Search Results (105)

As China’s third-largest lead–zinc ore field, the Xicheng Ore Field has significant potential for discovering concealed deposits. In this study, a tectono-geochemical survey was conducted, and 1329 composite samples (comprising 5614 subsamples) were collected from the central part of the field. The dataset was analyzed using staged factor analysis (SFA) and concentration–area (C–A) fractal model. Four geochemical factors were extracted from centered log-ratio (CLR)-transformed data: F_2-1 (Ag–Pb–Sb–Hg), F_2-2 (Mo–Sb–(Zn)), F_2-3 (Au–Bi), and F_2-4 (W–Sn). Known Pb–Zn deposits coincide with positive F_2-1 and negative F_2-2 anomalies, as identified by the C–A fractal model, suggesting these factors are reliable indicators of Pb–Zn mineralization. Five Pb–Zn exploration targets were delineated. Statistical analysis and anomaly maps for F_2-3 and F_2-4 also indicate the potential for Au and W mineralization. Notably, some anomalies from different factors spatially overlap, indicating the possibility of epithermal Pb–Zn mineralization at shallow depths and mesothermal to hyperthermal Au and W mineralization at great depths. Overall, the integration of tectono-geochemistry, targeted and composite sampling, SFA, and C–A fractal modeling proves to be an effective and economical approach for identifying and enhancing ore-related geochemical anomalies. Full article

As strategic critical metals, tungsten (W) and tin (Sn) require efficient exploration methods for effective resource development. This study implemented an advanced spread-spectrum induced polarization (SSIP) method in the Xitian mining district of southern China. Through optimized survey system configuration (maximum current electrode spacing of 5200 m, 12-channel acquisition, and five discrete frequency points), we achieved significant advancements: (1) a penetration depth of 1200 m, and (2) three- to five-times higher data acquisition efficiency compared to conventional symmetrical quadrupole arrays. Inversion results of resistivity and chargeability profiles from two parallel survey lines (total length 2.4 km) demonstrated an 85% spatial correlation between resistivity and chargeability anomalies, successfully identifying three mineralized veins. Drill-hole verification confirmed the presence of greisen veins (characterized by low resistivity <100 $\mathrm{\Omega }\cdot \mathrm{m}$ and high chargeability > 3%) and skarn veins (moderate resistivity 150–200 $\mathrm{\Omega }\cdot \mathrm{m}$ and chargeability 1.5–2%). The method exhibits a detection sensitivity of 0.5% chargeability contrast for deep-seated W-Sn polymetallic deposits, providing quantitative technical references for similar deposit exploration. Full article

Eocene magmatic systems contemporaneous with world-class Carlin-type Au deposits in Nevada (USA) have been proposed by some researchers as a key ingredient for Au mineralization, though evidence conclusively demonstrating their genetic relationship remains tenuous. This study provides the first direct evidence of the pre-eruptive metal budget of volatile- and metal-charged silicic magmas coincident in time (~41 to 34 Ma) and space (within 5 km) with Carlin-type Au deposits. We characterize the pre-eruptive metal fingerprints of these diverse magmatic systems to assess their potential as sources of metals for Carlin-type Au mineralization. Metal abundances from quartz-hosted melt inclusions (Au, Te, Ag, Sb, Tl, Mo, W, Sn, As, Pb, Co, Cu, Ni, and Zn) characterized in situ by SHRIMP-RG and LA-ICP-MS represent our best (and only) estimates for the pre-eruptive metal budget in these systems. Median metal concentrations are generally within one order of magnitude of average upper crust and average continental rhyolite values. But there are two notable exceptions, with median Au contents extending >1 order of magnitude higher than average upper crust and median Cu contents ranging >1 order of magnitude lower than upper crust. Despite this, melts contain lower Au/Cu (<0.1), Au/Ag (<5), and Au/Tl (<0.3) than most ore-grade Carlin-type rock samples and quartz-hosted fluid inclusions, regardless of their age and timing relative to nearby Carlin-type Au mineralization. The metal fingerprints of these magmatic systems, defined both by traditional and multivariate compositional data analysis techniques, are distinct from one another. Yet none are particularly specialized, e.g., high Au/Cu, in terms of being ideal ingredients as postulated by magmatic models for Carlin-type Au mineralization. Magmatic Au contents do not appear to be correlated with rhyolite “flavors” in the way that Cu, Sn, and Nb contents are. Fluid/melt partitioning modeling and magma volume estimates support the idea that a diverse array of non-specialized silicic magmas could feasibly contribute some or potentially all of the Au, Ag, and Cu in Carlin-type systems. The compositional diversity among contemporaneous magmatic systems could possibly contribute to some of the diversity observed across Carlin-type Au districts in Nevada. Full article

