minerals Article Indium Mineralization in the Xianghualing Sn-Polymetallic Orefield in Southern Hunan, Southern China Jianping Liu 1,2, Yanan Rong 1,2, Shugen Zhang 1,2, Zhongfa Liu 1,2,* and Weikang Chen 1,2 1 Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring (Central South University), Ministry of Education, Changsha 410083, China; [email protected] (J.L.); [email protected] (Y.R.); [email protected] (S.Z.); [email protected] (W.C.) 2 School of Geosciences and Info-Physics, Central South University, Changsha 410083, China * Correspondence: [email protected]; Tel.: +86-731-888-30616 Received: 28 July 2017; Accepted: 15 September 2017; Published: 18 September 2017 Abstract: Although numerous W–Sn–Pb–Zn polymetallic deposits are located in southern Hunan, and In-bearing deposits are related to W–Sn–Pb–Zn polymetallic deposits, Indium mineralization in southern Hunan is poorly studied. In order to investigate the In mineralization of the Xianghualing orefield, which is a typical orefield in southern Hunan, ore bulk chemistry, microscopic observation, and electron-probe microanalysis of vein-type (type-I) and porphyry-type (type-II) Sn–Pb–Zn orebodies were studied. The In contents of the type-I orebodies varies from 0.79 to 1680 ppm (avg. 217 ppm, n = 29), and that of the type-II orebodies varies from 10 to 150 ppm (avg. 64 ppm, n = 10). Although chalcopyrite and stannite contain trace amounts of In, sphalerite is the most important In-rich mineral in the orefield. Sphalerite in type-I orebodies contains from <0.02 to 21.96 wt % In, and in type-II orebodies contains from <0.02 to 0.39 wt % In. Indium-rich chemical-zoned sphalerite contains 7 to 8 wt % In in its core and up to 21.96 wt % In in its rim. This sphalerite may be the highest In-bearing variety in Southern China. The Cd contents of the In-rich sphalerite ranges from 0.35 to 0.45 wt %, which places it in the the “Indium window” of the Cu–In–S phases. The geological and structural features of the Xianghualing orefield indicate that the In mineralization of the two types of In-bearing Sn–Pb–Zn orebodies is related to the volatile-rich, In-rich, A-type granites, and is controlled by the normal faults of magmatic-diapiric activity extensional features. Keywords: indium; In-bearing sphalerite; Sn-polymetallic deposits; Xianghualing orefield; southern China 1. Introduction Indium is a dispersed scarce element with a low abundance of 0.05 ppm in the Earth’s crust [1]. Indium alloys are widely used in high-tech applications, e.g., flat-panel displays, solders, semiconductor materials, and photovoltaic solar cells [2]. Due to the demand for flat panel displays and photovoltaic solar cells, indium has become a high-priced commodity and is regarded as a critical and strategic mineral resource by many governments and organizations [3]. The geology and mineralogy of In-bearing deposits were studied during the last decade [4,5]. Major In deposits or mineralization regions have been identified throughout the world, such as Mount Pleasant in Canada [6–8], southwestern Bolivia [4,9], southern Finland and adjacent areas [10–12], southwestern England [13], the eastern Erzgebirge in Germany [14], the Iberian Pyrite Belt [15,16], Japanese Arc [5,17], the Southern Dahinggang Mountains in northern China [18,19], and southern China [20–24]. Two types of primary, industrial In-bearing deposits have been identified: (1) volcanic-hosted massive sulfide deposits, e.g., Kidd Creek in Canada and Neves Corvo in Minerals 2017, 7, 173; doi:10.3390/min7090173 www.mdpi.com/journal/minerals Minerals 2017, 7, 173 2 of 26 Portugal [4]; and (2) vein-type, disseminated-type, and skarn-type deposits in granitic terranes [5]. Minerals 2017, 7, 173 2 of 26 Indium-bearing polymetallic vein-type deposits are generally structurally controlled and occur within faultsPortugal systems [4]; [4]. and These (2) vein-type, types of deposits disseminated-type, are widely and distributed skarn-type arounddeposits the in granitic world andterranes are [5]. the most importantIndium-bearing In producing polymetallic deposits [4vein-type], e.g., the deposits Tosham are deposits generally in Japanstructurally [5], the controlled Bolivian Sn-polymetallicand occur depositswithin [9], faults and the systems Dajing [4]. deposit These types in Northern of deposits China are widely [19]. distributed around the world and are Southernthe most important China is oneIn producing of the richest deposits In mineralization[4], e.g., the Tosham areas deposits in the in world Japan [ 20[5],]. the Indium-bearing Bolivian Sn-polymetallic deposits [9], and the Dajing deposit in Northern China [19]. deposits are distributed in the Yunan, Guangxi, Guangdong, and Hunan provinces (Figure1a). Major Southern