Trace element compositions of pyrite and stibnite:implications for the genesis of antimony mineralization in the Yangla Cu skarn deposit,Northwestern Yunnan,China

The Yangla Cu skarn deposit is located in the central part of the Jinshajiang Suture Zone,southwest China,with a total reserve of 150 Mt Cu@1.03%.The newly discovered antimony orebodies at the depth of Yangla are strictly controlled by the stratum,structure,and lithology,which are lenticular and vein-like within the marble fracture zone,which can provide a window into multistage miner-alization and ore genesis at Yangla.Mineralization can be divided into three types,Cu–Pb–Zn(skarn)pyrite,galena,and sphalerite,Cu(porphyry)chalcopyrite and pyrite,and Sb(hydrothermal)stibnite and pyrite.The mineral assem-blages were stibnite+pyrite+calcite+quartz±minor scheelite in antimony ores.This study presents quantitative measurements of the trace element compositions of pyrite and stibnite from the Yangla antimony ores.Analysis of pyrite with electron probe microanalysis(EPMA)showed enrichment in Co,Ni,Sb,As,and Mo,and deficit in its S and Fe contents when compared to the stoichiometric con-centrations of S and Fe in pyrite.The Sb-related pyrite may belong to sedimentary-reworked genesis and may be modi-fied by hydrothermalfluids,thereby presenting a certain dif-ference(i.e.,crystal morphology,texture,and chemical com-position)compared to the skarn and porphyry Cu-related pyrite in the Yangla Cu skarn deposit.Analysis of stibnite with EPMA and inductively coupled plasma-mass spectrom-etry showed enrichment in As,Pb,Sn,Pb,Cu,and Zn,and presented much higher Sb contents and slightly lower S con-tents when compared to the stoichiometric concentrations of Sb and S in stibnite.Statistical analysis of the stibnite trace elements showed correlations for the elemental pairs Cu–Pb,As–Sb,and Sn–Pb,and the coupled substitution equations Sb^(3+)↔Cu^(+)+Pb^(2+),Sb^(3+)↔As^(3+),and Sn^(2+)↔Pb^(2+)may be the major factors governed the incorporating Cu,Pb,As and Sn within the stibnite.Moreover,this study preliminary shows that the antimony mineralization may belong to a car-bonate replacement hydrothermal genesis at Yangla.

Geochemical Behaviors of REE and Other Trace Elements during the Formation of Strata-bound Skarns and Related Deposits:A Case Study of the Dongguashan Cu(Au)Deposit,Anhui Province,China

REE and other trace elements in the altered marbles, massive skarns and ores, as well as garnet and quartz were determined in order to examine the behaviors of trace elements during hydrothermal alteration. It is demonstrated that the high-field-strength (HFS) elements Zr, Hf, Th and Nb were immobile while other trace elements were mobile during the formation of skarns and related deposits. REE and ore-forming elements such as Cu and Ag in hydrothermally-altered marbles and skarns were provided primarily by hydrothermal fluids. In the direction transverse of the strata, the more deeply the marbles were altered, the higher the total REE abundance and the larger the negative Eu anomalies would be. The chondrite-normalized REE patterns of skarns are similar to those of the marbles, but the former are distinguished by much higher REE contents and more remarkable negative Eu anomalies. Those patterns were apparently not inherited from the marble protolith, but were controlled by garnets, which were determined by the hydrothermal solutions involved in the infiltration metasomatism. The hydrothermal fluids are characterized by having slightly right-hand dipping REE patterns, being enriched in LREE and having strongly negative Eu anomalies. The uptake of REE from hydrothermal fluids during the growth of garnet crystals resulted in the garnets having similar REE patterns to the hydrothermal fluids. Based on the spatial variation of REE in skarns and the structures of the hosting strata, we can get a better understanding of the transport path and pattern of the fluids involved in the formation of skarns and their related deposits. REE geochemistry investigation can help elucidate the genesis of skarns and skarn-related deposits.

