Sb-Bi Alloys and Ag-Cu-Pb-Sb-Bi Sulphosalts in the Jialong Cu-Sn Deposit in North Guangxi, South China

minerals

Article Sb-Bi Alloys and Ag-Cu-Pb-Sb-Bi Sulphosalts in the Jialong Cu-Sn Deposit in North Guangxi, South China

Jianping Liu 1, Weikang Chen 1 and Qingquan Liu 2,* ID

1 Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, Ministry of Education, Central South University, Changsha 410083, China; [email protected] (J.L.); [email protected] (W.C.) 2 School of Resources and Safety Engineering, Central South University, Changsha 410083, China * Correspondence: [email protected]; Tel.: +86-731-888-30616

Received: 30 August 2017; Accepted: 8 January 2018; Published: 16 January 2018

Abstract: Although native bismuth is a relatively common mineral, native antimony is less abundant, and Sb-Bi alloys are relatively rare phases in Nature. Sb-Bi alloys and Ag-Cu-Pb-Sb-Bi sulphosalts have been discovered in the Jialong vein-type Cu-Sn deposit in North Guangxi, South China. The Jialong deposit is hosted by schist within the contact zone of a Neoproterozoic granite. Four stages of ore formation are recognised, with the Sb-Bi alloy- and sulphosalt-bearing assemblage formed during the third stage. Sulphosalts include Pb-Bi-Ag sulphosalts (pavonite), Sb-Bi sulphosalts (tintinaite, terrywallaceite), and Sb sulphosalt (ullmanite, freibergite, bournonite). Grains of Sb-Bi alloy measure 2–20 µm in diameter, show rounded margins and occur together with galena along the edges or internal fissures of sulphosalts. The Sb-Bi alloys do not coexist with bismuthinite, BiS (an unnamed mineral), or with native bismuth. Two phases of Sb-Bi alloys are identified based on back-scattered electron image observations and electron microprobe analysis. The textural and thermodynamic relationships indicate that Phase I was formed before Phase II. Phase I contains high Sb (69.15–80.12 wt %) and lower Bi (18.01–27.85 wt %), while Phase II contains low Sb (0.89–25.24 wt %) and high Bi (72.95–98.89 wt %). Cooling in the range of 270–400 ◦C and decreasing sulphur fugacity promote precipitation of Sb-Bi alloys and sulphosalts during the late stage of incursion of Sb- and Bi-bearing magmatic hydrothermal fluids.

Keywords: Sb-Bi alloys; sulphosalts; Jialong Cu-Sn deposit; south China

1. Introduction Bismuth-bearing minerals, including native bismuth, bismuth sulphosalts, and bismuth chalcogenides, occur in a variety of deposits [1], and have attracted signiﬁcant interest as a source of this useful metal. Bi and Sb are group V elements in the periodic table and occur within a range of sulphosalt minerals [2]. The complex substitution mechanisms of sulphosalts [3,4] are of particular geological interest for what they can reveal about the physico-chemical conditions of mineral formation [5–9]. Metallic Bi minerals include native bismuth, with some Pd-Bi (e.g., froodite PdBi2,[10,11]) and Au-Bi (e.g., maldonite Au2Bi, and Au0.53Bi0.47 [12]) alloys. However, Sb-Bi alloys are relatively rarely formed by geological processes. Much of the research on Sb-Bi alloys has involved materials science applications [13]. The reported occurrences of Sb-Bi alloys include antimonian bismuth in the Loddiswell quartz carbonate vein mine, southwest England [14], the Tanco pegmatite, Canada [15], the Skrytoe scheelite skarn deposit, Russia [16] and the Katerina coal mine in the Czech Republic [17], bismuthian antimony in the Viitaniemi pegmatite, Finland [18], and from the Sulitjelma VMS-type deposit in Norway [19]. Thus,

Minerals 2018, 8, 26; doi:10.3390/min8010026 www.mdpi.com/journal/minerals Minerals 2018, 8, 26 2 of 20 due to their limited geologic occurrence, the composition and mineralisation conditions of Sb-Bi alloys are poorly studied. The Jialong deposit is a small Sn-Cu deposit with metal reserves of 12,806 t Cu and 3000 t Sn [20] in North Guangxi Province, South China. This vein-type deposit is indium-bearing with abnormally high Bi and Sb contents (showing maximum Bi and Sb contents of 2010 ppm and 1155 ppm, respectively), which were observed during a recent study of indium mineralisation in the deposit (Jianping Liu’ unpublished data). After further mineralogical investigation, Sb-Bi alloys and several Ag-Cu-Pb-Sb-Bi sulphosalts were discovered. Therefore, this deposit allows us to assess how Sb-Bi alloys were formed during the mineralisation processes. In this study, mineralogical analysis of ores in the Jialong Sn-Cu deposit was ﬁrst performed, after which the mineral chemistry of the Sb-Bi alloys and Ag-Cu-Pb-Sb-Bi sulphosalts were obtained. We use these data to discuss the formation conditions of the Sb-Bi alloys.

2. Geological Setting The Jialong deposit is located in the Jiuwandashan-Yuanbaoshan region (JYR) in the southwest corner of the Jiangnan Orogenic Belt (Figure1a) [ 21]. The regional stratigraphy of the JYR comprises, in geochronological order, of the Paleoproterozoic Sibao Group, composed of regional low-grade metamorphic sandstone, sandy slate, phyllite, and mica schist; the Mesoproterozoic Danzhou Group, composed of metamorphic siltstone and phyllite; the Neoproterozoic Sinian sandstone, composed of siltstone and sandy slate; and Devonian limestone [22] (Figure1b). The Sibao Group including the Yuxi, Jiuxiao and Baidingyan Formations (from top to bottom), is a thick flysch formation of hemipelagic and pelagic facies terrigenous clastic sedimentary rocks interlayered with ultramafic volcanic and intrusive rocks [23]. Granites are widespread in the JYR, intruding into the Sibao Group, and underlain by the Danzhou Group [23]. Two types of granite are identified [24]: (1) 835–820 Ma granodiorite intrusions with minimal surface outcrops; and (2) 810–800 Ma biotite granite intrusions with widespread outcrop across the district (Figures 1b and 2). Geochemical features show that the granites are strongly peraluminous S-type granites with A/CNK > 1.1, and a CIPW (Cross, Iddings, Pirsson, Washington) normative corundum content of 1.53–3.85 vol % [24]. There are more than 30 Sn-polymetallic deposits in the JYR (Figure1b), with a total Sn reserve of 0.2 Mt [ 21,22]. These Sn deposits are hosted in the metamorphic rocks of the Sibao Group, and are related to type 2 granites [21]. The Jialong deposit is a vein-type deposit and is situated in the northeast of the Yuanbaoshan intrusion (Figures1b and2a). Contact metamorphism is local and only weakly affects the mining area. The deposit is hosted by the Yuxi Formation, which is composed of muscovite-quartz and chlorite-muscovite-quartz schist interlayered with leptinite and two-mica schist [20]. Orebodies occur in a silicified zone between the leptinite and muscovite schist of the Yuxi Formation (Figure2a). The mineralised silicified zone is approximately 500–600 m from the granite intrusion and approximately 1 km in length and 30–50 m in width, with an inclination of 45◦–60◦, and a steep dip of 55◦–60◦ [20]. Seven orebodies (Nos. 1–7) are outlined; the first three are the major orebodies. The number 3 ore-body, the largest in the deposit, is 677 m long and 3.0–4.5 m thick, extending 442 m along the dip [20]. Orebodies are layer-like, lamellar, and lenticular with grades of 0.45–0.70 wt % Cu and 0.2–0.3 wt % Sn [20]. Ore structures of the Jialong deposit comprise irregular veinlets (Figure3a) and veins with small amounts of massive ore (Figure3b). Minerals 2018, 8, 26 3 of 20 Minerals 2018, 8, 26 3 of 20

Figure 1. (a) Map of the tectonic units in south China (after reference [25]), showing the Figure 1. (a) Map of the tectonic units in south China (after reference [25]), showing the Jiuwandashan– Jiuwandashan–Yuanbaoshan Sn-polymetallic metallogenic area located in the southwestern corner Yuanbaoshan Sn-polymetallic metallogenic area located in the southwestern corner of the Jiangnan of the Jiangnan Orogen Belt; (b) Simplified geological map of the Jiuwandashan–Yuanbaoshan Orogen Belt; (b) Simpliﬁed geological map of the Jiuwandashan–Yuanbaoshan region, showing the region, showing the distribution of Sn-polymetallic deposits and the location of the Jialong deposit distribution of Sn-polymetallic deposits and the location of the Jialong deposit (after reference [23]). (after reference [23]).

Minerals 2018, 8, 26 4 of 20 Minerals 2018, 8, 26 4 of 20 Minerals 2018, 8, 26 4 of 20

Figure 2. (a) Simplified geological map of the Jialong deposit (after reference [20]); (b) Sketch of a Figure 2. (a) Simpliﬁed geological map of the Jialong deposit (after reference [20]); (b) Sketch of a representativeFigure 2. (a) Simplified section of geological the vein-following map of the drift Jialong at 440deposit m above (after seareference level (after [20]); reference(b) Sketch [20]), of a representative section of the vein-following drift at 440 m above sea level (after reference [20]), showing showingrepresentative the mineralisation section of the pattern vein-following of the Jialong drift deposit. at 440 m above sea level (after reference [20]), the mineralisation pattern of the Jialong deposit. showing the mineralisation pattern of the Jialong deposit.

Figure 3. Photographs of typical ore samples of the Jialong deposit: (a) irregular chalcopyrite (Ccp) andFigure arsenopyrite 3. Photographs (Apy) of veinlets typical infillingore samp granulite;les of the and Jialong (b) massivedeposit: ores(a) irregular composed chalcopyrite of arsenopyrite, (Ccp) Figure 3. Photographs of typical ore samples of the Jialong deposit: (a) irregular chalcopyrite (Ccp) chalcopyrite,and arsenopyrite and sphalerite(Apy) veinlets (Sp). infilling granulite; and (b) massive ores composed of arsenopyrite, and arsenopyrite (Apy) veinlets inﬁlling granulite; and (b) massive ores composed of arsenopyrite, chalcopyrite, and sphalerite (Sp). 3. Samplingchalcopyrite, and and Analytical sphalerite Methods (Sp). 3. SamplingIn our previous and Analytical study, more Methods than 20 ore samples were collected from the No. 3 ore-body, and 3. Sampling and Analytical Methods 10 polishedIn our previoussections werestudy, prepared more than for microsco20 ore samplespic observation were collected and electron-probe from the No. microanalyses.3 ore-body, and 10 InpolishedThe our previousore sections minerals study,were and prepared more textures than for 20weremicrosco ore identified samplespic observation wereusing collected standard and electron-probe from reflected-light the No. microanalyses. 3 ore-body,microscopy and 10techniques. polishedThe ore sections Analysis minerals were of and preparedchemical textures forcompositions microscopicwere identified of observationminerals using andstandard and X-ray electron-probe reflected-lightmapping were microanalyses. microscopyperformed usingtechniques.The a ore Shimadzu minerals Analysis EPMA-1720H and of textureschemical (Tokyo, were compositions identified Japan) electr usingof mineralson-probe standard and microanalyser reflected-light X-ray mapping (EPMA) microscopy were housed performed techniques. at the AnalysisSchoolusing a ofShimadzu Geosciences chemical EPMA-1720H compositions and Info (Tokyo,-physics, of mineralsJapan) Central electr South andon-probe X-ray Universi microanalyser mappingty (Changsha, were (EPMA) performedChina). housed The usingat BSE the a ShimadzuimagesSchool ofwere EPMA-1720H Geosciences obtained under (Tokyo,and Info 15Japan) -physics,kV accelerating electron-probe Central voltageSouth microanalyser Universiand 0.5 tynA (Changsha, beam (EPMA) current. housed China). Each at The theanalysis SchoolBSE ofusedimages Geosciences a 15 were kV accelerating andobtained Info-physics, under voltage, 15 Central kV a 10 accelerating nA South beam University current, voltage and and (Changsha, a 1-0.5μ mnA diameter beam China). current. electron The BSE Each beam. images analysis Count were times were 10 seconds each for peak and background. The X-ray lines, crystals used for analysis, obtainedused a 15 under kV accelerating 15 kV accelerating voltage, a voltage10 nA beam and current, 0.5 nA beamand a 1- current.μm diameter Each electron analysis beam. used Count a 15 kV standards, and detection limits are listed in Table 1. The resulting data were processed using the acceleratingtimes were voltage, 10 seconds a 10 each nA beamfor peak current, and background. and a 1-µm The diameter X-ray electronlines, crystals beam. used Count for timesanalysis, were atomicstandards, number and detection(Z), absorption limits are(A), listed and fluorescin Tableence 1. The (F) resultingeffects (ZAF) data werecorrection processed method. using X-ray the 10 seconds each for peak and background. The X-ray lines, crystals used for analysis, standards, and elementatomic number mapping (Z), was absorption performed (A), at a and15 kV fluoresc acceleratingence (F) voltage, effects and (ZAF) 60 nA correction beam current. method. X-ray detection limits are listed in Table1. The resulting data were processed using the atomic number (Z), element mapping was performed at a 15 kV accelerating voltage, and 60 nA beam current.

Minerals 2018, 8, 26 5 of 20 absorption (A), and ﬂuorescence (F) effects (ZAF) correction method. X-ray element mapping was performed at a 15 kV accelerating voltage, and 60 nA beam current.

