Main Ore Research Articles

Thermal enrichment of gold- bearing sulfide mineral material using centrifugal flotation

Depleted gold-containing sulfide mineral materials can be used in cement production, in the construction industry, in road construction and other sectors of the national economy. This will allow metallurgical enterprises to switch to low-waste or non-waste technology. Studies and practice of ore dressing with a high degree of sulfidity show that gold extraction is directly dependent on the degree of sulfidity of the ore and the content of the main ore sulfide minerals in it. To increase the efficiency of gold extraction, a device for enriching gold-containing sulfide materials using centrifugal flotation is proposed

Assessment of the Source of Anthropogenic Pollution Impact on the Hydro-chemical Runoff of the Main Ore Elements (Using the Example of Dumps at the Altai Mining and Processing Plant, Alei Сatchment)

The content of the main ore and associated elements in the material of the tailings of the Altai mining and processing plant, in the snow cover and surface waters of the dumps, as well as in the water filtrates of the dump material was studied. It was detected that the concentration of Cu in the substrates of the dumps of the Altai mining and processing plant varies from 970 to 7350 mg/kg and exceeds the background values of the copper content in the soils of Northwestern Altai up to 1000 times, the Pb content varies. from 850 to 2800 mg/kg and exceeds the background value up to 500 times, Zn – up to 200 times (content from 350 to 12170 mg/kg), Cd – up to 100 times. It was recorded that the Pb content in pound surface water on of tailings dumps exceeds the MPC of hazardous substances 2.5 times and is 79 μg/l, Cu – 52 times (52.3 mg/l), Zn – 250 times (254 mg/l), Cd – 940 times (0.94 mg/l). It was identified that in liquid media – lysimetric, surface and snow waters of the Altai mining and processing plant tailings pond – the ratio of pollutant concentrations to background and standards norms (Russian and foreign) is higher for more labile and easily leachable elements – cadmium and zinc. In solid components (substrates, snow dust), the concentrations of copper and lead noticeably exceed the background, clarke and standard concentrations.

The multiple sulfur isotope architecture of the Kambalda nickel camp, Western Australia

New data on the multiple sulfur isotope signature of Archean sulfides from country rocks and magmatic mineralization at the Moran deposit (Kambalda, Western Australia) were combined with previously published geochemical data to constrain the various stages of the dynamic evolution of this magmatic system, unveiling new insights into the transport mechanisms of sulfide liquids in komatiite magmas. Sulfides in the Archean magmatic and sedimentary host rocks of the komatiites display a unique mass-independent sulfur isotope signature (Δ33S), which records a photochemical reaction of sulfur in an oxygen-poor atmosphere prior to the Great Oxidation Event.Sedimentary rocks that are thought to be assimilated by komatiite show a distinctly positive Δ33S signature (+ 0.9 to + 2.4‰). Early ore sulfides situated above these sedimentary rocks contain relatively few valuable metals and display an overlapping Δ33S range (+ 0.6 to + 1.0‰). Subsequent but still early ore sulfides are situated above basalt, as the sedimentary rocks were thermo-mechanically eroded by the sulfide melt, displaying more mantle-like signatures (+ 0.2 to + 0.3‰) and valuable metal content - indistinguishable from the main ore deposit. This reflects a progressive dilution of the contaminant signature by the magmatic isotope signature of the komatiite liquid. Calculated volumes of the interaction of silicate melt and sulfide melt to explain the metal tenor of the ore and its Δ33S signature indicate a decoupling between chemical and isotopic signatures. This can be explained by upgrading the sulfide melt with valuable metals simultaneously with the dissolution of sulfur in the komatiite melt.

