Lower Yangtze River Metallogenic Belt Research Articles

Sulfur isotope and trace element geochemistry of sulfides from the unique Yaojialing Zn-Au-Cu deposit, Lower Yangtze River Metallogenic Belt, China: Implications for ore-forming process and exploration

The Yaojialing Zn-Au‑Cu deposit is a porphyry-skarn-epithermal vein-type compound deposit that consists of epithermal vein-type lead‑zinc‑silver orebodies, skarn Zn-Cu-Au orebodies, and porphyry CuAu orebodies from shallow level to depth. We decipher the source and metallogenic mechanism by studying the trace element and S isotopic compositions of sulfides (pyrite, sphalerite, chalcopyrite, and galena) from three types of orebodies. The collected pyrite can be divided into two types. PyI coexists with chalcopyrite, and PyII coexists with sphalerite or galena. In addition, PyI was further divided into PyIa (collected from porphyry copper bodies) and PyIb (collected from skarn copper bodies). PyII can be further divided into PyIIa (collected from skarn-type lead‑zinc ore body) and PyIIb (collected from vein lead‑zinc ore body in strata). Sphalerite and galena from skarn-type PbZn ore bodies and shallow vein-type PbZn ore bodies are named SpI and GnI, and SpII and GnII, respectively.Pyrite and sphalerite trace element thermometers revealed that the temperature of the ore-forming fluids decreased from 500 to 600 °C in the porphyry ore body to 300– 360 °C in the skarn ore body and then to 240– 280 °C in the shallow vein ore body. The decrease in the Co and Ni contents of pyrite collected from deep to shallow depths may indicate that meteoric water precipitated in the late ore-forming hydrothermal system. Rapid crystallization and variations in the physicochemical states (such as temperature, pH, fO2, and geochemical composition) of the fluids resulted in an obvious oscillating zone of euhedral PyI pyrite particles. It also affects the solubility of trace metal elements and leads to the selective entry of these elements into pyrite. PyII also shows obvious zonation characteristics rather than oscillating zonation, indicating that the growth rate of pyrite is relatively slow. Moreover, the relationships between the Au and As contents in the two types of pyrite are different. PyI is coupled, while PyII shows decoupling. We believe that this phenomenon is due to the high content of As in ore-forming fluid systems, which may inhibit the absorption of Au on the surface of pyrite rather than the decoupling of Au and As caused by rapid crystallization, based on the rapid increase in As content and non-oscillating zonation in PyII. According to the analysis of the sulfur isotopes of various sulfides, the solid evidences suggest that the ore-forming materials of each type of orebody in the Yaojialing deposit were mainly derived from magmatic-hydrothermal processes and that the fractionation of sulfur isotopes was the result of variations in physicochemical conditions caused by magma-hydrothermal evolution rather than the addition of foreign sulfur sources.

Non-magmatic sulfur source of hydrothermal colloform pyrite: Insights from the Jinshandian iron skarn deposit, Daye district, eastern China

Colloform pyrite occurs widely in many ore deposits in the Middle–Lower Yangtze River Metallogenic Belt (MLYRMB) in eastern China, but its genesis is still debated. In this study, we present detailed textures and geochemical compositions of newly identified colloform pyrite (Py1) and late coarse-grained pyrite (Py2) from the Jinshandian iron skarn deposit in the Daye district to decipher the genesis of the pyrite grains. Colloform pyrite is composed of nanometer-sized (<1 μm) grains, showing typical colloform textures, and occurs as interstitial fillings between magnetite grains. In contrast, Py2 commonly has a large grain size (up to 200 μm) and is usually distributed along the margins of colloform pyrite. These two types of pyrite have relatively high Co/Ni (1.24–13.36) ratios. δ34SCDT values of Py1 (17.22‰–20.63‰, mean 19.42‰) and Py2 (18.96‰–19.95‰, mean 19.43‰) are close to those of gypsum (anhydrite) from evaporites in the Daye district, indicating the incorporation of evaporite-derived materials into the formation of colloform pyrite. On the basis of the textures, trace-element compositions, and sulfur isotope characteristics of the colloform pyrite, it is inferred that this pyrite from the Jinshandian iron deposit is of hydrothermal origin. The sulfur isotope composition of colloform pyrite from Jinshandian is heavier relative to other magmatic-hydrothermal colloform pyrites, which indicates colloform pyrite could formed in diverse hydrothermal fluids (magmatic to no-magmatic fluid). Our study further confirmed that hydrothermal colloform pyrite has widely occurred in Fe and Cu-Au deposits associated with the Cretaceous magmatism in the MLYRMB.

