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The Xiaoqinling district, the second largest gold producer in China, is situated on the southern margin of the North China Craton and immediately to the north of the Qinling Orogen. The timing and genesis of the gold deposits have been hotly debated because the area has undergone multiple tectono-magmatic events since the stabilization of the North China Craton in the early Paleoproterozoic. Whether they are genetically related to the Triassic orogeny that formed the Qinling Orogen or associated with the early Cretaceous tectonic reactivation of the craton remains controversial. Here we present monazite U-Pb and molybdenite Re-Os dating results from the Hongtuling vein deposit in the eastern part of the Xiaoqinling district to provide new insights into the age and tectonic setting of gold mineralization . The Hongtuling deposit consists of gold veins at the top and minor molybdenum veins at the bottom, with molybdenum veins being locally crosscut by gold veins. Molybdenum veins mainly consist of calcite, quartz, K-feldspar, molybdenite, and pyrite with minor amounts of galena, and a variety of accessory minerals. Gold veins are dominated by quartz and pyrite, with minor to trace amounts of chalcopyrite, galena, sphalerite, and sericite. Monazite grains are well developed both in molybdenum and gold veins, and are intergrown with molybdenite and pyrite, respectively. Monazites from gold vein contain lower REEs contents, more prominent negative Eu anomalies, and higher Th/U ratios than those from molybdenum vein. The textural and geochemical evidence indicates that monazites from both veins precipitated from contrasting ore-forming fluids. Laser ablation ICP-MS U-Pb dating of monazite from the molybdenum vein yields a 206Pb/238U age of 203.5 ± 8.1 Ma (MSWD = 0.23, 2σ), which is statistically indistinguishable from the molybdenite Re-Os age of 204 Ma. In contrast, monazite from the gold vein has a significantly younger 206Pb/238U age of 130.4 ± 5.3 Ma (MSWD = 0.99, 2σ). Results presented here, combined with independent studies, suggest that the molybdenum and gold veins of the Hongtuling deposit, and by inference the other deposits in the district, formed in two discrete mineralization events in the late Triassic and early Cretaceous. The molybdenum mineralization is most likely related to the post-collisional magmatism associated with the Qinling orogeny, whereas gold mineralization occurred in an extensional setting associated with the decratonization of the North China Craton.

The West Qinling orogen in central China contains dozens of world-class sediment-hosted gold deposits, but the ages of these deposits and their relation to regional tectonism, magmatism, and metamorphism are poorly understood. Zaozigou, in the western zone of the Xiahe-Hezuo district, is one of the larger deposits in the orogen with 142 t Au at an average grade of 2.69 g/t. It is hosted in a middle Triassic turbidite sequence and swarm of crosscutting ilmenite-series intermediate to felsic dikes. Ore bodies are localized along subvertical, NE- or NS-striking faults. Gold occurs in fine-grained arsenian pyrite and arsenopyrite disseminated in hydrothermally altered sedimentary and igneous rocks and in subordinate sulfide-quartz-ankerite veinlets. Such mineralization is locally crosscut and overprinted by NW-striking, gently-dipping, auriferous stibnite-quartz veins. Zircon grains from gold mineralized granodiorite and quartz diorite porphyry dikes have U-Pb ages of 248.9 ± 1.4 to 244.8 ± 1.4 Ma, whereas a post-ore diorite porphyry dike has a U-Pb age of 237.5 ± 1.4 Ma. Two samples of sericite associated with disseminated arsenian pyrite and arsenopyrite in sedimentary and igneous host rocks yield plateau ages of 245.6 ± 1.0 Ma and 242.1 ± 1.0 Ma, that are bracketed by the zircon U-Pb ages on pre- and post-ore dikes. Field relationships and geochronological results, thus, constrain magmatism and gold mineralization at the early Triassic. Previous work has shown that the Au-Cu skarns and intrusion-related gold deposits exposed at a deeper level in the eastern zone of the Xiahe-Hezuo district are genetically related to early-middle Triassic ilmenite series intrusions generated in an extensional back-arc setting during rollback of the subducted paleo-Tethyan slab. Our U-Pb and Ar/Ar data show that the large Zaozigou gold deposit in the western zone of the Xiahe-Hezuo district is broadly coeval with the Au-Cu skarn and intrusion-related gold deposits in the eastern zone. This temporal consistency provides additional support for a genetic link between gold mineralization and magmatism in the Xiahe-Hezuo district. As such, this district may represent the only reduced intrusion related gold system in the West Qinling Orogen.

The West Qinling orogen in central China contains several dozens of gold deposits. However, absolute ages of gold mineralization and its relations to regional tectonism, magmatism, and metamorphism remain not tightly constrained for most of these gold deposits. Here we integrate 40Ar/39Ar dating of sericite from various hydrothermal alteration assemblages and U-Pb dating of zircon grains from magmatic rocks within and surrounding the Liziyuan gold deposit in the northern belt of the West Qinling orogen to provide new insights into the age and tectonic setting of gold mineralization. The Liziyuan gold deposit consists of six ore camps (Yuzigou, Liushagou, Jiancaowan, Kuangou, Suishizi, and Yingfang) that are hosted in Ordovician greenschist facies metamorphosed sedimentary-volcanic rocks and, less significantly, the Middle Triassic Tianzishan monzogranite pluton intruding the metamorphic rocks. Gold mineralization consists of auriferous quartz-pyrite veins and subordinate sulfide disseminations in hydrothermally altered wall rocks, with minor calcite-polymetallic sulfide veins in the monzogranite-hosted orebodies. Ore-related alteration assemblages are dominated by quartz, sericite, pyrite, chlorite, and calcite, with gold occurring mostly as native gold grains enclosed in or filling microfractures of pyrite and quartz. Barren alteration assemblages, dominated by K-feldspar, quartz, sericite, and pyrite, are locally developed along eastern margin of the Tianzishan monzogranite. Two sericite aggregates extracted from gold ores in the Liushagou camp yield well-defined 40Ar/39Ar plateau ages of 200.1 ± 1.2 and 198.8 ± 1.1 Ma (2σ), whereas those from barren alteration assemblages in the Tianzishan monzogranite, which hosts the Suishizi ore camp, give rise to older 40Ar/39Ar plateau ages of 211.9 ± 1.2 and 211.3 ± 1.3 Ma (2σ). The Tianzishan monzogranite pluton and several dioritic to granitic stocks and dykes in and surrounding the gold mines have zircon U-Pb ages ranging from 241.3 ± 1.2 to 212.4 ± 0.9 Ma (2σ). These new isotopic ages suggest that the Liziyuan gold deposit formed at the Triassic-Jurassic boundary, arguably representing the youngest orogenic-type gold mineralization event over the northern belt of the West Qinling orogen. Gold mineralization postdates magmatism in the Liziyuan gold deposit at least by about 10 million years, precluding a possible genetic relation between the two. Rather, the ore genesis was likely related to metamorphic fluids released from Paleozoic sedimentary and volcanic rocks in relation to the Qinling orogenesis. In contrast, the barren hydrothermal alteration assemblages were likely caused by fluids exsolved from a magma presumably represented by the ca. 212 Ma diorite dyke. Results presented here, when combined with independent geological and geochemical data, suggest that the Liziyuan gold deposit formed most likely under a post-collisional extensional setting related to the West Qinling orogeny.

