Post-orogenic,Carboniferous granite-hosted Sn–W mineralization in the Sierras Pampeanas Orogen,Northwestern Argentina

The Sierras Pampeanas orogen, in northwestern Argentina, hosts significant Sn–W mineralization in a variety of mostly epizonal granite stocks emplaced in variably metamorphosed country rocks. The San Blas, Huaco and El Durazno granite stocks in the Sierra de Velasco, the La Quebrada granite in the Sierra de Mazán, the Cerro Colorado granite in the Cerro Negro, and the Los Mudaderos and Sauce Guacho granite stocks in the Sierra de Ancasti, are largely peraluminous (ASI between 1.05 and 1.38) and represent S-type granites, are strongly fractionated (i.e., high Rb–Sr ratio), have a low oxidation state (low Fe₂O₃/Fe₂O₃ ratio) and are geotectonically linked to syncollisional magmatism. The U–Pb SHRIMP analyses on zircons from the Cerro Colorado and La Quebrada granites, located in the Cerro Negro and Sierra de Mazán, respectively, revealed ages from Lower Ordovician (Tremadocian) to Carboniferous. All granites display elevated LREE values, low HREE values and negative Eu anomalies. With regards to total REE values, two groups of granite stocks can be recognized. The granites with lower REE contents are highly evolved granites and are related to Sn–W mineralization. The mineralized granites display higher values of Sn, W and Rb, and lower values of Sr and Ba compared to barren granites. These trace element characteristics appear to be diagnostic for Sn–W mineralized granite stocks in the western Sierras Pampeanas. The western Sierras Pampeanas contains locally geochemically evolved Carboniferous granites, which are interpreted to be the main control of significant Sn–W mineralization. The Carboniferous age of western Sierras Pampeanas Sn–W mineralization sets it apart from the Triassic age of the Sn–W mineralization in the Eastern Tin belt of Bolivia.     

Geological,geochemical, and geochronological characteristics of Caledonian W–Sn mineralization in the Baiganhu orefield,southeastern Xinjiang,China

The newly discovered large-scale Baiganhu W–Sn orefield, consisting of the Kekekaerde, Baiganhu, Bashierxi, and Awaer deposits, is located in Ruoqiang County, southeastern Xinjiang, China. These deposits comprise mainly three types of W–Sn mineralization: early-stage skarn-type, middle-stage greisen-type, and late-stage quartz-vein-type. In this study, we classified seven major vertical zones on the basis of petrographic characteristics, roughly from the bottom of the parental granitic intrusions upward, as (A) fresh syenogranite, (B) argillic alteration, (C) muscovite-dominated greisenization, (D) tourmaline-dominated greisenization, (E) marginal facies (including K-feldspar pegmatite and fine-grained granite), (F) aplitic apophysis, and (G1) skarn or (G2) infilled silification zones. According to the alteration–mineralization assemblages and cross-cutting relationships, five stages of mineralization are recognized in the orefield (I, skarn stage; II, greisen stage; III, quartz vein stage; IV, argillic alteration stage; and V, supergene stage), and reverse alteration zonation in the altered intrusion is also observed.The W–Sn deposits are spatially associated with syenogranite, which is part of the Caledonian Bashierxi magmatic series. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon U–Pb dating of the syenogranite yields a weighted mean ²⁰⁶Pb/²³⁸U age of 413.6 ± 2.4 Ma (MSWD = 0.36, n = 30). Hydrothermal muscovite from three samples associated with W–Sn mineralization yields plateau ⁴⁰Ar/³⁹Ar ages of 411.7 ± 2.6 Ma (MSWD = 0.21), 412.8 ± 2.4 Ma (MSWD = 0.22), and 413.8 ± 2.6 Ma (MSWD = 0.22), which is consistent with the zircon U–Pb age, thus indicating a temporal link between the emplacement of the syenogranite and the W–Sn mineralization. Our age data and previously published ages, along with geochemical data, for the granitoids in the Bashierxi magmatic series show a nearly contemporaneous evolution of A- and S-type granites, which were emplaced in a post-orogenic setting at ca. 432–413 Ma. As compared with the A-type granites, the syenogranites with S-type affinities probably resulted from a lower degree of partial melting of metagreywackes, which was more likely to be enriched in the ore-forming elements W and Sn, as well as volatiles such as B and H₂O. In addition, the syenogranites exhibit low oxidation states and underwent high degrees of factional crystallization, both of which favor post-magmatic W–Sn mineralization. We suggest that more attention should be given to buried syenogranites of S-type affinities during mineral exploration in this area, and that the proposed model of a vertical alteration zoning can act as a guide to the targeting of similar ore systems.     

