Magmatic-hydrothermal Event Research Articles

Reworking of a Caledonian (Early Paleozoic) granodiorite porphyry in a collisional zone in South China and its contribution for tungsten mineralization

A newly discovered ore-bearing granodiorite porphyry in the Chuankou tungsten (W) ore field is the largest W deposit formed during the Indosinian (Triassic) collision event in South China. As such, its genesis and relationship to W mineralization in the region remains ambiguous. Zircon U–Pb dating demonstrates that the Chuankou granodiorite porphyry was emplaced at 436.1 ± 0.8 Ma, predating the Triassic W mineralization in the ore field. The granodiorite porphyry is characterized by low Zr + Nb + Ce + Y concentrations (100–294 ppm), 10000 Ga/Al values (2.09–2.62), indicating that it is a weakly fractionated I-type granite. Variably negative εHf(t) values of −10.2 to −2.48 and TDM2 values of 2.06–1.06 Ga suggest crystallization from a partial melt of amphibolite, with minor contributions of metasedimentary rock in the middle–lower crust during the Caledonian collisional event. Given its low degrees of differentiation, the Chuankou granodiorite porphyry is inferred to have low mineralization potential. The presence of abundant fluorite in the granodiorite porphyry, coupled with elevated whole-rock F contents (0.4–4.1 wt%), suggests that volatile (F) involvement in Indosinian W mineralization might partially originate from the Caledonian granodiorite porphyry. Furthermore, the elevated whole-rock W contents, which exceeds those of granites related to W mineralization from regional (including Indosinian granites in the Chuankou W ore field), and other regions worldwide, indicate that W in the granodiorite porphyry was likely added to the ore-forming fluids during Indosinian magmatic–hydrothermal events. Consequently, we infer that W in the Caledonian Chuankou granodiorite porphyry was mobilized by F-rich fluids and potentially served as a partial source for the Indosinian mineralization.

Zircon and cassiterite geochronology of Sn-polymetallic pegmatite from the Xianghualing ore field, South China: Implications for multi-stage magmatic-hydrothermal events

The Nanling metallogenic belt (South China) is one of the largest W-Sn polymetallic provinces in the world. The ore bodies are mainly hosted in Triassic-Jurassic granitoids which formed during a complex history of magmatic evolution. Among them, the Laiziling pluton, which forms the northern part of the Xianghualing district, is an example of Sn-polymetallic deposits that underwent multiple Mesozoic episodes. In this study, the first in-situ U-Pb age dating of zircon and cassiterite minerals, trace element, and Lu-Hf isotopic data are reported for Laiziling NYF-type pegmatites. Four types of pegmatites are identified: stock-like pegmatite, vein-type pegmatite, peripheral vein-type pegmatite, and cap/sill-like pegmatite. Zircon LA-ICP-MS U-Pb geochronology of pegmatites yields an age of ~150 Ma, which is consistent with the age of the associated mineralized granitic pluton. Results of cassiterite age dating indicate that the W-Sn mineralization took place at ca. 150 Ma coeval with pegmatite emplacement. Combined with structure and trace element composition, two young ages (i.e., ~130 and 90 Ma) can be identified from pegmatite veins, suggesting that the studied zircon crystals experienced two distinct periods of magmatic-hydrothermal evolution during the Cretaceous (related to Late Yanshanian magmatism). In addition, some zircon grains are obviously enriched in LREE, which is associated with hydrothermal metasomatism. Compared to the narrow range of magmatic zircons, a wide range of inherited zircons (Proterozoic to Paleozoic) are observed in the studied Late Jurassic pegmatite (Pg1 and Pg2b), suggesting that they were incorporated from pre-existing basement rocks during magma ascent and/or emplacement. Furthermore, U-Pb data for 14 disseminated cassiterite grains yield a 206Pb/238U age of 221.5 ± 4.2 Ma, documenting evidence of cassiterite inheritance during melt ascension from country rocks or representing the initial stage of Sn enrichment. The εHf values of magmatic zircons show negative εHf values from −4.4 to −16.6 and their crustal model ages (TDM2) vary between 1328 Ma to 2200 Ma, suggesting the parent magma of the Laiziling pegmatites were derived from partial melting of older crustal components (Proterozoic basement in the Cathaysian Block of South China) and the mixing of mantle materials. This study proposes that multi-stage magmatic-hydrothermal events may have occurred not only in the Xianghualing area but also in the whole Nanling Range, and provides fresh insights into the formation processes of rare metal-bearing pegmatites in South China.

New precise age constraints of the Hatu gold belt, west Junggar, NW China: Implications for a 300 Ma magmatic hydrothermal event in post-collisional setting

Abstract A 300 Ma magmatic hydrothermal ore-forming process is identified in the Hatu gold belt in west Junggar, northwest China, based on precise age constraint by secondary ion mass spectroscopy U-Pb dating of hydrothermal zircon and Ar-Ar dating of muscovite. The gold deposits in the Hatu belt (Hatu, Qi-V, Huilvshan, etc.) are similar in geology, with NE- and NW-trending orebodies composed of gold-bearing quartz veins and auriferous altered tuffaceous wall-rocks. Hydrothermal zircon grains separated from gold-bearing quartz veins in the Qi-V gold deposit provide a concordia age of 299.6 Ma and a nearly identical weighted mean 206Pb/238U age of 300 ± 2 Ma. Muscovite samples also from the gold-bearing quartz veins yield 40Ar/39Ar plateau ages of 299.6 ± 1.7 Ma, 299.9 ± 1.8 Ma, and 300.6 ± 1.9 Ma. By comprehensive compilation of geological and geochemical characteristics, tectonic evolution, and geochronology of the gold deposits in the Hatu gold belt, our new precise age data confirm that the gold deposits in the Hatu belt formed simultaneously at ca. 300 Ma, and likely formed during a post-collisional extensional setting by magmatic hydrothermal fluid from cooling magmatic sources.