Correlation between the surface morphology of the intrusions and the formation of mineralization within skarn deposits: A numerical simulation study of the Qiaomaishan skarn Cu deposit, Middle and Lower Yangtze River Metallogenic Belt, China

Skarn deposits are high grade hydrothermal deposits distributed throughout the world, containing multiple mineral resources. However, the formation of skarn deposits is extremely complex, hindering our in-depth understanding of these deposits with high economic value. The Qiaomaishan Cu deposit is a typical skarn deposit located in the Liqiao-Tongshan orefield, Middle-Lower Yangtze River Metallogenic Belt (MLYRMB). This study applied numerical simulation approach to quantitatively describe the formation of copper mineralization within the Qiaomaishan skarn deposit, and explored the correlation between the surface morphology of intrusion and the formation of mineralization. This numerical model links five main processes related to ore formation within hydrothermal ore-forming system and their complex coupled relationship, namely chemical reactions, heat conduction, rock deformation, fluid migration, and materials diffusion. Results show that rough surface morphology of the intrusions is an ore controlling factor within the Qiaomaishan skarn deposit. The uneven surface of the intrusions greatly affects the time spent in cooling, thereby affecting the generation and spatial distribution of chalcopyrite. The concave part of the surface of the intrusions lives a longer cooling period (1000–2500 years) than the convex part (110–160 years) from 310 to 260 °C, which directly causes the difference in the temporal-spatial distribution of chalcopyrite. Results also show that the factors involved in prospectivity modeling must undergo strict conditional independence analysis, and numerical simulation method can be used to effectively achieve this goal. However, there are also some problems unsolved, such as difficulties caused by lack of data and oversimplified ore-forming chemical reactions. Future development of both geological research and modification of the law of mass action will undoubtedly improve the accuracy and practicability of numerical simulation and our understanding of the Qiaomaishan as well as other skarn deposit, providing information for mineral deposit research from the perspective of computational geoscience.

Origin of the Yinshan Pb-Zn-Ag Deposit in the Edong District Section of the Middle–Lower Yangtze River Metallogenic Belt: Insights from In-Situ Sulfur Isotopes

The investigation into the enigmatic origin of Pb-Zn mineralization within the Middle-Lower Yangtze River Metallogenic Belt has long been marred by a paucity of prior studies. Seeking to alleviate this dearth of knowledge, our study meticulously scrutinizes the Yinshan Pb-Zn-Ag deposit nestled within the Edong district of the belt, endeavoring to cast an illuminating spotlight upon its enigmatic genesis. We identify two distinct epochs: (1) the pre-mineralization pyrite epoch (Epoch I) mainly characterized by colloform and massive pyrite, and (2) the hydrothermal mineralization epoch (Epoch II) which can be further divided into three stages: pyrite-arsenopyrite (stage 1), galena-sphalerite (stage 2), and vein pyrite (stage 3). We conduct in-situ sulfur isotope analyses on sulfide minerals from both epochs, revealing δ34S values ranging from −0.5 to 4.8‰ for Epoch I and varying from 2.2–4.9‰ (stage 1), 1.1–3.0‰, 4.2–7.1‰ (stage 2), and 2.1–3.8‰ (stage 3) for Epoch II. Integrating our sulfur isotope data with the geological characteristics of the deposit, we infer that Pb-Zn mineralization was related to a granite of ~130 Ma age. Additionally, our study suggests the possibility of coexisting Mo mineralization beneath the Pb-Zn mineralization. Our findings contribute to a better understanding of the origin of Pb-Zn mineralization in the Middle-Lower Yangtze River Metallogenic Belt.

Distribution of Co, Se, Cd, In, Re and other critical metals in sulfide ores from a porphyry-skarn system: A case study of Chengmenshan Cu deposit, Jiangxi, China

Chengmenshan Cu deposit is a large porphyry-skarn copper deposit, located in the Jiutui ore district, Middle–Lower Yangtze River metallogenic belt, Eastern China. The deposit is enriched in tellurium, selenium, rhenium and cadmium; however, the occurrence and distribution of these metals are unclear. In this study, we report cobalt, selenium, cadmium, indium, rhenium and other critical metals in pyrite, chalcopyrite, and sphalerite from sulfide ores of Chengmenshan deposit. In-situ LA-ICP-MS trace element analysis and mapping of minerals were conducted to determine their trace element concentrations and reveal the distribution and occurrence of critical metals in different sulfides. Three ore types have been identified in Chengmenshan deposit, named: porphyry ore, skarn ore and strata-bound ore. Based on mineral assemblages, ore fabrics, and crosscutting relationships between the veins, Chengmenshan deposit is divided into three mineralization stages: pre-ore stage of skarn mineralization, syn-ore stage of sulfide mineralization, and post-ore stage of carbonation. The pyrite and sphalerite can be divided into two generations: Py1, Py2, and Sp1, Sp2, respectively. The critical metals exhibited an uneven distribution and closely related to sulfide minerals. Telluride minerals in the deposit mainly include hessite, tetradymite, joseite. Rhenium is mainly enriched in molybdenite (128 to 496 ppm, average 276 ppm); cobalt is mainly enriched in pyrite, and the value of the three types of ore in the early stage (Py1) higher late stage (Py2); Se in chalcopyrite is slightly higher than pyrite and sphalerite; Cadmium is mainly enriched in sphalerite (up to 3000–6000 ppm), and is relatively low in pyrite and chalcopyrite; Indium is distributed in chalcopyrite and sphalerite, and the values of sphalerite are higher than chalcopyrite; the Ga distribution was sphalerite > chalcopyrite > pyrite. The enrichment and distribution of Co, Cd, In in Chengmenshan porphyry-skarn deposit system were mainly control by the fluid temperature. The Cu-Mo (Re), Cu-Fe (Co, Se) and Cu-Pb-Zn-Ag (Te, Cd, In, Tl) mineralizations constitute Chengmenshan porphyry-skarn mineralization system, and show a Mo-Re to Cu-Co-Se-Te-Ga to Cu-Pb-Zn-Ag-Te-Cd-In pattern from granite to distal stratum in space.

