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4A cartoon showing the evolution of ore-forming fluids in the iron skarn system of the Handan-Xingtai district. High-temperature, reducing, and Fe2+-rich magmatic-hydrothermal fluids were exsolved from cooling magmas represented by the dioritic intrusions in the district. Within the contact zones between the magmatic intrusions and middle Ordovician evaporite-rich marine carbonate, the magmatic-hydrothermal fluids interacted with the evaporites or mixed with external fluid components that had equilibrated with the evaporite units, leading to precipitation of voluminous magnetite. Abundant pyrite formed as a result of the redox reactions, as represented by dense to sparse pyrite disseminations in the magnetite ores and massive aggregates and veins of pyrite in marble close to the intrusion. Lack of magnetite ores associated with the Hongshan syenite is best interpreted in terms of the paucity of evaporites in the Carboniferous and Permian strata in which the Hongshan syenite was emplaced ()
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The Xishimen iron skarn deposit in the Handan-Xingtai district, North China Craton, contains 256 Mt @ 43 % Fe (up to 65 %). The mineralization is dominated by massive magnetite ore along the contact zone between the early Cretaceous Xishimen diorite stock and middle Ordovician dolomite and dolomitic limestones with numerous intercalations of evapor...
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Granulite-facies marbles are part of the Archaean crust of the In Ouzzal terrane (Western Hoggar). Besides calcite and dolomite, these marbles are characterized by forsterite, spinel, phlogopite, diopside, amphibole, and magnetite. High-Mn ilmenite (MnO: 19.43 wt%), pyrophanite (MnO: 25.83 wt%), dissakisite-(Ce) (containing 12.2–14.38 Ce2O3 wt% and...
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... The Handan-Xingtai area is located in the central part of North China Craton (NCC), adjacent to the Taihang Mountains fault zone in the east, where NNE/NWW trending faults and folds have developed. (Fig. 1a; Zhao et al., 2005;Wen et al., 2017;Cui et al., 2020). The main lithological units in this region and its surroundings consist of early Precambrian metamorphic basement rocks overlain unconformably by Phanerozoic sedimentary sequences. ...
... Generally, the solubility of Co and Ni in hydrothermal fluids exhibits strong positively correlated with temperature and salinity, both cooling and dilution processes can cause deposition of cobalt from hydrothermal fluids (Liu et al., 2011;Migdisov et al., 2011;Deditius et al., 2014;Brugger et al., 2016;Falkenberg et al., 2021). Data from fluid inclusions suggest a transition in the ore-forming fluid within the Handan-Xingtai area, shifting from medium-high temperature and salinity towards low temperature and salinity as mineralization progresses (Zheng, 2007;Wen et al., 2017;Qi, 2018;Zhang et al., 2019;Xi et al., 2022). Therefore, the decrease of temperature and salinity during the quartz sulfide stage facilitate the precipitation of Co and Ni. ...
... This led to a rapid decrease in pressure, subsequently inducing localized boiling of the hydrothermal fluid. This occurrence is prevalent in skarn deposits within the Handan-Xingtai area (Wen et al., 2017;Zhang et al., 2019;Xi et al., 2022). Fluid boiling and subsequent phase separation would cause Clpreferentially partition into the vapor phase, which results in the decrease of chloride concentrations in the liquid, as well as a reduction in temperature under adiabatic conditions (Bischoff et al., 1996;Simonson and Palmer, 1993;Velásquez et al., 2014). ...
... It is surrounded by the Central Asian Orogenic Belt to the north and the Central China Orogenic Belt to the south. The western boundary is the Qilian Orogenic Belt, and the eastern boundary is the Sulu Orogenic Belt [16]. The NCC is divided into three parts from west to east: the Western Block, the Central Zone, and the Eastern Block. ...
... This suggests that during the albite alteration process of the diorite body within the carbonate formation, high-temperature hydrothermal fluid disintegrates and eliminates dark minerals and magnetite in the rock mass, converting iron into iron-bearing hydrothermal fluid. Throughout the mineralization process, carbonate strata and gypsum strata contribute a significant number of Na + , Cl − , F − , H + , +CO 2 2− , and SO 4 2− ions as mineralizers [16,67,68] and form iron deposits [59]. The intricate interplay of alteration processes and mineralization conditions in the study area underscores the multifaceted nature of skarn-type iron ore formation. ...
