Silicic Alteration Research Articles

Mineralogical Study of Bauxite of Kenco Area, Landak District, West Kalimantan Province, Indonesia

Indonesia is a country with a tropical climate that allows for high levels of weathering. Bauxite is the result of weathering rocks that have high aluminum content, low iron content, and little quartz content. The formation of bauxite deposits is controlled by source rock which is rich in Al element, tropical climatic conditions, and geomorphological conditions that allow the formation of the accumulation of weathered source rock products. The altered silicate minerals due to weathering result in the silica element being released from the crystal bonds and some iron are released so that the aluminum element is concentrated as a residual precipitate. X-ray diffraction (XRD) analysis on 16 bauxite samples which are estimated to represent the overburden horizon, bauxite ore horizon, clay horizon, and source rock to establish the mineral composition of bauxite. Mineral groups in the overburden horizon, bauxite ore horizon, and clay horizon are alumina, iron, titanium, silicates, carbonates, sulfides, and sulfates, while mineral groups in source rock are iron, titanium, silicate, sulfide, and sulfate. The type of bauxite in the study area is gibbsite bauxite based on the dominant appearance frequency of gibbsite compared to mineral corundum as an alumina group.

Early Paleozoic tin mineralization in South China: Geology, geochronology and geochemistry of the Lijia tin deposit in the Miaoershan-Yuechengling composite batholith

Early Paleozoic Sn mineralization is rarely reported in South China. Here we carried out the detailed studies of deposit geology, cassiterite U-Pb dating, muscovite geochemistry and H-O isotopes on the Early Paleozoic Lijia Sn deposit in South China to constrain its genesis. The Lijia Sn deposit is hosted in the Yuechengling granitic batholith and characterized by greisen-type and quartz vein-type mineralization. Four stages of alteration and veining are recognized according to mineral assemblages and crosscutting relationships: pre-ore tourmalinization and silicification alteration of the Lijia granite (stage I), cassiterite-tourmaline-quartz vein and associated cassiterite greisen (stage II), and post-ore calcite-quartz-fluorite vein and calcite veinlet (stage III and IV, respectively). Two generations of the cassiterite in the cassiterite greisen, identified by cathodoluminescence imaging, yield the U-Pb concordant ages of 430.5 ± 3.7 Ma and 428 ± 2.2 Ma, respectively. The zircon U-Pb ages and geochemical features of the Lijia granite as well as the characteristics of alteration and mineralization indicate that the Lijia granite is Sn-bearing one and brings about the Sn mineralization. H-O isotopic compositions of the quartz from the Lijia granite reveal that the magmatic fluids have the δ18O values of 10.6–10.7‰ and the δD values of −57‰ to −62‰. The ore-forming fluids (δ18O 6.5–7.4‰, δD −64‰ to −69‰) responsible for cassiterite precipitation are derived from the mixing of magmatic fluids with minor meteoric water whereas more meteoric water is involved in the post-ore calcite-quartz-fluorite vein stage. Based on mineral assemblages, internal textures and chemical compositions, muscovite is divided into four generations from early to late: the Mus 1 and Mus 2 in the cassiterite greisen, the Mus 3 in the cassiterite-tourmaline-quartz vein and the Mus 4 in the phyllic alteration in the stage III. From the Mus 1 to the Mus 3, muscovite Rb, Cs, Zn, Li, V, Sc and Ga contents gradually decrease whereas boron shows an increasing trend, which might have been caused by the successive precipitation of hydrothermal minerals such as muscovite. Significantly higher Sr and Ba contents of the Mus 2 than the Mus 1 are likely related to the decomposition of the K-feldspar and plagioclase in the host granite. The combination of the precipitation of the early mineral phases, the decomposition of K-feldspar and the involvement of a large amount of meteoric water gives rise to the decrease of W, Sn, B, Rb, Cs and Sr contents and the increase of Ba, Ti, Mg, Li, Sc, V, Cr, Ga, Nb and Ta contents of the Mus 4 in the stage III. A key mechanism responsible for the formation of the Lijia Sn deposit is the interaction between the ore-forming fluids and the host granite. This study confirms the Early Paleozoic tin mineralization event in South China.

Garnets in the Yinachang Fe-Cu deposit, Kangdian region, China: Mineralogical and geochemical insights into fluid-rock dominated iron oxide-copper–gold (IOCG) mineralization

