Ore-forming Processes Research Articles

Two Epochs of Mineralization of Orogenic Gold Deposit in the East Kunlun Orogenic Belt: Constraints from Monazite U–Pb Age, In Situ Sulfide Trace Elements and Sulfur Isotopes in Wulonggou Gold Field

The Wulonggou Gold Field is one of the giant gold fields in the East Kunlun Orogenic Belt, northwestern China. Previous studies mainly focused on elementary mineral isotopic studies, fluid inclusions, and geological features in the Wulonggou Gold Field. In this study, we report some research on the precise age and the specific ore-forming process of the WGF: the hydrothermal monazite U–Pb ages; the way of gold precipitation; the composition, evolution, and source of ore-forming fluids of the Wulonggou Gold Field. Finally, we demonstrate a link between two-stage hydrothermal events and sequential episodes of crust-derived magmas, with implications for gold metallogeny in the East Kunlun Orogenic Belt. There are four hydrothermal stages that are recognized: a quartz–pyrite stage (stage 1), a quartz–pyrite–arsenopyrite–chalcopyrite stage (stage 2), a quartz–galena–sphalerite–pyrite stage (stage 3) and a quartz–stibnite–carbonate stage (stage 4). The monazite U–Pb ages of the Huanglonggou and Hongqigou deposits in the Wulonggou Gold Field were 422.2 ± 2.4 Ma and 236.7 ± 3.7 Ma, respectively, which support the opinion of two epochs of mineralization. Stages 1 and 2 are the main gold mineralization stages, wherein Au and As have a close genetic relationship. The Hongqigou and Huanglonggou deposits seem to have been formed in different metallogenic events due to the contrast on the trace element compositions in pyrite. The sources of the ore-forming materials and fluids of the Hongqigou and Huanglonggou deposits show apparent characteristics of orogenic gold deposit, and the magmatic events during Paleozoic and Mesozoic have an important contribution to the formation of the gold deposits. The gold deposits in the Wulonggou Gold Field can be interpreted as an orogenic gold system related to two-epoch tectonic–magmatic events.

Rift-induced structurally controlled hydrothermal barite veins in 1.6 Ga granite, Western Bastar Craton, Central India: Constraints from fluid inclusions, REE geochemistry, sulfur and strontium isotopes studies

Expressive granitic magmatism and a complex system of fault and shear zones are the main features associated with the crustal evolution and metallogeny in the Western Bastar Craton (WBC), Central India. The barite mineralization in WBC, Central India, occurs as veins and fracture fillings along faults are activated or reactivated as a consequence of rifting of – 1.5–1.6 Ga Pranhita-Godavari (PG) basin. The barite mineralization is hosted in ca. 1.6 Ga Mul granite of WBC. We present the first comprehensive, integrated field and laboratory studies approach using structural mapping, fluid inclusion, Sulfur, and Sr-Isotope geochemistry, mineral, and REE geochemistry to characterize barite mineralization ore-forming processes, a fluid source, and structural control. The host granite is intensely altered with evidence of hydrothermal mineralization in the form of silicification and hematitisation. Both sulfide-free (Brt-I) and sulfide-bearing (Brt-II) barites occur in the study area. Besides, barites with fluorite (Brt-III) were also observed in minor concentrations. The mineralization is associated with quartz-calcite vein, and the barite is accompanied by galena, pyrite, and chalcopyrite. Petrographic observations, fluid inclusion, and isotope data suggest a bimodal evolution of the mother brine viz. the oxidative source forms sulfide-free high-salinity brine and reductive low-salinity sulfide-bearing aqueous fluid formed by interaction with reducing agent causing hydrothermal barite mineralization in the study area. The source for the hydrotherms responsible for the formation of barite and galena in association with the quartz-barite vein is, in all probability, granitic magma. Incompatible elements like Ba, Pb and volatiles like S, preferentially concentrated in late magmatic hydrothermal fluids, got emplaced along the structurally weak zones in the interior of the granite pluton. The combined 87Sr/86Sr and δ34S‰ data suggest mixing fluids from diverse sources, including magmatic, marine, and crustal fluids. Low 87Sr/86Sr (<0.707) and high δ34S(>10‰) are indicative of alteration products of granite that were subsequently mixed with submarine hydrothermal fluid mobilized through the Mesoproterozoic PG rift system. This regional rifting event provided pathways for fluid flow and ore formation along faults/fracture systems (F2 and F3 fault systems) in the host Mul granite of WBC. The F2 fault system, sympathetic to the PG rift, is deep-seated and contains mainly barites of magmatic origin besides the minor marine signature. The F3 cross faults, developed across the gneissic foliation of TTG gneisses and charnockites, can be traced to the PG basin's younger marine sediments, host barites of dominantly marine signature.The Ba ± F mineralization in the study area is a perspective for regional exploration for REE-Ba-F in central India and elsewhere in a similar geological milieu. The epigenetic-submarine hydrothermal vein-type barite mineralization hosted in granite, WBC differs from Sedex, VMS, Carlin, or Orogenic type barite deposits, which has a great deal of replicability and suitability for future exploration targeting.