K–Ar ages of plutonism and mineralization at the Shizhuyuan W–Sn–Bi–Mo deposit,Hunan Province,China

The Qianlishan granite complex, situated 16 km southeast of Chenzhou City, Hunan Province, China, hosts the Shizhuyuan W–Sn–Bi–Mo deposit. This complex, which intruded the Protozoic metasedimentary rocks and the Devonian clastic sedimentary and carbonate rocks, consists of mainly medium- to coarse-grained biotite granites and minor amounts of fine-grained biotite granite in addition to granite and quartz porphyry. K–Ar ages suggest three episodes of plutonism: the medium- to coarse-grained biotite granite (before 152 Ma), the fine-grained biotite granite (137 Ma), and the granite porphyry (129–131 Ma). Muscovite ages of the greisen are 145–148 Ma, suggesting that the W–Sn–Bi–Mo mineralization was related to the main, medium- to coarse-grained biotite granites. The K–Ar age of the hydrothermal vein mineralization is 92 Ma and is probably related to the porphyries.     

Formation and geodynamic implication of the Early Yanshanian granites associated with W–Sn mineralization in the Nanling range,South China: an overview

ABSTRACT

The Nanling range (Nanling) is characterized by intense and widespread Mesozoic magmatism related large-scale W–Sn mineralization. A summary of geochemistry, geochronology, and petrogenesis for the W–Sn-bearing granites has been carried out in this study. A series of rock- and ore-forming ages in Nanling indicate that the W–Sn mineralization is closely related to the Early Yanshanian granitic magmatism both in temporal and spatial dimensions (165–150 Ma). Geochemical features show that both of the W- and Sn-bearing granites, which mainly belong to highly fractionated I-type granites with a few A-type granites, are characterized by high contents of SiO₂, Al₂O₃, Na₂O, and K₂O; enrichment in Rb, Th, U, Zr, Hf, and REE; depletion in Sr, Ba, P, and Ti; and high ratios of A/CNK. Furthermore, the different Sr–Nd–Hf isotopic compositions indicate that they are mainly originated from the partial melting of the Precambrian basement rocks of the Cathaysia Block at low oxygen fugacity, and the estimated temperatures for the tungsten-bearing and tin-bearing granites are ca. 700°C and ca. 800°C, respectively. The model of the mantle–crust interaction exhibits that different percentages of mantle-derived magma were likely involved in the generation of the tin-bearing granites and tungsten-bearing granites. In combination with previous studies, we propose that these granites in Nanling were emplaced in an extensional setting, as a response to the break-off and roll-back of the subducted Palaeo-Pacific Plate during 175–150 Ma.     

Metallogenic controls on the granite-related W–Sn deposits in the Hunan–Jiangxi region,China: evidence from zircon trace element geochemistry

The Nanling Range in South China is well known for its rich granite-related W–Sn deposits. To elucidate the controls of different granite-related W–Sn metallogenesis in the region, we chose five representative ore-related granites (Yanbei, Mikengshan, Tieshanlong, Qianlishan, and Yaogangxian intrusions) in the Hunan–Jiangxi region, and studied their magmatic zircon ages and trace element geochemistry. Our new zircon data showed the differences in ages, temperatures and oxygen fugacity of the ore-forming magmas. Zircon U–Pb ages of the Yanbei and Mikengshan intrusions are characterized by 142.4 ± 2.4 and 143.0 ± 2.3 Ma, respectively, whereas the Tieshanlong and Qianlishan intrusions are 159.5 ± 2.3 and 153.2 ± 3.3 Ma, respectively. The Sn-related intrusions were younger than the W-related intrusions. The Ti-in-zircon thermometry showed that there was no systematic difference between the Sn-related Yanbei (680–744 °C) and Mikengshan (697–763 °C) intrusions and the W-related Tieshanlong (730–800 °C), Qianlishan (690–755 °C) and Yaogangxian (686–751 °C) intrusions. However, the zircon Ce⁴⁺/Ce³⁺ ratios of the Yanbei (averaged at 18.3) and Mikengshan (averaged at 18.8) intrusions are lower than those of the Tieshanlong (averaged at 36.9), Qianlishan (averaged at 38.4) and Yaogangxian (averaged at 37) intrusions, indicating that the Sn-related granitic magmas might have lower oxygen fugacities than those of the W-related. This can be explained by that, in more reduced magmas, Sn is more soluble than W and thus is more enriched in the residual melt to form Sn mineralization. The difference in source materials between the Sn-related and the W-related granites seems to have contributed to the different redox conditions of the melts.

     

LA-ICPMS Zircon U–Pb and Molybdenite Re–Os Isotopic Dating of the Tungsten Deposits in the Dengfuxian W–Sn Orefield, Eastern Hunan Province, South China, and Their Geological Implications

Please refer to the attachment(s) for more details.     

