Main Mineralization Stage Research Articles

The role of hydrothermal alteration in uranium mineralization at the Xiaoshan uranium deposit, South China

Hydrothermal alteration can be utilized to constrain element migrations during mineralization, as it records the effects of fluid-rock interactions. Previous studies have suggested that uranium in deposits primarily originates from uranium-bearing granites; however, limited knowledge exists regarding the leaching mechamisms of this element and rare earth elements (REEs) from these rocks. In recent years, the Xiaoshan Deposit, a newly discovered medium-sized uranium deposit, has been discovered in the central part of the Lujing uranium ore field, South China. In this study, we examine this deposit to investigate hydrothermal alterations and their impact on elemental mass change. The deposit exhibits seven types of alteration including K-feldspar, albite, illite, sericite, muscovite, quartz and chlorite alteration. These alterations follow a certain sequence, starting from chlorite alteration, followed by widespread K-feldspar alteration, then to albite alteration, accompanied by muscovite alteration, and finally illite, sericite and quartz alteration. The main uranium mineralization stage was coeval with the late acid siliceous hydrothermal fluid, illite and sericite alteration. The pre-ore alkaline alteration (K-feldspar alteration) resulted in the leaching and extraction of uranium, leading to the precipitation of a significant amount of apatite in mineral interstices and initial uranium enrichment (ΔCi (U) = 16.52 ppm). This process facilitated material preparation for subsequent acidic alterations and localized ore enrichment. The original dense rock structure was disrupted, creating fractures/cavities that served as conduits for uranium mineralization. Moreover, under alkaline metasomatism, uranium and REEs was extensively leached out of uranium-bearing accessory minerals such as the apatite. According to apatite compositional variations and alteration geochemistry, these variations reveal the process of uranium dissolution, migration, and precipitation enrichment into ore bodies. Uranium was completely released during alkaline metasomatism, causing a sharp decline in U content from 53.1 ppm to 0.96 ppm. The formation of alkaline alteration fluids facilitates the extraction of uranium from the surrounding rocks (the Indosinian granite).

Hydrothermal rutile chemistry and U-Pb age fingerprinting of the formation of the giant Nurkazgan porphyry Cu-Au deposit, Central Kazakhstan

The porphyry Cu-related intrusions commonly comprise multiple phases such as the large Nurkazgan porphyry Cu-Au deposit in Central Kazakhstan, hosted in the Karagandinsky dioritic to granitic intrusive complex. Here, SHRIMP and LA-ICP-MS zircon U-Pb dating on the multiple ore-bearing intrusions from this complex confirms a punctuated magmatic history distributed over 35 m.y., and marked by three episodic porphyry events rather than a single event, with the oldest event being the early granodiorite and quartz diorite porphyries at ca. 437–440 Ma, the second being the quartz diorite porphyry at 429.7 ± 2.1 Ma, and the last being the late granodiorite and quartz diorite porphyries at 402.8 ± 3.7 Ma and 402.0 ± 3.9 Ma, respectively. The mineralization is related to the two younger episodic intrusions of quartz diorite porphyry at ∼ 430 Ma and ∼ 402 Ma, respectively. SIMS U-Pb dating of hydrothermal, Cu-rich (up to 20.9 ppm) rutile from the breccia-type ores directly constrains the timing of porphyry mineralization at 428.9 ± 6.9 Ma, which is coincident with the emplacement age of the ∼ 430 Ma quartz diorite porphyry, and thus demonstrates this porphyry as a causative intrusion generating main-stage mineralization. This close genetic link is also supported by the chondrite-normalized REE patterns of rutile, which show remarkably similar light REE-enrichments and moderate negative Eu anomalies to those of the ∼ 430 Ma quartz diorite porphyry. A molybdenite sample obtained from the main-ore stage vein, however, has a Re-Os age of 418.6 ± 1.8 Ma, which is slightly younger than the U-Pb age determinations of rutile. This indicates that the Re-Os isotope system was disturbed by the second (post-ore) thermal event related to ∼ 402 Ma quartz diorite porphyry. In line with published data, this study suggests that the rutile U-Pb age in combination with its REE patterns can be a powerful tool to trace the causative porphyry. Moreover, the typical LREE-enriched REE patterns coupled with the high Cu anomalies, inherited from the causative porphyry and related exsolving fluids, can be as diagnostic proxies for distinguishing the porphyry Cu-related hydrothermal rutile from those formed in orogenic gold deposits. Based on these two geochemical discriminators and U-Pb ages, rutile can serve as unique fingerprints to help improve porphyry copper exploration in green field or covered terranes to complement detrital zircon fertility indicators.

Sulfide trace element enrichments in the metamorphic basement-hosted Xinhua Pb-Zn-Cu vein-type deposit, eastern Guizhou province (SW China)

