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Earth's thermo-tectonic evolution determines the way the planet's interior and surface interact and shows temporal changes in both trends and periodic rhythms. By sampling the subcontinental lithospheric mantle that represents the interface between the convecting mantle and the crust, carbonatite and kimberlite should be ideal rock types for documenting this evolution. The first-order secular rise of kimberlites over time has been noted by researchers, but there is much debate over how to interpret this trend, and their second-order variability has received less attention. We compiled a comprehensive global carbonatite database and compared it with an existing kimberlite one. We find that the numbers of carbonatites and kimberlites have similar increasing secular trends, with accelerated growth after ca. 1 Ga, and show the same periodic rhythms that have been synchronized to the supercontinent cycle since ca. 2.1 Ga. We link these trends and rhythms to the long-term change of Earth and the supercontinent cycle, both of which have altered the temperature of, and the subduction-recycled volatile flux into, the subcontinental lithosphere. Such consistent records in carbonatite and kimberlite behavior provide critical evidence for the synchronous thermo-tectonic evolution of the entire subcontinental lithosphere.

The Au mineralization in the giant Jiaodong Au province is enigmatic and difficult to fit current classic mineralization models, primarily because of uncertainties as to the sources of ore-forming fluids and metals. The ca. 120 Ma Au mineralization has been previously proposed to have occurred during a magmatic lull, which would negate a magmatic-hydrothermal genetic model. However, recent drilling has revealed a buried mineralized monzonite equivalent in age to the Au mineralization in the Linglong goldfield. Here, we present comprehensive textural, geochemical [LA-(MC)-ICP-MS trace element, Nd and S isotopes] and geochronological (LA-ICP-MS U-Pb dating) analyses of titanite and pyrite from this previously unrecognized monzonite. Three types of titanite were distinguished, including magmatic Ttn1 and hydrothermal Ttn2 and Ttn3, which show indistinguishable U-Pb ages (120.7 ± 3.1 and 120.9 ± 2.6 Ma), REE patterns and Nd isotopes [εNd(t) = –14.7 to –12.9], implying that hydrothermal fluids were directly exsolved from the monzonitic magma, contemporaneous with the large-scale Au mineralization at ca. 120 Ma. The Nd isotopes of titanite potentially indicate a lower crustal source mixed with mantle materials for the monzonite. Four types of pyrite were analyzed, including magmatic Py1 from fresh biotite monzonite, hydrothermal Py2 from altered biotite monzonite, hydrothermal Py3 from quartz-pyrite veins with a monazite U-Pb age of 118.2 ± 4.6 Ma, and magmatic Py4 from mafic enclaves of the Gushan granite at ca.120 Ma. The δ34S values of magmatic Py1 and Py4 (+1.9 to +6.3‰, and +5.0 to +6.4‰, respectively) and hydrothermal Py2 and Py3 (+6.4 to +9.5‰ and +6.5 to +7.6‰, respectively) are consistent with sulfur isotopic fractionation between melt and fluid. Hydrothermal Py2 and Py3 also have higher Co, As, Ag, Sb, and Bi contents and submicrometer gold inclusions, implying that the magmatic-hydrothermal fluids were fertile for mineralization. This study highlights the importance of monzonite magmatism and exsolved fertile fluids in regional Au mineralization. Hydrous magmas at ca.120 Ma probably extracted Au efficiently from the lower crustal-mantle sources and released auriferous fluids at the late magmatic stage, leading to the formation of Au deposits in the Jiaodong province.

The gold deposits in the Jiaodong Peninsula constitute the largest gold mineralized province in China. The mineralization shows common characteristics in their tectonic setting, ore-forming fluid and metallogenic system. Sulfidation and fluid immiscibility are two important mechanisms controlling gold precipitation, both of which consume sulfur in the ore-forming fluids. The escape of H2S from the main ore-forming fluids and the decrease of total sulfur concentration not only lead to the efficient precipitation of gold, but also result in the crystallization of reducing minerals such as pyrrhotite and oxidizing minerals such as magnetite. Quartz solubility shows strong dependence on temperature, pressure, and CO2 content. The dependence of quartz solubility on pressure is weak at low temperatures, and progressively stronger at higher temperatures. Similarly, the temperature dependence of quartz solubility is relatively low at low pressures, but becomes gradually stronger at high pressures. The results of solubility modeling can constrain the dissolution and reprecipitation behavior of quartz in the ore-forming veins and the formation mechanism of different types of quartz veins. The multi-stage mineralization fluid activity resulted in the complex dissolution structure of quartz in the Jiaodong gold veins. Pyrite in the main metallogenic period in the Jiaodong gold deposits shows complex microstructure characteristics at single crystal scale. The trace elements (mainly the coupling of As- and Au-rich belt) and sulfur isotope composition also display a certain regularity. The As-rich fluids might have formed by the initial pulse of ore-forming fluids through As-rich metasedimentary strata, while the As-Au oscillation zone at the margin of pyrite grains is related to the pressure fluctuation caused by fault activity and the local phase separation of fluids. There is a temporal and spatial evolution of gold fineness in the Jiaodong gold deposits. Water/rock reaction (sulfidation) was the main ore-forming mechanism of early gold mineralization, forming relatively high fineness gold, while significant pressure drop in the shallow part accompanied by fluid phase separation promoted the late gold mineralization, forming low fineness gold. Under cratonic destruction setting, dehydration of the amphibolite and granulite facies metamorphic lower-crust resulted in the formation of Au-CO2-rich ore-forming fluids, which rose along the deep fault and secondary structure, and formed the largescale fault-controlled gold deposits in Jiaodong.

The origin of sediment-hosted copper-cobalt deposits (SCDs) within metamorphic terranes remains contentious, particularly in regard to the timing of mineralization relative to basin evolution. Here, we link the timing of Cu-Co mineralization in the Zhongtiao Mountains district, central China, to basin closure during development of the Trans-North China Orogen. Metamorphic apatite from meta-evaporite has a U-Pb age (1844 ± 25 Ma) within error of a Re-Os age for molybdenite from Cu- and Co-bearing veins (1819 ± 10 Ma), implying that mineralization and metamorphism were coincident. In situ trace element and Fe-S isotope analyses of deformed sedimentary pyrite (Py I) and younger euhedral metamorphic pyrite (Py II) in pyritic graphite schist indicate that Co was mobilized from Py I via fluid-mediated dissolution and reprecipitation. In the graphite schist, representing a sulfidic shale metamorphosed at upper greenschist facies conditions, relic Py I has high δ34S values (22.9 ± 0.4‰, n = 10) and δ56Fe values (0.90 ± 0.16‰, n = 8). These values are consistent with bacterial sulfate reduction and pyrite formation in a Paleoproterozoic sulfidic sea (i.e., after the first great oxygenation event). In addition, Py I has unusually high Co contents (0.8–3.0 wt.%), suggesting that transition metals, including Co and Ni, were originally concentrated in sedimentary pyrite in an evaporative setting. The evaporitic setting is supported by the presence of sylvite in sulfidic schists and adjacent scapolitic calc-silicates. Younger Co-poor Py II has slightly lower δ34S values (21.4 ± 0.2‰, n = 19) and higher δ56Fe values (1.61 ± 0.15‰, n = 9), supporting the hypothesis that Co was released from sedimentary sulfide during dissolution and reprecipitation. The great variability of δ34S (14.8 to 22.9‰) and δ56Fe (0.13 to 2.30‰) in hydrothermal pyrite (Py III) associated with Cu-Co mineralization suggests that an external Cu-rich oxidizing fluid was involved in the ore-forming process. Copper and Co in this type of deposit are typically both considered to be derived from fertile basement rocks. This study, however, highlights another potential source for the Co, with its enrichment in a sulfidic sea along an evaporative margin and its upgrading through mobilization during orogenesis that leads to formation of a relatively high-temperature group of SCDs. Tectonometamorphic processes causing such Co enrichments took place during the Paleoproterozoic and Neoproterozoic oxygenation events, implying that the most prospective targets for Co resources are concentrated in ca. 2.2–2.0 Ga and 0.9–0.7 Ga deformed passive margin marine sequences.

