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The subduction-related Sunda-Banda arc hosts several giant and major Cu–Au–Mo porphyry and epithermal Au systems, making it one of the most important magmatic-related metallogenic belts in Indonesia. They are accompanied by a number of smaller systems, one of which is the recently discovered Randu-Kuning porphyry Cu-Au deposit on Java Island. The present study investigates the geochemical characteristics of this deposit through whole-rock and mineral geochemistry and mineral geothermobarometry, focusing on three sequential dioritic intrusions that make up the host igneous complex, two barren and the third mineralized. Moreover, a comparative analysis is performed between other porphyry deposits in the Sunda-Banda arc and with Grasberg in Papua. This study shows that the older porphyry deposits have mostly similar geochemical characteristics to the younger deposits, suggesting the same magma source, which is mantle-derived oxidized I-type magma. Amphibole geothermobarometry shows that the formation of syn-ore intrusion in the older porphyry was higher in temperature and pressure than those at the younger porphyry. The halogen and oxygen fugacities inferred from biotite and amphibole chemistry indicate an oxidized, water- and halogen-rich melt. Our study shows that combining amphibole and biotite chemistry and whole-rock geochemical data is useful to fingerprint the magmatic-hydrothermal processes, especially where multiple magmatic phases occur. This research also provides valuable insights into the magmatic-hydrothermal physiochemical conditions during the formation of the mineralized system. [ABSTRACT FROM AUTHOR]

We present coupled textural, elemental, and boron isotopic data of tourmaline from the large Zhunuo–Beimulang collision-related porphyry copper deposits (PCDs) located within the western Gangdese, Tibet. Based on morphology and high-resolution mapping, the tourmaline is classified into three paragenetic generations. The first generation of schorlitic Tur-1 occurs in the monzogranite porphyry as disseminations intergrown with porphyritic K-feldspar and plagioclase. It shows decreasing Fe and Ca and increasing Mg and Al contents from core to rim and has relatively homogeneous δ11B values (− 9.9 to − 8.6‰); low Fe3+/(Fe2+ + Fe3+), Cu, F, H2O, and Sr/Y ratios; and high rare earth elements. These features indicate Tur-1 formed in a low fO2 and metal-poor granitic magma during the pre-mineralization stage. The second generation of porphyritic euhedral Tur-2 is hosted in diorite porphyry enclaves and dikes, where it is intergrown with plagioclase and biotite. It forms part of the schorl-dravite solid solution, with high Fe3+/(Fe2+ + Fe3+), Cu, F, H2O, Sr/Y, and δ11B (− 9.7 to − 5.1‰) values. These features indicate it crystallized from a hydrous, oxidized, metal-, and volatile-rich diorite magma. The third generation of Tur-3 is the most volumetrically important and occurs as veinlets and disseminations in the porphyry, or around Tur-1 and Tur-2. It shows radial and oscillatory zoning and is locally intergrown with chalcopyrite and pyrite within the main mineralization assemblage. It has δ11B values (− 10.5 to − 6.0‰) that overlap with Tur-1 and Tur-2 values. Tur-3 also has variable Fe3+/(Fe2+ + Fe3+), Cu, and volatiles (F and H2O), indicating it crystallized from oxidized to relatively reducing metal- and volatile-rich hydrothermal fluids. Overall, the three generations of tourmaline show a narrow range of δ11B values between − 10.5 and − 5.1‰ that are indicative of a single magmatic source. The high Cu, ferric iron, volatiles, and δ11B values in Tur-2 are interpreted to reflect injection of diorite magma into an open crustal magma storage system that led to the formation of an oxidizing and metal-volatile-rich porphyry system. The three stages of tourmaline formation reflect evolution of the magmatic–hydrothermal system from low fO2 conditions towards more oxidizing, volatile-rich conditions and then a return to more reducing conditions that accompanied Cu precipitation. Overall, the injection of oxidized metal-rich magma into a long-lived magma reservoir is a critical driving force for the development of collision-related PCDs. [ABSTRACT FROM AUTHOR]

The East Qinling Molybdenum Belt (EQMB), which is located on the southern margin of the North China Craton (NCC), is the largest Mo province in the world. This belt hosts a significant number of Mesozoic magmatic-hydrothermal Mo deposits and a small portion of pre-Mesozoic Mo deposits. Understanding the mineralization timing and mechanism of the unique pre-Mesozoic Mo deposits is essential to comprehend the evolution of the EQMB, the pre-Mesozoic Mo enrichment, and the Mesozoic Mo mineralization event. The recently discovered Zhaiwa deposit is a porphyry Mo deposit located in the Xiong'er Terrane of the EQMB. In this study, five molybdenite samples from the Mo-bearing quartz veins were analyzed for Re-Os isotopes composition. These samples yield an isochron age of 1794 ± 45 Ma, which represents the age of mineralization. The mineralization is mostly hosted within the biotite-amphibole plagiogneiss and granite porphyry. LA-ICP-MS U-Pb data of zircons constrain the crystallization age of the granite porphyry to be at 1791 ± 16 Ma. The close spatial and temporal association suggests that the granite porphyry is the causative rocks of the Mo mineralization. The δ34S values of pyrite vary from 5.3 to 6.8‰, suggesting that the S was mainly derived from magmatic source. The intrusion of magmas and associated Mo mineralization are contemporaneous to the regional Xiong'er volcanism that occurred during the late Paleoproterozoic. The Xiong'er volcanism was triggered by partial melting of lithospheric mantle in an extensional setting. The results of our study provide robust evidence for a late Paleoproterozoic Mo metallogenic event along the southern margin of the NCC. Future exploration should also consider the potential of late Paleoproterozoic porphyry Mo mineralization existing in the EQMB, which is closely associated with the Xiong'er volcanism. [ABSTRACT FROM AUTHOR]

Porphyry Cu, and porphyry Cu–Au deposits, are associated with arc magmatism and their ore-forming systems generally follow the magmatic evolution of typical arcs. However, most arc magmas are barren and giant economic porphyry Cu ± Au deposits are rare. In this study, we model variations in rare earth element concentrations in evolving arc magmas and giant porphyry Cu ± Au systems to quantify the percentage of the fractionating minerals required to produce the observed changes. We find that, during the andesitic stage of fractionation, ore-forming systems in thick crusts fractionate ~35% more amphibole than an average of thick arc magma systems (the thick-crust reference suite) and that ore-forming systems in thin crusts fractionate twice as much amphibole as their equivalent thin-arc magma reference suite. Thick-crust ore-forming suites also fractionate ~50% less plagioclase, and thin-crust ore systems ~40% less plagioclase, than their associated reference suites during the same andesitic stage of fractionation. Taken together, these observations imply that ore-producing magmas are appreciably wetter than their associated barren reference suites. Our modeling also shows that ~80% more amphibole is required to reproduce the andesite stage of fractionation in the thick-crust reference suite than in its thin-crust equivalent, suggesting that magmas produced under thick crusts are wetter than those produced under thin crusts. On the other hand, the chalcophile element contents of the thick- and thin-crust ore-forming systems are similar to and higher than those of the thick- and thin-crust reference suites, respectively. Therefore, we suggest that the high water content plays a critical role in the formation of giant porphyry Cu ore in thick crusts, whereas both high chalcophile contents and high water contents are required to form giant porphyry Cu–Au deposits in thin crusts. The high fraction of amphibole fractionation in giant economic porphyry suites, compared with their relevant reference suites, results in lower Y in the ore-associated suites and this difference increases with fractionation. As a consequence, plots of Y against MgO can be used to identify porphyries that have economic potential and are preferred to Sr/Y plots because they are less affected by the intense alteration associated with giant porphyry Cu ± Au deposits. [ABSTRACT FROM AUTHOR]

Continental subduction is the major cause of regional heterogeneities in the lithospheric mantle and contrasting types of magmatism and mineralization in post-collisional settings. We illustrate the relation between the nature of the subducted crust and the character of magmatism for the Late Miocene New Guinea Orogen that formed by the collision of the Australian continental margin with an island arc. The bipartite nature of the subducted Australian plate margin, with Precambrian crust in the west and Phanerozoic accreted arcs in the east, is reflected in the contrasting magmatism along the strike of the New Guinea Orogen. The chemical signature of the subducted crust is particularly prominent in small-volume Late Miocene–Quaternary ultrapotassic rocks of New Guinea. In the west, ultrapotassic lavas have low εNd values (−12.6 to −20.9), indicating the recycling of ancient continental material. Conversely, high εNd values of +3.5 to +4.5 are found in ultrapotassic lavas from eastern New Guinea. This suggests recycling of juvenile continental material, similar to the orthogneisses exposed in the Late Miocene ultrahigh-pressure metamorphic complex of the D'Entrecasteaux Islands. By comparison with ultrapotassic rocks from other orogenic belts, we show that crustal recycling is responsible for regionally contrasting redox conditions in the lithospheric mantle, which may explain why porphyry-type deposits are important in some regions but absent in others. [ABSTRACT FROM AUTHOR]

Porphyry-type molybdenum deposits, many of which are in China, supply most of the World's molybdenum. Of particular importance are the molybdenum deposits located in the Qinling-Dabie region that are responsible for more than half of China's molybdenum production. A feature that distinguishes this suite of deposits from the better-known Climax and Endako sub-types of porphyry molybdenum deposits is their formation from CO2-rich magmatic-hydrothermal fluids. The role of CO2, if any, in the transport of molybdenum by these fluids, however, is poorly understood. We conducted experiments on the partitioning of molybdenum between H2O-CO2, H2O-NaCl, and H2O-NaCl-CO2 fluids and a felsic melt at 850 °C and 100 and 200 MPa. Here we show that the exsolution of separate (immiscible) brine and vapor leads to the very high brine DMo values needed for efficient extraction of Mo from the magmas forming Dabie-type porphyry molybdenum deposits. Direct exsolution of immiscible CO2 vapour and brine from magma greatly enriches the brine in molybdenum, a likely factor in the genesis of the Dabie-type porphyry deposits that supply much of the World's molybdenum [ABSTRACT FROM AUTHOR]

Subduction zone magmatism is a major control of volcanism, the generation of modern continental crust and the formation of economically important porphyry Cu–(Mo–Au) deposits. Reading the magmatic record of individual arc segments and constraining the rates of magmatic changes are critical in order to fully understand and quantify the processes that drive magma evolution in subduction settings during arc growth. This study focuses on the San Francisco Batholith and the Rio Blanco-Los Bronces porphyry deposit cluster in central Chile, which provides an igneous rock record over ~13.5 Myr of arc evolution. We use whole-rock geochemistry, zircon geochronology and Hf isotope geochemistry to track changes in the crustal magmatic system of this arc segment during crustal thickening and porphyry Cu deposit formation. By combining the analytical dataset with Monte Carlo fractional crystallisation and assimilation fractional crystallisation modelling, we test a model for significant crustal involvement during magma evolution. Systematic and continuous increases in Dy/Yb, La/Yb, V/Sc and Sr/Y in the magmas over time indicate a transition in the main fractionation assemblage from plagioclase-dominated to amphibole-dominated that reflects deeper crystallisation and/or a higher meltwater content. Concomitant decreases in εHf and Th/La as well as increasing Ba/Th are best explained by assimilation of progressively deeper crustal lithologies from low (Chilenia) to high Ba/Th (Cuyania) basement terranes. Our study highlights that an increasingly hydrous magma and a deepening locus of crustal magma differentiation and assimilation, driven by crustal thickening contemporaneous with increased tectonic convergence and ingression of the aseismic Juan Fernandez ridge, can account for all investigated aspects of the multi-Myr magmatic evolution leading up to the formation of the Rio Blanco-Los Bronces porphyry Cu deposits. Our findings corroborate the importance of high-pressure differentiation of hydrous magma for the formation of Andean-style porphyry deposits. Once magmas favourable for porphyry Cu mineralisation were generated in the lower crust, multiple episodes of efficient magma migration into the upper crust fed several, discrete, shallow magmatic-hydrothermal systems over ~3.5 Myr to form the world's largest known Cu resource at Rio Blanco-Los Bronces. [ABSTRACT FROM AUTHOR]

