Ore Belt Research Articles

Prospecting potential evaluation based on geological factor analysis-a case study of Jiaojiacheng ore belt

Mineral forecasting is of great significance for social development. As an important aspect of geological exploration, its importance lies not only in its direct contribution to economic growth but also in how it employs precise technical methods for mineral exploration. This study utilizes a geological factor analysis method that combines various complex geological observation factors into a few dominant comprehensive factors, followed by causal research and multivariate statistical analysis for classification. Based on this, the study applies principles and methods of elemental geochemistry to identify the dispersion and concentration patterns of associated elements from the distribution characteristics of ordered accompanying factors, providing a scientific basis for mineralization forecasting. Using geochemical experimental data, geological survey comprehensive profiles, and factor score contour maps, this paper analyzes the southern extension segment of the Jiaojia gold mine mineralization belt through geological factor analysis. It was found that the anomalous distribution of chemical elements F4 (Hg, Au, Pb) exhibits certain regularities, which significantly indicate mineralization information and suggest the presence of two main longitudinal mineralization belts.

Joint Inversion of DC Resistivity and Gravity Data with Undulating Terrain Based on Deformed Hexahedral Mesh

In the field of mineral resource exploration, accurate imaging of subsurface structures is key to discovering and assessing potential mineral deposits. Traditional single geophysical methods, limited by terrain variations and their own constraints, can lead to divergent solutions and structural inconsistencies, affecting the reliability of exploration outcomes. To address these challenges, this paper presents a joint inversion method for three-dimensional direct current (DC) resistivity and gravity data based on a deformed hexahedral mesh. The article begins by outlining the current state of development of the method under study and proposes a research plan, followed by a detailed explanation of the theoretical basis and algorithmic implementation of the proposed method. Model tests confirm the advantages of the deformed hexahedral mesh in reducing terrain impacts and enhancing model resolution, demonstrating the optimization and complementarity of the resolution between the two methods after joint inversion. Finally, applying this method to actual data from the Huaniu Mountain area shows that joint inversion not only improves the consistency of the ore belt structure but also provides a more precise analysis for the quantitative interpretation of the distribution of underground mineral resources. This confirms the method’s effectiveness and potential in practical geological exploration.

The superposition of Cretaceous mineralization events leading to the formation of the large Baiyinnuoer Pb–Zn deposit in NE China

The Baiyinnuoer Pb–Zn deposit, estimated at 26.57 million metric tonnes (Mt) with grades of 1.77% Pb and 5.21% Zn, is situated in the southern Great Xing'an Range (SGXR) of northeast China. The deposit comprises southern and northern ore belts. The southern belt primarily contains skarn ore bodies (32% of reserves) associated with Triassic granodiorite, while the northern belt is dominated by skarn ore bodies (30% of reserves) related to Triassic diorite porphyry. In addition to Triassic skarn‐type mineralization, the deposit also exhibits Early Cretaceous mineralization. This includes vein‐type occurrences (36% of reserves) within volcanic tuff and syenite porphyry, alongside a small amount of skarn ore bodies (2% of reserves) related to syenite porphyry. LA‐ICP‐MS U–Pb dating of intrusive rocks and garnets was conducted to investigate the timing and genesis of these mineralization events, revealing two distinct stages of skarn‐type mineralization. The first stage, associated with Early Triassic granitoids, dates to 254.6 ± 1.4–241.7 ± 2.7 Ma, while the second stage is closely associated with Early Cretaceous syenite porphyry, constrained to 135.4 ± 1.1–135.2 ± 1.6 Ma. Garnet U–Pb dating in the syenite porphyry‐related skarn yielded an age of 134.9 ± 4.7 Ma; however, due to low U content, reliable dating of garnets associated with Early Triassic granitoid‐related skarn was not feasible. Micro‐thermometry and Laser Raman analyses of fluid inclusions within vein‐type ore bodies highlighted distinct differences between vein‐type mineralization and Early Triassic skarn‐type mineralization. Additionally, in situ sulfur isotope analyses of sphalerite from both Early Triassic and Early Cretaceous ore bodies indicate a magmatic origin for sulfur in both stages. Through comprehensive geological, geochronological, in situ sulfur isotope and fluid inclusion studies, the Baiyinnuoer Pb–Zn deposit is conclusively identified as a large deposit characterized by two distinct periods of mineralization (Early Triassic and Early Cretaceous), akin to several other significant polymetallic deposits in NE China.

