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Abstract The Heijianshan Fe–Cu (− Au) deposit is located in the Aqishan–Yamansu belt in Eastern Tianshan, NW China. As a typical Fe–Cu deposit in the region, Heijianshan is hosted in the Upper Carboniferous Matoutan Formation submarine volcanic/volcaniclastic rocks. Alteration styles, mineral assemblages and vein crosscutting relationships divide the hydrothermal alteration and mineralization processes into seven stages, namely the chromite (Stage I), epidote (Stage II), magnetite (Stage III), pyrite (Stage IV), Cu (–Au) (Stage V), late veins (Stage VI) and supergene (Stage VII) alteration/mineralization stages. Magnetite mineralization comprises the hematite (Stage III–A) and main magnetite (Stage III–B) mineralization sub-stages. The Heijianshan magnetite ores consist of massive (with mushketovite (MOM) or sulfides (MOS)), disseminated (DO) and magnetite clasts (with chromite (MWC) or without chromite (MNC)) ores. Magnetite in massive- and disseminated ores is featured by (1) depletion in Zr, Nb and Ta; (2) low Ti (< 2 wt.%) and Al (< 1 wt.%); and (3) Ni/Cr ≥ 1, which all reflect a hydrothermal origin. Moreover, magnetite in massive- and disseminated ores has lower Cr (MOM: 0–13.2 ppm; MOS: 0–12.9 ppm; DO: 3.57–133 ppm) than magnetite clasts ores (MNC: 849–2544 ppm; MWC: 835–44,132 ppm). However, the high Cr in the magnetite clasts ores may have been inherited from the chromite they replaced. From the magnetite clasts to disseminated/massive ores, formation temperature decreased and f O 2 increased, which may represent the major controls on the formation of the various magnetite ore types. Compositions of the ore fluids and host rocks, formation of coexisting minerals and other physicochemical parameters (such as T and f O 2) may have variably influenced the magnetite geochemistry in the different Heijianshan ore types, with fluid compositions probably playing the most important role. Discrimination diagrams, for instance, Cr vs. Co/Ni, Cr vs. Ti, V vs. Cr and Ni vs. Cr, may be useful for magnetite mineralization type differentiation in other submarine volcanic-hosted Fe/Fe–Cu deposits in the Aqishan–Yamansu belt. Geochemical discrimination diagrams, alteration and mineralization paragenesis indicate that the Heijianshan Fe–Cu (–Au) deposit is best classified as an IOCG-like deposit, which offers a new insight for classifying and characterizing ore genetic types for similar Fe and Fe–Cu deposits in Eastern Tianshan. Graphical abstract Image 1 Highlights • The Heijianshan magnetite from the massive-, disseminated- and most magnetite clasts ores are hydrothermal. • The Cr vs. Co/Ni, Cr vs. Ti, V vs. Cr and Ni vs. Cr diagrams can discriminate the different magnetite ores. • Temperature, f O2 and other factors control the element distribution in magnetite. • The Heijianshan Fe–Cu (–Au) deposit can be classified as an IOCG-like deposit. [ABSTRACT FROM AUTHOR]

The article presents a study for alteration and mineralization paragenesis of the Bailingshann iron (Fe)- copper (Cu) deposit located in Eastern Tianshan, China. Topics discussed include ore minerals found in the deposit include magnetite, hematite, and chalcopyrite, stages of alteration and mineralization including early skarn stage, late amphibole stage and quartz-sulfide stage, and field and petrographic studies which indicates that the Bailingshan Fe deposit is a metasomatic deposit.

