Alteration and mineralization styles of the orogenic disseminated Zhenyuan gold deposit, southeastern Tibet: Contrast with carlin gold deposit

Orogenic disseminated and Carlin gold deposits share much similarity in alteration and mineralization.The disseminated orogenic Zhenyuan Au deposit along the Ailaoshan shear zone,southeastern Tibet,was selected to clarify their difference.The alteration and mineralization from the different lithologies,including meta-quartz sandstone,carbonaceous slate,meta-(ultra)mafic rock,quartz porphyry and lamprophyre were researched.According to the mineral assemblage and replacement relationship in all types of host rocks,two reactions show general control on gold deposition:(1) replacement of earlier magnetite by pyrite and carbonaceous material;(2) alteration of biotite and phlogopite phenocrysts in quartz porphyry and lamprophyre into dolomite/ankerite and sericite.Despite the lamprophyre is volumetrically minor and much less fractured than other host rocks,it contains a large portion of Au reserve,indicating that the chemically active lithology has played a more important role in gold precipitation compared to structure.LA-ICP-MS analysis shows that Au mainly occurs as invisible gold in fine-grained pyrite disseminated in the host rocks,with Au content reaching to 258.95 ppm.The diagenetic core of pyrite in meta-quartz sandstone enriched in Co,Ni,Mo,Ag and Hg is wrapped by hydrothermal pyrite enriched in Cu,As,Sb,Au,Tl,Pb and Bi.Different host rock lithology has much impact on the alteration and mineralization features.Carbonate and sericite in altered lamprophyre show they have higher Mg than those developed in other of host rocks denoting that the carbonate and sericite incorporated Mg from phlogopite phenocrysts in the primary lamprophyre during alteration.The ore fluid activated the diagenetic pyrite in meta-quartz sandstone leading the hydrothermal pyrite enriched in Cu,Mo,Ag,Sb,Te,Hg,Tl,Pb and Bi,but the hydrothermal pyrite in meta-(ultra)mafic rock is enriched in Co and Ni as the meta-(ultra)mafic rock host rock contain high content of Co and Ni.However,Au and As shear similar range in both types of host rocks indicating that these two elements most likely come from the deep source fluid rather than the host rocks.It was shown in the disseminated orogenic gold deposit that similar hydrothermal alteration with mineral assemblage of carbonate (mainly dolomite and ankerite),sericite,pyrite and arsenopyrite develops in all types of host rocks.This is different from the Nevada Carlin type,in which alteration is mainly dissolution and silicification of carbonate host rock.On the other hand,Au mainly occur as invisible gold in both disseminated orogenic and Carlin gold deposits.

A Comparison of Carlin-type Gold Deposits：Guizhou Province,Golden Triangle,Southwest China,and Northern Nevada,USA

