Indium Mineralization in the Xianghualing Sn-Polymetallic Oreﬁeld in Southern Hunan, Southern China

: 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.


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].
Southern China is one of the richest In mineralization areas in the world [20].Indium-bearing deposits are distributed in the Yunan, Guangxi, Guangdong, and Hunan provinces (Figure 1a).Major In deposits in southern China occur in the western section of South China; e.g., the Dachang and Dulong deposits.Few In deposits occur in the eastern section; e.g., the Nanling metallogenetic belt [24].The southern Hunan district is the area with the most W-Sn-Pb-Zn mineralization in the Nanling metallogenetic belt [24,25].The Huangshaping, Xianghualing, and Yejiwei deposits (Figure 1b) in southern Hunan are also reported to contain In [5,26,27].In-rich sphalerite (9-10 wt % In) was 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 deposits [6,7,10].Thus, the southern Hunan district is an important In mineralization and exploration area in southern China.Portugal [4]; and (2) vein-type, disseminated-type, and skarn-type deposits in granitic terranes [5].Indium-bearing polymetallic vein-type deposits are generally structurally controlled and occur within faults systems [4].These types of deposits are widely distributed around the world and are the most important In producing deposits [4], e.g., the Tosham deposits in Japan [5], the Bolivian Sn-polymetallic deposits [9], and the Dajing deposit in Northern China [19].Southern China is one of the richest In mineralization areas in the world [20].Indium-bearing deposits are distributed in the Yunan, Guangxi, Guangdong, and Hunan provinces (Figure 1a).Major In deposits in southern China occur in the western section of South China; e.g., the Dachang and Dulong deposits.Few In deposits occur in the eastern section; e.g., the Nanling metallogenetic belt [24].The southern Hunan district is the area with the most W-Sn-Pb-Zn mineralization in the Nanling metallogenetic belt [24,25].The Huangshaping, Xianghualing, and Yejiwei deposits (Figure 1b) in southern Hunan are also reported to contain In [5,26,27].In-rich sphalerite (9-10 wt % In) was 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 deposits [6,7,10].Thus, the southern Hunan district is an important In mineralization and exploration area in southern China.[20]), showing the location of the Xianghualing Orefield in southern Hunan; (b) simplified regional 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 contains many types of deposits including granite-type Nb-Ta, skarn-type W-Sn-Be, vein-type Sn-Pb-Zn, and porphyry-type Sn-Pb-Zn deposits.According to previous studies [27], this orefield also hosts In-bearing ores, e.g., 15-52 ppm In in the Xinfeng deposit and 20-60 ppm In in the Paojinshan deposit [27].Therefore, the Xianghualing Orefield is a good deposit for the investigation of In mineralization in southern Hunan.In order to characterize the In metallogeny of the Xianghualing orefield, ore bulk geochemistry, ore petrology, and electron-probe microanalyses (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.[20]), showing the location of the Xianghualing Orefield in southern Hunan; (b) simplified regional 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 contains many types of deposits including granite-type Nb-Ta, skarn-type W-Sn-Be, vein-type Sn-Pb-Zn, and porphyry-type Sn-Pb-Zn deposits.According to previous studies [27], this orefield also hosts In-bearing ores, e.g., 15-52 ppm In in the Xinfeng deposit and 20-60 ppm In in the Paojinshan deposit [27].Therefore, the Xianghualing Orefield is a good deposit for the investigation of In mineralization in southern Hunan.In order to characterize the In metallogeny of the Xianghualing orefield, ore bulk geochemistry, ore petrology, and electron-probe microanalyses (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.

Stratigraphy and Structural Geology
The rocks of the Xianghualing orefield include Cambrian metamorphic rocks, Devonian-Permian carbonate-clastic rocks, Cretaceous red sandstones, and Quaternary covers (Figure 2).The Cambrian and mid-Devonian Tiaomajian, Qiziqiao, and ShetianqiaofFormations are the host rocks of the ore deposits in the Xianghualing Orefield [41].The Cambrian rocks are composed mainly of low-grade metamorphic rocks, slate and phyllite, which are located in the central part of the orefield, and contain quartz-vein-type W deposits [27,42].The Tiaomajian formation consists of neritic-littoral marine clastic rocks [41].The Qiziqiao and Shetianqiao formations consist of shallow-marine carbonate rocks, which are the host rocks of the Sn-Pb-Zn orebodies.