The mineralization within the North China Craton (NCC) is intricately linked to Mesozoic large-scale extension in eastern China and is a consequence of a unified geodynamic tectonic background. Despite previous attempts to elucidate the relationship between large-scale mineralization and magmatic activity in the NCC, a lack of systematic research has hindered the identification of connections among deposits with inconsistent metallogenic ages. This study focuses on the coal measures of the Huanghebei Coalfield (HHBC) in western Shandong, presenting a regional magmatic–hydrothermal metallogenic system with a genetic connection. It delves into the intricate interplay between the multi-mineral enrichment mechanism, metallogenic regularity, and the NCC’s destruction. The findings reveal that: (1) Various stages of magmatic intrusion during the Yanshanian period significantly influenced the Late Paleozoic coal measures in the HHBC. The coal measures exhibit distinct ranks, ranging from medium-rank bituminous C to A and high-rank anthracite C, resulting in noticeable differences in gas generation among different coal ranks. The shale between the coal seams C5 and C7 emerges as excellent with a good hydrocarbon-generating capacity during the middle-maturity stage. (2) The “Intrusion along the rock layer type” proves most conducive to shale gas enrichment, while the “laccolith type” is more favorable for shale gas enrichment compared to “dike type” intrusions, which have a limited impact on shale gas enrichment. (3) The mineralization process of CBM, shale gas, and iron ore is influenced by Yanshanian-period magma. The enrichment degree of CBM and shale gas exhibits an inverse correlation with the distance from the magmatic intrusion. Iron deposits demonstrate a close association with the magmatic intrusion, with enhanced enrichment along the rock layer. The results indicate that the destruction of the NCC triggered intense metasomatism in the deep cratonic fluids, serving as the primary driving mechanism for large-scale mineralization during the Yanshanian period. Magmatic intrusions bring hydrothermal fluids conducive to mineralization, and the heat release from these intrusions promotes thermal evolution, hydrocarbon generation, and the enrichment of organic-rich strata.
... Combined with geological evidence, sulfur isotope data, and garnet Th/U ratios from this study, we suggest that the incursion of stratigraphic sulfate has played an important role in magnetite mineralization for the Lazhushan deposit by increasing fluid fO 2 and facilitating the oxidation of Fe 2+ to precipitate magnetite. This role of evaporate sulfate for magnetite mineralization has also been recognized in Fe skarns elsewhere (Li et al., 2014;Wen et al., 2017). ...
... The middle Ordovician strata are highly oxidized evidenced by the occurrences of evaporate beds consisting of gypsum and anhydrate. The magmatic fluids interact with the evaporates would promote oxidization of the Fe 2+ to form magnetite (e.g., Li et al., 2014b;Zhu et al., 2015;Wen et al., 2017b), while sulfates from evaporates would be reduced to generate sulfides (e.g., pyrite), via the reaction: 22Fe 2+ + 2SO 4 2− + 20H 2 O = 7Fe 3 O 4 (Magnetite) + FeS 2 (pyrite) + 40H + (Reaction 1). The existence of this reaction is supported by the common presence of pyrite in magnetite ores with distinctively high δ 34 S values (>16 ‰, Table 1), whose sulfur is interpretated to be largely derived from evaporate sulfates (see discussion above). ...
... Most skarn deposits in the district exhibit similar alteration styles, characterized by Mg-rich skarn mineralogy in the contact zone and albitization in the orerelated intrusion. Additionally, sulfides from magnetite ores in these deposits show significant enrichment in δ 34 S (>10 ‰, Wen et al., 2017b and references therein), suggesting a sulfur derivation from evaporate sulfate for these sulfides. Our new isotopic data for the Baijian deposit, combined with previous findings, suggest extensive interactions between magmatic fluids and middle Ordovician evaporate-bearing carbonate on a regional scale for Fe mineralization. ...