Vanadium mineralization at Los Chihuidos sediment-hosted Cu–V deposit, Neuquén Basin, Argentina: An approach to vanadium ore forming processes

Vanadium mineralization at Los Chihuidos deposit of the Neuquén Basin is linked to the development of a redox front system related to the inflow of hydrocarbons into the red sandstone of the Huincul Formation. Interaction of hydrocarbons with oxidized red beds and connate water generated redox reactions where hematite was dissolved due to iron reduction resulting in the discoloration of the red strata. At the contact between oxidized red sandstone and reduced white sandstone, precipitation of specific mineral phases resulted in the V ore with minor amounts of Cu. With the implementation of the redox interface, abundant V-montmorillonite and V-hematite precipitated at the more oxidizing conditions and Cu-V-corrensite-type at the more reducing conditions of the redox front. As the redox front advanced with fluids constantly migrating into the reservoir, more reducing conditions were stablished, promoting chloritization and minor illitization with V-Cu incorporation and continuous upgrading of the ore. Main ore mineralogy consists of clay minerals including V-bearing montmorillonite, Cu-V-corrensite-type, V-di-trioctahedral chlorite and Cu-tri-trioctahedral chlorite with minor V-illite–smectite mixed-layer minerals and associated secondary V-hematite. Chloritization over illitization was favored due to high amounts of Fe and Mg in detrital clasts and in connate fluids and by low K availability related to low amounts of detrital K-feldspar. The spatial transition of V and /or Cu bearing clay minerals observed through the mineralized redox front at Los Chihuidos deposit (kaolinite → smectite → illite/smectite → corrensite-type → di- trioctahedral -chlorite → tri- trioctahedral -chlorite) and the related variation of V–Cu concentrations in bulk rock are indicative of increasing pH and decreasing Eh of resident solutions from red to white sandstones during the hypogene mineralization process. Late influx of Cu-rich oxidized basinal brines precipitated main copper ore with Cu-sulfides in the white sandstone up to the contact with the redox front in contact with hydrocarbons. During uplift and exhumation, percolation of meteoric water promoted remobilization of V and Cu and the precipitation of oxidized V–Cu ore.

Origin of Ag-Pb-Zn mineralization at Huanaote, Inner Mongolia, NE China: Evidence from fluid inclusion, H-O-S-Pb and noble gas isotope studies

The newly-discovered Huanaote Ag-Pb-Zn deposit, containing 1173 tons Ag with a grade of 154 g/t, is situated in the western part of the Great Xing’an Range metallogenic belt. The source of metals and the fluid evolution for this large metallogenic system are still ambiguous. Mineralized Ag-Pb-Zn veins are primarily hosted in Late Carboniferous monzogranite and Devonian slate. Three paragenetic stages of mineralization were recognized at Huanaote, including (stage I) early pyrite + arsenopyrite + quartz ± K-feldspar; (stage II) the main ore stage sulfide (sphalerite, galena, chalcopyrite and pyrite) + sulfosalt (freibergite, bournonite, wittichenite and tetrahedrite) + quartz + sericite + chlorite ± epidote ± fluorite; and (stage III) late pyrite + quartz + calcite. The homogenization temperatures of fluid inclusion assemblage for stages I and II range from 254 to 337 ℃ and 143 to 270 ℃, respectively, while the fluid salinity varied from 2.3 to 14.2 and 0.9 to 11.8 wt% NaCl equiv. for stages I and II, respectively. The fluid δ18OH2O and δDH2O values range from −0.4 to +6.2‰ and −116.8 to −104.8‰, respectively, indicating that the source of the fluids was primarily derived from a magma with less contribution from meteoric waters. Sulfur isotope analyses of sulfides exhibit δ34S values from −4.3 to +8.0‰, consistent with those observed in other Ag-Pb-Zn deposits in this region, suggesting the sulfur was mainly magmatic origin with minor sedimentary sulfur addition. Similarly, the Pb isotope compositions of sulfides resemble those of local Mesozoic magmatism, implying a Mesozoic magmatic source for the metals. Additionally, the noble gas isotope compositions, specifically the 3He/4He ratios (ranging from 4.41 to 7.18 Ra, mean of 5.56 Ra) for fluid inclusions,strongly support a deep magmatic fluid responsible for the formation of Huanaote deposit. Fluid cooling, mixing with meteoric waters and dilution are suggested to be important processes for Ag-Pb-Zn deposition at Huanaote.