Metallogeny of the northeastern Gangdese Pb–Zn–Ag–Fe–Mo–W polymetallic belt in the Lhasa terrane,southern Tibet

The northeastern Gangdese Pb–Zn–Ag–Fe–Mo–W polymetallic belt (NGPB), characterized by skarn and porphyry deposits, is one of the most important metallogenic belts in the Himalaya–Tibetan continental orogenic system. This belt extends for nearly four hundred kilometers along the Luobadui–Milashan Fault in the central Lhasa subterrane, and contains more than 10 large ore deposits with high potential for development. Three major types of mineralization system have been identified: skarn Fe systems, skarn/breccia Pb–Zn–Ag systems, and porphyry/skarn Mo–Cu–W systems. In this study, we conducted a whole-rock geochemical, U–Pb zircon geochronological, and in situ zircon Hf isotopic study of ore-forming rocks in the NGPB, specifically the Jiangga, Jiaduopule, and Rema skarn Fe deposits, and the Yaguila Pb–Zn–Ag deposit. Although some of these deposits (porphyry Mo systems) formed during the post-collisional stage (21–14 Ma), the majority (these three systems) developed during the main (‘soft collision’) stage of the India–Asia continental collision (65–50 Ma). The skarn Fe deposits are commonly associated with granodiorites, monzogranites, and granites, and formed between 65 and 50 Ma. The ore-forming intrusions of the Pb–Zn–Ag deposits are characterized by granite, quartz porphyry, and granite porphyry, which developed in the interval of 65–55 Ma. The ore-forming porphyries in the Sharang Mo deposit, formed at 53 Ma. The rocks from Fe deposits are metaluminous, and have relatively lower SiO₂, and higher CaO, MgO, FeO contents than the intrusions associated with Mo and Pb–Zn–Ag mineralization, while the Pb–Zn–Ag deposits are peraluminous, and have high SiO₂ and high total alkali concentrations. They all exhibit moderately fractionated REE patterns characterized by lower contents of heavy REE relative to light REE, and they are enriched in large-ion lithophile elements and relatively depleted in high-field-strength elements. Ore-forming granites from Fe deposits display ⁸⁷Sr/⁸⁶Sr_(i) = 0.7054–0.7074 and ε_Nd(t) = − 4.7 to + 1.3, whereas rocks from the Yaguila Pb–Zn–Ag deposit have ⁸⁷Sr/⁸⁶Sr_(i) = 0.7266–0.7281 and ε_Nd(t) = − 13.5 to − 13.3. In situ Lu–Hf isotopic analyses of zircons from Fe deposits show that ε_Hf(t) values range from − 7.3 to + 6.6, with T_DM(Hf)^C model ages of 712 to 1589 Ma, and Yaguila Pb–Zn–Ag deposit has ε_Hf(t) values from − 13.9 to − 1.3 with T_DM(Hf)^C model ages of 1216 to 2016 Ma. Combined with existing data from the Sharang Mo deposit, we conclude that the ore-forming intrusions associated with the skarn Fe and porphyry Mo deposits were derived from partial melting of metasomatized lithospheric mantle and rejuvenated lower crust beneath the central Lhasa subterrane, respectively. Melting of the ancient continental material was critical for the development of the Pb–Zn–Ag system. Therefore, it is likely that the source rocks play an important role in determining the metal endowment of intrusions formed during the initial stage of the India–Asia continental collision.     

Fluid evolution of the Hub Stock, Horní Slavkov–Krásno Sn–W ore district, Bohemian Massif, Czech Republic

The Horní Slavkov–Krásno Sn–W ore district is hosted by strongly altered Variscan topaz–albite granite (Krudum granite body) on the northwestern margin of the Bohemian Massif. We studied the fluid inclusions on greisens, ore pockets, and ore veins from the Hub Stock, an apical expression of the Krudum granite. Fluid inclusions record almost continuously the post-magmatic cooling history of the granite body from ～500 to <50°C. Rarely observed highest-temperature (～500°C) highest-salinity (～30?wt.% NaCl eq.) fluid inclusions are probably the result of secondary boiling of fluids exsolved from the crystallizing magma during pressure release which followed hydraulic brecciation of the gneissic mantle above the granite cupola. The greisenization was related to near-critical low-salinity (0–7?wt.% NaCl eq.) aqueous fluids with low amount of CO₂, CH₄, and N₂ (≤10?mol% in total) at temperatures of ～350–400°C and pressures of 300–530 bar. Crush-leach data display highly variable and negatively correlated I/Cl and Br/Cl values which are incompatible with both orthomagmatic and/or metamorphic origin of the fluid phase, but can be explained by infiltration of surficial and/or sedimentary fluids. Low fluid salinity indicates a substantial portion of meteoric waters in the fluid mixture that is in accordance with previous stable isotope data. The post-greisenization fluid activity associated with vein formation and argillitization is characterized by decreasing temperature (<350 to <50°C), decreasing pressure (down to ～50–100 bar), and mostly also decreasing salinity.     

