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The Yinachang Fe-Cu-Au-U-REE deposit is located in the Kangdian region at the southwestern margin of the Yangtze Block. This contribution presents petrological, geochronological, whole rock geochemical, and Rare Earth Elements (REE) geochemistry of zircons of gabbro and diorite dykes associated with the Yinachang Fe-Cu-Au-U-REE deposit, aiming to constrain the age of the mineralisation and help refine our understanding of the tectonic setting of the region. Zircons from diorite have a Palaeoproterozoic U-Pb age of 2014 ± 30 Ma, and zircons from the gabbro could not be dated because they are metamict, having a high concentration of uranium. The ca. 2014 Ma age of the zircons in the diorite indicates that the southwestern part of the Yangtze Block is partly synchronous with the Columbia Supercontinent. Geochemically, the diorite and gabbro are enriched in large-ion lithophile elements (LILEs) such as Rb and U, and depleted in high-field-strength elements (HFSEs) such as Nb, P, Ti, Ba, and Sr. The diorite is enriched in light REEs (LREEs) and has a slight to negligible Eu anomaly, which are characteristic of ocean-island basalts containing mantle-derived high potassic calc-alkaline rocks. In contrast, the gabbro is weakly enriched in LREEs and has a slightly negative Eu anomaly similar to those of potassic calc-alkaline enriched mid-ocean-ridge basalt. The average combined REE content of zircons from the gabbro is 19401 ppm and is significantly higher than that of the zircons from the diorite averaging 1020 ppm. This indicates that the gabbro is closely related with the REE mineralisation at the deposit. The geochemistry of the diorite indicates that it formed at the continental margin of a volcanic-arc. It also indicates that the magmatic rocks in the region have a possible mantle plume origin contaminated by crustal material and located at a transitional zone between a rift and an ocean-continent tectonic setting.

The Qiaoxiahala Fe-Cu-(Au) deposit (1.44 Mt ore @ 43–53% Fe, 0.55–2.21% Cu and 0.13–2.4 g/t Au) is located in the northern margin of East Junggar terrane, NW China. The deposit is hosted in the upper part of the Middle Devonian Beitashan Formation mafic and felsic volcanic rocks and sedimentary interbeds, and is spatially closely related to local fractures. Six hypogene hydrothermal stages have been identified, including (Stage I) early skarn, (Stage II) late skarn, (Stage III) magnetite mineralization, (Stage IV) magnetite-pyrite mineralization, (Stage V) chalcopyrite mineralization and (Stage VI) late veins. These six stages include three major mineralization events, as represented by the (Stage III) magnetite-epidote-K-feldspar-quartz-calcite, (Stage IV) magnetite-pyrite-garnet-quartz-calcite and (Stage V) chalcopyrite-chlorite assemblages. The Stage III magnetite mineralization fluids were likely of high temperature (354–386 °C), low-medium salinity (9.9–14.7 wt% NaCl equiv.), Mg/Fe-rich and organic-rich with lithostatic pressure of 1.3–1.5 kbar and corresponding depth of 4.3–4.8 km. Oxygen and hydrogen isotopes showed that the 18O-rich (9.7–11.2‰) and D-rich (−26.3‰) fluids were possibly modified from the Early Carboniferous seawater interacting with the Beitashan Formation organic-rich limestone or tuff. In comparison, the Stage IV magnetite-pyrite mineralization fluids were likely of medium-high temperature (272−453 °C), low-medium salinity (2.9–19.5 wt% NaCl equiv.), Mg/Fe-rich, with pressure of 0.8–1.2 kbar and corresponding depth of 2.6–4.0 km. The Stage V chalcopyrite mineralization fluids were likely of low-medium temperature (186−270 °C), low-medium salinity (1.4–21.8 wt% NaCl equiv.), Ca- or Na-rich, with pressure of 0.4–0.6 kbar and corresponding depth of 1–2 km. Hydrogen and oxygen isotopic compositions (Stage IV: δDwater = −141 to −92‰; δ18Owater = 8.9–11.1‰; Stage V: δDwater = −104‰; δ18Owater = 7.2‰) suggest that the ore fluids were of connate marine origin. Furthermore, Stage IV δ13Cwater values (−0.6 to 0‰) also indicate interactions between seawater and sedimentary wall-rocks. The negative sulfur isotopic compositions of chalcopyrite and pyrite (−4.2 to −0.2‰) may demonstrate a biogenic sulfur source. Compared with the arc-related IOCG deposits in the central Andean orogen, the Qiaoxiahala Fe-Cu-(Au) deposit shares many common features in geology, mineralization, alteration and various sources of fluids, indicating a possible IOCG-like mineralization-style and potential to discover other Late Paleozoic arc-related IOCG deposits in East Junggar.

