Geology Of Ore Deposits Research Articles

Compound criticality of bauxite production: implications for sustainability and trade neo-colonialism

We describe bauxite as having compound criticality. (1) It is a critical raw material (CRM) from which alumina and thereby aluminium are produced, and aluminium has the highest production levels of all metals deemed significant to the Clean Energy Transition. (2) Gallium is a by-product CRM, extracted during alumina refining. (3) Multiple other CRM by-products could be extracted during alumina refining: scandium, lithium, cobalt, titanium and REE. (4) Production is profoundly influenced by price inelasticity (for by-products), regime instability of bauxite production and supply chain bottlenecks. We review the geology of bauxite ore deposits as a function of complex CRM supply potential, and interrogate the trait of criticality using four of the world's dominant producer nations of bauxite and potential patterns of value addition from raw materials to refined products. Trade agreements and mitigation strategies to ensure security of supply in consumer regions prioritize removal of low-cost bauxite by large-scale mining operations and shipping of unprocessed ore at high CO 2 footprint from producer nations. Ore-refining nations have investments that are deemed extractive because they remove large quantities of raw material for export with minimal or no in-country processing and they can also place producer nations in debt. Opposition to neo-colonial debt-trap policies and extractive practices increases regime instability and thereby criticality. We highlight how societal-environmental-political interactions and the mineral-energy nexus in the bauxite-aluminium supply chain are subject to increasing turbulence, which may reshape the geographies of supply chains.

Preface to the Second Part of the Special Issue of the Journal Geology of Ore Deposits Dedicated to Porphyry and Related Deposits of Northern Eurasia

Preface to the Second Part of the Special Issue of the Journal Geology of Ore Deposits Dedicated to Porphyry and Related Deposits of Northern Eurasia

Kalyuzhnyite-(Ce), NaKCaSrCeTi(Si8O21)OF(H2O)3, a new mineral from the Darai-Pioz alkaline massif, Tien-Shan mountains, Tajikistan: mineral description, crystal structure and a new double (Si8O21) sheet

AbstractKalyuzhnyite-(Ce), ideally NaKCaSrCeTi(Si8O21)OF(H2O)3, is a new mineral from the Darai-Pioz alkaline massif, Tien-Shan mountains, Tajikistan. It occurs as equant grains up to 0.05 × 0.07 mm in a quartz–pectolite aggregate in a silexite-like peralkaline pegmatite. Associated minerals are quartz, fluorite, pectolite, baratovite, aegirine, leucosphenite, neptunite, reedmergnerite, orlovite, sokolovaite, mendeleevite-(Ce), odigitriaite, pekovite, zeravshanite, kirchhoffite and garmite. The mineral is colourless with a vitreous lustre and a white streak, and Dcalc. is 3.120 g/cm3. Kalyuzhnyite-(Ce) is monoclinic, P2/c, a = 18.647(4), b = 11.214(2), c = 14.642(3) Å, β = 129.55(3)° and V = 2360.9(11) Å3. The chemical composition of kalyuzhnyite-(Ce) is Nb2O5 0.53, TiO2 0.16, SiO2 43.85, Er2O3 0.13, Ho2O3 0.10, Gd2O3 0.09, Sm2O3 0.47, Nd2O3 6.22, Pr2O3 1.21, Ce2O3 6.34, La2O3 0.82, PbO 4.90, BaO 0.85, SrO 11.39, CaO 1.86, Cs2O 3.80, K2O 1.59, Na2O 2.99, H2O 5.24, F 1.55, O = F –0.65, total 100.31 wt.%. The empirical formula calculated on 26.11 (O + F) apfu is Na1.07K0.37Cs0.30Sr1.21Ca0.37Pb0.24Ba0.06(Ce0.43Nd0.41Pr0.08La0.06Sm0.03Gd0.01Er0.01Ho0.01)Σ1.04(Ti0.97Nb0.04)Σ1.01Si8.06O25.21F0.90H6.42, Z = 4. The simplified formula is (Na,□)(K,Сs)(Ca,Pb,Sr,Na)SrLn3+Ti(Si8O21)OF(H2O)3, where Ce is the dominant lanthanoid. The crystal structure was solved by direct methods and refined to an R1 index of 2.74%. In kalyuzhnyite-(Ce), the main structural units are a heteropolyhedral Na–Sr–Ce–Ti sheet, ideally [NaSrCeTiOF]7+, and a double (Si8O21)10– sheet parallel to (010). In the Si–O sheet, the Si tetrahedra form ten-membered rings. This is the first occurrence of such a double Si–O sheet in a mineral. The two sheets connect via common vertices of Na-, Sr-, Ce- and Ti-polyhedra and SiO4 tetrahedra to form a framework. The interstitial cations and H2O groups, ideally [(CaK)(H2O)3]3+, occur within the Si–O sheet. The mineral is named in honour of Vasily Avksentievich Kalyuzhny (1899–1993) in recognition of his contributions to the geology of ore deposits of Komi Republic (USSR) and the mineralogy of granitic pegmatites (Tajikistan).