The Dayingezhuang gold deposit in the Jiaodong district, eastern margin of the North China Craton is hosted in Mesozoic granitic rocks and consists of quartz-sulfide veins/veinlets and sulfide disseminations in alteration envelopes. Previous studies mainly focused on the geochronology, sources of ore-forming fluids and metals to investigate the ore genesis. However, enrichment mechanism of Au and other associated trace metals remain unclear. In this study, we present detailed textures and in-situ LA-ICP-MS trace-element compositions of different generations of pyrite, as well as EMP analysis of Au-bearing minerals to discuss the occurrence and enrichment mechanism of Au at this deposit. Three generations of pyrite (Py1, Py2 and Py3) formed during three hydrothermal ore stages (I, II, and III) at Dayingezhuang. Py1 occurs as disseminations in sericitic alteration assemblages and is characterized by low Au (mean 0.15 ppm), Ag, As and Te contents. The time-resolved depth-concentration profiles indicate that Au in Py1 mainly occurs as nanoparticles and/or micron-sized inclusions. Py2 can be further divided into the early undeformed Py2a and later Py2b, which is the product of deformed Py2a with different degrees of brittle to plastic deformation and recrystallization. Py2a in pyrite-siderite-quartz veins is relatively enriched in invisible Au (mean 0.41 ppm), Ag, As, and Te compared to Py1, and contains numerous micron-sized Au inclusions. In contrast, Py2b contains lesser invisible Au (0.21 ppm) and host abundant gold minerals along the grain boundaries and microfractures. Py3 in polymetallic sulfide veins has little Au. As a whole, Au in pyrite is positively correlated with Ag and Te, which is consistent with the results of EMP analysis showing the occurrence of Au as electrum, native gold and minor petzite in pyrite. Such evidences show that the deformation and recrystallization of auriferous Py2a potentially caused local remobilization of Au (mainly as micron-sized inclusion Au) via solid-state ductile flow and subsequent reconcentration of Au in microfractures of Py2b. The pyrite deformation and Au remobilization events were suggested to be related to the continuous reactivation of the regional Zhaoping Fault contemporaneous with gold mineralization. Our study highlights the importance of remobilization and reconcentration of Au triggered by syn-ore tectonic activities at Dayingezhuang and possibly other Au deposits in the Jiaodong district.

The Sangan iron skarn deposit is located on the eastern edge of the Sabzevar-Doruneh Magmatic Belt, northeastern Iran. Mineralization occurs at the contact between Eocene igneous rocks and Cretaceous carbonates. The silicate-dominant prograde skarn stage consists of garnet and clinopyroxene, whereas the retrograde stage is dominated by magnetite associated with minor hematite, phlogopite, pyrite, and chalcopyrite. Phase equilibria and mineral chemistry studies reveal that the skarn formed within a temperature range of ∼375° to 580 °C and that the mineralizing fluid evolved from a hot, low oxygen fugacity, alkaline fluid during the silicate-dominant stage to a fluid of relatively lower temperature and higher oxygen fugacity at the magnetite-dominant stage. The δ 18 O values of magnetite and garnet vary from +3.1 to +7.5‰ and +7.7 to +11.6‰, respectively. The calculated δ 18 O H2O values of fluid in equilibrium with magnetite and garnet range from +9.8 to +11.1‰ and +10.1 to +14.8‰, respectively. These elevated δ 18 O H2O values suggest interaction of magmatic water with 18 O-enriched carbonates. The high δ 34 S values (+10.6 to +17.0‰) of pyrite separates from the Sangan iron ore indicate that evaporites had an important role in the evolution of the hydrothermal fluid. Phlogopite separates from the massive ores yield 40 Ar/ 39 Ar plateau ages of 41.97 ± 0.2 and 42.47 ± 0.2 Ma, indicating that the skarn formation and associated iron mineralization was related to the oldest episode of magmatism in Sangan at ∼42 Ma. Eocene time marked a peak of magmatic activity and associated skarn in the post-collisional setting in northeastern Iran, whereas Oligo-Miocene magmatic activity and associated skarn in the Urumieh-Dokhtar Magmatic Belt are related to subduction. In addition, skarn mineralization in northeastern and eastern Iran is iron type, but skarn mineralization in the Urumieh-Dokhtar magmatic belt is copper – iron and copper type.

