Diorite Porphyry Research Articles

Geology and origin of the Zhunuo porphyry copper deposit, Gangdese belt, southern Tibet

The Zhunuo porphyry copper deposit in the Gangdese belt of southern Tibet contains 2.37 Mt at 0.57% Cu. In this deposit, Eocene rhyolite (51.6 ± 1.0 Ma) and quartz porphyry (49.1 ± 0.6 Ma) were intruded by monzogranite (14.7 ± 0.3 Ma) and monzogranite porphyry (14.5 ± 0.2 Ma) which commonly host mafic microgranular enclaves (14.9 ± 0.3 Ma). Late-mineralization diorite porphyry (14.2 ± 0.2 Ma) and post-mineralization lamprophyre dikes (12.2 ± 0.1 Ma) and granite porphyry (12.0 ± 0.2 Ma) crosscut the Miocene intrusions. Two quartz–molybdenittie veins yielded molybdenite Re-Os model ages of 14.8 ± 0.1 Ma and 14.4 ± 0.1 Ma, and another two quartz–muscovite–llite–pyrite–molybdenite veins yielded molybdenite Re-Os model ages of 14.2 ± 0.1 Ma and 13.5 ± 0.1 Ma. Zhunuo is characterized by early potassic alteration and associated quartz A veins centered on the monzogranite porphyry and adjacent monzogranite, distal propylitic alteration in the rhyolite, and late-stage phyllic alteration and associated quartz B veins, followed by D veins that affected quartz porphyry and potassic-altered rocks. Copper ores are mainly distributed in the potassic alteration zone that was overprinted by phyllic alteration. Copper mineralization likely occurred during potassic alteration stage and was locally remobilized and redeposited during phyllic alteration stage, or occurred during phyllic alteration stage. The post-mineralization granite porphyry has lower whole-rock Sr/Y ( 40; eNd(t) = − 6.9 to − 6.1; U/Yb = 1 to 10). Limited input of juvenile melts could explain the low potential for copper mineralization in the post-mineralization granite porphyry at Zhunuo.

Intraplate adakite-like rocks formed by differentiation of mantle-derived mafic magmas: A case study of Eocene intermediate-felsic porphyries in the Machangqing porphyry Cu-Au mining district, SE Tibetan plateau

Intraplate intermediate-felsic adakite-like rocks are widely considered to be generated via partial melting of the mafic lower crust. However, the genesis of phenocrysts of mafic minerals from some adakite-like rocks suggests that they can originate from mantle-derived magmas through assimilation and fractional crystallization (AFC) processes. In this study, we investigated the petrogenesis of three phases of Eocene porphyries, namely quartz diorite porphyry (QDP-I and QDP-II), granodiorite porphyry (GDP), and granite porphyry (GP), exposed in the Machangqing area of the western Yangtze Craton in the southeastern Tibetan plateau. These porphyries were formed at 34.2–35.2 Ma in an intracontinental extension setting and present adakitic affinities of high Sr/Y (50–95) and La/Yb (50–113) ratios. The similar characteristics of these Machangqing porphyries in terms of whole-rock trace elements and Sr–Nd isotopes, as well as in the mineralogy of amphibole phenocrysts and clinopyroxene antecrysts, indicate that these intermediate-felsic porphyries were derived from the same source. The important observation for investigating the parental magma of these intermediate-felsic porphyries is that they have close temporal and spatial correlations with mantle-derived mafic volcanic rocks. These intermediate-felsic porphyries have slightly enriched Sr–Nd isotopic compositions [(87Sr/86Sr)i = 0.7068–0.7077, εNd(t) = −5.1 to −6.6], affected by limited crustal assimilation, as compared to those of contemporaneous mafic volcanic rocks. The high-Al amphibole phenocrysts and clinopyroxene antecrysts in QDP-I have similar rare earth element (REE) patterns with clinopyroxene phenocrysts in the mafic volcanic rocks, which suggest that these rocks originated from the same mantle-derived mafic magma. In addition, the major elements of these intermediate-felsic and mafic igneous rocks in the Machangqing area show fractional crystallization trends with an increasing magma silica component. Simulations of the major and trace elements of these igneous rocks show that the sequence of fractional crystallization of olivine, clinopyroxene, garnet, amphiboles, biotite, feldspar, and apatite with time promoted the evolution of the magma series. As revealed by the calculated physicochemical conditions during crystallization of the phenocrysts, the initial mafic magmas were derived from depths of greater than 64 km through the partial melting of the metasomatic lithosphere mantle induced by Eocene intraplate extension in the western Yangtze Craton. These initial mafic magmas underwent three stages of fractional crystallization at three levels of the thickened crust: the first at the base of the lower crust (49–55 km); followed by fractional crystallization at the middle crust (24–32 km); and finally at the upper crust (4–5 km). These fractional crystallization processes caused the initial mafic magmas to evolve through the intermediate (roughly represented by QDP-I) to the felsic compositions (GDP and GP). Whole-rock and mineral geochemistry evidence demonstrates that fractional crystallization of mantle-derived magmas, with a small amount of crustal assimilation, generated these Eocene intraplate intermediate-felsic adakitic porphyries in the Machangqing area.

