Magmatic-hydrothermal Mineralization Research Articles

Genesis of the Weizigou Au Deposit, Heilongjiang Province, NE China: Constraints from LA-ICP-MS Trace Element Analysis of Magnetite, Pyrite and Pyrrhotite, Pyrite Re-Os Dating and S-Pb Isotopes

The Weizigou Au deposit in Heilongjiang Province, NE China, located in the southern Jiamusi Massif, shows similarities to IOCG deposits. To determine the mineralization age, sources of ore-forming materials and genetic type, pyrite Re-Os dating, S-Pb isotopic analysis, in situ sulfur analysis and LA-ICP-MS analysis of trace elements in magnetite, pyrite and pyrrhotite were conducted. Four pyrite samples yielded a Re-Os isochron age of 197 ± 11 Ma, implying the occurrence a metallogenic event in the Early Jurassic. The δ34S values of sulfides display a relatively narrow range from 4.70‰ to 12.83‰ (mainly 9.90‰ to 12.83‰), which may be accounted for the extensively exposed granitic gneiss and meta-gabbro, with δ34S values of 7.44‰ to 8.44‰ and 4.37‰ to 10.54‰, respectively. Sulfide lead isotopic compositions have 206Pb/204Pb = 18.605–20.136, 207Pb/204Pb = 15.637–15.710 and 208Pb/204Pb = 38.534–39.129, indicating that the lead was derived from a mixed source. Magnetite has the characteristics of a lower Ti content and higher Zn content, indicating that it should be of hydrothermal origin, which may be related to IOCG-type mineralization. Pyrite and pyrrhotite have a Co/Ni ratio greater than 1 and a lower As content, indicating that they are of magmatic hydrothermal origin. Integrating the above analysis results, we inferred that the Weizigou Au deposit experienced the IOCG-type mineralization in the Middle-Late Permian, associated with magmatic-hydrothermal mineralization in the Early Jurassic.

Textures and chemical compositions of the Narm iron oxide-apatite deposit in Kuh-e-Sarhangi District (Central Iran): Insights into the magmatic-hydrothermal mineralization

The Narm deposit is located in the Kuh-e-Sarhangi district which is a main part of the most significant Iranian iron mineralization belt, the Kashmar-Kerman Tectonic Zone (KKTZ) in Central Iran. The Narm deposit comprises an estimated total of ∼ 135000 tons of iron ore with an average grade of ∼ 55% Fe and is hosted in Early Cambrian volcano sedimentary rocks of the Rizu formation. Ore occurrences in this deposit consist of lens-shaped magnetite ore bodies, magnetite-apatite-actinolite veins and locally rare brecciated dolomite with magnetite clasts. Magnetite, pyrite, chalcopyrite and specularite associated with apatite, actinolite, biotite and carbonate minerals form the primary main mineral assemblage which is accompanied by hematite and goethite as the secondary minerals. Magnetite as the most current mineral of Narm deposit reveal the magmatic to hydrothermal evolution of mineralization. Magmatic magnetite minerals (Mag I) are dark-gray inclusion-rich magnetite spatially correlated with high temperature Ca-Fe alteration. The brighter inclusion-free hydrothermal magnetite groups (Mag II and Mag III) form during the temperature decreasing of the mineralizing fluid. According to the magnetite chemistry examination, most magnetite fall into the field for magnetite from iron-oxide apatite (IOA) deposits. Apatite minerals with F/Cl > 2, belong geochemically to the fluorapatite type. In addition to the primary dolomite, there are some hydrothermal Fe-rich dolomites and Mn bearing ones, indicating the hydrothermal fluid playing the important role for Fe-rich mineralization. In respect to fluid evolution, fluid inclusion analysis of calcite and apatite minerals form the magnetite paragenesis assemblage represent homogenization temperature range for fluid between 325 and 557℃. The salinity of fluid varied from 7.7 to 11.6 wt% NaCl equivalent and a cooling trend with the dominant chlorine complex as an agent for deposition of the Fe-rich ores. The geochemical characteristics of the δ18Ofluid values of magnetite (from + 6.1 to + 10.4‰) and δ18Ofluid values of actinolite (from + 7.7 to + 12.5‰) represent the magmatic-hydrothermal (δ18Ofluid > + 0.9 ‰) formation process. The iron rich Al-clinochlore composition from the alteration zone indicates a temperature range between 250 and 330℃ which points to a temperature reduction of hydrothermal fluids in this mineralizing zone. The integrated geochemical data from this investigation, including mineral chemistry, microthermometry of fluid inclusions and oxygen isotope data all reveal a magmatic-hydrothermal genesis for this deposit.

