Metallogenesis of the Carajás Mineral Province, Southern Amazon Craton, Brazil: Varying styles of Archean through Paleoproterozoic to Neoproterozoic base- and precious-metal mineralisation

The Itacaiúnas Belt of the highly mineralised Carajás Mineral Province comprises ca. 2.75 Ga volcanic rocks overlain by sedimentary sequences of ca. 2.68 Ga age, that represent an intracratonic basin rather than a greenstone belt. Rocks are generally at low strain and low metamorphic grade, but are often highly deformed and at amphibolite facies grade adjacent to the Cinzento Strike Slip System. The Province has been long recognised for its giant enriched iron and manganese deposits, but over the past 20 years has been increasingly acknowledged as one of the most important Cu–Au and Au–PGE provinces globally, with deposits extending along an approximately 150 km long WNW-trending zone about 60 km wide centred on the Carajás Fault. The larger deposits (approx. 200–1000 Mt @ 0.95–1.4% Cu and 0.3–0.85 g/t Au) are classic Fe-oxide Cu–Au deposits that include Salobo, Igarapé Bahia–Alemão, Cristalino and Sossego. They are largely hosted in the lower volcanic sequences and basement gneisses as pipe- or ring-like mineralised, generally breccia bodies that are strongly Fe- and LREE-enriched, commonly with anomalous Co and U, and quartz- and sulfur-deficient. Iron oxides and Fe-rich carbonates and/or silicates are invariably present. Rhenium–Os dating of molybdenite at Salobo and SHRIMP Pb–Pb dating of hydrothermal monazite at Igarapé-Bahia indicate ages of ca. 2.57 Ga for mineralisation, indistinguishable from ages of poorly-exposed Archean alkalic and A-type intrusions in the Itacaiúnas Belt, strongly implicating a deep magmatic connection.A group of smaller, commonly supergene-enriched Cu–Au deposits (generally < 50 Mt @ < 2% Cu and < 1 g/t Au in hypogene ore), with enrichment in granitophile elements such as W, Sn and Bi, spatially overlap the Archean Fe-oxide Cu–Au deposits. These include the Breves, Águas Claras, Gameleira and Estrela deposits which are largely hosted by the upper sedimentary sequence as greisen-to ring-like or stockwork bodies. They generally lack abundant Fe-oxides, are quartz-bearing and contain more S-rich Cu–Fe sulfides than the Fe-oxide Cu–Au deposits, although Cento e Dezoito (118) appears to be a transitional type of deposit. Precise Pb–Pb in hydrothermal phosphate dating of the Breves and Cento e Dezoito deposits indicate ages of 1872 ± 7 Ma and 1868 ± 7 Ma, respectively, indistinguishable from Pb–Pb ages of zircons from adjacent A-type granites and associated dykes which range from 1874 ± 2 Ma to 1883 ± 2 Ma, with 1878 ± 8 Ma the age of intrusions at Breves. An unpublished Ar/Ar age for hydrothermal biotite at Estrela is indistinguishable, and a Sm–Nd isochron age for Gameleira is also similar, although somewhat younger. The geochronological data, combined with geological constraints and ore-element associations, strongly implicate a magmatic connection for these deposits.The highly anomalous, hydrothermal Serra Pelada Au–PGE deposit lies at the north-eastern edge of the Province within the same fault corridor as the Archean and Paleoproterozoic Cu–Au deposits, and like the Cu–Au deposits is LREE enriched. It appears to have formed from highly oxidising ore fluids that were neutralised by dolomites and reduced by carbonaceous shales in the upper sedimentary succession within the hinge of a reclined synform. The imprecise Pb–Pb in hydrothermal phosphate age of 1861 ± 45 Ma, combined with an Ar/Ar age of hydrothermal biotite of 1882 ± 3 Ma, are indistinguishable from a Pb–Pb in zircon age of 1883 ± 2 Ma for the adjacent Cigano A-type granite and indistinguishable from the age of the Paleoproterozoic Cu–Au deposits. Again a magmatic connection is indicated, particularly as there is no other credible heat or fluid source at that time.Finally, there is minor Au–(Cu) mineralisation associated with the Formiga Granite whose age is probably ca. 600 Ma, although there is little new zircon growth during crystallisation of the granite. This granite is probably related to the adjacent Neoproterozoic (900–600 Ma) Araguaia Fold Belt, formed as part of the Brasiliano Orogeny.Thus, there are two major and one minor period of Cu–Au mineralisation in the Carajás Mineral Province. The two major events display strong REE enrichment and strongly enhanced LREE. There is a trend from strongly Fe-rich, low-SiO₂ and low-S deposits to quartz-bearing and more S-rich systems with time. There cannot be significant connate or basinal fluid (commonly invoked in the genesis of Fe-oxide Cu–Au deposits) involved as all host rocks were metamorphosed well before mineralisation: some host rocks are at mid- to high-amphibolite facies. The two major periods of mineralisation correspond to two periods of alkalic to A-type magmatism at ca. 2.57 Ga and ca. 1.88 Ga, and a magmatic association is compelling.The giant to world-class late Archean Fe-oxide Cu–Au deposits show the least obvious association with deep-seated alkaline bodies as shown at Palabora, South Africa, and implied at Olympic Dam, South Australia. The smaller Paleoproterozoic Cu–Au–W–Sn–Bi deposits and Au–PGE deposit show a more obvious relationship to more fractionated A-type granites, and the Neoproterozoic Au–(Cu) deposit to crustally-derived magmas. The available data suggest that magmas and ore fluids were derived from long-lived metasomatised lithosphere and lower crust beneath the eastern margin of the Amazon Craton in a tectonic setting similar to that of other large Precambrian Fe-oxide Cu–Au deposits.     