Cambrian carbonate formations are widespread in the western Hunan-eastern Guizhou (WHEG) region (southwestern China), which hosts many Mississippi Valley-Type (MVT) lead–zinc (Pb-Zn) deposits. Regional Pb-Zn mineralization is well developed in the low-grade metamorphic rocks of the basal Proterozoic Banxi Group. The mineralization is associated with quartz veins and generally distributed along NE-trending fault zones. Moreover, these deposits have an extensive distribution and high grade, and are associated with Cu-Ag endowment. However, geological and geochemical research on these Pb-Zn vein-type deposits is relatively limited, and their relationship with the regional MVT mineralization remains unclear. The representative Xinhua deposit in Danzhai district is selected as the study subject. We conducted in situ trace element analyses on the sphalerite and chalcopyrite from the various metallogenic stages, and compared them with published sphalerite trace element data from the MVT Pb-Zn deposits in the western Hunan-eastern Guizhou metallogenic belt. Seven orebodies in Xinhua Pb-Zn deposit have been discovered so far, with a metal resource of over 120,000 metric tonnes of Zn + Pb. Field geology and microscopic petrography have revealed two mineralization stages: An early-stage black sphalerite (Sp-I) followed by reddish-brown sphalerite (Sp-II) mineralization, which corresponds to the main chalcopyrite mineralization stage, and a later-stage light-yellow sphalerite (Sp-III), Cu ore-barren mineralization.LA-ICPMS data indicate that the sphalerite from Xinhua has similar trace element compositions to those from the MVT Pb-Zn deposits in the region. They are relatively enriched in Ga, Cd, and Ge, while depleted in Fe, Co, and Mn. Critical metal Ge and Ga are particularly enriched in sphalerite, especially in Sp-I (Ge max 937 ppm, Ga max 824 ppm). The substitution mechanism of Ge and Ga in sphalerite are likely 2Cu+ + Ge4+ ↔ 3Zn2+ and Cu+ + Ga3+ ↔ 2Zn2+. Indium and Sn are mainly present in Sp-I and Sp-III. Chalcopyrite contains Zn and Sn both exceeding 100 ppm. Contents of Se, Ag, In, and Sn in chalcopyrite are significantly higher than those in sphalerite. Calculation of the sphalerite trace element geothermometer (GGIMFis) suggests that the average sphalerite ore-forming temperatures are 164 °C (Sp-I), 156 °C (Sp-II), and 205 °C (Sp-III), implying medium- to low-temperature mineralization. This indicates a possible influx of high-temperature, in-bearing fluid during the late-stage mineralization.In summary, the faults-controlled vein-type Pb-Zn deposits (e.g., Xinhua) may have been products of the same Kwangsian orogeny as other strata bound MVT deposits, and the Xinhua deposit features two mineralization stages with multiple ore metal sources. During the ore-forming fluid ascent, some ore-forming materials may have precipitated in the fluid conduits. And exposed after the erosion of the shallower stratiform orebodies and strata. Consequently, the Xinhua Pb-Zn deposit represents the preserved ore-fluid conduit phase (in the basement strata) of the MVT mineralization.

Genesis of the Ulaan silver-lead–zinc deposit in Northeast Mongolia: Constraints from S and Pb isotopes, together with U-Pb and Rb-Sr geochronology

The Ulaan silver-lead–zinc deposit (hereinafter referred to as the Ulaan deposit) is identified as the largest silver-lead–zinc polymetallic deposit in Mongolia, with proved reserves including 2,240 tons of silver (Ag; average grade: 49 g/t), 440,000 tons of lead (Pb; average grade: 1.13 %), and 810,000 tons of zinc (Zn; average grade: 2.07 %). However, the genesis of this deposit remains unclear. The Ag-Pb-Zn ore bodies in the deposit, occurring as cylinders in shape within the Middle-Late Jurassic rhyolites, are governed by a concealed breccia pipe. The ore minerals include galena, sphalerite, and pyrite, followed by chalcopyrite, hematite, stibnite, and siderite. The primary alterations of the surrounding rocks include silicification, chloritization, kaolinization, argillization, carbonatization, and skarnization. The Rb-Sr dating of sulfide minerals and associated vein minerals in the ores yielded isochron ages varying in a range of 146 ± 3 Ma (n = 6, MSWD=1.3), suggesting mineralization during the Late Jurassic. The δ34S values of sulfide minerals in the ores range from 1.6 ‰ to 4.3 ‰, suggesting that the sulfur originated primarily from magmas or deep sources. The isotopic compositions of coexisting sphalerite-galena minerals in the deposit revealed mineralization temperature estimates ranging between 331 °C and 449 °C, indicating a medium- to high-temperature ore-forming conditions. The sulfide minerals exhibit 208Pb/204Pb ratios ranging from 38.138 to 38.301, 207Pb/204Pb ratios from 15.543 to 15.594, and 206Pb/204Pb ratios from 18.318 to 18.354, suggesting that ore-forming metals, represented by Pb, also originated primarily from mantle source. The zircon U-Pb dating of rhyolites in the ore-hosting strata and ore-controlling breccia pipes yielded ages of 160.6 ± 1.7 Ma (n = 24, MSWD=0.68) and 161.6 ± 1.6 Ma (n = 30, MSWD=0.89), respectively, indicating volcanic eruptions during the early Late Jurassic. These ore-hosting rhyolites exhibit characteristics of A-type rhyolites, suggesting that they were formed in an intracontinental extensional environment. These rhyolites share similar rare earth element (REE) distribution patterns with fluorite formed in the main mineralization stage, suggesting a genetic link between the mineralization and magmatic processes. This study proposes that the Ulaan deposit was a hydrothermal deposit formed in an extensional environment following the closure of the Mongol-Okhotsk Ocean, with ore-forming metals and hydrothermal fluids associated with volcanic rocks or magmatic-hydrothermal processes.

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.

Telluride Mineralogy of the Kochbulak Epithermal Gold Deposit, Tien Shan, Eastern Uzbekistan

The Kochbulak gold deposit is situated on the northern slope of the Kurama range of eastern Uzbekistan and is one of the largest Tellurium-rich epithermal gold deposits in the world. Based on a detailed field and petrological investigation, three stages of mineralization can be classified, including, from early to late, quartz–pyrite vein stage, quartz–telluride–sulfide–sulphosalt–native gold stage, and pyrite–chalcopyrite vein stage. Abundant tellurides, including tellurobismuthite, rucklidgeite, tetradymite, altaite, volynskite, and hessite, have been well recognized in the second (main) mineralization stage. Based on the mineral assemblages and petrogenetic occurrence, the sequence of tellurides in the second mineralization stage can be approximately identified as altaite+calaverite+native tellurium, calaverite+native gold, Bi-telluride (e.g., tellurobismuthite and rucklidgeite)+petzite+native gold, Ag-Bi telluride (e.g., volynskite), and Ag-telluride (e.g., hessite)+native gold. By depicting the Log ƒ(Te2)-Log ƒ(S2) relationship diagram of the Kochbulak gold deposit under 250 °C and 200 °C, the Log ƒ(S2) value ranges from −14.7 to −8.6 and from −16.7 to −10.9, respectively, with Log ƒ(Te2) value varies from −12.3 to −7.8 under 250 °C and ranges from −13.8 to −11.2 under 200 °C.

