11. Zoheir, Basem; Carr, Patrick; Xu, Xinyue; Zeh, Armin; Kraemer, Dennis; McAleer, Ryan; Steele-MacInnis, Matthew; Ragab, Azza; Deshesh, Fatma.The Igla Sn-(W-Be) deposit, Egypt: Prolonged magmatic-metasomatic processes during the middle stage evolution of the Arabian-Nubian Shield.Gondwana Research, 2025, 142: 20-43 The Igla Sn-(W-Be) deposit, Egypt: Prolonged magmatic-metasomatic processes during the middle stage evolution of the Arabian-Nubian Shield
The Igla Sn-(W-Be) deposit in the Central Eastern Desert of Egypt is associated with a suite of granitic rocks, including monzogranite, granophyric granite, and porphyritic leucogranite. These rocks belong to a calcic to calc-alkalic series, characterized by low Mg# values and low Ti and P concentrations. Monzogranite and granophyric granite show features typical of fractionated volcanic-arc I-type granites, while the leucogranite, with its distinct Rb/Ba, K/Rb, and Ga/Al ratios, is classified as a highly evolved A-type granite. Mineralization at Igla mine includes cassiterite and wolframite, along with minor molybdenite, arsenopyrite, columbite, and tourmaline, mainly hosted in beryl ± topaz-quartz veins and miarolitic cavities within greisen and silica-rich stockwork. Zircons from the monzogranite show LREE enrichment, moderate positive Ce anomalies, and moderately oxidizing conditions (ΔFMQ ≃ 1.75), while granophyric granite zircons exhibit higher HREE enrichment and more oxidizing conditions (ΔFMQ ≃ 1.04). Leucogranite zircons have the highest REE concentrations, more pronounced negative Eu anomalies, and distinctly reducing conditions (ΔFMQ ≃ -0.06). U–Pb dating of zircon and xenotime reveals concordant 206Pb/238U ages of 708.7 ± 2.0 Ma for monzogranite, 701.3 ± 1.5 Ma for the granophyric granite, and a noticeably younger age for the leucogranite (605.1 ± 2.4 Ma). Petrography and microchemistry of cassiterite reveal two distinct stages: an earlier generation (Cst-I) with straight oscillatory zoning, and a later chaotically zoned generation (Cast-II) that overgrows and crosscuts the former. U-Pb dating confirms two discernable age populations: Cst-I, with a weighted mean 206Pb/238U age of 637.4 ± 1.4 Ma; and Cst-II ages scatter from 605 to 588 Ma, partially overlapping with the leucogranite formation. Wolframite, although less precisely dated at 615.3 ± 4.3 Ma, suggests rejuvenated tectonics, magmatism, and hydrothermal activities, culminating in the formation of Cst-II. Primary aqueous fluid inclusions in quartz indicate deposition from a low-salinity aqueous fluid with undetectable dissolved gas, while trails of aqueous-carbonic inclusions with slightly higher salinity and appreciable gas (CO2, CH4) contents occur together in the same crosscutting trails with arsenopyrite and bismite inclusions. The variable contents of CO2 and CH4 in these inclusions suggest that carbon redox equilibria within the ore-forming fluid may have played a pivotal role in linking redox potentials, facilitating the deposition of arsenopyrite, bismite, and Cst-II. The improved age constraints highlight the role of highly evolved transcrustal magmatism in mobilizing and upgrading early rare metal concentrations, coinciding with the ∼ 650–600 Ma geodynamic transition in the Arabian-Nubian Shield. Crustal thinning, partial melting of older granitoids, and prolonged magmatic-hydrothermal interactions were key in ore formation and upgrading.Link DOI
10. Xinyue Xu, Wyatt M Bain, Fernando Tornos, John M Hanchar, Hector M Lamadrid, Bernd Lehmann, Xiaochun Xu, Jeffrey A Steadman, Ralph S Bottrill, Majid Soleymani, Abdorrahman Rajabi, Peng Li, Xuehai Tan, Shihong Xu, Andrew J Locock, Matthew Steele-MacInnis.Magnetite-apatite ores record widespread involvement of molten salts.Geology, 2024, 52 (6): 417–422 Magnetite-apatite ores record widespread involvement of molten salts
