Native Silver Research Articles

The carbonaceous phyllite rock-hosted Pedra Verde copper mine, Borborema Province, Brazil: Stable isotope constraints, structural controls and metallogenic evolution

The Pedra Verde Copper Mine is located in the Viçosa do Ceará municipality, State of Ceará, NE Brazil. The copper mineralization is hosted by the Pedra Verde Phyllite, which is a carbonaceous chlorite-calcite phyllite with subordinate biotite. It belongs to the Neoproterozoic Martinópole Group of the Médio Coreaú Domain, Borborema Province.The Pedra Verde deposit is stratabound and its ore zoning is conspicuous, according to the following sequence, from bottom to top: marcasite/pyrite, native silver, chalcopyrite, bornite, chalcocite, native copper and hematite. Barite and carbonaceous material are reported in ore zones. Zoning reflects the ore formation within a redox boundary developed due to the interaction between oxidized copper- and sulfate-bearing fluids and the reduced phyllite. Structural control on mineralization is evidenced by the association of the ore minerals with veins, hinge folds, shadow pressures, and mylonitic foliation. It was mainly exercised by a dextral transcurrent shear zone developed during the third deformational stage identified in the Médio Coreaú Domain between 590 Ma and 570 Ma. This points to the importance of epigenetic, post-metamorphic deformational events for ore formation. Oxygen isotopic composition (δ18OH2O = 8.94 to 11.28‰, at 250 to 300 °C) estimated for the hydrothermal fluids in equilibrium with calcite indicates metamorphic or evolved meteoric isotopic signatures. The δ13CPDB values (–2.60 to –9.25‰) obtained for hydrothermal calcite indicate mixing of carbon sources derived from marine carbonate rocks and carbonaceous material. The δ34SCDT values (14.88 to 36.91‰) of sulfides suggest evaporites as sulfate sources or a closed system in relation to SO42− availability to form H2S. Carbonaceous matter had a key role in thermochemical sulfate processes and sulfide precipitation.The Pedra Verde Copper Mine is considered the first stratabound meta-sedimentary rock-hosted copper deposit described in Brazil and shares similarities with the syn-orogenic copper deposits of the Congo-Zambian Copperbelt formed during the Gondwana amalgamation.

Specific composition of native silver from the Rogovik Au–Ag deposit, Northeastern Russia

The first data on native silver from the Rogovik Au–Ag deposit in northeastern Russia are presented. The deposit is situated in central part of the Okhotsk–Chukchi Volcanic Belt (OCVB) in the territory of the Omsukchan Trough, unique in its silver resources. Native silver in the studied ore makes up finely dispersed inclusions no larger than 50 μm in size, which are hosted in quartz; fills microfractures and interstices in association with kustelite, electrum, acanthite, silver sulfosalts and selenides, argyrodite, and pyrite. It has been shown that the chemical composition of native silver, along with its typomorphic features, is a stable indication of the various stages of deposit formation and types of mineralization: gold–silver (Au–Ag), silver–base metal (Ag–Pb), and gold–silver–base metal (Au–Ag–Pb). The specificity of native silver is expressed in the amount of trace elements and their concentrations. In Au–Ag ore, the following trace elements have been established in native silver (wt %): up to 2.72 S, up to 1.86 Au, up to 1.70 Hg, up to 1.75 Sb, and up to 1.01 Se. Native silver in Ag–Pb ore is characterized by the absence of Au, high Hg concentrations (up to 12.62 wt %), and an increase in Sb, Se, and S contents; the appearance of Te, Cu, Zn, and Fe is notable. All previously established trace elements—Hg, Au, Sb, Se, Te, Cu, Zn, Fe, and S—are contained in native silver of Au–Ag–Pb ore. In addition, Pb appears, and silver and gold amalgams are widespread, as well as up to 24.61 wt % Hg and 11.02 wt % Au. Comparison of trace element concentrations in native silver at the Rogovik deposit with the literature data, based on their solubility in solid silver, shows that the content of chalcogenides (S, Se, Te) exceeds saturated concentrations. Possible mechanisms by which elevated concentrations of these elements are achieved in native silver are discussed. It is suggested that the appearance of silver amalgams, which is unusual for Au–Ag mineralization not only in the Omsukchan Trough, but also in OCVB as a whole, is caused by superposition of the younger Dogda–Erikit Hg-bearing belt on the older Ag-bearing Omsukchan Trough. In practice, the results can be used to determine the general line of prospecting and geological exploration at objects of this type.