Multistage Genesis of the Haerdaban Pb-Zn Deposit, West Tianshan: Constraints From Fluid Inclusions and H-O-S-Pb Isotopes

The Haerdaban Pb-Zn deposit is located on the western edge of the Chinese Western Tianshan Orogen. This deposit consists of stratiform and veined mineralization hosted in Proterozoic carbonaceous and dolomitic limestone. Three metallogenic stages were recognized: an early sedimentary exhalative stage (stage 1), an intermediate metamorphic remobilization stage (stage 2), and a late magmatic-hydrothermal stage (stage 3). Fluid inclusions (FIs) present in stage 1 are liquid-rich aqueous, with homogenization temperatures of 206–246 C and salinities of 5.9–11.6 wt% NaCl eq. FIs present in stage 2 are also liquid-rich aqueous, with homogenization temperatures of 326–349 C and salinities of 3.4–6.6 wt% NaCl eq. FIs present in stage 3 include halite-bearing, vapor-rich aqueous, and liquid-rich aqueous FIs. Homogenization temperatures for these FIs span a range of 249–316 C. Halite-bearing, vapor-rich aqueous, and liquid-rich aqueous FIs yield salinities of 33.8–38.9, 2.6–3.5, and 4.2–8.1 wt% NaCl eq., respectively. Oxygen and hydrogen isotopic data (δ18OH2O = 2.6–13.6‰, δDH2O = −94.7 to −40.7‰) indicate that the ore-forming fluids of stages 1–3 were derived from modified seawater, metamorphic water, and magmatic-meteoric mixed water, respectively. Sulfur isotopic data (δ34S = 2.1–16.3‰) reveal that ore constituents were derived from mixing of marine sulfate and magmatic materials. Lead isotopic data (206Pb/204Pb = 17.002–17.552, 207Pb/204Pb = 15.502–15.523, 208Pb/204Pb = 37.025–37.503) reveal that ore constituents were derived from a mixed crust-mantle source. We propose that the Haerdaban deposit was a Proterozoic sedimentary exhalative deposit overprinted by later metamorphic remobilization and magmatic-hydrothermal mineralization.

Metal anomalies in zircon as a record of granite-hosted mineralization

Granite-hosted magmatic-hydrothermal mineral deposits are major sources of Cu, Mo, Sn, Li, and W, originating via mineralizing fluids exsolved from volatile-saturated magmas. We show how trace elements in zircon sampled from the granite-hosted Zaaiplaats tin deposit, Bushveld Complex, preserve a record of both the enrichment of incompatible metals during magma fractionation and those arising from magmatic-hydrothermal mineralization processes. The Zaaiplaats granites are subdivided into three groups; mineralized, altered, and unmineralized. Zircon trace element contents define two trends in a plot of Sn against Gd: Sn/Gd ratios in zircons from the unmineralized samples, as well as the majority of altered samples, define a magma fractionation trend with increasing Y at constant Sn/Gd, whereas those from the mineralized samples are displaced to high Sn/Gd ratios at similar Y. Elevated Sn in the Zaaiplaats zircons is attributed to the introduction of a Sn-rich mineralizing fluid during zircon growth, which occurred at an advanced stage of crystallization (>85%) of the host magma. This model is consistent with the preservation of whole-rock Sn zonation in the Zaaiplaats granites modelled by closed-system magma differentiation and the ensuing exsolution of an acidic, saline Sn-rich magmatic-hydrothermal fluid (Groves and McCarthy, 1978). A metal anomaly, Sn/Sn*, is defined which describes the deviation of Sn over that expected through magma fractionation alone (Sn*), and arises from Sn mobilization due to magmatic-hydrothermal mineralization processes. Identification of metal anomalies such as Sn/Sn* and Cu/Cu* in mineral archives or at the whole-rock level, provides an empirical link to the onset of mineralization processes in magmatic-hydrothermal systems, and can be coupled with geochemical proxies to yield a better understanding of the conditions leading up to, and subsequent to, volatile saturation.

Igneous rocks related to porphyry Cu‐Au mineralization at the Dizon mine, Philippines

AbstractThe Dizon Au‐rich porphyry Cu deposit, 0.67 Mt Cu and 174 t Au, is hosted by diorite and andesite porphyry intrusions, dated at ~2.5 Ma. Amphibole and Fe‐Ti oxides in relatively unaltered rocks were used to evaluate the magma conditions of intrusions. Parental magma for diorite porphyry was ~950°C at a depth of ~15 km, whereas the parental magmas for the andesite porphyry had lower temperatures, 760–820°C at a depth of ~5 km. The deposit formed at the locus of multiple intrusions, with evidence for injections of hot mafic magmas, including destabilization texture of plagioclase phenocrysts. Parental magmas at Dizon were oxidized, above FMQ + 2.0, and water‐rich, >5 wt%, comparable to conditions of many large porphyry deposits elsewhere in the world. The occurrence of thick opacitic bands of amphibole in the diorite porphyry at Dizon reflects the release of aqueous fluids from the magma; such magmatic fluids were likely responsible for magmatic hydrothermal mineralization of the Dizon porphyry deposit. Subduction of the Scarborough Seamount caused a compressive regime in the overlying plate, which likely contributed to favourable tectonic conditions for mineralization.