Early Cretaceous Wulong intermediate-mafic dike swarms in the Liaodong Peninsula: Implications for rapid lithospheric delamination of the North China Craton

The North China Craton (NCC) underwent a dramatic change in the lithospheric architecture, and more than 100 km of the ancient and refractory lithospheric mantle was removed. However, the timing and mechanism of the lithospheric thinning remain controversial. New zircon UPb ages and whole-rock/in-situ geochemical and isotopic data of the Early Cretaceous intermediate-mafic dike swarms in the Liaodong Peninsula have been carried out to decipher the timing and mechanism of lithospheric thinning of the NCC. The dike swarms are chemically subdivided into the ca. 126 Ma diorite porphyry and coeval (ca. 119 Ma) low-Ti (TiO2 < 1.20 wt%, Ti/Y < 375) and high-Ti (TiO2 > 1.90 wt%, Ti/Y > 580) diabase dikes. The diorite porphyries exhibit a moderate silica (56.71–61.13 wt%) and high-K calc-alkalic signature, with low TiO2 and total Fe2O3 and high Cr and Ni compositions. They are enriched in large ion lithophile elements (LILEs) (e.g., Rb, K, Pb, and Sr) and depleted in high field strength elements (HFSEs) (e.g., Nb, Ta, Ti, and P). They have high radiogenic Sr isotopes (whole-rock (87Sr/86Sr)i = 0.711553–0.714284, in-situ (87Sr/86Sr)i of plagioclase = 0.71392), low εNd(t) values (−19.9 to −14.5), and old Nd model ages (1.81–2.25 Ga). Meanwhile, some plagioclase phenocrysts have reverse zonings with Na-rich cores (An: 35–48) and Ca-rich rims (An: 48–57). These features imply that the diorite porphyries were generated by mixing between magmas from the Archean–Paleoproterozoic lower crust and the lithospheric mantle. The low-Ti diabase dikes are characterized by medium to high-K calc-alkaline series with high Al2O3 but low TiO2 contents. They show arc-like trace element signatures, such as enrichment in LILEs (Rb, K, Pb, and Sr) and depletion in HFSEs (Nb, Ta, Zr, Hf, Ti, and P). They also have relatively lower initial 87Sr/86Sr ratios (0.706331–0.708315 and 0.70837 for the whole-rock and in-situ Sr isotopes, respectively) compared to the porphyries and negative εNd(t) values (−13.6 to −5.0), indicating that they were derived from partial melting of an enriched lithospheric mantle. Their variable Th/Yb and Th/Nb ratios with constant Sr/Nd and U/Th values further suggest that the mantle source might have been previously modified by the subduction-related melt. In contrast, the high-Ti diabase dikes belong to the high-K calc-alkaline to shoshonitic series, with higher TiO2 and total Fe2O3 but lower Al2O3 contents. They have OIB-like trace elements (e.g., slight enrichments of Nb and Ta with no HFSE depletion, high Nb/U values (42 ± 5)) and SrNd isotopic compositions (e.g., positive whole-rock εNd(t) values (+3.1 to +4.3)), suggesting that they were generated from an asthenospheric mantle source. The coexisting Wulong low-Ti and high-Ti mafic dikes with similar formation ages (ca. 119 Ma) may indicate a transition from lithospheric to asthenospheric mantle source. In combination with previous studies on the Mesozoic–Cenozoic mafic rocks in the Eastern Block of the NCC, we propose that the lithospheric thinning beneath the Liaodong Peninsula initiated at ca. 119 Ma and this process beneath the NCC lasted for a narrow duration (ca. 13 Ma). The unsteady mantle flows due to the rapid subduction and rollback of the Paleo-Pacific plate might trigger the thickened, modified lithosphere to lose its gravitational stability, eventually leading to lithospheric delamination and thinning of the NCC.

Petrogenesis of Late Carboniferous intrusions in the Linglong area of Eastern Tianshan, NW China, and tectonic implications: Geochronological, geochemical, and zircon Hf–O isotopic constraints

The Linglong porphyry Cu deposit is located in the Dananhu–Tousuquan Arc Belt, adjacent to the large Tuwu–Yandong Cu deposits in Eastern Tianshan, northwest China. In this study, zircon U–Pb, whole rock geochemistry, and zircon Hf–O isotopic analyses were carried out on the Linglong intrusions (i.e., quartz albite porphyry and diorite porphyry). New SIMS zircon U–Pb dating and previous data indicate that the quartz albite porphyry occurred in the Late Carboniferous (318.6 ± 3.0 Ma), younger than emplacement of the diorite porphyry (338–340 Ma) and tonalite porphyry (332–335 Ma) in this area, as well large-scale copper mineralization (331–335 Ma) in Eastern Tianshan. The geochemistry of the quartz albite porphyry intrusions is consistent with calc-alkaline normal arc magmatism, characterized by high SiO2 (74.82–77.89 wt%), obvious Eu anomalies (0.42–0.52), high Y (21–25.9 ppm) and Yb (2.98–3.67 ppm) concentrations, moderate Mg# values (35–40), but relatively low Sr/Y (6.86–9.52)and low 10,000 Ga/Al values. In situ Hf–O isotopic analyses on zircons show that the quartz albite porphyry rocks have variable εHf(t) (+9.0 to + 13.9) and low δ18O values (4.72 to 5.84‰), suggesting a juvenile lower crust derived composition. However, the diorite porphyry intrusions show features of low SiO2 (57.51–61.12 wt%), minor Eu anomalies (0.82–1.15), strong depletion in high field strength elements (e.g., Nb, Ta, P and Ti), but enrichment in large ion lithophile elements (e.g., Rb, Ba, K and Pb). They also exhibit normal island arc magma geochemical signatures, with high Y (20.9–40.2 ppm), and Yb (2.75–4.64 ppm) concentrations, high Mg# (40–51), and relatively low (La/Yb)N (2.07–4.10) and Sr/Y (5.75–12.13) values, suggesting the melt was derived from the subduction-modified mantle mafic to ultramafic materials. Combined with regional tectonic evolution and our new data, we suggest that the Late Carboniferous magma was generated during the period of the northward subduction of the Paleo-Tianshan ocean plate beneath the Dananhu–Tousuquan island arc.