Garnet is an important metasomatic mineral in iron oxide-copper–gold (IOCG) ore systems, but its crystallization mechanisms and relationship to fluid evolution in IOCG are poorly understood. In this study, major and trace element analyses were conducted on garnets from the Yinachang IOCG deposit in the Kangdian region, southwest China, in order to reveal their characteristics and forming process.Garnet commonly occurs in the K-Fe ± REE mineralization stage and Cu ± Au mineralization stage of the Yinachang deposit. Three types of garnets are identified from this deposit, which generally have high almandine but low grossular and spessartine contents (Alm65-78Gro5-17Sp5-17). The type 1 garnet (Grt 1) in the ore bodies and the type 2 garnet (Grt 2) in the proximal silicate alteration zones are pink to purple, euhedral to subhedral grains. Grt 1 exhibit zoning pattern, and Grt 2 were altered into chlorite and was mainly crosscut by ore-bearing veins. They are both extremely depleted in LILEs and enriched in HFSEs, with low total rare earth element ∑REE contents but variable LREE vs HREE ratios. The type 3 garnets (Grt 3) in the intermediate garnet-biotite-quartz zones are purple-brown, anhedral grains with high LILE, HFSE, and ∑REE contents, and exhibit LREE-depleted and HREE-enriched patterns, with marked positive Eu anomalies. All three types garnets that formed during alteration and mineralization are hydrothermal, but their composition is controlled by different mechanisms due to different environments. Compositions of Grt 1 and Grt 2 are mainly related to substitution mechanism controlled by crystal chemistry, physicochemical conditions of the closed hydrothermal system, and buffering effects of carbonate wall rocks during slow infiltration metasomatism, whereas the composition of Grt 3 is mainly controlled by surface adsorption and related to the composition of external fluid during later rapid garnet growth. Decreases in temperature, pressure, and fO2 triggered by mixing of fluids could be responsible for the distinct mineralogical and geochemical characteristics of the three types of garnets.Garnets from IOCG deposits show various textual and geochemical characteristics worldwide. Generally, almandine and andradite are dominating end members for IOCGs. Andradite is typical for metasomatic origin. Although almandine garnet is generally considered to form during metamorphism, the occurrence of hydrothermal almandine in the alteration zones of IOCG deposits reveal a metasomatism between Fe-bearing fluid and Al-enriched pelite protolith in a sufficiently reduced environment. Also, it is possible that the metasomatism during mineralization has enriched the protolith with Fe, and the post-ore metamorphism formed almandine by providing high temperature and pressure.

Potassium silicate alteration in porphyry copper‑gold deposits: a case study at the giant maar-diatreme hosted Grasberg deposit, Indonesia

Potassium silicate alteration is a hallmark of the porphyry copper deposits that supply two thirds of the world's annual copper demand. These deposits formed in the cores of calc-alkaline to alkaline volcanic systems from the flux of magmatic gas that transported copper and other metals from source to the surface. The giant 3.2 Ma Grasberg CuAu deposit formed within a maar-diatreme complex following a resurgence in magmatism. The defined resources of this deposit occur from a few hundred metres depth to 1.7 km below the paleosurface which, uniquely in this deposit, is partially preserved as a section of maar tuffs.Potassium silicate alteration has commonly been interpreted as being the result of the addition of potassium to the porphyry copper host rocks via pervasive interaction with a large volume of a potassium-rich brine that is commonly presumed to be of magmatic origin. However, the data reported here show that alteration at the deposit scale is essentially isochemical with respect to the major rock-forming components and that only sulphur and the economic metals (Cu, Mo, Au, etc.) are added by flux of reactive magmatic gas containing SO2 and HCl from source intrusions at depth. Silicate solubilities are very low so that only a minor fraction of the total alkalis in the host rock are extracted by alteration reactions and then discharged at the paleo-surface. Reaction of the magmatic gas phase with plagioclase results in the coupled deposition of anhydrite (CaSO4) and disproportionation of SO2 to release H2S. The in-situ release of H2S immediately scavenges Cu and other chalcophile metals from the continuing magmatic gas flux to form the Cu-, Fe- and other sulphides that, in sufficient concentration, make up the economic reserve available to mining.The sequestration of Ca into anhydrite, along with deposition of silica into early quartz veins, increases the concentration of the other major components (K2O, Na2O, MgO, etc) in the remaining silicate assemblage within the porous host rock. The result is the development of intermingled potassium-enriched silicate and sulphur-rich (anhydrite-sulphide) sub-assemblages that constitute the mineralised phyllic or potassic alteration zones. These crystallise according to their pressure and depth into alteration assemblages dominated by potassic phyllosilicates, quartz and pyrite in the phyllic alteration zone, and alkali feldspar and phlogopitic-biotite plus minor andalusite and corundum in the central potassic zone. Dissolution and recrystallisation of primary magmatic biotite in the host rock releases K as well as Fe, the latter (along with amphibole and feldspar) providing iron for the formation of chalcopyrite, bornite and pyrite. The in-situ release of H2S through anhydrite formation, immediately scavenges Cu and other chalcophile metals from the continuing magmatic gas flux to form the CuFe sulphides that, in sufficient concentration, make up the economic reserve available to mining. Understanding of the alteration processes during porphyry copper formation also provides insights into gas-solid reactions processes inside active magmatic arc volcanoes but the magnitude of copper mineralisation is dependent on the original metal content of the source of the magmatic gas phase.