Textural and compositional evolution of quartz and cobalt-bearing minerals from the Wubaoshan Deposit, Jiangxi Province, South China: Implications for cobalt mineralization

Cobalt resources are primarily derived from hydrothermal-related deposits; however, our understanding of the mechanisms governing cobalt transportation and deposition, particularly for cobalt arsenides and sulfarsenides within hydrothermal fluids, remains limited. In this study, we present a comprehensive investigation into the Wubaoshan cobalt deposit located in the Qin-Hang ore Belt, South China. This deposit exhibits mineralization associated with multiple hydrothermal fluids, resulting in complex paragenesis and the formation of cobalt minerals. By employing a combination of petrographic and geochemical observations, we explore the conditions of the ore-forming fluid and the hydrothermal mechanisms underlying cobalt mineralization. Our analysis reveals three distinct hydrothermal stages of mineralization: Stage 1 is characterized by quartz-arsenopyrite-pyrite assemblages formed at relatively high temperatures (352–390 °C), neutral pH, and high fS2 (log fS2 = −6.9 ∼ −8.8); Stage 2, the pivotal stage for cobalt mineralization, displays various sulfides-sulfarsenides formed at lower temperatures (229 ± 6.0 °C), under acidic conditions, and low fS2 (log fS2 = −12.0 ∼ −14.0); and Stage 3 comprises minor sulfides and carbonates formed at relatively lower temperature and pH. Sulfur isotope analysis of pyrite from Stage 1 (+13.49 to +14.30 ‰) and sphalerite from Stage 2 (+5.53 to +9.21 ‰) suggests a mixed sulfur source derived from both Permian seawater sulfate and related magmatic rocks. Additionally, our results reveal that a transformation from cobalt arsenide to sulfarsenide during Stage 2, likely influenced by the change of As/S ratio in ore fluids, which is affected by the influx of external sulfur from magmatic hydrothermal fluids. Our findings, together with the previous thermodynamic modelling results, indicate that the variations of the ore fluid condition, particularly temperature and pH, govern the precipitation and dissolution of mineral during cobalt mineralization. These findings contribute to our understanding of the formation processes of the Wubaoshan deposit and provide valuable insights into the mechanisms of cobalt enrichment.

Characteristics and Mechanism of the Ore-Forming Fluids in the Shimensi Tungsten Polymetallic Deposit in Southeastern China

The Shimensi super-large tungsten polymetallic deposit is located in the Late Jurassic–Early Cretaceous Porphyry–Skarn tungsten ore belt in the south Yangtze metallogenic belt. There are three types of mineralization: veinlet-disseminated type, thick quartz vein type and hydrothermal cryptoexplosive breccia type. Based on geological studies, this paper presents new petrographic, microthermometric, laser Raman spectroscopic and hydrogen and oxygen isotope research on the fluid inclusions from the deposit. The results show that there are five different types of fluid inclusions: liquid-rich inclusions, vapor-rich inclusions, pure liquid inclusions, pure vapor inclusions, and fluid inclusions containing a solid crystal. The homogenization temperatures of the fluid inclusion range from 140 °C to 270 °C, the salinities are 3 wt.%–5 wt.% NaCleq and the densities of ore-forming fluid range from 0.64 g/cm3 to 0.99 g/cm3. For the analyses of laser Raman spectroscopy, the ore-forming fluids can be approximated by a Ca2+-Na+-SO42−-Cl− fluid system with small amounts of CO2, CH4 and N2. Otherwise, the data of the pressure, pH and Eh show a fluid metallogenic environment of low pressure, weak acid and weak reduction. The values of the homogenization temperature in the three types of orebodies suggest that the mineralization is characterized by a decrease in temperature under the conditions of fluid immiscibility. The H-O isotope values are interpreted to indicate that the ore-forming fluids are mainly composed of magmatic water, and meteoric water is added with the process of magma rising.

