Miarolitic cavities (MCs) serve as key indicators of volatile phase exsolution during magmatic differentiation, providing critical insights into the transition between igneous and hydrothermal regimes. Despite their metallogenic significance, the mechanisms controlling the selective extraction of metal-bearing fluids remain poorly understood. This study investigates the microstructural and geochemical characteristics of chalcopyrite- and molybdenite-dominated MCs in the Hongyuan porphyry Mo-Cu deposit (NW China). The cavities exhibit sulfide cores surrounded by graphic quartz-feldspar, aplitic, and K-alteration halos. Mass balance calculations reveal enrichments in Cu, Fe, Na, and Si during the magmatic-hydrothermal transition. The term "sulfide-silicate bulb" refers to silica-saturated fluid pockets or bubbles that develop during hypogene copper mineralization in porphyry deposits. The central sulfide-silicate bulbs represent hypersolidus mineral assemblages, with differential Cu-Mo precipitation linked to quartz growth rates. Late-stage meteoric water alteration further influences metal precipitation. We propose a genetic model wherein sulfide-silicate bulbs act as the primary vehicles for the extraction, transport, and focused precipitation of Cu- and Mo-rich fluids. Our results highlight the critical role of quartz growth rates and meteoric fluid influx in controlling metal segregation, providing a new framework for understanding the spatial zonation in porphyry Cu-Mo systems.
ABSTRACT The Sandu–Danzhai Au‐Hg‐Sb metallogenic belt is an essential constituent of the giant Mesozoic low‐temperature metallogenic domain of the South China Craton. Although many sediment‐hosted Au‐Hg‐Sb deposits have been discovered in this belt over decades, possible sources of ore‐forming elements (e.g., Au‐As‐S) and fluids remain controversial. This study presents chemical compositions and S isotopes of pyrites and C‐O isotopes of calcites collected from the Miaolong deposit in the central belt. Based on their petrographic features and Au‐As compositions, three generations of pyrites are classified in the deposit: syngenetic/diagenetic Py1, pre‐ore Py2, and ore Py3. From Py1 (As < 0.1%) to Py3 (As > 1%), the As, Au, and Cu concentrations increase gradually. This increase is greatest for As, indicating that As may be critical in the enrichment of Au and other trace elements. Au occurs in the form of lattice‐bound Au + , and the low Au/As ratios of the pyrite (< 1:100) indicate that the ore fluids are undersaturated in Au. Moreover, in situ S isotope analyses show that Py1 exhibits the largest variation in δ 34 S values (−21.65‰ to 34.97‰), consistent with a sedimentary origin. In contrast, Py2 and Py3 share similar and relatively homogeneous δ 34 S values (Py2 = 19.46‰–26.28‰, Py3 = 20.94‰–24.81‰). These positive δ 34 S values support an abiotic thermochemical sulfate reduction (TSR) of marine sulfate. As inferred from their C‐O isotopes (δ 18 O V‐SMOW = 15.11‰–24.43‰, δ 13 C V‐PDB = −3.95‰ to −1.52‰), the late‐ore calcite veins are likely derived from the dissolution and recrystallization of Cambrian marine limestone. In summary, a metamorphic model is proposed for Au mineralization in the Miaolong deposit, in which deep‐sourced metamorphic fluids from the Precambrian basement are essential in Au remobilization and deposition.
Myanmar hosts a rich diversity of ore deposits, ranging from numerous artisanal operations to several world-class mines. One of the important gold deposits is the Phayaung Taung mine, located in the northeastern part of the Mandalay region, central Myanmar. This gold deposit is hosted in the interbedded layers of quartzite and phyllite units of the Late Proterozoic Chaung Magyi Group in the Mergui Belt. Although the occurrence, geological setting, and ore mineralogy of the deposit have been previously studied, detailed Raman spectroscopy-based fluid inclusion investigations have not yet been conducted. Here, we present the results of the Raman analysis of CO2 bearing fluid inclusions and the pressure-depth relationships using the density and temperature range of the CO2 fluid inclusions. Raman analysis indicates a very minimum water content inside the bubbles in CO2 bearing fluid inclusions with density ranging from 288.82 to 969.68 kg/m3. Nitrogen (N2) is present only in trace amounts in the analyzed inclusions. The latest recrystallization entrapment pressures of CO2 bearing fluid inclusions were estimated at 7 MPa (approximate to 0.26 km) for low-density inclusions and 34 MPa (approximate to 1.28 km) for high-density inclusions. The low-pressure inclusions are interpreted to record uplift and deformation events associated with the Mergui Belt. This research classifies the Phayaung Taung deposit in the Mergui Belt as a mesozonal, structurally emplaced orogenic gold deposit, providing insights into its geological characteristics and formation processes.
