Log fO2 Values Research Articles

Quantitative redox measurements for hydrothermal experiments conducted in cold-seal pressure vessels

The cold-seal pressure vessel (CSPV) is a commonly-used apparatus for hydrothermal experiments performed at crustal temperature (T)–pressure (P) conditions. The redox states of the samples in CSPV hydrothermal experiments are normally controlled by the pressure medium, by using oxygen buffers, or with the Shaw membrane technique. Although these techniques have been widely used, the actual redox states of the samples are not necessarily the expected values and need to be quantitatively measured. In this study, by using CoPd, NiPd, and (NiMn)O redox sensors, quantitative redox measurements have been conducted in H2O-pressurized Ni-superalloy (Inconel 713 LC) CSPVs at 700–800 °C and 200 MPa. Oxygen fugacities (fO2) of the H2O pressure medium in three CSPVs used in this study were measured, and their log fO2 values were − 13.11 ± 0.06 (Ni–NiO (NNO) + 0.7), − 13.05 ± 0.06 (NNO + 0.8) and − 12.68 ± 0.07 (NNO + 1.1), comparable with those reported previously. By placing an open capsule containing Ni powder below the sample capsule, the fO2 of the H2O pressure medium can be adjusted to reach that of the NNO buffer (NNO to NNO + 0.2). For the MnO–Mn3O4, Ni–NiO, and Co–CoO oxygen buffers, a steady-state fO2 was always achieved for each buffer at a fixed P-T condition. Measured log fO2 values for the Ni–NiO and Co–CoO buffers are in good agreement with theoretical values calculated from thermodynamic data and also with previous results obtained from vessels pressurized with Ar. The log fO2 values determined for the MnO–Mn3O4 buffer, about 0.3 log unit lower than the theoretical values, are consistent with previous values obtained from vessels pressurized with Ar. These results suggest that the use of H2O pressure medium would not perturb the equilibrium redox states of the oxygen buffers. In addition, we developed a miniature sensor that is small enough to be loaded together with other sample material, allowing the monitoring of fO2 in actual experiments.

Zircon compositional systematics from Devonian oxidized I-type granitoids: examination of porphyry Cu fertility indices in the New Brunswick Appalachians, Canada

Zircon is a common, widely distributed accessory mineral in most igneous rocks and its refractory nature records magmatic evolution in terms of oxygen and U-Th-Pb isotopes, and trace-element contents all of which reflect the intrinsic physio-chemical evolution of the magmatic systems in which it crystallized. Zircon compositions can be used as an indicator of relative fertility of hypabyssal intrusions in terms Cu ± Mo ± Au porphyry mineralization. To further characterize syn- to post-collisional adakitic Devonian oxidized I-type granitoids in the New Brunswick (specifically, those with Cu ± Mo ± Au porphyry-style mineralization), LA-ICP-MS analyses (guided by µXRF-EDS mapping and SEM-BSE imaging of polished thin sections) of zircons from 13 granitoids was conducted. The zircons studied were similar in terms of their textures (homogenous cores, patchy zoning, oscillatory zoning, and some unzoned zircon); however, they have a wide range of trace- and minor-element (Hf, HREE, Y, Th, U) compositions. Specifically, Zr/Hf ranges between 24–60, whereas Th/U ranges between 0.15 and 5.37. The presence of inherited zircon affects the concentrations of Th and U, as well as other key elements. Estimated crystallization temperatures of granitoids, ranging from 737 to 899°C, were calculated via Ti-in-zircon geothermometry assuming reduced TiO2 and SiO2 activities. The calculated log fO2 values for zircons from some of these granitoids indicate a highly oxidized magmatic signature. Zr/Hf, Eu/Eu⁎, and (Eu/Eu⁎)/Y in zircon, as well as zircon (Ce/Nd)/Y are some of the best indicators of porphyry fertility. The Ce/Ce* in zircon exhibit a large range (1.1–590), with higher Ce/Ce* reflecting more metallogenically favourable oxidizing conditions. If Eu/Eu⁎ in zircon is ≥0.4 (relatively oxidized conditions), it indicates a high potential for an ore-forming porphyry Cu mineralizing system. Lower Eu contents reflect relatively reducing conditions, as Eu anomalies vary with oxygen fugacity as well, and the relative abundance of Eu2+ is higher, but does not substitute into the zircon lattice. The evidence extracted from analyzing the zircon composition within New Brunswick’s I-type granitoids indicates the fertility of these hypabyssal intrusions.

First identification of the Early Cretaceous Suolong Cu-rich porphyry in the Geji area, central Tibet: A new clue for regional porphyry Cu exploration

The Tibetan Plateau hosts the majority of porphyry Cu deposits in China. There are two large metallogenic belts, the Gangdese and Bangong-Nujiang belts, in the Lhasa Terrane, Central Tibet. The Lhasa Terrane experienced multistage magmatic activity from the Mesozoic to Cenozoic, and the subaerial volcanic areas of the western part of the terrane are regarded as favorable targets of porphyry Cu deposits. In this paper, we describe the geology of our newly identified Early Cretaceous Suolong Cu-rich porphyry in the western Lhasa Terrane and present new U–Pb ages, trace element and Hf isotopic compositions of zircon and whole-rock elemental and Sr–Nd isotopic compositions. The Suolong porphyry contains zircon grains with ages ranging from 136 to 135 Ma, εHf(t) values ranging from −1.5 ∼ +2.7 and logfO2 values ranging from −16.27 ∼ −9.92. Geochemically, the porphyry rocks are peraluminous in nature, with whole-rock εNd(t) values of −5.7 ∼ −5.4. We infer that the Suolong porphyry originated from a mixture of ∼53 % enriched lithospheric mantle and ∼47 % ancient lower crustal melt, triggered by the roll-back of the northward-subducting Neo-Tethyan Ocean. The conditions of high oxygen fugacity and water content and tectonic transition promoted the formation of the Suolong Cu-rich porphyry, but the condition of a thinned crust may have constrained the mineralization scale of the Cu deposits. This new identification of Early Cretaceous mineralization event provides important clues for identifying new potential exploration targets for porphyry Cu deposits in the western segment of the Lhasa Terrane.