Palladium, platinum, selenium and tellurium enrichment in the Jiguanzui-Taohuazui Cu-Au Deposit, Edong Ore District: Distribution and comparison with Cu-Mo deposits

The Jiguanzui-Taohuazui Cu-Au deposit is located in the Edong ore district, Middle–Lower Yangtze River metallogenic belt, eastern China. The deposit is palladium, platinum, selenium and tellurium enriched; however, the distribution of these metals is unclear. Three mineral assemblages of ore in the deposit have been identified, namely: a magnetite-bornite-chalcopyrite-(hematite) assemblage (Mt-Bn-Cp-Hm), a chalcopyrite-pyrite assemblage (Cp-Py), and a pyrite-chalcopyrite-(sphalerite) assemblage (Py-Cp-Sph). Forty-eight bulk ore assay results show high concentrations of up to 66.9 ppb for Pd, 5.9 ppb for Pt, 150 ppm for Se and 249 ppm for Te. The high temperature Mt-Bn-Cp-Hm assemblage (530–380 °C) is enriched in Pt and Pd, whereas the Py-Cp-Sph assemblage in the marble-replacement ore (300–220 °C) hosts the major Se and Te mineralization. Palladium, Pt, and Se are mostly hosted in sulfide minerals, whereas Te is hosted in tellurides and Bi-Te-S sulfosalt minerals. Building on previous experimental and thermodynamic calculations, we propose the major controls on the Pd and Pt distribution in the deposit are temperature and salinity, whereas the Se and Te mineralization is promoted by the precipitation of major sulfide phases such as pyrite, chalcopyrite and sphalerite.A comparison of the ores from the Jiguanzui-Taohuazui Cu-Au and Tongshankou Cu-Mo deposits in the Edong ore district shows that the Cu-Au deposit has higher PGE and Te, but similar Se concentrations. This scenario is consistent with the average grades and bulk ore contents of these elements from global (oxidized) porphyry (±skarn) Cu deposits. This suggests that the saturation of magmatic sulfides in the magma chamber as a result of higher proportion of crustal S-rich and/or reduced material contamination can be detrimental for PGE and Te enrichment processes, and thus, Cu-Au porphyry (±skarn) deposits have more potential for higher Pd and Te concentrations than the Cu-Mo deposits.

Geochemical study of the Tongshan intrusion in the Lower Yangtze River metallogenic belt, China: Significances of Cu-Au ore-forming

The Tongshan intrusion is located at the Guichi ore cluster field along the Lower Yangtze River metallogenic belt (LYRB) in eastern China. Elemental data and major elements of biotite are reported for Late Mesozoic plutons in the Guichi ore cluster in the Middle-Lower Yangtze River Region, attempting to explain their diagenetic age, petrogenesis, and tectonic implications. The Tongshan intrusion is dated at 146.3±3.2 Ma, with zircon εHf(t) average value of -5.23, illustrating that the Tongshan intrusion could be derived from crust mantle mixing magmatite provenance. The two-stage Hf model ages between 1184~1422 Ma is indicated magma source relationship with those of the Mesoproterozoic basement in south Anhui. The Tongshan intrusion is high-K calc-alkaline, and exhibit adakite-like geochemical feature, such as high Al2O3, Sr contents, Sr/Y value, low Y and Yb contents. The geochemical and reexplained published isotopic data indicate that these adakites are most likely from partial melting of subducted oceanic crust, and mixed with enriched lithospheric mantle components in the rising process.