Efficient manganese (Mn) removal from acidic mine drainage (AMD) is challenging due to its high solubility and slow oxidation kinetics. We investigate a mechanism that enables the efficient removal of Mn in a sand filter at an operational AMD treatment facility, with particular emphasis on naturally formed Mn oxides on sand grain surfaces (Mn-precipitated sand; MPS). Characterization of the filter media using x-ray fluorescence, x-ray diffraction, scanning electron microscopy, and transmission electron microscopy identified a coating of poorly crystalline birnessite (delta-MnO2) that formed in situ on the MPS and is absent on unprecipitated sand (UNS). X-ray absorption near-edge structure spectroscopy confirmed that this coating is composed mainly of tetravalent Mn(IV). Batch experiments simulating filtration conditions were performed to compare Mn removal kinetics using MPS, UNS, and commercial Mn oxide powder from thickener mine water and pure water with 2 mg/L dissolved Mn2+. The MPS removed > 99% of the dissolved Mn within 3 h from both mine and pure water, whereas UNS only removed some Mn (< 20% after 96 h). Microbial inhibition tests using UV-irradiated and ampicillin-treated MPS in pure water confirmed that this rapid Mn removal was dominated by abiotic physicochemical processes. This abiotic, autocatalytic oxidation mechanism proved effective even at a neutral pH, achieving > 96% removal. These findings reveal that Mn removal is driven by abiotic autocatalysis on a naturally formed, Mn(IV)-rich birnessite coating. The high efficiency of this process at a neutral pH presents a significant opportunity to optimize AMD treatment by lowering operational pH and reducing chemical consumption and sludge production for a more sustainable remediation strategy.
Fe-Cu skarns of the Loei Fold Belt have been poorly investigated in terms of lead isotopic signatures. We report the first MC-ICP-MS dataset from the belt, based on 15 ore samples from the Khao Thap Kwai deposit (Lop Buri, Thailand). Ores signatures display internally coherent yet dispersed signatures (206Pb/204Pb = 17.794-18.335, 207Pb/204Pb = 15.495-15.601, and 208Pb/204Pb = 37.628-38.256). The data plot between mantle and upper-crust evolutionary fields and overlaps the orogenic growth curve; binary mixing between hydrous mantle-derived arc melts and upper-crustal reservoirs provides a parsimonious explanation. Regionally, Khao Thap Kwai field partly overlaps the Chatree epithermal system but shows distinctly lower 208Pb/204Pb ratios, whereas ore deposits of the Truong Son Belt are more radiogenic, highlighting the utility of Pb isotopes for discriminating metallogenic provinces in western Indochina.
The Hu'u volcano is an eroded, medium K calc-alkaline basaltic andesite strato-volcano 15 km in diameter with a maximum elevation of about 850 m, with a central caldera about 6 km in diameter. Intra-caldera andesitic ash flow over 300 m thick fills the caldera and overlies older basaltic andesite to andesite flows and breccia. Overlying the ash flow tuff is fine laminar bedded tuff with accretionary lapilli, up to 50 m thick, formed in the caldera volcanic lake. This sequence is overlain by a relatively coarse crystal-crowded hornblende andesite-dacite dome 5.6 & times; 3.5 km in area, maximum thickness of 530 m, of low K calc-alkaline composition. This dome overlies and is likely co-magmatic with the Onto porphyry, which was intruded to near the base of the dome. The Onto porphyry system was formed at < 0.5 Ma and is remarkable for very deep overprinting by advanced argillic alteration that formed essentially together with high temperature porphyry alteration. The ore body comprises mainly gold-pyrite-covellite and minor enargite. From below the Onto dome the lithocap extends vertically over 1.8 km and is mushroom-shaped, centered directly on a composite porphyritic micro quartz diorite to granodiorite stock about 1.4 km in diameter. The upper part of the lithocap exhibits a maximum outflow of 2.5 km SE from the center of Onto. The lithocap exhibits a vertical zonation from (1) residual quartz-dickite-kaolinite, (2) alunite with minor pyrophyllite, (3) alunite-pyrophyllite-diaspore-zunyite, with pyrophyllite increasing relative to alunite with depth, and (4) andalusite-diaspore-anhydrite, with minor pyrophyllite-alunite, starting from 1400 m from below the top of the lithocap. At moderate to deep level the advanced argillic zone is enclosed by paragonite-albite-chlorite-high Al-smectite (beidellite), followed outward by epidote-chlorite. At deepest drilled levels, fluid inclusions are vapor-rich and multiphase, typical for porphyry systems. They are hosted by quartz-andalusite-diaspore, which is cut by narrow (cm) pyrite-enargite feeder veins, with pyrophyllite selvages.
