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Article Trace Element Geochemistry of : Implications for Genesis of the Huanggangliang Sn-Fe Deposit, Inner Mongolia, Northeastern China

Cheng Wang 1,2, Yongjun Shao 1,2, Xiong Zhang 3, Jeffrey Dick 1,2 ID and Zhongfa Liu 1,2,* 1 Key Laboratory of Metallogenic Prediction of Non-Ferrous and Geological Environment Monitoring (Central South University), Ministry of Education, Changsha 410083, China; [email protected] (C.W.); [email protected] (Y.S.); [email protected] (J.D.) 2 School of Geosciences and Info-, Central South University, Changsha 410083, China 3 416 Geological Team, Bureau of and Exploration and Development of Hunan Province, Zhuzhou 412007, China; [email protected] * Correspondence: [email protected]; Tel.: +86-731-888-30616

 Received: 29 December 2017; Accepted: 17 April 2018; Published: 4 May 2018 

Abstract: The Huanggangliang deposit is a super-large Sn-Fe deposit in the Huanggangliang– Ganzhuermiao metallogenic belt in the southern section of the Great Hinggan Range. The Sn-Fe deposits mainly occur in the contact zone and were formed via the interaction of biotite-bearing alkali with strata of the Permian Dashizhai and Zhesi Formations. Based on the intersecting relations among the ore-bearing veins and the different types of mineral assemblages within these veins, the Sn-Fe mineralization could be divided into two periods and four stages: the skarn period, which includes the garnet–diopside–magnetite (T1) stage (stage 1) and epidote–idocrase––magnetite (T2) stage (stage 2); and the –magnetite period, which can be divided into the quartz–cassiterite–magnetite (T3) stage (stage 3) and quartz–magnetite (T4) stage (stage 4). In this paper, we discuss the genesis of magnetite, controlling factors for magnetite compositions, and type of based on petrographic studies and LA-ICP-MS analyses of trace elements in these four types of magnetite from the Huanggangliang Sn-Fe deposit. The results demonstrate that the four types of magnetite are generally depleted in Ti (0.002–3.030 wt %), Al (0.008–1.731 wt %), and Zr (<1.610 ppm). In addition, the low Ni and Cr contents and relatively high and stable Fe contents in the four types of magnetite are indicative of hydrothermal genetic features. Compositions of the ore fluids and host rocks, formation of coexisting minerals, and other physical and chemical parameters (such as f O2) may have influenced the variable magnetite geochemistry in the different Huanggangliang ore types, with fluid compositions and f O2 probably playing the most important roles. The geological, petrographic, and geochemical characteristics of magnetite of the Huanggangliang Sn-Fe deposit us to conclude that the deposit is a skarn-type Sn-Fe deposit associated with Yanshanian medium-acidic magmatic activities.

Keywords: Huanggangliang Sn-Fe deposit; magnetite; trace elements; Huanggangliang- Ganzhuermiao metallogenic belt

1. Introduction The southern segment of the Great Hingan Range constitutes part of the eastern section of the Central Asian Orogenic Belt (Xingmeng Orogenic Belt) (Figure1A). The southern segment of the Great Hingan Range is separated from the northern margin of the North China block by the Xilamulun zone. It is bordered by the Erenhot-Hegenshan fracture zone to the north and by the Nenjiang fracture zone to the east (Figure1B). The southern segment of the Great Hingan Range is a

Minerals 2018, 8, 195; doi:10.3390/min8050195 www.mdpi.com/journal/minerals Minerals 2018, 8, 195 2 of 17 Minerals 2018, 8, x FOR PEER REVIEW 2 of 17 famousthe Nenjiang nonferrous fracture zone base to and the Pb-Zn-W-Mo-Sn-Feeast (Figure 1B). The polymetallicsouthern segment ore concentration of the Great Hingan area in northernRange Chinais a [famous1,2]. The nonferrous Huanggangliang–Ganzhuermiao metal base and Pb-Zn-W-Mo-Sn-Fe metallogenic polymetallic belt is in ore the concentration center of the area southern in northern China [1,2]. The Huanggangliang–Ganzhuermiao metallogenic belt is in the center of the segment of the Great Hingan Range. It is a polymetallic metallogenic belt characterized by the largest southern segment of the Great Hingan Range. It is a polymetallic metallogenic belt characterized by number of deposits, largest scale, and richest mineral types in the southern segment of the Great the largest number of deposits, largest scale, and richest mineral types in the southern segment of the Hingan Range [1–4]. Plenty of well-known deposits occur along the Huanggangliang–Ganzhuermiao Great Hingan Range [1–4]. Plenty of well-known deposits occur along the Huanggangliang– fracture zone (Figure1C), including the Haobugao Pb-Zn-Cu-Sn skarn deposit, the Baiyinnuoer Ganzhuermiao fracture zone (Figure 1C), including the Haobugao Pb-Zn-Cu-Sn skarn deposit, the Pb-Zn-AgBaiyinnuoer skarn Pb-Zn-Ag deposit, theskarn Dajing deposit, Cu-Sn the magmatic-hydrothermalDajing Cu-Sn magmatic-hydrothermal type deposit, vein thetype Aonaodaba deposit, Cu-Sn-Agthe Aonaodaba magmatic-hydrothermal Cu-Sn-Ag magmatic-hydrothermal vein type deposit, ve thein type Anle deposit, Sn-Cumagmatic-hydrothermal the Anle Sn-Cu magmatic- vein typehydrothermal deposit, and vein the type Huanggangliang deposit, and the Sn-Fe Huanggangliang deposit. Sn-Fe deposit.

Figure 1. Geological sketch map and distribution of deposits in central Inner Mongolia, adjacent areas Figure 1. Geological sketch map and distribution of deposits in central Inner Mongolia, adjacent areas (A,B) and the southern segment of the Great Hinggan Range (C), modified from Reference [3]. (A,B) and the southern segment of the Great Hinggan Range (C), modified from Reference [3]. The Huanggangliang deposit is a super-large Sn-Fe deposit in the Huanggangliang– GanzhuermiaoThe Huanggangliang metallogenic deposit belt. Previous is a super-large studies have Sn-Fe concentrated deposit inon thethe Huanggangliang–geochronology, Ganzhuermiaogeochemistry [5–9], metallogenic and geological belt. features Previous of studiesthe ore deposit have concentrated [10,11] as well on as thethe mineralogical geochronology, geochemistryfeatures [7,12–16], [5–9], timing and geological of mineralization features [7,9,17,18], of the ore fluid deposit inclusion [10,11 compositions] as well as [7,19,20], the mineralogical isotopic featuresgeochemistry [7,12–16 [20–22],], timing and of mineralizationore-controlling [factors7,9,17, 18of], the fluid granitic inclusion bodies compositions associated [7with,19,20 ], isotopicmineralization geochemistry [23]. The [20 following–22], and topics ore-controlling on the mineralization factors of and the graniticgenesis of bodies the Huanggangliang associated with mineralizationSn-Fe deposit [ 23are]. still The under following debate: topics (1) What on the are mineralization the relations andbetween genesis the ofCretaceous the Huanggangliang k-feldspar Sn-Fegranitic deposit , are stillPermian under Dashizhai debate: (1)group What and are Zhesi the group relations limestone between contact the Cretaceous , k-feldspar and graniticthe formation magma, of Permian the skarn Dashizhai Sn-Fe deposit group [3,6,7,9,14,19,20,22,24,25]? and Zhesi group limestone (2) The contactmetallogenesis metasomatism, of the anddeposit the formation is characterized of the skarnby a two-period Sn-Fe deposit meta [3llogenic,6,7,9,14 model,19,20, 22of, 24superimposition,25]? (2) The metallogenesisbetween the Permian sedimentary-exhalative process and the Yanshanian magmatic hydrothermal process. How of the deposit is characterized by a two-period metallogenic model of superimposition between does this model fit with the submarine hydrothermal exhalative-sedimentary series related to the the Permian sedimentary-exhalative process and the Yanshanian magmatic hydrothermal process. Paleozoic volcanic-sedimentary basin evolution [21,26,27]? (3) Important submarine hydrothermal How does this model fit with the submarine hydrothermal exhalative-sedimentary series related to the sedimentary-exhalative metallogenesis did occur during the Permian sedimentary basin evolution Paleozoic volcanic-sedimentary basin evolution [21,26,27]? (3) Important submarine hydrothermal process, and Yanshanian tectonic-magmatic activities also contributed to the formation of the deposit. sedimentary-exhalative metallogenesis did occur during the Permian sedimentary basin evolution The formation of the deposit experienced composite metallogenesis with superimposition of the process,Permian and exhalative-sedimentary Yanshanian tectonic-magmatic process and activities the Yanshanian also contributed magmatic to hydr theothermal formation process of the [18]. deposit. The formationMagnetite of commonly the deposit exists experienced in magmatic-type composite depo metallogenesissits and hydrothermal-type with superimposition deposits as of an the Permianaccessory exhalative-sedimentary mineral within igneous, process sedimentary, and the Yanshanianand metamorphic magmatic rocks hydrothermal [28–31], Magnetite process has [18 a]. typicalMagnetite spinel commonlystructure [30,32] exists and in is magmatic-type compatible with deposits trace elements—such and hydrothermal-type as Mg, Al, Ti, deposits V, Cr, Mn, as an accessoryCo, Ni, Zn, mineral and Ga—within within igneous, its structure sedimentary, [28,31]. andPrevious metamorphic studies proposed rocks [28 that–31 the], Magnetite structure and has a typicalcomposition spinel structure of the magnetite [30,32] are and sensitive is compatible to the ph withysical trace and elements—such chemical conditions as Mg, present Al, Ti, during V, Cr, its Mn, Co, Ni, Zn, and Ga—within its structure [28,31]. Previous studies proposed that the structure and Minerals 2018, 8, 195 3 of 17 composition of the magnetite are sensitive to the physical and chemical conditions present during its formation [28,29,32–38]. Recently, breakthroughs have been achieved in discriminating deposit genesis based on the structure and trace element composition of the magnetite [28,29,31,39]. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been proven to be a powerful tool for defining the separate generation events of magnetite and hydrothermal mineralization [40–42]. However, no equivalent research has been conducted for the Huanggangliang Sn-Fe deposits. In this paper, we report the results obtained from LA-ICP-MS analyses on from the Huanggangliang Sn-Fe deposit for the first time and discuss genesis and physical and chemical conditions to present a new understanding of ore deposit types.