Superimposed multi-stage mineralization in the Qingchengzi Pb-Zn ore district, North China: Evidence from geochronology and sulfide geochemistry

The Qingchengzi Pb-Zn polymetallic ore district in northern China records two stages of Pb-Zn mineralization in the Paleoproterozoic and Mesozoic, respectively. The Paleoproterozoic sedimentary-metamorphic stage (stage I) of mineralization was primarily recorded by stratiform ores, and the Mesozoic magmatic-hydrothermal stage (stage II) of mineralization mostly formed vein-type ores. The apatites coexisting with the stage I sulfides yield U-Pb isotopic ages of (1882–1857 Ma), corresponding to the regional metamorphism pervaded in the Paleoproterozoic in the Liaodong region. Zircons from a granite porphyry that is spatially associated with the stage-II mineralization have a U-Pb age of 228.5 ± 5.8 Ma.Stage-I fine-grained sulfides (Py1a and Sp1a) are of SEDEX origin and the fluid is fertile in metals such as Co, Ni, Zn, As, Mn and V. The metals are likely to be sourced from the Liaohe Group, which contains high concentration of those metals. Stage-I recrystallized sulfides (Py1b and Sp1b) show trace elements such as Co, Ni, Cu, As and Au of pyrite and the Cu, Cd, In, Ag, Sb of sphalerite were remobilized out from their crystal lattice under metamorphism. Stage-II sulfides (Py2 and Sp2) are more enriched in Au, As, Cu, Ag, Sb, Pb compared to stage-I sulfides. LA-ICP-MS mapping reveals multigenerational texture of Py2 which features a Cu and Zn enriched core (Py2a) and an overgrowth rim (Py2b) of enrichment in Au, As, Co and Ni. The compositionally distinct core and rim presumably suggest that two episodes of magmatic fluids are involved in the formation of stage-II sulfides. The sedimentary pyrite from Liaohe Group and the stage-I sulfides have δ34S value in the ranges of 10.4–17.04 ‰ and 4.10–9.37 ‰, respectively, suggesting that sulfur was probably derived from seawater sulfate reduction. The sulfur isotopes of stage-II sulfides (δ34S = 4.10–9.02 ‰) reflects a mixing of magmatic sulfur with sulfur leached from meta-volcanic-sedimentary source. This process was associated with the upward migration of magmatic hydrothermal fluids and subsequent fluid-rock interaction, which leached heavy sulfur isotopes along with Cu, Zn, Co, Ni, V metals from wall rocks of mica schist from the Dashiqiao and Gaixian Formations. Integrated mineral assemblage, sulfide texture, trace element and sulfur isotope signatures and geochronological constraints reveal the primary Paleoproterozoic SEDEX mineralization was intensively overprinted by later metamorphism and Mesozoic magmatic hydrothermal events for the Pb-Zn deposits in the Qingchengzi ore district.

Microfabrics, In Situ Trace Element Compositions of Pyrite, and the Sulfur Isotope Chemistry of Sulfides from the Xitieshan Pb-Zn Deposit, Qinghai Province, Northwest China: Analysis and Implications

The Xitieshan deposit, located in the central segment of the northern margin of the Qaidam Basin, is among the largest massive Pb-Zn sulfide deposits in China. This deposit, along with its ore-bearing rock series known as the Tanjianshan Group, underwent greenschist facies metamorphism due to subsequent orogeny. We investigated the in situ sulfur isotopes of sulfides with different occurrences to define the origin of ore-forming fluids. The δ34S values of sulfides from stratiform ores, massive ores in schist, stockwork ores in marble, schist and discolored altered rocks that constitute a typical double-mineralization structure range from −5.3‰ to +5.6‰ and from −1.7‰ to +32‰, respectively, indicating distinct biological and thermochemical reductions in seawater sulfates. These are similar to the sulfur isotopic characteristics of VSHMS deposits. Pyrite, whose LA-ICP-MS trace element compositions can provide significant information about metallogenic evolution and deposit genesis, is ubiquitous throughout the whole mineralization process. In these stratiform, massive and stockwork ores, three pyrite types were identified: colloform pyrite (Py0), fine-grained anhedral spongy pyrite (Py1) and coarse-grained euhedral pyrite (Py2). The contents of most metallogenic elements, such as Cu, Pb, Zn, Ag, Mo, Mn and Sn, decrease from Py0 to Py2 with the enhancement of metamorphic recrystallization. This suggests that the expelled elements appear as inclusions in primitive pyrite, contributing to the precipitation of new sulfide phases, such as sphalerite and galena. Orogenic metamorphism played an important role in controlling further Pb-Zn enrichment of the Xitieshan deposit. Moreover, there is another mineralization type, primarily occurring as sulfide veins in the undeformed Formation C siltstones of the Tanjianshan Group, which also crosscut early-formed sulfides, showing close-to-zero S isotopic compositions. In this mineralization type, pyrite (Py3) displays high Se/Tl (>10) and Co/Ni (>2.2) ratios, both indicating a minor superimposed post-orogenic magmatic–hydrothermal event.

