Vein Mineralization Research Articles

Genesis of the Ulaan silver-lead–zinc deposit in Northeast Mongolia: Constraints from S and Pb isotopes, together with U-Pb and Rb-Sr geochronology

The Ulaan silver-lead–zinc deposit (hereinafter referred to as the Ulaan deposit) is identified as the largest silver-lead–zinc polymetallic deposit in Mongolia, with proved reserves including 2,240 tons of silver (Ag; average grade: 49 g/t), 440,000 tons of lead (Pb; average grade: 1.13 %), and 810,000 tons of zinc (Zn; average grade: 2.07 %). However, the genesis of this deposit remains unclear. The Ag-Pb-Zn ore bodies in the deposit, occurring as cylinders in shape within the Middle-Late Jurassic rhyolites, are governed by a concealed breccia pipe. The ore minerals include galena, sphalerite, and pyrite, followed by chalcopyrite, hematite, stibnite, and siderite. The primary alterations of the surrounding rocks include silicification, chloritization, kaolinization, argillization, carbonatization, and skarnization. The Rb-Sr dating of sulfide minerals and associated vein minerals in the ores yielded isochron ages varying in a range of 146 ± 3 Ma (n = 6, MSWD=1.3), suggesting mineralization during the Late Jurassic. The δ34S values of sulfide minerals in the ores range from 1.6 ‰ to 4.3 ‰, suggesting that the sulfur originated primarily from magmas or deep sources. The isotopic compositions of coexisting sphalerite-galena minerals in the deposit revealed mineralization temperature estimates ranging between 331 °C and 449 °C, indicating a medium- to high-temperature ore-forming conditions. The sulfide minerals exhibit 208Pb/204Pb ratios ranging from 38.138 to 38.301, 207Pb/204Pb ratios from 15.543 to 15.594, and 206Pb/204Pb ratios from 18.318 to 18.354, suggesting that ore-forming metals, represented by Pb, also originated primarily from mantle source. The zircon U-Pb dating of rhyolites in the ore-hosting strata and ore-controlling breccia pipes yielded ages of 160.6 ± 1.7 Ma (n = 24, MSWD=0.68) and 161.6 ± 1.6 Ma (n = 30, MSWD=0.89), respectively, indicating volcanic eruptions during the early Late Jurassic. These ore-hosting rhyolites exhibit characteristics of A-type rhyolites, suggesting that they were formed in an intracontinental extensional environment. These rhyolites share similar rare earth element (REE) distribution patterns with fluorite formed in the main mineralization stage, suggesting a genetic link between the mineralization and magmatic processes. This study proposes that the Ulaan deposit was a hydrothermal deposit formed in an extensional environment following the closure of the Mongol-Okhotsk Ocean, with ore-forming metals and hydrothermal fluids associated with volcanic rocks or magmatic-hydrothermal processes.

Flotation separation mechanism of rutile and chlorite using CMC as depressant

In ores containing rutile, chlorite is the most common silicate gangue mineral. However, the flotation separation of rutile and chlorite has yet to be thoroughly studied. In this study, carboxymethyl cellulose (CMC) was used to depress chlorite when sodium oleate (NaOL) was used as the collector of rutile. The selective depression and its mechanism were investigated through micro-flotation experiments, zeta potential analyses, Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and particle video microscopy (PVM). Single mineral flotation showed selective depression of chlorite by CMC appeared at pH 7, NaOL concentration of 20 mg/L, and CMC concentration of 10 mg/L, when 88.39 % recovery difference between rutile and chlorite was obtained. The most effective concentration of CMC for the artificially mixed ore test was 15 mg/L, resulting in rutile recoveries and grades of 87.78 % and 75.28 % respectively. The results of Zeta, FTIR, and XPS tests indicate that the adsorption of CMC on chlorite surface is attributed to chemical and hydrogen bonding interactions, wherein the OH– and COOH– groups in CMC interact with hydroxyl groups of Fe2+ and Al3+ complexes, thereby diminishing chlorite floatability and impeding subsequent NaOL adsorption. PVM image further elucidates that hydration-repulsion interaction potentials between CMC-absorbed chlorite particles and gas bubbles deter particle adhesion. This markedly reduces chlorite ore carryover on bubble surfaces while minimally impacting rutile. This study can provide a theoretical basis for separating rutile and other vein minerals under the NaOL system.

