Placer Deposits Research Articles

Typomorphism of Native Gold (Geological-Industrial Types of Gold Deposits in the North-East of Russia)

This study presents the typomorphic features of native gold grains from three different geological-industrial types (GIT) of gold deposits in the North-East of Russia: (1) gold–arsenic-sulfide in black shale strata (Natalka, Degdekan, Karalveem, Maldyak deposits), (2) gold–quartz veins in granitoids (Dorozhnoye, Butarnoye, Shkolnoye, Maltan deposits), and (3) gold–silver adularia in volcanogenic strata (Kupol, Olcha, Kubaka, Burgali, Primorskoe, Dalnee deposits). The reliability of the geological interpretation is directly related to mineral associations, fineness variations, its internal structure and the content of microimpurities. Native gold is a reliable indicator for identifying various GIT of gold deposits at the early geological-prospecting stages of studying gold-bearing areas. Typomorphic features of native gold for each of the considered GIT are stable and do not depend on the age and scale of mineralization. It is shown that using an integrated approach obtains genetic information about a particular ore object, which makes it possible to predict the vertical range of mineralization and outline the technology for processing ores. The information obtained can also be effectively used in the search for placer deposits in nearby watercourses. Identification of typomorphic features of ore and placer native gold opens up wide opportunities for delineating the distribution areas of placer deposits.

Naryn-Gol Creek Sapphire Placer Deposit, Buryatia, Russia

A new gem corundum occurrence has been discovered in the Naryn-Gol Creek placer of the Dzhida volcanic field (Russia). In this placer deposit, sapphire associates with large crystals of garnet, spinel, augite, olivine, enstatite, ilmenite, Ti-magnetite, and alkali feldspar. Such a combination of minerals is typical for the placer deposits associated with alkali basalts widely distributed in Southeastern Asia and Australia. We have also found sapphire crystals in phonotephrites of the nearby Cenozoic alkali-basalt paleovolcano Barun Khobol Pravyi, and in basalt sample and trachybasalt from the valley flood basalts. The chemical composition of sapphire is generally typical for ‘basalt’ corundum: it is rich in Fe, and depleted in Ti and Cr. The δ18O SMOW values of corundum and related megacrysts range from 4.6 to 6.8 ‰, thus corresponding to the isotopic signature of igneous rocks. Etched and corroded surfaces of sapphire and other megacrysts indicate that they are in non-equilibrium with their host alkali basalts. Volatile components, CO2 in particular, played a significant role during sapphire formation as gas inclusions reveal.

Textural characteristics of surficial sediments along the Noakhali coast, Bangladesh: An implication for mineral placer deposits exploration

This study aimed to explore mineral placer deposits analyzing textural characteristics; mean size (Mz), standard deviation (σi), skewness (Ski), kurtosis (KG), and the depositional environments of surficial sediments deposited in the Noakhali coast along the Meghna River estuary. A total of nine sediment samples were collected, and the textural parameters were analyzed by a laser particle size analyzer (Microtrac S3500). The mean size of the sediment samples ranged from 3.063 Φ to 5.11 Φ, where the seven samples exhibited sandy-silt texture and only two samples silty-sand texture. However, all the samples presented unimodal grain size distribution. A minimal amount of clay (0.12–1.4%) had been found in three samples collected from Urir Char Island. Higher values of standard deviation (4.15 Φ to 5.76 Φ) indicated extremely poorly sorted sediments. Skewness value varied from 0.107 to 0.510 expressed fine to very fine skewness, and kurtosis value from 0.1033 to 1.525 exhibited a mesokurtic to very leptokurtic nature of the sediments. These textural characteristics indicated a low to moderate energy deposition of finer (mostly silt), unidirectional, and riverine sediments. Linear discriminant analysis (LDA) results revealed the littoral, shallow marine, and fluvial deposition of the sediments. CM pattern showed the deposition of sediments by graded suspension without rolling and uniform suspension. Both of these processes indicated low to moderate energy deposition of sediments. As the majority of samples were silt dominated, there are very low prospects of finding valuable heavy minerals except two locations (SP-04, 06) where sand is dominated, and minerals placers could be found there. Low to moderate depositional environments also indicated fewer prospects of finding mineral placer deposits in the studied area.