Gold mineralisation by pyrite recrystallisation and arsenopyrite sequestration in the Jiaochong Au deposit, Tongling ore district, eastern China: Implications for the formation of stratabound ore deposits

The Middle–Lower Yangtze River Valley metallogenetic belt (MLYRB) is a large and economically valuable porphyry–skarn Cu–Au ore belt in China with a total reserve of >600 tonnes of gold. Orebodies in the MLYRB are commonly stratabound and extend for several tens of metres in length and locally for more than 1000 m. However, the origin of the stratabound orebodies is uncertain, with proposals including a magmatic or sedimentary genesis, and the specific processes by which these gold deposits were formed are also unclear. Here we report a study of the representative stratabound Jiaochong Au deposit in the Tongling ore district, where stratified gold orebodies are hosted at the Triassic -Permian strata boundary. A detailed field survey, petrologic observations, in situ sulfur isotopic analysis, and major and trace element compositional analysis of gold and sulfide grains were carried out to determine how the gold was enriched. Field survey shows that precipitated sulphides exhibit obvious mineral and textural zonation from wall-rock to orebody centres as follows: Zone 1, colloform pyrite (Py1) ± sphalerite ± chalcopyrite → Zone 2, euhedral pyrite (Py2) ± pyrrhotite + arsenopyrite ± colloform pyrite (Py1) → Zone 3, pyrrhotite + arsenopyrite. From zone 1 to zone 3, the sulphides were progressively phase-transformed, with the earlier Py1 being gradually consumed and converted into Py2, which finally became pyrrhotite. The gold deposition occurs in Zones 2 and 3 and forms two generations of gold grains, one group being completely enclosed within euhedral Py2 with low As contents (<0.1 wt%) and another group infilling fractures between arsenopyrite and pyrrhotite or occurring as inclusions within arsenopyrite with high As contents (0.4 to 1.4 wt%). The comparable S-isotope compositions of the ore sulfides to those of Mesozoic intermediate-felsic intrusions and the veining characteristics of colloform pyrite in the Tongling ore district suggest that Mesozoic magmatic-hydrothermal fluids, rather than Carboniferous sedimentary rocks as usually thought, provided the principal ore-forming materials. The gold precipitation in this study followed two continuous processes: recrystallisation and arsenopyrite sequestration; in the first process, Au is remobilised from the pyrite structure at higher temperatures up to recrystallisation of fine-grained, colloform morphologies into euhedral crystals and formation of Au-bearing metallic particles (Au1); with the ongoing recrystallisation more As is released and accumulated into the equilibrated fluids, forming As-rich pyrite or arsenopyrite and a second period of gold deposition (Au2). The continuous sulphide zonation texture and phase transformation, similar to Jiaochong, have been observed in other gold deposits in the MLYRB, and our gold enrichment processes may also give an explanation for the formation of these stratabound gold deposits.