Petrogenesis of skarn in Shizhuyuan W-polymetallic deposit, southern Hunan,China:Constraints from petrology,mineralogy and geochemistry

Skarn is the main altered rock type and is of great importance to mineralization and ore-prospecting in the Shizhuyuan area of Hunan province, China. Its features of petrography, mineralogy and geochemistry were studied systematically. The results show that the skarn mainly consists of garnet skarn, secondary wollastonite-garnet skarn, tremolite-clinozoisite skarn, and few wolframine garnet skarn, idocrase-garnet skarn and wollastonite skarn with granoblastic texture, granular sheet crystalloblastic texture, and massive structure, disseminated structure, mesh-vein structure, comb structure, and banded structure. And, it is mainly composed of garnet, fluorite, chlorite, hornblende, epidote, tremolite, plagioclase, biotite, muscovite, plagioclase, quartz, idocrase, and calcite and so on. The chemical components mainly include SiO2, Al2O3, Fe2O3, MgO and CaO, and the trace elements and REEs consist of Li, Be, V, Co, Zn, Ga, Rb, Sr, Y, Ce, Nd, Pb and Bi, etc. And, the obvious fractionation exists between LREE and HREE, and it shows typical features of Nanling ore-forming granite for W？Sn polymetallic deposit. Skarn is derived from the sedimentary rock, such as limestone, mudstone, argillaceous rock, and few pelitic strips. It is affected by both Shetianqiao formation strata and Qianlishan granite during the diagenesis, indicating a strong reduction environment. The occurrence of skarn, whose mutation site is favorable to the mineralization enrichment, is closely related to the mineralization and prospecting.

Fluid-melt Inclusions in Fluorite of the Huanggangliang Skarn Iron-Tin Deposit and Their Significance to Mineralization

For the first time, fluid-melt inclusions are found in fluorite of the Huanggangliang skarn iron-tin deposit (HSID). The fluorite was formed in the main stage of mineralization, named the hydro-skarnization stage. The inclusions contain various components such as Fe, Mg and Cr from deep sources. The melts of primary inclusions are mainly Ca- and F-rich and those of secondary inclusions tend to become Si-rich. During this evolution process, the melts and iron daughter minerals decreased and even vanished. These facts reveal that the evolution of the primary mineralizing fluids and the differentiation of the fluids and melts are the main factors leading to the deposition of Fe, Sn and other elements. This discovery confirms the magmatic genesis of the HSID and has filled in the gaps in the research of magmatogenic skarn deposits and furnished new methods for such research. Furthermore, it has enlarged the scope of the research on fluid inclusions.

Genesis of Yangla Banded Skarn-Hosted Copper Deposit in Tethys Orogenic Belt of Southwestern China

Yangla copper deposit is the largest banded skarn hosted copper deposit found recently in the Tethys orogenic belt of Southwestern China. On the basis of the study of distribution, petrology and mineralogy as well as major element, REE and isotope geochemistry, the authors find that the banded skarn, which hosts the deposit, was precipitated from hydrothermal solutions in the form of exhalate sediment. Therefore, the banded skarn hosted copper deposit is a Sedex type deposit, with a series of stacked, conformable lenses underlain by at least one stringer zone. The deposit, intercalated at the contact of lower clastic rock and upper carbonate rock of Gajinxueshan Group, was formed in the Carboniferous ((296.1±7.0) Ma), contemporary to the host Gajinxueshan Group. The interpretation of the genesis of Yangla banded skarn hosted copper deposit is of fundamental exploration significance for the discovery of Sedex type copper deposit in the region.

DISCOVERY AND THE IMPLICATION OF A HYDROTHERMAL-METASOMATIC SKARN DEPOSIT IN GANGDISE TECTONIC ZONE,TIBET

Hydrothermal activity from a hydrothermal circulatory system is a special geological event, it is of importance to the formation of some massive sulfide deposits (hydrothermal deposits). The Authors think that Jiama polymetallic ore deposit in Gangdise tectonic zone, Tibet is a special skarn deposit i.e. a “hydrothermal\|metasomatic skarn deposit" bound up with benthonic hydrothermal circulatory system. Its important characteristics are as follows: 1 Evolution of the Gangdise island arc in studied area may be divided into three stages Middle Jurassic volcanic arc stage; Middle—Late Jurassic and Early Cretaceous inter arc sedimentary basin stage; and Eogene magmatic arc stage. The deposit is confined to the inter arc sedimentary basin. Existing data indicate that the volcanic arc provided Jiama deposit with abundant ore\|forming material; the inter arc sedimentary basin provided Jiama deposit with absolutely necessary space; the magmatic arc created reconcentration condition for the Jiama deposit.