2. Regional Geology The Great Hingan Range is in the strong transition zone between the NE-striking Paleozoic Asian tectono-metallogenic province and the NNE-striking Mesozoic–Cenozoic of the west Pacific Marginal tectono-metallogenic province (Figure1). The Huanggangliang–Ganzhuermiao metallogenic belt in the main part of the southern section of the Great Hinggan Range is outcrops mainly within different strata units such as the Lower Baoyintu Group; the Lower Paleozoic Wenduermiao and Bainaimiao Groups; the Carboniferous Benbatu and Amushan Formations; the Permian Dashizhai, Huanggangliang, and Linxi Formations; the Jurassic Hongqi, Wanbao, Xinmin, and Manketouebo Formations; the Cretaceous Manitu, Baiyingaolao, and Meiletu Formation; and deposits of the Quaternary [3]. The folds include the Huanggangliang–Ganzhuermiao anticlinorium, the Lindong synclinorium, and the Tianshan anticlinorium. These fold belts constitute the NE-striking basic tectonic framework of the Late Hercynian [4,21]. The Yanshanian structures are dominated by fractures. Deep systems have been formed along the axis of the Late Hercynian anticlinorium, forming a belt with a series of NE-striking fracture-intrusive rocks and a fracture- belt. Magmatic activities are well-developed in the area, dominated by Yanshanian granitoids, and have a few Late Hercynian rock bodies [3]. The Yanshanian intrusions include biotite-bearing and monzogranite. The Late Hercynian intrusions mainly include and , with occasional ultrabasic-basic stocks [4].

3. Ore Deposit Geology The Huanggangliang deposit of Inner Mongolia is in the NW wing of the Huanggangliang anticlinorium (Figure2A). From old to new strata, the exposed strata include and of the Lower Permian Qingfengshan Formation; , spilite and keratophyre, tuff, and other volcanic rocks of the Dashizhai Formation; marble, sandstone, and shale of the Zhesi Formation; and slate and sandstone of the Upper Permian Linxi Formation (Figure2A). The marbles of the Dashizhai Formation and the Zhesi Formation are the major ore-bearing strata in this area. Intrusive rocks of this area include the Early Cretaceous alkali granite and biotite-bearing alkali (Figure2A), which are all distributed in the western part of the deposit area, with an outcrop length of approximately 15.4 km and a width of 1.5–2.0 km. Minerals 2018, 8, 195 4 of 17 Minerals 2018, 8, x FOR PEER REVIEW 4 of 17

FigureFigure 2. Simplified 2. Simplified geological geological map map (A (A) and) and cross cross sections sections ((BB,,CC)) of of the the Huanggangliang Huanggangliang Sn-Fe Sn-Fe deposit. deposit. ModifiedModified from from Reference Reference [17]. [17 ].

The TheHuanggangliang Huanggangliang orebodies orebodies occur occur within within the contactcontact zone zone between between the the Yanshanian Yanshanian alkali alkali granitegranite and andthe thevolcaniclastic volcaniclastic rocks rocks of of the the Permian Permian Dashizhai Formation Formation or or the the rock strata strata of theof Zhesi the Zhesi Formation. Formation. The The ore ore bodies bodies exhibit exhibit st stratiform,ratiform, lenticular,lenticular, and and saddle saddle shapes. shapes. Near Near the the contactcontact areas areas between between the granite the granite intrusion intrusion and and the thema marble,rble, the the ore ore bodies bodies show show great great thickness, thickness, good continuity,good continuity, and high and grades high grades(Figure (Figure 2B,C).2B,C). A Fe A Feore ore body body and and Sn-Fe oreore body body are are the the two two major major orebodiesorebodies of the of thearea area (Figure (Figure 2B,C).2B,C). Sn Sn is found associatedassociated with with Fe Fe , ores, and and constitutes constitutes the mostthe most importantimportant associated associated mineral mineral within within the the deposit. deposit. Th Thee Sn contentscontents within within the the Fe Fe ore ore bodies bodies are beloware below industrial grade (<0.2%). The Sn content wihin the Sn-Fe ore body is much higher (Sn grade reaches industrial grade (<0.2%). The Sn content wihin the Sn-Fe ore body is much higher (Sn grade reaches 0.20–3.74%). Sn-Fe ore bodies are observed to cut through Fe ore body (Figure2B,C). Metallic minerals 0.20–3.74%). Sn-Fe ore bodies are observed to cut through Fe ore body (Figure 2B,C). Metallic in the ores include magnetite, cassiterite, , and . Non-metallic minerals include mineralsgarnet, in diopside, the ores epidote, include actinolite, magnetite, gokumite, cassiterite, ivaite, chlorite,sphalerite, hastingsite, and galena. quartz, Non-metallic fluorite, , minerals and includebiotite. garnet, Ore texturesdiopside, include epidote, idiomorphic-hypidiomorphic actinolite, gokumite, ivaite, granular chlorite, texture, hastingsite, xenomorphic quartz, granular , calcite,texture, and biotite. and Ore solution textures separation include idiomorphic-hypidiomorphic texture (Figure3). Ore structures granular include both texture, disseminated xenomorphic granularand massivetexture, structures. and solid Wall solution rock alterations separation are texture well-developed (Figure and3). includeOre structures silicified alteration,include both disseminatedhornfelsic and alteration, massive skarn structures. alteration, Wall fluoritization rock alterations alteration, are and well-developed carbonatization and alteration, include which silicified alteration,are developed hornfelsic in the alteration inner and, outerskarncontact alteration, zone betweenfluoritization the Yanshanian alteration, alkali and granite carbonatization and the alteration,Permian which strata are [16 ,developed20]. in the inner and outer contact zone between the Yanshanian alkali granite and the Permian strata [16,20].