First discovery of high-mercury silver in ores of the Rogovik gold–silver deposit (Northeastern Russia)

New data on mercurial mineralization are presented, and a detailed characteristic is given for the first discovery of mercurous silver in ores of the Rogovik gold–silver deposit (the Omsukchan trough, Northeastern Russia). It was found that native silver in the examined ores occurs as finely-dispersed inclusions in quartz filling microcracks and interstitions. It also occurs in associations with kustelite, Ag sulfosalts and selenides, selenitic acanthite, and argyrodite. The mercury admixture varies from “not detected” in the central parts of grains to 0.22–1.70 wt % along the edges, or, in independent grains, to the appearance of Ag amalgams containing 10.20–24.61 wt % of Hg. The xenomorph form of grains of 50 μm or less in size prevails. It is assumed that the appearance of mercurial mineralization is caused by the superposition of products of the young Hg-bearing Dogda–Erikit belt upon the more ancient Ag-bearing Omsukchan trough.

A New Zincian Greenockite Occurrence in the Saishitang Cu Skarn Deposit, Qinghai Province, Northwest China

Zn-Cd-S series minerals not only comprise industrial resources for Zn and Cd, but are also significant mineralogical indicators for hydrothermal ore-forming processes. Due to its unique formation conditions and rare occurrence, our understanding of the formation of zincian greenockite in natural systems is limited. Zincian greenockite was discovered during mineralogical studies in the Saishitang Cu skarn deposit, Qinghai Province, Northwest China. This provided an ideal opportunity to assess the occurrence and formation of zincian greenockite in skarn-type deposits. Ore minerals were observed using reflected-light microscopy, and the zincian greenockite was further analyzed using electron-probe microanalysis (EPMA) and X-ray diffraction (XRD). The zincian greenockite occurs in the bornite–chalcopyrite ores and is composed of subhedral to anhedral grains approximately 50 × 150 μm2 to 200 × 300 μm2 in size, replaces the bornite, and is replaced by native silver. Two phases (I and II) were identified based on back-scattered electron images, X-ray element-distributions maps, and EPMA data. The textural relationship indicated that Phase I was replaced by Phase II. Phase I contained high Zn (14.6 to 21.7 mol % ZnS) and low Cd (72.4 to 82.2 mol % CdS), while Phase II contained low Zn (5.6 to 9.1 mol % ZnS) and high Cd (85.4 to 89.9 mol % CdS). The zincian greenockite was formed at temperature of 300~270 °C during the transformation from a reducing environment to an oxidizing one in the late stage of the mineralization process in the Saishitang deposit.

The Kongsberg silver deposits, Norway: Ag-Hg-Sb mineralization and constraints for the formation of the deposits

The Kongsberg silver district has been investigated by microscopy and electron microprobe analysis, focusing primarily on the Ag-Hg-Sb mineralization within the context of the updated mineral paragenesis. The earliest mineralization stage is represented by sulfides, including acanthite, and sulfosalts. Native silver formed initially through breakdown of early Ag-bearing phases and later through influx of additional Ag-bearing fluids and silver remobilization. The first two generations of native silver were separated in time by the formation of Ni-Co-Fe sulfarsenides and the monoarsenide niccolite along rims of silver crystals. The presence of As-free sulfosalts and the absence of di- and tri-arsenides suggest a lower arsenic/sulfur activity ratio for the Kongsberg deposits compared to other five-element deposits. Native silver shows binary Ag-Hg and Ag-Sb solid solutions, in contrast to the ternary Ag-Hg-Sb compositions typical for other deposits of similar type. Antimonial silver together with allargentum, dyscrasite, and pyrargyrite was documented exclusively from the northern area of the district. Elsewhere, the only Sb-bearing minerals are polybasite and tetrahedrite/freibergite. Hg-rich silver (up to 21 wt% Hg) has been documented only in the central-western area. Myrmekite of freibergite and chalcopyrite reflects exsolution from an original Ag-poor tetrahedrite upon cooling, while myrmekite of pyrite and silver, forming through breakdown of low-temperature phases (argentopyrite or lenaite) upon heating, characterizes the Kongsberg silver district. Based on the stabilities of minerals and mineral assemblages, the formation of the silver mineralization can be constrained to temperatures between 180 and 250 °C.