Variability of lead-zinc sulfide ore slurry rheological properties and its influence on flotation conditions

We investigated how the rheological characteristics of a flotation slurry change in response to variations in mineral species, slurry concentration, and particle size; slurry pH; and trap and rheological control reagent concentrations using slurries containing galena, sphalerite, quartz, and kaolinite. The results indicate that reducing particle size and increasing slurry concentration leads to varying degrees of increase in apparent viscosity and yield stress. At the same particle size, the slurry exhibits the following order of apparent viscosity and yield stress: kaolinite > galena > sphalerite > quartz. In addition, as the slurry’s apparent viscosity and yield stress increase, the rheology decreases, creating progressively unfavorable conditions for the flotation of lead, zinc, and other target minerals. Furthermore, changes in pH have no significant effect on the slurry’s rheology when the slurry is comprised of vein minerals. Moreover, galena and sphalerite depict particle agglomeration in the slurry. Ultimately, the addition of sodium silicate as a rheological control reagent substantially enhances the slurry’s rheological properties. This results in a system where problematic minerals like kaolinite are more effectively dispersed, thereby promoting efficient lead-zinc mineral flotation. Regarding the flotation of lead sulfide and zinc minerals, the addition of kaolinite raises the apparent viscosity of the mixed slurry, hindering the flotation of the target minerals. Conversely, quartz lowers the apparent viscosity aiding the flotation separation process. Understanding the relationship between flotation conditions and the pulp’s rheological properties can provide valuable guidance for subsequent flotation tests.

MINERAL PARAGENESIS OF EARLY BIOTITE VEINS AT THE KUH-E JANJA Cu-Au PORPHYRY DEPOSIT, SOUTHEASTERN IRAN: IMPORTANCE OF MICROTEXTURAL OBSERVATIONS IN STUDIES CONSTRAINING THE RELATIVE TIMING OF HYPOGENE Cu MINERALIZATION

Abstract Veins consisting primarily of biotite are the earliest stockwork vein type recognized at the Kuh-e Janja Cu-Au porphyry deposit in southeastern Iran. These early biotite veins may contain quartz and minor amounts of sulfide minerals such as chalcopyrite and pyrite. Observations at the hand-specimen scale do not provide reliable constraints on the paragenetic relationships, as the early biotite veins have been repeatedly overprinted during the evolution of the magmatic-hydrothermal system. Microscopic investigations show that the sulfide minerals in the early biotite veins are texturally late, providing evidence that sulfide deposition did not occur at the high temperatures of biotite formation and potassic alteration of the host rocks. Chalcopyrite primarily occurs along hairline fractures that crosscut or refracture the earlier biotite veins. Biotite in contact with the chalcopyrite can be apparently unaltered or is replaced by chlorite, depending on the degree of wall-rock buffering of the magmatic-hydrothermal fluids that caused hypogene Cu mineralization. The findings add to the growing body of evidence that Cu mineralization in this deposit type occurs at temperatures close to the transition from ductile to brittle conditions (<450°C) following a drop in the pressure regime from lithostatic to hydrostatic conditions.

The Spatial and Temporal Evolution of the Sadisdorf Li-Sn-(W-Cu) Magmatic-Hydrothermal Greisen and Vein System, Eastern Erzgebirge, Germany

Abstract The Sadisdorf Li-Sn-(W-Cu) prospect in eastern Germany is characterized by vein- and greisen-style mineralization hosted in and around a small granite stock that intruded into a shallow crustal environment. The nature and origin of this mineral system are evaluated in this contribution by a combination of petrography and fluid inclusion studies, complemented by Raman spectroscopy and whole-rock geochemical analyses. The early magmatic-hydrothermal evolution is characterized by a single-phase low-salinity (7.0 ± 4 wt % NaCl equiv), high-temperature (>340°C), CO2-CH4–bearing aqueous fluid, which caused greisen alteration and mineralization within the apical portions of the microgranite porphyry. The bimodal distribution of brine and vapor fluid inclusions, and the formation of a magmatic-hydrothermal breccia associated with the proximal vein mineralization are interpreted to mark the transition from lithostatic to hydrostatic pressure. The vein- and stockwork-style mineralization (main stage) displays lateral zonation, with quartz-cassiterite-wolframite-molybdenite mineral assemblages grading outward into base-metal sulfide-dominated assemblages with increasing distance from the intrusion. Late fluorite-bearing veinlets represent the waning stage in the evolution of the mineral system. The similarity in the homogenization temperature (250°–418°C) of fluid inclusions in quartz, cassiterite, and sphalerite across the Sadisdorf deposit suggests that cooling was not a significant factor in the mineral zonation. Instead, fluid-rock interaction along the fluid path is considered to have controlled this zonation. In contrast to quartz-, cassiterite- and sphalerite-hosted fluid inclusions, which have a salinity of 0.0 to 10.0 wt % NaCl equiv, the fluid inclusions in late fluorite veins that overprint all previous assemblages have a salinity of 0.0 to 3.0 wt % NaCl equiv and homogenize at temperatures of 120° to 270°C, thus indicating cooling with or without admixture of meteoric fluids during the waning stage of the mineral system. The Sadisdorf deposit shares similar characteristics with other deposits in the Erzgebirge region, including a shallow level of emplacement, similar mineralization/alteration styles, and a hydrothermal evolution that includes early-boiling, fluid-rock interaction, and late cooling. In contrast to most systems in the region, both proximal and distal mineralization are well preserved at Sadisdorf. The recognition of such spatial zoning may be a useful criterion for targeting greisen-related Li and Sn resources.