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Figure 3. Mineral assemblages of the Huanggangliang Sn-Fe deposit. (a) Epidote skarn vein bearing Figure 3. Mineral assemblages of the Huanggangliang Sn-Fe deposit. (a) Epidote skarn vein disseminated magnetite (Mt2) cutting through banded garnet–diopside–magnetite (Mt1) ore body; bearing(b) banded disseminated garnet–diopside–magnetite magnetite (Mt2) cutting(Mt1) ore; through (c) fine-grain banded massive garnet–diopside–magnetite magnetite (Mt3) cements (Mt1) oreepidote body; skarn (b) banded bearing garnet–diopside–magnetite disseminated magnetite (Mt2); (Mt1) (d) fine-grain ore; (c) fine-grain magnetite massive (Mt3) cements magnetite epidote (Mt3) cementsskarn lenticles epidote skarnbearing bearing dissminated disseminated magnetite(Mt2); magnetite (Mt2);(e) coarse-grain (d) fine-grain massive magnetite magnetite (Mt3) cutting cements epidotethrough skarn epidote lenticles skarn bearing bearing disseminated dissminated magnetite( magnetite(Mt2);Mt2) which (e) is coarse-grain cemented by fine-grain massive magnetitemassive cuttingmagnetite through (Mt3); epidote (f) coarse-grain skarn bearing massive disseminated magnetite magnetite(Mt2) vein (Mt4) cutting which isthrough cemented epidote by fine-grain skarn massivecontaining magnetite disseminated (Mt3); magnetite; (f) coarse-grain (g) xenomorphic massive magnetite magnetite veinreplacing (Mt4) garnet cutting and through diopside, epidote and skarnlater containing replaced by disseminated cassiterite; ( magnetite;h) xenomorphic (g) xenomorphic magnetite replacing magnetite epidote replacing and garnet later replaced and diopside, by andcassiterite; later replaced (i) cassiterite, by cassiterite; magnetite, (h) and xenomorphic quartz assemblage; magnetite (j) replacing magnetite epidote occurring and with later idiomorphic replaced by cassiterite;texture, with (i) cassiterite, inter-granule magnetite, angels of and 120°, quartz showing assemblage; typical (triplej) magnetite junction occurring texture. Intersection with idiomorphic and ◦ texture,cutting with of later inter-granule -sphalerite; angels of 120 (,k showing) galena replacing typical triple hypi junctiondiomorphic texture. pyrite; Intersection (l) sphalerite and cuttingreplacing of later arseno-. chalcopyrite-sphalerite; Grt—garnet; Di—diopside; (k) galena replacing Ep—epidote; hypidiomorphic Mt—magnetite; pyrite; Cst—cassiterite; (l) sphalerite replacingCcp—chalcopyrite; arseno-pyrites. Sp—sphalerite; Grt—garnet; Gn—g Di—diopside;alena; Py—pyrite; Ep—epidote; Asp—. Mt—magnetite; Cst—cassiterite; Ccp—chalcopyrite; Sp—sphalerite; Gn—galena; Py—pyrite; Asp—arsenopyrite.

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Based on comprehensive studies of the intersection relations among the ore-bearing veins of the depositBased and on mineral comprehensive assemblages studies of different of the intersection types of ore-bearing relations among veins the(Figure ore-bearing 3a–f), the veins Sn-Fe of metallogenesisthe deposit and can mineral be divided assemblages into two of differentperiods and types 4 ofstages ore-bearing (Figure veins4). The (Figure skarn3a–f), period the can Sn-Fe be subdividedmetallogenesis into can the be dividedgarnet–diopside–magnetite into two periods and 4 stages(T1) stage (Figure (stage4). The 1) skarn and period the epidote–idocrase– can be subdivided cassiterite–magnetiteinto the garnet–diopside–magnetite (T2) stage (stage (T1) 2). stage The (stage quar 1)tz-magnetite and the epidote–idocrase–cassiterite–magnetite period can be subdivided into the quartz–cassiterite–magnetite(T2) stage (stage 2). The quartz-magnetite (T3) stage (stage period 3) can and be the subdivided quartz-magnetite into the quartz–cassiterite–magnetite (T4) stage (stage 4). (1) The garnet–diopside–magnetite(T3) stage (stage 3) and the quartz-magnetite stage is dominated (T4) stage by (stage the 4).formation (1) The garnet–diopside–magnetite of skarn minerals—such stage as wollastonite,is dominated bydiopside, the formation and garnet—with of skarn minerals—such the occurrence as wollastonite, of magnetites. diopside, Banded and garnet—with magnetite and the sparselyoccurrence disseminated of magnetites. ma Bandedgnetite magnetite are the major and sparsely ore types; disseminated (2) In the magnetite epidote–idocrase–cassiterite– are the major ore types; magnetite(2) In the epidote–idocrase–cassiterite–magnetite stage, a large amount of skarn minerals stage, occurs, a large such amount as epidote, of skarn idocrase, minerals hastingsite, occurs, such and as actinoliteepidote, idocrase, (Figure hastingsite,3h). The ores and have actinolite a densely (Figure disseminated3h). The ores structure; have a densely (3) In disseminatedthe quartz–cassiterite– structure; magnetite(3) In the quartz–cassiterite–magnetite stage, large amounts of hypidiomorphic stage, large amounts magnetites of hypidiomorphic occur, forming magnetites high-grade occur, forming ores thathigh-grade cross-cut iron the ores skarn that (Figure cross-cut 3c,d the). The skarn ores (Figure have a 3massivec,d). The structure. ores have Later, a massive cassiterite structure. replacement Later, ofcassiterite magnetite replacement could be ofobserved; magnetite (4) could In the be observed;quartz-magnetite (4) In the stage, quartz-magnetite large amounts stage, of largeidiomorphic- amounts hypidiomorphicof idiomorphic-hypidiomorphic magnetites occur. magnetites The ores occur.have a The massive ores havestructure. a massive The magnetite structure. Thegranules magnetite form ◦ anglesgranules of form120° anglesbetween of each 120 betweenother (Figure each other3j). (Figure3j).

Figure 4. Paragenetic sequence of minerals from the Huanggangliang Sn-Fe deposit. Figure 4. Paragenetic sequence of minerals from the Huanggangliang Sn-Fe deposit. 4. Sampling and Analyses 4. Sampling and Analyses

4.1. Sample Sites Ore samples were collected from boreholes and outcropsoutcrops of the no. 2–no. 22 orebodies in the the Huanggangliang deposit. The locations and types of samples are listed in Table1 1..

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Table 1.1. Location and descriptions ofof samplessamples fromfrom thethe HuanggangliangHuanggangliang deposit.deposit.

SampleSample No. No. Location Location Ore Ore Types Types Stage Stage Description Description HGL-153 1400 m level, no. 2–3 mineralized veins Garnet, diopside, magnetite, HGL-153 1400 m level, no. 2–3 mineralized veins Garnet, diopside, magnetite, DisseminatedDisseminated magnetite magnetite ores ores I I ZK581-7ZK581-7 133 133 m, m, drill drill hole hole ZK1401/587-7 cassiteritecassiterite HGL-149 1337.5 m level, no. 16–2 veins HGL-149 1337.5 m level, no. 16–2 veins Epidote,Epidote, chlorite, chlorite, gokumite, gokumite, DisseminatedDisseminated magnetite magnetite ores ores II II HGL-313HGL-313 1550 1550 m m level, level, no no.4.4 mineralized mineralized vein hastingsitehastingsite magnetite, magnetite, cassiterite HGL-220 1187.5 m level, no. 22 mineralized vein Massive magnetite ores III Quartz, magnetite, cassiterite HGL-220 1187.5 m level, no. 22 mineralized vein Massive magnetite ores III Quartz, magnetite, cassiterite HGL-54 1350 m level, no. 12 mineralized vein Massive magnetite ores IV Quartz, magnetite HGL-54 1350 m level, no. 12 mineralized vein Massive magnetite ores IV Quartz, magnetite

4.2. Electron-Probe Microanalyses 4.2. Electron-Probe Microanalyses The chemical composition of magnetite was analyzedanalyzed using a SHIMADZU EPMA-1720 electron microprobe (SHIMADZU, Tokyo, Japan)Japan) equippedequipped withwith fourfour wavewave lengthlength dispersivedispersive spectrometersspectrometers and energy-dispersive systemsystem atat the Key Laboratory of Metallogenic Prediction of Nonferrous Metals and GeologicalGeological Environment Environment Monitoring, Monitoring, Ministry Ministry of Education, of Education, China. China. Operating Operating conditions conditions include aninclude accelerating an accelerating voltage voltage of 15 kV, ofelectron 15 kV, electron beam current beam current of 10 nA, of 10 and nA, beam and diameterbeam diameter of 1 to of 2 µ1 m.to All2 μm. data All were data corrected were corrected using theusing atomic the atomic number-absorption-fluorescence number-absorption-fluorescence (ZAF) procedure.(ZAF) procedure.

