Conflicting evidence on the timing of mesothermal and paleoplacer gold mineralisation in early Proterozoic rocks from Southwest Ghana,West Africa

Rocks of early Proterozoic age (ca. 2100 Ma) host the major gold deposits in Ghana. The deposits are either located in mesothermal quartz vein systems or hosted in a quartz pebble conglomerate that represents a paleoplacer. Both types of mineralisation are largely confined to the Ashanti Belt, one of four parallel northeast-trending volcanic belts. While the stratigraphy and structure of the belts are similar, the Ashanti belt is characterised by a more tectonised northwest margin where most of the epigenetic gold deposits are located. In these deposits, gold mineralisation is located in faults that parallel the regional trend of the belts and were active late in the deformation history of the terrane. The auriferous quartz pebble conglomerate is part of a clastic sequence that is largely derived from the adjacent volcanic and plutonic rocks with the gold widely regarded as having originated from eroded vein deposits. Structural data, however, show that both the volcanic rocks and clastic sequence were deformed jointly prior to epigenetic gold mineralisation. Thus, the quartz vein deposits could not have been the source of the paleoplacer mineralisation. The paleoplacer gold could have originated from one of several possible sources but none has been unequivocally identified.     

Intrusion-related gold deposits associated with tungsten-tin provinces

An under-recognized and economically important class of intrusion-related gold deposits, which occur within magmatic provinces best known for tungsten and/or tin mineralization, is described with reference to seven major deposits (Fort Knox, Mokrsko, Salave, Vasilkovskoe, Timbarra, Kidston and Kori Kollo). These gold deposits contain a metal suite that includes some combination of bismuth, tungsten, arsenic, tin, molybdenum, tellurium and antimony, and contrasts with that found in the more widely-developed gold-rich porphyry copper and related deposits. The gold deposits associated with tungsten and/or tin provinces are located in cratonic margins, in a landward or back-arc position relative to continental margin arcs (where recognized), or within continental collisional settings. The deposits are related genetically to felsic domes, stocks or plutons of intermediate oxidation state, both magnetite- and ilmenite-series magmas are represented. The intrusion-hosted gold deposits are most commonly of sheeted vein/veinlet type, although greisen-like, disseminated and breccia deposits are also described. Gold may also be concentrated more distally (1–3 km) with respect to the intrusions, where deposits may be of skarn, disseminated replacement or vein types. K-feldspar, albite and/or sericitic alteration assemblages, commonly including carbonate, accompany the gold mineralization. In sheeted vein deposits, alteration is normally restricted to narrow envelopes around veins, whereas more pervasive alteration occurs in greisen-like, disseminated and shallow (<3 km) deposits. The gold mineralization is commonly present with low total sulphide contents (<3%), mainly pyrite and lesser arsenopyrite. In several deposits, bismuth minerals are closely associated with gold, and bismuth-gold and tellurium-gold correlations exist. Most deposits contain tungsten, tin, molybdenum and antimony, although generally these do not correlate with gold; tungsten and molybdenum concentrations may increase with depth or may occur in separate zones. Base metals generally are present in minor amounts (e.g. <100 ppm Cu). The distinct spatial association with felsic intrusions, combined with the consistent metal signature, suggests a magmatic-hydrothermal origin. Fluid inclusions studies indicate the presence of high-salinity fluids in some deposits, and low-salinity and carbonic fluids in most deposits, similar to the composition of fluids in intrusion-related tungsten deposits. Variations in mineralization style largely reflect depth of formation and location relative to the intrusive centre. Several deposits in this class contain >100 tonnes (3 million oz) of gold, thereby highlighting the gold potential of intrusion-related deposits beyond the more traditionally explored gold and copper provinces in arc terranes. Received: 13 March 1998 / Accepted 14 January 1999     