The Gudang Handak vein group of the Pongkor epithermal Au-Ag deposit in West Java comprises eight quartz-calcite veins that are hosted by volcanic rocks of the Bayah Dome Complex. This study aims to elucidate the mineralogical and geochemical characteristics of the GH-B and GH-C veins of the Gudang Handak vein group. Studied parts of the GH-B vein and the GH-C vein have Au grade from 0.31 to 56.0 g/t (ave. 9.67 g/t Au) and Ag grade from 0.02 to 655 g/t Ag (ave. 133 g/t Ag), and Au grade from 0.27 to 22.7 g/t (ave. 6.49 g/t) and Ag grade from 0.02 to 455 g/t (ave. 94.9 g/t), respectively. The major gangue minerals are quartz and calcite with local adularia. Quartz occurs with granular, zonal, comb, pseudo-bladed, pseudo-acicular, microcrystalline, mosaic, ghost-sphere, flamboyant, and feathery textures or forms. Calcite occurs as bladed, acicular, and granular forms. Adularia occurs as rhombic and sub-rhombic forms. Ore minerals include electrum, acanthite-aguilarite-naumannite solid solution, sphalerite, pyrite, pyrargyrite, chalcopyrite, and polybasite, and are hosted by the microcrystalline quartz and mosaic quartz, granular calcite, and rhombic adularia. The microcrystalline quartz associated with the ore minerals in both the GH-B and GH-C veins exhibits short-lived blue cathodoluminescence with a spectral peak at 380-390 nm. This CL characteristic is attributed to Al3+, where a couple substitution of Si4+ by Al3+ and Na+ is organized in addition to excess Al. Quartz in the veins with relatively high Au grade tends to have elevated Al, Na, K, and Rb contents, where the Al and Na contents demonstrate the most continuous positive correlation to the Au grade of the veins. The microthermometry of the fluid inclusions in quartz, calcite, and adularia revealed the formation temperatures of 190 degrees C-220 degrees C and salinities of 0.1-3.5 wt% NaCl eq. A part of the GH-B vein at 435 masl was formed by a boiling fluid at about 210 degrees C-220 degrees C or a little higher than that, and at depth estimated to be ca. 200-215 m below the paleo-water table. The other studied portions of the GH-B vein at 450 masl and 460 masl and the GH-C vein at 490 masl were plotted close to the boiling curve. One of the principal mechanisms of the gold deposition in the Gudang Handak vein group was likely the fluid boiling. The electrum tarnish method indicates log fS2 (in atm) ranging from -11.6 to -13.8 and -12.3 to -13.6 for the GH-B vein at 450 masl and the GH-C vein at 490 masl, respectively, and log fSe2 (in atm) ranging from -16.7 to -14.7 for the GH-B vein. The presence of aguilarite-naumannite solid-solution suggests that the Gudang Handak vein group at 435-490 masl formed under relatively higher fO2 conditions compared to those of other parts of the deposit.
The Akatani Fe deposit in the Ashio Belt, northern Japan, has been regarded as an iron skarn deposit which consists of iron-oxides in the skarn bodies in marble lenses near the Cretaceous Ninoujidake granite. The major ore mineral in this deposit is hematite, which is uncommon in typical Fe skarn deposits. Some of the orebodies are hosted by Miocene rhyolitic lavas and intrusions. The rhyolite intrusion complicates the understanding of the overall skarn deposit formation. We examined the formation model of the Akatani iron deposit through fieldwork, petrographic observations, apatite U-Pb geochronology, and mineralogical studies of the igneous rocks, skarn minerals, and iron oxides present in the deposit. The skarn mineralization at Akatani is classified into (1) early prograde stage represented by wollastonite, (2) early to late prograde stage represented by garnet and pyroxene, (3) early retrograde stage represented by hydrous skarn minerals represented by tremolite and/or actinolite, and (4) late retrograde stage represented by chlorite. Garnet shows the andradite-rich chemical composition and the zoning by a slight enrichment of grossular component, sometimes including a spessartine component. The hematite orebodies are classified into two main categories based on the petrographic occurrence and mineral assemblage: magnetized hematite (mushketovite)-bearing ores in the skarn zone and magnetite-free ores. Fluorapatites occurring in the magnetized hematite-bearing ores were used for U-Pb dating. These fluorapatites show euhedral to subhedral forms and occur within andradite coexisting with mushketovite, within tremolite formed by the alteration of clinopyroxene that coexists with andradite, or within mushketovite. The fluorapatites yielded U-Pb ages of 100 +/- 23 Ma (n = 3, MSWD = 1.2). This age is consistent with that of the Ninoujidake Granite. This geochronological evidence indicates that at least part of the hematite orebodies in the Akatani deposit formed during the Late Cretaceous. The petrological and geochronological studies suggests that hematite mineralization of the deposit resulted from multiple hydrothermal activities with early hematite formation during the prograde-retrograde skarn stage in the Late Cretaceous. Crystalline temperatures of graphite are calculated from carbonaceous material based on the geothermometer. The scarcity of reactive carbon in the host marble and hornfels may have prohibited the reduction of the hydrothermal fluids, resulting in hematite mineralization in the deposit. This study shows that the hematite orebodies at Akatani is composed by multiple mineralization stages at skarn mineralization, all of which are related to Fe skarn minerals formed by the oxidized hydrothermal fluids from the Cretaceous Ninoujidake granite.