The North China craton hosts numerous iron skarn deposits containing more than 2600 Mt of iron ores, mostly with an average grade of >45 wt% Fe, which have been among the most important source of high-grade iron ores for the last three decades in China. These deposits typically form clusters and can be roughly divided into the western and eastern belts, which are located in the middle of Trans-North China orogen and to the west of the Tan-Lu fault zone in the eastern part of North China craton, respectively. The western belt mainly consists of the southern Taihang district, as well as the Linfen and Taiyuan ore fields, whereas the eastern belt comprises the Luxi and Xu-Huai districts. The Zhangjiawa deposit in the Luxi district has proven reserves of 290 Mt at an average of 46% Fe (up to >65%). The iron mineralization occurs mainly along contact zones between the Kuangshan dioritic intrusion and middle Ordovician marine carbonate rocks that host numerous evaporite intercalations. Titanite grains from the mineralized skarn are closely intergrown with magnetite and retrograde skarn minerals including chlorite, phlogopite and minor epidote, indicating a hydrothermal origin. The titanite grains have extremely low REE contents and low Th/U ratios, consistent with their precipitation directly from hydrothermal fluids responsible for the iron mineralization. Ten hydrothermal titanite grains yield a weighted mean 206 Pb/ 238 U age of 131.0 ± 3.9 Ma (MSWD = 0.1, 1σ), which is in excellent agreement with a zircon U-Pb age (130 ± 1 Ma) of the ore-related diorite. This age consistency confirms that the iron skarn mineralization is temporally and likely genetically related to the Kuangshan intrusion. Results from this study, when combined with existing isotopic age data, suggest that iron skarn mineralization and associated magmatism throughout both the eastern and western belts took place coevally between 135 and 125 Ma, with a peak at ca. 130 Ma. As such, those deposits may represent the world's only major Phanerozoic iron skarn concentration hosted in Precambrian cratons. The magmatism and associated iron skarn mineralization coincide temporally with the culmination of lithospheric thinning and destruction of the North China craton, implying a causal link between the two.

The southern North China craton hosts numerous world-class porphyry Mo and Pb-Zn-Ag vein deposits. Whether or not the Pb-Zn-Ag veins are genetically associated with the porphyry Mo system remains contentious. Here we focus on the genetic relationships between the Sanyuangou Pb-Zn-Ag vein deposit and the world-class Donggou porphyry Mo deposit, and discuss the potential implications from the spatial and temporal relationships between porphyry and vein systems in the southern North China craton. At Sanyuangou, vein-hosted sulfide mineralization mainly comprises pyrite, sphalerite, and galena, with minor chalcopyrite, pyrrhotite, bornite, tetrahedrite, covellite, polybasite and argentite. The mineralization is hosted by a quartz diorite stock, which has a zircon U-Pb age of 1756 ± 9 Ma. However, sericite from alteration selvages of Pb-Zn-Ag sulfide mineralization yields a well-defined 40Ar/39Ar plateau age of 115.9 ± 0.9 Ma. Although nominally younger, the sericite 40Ar/39Ar age is similar to the age of the nearby Donggou porphyry Mo deposit (zircon U-Pb age of 117.8 ± 0.9; molybdenite Re-Os ages of 117.5 ± 0.8 Ma and 116.4 ± 0.6 Ma). Pyrite from Donggou has elevated contents of Mo and Bi, whereas pyrite from Sanyuangou is enriched in Cu, Zn, Pb, Ag, Au, and As. This trace element pattern is consistent with metal zonation typically observed in porphyry related metallogenic systems. Pyrite grains from Sanyuangou have lead isotopes overlapping those from Donggou (17.273–17.495 vs. 17.328–17.517 for 206Pb/204Pb, 15.431–15.566 vs. 15.408–15.551 for 207Pb/204Pb, and 37.991–38.337 vs. 38.080–38.436 for 208Pb/204Pb). Collectively, the geological, geochronological, and geochemical data support a magmatic-hydrothermal origin for the Sanyuangou Pb-Zn-Ag deposit and confirm that the Pb-Zn-Ag veins and the Donggou Mo deposit form a porphyry-related magmatic-hydrothermal system. Given the widespread Pb-Zn-Ag veins and Mo mineralized porphyries in many districts of the southern North China craton, the model derived from this study has broad implications for further exploration of Mo and Pb-Zn-Ag resources in the area.

Controversies in orogenic gold deposits remain, especially regarding the relative contribution of magmatic fluids to the mineralization. The Shuizhadonggou-Huanglonggou gold deposit in the Wulonggou gold field of the eastern Kunlun Orogen, western China consists mainly of sulfide disseminations in hydrothermally altered rocks with minor amounts of quartz-sulfide veins coeval to or overprinting the disseminated ores. Gold mineralization is hosted in diverse lithologies (i.e., Early Palaeozoic metamorphic rocks, Late Silurian syenogranite and Late Triassic porphyritic granodiorite and quartz diorite) and is structurally controlled by a second-order NW-trending sinistral-normal ductile shear zone and its subsidiary structures along the first-order Central Kunlun Fault. Gold-related hydrothermal alteration formed chlorite, sericite, quartz and calcite, with associated sulfide minerals dominated by pyrite, arsenopyrite, lollingite and pyrrhotite. Two types of hydrothermal sericite separates from a gold mineralized syenogranite yielded two 40Ar/39Ar ages of 237.0 ± 2.0 Ma and 230.8 ± 1.7 Ma, respectively, which postdated the Early Triassic regional metamorphism and ductile deformation by ~ 13 m.y. Field relationships suggest that gold mineralization also overprinted ~ 220 Ma porphyritic granodiorites and quartz diorites. These data indicate three gold mineralization events in the Late Triassic overlapped with post-collisional magmatism in the orogen. Gold-bearing sulfides have δ34S values mostly in the range of 2.0–5.5‰, consistent with a magmatic source of sulfur. Quartz from quartz-pyrite-sericite veins has calculated δ18OH2O values of 1.8–6.1‰ and δDH2O of − 63 to − 107‰. The stable isotopic and geochronological data suggest a magmatic origin for the ore-forming fluids. Therefore, the Shuizhadonggou-Huanglonggou and other gold deposits in the eastern Kunlun Orogen share many features of orogenic gold deposits (e.g., multiple-order ore-controlling structures, hydrothermal alteration, mineralization styles, close association between mineralization and magmatism, and H-O-S stable isotope compositions) and are genetically related to Late Triassic post-collisional magmatism.