Several Au deposits in Guizhou Province,southwest China,described as being similar to the highly productive Carlin-type gold deposits in northern Nevada.USA,were examined to identify similarities and differences between the two districts.Samples were collected along transects from lowto high-grade rock,where possible,and fram stockpiles at the Shuiyindong,Zimudang,Taipingdong,Yata and Jinfeng(formerly Lannigou)deposits.Methods used to examine ore and alteration minerals included hand-sample description:reflectance spectroscopy using an ASD Terraspec spectrometer;analyses of hand samples by carbonate staining with Alizaren red and potassium ferricyanide;transmitted and reflected light petrography;chemical analyses,mineral identification,and imaging using a JEOL.JSM-5610 scanning electron microscope:and quantitative chemical analyses using a JEOL JXA-8900 electron probe microanalyzer.Geochemical analyses of hand samples for 52 elements were done by ALS Chemex.Results indicate both similarities and differences between the two districts.Both districts have similar geologic histories.and deposits at both locations appear to have formed as a result of similar tectonic events.though the district in southwest China lacks evidence of eoeval felsic igneous activity;however,the ore-stage minerals and the fluids that produced the minerals and deposits have some significant differences.The Nevada deposits were dominated by fluid-rock reaction in which host rock Fe was sulfidized to form Au-bearing pyrite.Although ore fluids sulfidized host rock Fe in the Cuizhou deposits.the timing of Fe metasomatism is unknown,so whether the deposits formed in response to sulfidation or pyritization is unclear.Fluid-rock reaction between an acidic,aqueous fluid and highly reactive calcareous rocks in Nevada caused extensive decarbonatization of host rocks,jasperoid replacemerit of carbonate minerals,and alteration of silty rock components to illite and kaolinite.In Guizhou,CO2-bearing ore fluids with temperatures and pressures approaching 100℃ and 500 bars greater than temperatures and pressures detemained for ore fluids in the Nevada deposits,deposited Aubearing pyrite.In examined Guizhou deposits these fluids carbonatized host rocks and farmed both replacement and open-space-filling ore.The fluids,which may have been immiscible,were sufficiently overpressured to fracture wall rocks and to create significant open space filled by vein quartz.While deposit architecture,tectonic setting,and host rocks in Guizhou are quite similar to northern Nevada,ore and alteration minerals suggest that ore-forming processes in examined Guizhou deposits have important similarities to processes associated with formation of orogenic Au systems.The Guizhou deposits display characteristics of both Carlin-type and orogenic systems,perhaps indicating formation at conditions somewhat intermediate to conditions for Carlin-type deposits and orogenic systems.

In-situ sulfur isotope and trace element of pyrite constraints on the formation and evolution of the Nibao Carlin-type gold deposit in SW China

The fault-controlled Nibao Carlin-type gold deposit,together with the strata-bound Shuiyindong deposit,comprise a significant amount of the disseminated gold deposits in southwestern Guizhou Province,China.Five main types and two sub-types of pyrite at the Nibao deposit(Py1a/Py1b,Py2,Py3,Py4,Py5)were distinguished based on detailed mineralogical work.Py1,Py2and Py3 are Au-poor,whereas Py4 and Py5 are Au-rich,corresponding to a sedimentary and hydrothermal origin,respectively.Through systematic in situ analyses of NanoSIMS sulfur isotopes,the framboid pyrite Py1a with negative δ^34S values(-53.3 to-14.9%)from the Nibao deposit were found to originate from bacterial sulfate reduction(BSR)processes in an open and sulfate-sufficient condition while the superheavy pyrite Py1b(73.7–114.8%)is probably due to the potential influence of closed-system Rayleigh fractionation or the lack of preservation of deepsea sediments.Data of Py2 and Py3 plot within the area of S isotope compositions from biogenic and abiogenic sulfate reduction.In view of few coeval magmatic rocks in the mining district,the near zero δ^34S values of the Au-rich pyrites(Py4 and Py5)may discount the potential involvement of magmatic but metamorphic or sedimentary origin.LA-ICP-MS and TEM work show that Au in ore-related pyrite is present as both nanoparticles and structurally bound.LA-ICP-MS analyses show that the Au-rich pyrite also contains higher As,Cu,Sb,Tl and S than other types of pyrite,which inferred a distal manifestation of deep hydrothermal mineralization systems.

Metallogenic model and prognosis of the Shuiyindong super-large strata-bound Carlin-type gold deposit, southwestern Guizhou Province, China