Origin of the Early Cambrian Huayuan carbonate-hosted Zn-Pb orefield, South China: Constraints from sulfide trace elements and sulfur isotopes

The Huayuan Zn-Pb orefield in the southeastern Yangtze Craton contains over 20 Mt Zn + Pb metal resource @ 4%, including several large, Lower Cambrian carbonate-hosted deposits classified as Mississippi Valley-Type (MVT). The source of zinc and lead and the ore-forming processes involved are still unclear. Trace elements and sulfur isotope compositions of sulfides from the large-scale Limei and Danaopo Zn-Pb deposits in the orefield favor a fluid-mixing metallogenic hypothesis. Alteration/mineralization occurred in three stages (S1-S3), forming pale-yellow sphalerite (S1: Sp1), yellow–brown sphalerite and pyrite (S2: Sp2-Py2), and galena-pyrite (S3: Gn-Py3).Syn-sedimentary fine-grained pyrite (Py1) in the Lower Cambrian Qingxudong Formation (Fm.) algal limestone has high Co, Ni, and As concentrations, whereas hydrothermal Py2 and Py3 in sulfide-calcite veins are rich in Zn and Pb, respectively. All the pyrites have low Co/Ni ratios (<2), indicating that the Fe, Co, and Ni are from a sedimentary source. Sphalerites from Limei and Danaopo are rich in Cd, Cl, and Ge but poor in Fe, Mn, and Co. They were formed under low-medium temperature (134–236 °C; determined by the concentrations of Mn, Fe, Ga, Ge, In, and Sb) and in an acidic and low-fO2 hydrothermal system, which are consistent with typical MVT ores. Lower Cambrian algal limestone (δ34SΣS = 34.3–34.4‰) contributed most sulfur to the ore sulfides (δ34S = 29.3–37.2‰). Meanwhile, the Lower Cambrian Niutitang Fm. Pb-Zn-rich black shale is likely the main ore metal source, but its limited sulfate content may not be able to provide sufficient sulfur. We propose a mixing between metal-rich brines leached from the basal Niutitang Fm. black shale with H2S-rich fluid resulting from thermochemical sulfate reduction (TSR) of the Qingxudong algal limestone formation, thus destabilizing the base metal chloride complexes and precipitating the Zn-Pb ores.

Fluid origin and critical ore-forming processes for the giant gold mineralization in the Jiaodong Peninsula, China: Constraints from in situ elemental and oxygen isotopic compositions of quartz and LA–ICP–MS analysis of fluid inclusions

The Jiaodong Peninsula, China, is one of the largest gold provinces in the world. During a short time interval in the Early Cretaceous, over 5000 t of gold were accumulated there. The mechanisms controlling the focused Au deposition and the origins of massive amounts of auriferous fluids are still controversial. Quartz–sulfide lode mineralization (Linglong-type) and disseminated/stockwork mineralization (Jiaojia-type) are the two major mineralization styles in the Jiaodong Peninsula. Herein, we conducted in situ textural, elemental and oxygen isotopic analyses using scanning electron microscopy (SEM), laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS) and secondary ion mass spectrometry (SIMS) on quartz from different hydrothermal stages and depths for three representative Linglong-type (Linglong deposit) and Jiaojia-type (Xiadian and Jiangjiayao deposits) gold deposits in the northwestern Jiaodong Peninsula, with the aim to constrain the ore-forming processes. The LA–ICP–MS analysis of individual fluid inclusions was also conducted to unravel the origin of the auriferous fluids. The results show that from the pre-mineralization to the ore-forming stages in the Linglong-type mineralization, the homogenization temperatures and salinities of fluid inclusions and the δ18Oquartz values change slightly, but the Al concentrations of quartz decrease continuously. Combined with the coexistence of CO2- and H2O-rich fluid inclusion endmembers, these trends indicate the increase of pH induced by CO2 degassing (fluid–fluid unmixing), which led to focused Au deposition. The quartz grains from the Jiaojia-type mineralization typically show a homogeneous texture with well-correlated lithophile elements (e.g., K, Al and Rb), which are distinct from those of the Linglong-type that are characterized by oscillatory zoning with much higher Al concentrations and δ18Oquartz values. These phenomena indicate that enhanced fluid–rock interaction occurred in the Jiaojia-type mineralization. In addition, the δ18Oquartz values show an increase from deep to shallow depths. In combination with thermodynamic modelling, it suggests decreasing fluid–rock interaction with decreasing depth. The above results corroborate that multiple mechanisms led to the efficient Au deposition in the Jiaodong Peninsula. Fluid–fluid unmixing typically occurred in the Linglong-type mineralization, while fluid–rock interaction was dominant in the Jiaojia-type mineralization. The different mechanisms might render mining challenging due to the changeable locations of favorable Au unloading.The LA–ICP–MS results of fluid inclusions suggest that the ore-forming fluids are metamorphic fluids rather than magmatic–hydrothermal fluids. In combination with the isotopic compositions of ores showing considerable mantle affinities and large-scale mafic underplating occurring beneath the study region, we propose a new genetic model that accounts for the origin of the auriferous fluids. The new model invokes the devolatilization of previously emplaced H2O- and Au-rich amphibole cumulates through amphibolite- to granulite-facies metamorphism in the middle–lower crust. It suggests an alternative way to generate the ‘orogenic-like’ gold deposits.