西秦岭夏河—合作地区与还原性侵入岩有关的金成矿系统及其动力学背景和勘查意义

西秦岭造山带是我国最重要的金成矿带之一。以往研究大多认为造山型金矿床和(类)卡林型金矿床是西秦岭主要的金矿床类型,并且两类金矿床的金成矿作用主要与造山过程中的区域变质作用有关,而与岩浆活动不存在直接的成因联系。位于西秦岭造山带西段的夏河—合作地区大面积出露花岗岩类侵入体,其周缘发育有富金的夕卡岩型铜(钨)矿床。近年来该地区新发现的多个大型—超大型石英脉型金矿床和微细粒浸染型金矿床都与中酸性侵入岩的空间关系紧密,暗示这些金矿床可能和岩浆活动有成因联系。论文在作者研究结果以及总结前人成果基础上,综述了夏河—合作地区典型金(铜)矿床的地质矿化特征、地球化学特征、时空分布特征,以及中酸性侵入岩的岩性特征、形成时代和演化过程。年代学研究结果显示,夏河—合作地区的早子沟微细粒浸染型金矿床、德乌鲁夕卡岩型金(铜)矿床和老豆石英脉型金矿床均形成于250~240 Ma,与邻近的早中三叠世花岗闪长质石英闪长质侵入岩近于同时形成。拉布在卡等石英脉型金矿床略晚于区内中三叠世末期侵位的闪长玢岩脉(约230~225 Ma)形成。H、O、S、C、B、Pb等多种同位素地球化学特征指示该地区早中三叠世金矿床的成矿热液均为岩浆来源,并且显示低氧逸度的特征。早中三叠世中酸性侵入岩的还原性钛铁矿系列花岗岩类特征,以及同时代的多种金矿化类型和成矿分带性,表明夏河—合作地区在早中三叠世(约250~230 Ma)多期次侵位的钛铁矿系列I型中酸性岩浆是金成矿作用的成矿流体和成矿物质的主要来源,其中与250~240 Ma多期金成矿事件有关的准铝质弱过铝质、高钾钙碱性系列花岗岩类侵入岩均经历了幔源基性熔体和壳源酸性熔体的岩浆混合作用,而与约230 Ma的金成矿作用有关的闪长质岩浆岩则可能指示了更多幔源基性熔体的加入。与金(铜)成矿有关的早中三叠世还原性中酸性岩是在古特提斯洋俯冲过程中局部弧后伸展条件下交代富集地幔楔部分熔融形成的基性岩浆与壳源酸性岩浆混合作用的产物。夏河—合作地区形成于早中三叠世的夕卡岩型、电气石石英脉型、石英方解石脉型和微细粒浸染型金矿床共同构成了一个与还原性侵入岩有关的金成矿系统。夏河—合作地区与还原性侵入岩有关的金成矿系统的发现,丰富了西秦岭造山带区域成矿作用的类型,并为西秦岭西段其他早中三叠世岩浆岩分布区(如青海同仁地区)的金矿勘查工作提供了新的思想和方向。     

蒙古国巴彦洪戈尔地区金矿床地质特征及成因

巴彦洪戈尔地区位于蒙古中央地块南侧, 构造活动复杂, 发育有多期构造岩浆活动。区内发育有与花岗岩类有关金、铜等矿床。金矿床类型有石英脉型和斑岩型、矽卡岩型, 主要金和铜矿化与二叠纪磁铁矿系列花岗岩类密切相关, 与钛铁矿系列花岗岩类有关的矿化较少。成矿年代学研究显示, 金矿床的形成应早于三叠纪, 主要发生于石炭纪和二叠纪, 形成于微大陆碰撞期构造转换过程中的岩浆活动期间, 区内金矿床(点)构成蒙古国最具潜力的金成矿带。     

An overview of the relationship between granitoid intrusions and gold mineralisation in the Archaean Murchison Province,Western Australia

