Ore-related Granites Research Articles

Extension settings favour initial REE enrichment in the parent granites of ion-adsorption REE deposits: implication from Late-Permian to Triassic granites in South China

The mechanism of rare earth elements (REE) enrichment in granites is important to understand generation of ion-adsorption REE deposits. We investigated Late Permian to Triassic granites from South China to investigate these issues. The ore-related granites with high REE contents (192-467 ppm) intruded in Late Permian have high K 2 O and Zr+Ce+Nb+Y contents, high Ga/Al and K/Na ratios, and low CaO contents, which belong to aluminous A-type granite derived from melting of felsic igneous rocks at a high-temperature extensional setting. The ore-unrelated Triassic Pingtian granite with relatively low REE contents (81.7-127 ppm) is peraluminous with occurrence of muscovite, indicating a S-type affinity. Its high Rb/Sr and low CaO/Na 2 O ratios indicate magma origin from a metapelitic source related to the compressional setting due to the continental collision. In the extensional settings in South China, the high temperature condition promoting melting of REE-rich accessory minerals and F-rich conditions improving the solubility of REE in the melts could be the reasons for the initial REE enrichment in these granites. Given that parent rocks for ion-adsorption REE deposits are all generated in extensional settings, multiple tectonic stages and long-term extensional setting in South China contributed to generation of the specific ion-adsorption REE deposits in South China.

Features of ore-forming magma and fluid revealed by apatite and zircon geochemistry: A case study from the Huanggang skarn Fe-Sn deposit, NE China

The large-scale Huanggang Skarn Fe-Sn deposit is located in the southern part of the Great Xing’an Range (SGXR), NE China. The causative granitic rocks in the Huanggang ore district are characterized by consistently high SiO2 contents, low EuN/EuN* (0.02–0.24) and Sr/Y (0.2–1.9). The pre-ore granite porphyry and syn-ore syenogranite have been dated through zircon and monazite U-Pb dating at 144.6 ± 1.4 Ma and 138.6 ± 1.3 to 135.9 ± 0.8 Ma, respectively. The U-Pb dating of garnet from ore-associated skarn reveals that the mineralization was happened at 136.5 ± 1.3 Ma, which is consistent with the emplacement age of the ore-related syenogranite.Zircon geochemistry shows that the pre-ore granite porphyry has relatively low oxygen fugacity (average zircon Ce4+/Ce3+ = 14.74), whereas the syn-ore syenogranite is more oxidized (average zircon Ce4+/Ce3+ = 178.9). We suggest that the elevation of oxygen fugacity was most likely caused by degassing. The textural features indicate that apatite crystals from the pre-ore granite porphyry are magmatic in origin. In contrast, textural and chemical characteristics of apatite grains from syn-ore syenogranite reveal that they have been modified by hydrothermal fluids in different degrees. The apatite in both pre- and syn-ore granites display relatively high F and low Cl contents, and very low SO3 concentrations (i.e., <0.032 wt%), indicate extremely low content of S in the causative magma. Apatite from syn-ore syenogranite display more strong and variable enrichment of LREE relative to HREE compared to those from pre-ore granite porphyry. The extensive present of new REE mineral inclusions (monazite and xenotime) in the altered apatite suggests that the concentrations of Ca and Na must be low in the ore-forming fluid. Apatite from syn-ore syenogranite have higher concentrations of Mo, W, Zn, Sn, and Be than those from pre-ore granite porphyry.Combined with zircon and apatite geochemistry, and whole rock components of the ore-related granites in the Huanggang deposit, we propose that the ore-forming magma has undergone long-term evolution under relatively reduced conditions with extensive fractional crystallization of plagioclase. The reduced and S-poor evolved magma could have promoted the enrichment of Sn and prevented Fe from precipitating as sulfide. This study also reveals that the compositional characteristics of ore-forming fluid, such as the enrichment of ore-forming materials, could be revealed by altered apatite geochemistry.

Sulfide resorption contributes to porphyry deposit formation in collisional settings

Production of Cu-rich melts via melting of sulfide-bearing lower crustal cumulates is thought to contribute to porphyry Cu formation in the post-collisional Gangdese belt (Tibet). We present new whole rock, including platinum group elements (PGE) data, for ore-causative granites (OCG), ore-related granites (ORG) and barren granites (BG) from the Gangdese belt. The OCG, ORG and BG show indistinguishable Cu, PGE and Cu/Ag behavior during differentiation down to ∼2 wt% MgO. These systematics, together with the occurrence of sulfides, demonstrate that the propensity for some Gangdese magmas to be ore-associated is unrelated to melting of sulfide-bearing cumulates or the relative timing of sulfide fractionation. The behavior of chalcophile and siderophile elements during differentiation of the OCG, ORG and BG diverges when melts evolve past 2–3 wt% MgO and exsolve H2O, S and Cl: the BG show a decrease in Cu, whereas the OCG and ORG show highly variable Cu, Au, and PGE trends. Because S degassing causes melts to become sulfur undersaturated and because Cu is highly soluble in Cl-rich fluids, any sulfides in contact with the melt or magmatic fluids following volatile exsolution would dissolve. Continual injection, cooling and ascent of magmas through the Gangdese crust is expected to have resulted in the development of regions of crystal-rich partially molten crust beneath the intrusive granites. We suggest that prior to porphyry mineralization, extension and erosion caused exhumation of these long-lived sulfide-bearing mush zones. This exhumation may have caused a change in magmatism style from volatile exsolution after the melts transited sulfide-bearing mushes (i.e., the BG), to volatile exsolution during magma transit through sulfide-bearing mushes (i.e., the OCG). We suggest that only the magmas and that exsolved fluids during their ascent through sulfide-bearing mushes were able to assimilate sufficient Cu-rich sulfides to fuel the formation of porphyry Cu deposits in the region.