Geology of gold-bearing skarn deposits in the middle and lower Yangtze River Valley and adjacent regions

The middle and lower Yangtze River Valley and adjacent regions are the most important metallogenic belt of gold (and copper)-bearing skarn deposits in China. The total gold reserves in this belt have been estimated at more than 600 t. The gold-bearing skarns are mainly distributed in the southeastern Hubei, Tongling and northern Anhui regions. Favorable tectonic settings are depressions and fold zones of the platforms, i.e., mobile belts. These skarns are hosted by platformal limestone, dolomitic limestone and dolomite of the Triassic, Carboniferous-Permian and Middle to Lower Cambrian formations. The related intrusions are Yenshanian (180 to 113 Ma) calc-alkaline quartz monzodiorite, granodiorite, quartz monzonite, monzogabbro, and their hybabyssal facies. The intrusions have high Fe₂O₃/FeO (>0.5) and intermediate initial ⁸⁷Sr/⁸⁶Sr ratios (0.7046 to 0.7087). Their REE distribution patterns are LREE-enriched and exhibit smooth, right-dipping curves. These suggest that the source materials mainly came from upper mantle, with contamination by sialic crustal components. The auriferous skarns are both calcic and magnesian, but calcic skarns are most common. The constituent minerals of the calcic skarns are diopside, garnet, wollastonite, vesuvianite and scapolite, whereas magnesian skarns are dominated by forsterite, spinel, diopside, phlogopite, chondrodite and clinohumite, with abundant superimposed serpentine, clinochlore and brucite. The compositions of coexisting pyroxenes and garnets are diopside and andradite, indicating the high oxygen fugacity and low acidity conditions. Gold is closely associated with Cu (Pb, Zn) sulfides and exists mainly in the form of native gold and electrum. Arsenides, tellurides, bismuthides and selenides are present in many ore deposits. Therefore, Cu, As, Bi, Te, Ag, Pb, Zn, Se and Co are the major metals present in the deposits and are important geochemical ore-searching indicators. In some Au (Fe, Cu) magnesian skarns, magnesiomagnetite, magnesioferrite and ludwigite are locally abundant. The metasomatic zoning in many gold skarn deposits is very distinct consisting of an outward sequence of: Fe (Cu)→Cu (Mo)→Cu (Au)→Au (Cu)→Au (Pb, Zn). The geologic characteristics of Au (Cu) skarn deposits that formed in the mobile platformal setting of China have distinct differences compared to Au skarns formed in orogenic belts at convergent plate margins in British Columbia and the western USA.     

皖赣沿江地区中生代壳幔相互作用与多成因夕卡岩成矿过程研究综述

在皖赣沿江地区分布着大量中生代侵入岩体及其岩石包体和相关的夕卡岩矿床。本文在综合整理作者研究团队近30年来所获得的区内大部分侵入岩体及其岩石包体和夕卡岩矿床研究资料的基础上,聚焦区域中生代壳幔相互作用与多成因夕卡岩成矿过程分析,为发展壳幔成矿学打下一定基础。基性侵入岩和镁铁质岩石包体的同位素年代学和岩石地球化学资料表明,皖赣沿江地区在中生代发生了碰撞后(145~135 Ma)富铜金和造山后(130~120 Ma)富铁金幔源岩浆底侵作用和相应的壳幔混源岩浆作用。壳幔混源岩浆作用主要包括结晶分异作用、同化混染作用、岩浆混合作用和岩浆熔离作用。夕卡岩矿床地质调研和镜下观察结果显示,两期壳幔混源岩浆侵入晚古生代到早中生代围岩地层后引发了多成因夕卡岩成矿作用,形成了接触交代、层控、岩浆和复合叠加等多成因夕卡岩矿床。接触交代、层控、岩浆和复合叠加夕卡岩矿床分别以热液交代、沉积+热液交代、岩浆结晶+热液交代和沉积+岩浆结晶+热液交代矿物组合和结构构造为特征。在碰撞后酸性-中酸性侵入岩体中产有富Cu和Zn等成矿物质的元古宙变质岩包体,表明碰撞后富铜金的底侵玄武岩浆或其演化岩浆在浅位岩浆房中同化了元古宙变质基底成矿物质(铜锌等)储库导致铜进一步富集,从而形成更富铜的酸性-中酸性岩浆。在碰撞后中基性-基性侵入岩体中产有含大量Cu-Fe硫化物(黄铜矿和磁黄铁矿)和氧化物包裹体的深位和浅位堆积岩,表明碰撞后富铜金的底侵玄武岩浆在深位岩浆房中和其演化岩浆在浅位岩浆房中发生了强烈的结晶分异作用导致铜铁亏损,形成更富金的中基性-基性岩浆。酸性-中酸性侵入岩体中夕卡岩包体和夕卡岩中辉长岩-夕卡岩过渡包体的存在表明,碰撞后富铜金的底侵玄武岩浆在侵位处同化晚古生代含铜铁矿源层的碳酸盐地层导致铜进一步富集,形成更富铜的夕卡岩岩浆。更富铜的酸性-中酸性岩浆、更富金的中基性-基性岩浆和更富铜的夕卡岩岩浆是形成碰撞后时期接触交代和层控夕卡岩铜矿、接触交代夕卡岩金矿和岩浆夕卡岩铜矿的最重要控制因素。在造山后中基性-基性侵入岩体中产有含大量Cu-Fe硫化物(黄铜矿和磁黄铁矿)和氧化物包裹体的堆积岩,表明造山后富铁金的底侵玄武岩浆在深位岩浆房中发生了强烈的结晶分异作用导致铜铁亏损,从而形成更富金的中基性-基性岩浆。造山后富铁金的底侵玄武岩浆在侵位处同化晚古生代含铜铁矿源层的碳酸盐地层、早中生代铁矿源层或者早中生代铁硅矿源层,导致铁、铁和铁硅的进一步富集,分别形成更富铁的夕卡岩岩浆、基性岩浆和中基性岩浆。更富金的中基性-基性岩浆及更富铁的夕卡岩岩浆、基性岩浆和中基性岩浆是形成造山后时期接触交代夕卡岩金矿、岩浆夕卡岩铁矿、矿浆型铁矿和接触交代夕卡岩铁矿的关键控制因素。     

