Geology and Genesis of the Superlarge Jinchang Gold Deposit, NE China

The superlarge Jinchang gold deposit is located in the joint area between the Taipingling uplift and the Laoheishan depression of the Xingkai Block in both eastern Jilin and eastern Heilongjiang Province. Wall rocks of the gold deposits are the Neoproterozoic Huangsong Group of metamorphic rocks. Yanshanian magmatism in this region can be divided into 5 phases, the diorite, the graphic granite, the granite, the granite porphyry and the diorite porphyrite, which resulted in the magmatic domes and cryptoexplosive breecia chimney followed by large-scale hydrothermal alteration. Gold mineralization is closely related to the fourth and fifth phase of magmatism. According to the occurrences, gold ores can be subdivided into auriferous pyritized quartz vein, auriferous quartz-pyrite vein, auriferous polymetailic sulfide quartz vein and auriferous pyritized calcite vein. The ages of the gold deposit are ranging from 122.53 to 119.40 Ma. The ore bodies were controlled by a uniform tectono-magmatic hydrothermal alteration system that the ore-forming materials were deep derived from and the ore-forming fluids were dominated by magmatic waters with addition of some atmospheric water in the later phase of mineralization. Gold mineralization took place in an environment of medium to high temperatures and medium pressures. Ore-forming fluids were the K^＋-Na^＋-Ca^2＋-Cl^--SO4^2- type and characterized by medium salinity or a slightly higher, weak alkaline and weak reductive. Au in the ore-forming fluids was transported as complexes of [Au （HS）2]^-, [AuCl2]^-, [Au（CO2）]^- and [Au（HCO3）2]^-. Along with the decline of temperatures and pressures, the ore-forming fluids varied from acidic to weak acidic and then to weak alkaline, which resulted in the dissociation of the complex and finally the precipitation of the gold.     

Mobilization of gold into lake sediments from acid and alkaline mineralized environments in the southern Canadian Shield: Gold in lake sediments and natural waters

To be an effective indicator of mineralization in lake sediment surveys within the Canadian Shield, it is desirable that an element migrate in solution or adsorbed on suspensates. Given the low relief and disorganized drainage patterns of this region, dispersal in clastic form in drainage systems is limited and gives rise to erratic distributions. The purpose of this study was to discover whether Au shows significant hydromorphic mobility, which would justify the increasing use that is being made of this element in lake sediments as an indicator for gold mineralization.Waters and lake sediments were collected from Napier Lake, Ontario; PAP Lake, Saskatchewan; and Foster Lake, Manitoba, all of which contain Au-quartz vein mineralization and lie within the glaciated boreal forest zone of the Canadian Shield. In all three areas, profundal lake sediments down-drainage of mineralization contain Au concentrations higher than regional mean concentrations. Significant dissolution and transport of Au was found under oxidizing conditions associated with waters with pH that varied from acid to alkaline. Waters from drill holes penetrating mineralization contain up to 401 ng L⁻¹ Au (note; 1 ng L⁻¹ is equivalent to 1 part per trillion, 10⁻¹²). Surface waters overlying or near mineralization collected from bogs, seeps, ponds and streams contain up to 13 ng L⁻¹. The content of Au in lake waters is lower, with a maximum of 1.1 ng L⁻¹. There is also a detectable quantity of Au present in suspensates. Two samples of particulates (> 1 μm) filtered from lake water have Au equivalent to 0.17 ng L⁻¹ and 0.039 ng L⁻¹. While the contents of Au present in solution or as suspensates in lake and stream water are relatively small, they are sufficient, if precipitated, to generate anomalies in lake sediments. Thus for Reservoir Lake, in the Foster Lake area, water from the principal stream entering the lake carries 0.3 ng L⁻¹ Au. This provides an annual flux which far exceeds that required to generate the 7.3 ppb Au contained in profundal sediments of this lake; a content that is anomalous relative to the regional median content of < 1 ppb Au for lake sediments.Hydrogeochemical prospecting involving analysis for Au is one method for tracing the source of anomalous Au in lake sediments. Collection of 1 L samples without field treatment, followed by extraction of Au into MIBK, then analysis by graphite-furnace atomic absorption spectrophotometry, permits detection levels for Au of 0.5 ng L⁻¹. This is below the contents of Au found in some waters from mineralized areas. A detection limit of 0.3 ng L⁻¹ was obtained using larger water samples.     

