Vein Mineralization Research Articles

Mineralogická charakteristika barytové mineralizace z lokality Ruda-hájenka (hornoměstský rudní revír, silezikum)

The previously unknown remnants of old mining activity were recently found at the locality Ruda-hájenka in the SW part of the Horní Město Ore District (Northern Moravia, Czech Republic). Partly weathered fragments of baryte mineralization in association with acid metavolcanites of the Vrbno Group (Devonian, Silesicum) were found in the dump material. Baryte mineralization exhibits a fine-grained marble-like appearance and locally contains minor disseminated pyrite. A detailed mineralogical study also revealed the presence of trace amount of other hypogene sulphides (galena and sphalerite), whose chemical composition is similar to those reported from the Horní Město Ore District. In addition, baryte also contains individual grains or aggregates of quartz, K-feldspar, and muscovite, which are often corroded and replaced by baryte. The silicates contain negligible amount of Ba (up to 0.02 apfu), which is only slightly higher than those in the same mineral phases from the host metavolcanic rock. The isotope composition of sulphur in baryte and pyrite indicates at least two different sources of sulphur (marine sulphate and likely sulphur leached from wall rocks) and isotope disequilibrium between co-existing minerals. The texture and mineral composition of the studied mineralization resemble metamorphosed baryte mineralizations occurring in the wider area (including local stratiform baryte bodies), but the absence of elevated contents of Ba in feldspars and especially in mica contradicts with an idea of Variscan metamorphic re-crystallization of the studied mineralization together with its host rock environment under the greenschist facies conditions. Therefore, one cannot exclude the possibility that it can be a post-metamorphic vein mineralization, which experienced intense deformation and recrystallization at very low temperatures, associated with rejuvenation of fault-related tectonic activity. The supergene mineral phases are represented especially by limonite, less frequent are minerals of the hollandite group (hollandite, coronadite, cryptomelane), anglesite, cerussite, and a not very well identified Ce-mineral, most likely cerianite-(Ce). Supergene origin is also presupposed for rarely found acanthite.

Late orogenic faulting and associated vein mineralisation in Saxothuringian metasediments – implications for crustal strength estimates

Late orogenic faulting and associated vein mineralisation in Saxothuringian metasediments – implications for crustal strength estimates

Quartz veins and silver-containing crushing zones in the exocontact of Solur granite stock (Kularsky district, Yakutia)

The purpose of the work is a investigation of quartz varieties present in quartz veins and crushing zones in order to establish the formation conditions and the possibilities of using quartz varieties to study the distribution of mineralization during exploration. The work was stimulated by the discovery of gold and gold-silver mineralization in adjacent areas and the possibility of using some new methods for studying quartz. Research methods. Samples for the study were taken during the mineralogical mapping of the studied area in the course of work to assess the prospects for its ore potential. The characterization of quartz from veins and crushing zones was carried out on the basis of its field descriptions and laboratory microscopic study, as well as measurements of X-ray luminescence (RL) of vein quartz in the region of 350–550 nm. Fluid inclusions in quartz and sulfur isotope composition in sulfides from quartz veins were also studied. Results and conclusions. The granite stock, surrounded by a zone of contact hornfels with cordierite and andalusite, lies among terrigenous sedimentary rocks that have undergone metagenesis (anhimetamorphism). Veins of glassy coarse-grained quartz and recrystallized (granular) quartz are located directly in the granites, partially recrystallized gray quartz – among the contact cornea, and veins of deformed milky-white quartz - in terrigenous sedimentary rocks outside the contact halo. As the transition from veins located among granites to veins located outside the granite massif, the intensity of quartz RL decreases sharply. The nature of the RL indicates the probable presence in the crystal lattice of quartz from veins in granites of their own defects – vacancies of oxygen or silicon, and in gray and milkywhite quartz – cation-compensated [AlO4 /M+]-centers. Sulfide mineralization in quartz veins is mainly represented by arsenopyrite with an isotopic composition of sulfur close to the meteorite standard. In addition to quartz veins, later crushing zones with hydrothermal injection breccias are also common in the area. In breccia cement and in breccia-intersecting veins, early non-split hypidiomorphic quartz and later split comb-shaped and chalcedony quartz are present. In micro-cryptogrаined chalcedony quartz with grain size up to 0.05 mm contaminated with inclusions of finely crushed rock particles and kaolinite grains, the inclusions of the pyrargyrite – one of the main silver-containing minerals on a number of gold-silver deposits of the region – were found. Based on the known vertical zonality of epithermal gold-silver deposits with the confinement of kaolinite-containing ores and chalcedony quartz to the upper horizons of the deposits, and due to the presence of micro-cryptograined chalcedony quartz containing kaolinite and pyrargyrite in the considered crushing zones, it can be suggested that these crushing zones may be confined to the upper parts of the silver mineralization development zone.

