Ore Genesis Research Articles

Geology, fluid inclusions, and isotope signatures reveal hydrothermal evolution and genesis of the Aqishan Pb-Zn deposit in Eastern Tianshan and implications for exploration of skarn mineralization

The Aqishan deposit (1.97 Mt at 1.05 % Pb + Zn) is located in the Aqishan-Yamansu arc, on the southwest section of the Eastern Tianshan, Northwest China. Pb-Zn mineralization is mainly hosted by garnet skarn and the volcaniclastic rocks of the Yamansu Formation. To decipher the evolution of ore fluids and source(s) of ore-forming components, and constrain the ore genesis, a combination of geological work, fluid inclusions, and C-O-S-Pb isotope systematics is presented. Detailed field and microscopic observations reveal that the skarn alteration and ore formation at Aqishan could be divided into four hydrothermal stages, consisting of prograde skarn (I), retrograde skarn (II), quartz–sulfides (III), and carbonate stage (IV). Sphalerite and galena are the dominant ore minerals generally occurring as disseminations and veins with locally laminated ores in stage III. Fluid inclusion data show that the fluids responsible for prograde skarn are high-temperature (342–518 °C) and high-salinity (7.3–44.2 wt% NaCl equiv.), and recorded fluid phase separation from an intermediate-salinity supercritical fluid, which was exsolved from crystallizing granitic magma. Microthermobarometry results limit the retrograde alteration within the temperature range of 313 to 388 °C and trapping pressures of 98 to 241 bars (1.0–2.5 km), with pressure dropping from lithostatic to hydrostatic regimes associated with a phase separation event. The boiling fluid inclusions in ore stage quartz show that the Pb-Zn mineralization formed at 205–357 °C, with a decrease in temperature facilitating the precipitation of ore-forming metals from hydrothermal system. Carbon and oxygen isotope compositions of calcite indicate a predominantly magmatic source for ore fluids at Aqishan with later meteoric water involved. Bulk and in situ sulfur values of sulfides range from −6.4 to −0.7 ‰, consistent with a dominantly magmatic origin. Sulfides together with the granite porphyry and tuff, show relatively homogeneous Pb isotope compositions, indicating that abundant ore-forming metals were sourced from a magmatic reservoir with contribution from country rocks. Fluid inclusion study and available calcite C-O isotopes suggest that significant decrease in temperature and fluid-rock interactions remarkably contributed to the metal deposition at Aqishan. The skarn alteration with typical alteration assemblages of garnet–diopside is proposed as an effective mineral exploration target of skarn(–like) ores in Eastern Tianshan.

Low-temperature thermochronology of the Longmala - Mengya’a Pb-Zn deposits (southern Tibet): Implications for ore exhumation and preservation

The large Gangdese metallogenic belt, located in the southern part of the Tibetan Plateau, hosts a variety of magmatic-hydrothermal ore deposits. Previous works in the area primarily concerned the ore genesis, while the exhumation history of these ore deposit has received less attention. In this contribution we explore the multi-stage thermo-tectonic evolution of the Longmala and Mengya’a Pb-Zn deposits, two large magmatic-hydrothermal ore deposits in the central Lhasa sub-terrane. In more detail, the thermal history of granitoids and deformed Paleozoic sediments inside and on the periphery of the ore districts have been constrained by low-temperature thermochronological methods, including the zircon (U-Th)/He and apatite fission track thermochronology. Additionally, zircon U-Pb geochronology was conducted on granitic host rocks to determine their emplacement ages. Our thermochronological data and inverse thermal history modeling results reflect two phases of accelerated basement cooling during the Cenozoic (i.e., ∼46–41 Ma and ∼20–5 Ma), interpreted as exhumation phases. The ore body was exhumed to the near surface during the Miocene, which provides essential information for ore exploration in the region. We also explore the degrees of basement rock exhumation along the Gangdese metallogenic belt and their spatio-temporal relations to major ore deposit distributions. It is suggested that complex interactions between tectonic-structural activities and surface erosion occurred during the late Oligocene-Miocene (∼25–5 Ma), which resulting in widespread exhumation along the Gangdese batholith. During this period, the ore-bearing rocks were gradually (with medium to high cooling rates) exhumed to the near-surface from ∼3–4 km crustal depth, making these ore deposits feasible for commercial mining.