Petrogenesis of the Newly Discovered Neoproterozoic Adakitic Rock in Bure Area, Western Ethiopia Shield: Implication for the Pan-African Tectonic Evolution

The Neoproterozoic Bure adakitic rock in the western Ethiopia shield is a newly discovered magmatic rock type. However, the physicochemical conditions during its formation, and its source characteristics are still not clear, restricting a full understanding of its petrogenesis and geodynamic evolution. In this study, in order to shed light on the physicochemical conditions during rock formation and provide further constraints on the petrogenesis of the Bure adakitic rock, we conduct electron microprobe analysis on K-feldspar, plagioclase, and biotite. Additionally, we investigate the trace elements and Hf isotopes of zircon, and the Sr-Nd isotopes of the whole rock. The results show that the K-feldspar is orthoclase (Or = 89.08~96.37), the plagioclase is oligoclase (Ab = 74.63~85.99), and the biotite is magnesio-biotite. Based on the biotite analysis results, we calculate that the pressure during rock formation was 1.75~2.81 kbar (average value of 2.09 kbar), representing a depth of approximately 6.39~10.2 km (average value of 7.60 km). The zircon thermometer yields a crystallization temperature of 659~814 °C. Most of the (Ce/Ce*)D values in the zircons plotted above the Ni-NiO oxygen buffer pair, and the calculated magmatic oxygen fugacity (logfO2) values vary from −18.5 to −4.9, revealing a relatively high magma oxygen fugacity. The uniform contents of FeO, MgO, and K2O in the biotite suggest a crustal magma source for the Bure adakitic rock. The relatively low (87Sr/86Sr)i values of 0.70088 to 0.70275, positive εNd(t) values of 3.26 to 7.28, together with the positive εHf(t) values of 7.64~12.99, suggest that the magma was sourced from a Neoproterozoic juvenile crust, with no discernable involvement of a pre-Neoproterozoic continental crust, which is coeval with early magmatic stages in the Arabian Nubian Shield elsewhere. Additionally, the mean Nd model ages demonstrate an increasing trend from the northern parts (Egypt, Sudan, Afif terrane of Arabia, and Eritrea and northern Ethiopia; 0.87 Ga) to the central parts (Western Ethiopia shield; 1.03 Ga) and southern parts (Southern Ethiopia Shield, 1.13 Ga; Kenya, 1.2 Ga) of the East African Orogen, which indicate an increasing contribution of pre-Pan-African crust towards the southern part of the East African Orogen. Based on the negative correlation between MgO and Al2O3 in the biotite, together with the Lu/Hf-Y and Yb-Y results of the zircon, we infer that the Bure adakitic rock was formed in an arc–arc collision orogenic environment. Combining this inference with the whole rock geochemistry and U-Pb age of the Bure adakitic rock, we further propose that the rock is the product of thickened juvenile crust melting triggered by the Neoproterozoic Pan-African Orogeny.

Petrogenesis and oxidation state of biotite granite, and cassiterite u-pb age from the Debao Cu-Sn skarn deposit, southwestern China: Implications for coupled Cu-Sn mineralization

Copper and Sn mineralization are seldom formed from the same magmatism due to the distinct geochemistry of Cu and Sn (i.e., Cu and Sn mineralization are usually associated with oxidized mantle-derived intrusions and reduced crust-derived granites, respectively). Previous studies proposed that the formation of Cu-Sn deposits was due to injection of the oxidized mafic magma and/or associated fluids to the reduced magma chambers. The Debao skarn deposit in Guangxi (SW China) has uncommon coupled Cu-Sn mineralization, and it is unclear whether the Cu-Sn mineralization is associated with two different types of magmatism or not. This study presents zircon U-Pb dating, element and Hf-O isotopic data of mineralization-related granites, as well as cassiterite U-Pb ages for the Debao deposit, to constrain the genesis of the coupled Cu-Sn mineralization. The Cu-Sn mineralization is spatially associated with two types of biotite granites: the porphyritic and equigranular biotite granites which have zircon U-Pb ages of 442.5 ± 3.1 Ma to 439.0 ± 2.2 Ma and 439.1 ± 2.6 Ma, respectively. Cassiterite U-Pb dating yielded a mineralization age of 445.6 ± 3.2 Ma, coeval with the emplacement of both types of granites. The two granites have similar zircon δ18O values of 6.9–8.4 ‰, and variable εHf(t) values of − 9.9 to 6.1 (mostly − 3 to 3) with Hf model ages of 2042–1036 Ma, indicating that they were cogenetic and mainly derived from Mesoproterozoic metasedimentary rocks in the Sibao Group with some input of juvenile materials. The equigranular biotite granites have higher SiO2 contents (74.97–76.41 wt%) and Rb/Sr ratios (10.9–12.6), as well as lower Zr/Hf (23.4–24.6) and Nb/Ta ratios (4.4–5.3) than those of the porphyritic biotite granites (SiO2 = 70.70–73.27 wt%, Rb/Sr = 1.0–2.8, Zr/Hf = 23.4–36.7, Nb/Ta = 7.2–9.4), indicating that the former underwent a much higher degree of magmatic differentiation than the latter. Moreover, the two granites are relatively reduced, as indicated by low zircon Ce4+/Ce3+ ratios (5.1–113.9, mean 41.4) and calculated logfO2 values (−29.3 to − 12.7, mean − 20.9), which plot below the FMQ buffer. The Sn and Cu metals likely came from the Sn-rich metasedimentary rocks and the Cu-rich juvenile materials in the magma source region, respectively. Under the reduced and probably S-poor magma system, both the Sn and Cu are relatively incompatible and would be enriched in the residual melts. Therefore, we suggest that the Cu-Sn mineralization at the Debao deposit is genetically associated with the highly fractionated equigranular biotite granites, without the addition of oxidized mafic magma and/or associated fluids. Nevertheless, Cu endowment associated with such reduced magmas is expected to be small.