The Halasu III deposit, an important Cu deposit in the southernmost part of the Halasu porphyry Cu belt, is situated in the East Junggar block in NW China. Copper and Mo sulfide mineralization commonly occurs as disseminations or veinlets, and is mainly associated with Devonian granodiorite porphyry. Our detailed field geological investigation identified late-stage high grade Cu sulfide-bearing veining superimposed on the earlier porphyry Cu–Mo mineralization. Four hydrothermal alteration and mineralization stages were identified, namely the early epidote alteration (Stage I), porphyry-style alterations (Stage II comprising II-A potassic, II-B propylitic and II-C phyllic alteration sub-stages), late veining (Stage III) and supergene processes (Stage IV) in the northern- and southern mineralization zones at Halasu III. Multiphase granodiorite- and alkali granite dykes intruded the Beitashan Formation volcanic rocks, generating the early epidote alteration. Potassic alteration (Stage II-A) occurred in and around the NNW-treading granodiorite dykes, while the propylitic alteration (Stage II-B) occurred in the intrusions or volcanic wall rocks around the potassic zone. These early alteration assemblages were overprinted by the subsequent, structurally-controlled phyllic alteration (Stage II-C) confined within the granodiorite porphyry. Late veins (Stage III) include sulfide-bearing (Stage III-A) and sulfide-barren (Stage III-B) ones. Supergene process (Stage IV), represented by hematite and jarosite replacing primary sulfides, extends tens of meters down depth and is commonly fracture-controlled. Three fluid inclusion (FI) types were recognized, namely Type A (single-phase), B (liquid–vapor two-phase) and C (liquid–vapor–solid three-phase). For Type B FIs, those of potassic alteration homogenized at 183–347 °C, with corresponding salinities of 6.2–17.8 wt.% NaCl equiv. The propylitic and phyllic FIs homogenized at 172–425 °C and 231–352 °C, respectively, with the corresponding salinities of 0.9–14.0 wt.% NaCl equiv. and 0.4–10.5 wt.% NaCl equiv. The sulfide-bearing vein FIs homogenized at 243–410 °C (Stage III-A-1), 260–362 °C (Stage III-A-2) and 117–235 °C (Stage III-A-3), along with the corresponding salinities of 1.9–9.2 wt.% NaCl equiv., 1.1–6.7 wt.% NaCl equiv. and 6.5–17.1 wt.% NaCl equiv., respectively. The sulfide-barren vein FIs yielded homogenization temperatures of 260–380 °C (Stage III-B-1) and 114–297 °C (Stage III-B-2), with corresponding salinities of 1.7–9.8 wt.% NaCl equiv. and 0.2–13.6 wt.% NaCl equiv., respectively. We suggest that hydrothermal veins at Halasu III may have undergone complex and superimposing alteration due to the episodic reopening of the preexisting veins, with Stage III-A-3 veining overprinting the phyllic alteration and Stage III-A-2 veining. Stage III-B-2 veining superimposed on the potassic alteration, as well as on Stages III-A-1 and III-B-1 veining. Paragenetic sequence and fluid evolution at Halasu III indicate that these complex hydrothermal alteration stages were formed in accordance with the regional tectonic evolution. These various alteration and mineralization stages at Halasu III deposit reveal a prolonged history of magmatic and hydrothermal processes extending episodically from the Middle Devonian to Middle Permian, wherein early mineralization was overprinted by late hydrothermal events. Such superimposed mineralization may occur commonly in the Paleozoic Central Asia Orogenic Belt.