Relationship between cathodoluminescence response and trace element characterization of cassiterite from the Yunling tin deposit in western Yunnan, China: Implications for substitution mechanism and ore genesis

Cathodoluminescent (CL) imaging, combined quantitative geochemical analyses using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), was employed to study the cassiterite crystals from the Yunling tin deposit in western Yunnan Province, China. This investigation aimed to establish a connection between CL response with trace element compositions. The CL imaging of a well-formed centimeter-scale euhedral single crystal of cassiterite revealed two types of primary growth domains, namely oscillatory and sector zoning. High spatial resolution LA-ICP-MS spot analysis along three centimeter-scale profiles revealed that the oscillatory zoning patterns were primarily defined by the concentrations of Nb and Ta. The CL response associated with the oscillatory zoning was attributed to the interplay between activators such as Ti, Nb, Ta, and V, and quenchers like Fe. On the other hand, sector zoning exhibited significantly high W content, reaching three orders of magnitude greater than that in the oscillatory zoning. Consequently, the sectors displayed a dark CL response. Furthermore, U showed a sectoral preference, with contents within the sector zoning examined in this study reaching up to 10 ppm. The systematic variations in geochemical compositions suggest that the incorporation of trace elements in Yunling cassiterite involves a coupled substitutional mechanism of pentavalent and trivalent elements (e.g., Sc3+ + V5+ ↔ 2Sn4+) with H+ potentially serving as a compensating ion for the Fe3+ excess.It is worth noting that the trace element enrichment and potential substitution in the sector and non-sector regions of the single crystal may differ significantly. Therefore, the use of cassiterite trace elements as indicators of the mineralization environment requires careful consideration, particularly when analyzing randomly selected particles obtained from crushing. In such instances, it is recommended to utilize cassiterite samples that exhibit a preserved crystal texture extending from the core to the rim, such as cassiterite in thin sections or morphology-integral cassiterite separates. Moreover, the contrasting W contents observed between the sector and non-sector zones may provide an explanation for two trends in the Fe–W diagram of cassiterite associated with granite that were previously-unspecified.

Mineralization age of the Xiangshan uranium ore field, South China redefined by hydrothermal apatite U-Pb geochronology

The Xiangshan volcanic-related uranium ore field, located in the Ganzhou-Hangzhou Uranium-Polymetallic Metallogenic Belt (GHMB) in South China, has been the country’s largest historic uranium producer. Although this ore field has been intensely studied for decades, the absolute age of uranium ore formation was still debated. Conventional U-Pb dates on U-minerals (i.e., pitchblende, brannerite) and Ar-Ar dates on associated alteration minerals (i.e., illite) from different uranium deposits yield a wide range of ages (122 to 85 Ma). The uncertainty regarding the exact timing of uranium mineralization at Xiangshan has limited the development of accurate ore genesis models and precluded a better understanding of the links between metallogenesis and regional-scale geodynamics during the Cretaceous-Tertiary period in South China.In this work, we focus on applying in-situ LA-ICP-MS U-Pb geochronology to magmatic and hydrothermal apatite from two typical uranium ore deposits at Xiangshan, intending to indirectly constrain the exact timing of uranium mineralization and reconstruct the magmatic-hydrothermal history. U-Pb age determinations on magmatic zircon and apatite from the three types of ore-hosting volcanic rocks yielded precise crystallization ages of 133 to 136 Ma and 135 to 140 Ma, respectively. These results are identical within uncertainty to previously reported U-Pb dates obtained in the study area, and thereby tightly constrain the emplacement age of the Xiangshan volcanic complex that hosts uranium deposits. Moreover, the potassium feldspar-biotite Ar-Ar dating for the major volcanic rocks demonstrates that these host rocks were cooled and completely solidified through the biotite/potassium feldspar closure temperature (below 300 °C) at 133–131 Ma. Subhedral or anhedral aggregates of hydrothermal apatite ubiquitously formed in the high-grade uranium ores at the Shannan and Zoujiashan deposits and are commonly intergrown with fluorite, illite and uranium minerals. Relative to magmatic apatite from the host rocks, the hydrothermal apatite is typically characterized by much higher U and Th contents, depletion of LREEs, enrichment in HREEs and a much more pronounced negative Eu anomaly. As such, the hydrothermal apatite is unequivocal of hydrothermal origin and formed synchronously with uranium mineralization. LA-ICP-MS U-Pb dating of these hydrothermal apatite crystals yielded an absolute 206Pb/238U age of 126.7 ± 0.6 Ma for the Shannan deposit and 131.3 ± 7.2 Ma for the Zoujiashan deposit. The new ages are much older (>10 Ma) than those previously reported ages on ore or gangue minerals such as pitchblende and illite. Thus, one unidentified mineralization event likely occurred at ca. 131–127 Ma, soon after solidification and subsequent brittle deformation or faulting within the volcanic caldera. We, therefore, proposed that volcanic magmatism was highly likely to be the ‘heat engine’ driving hydrothermal fluid convection and possibly provide the essential conditions (i.e., magmatic fluids, U sources) for the formation of the U mineralization. Another implication of this study is that dating hydrothermal apatite with high U concentrations associated with uranium mineralization could be considered a complementary geochronological tool in the study of analogous hydrothermal uranium deposits worldwide.

