The genesis of the ores and granitic rocks at the Hongshi Au deposit in Eastern Tianshan,China: Constraints from zircon U–Pb geochronology,geochemistry and isotope systematics

The Hongshi gold deposit is located in the southwestern margin of the Kanggur–Huangshan ductile shear zone in Eastern Tianshan, Northwest China. The gold ore bodies are predominantly hosted in the volcanogenic metasedimentary rocks of the Lower Carboniferous Gandun Formation and the Carboniferous syenogranite and alkali-feldspar granite. The syenogranite and the alkali-feldspar granite yield SHRIMP zircon U–Pb ages of 337.6 ± 4.5 Ma (2σ, MSWD = 1.3) and 334.0 ± 3.7 Ma (2σ, MSWD = 1.1), respectively, indicating that the Hongshi gold deposit is younger than 334 Ma. The granitoids belong to shoshonitic series and are relatively enriched in large ion lithophile elements (Rb, K, Ba, and Pb) and depleted in high field-strength elements (Nb, Ta, P, and Ti). Moreover, these granitoids have high SiO₂, Al₂O₃, and K₂O contents, low Na₂O, MgO, and TiO₂ contents, low Nb/Ta ratios, and slightly positive Eu anomalies. The ε_Hf(t) values of the zircons from a syenogranite sample vary from + 1.5 to + 8.8 with an average of + 5.6; the ε_Hf(t) values of the zircons from an alkali-feldspar granite sample vary from + 5.0 and + 10.1 with an average of + 7.9. The δ³⁴S values of 10 sulfide samples ranged from − 11.5‰ to + 4.2‰, with peaks in the range of + 1‰ to + 4‰. The above-mentioned data suggest that the Hongshi granitoids were derived from the melting of juvenile lower crust mixed with mantle components formed by the southward subduction of the paleo-Tianshan ocean plate beneath the Aqishan–Yamansu island arc during the Early Carboniferous. The Hongshi gold deposit was formed by post-collisional tectonism during the Permian. The granitoids most likely acted as impermeable barriers that prevented the leakage and runoff of ore-bearing fluids. Thus, the granitoids probably played an important role in controlling gold mineralization.     

Zircon U–Pb geochronology and petrology of intrusive rocks in the C-North and Baghak districts,Sangan iron mine,NE Iran

Porphyritic granitoids that host the Sangan iron mine deposit belong to the Khaf–Kashmar–Bardaskan volcanoplutonic belt in northeastern Iran. These intrusive rocks, mostly quartz monzonite to syenogranite porphyries, have been divided into three groups on the basis of crosscutting relationships and zircon U–Pb dating: (1) group 1, 42.3 ± 0.8 Ma, (2) group 2, 40.0 ± 0.5 Ma, and (3) group 3, 39.2 ± 0.6 Ma. The group 1 and 2 rocks host magnetite mineralization, whereas the group 3 intrusions are interpreted as syn-mineralization. They have features typical of high-K alkali-calcic to calc-alkalic magnesian rocks and are metaluminous to weakly peraluminous formed in a volcanic arc setting. Mantle-normalized, trace-element spider diagrams display enrichment in large ion lithophile elements, such as Rb, Ba, K, and Cs, and depletion in high field strength elements, e.g., Nb, Ti, Ta, Zr, Y, and heavy rare earth elements, with moderate to strong light rare earth elements enrichment ((La/Yb)_N = 24.8–7.6) and a negative Eu anomaly. The parental magmas are probably derived from partial melting of mantle that had been metasomatized by a slab-derived fluid. During the upward migration of these melts, additional input of crustal materials could account for the high K characteristic for most of the intrusive rocks around the Sangan mine area.Textural evidence and mineral assemblages indicate the Sangan Fe-skarn is an oxidized magmatic-hydrothermal system caused by the group 3 intrusions.     

Mobility of elements in a continental subduction zone: evidence from the UHP metamorphic complex of the Kokchetav massif

We studied clastics of high-alumina garnet-kyanite-mica schists and garnet-kyanite-quartz granofelses, including diamond-bearing ones, found in the eluvial sediments near Lake Barchi. In contents of major elements the studied rocks correspond to argillaceous shales. The garnet-kyanite-quartz granofelses are poorer in K (0.49-1.35 wt.% K₂O) than the garnet-kyanite-mica schists (4.9-2.2 wt.% K₂O) but have the same contents of other major components. The REE patterns of most of the garnet-kyanite-phengite schists are similar to those of the Post-Archean Australian Shale (PAAS) (xLa/Yb = 13). All garnet-kyanite-quartz rocks are much stronger depleted in LREE (x_La/Yb = 1.4) and other incompatible elements. Our studies show that allanite and monazite are the main concentrators of LREE and Th in the garnet-kyanite-phengite rocks of the Barchi site. Monazite, occurring as inclusions in garnet, contains not only LREE but also Th, U, and Pb. Rutile of the nondepleted rocks is enriched in Fe and Nb impurities only. The garnet-kyanite-quartz granofelses bear rutile, apatite, and xenotime as accessory phases. Rutile of the depleted rocks shows wide variations in contents of Nb, Ta, and V impurities. In places, the contents of Nb and Ta reach 10.5 and 2.3 wt.%, respectively. The rutile decomposes into rutile with Nb (1.4 wt.%) and Fe (0.87 wt.%) impurities and titanium oxide rich in Fe (6.61 wt.%), Nb (up to 20.8 wt.%), and Ta (up to 2.81%) impurities. Based on the measured contents of incompatible elements in differently depleted high-alumina rocks, the following series of element mobility during UHP metamorphism has been established: Th > Ce > La > Pr > Nd > K > Ba > Rb > Cs > Sm > Eu. The contents of U, P, and Zr in the depleted rocks are similar to those in the nondepleted rocks. The studies have shown that metapelites subducted to the depths with diamond stability conditions can be depleted to different degrees. This might be either due to their exhumation from different depths of the subduction zone or to the presence of an external source of water controlling the temperature of dissolution of phengite and the formation of supercritical fluid/melt.     