Cassiterite deposition induced by cooling of a single-phase magmatic fluid: Evidence from SEM-CL and fluid inclusion LA-ICP-MS analysis

Cassiterite (SnO2), the principal ore mineral of tin, is mainly formed in granite-related magmatic hydrothermal systems. The precipitation mechanism of this mineral in hydrothermal veins is still debated due to lack of direct constraints on this specific mineralization process. Here, we present a detailed reconstruction of fluid evolution history from a high-grade cassiterite-quartz vein in the Weilasituo Sn-polymetallic deposit, North China, based on combined SEM-CL imaging with fluid inclusion microthermometry, Raman and LA-ICP-MS analysis of intergrown cassiterite and gangue minerals.Formation of the cassiterite-quartz vein at Weilasituo started from early topazization and muscovite deposition along vein walls and was followed by crystallization of topaz, quartz (Q1) and cassiterite in a general sequential order. Cassiterite deposition occurred within a restricted time period before complete crystallization of topaz and quartz. Shortly after cassiterite precipitation, the vein was fractured and overprinted by later quartz generations (Q2 & Q3) and fluorite. In situ microanalysis on primary and/or pseudosecondary fluid inclusions from the different crystallization stages indicates that an acid and reduced single-phase magmatic fluid of gradually dropping temperature but very consistent salinity was responsible for vein formation. Mixing of this magmatic fluid with a biotite-plagioclase gneiss buffered, deep-cycled underground water of lower temperature and salinity occurred at the final stage, but it is not related to Sn mineralization. The physical and chemical changes of fluids bracketing cassiterite deposition demonstrate that cassiterite precipitation at Weilasituo was predominately induced by the cooling of the hydrothermal fluid by at least 50 °C, and it is accompanied by the oxidation of Sn(II)-Cl complexes with CO2 and/or As(III) species as potential oxidants. Early stage fluid-rock interaction with feldspathic host rocks and the formation of muscovite coverage on the vein walls are perhaps important for providing a fluid-buffered environment ideal for such mechanism. However, our result argues against meteoric water mixing or fluid boiling being the triggers of cassiterite deposition, and this conclusion has been further supported by cassiterite oxygen isotope analysis on the same set of samples.Additionally, the maximum base metal endowment (Pb and Zn) calculated from initial metal contents of the premineralization fluid at the Weilasituo Sn-polymetallic deposit are far less than proven reserves found in the two adjacent base metal deposits, and therefore a genetic link between these deposits is not suggested. This finding may have important implications for the ongoing exploration in the ore district.

Hydrothermal fluorite solubility experiments and mobility of REE in acidic to alkaline solutions from 100 to 250 °C

Fluorite is a common vein mineral in critical mineral deposits that are overprinted by hydrothermal processes. Its chemistry potentially reflects the mobilization conditions of rare earth elements (REE) in these hydrothermal fluids. However, the controls of temperature and fluid chemistry (i.e., pH and salinity) on fluorite solubility and coupled REE mobilization is still uncertain. In this study, batch-type experiments were conducted to investigate REE mobility in aqueous fluids controlled by the solubility of fluorite at temperatures between 100 and 250 °C. Natural fluorite crystals from Cooke’s Peak (New Mexico) were equilibrated with aqueous solutions of variable starting pH (2–10), salinities (0 and 15 wt.% NaCl), and initial REE concentrations (0 and 0.5 ppm). Reacted fluorite crystals display dissolution-controlled reaction textures (i.e., etch pits and dissolution channels along fluorite cleavage planes), which are most pronounced in experiments conducted in acidic fluids and at elevated temperature. Addition of NaCl considerably enhances fluorite dissolution, in both acidic and alkaline solutions, which is also reflected by the compositions of the reacted solutions displaying an increase in Ca, F, and REE concentrations. The overall fluorite solubility is controlled by the association behavior of HF0 at acidic conditions, and by the formation of Ca chloride, Ca hydroxyl, and Na fluoride complexes, which become enhanced by addition of NaCl, including in mildly acidic and alkaline solutions. Mass balance calculations were used to compare the REE stoichiometry of unreacted fluorite crystals with measured REE concentrations in the reacted solutions, which reveal several possible controls on REE mobility: i) stoichiometric release of REE upon fluorite dissolution; ii) precipitation of secondary REE-depleted fluorite; and/or iii) precipitation of secondary light REE fluorides, which were observed to form on fluorite crystals surfaces in the REE-doped experiments. Fluorite solubility constants (Ksp) were regressed with available low temperature solubility data using the equation logKsp = A + BT + C/T + Dlog(T) (T, temperature in K) valid between 25–250 °C. Fitted coefficients yield: A = 171.180, B = 0.01477, C = −7794.10, D = −64.6634. The experimental results have important implications for geochemical modeling of natural systems, where fluorine controls the mobility of REE, and can be enhanced by addition of NaCl in both acidic and alkaline solutions. Therefore, the salinity of magmatic-hydrothermal fluids plays a crucial role in mobilizing REE during the formation of hydrothermal fluorite veins.