Fluid inclusion and He-Ar-Pb isotope studies of the Dabie-type Leimengou giant porphyry Mo deposit, Qinling Orogen

The Leimengou deposit is a Dabie-type porphyry Mo system in the Leimengou-Qiyugou orefield of Qinling Orogen. Orebodies host within the porphyry and the metasedimentary Taihua Supergroup. However, the characteristics and sources of ore-forming fluid, metal precipitation mechanism, and the sources of mineralizing substances remain unclear. In this contribution, by a comprehensive study comprising an investigation of deposit geology, fluid inclusion microthermometry, and He-Ar-Pb isotope, we discuss the source and evolution of ore-forming fluids and the molybdenum precipitation mechanism of the Leimengou deposit. The mineralizing process is divided into the Stage I quartz ± K-feldspar vein in potassic altered zone, Stage IIa molybdenite ± quartz vein, and Stage IIb molybdenite + quartz + pyrite ± purple fluorite vein in silicification-phyllic altered zone, Stage III quartz + pyrite + sphalerite + galena ± chalcopyrite ± green fluorite ± pink calcite in prophylitic altered zone and Stage IV quartz ± calcite vein in carbonatization zone based on cross-relationship. The Stage IIa and IIb veins characterize the main molybdenum mineralization stages. By microthermometry, CO2-bearing (C-), Water (WV- and WL-), and daughter minerals-bearing (S-) types of inclusions were recognized. The Stage I quartz contains C-type fluid inclusion assemblages (FIAs) with a salinity of 6.3 ± 1.4 wt% NaCl equiv., and a total homogenization temperature (Th, total) of 473 ± 3 °C. This suggests that the early fluids show characteristics of high temperature, CO2-rich, and moderate salinity, distinguishing them from those of Endako-type and Climax-type deposits. C-type and coexisting W-type FIAs from Stage IIa show similar salinity, ranging from 1.9 to 13.0 wt% NaCl equiv. and 1.9 to 14.1 wt% NaCl equiv., with Th, total of 349–376 °C and 327–392 °C, respectively. Moreover, C-type FIAs homogenize to distinct phases and also show similar homogenization temperatures, indicating fluid immiscibility. The FIAs in Stage IIb show an average salinity of 8.3 ± 7.4 wt% NaCl equiv. and a Th, total of 302 ± 14 °C. WL-type and WV-type FIAs coexist, with similar temperatures varying from 308 to 310 °C during this stage, indicating significant fluid boiling. These observations indicate that the decrease in temperature, fluid immiscibility, and decompression boiling collectively led to the precipitation of molybdenite. Trapping pressures are estimated to be 82–231 MPa for Stage IIa and 43–115 MPa for Stage IIb, corresponding to ore-forming depths of approximately 8.4 km and 4.3 km, respectively. Additionally, the He-Ar isotopes obtained from pyrite indicate a clear mixing trend of crustal fluids with mantle fluids at Stage IIb, with mantle-derived fluid components increasing during Stage III. This coincides with the tectonic shift from regional compression to extension, leading to the formation of many Dabie-type Mo deposits, alongside crustal thinning and the upwelling of asthenospheric mantle materials. Futhermore, Pb isotopes from the ore, ore-hosted gneiss, and ore-causative granitoids demonstrate that the Taihua Supergroup gneiss supplied ore-forming materials, suggesting a crustal origin for the Leimengou Mo deposit.

Hydrothermal alteration and its geochemistry of the Xiadian gold deposit, Jiaodong Peninsula, China: Implications for fluid-rock interaction processes and mineral exploration

The interaction between hydrothermal fluids and host rocks, along with associated alteration geochemistry within the Mesozoic Jiaodong gold system, presents significant gaps in our understanding. This study systematically examines the petrographic, mineralogical, and geochemical characteristics of alteration at the Xiadian gold deposit, including comprehensive whole-rock geochemistry analyses, mass balance calculations, and phase equilibria modeling. The alteration history of Xiadian could be divided into four stages. Amid Stage 1, the predominant process involves the replacement of plagioclase by K-feldspar-albite, accompanied by the simultaneous bleaching of amphibolite and associated significant depletion of MgO (ΔCi/CiO = −21.2 %) and Fe2O3 (−27.2 %) owing to the decomposition of mafic minerals. Stage 2a involves sericitization of albite and continued mafic mineral decomposition, resulting in the lowest recorded MgO (avg. 0.23 wt%) and Fe2O3 (avg. 0.92 wt%) contents in all alteration lithologies. Stage 2b is characterized by abundant chlorite vein formation, corresponding to the proximal enrichment of MgO (158.1 %) and Fe2O3 (108.2 %), accompanied by aMg2+/(aH+)2 decreased in the fluid. Stage 3, the main stage of gold mineralization, involves chlorite substitution with sericite during quartz-sericite-pyrite (QSP) alteration, suggesting mild acidification of the ore-forming fluid. Insights from phase equilibrium modeling suggest that sulfidation has contributed to gold precipitation, leading to increased fO2 and reduced fH2S (extending into quartz-carbonate alteration of stage 4). Mass balance calculations indicate gold is enriched compared to protolith at all stages, with the most intense enrichment in stage 3. This suggests that hydrothermal fluids at Xiadian were auriferous throughout their evolution. The process may induce fluid modifications, particularly through the dissolution of mafic minerals, more so in mafic mineral-rich rocks (e.g., amphibolite) than in granite, promoting the incorporation of hydrothermal chlorite into the Au system to contribute to sulfidation. Our results provide insights into lithology controls on gold mineralization at Xiadian, indicating that felsic rocks (Linglong granite and quartz porphyry) with lower initial CaO contents often develop K-metasomatism and Au-bearing QSP alteration, while mafic rocks (amphibolite and lamprophyre) with higher CaO contents develop carbonization. This is likely due to the influence of lower CaO contents on alteration minerals, which promote rock porosity, affecting rock deformation, pore-fluid flow, and reacting with wall rocks. Principal component analysis (PCA) results indicate that elements including Au, Ag, As, Bi, W, and Cu are proxies for Au mineralization, suggesting their mobilization and deposition together during the gold mineralization process. This highlights their significance as a proxy for gold exploration.