In the Archaean Murchison Province of Western Australia, granitoid batholiths and plutons that intruded into the ca. 2.7–2.8 Ga and ca. 3.0 Ga greenstone belts can be divided into three major suites. Suite I is a ca. 2.69 Ga monzogranite-granodiorite suite, which was derived from anatexis of old continental crust and occurs as syn-tectonic composite batholiths over the entire province. Suite II is a trondhjemite-tonalite suite (termed I-type) derived from partial melting of subducted basaltic crust, which intruded as syn- to late-tectonic plutons into the greenstone belts in the northeastern part of the province where most of the major gold deposits are situated. One of the Suite II trondhjemite plutons has a Pb−Pb isochron age of 2641±36 Ma, and one of the structurally youngest tonalite plutons has a minimum Pb−Pb isochron age of 2630.1±4.3 Ma. Suite III is a ca. 2.65–2.62 Ga A-type monzogranite-syenogranite suite which is most abundant in the largely unmineralised southwestern part of the province. Gold deposits in the province are mostly hosted in brittle-ductile shear zones, and were formed at a late stage in the history of metamorphism, deformation and granitoid emplacement. At one locality, mineralisation has been dated at 2636.8±4.2 Ma through a pyritetitanite Pb−Pb isochron. Lead and Sr isotope studies of granitoids and gold deposits indicate that, although most gold deposits have initial Pb isotope compositions most closely similar to those of Suite II intrusions, both Suite I and Suite II intrusions or their source regions could have contributed solutes to the ore fluids. These preliminary data suggest that gold mineralisation in the Murchison Province was temporally and spatially associated with Suite II I-type granitoids in the northeastern part of the province. This association is consistent with the concept that Archaean gold mineralisation was related to convergent-style tectonic settings, as generation of both Suite II I-type granitoids and hydrothermal ore fluids could have been linked to the dehydration and partial fusion of subducted oceanic crust, and old sialic crust or its anatectic products may also contribute solutes to the ore fluids. Integration of data from this study with other geological and radiogenic isotope constraints in the Yilgarn Block argue against direct derivation of gold ore fluids from specific I-type granitoid plutons, but favour a broad association with convergent tectonics and granitoid magmatism in the late Archaean.     

Magnetite/Ilmenite–series Classification and Magnetic Susceptibility of the Mesozoic-Cenozoic Batholiths in Peru

Abstract: Plutonic rocks of the Coastal Batholith of Peru were evaluated in terms of the granitoid-series classification using the bulk ferric/ferrous ratio from the literature and new measurements of magnetic susceptibility. The batholith is largely composed of magnetite-series plutonic rocks; the magnetite series make up 85% by number of chemical analyses (n=130) and 80% by measurement of magnetic susceptibility (n=210). The ilmenite-series rocks are mostly found in the felsic facies of the batholith. Asymmetrical distribution of magnetic susceptibility is not clear as in the Japanese Islands and Peninsular Range Batholith, but the magnetic susceptibility may decreases continentward (i. e., Peninsular Range type).
The Cordillera Blanca Batholith and stocks are also composed of mainly magnetite series plutonic rocks, but ilmenite-series rocks may be more predominant than in the Coastal Batholith, which is also indicated by the presence of Sn and W mineralizations.     

Granitoid Series and Mineralization in the Circum-Pacific Phanerozoic Granitic Belts

Abstract: Throughout the Phanerozoic Era, magnetite-series and ilmenite-series granitoids are heterogeneously distributed on both sides of the Pacific Ocean. Ilmenite-series granitoids are dominant in the western Pacific rim, while magnetite-series granitoids prediminate in the eastern Pacific orogenic belt. Regional distribution patterns of the two series of paired belt are also recognized differently, implying different tectonic and geochemical settings on both sides of the Pacific Ocean. The differences reflect on the predominance of Sn-W deposits in the western Pacific but sulfide-forming mineral commodities in the eastern Pacific rims. To determine redox state of granitoids is the first step in mineral exploration of granitoid affinity.     

Resource Evaluation and Some Genetic Aspects of Indium in the Japanese Ore Deposits

Abstract. There have been two primary sources for industrial indium; one from massive sulfides, while the other is dissemination-veins and skarns, related to felsic igneous rocks. The latter group of the In-bearing deposits is abundant in the Japanese Islands. Indium occurs as In-minerals such as sakuraiite, roquesite, laforetite and many unidentified minerals, but the majority is contained as an impurity in sphalerite, and tin and copper sulfides. Average grades of the ores from which indium has been extracted vary from a few ppm (e.g., Kosaka mine) to more than 300 ppm (Toyoha mine). The amount of indium in all the major basemetal deposits is estimated by analyzing representative samples. The main indium deposits are subvolcanic and tin-poly-metallic vein types. The largest one is Toyoha mine (4,700 tons hi) and the Ashio mine (ca. 1,200 tons In) was found to be the second largest. Many small occurrences, were recognized in the Miocene magnetite-series belt, besides the classic occurrences in the ilmenite-series granitic terrains of SW Japan, including the Ikuno and Akenobe tin(-tungsten) polymetallic veins, located in the northern margin of the late Cretaceous Sanyo ilmenite-series province. Magnetite-series magmas with deep source are necessary to concentrate sulfur in the magma chamber but sedimentary source rocks and their reducing agents are needed to collect and to precipitate indium. The Japanese islands are essentially accretionary terrains intruded by various deep oxidized magmas; thus forming magnetite/ilmenite-series paired belts, which are sometimes mixed. This unique geologic setting may be the most fundamental reason why indium is rich in vein-type deposits of the Japanese Island arcs.     