The Shuiyindong deposit is one of the largest (more than 100 tonnes of Au) and highest grade (more than 7×10-6-10×10-6), strata-bound Carlintype gold deposits in southwestern Guizhou Province, China. The deposit is controlled by both structure and favorable lithology. It is situated near the axis of the striking Huijiabao anticline and is hosted in bioclastic limestone of the Permian Longtan Formation. Gold mineralization occurred under low temperature with Th of 220℃± and is closely associated with decarbonation, silicification, sulfidation and dolomitization. The deposit has a characteristic elemental assemblage of Au-As-Hg-Tl. Studies of geochemistry and isotope compositions indicated that the ore-bearing materials and fluids of the gold deposit mainly originated from a plutonic source, and possess a mixing feature with the strata matter during transportation from mantle to crust. Fluid inclusions in vein quartz from the gold deposit are rich in volatile flux, indicating that metallogenic fluid is an overpres-sured one. The activity and geothermal state of the Earth's crust in the long period of time are favorable for the formation of overpressured fluids in a large area, and extensive structures would drive the fluids into ore-forming sys-tem and make gold deposits formed. The complexity of structural movement in the upper crust of southwestern Guizhou Province resulted in complicated gold mineralization. Through metallogenic prognosis and exploration, the proven reserves of the deposit increased by tens of tonnes of Au and the deposit has become a super-large strata-bound Carlin-type gold deposit.

S, C, O, H, and Pb isotopic studies for the Shuiyindong Carlin-type gold deposit, Southwest Guizhou, China: constraints for ore genesis

The Shuiyindong gold deposit is one of the most famous and largest Carlin-type gold deposits in China and is located in southwest Guizhou, in the eastern part of the Huijiabao anticline. The Shuiyindong's gold mineralization occurred in bioclastic limestone of the Permian Longtan Formation. Sulfur, carbon, hydrogen, oxygen, and lead isotopic compositions are reported in this paper. The properties and sources of ore-forming fluid have been discussed and a metallogenic model for the Shuiyindong gold deposit has been proposed. The d34 S values of stibnite, realgar, orpiment, pyrite from orebodies, and pyrite from quartz veins are similar to or slightly higher than the d34 S values of mantle sulfur. It is suggested that the sulfur of hydrothermal sulfides was likely of magmatic origin with minor heavy sulfur contributed from the country rocks. The measured d D values and calculated d18OH2 O values of inclusion fluid in quartz plotted within or below a magmatic hydrothermal fluid field far from the meteoric water line. This indicates that the ore-forming fluid for the main-stage gold mineralization could have been derived mainly from a magmatic source and mixed with a small amount of meteoric water. The carbon and oxygen isotopic compositions of calcites in the d18 O vs. d13 C diagram suggest that the CO2 in ore-forming fluid was derived from dissolution of bioclastic limestone and oxidation of sedimentary organic carbon in limestone. However, the d13 C values of ore-related calcites, which contain intergrown realgar and/or orpiment, are similar to those of mantle carbon. Although no igneous intrusive rock has been observed in the vicinity of the gold deposits, the possibility of mantle fluid integrated into the ore-forming fluid cannot be eliminated based on the d13 C values of ore-related calcites. The lead isotopes of sulfides are distributed near the growth curves of upper crust and orogenic belt in the plumbotectonic diagram. Their calculated Dc and Db values plotted within the magmatism field of crust-mantle subduction zone in the Dc- Db diagram. This suggests that the lead of sulfides has an intimate connection with magmatism. Our S, H, O, C, and Pb isotopic studies for the Shuiyindong Carlin-type gold deposit in Guizhou manifest a concordant possibility that the ore-forming fluid was mainly derived from magmatic fluid with minor contribution from the surrounding strata. With the integration of comprehensive geology and isotopic geochemistry, we have proposed a magmatic hydrothermal model for the origin of the Shuiyindong gold deposit.

Geochemical characteristics and metallogenesis of Carlin-type gold deposits in the Sandu-Danzhai metallogenic zone,Guizhou Province,China

