Ore Genesis Research Articles

Mineral Chemistry and In Situ LA-ICP-MS Titanite U-Pb Geochronology of the Changba-Lijiagou Giant Pb-Zn Deposit, Western Qinling Orogen: Implications for a Distal Skarn Ore Formation

The giant Changba-Lijiagou (Ch-L) Pb-Zn deposit is in the northeast part of the Xicheng ore cluster, Western Qinling Orogen. The ore genesis remains controversial; it could be either a sedimentary exhalative genetic type or an epigenetic hydrothermal genetic type. Here, in situ titanite U-Pb dating for the two kinds of titanite is presented, yielding ages of 212.8 ± 3.0 Ma in the mineralized skarn ore and 214.6 ± 5.1 Ma in the host rock. These ages conform to the previously reported magmatic zircon age (229–211 Ma) based on the in situ zircon U-Pb dating of plutons in this district and the time of large-scale magmatic–hydrothermal activities in Western Qinling Orogen (229–209 Ma). Titanites occurring in mineralized skarn and those that are calcite-hosted are similar to hydrothermal-origin titanites in major element characteristics. The Eu anomalies in the two types of titanite record oxidizing conditions during the mineralization process. A mineral assemblage of garnet, pyroxene, riebeckite, biotite, and potash feldspar, replacing the albite, is well-developed in the deposit. The mineralogical and geochronological characteristics indicate that the Ch-L Pb-Zn deposit is a distal skarn deposit and the result of intensive tectonomagmatic processes in the Xicheng ore cluster during the process of the Late Triassic orogeny.

Genesis of high-grade lode gold shoot dominated by ore fluid overprinting during a ductile-brittle shear event

Lode gold deposits hosted by ductile-brittle shear zones account for more than one-third of the world’s gold production. High-grade ore shoots from this type of deposit are the most critical exploration targets. The ore shoots can form through the post-depositional deformation of auriferous sulfides or overprinting of ore fluids accompanied by coupled dissolution-reprecipitation (CDR) reactions. However, the mechanism that dominates ore shoot genesis remains unknown, primarily due to the controversial single progressive or polyphase nature of ore-bearing shear zones. Here, we report on geological and geochemical analyses we conducted at the large Hetai goldfield, South China, to construct an accurate gold upgrading model for the formation of ore shoots. Stages 1−3 of mineralization at Hetai show features typical of ductile shearing, while Stage 4 is characterized by quartz-sulfide veinlets in brittle fractures. 40Ar/39Ar ages of ca. 184 Ma and 157 Ma for the mineralization of stages 1 and 4 overlap with the regionally dextral ductile-brittle shear that occurred during ca. 210−162 Ma. Thus, the gold event at Hetai should have been controlled by a single progressive ductile-brittle shear episode, rather than polyphase structural events. The auriferous fluids at Hetai precipitated minor invisible gold in pyrites (mean 0.173 ppm) produced during stages 1−4 through fluid-rock interaction. The systematic increase of elements Au, As, Sb, Bi, Ag, and Cu and δ34S values in ductile-deformed pyrites from stages 1−3 indicate that early invisible gold upgrading should be the result of the post-depositional remobilization of auriferous sulfides during the long-lived ductile-brittle transition. Cataclastic pyrites hosting invisible gold from Stage 4 have zoned and porous mantles with elevated invisible gold (mean 0.503 ppm) and Sb, Bi, Pb, Co, Ni, and Ti contents. These pyrites are further replaced by chalcopyrite and pyrrhotite with increasing invisible gold, Co, and Ni contents. In addition, numerous visible native gold grains in Stage 4 are included in sulfides formed by replacement and develop along the microfractures and grain boundaries of these sulfides. We suggest the late invisible and visible gold upgrading events in Stage 4 can be attributed to the auriferous fluid superposition and subsequent replacement of pyrite via CDR reactions in a brittle regime. Therefore, the gold upgrading process at Hetai is jointly caused by the early remobilization induced by ductile-brittle deformation and the late ore fluid superposition with accompanying CDR reactions within a brittle domain. As the ore fluid superposition and CDR reactions in Stage 4 produce a significant amount of visible gold, they exert a first-order control on the genesis of ore shoots at Hetai. The refined model may be widely applicable to lode gold deposits elsewhere and can be used to identify regions with promising exploration targets.