Metallogenic Age and Ore‐forming Material Sources of the Dahongshan Fe‐Cu Deposit, Yunnan Province: Insights from Molybdenite Re‐Os Dating and H‐O‐S‐Pb Isotopes

AbstractThe Dahongshan Fe‐Cu (‐Au) deposit is a superlarge deposit in the Kangdian metallogenic belt, southwestern China, comprising approximately 458 Mt of Fe ores (40% Fe) and 1.35 Mt Cu. Two main types of Fe‐Cu (‐Au) mineralization are present in the Dahongshan deposit: (1) early submarine volcanic exhalation and sedimentary mineralization characterized by strata‐bound fine‐grained magnetite and banded Fe‐Cu sulfide (pyrite and chalcopyrite) hosted in the Na‐rich metavolcanic rocks; (2) late hydrothermal (‐vein) type mineralization characterized by Fe‐Cu sulfide veins in the hosted strata or massive coarse‐grained magnetite orebodies controlled by faults. While previous studies have focused primarily on the early submarine volcanic and sedimentary mineralization of the deposit, data related to late hydrothermal mineralization is lacking. In order to establish the metallogenic age and ore‐forming material source of the late hydrothermal (‐vein) type mineralization, this paper reports the Re‐Os dating of molybdenite from the late hydrothermal vein Fe‐Cu orebody and H, O, S, and Pb isotopic compositions of the hydrothermal quartz‐sulfide veins. The primary aim of this study was to establish the metallogenic age and ore‐forming material source of the hydrothermal type orebody. Results show that the molybdenite separated from quartz‐sulfide veins has a Re‐Os isochron age of 831 ± 11 Ma, indicating that the Dahongshan Fe‐Cu deposit experienced hydrothermal superimposed mineralization in Neoproterozoic. The molybdenite has a Re concentration of 99.7–382.4 ppm, indicating that the Re of the hydrothermal vein ores were primarily derived from the mantle. The δ34S values of sulfides from the hydrothermal ores are 2‰–8‰ showing multi‐peak tower distribution, suggesting that S in the ore‐forming period was primarily derived from magma and partially from calcareous sedimentary rock. Furthermore, the abundance of radioactive Pb increased significantly from ore‐bearing strata to layered and hydrothermal vein ores, which may be related to the later hydrothermal transformation. The composition of H and O isotopes within the hydrothermal quartz indicates that the ore‐forming fluid is a mixture of magmatic water and a small quantity of water. These results further indicate that the late hydrothermal orebodies were formed by the Neoproterozoic magmatic hydrothermal event, which might be related to the breakup of the Rodinia supercontinent. Mantle derived magmatic hydrothermal fluid extracted ore‐forming materials from the metavolcanic rocks of Dahongshan Group and formed the hydrothermal (‐vein) type Fe‐Cu orebodies by filling and metasomatism.

Geochemistry of sulfide in mafic enclaves from Gushan granite: Implications for the role of contemporaneous mafic magma in the genesis of the large-scale Jiaodong gold province, eastern China

Studies have revealed the key role of deep-seated, ore-forming fluids and metals in the generation of the Early Cretaceous large-scale gold deposits in the Jiaodong gold province of eastern China. However, how the ore-forming materials were transported to shallow crustal levels remains unclear. Here, we investigate trace elements and sulfur isotopes of pyrite within mafic microgranular enclaves (MMEs) of Gushan granite to evaluate the role of the syn-mineralization of mafic enclaves in the transportation of ore-forming materials. Zircon U-Pb and molybdenite Re-Os dating indicate that the magmatic-hydrothermal event in the potassic-altered Gushan granite occurred at ca. 120 Ma, which is contemporaneous with the Jiaodong gold mineralization. The texture and geochemical compositions of pyrite indicate that pyrite grains hosted by Gushan MMEs are of deuteric hydrothermal origin and precipitated during or shortly after magma mixing. The distribution of elements (i.e., Co, Cu, Ni, Zn, As, Ag, Au, Pb, and Bi) and the sulfur isotope (4.14‰−8.8‰) data for pyrites from Gushan MMEs are quite identical to those of the Xiejia diorite intrusion (DI) and other ores from the Jiaodong gold province, which indicates a common source of these pyrites. The common origin of the pyrites, combined with evidence from previous work, suggest that the ore-forming fluids and materials originated from the metasomatized lithospheric mantle, which was the repository of water, sulfur, and volatiles from the subducted Paleo-Pacific plate, rather than by direct release from the subducted sediments of the Paleo-Pacific plate. Our results collectively show that the arc-like mafic magmas derived from the metasomatized lithospheric mantle at ca. 120 Ma were the intermediary that transported the gold and other ore-forming components from the deep mantle to the shallow crustal levels where gold and ore-related material were injected into the Weideshan granitic suite during magma mixing. Thus, the Weideshan granitic suite may have played a critical role by continuously transferring gold to the shallow crustal faults where it precipitated. Therefore, future research or deep-drilling exploration programs in the area should emphasize the Weideshan granitic suite rather than the Xiejia DI.

Geologic scenario from granitic sheet to Li-rich pegmatite uncovered by Scientific Drilling at the Jiajika lithium deposit in eastern Tibetan Plateau

The Jiajika pegmatite-type lithium deposit emplaced in Upper Triassic turbidites is located in the southeastern Songpan-Ganze terrane of the eastern Tibetan Plateau and is the largest hard-rock lithium deposit in China. The Jiajika Scientific Drilling Project (JSD) consists of the JSD-1 borehole, which is 3211 m deep, and two 1000 m boreholes, JSD-2 and JSD-3. The JSD-1 borehole is composed of the upper pelitic metasediment unit (0–900 m) and the lower are calc-silicate unit (900–3211 m). Pelitic metasediments at the depth of 0–400 m experienced Barrovian-Buchan metamorphism, while metasediments at the depth of 0–900 m were associated with domal deformation (D2). The calc-silicate unit below 900 m only experienced earlier orogenic deformation (D1). The mineralization of Li-Be and Nb-Ta occurs at a depth of 0–1200 m and 0–1800 m, respectively, while the Rb enrichment occurs throughout the whole borehole. Analyses of K-Fe-Ba-B-Li-Rb isotopes suggest that the Jiajika lithium deposit resulted from high-degree fractionation of the parent granitic magma and strong fluid immiscibility. The pegmatites may have crystallized from volatile-rich melts during two-stage magmatic-hydrothermal events at 205–210 Ma and 192–193 Ma. The JSD-1, JSD-2 and JSD-3 indicate that S-type granite related to the Jiajika lithium deposit was emplaced as multi-layer domal sheets, rather than as a deeply rooted pluton. The domal granitic sheets are surrounded by pegmatites and meta-sedimentary rocks. Therefore, we propose a “domal granitic sheet” model to interpret the geologic scenario from granite sheet to Li-rich pegmatite in the Jiajika ore field. The Upper Triassic turbidites in the Songpan-Ganze terrane underwent significant orogenic decollement at ∼ 230 Ma, followed by deep anatexis, basement doming, magma rising and emplacement of granitic sheets. Finally, the rare-metal-rich pegmatites intruded under domal decompression condition, forming a multi-layer architecture intercrossed by the granitic sheets and the meta-sediments.