Paleoproterozoic East Pana Layered Intrusion (Kola Peninsula, Russia): Geological Structure, Petrography, Geochemistry and Cu-Ni-PGE Mineralization

The East Pana intrusion is a part of the Paleoproterozoic Fedorova–Pana complex (FPC), which belongs to the group of Fennoscandian layered mafic–ultramafic massifs. This article discusses the magmatic stratification of the East Pana intrusion, as well as Cu-Ni and platinum-group elements (PGE) mineralization (PGE zones A, B and C) in its various parts with a total length of more than 20 km, including the East Chuarvy PGE deposit. Based on the whole-rock data on the distribution of major, trace, and ore-forming elements, it is assumed that PGE zone A belongs to the main ore–magmatic system of the FPC, while PGE zones B and C belong to the minor ore–magmatic systems. At the same time, additional magmatic injection played an important role in the formation of economic Cu-Ni-PGE mineralization (PGE zone B), characterized by high PGE concentrations and moderate palladium enrichment. On the normalized distribution spectra of trace elements, the crystallization products of this injection (Gabbronorite Zone 2) have a positive Zr-Hf anomaly, which distinguishes it from host rocks with an anomaly of the opposite sign (Gabbronorite Zone 1, Gabbro Zone). It is assumed that this portion of magma was intruded as a sill of crystal mush, the fractionation of which at depth led to its enrichment with residual liquid.

Evolution of an ancient VMS ore-forming system recorded by pyrite and sphalerite mineral texture, trace elements, and sulfur isotope: A case study from the Huangtupo Cu-Zn (-Au) deposit, Eastern Tianshan, NW China

The Huangtupo Cu-Zn (-Au) volcanogenic massive sulfide deposit is hosted in a suite of Early Paleozoic basic to acidic volcanic, volcaniclastic rocks in the Eastern Tianshan orogen, northwest China. The Cu-Zn orebodies are characterized by the zoning of metallogenic elements upward from a deep stockwork mineralized zone (Cu > Zn) to a shallow massive mineralized zone (Zn > Cu). Detailed petrographic and LA-ICP-MS analyses have identified five types of pyrite and three types of sphalerite. These sulfides can be distinguished in a paragenesis with four stages of sulfide mineralization. The preore stage (SⅠ) from the deep volcanic rock contains subhedral-euhedral pyrite (Py1) with high trace element contents (e.g., Co, Ni, and Ti; Average value of total trace elements: 16764 ppm), except for Sb, and Tl, indicating a euxinic and high-temperature environment. Both the disseminated and veined pyrite (Py2) from the early ore stage (SⅡ; stockwork zone) and the euhedral pyrite (Py3) from the main ore stage-1 (SIII-1) have a similar chemical signature, suggesting that they precipitated under similar physicochemical conditions. These two paragentic stages of pyrite contributed only minimally to the trace elements endowment, except for higher Se contents. The continuous convection of hydrothermal fluids caused a large accumulation of copper and zinc, forming massive orebodies. Pyrite within the Zn(Cu)-rich zone of the main ore stage-2 (SIII-2) comprises three sub-generations (Py4a ∼ c) which are characterized by enrichment in most trace elements such as Au, As, Cu, and Sb. Pyrite 4a ∼ c formed in a fluctuating sedimentary environment and recorded the injection of a short-term, gold-rich fluid, which dissolved and reprecipitated trace elements from earlier ores and surrounding rocks. Orebody deformation and local metamorphism played a key role in this gold enrichment event. Pyrite (Py5) from the late ore stage (SⅣ) is deficient in most elements but relatively enriched in Co, Ni, and Se. Three stages of sphalerite associated with the Py3 ∼ 4 have been distinguished in the SIII. From Sp1 to Sp3, the content of Fe, Ge, Mo, and Cd decreased gradually, but the Sp2 is relatively depleted in Ag, As, Au, Pb, and Sb compared to Sp1 and Sp3. The sensitive variation of As, Co, Ni, Se, Pb in pyrite and Fe, Cu, Mn, Sb, Cd in sphalerite provide significant information for reconstructing the hydrothermal evolution process. The sulfur isotopes of these pyrites determined by in situ LA-multicollector (MC)-ICP-MS analyses are concentrated around 0‰, but vary significantly from −2.3 to 5.8‰. The δ34S values of the sphalerite range from −3.5 to 4.0 ‰ and tends to decrease from Sp1 to Sp3. These results show that the metals of the SIII were most likely derived from the deep-seated Early Paleozoic subvolcanic intrusion and Daliugou Formation during the evolution of regional island arcs.Combining the chemical, and isotopic data and geological features, the ore-forming process of an ancient VMS deposit was deduced. These results constrain the texture, composition and sulfur isotopic signatures of sulfides in veins and deformed ore bodies, as well as the gold enrichment mechanism, and also reflect the vertical variation of trace elements at the scale of VMS deposits, supporting the existence of multiple depositional mechanisms.