The Handan-Xingtai district, situated in the central part of the North China craton, is one of the most important concentrations of Fe skarns in China. Baijian is the largest Fe skarn deposit in this district with significant Fe reserves being newly identified. This deposit is spatially related with a monzodiorite stock intruding the Middle Ordovician evaporate-bearing marine carbonates, with Fe mineralization occurring in the contact zone or within carbonate wall rocks. This paper conducts a comprehensive investigation encompassing geological, mineralogical, geochronological, and stable isotope analyses of the Baijian deposit. The goal is to provide insights into its formation and mineralization processes and offer a broader understanding of regional Fe metallogeny.
The skarn mineralogy in the Baijian deposit is predominantly characterized by Mg-rich minerals such as diopside, tremolite, serpentine, and phlogopite. Magnetite is the dominant metallic mineral, featuring low Ti contents (<0.11 wt%) and high Fe concentrations (>66.59 wt%), indicative of a hydrothermal origin. The majority of the magnetite trace element data are plotted in the skarn field on the Al + Mn versus Ti + V diagram. Pyrite, a notable component in ores, exhibits considerable variations in Co and Ni concentrations, with Co/Ni ratio generally higher than unity. Phlogopite 40Ar–39Ar dating constrains the formation of the Baijian Fe skarn deposit at ca. 128 Ma, aligning with zircon U-Pb ages (128.8 ± 0.9 Ma) of the associated monzodiorite. This temporal congruence suggests a genetic relationship between the magmatism and skarn mineralization. Combined with previous published geochronological data, this study identifies an increasing trend in Fe mineralization intensity within the Handan-Xingtai district, spanning from ca. 137 to 128 Ma. Geological and oxygen isotopic evidence advocates for a magmatic origin of the ore-forming fluids at the Baijian deposit. The δ18O values of these fluids experience elevation through interaction with carbonate wall rocks. The pronouncedly high δ34S values of pyrite (>16.1 ‰) in the Baijian magnetite ores underscore a substantial sulfur contribution from sulfate in evaporate beds. Drawing on geological, mineralogical, and isotopic evidence, the study suggests that the interaction between magmatic fluids and evaporate-bearing carbonate rocks plays an important role in magnetite precipitation at the Baijian deposit. This interaction serves to reduce fluid acidity and facilitate the oxidation of ferrous iron (Fe2+). The Fe skarn deposits in Handan-Xingtai district are mostly hosted in middle Ordovician evaporite-bearing carbonate strata with ore-related sulfides exhibiting strong 34S enrichment (δ34S > 10 ‰). The interaction of magmatic fluids with evaporate-bearing carbonates is likely a common process responsible for magnetite deposition in the Fe skarn deposits.
... Identification of possible sulfur sources requires consideration of the effects of sulfur isotope fractionation in the fluid from which pyrite was precipitated. However, the absence of sulfate minerals in the ore suggests that the sulfur isotopic composition of pyrite can be considered to be approximately equivalent to the isotopic composition of the fluids (δ 34 S ΣS ) from which it was precipitated (Wen et al. 2017). On the other hand, the relatively lower deposition temperatures of pyrite (late in the paragenetic sequence) and the high oxidation state of the ore (near the magnetite-hematite buffer) suggest that much of the sulfur was introduced in the form of sulfate (Barnes and Kullerud 1961). ...
... On the other hand, the relatively lower deposition temperatures of pyrite (late in the paragenetic sequence) and the high oxidation state of the ore (near the magnetite-hematite buffer) suggest that much of the sulfur was introduced in the form of sulfate (Barnes and Kullerud 1961). Such a sulfate-dominated solution must be significantly enriched in 34 S total sulfur (Ohmoto 1972) and likely originates from sources, such as trapped seawater sulfate (connate water) and/or evaporites (Zürcher et al. 2001;Zhu et al. 2015;Wen et al. 2017). Since there are no evaporite deposits in the Guydash area (Fig. 2), it is more likely that the sulfur originated from sulfate in connate water trapped in limestone host rocks. ...