Timing and origin of skarn-, greisen-, and vein-hosted tin mineralization at Geyer, Erzgebirge (Germany)

AbstractThis contribution presents new insights into the origin and age relationships of the Geyer tin deposit in the Erzgebirge, Germany. Tin mineralization occurs in skarns, greisen, and in cassiterite-bearing fluorite-quartz veins. Skarn alteration replaces marble layers of the Cambrian Jáchymov Group and occurs in two clearly distinct stages. The first skarn stage forms skarnoid textured assemblages of clinopyroxene, garnet, and wollastonite with no tin phases recognized. Garnet U-Pb ages of this skarn stage (~322 Ma) relate the earlier skarn stage to the emplacement of the Ehrenfriedersdorf granite (~324 to 317 Ma). The second stage of skarn alteration is marked by the occurrence of malayaite and cassiterite associated with garnet recording ages of 307 to 301 Ma. Greisen- and skarn-hosted cassiterite-bearing veins provide U-Pb ages in the range of 308 to 305 Ma, relating greisenization and vein formation to the same magmatic-hydrothermal event as the second skarn stage. This suggests that tin mineralization at Geyer is related to a distinctly younger magmatic-hydrothermal event, clearly postdating the Ehrenfriedersdorf granite, which was previously assumed as the source of the tin-rich fluids. Fluid inclusions show salinities in the range of 1.0 to 31.5 % eq. w(NaCl±CaCl2) and homogenization temperatures between 255 and 340 °C. Cassiterite-associated fluid inclusions show indications for heterogeneous entrapment and dilution of hydrothermal with meteoric fluids. Dilution of high-salinity fluids with low-salinity fluids and cooling of the system was probably a decisive process in the precipitation of cassiterite in the Geyer Sn system.

The geochronology of pegmatites in the Jiajika lithium deposit, western Sichuan, China: Implications for multi-stage magmatic-hydrothermal events in the Songpan-Ganze rare metal metallogenic belt

The Songpan-Ganze orogenic belt is a large-scale rare metal metallogenic belt in western China. Several large-scale granitic pegmatite-type lithium deposits are located in the Songpan-Ganze orogenic belt, which include the Jiajika Li deposit, one of the largest pegmatite-type Li deposits in China. The geochronological constraints of pegmatites and granite in Jiajika are still inadequate for revealing the relationships between mineralization and tectonothermal events. In this study, we performed columbite-group minerals (CGM) and cassiterite U–Pb dating on seven different pegmatite veins with different occurrences and deformation styles in the Jiajika deposit. These pegmatites yield CGM U–Pb ages of 213 to 208 Ma and cassiterite U–Pb ages of 199 to 192 Ma, regardless of their occurrences and deformation. Columbite-group minerals exhibit low Ta# (=Ta/(Ta + Nb)) cores and high Ta# rims, which were formed during the magmatic stage and the hydrothermal stage, respectively. The appearance of cassitertite is closely related with greisenization. Therefore, the CGM U–Pb ages, which were obtained from the low Ta# cores of CGM, are interpreted as magmatic crystallization age, while the cassiterite ages reflect another younger stage of magmatic-hydrothermal event. According to field observation, we consider that the occurrences and deformation of pegmatite veins are controlled by the development of various fracture systems formed during the ascent of the granitic pluton. Our results suggest long-lasting multi-stage magmatic-hydrothermal events in the Jiajika region. Geochronological data of other rare metal deposits located in the Songpan-Ganze orogenic belt and the Western Kunlun orogenic belt are comparable with those of the Jiajika Li ore deposit, indicating that the entire Songpan-Ganze rare metal metallogenic belt experienced long-lasting and multiple magmatic and fluid activities. The overlaps of the geochronological results of granites and pegmatites in the Songpan-Ganze rare metal metallogenic belt suggest that regional magmatism is closely related to Li mineralization. The enrichment of Li in the Songpan-Ganze rare metal metallogenic belt is possibly related to its unique geodynamic setting and the long duration of magmatic-hydrothermal activities.

Contrasting Nb-Ta mineralization between the Mufushan and Lianyunshan granites, South China: Evidence from whole-rock and zircon geochemistry and geochronology