Stratigraphy and Structural Geology
The rocks of the Xianghualing orefield include Cambrian metamorphic rocks, Devonian-Permian carbonate-clastic rocks, Cretaceous red sandstones, and Quaternary covers (Figure 2).The Cambrian and mid-Devonian Tiaomajian, Qiziqiao, and ShetianqiaofFormations are the host rocks of the ore deposits in the Xianghualing Orefield [41].The Cambrian rocks are composed mainly of low-grade metamorphic rocks, slate and phyllite, which are located in the central part of the orefield, and contain quartz-vein-type W deposits [27,42].The Tiaomajian formation consists of neritic-littoral marine clastic rocks [41].The Qiziqiao and Shetianqiao formations consist of shallow-marine carbonate rocks, which are the host rocks of the Sn-Pb-Zn orebodies.The Xianghualing orefield is located in the Tongtianmiao Dome, the core of which is composed of Cambrian rocks and is surrounded by Devonian, carboniferous, and Permian rocks (Figure 2).The dome contains NS and NE trending faults as well as a few NW trending faults (Figure 2).The NE trending F 1 , and F 101 faults and the NW trending F 2 fault are the main faults controlling the development of vein-type orebodies [27] (Figure 2).
The felsic dikes consist of granitic porphyry, ongonite, and lamprophyre that are distributed around the Laiziling intrusion (Figure 2).The ongonite dike, which is 1770 m long and 1.8-18 m wide, is Nb and Ta enriched (Figure 2) and is located to the east of the Laiziling intrusion.The EW trending granitic porphyry dikes are located to the west of the Laiziling intrusion hosted Sn-Pb-Zn mineralization and form porphyry-type orebodies [41].
Indium is always hosted within sulfides in these deposits [4,47].The first four types of deposits listed above contain little sulfide and are not economic In-rich deposits.The last two types contain abundant sulfides and are mainly In-rich deposits.Furthermore, the last two types, especially vein-types, are the deposits most exploited in the Xianghualing orefield.
Vein-Type Sn-Pb-Zn Orebodies (Type-I) The type-I orebodies, which are the most economic orebodies in the Xianghualing orefield, are distributed along faults F 1 and F 101 as well as suborder faults (Figure 2).The Xinfeng and Tangguanpu deposits are hosted in the F 1 fault zone in the north, and the Chashan and Paojinshan deposits are hosted in the F 101 fault zone in the south (Figure 2).The main orebodies of this type always occur within primary faults, while the secondary of this type of orebodies are hosted in suborder faults, e.g., the Xinfeng deposit (Figure 3a) and the Paojinshan deposit (Figure 3b).The size of the smaller orebodies is <200 m along strike, and that of larger orebodies is >1000 m.The type-I orebodies are 0.5-11 m thick with an average thickness of 2-3 m and extend more than 100-300 m along dips [27].The chemical composition of the orebodies varies base on locations, with Pb-Zn consistently dominatinges in shallower orebodies, Pb-Zn-Sn to and Sn-Pb-Zn dominatinge in intermediate depth orebodies, and dominant Sn dominating in deeper orebodies [48].The ore grade varies with an average of 0.66-1.72 wt % Sn, 1.14-3.03wt % Pb, and 1.94-5.24wt % Zn [27].The Pb-Zn ores in the shallower orebodies contain 3.34-8.94wt % Pb and 4.56-12.34wt % Zn [27].[27], and dips 45-75 • SW (Figure 3c) [49].The average ore grade of dikes No. II is 0.42 wt % Sn, 1.02 wt % Pb, and 1.54 wt % Zn [27].[27], and dips 45-75° SW (Figure 3c) [49].The average ore grade of dikes No. II is 0.42 wt % Sn, 1.02 wt % Pb, and 1.54 wt % Zn [27].[50]), (b) cross section of Line 9 in the Paojinshan deposit (after Ref. [51]), showing the occurrence of type-I orebodies, and (c) cross section of Line 306 in the Tangguanpu deposit (after Ref. [52]), showing the occurrence of type-II orebodies.