Age, petrogenesis, and tectonic setting of granitic gneiss and amphibolite from the Weizigou gold deposit, Heilongjiang Province, NE China: Constraints from geochronology and geochemistry

The Weizigou gold deposit is located in the western Jiamusi Massif, Northeast China. Gold mineralization is hosted in the amphibolite, which intruded the granitic gneiss. Although the deposit shows similarities to iron-oxide–copper–gold deposits, the detailed ore-forming process remains uncertain. To determine the formation age, petrogenesis, and tectonic setting of the granitic gneiss and amphibolite, LA–ICP–MS zircon, titanite, and monazite UPb dating, whole-rock major- and trace-element analyses, and LA–ICP–MS in situ zircon Hf isotope analyses were conducted on samples from these rocks. The granitic gneiss yielded two age populations of 951–882 Ma, and ca. 500 Ma, with a monazite UPb concordia age of 501.5 ± 5.1 Ma. The amphibolite yielded a crystallization age of 292 Ma, consistent with the results for magmatic titanite UPb dating, and a metamorphic age of 272–258 Ma. The granitic gneiss contains typical aluminum-rich minerals, such as garnet and muscovite, mean SiO2 = 73.31 wt%, and molar ratio Al2O3/(CaO + K2O + Na2O) values of 1.02–1.07, indicating an S-type granite protolith. The amphibolite belongs to the tholeiitic basalt series and has low SiO2 and high MnO contents. These results, together with εHf(t) values and two-stage model ages ranging from −9.5 to 2.3 and − 0.3 to 5.7, and from 2010 to 1659 Ma and from 1331 to 947 Ma, respectively, allow us to infer that the parental magmas of the granitic gneiss and amphibolite were derived from the partial melting of Paleoproterozoic lower crust and the partial melting of metasomatized depleted mantle, respectively. The granitic gneiss is characterized by positive Th and Hf anomalies, and negative Nb, Ta, Sr and Ti anomalies, whereas the amphibolite is enriched in K, Rb, and depleted in Ba, Nb, Ti, and Zr. These geochemical features suggest that the S-type granite was formed in an active continental margin during the Neoproterozoic and underwent granulite-facies metamorphism during the early Paleozoic. The protolith of the amphibolite was gabbro that formed in an extensional setting (e.g., a backarc basin) associated with westward subduction of the Paleo-Pacific oceanic plate beneath the eastern Jiamusi Massif during the early Permian. The gold mineralization can most likely be attributed to contact metasomatic metamorphism of gabbro during the middle–late Permian.

Fluid Inclusions and Stable Isotope Geochemistry of Gold Mineralization Associated with Fine-Grained Granite: A Case Study of the Xiawolong Gold Deposit, Jiaodong Peninsula, China

The Xiawolong gold deposit, located in the Muping–Rushan gold metallogenic belt (eastern Jiaodong Peninsula), is a newly discovered deposit that developed in the late Early Cretaceous as fine-grained granite. Gold mineralization, which mainly occurs in the middle of fresh fine-grained granite dikes, consists of stockwork-style and disseminated ores. They are characterized by middle-high-temperature mineral assemblages, such as molybdenite and magnetite, associated with gold-bearing pyrite. Four types of primary fluid inclusions, contained within the quartz grains from the gold-bearing disseminated and stockwork-style fine-grained granitic ores, were identified based on microthermometry and Raman spectroscopy. The types identified were type 1 aqueous inclusions with middle-high temperature (201 to 480 °C) and middle-low salinity of 0.18 to 17.00 wt.% NaCl equiv.; type 2 H2O–CO2 inclusions, which show middle-high temperatures (218 to 385 °C), middle-low salinities (1.23 to 13.26 wt.% equiv. NaCl), and variable XCO2 (0.031 to 0.044); type 3 daughter mineral-bearing inclusions with high temperature (416 to 446 °C) and relatively constant and high salinity (28.59 to 32.87 wt.% NaCl equiv.); and type 4 CO2 fluid inclusions, which possess a bulk density of 0.405 to 0.758 g/cm3 and a constant XCO2 (0.952 to 0.990) (according to the decreasing abundance of fluid inclusions). The δ18Owater range is between 3.4 and 5.9‰, and the range of the δD is from −97.1 to −77.4‰, which indicates that the ore-forming process is of a magmatic water origin. The δ34S values possess a narrow range between 4.5 and 9.3‰, indicating the source of the Mesozoic Kunyushan granitoids. The Pb isotopic compositions of pyrite show that the Mesozoic Kunyushan granitoids are the main lead source for pyrites. Types 1, 2, and 3 fluid inclusions coexist in the same view field of the quartz grain, which are suggested to occur as the result of fluid immiscibility because of the boiling of a single homogeneous NaCl-CaCl2-KCl-CO2-H2O system. The fluid immiscibility, rather the fluid mixing and wall-rock sulfidation, is the mechanism of gold precipitation in the Xiawolong deposit. Compared with both the “Linglong-type” and “Jiaojia-type” gold deposits in the Jiaodong Peninsula in terms of geological–petrographic evidence and all of the available geochemical data, it can be concluded the Xiawolong gold deposit is of magmatic hydrothermal origin, having a genetic relation to the fine-grained granite.

The effects of red beds on fluid flow and implications for the formation of volcanic-type uranium deposits in the Xiangshan basin, China

The South China uranium metallogenic province is an important hydrothermal uranium metallogenic region in China, which is spatially and temporally associated with the Cretaceous-Neogene red beds. Previous studies suggest that the red beds might have played critical role in the ore-forming processes by providing oxidizing fluids. However, the effects of the red beds on fluid flow are poorly understood. In this study, numerical modeling was conducted to investigate the roles of red beds on ore-forming fluid flow in the Xiangshan basin in Jiangxi Province, hosting the largest volcanic hydrothermal uranium deposit in China. The modeling results show that the variation of the slope gradient of the red beds greatly affects the fluid flow patterns, whereas the change of thickness and permeability of the red beds has little influence on fluid flow pattern. The fluid can circulate into the volcanic and basement rocks driven by topographic relief of the red beds. Furthermore, for models with fault, although the fluid velocities in the fault were more than one order of magnitude larger than those in the surrounding strata, the overall fluid flow patterns in the strata did not show great variation. The modelling results suggest that the topographic relief of the red beds may have driven the oxidizing fluids into the underlying rocks which are necessary for uranium mineralization in the Xiangshan basin.