Genesis of the Hajibolagh-Zalibolagh Cu-(Ag) intermediate-sulfidation epithermal deposit, Urumieh-Dokhtar magmatic arc, Iran: Evidence from ore geology, fluid inclusions, and stable isotopes

The Hajibolagh-Zalibolagh deposit located northeast of the city of Saveh in the central part of the Urumieh-Dokhtar magmatic arc of Iran, demonstrates vein and breccia vein style copper-(silver) mineralization hosted by Eocene volcano-sedimentary rocks. The main mineralization stage can be divided into four phases, respectively (1) jasperoid + quartz veins, chalcopyrite, and pyrite; (2) quartz veins along with chalcopyrite, bornite, chalcocite, arsenopyrite, and pyrite; (3) quartz-barite veins along with chalcopyrite, bornite, chalcocite and pyrite; and (4) veins of quartz, calcite, hematite, and oligist along with a small number of copper sulfides. The main stages of mineralization are cut by barren post-ore quartz and calcite veinlets. As a result of supergene processes, minerals are oxidized, and malachite, azurite, chrysocolla, chalcocite, covellite, goethite, and hematite are formed, presenting an important exploration guide. The hydrothermal alteration from the center of the vein-veinlets to the outside includes, respectively, silicification, sericitization, intermediate argillic, and propylitic. The average salinity and homogenization temperature (Th) of fluid inclusions is 14.2 wt% NaCl equiv. and 288 °C, respectively. The coexistence of the vapor phase, liquid-rich phase, and halite-bearing fluid inclusions is a sign of boiling in this hydrothermal system, which has contributed to copper saturation. Sulfur isotope values for pyrite, chalcopyrite, chalcocite, and bornite are mainly from –0.16 to 2.98 ‰, indicating a probable magmatic source for sulfur. Boiling, dilution, and mixing are the mechanisms for the ore deposition and facilitated the mineralization. The Hajibolagh-Zalibolagh deposit shows the highest similarity to intermediate-sulfidation epithermal deposits. The best environment for the mineralization and fluid circulation in these epithermal deposits is the intersection of faults with the Eocene volcanic and volcano-sedimentary rocks.

Machine learning model for deep exploration: Utilizing short wavelength infrared (SWIR) of hydrothermal alteration minerals in the Qianchen gold deposit, Jiaodong Peninsula, Eastern China

The Jiaodong Peninsula in the eastern North China Craton is renowned globally as a major gold province. Notably, the Jiaojia orefield is an important gold-producing district in this region, and its depths are inferred to offer substantial prospecting potential, underscoring the need for innovative exploration tools to uncover concealed orebodies. The Qianchen gold deposit in the southern part of the Jiaojia orefield is characterized by the disseminated-stockwork-style orebodies at depths of ca. –1000 to –1800 m, with three mineralization stages, namely (I) pre-ore K-feldspar-quartz stage, (II) quartz-sericite-gold-polymetallic sulfide stage (main Au mineralization stage), and (III) post-ore quartz-calcite stage. Systematic short-wavelength infrared (SWIR) spectral analysis reveals that sericite group minerals developing in Stage II are the predominant and wide-distributed alteration minerals at Qianchen. Their spectral characteristics demonstrate a shift in the Al-OH absorption feature wavelength positions (Pos2200) to longer wavelengths (>2205 nm) within the orebodies. This shift is likely due to strong water–rock interactions leading to Fe and Mg substituting for Al in octahedral sites. Orthogonal partial least squares discriminant analysis (OPLS-DA) indicates that the H2O, OH, and FeOH spectral bands (Variable Importance in the Projection (VIP) ≥ 1) of sericite are crucial for distinguishing between gold ores and barren wall rocks. Additionally, Long Short-Term Memory (LSTM) models demonstrate that spectral data of sericite can be used to predict ore samples with an accuracy of 82 %, validated by receiver operating characteristic analysis (84 %), and blind test results demonstrate that the predicted grade closely aligns with the actual grade. Therefore, it is concluded that SWIR spectral characteristics of sericite group minerals can serve as an effective indicator for prospecting the Qianchen concealed gold mineralization. This study highlights the potential of coupling between machine learning and SWIR spectral data of alteration minerals to uncover the concealed lode gold mineralization.