Indian Placer Deposits

Indian Placer Deposits

The Mineralogy of Pt-Fe alloys and phase relations in the Pt–Fe binary system

ABSTRACT A revised Pt–Fe phase diagram is proposed to replace those used in the materials science literature (e.g., Okamoto 2004), and to improve the one of Cabri & Feather (1975) by adding high-temperature phase equilibria data published in the mineralogical literature. The projected solid-solution fields at room temperature in the pure Pt–Fe system lie at the following approximate compositions: for γ(Pt,Fe) from Pt to Pt0.78Fe0.22, for Pt3Fe from Pt3.04Fe0.96 to Pt2.64Fe1.36, for PtFe from Pt1.16Fe0.84 to Pt0.67Fe0.33, and for PtFe3 from Pt1.26Fe2.94 to Pt0.68Fe3.32. The phase relations and phase boundaries are discussed and evaluated for Pt-Fe alloys occurring in pristine intrusive rocks and ores as well as in eluvial and placer deposits derived from the former by physical and chemical weathering over long periods of geologic time. In spite of the variable concentrations of minor and trace elements, the natural Pt-Fe alloy minerals correlate well with phase relations in the pure Pt–Fe binary system.

Evaluation of economic efficiency of mining technogenic deposits of placer gold with the formation of concentration zones

Currently, mineral reserves of gold placers are depleted largely due to a significant reduction of geological exploration. In view of the drop in gold production from placers, an important source of gold in many areas of the Far East Federal District becomes waste and natural-and-manmade placer deposits. By experts’ estimates, the resource potential of manmade placer deposits (waste) is very high. Billions of cubic meters of gold-bearing waste is accumulated in dumps. These are, first of all, dredge and sluice tailings dumps. The average gold content of such material mainly agrees with the modern economic standards. Sometimes, it is even comparable with the gold content of natural deposits. Obviously, effective development of manmade placer deposits is possible using new technologies, at selected and optimized design and process variables of mining and processing equipment subject to the whole set of influences. Creation of such technologies is an urgent scientific and technical task within the concept of efficient natural and manmade mineral resources management. The Institute of Mining, FB RAS formulates and accomplishes the research on development and theoretical justification of a geotechnology for manmade mineral deposits on the basis of concentration of valuable components inside waste dumps, which ensures formation of a pay zone nearby the bedrock. This study aims at the economic evaluation of the effectiveness of new organizational and engineering solutions to improve the level and completeness of gold recovery from manmade deposits.The studies were carried out using the resources of the Center for Shared Use of Scientific Equipment “Center for Processing and Storage of Scientific Data of the Far Eastern Branch of the Russian Academy of Sciences”, funded by the Russian Federation represented by the Ministry of Science and Higher Education of the Russian Federation under project No. 075-15-2021-663.

Structural Setting of the Sixtymile Gold District, Yukon, Canada: Insights into Regional Deformation and Mineralization from Field Mapping and 3D Magnetic Inversion

The Sixtymile gold district, Yukon, Canada has been mined for placer gold since the late 19th century. However, increasing demand for gold has prompted exploration of new lode deposits. Previous studies in the nearby Klondike gold district have shown correlation between placer deposits and bedrock occurrences. Poor bedrock exposure and a complex deformation history, however, make it difficult to determine structural controls on gold mineralization. Through structural analysis involving mesoscopic-scale field observations of fractures, faults, foliation, and folds, and 3D geophysical inversion, the goal of this study was to determine the structural setting of the Sixtymile district to enhance discovery success. Structural measurements in the Glacier Creek, Miller Creek, Bedrock Creek, and Sixtymile River areas show the relationships among the orientations of foliation, fractures, and veins. In most localities, veins are found both parallel and at high angles to foliation, and there is generally a weaker correlation between fractures and veins compared to between foliation and veins. This correlation between foliation and veins is corroborated by inferred gold-bearing horizons from gold assay data. Outcrops of oblique reverse and strike-slip faults, possibly related to a larger-scale thrust-zone, and to the left-lateral Sixtymile-Pika Fault, respectively, were documented for the first time in this study. The results of the 3D probabilistic inversion of total magnetic intensity data for magnetic susceptibility show that magnetic susceptibility highs are preferentially associated with volcanics, but also point to possible intrusive bodies or hydrothermal alteration zones associated with mineralization. A geologic cross-section through the lithologies demonstrates highly variable deformation styles, including extensive folding, possibly indicative of a multiphase deformational history necessitating further, more detailed investigations of the area.