新疆东准噶尔卡拉麦里造山型金成矿系统与区域构造演化

新疆东准噶尔卡拉麦里地区以金水泉、双泉、南明水、苏吉泉东等为代表的金矿床,构成了一套与晚古生代碰撞造山有关的金成矿系统。矿床夹持于区域性的卡拉麦里深大断裂和清水—苏吉泉大断裂之间,矿化受次级脆-韧性断层控制,以中等至陡倾斜的含金石英脉和破碎蚀变岩的形式产于晚古生代浅变质火山沉积岩中。流体包裹体、H-O-S-Pb同位素和热液锆石U-Pb年代学研究表明,成矿流体具中高温(集中于240~330 ℃)、低盐度(<6% NaCl_eq)、富CO₂的变质流体特征,成矿物质来自赋矿的火山沉积岩系,流体不混溶(相分离)和水-岩反应(围岩硫化作用)是导致金沉淀的主要机制,成矿深度变化于7~15 km之间,成矿时代约为314 Ma。晚石炭世至早二叠世,研究区的构造体制由挤压向走滑或走滑伸展转换,构造应力的释放导致深部变质脱水形成的低盐度CO₂-H₂O-NaCl±CH₄含金流体,沿走向NW至近EW向的走滑剪切断裂向地壳浅部流动,并在脆-韧性过渡带或脆性变形带的次级断裂中形成含金石英脉及蚀变岩型金矿石。     

云南墨江金矿床含金硅质岩的地球化学特征和成因

中石炭统金厂组（Ｃ２ｊ）下部含金硅质岩是云南墨江金矿庆的主要围岩之一,具有沉积结构构造,含热水沉积矿物。岩石的ＦｅＯ、Ｆｅ２Ｏ３、Ａｕ和Ａｇ含量高;Ｃｒ、Ｎｉ和Ｃｏ含量高、变化大;ＭｎＯ／ＴｉＯ２和ＴＦｅ／ＴｉＯ２比值较大;Ａｕ含量与ＮｉＣｒ含量相关性低,Ａｕ可能不是后期热液作用带入的。在判别硅质岩形成作用的一系列元素和微量元素关系图上,含金硅质岩位于热水沉积作用的范围内或接近于热水沉积作用。岩石     

Geochemical Features and Formation of the Auriferous Cherts in the Mojiang Gold Deposit,Yunnan

Auriferous cherts in the Middle Carboniferous Jinchang Formation are the dominant host rocks of auriferous quartz veins and mixed orebodies comprised of gold-bearing quartz veins and cherts in the Mojiang gold deposit.The rocks exhibit sedimentary texture and structure and are composed of hot-water deposited minerals.The FeO,Fe2O3,Au and Ag contents of the auriferous cherts are high;the Cr,Ni and Co contents are also high but significantly variable;MnO/TiO2 and TFe/TiO2 ratios are relatively higy.As viewed from a few diagrams that distinguish different chert formations,the auriferous cherts are in or near the range of hot-water deposited cherts.Because the correlation coefficients between Au contents and those of Cr, Ni of the rocks are negative,a great Au amount in the cherts might not be brought about by later hydrothermal alterations.The rare-earth elements,O and Si isotopic compositions of the auriferous cherts demonstrate that the cherts belong to hot-water deposited rocks.The later hydrothermal alterations made the petrochemical compositions of the cherts deviate from the characteristics of hot-water deposition.In general,the geological and geochemical features of the auriferous cherts demonstrate that the rocks were formed by hot water deposition.     