新疆西南天山金矿床主要类型、特征及成矿作用

文章在总结前人研究成果的基础上,综合论述了西南天山金矿的成矿地质背景、金矿床的时空分布和基本特征。根据矿床地质特征和控矿因素,将西南天山的金矿划分为与剪切带有关的金矿床、与侵入岩有关的金矿床(包括斑岩型)、石英-重晶石脉型金矿床、与火山岩有关的金矿床和矽卡岩型金矿床5类,其中与剪切带有关的金矿床是最重要的矿床类型。探讨了西南天山金矿的成矿时代、成矿物质和成矿流体来源,以及成矿地球动力学机制。提出与剪切带有关的金矿床成矿物质主要来源于岩浆和海相碳酸盐岩,成矿流体主要来源于岩浆水或主要来自大气降水,混合少量岩浆水。石英-重晶石脉型金矿床成矿物质来自容矿地层,成矿流体主要来源于沉积建造水。与剪切带有关的金矿、与侵入岩有关的金矿、石英重晶石脉型金矿和矽卡岩型金矿成矿时代主要集中在二叠纪—三叠纪,形成于后碰撞构造演化阶段。斑岩型和浅成低温热液型金矿床形成于岛弧挤压环境。     

Nature of gold mineralisation in the Walhalla Goldfield,southeast Australia

The Walhalla-Woods Point Goldfield in southeast Australia is characterised by large gold deposits associated with a Late Devonian dyke swarm. The setting of this goldfield is unique because unlike the major gold deposits in Victoria, it occurs close to the eastern margin of the Western Lachlan Orogen, and highlights the disparities between the evolving phases of orogenic gold mineralisation in the Western Lachlan Orogen, and the contrasts between sediment hosted, dyke-associated and dyke-hosted gold mineralisation. This study integrates existing and new data from renewed mapping of the geology and geochemistry of three gold deposits near the township of Walhalla, in the historically important yet under-explored and under-researched Walhalla-Woods Point Goldfield. The ten highest yielding deposits within the goldfield are either hosted within, or adjacent to, intrusions of the Woods Point Dyke Swarm. This is due to the greater chemical reactivity of the calc-alkaline dykes, and the greater rheological contrast between the dykes and surrounding low-grade metasedimentary units, which allowed for the formation of dyke-hosted quartz breccia veins that are consistently favourable sites for gold mineralisation in the Walhalla Goldfield. This is in contrast to historical production, which concentrated on visible gold within the shear zone-hosted laminated quartz veins. Gold and As assay results have highlighted the increased levels of invisible gold disseminated along dyke margins in proximity to shear zones and quartz reefs. The high-yielding gold deposits hosted wholly by the dyke intrusions of the Woods Point Dyke Swarm are orogenic gold deposits, as they are not associated with elevated levels of Bi, W, As, Mb, Te and Sb, typical of intrusion-related gold deposits.     

中国金矿资源特征及勘查方向概述

基于金矿成矿地球动力学环境以及矿床基本地质特征等,将中国金矿床类型归纳为11 类,其中以构造破碎带蚀变岩型、中深成侵入岩体内及其外接触带型、卡林-似卡林型、浅变质碎屑岩中热液型、陆相火山岩型等为主要找矿类型;成矿年代以中生代、新生代为主。在中国Ⅲ级成矿区带划分基础上,总结研究大地构造单元、地质演化、成矿地质条件、空间分布特征、金矿类型、区域成矿要素、资源量等,初步厘定42 个金矿集区,其空间呈集中分布特征。根据金矿勘查单位面积的钻探数量,初步将中国金矿集区划分为高、中、低工作程度区,高程度区主要分布在中东部地区;除砂金矿外,中国88.12%的岩金（伴生金） 矿探矿深度在500 m 以上,说明探矿钻探验证偏少、偏浅。文章还探讨了中国金矿集区资源找矿潜力,提出了勘查找矿方向和建议,指出中东部老矿山深部、外围和西部金矿集区特别是位于新疆、青海、西藏等地区的,是未来找矿潜力重点区域,未查明资源储量巨大。     