Rb–Sr Pyrite Dating and S–Pb Isotopes in the Fang’an Gold Deposit, Wuhe Area, Eastern Anhui Province

The Fang’an gold deposit in the Wuhe area, Anhui Province, is located in the area adjacent to the Bengbu Uplift and Wuhe Platform Depression in the southeastern part of North China. This study aimed to determine the deposit’s mineralization age and the source of its metallogenic materials and mineralization processes through investigations into its geological characteristics, Rb–Sr isotopes, and S–Pb isotopes. The orebodies of the Fang’an gold deposit in the Neoarchean Xigudui Formation primarily exhibit a vein-type structure. The ore-forming process can be divided into four stages: (i) the quartz stage (Py1); (ii) the quartz–pyrite stage (Py2); (iii) the polymetallic sulfide stage (Py3); and (iv) the carbonate stage. Of these, the main mineralization stage is also the main period in which gold mineralization occurs. In situ sulfur isotope results of pyrite (Py1 to Py3) in the first three mineralization stages, suggesting a contribution of sulfur from crust–mantle magmatic fluids. The δ34S values for Py2 (average 5.51‰) are higher than Py1 (average 4.45‰) and showed that the magmatic fluids mixed with meteoric waters. The δ34S values for Py3 (average 5.18‰) are lower than Py2 (average 5.51‰), revealing that it related fluid immiscibility. The lead isotopic compositions of sulfides within the ores possessed 206Pb/204Pb ratios ranging from 16.759 to 16.93, 207Pb/204Pb ratios ranging from 15.311 to 15.402, and 208Pb/204Pb ratios ranging from 37.158 to 37.548. These lead data were plotted close to the Xigudui Formation, relatively distant from the Mesozoic granites, indicating that the Xigudui Formation was the source of lead for the Late Mesozoic ores of the deposit. Taken together, due to the degassing of mantle-derived magma in the shallow parts of the crust, it can be determined that the sources of ore-forming sulfur and lead were crust–mantle magmatic activities in the Wuhe area. Rb–Sr dating of pyrite from Fang’an gold deposit reveals that the mineralization occurred at 126.89 ± 0.58 Ma. Considering the previous research into the dating of magmatic rocks in the Wuhe area, we propose that the genesis of the Fang’an gold deposit is closely associated with magmatic activities in the area at around 130 Ma.

Metallogenetic epoch and material source of Be-pegmatite differentiated from biotite granite in Mufushan complex

The Mufushan Complex (MFSC) is a significant rare metal mineralized in the central China district and is renowned for its marked economic value of rare metal deposits. While the main rare metal mineralization (RMM) stage in the MFSC relates to the magmatic event of two-mica monzogranite, the mineralization event related to biotite monzogranite remains unknown. To fill this gap, this study focuses on porphyritic biotite monzogranite and adjacent Be-rich pegmatite samples obtained from Changqing Pegmatite No. 1, which is situated in the southeastern part of the MFSC. We subjected these samples to zircon U–Pb dating and Hf isotope analysis using laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) and utilized an electron probe X-ray microanalyzer (EPMA) and LA–ICP–MS to examine the major and trace elements present in the muscovite samples. Our findings revealed precise chronological data for the geological history of Changqing, pinpointing the intrusion age of biotite monzogranite to 145.8 ± 1.1 Ma and the crystallization age of Be-rich pegmatite to 144.9 ± 1.1 Ma, firmly situating these events within the Late Jurassic to Early Cretaceous epoch. Regarding isotopic composition, zircon εHf (t) for granite ranged from −9.29 to −5.09, and their corresponding TDM2 ranged from 1788 to 1520 Ma. Similarly, zircon εHf (t) for pegmatite ranged from −7.89 to −5.47, and their corresponding TDM2 ranged from 1699 to 1544 Ma. These isotopic signatures strongly indicate a shared origin for the initial magma of granite and pegmatite. The partial melting of the thick Lengjiaxi Group tasedimentary strata serves as a material source for RMM. The transition from granite to pegmatite exhibits remarkable constancy in the primary components of muscovite. By examining its geochemical attributes, we observed synchronous decreases in FeO, MgO, SiO2, MnO, Be, Rb, and Cs, coupled with synchronous increases in Nb and Ta contents, along with Ta/Nb values. These findings strongly imply that the Changqing biotite monzogranite and Be-rich pegmatite originate from the continuous differentiation and evolution of a common magmatic source, establishing a clear genetic relationship between them. The MFSC has its origins in three distinct stages of magmatic activity and RMM spanning from 160 Ma to 120 Ma. Considering the distribution patterns of similar pegmatite veins, the metallogenic potential observed during the biotite granite stage may serve as an external indicator of marked mineralization within large batholiths.

Comparative lithology and alteration mineral chemistry of host rocks at the Seabee Gold Operation, northern Saskatchewan, Canada: Implications for a connected orogenic gold-mineralizing system

The Seabee Gold Operation, located in northern Saskatchewan, Canada, hosts the Santoy and Seabee gold deposits, as well as the Fisher property; the latter is an important exploration target. This gold mineralization is hosted in rocks of the Pine Lake greenstone belt that is within the Glennie domain of the larger Paleoproterozoic Trans-Hudson orogen. Mineralization is focused within shear zones, including the Santoy shear system that extends south onto the Fisher property. The role of ore-adjacent intrusions, systematics of gold mineralization, and relationship between the mineralization of the properties are largely undefined. In this study, hydrothermally-altered samples from locations along the Santoy shear system, namely the Santoy 7, Santoy Gap, and the Fisher property, were analyzed to identify and compare the mineralogical and geochemical characteristics related to sulfide-gold mineralization and associated alteration.The altered host rocks primarily comprise upper greenschist to lower amphibolite-grade sheared metabasalt to chlorite-hornblende-biotite ± garnet schist, and intrusive rocks dominated by granodiorite and tonalite. These lithologies are cut by similar quartz vein generations and are associated with similar alteration assemblages and mineralization, including (i) syn-late-D3 “distal” (∼0.4 to 3 m wide) sericite-biotite-chlorite-clinozoisite ± albite, titanite to vein-adjacent coarse-grained diopside-K-feldspar-albite-actinolite ± apatite, titanite calc-silicate alteration, associated with main-stage Py2a, 2b-Cpy2-Po1-Au (syn-late-D3) mineralization; (ii) remobilized, fracture-filling Py3-Po2-Cpy3-Au-BiTel (late-D3) mineralization within the calc-silicate assemblage; and (iii) early colloform Py1a (pre-syn-D3) and intrusion-hosted, inclusion-rich Py1b (pre-D3). Microprobe analyses reveal similar mineralogical trends between Fisher and Santoy alteration minerals typical of orogenic gold systems. Empirical geothermobarometric calculations of gold-associated vein-adjacent and vein-hosted chlorite and biotite exhibit orogenic-style formation conditions (∼320–330 °C, 3 kbar, ∼9 km depth). As such, these analyses suggest that the Fisher property and Santoy Mine Complex underwent inter-connected, multi-stage hydrothermal processes. These stages comprise (i) a potential early introduction of gold into the system closer to the timing of plutonism (Py1b magmatic-hydrothermal; pre-D1) or during the onset of gold mineralization (Py1a; orogenic; late-D2 to early-syn-D3) during the evolution of the Reindeer zone; (ii) orogenic main-stage mineralization (syn-late-D3) concurrent with late- to post- collisional deformation throughout the Reindeer zone; and (iii) remobilization during continuous deformation (late-D3) where elevated cyclical fluid fluxes and higher fracture density at Santoy produced higher-grade mineralization.