Geochronology of Gold Deposits and Its Implication for Metallogenesis in the Fengxian-Lixian Area, Qinling Orogenic Belt, China

Abstract: A series of super large‐scale and large‐scale Pb and Zn, and Au deposits are distributed in the Qinling orogenic belt, China. Gold deposits were generally ascribed to Carlin‐type originated from circular meteoric water. Visible and coarse‐grained gold (up to over 3mm in grain size) was recently identified in some gold deposits in the Fengxian‐Lixian area, Qinling. Au‐bearing quartz lodes related to magmatism were discovered in the Xiaogouli gold deposit. Two types of Au‐bearing quartz veins, i.e., NW‐trending quartz veins and NE‐trending quartz veins cutting strata are widely present in the Baguamiao gold deposit. Both are spatially associated with each other. The former is generally snake–like, S‐shape or zigzag, which was resulted from plastic deformation by ductile shearing, being generally cut by the latter. The latter is generally linear with widely developed bleaching alteration zones in its adjacent wall rocks, which symbolizes the superimposition of brittle deformation and filling and metasomatism of magmatic hydrothermal solution in ductile shear zones after uplifting of the shear zones near the surface. The NW‐trending quartz veins contain Au of lower than 3ppm. The NE‐trending quartz veins contain Au of more than 3 ppm, so that NE‐trending quartz veins and the adjoining altered rocks are important ores. The NW‐trending Au–bearing quartz vein was dated as 210.61.26 to 232.581.59 Ma by ⁴⁰Ar–³⁹Ar method, i.e., late Indosinian epoch (Triassic). The NE‐trending Au–bearing quartz vein was dated as 131.910.89 to 197.451.13 Ma by ⁴⁰Ar–³⁹Ar method, i.e., Yanshanian epoch (Jurassic). The ⁴⁰Ar–³⁹Ar age of the NW‐trending Au–bearing quartz veins represents the age of the ductile shear formation. The isotope data of the NE‐trending quartz veins indicate that gold mineralization was closely related to Indosinian and Yanshanian granite intrusives not only in time and space, but also in origin.     

Epithermal Gold Mineralization in the Trenggalek District,East Java,Indonesia

Gold‐mineralized quartz veins at the Trenggalek district of the Southern Mountains Range in East Java, Indonesia, are hosted by Oligo‐Miocene volcaniclastic and volcanic rocks, and are distributed close to andesitic plugs in the northern prospects (Dalangturu, Suruh, Jati, Gregah, Jombok, Salak, and Kojan) and the southern prospects (Sentul and Buluroto). The plugs are subalkaline tholeiitic basaltic‐andesite to calc‐alkaline andesite in composition. ⁴⁰Ar–³⁹Ar dating of a quartz‐adularia vein at the Dalangturu prospect yielded an age of 16.29 ± 0.56 Ma (2σ), and a crystal tuff of a limestone‐pyroclastic rock sequence at the southwest of the Dalangturu prospect was determined as 15.6 ± 0.5 Ma (2σ). Statistic overlap of ages suggests that the gold mineralization in the northern prospects took place in a shallow marine to subaerial transitional environment. Hydrothermal alteration of the host rocks is characterized by the replacement of quartz, illite and adularia. Quartz veins in surface outcrops are up to 50 cm wide in the northern prospects and up to 3 m wide in the southern prospects, showing a banded or brecciated texture, and are composed of quartz, adularia, carbonates with pyrite, electrum, sphalerite, galena, and polybasite. Gold contents of quartz veins are positively correlated with Ag, Zn, Pb, and Cu contents in both the northern and southern prospects. The quartz veins at the Jati, Gregah, and Sentul prospects have relatively lower gold‐silver ratios (Ag/Au = 23.2) compared to those at the Kojan, Dalangturu, Salak, and Suruh prospects (Ag/Au = 66.8). The quartz veins at the Dalangturu prospect are relatively rich in base metal sulfides. Ag/(Au+Ag) ratios of electrum in the Dalangturu prospect range from 45.2 to 65.0 at%, and FeS contents of sphalerite range from 1.2 to 6.4 mol%. Fluid inclusion microthermometry indicates ore‐forming temperatures of 190–200°C and 220–230°C at the Sentul and Kojan prospects, respectively. Widely variable vapor/liquid ratio of fluid inclusions indicates that fluid boiling took place within the hydrothermal system at the Sentul prospect. Salinities of ore‐fluids range from 0 to 0.7 wt% (av. 0.4 wt% NaCl equiv.) and from 0.5 to 1.4 wt% (av. 0.9 wt%) for the Sentul and Kojan prospects, respectively. The boiling of hydrothermal fluid was one of the gold deposition mechanisms in the Sentul prospect.     

