High-grade Gold Research Articles

The role of competitive fluid-rock interaction processes in the formation of high-grade gold deposits

Although forming one unified class, orogenic gold deposits may be associated with a range of ore mineral assemblages controlled by a variety of gold deposition processes that have a direct impact on gold grade. Whereas, a better understanding of the deposition process may be critical for effective targeting of highly-endowed gold deposits, it is challenging to establish a direct comparison between mineral systems formed under different conditions. Accordingly our ability to predict whether contrasted mineral associations may be more or less prospective for high grade mineralization remains poor. In this paper, we compare fluid-rock interaction processes that led to the coeval formation of two contrasting gold mineral assemblages within the world-class Callie orogenic gold deposit. Stratabound and vein-hosted lodes formed within the same structural framework but with contrasting grades (∼3 g/t Au and ∼8 g/t Au, respectively). The stratabound mineralization consists of bedding-parallel sulfides in which gold is preserved in arsenopyrite micro-fractures. The vein-hosted mineralization consists of locally very high-grade (up to 10,000 ppm Au) visible gold concentrated in quartz veins. Both mineralization styles are hosted within different metasedimentary stratigraphic horizons with contrasting compositions. The stratabound mineralization occurs in iron-oxide rich siltstones whereas the vein-hosted mineralization occurs in carbonaceous siltstones. We investigate the fluid-rock interaction mechanisms of the two styles of mineralization at the Callie deposit by combining petrographic observation with whole-rock geochemistry, quantitative chlorite and gold analyses and thermodynamic modeling. Our results show that the stratabound mineralization occurred in response to sulfidation of the host-rock whereas decarbonation alteration, associated with the vein-hosted mineralization, records oxidation of the host-rock. Our investigation shows that gold deposition induced by oxidation of the host-rock produces the valuable, locally very-high grade visible gold mineralization whereas the sulfidation process lead to the formation of lower grade gold mineralization disseminated within the sulphide ore assemblage. We conclude that the nature of the host-rock applies a first-order control on the gold deposition efficiency in metasedimentary-hosted gold deposits.

The extensive hydrocarbon-mediated fixation of hydrothermal gold in the Witwatersrand Basin, South Africa

There is a close spatial relation between high-grade gold mineralization in the Witwatersrand basin and carbonaceous nodules, veins and seams. Hydrocarbons thus may well have been essential in ore genesis. We have sampled four major gold-, uranium- and hydrocarbon-bearing ore horizons, namely the Carbon Leader, Vaal, B and Black reefs, to determine the role of hydrocarbons in the accumulation and hydrothermal fixation of gold. Our multipronged approach included high-resolution scanning and transmission electron microscopy (SEM, TEM), nanotomography with video clips, and geochemical modeling. Post-depositional hydrothermal activity at the peak of regional metamorphism produced an assemblage of quartz, phyllosilicates, brannerite, crandallite, florencite, monazite and gold in all four reefs. The gold, hydrocarbons and associated mineral assemblages are closely related on the micro to nano scale. Gold deposition occurred in interstices, as fracture fillings in detrital minerals, and on the surface of migrated solid hydrocarbon residues. The spherical to elliptical inclusions in the gold consist of an outer pyrobitumen phase and a central void space, partially associated with nanometric gold, uraninite, coffinite and silica. The hydrocarbon-bearing inclusion likely formed by the entrapment of a fossil liquid oil precursor during gold precipitation. The oil was subsequently thermally altered and converted into the final pyrobitumen and gaseous residues. Geochemical calculations to simulate the interaction of an invading hot hydrothermal fluid with the hydrocarbons in the reefs reveal that a very small amount of hydrocarbons will drastically decrease the aqueous solubility of gold and hence cause its instant precipitation.We extend our genetic model for the epigenetic formation of gold in the Witwatersrand. Regional metamorphism promoted the extensive and likely basin-wide circulation of hydrothermal fluids; these were capable of mobilizing substantial amounts of gold. The liquid, gaseous and solid hydrocarbons in the reefs acted as efficient chemical traps for the concentration of gold. Being strong chemical reductants, they caused the rapid precipitation and accumulation of gold on the surface of the fossil oil droplets and already solidified hydrocarbons. The release of the gases from accessible hydrocarbons into the sediments away from their source buffered the redox state of the hydrothermal solutions even at a considerable distance from the pyrobitumen seams and veins, likely resulting in the deposition of gold in the absence of visible hydrocarbons. Although our findings do not explain the ultimate origin and exceptional endowment of gold in the Witwatersrand, we do provide intriguing evidence for the large-scale hydrothermal mobilization, accumulation and fixation of gold mediated by hydrocarbons during post-depositional metamorphism.