Geochemistry of Cryogenian Datangpo manganese deposits in the southeastern Yangtze Platform of South China: implications for the origin of metallogenesis and depositional environment

ABSTRACT Sedimentary manganese (Mn) deposits in the southeastern Yangtze Platform of China have been newly discovered with considerable potential for resource exploration. Such deposits formed due to dynamic changes in the global environment, including the break-up of the supercontinent Rodinia, Snowball Earth glaciation, and the Neoproterozoic Oxygenation Event. The Mn-bearing sequences are hosted in the basal Datangpo Formation and are interbedded with black carbonaceous shale in a series of graben sub-basins in the Nanhua Rift Basin. We investigated the origin of these Mn deposits by analysing the major and trace elements, total organic carbon, and stable carbon and oxygen isotopes. Positive Eu anomalies were observed, indicating that the Mn was derived from a hydrothermal system. Redox-related elements, including Ce, Mo, U, V, S, and P, indicated that the depositional environment of the Mn layers was oxidative and that Mn2+ was initially oxidized to Mn oxides. However, the host rock (i.e. black carbonaceous shale) was deposited under dysoxic – anoxic and even sulfidic water conditions. The alternating distribution of Mn ore and host rock suggested alternating redox conditions in the sub-basins. A negative correlation between the Mn content and δ 13Ccarb values (−10‰–−7‰) and a deficiency of sulphide minerals indicate that the diagenetic degradation of organic matter (δ 13Corg from − 34‰ to − 31.9‰) took place through Mn oxide reduction rather than microbial sulphate reduction and can contribute to a considerable source of bicarbonates. The approximately homogeneous δ 13Ccarb depletion and their apparent discrepancy with δ 13Corg indicate that the post-depositional genesis of the Mn carbonate ore occurred in a relatively open early diagenetic pore water system with a considerable contribution from seawater-derived carbon sources.

Fluid evolution and ore genesis of Huaduoshan Cu–Mo prospect, Duobaoshan ore field, northeastern China: evidence from fluid inclusions, H–O–S–Pb isotopes, geochronology, and geochemistry

The Huaduoshan Cu–Mo prospect is in the Duobaoshan orefield, northeast China. The Cu–Mo mineralization occurs in the granodiorites as veinlet-disseminated. The ore-forming process can be divided into four mineralization stages: (I) quartz–pyrite–magnetite; (II) quartz–pyrite–chalcopyrite ± molybdenite; (III) quartz–pyrite–molybdenite–chalcopyrite–sphalerite; and (IV) quartz–calcite–minor pyrite. Liquid-rich two-phase aqueous (L-type), vapour-rich aqueous (V-type) and daughter-minerals three-phase (S-type) fluid inclusions (FIs) were identified at Huaduoshan. The last two types of FIs are absent in stages III and IV. The homogenization temperatures of FIs from stages I to IV are 375–438, 335–378, 283–335, and 223–267 ℃, with corresponding salinities of 2.4–50.4, 2.1–44.9, 2.7–10.1, and 1.7–7.3 wt. % NaCl eqv., respectively. The H–O isotope data of quartz in stages I (δ18OH2O = 6.1–8.0‰, δDH2O = −102.4–−94.6‰) show a magmatic origin of ore-forming fluid; the decreasing δ18OH2O (−6.8–3.2‰) and δDH2O (−117.1–−98.5‰) values of quartz in stage II–IV show the fluid mixing with meteoric water. The S–Pb isotopic values (δ34S = −2.7–0.8; 206Pb/204Pb = 18.236–18.599; 207Pb/204 Pb = 15.504–15.557; 208Pb/204Pb = 37.816–38.629) of pyrites indicate that the ore-forming materials are of magmatic origin. Fluid boiling and mixing may be the major mechanisms of ore precipitation. Zircon U–Pb age (172.1 ± 0.5 Ma) and geochemical data indicate that the ore-related granodiorites are I-type rocks formed in the subduction setting of the Paleo-Pacific Ocean Plate in the Early–Middle Jurassic. In conclusion, we propose that the Huaduoshan Cu–Mo prospect is a porphyry deposit and has potential for further exploration of porphyry Cu–Mo prospecting.

Multi-Isotopic Compositions of Ores from the Shizishan Cu–Au–Mo Orefield in the Tongling Region, Eastern China: Implications for Ore Genesis