Genesis of Makeng-type Fe-polymetallic deposits in SE China: New constraints by geochronological and isotopic data from the Dapai–Makeng metallogenic system

The southwestern Fujian depression belt (SFDB) is an economically important Mesozoic Fe metallogenic belt in South China and is renowned for its Makeng-type Fe deposits, in which stratified skarn Fe orebodies generally occur in or near the contact zone between late Paleozoic carbonate sequences and Mesozoic granites. However, the genesis and geodynamic setting of these deposits remain unclear because the characteristics of the widely distributed Pb–Zn–Cu and Mo orebodies in these deposits and the temporal, spatial, and genetic relationships between magmatism and mineralization are poorly defined. The Dapai Fe polymetallic deposit in the SFDB is a typical example of Makeng-type Fe deposits but also has regional significance, whereby the stratified skarn Fe orebodies have overprinted the stratabound Pb–Zn–Cu mineralization followed by final fissure-filling by vein-disseminated Mo mineralization. A detailed geological investigation suggests that episodic magmatic–hydrothermal events were involved in the formation process of the Dapai Fe polymetallic deposit.Pyrite and sphalerite from the Pb–Zn–Cu orebodies yield an Rb–Sr isochron age of 175.5 ± 3.3 Ma, which is regarded as the timing of Pb–Zn–Cu mineralization. Zircon grains from Fe-mineralized granodiorite porphyry and Mo-mineralized monzogranite yield weighted-mean 206Pb/238U ages of 146.3 ± 0.9 Ma and 131.7 ± 0.4 Ma, interpreted as the timings of Fe and Mo mineralization, respectively. Six zircons from granodiorite also yield a 206Pb/238U model age cluster of ∼184 Ma, which coincides reasonably with the timing of Pb–Zn–Cu mineralization and implies the existence of an unidentified ore-related intrusion in the Dapai deposit. Five further zircons from the porphyritic granodiorite yield an age cluster of ∼150 Ma, consistent with the timing of Fe mineralization. Galena, pyrite, and sphalerite from the Dapai and Makeng deposits have similar S–Pb isotopic compositions and suggest a magmatic source. Combining our results with published isotopic data for the SFDB, we suggest that the Pb–Zn–Cu mineralization in this area was derived from crustal magmas that mixed with mantle-derived magma prior to emplacement. The δ56Fe and δ57Fe values of magnetite from Dapai and Makeng are both slightly lower than those of the ore-related granites, suggesting that Fe in the initial fluid in both deposits was derived mainly from coeval granitic rocks. The Fe isotopic variation between intrusions and skarn Fe orebodies is interpreted as resulting from mass fractionation that occurred during fluid exsolution from melt. Contents of Re in molybdenite from published data for the SFDB indicate crust–mantle mixed sources of Mo and Re. The Makeng-type Fe polymetallic deposits formed as a result of three magmatic–hydrothermal episodes, generating Pb–Zn–Cu mineralization at 185–160 Ma, Fe–Mo mineralization at 150–140 Ma, and Mo–Fe mineralization at 135–130 Ma. The different metal associations formed during multiple stages of magmatism caused by ongoing subduction and rollback and/or retreat of the paleo-Pacific Plate.

Lamprophyre magmatism triggering the formation of the Zhuxi granites related to the world-largest scheelite skarn deposit in South China

The Zhuxi deposit (3.44 Mt. WO3 @0.54%) is the largest tungsten deposit in the world. Although ore-related granitic magmas are correlated with the partial melting of fertile supracrustal material, the heat source triggering the partial melting of fertile supracrustal material has been poorly constrained. To unravel the petrogenesis of the granites, we study the widespread lamprophyre dike swarms coeval with the ore-related granites. Phenocrysts within the lamprophyres are dominated by amphibole, plus a small amount of eastonite. The amphibole phenocrysts exhibit complex internal structures, but the similar geochemical characteristics reveal that they are “antecrysts” recycled from earlier stages of the same magma system that underwent the repeated injection of mafic magmas. Pressure estimates using the Al-in-amphibole geobarometer reveal that most amphibole crystals crystallized at depths of ∼22 km and/or ∼ 10 km, suggesting that lamprophyric magmas most likely ponded at depths of ∼22 km (i.e., the Conrad discontinuity) to form magmatic reservoirs, which in turn fed higher-level magmatic reservoirs that formed at depths of ∼10 km. Both calculations based on energy conservation and simulation results obtained from the quantitative energy-constrained assimilation fractional crystallization (EC-AFC) model consistently reveal that intense partial melting of metagraywackes above the Conrad discontinuity could occur in the temperature interval between 800 °C and 820 °C due to the underplating of lamprophyric magmas. In combination with previous studies showing that the ore-related granitic magmas of the Zhuxi deposit formed at depths of ∼22 km (∼6 kbar) through the biotite dehydration melting of fertile metagraywackes, it can be inferred that the underplating of lamprophyric magmas could have induced the effective partial melting of the overlying fertile supracrustal material, thus forming granitic magmas with significant W endowment. Therefore, the initial appearance of lamprophyres in a district with W-enriched metasedimentary basement rocks should serve as an important prospecting criterion for large-scale tungsten deposits.