Chelidonium majus L. is a species with a wide medicinal use, commonly found in anthropogenically degraded habitats, forest edges, and urban parks. This study aimed to determine the chemical composition of the leaves, stems, and roots of Ch. majus and the soil in its rhizosphere in terms of the content of the main elements (Fe, Ca, P, Mg, Al, Na, K, S), trace elements and rare earth minerals (Ti, Mo, Ag, U, Au, Th, Sb, Bi, V, La, B, W, Sc, Tl, Se, Te, Ga, Cs, Ge, Hf, Nb, Rb, Sn, Ta, Zr, Y, Ce, In, Be, and Li), and their comparison in the parts analyzed. The study was conducted in five urban parks in southern Poland in a historically industrialized area. The results showed that Ca has the highest content among the macroelements. Its leaf content ranges from 24,700 to 40,700 mg·kg⁻¹, while in soil, it ranges from 6500 to 15,000 mg·kg⁻¹. In leaves, low values of Al (100–500 mg·kg⁻¹) and Na (100 mg·kg⁻¹) were found in comparison to the other elements tested, while high values of Al (5100–9800 mg·kg⁻¹) were found in soils. Among the macroelements in the Ch. majus stems, K showed the highest concentration (>100,000 mg·kg⁻¹), while the Ca content was 3–4 times lower in the stems than in the leaves. Rhizomes of Ch. majus accumulate the most K and Ca, in the range of 22,800–29,900 mg·kg⁻¹ and 5400–8900 mg·kg⁻¹, respectively. Fe and Al in all locations have higher values in the soil than in the tissues. In turn, the content of Ca, P, Mg, K, and S is higher in plants than in the soil. Determining the elemental content of medicinal plants is important information, as the plant draws these elements from the soil, and, at higher levels of toxicity, it may indicate that the plant should not be taken from this habitat for medicinal purposes. Full article

Numerous skarn-type Sn and hydrothermal vein-type Pb–Zn–Ag deposits occur in the northern Yidun Terrane, China. The Gongjuelong skarn Sn polymetallic deposit, adjacent to the Haizishan granite, is situated in the central region of Yidun Terrane. The genesis of the Gongjuelong Sn deposit and its relationship with the adjacent Pb–Zn–Ag deposits remains controversial. The ore-forming process can be divided into three stages: the prograde stage (I), marked by the formation of garnet and pyroxene; the retrograde stage (II), which includes the epidote–actinolite sub-stage (II-1) and the quartz-cassiterite sub-stage (II-2); and the sulfide stage (III), consisting of the chalcopyrite–pyrrhotite sub-stage (III-1) and the arsenopyrite–sphalerite sub-stage (III-2). Two types of garnet (Grt-I and Grt-II) have been identified in stage I and both belong to the grossular–andradite solid solution. Grt-II (Gro_52-73And_25-45Spe+Pyr+Alm_2-3) contains slightly more Fe than Grt-I (Gro_64-76And_20-28Spe+Pyr+Alm_2-10). Grt-I is enriched in heavy rare-earth elements (HREEs) and depleted in light rare-earth elements (LREEs), whereas Grt-II is enriched in LREEs and depleted in HREEs. Grt-I has higher U contents and lower Th/U ratios than those of Grt II, indicating a lower oxygen fugacity for the earlier skarn alteration. In contrast to Grt-I, Grt-II shows a more significant negative Eu anomaly along with lower LREEs/HREEs. Therefore, Grt-I and Grt-II likely formed under mildly acidic and near-neutral conditions, respectively. The W (350–3015 ppm) and Fe (235–3740 ppm) contents and Zr/Hf ratios (18.7–49.4) of cassiterite from Gongjuelong are similar to those of cassiterite from the granite-related Sn deposits, as well as the Xiasai hydrothermal vein-type Pb–Zn–Ag deposit in the northern Yidun Terrane. The Ti/Ge ratio (0.06–1.13) and P contents (13.9–173 ppm) of quartz are also similar to those from the Xiasai Pb–Zn–Ag deposit, both of which resemble those of skarn-type deposits and Sn-associated quartz. Furthermore, the Ti/Zr ratio (average 33.2) of cassiterite at Gongjuelong are much higher than that of cassiterite at Xiasai (average 3.7), indicating that the Pb–Zn–Ag veins could represent the distal product of the “parent” granite. On the basis of combined evidence from geology, geochemistry, and published geochronology data, we propose that the proximal skarn-type Sn deposits and distal hydrothermal vein-type Pb–Zn–Ag±Sn deposits in the northern Yidun Terrane constitute an integrated ore system, which is genetically related to the late Cretaceous highly fractionated granites. This proposed hypothesis highlights the potential prospecting of Sn mineralization beneath the hydrothermal Pb–Zn–Ag veins, as well as the hydrothermal Pb–Zn–Ag veins controlled by faults/fractures within the strata around the Sn deposits and highly fractionated granites. Full article