Minerals 2018Table, 8, 26 1. Electron-probe microanalyser (EPMA) analysis conditions used in the study. 5 of 20

ElementsTable S 1. FeElectron-probe Ni microanalyser CuZn (EPMA) analysis As conditions Se used Ag in the Sb study. Pb Bi ElementsX-Ray Lines S Kα Fe Kα NiK α CuKα K Znα L Asα L Seα Lα AgLα Sb Mα Pb Mα Bi X-RayCrystals Lines Kα PETKα LiFKα LiF K LiFα LiFKα RAPLα RAPLα PETLα PETLα PETMα PETMα Crystals PET LiF LiF LiF LiF GalliumRAP RAP PET MetalPET PET NativePET Standards Pyrite Pyrite Pentlandite Chalcopyrite Sphalerite Guanajuatite Argentite Galena Galliumarsenide Sb bismuthNative Standards Pyrite Pyrite Pentlandite Chalcopyrite Sphalerite Guanajuatite Argentite Metal Sb Galena Detection 0.05 0.02 0.03 0.03 0.04arsenide 0.03 0.03 0.03 0.04 0.02 0.05bismuth DetectionLimits (wt %) 0.05 0.02 0.03 0.03 0.04 0.03 0.03 0.03 0.04 0.02 0.05 Limits (wt %) 4. Mineralogy and Mineral Chemistry 4. Mineralogy and Mineral Chemistry Based on microscopic observations and EPMA analyses, more than 27 minerals were identiﬁed. The parageneticBased on sequencemicroscopic of theobservations minerals isand summarised EPMA analyses, in Figure more4. Accordingthan 27 minerals to mineral were assemblagesidentified. andThe crosscutting paragenetic relationships, sequence of the the Jialong minerals deposit is summarised experienced in four Figure mineralisation 4. According stages to (Stagesmineral I, II, assemblages and crosscutting relationships, the Jialong deposit experienced four mineralisation III, and IV). Tourmaline, ﬂuorite, and quartz with trace cassiterite were formed in Stage I (oxide-silicate stages (Stages I, II, III, and IV). Tourmaline, fluorite, and quartz with trace cassiterite were formed in stage). In Stage II, cassiterite, arsenopyrite, pyrite, and pyrrhotite were formed (cassiterite-sulphide Stage I (oxide-silicate stage). In Stage II, cassiterite, arsenopyrite, pyrite, and pyrrhotite were formed stage). Next, chalcopyrite, sphalerite, stannite, Bi-, Sb-Bi-, and Sb-sulphosalts, galena I, and Sb-Bi (cassiterite-sulphide stage). Next, chalcopyrite, sphalerite, stannite, Bi-, Sb-Bi-, and Sb-sulphosalts, alloys were formed in Stage III. Finally, Stage IV marks the deposition of bismuthinite, galena II, BiS galena I, and Sb-Bi alloys were formed in Stage III. Finally, Stage IV marks the deposition of (an unnamed mineral), and native bismuth. bismuthinite, galena II, BiS (an unnamed mineral), and native bismuth.

Figure 4. Paragenetic sequence of minerals observed in the Jialong deposit. Figure 4. Paragenetic sequence of minerals observed in the Jialong deposit. 4.1. Sb-Bi Alloys and Native Bismuth Sb-Bi alloys display intergrowth with galena and sulphosalts, but are not intergrown with bismuthinite or native bismuth. The alloys grains are small and irregular and range from 1 μm to 20 μm in diameter (Figure 5). Two phases (I and II) of Sb-Bi alloys are identified based on

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4.1. Sb-Bi Alloys and Native Bismuth Sb-Bi alloys display intergrowth with galena and sulphosalts, but are not intergrown with bismuthinite or native bismuth. The alloys grains are small and irregular and range from 1 µm to 20 µm in diameter

(FigureMinerals5). 2018 Two, 8, phases26 (I and II) of Sb-Bi alloys are identiﬁed based on microscopic observations,6 of 20 back-scattered electron images (Figures5 and6), and EPMA analysis (Table2). Phase I is accompanied by galenamicroscopic I (see observations, Section 4.3 for back-scattered a description electron of the images two types (Figures of galena), 5 and tintinaite,6), and EPMA and analysis bournonite (Figure(Table6), 2). and Phase is replaced I is accompanied by Phase by II galena (Figure I (see5c). Section Phase 4.3 I contains for a description high Sb of (69.15–77.68 the two types wt of %) andgalena), low Bi tintinaite, (18.01–27.85 and bournonite wt %), while (Figure Phase 6), and II is contains replaced lowby Phase Sb (0.89–25.24 II (Figure 5c). wt Phase %) I and contains high Bi (72.95–98.89high Sb (69.15–77.68 wt %), displaying wt %) and a gap low in Bi composition. (18.01–27.85 wt In %), addition, while Phase Sb-Bi II alloys contains contain low Sb trace (0.89–25.24 amounts of Cu (<0.03–1.51wt %) and high wt %), Bi Fe(72.95–98.89 (0.07–1.48 wt wt %), %) anddisplaying S (<0.05–0.24 a gap in wt composition. %). We infer In from addition, mineral Sb-Bi textures alloys that contain trace amounts of Cu (<0.03–1.51 wt %), Fe (0.07–1.48 wt %) and S (<0.05–0.24 wt %). We infer Sb-Bi alloys formed after galena I (Figure5a–d), and galena I formed after the sulphosalts (Figure5d). from mineral textures that Sb-Bi alloys formed after galena I (Figure 5a–d), and galena I formed after The native bismuth comprises large grains ranging from 20–80 µm, which occur with pavonite, the sulphosalts (Figure 5d). The native bismuth comprises large grains ranging from 20–80 μm, freibergite, galena II (see Section 4.3), and bismuthinite (Figure7). The EPMA data shows that native which occur with pavonite, freibergite, galena II (see Section 4.3), and bismuthinite (Figure 7). The bismuthEPMA is data nearly shows pure that (Table native2). bismuth is nearly pure (Table 2).

Figure 5. Reflected light photomicrograph (a) and back-scattered electron (BSE) images (b–f) of FigureSb-Bi 5. Reflectedalloys and light associated photomicrograph minerals. (a)( aSb-Bi) and alloys back-scattered and galena electron I (Gn-I) (BSE) infilling images gaps ( bbetween–f) of Sb-Bi alloysstannite and associated (Stn) and minerals.tintinaite (Tnt), (a) Sb-Bi showing alloys the and di galenafferent Ireflectance (Gn-I) infilling of Phase gaps I (BS-I) between and stannite Phase II (Stn) and(BS-II) tintinaite of the (Tnt), Sb-Bi showing alloys; ( theb) enlarged different BSE reflectance image ofof Figure Phase 5a, I (BS-I)showing and the Phase different II (BS-II) brightness of the of Sb-Bi alloys;the( btwo) enlarged phases of BSE Sb-Bi image alloys; of Figure(c) Phase5a, Ishowing and Phase the II differentinfilling galena brightness I, with of growth the two of phases Phase II of on Sb-Bi alloys;the (cirregular) Phase Isurfaces and Phase of Phase II infilling I; (d) galenaPhase II I, infilling with growth galena of I, Phase together II on displacing the irregular stannite surfaces and of Phasetintinaite; I; (d) Phase (e) Phase II infilling II of Sb-Bi galena alloy I, togetherand galena displacing I infill on stannite the surface and of tintinaite; tintinaite ( eand) Phase bournonite II of Sb-Bi alloy(Bnn); and galenaand (f) IPhase infill II on and the galena surface I deposition of tintinaite on the and surface bournonite of tintinaite. (Bnn); and (f) Phase II and galena I deposition on the surface of tintinaite.

Minerals 2018, 8, 26 7 of 20 Minerals 2018, 8, 26 7 of 20 Minerals 2018, 8, 26 7 of 20

Figure 6. (a) Back-scattered electron images of Sb-Bi alloys and associated galena and bournonite Figure 6. a Figure(Bnn), showing6. ((a)) Back-scatteredBack-scattered Sb-Bi alloys electron electronand galena images images I infill of Sb-Biof Sb-Bialon alloysg altheloys and edge and associated and associated internal galena galenafissures and bournonite and of bournonite,bournonite (Bnn), (Bnn),showingand the showing later Sb-Bi formation alloysSb-Bi andalloys of galena Sb-Bi and alloysgalena I infill and alongI infill galena the alon edge comparedg the and edge internal to and bournonite; internal fissures fissures of(b bournonite,) enlarged of bournonite, image and the of later formation of Sb-Bi alloys and galena compared to bournonite; (b) enlarged image of Figure6a, andFigure the 6a, later showing formation Sb-Bi of alloys Sb-Bi and alloys galena and I galena(Gn-I) infillingcompared bournonite, to bournonite; and the (b) different enlarged brightness image of showing Sb-Bi alloys and galena I (Gn-I) infilling bournonite, and the different brightness of Phase I Figureof Phase 6a, Ishowing (BS-I) and Sb-Bi Phase alloys II and (BS-II); galena (c )I X-ray(Gn-I) element-distributioninfilling bournonite, andmap the of different Bi for the brightness area of (BS-I) and Phase II (BS-II); (c) X-ray element-distribution map of Bi for the area of Figure6b, showing ofFigure Phase 6b, I showing(BS-I) and Bi Phasecontent II from (BS-II); different (c) X-ray Sb-Bi element-distribution alloys. The Bi content map of ofPhase Bi forI is thelower area than of Bi content from different Sb-Bi alloys. The Bi content of Phase I is lower than that of Phase II, and Bi Figurethat of 6b,Phase showing II, and Bi Bi contentcontent fromof th edifferent Phase II Sb-Bigrains alloys. is variable; The Bi and content (d) X-ray of Phase element-distribution I is lower than content of the Phase II grains is variable; and (d) X-ray element-distribution map of Sb for the area of thatmap of of Phase Sb for II,the and area Bi of content Figure of 6b, th showinge Phase IIa highergrains isSb variable; content inand Phase (d) X-rayI than element-distributionin Phase II. Figure6b, showing a higher Sb content in Phase I than in Phase II. map of Sb for the area of Figure 6b, showing a higher Sb content in Phase I than in Phase II.

Figure 7. (a) Native bismuth (Bi) and galena II (Gn-II) infilling the boundaries between pyrrhotite Figure(Po) and 7. chalcopyrite(a) Native bismuth (Ccp); and(Bi) and(b) native galena bismuth, II (Gn-II) bismuthinite infilling the (Bmt), boundaries and chalcopyrite between pyrrhotite infilling Figure 7. (a) Native bismuth (Bi) and galena II (Gn-II) inﬁlling the boundaries between pyrrhotite (Po)interstitial and chalcopyrite cavities between (Ccp); muscovite and (b) native blades bismuth, (Ms) and bismuthinite cleavage planes. (Bmt), and chalcopyrite infilling (Po) and chalcopyrite (Ccp); and (b) native bismuth, bismuthinite (Bmt), and chalcopyrite inﬁlling interstitial cavities between muscovite blades (Ms) and cleavage planes. interstitial cavities betweenTable muscovite2. EPMA data blades for (Ms)Sb-Bi and alloys cleavage and native planes. bismuth. Table 2. EPMA data for Sb-Bi alloys and native bismuth. wt % apfu Σ1 Atom Analyses Cu Ag Fe Pb Biwt % Sb Se S Total Cu Ag Fe apfu Pb Σ 1 AtomBi Sb Se S Analyses Sb-Bi alloys (PhaseCu AgI) Fe Pb Bi Sb Se S Total Cu Ag Fe Pb Bi Sb Se S Sb-BiBs3 alloys (Phase0.36 I)- 0.36 0.85 18.01 78.66- 0.24 98.48 0.01 - 0.01 0.01 0.11 0.85 - 0.01 Gn61Bs3 0.36 0.11 -- 0.360.57 0.85- 18.01 18.32 78.66-80.12 - 0.240.18 98.4899.30 0.010.00 - - 0.010.01 0.01 - 0.110.11 0.850.86 -- 0.010.01 Gn61Bs13 0.110.20 - 0.570.40 - 18.3220.29 80.1277.68 0.04 - 0.18 0.12 99.3098.73 0.000.00 - - 0.010.01 - - 0.110.13 0.860.85 0.000.00- 0.01 Bs13Bs2 0.200.50 - 0.400.14 0.12- 20.2920.73 77.6876.70- 0.04 0.120.09 98.7398.28 0.000.01 - - 0.01 0.00 0.00 - 0.130.13 0.850.85 0.000.00 - 0.00 Bs2Bs5 0.500.59 - 0.140.07 0.120.14 20.7321.47 76.70-75.64- 0.090.12 98.2898.03 0.010.01 - - 0.00 0.00 0.00 0.00 0.130.14 0.850.84 - - 0.00 0.01 Gn64Bs5 0.59 0.53 -- 0.070.39 0.14- 21.47 23.14 75.64-74.04 - 0.120.14 98.0398.24 0.010.01 - - 0.000.01 0.00 - 0.140.15 0.840.82 -- 0.010.01 Gn64 0.53 - 0.39 - 23.14 74.04 - 0.14 98.24 0.01 - 0.01 - 0.15 0.82 - 0.01

Minerals 2018, 8, 26 8 of 20

Table 2. EPMA data for Sb-Bi alloys and native bismuth.