The large magma reservoirs underlying world-class porphyry deposits are one of the key factors in their formation, which thus led to the present study focusing on the unmineralized intrusive rocks underlying the porphyry molybdenum-copper orebody of the post-collisional Jiama porphyry-skarn copper-polymetallic deposit in southern Tibet. The Jiama porphyry intrusion comprises intermediate-silica quartz diorite, monzogranite, and granodiorite porphyries, as well a high-silica granite porphyry. The intrusive rocks suite exhibits similar whole-rock Sr-Nd isotopic compositions [εNd(t) = -3.9 to -0.8], suggesting a common, non-radiogenic magma source. Yet, these rocks have distinct geochemical characteristics. The intermediate-silica rocks are relatively enriched in Ba and Sr with minor Eu anomalies, and show adakite-like geochemical characteristics. In contrast, the high-silica granite porphyry is strongly depleted in Ba, Sr, and Eu, and lacks adakite-like geochemical characteristics. We propose that the high-silica granite porphyry represents highly fractionated melt extracted from a silicic mush reservoir (crystallinity of ∼40%-65%), and that the monzogranite and granodiorite porphyries constitute the complementary residual silicic cumulates. High crystallinity facilitates the formation of connected fluid pathways, allowing the efficient removal of volatiles from the remaining silicic melt and a rapid flux of the ore-forming fluids toward the apical parts of the large magma reservoir. Less-evolved mafic melt is believed to have repeatedly intruded the base of the magma reservoir, thereby releasing volatiles and water into the silicic mush systems. The volatiles migrated upward through the fluid channels and accumulated in the apical part of the magma reservoir, subsequently, as a result of the overpressure in the roof zone, ore-forming fluids and successive batches of magma were expelled together, thereby forming the Jiama porphyry-skarn deposit. [ABSTRACT FROM AUTHOR]

Most large-scale porphyry-style mineralization is genetically associated with oxidized, sulfur-rich, and hydrous magmas, the sources of which were enriched in mantlederived or juvenile crust--derived materials. Geochemical indices for these features can distinguish fertile magmas and barren magmas. However, fertile magmas that generate different-sized porphyry deposits are usually geochemically indistinguishable, and the factors controlling the size of porphyry mineralization are poorly understood. Here, we used zircon H2O contents and the compositions of apatite hosted in zircon, phenocrysts, and groundmass to compare the water contents and volatile evolution of fertile magmas in the Yulong ore belt, Tibet, which generated giant-, large-, and medium-sized porphyry deposits. We found that these porphyries have comparable major- and trace-element and zircon Hf-O isotope compositions, with high oxygen fugacity and sulfur contents. A negative correlation between XClAp/XOHAp versus XFAp/XClAp of apatites suggests that the magmas consistently achieved H2O saturation before zircon crystallization, and zircon hydroxyl contents reveal that the water contents of the melt positively correlate with the size of the deposits, consistent with larger deposits achieving H2O saturation at deeper crustal levels. The deeper H2O saturation also caused larger amounts of Cl extraction, as indicated by the trends of increasing XFAp/XClAp and decreasing XClAp/XOHAp with larger deposit sizes. These data sets can be reconciled by magmas forming larger deposits having higher H2O contents and suggest that the H2O content is a key control on their fertility. Our study highlights the utility of integrated hydrous and nominally anhydrous mineral analyses for constraining enigmatic magmatic volatile processes in magmatic ore-forming systems. [ABSTRACT FROM AUTHOR]

The genetic link between subduction- and collision-related porphyry Cu deposits (PCD) is still not well understood. The Gangdese porphyry Cu belt (GPCB) in southern Tibet hosts two parallel E–W-oriented metallogenic subbelts, including a southern Jurassic subduction-related and a northern Miocene post-collision PCD subbelt. In this study, we combine new and published whole-rock major and trace element data, Cu isotopic compositions and zircon trace element data of Jurassic magmatic rocks from the GPCB. Combined Sr/Y and La/Yb crustal thickness proxies confirm the south to north geometry of the Jurassic arc-back-arc system across the GPCB. The southern Jurassic magmatic arc rocks have systematically higher whole-rock V/Yb ratios, δ65Cu values and zircon Eu/Eu* ratios compared to those of the northern back-arc region. This suggests that Jurassic southern arc magmas had higher oxygen fugacity and H2O concentration than the contemporaneous northern back-arc magmas, which was controlled by a steep subduction geometry of the Neo-Tethyan oceanic slab. Hydrous and oxidized magmas resulted in Cu enrichment during magma evolution and generation of Jurassic PCD in the southern magmatic arc by inhibiting early sulfide saturation at deep crustal levels. In contrast, the northern back-arc magmas were less oxidized and less hydrous, which triggered early sulfide saturation, resulting in segregation of Cu-bearing sulfides in lower crustal cumulates that provided a favorable metal source for later Miocene PCD in the northern subbelt. Our study indicates that the Jurassic subduction geometry controlled the formation and distribution of Jurassic subduction-related and Miocene post-collision-related PCD in the GPCB. [ABSTRACT FROM AUTHOR]

The current debate on volcanic-plutonic connection is centered on whether eficient liquid-crystal segregation dominates the evolution of a mushy reservoir to produce evolved, crystal-poor rhyolite and cumulate leftover. However, magma recharge may remarkably influence the evolution of a mushy reservoir and obscure the evidence of liquid-crystal segregation. This complexity poses a challenge to exploring the connection of volcanic-plutonic rocks. This study investigates the Qinzhou Bay granitic complex (~250–248 Ma) from South China, which contains crystal-poor (<19 vol%) peraluminous rhyolites and subsequent crystal-rich (28–54 vol%) porphyries. Although the rhyolite and porphyry units have a close spatio-temporal link, they do not share a fractionation trend and similar whole-rock Sr-Nd-O isotopic compositions; thus, a direct connection is not evidenced. We further present textural analyses, mineral and melt inclusion compositions, thermobarometry (the combination of Ti-in-zircon thermometer and Ti-in-quartz thermobarometer), and thermodynamic modeling to examine the alternative interpretations, i.e., the two units may have intrinsically independent origins or the connection of the two units has been obscured. For the rhyolite unit, thermobarometric results reveal a polybaric storage system consisting of middle (>600 ± 80 MPa) and upper (~150 ± 40 and ~60 ± 20 MPa) crustal reservoirs. Variations in quartz Fe content and chlorine-rich, metaluminous melt inclusions suggest that magma hybridization with less-evolved metaluminous magmas occurred at both crustal levels. In particular, the elevated Fe contents in the quartz population that crystallized at the shallowest level (~60 ± 20 MPa) suggest that recharge magmas were directly injected into the shallowest reservoir. Deviation of the whole-rock composition from the liquid evolution trend recorded in melt inclusions suggests a combined efect of magma mixing and crystal-melt segregation processes in upper crustal reservoirs. Thermodynamic modeling and mass balance calculations suggest that the whole-rock composition of the rhyolite could be reproduced by mixing between regionally exposed dacites and segregated melts at crystallinities of 50–60% (using parental magma represented by the least-evolved melt inclusion). For the porphyry unit, thermobarometric results reveal magma storage at middle (more than 450 ± 40 to 550 ± 40 MPa) and upper (110 ± 20 to 140 ± 20 MPa) crustal levels. The small-scale oscillatory zonation of plagioclase, the pervasive resorption of quartz and alkali feldspar, and the presence of peraluminous microgranular enclaves in the porphyries suggest a recharge event of metasediment-sourced magmas, triggering reactivation and convection of the reservoir. Autoclastic and overgrowth textures of quartz, plagioclase, and alkali feldspar phenocrysts and development of columnar jointing suggest that the reactivated porphyritic magmas ascended and emplaced at ultrashallow levels (~30 ± 10 MPa). Because of the similar storage pressures, the porphyries may represent remobilized cumulates of rhyolitic magmas, whereas the texture and geochemistry of the cumulate-liquid pair were modified, a key factor rendering a cryptic connection between the rhyolite and porphyry. Alternatively, the plumbing systems feeding the rhyolite and porphyry units are horizontally independent or vertically discrete, but this circumstance is inconsistent with the same evolution trend of quartz Fe and Al contents of the rhyolite and porphyry. Our study highlights that whole-rock composition may record blended information of complex processes, and caution should be taken when whole-rock composition is used to extract information of a single process. Multi-method constraints are required to evaluate the influence of recharge processes on the modification of liquid-cumulate records, and big data analysis on the basis of geochemistry should be conducted with caution to avoid biased understanding. [ABSTRACT FROM AUTHOR]

The southern margin of the North China Craton (SNCC) contains 8 giant (> 0.5 Mt Mo resources), 4 large (0.1–0.5 Mt Mo resources) and many small (< 0.1 Mt Mo resources) porphyry Mo deposits. Their magmatism ages are concentrated within 150–131 Ma, but it is unclear what determines the size of porphyry Mo systems. Herein, we synthesize new and existing data for the Mo-bearing intrusions in the SNCC to investigate the optimal conditions for giant deposit formation. These intrusions share similar whole-rock geochemistry characteristics and highly differentiated features, with SiO2 and K2O contents ranging from 68.55 to 79.13 wt.% and 2.63 to 11.18 wt.%, respectively. They share similar lower crustal sources with a variable input of mantle materials. Their εNd(t) and εHf(t) values range from -19.1 to -12.7 and -29.5 to -9.3, respectively, and indicate no relationship with metal fertility. The similar ΔFMQ values calculated from zircon geochemistry also suggest that the porphyry Mo deposit size is unrelated to magma redox conditions. High magmatic water contents and high differentiation features (SiO2 > 73 wt.%) exhibit significant positive correlations with the deposit size. Therefore, we propose that magma with a high water content triggered by intensive fractional crystallization is the fundamental requirement to produce large Mo endowment in the SNCC. This conclusion is consistent with the criteria that pulsed release of mineralizing fluids from a large magma chamber through fractional crystallization play an important role in the formation of giant porphyry Mo deposits in other molybdenum belts in the world. [ABSTRACT FROM AUTHOR]

Porphyry copper ore-forming magmas worldwide are chemically distinguished from ordinary arc granitoids by lower Zr and by higher Sr/Zr ratios at equivalent SiO2 contents. Low ppm Zr in zircon-saturated melts and high whole-rock Sr/Zr in granitoid samples retaining igneous plagioclase are useful discriminants of Cu-fertile intrusive complexes. These and other chemical discriminants of porphyry-copper-forming melts of tonalite-granodiorite-adamellite composition cannot develop during crystallisation-differentiation at upper-crustal pressures. They indicate unusually high dissolved H2O (≥ 9 wt%) in residual melts at depths near the base of the crust. We compare Zr behaviour during mafic-to-felsic magmatic differentiation in orogenically deforming, copper-mineralised arc segments with behaviour during differentiation in non-orogenic, unmineralised arc segments laterally adjacent along the same subduction zones. In orogenically deforming segments, horizontal compressive stress provides resistance to opening of tensile dyke fractures and promotes entrapment of mantle-derived basaltic melts in magma chambers embedded in hot country rock at Moho-vicinity depths, where magmas cool slowly and residual melts tend to last long enough to experience intermittent chamber replenishment by basaltic melts from the deeper mantle. Over several cycles of replenishment and fractional crystallisation, residual melts acquire high concentrations of inherited chemical components that were largely excluded from cumulus minerals—H2O, Cl, CO2, SO3, etc. Accumulating H2O re-orders the high-pressure crystallisation sequence of igneous minerals in successive cycles and leads to early and prolific production of hornblende and early zircon saturation in mafic melts (< 60 wt% SiO2) of later cycles and leads to low Zr contents of zircon-saturated intermediate-composition residual melts. [ABSTRACT FROM AUTHOR]