Iron and Magnesium isotopes have been increasingly widely applied to trace mineralization processes of hydrothermal ore systems. In this study, Fe and Mg isotope compositions of whole-rocks, Fe-bearing minerals (pyrite and ankerite) and Mg-bearing mineral (ankerite) from the Shuangwang gold deposits are investigated to evaluate Fe and Mg isotope behaviors in a gold deposit hydrothermal system and provide new constraints on ore-forming processes. The results showed that the magmatic rocks in the Shuangwang gold deposit (mainly granodiorite , monzonitic granite and lamprophyre) yielded δ 56Fe values of 0.05–0.10‰ and δ26 Mg values concentrated in a narrow range from −0.23‰ to −0.21‰. The gold orebodies are hosted by a NW-trending breccia belt. The wall rock samples (mainly argillaceous limestone, carbonaceous slate and albitite) have higher δ 56Fe values of 0.12–0.29‰ and a wide δ26 Mg range from −2.54‰ to −0.35‰. Pyrite mineral separates show larger δ 56 Fe variation from −0.44‰ to 0.16‰, whereas ankerite has a small δ 56Fe range from −0.15‰ to −0.06 and a δ26Mg range from −0.66‰ to −0.35‰. The crystallization of magmatic rocks incorporated preferentially heavy Fe isotopes, resulting in enrichment of light Fe isotopes in the residual fluid exsolved from magma . The interactions between the wall rocks and the fluids resulted in increase of δ 56Fe value in fluids and resulted in decrease of δ56Fe value in the wall rocks. However, the fluid still had much lighter Fe isotope composition. Thus, Fe in the main ore-forming stages is regarded as derived from the magmatic stock. The opposite enrichment in Fe isotopes between pyrite and ankerite from stages II and III may be explained by equilibrium Fe isotope fractionation in an open system. In addition, the negative δ56Fe value in pyrite from stage IV is indicative of the equilibrium between FeS and dissolved Fe in a closed system. The exsolved fluid from magma has Mg isotope composition similar to magmatic rock, and the water–rock reaction led to the enrichment of heavy Fe isotopes in fluid. The evolutions of Mg isotopes in stages II and III precipitation matched well with the prediction of Rayleigh fractionation model. The Mg from wall rocks contributed to the composition of hydrothermal magnesium isotopes during the formation of the Shuangwang gold deposit. A multi-origin is supposed whereby the main stage ore-forming fluids were derived from metamorphic water and were affected by the influx of magmatic water.

The Badaguan porphyry Cu Mo deposit is located in the Derbugan metallogenic belt of northeastern Inner Mongolia, China. The host granodioritic porphyry and the wall rock granitic porphyry were emplaced at 230 Ma and 238 Ma, respectively. The granodioritic porphyry has ( 87 Sr/ 86 Sr) i values of 0.70535–0.70549, e Nd (t) values of 0.41–1.17, e Hf (t) values of 1.30–6.51, and two–stage model ages (T DM2 ) of 1131–848 Ma. In contrast, the granitic porphyry is characterized by e Hf (t) values from − 0.75 to 7.28 that yield T DM2 model ages of 1355–816 Ma. The geochemical and Sr Nd Hf isotopic data for the magmatic rocks associated with the Badaguan porphyry Cu Mo deposit indicate that these intrusions were generated by the partial melting of juvenile lower crust. The δ 18 O values of ore fluids from different mineralizing stages are between − 6.0‰ and + 1.5‰, and the fluid δD water values vary from − 119.3‰ to − 140.0‰, indicating a mixed fluid of magmatic and meteoric water, the S Pb isotopes show that the metal was mostly derived from a deep-seated magma that involved some crustal materials, with a narrow δ 34 S range (− 2.4‰ to + 3.5‰). We infer that the Badaguan porphyry Cu Mo deposit formed during a period of southeast–directed subduction of the Mongol–Okhotsk oceanic plate beneath the Erguna Block.