4.3. LA-ICP-MS Trace ElementElement MicroscopicMicroscopic InIn SituSitu AnalysisAnalysis LA-ICP-MS tracetrace element element microscopic microscopic in situin situ analysis analysis was conductedwas conducted at the Nanjingat the Nanjing Jupu Analysis Jupu TechnologyAnalysis Technology Co., Ltd. (Nanjing, Co., Ltd. China) (Nanjing, The LA-ICP-MSChina) The analysisLA-ICP-MS system analysis consists system of the Analyzeconsists Exciteof the 193Analyze nm ArF Excite Laser 193 Ablation nm ArF System Laser (LA) Ablation made System in the USA, (LA) and made the in Agilent the USA, 7700 ×andinduced the Agilent polarization 7700× plasmainduced mass polarization spectrum plasma (ICP-MS) mass made spectrum in Japan. (ICP-MS) During made laser in ablation, Japan. During the high laser intensity ablation, ultraviolet the high beamsintensity generated ultraviolet by thebeams laser generated generator by are the focused laser ongenerator the sulfide are throughfocused theon homogenizedthe through light path. the 2 Thehomogenized energy light path. is 4.0 The J/cm energy. The density beam diameter is 4.0 J/cm is2 40. Theµm. beam Each diameter analysis includesis 40 μm. aEach background analysis acquisitionincludes a background of approximately acquisition 20 s of (gas approximately blank) followed 20 s (gas by 40blank) s data followed acquisition by 40 froms datathe acquisition sample. Thefrom frequency the sample. is 7.0 The Hz. frequency The ICPMS-DataCal is 7.0 Hz. The software ICPMS-DataCal (China University software of (China Geosciences, University Wuhan, of China)Geosciences, is adopted Wuhan, for offlineChina) processing is adopted of for the analysisoffline processing data and includes of the analysis selection data of the and sample includes and blankselection signal, of the equipment sample and sensitivity blank signal, drift calibration, equipmentand sensitivity element drift content calibration, calculation. and Theelement LA-ICP-MS content analyticalcalculation. results The LA-ICP-MS are listed in Tableanalytical2. In-situ results LA-ICP-MS are listed analysis in Table on 2. the In-situ trace elementsLA-ICP-MS of the analysis magnetite on showsthe trace that elements the Al, Mg,of the Mn, magnetite Ti, Zr, Pb, shows Zn, Ni, that Co, the V, andAl, Mg, Cr contents Mn, Ti, ofZr, the Pb, four Zn,types Ni, Co, of magnetiteV, and Cr exceedcontents the of detection the fourlimit, types and of magnetite that the Sc, exceed Cu, Nb, the Ta, detection and Na contents limit, and of some that samplesthe Sc, Cu, approach Nb, Ta, or slightlyand Na exceedcontents the of detection some samples limit (Figure approach5). or slightly exceed the detection limit (Figure 5).

Figure 5. LA-ICP-MS analytical results from magnetite of Huanggangliang deposit, which are Figure 5. LA-ICP-MS analytical results from magnetite of Huanggangliang deposit, which are compared to the instrument limits of detection. compared to the instrument limits of detection.

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Table 2. Analytical results of selected ores from the Huanggangliang deposit.

Al2O3 SiO2 MnO FeO Mg Sc Ti V Cr Co Ni Zn Zr Nb Ta Pb Sample No. Stage wt % wt % wt % wt % ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm HGL-153 0.96 0.24 0.68 92.97 980 0.42 20 3.0 0.01 7.9 4.7 6960 0.87 0.38 0 0.23 HGL-153 2.71 13.49 0.41 74.59 37 1.7 24 6.8 2.7 6.5 6.8 720 1.6 0.95 0.01 1.3 zk1401/581-7 0.21 0.38 0.22 96.11 220 0.1 610 33 3.8 0.26 1.5 230 0.65 0.2 0.06 7.4 I zk1401/581-7 0.15 0.1 0.23 96.65 25 0.1 600 120 13 0.01 1.4 200 0.27 0.05 0 0.13 zk1401/581-7 0.2 0.19 0.24 96.49 52 0.11 650 71 8.9 0.1 1.1 22 0 0.02 0.01 0.38 zk1401/581-7 0.85 2.88 0.36 91.36 7600 0.48 380 46 5.7 2.9 3.1 1670 0.68 0.32 0.02 1.9 HGL-149 0.34 0.05 0.16 96.39 340 0.43 550 13 0.01 4.7 17 1130 0 0 0 2.2 HGL-149 0.52 0.14 0.2 95.95 460 0.78 610 15 7.8 4.3 13 2140 0.08 0.01 0 1.1 HGL-149 0.12 0.11 0.19 96.49 280 0.24 96 5.8 0.01 5.2 16 260 0.11 0.01 0 15 HGL-313II 0.59 0.04 1.47 93.82 3780 0.29 660 21 7.6 12 4.6 2960 0.06 0.22 0.06 2.03 HGL-313 0.53 0.05 1.5 93.98 4260 0 180 13 7.3 11 7.2 3020 0 0.05 0 3.6 HGL-313 0.44 0.07 3.53 92.02 4720 0 610 31 8.8 12 2.8 3000 0 0.05 0.02 0.1 HGL-313 0.42 0.08 1.18 94.77 2300 0.29 450 17 5.2 8.3 10.3 2080 0.04 0.06 0.01 4.0 HGL-220 0.26 0.11 0.14 96.31 18 0.44 830 32 0.01 0.04 9.8 610 0.03 0.03 0 13 HGL-220 0.2 0.38 0.09 96.4 35 0.59 260 9.8 30 1 55 240 0.48 0.08 0.02 8.3 HGL-220III 0.45 1.02 0.08 95.19 130 0.11 680 27 2.8 0.11 8.8 99 0.66 0.09 0 1.2 HGL-220 0.01 0.2 0 93.63 24 0.01 35 0.31 2.0 180 18 7.5 0.42 0.08 0 1.1 HGL-220 0.23 0.43 0.08 95.38 52 0.29 450 17 8.6 46 23 240 0.4 0.07 0 5.9 HGL-54 0.2 0.45 0.31 96 840 0.15 130 26 1.5 2.1 25 650 0.03 0.13 0.68 0.29 HGL-54 0.22 0.81 0.2 95.76 800 0 210 40 1.6 1.5 43 170 0.24 0.16 0.15 1.7 HGL-54 0.2 0.31 0.6 95.81 1480 0.16 55 6.6 2.3 2.3 12 860 0 0.06 0.26 0.17 IV HGL-54 0.32 0.42 0.55 94.93 1550 0.45 2710 79 38 1.7 37 1440 0.4 0.54 0.25 1.3 HGL-54 0.26 0.43 0.38 95.6 1160 0.15 920 88 29 1.9 51 860 0.63 0.64 0.09 1.0 HGL-54 0.24 0.48 0.41 95.62 1160 0.18 800 48 14 1.9 34 800 0.26 0.3 0.29 0.9 The concentration of Fe, Al, Si, and Mg are from EPMA. Minerals 2018, 8, 195 9 of 17