Source of Ore-Forming Fluids and Ore Genesis of the Batailing Au Deposit, Central Jilin Province, Northeast China: Constraints from Fluid Inclusions and H-O-C-S-Pb Isotopes

The Batailing Au deposit is a vein-type deposit in central Jilin Province, situated in the southern sector of the Lesser Xing’an–Zhangguangcai Range within the eastern Central Asian Orogenic Belt. NE-trending fault-controlled orebodies occur in the Upper Permian Yangjiagou Formation and quartz diorite–porphyrite. The mineralisation process was delineated into three stages: (I) quartz–arsenopyrite–pyrite, (II) quartz–polymetallic sulphides (main Au mineralisation stage), and (III) quartz–pyrite–carbonate. Fluid inclusions (FIs) in quartz were identified as four types: PC-type (pure CO2), C1-type (CO2-bearing), C2-type (CO2-rich), and W-type (aqueous two-phase). Raman spectroscopy analysis revealed that the vapor components of the FIs predominantly comprised CO2 with minor quantities of CH4 in stages I–II. Stages I and II encompassed four types of FIs with homogenisation temperature ranging from 264 to 332 °C and 213 to 292 °C and salinity spanning from 4.7 to 11.2 wt% and 1.8 to 11.6 wt%, respectively. Stage III exclusively contained W-type FIs with homogenisation temperature ranging from 152 to 215 °C and salinity spanning from 1.4 to 6.4 wt%. H-O isotopic values (δD = −84 to −79.6‰, δ18OH2O = 6.2 to 6.4‰ in stage I and δD = −96.4 to −90.4‰, δ18OH2O = 2.8 to 4.4‰ in stage II) and microthermometric data indicated that the ore-forming fluids are initially from a magmatic source, with later meteoric water input. Low C isotopic data from CO2 in FIs in quartz (−24.4 to −24.3‰ in stage I and −23.7 to −22.6‰ in stage II) indicated an organic carbon source. Ore precipitation is mainly attributable to fluid immiscibility. S-Pb isotopic data (δ34S = −3.5 to −1.6‰; 206Pb/204Pb = 18.325–18.362, 207Pb/204Pb = 15.523–5.562, 208Pb/204Pb = 38.064–38.221) revealed that ore metals primarily originated from magma. Based on this research, the origin of the Batailing Au deposit is of the mesothermal magmatic–hydrothermal lode type.

Geochronology, in-situ elements and sulfur isotopes of sulfides from the Songjiashan cobalt-iron deposit in the Zhongtiao mountains of North China Craton: Implications for cobalt occurrence and ore genesis

The Songjiashan Co-Fe deposit in the central part of the “Tongshan skylight” on the southeastern edge of the Zhongtiao Mountains is hosted by the volcanic-sedimentary rock series of the Paleoproterozoic Songjiashan Group. The spatial distribution of the orebodies is controlled by south-north trending rock units. Based on microscopic observations, the dominant ore minerals included magnetite, pyrite, chalcopyrite, carrollite, and linnaeite, while gangue minerals comprised quartz, calcite, sericite, and chlorite. Cobalt-iron ores had massive, banded, disseminated, and veinlet texture, and alteration of the host rocks included silicification, sericitization, pyritization, carbonation, and chloritization. Mineralization processes of the Songjiashan deposit were grouped into three periods: sedimentation, metamorphism, and hydrothermal. The Co concentrations in hydrothermal pyrite (Py-III) varied from 1.05 % to 3.75 %, with an average of 2.45 %. Cobalt in pyrite was homogeneously distributed and inversely correlated to Fe, indicating that Co isomorphically replaced Fe in pyrite. The characteristic Co/Ni ratio of pyrite varied greatly, ranging from 0.1 to 1000, reflecting various genetic types of sedimentation, metamorphism, and hydrothermal mineralization, with the main mineralization period primarily related to hydrothermal activities. Zircon U-Pb geochronology of the host rock and Re-Os isochron of Co-bearing pyrites indicate that Co mineralization mainly occurred at ∼2100 Ma. In-situ S isotopic analysis of sulfides reveals two peak δ34S values of 5–9 ‰ and 12–16 ‰. We interpret that the former value reflects the mixing of volcanic and marine sulfate sources, while the latter value is mainly artributted to marine sulfate sources. All δ34S values were lower than those of Proterozoic marine sulfates (15–20 ‰). Accordingly, we infer that thermochemical sulfate reduction plays a key role in marine sulfate reduction, and that the formation of Co-rich ore bodies in the Songjiashan deposit have undergone processes of initial sedimentation, metamorphism-deformation, and subsequent hydrothermal overprinting. Genetically, we suggest that the Songjiashan deposit belongs to a sedimentary-metamorphic hydrothermal superposition type Co-Fe deposit.

Geology and S-Pb isotope geochemistry of the Hatu gold deposit in West Junggar, NW China: Insights into ore genesis and metal source

Geology and S-Pb isotope geochemistry of the Hatu gold deposit in West Junggar, NW China: Insights into ore genesis and metal source

Genetic link between the Kangjiawan gold deposit and late Jurassic granitic magmatism, South China: Constraints from in situ calcite U-Pb dating, sulfur isotope and trace elements of pyrite