THE CHARACTERISTICS OF ORE MINERALIZATION IN THE WEISSWASSER COPPER DISTRICT, GERMANY

The research deals with drill core samples collected during exploration of copper in the Weisswasser area in Saxony. The area is the north-western part of the North-Sudetic Basin, the lithostratigraphic section of which is similar to the typical one known from the Lubin district. As a result of mineralogical observations using reflected light microscopy and scanning electron microscopy, the following minerals were identified: chalcopyrite, chalcocite, bornite, digenite, galena, sphalerite, native silver, Ag-amalgams, mckinstyite, anilite and betechtinite. Detailed characteristics of the occurrence of sulphide mineralization is presented, describing its form, mutual inclusions and paragenesis, relationship to microtectonic conditions, as well as implications of morphological changes on the bottom of the Zechstein. Three forms of mineralization were found: (1) horizontal, mid-layered copper sulphide lenses formed by hydraulic peeling along the sludge lamination surfaces caused by mineralized high-pressure solutions, (2) horizontal copper sulphide lenses replacing previous framboidal pyrite lenses, and (3) replacement of bioclasts. Copper sulphides were concentrated at the expense of sulphur deposited during sedimentation and early diagenesis as bacterial pyrite. Ore mineralization occurs in the thin horizon with an extensive microtectonic net. Two tectonic episodes can be distinguished: Mesozoic tectonic events that enabled seismic pumping of hot fluids, and microfractures that developed during ore minerals precipitation. Futhermore, single sharp-edged grains of chalcopyrite disturbing lamination of copper shale are observed. It indicates the displacement of grains from crushed conglomerate and resedimentation together with copper shale.

GEOCHEMICAL CHARACTERISTIC OF AG-BEARING MINERALS OCCURRING IN COPPER ORE DEPOSIT AT THE FORE-SUDETIC MONOCLINE

Silver is the most important associated element in the copper ore deposit of the Fore-Sudetic Monocline. Besides its own minerals, such as native silver, amalgams, stromeyerite, mackinstryite, jalpaite and Cu-Fe-Ag system sulphides, the silver occurs as isomorphic substitutions in copper minerals. The aim of this work included geochemical characterization of Ag-bearing minerals and correlation of the occurrence of Ag-enriched Cu sulphides with the areas of native silver and amalgam mineralization. Distribution of silver in the ore deposit distinctly correlates with Cu concentrations, and the areas of the strongest Cu mineralization are accompanied by high silver concentrations. Results of the scanning electron microscopy and electron microprobe analysis indicate that the Cu sulphides contain up to several wt.% Ag as isomorphic substitutions. Distribution of Ag in Cu sulfides does not show regularity, as demonstrated by wide diversity of Ag contents in various minerals, ranging from 0.0X to dozen wt.% Ag.

PRECIOUS METALS IN THE MORRISON DEPOSIT, SUDBURY, CANADA

The Morrison deposit, located in Sudbury Mining Camp, produces ore containing copper, nickel, platinum, palladium and gold. Chalcopyrite dominates the mineral assemblage, while the main Ni-bearing phases are pentlandite and millerite. Cubanite, mackinawite, pyrrhotite, magnetite, sphalerite and galena are present too. Bornite is the main mineral in the peripheral parts of veins, often containing native silver veinlets. Platinum occurs as discrete PGM minerals: composite grains of moncheite (PtTe2) with hessite (Ag2Te); maslovite (PtBiTe) and sperrylite (PtAs2) are rare. Palladium can occur as a substitution in pentlandite and as discrete PGM minerals: michenerite (PdBiTe) and paolovite (Pd2Sn). Tellurides and bismuth-tellurides often display Pt-Pd and Bi-Te substitutions. Gold is present as a native element and as electrum. A zonation in the occurrence of elements can be explained by fractional crystallization of magmatic sulphides. There is a possibility of partial remobilization of precious metals (especially gold and palladium) by later hydrothermal and/or metamorphic processes with associated authigenic quartz, silicates (epidote, amphiboles) and secondary magnetite containing sulphide inclusions.

Habitat structure influences the spider fauna of short-rotation poplar plantations more than forest age

Plantation forests comprise an important part of the forested areas in European countries. Intensive forestry management and short-rotation cycles of plantation forests reduce habitat diversity and change the composition of invertebrate assemblages, mainly by reducing the number of habitat specialist species. Here, we analysed the effect of vegetation structure, amount of dead organic matter (DOM) and plantation age on spider functional diversity and assemblage structure in short-rotation plantations of native silver poplar in Hungary. Three stages, representing young plantations, 6- to 10-year-old stands (five stands), middle-aged plantations, aged between 23 and 26 years (five stands) and mature, 35- to 37-year-old forests at commercial maturity (five stands) were sampled. Each sample consisted of the data of ten pitfall traps. Traps were installed 5 m from each other in a 2 × 5 grid. Functional diversity was positively related to vegetation structure. High functional diversity indicates a higher number of available niches and potential resources. The abundance of moist habitat species and forest specialist species was positively correlated with DOM. Furthermore, moist habitat species were also related to vegetation structure. The most important environmental parameters affecting spiders were factors attributed to trees (litter and DOM), understory vegetation structure and, to a lesser extent, forest age. Different-aged stands may be similar in terms of species composition of their spider fauna if they comprise the same habitat structural patterns. Our study emphasises that the simple habitat structure of plantation forests has a negative effect on spider communities.

