Au Sulfide Research Articles

The Raduzhnoe Au–Sulfide Deposit (Northern Caucasus): Geological Settings, Mineralogy, and Sources of Metals

The Raduzhnoe Au–Sulfide Deposit (Northern Caucasus): Geological Settings, Mineralogy, and Sources of Metals

Ultramafic-alkaline-carbonatite Tajno intrusion in NE Poland: A new hypothesis about the massif formation and related mineralization

This manuscript presents results of the newest petrographic, mineralogical and bulk chemical, as well as H, C and O stable isotope study of carbonatites and associated silicate rocks from the Tajno Massif (NE Poland). The Tajno Intrusion is a Tournaisian-Visean ultramafic-alkaline-carbonatite body emplaced within the Paleoproterozoic rocks of the East European Craton (EEC). Carbonatites of the Tajno Massif can be subdivided into the calciocarbonatite (calcite), ferrocarbonatite (ankerite), and breccias with an ankerite-fluorite matrix. Due to location at the cratonic margin and abundance in the REE, Tajno classifies (Hou et al., 2015) as the carbonatite-associated REE deposit (CARD), and more precisely as the Dalucao-Style orebody (the breccia-hosted orebody). High Fe2O3 (13.8 wt%), MnO (2.1 wt%), total REE (6582 ppm), Sr (43895 ppm), Ba (6426 ppm), F (greater than10000 ppm) and CO2 contents points for the involvement of the slab – including pelagic metalliferous sediments – in the carbonatites formation. Spatial relations and Sr isotope composition ((87Sr/86Sr)i = 0.7043–0.7048; Wiszniewska et al., 2020) of alkali clinopyroxenite and syenite suggest that these are products of differentiation of the magma, generated by the initial melting of the SCLM due to influx of F-rich fluids from subducted marine sediments. Carbonatites Sr isotope composition ((87Sr/86Sr)i = 0.7037–0.7038), and Ba/Th (16–20620) and Nb/Y (0.01–6.25) ratios, link their origin with a more advanced melting of the SCLM, triggered by CO2-rich fluids from the subducted AOC and melts from sediments. The Tajno Massif – and coeval mafic-alkaline intrusions – age, high potassic composition, and location along the craton margin nearly parallel the Variscan deformation front, are suggesting Variscan subduction beneath the EEC. The oxygen isotope compositions of clinopyroxene (δ18O value = 5.2‰) and alkali feldspar (δ18O value = 5.7‰), from alkali clinopyroxenite and foid syenite, respectively, are consistent with mantle-derived magmas. Isotopic compositions of carbonatites and breccias (carbonate δ18O = 8.7‰ to 10.7‰; δ13C = -4.8‰ to −0.4‰) span from values of primary carbonatites to carbonatites affected by a fractionation or sedimentary contamination. The highest values (δ18O = 10.7‰; δ13C = -0.4‰) were reported for breccia cut by numerous veins confirming post-magmatic hydrothermal alteration. The lowest carbonate δ18O (9.3‰ to 10.7‰) and δ13C (−5.0‰ to −3.8‰) values are reported for veins in alkali clinopyroxenites, whereas the highest δ18O (11.2‰) and δ13C (−1.2‰ to −1.1‰) values are for veins in syenites and trachytes. Isotopic composition of veins suggests hydrothermal origin, and interaction with host mantle-derived rocks, as well as country rocks. In silicate rocks of the Tajno Massif, fluid influx leads to the development of Pb, Zn, Cu, Ag, Au sulfide mineralization-bearing stockwork vein system, with carbonate, silicate and fluorite infilling the veins. Bulk-rock contents of molybdenum (925 ppm), rhenium (905 ppb) and palladium (29 ppb) are notable. The Re-rich molybdenite association with galena, pyrite and Th-rich bastnäsite in carbonate veins is similar as in Mo deposits associated with carbonatites, implying the mantle source of Mo and Re.

