Copper-gold Deposit Research Articles

Geology and market-dependent significance of rare earth element resources

China started to produce rare earth elements (REEs) in the 1980s, and since the mid-1990s, it has become the dominant producer. Rare earth element export quotas first introduced by the Chinese government in the early 2000s were severely reduced in 2010 and 2011. This led to strong government-created disparity between prices within China and the rest of the world. Industrialized countries identified several REEs as strategic metals. Because of rapid price increases of REE outside of China, we have witnessed a world-scale REE exploration rush. The REE resources are concentrated in carbonatite-related deposits, peralkaline igneous rocks, pegmatites, monazite ± apatite veins, ion adsorption clays, placers, and some deep ocean sediments. REE could also be derived as a by-product of phosphate fertilizer production, U processing, mining of Ti-Zr-bearing placers, and exploitation of Olympic Dam subtype iron oxide copper gold (IOCG) deposits. Currently, REEs are produced mostly from carbonatite-related deposits, but ion adsorption clay deposits are an important source of heavy REE (HREE). Small quantities of REE are derived from placer deposits and one peralkaline intrusion-related deposit. The ideal REE development targets would be located in a politically stable jurisdiction with a pro-mining disposition such as Canada and Australia. REE grade, HREE/light REE (LREE) ratio of the mineralization, tonnage, mineralogy, and permissive metallurgy are some of the key technical factors that could be used to screen potential development projects. As REEs are considered strategic metals from economic, national security, and environmental points of view, technical and economic parameters alone are unlikely to be used in REE project development decision-making. Recycling of REE is in its infancy and unless legislated, in the short term, it is not expected to contribute significantly to the supply of REE.

Timing of multiple hydrothermal events in the iron oxide–copper–gold deposits of the Southern Copper Belt, Carajás Province, Brazil

The Southern Copper Belt, Carajás Province, Brazil, hosts several iron oxide–copper–gold (IOCG) deposits, including Sossego, Cristalino, Alvo 118, Bacuri, Bacaba, Castanha, and Visconde. Mapping and U–Pb sensitive high-resolution ion microprobe (SHRIMP) IIe zircon geochronology allowed the characterization of the host rocks, situated within regional WNW–ESE shear zones. They encompass Mesoarchean (3.08–2.85 Ga) TTG orthogneiss, granites, and remains of greenstone belts, Neoarchean (ca. 2.74 Ga) granite, shallow-emplaced porphyries, and granophyric granite coeval with gabbro, and Paleoproterozoic (1.88 Ga) porphyry dykes. Extensive hydrothermal zones include albite–scapolite, biotite–scapolite–tourmaline–magnetite alteration, and proximal potassium feldspar, chlorite–epidote and chalcopyrite formation. U–Pb laser ablation multicollector inductively coupled mass spectrometry (LA-MC-ICP-MS) analysis of ore-related monazite and Re–Os NTIMS analysis of molybdenite suggest multiple Neoarchean (2.76 and 2.72–2.68 Ga) and Paleoproterozoic (2.06 Ga) hydrothermal events at the Bacaba and Bacuri deposits. These results, combined with available geochronological data from the literature, indicate recurrence of hydrothermal systems in the Southern Copper Belt, including 1.90–1.88-Ga ore formation in the Sossego–Curral ore bodies and the Alvo 118 deposit. Although early hydrothermal evolution at 2.76 Ga points to fluid migration coeval with the Carajás Basin formation, the main episode of IOCG genesis (2.72–2.68 Ga) is related to basin inversion coupled with Neoarchean (ca. 2.7 Ga) felsic magmatism. The data suggest that the IOCG deposits in the Southern Copper Belt and those in the Northern Copper Belt (2.57-Ga Salobo and Igarapé Bahia–Alemão deposits) do not share a common metallogenic evolution. Therefore, the association of all IOCG deposits of the Carajás Province with a single extensive hydrothermal system is precluded.