Exploring the structural and functional properties of the Lake Victoria food web, and the role of fisheries, using a mass balance model

Human and environmental factors have greatly challenged Lake Victoria ecosystem, especially in the last four decades. However, the lake continues to support the World's largest freshwater fishery, currently producing ca. one million tons of fish per year and directly supporting livelihoods of ca. four million people in three riparian countries. We used the Ecopath component of Ecopath with Ecosim modelling software to re-parameterise two existing mass balance models to reflect ecosystem state of Winam Gulf in 1971–1972 and 1985–1986, and construct a new model for the whole lake to reflect ecosystem state in 2014. The aim was to understand the structural and functional properties of Lake Victoria food web and the role of fisheries on the ecosystem. We found a decrease over time in productivity in relation with biomass and respiration, and food web connectivity, and an increase in biomass cycling. The total system throughput, decreased fivefold between 1971 and 1972 and 1985–1986, but was slightly higher in 2014 with a moderate shift from herbivory to detritivory. The implication of these changes on system maturity and resilience are discussed. The trophic level of catches increased between 1971 and 1972 and 1985–1986 due addition of high trophic level catches from the introduced piscivorous Nile perch (Lates niloticus) i.e. “fishing up”. However, the decline in trophic level of catches between 1985 and 1986 and 2014 seems to have been due to sequential addition of low trophic level catches, especially from the native Silver cyprinid (Rastrineobola argentea), a phenomenon termed “fishing through”, as opposed to a decline of high trophic level catches (or “fishing down”). Currently, exploitation is unbalanced and skewed to the least productive species at higher trophic level, with significantly less fishing occurring at the most productive species at lower trophic level, and the causes are discussed.

Mineralogy and genetic characteristics of the Rudnik Pb-Zn/Cu,Ag,Bi,W polymetallic deposit (Central Serbia) - New occurrence of Pb(Ag)Bi sulfosalts

The mineral aschamalmite, of heyrovskyite-like composition, but different in structure, from the Rudnik Pb–Zn/Cu,Ag,Bi,W polymetallic deposit in the central part of Serbia has been investigated. This polymetallic deposit includes over 90 hydrothermal and skarn-replacement orebody types, primarily hosted by Cretaceous sediments and occassionally by Oligocene dykes and sills of dacitic composition, and contact-metamorphic-metasomatic rocks. These rocks are host to an assemblage of pyrrhotite, colloform pyrite, chalcopyrite, galena, arsenopyrite, native bismuth and scheelite as well as minor pyrite, sphalerite, bismuthinite, argentopentlandite, and native silver. The chemical composition of the ore is very complex, where weight contents of valuable metals range as follows (%): Zn 0.49–4.49; Pb 0.90–5.66; Cu 0.08–2.18; WO 3 0.05–1.18; Ag 0.005–0.030; Bi 0.005–0.081; and Cd 0.002–0.016. In reflected light, aschamalmite is optically anisotropic, with moderately high bireflectance ranging from slightly greenish to slightly gray. Electron-microprobe analysis gave an average crystallochemical formulae of (Pb 5.82 Ag 0.20 ) Σ6.02 Bi 2.03 (S 8.93 Te 0.02 Se 0.01 ) Σ8.96 . The strongest diffraction maximums of the X-ray powder pattern [ d (in A)(I)] are 3.419(100), 3.382(92), and 3.334(66). Monoclinic unit cell parameters are a =13.727(7); b =4.122(3); c =31.32(2) A; β =90.72(5) o ; and V =1771.8(1) A 3 . Mineral assemblages and genesis of the Rudnik polymetallic deposit are discussed in detail and the sulfobismuthite mineralization has been compared with similar well-known global deposits.

Gold and silver minerals in low-sulfidaton ores of the Julietta deposit (northeastern Russia)

Gold- and silver-containing pyrites of the Tikhii area at the Julietta deposit (Engteri ore cluster, Magadan Region) were studied by optical and scanning electron microscopy and electron probe microanalysis. One- or two-phase rounded microinclusions consisting of electrum (450-680%c) and/or galena or of petrovskaite and/or uytenbogaardtite, galena, and sphalerite have been found in early pyrites. Later As-pyrites (up to 2.6 wt.% As) contain multiphase xenomorphic microinclusions of acanthite, uytenbogaardtite, freibergite, argentotetrahedrite-tennantite, naumannite, petzite, selenopolybasite-selenostephanite, tellurocanfieldite, and other ore minerals localized in pores, cracks, and interstices. Pyrites that underwent hypergene alterations have rims and veinlets formed by acanthite, goethite, anglesite, plattnerite, and native silver. The presence of rounded ore mineral microinclusions and large pores in the early pyrites suggests the participation of volatiles in the mineral formation and the uptake of large amounts of impurities by pyrite under high-gradient crystallization conditions. The thermobarogeochemical studies of fluid inclusions in quartz have shown that the ore zone formed under boiling-up of hydrothermal medium-concentration NaCl solutions at 230-105 °C. The results of thermodynamic calculations evidence that Ag-Au-S-Se minerals formed under decrease in temperature and fugacity of sulfur (log1Q/S2 = -22 to -9) and selenium (log1Q/Se2 = -27 to -14) and change of reducing conditions by oxidizing ones in weakly acidic to near-neutral solutions.