Magmatic-Hydrothermal Mineralization Processes at the Yidong Tin Deposit, South China: Insights from In Situ Chemical and Boron Isotope Changes of Tourmaline

Abstract Owing to the superimposition of water-rock interaction and external fluids, magmatic source signatures of ore-forming fluids for vein-type tin deposits are commonly overprinted. Hence, there is uncertainty regarding the involvement of magmatic fluids in mineralization processes within these deposits. Tourmaline is a common gangue mineral in Sn deposits and can crystallize from both the magmas and the hydrothermal fluids. We have therefore undertaken an in situ major, trace element, and B isotope study of tourmaline from the Yidong Sn deposit in South China to study the transition from late magmatic to hydrothermal mineralization. Six tourmaline types were identified: (1) early tourmaline (Tur-OE) and (2) late tourmaline (Tur-OL) in tourmaline-quartz orbicules from the Pingying granite, (3) early tourmaline (Tur-DE) and (4) late tourmaline (Tur-DL) in tourmaline-quartz dikelets in the granite, and (5 and 6) core (Tur-OC) and rim (Tur-OR), respectively of hydrothermal tourmaline from the Sn ores. Most of the tourmaline types belong to the alkali group and the schorl-dravite solid-solution series, but the different generations of magmatic and hydrothermal tourmaline are geochemically distinct. Key differences include the hundredfold enrichment of Sn in hydrothermal tourmaline compared to magmatic tourmaline, which indicates that hydrothermal fluids exsolving from the magma were highly enriched in Sn. Tourmaline from the Sn ores is enriched in Fe3+ compared to the hydrothermal tourmaline from the granite and displays trends of decreasing Al and increasing Fe content from core to rim, relating to the exchange vector Fe3+Al–1. This reflects oxidation of fluids during the interaction between hydrothermal fluids and the mafic-ultramafic wall rocks, which led to precipitation of cassiterite. The hydrothermal tourmaline has slightly higher δ11B values than the magmatic tourmaline (which reflects the metasedimentary source for the granite), but overall, the tourmaline from the ores has δ11B values similar to those from the granite, implying a magmatic origin for the ore-forming fluids. We identify five stages in the magmatic-hydrothermal evolution of the system that led to formation of the Sn ores in the Yidong deposit based on chemical and boron isotope changes of tourmaline: (1) emplacement of a B-rich, S-type granitic magma, (2) separation of an immiscible B-rich melt, (3) exsolution of an Sn-rich, reduced hydrothermal fluid, (4) migration of fluid into the country rocks, and (5) acid-consuming reactions with the surrounding mafic-ultramafic rocks and oxidation of the fluid, leading to cassiterite precipitation.

Genesis of the Donggushan tungsten polymetallic deposit, central Anhui Province: A clue of diagenetic and metallogenic system of a crustal source

• The W mineralization in the Donggushan was caused by the Late Cretaceous magmatism . • Diagenetic and metallogenic system was likely to be originated from a crustal source dominated by the Northern Dabie Terrane . • The REEs of scheelite are mainly controlled by the substitution mechanism Ca 2+ + W 6+ = REE 3+ +Nb 5+ . • The ore-forming fluids were modified by the intense fluid-rock interaction. The newly discovered large-scale Donggushan tungsten polymetallic deposit with resources of 70,000 t WO 3 and 38,000 t Mo, located at the Lujiang county, center of Anhui Province, East China. The deposit is characterized by skarn W-Mo mineralization, which is developed along the external contact zone between the biotite granites and carbonate rocks. Zircon U-Pb dating yields a Late Cretaceous age of 98.3 ± 1.6 Ma for the Donggushan biotite granite. The hidden biotite granites of Donggushan is characterized by high silica and alkali but low Mg, Fe. It is enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs: Rb, K, Th and U), but strongly depleted in heavy REEs, and high field strength elements (HFSEs: Nb, Ta and Ti), and Sr. This high-K granite has medium initial 87 Sr/ 86 Sr ratios (0.706518–0.707116) and low initial Pb isotopic ratios [( 206 Pb/ 204 Pb)i, 16.452–16.533; (207Pb/204Pb)i, 15.449–15.463; ( 208 Pb/ 204 Pb)i, 36.946.335–37.097], and is characterized by low εNd(t) and εHf(t) values (−22.1 to −16.1 and −21.3 to −15.1, respectively). All these data indicate that the Donggushan biotite granite is a high-K calc-alkaline fractionated I-type granitite. This granite may have derived from a crustal source, which is dominated by the Northern Dabie Complex (NDC) mixed with the basement materials of the Taihua Group. The magmatism in the Donggushan polymetallic deposit is quite different from those in the metallogenic belts of the Qinling-Dabie Mo belt (QDMB) and Middle-Lower Yangtze River Belt (MLYB). Based on the geochemical study of REEs of scheelite, it is proposed that the substitution mechanism of Ca2+ + W6+ = REE3+ +Nb5 + occurred during the formation of scheelite. Concentrations of Eu indicate that scheelite precipitated under the oxide conditions. The variations of the Mo concentrations might be caused by the changing of oxide reduction conditions. The Sr of the scheelite and S isotopes of pyrite in the Donggushan deposit reflect a complex magmatic-hydrothermal mineralization process within the intrusion and the country rocks.

