Unveil the Redox Evolution of Ore-forming Fluids using Sulfur Isotope:A Case Study of the Zhengguang Intermediate Sulfidation Epithermal Au-Zn Deposit,NE China

Oxygen fugacity(fO_(2))is a key intensity variable during the entire magmatic-hydrothermal mineralization courses.The redox state and its variations between different stages of the ore-forming fluids of intermediate sulfidation epithermal deposits are rarely deciphered due to the lack of appropriate approaches to determine fO_(2)of the fluids.Here,we reported theδ^(34)S of the sulfides from three different stages(stageⅠ,Ⅱ,Ⅲ)of Zhengguang,an Early Ordovician Au-rich intermediate sulfidation(IS)epithermal deposit,to decipher the redox evolution of the ore-forming fluids.The increasingδ^(34)S values from stageⅠpyrite(pyl,average-2.6‰)through py2(average-1.9‰)to py3(average-0.2‰)indicates a decrease of the oxygen fugacity of the ore-forming fluids.A compilation ofδ^(34)S values of sulfides from two subtypes of IS deposits(Au-rich and Ag-rich)from NE China shows that theδ^(34)S values of sulfides from Au-rich IS deposits are systematically lighter than those of Ag-rich IS Ag-Pb-Zn deposit,indicating the ore-forming fluids of the former are more oxidized than the latter.We highlight that sulfur isotopic composition of hypogene sulfides is an efficacious proxy to fingerprint the oxygen fugacity fluctuations of epithermal deposits and could potentially be used to distinguish the subtypes of IS deposits.

The first discovery of Xinlong epithermal gold deposit in southern margin of the Bangonghu-Nujiang metallogenic belt: A new expansion of gold prospecting in Northern Tibet

The Xinlong gold deposit is located in Niyma County,Naqu area of Tibet and was discovered by the Institute of Mineral Resources,Chinese Academy of Geological Sciences through the 1∶50000 mineral geological survey.The ore bodies occur in the Zenong Group volcanic rocks in the middle section of the central Lhasa subterrane and are structurally controlled by the NNW-striking faults.Four ore bodies have been found,exhibiting cloddy,dense-sparse,disseminated,and breccia structures.The ore minerals are mainly tetrahedrite group minerals,and other ore minerals include pyrite,chalcopyrite,nevskite,bornite,anglesite,native gold,and silver-gold bearing selenide,etc.The types of alteration are dominated by silicification,as well as middle-and high-graded argillization.The alteration mineral assemblages contain quzrtz,pyrophyllite,and kaolinite.The Zaliela Formation volcanic rocks of Zenong Group are silicified by later hydrothermal fluid with vuggy quartz in some fractured zones.The middle-and high-graded argillization are characterized by pyrophyllitization and kaolinization.The Xinlong gold deposit shows great metallogenetic potentiality and has been revealed by 1∶10000 geological mapping,IP sounding,and trial trenching in the mining area.Combined with the regional metallogenic geological setting,we suppose that a potential epithermal gold belt probably exists in the middle of the Lhasa terrane.The discovery of the Xinlong gold deposit opens a new chapter for the gold prospecting in Northern Tibet.

Geological Characteristics of Epithermal Ore Concentrated Areas and Epithermal Ore Deposits in China

The epithermal ore concentrated area is located in Southwestern China. We systematically study the regional geological characteristics such as the basement of Proterozoic, the capping bed, Moho, geothermal feature and tectonics, and discuss the relationship between distributed characteristics of the epithermal ore deposits and ore control factors in this paper. It is concluded that the conditions, under which the epithermal ore deposits form, are huge thick basement of Proterozoic, long time and wide scope developed capping bed and weak magmatic activity. The basement of Proterozoic that enriches volcanic matters and carbon and the carbonaceous bearing and paleo pool bearing capping bed provides main ore source. The large and deep faults and paleopool accordance with gravity anomaly gradient control the distribution of epithermal ore deposits. The lithologic assembles of microclastic rocks and carbonate rocks in the capping bed provide spaces of ore precipitation and create conditions of ore precipitation. The coincidence of many geological factors above forms the epithermal ore concentrated area.