The Triassic West Qinling orogen, which formed by the continental collision between the South China block and North China craton following the subduction and closure of the paleo-Tethyan ocean, hosts numerous gold deposits that have commonly considered as products of metamorphic dehydration during the oceanic subduction and subsequent continental collision. However, whether or not there are gold deposits that are genetically related to regional magmatism remains poorly understood. Here we present mineralogical, compositional, and geochronological data of the Dewulu Au-Cu skarn deposit in the Xiahe-Hezuo district to understand the ore genesis and its genetic link to many coeval sediment-hosted disseminated and magmatic-hosted vein gold deposits in the same district, which collectively reveal a possible intrusion-related gold system. The Dewulu Au-Cu skarn deposit in the eastern zone of the Xiahe-Hezuo district is associated with the early Triassic I-type, ilmenite-series Dewulu quartz diorite pluton that intrudes Permian marine clastic and carbonate rocks. Ore-related hydrothermal biotite separates yield a well-defined 40Ar/39Ar plateau age of 239.9 ± 1.4 Ma (2σ), which agrees with a previous zircon U-Pb age (238.6 ± 1.5 Ma at 2σ) of the Dewulu quartz diorite and thus demonstrates a temporal and likely genetic link between the two. Both prograde and retrograde skarn assemblages are well developed in the Dewulu Au-Cu deposit. Prograde garnet and pyroxene are compositionally dominated by grossularite and hedenbergite, respectively, indicating a reduced skarn system. Au-Cu mineralization is largely represented by the arsenopyrite-loellingite-chalcopyrite-pyrrhotite-bornite assemblage and is associated with retrograde skarns. Gold is mostly hosted in arsenopyrite, loellingite and chalcopyrite, and has close textural relations with native bismuth or bismuthides. Mineral stability relationships and fluid inclusion microthermometric data confirm that the prograde skarns formed at a low oxygen fugacity, high temperature (> 630 °C), and a depth range of 2.9 to 6.5 km. Arsenopyrite and chlorite geothermometers indicate that the retrograde skarns and late quartz-sulfide-calcite assemblages formed at 550 to 345 °C and

The Hongtuling Au-Mo deposit on the southern margin of the North China Craton consists of Au veins and minor Mo veins that formed at ~130 Ma and ~204 Ma, respectively. Mo mineralization is dominated by molybdenite that is associated with K-feldspar, quartz and calcite, whereas Au mineralization occurs mostly as auriferous quartz-sulfides veins associated with alteration assemblages consisting of pyrite ± sericite ± quartz. Laser ablation inductively coupled plasma mass spectrometry trace element analysis shows that pyrite from Mo veins (Py-Mo) is relatively enriched in Mo and Pb, whereas pyrite from Au veins (Py-Au) contains much higher Au, Ag, Te, Cu, Pb, and Ni. Sulfide minerals and celestine from Mo veins range in δ34S values from −13.4 to −8.89‰ (n = 24) and 5.26 to 7.76‰ (n = 8), respectively. Extrapolation of sulfur isotopes of coexisting sulfides and celestine to zero sulfide-celestine fractionation on Δ34SClt-Py versus δ34S diagram shows that the hydrothermal fluid from which molybdenite precipitated has δ34S of 2.49 ± 3.93‰. In comparison, Py-Au yields δ34S values of −6.23 ~ 0.16‰, with a mean of −2.60‰ (n = 20). The Py-Mo and Py-Au have significantly different lead isotopic compositions, which form two distinct groups on the 207Pb/204Pb versus 206Pb/204Pb diagram, with Py-Au plotting close to the lead growth curve of the subcontinental lithospheric mantle of the North China Craton at ~130 Ma. Combined with previous studies, our new trace element and S-Pb isotope data suggest that Mo mineralization at Hongtuling is most likely related to magmas derived from partial melting of Late Archean to Paleoproterozoic metamorphic basement rocks under a post-collisional setting related to the collision between the North China Craton and Yangtze Craton, whereas Au mineralization is genetically associated with mantle-derived magmas generated in an extensional setting due to thinning and destruction of subcontinental lithospheric mantle keel beneath the North China Craton. As such, the Triassic Mo and Early Cretaceous Au veins can both be classified as magmatic-hydrothermal mineralization but are affiliated with two distinct systems. This study highlights the utilization of pyrite trace element and isotopic compositions in distinguishing multiple mineralization events in a single deposit.

The North China Craton (NCC) hosts numerous gold deposits clustering in several districts, which combined have proven reserves of ~7000 t Au. Geochronological studies have shown that the craton-wide gold mineralization occurred mostly in the 140–120 Ma interval, coincident with the peak of thinning and destruction of the lithospheric keel beneath the NCC. Here we integrate geological relations with LA-ICP-MS zircon U-Pb dating to reveal a new gold mineralization event in the Jidong district, northern NCC. The Xiajinbao, Yu’erya and Jinchangyu gold deposits in this district are characterized by crosscutting relationships between gold veins and various dikes. This relation suggests that zircon U-Pb dating of the pre-ore and post-ore dikes can provide tight constraints on the time of gold veining. LA-ICP-MS zircon U-Pb dating of pre- and post-ore dikes from the three gold deposits yields concordant U-Pb dates of 165–163 Ma, 165–164 Ma and 165–164 Ma, respectively. These indistinguishable U-Pb dates within analytical uncertainty are interpreted as the timing of gold deposition (165–163 Ma) and thus reveal a previously unrecognized Late Jurassic gold mineralization event in the Jidong district. A large variety of mafic to intermediate dikes in the Jidong district have zircon U-Pb dates of 166 ± 1 to 164 ± 2 Ma, consistent with ages of the three gold deposits investigated. The temporal consistency and abundant sulfide inclusions hosted in the mafic-intermediate intrusions, along with the close spatial relations between gold veins and various dikes within and surrounding the mines, indicate a possible magmatic source for ore fluids. Synthesis of regional geological, geochemical and isotopic data led us to conclude that the Late Jurassic gold mineralization in the northern NCC is genetically related to lithosphere destruction of the NCC. An additional implication from this study is that the Mesozoic decratonization of the NCC and associated gold mineralization are spatially and temporally heterogeneous and much more prolonged than commonly thought.