Origin and evolution of hydrothermal fluids in epithermal Pb-Zn-Cu ± Au ± Ag deposits at Koru and Tesbihdere mining districts, Çanakkale, Biga Peninsula, NW Turkey

The Koru and Tesbihdere mining districts in Biga Peninsula, Northwestern Turkey, consist of twelve deposits covering approximately 12km2. The epithermal Au-Ag enriched base metal veins and associated low-grade breccia and stockwork at Koru and Tesbihdere are hosted by Oligocene subaerial and calc-alkaline volcanic rocks including basaltic andesite lavas, dacitic lava-tuffs, rhyolitic lava-domes and tuffs. NW- to N-trending strike-slip faults and E- and NE-trending faults constitute the most important ore-controlling structures in the Koru and Tesbihdere districts respectively. In the Koru mining district, galena is the dominant ore mineral in barite-quartz veins containing sphalerite, chalcopyrite, pyrite, bornite, enargite and tennantite. According to base metal content, the Tesbihdere mining district can be subdivided into sphalerite-galena dominated Tesbihdere mineralization and chalcopyrite-pyrite dominated Bakır and Kuyu Zones mineralization. Gold is present in small quantities with maximum 3.14g/t Au values either as free grains in quartz or as micro inclusions in pyrite and galena. The most widespread silver minerals are polybasite, pearceite, argentite and native silver which commonly occur as replacements of galena, sphalerite and pyrite, and other sulfides, or as fillings of microfractures in sulfides and quartz.Microthermometric measurements of primary liquid-rich fluid inclusions in sphalerite, barite and quartz in Koru indicate that the veins were formed at temperatures between 407 and 146°C from fluids with salinities between 0.7 and 12.5wt.% equiv. NaCl. Barite from the Tahtalıkuyu, Kuyutaşı and 5th Viraj mineralization show the highest homogenization temperatures. Fluid inclusion data for ore-stage quartz and sphalerite from the Tesbihdere mining district, indicate that these minerals were deposited at temperatures between 387 and 232°C from more diluted fluids with moderate salinities between 0.2 and 10.6wt.% NaCl equiv. Tahtalıkuyu and 5th Viraj mineralization show only boiling trends while Kuyutaşı, Tesbihdere, Bakır and Kuyu Zones mineralization show both boiling and isothermal mixing trends. The O and H isotope compositions of ore fluids from the Tahtalıkuyu (δ18O=−1.40 to 0.25‰; δD=−72.49 to −52.68‰) and Kuyutaşı (δ18O=−2.29 to 3.59‰; δD=−90.70 to −70.93‰) mineralization indicate that there was a major contribution from a magmatic component to ore genesis. Based on 9 quartz samples associated with orebodies at the Tesbihdere mining district, the relatively higher δ18O and lower δD isotope compositions from hydrothermal fluids could be attributed to a relatively dilute fluid derived by the mixing with meteoric water. The Pb isotope compositions also reveal that most of the lead in both mining districts is derived from the Oligocene-Miocene magmatic rocks, possibly with smaller contributions from the Eocene magmatic rocks.

English

Gastrointestinal tract (GIT) infections are major causes of mortality and morbidity world-wide, especially in developing countries. Cajanus cajan extracts possess therapeutic properties. In this study, the induced and non-induced antibacterial properties of C. cajan seeds were evaluated against bacterial strains implicated in GIT infections by Disc diffusion method and Micro-well dilution assay. C. cajan produced phytoalexins after the seeds were elicited with native flora and silver nitrate. At 100 mg/ml, the ethyl acetate extract produced zones of inhibition (14 to 16 mm) against Staphylococcus aureus (ATCC 25925), Klebsiella pneumoniae (ATCC 31488) and Salmonella typhimurium (ATCC 700030). The minimum inhibitory concentration (MIC) values obtained using micro well dilution method were 6.5, 12.5, and 12.5 mg/ml for S. aureus (ATCC 25925), K. pneumoniae (ATCC 4352) and S. typhimurium (ATCC 700030) and 25 mg/ml for all bacterial strains in the ethyl acetate extract (AgNO3 induced seeds), respectively. The results thus indicated that C. cajan seed extract do possess antibacterial activity. Key words: Seeds, antimicrobial, phytoalexins, phytoanticipins.