The Middle–Lower Yangtze Metallogenic Belt (MLYMB) hosts abundant porphyry–skarn–stratabound-type Cu–Au–Mo deposits. Despite extensive research, the origin of the stratabound-type deposits, which developed at the unconformity interface between the Devonian and Carboniferous strata in the MLYMB, remains controversial. The primary debate centers on whether these deposits are the result of Carboniferous sedimentary exhalative mineralization or Mesozoic magmatic–hydrothermal mineralization. In this paper, we examine three representative deposits in the Shizishan orefield: the Chaoshan skarn-type Au deposit, the Hucun porphyry–skarn-type Cu–Mo deposit, and the Dongguashan Cu–(Au) deposit, which has a disputed genesis of its stratiform orebodies. Economically important ore minerals, such as chalcopyrite, molybdenite, and pyrrhotite, and their associated quartz and calcite, were focused on, rather than the extensively studied pyrite in the Tongling region. The ore genesis and sources of mineralized elements in the Shizishan orefield were investigated using H, O, C, S, Pb, and Cu isotopes. The H–O isotopic compositions of hydrothermal quartz from the Chaoshan, Dongguashan, and Hucun deposits indicate that the ore-forming fluids were mainly magmatic water with some meteoric water input. The C–O isotopic compositions of calcite show a large difference from the local sedimentary carbonates. The S isotopic compositions of sulfides reveal a magmatic sulfur signature. The Pb isotopic compositions in the three deposits are similar to those of the Shizishan intrusions, suggesting a magmatic source for Pb. The Cu isotopic compositions of chalcopyrite and pyrrhotite demonstrate that Cu, the primary ore-forming element, was mainly derived from magmatic–hydrothermal fluids. The stratiform orebodies display H–O–C–S–Pb–Cu isotopes consistent with the porphyry orebodies in the Dongguashan deposit, as well as in the Chaoshan and Hucun deposits, indicating a common ore genesis. From these, we conclude that the porphyry–skarn–stratabound-type Cu–Au–Mo deposits in the Shizishan orefield can be classified as a unified Mesozoic magmatic–hydrothermal metallogenic system. The stratabound-type copper sulfide deposits and the porphyry–skarn-type copper deposits in the MLYMB have a strong similarity in the source and genesis of their ore-forming elements.

Rare native Ni, Fe, Cu, and Sn metals in Hemrin Basalt, northern Iraq: implications for mineral chemistry and ore genesis

Rare native Ni, Fe, Cu, and Sn metals in Hemrin Basalt, northern Iraq: implications for mineral chemistry and ore genesis

Integrated Geology, mineralogy, element and C–O–S–Pb isotopes characteristics elucidate ore genesis of the world-class huoshaoyun Zn–Pb deposit in Karakoram Area, Xinjiang, Northwest China

The Huoshaoyun carbonate-hosted non-sulfide Zn–Pb deposit in the Karakoram area, northwest China, provides an excellent setting for investigating the origin of this type of deposit. Here, geology, mineralogy, elements, and C–O–S–Pb isotopes evidence are presented to constrain the ore genesis of the Huoshaoyun deposit. Two orebodies occur in limestone of the Longshan Formation, which exhibit laminated, banded, and brecciated textures. Ore minerals of the Huoshaoyun deposit are dominated by smithsonite and cerussite, with subordinate galena and pyrite. From early to late, ore formation is divided into three stages, which are sulfide stage, oxidation stage I and oxidation stage II. The C–O isotopic compositions of smithsonite (δ13CPDB: –0.70‰ to 4.50‰, δ18OSMOW: 23.30‰ – 25.20‰), cerussite (δ13CPDB: –3.00‰ to –1.80‰, δ18OSMOW: 10.60‰ to 13.10‰), mineralization stage calcite (δ13CPDB: 0.90‰ to 2.80‰, δ18OSMOW: 12.40‰ to 24.80‰) and calcite within wall-rocks (δ13CPDB: –0.30‰ to 2.60‰, δ18OSMOW: 13.20‰ to 25.60‰) indicate that the carbon and oxygen source of the Huoshaoyun deposit are closely related to the sedimentary strata, and the minerals have experienced intense TSR effect of organic matter and influenced by meteoric water to a greater extent. Compared with gypsum in the Longshan Formation (δ34SV-CDT: 17.10‰ and 17.20‰) and veined gypsum near the orebodies (δ34SV-CDT: –26.30‰ to –18.50‰), galena and pyrite both enrich negative sulfur isotopes with δ34SV-CDT values ranging from –35.60‰ to –13.00‰, which reveal that the sulfur in the Huoshaoyun deposit was derived from low-temperature bacterial reduction of evaporative sulfate. The uniform Pb isotopic data of galena, cerussite, and anglesite (208Pb/204Pb: 38.857 – 38.935, 207Pb/204Pb: 15.677 – 15.694, 206Pb/204Pb: 18.515 – 18.552) from the Huoshaoyun deposit display linear trends in Pb isotope diagrams, which imply that the galena, cerussite, and anglesite should have been exposed to a series of cogenetic evolutionary processes and shared the same lead sources with significant upper crust and orogenic contribution. In comparison with Pb isotopic data of regional strata (208Pb/204Pb: 38.530 – 39.695, 207Pb/204Pb: 15.579 – 15.883, 206Pb/204Pb: 18.290 – 20.035), the combination of these regional strata can provide the enough metals for mineralization and induce the Pb isotopic characteristics evolving to the present model in the Huoshaoyun deposit. In summary, the ore-forming materials are mainly sourced from regional strata, and the Huoshaoyun deposit is a supergene MVT deposit-a new non-sulfide deposit type in China.

