Huanggang Fe-Sn deposit, Hexigten Banner (Keshiketeng Co.), Chifeng City (Ulanhad League; Chifeng Prefecture), Inner Mongolia, Chinai

Regional Level Types
Huanggang Fe-Sn deposit	Deposit
Hexigten Banner (Keshiketeng Co.)	County
Chifeng City (Ulanhad League; Chifeng Prefecture)	Prefecture-level City
Inner Mongolia	Autonomous Region
China	Country

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Skarn-type tin-iron deposit, occurring in the contact zone between carbonate rocks of the Early Permian Dashizai and Huanggangliang formations and two Cretaceous orthoclase granite intrusions (K-Ar isotopic age: 67-115 Ma), one in the western part of the area and one in its eastern part. At the contact, garnet diopside skarn and garnet amphibole biotite skarn are intensively developed. The ore minerals occur in masses, breccias, veinlets, and disseminations. Farther away from the contact, small veins occur in intraformational fissures in the skarn bodies. Late-stage sulphide minerals, amphibole, and epidote replace the skarn and early magnetite.

The deposit area is 0.5-2.5 km wide and 19.5 km long and is worked by seven mines. The western part of the area contains several isolated iron-rich skarn orebodies, which are worked by mines 1-4. In the eastern part of the area, a continuous band of tin-rich skarn lenses, about 6 km long, occurs in marble along the southern contact of the eastern intrusion. These orebodies are worked by mines 5-7.

The deposit is genetically related to the Anle deposit, which occurs in the contact aureole of the eastern intrusion. Both deposits form part of a metallogenic belt along a major EW-trending fault zone, which includes various skarn-type deposits with mineral associations that are similar to Huanggang (e.g., Haobugao and Hujiadian). A similar mineralization also occurs in the Sumugou deposit, which is located a little north of Huanggang.

The deposit is known for excellent and large (up to 20 cm) ilvaite crystals that came on the market around 2010. The locality is often erroneously given as "Baotou District" (Ottens, 2011).

Notes:
(1) Cassiterite mainly occurs as microscopic inclusions in other minerals or as fine-grained to colloidal disseminations. Visible crystals are very small (Wang et al., 2007).
(2) Some specimens sold as hedenbergite turned out to be amphiboles upon analysis (Rock Currier, pers. comm.).
(3) Datolite occurs in mine no. 2, but some datolite specimens in trade are actually from a mine near Linxi (Ottens & Neumeier, 2012).
(4) According to Zhou et al. (2011), garnets vary in composition from andradite to grossular, with andradite fractions ranging from 28.7 to 96.4 mol-% and grossular fractions ranging from 2.0 to 67.4 mol-%. Garnets formed in early stages are andradites of nearly end-member composition, while garnets in the major ore-forming stage are grossular. The latter is also dominant in retrograde skarn assemblages. Likewise, pyroxenes change in composition from diopside in early stages to hedenbergite in the ore-forming stage. Thus, hedenbergite can be associated with grossular, but not with andradite. It is also not likely that all garnet specimens are andradites, although they appear to be notoriously sold as such.

Most orebodies in the Huanggangliang deposit are distributed in SK I and SK III mining areas, which exhibit significant differences in wall rocks and mineral assemblages. Compared to SK III, the SK Ⅰ mining area is closer to the Luotuochangliang granite, and the orebodies are mainly hosted by the lower Permian upper Dashizhai Formation (andesite). In contrast, the SK Ⅲ mining area is closer to the 204 granite, and its orebodies are mainly hosted by the lower Permian lower Huanggangliang Formation (marble). In terms of orebody types, the SK Ⅰ mining area is mainly dominated by Fe orebodies, while the SK Ⅲ mining area features more Fe-Sn orebodies and Pb-Zn orebodies. The Huanggangliang Fe-Sn polymetallic deposit is a representative of such deposits, and it hosts 180 million tons (Mt) of Fe (ore) @ 38.29%, 0.456 Mt of Sn (metal) @ 0.29%, and 0.116 Mt of Zn (metal) @ 1.04%, along with economic occurrences of Pb, W, Mo, and Cu. These values make the Huanggangliang deposit the largest skarn-type Fe-Sn deposit north of the Yangtze River in China, and the only Fe-rich deposit in the southern Great Xing'an Range.

The Yanshanian magmatism was multi-phase and intense, leading to the emplacement of intrusions, which comprise the K-feldspar granite, granite porphyry, and a small amount of diorite. The Huanggang area hosts multiple intrusions, including the named Luotuochangliang intrusion, the 204 intrusion, and several smaller, unnamed intrusions. The Luotuochangliang intrusion, situated in the southwestern part of the area, covers an area of 4.6 km², which controls Ore Zones I, II, VI, and VII. The 204 intrusion is situated in the central-northeastern part of the area, covering an outcrop area of 2.0 km², which controls Ore Zones III and IV. The ore-related K-feldspar granite is massive and porphyroid in texture with a pale red color and mainly contains alkali feldspar (35~40%), quartz (25~30%), plagioclase (20%), and biotite (10%). Alkali feldspar mainly includes perthite, orthoclase, and microcline.
One hundred and eighty-five ore bodies were discovered, divided into seven ore zones. The lengths of ore bodies are 10–1475 m, with thicknesses of 2–118 m and plunge depths of up to 500 m. They generally dip to the north at 40–80°. Skarn alteration is dominant, which is predominantly developed along the contact zone between the granitoid intrusions and marble. Alteration and skarn in this area have the characteristics of zoning, there are silicified wall rocks, hornfels, green skarns, ore-barren skarns, and ore-bearing skarns (from the wall rock to skarns), with additional fluoritization, carbonatization, and silicification. The mineralization sequence is broadly divided into skarn and quartz-sulfide periods, which can be further subdivided into six distinct stages on the basis of minerals paragenesis and crosscutting relationships of veins, including: (I) anhydrous skarn, (II) hydrous skarn, (III) cassiterite-quartz-calcite, (IV) pyrite-arsenopyrite-quartz-fluorite, (V) polymetallic sulfides-quartz, and (VI) carbonate stages.

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Mineral List

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75 valid minerals.

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