Slab-derived fluid storage in the crust elucidated by earthquake swarm

Slab-derived fluids control crustal dynamics in the subduction zone. However, the slab-derived fluid budget has never been quantified beyond a geophysical and geological spatiotemporal resolution. Here, we target an intense earthquake swarm associated with the M9 Tohoku earthquake, which represented the critical dynamic behavior of slab-derived fluid. The fluid volume involved has been quantified, with a plausible range of 106−108 m3, by utilizing injection-induced seismicity insights. Comparisons with geological proxies suggest that the estimated fluid volume can be accumulated via supply from the lower crust within 102–104 y. Our study demonstrated such amount of aqueous fluid stored at the midcrustal level, which triggered consecutive swarm activity for ~2 y with the Tohoku earthquake, suggesting a possible link between earthquake swarms to M9 class earthquakes (103 y cycle) and mineral veins and deposits. This study has shed light on the quantitative understanding of the dynamic slab-derived fluid budget.

GEOLOGY AND ORE CHARACTERISTICS OF LOW SULFIDATION EPITHERMAL GOLD MINERALIZATION AT TAMBANG SAWAH, LEBONG, BENGKULU PROVINCE

Abstract –– Tambang Sawah Area, Lebong Regency, Bengkulu Province, is geologically located in the Barisan mountains and Sumatra fault zone. The prospect of Tambang Sawah area lies in the physiography of the central Sumatran mountains ranges composed by the igneous rocks of the Sunda – Banda magmatic arc. This study is aimed to understand the deposit geology and ore characteristics of the gold deposit at the study area. Quartz vein mineralization of Tambang Sawah occurred in granite rock intruded into andesitic breccia rocks, with the geological structure of mineralization control in the form of joint, breccia, dike, and fault, namely the Ketahun fault that forms extentional fracture zones which were filled by hydrothermal fluid in form of quartz veins. Hydrothermal alterations that appear at the study site are typical types of alterations found in epithermal gold deposits, namely, argillic, silicified and propylitic. Sulfide minerals markers of low sulfidation epithermal type gold deposits found, namely, pyrite, calcopyrite, covelite, sphalerite and galena with colloform vein texture, cockade-crustiform, moss, and brecciated texture. Gold is interpreted to be derived from the deposition of sulfide minerals and the deposition of quartz veins, the level of gold in rocks and veins varies greatly with an average 4,8 ppm. Based on the results of ore geochemical analysis of positively correlated gold with elements Ag, Cu, Pb and Zn.
 Keywords: Mineralization, low sulfidation epithermal gold, Tambang Sawah, Lebong, Bengkulu.

A review of natural hydrofractures in rocks

AbstractHydrofractures, or hydraulic fractures, are fractures where a significantly elevated fluid pressure played a role in their formation. Natural hydrofractures are abundant in rocks and are often preserved as magmatic dykes or sills, and mineral-filled fractures or mineral veins. However, we focus on the formation and evolution of non-igneous hydrofractures. Here we review the basic theory of the role of fluid pressure in rock failure, showing that both Terzaghi’s and Biot’s theories can be reconciled if the appropriate boundary conditions are considered. We next discuss the propagation of hydrofractures after initial failure, where networks of hydrofractures may form or hydrofractures may ascend through the crust as mobile hydrofractures. As fractures can form as a result of both tectonic stresses and an elevated fluid pressure, we address the question of how to ascertain whether a fracture is a hydrofracture. We argue that extensional or dilational fractures that formed belowc.2–3 km depth are, under normal circumstances, hydrofractures, but at shallower depth they may, but must not be hydrofractures. Since veins and breccias are often the products of hydrofractures that are left in the geological record, we discuss these and critically assess which vein structures can, and which do not necessarily, indicate hydrofracturing. Hydrofracturing can suddenly and locally change the permeability in a rock by providing new fluid pathways. This can lead to highly dynamic self-organization of crustal-scale fluid flow.