Trace Element Geochemistry of Magnetite and Its Relationship to Cu-Bi-Co-Au-Ag-U-W Mineralization in the Great Bear Magmatic Zone, NWT, Canada

The Paleoproterozoic Great Bear magmatic zone is the focus of ongoing exploration for iron oxide copper-gold (IOCG) deposits and also hosts iron oxide-apatite occurrences. Examples of IOCG deposits in the Great Bear magmatic zone include Sue-Dianne and NICO, and other smaller prospects, including Damp, Fab, and Nori/Ra. The past-producing Terra mine property hosts significant IOCG-like alteration that contains dome-shaped, iron oxide-apatite bodies. Petrographic study has identified multiple generations of magnetite at NICO, Fab, and Nori/Ra and, for the most part, a single generation of magnetite at Sue-Dianne, Damp, and Terra. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) documents important geochemical differences in V, Ni, Cr, and Co concentrations within the magnetite. Variations of trace elements in magnetite from the Great Bear magmatic zone could be a result of (1) host rock-fluid equilibration during regional metamorphism, (2) postmetamorphic hydrothermal metasomatism of Treasure Lake Group metasedimentary rocks, (3) preferential solubility of Co over Ni within the Fe-rich fluids, (4) changes in oxygen fugacity ( f O2), and (5) partitioning of elements into coprecipitating sulfides. Regionally, the Cr/Co ratio is higher in barren and pre-ore magnetite compared to magnetite coprecipitated with ore minerals and/or present in ore-rich veins and breccias. Locally, at the Nori/Ra prospect, the V/Ni ratio in magnetite differentiates between barren and ore-related magnetite, and at Damp and Sue-Dianne the Co/Ni ratio is extremely high and clearly different from that of other Great Bear magmatic zone magnetite samples. These results provide the first database for geochemically characterized magnetite from different stages of IOCG alteration and illustrate the potential use of magnetite as an indicator mineral in the exploration for IOCG deposits.

The Serra Pelada Au-Pd-Pt Deposit, Carajas, Brazil: Geochemistry, Mineralogy, and Zoning of Hydrothermal Alteration

The Serra Pelada Au-Pd-Pt deposit is located within the Carajas mineral province, which also hosts the world-class iron ore and iron oxide-hosted copper-gold deposits of the Amazon craton in Brazil. The unusual low-temperature hydrothermal mineralization at Serra Pelada is epigenetic, hosted by metasedimentary rocks of the Aguas Claras Formation and structurally localized in the Serra Pelada overturned syncline. The orebodies are controlled by the intersection of subvertical NE-trending fault zones with metasiltstones, mainly at the syncline’s hinge, with minor ore occurrences at the upper and lower limb. Intense tropical weathering over the last 70 m.y. has completely overprinted the shallow ore in and near the flooded open pit, but primary hydrothermal features are preserved in deeper drill core delineating the remaining resource. Gold, platinum, and palladium mineralization is associated with intense argillic alteration, hematite breccias, and silicification, with the highest grade ore hosted by brecciated metasiltstones that are highly enriched in amorphous carbon. Distal alteration zones comprise a reducing and oxidizing alteration front. The hydrothermal mineral paragenesis comprises kaolinite, quartz, sericite, amesite (Mg-rich Al-silicate), amorphous carbon, hematite, monazite, rutile, pyrite, and a complex assemblage of Bi-, Ag-, Pb-, Cu-, Co-, Ni-, Pt-, Pd-, and Au-bearing, chalcogenide (S, Se), and arsenide (As, Sb) minerals. Major element changes during hydrothermal alteration include C and Mg addition, K depletion, localized silica loss, and silicification with notable introduction of trace elements including light rare earth elements (LREE), Bi, Pb, U, V, Cu, Co, Ni, and As. The hydrothermal alteration and element association of the Serra Pelada deposit show geochemical similarities with unconformity-related uranium deposits, which may also be enriched in Au, Pd, and Pt and were formed by mixing of fluids that interacted with a highly oxidized cover sequence and highly reduced rock packages in structures of brittle-ductile strain.

Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, Chile

Fil: Austin, James. Commonwealth Scientific and Industrial Research Organisation; Australia

Long term production planning of open pit mines by ant colony optimization

The problem of long-term production planning of open pit mines is a large combinatorial problem. Application of mathematical programming approaches suffer from reduced computational efficiency due to the large amount of decision variables. This paper presents a new metaheuristic approximation approach based on the Ant Colony Optimization (ACO) for the solution of the problem of open-pit mine production planning. It is a three-dimensional optimization procedure which has the capability of considering any type of objective function, non-linear constraints and real technical restrictions. The proposed process is programmed and tested through its application on a real scale Copper–Gold deposit. The study revealed that the ACO approach is capable to improve the value of the initial mining schedule regarding the current commercial tools considering penalties and without, in a reasonable computational time. Several variants of ACO were examined to find the most compatible variants and the best parameter ranges. Results indicated that the Max–Min Ant System (MMAS) and the Ant Colony System (ACS) are the best possible variants based on the required less amount of memory. It is also proved that the MMAS is the most explorative variant, while the ACS is the fastest method.