MineralsThe two 2018 types, 8, x FOR of PEER disseminated REVIEW magnetite show big differences in geochemical characteristics.9 of 17 T1 magnetite shows positive correlations in Mn vs. Mg, Al vs. Mg, Si vs. Mg, Co vs. Mg, Ni vs. Co, The two types of disseminated magnetite show big differences in geochemical characteristics. andT1 V vs.magnetite Cr diagrams shows positive (Figure correlations6), while it in is Mn not vs. strongly Mg, Al linkedvs. Mg, withSi vs. ZnMg, or Co Mg. vs. Mg, Compared Ni vs. Co, with T2 magnetite,and V vs. Cr T1 diagrams magnetite (Figure has extremely6), while it highis not Alstrongly content linked (2.71 with wt %).Zn or Similar Mg. Compared to T1 magnetite, with T2 T2 magnetitemagnetite, shows T1 positivemagnetite correlations has extremely in Mnhigh vs. Al Mg,content Al vs.(2.71 Mg, wt Co%). vs. Simila Mg,r andto T1 V magnetite, vs. Cr diagrams, T2 andmagnetite is not strongly shows linkedpositive with correlations Cr or Ti in contents. Mn vs. Mg, However, Al vs. Mg, the Co Si vs. vs. Mg, Mg and and V Ni vs. vs.Cr Codiagrams, diagrams demonstrateand is not a strongly clear negative linked with correlation Cr or Ti and contents. extremely However, high Mnthe Si content vs. Mg (3.53 and wtNi %)vs. (FigureCo diagrams6). demonstrateSimilar to thea clear two negative types correlation of disseminated and extr oremely banded high Mn magnetite content (3.53 ores wt (T1 %) magnetite(Figure 6). and T2 magnetite),Similar the to massive the two magnetites types of disseminated (T3 magnetite or andbanded T4 magnetite)magnetite ores show (T1 positive magnetite correlation and T2 in the Mnmagnetite), vs. Mg the and massive Al vs. magnetites Mg diagram (T3 (Figure magnetite6), whileand T4other magnetite) minerals show show positive different correlation geochemical in the characteristics.Mn vs. Mg Besides,and Al vs. the Mg two diagram types of (Figure magnetites 6), wh alsoile showother differentminerals geochemicalshow different features geochemical with each characteristics. Besides, the two types of magnetites also show different geochemical features with other. Similar to T3 magnetite, T4 magnetite shows a negative correlation in the Ni vs. Co diagram. each other. Similar to T3 magnetite, T4 magnetite shows a negative correlation in the Ni vs. Co However, T4 magnetite shows a positive correlation in the Zn vs. Mg, Co vs. Mg, V vs. Cr, and Cr vs. diagram. However, T4 magnetite shows a positive correlation in the Zn vs. Mg, Co vs. Mg, V vs. Cr, Ti diagram,and Cr vs. while Ti diagram, it shows clearwhile negativeit shows correlationclear negative in thecorrelation Si vs. Mg in diagramthe Si vs. and Mg extremely diagram and high Ti contentextremely (54.76–2711.24 high Ti content ppm) (54.76–2711.24 (Figure6). ppm) (Figure 6).

Figure 6. Binary diagrams of (a) Mn vs. Mg, (b) Al vs. Mg, (c) Si vs. Mg, (d) Zn vs. Mg, (e) Ni vs. Co, Figure 6. Binary diagrams of (a) Mn vs. Mg, (b) Al vs. Mg, (c) Si vs. Mg, (d) Zn vs. Mg, (e) Ni (f) Co vs. Mg, (g) Cr vs. Ti, and (h) V vs. Cr for the Huanggangliang disseminated- and massive- vs. Co, (f) Co vs. Mg, (g) Cr vs. Ti, and (h) V vs. Cr for the Huanggangliang disseminated- and magnetite ores. massive-magnetite ores.

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5. DiscussionMinerals 2018, 8, x FOR PEER REVIEW 10 of 17

5.1.5. PetrographyDiscussion and Genesis of the Huanggangliang Magnetite The T1 and T2 magnetites were formed during the garnet–diopside–magnetite (T1) stage and 5.1. Petrography and Genesis of the Huanggangliang Magnetite the epidote–idocrase–cassiterite–magnetite (T2) stage during the skarn period (Figure3). Both coexist with theThe alteration T1 and mineralsT2 magnetites in the were typical formed skarn-type duringdeposits the garnet–diopside–ma (i.e., garnet, diopside,gnetite idocrase,(T1) stage epidote, and hastingsite).the epidote–idocrase–cassiterite–magnetite The T1 magnetites mainly occur (T2) within stage the during fissures the betweenskarn period the diopsides(Figure 3). andBoth thecoexist zoned garnetswith the or replacealteration the minerals early diopsides in the andtypical garnets skarn- andtype then deposits are later (i.e., replaced garnet, bydiopside, cassiterite. idocrase, The T2 magnetitesepidote, hastingsite). replace the The earlier T1 epidotesmagnetites and mainly diopsides occur andwithin are the later fissures replaced between by cassiterites the diopsides (Figure and3 ). the zoned garnets or replace the early diopsides and garnets and then are later replaced by cassiterite. The massive T3 magnetite ores are cemented with the magnetite that were formed during The T2 magnetites replace the earlier epidotes and diopsides and are later replaced by cassiterites the skarn period (i.e., T1 and T2 magnetites) (Figure3c,d). The T3 magnetite coexist with cassiterite (Figure 3). The massive T3 magnetite ores are cemented with the magnetite breccias that were formed and a small amount of quartz and replace the earlier hastingsite (Figure3). The T4 magnetite-bearing during the skarn period (i.e., T1 and T2 magnetites) (Figure 3c,d). The T3 magnetite coexist with ores mainly occur in massive structures. The T4 magnetite is cross-cut by later sulfides, indicating cassiterite and a small amount of quartz and replace the earlier hastingsite (Figure 3). The T4 thatmagnetite-bearing the magnetite mineralization ores mainly occur likely in predatedmassive structures. sulfides. The In addition, T4 magnetite the T4is cross-cut magnetite by shows later a ◦ goodsulfides, crystal indicating shape. Thethat idiomorphicthe magnetite magnetite mineralization granules likely form predat anglesed . of 120 Inbetween addition, each the other.T4 Currently,magnetite two shows models a good could crystal be adopted shape. The to explain idiomorphic the triple magnetite junction granules texture form of the angles T4magnetite: of 120° (1)between high-temperature each other. annealing Currently, in two a closed models system could (i.e., be adopted magmatic to explai magnetite,n the [triple43]), andjunction (2) fluid-assisted texture of recrystallization/replacementthe T4 magnetite: (1) high-temperature in an open annealing system in (i.e., a closed quartz, system [44,45 (i.e.,]). Themagmatic low Ni magnetite, and Cr contents [43]), andand relatively (2) fluid-assisted high and recrystallization/replacement stable Fe contents of the T4in an magnetite open system indicate (i.e., thatquartz, it does[44,45]). not The belong low to magmaticNi and Cr magnetite contents and [41 ].relatively Hydrothermal high and magnetite stable Fe contents bears relatively of the T4 lowmagnetite contents indicate of Ti that (<2300 it does ppm) comparednot belong with to magmatic magmatic magnetite magnetite. [41]. The Hydrothermal Ti and V contents magnetite of thebears magnetites relatively low of the contents area fall of Ti into the(<2300 ranges ppm) of 19.69–918.99 compared with ppm magmatic (with only magnetite. one extremely The Ti and high V contents value, 2711.24 of the magnetites ppm) and of 0.31–115.18 the area ppm,fall respectively.into the ranges In of addition, 19.69–918.99 fluid ppm inclusion (with on studiesly one extremely of garnet high and value, cassiterite 2711.24 in Huanggangliangppm) and 0.31– deposit115.18 demonstrateppm, respectively. that the In temperature addition, fluid of the inclusion skarn period studies and of magnetite-quartz garnet and cassiterite period in was belowHuanggangliang 400 ◦C[16,19 deposit,20]. The demonstrate fluid temperature that the temperature should not belongof the skarn to the period high-temperature and magnetite-quartz annealing systemperiod [40 was]. Thebelow polymetallic 400 °C [16,19,20]. sulfide The veins fluid within temper theature crack-seal should not textures belong that to the represent high-temperature open space fillingannealing are common system [40]. in the The massive polymetallic magnetite, sulfide suggesting veins within a localthe crack-seal extensional textures tectonic that regimerepresent [46 ]. Thisopen indicates space filling that the are triple common junction in the texture massive in the magn massiveetite, suggesting magnetites a were local probably extensional derived tectonic from regime [46]. This indicates that the triple junction texture in the massive magnetites were probably fluid-assisted recrystallization/replacement in an open system. derived from fluid-assisted recrystallization/replacement in an open system. Among the various magnetite ore types at Huanggangliang we distinguished the Ni vs. Cr and Among the various magnetite ore types at Huanggangliang we distinguished the Ni vs. Cr and V/Ti vs. Fe diagrams (Figure7a,b). Thus the Huanggangliang magnetite (banded-, disseminated-, and V/Ti vs. Fe diagrams (Figure 7a,b). Thus the Huanggangliang magnetite (banded-, disseminated-, massive magnetite ores) are hydrothermal. The depletions of Ti (<0.09 wt %), Al (0.008–1.731 wt %) and massive magnetite ores) are hydrothermal. The depletions of Ti (<0.09 wt %), Al (0.008–1.731 wt and%) Zr and (<1.610 Zr (<1.610 ppm) ppm) in magnetite in magnetite also also suggest suggest hydrothermal hydrothermal magnetite magnetite affinities affinities [28 [28,30,32,47].,30,32,47].

