Analysis of the Ore-Controlling Structure of Ductile Shear Zone Type Gold Deposit in Southern Beishan Area, Gansu, Northwest China

The ductile shear zone-type gold deposit is a kind that both the ore-forming mechanism and ore-controlling factors are closely related to the ductile shear zone and its evolution. Ductile shear zone develops in Beishan area, Gansu of Northwest China, and develops especially well in the south belt. The controls of the ductile shear zone on gold deposits are as follows. (1) The regional distribution of gold deposits (and gold spots) is controlled by the ductile shear zone. (2) The ductile-brittle shear zone is formed in the evolution process of ductile shear zone and both are only ore-bearing structures and con- trol the shape, attitude, scale, and distribution of mineralization zones and ore-bodies. (3) Com- presso-shear ductile deformation results in that the main kind of gold mineralization is altered mylonite type and the main alteralization is metasomatic. (4) Ore-bearing fracture systems are mainly P-type ones, some D-type and R-type ones, but only individual R’-type and T-type ones. (5) Dynamic differen- tiation and dynamic metamorphic hydrothermal solution resulting from ductile deformation is one of the sources of ore-forming fluid of gold mineralization, and this is identical with that ore-forming ma- terials are mainly from metamorphic rocks, and ore-forming fluid is mainly composed of metamorphic water, and with the fluid inclusion and geo-chemical characteristics of the deposit. (6) There is a nega- tive correlation between the gold abundance and susceptibility anisotropy (P) of the altered mylonite samples from the deposit, which shows that the gold mineralization is slightly later than the structural deformation. All above further expound the ore-forming model of the ductile shear zone type of gold deposits.     

Element Geochemistry and Petrogenesis of High—K Potassic Dike Rocks in Two Types of Gold Ore Fields in Northwest Jiaodong,Shandong,China

This paper deals with the high-K,potassic dike rocks in two types of gold ore fields at Linglong and Dayigezhuang,Northwest Jiaodong.The rocks can be divided into three types.i.e.,(1) lamprophyre,(2) andesite porphyrite,and (3) dacite porphyrite,based on their geological occurrence and space-time relationship with gold mineralization.These rocks were the products of early,synchronous and late mineralization.respectively,Element geochemistry shows that variations in chemical composition of major oxides follow the general rules of magmatic fractional crystallization.The fractional crystallization of mineral phases of augite in the early stage(namely in the lamprophyre stage)and hornblende and plagioclase in the late stge(namely from the andesite-porphyrite to dacite porphyrite stage)controlled the magma evolution.The rocks are enriched in alkili and have higher K2O and lower TiO2 contents,as well as strongly enriched in large ion lithophile elements such as Ba,Sr and Rb,and LREE but strongly depleted in transition elements such as Cr and Ni,Rb is depleted relative to Sr and Ba,and Rb/Sr ratios are low.Volatile constituents are abundant.These characteristics indicate that the initial magma originated from the metamorphic subduction ocean-crust that had been intensively contaminated by crustal materials,and retrogressive metamorphism is characterized by low-degree partial melting during back-arc spreading,Varying degrees of partial melting and different emplacement enviornments may be the main causes for the evolution of the rocks and mineralization in different degrees in the two gold ore fields at Linglong and Dayigezhuang,Shandong.     

Episodes of Cenozoic Gold Mineralization on the Eastern Margin of the Qinghai-Tibet Plateau:~(40)Ar/~(39)Ar Dating and Implication for Geodynamic Events