KUCUKDA : A NEW, HIGH SULFIDATION EPITHERMAL Au-Ag-Cu DEPOSIT AT THE TV TOWER PROPERTY IN WESTERN TURKEY

The Biga Peninsula in northwestern Turkey hosts a large number of high and low sulfidation epithermal gold-silver-(copper) and associated copper-gold porphyry deposits and prospects, associated with voluminous, Eocene-Miocene calc-alkaline volcanism and plutonism. Approximately 15 million gold-equiv oz have been discovered within the last 10 years in this area, with a number of new discoveries now in the drill-testing stage and two deposits in the development stage. At the TV Tower property in the central Biga Peninsula, Eocene(?) to Oligocene intermediate to felsic volcanic and volcaniclastic strata and associated intrusive rocks overlie metamorphosed basement rocks of the Camlica Group. The volcanic sequence is broadly divisible into a lower sequence of andesitic dikes and flows intruded by monzonite porphyry stocks and dikes, a middle sequence of andesitic breccias and flows, and an upper sequence consisting largely of dacitic tuffs, flows, and epiclastic strata. The middle and upper sequences are strongly altered over an area covering several tens of km2, including argillic, advanced argillic, and massive to vuggy quartz alteration, the latter largely manifested as ledges hosted in dacitic volcaniclastic rocks. Moderate- and high-angle normal and oblique faults are common in the area and may have influenced the distribution of mineralization. The Kucukdag zone was drill-tested in 2010 on the basis of strong surface soil and rock sample data. The second hole returned a near-surface intercept of 136.2 m averaging 4.30 g/t Au, 15.0 g/t Ag, and 0.68% Cu. As of the date of this communication, 169 holes have been drilled to test the zone, which measures approximately 600 × 400 m and consists of a lower gold-rich zone and an upper silver-rich zone. Total mineral endowment is estimated at 966,000 indicated and 351,000 inferred gold-equiv oz. Mineralization is strongly controlled by stratigraphy, with gold hosted primarily within a massive lithic lapilli-bearing tuff unit and silver largely constrained to an overlying fluvial-lacustrine sequence capped by andesite breccias. Copper is distributed throughout the zone in association with both gold and silver. The zone is located primarily in the hanging wall of a moderate-angle fault that separates the dacitic volcaniclastic sequence from andesite breccias in the footwall. Gold is associated with tectonic-hydrothermal breccias, zones of vuggy quartz and veins, and alteration minerals consisting primarily of alunite and dickite with sulfides including pyrite, enargite, and covellite. Spatially, silver is largely separate from gold, and is associated with silicification, very fine grained pyrite, and/or marcasite and enargite. Paragenetic evidence suggests that the silver event may predate the gold event, but that the two may have shared common fluid pathways. A number of other targets are currently being explored on the property, including silicified ledge or rib-style, vuggy quartz-hosted oxide gold, Cu-Au porphyry, and low sulfidation epithermal gold-silver veins.

The geochemical multi-fractal characteristics and mineralization of the Dehelongwa copper-gold deposit

The spatial distribution of ore-forming elements is the result of interaction and influence among multiple factors in the process of mineralization, and is the specific embodiment of non-linearity and coupling of mineralization. The fractal theory has such functions as to characterize non-lineariry and coupling, and can find out the deterministic law from the complicated coupling process. The primary geochemical fractal distribution of metallogenic elements such as Cu and Au possesses the characteristics of multi-fractal distribution in the Dehelongwa copper-gold deposit. Copper follows 2-d fractal distribution, and Au follows 3- or 4-d fractal distribution. The primary geochemical fractal distribution has a certain similarity on the same prospecting line, and this similarity is not obvious among different prospecting lines. The secondary geochemical fractal distribution of Cu and Au is higher in similarity, and simpler than the primary geochemical fractal distribution. These results show that the mineralization of Cu and Au is out of sync and also is inconsistent in this deposit, and the mineralization of Cu mainly experienced two mineralization stages, while the mineralization of Au experienced three to four mineralization stages. Besides the mineralization of Cu and Au shows a certain direction and along the strike of vertical orebodies it is relatively balanced. While along the strike of the ore bodies the mineralization of Cu and Au shows a significant difference. The hypergenic geologic process has a certain effect on the balance of spatial distribution of Cu and Au. From these it can be seen that the mineralization process of this deposit is well characterized by the geochemical fractal distribution of Cu and Au.