Morocco is rich in Mississippi Valley Type (MVT) copper deposits. Currently, geochemical surveying is being conducted in the Goulmima region in pursuit of breakthroughs in mineral exploration. This paper focuses on the delineation of prospecting targets in the Goulmima area based on the ongoing 1:100,000 geochemical survey work in Morocco. The study employs compositional data transformation to perform isometric log-ratio (ilr) transformations on raw data, followed by the Spectrum-Area (S-A) fractal processing, and then uses the Random Forest (RF) algorithm for mineral prediction. Finally, the prediction results are further delineated using the Concentration-Area (C-A) fractal model to identify high-probability areas, marking two prospecting targets. The results show: (1) the ilr transformation reduces the closure problem of the original data and improves their symmetry, thereby more effectively revealing the spatial structural features of the elements; (2) the principal component analysis (PCA) performed on the ilr-transformed data successfully identifies two main element combinations, representing high-temperature hydrothermal environments (Mo-Sn-Ti-W-U) and low-temperature mineralization environments (CaO-Pb-Zn), consistent with the regional mining history; (3) the application of the S-A multifractal model effectively distinguishes between anomalies and background distributions in the geochemical data of the study area, and combines fault buffer zones as the basis for mineral prediction; (4) the C-A fractal model further subdivides the prediction results, dividing potential mining areas into high, medium, and low probability zones, and ultimately identifies two prospecting targets. Full article

Molybdenite Re–Os and zircon U–Pb isotopic data are first obtained from the stockwork and disseminated-style gold-bearing ores and the fine-grained granite hosting these ores in the Xiawolong gold mine, respectively, which is located within the Muping–Rushan gold metallogenic belt, eastern Jiaodong Peninsula, so as to illustrate the genesis of gold mineralization and its implication for exploration. Four molybdenite samples yield a well-defined Re–Os isochron age of 118.4 ± 2.5 Ma (2σ), which is identical to the weighted average Re–Os model age of 118 ± 1.7 Ma (2σ). Integration of the new geochronologic data with those reported recently from the other gold mines in the Muping–Rushan gold metallogenic belt suggests that a discrete gold event occurred in Xiawolong ca. 4 m.y. older than that for the other gold mineralization at ca. 114 Ma in eastern Jiaodong. In addition, two fine-grained granite samples, measured using the LA-ICP-MS zircon U–Pb method, produce the first precise ages of 118 ± 2 to 117 ± 2 Ma (2σ), identical to the molybdenite Re–Os ages, within the margin of error and obtained in this study. The fine-grained granite has a similar lithology and emplacement age as those of the medium-grained monzogranite consisting of the marginal facies of the Sanfoshan batholith, and is considered to be the crystallization products of Sanfoshan granitic magma in the late stage. Combined with the previous S-Pb-D-O isotope, fluid inclusion and geological studies, which suggest that the ore-forming fluid of Xiawolong gold mineralization is from magmatic water, and the identification that the magnetite coexists with the gold-bearing pyrite and molybdenite in the gold ores, which indicates a high oxygen fugacity (fO₂) of both the magma and resultant hydrothermal fluids, it is logical to infer that the Xiawolong gold deposit is genetically in relation to the Sanfoshan granitic magmatism, which is high in fO₂ and rich in Au at the magmatic–hydrothermal transition stage, and the change in fO₂ mostly likely makes a significant contribution to the precipitation of Au. This result reveals that the late-stage granitic magma with high fO₂, which is crystallized into the fine-grained granite, probably is also rich in Au, except the W–Mo–Cu–Zn–U–Be–Li–Nb–Ta–Sn–Bi-elements. Therefore, based on the extensional tectonic regime for the early Cretaceous Jiaodong gold deposits, we propose that gold exploration in the Jiaodong should not only focus on the fault-hosted Au but also on the fine-grained granite-hosted Au around the apical portions of the late Early Cretaceous small-granitic intrusions with high fO₂. This model could also be important for prospecting in other gold ore districts, which have a similar tectonic setting. Full article