Temperatures of Vein Formation Associated With Plate Interface Deformation Constrained by Oxygen and Clumped Isotope Thermometry

AbstractTectonic mélanges, characterized by conditions reflective of modern subduction fault zones, preserve mineral veins formed through mass transfer, a mechanism influencing the slip behavior of subduction megathrusts. In this study, we apply secondary ion mass spectrometry quartz‐calcite oxygen isotope thermometry and clumped isotope thermometry to examine the temperatures of vein formations in six mélange units in the Cretaceous Shimanto belt and one mélange in the Kodiak accretionary prism. Calcite in the veins exhibits δ13CPDB values ranging from −17.2‰ to −6.8‰, indicative of a carbon source mixing with sedimentary carbonate and organic matter. δ18OSMOW values of calcite range from +11.1‰ to +17.2‰; quartz yields δ18OSMOW values of +14.9‰ to +21.7‰. Oxygen isotopic signatures in minerals reveal that most vein‐forming fluids are significantly affected by rock buffering, while some retain isotopic compositions of seawater and meteoric water. Temperature estimates, derived from both thermometers, fall within the range of 100–250°C. Notably, vein temperatures remain constant across diverse vein types and mélange units with distinct maximum temperatures. The combined temperature records and fluid isotopic compositions imply vein formations at shallower depths linked to the incorporation of seawater, meteoric water, and fluid released from early dehydration reactions. At greater depths, vein formations are associated with fluid released from clay dehydration and long‐distance fluid flow. Reduced vein formations between 250 and 350°C may correlate with a shift to fluid‐unsaturated conditions resulting from clay hydration reactions. Our study highlights potential mechanical and hydraulic variations within the thermal conditions of 100–350°C along the plate boundary driven by fluid‐mineral interactions.

Geology, fluid inclusion, 40Ar-39Ar geochronology, and isotope constraints on the ore genesis of the Ershiyizhan Cu–Au deposit, Heilongjiang Province, China

The Ershiyizhan Cu–Au deposit, located in the eastern part of the upper Heilongjiang metallogenic belt, north of the Great Xing'an Range, is composed of orebodies from the Mesozoic magmatic rocks and the Ershierzhan group. There are three metallogenic stages of this deposit, (1) Quartz-K-feldspar-polymetallic sulfide stage (stage Ⅰ), (2) quartz-polymetallic sulfide stage (stage II), and (3) quartz-calcite ± pyrite stage (stage Ⅲ). Three types of fluid inclusions (FIs) were discovered in the vein mineral assemblages, liquid-rich two-phase aqueous FIs (L-type), vapor-rich aqueous FIs (V-type), and multi-phase FIs (S-type) with daughter minerals, including S1-type inclusions homogenized through vapor disappearance and S2-type inclusions homogenized by halite dissolution. Quartz of stage I and stage II contains all of these FIs. In contrast, the L-type fluid inclusions of stage III veins are the only ones present in the calcite. The homogenization temperatures and salinities obtained from FIs in stages I, II, and III range from 330 to 563 °C, 223 to 423 °C, and 108 to 225 °C, and 0.88 to 66.18 wt%, 2.41 to 48.59 wt%, and 0.18 to 3.23 wt% NaCl equiv., respectively. δ18O and δD values obtained from stable isotope analyses of K-feldspar and quartz samples collected from stages I, II, and III range from −2.31 to 7.89 and −133.2 to −98.2, respectively. Microthermometry and H-O isotope data from FIs suggest that the ore-forming fluids of the deposit had a magmatic origin, characterized by high temperatures, low–high salinities, an H2O-NaCl fluid system and this fluid system evolved to a low temperature, low salinities fluid through the gradual combination of meteoric water from stages II to III. Trapping pressures estimated from boiling L-type, V-type, and S1-type fluid inclusions in stage Ⅰ were 100–500 bars, corresponding to a mineralization depth of 1.0 to 5.0 km, with fluid boiling and mixing likely being responsible for the precipitation of sulfides and gold. K-feldspar from an auriferous vein of stage I yielded an 40Ar/39Ar isotopic plateau age of 131.21 ± 0.52 Ma, suggesting that the mineralization of the deposit is closely associated with the Early Cretaceous quartz monzonite porphyry. The analysis of the S isotope of metal sulfides in this deposit demonstrate that the sulfur reservoir is primarily derived from a hybrid magma source consisting of both mantle-derived and crustal-derived materials. Lead radioactive isotopic analysis for metal sulfides and various wall rocks also implies the lead source is a mixed source of upper crust and mantle. Thus, S-Pb isotope studies indicate that a crust-mantle mixed source for the mineralization of the deposit, and ore-forming material may originate from both quartz monzonite porphyry and various surrounding rocks including Late Triassic-Early Jurassic monzogranite, granite, quartz syenite, and the Ershierzhan Formation. Considering the geology, geochronology, FI, and H-O-S-Pb isotopic characteristics, the Ershiyizhan Cu–Au deposit is classified as a porphyry deposit formed in an extensional environment due to the delamination of the thickened lower crust following the Mongolian-Okhotsk Ocean closure.