Anisim Efremovich Malakhov (1899–1989) and former malakhovite (now khesinite)

Anisim Efremovich Malakhov, a prominent specialist in the fi eld of geology of ore, non-ore and rare metal deposits of the Urals. For about 30 years he headed the Department of Geology of Ore Deposits and Coal and Non-Metal Deposits of the Faculty of Exploration Geology at the Sverdlovsk Mining Institute. In honor of Anisim Efremovich, a new mineral was named – malakhovite, calcium, magnesium and iron silicate, which was discovered by B. V. Chesnokov in the burnt dumps of the Chelyabinsk coal basin. The International Mineralogical Association did not approve it as a new mineral species, and recently a natural analogue of malachovite, hesinite, was found in Israel.

Current actual issues of gold meniralization of the Central Kyzylkum

As a result of the analysis of the data available and collected in recent years, in contrast to the well-established ideas about the polygenic and poly-stage nature of the mineralization, it is indicated that the gold mineralization of the Central Kyzyl Kum is formed as a result of the formation of a single ore-magmatic system, which develops in the same type regardless of the composition and age of the host rocks; during the formation of deposits, the most important thing is the presence of a process that promoted ore formation, which should serve as the basis for judgements in problems of the genesis and forecasting of industrial facilities. Some problematic issues on the geology of ore deposits are noted.

Gabbroids of the Bazhenov gabbro-hyperbasite massif (Middle Urals): Material composition and age

Research subject. Saussurite-amphibole rocks (metagabbroids) of the Bazhenov gabbro-hyperbasite massif (eastern sector of the Middle Urals).Materials and methods. The material composition of metagabbroids and their mineralogy were studied in the analytical laboratories of the Institute of Geological Geology, Ural Branch, Russian Academy of Sciences (Ekaterinburg), Urals State Mining University (Ekaterinburg), Institute of Mineralogy, Ural Branch, Russian Academy of Sciences (Miass), Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences (Moscow), and Moscow State University (Moscow). Isotope analyzes of zircon were performed on a SHRIMP-II ion microanalyzer at the Center for Isotope Research of VSEGEI (St.Petersburg).Results. The metagabbroids under study feature the following mineral composition: clinozoisite (zoisite, epidote), magnesian hornblende (pargasite, tremolite), albite, clinochlore, and dolomite. According to petro-geochemistry data, saussurite-amphibole rocks were formed after gabbronorites and olivine gabbro-norites, belonging to the alpine-type formation of gabbro-hyperbasite complexes. U-Pb dating showed the ancient age of zircons from metagabbroids, most of the analyzes are grouped below the concordia line, forming a discordia line, the upper intersection of which with the concordia corresponds to the age of 1992 Ma. Two points on the diagram located below the concordia line, although not falling on the continuation of the discordia line, apparently reflect the influence of intermediate stages of metamorphism, and two points with concordant ages of 256 and 251 Ma record the time of the last tectono-thermal episode.Conclusions. The formation of saussurite-amphibole rocks took place under the conditions of greenschist facies. In local areas of the massif, metamorphism reached the zeolite facies with signs of hydrothermal reworking. The primary gabbroids of the Bazhenov massif were most likely formed under the conditions of a suprasubduction basin. The age of zircons of about 2 Ga obtained by the U-Pb method indicates that the crystallization of the studied zircons occurred in the mantle rocks. It is not yet possible to unambiguously explain the presence of grains of these zircons in the metagabbroids of the Bazhenov massif; several possible explanations have been proposed. Zircons with the youngest age (256 and 251 Ma) were most likely formed as a result of metamorphic transformations under thermal influence from the nearby Aduy granite-leucogranite complex.

Pavel Ivanovich Kutyukhin (1899–1962) and former kutyukhinite (now kumtyubeite)

Pavel Ivanovich Kutyukhin, a prominent specialist in geology and mineralogy of gold, rare metal and tungsten deposits of the Urals. For about 15 years he headed the departments of exploration and geology of ore deposits of the Geological Exploration Faculty at the Sverdlovsk Mining Institute. In honor of Pavel Ivanovich, a new mineral was named – kutyukhinite, calcium fluorosilicate, which was discovered by B. V. Chesnokov in the burnt dumps of the Chelyabinsk coal basin. The International Mineralogical Association did not approve it as a new mineral species, and recently a natural analogue, kumtyubeite, was found in the North Caucasus.

