Statistical entropy of mineral intergrowths (Oleninskoe Gold ore occurrence, Murmansk region)

The Tianshan orogenic belt hosts several world-class gold deposits and is one of the largest gold provinces on Earth. The Katbasu Au-Cu deposit in the Chinese Western Tianshan is hosted in a granite intrusion. Previous researchers have shown that the main gold ores formed much later than the ore-hosting granite. However, the formation age of Cu mineralization and its possible link to Au mineralization remain poorly understood. This paper reports detailed mineralogical studies, combined with zircon U-Pb, in situ hydrothermal monazite as well as rutile U-Pb ages to constrain the timing of Cu mineralization and its possible link to Au mineralization. The two main ore types in the Katbasu deposit include Cu-Au ores with pyrite-chalcopyrite veins that crosscut the granite and Au ores with massive pyrite and quartz as the main minerals. The Cu-Au ores are spatially associated with diorite that intruded the granite, and they are overprinted by massive gold ores. Detailed mineralogical studies show that chalcopyrite is the main Cu-bearing mineral in the Cu-Au ores, and it is closely associated with some native gold, monazite, and rutile. Secondary ion mass spectrometer (SIMS) U-Pb dating of zircon grains from the ore-hosting granite and mafic enclave yielded concordant ages of 354.1 ± 1.6 and 355.8 ± 1.7 Ma, respectively. The diorite that intruded the granite has a zircon U-Pb age of 352.0 ± 3.2 Ma. The trace element compositions of the monazite suggest they were formed by hydrothermal fluids rather than inherited from the ore-hosting granite. Hydrothermal monazite coexisting with chalcopyrite and native gold yielded a concordant age of 348.7 ± 2.3 Ma, and the W-rich hydrothermal rutile grains associated with the chalcopyrite yielded a U-Pb age of 345 ± 27 Ma, indicating an early Cu-Au mineralization event prior to the major Au mineralization (ca. 323–311 Ma). The formation time of early Cu-Au mineralization is consistent with the emplacement age of the diorite and may be of magmatic-hydrothermal origin, whereas the main Au has no genetic associations with magmatic rocks in the ore district and may belong to the orogenic type. Monazite geochronology provided a more reliable age constraint than rutile in the Katbasu Au-Cu deposit, and we suggest hydrothermal monazite has advantages over rutile in dating the complex mineralization ages of gold deposits.

This study was undertaken to evaluate the relation between and gold deposition in the Screamer section of the Betze-Post Carlin-type deposit. We also attempted to determine the source of sulfur in the deposit and the possibility that more than one gold-depositing event contributed metal to the Screamer system. Gold ore at Screamer forms a generally stratiform body hosted largely by the Wispy member of the Devonian Popovich Formation and lacks obvious alteration of wall-rock gangue minerals. Gold at Screamer is hosted by arsenian pyrite that forms disseminated grains and overgrowths on diagenetic pyrite. A strong correlation is observed between the gold content of rock samples and their proportion of ore-related (arsenian) pyrite, as determined by point counts. Isocon plots show that mineralization at Screamer involved addition of both sulfur and iron, along with gold, arsenic, antimony, tungsten, and local silica, barium, and phosphorus. Fe/Al vs. S/Al plots show that most ore samples at Screamer do not contain enough sulfur to account for all of their iron as pyrite; petrographic examination shows that the iron occurs in pyrite, ferroan dolomite, and iron-bearing micas in order of decreasing abundance. The Fe/Al vs. S/Al plots also show that Screamer samples with high gold contents contain more pyrite than samples with low gold contents and that samples inside the ore zone have more pyrite than those in the surrounding area. These relations are interpreted to indicate that Screamer has undergone at least two pyrite-forming events. The first event, which probably took place during diagenesis, involved incomplete that left some iron in carbonate and silicate minerals. The second event, which probably took place during gold mineralization, sulfidized most remaining iron and added pyrite in the Screamer ore zone. The δ 34 S values of chemically extracted sulfur from disseminated pyrite at Screamer range from –13.8 to 16.5 per mil, and δ 34 S values for hand-picked separates of pyrite and other sulfides in veins cutting these rocks range from –21.2 to 11.7 per mil. A significant fraction of samples with high gold contents and of samples in the ore zone regardless of gold content have δ 34 S values between –1 and 5 per mil. These data suggest that early diagenetic sulfur with a wide range of δ 34 S values was overprinted by sulfur with isotopic compositions in the –1 to 5 per mil range that was associated with gold mineralization. The δ 34 S values for gold-related sulfur at Screamer are lower than those reported for bulk mineral separates from most other Carlin-type deposits and from SIMS analyses of sulfides from the proximal Post part of the Betze-Post system and could be magmatic. Limited evidence can be found for multiple gold-forming events in the Screamer zone. Tungsten, which might have been introduced by the Jurassic-age Goldstrike stock, is widespread in the deposit and correlates closely with gold. A few samples with high tungsten/gold ratios found along fault zones might be part of an earlier phase of mineralization related to the Goldstrike stock. A δ 34 S value for pyrite in one of these samples is similar to the high values reported for sulfides in auriferous, polymetallic mineralization in the Post section of the deposit, but this mineralization is not reported to contain tungsten. Other veins containing sphalerite have lower δ 34 S values and lack consistent gold values. Whereas there is no correlation between gold values and the degree to which the host rocks have undergone sulfidation, there is a strong and highly significant correlation between gold values and the abundance of ore-related pyrite. This shows that simple of immediately adjacent wall rock cannot account alone for gold deposition at Screamer and it might not be the only ore-depositing process in some other Carlin deposits. A more general, extended sulfidation process could be important, however. One likely process involves mixing of an invading, mineralizing fluid containing sulfur and gold with a wall-rock fluid containing iron derived from adjacent or distal wall rocks. Recognition of the source(s) for this iron and fluid flow pathways responsible for introducing it to the ore zone could provide useful guidance in exploration for the next Carlin trend.