The origins of magnetite-apatite deposits are controversial, and the crux of the debate is what types of fluids form these rocks. We present evidence from 20 magnetite-apatite deposits worldwide showing ubiquitous involvement of molten salts. The studied deposits are distributed globally, from various tectonic settings, and from Precambrian to Quaternary in age. In every case, water-poor polycrystalline melt inclusions in ore-stage minerals are dominated by sulfate, chloride, and carbonate components plus variable proportions of calc-silicates, phosphates, and iron ± titanium oxides that re-melt between 285 °C and 1100 °C. These fluids are very different from what is generally expected in most geologic settings, but their ubiquitous presence in magnetite-apatite rocks indicates that molten salts are widespread and essential to the formation of these deposits. DOI
9. Matthew Steele-Macinnis, Xinyue Xu.Molten Salts: Novel Agents of Transport and Deposition of Rare Earth and High Field-Strength Elements.AGU Fall Meeting Abstracts, 2023, V44A-01 Molten Salts: Novel Agents of Transport and Deposition of Rare Earth and High Field-Strength Elements
Magnetite-apatite deposits have been historically mined primarily for iron, but they are of growing interest as sources of rare earth and high field-strength elements (REE and HFSE) because they commonly host exceptionally REE-rich apatite and a number of HFSE-rich minerals. However, the formation mechanisms of these deposits are still poorly understood and deeply controversial, leaving major unknowns about the fluids that generate such REE and HFSE enrichment. Analysis of fluid and melt inclusions in magnetite-apatite mineral deposits from around the world and from Archean to recent times reveals that a hitherto unexpected and largely unknown type of mineralizing fluid—namely, non-aqueous ionic liquids, or molten salts—played a pivotal role in forming all of them. In other words, involvement of such molten salts is a ubiquitous and critical factor in forming REE-and HFSE-enriched magnetite-apatite …
8. Xinyue Xu, Matthew Steele-Macinnis.Melt Inclusion Evidence for Sulfate-Carbonate Melts in Iron Oxide-Apatite Deposit.GSA Connects 2023 Meeting in Pittsburgh, Pennsylvania, 2023, 55, 393425 Melt Inclusion Evidence for Sulfate-Carbonate Melts in Iron Oxide-Apatite Deposit
The type of fluids involved in the iron oxide–apatite (IOA) deposits are the crux of the debate about their origins. We report the ubiquitous occurrence of high-temperature, polycrystalline melt inclusions in IOA deposits from around the world, revealing a direct genetic links between molten salts and these deposits. We studied the petrographic characteristics of thousands of inclusions at room temperature, identified their phases by Raman spectroscopy and EDS, and conducted microthermometry experiments to re-melt these inclusions in the lab. These polycrystalline inclusions show complex compositions of chlorides, sulfates, carbonates, silicates, calc-silicates, and metal sulfides and oxides. Four main types of polycrystalline inclusions with end-member components are summarized based on their compositions: (i) chloride melt inclusions (including sylvite, halite, hibbingite, etc.); (ii) sulfate melt inclusions (including anhydrite, barite, cesanite, and gypsum); (iii) calc-silicate melt inclusions (including diopside, wollastonite, garnet, and tremolite/ actinolite); and (iv) carbonate melt inclusions (including calcite, dolomite, natrite and trona). Although some examples of end-member type inclusions are reported, most studied inclusions are transitional between different types, underscoring that all four types are intimately related and represent different flavors of a broader category of salt melts. Polycrystalline inclusions across all studied deposits melt between 585 °C and 1200 °C, and thus represent high-temperature ionic liquids. These high-temperature inclusions are widely distributed in all deposits studied, and seem to be a fundamental feature of IOA systems. Although the detailed characteristics, types, and distribution of inclusions vary between different deposits, taken together they suggest a key role of magma contamination and immmiscibility. Therefore, we argue that these results reveal consistent involvement of hitherto unexpected molten salts in forming magnetite-apatite rocks worldwide. DOI
7. Xinyue Xu, Matthew Steele-Macinnis.Calc-Silicate Magmas Generated by Limestone Assimilation to Form" magmatic Skarn".GSA Connects 2023 Meeting in Pittsburgh, Pennsylvania, 2023, 55, 393047 Calc-Silicate Magmas Generated by Limestone Assimilation to Form" magmatic Skarn"