The Bahariyeh iron oxide copper–gold deposit, Khaf-Khashmar-Bardaskan magmatic belt, NE Iran: Constraints from geochemical, fluid inclusions, and O-S isotope studies

The Bahariyeh deposit is located in the central segment of the Khaf-Kashmar-Bardaskan magmatic belt (KKBMB), northeast Iran. Previous U-Pb data on zircon revealed an age of 38–41 Ma for the felsic-intermediate intrusions. The stockwork like vein orebodies are hosted in Eocene monzodiorite porphyry rocks which have strong structural controls imposed by the Great Dorouneh Fault System. Hydrothermal alteration is dominated by silicification, propylitic (chloritization), argillic, and sericitic zones. The mineralized veins in the Bahariyeh deposit can be divided into seven types: 1) quartz ± pyrite; 2) quartz + specular hematite + pyrite ± gold; 3) quartz + chalcopyrite + pyrite; 4) quartz + specular hematite + chalcopyrite + pyrite ± sphalerite ± galena ± gold; 5) chalcopyrite + specular hematite + pyrite ± gold; 6) specular hematite ± pyrite; and 7) chalcopyrite + pyrite. The various vein-style orebodies contain high concentrations of Cu, Au, Pb, Zn, and Ag. Microthermometric measurements of fluid inclusions in mineralized veins demonstrate homogenization temperatures in the range of 271–500 °C (mode of 300 °C), and corresponding salinities in the range of 7.9–26.3 wt% NaCl equivalent. The δ18OWater values calculated from δ18O of quartz, and the δ34S values of chalcopyrite reveal a dominantly magmatic origin for the ore-forming fluids. The fluid inclusions indicate that mixing between magmatic fluids and meteoric water, together with cooling, are the dominant mechanisms for metal deposition in the Bahariyeh district. The combination of ore deposit geology, alteration type, fluid evolution processes, and O–S isotope data suggest that the Bahariyeh deposit be classified as a Cu ± Au-rich iron oxide-copper–gold (IOCG) system.

Geology and Structural Evolution of the La Huifa Ore Deposit, Central Chile: A Newly Discovered Porphyry Cu-Mo System in the El Teniente District

Abstract La Huifa is a breccia-related Cu-Mo porphyry deposit located in the Andes of central Chile, 3 km northeast of the giant El Teniente porphyry Cu-Mo orebody. It was discovered as part of CODELCO’s (Corporación Nacional del Cobre de Chile) brownfield exploration activities in the El Teniente district. It is the first major discovery in the area, and this work presents its first detailed geologic description. The La Huifa orebody is related to a complex of late Miocene diorite and granodiorite intrusions and hydrothermal breccias, the latter characterized by abundant tourmaline-anhydrite cement, emplaced in middle to late Miocene volcanic and subvolcanic rocks. The structural architecture of La Huifa is dominated by WNW-and NE-striking high angle faults. Usually, slip on the WNW-striking faults involves a sinistral component, whereas slip on the NE-striking faults is predominantly dextral. The main hydrothermal breccia body at La Huifa is located at the intersection of WNW- and NE-striking faults. Four stages are proposed for the tectono-magmatic-hydrothermal evolution of La Huifa:Premineralization, involving tourmaline-albite veins and sodic calcic alteration emplaced under a transpressive tectonic regime with a subhorizontal, ~E-W–trending σ1 (~N-S–trending σ3);Early mineralization, involving a polydirectional vein system associated with poorly developed potassic and transitional alteration zones with a scarce presence of Cu and Mo sulfides;Main mineralization, involving Cu- and Mo-rich anhydrite-tourmaline hydrothermal breccias and polydirectional veins associated with strong chlorite-sericite alteration with a 270° to 290°C emplacement temperature, obtained from chlorite geothermometry. The regional stress field during this period was exceeded by the local fluid pressure. These breccias and veins are followed by the emplacement of NE-striking C and D type veins associated with gray and white sericite alteration, respectively, which show a similar temperature range.Late mineralization, involving a NE-striking, carbonate-rich vein system containing polymetallic sulfides. It is associated with argillic alteration, whose temperature was 200° to 260°C. This stage occurred under a compressive tectonic regime with NE-trending σ1. The relatively low temperature at which mineralization was introduced in this deposit (~270°–290°C) and the predominantly vertical fluid flow pattern typical of hydrothermal breccia systems allow us to infer the presence of more mineralized rock at depth, below the recognized portion of the system. The association of Cu and Mo enrichment with chlorite-sericite alteration, instead of higher-temperature potassic or gray sericite alteration events, makes La Huifa a unique case among the porphyry deposits of central Chile and broadens the scope of mineralization styles that could be targeted in this belt. Finally, the intersection of arc-oblique, high-angle faults and, in particular, the presence of fault systems orthogonal to the main compression direction, favorable for magma storage and differentiation and metal concentration, constitute a valuable tool for exploring porphyry Cu deposits in similar geologic contexts.