Spatial coupling relationship between faults and gold deposits in the Jiaodong ore concentration area and the effect of thermal doming-extension on mineralisation

As the third largest gold ore-forming province in the world, the deep metallogenic potential of and exploration strategies for Jiaodong gold deposits have attracted substantial attention. By applying three-dimensional (3D) geological modelling to these super-giant and giant gold deposits, this study reveals the 3D morphological characteristics of the ore-bearing faults and the ore-related granites, analyses the relationships between ore body locations and slope dip angle changes in the faults, and discusses the coupling relationships among gold mineralisation, ore-controlling faults, and magmatic activities. In the 3D model, the dip angles of ore-controlling faults gradually decrease downwards and alternate between steep and gentle along the fault dip direction. The ore bodies mainly occur in areas with relatively high fault-dip-angle change rates. Hence, positions with fault dip angles of 20°–50° and change rates of ≥0.91 should be considered as target areas for prospecting deep gold ore bodies. In-depth analysis suggests that the ore-hosting faults, granites, and gold mineralisation resulted from regional thermal doming and extensional movements. Gold ore bodies in the Jiaodong Peninsula occur inside or on the periphery of Mesozoic granite. Strong magmatic activities during the transition from enriched to depleted mantle provided the necessary metallogenic and thermal dynamic environment for gold mineralisation. In particular, the magmatic evolution provided abundant ore-forming materials. The detachment faults with varied dip angles provided favourable space for gold mineralisation, as the fluctuations of ore-forming fluid pressure caused by sudden changes in these dip angles served as the primary mechanism underlying the step-like gold mineralisation pattern.

Petrogenesis of the Alubaogeshan intrusion in the Maodeng–Xiaogushan area, southern great xing'an range, NE China: Implications for magma evolution and tin–polymetallic mineralization

• The Alubaogeshan intrusion formed at ca. 134 Ma and belongs to transitional I–A 2 -type granite . • The Alubaogeshan intrusion was formed by partial melting of a Neoproterozoic juvenile crust. • The syenogranite porphyry evolved from the porphyritic monzogranite. • Fluid–melt interaction is crucial for W mineralization. • The magma evolutionary degree influences the size of the Sn–polymetallic deposits in the SGXR. The Alubaogeshan intrusion, consisting of porphyritic monzogranite in the central part and syenogranite porphyry in the edge, is genetically related to the Maodeng–Xiaogushan Sn–polymetallic deposit. This paper aims to investigate the genetic link between these two granite phases and the relationship between magma evolution and Sn mineralization. LA-ICP-MS zircon U–Pb dating of the porphyritic monzogranite and syenogranite porphyry yielded ages of 134 ± 1.0 Ma and 133 ± 0.5 Ma, respectively. The Alubaogeshan intrusion has high SiO 2 and total alkali (Na 2 O + K 2 O) contents, with low Al 2 O 3 , Fe 2 O 3 , FeO, and MgO contents, belonging to high-K calc-alkaline metaluminous–weakly peraluminous granites. Chondrite-normalized rare earth element (REE) patterns are characterized by light REE enrichment and heavy REE depletion, with extremely negative Eu anomalies. In addition, the intrusion was also enriched in Rb, Th, U, K, Zr, Hf, and light REE and strongly depleted in Ba, Sr, P, and Ti. Mineralogical and geochemical characteristics, together with high zircon saturation temperature, indicate that the Alubaogeshan intrusion belongs to transitional I–A 2 -type granites. Compared with the porphyritic monzogranite, the syenogranite porphyry reveals higher SiO 2 content and lower TiO 2 , Al 2 O 3 , Fe 2 O 3 , FeO, CaO, MgO, and P 2 O 5 contents, with more obvious negative anomalies of Eu, Ba, Sr, P, and Ti. The temporal and spatial relationship and geochemical characteristics of the two rocks indicate that the syenogranite porphyry evolved from the porphyritic monzogranite. The modeling results show that the fractional crystallization of amphibole, plagioclase, K-feldspar, biotite, apatite, monazite, and allanite occurred during the magma evolution. The granitic magma differentiation plays a key role in the formation of the Maodeng–Xiaogushan Sn–polymetallic deposit. The ε Hf ( t ) values of zircon range from 2.58 to 7.08, and the two-stage Hf model ages range from 619 Ma to 850 Ma, implying that the Alubaogeshan intrusion was predominantly derived from partial melting of a Neoproterozoic juvenile crust. The TE 1,3 values of the ore-related granites from W–(Sn) deposits are generally higher than 1.1, suggesting that fluid–melt interaction is crucial for W mineralization. The degree of magmatic evolution is one of the controlling factors for the size of Sn–polymetallic deposits in the southern Great Xing′an Range.