Skarn deposits related to porphyry systems are generally considered to be products of hydrothermal metasomatism. However, at the Chating porphyry deposit (China), we find evidence for the formation of “magmatic skarn” by pervasive, infiltrative chemical exchanges between silicate melts and carbonate rocks in a shallow porphyry setting driven by assimilation, melting, and complex liquid immiscibility. In pods of endoskarn and associated veins from Chating, we find melt inclusions rich in sulfate and calc-silicate minerals (diopside + garnet + wollastonite + epidote). These inclusions were remelted in the heating experiments showing a variety of liquid immiscibility and often coexisting with chloride-rich salt melt inclusions and CO2 vapor inclusions. We argue that skarn at Chating was formed by fractional crystallization of an immiscible, calc-silicate-rich melt, and these melts were generated by the assimilation of limestones with interbedded gypsum evaporites, followed by coupled decarbonation and desilication. The coeval assemblages of anhydrous salt-melt inclusions found in Chating, as well as the occurrence of phases such as thenardite, celestine, apatite, and chondrodite in the calc-silicate-bearing melt inclusions, suggests that the skarn-forming melts were stabilized by a variety of fluxes including elevated Na+, Sr2+, Cl–, F–, PO43– and SO42–. Meanwhile, the coeval vapor inclusions represent the products of decarbonation of the assimilated material and degassing of the CO2 thus produced. Moreover, the calc-silicate bearing melt inclusions commonly contain sulfide daughter minerals, suggesting that these melts were rich in metals, and therefore may have played a role in ore mineralization. Based on these results, we argue that at Chating—and probably other skarn deposits where evaporites are part of the host sedimentary package—assimilation of carbonate rocks and generation of calc-silicate-rich melts was a key process of skarn formation. DOI
6. Xinyue Xu, Matthew Steele-Macinnis.Metasomatism driven by carbonate-rich melt: evidence from melt inclusions.AGU Fall Meeting Abstracts, 2023, V41F-0158 Metasomatism driven by carbonate-rich melt: evidence from melt inclusions
Metasomatism is traditionally regarded as a primarily hydrothermal process, wherein mineral replacement reactions involve coupled dissolution and precipitation from an aqueous fluid phase. "Flame" perthite is a fairly common texture in high-grade metamorphic rocks, wherein sharp and irregular zones of albite appear to invade and replace preexisting K-feldspar. The usual interpretation is that these albite "flames" represent hydrothermal-metasomatic alkali exchange between aqueous fluid and alkali feldspar. However, here, we present a unique example of flame perthites in which the fluid medium that drove replacement of alkali feldspar and fostered growth of albite flames was in fact a carbonate-rich melt. Polymineralic, crystallized melt inclusions of are hosted only within albite flame lamellae and are absent from the surrounding K-feldspar. Petrography and Raman spectroscopy show that these inclusions are composed of calc-silicate and carbonate minerals that re-melt during laboratory heating, and thus represent aliquots of contaminated silicate-carbonate melts. Such liquids are known to have high interconnectivity, low density, and low viscosity relative to silicate melts, and as such can be capable of infiltrating and replacing alkali feldspar in a way analogous to a reactive hydrothermal fluid. DOI
5. Xinyue Xu, Xiaochun Xu, Marko Szmihelsky, Jun Yan, Qiaoqin Xie, Matthew Steele-MacInnis.Melt inclusion evidence for limestone assimilation, calc-silicate melts, and “magmatic skarn”.Geology, 2023, 51 (5): 491–495 Melt inclusion evidence for limestone assimilation, calc-silicate melts, and “magmatic skarn”