Textures and trace element geochemistry of pyrite in Gaoloushan ore section of the Yangshan gold belt, West Qinling: Implications for ore genesis

The Devonian Sanhekou Group phyllite in the Yangshan gold belt includes multiple stages of pyrite development, and Au is mainly distributed within the pyrite. Bodies within the Gaoloushan ore section of the gold belt are located in the broken and altered carbonaceous phyllite and granitic rock dykes, where quartz vein-type gold ores are more common as compared to other ore sections (Anba, Getiaowan). Studying the trace element distribution characteristics of gold-bearing and non-gold-bearing pyrite can constrain the evolution of ore-forming fluids and the types of ore deposit genesis. Based on detailed fieldwork and microscopic identification, 48 pyrite samples from the 69th exploration line of the Gaoloushan ore section were analyzed in situ by LA-ICP-MS. The following conclusions were drawn: (1) The gold-bearing pyrite formed during the ore-forming stage while the non-gold-bearing pyrite formed during the sedimentary and metamorphic period. The morphology of the pyrites differs, with gold-bearing pyrite mainly characterized by medium-fine grains, impregnation, fine veins, and reticulate structure, with crystal morphology mainly pentagonal dodecahedra or pentagonal octahedra, whereas non-gold-bearing pyrite is mainly characterized by a medium or medium-coarse grains, with stellate, strawberry, or cluster structures, and crystal morphology mainly in the form of cubes or pentagonal octahedra; (2) The As and Te content of the sedimentary pyrite is low, locally below the detection limit, and the Co and Ni contents and ratios vary greatly, with a distribution of 117–945 ppm and ratio distribution of 0.11–1.92. Pyrite from the ore-forming stage is primarily characterized by high As, Pb, Co, Ni, Cu, Sb, Zn, and Se concentrations, with Bi, Au, and trace amounts of Tl, Te, and Sn observed in later formations; (3) Au and As are positively correlated. The average Au content of 60.53 ppm in pyrite from granite dykes is higher than the average Au 15.97 ppm in carbonaceous phyllite. Pyrite particles with Au contents below the detection limit are sourced in carbonaceous phyllite. In addition, the higher As enrichment is observed in pyrite from granite dykes, averaging 35 770.60 ppm with a maximum value of 72 930.19 ppm. In comparison, the average As content in carbonaceous phyllite is 8974.66 ppm, with a maximum of 69 800.50 ppm, and the Au-As diagram indicates that gold in the Gaoloushan ore section is mainly in the form of solid solution gold within the pyrite lattice; (4) Statistical analysis of the Co/Ni ratio variation in the different lithologies and pyrite stages reveals an initial increase followed by a decrease. The median Co/Ni ratio variations during the mineralization stages of Py1s (0.51–0.7), Py1m (1.35–2.25), Py2 (1.43–1.87), Py1-2 m (1.53), Py2a (1.59), Py2b (1.4), Py2s (1.2), Py2m (1.63), and Py3 (0.19–1.40) suggest that magmatic-hydrothermal fluids dominated during the early stage of mineralization in the gold belt and metamorphic fluids during the main mineralization stage, with deep-seated metamorphic fluids playing a significant role in the late mineralization stage. The varying proportions of ore-forming fluids are likely to have been crucial in controlling gold mineralization in the Yangshan gold belt.

Characteristics and evolution of quartz-calcite-sulfide veins in the Nazca-Ocoña belt, Peru

The Nazca-Ocoña metallogenic belt in southern Peru host about 70 recognized Au-Ag and base metal (Pb-Cu-Zn) deposits such as Orión, Caravelí, Ishihuica, Calpa, Arirahua, Mollehuaca, and San Juan de Chorunga. These deposits are spatially associated with Cretaceous intrusive rocks of the coastal Batholith in a zone that extends more than 350 km along the Central to Southern part of Peru. Gold and silver are structurally controlled in mineralized NW-SE, N-S and W-E-trending fault-fill veins that are less than one-meter wide, crosscutting granodiorite and diorite bodies. The origin of the veins is still debated, and they may be classified as intrusion-related gold deposits (IRGD), orogenic or mesothermal deposits. In this study, we focus on two representative deposits in the Nazca-Ocoña metallogenic belt: Mollehuaca and San Juan de Chorunga. At both sites, the mineralization is composed of quartz-calcite sulfide veins hosted in Cretaceous Coastal Batholith intrusions. Petrographic and chemical analyses on pyrite were performed with field-emission scanning electron microscopy (FE-SEM), electron microprobe analysis (EMPA), nano-scale secondary ion mass spectrometry (NanoSIMS), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).Native gold and Au-rich silver are disseminated throughout the veins as micro to sub-micron inclusions in pyrite and chalcopyrite, and in pyrite as cavity and fracture fill. The are three pyrite generations and these have complex internal zonation and are host to precious (Au, Ag) and base metals (Co, Ni, Cu) metals, and also metalloids (As, Sb) as lattice-bound impurities and micron inclusions. The San Juan de Chorunga pyrite has δ34S values ranging from 0.4 to 1.4 ‰, and the Mollehuaca pyrite δ34S from 5.8 to 7.4 ‰. In both San Juan de Chorunga and Mollehuaca, the highest Au concentrations occur in pyrite zones with the heaviest δ34S values. Fluid inclusion petrography of these veins shows recrystallized, wispy quartz with implosion and explosion fluid inclusion textures, indicative of pressure variations during quartz vein formation. The presence of CO2 in these inclusions requires mid-crustal pressure conditions. However, the main stage of gold mineralization occurs with carbonate, chlorite, and euhedral quartz crystals lacking post-entrapment recrystallization textures or CO2. Our observations suggest that most of the gold in these veins formed in association with a shallower hydrothermal event, potentially in association with the emplacement of batholiths and shallower intrusions in the Late Cretaceous.