Petrogenesis and metallogenic potential of granodiorite porphyry in the Kalatag district, East Tianshan, NW China: Constraints from geochronology, mineral geochemistry, Sr–Nd–Hf–O–S isotopes and sulfide trace elements

The Hongshi epithermal Cu deposit is located in the northern margin of the Dananhu arc in the East Tianshan Orogenic Belt, NW China. The Hongshi deposit is hosted by andesite and is famous for its lode type sulfide ores. Recently, the deep drill hole exploration shows a porphyry Cu mineralization and is predominantly hosted in granodiorite porphyry in the Hongshi. As for porphyry mineralization, the metallic minerals mainly include chalcopyrite, magnetite, and pyrite, with minor amounts of molybdenite. Ore minerals occur as dense dissemination and veins. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb dating of zircons showed that the ore-bearing granodiorite porphyry was emplaced at ca. 434 Ma, recording the early subduction of the Paleo-Tianshan oceanic plate. Major element geochemical characteristics show that granodiorite porphyry samples have A/CNK values of 1.04–1.10 and moderate Mg# values of 45–49, indicating an I-type granitoid attribute. Trace element geochemical analysis indicates that ore-bearing granodiorite porphyry samples exhibit obvious large ion lithophile elements (LILEs) enrichment, high field strength elements (HFSEs) depletion, together with mantle-like bulk Sr–Nd ((87Sr/86Sr)i = 0.706417–0.708601; εNd(t) = 6.3–7.0) and zircon Hf–O isotope signatures (εHf(t) = 15.5–21.7, δ18O = 3.8 ‰–4.7 ‰), indicating that they were generated from partial melting of metasomatized mantle by the subducted slab fluids. In situ S isotope results of pyrite (1.46 ‰–2.07 ‰) and chalcopyrite (0.79 ‰–1.93 ‰) imply that granodiorite porphyry magmas and volcanic rocks provided ore-forming components (S and metals) for porphyry Cu mineralization in the deep drill hole ZK7501. The ore-bearing granodiorite porphyry samples have high logfO2 values ranging from − 12.4 to − 10.7, corresponding to ΔFMQ values of 0.6–5.2 (FMQ is the fayalite-magnetite-quartz buffer). Zircons from granodiorite porphyry have high Ce4+/Ce3+ ratios ranging from 74 to 187 and high Ti-in-zircon temperatures (764 to 869 °C). Electron microprobe analyses (EPMA) composition results of plagioclase, apatite and amphibole reveal that granodiorite porphyry magma had systematically high oxygen fugacity, high water contents (7.6–8.4 wt%), and low Cl contents (0.08–0.27 wt%), further demonstrating that granodiorite porphyry may be beneficial to the porphyry Cu mineralization in the deep drill hole ZK7501. Pyrite in the deep drill hole ZK7501 is enriched in Co, Ni, Ag, Cu, As, and Pb, but poor in Mn, Ga, Ge, Cd, In, Sn. Mn, As, Tl, Pb and Sb in pyrite substituted Fe2+ by coupled mechanisms, while Ag and Cu can enter the mineral lattice in the form of solid solution or micro-inclusions, which was also demonstrated by LA–ICP–MS mapping and textural studies. Pyrite shows variable Co/Ni ratios ranging from 10 and 455, indicating that ore-forming fluid originated from a magmatic source. The involvement of highly oxidized magmas is fundamental for the formation of porphyry Cu mineralization in an arc tectonic setting. Additionally, water concentrations also play an important factor that controlled metal fertility of the Early Paleozoic porphyry Cu mineralization in the Kalatag district.

Reaction between volatile-bearing eclogite and harzburgite as a function of degree of interaction: Experimental constraints at 4 GPa

Abstract The mantle is known to be heterogeneous, mainly composed of peridotite and eclogite. Eclogite-derived hydrous melts may interact with harzburgite at the slab-mantle interface in subduction zones or in the sub-continental lithospheric mantle. In this study, such interactions were simulated by performing hybridization experiments in which a layer of eclogite was juxtaposed to a layer of harzburgite in the presence of H2O-CO2 at 4 GPa and 1200 °C, conditions where eclogite is super-solidus while harzburgite is sub-solidus. A diamond trap was placed in between the two layers to trap the fluid or melt phase, allowing direct determination of their composition. The multi-anvil was rotated at different frequencies to examine the effect of increasing degree of interaction on the melt composition as well as the mineral compositions. The interaction of eclogite-derived hydrous melt and harzburgite results in a reaction layer at the interface between the two lithologies, composed of Opx and garnet. The harzburgite above the reaction layer is metasomatized, containing various amounts of olivine, Opx, Cpx, and garnet. The eclogitic melt is modified during this interaction. With increasing interaction, a thicker reaction layer is formed. Both the eclogitic and the peridotitic garnet compositions approach each other and become intermediate between the composition of the garnet in the eclogite+H2O+CO2 system and the garnet in the harzburgite+H2O+CO2 system at these conditions. The Mg# of the peridotitic olivine and Opx decreases with increasing interaction. The initial basaltic melt in equilibrium with eclogite is metaluminous, turning to a peralkaline melt with increasing interaction with the harzburgite. The metasomatizing effect of the eclogite-derived hydrous melt on the harzburgite is observed by increasing the mode of the peridotitic Opx, Cpx, and garnet at the expense of peridotitic olivine and eclogitic garnet. A slight increase in melt fraction occurs as well. This interaction also results in a gradient in the log fO2. Relatively more oxidizing conditions occur near the reaction layer, becoming more reduced into the peridotite, suggesting that the reaction zones act as partial barriers for the melt to travel through the peridotite. Increased interaction leads to higher log fO2 values. These experiments demonstrate the influence of the degree of interaction on the range of melt compositions found in volcanic arcs as well as the degree of metasomatism in the mantle found in the sub continental lithospheric mantle.

The role of uranyl complex decomposition and redox conditions in the precipitation of hydrothermal uranium deposits: Insights from chlorite mineralogy and geochemistry in the Shazhou uranium deposit, Xiangshan, SE China