Intermediate‐sulfidation epithermal mineralization at Monterado goldfield in Western Borneo (Indonesia): Geological, mineralogical, and fluid inclusion microthermometric perspectives

Gold mining in Western Borneo can be traced back over a century in the Dutch era. Many of these gold deposits are hosted in auriferous quartz veins, yet their geology and alteration/mineralization features have never been well documented. In this study, we present the first detailed account on gold mineralization in Western Borneo, using the Monterado goldfield as an example. Our results reveal that the auriferous quartz veining occurred in both intrusions (Mensibau granodiorite and Sintang Suite diorite porphyry) and volcanic‐sedimentary sequences (Raya Volcanics and Hamisan Formation), and wallrock alterations are well developed. Distributions of the veins are controlled largely by N‐S‐trending (tensional veins, e.g., Nek Rimban and Muisan) and NW‐SE (en‐échelon tensional gash veins, e.g., Mertua, Lipan, and Sekar) structures. Vein textures include mainly massive, breccia, comb, drusy, and stockwork. Advanced Mineral Identification and Characterization System mineral mapping on the ore veins and mineralized wallrocks show the presence of electrum, acanthite, pyrite, chalcopyrite, bornite, sphalerite, galena, and supergene products such as malachite, covellite, cuprite, chalcocite and rosasite. Polymetallic sulfide mineralization is spatially associated with adularia within auriferous quartz veins and silicic alteration. Ore chemistry on 285 vein ore samples yielded on average 1.46 g/t Au and 6.58 g/t Ag. Fluid inclusion microthermometry indicates that the homogenization temperature ranges from 273 to 362°C (avg. 338°C), with salinities of 1.1–8.7 wt% NaCl eq. (avg. 4.4 wt% NaCl eq.). Accordingly, the Monterado Au–Ag quartz vein‐type mineralization is best classified as intermediate‐sulfidation epithermal style.

Mechanism of olivine and glass alteration under experimental H2O-CO2 based supercritical gas: Application to modern and ancient Venus

Extreme conditions encountered in some geological contexts (deep serpentinization, interaction of Venus atmosphere with its basaltic surface, volcanic degassing) activate mechanisms and rates of silicate alteration that are poorly understood. In the present study, we investigate the mechanisms of mineral reactions in a natural geological system at high temperature, under conditions where the low solvation of cations by fluids likely promotes surface reactions such as surface diffusion and/or local recrystallization. We focus on vitreous glasses and olivine, reputed to be the most alterable phases in volcanic rocks, by reacting samples for one week in a Ni-based alloy experimental vessel. For the framework of our experimental study, we chose to apply the deep atmosphere conditions on Venus: 470 °C and 90 bar of reconstituted Venus-like gas. We also tested the effect of water (Early Venus or wet volcanic degassing) by adding water vapor at up to 320 bar total pressure. The mineral reactions affecting the samples were identified by a set of spectroscopic surface analyses of the altered samples: Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Diffraction in grazing incidence mode, X-ray Photo electron Spectroscopy and Raman spectroscopy.Samples of obsidian and tholeiitic glasses are found to be sensitive to a threshold water pressure, depending on glass composition, below which the reaction is limited to some elemental mobility in the glass (alkali enrichment, calcium loss) leading to a possibly more stable surface layer of tens to hundreds of microns. Above this threshold water pressure (ca. 50 bar H2O for the obsidian but >250 bar H2O for the tholeiitic glass), water promotes the depolymerization of the glass and the crystallization of stable minerals. This crystalline rim is less protective that the chemically modified layer.Olivine samples react differently depending on whether the olivine is isolated or included in a basaltic rock. In the latter case only, iron coatings are formed, which are identified as hematite, suggesting that this phase is not fed by olivine itself but rather by surface diffusion from neighboring Fe-rich phases. This supports the conclusions from experimental studies and orbital observations on the short-term visibility of unaltered olivine in Venus lava flows: such a coating is enhanced when Fe-bearing minerals are in the proximity of olivine. Under high water vapor pressure, Fe-bearing talc (and not serpentine) forms by a likely topotactic reaction that also incorporates silica from the gas. This talc layer may form a protective layer, implying that serpentinization of ultramafic rocks at high temperature may not be as prevalent as one might think in a gas-dominated system like the Early Venus surface.

Carbonatite-melilitite-phosphate immiscible melts from the aragonite stability field entrained from the mantle by a Pliocene basalt

A plagioclase megacryst containing composite crystal-glass inclusions was ejected in a Pliocene basaltic diatreme in the Carpathian back-arc basin (Pannonian Basin). The megacryst grew from phonolitic melt, relics of which are preserved in the crystal-glass inclusions. Most of the pristine melt has undergone substantial compositional resetting by interaction with several batches of a low-viscosity carbonated, P-rich melilitite melt, which infiltrated and largely replaced the original inclusion content. The melilitite melt also caused partial resorption of the host megacryst and crystallisation of new calcic plagioclase forming stringers and palisades. A P-rich calcic carbonatite melt exsolved from the melilitite and later crystallised to aragonite at ~ 800 °C and 1.9 GPa. The phosphate melt fraction exsolved from the carbonatite and solidified as CO32−-rich A-B type apatite. At a very late evolutionary stage, K- and Si-rich fluids caused potassic and silicic alteration of the solidified melilitite glass along cracks and interfaces between calcic carbonate globules and glass at temperatures below 680 °C. The oxygen isotope composition of the plagioclase megacryst (6.2 ‰ V-SMOW; Vienna Standard Mean Ocean Water) and the 87Sr/86Sr isotope ratio of carbonates in the inclusions (0.7034) are consistent with a mantle-derived melt. 87Sr/86Sr isotope ratios (0.7047–0.7051) in interstitial carbonates from associated syenite and carbonatite xenoliths indicate a metasomatised mantle source contaminated with radiogenic crustal material or altered marine carbonate. The O-isotope ratios in the carbonates, 22.7 ± 0.6 ‰ V-SMOW in calcite and 23.6 ± 0.7 ‰ V-SMOW in aragonite, are also consistent with a sedimentary precursor. Contrasting δ13C values in the calcite, -12.7 ± 0.5 ‰ V-PDB (Vienna PeeDee Belemnite), and the aragonite (-4.6 ± 0.5 ‰ V-PDB) indicate low-temperature modification of calcite assisted by delta13C-depleted CO2 and preservation of primary magmatic delta13C values in aragonite. The microstructural and geochemical evidence points towards heterogeneous silicate-carbonate melt fractions generated during the metasomatism and partial melting of a supra-subduction mantle wedge.