Geology, hydrothermal alteration and mineralization of the Carlin-type gold deposit at South Ratatotok, Southeast Minahasa Regency, North Sulawesi Province, Indonesia

South Ratatotok in North Sulawesi, Indonesia is one of the regions that was once a gold-producing region in North Sulawesi. Mesel gold deposit in this region is approved as Carlin type gold deposit with a total of resources of 12.25 Mt @5.21 g/t Au. Near the Mesel deposit, gold mineralization is currently discovered prospects such as Leon, Bulex Hill, Heind’s Find and Monkey Forest. This study is aimed to elucidate the types and distribution of hydrothermal alteration and ore mineralization encountered in these four prospect areas. Research methods including field work (including geological and hydrothermal alteration mapping, rocks and ore sampling) and various laboratory works consisting of petrographic analysis, ore microscopy, X-Ray Diffraction (XRD) and fire assay were performed. As a result, the study area is composed of several lithological units including limestone, volcanic breccia, porphyritic andesitic intrusion units as well as colluvial deposit. The wall rocks have been suffered by various hydrothermal alteration as follows: silicification in limestone, carbonatization in volcanic breccia, argillic alteration in volcanic breccia and propylitic alteration developed in porphyritic andesitic intrusion, minor decarbonatization associated with limestone and minor oxidation in volcanic breccia. Gold mineralization is present as a replacement type in very fine size of sulphides and gold is closely associated with silicified limestone. Ore chemistry by fire assay analysis indicates that gold and silver contents vary from 0.012 g/t to 2.41 g/t Au, and <0.5 g/t to 2.1 g/t Ag, respectively. The increase of gold content is geochemically followed by high values of Ag, As, Sb, Cu, Pb, Zn and by low value of Hg because of oxidation. Supergene process was also the key factor in the enrichment of gold where the oxidized ore has relatively higher gold grade than in non-oxidized ore.

Characterization of high-grade gold deposits of the northeast of Antioquia-Colombia

Mineralogical characterization is a fundamental stage when designing and implementing metallurgical extraction processes; in the case of gold mining, knowing the way the metal occurs and its mineralogical associations is a fundamental tool when minimizing losses or designing processes. The northeast of the department of Antioquia has distinguished itself as one of the main areas of Colombia in terms of gold production. In the present work, a characterization of different samples from this Colombian region was made using XRD, XRF, QUEMSCAN, SEM-EDX, fire assay, conventional cyanidation and froth flotation tests. The analyses performed classify these deposits as high grade, with values up to 81 g/t of gold. Quartz is the most common mineral followed by the presence of muscovite, pyrite and potassium feldspar. Regarding gold, it was found in the form of electrum associated with sulphide minerals, a conventional flotation process is proposed, with an average recovery of 90%.

Surface structure of Amur region high grade native gold

The purpose of the research is to study the surface structure of high grade gold. The subject of research is gold ore fields in the Amur region. The object of the study is samples of native high grade gold grains from these fields. The study uses the methods of thermodynamics and X-ray electron microscopy. The study results in revealing a multilayer structure of the surface of high grade minerals of the Amur region native gold with the following levels: a boundary layer with zero oxidation degree Au0 in the form of yellow metallic gold; an oxide layer with the oxidation degree Au+1in the form of purple Au2O; an oxide layer with the oxidation degree Au+3in the form of a yellow-brown Au2O3; a hydrated oxide layer with the oxidation degree Au+3in the form of a red-yellow-brown Au(OH)3. The methods of electron microscopy have allowed to identify external surface structures – dense oxide layers of the form of Au2O3and loose hydrated layers of the form of Au(OH)3, whereas the inner layers of metallic and monovalent gold are not visible. Important thermodynamic characteristics of the presented levels are the values of standard oxidation-reduction potentials (E°), which determine their physicochemical properties: for metallic gold E° = +1.68 V; for the oxide layer with the oxidation degree Au+1in the form of Au2O – E° = +0.32 V; for the oxide layer with the oxidation degree Au+3in the form of Au2O3– E° = +1.36 V; for the hydrated oxide layer with the oxidation degree Au+3in the form of Au(OH)3– E° = +0.7 V. The results of the conducted studies indicate that the surface structure has several layers that lower the oxidation-reduction potential, which explains the generation and formation of migratory forms of gold in humid hypergene conditions of natural environment.

Types, structure and location of fractured gold pockets

Fractured gold ore pockets of various types are classified and their structure is described in detail. This will allow explorationists to confirm high-grade gold ores, which is especially important in underground deposit mining. Gold pockets were mapped and analyzed by the author at deposits in Uzbekistan (Muruntau, Daugyz, Charmitan, Kokpatas), eastern Trans-Baikal region (Darasun, Balei, etc.) and Kochkarskoye (South Urals). Also, the paper describes the material collected by the author at gold pockets in Natalkinskoye, Nezhdaninskoye, Pavlik and Kyuchus deposits in Yakutia, Berikul in Western Siberia, Bakyrchik in Kazakhstan as well as deposits from Australia (Kalgoorlie, Northman, etc.), USA (Comstock, etc.), Canada (Porcupine), among others.