Geochronology and Geochemistry of Volcanic and Intrusive Rocks from the Beizhan Iron Deposit, Western Xinjiang, NW China: Petrogenesis and Tectonic Implications

The Awulale Iron Metallogenic Belt (AIMB) located in Central Tianshan is a significant iron ore belt in China. The Beizhan area exhibits extensive volcanic and intrusive rocks that formed during or close to the iron mineralization period. The iron ores in Beizhan are found in Early Carboniferous rhyolite and dacite tuff. The rhyolite is enriched in LILEs and LREEs, depleted in HFSEs, and shows high positive εNd(t) values (+3.0–+4.0). Late Carboniferous intrusive rocks include a granite stock and diabase and diorite dykes. The zircon grains from the granite yield a weighted mean 206Pb/238U age of 311.8 ± 2.6 Ma. The geochemical features of the granite are similar to those of rhyolite, but with pronounced negative anomalies of Eu, Sr, P, and Ti and higher positive εNd(t) values (+4.9–+5.1). The zircons in the diorite dyke yield a weighted mean 206Pb/238U age of 299.2 ± 1.4 Ma. Both the diabase and diorite dykes show an enrichment of LREEs and depletion of HFSEs with high positive εNd(t) values (+3.3–+7.3 and +2.3–+2.6, respectively), although the Eu, Th, and Sr anomalies are more negative in the diorite compared to the diabase. The rhyolite displays high positive εNd(t) values and young Nd model ages (TDM2 = 760–838 Ma) and has Nb/Ta ratios (11.3–12.8) close to that of the continental crust, indicating that it originated from the partial melting of the juvenile lower crust. The granite has similar geochemical characteristics (TDM2 = 656–673 Ma and Nb/Ta ratio = 8.7–10.9) and is also believed to have originated mainly from the partial melting of the juvenile lower crust. The diabase and diorite dykes have low (Tb/Yb)N ratios (&lt;2) and high Ba/Th (31.8–353.2 and 185.3–251.3, respectively) and Sr/Th (113.8–312.9 and 144.7–163.1) ratios, and exhibit a pronounced depletion of HREEs and Y and negative Th anomalies, suggesting that they originated from a spinel-garnet lherzolite mantle source. The Early Carboniferous rhyolite erupted in a continental arc setting, whereas the Late Carboniferous granites, diabase dykes, and diorite dykes formed in an extensional setting associated with the upwelling of the asthenosphere. Therefore, the magmatism and Fe mineralization in the AIMB are correlated with an extensional setting associated with oceanic slab breakoff.

Porphyry and Related Deposits of Northern Eurasia

It is hard to overestimate the economic importance of the ore deposits of the “porphyry family” and related ones, in particular, epithermal, in the modern world. These deposits are represented by industrial concentrations of a wide range of metals, mainly copper, gold, molybdenum, tin, etc. In Northern Eurasia, they are localized in terranes of different ages—from the Early-Middle and Late Paleozoic (for example, in the Urals and other segments of the Central Asian orogenic belt) to the Mesozoic (Transbaikalia), Mesozoic-Cenozoic (Pacific Ore Belt) and Cenozoic (Kamchatka). The tectonic nature of the corresponding terranes varies from island-arc and marginal-continental in connection with subduction zones along ancient convergent continental margins to post-collision segments and zones of intraplate development (tectonic-magmatic activation) of consolidated continental structures. The history of the study of porphyry copper and related deposits in Northern Eurasia covers the period from 1901 (Turya district of the Northern Urals and Kedabek deposit in Transcaucasia) to the present. In Soviet period, the largest gold-molybdenum-copper-porphyry deposits of Kounrad (Kazakhstan), Almalyk (Uzbekistan) and Kajaran (Armenia) were discovered and studied, as well as in Russia—Peschanka (Chukotka), and in the post-Soviet years—Malmyzh (Khabarovsk Krai). In the overall balance of copper reserves in Russia, porphyry copper deposits take the leading positions, second only to the reserves of sulfide copper-nickel deposits. Porphyry copper deposits play a much more significant role in the structure of the mineral resource base of copper in Kazakhstan, and the predominant one— in Uzbekistan. The main focus of this thematic issue is on gold-copper-porphyry and related deposits. In recent years, new perspectives have been opening up for studying natural associations of different types of porphyry mineralization.