Early orogenic gold mineralization event in the West Qinling related to closure of the Paleo-Tethys Ocean – Constraints from the Ludousou gold deposit, central China

The West Qinling Orogen experienced a complex orogenic history and developed related orogenic gold deposits. Most known orogenic gold deposits in West Qinling are hosted by brittle to ductile shear zones and mainly formed during 220–190 Ma. The Ludousou gold deposit, located in the northwesternmost segment of West Qinling, has breccia gold ores controlled by E-W, NE-, NW-, and N-S trending faults, and is hosted by tuff and quartz diorite porphyry. Uranium-Pb zircon investigations indicate that tuff and quartz diorite porphyry were emplaced at 252.9 ± 4.1 Ma and 247.0 ± 2.2 Ma. Magmatic apatites from the same quartz diorite porphyry crystallized at 243.5 ± 4.8 Ma indicating a rapid cooling history. Hydrothermal sericite coexisting with gold-bearing pyrite and arsenopyrite from mineralized quartz diorite porphyry provided 40Ar/39Ar plateau and inverse isochron ages of 235.68 ± 0.29 Ma and 235.61 ± 0.41 Ma. Hydrothermal apatite separated from the same mineralized quartz diorite porphyry yielded concordant U-Pb age of 235.7 ± 4.9 Ma. Such data bracketed that the Ludousou gold mineralization event occurred at ca. 236 Ma postdating the 252–247 Ma magmatism by approximately 8–11 million years. Combined present field observations and geochronological data with sulfur isotopic and fluid inclusion investigations in literatures, we therefore propose that ore-forming fluids may not be derived from ore-hosting tuff and quartz diorite porphyry, and such rapid cooled host-rocks might even provide little heat source during ore formation. The Ludousou gold deposit is best classified as an orogenic gold deposit, and probably can extend the orogenic gold mineralization event in the West Qinling related to closure of the Paleo-Tethys Ocean tracing back to ca. 236 Ma.

Reduced fluids in porphyry copper-gold systems reflect the occurrence of the wall-rock thermogenic process: An example from the No.1 deposit in the Xiongcun district, Tibet, China

High fO2 conditions characterize the majority of global porphyry copper deposits and contain highly oxidized minerals, such as magnetite and anhydrite. In contrast, the No. 1 porphyry Cu–Au deposit in the Xiongcun district (Tibet, China) has abundant pyrrhotite, reduced fluids (CH4 ≫ CO2), and a relative lack of highly oxidized minerals, which are indicative of low fO2 conditions. Scanning electron microscopy, fluid inclusion, C–H–O–He–Ar isotopes, and whole-rock organic carbon contents and isotope analysis were used to constrain the evolution of ore-forming fluid, the origin of CH4 and metal deposition mechanisms for the No. 1 deposit. The He–Ar isotopic compositions (3He/4He = 0.11–0.96 Ra, 40Ar/36Ar = 418.7–2920.2) suggest that the ore-forming fluids predominantly derived from crust source with minor mantle input. The H–O isotopic analysis results (δ18OH2O = −1.8 to +5.2‰, δD = −106 to −89.9‰) indicate that the ore-forming fluids were derived from a magmatic source that mixed with some meteoric waters. The element compositions of zircons and fluid/melt inclusions from the mineralized Middle Jurassic quartz diorite porphyry reveal that the primary magma was characterized by high log fO2 (>NNO) conditions. The quartz diorite porphyry intruded into the carbon-bearing wall rocks produced abundant CH4 by thermal decomposition of organic matter (δ13CCH4 = −26.3 to −28.5‰), which changed the redox state of the porphyry copper system from oxidized to reduced condition. Ore elements were deposited via fluid boiling as a consequence of the rapid decrease in temperature and pressure.

Late Palaeozoic tectonic evolution of North Tianshan Orogenic Belt: Perspectives from geochronology and geochemistry of the Tulasu pluton in the Tulasu Basin

The Tulasu pluton is located in the northeast of the Tulasu Basin, North Tianshan, which is composed of three rock types including quartz diorite porphyry, pyroxene diorite porphyry, and granite. Zircon U‐Pb dating indicates that the quartz diorite porphyry and pyroxene diorite porphyry were crystallized in the Late Devonian (with ages at 360.3 ± 7.8 and 375.4 ± 6.2 Ma, respectively), while the granitic rocks was formed in the Late Carboniferous (at 305.9 ± 5.9 Ma), suggesting that the Tulasu pluton was the product of two magmatic episodes. The Late Devonian quartz diorite and pyroxene diorite porphyry are metaluminous and belong to calc‐alkaline to high‐K calc‐alkaline series. Quartz diorite porphyry and pyroxene diorite porphyry are characterized by the prominent enrichment in LILEs, such as Rb, Th, U, and K, and depletion in HFSEs, such as Nb, Ta, P, and Ti, which is similar to typical subduction‐related arc magma. The εHf(t) values of quartz diorite porphyry and pyroxene diorite porphyry are +4.5–+8.8 and +2.0–+6.4, respectively, indicating that they are derived from depleted mantle wedge. Their TDM2 ages are 814–1,087 Ma and 955–1,227 Ma, respectively, which shows that the Mesoproterozoic to the Neoproterozoic crustal materials were involved. Their high Ba/La (10.26–17.92), low Th/Yb (1.96–5.80), and relatively low Ce/Th (3.16–7.34) and Ba/Th (18.29–38.92) ratios indicate that they were probably produced by partial melting of depleted mantle wedge metasomatized by slab‐derived aqueous fluids, with involvement of subducted sediment. Geochemical characteristics indicate that the Late Devonian dioritic magma was generated in an arc‐related tectonic setting. The Late Carboniferous granitic rocks were composed of granodiorite porphyry and granite porphyry. The granodiorite porphyry samples are high‐K calc‐alkaline and peraluminous, while the granite porphyry samples are in the boundary zones of shoshonite and high‐K calc‐alkaline, as well as metaluminous and weakly peraluminous. Granodiorite porphyry shows features of I‐type granite, while granite porphyry has the characteristics of A‐type granite. High 176Hf/177Hf ratios (0.282600–0.282833) and εHf(t) values (+0.4–+8.7) indicate that granitic rocks have affinities with both depleted mantle and crust. Geochemical characteristics suggest that the Late Carboniferous granitic magma was formed in post‐collisional setting.