New insights into the petrogenesis of rhyolites and evolution of volcanic‐hosted massive sulphide mineralization from shallow borehole core, Betul Belt, Central India

Shallow borehole drilling has been conducted at the Sarni area of Betul Belt, Central India to understand the subsurface geology and nature of mineralization. The predominant lithounits are ferruginous quartzites, felsic volcanic rocks, and with minor intrusions of amphibolites. The encountered felsic volcanic rocks are rhyolites varying from pink (rich in K‐feldspar) to grey (rich in Na‐feldspar and amphiboles). The rhyolitic rocks have undergone intense hydrothermal alteration. The alteration zones are defined by the presence of biotite‐chlorite‐garnet‐gahnite; biotite‐sericite‐chlorite‐anthophyllite and anthophyllite‐actinolite‐tremolite‐carbonate mineral assemblages. Sulphide pits, highly leached zones with occasional bluish tinges, limonitic patches are present in the felsic volcanic rocks, followed by semi‐massive to disseminated sulphide mineralization indicative of Kuroku‐ type Zn–Cu–Pb volcanic‐hosted Massive Sulphide (VHMS) mineralization. Scanning electron microscope and energy‐dispersive x‐ray spectroscopy studies documented sphalerite, pyrite, chalcophyrite, arsenopyrite, pyrrhotite, and minor Au–Ag phases. The Sarni rhyolites exhibit chalcopyrite disease in sphalerite, replacement, and overgrowth ore‐textures. The high HFSE, low Zr/Y ratio, pronounced negative Eu anomalies characterize the felsic volcanic rocks as FIIIb type with high zircon saturation temperatures of 856–931°C. These rhyolites are formed at a back‐arc rift setting in an ensialic island‐arc tectonic regime. The synvolcanic structures facilitated the magma ascent to the surface. The hydrothermal circulation due to adequate heat flow in the back‐arc rift environment, in an episodic multicyclic process provided sufficient time for accumulation of sulphides from the seafloor, which was later deposited to form a VHMS mineralization. We also report tungsten (W) mineralization in the quartz veins of these felsic volcanic rocks. It is suggested that the felsic magma has interacted with metasedimentary sequences and assimilated W‐ore bearing fluids, and during remobilization in the later stages of tectonic activity enabled the deposition of tungsten in these quartz veins.

Sealing fractures to increase underground storage security: Lessons learned from a multiscale multimodal imaging study of a syntaxial vein in a mudrock

Veins recovered from deep sedimentary formations offer insights into mineral precipitates and processes that lead to sealing of underground fractures. These processes are of interest in the context of subsurface negative emissions technologies such as geologic carbon storage, where fractures are potential pathways for unwanted fluid migration. In this study, we characterized the mineralogy and porosity of a syntaxial vein in a mudrock sample from the Wolfcamp formation in Texas. The original fracture had an aperture of 5 mm and is now filled with distinct zones of minerals and vuggy regions. Thin sections from cuts across the vein were examined at micron scale resolution using scanning electron microscopy, energy dispersive X-ray spectroscopy, QEMSCAN, and polarized light microscopy. Larger-scale analyses were done using synchrotron X-ray fluorescence. Collectively, these methods reveal elongated crystals of dolomite as large as 900 μm, overlain with a mixture of smaller crystals including calcite and ferroan dolomite. Silica fills some of the void space. Mineral identification was corroborated using powder X-ray diffraction. Quantitative analysis of a 3D X-ray computed tomography image indicates that the vein volume contains 62% elongate dolomite crystals, 33% mixed ferroan dolomite and calcite, 1% silica, and 4% vuggy void space. Synchrotron small and ultra-small angle X-ray scattering reveals that the vein mineral precipitates have ~1% porosity. This is much smaller than the porosity of the mudrock matrix. The findings in this study suggest that as the formation formed and subsided, fracture fluids migrated vertically and experienced pressure reduction causing exsolution of CO2. A geochemical simulation demonstrated how this could have led to carbonate precipitation in the veins. A fundamental understanding of the sequence of vein mineral precipitation and the associated reduction in porosity may inspire strategies designed to induce fracture sealing, thus preserving the integrity of underground fluid storage. Changes that would lead to CO2 exsolution, carbonate supersaturation, and mineral precipitation include increasing the pH, addition of divalent cations, enabling vertical migration with subsequent depressurization, and heating to reduce carbonate solubility.