(Meta)sedimentary rock-hosted gold (Au) deposits are globally important Au resources, of which ore genesis and mineral exploration have been attracted considerable attention. However, the precise dating of Au mineralization of those Au deposits remains challenging due to the absence of suitable dating minerals, thus impeding a comprehensive understanding of their genesis. The Kangjiawan Au deposit, situated in the southern Hunan Province, South China, is one of representative (meta)sedimentary rock-hosted Au deposits. Due to the lack of mineralization age, the genesis of Kangjiawan Au deposit is still a matter of debate. Here we report the data of in situ calcite U-Pb dating, in situ trace elements and sulfur isotope analysis of pyrite, to further constrain the mineralization timing and the sources of ore-forming materials of the Kangjiawan Au deposit. Based on the detailed field investigation and petrographic observations, three mineralization stages have been identified: pyrite (Py1) + quartz (Stage I), gold-bearing pyrite (Py2) + polymetallic sulfides + quartz + calcite (Stage II), and gold-bearing pyrite (Py3) + calcite (Stage III). The results of mineralogical and trace elemental analyses indicate that Au are mainly hosted in Py2 (average 14.19 ppm) and Py3 (average 4.80 ppm), primarily as the form of “invisible gold”. In situ LA-ICP-MS U-Pb dating on calcite intergrowth with the gold-bearing pyrite (Py3) yields a Tera-Wasserburg lower intercept age of 151.7 ± 5.4 Ma. This age is well consistent with the published zircon U-Pb age (158.3 ± 1.2 Ma) of the nearby Shuikoushan granodiorite, the molybdenite Re-Os age (157.8 ± 1.4 Ma) of the Laoyachao skarn Pb-Zn deposit in the Shuikoushan ore field, and the garnet U-Pb age (159.1 ± 1.9 Ma) of the skarn Pb-Zn ore in depth of the Kangjiawan Au deposit. These suggested that the Au mineralization of the Kangjiawan deposit is coeval with the emplacement of the Shuikoushan granodiorite and Laoyachao Pb-Zn mineralization, which are important parts of the large-scale Middle-Late Jurassic Cu-Au-Pb-Zn Metallogenic event of the Qin-Hang Metallogenic Belt, South China. In addition, trace elemental contents, such as relative low Co, Ni, and Se (i.e., <0.01 to 100 ppm), and a narrow δ34S range of −2.94 ‰ ∼ +3.03 ‰ of pyrite, indicate that ore-forming materials were mainly derived from granitic magmas. Integrated with previous studies, it is suggested that the Au mineralization in the Kangjiawan deposit is genetically associated with the late Jurassic granitic magmatism and is probably as the distal products of the deep-seated concealed granitic intrusions and related proximal skarn Pb-Zn ore.

In-situ geochemical and isotopic analyses of multiple pyrite generations: Insights for the giant Beiya Au polymetallic ore genesis in southwestern China

The Beiya giant Au polymetallic deposit is located in the Sanjiang Tethyan Orogen, northwestern Yunnan (SW China). The ores occur as disseminations or veinlets in granite porphyry. To unravel the ore genesis at Beiya, we analyzed the ore-related sulfide trace elements and sulfur isotopes. Py-1 is mainly euhedral-subhedral medium-/coarse-grained (size: > 100 μm), with relatively smooth surface and some pores. Py-2 is mostly coarse grained (size: 50–200 μm), with well-developed pores and inclusions. The pyrite is usually Co-Cu rich and V-Ti-Sb poor, resembling typical magmatic-hydrothermal pyrite. In addition, the Co/Ni ratios decrease from pyrite-1 (Py-1) to pyrite-2b (Py-2b), suggesting that their chemical compositions are controlled by magma fractionation. We found that Co, Ni, As, and Se occurred as solid solution in the pyrite lattice, while Pb, Bi, Ag, and Mn occurred mainly in inclusions in the pyrite. Pb and Bi display good positive correlation, suggesting that they occurred as inclusions or nano-particles in pyrite lattice. The pyrite samples have sulfur isotope value (δ34S) of 0.62–3.45 ‰ (avg. 2.35 ‰) for Py-1, 0.18–3.12 ‰ (avg. 1.85 ‰) for Py-2a, and 0.62–4.18 ‰ (avg. 2.51 ‰) for Py-2b. These characteristics may have played a vital role in the initial enrichment of Cu, Mo, Au, and ultimately formed the complex polymetallic system at Beiya.

Dual-mineralization in the intracontinental Jiangnan Orogen, South China: Evidence from textures and in-situ trace elements and oxygen analysis of quartz from the Woxi Au-Sb-W deposit