Geology and K-Ar Ages of the South, Huh Bulgiin Hundii, Saran Uul, Taats Gol and Han Uul deposits in the Bayankhongor Region, Mongolia

Abstract: The Bayankhongor region in central Mongolia consists of a Paleozoic subduction system including Precambrian microcontinents (Baidrag and Burd Gol zones), obducted ophiolites and accretionary sedimentary rocks (Bayankhongor and Dzag zones), and forearc sedimentary rocks (Khangay zone). Arc magmatism in the Bayankhongor region is characterized by dominance of Early Paleozoic ilmenite-series and Late Paleozoic magnetite-series granitoids. These granitoids accompany many hydrothermal deposits of such various types as porphyry, skarn and vein. K-Ar dating on four deposits in the region revealed that the South porphyry Cu-Au, Huh Bulgiin Hundii skarn Cu-Au, Han Uul shear zone-hosted Au and Taats Gol pegmatite W-Au deposits formed at 240±5 Ma, 252±5 Ma, 283±6 Ma and 329±7 Ma, respectively.
Thus the former three are related to the Permian to earliest Triassic magnetite-series granitoids, whereas the W-Au pegmatite at Taats Gol to the Early Carboniferous ilmenite-series granitoids. Porphyry and skarn Cu-Au mineralization occurred at latest Permian to earliest Triassic, when the Andean-type arc magmatism was immediately followed by the collision between the Baidrag and Tarbagatai microcontinents.     

Implications of pyrite geochemistry for gold mineralisation and remobilisation in the Jiaodong gold district,northeast China

The Jiaodong gold district of eastern China, the largest gold producing district in China, is located on the eastern margin of the North China Craton. It consists of three mineralisation belts: the western Zhao-Ye belt, the middle Qixia belt, and the eastern Muping–Rushan (Muru) belt. Over 85% of mineralisation is hosted in the Zhao-Ye belt, which is bordered by the mantle-tapping Tan Lu fault zone. Pyrite crystals from three deposits in the Zhao-Ye belt and three deposits in the Muru belt were studied using a combination of optical petrography, bulk pyrite geochemistry, and in-situ laser ablation ICP-MS. Results show that although mineralisation is broadly similar between the two belts, there are significant differences in ore and gangue mineral textures, pyrite geochemistry, and style of gold mineralisation.Texturally, pyrite grains from the Zhao-Ye belt are generally cubic and do not exhibit zoning. In contrast, Muru pyrite grains are more often pyritohedral, commonly exhibit well-defined concentric zoning, and display textures in ore and gangue minerals indicative of open space growth. Bulk pyrite geochemistry suggests a distinct enrichment in Pb, Bi, Au, Ag and Te in the Zhao-Ye belt, whereas the Muru belt pyrite is significantly enriched in As, Cu and Co. In situ pyrite geochemistry indicates that Au and As are variably correlated in the Zhao-Ye belt, typically only exhibiting correlation at low Au concentrations. Most gold occurs as visible electrum along pyrite fractures and grain boundaries, with a minor generation of invisible gold formed through As-facilitated uptake into pyrite. In the Muru belt, Au and As have a strong correlation and there is limited occurrence of gold particles, indicating that most gold in the Muru belt is invisible gold contained in the crystal structure of As-rich pyrite.The differences in style of gold mineralisation between the belts indicates an inherent difference in timing of gold introduction: in the Zhao-Ye belt, the visible electrum accounting for most of the gold endowment is formed post-pyrite, whereas the invisible gold in the Zhao-Ye and Muru belts is formed syn-pyrite. The heterogeneity in gold distribution in the Jiaodong district is attributed to melting of metallogenically fertile Archean crust at the base of the well-endowed Zhao-Ye belt, and the lack of a similarly fertile source region beneath the Muru belt.     