The propagation paths of fluid-driven fractures in layered and faulted rocks

AbstractFractures that form when fluid pressure ruptures the rock are referred to as fluid-driven fractures or hydrofractures. These include most dykes, inclined sheets and sills, but also many mineral veins and joints, as well as human-made hydraulic fractures. While considerable field and theoretical work has focused on the geometry and arrest of hydrofractures, how they select their propagation paths, particularly in layered and faulted rocks, has received less attention. Here I propose that of all the possible paths that a given hydrofracture may follow, it selects the path of least (minimum) action as determined by Hamilton’s principle. This means that the selected path is that along which the energy transformed (released) multiplied by the time taken for the propagation is a minimum. Hydrofractures advance their tips/fronts in steps, with a time lag between the fracture front and the fluid front. In the present framework, each step is then controlled by Hamilton’s principle. The results suggest that when the hosting rock body is regarded as homogeneous, isotropic and non-fractured, hydrofracture paths are everywhere perpendicular to the trajectories of the minimum compressive (maximum tensile) principal stress σ3 and follow the trajectories of the maximum principal compressive stress σ1. When applied to layered and faulted rock body, the results indicate that hydrofracture paths may follow existing faults for a while, depending primarily on (1) the dip of the fault (steep faults are the most likely to be used by vertically propagating hydrofractures), and (2) the tensile strength across the fault compared with the tensile strength of the host rock along a path following the direction of σ1. The results suggest that hydrofractures may use faults as parts of their paths primarily if the fault is steeply dipping and with close to zero tensile strength.

Transport of Geothermal Fluids along Dikes and Fault Zones

Field observations of active and fossil natural geothermal fields indicate that geothermal fluids are primarily transported along dikes and fault zones. Fluid transport along dikes (commonly through fractures at their margins) is controlled by the cubic law where the volumetric flow rate depends on the aperture of the fracture in the 3rd power. Dikes (and inclined sheets) also act as heat sources for geothermal fields. In high-temperature fields in volcanoes in Iceland dikes and inclined sheets constitute 80–100% of the rock at crustal depths of 1.5–2 km. Holocene feeder-dikes are known to have increased the activity of associated geothermal fields. Fault zones transport geothermal fluids along their two main hydromechanical units, the core and the damage zone. The core is comparatively thin and primarily composed of breccia, gouge, and clay and related low-permeability porous materials. By contrast, the fault damage zone is characterised by fractures whose frequency is normally highest at the contact between the core and the damage zone. Fluid transport in the damage zone, and in the core following fault slip, is controlled by the cubic law. During non-slip periods fluid transport in the core is primarily controlled by Darcy’s law. Secondary mineralisation (forming mineral veins and amygdales) tends to reduce the fault-zone permeability. Repeated earthquake activity is thus needed to maintain the permeability of fault zones in active natural geothermal fields.

U–Pb and Re–Os geochronology of the Yundukala Au–Cu–Co deposit in East Junggar, NW China: Constraints on the timing of mineralization and ore‐bearing rocks

East Junggar is an important part of the Central Asia Orogenic Belt and has developed a multi‐epoch and multi‐type metallogenic system. Yundukala is a recently discovered large intrusion‐related Au–Cu–Co deposit. The No. 1 main mineralization zone mainly occurs in the contact area between fine‐grained diorite and basalt. Massive and vein mineralization have developed there, but the ore‐bearing stratum, ore‐bearing intrusive rocks, and metallogenic ages are not clear. Zircon SHRIMP U–Pb dating of the porphyritic diorite and fine‐grained diorite yields ages of 416.1 ± 3.9 Ma and 411.1 ± 7.5 Ma, respectively. The dioritoid intruded into the ore‐bearing stratum, indicating that this formation is part of the Early Palaeozoic strata rather than the Middle Devonian Beishan Formation. The Re–Os isochron age of the chalcopyrite in the massive mineralization is 402.6 ± 5.2 Ma; thus, the massive mineralization is related to fine‐grained diorite and formed in the Early Devonian. Six sulphides and four sulphides from the vein mineralization yield Re–Os isochron ages of 352.8 ± 1.8 Ma and 354 ± 23 Ma, respectively, and the limited vein mineralization was formed during 353–354 Ma. The massive and vein mineralizations in the Yundukala deposit were formed in the Early Devonian and Early Carboniferous.