The Jiangnan Orogenic Belt (JOB), situated in the interior of the South China Block (SCB), harbors numerous gold-polymetallic deposits, but the ore genesis has been a long-standing controversy. This study examines the Woxi super-large gold deposit in the middle JOB, which is characterized by simultaneous large-scale antimony-tungsten mineralization. The investigation shows that the Woxi ore deposit have developed multiple-stage quartz, i.e., Qz1 (early quartz-carbonate, stage I), Qz2 (quartz-wolframite-scheelite, stage II), Qz3a (quartz-gold-pyrite, early stage III), Qz3b (quartz-stibnite-scheelite, late stage III) and Qz4 (late quartz-carbonate, stage IV). We conducted SEM-CL texture imaging, LA-ICP-MS trace element, and SIMS oxygen isotope analysis on the quartz samples from the main mineralization stages (mainly Qz2 and Qz3). The results reveal a dual mineralization process of the Woxi gold-antimony-tungsten deposit. In the initial stage, the quartz (Qz2) exhibits intense brightness in CL imaging and spiderweb-like texture, shows high concentrations of trace elements, especially Ge, Al and Ti, and has δ18Ofluid values ranging from 10.84 ‰ to 11.64 ‰. These characters are consistent with a magmatic fluid that is acidic (pH<3), reducing, and of relatively high-temperature. In the second stage, the quartz (including Qz3a, Qz3b and Qz4) shows relatively darker CL image and band texture or cobweb mosaic coexistence texture, low concentrations of trace elements, especially Al and Ti, and a low δ18Ofluid values (8.01 ‰ to 9.19 ‰ for Qz3a and 5.83 ‰ to 6.51 ‰ for Qz3b) consistent with characteristics of mantle-derived fluids. The results of this study supports an “intracontinental reactivation metallogenic model”, in which the gold-polymetallic deposits in the JOB formed from a dual-stage mineralization related to tectono-magmatic activities in a back-arc setting. The dual ore-forming processes revealed in this study provide important insights for a comprehensive understanding of the gold-polymetallic deposits in the JOB, and it may be a significant mechanism in the formation of large to super-large gold-polymetallic deposits in this region, which is indicative perspective for exploration of the gold-polymetal deposits. Our work also demonstrates that quartz is an effective tool for identifying the mineralization in the JOB.

Features of the genesis of manganese ores of the Kvirila deposit, Georgia (according to the data carbon and oxygen isotope composition and rare earth elements geochemistry)

Features of the genesis of manganese ores of the Kvirila deposit, Georgia (according to the data carbon and oxygen isotope composition and rare earth elements geochemistry)

Iron isotope constraints on the genesis of giant Beiya Au-base metal deposits, Yunnan, Southwest China

The Beiya Au-base metal deposit in southwest China is characterised by a huge amount of iron associated with gold mineralization. The formation of the Beiya deposit is generally thought to be related to Tertiary potassic intrusion, as porphyry- and skarn-type mineralization are the two most important types of mineralization in the region. However, the lack of direct evidence to constrain the source of iron and gold as well as other metals makes it difficult to accurately conceptualise the ore genesis model. In this study, we report high-precision (0.03 ‰; 2sd) Fe isotope data on Fe-bearing minerals including magnetite, pyrite and chalcopyrite, and major igneous rocks exposed in the area, including monzogranite porphyry (MGP), mafic microgranular enclave (MME), lamprophyre and basalt. Magnetites have a wide range of δ Fe from 0.15 to 0.64 ‰, reflecting substantial isotopic fractionation at different mineralization stages. MMEs have heaviest Fe isotopic composition (0.35 ‰ to 0.88 ‰) compared to MGPs (0.19 ‰ to 0.48 ‰), lamprophyre (∼0.2 ‰) and basalt (∼0.0 ‰). A negative correlation between δ56Fe and TFe2O3 is found for both MPGs and MMEs, which indicates the leaching of iron by hydrothermal fluids mobilizes light Fe and leaves behind isotopically heavy Fe in the remaining source rock. Fe isotopic compositions of MPG and MME overlap with those of magnetite, both of which are proposed to be the source of Fe in magnetite. The basalt has δ56Fe value of 0 ± 0.03 ‰, similar to those of global basalts, suggesting a negligible contribution to the formation of iron ores. Therefore, we propose that magmas parental to the MGP and MME may be the main source of iron to form the Beiya deposit; post-magmatism hydrothermal activities play a key role in leaching the metals out and transporting them to the mineralization area.

New discovery of the Early Paleozoic carbonatite in Bayan Obo (China): Insights into the giant REE accumulation

The Bayan Obo deposit in China hosts the world’s largest rare earth element (REE) resource. Age dating results for Bayan Obo range across approximately one billion years (from ∼1.4 to 0.3 Ga), with three age groups (∼1.3 Ga, ∼0.45–0.40 Ga, and 0.28–0.26 Ga). Carbonatite dated to around 1.3 Ga and granitoids to approximately 270 Ma have been identified. The Early Paleozoic vein-type mineralization is widespread in the deposit. However, magmatic activity related to the highest age peak at ∼0.4 Ga has not well been identified in the deposit, complicating the interpretation of the ore genesis. In this study, we report a zircon 232Th-208Pb age of 435.2 ± 4.6 Ma (MSWD = 1.9, N = 26) from carbonatite in Bayan Obo. The zircon morphology, characterized by bipyramidal crystal forms, low U concentrations (mostly < 1 ppm), high Th/U ratio, and carbonatite-like oxygen isotopes (5.92 ± 0.31 ‰), demonstrates that the zircon crystallized from carbonatitic magmas, thus their ages represent the timing of magmatic activity. Although remelting of the Mesoproterozoic carbonatite during Paleozoic carbonatite has been previously documented, the newly identified Early Paleozoic carbonatite derives from a different mantle source, as indicated by their more radiogenic Hf isotope compositions. This suggests that the Bayan Obo deposit experienced multiple carbonatitic activities. The Early Paleozoic carbonatitic activity may have facilitated element mobilization and mineral recrystallization, improving the exploitable levels of the world’s largest REE deposit.