Postcaldera intrusive magmatism at the Platoro caldera complex, Southern Rocky Mountain volcanic field, Colorado, USA

The Oligocene Platoro caldera complex of the San Juan volcanic locus in Colorado (USA) features numerous exposed plutons both within the caldera and outside its margins, enabling investigation of the timing and evolution of postcaldera magmatism. Intrusion whole-rock geochemistry and phenocryst and/or mineral trace element compositions coupled with new zircon U-Pb geochronology and zircon in situ Lu-Hf isotopes document distinct pulses of magma from beneath the caldera complex. Fourteen intrusions, the Chiquito Peak Tuff, and the dacite of Fisher Gulch were dated, showing intrusive magmatism began after the 28.8 Ma eruption of the Chiquito Peak Tuff and continued to 24 Ma. Additionally, magmatic-hydrothermal mineralization is associated with the intrusive magmatism within and around the margins of the Platoro caldera complex. After caldera collapse, three plutons were emplaced within the subsided block between ca. 28.8 and 28.6 Ma. These have broadly similar modal mineralogy and whole-rock geochemistry. Despite close temporal relations between the tuff and the intrusions, mineral textures and compositions indicate that the larger two intracaldera intrusions are discrete later pulses of magma. Intrusions outside the caldera are younger, ca. 28–26.3 Ma, and smaller in exposed area. They contain abundant glomerocrysts and show evidence of open-system processes such as magma mixing and crystal entrainment. The protracted magmatic history at the Platoro caldera complex documents the diversity of the multiple discrete magma pulses needed to generate large composite volcanic fields.

Iron Isotopes and Trace Element Compositions of Magnetite from the Submarine Volcanic-Hosted Iron Deposits in East Tianshan, NW China: New Insights into the Mineralization Processes

The Aqishan-Yamansu metallogenic belt (AYMB) in East Tianshan hosts abundant submarine volcanic-hosted iron deposits. Although there is agreement with the magmatic source of the ore-forming materials and the role of hydrothermal replacement in iron ore formation, the mineralization processes of these iron deposits remain uncertain. Three ore types are identified on the basis of the geological occurrences of minerals and the sequence of mineral in ores. The type I ores are characterized by magnetite, diopside, amphibole with a few pyrite, and chalcopyrite. The type II ores are mainly composed of magnetite, garnet, chlorite with a few pyrite, while the type III ores are mainly composed of magnetite, quartz, calcite with a few pyrite. In order to constrain the mineralization processes of these ore types, we performed iron isotopes and trace element compositions of magnetite from three typical iron deposits (Yamansu, Duotoushan and Luotuofeng). Trace element and Fe isotope investigations of the three ore types reveal two major groups. The group I consists of analyses of the type I and II ores, with both showing a narrow range of positive δ56Fe values (+0.08‰ to +0.22‰ for type I ores and +0.15‰ to +0.22‰ for type II ores) and plotting in the range of the ortho-magmatic field. In contrast, the group 2 is composed merely of the type III ores, showing a wider range of negative δ56Fe values (-0.49‰ to -0.01‰), which is similar to the features of Fe-skarn magnetite. As shown in the binary diagrams of magnetite trace elements and a fractionation of the Fe isotopes, different ore types were likely produced during gradually changing ore-forming stages from magmatic to hydrothermal. Collectively, the submarine volcanic-hosted iron deposits in the East Tianshan are likely the results of a continuous magmatic-hydrothermal mineralization process.

Genesis of the Hongtuling Au-Mo deposit in the southern North China Craton revealed from pyrite trace element compositions and S-Pb isotopes

The Hongtuling Au-Mo deposit on the southern margin of the North China Craton consists of Au veins and minor Mo veins that formed at ~130 Ma and ~204 Ma, respectively. Mo mineralization is dominated by molybdenite that is associated with K-feldspar, quartz and calcite, whereas Au mineralization occurs mostly as auriferous quartz-sulfides veins associated with alteration assemblages consisting of pyrite ± sericite ± quartz. Laser ablation inductively coupled plasma mass spectrometry trace element analysis shows that pyrite from Mo veins (Py-Mo) is relatively enriched in Mo and Pb, whereas pyrite from Au veins (Py-Au) contains much higher Au, Ag, Te, Cu, Pb, and Ni. Sulfide minerals and celestine from Mo veins range in δ34S values from −13.4 to −8.89‰ (n = 24) and 5.26 to 7.76‰ (n = 8), respectively. Extrapolation of sulfur isotopes of coexisting sulfides and celestine to zero sulfide-celestine fractionation on Δ34SClt-Py versus δ34S diagram shows that the hydrothermal fluid from which molybdenite precipitated has δ34S of 2.49 ± 3.93‰. In comparison, Py-Au yields δ34S values of −6.23 ~ 0.16‰, with a mean of −2.60‰ (n = 20). The Py-Mo and Py-Au have significantly different lead isotopic compositions, which form two distinct groups on the 207Pb/204Pb versus 206Pb/204Pb diagram, with Py-Au plotting close to the lead growth curve of the subcontinental lithospheric mantle of the North China Craton at ~130 Ma.Combined with previous studies, our new trace element and S-Pb isotope data suggest that Mo mineralization at Hongtuling is most likely related to magmas derived from partial melting of Late Archean to Paleoproterozoic metamorphic basement rocks under a post-collisional setting related to the collision between the North China Craton and Yangtze Craton, whereas Au mineralization is genetically associated with mantle-derived magmas generated in an extensional setting due to thinning and destruction of subcontinental lithospheric mantle keel beneath the North China Craton. As such, the Triassic Mo and Early Cretaceous Au veins can both be classified as magmatic-hydrothermal mineralization but are affiliated with two distinct systems. This study highlights the utilization of pyrite trace element and isotopic compositions in distinguishing multiple mineralization events in a single deposit.