Geochemistry and evolution of ore-forming fluids of the Yueshan Cu–Au skarn- and vein-type deposits, Anhui Province, South China

The Yueshan mineral belt is geotectonically located at the centre of the Changjiang deep fracture zone or depression of the lower Yangtze platform. Two main types of ore deposits occur in the Yueshan orefield: Cu–Au–(Fe) skarn deposits and Cu–Mo–Au–(Pb–Zn) hydrothermal vein-type deposits. Almost all deposits of economic interest are concentrated within and around the eastern and northern branches of the Yueshan dioritic intrusion. In the vicinity of the Zongpu and Wuhen intrusions, there are many Cu–Pb–Zn–Au–(S) vein-type and a few Cu–Fe–(Au) skarn-type occurrences.Fluid inclusion studies show that the ore-forming fluids are characterised by a Cl⁻(S)–Na⁺–K⁺ chemical association. Hydrothermal activity associated with the above two deposit types was related to the Yueshan intrusion. The fluid salinity was high during the mineralisation processes and the fluid also underwent boiling and mixed with meteoric water. In comparison, the hydrothermal activity related to the Zongpu and Wuhen intrusions was characterised by low salinity fluids. Chlorine and sulphur species played an important role in the transport of ore-forming components.Hydrogen- and oxygen-isotope data also suggest that the ore-forming fluids in the Yueshan mineral belt consisted of magmatic water, mixed in various proportions with meteoric water. The enrichment of ore-forming components in the magmatic waters resulted from fluid–melt partitioning. The ore fluids of magmatic origin formed large Cu–Au deposits, whereas ore fluids of mixed magmatic-meteoric origin formed small- to medium-sized deposits.The sulphur isotopic composition of the skarn- and vein-type deposits varies from − 11.3‰ to + 19.2‰ and from + 4.2‰ to + 10.0‰, respectively. These variations do not appear to have been resulted from changes of physicochemical conditions, rather due to compositional variation of sulphur at the source(s) and by water–rock interaction. Complex water–rock interaction between the ore-bearing magmatic fluids and sedimentary wall rocks was responsible for sulphur mixing. Lead and silicon isotopic compositions of the two deposit types and host rocks provide similar indications for the sources and evolution of the ore-forming fluids.Hydrodynamic calculations show that magmatic ore-forming fluids were channelled upwards into faults, fractures and porous media with velocities of 1.4 m/s, 9.8 × 10^− 1 to 9.8 × 10^− 7 m/s and 3.6 × 10^− 7 to 4.6 × 10^− 7 m/s, respectively. A decrease of fluid migration velocity in porous media or tiny fractures in the contact zones between the intrusive rocks and the Triassic sedimentary rocks led to the deposition of the ore-forming components. The major species responsible for Cu transport are deduced to have been CuCl, CuCl₂⁻, CuCl₃²⁻ and CuClOH, whereas Au was transported as Au₂(HS)₂S²⁻, Au(HS)₂⁻, AuHS and AuH₃SiO₄ complexes. Cooling and a decrease in chloride ion concentration caused by fluid boiling and mixing were the principal causes of Cu deposition. Gold deposition was related to decrease of pH, total sulphur concentration and fO₂, which resulted from fluid boiling and mixing.Geological and geochemical characteristics of the two deposit types in the Yueshan mineral belt suggest that there is a close genetic relationship with the dioritic magmatism. Geochronological data show that the magmatic activity and the mineralisation took place between 130 and 136 Ma and represent a continuous process during the Yanshanian time. The cooling of the intrusions and the mineralisation event might have lasted about 6 Ma. The cooling rate of the magmatic intrusions was 80 to 120 °C my^− 1, which permitted sufficient heat supply by magma to the ore-forming system.     

Overview of some Colombian gold deposits and their development potential

Source rock gold deposits in Colombia include Proterozoic unconformity-related paleoplacers, Palaeozoic stratabound Au/Ag-Cu-Pb-V-U red bed-type ores, and Mesozoic/Tertiary hydrothermal vein systems of Cordilleran magmatic arcs. The younger metallogenic episode occurred some 8 Ma ago in the Western Cordillera. Epithermal deposits are generally small (> 10,000–1 Mt grading 5–10 g/t Au) and the precious-base metal (Cu, Zn, Fe) association was probably deposited within the temperature range 180–300 °C. Widespread palaeoplacers in Quaternary terraces with enrichment in old channels, as well as extensively dredged alluvial deposits in presently active sediments, are connected with ongoing Andean uplift and erosion. Palaeochannel and alluvial gold concentrations represent the most promising targets for future exploration. An additional output could also derive from the clastic-hosted, stratiform deposits of the shield and E Cordillera.     

The copper–gold and gold deposits of the Neoproterozoic Mara Rosa magmatic arc, central Brazil

Mineral exploration in the Neoproterozoic Goiás Magmatic Arc, central Brazil, dates back to the beginning of the 1970s. The Goiás Magmatic Arc extends for more than 1000 km in the western and northern parts of Goiás, into Tocantins, and disappears under the Phanerozoic Parnaíba Basin. Two main areas of Neoproterozoic juvenile crust, the Arenópolis and the Mara Rosa arcs, are identified. They lie in the southern and northern sectors of the Goiás Arc, respectively, and are relatively well studied.The Goiás Magmatic Arc dominantly comprises tonalitic/dioritic orthogneisses and narrow NNE-striking volcano-sedimentary belts. Recent U–Pb zircon data indicate crystallization of the tonalite protoliths in two main episodes: the older between ca. 890 and 790 Ma and the younger at 670–600 Ma. Nd isotopic data indicate the very primitive nature of the original magmas, with T_DM model ages mostly within the interval between 0.9 and 1.0 Ga and _Nd(T) values between +3.0 and +4.6. In the Chapada–Mara Rosa area, the supracrustal rocks form three individual NNE belts, known as the eastern, central and western belts, separated from each other by metatonalites/metadiorites.Gold and Cu–Au deposits of the Mara Rosa area occur in four main associations: (i) Au–Ag–Ba (e.g., Zacarias), which are interpreted as stratiform, disseminated volcanogenic deposits, (ii) Cu–Au (e.g., Chapada) which has been interpreted either as volcanogenic or as a porphyry-type deposit, (iii) Au-only deposits (e.g., Posse), interpreted as an epigenetic disseminated deposit controlled by a mesozonal shear zone and (iv) Au–Cu–Bi (e.g., the Mundinho occurrence), which are considered as vein-type deposits controlled by magnetite-rich diorites.The gold and Cu–Au deposits located within the Goiás Magmatic Arc can be spatially and temporally related to the magmatic evolution of a collisional belt or, in other words, to an orogenic gold deposit model. These models are based on the continuous evolution of collisional plates, which can be subdivided into four stages with distinct magmatic characteristics: (i) subduction stage, (ii) syntectonic collisional magmatism stage, (iii) post-tectonic collisional magmatism stage and (iv) post-orogenic extension stage.     