A lot of new gold deposits have been found on the eastern margin of the Qinghai-Tibet Plateau during the past two decades. Among them, three main types of gold deposits have been recognized, including quartz-vein-type, shearzone-type and porphyry-type. The former two types of gold deposits are mainly hosted within metamorphic rocks, while the latter is related to Cenozoic magmatism. Although all of these gold deposits are believed to have been formed during the uplift process of the Qinghai-Tibet Plateau in the Cenozoic era (Wang et al., 2002b), precise isotopic age constraints have still been lacking until quite recently. This paper presents new ^40Ar/^39Ar data of some gold deposits on the eastern margin of the Qinghai-Tibet Plateau, which indicate that gold mineralization in the region occurred in response to the episodic stages of the orogenies. Recently obtained ^40Ar/^39Ar data on quartz and feldspars from several gold deposits, such as the Sandiao deposit, the Baijintaizi deposit, the Pusagang deposits, provide new constraints on gold mineralization on the eastern margin of the Qinghai-Tibet Plateau. Geochronological studies of gold deposits along the Daduhe River indicate that there are three stages of gold mineralization. The early two stages occurred as early as 65.1 Ma in the Shuibaiyang deposit and 58.95 Ma in the Ruoji deposit, while the latter stage occurred as late as 25.35 Ma in Baijintaizi and 24.70 Ma in Sandiao. Isotopic dating of three plagioclases from the Beiya deposit, Zhifanggou deposit and Luobodi deposit and a K-feldspar from the Jinchangqing deposit in Yunnan Province indicates that these deposits were formed at two stages. The Zhifanggou and Jinchangqing deposits have early stage records as old as 58.82 Ma in Zhifanggou and 55.49 Ma in Jinchangqing, but all of the above four deposits in Yunnan have late stage records of 23.18 Ma in Jinchangqing, 24.54 Ma in Zhifanggou, 24.60 Ma in Luobodi and 24.56 Ma in Hongnitang. The above results suggest that the gold deposits on the eastern margin of the Qinghai-Tibet Plateau were formed concentratedly at two main episodes, i.e. the end of the Paleocene (about 58 Ma) and the boundary between the Paleogene and the Neogene (about 25 Ma). The later episode appears to be looks like more important and was coupled with the Sichuan movement, which was extensively activated at that period. The beginning of the Cenozoic Era (about 65 Ma) might be another episode of gold mineralization, but only one deposit (Shuibaiyang) in this study has been proved to have been be formed at this stage and might be earlier than the initial collision between the Indian Plate and the Eurasia Plate. In view of geology, the above three episodes of gold mineralization are associated with three events of tectonicmagmatism and/or fluid events. Even though the gold deposits (for example, the Shuibaiyang deposit, Ruoji deposit and Pusagang deposit) were formed at different episodes, all of them are genetically related to tectonic movements in largescale shear zones. It looks like theat tectonic events (including large-scale strike-slip) between Paleogene and Neogene had a wide influence upon gold mineralization, with new deposits formed and old deposits enriched or superimposed to be a higher grade by new stage of mineralization. The above data suggest that gold deposits were not only concentrated in some areas, but also formed mainly at different boundaries of geological times, indicating that there existed some peak stages of gold mineralization (metallogenic episodes), and that the gold deposits were formed mainly by episodic mineralization.     

Trace element and REE geochemistry of the Zhewang gold deposit,southeastern Guizhou Province,China

The quartz vein-type gold deposits are widely hosted by the Neoproterozoic （Xiajiang Group） epimeta- morphic clastic rock series in southeastern Guizhou Province, China. The Zhewang gold deposit studied in this paper occurs in the second lithologieal member of the Pinglue Formation of the Xiajiang Group. Trace element geochemis- try of host rocks, quartz veins and arsenopyrite has revealed that ore-forming fluid was enriched in sulphophile ele- ments such as Au, Ag, As, Sb, Pb and Zn, and simultaneously concentrated some magmaphile elements such as W and Mo, which probably provides some evidence for multi-stage mineralization or overprinting of magmatic hydro- therm. Quartz veins and arsenopyrite were characterized by depletion in HFSE and enrichment in LREE. Hf/Sm, Nb/La and Th/La imply that the ore-forming fluid was probably a NaC1-H20 solution system enriched in more C1 than F; Th/U values reflect the strong reducibility of the ore-forming fluid, coincident with the sulfide assemblages. The values of Co/Ni reflect that magmatic fluids may have partly participated in the ore-forming process and Y/Ho values have proved that the ore-forming fluid was associated with metamorphism and exotic hydrotherm which has reformed former quartz veins during late mineralization. The concentrations of REE, Eu anomalies and Ce anomalies of this deposit display that ore-forming elements mainly were derived from host rocks and possibly from a mixed deep source, and the ore-forming fluid was mixed by dominant metamorphic fluid and minor other sources. The physical-chemical conditions of ore-forming fluid changed from the initial stage to the late stage. The metamorphic fluid is responsible for the mineralization. Therefore, the Zhewang gold deposit is classified as a quartz vein-type gold deposit which may have been reformed by magmatic fluids during the late stage.     