Geological characteristics and genetic types of antimony deposits in the Weishan Yongping ore concentration area of Yunnan Province

The Weishan Yongping ore concentration area is located at the southern end of the "Jubao Basin" in the Lanping Basin, and is part of the Lanping-Simao mineralization belt. It is an important antimony ore belt in Yunnan Province. This article analyzes the geological characteristics of antimony deposits in the ore concentration area from the perspectives of regional geology and typical deposit characteristics, explores their genetic types, and provides a basis for the exploration and development of antimony resources in the area.

Characteristics, geochronology, and formation conditions of W mineralization and its relationship with Au mineralization in the Zhaishang gold deposit, West Qinling Orogen, China

The West Qinling Orogen is an important Au-W ore belt; however, the spatio-temporal and genetic relationships of W and Au ores remain unclear. This study takes the Zhaishang deposit, one of the largest Au-W deposits in the West Qinling Orogen, to trace their connections. The geological observation reveals that high-grade W ores are commonly characterized by extensional hydrothermal veins. In contrast, high-grade Au ores are hosted by breccia zones, which cut the W ore-controlling structures, even though the W and Au ores overlap locally. The mineral assemblages of W ores associated with carbonatization and silicification consist of scheelite and pyrite with few polymetallic sulfides, in contrast to the abundance of polymetallic sulfides and native gold in Au ores linked with silicification. Textural and in situ trace element analyses reveal that the scheelites show a decrease in Na, U, Mo, Nd, and calculated Eu anomaly values and an increase of Th concentrations and Ce anomaly values from early- to late-generation scheelites. This finding, in conjunction with mineral assemblages and previous thermodynamic modeling, suggests a decrease in salinity and oxygen fugacity (fO2) of the oxidized ore-forming fluids of W mineralization, as opposed to the reduced fluids of Au mineralization. The plots of scheelite at Zhaishang in the ternary LREE-MREE-HREE diagram are compatible with those of W deposits related to magmatic-hydrothermal fluids. In situ U-Pb dating of scheelite from W ores constrains the precise timing of W mineralization at ca. 227.9 ± 2.3 and 225.6 ± 3.0 Ma in a collisional orogenic setting. The unequivocal crosscutting relationship, contrasting mineral assemblages, and physiochemical conditions suggest that the W and Au mineralization at Zhaishang are due to two separate mineralization events. The identification of overlapped W and Au mineralization events at Zhaishang is crucial for guiding the regional exploration of W and Au deposits.

A Study on The Tectonic Control and Metallogenic Regularity of The Sanjiang Sanjiang Metallogenic Belt Cobalt Deposit in Yunnan Province

The Sanjiang region of Yunnan is rich in minerals, especially known for gold, copper, lead zinc, and iron ore deposits. There are many genetic types of ore deposits, and most of the ore deposits (points) and anomalies are controlled by the northwest north-south structural belt. The regional tectonic activity is strong and the metallogenic conditions are superior. In this paper, the structural ore-controlling effect and metallogenic regularity of Sanjiang Metallogenic Belt cobalt deposit in Yunnan Province are further studied. The mineralization of the ore belt is most closely related to the Caledonian submarine hydrothermal sedimentation, and after mineralization, it was obviously transformed by Indosinian metamorphism and hydrothermal superposition. Some scholars have carried out relevant research on the geological and geochemical characteristics and genesis of the deposit, and think that the deposit is stratabound-reformed, jet sedimentary, hydrothermal sedimentary-tectonic reformed, etc. However, the chemical properties of ductile rocks are inactive and the permeability is poor, which makes the ore-forming fluid difficult to lose, which is beneficial to the full water-rock reaction between minerals in hydrothermal solution and surrounding rocks flowing through carbonate rocks, resulting in a large number of minerals precipitation and enrichment. When the soft and hard rocks alternate with each other, it is beneficial to form bedding detachment structure to become ore storage space, and it is also beneficial to the precipitation of minerals along the chemical interface and the enrichment of minerals.