Ores of Type-I Orebodies
The ore structure of the type-I orebodies is characterized as massive and disseminated with veins in different locations.Ore minerals include cassiterite, arsenopyrite, pyrrhotite, chalcopyrite, sphalerite, galena, lillianite, native bismuth, and bismuthinite.Based on the major mineral (cassiterite, sphalerite, and galena) contents, the ores of the type-I orebodies can be divided into Sn, Sn-Pb-Zn, and Pb-Zn ores (Figure 4).According to mineral assemblages and textural relationships, the type-I orebodies experienced four stages of mineralization (stage 1 to stage 4) (Figure 5).Stage 1 is the oxide mineral stage, in which wolframite, scheelite, and a small amount of cassiterite form.Stage 2 is the cassiterite-sulfide stage, in which cassiterite, arsenopyrite, pyrite, and pyrrhotite form as well as gangue minerals including quartz, fluorite, and chalorite.Stage 3 is the Cu-Pb-Zn sulfide stage, in which chalcopyrite, sphalerite, and galena form as well as trace amounts of stannite, bismuthinite, native bismuth, and lillianite (Figure 6).Stage 4 is the calcite stage, in which quartz, calcite and trace amounts of galena form.[50]), (b) cross section of Line 9 in the Paojinshan deposit (after Ref. [51]), showing the occurrence of type-I orebodies, and (c) cross section of Line 306 in the Tangguanpu deposit (after Ref. [52]), showing the occurrence of type-II orebodies.

Ores of Type-I Orebodies
The ore structure of the type-I orebodies is characterized as massive and disseminated with veins in different locations.Ore minerals include cassiterite, arsenopyrite, pyrrhotite, chalcopyrite, sphalerite, galena, lillianite, native bismuth, and bismuthinite.Based on the major mineral (cassiterite, sphalerite, and galena) contents, the ores of the type-I orebodies can be divided into Sn, Sn-Pb-Zn, and Pb-Zn ores (Figure 4).According to mineral assemblages and textural relationships, the type-I orebodies experienced four stages of mineralization (stage 1 to stage 4) (Figure 5).Stage 1 is the oxide mineral stage, in which wolframite, scheelite, and a small amount of cassiterite form.Stage 2 is the cassiterite-sulfide stage, in which cassiterite, arsenopyrite, pyrite, and pyrrhotite form as well as gangue minerals including quartz, fluorite, and chalorite.Stage 3 is the Cu-Pb-Zn sulfide stage, in which chalcopyrite, sphalerite, and galena form as well as trace amounts of stannite, bismuthinite, native bismuth, and lillianite (Figure 6).Stage 4 is the calcite stage, in which quartz, calcite and trace amounts of galena form.

Ores of Type-II Orebodies
Based on their structure, the ores in the type-II orebodies in the granitic porphyry dikes can be divided into disseminated ores (Figure 7a) and veinlet ores (Figure 7b).The disseminated ores are located in the western dikes, while veinlet ores are located in the eastern dikes.The ore minerals of type-II orebodies include cassiterite, arsenopyrite, pyrite, pyrrhotite (Figure 8a), chalcopyrite, sphalerite (Figure 8b), galena, and boulangerite (Figure 8b,c).Gangue minerals contain quartz, topaz, fluorite, schorl (Figure 8c), and calcite.According to textural relationships between these minerals, the type-II Sn-Pb-Zn orebodies experienced four stages of mineralization (stage 1 to stage 4).Stage 1 is the oxide mineral stage, in which topaz, schorl, flurite, quartz, and trace amounts of scheelite and cassiterite form.Stage 2 is the cassiterite-sulfide stage, in which scassiterite, arsenopyrite, pyrite, and pyrrhotite form as well as gangue minerals including quartz and fluorite.Stage 3 is the Pb-Zn sulfide stage, in which sphalerite, galena and chalcopyrite with trace amounts of tetrahedrite and stannite form.Stage 4 is the boulangerite-calcite stage, in which abundant boulangerite forms.The paragenetic sequences of minerals in the type-II orebodies are summarized in Figure 9.

Ores of Type-II Orebodies
Based on their structure, the ores in the type-II orebodies in the granitic porphyry dikes can be divided into disseminated ores (Figure 7a) and veinlet ores (Figure 7b).The disseminated ores are located in the western dikes, while veinlet ores are located in the eastern dikes.The ore minerals of type-II orebodies include cassiterite, arsenopyrite, pyrite, pyrrhotite (Figure 8a), chalcopyrite, sphalerite (Figure 8b), galena, and boulangerite (Figure 8b,c).Gangue minerals contain quartz, topaz, fluorite, schorl (Figure 8c), and calcite.According to textural relationships between these minerals, the type-II Sn-Pb-Zn orebodies experienced four stages of mineralization (stage 1 to stage 4).Stage 1 is the oxide mineral stage, in which topaz, schorl, flurite, quartz, and trace amounts of scheelite and cassiterite form.Stage 2 is the cassiterite-sulfide stage, in which scassiterite, arsenopyrite, pyrite, and pyrrhotite form as well as gangue minerals including quartz and fluorite.Stage 3 is the Pb-Zn sulfide stage, in which sphalerite, galena and chalcopyrite with trace amounts of tetrahedrite and stannite form.Stage 4 is the boulangerite-calcite stage, in which abundant boulangerite forms.The paragenetic sequences of minerals in the type-II orebodies are summarized in Figure 9.