The Sin Quyen iron oxide-copper–gold (IOCG) deposit in northwestern Vietnam contains a proven reserve of 52.8 Mt ores at 14% Fe, 0.91% Cu, 0.7% REEs (rare earth elements), and 0.44 g/t Au. REEs mineralization is hosted within Ca-silicate alteration zone and associated with Fe-Cu ore bodies in the gneiss, mica schist, and marble of the Upper Sin Quyen Formation. Two mineralization episodes are identified based on the field and petrographic relations. The first episode includes sodic alteration (stage I-1), calcic alteration and associated REE mineralization (stage I-2), and localized K-Fe alteration (stage I-3). The second episode is main stage mineralization and contains four main stages of alteration: pre-ore Na alteration (stage II-1), Ca-Fe alteration and the associated Fe-REE mineralization (stage II-2), K-Fe alteration and associated Cu-Au mineralization (stage II-3), and the final carbonate stage of quartz-carbonate veins (stage II-4) crosscutting the above-mentioned alteration phases and ores. Primary allanite and type 1 titanite (Tnt-1) from episode 1 yield weighted mean 206Pb/238U ages of 882 ± 3 Ma and 881 ± 8 Ma (2σ), respectively, which are interpreted as the timing of REE mineralization in episode 1. Secondary allanite and type 2 titanite (Tnt-2) associated with iron-oxide and Cu-Au ores, however, have U-Pb ages of 840 ± 7 Ma and 838 ± 5 Ma (2σ), respectively. These ages are hence considered to represent the timing of polymetallic IOCG mineralization in episode 2. ~880 Ma titanite grains have eNd(t) values ranging from −7.00 to −5.43, which are intermediate between the Neoproterozoic felsic intrusions and ore-hosting meta-sedimentary rocks in the region and likely reflect interaction between magmatic fluids and ore-hosting rocks. In contrast, ~840 Ma titanite have eNd(t) values ranging from −4.31 to −1.97, similar to those of the Neoproterozoic felsic intrusions, indicating a possible magmatic fluid source for the episode II IOCG mineralization. Multiple episodes of mineralization at Sin Quyen were likely formed during the prolonged tectonothermal events related to backarc extension during the Neoproterozoic subduction along the western margin of the Yangtze Block.

Large variations in Mo isotopes (up to ~2‰ δ98Mo) of molybdenite from many porphyry ore deposits have been reported. However, the mechanisms of Mo isotopic fractionation and their implications for mineralization processes remain poorly understood. Here we report contrasting Mo isotopes of molybdenite formed in two discrete, successive mineralizing stages of the giant Yulong porphyry Cu-Mo deposit in eastern Tibet which, when combined with available fluid inclusion data and high-precision molybdenite Re-Os ages, provide a better understanding in the mechanisms of Mo isotopic fractionation and molybdenite precipitation. The initial ore-forming fluids of both mineralizing stages at Yulong exsolved from magmas as a single-phase, intermediate-density fluid, which subsequently separated into coexisting brine and vapor phases upon ascent and decompression. The relatively uniform Mo isotopes (δ98Mo = 0.03–0.18‰) of the early Cu-Mo stage is consistent with the precipitation of molybdenite from relatively stagnant, high-density brines at shallow levels after phase separation. In contrast, the large spread of Mo isotopes (δ98Mo = −0.16–0.60‰) of the transitional Mo stage requires a process similar to instantaneous Rayleigh fractionation and suggests molybdenite precipitation from rapidly ascending single-phase fluids before phase separation in deep parts of the deposit . These arguments imply that the amount of Mo precipitation from the single-phase fluids likely determines the degree of Mo isotopic fractionation. Further quantitative modeling results suggest that the relatively large Mo isotope variation of molybdenite in many porphyry ore deposits may be simply explained by the precipitation of significant amount of Mo from the initial single-phase fluids. Therefore, apart from the precipitation of molybdenite with economic importance from metal-enriched brines that condensed from the single-phase fluids, the direct precipitation of molybdenite from the single-phase fluids may represent another significant mechanism of molybdenite precipitation in porphyry ore systems.

The West Qinling orogen, central China is endowed with dozens of world-class sediment-hosted gold deposits, most of which have formed from metamorphic fluids released from Paleozoic sedimentary rocks during the Triassic collisional orogeny. Here we present trace element and sulfur isotope data of gold-bearing pyrite and arsenopyrite, along with oxygen and hydrogen isotopes of ore-related sericite, to show that the Early Triassic Zaozigou gold deposit (142 t) in the Xiahe-Hezuo district may have contrasting origin. Gold mineralization at Zaozigou is dominated by fine-grained pyrite and arsenopyrite disseminations (Py1 and Asp1) in hydrothermally altered Triassic flysch and, less significantly, in Early Triassic granitoid dike swarm. The disseminated ores are overprinted by quartz-sulfide-ankerite-sulfide vein/veinlets, which contain less abundant, coarser pyrite and arsenopyrite (Py2 and Asp2) and are less economically significant. Gold occurs as invisible gold in fine-grained arsenian pyrite and arsenopyrite of the disseminated ores, with subordinate native gold grains locally observed in the quartz-sulfide-ankerite vein/veinlets. The two types of pyrite (Py1 vs. Py2) and arsenopyrite (Asp1 vs. Asp2) are consistently enriched in As, Au, Co, Ni, Mn, Cu, Zn, Ag, Sb, W, Pb, Te, and Bi and have well comparable δ34S values ranging from −12.0‰ to −5.5‰. Grain-scale variation has been observed for Au and other trace elements both in Py1 and Py2, likely reflecting changes in physio-chemical conditions such as fO2, fS2 and temperature due to fluid-rock interactions and/or fluid mixing. The δ34S values are broadly consistent with sulfur isotopic compositions of many Early Triassic ilmenite-series intrusions in the Xiahe-Hezuo district, and thus suggest a magmatic sulfur derivation from the reduced magmas that have assimilated carbonaceous sedimentary rocks. The δD and δ18O values of ore-fluids calculated from isotopic compositions of ore-related sericite range from −56 to −76‰ and 10.1 to 12.4‰, respectively, indicating a magmatic fluids exsolved from the above-mentioned ilmenite-series magma or a mixture of such as fluid with a metamorphic derived component. Synthesis of geochronological and geochemical data throughout the Xiahe-Hezuo district led us to conclude that the Zaozigou gold deposits can be considered as a shallow-seated, distal product of a reduced intrusion-related gold system.