Chemical exchange between silicate magmas and carbonate rocks has major implications for igneous fractionation, atmospheric CO2 flux, and formation of mineral deposits. However, this process is only partly understood, and long-standing questions of whether, where, and how carbonate rocks can be digested by silicate melts remain controversial. We describe evidence for pervasive chemical exchange between silicate melt and carbonate rock in a shallow porphyry setting driven by limestone assimilation. Melt inclusions in endoskarn from the Chating Cu-Au deposit in eastern China reveal that the calc-silicate assemblage (diopside + andradite ± wollastonite ± epidote) was molten at the time of skarn formation and coexisted with CO2 vapor as well as sulfate- and chloride-salt melts. Hence, we argue that endoskarn at Chating formed by crystallization of an immiscible calc-silicate melt produced by assimilation of carbonate rock, aided by the presence of sulfate and other fluxes, which in turn promoted desilication of the intruding magma and drove vigorous CO2 release. DOI
4. Xinyue Xu, Xiaochun Xu, Qiaoqin Xie, Zhongyang Fu, Sanming Lu, Lili Zhao.Geological features and ore-forming mechanisms of the Chating Cu–Au deposit: A rare case of porphyry deposit in the Middle–Lower Yangtze River metallogenic belt.Ore Geology Reviews, 2022, 144, 104860 Geological features and ore-forming mechanisms of the Chating Cu–Au deposit: A rare case of porphyry deposit in the Middle–Lower Yangtze River metallogenic belt
The Chating Cu–Au deposit is an important porphyry deposit located in the Middle–Lower Yangtze River Metallogenic Belt (MLYMB) of eastern China. Drill core logging and ore petrographic observations were systematically employed to recognize the geological features of the deposit. Several important and peculiar geological characteristics are revealed as fellows: (1) the ore-bearing quartz diorite porphyry emplaced within carbonate-dominated strata rather than clastic strata and volcanic rocks, (2) the ore-hosting location confined in the whole cryptoexplosive breccia pipe inside the porphyry stock, and (3) large-scale and barren marbles, marbled limestones, and hornfels almost encircling the porphyry stock and sporadic and barren skarns scattered within the porphyry stock. The fluid-inclusion study at the deposit reports a wide range of homogenization temperatures (161.4 °C–454.2 °C) and salinities (0.2–54.7 wt% NaCl eq) for the ore-forming fluids, and two fluid boiling events as suggested by the coexistence of halite-bearing liquid-rich inclusions and vapor-rich inclusions. In contrast with classical porphyry deposits, the Chating deposit has similar characteristics in the close relationships between the mineralization and the porphyry stock, the hydrothermal alteration zonation, and the fluid evolution process, while the wall-rock strata and ore-hosting position mark outstanding differences of the Chating deposit. The comprehensive geological and geochemical research in this study has been integrated to explore the ore-forming mechanisms of the deposit. The carbonate wall-rock strata were baked by early magma to form low-permeability thermal metamorphic shield at the contact zone, which prevents the migration and loss of the ore-forming fluids and avoid hydrothermal metasomatism for skarn ores. After that, the cryptoexplosions open up the porphyry system and promote the magmatic hydrothermal fluids mixing with the meteoric water, which successively induce the ore-forming fluids boiling and further cause ore-forming materials unloading and precipitation in the cryptoexplosive breccia pipe. DOI
3. Xie Qiaoqin, Sun Rui, Xu Xiaochun, Xu Xinyue, An Yuhua, Qian Shilong.Characteristics of cryptoexplosive breccia from the Chating copper-gold deposits, Xuancheng, Anhui province and its metallogenic significance.Geological Journal of China Universities, 2020, 26 (3): 255-264 Characteristics of cryptoexplosive breccia from the Chating copper-gold deposits, Xuancheng, Anhui province and its metallogenic significance