Zircon O and Lu-Hf isotope evidence of mantle and supracrustal origins of Tasmanian Devonian granites

The Tasmanian Devonian granites were emplaced during the Tabberabberan Orogeny when the East and West Tasmania Terranes were sutured. The primary aim of this study is to determine zircon O and Lu-Hf isotope constraints on, and relationships between, the magmas forming these granites. A second aim is to determine if these zircon isotopic compositions can be used to inform granite-related ore endowment. Several granites (n = 11 in East Tasmania Terrane, n = 1 West Tasmania Terrane) were previously dated by U-Pb geochronology using SHRIMP, and the zircon pits from the dating analyses were targeted firstly in O and later in Lu-Hf isotope analyses. The magmatic zircon δ18OVSMOW results ranged from mantle-like values (<5.7‰) to values like supracrustal rocks (∼12‰). The granites with the lowest most mantle-like zircon δ18O are all I-types, and these include the relatively mafic Lisle to the very felsic and highly fractionated Mt Stronach and Tombstone Creek plutons. The Tombstone Creek zircon εHfi results are significantly lower than those of Lisle and Mt Stronach, indicating distinct melt sources from which the zircons crystallized. The magmatic zircon δ18O and εHfi results revealed two distinct paths of infracrustal to upper crustal rock εHfi– δ18O melt evolution: one “high εHf” path linking the results from the Lisle, Mt Stronach, Hazards, Henbury, Lottah, Gipps Creek and Royal George granites, and the other “low εHf” path linking those from Tombstone Creek, Meredith, Poimena, Bicheno and Ansons Bay granites. The paths are statistically different and modeled results are consistent with mixing of Mathinna Supergroup rocks with different isotopically defined infracrustal/mantle-like components. The high εHf group of granites are strongly associated with granite-related Au, Sn, and Sn–W ore deposits.

In situ U-Pb geochronology, elemental and Nd isotopic compositions of titanite from the Mesozoic porphyry Mo deposits, NE China

Northeastern (NE) China is one of the most important regions for Mo resources in China with more than 80 porphyry/skarn Mo deposits, most of which were formed in the Mesozoic. Geology, geochemistry and geochronology of individual deposits have been studied and a large amount of data was accumulated, but the factors controlling large-scale Mo mineralization in this region is still debated. To better understand the factors controlling the Mo mineralization, three typical large to giant Mesozoic porphyry Mo deposits located in NE China, namely the Daheishan (DHS), Fu’anpu (FA) and Luming (LM) deposits have been selected. In this paper, U-Pb age, elemental and Nd isotopic compositions of titanite from these deposits have been analyzed to reveal their chemical and isotopic compositions, which provide insights into the nature of source magmas and unravel the physical and chemical conditions of Mo mineralization. In-situ titanite Nd isotopic compositions from all the ore-related granites indicate that they originate from a juvenile crustal source. Titanite occurring as euhedral grains in DHS, FA and LM ore-related granites are characterized by high Th/U and LREE/HREE ratios, as well as low Lu/Hf and 147Sm/144Nd ratios, indicate a magmatic origin. In the LM-barren granite, titanite occurs as magmatic and hydrothermally altered type. The euhedral envelope-shaped magmatic titanite has the same characteristics as the titanite in DHS, FA and LM ore-related granites, with higher Th/U and LREE/HREE ratios and lower147Sm/144Nd ratios. In contrast, hydrothermally altered titanite in the LM-barren granite has lower Th/U and LREE/HREE ratios, as well as higher Lu/Hf and 147Sm/144Nd ratios, distinct Eu anomaly and tetrad effect than the magmatic titanite. In-situ magmatic titanite U-Pb dating of DHS, FA, LM ore-related granite yields crystallization ages of ca.168 Ma, ca.166 Ma and ca.178 Ma, respectively, which are consistent with the mineralization ages within error. Hydrothermally altered titanite in the LM-barren granite yields a crystallization age of 177.9 ± 2.3 Ma (MSWD = 2.3), which is indistinguishable from the LM-ore granites and molybdenite Re-Os age, implying that the formation of the Luming porphyry Mo deposit was coeval with the wall-rock alteration. Relatively homogeneous and consistent Nd isotopic compositions of magmatic titanite from LM-ore granite and hydrothermally altered titanite from LM-barren granite suggest that the hydrothermal fluids have the same origin with the granite and could be directly exsolved from the ore-forming magma. Trace element characteristics of magmatic titanite from these porphyry Mo deposits show that the magma of ore-related granite has higher oxygen fugacity and water contents than those of the LM-barren granite. Hydrothermally altered titanite in the LM-barren granite shows higher F contents than that in the magmatic titanite. The results from this study show that high Mo content in the source region is a prerequisite for the formation of porphyry Mo deposits but the specific magma composition (e.g., with abnormally high Mo contents) may be not critical. Other factors such as the higher F, oxygen fugacity and water contents are also important for Mo mineralization, which could lead to the magma evolution and accumulation of metal elements.

Fluid-rock interaction and fluid mixing in the large Furong tin deposit, South China: New insights from tourmaline and apatite chemistry and in situ B-Nd-Sr isotope composition