ПЕРВЫЕ ДАННЫЕ О ЮТЕНБОГААРДИТЕ В РУДЕ ТАСЕЕВСКОГО ЗОЛОТОСЕРЕБРЯНОГО МЕСТОРОЖДЕНИЯ В ВОСТОЧНОМ ЗАБАЙКАЛЬЕ (РОССИЯ)

The relevance lies in the need to have complete data on the features of the mineralogy of the unique in terms of gold and silver content ores of shallow gold-silver formation deposits, one example of which is the Taseevskoye deposit in the Baleisky ore field in Eastern Transbaikalia. The purpose of the study is to determine the mineral composition of the rich gold-silver ores of the Taseevsky deposit. The object of the study is a hessite-uytenbogaardite-electrum-chalcopyrite-calcite-quartz mineral association. The subject of the study is the chemical composition and forms of isolation of uytenbogaardite. Method and methodology used are optical and electron microscopy with the determination of forms of precipitation and variations in the chemical composition of uytenbogaardite. The results are the following: for the first time, the rare Au and Ag sulfide uytenbogaardite was identified in the gold-silver ore of the Taseevskoye deposit, its chemical composition was determined, and it was found that it is in association with electrum, chalcopyrite, sphalerite, hessite, quartz, acanthite, cervelite, and petzite. Subspherical forms of aggregates predominate, less often lenticular and veinlets. The size of its crystals and their intergrowths is 0.005 - 0.5 mm. All crystals are nonstoichiometric. The content of the main chemical elements varies within (wt.%): Ag 52.43 - 64.76; Au 22.57 - 37.35; S 7.32 - 12.84. Among the studied individuals of uytenbogardite, three contain from 2.98 to 5.18% Te. Low grade Au, which is associated with uytenbogardite, contains from 43.32 to 56.42% Ag and is electrum by their ratio. Uytenbogaardite was found only in the upper part of the ore zone of the Taseevskoe deposit. This may be a typomorphic feature for determining whether the chalcedony-like quartz containing it belongs to the supra-ore zone of a deposit of a shallow gold-silver formation

Chlorite as an exploration indicator for concealed skarn mineralization: Perspective from the Tonglushan Cu–Au–Fe skarn deposit, Eastern China

Compositional variations of chlorite have been increasingly used to trace the magmatic–hydrothermal fluid evolution, as well as exploration vector toward concealed orebodies. This method has been widely applied to porphyry Cu (–Au) systems, but related research on skarn systems remain scarce. The Tonglushan Cu–Au–Fe deposit (86.3 Mt @ 1.66% Cu, 0.94 g/t Au and 39.4% Fe) is one of the largest Cu–Au polymetallic skarn deposits in the Middle–Lower Yangtze River metallogenic belt (MLYRB, Eastern China). Based on detailed petrographic observation, we present new EPMA and LA–ICP–MS elemental data for the Tonglushan chlorite, and discuss their implications on hydrothermal fluid evolution and exploration of concealed skarn orebodies there. At Tonglushan, chlorite alteration is well developed in the main Cu–Au sulfide ore stage. Three types of chlorite have been identified, i.e., disseminated chlorite replacing biotite and/or hornblende in the ore-causative quartz monzodiorite (porphyry), vein-type chlorite in quartz–chlorite–sulfides veins along/near the internal and external intrusive contact, and replacement-type chlorite that replaced garnet, diopside, epidote and Fe oxides in the skarn mineralization center.All the Tonglushan chlorite samples belong to trioctahedral chlorite and have similar crystallization temperatures (163–351 °C). The substitution mechanisms of Fe2+ ⇔ Mg2+, Tschermark (AlivAlvi ⇔ Si (Mg2+, Fe2+)) and di-trioctahedral (3(Mg2+, Fe2+) ⇔ □ + 2Alvi) are likely important for the Tonglushan chlorite formation. Replacement-type chlorite shows higher contents of FeOT, mobile elements (e.g., Ca, Na, B, Sr, Pb, Zn and Sn) and ore-forming elements (e.g., Cu and Co), whereas the disseminated chlorite has higher contents of Ti, Li, LILEs (e.g., K, Rb, Ba and Cs) and incompatible elements (e.g., V, Sc, Co and Ni). Meanwhile, the vein-type chlorite has similarly high contents of Ti, Li, V, Sc and Ni to the disseminated chlorite, but has higher FeOT and Cu contents but lower MgO content than the latter. Such compositional differences may have mainly attributed to the protolith (or precursor minerals) and hydrothermal fluid chemistry. Integrating the chlorite petrographic features and chemical compositions, we suggest that elevated FeOT and B contents and Fe/(Fe + Mg) ratios, and lower MgO, Al2O3, Ti, V and Sc contents can serve as proximal indicator for exploring concealed skarn orebodies at Tonglushan, as well as other similar Cu–Au–Fe skarn deposits in the MLYRB.