Geochemical studies of the Paiting and Miaolong Carlin-type gold deposits in the Sandu-Danzhai metal-logenic zone,Guizhou Province,have shown that the mineralized-altered rocks show LREE-enrichment patterns,generally displaying negative Eu anomalies(δEu=0.51?0.97) and unobvious negative Ce anomalies(δCe=0.86?0.99).Calcite and fluorite in relation with metallogenesis show MREE-enrichment patterns,generally displaying rather weak negative Eu anomalies(δEu=0.74?0.93) and weak negative Ce(δCe=0.70?0.98) anomalies.The δ13CPDB values of carbon in calcite are-1.61‰?-5.82‰,the δ18OSMOW values of oxygen are 13.97‰?19.24‰,and the δ34SCDT values of sulfur in stibnite are 17.72‰?21.68‰.In regard to δD and δ18O,ore-forming fluids pos-sess the characteristics of metamorphic water.The process of metallogenesis of the Carlin-type gold deposits is con-trolled by the Yanshanian tectonic activities.The Yanshanian movement promoted the migration and mobilization of metamorphic fluids in the extensively developed medium-to high-grade metamorphic rocks in this region,carrying primarily enriched gold and associated elements such as Hg,As,and Sb in the Sinian metamorphosed black shales and Lower Cambrian black shales.The ore-forming fluids found their way into a suitable metallogenic environment along the fault zone,followed by gold precipitation to form gold deposits.

A study on the genetic relations between Permian Longtan Formation coal series strata and Carlin-type gold deposits,southwestern Guizhou Province,China

A large number of the Carlin-type gold deposits occur in the Longtan Formation in southwestern Guizhou Province.The Long-tan Formation contains abundant basalt,tuff and siliceous rocks.All rocks of the Longtan Formation are enriched in gold,which were deposited in a limited platform environment in the transition zone from marine to continental.The process of sedimentation was accompanied by the eruption of Emeishan basalt and hydrothermal deposition controlled by co-sedimentary submarine deep faults in the west,which led to the formation of a peculiar gold-bearing formation with coal series strata.This formation controlled the occurrence of the Carlin-type gold deposits in southwestern Guizhou Province.In response to the remobilization of the Emei mantle plume during the Yanshanian period,As,Au and other ore-forming materials were continuously extracted by deeply circulating waters from the Emeishan basalt and coal seams,thereafter forming ore-forming hydrothermal solutions.When these elements were transported in the coal seams,large amounts of As,Au and other elements were enriched in pyrite within the coal seams,thus forming high-As coal and Carlin-type gold deposits in the Longtan Formation coal series strata.

Geochemical Tracing of Ore-forming Material Sources of Carlin-type Gold Deposits in the Yunnan-Guizhou-Guangxi Triangle Area --A Case Study of the Application of the Combined Silicon Isotopes Geochemistry and Siliceous Cathodoluminescence Analysis

Abstract This paper deals with characteristics of silicon isotope compositions and siliceous cathodoluminescence of host rocks, ores and hydrothermal silicified quartz of the Carlin-type ore deposits in the Yunnan-Guizhou-Guangxi triangle area. The study shows that primary silicified quartz is nonluminescent but quartz in host rocks and secondary silicified quartz are luminescent by the action of cathode rays. Correspondingly, silicon isotope compositions of host rocks, ores and hydro6thermal quartz veins are clearly distinguished. In strata from the Middle Triassic to the “Dachang” host bed, δ30Si of the host rocks ranges from 0.0% ?0.3%, while that of primary ore-forming silicified fluids from ?0.1% to ?0.4%; in the Upper Permian and Lower Carboniferous strata and Indosinian diabase host beds, δ30Si of the host rocks is from ?0.1% to ?0.2% and that of the primary silicified quartz veins from 0.3 % ?0.5 %. This pattern demonstrates the following geochemical mineralization process, primary ore-forming siliceous fluids migrated upwards quickly along the main passages of deep-seated faults from mantle to crust and entered secondary faults where gold deposits were eventually formed as a result of permeation and replacement of the siliceous ore-forming fluids into different ore-bearing strata. This gives important evidence for the fact that ore-forming fluids of this type of gold deposits were mainly derived from upper mantle differentiation and shows good prospects for deep gold deposits and geochemical background for large and superlarge gold deposits.