AbstractThe Furong tin deposit (South China) is genetically associated with the multiphase Qitianling batholith that consists of main-phase and minor, but more fractionated, late-phase granites. Several tourmaline and apatite generations are distinguished. Tourmaline (Tur) variants comprise pre-ore Tur-1 as disseminations and nodules in the late-phase granite, pre- to syn-ore Tur-2 as replacements in nodules and as veins crosscutting the late-phase granite and nodules, syn-ore Tur-3 in tin greisens, pre- to syn-ore Tur-4 as veins in the altered main-phase granite, and syn-ore Tur-5 from tin skarns in a distinct Ca-rich environment. Apatite (Ap) generations include accessory Ap-G in the main-phase granite, and Ap-I to Ap-III from three stages related to skarn-type mineralization (garnet-diopside stage-I, pargasite-phlogopite-cassiterite stage-II, and sulfide-rich stage-III). Textural and compositional features suggest that all tourmaline variants are hydrothermal in origin with alkali and schorl to foitite composition and minor extensions to calcic and X-site vacant tourmaline groups, whereas all apatite generations belong to fluorapatite with Ap-G crystallizing from the magma and Ap-I to Ap-III being hydrothermal in origin. The narrow range of tourmaline δ11B values (–14.8 to –10.4‰) suggests a single magmatic boron source in the ore-forming fluids. The similar rare earth element patterns and εNd(t) values (–8.2 to –5.9 for Ap-G and –8.0 to –7.3 for Ap-I) between magmatic and hydrothermal apatite indicate that the skarn-forming fluids are dominantly derived from granites. The 87Sr/86Sr ratios of Ap-I to Ap-III (0.70733–0.70795) are similar to the carbonate wall rocks, but distinctly different from the more radiogenic granites, indicating Sr exchange with carbonate rocks. Integrating previous H-O isotopic data, the tourmaline and apatite elemental and B-Sr-Nd isotope results suggest that the greisen-type ore formed by interaction of B-, Na-, Li-, Zn-, and Sn-rich magmatic fluids with the late-phase granite in a closed and reduced feldspar-destructive environment, whereas the tin skarns resulted from mixing of magmatic fluids with meteoric water and interaction with the carbonate wall rocks in an open system where oxygen fugacity changed from reduced to oxidized conditions. During fluid-rock interactions and fluid mixing, considerable Ca, Mg, V, Ni, and Sr from the host rocks were introduced into the ore system. Coupled hydrothermal minerals such as tourmaline and apatite have great potential to fingerprint the nature, source, and evolution of fluids in granite-related ore systems.

Geology of late-Variscan Sàrrabus pluton (south-eastern Sardinia, Italy)

ABSTRACT This paper deals with the geological mapping of the late-Variscan Sàrrabus pluton, (south-eastern Sardinia), a shallow multiple and composite igneous complex dominated by several generations of granodiorites, metaluminous and peraluminous granites and repeated pulses of mantle-derived mafic magmas. The map has been compiled based on geological surveys at 1:10,000 and 1:5,000 scales, assisted by in situ gamma-ray spectrometry and detailed petrographic investigations. Granite-related ore deposits have been also reported. The emplacement age of the pluton can be constrained by U/Pb dating on zircons of Cala Regina granodiorite, yielding an age of 286 ± 9 Ma. The resulting scenario documents a bimodal magmatism controlled by an EW trending shear zone, followed by the shallower emplacement of several pulses of independent granite magmas.

Magmatic-hydrothermal tin deposits form in response to efficient tin extraction upon magma degassing

Most of the global Sn resources are from granite-related ore deposits, which form in response to cassiterite precipitation from hydrothermal fluids. However, the physical and chemical controls on the efficiency of Sn extraction from upper crustal plutons by exsolving magmatic fluids are still unclear. In this study, we determine the partition coefficient of Sn between aqueous fluids and granitic melts (DSnfluid/melt) at 800 °C, 150 MPa and the fO2 of the Ni-NiO buffer. To obtain equilibrium partition coefficients, a new experimental method has been used relying on local equilibrium between silicate melt and microscopic-sized fluid bubbles. The latter formed synthetic fluid inclusions in the quenched glasses, which in turn were analyzed by laser ablation inductively coupled plasma mass spectrometry along with the enclosing glass. The results show that at constant aluminum saturation index (ASI = 1.05–1.08) of the silicate melt, DSnfluid/melt increases from 1.9 to 35.0 as the total Cl concentration (mCltotal) in fluid increases from 1.0 to 16.6 mol/kg H2O. At a fixed mCltotal = 2 mol/kg H2O, DSnfluid/melt increases from 4.3 to 10.6 as the HCl concentration in the solution increases from 0.15 to 0.79 mol/kg H2O, which in turn is a function of the ASI of the melt (ASI = 1.06–1.29). Numerical modeling suggests that Sn is extracted by magmatic fluids from upper crustal plutons most efficiently at the late stage of crystallization and degassing. At a similar degree of crystallization, granitic magma with lower initial water concentration and higher ASI will separate a fluid phase with higher Sn concentration and thus has higher Sn mineralization potential. Due to the relatively high DSnfluid/melt value, fluids exsolved from highly evolved magmas can sequester enough Sn to form Sn deposits and the sub-solidus remobilization of Sn from granite bodies is not a pre-requisite for ore genesis.

Metallogenic ages and sulfur sources of the giant Dahutang W–Cu–Mo ore field, South China: Constraints from muscovite 40Ar/39Ar dating and in situ sulfur isotope analyses