Magmatic–hydrothermal rare-element mineralization in the Songshugang granite (northeastern Jiangxi,China): Insights from an electron-microprobe study of Nb–Ta–Zr minerals

The Songshugang granite, hidden in the Sinian metasedimentary stratum, is a highly evolved rare-element granite in northeastern Jiangxi province, South China. The samples were systematically taken from the CK-102 drill hole at the depth of 171–423 m. Four types of rocks were divided from the bottom upwards: topaz albite granite as the main body, greisen nodules, topaz K-feldspar granite and pegmatite layer. Electron-microprobe study reveals that the rare-element minerals of the Songshugang granite are very different from those of other rare-element granites. Mn^# [Mn/(Fe + Mn)] and Ta^# [Ta/(Nb + Ta)] of columbite-group minerals and Hf^# [Hf/(Zr + Hf)] of zircon are nearly constant within each type of rocks. However, back-scattered electron imaging revealed that Nb–Ta oxides and zircon of the Songshugang granite, especially those of topaz albite granite, topaz K-feldspar granite and greisen, are commonly characterized by a specific two-stage texture on the crystal scale. The early-stage Nb–Ta oxide is simply subhedral-shaped columbite-(Fe) (CGM-I) with low Mn^# (0.16–0.37) and Ta^# (0.05–0.29). Columbite-(Fe) is penetrated by the later-stage tantalite veinlets (CGM-II) or surrounded by complex Nb–Ta–Sn–W mineral assemblages, including tantalite-(Fe), wodginite (sl), cassiterite, and ferberite. Tantalite has wide range of Mn^# values (0.15–0.88) from Fe-dominance to Mn-dominance. Wodginite with Ta>Nb has large variable concentrations of W, Sn and Ti. Cassiterite and ferberite are all enriched in Nb and Ta (Nb₂O₅ + Ta₂O₅ up to 20.12 wt.% and 31.42 wt.%, respectively), with high Ta^# (>0.5). Similar to Nb–Ta oxides and Nb–Ta–Sn–W mineral assemblages, the early-stage zircon is commonly included by the later-stage zircon with sharply boundary. They have contrasting Hf contents, and HfO₂ of the later-stage zircon is up to 28.13 wt.%. Petrographic features indicate that the early-stage of columbite and zircon were formed in magmatic environment. However, the later-stage of rare-element minerals were influenced by fluxes-enriched fluids. Tantalite, together with wodginite, cassiterite, and ferberite implies a Ta-dominant media. An interstitial fluid-rich melt enriched in Ta and flux at the magmatic–hydrothermal transitional stage is currently a favored model for explaining the later-stage of rare-element mineralization.     

Whole rock geochemistry,molybdenite Re-Os geochronology,stable isotope and fluid inclusion investigations of the Siah-Kamar deposit,western Alborz-Azarbayjan: New constrains on the porphyry Mo deposit in Iran

The Siah-Kamar porphyry Mo deposit, located in the western Alborz-Azarbayjan magmatic belt, is the first and largest Mo deposit in the Iran. This deposit is mainly hosted by an I-type, shoshonitic quartz monzonite to monzonite intrusion and also extends in the surrounding lower to middle Eocene volcanic rocks. The geochemical features of the Siah-Kamar intrusion show enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE), and significant negative anomalies of Nb, Ta and Ti analogues to the magmas derived from metasomatized sub-continental mantle. Porphyry molybdenum mineralization is associated with potassic, sericitic, argillic, and propylitic alteration zones. Mineralization occurs in disseminated form, in veins/veinlets and in hydrothermal breccias. The main ore minerals comprise molybdenite, chalcopyrite and bornite. The Microthermometric analyses at Siah-Kamar deposit showed that the halite-bearing inclusions contain high salinity (30.9–60.7 wt% NaCl eq.) with homogenization temperature ranging from 226 °C to 397 °C. The homogenization temperature of two phase liquid-rich inclusions range between 224 °C and 375 °C. The salinity of this type inclusions range from 0.6 to 7.5 wt% NaCl equivalent. The two-phase vapor-rich fluid inclusions homogenized at 270 °C to 397 °C. The salinity of this type fluid inclusions lie within the range of 0.6 to 4.24 wt% NaCl equivalent. Coexisting two phase V-rich and L-rich fluid inclusions in quartz associated with molybdenite provide evidence for boiling at 270 °C to 400 °C. The δ¹⁸O_water values of quartz in the molybdenite-bearing veins vary from +2.16 to +4.05‰, suggesting a magmatic origin for the ore-forming fluids. Re-Os isotopic dating of molybdenite indicated a mineralization age of 41.9 ± 3.6 Ma. The Re concentration in molybdenite suggests incorporation of mantle derived melt with crustal materials. The late Eocene magmatism along the western Alborz-Azarbayjan magmatic zone resulted from the Neo-Tethys subduction beneath the Iranian plateau. The Siah-Kamar monzonitic intrusion hosting the Mo deposit, could be considered as an example among the late Eocene intrusions within the western Alborz-Azarbayjan magmatic zone for any further exploration in this zone.     