The research was conducted in Bukit Nunggal Air Mesu Village, Pangkalan Baru District, Central Bangka Regency, an IUP PT Tanjung Bukit Nunggal with a height of ± 210 meters. This study is to find out more details about the type of granitoid rock which is a unitary hill but it is estimated that it is the intrusion body of several types of granitoid rock. The research method includes analysis of mineralization content and geochemical analysis in the form of XRF. The steps to be taken include literature studies, field research, laboratory analysis including mineralogical analysis and microscopic observations as well as geochemical testing of rock samples using XRF. The sampling procedure for analysis is carried out based on the height and changes in rock texture, on the number of rock types / lithologies available to be observed and examined for their mineralization content. Regionally, the study area consists of a hill which is interpreted as a potential rock for construction mining. It is hoped that this research can produce an analysis of the existing granitoid types by studying the lithology / rock, geological structure and mineral textures. There are 2 types of granite found in Nunggal Hill, namely granite and granite alterated (gneiss), with its main minerals are quartz, feldspar, biotit, opaq and sericytic and chlorite minerals.

The article presents the results of studying the metallogenic features of the Central Donbass. The relevance of the research is determined by the need to develop scientific and methodological foundations for creating predictive prospecting models of gold deposits adapted to the conditions of the Central and Eastern Donbass. Metallogenic analysis was used as the main research method. It has been established that the metallogenic feature of the Central Donbass is the selective occurrence of gold deposits and ore occurrences in a series of brachymorphic folds formed as a result of undulation of the hinge of the Main Anticline of Donbass, as well as similar parallel anticlines and transverse uplifts, in the complete absence of magmatism. The ore-bearing complex is represented by strata of interlacing pelitic, silty and psammitic sedimentary rocks in a earboniferous coal-bearing formation containing dispersed organic matter and scattered pyrite inclusions in the main mineral tissue. The ore-bearing rocks underwent postsedimentation transformations under conditions of early and late catagenesis and metagenesis, in the absence of signs of near-ore metasomatic changes. A variety of ore mineralizations and their zonal distribution have been revealed. The main gold mineralization zone is highlighted. Up to the ore column, through the transitional subzone of gold-polymetallic ores, it is replaced by a zone of mercmy-antimony mineralization. It is shown that the localization of the gold ore bodies of the Bobrikovskoe deposit is confined to a brachymorphic anticline composed of black shale rocks of the ore-bearing complex and complicated by faults of upsurge-shear kinematics, with the complete absence of signs of magmatism. The ore bodies are represented by volumetric quartz-vein-veined and sulfide-interspersed mineralizations located one below the other at depths from 0 to 270 m and from 570 to 1200 m, respectively. The main useful minerals are native gold and electrum, small particles of which are localized in pyrite and arsenopyrite in association with galena, sphalerite and sulfosalts. The metallogenic features of the region indicate the possibility of classifying gold ore objects to the so-called black shale type.