AMT survey in the Outokumpu ore belt, eastern Finland

ABSTRACTThe Outokumpu belt in eastern Finland is known for numerous polymetallic (Cu–Co–Zn–Ni–Ag–Au) sulphide ore deposits and it is a potential area for new discoveries. Audiomagnetotelluric (AMT) data have recently been collected to image the subsurface conductivity structure of the belt. The data were acquired along five profiles aiming to explore deep conductors, study their geometry and investigate the deep conductivity structure of the belt.The acquired AMT data were mostly adequate for 2D inversion, as the survey area is characterised by thin, laterally extensive conductors indicated by airborne electromagnetic data, deep drillings and regional strike analysis of the impedance tensor data. 2D smooth inversion was carried out jointly for transverse electric and transverse magnetic data. The results show southeast-dipping and sub-horizontal continuous conductors southeast of the Outokumpu old mine, suggesting the presence of prospective Outokumpu assemblage rocks. One ∼ 1 km deep sub-horizontal conductor is verified by a deep drill-hole located ∼ 8 km southeast of the mine. The results demonstrate a similar southeast-dipping structure in the Vuonos mine area, which is located ∼ 7 km northeast of the Outokumpu old mine. An eastwards-dipping conductor detected in the Miihkali serpentinite area indicates deep exploration potential in this area. Besides the smooth 2D inversion, a sharp-boundary 2D inversion was performed and the resulting model was assessed with the existing geological interpretation of the Miihkali area. In the area of the Sotkuma gneiss inlier, conductors are absent from the uppermost ∼ 6 km. This feature may represent an uplifted fault block rather than a thin thrust sheet of Archaean basement rocks.

Surface Typochemistry of Native Gold

Using the methods of electron spectroscopy of the surface and SEM–EDS, it is shown that native gold of the deposit related to the epithermal Au–Ag ore formation contains oxidized gold with an oxidation degree of Au (I) or higher on the surface. A thin layer (~15 nm) with high concentrations of Ag and S and an underlying SiO2-bearing layer with a thickness of ~30–60 nm play a protective role providing preservation of Ag and Au sulfides in the surface parts of the Au–Ag grains under the oxidizing conditions. S-rich marginal parts of native gold particles may be represented by solid solutions Ag2–xAu x S or (with a lack of S) by agglomerates of Ag n Au m S clusters. The formation of surface zoning in the nanoscale on the surface of native Au is abundant in nature and may be applied in prospecting.

The fabrication of high sensitivity gold nanorod H2S gas sensors utilizing the highly uniform anodic aluminum oxide template

Gold nanorod were fabricated using anodic alumina oxide template for H2S gas detection. The nanorod gas sensor exhibits high surface density and contact area, which can increase detection sensitivity. The anodic alumina oxide template contains an array of pores, with a width of 70 nm and a length of 27μm. Au nanorod were obtained through electro-deposition under a pulse bias of −1 V. The resistance of the Au nanorod was recorded upon exposure to various concentrations of H2S. The resistance could be attributed to the high electron affinity between sulfide and Au nanorod. Au–sulfide bonds provide strong bonding, which could alter the conductivity of the sensor. The gas sensor exhibits high sensitivity and short response time for H2S detection at room temperature.

Tectono-metallogenic settings of the formation and convergence of disseminated Au–sulfide mineralization

Large Au-sulfide deposits (GSDs) of disseminated ores occur worldwide in metallogenic provinces of various ages (from Precambrian to Pliocene). The studies performed showed that the great genetic diversity of GSD is determined by the similar oregenesis conditions that appear in different tectono-metallogenic settings (TMSs). A GSD is included in a certain TMS by the respective changes in the mineral and geochemical assemblages of ores. However, in the majority of cases, the GSDs of different TMSs are convergent (quasi-identical) in the texture, structure, and mineral composition of ores. All types of the above TMSs are found in Russia, which allows forecasting the discovery of new GSDs in each setting.

Polymetallic mineralisation associated with Carboniferous I-type granitoids in central Stewart Island, New Zealand