P-wave velocity structure in the crust and the uppermost mantle of Chao Lake region of the Tan-Lu Fault inferred from teleseismic arrival time tomography

Chao Lake is a Geoheritage site on the active Tan-Lu Fault between the Yangtze craton, the North China craton, and the Dabie orogenic belt in the southeast. This segment of the fault is not well constrained at depth partly due to the overprinting of the fault zone by intrusive materials and its relatively low seismic activity and sparse seismic station coverage. This study took advantage of a dense seismic array deployed around Chao Lake to delineate the P-wave velocity variations in the crust and uppermost mantle using teleseismic earthquake arrival time tomography. The station-pair double-difference with waveform cross-correlation technique was employed. We used a multiscale resolution 3-D initial model derived from the combination of high-resolution 3-D vS models within the region of interest to account for the lateral heterogeneity in the upper crust. The results revealed that the velocity of the upper crust is segmented with structures trending in the direction of the strike of the fault. Sedimentary basins are delineated on both sides of the fault with slow velocities, while the fault zone is characterized by high velocity in the crust and uppermost mantle. The high-velocity structure in the fault zone shows characteristics of magma intrusion that may be connected to the Mesozoic magmatism in and around the Middle and Lower Yangtze River Metallogenic Belt (MLYMB), implying that the Tan-Lu fault might have formed a channel for magma intrusion. Magmatic material in Chao Lake is likely connected to the partial melting, assimilation, storage, and homogenization of the uppermost mantle and the lower crustal rocks. The intrusions, however, seem to have suffered severe regional extension along the Tan-Lu fault driven by the eastward Paleo-Pacific plate subduction, thereby losing its deep trail due to extensional erosion.

Titanite geochemistry and its indicators for Cu-mineralized magmas: Insight from three dioritic intrusions in the Tongling area of the Lower Yangtze River metallogenic belt

Titanite has been regarded as a potential petrogenetic and metallogenic indicator owing to its stability and enrichment of trace elements. To verify the availability of geochemical titanite proxies in the Cu-mineralized magma system and to reveal magmatic constraints on Cu mineralization related to magmatic hydrothermal fluid, in situ major and trace element abundances and Nd isotopes of igneous titanite were determined for three Mesozoic diorite intrusions in the Tongling ore district of eastern China. The investigated intrusions were the Tongguanshan, Fenghuangshan, and Hucun intrusions, all of which host porphyry-skarn Cu deposits. Our study shows that the titanite δEu value and Fe/Al ratio, rather than the δCe and Ga content, are more effective indicators of the magma oxidation state in all three intrusions. Based on the titanite δEu value and Fe/Al ratio, the causative magma of the Fenghuangshan intrusion (titanite δEu = 0.50 ± 0.08; Fe/Al = 0.21 ± 0.07) was identified as being less oxidized than those of the Tongguanshan (titanite δEu = 0.64 ± 0.09; Fe/Al = 0.93 ± 0.15) and Hucun (titanite δEu = 0.80 ± 0.03; Fe/Al = 0.91 ± 0.04) intrusions. This result was consistent with the zircon Ce4+/Ce3+ ratio. Moreover, owing to the limited effect of fluid exsolution and fractional crystallization on the F content of the investigated titanite, the higher titanite F content of the Fenghuangshan intrusion (titanite F = 0.40 ± 0.09 wt%) implies that the parental magma of this intrusion is more F-enriched than those of the Hucun (titanite F = 0.17 ± 0.09 wt%) and Tongguanshan (titanite F = 0.10 ± 0.07 wt%) intrusions; however, titanites from all three Cu-mineralized intrusions had similar or lower F content than those from intrusions without Cu mineralization. The above findings indicate that magmas with high oxygen fugacity have relatively high potential for porphyry-skarn Cu mineralization, while the high enrichment of F is not necessary for Cu mineralization. Additionally, we found that titanite εNd(t) values can inherit whole-rock εNd(t) values and thus can be used to investigate petrogenesis. This study confirms that titanite geochemistry is an efficient petrogenetic and metallogenic indicator for Cu-mineralized magma systems when the prerequisites are met.

Three-Dimensional Mineral Prospectivity Modeling for Delineation of Deep-Seated Skarn-Type Mineralization in Xuancheng–Magushan Area, China

The Middle–Lower Yangtze River Metallogenic Belt is an important copper and iron polymetallic metallogenic belt in China. Today’s economic development is inseparable from the support of metal mineral resources. With the continuous exploitation of shallow and easily identifiable mines in China, the prospecting work of deep and hidden mines is very important. Mineral prospectivity modeling (MPM) is an important means to improve the efficiency of mineral exploration. With the increase in resource demands and exploration difficulty, the traditional 2DMPM is often difficult to use to reflect the information of deep mineral deposits. More large-scale deposits are needed to carry out 3DMPM research. With the rise of artificial intelligence, the combination of machine learning and geological big data has become a hot issue in the field of 3DMPM. In this paper, a case study of 3DMPM is carried out based on the Xuancheng–Magushan area’s actual data. Two machine learning methods, the random forest and the logistic regression, are selected for comparison. The results show that the 3DMPM based on random forest method performs better than the logistic regression method. It can better characterize the corresponding relationship between the geological structure combination and the metallogenic distribution, and the accuracy in the test set reaches 96.63%. This means that the random forest model could provide more effective and accurate support for integrating predictive data during 3DMPM. Finally, five prospecting targets with good metallogenic potential are delineated in the deep area of the Xuancheng–Magushan area for future exploration.