Geology, mineralogy and geochemistry of manganese ore deposits of the Um Bogma Formation, south-western Sinai, Egypt: genesis implications

Purpose.This paper aims to understand the genesis and nature of the manganese ore deposits associated with the Ras Samra Member of the Um Bogma Formation in the southwest of Sinai. Methods. Mineralogical and geochemical studies of 50 selected samples of manganese ores and host shale have been conducted. These samples have been taken from different sites representing the Ras Samra Member. Findings. The dominant manganese minerals are pyrolusite and hausmannite. In most samples, helvite and hematite are noted in association with pyrolusite. In the investigated manganese ores, wide ranges of MnO (17.70-81.90 wt. %) and Fe2O3 (1.16-65.49 wt. %) concentrations are observed. Based on their Mn/Fe ratio, they can be classified into high-Mn ore content (76.94-6.46%), medium-Mn ore content (4.87-2.58%), and low-Mn ore content (1.51-0.30%). Originality. The compositions of major and trace elements in Ras Samra manganese ores, together with their textures and mineralogical compositions, suggest an epigenetic hydrothermal contribution for high-Mn ores, as well as syngenetic sedimentary precipitation for medium- Mn and low-Mn ores. The epigenetic nature of the high-Mn samples may be related to a younger phase of hydrothermal activity associated with Tertiary basalt flows. Ore-bearing hypogene solutions, which penetrate the bedding planes, have impregnated and cemented non-diagenetic terrigenous sandstones and shale. Practical implications. In contrast to low-Mn ores, high-Mn and medium-Mn ores of Um Bogma are preferable for obtai-ning a significant economic effect in the production of ferromanganese alloys. However, low-Mn ores need to be processed appropriately to achieve the desired quality in order to meet the present level of manganese demand in Egypt.

Using titanite to constrain geochronology and physicochemical conditions of hydrothermal mineralization events: A case study of the Duotoushan Fe–Cu deposit, Eastern Tianshan, NW China

As a common Ca‐ and Ti‐ bearing silicate mineral in many types of hydrothermal deposits, titanite usually contains high concentrations of trace elements. Its mineral chemistry and U–Pb isotope can reveal the physicochemical conditions and geochronology of the ore‐forming systems. In this contribution, we present a detailed study on titanite which precipitated during the Fe mineralization in the Duotoushan deposit. Due to coexistence with hydrothermal minerals, low Th/U ratios (0.02–0.3), and depletion in rare earth elements (REE), all the studied titanites are classified into a hydrothermal group. The negative correlation between [REE3+ + (Al, Fe)3+] and [Ca2+ + Ti4+] indicates that REE mainly entered the lattice of titanite via the mechanism of substitution. In addition, titanite grains are characterized by HREE, Zr, and Nb enrichments with LREE depletion, suggesting that the complexation of F− at neutral to alkaline pH conditions may have caused the fractionation of REE. At Duotoushan, the titanite grains coexist with quartz, epidote, amphibole, and magnetite, and exhibit positive Eu anomalies (δEu = 1.04–1.31) but lack Ce anomalies, indicating that ore‐forming fluids may have been derived from a relatively low oxygen fugacity and high fH2O environment. Titanite yielded an in‐situ U–Pb lower‐intercept age of 307.2 ± 4.8 Ma (MSWD = 0.97), consistent with the syn‐ore amphibole 40Ar‐39Ar plateau age (305 ± 6 Ma). Since the mineralization ages are obviously younger than country rocks, the previous syn‐sedimentary ore‐forming model for Duotoushan Fe–Cu mineralization can be excluded. Integrating the characteristics from ore deposit geology, periods of mineralization events, and spatial–temporal distribution of magmatism, we proposed that the Duotoushan Fe–Cu mineralization event may be linked with a hidden granite in its orefield.

Zn–S isotopic fractionation effect during the evolution process of ore-forming fluids: A case study of the ultra-large Huize rich Ge-bearing Pb–Zn deposit

The fluid evolution process is a key research subject in the field of ore deposit geology. An accurate inversion of the evolution history of ore-forming fluids (OFFs) can play a crucial role in the investigation of mineralisation processes and metallogenesis. In addition, analysing the combination of Zn–S isotopes eliminates the uncertainty and unilaterality of monoisotopic tracing and provides a more accurate interpretation of the evolution of OFFs during the mineralisation process. To trace the migration direction and evolution process of OFFs, based on a collected and tested batch of Zn–S isotope compositions, the characteristics of Zn–S isotopic fractionation and the type of metallogenesis were comprehensively analysed to determine the basis for building a metallogenic model of the Ultra-large scale Huize rich Ge-bearing Pb–Zn Deposit, composed of Kuangshanchang deposit and Qilinchang deposit. Previous studies have shown that OFFs migrate upward from deep sections, whereas stratum brine and atmospheric precipitation containing reduced S migrate downward from shallow sections. Rayleigh fractionation of Zn–S isotopes occurred during the migration and evolution of OFFs, resulting in the accumulation of the heavier isotopes of Zn and S present in the fluids. For example, from shallow to deep sections, δ34S values were 5–9‰ (2400–2200 m), 8.5–17.2‰ (1900–1400 m), and 13.6–15.2‰ (1274 m), the δ66Zn values of ore minerals in Qilinchang were 0.205–0.307‰ (1832–1840 m) and 0.203–0.247‰ (1261 m), while the δ66Zn values of ore minerals in Kuangshanchang were 0.290–0.424‰ (1752 m), 0.169–0.3157‰ (1463 m), and 0.033–0.123‰ (1274 m), respectively. Consequently, the isotopic composition of sulfides exhibited an obvious spatiotemporal zoning. Heavier Zn isotopes and lighter S isotopes gradually accumulated in the sulfides at increasingly shallow depths; temporally, the sulfides gradually enriched in heavier isotopes between the early and late stages of mineralisation.