Spatio-Temporal Shifts in Magmatism and Mineralization in Northern Colorado Beginning in the Late Eocene

AbstractMagmatism in northern Colorado beginning in the late Eocene is associated with the formation of Pb-Zn-Ag carbonate-replacement and polymetallic vein deposits, the onset of caldera-forming magmatism, and eventually, the formation of rift-related, F-rich Mo porphyries (“Climax-type” intrusions). We use high-precision U/Pb zircon geochronology to better evaluate the temporal framework of magmatism and mineralization in the region. Our results demonstrate that mineralization in the Leadville area occurred between 43.5 and 39.7 Ma and was followed by mesothermal mineralization in the Montezuma area at approximately 38.7 Ma. Mineralization is associated with a suite of approximately 43 to 39 Ma intermediate magmatic centers that extended from Twin Lakes through Montezuma. The oldest porphyries associated with F-rich Mo prospects and deposits (Middle Mountain; 36.45 Ma) intruded 900 kyr after the start of the ignimbrite flare-up in the region. Spatiotemporal analyses reveal that the pattern of magmatism shifted in orientation between 40 and 35 Ma. We propose a model wherein magmatism before 39 Ma was the result of fluids evolved from the subducted Farallon slab being focused through weak zones in the lithospheric mantle and into the lower crust. This was followed by a more diffuse and higher power melting event that corresponds to a distinct change in the spatial patterns of magmatism. Our data suggest that low-grade Mo porphyry deposits can form close in time to calderas. We hypothesize that the transition from subduction to extensional tectonics in the region was responsible for this more widespread melting and a distinct shift in the style of magmatic-hydrothermal mineralization.

Discriminate between magmatic- and magmatic-hydrothermal ore deposits using Fe isotopes

Although discriminating high temperature mineral systems, for example, magmatic- vs magmatic-hydrothermal origin Fe deposits, is challenging, the emerging Fe isotope systematics have shown good potentials to provide crucial information on resolving the problem. Here, Fe isotopes of multiple types of samples from one iron oxide-apatite (IOA) deposit and two skarn Fe deposits are measured, aiming to study their behaviors in high temperature magmatic and magmatic-hydrothermal environments. The primary observation of this study is that magnetite samples from high grade ores of magmatic origin IOA deposits has a heavier Fe isotopic signature relative to the associated igneous rocks, whereas a lighter Fe isotopic composition in magnetite samples from magmatic-hydrothermal origin skarn deposits relative to the causative intrusions. Another distinctive feature is that δ56Fe values of the causative intrusions in the magmatic origin IOA deposits are lighter than that of non-fertile intrusions, whereas the ore-associated intrusions of the magmatic-hydrothermal deposit are heavier in δ56Fe than that of non-fertile igneous rocks. The above two observed scenarios suggest that Fe isotope fractionation exists in both magmatic immiscibility and hydrothermal fluid exsolution processes. Magma immiscibility leads to heavy Fe isotope enrichment in immiscible Fe-rich melt phase, and resulting light Fe enrichment in Si-rich melt phase. Hydrothermal fluid exsolution results in lighter Fe isotope enrichment in the exsolved liquid phase, with a heavy Fe isotope enrichment in the residual magma. Fe isotopes behave in different ways in magmatic and magmatic-hydrothermal mineralization processes, which makes Fe isotopes an effective tool to discriminate mineral deposits of magmatic origin from those formed by magmatic-hydrothermal processes.

Dating the Xiaobaishitou skarn W–(Mo) deposit, Eastern Tianshan, NW China: Constraints from zircon U–Pb, muscovite 40Ar–39Ar, and molybdenite Re–Os system

The Xiaobaishitou deposit (36,264 tonnes @ 0.78 wt% WO3) in the Eastern Tianshan orogenic belt is a medium-sized skarn deposit characterized by W–(Mo) ore bodies that developed along contacts between Triassic biotite granite and Mesoproterozoic carbonaceous rocks. Scheelite and molybdenite are the dominant metallic minerals in this deposit and mostly precipitated during the retrograde stage and/or quartz–sulfide stage, respectively. Laser ablation multi-collector inductively coupled plasma mass spectrometry (LA–MC–ICP–MS) zircon U–Pb dating of the mineralization-related biotite granites from underground openings and outcrops yields ages of 247.9 ± 1.7 Ma (1σ; N = 22; MSWD = 0.69) and 252.2 ± 3.0 Ma (1σ; N = 12; MSWD = 1.60), implying they were emplaced in the Early Triassic. A muscovite 40Ar/39Ar weighted plateau age of 247.6 ± 2.3 Ma (2σ; MSWD = 2.03) and molybdenite Re–Os model ages ranging from 235.8 ± 5.7 Ma to 249.6 ± 3.6 Ma (weighted mean age = 251.1 ± 1.6 Ma; 2σ; MSWD = 0.70) are interpreted as the time of the hydrothermal activity mineralization. The excellent agreement among the U–Pb, 40Ar–39Ar, and Re–Os chronometers confirms that the Xiaobaishitou deposit formed in the Early Triassic. The Re contents of the molybdenites range from 18,477 to 130,447 ng/g, suggesting that the ore-forming materials were derived from continental crust together with the involvement of abundant mantle components. As one of the representative Triassic deposit in Eastern Tianshan, the Xiaobaishitou provides important chronological evidence for metallogenic regularity in the Eastern Tianshan and the Central Asian Orogenic Belt. The new ages reported here confirm that the Xiaobaishitou deposit represents one of the magmatic–hydrothermal mineralization events that occurred in the Eastern Tianshan orogenic belt in lithospheric extension during the Triassic. It is suggested that mantle material played a role in producing the Triassic mineralization and associated magmatism.