Artificial weathering of an ordinary chondrite: Recommendations for the curation of Antarctic meteorites

AbstractMeteorites are prone to errestrial weathering not only after their fall on the Earth’s surface but also during storage in museum collections. To study the susceptibility of this material to weathering, weathering experiments were carried out on polished sections of the H5 chondrite Asuka 10177. The experiments consisted of four 100‐days cycles during which temperature and humidity varied on a twelve hours basis. The first alteration cycle consisted of changing the temperature from 15 to 25 °C; the second cycle consisted of modifying both humidity and temperature from 35 to 45% and 15 to 25 °C, respectively; the third cycle consisted of varying the humidity level from 40 to 60%; and the fourth cycle maintained a fixed high humidity of 80%. Weathering products resulting from the experiments were identified and characterized using scanning electron microscopy–energy dispersive spectroscopy and Raman spectroscopy. Such products were not observed at the microscopic scale after the first cycle of alteration. Conversely, products typical of the corrosion of meteoritic FeNi metal were observed during scanning electron microscope surveys after all subsequent cycles. Important increases in the distribution of weathering products on the samples were observed after cycles 2 and 4 but not after cycle 3, suggesting that the combination of temperature and humidity fluctuations or high humidity (>60%) alone is most detrimental to chondritic samples. Chemistry of the weathering products revealed a high degree of FeNi metal corrosion with a limited contribution of troilite corrosion. No clear evidence of mafic silicate alteration was observed after all cycles, suggesting that postretrieval alteration remains limited to FeNi metal and to a lesser extent to troilite.

Microbial Alkalinity Production and Silicate Alteration in Methane Charged Marine Sediments: Implications for Porewater Chemistry and Diagenetic Carbonate Formation

A numerical reaction-transport model was developed to simulate the effects of microbial activity and mineral reactions on the composition of porewater in a 230-m-thick Pleistocene interval drilled in the Peru-Chile Trench (Ocean Drilling Program, Site 1230). This site has porewater profiles similar to those along many continental margins, where intense methanogenesis occurs and alkalinity surpasses 100 mmol/L. Simulations show that microbial sulphate reduction, anaerobic oxidation of methane, and ammonium release from organic matter degradation only account for parts of total alkalinity, and excess CO2 produced during methanogenesis leads to acidification of porewater. Additional alkalinity is produced by slow alteration of primary aluminosilicate minerals to kaolinite and SiO2. Overall, alkalinity production in the methanogenic zone is sufficient to prevent dissolution of carbonate minerals; indeed, it contributes to the formation of cemented carbonate layers at a supersaturation front near the sulphate-methane transition zone. Within the methanogenic zone, carbonate formation is largely inhibited by cation diffusion but occurs rapidly if cations are transported into the zone via fluid conduits, such as faults. The simulation presented here provides fundamental insight into the diagenetic effects of the deep biosphere and may also be applicable for the long-term prediction of the stability and safety of deep CO2 storage reservoirs.

Authigenic anatase nanoparticles as a proxy for sedimentary environment and porewater pH

Abstract Titanium (Ti) has long been considered to be immobile during weathering and diagenetic processes, and it is widely used for the normalization of elemental concentrations in weathering profiles. However, our study demonstrates that authigenic titania is commonly formed in fine-grained siliciclastics of a wide variety of facies through weathering of Ti-bearing silicates, authigenic euhedral anatase is present ubiquitously as nanoparticles, and its morphology varies in a predictable manner over a range of depositional environments. The crystal habit of authigenic anatase nanoparticles is controlled primarily by porewater pH during the early diagenetic alteration of Ti-bearing silicates. Authigenic anatase nanoparticles exhibit a distinct tetragonal tabular morphology in deep-marine facies, a tetragonal bipyramidal shape in shallow-marine facies, an irregular morphology with sponge-like aggregates in terrestrial-marine transitional to paludal facies, and euhedral short tetragonal prisms in lacustrine facies. Also, authigenic anatase is observed to form in organic-free glacial deposits, attesting its formation as an inorganic precipitate and demonstrating diagenetic remobilization of titanium in the absence of organic matter. Our findings suggest that authigenic anatase could be a sensitive proxy for the sedimentary environment and sedimentary porewater chemistry, and it will likely prove useful in depositional facies analysis.