Стадийность формирования кварц-альбит-алланит-фукситовых прожилков на Au-Pd-месторождении Чудное (Приполярный Урал)

The gold-palladium mineralization of the Chudnoe deposit is represented by mineralized veined zones in fractured and brecciated rhyolites of the Riphean-Vendian age. Native gold and palladium minerals are concentrated mainly in veins of Cr-containing muscovite (fuchsite), in which allanite is present in small amounts; quartz, albite, calcite, potassium feldspar, titanite, apatite, zincochromite and other minerals are also found. Veins of allanite-albite-quartz composition are found in ore zones, in some cases containing abundant fuchsite secretions. It has been established that quartz-albite-allanite-fuchsite and other fuchsite-containing veins are the result of the superposition of quartz-albite vein execution on previously formed gold-bearing fuchsite veins. Quartz-albite vein material fills central parts of the combined veins and cements fragments (xenoliths) of fuchsite, while in some cases part of the gold was redeposited and fixed in the quartz-albite part of the veins. Based on the study of the decomposition structures of solid solutions in native gold, it was previously established that the temperature of gold formation in fuchsite veinlets exceeded 220 °C. The deposition temperature of the main part of the quartz-albite veins was noticeably lower. The homogenization temperature of fluid inclusions in vein minerals (quartz, albite, allanite, calcite) was mainly in the range of 96—168 °C, solutions were enriched with magnesium and calcium chlorides. Under these conditions, allanite, apatite, monazite, xenotime, and molibdosheelite were formed and redeposited, and fuchsite recrystallized.

Mineral precipitation sequence from multi-stage fluids released by eclogite during high-pressure metamorphism

Abstract Arc magmas above subduction zones hold abundant fluid-mobile elements attributed to fluids released from the dehydrating subducted oceanic crust. However, the quantity of trace elements in the fluids and their evolution with the metamorphic processes during subduction and exhumation are still unclear. The precipitation sequence of vein minerals preserves the nature of multi-stage high-pressure (HP) metamorphic fluids and the fingerprint of mass exchange in deep subduction zones. In this contribution, we conducted detailed petrological studies and phase equilibria modeling on a unique HP omphacite-rich vein and its host eclogite from the Chinese southwestern Tianshan. The host eclogite consists mainly of garnet, omphacite, epidote, glaucophane, phengite, quartz, and rutile. Garnet in the eclogite records prograde subduction and early exhumation characterized by decompression heating at P-T conditions of ~2.4–2.6 GPa and 460–540 °C. The embedded omphacite-rich vein has similar mineral assemblage to the host eclogite. Garnet grains in this vein are predominantly distributed along or intersect the vein wall, which record similar eclogite-facies metamorphic conditions to that of the host eclogite. Omphacite is dominant in the vein, while epidote and glaucophane occur interstitially. Phase equilibria modeling reveals a sequential growth of garnet-dominated, omphacite-dominated, and epidote-dominated assemblages from fluids originating from the breakdown of different hydrous minerals. These lines of evidence suggest that the formation of multi-stage HP fluids are a continuous long-term process with a spontaneously short-distance transport and sequential mineral precipitation. Calculated fluid compositions demonstrate that the fluids released by lawsonite breakdown during exhumation have great potential to modify the trace element systematics of arc magmas. Our findings reveal the nature and evolution of multi-stage HP metamorphic fluids from internal sources during subduction and exhumation of oceanic crust, providing valuable insights into the chemical compositions of arc magmas.