大兴安岭南段锡多金属成矿系列

大兴安岭南段是我国北方最重要的锡-多金属成矿集中区.根据成矿花岗岩和成矿元素组合的不同,可分为3个成矿系列:锡(钨)成矿系列(Sn-W-Nb-Ta-Be)、锡-多金属系列(Sn-Ag-Cu-Pb-Zn)和含锡的多金属系列(Pb-Zn-Cu-Ag),3个系列的成矿时代相同(130～150Ma),均与大兴安岭南段燕山期花岗质岩浆作用有关.与锡(钨)成矿系列有关的花岗岩,主要是钾长花岗岩-花岗斑岩,具有钛铁矿系列花岗岩的特征;与含锡的多金属系列有关的花岗岩,主要是花岗闪长岩-石英二长岩类,具有I型或磁铁矿系列花岗岩的特征;而当钾长花岗岩类与花岗闪长岩-二长斑岩等构成花岗质杂岩体或定位在相近空间时,常形成锡-多金属共生组合.研究表明,锡-多金属系列是与含锡的钛铁矿系列和含多金属的磁铁矿系列两种不同花岗岩类有关的含矿热液同位叠加成矿的结果.高成熟度、富锡的锡林浩特元古宙变质岩的重融-分异演化,可能是形成大兴安岭南段锡富集的主要原因.     

澳大利亚造山型金矿和侵入岩有关金矿系统流体包裹体资料和矿化过程的比较

We have examined the fluid inclusion data and fluid chemistry of Australian orogenic and intrusion-related gold deposits to determine if similar mineralization processes apply to both styles of deposits.The fluid inclusion data from the Yilgarn craton,the western subprovince of the Lachlan orogen,the Tanami,Tennant Creek and Pine Creek regions,and the Telfer gold mine show that mineralization involved fluids with broadly similar major chemical components(i.e.H_2O NaCl CO_2±CH_4±N_2).These deposits formed over a wide range of temperature-pressure conditions(<200 to>500℃,<100～400MPa).Low salinity, CO_2-bearing inclusions and low salinity aqueous inclusions occur in both systems but the main difference between these two types of deposits is that most intrusion-related gold deposits also contain at least one population of high-salinity aqueous brine.Oxygen and hydrogen isotope data for both styles of deposit usually cannot distinguish between a magmatic or metamorphic source for the ore-bearing fluids.However,sulfur and lead isotope data for the intrusion-related gold deposits generally indicate either a magmatic source or mixing between magmatic and sedimentary sources of fluid.The metamorphic geothermal gradients associated with intrusion-related gold deposits are characterized by low pressure,high temperature metamorphism and high crustal geothermal gradients of>30/km.Where amphibole breakdown occurs in a granite source region,the spatially related deposits are more commonly associated with Cu-Au deposits rather than Au-only deposits that are associated with lower temperature granites.The dominant processes thought to cause gold precipitation in both types of deposits are fluid-rock interaction(e.g.desulfidation)or phase separation.Consideration of the physical and chemical properties of the H_2O-NaCl-CO_2 system on the nature of gold precipitation mechanisms at different crustal levels infers different roles of chemical(fluid-rock interaction)versus rheological(phase separation and/or fluid mixing)host-rock controls on gold deposition.This also implies that at the site of deposition,similar precipitation mechanisms operate at similar crustal levels for both orogenic and intrusion-related gold deposits.     

Cenozoic metallogeny of Greece and potential for precious,critical and rare metals exploration

The Cenozoic metallogeny in Greece includes numerous major and minor hydrothermal mineral deposits, associated with the closure of the Western Tethyan Ocean and the collision with the Eurasian continental plate in the Aegean Sea, which started in the Cretaceous and is still ongoing. Mineral deposits formed in four main periods: Oligocene (33–25 Ma), early Miocene (22–19 Ma), middle to late Miocene (14–7 Ma), and Pliocene-Pleistocene (3–1.5 Ma). These metallogenic periods occurred in response to slab-rollback and migration of post-collisional calc-alkaline to shoshonitic magmatism in a back-arc extensional regime from the Rhodopes through the Cyclades, and to arc-related magmatism along the active south Aegean volcanic arc. Invasion of asthenospheric melts into the lower crust occurred due to slab retreat, and were responsible for partial melting of metasomatized lithosphere and lower crustal cumulates. These geodynamic events took place during the collapse of the Hellenic orogen along large detachment faults, which exhumed extensive metamorphic core complexes in mainly two regions, the Rhodopes and the Cyclades. The detachment faults and supra-detachment basins controlled magma emplacement, fluid circulation, and mineralization.The most significant mineralization styles comprise porphyry, epithermal, carbonate-replacement, reduced intrusion-related gold, intrusion-related Mo-W and polymetallic veins. Porphyry and epithermal deposits are commonly associated with extensive hydrothermal alteration halos, whereas in other cases alteration is of restricted development and mainly structurally controlled. Porphyry deposits include Cu-Au-, Cu-Mo-Au-Re, Mo-Re, and Mo-W variants. Epithermal deposits include mostly high- and intermediate-sulfidation (HS and IS) types hosted in volcanic rocks, although sedimentary and metamorphic rock hosted mineralized veins, breccias, and disseminations are also present. The main metal associations are Cu-Au-Ag-Te and Pb-Zn-Au-Ag-Te in HS and IS epithermal deposits, respectively. Major carbonate-replacement deposits in the Kassandra and Lavrion mining districts are rich in Au and Ag, and together with reduced intrusion-related gold systems played a critical role in ancient economies. Finally hundreds of polymetallic veins hosted by metamorphic rocks in the Rhodopes and Cyclades significantly add to the metal endowment of Greece.     