In-situ S–Pb isotopic and trace elemental compositions of sulfides from the Habo Au polymetallic deposit: Evidences for vein-type Au mineralization in the Ailaoshan Au belt

The Habo Au polymetallic deposit is located in the south of the Ailaoshan-Red River tectonic zone. Mineralization is controlled by a strike-slip fault, which was intruded by aplite. Ore minerals are dominated by pyrite and arsenopyrite. Gold is invisibly and ionically bound in pyrite and arsenopyrite. Three hydrothermal alteration-mineralization stages can be identified: quartz-pyrite (py1) ± arsenopyrite vein associated with sericite alteration (I), quartz-pyrite (py2)-polysulfide (II) and quartz-calcite (III). The aplite yielded zircon U − Pb ages of ca. 35.4 Ma while the sericite in pyritized siltstone yielded an Ar-Ar age of ca. 37.5 Ma, constraining the mineralizing age. In situ S–Pb isotopic compositions for sulfides were measured by fs-LA-MC-ICP-MS. Sulfides from the deposit show uniform δ34S values ranging from –5.1‰ to + 2.5‰, a typical characteristic of magmatic-derived S. Pb isotopic compositions of galena are similar to those of the granite in the Habo granite complex, suggesting that the metal is probably sourced from the Habo granite complex. In-situ LA-ICP-MS spot analysis indicates that py1 has high Ni, Co, As and Se concentrations while py2 contains higher concentrations of Au, As, Cu, Pb and Zn. These characters reveal that the ore-forming fluids are As-rich and largely unsaturated with respect to Au. Based on the ore deposit geology, dating and isotopic data, the Habo Au polymetallic deposit mineralization is similar to typical intrusion-related vein-type deposit, formed by fluids originated from magma differentiations of the Habo granite complex.

Geology and geochemistry of Bukan iron ore deposits, Ductile Shear Zone, Northwest Iran

Geology and geochemistry of Bukan iron ore deposits, Ductile Shear Zone, Northwest Iran

Mechanisms for invisible gold enrichment in the Liaodong Peninsula, NE China: In situ evidence from the Xiaotongjiapuzi deposit

Mechanisms for invisible gold enrichment hosted within Paleoproterozoic Fe-rich metamorphic rocks (marble, biotite schist, and quartz-feldspar schist) in the Liaodong Peninsula, NE China are still unclear. In this study, we choose the Xiaotongjiapuzi deposit as a case study, and present a detailed ore deposit geology and dataset of in situ chemical compositions of Fe-sulfides to address this issue. Fe-sulfides have the following paragenesis: metamorphic pyrite (Py0), first-ore stage pyrite (Py1, Py2), and a second-ore stage comprising arsenopyrite (Apy1, Apy2) and two phases of marcasite (Mas(a-b)). Early metamorphic pyrite (Py0) has relatively low concentrations of Au (<0.06–0.17 ppm). The significantly higher concentrations of Au in Py2 (1.55–423 ppm) and Apy2 (105–341 ppm) than those of Py1 (0.068–0.123 ppm) and Apy1 (2.90–7.70 ppm) suggest that gold prefers to incorporate into non-stoichiometric hydrothermal Fe-sulfides. Substitution of As1- and As3+ in Fe-sulfides may account for the coupled geochemical behavior between As and Au, Ag, Pb, Zn, Cu. Replacement led to fractured Py1 becoming enriched in Au, As, Ag, Cu, Sb and Pb, and Py0 being replaced by Au, As, Ag, Cu, Sb and Pb-rich marcasite. In situ sulfur analysis shows that Py0 has highly positive δ34S values (+13.62 to +18.55‰), suggesting it is associated with metasediments (+14 to +20‰). Py1, Py2, Apy1, and Apy2 are isotopically homogeneous and have δ34S values of +3.67 to +7.50‰, indicative of a magmatic phase. Both generations of marcasite, which replaced Py0, have yielded mixed sulfur isotopic signatures (δ34S values of +8.66 to +13.18‰). The gold mineralization in the Xiaotongjiapuzi gold deposit was the result of magmatic-hydrothermal processes. We propose two key factors: i) abundant defects in non-stoichiometric Fe-sulfides, and ii) replacement processes can cause invisible gold enrichment in Fe-sulfides in the Liaodong Peninsula. This provides a new perspective for invisible gold mineralization in other similar regions worldwide.