Physico-chemical constraints associated with hypogene hydrothermal alteration and supergene oxidation at the Farallón Negro intermediate-sulfidation epithermal Au-Ag deposit, NW Argentina

The Farallón Negro deposit is located in the Farallón Negro Volcanic Complex (FNVC; ∼9.40 to 4.88 Ma) in NW Argentina and includes intermediate-sulfidation, epithermal Au-Ag mineralization in the Alto de la Blenda deposit. Detailed mineralogical and geochemical investigations of the Esperanza-Esperanza Sureste, Cecilia veins, both hosted in the Alto de la Blenda monzonite, and the Laboreo vein, hosted in the volcaniclastic Morada Central andesitic breccia, reveal four hypogene vein stages. Each of these four stages are comprised of a texturally early quartz, followed by a sulfide-sulfosalt and a late Mn-carbonate sub-stage. Stage 1 is characterized by a quartz, base metal and Mn-carbonate sub-stage showing high δ18OVSMOW (δ18OQuartz = 13.7 ± 0.4‰ and δ18OMn-Calcite = 11.6 ± 0.2‰) and low δ13CVPDB values (δ13CMn-Calcite = –4.7 ± 0.2‰). Stage 2 includes most gold and silver minerals in a tennantite-tetrahedrite-sphalerite-pyrite-galena±electrum sub-stage. Fluid inclusions trapped in vein-anhydrite, only associated with stage 2, record the highest temperatures (TEntrapment = 327–335°C) and highest salinity (3.8NaCleq.wt.%) when compared to all other stages. Stage 2 quartz (δ18OQuartz = 9.9 to 11.9‰) and carbonate display lower δ18OVSMOW (δ18OMn-Calcite = 7.9 to 10.3‰), as well as lower δ13CVPDB values (δ13CMn-Calcite = -5.2 to 4.7‰) than all other stages. Stages 3 and 4 consist of barren quartz and carbonate sub-stages that show lower temperatures (TEntrapment = 187–262°C) and higher δ18OVSMOW (δ18OQuartz = 13.4 to 13.9‰ and δ18OMn-Calcite = 10.7 to 11.8‰) and δ13CVPDB values (δ13CMn-Calcite = –3.5 to −3.9‰) when compared to earlier stages.Petrographic, sulfide mineral chemistry, microthermometric, and stable isotope data combined with distinct alteration mineral assemblages allow the reconstruction of a model for the Alto de la Blenda deposit. During the hypogene hydrothermal fluid flow stage, around 7.16 Ma, at ∼2.2 km depth (PHYDROSTATIC = 220 bars), the high temperature alteration mineralogy, low fluid salinities and 18O and 13C isotope compositions indicate cooling of ascending magmatic-hydrothermal fluids. These fluids were derived from a contracted magmatic vapor phase that exchanged with unexposed sedimentary rocks of the Sierras Pampeanas. Hypogene quartz-R3 illite/smectite-chlorite-calcite-pyrite alteration in the andesitic-breccia and quartz-illite-R3 illite/smectite-chlorite-calcite-pyrite alteration in the monzonite are temporally and spatially to the hydrothermal vein minerals deposited between 187 and 335°C. During the post-hydrothermal supergene weathering event, around 2.70 Ma, sulfuric acids generated by meteoric fluids and supergene oxidation of hypogene sulfides, particularly pyrite, descended along normal fault zones and related vein and fracture networks to at least 450 m depth below the surface level, forming the supergene alteration assemblage of dioctahedral smectite-kaolinite-Mn-/Fe-oxides/-hydroxides-gypsum±interstratified chlorite/smectite±interstratified R1 illite/smectite in both wall rock types at temperatures <50°C.The dominant hypogene alteration assemblage, present in the monzonite and volcaniclastic andesitic breccia, may be indicative of deeper-seated, transitional magmatic-hydrothermal systems (>1 km depth), generally controlled by fluid cooling, as is the case at Farallón Negro. Pervasive supergene alteration can conceal these systems but the identified supergene alteration assemblage of dioctahedral smectite-kaolinite-interstratified chlorite/smectite-interstratified R1 illite/smectite that replaces the hypogene alteration assemblage along the permeable fault, vein and fracture zone network may present a useful vectoring tool towards concealed, deeper-seated, epithermal Au-Ag mineralization in arid climates.

Petrogenesis of the alkaline complex in the Weishan REE deposit, Luxi Block, eastern North China Craton: Implications for REE mineralization