The arsenic-bearing gold ore in Anhui, China is an extremely refractory gold ore, and the cyanide leaching rate of gold concentrate is only 30%. The mineralogical factors of the low leaching rate were discussed by process mineralogical analysis. The results demonstrate that the gold concentrate contains 20.30 g/t gold, 3.39% arsenic, 29.80% sulfur, and 4.10% iron. Gold exists in the occurrence states of metallic mineral-wrapped gold, gangue mineral-wrapped gold, and fissure gold, which account for 64.90%, 8.31%, and 26.79% respectively. Pyrite, arsenopyrite, realgar, sphalerite, and pyrrhotite are the main metallic minerals in the gold concentrate. Among them, pyrite accounts for 51.20%, and arsenopyrite accounts for 24.30%. Gangue minerals include feldspar, sericite, quartz, calcite, and chlorite. Among them, feldspar, sericite, and quartz account for 30.30%, 22.70%, and 22.10% respectively. In addition, the grain size distribution and distribution characteristics of various minerals are obtained, and the texture and structure of the gold ore are analyzed. Pyrite and arsenic phase are the main factors causing the low gold leaching rate. The presence of carbonate minerals and clay minerals also has an effect on the rate of gold leaching. The oxidation pretreatment can increase the gold leaching rate to about 94%. The findings provide a theoretical foundation for the selection of manufacturing techniques in businesses and play an important guiding role in the development of similar ores.

Mineralogical characteristics and recovery process optimization analysis of a refractory gold ore with gold particles mainly encapsulated in pyrite and Arsenopyrite

The weathering process of the Pan African granitic rock of Batie was mineralogically investigated by means of Microprobe analysis (EPMA), X-ray diffraction (XRD), X-ray fluorescent (XRF), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The porphyritic granite is composed of biotite, feldspar and quartz as main minerals, whereas epidote, chlorite, kaolinite and mica clay mineral are secondary products. Mica clay mineral and kaolinite are main constituent clay minerals in the granite saprolite (weathered granite). Mica clay mineral predominantly occurs at the lower part of the investigated profile associating with a small amount of kaolinite. The granite saprolite at the top part of the profile consists mainly of platy kaolinite with a small amount of lath shape mica clay mineral. Mica clay mineral was formed in the hydrothermal clay veins occurring in the weathering profile. It is inferred that mica clay mineral occurred in the altered granite was formed by hydrothermal activity. Detailed observations of morphological variation by TEM with X-ray analysis revealed that crystal size and shape reasonably explain the transformation sequence of kaolinite as weathering proceeds. Close relationship between crystal size and morphology is obtained. Etch pits developed on quartz and K-feldspar grains are commonly observed. However, shape and size of the etch pits are quite complicated suggesting none monotonous micro-weathering condition. Etch pits found in the upper part are much rougher than those of the lower part. Based on the results obtained, weathering condition of the Batie granite was discussed mainly from the standpoint of clay mineralogy.

Copper sulfide ores often contain significant amounts of silica and sulfur-bearing gangue minerals, complicating flotation efficiency. However, these challenges can be mitigated through collectorless flotation, which exploits the natural floatability of chalcopyrite and the hydrophilicity of silica minerals. Pyrite, the main sulfur gangue mineral, is also depressed under these conditions, improving concentrate quality by reducing the sulfur and iron content. Air exposure and pulp pre-aeration techniques can enhance chalcopyrite floatability, resulting in high recovery and grade. However, further processing of chalcopyrite concentrate using direct leaching remains challenging due to sulfur passivating layers. To overcome this, additive roasting is used as a pretreatment to improve the leachability of chalcopyrite. This study explored a combined collectorless flotation and additive roasting-leaching method using copper sulfide ore with chalcopyrite, quartz, and pyrite as the main minerals. Collectorless flotation achieved 94.5% recovery and a concentrate of 7.12% Cu from an initial 0.94%. Roasting this concentrate with additives like KCl and NaOH at 600 °C for 1 h, followed by leaching in 0.1 M H2SO4 at 25 °C with a hydrogen peroxide (H2O2) addition, resulted in copper dissolutions of 97% and 96.5%, respectively, with low iron dissolution. The proposed process achieved an overall copper recovery of 92%, demonstrating the effectiveness of combining collectorless flotation with additive roasting and atmospheric leaching.