Occurrence of Manganese Mineralization in Rayavalasa and Tudi Villages of Eastern Ghat Mobile Belts, Andhra Pradesh

In this paper, we have reported small bands of Manganiferous quartzite at S. Gopalapuram, Tudi, .Some other small occurrences also observed as float ore/boulders and/or small manganese ore observed north of Nandala-meta, Tangidi and Rayavalasa The pockets of Mn ores are lithologically controlled but the disposition of manganese bands are structur-ally controlled, localized near the hinge zones and at some parts in the limb areas. The Mn-rich silicates are converted to manganese ore due to leaching or oxidation. The relict phases of silicate with Mn-rich rim and inclu-sions indicate that they were derived during leaching. Some features such as colloform bands, relict silicates and rare pseudomorphs, indicate its secondary nature formed due to the alteration of manganiferous silicates. Braunite, and psilomelane are represented as the primary minerals. secondary minerals are made up of psilomelane, cryptomelane, py-rolusite, and goethite and are formed in the low grades of metamorphism. Analytical val-ues of manganese (Mn) in bedrock samples collected from the Mn-enriched horizons of calc-granulite and khondalite rock types range from 0.16% to 39.70%. The analytical results of float ore samples have maximum values of upto 23.64%

Experimental investigation of Fe-clay/organic interactions under asteroidal conditions

Carbonaceous chondrites contain both soluble and insoluble organic materials (SOM and IOM) which may have been produced in different environments via different processes or share possible genetic relationships. The SOM may have been produced from IOM during hydrothermal episodes on asteroids, and vice versa. The potential role played by the mineral matrix during these episodes (clay minerals of variable crystallinity) remains to be constrained. Here, we exposed a mixture of formaldehyde and glycolaldehyde with ammonia-bearing liquid water together with Fe-rich smectitic minerals to hydrothermal conditions mimicking asteroidal conditions. We used both amorphous gel of smectite or crystalline smectites in order to understand the influence of the crystallinity on the evolution of OM. The organo-mineral experimental residues were characterized at a multiple length scales using X-ray diffraction and microscopy/spectroscopic tools. Results evidence that some IOM polymerizes/condenses in the absence of Fe-rich smectites. Yet, the presence of Fe-rich smectites inhibits this production of IOM. Indeed, the interactions between the SOM and clay surfaces (interlayers or edges) reduce the concentration of SOM available for polymerization/condensation reactions, a necessary step for the production of IOM. In addition, the presence of OM disorganizes the crystallization of the Fe-rich amorphous silicates, leading to smaller crystal sized particles exhibiting a lower permanent charge. This might suggests that the smectite permanent charge distribution may help better constraining the origin and evolution of chondritic clay minerals. Altogether, the present study sheds new light on the organo-mineral interactions having occurred during hydrothermal episodes onto/within chondritic asteroids. Indeed, IOM formation from OM-rich aqueous fluids does not occur during the alteration of amorphous silicates. This would mean that IOM is either produced within pockets free of clay minerals or initially accreted as IOM-rich grain. Last, about ∼50 wt% of the initial C could not be removed from the clay minerals at the end of the experiments using classical solvent extraction protocols, demonstrating that a high fraction of the SOM in carbonaceous chondrites may have been overlooked.

Integration of geological and geophysical studies in order to mineral exploration at the Zaveh mineralization area, Khorasan Razavi Province, Iran

The copper deposit of Zaveh lies in the SE of the city of Torbat-e-Heydarieh and in middle of the Khaf-Kashmar-Bardaskan Magmatic Belt (KKBMB) in the Khorasan-e-Razavi Province. The lithology of the area consist of Jurassic and Cretaceous sedimentary rocks and Eocene volcanic units. Ore-formation is controlled by fault activity, representing vein-veinlet style E-W trending, formed within a conglomerate rich in quartz. Primary minerals are chalcopyrite, pyrite and arsenopyrite and secondary minerals contain malachite, azurite chalcocite, bornite, covellite, Cu sulphates, wad (Mn hydroxide), haematite, goethite, jarosite, limonite and (to a lesser extent) chrysocolla. The predominant alteration is silification which is associated with vein ore-formation. The volcanic units host propylitic, sericite, carbonate and silicification alterations. The ore-formation itself represents anomalies of Cu (2.1 % max), As (>1%), Sb (~105 gr/T), Pb (4371 gr/T) and Zn (1.1% max). Induced polarization and electrical resistivity (IP/RS) surveys unveil that the most chargeability anomaly corresponds to center of ore-forming vein and fault zone.The chargeability anomaly extends and amplifies with depth. The most amount of specific electrical resistance has been observed in the quartz-rich conglomerate. Interpretation of IP/RS data reveals that the chargeable source is extending in deeper beds (presumably sulphid ore-formation) which needs to be verified by boring operation. Geophysical surveys are significantly commensurate with field observations, ore-forming and geochemical data. Utilization Geophysical methods in different style of ore-deposits and interpretation of obtained information by means of geological, ore-forming and geochemistry data is considered to be a big step towards subterranean exploration and deposits modeling.