The Biggenden gold-bearing Fe skarn deposit in southeast Queensland, Australia, is a calcic magnetite skarn that has been mined for Fe and gold (from the upper portion of the deposit). Skarn has replaced volcanic and sedimentary rocks of the Early Permian Gympie Group, which formed in different tectonic settings, including island arc, back arc, and mid-ocean ridge. This group has experienced a hornblende-hornfels grade of contact metamorphism due to the intrusion of the Late Triassic Degilbo Granite. The intrusion is a mildly oxidized I-type monzogranite that has geochemical characteristics intermediate between those of granitoids typically associated with Fe-Cu-Au and Sn-W-Mo skarn deposits. The skarn mineralogy indicates that there was an evolution from prograde to various retrograde assemblages. Prograde garnet (Adr_11-99Grs_1-78Alm_0-8Sps_0-11), clinopyroxene (Di_30-92Hd_7-65Jo_0-9), magnetite, and scapolite formed initially. Epidote and Cl-bearing amphibole (mainly ferropargasite) were the early retrograde minerals, followed by chlorite, calcite, actinolite, quartz, and sulfides. Late-stage retrograde reactions are indicated by the development of nontronite, calcite, and quartz. Gold is mainly associated with sulfide minerals in the retrograde sulfide stage. The fluids in equilibrium with the ore-stage calcites had δ¹³C and δ¹⁸O values that indicate deposition from magmatically derived fluids. The calculated δ¹⁸O values of the fluids in equilibrium with the skarn magnetite also suggest a magmatic origin. However, the fluids in equilibrium with epidote were a mixture of magmatic and meteoric water, and the fluids that deposited chlorite were at least partly meteoric. δD values for the retrograde amphibole and epidote fall within the common range for magmatic water. Late-stage chlorite was deposited from metasomatic fluids depleted in deuterium (D), implying a meteoric water origin. Sulfur isotopic compositions of the Biggenden sulfides are similar to other skarn deposits worldwide and indicate that sulfur was most probably derived from a magmatic source. Based on the strontium (⁸⁷Sr/⁸⁶Sr) and lead (²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb) isotope ratios, the volcanic and sedimentary rocks of the Gympie Group may have contributed part of the metals to the hydrothermal fluids. Lead isotope data are also consistent with a close age relationship between the mineralization at Biggenden and the crystallization of the Degilbo Granite. Microthermometric analysis indicates that there is an overall decrease in fluid temperature and salinity from the prograde skarn to retrograde alterations. Fluid inclusions in prograde skarn calcite and garnet yield homogenization temperatures of 500 to 600 °C and have salinities up to 45 equivalent wt % NaCl. Fluid inclusions in quartz and calcite from the retrograde sulfide-stage homogenized between 280 and 360 °C and have lower salinities (5–15 equivalent wt % NaCl). In a favored genetic model, hydrothermal fluids originated from the Degilbo Granite at depth and migrated through the shear zone, intrusive contact, and permeable Gympie Group rocks and leached extra Fe and Ca and deposited magnetite upon reaction with the adjacent marble and basalt. Full article