Isotopic dating studies have revealed that many carbonatite-related REE ore systems have protracted and complex temporal evolution histories. The mechanisms that cause these complex dating results remain poorly understood. Here, we present an in-situ Sm-Nd and Th-Pb isotopic investigation of monazite and bastnasite from a geologically-complicated deposit, the world-class Bayan Obo REE deposit of China, with the aim of defining the general mechanisms accounting for the protracted age spread observed in this and many other REE deposits. Monazite and bastnasite are two principle REE ore minerals in the Bayan Obo deposit. Most of the studied monazite and bastnasite grains have experienced fluid-aided modification. The modified grains have generally homogeneous Sm and Nd contents and Sm-Nd isotopic compositions, implying low mobility of Sm and Nd during the modification process. Thus, the Sm-Nd chronometer can be used to constrain the primary crystallization timing of the REE minerals at 1293 ± 48 Ma. However, altered REE minerals have apparent 208Pb-232Th ages (1248–261 Ma) that are variably younger than the primary crystallization age. In most samples, Th contents have no correlations with 208Pb-232Th ages, while Pb contents tend to decrease along with the younging trend of 208Pb-232Th ages. NanoSIMS mapping shows that 208Pb and 208Pb/232Th are heterogeneous, and irregularly distributed in the altered grains. Such results are indicative of variable Pb loss during the fluid-aided modification process. Thus, many Th-Pb ages represent partial isotopic resetting and, hence, are geologically meaningless. Completely reset ages cluster at 450–400 Ma or 280–260 Ma, representing two discrete episodes of post-ore hydrothermal activity. Small amounts of monazite and bastnasite that were newly crystallized during these two overprinting episodes have initial Nd isotopic signatures approaching the time-evolved isotopic compositions of primary ores, which suggests insignificant REE input to the primary ores during these events. This study provides critical evidence to resolve complex dating results and disparate ore genesis models for the giant Bayan Obo deposit. Moreover, our results indicate the resistance of Sm-Nd isotopes, but the susceptibility of Th-(U)-Pb isotopes, to fluid-aided modification. Therefore, younger Th-U-Pb dates in geologically-complicated deposits should be treated with caution as they may represent partial resetting results and/or may not represent events of increased metal tenor.

Hydrothermal fluids in orogenic and intrusion-related (mesothermal) gold deposits are dominated by saline-aqueous-carbonic fluids, commonly represented by the ternary system H2O-NaCl-CO2. The phase equilibria, thermodynamic properties (PVTx, density, compositions of fluid phases) and quartz dissolution-precipitation behavior in the H2O-NaCl-CO2 system, which are still poorly constrained, are of great importance to understanding the process of hydrothermal gold mineralization. Here, we conducted thermodynamic modeling to constrain the fluid properties under single- and two-phase conditions in the H2O-NaCl-CO2 system at temperatures of 300 to 500 °C and pressures of 0.001 to 3.5 kbar. Our results illustrate thermodynamic controls rooted in the equilibria of the H2O-NaCl-CO2 system. Increasing CO2 and/or NaCl contents shift the solvus to higher pressures and temperatures, expanding the pressure–temperature region of L + V immiscibility. Calculated isopleths of CO2 content in coexisting, immiscible vapor and liquid describe the maximum amount of CO2 that may be present in fluid inclusions through the studied P-T-x ranges. Quartz solubility in the H2O-NaCl-CO2 fluids shows strong dependence on temperature, pressure, and CO2 content, with several potential triggers for vein mineral deposition. Specifically, solubility of quartz generally decreases with decreasing temperature, pressure, and increasing CO2 content both in the single- and two-phase fluids, but exhibits retrograde behavior in the L + V field or at the phase-transition boundary. In detail, the dependence of quartz solubility on pressure is weak at low temperatures (300 °C), and becomes progressively stronger at high temperatures (400 °C and 500 °C), vice versa for temperature dependency at different pressures. The present study reviews two mechanisms of fluid immiscibility and constrain the conditions at which distinct fluid inclusion types, bedding-parallel shear veins and fault-related extension veins are formed in mesothermal gold deposits. Thermodynamic modeling of the solvus of the H2O-NaCl-CO2 system is consistent with the hypothesis that decompression is an efficient mechanism driving fluid immiscibility at specific ranges of temperature and composition, producing coexisting liquid- and vapor-phase fluids, both with low density and relatively low content of CO2. For fluids with high CO2 contents (>10 mol. %), cooling at relatively high pressure may also lead to fluid immiscibility, producing a liquid with low CO2 content in equilibrium with a vapor of medium to high CO2 content. Very CO2-rich, or “pure CO2” fluid inclusions (>90 mol. % CO2, type I) cannot be produced by immiscibility under these conditions, but may rather be the result of decrepitation of primary H2O-NaCl-CO2 fluid inclusions. Within the P-T-x ranges studied here, cooling-dominated phase separation accounts for the formation of fluid inclusions with moderate to high CO2 contents (50–80 mol. % CO2, type IIa). Fluid inclusions with low to moderate CO2 contents (5–30 mol. % CO2, type IIb) can represent the original ore-forming fluids, or can be produced by decompression-dominated phase separation. And H2O-NaCl fluid inclusions (type III) generally represent the latest-stage ore-forming fluids, or can be produced by decompression-induced immiscibility at high temperature. In orogenic (mesothermal) gold deposits, decompression-induced quartz precipitation during pressure fluctuation is dominant in bedding-parallel shear veins. Fault-related extension veins are associated with initial decompression-induced quartz precipitation and subsequent cooling-dominated deposition.

Structural network studies could give appropriate opportunities to understanding structural/hydrothermal events, transportation of ore-forming fluids and water/rock interaction process. Four structural deformation/hydrothermal events have been identified in the Jiaojia fault zone according to microtexture and deformation of quartz and feldspars. Plagioclase experienced ductile deformation period with bended polysynthetic twin stripes (>450 °C) in the early stage, followed by K-feldspar alteration period with ductile-brittle deformation and subgrain rotation recrystallization of quartz (380–450 °C). Then, sericitization period occurred extensive ductile-brittle deformation (350–420 °C) and extensive subgrain rotation recrystallization with a little bulging recrystallization in quartz. In the last, gold precipitation-related pyrite-sericite-quartz alteration was dominated by brittle deformation (300–380 °C) and total bulging recrystallization of quartz. From the K-feldspar alteration zone and sericitization zone to pyrite-sericitequartz alteration zone, fractal dimension values of dynamically recrystallized quartz grains increase from 1.07 and 1.24 to 1.32, the calculated paleo strain rate values of dynamically recrystallized quartz range from 10−10.7 (380 °C)−10−96 (450 °C) and 10−9.3 (350 °C)−10−82 (420 °C) to 10−9.5 (300 °C)−10−80 (380 °C), and the paleo differential stress values increase from 36.9 and 39.3, to 121.3 MPa. The increase of fractal dimension values and decrease of grain size from pyrite-sericite-quartz alteration zone and sericitization zone to K-feldspar alteration zone decreased average water/rock ratio values, which could lead to different acidity and redox conditions of ore-forming fluids and mineralization differences. Two kinds of orecontrolling fractures have been distinguished which include the gentle dip types (18°–50°) with NW (315°–355°) and SW (180°–235°) dip hosting No. I orebodies and the steep dip types (74°–90°) with NE (45°–85°) and SE (95°–165°) dip hosting No. III orebodies. These faults/fractures crosscut altered Linglong granite of footwall of the Jiaojia fault zone as rhombohedrons that promoted the connection between fractures in the K-feldspar alteration zone and fluid flow passages near the main fault face. Research results indicate No. I and No. III orebodies should be derived from the same mineralization event and belong to different orebody types in different mineralization sites under the same structural networks.

The supplementary datasetincludes six tables. They are composed ofwhole-rock geochemical compositions of the Late Cretaceous lamprophyre dykes (Table S1),compositions of groundmass mineralsanalyzed by EPMA (Table S2),normal clinopyroxene phenocrysts and compositionally zoned olivine compositionsdetermined byEPMA(Table S3),compositions of minerals from textually zoned grainsanalyzed by EPMA (Table S4),LA-ICP-MS trace and rare-earth element analyses of minerals from phenocryst-sized grains(Table S5), and in situ Sr isotopic compositions of clinopyroxenedetermined by LA-MC-ICPMS(Table S6).

The supplementary datasetincludes six tables. They are composed ofwhole-rock geochemical compositions of the Late Cretaceous lamprophyre dykes (Table S1),compositions of groundmass mineralsanalyzed by EPMA (Table S2),normal clinopyroxene phenocrysts and compositionally zoned olivine compositionsdetermined byEPMA(Table S3),compositions of minerals from textually zoned grainsanalyzed by EPMA (Table S4),LA-ICP-MS trace and rare-earth element analyses of minerals from phenocryst-sized grains(Table S5), and in situ Sr isotopic compositions of clinopyroxenedetermined by LA-MC-ICPMS(Table S6).