Trace Element Characteristics of Pyrite and Arsenopyrite from the Golden Ridge Gold Deposit, New Brunswick, Canada: Implications for Ore Genesis

The Golden Ridge gold deposit is located in southwestern New Brunswick, in the Canadian Appalachians. Gold mineralization is consistently associated with acicular arsenopyrite, and to a lesser degree with pyrite, disseminated in host rocks, sulphide veinlets, quartz-carbonate veins, and the breccia matrix. According to petrographic-based textural differences, four types of pyrite and two types of arsenopyrite are recognized with associated assemblages. Based on SEM-BSE imaging and LA-ICP-MS spot analyses of the different types of pyrites and arsenopyrites, “invisible gold” (solid solution in the crystal lattice of pyrite and arsenopyrite or <100 nm nanoparticles) and micrometer-size inclusions were identified as the main forms of Au. Four syn-gold mineralization pulses of fluid are suggested. The initial hydrothermal fluid, which generated low-grade pyrite (Py-I) enriched in Sb, Pb, Cu, Co, Ni, and Bi, was followed by a second pulse of fluid enriched in arsenic and gold, generating coprecipitated Py-II and Asp-I. The third and fourth pulses were enriched in both arsenic and gold and precipitated Py-III, then coprecipitated Py-IV and Asp-II, which constitute the most important Au depositional episodes. The repeated occurrence of growth zones with Au enrichment in the arsenian pyrites (Py-II, Py-III, and Py-IV) indicate surface growth during metal deposition and disequilibrium crystallization processes.

Mantle-to-crust metal transfer by nanomelts

The transfer of chalcophile metals across the continental lithosphere has been traditionally modeled based on their chemical equilibrium partitioning in sulfide liquids and silicate magmas. Here, we report a suite of Ni-Fe-Cu sulfide droplets across a trans-lithospheric magmatic network linking the subcontinental lithospheric mantle to the overlying continental crust. Petrographic characteristics and numerical calculations both support that the sulfide droplets were mechanically scavenged from the mantle source during partial melting and transported upwards by alkaline magmas rising through the continental lithosphere. Nanoscale investigation by high-resolution transmission electron microscopy (HR-TEM) documents the presence of galena (PbS) nanoinclusions within the sulfide droplets that are involved in the mantle-to-crust magma route. The galena nanoinclusions show a range of microstructural features that are inconsistent with a derivation of PbS by exsolution from the solid products of the Ni-Fe-Cu sulfide liquid. It is argued that galena nanoinclusions crystallized from a precursor Pb(-Cu)-rich nanomelt, which was originally immiscible within the sulfide liquid even at Pb concentrations largely below those required for attaining galena saturation. We suggest that evidence of immiscibility between metal-rich nanomelts and sulfide liquids during magma transport would disrupt the classical way by which metal flux and ore genesis are interpreted, hinting for mechanical transfer of nanophases as a key mechanism for sourcing the amounts of mantle-derived metals that can be concentrated in the crust.

Robust dating of Pb–Zn skarn systems by LA–ICP–MS garnet U–Pb geochronology

Lawu and Yaguila are two Pb–Zn skarn deposits in the eastern Nyainqêntanglha metallogenic belt, central Lhasa subterrane, Tibet. The genesis of Pb–Zn deposits in this belt and the crustal processes leading to their formation remain ill-constrained, mostly because of the lack of precise mineralization ages. We integrate textural information, geochemistry, and in-situ garnet U–Pb geochronology to constrain the timing and genesis of Pb–Zn mineralization. Garnets from the two deposits display oscillatory compositional zoning (And14Gr86 to And100) and contain variable U contents (0.07–5.3 ppm). Aluminum-rich garnet displays a chondrite-normalized rare earth element (REE) fractionation pattern in which LREEs are depleted relative to flattish HREE segments. In contrast, Fe-rich garnet shows LREE-enriched, relatively HREE-poor patterns with positive Eu-anomalies. Uranium concentration is correlated with total REE and Fe components in garnets, implying that U incorporation is largely controlled by coupled substitution mechanisms. The same garnets also contain measurable contents of other metals (up to hundreds of ppm), such as Sn, W, and In. The distribution and fractionation of major and trace elements in zoned garnets record periodic fluid pluses with different compositions during hydraulic fracturing. The new garnet U–Pb data show that the Yaguila deposit formed between 68.5 ± 3.4 and 65.0 ± 4.7 Ma, and the Lawu deposit formed at 54.6 ± 2.9 Ma. Within the geochronological framework of igneous rocks and Pb–Zn mineralization in the Nyainqêntanglha metallogenic belt, the new garnet ages suggest a magmatic-hydrothermal origin for related mineralization, with the causative magma likely derived from partial melting of ancient continental material due to rollback and subsequent breakoff of the Neo-Tethys oceanic slab during India–Asia continental collision. This study highlights the opportunities offered by garnet U–Pb dating for elucidating the formation age and ore genesis of base metal skarn systems.