He-Ar-S-Pb Isotopic Compositions of Pyrite：Constraints on the Source of Ore-forming Materials of the Chengchao Skarn Iron Deposit,SE Hubei Province,Eastern China

The Chengchao iron deposit,the largest high-grade skarn iron deposit in southeastern Hubei Province,contains considerable amounts of magnetite and by-product anhydrite.To obtain better understanding of the ore-formation process,this study carried out He-Ar-S-Pb multi-isotopic analyses on the pyrites formed during two stages of mineralization.The results indicate that the δ34S values（ranging from 14.0‰ to 17.6‰） of pyrites formed from the two stages have no obvious differences,suggesting that they were not derived from a single magmatic sulfur source.The δ34S values of anhydrite mostly range from 21.9‰ to 28.4‰,similar to that of the Middle Triassic sedimentary anhydrite in the Middle-Lower Yangtze River metallogenic belt（MLYRB）.The Pb isotopic compositions of the pyrites of both stages are homogeneous,with values of 208Pb/204Pb,207Pb/204Pb,and-206Pb/204Pb being 38.006-38.257,15.523-15.556,and 17.806-18.052,respectively,indicating a mixed crust-mantle source.The He-Ar results exhibit different compositions of the two stages：the -3He/-4He（R/Ra） and 40Ar/-36Ar values for the early-stage pyrite are 0.46-0.63 and 311-322,respectively,whereas the values for late-stage pyrite are 0.23-0.34 and 305-361,respectively.Both stages of pyrites indicate the multiple sources of the ore-forming fluids,with decreasing amount of magmatic water and increasing amount of modified meteoric water（MASW） during fluid evolution.The Triassic evaporites played an important role in the mineralization process.

Skarn mineralogy and its geological significance for the Tayuan (Cu-Mo)-Pb-Zn deposit, northern Daxinganling metallogenic belt

The Tayuan(Cu-Mo)-Pb-Zn deposit is located in the northern part of Daxinganling,NE China.Lenticular ore body occurs in the skarn zone.The skarn minerals mainly include garnet,pyroxene,epidote and wollastonite.Electron microprobe analysis shows that the end member of garnet is mainly andradite(Ad_(62-97)Gr_(11-45),the pyroxene is mainly diopside,and epidote is mainly clinozoisite.These characteristics indicate that the Tayuan polymetallic skarn deposit is mainly calcareous skarn.Sometimes the content zonation can be observed in garnets.With one garnet crystal,content is shifty from the core to the rim.In general,the iron content in the core is higher than in the edge.The content in the garnet shows that the garnet in the Tayuan deposit formed from weak oxidation in alkaline environment with the oxygen fugacity increasing,suggesting that the hydrothermal fluid evolved from an acidic to a slight alkaline state.In the Tayuan polymetallic deposit,the ratio of Mn/Fe in pyroxene is about 1.3,and of Mg/Fe,it is about 2.The components of garnet in the Tayuan deposit plot in the field of the typical skarn Zn,Cu,Mo deposits in the world.

Quantitative analysis of intrusive body morphology and its relationship with skarn mineralization——A case study of Fenghuangshan copper deposit, Tongling, Anhui, China

The shapes of intrusive body and contact zone might influence the formation and distribution of orebodies in skarn deposit.By taking Xinwuli intrusive body in Fenghuangshan copper deposit,Tongling,Anhui,China,as the research object,a new method was used to obtain the quantitative relationship between intrusion morphology and skarn mineralization.The first step of the method was to extract morphological characteristic parameters based on mathematical morphology and Euclidean distance transformation;then the quantitative relationship between the parameters and orebodies was analyzed;finally correlational analyses between the parameters and mineralization indices were conducted.The results show that morphological characteristic parameters can effectively indicate the location of concealed ore bodies in skarn deposit,with the following parts as advantageous positions of skarn mineralization:(1)the parts away from the1st trend surface in the range from?25to50m;(2)the convex parts about200m away from the2nd trend surface,around which the tangent plane of the intrusive body is approximately consistent with the trend surface;(3)the contact zones with angle between intrusive body original contact surface and trend contact surface ranging from35°to70°;(4)the parts with angle between intrusive body original contact surface and regional extruding far crustal stress ranging from50°to60°.These knowledge can be applied to more skarn deposits for future mineral exploration.