Laumontitization as an Exploration Indicator of Epithermal Gold Deposits: A Case Study of the Axi and Other Epithermal Systems in West Tianshan, China

In the light of field investigation, microscopic study, X\|ray phase analysis and mineral infrared spectral analysis, it is considered that laumontitization is of extensive occurrence in the Axi gold orefield. The development of laumontitization and its relationship to mineralization show that the laumontitization appeared mainly at the top of and in the periphery of orebodies, and occurred at the edge of the epithermal system or at the late stage of epithermal system evolution. Therefore, laumontitization can be used as an exploration indicator of epithermal gold deposits. The fluids responsible for laumontitization in the Axi gold orefield are similar to those producing hot spring\|type gold deposits or those from modern geothermal fields. Epithermal mineralization of the Axi gold deposit was dated at Carboniferous, indicating that the West Tianshan of China is a region favorable to epithermal\|type gold mineralization and preservation. Hence the West Tianshan of China is a target area for exploring epithermal gold deposits.

Epithermal Ageing Mechanism of Gussasphalt

The normal asphalt index test, DSR test, FTIR and the GPC distribution analysis of molecular weight on the extraction and recovery of asphalt of the gussasphalt, SMA extraction and recovery of asphalt and the rotary-thin-film-oven-aged asphalt above 240 ℃ were introduced. The results indicate the rutting factor and fatigue factor of the extraction and recovery of asphalt of the gussasphalt are greatly improved, and an obvious absorption peak of carbonyl and a further decrease of the SBS molecular weight of the gussasphalt are found.

Genesis of the Ciemas Gold Deposit and Relationship with Epithermal Deposits in West Java,Indonesia:Constraints from Fluid Inclusions and Stable Isotopes

The Ciemas gold deposit is located in West Java of Indonesia, which is a Cenozoic magmatism belt resulting from the Indo-Australian plate subducting under the Eurasian plate. Two different volcanic rock belts and associated epithermal deposits are distributed in West Java： the younger late Miocene-Pliocene magmatic belt generated the Pliocene-Pleistocene epithermal deposits, while the older late Eocene-early Miocene magmatic belt generated the Miocene epithermal deposits. To constrain the physico-chemical conditions and the origin of the ore fluid in Ciemas, a detailed study of ore petrography, fluid inclusions, laser Raman spectroscopy, oxygen-hydrogen isotopes for quartz was conducted. The results show that hydrothermal pyrite and quartz are widespread, hydrothermal alteration is well developed, and that leaching structures such as vuggy rocks and extension structures such as comb quartz are common. Fluid inclusions in quartz are mainly liquid-rich two phase inclusions, with fluid compositions in the NaCI-H2O fluid system, and contain no or little CO2. Their homogenization temperatures cluster around 240℃-320℃, the salinities lie in the range of 14-17 wt.% NaCI equiv, and the calculated fluid densities are 0.65-1.00 g/cm^3. The values of δ18OH2O-VSMOW for quartz range from ＋5.5%0 to ＋7.7‰, the δDVSMOW of fluid inclusions in quartz ranges from -70‰ to -115‰. All of these data indicate that mixing of magmatic fluid with meteoric water resulted in the formation of the Ciemas deposit. A comparison among gold deposits of West Java suggests that Miocene epithermal ore deposits in the southernmost part of West Java were more affected by magmatic fluids and exhibit a higher degree of sulfidation than those of Pliocene-Pleistocene.