Magnetite mineralization accompanied by minor hematite, pyrite, chalcopyrite, tetrahedrite, tennantite, and goethite, occurs in the Guydash iron skarn deposit in East Azarbaijan province, Iran. Geologically, it is located in the northwestern part of the Sanandaj-Sirjan zone. The skarn was formed by the intrusion of igneous bodies, especially porphyritic diorites, in contact with Middle-Upper Jurassic limestones and lesser Eocene pyroclastics. During skarn formation, four paragenetic stages of mineralization are distinguished: the prograde, retrograde, sulfidic and supergene stages, with magnetite deposited in the retrograde stage. Microthermometric data from fluid inclusions in calcite and quartz showed that the retrograde mineraliza-tion stage occurred at low to moderate temperatures (159.7-299.5 °C), a maximum pressure of 95 bar, and a maximum depth of 1 km. The fluids responsible for mineralization in this stage were aqueous and had low to high salinity (2-34 wt% NaCl equivalent). Fluid inclusion data indicate that the mineralizing fluid in the Guydash deposit was derived from a mixture of magmatic, meteoric, basinal, and metamorphic waters. The δ 18 O values in magnetite range from + 5.8 to + 10.2‰. The δ 18 O values of water in equilibrium with magnetite at an average homogenization temperature of 230 °C were calculated to range from-2.43‰ to 1.97‰. The O isotope values in magnetite revealed that the mineralizing fluids were mainly from magmatic waters. The δ 34 S values in pyrite from sulfidic stage range from + 10.2 to + 12.6‰, indicating that the sulfur was supplied from seawater sulfate source. Geological, mineralogical, fluid inclusion and isotopic data suggest that the Guydash deposit is a typical calcic-type Fe skarn deposit related to the intrusion of dioritic rocks into the Jurassic limestones.
... T.J. Boothe et al. oxygenated meteoric fluids (Simon et al., 2013;Wen et al., 2016). Meteoric water may have become highly oxygenated through interaction with gypsum deposits located south of the study area resulting in increasing fO 2 and fS in the form of SO 4 2− (Newton and Manning, 2004;Jansson and Allen, 2013;Wen et al., 2016). ...
... T.J. Boothe et al. oxygenated meteoric fluids (Simon et al., 2013;Wen et al., 2016). Meteoric water may have become highly oxygenated through interaction with gypsum deposits located south of the study area resulting in increasing fO 2 and fS in the form of SO 4 2− (Newton and Manning, 2004;Jansson and Allen, 2013;Wen et al., 2016). ...
... The δ 34 S values of sulfides from the Zhangjiawa deposit range 16.4‰ from 21.1‰, much higher than those (0.0‰ to 10.8‰) of the Jinling deposit (Fig. 12). This is consistent with the widespread Ordovician marine strata in the Zhangjiawa deposit, which contain high-δ 34 S sulfates (Wen et al., 2017;Duan, 2019). ...
Apatite commonly contains abundant halogens and trace elements, which can occur in both the magmatic and hydrothermal stages, becoming favorable for recording the magmatic-hydrothermal properties and processes. Skarn-type iron deposits associated with high-Mg diorites are widespread in the Luxi Block, eastern North China Craton. Their ore-forming processes, especially how the different wallrocks (limestones and dolomites) controlled the formation of high-grade iron ores, have been poorly constrained. To unravel the mechanisms, in this contribution, in-situ textural, geochronological (U-Pb dating) and geochemical (halogens and trace elements) analyses by SEM, EPMA and LA-ICP-MS were conducted on apatite from the representative Fe skarn deposits (Jinling and Zhangjiawa deposits) in the Luxi Block. Three generations of apatite were identified in the Jinling deposit, which occur in the feldspathization (Ap1), garnet–pyroxene skarns (Ap2) and massive magnetite ores (Ap3), respectively. One generation of apatite occurring in the massive magnetite ores (Ap-3) was identified in the Zhangjiawa deposit. The Ap2 and Ap-3 apatite grains show patchy textures composed by residual bright zones (Ap2a and Ap-3a) and newly-formed grey to dark zones (Ap2b and Ap-3b), which indicate fluid metasomatism. LA-ICP-MS U-Pb dating shows that the Ap1, Ap2a and Ap3 apatite in the Jinling deposit formed at 130.4±0.9 Ma (2σ), 128.5±2.4 Ma and 128.3±9.2 Ma, respectively, whereas the Ap-3a in the Zhangjiawa deposit formed at 128.1±4.2 Ma. These ages are well consistent with the intrusive ages of the spatially associated high-Mg diorites within errors, corroborating the ore-forming fluids originating from the high-Mg rocks. All the studied apatite grains show F/Cl ratios higher than 1, especially in the early-stage apatite (e.g., 5-19 in Ap1), indicating that the originally exsolved fluids were enriched in F. The high F contents probably played a significant role in leaching Fe from the high-Mg rocks by enhancing rock porosities. The Eu/Eu* ratios of apatite increase from Ap2a to Ap3 while