Metallogenic potential of porphyries in Tulasu basin, Northwest Tianshan: Insight from magma nature and crustal thickness

Tulasu basin in Northwest Tianshan hosts a lot of Late Paleozoic epithermal deposits, such as Axi, Jingxi-Yelmand, and Tawuerbieke deposits. Epithermal deposits are considered as telescoped systems of porphyry deposits. However, porphyry deposits are not discovered in Tulasu basin, though granitoid porphyries are widespread in this region. Tulasu pluton complex, as one of the largest intrusions located in northeast part of Tulasu basin, is composed of the Late Devonian quartz diorite porphyry and pyroxene diorite porphyry, and the Late Carboniferous granodiorite porphyry and granite porphyry. The metallogenic potential of each rock type is evaluated in terms of magma nature and crustal thickness of source. The magma nature including magmatic oxygen fugacity and water content is estimated based on trace elements compositions of zircons, amphibole hygro-barometer and ilmenite-magnetite mineral pairs. The mean Ce4+/Ce3+ ratio, magmatic oxygen fugacity and water content of the Late Devonian quartz diorite porphyry are 291, ΔFMQ = 1.0–1.8, ΔFMQ = −0.2–1.5 and 0.9–2.2 wt%, respectively, while those of pyroxene diorite porphyry are 96, ΔFMQ = 2.6–3.3 and 0.2–1.3 wt%. The Late Carboniferous granodiorite porphyry has a mean Ce4+/Ce3+ ratio of 138. The crustal thicknesses in the Tulasu area are estimated to be 30–35 km at the Late Devonian and ~40 km at the Late Carboniferous, based on whole rock geochemistry of the Late Devonian dioritic rocks and the Late Carboniferous granitic rocks. Considering magmas associated with typical porphyry deposits which have high oxygen fugacity of ΔFMQ = +1.5 to +3 and water content (>4.5 wt%), and are derived from crustal thickness of >30 km, we think both dioritic and granitic rocks of Tulasu porphyries have favorable conditions of oxidation state and crustal thickness for porphyry deposit formation. However, the magmatic water contents of these rocks are relatively low. Therefore, the Tulasu porphyries have low potential in forming porphyry Cu deposits.

Age and Tectonic Setting of Mesothermal Magmatic Hydrothermal Vein‐Type Pb–Zn–(Ag) Mineralization in the Xiaohongshilazi Deposit, Central Jilin Province, Northeast China

AbstractThe Xiaohongshilazi deposit located in central Jilin Province, Northeast China, is a newly discovered and medium‐scale Pb–Zn–(Ag) deposit with ore reserves of 34,968 t Pb, 100,150 t Zn, and 158 t Ag. Two‐stage mineralization has been identified in this deposit. Stratiform volcanic‐associated massive sulfide (VMS) Pb–Zn mineralization interbedding with the marine volcanic rocks of the Late Carboniferous–Early Permian Daheshen Formation was controlled by the premineralization E–W‐trending faults. Vein‐type Pb–Zn–(Ag) mineralization occurs within or parallel to the granodiorite and diorite porphyries controlled by the major‐mineralization N–S‐trending faults that cut the stratiform mineralization and volcanic rocks. To constrain the age of vein‐type Pb–Zn–(Ag) mineralization and determine the relationship between mineralization and magmatism, we conducted LA–ICP–MS U–Pb dating on zircon from the ore‐bearing granodiorite and diorite porphyries and Rb–Sr dating on metal sulfide. Granodiorite and diorite porphyries yield zircon U–Pb weighted‐mean 206Pb/238U ages of 203.6 ± 1.8 Ma (Mean Standard Weighted Deviation [MSWD] = 1.8) and 225.6 ± 5.1 Ma (MSWD = 2.3), respectively. Sulfides from four vein‐type ore samples yield a Rb–Sr isochron age of 195 ± 17 Ma (MSWD = 4.0). These results indicate a temporal relationship between the granodiorite porphyry and vein‐type Pb–Zn–(Ag) mineralization. The granodiorite associated with vein‐type mineralization has high SiO2 (68.99–70.49 wt.%) and Na2O (3.9–4.2 wt.%; Na2O/K2O = 1.07–1.10) concentrations, and A/CNK values of 0.95–1.04; consequently, the intrusion is classified as a high‐K, calc‐alkaline, metaluminous I‐type granite. The granodiorite porphyry is enriched in large‐ion lithophile elements (e.g. Rb, Th, U, and K) and light REE and is depleted in high‐field‐strength elements (e.g. Nb, Ta, P, and Ti) and heavy REE, indicating that it represents a subduction‐related rock that formed at an active continental margin. Furthermore, the granodiorite porphyry has Mg# values of 31–34, indicating a lower crustal source. Based on petrological and geochemical features, we infer that the ore‐bearing granodiorite porphyry was derived from the partial melting of the lower crust. In summary, mineralization characteristics, cross‐cutting relationships, geochronological data, and regional tectonic evolution indicate that the region was the site of VMS Pb–Zn mineralization that produced stratiform orebodies within the Late Carboniferous–Early Permian marine volcanic rocks of the Daheshen Formation, followed by mesothermal magmatic hydrothermal vein‐type Pb–Zn–(Ag) mineralization associated with granodiorite porphyry induced by the initial subduction of the Paleo‐Pacific Plate beneath the Eurasia Plate during the Late Triassic–Early Jurassic.