Water-susceptible primordial noble gas components in less-altered CR chondrites: A possible link to cometary materials

We report detailed characterizations of the petrology, mineralogy, and noble gas signatures of Renazzo-type (CR) chondrites EET 92048, MIL 090657, NWA 801, and hydrothermally treated MIL 090657 samples to investigate primordial noble gases hosted by water-susceptible materials in aqueously less-altered CR chondrites. The noble gases were extracted by a stepwise heating method. The hydrothermal treatment on MIL 090657 resulted in the alteration of amorphous silicates in the matrix and the removal of large amounts of He and Ne that were released at low temperature from the untreated sample. The 36Ar/132Xe ratios in EET 92048 and MIL 090657 are ~5 times higher than that of the Q noble gas component, although both meteorites do not show any evidence for solar wind noble gases. The analyses revealed that aqueously less-altered CR chondrites contain two distinct primordial noble gas components hosted by water-susceptible materials: an isotopically Q-like Ne-rich component and an Ar-rich component. The characteristics of the Q-like Ne-rich component are consistent with those of Q-like Ne in cometary materials. We propose that the CR chondrites formed at a greater heliocentric distance and share similar materials hosting the Q-like Ne-rich component with comets. The presence of the Ar-rich component in the CR chondrites, as well as in ordinary chondrites and other anhydrous carbonaceous chondrites, provides evidence of the global distribution of the Ar-rich carriers in the ordinary and carbonaceous chondrite forming regions.

Release of chromite nanoparticles and their alteration in the presence of Mn-oxides

Abstract The discovery of chromite nanoparticles in silicates of ultramafic rocks may change our approach on the environmental risk assessment of mine waste associated with chromitite mining. This experimental study shows for the first time that the alteration of Cr-rich silicates results in the release of chromite nanoparticles and that their interaction with oxidizing Mn-oxide nanoparticles causes the dissolution of chromite and Mn-oxide nanoparticles and the precipitation of Fe3+- and Cr3+-hydroxides. Transmission electron microscopy (TEM) in combination with ultra-microtomy, centrifugation, chromatography, ICP-MS, and UV-VIS is used to characterize release and alteration of chromite nanoparticles and the concentrations and speciation of Cr aqueous species. Alteration of clinochlore grains containing chromite nanoparticles results in the release of the nanoparticles and their attachment to Si-bearing Alhydroxide colloids. Chromite nanoparticles with the end-member composition FeCr2O4 are synthesized, and their interaction with Mn-oxide nanoparticles (hausmannite, Mn3O4), Fe2+-silicates (chamosite, [(Fe3.9Mg0.62Al0.48)Al(Si3Al)O10(OH)8] and organic matter is studied over a period of six to nine months in suspensions of pH = 5. The interaction of chromite and hausmannite nanoparticles is facilitated by the aggregation of the nanoparticles and dissolution-precipitation processes. Processes on the surfaces of the hausmannite nanoparticles include the reductive dissolution of the substrate (reduction of Mn3+ to Mn2+ by Fe2+ species) and its replacement by amorphous or nanocrystalline Cr3+-bearing Fe3+-hydroxides. Processes on the surfaces of the chromite nanoparticles involve the attachment of hausmannite nanoparticles, the oxidative dissolution of the substrate (oxidation of Fe2+ and perhaps Cr3+ by Mn3+ species), its replacement by an amorphous or nanocrystalline Mn-bearing Cr3+-hydroxide matrix and the formation of the Cr3+-hydroxides bracewellite and grimaldite within the latter matrix. Analyses of the suspensions indicate only minor amounts of Cr6+ in the suspensions (<5 µg kg−1) suggesting that formation or occurrence of Cr6+ species can be limited in complex geochemical and mineralogical systems even in the presence of hausmannite nanoparticles.

Re-Os Age and Stable Isotope (O-H-S-Cu) Geochemistry of North Eastern Turkey’s Kuroko-Type Volcanogenic Massive Sulfide Deposits: An Example from Cerattepe-Artvin