No Unique Scaling Law for Igneous Dikes

AbstractIn linear elastic fracture mechanics (LEFM), veins, dikes, and sills grow in length when the stress intensity factor at the tip reaches a critical value: the host rock fracture toughness . This criterion is applied broadly in LEFM models for crack growth and it is often assumed that the pressure inside the crack is uniform. When applied to intrusion length versus thickness scaling, a significant issue arises in that derived , which is about 100–1,000 times that of measured values for rocks at upper crustal depths. The same scaling relationships applied to comparatively short mineral vein data gives , approaching the expected range. Here we propose that intrusions preserve non‐equilibrated pressures as cracks controlled by kinetics, and therefore cannot be treated in continuum with fracture‐controlled constant pressure (equilibrium) structures such as veins, or many types of scaled analogue model. Early stages of dike growth (inflation) give rise to increasing length and thickness, but magma pressure gradients within intrusions may serve to drive late‐stage lengthening at the expense of maximum thickness (relaxation). For cracks in 2D, we find that intrusion scaling in non‐equilibrium growth is controlled by the magma injection rate and initial dike scaling, effective (2D) host rock modulus, magma viscosity and cooling rate, which are different for all individual intrusions and sets of intrusions. A solidified intrusion can therefore achieve its final dimensions via many routes, with relaxation acting as a potentially significant factor, hence there is no unique scaling law for dike intrusions.

Effects of dissolved fluoride in phosphate ore flotation systems on the surfaces properties of dolomite

Fluoride is an important component phosphate ore, and the leaching and migration behavior of fluoride during the phosphate ore flotation and slurry transfer processes affects the surface properties of its vein minerals in phosphate ore. This study investigates the effects of this behavior on the surface properties of dolomite. The results showed that the fluoride concentration in the slurry gradually decreased with increases in the slurry-making time and temperature. Adsorption experiments and contact angle tests showed that F- could adsorb on the dolomite surface, which reduced the hydrophobicity of this surface when sodium oleate (NaOL) was the collector. Zeta potential tests, solution chemistry calculations and X-ray photoelectron spectrometry (XPS) analysis showed that F- reacted with Ca2+ and Mg2+ on the dolomite surface to form CaF2 and MgF2, both of which inhibited NaOL from interacting with dolomite, thus decreasing the hydrophobicity of the dolomite surface.

Fluid inclusions and C–H–O–S–Pb isotope systematics of the Senj Mo–Cu deposit, Alborz magmatic belt, northern Iran: implications for fluid evolution and regional mineralization

AbstractThe Middle Eocene Senj Mo–Cu deposit (1.3 Mt at 1.5 wt % Cu and 0.2 wt % Mo) is located in the central Alborz magmatic belt, northern Iran. Mineralization is characterized by multistage veins, which are hosted in volcanic and volcano-sedimentary strata of the Karaj Formation (c. 41–45 Ma), genetically associated with the Senj Mafic Sill (c. 40 Ma). Four generations of veins are documented based on mineral assemblages and cross-cutting relationships, sequentially: quartz–biotite–chalcopyrite (QBC veins), quartz–molybdenum (QM veins), quartz–pyrite (QP veins) and late calcite (LC veins). Three types of fluid inclusions (FIs) are present in multistage veins: liquid-rich two-phase (L-type), vapour-rich two-phase (V-type) and solid-bearing multi-phase (S-type) inclusions. FIs in the QBC and QM veins are predominantly V-type and S-type, together with minor L-type, whereas the QP and LC vein minerals only contain L-type fluid inclusions. The homogenization temperatures of FIs from QBC to LC veins vary from 320 to 425 °C, 308 to 390 °C, 214 to 288 °C and 145 to 243 °C, and their salinities range from 5.3 to 49.0, 6.2 to 39.7, 5.7 to 13.0, and 2.1 to 7.2 wt % NaCl equiv., respectively. The H–O–C isotope compositions favour a dominantly magmatic origin for the hydrothermal fluids, which were gradually diluted by meteoric waters. The S–Pb isotope data of sulphide minerals indicate that the sulphur and metals were sourced from a deep-seated magmatic reservoir. The Senj Mafic Sill and associated Mo–Cu mineralization was developed in a back-arc extension regime, which faults and crustal fracture systems served as conduits for hydrothermal fluid circulation and Mo-rich veining.