Amphibole and phlogopite in “hybrid” metasomatic bands monitor trace element transfer at the interface between felsic and ultramafic rocks (Eastern Alps,Italy)

Ultramafic rocks in contact to gneisses in the Mt. Hochwart HP mélange (Eastern Italian Alps) preserve a series of metasomatic mineral zones. A phlogopitite with minor tremolite and accessory zircon and apatite forms close to the gneiss (Zone 1). Zone 2 consists of tremolite, phlogopite and anthophyllite followed by Zone 3 with anthophyllite plus minor chlorite and talc. Zone 3 grades into an amphibole–garnet peridotite lens. This reaction zone has been generated by infiltration of hydrous fluids at T of 660–700 °C and P < 1.2 GPa, which occurred during exhumation of coupled continental crust and mantle peridotites.The reaction zone between a trace element-rich (gneiss) and a trace element depleted reservoir (peridotite) allows assessment of local trace element mobility in aqueous fluids. We present the results of in situ LA-ICP-MS trace element analysis of minerals from the reaction zone. Phlogopite is the main host for Large Ion Lithophile Elements (LILE) and contributes significantly to the Li, Ti, Nb, Ta, Pb and Sc budget. Anthophyllite is the main host for Li whereas all other trace elements including Rare Earth Elements (REE) are preferentially incorporated into tremolite. Combined with the abundance of these minerals over the contact zone, the mineral trace element data suggests that the LILE and REE were mobile on a small scale of a few centimetres only. Limited mobility of Ta, which is generally regarded as barely mobile in fluids, is documented in elevated contents of Ta in anthophyllite coupled with low Nb/Ta. The high Li content in minerals throughout the reaction zone suggests that Li was the most mobile element.The studied metasomatic zones mirror geochemical processes occurring in subduction zones at the slab–mantle interface. Phlogopite crystallization at the slab–mantle interface is an efficient mechanism to filter LILE from the aqueous fluid. Thus, such reaction zones, forming at temperatures < 660–700 °C, likely prevents that the typical slab signature with enriched LILE is transported by aqueous fluids over long distances in the mantle wedge. However, if coupled to the downgoing slab, phlogopite- and tremolite-rich rocks from such reaction zones might be able to act as carriers of trace elements and water into deeper parts of the subduction zone.     

Zr-in-rutile thermometry of eclogites from the Karakaya Complex in NW Turkey: Implications for rutile growth during subduction zone metamorphism

Eclogites occur as a tectonic slice within a metabasite-phyllite-marble unit of the Karakaya Complex in northwest Turkey. The high-pressure mineral assemblage in eclogite is mainly composed of garnet + omphacite + glaucophane + epidote + quartz. Trace element characteristics of rutile and Zr-in-rutile temperatures were determined for eclogites from the Karakaya Complex. Core-rim analyses of rutile grains yield remarkable trace element zoning with lower contents of Zr, Nb and Ta in the core than in the rim. The variations in Zr, Nb and Ta can be ascribed to growth zoning rather than diffusion effects. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents, which could be ascribed to the effect of metamorphic dehydration in subduction zones on rutile Nb/Ta differentiation. The rutile grains from eclogites in the Karakaya Complex are dominated by subchondritic Nb/Ta and Zr/Hf ratios. It can be noted that subchondritic Nb/Ta may record rutile growth from local sinks of aqueous fluids from metamorphic dehydration.The Zr contents of all rutile grains range between 81 and 160 ppm with an average of 123 ppm. The Zr-in-rutile thermometry yields temperatures of 559–604 °C with an average temperature of 585 °C for eclogites from the Karakaya Complex. This average temperature suggests growth temperature of rutile before peak pressure during the subduction. However, some rutile grains have higher Zr contents in the outermost rims compared to the core. Zr-in-rutile temperatures of the rims are about 20 °C higher than those of the cores. This suggests that the outermost rims would have grown from a distinct fluid at higher temperatures than that of the cores. Moreover, Zr contents and calculated temperatures in both inclusion rutile and matrix rutile from eclogites are identical, which suggests that eclogites within the Karakaya Complex belong to the same tectonic slice and underwent similar metamorphic evolution.     

Neoproterozoic magmatic events in the South Qinling Belt,China: Implications for amalgamation and breakup of the Rodinia supercontinent