Spectral Angle Mapping and AI Methods Applied in Automatic Identification of Placer Deposit Magnetite Using Multispectral Camera Mounted on UAV

The use of drones in mining environments is one way in which data pertaining to the state of a site in various industries can be remotely collected. This paper proposes a combined system that employs a 6-bands multispectral image capturing camera mounted on an Unmanned Aerial Vehicle (UAV) drone, Spectral Angle Mapping (SAM), as well as Artificial Intelligence (AI). Depth possessing multispectral data were captured at different flight elevations. This was in an attempt to find the best elevation where remote identification of magnetite iron sands via the UAV drone specialized in collecting spectral information at a minimum accuracy of +/− 16 nm was possible. Data were analyzed via SAM to deduce the cosine similarity thresholds at each elevation. Using these thresholds, AI algorithms specialized in classifying imagery data were trained and tested to find the best performing model at classifying magnetite iron sand. Considering the post flight logs, the spatial area coverage of 338 m2, a global classification accuracy of 99.7%, as well the per-class precision of 99.4%, the 20 m flight elevation outputs presented the best performance ratios overall. Thus, the positive outputs of this study suggest viability in a variety of mining and mineral engineering practices.

Seabed mining and blue growth: exploring the potential of marine mineral deposits as a sustainable source of rare earth elements (MaREEs) (IUPAC Technical Report)

Abstract The expected growth of the global economy and the projected rise in world population call for a greatly increased supply of materials critical for implementing clean technologies, such as rare earth elements (REEs) and other rare metals. Because the demand for critical metals is increasing and land-based mineral deposits are being depleted, seafloor resources are seen as the next frontier for mineral exploration and extraction. Marine mineral deposits with a great resource potential for transition, rare, and critical metals include mainly deep-sea mineral deposits, such as polymetallic sulfides, polymetallic nodules, cobalt-rich crusts, phosphorites, and rare earth element-rich muds. Major areas with economic interest for seabed mineral exploration and mining are the following: nodules in the Penrhyn Basin-Cook Islands Exclusive Economic Zone (EEZ), the Clarion–Clipperton nodule Zone, Peru Basin nodules, and the Central Indian Ocean Basin; seafloor massive sulfide deposits in the exclusive economic zones of Papua New Guinea, Japan, and New Zealand as well as the Mid-Atlantic Ridge and the three Indian Ocean spreading ridges; cobalt-rich crusts in the Pacific Prime Crust Zone and the Canary Islands Seamounts and the Rio Grande Rise in the Atlantic Ocean; and the rare earth element-rich deep-sea muds around Minamitorishima Island in the equatorial North Pacific. In addition, zones for marine phosphorites exploration are located in Chatham Rise, offshore Baja California, and on the shelf off Namibia. Moreover, shallow-water resources, like placer deposits, represent another marine source for many critical minerals, metals, and gems. The main concerns of deep-sea mining are related to its environmental impacts. Ecological impacts of rare earth element mining on deep-sea ecosystems are still poorly evaluated. Furthermore, marine mining may cause conflicts with various stakeholders such as fisheries, communications cable owners, offshore wind farms, and tourism. The global ocean is an immense source of food, energy, raw materials, clean water, and ecosystem services and suffers seriously by multiple stressors from anthropogenic sources. The development of a blue economy strategy needs a better knowledge of the environmental impacts. By protecting vulnerable areas, applying new technologies for deep-sea mineral exploration and mining, marine spatial planning, and a regulatory framework for minerals extraction, we may achieve sustainable management and use of our oceans.

Metal recycling tracked by mercury and helium isotopes in platinum–palladium nuggets from Córrego Bom Sucesso, Brazil

The enigmatic botryoidal nuggets of platinum (Pt) and palladium (Pd) from Córrego Bom Sucesso in the southern Serra do Espinhaço, Minas Gerais, Brazil, are considered to have formed during supergene alteration of placer deposits. This requires hitherto unidentified precious-metal enrichment processes and is inconsistent with Pt–Os age of 180 Ma that entails formation at depth, as recently proposed. Here we report the first mercury (Hg) and helium (He) isotopic determinations of Pt–Pd nuggets. Mercury isotopic compositions have a mass-independent fractionation (MIF) signature with an odd-mass deficit (Δ199Hg = − 0.22 ± 0.04; 1SD, n = 15), which requires aqueous photochemical reduction of Hg (II). Extremely low 3He/4He (<0.001 Ra) and extremely high concentrations of He (up to 1.9 × 1017 at/g) are indicative of nugget formation from He-enriched fluids within the quartzite sequence of the Espinhaço basin, not from meteoric surface water. The data are consistent with a nugget-forming setting in the deep biosphere, as a result of groundwater interaction with Pt–Pd–Hg minerals in Pan-African-Brasiliano post-orogenic veins. We propose that the negative Hg-MIF signature was inherited from the vein minerals that originally acquired their Hg from Earth's surface during the intracratonic sedimentation of the Proterozoic Espinhaço basin.