wt % apfu Σ1 Atom Analyses Cu Ag Fe Pb Bi Sb Se S Total Cu Ag Fe Pb Bi Sb Se S Sb-Bi alloys (Phase I) Bs3 0.36 - 0.36 0.85 18.01 78.66 - 0.24 98.48 0.01 - 0.01 0.01 0.11 0.85 - 0.01 Gn61 0.11 - 0.57 - 18.32 80.12 - 0.18 99.30 0.00 - 0.01 - 0.11 0.86 - 0.01 Bs13 0.20 - 0.40 - 20.29 77.68 0.04 0.12 98.73 0.00 - 0.01 - 0.13 0.85 0.00 0.00 Bs2 0.50 - 0.14 0.12 20.73 76.70 - 0.09 98.28 0.01 - 0.00 0.00 0.13 0.85 - 0.00 Bs5 0.59 - 0.07 0.14 21.47 75.64 - 0.12 98.03 0.01 - 0.00 0.00 0.14 0.84 - 0.01 Gn64 0.53 - 0.39 - 23.14 74.04 - 0.14 98.24 0.01 - 0.01 - 0.15 0.82 - 0.01 Bs11 0.10 0.04 0.49 - 23.46 73.87 - 0.14 98.10 0.00 0.00 0.01 - 0.15 0.83 - 0.01 Bs8 0.18 - 0.29 0.11 24.48 74.67 - 0.09 99.82 0.00 - 0.01 0.00 0.16 0.83 - 0.00 Gn62 0.38 - 0.16 - 24.55 72.92 - 0.07 98.08 0.01 - 0.00 - 0.16 0.82 - 0.00 Bs15 1.51 - 1.05 0.07 25.72 71.03 - 0.16 99.54 0.03 - 0.02 0.00 0.16 0.77 - 0.01 Bs12 0.17 - 0.17 0.08 27.34 70.21 0.08 0.04 98.09 0.00 - 0.00 0.00 0.18 0.81 0.00 0.00 Gn67 0.15 - 0.31 0.10 27.85 70.46 - 0.11 98.98 0.00 - 0.01 0.00 0.18 0.80 - 0.00 Bs7 0.21 - 1.48 - 27.85 69.15 - 0.14 98.83 0.00 - 0.04 - 0.18 0.77 - 0.01 Sb-Bi alloys (Phase II) Gn41 0.07 - 0.23 - 72.95 25.24 0.05 - 98.54 0.00 - 0.01 - 0.62 0.37 0.00 - Gn42 0.12 - 0.41 - 73.43 24.21 0.04 0.07 98.28 0.00 - 0.01 - 0.63 0.35 0.00 0.00 Gn59 0.20 - 0.34 - 75.21 22.47 - 0.05 98.27 0.01 - 0.01 - 0.65 0.33 - 0.00 Gn43 0.20 - 0.23 - 75.67 22.31 - - 98.41 0.01 - 0.01 - 0.66 0.33 - - Gn65 0.37 - 0.19 - 76.93 22.51 - 0.08 100.08 0.01 - 0.01 - 0.65 0.33 - 0.00 Gn33 0.10 - 0.82 - 77.59 19.36 - 0.14 98.01 0.00 - 0.03 - 0.67 0.29 - 0.01 Gn66 0.36 0.09 0.65 - 77.96 20.59 - 0.13 99.78 0.01 0.00 0.02 - 0.66 0.30 - 0.01 Gn66 0.51 0.03 0.98 - 78.94 20.98 - 0.12 101.56 0.01 0.00 0.03 - 0.65 0.30 - 0.01 Gn44 0.10 - 0.16 - 79.27 19.83 - 0.05 99.41 0.00 - 0.01 - 0.69 0.30 - 0.00 Gn35 0.09 0.07 0.21 - 79.53 19.09 0.04 - 99.03 0.00 0.00 0.01 - 0.70 0.29 0.00 - Gn40 - - 0.65 - 80.34 17.39 - 0.10 98.48 - - 0.02 - 0.71 0.26 - 0.01 Gn12 0.08 - 0.66 - 85.20 15.64 - 0.10 101.68 0.00 - 0.02 - 0.74 0.23 - 0.01 Gn60 0.09 0.06 0.33 - 88.19 11.60 - 0.11 100.38 0.00 0.00 0.01 - 0.80 0.18 - 0.01 Gn37 - - 0.48 - 88.42 10.85 0.05 0.05 99.85 - - 0.02 - 0.81 0.17 0.00 0.00 Gn30 0.54 - 0.35 - 89.24 9.94 - 0.11 100.18 0.02 - 0.01 - 0.81 0.15 - 0.01 Bs1 - - 0.82 - 89.57 10.51 - 0.13 101.03 - - 0.03 - 0.80 0.16 - 0.01 Gn32 0.76 - 0.78 - 91.36 8.80 - 0.10 101.80 0.02 - 0.03 - 0.81 0.13 - 0.01 Gn15 0.38 0.04 0.71 - 93.31 4.32 0.04 0.22 99.02 0.01 0.00 0.02 - 0.88 0.07 0.00 0.01 Gn29 0.16 - 0.76 - 94.27 4.37 - 0.17 99.73 0.00 - 0.03 - 0.89 0.07 - 0.01 Gn31 0.53 - 0.49 - 94.72 5.05 - 0.14 100.93 0.02 - 0.02 - 0.88 0.08 - 0.01 nBi1 0.13 - 0.24 - 96.84 3.01 - - 100.22 0.00 - 0.01 - 0.94 0.05 - - nBi2 0.17 - 0.14 - 97.62 3.46 - 0.06 101.45 0.01 - 0.00 - 0.93 0.06 - 0.00 Gn72 0.06 - 0.38 - 97.83 0.96 - - 99.23 0.00 - 0.01 - 0.97 0.02 - - Gn71a 0.37 - 0.24 - 98.51 1.00 - - 100.12 0.01 - 0.01 - 0.96 0.02 - - Gn73 0.57 - 0.54 - 98.69 1.29 - 0.05 101.14 0.02 - 0.02 - 0.94 0.02 - 0.00 Gn84 0.31 0.04 0.23 - 98.78 1.37 0.04 - 100.77 0.01 0.00 0.01 - 0.96 0.02 0.00 - Gn71b 0.30 - 0.20 - 98.83 0.89 - - 100.22 0.01 - 0.01 - 0.97 0.01 - - Gn74 0.32 - 0.21 - 98.89 1.05 0.04 - 100.51 0.01 - 0.01 - 0.96 0.02 0.00 - Native bismuth nBi5 - - 0.04 - 99.66 - - - 99.70 - - 0.00 - 1.00 - - - nBi11 - - 0.09 - 98.69 0.05 - - 98.83 - - 0.00 - 1.00 0.00 - - nBi8 0.03 - 0.02 - 99.11 - - - 99.16 0.00 - 0.00 - 1.00 - - - nBi9 - - 0.03 - 99.45 - - - 99.48 - - 0.00 - 1.00 - - - nBi6 0.10 - 0.10 - 99.49 - - - 99.69 0.00 - 0.00 - 0.99 - - - nBi12 - - - - 100.35 - 0.04 - 100.39 - - - - 1.00 - 0.00 - nBi3 - - 0.02 - 100.37 - - - 100.39 - - 0.00 - 1.00 - - - nBi13 0.05 - - - 100.65 - - - 100.70 0.00 - - - 1.00 - - - nBi7 0.05 - 0.03 - 100.79 - 0.05 - 100.92 0.00 - 0.00 - 1.00 - 0.00 - nBi10 - 0.04 - - 101.01 0.05 - - 101.10 - 0.00 - - 1.00 0.00 - - Mean 0.06 0.04 0.05 - 99.94 0.05 0.05 - 100.19 0.00 0.00 0.00 - 0.99 0.00 0.00 - (n = 10) “-” below detection limits.

4.2. Sulphosalt Minerals Sulphosalts of the late stage-III mineralisation can be categorised as Bi-sulphosalts (pavonite), Sb-Bi-sulphosalts (tintinaite and terrywallaceite), and Sb-sulphosalts (freibergite, ullmannite, and bournonite). These minerals are discussed in the following subsections. Minerals 2018, 8, 26 9 of 20 Minerals 2018, 8, 26 9 of 20

4.2.1. Pavonite [(Ag,Cu)(Bi,Pb) S ] 4.2.1. Pavonite [(Ag,Cu)(Bi,Pb)3S55] µ Pavonite is is a rarea rare ore ore mineral, mineral, which which occurs occurs with galena withII galena and native II and bismuth native as grainsbismuth ofbetween as grains 5 mof µ andbetween 40 m 5 inμm size and (Figure 40 μm8). in The size BSE (Figure images 8). indicate The BSE that images pavonite indicate formed that earlier pavonite than formed galena IIearlier and nativethan galena bismuth II (Figureand native8b). Thebismuth EPMA (Figure data (Table 8b). 3The) shows EPMA that data pavonite (Table contains 3) shows 67.23–70.24 that pavonite wt % Bi,contains 11.50–12.10 67.23–70.24 wt % wt Ag, % Bi, and 11.50–12.10 18.84–19.43 wt wt % %Ag, S, and with 18.84–19.43 trace amounts wt % S, of with Cu (0.08–0.52trace amounts wt %), of FeCu (0.02–0.43(0.08–0.52 wt wt %), %), Pb Fe (<0.02–0.43 (0.02–0.43 wt wt %), %), and Pb Se(<0.02–0.43 (<0.03–0.19 wt wt %), %), and and Se an (<0.03–0.19 average chemical wt %), formulaand an of Ag Cu Fe Bi Pb S Se . average0.95 chemical0.03 0.03formula2.83 of 0.01Ag0.955.14 Cu0.030.02Fe0.03Bi2.83 Pb0.01S5.14Se0.02.

Figure 8. (a) Reflected light photomicrograph of pavonite (Pv) occurring with bismuthinite (Bmt), Figure 8. (a) Reﬂected light photomicrograph of pavonite (Pv) occurring with bismuthinite (Bmt), galena II (Gn-II), and native Bi. Pavonite and associated minerals occur as infilling gangue minerals; galena II (Gn-II), and native Bi. Pavonite and associated minerals occur as inﬁlling gangue minerals; (b) enlarged BSE image of Figure 8a, indicating earlier formation of pavonite than galena II and (b) enlarged BSE image of Figure8a, indicating earlier formation of pavonite than galena II and native bismuth. native bismuth.

Table 3. EPMA data for pavonite. Table 3. EPMA data for pavonite. wt % apfu ∑9 Atoms Analyses wt % apfu ∑9 Atoms Analyses Cu Ag Fe Pb Bi Sb Se S Total Cu Ag Fe Pb Bi Sb Se S pav1 0.11 Cu11.56 Ag 0.07 Fe - Pb70.24 Bi - Sb Se- 19.02 S 100.99 Total Cu0.02 Ag 0.93 Fe 0.01 Pb - Bi2.91 Sb - Se - S 5.13 pav1 0.11 11.56 0.07 - 70.24 -- 19.02 100.99 0.02 0.93 0.01 - 2.91 -- 5.13 pav2pav2 0.32 0.3211.9811.98 0.430.43 0.34 0.34 68.9968.99 - - 0.120.12 19.2419.24 101.42101.42 0.04 0.04 0.95 0.95 0.07 0.07 0.01 0.01 2.81 2.81- -0.01 0.01 5.11 5.11 pav3pav3 0.15 0.1511.7811.78 0.180.18 0.24 0.24 70.1470.14 - - 0.190.19 19.2119.21 101.88101.88 0.02 0.02 0.93 0.93 0.03 0.03 0.01 0.01 2.87 2.87- -0.02 0.02 5.12 5.12 pav4pav4 0.04 0.0412.0012.00 0.020.02 - - 68.6868.68 - -- - 19.0319.03 99.77 0.000.00 0.97 0.97 0.00 0.00- - 2.862.86-- - -5.16 5.16 pav5 0.52 12.10 0.25 - 68.09 -- 19.43 100.39 0.07 0.96 0.04 - 2.78 -- 5.16 pav5pav6 0.52 0.0812.1011.50 0.250.20 - 0.4368.0967.23 - - 0.16 - 19.4318.84 100.3998.44 0.01 0.07 0.94 0.96 0.03 0.04 0.02 - 2.832.78- -0.02 - 5.16 5.16 pav6Mean (n = 6)0.08 0.2211.5011.87 0.200.22 0.43 0.33 67.2368.62 - - 0.160.15 18.8419.15 100.38 98.44 0.03 0.01 0.95 0.94 0.03 0.03 0.01 0.02 2.83 2.83- -0.02 0.02 5.14 5.16 Mean (n = 6) 0.22 11.87 0.22 0.33 68.62“-” - below 0.15 detection 19.15 limits. 100.38 0.03 0.95 0.03 0.01 2.83 - 0.02 5.14 “-” below detection limits. 4.2.2. Tintinaite 4.2.2. Tintinaite Tintinaite is widely distributed in the Jialong ores. It predominantly occurs together with Sb-Bi alloys,Tintinaite and a small is widely amount distributed is found with in the native Jialong bismuth. ores. It Grains predominantly are variable occurs in diameter, together ranging with Sb-Bi from severalalloys, andµm toa moresmall thanamount 500 µ ism, found and are with euhedral native to bismuth. subhedral Grains (Figure are9). variable Tintinaite in compositiondiameter, ranging varies andfrom can several be divided μm to into more two than types 500 based μm, on and EPMA are data euhedral (Table 4to): Cu-bearingsubhedral (Type-I)(Figure and9). Tintinaite Cu-poor (Type-II).composition Type-I varies contains and can 1.08–1.33 be divided wt % Cu,into 0.48–0.59 two types wt based % Ag, on 38.06–39.15 EPMA data wt % (Table Pb, 19.50–20.94 4): Cu-bearing wt % Bi,(Type-I) 17.51–18.79 and wtCu-poor % Sb, and(Type-II). 19.26–19.67 Type-I wt %contains S. The average 1.08–1.33 chemical wt formula,% Cu, 0.48–0.59 calculated onwt the% basisAg, 38.06–39.15 wt % Pb, 19.50–20.94 wt % Bi, 17.51–18.79 wt % Sb, and 19.26–19.67 wt % S. The average of ΣS + Se = 35 at., is Cu1.05Fe1.64Pb10.58Ag0.28 Bi5.52Sb8.46S34.54Se0.46. Type-II contains <0.03–0.14 wt % Cu,chemical 36.74–37.53 formula, wt %calcul Pb, 13.37–15.07ated on the wt %basis Bi, 23.71–25.32 of ΣS + wtSe % = Sb, 35 and at., 20.87–21.71 is Cu1.05 wtFe1.64 %Pb S,10.58 withAg an0.28 Bi5.52Sb8.46S34.54Se0.46. Type-II contains <0.03–0.14 wt % Cu, 36.74–37.53 wt % Pb, 13.37–15.07 wt % Bi, average chemical formula of Cu0.04Fe2.51Pb9.35Bi3.53Sb10.67S34.62Se0.38 based on ΣS + Se = 35 at. 23.71–25.32 wt % Sb, and 20.87–21.71 wt % S, with an average chemical formula of Cu0.04Fe2.51Pb9.35Bi3.53Sb10.67S34.62Se0.38 based on ΣS + Se = 35 at.