Mineral chemistry of magmatic and hydrothermal biotites from the Bangpu porphyry Mo (Cu) deposit, Tibet

The Bangpu deposit, located in the eastern part of the Gangdese porphyry copper belt, Tibet, is a porphyry Mo (Cu) deposit in a continental collisional orogenic belt. The Mo (Cu) mineralization occurs mainly in monzogranite porphyry, whereas the Cu (Mo) mineralization occurs mainly in diorite porphyry. Most magmatic and hydrothermal biotites from the Bangpu deposit are Mg-rich, plotting in the phlogopite and Mg-biotite compositional fields. The Bangpu magmatic biotite has high BaO (>0.1 wt%) and TiO2 (>3 wt%), while the hydrothermal biotite has low BaO (<0.1 wt%) and TiO2 (<3 wt%). Hydrothermal biotite from the Bangpu Mo (Cu) mineralization system has higher Al2O3, SiO2, MgO, K2O, Na2O and F contents and lower TiO2, FeOtot, MnO and Cl contents than hydrothermal biotite from the Cu (Mo) mineralization system. Crystallization temperatures range from 757 °C to 827 °C and 687 °C to 740 °C for magmatic biotite in monzogranite porphyry and biotite monzogranite, respectively. Hydrothermal biotite geothermometry yields a temperature range from 362 °C to 547 °C for the Mo (Cu) mineralization system and 302 °C to 410 °C for the Cu (Mo) mineralization system. Calculated oxygen fugacity, relative F and Cl contents, and fugacity ratios indicate that the Cu (Mo) and Mo (Cu) mineralization systems formed from different magmatic-hydrothermal fluids. The Mo (Cu) mineralization system formed from F-rich high oxygen fugacity (above NNO) magmatic-hydrothermal fluids favorable for extracting Mo from the melt and transporting Mo, whereas the Cu (Mo) mineralization system formed from Cl-rich high oxygen fugacity (above NNO) magmatic-hydrothermal fluids favorable for extracting Cu from the melt and transporting Cu. The Bangpu porphyry Mo (Cu) deposit is the result of two different superimposed magmatic-hydrothermal fluids.

A genetic link between iron oxide-apatite and iron skarn mineralization in the Jinniu volcanic basin, Daye district, eastern China: Evidence from magnetite geochemistry and multi-mineral U-Pb geochronology

Abstract Various styles of ore deposits may form from a single magmatic-hydrothermal system. Identification of a possible genetic link between different ore types in a region is not only of critical importance for a better understanding of the magmatic-hydrothermal processes, but can also help in successful mineral exploration. Both iron oxide-apatite (IOA) and iron skarn deposits are closely associated with intrusive rocks of intermediate to felsic in composition, but whether these two ore types can form from the same magmatic intrusion remains poorly understood. In this study, we present a comparative study between a newly identified subsurface IOA ore body located at the apex of a diorite porphyry and the iron skarn ore bodies located immediately above it in the Jinniu volcanic basin of the Daye district, Middle-Lower Yangtze River metallogenetic belt (MLYRMB), eastern China in order to highlight a genetic link between these two styles of mineralization. The IOA ores are dominated by Ti-rich magnetite with variable amounts of fluorapatite, diopside, and actinolite. This mineralogical assemblage is distinctly different from the iron skarn ores, which consist mainly of Ti-depleted magnetite and subordinate pre-ore garnet and diopside, and post-ore quartz, chlorite, calcite, and pyrite. In addition, magnetite from the IOA ores is characterized by well-developed ilmenite lamellae and has high concentrations of Ni, V, Co, and Ga, consistent with high temperature crystallization, whereas magnetite grains from the iron skarn ores usually exhibit oscillatory growth zones and contain much lower Ni, V, Co, and Ga, indicating their formation under relatively low temperatures. Titanite and fluorapatite from the IOA ores have U-Pb ages of 132.5 ± 2.4 Ma to 128.4 ± 3.0 Ma, which match a titanite U-Pb age for the associated iron skarn ores (132.3 ± 2.0 Ma), and are consistent with zircon U-Pb ages for the ore-hosting diorite porphyry (130.4 ± 0.7 Ma to 130.3 ± 0.5 Ma). This age consistency supports a possible genetic link among the diorite porphyry, IOA ores, and iron skarn ores. We propose that the IOA and skarn ores are the products of two consecutive mineralization stages of the same magmatic-hydrothermal system, involving a high-temperature, hypersaline fluid coexisting with the diorite porphyry magma during emplacement and a subsequent low temperature, diluted hydrothermal fluid. Other IOA and iron skarn deposits of similar ages (130 Ma) are found in a series of volcanic basins in the MLYRMB, which forms one of the world’s largest IOA metallogenic belts. The close association of the two ore styles identified at Daye provides a useful exploration guide for IOA and iron skarn deposits both on a local and regional scale.

Geochronology, geochemistry, and Pb–Hf isotopes of mineralization-related magmatism in the Dongyang gold deposit, Fujian Province, southeastern China

The recently discovered Dongyang low-sulphidation epithermal Au deposit is located in Fujian Province. The Au mineralization hosted in rhyolite porphyry and the Lower Jurassic Nayuan Formation continental volcanic rocks is considered to be related to intermediate–acidic intrusions (rhyolite porphyry, quartz diorite porphyry, and dacite porphyry). The zircon U–Pb ages of these samples are 160.3 ± 0.8, 156.6 ± 0.8, and 154.1 ± 0.6 Ma, respectively, and the sulphide Rb–Sr isotope isochron age is 152.4 ± 1.7 Ma, indicating a temporal link between porphyry emplacement and Au mineralization. Porphyries are enriched in large-ion lithophile elements and light rare earth elements and slightly depleted in heavy rare earth elements and high field strength elements, belong to the high-potassium calc-alkaline or shoshonitic series, and show characteristics of volcanic arcs or active continental margins. Moreover, the εHf(t) values of the porphyries range from −11.6 to −7.6, −11.2 to −5.4, and −9.8 to −4.6, respectively. The 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb values of the ore minerals are from 38.417 to 38.406, 15.603, and from 18.179 to 18.175, respectively. Pb and Hf isotopes indicate that the intermediate–acidic magma related to mineralization originated from Mesoproterozoic lower crust. Consequently, these data favour an intermediate–acidic magma origin for Au mineralization in the Dongyang deposit. Integrating new and published data on the tectonic evolution, we suggest that the rhyolite porphyry, quartz diorite porphyry, dacite porphyry, and associated Au mineralization in the Dongyang deposit formed at 160–152 Ma in an extensional environment related to subduction of the Palaeo-Pacific Plate beneath the South China block.