Geochemistry,Sr–Nd–Pb–Hf isotopes systematics and geochronological constrains on petrogenesis of the Xishan A-type granite and associated W–Sn mineralization in Guangdong Province,South China

The Xishan deposit, located in the western Guangdong Province in South China, is a quartz-vein type W-Sn deposit with an average Sn grade of 0.1–0.4 wt%. The deposit is temporally and spatially associated with Xishan alkali feldspar granite. The W–Sn mineralization is present mainly as veins that are hosted by the granite. In this paper we present new zircon U–Pb age, whole-rock geochemical data, Sr–Nd–Pb–Hf isotopic data and Re–Os age in order to constrain the nature and timing of magmatism and mineralization in the Xishan mining district with implications on geodynamic settings. LA–ICP–MS zircon U–Pb analyses yielded an age of 79.14 ± 0.31 Ma for the alkali feldspar granite, consistent with the molybdenite Re–Os age of 79.41 ± 1.11 Ma. The alkali feldspar granite shows high contents of SiO₂ (71.52–76.25 wt%), high total alkalis (Na₂O + K₂O = 9.35–13.51 wt%), high field strength elements (e.g. Zr = 95.4–116 ppm, Y = 97.1–138 ppm, Nb = 36.1–55.5 ppm, Ga = 97.1–138 ppm), and rare earth elements (total REE = 171.8–194.0 ppm) as well as high Ga/Al ratios (10,000 × Ga/Al = 3.23–3.82) suggesting that it has the geochemical characteristics of A-type granite and shows an A₂ subtype affinity. Sr–Nd isotopes of the alkali feldspar granite show that (⁸⁷Sr/⁸⁶Sr)_i values range from 0.7111 to 0.7183, and the ε_Nd(t) values and Nd model ages (T_2DM) vary from −6.8 to −6.5 and 1414 to 1433 Ma, respectively. The Pb isotopic compositions are variable, with ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb values ranging from 18.783 to 18.947, 15.709 to 15.722 and 38.969 to 39.244, respectively, indicating that the alkali feldspar granite was derived from a mantle-crust mixed source. In situ Hf isotopic analyses reveal that the alkali feldspar granite has ε_Hf(t) values ranging from −9.69 to −0.04 and two-stage Hf model ages from 1145 Ma to 1755 Ma, indicating that the alkali feldspar granite was formed by the partial melting of Mesoproterozoic crusts of the Cathaysia Block with additions of mantle-derived materials. These results, together with previously presented regional geological relationships, suggest that the formation of the Xishan granite and associated W–Sn mineralization is related to lithospheric extension and asthenospheric upwelling that are attributed to a directional change of Pacific plate motion.     

Variscan Sn–W–Mo metallogeny in the gravity picture of the Krušné hory/Erzgebirge granite batholith (Central Europe)

Late Variscan wolframite (± molybdenite) and cassiterite–wolframite greisen, skarn and vein deposits occur in a close spatial association with the granites of the Krušné hory/Erzgebirge batholith (KHEB) in Central Europe. We examined the distribution of the deposits in relation to the gravity field affected by Late Variscan granites using the data from previous gravity and metallogenic studies. Late Variscan granites are differentiated into earlier biotite monzogranites (low-F granites) and later biotite or lithium mica syenogranites (high-F granites) in accordance with the previous classifications. All the outcrops of granites in the KHEB region and their hidden continuation are confined to the Bouguer anomaly contour of − 20 mGal. The Sn–W–Mo (rare metal) deposits and occurrences are within the gravity contour of − 30 mGal with the exception of the Grossschirma stratiform tin deposit in the Freiberg polymetallic ore district. We constructed a geological model based on the gravity data along two profiles across the KHEB showing the position of some rare metal deposits and of outcropping and hidden granite bodies. The models show that the overlapping of earlier and later granites is in the areas of the most intense regional gravity minima. These coincide with the Eastern Volcano-Plutonic Complex (Altenberg minimum), which encloses large volumes of felsic extrusives, microgranite dikes and granites, and the Western Plutonic Complex (Eibenstock minimum), with small volumes of felsic dikes and predominance of earlier and later granites, with no extrusives preserved. There is no distinct relationship between the masses of Late Variscan granites and the distribution and the sizes of associated W ± Mo and Sn–W deposits. We prefer the idea that rare metal mineralization was formed by hydrothermal fluids derived from outside of presently outcropping granites. It originated in two cycles: one connected with the formation of earlier granites producing W ± Mo associations and the other one associated with later granites connected with Sn–W mineralization. Mineralizing fluids were probably generated by mantle–crustal interaction in the crust near the mantle–crust boundary as also indicated by lamprophyric intrusions coeval with the Late Variscan granitic magmatism.     