Transport and coarsening of gold nanoparticles in an orogenic deposit by dissolution\u2013reprecipitation and Ostwald ripening

The role of nanoparticle gold in the formation of gold deposits has long been debated. Evidence in support of this process is generally limited to epithermal-, Carlin- and seafloor massive-sulfide-type deposits where gold nanoparticles are associated with primary fluid related processes. At the Kenty orogenic deposit in Ontario, Canada, gold has been remobilized from early pyrite through secondary coupled dissolution-reprecipitation processes to form high-grade gold external to pyrite. Here we report gold nanoparticles and related textures that help document this gold coarsening process. A combination of focused ion beam technology and transmission electron microscopy provides a rare glimpse of gold coarsening frozen in time, which includes nanoparticles trapped in iron oxides and rutile and non-oriented attachment of gold nanoparticles to bulk gold suggesting coarsening via Ostwald ripening. The processes documented are applicable to orogenic deposits formed through Earth’s history, and may explain the formation of ultra high-grade ore zones.

Structural Control of High-Grade Gold Shoots at the Reward Mine, Hill End, New South Wales, Australia

Abstract The Reward mine at Hill End hosts structurally controlled orogenic gold mineralization in moderately S plunging, high-grade gold shoots located at the intersection between a late, steeply W dipping reverse fault zone and E-dipping, bedding-parallel, laminated quartz veins (the Paxton’s vein system). The mineralized bedding-parallel veins are contained within the middle Silurian to Middle Devonian age, turbidite-dominated Hill End trough forming part of the Lachlan orogen in New South Wales. The Hill End trough was deformed in the Middle Devonian (Tabberabberan orogeny), forming tight, N-S–trending, macroscopic D2 folds (Hill End anticline) with S2 slaty cleavage and associated bedding-parallel veins. Structural analysis indicates that the D2 flexural-slip folding mechanism formed bedding-parallel movement zones that contained flexural-slip duplexes, bedding-parallel veins, and saddle reefs in the fold hinges. Bedding-parallel veins are concentrated in weak, narrow shale beds between competent sandstones with dip angles up to 70° indicating that the flexural slip along bedding occurred on unfavorably oriented planes until fold lockup. Gold was precipitated during folding, with fluid-flow concentrated along bedding, as fold limbs rotated, and hosted by bedding-parallel veins and associated structures. However, the gold is sporadically developed, often with subeconomic grades, and is associated with quartz, muscovite, chlorite, carbonates, pyrrhotite, and pyrite. East-west shortening of the Hill End trough resumed during the Late Devonian to early Carboniferous (Kanimblan orogeny), producing a series of steeply W dipping reverse faults that crosscut the eastern limb of the Hill End anticline. Where W-dipping reverse faults intersected major E-dipping bedding-parallel veins, gold (now associated with galena and sphalerite) was precipitated in a network of brittle fractures contained within the veins, forming moderately S plunging, high-grade gold shoots. Only where major bedding-parallel veins were intersected, displaced, and fractured by late W-dipping reverse faults is there a potential for localization of high-grade gold shoots (&amp;gt;10 g/t). A revised structural history for the Hill End area not only explains the location of gold shoots in the Reward mine but allows previous geochemical, dating, and isotope studies to be better understood, with the discordant W-dipping reverse faults likely acting as feeder structures introducing gold-bearing fluids sourced within deeply buried Ordovician volcanic units below the Hill End trough. A comparison is made between gold mineralization, structural style, and timing at Hill End in the eastern Lachlan orogen with the gold deposits of Victoria, in the western Lachlan orogen. Structural styles are similar where gold mineralization is formed during folding and reverse faulting during periods of regional east-west shortening. However, at Hill End, flexural-slip folding-related weakly mineralized bedding-parallel veins are reactivated to a lesser degree once folds lock up (cf. the Bendigo zone deposits in Victoria) due to the earlier effects of fold-related flattening and boudinage. The second stage of gold mineralization was formed by an array of crosscutting, steeply W dipping reverse faults fracturing preexisting bedding-parallel veins that developed high-grade gold shoots. Deformation and gold mineralization in the western Lachlan orogen started in the Late Ordovician to middle Silurian Benambran orogeny and continued with more deposits forming in the Bindian (Early Devonian) and Tabberabberan (late Early-Middle Devonian) orogenies. This differs from the Hill End trough in the eastern Lachlan orogen, where deformation and mineralization started in the Tabberabberan orogeny and culminated with the formation of high-grade gold shoots at Hill End during renewed compression in the early Carboniferous Kanimblan orogeny.