Geological and Fluid Inclusion Constraints on Gold Deposition Processes of the Dayingezhuang Gold Deposit,Jiaodong Peninsula,China

The Dayingezhuang gold deposit, hosted mainly by Late Jurassic granitoids on Jiaodong Peninsula in eastern China, contains an estimated 170 t of gold and is one of the largest deposits within the Zhaoping fracture zone. The orebodies consist of auriferous altered pyrite–sericite–quartz granites that show Jiaojia-type (i.e., disseminated and veinlet) mineralization. Mineralization and alteration are structurally controlled by the NE- to NNE-striking Linglong detachment fault. The mineralization can be divided into four stages: (K-feldspar)–pyrite–sericite–quartz, quartz–gold–pyrite, quartz–gold–polymetallic sulfide, and quartz–carbonate, with the majority of the gold being produced in the second and third stages. Based on a combination of petrography, microthermometry, and laser Raman spectroscopy, three types of fluid inclusion were identified in the vein minerals: NaCl–H2O (A-type), CO2–H2O–NaCl (AC-type), and pure CO2 (PC-type). Quartz crystals in veinlets that formed during the first stage contain mainly AC-type fluid inclusions, with rare PC-type inclusions. These fluid inclusions homogenize at temperatures of 251°C–403°C and have low salinities of 2.2–9.4 wt% NaCl equivalent. Quartz crystals that formed in the second and third stages contain all three types of fluid inclusions, with total homogenization temperatures of 216°C–339°C and salinities of 1.8–13.8 wt% NaCl equivalent for the second stage and homogenization temperatures of 195°C–321°C and salinities of 1.4–13.3 wt% NaCl equivalent for the third stage. In contrast, quartz crystals that formed in the fourth stage contains mainly A-type fluid inclusions, with minor occurrences of AC-type inclusions; these inclusions have homogenization temperatures of 106°C–287°C and salinities of 0.5–7.7 wt% NaCl equivalent. Gold in the ore-forming fluids may have changed from Au(HS)0 as the dominant species under acidic conditions and at relatively high temperatures and fO2 in the early stages, to Au(HS)2– under neutral-pH conditions at lower temperatures and fO2 in the later stages. The precipitation of gold and other metals is inferred to be caused by a combination of fluid immiscibility and water–rock interaction.     

Dating and Fluid Geochemistry of the Sarkobu Gold Deposit in Altay, Xinjiang, China

The dating of fluid inclusions of quartz yields an Ar-Ar isochrone age of 320.4±6 Ma. Three types of fluid inclusions have been identified with the homogenization temperature ranging from 157℃ to 362℃. The homogenization temperature consists of two groups. The first group varies from 157℃ to 166℃, and the second from 232℃ to 362℃. Their chemical composition is dominated by Na+-Ca2+-Mg2+ and Cl-. The relative concentration of ions is characteristic by Na+>Ca2+>K+>Mg2+ and C1->SO42-> F-. The δD and δ18O values indicate that the ore-forming fluid originates from mixing of multi-source water. The Sarkobu gold deposit has experienced two mineralization stages: gold was enriched during the volcanic-exhalative-sedimentary process in the early stage, while the gold deposit was finally formed under compression-shearing during the orogenic period.     

A Three—Stage Metallogenic Model for Gold Deposits in Metamorphosed Microclastic Rocks

Gld deposits occurring in metamorphosed microcelastic rocks are distributed extensively at home and abroad.Some deposits of this type are of superlarge tonnage.The formation of gold deposits in metamorphosed microclastic rocks involves three stages:the sedimentary stage,the regionally metamorphic stage,and the ore-forming stage.At the first stage,microclastic sedimentary source rocks were developed in a relatively semi-enclosed reducing sea basin and were enriched in carbon,sulfur and gold.At the second stage,the gold adsorbed on organic matter and clay minerals was relesed and poorly concentrated during the destruction of organic matter and the depletion of clay minerals by regional metamorphism with increase temperature and pressure.At the third stage,a tectono-hydrothermal event took place.As a result,gold was leached from metamorphosed microclastic rocks,transported to ore depositional locus and/or mixed with gold of other sources in the course of migration,and finally precipitared as ores.Gold deposits of this type were eventually formed at the third stage,and they also can be classified as the orogenic belt type and the activation zone type.The gold deposits occurring in metamorphosed microcalastic rocks are the products of reworking processes and the influence of magmatism should be taken into consideration in some cases.     