Several recent studies have shown that garnet U-Pb dating may potentially provide robust constraints on the ages of carbonatite, alkaline magmatism and skarn ore formation. Here we present textural, trace element, and laser ablation inductively coupled plasma mass spectrometry U-Pb isotope data of garnet from the Yinan Au-Cu skarn deposit in Luxi District, eastern North China Craton, to place tight constraints on the timing of mineralization. Three hydrothermal andradite-rich garnet samples (JL-8, THZ-38 and TJ-13) collected respectively from Jinlong, Tonghanzhuang and Gongquan ore segments of the Yinan Au-Cu skarn deposit, contain 2.31–10.36 ppm U and are characterized by flat time-resolved depth profiles for U, indicating that this element is hosted in crystallographic lattice in the garnets. The positive correlation between U and LREEs concentration suggests that the incorporation of U into the garnet is largely controlled by substitution mechanisms. The three garnet samples yield weighted mean 206Pb/238U dates of 127 ± 3 Ma, 127 ± 5 Ma and 126 ± 7 Ma (2σ), respectively. These ages are reproducible within analytical uncertainties and are consistent with a zircon U-Pb age of 129 ± 2 Ma of the ore-related diorite intrusion, and thus, are interpreted as the age of Au-Cu mineralization at Yinan. The results presented here, when combined with existing isotopic age data, demonstrate that Au-Cu skarn mineralization throughout the southeastern Luxi District occurred, coevally, in the Early Cretaceous and is genetically associated with the Tongjing and Jingchang granitic-dioritic complexes. The Au-Cu mineralization and associated magmatism coincide in time with the iron skarn mineralization and associated magmatism (134–126 Ma) across the Luxi District, strongly suggesting a causal link between the district-wide skarn mineralization and pervasive intermediate to felsic magmatism; both are products of destruction of lithospheric mantle beneath the North China Craton. This study confirms that garnet U-Pb dating can be a robust geochronometer for garnet-bearing hydrothermal deposits and can elucidate associated geological processes.

In this paper, we present U–Pb ages and trace element compositions of titanite from the Ruanjiawan W–Cu–Mo skarn deposit in the Daye district, eastern China to constrain the magmatic and hydrothermal history in this deposit and provide a better understanding of the U–Pb geochronology and trace element geochemistry of titanite that have been subjected to post-crystallization hydrothermal alteration. Titanite from the mineralized skarn, the ore-related quartz diorite stock, and a diabase dike intruding this stock were analyzed using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Titanite grains from the quartz diorite and diabase dike typically coexist with hydrothermal minerals such as epidote, sericite, chlorite, pyrite, and calcite, and display irregular or patchy zoning. These grains have low LREE/HREE and high Th/U and Lu/Hf ratios, coupled with negative Eu and positive Ce anomalies. The textural and compositional data indicate that titanite from the quartz diorite has been overprinted by hydrothermal fluids after being crystallized from magmas. Titanite grains from the mineralized skarn are texturally equilibrated with retrograde skarn minerals including actinolite, quartz, calcite, and epidote, demonstrating that these grains were formed directly from hydrothermal fluids responsible for the mineralization. Compared to the varieties from the quartz diorite stock and diabase dike, titanite grains from the mineralized skarn have much lower REE contents and LREE/HREE, Th/U, and Lu/Hf ratios. They have a weighted mean 206 Pb/ 238 U age of 142 ± 2 Ma (MSWD = 0.7, 2σ), in agreement with a zircon U–Pb age of 144 ± 1 Ma (MSWD = 0.3, 2σ) of the quartz diorite and thus interpreted as formation age of the Ruanjiawan W–Cu–Mo deposit. Titanite grains from the ore-related quartz diorite have a concordant U–Pb age of 132 ± 2 Ma (MSWD = 0.5, 2σ), which is 10–12 Ma younger than the zircon U–Pb age of the same sample and thus interpreted as the time of a hydrothermal overprint after their crystallization. This hydrothermal overprint was most likely related to the emplacement of the diabase dike that has a zircon U–Pb age of 133 ± 1 Ma and a titanite U–Pb age of 131 ± 2 Ma. The geochronological results thus reveal two hydrothermal events in the Ruanjiawan deposit: an early one forming the Wu–Cu–Mo ores related to the emplacement of the quartz diorite stock and a later one causing alteration of the quartz diorite and its titanite due to emplacement of diabase dike. It is suggested that titanite is much more susceptible to hydrothermal alteration than zircon. Results from this study also highlight the utilization of trace element compositions in discriminating titanite of magmatic and hydrothermal origins, facilitating a more reasonable interpretation of the titanite U–Pb ages.