Sample Sites
Ore samples were collected from underground workings of the Xinfeng, Tangguanpu, Chashan, and Paojinshan deposits.The locations, types, and ore minerals compositions of samples are listed in Table 1.

Sample Sites
Ore samples were collected from underground workings of the Xinfeng, Tangguanpu, Chashan, and Paojinshan deposits.The locations, types, and ore minerals compositions of samples are listed in Table 1.

Whole-Rock Geochemical Analyses
A total of 39 representative ores samples from the Xianghualing orefield were analyzed at Australia Laboratory Services (ALS), ALS Chemex in Guangzhou, China.Bulk samples were processed using perchloric, nitric, hydrofluoric, and hydrochloric acids (four acids), digested, and then the In contents were measured using inductively-coupled plasma-mass spectrometry, with detection limits of 0.005 to 500 ppm.Other elements, including S, Ti, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Ag, Cd, Sn, Sb, W, Pb, and Bi, were processed with four acids and sodium peroxide flux and were analyzed using inductively-coupled plasma-atomic emission spectroscopy.

Electron-Probe Microanalyses
Minerals were identified in polished thick sections using standard reflected-light microscopy techniques.The results of the bulk-rock geochemistry were used to select In-rich samples for detailed mineralogical and in situ compositional studies.Electron-probe microanalyses (EPMA) with backscattered electron images observation and X-ray elemental mapping were conducted using a Shimadzu EPMA-1720H electron microprobe at the School of Geosciences and Info-physics, Central South University, Changsha, China.The operating conditions of the electron microprobe were as follows: 15-kV accelerating voltage, 60-nA beam current, and 1-µm diameter electron beam.The X-ray lines used to analyze the different elements were as follows: S (Kα), Mn (Kα), Fe (Kα), Cu (Kα), Zn (Kα), Ga (Lα), Cd (Lα), In (Lα), and Sn (Lα).Mineral and metal standards used for elemental calibrations included chalcopyrite (S, Fe, and Cu), metallic manganese (Mn), sphalerite (Zn), gallium arsenide (Ga), greenockite (Cd), indium antimonide (In), and herzenbergite (Sn).The resulting data was corrected by the atomic number (Z), absorption (A) and fluorescence (F) effects (ZAF)-method using proprietary Shimadzu software.The minimum detection limit of Cu and In was 0.02 wt %, that of Zn, Fe, Cd, and Ga was 0.03 wt %, that of Mn was 0.04 wt %, and that of Sn was 0.07 wt %.

Chemical Composition of Ores
Twenty-nine samples of Sn ores, Sn-Pb-Zn ores, and Pb-Zn ores from the type-I orebodies and ten samples of disseminated ores and veinlet ores from the type-II orebodies were analyzed for In and related elements.The results are listed in Table 2.

Correlations among Significant Elements
In the In-Sn, In-Cu, and In-Zn binary diagrams (Figure 10a-c), the In/Sn, In/Cu, and In/Zn ratios of the type-II orebodies are characterized by a narrower range than that of the type-I orebodies.In addition, Cd and Zn are positively correlated with Cd/Zn from 0.005 to 0.05 (Figure 10d).

Correlations among Significant Elements
In the In-Sn, In-Cu, and In-Zn binary diagrams (Figure 10a-c), the In/Sn, In/Cu, and In/Zn ratios of the type-II orebodies are characterized by a narrower range than that of the type-I orebodies.In addition, Cd and Zn are positively correlated with Cd/Zn from 0.005 to 0.05 (Figure 10d).

Chemistry of Ore Minerals
Sphalerite, chalcopyrite and stannite were analyzed for both types of orebodies.

Sphalerite
A total of 100 spots of sphalerite were analyzed for the two types of orebodies in the orefield.The results are listed in Table 3.The In contents of the sphalerite in the type-I orebodies varies from <0.02 to 21.96 wt %.The sphalerite from the Sn ores in the Xinfeng deposit (i.e., sample No. x21d1-x25d4) contains high In (0.98-21.96 wt %).The sphalerite from the Sn-Pb-Zn ores in the Tangguanpu deposit contains 0.26-0.35wt % In, and while that from the Paojinshan deposit contains 0.06-0.70wt % In.The sphalerite from the Pb-Zn ores contains low In, e.g., <0.02-0.18wt %

Chemistry of Ore Minerals
Sphalerite, chalcopyrite and stannite were analyzed for both types of orebodies.