The Mufushan (MFS) and Lianyunshan (LYS) granitic complexes are located in northeastern Hunan (South China) and host important Nb-Ta mineralization. Fine-grained muscovite granites (FGMGs) occur as intrusions within the Lengjiaxi Group and show a spatial relationship with the ore-bearing pegmatites. Here, geochemical, geochronological, and isotopic investigations were carried out on the FGMGs of the MFS and LYS complexes to compare their magma sources and metallogenic potential. The MFS and LYS FGMGs are strongly peraluminous (A/CNK > 1.5) and highly fractionated S-type granites. Comparatively, the MFS FGMGs possess more negative Eu (Eu/Eu* = 0.19–0.60), Ba (3.3–360 ppm), Sr (6.2–156 ppm), and Zr (4–26 ppm) anomalies, and more positive Ta (1.1–15.8 ppm) anomalies than the LYS FGMGs, suggesting a stronger magma differentiation. In addition, the zircons from the MFS FGMGs exhibit higher contents of Hf (MFS = 34336 to 60010 ppm, LYS = 6795 to 28937 ppm), Nb (MFS = 16.49 to 401.56 ppm, LYS = 1.12 to 20.22 ppm), Ta (MFS = 33.45 to 138.65 ppm, LYS = 1.11 to 7.19 ppm), Th (MFS = 458 to 3630 ppm, LYS = 11 to 710 ppm), and U (MFS = 8400 to 30100 ppm, LYS = 1285 to 5220 ppm) than those from the LYS FGMGs, suggesting that the MFS FGMGs are more fractionated and their zircons have undergone hydrothermal alteration. Zircon U-Pb dating yielded concordant ages of 140.6 ± 0.5 Ma and 139.9 ± 0.7 Ma for the MFS and LYS FGMGs, respectively, implying an Early Cretaceous magmatic-hydrothermal event. Moreover, the geochemical and isotopic (whole-rock Sm-Nd and zircon Lu-Hf) compositions show younger sources for the MFS FGMGs compared to the LYS FGMGs, which were derived from the partial melting of Paleoproterozoic basement rocks with clay-rich material in a post-collision extensional setting. Our results, combined with previous studies, indicate that the studied FGMGs are the parental rocks of extensive Nb-Ta mineralization, and the highly fractionated MFS FGMGs are more conducive to hosting Nb-Ta mineralization than the LYS FGMGs. The strongly peraluminous and highly-fractionated S-type FGMGs can be used as good targets for further exploration of Nb-Ta deposits in South China and elsewhere.

Metallogeny of the Xiaotongjiapuzi gold deposit, Liaodong Peninsula (Eastern China): Perspective from sulfide trace element geochemistry and sulfur isotopes

Most gold ores have variable sulfur isotopic and trace elemental compositions at micro-/nano-scale, which makes the understanding of the gold formation process more challenging. The advancement of in-situ analytical techniques offer opportunity to gain insight into gold mineralization processes and ore-material source. The Xiaotongjiapuzi is a representative intrusion-related gold deposit in the Qingchengzi orefield of the Liaodong Peninsula, Eastern China. Alteration and gold mineralization comprise four stages: (I) quartz-pyrite-Au, (II) quartz-pyrite-biotite-Au, (III) Au-barren quartz-pyrite, and (IV) post-ore quartz-calcite. Detailed scanning electron microscope (SEM) backscattered electron (BSE) imaging, electron probe microanalysis (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) elemental and LA–multi-collector (MC)–ICP–MS sulfur isotope analyses were conducted to reveal the ore-material source and mineralization process. Three texturally distinct auriferous pyrite generations were identified: Py1 and Py2 (in both stage I and II) and Py3 (in stage II and III). Py1 is porous and weakly fragmented, poorly crystallized, and overgrown by Py2. Py2 is commonly intergrown with arsenopyrite and marcasite, whilst Py3 overgrew around Py2 or replace it.Gold exists mainly as solid solution (Au+) in the pyrite lattice and nanoparticles (Au0), as well as (rare) micron-scale inclusions along the Py2-Py3 interface. Py2 has the highest gold content (mean 47 ppm, max 344 ppm), especially when intergrown with marcasite (Mrc1). The δ34S values of pyrite (5.71–15.31‰, n = 18) and marcasite (-19.59 to 7.45‰. n = 6) are the highest and lowest, respectively, and the values increase steadily from Py1 to Py3 (Py1: 5.71–7.54‰ → Py2: 7.44–9.55‰ → Py2 + Mrc1: 12.88–13.92‰ → Py3: 15.17–15.31‰). The Paleoproterozoic Dashiqiao and Gaixian formation host rocks contain large amount of sulfate minerals (e.g., barite and gypsum), and the coeval global sulfate has heavy sulfur isotope enrichment, suggesting that sulfate reduction may have provided H2S-rich fluids [Au(HS)2- and/or Au(HS)0] for the Mesozoic mineralization. For the multistage gold enrichment at Xiaotongjiapuzi, we suggest that the Paleoproterozoic sedimentary and metamorphic rocks may have formed the initial sulfur reservoir, which was then reactivated by Mesozoic magmatic-hydrothermal events.

Genesis of Makeng-type Fe-polymetallic deposits in SE China: New constraints by geochronological and isotopic data from the Dapai–Makeng metallogenic system

The southwestern Fujian depression belt (SFDB) is an economically important Mesozoic Fe metallogenic belt in South China and is renowned for its Makeng-type Fe deposits, in which stratified skarn Fe orebodies generally occur in or near the contact zone between late Paleozoic carbonate sequences and Mesozoic granites. However, the genesis and geodynamic setting of these deposits remain unclear because the characteristics of the widely distributed Pb–Zn–Cu and Mo orebodies in these deposits and the temporal, spatial, and genetic relationships between magmatism and mineralization are poorly defined. The Dapai Fe polymetallic deposit in the SFDB is a typical example of Makeng-type Fe deposits but also has regional significance, whereby the stratified skarn Fe orebodies have overprinted the stratabound Pb–Zn–Cu mineralization followed by final fissure-filling by vein-disseminated Mo mineralization. A detailed geological investigation suggests that episodic magmatic–hydrothermal events were involved in the formation process of the Dapai Fe polymetallic deposit.Pyrite and sphalerite from the Pb–Zn–Cu orebodies yield an Rb–Sr isochron age of 175.5 ± 3.3 Ma, which is regarded as the timing of Pb–Zn–Cu mineralization. Zircon grains from Fe-mineralized granodiorite porphyry and Mo-mineralized monzogranite yield weighted-mean 206Pb/238U ages of 146.3 ± 0.9 Ma and 131.7 ± 0.4 Ma, interpreted as the timings of Fe and Mo mineralization, respectively. Six zircons from granodiorite also yield a 206Pb/238U model age cluster of ∼184 Ma, which coincides reasonably with the timing of Pb–Zn–Cu mineralization and implies the existence of an unidentified ore-related intrusion in the Dapai deposit. Five further zircons from the porphyritic granodiorite yield an age cluster of ∼150 Ma, consistent with the timing of Fe mineralization. Galena, pyrite, and sphalerite from the Dapai and Makeng deposits have similar S–Pb isotopic compositions and suggest a magmatic source. Combining our results with published isotopic data for the SFDB, we suggest that the Pb–Zn–Cu mineralization in this area was derived from crustal magmas that mixed with mantle-derived magma prior to emplacement. The δ56Fe and δ57Fe values of magnetite from Dapai and Makeng are both slightly lower than those of the ore-related granites, suggesting that Fe in the initial fluid in both deposits was derived mainly from coeval granitic rocks. The Fe isotopic variation between intrusions and skarn Fe orebodies is interpreted as resulting from mass fractionation that occurred during fluid exsolution from melt. Contents of Re in molybdenite from published data for the SFDB indicate crust–mantle mixed sources of Mo and Re. The Makeng-type Fe polymetallic deposits formed as a result of three magmatic–hydrothermal episodes, generating Pb–Zn–Cu mineralization at 185–160 Ma, Fe–Mo mineralization at 150–140 Ma, and Mo–Fe mineralization at 135–130 Ma. The different metal associations formed during multiple stages of magmatism caused by ongoing subduction and rollback and/or retreat of the paleo-Pacific Plate.