Uranium precipitation involves the decomposition of uranyl complexes and the reduction of hexavalent uranium, which can occur sequentially or simultaneously within one redox reaction. The redox condition of hydrothermal fluid plays a vital role in controlling the migration and precipitation of uranium in hydrothermal uranium deposits. However, little attention has been paid to the role of uranyl complex decomposition in uranium precipitation. In this study, chlorite mineralogy and geochemistry were examined to clarify the process of uranium precipitation in the Shazhou deposit, Xiangshan uranium orefield, Southeast China. Based on comprehensive petrographic and mineral chemistry studies of chlorites obtained from altered granite porphyries and uranium ores, five types of chlorites were identified: (1) chlorite present in the form of pseudomorphous biotite, which was produced by the hydrothermal alteration of biotite in rocks that underwent hematitization and chloritization (Chl-I); (2) chlorite filling the cleavage cracks in biotite in rocks that underwent hematitization and chloritization (Chl-II); (3) chlorite occurring in pyrite veins (Chl-III); (4) chlorite intergrown with pitchblende in ore veins (Chl-IV); and (5) chlorite occurring in calcite veins (Chl-V). Chlorite geothermometry revealed that the formation temperatures of the five types of chlorites ranged from 219 °C to 254 °C. Mineral chemistry analyses revealed that the five types of chlorites formed in a reductive fluid environment, where the oxygen fugacity at different stages is similar, with log fO2 values ranging from −41.6 to −39.1. Uranium precipitation started only in stage Chl-IV. The examination of the mineral assemblage revealed that the ore-forming fluid was rich in F−, HPO32−, and CO32−. Comprehensive investigation of chemistry and physicochemical conditions of the ore-forming fluid revealed that oxidized uranium (UO22+) could be complexed with HPO42− and F−, and uranyl phosphate and the uranyl fluoride complexes were the main uranium species when uranium precipitation and the decomposition occurred at stage Chl-IV. However, the assessment of oxygen fugacity of the solution equilibria between the UO2(s) and the uranyl phosphate and uranyl fluoride complexes revealed that the reducibility of the fluid favoring the reduction of uranyl ions (UO22+) to U4+ was insufficient to reduce the uranyl phosphate and uranyl fluoride complexes. This indicates that the breakup of uranyl phosphate and the uranyl fluoride complexes to release uranyl ions should occur first at stage Chl-IV, reducing uranyl ions to U4+, and leading to uranium precipitation. Hence, the decomposition of uranyl complexes played an important role in uranium precipitation. With the increase in pH, uranyl phosphate and the uranyl fluoride complexes gradually decomposed and became reducible. Moreover, the decrease in ligand concentration was conducive to the decomposition of uranyl phosphate and the uranyl fluoride complexes. During the formation of the Shazhou deposit, the fluid boiling process induced the loss of volatiles, such as CO2, CH4, HF, and H2S, leading to an increase in pH and decrease in HPO42−, F−, and CO32− concentrations in the fluid. These factors also led to the decomposition of uranyl fluoride and the uranyl phosphate complexes and the precipitation of fluorapatite and calcite. Uranium was then reduced by the action of Fe2+ and S− (pyrite) from a hexavalent to a tetravalent, and finally, uranium was precipitated to form uranium ores.

Early Cretaceous Ningguo-Guangde weakly fractionated I-type granitoids, Jiangnan tungsten belt, China: Implications for petrogenesis and W[sbnd]Mo mineralization

Most W mineralization in the world is genetically related with highly fractionated granitoids, but little is known about petrogenesis of weakly fractionated granitoids and its relationship with W mineralization. To reveal the petrogenesis of the weakly fractionated granitic rocks and related mineralization, a combined study of zircon UPb ages, whole-rock major-trace elements and Sr-Nd-Pb isotopes as well as apatite in-situ geochemistry was carried out for the Ningguo-Guangde granitoids in the world-class Jiangnan W belt (total resource of approximately 6.06 Mt WO3), China. Zircon UPb ages indicate that the Ningguo-Guangde granitoids were emplaced in the Early Cretaceous (ca. 138–125 Ma). These samples with moderate silicon (SiO2 = 65.5–68.4 wt%) mainly consist of high-K calc-alkaline granodiorites and monzogranites, which exhibit an affinity for the weakly fractionated I-type granite, with enrichment in light rare earth elements (LREEs), Rb, Th and U, and negative Eu (δEu = 0.64–0.91), Nb, P and Ti anomalies. All samples have Mg# values of 40.3–51.2, Sr contents of 266–411 ppm and Sr/Y ratios of 9.11–29.6, negative whole-rock εNd(t) values (−6.6 to −5.1), high radiogenic Pb isotopic compositions, and high logfO2 values (−21.7 to −12.0). The integrated interpretation of geochemical data show that the Ningguo-Guangde granitoids were likely originated from Neoproterozoic crustal components mixing with metasomatized mantle-derived magmas. A comprehensive discriminant analysis indicates that metal-rich magma source, shallow fractional crystallization and high oxygen fugacity were favorable factors for the weakly fractionated I-type granite-related WMo mineralization in southern region of Anhui Province, eastern China. Furthermore, porphyry or skarn WMo deposits can be regarded as important exploration targets in the Ningguo-Guangde region.

High degree partial melting of the metasomatized mantle: A possible source for the Eocene-Oligocene porphyry Cu-Au-Mo deposits in Lut block, Eastern Iran

The small (<50 Mt) Eocene porphyry Cu-Au deposits of Maher abad and Khupic and the Oligocene Cu-Mo deposits of ChahShaljmi and DehSalam are attributed to the subduction of the Sistan ocean crust beneath the Lut block of eastern Iran. The calculated Ce4+/Ce3+ ratios of Dehsalm and ChahShaljami zircons are clustered around 10–50 and 75–155, and the values for Maher abad and Khupic are clustered around 120–300 and 50–150, respectively. The calculated logfO2 values indicate FMQ buffer conditions for Eocene and Oligocene magmas (ΔFMQ < 2; ΔFMQ −1.8 to + 0.6 ± ∼1.5 for ChahShaljami; ΔFMQ −1.3 to −0.4 ± ∼1.5 for Dehsalm, and ΔFMQ −3.2 to −2.1 ± ∼1.5 for Maher abad; ΔFMQ −2.6 to −1.3 ± ∼1.5 for Khupic), which never reached the ideal values of the worldwide giant to large porphyries (ΔFMQ < 4; HM buffer). The 30–60% partial melting of a slab (∼10–25% garnet) can explain ChahShaljami and Dehsalm, while it is > 60% partial melting of a slab (garnet > 50%) + ∼10% of metasomatized garnet-lherzolite (∼10% garnet) for Maher abad and Khupic. High partial melting of a slab has produced magma poor in copper in the magmatic subarc of the Lut block. Our zircon data and whole-rock geochemical characteristics of the Eocene and Oligocene ore-bearing intrusions along with the kinematics studies of the subduction zones are well consistent with a west-directed subduction system in eastern Iran. In such a system, a higher subduction rate > convergence rate causes deep steep subduction and in the continuation roll-back of the slab occurs in response to the opening and closing of the back-arc basin. This event caused the thinning of the Lut continental crust, mantle delamination and hot asthenospheric upwelling. The ascent of magmas resulting from the partial melting of a hydrous slab through a hot mantle and thinned continent caused widespread volcanism, and large amounts of water, sulfur and, volatiles were released to the atmosphere in an island arc regime during the middle-upper Eocene. The poor in metal low-volume magmas resulting from the high partial melting of a low water warm/hot deepest slab slightly metasomatized the mantle that subsequently amphibole-FC process with low contamination in the MASH zones and their emplacement during the transition from the island- to normal continental arc in the upper Eocene-Oligocene formed upper Eocene high-K calc-alkaline I/A-type (ferroan) arc magmatism and lower Oligocene adakite-like high-K calc-alkaline-Shoshonitic I-type (magnesian) arc magmatism, led to the formation of small Cu-Au and Cu-Mo porphyry deposits in Lut block, respectively. These events occur in a particular tectonic condition where subduction and collision were accompanied by rotation of the block affected by both Indo-Asian and Arabian-Eurasian collisions. Our study implies that W-directed subduction systems do not have favorable conditions for the formation of large porphyry deposits such as the ideal down-dip thermal gradient of the oceanic slab, water content, depth of dehydration, degree of partial melting of oceanic slab, and thickened continental crust.