Fluid Inclusion Characteristics of Tungsten Mineralization in the Agargaon Area of Sakoli Fold Belt, Central India

The Lower to Middle Proterozoic Sakoli fold belt in Central India forms a triangular belt with significant mineralization of strategic minerals. The Sakoli fold belt comprises metasediments, felsic and mafic volcanics with metabasalts bounded by the gneissic-migmatitic terrain. The last pulses of granitic activity in the form of quartz lenses intrude the metasediments and are associated with tungsten mineralization. The metasediments are intruded by the quartz veins and tourmaline breccias trending 60°N to 65°E and 60°S to 65°W and are parallel to the regional structural foliations. The tungsten mineralization in this area is restricted to tourmaline-quartz mica greisens and quartz veins. The NE-SW trending foliated contact zones of chlorite mica schist and porphyritic granite/gneisses have served as easy channels for the mineralizing vapours and solutions to percolate, which formed ore bearing greisens and quartz veins. This mineralization is erratic and manifested by sparse and sporadic disseminations of wolframite and scheelite associated with minor amount of molybdenite and chalcopyrite. The fluid inclusion microthermometry on mineralized quartz veins and quartz-tourmaline veins reveals the existence of a metamorphogenic aqueous- gaseous (H2O-CO2+NaCl) fluid that underwent phase separation and gave rise to gaseous (CO2) inclusion. The salinity of tungsten mineralizations varies from low to high (1.32 wt.% to 40.44 wt.% NaCl eq.). The estimated P-T range of tungsten mineralization varies from 1.2 to 2.2 kbar at 280 to 390 °C. Raman spectroscopy reveals that the fluid inclusions mainly contain H2O and CO2 with rarely H2S and CH4. Stable isotopic data reveal that the sulfur isotope fractions from the deposits δ34S ranging from +3.1‰ to +3.35‰, suggesting the deep crustal source for the sulfur, which can be further interpreted as a single (magmatic) supply of sulfur during magmatic-hydrothermal mineralization. The studies reveal the presence of chlorides such as FeCl2/MgCl2 and CaCl2, indicating the involvement of chloride complexes in transportation of tungsten to the fluid system and the evolution of the ore-forming fluids by mixing or immiscibility of high-temperature, high-salinity magmatic fluids and low-temperature, low-salinity fluids in hydrothermal system, and also representing magmatic-hydrothermal interactions contributed wolframite and scheelite with minor amount of molybdenite and chalcopyrite.

Evaluating the Changes from Endogranitic Magmatic to Magmatic-Hydrothermal Mineralization: The Zaaiplaats Tin Granites, Bushveld Igneous Complex, South Africa

The stanniferous granites of the Zaaiplaats Tin Field are part of the A-Type Lebowa Granite Suite, within the greater Bushveld Igneous Complex of northeast South Africa. The tin field comprises three granites: (1) the Nebo, a leucocratic, equigranular biotite granite; (2) The brick-red hypidiomorphic Bobbejaankop granite, which is extensively microclinized with chloritized biotite and characteristic synneusis-textured quartz; and (3) The variably altered roof facies of the Bobbejaankop granite known as the Lease microgranite. The Bobbejaankop and Lease granites were both extensively mined for cassiterite until 1989. The cassiterite is hosted in disseminations, miarolitic cavities, and within large hydrothermal, tourmalinized, and greisenized pipes and lenticular ore-bodies. An extensive petrological and whole-rock XRF and ICP-MS geochemical study, has provided new insight into the magmatic and magmatic-hydrothermal mineralization processes in these granites. Trace elements and Rayleigh Fractionation modelling suggest the sequential fractionation of the Nebo granite magma to be the origin of the Bobbejaankop granite. Incompatible elemental ratios, such as Zr/Hf and Nb/Ta, record the influence of internally derived, F-rich, hydrothermal fluid accumulation within the roof of the Bobbejaankop granite. Thus, the Lease granite resulted from alteration of the partially crystallized Bobbejaankop granite, subsequent to fluid saturation, and the accumulation of a magmatic-hydrothermal, volatile-rich fluid in the granite cupola. The ratio of Nb/Ta, proved effective in distinguishing the magmatic and magmatic-hydrothermal transition within the Bobbejaankop granite. Elemental ratios reveal the differences between pre- and post-fluid saturation in the mineralizing regimes within the same pluton. Thus highlighting the effect that the location and degree of hydrothermal alteration have had on the distribution of endogranitic tin mineralization.