Geology of the Riacho do Pontal iron oxide copper-gold (IOCG) prospect, Bahia, Brazil: hydrothermal alteration approached via hierarchical cluster analysis

The Riacho do Pontal prospect is situated on the border between the Borborema Province and the São Francisco Craton, in Bahia state. It comprises rocks polydeformed during the Neoproterozoic. The prospect area includes migmatites and gneissic rocks intruded by several sin- to post-tectonic granites. Structural analysis indicates a strong relationship between the development of ductile to brittle-ductile shear zones and associated hydrothermalism. The main tracts of high-strain rate are represented by the Riacho do Pontal (north) and Macururé (south) shear zones. Several copper occurrences have been mapped within the Riacho do Pontal prospect along secondary shear zones. In these areas, the gneissic rocks were affected by intense hydrothermal alteration. Hierarchical cluster analysis permitted the identification of the main hydrothermal mineral associations present in these rocks, which resulted from potassic (biotite) and sodic-calcic (amphibole-albite) alteration, in addition to silicification and iron alteration (hematite). These hydrothermal alteration types are similar to those typically found in iron oxide copper-gold deposits developed at intermediate crustal levels. Hematite-quartz-albite-chalcopyrite-pyrite hydrothermal breccias host the highest-grade copper ore (chalcopyrite-pyrite-chalcocite) zones. The spatial relationship between copper deposits and shear zones improves the metallogenic potential for copper of the Borborema Province and has important implications for mineral exploration in the region.

Elements Spatial Distribution and Ore Prospecting of the No.II Porphyry Copper - Gold Deposit in the Xiongcun District, Tibet

Xiongcun district is located in the western segment of the Gangdese porphyry copper belt, Tibet. Exploration activities in the No.I, No.II and No.III deposits in the past decade suggest that it would be a large prospective for porphyry copper-gold resources. In this paper, we focus on the systematical research of the elements spatial distribution of the No.II porphyry copper-gold deposit in the Xiongcun district. The results show, from center to the outer parts of the orebody, the elements distribution can be divided into Cu, Au, Ag, K, Mo and Ba → Co, Ni and Mn → Na and Ca → Pb, Zn, Cd, Bi, Sb and As. The No.II deposit is still open down-dip to the north and along the NW-striking, it need to conduct additional exploration.

Characteristics of Magnetic Susceptibility of the Cores in Yinmin Mining Area

Through the work of measuring magnetic susceptibility of the cores in Yinmin mining area, Yunnan, one can draw a conclusion that different strata have different magnetic susceptibility, and variations of magentic susceptibility as a whole have significant changes, concerned primarily with mafic ferruginous lava, iron ore, ferruginous dolomite and fine grained diabase in the Luoxue Group and the Yinmin Group. The study of magnetic susceptibility of the rocks is not only relevant to magnetic prospecting and the boreholetricomponent magnetic, but also a rapid and effective means of geological exploration for the iron-oxide copper gold (IOCG) deposit in Yinmin mining area.

Mineralization and structural features of Kalchouyeh copper-gold deposit (west-central Iran)

The Kalchouyeh copper deposit is located about 110 km east of Isfahan, in the Urumieh-Dokhtar magmatic assemblage (UDMA) arc of Iran. Mineralization is closely associated with the calc-alkaline volcanism of the UDMA arc and controlled by northwest–southeast trending strike-slip faults (Qom-Zefreh and Nain-Baft faults). A pull-apart basin along these strike-slip faults has facilitated the localization of magma and related hydrothermal systems and eventually the development of Kalchouyeh mineralization. Copper mineralization occurs mainly as veins and veinlets and is related to two distinct main stages of hypogene and supergene. Hypogene mineralization includes Cu and Pb sulfides (chalcopyrite, pyrite, galena) and Fe oxide (magnetite). Chalcocite and covellite are found in supergene mineralization. Microthermometric measurements of fluid inclusions on two mineralized veins show the presence of two different kinds of ore fluids: (1) low temperature and salinity in relation to vein A (homogenization temperature 175–252 °C, salinity 0.82–4.23 wt.% NaCl) and (2) low to moderate temperature and salinity in relation to vein B (homogenization temperature 255–324 °C, salinity 0.16–9.32 wt.% NaCl). Copper mineralization at Kalchouyeh appears to be epithermal and low-sulfidation in style, and ore deposition was the result of cooling and surface fluid dilution.