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 modem 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.     

Geochemistry of Ore Fluids and Rb-Sr Isotopic Dating for the Wulong Gold Deposit in Liaoning, China

On the basis of detailed geological studies of the Wulong gold deposit, three metallogenic stages can be identified. With quartz fluid inclusions as an object of study, the authors investigated phase characteristics, compositional variations, temperature and pressure changes, fluid evolution, Pb isotope tracing and Rb-Sr isotopic dating of fluid inclusions entrapped in the above three metallogenic stages. The results show that Na+ is decreased obviously with metallogenic evolution, while K+ and other cations and gas compositions (H2, CO, CH4 and CO2) are increased slightly, and that the temperature and salinity vary in a pulsating manner along with the metallogenic evolution. Inverse calculation of hydrogen and oxygen isotopes indicate that at the first metallogenic stage the fluids were magmatic water, at the second stage they were dominated by magmatic water with a minor amount of meteoric water involved, and at the third stage, i.e., the final stage of metallogenesis, the fluids were composed complete     

Microthermometry, Raman and LA-ICP-MS of Fluid Inclusions Constrain on Fluids Chemistry and Evolution of Carlin-Type Gold System, Guizhou, China: Implications for Ore Genesis

The Shuiyindong and Yata Carlin-type gold deposits, located in Southwestern Guizhou, China, are hosted by Permianbioclastic limestone in the form of stratabound mineralization and Middle Triassic calcareous clastic rocks as fault-controlled mineralization, respectively. In these deposits, quartz crystals in the veins or veinlets associated with mineralization have contained several populations of fluid inclusions with relatively quite big size and clear paragenetic relationship of entrapment. Petrography, microthermometry, Raman and LA-ICPMS of fluid inclusions analyses are used to characterize fluids chemistry and their evolution of Carlin-type system in Guizhou.     

江西金山剪切带型金矿床两类矿石的地球化学特征—兼论两阶段成矿机制

金山剪切带型金矿床主要发育含金硅质糜棱岩和含金石英脉两类矿石，它们分别在矿化第一和第二阶段形成。含金硅质糜棱岩与围岩－双桥山群上亚群具有一致的稀土和微量元素分布特征及相近的元素比值，后者为矿床第一阶段矿化的形成提供了物质来源。含金石英脉中流体包裹体的化学和同位素组成特征表明，矿化第二阶段的成矿流体为源于大气降水的地下热水，引起自然金沉淀的因素主要是流体的相分离。     

粤西河台金矿床构造控矿规律研究

本文是在全面调查了粤西河台金矿区内构造特征与成矿特征之后,对该区构造发育规律及控矿规律所做的系统总结.文中对矿区存在的一个重要构造型式——拐肘构造及其对金矿的控制作用作了论述,对成矿的物质来源、成矿期次与构造演化的关系进行了讨论,提出了三期成矿的观点和构造矿源带的概念,总结了该区的构造成矿模式.     

新疆东天山红山金矿成矿时代研究

红山金矿区位于秋格明塔什—黄山韧性剪切带东段北缘,矿床成因研究表明,红山金矿的形成严格受该韧性剪切带控制,属于与韧性剪切带有关的糜棱岩型、超糜棱岩型矿床。花岗质糜棱岩中角闪石276.3Ma的Ar-Ar坪年龄给出了红山金矿床成矿事件的时代上限。金矿石样品中绢云母246.9Ma和246.5Ma的Ar-Ar坪年龄记录了金矿床主成矿期的时代。糜棱岩中新生白云母246.5Ma的Ar-Ar坪年龄,在误差范围内和金矿石样品中绢云母的Ar-Ar坪年龄完全一致,不仅为红山金矿床的剪切带型成因提供了进一步的佐证,也对金成矿时代给予了进一步的限定。     

中国南天山萨恨托亥-大山口成矿带韧性剪切带与金成矿作用

以南天山中段萨恨托亥-大山口成矿带内控矿韧性剪切带为例,对韧性剪切带的金成矿作用进行了初步探讨.通过对地质体的构造变形特点、变形演化过程的分析表明,韧性剪切带的构造属性控制了金矿的产状及规模,金矿化阶段与韧性剪切带的变形演化过程密切相关.矿化类型、矿化强度及矿化方式受韧性剪切带发展阶段制约,剪切带内物质组分迁移变化揭示出韧性剪切带与金在剪切带内的迁移富集、沉淀成矿的内在联系.韧性剪切带成矿作用是南天山成矿带中段重要的金矿成矿作用.     