Genesis of carbonate-hosted Zn-Pb deposits in the Late Indosinian thrust and fold systems: An example of the newly discovered giant Zhugongtang deposit, South China

The Sichuan-Yunan-Guizhou triangle region contains numerous economically important carbonate-hosted Zn-Pb deposits that occur in the Late Indosinian thrust and fold system rather than foreland basin. In this paper, we investigate the thrust-controlled Zhugongtang deposit (>30.0 Mt ores @ 6.76 wt% Zn and 2.27 wt% Pb) as a case study, using ore deposit geology, in-situ trace elements and isotopes in sulfides, to provide new insights into the ore genesis of the MVT deposits in the thrust belts. The sulfide orebody is structurally controlled by a kilometer-scale thrust system and occurs as open-space fillings, vein or replacement structures. Trace elements in pyrite show a low concentration of Co, Ni, Tl and Se, suggesting that the sulfides were formed under low-temperature (100–250 °C) and slightly reduced conditions. The δ13CPDB values (−7.53 to +1.73‰) in calcite lie between the marine carbonate rocks and sedimentary organic matter, and the calculated δ18Ofluid values (+3.40 to +13.36‰) are different from that of marine carbonate rocks but partly overlap with the basinal brines. Such C-O isotope signature indicates that the carbon was mainly derived from the host rocks (limestone) with additional contribution from organic carbon. The oxygen isotope values suggest mixing of the basinal brine and the limestone. The δ34S values of sulfides within Permian strata (+12.2 to +15.3‰) and Devonian strata (+18.5 to +23.8‰) are similar to the coeval seawater sulfate within the ore-hosting strata, respectively. This indicates that the reduced sulfur is originated from evaporative sulfate within host rocks by thermo-chemical reduction in the near-close system. In-situ Pb isotopic ratios of galena (206Pb/204Pb = 18.566–18.758, 207Pb/204Pb = 15.757–15.769 and 208Pb/204Pb = 39.061–39.366) are comparable with the Proterozoic basement and the country rocks, indicating the mineralizing metals were mainly derived from basement rocks and partly extracted from country rocks via fluid-rock interaction. Regional geological evidence indicates the timing of Zn-Pb mineralization of Zhugongtang is Late Triassic to Early Jurassic and related to the Indosinian orogeny. Overall, the newly obtained trace element and isotopic data together with geological evidence suggest that the Zhugongtang deposit is an MVT deposit formed in the orogenic thrust belt and that fluid mixing was critical for the ore formation.

Geology, alteration geochemistry, and exploration geochemical mapping of the Ertsberg Cu-Au-Mo district in Papua, Indonesia

The Ertsberg-Grasberg district hosts the world's largest Cu-Au(Mo) skarn system. The mineralization is related to the Pliocene Ertsberg- and Grasberg intrusive complexes, which intruded the Jurassic-Cretaceous Kembelangan Group siliciclastics and Cenozoic New Guinea Limestone Group. Despite previous studies, elemental migration across the porphyry-skarn system and across the different ore stages is still unclear. Here, we attempt to tackle this issue by integrating ore deposit geology, alteration/mineralization paragenesis, whole-rock geochemistry of the Ertsberg granitoids and carbonate wallrocks, together with spatial mapping of hydrothermal minerals and target/pathfinder trace elements at the Deep Mill Level Zone of Ertsberg. Ores at Ertsberg are mainly skarn-hosted, whose formation comprises five stages: (I) prograde skarn; (II) retrograde alteration; (III) massive anhydrite replacement; (IV) late hydrothermal veining; (V) supergene alteration. Massive magnetite and main CuAu mineralization occurred in Stage II and III, respectively, although minor Cu mineralization persisted to Stage IV.The Ertsberg granitoids have medium SiO2 and high Al2O3 contents, and consist mainly of (quartz-)monzonite and minor (monzo)diorite. Least-altered samples have upper crust-normalized enrichments in certain large ion lithophile elements (LILEs, e.g., U and K) and depletions in all high field strength elements (HFSEs, e.g., Ti, Y, and Yb). The samples are fresh to moderately-altered, featured by garnet-diopside skarn and/or porphyry-style (potassic, propylitic, phyllic) alterations and anhydrite replacement. Elemental mass balance calculation indicates that the porphyry-style alteration zones are featured by feldspar destruction and the accompanying alkali depletions, although the loss of KRb (in potassic and phyllic zones) and Ca-Ba-Sr (in propylitic zone) are balanced by their respective capturing in secondary K-feldspar-mica and actinolite-epidote-anhydrite. Decarbonation of the dolomitic wallrocks likely released Mg-Ca-Sr, which facilitated the subsequent forsterite-diopside exoskarn and anhydrite alteration. The enrichments of various ore-related target/pathfinder elements in these altered samples are consistent with their mineralized nature, e.g., FeMn (magnetite), Cu-Fe-Bi-Se-Te (bornite), MoRe (molybdenite), Au-Ag-As-Bi-Te (auriferous pyrite/arsenopyrite), Zn-Fe-Mn-Sn-In (sphalerite), and Pb-Ag-Bi (galena).Alteration mineral and target/pathfinder elemental distribution patterns show that the ore fluids were likely originated from the porphyry hydrothermal (potassic) centers near the Ertsberg pluton margin. The fluids then spread out from the potassic centers, forming the surrounding propylitic zone, and migrated along the largely NW-SE-oriented intrusive contact and fault zones. This formed the endoskarn in the Ertsberg pluton, the forsterite-diopside exoskarn in the Waripi Formation dolomite, and the garnet-diopside exoskarn in the Ekmai Formation limestone/calcareous sandstone-siltstone. As the hydrothermal system started to wane, the prograde skarn formation is partially overprinted/enveloped by retrograde serpentine and actinolite/tremolite-epidote-chlorite alterations, and then by magnetite mineralization and massive anhydrite replacement in the carbonate wallrocks. The texturally-destructive skarn formation, and the dissolution of carbonate wallrocks and hydrothermal anhydrite were likely pivotal in creating the highly-fractured Broken Zone, which served as a structural trap for the high-grade Cu-Au-Mo ore deposition.