China has a rich reserve of iron ores and hosts most of the major types of iron deposits recognized worldwide. However, among these, the banded iron formation (BIF), skarn, apatite–magnetite, volcanic-hosted, sedimentary hematite and magmatic Ti–Fe–(V) deposits constitute the most economically important types. High-grade iron ores (> 50% Fe) are relatively rare, and are mostly represented by the skarn-type. Most of the BIF deposits formed in the Neoarchean, with a peak at ~ 2.5 Ga, and are mainly distributed in the North China Craton. The majority of these is associated with volcanic rocks, and therefore belongs to the Algoma-type. The superior-type BIF deposits formed during the Paleoproterozoic occur subordinately (ca. 25%), and are related mainly to rifts (or passive continental margins). In addition, minor Superior-type BIF deposits have also been recognized. The skarn iron deposits are widely distributed in China, especially in the uplifted areas of eastern China, and form several large iron ore clusters. These ore deposits are genetically associated with intermediate, intermediate-felsic and felsic intrusions with a peak age of formation at ca. 130 Ma. They display common characteristics including alteration and nature of mineralization. The apatite–magnetite deposits occurring in the Ningwu and Luzong Cretaceous terrigenous volcanic basins along the Middle–Lower Yangtze River Valley, are spatially and temporally associated with dioritic subvolcanic intrusions. The ores in this type are characterized by magnetite and apatite. The volcanic-hosted iron deposits are associated with submarine volcanic-sedimentary sequences, and are widely distributed in the orogenic belts of western China, including Western Tianshan, Eastern Tianshan, Beishan, Altay, Kaladawan area in the eastern part of the Altyn Tagh Mountain and southwestern margin of South China Block. These deposits show a considerable age range, from Proterozoic to Mesozoic, but with more than 70% were formed in the Paleozoic, especially during the Late Paleozoic. The metallogenesis in these deposits can be correlated to the space–time evolution of the submarine volcanism, and their relationship to volcanic lithofacies variation, such as central, proximal and distal environments of ore formation. The sedimentary hematite deposits are widespread in China, among which the “Xuanlong-type” in the North China Craton and the “Ningxiang-type” in the South China Block are the most economically important. All these deposits formed during transgressions in a shallow-marine environment. Magmatic Ti–Fe–(V) deposits are dominantly distributed in the Panxi area in Sichuan province and Chengde area in Hebei province. They are dominated low-grade disseminated ores, and unlike the other types of iron deposits, associated sulfide deposits are absent, with magnetite, titanomagnetite and ilmenite as the dominant ore minerals. In the Panxi area in the central Emeishan large igneous province along the western margin of South China Block, the ores are hosted in the ca. 260 Ma mafic layered intrusions, whereas the ores in the Chengde area are associated with the Mesoproterozoic anorthosite complex. The distinct spatio-temporal characteristics of the various iron deposits in China correlate with the multiple tectono-magmatic events associated with the prolonged geological history of the region involving accretion, assembly and rifting.

The Daye District represents one of the largest concentrations of Cu–Fe–Au skarn deposits in China, with additional porphyry Cu–Mo deposits. These deposits are closely associated with late Mesozoic intrusions of intermediate to felsic composition. Previous studies have yielded important age constraints for several deposits, timing and history of metallogenesis for the entire district, however, remain not well understood. In this paper, we present twenty-five new ages (Re–Os, 40Ar/39Ar, and U–Pb) to better understand the temporal framework of the district-wide polymetallic mineralization. These ages, when combined with existing data, indicate a prolonged history of mineralization lasting 25 million years from late Jurassic to early Cretaceous (157–132 Ma), and that most ore deposits of the district are results of multistage hydrothermal activity. Discrete episodes of ore formation coincide well with emplacement ages of granitoid intrusions within the district as revealed by recent zircon U–Pb dating. This age consistency substantiates a genetic relationship between ore formation and intrusive magmatism. Prolonged and episodic magmatic and hydrothermal activities must have played significant roles in the formation of polymetallic ore deposits in the district by repeatedly supplying heat, fluids, and metals. Previous studies have demonstrated that the Daye District was dominated by lithospheric extension during late Jurassic to early Cretaceous, when extensive magmatism and mineralization took place. Under the extensional setting, the area could have experienced significant uplift or extensional exhumation that would have brought early-stage intrusions and associated ore deposits to shallower levels, with ore bodies formed by subsequent magmatic–hydrothermal events tending to be localized at greater depth. This in turn indicates potentials to find new ore bodies at depth of known deposits, especially for those formed by episodic magmatic–hydrothermal processes. This view is partly confirmed by the recent success in deep exploration beneath the Tieshan Fe–Cu and Tonglushan Cu–Au–Fe deposits.

The Dahu lodegold deposit is situated in the Xiaoqinling district, hosted in the east-west-trending shear zones, and characterized by auriferous quartz vein-type. Based on the morphology and paragenetic assemblage, three generations of pyrite (termed as first-generation pyrite (Py1), Py2, and Py3) can be classified. The Py2 can be further identified as brittle fractured pyrite (Py2-B) and ductile deformed pyrite (Py2-D). The different generations of pyrites feature distinct contents and distribution patterns of Au and other trace elements. The coarse-grained, euhedral Py1, disseminating in the early formed pyrite-poor quartz veins, contained negligible to extremely low levels of Au and associated trace elements, probably indicating a slow growth rate from a hydrothermal fluid unsaturated with respect to Fe, S, and Au and other trace elements, such as Cu, Pb, Bi, and Te, during the early orestage. Py2, occurring as laminations in the auriferous quartz veins, consistently contained significant amounts of Au, Bi, and Te, with a strong positive correlation between these elements, probably indicating a rapid growth rate and concentrated precipitation process of pyrite due to a hydrothermal fluid supersaturated with respect to Fe, S, Au, and other trace elements during the pyrite-rich auriferous quartz veining. Py3, which precipitated in the polymetallic sulfide orestage, contained a small amounts of Ag and a dramatically decreased content of Au, Bi, Te, and ratios of Bi/Ag. The results of electron back-scattered diffraction analysis on the Py2 revealed that Py2-B was characterized by predominantly brittle deformation with a limited local plastic deformation by dislocation glide on a simple slide system, whereas the Py2-D displayed a significant crystal plastic deformation through a lattice rotation on two separate 〈1 0 0〉 axes and local dislocation creep. Microscopic petrography and laser ablation inductively coupled plasma mass spectrometry analyses revealed that the brittle fracturing-dominated Py2-B generally displayed homogenous distribution patterns of Au and other trace elements and scarce visible gold grains, whereas the plastically deformed Py2-D generally exhibited an inhomogeneous distribution pattern of trace element and commonly contained fine-grained irregular-shaped visible native gold and other sulfide inclusions in the low-angle boundaries and dislocation sites within Py2-D, possibly suggesting the significant influence of ductile deformation on remobilization and reprecipitation of Au and associated trace elements once locked in Py2. The corrosion of Au-Te-Bi-bearing Py2 by the late polymetallic sulfide assemblage led to a liberation of invisible Au and other trace elements and reprecipitation of visible native gold and other Bi–Pb minerals. The results indicate that brittle deformation exhibited no essential effects on the crystal structure and chemical component of pyrite, whereas the plastic deformation can cause the readjustment of crystal lattices and liberation of impurities (e.g., Au, Te, Bi, and Cu) from the crystal lattices of pyrite. The plastic deformation and dissolution–remobilization of pyrite are the important mechanisms responsible for the visible discrete gold grain formation in auriferous quartz veins. Macroscopically, a preferred constant E–W extending orientation and typical lamination structure of the auriferous quartz veins suggest a channeled fluid flowing along the closed and connected fractures under a syn-mineralization S–N oriented extensional tectonic regime related to the Xiaoqinling metamorphic core complex. Here, we report that the microstructures of ductile deformation and brittle fracturing of the auriferous quartz veins are probably indicative of the continuous shearing activation of the ore-hosting normal fault.