Sulfide micro-textures and in-situ compositions from the Wulong gold deposit, northeastern North China Craton: Implication for ore-forming processes

Lode gold deposits in the North China Craton (NCC) form the only known giant late Mesozoic gold province in the world’s Precambrian cratons. Understanding the ore genesis for these deposits is of great scientific and economic importance. In order to provide constraints on the ore-forming processes, this study presents a combination of micro-textures and in-situ compositions of sulfide from the Wulong gold deposit (80 t @ 5.35 g/t Au; 127–122 Ma), northeastern NCC. Five sub-generations of pyrite (Py1–Py5) are identified based on micro-textural observations and EPMA results. In-situ trace elemental concentrations show that pyrite from the stage 1 (Py1) has high Co and Ni contents but no Au (<0.02 ppm). In contrast, euhedral Py2 and porous Py3 from stage 2 exhibit much higher Au (average 3.08 ppm and 1.66 ppm), As (average 1400 ppm and 946 ppm), and Ag (average 2.81 ppm and 3.21 ppm). Anhedral Py4 from stage 3 shows lower Au (average 0.31 ppm) and As (average 337 ppm) concentrations when compared to Py3. However, Py5 from stage 3 exhibits significant increases of As (average 7102 ppm) and Au (average 5.46 ppm) again and is featured by the alternation of Co-Ni- and Au-As-rich zones. Other sulfides, including pyrrhotite, chalcopyrite, and sphalerite, are poor in Au and As. Apart from visible gold grains related to Bi-rich melts, LA-ICP-MS spot and mapping analyses reveal that invisible gold hosted in Py2 to Py5 occurs dominantly as lattice-bound solid solutions (Au+). Direct gold precipitation from anomalously As-rich auriferous fluids induced by fluid immiscibility is proposed as the dominant mechanism of invisible gold enrichment. In-situ δ34S values of Py1 to Py4 exhibit narrow ranges of 1.0 to 3.8 ‰, indicating a deep-seated magmatic sulfur source. The elevated δ34S values (2.3–6.3 ‰) of Py5 are ascribed to some wall-rock contributions during fluid-rock interaction. These findings shed new light on the link between multistage fluid immiscibility and the chemical and micro-textural fingerprints of pyrites and the role of fluid immiscibility in the deposition of invisible gold.

Genesis of the Xinfang magmatic-hydrothermal gold deposit, Liaodong Peninsula, China: Constraints from pyrite Re-Os isotopes, C, O, S, Pb, Si, He and Ar isotopes

The Xinfang gold deposit (>20 t@ 2.85 g/t) is situated in the southwest of the Liaodong Peninsula. Ore bodies are hosted by the Archean gneiss in the footwall and Neoproterozoic metasandstone in the hangingwall of the Xinfang Metamorphic Core Complex. Here, we conduct pyrite Re-Os dating, C, O, Si, He-Ar, S, and Pb isotopes in order to constrain the ore-forming age and genesis of the deposit. Field observations show that three ore-forming processes are recognized: (1) quartz- coarse-grained pyrite stage (stage Ⅰ), (2) quartz-polymetallic sulfide-gold stage (stage Ⅱ), and (3) quartz – calcite ± pyrite stage (stage III). Pyrite from the quartz-polymetallic sulfide-gold vein yielded Re-Os isochron age of 121.1 ± 1.2 Ma (Initial 187Os/188Os = 1.49 ± 0.01, MSWD = 1.2), which is interpreted to be the ore-formation age.Theδ13CV-PDB and 18Ov-SMO W values of calcite from stage III range from −5.1‰ to −4.9‰ and from 9.7‰ to 10.1‰, and the δ30Si values of quartz from stage Ⅰto stage III range from −0.5‰ to −0.4‰, −0.1‰ to −0.3‰, and −0.2‰ to −0.1‰, respectively, indicating that ore-forming fluids were derived from a magmatic-hydrothermal source. Sulfur isotopic compositions of sulfides between −1.9 ‰ and 4.4 ‰ (mean = 2.4 ‰), are consistent with that of magmatic sulfur. The galena yielded a wide range of lead isotopic composition (206Pb/204Pb = 16.995–17.252, 207Pb/204Pb = 15.335–16.343, 208Pb/204Pb = 37.461–37.580) suggesting an external lead source. The He and Ar isotope compositions of pyrite and galena (3He/4He = 0.14Ra-0.62Ra), indicate a crustal source with minor mantle contributions. Combining all available data results, we propose that a magmatic -hydrothermal source for the Xinfang gold deposit and the ore formation was related to the subduction of the Paleo-Pacific Plate beneath Eurasia.

Colloids and Nanoparticles: Implications for Hydrothermal Precious Metal Ore Formation

Abstract Research on nanoscale processes is expanding in many scientific and technical disciplines, and economic geology is no exception. The idea that colloidal gold particles (or nanoparticles) may have played a significant role in ore formation was initially based on textural evidence from high-grade epithermal veins. More recently, the discovery of gold nanoparticles in some present-day geothermal systems and several orogenic gold deposits suggests that their formation could be a common process in gold-supersaturated hydrothermal solutions. Rare laboratory studies indicate that gold nanoparticles typically aggregate to form dendritic clusters. Over time, these dendrites perhaps can evolve to form coarser-grained crystals as subsequent annealing and recrystallization occurs. Due to the ephemeral nature and later recrystallization of dendrites, evidence of their former existence is commonly obscured. However, newer nanoscale imaging technologies have resulted in an increased recognition of their presence in hydrothermal gold ores, and thus their role in ore-forming processes merits further research. In particular, does their nucleation and deposition lead to forming higher-grade ores?