Magnetite is a common mineral in many ore deposits and their host rocks, and contains a wide range of trace elements (e.g., Ti, V, Mg, Cr, Mn, Ca, Al, Ni, Ga, Sn) that can be used for deposit type fingerprinting. In this study, we present new magnetite geochemical data for the Longqiao Fe deposit (Luzong ore district) and Tieshan Fe–(Cu) deposit (Edong ore district), which are important magmatic-hydrothermal deposits in eastern China. Textural features, mineral assemblages and paragenesis of the Longqiao and Tieshan ore samples have suggested the presence of two main mineralization periods (sedimentary and hydrothermal) at Longqiao, among which the hydrothermal period comprises four stages (skarn, magnetite, sulfide and carbonate); whilst the Tieshan Fe–(Cu) deposit comprises four mineralization stages (skarn, magnetite, quartz-sulfide and carbonate). Magnetite from the Longqiao and Tieshan deposits has different geochemistry, and can be clearly discriminated by the Sn vs. Ga, Ni vs. Cr, Ga vs. Al, Ni vs. Al, V vs. Ti, and Al vs. Mg diagrams. Such difference may be applied to distinguish other typical skarn (Tieshan) and multi-origin hydrothermal (Longqiao) deposits in the MLYRB. The fluid–rock interactions, influence of the co-crystallizing minerals and other physicochemical parameters, such as temperature and f O 2 , may have altogether controlled the magnetite trace element contents of both deposits. The Tieshan deposit may have had higher degree of f O 2 , but lower fluid–rock interactions and ore-forming temperature than the Longqiao deposit. The TiO 2 –Al 2 O 3 –(MgO + MnO) and (Ca + Al + Mn) vs. (Ti + V) magnetite discrimination diagrams show that the Longqiao Fe deposit has both sedimentary and hydrothermal features, whereas the Tieshan Fe–(Cu) deposit is skarn-type and was likely formed via hydrothermal metasomatism, consistent with the ore characteristics observed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two generations of garnets are identified in the Shuanglong Fe-Cu and Shaquanzi Fe deposit, respectively. • Physicochemical conditions of multiple episodes of hydrothermal fluids are constrained. • The transition from volcanic-hosted Fe deposits to intrusion-related skarn or IOCG type Fe-Cu deposits occur. The Aqishan-Yamansu Fe-Cu-Au metallogenic belt in the Eastern Tianshan, NW China, hosts numerous Fe and Fe-Cu deposits that may have different genetic models, such as volcanic-hosted and skarn/IOCG types. These variations in genetic models are attributed to whether the mineralization is associated with hydrothermal activity related to volcanic or intrusive rocks. This study primarily focuses on garnets formed during the early skarn alteration in the Shuanglong Fe-Cu and Shaquanzi Fe deposits within this belt. Garnets from the Shuanglong deposit can be divided into two types and exhibit general homogeneity, with SL-Grt1 being Fe-rich and subsequently replaced by the Fe-poor SL-Grt2. Garnets from the Shaquanzi deposit display complex zonation patterns, SQZ-Grt1 show core–oscillatory zoned rim and SQZ-Grt2 show core–mantle–oscillatory zoned rim. Laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) dating of SL-Grt1 and SL-Grt2 produced lower intercept 206Pb/238U ages ranging from 318.0 ± 6.4 Ma to 303.7 ± 16.4 Ma, coinciding with the multi-stage granite occurrence. In contrast, SQZ-Grt1 and SQZ-Grt2 yielded ages between 328.0 ± 2.6 Ma and 320.4 ± 1.7 Ma, corresponding to the timing of the hosted rhyolite. SL-Grt1 show light rare earth element (LREE) enrichment, and low concentrations of high field strength elements (HFSE), such as V and Zr, and appears to have formed rapidly within an open system. Conversely, SL-Grt2 is characterized by heavy rare earth element (HREE) enrichment and elevated HFSE contents, which could be formed slowly in a closed system. The variable composition in the SQZ-Grt1 and SQZ-Grt2 record cyclical changes in fluid kinetics (vigorous fluid flow vs. fluid stagnation). The cyclical zones in SQZ-Grt2 with HREE and HFSE concentrations below the detection limit indicate multiple inputs of external seawater. The distinct characteristics between Shuanglong and Shaquanzi garnets may reflect the difference between the single magma intrusion and complex volcanic activity. Combining previously published chronological data, this study elucidates a transition from the Middle Carboniferous volcanic-hosted Fe deposits (335–320 Ma) to the Late Carboniferous intrusion-related skarn or IOCG type Fe-Cu deposits (310–300 Ma) in the Aqishan-Yamansu belt. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sedimentary formation waters are the major fluids in the Qiaoxiahala deposit. • Genesis and evolution of formation waters in Fe and Cu-Au stages are different. • Two-stage mineralization and non-magmatic fluids indicate an IOCG-type deposit. • A basin inversion setting is beneficial to the formation of IOCG deposits. The Qiaoxiahala deposit is a significant Paleozoic Fe-Cu-Au deposit in the northern margin of East Junggar, NW China, which has been confirmed to form in a basin inversion setting (dying back-arc basin). The composition of noble gases (Ar, Kr, and Xe) and halogens (Cl, Br, and I) extracted from fluid inclusions, hosted in quartz, calcite, and epidote from various mineralization stages of Qiaoxiahala, are investigated to trace the sources of ore fluids and discuss the ore genesis. Significant multistage mineralization at Qiaoxiahala is identified as magnetite mineralization (stage III), magnetite-pyrite mineralization (stage IV), and chalcopyrite mineralization (stage V). Syn-ore fluid inclusions show salinities varying from 13.2 to 15.3 wt% (NaCl eq.) associated with elevated I/Cl ratios (214 × 10−6 to 3950 × 10−6), uniformly low Br/Cl ratios (0.78 × 10−3 to 1.30 × 10−3), and low 40Ar/36Ar ratios (<700). The low 40Ar/36Ar ratios and Br/Cl ratios preclude the involvement of magmatic or metamorphic fluids (high 40Ar/36Ar), and sub-aerial evaporation bittern brines (elevated Br/Cl). The predominance of sedimentary formation water modified by organic-rich sediments is supported by the high I/Cl ratios, low 36Ar concentrations (less than or equal to that of Air Saturated Water, ASW), and the constant 40Ar E /Cl slopes (10−5 to 10−4) of fluid inclusions from various mineralization stages in Qiaoxiahala. The elevated δ18O water values (7.2–11.1‰) of the ore-forming fluids and the common presence of organic matter (e.g. C 4 H 6 , C 2 H 2 and CH 4) in fluid inclusions further indicated the involvement of organic-rich materials. However, different δD water values and a significant gap between halogen and noble gas data in stages III and IV-V indicate that different sedimentary formation fluids are involved during these stages, i.e., extensive water-wall rock interactions between seawater and Beitashan Formation in stage III and formation waters formed by diagenesis and compaction in stages IV-V. Multistage mineralization, i.e., Fe-oxide and chalcopyrite (-gold), and the mixing of different non-magmatic fluids with variable origins in Qiaoxiahala are similar to many iron oxide-Cu-Au deposits (IOCGs) from the Central Andes, indicating an IOCG-like type deposit for Qiaoxiahala. These finding further suggest that non-magmatic fluids dominate the formation of IOCG deposits in the basin inversion setting at the northern margin of East Junggar. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Basin inversion occurred in the Late Carboniferous in the Aqishan-Yamansu belt. • Fe-Cu mineralization may have occurred during the basin inversion. • Fe and Cu mineralization was separated. • External sulfur would be involved in the Cu mineralization. Abstract The formation of the Eastern Tianshan orogen (northern Xinjiang, NW China) with a number of EW-trending mineralization belts was closely linked to the evolution of the Junggar and South Tianshan oceans, probably part of the Paleo-Asian Ocean. Among these Eastern Tianshan mineralization belts, the Carboniferous Aqishan-Yamansu Fe (-Cu) belt hosts a total reserve of 207 Mt Fe and economic Cu endowments for many deposits. These Fe (-Cu) deposits are hosted in submarine volcanic rocks (Lower Carboniferous Yamansu Formation and Upper Carboniferous Tugutublak Formation) and are featured by the presence of extensive skarn alteration without apparently-causative intrusive rocks, which leads to debates over their genesis. In this paper, we have summarized the ore deposit geology, geochemistry and stable isotopes of the Aqishan-Yamansu Fe (-Cu) deposits and discuss their genesis under the regional tectonic framework. We suggest that the Carboniferous Aqishan-Yamansu belt may have been a forearc basin formed by the south-dipping subduction of the Kangguer Ocean beneath the Central Tianshan massif. The Yamansu Formation volcanic rocks and some syngenetic Fe deposits may have formed during the opening of the forearc basin. The Tugutublak Formation volcanic rocks and most Fe (-Cu) deposits may have formed during the subsequent Late Carboniferous basin inversion. In these Aqishan-Yamansu Fe (-Cu) deposits, the Fe mineralization occurred earlier and was likely formed directly from the magmatic-hydrothermal fluids, whereas the subsequent Cu mineralization was likely caused by the gradual increase of seawater or basinal brine influx into the fluid system (external sulfur). The probable external sulfur input, the absence of clear plutonic link, and the temporal coincidence of peak mineralization and basin inversion for the Carboniferous Aqishan-Yamansu Fe-Cu mineralization are comparable to the Mesozoic IOCG mineralization in the Central Andes. [ABSTRACT FROM AUTHOR]