The Xinjiazui gold deposit marks a notable significance in prospecting within the Back-Longmenshan tectonic belt, located on the northwest margin of the Yangtze Block, China. Despite the extensive studies conducted on this deposit, the source of the ore-forming materials remains unclear, leading to ongoing debates regarding the genesis of this deposit. This study analyzed in situ (EPMA and LA-ICP-MS) trace elements and S-Pb isotopes of arsenopyrite, solely from the principal metallogenic stage and paragenetic with native gold. The results show that the gold in arsenopyrite occurs as invisible gold (Au³⁺), with an average concentration of 9.38 ppm, whereas the concentrations of magma-related elements, such as W, Sn, Mo, and Bi, are very low. The sulfur isotopes (³⁴S) of arsenopyrite range from 8.32‰ to 10.16‰, aligning closely with the deep metamorphic basement (Pt₃l). Meanwhile, the lead isotopes in arsenopyrite display characteristics typical of those found in orogenic belts. A comprehensive analysis of the abundance of gold indicated that the metallogenic materials (sulfur and gold) primarily originated from Pt₃l. Additionally, the arsenopyrite thermobarometer indicated that the Xinjiazui gold deposit formed in a medium–low-temperature, medium metallogenic environment (5.57–8.69 km), with a sulfur fugacity (log f (S₂)) below −8.4. Combined with previous research results, this study proposes that the Xinjiazui gold deposit is a subduction-related mesozonal orogenic gold deposit. In gold prospecting and exploration in the Back-Longmenshan tectonic belt, it is essential to focus on the distribution of brittle-ductile shear zones and location of the quartz veins associated with pyrite and arsenopyrite mineralization. Full article

To explore the potential of plant trace elements as indicators in the search for concealed deposits within the W–Sn polymetallic mining area of Shizhuyuan, Hunan Province, this study focused on the geochemical characterization of 21 trace elements, including Ag, As, B, Bi, Cd, Mo, Ni, Pb, and U, in the stem and leaf tissues of three predominant plants in the area. A total of 126 plant samples were collected, covering an area of about 10 km², and analyzed using ICP-MS. The best indicator plants and sampling sites were selected using multiple indicators, including the biological absorption coefficient (X_BAC), the enrichment coefficient (K_NJ), and the contrast coefficient (K_CD). The results showed that plant leaf tissues represent the most effective sampling components for phyto-geochemical surveys in this region. Dicranopteris dichotoma exhibited markedly pronounced geochemical anomalies of Ag (0.137 µg/g), As (86.12 µg/g), Mo (0.963 µg/g), Pb (15.4 µg/g), Sb (2.03 µg/g), and Se (0.547 µg/g) and demonstrated superior absorption capabilities for Ni, Sn, Sb, Pb, and Bi in the soil, with X_BAC values of 12.0, 54.2, 23.3, 2.9, and 83.9, respectively. R-type cluster analysis and factor analysis identified four distinct mineralization element combinations: (1) Sn–As, (2) Ag–Cu–Mo, (3) Pb, and (4) Bi–Sb–Se. Consequently, D. dichotoma is a viable indicator plant for the phyto-geochemical detection of concealed Ag, Bi, Mo, Pb, Sb, Se, and Sn mineralization in mining areas. The results demonstrate that using phyto-geochemical methods for mineral prospecting is feasible and has significant application value in the Shizhuyuan mining area, which is characterized by dense vegetation and complex geological conditions. Full article