Remote sensing and GIS-based prediction and assessment of copper-gold resources in Thailand

Quantitative integration of geological information is a frontier and hotspot of prospecting decision research in the world. The forming process of large scale Cu-Au deposits is influenced by complicated geological events and restricted by various geological factors (stratum, structure and alteration). In this paper, using Thailand's copper-gold deposit district as a case study, geological anomaly theory is used along with the typical copper and gold metallogenic model, ETM+ remote sensing images, geological maps and mineral geology database in study area are combined with GIS technique. These techniques create ore-forming information such as geological information (strata, line-ring faults, intrusion), remote sensing information (hydroxyl alteration, iron alteration, linear-ring structure) and the Cu-Au prospect targets. These targets were identified using weights of evidence model. The research results show that the remote sensing and geological data can be combined to quickly predict and assess for exploration of mineral resources in a regional metallogenic belt.

Geology and District-Scale Setting of Tilted Alkalic Porphyry Cu-Au Mineralization at the Lorraine Deposit, British Columbia

Lorraine is a copper-gold porphyry deposit (6.4 Mt indicated resource at 0.61% copper and 0.23 g/t gold, and 28.8 Mt inferred resource at 0.45% copper and 0.19 g/t gold) in north-central British Columbia—one of the youngest known alkalic porphyry deposits within the Triassic-Jurassic Quesnel arc. The deposit is hosted by the Early Jurassic Duckling Creek Syenite Complex, an alkalic multiphase intrusive dike complex of pyroxenite, syenite, and monzonite composition. The southern part of the complex hosts numerous copper-gold porphyry prospects in addition to Lorraine; together, they constitute the Duckling Creek district. Main-stage Cu-Au porphyry mineralization at Lorraine is hosted by phase 1 of the Duckling Creek Syenite Complex, an SW-dipping, early intrusive suite of silica-undersaturated pyroxenites and syenites. Mineralized zones are up to 2.5 km long by 500 m wide, in the form of northwesterly elongate, SW-dipping panels that generally parallel the phase 1 intrusive contacts. Mineralization is attributed to “blind” porphyries within the phase 1 sequence, which was tilted after main-stage mineralization. Copper sulfides define deposit-scale zonation patterns of bornite-chalcocite cores rimmed by chalcopyrite-rich and outer, weakly developed pyrite-dominated domains. Alteration patterns and intensity are consistent across mineralized zones. Strong, pervasive K-feldspar-biotite (potassic) core zones are rimmed by albite-diopside-magnetite (calc-potassic) alteration that is pervasive near the center of the zones, but varies laterally outward to vein-style alteration. Pervasive albite alteration (sodic) is locally present and is interpreted to be an early alteration event. Mineralization at Lorraine has been cut by later phases of the Duckling Creek Syenite Complex. A second cycle of pyroxenite-syenite-monzonite intrusion (phase 2) is mineralogically similar to phase 1, but is unmineralized and has vertical intrusive contacts that strike northwest. A change to late, silica-saturated intrusions is marked by subvertical phase 3 silica-saturated leucosyenite and pegmatite dikes. U-Pb zircon and Ar-Ar geochronology constrain the timing of main-stage mineralization at Lorraine to an approximately 1.5 m.y. interval between 180 Ma and 178.5 Ma. Phase 1 intrusions are as old as 181.68 ± 0.95 Ma based on an Ar-Ar age on biotite from pyroxenite, but may range to as young as 180.2 ± 0.28 Ma based on a U-Pb zircon age from a mineralized phase 1 syenite. The upper age limit for mineralization is 178.75 ± 0.21 Ma, based on U-Pb data for a postmineral phase 2 syenite. An alternate interpretation considers the presence of zircon antecrysts in an analyzed phase 1 rock, which leads to a more narrow time window of 0.31 m.y. that includes phase 1 intrusion, main-stage porphyry mineralization, and structural tilting, which was followed by phase 2 intrusion. Magmatic and hydrothermal activity in the Lorraine area persisted until at least 176 Ma, based on the U-Pb zircon age of 176.77 ± 0.36 Ma from a phase 3 leucosyenite dike, and a late biotite-albite-apatite vein with an Ar-Ar biotite age of 175.21 ± 0.91 Ma. Several intrusive-hosted porphyry prospects within the Duckling Creek district share mineralogical and alteration characteristics, as well as relative igneous paragenesis, with Lorraine. The model for magmatic and hydrothermal development at Lorraine may broadly be applied to the district as a whole, providing a geologic framework upon which to base future exploration in the district.