Evolution of the magmatic–hydrothermal system and formation of the giant Zhuxi W–Cu deposit in South China

The Zhuxi deposit is a recently discovered W–Cu deposit located in the Jiangnan porphyry–skarn W belt in South China. The deposit has a resource of 3.44 million tonnes of WO3, making it the largest on Earth,however its origin and the evolution of its magmatic–hydrothermal system remain unclear, largely because alteration–mineralization types in this giant deposit have been less well-studied, apart from a study of the calcic skarn orebodies. The different types of mineralization can be classified into magnesian skarn, calcic skarn, and scheelite–quartz–muscovite(SQM) vein types. Field investigations and mineralogical analyses show that the magnesian skarn hosted by dolomitic limestone is characterized by garnet of the grossular–pyralspite(pyrope, almandine, and spessartine) series, diopside, serpentine,and Mg-rich chlorite. The calcic skarn hosted by limestone is characterized by garnet of the grossular–andradite series, hedenbergite, wollastonite, epidote, and Fe-rich chlorite. The SQM veins host highgrade W–Cu mineralization and have overprinted the magnesian and calcic skarn orebodies. Scheelite is intergrown with hydrous silicates in the retrograde skarn, or occurs with quartz, chalcopyrite, sulfide minerals, fluorite, and muscovite in the SQM veins.Fluid inclusion investigations of the gangue and ore minerals revealed the evolution of the ore-forming fluids, which involved:(1) melt and coexisting high–moderate-salinity, high-temperature, high-pressure(>450 ℃and >1.68 kbar), methane-bearing aqueous fluids that were trapped in prograde skarn minerals;(2) moderate–low-salinity, moderate-temperature, moderate-pressure(~210–300 ℃and ~0.64 kbar),methane-rich aqueous fluids that formed the retrograde skarn-type W orebodies;(3) low-salinity,moderate–low-temperature, moderate-pressure(~150–240 ℃and ~0.56 kbar), methane-rich aqueous fluids that formed the quartz–sulfide Cu(–W) orebodies in skarn;(4) moderate–low-salinity,moderate-temperature, low-pressure(~150–250 ℃and ~0.34 kbar) alkanes-dominated aqueous fluids in the SQM vein stage, which led to the formation of high-grade W–Cu orebodies. The S–Pb isotopic compositions of the sulfides suggest that the ore-forming materials were mainly derived from magma generated by crustal anatexis, with minor addition of a mantle component. The H–O isotopic compositions of quartz and scheelite indicate that the ore-forming fluids originated mainly from magmatic water with later addition of meteoric water. The C–O isotopic compositions of calcite indicate that the ore-forming fluid was originally derived from granitic magma, and then mixed with reduced fluid exsolved from local carbonate strata. Depressurization and resultant fluid boiling were key to precipitation of W in the retrograde skarn stage. Mixing of residual fluid with meteoric water led to a decrease in fluid salinity and Cu(–W) mineralization in the quartz–sulfide stage in skarn. The high-grade W–Cu mineralization in the SQM veins formed by multiple mechanisms, including fracturing, and fluid immiscibility, boiling, and mixing.     

Late Jurassic Sn metallogeny in eastern Guangdong,SE China coast: Evidence from geochronology,geochemistry and Sr–Nd–Hf–S isotopes of the Dadaoshan Sn deposit

The newly discovered Dadaoshan Sn deposit is located in the eastern Guangdong Sn–W province, coastal SE China. The Sn mineralization, hosted in Jurassic porphyritic granite and the Lower Jurassic Jinji Formation sedimentary wall rocks, is considered to be granite-related. In this study, the porphyritic granite was LA–ICP–MS zircon U–Pb dated to be 153.2 ± 1.2 Ma, consistent with the syn-mineralization molybdenite Re–Os age of 152.6 ± 1.8 Ma. The porphyritic granite samples are weakly peraluminous (A/CNK = 1.0–1.1) and high-K calc-alkaline. The rocks contain high SiO₂ (72.9–75.6 wt%), moderate Rb/Sr (5–9) and low ΣREE (136–223 ppm). They are enriched in F, Li, Rb and Sn, depleted in Ba, Sr, P, Zr, Th, Nb and Y, and have distinct negative Eu anomalies (δEu = 0.09–0.18), suggesting that the porphyritic granite is highly fractionated I-type granite. The calculated initial ⁸⁷Sr/⁸⁶Sr (0.711582–0.715173), relatively low ɛ_Nd(t) (−9.48 to −8.54; T_DM2 = 1638–1814 Ma), and the zircon ε_Hf(t) (−14.2 to −5.1; two-stage model ages = 1528–2103 Ma) all suggest that the granite was mainly crustal-derived with little mantle input. Sulfur isotopic compositions for the sulfides (arsenopyrite and chalcopyrite: δ³⁴S = −1.1 to 1.4‰, average = −0.1) imply a dominantly magmatic sulfur source. The calculated zircon Ce⁴⁺/Ce³⁺ and Eu_N/Eu_N¹ ratios of the Dadaoshan granite range from 1.0 to 112 (mean = 31.7) and from 0.04 to 0.37 (mean = 0.14), respectively, indicating a low oxygen fugacity for the magma. The reducing and highly fractionated nature of the Dadaoshan granitic magma may have played a key role in the Sn mineralization.It was previously argued that the Jurassic Sn–W mineralization and its causative magmatism were largely confined in the South China interior, e.g., the Nanling Range. Our new data suggest that the Late Jurassic Sn–W mineralization and its causative magmatism actually extended to the SE China coastal area. The Dadaoshan granite may have been generated from partial crustal melting led by underplating of mantle-derived magmas in an extensional environment. Regional extension may have been related to the west-directed, flat-slab subduction and delamination of the Paleo-Pacific (Izanagi) plate beneath the South China block. Another suite of Early Cretaceous Sn–W-bearing granitic rocks in eastern Guangdong may have mainly been crustal-derived with minor mantle input, and likely occurred under back-arc extensional setting led by the Paleo-Pacific subduction rollback.     