Multiple pulses of fluids involved in the formation of carbonatite-related REE deposits as revealed by fluorite

Formation of carbonatite-related REE deposits generally associated with hydrothermal fluids exsolved from carbonatite melts. Deciphering the nature and evolution of the fluids is critical for establishing ore-formation models, and was mostly benefited from multi-analytical investigation of specific minerals presenting in multi-generation veins. However, there is a risk that the minerals in specific-generation veins not always precipitated solely from the single-stage fluids particularly for a dynamic mineralizing system. In order to evaluate this potential risk, this study conducted a combined textural, in situ trace elemental and fluid inclusion investigation of fluorite from multiple generations of veins in the Muluozhai carbonatite-related REE deposit, SW China. The veins dominate the mineralization system of the deposit, and include four generations/stages: fenitization (Stage I), pre-REE (Stage II), early REE (Stage III) and late REE (Stage IV) stages in which the ore minerals are all dominated by bastnäsite. Fluorite grains are widely present in these generations of veins, but high-resolution CL imaging reveal that most of them display complex internal textures composed commonly of core, mantle and rim domains from center outward. These domains exhibit different CL-intensities that are well correlated with chemical compositions and even types of fluid inclusions they hosted. This study confirmed that the “core-mantle-rim” textures of fluorite are essentially responses to interaction of early grains (i.e., represented by cores) with multi-stage fluids through dissolution-reprecipitation processes. Trace elemental and fluid-inclusion microthermometric results show that the cores (also for mantles or rims) in fluorite from Stages I to III veins have comparable REE concentrations and patterns and homogenization temperatures of fluid inclusions, strongly suggesting that the core-mantle-rim fluorite grains in these veins are originally formed at Stage I, and were variably captured or metasomatized by fluids of Stage II or III during development of these generations of veins. Similar core-mantle-rim fluorite grains are also present in Stage IV veins, and thus are constrained to be also “xenocrysts” formed in a similar manner. They are surrounded or even locally disturbed by a number of euhedral and/or slightly oscillatory fluorite grains which are supposed to be formed from a different manner. On the basis of their close association with bastnäsite and relatively high homogenization temperatures of fluid inclusions they host, we proposed that these euhedral fluorite grains are products of Stage IV fluids.Clear understanding of the internal textures and paragenesis of fluorite allows us to propose a genetic model for the Muluozhai deposit that the REE mineralization in Stages III and IV involves likely different pulses of carbonatite-related REE-rich fluids, and REE deposition was possibly mainly triggered by incursions of external fluids (e.g., meteoric water). This study also highlights that the phenomenon regarding presences of early-stage “xenocrysts” in late-generation veins of carbonatite-related vein systems may be more common than previously thought, and thus investigation in a textural context is critical for deciphering ore genesis.

Chronolgy and Geochemistry of the Sijiaying Iron Deposit in Eastern Hebei Province, North China Craton: Implications for the Genesis of High-Grade Iron Ores

The Sijiaying iron deposit is located in the Eastern Hebei area of the southern section of the northern margin of the North China Craton (NCC) and is the largest single iron deposit in China. The deposit contains many banded iron formations (BIFs) and was proven to have more than 3 million tons of high-grade iron ore resources. This study carried out geochemistry and zircon U–Pb analysis of normal-grade iron ore, high-grade iron ore, and wall rock (biotite–leptynite, chlorite–sericite schist) in the Sijiaying deposit and discussed the genesis and metallogenic age of high-grade iron ore. BIFs have low concentrations of Al2O3 and TiO2 and high field strength element (HFSE) depletion, indicating almost no contamination via terrestrial debris. The standardized post-Archean Australian shale (PAAS) rare earth element (REE) distribution pattern indicates that the iron formation exhibits positive Eu, Y, and heavy rare earth element (HREE) anomalies and lacks negative Ce anomalies, indicating that the Sijiaying BIF was enriched with iron sources via high-temperature hydrothermal fluids from the seabed and deposited in an anoxic ancient marine environment. In addition, geological field work identified two types of high-grade iron ore in the mining area: primitive sedimentary and hydrothermally altered high-grade iron ore. Further ore geochemical research showed that the primitive sedimentary-type iron ore is similar in geochemistry to the BIF. In addition to low Eu/Eu* values, the hydrothermally altered high-grade iron ore shows geochemical characteristics similar to those of the BIF, suggesting that they share the same iron source but did not form at the same time. The total large ion lithophile element (LILE) (Sr, Ba, Pb) contents in primitive sedimentary-type high-grade iron ore are higher than those in hydrothermally altered high-grade iron ore, indicating that LILEs are carried away via fluids during the hydrothermal alteration process in normal-grade iron ore. The geochemical characteristics of biotite–leptynite and chlorite–sericite schist include high contents of SiO2 and Al2O3, light rare earth elements (LREEs), LILE enrichment (Rb, Ba, Sr, Zr), and HFSE depletion (Nb, Ta, P, Ti), characteristics that are similar to island arc volcanic rocks. The reconstruction of the original rock indicates that the wall rock is a product of volcanic sedimentary cycles in an island arc setting. Zircon cathodoluminescence images and LA–ICP–MS zircon U–Pb dating can be divided into four age groups (3283 Ma, 2547 Ma, 2500 Ma, and 2407 Ma), which correspond to the earliest volcanic activity in eastern Hebei, the main mineralization age of the Sijiaying BIF (the mineralization age of primitive sedimentary high-grade iron ore), a regional tectonic–metamorphic event, and the occurrence of migmatization (the mineralization age of hydrothermally altered high-grade iron ore), respectively. Therefore, the Sijiaying BIF and primitive sedimentary high-grade iron ores were deposited and mineralized at 2547 Ma, and the iron orebody was later altered via the hydrothermal solution at 2407 Ma, forming large-scale high-grade iron ores.