Figure 7. Binary diagrams of (a) Ni vs. Cr (after Reference [30]).and (b) V/Ti vs. Fe (after Reference Figure 7. Binary diagrams of (a) Ni vs. Cr (after Reference [30]).and (b) V/Ti vs. Fe (after Reference [42]) [42]) for the Huanggangliang magnetite from the different ore types. for the Huanggangliang magnetite from the different ore types.

Minerals 2018, 8, 195 11 of 17 Minerals 2018, 8, x FOR PEER REVIEW 11 of 17

5.2.5.2. ControllingControlling FactorsFactors forfor MagnetiteMagnetite CompositionsCompositions FactorsFactors affectingaffecting thethe tracetrace elementelement compositionscompositions ofof magnetitemagnetite inin thethe hydrothermalhydrothermal fluidsfluids includeinclude fluidfluid compositions,compositions, hosthost rockrock compositions,compositions, coexistingcoexisting minerals,minerals, temperature,temperature, andand oxygenoxygen fugacityfugacity ((ffO2))[ [28,30,31,48,49].28,30,31,48,49].

5.2.1.5.2.1. CoexistingCoexisting Minerals,Minerals, FluidFluid andand HostHost RockRock CompositionsCompositions Micro-inclusionsMicro-inclusions inin magnetitemagnetite cancan influenceinfluence the bulk magnetite geochemistry detected (Table 2 2).). TheThe fewfew anomalouslyanomalously highhigh Si,Si, Al,Al, Mn,Mn, Mg,Mg, Ti,Ti, andand ZnZn magnetitemagnetite grainsgrains maymay pointpoint toto thethe presencepresence ofof Mn-bearingMn-bearing phases,phases, Ti-bearingTi-bearing phases,phases, sphaleritesphalerite inclusions,inclusions, and/orand/or silicate (Figure8 8).).

FigureFigure 8.8. Time-resolvedTime-resolved analyticalanalytical signalssignals ofof aa LA-ICP-MSLA-ICP-MS analysis from disseminated- and massive- magnetitemagnetite ores.ores. (a)) DisseminatedDisseminated magnetitemagnetite oresores (T2);(T2); ((bb)) MassiveMassive magnetitemagnetite oresores (T3);(T3); ((cc)) MassiveMassive magnetitemagnetite oresores (T4).(T4). SuspectedSuspected fluidfluid inclusionsinclusions are characterizedcharacterized by high Si, Al, Mn,Mn, Mg,Mg, Ti,Ti, andand ZnZn intensitiesintensities (cps(cps countscounts perper second).second).

Fluid-rock interactions enabled the hydrothermal magnetite to inherit some geochemical Fluid-rock interactions enabled the hydrothermal magnetite to inherit some geochemical features features of the altered wall rock or altered minerals [30,48]. In Figure 9, the T1 and T2 magnetites are of the altered wall rock or altered minerals [30,48]. In Figure9, the T1 and T2 magnetites are formed formed during the skarn period. Both might be the products of the same metallogenic fluid system. during the skarn period. Both might be the products of the same metallogenic fluid system. The T1 The T1 magnetite was formed during the garnet–diopside–cassiterite–magnetite stage, which marked magnetite was formed during the garnet–diopside–cassiterite–magnetite stage, which marked the the beginning of metallogenesis in the area. The Co/Ni ratio varies in the range of 0.01–1.67, averaging beginning of metallogenesis in the area. The Co/Ni ratio varies in the range of 0.01–1.67, averaging 0.58. 0.58. The sample points fall into the range between magnetite-forming fluids (low Co/Ni = 0.01, The sample points fall into the range between magnetite-forming fluids (low Co/Ni = 0.01, [50,51]) and [50,51]) and the Permian Dashizhai marine and skarn, suggesting that the formation of the the Permian Dashizhai marine sediments and skarn, suggesting that the formation of the T1 magnetite T1 magnetite was due to the fluid-rock interactions between the magnetite-forming fluids, Permian was due to the fluid-rock interactions between the magnetite-forming fluids, Permian Dashizhai marine Dashizhai marine sediments and the early skarn minerals (such as garnet and diopside). The Co/Ni sediments and the early skarn minerals (such as garnet and diopside). The Co/Ni values of the T2 values of the T2 magnetites vary in the range of 0.27–4.41, averaging 1.58, which is higher than those magnetites vary in the range of 0.27–4.41, averaging 1.58, which is higher than those of the T1 magnetite. of the T1 magnetite. In the diagram (Figure 9), the sample points fall into the skarn range, suggesting In the diagram (Figure9), the sample points fall into the skarn range, suggesting that the formation that the formation of the T2 magnetite occurred simultaneously with petrogenesis (i.e., epidote– of the T2 magnetite occurred simultaneously with petrogenesis (i.e., epidote–diopside–wollastonite diopside–wollastonite skarn). The T3 and T4 magnetites were formed during the quartz-magnetite skarn). The T3 and T4 magnetites were formed during the quartz-magnetite period. The T3 magnetite period. The T3 magnetite was formed during the early stage of the quartz-magnetite period and has was formed during the early stage of the quartz-magnetite period and has a wide range of Co/Ni a wide range of Co/Ni ratios (0.01–9.56, averaging 2.50). The sample points are distributed over a ratios (0.01–9.56, averaging 2.50). The sample points are distributed over a wide range, with a few wide range, with a few sample points falling out of the range of skarn and the Permian Dashizhai sample points falling out of the range of skarn and the Permian Dashizhai Formation marine sediments Formation marine sediments (Figure 9). Its formation might be the result of interactions between the (Figure9). Its formation might be the result of interactions between the magnetite-forming fluids and magnetite-forming fluids and the preexisting skarn, as well as the Permian Dashizhai marine the preexisting skarn, as well as the Permian Dashizhai marine sediments and other strata. The T4 sediments and other strata. The T4 magnetite was formed during the late stage of the quartz- magnetite was formed during the late stage of the quartz-magnetite metallogenic period. The Co/Ni magnetite metallogenic period. The Co/Ni ratios vary over the range of 0.04–0.18, averaging 0.08. The ratios vary over the range of 0.04–0.18, averaging 0.08. The sample points are relatively concentrated sample points are relatively concentrated in the range of magnetite-forming fluids and skarn (Figure in the range of magnetite-forming fluids and skarn (Figure9), suggesting that its formation is related 9), suggesting that its formation is related to the fluid-rock interaction between the magnetite-forming to the fluid-rock interaction between the magnetite-forming fluids and the preexisting skarn. fluids and the preexisting skarn.