Fluid Inclusion Investigations of the Masjed Daghi Copper-Gold Porphyry-Epithermal Mineralization, East Azerbaijan Province, NW Iran

The Masjed Daghi mineralization is located 30 km southeast of Jolfa city at the bank of Araxes River, northwest Iran. This area is situated in the Alborz-Azarbaijan structural zone of Iran. The most widespread rocks in the mineralization area are andesite and trachyandesite, while there are rock units of latite tuff, andesitic agglomerate, and hornblende porphyry basalt in eastern hills and Eocene flysch in the southern part of the area. Several intrusive bodies are present in the study area, from which the dominant intrusive rock hosting the mineralization is diorite porphyry. The mineralized rock units of the area are cut by different diorite ad mafic dikes. The most prevalent texture of mineralization is dissemination, while open space filling textures including veins and veinlets, are common as well. Diverse types of alteration including potassic, phyllic, argillic, silicification, and a little of carbonatization were recognized in the field and microscopic observations as well as by XRD. In addition to thick silica veins and stockwork zones, some silica, barite, sulfide, and calcite veins and veinlets have occurred in the Masjed Daghi mineralization area. In this research, 26 doubly polished thin sections (wafers) were prepared and investigated. Four samples were taken from surface veins, while 22 samples were chosen from core samples (of 6 boreholes) of white and grey-white silica, and silica-barite veins. The fluid inclusion studies on 105 primary fluid inclusions indicated five phases for inclusions including: 1) liquid or gas, 2) liquid and gas, 3) liquid, gas, and solid, 4) liquid, gas, halite, and solid, and 5) liquid, gas, halite, and two types of solids. The data gained from fluid inclusions approved two mineralization fluids which caused porphyry and epithermal mineralizations. The porphyry fluid inclusions were homogenized in temperatures of 122°C to 550°C with a maximum of 700°C and average salinity of 55 wt% NaCl equivalent, while the epithermal inclusions indicated an average homogenization temperature of 186°C with an average salinity of 6.23 wt% NaCl equivalent.

Comparison of U-spatial Statistics Method with Classical Statistics Results in the Determination of Geochemical Anomalies of Epithermal Gold in Khoshnameh Area, Hashtjin, Iran

In this study,methods based on the distribution model(with and without personal opinion)were used for the separation of anomalous zones,which include two different methods of U-spatial statistics and mean plus values of standard deviation(X+nS).The primary purpose is to compare the results of these methods with each other.To increase the accuracy of comparison,regional geochemical data were used where occurrences and mineralization zones of epithermal gold have been introduced.The study area is part of the Hashtjin geological map,which is structurally part of the folded and thrust belt and part of the Alborz Tertiary magmatic complex.Samples were taken from secondary lithogeochemical environments.Au element data concerning epithermal gold reserves were used to investigate the efficacy of these two methods.In the U-spatial statistics method,and criteria were used to determine the threshold,and in the method,the element enrichment index of the region rock units was obtained with grouping these units.The anomalous areas were identified by,and criteria.Comparison of methods was made considering the position of discovered occurrences and the occurrences obtained from these methods,the flexibility of the methods in separating the anomalous zones,and the two-dimensional spatial correlation of the three elements As,Pb,and Ag with Au element.The ability of two methods to identify potential areas is acceptable.Among these methods,it seems the method with criteria has a high degree of flexibility in separating anomalous regions in the case of epithermal type gold deposits.

Characterization of Arroyo Verde Epithermal Deposit:Paragenesis,Mineral Geochemistry,Geochronology and Fluid Inclusions in Lower Chon Aike Volcanism,Argentina