Fluid Evolution and Ore Genesis of the Songjianghe Au Deposit in Eastern Jilin Province, NE China: Constraints from Fluid Inclusions and H-O-S-Pb Isotope Systematics

The medium-sized Songjianghe Au deposit is located in the southeastern part of the Jiapigou-Haigou gold belt (JHGB) in central eastern Jilin Province, NE China. The gold mineralization is primarily characterized by disseminated-style ores and hosted in the low-/medium-grade metamorphic rocks of the Seluohe Group. The ore bodies are governed by NNW-striking brittle-ductile structures and spatially correlated with silicic and sericitic alterations. Four alteration/mineralization stages have been distinguished: (I) Quartz-pyrrhotite-pyrite, (II) quartz-polymetallic sulfides, (III) quartz-pyrite, and (IV) quartz-calcite. The fluid inclusion (FI) assemblage in quartz from Stage I comprises C1-type, C2-type, C3-type, and VL-type FIs, with total homogenization temperatures (Th-total) of 292.8 to 405.6 °C and salinities of 2.8 to 9.3 wt% NaCl eqv. Quartz from Stage II (main ore stage) developed C2-, C3-, and VL-type FIs, with a Th-total of 278.5 to 338.9 °C and salinities of 2.8 to 8.1 wt% NaCl eqv. Stage III is characterized by coexisting C3- and VL-type FIs in quartz, with a Th-total of 215.9 to 307.3 °C and salinities of 2.4 to 7.2 wt% NaCl eqv. Only VL-type FIs are observed in Stage IV, with a Th-total of 189.5 to 240.4 °C and salinities of 3.7 to 5.7 wt% NaCl eqv. The Laser Raman spectroscopic results demonstrated minor CH4 in the C-type FIs from Stages I and II. The results suggest that ore fluids may have evolved from a medium-high temperature, low-salinity immiscible CO2-NaCl-H2O ± CH4 system to a low temperature, low-salinity homogeneous NaCl-H2O system. Fluid immiscibility caused by the rapid drop in pressure may have been the main trigger for gold-polymetallic sulfide precipitation. The Songjianghe Au deposit may have been formed under 352–448 °C and 850–1380 bar pressure, based on the isochore intersection for Stage II fluid inclusions. The H-O isotopic compositions (Stage I: δ18Ofluid = 5.6 to 5.8‰, δD = −96.2 to −95.7‰; Stage II: δ18Ofluid = 3.7 to 4.2‰, δD = −98.7 to −89.8‰; Stage III: δ18Ofluid = 1.2 to 1.4‰, δD = −103.5 to −101.2‰) indicate that the hydrothermal fluids are dominated by magmatic water in the early stages (Stages I and II) and mixed with meteoric water since Stage III. The pyrite S-Pb isotope data (δ34S: −2.91 to 3.40‰; 206Pb/204Pb: 16.3270 to 16.4874; 207Pb/204Pb: 15.2258 to 15.3489; 208Pb/204Pb: 36.6088 to 36.7174), combined with Pb isotopic compositions of the intrusive rocks and wall rocks (the Seluohe Group) in the ore district, indicate that the ore-forming materials at Songjianghe are predominantly from a magmatic source and may have been affected by the contamination of the Seluohe Group. In accordance with the features of ore geology, ore-forming fluids and metals, and geodynamic setting, the Songjianghe Au deposit belongs to a mesothermal magmatic hydrothermal vein gold deposit, which formed in the intermittent stage of Paleo-Pacific plate subduction during the Late Jurassic.