Minerals 2018, 8, 26 10 of 20 Minerals 2018, 8, 26 10 of 20

Figure 9. Back-scattered electron image showing euhedral to subhedral tintinaite crystal (Tnt) Figure 9. Back-scattered electron image showing euhedral to subhedral tintinaite crystal (Tnt) inﬁlling infilling arsenopyrite (Apy) and pyrrhotite (Po), and partially replaced by galena I (Gn-I) and Sb-Bi arsenopyrite (Apy) and pyrrhotite (Po), and partially replaced by galena I (Gn-I) and Sb-Bi alloys along alloys along the edges and internal fissures of tintinaite and gudmundite (Gd). the edges and internal ﬁssures of tintinaite and gudmundite (Gd). Table 4. EPMA data for tintinaite. Table 4. EPMA data for tintinaite. wt % apfu ΣS + Se 35 Atoms Analyses Cu Fe Pb Ag Bi wt % Sb S Se Total Cu Fe apfu PbΣS + Ag Se 35Bi Atoms Sb S Se Analyses Type-I Cu Fe Pb Ag Bi Sb S Se Total Cu Fe Pb Ag Bi Sb S Se gn18 1.11Type-I 2.53 38.510.48 19.50 18.79 19.67 0.55 101.14 0.98 2.55 10.48 0.25 5.26 8.70 34.61 0.39 tnt4 gn181.33 1.391.11 39.150.562.53 38.51 0.4819.5619.50 18.39 18.79 19.31 19.67 0.550.55 100.25101.14 1.20 0.98 2.551.43 10.48 10.85 0.25 0.30 5.26 5.388.70 8.6834.61 34.60 0.39 0.40 Tnt5 tnt41.08 1.441.33 37.850.591.39 39.15 0.5620.9419.56 17.54 18.39 19.26 19.31 0.740.55 99.45100.25 0.98 1.201.43 1.48 10.85 10.48 0.30 0.32 5.38 5.758.68 8.2634.60 34.46 0.40 0.54 Tnt5 1.08 1.44 37.85 0.59 20.94 17.54 19.26 0.74 99.45 0.98 1.48 10.48 0.32 5.75 8.26 34.46 0.54 Gn53 Gn531.14 1.071.14 38.060.491.07 38.06 0.4920.9120.91 17.51 17.51 19.38 19.38 0.680.68 99.23 99.23 1.021.02 1.09 10.49 10.49 0.26 0.26 5.71 5.718.21 8.2134.51 34.51 0.49 0.49 Mean (nMean = 4) (n 1.17 = 4) 1.611.17 38.391.61 38.39 0.53 0.53 20.2320.23 18.06 18.06 19. 19.4040 0.630.63 100.01100.01 1.05 1.05 1.64 10.58 10.58 0.28 0.28 5.52 5.528.46 8.4634.54 34.54 0.46 0.46 Type-IIType-II tnt3 tnt30.08 3.130.08 37.090.003.13 37.09 0.0014.2614.26 23.71 23.71 20.93 20.93 0.550.55 99.76 99.76 0.060.06 2.979.49 9.49 0.000.00 3.62 3.62 10.33 10.33 34.63 34.63 0.37 0.37 Gn27 Gn270.07 2.500.07 37.530.002.50 37.53 0.0013.3713.37 25.08 25.08 21.25 21.25 0.380.38 100.17100.17 0.06 0.06 2.359.50 9.50 0.000.00 3.35 3.35 10.80 10.80 34.75 34.75 0.25 0.25 Gn24 Gn240.08 2.690.08 37.130.002.69 37.13 0.0015.0715.07 24.04 24.04 21.12 21.12 0.660.66 100.79100.79 0.07 0.07 2.539.40 9.40 0.000.00 3.78 3.78 10.36 10.36 34.56 34.56 0.44 0.44 Gn28 0.00 2.57 37.13 0.00 13.39 25.65 21.71 0.44 100.88 0.00 2.36 9.19 0.00 3.28 10.80 34.71 0.29 Gn28 Gn30.00 2.570.14 37.130.002.54 37.08 0.0013.3914.22 25.65 25.20 21.71 21.19 0.440.72 100.88101.09 0.00 0.122.38 2.369.35 9.19 0.000.00 3.55 3.28 10.81 10.80 34.52 34.71 0.48 0.29 Gn3 Gn10.14 2.540.03 37.080.002.66 37.03 0.0014.2214.28 25.20 24.69 21.19 20.87 0.720.67 101.09100.23 0.12 0.032.53 2.389.49 9.35 0.000.00 3.63 3.55 10.76 10.81 34.55 34.52 0.45 0.48 Gn23 0.01 2.88 36.96 0.00 14.39 24.73 21.20 0.62 100.79 0.01 2.70 9.33 0.00 3.60 10.62 34.59 0.41 Gn1 Gn20.03 2.660.04 37.030.002.57 36.94 0.0014.2813.92 24.69 25.32 20.87 21.23 0.670.62 100.23100.64 0.03 0.032.40 2.539.31 9.49 0.000.00 3.48 3.63 10.86 10.76 34.59 34.55 0.41 0.45 Gn23 Gn260.01 2.880.00 36.960.002.58 36.74 0.0314.3914.18 24.73 25.27 21.20 21.56 0.620.45 100.79100.81 0.01 0.002.38 2.709.15 9.33 0.010.00 3.50 3.60 10.71 10.62 34.71 34.59 0.29 0.41 Gn2Mean (n0.04 = 9) 2.570.05 36.940.002.68 37.07 0.0013.9214.12 25.32 24.85 21.23 21.23 0.620.57 100.64100.57 0.03 0.042.51 2.409.35 9.31 0.000.00 3.53 3.48 10.67 10.86 34.62 34.59 0.38 0.41 Gn26 0.00 2.58 36.740.03 14.18 25.27“-” below 21.56 detection 0.45 100.81 limits. 0.00 2.38 9.15 0.01 3.50 10.71 34.71 0.29 Mean (n = 9) 0.05 2.68 37.07 0.00 14.12 24.85 21.23 0.57 100.57 0.04 2.51 9.35 0.00 3.53 10.67 34.62 0.38 4.2.3. Terrywallaceite “-” below detection limits.

4.2.3.Terrywallaceite Terrywallaceite is a very rare mineral that occurs in assemblages of galena II and native bismuth. Terrywallaceite was ﬁrst discovered in 2011 [26], and the Jialong deposit is the ﬁrst reported occurrence Terrywallaceite is a very rare mineral that occurs in assemblages of galena II and native in China. Texturally, terrywallaceite formed earlier than galena II and native bismuth (Figure 10). bismuth. Terrywallaceite was first discovered in 2011 [26], and the Jialong deposit is the first EPMA data for terrywallaceite (Table5) indicates that Pb, Ag and S contents are relatively constant reported occurrence in China. Texturally, terrywallaceite formed earlier than galena II and native (20.13–24.36 wt % Pb, 9.49–10.26 wt % Ag, 18.04–20.03 wt % S), while Bi and Sb contents are variable bismuth (Figure 10). EPMA data for terrywallaceite (Table 5) indicates that Pb, Ag and S contents are (27.43–41.33 wt % Bi, 8.74–19.08 wt % Sb). In addition, terrywallaceite contains trace amounts of Fe relatively constant (20.13–24.36 wt % Pb, 9.49–10.26 wt % Ag, 18.04–20.03 wt % S), while Bi and Sb (0.15–1.13 wt %), Cu (0.04–0.96 wt %), As (0.14–0.31 wt %), and Se (0.53–1.18 wt %), with an average contents are variable (27.43–41.33 wt % Bi, 8.74–19.08 wt % Sb). In addition, terrywallaceite contains chemical formula of Ag0.91Pb1.04Cu0.07Fe0.10Bi1.64Sb1.15As0.03S5.96Se0.10, similar to the ideal chemical trace amounts of Fe (0.15–1.13 wt %), Cu (0.04–0.96 wt %), As (0.14–0.31 wt %), and Se formula of AgPb(Sb,Bi)3S6. (0.53–1.18 wt %), with an average chemical formula of Ag0.91Pb1.04Cu0.07Fe0.10Bi1.64Sb1.15As0.03S5.96Se0.10, similar to the ideal chemical formula of AgPb(Sb,Bi)3S6.

Minerals 2018, 8, 26 11 of 20

Figure 10. Reflected light photomicrograph (a) and back-scattered electron image (b) of Figure 10. Reflected light photomicrograph (a) and back-scattered electron image (b) of terrywallaceite. terrywallaceite. (a) Terrywallaceite (Trr) with galena II (Gn-II) and native bismuth (nBi) infill along (a) Terrywallaceitethe edge of chalcopyrite (Trr) with (Ccp) galena and pyrrhotite II (Gn-II) (Po); and (b native) enlarged bismuth BSE image (nBi) of infill Figure along 10a, showing the edge of chalcopyritegalena II replacing (Ccp) and terrywallaceite pyrrhotite (Po);and native (b) enlarged bismuth infilling BSE image terrywallaceite of Figure and10a, chalcopyrite. showing galena II replacing terrywallaceite and native bismuth infilling terrywallaceite and chalcopyrite. Table 5. EPMA data for terrywallaceite. Table 5. EPMA data for terrywallaceite. wt % apfu Σ11 Atoms Analyses Pb Ag Fe Cu Bi Sb As Se S Total Pb Ag Fe Cu Bi Sb As Se S wt % apfu Σ11 Atoms Gn77aAnalyses 20.53 9.76 0.810.37 41.33 8.74 0.14 1.18 18.04 100.90 1.03 0.94 0.15 0.06 2.05 0.75 0.02 0.16 5.85 Gn78a 20.13Pb 9.86 Ag 0.820.27 Fe Cu 38.93 Bi 11.29 Sb 0.17 As 0.70 Se 18.72 S 100.89 Total 0.99 Pb 0.93 Ag 0.15 Fe 0.04 Cu 1.89 Bi 0.94 Sb 0.02 As Se0.09 5.94 S Gn79aGn77a 21.3620.53 10.129.76 0.800.81 0.960.37 30.6941.33 16.508.74 0.230.14 0.691.18 19.6218.04 100.97 100.90 1.00 1.03 0.91 0.94 0.14 0.15 0.15 0.06 1.43 2.05 1.32 0.75 0.03 0.02 0.160.09 5.85 5.94 Gn81aGn78a 20.4720.13 9.909.86 0.150.040.82 0.27 34.8238.93 14.24 11.29 0.23 0.17 0.590.70 19.4118.72 99.84 100.89 0.99 0.99 0.92 0.93 0.03 0.15 0.01 0.04 1.68 1.89 1.18 0.94 0.03 0.02 0.090.08 5.94 6.09 Gn79a 21.36 10.12 0.80 0.96 30.69 16.50 0.23 0.69 19.62 100.97 1.00 0.91 0.14 0.15 1.43 1.32 0.03 0.09 5.94 Gn85aGn81a 21.9220.47 10.269.90 0.490.15 0.180.04 27.7734.82 19.08 14.24 0.31 0.23 0.570.59 20.0319.41 100.6099.84 1.020.99 0.92 0.92 0.09 0.03 0.03 0.01 1.28 1.68 1.51 1.18 0.04 0.03 0.080.07 6.09 6.04 Gn86aGn85a 20.2921.92 10.22 10.26 0.42 0.49 0.610.18 34.4427.77 14.30 19.08 0.20 0.31 0.640.57 19.0920.03 100.20 100.60 0.98 1.02 0.95 0.92 0.08 0.09 0.10 0.03 1.65 1.28 1.18 1.51 0.03 0.04 0.070.08 6.04 5.96 Gn87aGn86a 20.4620.29 9.83 10.22 1.130.25 0.42 0.61 36.8634.44 12.24 14.30 0.24 0.20 0.530.64 19.0019.09 100.54 100.20 0.99 0.98 0.92 0.95 0.20 0.08 0.04 0.10 1.77 1.65 1.01 1.18 0.03 0.03 0.080.07 5.96 5.96 Gn106aGn87a 20.4120.46 9.669.83 0.420.401.13 0.25 37.5936.86 11.71 12.24 0.17 0.24 0.960.53 18.7419.00 100.05 100.54 1.01 0.99 0.91 0.92 0.08 0.20 0.06 0.04 1.84 1.77 0.98 1.01 0.02 0.03 0.070.12 5.96 5.97 Gn107aGn106a 24.3620.41 9.499.66 0.350.460.42 0.40 27.4337.59 17.54 11.71 0.25 0.17 1.030.96 19.3818.74 100.28 100.05 1.16 1.01 0.87 0.91 0.06 0.08 0.07 0.06 1.29 1.84 1.42 0.98 0.03 0.02 0.120.13 5.97 5.96 Gn107a 24.36 9.49 0.35 0.46 27.43 17.54 0.25 1.03 19.38 100.28 1.16 0.87 0.06 0.07 1.29 1.42 0.03 0.13 5.96 Mean (n = 9) 21.38 9.80 0.58 0.43 34.08 13.95 0.21 0.79 19.05 100.27 1.04 0.91 0.10 0.07 1.64 1.15 0.03 0.10 5.96 Mean (n = 9) 21.38 9.80 0.58 0.43 34.08 13.95 0.21 0.79 19.05 100.27 1.04 0.91 0.10 0.07 1.64 1.15 0.03 0.10 5.96 4.2.4. Freibergite 4.2.4. Freibergite Freibergite is abundant within the Jialong ores and occurs together with native bismuth. FreibergiteFreibergite grains is abundant are irregularly within shaped the Jialong and range ores from and several occurs μ togetherm to 100 with μm nativein diameter. bismuth. FreibergiteTexturally, grains freibergite are irregularly is incorporated shaped in, and but range formed from earlier several than,µm galena to 100 IIµ (Figurem in diameter. 11). Freibergite Texturally, freibergite(Table 6) is incorporatedcontains 20.85–23.06 in, but wt formed % Cu, earlier 19.44–22.09 than, galenawt % IIAg, (Figure 25.77–27.64 11). Freibergite wt % Sb, (Tableand 6) contains23.22–24.26 20.85–23.06 wt % S, wt with % Cu, small 19.44–22.09 amounts of wt Fe % (5.46– Ag, 25.77–27.646.26 wt %), As wt (0.43–0.53 % Sb, and wt 23.22–24.26 %) and Bi (0.15–0.26 wt % S, with smallwt amounts %), and has of Fean mean (5.46–6.26 chemical wt %),formula As (0.43–0.53 of Ag3.40Cu wt6.32Fe %)1.92 andB0.02Sb Bi3.95 (0.15–0.26As0.12S13.27Se wt0.01 %),. and has an mean chemical formula of Ag3.40Cu6.32Fe1.92B0.02Sb3.95As0.12S13.27Se0.01. Minerals 2018, 8, 26 Table 6. EPMA data for freibergite. 12 of 20