Mantle plumes of Central Asia (Northeast Asia) and their role in forming endogenous deposits

The Phanerozoic within-plate magmatism and the related deposits of Siberia are reviewed. The formation of post-perovskite at about 2.5 Ga in the Earth’s interior and the isotope characteristics of within-plate igneous rocks have shown that plate tectonics and deep geodynamics started to operate at about 2–2.5 Ga. The assembly and breakup of supercontinents under the effect of the superplumes formed in layer D″ is considered. Thus, the supercontinent–superplume cycles spanning about 700 Ma are recognized in the Earth’s history.The manifestations of the within-plate magmatic activity are found throughout the whole Phanerozoic. It was demonstrated earlier that between 570 and 160 Ma, the Siberian continent drifted within the African hot mantle field or large low shear velocity province (LLSVP). At least four plumes, excluding the superplume leading to the breakup of Rodinia at 750 Ma, interacted with the Siberian continent. The superplume leading to the breakup of Rodinia was also responsible for the origin of ultramafic intrusions with carbonatites hosting rare-metal (Nb, Ta, REE) mineralization as well as ultramafic–mafic intrusions with Cu–Ni–Pt mineralization localized along the rift zones.The plumes originated in other Phanerozoic cycles formed most likely at the lower-upper mantle boundary, where most of the stagnant slabs is accumulated. Those plumes were responsible for the origin of within-plate igneous rocks. The granitic batholiths formed in the centers of zonal area surrounded by rift zones containing abundant rare-metal intrusions with rare-metal mineralization. Gold, tin, base metal, and porphyry copper deposits are also related to these zonal area.The studies have shown that the formation of folded zones and related deposits which surround these zones as well as the structures of cratons and their metallogenic specialization should be considered in terms of both plate tectonics and plume tectonics.

Structural and Lithological Controls on Iron Oxide Copper-Gold Deposits of the Southern Selwyn-Mount Dore Corridor, Eastern Fold Belt, Queensland, Australia

The Eastern fold belt of the Proterozoic Mount Isa inlier has undergone numerous episodes of deformation, hydrothermal alteration, and iron oxide copper-gold mineralization. The structural and lithological controls on the location and geometry of five iron oxide copper-gold deposits (Starra, Mount Elliott, SWAN, Mount Dore, and Lady Ella) in the Selwyn-Mount Dore corridor were studied through geologic mapping, core logging, structural analysis, and examination of 3-D grade distribution. All the deposits in this area occur in close proximity to the Selwyn shear, a long-lived, regional structure which developed at the contact between carbonate-rich and siliciclastic-dominated rock packages. This fault and a series of subparallel structures have been the focus of multiple reactivation events and have controlled the distribution of alteration and mineralization, which occurred in this area at ~1595, 1570, 1530, 1515, 1500, and 1485 Ma. Ironstone-hosted mineralization at Starra developed in a preexisting zone of sodic and iron oxide alteration along the N-striking Starra shear. Kinematic indicators along the Starra shear reveal that it has been reused numerous times; early D2 thrusting, post-D2 sinistral shearing, and pre-D4 (syn-D3?) dextral brittle faulting were all associated with sodic, sodic-calcic, and iron oxide alteration. Either the post-D2 or pre-D4 strike-slip faulting events can explain the steeply plunging nature of the orebodies at Starra. However, the dextral pre-D4 event produces dilational structures in ironstones and is associated with regionally important sodic and iron oxide alteration along NE- to ENE-trending faults, which intersect the Starra shear close to the main orebodies; we consider this the more likely main mineralizing event at Starra. Both strike-slip faulting events correspond with a change from E-W–oriented compression during the main phase of the Isan orogeny to transpression that may have been driven by crustal overthickening during orogenesis. At Mount Elliott and SWAN, mineralization is associated with post-D4 dextral and reverse movement across a sinistral fault jog along the NNW-striking Mount Elliott fault during transpression. Mineralization, alteration, and veins at these deposits clearly overprint all ductile structural features. Overall, the orebody geometry is controlled by the orientation of the Mount Elliott fault, but high-grade ore shoots are controlled by breccia formation in elongate pods which are parallel to preexisting F2 fold axes. In contrast, gently plunging grade shells at the slightly younger Mount Dore and Lady Ella deposits formed in response to renewed E-W compression and reverse displacement along N- to NE-striking fault segments of the Mount Elliott fault and newly formed subparallel faults. Examination of the structural setting of Mount Dore and Lady Ella also demonstrates that strain partitioning between mechanically heterogeneous rock sequences (metasedimentary rocks, metabasalts, granite, and strongly silicified rock types) exerted strong controls on the location of later mineralized systems. The important episodes of iron oxide copper-gold mineralization in the Eastern fold belt between 1595 and 1485 Ma appear to be associated temporally with compressive or transpressive structural regimes. These events developed in response to far-field tectonic stresses that evolved in response to the collision of Laurentia with the proto-Australian continent during the Isan orogeny. Late in the orogenic history, the emplacement of voluminous A-type batholiths associated with hot-spot plume activity likely generated localized transient shortening events, which are also associated with iron oxide copper-gold mineralization. This unique geodynamic evolution was responsible for the large-scale metal enrichment and remobilization into suitable chemical and structural traps over significant time periods in the Eastern fold belt iron oxide copper-gold district.