Neoproterozoic magmatic rocks in the South Qinling Belt of China provide important clues for understanding the mechanism and timing of the amalgamation and breakup of the Rodinia supercontinent. Here we report new geochemical and high-precision LA-ICP-MS zircon U–Pb–Hf isotopic analyses on magmatic suites from the Liuba and Zhashui areas in the South Qinling Belt. Our data show that the crystallization ages of the granitic intrusions from Tiefodian and Tangjiagou in the Liuba area are 863 ± 22 Ma and 794 ± 11 Ma, respectively, whereas those of the dioritic and gabbroic intrusions at Chishuigou in the Zhashui area are 925 ± 28 Ma and 832.6 ± 4.0 Ma, respectively. The diorites at Chishuigou display arc-related geochemical affinity, characterized by strong depletion in Nb, Ta, P and Ti, and enrichment in large-ion lithophile elements (i.e., Rb, Ba, Th and U), indicating a subduction-related arc setting at ca. 925 Ma. The Tiefodian granitic rocks have high SiO₂ (68.46–70.98 wt.%), Na₂O (3.87–4.51 wt.%), and low K₂O (1.34–2.61 wt.%) contents with TTG affinity. However, their Cr, and Ni contents and Cr/Ni, Nb/Ta ratios are similar to those of continental crust, and together with high negative ε_Hf(t) values (− 4.87 to − 14.84), suggesting a continental margin arc at ca. 863 Ma. The gabbros at Chishuigou have high TiO₂ content (2.74–3.14 wt.%), Zr/Y (3.93–4.24), Ta/Yb (0.19–0.25) ratios and low Zr/Nb ratios (11.37–13.17), similar to the features of within-plate basalts, indicating an intra-continental rift setting at ca. 833 Ma. The granitoids at Tangjiagou exhibit enrichment of LREE, K and Pb, and depletion of Nb, Ta, P and Ti, suggesting an extensional tectonic environment at ca. 794 Ma.The results indicate that Neoproterozoic magmatic rocks in the South Qinling Belt formed before ca. 833 Ma and might represent the amalgamation of the Rodinia supercontinent in an arc-related subduction environment, whereas the magmatic events with the peak ages at ~ 740 Ma during ca. 833–680 Ma represent the breakup of Rodinia. Integrating our new data with those from previous works, we propose a new tectonic model for the evolutionary history of the South Qinling Belt in the Neoproterozoic, including four key stages: 1) an ocean that separated the South Qinling Belt and the Yangtze Block in the Early Neoproterozoic (ca.1000–956 Ma); 2) bidirectional subduction of the oceanic lithosphere during ca. 956–870 Ma; 3) subduction and collision between the South Qinling Belt and the Yangtze Block during ca. 870–833 Ma, thus suggesting that the South Qinling Belt was as a part of the Yangtze Block from this period; and 4) intra-continental rifting during ca. 833–680 Ma, although the blocks were not entirely rifted apart.     

Geochronological and geochemical constraints on the petrogenesis of alkaline ultramafic dykes from southwest Guizhou Province,SW China

Geochronological, geochemical and whole-rock Sr–Nd isotopic analyses have been completed on a suite of alkaline ultramafic dykes from southwest (SW) Guizhou Province, China with the aim of characterising their petrogenesis. The Baiceng ultramafic dykes have a LA-ICP-MS zircon ²⁰⁶Pb/²³⁸U age of 88.1 ± 1.1 Ma (n = 8), whereas two phlogopites studied by ⁴⁰Ar/³⁹Ar dating methods give emplacement ages of 85.25 ± 0.57 Ma and 87.51 ± 0.45 Ma for ultramafic dykes from Yinhe and Lurong, respectively. In terms of composition, these Late Mesozoic ultramafic dykes belong to the alkaline magma series due to their high K₂O (3.31–5.04 wt.%) contents. The dykes are characterised by enrichment of light rare earth element (LREE) and large-ion lithosphile elements (LILEs) (Rb and Ba), negative anomalies in high field strength elements (HFSEs), such as, Nb, Ta and Ti relative to primitive mantle, low initial ⁸⁷Sr/⁸⁶Sr ratios (0.7060–0.7063) and positive ε_Nd(t) values (0.3–0.4). Such features suggest derivation from low degree (< 1%) partial melting of depleted asthenospheric mantle (garnet-lherzolite), and contamination to various degrees (～ 10%) by interaction with upper crustal materials.     

Rutile geochemistry and thermometry of eclogites and associated garnet-mica schists in the Biga Peninsula,NW Turkey

In northwest Turkey, high-pressure metamorphic rocks occur as exotic blocks within the Çetmi mélange located on the south of the Biga Peninsula. Rutile chemistry and rutile thermometry obtained from the eclogite and associated garnet-mica schist in the Çetmi mélange indicate significant trace element behaviour of subducted oceanic crust and source-rock lithology of detrital rutiles. Cr and Nb contents in detrital rutile from garnet-mica schist vary from 355 to 1026 μg/g and 323 and 3319 μg/g, respectively. According to the Cr-Nb discrimination diagram, the results show that 85% of the detrital rutiles derived from metapelitic and 15% from metamafic rocks. Temperatures calculated for detrital rutiles and rutiles in eclogite range from 540 °C to 624 °C with an average of 586 °C and 611 °C to 659 °C with an average of 630 °C at P = 2.3 GPa, respectively. The calculated formation temperatures suggest that detrital rutiles are derived from amphibolite- and eclogite-facies metamorphic rocks. Amphibolite-facies rocks of the Kazdağ Massif could be the primary source rocks for the rutiles in the garnet-mica schist from the Çetmi mélange. Nb/Ta ratios of metapelitic and metamafic rutiles fall between 7–24 and 11–25, respectively. Nb/Ta characteristics in detrital rutiles may reflect a change in source-rock lithology. However, Nb/Ta ratios of rutiles in eclogite vary from 9 to 22. The rutile grains from eclogites are dominated by subchondritic Nb/Ta ratios. It can be noted that subchondritic Nb/Ta may record rutile growth from local sinks of aqueous fluids from metamorphic dehydration.     