wt % apfu Σ29 Atoms Analyses Cu Ag Fe Pb Bi Sb As Se S Total Cu Ag Fe Pb Bi Sb As Se S Yc9 22.65 19.48 5.89 0.12 0.26 25.94 0.51 0.05 23.76 98.65 6.44 3.26 1.90 0.01 0.02 3.85 0.12 0.01 13.38 Yc17 22.98 19.44 5.99 0.05 0.22 25.77 0.43 0.05 23.33 98.26 6.57 3.27 1.95 0.00 0.02 3.85 0.10 0.01 13.22 Gn94a 21.40 22.09 6.26 0.06 0.20 25.65 0.48 - 23.57 99.71 6.08 3.70 2.02 0.00 0.02 3.80 0.12 - 13.27 Gn95a 20.85 21.96 5.99 - 0.16 27.31 0.50 0.06 23.51 100.33 5.93 3.68 1.94 - 0.01 4.05 0.12 0.01 13.25 Yc11 22.93 19.29 6.02 - 0.09 26.08 0.53 0.04 23.51 98.48 6.53 3.24 1.95 - 0.01 3.87 0.13 0.01 13.27 Yc14 22.39 20.15 5.78 0.03 0.17 27.64 0.48 - 23.43 100.08 6.36 3.37 1.87 0.00 0.01 4.09 0.12 - 13.18 Yc13 21.99 20.37 5.46 0.07 0.15 27.33 0.51 - 23.22 99.10 6.32 3.45 1.78 0.01 0.01 4.10 0.12 - 13.21 Yc16 21.82 20.44 6.05 - 0.15 27.51 0.48 0.03 23.54 100.02 6.19 3.42 1.95 - 0.01 4.07 0.12 0.01 13.23 Yc16 22.03 20.72 6.19 0.02 0.24 25.40 0.51 - 23.44 98.56 6.29 3.49 2.01 0.00 0.02 3.79 0.12 - 13.27 Yc18 23.06 19.94 5.91 0.11 0.20 27.56 0.44 0.05 24.26 101.53 6.40 3.26 1.87 0.01 0.02 3.99 0.10 0.01 13.34 Yc17 22.53 19.80 5.77 - 0.16 27.29 0.52 0.04 23.73 99.84 6.37 3.30 1.86 - 0.01 4.03 0.12 0.01 13.30 Mean (n = 11) 22.24 20.33 5.94 0.07 0.18 26.68 0.49 0.05 23.57 99.50 6.32 3.40 1.92 0.01 0.02 3.95 0.12 0.01 13.27 “-” below detection limits. Figure 11. Reflected light photomicrograph of freibergite (Fr) associated with galena II (Gn-II) and Figurenative 11. bismuthReﬂected (Bi), light infilling photomicrograph cavities between of pyrr freibergitehotite (Po) (Fr) crystals associated and partially with galena replacing II (Gn-II) them. and nativeThe bismuth image shows (Bi), freibergite inﬁlling cavities grains enclosed between by pyrrhotite galena II. (Po) crystals and partially replacing them. The image shows freibergite grains enclosed by galena II. 4.2.5. Ullmannite Ullmannite is scarce in the Jialong ore samples and occurs with galena II and native bismuth in the interstices of pyrrhotite crystals (Figure 12). Ullmannite has a higher reflectance than galena and a lower hardness than pyrrhotite. The analyses shows amounts of 0.42–0.87 wt % Fe, 0.43–1.64 wt % Bi, 1.01–1.16 wt % As and 0.20–0.40 wt % Se (Table 7), with an average chemical formula of Ni0.97Fe0.02Sb0.97As0.03Bi0.01S1.00Se0.01.

Table 7. EPMA data for ullmannite.

Figure 12. Reflected light photomicrograph of ullmannite (Ul), showing ullmannite infill in pyrrhotite fissures (Po). Mineral abbreviation: Fr = freibergite, Gn-II = galena II, and Bi = native bismuth.

Minerals 2018, 8, 26 12 of 20

Figure 11. Reflected light photomicrographTable 6. EPMA of freibergite data for freibergite. (Fr) associated with galena II (Gn-II) and native bismuth (Bi), infilling cavities between pyrrhotite (Po) crystals and partially replacing them. The image shows freibergite grainswt enclosed % by galena II. apfu Σ29 Atoms Analyses Cu Ag Fe Pb Bi Sb As Se S Total Cu Ag Fe Pb Bi Sb As Se S 4.2.5. UllmanniteYc9 22.65 19.48 5.89 0.12 0.26 25.94 0.51 0.05 23.76 98.65 6.44 3.26 1.90 0.01 0.02 3.85 0.12 0.01 13.38 Yc17 22.98 19.44 5.99 0.05 0.22 25.77 0.43 0.05 23.33 98.26 6.57 3.27 1.95 0.00 0.02 3.85 0.10 0.01 13.22 Gn94aUllmannite21.40 is scarce 22.09 6.26 in 0.06the Jialong 0.20 25.65 ore 0.48samples- and23.57 occurs99.71 6.08with 3.70 galena 2.02 0.00 II and 0.02 native 3.80 0.12 bismuth- 13.27 in Gn95a 20.85 21.96 5.99 - 0.16 27.31 0.50 0.06 23.51 100.33 5.93 3.68 1.94 - 0.01 4.05 0.12 0.01 13.25 the intersticesYc11 22.93 of pyrrhotite 19.29 6.02 crystals- 0.09 (Figure26.08 0.5312). 0.04Ullmannite23.51 98.48 has 6.53a higher 3.24 1.95 reflectance- 0.01 3.87 than 0.13 galena 0.01 13.27 and a lowerYc14 hardness22.39 than 20.15 pyrrhotite. 5.78 0.03 0.17The 27.64analyses 0.48 sh- ows23.43 amounts 100.08 6.36of 0.42–0.87 3.37 1.87 0.00 wt 0.01% Fe, 4.09 0.43–1.64 0.12 - 13.18wt % Yc13 21.99 20.37 5.46 0.07 0.15 27.33 0.51 - 23.22 99.10 6.32 3.45 1.78 0.01 0.01 4.10 0.12 - 13.21 Bi, 1.01–1.16Yc16 21.82wt % 20.44 As 6.05and -0.20–0.40 0.15 27.51 wt % 0.48 Se0.03 (Table23.54 7), 100.02 with 6.19 an 3.42 average 1.95 - chemical0.01 4.07 0.12 formula 0.01 13.23 of Yc16 22.03 20.72 6.19 0.02 0.24 25.40 0.51 - 23.44 98.56 6.29 3.49 2.01 0.00 0.02 3.79 0.12 - 13.27 0.97 0.02 0.97 0.03 0.01 1.00 0.01 Ni FeYc18 Sb 23.06As 19.94Bi S 5.91 Se0.11. 0.20 27.56 0.44 0.05 24.26 101.53 6.40 3.26 1.87 0.01 0.02 3.99 0.10 0.01 13.34 Yc17 22.53 19.80 5.77 - 0.16 27.29 0.52 0.04 23.73 99.84 6.37 3.30 1.86 - 0.01 4.03 0.12 0.01 13.30 Mean (n = 11) 22.24 20.33 5.94 0.07 0.18Table26.68 7. EPMA 0.49 0.05 data 23.57for ullmannite.99.50 6.32 3.40 1.92 0.01 0.02 3.95 0.12 0.01 13.27 “-” below detection limits. wt % apfu Σ3 Atoms Analyses Ni Fe Zn Bi Sb As S Se Total Ni Fe Zn Bi Sb As S Se 4.2.5.Gn89a Ullmannite 27.41 0.540.06 0.47 56.46 1.13 15.08 0.24 101.40 0.98 0.02 0.00 0.00 0.97 0.03 0.99 0.01 Gn92dUllmannite 26.53 is scarce0.420.08 in the0.43 Jialong 56.06 ore 1.07 samples 15.04 0.20 and 99.82occurs 0.96 with 0.02 galena 0.00 II 0.00 and native0.98 0.03 bismuth 1.00 0.01 in theGn90a interstices 26.89 of pyrrhotite 0.87- crystals1.64 55.801.13 (Figure 12 15.18). Ullmannite 0.40 101.89 has a0.96 higher 0.03 reﬂectance - 0.02 0.96 than 0.03 galena 0.99 and 0.01 a Gn92b 27.22 0.56- 0.53 53.891.16 15.26 0.35 98.99 0.98 0.02 - 0.01 0.94 0.03 1.01 0.01 lower hardness than pyrrhotite. The analyses shows amounts of 0.42–0.87 wt % Fe, 0.43–1.64 wt % Gn92a 26.47 0.450.07 0.69 56.04 1.01 15.03 0.26 100.03 0.96 0.02 0.00 0.01 0.98 0.03 1.00 0.01 Bi, 1.01–1.16 wt % As and 0.20–0.40 wt % Se (Table7), with an average chemical formula of Mean (n = 5) 26.90 0.57 0.07 0.75 55.65 1.10 15.12 0.29 100.43 0.97 0.02 0.00 0.01 0.97 0.03 1.00 0.01 Ni Fe Sb As Bi S Se . 0.97 0.02 0.97 0.03 0.01 1.00 0.01 “-” below detection limits.

Figure 12. Reflected light photomicrograph of ullmannite (Ul), showing ullmannite infill in Figure 12. Reflected light photomicrograph of ullmannite (Ul), showing ullmannite infill in pyrrhotite pyrrhotite fissures (Po). Mineral abbreviation: Fr = freibergite, Gn-II = galena II, and Bi = native fissures (Po). Mineral abbreviation: Fr = freibergite, Gn-II = galena II, and Bi = native bismuth. bismuth.