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Figure 9. Binary diagrams of Mg (wt %) vs. Co/Ni for the Huanggangliang magnetite from the Figure 9. Binary diagrams of Mg (wt %) vs. Co/Ni for the Huanggangliang magnetite from the different ore types. different ore types.

5.2.2. Temperature and Fugacity (fO2) 5.2.2. Temperature and Oxygen Fugacity (f O2) Temperature could affect the trace element composition of the hydrothermal magnetite [30,31]. Temperature could affect the trace element composition of the hydrothermal magnetite [30,31]. Experimental studies indicated that Zn and Mn would be the priorities for entering magnetite in the Experimental studies indicated that Zn and Mn would be the priorities for entering magnetite in the condition of lower temperatures [52]. In the Huanggangliang deposit, the Zn contents in the four condition of lower temperatures [52]. In the Huanggangliang deposit, the Zn contents in the four types of types of magnetite are 1560.96–4661.93 ppm, avg. 3169.99 ppm in T1; 1216.63–27364.18 ppm, avg. magnetite are 1560.96–4661.93 ppm, avg. 3169.99 ppm in T1; 1216.63–27364.18 ppm, avg. 9101.14 ppm in 9101.14 ppm in T2; 1673.99–5301.95 ppm, avg. 2768.82 ppm in T3; and 9.93–1093.55 ppm, avg. 593.50 T2; 1673.99–5301.95 ppm, avg. 2768.82 ppm in T3; and 9.93–1093.55 ppm, avg. 593.50 ppm in T4. The Mn ppm in T4. The Mn contents are T1（166.14–1444.24 ppm, avg. 794.72 ppm), T2 (259.45–3016.06 ppm, contents are T1(166.14–1444.24 ppm, avg. 794.72 ppm), T2 (259.45–3016.06 ppm, avg. 2085.73 ppm), avg. 2085.73 ppm), T3 (195.33–6958.99 ppm, avg. 1665.85 ppm), and T4 (7.54–611.12 ppm, avg. 238.45 T3 (195.33–6958.99 ppm, avg. 1665.85 ppm), and T4 (7.54–611.12 ppm, avg. 238.45 ppm). The Mn and ppm). The Mn and Zn contents of the four types of magnetites differ from each other, which might Zn contents of the four types of magnetites differ from each other, which might have been the result of have been the result of different temperatures during the precipitation of magnetites. However, fluid different temperatures during the precipitation of magnetites. However, fluid inclusion studies of the inclusion studies of the garnet and cassiterite demonstrate that the formation temperatures of the garnet and cassiterite demonstrate that the formation temperatures of the four types of fluid inclusions four types of fluid inclusions vary over the range of 349 to 432 °C [16], showing a small range of vary over the range of 349 to 432 ◦C[16], showing a small range of variation. The difference in Zn and variation. The difference in Zn and Mn contents might be due to the Mn-bearing and Zn-bearing Mn contents might be due to the Mn-bearing and Zn-bearing inclusions (Figure7). The within inclusions (Figure 7). The titanium within the magnetite is generally believed to be positively related the magnetite is generally believed to be positively related to its formation temperature [29,32,53]. In the to its formation temperature [29,32,53]. In the (Al + Mn) vs. (Ti + V) diagram (Figure 10a), the (Al + Mn) vs. (Ti + V) diagram (Figure 10a), the magnetites of the different Huanggangliang ore types magnetites of the different Huanggangliang ore types show similar distribution patterns, suggesting show similar distribution patterns, suggesting that the temperature had little effect on the compositions that the temperature had little effect on the compositions of the magnetites. of the magnetites. MineralsVanadium 2018, 8, x FOR exists PEER mostly REVIEW in the form of (+3, +4, +5) in fluids. Only V3+ could enter the crystal13 cube of 17 of magnetite [31,38,54], i.e., the increase in content in magnetite represents the decrease in oxygen fugacity [38,41,55]. In Figure 10b, the variation range of V tends to become lower from T1 to T3 magnetite, suggesting that the oxygen fugacity of the metallogenic fluids increased as the metallogenesis proceeded. The V content in the T4 magnetite tends to increase, indicating that the oxygen fugacity of the metallogenic fluids tends to decrease. As the metallogenesis proceeded to the quartz-magnetite stage (Stage 4), the oxygen fugacity of the metallogenic fluid system weakened, and the reduction of the system became stronger. The metallogenesis tended to transition toward the quartz-sulfide period.

Figure 10. (a) Al + Mn vs. Ti + V correlation diagram; (b) Mg vs. V plot. Figure 10. (a) Al + Mn vs. Ti + V correlation diagram; (b) Mg vs. V plot.

5.3. Indications for the Genesis of the Deposit The stratiform and lenticular ore bodies of the Huanggangliang Sn-Fe deposit are clearly associated with the skarn belt in the contact zone between the Yanshanian alkali granite and the wall rock (Figure 2). The LA-ICP-MS ages of the Huanggangliang k-feldspar granite are in the range of 136.7–139.9 Ma [6,9]. The corresponding (quartz-sulfide period) has Re-Os isochron ages in the range of 135.3–134.9 Ma [7,9]. The metallogenic age of the Huanggangliang deposit is similar to the age of the rock body and is remarkably different from the age of the ore-hosting Permian Zhesi Formation strata. Therefore, the deposit is unlikely to be a sedimentary-exhalative deposit. Magnetite is a key ore mineral in Fe-dominated deposits, including (BIF), -type magmatic Fe-Ti , and Fe skarn deposits [28,32], as well as in other types of hydrothermal deposits such as -- (IOCG) and Cu-Au systems [56,57], which are mostly sub-economic. The high Ni/Cr ratios of the four types of magnetite are all similar to the magnetite of the typical magmatic hydrothermal/hydrothermal deposits (i.e., skarn, IOCG, porphyry-type and Ag-Pb-Zn vein type deposits) (Figure 11a). Therefore, it is difficult to precisely identify the genesis of the deposit based on the Ni/Cr ratios within the four types of magnetites. The relatively low Ti + V (wt %) content, Ni/(Cr + Mn) ratio and high Al + Mn (wt %) content (Figure 11b,c) all demonstrate that the four types of magnetites in the deposit share similar features with skarn deposits, which are remarkably different from those of IOCG, porphyry-type and BIF deposits.

Figure 11. Magnetite discrimination diagrams (a) Ti vs. Ni/Cr (after Reference [30]); (b) Ni/(Cr + Mn) vs. (Ti + V) (after Reference [28]); (c) (Ti + V) vs. (Al + Mn) (after Reference [28]).

In the multi-element diagram (Figure 12), the four types of magnetites share similar distribution patterns, which suggests similar sources. The four types of magnetites show different degrees of depletion in Zr, Nb, Mg, and Co, and slight enrichment of Mn and Zn. These features are similar to those of the magnetites in the skarn and IOCG deposits, while they are different from the magnetite of BIF-type deposits. However, the enrichment of Al and depletion of Sc, V, Ni, and Cr are different from the features of the IOCG-type deposit. In addition, the epidotizaton, tourmalinization, and

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Vanadium exists mostly in the form of (+3, +4, +5) in fluids. Only V3+ could enter the crystal cube of magnetite [31,38,54], i.e., the increase in vanadium content in magnetite represents the decrease in oxygen fugacity [38,41,55]. In Figure 10b, the variation range of V tends to become lower from T1 to T3 magnetite, suggesting that the oxygen fugacity of the metallogenic fluids increased as the metallogenesis proceeded. The V content in the T4 magnetite tends to increase, indicating that the oxygen fugacity of the metallogenic fluids tends to decrease. As the metallogenesis proceeded to the quartz-magnetite stage (Stage 4), the oxygen fugacity of the metallogenic fluid system weakened, and the reduction of the system became stronger. The metallogenesis tended to transition toward the quartz-sulfide period.Figure 10. (a) Al + Mn vs. Ti + V correlation diagram; (b) Mg vs. V plot.