Improvement and systematization of principles and process flows in mineral mining in the Republic of Kazakhstan

The methods and economic parameters of mineral mining are interrelated with the applied technological, structural and organizational solutions. The parameters of individual ore bodies, their occurrence conditions and the totality of natural ore-forming processes govern these engineering solutions. Considering the relationship between such concepts as the integrity, structures and components of a subsoil use system, the basic principles defining a set of production processes for extracting minerals (or commercial component) from the subsoil are formulated. Due to the improvement of tools and technology, the scopes of the synonymic &ldquo;mineral mining&rdquo; and &ldquo;mineral production&rdquo; concepts expanded. The technological evolution was accompanied by fundamental clarifications and new understanding of the key concepts in scientific cognition and production management. The scientific relevance of the set of systemic principles rested on their application as a practical guide in mining. The key definitions included the validated series of the components and their contents. The proposed formulations have a significant weight both in science and technology as they provide more economically efficient and safe level of organization of underground mining with the system-founded and fool-proof selection of mining methods.

Балыгычано-Сугойский континентальный рифт: строение, основные черты развития и металлогении

The Balygychan-Sugoy structure was formed in the zone of expansion, presumably resulting from the reverse of the Omolon microcontinent northern flank to the south and southeast along the Omsukchan deep fault, and developed as a continental rift. By the end of the Early Cretaceous, the rift was filled with thick coal-bearing molasse. Volcanic, intrusive , and various ore formation processes were actively occurring in the rift zone. The data on the geological structure and the history of the structure development confirm its rift nature.

Geology, mineralogy and pyrite trace elements constraints on gold mineralization mechanism at the giant Dayingezhuang gold deposit, Jiaodong Peninsula, China

Identifying the mechanism of gold deposition is important to reveal ore-forming processes and genesis. The giant Dayingezhuang gold deposit, with 283 tons of proven gold resources, is located in the northwestern of the Jiaodong gold province, China. Pyrite is the dominant sulfide minerals and visible gold dominates Au resources. Five types of pyrite were identified at the Dayingezhuang gold deposit: (1) Py-1a is euhedral grain with Co– and Ni-rich content; (2) Py-1b is subhedral to anhedral grain with intermediate rich in Co, Ni, As and minor Te; (3) Py-2a is rich in As and crystalizes with a mass of mineral inclusions; (4) Py-2b is also rich in As but glossy; and (5) Py-3 is mainly euhedral grain and crystalizes with much more galena.Laser ablation spectra commonly shows Au and Ag-Bi-Pb spikes in Py-1b, Py-2a, Py-2b and Py-3, reflecting the occurrence of nanoparticles in pyrite. LA-ICP-MS mapping analysis shows elemental zoning of Co, Ni and As, which is considered as the element depletion (Co and Ni) of pre-existing Py-1a and enrichment (As) from ore-forming fluid via coupled dissolution-reprecipitation (CDR) mechanism. Au in pyrite is totally below 1 ppm (average 0.154 ppm and median 0.264 ppm) and without arresting variation in different pyrites, and mass balance indecates that invisible gold mobilized from pyrite may not interpret the formation of world-class gold deposit in the Jiaodong gold province. Most of the gold grains distribute in the microfractures of pyrites which is caused by brittle deformation. Fracture of rocks and minerals significantly improve the efficiency of water–rock interaction and result in sudden drop of fluid pressure. A probable model is that a fluid with extremely different physicochemical conditions and high As-Au-Cu-Pb-Bi-Te content give rise to Au mineralization, and visible gold precipitate in a gold-supersaturated hydrothermal fluid which is attributed to sulfidation and fluid phase separation via hydrofracturing. In addition, similar occurrences of gold and silver (individual minerals in microfractures of pyrites and spikes on laser ablation spectra of pyrite) and paragenetic sequence indicate that gold and silver mineralization belong to single geological event.

Textural features and in situ trace element analysis of fluorite from the Wujianfang fluorite deposit, Inner Mongolia (NE China): Insights into fluid metasomatism and ore-forming process

The Wujianfang fluorite deposit shows a four-stage mineralization history: (1) pre-ore stage of disseminated fluorites, (2) early-ore stage of fluorite-muscovite-pyrophyllite, (3) main-ore stage of fluorite-pyrophyllite, and (4) late-ore stage of fluorite-albite-quartz. Detailed cathodoluminescence imaging, fluid inclusion study, and in-situ LA-ICP-MS trace element analysis of fluorite in different stages or mineral assemblages were applied to reveal the fluorite mineralization and metasomatic history of this deposit. These data show that water-rock reaction between hydrothermal fluids and wall rocks not only provides the dominant ore-forming materials for fluorite mineralization, but also promotes the precipitation of fluorite by changing the pH of ore-forming fluids. Temperature change also plays an important role in fluorite precipitation. Fluorite grains from the pre-, early-, and main-ore stages have been variably metasomatized by a coupled dissolution-reprecipitation-recrystallization mechanism, which is characterized by complex petrographic and chemical zones. During this process, many trace elements were leached from the primary fluorite grains or other accompanied minerals, and parts of these elements were immediately reprecipitated into the new phases. Then, the recrystallized phases were formed from the leachate solutions of primary minerals. Our study highlights that fluorite generally has a complex growth history due to metasomatic alteration by hydrothermal fluids during the ore-forming process. Thus, in-situ microanalysis is essential and necessary to obtain effective and accurate constraints on hydrothermal evolution, and most of the interpretations based on bulk analysis of fluorites crystals should be cautioned.