The eastern Pontide tectonic belt (EPTB) contains greater than 350 identified Kuroko type volcanogenic massive sulfide deposits/mineralization/occurrences (VMSD). The deposits are associated with Late Cretaceous felsic volcanics consisting mainly of dacitic and rhyolitic lavas and pyroclastics that outcrop within a narrow zone running parallel to the eastern Black Sea coast and represent the axial zone of a paleo-magmatic arc. The Cerattepe deposit is the second-largest and is a hybrid VMS system with some epithermal features. To date, no geochemical research constrains the origin and timing of mineralization in the Cerattepe VMS deposit. Here, we provide Cu, O, H and S, isotope analysis of ores and alteration minerals to understand the hydrothermal history of the deposit and date the massive ore with Re-Os geochronology. Secondary weathering mobilized and redistributed metals in the deposit. The copper isotope signatures of shallow ores in the gossan follow patterns resulting from oxidative weathering of copper minerals with gossan Fe oxides of δ65Cu = −2.59‰, enrichment zone copper sulfide of d65Cu = +2.23 and +1.73‰, and primary ores of δ65Cu = +0.71 and +0.41‰. At the boundary of the enrichment zone, further cycling and migration of enrichment zone copper are evidenced by two samples having larger ranges of the δ65Cu = +3.59‰, and −2.93‰. Evidence for a magmatic source for fluids and S are evidenced by the O and H isotope values from quartz veins (δ18O = +7.93‰ to +10.82‰, and δD = −78‰ and −68‰) and sulfides that possess δ34S ratios of –5 and 0‰ from drill core samples. 187Os/188Os–187Re/188Os ratios from drill core sulfide samples of Cerattepe VMS deposit yields a 62±3 Ma isochron age and a highly radiogenic Os initial ratio. This age is compatible with silicate alteration ages from a proximal deposit and clearly shows mineralization occurs at a much younger time than previously proposed for VMS mineralization in the eastern Pontides. The new Re-Os age and source of Os imply that mineralization in the area occurs at a distinctly younger interval in the back-arc basin and metals could be sourced from the surrounding host rocks.

Preservation of Xiuwacu W-Mo deposit and its constraint on the uplifting history of Eastern Tibetan Plateau

Thermochronology has become an increasingly effective tool to reveal the post-mineralization uplift and exhumation history of ore deposits. In this paper, we studied the exhumation history and preservation conditions of the Xiuwacu tungsten-molybdenite deposit (resource: 24,000 t Mo and 23,000 t WO3), which is located on the southern Yidun Terrane (SYT), Eastern Tibetan Plateau. At Xiuwacu, both the eastern and western ore zones contain quartz-vein-type orebodies in the K-feldspar, greisen, and silicic alteration zones. The orebodies distributed in a northwestward trend along regional faults, with ore minerals including mainly molybdenite, scheelite, chalcopyrite, and pyrite.The mineralization at Xiuwacu occurred in 86–82 Ma, coeval with the emplacement of the ore-causative Xiuwacu porphyry monzogranite. The deposit likely underwent rapid cooling from 750 − 800 °C (magmatic zircon U-Pb age) to ~ 300 °C during 90–86 Ma (molybdenite Re-Os mineralization age). After that, the temperature slowly and continuously cooled to ~ 180 °C from the Late Cretaceous to 25 Ma, and then rapidly cooled to ~ 125 °C in 25–17 Ma, and eventually to 125–60 °C during 17–5 Ma (apatite fission-track ages; n = 8).The thermochronologic history of the Xiuwacu intrusive complex was reconstructed by inverse modelling based on the apatite fission-track ages and lengths. There was 6426–6915 m (average 6650 m) uplift, while only 1982–2471 m (average 2200 m) exhumation. Considering the depth of current exploration and typical depth of granitoid-related W-Mo mineralization, we infer that there is still great potential to discover concealed W-Mo orebodies beneath the current mining level at Xiuwacu.

Hydrothermal alteration and mineralization of Baiyun gold deposit in Liaodong Peninsula, North China Craton

Baiyun deposit is a large gold deposit in the Liaodong Peninsula (North China Craton), containing over 31.7 t of gold. Silicic alteration, K‐feldspar alteration, and pyritization are well developed and closely related with mineralization in Baiyun deposit. Based on field and optical microscopic observations, the alteration styles include quartz + K‐feldspar zone, pyrite + sericite +quartz zone, and chlorite zone from orebody outward. In this study, the quartz, K‐feldspar, and pyrite of pre‐ore, syn‐ore stages 1 and 2 were selected for LA‐ICP‐MS trace element analysis and electron probe microanalysis (EPMA) to reveal the alteration‐mineralization link. Results show that the albite was altered to mainly K‐feldspar and minor secondary quartz at syn‐ore stage 1. Fluid‐rock reaction of the silicic‐potassic alteration may have decreased the fluid oxygen fugacity (fO2), which triggered the gold precipitation. Most of invisible gold occurred in the form of solid solution. At syn‐ore stage 2, albite altered to mainly quartz and minor K‐feldspar. The syn‐ore stage 1 K‐feldspar also altered to minor secondary quartz at syn‐ore stage 2. In addition, the release of sulphur from the syn‐ore stage 1 pyrite was likely another trigger for the gold precipitation. Most of syn‐ore stage 2 invisible gold occurred as nano‐particles. The ore‐forming fluids consist mainly of primary magmatic fluids mixed with minor metamorphic fluids. The ore metals may have sourced mainly from the magmatic fluid and the sillimanite‐mica schist of the Gaixian Formation.