Hydrothermal fluid signatures of the Yulong porphyry Cu-Mo deposit: Clues from the composition and U-Pb dating of W-bearing rutile

AbstractHydrothermal rutile (TiO2) is a widely distributed accessory mineral in hydrothermal veins or alteration assemblages of porphyry deposits and provides important information for further understanding hydrothermal fluid signatures. This study determines the geochemical composition and U-Pb dates of hydrothermal rutile from the Yulong porphyry Cu-Mo deposit in east Tibet, China. Three types of TiO2 polymorphs have been identified based on their Raman spectroscopic, textural, and chemical characteristics. (1) Brookite and anatase pseudomorphs after titanite in a fine-grained matrix, indicating low-temperature hydrothermal fluids destabilizing primary Ti-bearing minerals during argillic alteration (type-I). (2) Elongated and prismatic rutile present in hydrothermal veins or in clusters in accompanying alteration envelope characterized by weak zoning (type-II). And (3) rutile intergrown with sulfides in hydrothermal veins, characterized by well-developed patchy and sector zoning (type-III). In contrast to the type-I and type-II TiO2 polymorphs, tungsten is enriched in backscattered bright patches and sector zones in type-III rutile, which is due to the substitution of W6+ in the Ti4+ octahedral site. The mechanism of the enrichment of tungsten is effectively driven by the halogen-rich (F, Cl) aqueous fluids during hydrothermal mineralization. In situ U-Pb dating of the type-III rutile yields a lower intercept age of 41.8 ± 1.2 Ma, which brackets the timing of the Cu-Mo mineralization. The relationship between rutile textures and composition indicates that W-bearing rutile can serve as a recorder of hydrothermal processes in porphyry Cu deposits.

Vein and Wehrlite Formation in the Lithospheric Mantle Below the West Eifel Volcanic Field: Modelling the Effects of Pressure, Temperature and Peridotite/Melt Ratio on Magma-Peridotite Interaction Using pMELTS and a Melt Infiltration Experiment

Abstract The mantle peridotite xenoliths of the West Eifel Volcanic Field in Germany preserve evidence of multiple phases of metasomatism. The most recent metasomatic episode produced a variety of veins in the peridotite: high temperature (>1150°C), phlogopite–clinopyroxenite intermediate temperature (~1150°C), olivine clinopyroxenite and relatively low temperature (<1100°C) hornblendite together with marginal reaction zones of wehrlite and dunite. The veins and associated reaction zones have been interpreted as products of crystallization of magmas similar to those that transported the xenoliths to surface. We describe a high temperature melt infiltration experiment and thermodynamic (pMELTS) models that examine the origin of high temperature phlogopite–clinopyroxenite veins and the evolution of the wall rock adjacent to the veins and compare the result to the major and trace element signatures of the minerals in the veins. The infiltration experiment replicates the common reaction textures such as partially dissolved orthopyroxene and sieved secondary clinopyroxene that are found associated with veins. In the thermodynamic model, we calculated the equilibrium assemblages and mineral compositions for peridotite–melt mixtures ranging from peridotite only to melt only over the range of 1150 to 1350°C and 1 GPa to 2 GPa. The models reproduce the composition of vein minerals at a small peridotite/melt ratio, whereas at larger peridotite/melt ratios they produce wehrlite/dunite assemblages that are similar both in modal mineralogy and composition to the natural samples. The models show that olivine clinopyroxenite veins may have been produced at a higher pressure than the phlogopite–clinopyroxenite veins. Our models show that interaction of magma with a trace element signature indicative of a garnet-bearing source with spinel facies mantle will result in a dilution of the trace element garnet signature with little to no variation in the major oxide composition.