K–Ar geochronology of orogenic gold mineralization in the Vangtat gold belt, southeastern Laos: Effect of excess argon in hydrothermal quartz

AbstractThe Thongkai‐Ok gold deposit is one of several actively mined deposits in a newly discovered orogenic gold belt in southeastern Laos. At a district scale, gold mineralization occurs within the Vangtat shear zone, one of the tectonic structures of the Poko suture zone that marks the collision between the Indochina Terrane and the Kontum Massif in southern Laos‐central Vietnam. High grade gold mineralization is associated with quartz–pyrite–white mica veins and silicified zones up to 10 m thick, hosted by strongly deformed and sheared pelitic schist. Lower‐grade gold mineralization occurs in a graphite–carbonate–quartz–sulfide hydrothermal alteration envelope that grades into sub‐economic/barren altered pelitic schist. The objective of this study is to establish the age of mineralization in the Vangtat orogenic gold belt by K–Ar dating of hydrothermal white mica in the gold‐bearing quartz‐sulfide veins in order to better understand its spatial and temporal relation to other gold deposits in Southeast Asia and to regional tectonic events. Three‐white mica bearing quartz–pyrite samples were collected from the open pit at Thongkai‐Ok. The dominant white mica phase in the samples is 2M1 muscovite and the K2O content measured by electron microprobe techniques in individual white mica crystals ranged between 8.61 and 9.79 wt%. Two of the three vein samples were separated by gravity settling into four size fractions, &lt;2, 2–4, 4–10, and 10–40 μm, respectively. The results of potassium measurements by flame photometry in the K–Ar sample aliquots show a range in potassium content which reflects the amount of quartz present in each sample as an impurity. With one exception, a correlation was observed between potassium concentration in the samples, including the size fraction separates, and the calculated K–Ar age. The large range of calculated ages, from 348 to 206 Ma, is interpreted to reflect excess argon contained in fluid inclusions in the hydrothermal quartz present in the analyzed samples. We interpret the youngest age of the quartz‐free samples, 206 ± 4 Ma, as closest to the age of mineralization in the Vangtat gold belt. The age could be as young as ~170 Ma if the age versus potassium content relation is extrapolated to the average potassium content of white mica in the samples analyzed.

Grade estimation by a machine learning model using coordinate rotations

ABSTRACT Machine learning (ML) models provide useful tools to generate spatial estimations of geological features, but they do not consider the spatial dependence among the observations and they primarily use coordinates as predictors. Thus, many ML models produce visible artifacts in the resulting estimates along the coordinate directions. To overcome this significant problem, this paper presents an ensemble super learner (ESL) model which uses the super learner (SL) model as the ML model. In the ESL model, numerous training sets are created from the original dataset by a coordinate rotation strategy and then the estimates obtained from the fitted SL models are ensembled to produce a final estimate. A dataset from a high-grade gold deposit demonstrates the approach and compares the results to kriging and the SL model. The results demonstrate that the ESL model manages artifacts in ML spatial estimation. It also provides better results than the kriging and SL model in terms of estimation accuracy.

The tungsten-gold veins of Bonnac (French Massif central): new constraints for a Variscan granite-related genesis

In the Brioude-Massiac district (French Massif Central: FMC), a network of W-As-Bi-Au quartz veins constitutes the Bonnac deposit, where tungsten is the major economic element, together with high-grade gold (up to 15 g/t Au). The evolution of this mineralization has been divided into 3 stages: (i) an early deep-seated wolframite-löllingite stage formed between 12 to 9 km, at up to 400 °C; (ii) a ductile/brittle deformation stage associated with scheelite and arsenopyrite deposition, with an estimated temperature of 480–300 °C; (iii) a late stage controlled by fluid-overpressure potentially triggered by fault-valve mechanism, at a depth of 7 to 5 km, and a temperature estimated between 266 to 240 °C, is marked by micro-fracturing infilled by native bismuth, bismuthinite, hedleyite, electrum, pyrite and base-metals. Structural analysis and apatite LA-ICP-MS U/Pb dating demonstrate a spatial and temporal link between the emplacement of the peraluminous leucogranitic dykes and the Bonnac mineralization. In more details, the mineralization was deposited between 321–316 Ma, during, or just after, the emplacement of the peraluminous dykes estimated around 329–315 Ma, suggesting a magmatic-hydrothermal transition for the ore-forming process. In the proposed model, the cooling of a hidden two-mica granitic pluton could have generated a magmatic fluid, and acted as the heat source responsible for fluid flow towards inherited permeability zones. The magmatic fluid could have then re-equilibrated at high temperature by fluid-rocks interaction. The sharp changes in pressure, associated with the decrease of the temperature, and sulfide-fugacity generated by a late input of meteoric fluid were responsible for the deposition of the late gold-stage. At the regional scale, the tungsten-gold event is ascribed to an early hydrothermal stage, dissociated from the formation of the antimony event in the district. The leucogranitic dykes and Bonnac quartz veins are controlled by a NW-SE stretching direction, interpreted as an expression of the Serpukhovian-Bashkirian syn-orogenic extension (D4 event of the FMC). These new data provide evidence for an early tungsten and gold metallogenic event in the FMC, prior the “Or300” event. The genetic classification of the Bonnac mineralization is equivocal. The W-As-Bi-Au-quartz veins exhibit the features of both an “orogenic gold” deposit at a relatively deep emplacement level (mesozonal), and an Intrusion-Related-Gold-Deposit (IRGD) type with a spatial-temporal link with the peraluminous intrusion emplacement. We propose that the Bonnac deposits represent an intermediate type between a typical orogenic-gold deposit and an IRGD. We argue that the presence of economic high-grade gold content in tungsten vein-type, and more generally the IRGD deposits, have been underestimated in the Variscan French Massif Central.