Sphalerite
A total of 100 spots of sphalerite were analyzed for the two types of orebodies in the orefield.The results are listed in Table 3.The In contents of the sphalerite in the type-I orebodies varies from <0.02 to 21.96 wt %.The sphalerite from the Sn ores in the Xinfeng deposit (i.e., sample No. x21d1-x25d4) contains high In (0.98-21.96 wt %).The sphalerite from the Sn-Pb-Zn ores in the Tangguanpu deposit contains 0.26-0.35wt % In, and while that from the Paojinshan deposit contains 0.06-0.70wt % In.The sphalerite from the Pb-Zn ores contains low In, e.g., <0.02-0.18wt % (mostly below 0.09 wt %) in Xinfeng (i.e., sample No. x3a1-x17b5) and below the detection limits in Chashan.The In contents of the sphalerite from the type-II orebodies ranges from <0.02 to 0.39 wt %, with an average of 0.19 wt %.
In the type-I orebodies, In is highly positively correlated with Ga (Figure 11a).The sphalerite from the type-I orebodies in Xinfeng contains high Cu, and there is a high correlation between In and Cu (Figure 11b).Indium correlates poorly with Fe (Figure 11c) and negatively with Fe + Zn (Figure 11d).Indium is poorly correlated with Cd (Figure 11e).The In-rich sphalerite contains 0.35-0.45wt % Cd (Figure 11e), exhibiting an "Indium window" in the Cu-In-S phases [55].In addition, Cu is negatively correlated with (Zn + Fe) in sphalerite (Figure 11f).
In sphalerite from the type-II orebodies, there is a poor correlation between In and Ga, Cu, Fe, Zn and Cd (Figure 11a-d), but there is a strong negative correlation between Cu and Zn (Figure 11f).
Indium-rich sphalerite from the Sn ores in Xinfeng was mapped to produce X-ray element-distribution maps for In, Zn, Cu, and Fe (Figure 12).The sphalerite was found to be enriched in Zn in the core (Figure 12d) and enriched in In (Figure 12c) and Cu in the rim (Figure 12e).In the In sphalerite from the type-II orebodies, there is a poor correlation between In and Ga, Cu, Fe, Zn and Cd (Figure 11a-d), but there is a strong negative correlation between Cu and Zn (Figure 11f).
Indium-rich sphalerite from the Sn ores in Xinfeng was mapped to produce X-ray element-distribution maps for In, Zn, Cu, and Fe (Figure 12).The sphalerite was found to be enriched in Zn in the core (Figure 12d) and enriched in In (Figure 12c) and Cu in the rim (Figure 12e).In the interior of the sphalerite Cu and Fe (Figure 12e,d) are inhomogeneously due to the effects of fine chalcopyrite inclusions.

Chalcopyrite
Chalcopyrite is common in both types of orebodies, but especially in the type-I orebodies.EPMA data for chalcopyrite from the type-I orebodies in the Xinfeng, Tangguanpu, Chashan and Paojinshan deposits are listed in Table 4. Chalcopyrite from the Xinfeng deposit contains slightly higher In than the chalcopyrite from the other deposits, ranging from 0.04 to 0.40 wt %.The In content of chalcopyrite from the Tangguanpu deposit ranges from <0.02 to 0.07 wt %, form the Paojinshan deposit ranges from 0.02 to 0.10 wt %; and from the Chashan deposit, the value was below the detection limits.In addition, the chalcopyrite contains trace amounts of Zn (<0.03-0.79wt %).Except for the influence of fine sphalerite inclusions, In and Zn were homogeneous in the chalcopyrite phenocrysts based on the X-ray element-distribution maps for In and Zn (Figure 13).    5.The In content of the stannite from the type-I orebodies ranges from <0.02 to 3.68 wt %, while that in the stannite from the type-II orebodies ranges from <0.02 to 0.26 wt %.In addition, the stannite contains a small amount of Zn (0.83-5.00 wt %) and trace Cd (<0.03-0.25 wt %).   5.The In content of the stannite from the type-I orebodies ranges from <0.02 to 3.68 wt %, while that in the stannite from the type-II orebodies ranges from <0.02 to 0.26 wt %.In addition, the stannite contains a small amount of Zn (0.83-5.00 wt %) and trace Cd (<0.03-0.25 wt %)."-" below detection limits.