Geology,mineralization, and fluid inclusion characteristics of the Chorukh-Dairon W–Mo–Cu skarn deposit in the Middle Tien Shan,Northern Tajikistan

The Chorukh-Dairon deposit is part of the metallogenic belt of WMo, CuMo, AuW, and Au deposits along the Late Paleozoic active continental margin of the Tien Shan. It is related to the Late Carboniferous multiphase pluton, with successive intrusive phases of early monzogabbro through monzonite-quartz monzonite to monzogranite and leucogranite, and the latest lamprophyre dikes. The deposit is an example of complex W–Mo–Cu magmatic-hydrothermal system related to magnetite-series shoshonitic igneous suite. It contains zones of W–Cu–Mo oxidized prograde and retrograde skarns, with abundant scapolite, plagioclase, K-feldspar, andradite garnet, magnetite, as well as molybdoscheelite and minor chalcopyrite, and molybdenite. Skarns are overprinted by hydrosilicate alteration assemblages, with amphibole, chlorite, epidote, quartz, calcite, scapolite, albite, scheelite, and chalcopyrite, and are cut by quartz-carbonate-barite-fluorite-sulfide veins.The fluid evolution included a release of high temperature (~ 400–500 °C), high pressure (900–1100 to 700–800 bars), high salinity magmatic-hydrothermal aqueous chloride fluid, with its direct separation from crystallizing magma and formation of prograde and retrograde skarns. Fluid enrichment in Ca (up to 15–22 wt.% CaCl₂) at the retrograde skarn stage was possibly related to magmatic differentiation and provided intense molybdoscheelite deposition from a homogenous fluid. In contrast, hydrosilicate alteration assemblages were formed at lower temperatures (~ 350–400 °C) initially from a homogenous and then from a boiling Ca-rich (20–22 wt.% CaCl₂) magmatic-hydrothermal fluid, with the latter contributing to the most intense scheelite deposition. The stable isotope data (δ¹³C_CO2 = − 3.0 ± 0.5‰ and δ¹⁸О_H2O = + 6.5 ± 0.5‰, δ³⁴S = + 7.5 to + 7.7‰) obtained for the hydrosilicate stage minerals suggest significant fluid sourcing from magmatic and meteoric waters as well as from sedimentary rocks enriched in seawater sulfate, possibly evaporites, although a strongly homogenous character of the isotopic composition reveals intense isotope homogenization in a magmatic chamber. Some light sulfur isotope enrichment of sulfides from the quartz-carbonate-barite-fluorite-sulfide veins (δ³⁴S = + 6.0 to + 6.1‰) may be linked to the evolution of the magmatic source toward more mantle-related sulfur species, as these veins were formed after emplacement of the late mafic (lamprophyre) dikes.     

The role of E–W basement faults in the Mesozoic geodynamic evolution of the Gafsa and Chotts basins,south-central Tunisia

The Gafsa and Chotts intracratonic basins in south-central Tunisia are transitional zones between the Atlasic domain to the north and the Saharan platform to the south. The principal aim of this paper is to unravel the geodynamic evolution of these basins following an integrated approach including seismic, well log and gravity data. These data are used to highlight the tectonic control on the deposition of Jurassic and Lower Cretaceous series and to discuss the role of the main faults that controlled the basin architecture and Cretaceous–Tertiary inversion. The horizontal gravity gradient map of the study area highlights the pattern of discontinuities within the two basins and reveals the presence of deep E–W basement faults. Primary attention is given to the role played by the E–W faults system and that of the NW–SE Gafsa fault which was previously considered active since the Jurassic. Facies and thickness analyses based on new seismic interpretation and well data suggest that the E–W-oriented faults controlled the subsidence distribution especially during the Jurassic. The NW–SE faults seem to be key structures that controlled the basins paleogeography during Late Cretaceous–Cenozoic time. The upper Triassic evaporite bodies, which locally outline the main NW–SE Gafsa fault, are regarded as intrusive salt bodies rather than early diapiric extrusions as previously interpreted since they are rare and occurred only along main strike-slip faults. In addition, seismic lines show that Triassic rocks are deep and do not exhibit true diapiric features.     