The Southern Hunan area is located in the superposition of the Qin-Hang Cu-Pb-Zn polymetallic ore belt and the Nanling W-Sn-Mo polymetallic ore belt, which is an important window to study the mineralization of W-Sn-Mo and Cu-Pb-Zn polymetallic deposits. The Baoshan deposit is a large Cu-Pb-Zn polymetallic deposit in Southern Hunan Province with obvious zones of Cu mineralization and Pb-Zn mineralization: the central part of the Baoshan deposit demonstrates contact metasomatic (skarn) Cu mineralization, while the western, northern and eastern parts demonstrate hydrothermal vein Pb-Zn mineralization. However, the origin and evolution of the ore-forming fluid and mechanism of Cu and Pb-Zn mineral precipitation are still unclear. The metallogenic process of the Baoshan Cu-Pb-Zn deposit can be divided into four stages: (1) the early skarn stage (S₁); (2) the late skarn stage (S₂); (3) the Cu-Fe sulfide stage (S₃); and (4) the Pb-Zn sulfide stage (S₄). The results of microtemperature measurements and a Raman spectrometric analysis of fluid inclusions show that the ore-forming fluid was the H₂O-NaCl (-CO₂ ± N₂ ± C₂H₆) system in the skarn stages (S₁ + S₂) and changed into the H₂O-NaCl-CO₂ (±N₂ ± C₂H₆) system in the sulfide stages (S₃ + S₄). The temperature (S₁: 436.6~548.2 °C; S₂: 344.1~435.1 °C; S₃: 134.1~413.1 °C; S₄: 183.9~261.0 °C) and salinity (S₁: 17.4~51.2 wt.%NaClequiv; S₂: 13.6~41.7 wt.%NaClequiv; S₃: 1.2~32.3 wt.%NaClequiv; S₄: 1.8~9.6 wt.%NaClequiv) showed a downward trend from the early to late stages. From the skarn stages (S₁ + S₂) to the sulfide stages (S₃ + S₄), the ore-forming pressure results from the static rock pressure and the hydrostatic pressure, and the ore-forming depth is estimated to be about three to six km. The C-H-O isotopic compositions of hydrothermal minerals such as quartz and calcite indicate that the ore-forming fluid is predominately magmatic fluid, but a significant amount of meteoric water is added in the Pb-Zn sulfide stage (S₄). The formation of the mineralization zonation of the Baoshan deposit is the result of many factors (e.g., stratigraphy, structure and metal precipitation mechanism): the Cu mineralization is controlled by the contact zone, and the Pb-Zn mineralization is controlled by the fault. In addition, the precipitation of Cu is mainly controlled by fluid boiling, while the precipitation of Pb and Zn is mainly controlled by the mixing of magmatic fluid and meteoric water. Full article

Lithium is a strategic metal due to its use in green technologies, particularly battery manufacturing. It is on the US List of Critical Minerals and the European Union’s List of Critical Raw Materials. In Mongolia, there are three major types of potentially economic Li deposits: (1) Deposits related to granites, granitic pegmatites and associated rocks; (2) Li-rich clay deposits; (3) Salar (Li brine) deposits. The first type of mineralization is associated with the lithium–fluorine-rich peraluminous A-type granites and related rocks (greisens, pegmatites, ongonites, ongorhyolites). The mineralization includes Li and also Sn, W, Ta and Nb. Lithium is hosted in Li-rich micas, unlike the world-class Li-bearing pegmatite deposits where the bulk of Li is in spodumene. In Mongolia, particularly promising are Li brines of endorheic basins in the Gobi Desert with an arid environment, high evaporation rates and low precipitation. Full article

The Baoshan Cu-Pb-Zn deposit is situated at the intersection of the Qin-Hang Cu polymetallic and Nanling W-Sn polymetallic metallogenic belts. The age, lithology, petrogenesis, and tectonic setting of granodiorite porphyry within the deposit remain subjects of debate. Additionally, there is a lack of comparative studies with the W-Sn-related granites in the region. This study conducted whole-rock major and trace element analysis, Sr-Nd isotope analysis, and zircon U-Pb dating on the Baoshan granodiorite porphyry. The zircon U-Pb age of the granodiorite porphyry is 162 ± 1 Ma. The whole-rock SiO₂ and K₂O contents range from 65.87 to 68.21 wt.% and 3.42 to 5.62 wt.%, respectively, indicating that the granodiorite porphyry belongs to high-potassium calc-alkaline I-type granite. The granodiorite porphyry is characterized by enrichment in LREE and depletion in HREE (LREE/HREE ratio = 6.2–21.2). The samples of granodiorite porphyry generally exhibit weak negative Eu anomalies or no Eu anomalies (δEu = 0.62–1.04, mean = 0.82). The (⁸⁷Sr/⁸⁶Sr)_i and ε_Nd(t) values are 0.707717–0.709506 and −7.54 to −4.87, respectively. The whole-rock geochemical composition and Sr-Nd isotopic values indicate that the magma originated from the partial melting of the Mesoproterozoic ancient crust and Neoproterozoic mafic juvenile lower crust, with the addition of high oxygen fugacity and water-rich lithospheric mantle melts. The source of the granodiorite porphyry in the Baoshan deposit is significantly different from the crust-derived metapelite source of the W-Sn-related granite in the area, indicating that different magma sources might be the main reason for the co-spatial and nearly contemporaneous development of Cu-Pb-Zn and W-Sn mineralization in the southern Hunan region. Full article