Mineral assemblages of the Francisco I. Madero Zn–Cu–Pb–(Ag) deposit, Zacatecas, Mexico: Implications for ore deposit genesis

The Francisco I. Madero deposit, central Mexico, occurs in the Mesozoic Guerrero Terrane, which hosts many ore deposits, both Cretaceous (volcanogenic massive sulfides) and Tertiary (epithermal and skarn deposits). It is hosted by a 600 m-thick calcareous-pelitic unit, of Lower Cretaceous age, crosscut by porphyritic dikes that strike NW–SE. A thick felsic volcanic Tertiary sequence, consisting of andesites and rhyolitic ignimbrites, unconformably overlies the Cretaceous series. At the base, the mineralization consists of several mantos developed within calcareous beds. They are dominantly composed of sphalerite, pyrrhotite and pyrite with minor chalcopyrite, arsenopyrite and galena. At the top of the orebody, there are calcic skarns formed through prograde and retrograde stages. The resulting mineral assemblages are rich in manganoan hedenbergite (Hd_75–28Di_40–4Jh_40–20), andraditic garnets (Adr_100–62Grs_38–0), epidote (Ep_95–36Czo_60–5Pie_8–0), chamosite, calcite and quartz. The temperature of ore deposition, estimated by chlorite and arsenopyrite geothermometry, ranges from 243° to 277 °C and from 300° to 340 °C, respectively. The pressure estimated from sphalerite geobarometry averages 2.1 kbar. This value corresponds to a moderately deep skarn and agrees with the high Cu content of the deposit. Paragenesis, P–T conditions and geological characteristics are compatible with a distal, dike-related, Zn skarn deposit. Its style of mineralization is similar to that of many high-temperature carbonate replacement skarn deposits in the Southern Cordillera.     

Correlation between local structure and molar ratio of Au (III) complexes in aqueous solution: An XAS investigation

The local and geometrical structure around gold (III) e.g., Au³⁺ ions in aqueous solution with different OH⁻/Cl⁻ molar ratios, has been investigated by X-ray absorption spectroscopy (XAS). X-ray absorption near-edge structure (XANES) spectra of [AuCl_n(OH)_4−n]⁻ solutions have been calculated and the multiple-scattering spectral features have been attributed to Cl d-states, axial water molecules and the replacement of Cl⁻ ligands by OH⁻ ligands. A square–planar geometry for [AuCl_n(OH)_4−n]⁻ with two axial water molecules has been identified. Moreover, a spectral correlation between XANES features and the type of planar atoms has been identified. By extended X-ray absorption fine structure spectra (EXAFS), the planar Au bond distances in the solutions have also been determined, e.g., 2.28 Å for Au–Cl and 1.98 Å for Au–O, respectively. The same EXAFS analysis provides evidence that the peak at about 4.0 Å in solutions with the lowest OH⁻/Cl⁻ molar ratio arises from collinear Cl–Au–Cl multiple-scattering contributions. For the first time, a complete detailed reconstruction of the hydration structure of an Au ion at different pH values has been achieved.     

LA-ICP-MS mineral chemistry of titanite and the geological implications for exploration of porphyry Cu deposits in the Jinshajiang – Red River alkaline igneous belt,SW China

The Jinshajiang–Red River alkaline igneous belt in the eastern Indian–Asian collision zone, of southwestern China, hosts abundant, economically important Cu–Mo–Au mineralization of Cenozoic age. Major- and trace-element compositions of titanites from representative Cu-mineralized intrusions determined by LA-ICP-MS show higher values for Fe₂O₃/Al₂O₃, ΣREE?+?Y, LREE/HREE, Ce/Ce*, (Ce/Ce*)/(Eu/Eu*), U, Th, Ta, Nb and Ga, and lower values for Al₂O₃, CaO, Eu/Eu*, Zr/Hf, Nb/Ta and Sr than those for titanites from barren intrusions. Different ΣREE?+?Y, LREE/HREE, U, Th, Ta and Nb values of titanites between Cu-mineralized and barren intrusions were controlled mainly by the coexisting melt compositions. However, different Sr concentrations and negative Eu anomalies of titanites between Cu-mineralized and barren intrusions were most probably caused by different degrees of crystallization of feldspar from melts. In addition, different Ga concentrations and positive Ce anomalies of titanites between Cu-mineralized and barren intrusions were most likely caused by different magmatic fO₂ conditions. Pronounced compositional differences of titanites between Cu-mineralized and barren intrusions can provide a useful tool to help discriminate between ore-bearing and barren intrusions at an early stage of exploration, and, thus, have a potential application in exploration for porphyry Cu deposits in the Jinshajiang – Red River alkaline igneous belt, and to other areas.     