5.3.5.3. Indications for the Genesis of thethe DepositDeposit TheThe stratiformstratiform andand lenticularlenticular oreore bodiesbodies ofof thethe HuanggangliangHuanggangliang Sn-FeSn-Fe depositdeposit are clearlyclearly associatedassociated with the the skarn skarn belt belt in in the the contact contact zone zone between between the theYanshanian Yanshanian alkali alkali granite granite and andthe wall the wallrock rock(Figure (Figure 2). The2). LA-ICP-MS The LA-ICP-MS zircon zircon ages of ages the Huanggangliang of the Huanggangliang k-feldspar k-feldspar granite are granite in the are range in theof 136.7–139.9 range of 136.7–139.9 Ma [6,9]. The Ma [corresponding6,9]. The corresponding molybdenite molybdenite (quartz-sulfide (quartz-sulfide period) has period) Re-Os has isochron Re-Os isochronages in the ages range in the of range135.3–134.9 of 135.3–134.9 Ma [7,9]. MaThe [7me,9].tallogenic The metallogenic age of the ageHuanggangliang of the Huanggangliang deposit is depositsimilar to is similarthe age toof thethe agerock of body the rock and bodyis remarkab and is remarkablyly different from different the age from of the the age ore-hosting of the ore-hosting Permian PermianZhesi Formation Zhesi Formation strata. Therefore, strata. Therefore, the deposit the is deposit unlikely is unlikelyto be a sedimentary-exhalative to be a sedimentary-exhalative deposit. deposit.Magnetite Magnetite is a key isore a keymineral ore mineral in Fe-dominated in Fe-dominated deposits, deposits, including including banded banded iron formation iron formation (BIF), (BIF),Kiruna-type Kiruna-type magmatic magmatic Fe-Ti Fe-Tioxide, oxide, and andFe skarn Fe skarn deposits deposits [28,32], [28,32 as], aswell well as as in in other other types ofof hydrothermalhydrothermal depositsdeposits suchsuch as iron oxide-copper-goldoxide-copper-gold (IOCG) and porphyry Cu-Au systems [56,57], [56,57], whichwhich areare mostlymostly sub-economic.sub-economic. TheThe highhigh Ni/CrNi/Cr ratios of the four types of magnetite are allall similarsimilar toto thethe magnetitemagnetite ofof thethe typicaltypical magmaticmagmatic hydrothermal/hydrothermalhydrothermal/hydrothermal deposits (i.e., skarn, IOCG, porphyry-typeporphyry-type and Ag-Pb-ZnAg-Pb-Zn vein typetype deposits)deposits) (Figure 1111a).a). Therefore, it is difficultdifficult to preciselyprecisely identifyidentify the genesis genesis of of the the deposit deposit based based on on the the Ni/C Ni/Crr ratios ratios within within the thefour four types types of magnetites. of magnetites. The Therelatively relatively low lowTi + TiV (wt + V %) (wt content, %) content, Ni/(Cr Ni/(Cr + Mn) +ratio Mn) and ratio high and Al high + Mn Al (wt +Mn %) (wtcontent %) content(Figure (Figure11b,c) all 11 b,c)demonstrate all demonstrate that the that four the fourtypes types of of magnetitesites in the in the deposit deposit share share similar similar features features with skarnskarn deposits,deposits, which are remarkably different from those of IOCG, porphyry-type and BIF deposits.

FigureFigure 11.11. Magnetite discriminationdiscrimination diagramsdiagrams( a(a)) Ti Ti vs. vs. Ni/Cr Ni/Cr (after(after ReferenceReference [[30]);30]); ((bb)) Ni/(Cr Ni/(Cr ++ Mn) vs.vs. (Ti ++ V) (after Reference [[28]);28]); ((cc)) (Ti(Ti ++ V)V) vs.vs. (Al + Mn) Mn) (after Reference [28]). [28]).

In the multi-element diagram (Figure 12), the four types of magnetites share similar distribution In the multi-element diagram (Figure 12), the four types of magnetites share similar distribution patterns, which suggests similar sources. The four types of magnetites show different degrees of patterns, which suggests similar sources. The four types of magnetites show different degrees of depletion in Zr, Nb, Mg, and Co, and slight enrichment of Mn and Zn. These features are similar to depletion in Zr, Nb, Mg, and Co, and slight enrichment of Mn and Zn. These features are similar to those of the magnetites in the skarn and IOCG deposits, while they are different from the magnetite those of the magnetites in the skarn and IOCG deposits, while they are different from the magnetite of BIF-type deposits. However, the enrichment of Al and depletion of Sc, V, Ni, and Cr are different of BIF-type deposits. However, the enrichment of Al and depletion of Sc, V, Ni, and Cr are different from the features of the IOCG-type deposit. In addition, the epidotizaton, tourmalinization, and from the features of the IOCG-type deposit. In addition, the epidotizaton, tourmalinization, and sericitization of the deposit all occurred during the metallogenic period. In the case of IOCG deposits, these types of alterations mostly occur before the metallogenic period [56,58,59]. To summarize, we Minerals 2018, 8, x FOR PEER REVIEW 14 of 17 Minerals 2018, 8, 195 14 of 17 sericitization of the deposit all occurred during the metallogenic period. In the case of IOCG deposits, these types of alterations mostly occur before the metallogenic period [56,58,59]. To summarize, we believe that the Huanggangliang deposit is a skar skarn-typen-type Sn-Fe deposit whose genesis is related to Yanshanian medium-acidicmedium-acidic magmaticmagmatic activities.activities.

Figure 12. Multi-element diagram for the Heijianshan magnetite, normalized to bulk continental Figure 12. Multi-element diagram for the Heijianshan magnetite, normalized to bulk continental . crust. Data for IOCG from the Ernest Henry deposit [30], BIF from the Sokoman Fe formation [60], Data for IOCG from the Ernest Henry deposit [30], BIF from the Sokoman Fe formation [60], skarn from skarn from the Tengtie skarn Fe [61], and Vegas Peledas calcic skarn Fe [30] deposits are shown for the Tengtie skarn Fe [61], and Vegas Peledas calcic skarn Fe [30] deposits are shown for comparison comparison (normalization values from Reference [62]). (normalization values from Reference [62]).

6. Conclusions 6. Conclusions (1) Petrographic characteristics and geochemical parameters of magnetite suggest that the four (1) Petrographic characteristics and geochemical parameters of magnetite suggest that the four types types of magnetites all belong to hydrothermal magnetite. of magnetites all belong to hydrothermal magnetite. (2) Compositions of the ore fluids and host rocks, formation of coexisting minerals, and other (2) Compositions of the ore fluids and host rocks, formation of coexisting minerals, and other physical physical and chemical parameters (such as fO2) may have variably influenced the magnetite and chemical parameters (such as f O2) may have variably influenced the magnetite geochemistry geochemistry in the different Huanggangliang ore types, with fluid compositions and fO2 in the different Huanggangliang ore types, with fluid compositions and f O probably playing the probably playing the most important role. 2 most important role. (3) Geological characteristics, micro-structural features, and trace element traits of the (3) Geological characteristics, micro-structural features, and trace element traits of the Huanggangliang Sn-Fe deposit indicate that the deposit is a skarn-type Sn-Fe deposit associated Huanggangliang Sn-Fe deposit indicate that the deposit is a skarn-type Sn-Fe deposit associated with Yanshanian medium-acidic magmatic activities. with Yanshanian medium-acidic magmatic activities. Author Contributions: C.W., Y.S., and Z.L. conceived and designed the experiments; C.W. performed the experiments;Author Contributions: X.Z. and J.D.C.W., helped Y.S., editing and Z.L.and conceivedimproved English and designed wording the and experiments; language style; C.W. allperformed authors wrote the theexperiments; paper. X.Z. and J.D. helped editing and improved English wording and language style; all authors wrote the paper. Acknowledgments: ThisThis workwork was was supported supported by theby the Innovation-driven Innovation-driven Plan ofPlan Central of Central South UniversitySouth University (Project 1053320180985)(Project 1053320180985) and the Nationaland the National Natural ScienceNatural FoundationScience Foundation of China of (Grant China no. (Grant 41702078). no. 41702078). ConflictsConflicts of Interest: The authors declare no conflictconflict ofof interest.interest.

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