In contrast to most Mesozoic granite-hosted gold deposits in the giant Jiaodong gold province (China), the Majiayao deposit represents a significant example hosted in the Archean high-grade metamorphic terrane. The mineralization is characterized by auriferous quartz-sulfide veins together with notable Fe-bearing carbonates (ankerite and siderite), iron oxides and barite. In this study, the comprehensive in-situ analyses of vein-hosted hydrothermal minerals (such as: xenotime U-Pb dating, ankerite Rb-Sr isotopes and monazite Sm-Nd isotopes) and sulfur isotopic analyses of gold-bearing sulfides are used to constrain the timing of mineralization and to better understand the ore genesis. The syn-ore hydrothermal xenotime yielded a U-Pb age of 120.0 ± 1.2 Ma marking timing of gold mineralization, which is much younger than wallrocks’ latest metamorphism at 1950 to 1850 Ma. The relatively higher and variable initial 87Sr/86Sr ratios (0.715809–0.718753) of ore-related ankerite may be leached from ore-hosting Archean metamorphic rocks and/or regional Neoproterozoic Penglai Group low-grade metasedimentary rocks via extensive fluid-rock interactions. This inference is also supported by the newly reported near-zero δ34S values (–1.2 to 1.4‰) of pyrite from altered wallrocks, which are significantly comparable to the surrounding Archean plagioclase amphibolite. The monazite has relatively homogenous εNd(t=120Ma) values ranging from –19.3 to –17.6, which are much higher than the Nd isotope compositions of the ore-hosting Archean high-grade metamorphic rocks. Combining the widespread mafic dykes and previous relevant geochemical studies, it is proposed that the ore-forming fluids were probably derived from deeply mantle-related contents, followed by intense interaction with Archean basements at the shallow crustal level. In addition, the progressive decrease of δ34S values of pyrite and more appearances of iron oxides and barite from early to late mineralization stages, are ascribed to gradual fluid oxidation by extensive carbonatization of Fe-rich Archean wallrocks.

The Wulonggou Au district in the East Kunlun Orogen is one of the most important Au producing regions in China. The Yanjingou Au deposit occurs within a shear zone in the northeastern Wulonggou Au district. Based on detailed field investigations, geochemical data for the primary halo, and in situ thermoelectric data for pyrite, the following key results were obtained: (1) the Yanjingou Au deposit has the fractured-altered-rock type gold mineralization that is arsenopyrite-rich, (2) elemental correlations and cluster analysis show that Au and As are the most diagnostic elements, (3) geochemical data for the primary halo indicate the deposit is a shallow supra-ore halo ore body, and (4) in situ pyrite thermoelectric data show that the proportion of P-type pyrite is &gt, 80% and the detachment rate is 50%, which can be inferred that the location of the ore body is shallow. Based on our data, we present a mineralization prediction model for the ore body. The Yanjingou Au deposit has a good mineralization and high prospecting potential, with at least half of the ore body being concealed at depth, which has important scientific guiding significance for the breakthrough of prospecting and exploration.

The Bayan Obo deposit in China is endowed with the largest rare earth element (REE) resource in the world. The mechanism resulting in this REE enrichment has been the focus of many studies. Carbonatite is known globally as the most favorable carrier of REE ores. In the Bayan Obo deposit, REE ores are hosted in dolomites (including coarse-grained and fine-grained varieties), and many carbonatite dikes (ferroan, magnesian, and calcic) have been identified. All of the dolomites and carbonatite dikes appear to be broadly coeval and possess similar geochemical characteristics. The Sm-Nd isochron age of apatite (1317 ± 140 Ma) from coarse-grained dolomite is consistent with the Th-Pb age of monazite (1321 ± 14 Ma) from a calciocarbonatite dike. The εNd(t) values and initial 87Sr/86Sr ratios at 1.3 Ga of apatite from coarse-grained dolomite show a tight cluster between −2.5 and +1.0 and between 0.70266 and 0.70293, respectively. The δ18OVSMOW values (relative to Vienna standard mean ocean water) of apatite also vary narrowly from 5.0‰ to 6.2‰. These results are consistent with primary mantle-derived carbonatite and prove a magmatic origin for the ore-hosting dolomite. Furthermore, the rim and core texture of dolomite and calcite in the magnesian and calcic carbonatite dikes shows that carbonatite at Bayan Obo has an evolutionary sequence from ferroan through magnesian to calcic in nature. There is a clear negative correlation between the iron content and REE concentration in different stages of carbonatite. Intense magmatic differentiation of carbonatite is likely the critical factor for the giant REE accumulation.

The Jiaobei Terrane in the southeastern North China Craton (NCC) witnessed intense magmatic pulses during Mesozoic in response to lithospheric thinning. These include sporadic felsic-porphyritic dikes which preserve important information on the magmatic processes and of its implications on lithospheric thinning. Here we present a detailed investigation of representative felsic-porphyritic dikes based on whole-rock geochemical analysis, zircon LA-ICPMS U-Pb geochronology, trace elements and hafnium isotopic compositions. Our results identify stages of felsic dikes in the Jiaobei Terrane with ages in the range of 131–127 Ma and 123–116 Ma. The early stage felsic dikes (ESFDs) have negative zircon ɛHf(t) (−22.4 to −11.1), high zircon EuN/EuN* (0.41–0.92) and Ce4+/Ce3+ (62–944), low Ti-in-zircon crystallization temperatures (524–738 °C), and are geochemically comparable to the coexisting Guojialing granodiorite. Abundant inherited zircons and scattered zircon Hf, Yb/Gd, Th/U, and Ce/Sm values suggest that the magmas from which the dikes formed involved crustal contamination. They are interpreted to be the hypabyssal phase of the Guojialing suite sourced from the Paleoproterozoic lower crust of the eastern NCC with input of mantle components, associated with extensive crust-mantle interaction during the peak lithospheric thinning. The late stage felsic dikes (LSFDs) are characterized by variable zircon ɛHf(t), EuN/EuN* and Ce4+/Ce3+ values (−20.1 to −12.2, 0.38–0.88 and 64–956 for the granodiorite- and quartz-porphyritic dikes; −27.6 to −16.2, 0.17–0.75 and 22–503 for the monzogranite-porphyritic dikes), low Ti-in-zircon crystallization temperatures (562 to 774 °C), and display geochemical similarity with the Aishan granitoids. Systematic variations of zircon Hf, Yb/Gd, Th/U and Ce/Sm suggest that fractional crystallization of hornblende played a significant role in the formation of the late dikes. The LSFDs originated from the Neoarchean-Paleoproterozoic lower crust of the NCC with heterogeneous involvement of lesser amounts of mantle materials than the early dikes, consistent with weak crust-mantle interaction during the waning stage of lithospheric thinning. In the LSFDs, the granodiorite and monzogranite porphyries are broadly coeval (123–118 Ma) with large scale gold mineralization in the area as also favored by the high zircon Ce4+/Ce3+ ratios. Our study also provides new insights into the formation of gold deposits.

The Daliuhang gold deposit (> 20 t gold) is located in the central Penglai-Qixia belt of the giant Jiaodong gold province, eastern China. The ore-hosting Guojialing granodiorite and pegmatite were formed at 129.0 ± 0.6 Ma and 126.2 ± 0.6 Ma, respectively. Syn-ore monazite, with a U–Pb age of 120.5 ± 1.7 Ma, represents the timing of gold mineralization. Given at least 5 m.y. between magmatism and mineralization, a genetic relationship to magmatic-hydrothermal activity is negated. Noble gas isotopes of pyrite have crust-mantle-mixed 3He/4He (1.13 to 1.50 Ra) and air-like 40Ar/36Ar (327–574). Together with the broadly positive correlation between 3He and 36Ar, it is inferred that the initial ore-forming fluids were deeply sourced from the sedimentary wedge overlying the subducted plate and overlying mantle during early Cretaceous paleo-Pacific plate subduction. The pre-ore and post-ore pyrites have low δ34S values (3.7–5.6‰ and 5.3–6.4‰, respectively), whereas ore-related pyrites have higher δ34S values, especially in As–Au-rich domains (7.8–8.3‰). These positive δ34S values also suggest that the initial ore fluid and some of the sulfur component were derived via subduction-related devolatilization. The elevated δ34S values of the ore-related pyrite are partly ascribed to mass fractionation and partly to a contribution from sulfur leached from crustal host rocks. This interpretation is also supported by neodymium isotope ratios of monazite (eNd (~ 120 Ma) = − 13.7 to − 11.6), which correlate well with the ore-hosting Guojialing granodiorite. This study highlights the combined roles of deeply derived fluids and intense interaction with upper crustal rocks in the formation of Jiaodong gold deposits.

Late Mesozoic granitoids are widely distributed in the Jiaobei Terrane, southeastern North China Craton (NCC) and crucial to understanding the processes and mechanisms of the lithospheric thinning. Here we present petro-geochemical, zircon U Pb, Lu Hf and O isotopic constrains on three stages of granitoids, building an integrated model of lithospheric thinning from beginning through peak to waning stages. The early stage Linglong granite (166–158 Ma) is geochemically comparable to adakitic rocks with negative ɛNd(t) (−21.3 to −19.2), zircon ɛHf(t) (−26.8 to −18.7), and high zircon δ18O (6.7–8.3‰). It was originated from the subduction-thickened lower crust of the eastern NCC, with minor contribution from the subducted Yangtze Block, in an extensional setting, representing the beginning of lithospheric thinning. The middle stage Guojialing granodiorite (130–128 Ma), characterized by higher Sr/Y, Ba (898–5075 ppm), Sr (657–2256 ppm), ɛNd(t) (−19.1 to −11.5), zircon ɛHf(t) (−19.0 to −11.6) and δ18O (7.5–8.7‰) than the Linglong granite, addressing a fluid-metasomatized lithospheric mantle and extensive crust-mantle interaction in the Paleoproterozoic crustal source, is coeval with peak lithospheric thinning due to roll-back of the subducted Pacific plate. The late stage Aishan complex (118–115 Ma), which is composed of granodiorite, syenogranite, porphyritic quartz syenogranite, alkali granite and monzodiorite, exhibits slightly lower ɛNd(t) (−17.9 to −16.2), zircon ɛHf(t) (−21.4 to −15.3) and δ18O (6.6–7.9‰) than the Guojialing granodiorite. It was derived from the melting of Neoarchean- Paleoproterozoic crust with limited crust-mantle interaction and experienced crustal assimilation and fractional crystallization, indicating an extended process associated with the waning stage of lithospheric thinning. We document the magmatic responses to the lithospheric thinning at different stages which account for the genesis and evolution of the continental adakitic rocks and decratonization of the NCC.