The paragenesis of silver minerals in the Pb-Zn Stan Terg deposit, Kosovo - an example of precious metal epithermal mineralization.

This study reports silver mineral association found recently in the Stan Terg lead and zinc mine, located in the Vardar Zone (in the northern Kosovo). The described mineralization comprises pyrargyrite, freieslebenite, high-Ag bearing tetrahedrite, freibergite and native compounds (electrum, native silver, native antimony). Ag-minerals occur in vuggs and cracks in massive galena ore, and have signs of the latest precipitated minerals in the deposit. The chemical composition of those minerals was confirmed by the electron microprobe. Freibergite from the Stan Terg deposit reveals zonality and contains between 13.91-20.28 at. % of Ag. High Ag solutions are indicated also by relatively high silver content in electrum, which is between 47.02 and 73.19 at. % of Ag. The Ag association is supposed to be an epithermal equivalent of precious metal mineralization which could be located in the external part of the Stan Terg hydrothermal system. This association occurs in low temperatures, below 200˚C. The Ag-minerals can be part of epithermal veins from the external part of the Stan Terg hydrothermal system. Similarly to the other know Pb-Zn-Ag hydrothermal system, silver association is related to formation of the rhodochrosite banded ore and Ag-Au-Sb±Hg dominated mineralization.

World-class Xincheng gold deposit: An example from the giant Jiaodong gold province

The Jiaodong gold deposits are currently the most important gold resources (with Au reserves of >4000 t) in China, and the leading gold-producing country globally (with Au production of ∼428 t in 2013). Jiaodong is also considered as perhaps the only world-class to giant gold accumulation on the planet where relatively young gold ores (ca. 130–120 Ma) were deposited in rocks that are 2 Ga older. The Xincheng world-class high-grade gold deposit, with a proven reserve of >200 t gold, is one of the largest deposits in the giant gold province of the Jiaodong Peninsula. It is located in the northwestern part of the Jiaobei Uplift, and hosted by ca. 132–123 Ma Xincheng quartz monzonites and monzogranites. Ore zones are structurally controlled by the NE-trending and NW-dipping Jiaojia Fault and subsidiary faults, and are mainly restricted to the footwall of the fault. The dominant disseminated- and stockwork-style ores are associated with strong sericitization, silicification, sulfidation and K-feldspathization, and minor carbonate wallrock alteration halos. The four mineralization stages are pyrite–quartz–sericite (stage 1), quartz–pyrite (stage 2), quartz–polysulfide (stage 3) and quartz–carbonate (stage 4). Gold occurs dominantly as electrum, with lesser amounts of sulfide-hosted native gold and rare native silver and argentite, normally associated with pyrite, chalcopyrite, galena and sphalerite: the latter with proven resources of about 105 t Ag, 713 t Cu, and 5100 t S.There are three types of ore-related fluid inclusions: type 1 aqueous-carbonate (H2O–CO2), type 2 aqueous (liquid H2O + vapor H2O), and type 3 CO2 (liquid CO2 and vapor CO2) inclusions. Homogenization temperatures range from 221 to 304 °C for type 1 inclusions, with salinities of 2.4–13.3 wt.% NaCl eq., and bulk densities of 0.858–1.022 g/cm3. The δ34SCDT values of hydrothermal sulfides are 4.3–10.6‰ and δ18O values of hydrothermal quartz have a median value of 13.0‰. δD values of fluid inclusions in hydrothermal quartz have a median value of −75‰. Calculated δ18Owater has a median value of 5.2‰. The timing of gold mineralization at the Xincheng gold deposit is younger than 123 ± 1 Ma, and likely between 120.9 and 119.9 Ma.A minerals system genetic model for the probable epizonal orogenic Xincheng deposit suggests an initial medium temperature, CO2-rich, and low salinity H2O–CO2 deeply sourced metamorphic ore fluid associated with dehydration and decarbonization of subducting Paleo-Pacific lithosphere. The Jiaojia Fault constrained the migration of ore-forming fluids and metals at the brittle–ductile transition. Fluid immiscibility, caused by episodic pressure drops, led to significant high-grade gold deposition in the giant Xincheng gold deposit.