Table 7. EPMA data for ullmannite.

wt % apfu Σ3 Atoms Analyses Ni Fe Zn Bi Sb As S Se Total Ni Fe Zn Bi Sb As S Se Gn89a 27.41 0.54 0.06 0.47 56.46 1.13 15.08 0.24 101.40 0.98 0.02 0.00 0.00 0.97 0.03 0.99 0.01 Gn92d 26.53 0.42 0.08 0.43 56.06 1.07 15.04 0.20 99.82 0.96 0.02 0.00 0.00 0.98 0.03 1.00 0.01 Gn90a 26.89 0.87 - 1.64 55.80 1.13 15.18 0.40 101.89 0.96 0.03 - 0.02 0.96 0.03 0.99 0.01 Gn92b 27.22 0.56 - 0.53 53.89 1.16 15.26 0.35 98.99 0.98 0.02 - 0.01 0.94 0.03 1.01 0.01 Gn92a 26.47 0.45 0.07 0.69 56.04 1.01 15.03 0.26 100.03 0.96 0.02 0.00 0.01 0.98 0.03 1.00 0.01 Mean (n = 5) 26.90 0.57 0.07 0.75 55.65 1.10 15.12 0.29 100.43 0.97 0.02 0.00 0.01 0.97 0.03 1.00 0.01 “-” below detection limits. Minerals 2018, 8, 26 13 of 20 Minerals 2018, 8, 26 13 of 20 4.2.6. Bournonite 4.2.6. Bournonite Bournonite is a common sulphosalt in the Jialong ores with a variable size from several µm Bournonite is a common sulphosalt in the Jialong ores with a variable size from several μm to to more than 300 µm. Texturally, grain contacts of bournonite are inﬁlled by tintinaite, galena I, more than 300 μm. Texturally, grain contacts of bournonite are infilled by tintinaite, galena I, and and Sb-Bi alloys (Figure 13). According to the EPMA data, the mineral contains 40.29–41.27 wt % Sb-Bi alloys (Figure 13). According to the EPMA data, the mineral contains 40.29–41.27 wt % Pb, Pb, 12.02–13.18 wt % Cu, 23.14–24.56 wt % Sb, and 19.84–20.69 wt % S, with trace amounts of Bi 12.02–13.18 wt % Cu, 23.14–24.56 wt % Sb, and 19.84–20.69 wt % S, with trace amounts of Bi (0.72–1.17 wt %), Fe (0.15–1.10 wt %), As (0.33–0.44 wt %) and Se (0.43–0.77 wt %) (Table8), and an (0.72–1.17 wt %), Fe (0.15–1.10 wt %), As (0.33–0.44 wt %) and Se (0.43–0.77 wt %) (Table 8), and an average chemical formula of Pb0.95Cu0.96Fe0.04Bi0.02Sb0.94As0.02S3.03Se0.04. average chemical formula of Pb0.95Cu0.96Fe0.04Bi0.02Sb0.94As0.02S3.03Se0.04.

Figure 13. Back-scattered electron images of bournonite and associated minerals. (a) Bournonite Figure 13. Back-scattered electron images of bournonite and associated minerals. (a) Bournonite (Bnn) (Bnn) infilled by Sb-Bi alloys and galena I along edges and internal fissures; and (b) irregular infilled by Sb-Bi alloys and galena I along edges and internal fissures; and (b) irregular bournonite bournonite replaced or infilled by galena I and Sb-Bi alloys. replaced or infilled by galena I and Sb-Bi alloys. Table 8. EPMA data for bournonite. Table 8. EPMA data for bournonite. wt % apfu Σ6 Atoms Analyses Pb Bi Cu Fe Ag Sbwt %As S Se Total Pb Bi Cu apfu Fe ΣAg6 Atoms Sb As S Se Analyses Gn9a 41.27 1.05Pb 12.560.36 Bi Cu Fe- 23. Ag62 0.41 Sb 19.90 As S 0.77 Se 99.92 Total 0.97 Pb 0.02 Bi 0. Cu96 0.03 Fe Ag- Sb0.94 As 0.03 S 3.01 Se 0.05 Gn10a Gn9a40.86 0.8141.27 12.730.391.05 12.56 0.36- 23. -39 23.620.34 19.84 0.41 19.90 0.680.77 99.04 99.92 0.960.97 0.02 0.02 0. 0.9698 0.03 0.03 - - 0.940.94 0.03 0.02 3.01 3.01 0.05 0.04 Gn11aGn10a 40.32 0.9140.86 13.180.270.81 12.73 0.39- 23. -19 23.390.33 19.93 0.34 19.84 0.570.68 98.69 99.04 0.950.96 0.02 0.02 1. 0.9801 0.02 0.03 - - 0.940.93 0.02 0.02 3.01 3.02 0.04 0.03 Gn11a 40.32 0.91 13.18 0.27 - 23.19 0.33 19.93 0.57 98.69 0.95 0.02 1.01 0.02 - 0.93 0.02 3.02 0.03 Gn17aGn17a 40.29 1.1740.29 12.021.101.17 12.02 1.10- 23. -32 23.320.36 20.39 0.36 20.39 0.630.63 99.27 99.27 0.930.93 0.03 0.03 0. 0.9191 0.09 0.09 - - 0.920.92 0.02 0.02 3.05 3.05 0.04 0.04 Gn51aGn51a 41.17 0.7241.17 12.670.72 0.8812.67 0.88 - 23.14 - 23.140.44 20.69 0.44 20.69 0.580.58 100.29100.29 0.94 0.94 0.02 0.02 0.95 0.95 0.07 0.07 - - 0.900.90 0.03 0.03 3.06 3.06 0.03 0.03 Gn52a 41.08 0.94 12.21 0.20 - 25.15 0.37 20.65 0.69 101.28 0.94 0.02 0.91 0.02 - 0.98 0.02 3.06 0.04 Gn52aGn54a 41.08 0.9440.76 12.211.15 0.2013.09 0.15 - 25.15 - 24.560.37 20.65 0.42 20.01 0.690.43 101.28100.57 0.94 0.95 0.02 0.03 0.91 0.99 0.02 0.01 - - 0.970.98 0.03 0.02 3.00 3.06 0.03 0.04 Gn54aGn56a 40.76 1.1540.78 13.091.15 0.1513.03 0.28 - 24.56 - 24.470.42 20.01 0.36 19.93 0.430.52 100.57100.54 0.95 0.95 0.03 0.03 0.99 0.99 0.01 0.02 - - 0.970.97 0.02 0.03 2.99 3.00 0.03 0.03 Gn56aMean 40.78 (8) 1.1540.81 13.030.99 0.2812.69 0.45 - 24.47 - 23.860.36 19.93 0.38 20.17 0.520.61 100.54 99.95 0.950.95 0.03 0.02 0.99 0.96 0.02 0.04 - - 0.940.97 0.02 0.02 3.03 2.99 0.04 0.03 Mean (8) 40.81 0.99 12.69 0.45 - 23.86 0.38“-” below 20.17 detection 0.61 99.95 limits. 0.95 0.02 0.96 0.04 - 0.94 0.02 3.03 0.04 “-” below detection limits. 4.3. Associated Sulphides and Rare Minerals 4.3. Associated Sulphides and Rare Minerals Other minerals associated with Sb-Bi alloys and sulphosalts are galena, gudmundite bismuthinite Other minerals associated with Sb-Bi alloys and sulphosalts are galena, gudmundite (Bi2S3), unnamed (BiS), and scarce nisbite. bismuthinite (Bi2S3), unnamed (BiS), and scarce nisbite. 4.3.1. Galena 4.3.1. Galena Galena is widely distributed in the Jialong ore samples and mostly comprises anhedral grains rangingGalena from is widely several distributed to tens of micrometres.in the Jialong ore According samples toand mineral mostly assemblagescomprises anhedral and chemical grains rangingcompositions, from several two types to oftens galena of micrometres. are identified According (galena I to and mineral galena assemblages II). Galena I and is intergrown chemical withcompositions, Sb-Bi alloys two and types contains of galena 0.30–0.47 are identified wt % Bi (galena and 0.87–1.49 I and galena wt % II). Se, Galena while galena I is intergrown II occurs with Sb-Bibismuthinite alloys and and contains native bismuth, 0.30–0.47 and wt contains% Bi and 1.66–2.80 0.87–1.49 wt wt % Bi% andSe, while 1.92–3.14 galena wt %II occurs Se (Table with9). bismuthiniteIn addition, galenaand native II has bismuth, more Ag and than contains galena 1.66–2.80 I. The data wt % show Bi and some 1.92–3.14 substitutions wt % Se of (Table Bi and 9). Ag In addition,for 2 Pb. galena II has more Ag than galena I. The data show some substitutions of Bi and Ag for 2 Pb.

Minerals 2018, 8, 26 14 of 20 Minerals 2018, 8, 26 14 of 20

TableTable 9. 9.EPMA EPMA data for for galena. galena. wt % apfu ∑2 Atoms Analyses wt % apfu ∑2 Atoms Analyses Pb Fe Cu Ag Bi Sb Se S Total Pb Fe Cu Ag Bi Sb Se S Galena I Pb Fe Cu Ag Bi Sb Se S Total Pb Fe Cu Ag Bi Sb Se S GalenaG13 I 84.09 0.180.25 0.06 0.36- 1.4213.48 99.84 0.95 0.01 0.01 0.00 0.00 - 0.04 0.98 G13G14 84.0983.680.18 0.380.19 0.25 0.06 0.06 0.360.47- - 1.3713.73 1.42 13.48 99.8899.84 0.940.95 0.02 0.01 0.010.01 0.000.00 0.01 0.00 - -0.04 0.04 0.990.98 G14G15 83.68 84.320.38 0.63 0.19 - 0.060.12 0.470.47 - - 1.48 1.37 13.5713.73 100.5999.88 0.940.94 0.03 0.02 0.01 - 0.000.00 0.01 0.01 - -0.04 0.04 0.980.99 G15 84.32 0.63 - 0.12 0.47 - 1.48 13.57 100.59 0.94 0.03 - 0.00 0.01 - 0.04 0.98 G16 83.88 0.290.13 0.10 0.42 0.07 1.49 13.71 100.09 0.94 0.01 0.00 0.00 0.00 0.00 0.04 0.99 G16 83.88 0.29 0.13 0.10 0.42 0.07 1.49 13.71 100.09 0.94 0.01 0.00 0.00 0.00 0.00 0.04 0.99 G39G39 84.6384.630.44 0.44- - -- 0.310.31- - 1.3513.27 1.35 13.27100.00 100.00 0.96 0.96 0.02 0.02 - -- - 0.000.00 - -0.04 0.04 0.970.97 G45G45 84.4384.430.27 0.270.18 0.18 0.08 0.08 0.330.33- - 1.3313.24 1.33 13.24 99.8699.86 0.960.96 0.01 0.01 0.010.01 0.000.00 0.00 0.00 - -0.04 0.04 0.970.97 G46G46 84.87 84.870.23 0.23 - - 0.170.17 0.300.30 - - 0.87 0.87 13.8713.87 100. 100.3131 0.95 0.95 0.01 0.01 0.000.00 0.000.00 0.00 0.00 - -0.03 0.03 1.011.01 MeanMean (n = (n 7) = 7)84.27 84.270.35 0.35 0.19 0.19 0.10 0.10 0.38 0.38 0.07 1. 1.3333 13.5513.55 100.20 100.20 0.95 0.95 0.01 0.01 0.010.01 0.000.00 0.00 0.00 0.000.00 0.04 0.04 0.980.98 GalenaGalena II II 0.990.99 G2 G2 81.69 81.69- - 0.180.18 0.96 0.96 2.112.11 - - 2.27 2.27 13.0913.09100.30 100.30 0.92 0.92 -- 0.01 0.01 0.020.02 0.02 0.02 - -0.07 0.07 0.960.96 G4 G4 80.05 80.05- - - - 1.161.16 2.802.80 - - 3.14 3.14 12.6412.64 99.99.7979 0.920.92 --- - 0.030.03 0.03 0.03 - -0.09 0.09 0.930.93 G5 G5 79.17 79.170.08 0.08 - - 1.131.13 2.712.71 - - 2.74 2.74 12.7212.72 98.98.5555 0.910.91 0.00 0.00 - - 0.020.02 0.03 0.03 - -0.08 0.08 0.950.95 G6 82.09 0.50 0.13 0.85 1.66 - 2.11 13.14 100.48 0.92 0.02 0.00 0.02 0.02 - 0.06 0.95 G6 82.09 0.500.13 0.85 1.66- 2.1113.14 100.48 0.92 0.02 0.00 0.02 0.02 - 0.06 0.95 G7 82.68 0.74 0.20 0.60 1.82 - 1.92 13.33 101.29 0.92 0.03 0.01 0.01 0.02 - 0.06 0.96 G8 G7 82.4082.680.36 0.740.20 0.17 0.84 0.60 2.031.82- - 1.9213.33 2.31 12.99101.29 101.10 0.92 0.93 0.03 0.02 0.010.01 0.010.02 0.02 0.02 - -0.06 0.07 0.960.94 G9 G8 82.6182.400.27 0.360.17 0.25 0.70 0.84 1.452.03- - 2.3112.99 2.01 13.48101.10 100.77 0.93 0.92 0.02 0.01 0.010.01 0.020.01 0.02 0.02 - -0.07 0.06 0.940.97 G10 G9 82.0382.610.77 0.270.25 0.21 0.89 0.70 1.951.45- - 2.0113.48 2.13 13.41100.77 101.39 0.92 0.90 0.01 0.03 0.010.01 0.010.02 0.02 0.02 - -0.06 0.06 0.970.95 G76G10 82.8282.030.54 0.770.21 0.06 0.79 0.89 1.881.95- - 2.1313.41 2.14 13.12101.39 101.35 0.90 0.93 0.03 0.02 0.010.00 0.020.02 0.02 0.02 - -0.06 0.06 0.950.95 G82 81.84 0.88 0.05 0.80 1.84 - 2.33 12.93 100.67 0.92 0.04 0.00 0.02 0.02 - 0.07 0.94 G88G76 80.7282.820.72 0.540.06 0.20 0.81 0.79 1.901.88- - 2.1413.12 2.22 13.14 101.3599.71 0.930.91 0.02 0.03 0.000.01 0.020.02 0.02 0.02 - -0.06 0.07 0.950.95 G82 81.84 0.880.05 0.80 1.84- 2.3312.93 100.67 0.92 0.04 0.00 0.02 0.02 - 0.07 0.94 Mean (n = 11) 81.65 0.54 0.16 0.87 2.01 - 2.30 13.09 100.62 0.92 0.02 0.01 0.02 0.02 - 0.07 0.95 G88 80.72 0.720.20 0.81 1.90- 2.2213.14 99.71 0.91 0.03 0.01 0.02 0.02 - 0.07 0.95 “-” below detection limits. Mean (n = 11) 81.65 0.54 0.16 0.87 2.01 - 2.30 13.09 100.62 0.92 0.02 0.01 0.02 0.02 - 0.07 0.95 “-” below detection limits. 4.3.2. Gudmundite 4.3.2. Gudmundite Gudmundite is rarely distributed in the Jialong ore samples. The euhedral grains up to 150 µm are enclosedGudmundite by quartz is rarely or are distributed located at in the the grain Jialong boundaries ore samples. of The arsenopyrite euhedral grains and up gangue to 150 mineralsμm (Figureare 14enclosed). Gudmundite by quartz or contains are located 26.20–27.66 at the grai wtn boundaries % Fe, 56.07–57.06 of arsenopyrite wt % and Sb, gangue 15.67–16.17 minerals wt % S, (Figure 14). Gudmundite contains 26.20–27.66 wt % Fe, 56.07–57.06 wt % Sb, 15.67–16.17 wt % S, and and trace Pb (<0.02–0.05 wt %), Cu (<0.03–0.08 wt %), Bi (<0.05–0.36 wt %), and Se (<0.04–0.11 wt %) trace Pb (<0.02–0.05 wt %), Cu (<0.03–0.08 wt %), Bi (<0.05–0.36 wt %), and Se (<0.04–0.11 wt %) (Table 10), with an average chemical formula of Fe1.00Sb0.96S1.03. (Table 10), with an average chemical formula of Fe1.00Sb0.96S1.03.