In Situ Trace Element and Fe-O Isotope Studies on Magnetite of the Iron-Oxide Ores from the Takab Region, North Western Iran: Implications for Ore Genesis

The early Cambrian Takab iron ore deposit is situated in the northern part of the Sanandaj-Sirjan zone, western Iran. It consists of banded, nodular and disseminated magnetite hosted in folded micaschists. Trace element and Fe and O isotopic experiments reveal various hydrothermal precipitation environments under reduced to slightly oxidizing conditions. Disseminated magnetite has high Ti (945–1940 ppm) positively correlated with Mg + Al + Si, and heavy Fe (+0.76 to +1.86‰) and O (+1.0 to +4.07‰) isotopic compositions that support a magmatic/high-T hydrothermal origin. Banded magnetite has low Ti (15−200 ppm), V (≤100 ppm), Si and Mg (mostly ≤300 ppm) and variable Al. The ∂56Fe values vary from −0.2‰ to +1.12‰ but most values also support a magmatic/high-T hydrothermal origin. However, variable ∂18O (−2.52 to +1.22‰) values provide evidence of re-equilibration with lower-T fluid at ~200–300 °C. Nodular magnetite shows high Mn (≤1%), and mostly negative ∂56Fe values (average, −0.3‰) indicative of precipitation from an isotopically light hydrothermal fluid. Re-equilibration with carbonated rocks/fluids likely results in a negative Ce anomaly and higher ∂18O (average, +6.30‰). The Takab iron ore deposit has, thus, experienced a complex hydrothermal history.

Big data mining on trace element geochemistry of sphalerite

The determination of ore genesis is a main challenge in ore deposit research. Advanced and rapid analytical techniques have given rise to the accumulation of massive amounts of geoscientific data. Therefore, it is imperative to conduct data mining on ore geochemical data to efficiently extract useful metallogenic information. In this contribution, 4095 sets of sphalerite trace element data from 86 deposits of different origins (VMS, MVT, porphyry, epithermal, SEDEX, and skarn) were compiled and analyzed. Factor analysis revealed the effects of physicochemical conditions on sphalerite trace element compositions. Specifically, the high Mn-Fe-Cu-Co-In but low As-Ga-Ge-Sb-Pb concentration of sphalerite is commonly related to decreasing pH or increasing temperature; high sulfur fugacity favors the entry of Fe and Co (but not Ga or Sn) into the sphalerite lattice; and high salinity causes enrichment in Cd-Ga-Ge-Mn, but depletion in Ag-Cu-In-Sb. Multivariate statistical analysis reveals that the Mn-Ge-Sn contents in sphalerite have good potential to differentiate among ore genetic types, the Mn-Ge-In are used to determine between magmatic-hydrothermal and non-magmatic-hydrothermal deposits. Furthermore, machine learning models demonstrate high accuracy of sphalerite trace element data in distinguishing ore types, i.e., 93.02 % (random forest) and 92.82 % (gradient boosting), and its reliability was validated by receiver operating characteristics. Additionally, the blind tests by machine learning on sphalerite trace elements indicate that the Qingshuitang deposit (in the Qin-Hang metallogenic belt, South China), have been an MVT deposit, which is also supported by its low-temperature and high-salinity fluids, wallrock alterations (esp. bariteization), and the obvious age distinction between mineralization and local magmatism. This study highlights that machine learning and multivariate statistical analysis on sphalerite trace-element data can differentiate metallogenic origin and conditions.