In-situ monazite Nd and pyrite S isotopes as fingerprints for the source of ore-forming fluids in the Jiaodong gold province

The giant Jiaodong gold province has attracted a large amount of research on its geological features, ore-forming processes and genesis. Uncertainties as to the primary sources of ore-forming fluids, and whether host rocks contribute materials to gold mineralization, are still subject to intense debate. Here, we present comprehensive in-situ sulfur isotopic studies of pyrite from the Qujia and Xincheng gold deposits, and neodymium isotopic studies of monazite from the Xiadian, Zhuangzi, Hushan, Daliuhang, and Muping gold deposits, whose timing of gold mineralization has been constrained to ca. 120 ± 5 Ma using in-situ monazite U-Pb dating. The δ34S values among Py1 (+9.0 to +9.9‰), Py2 (+8.4 to +10.7‰) and Py3 (+6.9 to +12.3‰) are similar, showing consistence with that of other deposits in the Jiaodong gold province. It indicates that these gold deposits share the same dominant sources of sulfur and/or ore-forming fluids, potentially being exsolved from the contemporaneous magmas. Slightly wide range of δ34S for Py3 is likely due to the partially closed deposition spaces and intensive fluid-rock interaction. Hydrothermal monazite is intergrown with pyrite in the orebodies, suggesting that they were precipitated simultaneously from the same fluids. Our newly published Sm-Nd isotopic studies on monazite yielded inconsistent values of εNd (t = 120 Ma) among the Zhuangzi (−25.5 to –22.6), Xiadian (–23.3 to −20.2), Hushan (−20.6 to −18.4), Muping (−20.5 to −17.3) and Daliuhang (−13.7 to −11.6) gold deposits. These in-situ monazite Nd isotopes overlap with whole-rock Nd isotopes of their corresponding host rocks, indicating the material contribution of host rocks to the gold mineralization. This study provides robust evidences showing that the ore-forming fluids of the Jiaodong gold deposits share the same primary origin, but incorporate nonnegligible abundance of materials (REE, and potentially ore-related elements, such as Au, As, Fe) from the host rocks upon ascending, due to intensive fluid-rock interaction.

Fluid evolution characteristics and ore genesis in the Jinqu Au deposit, Qinling Orogen, China: Implications for ore genesis

The Jinqu Au deposit is located in the central Xiaoqinling gold field along the southern margin of the North China Craton. Ore-bearing auriferous quartz veins in the deposit are controlled by E–W trending structures within amphibolite facies metamorphic rocks of the Archean Taihua Group. The ore-forming process in this deposit can be divided into four stages represented by feldspar-quartz, pyrite-quartz, polymetallic sulfide-quartz, and carbonate-quartz veins and veinlets. Here we present fluid inclusion and isotopic data of the Jinqu Au deposit. Four types of fluid inclusions in quartz and calcite are identified, including carbonic-aqueousinclusions (type-1), aqueousinclusions (type-2), solid-bearinginclusions (type-3) and pure carbonic inclusions (type-4) varieties, based on petrography and laser Raman spectroscopy. Quartz in stage I contains type-1 fluid inclusions (FIs) which homogenized to aqueous or carbonic phase at temperature 361 to 406 ℃ and 385 to 400 ℃ respectively, and have salinities of 10.3 to 17.9 wt% NaCl equiv. Type-2 FIs show homogenization temperatures of 347 to 410 ℃ into the liquid phase, with high salinities of 11.6 to 18.6 wt% NaCl equiv. Quartz in stage II is the major host of type-1 FIs, with minor type-4 FIs, the former showing homogenization at temperatures of 305 to 390 ℃ into the carbonic phase and 280 to 410 ℃ into the aqueous phase, with variable salinities of 4.5 to 19.8 wt% NaCl equiv. The stage III quartz contains all the four types of FIs (homogenizing to carbonic or aqueous phase at temperature 309 to 360 ℃ and 295 to 400 ℃, with salinities of 6.6 to 19.9 wt% NaCl equiv for type-1, and homogenizing to liquid at temperature 308 to 326 ℃ with salinities of 12.5 to 13.2 wt% for type-2 Fls). In stage IV, type-2 FIs are the major type in quartz and calcite with total homogenization temperatures of 213 to 280 ℃ into the liquid phase and variable salinities of 5.3 to 18.6 wt% NaCl equiv. Our data show that the ore-forming fluids of the Jinqu Au deposit are generally characterized by moderate to high homogenization temperatures and variable salinities, belonging to the CO2-H2O-NaCl ± CH4 system. Based on fluid inclusion data, we infer that fluid immiscibility occurred in stages II and III, and the estimated trapping pressures for stages II and III fluids are between 81 and 275 MPa.The CHO isotopic values of fluids (δ18Owater = 1.2 to 6.4 ‰; δDV-SMOW = − 68.5 to − 56.0 ‰; δ13CCO2 = − 12.4 to − 3.4 ‰) in stage I to IV and δ13CV-PDB values for calcite (δ13CV-PDB = − 7.6 to − 4.3 ‰) in stage IV suggest that the ore-forming fluids were composed of a mixture of metamorphic water and mantle-derived fluids with minor involvement of meteoric water. Fluid inclusions in pyrite of stage II and III yield 3He/4He ratios of 0.88 to 1.39 Ra, and considerable 40Ar/36Ar ratios range from 2287.6 to 5669.9, suggesting the mixing of mantle and crustal components. The δ34SV-CDT values of sulfide samples in stages II and III range from − 5.8 to 4.5 ‰ (except for a pyrite grain within calcite that shows − 28.5 ‰). The values of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb of pyrite samples in stages II and III are from 16.919 to 17.321, 15.340 to 15.539, and 37.303 to 37.971 respectively. Our data suggest that the Taihua Group was possibly a major source for the ore-forming metals of the Jinqu Au deposit. Integrating the data from ore geology, fluid inclusions, isotope geochemistry and regional setting, we propose that the Jinqu Au deposit is an orogenic-type deposit which formed within the continental collision setting of the North China and Yangtze Cratons.