Acid drainage from sulfides hosting gold mineralization (Furtei, Sardinia)

 The past mining activity for kaolin minerals left several abandoned quarries in the area of Furtei (southern Sardinia). Recently, gold mineralization has been found in association with intensely altered andesitic rocks, and an open-pit gold mine is expected to open in the near future. Twenty-one water samples were analyzed for a wide range of major and trace elements, in order to define the present hydrochemical situation before exploitation starts. Waters interacting with the altered andesitic rocks had higher salinity and metal concentrations than waters in contact with nonaltered rocks. Acid drainage and high concentrations of metals (Al, Fe, Mn, Zn, Cu, As) in solution were observed in waters leaching the mineral deposit. An environmental impact study is urgently called for since the waste material derived from the exploitation is expected to enhance acidification and metal-releasing processes, due to the increase in the specific yield, which favors the oxidation of sufide minerals. Received: 15 February 1995 · Accepted: 10 October 1995     

Form and distribution of gold mobilized into surface waters and sediments from a gossan tailings pile,Murray Brook massive sulphide deposit,New Brunswick,Canada

Stream waters and sediments draining a gossan tailings pile at the Murray Brook massive sulphide deposit were collected to investigate Au mobility. Weathering of the massive sulphides at Murray Brook during the Late Tertiary period resulted in the concentration of Au in the gossan cap overlying the supergene Cu and unoxidized massive sulphide zones of the deposit. The gossan was mined between 1989 and 1992, and Au and Ag were extracted using a cyanide vat leach process. Although stream sediments prior to mining had Au<5 ppb (the detection limit), sediments collected in 1997 had Au contents ranging up to 256 ppm with values up to 6 ppm more than 3 km downstream from the deposit. Dissolved Au contents were similarly anomalous, up to 19 μg/L and in excess of 3 μg/L 3 km downstream. The elevated Au contents in the waters and sediments are interpreted to reflect complexation of Au (as Au(CN)₂⁻) by cyanide hosted within the gossan tailings pile. Precipitation recharges through the tailings pile with groundwater flow exiting to Gossan Creek. Degradation of cyanide along the flow path and within Gossan Creek allows colloidal Au to form via reduction of Au(I) by Fe²⁺, consistent with SEM observations of Au as <1 μm subrounded particles. In the surface waters, the majority of the Au must be in a form <0.45 μm in size to account for the similarity in Au contents between the <0.45 μm and unfiltered samples. The very elevated stream sediment Au values close to the headwaters of Gossan Creek near the tailings indicate that upon exiting to the surface environment, Au(CN)₂⁻ complexes are rapidly destroyed and Au removed from solution. However, the high Au_{<0.004 μm}/Au_total in the headwaters and the extended Au dispersion in Gossan Creek waters and sediments suggest that Au(CN)₂⁻ complexes persist for the full length of Gossan Creek. The decrease in aqueous Au which is less than 0.004 μm indicates that Au is converted from a complexed form to a colloidal form with increasing distance downstream, consistent with dissolved NO₃⁻ contents which decrease from 5210 μg/L near the headwaters to 1350 μg/L at the lower end of the stream.     

福建尤溪肖板金矿床金的赋存状态及金矿物特征

肖板金矿床属受构造控制的中低温岩浆热液矿床,矿化类型为构造蚀变岩型。金多呈独立金矿物形式出现,少许呈分散状;金矿物以自然金为主,平均成色９３０,有少量银金矿和碲金矿。金矿物以包体金、裂隙金、连生金和粒间金等形式嵌布于黄铁矿、黄铜矿、石英、方铅矿及方解石等主要载金矿物中,且石英、方解石中较金属硫化物中占优势。金矿物形态各异,粒度以中细粒为主。     

Gold mineralisation and advanced argillic alteration at the Dobroyde prospect,central New South Wales