Indiumenriched Orebody Distribution in the Xianghualing Orefield
The type-I In-enriched Sn-Pb-Zn orebodies are controlled by both the faults and the intrusions in the orefield.The orebodies are located in the fault zone, are adjacent to the granites, and show ore zonation: (Sn→Sn-Pb-Zn→Pb-Zn-Sn→Pb-Zn mineralization from the proximal to the distal regions) [48,56,57], e.g., the Xinfeng and Paojinshan deposits.The major In-bearing orebodies are distributed along the NE trending F 1 and F 101 faults and suborder faults.The In grade of the type-I orebodies of the four deposits studied varied dramatically.High In grade ores occur in the Tangguanpu and Paojinshan deposits; i.e., 1680 ppm and 620 ppm, respectively.The average In contents of type-I orebodies in the Xinfeng, Tangguanpu, Paojinshan, and Chashan deposits are 134 ppm, 376 ppm, 143 ppm and 328 ppm, respectively.The In contents of the type-I orebodies in the Xianghualing Orefield are higher than those of the skarn-type orebodies in the Yejiwei deposits in southern Hunan (avg.114 ppm In, [24]).The vein-type orebodies in the Xianghualing Orefield are the richest In orebodies in southern Hunan.These type-II orebodies are controlled by the NE-EW trending granitic porphyry dikes.The In content of the type-II orebodies ranges from 10 to 152 ppm with an average of 64 ppm and is higher than that of the porphyry-type Sn orebodies (avg.17 ppm In [24]) in the Yejiwei deposit in southern Hunan.Therefore, the two types of orebodies present in the Xianghualing ore system are significantly more enriched in In than other orebodies in southern Hunan.Despite have a geological setting similar to that of the other deposits in southern Hunan [30,38], the Xianghualing orefield is characterized as being suitable, having a magmatic-diapiric extensional structure [58].
The In-enriched vein and porphyry-type Sn-Pb-Zn orebodies were formed in normal faults and the associated suborder faults of the structure.

Indium Enriched Minerals in the Xianghualing Orefield
Discrete roquesite phenocrysts always occur in Zn-poor or zinc-free ores [4,10].The ores in the two types of orebodies discussed are Zn-rich, and no roquesite was found in this study.Similar to most In-bearing deposits, In-bearing sphalerite is the most significant In-bearing mineral in the Xianghualing orefield.The EPMA data shows that sphalerite from the two types of orebodies contains variable In contents due to their locations and generation.In the type-I orebodies, the sphalerite from Sn ores contains a high In content, ranging from 2 to 8 wt % In and up to 21.96 wt % In on the rim of the sphalerite phenocrysts (Table 3).Sphalerite from Pb-Zn ores contains <0.10 wt % In.In the type-II orebodies, the sphalerite contains slightly higher In than that from the Pb-Zn ores of the type-I orebodies, e.g., sphalerite from disseminated ores contains 0.10-0.22wt % In, and that from veinlet ores contains <0.02-0.39wt % In.The chemical composition of the In-rich sphalerite from the Xianghualing orefield shows a positive correlation between In and Cu (Figure 11b) and the Sn content is very low, indicating cation replacement within the sphalerite: (2Zn 2+ ) ↔ (Cu + , In 3+ ) [59].Furthermore, the Cd content of the In-rich sphalerite ranges from 0.35-0.45wt % Cd, showing characteristics of an "Indium window" in the Cu-In-S phase (Figure 16e) [55].The In-bearing sphalerite contains chalcopyrite in solid solution (Figure 6a,b, and Figure 8d), which is similar to observation of other In deposits [14].Chalcopyrite is a common and In-enriched mineral in In-bearing deposits [13,47].The EPMA data shows that the chalcopyrite in the type-I orebodies contains <0.02-0.40wt % In.The In contents of chalcopyrite and sphalerite are synchronously enriched.The In content of sphalerite from the Xinfeng and Paojinshan deposits is relatively high, and the In content of the chalcopyrite is also high.The In content of the sphalerite from the Chashan deposit is relatively low, and the In content of the chalcopyrite is also low.Stannite, a secondary mineral in the Sn-Pb-Zn deposits, consistently contains a small amount of In [4,13,24].The type-I and type-II orebodies contain trace stannite.The EPMA data shows that the stannite contains <0.02-3.68wt % In.Stannite from the type-I orebodies of the Paojinshan deposit contains higher In (<0.02-3.68wt % In) than that of the type-II orebodies of the Tangguanpu deposit (<0.02-0.26wt % In).Cassiterite, a major mineral in the In-rich Sn deposits, contains trace In, e.g., Sn-sulfide veins in far-eastern Russia contain 80-485 ppm In [54].Unfortunately, the In line experiences interference from the Sn line during the EMPA analysis of cassiterite, so it is difficult to obtain an accurate In content for cassiterite [13].Based on the mineral contents of ores and the In contents of thier minerals, sphalerite and chalcopyrite are the main In-enriched minerals in the Xianghualing orefield.