The Weishan REE deposit is one of the largest LREE deposits in China, which is hosted by the Weishan alkaline complex (WSAC) and late Archean gneisses. Two types of mineralization including vein-type and disseminated-type occur in this deposit, of which the former is characterized by large quartz-sulfate-calcite-REE mineral veins cutting all kinds of wallrocks, while the latter is featured by REE minerals disseminated in the alkaline rocks. The vein-type mineralization commonly occurs at shallow depths and has been numerously studied. The disseminated-type mineralization typically occurs at deeper depths, which was newly discovered by drilling exploration and has been poorly studied. In this contribution, zircon U-Pb dating and Hf isotopic analysis as well as whole-rock geochemistry and Sr-Nd isotopic analyses were conducted on the deeply drilled alkaline rocks, combined with molybdenite Re–Os dating on the disseminated ore, with the aim to unravel the petrogenesis of the alkaline rocks and their contributions to the REE mineralization. Zircon U–Pb dating suggests an intrusive age of 119.9 ± 0.9 Ma for the WSAC, which is quite consistent the Re–Os age of 120.0 ± 1.8 Ma for the disseminated ore, corroborating their close genetic correlation. The studied alkaline rocks show enrichment of LILEs, depletion of HFSEs and strong fractionation between LREEs and HREEs, indicating a crustal involvement in the magmas or a metasomatized mantle source. They are characterized by higher Hf (εHf(t) = -6.7 to −12.2) and Nd (εNd(t) = -8.8 to −9.7) isotopic compositions compared with those of the contemporaneous subcontinental lithospheric mantle (SCLM). Based on the above features, it is inferred that the parental magmas of the WSAC were mainly derived from an enriched SCLM with some involvement of asthenospheric mantle-derived materials. The mantle source was likely metasomatized by the subducted Paleo-Pacific oceanic plate, leading to the enrichment of REE and carbonate. Rollback of the oceanic slab during the early Cretaceous resulted in an extensional setting in the study region, which was favorable for partial melting of the metasomatized mantle and thus generated the REE-rich alkaline magmas.

Fluorite-bearing vein mineralization from Bartoušov near Havlíčkův Brod: a complex fluid history related to post-Variscan uplift of the Moldanubian basement (Bohemian Massif, Czech Republic)

Fluorite-bearing vein mineralization from Bartoušov near Havlíčkův Brod: a complex fluid history related to post-Variscan uplift of the Moldanubian basement (Bohemian Massif, Czech Republic)

Co enrichment and Au–Cu–Co association in the Yundukala deposit in East Junggar, NW China: An in situ LA-ICP-MS study

The Yundukala deposit is a newly discovered Au–Cu–Co deposit located in the northern margin of Junggar in the Central Asian Orogenic Belt. The Au–Cu–Co mineralization is associated with the contact zone between a dioritic intrusion and basalt. The formation of the vein mineralization can be divided into three mineralization stages: chlorite + pyrite, quartz + polymetallic sulfide, and quartz + calcite. Ore microscopy and in-situ laser ablation inductively coupled plasma mass spectrometry were used to investigate textural and compositional relationship between pyrite, chalcopyrite, arsenopyrite, and cobaltite. The gold in the deposit is present in two main mineralogical forms: native gold (micron inclusions of the gold) and invisible gold (solid solution of gold). Cobalt in the vein mineralization is primarily associated with cobaltite, whereas pyrite, chalcopyrite, arsenopyrite, and pyrrhotite contain small amounts of cobalt. There is a positive correlation between As and Au in Py-Ⅱ (R2Au-As = 0.9211; R2Au-As = 0.4306) and cobaltite and a positive correlation between Co and Au in cobaltite (R2Au-Co = 0.8168). This relationship supports a model in which arsenic plays a role in the occurrence of gold. The correlation of trace elements in minerals and the formation sequence and interpenetration relationship between minerals indicate the progressive geochemical evolution of a single ore-forming fluid arising from a single vein mineralizing event. Hydrothermal processes led to alteration of the surrounding rocks while simultaneously extracting Au, Cu, and Co, forming ore-forming fluids. As physical conditions changed, minerals began to precipitate, ultimately resulting in the formation of ore deposits during the Carboniferous period (354–353 Ma).

Evolution of skarn to quartz-vein mineralization: Insights from the Tongshanling Cu–Pb–Zn deposit, South China