Fluid inclusion and isotope evidence for magmatic-hydrothermal fluid evolution in the Tuwu porphyry copper deposit, Xinjiang, NW China

The Tuwu deposit (557 Mt at 0.58% Cu) is the most typical and economically significant one of several porphyry copper deposits in the Dananhu-Tousuquan Arc Belt near the Turpan-Hami Basin, northwest China. The mineralization occurs as chalcopyrite and minor bornite in quartz-bearing veins and host porphyries (i.e. diorite porphyry and tonalite porphyry), and is closely associated with potassic (e.g. K-feldspar, magnetite, and hematite) and phyllic (e.g. sericite, pyrite, albite and chlorite) alterations. Fluid inclusions were studied in different generations of quartz, defined as QzIA+IB, QzII, QzIII, and QzIV. Four types of fluid inclusions were recognized, namely liquid-rich biphase (L0), vapor-rich biphase (V0) and triphase (V1, with one opaque mineral), as well as brine-rich (B0; with or without an opaque mineral) inclusions. Based on fluid inclusion microthermometry using FIA method, the fluids associated with QzIB (early ore stage) are characterized by relatively high temperatures (306–458 °C) and salinities (50.3–62.1 and 6.5–22.6 wt% NaCl + CaCl2 equiv. for B0 and L0 inclusions, respectively), under lithostatic pressure of 167 to 444 bars (depth of 0.6–1.6 km), and the fluids associated with QzII and QzIII (main ore stage) have progressively decreasing temperatures from 201° to 345 °C, under hydrostatic pressure of about 90 bars (depth of 0.9 km), which induced to large-scale mineralization at Tuwu. Mineralogy and physicochemical calculations suggest that the early stage occurred at alkaline and high-oxidized fluid environment (pH = 9.6 to 11.5; logfO2 = −26.4 to − 24.3), whereas the main ore stage took place at acidic and low-oxidized conditions (pH = 4.0 to 5.0; logfO2 = −30.8). The fluids associated with QzIV (late ore stage) show low homogenization temperatures (<204 °C) and salinities (0.6–4.2 wt% NaCl + CaCl2 equiv.), implying addition of meteoric water. The δ18O values of quartz and chlorite separates range from 7.7 to 12.1‰ (n = 21), with the calculated δ18Ofluid values of − 5.4 to 9.0‰, and the δD values of fluids range from −99 to −45‰. All these observations combined with previous geochronological and geochemical results reveal that the Tuwu deposit was formed by magmatic-hydrothermal fluids related to the Late Carboniferous felsic magmatism (i.e. tonalite porphyry magma) in a subduction setting. The Cu concentration in magma source is probably the key factor controlling the anomalous Cu mineralization at Tuwu, and the oxygen fugacity and temperature decreasing of the fluids resulted in abundant precipitation of Cu-riched sulfides.

Alteration mapping with short wavelength infrared (SWIR) spectroscopy on Xiaokelehe porphyry Cu-Mo deposit in the Great Xing’an Range, NE China: Metallogenic and exploration implications

The newly discovered Xiaokelehe porphyry Cu-Mo deposit (PCD) is situated in northern part of the Great Xing’an metallogenic belt, northeastern China. The syn-mineralization granodiorite porphyry was intruded by multiple phases of post-ore barren monzonite, diorite porphyry and granite porphyry, leading to complex and overprinting hydrothermal alteration patterns. This paper present new data on the alteration mineralogy, vein paragenesis, sulfide assemblages and SWIR (short wavelength infrared) spectroscopy at Xiaokelehe, and discuss how SWIR spectral data can help to understand hydrothermal fluid evolution and assist PCD exploration.At Xiaokelehe, oligoclase-epidote alteration is distributed at the deeper levels of the granodiorite porphyry but played little role in mineralization. The following potassic alteration (hydrothermal biotite and K-feldspar) was developed in the granodiorite porphyry with the main Cu-Mo mineralization. Drill core logging suggests that the subsequent chlorite-illite alteration affected almost the entire granodiorite porphyry, and is spatially and genetically associated with minor Cu mineralization. The youngest quartz-muscovite-pyrite alteration dominated in the upper level and outer parts of the PCD, and overprints the earlier alteration phases with only very minor mineralization.The short wavelength infrared (SWIR) analysis results indicate that chlorite and white micas (illite and muscovite) are the most abundant alteration minerals at Xiaokelehe. The wavelengths of Fe-OH band (Pos2250) of chlorite show a decreasing trend away from the granodiorite porphyry into the surrounding sedimentary wall rocks, probably reflecting a drop in temperature and Fe contents of the hydrothermal fluids. The Illite crystallinity (IC) values of white micas show a reverse trend, different from many PCDs, which is likely caused by the distribution pattern of illite and muscovite formed in the ore-proximal chlorite-illite and ore-distal quartz-muscovite-pyrite alteration, respectively.At Xiaokelehe, Cu and Mo mineralization is mainly distributed in quartz veins or disseminated within the potassic alteration zones, resembling typical PCDs. Meanwhile, chlorite-illite alteration is also associated with minor Cu mineralization. Thus, areas with intensive chlorite-illite alteration overlapping on potassic alteration likely represent the best exploration targets for high grade Cu-Mo mineralization. These target areas coincide spatially with areas of lower IC (<0.8) and higher Pos2250 (>2245 nm) values, suggesting the latter two are effective vectoring tools for PCD exploration at Xiaokelehe.