Some metallogenic features of gold and copper deposits related to alkaline rocks and consequences for exploration

Porphyry copper-gold, skarn copper-gold, sediment-hosted (Carlin-style) gold, breccia pipe, low-sulphidation epithermal gold, pluton-related (mesothermal or orogenic) gold vein and volcanogenic massive sulphide deposits associated with alkaline rocks are commonly broadly similar to those hosted by their calc-alkaline counterparts. In contrast, porphyry molybdenum-gold deposits are confined to alkaline igneous centres. Alkaline suites are notably deficient in high-sulphidation epithermal gold deposits and even in the advanced argillic lithocaps which host them. This is surprising, given that the required oxidised sulphur species are seemingly more abundant than in calc-alkaline igneous centres. Highly efficient buffering of acidic fluid by metasomatised alkaline rocks may offer a viable explanation. All types of intrusion-related zinc deposits also appear to be poorly developed in alkaline provinces. The characteristics of several gold and copper deposits associated with alkaline rocks, including the giant Porgera, Cripple Creek, Ladolam, Olympic Dam and Phalaborwa examples, are judged to diverge appreciably from their most closely related deposit types, rendering them arguably unique. Most of these aberrant mineralisation styles may be due to variations in magmatic-fluid compositional and liberation characteristics consequent upon the extreme diversity of ore-related alkaline magmas. Most types of gold and copper deposits developed in calc-alkaline provinces also constitute exploration targets in and around alkaline igneous centres, although porphyry copper-gold and low-sulphidation epithermal gold deposits are considered to possess the greatest potential. Perhaps of even greater interest, however, is the possibility of encountering unconventional giant gold and copper deposits which lack closely analogous examples. If already-defined aberrant deposits are truly unique, then exploration designed specifically to detect additional examples is pointless. Furthermore, exploration for new unique deposits is difficult because their defining geological parameters are unknown. Alkaline rocks within or behind calc-alkaline arcs at convergent plate boundaries probably offer the greatest exploration potential, although anorogenic intracontinental extensional settings should not be ignored.     

新疆东部金矿床类型、成矿特点及找矿方向

据金矿类型划分标准，结合新疆东部金成矿特点，划分出韧性剪切带型金矿、浅成低温热液型金矿、岩浆热液型金矿、斑岩型金（铜）矿、硅化帽型金矿及变质岩型或绿片岩型银金矿6种成因类型，8种工业类型。通过研究，划分出以斑岩型金矿为主的大南湖－三岔口成矿带、以韧性剪切带型金矿为主的康古尔塔格－黄山成矿带、以浅成低温热液型金矿为主的马庄山－南金山成矿带、以绿片蚀变岩型银金、铅锌矿以及硅铁建造型金矿为主的玉西－铅炉子成矿带、以岩浆热液型金矿为主的金窝子－照壁山成矿带和依热达坂－红山成矿带、以韧性剪切带型和硅帽型金矿为主的头苏泉－塔林成矿带7个金矿成矿带，在此基础上确定该区区找矿主要类型和远景区。     

A geochronological framework for orogenic gold mineralisation in central Victoria, Australia