Genetic Considerations
The type-I orebodies of the Xianghualing orefield have been well-studied and exploited [48,50,56,57,60].The δ 34 S of the sulfides in the vein-type orebodies is −2.7‰-+6.7‰[46] with an average of +2.5‰, indicating the sulfur is derived from magmatic rocks.The H-O isotopes of quartz in the ores indicates that the fluid of the early stage originated from magmatic water, while the isotopes of the later stages indicated added meteoric water [46].Isotopic data for the type-I orebodies has not been obtained.
The biotite granite and granitic porphyry dikes, which are related to the vein and porphyry-type orebodies, respectively, are products of the same magma chamber.The petrology and geochemistry of the biotite granite indicates that it is an A-type granite [43].The Xianghualing orefield is located in the northern Guangxi southern Hunan A-type granite belt [28,29].Mineralization-related granitic intrusions in southern Hunan, e.g., the Qianlishan granite in the Shizhuyuan orefield [61] and granites in the Huangshaping deposit [36], formed during 160-150 Ma in a post-orogenic extensional and thinning tectonic environment [28,33].The magmatic rocks originated from metasomatized Neoproterozoic volcanic-sedimentary materials [29,33] mixed with lithospheric-mantle-derived magmas [28].Important magmatic-hydrothermal In-bearing deposits around the world, e.g., Mount Pleasant in Canada [7], the Wiborg batholith in Finland [10,11], and the Freiberg district in Germany [14], are specific to A-type granites.The In content of the Laiziling intrusion ranges from 0.141 to 0.616 ppm (Liu Jianping, unpublished data), which is higher than the In content of the crust (0.05 ppm, [1]), indicating that the granites of the Xianghualing orefield are In-enriched.Furthermore, the granites of the Xianghualing Orefield contain high F (0.85-1.60 wt %, [43]).Ore minerals also include F-and B-bearing minerals, e.g., fluorite, topaz, and schorl.F and B play an important role during the mineralization of In and Sn [14].Thus, the Xianghualing Orefield has a suitable intrusive magmatic setting for In mineralization.
In summary, the Xianghualing orefield has volatile-rich, In-rich A-type granites and normal faults in a magmatic-diaper extensional structural setting.These are two significant factors for the formation of the two types of In-enriched Sn-Pb-Zn orebodies.

Conclusions
Based on the geology, the petrology of the ores, the bulk chemistry of the ores, and the EPMA analysis of the two types of Sn-Pb-Zn orebodies in the Xianghualing orefield, the In mineralization features of the orefield can be summarized as follows: (1) The Xianghualing orefield contains vein and porphyry-type Sn-Pb-Zn orebodies.The former occur in the main faults and are the most In-enriched orebodies, while the latter occur in the granitic porphyry dikes.

Figure 1 .
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 geologic map of southern Hunan, showing the important W-Sn-Pb-Zn deposits (after Ref. [30]).

Figure 1 .
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 geologic map of southern Hunan, showing the important W-Sn-Pb-Zn deposits (after Ref. [30]).
Sn-Pb-Zn Orebodies (Type-II) Ten granitic porphyry dikes, including two large dikes (No.I & II), are distributed located in the Tangguanpu deposit in the northern part of the orefield.All of the granitic porphyry dikes have Sn-Pb-Zn mineralization.Dike No.I is 760 m long and 5-13 m (avg.4.5 m) wide, strikes E-W, and dips 65 • -85 • S. The average ore grade of dike No.I is 0.33 wt % Sn, 1.20 wt % Pb, and 0.52 wt % Zn.Dike No. II is 1850 m in length, 1.05-18.92m in width (avg.7.94 m) Sn-Pb-Zn Orebodies (Type-II) Ten granitic porphyry dikes, including two large dikes (No.I & II), are distributed located in the Tangguanpu deposit in the northern part of the orefield.All of the granitic porphyry dikes have Sn-Pb-Zn mineralization.Dike No.I is 760 m long and 5-13 m (avg.4.5 m) wide, strikes E-W, and dips 65°-85° S. The average ore grade of dike No.I is 0.33 wt % Sn, 1.20 wt % Pb, and 0.52 wt % Zn.Dike No. II is 1850 m in length, 1.05-18.92m in width (avg.7.94 m)

Figure 3 .
Figure 3. (a) Cross section of Line 49 in the Xinfeng deposit (after Ref. [50]), (b) cross section of Line 9 in the Paojinshan deposit (after Ref. [51]), showing the occurrence of type-I orebodies, and (c) cross section of Line 306 in the Tangguanpu deposit (after Ref. [52]), showing the occurrence of type-II orebodies.