Gold mineralisation at the Dobroyde prospect in central New South Wales is hosted by a zoned alteration system characterised by peripheral propylitic alteration, grading inwards through argillic and advanced argillic alteration to a siliceous altered core. Overprinting textures indicate that propylitic, argillic, advanced argillic and siliceous assemblages were successively superimposed on each other. Au grades between 0.3–0.8 ppm are associated with siliceous alteration and cross‐cutting pyrite veinlets. Higher Au grades are associated with barite veins that cut the pyrite veinlets. Native Au, native Te, Au, Pb and Hg tellurides, Pb selenide, chalcopyrite, Zn‐sphalerite and tennantite‐tetrahedrite occur in the barite veins. Microscopic pyrophyllite shears cut the barite veins. The location of the Dobroyde prospect, the orientation of its internal alteration zonation and the orientation of auriferous barite veins in the core of the prospect are controlled by a 330°‐striking fault. Movement on this fault, synchronous with hydrothermal activity, at some time between the Late Ordovician and mid‐Devonian controlled the development of successive phases of brecciation, siliceous alteration, pyrite and later barite‐Au veining in the prospect core. The restricted distribution of auriferous barite veins within the siliceous altered core of the prospect is inferred to be controlled by the relatively brittle rheology of this assemblage during deformation, and its location on the fault that formed the main hydrothermal fluid conduit. Alteration zones distal from this fault remain unmineralised. The Dobroyde prospect may be a product of the same Early Devonian metallogenic epoch as the paragenetically similar Temora and Peak Hill deposits. All three deposits/prospects appear to be localised in splays of either the Gilmore Fault Zone or the Parkes Thrust.     

Geology, mineralization, and geochronology of the Qianhe gold deposit, Xiong’ershan area, southern North China Craton

The Qianhe gold deposit in the Xiong’ershan area is located along the southern margin of the Archean-Paleoproterozoic North China Craton. The deposit consists of six orebodies that are hosted in Paleoproterozoic andesites to basaltic andesites and structurally controlled by roughly EW-trending faults. Individual orebodies comprise auriferous quartz veins and disseminated Au-bearing pyrite within hydrothermally altered rocks on both sides of, or close to, the veins. Ore-related hydrothermal alteration has produced various mixtures of K-feldspar, quartz, sericite, chlorite, epidote, carbonate, and sulfides. Pyrite is the most important ore mineral, associated with minor amounts of galena, sphalerite, and chalcopyrite. Other trace minerals include molybdenite, arsenopyrite, scheelite, rutile, xenotime, and parisite. Gold occurs mostly as native gold and electrum enclosed in pyrite or along microfractures of sulfides and quartz. Microthermometric measurements of primary inclusions in auriferous quartz suggest that gold and associated minerals were precipitated in the range of 160–305 °C from aqueous or carbonic-aqueous fluids with salinities of 6–22 wt% NaCl equiv. Samples of molybdenite coexisting with Au-bearing pyrite have Re–Os model ages of 134–135 Ma, whereas ore-related hydrothermal sericite separates yield ⁴⁰Ar/³⁹Ar plateau ages between 127 and 124 Ma. The Re–Os and ⁴⁰Ar/³⁹Ar ages are remarkably consistent with zircon U–Pb ages (134.5?±?1.5 and 127.2?±?1.4 Ma; 1σ) of the biotite monzogranite from the Heyu-intrusive complex and granitic dikes in and close to the Qianhe gold mine, indicating a close temporal and thus possibly genetic relationship between gold mineralization and granitic magmatism in the area. Fluid inclusion waters extracted from auriferous quartz have δD values of ?80 to ?72 ‰, whereas the calculated δ ¹⁸O_H2O values range from 3.1 to 3.8 ‰. The hydrogen and oxygen isotopes from this study and previous work indicate that ore fluids were likely derived from degassing of magmas, with addition of minor amounts of meteoric water. Gold mineralization at Qianhe is temporarily coincident with pervasive bimodal magmatism, widespread fault-basin formation, and well development of metamorphic core complexes in the whole eastern North China Craton that have been interpreted as reflecting reactivation of the craton in the late Mesozoic after prolonged stabilization since its formation in the late Paleoproterozoic. It is therefore concluded that the Qianhe gold deposit formed as a result of this craton reactivation event.     