ABSTRACTCarboniferous granitoids in central Stewart Island host two metalliferous hydrothermal systems that formed during emplacement of the c. 306 ± 2 Ma old Euchre Pluton and 303 ± 2 Ma Hill 267 leucogranitoid, respectively. The Ogles Creek–Silvertown Hydrothermal System (OST) on the eastern side of South West Arm, Paterson Inlet is centred on the scheelite-bearing, ilmenite-syenogranite core of the Euchre Pluton. Here pyritic-potassic alteration and related veins contain Mo, Bi, Ag, Co, Cu, W, Pb, Zn, U–Th and rare Earth element (REE) sulphide, telluride, oxide and phosphate minerals. Peripheral quartz-rich veins contain various Ag, Au, Pb and Zn-bearing sulphide, telluride and oxide minerals. The Hill 267 Hydrothermal System (HHS) is centred on the ridge between the Scott Burn and Forked Creek where strongly altered leucogranitoid riddled with miarolitic cavities contains pyrite, W- and Nb-bearing rutile, molybdenite, tourmaline and 2–10 times background Bi, Ag, Te, Cu and Se. More prospective parts of both systems have probably been removed by erosion, but less deeply eroded correlative hydrothermal systems may be present elsewhere in New Zealand near the outboard margin of the Takaka Terrane.

Extreme enrichment of Se, Te, PGE and Au in Cu sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion, east Greenland

The Platinova Reef, in the Skaergaard Intrusion, east Greenland, is an example of a magmatic Cu–PGE–Au sulfide deposit formed in the latter stages of magmatic differentiation. As is characteristic with such deposits, it contains a low volume of sulfide, displays peak metal offsets and is Cu rich but Ni poor. However, even for such deposits, the Platinova Reef contains extremely low volumes of sulfide and the highest Pd and Au tenor sulfides of any magmatic ore deposit. Here, we present the first LA-ICP-MS analyses of sulfide microdroplets from the Platinova Reef, which show that they have the highest Se concentrations (up to 1200 ppm) and lowest S/Se ratios (190–700) of any known magmatic sulfide deposit and have significant Te enrichment. In addition, where sulfide volume increases, there is a change from high Pd-tenor microdroplets trapped in situ to larger, low tenor sulfides. The transition between these two sulfide regimes is marked by sharp peaks in Au, and then Te concentration, followed by a wider peak in Se, which gradually decreases with height. Mineralogical evidence implies that there is no significant post-magmatic hydrothermal S loss and that the metal profiles are essentially a function of magmatic processes. We propose that to generate these extreme precious and semimetal contents, the sulfides must have formed from an anomalously metal-rich package of magma, possibly formed via the dissolution of a previously PGE-enriched sulfide. Other processes such as kinetic diffusion may have also occurred alongside this to produce the ultra-high tenors. The characteristic metal offset pattern observed is largely controlled by partitioning effects, producing offset peaks in the order Pt+Pd>Au>Te>Se>Cu that are entirely consistent with published D values. This study confirms that extreme enrichment in sulfide droplets can occur in closed-system layered intrusions in situ, but this will characteristically form ore deposits that are so low in sulfide that they do not conform to conventional deposit models for Cu–Ni–PGE sulfides which require very high R factors, and settling of sulfide liquids.

Origin of the Luping Pb deposit in the Beiya area, Yunnan Province, SW China: Constraints from geology, isotope geochemistry and geochronology

The Luping Pb deposit, a newly discovered Pb–(Fe–Au–Ag–Zn) polymetallic deposit close to the Cenozoic Beiya porphyry-related Au–(Fe–Cu–Pb–Zn–Ag) deposit, is located in the central Sanjiang (three rivers: Jinshajiang, Lancangjiang and Nujiang) region (western Yangtze Block) in southwestern China. Ore bodies of the Luping deposit are mainly stratiform type, host in the Middle Triassic Beiya Formation limestone and Lower Triassic Qingtianbao Formation sandstone, and occur along NNW-trending bedding-plane faults within axis of Beiya–Qinghe syncline. Three ore types, namely the Pb–Au sulfide, Fe–Au, and Au ores, can be discerned regarding their ore metal association with reserves of 2.7million tonnes (Mt) (average grade: 3.06wt.% Pb, 0.66g/t Au, 41g/t Ag, and 0.82wt.% Zn), 3Mt (average grade: 30wt.% Fe, 0.96g/t Au and 31g/t Ag), and 0.67Mt (average grade: 2.16g/t Au and 13g/t Ag), respectively. Pb–Au sulfide ores contain mainly galena, siderite, native gold, sphalerite, and pyrite, with minor chalcopyrite, pyrrhotite and arsenopyrite, and gangue minerals such as quartz, calcite and dolomite. Sulfide ore textures include mainly brecciated, banded and vein, and minor massive and disseminated. LA-ICP-MS zircon U–Pb dating of alkali-rich quartz syenite porphyry from drill holes yielded a Late Eocene (Priabonian) age (36.2±0.4Ma), broadly coeval to the zircon U–Pb ages (ca. 38Ma–31Ma) of alkaline porphyries and molybdenite Re–Os age (36.9±0.3Ma) from the Beiya deposit near Luping. Calcite separates have δ13CPDB and δ18OSMOW values ranging from −5.8‰ to −5.1‰ (average: −5.6‰) and +13.2‰ to +14.7‰ (mean: +13.6‰), respectively, suggesting association with the mantle. The sulfides have a narrow range of δ34SCDT values (+0.8‰–+2.8‰, mean +1.8‰), which is similar to that of mantle-derived S (0±3‰). 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of the sulfides range from 18.62 to 18.69, 15.66 to 15.70 and 38.92 to 39.08, respectively, similar to those of the porphyry whole-rock (206Pb/204Pb 36 Ma=18.61–18.71, 207Pb/204Pb 36 Ma=15.64–15.77 and 208Pb/204Pb 36 Ma=38.88–39.32). Ore deposit geology and C–O–S–Pb isotopic data suggest that the sources of metals and ore-forming fluids were likely to be derived from the alkali-rich porphyries in the Beiya area. We propose that the Luping deposit is best classified as an epithermal Pb polymetallic deposit associated with the Beiya alkaline porphyries (ca. 36Ma–31Ma). Similar to other deposits related to the Cenozoic alkaline porphyries in the Jinshajiang–Red River (Ailaoshan) metallogenic belt, the Luping deposit may have been formed in the India–Eurasia post-collisional setting, when partial melting occurred in the Triassic stagnant slab that thickened the lower crust and the upper mantle, producing the alkaline magmatism and its associated mineralization.