Fluorine-rich granites and rhyolites occur throughout the southern Rocky Mountains, but the origin of F-enrichment has remained unclear. We test if F-enrichment could be inherited from ancient mafic lower crust by: (1) measuring amphibole compositions, including F and Cl contents, of lower crustal mafic granulite xenoliths from northern Colorado to determine if they are unusually enriched in halogens; (2) analyzing whole-rock elemental and Sr, Nd, and Pb isotopic compositions for upper crustal Cretaceous to Oligocene igneous rocks in Colorado to evaluate their sources; and (3) comparing batch melting models of mafic lower crustal source rocks to melt F and Cl abundances derived from biotite data from the F-rich silicic Never Summer batholith. This approach allows us to better determine if the mafic lower crust was pre-enriched in F, if it is concentrated enough to generate F-rich anatectic melts, and if geochemical data support an ancient lower crustal origin for the F-rich rocks in the southern Rocky Mountains. Electron microprobe analyses of amphibole in lower crustal mafic granulite xenoliths show they contain 0.56–1.38 wt% F and 0.45–0.73 wt% Cl. Titanium in calcium amphibole thermometry indicates that the amphiboles equilibrated at high to ultrahigh temperature conditions (805 to 940 °C), and semiquantitative amphibole thermobarometry indicates the amphiboles equilibrated at 0.5 to 1.0 GPa prior to entrainment in magmas during the Devonian. Mass balance calculations, based on these new measurements, indicate parts of the mafic lower crust in Colorado are at least 3.5 times more enriched in F than average mafic lower crust. Intrusions coeval with the Laramide Orogeny (75 to 38 Ma) pre-date F-rich magmatism in Colorado and have Sr and Nd isotopic compositions consistent with mafic lower crust ± mantle sources, but many of these intrusions contain elevated Sr/Y ratios (>40) that suggest amphibole was a stable phase during magma generation. The F-rich igneous rocks from the Never Summer igneous complex and Colorado Mineral Belt also have Sr and Nd isotopic compositions that overlap with the lower crustal mafic granulite xenoliths, but they have lower Sr/Y, higher Nb and Y abundances, and distinctly less radiogenic 206Pb/204Pbi compositions than preceding Laramide magmatism. Batch melt modeling indicates low-degree partial melts derived from rocks similar to the mafic lower crustal xenoliths we analyzed can yield silicic melts with >2000 ppm F, similar to estimated F melt concentrations for silicic melts that are interpreted to be parental to evolved leucogranites. We suggest that F-rich silicic melts in the southern Rocky Mountains were sourced from garnet-free mafic lower crust, and that fluid-absent breakdown of amphibole in ultrahigh temperature metamorphic rocks was a key process in their generation. Based on the composition of high-F amphibole measured from lower crustal xenoliths, the temperature of amphibole breakdown and melt generation for these F-enriched source rocks is likely >100 °C higher than similar lower crust with low or average F abundances. As such, these source rocks only melted during periods of unusually high heat flow into the lower crust, such as during an influx of mantle-derived magmas related to rifting or the post-Laramide ignimbrite flare-up in the region. These data have direct implications for the genesis of porphyry Mo mineralization, because they indicate that pre-enrichment of F in the deep crust could be a necessary condition for later anatexis and generation of F-rich magmas. [ABSTRACT FROM AUTHOR]

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We constrain the magma sources of representative post‐collisional ore‐associated and barren suites in the Sanjiang metallogenic belt, Southwest China. The ore‐associated suites generally have higher Mg# and Cr and Ni contents than the crustal melts. Also, they show wide ranges of whole‐rock Nd and zircon Hf isotopes that are similar to the subduction‐modified mantle‐derived alkaline volcanic rocks in the region. Combing with the geochemical model, we suggest that the ore‐associated suites dominantly originated from partial melts of subduction‐metasomatised mantle by fractional crystallisation. In contrast, the barren suites are mainly characterised by low Mg# and Cr and Ni contents that are comparable to the crustal melts and they have enriched whole‐rock Nd and zircon Hf isotopes, indicating a metasomatised lower crustal origin. The different magma sources play an important role in controlling the fertility of contemporary ore‐associated and barren magmatic suites during post‐collisional porphyry ore formation. [ABSTRACT FROM AUTHOR]

Volatile element abundance is a crucial factor triggering mineralization and controlling the enrichment of molybdenum in porphyry deposits. The Chalukou deposit is the largest porphyry Mo deposit in NE China, with an average grade of 0.087% Mo. In this contribution, we present petrology, bulk geochemistry, zircon U–Pb geochronology and Lu–Hf isotopes, and apatite geochemistry for the Chalukou deposit. The intrusive rocks include pre‐mineralization monzogranite, syn‐mineralization quartz porphyry, fine‐grained porphyry and granite porphyry, and post‐mineralization monzogranite and feldspar porphyry. These granitoids are metaluminous to peraluminous, and belong to alkali‐calcic to calc‐alkalic series. Zircon εHf(t) values of granitoids range from +0.2 to +5.7 with corresponding Hf crustal model ages of 805–1170 Ma, indicating a Mesoproterozoic juvenile crustal source modified by mantle‐derived magma. They are characterized by logf(O2) of −16.1 to −9.4, with an average of −12.5, ΔFMQ of +0.8 to +7.9, with an average of +4.5, showing a relatively high oxidation state for the syn‐mineralization magma. The apatites in quartz porphyry have the highest F contents, ranging from 3.61 to 4.62 wt%. At Chalukou, F‐rich magma is conducive to the convection of magma and promotes the efficient separation of differentiation magma, making the magmatic‐hydrothermal fluid circulate many times, eventually resulting in the accumulation of ore‐forming materials on the top of the magma chamber and gradually aggravating mineral enrichment processes. [ABSTRACT FROM AUTHOR]

Whole-rock geochemical signals of porphyry intrusions can provide clues for key metallogenetic processes and the potential for porphyry Cu deposits (PCDs). However, it cannot be guaranteed that these signals are the best choices, because they are proposed more based on the individual experience of researchers or some local and limited research data. In this study, it was found that the fertility potential for contemporaneous porphyry intrusions from different locations (fertility field) could be identified according to the composition statistics of the porphyry intrusions in the southern Sanjiang Tethyan Orogen. Therefore, a crucial signal-ranking Monte Carlo-based framework was implemented using the feature importance acquired from a random forest machine learning method. The first six crucial variables among 31 oxides and elements for fertile magma identification were then grouped into three sets using principal component analysis and hierarchical cluster analysis. Several optimal two-dimensional discrimination plots were built based on the k-nearest neighbor classification method according to the three sets of oxides and elements. The results indicate that the fertile magmas have signatures of high Sr, Ba, and P2O5 and low heavy rare earth elements (REEs) and SiO2. These signatures indicate that hydrous, oxidized, and volatile-rich Cu-fertile magmas originated from a thick arc crustal environment and underwent amphibole and garnet fractionation in the deep crust and the subsequent addition of mafic melt in shallow chambers. The application of these discrimination plots in the Paleo-Tethyan shows that the Zhongdian Triassic–Jurassic PCDs that developed in the sub-Paleo-Tethyan subduction zones are special cases. [ABSTRACT FROM AUTHOR]

Large volume, intermediate-felsic magma reservoirs are the source of melt and mineralising fluids which generate porphyry copper deposits. Cooling and crystallisation of hydrous magmas drives the exsolution and expulsion of a magmatic volatile phase—a process which remains challenging to constrain in porphyry Cu systems where the record of magma volatile compositions is rarely preserved. Here, we use the halogen compositions of apatite inclusions shielded as inclusions within zircon to constrain volatile evolution in magma reservoirs which pre-date and are synchronous with porphyry Cu mineralisation at Quellaveco, Southern Peru. Geochemical and textural data confirm that the zircon-included apatites escaped re-equilibration with hydrothermal fluids, unlike apatites found in the groundmass of the same rocks. We, therefore, recommend that future studies attempting to reconcile magmatic volatile budgets using apatite in porphyry Cu systems should focus on apatite inclusions in zircon. By combining the apatite inclusion data with numerical modelling, we find evidence that the magma reservoir sourcing porphyry Cu mineralisation remained fluid-saturated for the entire period recorded by apatite crystallisation. By contrast, the pre-mineralisation batholith shows more variable, potentially fluid-undersaturated behaviour. Our modelling suggests that in order to attain the porphyry melt volatile compositions inferred from apatite, the magma reservoir must have exsolved a large proportion of its volatile budget, consistent with having been held at high crystallinity (40–60% crystals). This crystallisation interval coincides with peak chlorine and copper extraction from intermediate-felsic magmas, and would have permitted efficient fluid migration and accumulation at the roof of the system. We suggest that the storage of large-volume, long-lived, crystal-rich magma reservoirs in magmatic arcs may be a critical step in generating world-class porphyry copper deposits. [ABSTRACT FROM AUTHOR]

The origin of intermediate to felsic potassic magmas is debated, and not much is known about the volatile content of potassic magmas associated with porphyry Cu (Au, Mo) deposits. To better understand the liquid line of decent of mafic potassic magmas and the behavior of volatiles during magma differentiation, we performed 19 experiments at 1.0 GPa and 1150 °C to 850 °C using piston cylinder presses. We developed a new experimental technique that involves a capsule liner made of single-crystal zircon to prevent the loss of Fe and S in the starting material to the noble metal capsule. The starting material is a high-Mg, basaltic trachyandesite (52 wt% SiO2, 12 wt% MgO, 1.9 wt% Na2O and 5.3 wt% K2O) from the Sanjiang region in southwestern China, doped with geologically realistic amounts of volatiles (i.e. 4.0 wt% H2O, 0.34 wt% CO2, 0.27 wt% Cl and 0.25 wt% S). The addition of 0.25 wt% S in the form of anhydrite internally buffered the experiments at an oxygen fugacity of 2.0 ± 0.5 log units above the fayalite–magnetite–quartz buffer, which is similar to the redox state of the Sanjiang variously evolved potassic magmas. The experimentally produced silicate melts match well with the Sanjiang intermediate to felsic magmas in terms of major, minor and trace element compositions, and also with regard to the S and Cl contents. The sequence of crystallizing minerals (olivine + clinopyroxene –> biotite ± orthopyroxene –> apatite –> K-feldspar) also fits with the one observed in the Sanjiang mafic to intermediate magmas. These results suggest that the Sanjiang intermediate to felsic magmas, including the porphyry Cu (Au, Mo)-forming magmas, can form solely by differentiation of potassic mafic magmas without any involvement of old crustal material. During experimental differentiation at 1.0 GPa, the S content of the evolving silicate melt first increased until ~57 wt% melt SiO2, and then decreased in response to precipitation of sulfides, sulfate melt and/or anhydrite, whereas the H2O and Cl contents of the evolving silicate melt increased exponentially until saturation in a CO2-rich fluid was reached at 60 to 65 wt% melt SiO2 and ~ 8 wt% melt H2O. During further magma differentiation the H2O and Cl contents of the evolving silicate melt remained constant until ~70 wt% melt SiO2, after which point the Cl content of the silicate melt decreased due to increased partitioning of Cl into the fluid phase ± increased fluid/melt ratio. Based on these experimental results and petrographic and geochemical evidence from natural samples, the Sanjiang porphyry Cu (Au, Mo)-forming magmas (65–70 wt% SiO2) are interpreted to have formed through differentiation of primitive, mantle-derived, potassic magmas in the lower crust (≥1.0 GPa), and to have ascended ±directly from the lower crust to shallow crustal levels. They likely contained 8 to 13 wt% H2O, 0.37 to 0.90 wt% Cl and 0.07–0.29 wt% S. This case study on the magma evolution in the Sanjiang region may have implications for the origin and nature of intermediate to felsic potassic magmas in various tectonic settings. [ABSTRACT FROM AUTHOR]