The Lugiin Gol deposit is one of four REE deposits (Khalzan Burged, Mushigai Khudag, and Khotor) in Mongolia. It consists of a nepheline syenite stock, equivalent dike rocks, and more than 400 carbonatite veins within an area of approximately 13 km(2). This study focuses mainly on the western part of the Lugiin Gol deposit. The western Lugiin Gol deposit consists of many carbonatites that fill NE-trending fractures in sedimentary rock. The minerals in the carbonatites include calcite, dolomite, strontianite, kutnohorite, ankerite, fluorite, synchysite-(Ce), bastnaesite-(Ce), parisite-(Ce), synchysite-bastnaesite intergrowths, rutile, apatite, goyazite, quartz, K-feldspar, muscovite, chlorite, Al-Si mineral, Na-Si mineral, pyrite, sphalerite, chalcopyrite, galena, Fe hydroxide, and graphite. Synchysite-(Ce), bastnaesite-(Ce), parisite-(Ce), and synchysite-bastnaesite intergrowths are REE fluorocarbonates. Synchysite-(Ce), the most abundant REE fluorocarbonate, occurs as disseminated euhedral crystals in carbonates, Fe hydroxide, and K-feldspar. It is LREE-dominant, with La/Ce ratios ranging from 0.47 to 0.84, and its LREE abundance decreases in the order Ce > La > Nd > Gd > Sm > Eu. Bastnasesite-(Ce), the second most abundant REE fluorocarbonate, occurs as granular crystals closely intergrown with synchysite-(Ce). It is also LREE-dominant, with La/Ce ratios ranging from 0.68 to 0.91, and LREE abundances in the order Ce > La > Nd > Gd > Eu > Sm. Parisite-(Ce), the third most abundant REE fluorocarbonate, occurs as anhedral or granular crystals that are closely intergrown with or replaced by synchysite-(Ce). It is LREE-dominant, with La/Ce ratios ranging from 0.38 to 0.61, and LREE abundances in the order Ce > La > Nd > Gd > Sm > Eu. The synchysite-bastnaesite intergrowths occur as granular crystals and are LREE-dominant, with La/Ce ratios ranging from 0.81 to 0.97, and LREE abundances in the order Ce > La > Nd > Gd > Eu. The grain size and intergrowth textures of the REE minerals govern the grinding fineness required to achieve sufficient mineral liberation. REE mineral grains in this deposit range from fine (< 150 mu m) to moderately coarse (< 400 mu m), but they commonly occur locked with gangue minerals. This indicates that the ore must be ground sufficiently fine to break the intergrowths and liberate the REE minerals. Based on the observed REE mineral textures, REE mineralization was formed by the addition of Ca and a decrease in temperature in ore-bearing fluids (from approximately 100 degrees C to over 400 degrees C) at relatively low pressures. Therefore, information on the occurrence and chemical composition of REE minerals can be used as basic data for understanding REE minerals genesis and improving their recovery rates.
In Central Tunisia, the Jebel Kohl Sr-(Pb-Zn) salt-related mineralization is located at the southern edge of the North-South Axis within the Maknassy-Mezzouna Triassic corridor. The mineralization, comprising celestine, galena and late-stage schalenblende, is mainly hosted in N-S to N40 degrees E-trending fractures and faults in the sandy marl and limestone of the Abiod Formation (Campanian-Maastrichtian) and in carbonate breccias of the Zebbag Formation (Albian-Turonian). These structures reflect Atlasic-driven stress and halokinetic activity that guided metal-bearing fluids. The paragenesis-celestine (Clt1 -> Clt2) -> galena -> schalenblende-records a multi-stage hydrothermal evolution with episodic fluid influx and redox fluctuations. Colloform textures and replacement features indicate rapid precipitation linked to fluid mixing between basinal brines and cooler fluids, as well as wall-rock interaction. NW-SE lineaments localized mineralization by facilitating Triassic evaporite rise and channeling metal-bearing brines. Reactivated Mesozoic faults during compressional phases promoted fracture networks around diapirs, enhancing fluid circulation. Although halokinesis has been long-lived in the region, the structural style, mineral assemblage, and deformation pattern are most consistent with ore emplacement during Eocene-Miocene Alpine compressional phases, when major NW-SE faults were reactivated and diapiric uplift intensified. Despite its peridiapiric setting, the stratabound geometry, low-temperature assemblage, and strong structural control align with Mississippi Valley-Type (MVT) characteristics. Jebel Kohl deposit illustrates how salt tectonics and orogenic deformation interact to focus Sr-(Pb-Zn) mineralization in diapiric terrains, highlighting a broader metallogenic potential of Central Tunisia.