The Lepanto Cu–Au deposit, Philippines: A fossil hyperacidic volcanic lake complex

Hyperacidic lakes and associated solfatara in active volcanoes are the expression of magmatic gas expansion from source to surface. Here we show for the first time, that the vein system that comprises the~2Ma high-sulfidation, Lepanto copper–gold deposit in the Mankayan district (Philippines) was associated with a contemporary hyperacidic volcanic lake complex—possibly the first such lake recognized in the geological record. A 15–20‰ difference in sulfur isotopic composition between barite and sulfides and sulfosalts in the vent fumarole encrustations supports the interpretation that SO2-rich volcanic gas vented into the base of the lake and marginal to it and ties the mineralization directly to magmatic gas expansion, fracture propagation, and mineralization that occurred through a series of decompression steps within the feeder fracture network. These data confirm that crater lake environments such as Kawah Ijen (Java, Indonesia) provide modern day analogs of the Lepanto and other high sulfidation Cu–Au depositing environments.We also provide extensive analysis of sulfosalt–sulfide reactions during vein formation within the hyperacidic lake complex. Pyrite± silica deposited first at high temperature followed by enargite that preserves the vapor–solid diffusion of, for example, antimony, tin, and tellurium into the vapor from the crystallizing solid. Subsolidus, intra-crystalline diffusion continued as temperature declined. Pyrite and enargite are replaced by Fe-tennantite in the lodes which initially has low Sb/(Sb+As) atomic ratios around 13.5% close to the ideal tennantite formula, but evolves to higher ratios as crystallization proceeds. Fumarole encrustation clasts and sulfosalts in the lake sediment are more highly evolved with a larger range of trace element substitutions, including antimony. Substitution of especially Zn, Te, Ag, and Sn into tennantite records metal and semi-metal fractionation between the expanding magmatic gas and deposited sulfide sublimates provides a rare insight into the fate of metals and semi-metals in the shallower parts of fracture arrays that feed modern hyperacidic lakes.These data support a growing understanding of the formation of high-sulfidation gold deposits as the consequence of single-phase expansion of gas from magmatic-gas reservoirs beneath the surface of active volcanoes without the intervention of a later aqueous fluid including groundwater. Aggressive sulfide–sulfosalt reactions, including pitting and the almost complete dissolution of earlier minerals, are persistent characteristics of the vein assemblages and precious metals typically occur late in pits or along brittle fractures. These characteristics support a hypothesis of mineral deposition at temperatures of the order of 600°C in contrast to available fluid inclusion data from enargite that record temperatures following phase transitions in the sulfosalt during the retrograde devolution of the deposit in the presence of groundwater.