Refertilized continental root controls the formation of the Mianning–Dechang carbonatite-associated rare-earth-element ore system

Rare earth element ore deposits associated with carbonatite derived from Earth’s mantle supply half of the world’s rare earth element. However, the formation of carbonatite and initial enrichment and transport of rare earth element in the mantle, is unclear. Here, we image the lithospheric architecture of a Cenozoic rare earth element ore belt in southwestern China by integrating seismic tomography with geochemical data. The subduction of the Indian continent caused vertical upwelling and lateral flow of the asthenosphere, which triggered the melting of the overlying subcontinental lithospheric mantle to generate carbonatites. Such a mantle source that previously metasomatized by fluids from recycled marine sediments is a precursor process critical for forming a giant rare earth element system. For the studied ore belt, three key factors are prerequisites to generating ore-forming carbonatites: thick lithosphere with a continental root; prior fertilization of the subcontinental lithospheric mantle; and trans-lithospheric weakness for magma ascent.

Petrographic Analysis of Brecciated Iron Deposit (BID) of Bonai-Keonjhar Iron Ore Belt of Odisha, India

Petrographic Analysis of Brecciated Iron Deposit (BID) of Bonai-Keonjhar Iron Ore Belt of Odisha, India

Advances in metallogeny and tectonics of the Eastern Tethyan Realm: Introduction

The Tethys domain preserves one of the largest continent‐continent collisional orogenic belts on Earth. This belt can be divided into the Proterozoic to Palaeozoic Proto‐Tethyan orogenic belt, Late Palaeozoic to Triassic Palaeo‐Tethyan orogenic belt and Triassic to Cenozoic Meso‐ and Neo‐Tethyan orogenic belts. The Tethyan metallogenic domain, representing one of the three major metallogenic domains in the world, extends more than 10,000 km from east to west and has developed world‐class ore belts, such as the South‐east Asia tin ore belt, Sanjiang metallogenic belt in South‐west China, Gangdese–Pakistan–Iran porphyry copper belt and South‐east Europe epithermal gold belt. The geology of the Tethys domain has been studied for more than 100 years and many important advances have been made recently, although scientific issues remain controversial. This thematic section of Geological Journal contains 10 articles focusing on the formation of rocks and ore deposits, including petrology and geochemistry of magmatic, metamorphic and sedimentary rocks, and the formation mechanism of mineral deposits in the Eastern Tethyan Realm. These articles reflect new progress in related studies and provide important reference for future studies.

Реализация принципов безопасности труда при подземной разработке сложноструктурных рудных месторождений

Most of the metal ores are mined from the rock deposits by technologies with natural control of the state of rock massifs. Rationalization of the methods for controlling the state of an ore-bearing massif, considering their geomechanics, is becoming a priority direction for improving technologies for the development of complex structure ore deposits. The purpose of the study is to substantiate the possibility of managing the state of massifs based on the combination of filling mixtures in the conditions of the Sadon ore belt deposit. The complex of studies includes the engineering division of the massif with the allocation of engineering structural sections. By modeling on equivalent materials, a mechanism for the development of stresses in the vicinity of a working was established. It is determined that the studied massif is discrete with a gravitational-tectonic-structural stress field. Based on the experimental data, a model of the intensity of the ore-bearing massif is built on the basis of the hypothesis of wedging of the rocks of the bearing layer. The role of expansion stresses and backfill strength in the input of the massif into the volumetric compression mode is determined. A stress control technique is proposed by dividing the massif into geomechanically safe areas. It was proven that backfilling systems ensure the recovery of reserves, improve the quality of ores and preserve the earth surface, protecting the region from the negative impact of mining. The complexity of exploitation of ore-bearing massifs determines the need to monitor the geomechanics of ore-bearing rocks. The combination of technologies is a real step in improving mining production, as it allows to reduce ore dilution, increase labor productivity, and also improve the safety conditions of workers by increasing the reliability of technology parameters.