The magmatic process within upper crust encompasses various contents such as the transition between magmatic and hydrothermal systems and changes in oxygen fugacity (ƒO2), which ultimately play key roles in the formation of porphyry Cu deposits (PCDs). However, tracing these magmatic processes, especially in porphyry systems, is not an easy task. This study reported the detailed process of magmatic fluid exsolution and systematical variation of magmatic ƒO2 within the upper crust of a Tongchang–Chang'anchong porphyry Cu deposit, based on detailed investigations of mineral crystallization sequences and compositional features of the minerals in the fertile porphyries. Results indicate that the fertile porphyries show a high initial ƒO2, with ΔFMQ ≥ +3.0 (ΔFMQ is the deviation of logƒO2 from the fayalite–magnetite–quartz (FMQ) buffer). The magmatic ƒO2 (ΔFMQ) continued to decrease to ~+2 until fluid exsolution occurred at ~790 °C due to wall-rock contamination. The magmatic fluid exsolution process caused a temporary increase in the ƒO2 (to ΔFMQ = ~+3.4). The high magmatic ƒO2 during this process (790–750 °C) resulted in a higher content of ore-forming materials in the exsolved magmatic fluid. When the temperature dropped below 750 °C, the magmatic ƒO2 began to continuously decrease and eventually reached ΔFMQ = ~+0.6. The lower magmatic ƒO2 hindered the further migration of ore-forming materials through the exsolved fluid during this process (< 750 °C). Results of this study indicate that the initial magma during the upper crustal magmatic process of PCDs generally has a high ƒO2, and the contamination of reduced components can significantly decrease the magmatic ƒO2. The early magmatic fluid exsolution process can maintain a high magmatic ƒO2 condition, thereby efficiently extracting ore-forming minerals and producing ore-forming fluids, which is the key to the formation of PCDs. The latter continuous decrease in magmatic ƒO2 during the fluid exsolution process may be the reason preventing the Tongchang–Chang'anchong porphyry Cu deposit to form a giant PCD. [ABSTRACT FROM AUTHOR]

The origin of the anorthosite-rapakivi granite-bearing rock complexes was a topic of research for geologists for more than a century. Magmatic systems that produce these complexes were widely developed in the Precambrian and have no direct analogues in modern times. The main goal of this study was to characterize the conditions under which primitive granitoids formed and to shed light on the history of ore matter transport during these stages. The object of the research was granite porphyry dikes—a subeffusive analogue of rapakivi granite from the Salmi batholith in the Fennoscandian Shield. Characteristic solid-phase inclusions of a mineral paragenesis of mafic rocks, as well as inclusions of sulfide melts, were found in zircon from this type of rock. These sulfide inclusions were homogenized by heating, and subsequently, the trace element composition was determined by the LA-ICP-MS method. The geochemistry of zircons was studied by the SIMS method, and the temperature of their formation was determined using a Ti-geothermometer. The temperature of the studied zircon grain formation varied from 925 to 765 °C. The values of ƒO2 for the early stages of the rock formation were in the region below the boundary of the FMQ buffer. The presence of two sulfide melts at the time at which the sulfide inclusions were captured by the zircon, pyrrhotite-chalcopyrite, and sphalerite-chalcopyrite compositions was established. The capture of sulfide inclusions from the pyrrhotite-chalcopyrite composition occurred above 841 °C, while in sphalerite-chalcopyrite, they occurred at a lower temperature of 765 °C. The connection between the formation of granite porphyry with mafic melts that form rocks of the gabbro and anorthosite types was established. [ABSTRACT FROM AUTHOR]

The world's largest current Cu resource is volcanic arc-hosted, porphyry copper deposits. Whether unusual parental magmas or fortuitous combinations of processes accompanying emplacement of common parental arc magmas (e.g., basalt) is required for ore deposit formation, remains unclear. Spatial and tectonic associations of adakite (andesite with high La/Yb, Sr/Y) with porphyries exist, but genetic links are debated. Delayed saturation with Cu-bearing sulfides consequent to elevated redox state seems essential for late-stage exsolution of Cu-bearing hydrothermal fluids. Partial melting of igneous layers of subducted, hydrothermally altered oceanic crust in the eclogite stability field are invoked to account for andesitic compositions, residual garnet signatures, and the putative oxidised character of adakites. Alternative petrogeneses include partial melting of lower crustal, garnet-bearing sources and extensive intra-crustal amphibole fractionation. Here we demonstrate mineral-hosted, adakite glass (formerly melt) inclusions in lavas erupted subaqueously in the New Hebrides arc are oxidised relative to island arc (and mid-ocean ridge) basalts, are H2O-S-Cl-rich, and moderately enriched in Cu. Polynomial fitting of chondrite-normalised, rare earth element abundance patterns shows the precursors of these erupted adakites were unequivocally derived from partial melting of subducted slab, and represent optimal porphyry copper progenitors. [ABSTRACT FROM AUTHOR]

The Dongxiang tungsten–copper deposit is a large W–Cu deposit located in the northeast of Jiangxi province in south China. Previous studies have mainly considered the geochemical and isotopic attributes of the ore deposit, but information is still lacking on the genesis and setting of Dongxiang W–Cu mineralization-related intrusive rocks. This paper presents systematic elements and Sr–Nd–Hf isotopic data of the Dongxiang granodiorite porphyry. The Dongxiang granodiorite porphyry is intermediate–acidic in composition, with SiO2 contents of 60.00–75.16 wt.%, Al2O3 contents of 10.15–18.53 wt.%, an K2O contents of 2.95–4.28 wt.%. The REEs content ranges from 64.2 to 198.1 ppm, with LREE/HREE ratios of 7.67–17.47. It is characterized by adakitic geochemical affinities with high Sr/Y and (La/Yb)N ratios but low Y and Yb contents. A slight Eu anomaly, extreme depletion in Y and Yb, relatively low MgO content, and relatively high 207Pb/204Pb ratios together indicate that the Dongxiang granodiorite porphyry was likely derived from partial melting of the thickened lower continental crust. Based on zircon εHf(t) values (−11.8–−4.5), two-stage Hf model ages (1.33–1.94 Ga), and the regional geological setting, it can be inferred that Dongxiang granodiorite porphyry magma is mainly derived from Neoproterozoic juvenile crust with the involvement of Paleoproterozoic ancient crust. [ABSTRACT FROM AUTHOR]

Magmatic sources of porphyry deposits in postcollisional settings remain controversial. We have used new and published petrological and geochemical data for the Eocene–Oligocene porphyry Cu ± Mo ± Au deposits in the Sanjiang region, SW China, to address this outstanding issue. New data for three deposits (Machangqing, Tongchang, and Beiya) in the Ailaoshan–Red River porphyry Au-Cu-Mo belt (southern part of the Sanjiang region) suggest that ore-forming porphyries were emplaced at ~ 35 Ma, have high (87Sr/86Sr)i (0.7068–0.7071) and negative εNd(t) (− 6.9 to − 5.0), low zircon εHf(t) (− 5.3 to 4.5), and relatively high δ18O (5.9–9.0‰). Magmatic amphibole phenocryst compositions indicate that the parental magmas are all relatively oxidized (ΔFMQ = 1.7 ± 0.6), and H2O-rich (3.8 ± 0.3 wt% H2O). These results are consistent with those estimated from zircon compositions (ΔFMQ = 1.8 ± 0.8) and high whole-rock Sr/Y ratios (75 ± 31), respectively. Based on the new and published data, we suggest that the parental magmas for the Ailaoshan–Red River porphyry Au-Cu-Mo belt were derived from a preserved juvenile arc lower-crust and the underlying metasomatized subcontinental lithospheric mantle (SCLM) attributed to a Neoproterozoic subduction event, whereas the parental magmas for the Yulong porphyry Cu-Mo belt (northern part of the Sanjiang region) originated from the Permian–Triassic juvenile arc lower-crust and metasomatized SCLM. Additionally, parental magmas for these porphyry deposits are all oxidized and H2O-rich, and we attribute such characteristics to inheritance from mixed mantle-crust sources that were modified by previous oceanic slab subduction. [ABSTRACT FROM AUTHOR]

The controversial topic of genetic relationships of shallow magmatogenic ore deposits with associated complexes of small intrusive bodies or separate syn-ore bodies is discussed in this article. Materials of the field study by the authors of four epithermal gold deposits of the Amur region are used. These materials are supplemented by an analysis of published data on the conditions and geological settings of the localization of a number of other epithermal and shallow Cu-Mo-porphyry deposits in various regions of Russia and other countries. The active thermal participation signs of syn-ore stocks and sill in retraction to intrusions and initiation of near-intrusive convection of deep-seated fluids during ore formation at epithermal gold deposits of the Amur region (Pokrovskoe, Pioner, Zheltunak, Bamskoe, and Mnogovershinnoe) have been established and confirmed by model experiments. These signs and zoning of metal deposition are also established at epithermal and porphyry deposits in other regions of Russia (Ural, Transbaikalia, and Kamchatka) and in other countries. Favorable conditions for ore accumulations have been identified. These conditions are associated with shallow syn-ore small intrusions and magma chambers at 11 characteristic deposits, including large and unique ones (Pioner, Mnogovershinnoe, Bingham, and Klaimax). [ABSTRACT FROM AUTHOR]

Sulfide-rich hydrous arc cumulates in the lower crust are considered a likely source for porphyry Cu-forming magmas in post-subduction settings. However, it remains controversial whether or not post-subduction porphyry Cu magmas can be produced by partial melting of lower crustal arc cumulates. Here we performed detailed petrographic and geochemical studies on exhumed lower to middle crustal cumulates from the Gangdese and Kohistan arc sections, and then conducted partial melting experiments of the Gangdese sulfide-rich lithologies at 1.5 GPa and 800°C–1150°C using a piston cylinder press. Both the Gangdese and the Kohistan arc-root samples formed as cumulates in the lower to middle crust, but the Kohistan samples were subsequently brought into the garnet stability field during the India–Eurasia continental collision. Most of the Gangdese samples contain relatively high abundances of magmatic sulfides preserved in the form of Cu-poor monosulfide solid solution. In contrast, most of the Kohistan samples contain very low abundances of Cu-rich sulfides preserved as inclusions in garnet, probably due to intense metamorphic dehydration and up to 2 wt% partial melting in the garnet stability field. The original magmatic sulfides at Kohistan appear to have been removed mainly by metamorphic fluids rather than by partial melts, as the arc-root samples could have experienced only very low degree of partial melting and the sulfur solubility in experimentally produced partial melts is low (≤0.1 wt%) even at oxygen fugacities two log-units above the fayalite-magnetite-quartz buffer. Furthermore, the experimental partial melts contain much less K2O, MgO, Cl and ±S than typical post-subduction porphyry Cu-forming magmas. Hence, we conclude that the role of sulfide-rich arc cumulates in the formation of post-subduction porphyry Cu magmas has been severely overestimated. [ABSTRACT FROM AUTHOR]

Porphyry-type deposits are a vital source of green technology metals such as copper and molybdenum. They typically form in subduction-related settings from large, long-lived magmatic systems. The most widely accepted model for their formation requires that mantle-derived magmas undergo an increase in volatiles and ore-forming constituents in mid- to lower crustal reservoirs over millions of years, however, this is mostly based on observations from shallow, sporadically exposed parts of porphyry systems. To examine this paradigm, we have evaluated the timeframe and geochemical signatures of magmatism in a ~ 8 km palaeodepth cross-section through plutonic and volcanic rocks of the classic Yerington magmatic system, Nevada. We show that the magmas in the upper parts of the system (< 8 km) underwent a major and rapid change in chemistry over a period of < 200 kyrs that is coincident with the initiation of ore formation. We attribute this change to a shift from extraction of quartz monzodiorite and quartz monzonite magmas evolving in mid-crustal reservoirs, and that had relatively poor ore-forming potential, to extraction of volatile-rich granitic magmas from greater (~ 30 km) depths. As the granites crystallised, late stage melts were intruded through the carapace as aplite dykes which contain traceable expressions of the porphyry deposit-forming fluids. The rapid nature of the shift in ore-forming potential narrows the temporal-geochemical footprint of magmas associated with porphyry mineralisation and provides new constraints for exploration models. [ABSTRACT FROM AUTHOR]