The Leon gold deposit in the Ratatotok district, North Sulawesi, Indonesia, is hosted by the Middle to Late Miocene Ratatotok Limestone Formation overlying Early to Middle Miocene volcanic rocks. This study aims to elucidate the mode of occurrence of ores, and the conditions and genesis of ore formation of the deposit, based on morphological characteristics, trace elements, and sulfur isotope compositions of sulfide minerals. Four stages of sulfide mineralization associated with sedimentary and hydrothermal processes were identified. Stage 1 is characterized by disseminated framboidal pyrite (pyrite 1; a number after mineral name hereafter indicates its mineralization stage) of sedimentary origin. Stages 2-4 record hydrothermal overprinting, with successive formation of euhedral to subhedral pyrite 2 and marcasite 2, euhedral to anhedral pyrite 3 and arsenopyrite 3, and anhedral pyrite 4. Pyrite 1, pyrite 2, and marcasite 2 have lower Au and As contents, < 0.24 ppm Au and < 1.13 wt% As, compared to those of pyrite 3 with 69 ppm Au and 7.04 wt% As. Much higher Au and As contents were observed in arsenopyrite 3 in the limestone (ave. 110 ppm Au and 44.1 wt% As), the brighter and darker arsenopyrite 3 in the porphyritic andesite (90 ppm Au and 44.3 wt% As, and 80 ppm Au and 41.3 wt% As, respectively), and pyrite 4 (ave. 140 ppm Au and 4.41 wt% As). Gold in the sulfides was likely deposited from Au-unsaturated hydrothermal fluids at the Leon deposit as gold occurs only as solid solution (Au+) in the sulfides. Gold and As were incorporated into pyrite as coupled partitioning. Temperature and sulfur fugacity (in atm) during the mineralization of arsenopyrite 3 were similar to 303 degrees C-399 degrees C and log fS(2) = -10.6 to -6.6. delta S-34(CDT) values of hydrothermal pyrite in stages 2-4 vary from -3.1 parts per thousand to +1.2 parts per thousand, indicating a predominant magmatic source for S. The Leon deposit is a sediment-hosted gold deposit with probably a distal intrusion-centered setting.
The South Kitakami Belt of Japan yields a number of mesothermal auriferous vein deposits, hosted in Paleozoic-Mesozoic sedimentary rocks in the vicinity of Cretaceous intrusive rocks. We investigated lithology, mineralogy, and chemistry of the host sedimentary rocks (Late Triassic Isatomae Formation) in the Ishinomaki district to evaluate gold mineralizing potential in the belt. The formation consists of shallow-marine continental shelf sedimentary rocks that underwent prehnite-pumpellyite facies of contact metamorphism. The analyzed three representative slate samples of the formation contain diagenetic-metamorphic minerals such as calcite, K-feldspar, albite, pumpellyite, titanite, and apatite, in addition to micro-nodules and seams consisting of carbonaceous matter (CM) and/or sulfides. The carbonaceous matter in the nodules and seams was partly or mostly substituted by sulfides; pyrite with minor cobaltite and pyrrhotite, which occur as framboids, compact spheres, and compact anhedral grains. Cobaltite contains rarely electrum grains. These samples are characterized by high Ca contents, and are depleted in Mg, Fe, Na, and K, compared to the underlying Paleozoic and Mesozoic shale and overlying Jurassic sedimentary rocks of the belt. A sulfide nodule-bearing sample is enriched in metals such as As, Cr, Co, Ni, Cu, and Sb. Depletion of sulfur mole ratio of the pyrites, in particular, framboidal/spherical pyrite, compared to the stoichiometric ratio, suggests that the pyrites formed from monosulfides. Most of the trace elements such as As, Bi, Pb, Tl, Sb, and Mo are more enriched in pyrite than pyrrhotite. These analytical results of the Isatomae Formation indicate that this slate was accumulated in an anoxic seawater environment and enriched in metallic elements, which may have been adsorbed to Fe-oxyhydroxide particles originally. The successive diagenetic reaction with pore water sulfurized the Fe-oxyhydroxides to monosulfides, which finally transformed into pyrite. The narrow and enriched range (+0.3 parts per thousand to +0.5 parts per thousand) delta 34S values of sulfides in the Isatomae slate suggest that this diagenetic reaction occurred in a closed system, where seawater sulfate hardly diffused into the sediments. Subsequent prehnite-pumpellyite metamorphism transformed pyrite to pyrrhotite, during which metamorphism, the trace elements including Au may have exsolved into metamorphic fluids. These results show a gold mineralizing potential for the Isatomae Formation.
The Pilok Sn-W deposit in western Thailand is hosted by peraluminous S-type granites that intruded Silurian-Devonian metasedimentary rocks. This study presents whole-rock geochemistry, zircon U-Pb geochronology, and trace element data to constrain the timing of emplacement, petrogenesis, and regional metallogenic processes. Two granite types occur in the deposit: biotite-muscovite granite and tourmaline-biotite-muscovite granite, both showing high SiO2 (72.6-75.2 wt%) and Sn (12.8-27.4 ppm) contents, strongly peraluminous characteristics (A/CNK = 1.20-1.38), pronounced negative Eu anomalies (Eu/Eu* = 0.13-0.27), and elevated Rb/Sr ratios (14.1-22.6), indicating extensive fractional crystallization. Zircon textures and chemistry of the host granites reveal four distinct types: Types I and II zircons displaying magmatic oscillatory zoning and heavy REE-enriched patterns, and Types III and IV zircons showing hydrothermal characteristics with LREE enrichment in chondrite-normalized REE patterns. U-Pb dating of magmatic zircons from four granite samples yielded 206Pb/238U ages of 208 +/- 5.3 to 212 +/- 1.5 Ma, synchronous with the granites in the Late Triassic tin metallogenic belt in Southeast Asia. Ti-in-zircon thermometry indicates crystallization temperatures of 698 degrees C-829 degrees C (average 754 degrees C), and trace elements of zircon indicate strongly reduced conditions (Delta FMQ: -0.8 to -4.5, average -1.9), which were favorable conditions to retain Sn2+ in a residual melt. REE patterns of zircon suggest a magmatic to hydrothermal transition, recording late-stage fluid exsolution that mobilized Sn and W. The combination of Late Triassic ages, S-type peraluminous geochemistry, extreme fractional crystallization, and reduced magmatic conditions can be used as criteria for identifying tin-fertile granites in the Sibumasu Terrane and other terranes with similar tectonic settings.
