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

Skarn-typetin-irondeposit, occurring in the contact zone betweencarbonate rocks of the Early Permian Dashizai and Huanggangliangformations and two Cretaceousorthoclasegraniteintrusions (K-Ar isotopic age: 67-115 Ma), one in the western part of the area and one in its eastern part. At thecontact,garnetdiopsideskarn andgarnetamphibolebiotiteskarn are intensively developed. Theore minerals occur in masses,breccias,veinlets, and disseminations. Farther away from thecontact, smallveins occur inintraformationalfissures in theskarn bodies. Late-stagesulphide minerals,amphibole, andepidote replace theskarn and earlymagnetite.

Thedeposit area is 0.5-2.5 km wide and 19.5 km long and is worked by sevenmines. The western part of the area contains several isolatediron-richskarn orebodies, which are worked by mines 1-4. In the eastern part of the area, a continuous band oftin-richskarnlenses, about 6 km long, occurs inmarble along the southerncontact of the easternintrusion. These orebodies are worked bymines 5-7.

Thedeposit is genetically related to theAnle deposit, which occurs in thecontactaureole of the easternintrusion. Bothdeposits form part of a metallogenicbelt along a major EW-trendingfault zone, which includes variousskarn-typedeposits with mineral associations that are similar to Huanggang (e.g.,Haobugao andHujiadian). A similar mineralization also occurs in theSumugoudeposit, which is located a little north of Huanggang.

Thedeposit 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 microscopicinclusions in other minerals or as fine-grained tocolloidal disseminations. Visible crystals are very small (Wang et al., 2007).
(2) Some specimens sold ashedenbergite turned out to beamphiboles upon analysis (Rock Currier, pers. comm.).
(3)Datolite occurs in mine no. 2, but somedatolite specimens in trade are actually from a mine near Linxi (Ottens & Neumeier, 2012).
(4) According to Zhou et al. (2011),garnets vary in composition fromandradite togrossular, withandradite fractions ranging from 28.7 to 96.4 mol-% andgrossular fractions ranging from 2.0 to 67.4 mol-%.Garnets formed in early stages areandradites of nearly end-member composition, whilegarnets in the major ore-forming stage aregrossular. The latter is also dominant in retrogradeskarn assemblages. Likewise,pyroxenes change in composition fromdiopside in early stages tohedenbergite in the ore-forming stage. Thus,hedenbergite can be associated withgrossular, but not withandradite. It is also not likely that allgarnet specimens areandradites, although they appear to be notoriously sold as such.

Most orebodies in the Huanggangliangdeposit are distributed in SK I and SK III mining areas, which exhibit significant differences inwall rocks and mineral assemblages. Compared to SK III, the SK Ⅰ mining area is closer to the Luotuochanglianggranite, and the orebodies are mainly hosted by the lower Permian upper DashizhaiFormation (andesite). In contrast, the SK Ⅲ mining area is closer to the 204granite, and its orebodies are mainly hosted by the lower Permian lower HuanggangliangFormation (marble). In terms oforebody 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 polymetallicdeposit is a representative of suchdeposits, 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 Huanggangliangdeposit the largestskarn-type Fe-Sndeposit north of the Yangtze River in China, and the only Fe-richdeposit 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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China Minerals trip: HuangGang mine,Keshiketeng Qi,ChiFeng,Inner Mongolia,2011 J by John Chen

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References