Paleoproterozoic gold deposits in the Bald Hill and Coyote areas, Western Tanami, Western Australia

Significant gold deposits in the western Tanami region of Western Australia include deposits in the Bald Hill and Coyote areas. The ca. 1,864 Ma Bald Hill sequence of turbiditic and mafic volcanic rocks hosts the Kookaburra and Sandpiper deposits and a number of smaller prospects. The ca. 1,835 Ma turbiditic Killi Killi Formation hosts the Coyote deposit and several nearby prospects. The Kookaburra deposit forms as a saddle reef within a syncline, and the Sandpiper deposit is localized within graphitic metasedimentary rocks along a limb of an anticline. Gold in these deposits is hosted by anastomosing quartz–(–pyrite–arsenopyrite) veins within quartz–sericite schist with disseminated arsenopyrite, pyrite, and marcasite (after pyrrhotite). Based on relative timing relationships with structural elements, the auriferous veins are interpreted to have been emplaced before or during the ca. 1,835–1,825 Ma Tanami Orogeny (regional D₁). Gold deposition is thought to have been caused by pressure drops associated with saddle reef formation (Kookaburra) and chemical reactions with graphitic rocks (Sandpiper). The Coyote deposit, the largest in the western Tanami region, consists of a number of ore lenses localized along the limbs of the Coyote Anticline, which formed during the Tanami Orogeny. The largest lenses are associated with the Gonzalez Fault, which is located along the steeply dipping southern limb of this fold. Gold was introduced at ca. 1,790 Ma into dilatant zones that formed in local perturbations along this fault during later reactivation (regional D₅) towards the end of a period of granite emplacement. Gold is associated with quartz–chlorite–pyrite–(arsenopyrite–galena–sphalerite) veins with narrow (<?5 mm) chloritic selvages. A quartz–muscovite–biotite–K–feldspar–(tourmaline–actinolite–arsenopyrite) assemblage, which is interpreted to relate to granite emplacement, overprints the regional greenschist facies metamorphic assemblage. The mineralogical similarity between this overprinting assemblage and the vein assemblage suggests that the auriferous veins at the Coyote deposit are associated with the granite-related metamorphic–metasomatic assemblage. Gold deposition is thought to have been caused by pressure drops within dilatant zones.     

Hydrogeochemical baseline studies prior to gold mining: A case study in Sardinia (Italy)

An epithermal gold deposit is planned to be exploited in the Osilo area (North Sardinia). A detailed hydrogeochemical study was carried out to evaluate the water quality prior to mining, and to assess the potential impact of mining on the aquatic system. Forty-eight surface and ground waters were sampled at different seasonal conditions. A large set of chemical components was determined, taking into account the composition of ore and host rocks, as well as those components, such as cyanide, planned to be used in the mineral processing. Waters show different salinity and element concentrations depending on the composition of rocks drained, the time of circulation, the interaction with mineralised bodies, and climatic conditions. Most waters show relatively low concentrations of toxic or potentially harmful elements.Waters interacting with the ore deposit are generally non acidic, likely due to the low sulphidation system, the limited extension of the ore veins, the presence of calcite in the hydrothermal alteration assemblage, and the weathering of silicate rocks, which appears to contribute in buffering the acidity produced by the oxidation of sulphide minerals, especially pyrite. The nonacid environment does not favour the mobility of elements associated with the mineralisation, such as Cd, Co, Ni, Pb, Zn, and As. In addition, aqueous transport of these elements seems limited by the precipitation of ferrihydrite, which is able to reduce or remove these elements, particularly As, from solution. However, considering that exploitation will expose large quantities of mineralised materials to weathering, an adequate disposal of waste dumps and tailings needs to be carefully planned to prevent the potential dispersion of contaminants.     

Rare-earth element mobility during ore-forming hydrothermal alteration: A case study of Dongping gold deposit Hebei Province,China