25 years of mineral exploration and discovery in Indonesia

This paper traces the history of mineral exploration in Indonesia between 1967 and 1992, and discusses various technical aspects, such as area selection, exploration and discovery methods, and significant geologic features of the more important new discoveries.Exploration activity over the past 25 years can be divided into four main phases. Phase 1 (1967–1976) mostly involved investigations of mineral prospects and districts previously identified by the Dutch. These investigations resulted in many discoveries, including: a major copper-gold district (skarn-porphyry copper) in Irian Jaya, where exploration is still in progress (resources identified to date: 28 Mt Cu and 2,700 t Au); large nickel resources in Eastern Indonesia (13 Mt Ni); significant onshore and offshore tin resources in the Sumateran tin belt (0.13 Mt Sn); and large but low grade bauxite deposits in West Kalimantan (300 Mt Al₂O₃). Of the eight Contracts of Work signed between 1967 and 1972, six reached the mining stage. Phase 2 (1970–1975) consisted of an extensive porphyry copper search in the Sunda arc, the western arc of Sulawesi and the central belt of Irian Jaya. Best results were obtained from northern Sulawesi, where follow-up between 1976 and 1982 identified three potentially economic copper-gold deposits (1.7 Mt Cu and 140 t Au) and one subeconomic molybdenum porphyry system (0.8 Mt Mo). During Phase 3 (1981–1988) extensive coal exploration in South and East Kalimantan delineated over 5,000 Mt of coal of varying rank and quality, including 1,500 Mt as measured reserves in 17 deposits, eight of which have been developed to date. Phase 4 (1984–1990) involved a major gold rush, focused primarily on the Cenozoic magmatic belts of Kalimantan, Sulawesi, Moluccas and the Sunda arc. Over 80 primary and alluvial gold prospects were drill tested. Five of these were brought into production (two alluvial deposits, two new hard rock discoveries and one Dutch mine), containing approximately 135 tonnes of mineable gold, and several other projects are under development or undergoing feasibility studies. Total geological resources identified to date are estimated to contain about 700 tonnes of gold. Exploration during phase 4 also resulted in several gold-rich porphyry copper discoveries, including a major deposit in Sumbawa (2.7 Mt Cu and 250 t Au). Intermittent exploration for uranium, diamonds and lead/zinc since 1969 has been largely unsuccessful.Exploration is now passing to the next phase, which is likely to be multi-commodity in nature with a strong focus on gold, copper and coal. A number of deposits outlined during earlier phases will be developed.The unprecedented high level of mineral exploration activity over the past 25 years can be attributed to Indonesia's mineral prospectivity and favourable investment climate. Given a continued competitive commercial environment and sustained commodity prices, the next 25 years should see further strong development of the country's mineral resources.     

Metallogeny and tectonic development of the Tasman Fold Belt System in New South Wales

The northwestern corner of New South Wales consists of the paratectonic Late Proterozoic to Early Cambrian Adelaide Fold Belt and older rocks, which represent basement inliers in this fold belt. The rest of the state is built by the composite Late Proterozoic to Triassic Tasman Fold Belt System or Tasmanides.In New South Wales the Tasman Fold Belt System includes three fold belts: (1) the Late Proterozoic to Early Palaeozoic Kanmantoo Fold Belt; (2) the Early to Middle Palaeozoic Lachlan Fold Belt; and (3) the Early Palaeozoic to Triassic New England Fold Belt. The Late Palaeozoic to Triassic Sydney—Bowen Basin represents the foredeep of the New England Fold Belt.The Tasmanides developed in an active plate margin setting through the interaction of East Gondwanaland with the Ur-(Precambrian) and Palaeo-Pacific plates. The Tasmanides are characterized by a polyphase terrane accretion history: during the Late Proterozoic to Triassic the Tasmanides experienced three major episodes of terrane dispersal (Late Proterozoic—Cambrian, Silurian—Devonian, and Late Carboniferous—Permian) and six terrane accretionary events (Cambrian—Ordovician, Late Ordovician—Early Silurian, Middle Devonian, Carboniferous, Middle-Late Permian, and Triassic). The individual fold belts resulted from one or more accretionary events.The Kanmantoo Fold Belt has a very restricted range of mineralization and is characterized by stratabound copper deposits, whereas the Lachlan and New England Fold Belts have a great variety of metallogenic environments associated with both accretionary and dispersive tectonic episodes.The earliest deposits in the Lachlan Fold Belt are stratabound Cu and Mn deposits of Cambro-Ordovician age. In the Ordovician Cu deposits were formed in a volcanic are. In the Silurian porphyry Cu---Au deposits were formed during the late stages of development of the same volcanic are. Post-accretionary porphyry Cu---Au deposits were emplaced in the Early Devonian on the sites of the accreted volcanic arc. In the Middle to Late Silurian and Early Devonian a large number of base metal deposits originated as a result of rifting and felsic volcanism. In the Silurian and Early Devonian numerous Sn---W, Mo and base metal—Au granitoid related deposits were formed. A younger group of Mo---W and Sn deposits resulted from Early—Middle Carboniferous granitic plutonism in the eastern part of the Lachlan Fold Belt. In the Middle Devonian epithermal Au was associated with rifting and bimodal volcanism in the extreme eastern part of the Lachlan Fold Belt.In the New England Fold Belt pre-accretionary deposits comprise stratabound Cu and Mn deposits (pre-Early Devonian): stratabound Cu and Mn and ?exhalite Au deposits (Late Devonian to Early Carboniferous); and stratabound Cu, exhalite Au, and quartz—magnetite (?Late Carboniferous). S-type magmatism in the Late Carboniferous—Early Permian was responsible for vein Sn and possibly Au---As---Ag---Sb deposits. Volcanogenic base metals, when compared with the Lachlan Fold Belt, are only poorly represented, and were formed in the Early Permian. The metallogenesis of the New England Fold Belt is dominated by granitoid-related mineralization of Middle Permian to Triassic age, including Sn---W, Mo---W, and Au---Ag---As Sb deposits. Also in the Middle Permian epithermal Au---Ag mineralization was developed. During the above period of post-orogenic magmatism sizeable metahydrothermal Sb---Au(---W) and Au deposits were emplaced in major fracture and shear zones in central and eastern New England. The occurrence of antimony provides an additional distinguishing factor between the New England and Lachlan Fold Belts. In the New England Fold Belt antimony deposits are abundant whereas they are rare in the Lachlan Fold Belt. This may suggest fundamental crustal differences.     