the Ce/Ce* ratios decrease. This suggests an increase of oxygen fugacity. The Sr concentrations in Ap3 are much higher than those in Ap-3a, correlating well with the wallrocks that limestones are developed in the former while dolomites in the latter. The above features indicate that fluid-rock interaction likely led to the increase of oxygen fugacity, which controlled the massive Fe deposition. In the Jinling deposit, the altered apatite grains (Ap2b) show much lower REE+Y but higher F contents than those of the unaltered (Ap2a), not only indicating the REEs being easily mobilized during metasomatism, but also suggesting that the high F contents likely contributed to the formation of high-grade ores by leaching additional Fe from the previously formed Fe-rich skarns. In the Zhangjiawa deposit, the altered apatite grains (Ap-3b) shows lower Cl contents than those of the unaltered (Ap-3a). This probably indicates the mixing of low-salinity fluids (e.g., recycling meteoric water), leading to the loss of Fe and thus lowering the Fe grade. The above results indicate that metasomatism is common in the skarn deposits, which can either elevate or lower the metal grade. The processes can be well recorded by apatite.
... This model is widely accepted as applicable to IOCG and IOA deposits, but less so for skarn deposits, which are the products of fluid-rock interaction at the contact between a granitoid and carbonate-bearing protoliths, each of which has distinct geochemical features (e.g., Einaudi et al., 1981;Ciobanu and Cook, 2004;Meinert et al., 2005). There is, however, increasing geological and geochemical evidence to suggest that the involvement and importance of evaporites for Fe skarn systems (Zhu et al. 2015;Wen et al., 2017; ~130 Ma by U/Pb dating of skarn titanite (Zhu et al., 2017), thus confirming the genetic link between the Jinshandian pluton and Fe mineralization. Rocks of the Jinshandian pluton display a wide range of SiO 2 content (48.45−73.89%), ...
Increasing volumes of geological and geochemical evidence suggest that evaporites can be involved in the formation of Fe skarn systems and may play a critical role in ore-forming processes. Despite this, the timing and mechanisms of evaporite assimilation and its consequences for the Fe mineralization remains poorly constrained. Jinshandian (Edong district, eastern China) is an iron skarn formed by the intense interplay between magmatic-hydrothermal fluids and evaporite-bearing wall rocks. Petrographic, geochemical, and in-situ Srsingle bondNd isotope signatures of apatite from the causative intrusion and through early prograde to late retrograde skarn reveals the evolution and sequence of magmatic and hydrothermal fluid processes involved in formation of the Jinshandian deposit. Three sub-types of apatite (igneous, primary hydrothermal, and secondary hydrothermal) are distinguished according to their association, contained mineral inclusions, textures and relationships with other minerals, and the correlative relationships among trace elements, as well as their relative concentrations. Volatile components (F, Cl, SO3) suggest that igneous apatite from the quartz monzonite formed prior to vapor saturation whereas that from the quartz diorite crystallized during vapor saturation. Correlations between Sr and Mg, V, Mn, Fe, Ge, Y, Zr, and REE + Y in igneous apatite suggest that fractional crystallization exerts a primary control on trace element incorporation into apatite. All sub-types of apatite show chondrite normalized REE + Y fractionation patterns and negative Eu anomalies that are comparable with their host magmatic rocks, suggesting that signatures specific to the magmatic history are retained in hydrothermal apatite. A limited evaporite component has been assimilated during the magmatic stage, resulting in the observed wide variation in Sr content (148–1054 ppm), signatures of Nd isotopes (εNd (t) = −12.33 to −7.85), and radiogenic Sr isotopes (87Sr/86Sr = 0.70721 to 0.70948) measured in igneous apatite. Primary hydrothermal apatite shares a similar Sr isotope signature (87Sr/86Sr = 0.70819 to 0.70989), consistent with sedimentary sulfates (gypsum and anhydrite) from wall rocks, indicating continued input of evaporite components during the hydrothermal stage. Assimilation of evaporite components into the magma facilitated partitioning of Cl and Fe2+ into exsolved fluid. The continued involvement of evaporites at the hydrothermal stage drove the hydrothermal fluid toward oxidized conditions as the system evolved, consequently leading to precipitation of large amounts of magnetite. These results highlight both the critical role played by evaporites in facilitating formation of magmatic-hydrothermal Fe deposits and the efficacy of apatite to fingerprint complex petrological and ore-forming processes (e.g., assimilation, fractional crystallization, fluid exsolution, and metasomatism).