REE mobility during hydrothermal ore-forming processes has been extensively investigated in recent years and the potential of REE to provide information about ore forming processes has commonly been recognized.The Dongping gold deposit,which is located in northwestern Hebei Province,China,occurring in the inner contact zone of the Shuiquangou syenite complex,is spatially,and probably genetically,related to the syenite,the deposit was formed under the moderate to high temperature(220℃ to 320℃),weakly acidic to weakly alkaline,rather high fo2(lgfo2=-30～-34)environment.The REE study of the host rocks,altered wall rocks,ores and gangue minerals from the deposit suggests that the REEs have been mobilized and differentiated during K-feldspathization and silicification.The extremely altered syenite enveloping auriferous quartz vein shows positive Ce anomaly and larger LREE/HREE ratio than that of the unaltered syenite.The REE concentrations and patterns of the ores are determined by the ore types and mineral assemblages,LREE/HREE ratios in the gangue quartz and hydrothermal Kfeldspars are relatively low.The most significant observation is that the gangue quartz shows significant positive Eu anomaly,whereas the hydrothermal K-feldspars show less significant or no positive Eu anomaly at all relative to the primary feldspar in the unaltered syenite. It is evident that the REEs are mobile during K-feldspathization and silicification in the ore forming process.Weak to moderate K-feldspathization caused REE mobility without apparent differentiation with the exception of extreme K-feldspathization and silicification which resulted in significant depletion of HREE and Eu and relative enrichment of Ce.The REE,Y,U,Th and Au contents of the syenite decrease as the degrees of K-feldspathization and silicification of the rocks increase towards the auriferous quartz veins.As the ores were deposited under a rather oxidized environment,Ce^4 predominated over Ce^3 .The precipitation of the former in the form of CeO2 or absorpted onto the secondary mineral assemblage resulted in the inconsistent removal of the REE and the relative Ce enrichment in the strongly altered rocks.in contrast,Eu was present mainly in a low valence state (Eu^2 ).The geochemical differences from the other REE^3 and much less sites in the secondary minerals to accommodate the Eu released form the original minerals resulted in the enrichment of Eu in the fluids.The mobility and differentiation of REE and the coherent mobilities of Y,U,Th and Au also support the argument that the syenite is one of the source rocks for gold mineralization.The REE contents and patterns of the altered rocks enveloping the auriferous quartz vein could be used as a guide for locating ore veins in mineral exploration.     

Mineralogy and microchemistry of the Egat gold deposit, South Eastern Desert of Egypt

Gold-bearing quartz lodes from the Egat gold mine, South Eastern Desert of Egypt, are associated with pervasively silicified, highly sheared ophiolitic metagabbro and island-arc metavolcanic rocks. The mineralized quartz veins and related alteration haloes are controlled by NNW-trending shear/fault zones. Microscopic and electron probe microanalyses (EPMA) data of the ore and gangue minerals reveal that fine-grained auriferous sulfarsenides represent early high-temperature (355–382 °C) phases, with formation conditions as (fS₂?=??10, and fO₂ around ?31). A late, low-temperature (302–333 °C) assemblage includes coarse pyrite, arsenopyrite, and free-milling gold grains (88–91 wt.% Au), with formation conditions as (fS₂?=??8 and fO₂ around ?30). Gold was impounded within early sulfarsenides, while free-milling gold blebs occur along microfractures in quartz veins and as inclusions in late sulfides. Infiltration of hydrothermal fluids under brittle–ductile shear conditions led to mobilization of refractory Au from early sulfarsenide phases and reprecipitated free gold, simultaneous with silicification of the host rocks. The positive correlation between Au and As favors and verifies the use of As as the best pathfinder for gold targets, along the NNW-trending shear zones.     

青田-仙居地区金银矿化特征及找矿远景分析

浙江青田-仙居地区位于华南褶皱系浙东南褶皱带之温州-临海拗陷内.金银矿化的直接围岩是上侏罗统西山头组晶屑、玻屑熔结凝灰岩.主控矿构造为火山机构及有关的断裂构造.多期次的火山活动、岩浆侵入活动为金银成矿提供热源、热液及成矿物质来源.该区与龙泉遂昌金银成矿带同处于地幔陡变带内,深部构造特征相同或相似.区内构造活动、火山喷发及岩浆侵入频繁而强烈,伴随的多期次热液活动明显.基底岩系为含金变质岩系(陈蔡群、龙泉群),盖层岩系是由基底含金变质岩系重熔或部分同熔形成的中生代火山喷发-沉积岩系.在基底岩系演化过程中,金银等成矿物质发生了活化、迁移、富集或再分配作用,部分在构造有利部位富集成矿,部分则以自然态、游离吸附态赋存在凝灰质岩石中,经多期次热液作用再次被活化、迁移,最终在成矿有利部位沉淀富集成矿.因此,青田-仙居地区具备较好的金银成矿条件,是金银矿找矿的良好远景区.     