Dynamics of Ore-Forming Processesof the Stratabound Skarn Copper Depositsof Tongling, Anhui Province

The skarn and ore bodies of the stratabound skarn copper deposits of Tongling, Anhui Province, are both controlled by definite stratigraphic horizons, and they are concordant with the strata. They occur as layers and layer-like bodies in permeable carbonate rocks of the Middle-Upper Carboniferous Huanglong and Chuanshan Formations which are underlain by impermeable shale or siliceous rocks of the Upper Devonian Wutong Formation. The authors study the dynamics of ore-forming processes of the ore deposits with the dynamic model of coupled transport and reaction, and the following results are obtained: The salinity gradient and flow rate of the ore-forming fluids can both promote the mixing and reaction of juvenile water and formation water, and the permeable strata are favourable sites for the intense transport-reaction of mixing and the formation of deposits. (2) As isothermal transport-reaction took place along the bedding of strata, the moving transport-reaction front formed at the contact between the ore-forming fluids and the rocks advanced slowly along the permeable strata, and then stratiform skarn and ore bodies concordant with the strata were formed. (3) The gradient transport-reaction taking place across the isotherms in the cross-bedding direction caused the mineralogical composition to alter gradually from magnesian skarn to sulphide ore bodies.

Origin of the Oligocene Tuolangla porphyry-skarn Cu-W-Mo deposit in Lhasa terrane,southern Tibet

Although some porphyry-skarn deposits occur in post-collisional extensional settings,the post-collisional deposits remain poorly understood.Here the authors describe the igneous geology,and mineralization history of Tuolangla,a newly-discovered porphyry-skarn Cu-W-Mo deposit in southern Tibet that belongs to the post-collisional class.The deposit is associated with Lower Cretaceous Bima Formation.It was intruded by granodiorite porphyry intrusions at about 23.1 Ma.Field investigation indicated that mineralization is spatially and temporally associated with granodiorite porphyry.Molybdenite yielded a Re-Os weighted mean age of 23.5±0.3 Ma and is considered to represent the age of skarn mineralization at the deposit.Theδ^34S values of sulfides,concentrated in a range between 0.6‰to 3.4‰,show that the sulfur has a homogeneous source with characteristics of magmatic sulfur.The Pb isotopic compositions of sulfides indicate that ore-forming metal materials were derived from the mantle and ancient crust.The granodiorite porphyry displays high SiO2(68.78%–69.75%)and K2O(3.40%–3.56%)contents,and relatively lower Cr(2.4×10^-6–4.09×10^-6),Ni(2.79×10^-6–3.58×10^-6)contents,and positiveεHf(t)values(7.7–12.9)indicating that the mineralization porphyry was derived from the partial melting of juvenile lower crust.The Tuolangla deposit is located in the central part of Zedang terrane.This terrane was once considered an ancient terrane.This terrane is in tectonic contact with Cretaceous ophiolitic rocks to its south and Mesozoic continental margin arc volcanics and intrusions of the Gangdese batholith of the Lhasa terrane to its north.Thus,the authors proposed that the Oligocene porphyry skarn Cu-W-Mo mineralization is probably associated with the Zedang terrane.This finding may clarify why the Oligocene(about 23 Ma)deposits are found only in the Zedang area and why mineralization types of the Oligocene mineralization are considerably different from those of the Miocene(17–14 Ma)mineralization.