Data mining for geochemical signatures of volcanic-type uranium mineralization, Duolun-Guyuan prospect, North China

Application of advanced data mining methods to various types of geochemical data is able to fingerprint valid signatures of mineralization, thus unveiling ore genesis and discovering new minerals. But individual studies that apply data mining methods to both local- and regional-scale, both sediment and whole-rock multi-element geochemical data sets are relatively scarce. Here, we applied data mining methods, including multivariate statistical analysis (principal component analysis), spatial analysis (trend surface analysis), unsupervised machine learning algorithm (K-means clustering), supervised algorithms (random forest and deep neural network) to both regional sediment geochemical and local lithogeochemical data from the Duolun-Guyuan prospect, in order to determine the geochemical signatures of volcanic-type uranium mineralization through characterizing: (1) representative element associations; (2) axial zonation of primary haloes; (3) element distribution patterns; and (4) crustal structures (via deep learning-based predictive hafnium (Hf) isotopic mapping). Results of principal component analysis and random forest show that samples from known ore districts (e.g., Zhangmajing and Daguanchang) exhibit a distinct combination of major ore-forming elements (U and Mo), chalcophile elements (Ag, Hg, Pb, Sb and As), rare and rare earth elements (Be, Li, La, Nb and Y), tungsten (W), bismuth (Bi), and rock-forming elements (SiO2, K2O, Na2O and Al2O3), differing from samples of both the mineralized and barren areas. The axial zonation of primary haloes in Daguanchang is comprised of supra-ore haloes (rare earth elements, Th, Nb, Zr, Hf, Ga and Rb), near-ore haloes (U, Mo, Pb, Zn, Cd and Sb), and sub-ore haloes (Li, Be, Sc, V, Cu, Sr, Cs, Ba, W and Bi). Moreover, trend surface analysis shows that in the study area, the spatial distribution pattern of the supra-, near-, and sub-ore elements forms a northwesterly alignment, with the supra-ore elements concentrated in the southeast, the sub-ore elements in the northwest, and the near-ore elements in between. Finally, deep learning-based predictive hafnium (Hf) isotopic mapping reveals that the Duolun-Guyuan prospect is dominated by negative mean zircon εHf(t) values ranging from −17 to 0, except for some local areas in the west and southwest of Duolun and the north of Weichang. The above results may indicate critical signatures of volcanic-type U mineralization, consisting of meta- or pera-luminous, alkaline rhyolite resulted from crustal reworking, surrounding mantle-derived igneous rocks, proximal heat source, accompanying epithermal deposits (e.g., Ag, Au, etc.), and anomalous concentrations of U, Mo and relevant elements particularly Th, W, Bi, Ag and Sb etc. Our study will effectively provide new exploration geochemical indicators of volcanic-type U deposit.

Deciphering ore genesis with oxygen and sulfur isotope signatures: A case study from the Singhbhum Shear Zone, Eastern India

The importance of light-stable isotopes and their mass-dependent fractionations in understanding past geological processes is enormous. The present research delivers precise, high-resolution, in-situ oxygen (18/16O) and triple sulfur (32/33/34S) isotope ratios from quartz and sulfide minerals found in the CuAu Kendadih deposit located along the Mesoproterozoic (∼1.6 Ga) Singhbhum Shear Zone (SSZ) in eastern India. Oxygen and sulfur isotope analyses were carried out on quartz and pyrite-chalcopyrite pairs that are in textural equilibrium, using the most advanced Large Geometry-Secondary Ion Mass Spectrometer (LG-SIMS; CAMECA IMS-1300HR3). The results show restricted ranges for δ18Oquartz (+6 to +7.7‰; average: 6.9 ± 0.9‰, n = 50) and δ34Schalcopyrite-pyrite (+11.4 to +11.9‰; average: 11.79 ± 0.2‰, n = 62). This isotopic homogeneity suggests a single, uniform fluid source for the ore-forming metals. The combined oxygen, sulfur isotope ratios, and fluid inclusion data are consistent with a hydrothermal fluid derived from an “I-type” granitic melt. This study incorporates existing fluid inclusion, stable, and radiogenic isotope data from temporally similar deposits within the shear zone, reevaluating their implications in light of the new findings. It proposes that, around 1.6 billion years ago, underplating the Singhbhum Craton by the Dalma Plume resulted in the remelting of the lower crust. This remelting is attributed to the plume's introduction of a significantly elevated thermal perturbation. The process is hypothesized to have led to the generation of second-order granitic melts. Upon emplacement in the lower crust, these granitic melts became the potential source for essential metals, ligands, and hydrothermal fluids, contributing to mineralization within the deep-seated Singhbhum Shear Zone. This research attempts to comprehensively describe the “source-to-sink” ore genesis model by proposing potential magma chamber processes that concentrate metals and ligands at the roof zone, followed by the separation of metal-rich hydrothermal fluids, fluid-rock interaction, and the physicochemical conditions governing the deposition of the extensive polymetallic deposit. This work offers novel insights into the Mesoproterozoic metallogenesis along the Singhbhum Shear Zone, challenging existing paradigms that favored evaporite or seawater brine sources. Furthermore, it sheds light on the Mesoproterozoic sub-crustal processes beneath the Indian Craton in this region.