Figure 14. Back-scattered electron images of gudmundite. (a) Euhedral to subhedral gudmundite Figuregrains 14. Back-scattered(Gd) enclosed by electron quartz (Qtz); images (b) ofgudmundite gudmundite. infills ( acavities) Euhedral between to subhedral arsenopyrite gudmundite (Apy) grainsand (Gd) muscovite enclosed (Ms) by or quartz cleavage (Qtz); planes (b) of gudmundite muscovite, and inﬁlls is infilled cavities by betweengalena I (Gn-II). arsenopyrite (Apy) and muscovite (Ms) or cleavage planes of muscovite, and is inﬁlled by galena I (Gn-II). Table 10. EPMA data for gudmundite.

4.3.3. Bismuthinite and Unnamed BiSwt % apfu Σ3 Atoms Analyses Fe Pb Cu Bi Ag Sb Se S Total Fe Pb Cu Bi Ag Sb Se S Bismuthinite is associated with native bismuth, galena II, bismuthinite and unnamed BiS, all of Gn19 27.66 - - - - 56.160.07 16.17 100.07 1.02 - - - - 0.95 0.001.04 which appearGn20 filling 27.14 cavities- 0.04 between0.06 - 56.95 chalcopyrite - 15.93 and 100.11 gangue 1.00 minerals - 0.00 0.00 (Figure - 0.97 15 ).- Galena1.03 II, bismuthinite, and unnamed BiS have similar reflectance values (Figure 15). Based on BSE images, the paragenetic sequence of sulphides is: chalcopyrite→bismuthinite→galena II→unnamed BiS→native bismuth. (Figure 15b). The bismuthinite grains, around 40 µm in size, are incorporated in galena II, and fissures in bismuthinite are filled by native bismuth. The bismuthinite contains trace amounts of Minerals 2018, 8, 26 15 of 20 Minerals 2018, 8, 26 15 of 20 Gn21 27.42 - 0.03 0.17 - 56.46 - 15.98 100.06 1.01 - 0.00 0.00 - 0.96 - 1.03 Gn22 27.38 - 0.05 0.36 0.04 56.28 0.11 16.04 100.25 1.01 - 0.00 0.00 0.00 0.95 0.00 1.03 Cu (0.03–0.32Gn25 wt %), 27.59 Fe (<0.02–0.110.050.08 - wt - %),56.99 and Se - (0.08–0.1916.04 100.75 wt 1.01 %), 0.00 with 0.00 an average- - 0.96 chemical - 1.03 formula Gn47 26.33 0.02- - - 57.060.04 15.67 99.12 0.99 0.00 - - - 0.98 0.00 1.03 of Bi1.89Cu0.01S3.09Se0.01 (Table 11). Unnamed BiS is subhedral with grains of 10–30 µm, and formed Gn48 26.47 - - - - 56.73 - 15.78 98.98 0.99 - - - - 0.98 - 1.03 earlier than native bismuth (Figure 15b). Unnamed BiS contains 87.26–89.10 wt % Bi, 11.12–11.36 wt % Gn49 26.20 0.04- - - 56.07 - 15.73 98.04 0.99 0.00 - - - 0.97 - 1.04 S, and traceMean amounts(n = 8) 27.02 of Fe 0.04 (<0.02–0.10 0.05 0.20 0.04 wt %),56.59 Cu 0.07 (<0.02–0.15 15.92 99.91wt 1.00 %), 0.00 and 0.00 Se (<0.02–0.09 0.00 0.00 0.96 wt 0.00 %) 1.03 (Table 11), with an average chemical formula of Bi1.09“-”S below0.90. Thedetection Bi:S limits. ratio is close to 1:1.

4.3.3. Bismuthinite and UnnamedTable BiS 10. EPMA data for gudmundite. Bismuthinite is associated with native bismuth, galena II, bismuthinite and unnamed BiS, all of wt % apfu Σ3 Atoms Analyseswhich appear filling cavities between chalcopyrite and gangue minerals (Figure 15). Galena II, bismuthinite,Fe and Pb unnamed Cu Bi BiS Aghave similar Sb Se reflectance S Total values Fe (Figure Pb 15). Cu Based Bi on Ag BSE Sbimages, Se S Gn19the paragenetic27.66 ---- sequence of sulphides56.16 0.07is: chalcopyrite16.17 100.07→bismuthinite 1.02 - -→galena - -II→unnamed 0.95 0.00 1.04 Gn20BiS→native27.14 bismuth.- 0.04 (Figur 0.06e 15b). - The56.95 bismuthinite- 15.93 grains, 100.11 around 1.00 40- μm 0.00 in size,0.00 are -incorporated 0.97 - 1.03 Gn21 27.42 - 0.03 0.17 - 56.46 - 15.98 100.06 1.01 - 0.00 0.00 - 0.96 - 1.03 Gn22in galena27.38 II, and- fissures 0.05 0.36in bismuthinite 0.04 56.28 are0.11 filled16.04 by 100.25native bismuth. 1.01 - Th 0.00e bismuthinite0.00 0.00 0.95contains 0.00 1.03 Gn25trace amounts27.59 0.05of Cu 0.08(0.03–0.32 - wt -%), Fe56.99 (<0.02–0.11- 16.04 wt %), 100.75 and Se 1.01 (0.08–0.19 0.00 0.00 wt %), - with - an 0.96 average - 1.03 Gn47 26.33 0.02 - - - 57.06 0.04 15.67 99.12 0.99 0.00 - - - 0.98 0.00 1.03 chemical formula of Bi1.89Cu0.01S3.09Se0.01 (Table 11). Unnamed BiS is subhedral with grains of Gn48 26.47 ---- 56.73 - 15.78 98.98 0.99 - - - - 0.98 - 1.03 Gn4910–30 μm,26.20 and0.04 formed - earlier - - than56.07 native- bism15.73uth98.04 (Figure0.99 15b). 0.00 Unna-med - -BiS 0.97contains - 1.04 87.26–89.10 wt % Bi, 11.12–11.36 wt % S, and trace amounts of Fe (<0.02–0.10 wt %), Mean (n = 8) 27.02 0.04 0.05 0.20 0.04 56.59 0.07 15.92 99.91 1.00 0.00 0.00 0.00 0.00 0.96 0.00 1.03 Cu (<0.02–0.15 wt %), and Se (<0.02–0.09 wt %) (Table 11), with an average chemical formula of “-” below detection limits. Bi1.09S0.90. The Bi:S ratio is close to 1:1.

Figure 15. Reflected light photomicrograph (a) and BSE image (b) of the mineral association of Figure 15.nativeReﬂected bismuth light(Bi), photomicrographgalena II (Gn-II), bismuthinite (a) and BSE (Bmt) image and (bthe) of unnamed the mineral BiS mineral, association which of native bismuthappears (Bi), galena filling cavities II (Gn-II), between bismuthinite chalcopyrite (Bmt) (Ccp) and and the gangue unnamed minerals. BiS mineral, which appears ﬁlling cavities between chalcopyrite (Ccp) and gangue minerals. Table 11. EPMA data for bismuthinite and unnamed BiS. Table 11. EPMAwt data % for bismuthinite and unnamed apfu BiS. Σ3 Atoms Analyses Cu Fe Bi Se S Total Cu Fe Bi Se S Bismuthinitewt % apfu∑Σ53 Atomsatoms Analyses Gn98 0.16Cu 0.02 Fe 80.27 Bi 0.12 Se 20.15 S Total100.72 Cu0.01 Fe0.00 Bi1.89 Se0.01 S3.09 Gn99 0.17 Bismuthinite - 80.91 0.15 20.05 101.28 0.01 - ∑5 atoms 1.90 0.01 3.07 Gn100Gn98 0.11 0.16 0.06 0.02 80.09 80.27 0.13 0.12 20.1520.04 100.72100.43 0.010.01 0.000.01 1.891.89 0.010.01 3.093.09 Gn102Gn99 0.22 0.17 0.11 - 79.66 80.91 0.17 0.15 20.0520.08 101.28100.24 0.010.02 -0.01 1.901.88 0.010.01 3.073.08 Gn100 0.11 0.06 80.09 0.13 20.04 100.43 0.01 0.01 1.89 0.01 3.09 Gn103 0.10 0.04 80.41 0.18 20.41 101.14 0.01 0.00 1.88 0.01 3.10 Gn102 0.22 0.11 79.66 0.17 20.08 100.24 0.02 0.01 1.88 0.01 3.08 Gn104Gn103 0.03 0.10 0.05 0.04 80.43 80.41 0.19 0.18 20.4120.06 101.14100.76 0.010.00 0.000.00 1.881.90 0.010.01 3.103.08 Gn105Gn104 0.32 0.03 0.02 0.05 79.62 80.43 0.08 0.19 20.0620.30 100.76100.34 0.000.02 0.000.00 1.901.87 0.010.00 3.083.10 Gn105 0.32 0.02 79.62 0.08 20.30 100.34 0.02 0.00 1.87 0.00 3.10 Gn106 0.18 0.05 80.58 0.08 19.97 100.86 0.01 0.00 1.90 0.01 3.07 Gn106 0.18 0.05 80.58 0.08 19.97 100.86 0.01 0.00 1.90 0.01 3.07 Mean (n = 8) 0.16 0.05 80.25 0.14 20.13 100.73 0.01 0.00 1.89 0.01 3.09 Mean (n = 8) 0.16 0.05 80.25 0.14 20.13 100.73 0.01 0.00 1.89 0.01 3.09 Unnamed BiS apfu ∑2 atoms Unnamed BiS apfu ∑2 atoms

Gn96a 0.15 - 88.71 0.06 11.36 100.28 0.01 - 1.09 0.00 0.91 Gn107 0.11 0.02 88.31 0.09 11.21 99.74 0.00 0.00 1.09 0.00 0.90 Gn108 0.04 - 89.10 0.06 11.16 100.36 0.00 - 1.10 0.00 0.90 Gn109 0.14 0.10 88.55 0.05 11.51 100.35 0.01 0.00 1.08 0.00 0.91 Gn110 - - 88.34 0.08 11.12 99.54 - - 1.10 0.00 0.90 Gn111 - 0.06 87.26 - 11.34 98.66 - 0.00 1.08 - 0.92 Mean (n = 6) 0.11 0.06 88.38 0.07 11.28 99.90 0.00 0.00 1.09 0.00 0.90 “-” below detection limits. Minerals 2018, 8, 26 16 of 20

Gn96a 0.15 - 88.71 0.06 11.36 100.28 0.01 - 1.09 0.00 0.91 Gn107 0.11 0.02 88.31 0.09 11.21 99.74 0.00 0.00 1.09 0.00 0.90 Gn108 0.04 - 89.10 0.06 11.16 100.36 0.00 - 1.10 0.00 0.90 Gn109 0.14 0.10 88.55 0.05 11.51 100.35 0.01 0.00 1.08 0.00 0.91 Gn110 - - 88.34 0.08 11.12 99.54 - - 1.10 0.00 0.90 Gn111 - 0.06 87.26 - 11.34 98.66 - 0.00 1.08 - 0.92 Mean (n = 6) 0.11 0.06 88.38 0.07 11.28 99.90 0.00 0.00 1.09 0.00 0.90 Minerals 2018, 8, 26 “-” below detection limits. 16 of 20

4.3.4. Nisbite 4.3.4. Nisbite Nisbite is a trace mineral in the Jialong ores that coexists with Sb-Bi alloys and native bismuth. Nisbite is a trace mineral in the Jialong ores that coexists with Sb-Bi alloys and native bismuth. It occurs as small grains of 3–20 μm in diameter. Nisbite is surrounded by native bismuth, galena (I It occurs as small grains of 3–20 µm in diameter. Nisbite is surrounded by native bismuth, galena (I or II) or Sb-Bi alloys in complex aggregates that infill interstitial cavities between pyrrhotite grains. or II) or Sb-Bi alloys in complex aggregates that infill interstitial cavities between pyrrhotite grains. The pyrrhotite is partially corroded and infilled by native bismuth (Figure 16a), which also infills The pyrrhotite is partially corroded and infilled by native bismuth (Figure 16a), which also infills galena galena I and Sb-Bi alloys (Figure 16b). Nisbite contains 18.41–19.46 wt % Ni and 77.70–79.82 wt % Sb I and Sb-Bi alloys (Figure 16b). Nisbite contains 18.41–19.46 wt % Ni and 77.70–79.82 wt % Sb with trace with trace amounts of Fe (0.75–2.03 wt %) (Table 12), and an average chemical formula of amounts of Fe (0.75–2.03 wt %) (Table 12), and an average chemical formula of Ni0.99Fe0.09Sb1.90S0.02. Ni0.99Fe0.09Sb1.90S0.02.