Knowledge-driven based three-dimensional prospectivity modeling of Fe–Cu skarn deposits; a case study of the Fanchang volcanic basin, anhui province, Eastern China

Mineral exploration at depth is becoming increasingly important as a result of the decades of discovery and mining of surficial or near-surface mineralization, leading to targeting of deeper-seated mineralization and mineral systems. The numerous challenges posed by this transition to deeper exploration can be partly overcome by the application of 3D prospectivity modeling. This study provides an outline of this type of prospectivity modeling and focuses on the under-explored Fanchang volcanic basin, an area prospective for skarn-type Fe–Cu mineralization within the Middle–Lower Yangtze River Metallogenic belt (MLYRB) of eastern China. The approach used utilizes a 3D geological model of the Fanchang volcanic basin that enables the identification and extraction of favorable elements for mineralization using 3D spatial and mathematical morphology analysis methods. A 3D distance field method was also used to obtain distance field information for the favorable ore-forming factors delineated during this study. The limited exploration to date in the study area means that there is a lack of specific information (e.g., location, size, grade) for the mineralization in this region. As such, knowledge-driven Index Overlay with Multi-Class (IOMC), Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS), and Fuzzy Comprehensive Evaluation (FCE) approaches were used to generate 3D prospectivity models for the Fanchang volcanic basin. The resulting weight coefficients relating to favorable ore-forming factors were quantified using an Analytic Hierarchy Process (AHP) approach, yielding random consistency ratio (CR) values of 0.0125. These are all less than a value of 0.1, which would indicate inconsistencies between the matrix values and values for the entirety of the hierarchy, indicating that our calculated weighting coefficients are precise and accurate. Comparison of the 3D prospectivity modeling results of the three methods using a prediction area (P–A) plot indicates that 88% of the known mineralization and mineralized occurrences within the basin were located within an area of only 12% of the study area considered prospective during modeling using the IOMC method. In comparison, TOPSIS and FCE modeling positively identified 82% (18% of the study area) and 91% (9% of the study area) of the mineralization in the study area, respectively. These results indicate that these approaches are viable tools for exploration targeting in relatively unexplored areas without specific orebody size, location, and grade data, and the FCE method appears more efficient and reliable than the other two methods in predicting locations to explore for Fe–Cu skarn mineralization. The approaches outlined during this study are widely applicable for exploration for other mineralizing systems in under-explored regions elsewhere and the specific high prospectivity targets identified during this study and the links between exploration indicators and high prospectivity regions also provide key areas and insights for both future modeling and mineral exploration within the Fanchang volcanic basin and the wider MLYRB.

REE and cathodoluminescence features of scheelites from the Tongshankou Cu–Mo deposit in Eastern China

The Tongshankou porphyry-/skarn-type Cu–Mo deposit is located in the Edong ore district, the largest district of the Middle–Lower Yangtze River Metallogenic Belt (MLYRMB) in Eastern China. From the ore-causative granodiorite porphyry and skarn at Tongshankou, three types of scheelite are recognized (Sch1 to Sch3): Sch1-subhedral–anhedral, occurring in the chalcopyrite ores within the porphyry; Sch2-granular, occurring inside garnet in the endoskarn and Sch3-subhedral–anhedral, occurring in calcite veins in the exoskarn. Sch2 and Sch3 have different internal texture according to CL images: Sch2-Dark core and bright rim, with the heterogeneous dark core; Sch3-Dark core and narrow dark rim, showing patches of different brightness in core. In addition, three REE types have been differentiated: 1) REE-Type1: LREE-enriched, HREE-depleted, and negative Eu anomalies patterns (Sch1), which is related to the porphyry system; 2) REE-Type2: No apparent fractionation between LREE and HREE, with positive Eu anomalies (Sch2), which is related to the endoskarn; 3) REE-Type3: Higher LREE and lower HREE with extremely positive Eu anomalies (Sch3), which is related to the exoskarn. The negative MoO3 vs. WO3 correlation for the Tongshankou scheelites suggests Mo-W substitution in the scheelite crystal lattice. No humped pattern (MREEs-enriched) of REE, lower Na content and the lack of correlation between Na and REE at Tongshankou excluded the Na substitute into the Ca site. The positive correlation with Nb and REE for Sch 1 and 3, suggests equation [2] and [3] should be more plausible mechanism to generate the Tongshankou scheelite REE patterns.