Geochronology, petrogenesis and metallogenic implications of granitoids in the Xiaotuergen Cu deposit, Northern Chinese Altai Orogen, NW China: Constraints from zircon, apatite and whole-rock geochemistry

The Xiaotuergen Cu deposit is the first Cu deposit described in the Northern Chinese Altai Orogen, Xinjiang, NW China. The multiple phases of granitic intrusions occur in the Xiaotuergen region, including the intrusions of granodiorite porphyry, granite porphyry, and biotite monzogranite. Among these types of intrusions, Cu mineralization is considered to be closely related to the early Hercynian granodiorite porphyry. However, the precise emplacement ages, petrogenesis, redox states, and tectonic setting of the three Xiaotuergen granitoids and the relationship between these granitoids and mineralization was unclear. To resolve these issues, zircon U–Pb dates, zircon in situ trace element concentrations, Hf isotopic compositions, apatite in situ major element concentrations, and whole-rock geochemistry were determined in this study. Three different intrusive phases are recognized within the district; in order of deceasing age, these phases are biotite monzogranite, granodiorite porphyry, and granite porphyry, which have the ages of 400.2 ± 1.6 Ma to 399.6 ± 2.4 Ma, 390.3 ± 1.6 Ma to 377.1 ± 1.6 Ma, 381.0 ± 2.0 Ma to 378.7 ± 1.2 Ma, respectively, suggesting that they were emplaced during the Early-Middle Devonian. Geochemical data show that these intrusions are metaluminous to weakly peraluminous (A/CNK = 0.91–1.28), calc-alkalic to shoshonitic I-type granitoids. The two Harker plot trends reveal derivation from two magma sources (biotite monzogranite vs granodiorite porphyry and granite porphyry) that experienced different evolutionary processes. Multiple indicators, including the zircon Ce4+/Ce3+ ratio and oxygen fugacity (logfO2) values, apatite Mn oxybarometer, and whole-rock Fe2O3/FeO ratio, consistently indicate that the parental magma of the fertile granodiorite porphyry was more oxidized than that of the two barren intrusions (biotite monzogranite and granite porphyry). Furthermore, apatite grains from the fertile granodiorite porphyry have higher Cl contents and Cl/F ratios than those of the ore-barren biotite monzogranite and granite porphyry, which may have resulted from the higher water content of the parental magma and increased lithospheric mantle-derived fluid involvement in their generation. Thus, higher Cl/F ratios of apatite can be used to discriminate fertile granitoid intrusions that host Cu mineralization in the Northern Altai orogen. Zircon Hf isotopic compositions show widely ranging and mostly positive εHf (t) values (−4.2 to +11.4, mainly concentrated between +2 and +8). These isotope characteristics in combination with young zircon TDMC (Hf) ages (655–1,659 Ma; mainly concentrated between 850 Ma and 1250 Ma) indicate that the Xiaotuergen granitoids were most likely derived from the partial melting of juvenile lower crust, with some interaction of mantle materials from the underlying mantle wedge. The three Xiaotuergen granitoids were enriched in light rare earth elements and large ion lithophile elements, depleted in heavy rare earth elements, and showed negative Nb, Ta, Sr, P, and Ti anomalies, displaying typical arc geochemical affinities. Combined with the regional tectonic evolution, we propose that the Xiaotuergen granitoids were generated in a continental arc setting associated with subduction processes, which were the products of syn-accretion orogenic processes.

Petrogenesis of neoproterozoic Mo-bearing A-type granites in the Gattar area, northern Eastern Desert, Egypt: Implications for magmatic evolution and mineralization processes

Three Mo-bearing granitic intrusions, namely: Gattar, Abu Harba and Abu Marwa occur at the Gattar area in the North Eastern Desert of Egypt. These late tectonic granites intrude Neoproterozoic rocks of island arc metavolcanics and metagabbro-diorite complexes in addition to post-collision molasse-type sediments (Hammamat Group) and Dokhan-type volcanic rocks. U–Pb zircon geochronology yielded ages of 630 ± 27 Ma, 600.1 ± 8.5 Ma, and 601.1 ± 2.4 Ma for the Gattar, Abu Harba, and Abu Marwa granite intrusions, respectively.Whole-rock geochemical data showed the granites to be alkaline to peralkaline post-collision A-type granites. The three granite intrusions are considered co-magmatic as indicated by their similar ages and the continuous variation of major and trace elements on the variation diagrams. The inferred crystallization temperatures, as calculated from zircon geothermometry according to Watson et al. (2006), fall in the range of 616–690 °C, (average = 662 °C), 592–720 °C, (average = 653 °C), and 592–894 °C, (average = 706 °C) for the Gattar, Abu Harba, and Abu Marwa granite intrusions, respectively. This indicates that the Abu Marwa granite is the least evolved, followed by the Gattar and Abu Harba granites. The calculated logfO2 values for zircons from all the studied granites show highly oxidized magmatic features. The Abu Marwa granite (average logfO2 = −12.62) has the strongest oxidized state, whereas Gattar granite (average logfO2 is −15.46) and Abu Harba granite (average logfO2 = −15.99) have moderate logfO2 values implying moderate oxidized states. Guided by the tectonic evolution of the post-collision stage in the Arabian-Nubian Shield, it is suggested that the original magma of the granites in the Gattar area was formed by partial melting of an underplated crustal source, which had been fertilized by alkali-, HFSE-, and REE-rich fluids released and metasomatized by an underplating mantle-derived magma.Fractional crystallization and fluid differentiation/metasomatism were major processes in the petrogenetic evolution of these granite intrusions. Fluorine-complexing of HFSEs and REEs was involved in the early stages of fractional crystallization (i.e., crystallization of the Abu Marwa granite intrusion), resulting in a HFSE- and REE-rich residual melt that form the more evolved alkali feldspar granite of Gattar and Abu Harba intrusions. The late magmatic ore-forming fluids enhance the Gattar granite intrusion’s ability to become enriched in molybdenum relative to Abu Harba and Abu Marwa granites. The reason of the different degrees of molybdenite enrichment in the three intrusions depended on many factors (e.g., degree of fractionation and oxygen fugacity of the granitic magma).