The Tongshanling Cu–Pb–Zn deposit, situated within the Qin-Hang intra-continental porphyry-skarn metallogenic belt in South China, presents a valuable case study of intrusion-related ore systems. This deposit is characterized by skarn mineralization closely associated with subsequent quartz-vein sulfide mineralization. While considerable research has been devoted to understanding the origin and evolution of the intrusions and mineralization processes, limited attention has been given to elucidating the relationship between the skarn and quartz-vein mineralization, along with the physicochemical conditions governing their formation. Here, we conducted a comprehensive mineralogical and isotopic investigation of sulfides, and a thorough analysis of fluid inclusion assemblages. We aimed to discern disparities in the sources of ore-forming materials, formation temperature, sulfide fugacity, and precipitation-alteration mechanisms of hydrothermal fluids for these two distinct orebodies. Although same sulfide species including arsenopyrite, pyrite, chalcopyrite, and sphalerite, some silicate minerals such as garnet, chlorite, and epidote are exclusive to the skarn orebodies and absent in the quartz veins.The homogeneous temperatures of fluid inclusions in the skarn orebody, ranging from the early to late stages of evolution, decrease from ∼310 to ∼290 °C. Simultaneously, salinity varies from 5.5 to 3.1 wt% NaCl eqv. In the quartz vein mineral body, the temperature reduction is more pronounced, decreasing from ∼270 to 186 °C, with salinity ranging from 3.6 to 1.4 wt% NaCl eqv. Sphalerite geothermometer indicates that peak hydrothermal fluid temperature in the skarn orebodies (∼300–340 °C) was relatively higher than that in the quartz-vein orebodies (<300 °C). Nevertheless, temperatures in both hydrothermal fluid systems declined as mineral precipitation proceeded, corresponding to a decrease in sulfur fugacity. The final stage of sphalerite represents the lowest temperature, salinity and sulfur fugacity with associated quartz displaying the lowest salinity across the entire hydrothermal fluid spectrum at the Tongshanling deposit, suggestive of meteoric water incorporation. This study delves into the multifaceted history of mineralization at the Tongshanling deposit, providing a fresh perspective on the origin and evolutionary relationships of Cu-polymetallic deposits associated with intrusions, particularly those involving multiple stages of mineralization in skarns and quartz veins, contributing to a better understanding of similar deposits worldwide.

Eclogite dehydration and melt‐induced embrittlement at high‐pressure conditions

AbstractWe document the complex interaction between metamorphic reactions and deformation behaviour at high‐pressure conditions by combining (micro‐) structural, petrographical and geochemical data from an eclogite body. The well‐equilibrated eclogite fabric is crosscut by mineral veins. Precipitated veins host the eclogitic high‐pressure assemblage with variation in modal composition, indicating that fracturing occurred at eclogite facies conditions. Deflection of the eclogite fabric adjacent to the veins implies ductile reactivation of the veins as flanking structures and strain localization under continuous aseismic shearing. In consequence, the reactivated veins are characterized by undulatory extinction and subgrain formation in quartz indicating crystal plasticity. We show that prograde post‐eclogitization metamorphism resulted in progressive dehydration and melting of the eclogite. Subsequent increase in pore‐pressure‐induced rock failure. The mesoscopic to microscopic characteristics of eclogite‐facies veins indicate a cyclic behaviour of fracturing, vein formation and crystal‐plasticity which demonstrates the strong interaction of chemical and mechanical processes operating at depth.

The "Creuseurs" ("Diggers"), at the Center of the World's Push for EVs, are in Peril: Part One-The Precarious Reality of Artisanal Mines.

Electronics Watch travelled to Kolwezi in the province of Lualaba, in the south of the Democratic Republic of Congo. Two worlds live side by side here, without ever crossing paths. On the one hand, the world of industrial mines, with their huge machines. On the other, the tens of thousands of "diggers" in small-scale artisanal mines, armed with a simple crowbar to exploit a mineral vein, in extremely dangerous conditions. The DRC alone has 80% of the world's cobalt stocks needed to manufacture batteries to serve the demand for electric vehicles, and no less than 30% of this stock is mined in an artisanal way. One to two million Congolese people depend on this production directly or indirectly, while world demand is booming.

First‐principles study on the surface properties and floatability of magnesite tailings and its main gangue

AbstractThe accumulation of magnesite tailings (MT) poses challenges such as resource wastage, land occupation, dust generation, and environmental pollution, thereby jeopardizing both physical and mental health. Urgent attention is required for the proper treatment of this solid waste material. An in‐depth investigation into enhancing the flotation processes of MT is essential. A comprehensive comprehension of the surface properties of MT and its principal gangue minerals assumes paramount importance in facilitating the desilication and decalcification of MT via flotation. In this investigation, a first‐principles study grounded in density functional theory was employed to scrutinize the surface properties, as well as the similarities and differences in flotability, of four minerals‐quartz, magnesite, dolomite, and calcite. The findings reveal that quartz's primary cleavage plane is (1 0 1), whereas that of magnesite, dolomite, and calcite is (1 0 4). The surfaces of magnesite, dolomite, and calcite exhibit chemical similarities, with Ca atoms demonstrating higher reactivity than Mg atoms. The hydrogen bonding between dodecylamine and quartz emerges as the most robust, while adsorption energies with the three carbonate minerals exhibit minimal disparity. The ongoing focus lies on the selection and optimization tests of decalcification reagents. A moderate quantity of dodecylamine manifests a certain desilication effect. However, excessive dosage compromises selectivity. The first‐principles approach offers guiding significance for elucidating the surface properties of MT and its primary vein minerals, along with investigating the adsorption mechanisms of flotation regents.