This study provides the first comprehensive assessment of rare earth element (REE)-niobium (Nb) mineralization in the Jashora Ultrabasic Alkaline Complex (JUAC), northeastern India, addressing a critical knowledge gap in understanding the genesis and economic potential of enriched ultrabasic rocks. The JUAC hosts pyroxenites and magnetite-perovskite cumulates with exceptionally high concentrations of light REE (LREE; up to 20,000 ppm) and Nb (up to 1700 ppm). This study integrates field observations, petrography, whole-rock geochemistry, and in situ mineral chemistry to unravel the formation mechanism and mineralogical controls on REE-Nb enrichment in JUAC rocks. Perovskite (CaTiO3) is identified as the principal host mineral, contributing 58%-66% of total LREE and 48%-63% of Nb in pyroxenites, and 74%-94% (LREE) and 84%-94% (Nb) in magnetite-perovskite cumulates. This enrichment is explained by coupled substitution mechanisms (2Ca(2+) reversible arrow Na+ + REE3+ and 2Ti <-> Nb5+ + Fe3+) on the perovskite A and B sites during magmatic crystallization. Accessory minerals such as ancylite, bastn & auml;site, strontianite, apatite, and pyrochlore precipitated at late-stage carbonatite vein boundaries, collectively contributing 35%-40% of LREE in pyroxenites and 10%-25% in cumulates, and up to 50% of total Nb despite their low modal abundance (< 1 vol%). The REE-Nb mineralization in JUAC results from magmatic segregation and gravity settling of magnetite-perovskite cumulates crystallized from a Ca-Ti-REE-enriched, silica-undersaturated magma under moderately oxidizing conditions, followed by metasomatic alteration linked to carbonatite intrusion. Geochemical signatures and mineralogy of JUAC closely resemble global alkaline-carbonatite complexes such as the Kola Province (Russia), indicating similar magmatic differentiation and metasomatic processes. Given the rising global demand for REE and Nb in technology and clean energy sectors, JUAC stands out as an important and unexplored resource for critical minerals. Our findings provide new insights into REE-Nb enrichment mechanisms in alkaline ultrabasic systems and also highlight the need for further exploration and resource evaluation in the alkaline complexes of north-east India.
We integrated drill core observations, petrography, whole-rock geochemistry, and C and O stable isotope analyses of the late Cretaceous Kangankunde Carbonatite to understand its magmatic evolution with respect to its significance for rare earth element (REE) mineralization. The Kangankunde Carbonatite was emplaced as a ring structure and comprises four carbonatite types: beforsite, magnesio-carbonatite, ferro-carbonatite, and ferruginous calcio-carbonatite. The carbonatite is depleted in Nb and Zr relative to mantle values. The abundance of dolomite and apatite in the Kangankunde Carbonatite suggests a Mg- and P-rich initial magma. The bulk SrO contents decrease from magnesio-carbonatite (0.7-8.8 wt.%), ferro-carbonatite (0.7-6.9 wt.%), to ferruginous calcio-carbonatite (0.4-2.0 wt.%). On the other hand, the MnO contents increase from magnesio-carbonatite (1.8-6.0 wt.%) to ferro-carbonatite (5.0-10.1 wt.%), while in ferruginous calcio-carbonatite it ranges from 2.2 to 4.1 wt.%. We suggest two trends of differentiation of carbonatite magma. The first differentiation trend was from beforsite through magnesio-carbonatite to ferro-carbonatite. The second trend was possibly from beforsite to ferruginous calcio-carbonatite. The two identified differentiation trends are consistent with the observed mineral paragenetic sequence. The delta 13CVPDB and delta 18OVSMOW values of ankerite and calcite from ferruginous calcio-carbonatite range from -0.5 parts per thousand to -4.0 parts per thousand and 14.8 parts per thousand to 26.7 parts per thousand, while those of strontianite from magnesio-carbonatite are -4.3 parts per thousand and 12.0 parts per thousand, respectively. Assuming that the effect of weathering was minor, the wide variation of stable isotopes is suggestive of the differentiation of carbonatite magma from magnesio-carbonatite to ferruginous calcio-carbonate. The main REE-bearing mineral in Kangankunde is monazite. Minor REE-bearing minerals include apatite, synchysite, goyazite, and daqingshanite. The REE mineralization in the Kangankunde Carbonatite occurs as dissemination, wispy veinlets, and patchy forms within almost all identified carbonatite rocks, as well as acicular forms in magnesio-carbonatite, and is classified into primary magmatic and late hydrothermal stages. The primary REE mineralization occurred during magmatic differentiation, evidenced by the occurrence of monazite in interstitial spaces between subhedral dolomite and monazite inclusions in dolomite. The late hydrothermal mineralization is considered localized and is characterized by wispy veins of monazite with spherulitic texture, monazite overprinting dolomite or quartz, and strontianite enveloping primary monazite. Geochemical data show decreasing La/Yb ratios normalized to chondrite from magnesio-carbonatite (6020), ferro-carbonatite (5139), to ferruginous calcio-carbonatite (846). The total REE contents decrease from more evolved magnesio-carbonatite, which appears relatively hydrothermally altered, to ferro-carbonatite with similar characteristics, to the less evolved ferruginous calcio-carbonatite. These petrography and geochemical data suggest that magmatic processes played a significant role in REE enrichment at Kangankunde Carbonatite, while hydrothermal processes and re-equilibration of REE were possibly localized.