Characteristics of Ore-Forming Fluids and Genesis of the First Mining Area and Eastern Ore Section of the Pulang Porphyry Copper Deposit, Southeastern China: A Comparative Study

The Pulang copper deposit, formed in the Late Triassic, is the largest porphyry Cu-Mo-Au deposit in the eastern Tethys, and its genetic type and mineralization potential have received widespread attention. Identifying the characteristics of ore-forming fluids and the sources of ore-forming materials in the deep and peripheral ore bodies of Pulang is particularly important for constructing a complete porphyry copper mineralization system. Based on detailed core logging and geological observations, this article provides extensive petrographic, fluid inclusion micro-thermometry, laser Raman spectroscopy, and H-O-S isotope data on the veins of the main mineralization stage (B veins) in the first mining area and eastern ore section of the Pulang porphyry copper deposit. The genetic correlation between the eastern ore section and the first mining area is clarified, and their mineralization potential is inferred. The results indicate that the deep vein bodies in the first mining area exhibit multi-stage characteristics, and the fluid in B veins exhibits both high-temperature and salinity characteristics. The magma-derived early ore-forming fluids underwent processes such as boiling and experienced immiscibility during meteoric water mixing, which could be the primary mechanism of the precipitation of Cu, Mo, Au, and other metals. The outer eastern ore section is located in a medium-to-low-temperature hydrothermal mineralization zone far from the mineralization center. This outer eastern ore section is a distant part of the magmatic–hydrothermal system of the first mining area.

Mineralogical characteristics and fluid inclusions of the Dashuixiabei crystalline graphite deposit in the Dunhuang block

AbstractGraphite is a strategic mineral resource of the world. The Dashuixiabei (DSXB) crystalline graphite deposit is located in the Dongbatu area in the Altyn crystalline graphite metallogenic belt. This study presents data from x‐ray diffraction (XRD), scanning electron microscopy (SEM), laser Raman spectroscopy, and fluid inclusions analysis conducted on the DSXB crystalline graphite deposit. The graphite is flake shaped, with a diameter of 0.1–0.4 mm. A group of extremely complete cleavage was observed under SEM, and the overall distribution was a flake. The C content in graphite is greater than 90 wt%, followed by N, O, and so on. The results of XRD analysis show that the lattice parameters of the DSXB crystalline graphite is a = 0.246–0.2465 nm, c = 0.6714–0.6715 nm, and V = 0.03519–0.03532 nm3. The degree of graphitization ranges from 0.8490 to 0.8519, indicating that the graphite crystal structure is relatively intact, the average metamorphic temperature is 552°C, and the content of 3R polytypes ranges from 13.16% to 13.25%. It is concluded that the metamorphic rocks of the DSXB crystalline graphite deposit have undergone medium‐grade metamorphism. The Raman spectral peaks show that DSXB crystalline graphite has a high degree of crystallinity. The DSXB crystalline graphite ore is dominated by hydrothermal fluids with medium‐low temperature and medium‐low salinity, and the vapor phase of the fluid inclusions is composed of CH4. There may be a superposition of the main and secondary mineralization stages. The crystalline graphite from the DSXB deposit shows high quality and stable ore quality, which has good metallogenic conditions and development and utilization prospects.

The Occurrence and Chemical Composition of Bismuth-Bearing Minerals in the Niuxingba-Liumukeng Ag-Pb-Zn Deposit, Jiangxi Province, South China

The Niuxingba-Liumukeng deposit, located in the Yinkeng ore field (Jiangxi province, South China), is a typical Ag-Pb-Zn deposit hosted in the Yudu-Ganxian metallogenic belt. Based on the field investigation and mineralogical studies, the mineralization of this deposit can be divided into three stages: quartz-pyrite-arsenopyrite stage (I), quartz-galena-sphalerite-sulfosalt stage (II), and quartz-carbonate stage (III), with stage II being the main Ag mineralization stage. In this contribution, we reported the occurrence of bismuth-bearing minerals in this hydrothermal deposit and its implications for ore formation. Based on the results of electron microprobe analyses, we infer that the dominant occurrence of bismuth at Niuxingba-Liumukeng is primarily marked by solid solutions within the crystal lattice of galena and as visible independent bismuth-bearing minerals. The independent bismuth minerals consist of berryite [Pb3(Ag,Cu)5Bi7S16], emplectite (CuBiS2), and aikinite (PbCuBiS3). Most bismuth minerals replace chalcopyrite or fill in the cracks of pyrite and chalcopyrite. Meanwhile, we found a large number of Bi-bearing minerals closely coexisting with Ag-bearing minerals, indicating that bismuth may have played a crucial role in silver deposition from hydrothermal fluids. We considered that the existence of bismuth-rich melts associated with the ore-forming hydrothermal systems could help to promote the enrichment and precipitation of silver to form economic ores.