Mineral exploration and active mining relies on extensive drilling campaigns that produce large numbers of drill cores. LIBS is ideally suited for their fast and effective measurement, but matrix effects complicate quantitative geological LIBS applications due to the extensive amount of different minerals, rock types, and lithologies, as well as all textural and optical parameters increasing physical matrix effects. This is challenging for the application of LIBS in geological exploration, since LIBS data processing highly depends on matrix-matched models. The fast acquisition of new data is in conflict with the large amount of existing minerals and lithologies. As a result, new appearances are common during ongoing drilling campaigns, resulting in incomplete train sets for supervised classification and quantification.This paper presents a novel semi-supervised learning (SSL) classification model to resolve related issues by separating known minerals in geological drill cores based on a set of train samples, while also detecting unknown material, i.e. new lithologies and/or minerals not in the train set. Using a combination of supervised Linear Discriminant Analysis (LDA) and semi-supervised One-Class Support Vector Machines (OC-SVM), main minerals and known accessory minerals were effectively separated from unknown material in LIBS mappings of Spodumene and Muscovite pegmatite, as well as from Metagreywacke in drill cores from the Rapasaari lithium deposit in Finland. Self-learning was applied to automatically increase the number of train samples, which effectively decreased the number of unknowns due to physical matrix effects in coherent crystals.Validation with respect to the main minerals revealed an almost perfect classification of albite, spodumene, K-feldspar, quartz, and muscovite. Measurement points of Metagreywacke, which were only included in the test set, were correctly detected as unknown. Transferring the developed model onto LIBS mappings and drill core profile measurements displayed excellent classification results for main and accessory minerals included in the train set. Mixed spectra at mineral borders, as well as accessory minerals not in the train set were correctly identified as unknown.

Spectroscopic characterization of iron ores formed in different geological environments using FTIR, XPS, Mössbauer spectroscopy and thermoanalyses

Recent research has discovered high-grade Au ores in NNE-SSW trending shear zones in metamorphic proterozoic and palaeozoic terranes, some 40 km NW of Santiago de Compostela (NW Spain). The orebodies are bound to late-stage Hercynian structures, mainly due to brittle deformation, which are superimposed on earlier ductile shear zones, cutting through various catazonal lithologies, including ortho- and paragneisses, amphibolites, eclogites, and granites. Ore mineralogy, alteration, and ore textures define a frame whose main features are common to all prospects in the area. Main minerals are arsenopyrite and pyrite — accompanied by quartz, adularia, sericite, ± (tourmaline, chlorite, carbonates, graphite), as main gangue minerals -with subordinate amounts of boulangerite, bismuthinite, kobellite, jamesonite, chalcopyrite, marcasite, galena, sphalerite, rutile, titanite, scheelite, beryl, fluorite, and minor native gold, electrum, native bismuth, fahlore, pyrrhotite, mackinawite, etc., defining a meso-catathermal paragenesis. Detailed microscopic study allows the author to propose a general descriptive scheme of textural classification for this type of ore. Most of the ores fill open spaces or veins, seal cracks or cement breccias; disseminated ores with replacement features related to alteration (mainly silicification, sericitization, and adularization) are also observed. Intensive and repeated cataclasis is a common feature of many ores, suggesting successive events of brittle deformation, hydrothermal flow, and ore precipitation. Gold may be transported and accumulated in any of these events, but tends to be concentrated in later ones. The origin of the gold ores is explained in terms of hydrothermal discharge, associated with mainly brittle deformation and possibly related to granitic magmas, in the global tectonic frame of crustal evolution of West Galicia. The mineralogical and textural study suggests some criteria which will be of practical value for exploration and for ore processing. Ore grades can be improved by flotation of arsenopyrite. Non-conventional methods, such as pressure or bacterial leaching, may subsequently obtain a residue enriched in gold.