Figure 3 .
Figure 3. (a) Cross section of Line 49 in the Xinfeng deposit (after Ref. [50]), (b) cross section of Line 9 in the Paojinshan deposit (after Ref. [51]), showing the occurrence of type-I orebodies, and (c) cross section of Line 306 in the Tangguanpu deposit (after Ref. [52]), showing the occurrence of type-II orebodies.

Figure 5 .
Figure 5. Paragenetic sequences of the minerals in the type-I orebodies.

Figure 5 .
Figure 5. Paragenetic sequences of the minerals in the type-I orebodies.Figure 5. Paragenetic sequences of the minerals in the type-I orebodies.

Figure 5 .
Figure 5. Paragenetic sequences of the minerals in the type-I orebodies.Figure 5. Paragenetic sequences of the minerals in the type-I orebodies.

Figure 9 .
Figure 9. Paragenetic sequences of the minerals of the type-II orebodies.

Figure 10 .
Figure 10.Binary diagrams of (a) In-Sn, (b) In-Cu, (c) In-Zn, and (d) Zn-Cd for ores, showing the variation of the two types of orebodies.

Figure 10 .
Figure 10.Binary diagrams of (a) In-Sn, (b) In-Cu, (c) In-Zn, and (d) Zn-Cd for ores, showing the variation of the two types of orebodies.

Figure 12 .
Figure 12.(a) Photomicrographs; (b) backscattered electron images, and X-ray element-distribution maps for (c) In; (d) Zn; (e) Cu, and (f) Fe of high In-bearing sphalerite, showing In and Cu in the rim are richer than in the core, while Zn is richer in the core than in the rim.

Figure 13 .
Figure 13.(a) Photomicrographs, (b) backscattered electron images, and X-ray element-distribution maps for (c) In and (d) Zn for chalcopyrite, showing that In and Zn are homogeneous in chalcopyrite except for the sphalerite inclusions.

4. 2 . 3 .
StanniteStannite, a trace mineral, was observed in the type-I orebodies of the Tangguanpu and Paojinshan deposits and in the type-II orebodies of the Tangguanpu deposit.The EPMA data for stannite are listed in Table

Figure 13 .
Figure 13.(a) Photomicrographs, (b) backscattered electron images, and X-ray element-distribution maps for (c) In and (d) Zn for chalcopyrite, showing that In and Zn are homogeneous in chalcopyrite except for the sphalerite inclusions.

4. 2
.3.Stannite Stannite, a trace mineral, was observed in the type-I orebodies of the Tangguanpu and Paojinshan deposits and in the type-II orebodies of the Tangguanpu deposit.The EPMA data for stannite are listed in Table

( 2 )
Bulk chemical analysis of the ores shows the In content of the vein-type Sn-Pb-Zn orebodies varies from 0.79 to 1680 ppm (avg.217 ppm, n = 29), and that of the porphyry-type orebodies varies from 10 to 150 ppm (avg.64 ppm, n = 10).(3)The EPMA data shows that sphalerite, chalcopyrite, and stannite are In-rich minerals, and sphalerite is the most significant In-rich mineral in the orefield.The most enriched sphalerite contains 7-8 wt % In in its core and up to 21.96 wt % In in its rim, which makes it the most In-enriched sphalerite in southern China.The Cd content of the In-rich sphalerite ranges from 0.35 to 0.45 wt % and exhibits an "Indium window" in the Cu-In-S phases.(4) The In mineralization of the two types of In-bearing Sn-Pb-Zn orebodies was related to the intrusion of volatile-rich, In-rich, A-type granites and was controlled by normal faults within a magmatic-diapiric extensional structure.

Table 1 .
Location, types, and ore minerals of the analyzed samples from the Xianghualing orefield.

Table 1 .
Location, types, and ore minerals of the analyzed samples from the Xianghualing orefield.

Table 2 .
Analytical results of selected ores from the Xianghualing orefield.