REE mineralization age and geodynamic setting of the Huanglongpu deposit in the East Qinling orogen, China: Evidence from mineralogy, U–Pb geochronology, and in-situ Nd isotope

The Huanglongpu deposit is one of the most representative igneous carbonatite-type molybdenum-rare earth element (Mo-REE) deposits in the eastern Qinling metallogenic region. The molybdenum resources exceed 180 kt, whilst the total rare earth resources are about 37.8 kt. However, the age of REE mineralization, sources of ore-forming minerals, and tectonic setting are not well characterized. Therefore, this study carried out detailed mineralogical, geochronological, and geochemical analyses to provide new insights. Monazite, bastnäsite, parisite, and xenotime were found to be the dominant REE-bearing minerals in the Huanglongpu deposit. LA-ICP-MS U-Pb dating of the REE minerals revealed a two-stage REE mineralization: monazite formed at 219.4 Ma, whereas bastnäsite and xenotime formed at 145.9 Ma and 142.6 Ma, respectively. The carbonatites, as the main ore host, were characterized by a strong enrichment of light rare earth element (LREE) and moderately high heavy rare earth element (HREE) contents. Monazite showed different Nd isotopic compositions, with lower εNd(t) values ranging between −7.12 and −4.18, while the εNd(t) values of bastnäsite and xenotime ranged from −9.57 to −6.49 and from −11.13 to −6.28, respectively. These contrasting geochemical and isotopic signatures suggest that the Huanglongpu REE mineralization occurred over multiple magmatic-hydrothermal events and that the ore-forming material was unlikely to have stemmed from a single enriched mantle (EMI) source. The early REE mineralization stage (219.4 Ma) was closely associated with carbonatite-related Mo mineralization, both of which were products of magmatic mineralization during the crystallization of the host carbonatite emplaced in an extensional environment after the Late Triassic collision. The ore-related magmas may have originated from a hybrid source composed of EMI and partial melting of the lower crust. In contrast, due to the extensive Yanshanian magmatism which could provide massive heat, the later REE mineralization stage (145.9–142.6 Ma) in the Huanglongpu deposit was likely driven by the reactivation and recrystallization of early-formed REE minerals within the host carbonatites, hence representing a hydrothermal redistribution of the primary magmatic ore.

Paleoproterozoic gold deposits at Alta Floresta Mineral Province, Brazil: two overprinted mineralizing events?

Abstract Large gold provinces commonly show complicated mineralization histories, and the Paleoproterozoic Alta Floresta, one of Brazil's most exciting Au–Cu mineral provinces, is a good example. The current models defined four deposit types, all connected to a single (1.88–1.75 Ga) magmatic–hydrothermal event. However, long Province history, diverse geodynamic environment and older ages of Type-1mineralization weaken the single metallogenic event and enable the hypothesis of overprinted mineral events. By scale-integrated analyses, we revise the tectonic–geological context, structural–hydrothermal alterations and chlorite–white mica geothermobarometry and propose the Type-1 as an older, granitoid-hosted orogenic mineralization, with subsequent overprinting by the magmatic–hydrothermal event. The older orogenic gold event developed orogenic gold deposits on WNW-trending shear zones in the Peixoto de Azevedo domain granitic–gneiss rocks. Phengite, biotite and chlorite–carbonate phyllonites (3.3–6.1 kbar, 300–420°C) host fault-fill quartz veins (pyrite–chalcopyrite–magnetite–pyrrhotite–gold–Bi–Ag tellurides). Mg-rich chlorite–phengite is the main alteration footprint for this mineralization type. A younger magmatic–hydrothermal event in the Juruena magmatic-arc rocks produced Fe-rich chlorite–white mica alteration zones (0.6–4.6 kbar, 120–380°C) and disseminated and stockwork–breccia ore (pyrite–chalcopyrite–gold–molybdenite–Ti minerals–allanite) in porphyry–epithermal deposits. Where the younger mineralization overprints the older, phyllic alteration destroyed the phengite orogenic gold phyllonite S n +1 foliation. The ages of two pyrite populations (1979 and 1841 Ma) in the older fault-fill veins and molybdenite in late fractures (1805–1782 Ma) or disseminated in the c. 1.79 Ga syenogranite porphyry suggest more than two episodes of mineralization. These two events differ in their alteration styles, P–T conditions and structural, mineralogical and textural ore styles. The multiscale approach sheds light on the relationships between the various mineralization events, allowing a new explorational potential within the province. Supplementary material: Chlorite and white mica complete chemical composition data and other characteristics of the studied deposits are available at https://doi.org/10.6084/m9.figshare.c.6056324