Late-Hercynian intrusion-related gold deposits: An integrated model on the Tighza polymetallic district, central Morocco

Gold have been recently recognized in the Tighza (formerly Jebel Aouam) district, in the Hercynian belt of central Morocco. This district has long been known for its W mineralization, as well as major Pb–Ag–Zn, and minor Sb–Ba deposits, all geographically associated with late-Hercynian calc-alkaline magmatism. Gold mineralization in the district is mainly hosted by thick W–Au quartz veins located around the “Mine granite” small granitic plug. Within the veins, gold grade is highest (up to 70g/t) close to the granite but rapidly decreases going outward from the granite, defining a perigranitic zoning. Anomalous gold grades have also been measured in hydrothermal skarn layers close to two other granitic plugs (Kaolin granite and Mispickel granite), associated with disseminated As–Fe sulfides. The paragenetic sequence for the W–Au quartz veins shows three stages: (1) an early oxidized stage with wolframite-scheelite associated with early quartz (Q1), (2) an intermediate Bi–As–Te–Mo–Au sulfide stage with loellingite, bismuth minerals and native gold with a later quartz (Q2), restricted to a narrow distance from the granite, and (3) a late lower temperature As–Cu–Zn–(Pb) stage with abundant massive pyrrhotite, arsenopyrite and sphalerite, locally forming independent veins (“pyrrhotite vein”). Both Q1 hyaline and Q2 saccharoidal gold-bearing quartz display aqua-carbonic fluids with minor H2S and Cu and an homogeneous composition (81mole% H2O, 18mole% CO2 and about 1mole% NaCl). The trapping pressure is estimated to 1.5–2kbar with temperature ranging from 300 to 350°C. Q1 inclusions have exploded indicating an uplift of the Tighza block, that lead to saccharoidal Q2 quartz deposition with multiphase NaCl-saturated fluid inclusions. 40Ar/39Ar dating demonstrates that the “Mine granite”, tungsten skarnoid, scheelite-molybdenite veins, and very likely gold-bearing veins are coeval, emplaced at 286±1Ma. Multiple and widespread metal sources are indicated by radiogenic isotope studies. Nd and Sr isotope compositions of scheelite and granites suggest the participation of a juvenile component while lead isotopes demonstrate a major participation of the basement.Both gold mineralization and zoning suggest that the system developed at the end of the magmatic activity, accompanying a major transition in magmatic fluid composition. The morphology of the gold-bearing mineralization is dependent of the permeability and the reactivity of host-rocks: focus circulation of fluids through pre-existing tectonic corridors, reactivated by late-Hercynian intrusions favor the formation of large W-type gold veins, while infiltration of fluid within reactive stratigraphic layers gives rise to skarn mineralization. A 40Ar/39Ar date (W1 north vein: 291.8±0.3Ma) indicates that hydrothermal circulation predates gold and tungsten deposition in open fractures as well as Mine granite emplacement.The W–Au mineralization preceded the onset of a large convective hydrothermal cell around the intrusion that led to the formation of the Pb–Ag–Zn mined veins. The Tighza polymetallic district displays numerous similarities with the R-IRG model that was defined in the American Cordillera, such as thermal and zonation patterns, carbonic hydrothermal fluids and chronology of intrusion and related deposits, but also provides new insight to the R-IRG model such as wide Au-quartz veins instead of sheeted Au-veins, oxidation state of the magma, and Sr–Nd isotopic data. These results establish a major magmatic contribution and discard a direct genetic relationship between gold mineralization and major neighboring Pb–Ag–Zn veins. A large number of classic Pb–Zn district of the Western Hercynides belong to the same clan.