New ⁴⁰Ar/³⁹Ar geochronological data support, and significantly expand upon, preliminary age data that were interpreted to suggest an episodic and diachronous emplacement of gold across the western Lachlan fold belt, Australia. These geochronological data indicate that mineralisation in the central Victorian gold province occurred in response to episodic, eastward progressing deformation, metamorphism and exhumation associated with the formation of the western Lachlan fold belt. Initial gold formation throughout the Stawell and the Bendigo structural zones can be constrained to a broad interval of time between 455 and 435 Ma, with remobilisation of metals into new structures and/or new pulses of mineralisation occurring between 420 and 400 Ma, and again between 380 and 370 Ma, linked to episodic variations in the regional stress-field and during intrusion of felsic dykes and plutons. This separation of ages is incompatible with the view that gold emplacement in the western Lachlan fold belt was the result of a single, orogen-wide event during the Devonian. A distinct phase of gold mineralisation, characterised by elevated Cu, Mo, Sb or W, is associated with both Late Silurian to Early Devonian (~420 to 400 Ma) and Middle to Late Devonian (~380 to 370 Ma) magmatism, when crustal thickening and shortening during the ongoing consolidation of the western Lachlan Fold Belt led to extensive melt development in the lower crust and resulted in widespread magmatism throughout central Victoria. These ~420 to 400 Ma and ~380 to 370 Ma occurrences, best exemplified by the Wonga deposit in the Stawell structural zone and many of the Woods Point deposits in the Melbourne structural zone, but also evidenced by occurrences at Fosterville and Maldon in the Bendigo structural zone, clearly formed synchronous with, or post-date, the emplacement of plutons and dykes, and thus are spatially (if not genetically) related to melt generation at depth. This later, magmatic-associated and polymetallic type of gold mineralisation is economically subordinate to the earlier, metamorphic-associated type of gold deposition in the Stawell and Bendigo structural zones, but tends to be the dominant style in the Melbourne Zone. These new geochronological constraints, together with zircon U-Pb data from felsic intrusive rocks of known relationship to gold mineralisation, demonstrate that initial hydrothermal alteration associated with gold emplacement in the western Lachlan fold belt was metamorphic-related, predating the emplacement of granite plutons by as much as 80 million years. This timing differs from other important orogenic gold districts where gold deposition is closely associated spatially with felsic magmatism. The early introduction of metamorphically derived fluids well before magmatism may reflect variations in the timing of peak metamorphic conditions at different crustal levels in an accretionary prism undergoing simultaneous deformation and erosion. Consequently, no genetic link exists between the main phase(s) of gold mineralisation and magmatism in the central Victorian gold province. With the exception of formation of a minor magmatism-related and geochemically-distinct mineralisation style at about 420 to 400 Ma, and again at about 380 to 370 Ma, the apparent spatial relationship between gold mineralisation and felsic intrusions is merely the result of melts and fluids being channelised along the same structures.     

Granitoid Series in Terms of Magnetic Susceptibility: A Case Study from the Barberton Region,South Africa

Magnetic susceptibilities were measured on a representative collection of Archaean granitoids of the Barberton region using a portable KT5 magnetic susceptibility meter. The studied granitoids comprise, (1) syn-tectonic tonalite-trondhjemite-granodiorite (TTG) granitoids (132 samples), (2) late-tectonic calc-alkaline granitoids (402 samples) and (3) post-tectonic low-Ca and high-Ca granitoids (12 samples). Most of the early-stage syn-tectonic granitoids (∼3450 Ma) have low magnetic susceptibilities, less than 3 × 10⁻³ SI units, and correspond to ilmenite-series granitoids. The late-stage Kaap Valley tonalite pluton (∼3230 Ma) contains sporadically distributed higher magnetic susceptibility values (greater than 3 × 10⁻³ SI units), which are less than one-third in magnetic susceptibility of typical magnetite-series TTG of the Japanese Island Arc and thus strictly belong to an intermediate series. The Barberton TTG suite is essentially derived from reduced amphibolitic lower crust that reflects the anoxic nature of the Earth surface during the Archaean Eon. The more oxidized nature of the Kaap Valley tonalite may be generated in an oxidized lower crust by fluids squeezed out of the subducting plate.Late-tectonic granodiorite - adamellite batholithic complexes (∼3105 Ma) belong mostly to the magnetite series, and seem to suggest that relatively oxidized continental crust, reflecting oxic atmosphere and subduction mechanism operating, had evolved it by this time. Post-tectonic granitic plutons formed largely between circa 2900 Ma and 2700 Ma can be subdivided into low-Ca ilmenite series and high-Ca magnetite series.