Trace Elements in Fluid Inclusions in the Carlin-Type Gold Deposits, Southwestern Guizhou Province

Fluid inclusions in quartz from the Lannigou and Yata Carlin\|type gold deposits in southwestern Guizhou were analyzed by inductively coupled plasma\|mass spectrometry for their trace elements (Co, Ni, Cu, Pb, Zn, Pt, etc.). The results show that quartz fluid inclusions entrapped at different ore\|forming stages contain higher Co, Ni, Cu, Pb and Zn. It has been found for the first time that the ore\|forming fluids responsible for the Carlin\|type gold deposits are rich in Pt. From this it can be concluded that basic volcanic rocks seem to be one of the important sources of ore\|forming materials for the Carlin\|type gold deposits.

Carlin-Type Gold Deposits in Qinling and Some Related Problems

The sediment hosted disseminated gold deposits in the Qinling region are of sedimentation slight metamorphic origin superimposed by hydrothermal reworking at moderate low temperatures and are well comparable with the typical Carlin gold deposits in the United States. In view of the confusing concept concerning the \!sediment hosted" and \!Carlin type" gold deposits, the authors propose that the term \!sediment hosted gold deposit" should be used in a broad sense which encompasses at least the four subtypes, i.e., the Carlin type, the metamorphic fine clastic type, the hydrothermal sedimentary type and the vein type. In other words, the \!Carlin type" should not be used as a synonym for \!sediment hosted" but is recommended as a subtype under the general category of \!sediment hosted gold deposits".

The conjunction of factors that lead to formation of giant gold provinces and deposits in non-arc settings

It is quite evident that it is not anomalous metal transport,nor unique depositional conditions,nor any single factor at the deposit scale,that dictates whether a mineral deposit becomes a giant or not.A hierarchical approach thus is required to progressively examine controlling parameters at successively decreasing scales in the total mineral system to understand the location of giant gold deposits in non-arc environments.For giant orogenic,intrusion-related gold systems（IRGS） and Carlin-type gold deposits and iron oxide-copper-gold（IOCG） deposits,there are common factors among all of these at the lithospheric to crustal scale.All are sited in giant gold provinces controlled by complex fundamental fault or shear zones that follow craton margins or,in the case of most Phanerozoic orogenic giants,define the primary suture zones between tectonic terranes.Giant provinces of IRGS,IOCG,and Carlin-type deposits require melting of metasomatized lithosphere beneath craton margins with ascent of hybrid lamprophyric to granitic magmas and associated heat flux to generate the giant province.The IRGS and IOCG deposits require direct exsolution of volatile-rich magmatic-hydrothermal fluids,whereas the association of such melts with Carlin-type ores is more indirect and enigmatic.Giant orogenic gold provinces show no direct relationship to such magmatism.forming from metamorphic fluids,but show an indirect relationship to lamprophyres that reflect the mantle connectivity of controlling first-order structures.In contrast to their province scale similarities,the different giant gold deposit styles show contrasting critical controls at the district to deposit scale.For orogenic gold deposits,the giants appear to have formed by conjunction of a greater number of parameters to those that control smaller deposits,with resultant geometrical and lithostratigraphic complexity as a guide to their location.There are few giant IRGS due to their inferior fluid-flux systems relative to orogenic gold deposits,and those few giants are essentially preservational exceptions.Many Carlin-type deposits are giants due to the exceptional conjunction of both structural and lithological parameters that caused reactive and permeable rocks,enriched in syngenetic gold,to be located below an impermeable cap along antiformal ＂trends＂.Hydrocarbons probably played an important role in concentrating metal.The supergiant Post-Betze deposit has additional ore zones in strain heterogeneities surrounding the pre-gold Goldstrike stock.All unequivocal IOCG deposits are giant or near-giant deposits in terms of gold-equivalent resources,partly due to economic factors for this relatively poorly understood,low Cu-Au grade deposit type.The supergiant Olympic Dam deposit,the most shallowly formed deposit among the larger IOCGs,probably owes its origin to eruption of volatile-rich hybrid magma at surface,with formation of a large maar and intense and widespread brecciation,alteration and Cu-Au-U deposition in a huge rock volume.