Insights into the skarn Cu mineralization processes of an intracontinental setting: A case study of the Xiaohekou deposit, southern Qinling Orogen, China

Traditional metallogenic models posit that porphyry–skarn Cu systems form in subduction and collision zones. However, in eastern China, many important Late Mesozoic porphyry–skarn deposits have formed in intracontinental settings related to lithospheric break-up during the celebrated tectonothermal, Yanshanian event. The Xiaohekou Cu skarn deposit in the southern Qinling Orogen presents an ideal case study to describe such ore deposit geology, using mineral and fluid inclusion analysis, in addition to sulfide and granitoid SPb isotope studies. A detailed metallogenic process model for the intracontinental skarn Cu deposit is proposed.The authors recognize four main paragenetic stages: (I) anhydrous skarn, (II) hydrous skarn–Fe oxide, (III) quartz–polymetallic sulfide, and (IV) carbonate–quartz. Stage I is characterized by high temperatures (346–547 °C), high to moderate salinities (6.74–49.2 wt% NaCleqv), together with acidic and oxidizing H2O-NaCl fluids. From early to late anhydrous skarn stage, un-zoned grossular (Adr24–31Gr68–74), a grossular–andradite alternation series with wide zones (Adr26–68Gr31–72) and diopside (Di73–91Hd8–24)–pure andradite with dense oscillation zones (Adr68–100Gr0–30) crystallized sequentially, representing a gradual shift toward higher fO2 conditions. Diopside-hosted fluid inclusions (FIs) contain halite-bearing three phase (H-type), liquid-rich two-phase (L-type), and vapor-rich two-phase (V-type) inclusions, suggesting such fluids were sourced from a silicate melt and stage I & II boiling of magmatic-hydrothermal fluids at lithostatic depths of 1.1–3.3 km.. The FIs in actinolite (stage II) are characterized by homogenization temperatures (Th) of 273–502 °C and salinities of 4.34–42.8 wt% NaCleqv. Cooling and dilution of the ore-forming hydrothermal fluid, as well as the high fO2 conditions were responsible for the hydrous skarn alteration in addition to magnetite and specularite deposition. Stage III constitutes the principal Cu mineralizing event. Quartz from this stage contains distinctive liquid-rich inclusions, with Th of 143–423 °C and salinity of 2.07–17.8 wt% NaCleqv. Their Th values include two populations (210–270 °C and 303–359 °C) suggesting a commingling of hot magmatic-hydrothermal fluid and meteoric water accompanied by a significant fO2 decrease and pH increase was a principal factor behind chalcopyrite-pyrite-pyrrhotite deposition. The fluids in stage IV (81–218 °C and 0.18–14.1 wt% NaCleqv) are likely be the chilled equivalent of fluid from the Cu mineralization stage which equilibrated with marble. SPb isotopes reveal that the metals were derived from the granitic rocks and produced by hybrid (mantle+crust)-derived magmas. We propose hydrothermal fluids exsolved from the cooling granitic magma contributed the majority ore-forming materials. Whereas ore-forming fluids clearly interacted with country rocks affecting ore precipitation, skarn development and deposit geometry and emplacement. Devonian host rocks donated little if any of either sulfur or base metals to the mineralization process.