... Such features are particularly well displayed by microthermometric results obtained in garnet and pyroxene, which tend to be located way apart into two distinctive regions in the temperature of homogenization vs. salinity space (Fig. 9). Such extremely high salinity fluids are common in IOCG deposits of any type, particularly those whose formation occurred relatively close to the parental intrusive bodies, which includes the IOCG skarn kind (e.g., Borrok et al., 1998;Davidson et al., 2007;Baker et al., 2008;Wen et al., 2017). We recorded no evidence for pre-boiling fluids, neither did we observe any fluid inclusions that homogenized into a supercritical phase, despite the representativeness of sampling, which suggests that this "first boiling" did not require a preexisting supercritic fluid. ...
The Miocene skarn deposits at Tatatila–Las Minas are found in central-eastern Veracruz state, east Mexico, near the Palma Sola massif. These deposits are geologically associated with the early stages of the Trans-Mexican Volcanic Belt (TMVB) intruded Mesozoic carbonate rocks of the Sierra Madre Oriental. Skarn associations are distributed in the classic evolution from prograde to retrograde mineralization stage. Prograde associations consist mainly of grossular-andradite, clinopyroxene, quartz, wollastonite, clinopyroxene, potassium feldspar, quartz, epidote, chromian muscovite, and are rich in magnetite, whereas retrograde associations are richer in hematite than magnetite, chlorite, fuchsite, hornblende and additionally contain chalcopyrite, pyrite, bornite, and native gold. The systematic study of fluid inclusions shows a broad variety of petrographic and microthermometric features. Fluid inclusion associations in early prograde minerals show evidence for boiling and effervescence, which are hereby interpreted as deep boiling in the -magmatic environment (or “first boiling”) with no evidence for supercritic fluids. Such a process would account for the generation of two distinct brines at ≤650 °C (a) up to ∼20 wt% NaCl equiv. and (b) up to ∼70 wt% NaCl. Both brines have cooled down independently until the brittle-ductile transition (∼400 °C) bypassed it and were able to interact with other fluids, and perhaps between with each other. Later on, deep isothermal mixing would have occurred between both brines and deeply evolved meteoric water (thermally equilibrated with host rocks). REE geochemistry of garnet suggests that mineralizing fluids at prograde stage evolved from near neutral pH and oxidizing conditions to mildly acidic and reducing conditions, perhaps reflecting the entrainment of shallow fluids. Both brines or their mixed products have experienced further dilution leading to the precipitation of retrograde associations. The most noticeable features in the retrograde stages, however, are conductive cooling and shallow isothermal mixing, this time between the products of the two pathways that originated as two distinct types of magmatic brines. The occurrence of magmatic fluids is corroborated by C and O isotope geochemistry, in which such source presents different types of water/rock interaction with sedimentary C and O from local limestones (δ¹³CVPDB between 0.9 and 3.7‰ and δ¹⁸OVPDB between −7.5 and −3.7‰), thus drawing an isotopic zonation that parallels the marble front associated with skarns (endoskarn calcite, δ¹³CVPDB between −8.5 and −3.5‰, and δ¹⁸OVPDB between −22.4 and −15.0‰). δ³⁴SVCDT values from pyrite, chalcopyrite and galena in retrograde associations (between −3 and 4.2‰) also indicate a dominant magmatic source for sulfur, with a minor sedimentary/metasedimentary contribution. Low H2S concentrations enhanced magnetite deposition in prograde stages, and the progressive increase in H2S concentrations, coupled with a decrease in temperature by conductive cooling, led to sulfide and gold precipitation during retrograde stages. These deposits are hereby classified as IOCG skarn that were developed in association with the regional adakitic stage of the TMVB.