New near-mine prospecting approach using multivariate analysis and reflectance spectroscopy to define surface footprint: A case study of the Pequizão Gold Deposit, Crixás Greenstone Belt, Central Brazil

The Pequizão gold deposit in the Crixás greenstone belt, central Brazil, is structurally-controlled mineralization hosted mainly in carbonaceous phyllite with pervasive hydrothermalized zones and large amounts of disseminated sulfides and gold. Usually, regoliths of Au deposits are either unstudied or understudied in exploration surveys because of lower Au content and the difficulty and complexity of soil profiles. However, such investigation can be beneficial in brownfield exploration to assess larger areas than drilling. In this work, results of clustering and machine learning of soil geochemistry and reflectance spectroscopy integrated with a multivariate approach to determine soil footprints and to target new deposits in the surface of the Crixás greenstone belt. Reflectance spectroscopy was applied in 939 soil samples and is a valuable tool in mineral exploration for an immediate investigation of mineral assemblage from the target. It was calibrated with X-ray diffraction, geochemical, and multivariate approaches providing consistent vectors toward mineralization, with Pequizão soil samples developing gibbsite and phengitic-white mica as minerals related to mineralized samples. Multivariate analysis reveals that the deposit has a typical orogenic gold deposit chemical signature. Principal components and factor analysis first defined samples derived from carbonaceous phyllite and dolomite as the main ore hosts. The chemical aspects of hydrothermal alteration are As, Ag, Te, Ca, and Mg, with enrichment of Sb, V, Na, Ba, and W and depletion of Zn, Ga, and Pb that, according to ensemble learning, they have significant importance in the detection of gold. Understanding surface footprints of known deposits can be an exploratory guide for finding new soil geochemical halos related to mineralization zones. The research revealed new associations of minerals and chemical elements that can be determined as exploration vectors. It was possible to clarify further the knowledge about the footprint of mineralization in soil. Combining the soil-related methods applied in this study and a broad-coverage spectral approach in soil and drill cores can enhance success in prospecting in brownfield areas and expand to greenfields.

LA-ICP-MS analyses of trace elements in zoned sphalerite: A study from the Maoping carbonate-hosted Pb-Zn(-Ge) deposit, southwest China

In southwest China, many Pb-Zn deposits are described as low temperature carbonate-hosted deposits or Mississippi Valley-type (MVT) deposits. But trace element distribution and concentration in sphalerite between deposits may significantly vary and could possibly imply alternative deposit-types. An investigation was carried out on sphalerite (Sp-II) in the main ore stage of the Maoping carbonate-hosted Pb-Zn(-Ge) deposit (Southwest China), based on laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Here, Sp-II is divided into the dark red, yellow–brown, and light-yellow zones. Principal component analysis revealed element clusters distributed within distinct zoning types in Sp-II: the dark red zones are enriched in Mn, Fe, and Cd; the yellow–brown zones are enriched in Cu, Ge, Ag, and Sb; the light-yellow zones are enriched in Ga. Trace elements in Sp-II record temperature and sulfur fugacity (fS2) evolution of ore-forming fluid system, which tends to decrease from the dark red to yellow–brown to light-yellow zones. The formation of Sp-II may be an external process resulting from the varieties of temperature and fS2 in the ore-forming fluid, which may be driven by rock buffer. Here, Manganese, Fe, and Cd are preferentially incorporated in the relatively higher temperatures and fS2, whereas Ga is preferentially incorporated in the relatively lower those. Regardless of the zoning type, strong binary correlations between Ge and Cu as well as the high similarity of their concentration distribution in mapping images suggest coupled substitutions as Ge4+ + 2Cu+ ↔ 3Zn2+ and/or Ge2+ + 2Cu+ ↔ 2Zn2+ + vacancy. A trace element comparison of various Pb-Zn deposits in the world, including our new data from Maoping shows a distinctive signature for the Maoping deposit. Homogenization temperatures (217–430 ℃, mean 298 ℃) of the newly discovered ore body (No. VI) support that Maoping is a medium–high temperature carbonate-hosted deposit.