The Chating copper-gold ore in Xuancheng region is a newly discovered large ore deposit in the Mesozoic-Cenozoic volcanic-sedimentary Nanling-Xuancheng basin in recent years, where the deposits are located at shallow depths of the Middle-Lower Yangtze River. This study is focused on the cryptoexplosive breccia pipe developed in the intrusives of quartz-dioriticporphyrite in the Chating copper-gold ore deposits. Based on the detailed core observations and petrographic analysis, characteristics and types of cryptoexplosive breccia are determined, and the relationship between the cryptoexplosive breccia and the copper-gold mineralization is discussed. The cryptoexplosive breccia in the ore deposits can be divided into three types: cryptoexplosivemelt-crystal-lithicbreccia, cryptoexplosive hydrothermal breccia, and cryptoexplosive fracture breccia based on its textures, compositions and abundance of rubbles. The cryptoexplosive breccia appears as an irregular pipe enveloped by the quartz-dioriticporphyrite and shows a regular spatial distribution. From the center of breccia to wall-rock are quartz-dioriticporphyrite, cryptoexplosivemelt-crystal-lithicbreccia, the cryptoexplosive hydrothermal breccia, and the cryptoexplosive fracture breccia, respectively. The spatial relationship between the alterated, mineralized and the cryptoexplosive breccia pipe shows that there exists a genetic link between formation of cryptoexplosive breccia and mineralization. The cryptoexplosion of the melt, liquid and gas originated from intermediate-acid magma induced the DOI
2.Xu Xiaochun, An Yuhua; Xu Xinyue, Fu Zhongyang.Zircon U-Pb ages and element geochemistry characteristics of magmatic rocks in Nanling-Xuancheng area of Anhui, China.Journal of Earth and Environment, 2020, 42(1): 15-35 Zircon U-Pb ages and element geochemistry characteristics of magmatic rocks in Nanling-Xuancheng area of Anhui, China
The Nanling-Xuancheng area of Anhui, which is a Meso-Cenozoic volcanic-sedimentary basin, is located in the southeastern limb of the northeastern part of middle-lower Yangtze river valley tectonic-magmatic-metallogenic belt. Zircon U-Pb dating, and major, trace and rare earth elements of the magmatic rocks in Nanling-Xuancheng area were focused, and compared with those of the magmatic rocks in other areas of middle-lower Yangtze river valley tectonic-magmatic-metallogenic belt, for determining the age, and discussing the petrogenesis of the magmatic rocks and the relationship between the magmatism and mineralization. In Nanling-Xuancheng area, a part of the magmatic rocks intruded into the basement of the basin or erupted as the cover rocks of the basin, and the other part of the magmatic rocks occurred in the nappe above the basin. The intrusive rocks are mainly granite, granodiorite, quartz diorite and pyroxene diorite, and the volcanic rocks are dacitic pyroclastic rocks and lavas. The results show that the zircon U-Pb ages of the intrusive rocks are between 138 Ma and 135 Ma, and the ages of the volcanic rocks are all less than 134 Ma, suggesting that the magmatism occurred in Early Cretaceous of Late Mesozoic(Late Yanshanian). The characteristics of major elements show that the magmatic rocks are high for Si and K, belonging to sub-alkaline and high-K calc-alkaline series; the characteristics of trace elements show that the magmatic rocks are rich in Rb, Th, U and K, and poor in Ti, Nb and Ta, the volcanic rocks are more deficient from intrusive rocks in Sr and P; the chondrite-normalized REE patterns show that the magmatic rocks are rich in LREE and have weak negative Eu anomalies. The element geochemical characteristics indicate that the magmatic rocks have the characteristics of crust-mantle mixed and mainly mantle-derived. Zircon U-Pb dating, and geological and geochemical characteristics of the magmatic rocks in Nanling-Xuancheng area indicate that the Late Mesozoic magmatism in the area has the dual characteristics of those in upwelling areas and depression areas of the middle-lower Yangtze river valley tectonic-magmatic-metallogenic belt, that is, the study area not only develops intrusive rocks in the upwelling area(such as Tongling area), but also develops volcanic rocks in the depression area(such as Luzong and Ningwu basins). The duality of magmatism may imply the duality of mineralization, that is, the study area may develop hydrothermal porphyry-type, skarn-type and vein-type Cu-Au and other polymetallic deposits related to intrusive magmatism, also porphyry-type Fe(S)deposits associated with volcanic-subvolcanic rocks.