Type of Gold Deposit in Arinem Cisewu and Its Surrounding Garut Regency, West Java, Indonesia

Gold deposit based on the mineralization of gold and other ore minerals in Arinem area and its surrounding was found in the quartz vein. The research area is in Arinem area and its surrounding, Garut Regency, West Java. Arinem and the vicinity was the location for early stage of research program of mineralization in Papandayan area. This area has good mineralization, and according to previous studies, is a low sulfidation area with the presence of pyrite, chalcopyrite, galena and sphalerite (Antam, 2014). The presence of galena and sphalerite mineral has suggested that instead of low sulfidation, the area may be in intermediate sulfidation zone state supported by other data such as quartz breccia, banded quartz and shear as control structure. Lithology in the area consists of breccia Quaternary and lava unit of Jampang formation in Miocene and unit of andesite and basaltic in Quaternary and intrusion of dacite, andesite and diorite. The alteration and mineralization of research area was classified as propylitic alteration zone with the presence of chlorite, epidote and calcite mineral, argillic alteration zone with montmorillonite, kaolinite mineral, silicic alteration zone with the presence of quartz-sericite, a bit of calcite mineral. The observed ore minerals are pyrite, chalcopyrite, galena, sphalerite. The geological structure was controlled by horizontal fault in almost north-south direction of N 170O-180O E and northeast – southwest horizontal fault in N 40O – 50O E, while the mineralization zone was controlled or following fault pattern of N 170O - 175O E. The epithermal deposit of the study area can be classified as intermediate sulfidation epithermal deposit for zones with galena and sphalerite mineral particularly on several locations near fault zones and brecciated quartz. Meanwhile, the study area is generally low sulfidation epithermal type deposit.

Geology, geochemistry and geochronology of Lindero porphyry gold deposit in the Southern Puna plateau, Argentina

The Lindero gold deposit is located in the Southern Puna plateau, northwest Argentina. The deposit is centered in a cluster of six subvolcanic intrusions emplaced at the margin of the Arizaro Basin. Three alteration types were recognized: (i) Ca–Na silicate (clinopyroxene + magnetite + K-feldspar + quartz + calcite ± plagioclase), (ii) K-silicate (K-feldspar + quartz + magnetite ± biotite ± anhydrite) and (iii) chlorite-calcite alteration. The highest ore grades are linked to the K-silicate alteration. The proven plus probable reserves of Lindero are 84,226 t with average grades of 0.63 g/t Au and 0.11% Cu. A previous study assigned Lindero to the iron oxide copper-gold (IOCG) deposit type but many features of Lindero suggest that it is a porphyry gold deposit, including (i) the temporal and spatial link between alteration and the intrusive bodies, (ii) the alteration distribution pattern, particularly the small volume of rock affected by Ca–Na silicate alteration, (iii) the Au-rich and Cu-poor mineralization style.The magmatic complex at Lindero comprises an early-mineral unit (FPD), four inter-mineral units (CPD1, PBFD, CPD2 and DDP) and one post-mineral unit (PMI). In-situ U/Pb SIMS dating of the oldest (FPD), an intermediate (PBFD) and the youngest (DDP) intrusive units, confirms a middle Miocene age. The weighted mean ages of the oldest and youngest units are indistinguishable, with 15.36 ± 0.13 Ma (n = 21) and 15.47 ± 0.11 Ma (n = 16), respectively. Individual ages from each unit range by ~1 m.y. and the overall spread of zircon ages is 15.92 ± 0.23 to 14.44 ± 0.33 Ma. We suggest that emplacement of the subvolcanic stocks took place within this span time, likely at the lower end of this range (15.0–14.4 Ma). Two 40Ar/39Ar ages of hydrothermal biotites from the K-silicate alteration (14.99 ± 0.16 Ma and 14.93 ± 0.12 Ma) indicate that hydrothermal alteration began practically simultaneously with the emplacement of the porphyry units.All of the intrusive units are similar compositionally. They show a fine- to medium-grained porphyric texture (1–4 mm) comprising plagioclase, amphibole, clinopyroxene and scarce quartz phenocrysts (40–55 vol % of phenocrysts) in a K-feldspar ± quartz microcrystalline (0.02–0.07 mm) groundmass, except in the post-mineral unit which has a cryptocrystalline groundmass. Whole-rock analyses reveal a narrow range of dioritic composition (58.6–61.9 wt % SiO2) and high-K calc-alkaline character for all units. Trace element features (low Ba/Nb ratios, high Nb) of the Lindero magmas indicate a back-arc affinity, similar to those from the Southern Puna and distinct from the Central Volcanic Zone (CVZ) frontal arc. The Sr and Nd isotope ratios (87Sr/86Sr = 0.706042 to 0.706607; 143Nd/144Nd = 0.512501 to 0.512582) from Lindero intrusives are also similar to Southern Puna back-arc volcanic rocks. The Pb isotope ratios of Lindero (206Pb/204Pb = 18.79 to 18.83; 207Pb/204Pb = 15.60 to 15.63; 208Pb/204Pb = 38.66 to 38.74) overlap with both back-arc and arc magmas in the CVZ. The narrow age range, spatial association and uniform chemical and isotopic composition of Lindero porphyry units suggest that were derived from a common magma source, which underwent fractionation and/or crustal assimilation before emplacement as suggest by the low concentrations of Mg, Cr, Ni and Sr. The Lindero porphyry units show chemical and isotopic similarities with those from porphyry gold deposits in the Maricunga belt, Chile, and with the porphyry copper deposits of Argentina located in a back-arc setting; however, they differ from porphyry copper deposits in the frontal-arc setting of Chile, notably by the lack of an adakite-like signature (high Sr/Y ratio).