... For example, the trace element characteristics of magnetite in porphyry and skarn deposits are transitional, rather than exhibiting a clear boundary (Nadoll et al., 2015). The dissolution and reprecipitation or component re-equilibrium processes of magnetite will also change its trace element characteristics (Hu et al., 2015;Wen et al., 2017a;Wen et al., 2017b). Liu (2019) proposed that the change trends of trace elements in magnetite can reflect its fluid evolution process, and thus can indicate the deposit type. ...
... This overlap has usually been interpreted as the result of the dissolution and reprecipitation of magnetite in IOA deposits (Palma et al., 2020). Although the dissolution and reprecipitation of magnetite are common in IOA and skarn deposits (Hu et al., 2015;Heidarian et al., 2016;Wen et al., 2017a;Wen et al., 2017b;Huang and Beaudoin, 2019), there is still some controversy regarding how this process can explain a situation whereby all magnetite samples present in an IOA deposit fall into the IOCG region. ...
... The iron oxides in these deposits mainly comprise magnetite, followed by small amounts of martite. Numerous studies have investigated the chronology, fluid inclusions and C-O-S isotopes in these deposits, revealing that most iron deposits in the belt experienced strong assimilation of Triassic evaporites during their ore-forming processes (Zhou et al., 2011;Li et al., 2015;Wen et al., 2017a;Wen et al., 2017b;Zeng et al., 2016;Li et al., 2019a;Li et al., 2019b). The Luzong volcanic basin is an important part of the Middle and Lower reaches of the Yangtze River Metallogenic belt (MLYB) (Chang et al., 1991); the Daling iron deposit is located in the northern part of the basin. ...
In recent years, magnetite trace elements have increasingly been applied in studies into ore deposits. The magnetite trace element characteristics of different deposit types have been summarized, but to date no satisfactory explanation has been obtained as to why magnetite samples from some iron oxide-apatite (IOA) deposits exhibit similar trace element characteristics to those in iron-oxide copper gold (IOCG) deposits, or even skarn deposits. The Daling IOA deposit is located in the Luzong volcanic basin, Eastern China. Multi-stage magnetite have developed within the deposit; which provides a good opportunity to study the evolution process of magnetite trace elements in an IOA deposit. Here, sensitive high-resolution ion microprobe (SHRIMP) in situ sulfur isotope analysis was carried out for pyrites at different depths in the deposit. Pyrites at different locations exhibited similar sulfur isotope compositions, falling within the magmatic sulfur range (0.1‰–5.2‰), indicating that the ore-forming fluid of the Daling deposit was not affected by the Triassic evaporite, and that the trace element characteristics of its magnetite were mainly controlled by its magmatic-hydrothermal evolution process. Magnetite within the deposit can be divided into three sub-stages. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis revealed that magnetite (Mag-a) in vertical veinlets exhibits the highest Ti, V, Mn, and Zn contents; magnetite (Mag-b), which is associated with diopside and tremolite in coarse veinlets, exhibits the highest Mg, Al, Co, and Ni contents and brecciated magnetite (Mag-c) exhibits the lowest V content, the highest Mn and Zn contents, and similar Mg, Al, Ti, and Co contents to those of Mag-b. Comparing the trace elements of the three types of magnetite revealed that hydrothermal fluid can assimilate and absorb albite-diopside altered rock that forms in the early stage, resulting in hydrothermal fluid that is rich in Mg, Al and Si. Thus, magnetite samples in IOA deposits can exhibit similar features to those in skarn deposits through multi-stage, long-distance fluid evolution. Therefore, before using magnetite trace elements to discuss the characteristics of hydrothermal fluid, it is important to carefully investigate the basic geological characteristics of a given deposit and the mineralogical characteristics of its magnetite.