Technogenic Placer Deposits of the Artic Zone of Yakutia

The northern parts of the Arctic Zone of the Sakha Republic (Yakutia) are the most industrialized regions of the Republic. Since the 1930s, there has been intensive mining of alluvial and primary tin and gold placers. The 60-70-year mining operation has accumulated huge mining residues in the region, leaving behind useful components owing to deficiencies in mining technology at the time and deviations from mining technology. These wastes are considered technogenic placer deposits. The study of these wastes has identified the following types of technological s: 1 – technogenic placers of tin and gold; 2 - technogenic combined placers of gold and kularit; 3 - technogenic placers of tailings ponds consisting of mining wastes of gold and tin ore placers.

Assessment of the Ecological State of Soils Near the Platinum Deposit

The research is devoted to the ecological state of soil resources in the area of the Konder platinum placer deposit in the Khabarovsk Territory. The environmental impact of the Konder mine activities was established based on chemical analyses performed. In general, the study has demonstrated that the Konder field development and operation cause a complex multicomponent pollution of the landscapes. The pollution is more than local in nature, since the environmental problem related to violation of soil resources and to chemical contamination of soils and natural watercourses in areas of mineral development is becoming increasingly acute. As a result of the studies, geochemical features of the soil space and the main sources and factors of the soil contamination have been determined.

Sedimentology, geomorphology, structural controls, and detrital zircon ages of the Itiquira River diamond placer deposits, Mato Grosso, western Brazil

The Itiquira River, Mato Grosso state (western Brazil), hosts several diamond placer deposits, mined intermittently over the last century. It runs over volcanic and sedimentary rocks of the Paraná Basin until it discharges in the northern Pantanal Basin. The bedrocks were deposited in marine, continental desertic, alluvial deltaic, and fluvial environments. The meanders of the Itiquira River are controlled by NE-SW, ENE-WSW, NNW-SSE, N–S, and NW-SE fractures and normal faults, developed in response to the evolution of the Paraná Basin and by neotectonics, linked with the development of the Pantanal Basin since the Paleogene. The Itiquira River middle valley, in which the diamondiferous placers are found, is controlled by NE-SW structures inherited from the Neoproterozoic Transbrasiliano Lineament. The landscape comprises dissected plateaus and structure-controlled valleys formed by Cretaceous, Paleogene, and Neogene planation processes. The diamonds occur in the muddy-sandy matrix of the current stream bed and older terraces gravels. In the Itiquira River, the diamond deposits are related to the following traps: point bars, cut-and-fill channels, pockets, and potholes. Sapphire, garnet (including kimberlitic), ilmenite, zircon, rutile, gold, and iron oxides are documented as heavy minerals in the gravels. Detrital zircon dating of grains extracted from the Itiquira River diamond deposits resulted in the ages of 2057, 1184, 873, 645–508, 307–207, and 144-142 Ma. The potential zircon sources are the Goiás Magmatic Arc granitoids, Paraguay Belt metavolcanics and granites, and Serra Geral Formation volcanics. The ages between 307 and 207 Ma are likely to be from an unknown (possibly kimberlitic) source. The Itiquira River tectonic, geomorphological, and sedimentological evolutions suggest potential sources for the diamond placers and paleoplacers.

Chemistry and mineralogy of Zr- and Ti-rich minerals sourced from Cox’s Bazar beach placer deposits, Bangladesh: Implication of resources processing and evaluation

