent geophysical exploration and drilling in the Tonglushan mines, there is potential for new deposits at deeper levels, specifically exoskarn ores containing >100,000 t Cu and 3 Mt Fe.
Metal resources: 1.08 Mt Cu (@1.78%), 60 Mt Fe (@41%), 70 t Au (@0.38 g/t), and 508 t Ag.

Magmatic-hydrothermal mineralization processes exert influence upon various host rocks, leading to the formation of three distinct ore types, including porphyry type ores, characterized by mineralization within intrusive rocks; skarn type ores, with mineralization primarily occurring in exoskarn; and carbonate-replacement type ores, which are situated distal to the contact zone. Besides, cryptoexplosive breccias, which are closely linked to mineralization, are prevalent in skarn type ores. The dimensions of the ore bodies range from 150 to 600 m in length, several tens to hundreds of meters in thickness, and exhibit varying dip angles between 50° to 80°. The No. XIII orebodies represent the largest Cu-Fe-Au orebody with over 600 m long and 57 m width, and contribute about 20 % of the Cu-Fe-Au resource, encompassing all three types of ores.
The mineral paragenetic sequence is divided into four stages: (1) Prograde stage, which is exclusively developed in skarn type ores, comprising garnet (grossular and andradite) and pyroxene (mainly diopside). These minerals nearly absent in porphyry and carbonate-replacement type ores. (2) A retrograde stage primarily evolves in skarn and carbonate-replacement ores, characterized by biotite, phlogopite, serpentine, and talc, accompanied by chlorite, quartz, and calcite, with minor epidote and actinolite. The ore minerals are predominantly magnetite and hematite. These mineral associations are mainly observed in skarn-type and carbonate-replacement type ores, while the latter shows fine grained textures; (3) The quartz-sulfide stage can be further divided into two sub-stages: the early stage consists of pyrite (Py1a, Py1b) + chalcopyrite ± bornite ± sphalerite (Sp1) ± molybdenite, and the late stage consists of chalcopyrite + bornite ± pyrite (Py2) ± covellite ± digenite ± sphalerite (Sp2) ± galena. The gangue minerals formed during this stage are quartz, calcite, and chlorite. Notably, porphyry type ores only developed in the early sulfide stage. This is marked by an elevated presence of molybdenite and a decreased quantity of Cu-bearing minerals, occurring alongside potassic alteration (K-feldspar ± biotite). Conversely, carbonate-replacement type ores are characterized by a more considerable concentration of Cu-bearing minerals, as well as sphalerite and galena; (4) The carbonate stage is characterized by primarily calcite, with minor pyrite (Py3) and marcasite, which occur as veinlets crosscutting the earlier three stage mineral assemblages.

Over 14 main orebodies were discovered in the Tonglushan deposit with most of them being exposed to the surface. These orebodies are divided into three mineralization zones according to their trend. Most of the large-sized orebodies are striking along ∼22° while few of them go along ∼60° or 340–345°. Orebodies of Tonglushan are mostly present at depths from the surface (∼40 m) to 800 m while XIII and XIV orebodies are developed between 700 and 1200 m below the sea level. Individual orebodies are mainly lenticular or vein-like in shape and range from 165 to 520 m along strike with width from 18 to 85 m. These orebodies have a combined length of approximately 2.1 km and a width of over 350 m.

The Tonglushan deposit represents one of the largest Cu–Au polymetallic skarn deposits in the MLYRB, containing about 10,000 t of cobalt metal with an average grade of 0.012 %.


Note:
Although referred to as "Tonglushan" occasionally, the Chinese name of the deposit transliterates to "Tonglüshan" (or, "Tonglvshan", which is an alternative spelling).

Chalcopyrite 'balls' controversy
Highly unusual specimens of chalcopyrite, as single balls with an iridescent surface or clusters of connected balls have appeared on the market in recent years. It must be noted that doubt has been raised about the authenticity of these specimens, for example analysis by the Smithsonian Museum showed unexpected inclusions of both calcium sulfide and calcium sulfate. The material seems to be made up of spherules of chalcopyrite bonded together. It has been suggested by Chinese mineral experts that these may be sintered chalcopyrite pellets produced from chalcopyrite powder industrially rather than mineral specimens.

Other Regions, Features and Areas containing this locality

References