Geological Characteristics and Exploration Potential of the NO.III Deposit in the Xiongcun District, Tibet, China

The Xiongcun district is located along the south margin of the Gangdese porphyry copper belt, approximately 53 km west of the Xigaze. No.III deposit is a newly discovered porphyry copper-gold deposit in the Xiongcun district. This paper first reports geological characteristics and exploration potential of No.III deposit. No.III deposit is hosted by Early Jurassic hornblende quartz diorite porphyry. Pervasive alteration is dominated by a well-mineralized potassic alteration. Major ore-bearing vein types include quartz-sulfide and chlorite-sulfide veins. Drilling holes and geochemical anomaly indicated the No.III deposit has excellent potential for exploration.

Petrogenesis and mineralization of the Fenghuangshan skarn Cu–Au deposit, Tongling ore cluster field, Lower Yangtze metallogenic belt

The Fenghuangshan copper–gold deposit, located in the Tongling ore cluster field along the Lower Yangtze metallogenic belt (LYRB) in eastern China, mainly consist of skarn ores hosted in granodiorite. U–Pb dating of magmatic zircons from Fenghuangshan granodiorite yields a weighted mean 206Pb/238U age of 143.1±1.6Ma. Five molybdenite samples collected in the Fenghuangshan deposit yield a Re–Os isochron age of 141.7±0.8Ma, demonstrating that the ore formation event is coeval with the Fenghuangshan granodiorite intrusion. The magmatic zircon ƐHf(T) values vary from −12.0 to −28.3, corresponding two-stage Hf model ages between 1.6Ga to 2.4Ga. Geochemical and isotopic signatures suggest that the Fenghuangshan granodiorite resembles adakite, which was derived from partial melting of the subducted oceanic crust towards LYRB during the early Cretaceous. The occurrence of inherited zircons shows the intrusive granodiorite was assimilated by old crustal materials during its emplacement. The biotite thermobarometry, zircon Ce(IV)/Ce(III) ratios and Eu anomalies coincidently demonstrate that the magma source of granodiorite was under high to moderate oxidized condition, conducive to Cu–Au mineralization. The sulfide ores in Fenghuangshan deposit are enriched in Pd and Pt, which could also be a consequence of the high oxidized magma source. The high Re abundance in molybdenite and platinum group element (PGE) contents of sulfide ores suggest that the ore-forming materials are characterized by mixed sources from the mantle and crust, and were slightly affected by hydrothermal alteration.

In situ LA–MC–ICP–MS U–Pb geochronology of igneous rocks in the Ashele Basin, Altay orogenic belt, northwest China: Constraints on the timing of polymetallic copper mineralization

The Altay orogenic belt of Kazakhstan hosts a world-class polymetallic copper volcanogenic massive sulfide (VMS) metallogenic belt, and the eastern margin of this belt extends into the southern Chinese Altay. The Ashele Basin is located at the western end of the Chinese Altay and borders Kazakhstan. The basin hosts the large Ashele copper–zinc deposit, which is a typical VMS deposit and the largest deposit in the Ashele Basin, and it hosts the subvolcanic-hosted medium-sized Sarsuk polymetallic gold deposit. Both of these deposits are hosted in the Ashele Formation volcanic sequence. The Ashele copper–zinc orebodies are stratabound orebodies located between basalt and tuff units, and were formed during exhalative sediment deposition; in comparison, the Sarsuk gold–copper–lead–zinc orebodies are hosted by rhyolite porphyry that contains disseminated, veinlet, and veinlet–stockwork ore that formed during intrusion of the rhyolite porphyry. This study presents new zircon LA–MC–ICP–MS U–Pb analyses of six volcanic and subvolcanic units, and dikes associated with the Sarsuk and Ashele deposits. The ore-bearing rhyolite porphyry, diabase dike, basalt, tuff, and dacite porphyry samples analyzed during this study yielded ages of 382.0–382.8, 381.7, 388.2, 387.0, and 379.4Ma, respectively. These data indicate that the Ashele Formation formed during the Early–Mid-Devonian (375–402Ma), whereas the Ashele copper–zinc deposit formed during the Middle Devonian (388–387Ma) and the Sarsuk polymetallic copper–gold deposit formed during the latest Middle Devonian (382Ma). Inherited zircons within the six samples analyzed during this study yielded U–Pb ages of 618–2294Ma, suggesting the presence of Precambrian crystalline basement within the Altay orogenic belt.