The perigranitic W-Au Salau deposit (Pyrenees, France): polyphase genesis of a late Variscan intrusion related deposit

A field study combined with a laboratory study and 3D modeling have been performed in order to decipher the genesis of the Salau deposit W-Au mineralization (Pyrenees, France), one of the most important for tungsten in Europe. Results show the existence of two superimposed ore types, emplaced ca. 10 km depth and within decreasing temperature conditions: a calcic silicates skarn with rare scheelite and disseminated sulphides followed by a mineralized breccia with massive sulphides (pyrrhotite and chalcopyrite dominant), coarse-grained scheelite and gold, representing the main part of the ore mined in the past. This breccia is localized in ductile-brittle shear-zones which crosscut the granodiorite. U/Pb dating on zircon, apatite and scheelite, previously realized, confirmed this polyphase evolution. These two types of mineralization, linked to the emplacement of two successive intrusions as confirmed by sulphur isotopic analysis, granodioritic then leucogranitic, can be classified as belonging to the Intrusion-Related Gold Deposit type (IRGD). The emplacement of the high-grade gold and scheelite breccia was initiated by the progressive localization of the regional deformation in the Axial Zone of the Pyrenees during the Permian within E-W dextral-reverse faults.

High REE and Y Concentrations in Mo-Au Ores of the Kis-Kuel IOCG Deposit, East Yakutia (Russia)

This paper presents the results of an updated from 2008-2019 study of the Kis-Kuel promising area and is devoted to the discovered unusual molybdenite + gold bearing mineralizing system of the Kis-Kuel Iron Oxide Copper-Gold deposit in Eastern Yakutia (Russia). Economic mineralization is localized within the apical zone of a granodiorite-diorite stock and represented by hematite, goethite, quartz, chalcopyrite, molybdenite, arsenopyrite, pyrite, native gold and bismuth (no signs of any ore mineralization were found outside the Kis-Kuel intrusive). The intrusive has a Late Cretaceous crystallization age (K-Ar) of 103 Ma. The Mo-bearing quartz vein yields a mineralization age (Ar-Ar) of 99.9±1.1 Ma and genetically relates to the granodiorite. Kis-Kuel breccia complex (KKBC) consists of a manto-type irregular shaped breccia body with arrays of variably mineralized veins and veinlets inside. The KKBC has a complete gradation from hematite-goethite altered granodiorites and more locally -diorites to intensely brecciated and hematite-goethite breccias. Multiple episodes of brecciating and veining with Fe-oxide-Cu-Au±Ag, porphyry Cu-Au±Bi, Ag-Pb and Mo+REE±Au mineralization occur in Kis-Kuel intrusive. In order to obtain more resources, the research Kis-Kuel target with IOCG mineralization was studied for molybdenum and rare earth minerals. Mainly, ore is quartz-bearing, Mo-Au-mineralized and strongly enriched in the rare earth elements (REE) material. The textures of REE minerals indicate crystallisation of monazite-(Ce) and xenotime as hydrothermal phases together with molybdenite and arsenopyrite. Analysis of quartz-molybdenite ore from the Kis-Kuel diorite-granodiorite intrusive shows previously unknown high concentrations of REE and Y, averaging 4.76 wt percent ∑REE + Y. Ore additionally contains 2.42 wt percent Mo, 8.8 g/t Au and 231 g/t Ag. We propose that one of the basic factors for mineralization styles at Kis-Kuel consists in the granitoids evolution and strongly differs from unevolved and mantle compatible compositions to highly evolved and fractionated intrusive rocks. The calc-alkaline evolution trend of the Kis-Kuel magmatic rocks is influenced by the accumulation of iron in ore. A significant part of the iron did not fractionated into high-iron melts, and separated into hydrothermal solutions with high grade gold concentrations. An extensively revised paragenetic model for Kis-Kuel deposit incorporates next four stages. Stage 1 dominated by widespread brecciating and iron metasomatism, which converted granodiorite rocks to Fe-oxide-Cu-Au ore. Stage 2 comprises chloritic and sericitic alteration and associated systems of linear quartz veins with Cu-Au-porphyry and Au-Bi mineralization. Stage 3 includes sericitic alteration and veining with quartz-molybdenite-native gold-REE minerals. Stage 4 consists of Ag-Pb veins.