Geochronology and geochemistry of the granites from the Jiabusi Ta-Nb-(Li-Rb-Cs) deposit at the northern margin of the North China Craton

The newly discovered Jiabusi Ta-Nb deposit occurs within the latest Jurassic-Early Cretaceous multiphase granites, which are composed of felsic, peraluminous intrusions including biotite, two-mica, Li-mica, and topaz-lepidolite granites (abbreviated as BG, TMG, LAG, and TLG, respectively). Ore mineralizations are mainly hosted in the LAG and TLG, with subordinate mineralization occurring in the pegmatitic dykes. In this contribution, we present a systematic work of geochronology, whole-rock geochemistry, and Sr-Nd-Hf isotope composition for determining the timing of mineralization, petrogenesis, geodynamic setting, and ore-forming processes. Zircon U-Pb dating constrains the emplacement ages of 148–151 Ma for the BG, TMG, and LAG and reveals at least three episodes of Ta-bearing granitic pegmatites formed at ∼150 Ma, 127 Ma, and ∼100 Ma, respectively. Disseminated cassiterite grains from the LAG, TLG, and KPD yielded U-Pb ages of 149, 149, and 104 Ma, respectively. These granites have similar and limited features of (87Sr/86Sr)i = 0.7099, εNd(t) = −2.8 to −5.1, and εHf(t) = −4.7 to +5.5 and relative old Nd and Hf model ages of 1166–1442 Ma and 840–1500 Ma, respectively, indicating that Jiabusi multiphase granites are likely derived from the same magma reservoir by the partial melting of Mesoproterozoic crust in the destroyed northern margin of the NCC and are characterized by having involved significantly juvenile crustal materials.From the BG, TMG to LAG and TLG, bulk-rock Li, Rb, Cs, Be, Sn, Nb, and Ta contents increase with decreased Zr/Hf, Nb/Ta, and K/Rb ratios. Such systematic variations denote that these multiphase granites are cogenetic and that the LAG and TLG have experienced a higher degree of magmatic fractionation than the BG and TMG. The decrease in bulk-rock (La/Yb) N ratios, ΣREE, and Sr-Ba concentrations from the BG to TMG and LAG suggest an evolution involving the fractional crystallization of monazite and feldspar. The remarkable M−type lanthanide tetrad effect (TE1,3 = 1.22–1.75) matches low Nb/Ta (<1.2) and Zr/Hf (<5.0) ratios, indicating both the magmatic fractionation and melt-hydrothermal interaction were closely associated with Ta-Nb super enrichment in the LAG and TLG stocks. The combined evidence of compositional gaps and geologic spatial relationship between the BG batholith and Ta-bearing plutons confirm that the western part of the Jiabusi LAG stock and its surrounding concealed muscovite granites (MSG) are the further prospecting targets for Ta-Nb and W deposits.

A study of iron carbonates and clay minerals for understanding the origin of marine ooidal ironstone deposits

A detailed study of cement and matrix of ooidal ironstones of the Bakchar deposit (Western Siberia) was carried out to assess the factors influencing ore-forming processes. This research focusses on a debated issue about iron sources for Phanerozoic ooidal ironstone. Siderite, the main cementing mineral in the ironstones, is of two varieties that differ in morphology, chemical and isotopic composition, and types of fluid inclusions. The first variety of siderite occurs either as veinlet or as anhedral cement, consisting of isotopically light carbon and oxygen (δ13C from −39.5 to −29.7‰ and δ18O from −15.2 to −5.1‰). Fluid inclusions show a relatively high homogenization temperature (170–320 °C) and methane in the gas phase, corresponding to methane-bearing hydrothermal fluids. The second variety of siderite occurs as aggregates of small crystals in the ironstone matrix and is relatively enriched in heavier stable carbon and oxygen isotopes (δ13C from −28.1 to −12.2‰ and δ18O from −28.4 to −2.1‰), suggesting its formation on the seafloor under the combined influence of methane flux and seawater. The zone of the ooidal ironstone most proximal to the most intense ore-mineralization, an area of intense diffusion of metals and methane through marine sediments, is marked by the first variety of siderite, with rare authigenic minerals, a low clay content (kaolinite, chlorite, nontronite) and a high Fe content of the smectites. The authigenic mineral associations reflect the transition from methanic (sulfate-methane transition zone) to ferruginous (iron reduction zone) through sulfidic environment. The intermediate zone is dominated by montmorillonite-illite-saponite-nontronite and the second variety of siderite. The distal zone of the ore deposit is relatively unaltered, and is marked by illite-montmorillonite (illite-smectite), with rare second variety of siderite. The ratio of 1 M phyllosilicates (kaolinite) to the main swelling 2 M phyllosilicates in the clay fraction (K/M mineral index) decreases from the proximal zone of the intense iron-mineralization to the distal zone. The trend of clay mineral changes reflects the decreasing alteration of sediment matrix away from the main iron-rich and/or carbonate-bearing fluid influx. This study shows the expected lateral and vertical variation in authigenic minerals associated with marine Phanerozoic ironstone deposits, related to variable flux of metal- and methane-bearing fluids.