Mafic–intermediate igneous rocks in the East Kunlun Orogenic Belt, northwestern China: Petrogenesis and implications for regional geodynamic evolution during the Triassic

Mafic–intermediate igneous rocks can provide important insights into the geodynamic evolution of orogenic belts. Here, we investigate the petrogenesis of mafic–intermediate intrusive igneous rocks in the East Kunlun Orogenic Belt (EKOB) to constrain regional geodynamic and magmatic evolution. These intrusive rocks are all located in the Permian-Triassic magmatic arc and parallel to the Paleo-Tethys ophiolite belt. Zircon UPb dating results indicate that these various igneous rocks crystallized during the Triassic. The 250–248 Ma appinites display low SiO2 contents, high MgO contents, and marked enrichments in large-ion lithophile elements and depletions in high-field-strength elements; combined with their enriched εHf(t) values, these appinites were considered to be derived from lithospheric mantle modified by subducted slab-derived fluids. The Harizha host granodiorites and MMEs have indistinguishable crystallization ages of 235 Ma but distinct SiO2 contents and δ18OSMOW values, which, together with enriched Sr–Nd–Hf–Pb isotopes, suggest that their primary magmas were derived from the Mesoproterozoic lower crust (MLC) and subduction-modified lithospheric mantle (SMLM), respectively. The 241 Ma Baidungou quartz diorite and the 218 Ma Huanglonggou diorite porphyry show characteristics of medium SiO2 contents, moderate Mg# and εHf(t) values relative to contemporaneous mafic and granitic rocks; therefore they probably represent the mixing products of MLC-derived felsic and SMLM-derived mafic magmas. Different from the Baidungou diorite and Harizha granodiorite, the Huanglonggou diorite porphyries have adakitic characteristics, which suggests crustal thickening during the Late Triassic. A synthesis of these new data with previous researches shows that the EKOB undergone three magmatic peaks corresponding to three extension events (slab-rollback, slab-breakoff, and delamination) during the Triassic evolution.

Origins and tectonic implications of Late Cretaceous adakite and primitive high-Mg andesite in the Songdo area, southern Lhasa subterrane, Tibet

Late Cretaceous igneous rocks in the southern Lhasa subterrane, Tibet, include primitive high-Mg andesites and adakites, which provide important constraints on the tectonic evolution of the Neo-Tethys Ocean. Here, we present detailed zircon UPb and Hf isotopic and whole-rock geochemical data for granodioritic and dioritic porphyry samples from the Songdo area in the southern Lhasa subterrane. Zircon UPb dating indicates that the granodiorite crystallized at 88 Ma, whereas the diorite yields ages of 68 and 66 Ma. The granodiorite has adakite-like geochemical characteristics, including high Sr (801–1005 ppm) and low Y (6.8–15.2 ppm) and Yb (0.6–1.3 ppm) concentrations, and high Sr/Y (62–145) and La/Yb (39–93) ratios. We infer that the adakitic granodiorites formed through partial melting of subducted oceanic crust. The dioritic porphyry has intermediate moderate SiO2 (53–58 wt%) and high MgO (5.6–8.2 wt%) contents, and high Mg# (66.4–69.5) values, and is therefore classified as a primitive high-Mg andesite that was derived from interaction between subducted sediment and mantle. The presence of coeval adakite and charnockite, as well as high-temperature granulite-facies metamorphism, indicates that mid-ocean ridge subduction occurred at 100–80 Ma, followed by a 10 Myr hiatus in magmatism and subsequent rollback of the Neo-Tethys slab at 68 Ma. These processes resulted in significant crustal growth within the Lhasa terrane.

Rb–Sr geochronology and geochemistry of pyrite from the Shihu gold deposit, central North China Craton: Implication for the timing and genesis of gold mineralization

The Shihu quartz vein‐type gold deposit in the central North China Craton occurs within Neoarchean TTG (tonalite‐trondhjemite‐granodiorite) gneisses and shows spatial relationship with quartz diorite porphyry. The occurrence of the ore body is controlled by the N‐S fracture. Primary mineral assemblage of the ore body is composed of quartz, calcite, and base‐metal sulphides, including pyrite, galena, sphalerite, chalcopyrite, and pyrrhotite. Eight pyrite samples from veins of the main mineralization stage yield an isochron age of 129 ± 3 Ma (MSWD = 1.6), coinciding with the major Early Cretaceous magmatic event, and associated lithospheric thinning recognized in the NCC. The (87Sr/86Sr)i values of the pyrite (0.7102 ± 0.0006) are lower than the continental crust mean value (0.719) and higher than that of the mantle initial ratio (0.707), suggesting mixed crust–mantle source for the metallogenic components. Three types of hydrothermal pyrite from the early to major ore‐forming stages were identified in the quartz vein, including Py(I) as disseminated euhedral grains, Py (II) as dense bulks, and Py (III) as intergrowth with base‐metal sulphides. Electron microprobe analysis of the pyrite grains indicates a trend from S‐deficient to S‐enriched and from Fe‐enriched to Fe‐deficient stages, suggesting an increase in sulphur fugacity and reducing conditions. The arsenic in pyrite shows decrease against increasing Au during Stages II and III, implying that As is not the only trigger of gold precipitation, but electrochemical‐geochemical barrier played a major role in the formation of the ore. The Co and Ni concentrations, as well as Co/Ni ratios in pyrite, are relatively high, which provide an additional clue to the link with the regional magmatic event. Combined with the textural features, we propose a wider potential for gold exploration in this region, linking the mineralization with a major transitional tectonic regime.