Arroyo Verde epithermal deposit,in the North Patagonia region of Argentina,is located within the Lower Chon Aike volcanism and is developed between 192.6±2.5 Ma(mineralization host rock)and 189.5±2.6 Ma(overlying lava).Marifil volcanic complex is the host rock for these veins,veinlets and breccias.This particular small deposit has developed low to intermediate sulphidation characteristics,with gangue mineral textures associated with several ore minerals.Electron probe microanalysis determines electrum,silver minerals such as acanthite,and tetrahedrite,related Ag-Cu minerals like jalpaite,mckinstryite,stromeyerite,and base metals like chalcopyrite,sphalerite,galena and pyrite.Fluid inclusions in quartz of two out of five events indicate that these Low Jurassic veins were formed due to subtle boiling and dilution mechanisms and by low-salinity(3.4 wt.%to 6.7 wt.%NaCl Eq)magmatic-hydrothermal fluid at 225 to 310℃.The fluid inclusion measurements that indicate boiling(Event 3)were plotted,and based on this data,we interpret that the Arroyo Verde deposit has been eroded between 550 and 700 m.This particular character has not been previously recorded for other sectors of the eastern north Patagonian region.

Fluid-rock interactions leading to the formation of the epithermal Ag-Pb-Zn veins:A perspective of thermodynamic modeling

Although vein-type silver-lead-zinc ore deposits have been extensively studied,the factors controlling their formation are still poorly understood and their genesis is a matter of ongoing debate.In this contribution,I present new mineralogical data and the results of thermodynamic modeling that constrain the conditions of metal transport and deposition for the Aerhada epithermal Pb-Zn-Ag deposit(reserves of>1,000 t Ag@58 g/t and 1.0 Mt Pb+Zn@5.2%)in NE China.Three primary paragenetic stages have been identified,the second of which(Stage II)is the main base metal and silver mineralization.Freibergite,argentite,pyrargyrite,and canfieldite are the main Ag-bearing minerals and are spatially associated with an alteration assemblage of quartz-muscovite±chlorite±epidote.Dissolution textures and evidence of compositional heterogeneity for freibergite suggest that its decomposition may have redistributed the Ag and contributed in part to the high Ag grade ores in the deposit.Thermodynamic calculations indicate that there was extensive silver ore deposition from a strongly reducing(e.g.,∆log fO_(2)(HM)of<-8.6 to-2.4)and nearly neutral to weakly alkaline(e.g.,pH of 5.5 to 6.8)aqueous fluid at temperatures between 220℃ and 170℃.These calculations reveal that a reduction in fO_(2)and decreasing temperature,both as a result of fluid-rock interactions,were the key factors leading to silver and base metal mineral deposition.Further path modeling showed that the sole evolution of a magmatic-derived fluid is capable of forming the large Ag-Pb-Zn veins via fluid-rock interactions,which is contrary to the conclusions of some other studies that the mixture of an externally derived fluid is required to explain their formation.The genetic model for Ag-Pb-Zn ore formation developed in this study is applicable to other polymetallic vein-type deposits in comparable geological settings elsewhere.

The fluid regime of formation of epithermal ore mineralization in the eastern part of the Aldansky shield (Russian Far East)

IN the eastern part of the Aldansky shield, on the territory of volcanic and sedimentary basins of Proterozoic age, many deposits and ore occurrences of Au, Ag, Mo, U, V, Ni, Co, Ba and Th are revealed.Petrographic, geochemical and fluid inclusion study indicate their low temperature (epithermal) genesis.It is supposed that these ores were formed in the grenville metallogenic epoch (Upper Proterozoic). The epithermal ores in this region are connected with: (i) eisite (apatite-albite metasomatites)and (ii) argilliceous-white mica metasomatites (argillisites and beresites). Apatite-albite metasomatitesare associated with rare-earth ores. As a rule, metasomatite bodies are controlled by steeply-dipping fractures. Albite, quartz and fine-grained hematite form a typical mineral assiciation. The ore bearing metasomatites were formed at pH = 4 and T≤300℃. The beresite type argillaceous-white mica alterations are widespread in volcanic rocks of the Ulkansky basin and in the sedimentary suites of the Uchursky basin. They are distinguished on all stratigraphiclevels, but especially often in a zone of structural-stratigraphic unconformity (SSU) of AR-PR. Au, Ag,Mo, V and U deposits and occurrences are connected with this type of alterations. Their structural pos-