Computer thermodynamic modeling of the transport and deposition of Sb and Au during the formation of Au-Sb deposits

Using the Chiller computer program, we performed modeling of the mechanisms of the joint transport and deposition of Au and Sb from various ore-forming solutions during the formation of Au-Sb deposits. Three models are considered by the example of the Uderei Au-Sb deposit in the Yenisei Ridge: (1) simple cooling (cooling only), (2) iso-enthalpy boiling (P = f(T)), and (3) solution–rock interaction (rock titration model). The behavior of Sb(III) and Au(I) in the system Au–Sb–Fe–Cu–Pb–Zn–As–H₂O–Cl–H₂S–CO₂ under hydrothermal conditions was studied. It is shown that both weakly alkaline (near-neutral) and reduced acidic Fe_aq²⁺-enriched low-chloride high-CO₂ and high-chloride hydrothermal solutions play a crucial role in the formation of gold parageneses of Au-Sb ores.     

Partitioning of platinum-group elements and Au in the Fe−Ni−Cu−S system: experiments on the fractional crystallization of sulfide melt

Partitioning of platinum-group elements (PGE) between sulfide liquid and monosulfide solid solution (mss) has been investigated by crystallizingmss from Fe–Ni–Cu sulfide liquid at 1,000–1,040° C, using bulk compositions and PGE contents typical of magmatic sulfides associated with mafic and ultramafic systems. Products were analyzedin situ for PGE and Au using SIMS. Sulfide liquid compositions were more Ni- and Cu-rich than coexistingmss. Liquid/mss partition coefficients are: Os-0.23±0.04, Ir-0.28±0.11, Ru-0.24±0.05, Rh-0.33±0.06, Pt-4.8±0.7, Pd-4.8±1.9, Au-11.4. Partitioning of PGE is independent of PGE concentration and Ni content in the composition range investigated. Additionally, Henry's law appears to be obeyed up to minor-element contents in the sulfide liquid andmss. Osmium, Ir, Ru, and Rh are compatible elements in the anhydrous Fe–Ni–Cu–S system, whereas Pt, Pd and Au are incompatible elements. These affinities correspond to the partitions of PGE between massive and Cu-rich magmatic sulfides. However, the detailed precious-metal compositions of the Cu-rich sulfides of mafic rock systems, disseminated ores of komatiites and Cu-rich assemblage of droplet ore from the Noril'sk-Talnakh deposits are not consistent with those expected for pristine fractionated sulfide liquids.     

Hostrocks to the stratabound iron-formation-hosted Starra gold-copper deposit,Australia

This paper documents the timing, geochemistry and possible origin of sodium enrichment associated with Proterozoic iron formation-hosted copper-gold ore lenses at the Starra deposit, Australia. The ore lenses are immediately underlain by variably sheared albitemagnetite-hematite-pyrite-bearing rocks, and overlain by mainly unaltered, less-sheared, meta-sediments. Evidence indicating that albite was abundant prior to deformation, and also prior to the main hydrothermal addition of Fe, S, Cu and Au, includes (1) regional albite development at this stratigraphic level; (2) alteration of albite by ore-related sericite; and (3) inclusion of unfoliated inclusions of albite and hematite in ore-related pyrite. Nevertheless, albite also developed around dolerites and within hangingwall shears during metamorphism and deformation. Least altered albite footwall rocks have SiO₂ (67.31–73.13 wt.%), Al₂O₃(9.89–12.51 wt.%), total alkali elements (6.40–9.43 wt.%) and HFS elements (e.g., Zr = 179–275 ppm; Ti/Zr = 7.6–14.1) comparable with felsic volcanics, but have high relative Na₂O contents (5.08–5.81 wt. %), and variable to high Na₂O/K₂O ratios (0.05–68.37). An episode of alkali alteration by high-Na fluids prior to the ore-related alteration is postulated to account for sodic compositions, after chemical consideration of the alternatives (1) arkosic sediments; (2) trondhjemitic volcaniclastics; and (3) Na-metasomatism of Staveley Formation sediments. During the most intense ore-alteration, isocon analysis indicates a density increase of 23% compared to the least altered albitised hostrocks. Cu, Fe, Au, Sn, W, Zn, K, Ba and Rb were enriched during the mineralising process, whereas Mn, Ca, Si, Nb and Zr were lost, and Al, Ti and Y were not changed (and were used to define the isocon). The loss of some high field strength elements during this alteration indicates that igneous rock classification diagrams based on immobile element ratios should be used with caution for albitemuscovite magnetite-pyrite assemblages associated with iron formation-hosted copper-gold deposits. Zircon was partially soluble, whereas titanium oxides were probably stable in the saline, high temperature (260°–380 °C), acid (pH = 3.9–6.0) fluids envisaged for ore-related alteration.     

Geological, mineralogical and geochemical characteristics of the Radzimowice Au–As–Cu deposit from the Kaczawa Mountains (Western Sudetes, Poland): an example of the transition of porphyry and epithermal style