The giant Shangfanggou skarn-porphyry Mo–Fe deposit, one of the largest Mo deposits in the East Qinling Orogen, is hosted by the Neoproterozoic Luanchuan Group on the southern margin of the North China Craton. The mineralization occurs mainly as veinlets and in veinlet-disseminated form within altered schists, skarns, hornfelses, and/or marbles. The hydrothermal alteration and mineralization at Shangfanggou took place over four stages. Stage 1 involved potassic alteration and silicification in the porphyry, skarnization and magnetization in carbonate strata, and hornfelsization in schists. Quartz–molybdenite veins associated with phyllic alteration were produced in the porphyry during stage 2, along with sericitization, chloritization, serpentinization, and silicification in the skarns, hornfelses and/or marbles. Quartz–polymetallic sulfide veins related to phyllic alteration were produced during stage 3, and ore-barren quartz ± calcite ± pyrite veins associated with weak carbonatation were produced during stage 4. C, O, and D isotope compositions of hydrothermal calcite, dolomite, magnetite, phlogopite, and quartz from different stages of mineralization during the formation of the Shangfanggou deposit range from − 12.9‰ to + 8.8‰, − 3.2‰ to + 22.7‰, and − 100‰ to − 80‰, respectively. Sulfur isotope compositions of sulfides from the ores of the Shanfanggou deposit range from 3.6‰ to 4.4‰. 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb ratios of 17.648 to 18.742 (apart from one magnetite with a value of 20.78), 15.526 to 15.690, and 38.197 to 39.823 in the Shanfanggou deposit. The evolution of the ore-forming fluids in the Shangfanggou deposit, as revealed by δ 18 O, δD, and δ 13 C isotope studies, was one of progressive modification of the magmatic fluids through fluid–wall rock interactions along conduits during fluid ascent, and this signifies the involvement of formation/strata water during the earlier stages of mineralization, and the predominance of meteoric waters over magmatic fluids in the later stages. The carbon, sulfur, and lead isotope compositions suggest mixing took place between the magmas and the host rocks within the region. Integrating the data obtained from studies of the regional geology, ore geology, fluid inclusions, and C–H–O–S–Pb isotope geochemistry, we conclude that the Shangfanggou Mo–Fe deposit is a porphyry-skarn type system that formed during a transition from compressional to extensional tectonics during the Jurassic–Early Cretaceous continental collision between the North China Craton and Yangtze Craton. The ore materials were sourced from magmatic ore-forming fluids that mixed with components derived from carbonaceous wall rocks during their ascent, and which were gradually mixed with meteoric waters, especially in the later stages.

The Halasu porphyry copper belt situated in the East Junggar is one of the major porphyry copper belts in Xinjiang Uygur Autonomous Region, northwest China. Copper and molybdenum mineralization occurs as disseminated sulfides or veinlets mainly in granodiorite porphyry and diorite porphyry, with the intense development of zoned alteration from potassic, through sericitic to an outer zone of propylitic alteration. New LA–ICP-MS zircon U–Pb dating reveals that magmatism in the belt can be divided into three periods during the Middle Devonian and Early Carboniferous, namely the pre-mineralization stage of 390 Ma, syn-mineralization stage of 382–372 Ma, and post-mineralization stage of 350–320 Ma. The syn-mineralization intrusions are calc-alkaline, whereas pre- and post-mineralization intrusions are shoshonitic and high-K calc-alkaline. The syn-mineralization intrusions are enriched in highly incompatible trace elements but depleted in Nb, Ta, Hf and Ti relative to the pre- and post-mineralization intrusions. Zircon trace elements analyses demonstrate a negative correlation between Ti-in-zircon temperatures and oxygen fugacity. Ore-bearing syn-mineralization granitoids are characterized by higher water content, oxygen fugacity and low temperatures with higher mineralization potential than pre- and post-mineralization ones. These characteristics, together with the geochemical signature of the intrusions, suggest that the ore-bearing porphyries are derived from relative high ƒH2O magma reservoir. The remarkably homogeneous Hf isotopic compositions (eHf(t) = 8 to 13) from syn-mineralization intrusions span over 10 m.y., suggesting the existence of a long-lived reservoir beneath Halasu belt during the Middle Devonian. All the intrusions have low initial 87Sr/86Sr values (0.703935 to 0.707172), high eNd(t) values (4.7 to 5.5) and young crustal model ages (650 to 750 Ma). Combined with the mantle-derived Pb isotope characteristics, the Sr–Nd–Hf data suggest that the parental magma was probably derived from flat subduction triggered partial melting of juvenile crust generated during subduction–accretionary process with no significant input of old crust, whereas pre-mineralization and post-mineralization intrusions are supposed to emplaced in immature island arc setting and post-orogenic setting, respectively.