Study on the Leaching Conditions of the Shihongtan Uranium Deposit

CO2 + O2 is a relatively mature, neutral, in situ leaching process that has been widely used. However, the decrease in uranium concentration in the leaching solution during production has become a serious problem in the western section of the south ore belt of the Shihongtan deposit in Xinjiang, China. In order to solve this problem, mineralogy and batch tests were carried out to explore the reason for the low uranium resource leaching efficiency and determine better leaching process parameters. A total of 16 tests were carried out under different conditions of CO2/O2 ratios and HCO3− concentrations. The results show that: (1) The uranium minerals in the ore were mainly pitchblende and titanium-bearing uranium mineral. Part of the uranium resources were mixed in quartz, which were difficult to activate and recover. The high content of calcium carbonate and clay minerals in ore and the high TDS (total dissolved solid) content in groundwater would cause a reduction in porosity. (2) According to the uranium concentration and uranium leaching rate, a better leaching efficiency was obtained when the pH was lower than 6.6, and the HCO3− concentration was 800 mg/L. This result could serve as a reference for production in other similar mines.

Formation Model of the Gold-Sulfide Deposits of the Western Kalba and Its Main Forecast and Search Criteria

The West Kalba Gold ore Belt (WKB), located within the Greater Altai, is a unique gold ore province on a global scale. It contains about 500 known gold occurrences and deposits. The main industrial type for the WKGB are gold-bearing sulfide deposits. The article presents a model for the formation of gold sulfide deposits in West Kalba. The main predictive-search criteria are considered, which make it possible to assess the prospects of areas for the presence of potential gold-sulfide objects within the described territory. The aim of the work is to clarify the main predictive and prospecting criteria specific to the considered field model. The given data is highlighted using descriptive analytics methods.

Determining the impact of magma water contents on porphyry Cu fertility: Constraints from hydrous and nominally anhydrous mineral analyses

Most large-scale porphyry-style mineralization is genetically associated with oxidized, sulfur-rich, and hydrous magmas, the sources of which were enriched in mantle-derived or juvenile crust−derived materials. Geochemical indices for these features can distinguish fertile magmas and barren magmas. However, fertile magmas that generate different-sized porphyry deposits are usually geochemically indistinguishable, and the factors controlling the size of porphyry mineralization are poorly understood. Here, we used zircon H2O contents and the compositions of apatite hosted in zircon, phenocrysts, and groundmass to compare the water contents and volatile evolution of fertile magmas in the Yulong ore belt, Tibet, which generated giant-, large-, and medium-sized porphyry deposits. We found that these porphyries have comparable major- and trace-element and zircon Hf-O isotope compositions, with high oxygen fugacity and sulfur contents. A negative correlation between [see PDF for equation] versus [see PDF for equation] of apatites suggests that the magmas consistently achieved H2O saturation before zircon crystallization, and zircon hydroxyl contents reveal that the water contents of the melt positively correlate with the size of the deposits, consistent with larger deposits achieving H2O saturation at deeper crustal levels. The deeper H2O saturation also caused larger amounts of Cl extraction, as indicated by the trends of increasing [see PDF for equation] and decreasing [see PDF for equation] with larger deposit sizes. These data sets can be reconciled by magmas forming larger deposits having higher H2O contents and suggest that the H2O content is a key control on their fertility. Our study highlights the utility of integrated hydrous and nominally anhydrous mineral analyses for constraining enigmatic magmatic volatile processes in magmatic ore-forming systems.