Large-scale quart-vein and structurally-controlled gold mineralization is intensely developed in the Jiaodong Peninsula, North China Craton and is typified by the Linglong and Jiaojia deposits, respectively. In this work, zircons from typical gold-bearing ores of the Sanshandao Northern Sea (SNS), Jiuqu (JQ) and Canzhuang (CZ) gold deposits were compared in terms of texture, U–Pb age, trace element content and Hf isotopic signatures in order to discern whether zircon from ore samples can be used as an indicator of ore genesis and grade. Most studied zircons are magmatic in origin with a hydrothermal overprint (i.e., zircons with core-rim assemblages, fractured-dissolution textures and hydrothermal activity-related fluid/mineral inclusions). Three zircon age clusters were differentiated: ~120 Ma, ~150 Ma and >2000 Ma. The ~120 Ma zircons show evidence of hydrothermal alteration (dark in cathodoluminescent images with hydrothermal rim textures) and are characterized by high LREE, P, Ti and eHf(t) (−21 to −15) and young TDMC (2100–2500 Ma). This suggests an interaction between the mantle and crust at the magma source, and that a P/Ti-rich, Al-poor, high temperature, high fO2, wet late-stage residual granitic melt and intense hydrothermal alteration played an important role in the formation of gold mineralization. The ~150 Ma zircons have high Y, Nb, Ta and U contents, low eHf(t) (−26 to −20) and old TDMC (2300–3000 Ma) ages, and HREE-enriched patterns with pronounced Ce and Eu anomalies. These features indicate a reduced, cool and Al-rich magma which did not favor gold mineralization, even though it was highly evolved. This also implies that the degree of magma differentiation is not the key factor that led to gold mineralization in the Jiaodong gold province. The >2000 Ma zircons are primarily limited to gold ores with high Pb contents, HREE-enriched patterns and variable Ce and Eu anomalies, indicating that they were inherited from the Paleoproterozoic (2000–2200 Ma) basement. In addition, the SNS high-grade ores yielded zircon with the greatest U-Pb age range (mainly 110–180 Ma) and the most pronounced hydrothermal overprinting, indicating that large-scale mineralization resulted from multi-stage granitic intrusion, with intense fluid dissolution and metasomatism. This research highlights that correlations between zircon age populations, Hf isotope signatures, internal structures and trace element patterns can provide insights into ore genesis and fluid evolution in gold mineralization systems.

The Dayingezhuang gold (silver) deposit in the Jiaodong district, eastern margin of North China Craton, is hosted in the NE to NNE-trending Zhaoping Fault along the contact between Precambrian metamorphic rock (Jiaodong Group) and Mesozoic intrusion (Linglong granite). Although many studies have addressed the genesis of this deposit, the mineralization age, the sources of ore-forming fluids and materials, the ore genesis is still controversial, particularly on the relationship between Au and Ag. In this paper, new dating and in-situ isotopic data are presented to provide tight constraints on the timing and ore-forming processes of the Dayingezhuang deposit. Mineral assemblages of Dayingezhuang deposit can be divided into four stages: the quartz-pyrite stage (I), the Au-bearing quartz-siderite-pyrite stage (II), the Ag-bearing quartz-siderite-polymetallic sulfide stage (III), and the quartz-carbonate stage (IV). The Ag mineralization is texturally later than the gold mineralization, and only develops locally in the orebody I. Sericite from sulfide-bearing ores has a 40Ar/39Ar plateau age of 119.1 ± 1.2 Ma, and pre-ore mafic dikes yield a zircon U-Pb age of 122.7 ± 2.6 Ma. The new dating results consistently indicate that the Dayingezhuang deposit formed at ~120 Ma and is synchronous with the regional gold mineralization event in the Jiaodong district. The C and O isotopic values of siderite and calcite from stage II to IV vary from −5.4 to −2.2‰ (δ13CV-PDB) and 7.8 to 12.1‰ (δ18OV-SMOW), respectively, and the calculated values of them for ore-forming fluids are −7.1 to −2.9‰ and −4.1 to 5.7‰, respectively. The δ34SCDT values of pyrite from stage I to III range from 4.8 to 9.0‰. Pyrite from stage I to III has 206Pb/204Pb values of 17.181–17.339, 207Pb/204Pb of 15.414–15.504, 208Pb/204Pb of 37.729–37.984. These isotopic results combined with geological and geochronological evidence collectively indicate that the ore-forming fluids and metals of Dayingezhuang were mainly derived from the deep mantle-derived magma typically represented by intermediate-mafic dikes, and mixed with meteoric water subsequently. These data also indicate that the stage III Ag mineralization was not a late event independent from the stage I and II Au mineralization. The Dayingezhuang deposit may not be related to the activation of detachment faults around the Linglong massif at 130 ± 4 Ma as previously suggested, but a product of the destruction of NCC accompanied with the crust-mantle interaction and lithospheric thinning at ~120 Ma.