A current mineral exploration focus is the development of tools to identify magmatic districts predisposed to host porphyry copper deposits. In this paper, we train and test four, common, supervised machine learning algorithms: logistic regression, support vector machines, artificial neural networks (ANN) and Random Forest to classify metallogenic 'fertility' in arc magmas based on whole-rock geochemistry. We outline pre-processing steps that can be used to mitigate against the undesirable characteristics of geochemical data (high multicollinearity, sparsity, missing values, class imbalance and compositional data effects) and therefore produce more meaningful results. We evaluate the classification accuracy of each supervised machine learning technique using a tenfold cross-validation technique and by testing the models on deposits unseen during the training process. This yields 81–83% accuracy for all classifiers, and receiver operating characteristic (ROC) curves have mean area under curve (AUC) scores of 87–89% indicating the probability of ranking a 'fertile' rock higher than an 'unfertile' rock. By contrast, bivariate classification schemes show much lower performance, demonstrating the value of classifying geochemical data in high dimension space. Principal component analysis suggests that porphyry-fertile magmas fractionate deep in the arc crust, and that calc-alkaline magmas associated with Cu-rich porphyries evolve deeper in the crust than more alkaline magmas linked with Au-rich porphyries. Feature analysis of the machine learning classifiers suggests that the most important parameters associated with fertile magmas are low Mn, high Al, high Sr, high K and listric REE patterns. These signatures further highlight the association of porphyry Cu deposits with hydrous arc magmas that undergo amphibole fractionation in the deep arc crust. [ABSTRACT FROM AUTHOR]

[Display omitted] • Gangjiang porphyry Cu–Mo mineralization is associated with adakitic intrusions. • Copper-Mo orebodies are hosted in the potassic and phyllic alteration zones. • Intrusions were derived from the mixture of crust and metasomatized juvenile mantle. • The mantle components increased from the west section to the east section of the Gangdese. The Gangjiang Cu–Mo deposit is located in the central Gangdese porphyry Cu belt (GPCB), south Tibet. Geological investigation reveals that the Gangjiang deposit is characterized by early potassic alteration, followed by late phyllic and argillic alteration. Late alteration has different degrees of overprinting over the potassic alteration zone. Copper-Mo orebodies are predominantly hosted in the potassic and phyllic alteration zones of the Miocene monzogranite porphyry (MGP) and granodiorite porphyry (GDP). In this study, we present the chemistry and Sr–Nd–Pb–Hf–O isotope compositions of fertile MGP and GDP, barren tonalite porphyrite (TP), and microgranular mafic enclaves (MMEs). Chemical compositions indicate that these intrusions are I-type granites that show high–K calc-alkaline signatures. The negative correlation between Dy/Yb and SiO 2 indicates that the intrusions experienced fractionation of amphibole. They have high Sr/Y (>70) and La/Yb (>38) ratios, strong negative Nb–Ta–Ti anomalies, and positive Pb anomalies are typical for arc magma. The high Mg# of various porphyry intrusions (43–65) and MMEs (47–58) indicate the input of mafic components. Various intrusions have whole-rock 87Sr/86Sr (t=13Ma) ratios of 0.70529 to 0.70674, negative εNd (t=13Ma) (−5.0 to −1.2), positive zircon εHf(t) (1.2–9.8), and homogeneous δ18O (5.8–7.1 ‰, mean 6.6 ‰). The MMEs have similar Sr–Nd–Pb–Hf–O isotopic compositions with their host rocks. The features reveal that the Gangjiang adakite-like intrusions and MME samples were derived from the partial melting of the Lhasa Paleoproterozoic crust, with contributions from the juvenile mantle that has been metasomatized by subducted sediments-derived melts. Note, the MGP, GDP, and two types of MMEs have slightly lower δ18O values (down to 4.76 ‰) but higher εNd (t) (up to −1.2) than barren TP, indicating their formation involves more mantle components. Furthermore, the MMEs in the TP and MGP have high Cu contents (up to 1485 ppm), similar to the phenomenon occurs in the Qulong deposit. The Cu-rich MME is probably formed by Cu-refertilization by the underplate arc magma in the juvenile crust. The εHf(t) and εNd(t) values of fertile porphyries increased from the Jiru, Gangjiang, to Qulong deposit indicating increased mantle material additions from the west to the east section of the GPCB. These variations in mantle components have led to an increase in the size of the porphyry Cu deposits from Jiru to Gangjiang, and then to Qulong. [ABSTRACT FROM AUTHOR]

• Recognition of two distinct stages of A-type magmatism at 1.65 Ga and 1.60 Ga in the North China Craton. • Geochemical and isotopic compositions of the two stages A-type granites indicate gradual crustal extension and asthenosphere upwelling processes. • Tectonic transition from post-orogenic to anorogenic settings took place at the late Paleoproterozoic. Paleoproterozoic and Mesoproterozoic A-type granites occur on many cratons and possess important information for our understanding of the formation and breakup history of the supercontinent Columbia. It was argued previously, that Proterozoic A-type granites (∼1.8–1.5 Ga), exposed along the southern margin of the North China Craton formed in a post-collisional or anorogenic setting related to the final amalgamation of the North China Craton or to the breakup of Columbia. In the present study, we report zircon ages and geochemical data of the Maping A-type granite. This intrusion consists of a quartz monzonite porphyry and a granite porphyry that, based on U-Pb age dating, formed at ∼ 1.65 and ∼ 1.60 Ga, respectively. The granites show high contents in alkaline and high field strength elements, high Ga/Al and Fe/Mg ratios. The quartz monzonite porphyry of the early stage is metaluminous and relatively depleted in Hf-Nd isotopic compositions (whole-rock initial ε Nd values −5.4 to −4.5; zircon initial ε Hf values −8.5 to −1.5), while granite porphyry of the late stage is peraluminous and has lower initial ε Nd and ε Hf values (−6.4 to −5.9; −9.6 to −3.3). Inherited zircon grains in the Maping intrusion have relatively high initial ε Hf values (>-0.7), likely originating from juvenile crust. The Pb isotopes of the quartz monzonite porphyry show characteristics similar to the lower crust, whereas the granite porphyry has more radiogenic Pb isotopic compositions. Apatite grains from the quartz monzonite porphyry have initial 87Sr/86Sr ratios of ∼ 0.7109–0.7133 and those from the granite porphyry have noticeably high initial 87Sr/86Sr ratios of ∼ 0.7862–0.8812. These isotopic characteristics imply the presence of various crustal rocks underneath the North China Craton with variable isotopic compositions. From the early to late magmatic stages, the Sr/Y ratios of granitic rocks decrease from 1.6 – 7.6 to 0.2–0.4, while the estimated magma temperatures, calculated from whole-rock compositions, slightly increase from approximately 900 °C to about 930 °C. These concurrent changes in temperature and chemical composition reflect ongoing asthenospheric mantle upwelling during crustal extension. This suggests a transition in the southern margin of the North China Craton from a post-collisional setting before 1.65 Ga to an anorogenic setting by 1.6 Ga. [ABSTRACT FROM AUTHOR]

Volatile-bearing minerals, such as apatite, Ca 5 (PO 4) 3 (OH,F,Cl), can record changes in dissolved magmatic volatile species during differentiation and, unlike melt inclusions, are sensitive to the presence of an exsolved fluid phase. Populations of apatite crystals from an individual sample can therefore be used to define the progressive volatile evolution of melt ± fluid during magma differentiation. Despite the importance of fluid chemistry in mineralisation processes, this approach remains relatively underdeveloped for porphyry mineralisation scenarios. Here, we present a model, including a standalone MATLAB app, for melt + apatite ± fluid fractionation that incorporates non-ideal, temperature-dependent K D s for OH-Cl-F exchange and permits an analysis of uncertainty arising from non-unique parameter combinations. We apply the model to apatite from the Fe-Cu-Au Corrocohuayco porphyry-skarn system and analyse differences in volatile saturation state and fluid salinity between different units. We find that there is little difference in the overall fluid salinity, and thus the fluid copper loads, but that the more primitive unit (i.e. the gabbrodiorites) reached fluid saturation much later (after around 50% crystallisation) than the more evolved units, implying that the melt volatile concentration recorded by the apatites in the gabbrodiorites is not representative of the initial magma volatile budget. This work demonstrates that apatite can be a good alternative means of reconstructing the evolving magmatic fluid salinity within mineralising systems, and linking this to the trace metal content of the melt. • A MATLAB app for non-ideal, temperature-dependent melt + apatite ± fluid fractionation and sensitivity analysis • Gabbrodiorites reached fluid saturation much later than evolved porphyry units. • Fluid salinities calculated independently from apatite are ∼4–10 wt% NaCleq. • Apatite can be used to reconstruct evolving melt composition and fluid salinity. [ABSTRACT FROM AUTHOR]

A 3-D lithospheric resistivity model is obtained with 699 MT stations. The upper-mantle low-resistivity anomalies beneath the eastern SCB show a spatial distribution that is gradually shallowing from south to north, probably indicating that the asthenospheric materials are upwelling from south to north, corresponding with the changing progressively of magma and metallogenic activities. [Display omitted] • The 3-D lithospheric resistivity structure of the lithosphere in South China is obtained by inverting 699 MT stations. • The resistivity structure and disposition of four metallogenic belts in the South China Block are outlined. • The upper-mantle low-resistivity anomalies show a spatial distribution of gradual shallowing, indicating the asthenospheric upwelling from south to north. The South China Block (SCB) is located at the junction of the Pacific, Eurasian, and Indo-Australian plates. Their interaction led to large-scale multi-stage mineralization in the SCB during the Mesozoic. Several regional ore-concentration areas, such as the Middle-Lower Yangtze Metallogenic Belt (MLYMB), the Qinzhou-Hangzhou Metallogenic Belt (QHMB), the Wuyishan Metallogenic Belt (WYMB), and the Nanling Metallogenic Belt (NLMB) were formed during this process. However, the dominant mineral types of these metallogenic belts are different. To study the deep mechanisms of the different metallogenic types developed in the same tectonic background at almost the same period, the magnetotelluric sounding (MT) data from 691 sites located mainly within the eastern SCB are employed to obtain a regional lithospheric 3-D resistivity model. It could be concluded from the resistivity model that deep low-resistivity anomalies and mantle upwelling channels mainly controlled almost all the Mesozoic deposits. Large-scale low-resistivity bodies extend from the crust to the upper mantle beneath the MLYMB and the QHMB, interpreted as channels of mantle-derived magma and melts/fluids containing metallogenic elements upwelling. However, the MLYMB and the QHMB have different upper crustal ore-conducting and ore-controlling structures, thus forming porphyry copper and copper-bearing tungsten deposits. Small-scale low-resistivity anomalies are invading the high-resistivity crust in the NLMB. And remelting the upper crust, mixing, and intrusion of crust-source magma, enriching tungsten-tin elements near the NLMB. Larger-scale low-resistivity anomalies exist deep in the WYMB, remelting the lower crust and resulting in the formation of porphyry copper in it. Significantly, the upper-mantle low-resistivity anomalies beneath the eastern SCB show a spatial distribution that is gradually shallowing from south to north, probably indicating that the asthenospheric materials are upwelling from south to north, corresponding with the changing progressively of magma and metallogenic activities. We propose that the lithospheric delamination and asthenospheric upwelling caused by the far-field effects of the Paleo-Pacific Plate subduction are the sources of solid magmatic activities and related metallogeny. [ABSTRACT FROM AUTHOR]