Source of ore-forming materials and ore genesis of the Liangyan lead-zinc deposit in the northwestern Guizhou

Source of ore-forming materials and ore genesis of the Liangyan lead-zinc deposit in the northwestern Guizhou

Genesis of W mineralization in the Yangla Cu-polymetallic deposit (NW Yunnan, China): Constraints from scheelite microstructure, trace element, U-Pb dating and Sr isotope geochemistry

The Yangla Cu-polymetallic deposit is the largest skarn Cu deposit in the Jinshajiang suture zone. Recently, an new W orebody was identified in the depths of the Cu orebodies. However, the genetic relationship between W and Cu orebodies, along with the tungsten ore-forming processes, remains unclear. This study delves into the careful investigation of three types of scheelites focusing on microstructure, trace element compositions and Sr isotope geochemistry. The aim is to elucidate the source and evolution of ore-forming fluids and ore genesis in the multi-episodic metallogenic systems. Primary scheelite (Sch-I) generally displays oscillatory zoning in CL images with the lowest REE (3.8–142 ppm) and highest Sr (604–1480 ppm) contents. Secondary scheelite (Sch-III), commonly precipitated as overprinting rims on primary crystal, has the highest REE (145–1071 ppm) and lowest Sr (376–793 ppm) contents. In contrast, Sch-II represents a transitional stage from primary to secondary, with REE and Sr contents at intermediate levels. Sch-I is characterized by LREE enrichment and a positive Eu anomaly in the chondrite-normalized REE patterns, whereas Sch-III shows MREE-rich patterns with a weak positive Eu anomaly. Scheelite U-Pb dating (30.3 ± 1.5 Ma) indicates that the W mineralization is not genetically related to Triassic granitoids in the Yangla district. Instead, it is likely associated with magmatic activities and tectono-thermal events in the Jinshajiang fault zone during the Cenozoic. The high initial 87Sr/86Sr ratios (0.71771–0.72229) in the scheelite, significantly higher than those of Triassic granites and ore-hosting marble, suggest that the geochemical features of Sch-I are inherited from the parental ore-forming fluids. These fluids are likely derived from the mixed hydrothermal fluids involved by the Neoproterozoic strata and/or concealed magmatism.

Fluid source and ore-forming process of the Lishupo Au deposit, NE Hunan: Constraints from fluid inclusions, SIMS oxygen isotope, LA-ICP-MS pyrite trace elements and fsLA-ICP-MS quartz trace elements

The Lishupo Au deposit (4.3 t @ 4.76 g/t) is located in the central Jiangnan Orogen. The processes and origins of regional gold mineralization, as well as the characteristics of the ore-forming fluids, continue to be poorly understood. This study integrates field geology, fluid inclusions, secondary ion mass spectrometry (SIMS) O isotope, femtosecond laser ablation inductively coupled plasma mass spectrometry (fsLA-ICP-MS) trace elements analysis for quartz, and LA-ICP-MS for trace elements study of pyrite to constrain the nature and source of ore-forming fluids, mechanism of gold precipitation, and ore genesis. Field investigations and microscopic observations reveal three mineralization stages at Lishupo: (1) the quartz-pyrite (Qtz1-Py1) stage; (2) the quartz-dolomite-polymetallic sulfides-gold (Qtz2-Py2) stage; and (3) the quartz-carbonate-pyrite (Qtz3-Py3) stage.Cathodoluminescence (CL) observations reveal that Qtz1 and Qtz2 have a homogeneous texture, while Qtz3 exhibits oscillatory zoning. Fluid inclusions in quartz suggest a CO2-H2O-NaCl ± N2 ± CH4 fluid system, which comprise H2O-CO2-NaCl, CO2-rich, and aqueous types. Microthermometry of fluid inclusions indicates low salinity (stage 1: 3.7–7.9 wt% NaCl equiv.; stage 2: 2.2–7.5 wt% NaCl equiv.; stage 3: 1.4–3.9 wt% NaCl equiv.) and medium to low temperature (stage 1: 313–341 °C; stage 2: 209–286 °C; stage 3: 139–198 °C) for ore-forming fluids, consistent with the low Ti content (<10 ppm) found in the quartz. The low Al content (7.99–20.7 ppm) of Qtz1 suggests that the ore-forming fluids were saturated with CO2 and had a near-neutral pH. The Al contents are higher and more variable in Qtz2 (10.7–1959 ppm) and Qtz3 (21.6–713 ppm), which may imply fluctuations in fluid pH. δ18OFluid values for various types of quartz (Qtz1: 9.02–10.95 ‰, Qtz2: 6.30–7.68 ‰, Qtz3: 3.45–3.94 ‰) indicate a metamorphic fluid origin for stages 1 and 2 fluids, which were mixed with the meteoric water during stage 3. The highest concentrations of Au and As in Py2 suggest that the Qtz2-Py2 stage is the primary ore stage. The Co/Ni ratios of all types of pyrite are less than 1, indicating that the ore-forming materials are derived from metamorphic sedimentary rocks. Fluid inclusion microthermometry suggests that fluid immiscibility was responsible for the gold deposition during the Qtz2-Py2 stage. Fluid immiscibility destabilizes Au(HS)2-, leading to the precipitation of native gold. These data strongly suggest that the Lishupo gold deposit is classified as an orogenic-type deposit. Integrating the existing geochronology data and geological context, we emphasize the presence of the Late Triassic orogenic gold deposit in the Jiangnan orogen. This highlights a significant exploration target area within this zone for future gold prospecting.