Hydrothermal injection breccia with organic carbon and nitrogen in the fossil hydrothermal system of Harghita Bãi, East Carpathians, Romania: an example of magmatic and non-magmatic element mobility in the upper continental crust

AbstractOrganic carbon and nitrogen fixed in illite (I) clays were identified in a hydrothermal breccia structure from the Harghita Bãi area of the Neogene volcanism of the East Carpathians. The potassium-illite (K-I) alteration related to an early magmatic-hydrothermal event (9.5 ± 0.5 Ma) was later replaced by ammonium-illite (NH4-I) (6.2 ± 0.6 Ma) owing to circulation of an organic-rich fluid. Several textural evolutions of breccia structures were recognized, such as ‘shingle’, ‘jigsaw’, ‘crackle’ and hydraulic in situ fractures. The high-field-strength element behaviours of the K-I and NH4-I argillic altered andesite are close to chondritic ratios, indicating no contribution of hydrothermal fluid, especially on NH4-I andesite alteration and the CHArge-and-RAdius-Controlled (CHARAC) behaviour within silicate melts. The rare earth element normalized patterns show two distinct trends, one with a Eu* anomaly (K-I) and the other with a Nd* anomaly (NH4-I), indicating a boundary exchange with the organic-rich fluid. The strongly depleted δ13C (V-PDB) measured for the NH4-I clays reflects values (−24.39 to −26.67 ‰) close to CH4 thermogenic oxidation, whereas the δ15N (‰) from 4.8 to 14.8 (± 0.6) confirmed that the N2 originated from post-mature sedimentary organic matter. The last volcanism (6.3 to 3.9 ± 0.6 Ma) and simultaneous volcano-induced tectonics in the proximity of the eastern Transylvanian basin basement increased the heat flow, generating lateral salt extrusion, diapirism and increased pressure in the gas reservoir. New pathways were opened that provided new circulation routes for basinal fluids to new and old permeable zones and expelled seeps from the biogenic petroleum system.

Multiple skarn generations related to composite leucogranites in the Cuonadong Sn-W-Be deposit, Himalaya

The newly discovered Cuonadong Sn-W-Be skarn deposit is related to fractionated leucogranitic intrusions hosted in the Cenozoic Himalayan gneiss dome, Tibet, however, temporal and genetic relationships between composite magmatism, skarn and mineralization remain unclear. Based on age and compositional features, three types of titanite were identified: Ttn1 and Ttn2 in the diopside-dominated skarn and adjacent greisenized granitic dike, and Ttn3 (subdivided into Ttn3a and 3b) in the Sn-mineralized garnet skarn. Ttn1 has a higher Ti content and yielded a U-Pb age of ∼35 Ma, consistent with the U-Pb ages of monazite from the pegmatitic granite (35.0 ± 0.6 Ma). Younger, recrystallized Ttn2 (∼28–27 Ma) is characterized by higher Al, F, Ta, Nb, Sn and Y contents and was likely formed by interaction between early Ttn1 and late fluids as indicated by the monazite U-Pb age of two-mica granite (28.8 ± 0.3 Ma). These two types of hydrothermal titanite are confined to the Oligocene unmineralized skarn and adjacent greisenized granitic dike.Titanite from the garnet-bearing Sn-mineralized skarn (Ttn3) provides the age of mineralization (16.8 ± 1.6 Ma), slightly younger than the emplacement age of the Miocene granite (monazite U-Pb age: 19.9 ± 0.3 Ma and columbite: 19.0 ± 0.4 Ma). The Sn-rich Ttn3b coexisting with garnet and interstitial cassiterite shows a deficit of Y and HREE and a high (Dy)N/(Yb)N ratio, implying that hydrothermal Sn metasomatism of Ttn3 occurred after garnet crystallization. Overall, our results shows that the Cuonadong multigenerational skarns were generated during three episodic magmatic-hydrothermal events, and mineralization occurred in the Miocene.

Discrete late Jurassic Sn mineralizing events in the Xianghualing Ore District, South China: Constraints from cassiterite and garnet U-Pb geochronology

Abstract Numerous skarn-type Sn deposits have been identified in the Nanling Range (South China), of which the Shizhuyuan W-Sn-Bi-Mo, Xianghualing Sn, Jinchuantang Sn-Bi, and Hehuaping Sn deposits are the largest. The Xianghualing deposit, which is the focus of this study, hosts a resource of 0.17 Mt Sn grading 0.93–1.39 wt% SnO2. Whether the distal skarn-type mineralization and the cassiteritesulfide vein-type orebody in the Xianghualing district are genetically related to the Laiziling granitic pluton, which produced the proximal skarn-type Sn mineralization, however, is still unknown. The Xianghualing Sn mineralization occurs exclusively as cassiterite and has been subdivided into four ore-types: (1) lenticular proximal skarn ore (Cst I) containing the mineral assemblage cassiteritepyrrhotite-chalcopyrite-actinolite-wollastonite; (2) layered distal skarn ore (Cst II) containing the mineral assemblage cassiterite-pyrrhotite-chalcopyrite-actinolite; (3) vein cassiterite-sulfide ore (Cst III) distal from the skarn and associated granite containing the mineral assemblage cassiterite-arsenopyrite-pyrrhotite-muscovite-fluorite; and (4) veinlet Sn-Pb-Zn ore (Cst IV) distal from the skarn and associated granite containing the mineral assemblage cassiterite-galena-sphalerite-topaz-quartz. Here, we report the results of in situ laser ablation inductively coupled plasma mass spectrometric (LA-ICPMS) U-Pb age determinations for garnet from the Xianghualing skarn and the above four types of cassiterite. Our age determinations indicate that there were two independent magmatic-hydrothermal events at ~160 and 156~150 Ma, both of which led to Sn mineralization. The first Sn mineralization event at ~160 Ma (Cst IV U-Pb ages of 159.6 ± 1.4 to 158.5 ± 0.8 Ma) is interpreted to have been associated with a speculative unexposed granitic pluton, which is coeval with the nearby Jianfengling granite intrusion. The second Sn mineralization event at 156~150 Ma (Cst I to Cst III U-Pb ages of 155.9 ± 0.7 to 152.3 ± 1.1 Ma and garnet U-Pb ages of 153.6 ± 7.6 to 151.5 ± 3.5 Ma) is genetically related to the adjacent Laiziling granitic intrusion (152.8 ± 1.2 Ma, zircon U-Pb age). This event was responsible for the bulk of the Sn resource (>95%). Our age determinations provide convincing evidence for superimposed Jurassic Sn mineralizing systems at Xianghualing. They also show the value of combining garnet and cassiterite U-Pb age determinations to constrain the timing of skarn and Sn mineralization and distinguish discrete Sn mineralizing events in a protracted metallogenic history.