Arc basalts with high H 2 O content are expected to evolve into highly hydrated felsic melts saturated with aqueous fluids at lower crustal pressures, which are potentially important in providing sulfur (S) and metals for porphyry deposit formation. However, the role of such highly hydrated and fluid-saturated magmas in the transfer of S (and metals) remains rarely studied. To investigate the S dissolution capacity of highly hydrated felsic magmas saturated with fluids at the lower crustal conditions, this study performed experiments with dacite + 10 wt% FeS at H 2 O contents of 10, 15, and 20 wt%. All the experiments were performed in piston-cylinder apparatus at 1.0 GPa and 950 °C with f O 2 conditions imposed by the following solid-state buffers: cobalt-cobalt oxide (CCO), nickel-nickel oxide (NNO), rhenium-rhenium oxide (RRO), MnO-Mn 3 O 4 (MMO), and hematite-magnetite (HM), resulting in a f O 2 range of FMQ−1.5 to FMQ+3.3 log units (FMQ = fayalite + magnetite + quartz oxgen buffer). The experimental results show that the H 2 O content in the felsic melt, in addition to f O 2 and melt composition, has a strong effect on the concentration of S in the silicate melt at sulfide ± anhydrite saturation. At a given f O 2 , the S concentration in the melt increases with increasing H 2 O content (hydration), resulting in a S concentration of up to ∼8000 ppm in the highly hydrated dacitic melts at f O 2 ∼ FMQ+2. We found that high melt hydration at an intermediate f O 2 not only dramatically increases sulfide and anhydrite solubilities in the dacitic melts but also promotes the saturation of S-rich fluids. The S concentration in the fluid that corresponds to the highest measured S concentrations in the melt (∼8000 ppm) are ∼5 wt%. These results show that highly hydrated felsic magmas saturated with fluids have a high capacity for S dissolution. Therefore, injection of such fluid-saturated magmas from lower crustal to shallow magma reservoirs is a potential mechanism for the effective transport of S (and perhaps metals) to facilitate subsequent porphyry ore deposit formation. [ABSTRACT FROM AUTHOR]

Porphyry Mo deposits have traditionally been classified into two major classes, arc-related and Climax-type, based on the tectonic setting and chemistry of associated intrusions. Although there is a consensus that porphyry Mo systems were formed by the optimal coincidence of geological processes operating at different scales, it is unclear what key parameter(s) render systems productive and whether the two classes of porphyry Mo deposits are unique in their mode of formation, or if they share fundamentally similar geological processes. These questions are important as a clearer understanding of the optimum conditions for the formation of porphyry Mo deposits is a prerequisite for more efficient exploration. This contribution presents a detailed assessment of the factors affecting the formation of porphyry Mo deposits through the investigation of barren and mineralized intrusions from the arc-related Songbei-Yangjiazhangzi-Lanjiagou (SYL) ore zone and the Climax-type Hashitu deposit of northeastern China. Our results show that the syn-mineralization intrusions from the SYL ore zone are quite evolved (SiO2 ~ 75 wt%; Na2O+K2O ~ 8.7 wt%) and are characterized by apparent light rare earth element (LREE) enrichments (LaN/YbN = 2.7–33.1) and moderate negative Eu anomalies (Eu/Eu* = 0.4–0.7). They show enriched zircon Hf isotopic compositions [εHf(t) = –11.9 to –4.8], indicating their parental magmas were likely derived from an ancient crustal source. Melt inclusions from the SYL syn-mineralization intrusions contain negligible F and Cl. In contrast, Hashitu syn-mineralization intrusions are characterized by weak LREE enrichments (LaN/YbN = 2.2–6.9) and strong negative Eu anomalies (Eu/Eu* = 0.02–0.10), with SiO2 and Na2O+K2O contents similar to the SYL syn-mineralization intrusions. They show depleted zircon Hf isotopic compositions [εHf(t) = 3.1–5.0], indicating their parental magmas were likely derived from a juvenile crustal source. Melt inclusions from the Hashitu syn-mineralization intrusions contain up to 0.4 wt% F and 0.03 to 0.09 wt% Cl. However, in both cases, the syn-mineralization intrusions are Mo-poor (1–7 ppm Mo), oxidized (above the quartz-fayalite-magnetite buffer), water-saturated (4.4–7.8 wt% H2O), and were emplaced at palaeodepths of 3.3 to 8.3 km. These data imply that magma source composition is not a key factor in the formation of porphyry Mo deposits. In contrast, magma oxygen fugacity, water content, and emplacement depth appear to play fundamental roles in the formation of porphyry Mo deposits of both arc-related and Climax-type. Within individual deposits, no systematic differences between pre- and syn-mineralization intrusions are observed in terms of magma source, fractionation degree, oxygen fugacity, emplacement depth, and volatile and Mo contents. Instead, a crucial apparent difference lies in the geometry of the intrusions, i.e., pre-mineralization intrusions generally occur as flat, ponded bodies, whereas syn-mineralization intrusions commonly develop as small stocks or dikes. Our results, in combination with an examination of other porphyry Mo systems, suggest that the sudden depressurization of magma chambers and subsequent venting of voluminous fluids along focusing structures (such as small stocks or dikes) most likely plays a critical role in the formation of porphyry Mo deposits of both arc-related and Climax-type. The findings of this study indicate that fluid processes in the shallow crust are pivotal for the formation of porphyry Mo deposits and that settings with ideal magmatic-hydrothermal architectures are most likely to develop into productive porphyry Mo systems. [ABSTRACT FROM AUTHOR]

Large and easily accessible porphyry Cu deposits have already been identified, exploited, and gradually exhausted. Novel strategies, therefore, are required to identify new, deeply buried deposits. Previous studies have proposed several lithogeochemical and mineralogical approaches for identifying porphyry Cu systems. Most of these methods, however, require significant a priori knowledge of the exploration region and are, generally, of low effectiveness. In this study, machine learning models using Random Forest and Deep Neural Network algorithms are utilized to characterize magma fertility. The two models have first been trained using a large trace‐element data set of magmatic zircon and then validated on unseen data set during the training process. The performance of both models was evaluated using a fivefold cross‐validation technique, which demonstrates that the models provide consistent results and yield good classification accuracy (∼90% on average) with low false positive rates. Feature importance analysis of the models suggests that Eu/Eu*, Eu/Eu*/Y, Ce/Nd, Ce/Ce*, Dy, Hf, and Ti are the important parameters that distinguish fertile and barren zircons. The real‐world applicability of the validated models was evaluated using two well‐characterized porphyry Cu deposits in subduction and postcollisional settings—the Highland Valley porphyry Cu district (south‐central British Columbia, Canada) and the southern Gangdese belt (Tibet, China), respectively. The results demonstrate that our generalized models can discriminate zircon from igneous rocks associated with porphyry Cu deposits from those in nonmineralized systems with high accuracy and independent of geological setting, suggesting that this new approach can be used effectively in greenfield and brownfield exploration. Plain Language Summary: Mineral resources, which are important to the development of human society, are increasingly being consumed as our need for technological advancement increases. With this consumption comes the need to identify additional resources, many of which may be invisible at the Earth's surface. This challenges current exploration methods, requiring novel techniques to be developed to identify variably mineralized rock below Earth's surface. In this study, machine learning methods are trained using a global data set of zircon chemistry to evaluate the prospectivity of porphyry Cu mineralization in magmatic districts. This work demonstrates that machine learning methods provide a robust, accurate, and effective approach to identifying porphyry Cu mineral resources. Key Points: A global data set of magmatic zircon trace‐element chemistry is used to train two separate machine learning algorithmsThe Eu/Eu*, Eu/Eu*/Y, Ce/Nd, and Ce/Ce* ratios, and Dy, Hf, and Ti contents are important for distinguishing fertile and barren zirconsThe performance of the machine learning models is not affected by regional differences and geological setting [ABSTRACT FROM AUTHOR]

New LA‐ICP‐MS zircon U–Pb geochronology, whole‐rock geochemistry and Hf isotopic data have been studied on the Taipingtun granite porphyry to determine its petrogenesis and constrain the tectonic setting of the central Great Xing'an Range, northeastern China, during the Early Cretaceous. The results of zircon U–Pb dating suggest that the Taipingtun granite porphyry was emplaced during the Early Cretaceous (122–123 Ma). Geochemically, the granite porphyries have high contents of SiO2 (75.76–78.66 wt%) and (K2O + Na2O) (7.14–8.29 wt%), and low Al2O3 (11.09–12.81 wt%) and CaO (0.15–0.29 wt%), indicating peraluminous and high‐K calc‐alkaline features. Additionally, these rocks are characterized by strong Th, U, K, and Rb enrichment; Ba, Sr, P and Ti depletion; high Ga/Al ratios (10,000*Ga/Al = 2.60–4.92) and negative Eu anomalies (δEu = 0.02–0.13). According to the zircon saturation thermometer results, zircon saturation temperatures range from 756 to 959°C with an average of 823°C, displaying high magmatic temperature for the parental magma. Based on these geochemical characteristics, it can be reasonably inferred that the initial composition of the Taipingtun granite porphyry melts exhibited an A‐type magmatic affinity. Furthermore, zircon grains within the Taipingtun granite porphyry have εHf(t) values of 7.12 to 10.99 and TDM2 model ages of 476–726 Ma. The Ba/La (average 3.89), Nd/Th (average 2.25), Zr/Hf (average 22.55), Ti/Zr (average 2.96) and Rb/Sr (average 4.21) values display the characteristics of crust‐derived magmas. Moreover, these rocks have obviously negative Eu anomalies (average 0.13) and relatively high Y (average 37.83 ppm) and Yb (average 4.15 ppm) contents, suggesting the magmas are generated in a low‐pressure environment. Thus, we consider the primary magmas of the Taipingtun granite porphyry may have been predominantly derived from the partial melting of juvenile crustal rocks at low pressure. Combined with the regional geological data, we suggest that the Taipingtun granite porphyry was formed in an extensional tectonic environment, and possibly related to the subducted Palaeo‐Pacific Ocean Plate in the Early Cretaceous. [ABSTRACT FROM AUTHOR]

The Rio Blanco deposit, which is one of the largest porphyry Cu–Mo deposits in northern Peru, formed coevally with the subduction of the Inca Oceanic Plateau at 12–10 Ma. However, the genetic relationship between the subduction of oceanic plateaus and the porphyry deposit formation remains unclear. Igneous rocks emplaced at 23–12 Ma in northern Peru, including the Portachuela batholith (which hosts the Rio Blanco porphyry complex), are normal calc-alkaline to weakly adakitic. In comparison, the 12–8 Ma igneous rocks, including the ore-related Rio Blanco porphyry complex, have typical adakitic signatures, such as high Sr/Y ratios (up to 180) and LaN/YbN ratios (up to 32). The Rio Blanco igneous rocks (Portachuela batholith and Rio Blanco porphyry complex) have uniform zircon εHf(t) values (+0.3 ± 1.2) and δ18O values (6.5 ± 0.14‰). These geochemical characteristics indicate that the Rio Blanco igneous rocks evolved from mantle-derived parental melts in a long-lived, stable, homogeneous isotopic reservoir at the crust–mantle boundary. However, whereas both the Portachuela batholith and the Rio Blanco porphyry complex formed from hydrous parental magmas (>5 wt %; based on plagioclase hygrometry), the ones of the Rio Blanco porphyry complex seem to be more oxidized, hydrous, and sulfur-rich compared with the older batholitic rocks. Reverse zoning in plagioclase phenocrysts, with a systematic core–mantle–rim variation in An (anorthite) and Fe (total iron) contents, are common in the intermineralization rocks. The An content of the mantles of the plagioclase phenocrysts correlates positively with the Fe content, but in the rims, the An contents significantly decrease while Fe remains constant. The apatite inclusions in the mantles are richer in S (0.24 ± 0.06 wt %) and Cl (1.42 ± 0.32 wt %) than those in the phenocryst cores (S: 0.09 ± 0.07 wt %; Cl: 1.03 ± 0.56 wt %) and rims (S: 0.14 ± 0.09 wt %; Cl: 0.83 ± 0. 35 wt %). These systemic geochemical variations in the plagioclase phenocrysts suggest recharge by S- and Cl-rich melts followed by fluid exsolution. This magma recharge and subsequent fluid exsolution may have triggered porphyry Cu mineralization at Rio Blanco. The coincidence of timing between the geochemical transition and collision (initial subduction) of the Inca Oceanic Plateau with the South American plate may indicate a change in the tectonic regime to a compressional state of stress and a thickening of the crust during the collision. The tectonic transition would have facilitated the fractionation of mantle-derived magma in a deep crustal hot zone, resulting in oxidized, volatile-rich residual melts. Replenishment of the upper-crustal magma chamber by such volatile-rich magmas and the subsequent discharge of fluids are interpreted to be fundamental for porphyry Cu mineralization at Rio Blanco and plausibly for the formation of Late Miocene porphyry ore deposits in northern Peru in general. [ABSTRACT FROM AUTHOR]