Hydrogeochemical prospecting of gold in an alpine bald mountain zone

The investigation was conducted within highly and moderately separated highlands and high plateaus where glaciers, stone streams, solifluction, and glacial and fluvio-glacial deposits are widely developed. A capping of Miocene basalts remains in the divides over the Au ore deposits and their oxidation zones. Young water-filled fractures traverse the ore-bearing structures and control the direction of the glacial and river valleys, as well as the location of the lakes, springs, and icings.Gold occurs in small- to average-sized sulphide-Au-quartz veins and in a sulphidized black shale series of Precambrian and Paleozoic age. Both mechanical and hydromorphic dispersion of Au are exhibited clearly in the highlands. The latter is due to the processes of modern oxidation of the Au-bearing sulphide minerals. The anomalies of Au in streams and small lakes are related to supra- and sub-ice waters. In the water of streams Au is present in three forms; colloidal, dissolved, and sorbed. Gold in colloidal form comprises the most ample and contrasty anomalies. The truly dissolved Au is more local and manifests itself close to the source of the stream. Gold sorbed on suspended matter is evident because of a significant removal from the source into the solution. Migration of Au and formation of long (up to 2.5 km) and contrasty dispersions in waters of low dissolved solids is favoured by the presence of organic matter and argillaceous and ferruginous suspensions as well as other sorbents. The anomalies of Au in water either coincide with anomalies in stream sediments over mineralized zones or indicate new mineralized areas not reflected in stream sediments.     

金窝子金矿金的赋存状态和金矿物特征

金窝子金矿属于岩浆热液型金矿床,金矿化类型有石英脉型和蚀变糜棱岩型.金多呈独立金矿物形式出现,少许呈分散状,以银金矿为主,次为自然金,平均成色782.金矿物以粒间金、裂隙金、连生金和包体金等形式嵌布于黄铁矿、石英、方铅矿及闪锌矿等主要载金矿物中,且黄铁矿、石英较金属硫化物中占优势,黄铜矿中未见金矿物.金矿物形态各样,粒度以中细粒为主.金矿物特征反映出本区金矿床的成矿物质主要来源于变质岩,成矿作用与华力西、燕山期中酸性侵入岩有关.这与地质地球化学研究所获得的矿床成因认识相一致.     

The Crater Mountain Deposit,Papua New Guinea: Porphyry‐related Au–Te System

Ore mineralization and wall rock alteration of Crater Mountain gold deposit, Papua New Guinea, were investigated using ore and host rock samples from drill holes for ore and alteration mineralogical study. The host rocks of the deposit are quartz‐feldspar porphyry, feldspar‐hornblende porphyry, andesitic volcanics and pyroclastics, and basaltic‐andesitic tuff. The main ore minerals are pyrite, sphalerite, galena, chalcopyrite and moderate amounts of tetrahedrite, tennantite, pyrrhotite, bornite and enargite. Small amounts of enargite, tetradymite, altaite, heyrovskyite, bismuthinite, bornite, idaite, cubanite, native gold, CuPbS₂, an unidentified Bi‐Te‐S mineral and argentopyrite occur as inclusions mainly in pyrite veins and grains. Native gold occurs significantly in the As‐rich pyrite veins in volcanic units, and coexists with Bi‐Te‐S mineral species and rarely with chalcopyrite and cubanite relics. Four mineralization stages were recognized based on the observations of ore textures. Stage I is characterized by quartz‐sericite‐calcite alteration with trace pyrite and chalcopyrite in the monomict diatreme breccias; Stage II is defined by the crystallization of pyrite and by weak quartz‐chlorite‐sericite‐calcite alteration; Stage III is a major ore formation episode where sulfides deposited as disseminated grains and veins that host native gold, and is divided into three sub‐stages; Stage IV is characterized by predominant carbonitization. Gold mineralization occurred in the sub‐stages 2 and 3 in Stage III. The fS₂ is considered to have decreased from ～10^?2 to 10^?14 atm with decreasing temperature of fluid.