Metallogeny of the Xiaotongjiapuzi gold deposit, Liaodong Peninsula (Eastern China): Perspective from sulfide trace element geochemistry and sulfur isotopes

Ukraine possesses a significant gold ore potential with total resources of precious metal exceeding 3000 tons, of which about 2400 tons are concentrated in the Ukrainian Shield. Among the list of potentially industrial deposits, the Mayske deposit stands out as a crucial site within the Savran gold ore field (SaRF) in the Pobuzhia ore district. This article examines the geological and structural setting of the SaRF and provides data on its prospective and forecasted gold resources, which have been tested and approved during the period from 2011 to 2023 by the Expert Commission on Monitoring the Resource Base of Ore, Non-metallic, and Solid Combustible Minerals. The Savran ore field comprises 11 gold ore sites with varying degrees of exploration, including the Mayske deposit and the ore occurrences of Kvitka, Kapustianka, Chemerpil, Mohylne, Baksha, Savran, Polyanetske, Nedilkove, Bohdanivka, and Zavallia. Among these, the Mayske deposit and the Kvitka ore occurrence are the most thoroughly studied and are included in the Subsoil User’s Investment Atlas. The total resource potential of gold in the SaRF is estimated to be over 470 tons. By considering the spatial location, geological criteria, and similar exploration indicators, it is recommended to treat these deposits as a single investment project. This strategy would not only streamline the exploration and development process but also maximize resource utilization and economic returns. The favorable mining conditions of the weathering crusts, including their shallow depth and higher gold content, make them particularly attractive for investment, ensuring lower costs and higher efficiency in extraction and processing. Special attention should be given to gold ore deposits in weathering crusts, which are characterized by shallow ore body occurrence, relatively high gold content, and less expensive processing and enrichment compared to basement rock mineralization. This approach would facilitate a streamlined exploration and development process, maximizing resource utilization and economic returns.

Ore textures in Australian BIF-derived ores are quite complex and have formed the basis for ore genesis models, which includes hypogene upgrading or supergene upgrading then regional metamorphism for the microplaty hematite ores and supergene upgrading for the martite-goethite ores. Despite a high level of ore texture knowledge, little is known about the spatial distribution of ore textures within deposits or their relationship to downstream processing. This paper describes a new iron ore texture classification system to understand better the vertical textural zonation characteristics of Australian BIF-derived deposits, the interpreted role of recent supergene upgrading processes on modifying primary ore textures and their implications for downstream mineral processing. The iron ore textural classification scheme presented uses textural groupings defined on the basis of similarities in mineralogy, ore texture, porosity, mineral associations and hardness. The scheme is non-genetic and has been successfully applied to deposits in the Pilbara, Yilgarn and Gawler cratons. The main ore texture groups include dense martite/hematite, microplaty hematite, microplaty hematite-goethite, martite-goethite, goethite-martite and goethite-rich. Each group can be further subdivided into physically hard to softer subcategories. The ore textural groups can be divided into those interpreted to be associated with primary replacement of BIF and secondary textures resulting from more recent modification by near-surface hydration or dehydration processes. A schematic vertical section through BIF-derived deposits consists (from the surface) of detritals underlain by a carapace, both of which may have been eroded, followed by a hydrated zone with replacement of primary ore martite and microplaty hematite by vitreous goethite. The hydrated zone is underlain by 0·2-6 m thick zones of intense dehydration and textural infilling of porosity with hematite and hydrohematite. Immediately below the dehydration zone is a strong zone of leaching, where more porous and friable ore textures occur,followed underneath by a gradational contact with primary ore. Secondary supergene processes can impact on beneficiation with hydration and leaching resulting in more difficult density separations at the concentrator stage due to reductions in density differences between ore and gangue and loss of heavy media into pores. Supergene modification of primary BIF-derived ore textures can substantially change lump metallurgical properties, with hydration and dehydration favourably increasing lump yield, but reducing resistance to thermal shock whilst leaching will give the opposing outcome. The lump properties of ore textural groups appear to be relatively consistent within and between the iron ore deposits examined.

Isolation and characterization of mineral oxidizing bacteria from the Obuasi gold mining site, Ghana