Rb–Sr geochronology and geochemistry of the Xiaotongchang basalt-hosted copper deposit in the Jinping area, SW China

The Xiaotongchang basalt-hosted copper deposit in Jinping, southern Yunnan Province, SW China, is located in the southern part of the Emeishan large igneous province. Here, we use Rb–Sr, Re–Os and S–Pb–C–O isotope data to constrain the age and genesis of the deposit. Petrological investigations reveal two main stages of mineralization. The early-stage is characterized by disseminated or massive sulfides in an assemblage of pyrite + chalcopyrite + quartz + albite + calcite. Rb-Sr isotopic dating of early-stage chalcopyrite yields an age of 256 ± 9.4 Ma (MSWD = 5.4), which is slightly younger than the eruption age of the Jinping basalts. The δ34SCDT values of the sulfides range from +5.8‰ to +7.7‰, suggesting that the metals of the early-stage copper mineralization originated from the Emeishan basalts and that the ore-forming fluids were contaminated by crustal rocks. These units may indicate that the early-stage orebodies represents syngenetic hydrothermal mineralization related to the eruption of Emeishan flood basalts. The late-stage mineralization is characterized by a pyrite + chalcopyrite + bornite + chalcocite + quartz + calcite assemblage that is developed in veins or breccia. The Re-Os isotopic dating of late-stage chalcopyrite samples reveals that they formed at 240–231 Ma. The Pb isotopic compositions ((206Pb/204Pb)t = 17.521–19.227, (207Pb/204Pb)t = 15.480–15.760, and (208Pb/204Pb)t = 37.778–38.731; t = 235 Ma) show that the late-stage copper orebodies have a heterogeneous source and originated mainly from the crust. The late-stage sulfides have higher δ34SCDT values (+7.9‰ to +10.7‰) than the early-stage sulfides. The narrow range of sulfur isotopic compositions of the sulfides associated with both stages and the Pb isotopic compositions of late-stage chalcopyrite indicate that some of the metals associated with late-stage mineralization originated from the Jinping basalts. The C–O isotopic compositions of calcite samples show that the magmatic hydrothermal fluids in the late stage flowed through and were contaminated by the Maokou limestone. Therefore, we suggest that the late-stage orebodies represent magmatic hydrothermal mineralization associated with the Late Triassic rhyolite porphyry and that the tectono-magmatic hydrothermal fluid remobilized copper from the basalts. The copper deposits formed at favourable interfaces within the basalt stratigraphy or in favorable structural locations.

Geochemical Characteristics of A-Type Granite near the Hongyan Cu-Polymetallic Deposit in the Eastern Hegenshan-Heihe Suture Zone, NE China: Implications for Petrogenesis, Mineralization and Tectonic Setting

In the eastern Hegenshan-Heihe suture zone (HHSZ) of NE China, Cu-Au hydrothermal mineralization at the newly discovered Hongyan deposit is associated with the Shanshenfu alkali-feldspar granite (SAFG). Zircon U-Pb dating showed that the inner phase and outer phase of the SAFG were formed at 298.8 ± 1.0 Ma and 298.5 ± 1.0 Ma, respectively. Whole rock geochemistry suggests that the SAFG can be classified as an A-type granite. Halfnium isotopes and trace elements in zircon suggest that the SAFG has high Ti-in-zircon crystallization temperature (721–990 °C), high magmatic oxygen fugacity and largely positive εHf(t) (from +6.0 to +9.9). We proposed that the SAFG was derived from crustal assimilation and fractional crystallization of juvenile crust metasomatized by subducting oceanic crust. The high oxygen fugacity of the SAFG suggests the chalcophile elements (e.g., Cu, Au) remained in the magma as opposed to the magma source. An arc-related juvenile source favors enrichment of Cu and Au in the resulting magma. Combined, these magmatic characteristics suggest Cu ± Au exploration potential for magmatic-hydrothermal mineralization related to the SAFG, and similar bodies along the HHSZ. The results obtained combined with regional geological background suggest that the Permian A-type granites and related mineralization along the HHSZ were formed in a post-collisional slab break-off process.

Characteristics of REEs and trace elements in scheelite from the Zhuxi W deposit, South China: Implications for the ore-forming conditions and processes