Discovery of Lorandite TlAsS_2 at the Distal Au-Tl Deposit in a Skarn system,Fengshan Area,Middle-Lower Yangtze River,Eastern China

Thallium has been used geochemical exploration of gold deposits. However, as an indicator element in searching for hydrothermal the T1 minerals and mineralization are rare in nature. Lorandite T1AsS2, a relatively uncommon mineral, has been dominantly discovered in some Carlin gold deposits, and minor Sb- Hg, U and Pb-Zn-Ag deposits.

Ilvaite as a thermodynamic recorder of multistage retrograde alteration in large Galinge skarn Fe deposit, western China

The ilvaite-bearing skarn associations in the Galinge skarn deposit were studied to determine their physicochemical formation conditions.A thermodynamic model setting pressure of 50 MPa(Pf=Ps=50 MPa)was set up to trace the skarn evolution.Petrographic evidence for replacement of garnet and magnetite by ilvaite in the early retrograde stage(Stage I)combined with thermodynamic modeling suggests that the alteration may have occurred at 400470°C under moderately high fO withΔlgfO(HM)ranges from 4 to 4.2.The model is based on a maximum 22 pressure of 50 MPa calculated from magmatic amphibole geobarometer.The continuous breakdown of ilvaite with quartz to form ferro-actinolite and magnetite occur in the late retrograde stage(Stage II).The reactions occurred at 400440°C under moderate fO(ΔlgfO(HM):4 to 4.4).In Stage III,the breakdown of ilvaite to form calcite,pyrite 22 and ferroactinolite depends on XCO which can be estimated to be in a range of 0.005 to 0.05,and the reaction would 2 occur at higher temperatures with increasing XCO.Under these conditions,the breakdown occurs at 270350°C and 2 low fO(ΔlgfO(HM):up to 5.2).The thermodynamic model for continuous evolution from Stage I to Stage III 22 completely records the conditions of the retrograde alteration,which is inconsistent with the thermobarometry imprints of fluid inclusions.Therefore,the petrography and phase relations of ilvaite are useful indicators of reaction conditions in various skarn deposit types.

Molybdenite Re-Os,titanite and garnet U-Pb dating of the Magushan skarn Cu-Mo deposit,Xuancheng district,Middle-Lower Yangtze River Metallogenic Belt

The Magushan skarn Cu-Mo deposit is a representative example of the skarn mineralization occurring within the Xuancheng ore district of the Middle-Lower Yangtze River Metallogenic Belt of eastern China.The precise age of an ore deposit is important for understanding the timing of mineralization relative to other geological events in a region and to fully place the formation of a mineral deposit within the geological context of other processes that occur within the study area.Here,we present new molybdenite Re-Os and titanite and andradite garnet U-Pb ages for the Magushan deposit and use these data to outline possible approaches for identifying genetic relationships in geologically complex areas.The spatial and paragenetic relationships between the intrusions,alteration,and mineralization within the study area indicates that the formation of the Magushan deposit is genetically associated with the porphyritic granodiorite.However,this is not always the case,as some areas contain complexly zoned plutons with multiple phases of intrusion or mineralization may be distal from or may not have any clear spatial relationship to a pluton.This means that it may not be possible to determine whether the mineralization formed as a result of single or multiple magmatic/hydrothermal events.As such,the approaches presented in this study provide an approach that allows the identification of any geochronological relationships between mineralization and intrusive events in areas more complex than the study area.Previously published zircon U-Pb data for the mineralization-related porphyritic granodiorite in this area yielded an age of 134.2±1.2 Ma(MSWD=1.4)whereas the Re-Os dating of molybdenite from the study area yielded an isochron age of 137.7±2.5 Ma(MSWD=0.43).The timing of the mineralizing event in the study area was further examined by the dating of magmatic accessory titanite and skarn-related andradite garnet,yielding U-Pb ages of 136.3±2.5 Ma(MSWD=3.2)and 135.9±2.7 Ma(MSWD=2.5),respectively.The dating of magmatic and hydrothermal activity within the Magushan area yields ages around 136 Ma,strongly suggesting that the mineralization in this area formed as a result of the emplacement of the intrusion.The dates presented in this study also provide the first indication of the timing of mineralization within the Xuancheng district.providing evidence of a close genetic relationship between the formation of the mineralization within the Xuancheng district and the Early Cretaceous magmatism that occurred in this area.This in turn suggests that other Early Cretaceous intrusive rocks within this region are likely to be associated with mineralization and should be considered highly prospective for future mineral exploration.This study also indicates that the dating of garnet and titanite can also provide reliable geochronological data and evidence of the timing of mineralization and magmatism,respectively,in areas lacking other dateable minerals(e.g.,molybdenite)or where the relationship between mineralization and magmatism is unclear,for example in areas with multiple stages of magmatism,with complexly zoned plutons,and with distal skarn mineralization.