The world-class giant gold province (>4000 t) in the Jiaodong Peninsula has attracted global attention and extensive studies for decades. However, most of the works have been focused on the western Zhaoyuan-Laizhou and eastern Muping-Rushan gold metallogenic belt, leaving the middle Penglai-Qixia belt largely unexplored. The Hushan gold deposit in the Penglai-Qixia belt shows a unique two-stage gold mineralization, i.e., an early-stage pyrite-sericite-quartz altered-rock type mineralization and a late-stage pyrite-pyrrhotite vein type mineralization. Hydrothermal monazite coexisting with Au-bearing pyrite is observed in the early-stage mineralization. The widespread “circular zoned” metasomatic relict structures indicate that monazite was formed by the strong interaction between (Ca, P, REE)-rich fluids and feldspars (plagioclase and K-feldspar). Therefore obtained in-situ U-Pb age of 120.0 ± 3.1 Ma for the “pure” monazite without mineral inclusions (such as feldspars) can represent the timing of the early-stage gold mineralization. The in-situ monazite e Nd (t) (t = 120 Ma) values vary from −20.6 to −18.4, well corresponding to Nd isotopes of the late Jurassic Linglong granite. It is inferred that the REE-rich components in the ore-forming fluids were extracted during the process of primary mineralizing fluids passing through the lower Linglong granite body, and that the Nd isotopic compositions were altered due to the strong fluid-rock interaction. In this regard, Linglong granite contributes some ore-forming materials to the mineralizing fluids during fluid-rock interaction. The early-stage altered-rock type gold mineralization indicates a compressional (closed) ore-forming system, whereas the late-stage pyrite-pyrrhotite vein type mineralization and the occurrences of fracture, geode and hole in the ore samples reflect an extensional (open) ore-forming system. The presence of barite and magnetite in the late-stage mineralization also suggests an increase of oxidation state during the process. Furthermore, pyrites in the late stage generally have lower δ 34 S values (5.69–6.98‰, av. = 6.47‰) than pyrites in the early stage (δ 34 S values = 7.06–7.85‰, av. = 7.42‰), which can also be well explained by the increase of oxidation state. Therefore, the Hushan gold deposit uniquely records a metallogenic environmental transition from compressional, reduced to extensional, oxidized at ∼120 Ma. In addition, the mineralizing fluids with higher oxidation state in the late-stage is supposed to superimpose on the early-stage mineralization, dissolve and rework previously crystalized pyrite to form the high-grade gold mineralization. Unlike the gold deposits in the western and eastern belts, the Hushan gold deposit temporally preserves two types of mineralization in one single deposit, as a response to regional stress field transition.

The Guojialing and Aishan plutons in the northern Jiaobei Terrane represent the magmatic products of the lithospheric thinning of the North China Craton in the Early Cretaceous. The exhumation history of the terrane in response to the thinning process and its effect on the formation and preservation of coeval gold deposits remain poorly constrained. Granodiorites from the Guojialing pluton and monzogranites from the Aishan pluton contain zircon grains with U-Pb ages of ca. 130 Ma and ca. 116 Ma, respectively. Using the Al-in-hornblende barometry, the Guojialing and Aishan plutons had crystallization pressures of 3.2–5.4 kbar (∼12 km) and 1.5–2.6 kbar (∼5 km), respectively. Using the hornblende-plagioclase thermometry, the Guojialing and Aishan plutons had crystallization temperatures of 628–697 °C and 702–745 °C, respectively. Fluid inclusion microthermometric data show that auriferous quartz veins in the Daliuhang deposit formed at temperatures between 243 and 322 °C at a depth of 7–11 km which was similar to the emplacement depth of the Aishan pluton. These thermobarometric and geochronological data reveal ∼7 km uplift between 130 Ma and 116 Ma, but negligible exhumation for the gold deposits after its formation until 116 Ma. Combining previous results, we envisage that the exhumation magnitude of the Guojialing intrusions were nearly the same in the wide area with slight differences between the core and margin of a single pluton. Numerous gold deposits in the Jiaobei Terrane formed during or after the late stage of rapid exhumation of granitoids, and were uplifted with similar depths to the Aishan pluton since ca. 116 Ma. The rapid exhumation of the Guojialing pluton was with the regional extension, and might be genetically associated with the intensive delamination of destabilized lithospheric root and dense residues.

The Jintingling gold deposit, located in the Jiaodong peninsula, north China, contains vein-, dissemination- and stockwork-style ores hosted in the Jurassic Linglong granitic pluton. Hydrothermal activities in this deposit are divided into seven stages, including pre-ore massive K-feldspar alteration, specularite-quartz vein (V1), milky quartz ± sulfide vein (V2), quartz-pyrite vein (V3), massive quartz-sericite-pyrite alteration and gold mineralization, quartz-polymetallic sulfide vein (V4), and quartz-calcite vein (V5). Rhenium-Osmium dating was conducted on molybdenite from V2, yielding an isochron age of 123.3 ± 3.6 Ma. LA-ICP-MS zircon U-Pb dating yielded 121.5 ± 1.5 Ma (1σ, MSWD = 0.010) for a pre-ore diorite porphyrite dyke and 117.6 ± 1.2 Ma (1σ, MSWD = 0.018) for a post-ore diorite porphyry dyke, respectively. Thus, gold mineralization occurred at 122–118 Ma. Four types of fluid inclusions were identified in quartz veins, including CO2-H2O ± CH4 inclusions (type I), pure CO2 inclusions (type II), mineral-bearing inclusions (type III) and aqueous inclusions (type IV). Fluid inclusion studies demonstrate that the primary ore-forming fluids contain CO2-rich vapor (357–420 °C, 7.2–11.3 wt% NaCl equivalent) and critical fluids (368–400 °C). The two phases were likely formed by immiscibility of magmatic-hydrothermal fluids. Later on, the fluids evolved to a H2O-CO2-NaCl ± CH4 system which had temperatures of 300–364 °C and salinities of 2.0–9.7 wt% NaCl equivalent. The H2O-CO2-NaCl ± CH4 fluid system may experience phase separation, forming coexisted CO2-H2O ± CH4 inclusions (homogenized to vapor or liquid at temperature of 265–309 °C and 265–287 °C, salinities of 3.1–7.1 wt% and 4.3–7.1 wt% NaCl equivalent, respectively) and aqueous inclusions (homogenized to liquid at temperature of 255–294 °C and 3.7–7.6 wt% NaCl equivalent). Along with further evolution, the fluids shifted to a H2O-NaCl system, with temperatures of 163–258 °C and salinities of 0.5–9.0 wt% NaCl equivalent. Pyrite from the Jintingling deposit has δ34S values (5.5‰–6.1‰) similar to those of pyrite from other gold deposits in the Jiaodong district, indicating that they were related to the same hydrothermal ore-forming system. The δ13CPDB values of calcite (−4.5‰ to −5.4‰) in V5 are generally located in the range of magmatic-derived carbon. Fluids of V2, V3, V4 have δD from −64.4‰ to −87.1‰, and δ18O from 8.4‰ to 0.2‰, located in the compositional fields between magmatic water and meteoric water. Collectively, microthermonetric results and isotopic data indicate that the primary ore-forming fluids were most probably magmatic in origin, with incorporation of meteoric water in the later ore-forming stage. Precipitation of gold was triggered by cooling of fluids, fluid immiscibility and decrease of sulfur in the fluids.

The Mesozoic (∼120 Ma) Heilan’gou gold deposit, located in the Jiaodong gold province, eastern margin of the North China Craton (NCC), consists of several ultra-high grade (up to 600 g/t) auriferous quartz veins in the early Cretaceous Guojialing granodioritic pluton. Ore-related pyrite crystals from this deposit show complex textures. In this study, EMP, Nano-SIMS trace element mapping and in-situ sulfur isotope analyses were conducted to characterize the textural and compositional features. Two types of pyrite were identified. Type I crystals (Py-I), hosted in gold-quartz-pyrite veins, are generally homogeneous in chemical composition. They contain low concentrations of As ( Based on the distinctive textural and compositional signatures between Py-IIa and Py-IIb, it is proposed that anomalously As-Au-rich fluids were injected into hydrothermal systems during the late ore-forming stage, which may have intensively interacted with certain sedimentary rocks. The involvement of these fluids, firstly documented in this study, can largely explain the occurrence of native gold ore shoots at Heilan’gou. In addition, the intimate association between As and Au highlights the important roles of As in enrichment of Au in the Jiaodong gold district.