Petrology and biotite geochemistry of Mengku granitoids in the Changning-Menglian suture zone, southwest China: Insights into magma evolution and Sn mineralization

The Changning-Menglian suture zone (CMSZ) is one of the major Sn metallogenic zones related to Triassic granitoids. However, the genetic relationship between magmatic petrogenesis and metallogeny is not well-constrained. Highly evolved granitoids are an important type of granitic rocks, given their close relationship with Sn mineralization. Here we provide monazite U-Pb data and comprehensive major-trace element (including halogen) data for biotites from the Mengku granitoids, to constrain their magma evolution and link to regional Sn metallogeny. Our U-Pb dating on monazite from the highly evolved granitoids yielded weighted mean age of 223.6 ± 1.4 Ma (n = 20, MSWD = 1.3). The new geochronologic results, coupled with recently reported ages from the Lincang batholith, suggest that most of the Lincang granitoids formed within a relatively consistent period at ca. 230–215 Ma. Geochemically, these Triassic granitoids can be divided into three groups. Group 1 granitoids display low Al2O3, P2O5, FeOT + MgO, Eu, Sr and Zr contents with high differentiation index (DI = 88–94) and A/CNK (1.07–1.17), consistent with the features of highly evolved granites. In contrast, Group 2 monzogranites and Group 3 dioritic enclaves have higher TiO2, P2O5, FeOT + MgO, Eu, Sr and Zr contents, comparable to I-type granites. All magmatic biotite grains are Mg-rich in composition (XMg = 0.44–0.60). A positive correlation between F and MnO contents in biotites from Mengku granitoids indicate that more evolved Group 1 magmas underwent fractional crystallization. The most evolved magmas (Group 1) have relatively low log(fH2O/fHF) values (4.34–5.05) and high log(fHF/fHCl) values (4.85–5.39), suggesting lower Cl contents and higher F contents than other magmas. Oxygen fugacities (logfO2) calculated from biotite equilibria for the Mengku granitoids are –22.2 to −17.7, straddling on the NNO and QFM buffers. Low log(fO2) values and positive correlation between Sn and log(fHF/fHCl) suggest that relatively reduced condition, highly evolved and F-rich granitic magmas are conducive to Sn mineralization in the CMSZ.

Geochronology and Geochemistry of the Granite Xenolith within the Lamprophyre at the Zhenyuan Gold Deposit (Yunnan Province, SW China)

AbstractThe xenoliths in host rocks of hydrothermal gold deposits can generally provide much geochemical information of the deep rocks, which may have an implication for the sources of ore‐forming materials. Geochronology and geochemical characteristics are reported for a granite xenolith, which is enclosed by the lamprophyre in the Zhenyuan gold deposit (Yunnan Province, SW China). This granite xenolith mainly consists of K‐feldspar, quartz, and plagioclase with trace amounts of magnetite, titanite, apatite, zircon, and sulfides. Zircons from the granite xenolith yield a weighted average U‐Pb age of 281.1 ± 1.3 Ma (MSWD = 2.1), which could represent the crystallization age of this granite xenolith. The Ti‐in‐zircon geothermometer and the Mn concentration in apatite calculate that this granite xenolith formed at 685 ± 43°C with the logfO2 values ranging from NNO + 3.7 to NNO + 6.4. The zircons in the granite xenolith have a restricted range of positive ∊Hf(t) values ranging from +9.4 to +10.8, and the corresponding Hf TDM2 model ages range from 588 to 678 Ma. The zircon U‐Pb age and the Hf isotopic compositions indicate this granite xenolith within the lamprophyre is mainly derived from partial melting of juvenile crustal rocks before the completed closure of the Ailaoshan Ocean. The pyrites in the granite xenolith have higher Bi concentrations, and lower As, Sb, and Tl concentrations than the gold‐bearing pyrites of the ores in the Zhenyuan gold deposit. The low Au concentrations of the pyrites together with the ore‐forming age of the Zhenyuan gold deposit (Oligocene) indicate the granite xenolith may have limited contribution to the gold mineralization of the Zhenyuan gold deposit.

Zircon trace elements and oxygen fugacities of parental magma of Maher abad and Khopik Cu porphyries, Lut block

The Maher abad and Khopik porphyry Cu deposits occurred in the Upper Eocene (39-37 Ma) in Lut block. All of them associated with intermediate (mostly monzonite) rocks. Porphyry deposits are closely associated with oxidized magmas. Oxygen fugacity (fO2) is a key factor that controls the formation of porphyry Cu deposits. The composition of the major and trace elements of zircon grains related to several ore-bearing monzonite were measured in Maher abad and Khopik porphyry copper indices. Zircon grains show moderate to low Ce4+/Ce3+ with a range of 19 to 610 and an average of 155. The average of oxygen fugacity (logfO2) values of Meher abad and Khopik ore-bearing magmas, range ∆FMQ -3.2 to MFMQ -1.3 with mean ∆FMQ -2.2, indicate formation under moderate oxidation conditions (between Ni-NiO (NNO) and Faylite magnetite-quartz (FMQ) buffers, but magnetite-hematite (HM) buffer, which ), which is not ideal for the formation of porphyry deposits. This is supported by whole-rock and Sr-isotopic data, and absence of high oxidation minerals such as hematite, and the poor adakitic charactristic of rocks in both deposits, which are due to factors involved in magma origin such as rock type and partial melting rate (possibly peridotite with low participation of slab).