Compared with the porphyry Cu-epithermal Au mineralization system, detailed studies on the porphyry Mo-epithermal Pb–Zn–Ag–Au mineralization are rare due to limited exposures. The Shipingchuan polymetallic deposit, located in the South China Mo Province (SCMP) represents a typical example containing both porphyry Mo and epithermal Pb–Zn–Ag mineralization. The Mo mineralization mainly occurs as molybdenite-quartz veins in veinlets or as disseminated molybdenite within the potassic, silicic, and sericitic syenogranite. The Pb–Zn–Ag mineralization is characterized by veinlet-type sphalerite–galena–pyrite–quartz–calcite vein within the volcanic rocks accompanied with silicification and propylitization. Five molybdenite samples yield a Re–Os isochron age of 104.7 ± 0.7 Ma that is consistent with the zircon age (107.5 ± 2.1 Ma) of the ore-bearing syenogranite within errors. Together with previous reported Ar–Ar ages (106.6–121.8 Ma) of Pb–Zn–Ag related volcanic rocks, the Mo and Pb–Zn–Ag mineralization belong to a magmatic-hydrothermal event in the Early Cretaceous. Meanwhile, the total Re contents of molybednite range from 1.28 to 45.55 ppm, indicating the ore-forming materials were from a mixture between the mantle and crustal material. Moreover, previous sulfur isotopic values (3.7–4.3‰) of the pyrites from the porphyry Mo mineralization were consistent with the reported range of 4.0–6.1‰ of the sphalerites from the Pb–Zn–Ag mineralization, implying that the sulfur of two-types of mineralization was derived from magma. The above-mentioned spatial, temporal, and isotopic lines of evidence suggest that the Mo and Pb–Zn–Ag mineralization of the Shipingchuan deposit was formed from the same metallogenic system. In consideration of regional tectonic evolution history, we propose that the porphyry Mo-epithermal Pb–Zn–Ag mineralization formed in an extensional tectonic setting caused by the continued rollback and the eventual slab break-off of the subducting Paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

Mount Hagen is a mid-Pleistocene stratovolcano located in the Papua New Guinea Highlands. It was selected for this study because of (1) its close location to several giant Cu–Au porphyry deposits in the region; (2) its high-K calc-alkaline character (absarokite–shoshonite) and (3) its wide compositional range (2 to 12 wt % MgO). Whole-rock geochemistry, petrography and QEMSCAN observations are consistent with fractional crystallisation of the evolving magma being controlled by the phases now represented by the megacrysts in the lavas: olivine and clinopyroxene at high MgO and hornblende and plagioclase at low MgO. However, the role of plagioclase is enigmatic. Although it is an abundant megacryst phase in the low-MgO samples, plagioclase has little or no influence on fractional crystallisation, suggesting that it may be an antecryst. The appearance of plagioclase megacrysts does not slow the rate of increase in Al2O3 or Sr with decreasing sample MgO and the low-MgO samples do not have Eu anomalies. At ~5.5 wt % MgO, there are significant changes in the system that are inconsistent with simple fractional crystallisation. These changes include hornblende and plagioclase replacing olivine and clinopyroxene as the principal megacryst phases, a sharp rise in platinum-group elements (PGE) concentrations, the brief reappearance of high Fo olivine megacrysts and reversed zoning in the plagioclase megacrysts. These changes are interpreted to have resulted from a new pulse of magma entering the system, with higher water, MgO, SiO2 and PGE concentrations than the original parent magma. Scatter in the PGE data is attributed to the presence of micronuggets in all samples, including the most mafic samples. We conclude that the magma system became sulphide saturated during an early stage in its fractionation history, probably before leaving the crust to deep crustal magma chamber, and then became undersaturated as a consequence of decreasing pressure as magma ascended into a mid-crustal magma chamber. The early saturation episode had a pronounced influence on PGE concentration but had little affect Cu and Au, due to their lower partition coefficient into sulphides. The magma became sulphide saturated again in the crustal magma chamber at ~8.5 wt % MgO, this time affecting all chalcophile elements. Given the early episodes of sulphide saturation, depletion in Au in the Mount Hagen magma system and the absence of a known porphyry system, it is unlikely that Mount Hagen produced economic porphyry mineralisation. [ABSTRACT FROM AUTHOR]

Porphyry deposits supply most of the world's Cu and Mo resources. Most porphyry deposits are developed in magmatic arcs above subduction zones. However, abundant Miocene porphyry Cu-Mo deposits have been found in the post-collision stage in Tibet, more than ∼30 Myr after the Indian-Eurasian continental collision. The magma source and the enrichment process of ore-forming elements for these post-collision porphyry deposits remain controversial. Here, we present Sr-Nd-Mo isotope compositions of a suite of mineralized and barren igneous rocks from the Rongmucuola pluton in the Miocene post-collisional Qulong porphyry Cu-Mo deposit in Tibet to reveal their magma sources and ore-forming processes. Our results indicate that the mineralized and barren igneous rocks in the Qulong deposit were derived from a cogenetic source with similar Sr-Nd isotope compositions (87Sr/86Sr (i) = 0.7049–0.7050 and ε Nd (t) = −0.24 to 0.20). However, the mineralized igneous rocks have large variations in δ98/95Mo values (−0.30‰ to 0.74‰; relative to NIST SRM 3134) and Mo/Ce ratios (0.01 to 4.84) compared to those of the barren igenous rocks (δ98/95Mo = −0.74‰ to −0.02‰; Mo/Ce = 0.01 to 0.04). In combination with the higher LOI values, Mo/Ce and Cs/Ta ratios and Cu concentrations and lower Ce/Pb ratios of the mineralized igneous rocks relative to the barren igneous rocks, we propose the mineralized igneous rocks were affected by ore-forming hydrothermal fluids originated from the exsolution of later co-genetic magmas, which significantly changed the isotopic and elemental compositions of intrusions and resulted in Mo mineralization. The fluid-rock interaction modeling supports this interpretation and successfully reproduce the observed δ98/95Mo and Mo/Ce compositions of mineralized igneous rocks. Our study indicates that the exsolved magmatic-hydrothermal fluids have heavy Mo isotopes, and the fluids with a slightly heavier Mo isotope composition have the greatest potential for mineralization. As the water-rock reaction progresses, leading to the precipitation of Mo-rich minerals, ore-forming fluids with a heavier Mo isotope composition may not have significant mineralization potential. This highlights that Mo isotope system is an effective tool to study the ore-forming processes of porphyry deposits. [ABSTRACT FROM AUTHOR]

Numerous studies have argued that the andesitic model (i.e., the arc directly produces andesitic magmas) rather than the basaltic-input model (i.e., andesitic magmas were derived by fractionation from basaltic magmas) better explains the composition of continental crust. However, it remains controversial as to how andesitic magmas are directly produced in subduction zones, and this weakens the basis of the andesitic model. Recently, the mélange-diapir model has been increasingly considered to be an important mechanism for the direct generation of arc andesites, and would thus support the andesitic model for crustal growth. Moreover, melting experiments on mélange rocks show that varying the composition of mélange rocks (e.g., serpentinite-dominated and sediment-dominated mélange) can produce a range of primary andesitic arc magmas, from tholeiitic, calc-alkaline, to high-K calc-alkaline and shoshonitic magma types. However, it remains challenging to determine the different mélange sources for low-K to high-K arc andesites. Here we verify these experimental results using data from early Cretaceous dioritic porphyries in the southern Qiangtang block of central Tibetan plateau. The generation of these dioritic rocks cannot be linked to any coeval basaltic rocks in this region and so they may represent primary andesitic magmas. These dioritic porphyries are divided into low-K type-1 and high-K type-2. Type-1 has higher δ26Mg values (−0.16 to −0.08‰) than MORBs (mid-ocean ridge basalt, δ26Mg = −0.25 ± 0.06‰), which can be ascribed to the contribution of subducted bulk/un-differentiated serpentinite in their source. Combined with their low K contents and La/Sm ratios, and high Nd Hf isotope ratios (εNd(t) = 3.36–5.03; εHf(t) = 12.88–13.76), we suggest a serpentine-dominated mélange for their origin. The type-2 and type-1 rocks have similar trace-element distribution patterns, the same ages (∼124 Ma), and are indistinguishable in field outcrops, indicating their common petrogenesis. However, compared to type-1, type-2 has higher K and Th contents, and La/Sm and Th/Nd ratios with lower Nd Hf isotope values (εNd(t) = −1.61 to +0.30; εHf(t) = 3.78–4.39), and mantle-like δ26Mg values (−0.28 to −0.17‰). This likely indicates derivation from a sediment-dominated mélange for type-2. This study thus verifies the experimental results of melting of different mélange from natural rock record and shows that the mélange model provides an important mechanism for generating variable andesitic arc magmas and so the formation of the andesitic continental crust. • Gerze ∼124 Ma dioritic porphyry dykes in Tibetan plateau represent primary andesitic magmas and are divided into two types. • Low-K and high-K rocks originated from serpentinite-dominated mélange and sediment-dominated mélange, respectively. • This study verifies experimental results of melting of different mélange rocks, arguing for andesitic crustal growth. [ABSTRACT FROM AUTHOR]

Explanation: From Lakange Mo (Cu) deposit to Jiama Cu polymetallic deposit to Bangpu Mo mineralization to Qulong Cu-Mo deposit to Bangpu Cu mineralization, the Cl contents in apatite gradually increase, but the F contents in apatite gradually decrease, and the S content is similar but variation. It indicates that the Mo-dominated porphyry deposit formed from F-S-rich magma, whereas the Cu-dominated porphyry deposit formed from Cl-S-rich magma. [Display omitted] • There are two different magmatic-hydrothermal systems that formed the Bangpu Mo-Cu deposit. • Cu and Mo mineralization contain zircon and apatite with different geochemical features. • Cu mineralization was related to Cl-rich porphyry system, whereas Mo-mineralization was related to F-rich porphyry system. 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. Cu and Mo mineralization occurred separately in the Bangpu deposit. Mo (Cu) mineralization occurred mainly in the monzogranite porphyry (MP), while Cu (Mo) mineralization occurred mainly in the diorite porphyry (DP). The cause of such spatial differences in Cu and Mo mineralization in the Bangpu deposit remains unclear. In this study, the mineral chemistry of apatite and zircon was investigated to reveal the differences in the nature of ore-forming magma between Cu (Mo) and Mo (Cu) mineralization in the Bangpu deposit. The chondrite-normalized REE patterns of the apatite grains from the MP were enriched in LREEs with negative Eu anomalies, whereas those from the DP and biotite monzonitic granite (BM) had strong negative Eu anomalies with no obvious differentiation between LREEs and HREEs. The DP, MP, and BM have a low T TiZ range from 657 °C to 917 °C and a high AST range from 687 °C to 1079 °C. The zircon grains from the DP and MP had different Th/U ratios and T TiZ values, indicating that these porphyry samples probably experienced different magma crystallization or crystal fractionation histories. The zircon Ce4+/Ce3+ and Eu/Eu* ratios indicate that the ore-bearing DP and MP have higher oxygen fugacity than the BM. The F, Cl, and S contents in the apatite showed that the DP magmas were Cl- and S- rich, whereas the MP magmas magmas were F- and S- rich. The Bangpu porphyry Mo-Cu deposit results from two superimposed magmatic-hydrothermal systems. Mo was mainly partitioned into the F-rich magmatic-hydrothermal system released from the MP, and Cu was mainly partitioned into the Cl-rich magmatic-hydrothermal system released from the DP. Our results show that zircon and apatite geochemistry can be used to explain the spatial distribution of Cu and Mo mineralization in porphyry Cu-Mo systems. [ABSTRACT FROM AUTHOR]