Duplex Underplating, Sediment Dehydration and Quartz Vein Mineralization in the Deep Tremor Source Region

AbstractDeep tectonic tremor downdip of the seismogenic zone in warm subduction zones is thought to occur in the region of high fluid pressures. However, the deformation and fluid processes responsible for tremor are poorly understood. We examined the Tomuru metamorphic rocks on Ishigaki Island, southern Ryukyu Arc, deformed at ∼40 km depth and ∼450°C under epidote‐blueschist metamorphism comparable to the tremor source region in northern Cascadia subduction zone. Here, quartz vein‐rich metapelite and metabasite are repeated many times as a result of duplex underplating. The spatiotemporal relationship between clustered quartz veins and the juxtaposition of metapelite and metabasite suggests that quartz vein formation and duplex underplating are contemporaneous. Viscous shear in metapelite is accommodated by dissolution‐precipitation creep. Metabasite records heterogeneous dehydration, resulting in rheological heterogeneity characterized by greenschist lenses in the foliated blueschist matrix. Viscous shear in the blueschist matrix was mainly accommodated by dissolution‐precipitation creep of glaucophane. Geochemical and strontium‐neodymium isotope analyses indicated that quartz veins were derived from sediment dehydration, whereas dehydration from oceanic crust contributed neither to quartz vein formation nor to fluid overpressures. We suggest that high fluid pressure in the deep tremor source region is primarily controlled by dehydration of subducting sediments, and the clustered quartz veins in underplated rocks correlate with the overpressured tremor source in low shear‐wave velocity zones.

Seismic faulting and CO2-rich fluid interactions: Evidence from carbonate spherulitic grains in ultramafic fault damage zones

Faults and shear zones in the metamorphic ultramafic rocks of the Voltri Massif (Ligurian Alps, NW Italy) are often accompanied by intense or complete carbonation of the host rocks. One of these fault zones, hosted in peridotite and serpentinite, is characterized by distinctive structural features that can be related to a fluid-assisted multistage brittle deformation, indicative of paleoseismic activity. The fault rocks contain cataclasite and breccias with layers of coseismic spherulitic grains of dolomitic composition, silica/calchedony veins and cement, and saponite bearing gouge. The fault is part of a system of regional structures associated with gold mineralization in quartz veins and various stages of hydrothermal alterations.Here we present a multiscale study of this fault zone combining field observations, microstructural analysis, SEM-EDS, and electron backscattered diffraction (EBSD). Focus is on the microstructures of the fault core and the significance of the characteristic carbonate spherulite layers in association with silica/chalcedony cement and veins. Our results show that these structures are indicative of the interaction between CO2-rich fluids released during coseismic and interseismic phases of faulting, i.e., during cycles of fluid pressure build-ups, faulting, fluid flushing, and mineral precipitation and sealing during seismic failure of the fault.

The effect of weathering on cohesion in granitic fault rocks: A case study from the Yeongdeok Fault, South Korea

Weathering can alter fault-rock cohesion, which is an important criterion in the classification of fault rocks, and can also alter fault-rock mechanical and hydraulic properties. To investigate the effects of weathering on fault rocks, we studied relatively fresh and weathered fault rocks collected from a drill core and outcrop, respectively, of a granitic fault zone (the Yeongdeok Fault, a northern branch of the Yangsan Fault) on the southeastern Korean Peninsula. At the studied outcrop, the Yeongdeok Fault has juxtaposed Triassic granite against Cretaceous sedimentary rocks. Granitic fault rocks in the outcrop are incohesive, whereas the drill core includes both cohesive and incohesive granitic fault rocks. A detailed correlation of the fault rocks from the drill core with those from the outcrop reveals that some incohesive fault rocks from the outcrop are weathered cataclasite. Cataclasites from the drill core are composed of feldspar, plagioclase, and quartz fragments embedded in a matrix of quartz, plagioclase, muscovite, and chlorite. Locally, foliation defined by the preferred orientation of muscovite is developed. The weathered cataclasite comprises quartz, plagioclase, and feldspar fragments, with a fine-grained matrix composed mostly of clay minerals. The measured Chemical Index of Alteration (CIA) values for cataclasite and weathered cataclasite are 47–49 and 60–67, respectively. Measurements of hydraulic properties show that weathered cataclasite has higher porosity and permeability compared with unweathered cataclasite. Physical and chemical weathering are interpreted to have increased the fracture density of the weathered cataclasite and enhanced the dissolution of vein minerals, respectively. These processes have not only contributed to the higher permeability and porosity of the weathered (cf. unweathered) cataclasite but have also resulted in a loss of cohesion. When cohesion is lost due to weathering, distinguishing between cataclasite and fault breccia becomes challenging. Our study demonstrates that the cohesion-based classification of fault rocks becomes limited for fault rocks with CIA value more than 60.