Fenitization, a unique type of alkali metasomatism related to carbonatite or alkaline igneous rocks, is widely distributed around the Mesoproterozoic carbonatite dykes in the Bayan Obo giant REE-Nb-Fe deposit. Meanwhile, represented by alkali silicates (sodic amphibole or aegirine) enriched REE-(Fe) ores, there is extensive alkali alteration in ores at Bayan Obo, whose similarity to fenitization has been proposed. Fenitization associated with carbonatite is an appropriate indicator of REE mineralizing process. Alkali silicates (sodic amphibole, aegirine and phlogopite) from the East and Main open pits, and fenite around the Wu dyke at Bayan Obo were collected for EMPA and laser ablation ICPMS analyses. Aegirine and phlogopite from the open pits and fenite around the Wu dyke contain similar major components. Sodic amphiboles from those two localities contain comparable trace element composition but with different Cao, MgO and F contents. Alkali silicates from fenites around the Wu dyke show systematic enrichment of Zr, Hf and Ti over alkali silicates from the open pits. Considering different wallrocks and other factors influencing the composition, combined with previous results of geochronology, mineralogy and fluid inclusion, the alkali alteration in the open pits is essentially fenitization in ore-hosting dolomite. A two-stage fenitization process is supported by the zonal texture of sodic amphiboles from Wu carbonatite dyke. The early stage fenitization was Mg, Na, K, F rich and Fe, La, Ce depleted, distributed in alkali silicates from the banded REE-Fe ores and in the core of sodic amphiboles from the Wu dyke. The late stage was Fe, LREE rich and Mg, Na, K, F depleted, distributed in the massive REE-(Fe) ores and the rim of sodic amphiboles from the Wu dyke. The initial alkali fluids derived from carbonatite commonly exhibits LREE-rich patterns. Therefore, the LREE-depletion and low La/Nd ratio of the early stage silicates indicates intense LREE-bearing mineral precipitation and the REE mineralization gradually weakened in the late stage when alkali fluids kept the initial REE patterns unchanged.

The Jiaodong Peninsula in the eastern North China Craton (NCC) hosts some of the world-class gold deposits. Among these, the Shangzhuang gold deposit represents a typical fault-zone hosted disseminated- and stockwork-style gold mineralization. The mineralization is characterized by intense hydrothermal alteration halos in the wallrocks with the mineralized veins intruding into altered wallrocks. Zircon U-Pb isotope dating constrains the timing of emplacement of the Guojialing granodiorite as 130 ± 1 Ma. Five molybdenite samples from the main mineralization stage veins yielded a well-fitted isochron age of 126 ± 2 Ma (MSWD = 1.3), marking the timing of gold mineralization. Four types of fluid inclusions are identified at Shangzhuang, and their petrographic and microthermometric features suggest fluid immiscibility followed by fluid mixing. This inference is also supported by oxygen and hydrogen isotopic data of quartz veins from stage III. The measured δ 18 O values of quartz are + 12.3 to + 13.7‰ for stage II and + 11.7 to + 12.0‰ for stage III, with calculated δ 18 O fluid values for stage II ranging from + 5.9 to + 7.3‰ and for stage III from + 3.4 to + 3.7‰. δD values for stage II and III quartz range from − 65.3 to − 75.2‰ and − 70.6 to − 74.7‰, respectively. The data suggest that the ore-forming fluids were initially derived from magmatic sources, followed by mixing with meteoric water. SIMS in-situ sulfur isotope analyses of two types of pyrite (Py I and Py II) from different mineralization stages show different sulfur isotope features. The δ 34 S values for Py I (+ 10.2 to + 11.3‰, mean = + 10.8‰, n = 25) are higher than those of the later mostly gold-related Py II (+ 4.1 to + 6.8‰, mean = + 5.4‰, n = 27). The higher δ 34 S values of Py I are correlated to degassing of mantle wedge metasomatized by the slab fluids. The relatively lower δ 34 S values of Py II might suggest increasing of f O2 through fluid mixing between ore-forming fluids and meteoric water. The temporal, spatial and tectonic relations between the giant gold mineralization and destruction of the NCC suggest a genetic linkage. The gold mineralization between 126 and 117 Ma at Jiaodong was probably initiated at the peak of decratonization (ca. 125 Ma) of the eastern NCC. Phanerozoic craton margin orogeny also played a critical role in the generation of the early Cretaceous giant gold deposits in the eastern NCC. Integrated geological characteristics, mineralization features, metallogenic age, sources of ore-forming fluids and sulfur, and tectonic settings favor a decratonic gold mineralization model for the Shangzhuang gold deposit. The geodynamic scenario proposed for the early Cretaceous giant gold mineralization event in the eastern NCC includes the paleo-West Pacific plate subduction, asthenospheric upwelling, multiple subduction-collision processes along the margins.

Epigenetic hydrothermal Cu-(Co) deposits are widely distributed in the Zhongtiao Mountains within the Paleoproterozoic Trans-North China Orogen in the North China Craton. Here we investigate the Henglingguan Cu deposit hosted in metasediments to gain insights on the fluid evolution characteristics associated with the ore formation. This Cu deposit is characterized by early disseminated mineralization and late quartz-vein type mineralization. The negative sulfur isotope values (about −10‰) of the vein sulfides suggests a sedimentary rock source for sulfur associated with the hydrothermal Cu mineralization. The coexistence of CO2-rich carbonic inclusions and halite-bearing inclusions within a single fluid inclusion assemblage suggests fluid immiscibility in the H2O-NaCl-CO2 system. Based on the fluid phase analysis, our data show that the parent ore fluid was characterized by X(NaCl) of 10 to 20 mol.% (salinity of around 23 to 41 wt% NaCl) and X(CO2) of 10 to 15 mol.% before fluid immiscibility. The estimated temperature–pressure conditions of 320 to 340 °C and 3.5 to 4.0 kbar based on the carbonic fluid inclusions is suggested to be close to the conditions of fluid immiscibility. In-situ composition analyses of fluid inclusions by LA-ICP-MS show that the ore fluids contained Na, Ca, Fe and Mn, and evolved towards Sr-Ba enrichment. The data are consistent with a metamorphic brine derived from the sedimentary rocks. The brine-rich metamorphic fluids were likely derived from the dehydration and decarbonation of evaporitic carbonate rocks developed on the basin margin or a passive continental margin. The decompression during post-collisional exhumation triggered fluid immiscibility resulting in the quartz vein-type Cu mineralization.

The giant Bayan Obo REE deposit bears a large amount of iron resources as well. However, the genesis of iron mineralization is still highly controversial with limited research. In this study, new data of trace elements of magnetite from Bayan Obo ores, Eastern contact zone skarn and Heinaobao BIF are obtained by Laser ablation (LA) ICP-MS analyses, revealing the genesis of Bayan Obo iron resources through comparing study. The Bayan Obo deposit contains disseminated, banded and massive ores, and in which magnetite is associated with REE minerals, fluorite, aegirine, riebeckite, and biotite. Euhedral magnetite in the skarn of Eastern contact zone is usually associated with pyrite, biotite, fluorite, and bastnaesite. There are two types of magnetite in the Heinaobao BIF: (1) euhedral to subhedral magnetite associated with quartz and a small amount of amphibole; (2) anhedral magnetite associated with quartz, garnet, plagioclase, amphibole and biotite. Magnetite in the Bayan Obo is enriched in Ni, but depleted in Mg, Al, Ti, Ge, Mn, Ga and Zn, showing low and variable concentrations, which is similar to the hydrothermal magnetite. The contents of some trace elements (e.g. Ti, Mn, Sc, Zn, Nb and REE) of magnetite from the skarn ores are generally higher, indicating a relatively high formation temperature. Magnetite in the Heinaobao BIF is generally characterized by low and uniform trace element contents, except for the abnormal values of Ti, Al, Cr and Mn, suggesting the involvement of terrigenous clastic materials. Compared with Bayan Obo magnetite, the skarn magnetite has the highest Sn/Ga, Co/Ni, Nb/Ta, La/Yb, Ti/V and Ti/Al ratios, while magnetite in the BIF has the highest Al/Co and lowest Nb/Ta ratios. The significant difference in mineralogical and trace element characteristics among the three types of magnetite indicates that the iron resources in Bayan Obo deposit are unlikely to be a skarn Fe deposit nor a BIF deposit. However, the Bayan Obo magnetite shows similar geochemical characteristics to hydrothermal magnetite related to carbonatite, both of which are depleted in high field strength elements, such as Zr, Hf and Ta, and show strong positive anomalies of Mn and Zn and negative anomalies of Co and Ga. In addition, in the diagrams of Ti vs. Nb + Ta and Ti vs. Zr + Hf, the Bayan Obo magnetite falls into the field of hydrothermal magnetite associated with carbonatite. In conclusion, it is recommended that the Bayan Obo iron deposit is a typical hydrothermal deposit related to carbonatite. In this contribution, the skarn magnetite formed at high temperature and the BIF magnetite was contaminated by terrigenous materials deviating from the expected region in discriminant diagrams. It is therefore proposed that the validity of these diagrams depends on a full understanding of mineralogical characteristics of samples and magnetite precipitation environment, and that multiple discrimination diagrams should be used in combination.