ORE FLUID GEOCHEMISTRY OF THE JINLONGSHAN CARLIN-TYPE GOLD ORE BELT IN SHAANXI PROVINCE, CHINA

The Jinlongshan gold ore belt in southern Shaanxi Province contains a number of Carlin-type gold deposits in the Qinling collisional orogenic belt. Their fluid inclusions are of the Na-Cl- type. From the main metallogenic stage to later stages, the total quantity of anions and cations, temperature and deoxidation parameter (R) for fluid inclusions all gradually decreased, suggesting the gradual intensification of fluid oxidation, the reduction of metallogenic depth and the input of meteoric water and organic components. The deposits were formed during crustal uplifting and hence had similar tectonic settings to orogenic gold deposits. The CO-2 contents and CO-2/H-2O values of the ore fluid increased from early to late stages, and the wall-rock alteration is represented by decarbonation, which is inconsistent with the characteristics of orogenic gold deposits. It is also discovered that Na, K, SO{2-}-4, Cl- and the total amounts of anions and cations in the inclusions in quartz are higher than those in the coexisting calcite. The H, O and C isotope ratios indicate that the ore fluid was sourced from meteoric water and metamorphic devolatilisation of the sedimentary rocks that host the ores. The high background {δ{}{18}O} and {δ{}{13}C} values of wall rocks resulted in high {δ{}{18}O} and {δ{}{13}C} values of ore fluid and also high {δ{}{18}O} and {δ{}{13}C} values of hydrothermal minerals such as quartz and carbonate. The carbon in ore fluid stemmed largely from the hosting strata. The {δ{}{18}O} and {δ{}{13}C} values of Fe-calcite and the δD values of fluid inclusions are lower than those of calcite and quartz. In terms of the theory of coordination chemistry, all these differences can be ascribed to water-rock interaction in the same fluid system, instead, to the multi-source of ore fluid.

Red Clay Type Gold Deposits in China

Red clay type gold deposits,located in the south of China,are situated not only in orogenic belts,but also in inner cratons,where climate is tropical-subtropical with clear arid and humid.The lateritic weathering crust often can be divided into five zones,including topsoil,siliceous duricrust zone,multi-color zone(or red clay zone in some deposits),pallid zone and saprolite zone from surface to the base rock,several of which are absent in some deposits.The base rocks are composed mainly of carbonate rocks with minor clastic rocks,intermediate-basic volcanic rocks and intermediate-acid and alkalic intrusions.The orebodies are mainly located in the multi-color zone with part of them in the pallid and saprolite zones.The ore sources include orebodies of Carlin-type gold deposits and porphyry gold deposits,as well as gold-rich base rocks.The red clay type gold deposits experienced early-stage endogenic gold mineralization and laterization during the Tertiary and Quaternary.The areas with endogenic gold deposits,especially Carlin-type gold deposits and porphyry gold deposits in karst depressions on the plateau,structual erosional platforms in the middle-lower mountains,and intermountain basins in southern China are well worth studying to trace red clay type gold deposits.

Geological and geochemical characteristics of the Baogudi Carlintype gold district(Southwest Guizhou, China) and their geological implications