Geology and Geochronology of Magmatic–Hydrothermal Breccia Pipes in the Yixingzhai Gold Deposit: Implications for Ore Genesis and Regional Exploration

Magmatic–hydrothermal breccia pipes are widespread in numerous major porphyry and epithermal gold deposits globally, representing significant repositories of metal resources and serving as potential indicators for exploration targeting. More than ten breccia pipes occur in the Central Taihangshan District (CTD) of the North China Craton. Some of these breccia pipes host gold mineralization and are proposed to be related to the adjacent lode gold mineralization. However, the lack of detailed geological constraints make this hypothesis ambiguous. To address this, the present study conducted comprehensive field observations, drill core logging, an in situ sulfur isotope analysis of pyrite, and the 40Ar/39Ar dating of adularia along a 1400 m section of the Tietangdong breccia pipe at Yixingzhai. Three distinct breccia facies were identified at Tietangdong, exhibiting variable proportions across the entire section, including a massive skarn breccia; polymictic, skarn matrix-supported breccia; and polymictic, intrusive rock cement chaotic breccia. Furthermore, adularia 40Ar/39Ar dating indicates a syn-/post-gold mineralization age of 136 ± 1.5 Ma, coinciding with the age of post-breccia felsite dike. The deepest sampled pyrite displays δ34S values of ~2.7‰, strongly indicating a magmatic–hydrothermal signature. These results, when combined with the geological, geochronological, and isotopic studies on the adjacent lode gold mineralization, further suggest a close genetic relationship between the breccia pipes and the lode Au mineralization, paving the way for their utilization as effective indicators for gold targeting within the CTD.

Multi-stage magmatism and Sn-polymetallic mineralization in the Shuicheng Region, SW China

The economically important tin‑tungsten mineralization in southwestern China has attracted much interest in recent years, yet its age, tectonic setting, and genetic relationship to the host granites remain uncertain in most regions. Our focus in this study is the Shuicheng tin-polymetallic deposit, situated in the western sector of the Diantan Batholith, within the northern Tengchong Block. The granites in this area consist of two intrusive units, i.e., 1) biotite monzogranite (T1), with LA-ICP-MS zircon UPb ages ranging from 76.88 ± 0.43 Ma to 74.69 ± 0.57 Ma, whole-rock εNd(t) values ranging from −9.75 to −8.11, and zircon εHf(t) values from −12.19 to −8.85; and 2) alkali-feldspar granite (T2), with an LA-ICP-MS zircon UPb age of 52.16 ± 0.23 Ma, whole-rock εNd(t) values of −10.15 to −8.25, and zircon εHf(t) values of −9.64 to −8.06. These two intrusive events have been linked to prolonged low-angle subduction and retreat of the subducting Neo-Tethys Ocean Plate, respectively. The Shuicheng granites exhibit high concentrations of SiO2 and Al2O3, contrasted with low levels of FeOT, CaO, MgO, TiO2, and P2O5, suggesting that they are highly fractionated S-type granites. High abundances of Rb, K, U, and Hf, along with low contents of Ba, Sr, and Ti, further indicate significant fractionation and crystallization processes during magma evolution. Importantly, a transition from purely magmatic conditions to a magmatic-hydrothermal state occurred during the latter stages of magmatic evolution. This transition, associated with an amplified potential for tin mineralization, provides fresh insight into the role of magmatic processes in ore genesis, enriching our understanding of the tin‑tungsten mineralization history of the Tengchong region.