Microporous gold is common in many Te-Au deposits. Experimental formation and textures of microporous gold have recently been studied. However, few studies have worked on naturally occurring microporous gold. At the Dongping gold deposit, which is one of the most studied Au-Ag-Te deposits in China natural microporous gold is widely distributed in both primary and oxidized ores. This provides a good opportunity to study the textures and the formation of microporous gold in nature. This gold is pseudomorphous in addition to being porous, indicating that it formed via interface coupled dissolution-reprecipitation (ICDR) reactions. Four textures that were not described previously in experiments were observed in samples from this deposit. (1) A hackly interface between the microporous gold and parent calaverite. Te content shows a decreasing trend with increasing distance from the interface. This texture may result from diffusion of excess surface energy as the ICDR reaction moves towards equilibrium. (2) A less-porous band exists in the microporous gold. The band has fewer pores, smaller crystal sizes and similar chemical composition with the surrounding microporous gold. It likely formed due to the fluctuation of the fluid physicochemical conditions (including decreasing temperature, αO2(aq) and increasing pH) that changes the dissolution rate of calaverite. (3) Microporous gold precipitated between quartz and calaverite. As well, gaps developed between gold and remnant calaverite. This texture is derived from catalytic effects of a heterogeneous nucleation or recrystallization process. It is helpful for extraction and aqueous processing of Au-Te ores, and accounts for the phenomenon that quartz can accumulate gold in some hydrothermal gold deposits. (4) Petzite coexists with Ag-bearing microporous gold, indicating that petzite may also decompose to microporous gold under hydrothermal conditions. Calaverite could be dissolved without altered pyrite at high-temperature (>200 °C) conditions, but under weathering conditions, pyrite would be altered first. In primary ores, microporous gold coexists with pyrite and baryte, indicating that it was formed during the late-stage mineralization. In oxidized ores, microporous gold coexists with limonite and baryte, indicating it may have generated during late-stage mineralization and then altered by weathering. Hydrothermal fluids derive from late-stage mineralization may play the main role in the formation of microporous gold compared to weathering processes. This observation also leads us to reappraise the importance of hydrothermal fluids in the weathering dominated ICDR geological processes.

The Haoyaoerhudong gold deposit in the northern margin of the North China Craton (NCC) is a large tonnage lower-grade deposit with a reserve of about 148 tons of gold. Gold mineralization is characterized by pyrite and pyrrhotite films and thin veins on the schistosity plane of the Proterozoic black shales. The orebodies, strictly controlled by a near EW-trending shear zone, are stratabound within carbonaceous phyllite and andalusite-garnet schist of the Bilute Formation. Hydrogen and oxygen isotopic data show that the ore-forming fluid was derived from a magmatic source and mixed with meteoric water. Sulfur and carbon isotope data indicate that most of the sulfur and carbon came from the black shale strata. Well-defined biotite Ar-Ar plateau age and inverse isochron age show that the deposit formed at ca. 270Ma, which suggests a probable link between Hercynian magmatism and gold mineralization. Studies on regional geology, ore geology, isotope geochemistry, and ore-forming age substantiate a complex evolutionary history of the deposit. The Proterozoic black shales rich in gold, sulfur, and organic matter, which were deposited in the Proterozoic continental margin rifts, comprised the source bed for gold mineralization. EW-ENE-structures, products of Palaeozoic orogenic process, provided pathways and mineralization space for ore-forming fluids. Hercynian tectono-magmatism and subsequent hydrothermal events remobilized gold and drove the ore-forming fluids to dilatational fracture zones. Related to postcollisional magmatic hydrothermal events, the Haoyaoerhudong gold deposit is considered as a special type of orogenic gold deposit formed in the compression–extension transition stage.