Natural Amalgam of Gold in Placers of the Ebelyakh Area -Indicator of Tectono-Fluid Activation (North-Eastern Siberian Platform)

The results of studying the typomorphic features of placer gold in the unique diamond-bearing placers of the Ebelakh river basin (Anabar diamond-bearing region) are given. Detailed study of the morphology, micro-relief of the surface and internal structure of the gold and photographing was performed using a scanning electron microscope JEOLJSM-6480LV. The gold fineness was determined using the Camebax-Micro microanalyzer and the JEOL OXFORD INCA-sight energy spectrometer. The internal structure of native gold was studied by etching gold in mounted thin sections using a proven method, using a reagent: HCl + HNO3 + FeCl3 × 6H2O + CrO3 + thiourea + water. It is determined that, modern placer occurrences were formed mainly due to the redeposition of fine high-grade gold from ancient gold-bearing intermediate sources. At the same time, in the placer of the Kamenisty creek a natural amalgam of gold is discovered, which is an aggregate consisting of several cemented rounded gold particles of small size (-0.25 mm) of various morphology. The cement is superimposed medium-grade gold with Hg content of up to 13.3%. Its internal structure is porous, and zoning is noted due to the uneven distribution of Hg. The surface of mercury gold is characterized by a brain-like microsculpture. Along with this, in some placers of the studied area, it was possible to find small (>0.2 mm) gold particles with a specific surface with the thinnest (first microns) fringe of mercury (ртутистого) gold. Obviously, these are single grains of the disintegrated aggregates of auro amalgam. We also found gold particles in an aluminosilicate film of variable Al, Si, K, Fe composition, and the smallest (1-2 microns) mineral phases of gold, sphalerite, galena, zincite and zinc-containing iron are identified on this film. It is assumed that natural amalgamation of placer gold occurred as a result of migration of mercury-containing gold-bearing hydrothermas on fault zones during tectonomagmatic activation. Based on the above-mentioned, it is assumed that there are adjacent sources of supply - low-temperature hydrothermal ore occurrences confined to the faults and formed as a result of tectonomagmatic activation processes. This proposition is confirmed by the identification of hydrothermal-metasomatic formations of K-spar-quartz-pyrite composition with disseminated gold-sulfide mineralization on the studied territory. The similarity of geological conditions of localization and the material composition of apocarbonate hydrothermal-metasomatic formations of the Ebelyakh area with the gold-bearing rocks of the Central Aldan ore district allow to estimate positively the prospects for their further study.

KARAKTERISTIK ALTERASI DAN TEKSTUR URAT KUARSA PADA PIT BARANI, CEBAKAN EMAS MARTABE, KABUPATEN TAPANULI SELATAN, PROVINSI SUMATRA UTARA

Pit Barani merupakan bagian dari wilayah kontrak karya PT Agincourt Resources yang terletak di Kelurahan Aek Pining, Kecamatan Batangtoru, Kabupaten Tapanuli Selatan, Sumatra Utara. Pit Barani berupa tambang terbuka, dengan tipe cebakan epitermal berupa urat-urat yang menjadi tempat konsentrasi lebih banyak unsur logam. Penelitian bertujuan untuk mengetahui karakteristik alterasi dan variasi tekstur urat kuarsa yang banyak terdapat pada daerah Pit Barani dan mengidentifikasi tekstur urat kuarsa pembawa mineralisasi yang ekonomis. Pengambilan conto batuan dilakukan pada saat pemetaan pit dan identifikasi mineral alterasi menggunakan analisis laboratorium berupa analytical spectral devices (ASD), serta analisis geokimia untuk mengetahui kadar unsur Au, Ag, dan Cu. Hasil penelitian menunjukkan zona alterasi yang berkembang terdiri dari zona alterasi argilik (kaolinit+illit+smektit), argilik lanjut (kuarsa+kaolinit+dikit), dan silisifikasi (kuarsa+kalsedon+kaolinit). Tekstur urat kuarsa yang berkembang pada daerah penelitian terdiri dari masif, crustiform, crustiform-colloform, brecciated, bladed, dan saccharoidal. Tekstur urat kuarsa pembawa mineralisasi dengan kadar emas tinggi berupa crustiform-colloform, banded diikuti oleh massive quartz oxide, dan lattice bladed. Urat kuarsa tersebut berasosiasi dengan mineral lempung kaolinit+dikit dengan tingkat oksidasi sedang sampai tinggi, serta berasosiasi dengan sulfida abu-abu yang mengandung kadar tertinggi mencapai Au 76,65 ppm dan Ag 34 ppm.