The Perron deposit, located in the northern part of the Archean Abitibi belt, bears some of the highest gold-grade mineralization for orogenic-vein-type deposits worldwide (High-Grade Zone: HGZ). More than 13 gold-bearing zones with different sulfide assemblages, hydrothermal alterations, and gold grades have been recently outlined, and they range from volcanogenic to orogenic in origin. In addition, seven zones are hosted in a restricted volume of ~1 km³, which is called the Eastern Gold Zone. Pyrite, sphalerite, pyrrhotite, and chalcopyrite—each from a different gold-bearing zone—were analyzed with LA-ICP-MS to decipher their genetic links, mineralizing processes, and temperature of formation. The temperatures calculated with the sphalerite GGIMFis thermometer range from 348 to 398 °C. All gold-bearing zones recorded volcanogenic hydrothermal inputs at different intensities, manifested by pyrrhotite. Pyrite was late-metamorphic and related to the orogenic gold system induced by the contact metamorphism of amphibolite facies. The pyrrhotite grains had very homogeneous trace element signatures in all zones, which is a characteristic of metamorphic recrystallization, exhibiting a loss of mobile elements (Au, Te, Bi, Tl, Sn, W, In) but high concentrations of Ni, Co, and As. Conversely, the pyrite was systematically enriched with all elements depleted from pyrrhotite, bearing five specific signatures of element enrichments: W, Tl, Sn, In-Cd-Zn, and Bi-Te-Au. For gold-rich zones (e.g., the HGZ), gold was linked to the Bi-Te-Au signature of pyrite, with Bi enrichment occurring at up to 72,000 times the background level in Archean shale pyrite. It was concluded that gold was transported, at least in part, as Bi-Te melts in the previously documented non-aqueous orogenic fluids, hence accounting for the very-high-grade gold content of the HGZ. Genetically, the metamorphism of primary gold-bearing volcanogenic mineralizations was the main source of gold during the overprinting of amphibolite (600 °C) in a metamorphically induced orogenic mineralizing event. A strong volcanogenic pre-enrichment is considered the main factor accounting for the gold endowment of the Eastern Gold Zone. Full article

Mineralogy and formation conditions were studied in a newly found vein wolframite mineralization, cutting migmatitized paragneisses in the exocontact of a small Carboniferous granite body in the Pohled quarry, Moldanubian Zone of the Bohemian Massif, Czech Republic. The early stage of the rich mineral assemblage (36 mineral species) involves wolframite, columbite-group minerals, molybdenite, and scheelite hosted by quartz–muscovite–chlorite gangue, which was followed by base-metal sulfides in a quartz gangue, whereas the last stage included calcite gangue with fluorite and minor sulfides. The mineral assemblage points to the mobility of usually hardly soluble elements, including W, Sn, Zr, Nb, Th, Ti, Sc, Y, and REEs. A fluid inclusion study indicates a significant decrease in homogenization temperatures from 350–370 °C to less than 100 °C during vein formation. Fluids were aqueous, with a low salinity (0–12 wt. % NaCl eq.) and traces of CO₂, N₂, CH₄, H₂, and C₂H₆. The δ¹⁸O values of the fluids giving rise to quartz and scheelite are positive (min. 4‰–6‰ V-SMOW). The Eh and pH of the fluid also changed during evolution of the vein. Both wolframite and columbite-group minerals are anomalously enriched in Mg. We suggest that the origin of this distinct mineralization was related to the mixing of Mo,W-bearing granite-derived magmatic fluids with external basinal waters derived from contemporaneous freshwater (but episodically evaporated) piedmont basins. The basinal waters infiltrated into the subsurface along fractures formed in the extensional tectonic regime, and their circulation continued even after the ending of the activity of magmatic fluids. The studied wolframite mineralization represents the most complete record of the ‘hydrothermal’ history of a site adjacent to a cooling granite body in the study area. Moreover, there are broad similarities in the mineral assemblages, textures, and chemical compositions of individual minerals from other occurrences of wolframite mineralization around the Central Moldanubian Plutonic Complex, pointing to the genetic similarities of the Variscan wolframite-bearing veins in this area. Full article