Arc magmas globally are H2O-Cl-S-rich and moderately oxidized (ΔFMQ = +1 to +2) relative to most other mantle-derived magmas (ΔFMQ = 0). Their relatively high oxidation state limits the extent to which sulfide phases separate from the magma, which would otherwise tend to deplete the melt in chalcophile elements such as Cu (highly siderophile elements such as Au and especially platinum-group elements are depleted by even small amounts of sulfide segregation). As these magmas rise into the crust and begin to crystallize, they will reach volatile saturation, and a hydrous, saline, S-rich, moderately oxidized fluid is released, into which chalcophile and any remaining siderophile metals (as well as many other water-soluble elements) will strongly partition. This magmatichydrothermal fluid phase has the potential to form ore deposits (most commonly porphyry Cu ± Mo ± Au deposits) if its metal load is precipitated in economic concentrations, but there are many steps along the way that must be successfully negotiated before this can occur. This paper seeks to identify the main steps along the path from magma genesis to hydrothermal mineral precipitation that affect the chances of forming an ore deposit (defined as an economically mineable resource) and attempts to estimate the probability of achieving each step. The cumulative probability of forming a large porphyry Cu deposit at any given time in an arc magmatic system (i.e., a single batholith-linked volcanoplutonic complex) is estimated to be ~0.001%, and less than 1/10 of these deposits will be uplifted and exposed at shallow enough depths to mine economically (0.0001%). Continued uplift and erosion in active convergent tectonic regimes rapidly remove these upper-crustal deposits from the geological record, such that the probability of finding them in older arc systems decreases further with age, to the point that porphyry Cu deposits are almost nonexistent in Precambrian rocks. A key finding of this paper is that most volcanoplutonic arcs above subduction zones are prospective for porphyry ore formation, with probabilities only falling to low values at late stages of magmatic-hydrothermal fluid exsolution, focusing, and metal deposition. This is in part because of the high threshold required in terms of grade and tonnage for a deposit to be considered economic. Thus, the probability of forming a porphyry-type system in any given arc segment is relatively high, but the probability that it will be a large economic deposit is low, dictated to a large extent by mineral economics and metal prices. [ABSTRACT FROM AUTHOR]

Melt inclusion (MI) homogenization experiments are essential for determining the pressure-volume-temperature-composition (P-V-T-X) parameters of magma systems. The hydrothermal diamond-anvil cell (HDAC) is currently the only equipment that can exert external pressure on MIs while allowing in situ observation of MI phase changes during heating. The HDAC's pressure potentially prevents the MI diffusion that, under heating at one atmosphere, produces artificially elevated measurements of phase transition temperatures. It is important to compare the phase transition temperatures measured using HDAC at elevated external pressure with those obtained using conventional equipment at one atmosphere. Such a comparison not only helps assess the reliability of HDAC phase transition temperatures but also helps determine phase transition temperatures that are naturally occurring in MI during the natural history of cooling. In this study, we homogenized MIs hosted in quartz from the granitic porphyry in the Yixingzhai Au deposit, China, using HDAC at an elevated pressure of ~(140–230) MPa. We compared our experimental results with published data measured using a Linkam TS1500 stage at one atmosphere. The experiments show that the initial melting temperature (TIniM), total melting temperature (TTotM), and total homogenization temperature (ThTot) of the MIs are 695 ± 20, 780 ± 15, and 833 ± 17 °C, respectively. These phase transition temperatures are as much as 374 °C lower than the corresponding values measured at one atmosphere using the Linkam stage. Moreover, the temperatures measured using HDAC agree with actual values estimated using the linear extrapolation method based on correlations of MI size with phase transition temperatures measured using the Linkam stage. Based on the experimental HDAC results, we estimate that MIs in the Yixingzhai Au deposit were trapped at ~140 Ma and contained ~2 wt% H2O. These values are consistent with previously estimated emplacement pressures and H2O contents of granitic magmas in granitic porphyry-type Cu-Au deposits. Our results demonstrate that MI-homogenization experiments using HDAC at suitably elevated pressures can yield reliable naturally occurring phase transition temperatures in MI during the melt cooling process. [ABSTRACT FROM AUTHOR]

Along the eastern margin of the Mesoproterozoic Namaqua metamorphic province (NMP) of southern Africa are a bimodal volcano-sedimentary succession, the ∼1.13–1.10 Ga Koras Group, composed of rhyolitic porphyries and basaltic andesites, and the ∼1.11–1.07 Ga late- to post-tectonic granitoids of the Keimoes Suite. This review examines existing whole-rock major- and trace-element data, along with isotope chemistry (with some new isotopic data), to investigate the role these two magmatic successions played in terms of post-collisional magmatism of the eastern NMP near the boundary with the Archean Kaapvaal Craton. The Keimoes Suite comprises variably porphyritic biotite monzogranites and granodiorites, with a charnockitic member. They are metaluminous to weakly peraluminous, ferroan, and calc-alkalic. They exhibit large ion lithophile (LIL) element enrichment relative to the high field strength elements (HFSE) with depletions in Ba, Sr, Nb, P, Eu and Ti, and enrichments in Th, U and Pb. Isotopic values (εNd(t): 2.78 to -2.95, but down to -8.58 for one granite, depleted mantle Nd model ages (TDM): 1.62–1.99 Ga, but up to 2.55 Ga; initial 87Sr/86Sr: 0.652 82–0.771 30) suggest derivation from weakly to mildly enriched (and radiogenic) sources of Meso- to Paleoproterozoic age, the former of more juvenile character. The Koras Group is characterized by a bimodal succession of calcic to calc-alkalic, magnesian and tholeiitic basaltic andesites and mostly metaluminous to peralkaline rhyolitic porphyries. Two successions are recognised, an older, lower succession that extruded at ∼1.13 Ga, and a younger, upper succession at ∼1.10 Ga. The rhyolitic porphyries of both successions show similar LILE/HFSE enrichment and the same element enrichments and depletions as the Keimoes Suite granitoids. The upper succession is consistently more fractionated in terms of both whole-rock major and trace element chemistry, and, isotopically, has a greater enriched source component (εNd(t)}: −0.69 to −4.26; TDM: 1.64–2.44 Ga), relative to the lower succession (εNd(t): 0.74–5.62; TDM: 1.28–2.12 Ga). Crystal fractionation of plagioclase and K-feldspar appears to have played a role in bringing about compositional variation in many of the granites. These were derived from partial melting of mainly igneous with subordinate sedimentary sources from mostly lower crustal depths, although some granitoids have indications of a possible mantle source component. The lower succession of the Koras Group was derived by partial melting of subduction-influenced enriched mantle giving rise to mafic magmas that fractionated to give rise to the rhyolitic porphyries. The upper succession rhyolites were derived by crustal melting due to the input of mafic magmatism. Crystal fractionation was the main compositional driver for both successions. The Keimoes Suite granitoids and the Koras Group are associated with extensional regimes subsequent to the main deformational episode in the eastern NMP. [ABSTRACT FROM AUTHOR]

Magmatic-hydrothermal gold–copper deposits in post-subduction settings represent essential targets for mineral exploration, but controls on their formation remain controversial. The early Cretaceous lode Au districts that formed during lithosphere destruction of the North China Craton provide an ideal opportunity to better understand the key tectono-magmatic factors responsible for the genesis of Au-rich deposits in post-subduction settings. Here, we present a LA-ICP-MS study of silicate melt inclusions and sulfide inclusions from ore-related mafic to intermediate rocks in the central Taihangshan Au district in the interior of the North China Craton to constrain the content and evolution of magmatic ore metals ± volatiles. The results, combined with numerical modeling, suggest that the ore-related magmas contained only a few ng/g Au, which is similar to the Au content of non-mineralization-related mafic to intermediate magmas worldwide. The low Au content of the lode Au-related magmas suggest that large volumes of magmas had to accumulate in the middle to lower crust through trans-lithospheric fault systems to produce the lode Au deposits. It is further suggested that the lode Au-related magmas were alkali-rich, hydrous, oxidized and relatively rich in sulfur and chlorine (mafic melt inclusions contain 0.14‒0.24 wt% S and 0.1‒0.2 wt% Cl). These properties are considered critical for the generation of auriferous ore fluids. By comparing the tectono-magmatic setting of the giant Jiaodong Au province (~ 4000 t Au) with the central Taihangshan district (~ 150 t Au), we propose that the much larger total Au tonnage of the Jiaodong district results from the accumulation of a much larger volume of ore-forming magmas at deep crustal levels, induced by a stronger degree of lithosphere modification. In addition, given that the composition of lode Au-related magmas is similar to that of porphyry Cu–Au-related magmas, the lack of giant, early Cretaceous porphyry Cu–Au deposits in the North China Craton suggests that strong extensional settings favor the formation of lode Au deposits instead of porphyry Cu–Au deposits. The present study, therefore, has general implications for the genesis of Au-rich deposits in strongly extensional settings. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Northparkes district, central New South Wales, hosts several economic Cu–Au deposits associated with discrete, thin, porphyry intrusive complexes emplaced in the Late Ordovician during formation of the Macquarie Arc. The recently discovered Two-Thirty Cu–Au–(Mo) prospect is a mineralised magmatic–hydrothermal breccia complex that is hosted by the moderately east-dipping Goonumbla Volcanic Complex on the western limb of the Milpose Syncline ∼15 km south of the Northparkes porphyry district. Generation of the magmatic–hydrothermal breccia complex is interpreted to be related to the 448.0 ± 4.4 Ma emplacement of the Two-Thirty porphyry. However, Re–Os dating of molybdenite from the breccia complex indicates a potential for a ca 440 Ma mineralising event that has similar timing to economic porphyry mineralisation in the Northparkes district. The discovery of the Two-Thirty prospect has important implications for exploration in the Northparkes district and the broader Macquarie Arc. Two-Thirty is only the second known occurrence of magmatic-hydrothermal breccia-hosted mineralisation discovered within the Macquarie Arc, with the other being Cadia Quarry. Mineralisation at Two-Thirty is potentially older than the Northparkes and Cadia deposits, and younger than the epithermal and calc-alkaline deposits at Cowal, Marsden and Ridgeway. The Two-Thirty is a polyphase magmatic–hydrothermal breccia complex that hosts Cu–Au (Mo). The Two-Thirty is the first significant breccia-hosted mineralisation found in the Northparkes district. U–Pb zircon crystallisation ages of the causative intrusion at Two-Thirty pre-date mineralisation at Northparkes. Re–Os dates of molybdenite from the Two-Thirty breccia complex are coeval with syn-mineralisation at Northparkes, supporting the model of periodic release of melts and fluids from underlying magma chambers during the formation of porphyry mineralisation in the Northparkes district. [ABSTRACT FROM AUTHOR]