Epithermal gold deposits in China and potential assessment

THE epithermal gold deposit (epi-gold) is one of the most important types in various gold deposits all overthe world. The discovery of several superlarge deposits of this type around the circum-Pacific Rim duringthe 1980s, greatly stimulated the interest in searching for epi-golds in the world as well as in China. Theepi-gold has become a major target in gold exploration in China during last two-decade "Golden Rush.The discovery of the Zijinshan Cu (Au) deposit in SE China and the Axi and other Au deposits in NWChina is the significant success in gold prospecting in this field. The author suggested that it is the timeto do an overview and the potential assessment of epi-golds in China Some people are holding an optimistic idea on this topic mainly based on the following considerations: (i) as a host rock, the subaerial volcanic rocks of Mesozoic are widespread in East China; (ii)

Alkalic-type epithermal gold mineralization associated with Tongshi complex in Pinyi County, Shandong Province

THE alkali-rich subvolcanic complex of Tongshi and the associated gold mineralization are located at thesouth boundary of Pinyi Mesozoic volcanic depression in western Shandong Province. There are morethan 30 gold deposits and mineralization locations around the complex, in which Guilaizhuang gold deposit and Zhuojiazhuang bonanza gold deposit with important economic value are included. This area isbecoming a perspective target of superlarge gold deposit. In the mine area, there crop out Archeangranitic gneisses, Paleozoic carbonates and Jurassic clastic rocks, which was intruded by Tongshi complexwith 30 km. The complex consists of K-high igneous rocks formed by two stages of magmatism. In thefirst stage, the monzonitic dioritic porphyrys, which belong to K-high calc-alkalic rocks, were formed andin the second stage, monzonitic-syenitic porphyrys, which belong to K-high alkalic rocks, were formed.Their Ar-Ar ages are 189 Ma and 188 Ma, respectively. At the end of the second stage, a lot of theexplosive breccias were formed. The gold mineralization in this area is closely associated in time andspace with the second stage monzonitic-syenitic porphyrys. Based on the characteristics of

Regularities controlling the distribution of halogens in the Danzhai epithermal Hg-Au deposit in Guizhou and their significance

HALOGENS, as mineralizer elements, have been attracting ever increasing attention of geological workers inpetrogenetically experimental and ore-forming fluid geochemical studies. However, little research workhas been done on the contents, variation characteristics and significance of halogens in solid ores(rocks). It is found in the study of the Danzhai Hg-Au deposit that (i) variations in the contents ofhalogens and their distribution regularities in solid rocks and ores can shed light on the formation of thedeposit; and (ii) halogens can serve the function of indicator elements in search of buried orebodies. 1 Main characteristics of the ore

Tracer system on halogen mineralizer from the epithermal deposits in Guizhou Province

HALOGENS are typical mineralizer elements and play a very important role in remobilization and resettlement of the ore-forming mental elements in the hydrothermal deposits. Studies of tracer system on halogens mineralizer include the following aspects: (i) halogens’ role as mineralizer in ore-forming action;(ii) halogens importance as tracer elements in formation and evolution of the epithermal ore deposit;(iii) halogens’ significance as guidance in looking for the buried orebodies. Guizhou is a concentrated area of epithermal Hg, Sb and Au deposits, where are distributed famousepithermal deposits such as the Wanshan Hg deposit, the Banpo Sb deposit, the Danzhai Hg-Au depositand the Lannigou Au deposit. Many researches into geological and geochemical characteristics of thesedeposits have been done, but few study on halogen mineralizer.

Characteristics and metallogenesis of epithermal gold (copper)deposits in the middle-south parts of Tancheng-Lujiang deep fault zone and its vicinity, eastern China

EPITHERMAL gold (copper) deposits distributed in the middle-south parts of Tancheng-Lujiang deep faultzone and its vicinity have close relation to Mesozoic shoshonitic magmatism. According to their metallogenic features and ore-forming conditions, these deposits can be divided into three types; tellurium-goldtype Au deposit, quartz-adularia type Au deposit and quartz-manganoansiderite type Au-Cu deposit. Therepresentative deposits of them are Guilaizhuang, Dongxi and Tiantoushan. In this note, the general features of the three typical epithermal gold (copper) deposits are outlined and the relationship between mineralization and types of volcanic basins is discussed preliminarily.