Laser Ablation ICP-MS Titanite U-Th-Pb Dating of the Tonglushan Cu-Fe-Au Skarn Deposit,Southeastern Hubei Province

Titanite(CaTi2SiO5) is an important accessory mineral not only in magmatic and metamorphic rocks,but also commonly in hydrothermal mineral deposits. It incorporates appreciable amounts(usually 10×10-6 s to 100×10-6 s) of U and Th into its structure and has a closure temperature of Pb diffusion higher than 660～700 ℃(Scott and St-Onge,1995) ,making it an ideal U-Th-Pb geochronometer. The Daye metallogenic district is located in the west of the giant Middle-Lower Yangtze River(MLYR) Cu-Fe-Au province,eastern China and is well endowed with Fe,Cu,and polymetallic skarn deposits.

Carbon–oxygen isotopic covariations of calcite from Langdu skarn copper deposit, China: implications for sulfide precipitation

The Langdu skarn copper deposit in the Zhongdian area, Yunnan Province, China, has an average Cu grade of 6.49 %. The deposit is related to a porphyry intrusion(*216 Ma), which was emplaced in the Upper Triassic sedimentary rocks of the Tumugou and Qugasi Formations.At the Langdu skarn copper deposit, carbon and oxygen isotope ratios of fresh limestones(d18O = 3.0–5.6 % relative to V-SMOW; d13 C = 24.5–25.7 % relative to PDB)and partly altered limestones(d18O = 27–7.2 to-1.9 %;d13C = 11.8–15.2 %) indicated that the deposit was a typical marine carbonate source. Oxygen and carbon isotope values for calcites formed at different hydrothermal stages are-9.1 to 0.2 and 10.1–16.3 %, respectively. Moreover,the carbon–oxygen isotopic composition of an ore-forming fluid(d18O = 5.0–9.5 %, d13 C =-7.3 to-5.3 %) suggested the presence of magmatic water, which most likely came from the differentiation or melting of a homologous magma chamber. The deposition of Calcite I may arise from metasomatism in an open system with a progressively decreasing temperature.Later, the minerals chalcopyrite, pyrrhotite, quartz and Calcite II were precipitated due to immiscibility. Water–rock interaction could potentially be responsible for Calcite III precipitation in the post-ore stage.

Geology and geochemistry of Huanggangliang stratabound skarn deposit in Inner Mongolia,China