The composition and genesis of the Mesoarchean Dagushan banded iron formation (BIF) in the Anshan area of the North China Craton

The Dagushan BIF-hosted iron deposit in the Anshan–Benxi area of the North China Craton (NCC) has two types of iron ore: quartz–magnetite BIF (Fe₂O₃^T < 57 wt.%) and high-grade iron ore (Fe₂O₃^T > 90 wt.%). Chlorite-quartz schist and amphogneiss border the iron orebodies and are locally present as interlayers with BIFs; chlorite-quartz schist and BIFs are enclosed by amphogneiss in some locations. The quartz–magnetite BIFs are enriched in HREEs (heavy rare earth elements) with positive La, Eu and Y anomalies, indicating their precipitation from marine seawater with a high-temperature hydrothermal component. Moreover, these BIFs have low concentrations of Al₂O₃, TiO₂ and HFSEs (high field strength elements, e.g., Zr, Hf and Ta), suggesting that terrigenous detrital materials contributed insignificantly to the chemical precipitation. The high-grade iron ores exhibit similar geochemical signatures to the quartz–magnetite BIFs (e.g., REE patterns and Y/Ho ratios), implying that they have identical sources of iron. However, these ores have different REE (rare earth element) contents and Eu/Eu* values, and the magnetites contained within them exhibit diverse REE contents and trace element concentrations, indicating that the ores underwent differing formation conditions, and the high-grade ores are most likely the reformed product of the original BIFs.The chlorite-quartz schist and amphogneiss are characterized by high SiO₂ and Al₂O₃ contents and exhibit variable abundances of REEs, enrichment in LREEs (light rare earth elements), negative anomalies in HFSEs (e.g., Nb, Ta, P and Ti) and positive anomalies in LILEs (large ion lithophile elements, e.g., Rb, Ba, U and K). A protolith reconstruction indicates that the protoliths of the chlorite-quartz schist are felsic volcanic rocks. SIMS and LA-ICP-MS zircon U–Pb dating indicate that this schist formed at approximately 3110 to 3101 Ma, which could represent the maximum deposition age of the Dagushan BIF. However, two groups of zircons from the amphogneiss are identified: 3104 to 3089 Ma zircons that are most likely derived from the chlorite-quartz schist and 2997 to 2995 Ma zircons, which are interpreted to represent the time of protolith crystallization. Thus, the Dagushan BIF most likely formed before 2997 to 2995 Ma. The ~ 3.1 Ga zircons yield ε_Hf(t) values of − 8.07 to 5.46, whereas the ~ 3.0 Ga zircons yield ε_Hf(t) values of − 3.96 to 2.09. These geochemical features suggest that the primitive magmas were derived from the depleted mantle with significant contributions of ancient crust.     

Geochemistry,geochronology and Sr–Nd–Pb–Hf isotopic compositions of Middle to Late Jurassic syenite–granodiorites–dacite in South China: Petrogenesis and tectonic implications

In situ zircon U–Pb ages and Hf isotope data, major and trace elements and Sr–Nd–Pb isotopic compositions are reported for coeval syenite–granodiorites–dacite association in South China. The shoshonitic syenites are characterized by high K₂O contents (5.9–6.1 wt.%) and K₂O/Na₂O ratios (1.1–1.2), negative Eu anomalies (Eu/Eu* = 0.65 to 0.77), enrichments of Rb, K, Nb, Ta, Zr and Hf, but depletion of Sr, P and Ti. The adakitic granodiorite and granodiorite porphyry intrusions are characterized by high Al₂O₃ contents (15.0–16.8 wt.%), enrichment in light rare earth elements (LREEs), strongly fractionated LREEs (light rare earth elements) to HREEs (heavy rare earth elements), high Sr (438–629 ppm), Sr/Y (29.2–53.6), and low Y (11.7–16.8 ppm) and HREE contents (e.g., Yb = 1.29–1.64 ppm). The calc-alkaline dacites are characterized by LREE enrichment, absence of negative Eu anomalies, and enrichment of LILEs such as Rb, Ba, Th, U and Pb, and depletion of HFSEs such as Nb, Ta, P and Ti.Geochemical and Sr–Nd–Hf isotopic compositions of the syenites suggest that the shoshonitic magmas were differentiated from parental shoshonitic melts by fractional crystallization of olivine, clinopyroxene and feldspar. The parent magmas may have originated from partial melting of the lithospheric mantle with small amount contribution from crustal materials. The adakitic granodiorite and granodiorite porphyry have Sr–Nd–Pb isotopic compositions that are comparable to that of the mafic lower crust. They have low Mg# and MgO, Ni and Cr contents, abundant inherited zircons, low ε_Nd(t) and ε_Hf(t) values as well as old whole-rock Nd and zircon Hf model ages. These granodiorites were likely generated by partial melting of Triassic underplated mafic lower crust. The Hf isotopic compositions of the dacites are relatively more depleted than the Cathaysia enriched mantle, suggesting those magmas were derived from the partial melting of subduction-modified mantle sources. The coeval shoshonitic, high-K calc-alkaline and calc-alkaline rocks in Middle to Late Jurassic appear to be associated with an Andean-type subduction. This subduction could have resulted in the upwelling of the asthenosphere beneath the Cathaysia Block, which induced partial melting of the mantle as well as the mafic lower crust, and formed an arc regime in the coastal South China during Middle to Late Jurassic.     

The genesis of the ores and intrusions at the Yuhai Cu–Mo deposit in eastern Tianshan,NW China: Constraints from geology,geochronology, geochemistry,and Hf isotope systematics