Mesozoic porphyry Cu–Au mineralization and associated adakite-like magmatism in the Philippines: insights from the giant Atlas deposit

The Atlas porphyry Cu–Au deposit is located in central Cebu Island in the Philippines, with a proven mineral reserve of 1420 Mt at 0.45% Cu, 0.24 g/t Au, 0.018 g/t Mo, and 1.8 g/t Ag. It is associated with the Lutopan quartz diorite porphyry stock that was emplaced into the Cretaceous volcano-sedimentary sequences of the Cansi Formation. Two stages of hypogene alteration have been identified at Atlas: stage I quartz–magnetite ± chalcopyrite ± pyrite veins associated with potassic and propylitic alteration and stage II anhydrite–pyrite–chalcopyrite ± specularite veins associated with phyllic alteration. Supergene gypsum veins are also present. Mineralization is mainly associated with the stage I and stage II veins. The Lutopan quartz diorite porphyry yielded a zircon U–Pb age of 108.5 ± 1.6 Ma and is characterized by high Sr/Y (54–69), with the corresponding magma having high oxygen fugacity (avg. ΔFMQ +2.7, avg. Ce4+/Ce3+ of zircon = 439) and H2O concentrations (presence of amphibole and biotite phenocrysts) and low magmatic temperatures (avg. Ti-in-zircon thermometry = 706 °C). The relatively low La/Yb ratios (9–11), listric-shaped normalized REE patterns with weak or absent Eu anomalies, together with zircon eHf(t) values of 3.4 to 10.0, whole-rock ISr values of 0.70373–0.70382, eNd(t) values of 2.4–3.4 and Mg numbers of 49–53 suggest that the Lutopan quartz diorite porphyry was likely derived from partial melting of young lower continental crust or interaction between asthenospheric melts and lower crust melts, that evolved to adakite-like trace element compositions through amphibole fractionation. Stage I veins yielded a pyrite Re–Os isochron age of 110.2 ± 5.6 Ma, making Atlas the only Mesozoic porphyry deposit discovered in the Philippines.

Late Miocene adakites associated with the Tangse porphyry Cu-Mo deposit within the Sunda arc, north Sumatra, Indonesia

Porphyry deposits are generally found at convergent margins, especially above active subduction zones where adakite may be a great exploration target for porphyry-type Cu (-Mo and/or -Au) deposits. The Sunda arc is one of the recent island arcs in the world. The quartz diorite porphyry from the Tangse porphyry Cu-Mo deposit, west end of the Sunda arc, shows an emplacement age of 8.7 Ma and is characterized by high Sr/Y (23.9–32.9) and moderate Y (11.11–16.78), and obviously positive Eu anomalies (δEu = 1.10–1.35), which belongs to adakite with calc-alkaline affinities. This hypabyssal intrusion has the dominantly positive zircons εHf(t) values (+12.57 to +16.70) and whole-rock εNd(t) values (+3.8 to + 5.5). Slightly low 87Sr/86Sr values (0.70439 to 0.70449) and 143Nd/144Nd (0.512829 to 0.512914) of porphyries indicate that they have the sources similar to the Batu Hijau deposit in east end of the Sunda arc. Our study further displays that the mineralization of the Tangse Cu-Mo deposit is related to Indian ocean plate northward subduction during Late Miocene. The parental magma of the quartz diorite porphyry resulted from dehydration partial melting of subducted oceanic crust (including marine sediments) and subsequent contamination of mantle wedge material. The Tangse quartz diorite porphyry is characterized by high oxygen fugacities (ΔFMQ = +5.0 to +9.4), which has a good potential for the exploration of porphyry Cu-Mo deposit.

Zircon U–Pb geochronology and Sr–Nd–Pb–Hf isotopic constraints on the timing and origin of the Early Cretaceous igneous rocks in the Yongxin gold deposit in the Lesser Xing'an Range, NE China

The Lesser Xing'an Range in NE China is an important gold district. However, the age and genesis of Early Cretaceous magmatic rocks that are coeval with gold mineralization remain obscure. A suite of Early Cretaceous igneous rocks in a newly discovered gold deposit at Yongxin was conducted zircon U–Pb dating and Hf isotope and bulk‐rock geochemistry and Sr–Nd–Pb isotope analyses. A dacite of the Guanghua Formation and an andesite of the Longjiang Formation have zircon U–Pb ages of 111.7 ± 1.5 Ma and 119.7 ± 1.9 Ma, respectively. The dacite has zircon εHf(t) values of 5.4 to 12.0 and depleted bulk‐rock Sr–Nd–Pb isotopes ((87Sr/86Sr)i = 0.7049 to 0.7056, εNd(t) = 1.2 to 2.5, (206Pb/204Pb)i = 18.202 to 18.320). The andesite has zircon εHf(t) values of 5.6 to 13.6, (87Sr/86Sr)i of 0.7049 to 0.7051, εNd(t) of 1.0 to 1.6, and (206Pb/204Pb)i of 18.199 to 18.297. The ~120 Ma diorite porphyry and granite porphyry have zircon εHf(t) values of 3.7 to 10.0 and 3.6 to 10.2, respectively. These two units show large variations of 87Rb/86Sr ratios (&lt;1) and similar Sr–Nd–Pb isotopes compositions. All rock units are enriched in light rare earth elements and large‐ion lithophile elements and depleted in high‐field‐strength elements. The formation of Yongxin Early Cretaceous igneous rocks was related to variable degrees of partial melting from Jurassic basalt in the lower crust with significant contribution from ancient continental materials. The low Sr/Y ratios (2–24) and negative correlations between Sr, Eu/Eu, and SiO2 indicate that magmas of the Early Cretaceous igneous rocks at Yongxin have low water content and thus have low potentiality for porphyry copper mineralization.