The newly discovered Baogudi gold district is located in the southwestern Guizhou Province,China,where there are numerous Carlin-type gold deposits.To better understand the geological and geochemical characteristics of the Baogudi gold district,we carried out petrographic observations,elemental analyses,and fluid inclusion and isotopic composition studies.We also compared the results with those of typical Carlin-type gold deposits in southwestern Guizhou.Three mineralization stages,namely,the sedimentation diagenesis,hydrothermal(main-ore and late-ore substages),and supergene stages,were identified based on field and petrographic observations.The main-ore and late-ore stages correspond to Au and Sb mineralization,respectively,which are similar to typical Carlin-type mineralization.The mass transfer associated with alteration and mineralization shows that a significant amount of Au,As,Sb,Hg,Tl,Mo,and S were added to mineralized rocks during the main-ore stage.Remarkably,arsenic,Sb,and S were added to the mineralized rocks during the late-ore stage.Element migration indicates that the sulfidation process was responsible for ore formation.Four types of fluid inclusions were identified in ore-related quartz and fluorite.The main-ore stage fluids are characterized by an H2O–NaCl–CO2–CH4±N2system,with medium to low temperatures(180–260℃)and low salinity(0–9.08%NaCl equivalent).The late-ore stage fluids featured H2O–NaCl±CO2±CH4,with low temperature(120–200℃)and low salinity(0–7.48%Na Cl equivalent).The temperature,salinity,and CO2and CH4concentrations of ore-forming fluids decreased from the main-ore stage to the late-ore stage.The calculated δ^13C,d D,and δ^18O values of the ore-forming fluids range from-14.3 to-7.0%,-76 to-55.7%,and 4.5–15.0%,respectively.Late-ore-stage stibnite had δ^34S values ranging from-0.6 to 1.9%.These stable isotopic compositions indicate that the ore-forming fluids originated mainly from deep magmatic hydrothermal fluids,with minor contributions from strata.Collectively,the Baogudi metallogenic district has geological and geochemical characteristics that are typical of Carlin-type gold deposits in southwest Guizhou.It is likely that the Baogudi gold district,together with other Carlin-type gold deposits in southwestern Guizhou,was formed in response to a single widespread metallogenic event.

Fluid inclusion, siliceous rock geochemistry of Shewushan lateritic gold deposit, Hubei Province, eastern China: Implication for the genesis of primary orebody

The Shewushan gold deposit is located 16 km southwest of Jiayu County, Hubei Province, eastern China, which is the largest lateritic gold deposit in Asia, consisting of a series of mineralized faults containing gold grades of 1.0–19.5 g/t set within a larger, lower-grade(0.2–1.0 g/t) zone. According to the fluid inclusions study, the homogenization temperature ranges from 70–350℃, and concentrates between 140–220℃. The laser Rama results show that the CO2 and CH4 exist in mineralized fluid. In addition, the major and trace element and REE geochemical data show that the genesis of the siliceous rocks is hydrothermal genesis, formed by mineralized fluid bearing SiO2 transmitted along faults to the surface, and replace the carbonate rocks to begin deposition. Primary gold mineralization is attributed to hydrothermal activity that followed the main period of tectonic deformation of the Indosinian orogeny, which caused the regional detachment regime in southeast Hubei. The reversed fold and the fault system formed the fluid migration channel in the Shewushan area. EPMA results show that Au exists in arsenopyrite(850×10-6–1550×10-6 Au) and pyrite(470×10-6–1340×10-6 Au). Therefore, based on the above results and combined with the field observation, we suggest that the genesis of primary orebody in Shewushan deposit is carlin type, while not weathered residual type.

Physicochemical Conditions of Differential Mineralization of Au and As in Gold Deposits,Southwest Guizhou Province, China

The conditions under which gold and arsenic are enriched separately during mineralization in gold deposits in southwestern Guizhou Province were described and the thermodynamic calculations gave: 200-150℃ at 400×10-6-300×10 6 Pa （corresponding to a depthbetween 1 .6 km and 1 .2 km）; lgfO2-40 t0 - 35 Pa; lgfs2- 20 to -16 Pa; pH 5. 0 -4. 2 and Eh - 0. 53 V.

基于证据权重法广西金牙-明山一带金矿产定量预测

广西金牙-明山一带存在多个大中型卡林型金矿床,具备良好的金矿找矿潜力。前人工作获得了该地区地质、矿产、物、化探等多元资料,但缺乏对相关资料找矿信息的深度定量挖掘。本文基于证据权重法在广西金牙-明山一带开展卡林型金矿矿产定量预测。在系统分析金牙-明山一带区域地质背景与卡林型金矿成矿地质条件的基础上,建立研究区区域找矿模型。依据此模型选择并利用MRAS软件系统提取了成矿有利地层、岩浆岩、断裂、断裂交点、围岩蚀变和Au、As、Sb、Hg元素化探异常等多个证据因子;并基于这些证据因子计算区内各单元格(500 m×500 m)的成矿后验概率。综合成矿后验概率和已有的资料,在研究区圈定出19个找矿靶区。这些靶区包含了区内绝大多数矿床点所在位置,表明该预测成果的可信度较高;同时多处靶区范围包含重点矿区外围及空白区,这为该区的卡林型金矿后续找矿部署提供依据。