Erentaolegai silver deposit in Inner Mongolia as an example of epithermal deposit

1 Comparison with the characteristics of geology and geochemistry of typical epithermal silverdeposit Erentaolegai silver deposit is located to the west bank of Kelulun river in the Xibarhuyou Banner,south-west of Manzhouli. The geotectonic is the joint of Hailar basin and Manzhouli-Xinbarhuyou Banner’svolcanic mole track. The stratas in the mining area are upper Jurassic Tamolangou formation andShangkuli formation: the former consists of andesite mainly and the latter is divided into three parts fromtop to bottom, namely rhyolite, decite, trachyte. The types of igeous rock in the mining area are graniteand quartz porphyry, both with age (120 ±6) Ma as determined by the Rb-Sr isochron. The principalstructures in the mining areas are faults, trending SN, NW, NE, mainly SN. The ore bodies are controlledby faults. It is a large-scale silver deposit found recently. Many years’ research shows that it is a silverepithermal deposit. Table 1 lists a comparison with the typical silver epithermal deposits.

Kinetics of ore-forming fluids in epithermal systems

As verified by the data of fluid inclusions in minerals in some paleo-hydrothermal systems, a lowering intemperature of the ore-forming fluids and a decrease in salinity occurred simultaneously from the centralzone （deep part） of the deposit profile to its outer zone （shallow part）. The usual situation shown byexperimental data is that solubility rises with an increase in temperature, as shown by quartz and manyore minerals. However, the solubility of some minerals increases as the temperature decreases within acertain temperature range. Therefore, continuous deposition cannot be achieved as the temperature of thesystem decreases, as in the cases of calcite, fluorite, and anhydrite. In water and NaCl-H2O systems,the solubility of calcite （or anhydrite） decreases with a rise in temperature at 【 300℃ (or 【 450℃

Comparison of two end-member styles of epithermal Au-(Cu)deposits

EPITHERMA Au-(Cu) deposits occur largely in volcano-plutonic arcs (island arcs as well as continentalarcs) associated with subduction zones, with ages similar to those of volcanism. These deposits form atshallow depth,【1 km, and are hosted mainly by volcanic rocks. Modern volcanic-hydrothermal systems provide an analogue to the environment for the ancient intrusion-related and volcanic epithermal deposits. Recent studies also indicate that the volcanic epithennalore deposits are formed from magmatic fluids, although the magmatic signatures have been largely erasedby meteoric water. At depth (fig. 1), the magmatic fluid from the high-level intrusive magma will result in the formation of intrusion-related deposits (e.g. porphyry Cu, Au, Mo deposits). Detailed studies of fluid inclusions and stable isotopes indicate that the hydrothermal system that form these deposits are initially

The relationship between epithermal and low temperature mineralizations

THE term epithermal as a kind of hydrothermal mineralization was first used by Lindgren in 1933. It describes those ore-forming systems occurring at depths mainly less than 1 km, and at temperatures less than300℃. Epithermal deposits of Cenozoic ages are widely distributed in the Circum-Pacific belt, especiallyin the Southwest Pacific area. From the 1980s on, the study of epithermal ore deposits became an important field of mineral deposit research. Hayba et al.and Hedenquist classified the epithermal systemas adularia-sericite or acid-sulphate types, and low sulphidation or high sulphidation types, respectively.The low temperature mineralization, which was exemplified by the deposits in southwest China, refers tothe system at temperature mainly less than 200℃. Besides the distinction in temperature, however, thereexist many differences between epithermal and low temperature mineralizations.