The sheeted quartz–sulfide veins of the Radzimowice Au–As–Cu deposit in the Kaczawa Mountains are related to Upper Carboniferous post-collisional potassic magmatism of the composite Zelezniak porphyry intrusion. Multiple intrusive activity ranges from early calc-alkaline to sub-alkaline and alkaline rocks and is followed by multiple hydrothermal events. Early crustally derived dacitic magma has low mg# (<63) and very low concentrations of mantle-compatible trace elements, high large-ion lithophile elements (LILE), moderate light rare-earth elements (LREE), and low high-field-strength elements (HFSE). Later phases of more alkaline rocks have higher mg# (60–70), and LILE, LREE, and HFSE characteristics that indicate mafic magma contributions in a felsic magma chamber. The last episode of the magmatic evolution is represented by lamprophyre dikes which pre-date ore mineralization and are spatially related to quartz–sulfide–carbonate veins. The dikes consist of kersantite and spessartite of calc-alkaline affinity with K₂O/Na₂O ratios of 1.1–1.9, mg# of 77–79, and high abundances of mantle-compatible trace elements such as Cr, Ni, and V. They have high LILE, low LREE, and low HFSE contents suggesting a subduction-related post-collisional arc-setting. The mineralization started with arsenopyrite that was strongly brecciated and overprinted by multiple quartz–carbonate phases associated with base-metal sulfides and Au–Ag–Bi–Te–Pb±S minerals. The sulfur isotope composition of sulfides ranges from –1.1 to 2.8 ³⁴S and suggests a magmatic source. At least two generations of gold deposition are recognized: (1) early refractory, and (2) subsequent non-refractory gold mineralization of epithermal style. Co-rich arsenopyrite with refractory gold and pyrite are the most abundant minerals of the early stage of sulfide precipitation. Early arsenopyrite formed at 535–345°C along the arsenopyrite–pyrrhotite–loellingite buffer and late arsenopyrite crystallized below 370°C along the arsenopyrite–pyrite buffer. Non-refractory gold associated with base-metal sulfides and with Bi–Te–Ag–Pb–S mineral assemblages has an average fineness of about 685, and is represented by electrum of two generations, and minor maldonite (Au₂Bi). Fluid inclusions from various quartz generations co-genetic with base-metal sulfides and associated with carbonates, tellurides and non-refractory gold indicate fluids with moderate salinity (9–15 wt% NaCl equiv.) and a temperature and pressure drop from 350 to 190°C and 1.2 to 0.8 kbar, respectively. According to the result of the sulfur isotope fractionation geothermometer the temperature of base-metal crystallization was in the range from 322 to 289°C. Preliminary results of oxygen isotope studies of quartz from veins indicate a gradual increase in the proportion of meteoric water in the epithermal stage. The gold to silver ratio in ore samples with >3 ppm Au is about 1:5 (geometric mean). Hydrothermal alteration started with sericitization, pyritization, and kaolinitization in vein selvages followed by alkaline hydrothermal alteration of propylitic character (illitization and chloritization), albitization and carbonatization. The mineralization of the Radzimowice deposit is considered as related to alkaline magmatism and is characterized by the superposition of low-sulfidation epithermal mineralization on higher-temperature and deeper-seated mesothermal/porphyry style.Editorial handling: B. Lehmann     

U–Pb (zircon) and geochemical constraints on the age,origin, and evolution of Paleozoic arc magmas in the Oyu Tolgoi porphyry Cu–Au district,southern Mongolia

Uranium–Pb (zircon) ages are linked with geochemical data for porphyry intrusions associated with giant porphyry Cu–Au systems at Oyu Tolgoi to place those rocks within the petrochemical framework of Devonian and Carboniferous rocks of southern Mongolia. In this part of the Gurvansayhan terrane within the Central Asian Orogenic Belt, the transition from Devonian tholeiitic marine rocks to unconformably overlying Carboniferous calc-alkaline subaerial to shallow marine volcanic rocks reflects volcanic arc thickening and maturation. Radiogenic Nd and Pb isotopic compositions (ε_Nd(t) range from + 3.1 to + 7.5 and ²⁰⁶Pb/²⁰⁴Pb values for feldspars range from 17.97 to 18.72), as well as low high-field strength element (HFSE) contents of most rocks (mafic rocks typically have < 1.5% TiO₂) are consistent with magma derivation from depleted mantle in an intra-oceanic volcanic arc. The Late Devonian and Carboniferous felsic rocks are dominantly medium- to high-K calc-alkaline and characterized by a decrease in Sr/Y ratios through time, with the Carboniferous rocks being more felsic than those of Devonian age. Porphyry Cu–Au related intrusions were emplaced in the Late Devonian during the transition from tholeiitic to calc-alkaline arc magmatism. Uranium–Pb (zircon) geochronology indicates that the Late Devonian pre- to syn-mineral quartz monzodiorite intrusions associated with the porphyry Cu–Au deposits are ~ 372 Ma, whereas granodiorite intrusions that post-date major shortening and are associated with less well-developed porphyry Cu–Au mineralization are ~ 366 Ma. Trace element geochemistry of zircons in the Late Devonian intrusions associated with the porphyry Cu–Au systems contain distinct Th/U and Yb/Gd ratios, as well as Hf and Y concentrations that reflect mixing of magma of distinct compositions. These characteristics are missing in the unmineralized Carboniferous intrusions. High Sr/Y and evidence for magma mixing in syn- to late-mineral intrusions distinguish the Late Devonian rocks associated with giant Cu–Au deposits from younger magmatic suites in the district.     

The timing and isotopic character of regional hydrothermal alteration and associated epigenetic mineralization in the western sector of the Kaapvaal Craton (South Africa)

The Kaapvaal Craton of South Africa comprises an Archaean core of ≈3.5 Ga lithospheric and crustal rocks surrounded by younger accreted terrains of ≈3.0–2.7 and ≈2.1–1.9 Ga. The craton is covered by relatively undeformed 3.0–2.4 Ga supracrustal rocks, which show the effects of thermal and hydrothermal interaction. Part of this activity is manifested by a large number of epigenetic Pb–Zn (±Ag, Au, Cu, F) deposits in the cover rocks of the Kaapvaal Craton. These include small volcanic and breccia hosted deposits in mafic and felsic volcanic rocks of the 2.7 Ga Ventersdorp Supergroup and the Mississippi Valley-type (MVT) deposits in the carbonates of the Transvaal Supergroup.MVT mineralization at the Pering (and other Zn–Pb deposits) is hosted in fracture-generated N–S breccia bodies in the Paleoproterozoic carbonate succession of the western Kaapvaal Craton. The fluids carrying the metals were focused in vertical bodies within the fracture zones (FZ), the metals and the sulphur being carried together and precipitated in organic-rich sectors of the basin. Two small Pb–Zn deposits within mafic rocks of the Ventersdorp Supergroup, stratigraphically below the basin-hosted MVTs on the southwestern part of the Kaapvaal Craton have secondary chlorite which is extremely Rb-rich, associated with the mineralization. This chlorite and the associated altered basaltic host rocks give a Rb–Sr date of ≈1.98 Ga, and the associated galena Pb isotope data plot on the same array as those of other Pb–Zn deposits, the radiogenic intercept giving a date of ≈2.0 Ga. We interpret these data to indicate a craton-wide epigenetic fluid-infiltration event, which exploited the Maquassie Quartz Porphyry (MQP) as the aquifer and metal source.Sr isotopic results for the ore-zone gangue minerals show highly radiogenic ⁸⁷Sr/⁸⁶Sr ratios (>0.710) which support earlier models that the origin of radiogenic Sr isotopic composition in the calcite cements is the felsic tuffs (MQP) of the Ventersdorp Supergroup occurring at deeper levels within the basin. Relationships between δ¹⁸O and δ¹³C performed on carbonate cements within the aquifers are complex: the range in δ¹³C for some of the cements represents a mixture from two sources and with a progression from heavy carbon in the host to somewhat lighter carbon in the cements. Similarly, the lighter δ¹⁸O values have a narrow range indicative of rapid exchanges between hydrous fluid and rock.     