The Wulonggou gold district is one of the most important gold producers of the East Kunlun metallogenic belt in China. Due to its complex geological background and limited investigations, the age of mineralization and ore-forming process remain unclear. Here, we focus on the Yanjingou gold deposit which is the largest and most typical deposit in the Wulonggou gold district, with a view to investigate the metallogenic mechanism and timing of ore formation with a view to evaluate the ore-forming processes and sources through a comprehensive study of the ore mineralogy, monazite and zircon U-Pb dating, in situ trace element analysis and mapping, and in situ S isotopes. Our results show that the magmatism and mineralization were coeval, during 239 Ma and 244 Ma in the Middle Triassic. Four stages of mineralization are identified with distinct textures, mineral assemblages, trace element characteristics and S isotopes. Stage 1 is represented by euhedral pyrite bearing quartz veins, which originated from deep metamorphic fluid, and was rarely affected by magmatic hydrothermal fluids. Stage 2 is characterized by the occurrence of abundant oriented arsenopyrite, which originated from the mixture of deep metamorphic fluid and magmatic hydrothermal fluid. Stage 3 is characterized by the occurrence of polymetallic sulfide of copper, with two generation of pyrite (stage 3 Py1 and Py2). Stage 3 Py1 formed from magmatic hydrothermal fluids whereas Py2 originated from deep metamorphic fluid and was also slightly influenced by magmatic hydrothermal fluids. Stage 4 is represented by late calcite and pyrite combination, which originated from another stage of deep metamorphic fluid. Stage2 and 3 are the main gold mineralization stages, and Au has a close relationship with As, and an obvious inverse correlation with Co and Ni. Combined with the trace element characteristics, we infer that the denudation degree of the Yanjingou gold deposit is very shallow with good prospects for exploration. Through multi-proxy investigation of the different stages and types of pyrite, we postulate that the Yanjingou gold deposit is an orogenic gold deposit related to intrusive rocks formed during Middle Triassic compressional transformation.

The Bayan Obo REE-Nb-Fe deposit with giant rare earth reserves, still has no unified understanding of the REE and Nb-bearing mineral evolution and the division of mineralization stages, due to the complicated metallogenic process and the huge controversy on the important issues such as the origin of ore-hosting dolomite. In this work, the whole process of carbonatite magma solidification and mineralization is divided into six stages: coarse dolomitic facies, fine dolomitic facies, disseminated mineralization, banded mineralization, massive mineralization and vein mineralization. The mineralogical composition and paragenesis of various types of rocks and ores have been systematically studied using the automatic mineral analysis technology-Advanced Mineral Identification and Characterization System (AMICS), supplemented by optical microscopy and cathodoluminescence. In order to establish the internal relationship between different stages, trace elements of six kinds of rocks and ores were analyzed. The mineralogical studies show that the rare earth minerals appear in the order of transition from the phosphate minerals in the brine-melt stage (fine dolomitic facies), through the fluorcarbonate minerals in the hydrothermal stage (disseminated, banded and massive mineralization), to the Ba-fluorcarbonate minerals in the Paleozoic vein mineralization, and all of these are generally associated with apatite, baryte, fluorite, aegirine and quartz. The distribution of niobium minerals in all kinds of ores is in the form of disseminated grains, and there is no obvious paragenetic relationship with other minerals, which indicate that niobium mineralization may only be related to the content of niobium in hydrothermal solution. The geochemical data show that all types of rocks and ores have positive anomalies of Ba and Nb, negative anomalies of U, Ta, Sr, Zr and Y. From coarse dolomitic facies to massive mineralization, the content of REE, Nb and Th increases, the content of Sr decreases, and the ratio of (La/Yb)N and (La/Nd)N increases, all of which change continuously. Vein mineralization has similar (La/Nd)N and (La + Ce + Pr)N/REE ratios compared with coarse dolomitic facies and has a wide range of Sr, Th, Nb and REE compositions, and elemental ratio and content of vein mineralization are within the distribution range of ore-hosting dolomite and different types of mineralization. Based on the above, it is considered that the main mineralization body at Bayan Obo was formed in the process of auto-metasomatism of Mesoproterozoic igneous carbonatite, while vein mineralization was the product of homogenization and re-precipitation of early ore-forming material by the Paleozoic fluids, without the addition of exogenous metallogenic materials.

The Bayan Obo deposit in China hosts the largest REE resource in the world. However, the genesis of this deposit is still highly debated, largely due to a lack of consensus on the mineralization age. The Banyan Obo deposit has experienced intensive post-ore metamorphic and metasomatic overprints, so it is crucial to choose robust chronometers to determine the primary mineralization age. In this study, zircon is identified in the REE ore of the Bayan Obo deposit. The zircon grains are in contact with or contain inclusions of hydrothermal minerals (e.g., magnetite, biotite, monazite, allanite, apatite and ilmenorutile). They have variable Th contents (14 to 1139 ppm) and are poor in U ( Thorium-lead dating was also conducted on monazite from the zircon-bearing sample, yielding 208Pb-232Th ages (993 to 319 Ma) variably younger than that of zircon. The younger monazite Th-Pb ages could have resulted from disturbance of the Th-Pb isotopic system during post-ore modification process. Similarly, monazite has younger Th-U-Pb dates than zircon in many other geologically-complicated carbonatites or REE deposits. Such a phenomenon implies that the zircon Th-U-Pb chronometer is robust even if the host-rocks have experienced intensive modification, whereas monazite Th-U-Pb chronometer is more susceptible to modification. Therefore, younger Th-U-Pb dates of monazite should be interpreted with caution as they may record the timing of post-ore modification event or represent partial resetting, and hence geologically meaningless results.

The Asiha vein-type gold deposit, located in the Eastern Kunlun Orogenic Belt, provides an excellent opportunity for deciphering sources of metals and origins of orogenic intrusion-related gold systems. Within this deposit, four types of pyrite have been distinguished in three stages of hydrothermal activities. Pyrite (Py1) occurs in quartz-pyrite veins (stage I); pyrite (Py2), consisting of core (Py2a) and rim (Py2b), occurs in quartz-polymetallic sulfide veins (stage II); pyrite (Py3) occurs in quartz-pyrite-chalcopyrite veins (stage III). Py1 contains high concentrations of As (median of 2090 ppm) and Au (0.1 ppm). Py2a is enriched in Co (43.1 ppm) and Ni (50.9 ppm), but depleted in As and Au. By contrast, Py2b is enriched in As (7894 ppm) and Au (0.5 ppm), but depleted in Co and Ni. Although, Py3 shows enrichment in Co (1319 ppm) and Ni (1783 ppm), it is usually accompanied with chalcopyrite and visible gold. Three generations of gold-associated pyrite indicate three stages of hydrothermal mineralization, and the variation of metals in pyrite suggest that the ore-forming materials were predominantly derived from felsic magma mixed with different proportion of mafic-volcanic host rocks. U-Pb dating on hydrothermal monazite from stage III constrains the mineralization age at 227 ± 7 Ma, which is coeval with the concealed granite porphyry (228 Ma). The δ34S values of the pyrites vary from +4.8‰ to +8.9‰, which are slightly higher than magmatic pyrite in porphyry (+4.2‰ to +5.6‰). We tentatively propose that the ore-forming materials are closely related to the granite porphyry and the evolved magmatic hydrothermal fluids.