The Kupol Epithermal Au-Ag Vein District, Chukotka, Far Eastern Russia

Abstract The Kupol epithermal Au-Ag vein district is located in the northern part of the Okhotsk-Chukotka volcanic belt, a Late Cretaceous subduction-related continental volcanic arc exposed for >3,000 km along the eastern coast of Russia. High-grade veins are hosted in the Kupol andesite sequence, a 300- to 1,000-m-thick, subhorizontal, layered sequence of andesite flows, sills, and ash tuffs, dated at 97 to 96 Ma (Cenomanian). The Kupol andesite sequence is underlain by mixed mafic-felsic volcanic units plus sedimentary rocks (“older volcanics”) and overlain by a >1-km-thick “upper felsic” sequence of dacitic-rhyolitic tuffs and associated dikes and flow domes, dated at 95 to 85 Ma, with local sequences of fluvio-lacustrine sedimentary rocks. The epithermal veins occupy N-striking, steeply dipping normal faults that cut thick coherent andesite flows and sills in the central-upper part of the Kupol andesite sequence. The district is dominated by the large Kupol vein (180.7 tonnes (t) Au and 1,986 t Ag produced to 2020), hosted by the 5.5-km-long Kupol fault, which accommodates normal, east-side-down displacement of up to 190 m. The Moroshka and Providence veins, 5 km east-southeast of Kupol, occupy shorter faults (1- to 2-km strike) with smaller vertical displacements (to 70 m). The Moroshka vein is dated at 93.5 ± 1.5 Ma (Turonian; 40Ar/39Ar method on adularia), and the timing of vein mineralization here and at Kupol overlaps with the early stage of upper felsic sequence magmatism. Veins contain subhorizontal ore shoots, controlled by the intersection of the steep faults with flat-lying Kupol andesite sequence stratigraphy and by steepening of the faults to a more dilational orientation as the inferred paleosurface is approached. Local structural controls are also evident, reflecting a component of oblique slip on the Kupol fault, with the thickest vein segments at steeply pitching jogs and relays. Main-stage veins grew via repeated encrustation by quartz-chalcedony ± amethyst ± lattice bladed calcite (replaced by quartz), with Au-Ag–bearing crustiform adularia ± clays ± sulfides/sulfosalts/electrum ± chlorite ± hematite bands. The main controls on Au grade are inferred to have been boiling, resulting in sharp vertical limits to high metal grades typical of epithermal veins, coupled with optimal dilation of the vein system where the hosting normal fault steepens near surface with decreasing differential stress. Although much of the displacement on the controlling faults is pre-mineralization in timing, lithified cataclastic breccia, coeval with some vein stages, and vein geometry patterns indicate that some vein development occurred contemporaneously during late normal displacement along the fault system. Waning of the hydrothermal system is marked by late carbonate fill, initially Fe dolomite, then coarse calcite as veins, matrix to vein breccia, and central vein cavity fill. The Kupol district veins have proximal adularia-quartz alteration (haloes meters wide), within an extensive (hundreds of meters in scale) clay alteration halo. Clays are zoned both vertically and laterally with respect to veins, with inner illite-chlorite that was magnetite-destructive (at highest paleotemperature; >220°C), grading outward and upward to illite/interlayered illite-smectite with kaolinite, then to an outer zone (or upper blanket) of smectite, at lowest paleo-temperature (<150°C). The boundary between the illite and smectite zones is interpreted to mark the interaction limit of paleo-hydrothermal systems with cooler groundwater. District-scale pathfinder element zonation correlates with clays, with S-Te-Bi-As in the illite-chlorite core and Sb-Cs-Tl(-As-Li) in the smectite blanket. Pathfinder zonation patterns at Kupol point to a magmatic source at depth or, more likely given the scale of the anomalies, multiple magmatic sources, with the surface clay zonation indicating the extent of coalesced paleo-hydrothermal systems associated with upflow plumes. This is the best-defined alteration record with geochemical signature for a complete district hosting a large, high-grade vein deposit. Early definition of clay and pathfinder element patterns across an entire epithermal district can be carried out at low cost to provide useful constraints on vein targeting.

Elemental Mapping for Characterizing of Thorium and Rare Earth Elements (REE) Bearing Minerals Using µXRF

Thorium (Th) anomaly was found in Adang Volcanic Complexes, Mamuju Area, West Sulawesi. This element is associated with high-value elements, the rare earth elements (REE). The minerals containing Th and REE were found in veins mineralization with various types of minerals which are very difficult to identify by conventional method. This research aims to understand the distribution and characterization of Th and REE in individual minerals, using Micro X-Ray Fluorescence (µXRF) analysis and completed by Advanced Minerals Identification and Characterization System (AMICS) software. The samples were collected from vein mineralization in Hulu Mamuju Sector. The contents of Th and REE that were analyzed using X-Ray Fluorescence (XRF) completed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) are 11,550-74,480 ppm and 6,244.15-48,036.87 ppm, respectively. The minerals that contain Th and REE are britholite ((Ce,Ca) 5 (SiO 4 ) 3 OH), aeschynite (Ce,Ca,Fe,Th)(Ti,Nb) 2 (O,OH) 6 , cerite (Ce,Ca) 9 (Mg,Fe)(SiO 4 ) 3 (HSiO 4 ) 4 (OH) 3 , monazite (REE,Th(PO 4 )), thorite (Th(SiO 4 )), and thorutite (Th,U,Ca)Ti 2 (O,OH) 6 associated with other minerals such as pyrite, actinolite, apatite, ilmenite, hematite, zircon and ankerite. Some minerals are uncommon minerals and are only characterized by detailed elemental mapping. The variety of minerals shows the condition of mineralization influenced by carbonatite magma and the hydrothermal process of mineralization Normal 0 false false false EN-ID JA AR-SA /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabel Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-pagination:widow-orphan; mso-hyphenate:none; font-size:10.0pt; font-family:"Times New Roman",serif; mso-fareast-language:EN-US;}