The Zhuxi W deposit in Jiangxi, South China, with a resource of 2.86 Mt W and an average grade of 0.54% WO3, is the largest W deposit in the world. The deposit occurs at the contact between a late Mesozoic granitic intrusion and Carboniferous – Permian carbonate rocks and Neoproterozoic metamorphic rocks. The ores are divided into three types: skarn ore (dominant), sulfide ore and greisen ore. Based on occurrences and petrographic relationships, scheelite (the dominant ore mineral) is classified into three types, i.e. type I (greisen), type II (skarn, specifically in the retrograde stage), and type III (hydrothermal sulfides). Type I and type II are time equivalent but spatially separated, whereas type III is later. The different types of scheelite have distinctly different REE and trace element compositions. Type I scheelite is characterized by an average ΣREE of 67.9 ppm, LREE/HREE ratio of 24.4, δEu of 8.5, Mo of 0.1 ppm and Sr of 1058 ppm, whereas type II scheelite features an average ΣREE of 48.1 ppm, LREE/HREE ratio of 10.6, δEu of 0.67, Mo of 1892 ppm and Sr of 90.1 ppm. Type III scheelite has an average ΣREE of 53.9 ppm, LREE/HREE ratio of 4.8, δEu of 17.5, Mo of 92.9 ppm and Sr of 37.1 ppm. The extremely high concentrations of Sr and highly positive Eu anomalies in type I scheelite are likely related to release of these elements from plagioclase in the granite during greisenization, whereas the extremely low concentrations of Mo may be related to the reducing and high-temperature nature of the magmatic fluid – Mo probably was mainly in the Mo4+ state and could not replace W6+ in the scheelite lattice. In contrast, the negative Eu anomalies and high Mo concentrations in type II scheelite suggest that the mineralizing environment in the retrograde alteration stage was relatively oxidizing, causing Eu to exist mainly as Eu3+, which is difficult to replace Ca2+ in scheelite, and Mo mainly as Mo6+, which is easy to replace W6+ in scheelite. In the sulfide mineralization stage, the fluid became relatively reducing again, and Eu2+ could easily replace Ca2+ in scheelite causing positive Eu anomalies, whereas Mo mainly exists as Mo4+ and precipitated as molybdenite, and so has limited substitution for W6+ in scheelite. The REE and trace element compositions of the dominant W mineral (type II scheelite), characterized by high concentrations of Mo, high LREE/HREE ratios and negative Eu anomalies, indicate that the ore-forming materials were mainly derived from the granitic intrusions. The variation of REE and trace elements in scheelite in time and space reflects a complex magmatic-hydrothermal mineralization process involving various fluid-rock reactions within the intrusion and in the country rocks. The formation of the Zhuxi W deposit is linked with a large fertile granitic intrusion, which delivered a large amount of W to the site of mineralization through convection within the magma chamber, and W precipitation in the skarn was largely caused by an abrupt drop in temperature and increase in pH of the ore-forming fluid.

Ore-Forming Fluids Characteristics and Metallogenesis of the Anjing Hitam Pb-Zn Deposit in Northern Sumatra, Indonesia

The Anjing Hitam Pb-Zn deposit in northern Sumatra (Indonesia) is one of the largest Pb-Zn deposits in the region. The stratiform orebodies are mainly hosted in the middle member of the Carboniferous-Permian Kluet Formation of the Tapanuli Group. Mineral paragenesis and crosscutting relationships suggest a two-stage Pb-Zn mineralization: (I) sedimentary and (II) hydrothermal mineralization. Ore-related calcite from both stages I and II contains mainly liquid- and gas-liquid two-phase-type fluid inclusions (FI). For stage I ore-forming fluids, FI homogenization temperatures (Th) are 105 to 199 °C, and the salinities are 9.6 wt.% to 16.6 wt.% NaCleqiv, reflecting low temperature and medium-low salinity; whereas in stage II, the Th (206 to 267 °C) and salinity (19.0 wt.% to 22.5 wt.% NaCleqiv) are considerably higher. Fluid inclusion and C-O isotope characteristics suggest that the stage I ore-forming fluids were mainly derived from a mixture of seawater and magmatic fluids (probably from deep-lying plutons), whereas the stage II ore-forming fluids were likely magmatic-derived with wall rock input. We propose that the Anjing Hitam deposit was a Carboniferous exhalative sedimentary (SEDEX) deposit overprinted by the Pleistocene vein-style magmatic-hydrothermal mineralization.

Muscovite 40Ar/39Ar and in situ sulfur isotope analyses of the slate-hosted Gutaishan Au–Sb deposit, South China: Implications for possible Late Triassic magmatic-hydrothermal mineralization

The Gutaishan deposit is a slate-hosted Au–Sb deposit in the Xiangzhong metallogenic province, South China. The deposit has proven reserves of ca. 9 tonnes (t) of gold with an average grade of 13 g/t and 2,500 t of Sb with an average grade of 10%. In this study, muscovite 40Ar/39Ar and in situ sulfur isotope analyses of pyrite and arsenopyrite were performed to determine the mineralization age and the plausible source of S and Au. The 40Ar/39Ar dating result of muscovite limits the formation age of the Gutaishan deposit to ca. 223.6 ± 5.3 Ma, coeval with the adjacent Baimashan granite (223–204 Ma). The in situ34S values of pyrite and arsenopyrite coexisting with native gold lie in a range between −3.7 and +2.1‰ with a mean value of -0.8‰, and these values are markedly different from those of sedimentary pyrite (+7.0 to +23.3‰), indicating a contribution from magmatic sulfur. A magma-derived genetic model may therefore be suitable for the Gutaishan deposit. Integrating the available ages of the Au–Sb and Sb–Au deposits and granites in the Xiangzhong metallogenic province, we propose that a widespread Late Triassic magmatic-hydrothermal Au–Sb mineralization event occurred.