The Gouli goldfield is the most important gold producers of the East Kunlun metallogenic belt. Gold mineralization in this region is enigmatic, primarily because of uncertainties as to the mineralization processes, and the nature and sources of ore-forming fluids. Here, we investigate the ore-forming fluids and processes through a comprehensive study of the texture and geochemistry (LA-(MC)-ICPMS trace element analysis, mapping, S isotopes, and He-Ar isotopes) of pyrite from the Guoluolongwa gold deposit, the largest deposit in the Gouli goldfield. Four types of pyrite with distinct textures, trace element contents and sulfur isotopes were identified, and provide evidence for a multi-stage hydrothermal fluid evolution. The sedimentary-diagenetic Py0, representing the pre-ore stage, is characterized by high contents of Co and Ni, and negative δ34S values (−11.6‰ to −4.0‰), which are notably different from the subsequent hydrothermal Py1 to Py3. Hydrothermal Py1, comprising subtypes Py1a and Py1b, was deposited in pyrite-quartz veins during stage I. The Py1a subtype shows characteristic Co-Ni-As oscillatory zoning that replaced Py0 via dissolution-reprecipitation, and hence inherited high concentrations of Co and Ni from Py0. In contrast, the Py1b subtype was devoid of Py0 influence and represented the initial ore-forming fluid with low concentrations of Co and Ni, moderate Cu, Pb, Zn, Sb, and Bi, but high As, Au, and Ag. The next stage, Py2, formed in the quartz-pyrite veins during stage II and showed clear textural and compositional contrasts to Py1. Specifically, Py2 has elevated Cu, Pb, Zn, Ag, and Bi contents and somewhat lower δ34S values (+1.5‰ to +3.2‰) compared to Py1 (+1.6‰ to +5.6‰). In addition, Py2 shows irregular compositional zones, which we attribute to fluid phase separation caused by pressure fluctuation. Abundant Py2 precipitation triggered native gold deposition due to desulfidation of the ore-forming fluid. The next stage, Py3 in polymetallic sulfides-calcite-quartz veins at stage III, implies a new pulse of Cu-Pb-Zn-As-Au-Ag-rich and Bi-poor ore-forming fluid. This latter pyrite is characterized by inclusion-rich cores (Py3c), which contain abundant inclusions of chalcopyrite, galena, sphalerite, and native gold, and inclusion-free rims (Py3r). The cores, Py3c, likely represent abrupt destabilization of metal complexes and rapid precipitation during vigorous phase separation, whereas the euhedral Py3r rims formed under steadier physico-chemical conditions, contributing to lower δ34S values of Py3c (+0.5‰ to +3.0‰) than Py3r (+1.9‰ to +3.6‰). Noble gas isotopes of Py1-Py3 have crust-dominated 3He/4He (0.04–0.4 Ra) and 40Ar/36Ar (623–2081), mixed with minor mantle components. Sulfur isotopes and low Co and Ni contents of hydrothermal pyrite, and He-Ar isotopes of fluid inclusions in pyrite, are consistent with a model in which multiple pulses of ore-forming fluids were exsolved during sequential episodes of primarily crustal-derived felsic magmatism with lesser mantle influences. This model is also supported by previous H-O isotope analyses, as well as widespread granitoid magmatism in the eastern Central East Kunlun Belt.

The stratabound Cu deposits in the Zhongtiao Mountains district contain good records about the Precambrian tectonic evolution in the central North China Craton. Five stages of metamorphic and metallogenic processes are identified and the P-T conditions are constrained using mineral geothermobarometry and P-T pseudosection. Results revealed a prograde metamorphism (stage M − 1) from 565 to 630 °C, and peak metamorphism of 6.5 ± 0.5 kbar and 610 ± 20 °C (stage M − 2). The post-peak metamorphism consisted of a continued retrogression (stage M − 3) at 545 ± 5 °C and 6.0 ± 0.1 kbar, and Cu mineralizations (stages M − 4 and M − 5). Two distinct mineral assemblages of arsenopyrite-pyrrhotite-pyrite-chalcopyrite and bornite-chalcopyrite-parkerite- wittichenite-bismuth are observed in veinlets. The Cu mineralization occurred from 446 to 341 °C at a pressure of ∼5.0 to 4.4 kbar. We obtained laser ablation ICPMS monazite U-Pb ages of 1881 ± 15 Ma and 1863 ± 17 Ma for staurolite schist and mineralized veins, respectively. A Nano-secondary ion mass spectrometer zircon U-Pb age of 1815 ± 32 Ma for fluid-modified zircon rims from host schist. These ages are interpreted as the timing for the stages M − 2, M − 4 and M − 5, respectively. These results define a clockwise P-T-t path that displays nearly parallel prograde and retrograde trajectory (Franciscan type). The retrograde portion is similar to near-isobaric cooling (IBC) stage, which supports a relatively slow exhumation following a continental collision. It is proposed that the ore materials were mainly derived from the host rocks, which might have been pre-enriched. Cu mineralization formed during the retrograde cooling stage at greenschist facies, and was likely related to a post-orogenic sluggish exhumation at a rate of 0.31–0.05 mm/yr.

Mesozoic granitoids were extensively altered by hydrothermal fluids in the northwest Jiaodong Peninsula, and gold precipitated from the fluids developing prevalent mineralization in this district. The 160–158 Ma Linglong granite and 130–120 Ma Guojialing granodiorite are the major Mesozoic granitoids in this district, both of which are hydrothermally altered and intimately associated with gold mineralization. Although numerous studies were carried out by previous researchers, mainly focusing on tectonics, lithology, mineralogy, geochronology, and fluid geochemistry, knowledge about hydrothermal alteration processes of these granitoids and their gold mineralization efficiency (i.e. which one is more effective to precipitate the gold from its parent solution) is far beyond clear illumination. Geochemical simulation software GEM-Selektor (based on the Gibbs energy minimization algorithm) was applied in this study, which aims to test the gold mineralization efficiency of these two granitoids during the hydrothermal alteration processes. Simulation results indicate that solutions in equilibrium with the Linglong granite are capable of hosting more sulfur than that with the Guojialing granodiorite, since the latter contains more Fe. However, the solutions with these two granitoids display similar gold solubility. “Bulk cooling” simulation results show that the gold mineralization pattern is similar between the Linglong and Guojialing case; “Rock titration” simulation results reveal that the Guojialing granodiorite is prone to precipitate gold more strongly than the Linglong granite, as gold-bearing solutions (or ore-forming fluids) flowing-through at high temperature, equivalent to a deeper level, implying that if the gold mineralization is developed at depth, the Guojialing rock will precipitate more gold. If the gold-bearing solution flow-through the wall rocks relatively fast, and gold mineralization fails to take place, then the Guojialing granodiorite is probably unfavorable for subsequent gold enrichment of the ore-forming fluid. The Linglong granite will precipitate the gold more efficiently from its parent solution at low temperature or at a shallower level, and this is consistent with previous mining prospecting results. Therefore, we suggest that the Guojialing granodiorite should be treated as the main target during future deep prospecting project.

The Sanshandao gold deposit contains an estimated Au resource of >1500 tons, however little is known about the history of exhumation, and the magnitude of displacement on the ore-hosting fault. Structural measurement revealed two phases of normal and one phase of sinistral movement on the fault. Despite of intra-sample dispersions, (U-Th)/He ages from two sub-vertical profiles show decreasing trends from the surface down to −3560 m (zircon: 123 Ma to 55 Ma; apatite 103 Ma to 0.3 Ma). Over-dispersion of AHe ages likely reflects the presence of undetected inclusions. According to the age-depth pattern, we infer that the deposit underwent an early phase of rapid cooling in the late Early Cretaceous, which was followed by a short period of thermal stagnation and a revived rapid cooling between 75 Ma and 55 Ma in response to a combined effects of late normal movement and erosion. Since the Eocene, the deposit has experienced a slow monotonic cooling. Exhumation magnitude estimates suggest that the deposit have been denudated > 5.1 km. The two phases of normal displacement along the fault occurred in the late Early Cretaceous and Late Cretaceous to Paleocene, leading to a total offset magnitude of 0.5–2.3 km.

The Xiadian gold deposit, located in the Zhaoyuan–Laizhou belt of the Jiaodong gold province, is a typical Jiaojia-type gold deposit, which is characterized by disseminated and stockwork ores enclosed by hydrothermally altered wall rocks. The exact age and the genesis of the gold deposit remain controversial. Here, we present precise in-situ monazite U-Pb dating to constrain the age of the gold mineralization, which we integrate with published geochronological work on the associated geological events to understand the genesis of the gold deposit. The Linglong granite represents the earliest magmatic event at Xiadian, and yielded a zircon LA–ICPMS U-Pb age of 159.5 ± 0.9 Ma (2σ, MSWD = 0.63). Subsequent geologic events were recorded by minor amounts of quartz–pyrite–molybdenite veins which are dated at 124.8 ± 2.1 Ma (2σ, MSWD = 0.01) by molybdenite Re–Os dating in a granitic pegmatite. The formation of such veins was close to the emplacement of adjacent Guojialing granodiorite (~130 Ma), and thus may be considered as a product of post–magmatic hydrothermal activity. It is proposed that the molybdenum–bearing hydrothermal fluids acted as a prelude to gold mineralization and participated in the formation of the latter ore fluids. Gold mineralization took place at 120.0 ± 1.4 Ma (2σ, MSWD = 0.59), determined by LA–ICPMS U–Pb dating on hydrothermal monazite from quartz–polymetallic sulfide veins. Prior to and post mineralization, voluminous hydrothermally altered porphyritic diorite and fresh quartz diorite porphyry dykes were emplaced, which yielded U–Pb ages of 121.3 ± 1.4 Ma (2σ, MSWD = 0.28) and 115.8 ± 1.9 Ma (2σ, MSWD = 0.71), respectively. Based on these geochronological data, we have established a comprehensive geochronologic framework, which suggests that the genesis of the Xiadian deposit might be related to the craton destruction and lithosphere thinning in the North China Craton.