Lepidolite-bearing pegmatite, recently recognized as a major lithium (Li) resource, is exposed in Phang Nga, southern Thailand. This study investigates the geological relationships between Li-pegmatites and granitic rocks and their formation processes within the tectonic evolution of the study area, using petrological, geochemical, and geochronological data. The granitic rocks in the study area are classified into three types: I-type biotite granite, both I- and S-type biotite-muscovite granite, and S-type tourmaline granite. The Li-pegmatite shows S-type characteristics with peraluminous features. The primitive mantle-normalized spider diagram of Li-pegmatite and tourmaline granite reveals similar patterns, with enrichment in large-ion lithophile elements (e.g., Cs, Rb, Li, and U) and depletion in Ba, Nb, and Sr, suggesting that the Li-pegmatite evolved from a highly fractionated tourmaline granitic melt. Zircon U-Pb dating of the granites indicates three main magmatic events: Late Triassic biotite granite and tourmaline granite (216-214 Ma), Late Cretaceous biotite-muscovite granite and tourmaline granite (83-81 Ma), and Paleocene biotite granite (60-58 Ma). The cassiterite U-Pb ages of Li-pegmatites are 81 and 69 Ma, which are coeval with the Late Cretaceous tourmaline granite. Newly found Late Triassic granites in the Western Granitoid Belt suggest that the Triassic granitic magmatism of the Central Granitoid Belt may extend further into southern Thailand than previously known. The formation of the Late Triassic biotite granite and tourmaline granite is related to the collision events between the Sibumasu and Indochina Terranes following the closure of the Paleo-Tethys Ocean. Subsequently, during the Late Cretaceous, biotite-muscovite granite, tourmaline granite, and associated Li-pegmatites formed due to the West Burma-Sibumasu collision and the subduction of the Neo-Tethys oceanic plate beneath the western Sibumasu Terrane. The Paleocene biotite granite likely resulted from asthenospheric upwelling caused by the rollback of the Neo-Tethys oceanic plate.
The aim of this study is to identify the patterns of gold distribution and the mineral composition of placers in the Shagan-Oba River (Eastern Kazakhstan) area in order to clarify their genesis and assess the prospects for further exploration. The study employed methods of panning sampling, mineralogical analysis, and electron microprobe investigation of heavy minerals. The results show that the distribution of gold is closely related to the morphology of alluvial terraces and the composition of heavy mineral assemblages. Elevated gold contents were recorded in certain grain-size fractions (0.25 mm and 0.5-1.0 mm); the concentrates are dominated by quartz, magnetite, ilmenite, and titanite. The morphology of gold grains and their association with accessory minerals indicate a mixed origin, caused both by the re-deposition of ancient placers and by the influx of gold from nearby primary sources. The ancient placers, identified on terrace-like ledges of bedrock and on the valley slopes of the Shagan-Oba River, represent remnants of eroded alluvium resting on a bedrock floor.
The Miocene low-sulfidation epithermal deposits of the Omu camp in the Kitami region of northeast Hokkaido, Japan, are small past producers of precious metals that represent significant exploration targets for high-grade Au and Ag ores. Following changes in the Japanese mining law, Irving Resources initiated a camp-scale exploration program in 2016. Exploration resulted in the early recognition of a previously undescribed silica sinter outcrop along the Otoineppu River. Rock chip sampling combined with mapping of the sinter and related surficial deposits, as well as a camp-scale stream sediment survey, highlighted the potential for mineralization associated with the discovered silica sinter. Regional gravity and magnetic surveys indicated that Otoineppu Sinter occurs at the eastern edge of a major inferred graben, trending north northeast-south southwest. Subsequent controlled-source audio-frequency magnetotelluric and moving-loop electromagnetic surveys suggested that the sinter is located in the structural hanging wall of a major normal fault, a possible focus of fluid flow to the surface, providing a target of a potential mineralized zone at depth. The geophysical surveys provided critical information as the exploration area is heavily vegetated and partially covered by young sedimentary deposits, with only limited surface exposure. Drilling in 2019 and 2020 proved the existence of a mineralized zone having high Au and Ag grades beneath the silica sinter. The discovery history of Otoineppu Sinter serves as an example of data integration during brownfields exploration of a historic mining camp. The existence of an undocumented silica sinter within a heavily vegetated area highlights the prospectivity of the Kitami region for low-sulfidation epithermal deposits.