• In-situ sulfur isotope compositions of sulfides imply a magmatic origin for sulfur. • The hydrothermal breccia in the Shimensi deposit formed at 142.0 ± 0.6 Ma and was triggered by the BGP . • The coarse quartz vein-type mineralization in the Shiweidong deposit formed at 136.1 ± 0.5 Ma and was caused by the early episode of CPTG. • The W–Cu–Mo mineralization and ore-related granites in the Dahutang ore field formed in a compression–extension transitional setting. The giant Dahutang W–Cu–Mo ore field is one of the largest tungsten ore fields worldwide. Three main types of mineralization are developed at Dahutang, comprising veinlet-disseminated, hydrothermal breccia, and coarse quartz vein-type mineralization. In this study, precise muscovite 40 Ar/ 39 Ar ages and systematic in situ sulfur isotope compositions of sulfides from the Shimensi and Shiweidong deposits were presented to determine the ore-forming ages and mineralizing intrusions of the hydrothermal breccia type and coarse quartz vein-type mineralization, sources of sulfur in the mineralization, and tectonic setting of the Dahutang ore field. The precise muscovite 40 Ar/ 39 Ar dating suggested that the hydrothermal breccia in the Shimensi deposit formed at 142.0 ± 0.6 Ma and was triggered by the biotite granite porphyry (BGP), while the coarse quartz vein-type mineralization in the Shiweidong deposit formed at 136.1 ± 0.5 Ma and was caused by an early episode of coarse-grained porphyritic two-mica granite (CPTG; 144.2–137.5 Ma) and destroyed by the late episode of CPTG (130–128 Ma). The in situ sulfur isotope compositions of sulfides showed that the hydrothermal breccia type and the coarse quartz vein-type mineralization had a narrow range of sulfur isotope compositions (−3.38–+0.39‰), implying a magmatic origin for sulfur. The increased sulfur isotopes in the sulfides from early to late stages were probably caused by a reduction in the oxygen fugacity of ore-forming fluids in the hydrothermal breccia mineral system. The main W–Cu–Mo mineralization event at Dahutang occurred in the 146–136 Ma interval and was only associated with the early episode of magmatism (149–138 Ma), which coincided well with the Cu–Au–Mo–Fe mineral system in the neighboring Middle–Lower Yangtze River Metallogenic Belt (148–135 Ma). The late episode of magmatism (138–128 Ma), however, was commonly emplaced after the tungsten polymetallic mineralization and even destroyed early formed orebodies as ore-barren intrusions. Combined with the regional tectonic evolution, we proposed that the W–Cu–Mo mineralization and ore-related granites in the Dahutang ore field formed in a transitional setting from a compressional regime to an extensional regime.

Magmatic processes recorded in plagioclase and the geodynamic implications in the giant Shimensi W–Cu–Mo deposit, Dahutang ore field, South China

• The two magma chambers experienced chemically closed magmatic evolution. • The calcium needed for the scheelite mineralization may have been provided by the BG . • The highly evolved felsic magma chamber is critical to the formation of the giant Shimensi deposit. The Shimensi W–Cu–Mo deposit is one of the largest tungsten deposits in the world. Despite numerous geochemical studies conducted on ore-related granites in the district, few studies have concerned magma chambers processes. In this study, systematic in-situ major- and trace-element studies across plagioclase crystals from the ore-related Mesozoic granites as well as whole-rock Sr–Nd isotopic compositions of such granites in the Shimensi deposit were used to constrain the sources of calcium, the dynamics of the magmatic system and the metallogenic geodynamic setting. In-situ analyses of plagioclase showed no obvious positive correlations between An and FeO, while Sr was positively correlated with Ba, indicating that the magma chambers in the Shimensi deposit may have experienced chemically-closed evolution affected only by thermal mixing and/or decompression, without chemical mixing with mafic magma from the mantle. This conclusion was also supported by whole-rock Sr–Nd isotopic characteristics of high ( 87 Sr/ 86 Sr) i (0.71664–0.73689) and negative ε Nd (t) values (−9.81 to −5.07). It was found that the calcium needed for scheelite mineralization may have been predominantly provided by biotite granodiorite (BG) because of its high calcium content and large size, while ore-forming metals should mainly have been derived from the magma sources of pelites and basic volcanic rocks in the Shuangqiaoshan Group instead of the recharging of mafic magma. Moreover, change of the stress environment likely facilitated the formation of long-term stable, large-volume, highly evolved felsic magma chambers in the shallow crust, which would have been critical to the formation of the giant Shimensi W–Cu–Mo deposit.

Petrogenesis of Scheelite-Bearing Albitite as an Indicator for the Formation of a World-Class Scheelite Skarn Deposit: A Case Study of the Zhuxi Tungsten Deposit

Abstract Scheelite-bearing albitite is present in the form of rare, highly fractionated felsic dikes in the world-class Zhuxi tungsten deposit. Morphologically, the Zhuxi albitite forms individual dikes with thicknesses from 0.01 to 5.1 m in the orebodies. Additionally, the Zhuxi albitite is characterized by high sodium concentrations (Na2O = 6.08–8.04 wt %), low silicon (SiO2 = 56.81–62.56 wt %) and potassium concentrations (K2O = 1.44–2.62 wt %), and increasing P2O5 (0.1–0.7 wt %), Y (2.72–8.62 ppm), and rare earth element (8.28–28.89 ppm) concentrations from the tops to the bottoms of the dikes, which are controlled by the heterogeneous distribution of apatite grains in the albitite. The trace element geochemical characteristics and Sr-Nd isotope compositions of the albitite and the geochemistry of plagioclase, muscovite, apatite, and scheelite that formed in both the albitite and ore-related (altered) granites strongly suggest a genetic relationship between the two rocks. Given our new data and previous experimental data, as well as natural examples from around the world, we propose that the Zhuxi albitite is the product of a silicate-poor, H2O-rich melt that formed by melt–melt-liquid immiscibility processes in an extremely fractionated residual magma. A deep-seated (&amp;gt;3 kbar) granitic magma reservoir was directly related to the formation of these rare scheelite-bearing albitite dikes. Albitite dikes are the product of extreme fractionation of a granitic magma, and W is highly incompatible during magma evolution regardless of oxygen fugacity; therefore, intense tungsten mineralization development within albitite dikes should serve as an important criterion for judging the tungsten metallogenic potential.