Tectonic-magmatic setting for Early Cretaceous low-sulfidation epithermal gold deposits in the Xing–Meng Orogenic Belt: Constraints from zircon U–Pb and Hf isotopic data of wulaga deposit, NE China

The Xing–Meng Orogenic Belt hosts an amount of low-sulfidation epithermal gold deposits. However, the tectonic-magmatic setting remains problematic, which hinders understanding the factors that control the gold endowment in the region. Wulaga deposit is the largest low-sulfidation epithermal gold deposit in the northeastern Xing–Meng Orogenic Belt. Gold mineralization occurs in the crypto-explosive breccia zone of subvolcanic granodiorite porphyry. Zircon U–Pb ages of three granodiorite apophyses and previous pyrite Rb–Sr dating (113.8 ± 4.4 Ma) indicate granodiorite porphyry and gold mineralization was coeval. The ore-related granodiorite porphyry is moderate SiO2, high-K calc-alkaline, and metaluminous, suggesting an I-type granite. Moreover, Wulaga granodiorite porphyry displays low initial 87Sr/86Sr ratios and positive εNd(t) values with TDM2(Nd) of 799.7–897.4 Ma and εHf(t) values with TDM2(Hf) of 652–785 Ma, indicating that it was derived from partial melting of the Neoproterozoic juvenile mafic lower crust. Ti-in-zircon thermometry, medium–high Sr/Y ratio, high Ba/La, and fO2 value indicate that Wulaga granodiorite porphyry formed at relatively low temperatures (∼700 °C), rich water, and high fugacity within the stability field of garnet in the juvenile lower crust. Combined with ore-related tectonic-magmatic activities in the Wulaga, Dong'an, and Sandaowanzi gold deposits, the Early Cretaceous low-sulfidation epithermal gold deposits in the Xing–Meng Orogenic Belt were formed from magmatic-hydrothermal events triggered by mutual interaction between post-orogenic lithospheric extension related to the closure of the Mongol-Okhotsk Ocean and arc-back extension associated with rollback of the Paleo-Pacific Ocean plate. These data indicate the potential existence of the Early Cretaceous epithermal gold deposits that are related to the contemporaneous igneous activity.

The role of crystal mush in porphyry systems: A case study from the Baishiya ore field, East Kunlun orogenic belt, northern Qinghai-Tibet plateau

Since a cold storage crystal mush reservoir has been gradually used to describe magmas in shallow crust, traditional mechanisms, such as wall-rock assimilation, melt-crystal separation, as well as magma mixing and mingling, must be used with caution because recycled antecrysts can play a significant role. As a result, magmatic processes accounted for texture, geochemistry, and mineralization diversity among ore-related porphyry, overlying (sub)volcanic rocks, and underlying pluton in porphyry systems remain ambiguous. The Baishiya igneous suite (East Kunlun orogenic belt, China) with porphyry-related skarn mineralization provides an opportunity to resolve this issue. Within the crystal mush concept, we propose a comprehensive model based on the subtle changes. First and foremost, large K-feldspar grains characterized by high Sr/Y ratios (52–134) in the top area of granodiorite have a slightly enriched lead isotopic signature, indicating a previously existed crystal mush equilibrated with K-feldspar. The locked crystal mush was injected by mantle-derived mafic melts, leading to a transfer in heat and volatiles from hot melts to cold crystal mush. The buoyant volatiles and loaded metals introduced by episodic mafic replenishments concentrated on the roof, providing a fluid-rich and thermal cycling condition for K-feldspar coarse graining. Some enlarged K-feldspar grains sunk into the bottom area due to gravity, and subsequently reacted with upwelling hot melts to form rapakivi textures. As a gradually waning of injection of mafic melts, crystallization drove fluid exsolution, forming magmatic-hydrothermal events. The finally solidified granodiorite acted as a host rock for a newly produced magma reservoir, but the following development was different. Catastrophic eruptions induced by tectonic stress transition led to a strong depletion of volatiles and associated metal endowment in the underlying magma reservoir, and subsequently left a barren magma source, terminating potential mineralization events. The residual felsic melts migrated upwards along previously formed magma conduits, and thus emplaced as barren porphyry dike. Our work reveals that recycling of K-feldspar antecryst induced by mafic injection contributes to high Sr/Y ratio in ore-related porphyritic granodiorite. Within a long-lived replenishment of mantle-derived magma, a crystal mush reservoir at shallow crustal levels can act as a ‘cooling pond’ to quench these hot melts, but accept volatiles and loaded ore-forming elements, concentrating metals by volatile buoyancy with the help of a compressional stress, which is presumably essential for late fluid exsolution from the reservoir’s roof.