Comparative studies on stratabound and skarn-type deposits, Tongling region, lower Yangtze River metallogenic Belt: Constraints from pyrite geochemistry

The Xinqiao and Baoshantao deposits in the Tongling ore-cluster region, Middle-Lower Yangtze River Metallogenic Belt (MLYRMB) are typical stratabound and skarn Cu-Au deposits, respectively. The genetic model of skarn deposits has been fully studied and well established, while the genesis of stratabound deposits remains ambiguous. Two principal viewpoints include a late Carboniferous seafloor exhalative formation and Yanshanian magmatic-hydrothermal origin. In this study, three types of pyrite samples are recognized and collected, they are defined as Py A, Py B and Py C, characterized by fine-grained and anhedral, medium-grained and subhedral, and coarse-grained and euhedral, respectively. EPMA, LA-ICP-MS, and LA-MC-ICP-MS were used to detect major elements, trace elements, and S isotopes of these different pyrites. Ratios of Fe/S (0.99 ∼ 1.05, in mol %), Co/Ni (mostly greater than 1) suggest that both the Xinqiao and Baoshantao deposits were formed in the Yanshanian magmatic-hydrothermal system. The Xinqiao stratabound deposit was formed in a more oxidizing environment and have relatively lower δ34SCDT value (2.57 ∼ 5.95‰) than the Baoshantao skarn deposit (4.97 ∼ 9.57‰), indicating that the ore-forming contribution of strata in Xinqiao deposit is dominated. Combined with regional geological background, it is believed that the ore-hosting strata as well as migrations of magmatic-hydrothermal fluids are two important factors, affecting differences of formation and mineralization between the two types of deposits. Our results directly provide important enlightenments for understanding regional metallogenic mechanism and application of pyrite geochemical exploration.

Geological features and ore-forming mechanisms of the Chating Cu–Au deposit: A rare case of porphyry deposit in the Middle–Lower Yangtze River metallogenic belt

The Chating Cu–Au deposit is an important porphyry deposit located in the Middle–Lower Yangtze River Metallogenic Belt (MLYMB) of eastern China. Drill core logging and ore petrographic observations were systematically employed to recognize the geological features of the deposit. Several important and peculiar geological characteristics are revealed as fellows: (1) the ore-bearing quartz diorite porphyry emplaced within carbonate-dominated strata rather than clastic strata and volcanic rocks, (2) the ore-hosting location confined in the whole cryptoexplosive breccia pipe inside the porphyry stock, and (3) large-scale and barren marbles, marbled limestones, and hornfels almost encircling the porphyry stock and sporadic and barren skarns scattered within the porphyry stock. The fluid-inclusion study at the deposit reports a wide range of homogenization temperatures (161.4 °C–454.2 °C) and salinities (0.2–54.7 wt% NaCl eq) for the ore-forming fluids, and two fluid boiling events as suggested by the coexistence of halite-bearing liquid-rich inclusions and vapor-rich inclusions. In contrast with classical porphyry deposits, the Chating deposit has similar characteristics in the close relationships between the mineralization and the porphyry stock, the hydrothermal alteration zonation, and the fluid evolution process, while the wall-rock strata and ore-hosting position mark outstanding differences of the Chating deposit. The comprehensive geological and geochemical research in this study has been integrated to explore the ore-forming mechanisms of the deposit. The carbonate wall-rock strata were baked by early magma to form low-permeability thermal metamorphic shield at the contact zone, which prevents the migration and loss of the ore-forming fluids and avoid hydrothermal metasomatism for skarn ores. After that, the cryptoexplosions open up the porphyry system and promote the magmatic hydrothermal fluids mixing with the meteoric water, which successively induce the ore-forming fluids boiling and further cause ore-forming materials unloading and precipitation in the cryptoexplosive breccia pipe.

Enrichment mechanisms and occurrence regularity of critical minerals resources in the Yaojialing Zn skarn polymetallic deposit, Tongling district, eastern China

Critical minerals resources are widely used in emerging industries, and their mineralization characteristics and metallogenic regularity are of high importance. Skarn deposits are one of the important sources of critical minerals resources. Yaojialing deposit is a typical large skarn zinc polymetallic deposit in Tongling district of the Middle and Lower Yangtze River metallogenic belt. The ore bodies are mainly lenticular and veined occurrence along the proximal skarn zone and structural or lithologic contacts, respectively. We recognize five hydrothermal stages in the deposit: skarn stage, oxide stage, early sulfide stage, late sulfide stage and carbonate stage. The early and late sulfide stages are the main ore-forming stages. In addition to the production of zinc, gold and copper, the deposit also contains critical element resources such as cadmium, cobalt, selenium, and tellurium. Taking the Yaojialing deposit as an example, this paper shows the occurrence and distribution of critical minerals resources in a typical skarn deposit by using scanning electron microscope, TESCAN integrated mineral analyzer (TIMA), and sulfide LA-ICP MS analysis. Although there are no cadmium minerals in Yaojialing deposit, cadmium can incorporated in the sphalerite lattice, and sphalerite in veins has elevated cadmium content (average 5478.78 ppm). Tellurium content in various sulfides is very low, and it does not enter into the sulfide lattice. It mainly forms tellurobismuthite, hessite and tetradymite, which occur in Cu-Zn ore formed in the early sulfide stage, there are 227 tetradymite grains in a single rock section. Selenium occurs as naumannite in vein ore in the distal of the deposit; selenium can also incorporated the lattice of chalcopyrite and sphalerite, and the selenium content is elevated in sphalerite formed in the early sulfide stage (average 226.80 ppm). The cobalt mineral glaucodot is only found in skarn ore; cobalt easily incorporated the lattice of pyrite and sphalerite, and pyrite and sphalerite formed in the early sulfide stage are enriched in cobalt (average 1962.18 ppm). The characteristics of trace elements in pyrite and sphalerite show that temperature is the main factor affecting the distribution of critical minerals resources, high temperature is conducive to the enrichment of cobalt, selenium and tellurium, while low temperature is conducive to the enrichment of cadmium. Cadmium, cobalt, selenium, and tellurium have high content in specific parts of the deposit, which makes them potentially amenable to recovery.