Petrology,Geochemistry, and Fluid Inclusion Microthermometry of Sphalerite from the Laloki and Federal Flag Strata‐Bound Massive Sulfide Deposits,Papua New Guinea: Implications for Gold Mineralization

The Laloki and Federal Flag deposits are two of the many (over 45) polymetallic massive sulfide deposits that occur in the Astrolabe Mineral Field, Papua New Guinea. New data of the mineralogical compositions, mineral textures, and fluid inclusion studies on sphalerite from Laloki and Federal Flag deposits were investigated to clarify physiochemical conditions of the mineralization at both deposits. The two deposits are located about 2 km apart and they are stratigraphically hosted by siliceous to carbonaceous claystone and rare gray chert of Paleocene–Eocene age. Massive sulfide ore and host rock samples were collected from each deposit for mineralogical, geochemical, and fluid inclusion studies. Mineralization at the Laloki deposit consists of early‐stage massive sulfide mineralization (sphalerite‐barite, chalcopyrite, and pyrite–marcasite) and late‐stage brecciation and remobilization of early‐stage massive sulfides that was accompanied by late‐stage sphalerite mineralization. Occurrence of native gold blebs in early‐stage massive pyrite–marcasite‐chalcopyrite ore with the association of pyrrhotite‐hematite and abundant planktonic foraminifera remnants was due to reduction of hydrothermal fluids by the reaction with organic‐rich sediments and seawater mixing. Precipitation of fine‐grained gold blebs in late‐stage Fe‐rich sphalerite resulted from low temperature and higher salinity ore fluids in sulfur reducing conditions. In contrast, the massive sulfide ores from the Federal Flag deposit contain Fe‐rich sphalerite and subordinate sulfarsenides. Native gold blebs occur as inclusions in Fe‐rich sphalerite, along sphalerite grain boundaries, and in the siliceous‐hematitic matrix. Such occurrences of native gold suggest that gold was initially precipitated from high‐temperature, moderate to highly reduced, low‐sulfur ore fluids. Concentrations of Au and Ag from both Laloki and Federal Flag deposits were within the range (<10 ppm Au and <100 ppm Ag) of massive sulfides at a mid‐ocean ridge setting rather than typical arc‐type massive sulfides. The complex relationship between FeS contents in sphalerite and gold grades of both deposits is probably due to the initial deposition of gold on the seafloor that may have been controlled by factors such as Au complexes, pH, and fO₂ in combination with temperature and sulfur fugacity.     

陕西山阳县夏家店金矿物质组分和成矿流体特征及成矿物质来源探讨

夏家店金矿主要含矿岩石是由泥、铁、炭硅质板岩及硅质岩、硅化碎块组成的角砾岩,与金矿化关系密切的围岩蚀变为硅化.金主要以裂隙金为主,其次是粒间金,包裹金较少;金的独立矿物是自然金.成矿流体包体比较发育,随着成矿作用的进行,成矿温度逐渐降低,成矿溶液由H2O-CO2-KCl为主的热液体系向以H2O-CO2-NaCl为主的热液体系转化.金主要来源于炭硅质板岩.     

Analysis of Ore-controlling Structure in the Qifengcha-Detiangou Gold Deposit, Huairou County, Beijing

The Qifengcha-Detiangou gold deposit is a medium-sized deposit recently found in Huairou County, Beijing. It belongs to the altered mylonite type with superimposed quartz vein type and is related to the early Yanshanian magmatic activity. Characterized by multiperiodic activity, the NE-trending Qifengcha fault is a regional ore-controlling structure in the area, and gold mineralization develops only in its southeastern part. Meanwhile, gold mineralization is controlled by the Yunmengshan metamorphic core complex. The nearly N-S- and E-W-trending low-angle detachment faults, reformed by the Qifengcha fault in the northwestern part of the core complex, are the main ore-bearing faults. All discovered gold deposits are located within an area 1.5-4.0 km away from the boundary of the upwelling centre. The N-S- (NNE-) and E-W-trending ore-bearing faults are ductile-brittle structural zones developing in shallow positions and subjected mainly to compressive deformation. The structural ore-controlling effects ar     