The Ni–Antimonide Mineral Assemblage: A Product of Recrystallization of Sn–Pb–Zn Ores of the Yuzhnoe Deposit,Sikhote-Alin,Russia

Doklady Earth Sciences - A mineral assemblage with nisbite NiSb2 and breithauptite NiSb unique for a Mesozoic (Sn)–Pb–Zn vein deposit is found during mineralogical–geochemical...     

Zircon U–Pb,molybdenite Re–Os and muscovite Ar–Ar isotopic dating of the Xitian W–Sn polymetallic deposit,eastern Hunan Province,South China and its geological significance

The Xitian tungsten–tin (W–Sn) polymetallic deposit, located in eastern Hunan Province, South China, is a recently explored region containing one of the largest W–Sn deposits in the Nanling W–Sn metallogenic province. The mineral zones in this deposit comprise skarn, greisen, structurally altered rock and quartz-vein types. The deposit is mainly hosted by Devonian dolomitic limestone at the contact with the Xitian granite complex. The Xitian granite complex consists of Indosinian (Late Triassic, 230–215 Ma) and Yanshanian (Late Jurassic–Early Cretaceous, 165–141 Ma) granites. Zircons from two samples of the Xitian granite dated using laser ablation-inductively coupled mass spectrometer (LA-ICPMS) U–Pb analysis yielded two ages of 225.6 ± 1.3 Ma and 151.8 ± 1.4 Ma, representing the emplacement ages of two episodic intrusions of the Xitian granite complex. Molybdenites separated from ore-bearing quartz-veins yielded a Re–Os isochron age of 149.7 ± 0.9 Ma, in excellent agreement with a weighted mean age of 150.3 ± 0.5 Ma. Two samples of muscovites from ore-bearing greisens yielded ⁴⁰Ar/³⁹Ar plateau ages of 149.5 ± 1.5 Ma and 149.4 ± 1.5 Ma, respectively. These isotopic ages obtained from hydrothermal minerals are slightly younger than the zircon U–Pb age of 151.8 ± 1.4 Ma of the Yanshanian granite in the Xitian area, indicating that the W–Sn mineralization is genetically related to the Late Jurassic magmatism. The Xitian deposit is a good example of the Early Yanshanian regional W–Sn ore-forming event (160–150 Ma) in the Nanling region. The relatively high Re contents (8.7 to 44.0 ppm, average of 30.5 ppm) in molybdenites suggest a mixture of mantle and crustal sources in the genesis of the ore-forming fluids and melts. Based upon previous geochemical studies of Early Yanshanian granite and regional geology, we argue that the Xitian W–Sn polymetallic deposit can be attributed to back-arc lithosphere extension in the region, which was probably triggered by the break-off of the flat-slab of the Palae-Pacific plate beneath the lithosphere.     

Combined garnet,scheelite and apatite U–Pb dating of mineralizing events in the Qiaomaishan Cu–W skarn deposit,eastern China

Determining the precise timing of mineralization and mineralizing events is crucial to understanding regional mineralizing and other geological events and processes. However, there are a number of mineralogical and analytical limitations to the approaches developed for the absolute dating of mineralizing systems, such as molybdenite Re–Os and zircon and garnet U–Pb, among others. This means that the precise and accurate dating of mineralizing systems that may not contain minerals suitable for dating using existing approaches requires the development of new (and ideally in situ) approaches to absolute dating. This study outlines a new in situ analytical approach that has the potential to rapidly and accurately evaluate the timing of ore formation. Our study employs a novel application of in situ scheelite U–Pb dating analysis using laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) and samples from the Qiaomaishan deposit, a representative example of skarn mineralization within the Xuancheng ore district of eastern China. Our approach to scheelite dating of the deposit is verified by cross-comparison to dating of cogenetic garnet and apatite, proving the effectiveness of this approach. Our new approach to dating of scheelite-bearing geological systems is rapid, cheap, requires little sample preparation, and is undertaken in situ, allowing crucial geological and mineralogical context to be retained during analysis. The approaches outlined here not only allow the determination of the absolute timing of formation of the Qiaomaishan deposit through the U–Pb dating of scheelite [138.6 ± 3.2 Ma, N = 39, mean square weighted deviation (MSWD) = 1.17], garnet (138.4 ± 1.0 Ma, N = 40, MSWD = 1.3), and apatite (139.6 ± 3.3 Ma, N = 35, MSWD = 0.72), but also further supports the theoretical genetic links between this mineralization and the emplacement of a proximal porphyritic granodiorite intrusion (zircon U–Pb age: 139.5 ± 1.2 Ma, N = 23, MSWD = 0.3). Moreover, our research indicates that the higher the concentrations of U within scheelite, the more suitable that scheelite is for U–Pb dating, with the main factor controlling the U content of scheelite seemingly being variations in oxygen fugacity conditions. This novel approach provides a potentially powerful tool, not just for the dating of skarn systems but also with potential applications in orogenic and intrusion-related gold, porphyry W–Mo, and greisen mineralizing systems as well as other scheelite-bearing geological bodies or geological systems.     