Constraints on Ore Genesis from Trace Ore Mineralogy: A New Occurrence of Kupčíkite and Paděraite from the Zhibula Cu Skarn Deposit, Southern Tibet

Mineral assemblages containing Cu-Bi sulfosalts, Bi chalcogenides, and Ag-(Au) tellurides have been identified in the mid-Miocene Zhibula Cu skarn deposit, Gangdese Belt, southern Tibet. Different mineral assemblages from three locations in the deposit, including proximal massive garnet skarn, proximal retrogressed pyroxene-dominant skarn in contact with marble, and distal banded garnet–pyroxene skarn hosted in marble, are studied to constrain the evolution of the mineralization. Hypogene bornite contains elevated Bi (mean 6.73 wt.%) and co-exists in proximal andradite skarn with a second bornite with far lower Bi content, carrollite, Au-Ag tellurides (hessite, petzite), and wittichenite. This assemblage indicates formation at relatively high temperatures (&gt;400 °C) and high fS2 and fTe2 during prograde-stage mineralization. Assemblages of Bi sulfosalts (wittichenite, aikinite, kupčíkite, and paděraite) and bismuth chalcogenides (e.g., tetradymite) in proximal pyroxene skarn are also indicative of formation at relatively high temperatures, but at relatively lower fTe2 and fS2 conditions. Within the reduced distal skarn (chalcopyrite–pyrrhotite-bearing) in marble, cobalt, and nickel occur as discrete minerals: cobaltite, melonite and cobaltic pentlandite. The trace ore mineral signature of the Zhibula skarn and the distributions of precious and critical trace elements such as Ag, Au, Co, Te, Se, and Bi support an evolving magmatic–hydrothermal system in which different parts of the deposit each define ore formation at distinct local physicochemical conditions. This is the first report of kupčíkite and paděraite from a Chinese location. Their compositions are comparable to other occurrences, but conspicuously, they do not form nanoscale intergrowths with one another.

Geology, fluid inclusion, 40Ar-39Ar geochronology, and isotope constraints on the ore genesis of the Ershiyizhan Cu–Au deposit, Heilongjiang Province, China

The Ershiyizhan Cu–Au deposit, located in the eastern part of the upper Heilongjiang metallogenic belt, north of the Great Xing'an Range, is composed of orebodies from the Mesozoic magmatic rocks and the Ershierzhan group. There are three metallogenic stages of this deposit, (1) Quartz-K-feldspar-polymetallic sulfide stage (stage Ⅰ), (2) quartz-polymetallic sulfide stage (stage II), and (3) quartz-calcite ± pyrite stage (stage Ⅲ). Three types of fluid inclusions (FIs) were discovered in the vein mineral assemblages, liquid-rich two-phase aqueous FIs (L-type), vapor-rich aqueous FIs (V-type), and multi-phase FIs (S-type) with daughter minerals, including S1-type inclusions homogenized through vapor disappearance and S2-type inclusions homogenized by halite dissolution. Quartz of stage I and stage II contains all of these FIs. In contrast, the L-type fluid inclusions of stage III veins are the only ones present in the calcite. The homogenization temperatures and salinities obtained from FIs in stages I, II, and III range from 330 to 563 °C, 223 to 423 °C, and 108 to 225 °C, and 0.88 to 66.18 wt%, 2.41 to 48.59 wt%, and 0.18 to 3.23 wt% NaCl equiv., respectively. δ18O and δD values obtained from stable isotope analyses of K-feldspar and quartz samples collected from stages I, II, and III range from −2.31 to 7.89 and −133.2 to −98.2, respectively. Microthermometry and H-O isotope data from FIs suggest that the ore-forming fluids of the deposit had a magmatic origin, characterized by high temperatures, low–high salinities, an H2O-NaCl fluid system and this fluid system evolved to a low temperature, low salinities fluid through the gradual combination of meteoric water from stages II to III. Trapping pressures estimated from boiling L-type, V-type, and S1-type fluid inclusions in stage Ⅰ were 100–500 bars, corresponding to a mineralization depth of 1.0 to 5.0 km, with fluid boiling and mixing likely being responsible for the precipitation of sulfides and gold. K-feldspar from an auriferous vein of stage I yielded an 40Ar/39Ar isotopic plateau age of 131.21 ± 0.52 Ma, suggesting that the mineralization of the deposit is closely associated with the Early Cretaceous quartz monzonite porphyry. The analysis of the S isotope of metal sulfides in this deposit demonstrate that the sulfur reservoir is primarily derived from a hybrid magma source consisting of both mantle-derived and crustal-derived materials. Lead radioactive isotopic analysis for metal sulfides and various wall rocks also implies the lead source is a mixed source of upper crust and mantle. Thus, S-Pb isotope studies indicate that a crust-mantle mixed source for the mineralization of the deposit, and ore-forming material may originate from both quartz monzonite porphyry and various surrounding rocks including Late Triassic-Early Jurassic monzogranite, granite, quartz syenite, and the Ershierzhan Formation. Considering the geology, geochronology, FI, and H-O-S-Pb isotopic characteristics, the Ershiyizhan Cu–Au deposit is classified as a porphyry deposit formed in an extensional environment due to the delamination of the thickened lower crust following the Mongolian-Okhotsk Ocean closure.