Mineral Exploration Based on Quantified Spatial Relationships between Gold Deposits and Ore Genesis in Malaysia

Mineral Exploration Based on Quantified Spatial Relationships between Gold Deposits and Ore Genesis in Malaysia

Boron Isotopic Systematics and Its Significance in Natural Processes: An Overview

In recent years, interest in boron has expanded from microscopic to macroscopic levels, and several studies have contributed to understanding the role of boron in earth and natural processes. The boron isotopic composition provides a unique perspective into the crystallization process in granites, pegmatites, and temperature variations. Boron isotopic studies have been used as a tracer to understand geothermal systems, rivers, rock processes, reconstruction of pH and pCO2, groundwater pollution, and further help in understanding the changes which have occurred in oceans through geological time. Furthermore, boron isotopes have also been utilized to understand the genesis of ores and understanding subduction processes and as a tracer in groundwater pollution. In plants, it acts as a micronutrient. However, its deficiency and the excessive amount may inhibit the growth of plants, bacteria, and fungi and may also affect the soil and aquatic microflora. Boron maintains and regulates several metabolic pathways, and its quantity above a certain level may prove detrimental to the environment. This overview explains boron isotope variations and their implications in earth sciences and natural processes.

Geochronology, Geochemistry and Petrogenesis of the Bangbule Quartz Porphyry: Implications for Metallogenesis

AbstractThe Bangbule skarn lead‐zinc (Pb‐Zn) deposit (>1 Mt Zn + Pb) is located in the western Nyainqentanglha polymetallic metallogenetic belt, central Tibet. Lenticular orebodies are all hosted in skarn and developed in the contact zone between the quartz porphyry and carbonate strata of the mid Paleozoic Middle to Upper Chaguoluoma Formation as well as in carbonate and sandstone beds of the Upper Paleozoic Laga Formation. As a newly discovered skarn deposit, the geological background and metallogenesis of this deposit remain poorly understood. Detailed petrological, geochemical and geochronological data of the ore‐related quartz porphyry, helps constrain the mineralization age and contributes to discussion on the ore genesis of the Bangbule deposit. Both endoskarn and exoskarn are identified in the Bangbule deposit. From quartz porphyry to carbonate formation, the exoskarn is zoned from proximal garnet skarn to distal pyroxene skarn. Zircon U‐Pb dating results show that the quartz porphyry formed at 73.9 ± 0.8 Ma. Geochemical analysis results show that the quartz porphyry has high contents of SiO2 (71.40–74.94 wt%) and K2O + Na2O (3.76–8.46 wt%) with A/CNK values of 0.69 to 1.06. Besides, the quartz porphyry is enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and have low εNd(t) (from –8.25 to –8.19) and high initial (87Sr/86Sr)i values (0.713611–0.714478). Major, trace elements and whole‐rock F concentration analysis results from the endoskarn samples show higher TFe2O3, MgO, CaO, Pb + Zn, W, Sn, Mo and F etc., and lower alkalis (K2O, Na2O, Sr and Ba) than those of fresh quartz porphyry, indicating that the early ore‐forming fluids were an Ca‐Fe‐F‐enriched fluid. Massive ore in the proximal skarn might be related to the high F content in the magma, which lowered the solidus temperature of the quartz porphyry magma and caused a lower temperature of the ore‐forming fluids, as well as facilitating the precipitation of sphalerite and galena. Based on the geochemical characteristics presented in this study, we propose that the ore‐related quartz porphyry was formed by partial melting of crust materials with some juvenile crustal component input. The partial melting of the middle‐upper crust after the initial enrichment of lead and zinc elements are important for the formation of Pb‐Zn deposits. The case study of the Bangbule deposit has proven that there is still a crust‐derived magmatic source region in the western segment of the central Lhasa terrane. Therefore, there is still great potential for Pb‐Zn mineralization and Pb‐Zn exploration.

Geology, Fluid Inclusions, and C–H–O–S–Pb Isotope Geochemistry of Pb–Zn Deposits within the Tuotuohe Region of the Tibetan Plateau: Implications for Ore Genesis

The Tuotuohe region is a highly prospective area for Pb and Zn mineral exploration. This paper contributes to our comprehension of the ore-controlling structures, fluid inclusions, and C–H–O–S–Pb isotope geochemistry of Pb–Zn deposits in this region. These deposits are generally hosted by carbonates and controlled by fractures. The principal homogenization temperatures of quart- and calcite-hosted inclusions ranged predominantly between 120 and 220 °C, with salinities varying from 6 to 16 wt.% NaCl equivalent. The Pb isotope compositions of the ore deposits are comparable to those of Cenozoic volcanic rocks in the region but differ significantly from those of the host rocks, indicating that the Pb within these deposits was derived from the mantle. The C, O, and S isotope compositions of samples exhibit a bimodal distribution based on whether they were derived from magma or host rocks, implying that magma-derived fluids underwent an isotopic exchange with the host rocks. The H-O isotope compositions of samples also indicate that ore-forming fluids were originally magmatic but were depleted by combining with meteoric water. These findings are also supported by variations in fluid inclusion homogenization temperatures and salinities. Taken together, these findings suggest that the Pb–Zn deposits of the Tuotuohe region developed from magma to hydrothermal fluids at medium–low temperatures.