Porphyry Cu–Au and associated polymetallic Fe–Cu–Au deposits in the Beiya Area, western Yunnan Province, south China

The Alkaline porphyries in the Beiya area are located east of the Jinshajiang suture, as part of a Cenozoic alkali-rich porphyry belt in western Yunnan. The main rock types include quartz-albite porphyry, quartz-K-feldspar porphyry and biotite–K-feldspar porphyry. These porphyries are characterised by high alkalinity [(K₂O + Na₂O)% > 10%], high silica (SiO₂% > 65%), high Sr (> 400 ppm) and ⁸⁷Sr/⁸⁶Sr (> 0.706)] ratio and were intruded at 65.5 Ma, between 25.5 to 32.5 Ma, and about 3.8 Ma, respectively. There are five main types of mineral deposits in the Beiya area: (1) porphyry Cu–Au deposits, (2) magmatic Fe–Au deposits, (3) sedimentary polymetallic deposits, (4) polymetallic skarn deposits, and (5) palaeoplacers associated with karsts. The porphyry Cu–Au and polymetallic skarn deposits are associated with quartz–albite porphyry bodies. The Fe–Au and polymetallic sedimentary deposits are part of an ore-forming system that produced considerable Au in the Beiya area, and are characterised by low concentrations of La, Ti, and Co, and high concentrations of Y, Yb, and Sc.The Cenozoic porphyries in western Yunnan display increased alkalinity away from the Triassic Jinshajiang suture. Distribution of both the porphyries and sedimentary deposits in the Beiya area are interpreted to be related to partial melting in a disjointed region between upper mantle lithosphere of the Yangtze Plate and Gondwana continent, and lie within a shear zone between buried Palaeo-Tethyan oceanic lithosphere and upper mantle lithosphere, caused by the subduction and collision of India and Asia.     

Geochemistry of the kaolin deposits of Swat (Pakistan)

Kaolin deposits of the Swat District in Pakistan are indicated to have derived by hydrothermal alteration of more feldspathic parts of felsic intrusives, which occur enclosed in orthoamphibolites and orthogneisses of the Cretaceous Kohistan Island Arc terrane. These latter “country rocks” formed under epidote–amphibolite conditions that prograde northwards to amphibolite facies, and locally manifest slight metamorphic differentiation. The felsic intrusives exhibit a general decrease in siliceous character from west to east, but are less siliceous than most hosts of world kaolins. They are composed of chemically allied quartz diorite, tonalite, trondhjemite and pegmatoids, which evolved mainly by an orthomagmatic crystal fractionation. These parental rocks are calc-alkaline in nature, and kaolinization has proceeded in Ca-richer environment. This is in variance with the occurrence of most known kaolin deposits over potassic granites or rhyolites. Ca-metasomatism of the “host rocks” is in evidence. Kaolin formation by a supergene process is not displayed.The raw kaolin with contained unaltered plagioclase is characterized by a rather low silica (46.54–50.93%) and potash (<1%), and high alumina (23.54–26.77%), Fe₂O₃ (1.73–5.45%) and lime (8.13–16.93%) content. Kaolinization proceeded with a decrease in SiO₂ and concomitant increase in Al₂O₃. The same trend is followed with fineness of grain size of washed fractions, in resemblance to other known kaolin deposits of primary as well as secondary origin.     

Thermodynamic study of the association and separation of copper and gold in the Shizishan ore field, Tongling, Anhui Province, China

The Shizishan ore field is the largest gold–copper ore field in the Tongling ore district of Anhui Province, China. Copper and gold deposits in the district are present as one-commodity deposits or as deposits with both commodities. Copper and gold mineralization are either cogenetic or are temporally and spatially distinct. We present the results of systematic geochemical analysis of fluid inclusions from typical Au–Cu deposits in the Shizishan ore field; these data are used to determine the solubility of Cu and Au in the ore-forming fluids and to ascertain the mechanisms and factors that controlled variations in the association and separation of copper and gold mineralization. Our results indicate that copper in the ore-forming fluids was transported as CuCl₂⁻ and CuCl⁰ complexes and that the solubility of copper was controlled by variations in Cl⁻ concentration. In addition, the precipitation of copper was controlled by changes in temperature, pH, fO₂, and fO₂. In comparison, gold in the ore-forming fluids was transported as Au(HS)₂⁻ and Au₂S(HS)₂²⁻ complexes, and the solubility of gold was controlled by variations in total sulfur concentration; the precipitation of gold was controlled by temperature, pH, fO₂, and fO₂. These differences between the two elements meant that copper and gold in the ore-forming fluids responded in different ways to changes in physicochemical conditions. Copper precipitated under relatively acidic conditions at high temperatures, while gold precipitated under weakly alkaline conditions at relatively low temperatures; this dissociation resulted in the temporal and spatial separation and zonation of copper and gold mineralization in the Shizishan ore field.