Zircon is always found in association with Ti-rich minerals; therefore, it is produced mainly as a co-product in the production of ilmenite and rutile from placer mining operations. In Cox’s Bazar beach sands, they contain at 2.8, 12.1 and 2.7 wt% (average) respectively in the heavies. In order to scrutinize mineralogical and geochemical variability among Zr- and Ti- rich minerals, XRF, XRD, SEM and EPMA were implemented. Petrogenesis manifests the nature of impurities in mineral concentrates where they included through cationic substitution during alteration and metamictization, whereas their coating and pore filling occurred by hydraulic action in fluvial process. The impurities of oxides, silicates and phosphates gangue mineral phases degrade the quality of zircon concentrate (ZrO2 + HfO2 = 63.73 wt%) in achieving premium grade. Although the process of hot acid leaching (HAL) upgrades the quality enhancing ZrO2 + HfO2 (69.10 wt%) content, yet to be eliminated Fe and U to reach premium grade. Thermal annealing and calcining treatment is suggested to fully recover the zircon prior to industrial use. Similar to zircon, ilmenite and rutile they both contain trace levels of gangue mineral phases. The content of TiO2 and Ti/(Ti + Fe) (48.1 wt% and 0.5 respectively) indicates unaltered ilmenite. Therefore, upgrading the unaltered low grade ilmenite concentrate to chlorination feedstock, ilmenite smelting and the synthetic rutile routes are suggested. In addition, the TiO2 (83.84 wt%) content in the bulk rutile concentrate shows as much as the high grade ilmenite display due to contaminants. Mentioning, two of the major impurities such as tin and zirconium occurred as mineral grain cassiterite and zircon and as substitutions for titanium (Ti ⇌ Sn, Zr) in crystal lattice. The way of acid leaching can be instrumental not only for upgrading rutile but also for extracting Sn and Zr as byproduct of Ti metal/ TiO2 pigment.

Platinum–group minerals in the placer deposit in northwestern Hokkaido, Japan: description of a new mineral, tomamaeite

Platinum–group minerals in the placer deposit in northwestern Hokkaido, Japan: description of a new mineral, tomamaeite

Current state, prospects and problems of the gold mining industry of the Trans-Baikal Territory

The article considers the current state, problems and prospects of gold mining in the Trans-Baikal Territory. There has been an increase in the volume of gold production from ore and placer deposits over the past 5 years. Placer deposits make up a significant part of the total production volume. The reduction of reserves in placers and the decrease in the quality of minerals in them open up new prospects for the extraction of precious metals, namely in ore gold mining. The extraction of placer gold, even with the best existing technologies, remains a sector of high environmental risk, in many settlements there is a gradual decline in the population and the “extinction” of settlements, as well as illegal gold mining is gaining momentum. Neither regional nor federal environmental supervision bodies have the opportunity to resist the destruction and degradation of nature from the extraction of placer gold. In general, this leads to an increase in the negative impact of placer gold mining on natural complexes and socio-economic sustainable development of regions and municipalities on the territory of which this type of activity is carried out, an increase in accumulated environmental damage.

МЕЗОЗОЙ-КАЙНОЗОЙСЬКИЙ МОРФОЛІТОГЕНЕЗ УКРАЇНСЬКОГО ЩИТА (В МЕЖАХ ІРШАНСЬКОГО РОЗСИПНОГО ПОЛЯ)

The article presents the results of the study of Mesozoic-Cenozoic motpholithogenesis of the of the Ukrainian shield, within the Irshansky placer development field of titanium deposits of the Ukrainian sub-province of placer province of Eastern Europe. The morpholitogenetic approach expands the methodology and methodical possibilities of geomorphological research. The method of processing analyzes of granulometry and chemical composition of ilmenite, calculation of quantitative indicators that parameterize the granulometric field and the field of variability of ilmenite, integrating the root rocks-weathering crust - mesozoic-cenozoic sedimentary deposits within the placers. Analysis of the static and dynamic parameters of these fields revealed their evolutionary trends within the placers of the Irshansky placer field. The empirically revealed relationship between the average size and the degree of variability of ilmenite can be used in modeling the processes of morpholitogenesis and oregenesis of titanium placer deposits. Interpretations of the obtained results were carried out on a broad paleogeographical basis, taking into account tectonics, paleorelief, and paleoclimates.

Methodology for determining the dilution of sands in the bottom of the dredging waste during the dredging development of placer deposits

Methodology for determining the dilution of sands in the bottom of the dredging waste during the dredging development of placer deposits

Ways of solving the problems of rational nature management in the areas of alluvial deposits development

A characteristic feature of the developed placer deposits is that most of them (up to 90–95%) are hard to develop, and the sands included in them are hard to enrich, due to their location in the geographic and climatic zones with a harsh climate, where perennial and deep seasonal permafrost is widespread almost everywhere. About 40% of alluvial deposits are clayey, highly clayey or cemented. As a consequence, there are significant losses of the valuable component and a large negative impact on the environment, including due to repeated re–mining. The studies presented in this paper help to significantly reduce losses and increase the productivity of the dredge, thereby increasing metal recovery.

Thoron Equilibrium Factor Observed around Chhatrapur Placer Deposit, a High Background Radiation Area in Odisha, India

Thoron Equilibrium Factor Observed around Chhatrapur Placer Deposit, a High Background Radiation Area in Odisha, India