Formation of the Lened W-(Be) Skarn Deposit by Neutralization of a Magmatic Fluid—Evidence from H3BO3-Rich Fluids

Magmatic-hydrothermal systems, especially those causing the formation of tungsten deposits, may be enriched in boron, as is suggested by the presence of hydrothermal tourmaline. This study examines the boron and metal (including tungsten) concentrations of quartz-hosted fluid inclusions in the Lened W-(Be) deposit of the Canadian Cordillera and resolves (i) the analytical challenges involved during fluid salinity calculations of B-rich fluids and (ii) the relationship between fluid chemical composition and ore-forming processes involved at Lened. The aqueous fluid inclusions from this study have high CO2 and boron contents, indicated by the presence of a carbonic phase and sassolite crystals (H3BO3) in fluid inclusions. The boron content of the aqueous liquid phase (0.5 wt. %) was determined using microthermometric and Raman spectroscopic analyses. Boron was judged the most appropriate internal standard for quantifying the LA-ICP-MS data from these inclusions after calculation of salinity in the H2O-NaCl-H3BO3 system (3.5 to 5 wt. % NaCleq). Trace element data of the fluids show relatively high concentrations of Li (40 to 474 ppm), Al (56 to 1003 ppm), As (36 to 490 ppm) and Cs (68 to 296 ppm); and lower concentrations of Rb (3.6 to 77 ppm), Sr (0.4 to 23 ppm), Sb (1 to 32 ppm), Ba (0.6 to 163 ppm), Mg (6.9 to 7.6 ppm) and other metals, such as Be (2.4 to 10.2 ppm), W (2.4 to 27 ppm) and Cu (5.1 to 73 ppm). The high Cs and Li concentrations suggest a magmatic origin of the metals, while the moderate concentrations in Sr and Ba are indicative of fluid–rock interaction with the surrounding limestone. The presence of sassolite suggests that these fluids were highly acidic. The neutralization of this fluid through interaction with the surrounding limestone is the most probable trigger for scheelite precipitation. The presence of such high boron content in the magmatic fluid at Lened indicates the potential role in the enrichment of the source melt before fluid exsolution.

Geology, geochemistry, and genesis of REY minerals of the late Cretaceous karst bauxite deposits, Zagros Simply Folded Belt, SW Iran: Constraints on the ore-forming process

The present study focuses on the geochemistry and occurrence of REY (rare earth elements and yttrium)-bearing minerals in the Late Cretaceous karst bauxite deposits in the central part of the Zagros Simply Fold Belt (ZSFB), SW Iran. The ore bodies comprise a series of individual pods and/or contiguous lenses that occur as infills of deep karst cavities, depressions, and fractures within the upper neritic carbonates of the Cenomanian–Turonian Sarvak Formation. Karst bauxites from the ZSFB show, overall, the same mineral components, which consists of boehmite, hematite (commonly occurring as Al-rich), anatase, and kaolinite, with lesser amounts of diaspore, goethite, chamosite, rutile, and zircon. Among minor constituents, single crystals rich in rare earth elements (REEs) occur mainly in the form of authigenic REY fluorocarbonate, phosphate, and oxide minerals (bastnasite, parisite, rhabdophane, churchite and cerianite). Some textural features, such as spheroidal concretions, pisoids with cortexes lacking radial and circular fractures, growth of simple cortex around earlier pisoids, and pelitomorphic matrix suggest the ores are mostly autochthonous in origin. R-mode factor analysis revealed several significant interelemental relationships including: (i) significant and positive weightings for TiO2, Al2O3, Cr2O3, Ni, Zr, Nb, Hf, Ta, W, and Th, and a significant, negative weighting for SiO2 represent a later bauxitization stage involving silica depletion under drier conditions, promoting formation and stability of a range of minerals including detrital minerals and Al and Ti oxyhydroxides which also control, through scavenging, cations of first-row transition metals such as Ni2+ and Cr6+; (ii) Supergene conditions, mainly acidic pH, probably played an efficient role in the formation of secondary REE-rich phosphates and Ga-hydroxide; (iii) similar and meaningful weightings for U and V suggest that the redox environment would be most important in controlling the U and V mineral phases; and (iv) the scandium co-variance with Fe2O3 represents the control exerted by iron oxy-hydroxides on the critical metal Sc. In the ZSFB bauxites, the most frequent authigenic REE-bearing minerals are light REE (LREE) fluorocarbonates of the bastnaesite group that forms a solid solution series between end members parisite [CaCe2(CO3)3F2] and bastnäsite (CeCO3F). The mode of occurrence of bastnäsite-Ce and parisite-Ce suggests that cerium as fluoride and/or carbonate–fluoride complexes were readily leached by acidic downward solutions and finally precipitated on the geochemical barrier of the carbonate bedrock under alkaline and reducing conditions. Rhabdophane [(Ce, La) PO4·H2O] as an LREE phosphate mineral appears in two generations with different chemical compositions, an early one as irregular and/or acicular particles within the cavities and a later one along the margin of a goethite microvein that cuts the pelitomorphic matrix. Cerianite (CeO2) occurs mainly as sub-micrometer to micrometer grains in the porous aggregates of the aphanitic matrix and as microdomains or microveins that coexist with Al-oxyhydroxide and goethite. Cerianite precipitation may occur due to the predominance of acidic/oxidizing conditions and the dissolution of Ce-rich fluorocarbonates in the bauxitic profile, respectively. The only heavy REE (HREE) phosphate mineral within the ZFSB bauxite deposits is churchite[Y(PO4)·2(H2O)] that forms as single euhedral crystals at the core of the sub-spheroidal structures under an acidic condition.