Geochemistry of zircon and apatite from the Mo ore-forming granites in the Dabie Mo belt, East China: Implications for petrogenesis and mineralization

The Dabie molybdenum (Mo) belt in east China is an important Mo belt in both China and the world. All of the Mo deposits in the Dabie area are porphyry (-skarn) type. The ore-related granite samples from the Qian’echong, Tangjiaping, and Doupo Mo deposits in the Mo belt have been collected for zircon and apatite trace elements analysis. Additionally, the Doupo ore-related granite has also been chosen for zircon U-Pb dating. LA-ICP-MS zircon U-Pb dating of the ore-related granite in the Doupo Mo deposit yields a crystallization age of 127 ± 1 Ma, which is consistent with the molybdenite Re-Os age of the deposit. The chondrite-normalized patterns of all zircons are characterized by positive Ce anomalies with variable negative Eu anomalies. The ore-related granites in the Qian’echong and Tangjiaping Mo deposits show relatively high magmatic oxygen fugacity (ΔFMQ ≥ +1.5), whereas the Doupo ore-related granite has a relatively low magmatic oxygen fugacity (ΔFMQ − 0.3), which might have caused it to have relatively small Mo reserve compared to the Qian’echong and Tangjiaping deposits. All of the apatites from the three Mo deposits are characterized by LREE-enriched and HREE-depleted chondrite-normalized patterns, with various degrees of Eu depletion and Ce enrichment. Not only redox condition but also other factors could have influenced the Eu/Eu* or/and Ce/Ce* of apatite in this study, and the anomalies of Eu and Ce of apatites from the ore-related granites in this study could not be used to evaluate the magma redox states. The geochemical characteristics of apatite indicate that the ore-forming magmas of the Mo deposits in this study are oxidized and metaluminous I or A type magmas. During the Early Cretaceous regional extension and asthenospheric upwelling in the Dabie orogen, partial melting of the crustal rocks generated oxidized Mo-bearing magma. Relatively oxidized condition prevents Mo from incorporating into sulfides or silicates in the magma, and finally leads to Mo precipitation from the ore-forming fluids, which released from the magma.

Genesis of W–Mo mineralization in the Xiaoliugou and Ta’ergou ore fields, North Qilian Orogen (NW China): Constraints from fluid inclusions and S–Pb[sbnd]H[sbnd]O[sbnd]Nd isotopes

Tungsten–molybdenite (W–Mo) polymetallic mineralization are intensely developed in the western section of the North Qilian Orogen (NW China), represented by the Xiaoliugou and Ta’ergou ore fields. In this study, fluid inclusion microthermometric and S–PbHONd isotopic analyses were conducted on the W–Mo ores to shed insights into the genesis of the mineralization belt. The ore fields are characterized by abundant liquid-vapor two-phase inclusions which have medium–high temperature-salinity (200–320 °C and 4–10 wt% NaCl equiv.). The consistent δ18OV-SMOW (7.7‰ to 13.1‰) and δ2HV-SMOW (−88.1‰ to −49.4‰) values of quartz and muscovite indicate that the ore-forming fluid originated from granitic intrusion but mixed with meteoric water. Typical δ34S values of their sulfide ores range from 6 to 18‰, and the ore-related granites (206Pb/204Pb = 18.18–26.61, 207Pb/204Pb = 15.51–16.02, 208Pb/204Pb = 37.60–39.77) and sulfides (206Pb/204Pb = 17.97–20.06, 207Pb/204Pb = 15.42–16.64, 208Pb/204Pb = 37.39–41.06) have variable Pb/Pb ratios, indicating both magmatic rocks and meta-sedimentary rocks contributed to the mineralization. The negative Nd values (εNd(t) = −9.0 to −3.2) and old two-stage Nd model ages (TDM2 = 1517 to 1901 Ma) of the scheelites suggest that the ore-forming materials may have been derived from old crust together with the granitic magma. An isochron age of 422 ± 42 Ma (initial 143Nd/144Nd = 0.511701 ± 0.000046) has been yielded by the scheelite Sm-Nd dating from the Ta’ergou ore field, implying the 450–420 Ma magmatic–hydrothermal event resulted in the intense W–Mo mineralization in the North Qilian, especially in the western section of this orogen. Consequently, we propose a multi-metal coupled mineralization model to illustrate the mineralization process of the ore fields, which involving the formation of ore source beds (wall-rocks) in Proterozoic and the intrusion of granites in Early Paleozoic. This research highlights the use of multiple isotopic methods in revealing complex fluid evolutionary process of large-scale W–Mo deposits.