The Yuhai porphyry Cu–Mo deposit is located in the eastern Tianshan orogenic belt of the southern Central Asian Orogen Belt, being an economically important porphyry Cu deposit in NW China. The deposit comprises sixteen buried orebodies that are predominantly associated with dioritic and granodioritic intrusions and are structurally controlled by roughly NE-trending faults. LA-ICP-MS zircon U–Pb dating yielded crystallization ages of 441.6 ± 2.5 Ma (MSWD = 0.03, n = 24) for diorite and 430.4 ± 2.9 Ma (MSWD = 0.04, n = 19) and 430.3 ± 2.6 Ma (MSWD = 0.09, n = 24) for granodiorite. In situ zircon Hf isotope data on a diorite sample show ε_Hf(t) values from + 8.7 to + 18.6, and two granodiorite samples exhibit similar ε_Hf(t) values from + 12.6 to + 19.6 and + 12.6 to + 18.9, respectively. The dioritic and granodioritic intrusions belong to a low-K tholeiite series and are relatively enriched in large ion lithophile elements (K, Ba, Pb, and Sr) and are depleted in high field strength elements (Th, Nb, Ta, and Ti). Moreover, these intrusions have high SiO₂, Al₂O₃ and MgO contents, low Na₂O, P₂O₅ and TiO₂ contents, low Nb/Ta ratios, and slightly positive Eu anomalies. Re–Os dating of molybdenite intergrowth with chalcopyrite yielded a well-constrained ¹⁸⁷Re–¹⁸⁷Os isochron age of 351.7 ± 2.9 Ma (MSWD = 1.5) with a weighted average age of 355.7 ± 2.4 Ma (MSWD = 0.69) Ma, indicating that the Yuhai Cu–Mo deposit is younger than the intrusion of the diorite and granodiorite. Combined with the regional geological history and above-mentioned data, we suggest that the Yuhai intrusions were most likely derived from the partial melting of mantle components that were previously metasomatized by slab melts formed by the northward subduction of the ancient Tianshan ocean plate beneath the Dananhu–Tousuquan island arc during the Silurian to Carboniferous. Under the subduction-related tectonic setting, the metasomatized mantle magma was emplaced into the shallow crust and induced the formation of the Early Carboniferous Yuhai Cu–Mo deposit, and the hydrothermal fluids of enriched sulfides probably played an important role in the Cu–Mo mineralization.     

In situ U–Pb isotopic dating of columbite–tantalite by LA–ICP–MS

Columbite–tantalite (Coltan) is the most important niobium (Nb)- and tantalum (Ta)-bearing economic mineral, commonly occurring in rare metal granite and pegmatite, alkaline granite, syenite and carbonatite. Its high U but low common Pb contents make it an ideal mineral for U–Pb isotopic dating of Nb–Ta mineralization. In order to establish a feasible coltan dating method by in situ laser-ablation (LA) ICP–MS, we determined the U–Pb ages of five coltan samples from different pegmatites and rare-metal granites in China. In order to evaluate the potential matrix effect between different minerals, a 91500 zircon was used as external standard during analyses. The results show that, compared to the recommended ages, approximately 7–15% younger ages were yielded for the analyzed coltan samples in both single spot and line raster scan analytical methods, indicating a significant matrix effect between coltan and zircon. However, by using a coltan standard from Namibia (Coltan139), the coltan sample from Dahe pegmatite (SNNT) has a weighted mean ²⁰⁶Pb/²³⁸U age of 363 ± 4 Ma (2σ, n = 25) and 357 ± 5 Ma (2σ, n = 20) in single spot and line raster scan analytical methods, respectively; the coltan samples from Altai No.3 pegmatite (713-79), Yichun topaz-lepidolite granite (Yi-1) and Huangshan albite granite (LS-15) have weighted mean ²⁰⁶Pb/²³⁸U ages of 218 ± 2 Ma (2σ, n = 20), 160 ± 1 Ma (2σ, n = 20) and 130 ± 1 Ma (2σ, n = 20), respectively, in single spot mode. These ages agree well with the previously published data, and hence support the reliability of our analytical method. Although the analyzed coltan minerals show a large variation of chemical compositions, no significant matrix effect was observed, which suggests that a coltan material should be used as an external standard for U–Pb dating of coltan by LA–ICP–MS. Using the established analytical protocol, we date the Nanping pegmatite (NP155), a main Nb–Ta deposit in China without known age, and obtain a weighted mean ²⁰⁶Pb/²³⁸U age of 391 ± 4 Ma (2σ, n = 20), which is considered as the best estimation of Nb–Ta mineralization time in the area.     

Chronology and geochemistry of Mesozoic granitoids in the Bengbu area,central China: Constraints on the tectonic evolution of the eastern North China Craton

We performed zircon U–Pb dating and analyses of major and trace elements, and Sr–Nd–Pb isotopes for granitoids in the Bengbu area, central China, with the aim of constraining the magma sources and tectonic evolution of the eastern North China Craton (NCC). The analyzed zircons show typical fine-scale oscillatory zoning, indicating a magmatic origin. Zircon U–Pb dating reveals granitoids of two ages: Late Jurassic and Early Cretaceous (²⁰⁶Pb/²³⁸U ages of 160 Ma and 130–110 Ma, respectively). The Late Jurassic rocks (Jingshan intrusion) consist of biotite-syenogranite, whereas the Early Cretaceous rocks (Huaiguang, Xilushan, Nushan, and Caoshan intrusions) are granodiorite, syenogranite, and monzogranite. The Late Jurassic biotite-syenogranites and Early Cretaceous granitoids have the following common geochemical characteristics: SiO₂ = 70.35–74.56 wt.%, K₂O/Na₂O = 0.66–1.27 (mainly < 1.0), and A/CNK = 0.96–1.06, similar to I-type granite. The examined rocks are characterized by enrichment in light rare earth elements, large ion lithophile elements, and U; depletion in heavy rare earth elements, Nb, and Ta; and high initial ⁸⁷Sr/⁸⁶Sr ratios (0.7081–0.7110) and low ε_Nd (t) values (? 14.40 to ? 22.77), indicating a crustal origin.The occurrence of Neoproterozoic magmatic zircons (850 Ma) and inherited early Mesozoic (208–228 Ma) metamorphic zircons within the Late Jurassic biotite-syenogranites, together with the occurrence of Neoproterozoic magmatic zircons (657 and 759 Ma) and inherited early Mesozoic (206–231 Ma) metamorphic zircons within the Early Cretaceous Nushan and Xilushan granitoids, suggests that the primary magmas were derived from partial melting of the Yangtze Craton (YC) basement. In contrast, the occurrence of Paleoproterozoic and Paleoarchean inherited zircons within the Huaiguang granitoids indicates that their primary magmas mainly originated from partial melting of the NCC basement. The occurrence of YC basement within the lower continental crust of the eastern NCC indicates that the YC was subducted to the northwest beneath the NCC, along the Tan-Lu fault zone, during the early Mesozoic.     