燕山北部崇礼-隆化-阜新构造带形变特征及其控矿作用

崇礼-隆化-阜新构造带是燕山北部重要的控岩控矿构造。晚华力西期-印支期,该构造带以韧性剪切变形为主,形成一系列近EW向断续分布的韧性剪切带。燕山期,该构造带以韧脆性-脆性断裂变形为主,在早期韧性剪切变形的基础上叠加一系列同方向的高角度压性-压扭性逆冲断裂。喜马拉雅期,该构造带仍有一定的继承性活动,以张扭性-扭性断裂活动为主。
崇礼-隆化-阜新构造带对金矿化分布有明显的制约作用。在空间上,该构造带控制了张家口-隆化-阜新金矿带及其中5个金矿化集中区的展布;在时间上,该构造带不同类型的形变伴有不同类型的金矿化。该构造带与NE向、NW向断裂带的复合部位是金矿成矿的有利部位.      

浙西金鸡岩金矿床成矿特征与成矿机理研究

对浙西金鸡岩金矿进行了流体包裹体、岩石和矿石地球化学研究,以阐明其成矿特征和成矿机理．金鸡岩金矿是由多阶段成矿作用形成的,第一阶段以钼矿化为主,成矿温度较高;第二和第三阶段以金矿化为主,成矿温度较低．该金矿的成矿压力小、深度浅．成矿流体具低盐度、弱酸性及较高矿化度的特点,其中尚有大量大气水的混入．区内的前寒武纪浅变质岩系属于原始矿源层,而中生代火山岩,特别是次火山岩属于直接矿源岩．就成矿机理来看,金主要是呈金硫络合物形式迁移的,其次是被硅胶吸附呈胶体状态迁移的,而成矿流体的温度和压力下降、ｐＨ值降低以及溶液的氧化还原电位改变是导致金沉淀的重要因素．区内胶体金的沉淀主要是由于温度的降低和电解质的加入引起凝胶作用,使金随硅胶一同沉淀的．     

Two stages of gold mineralization at Hutti mine, India

The Hutti gold mine is located in a high-angle, NNW–SSE-trending shear zone system, which hosts nine discrete auriferous shear zones (reefs). On a clockwise, retrograde PT path two separate stages of deformation/metamorphism (D₂/M₂ and D₃/M₃) occurred synchronous with two distinct stages of gold mineralization, both of which were associated with different fluid types. Stage 1 mineralization developed during D₂/M₂, where the amphibolite host rocks were altered by a metamorphic fluid with a $ {{\delta }^{{18}}}{{O}_{{{{H}_2}O}}} $ of 7.5–10.1?‰, rich in K, S, As, and Au at pressure and temperature conditions of around 3 kbar and 530?+?20/?30°C, respectively. The stage 1 auriferous shear zones are enveloped by a zoned alteration consisting of a distal biotite–chlorite and proximal biotite–plagioclase assemblage. Subsequently, D₂/M₂ was overprinted by D₃/M₃ deformation and metamorphism at 300–400°C and <2 kbar that formed the stage 2 mineralization. The stage 2 mineralizing fluid which originated from outside the greenstone belt (δ¹⁸O_fluid of 3.2–6.8?‰) was rich in Si, Au, and W. This mineralization stage is distinct by the emplacement of laminated quartz veins central to the shear zone, containing locally visible gold at concentrations of up to 1 kg Au/t. The laminated quartz veins are surrounded by a millimeter-scale chlorite₂–K-feldspar alteration halo, which replaced the stage 1 biotite–plagioclase assemblage. The oxygen isotopic composition of the stage 2 fluid suggests a mixture of a magmatic fluid with an oxygen isotopic composition in the range of 6 to 10?‰ and an isotopically light formation fluid that resulted from fluid–rock interaction in the greenstone pile. The two fluid fluxes at stages 1 and 2 both contributed to the overall gold mineralization; however, it was the second fluid pulse, which gave the Hutti mine its status as the largest gold mine in India. The metamorphic evolution was thereby important for the first stage, whereas the second stage was controlled by tectonism and intrusion of the high-heat production Yellagatti granite that re-established the fluid plumbing and mineralizing system.