Spatiotemporal relationship between hydrocarbon fluid and sandstone‐hosted uranium deposits in the Qianjiadian area, Songliao Basin

The spatiotemporal coupling relationship between deep hydrocarbon fluid and sandstone uranium mineralization within the shallow buried red‐variegated clastic rocks in the Qianjiadian area of the Songliao Basin remains a topic of controversy. This paper aims to provide a comprehensive understanding of the source, nature and exudative age of deep exotic hydrocarbon, as well as the interaction mechanism and alteration process between hydrocarbon fluid and clastic rock. To achieve this, various methods were employed, including acidolysis hydrocarbon test (AHT), clay x‐ray diffraction (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), carbon isotope analysis (CIA) and LA‐ICP‐MS U–Pb isotopic dating. The results indicate that some tight sandstones from the Qingshankou Formation in Dalin uranium deposit exhibit high acidolysis hydrocarbon content (AHC), reaching n × 104 μL/kg, and predominantly consisting of low mature oil‐type gas. Local microscopic observations reveal pore fluorescence and hydrocarbon‐bearing inclusions with nattier blue tone. Furthermore, the kaolinites present in the ore area's sand‐bodies show a significantly higher content anomaly, commonly exceeding &gt;50%, compared to the same layer in peripheral regions. Extensive dissolutions of lithic grains and feldspars are observed, along with the widespread occurrence of ferro‐dolomites and colloidal pyrites. Additionally, exotic asphaltenes are sporadically developed in localized areas. These findings provide evidence that the sand‐bodies experienced a significant exfiltration event of external gaseous fluids. The light carbon isotopes (δ13CV‐PDB ranging from −33.26‰ to −30.06‰) of group components and n‐Alkane suggest that the hydrocarbon originates from the source rock of the Lower Cretaceous Jiufotang Formation. A detailed two‐stage alteration sequence caused by acidic and reducing hydrocarbon is clarified, encompassing acidic corrosion, kaolinization, pyritization, silification and asphaltization during the exudation stage, followed by ferro‐dolomitization in the later cessation stage. Notably, vermicular secondary kaolinites, formed through the interaction between acidic hydrocarbon fluid and low‐temperature meteoric groundwater, serve as significant markers for the exfiltration of deep hydrocarbon fluid. In‐situ U–Pb dating of hydrocarbon‐bearing ferro‐dolomite yielded absolute exfiltration ages of 63.54 ± 4.13 and 65.93 ± 3.35 Ma. By integrating the tectonic–sedimentary–fluid evolution history and uranium mineralization characteristics in the study area, a three‐stage superimposed metallogenic model is proposed for the Upper Cretaceous red‐variegated layers: (1) the sedimentary and diagenetic stage of the target layer during the Late Cretaceous, (2) the predominant hydrocarbon exudation stage at the end of the Late Cretaceous, and (3) the main uranium mineralization stage since the Paleogene. This study enhances our understanding of coupled‐genetic sandstone‐type uranium deposit in a sedimentary basin and provides valuable guidance for prospecting similar red‐variegated beds in the Songliao Basin and other sedimentary basins worldwide.

Magmatic‐hydrothermal evolution and mineralization mechanisms of the Wangjiazhuang Cu (‐Mo) Deposit in Zouping Volcanic Basin, Shandong Province, China: Constraints from Fluid Inclusions

AbstractWangjiazhuang Cu (‐Mo) deposit, located within the Zouping volcanic basin in western Shandong Province, China is the only one with economic value found in the area so far. In order to expound the metallogenetic characteristics of this porphyry‐like hydrothermal deposit a detailed fluid inclusion study has been conducted employing the techniques of representative sampling, fluid inclusion petrography, microthermometry, Raman spectroscopy, La‐ICP‐Ms analysis of single fluid inclusions, as well as cathode fluorescence spectrometer analysis of host mineral quartz. The deposit contains mainly two types of orebodies, i.e. veinlet‐dissemination‐stockwork orebodies in the K‐Si alteration zone and pegmatitic‐quartz sulfide veins above them. In addition, minor breccia ore occurs locally. Four types of fluid inclusions in the deposit and altered quartz monzonite are identified: L‐type one‐ or two‐phase aqueous inclusions, V‐type vapor‐rich inclusions with V/L ratios greater than 50‐90%, D‐type multiphase fluid inclusions containing daughter minerals or solids and S‐type silicate‐bearing fluid inclusions containing mainly muscovite and biotite. Ore petrography and fluid inclusion study has revealed a three‐stage mineralization process driven by magmatic‐hydrothermal fluid activity as follows. Initially a hydrothermal fluid separated from the parent magma infiltrated into the quartz monzonite, resulting in its extensive K‐Si alteration as indicated by silicate‐bearing fluid inclusions trapped in altered quartz monzonite. This is followed by the early mineralization, the formation of quartz veinlets and dissemination‐stockwork ores. During the main mineralization stage due to the participation and mixing of meteoric groundwater with the magmatic‐sourced hydrothermal fluid the cooling and phase separation caused deposition of metals from the hydrothermal fluids. As a result the pegmatitic‐quartz sulfide‐vein ores formed. In the late mineralization stage, decreasing in fluid salinity has led to the formation of L‐type aqueous inclusions and chalcopyrite‐sulfosalt ore. Coexistence of V‐type and D‐type inclusions and their similar homogenization temperatures but different homogenization modes suggest that phase separation or boiling of the ore‐forming fluids once took place during the early and the main mineralization stages. The formation P‐T conditions of S‐type inclusions, and the early and the main mineralization stages are estimated as ca. 156 ∼ 182 MPa and 450 ∼ 650 °C, 350‐450 °C, 18‐35 MPa and 280‐380 °C, 8‐15 MPa, respectively based on the microthermometric data of the fluid inclusions formed at the individual stages.