Multi-stage alteration, rheological switches and high-grade gold mineralization at Sheba Mine, Barberton Greenstone Belt, South Africa

Structural, petrographic and geochemical data from Sheba Gold Mine in the Barberton Greenstone Belt of South Africa indicate that gold mineralization formed at the end, and as the result of a multi-stage structural, fluid flow and alteration history. This multi-stage evolution is a prerequisite for the formation of high-grade (>40 g/t Au) ore bodies. The Sheba Mine is situated in well-bedded metaturbidites of the Mesoarchaean Fig Tree Group and structurally infolded ultramafic lavas in the first-order, refolded Ulundi syncline in the northern parts of the belt. Original komatiitic lava flows are pervasively altered to talc-carbonate greyschist. This regionally widespread alteration relates to an early phase of deformation and associated fluid flow. The reaction softening associated with this alteration accentuates rheological anisotropies within the heterogeneous wall-rock sequence. This results in the localization of strain along the contact between talc-carbonate greyschist and overlying, massive greywacke and chert units during later-stage refolding and associated flexural slip. Pervasive quartz veining, silicification, K-enrichment and the progressive replacement of the earlier talc-carbonate assemblages by a high-variance quartz-fuchsite green schist alteration testify to the localized fluid flow along this contact. The newly formed, finely intergrown green schist assemblage leads, in turn, to a reaction hardening and embrittlement of the former greyschist-chert contact. High-grade gold mineralization is hosted by brittle quartz-carbonate vein networks and breccias developed along brittle-ductile structures that cross-cut the competent green schist at high angles. The siting of gold and predominance of free gold suggest that gold precipitation is related to extreme fluid pressure cycling and phase separation of the mineralizing fluid during the formation of the brittle fracture networks. The thrust kinematics of the late-stage controlling structure studied here indicate that the mineralized structure accommodated regional NW-SE subhorizontal shortening when further tightening of the Ulundi syncline passed the lock-up stage could no longer be accommodated by flexural slip. The results highlight that the formation of favourable conditions for high grade mineralization, such as those at Sheba Mine, may be the result of the interaction of temporally distinct fluid flow and alteration events and lithological heterogeneities during the progressive structural evolution of a region.

Paragenetic relationships between low- and high-grade gold mineralization in the Cripple Creek Au-Te deposit, Colorado: Trace element studies of pyrite

The Cripple Creek alkaline igneous rock-related low-sulfidation epithermal gold telluride deposit is hosted in a 10 km wide Oligocene alkaline volcanic diatreme in Proterozoic rocks. Periods of phreatic eruptions and progressively more mafic alkaline magma emplacement created the diatreme and breccias that host the gold ore, followed by breccia pipe creation, and later by the emplacement of phonolite and later lamprophyre dikes throughout the diatreme. Pervasive potassic alteration affected much of the diatreme, and is spatially related to the late-stage veins containing native gold and precious metal tellurides. Previous studies have mainly focused on the high-grade gold veins primarily located toward the center of the diatreme. The current study evaluates the mineralogy and paragenesis of low-grade mineralization in the currently mined Wild Horse Extension (WHEX), Globe Hill, and Schist Island pits, and the Galena Embayment along the margin of the diatreme next to the WHEX pit, as well as high-grade mineralization in the WHEX and Cresson pits. Given the variable paragenesis of mineralizing stages in different locations in the Cripple Creek deposit, a simplified three stage paragenesis (stages 1, 2, and 3) is recognized here involving low- and high-grade gold mineralization.Scanning electron microscopy, electron microprobe, and laser ablation-inductively coupled plasma-mass spectrometry analyses are used to compare the trace element compositions of pyrite in low- and high-grade gold mineralization. These analyses reveal a complex trace element pattern with variability in Ag, As, Au, Co, Ni, Sb, and Te in the rims, cores, and zones (area between the core and the rim) of stages 2 (Py2) and 3 pyrite (Py3) and spatially between the pits currently being mined. Trace element concentrations in stage 1 pyrite (Py1) are lower than those in Py2 and Py3 and the patterns are uniform. Trace elements reside within the lattice structure of pyrite and as micro- and nano-inclusions (e.g., up to 48,220 ppm As, 6983 ppm Co, 12,250 ppm Ni, and 10,860 ppm Sb). The trace element patterns from the final stage of pyrite growth in high-grade gold telluride veins indicate enrichment in Ag, As, Au, Cu, Pb, Sb, and Te.The paragenesis and compositional zoning of pyrite associated with high-grade ore contrast with those associated with pyrite from low-grade ore, which preceded the formation of high-grade gold telluride veins. This suggests that metallic mineralization occurred in multiple episodes and that low-grade ore did not form from the same hydrothermal fluids that precipitated the high-grade ore. Early pyrite formed under passive, non-boiling conditions, followed by a transition to vigorous boiling in Py2 and Py3, ending with non-boiling conditions recorded in the Au and As-rich rims of Py3. This enrichment in Au and As on the rims of pyrite is consistent with other alkaline igneous rock-related epithermal Au deposits, as are the concentrations of trace elements throughout the pyrite grains. The presence of As, Ag, Co, Cu, Mo, Ni, Sb, Te, and Tl in pyrite are considered vectors to high-grade Au ore in the Cripple Creek deposit.