Copper, zinc, and iron bioleaching from polymetallic sulphide concentrate

Bioleaching of low-grade complex Cu–Zn–Pb–Fe–Ag–Au sulphide concentrate (of Majdanpek ore body, RTB Bor, Serbia) was carried out in an aerated bioleach reactor in the presence of mesophilic mixed bacterial culture of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirillum ferrooxidans. A mesophilic acidophiles culture was isolated from the acidic solution of the underground copper mine of Bor, Serbia. The nutrient medium was 9K at pH 1.6. 87% of the particles were <10 µm in size, with a pulp density of 8% (w/v). Bioleaching efficiencies of 89% for zinc, 83% for copper, and 68% for iron can be achieved in the examined conditions. Kinetic analysis shows that the change in leaching corresponds to the Spencer-Topley kinetic model for diffusion-controlled topochemical reactions.

Process Mineralogy of Jinshan Gold Ore Based on Mineral Liberation Analysis System

Traditional measurement and modern SEM-based mineral liberation analysis (MLA) system were employed to obtain the process mineralogy characteristic of Jinshan gold ore which had high Au (6.20g/t) and low sulfide (0.25%). XBSE, XBSE_STD and SPL_Lt MLA modes are used in this case, which make the results timely, reliable and quantitative. The gold behaves irregular granular native gold or silver-bearing native gold of which the Au content ranging from 93%to 100%. Gold mainly occurred as liberated or in gold-carrying gangue minerals, such as quartz and biotite,rarely in pyrite in the form of fissure gold, inter-crystalline gold or inclusion gold . The particle size of the Gold minerals range from 0.001mm to 0.010mm , which is too fine to recover from beneficiating method. Combined process should be adopted.

Structure of the Outokumpu ore district and ophiolite-hosted Cu–Co–Zn–Ni–Ag–Au sulfide deposits revealed from 3D modeling and 2D high-resolution seismic reflection data

The Outokumpu district within the North Karelia Schist Belt in eastern Finland hosts a number of Cu–Co–Zn–Ni–Ag–Au sulfide deposits that are associated with Palaeoproterozoic ophiolitic metaserpentinites derived from depleted mantle peridotites that were subsequently tectonically interleaved with allochthonous metaturbidites. The metaperidotites have been extensively metasomatized to quartz–carbonate–calc–silicate rocks of the Outokumpu assemblage. The Outokumpu area has been affected by a multiple-phase tectonic history comprising various phases of folding and shearing followed by several faulting events. Future exploration has to expand the search into deeper areas and requires knowledge of the subsurface geology. In order to unravel the complex structure 3D geologic models of different scales have been built using a variety of information including geological aeromagnetic and gravity maps, digital terrain models, and mine cross sections as well as data like drill core logs combined with observations from underground mine galleries, structural measurements, aeromagnetic data, and seismic surveys. For crustal structures, data from seismic surveys lines have been reprocessed for our purpose. Both deposit-scale and regional-scale models allow the reconstruction of a sequence of structural events. The mined ore has formed during remobilization of a proto-ore and is closely related to shear zones (thrusts) that truncate the Outokumpu assemblage. Later faults dismembered the ore explaining the variable depth of the different ore bodies along the Outokumpu ore zone. On larger scale at least four km-scale thrust sheets, separated by major listric shear zones can be identified in the ore belt, which are internally further imbricated by subordinate shear zones. These thrusts separate a number of lens-shape metaperidotite bodies that are probably surrounded by Outokumpu assemblage rocks. Thrust stacking was followed by at least three stages of faulting that divided the ore belt into fault-bounded blocks with heterogeneous displacements: (i) faulting along NW-dipping faults with unresolved kinematics, (ii) reverse faulting along c. 50°–60° SE-dipping faults, and (iii) SW–NE to SSW–NNE striking faults which may have formed at an earlier stage and have been reactivated.The specific Outokumpu alteration assemblage around metaperidotite bodies combined with shear zones acting as path ways for fluids are the main vectors to mineralization. Seismic reflection data do not provide a simple tool to directly detect the sites of Outokumpu assemblage bodies at depth but they identify strong reflector zones which are characteristic for though not exclusive to the assemblage, shear zones can be recognized as curved dislocations in the seismic lines. Our study shows that 3D modeling, when used in combination with surface geology and other geophysical data and good knowledge about the structural evolution clearly improves the interpretation of reflectors and enables the identification of strong reflector packages as Outokumpu assemblage that, due to absent geological control, have first been mapped as “unknown reflector”. It thus enhances the chances for locating potentially economic horizons at depth and to delineate target areas for detailed exploration.