China is one of the richest In mineralization areas in the world [20]. Indium-bearing In depositsdeposits in are southern distributed China in the occur Yunan, in the Guangx westerni, Guangdong, section of and South Hunan China; provinces e.g., the (Figure Dachang 1a). and DulongMajor deposits. In deposits Few in Insouthern deposits China occur occur in in thethe western eastern section section; of South e.g., theChina; Nanling e.g., the metallogenetic Dachang belt [24and]. TheDulong southern deposits. Hunan Few In district deposits is occur the area in th withe eastern the section; most W–Sn–Pb–Zn e.g., the Nanling mineralization metallogenetic in the Nanlingbelt metallogenetic [24]. The southern belt Hunan [24,25 ].dist Therict Huangshaping, is the area with the Xianghualing, most W–Sn–Pb–Zn and Yejiwei mineralization deposits in (Figure the 1b) in southernNanling Hunan metallogenetic are also belt reported [24,25]. The to contain Huangshaping, In [5,26 Xianghualing,,27]. In-rich and sphalerite Yejiwei deposits (9–10 wt (Figure % In) was discovered1b) in southern in the Yejiwei Hunan depositare also reported [24]. Furthermore, to contain In [5,26,27]. the southern In-rich Hunansphalerite district (9–10 wt is % located In) was in the discovered in the Yejiwei deposit [24]. Furthermore, the southern Hunan district is located in the NE-trending North Guangxi–South Hunan A-type granite belt [28,29], which is related to In-bearing NE-trending North Guangxi–South Hunan A-type granite belt [28,29], which is related to In-bearing depositsdeposits [6,7,10 [6,7,10].]. Thus, Thus, the southern the southern Hunan Hunan district district is an importantis an important In mineralization In mineralization and exploration and area inexploration southern China.area in southern China. Figure 1. (a) Distribution of major In-bearing base metal deposits in southern China (after Ref. [20]), Figure 1. (a) Distribution of major In-bearing base metal deposits in southern China (after Ref. [20]), showing the location of the Xianghualing Orefield in southern Hunan; (b) simplified regional showinggeologic the location map of southern of the Xianghualing Hunan, showing Orefield the important in southern W–Sn–Pb–Zn Hunan; deposits (b) simplified (after Ref. regional [30]). geologic map of southern Hunan, showing the important W–Sn–Pb–Zn deposits (after Ref. [30]). The Xianghualing Orefield is a typical Sn-ploymetallic orefield in southern Hunan. The orefield Thecontains Xianghualing many types Orefield of deposits is a typical including Sn-ploymetallic granite-type Nb–Ta, orefield skarn-type in southern W–Sn–Be, Hunan. vein-type The orefield Sn–Pb–Zn, and porphyry-type Sn–Pb–Zn deposits. According to previous studies [27], this orefield contains many types of deposits including granite-type Nb–Ta, skarn-type W–Sn–Be, vein-type also hosts In-bearing ores, e.g., 15–52 ppm In in the Xinfeng deposit and 20–60 ppm In in the Sn–Pb–Zn,Paojinshan and porphyry-type deposit [27]. Therefore, Sn–Pb–Zn the Xianghualing deposits. According Orefield tois a previous good deposit studies for the [27 ],investigation this orefield also hosts In-bearingof In mineralization ores, e.g., in 15–52 southern ppm Hunan. In in the In Xinfeng order to deposit characterize and 20–60the In ppm metallogeny In in the of Paojinshan the depositXianghualing [27]. Therefore, orefield, the ore Xianghualing bulk geochemistry, Orefield ore petrology, is a good and deposit electron-probe for the investigationmicroanalyses of In mineralization(EPMA) of in the southern In-bearing Hunan. minerals In in order the vein-type to characterize (type-I) and the porphyry-type In metallogeny (type-II) of the Sn–Pb–Zn Xianghualing orefield,orebodies ore bulk were geochemistry, studied, and In oregenesis petrology, is investigated and electron-probeand discussed in this microanalyses paper. (EPMA) of the In-bearing minerals in the vein-type (type-I) and porphyry-type (type-II) Sn–Pb–Zn orebodies were studied, and In genesis is investigated and discussed in this paper. Minerals 2017, 7, 173 3 of 26 Minerals 2017, 7, 173 3 of 26 2. Geologic Setting 2.The Geologic Xianghualing Setting orefield is located in the southwestern corner of the southern Hunan metallogeneticThe Xianghualing belt (Figure orefield1b). The is outcroppinglocated in the strata southwestern in the belt corner consists of the of Siniansouthern to CambrianHunan low-grademetallogenetic metamorphic belt (Figure rocks, 1b). Devonian The outcropping to Lower strata Triassic in the limestone belt consists intercalated of Sinian with to Cambrian clastic rocks, andlow-grade Upper Triassic metamorphic to Tertiary rocks, sandstone Devonian and to Lower siltstone. Triassic The limestone Yangshanian intercalated granites