Figure 16. Back-scattered electron images of nisbite. (a) Fine nisbite (Ns) incorporated in native bismuthFigure 16. (Bi);Back-scattered (b) nisbite electronfilling pyrrhotite images of nisbite.(Po) fissures (a) Fine and nisbite infilled (Ns) incorporatedby galena I in(Gn-I). native bismuthMineral abbreviation:(Bi); (b) nisbite Fr filling= freibergite, pyrrhotite Bnn (Po)= bour fissuresnonite, and BS-II infilled = Phase by II galena of Sb-Bi I (Gn-I).alloys. Mineral abbreviation: Fr = freibergite, Bnn = bournonite, BS-II = Phase II of Sb-Bi alloys. Table 12. EPMA data for nisbite. Table 12. EPMA data for nisbite. wt % apfu Σ3 Atoms Analyses wt % apfu Σ3 Atoms Analyses Ni Fe Zn Sb Bi S Se Total Ni Fe Zn Sb Bi S Se Gn93 18.88Ni 0.83 Fe 0.13 Zn 79.70 Sb Bi0.21 S 0.20 Se 0.06 Total 100.00 Ni 0.96 Fe 0.04 Zn 0.01 Sb 1.96 Bi 0.00 S 0.02 Se 0.00 Ns1 Gn93 19.1018.88 1.450.83 0.13- 79.8279.70 0.21- 0.200.17 0.06 - 100.00100.540.96 0.96 0.04 0.08 0.01 1.96 - 1.94 0.00 0.02- 0.020.00 - Ns1 19.10 1.45 - 79.82 - 0.17 - 100.54 0.96 0.08 - 1.94 - 0.02 - Ns2 Ns2 18.8118.81 1.951.95 0.04 0.04 77.8277.82 0.080.08 0.25 0.25- - 98.94 98.940.96 0.96 0.10 0.10 0.00 0.00 1.91 1.91 0.00 0.020.00 0.02- - Ns3 19.46 0.75 - 79.03 - 0.13 - 99.37 1.00 0.04 - 1.95 - 0.01 - Ns3 Ns4 19.4618.41 0.752.03 0.22- 79.0377.71 - - 0.360.13 0.08 - 98.81 99.370.94 1.00 0.11 0.04 0.01 1.91 - 1.95- 0.03- 0.010.00 - Ns4Mean (n = 5) 18.4118.93 2.031.40 0.22 0.13 77.7178.82 0.14- 0.220.36 0.07 0.0899.71 98.810.96 0.94 0.07 0.11 0.01 0.01 1.93 1.91 0.00 0.02- 0.030.00 0.00 Mean (n = 5) 18.93 1.40 0.13 78.82 0.14“-” below 0.22 detection 0.07 limits. 99.71 0.96 0.07 0.01 1.93 0.00 0.02 0.00 “-” below detection limits. 5. Discussion 5. Discussion 5.1. Compositional Variations of the Sb-Bi Alloys 5.1. Compositional Variations of the Sb-Bi Alloys Native bismuth is widely distributed in various deposits, e.g., W-Sn deposits [7,16,27,28], Pb-Zn depositsNative [29 bismuth–31], and is widely Au deposits distributed [4,32– in36 various]. On the deposits, other hand,e.g., W-Sn native deposits Sb is [7,16,27,28], less common Pb-Zn and depositsoccurs mostly [29–31], in and Au-Sb Au or deposits Au deposits [4,32–36]. [37– On40], th ande other in trace hand, amounts native Sb in Pb-Znis less common deposits [and41,42 occurs] and mostlySn-polymetallic in Au-Sb deposits or Au [deposits43]. However, [37–40], Sb-Bi and alloys in trace are rarelyamounts reported in Pb-Zn in deposits deposits [15 [41,42]]. Previous and Sn-polymetallicstudies have shown deposits that, in[43]. geological However, processes, Sb-Bi alloys small are amounts rarely ofreported bismuthian in deposits antimony [15]. [15 Previous,17,18] or studiesantimonian have bismuthshown that, [13,15 in, 19geological] are formed. processes, Only tracesmall amounts amounts ofof antimonian bismuthian bismuthantimony (containing [15,17,18] 1.5–13.8 wt % Sb) and bismuthian antimony (containing 13.4 wt % Bi) are present in the Tanco pegmatite in Canada [15]. The Jialong is a rare deposit containing a high abundance of Sb-Bi alloys. The Sb-Bi alloys contain variable Sb and Bi contents ranging from 20.72 wt % to 98.89 wt % Bi and 0.89 wt % to 77.68 wt % Sb. Two phases of Sb-Bi alloys separated by a composition gap are identified (Figure 17a). However, thermodynamic calculations show that Sb-Bi solid solution is a continuous solution [44] that includes the compositions of Phase I and Phase II (Figure 17b). The crystallisation temperature during cooling Minerals 2018, 8, 26 17 of 20 or antimonian bismuth [13,15,19] are formed. Only trace amounts of antimonian bismuth (containing 1.5–13.8 wt % Sb) and bismuthian antimony (containing 13.4 wt % Bi) are present in the Tanco pegmatite in Canada [15]. The Jialong is a rare deposit containing a high abundance of Sb-Bi alloys. The Sb-Bi alloys contain variable Sb and Bi contents ranging from 20.72 wt % to 98.89 wt % Bi and 0.89 wt % to 77.68Minerals wt2018 % Sb., 8, 26 Two phases of Sb-Bi alloys separated by a composition gap are identified (Figure17 17a). of 20 However, thermodynamic calculations show that Sb-Bi solid solution is a continuous solution [44] that includes the compositions of Phase I and Phase II (Figure 17b). The crystallisation temperature is higher for Phase I (Sb-rich member) than Phase II (Bi-rich member) (Figure 17b). Phase I is formed during cooling is higher for Phase I (Sb-rich member) than Phase II (Bi-rich member) (Figure 17b). earlier than Phase II according to textural analysis (Figure5c); the earlier formation also indicates Phase I is formed earlier than Phase II according to textural analysis (Figure 5c); the earlier formation higher formation temperatures for Phase I. Because continuous slow cooling would precipitate the also indicates higher formation temperatures for Phase I. Because continuous slow cooling would full range of solid solutions, the presence of two phases implies multiple steps of non-continuous precipitate the full range of solid solutions, the presence of two phases implies multiple steps of temperature decrease during formation. non-continuous temperature decrease during formation.

Figure 17. (a) In a Diagram of Bi (apfu) versus Sb (apfu) for the Sb-Bi alloys (Phase I and Phase II) Figure 17. (a) In a Diagram of Bi (apfu) versus Sb (apfu) for the Sb-Bi alloys (Phase I and Phase II) showing showing the compositional gap between them. The data of the Loddiswell mine and the Tanco the compositional gap between them. The data of the Loddiswell mine and the Tanco pegmatite pegmatite are from [14] and [15], respectively; (b) Sb-Bi phase diagram (after [45,46]), showing the are from [14,15], respectively; (b) Sb-Bi phase diagram (after [45,46]), showing the temperature temperature and composition gap between Phase I and Phase II. Note that the temperatures that and composition gap between Phase I and Phase II. Note that the temperatures that stabilise the stabilise the Sb-Bi alloys in the pure Sb-Bi system in laboratory conditions are higher than those for Sb-Bi alloys in the pure Sb-Bi system in laboratory conditions are higher than those for the natural the natural metallogenic system. metallogenic system. 5.2. Formation of Sb-Bi Alloys and Sulphosalts during Mineralisation 5.2. Formation of Sb-Bi Alloys and Sulphosalts during Mineralisation The Cu-Sn orebodies in the Jialong deposit are located in the external contact zone of the The Cu-Sn orebodies in the Jialong deposit are located in the external contact zone of the Yuanbaoshan granitic intrusion. All orebodies are less than 600 m from the intrusion boundary. Yuanbaoshan granitic intrusion. All orebodies are less than 600 m from the intrusion boundary. They strike northwest and are controlled by faults. Some studies suggest that ore genesis is related to They strike northwest and are controlled by faults. Some studies suggest that ore genesis is related the presence of ultramafic rocks [47–50] in the JYR. However, because the orebodies are present in to the presence of ultramafic rocks [47–50] in the JYR. However, because the orebodies are present in the contact zone of granite intrusions, the genesis of the Cu-Sn mineralisation system is linked to the the contact zone of granite intrusions, the genesis of the Cu-Sn mineralisation system is linked to the granite intrusions [21,22,51]. granite intrusions [21,22,51]. The analysis of ore petrology in this study indicates that the Jialong deposit experienced four The analysis of ore petrology in this study indicates that the Jialong deposit experienced four mineralisation stages. The Sb-Bi alloys and sulphosalts were formed in Stage III, and infilled cavities mineralisation stages. The Sb-Bi alloys and sulphosalts were formed in Stage III, and infilled cavities in chalcopyrite and pyrrhotite, while bismuthinite, unnamed BiS, and native bismuth formed in in chalcopyrite and pyrrhotite, while bismuthinite, unnamed BiS, and native bismuth formed in Stage IV. Our petrographic evidence shows that the Sb-Bi minerals were formed during the late Stage IV. Our petrographic evidence shows that the Sb-Bi minerals were formed during the late stages of magmatic hydrothermal evolution. This situation is consistent with studies on other Sb-Bi stages of magmatic hydrothermal evolution. This situation is consistent with studies on other Sb-Bi mineral-bearing deposits [7]. In addition, Sb-Bi alloys are not intergrown with bismuthinite, mineral-bearing deposits [7]. In addition, Sb-Bi alloys are not intergrown with bismuthinite, unnamed unnamed BiS, or native bismuth in the Jialong deposit, which implies that Sb-Bi alloys and native BiS, or native bismuth in the Jialong deposit, which implies that Sb-Bi alloys and native bismuth were bismuth were formed at different times. formed at different times. The Sb-Bi phase diagram shows that the formation temperature of Sb-Bi alloys is higher than The Sb-Bi phase diagram shows that the formation temperature of Sb-Bi alloys is higher than that that of native bismuth (Figure 17b). Experiments and evidence from many geological deposits of native bismuth (Figure 17b). Experiments and evidence from many geological deposits indicate that indicate that Bi sulphosalts formed at temperatures of >400–300 °C [1,4,9], while native bismuth and Bi sulphosalts formed at temperatures of >400–300 ◦C[1,4,9], while native bismuth and bismuthinite formed below 271 ◦C. Thus, sulphosalts and Sb-Bi alloys formed at temperatures of 271 to >400 ◦C. Additional evidence shows that the Bi-bearing galena in Stages III and IV formed at higher temperatures than pure galena [1]. Sb-Bi mineral precipitation is affected by temperature, sulphur fugacity, oxygen fugacity, pH, and the solubility of Bi and Sb ions [7]. The precipitation of many sulphides and sulphosalts during the late third stage depleted the fluid of S. This low fS2 fluid could Minerals 2018, 8, 26 18 of 20 then precipitate Sb-Bi alloys and trace amounts of nisbite at high temperature. After formation of Sb-Bi alloys, a later mineralisation stage formed bismuthinite, galena II, unnamed BiS, and native bismuth. The formation of additional sulphur minerals indicates that the fourth stage experienced decreasing fS2, which could support the deposition of native bismuth at lower temperature.

6. Conclusions (1) The Sb-Bi alloys in the Jialong Cu-Sn deposit are 1–20 µm and intergrown with earlier-formed sulphosalts. The alloys formed during the late stages of hydrothermal mineralisation. (2) Seven sulphosalts were identified in the Jialong deposit, including Bi sulphosalt (pavonite), Sb-Bi sulphosalts (tintinaite and terrywallaceite), and Sb sulphosalts (freibergite, ullmanite, bournonite). (3) Two phases of Sb-Bi alloys were identified. The textural relationship indicate that Phase I was formed before Phase II. The composition of Phase I is dominated by Sb, while that of Phase II is dominated by Bi. It is inferred that Sb-Bi alloys formed in a high temperature (271–400 ◦C) and low fS2 environment. The presence of the two phases may indicate multiple steps of cooling during mineralisation. (4) The Jialong deposit is related to granite intrusions. Sulphosalts, Sb-Bi alloys, bismuthinite, and native bismuth were precipitated from the late Sb-Bi-rich fluid during cooling and fluctuating fS2 conditions.

Acknowledgments: This work was jointly supported by the National Natural Science Foundation of China (Grant 41302048) and the Innovation-driven Plan of Central South University (Grant 2015CX008). Jeffrey M. Dick of Central South University is thanked for English polishing. Author Contributions: Jianping Liu, Weikang Chen, and Qingquan Liu conceived and designed the experiments; Weikang Chen performed the experiments; all authors wrote the paper. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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