Carboniferous magmatism and mineralization in the area of the Fuxing Cu deposit,Eastern Tianshan,China: Evidence from zircon U–Pb ages,petrogeochemistry, and Sr–Nd–Hf–O isotopic compositions

The newly discovered Fuxing porphyry Cu deposit is located in the Dananhu–Tousuquan arc, adjacent to the Tuwu–Yandong Cu deposits of Eastern Tianshan, in the southern Central Asian Orogenic Belt. The Fuxing deposit is hosted by volcanic rocks (basalt and dacite) in the Early Carboniferous Qi'eshan Group and Carboniferous felsic intrusions (plagiogranite porphyry, monzogranite, and quartz diorite). New SIMS zircon U–Pb dating indicates that the plagiogranite porphyry and monzogranite emplaced at 332.1 ± 2.2 Ma and 328.4 ± 3.4 Ma, respectively. The basalts are characterized by low SiO₂ contents (47.47–54.90 wt.%), a lack of Eu anomalies, strong depletion of Na, Ta, and Ti elements but positive Sr, U, and Pb anomalies, high Y (20.8–28.2 ppm) and HREE concentrations (Yb = 2.23–3.06 ppm), and relatively low (La/Yb)_N (2.20–3.92) values; the dacite samples have high SiO₂ contents (66.13–76.93 wt.%), clearly negative Eu anomalies, high Mg^# values (36–51), and high Y (41.8–54.9 ppm) and Yb (5.76–8.98 ppm) concentrations. The basalts and dacites exhibit similar signatures as normal arc rocks, and were considered to be derived from partial melting of mantle-wedge peridotite that was previously metasomatized by slab melts. In contrast, the plagiogranite porphyry, monzogranite, and quartz diorite show the same geochemical affinity with modern adakites, which are characterized by high SiO₂ contents (67.55–79.00 wt.%), minor negative to positive Eu anomalies, strong depletion of heavy rare earth elements (Yb = 0.17–1.19 ppm) and Y (1.86–10.1 ppm), positive K, Rb, Sr, and Ba but negative Nb, Ta, Th, and Ti anomalies, and high (La/Yb)_N ratios and Mg^# values. Moreover, these adakitic felsic intrusions display relatively high positive zircon ε_Hf(t) values (+ 11.4 to + 18.3), low ⁸⁷Sr/⁸⁶Sr (0.706080–0.711239), high ¹⁴³Nd/¹⁴⁴Nd (0.512692–0.512922) ratios, and consistent zircon δ¹⁸O values (4.41‰–5.48‰), suggesting that their parental magma were most likely derived from partial melting of the subducted oceanic crust followed by mantle peridotite interaction. Based on the whole-rock geochemical and Sr–Nd–Hf–O isotopic data, as well as detailed petrographic analyses, we further suggest that the Fuxing igneous rocks and associated porphyry Cu mineralization were generated by the northward subduction of the paleo-Tianshan oceanic plate beneath the Dananhu–Tousuquan island arc during the Early Carboniferous.     

Adakite-like signature of porphyry granitoid stocks in the Meiduk and Parkam porphyry copper deposits,NE of Shahr-e-Babak,Kerman, Iran: Constrains on geochemistry

The Middle Miocene porphyry granitoid stocks of Meiduk and Parkam porphyry copper deposits are intruded in the north-western part of the Dehaj-Sarduiyeh volcano-sedimentary belt in the south-eastern extension of the Urumieh-Dukhtar Magmatic Arc (UDMA) in Iran. The porphyritic to microgranular granitoids are mainly consist of quartz diorite, granodiorite and diorite. The whole rock geochemical analyses of these rocks reveals sub-alkaline, calc-alkaline, meta-peraluminous and I-type characteristics. Their geochemical characteristics such as Al₂O₃ content of 13.51–17.05 wt%, high Sr concentration (mostly >400 ppm), low Yb (an average of 0.74 ppm) and Y (an average of 9.02 ppm) contents, strongly differentiated REE patterns (La/Yb ≥ 20), lack of Eu anomaly (Eu/Eu¹ ≥ 1) are indicative of adakitic signature. Their enrichment in low field strength elements (LFSE) and conspicuous negative anomalies for Nb, Ta and Ti are typical of subduction related magmas. Detailed petrological studies and geochemical data indicated that Meiduk and Parkam porphyry granitoids were derived from amphibole fractionation of hydrous melts at a depth of >40 km in a post-collisional tectonic setting.     