Mineral and geochemical compositions, regularities of distribution, and specific formation of ore mineralization of the Rogovik gold-silver deposit (northeastern Russia)

New data on the mineral composition and the first data on the geochemical composition of ores of the Rogovik gold-silver deposit (Omsukchan ore district, northeastern Russia) have been obtained. Study of the regularities of the spatial distribution of ore mineralization shows that the deposit ores formed in two stages. Epithermal Au-Ag ores of typical poor mineral and elemental compositions were generated at the early volcanic stage. The major minerals are low-fineness native gold, electrum, acanthite, silver sulfosalts, kustelite, and pyrite. The typomorphic elemental composition of ores is as follows: Au, Ag, Sb, As, Se, and Hg. The content of S is low, mostly <1%. Silver ores of more complex mineral and elemental compositions were produced under the impact of granitoid intrusion at the late volcanoplutonic stage. The major minerals are high-Hg kustelite and native silver, silver sulfosalts and selenides, fahlore, pyrite, chalcopyrite, galena, and sphalerite. The typomorphic elemental composition of ores is as follows: Ag, As, Sb, Se, Hg, Pb, Zn, Cu, and B. The content of S is much higher than 1%. The ores also have elevated contents of Mo, Ge, F, and LREE (La, Ce, and Nd). At the volcanoplutonic stage, polychronous Au-Ag ores formed at the sites of the coexistence of silver and epithermal gold-silver mineralization. Their specific feature is a multicomponent composition and a strong variability in chemical composition (both qualitative and quantitative). Along with the above minerals, the ores contain high-Hg gold, hessite, argyrodite, canfieldite, orthite, fluorapatite, and arsenopyrite. At the sites with strongly rejuvenated rocks, the ores are strongly enriched in Au, Ag, Hg, Cu, Pb, Zn, Ge, Se, La, Ce, Nd, S, and F and also contain Te and Bi. The hypothesis is put forward that the late silver ores belong to the Ag-complex-metal association widespread in the Omsukchan ore district. A close relationship between the ores of different types and their zonal spatial distribution have been established. In the central part of the Rogovik deposit, epithermal Au-Ag ores are widespread in the upper horizons, Ag ores are localized in the middle horizons, and rejuvenated polyassociation Au-Ag ores occur at the sites (mostly deep-seated) with ore-bearing structures of different ages.

Metal-dielectric-metal resonators with deep subwavelength dielectric layers increase the near-field SEIRA enhancement.

Plasmonic nanostructures presenting either structural asymmetry or metal-dielectric-metal (M-D-M) architecture are commonly used structures to increase the quality factor and the near-field confinement in plasmonic materials. This characteristic can be leveraged for example to increase the sensitivity of IR spectroscopy, via the surface enhanced IR absorption (SEIRA) effect. In this work, we combine structural asymmetry with the M-D-M architecture to realize Ag-Ag(2)O-Ag asymmetric ring resonators where two Ag layers sandwich a native silver oxide (Ag(2)O) layer. Their IR response is compared with the one of fully metallic (Ag) resonators of the same size and shape. The photothermal induced resonance technique (PTIR) is used to obtain near-field SEIRA absorption maps and spectra with nanoscale resolution. Although the native Ag(2)O layer is only 1 nm to 2 nm thick, it increases the quality factor of the resonators' dark-mode by ≈27% and the SEIRA enhancement by ≈44% with respect to entirely Ag structures.