Over the recent three decades, exploration of a large-size Sn-Fe polymetallic ore deposit at the Huanggangliang, the Da Hinggan Mountains, Inner Mongolia, China, has been largely focused on the premise that the mineralization represents epigenetic magmatic hydrothermal ore deposit in genetic connection with the Mesozoic magmatism. The Huanggangliang Sn-Fe polymetallic ore deposits occurred in Permian strata, with silt- stone/marble of the Zhesi Formation and spilite/andesite/tuff of the Dashizhai Formation. The characteristics of geological and geochemical data demonstrated that sedimentary hydrothermal mineralization occurred during the basin evolution at the Permian, rather than representing epigenetie magmatic hydrothermal genesis with the following evidences. The ore-bearing skarus are stratiform with underlying metasedimentary rocks and overlying volcanic sedimentary rocks. Sedimentary hydrothermal textures and structures are observed in the stratabound ore-bearing skarn such as bedded-laminated skarn and magnetite ores with small-size folding or soft deforma- tion, synsedimentary breccia of skarn and magnetite ores and concentric shell structure of magnetite ores. So the stratabound ore-bearing skarns associated with magnetite ore and micro-disseminated tin, are peculiar examples of exhalite. The REE contents of the stratabound ore-bearing skarns display ∑LREE-rich （36.91×10^-6） but EHREE-depletion （6. 42 ×10^-6） , with positive Eu anomaly （Eu/Eu ＊ 1.28） and negative Ce anomaly （Ce/ Ce ＊ 0.88 ） , which is totally different from REE pattern of the Huanggang magmatic rocks（ with ∑REE 277.73 ×10^-6, ELREE 220.24 ×10^-6, ∑HREE 57.49 ×10^-6, Eu/Eu＊ 0.06, Ce/Ce＊ 1.52） , which is comparable with modern sea-floor hydrothermal fluid,sedimentary hydrothermal ore deposit and associated hydrothermal sedimentary rocks. Calcite samples with δ13CPDB from -5. 400 ‰ to -4. 397 ‰ and δ18SOSMOW from 9. 095 ‰ to 9. 364 ‰ in the stratabound ore-bearing skarns show sedimentary hydrothermal genesis of the Huanggangliang deposit. This proposition is useful not only for interpretation of the genesis of the Huanggangliang large Sn-Fe polymetallic ore deposit but also significant for mineral exploration in the area especially for finding large deposits caused by sedimentary exhalative mineralization processes.

METALLOGENIC CONDITIONS OF GOLD-BEARING SKARN DEPOSITS ALONG THE MIDDLE-LOW ER REACHES OF THE YANGTZE RIVER

The authors discussed the metallogenic conditions of goldbearing skarn deposits along the middlelower Yangtze River reaches. Gold was enriched in mantleoriginated magmas while copper was enriched in crustoriginated magmas. So the enrichment of gold in skarn deposits was decided by the M/C ratios of the intrusive rocks. The distribution of these deposits was controlled not only by the localization of the intrusive rocks which were decided by Mesozoic Eradeveloped largescaled and deepseated faults, but also by the favorable stratigraphic horizons.

Analyzing the Characteristics and Available Attributes of Skarn Gold Deposit Tailings

Skarn gold deposit tailings is a kind of tailings which is difficult to be utilized effectively. Taking a skarn gold deposit tailings from Hubei province, in China, as an example, the paper has tested and analyzed the tailings, and studied the characteristics and available attributes of the tailings, and provided scientific and efficient utilization approaches of tailings in the area of building materials further. The results showed that major mineral phases in the tailings is quartz, particle sizes of the tailings mainly exist in 10–100 μm, and the tailings has no pozzolanic activity. As a result, this kind of tailings can be used for building sand, and can be used as supplementary cementing material of concrete based on

Mineral Deposit Model of Cu-Fe-Au Skarn System in the Edongnan Region, Eastern China

Cu and Fe skarns are the world's most abundant and largest skarn type deposits,especially in China,and Au-rich skarn deposits have received much attention in the past two decades and yet there are few papers focused on schematic mineral deposit models of Cu-Fe-Au skarn systems.Three types of Au-rich deposits are recognized in the Edongnan region,Middle-Lower Yangtze River metallogenic belt:~140 Ma Cu-Au and Au-Cu skarn deposits and distal Au-Tl deposits.137-148 Ma Cu-Fe and 130-133 Ma Fe skarn deposits are recognized in the Edongnan region.The Cu-Fe skarn deposits have a greater contribution of mantle components than the Fe skarn deposits,and the hydrothermal fluids responsible for formation of the Fe skarn deposits involved a greater contribution from evaporitic sedimentary rocks compared to Cu-Fe skarn deposits.The carbonate-hosted Au-Tl deposits in the Edongnan region are interpreted as distal products of Cu-Au skarn mineralization.A new schematic mineral deposit model of the Cu-Fe-Au skarn system is proposed to illustrate the relationship between the Cu-Fe-Au skarn mineralization,the evaporitic sedimentary rocks,and distal Au-Tl deposits.This model has important implications for the exploration for carbonate-hosted Au-Tl deposits in the more distal parts of Cu-Au skarn systems,and Fe skarn deposits with the occurrence of gypsum-bearing host sedimentary rocks in the MLYRB,and possibly elsewhere.