Geochronology and geochemistry of the Late Jurassic Wujiaping Sn deposit, Dayishan ore field, South China: Implications to the petrogenesis and Sn mineralization

The Wujiaping Sn deposit is located at the northern Dayishan ore field, South China, whose ore veins are mainly hosted in the Dayishan pluton. LA–ICP–MS zircon U–Pb dating for the medium-fine grained- and medium-coarse grained-biotite monzogranite of Dayishan pluton yields emplacement ages of 154.5 ± 1.6 Ma (MSWD = 2.0) and 155.5 ± 0.5 Ma (MSWD = 1.9), respectively, which are consistent with the muscovite 40Ar-39Ar plateau age of 150.4 ± 0.9 Ma for the quartz vein type ore veins. It is indicated that the Sn mineralization in the Wujiaping deposit is related to the Late Jurassic granitic magmatism. These granites show the geochemical features of highly fractionated S-type granite: 1) low Zr + Nb + Ce + Y contents (<209 ppm); 2) high A/CNK ratios (>1.1); 3) low crystallization temperature (mean = 688 °C); 4) high Rb/Sr ratios (mostly > 48); 5) high differentiation index (DI > 90); and 6) low CaO, P2O5, Sr, and Eu contents. Whole rocks isotopes show that these granites shows variable initial 87Sr/86Sr ratios (0.70251–0.71208), negative εNd(t) values (−7.94–5.62) and old two stage Nd model ages of 1491–1563 Ma. LA–MC–ICP–MS zircon Lu–Hf isotopes show that the medium-fine-grained monzogranite have positive εHf(t) values of 0.37–8.5 and two stage Hf model ages of 662–1180 Ma, whereas the medium-coarse grained-biotite monzogranite have negative εHf(t) values of −6.42–3.55 and two stage Hf model ages of 1431–1599 Ma. It is proposed of that these granites are originated from melts mixed by crustal- and mantle-constituents and are formed in an extensional setting caused by the subduction of the Palaeo-pacific plate. The low LogfO2 values calculated through zircons (−21.2–13.1) and high F contents (3630–5120 ppm) indicate the granites derived from reduced and F-rich melts. Therefore, the reduced melt is highly fractionated and enriched in Sn and F, resulting in the large scale Sn mineralization in the Dayishan ore field.

Remelting of a Neoproterozoic arc root: origin of the Pulang and Songnuo porphyry Cu deposits, Southwest China

The reduced nature of the subducting slab has been used to explain the relatively poor endowment of economic porphyry copper deposits in Paleo-Tethyan arc systems. The presence of numerous porphyry Cu deposits in the southern Yidun terrane potentially challenges this model, because these deposits are thought to be the product of Paleo-Tethyan subduction. To investigate this, two representative deposits (i.e., Pulang and Songnuo porphyry Cu deposits) from the southern Yidun terrane have been studied. Zircon U-Pb ages of pre- and syn-mineral porphyries in Pulang are 221 ± 2 Ma (MSWD = 0.89) and 215 ± 2 Ma (MSWD = 1.50), respectively. Zircon and garnet U-Pb ages of the Songnuo syn-mineral porphyry are 217 ± 2 Ma (MSWD = 1.15) and 223 ± 5 Ma (MSWD = 0.97), respectively. The Pulang and Songnuo porphyries both have high whole-rock Sr/Y ratios with minor or no negative Eu anomalies, consistent with derivation from hydrous magmas that underwent minor early plagioclase crystallization but abundant amphibole fractionation. The two porphyry intrusions are characterized by high large-ion-lithophile elements (LILE: Th, U, Ba, Rb) abundances, and low concentrations of high-field-strength elements (HFSE: Nb, Ta, Ti, Zr, Hf). They have similar initial Sr isotope ratios from 0.7055 to 0.7073, ƐNd (t) values from − 4.3 to − 1.6 and zircon ƐHf (t) values of − 1.81 ± 1.34 (n = 47) that are distinct from published results for the Permian–Early Triassic Paleo-Tethyan arc granitoids in the Sanjiang region but similar to the Neoproterozoic arc intrusions in the nearby western Yangtze craton. The Pulang and Songnuo porphyries have relatively high zircon EuN/EuN* ratios (0.59 ± 0.04, n = 52) and calculated Δ log fO2 (FMQ) values (1.61 ± 0.23, n = 52), consistent with relatively oxidized magmas. This feature is similar to the published data for the Neoproterozoic arc intrusions (EuN/EuN* = 0.55 ± 0.08; Δ log fO2 (FMQ) = 2.14 ± 0.60), but distinct from the published data for the reduced normal Paleo-Tethyan arc magmas (EuN/EuN* = 0.29 ± 0.10; Δ log fO2 (FMQ) = − 0.68 ± 0.88). Given that the most recent tectonic reconstruction models suggest that the Paleo-Tethys Ocean closed before ~ 220 Ma, we propose that the Pulang and Songnuo porphyries Cu deposits were formed in a postsubduction setting from oxidized melts generated by reactivating the Neoproterozoic arc root, unrelated to Paleo-Tethyan subduction.

Constraints on Archean crust recycling and the origin of mantle redox variability from the δ44/40Ca – δ18O – fO2 signatures of cratonic eclogites

The nature of the deep calcium geochemical cycle through time is unresolved, in part due to the dearth of information about the calcium isotope composition of Archean recycled oceanic crust. Remnants of such ancient oceanic crust are preserved in the form of cratonic mantle eclogites, brought to surface as xenoliths in kimberlite magma eruptions. The δ44/40Ca of fresh mantle-derived eclogite xenoliths (i.e., garnet and omphacite mineral separates) from the Bellsbank kimberlite on the Kaapvaal craton in South Africa are presented here in combination with their trace element compositions, garnet Fe3+ contents and δ18O values.The studied Bellsbank eclogite xenoliths have geochemical compositions that indicate oceanic crustal protoliths, with bulk Al2O3 from 15 to 27 wt.%, Eu anomalies from 0.8 to 2.6 and, significantly, garnet δ18O values from +2.7 to +6.2‰. Garnet Fe3+/ΣFe contents yield logfO2(ΔFMQ) values between −4.0 and −1.2 for a depth range of 110–180 km, recording strong redox heterogeneity of the eclogite component within the Archean Kaapvaal mantle lithosphere. Reconstructed bulk eclogite MgO contents correlate negatively with fO2, suggesting that the redox compositions are related to magmatic differentiation during oceanic crust formation, excluding secondary metasomatic overprints. These data may thus emphasize that Archean basaltic oceanic crust had a similarly variable redox composition to modern MORB-type crust.Reconstructed bulk δ44/40Ca values for the Bellsbank eclogites range from +0.28 to +1.56‰. Although some of the xenoliths have δ44/40Ca values that overlap with the average mantle composition and modern MORB (+0.94 ± 0.1 and +0.83 ± 0.05‰), half of our dataset shows excursions to more extreme Ca isotopic compositions. Both higher and lower δ44/40Ca relative to mantle compositions are recorded by the eclogites, with a general negative correlation with δ18O suggestive of seawater-alteration of oceanic crust. The combined low δ44/40Ca (+0.28‰) and δ18O (+3.4‰) measured for one eclogite xenolith may record a subtle imprint by carbonate-rich mantle melts, which are known to contain isotopically light calcium contributed by recycled sediments. In contrast, the high δ44/40Ca of up to +1.56‰ for some eclogite xenoliths, coupled with strong LREE depletion, can be explained by calcium isotope fractionation during partial melting.The protracted history of recycled oceanic crust as probed by cratonic mantle eclogites is recorded by their highly variable δ44/40Ca–δ18O–fO2 signatures. Whereas some of this heterogeneity can be linked to processes that operated on the Archean ocean floor such as seawater-alteration of basaltic crust, other sources of compositional variability are introduced by loss and addition of melts during subduction recycling and mantle residence. The observed δ44/40Ca complexity of ancient recycled oceanic crust components at the scale of a single mantle-derived eclogite xenolith suite implies that mantle plume sourced intraplate magmas should reveal similarly strong calcium isotope variations contributed by apparently essential recycled crust components – as observed in the global oceanic island basalt record.