Genetic Pd, Pt, Au, Ag, and Rh mineralogy in Noril’sk sulfide ores

The undeformed ore-bearing intrusions of the Noril’sk ore field (NOF) cut through volcanic rocks of the Late Permian–Early Triassic trap association folded in brachysynclines. Due to the nonuniform load on the roof of intrusive bodies, most sulfide melts were squeezed, up to the tops of ore-bearing intrusions; readily fusible Ni–Fe–Cu sulfide melts were almost completely squeezed. In our opinion, not only one but two stages of mineralization developed at the Noril’sk deposits: (i) syntrap magmatic and (ii) epigenetic post-trap metamorphic–hydrothermal. All platinum-group minerals (PGM) and minerals of gold are metasomatic in the Noril’sk ores. They replaced sulfide solid solutions and exsolution structures. All types of PGM and Au minerals occur in the ores, varying in composition from pyrrhotite to chalcopyrite, talnakhite, mooihoekite, and rich in galena; they are localized in the inner and outer contact zones and differ only in the quantitative proportions of ore minerals. The aureoles of PGM and Au–Ag minerals are wider than the contours of sulfide bodies and coincide with halos of fluid impact on orebodies and adjacent host rocks. The pneumatolytic PGM and Au–Ag minerals are correlated in abundance with the dimensions of sulfide bodies. Their amounts are maximal in veins of late fusible ore composed of eutectic PbSss and iss intergrowths, as well as at their contacts. The Pd and Pt contents in eutectic sulfide ores of NOF are the world’s highest. In the process of noble-metal mineral formation, the fluids supply Pd, Pt, Au, As, Sb, Sn, Bi, and a part of Te, whereas Fe, Ni, Cu, Pb, Ag, Rh, a part of Te and Pd are leached from the replaced sulfide minerals. The pneumatolytic PGM of the early stage comprises Pd and Pt intermetallic compounds enriched in Au along with Pd–Pt–Fe–Ni–Cu–Sn–Pb(As) and (Pd,Pt,Au)(Sn,Sb,Bi,Te,As) solid solutions. Pneumatolytic PGM and Au minerals of the middle stage are products of solid-phase transformation and recrystallization of early PGM in combination with the newly formed mineral species Sb-paolovite–insizwaite–geversite–maslovite, niggliite, tetraferroplatinum, rustenburgite–atokite–zvyagintsevite, moncheite, majakite, plumbopalladinite, polarite in association with altaite. The late minerals of the middle stage include stannopalladinite, tatianaite–taimyrite, Ag–Pd–Pt tetraauricupride, and cuproauride. PGM and Au–Ag minerals of the late stage are represented by sobolevskite–sudburyite–kotulskite, maslovite–michenerite, low-Sb paolovite, hessite, cabriite, Au–Ag minerals with fineness of 870–003, froodite, Sb-free insizwaite, Bi-free geversite, and Sb-free niggliite. Electrum and kustelite in PGM aggregates are not zoned. Crystals of Au–Ag minerals that grow over PGM minerals are smoothly zoned. Their zoning may be direct (crystal margins are enriched in Ag), inverse, oscillatory, and complex. Despite favorable annealing conditions, exsolution structures are not identified in Au–Ag minerals from the Noril’sk ores. Sperrylite—the latest of pneumatolytic PGM—occurs as metacrysts up to 14 cm in size. Sperrylite, which replaces high-Sb minerals, contains up to 11 wt % Sb. Pneumatolytic noble-metal minerals originated under the effect of the fluids released during crystallization of sulfide melts in an extremely reductive setting and at extremely low fS2; temperature drops from ~450 to ~350°C. Metamorphic–hydrothermal Ag mineralization (native silver, Hg-silver, sulfides and selenides, chalcopyrite–lenaite solid solutions, argentopentlandite), Pd mineralization (vysotskite, palladoarsenide, vincentite, Sb-free Ag-paolovite, malyshevite, native palladium), and Pt mineralization (kharaelakhite, cooperite, native platinum) develop in those parts of orebodies that are affected by low-grade metamorphism.

GEOLOGY AND ORE MINERALISATION OF NEOGENE SEDIMENTARY ROCK HOSTED LS EPITHERMAL GOLD DEPOSIT AT PANINGKABAN, BANYUMAS REGENCY, CENTRAL JAVA, INDONESIA

Low suphidation (LS) epithermal gold deposits were recently found in the Paningkaban area, Central Java province, Indonesia, with more than five hundred artisanal gold miners currently operating in the area. This study is aimed to understand the geological factors controlling the gold mineralization and to characterize the alteration and ore mineralogy of the deposit. Several epithermal veins/veinlets trending N–S, NW–SE, and NE–SW are hosted by Tertiary turbiditic volcanoclastic sedimentary rocks of the Halang formation. This formation is composed of looping gradation of sandstone and siltstone units. Pre- and syn-mineralization structures such as extension joints, normal sinitral fault and sinitral fault control the gold mineralization. Fault movements formed dilational jogs manifested by NW-SE-trending en-echelon tension gash veins. Four main alteration zones are identified: (a) phyllic, (b) argillic, (c) sub propylitic and (d) weak subpropylitic. Ore minerals consist of native gold, electrum, native silver, pyrite, chalcopyrite, sphalerite, galena, arsenopyrite, cubanite, marcasite, covellite and tennantite, which are commonly associated withargillic alteration. Vein structures such as massive, swarm and low angle veins, stockwork and veins dispersed in diatreme breccia are present. Normal banded, cockade, crustiform, bladed carbonates as well as, comb and saccharoidal features are the typical vein textures. It is noteworthy that the veins are basically composed of carbonate with minor quartz at gold grades of up to 83 g/t Au. Based on the vein structures and textures, four stages of ore mineralization were developed consisting of (a) early stage (fluidized breccia and quartz vein), (b) middle stage (carbonate base metal), (c) late stage (late carbonate), and supergene stage. Gold mineralization originated mainly during middle and late stages, particularly in association with cockade, crustiform, bladed carbonate base metal veins. Based on those various features, the LS epithermal deposit in the study area is categorized as carbonate-base metalgold mineralization type.