Magmatic-hydrothermal origin for Carlin-type Au deposits: Evidences from in-situ S-Pb isotopic compositions of sulfides, the Chang’an Au deposit, southern Ailaoshan tectonic zone

The Chang’an Au deposit is a large Au deposit located in the south of the Ailaoshan-Red River tectonic zone, southwestern margin of the South China block. The deposit exhibit characters similar to Carlin-type Au deposits in Nevada and Dian-Qian-Gui “Golden Triangle”, including tectonic evolution (deformed and rifted cratonic margins), orebody controlled by lithology and structure and invisible Au ionically bound in arsenian pyrite and pyrite. Mineralization is controlled by a strike-slip fault and occurs as barren milky quartz veins, disseminated gold-bearing pyrite and arsenopyrite in the Early Paleozoic sandstone, siltstone and limestone. Gold is invisibly and ionically bound in arsenopyrite and pyrite or locally occurs as isolated native gold crystals (micron scale). Wall rock alteration includes sulfide, silicic, sericite and decarbonized alterations. Three hydrothermal mineralizing stages (I, II, III) can be identified: milky quartz-pyrite (I), quartz-sericite-pyrite-arsenopyrite (II) and dolomite-calcite-quartz (III). Different from those deposit in Dian-Qian-Gui, numerous plutons intruded in and around the mine. The syenite dikes are pyritized, thus, formed prior to the mineralization while lamprophyre dikes are unaltered and crosscut by the syenite dikes. The syenite dikes yielded zircon U − Pb ages of ca. 35.8 Ma and the lamprophyre yielded similar Ar-Ar age of ca. 36.6 Ma, largely constraining the age of Au mineralization. In situ S–Pb isotopic compositions for ore pyrite and arsenopyrite were measured by fs-LA-MC-ICP-MS. Sulfides from Chang’an show a uniform range from –6.4‰ to + 4.6‰, a typical characteristic of magmatic-derived S. Such sulfur isotopic compositions are similar to those of sulfides from Carlin-type Au deposits, but different from those of sulfides from orogenic-type deposit, which commonly exhibit a wide range of δ34S values. Pb isotopic ratios of pyrite and arsenopyrite are similar to those of the intrusive rocks in the deposit with more radiogenic Pb, suggesting that the metal is probably sourced from the coeval intrusive rocks and sedimentary wall rocks. Combined with the low Au concentrations of the sedimentary wall rocks, Au in the Chang’an deposit are probably sourced from the intrusive rocks. Differences between the Chang’an deposit and typical orogenic-type Au deposit include: (1) Orebodies in the Chang’an deposit exhibit transitional contact relationship with the host rocks and boundaries between them are defined by cut-off grade while these boundaries in typical orogenic-type deposits are clearly defined. (2) Sulfidized and decarbonized alterations are quite significant in the Chang’an deposit but commonly absent in typical orogenic-type deposits. (3) The Chang’an deposit have lower CO2 contents of ore-forming fluids and more shallow ore-forming depth relative to typical orogenic-type deposits. Based on the ore deposit geology, dating and isotopic data, the Chang’an mineralization is similar to typical Carlin-type gold deposit, formed by ore fluids originated from a deep magmatic S source in an post-collisional intracontinental setting at ca. 36 Ma.

Petrogenesis of the Cretaceous Intraplate Mafic Intrusions in the Eastern Tianshan Orogen, NW China

In this study, we conducted zircon U-Pb dating, and whole-rock geochemical and Sr-Nd isotope analyses on the Late Mesozoic dolerite dykes in the Bailingshan Fe deposit (Eastern Tianshan Orogen, NW China) to unravel their petrogenesis and regional tectonic significance. Zircon U-Pb dating on the dolerite yielded an Early Cretaceous age of 129.7 ± 1.4 Ma. The dolerite is calc-alkaline sodic (Na2O/K2O = 4.71 to 6.80), and enriched in LILEs (Rb, K, Sr, and Pb) but depleted in HFSEs (Nb, Ta, and Ti). The intermediate Nb/U (16.7 to 18.5) and Ce/Pb (6.33 to 6.90) values, and the presence of xenocrystic zircons in these dolerite dykes suggest crustal assimilation during the magma evolution. Petrological modeling suggests fractionation of olivine, pyroxene, garnet, and spinel. All the dolerite samples have low initial 87Sr/86Sr (0.7041 to 0.7043) and positive εNd(t) (+ 4.6 to + 5.1) values, indicative of a depleted asthenospheric mantle source. Partial melting modeling suggests that the melting has occurred in the spinel-garnet stability field. Integrating the data from ore deposit geology, geochronology, geochemistry and Sr-Nd isotopes, we proposed that the Late Cretaceous Eastern Tianshan mafic magmatism was developed in an intraplate extension setting.