Re–Os geochronology of Cu and W–Mo deposits in the Balkhash metallogenic belt, Kazakhstan and its geological significance

The Central Asian metallogenic domain (CAMD) is a multi-core metallogenic system controlled by boundary strike-slip fault systems. The Balkhash metallogenic belt in Kazakhstan, in which occur many large and super-large porphyritic Cu–Mo deposits and some quartz vein- and greisen-type W–Mo deposits, is a well-known porphyritic Cu–Mo metallogenic belt in the CAMD. In this paper 11 molybdenite samples from the western segment of the Balkhash metallogenic belt are selected for Re–Os compositional analyses and Re–Os isotopic dating. Molybdenites from the Borly porphyry Cu deposit and the three quartz vein-greisen W–Mo deposits—East Kounrad, Akshatau and Zhanet—all have relatively high Re contents (2712–2772 μg/g for Borly and 2.267–31.50 μg/g for the other three W–Mo deposits), and lower common Os contents (0.670–2.696 ng/g for Borly and 0.0051–0.056 ng/g for the other three). The molybdenites from the Borly porphyry Cu–Mo deposit and the East Kounrad, Zhanet, and Akshatau quartz vein- and greisen-type W–Mo deposits give average model Re–Os ages of 315.9 Ma, 298.0 Ma, 295.0 Ma, and 289.3 Ma respectively. Meanwhile, molybdenites from the East Kounrad, Zhanet, and Akshatau W–Mo deposits give a Re–Os isochron age of 297.9 Ma, with an MSWD value of 0.97. Re–Os dating of the molybdenites indicates that Cu–W–Mo metallogenesis in the western Balkhash metallogenic belt occurred during Late Carboniferous to Early Permian (315.9–289.3 Ma), while the porphyry Cu–Mo deposits formed at 316 Ma, and the quartz vein-greisen W–Mo deposits formed at 298 Ma. The Re–Os model and isochron ages thus suggest that Late Carboniferous porphyry granitoid and pegmatite magmatism took place during the late Hercynian movement. Compared to the Junggar-East Tianshan porphyry Cu metallogenic belt in northwestern China, the formation of the Cu–Mo metallogenesis in the Balkhash metallogenic belt occurred between that of the Tuwu-Yandong in East Tianshan and the Baogutu porphyry Cu deposits in West Junggar. Collectively, the large-scale Late Carboniferous porphyry Cu–Mo metallogenesis in the Central Asian metallogenic domain is related to Hercynian tectono-magmatic activities.     

Nb–Ta–(Ti–Sn) oxide mineral chemistry as tracer of rare-element granitic pegmatite fractionation in the Borborema Province,Northeastern Brazil

The Borborema Pegmatitic Province (BPP), northeastern Brazil, is historically important for tantalum mining and also famous for top-quality specimens of exotic Nb–Ta oxides and, more recently, for the production of gem quality, turquoise blue, ‘Paraíba Elbaite.’ With more than 750 registered mineralized rare-element granitic pegmatites, the BPP extends over an area of about 75 by 150 km in the eastern part of the Neoproterozoic Seridó Belt. The Late Cambrian pegmatites are mostly hosted by a sequence of Neoproterozoic cordierite–sillimanite biotite schists of the Seridó Formation and quartzites and metaconglomerates of the Equador Formation. The trace-element ratios in feldspar and micas allow to classify most pegmatites as belonging to the beryl–columbite phosphate subtype. Electron microprobe analyses (EMPA) of columbite, tapiolite, niobian–tantalian rutile, ixiolite and wodginite group minerals from 28 pegmatites in the BPP are used to evaluate the effectiveness of Nb–Ta oxide chemistry as a possible exploration tool, to trace the degree of pegmatite fractionation and to classify the pegmatites. The columbite group mineral composition allows to establish a compositional trend from manganoan ferrocolumbite to manganocolumbite and on to manganotantalite. This trend is typical of complex spodumene- and/or lepidolite-subtype pegmatites. It clearly contrasts with another trend, from ferrocolumbite through ferrotantalite to ferrowodginite and ferrotapiolite compositions, typical of pegmatites of the beryl–columbite phosphate subtype. Large scatter and anomalous trends in zoned crystals partially overlap and conceal the two main evolution patterns. This indicates that a large representative data set of heavy mineral concentrate samples, collected systematically along cross-sections, would be necessary to predict the metallogenetic potential of individual pegmatites. Other mineral species, e.g. garnets and/or tourmaline, with a more regular distribution than Nb–Ta oxides, would be more appropriate and less expensive for routine exploration purposes. The currently available Nb–Ta oxide chemistry data suggest the potential for highly fractionated Ta–Li–Cs pegmatites in the BPP, so far undiscovered, and encourages further, more detailed research.