Late Paleozoic subduction system in the southern Central Asian Orogenic Belt: Evidences from geochronology and geochemistry of the Xiaohuangshan ophiolite in the Beishan orogenic belt

The Xiaohuangshan ophiolite of the Beishan (Inner Mongolia) is located in the southern margin of the Central Asian Orogenic Belt. It consists of several blocks composed dominantly of serpentinized ultramafic rocks, cumulative gabbros and basalts. The geochemical data of gabbros and basalts obtained from the Xiaohuangshan ophiolite are similar to tholeiitic rocks. They all have low TiO₂ and high Al₂O₃ contents. Their light rare earth elements are slightly enriched, (La/Yb)_N = 3.62–6.80, similar to the typical enriched mid-ocean ridge basalts. The mafic rocks display enrichments in large ion lithophile elements and depletions in high field strength elements, as well as significant Nb–Ta–Ti negative anomalies, similar to subduction-derived rocks. All these geochemical characteritics indicate that the Xiaohuangshan ophiolite would form in a subduction zone from a slightly enriched mantle source. Ion microprobes (SHRIMP) U–Pb dating were conducted on zircons from the basalt and gabbro. The weighted mean ages are 336.4 ± 4.1 Ma and 345 ± 14 Ma, which are considered as the crystallization ages of the basalt and gabbro, respectively. Together with other two units, the Dongqiyishan arc belt and the Yueyashan–Xichangjing ophiolite, the Xiaohuangshan ophiolite forms a Late Paleozoic arc-basin system, indicating that the Paleo-Asian Ocean did not close in the early Carboniferous. Based on the geochemical characteristics of adjacent geological bodies and their settings, the Xiaohuangshan ophiolite is considered as an indicator of a suture zone between the different epicontinental belts in the Beishan region.     

Early to Middle Paleozoic tectonometamorphic evolution of the Hongseong area,central western Korean Peninsula: Tectonic implications

The migmatized gneiss (viz. Gwangcheon gneiss) of the southern Hongseong area, central–western Korean Peninsula underwent intermediate to high granulite-facies metamorphism (ca. 9.2–12.0 kbar and 770–870 °C) during Early Silurian to Early Devonian in age. Field and petrographic evidences from the Gwangcheon migmatite provide a clear indication of partial melting. Particularly the migmatized paragneiss is juxtaposed with arc-related doleritic metagabbro, which might be related to the heat source of the migmatization. The migmatized paragneiss has similar arc-related geochemical characteristics, such as depletions in Ta–Nb, Sr, P, and Ti and enrichments in large ion lithophile elements (LILE) caused by the partial melting effect related to the doleritic metagabbro. Sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb dating of the migmatized paragneiss yielded ages of 432 ± 6 Ma, 431 ± 10 Ma, 421 ± 3 Ma, and 403 ± 3 Ma. The U–Pb ages of inherited zircons from the migmatized paragneiss yielded an age spectra from Neoarchean to Early Paleozoic, with a dominant age population at Neoproterozoic. In contrast, new-growth and recrystallized equant zircons showed dominant concordant Early Silurian to Early Devonian ages that provide critical evidence on the timing of migmatization. These age results and the tectonic signatures are similar to those reported from the Central China Orogenic Belt in China, indicating their tectonic linkage at the northeastern margin of eastern Gondwana during Early to Middle Paleozoic in age.     

Effects of fluorine on the solubilities of Nb,Ta, Zr and Hf minerals in highly fluxed water-saturated haplogranitic melts

The effect of fluorine on the solubilities of Mn-columbite (MnNb₂O₆), Mn-tantalite (MnTa₂O₆), zircon (ZrSiO₄) and hafnon (HfSiO₄) were determined in highly fluxed, water-saturated haplogranitic melts at 800 to 1000 °C and 2 kbar. The melt composition corresponds to the intersection of the granite minimum with the albite–orthoclase tieline (Ab₇₂Or₂₈) in the quartz–albite–orthoclase system (Q–Ab–Or), which is representative of a highly fluxed melt, from which high field strength element minerals may crystallize. The melt contains 1.7 wt.% P₂O₅, 1.05 wt.% Li₂O and 1.83 wt.% B₂O₃. The main purpose of this study is to examine the effect of F on columbite, tantalite, zircon and hafnon solubility for a melt with this composition. Up to 6 wt.% fluorine was added as AgF in order to keep the aluminum saturation index (ASI, molar Al/[Na + K]) of the melt constant. In an additional experiment F was added as AlF₃ to make a glass peraluminous. The nominal ASI of the melts are close to 1 for the minimum composition and approximately 1.32 in peraluminous glasses, but if Li is considered as an alkali, the molar ratio Al/[Na + K + Li] of the melts are alkaline (0.87) and subaluminous (1.09), respectively.The molar solubility products [MnO] 1 [Nb₂O₅] and [MnO] 1 [Ta₂O₅] are nearly independent of the F content of the melt, at approximately 18.19 ± 1.2 and 43.65 ± 2.5 × 10^− 4 (mol²/kg²), respectively for the minimum composition. By contrast, there is a positive dependence of zircon and hafnon solubilities on the fluorine content in the minimum composition, which increases from 2.03 ± 0.03 × 10^− 4 (mol/kg) ZrO₂ and 4.04 ± 0.2 × 10^− 4 (mol/kg) HfO₂ for melts with 0 wt.% F to 3.81 ± 0.3 × 10^− 4 (mol/kg) ZrO₂ and 6.18 ± 0.04 × 10^− 4 (mol/kg) HfO₂ for melts with 8 wt.% F. Comparison of the data from this work and previous studies indicates that ASI of the melt seems to have a stronger effect than the contents of fluxing elements in the melt and the overall conclusion is that fluorine is less important (relative to melt compositions) than previously thought for the control on the behavior of high field strength elements in highly evolved granitic melts. Moreover, this study confirms that although Nb, Ta, Zr and Hf are all high field strength elements, Nb–Ta and Zr–Hf are complexed differently in the melt.