The Xiaowangjiaduan copper-polymetallic deposit in Inner Mongolia, northern China, is a recent discovery in the Da Xing'an Ling metallogenic belt. Geological and geo-electrical studies to search and explore new resources were carried out in the Xiaowangjiaduan area. The Xiaowangjiaduan deposit is located within a large alteration zone, which is covered by slate, pyroclastic rocks, silicalite and Quaternary sediments. In this case study, a comprehensive exploration work was carried out, including surface geological mapping, measurement of induced polarization (IP) intermediate gradient arrays survey, EH4 magnetotelluric measurements sounding, and large-power IP sounding. The IP intermediate gradient arrays survey revealed the mineralization-alteration system that exhibits obvious low-resistance and high-polarization anomalies, with a width of 350-650 m and a length exceeding 1500 m. The stratagem EH4 sounding profiles indicate that the mineralization system is characterized by a medium-low resistivity anomaly, and is stable within the depth range of 300-600 m below the surface. The large-power IP sounding reveals that the mineralized zone above -200 m is characterized by low resistivity and high chargeability, while the zone continues below the level of -200 m, where it is characterized by high resistivity and high chargeability. The integration of these methods provides a robust strategy for identifying a concealed mineralization zone, demonstrating their effectiveness in reducing exploration uncertainties and improving target accuracy.
The South Kitakami Belt of Japan yields a number of Mesozoic vein-type gold deposits, which have been classified as a 'mesothermal' type, related to the intrusions of Cretaceous granitic rocks. We investigated the Mano deposit, one of the gold deposits in the belt, to reveal the type and mineralization process of the deposit. The Mano deposit consists of thin auriferous quartz veins hosted by pyroxene hornfels that was metamorphosed from sandstone and mudstone of the Triassic Isatomae Formation by the intrusion of the Cretaceous Numazu gabbroic pluton. The pyroxene hornfels in the Mano deposit contains relatively less metamorphosed dark-gray pockets, which consist mainly of quartz, plagioclase, orthoclase, prehnite, calcite, chlorite, clinopyroxene, clinozoisite, carbonaceous matters, and sulfides in the white-colored completely metamorphosed hornfels. The mineral assemblage of the completely metamorphosed hornfels is similar to that of the less metamorphosed hornfels; although it contains titanite in addition to the minerals above, it is characterized by less amounts of sulfides and hydrous minerals. The bulk chemical compositions of the less metamorphosed and completely metamorphosed hornfels are both characterized by high concentrations of CaO (8.56-11.23 wt%); although the completely metamorphosed hornfels is more depleted in loss on ignition (including C, H and S) Co, Cu, Mo, and As, and has higher concentrations of Ca, K, Ba, Sr, and Rb, compared with the less metamorphosed hornfels. The sulfide minerals disseminated in the less metamorphosed hornfels are pyrrhotite, arsenopyrite, and chalcopyrite, with trace amounts of pyrite and alloclasite. Pyrrhotite contains trace amounts of Co, Ni, and Cu, while arsenopyrite contains trace amounts of Pb, Te, Co, Ni, Sb, Bi, and Au. The arsenopyrite geothermometer indicates an equilibrium temperature range of 460 degrees C-485 degrees C, which is slightly lower than the temperatures estimated from the crystallinity of carbonaceous matter (513 degrees C to 539 degrees C). The ore minerals in the quartz veins of the deposit are gold, bismuth, jos & eacute;ite-A, jos & eacute;ite-B, hedleyite, and Bi-Au +/- Te alloys, with trace galena and arsenopyrite. These minerals are oxidized from the grain margins to form various oxides. A large smirnite grain is associated with 1-20 mu m size droplets of gold and Bi minerals that form trails aligning on planes together with a few micron-size fluid inclusions. The lithology, mineralogy, and chemistry of the host rocks show that the hornfels metamorphism attained temperatures of 460 degrees C to > 500 degrees C. The chemistry of the sulfide minerals in the hornfels indicates that during this metamorphism, Bi and Te, the major low-melting chalcophile elements included in sulfides, were scavenged into the metamorphic fluid as melts, together with other elements such as Au, As, Cu, Pb, Co, and Mo. These metal melts in the fluid precipitated gold, various Bi-Te-(Se + S) minerals, and Bi-Au-Te alloys in the quartz veins close to and/or within the source rock at the temperature range of 240 degrees C-300 degrees C. The Au mineralization at Mano could be categorized into an "orogenic type", although it is related to contact metamorphism, which is uncommon in the orogenic gold deposits.