Noble-metal ore genesis and mantle–crust interaction

The mineral and geochemical compositions of noble-metal (first of all, gold) deposits of the Fennoscandian, Siberian, and Northeast Asian orogenic belts are considered. These deposits are of several types: Au (disseminated Au–sulfide and Au–quartz), Au–Bi, Au–Ag, Au–Sb, Ag–Sb, Au–Sb–Hg, and Ag–Hg. They formed in different geodynamic settings as a result of the active motion of crustal tectonic blocks of different nature. Subduction processes (both at the front and at the rear of continent-marginal and island-arc magmatic arcs) resulted in Au–Ag, Ag–Sb, Ag–Hg, Au–Sb–Hg, and Au–Bi deposits. Collision events gave rise to Au and Au–Bi deposits. Intraplate continental rifting and formation of orogenic belts along the boundaries of block (plate) sliding led to the origin of Au and Au–Bi ores in association with Au–Ag, Au–Sb–Hg, and complex ores. In all cases, the formation of noble-metal mineralization was accompanied by magmatism of different types and metamorphism. Because of this diversity of ores, there is no single concept of the genesis of noble-metal mineralization. Several competing models of genesis exist: hydrothermal-metamorphic, pluton-metamorphic, plutonic, activity of mantle fluid flows, and multistage concentration during the crust–mantle interaction with the leading role of sedimentary complexes.

Seawater contribution to polymetallic Ni–Mo–PGE–Au mineralization in Early Cambrian black shales of South China: Evidence from Mo isotope, PGE, trace element, and REE geochemistry

The Early Cambrian black shale sequence of the Niutitang Formation in South China hosts a synsedimentary, organic carbon-rich, polymetallic sulfide layer with extreme metal concentrations, locally mined as polymetallic Ni–Mo–PGE–Au ore. In combination with previously reported data, we present Mo isotope, platinum-group element (PGE), and trace and rare-earth element (REE) data for the polymetallic sulfide ores and host black shales from four mine sites (Dazhuliushui and Maluhe in Guizhou Province, and Sancha and Cili in Hunan Province, respectively), several hundred kilometers apart. The polymetallic sulfide ores have consistently heavy δ98/95Mo values of 0.94 to 1.38‰ (avg. 1.13±0.14‰, 1σ, n=11), and the host black shale and phosphorite have slightly more variable δ98/95Mo values of 0.81‰ to 1.70‰ (n=14). This latter variation is due to variable paleoenvironmental conditions from suboxic to euxinic, and partly closed-system fractionation in isolated marine sedimentary basins. Both the polymetallic sulfides and host black shales show PGE distribution patterns similar to that of present-day seawater, but different from those of ancient submarine-hydrothermal deposits and modern submarine hydrothermal fluids. The polymetallic sulfide bed has a generally consistent metal enrichment by a factor of 107 compared to present-day seawater. PAAS-normalized REE+Y patterns of the polymetallic sulfide bed are characterized by a remarkably positive Y anomaly, consistent with an origin of the REE predominantly from seawater. Small positive Eu anomalies in some of the sulfide ores could reflect minor hydrothermal components involved. The Mo isotope, PGE, and trace and rare-earth element geochemical data suggest that metals in the polymetallic Ni–Mo–PGE–Au sulfide ore layer were scavenged mostly from Early Cambrian seawater, by both in-situ precipitation and local re-deposition of sulfide clasts.