Petrogenesis and Mo prospecting significance of Sadaigoumen granites on the northern margin of the North China Craton

The Sadaigoumen porphyry Mo deposit lies on the northern margin of the North China Craton. Molybdenum mineralization occurs mainly as veins and veinlets, or is disseminated within alkali feldspar granite and granite porphyry, which yield weighted-mean 206Pb/238U ages (±2σ) of 243.7 ± 1.6 to 242.2 ± 2.0 Ma and 240.0 ± 1.7 Ma, respectively. ReOs dating of molybdenite from Stage 3 mineralization yields an isochron age of 238.0 ± 1.9 Ma. The Sadaigoumen ore-related granites have petrological, mineralogical, and geochemical characteristics of I-type granite. Ore-related granites exhibit low (87Sr/86Sr)i ratios of 0.710256–0.711463, negative εNd(t) values of −16.4 to −15.4 with corresponding TDM2 (Nd) ages of 2061–1870 Ma, and negative εHf(t) values of −21.2 to −11.2 with corresponding TDM2 (Hf) ages of 2614–1983 Ma, indicating that the primary magma was derived by partial melting of ancient lower crust. In chondrite- and primitive-mantle-normalized trace element diagrams, the Sadaigoumen ore-related granites are characterized by moderate enrichment of light rare earth elements (REE) relative to heavy REE, moderate to strong negative Nb, Ta, Zr, Hf, and Ti anomalies, and increasing Rb/Sr ratios with decreasing Sr content, all attributed to fractional crystallization. Fractionation of amphibole, muscovite, and possibly minor biotite and garnet (and/or zircon) produced the variations in most elements. Together with the regional geology, the data imply that the Sadaigoumen ore-related granites and corresponding mineralization formed in a syn-collision to post-collision transitional setting during the Early–Middle Triassic. These fractionated Triassic alkaline granites or syenogranites potentially contain new porphyry Mo deposits.

Genesis and timing of the Sungai Lembing tin deposit in Pahang, East Malaysia: Constraints from LA–ICP–MS zircon and cassiterite U–Pb dating, geochemical compositions and Sr–Nd–Hf isotopes

The Sungai Lembing tin (Sn) deposit is one of the largest primary Sn deposits in Malaysia, and is a typical hydrothermal vein-type deposit with strong spatial and genetic relationship with the underlying granites. In-situ LA-ICP-MS cassiterite U-Pb dating of the Sn-bearing polymetallic sulfide stockworks yields a weighted average age of 264.2 ± 2.0 Ma, consistent to the zircon U-Pb ages (ca. 260.3–263.0 Ma) for the granites there, showing that the Late Permian mineralization was co-magmatic. The ore-related granites are featured by high SiO2, Al2O3, Na2O, K2O, and low P2O5 contents, with low A/CNK ratios, indicating that these granites are peraluminous I-type high-K calc-alkaline. These granites are enriched in Rb, U, Nd, Zr, Hf and light rare earth elements (LREEs), and relatively depleted in Ba, Nb, Sr, P, Ti and heavy rare earth elements (HREEs), accompanied by negative Eu anomalies. The relatively low whole-rock initial 87Sr/86Sr ratios (0.704199–0.708692), moderately high εNd(t) (−5.30 to −1.88), and old two- stages Nd model ages (1.05–1.28 Ga), together with the negative zircon εHf(t) (−3.2 to −0.3) and old two-stages Hf model ages (1.29–1.48 Ga), indicate that the granites were sourced from the magma generated by the partial melting of Proterozoic meta-igneous rocks of the Indochina Block. The extensive emplacement of Permian granites and Sn mineralization in the Eastern Granite Belt of Peninsular Malaysia may have been resulted from the east-dipping subduction of the Paleotethys beneath the western Indochina Block.

The Permian Sn metallogenic event and its geodynamic setting in East Kunlun, NW China: Evidence from zircon and cassiterite geochronology, geochemistry, and Sr–Nd–Hf isotopes of the Xiaowolong skarn Sn deposit

Abundant granitoids are exposed along the East Kunlun orogenic belt (EKOB), and many skarn deposits occur at the contacts between intrusions and strata. One such is the Xiaowolong deposit, a skarn-type tin polymetallic deposit that is temporally and spatially associated with porphyry monzogranite. Tin mineralization is mainly hosted by the skarn. In this study, we reported zircon and cassiterite U–Pb ages, whole-rock geochemistry, and Sr–Nd–Hf isotopic data, and used these to constrain the timing of intrusion and mineralization in the Xiaowolong deposit and identify the origin of the ore-related granites and the link between Sn mineralization and granitic magmatism. Age determinations by LA-ICP-MS U–Pb zircon dating indicated that the porphyry monzogranite formed at 260.0 ± 0.7 Ma. Cassiterite from the ore-bearing skarn yielded a Tera-Wasserburg U–Pb lower intercept age of 258.0 ± 3.7 Ma. These ages suggested that both granitic intrusion and related Sn mineralization in the Xiaowolong deposit were initiated during the Permian (ca. 260 Ma). The porphyry monzogranites had high SiO2 (71.26–73.13 wt%) and Al2O3 (13.84–14.46 wt%) contents, were alkali-enriched (K2O + Na2O = 7.08–7.69 wt%), had A/CNK values that ranged from 1.01 to 1.05, were enriched in light REEs and large ion lithophile elements such as Rb, Th, U and K, were depleted in high field strength elements, and had relatively low Zr, Nb, Y and Ce contents. They thus exhibited the geochemical characteristics of I-type granite. The porphyry monzogranite had consistent negative whole rock ɛNd(t) (−6.8 to −7.1) and magmatic zircon ɛHf(t) values ranging from −7.4 to −1.6, and two-stage Hf model ages ranging from 1393 Ma to 1758 Ma. Detailed elemental and isotopic data demonstrated that the porphyry monzogranite were derived from partial melting of ancient crustal source, and emplacement in a subduction tectonic setting. The Xiaowolong tin mineralization event indicated that the EKOB has great potential for exploration focusing on Permian-Triassic Sn skarn deposits.