The rare earth elements (REEs) have unique and diverse properties that make them function as an “industrial vitamin” and thus, many countries consider them as strategically important resources. China, responsible for more than 60% of the world’s REE production, is one of the REE-rich countries in the world. Most REE (especially light rare earth elements (LREE)) deposits are closely related to carbonatite in China. Such a type of deposit may also contain appreciable amounts of industrially critical metals, such as Nb, Th and Sc. According to the genesis, the carbonatite-related REE deposits can be divided into three types: primary magmatic type, hydrothermal type and carbonatite weathering-crust type. This paper provides an overview of the carbonatite-related endogenetic REE deposits, i.e., primary magmatic type and hydrothermal type. The carbonatite-related endogenetic REE deposits are mainly distributed in continental margin depression or rift belts, e.g., Bayan Obo REE-Nb-Fe deposit, and orogenic belts on the margin of craton such as the Miaoya Nb-REE deposit. The genesis of carbonatite-related endogenetic REE deposits is still debated. It is generally believed that the carbonatite magma is originated from the low-degree partial melting of the mantle. During the evolution process, the carbonatite rocks or dykes rich in REE were formed through the immiscibility of carbonate-silicate magma and fractional crystallization of carbonate minerals from carbonatite magma. The ore-forming elements are mainly sourced from primitive mantle, with possible contribution of crustal materials that carry a large amount of REE. In the magmatic-hydrothermal system, REEs migrate in the form of complexes, and precipitate corresponding to changes of temperature, pressure, pH and composition of the fluids. A simple magmatic evolution process cannot ensure massive enrichment of REE to economic values. Fractional crystallization of carbonate minerals and immiscibility of melts and hydrothermal fluids in the hydrothermal evolution stage play an important role in upgrading the REE mineralization. Future work of experimental petrology will be fundamental to understand the partitioning behaviors of REE in magmatic-hydrothermal system through simulation of the metallogenic geological environment. Applying “comparative metallogeny” methods to investigate both REE fertile and barren carbonatites will enhance the understanding of factors controlling the fertility.

The Sanshandao gold deposit is located at the northwestern edge of the Jiaodong peninsula, North China Craton. It is mainly hosted in the Mesozoic granitoids. Gold mineralization occurs as disseminated- and stockwork-style ores, typically enveloped by broad alteration selvages. Mineralization and alterations are structurally controlled by the Sanshandao–Cangshang fault. Three paragenetic stages were identified with the early stage represented by quartz ± pyrite, the middle stage by gold + quartz + pyrite or gold + quartz + base metal sulfides, and the late stage by quartz + carbonate ± pyrite, respectively. Four types of fluid inclusions were distinguished, including (1) pure CO 2 fluid inclusions (type I), (2) H 2 O–CO 2 –NaCl fluid inclusions (type II), (3) H 2 O–NaCl fluid inclusions (type III), and (4) daughter mineral-bearing or multiphase fluid inclusions (type IV). The early- and middle-stage quartz mainly contain primary type II fluid inclusions that completely homogenized at temperatures of 241–390 °C with salinities of 2.96–18.39 wt.% NaCl equivalent, and temperatures of 207–336 °C with salinities of 2.06–17.57 wt.% NaCl equivalent, respectively. A few primary type I fluid inclusions can be observed in the early-stage quartz, while the middle-stage quartz contains a few primary type I, type III and type IV fluid inclusions. In contrast, the late-stage quartz only contains type III fluid inclusions showing homogenization temperatures of 101–268 °C, and salinities of 0.17–15.47 wt.% NaCl equivalent. CH 4 , derived from extensive water–rock interaction between the ore-forming fluids and wall rocks in the main fault, is the key factor controlling the gold mineralization. CH 4 changed the physico-chemical conditions of the ore fluids, and led to gold precipitation. Oxygen and hydrogen stable isotopic analyses for quartz from different ore-forming stages show that the ore-forming fluids are of magmatic origin, with gradual incorporation of meteoric water during/after mineralization. δ 34 S values of pyrite from different ore-forming stages vary between 1.9‰ and 11.9‰. 3 He/ 4 He ratios of fluid inclusions in the middle-stage pyrite mainly range from 0.14 to 2.94 Ra, while it is from 675.10 to 5926.44 for 40 Ar/ 36 Ar. All these isotopic signatures suggest that the ore fluids could be derived from a combination of crustal and mantle components.

Dexing porphyry Cu–Mo–Au deposit, one of the largest copper deposits in China, is located adjacent to the Neoproterozoic suture of South China Block. It has similar characteristics in terms of hydrothermal vein and alteration types to those of typical porphyry copper deposits, but differs in fluid compositions and properties. Through petrographic observation on the mineralized veins and phenocryst quartz, five types of fluid inclusions were recognized, i.e. multi-phase high salinity inclusions (A type) which was subdivided into A 1 (containing only halite as daughter mineral) and A 2 (containing halite and opaque daughter minerals) subtypes, vapor-rich inclusions (B type), CO 2 -bearing inclusions (C type), LV inclusions with vapor to liquid ratio of ~ 20% (D type) and LV inclusions with vapor to liquid ratio less than 10% (E type). The earliest barren quartz veins with potassic halos contain primary A 1 and C type inclusions; primary fluid inclusions in the Q + Py + Mo ± Cp veins consist of C type inclusions in coexistence with minor A 1 type inclusions; primary inclusions in the Q + Py + Cp ± Cc veins with sericitic selvages are A 2 and B type inclusions; fluid inclusions in phenocryst quartz are secondary, and consist of D, A 2 , B and E type inclusions. Laser Raman spectroscopic investigation revealed that daughter minerals within the A type inclusions include anhydrite, siderite and magnetite; vapor in B type inclusions contains CO 2 . Microthermometry revealed that A type inclusions were predominantly homogenized by halite dissolution. These inclusions exhibit variations in both halite melting temperatures (T m, halite ) and liquid to vapor homogenization temperatures (Th L–V ). They are interpreted to originate from heterogeneous trapping of halite-saturated solutions, and subjected to post-entrapment stretching. Pressure calculations suggest that A and C type inclusions formed at great pressures of > 150 MPa, which resulted in the retention of more CO 2 in the exsolved fluids than those of shallow porphyry Cu systems. Compositions of hydrothermal fluids were possibly in the “L + V + H” field of the H 2 O–NaCl–CO 2 ternary system, thus leading to immiscibility to produce halite-saturated solution, halite crystals and CO 2 -bearing vapor. The barren quartz veins and potassic alteration represented by A 1 subtype and C type inclusions formed at a temperature range of 450 to 500 °C and pressure of ~ 265 to 300 MPa. Later, a decrease in temperature to 300–400 °C and pressure to ~ 220 MPa resulted in the precipitation of molybdenite. Subsequently, a decrease in temperature (to ~ 200–250 °C) and pressure (to ~ 150 MPa) occurred during chalcopyrite precipitation and pervasive sericitic alteration. Pyrite-dominated veins and barren carbonate quartz veins formed in response to influx of meteoric waters, and were the last stage hydrothermal activities at Dexing.

Sanshandao deposit, located in the western end of the Jiaodong Peninsula, is a typical altered-rock type gold deposit. The hydrothermal alteration in the deposit commences from potassic alteration with mineral assemblage mainly composed of K-feldspar and quartz, with minor sericite. The potassic alteration is followed by silicification that is always weakly developed in this district with minor sericite and gold-absent pyrite. As sericite content increases, the silicification alteration is gradually giving its way to sericitization. Fine sulfide crystals occur in this zone scattering in sericite and quartz matrix, which turns to be sulfidation as hydrothermal alteration proceeding. Gold mineralization is mainly associated with the sulfidation, predominantly hosted by pyrite. The latest hydrothermal alteration and veins consist of quartz-calcite-siderite(-ankerite) crosscutting the former alteration zones. Some auriferous sulfide-quartz veins fill the fractures in the alteration zones, but its gold reserve is limited. Geochemical modeling is applied to examine the hydrothermal alteration and gold precipitation processes in the Sanshandao deposit. Modeling shows that a gold-bearing fluid is potential to form an economic gold deposit via various paths, including fluid cooling, water-rock interaction, and fluid mixing with groundwater. The simulation results indicate that the auriferous quartz veins located in the alteration zones are probably generated by fluid cooling and mixing, whereas gold mineralization in the sulfide-sericite alteration stage is primarily caused by water-rock reaction that also produces the hydrothermal alteration following the potassic alteration. To evaluate the roles of water-rock interaction in gold mineralization at different temperatures, we execute simulations at T = 400 °C and 300 °C at pressure of 2 kbar. Gold precipitation at >400 °C is driven by strong water-rock reaction with low water/rock ratio, during which the gold precipitation is associated with pyrrhotite rather than pyrite, and thus the pyrite at this temperature scale is always gold-absent; at low temperature (∼300 °C), the water-rock interaction is effective to precipitate gold from the fluids, and gold mineralization links to pyrite precipitation. The comparison between these two simulations with different temperatures indicates that water-rock interaction at moderate temperature is prior to precipitate gold from hydrothermal fluid, which can be invoked to interpret the fact that gold mineralization is always intense in shallow level and host majority of gold reserve in this deposit. The modeling suggests that pyrrhotite should be paid more attention in future deep exploration since its ability to host certain gold budget at relatively high temperature.