References: DOI
1. XU XiaoChun, XU XinYue, XIE QiaoQin, FU ZhongYang, QIAN ShiLong, XIE ZuJun.Geological and geochemical characteristics and genesis of the Chating copper-gold deposit in Xuancheng City, Anhui Province.Acta Petrologica Sinica, 2019, 35(12); 3659-3676 Geological and geochemical characteristics and genesis of the Chating copper-gold deposit in Xuancheng City, Anhui Province
The Chating Cu-Au ore deposit in the Xuancheng City of Anhui Province is a large deposit newly discovered in shallow overburden area of the Middle and Lower Yangtze River Valley Metallogenic Belt. It is located in the central uplift of Nanling-Xuancheng Meso-Cenozoic volcanic-sedimentary basin. The geological study of the deposit indicates that the ore bodies occur in the concealed quartz diorite porphyritic intrusion formed in Early Cretaceous. The strong mineralization keeps obviously with the crypto-explosive breccia pipe and the range of the former is slightly larger than that of the latter. The alteration types are dominated by silication, potash-feldspathization, biotization, sericitization (muscovitization), and pyritization, with obvious zoning characteristics, while skarnization, chlorinization and kaolinization scattered in the mineralization area as strip belts or gobbets. The ores have brecciated, veined, veinlet-stockwork, fine granular disseminated structures, and replacement remnant texture, exsolution texture, etc. Magnetite-hematite and skarn minerals grow in the brecciated and veined ores. Especially anhydrite develops in veins and even forms anhydrock. The metallic minerals in the ores are dominated by pyrite and chalcopyrite as well as a small amount of bornite, tetrahedrite, tennatite, etc. The breccia in cryptoexplosion breccia is mainly composed of quartz diorite porphyrite, and the cementation mainly has two types. One is rock debris or rock powder which has similar composition with quartz diorite porphyrite. Another is hydrothermal minerals mainly including quartz and anhydrite. Three types inclusions like aqueous, vapor-aqueous, and daughter mineral-bearing inclusions are found in the quartz, and the component of vapor phase in the inclusions is mainly water. The daughter mineral-bearing inclusions are mainly found in quartz paragenesis with pyrite which has crakes formed in the earlier stage, with homogenization temperature range from 360°C to 420°C and higher salinity and density. There two homogenization temperature rages, 270C~300C and 190C~220C were gained from the vapor-aqueous and aqueous inclusions developed at the main metallogenic stages of copper and gold, corresponding with lower salinity and density. The geochemical characteristics of H-O, C-O, S and Pb isotopes indicate that the ore-forming fluids, the ore-forming metal elements and the compound elements are mainly from magma or magmatic rocks, while sedimentary strata and atmospheric precipitation also contribute to mineralization, but play a relatively small role. The Re-Os age of pyrite is consistent with the U-Pb age of the zircon in quartz diorite porphyrite within the margin of error, indicating that its mineralization is closely related to the magmatic intrusion and hydrothermal activity of the metallogenic area in late Yanshanian. Based on the comprehensive geological and geochemical characteristics of the deposit, comparing with the porphyry deposit and volcanic-subvolcanic (epithermal) deposit, it is considered that the Chating Cu-Au ore deposit in the Xuancheng City is a cryptoexplosive breccia type deposit related to the Early Cretaceous hypabyssal intrusive of quartz diorite porphyrite, which is a new type deposit in the Middle and Lower Yangtze River Valley Metallogenic Belt. DOI