右江盆地卡林型金矿成矿年代学研究进展

右江盆地是全球仅次于美国内华达地区的第二大卡林型金矿床集中分布区。由于成矿时代的不确定性,盆地内卡林型金矿床的成矿动力学背景一直不清。为准确确定这些金矿床的成矿时代,近四十年来国内外矿床学家进行了孜孜不倦的探索,从早期以石英裂变径迹和流体包裹体Rb-Sr等时线法为代表的定年,到中期以硫化物Re-Os等时线法为代表的单矿物溶样法定年,再到最新以热液金红石、独居石和磷灰石U-Th-Pb法为代表的微区原位定年,其定年对象和方法见证了同位素地质年代学的发展历程。现已基本明确,右江盆地主要发育两期卡林型金矿成矿作用,分别为215~200 Ma和155~140 Ma,相当于印支期和燕山期,其动力学背景分别对应于印支-华南-华北地块碰撞后的印支期陆内造山过程以及燕山期软流圈上涌诱发的岩石圈伸展作用。

The Existence of the Negative Charge of Gold in Sulphide Minerals and Its Formation Mechanism

Through a study, particularly an X-ray photoelectron spectroscopy (XPS or ESCA) analysis, of gold-bearing arsenopyrite and pyrite in Carlin-type gold deposits of Guangxi, China, and hydrothermally synthesized gold-bearing pyrite and marcasite, the authors have found that these minerals contain 'invisible gold' whose binding energy is lower than that of native gold (Au°). Therefore they suggest that gold occurs in a negative charge state in these sulphide minerals as it replaces some sulphur and is combined with sulphur with the covalent bond. This paper also preliminarily discusses the possibility of its formation from the chemistry and geochemistry of gold, crystal chemistry of arsenopyrite, pyrite and marcasite and geochemical environment.

郑明华矿(Zhengminghuaite):黔西南卡林型金矿床中新矿物的发现及其成矿学意义

郑明华矿是最近在黔西南紫木凼卡林型金矿床中发现的一种硫盐类新矿物。文章在概述郑明华矿产出状态、物理性质、光学特征、化学组成和晶体结构基础上,侧重介绍该新矿物形成的地质背景、显微组构特征及与同型系列其他矿物的关系,并结合矿物共生组合特征,探讨其形成的物理化学条件。郑明华矿产于受断层破碎带控制的角砾状金矿石中,与其共生或伴生的矿物为成矿晚阶段石英、雄黄和方解石,以及少量至微量As-Sb-Hg-Tl的硫化物和硫盐。郑明华矿为不透明矿物,金属光泽,性脆易碎,无解理,莫氏硬度约为4;反射色为浅灰色,双反射和反射多色性不显至微弱,非均质性微弱,反射率为23%~29%(546 nm);理想化学式为Cu_(6)Fe_(3)As_(4)S_(12),三方晶系,空间群R3,晶胞参数:a=13.5373(17)Å,c=9.2354(13)Å,V=1465.7(4)Å^(3)(Z=3),属硫砷锌铜矿同型系列的新矿物。郑明华矿形成于成矿主阶段含金富砷黄铁矿、毒砂等Fe硫化物沉淀后的成矿晚阶段,但主要形成于雄黄等As硫化物大量沉淀前,在此期间成矿流体的硫逸度(f(S_(2)))升高了1~2个对数单位,温度降低了60~100℃。郑明华矿的发现及与其他热液矿物的共生组合关系,为揭示卡林型金矿床的成矿过程和成矿物理化学条件提供了重要信息。