Titanite Geochemistry and its Implications for Cu Ore Genesis: Insight from Three Diorite Intrusions in the Tongling Ore District of the Middle–Lower Yangtze River Metallogenic Belt

Titanite Geochemistry and its Implications for Cu Ore Genesis: Insight from Three Diorite Intrusions in the Tongling Ore District of the Middle–Lower Yangtze River Metallogenic Belt

A comprehensive overview on the origin of intrusive rocks and polymetallic mineralization in the Tongling ore-cluster region, lower Yangtze River Metallogenic Belt: Geological and geochemical constraints

The Tongling ore-cluster region is one of the most important Cu-Au polymetallic producers in the famous Lower Yangtze River Metallogenic Belt (LYRMB) in eastern China. The Cu-Au polymetallic ore deposits can be divided into four types, i.e., skarn, strata-bound hydrothermal, porphyry, and cryptobreccia, closely related to the Late Jurassic to Early Cretaceous magmatism. We summarize the geology of the Mesozoic Cu-Au deposits in Tongling, eastern China, and revisit the age distributions and geochemical characteristics of associated Mesozoic intrusions, by integrating a large number of published geochemical data (including major and trace elements for both early-stage and late-stage intrusions, whole-rock Sr-Nd-Pb isotopes, and zircon U-Pb age and Hf isotopes for early-stage intrusions), to reveal their sources and genesis.According to the U-Pb ages of intrusions, the main magmatic events in the area can be divided into two stages, i.e., 152–135 Ma and 135–124 Ma, respectively. The early-stage magmatism mainly produced Cu-Au mineralization-related dioritic intrusions, including pyroxene diorite-pyroxene monzodiorite, quartz diorite-quartz monzodiorite, and granodiorite, showing unobvious geochronological order. Geochemical data of Late Jurassic-Early Cretaceous intrusions from the early-stage magmatism suggest that they are all derived from a similar source composed of different proportions of slab-derived melt, metasomatized lithospheric mantle, and a lesser content of lower crust materials. Among them, the key differences lie in that more lower crust materials are incorporated in the source of intermediate-felsic rocks compared to intermediate-basic rocks. The late-stage magmatism produced a wide variety of rocks (diorite porphyry, syenite porphyry, granite porphyry, monzonite, and granite porphyry), which are related to Pb-Zn deposits. The late-stage igneous rocks may evolve from the early-stage rocks and have experienced fractional crystallization of apatite, ilmenite, and other minerals. Both early and late-stage magmatic events in the Tongling region were formed in the subduction setting, and corresponding to compression and extensional setting, respectively.Besides, the H-O isotopes of different kinds of minerals suggest that the ore-forming fluids of most ore deposits were mainly derived from the magma and mixed with a small amount of meteoric water in the late-stage mineralization. The S isotopes of sulfides show that the ore-forming materials come from the magma, accompanied by the addition of original sediments.

Numerical modeling of mineralizing processes during the formation of the Yangzhuang Kiruna-type iron deposit, Middle and Lower Yangtze River Metallogenic Belt, China: Implications for the genesis and longevity of Kiruna-type iron oxide-apatite systems