Role of Au Nanoparticles and NiTiO&lt;SUB&gt;3&lt;/SUB&gt; Matrix in H&lt;SUB&gt;2&lt;/SUB&gt;S Sensing and Its Catalytic Oxidation to SO&lt;SUB&gt;&lt;I&gt;x&lt;/I&gt;&lt;/SUB&gt;

The role of Au nanoparticles inside TiO2-NiO sol-gel thin films for hydrogen sulfide optical detection has been assessed by combining optical spectroscopy, X-ray diffraction (XRD), reaction products analysis and X-ray photoemission spectroscopy (XPS) data. Sulfur oxides (i.e., SO2 and SO3, hereafter SOx) are clearly distinguished as reaction products and SOx species are detected on the surface of the samples by XPS. After exposure to H2S, no metal sulfide species can be detected, neither by XRD nor XPS, so we propose that the reaction mechanism does not involve the formation of Ni, Ti or Au sulfides, but a direct catalytic oxidation of H2S to SOx. The role of Au is to provide an optical probe sensitive to the H2S presence, while the oxide matrix is responsible for the conversion of H2Sto SOx.

Understanding the initial stages of precious metals precipitation: Nanoscale metallic and sulfidic species of gold and silver on pyrite surfaces

The nanoscale products deposited on pyrite at room temperature from 0.1 mM tetrachloroaurate or silver nitrate aqueous solutions and colloidal solutions (sols) of Au 0, Ag 0 and gold sulfide nanoparticles, which were prepared beforehand by the reduction of the Au(III) and Ag(I) complexes with sodium citrate, borohydride or sulfide, have been studied using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), scanning tunneling microscopy (STM) and tunneling spectroscopy (STS). The quantity of metals spontaneously immobilized from the solutions is basically higher than from the sols and depends on the reaction conditions. In particular, the surface concentration of gold passes a maximum at the initial molar ratio Na 2S to HAuCl 4 of about 2 in the sulfidic sols. Ag and Au sulfide phases deposit as plain islands of 10–30 nm in the lateral size while elemental metals form nanoparticles. Although XPS showed predominant lines of metallic gold in all the cases, XAS in the transmission mode revealed that disordered gold sulfide is the main product after the interaction of pyrite with the media with Na 2S to HAuCl 4 ratios more than 1.5–2. The discrepancy was rationalized in terms of decomposition of surface layer of Au 2S yielding Au 0 in air and the spectrometer vacuum. Silver spontaneously deposits preferentially as Ag 2S, and metallic nanoparticles arise with increasing reaction time; the precipitation of Ag nanoparticles (NPs) from their sols results also in some silver sulfide. A sharp current surge was found in tunneling spectra at silver sulfide and Ag NPs under positive or both positive and negative threshold biases of several tenths of a volt, respectively. The effect is most likely due to an increase in the local conductance (known as resistive switching) as a result of enrichment of acanthite (α-Ag 2S) by Ag producing conducting argentite (β-Ag 2S) and then Ag 0. The switching allows identifying Ag 0 and Ag 2S phases on nanoscale; it can play an important role in surface reactions of silver in the ore deposition and processing.

The nature and genesis of marginal Cu–PGE–Au sulphide mineralisation in Paleogene Macrodykes of the Kangerlussuaq region, East Greenland

The Kangerlussuaq region of East Greenland hosts a variety of early Tertiary extrusive and intrusive igneous rocks related to continental break up and the passage of the ancestral Iceland plume. These intrusive bodies include a number of gabbroic macrodykes, two of which—the Miki Fjord Macrodyke, and the newly discovered Togeda Macrodyke—contain Cu–PGE–Au sulphide mineralisation along their margins. Sulphides occur as disseminated interstitial blebs and rounded globules of chalcopyrite and pyrrhotite with some Fe–Ti oxides and platinum-group minerals, comprising largely Pd bismuthides and tellurides. The globules are interpreted to have formed from fractionation of trapped droplets of an immiscible Cu- and Pd-rich sulphide melt and show geopetal indicators. Sulphur isotopes imply a local crustal source of S in these from pyritic sediments of the Kangerlussuaq Basin. Thus, generation of these sulphide occurrences was controlled by local country rock type. Low Ni/Cu and Pt/Pd ratios, also present in the Platinova reefs in the Skaergaard Intrusion, indicate that early fractionation of olivine may have depleted the magma of Ni and suggest the likely presence of a large magma chamber at depth. Xenoliths of Ni-rich olivine cumulates in the Miki Fjord Macrodyke may have been sourced from such a body. The location of thus far unidentified conduit or feeder zones to the macrodykes beneath the present day surface may represent potential targets for more massive sulphide orebodies.