Gold composition and conditions of Southern Ak-Dag gold-sulfide-quartz ore occurrence formation (Western Tuva)

Research subject. The paper presents data on the mineralogical, geochemical and fluid inclusion features of the Southern Ak-Dag gold-sulphide-quartz ore occurrence in Western Tuva.Methods. Mineral formation temperatures, salt composition and fluid salinity were examined using a Linkam TMS-600 cryostage and an Olympus BX 51 microscope. The chemical composition of samples was identified using a MIRA 3 LMU (Tescan Orsay Holding) scanning electron microscope equipped with INCA Energy 450+XMax 80 and INCA Wave 500 microanalysis systems; BSE photos were taken by Tescan Vega 3 and Hitachi ТМ-1000 SEM instruments.Results. The ores under study were found to contain both high-grade and medium-grade gold with an Ag content of up to 17.05 wt %. The average gold fineness comprised 904 ‰, ranging from 830 to 928 ‰. According to fluid inclusion data, gold-sulphide-quartz veins were formed at temperatures of 280–240 °C and pressures of 0.8–1.2 kbar from aqueous fluids having a salinity of 8.6–6.4 wt % NaCl eq. The narrow range of fluid salinity at decreasing temperatures and the prevalence of high-grade gold in sulphide-quartz veins indicate a relatively high rate of mineral formation in a narrow permeable zone without any significant interaction with host rocks or mixing with meteoric waters.Conclusions. Gold mineralization in the Southern Ak-Dag ore occurrence, which was formed within one ore substage, corresponds to the type of gold-galena-chalcopyrite with barite. The established similarity of native gold in the Southern Ak-Dag occurrence and other deposits in the Aldan-Maadyr ore cluster in terms of P-T parameters of ore formation and mineralogical and geochemical features, as well as association of the ore mineralization with beresites, indicate the possibility of discovering industrial ore deposits in the region and confirm its paragenetic relation with Devonian magmatic activity.

Association between serum CCL-18 and IL-23 concentrations and disease progression of chronic obstructive pulmonary disease

This study aimed to investigate the association between serum concentrations of chemokine (C–C Motif) ligand 18 (CCL-18) and interleukin 23 (IL-23) and clinical parameters of chronic obstructive pulmonary disease (COPD). The serum concentrations of CCL-18 and IL-23 were tested by enzyme linked immunosorbent assay (ELISA). The association between their concentrations and clinical parameters of COPD patients were analyzed by linear regression, logistic regression and ROC curve. The results showed that the serum concentrations of CCL-18 and IL-23 in COPD patients were increased compared with healthy people (P < 0.001) and that patients with acute exacerbation of COPD (AECOPD) had higher serum CCL-18 and IL-23 concentrations than stable patients (P < 0.001). Synergistic increase of CCL-18 and IL-23 in COPD patients was positively correlated with COPD patients' higher GOLD grade (P < 0.001), higher mMRC score (P < 0.001) and longer medical history (P < 0.001), but negatively correlated with the forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) (P < 0.001) and FEV1% predicted (P < 0.001). The serum concentrations of CCL-18 and IL-23 were most related to the GOLD grade (OR = 2.764 for CCL-18 and OR = 4.215 for IL-23) and detection of both showed considerable sensitivity (72.57% for CCL-18 and 76.92% for IL-23) and specificity (92.50% for CCL-18 and 77.5% for IL-23) in identifying COPD. Increased serum concentrations of CCL-18 and IL-23 correlated with the disease progression of COPD and they could be used as biomarkers for disease evaluation of COPD.

Geology of the Yeşilyurt (Malatya) fluorite-gold deposit: an example of low-angle normal fault related mineralization, Eastern Anatolia-Turkey

Yeşilyurt gold mineralization is located within the provincial borders of Malatya and Adıyaman in the East Anatolian Region. This mineralization is one of the gold deposits which correlated with low-angle normal/detachment fault. Low-angle normal fault associated with a tectonic setting which is potential extensional in Paleogene-Neogene (?) term. Marble-recrystallized limestone which belongs to the metamorphic core is the dominant rock (footwall) type in the bottom plate of the fault zone. There are deformed graphitic calc-schists (hanging wall) in the upper plate of the fault zone. The fault zone is characterized by fault gauge, cataclasite, and breccia. While the cataclasite, and breccia are the principal ore host, there is weaker mineralization in fault gauge. Alteration assemblages are: (1) silica replacements/veinlets and, (2) quartz-pyrite replacements / veinlets. High gold contents are closely related to silicification and quartz-pyrite alteration which damaged the primary textures. Small volume syn-tectonic magmatic rocks are simultaneous and typically monitored in the silicified areas which are border on the high-grade gold mineralization. Mineralization is a non-base metalliferous Au depositthat contains Au/Ag ~ 1.07, As (~0.27%), F (1.59%), and a trace amount of Sb. This deposit will lead to finding new gold deposits in Eastern Taurus Orogenic Belt.