The Yangzhuang iron deposit is a Kiruna-type iron oxide-apatite (IOA) deposit within the Ningwu mining district of the Middle and Lower Yangtze River Metallogenic Belt (MLYRMB), China. This study applies a numerical modeling approach to identify the key processes associated with the formation of the deposit that cannot be easily identified using traditional analytical approaches, including the duration of the mineralizing process and the genesis of iron orebodies within intrusions associated with the deposit. This approach highlights the practical value of numerical modeling in quantitatively analyzing mineralizing processes during the formation of mineral deposits and assesses how these methods can be used in future geological research. Our numerical model links heat transfer, pressure, fluid flow, chemical reactions, and the movement of ore-forming material. Results show that temperature anomaly and structure (occurrence of the contact of intrusion and the Triassic Xujiashan group) are two key factors controlling the formation of the Yangzhuang deposit. This modeling also indicates that the formation of the Yangzhuang deposit only took some 8000 years, a reaction that is likely to be controlled by temperature and diffusion rates within the system. The dynamic changes of temperature and the distribution of mineralization also indicate that the orebodies located inside the intrusions most likely formed after magma ascent rather than representing blocks of existing mineralization that descended into the magma as a result of stoping or other similar processes. All these data form the basis for future research into the forming processes of Kiruna-type IOA systems as well as magmatic–hydrothermal systems more broadly, including providing useful insights for future exploration for these systems. The simulation approach used in this study has several limitations, such as oversimplified chemical reactions, uncertainty of pre-metallogenic conditions and limitation of 2D model. Future development into both theories and methods will definitely improve the practical significance of numerical simulation of ore-forming processes and provide quantitative results for more geological issues.

Petrogenesis and metallogeny of the Dongguashan Cu-Au deposit in the Tongling ore-cluster region, the Lower Yangtze River Metallogenic Belt: Constraints from geochemistry and geochronology

The Dongguashan Cu-Au deposit located in the eastern portion of the Tongling mining district, the Lower Yangtze River Metallogenic Belt (LYRB), Eastern China is a typical one associated with the Qingshanjiao quartz monzodiorite, including porphyry, skarn, and stratabound ores. In order to constrain the petrogenesis of the intrusive rocks and associated Cu-Au mineralization, detailed analyses of the zircon geochronology and geochemistry, whole-rock geochemistry and Sr-Nd-Pb isotopes, and zircon Lu-Hf isotopes were performed. Magmatic zircons from quartz monzodiorite yield U-Pb ages of 136–138 Ma, revealing their formation ages of early Cretaceous. Geochemical characteristics of the quartz monzodiorites (SiO2 = 63.6–66.2 wt%, high Sr, low Y and Yb concentrations) discriminate their adakitic affinity. They are enriched in LILE and LREE, depleted in HFSE and HREE, and has no or slightly negative Eu anomalies. These geochemical characteristics indicate that the monzodiorites may be primarily derived from the magma mixing of mantle- and LCC-derived melts. The relatively low εNd(t) values (−11.7 to −10.7) and high (87Sr/86Sr)i ratios (0.7075 to 0.7078) may be plausibly interpreted by contamination of enriched mantle materials and/or continental crust. The high radiogenic Pb isotopes with (206Pb/204Pb)i = 17.98–18.09, (207Pb/204Pb)i = 15.51–15.53, and (208Pb/204Pb)i = 38.18–38.26 plot in the field of MORB, near the intersection of EM-1 and EM-2, and are considerably different from those of the upper and lower continental crust and the Dabie adakites, which exclude major contamination from the continental crust. Ti-in-zircon temperatures and calculated Ce4+/Ce3+ values fall within the field between MH and FMQ. The results indicate that the intrusive rocks and associated large-scale Cu-Au mineralization in the Dongguashan deposit are resulted from the magma mixing of mantle- and LCC-derived melts. in a lower magma temperature, yet higher fO2 and water content environment.

The role of evaporite layers in the ore-forming processes of iron oxide-apatite and skarn Fe deposits: Examples from the middle-lower Yangtze River metallogenic Belt, East China

Iron oxide – apatite (IOA) and skarn Fe deposits are important sources of Fe in China. During the Mesozoic, a large number of large IOA and skarn Fe deposits formed in the Middle–Lower Yangtze River Metallogenic Belt (MLYRMB) in a short period. These deposits genetically show a close spatial relationship to Triassic evaporite layers. In this study, the S isotope values of IOA deposits and Fe skarn deposits in the MLYRMB were collected and summarized. Most of the sulfides from Fe deposits have higher S isotope values (5–10‰), and the sulfates have S isotope values (17–21‰) that are similar to those of the evaporite layers (28–30‰), indicating the involvement of the evaporite layers. The effects of the evaporite layers on the mechanism of Fe ore formation are discussed. Evaporite layers are the most important oxidation barrier in the formation of Fe ores, as they can oxidize Fe2+ to Fe3+ in magmatic melts and magmatic-hydrothermal fluids, promoting Fe accumulation. Evaporite layers can also provide Na, Ca, K, Cl, and other agents of mineralization that facilitate the formation and transformation of Fe-bearing fluids and cause the deposits to display large-scale Na and Cl alterations. When sulfate from evaporite layers oxidizes Fe2+ to Fe3+, S6+ is reduced to S2−, becoming a major sulfur source for the formation of either sulfide ores or pyrite deposits after Fe mineralization. Sulfate (gypsum) from evaporite layers could be activated and transferred to the upper or side part of the ore system, forming anhydrite/gypsum ores (veins). Therefore, pyrite, anhydrite, and Fe ores often appear in single deposit.