Petrogenesis and geodynamic setting of granitoids at Machangqing Cu–Mo (Au) deposit, western Yangtze craton, southwestern China: constraints from zircon U–Pb and molybdenite Re–Os geochronology, Lu–Hf isotopes, and geochemistry

The Machangqing Cu–Mo (Au) deposit is located in the central part of the Jinshajiang – Red River belt in the Sanjiang orogen, which lies across the Qiangtang terrane and western Yangtze craton, southwestern China. Zircon U–Pb dating constrains that the granite porphyry and porphyritic granite emplacements occurred at 35.92 ± 0.31 Ma and 34.92 ± 0.31 Ma, respectively. The Re–Os model ages of molybdenite are 34.94 ± 0.38 Ma. The new ages presented here, along with previously published data in the region, define a short duration of potassic magmatism and mineralization from 37 Ma to 34 Ma in the Jinshajiang – Red River belt. Zircon Ce4+/Ce3+ values of the porphyritic granite and granite porphyry vary from 50.32 to 1579.20 (averaging 481.01) and 33.18 to 1511.80 (averaging 452.98), respectively, and the log(fo2) values vary from –6.66 to −23.86 and −9.88 to −25.18, respectively, which plot within the range of the fayalite–magnetite–quartz buffer curve to the magnetite–hematite buffer curve, indicating an oxidized magma source, which may have facilitated the Cu–Au enrichment. Zircons from granitoids show εHf(t) values ranging from −0.75 to +2.33 and crustal model ages between 0.9 and 1.1 Ga. The features of Lu–Hf isotopes and wide range of Mg#, Cr, and Ni contents imply that the magmas of the Machangqing granitoids were probably derived from partial melting of juvenile lower crust and mixed with some mantle melts. Combined with the features of the Machangqing granitoids, the following evolution process are concluded. During the Cenozoic, the India–Asia continental collision triggered upwelling of hot asthenosphere and underplating of the thickened juvenile lower crust, which caused the formation of mafic and felsic magmas. Those magmas ascended, mixed, crystallized, and formed Machangqing ore-bearing granitoids in an intracontinental extension setting.

Primary magmatic biotite in granitoid intrusions associated with Late Mesozoic Jinchanggouliang-Erdaogou lode gold deposits, North China Craton: Linkage to gold mineralization

The Late Mesozoic Jinchanggouliang and Erdaogou lode gold deposits in the central segment of the northern North China Craton are mainly hosted in Late Archaean metamorphic rocks of the Jianping Formation and Jurassic volcanic-sedimentary rocks. These deposits are spatially and temporally associated with a series of I-type granitoid intrusions: i.e., the 128–136 Ma Duimiangou granodiorite complex with a massive margin and a porphyritic center at Jinchanggouliang, the 161.4 ± 1.1 Ma Loushang quartz diorite intrusion and numerous syenite porphyry dykes (160.9 ± 1.0 Ma) at Erdaogou, and the ~ 227–217 Ma Xitaizi monzogranite batholith. Compositions of primary magmatic biotite in these granitoid intrusions have been used to investigate the nature of granitoid magmas and the evolution of magmatic processes and to identify possible linkages between gold mineralization and granitoid magmatism. All primary magmatic biotite grains are Mg-rich in composition (XMg = Mg/(Mg + Fe) = 0.41–0.69). The Cl contents of biotite (0.09–0.42 wt%) in the Loushang quartz diorite and the Duimiangou massive granodiorite correlate negatively with XMg and are consistent with the “Mg-Cl avoidance” rule. The Cl contents of biotite (0.01–0.14 wt%) in the Duimiangou porphyritic granodiorite, syenite porphyry and Xitaizi monzogranite, on the other hand, remain relatively constant and may be affected by multiple variables such as Cl-rich fluids and subtle changes in temperature. Halogen fugacity of the parental magma calculated from biotite shows that the Duimiangou granodiorite complex at Jinchanggouliang and syenite porphyry dykes at Erdaogou have the log(fHF/fHCl) ranges of −0.71 to −0.27 and −2.16 to −1.08, respectively, and have similar log(fH2O)/(fHCl) values from 3.53 to 4.23. Oxygen fugacities (logfO2) calculated from biotite equilibria for the Duimiangou granodiorite complex and syenite porphyry dykes are −13.7 to −7.2, straddling on the nickel-nickel oxide and hematite-magnetite buffers. The Xitaizi monzogranite and the Loushang quartz diorite have lower log(fO2) values from −14.9 to −12.4, between the nickel-nickel oxide and hematite-magnetite buffers. The Duimiangou granodiorite complex and syenite porphyry dykes with high oxygen fugacities are similar to oxidized magmas associated with porphyry Cu-Mo-Au deposits. These results suggest that multiple episodes of I-type granitoid magmas in the study area were rich in Cl and high in oxygen fugacity, especially those associated with the Duimiangou granodiorite complex and syenite porphyry dykes. The I-type melts represented by the Duimiangou granodiorite complex and syenite porphyry dykes as well as their related Cl-rich, oxidizing fluids were likely efficient in dissolving, transporting and precipitating gold for the formation of the Jinchanggouliang and Erdaogou lode gold deposits.