Ore-forming processes of the Baisong carbonate-hosted Pb-Zn deposit, SW China: Constraints from in-situ sphalerite trace element and sulfide S-isotopic compositions

The western Hunan-eastern Guizhou (WHEG) Pb-Zn ore belt in the southwestern Yangtze block is a main Pb-Zn province in China. The metallogenic characteristics of this ore belt were widely reported, but the ore-forming process is still poorly understood. The lower Cambrian carbonate-hosted Baisong deposit is a representative Pb-Zn deposit in the southern WHEG belt. Sphalerite trace elements and sulfur isotopic compositions from the Baisong Pb-Zn deposit could reveal the ore-forming fluid source and metallogenic processes. Four types of sphalerites have been distinguished (black colloidal sphalerite (Sp) I, light-colored sector Sp II, red zoned Sp III and brown zoned Sp IV, indicating four sulfide mineralization stages from the early ore phase. Sp I (66-117℃, δ34S: +24.8 to + 27.8‰) has the highest Cd-Ga-Ag-Cu contents among the four sphalerite types, and commonly overgrow with marcasite. This suggests that Sp I was formed from acidic fluids under high precipitation rate. The trace elements and sulfur isotopic compositions of Sp II (80-128℃, δ34S: +26.5 to + 28‰) are similar to Sp I. Sp II was likely formed by a decrease in oversaturation and precipitation rate with fluid pH increase. Sp III (127-164℃, δ34S: +31 to + 32.5‰), commonly overgrow on pyrite (Py I), has higher Mn-Fe-Ge but lower Cd-Cu-Ga-Ag contents and heavier sulfur isotopes than Sp II. Changes in precipitation environment and fluid compositions are likely major factors in forming Sp III (temperature increase, pH increase and more reduced). The forming of Sp III and Py I likely consumed the Fe and Ge in the fluid, depriving those elements from the later-formed Sp IV (97-141℃, δ34S: +25.7 to + 29.8‰). The sulfide δ34S value (+22.5 to + 46.3‰) implies that the S2- at Baisong was sourced from seawater sulfates via thermochemical sulfate reduction (TSR). Sphalerite trace element features reflect that the Baisong is an MVT deposit.

Origin and evolution of the ore-forming fluids of the Bajiazi gold deposit in the Jiapigou gold ore belt, NE China: Constraints from fluid inclusions, H-O-S isotopes, and pyrite trace element concentrations

The Bajiazi gold deposit, located within the southeastern Jiapigou gold ore belt (JGB) along the northeastern corner of the North China Craton (NCC), contains > 6 tons of gold at an average grade of 24 g/t. More than 20 total auriferous quartz veins are hosted in the Neoarchean basement gneiss and amphibolite and are spatially and temporally associated with Mesozoic intermediate-acid dikes. The distribution of the gold orebodies is mainly controlled by NNE-trending brittle–ductile shear zones and faults. Three hydrothermal stages were identified, namely, quartz–pyrite (stage I), quartz–gold–polymetallic sulfide (stage II), and quartz–carbonate (stage III). Three types of fluid inclusions (FIs) were identified: H2O–NaCl (W-type), CO2–H2O (C-type), and pure CO2 (PC-type) FIs. From stage I to stage III, the FI suite changes from W-type and C-type in stage I to all three types in stage II and to only W-type in stage III. The FIs in the quartz of stages I to III mainly homogenized at temperatures (Th) of 283–395 °C, 183–287 °C and 116–186 °C, respectively, with salinities of 3.87 to 13.01 wt% NaCl equiv, 4.65 to 18.55 wt% NaCl equiv, and 3.83 to 9.68 wt% NaCl equiv, respectively. The ore-forming fluids of the Bajiazi gold deposit evolved from a H2O–NaCl–CO2 system in stages I and II to a H2O–NaCl system in stage III. Fluid immiscibility is an important mechanism leading to rapid precipitation of sulfides and gold. H–O–S isotope signatures indicate that the initial ore-forming fluids and materials were originally derived from magmatic sources. Electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) data on pyrite grains show that abundant gold mineralization occurred in the middle hydrothermal stage. The high Co/Ni ratios of pyrite are consistent with a magmatic–hydrothermal origin. The results, combined with previous regional studies, indicate that the Bajiazi gold deposit is a mesothermal magmatic–hydrothermal lode gold deposit.