Copper technology at the Early Iron Age fortified settlements near Lakes Itkul and Irtyash, middle Trans-Urals

During the EIA (7th-3rd c. BCE), the middle Trans-Urals were populated by the Itkul culture of metalworkers. Most of the Itkul sites were excavated in 1960-1980′s, and ever since then the copper smelting technology, and exploited ore sources remained limitedly understood. To provide insight into these questions, we consider the archaeological context of copper production and apply methods of OM, SEM-EDS and LA ICP-MS to analyse copper slag, technical ceramics and ores from the Itkul culture settlement of Dautovo-1 (Itkul-1). This data is considered against the analyses of ores from the EIA sites and the Gumeshevsky mine in the Polevskoy area located 35 km from Dautovo, and the formerly investigated copper slags (Stepanov et al., 2021) from the site of Irtyash-1 located 50 km apart. The obtained results confirm that secondary copper ores of the Gumeshevsky mine, long regarded as the main ore source of the Itkul culture, were smelted at the site of Dautovo-1. We also identify the plate slag as the residue attesting to the most frequently used smelting technique, which consisted of the smelting of secondary copper ores in shallow open furnaces or crucibles and under moderately reducing conditions. The smelt ended with the removal and fast-cooling of slag outside the furnace. In contrast to Dautovo-1, only slags from secondary metallurgical operations were found at the site of Irtyash-1, which aligns with the dominance of secondary copper-working remains at the latter site. The production probably was likely performed on a seasonal basis, the metalworking society was divided into smelters and copper-workers, and the copper supply was likely oriented at both domestic and external (nomadic) markets.

Tin transport and cassiterite precipitation from hydrothermal fluids

Cassiterite (SnO2) is the main ore mineral of tin in magmatic–hydrothermal tin deposits, but tin transport and precipitation mechanisms from hydrothermal fluids remain poorly understood. We critically evaluated aqueous tin speciation in hydrothermal fluids from extensive experimental data and thermodynamic modeling. Sn(II) chloride complexes in hydrothermal fluids exist mainly as SnCl+, SnCl2(aq), and SnCl3−. The revised Helgeson–Kirkham–Flowers model parameters of these three tin species and two tin ions (Sn4+ and Sn2+) were derived from the correlation algorithms among these parameters, and the standard molar properties of cassiterite were optimized to be internally consistent with the available thermodynamic dataset. These thermodynamic parameters, together with the available equilibrium constant equation of Sn(IV) chloride complexes, could reproduce the available solubility data of cassiterite in acidic solutions at 400–700 °C under oxygen fugacity (fO2) levels buffered by hematite–magnetite (HM) or nickel–nickel oxide (NNO). These comparisons allow modeling chemical systems of SnO2–NaCl–HCl–H2O (liquid phase) to examine tin transport and cassiterite precipitation mechanisms under tin-mineralizing conditions: 300–500 °C, 50–150 MPa, 2 molal NaCl, and fO2 levels from QFM (quartz–fayalite–magnetite) to HM. Sn(II) chloride complexes are commonly interpreted to dominate in aqueous tin speciation under fO2 = NNO, but our modeling results indicate that considerable contents of Sn(IV) chloride complexes also exist in those reduced fluids with high HCl contents, consistent with recent in situ high-temperature experiments and molecular dynamic simulations. The Sn(II)/Sn(IV) ratios in fluids depends on fO2, temperature, and HCl contents. A considerable amount of Sn(IV) possibly exist in an early mineralization stage even under fO2 = NNO; if so, redox reactions are unnecessary to precipitate cassiterite from these mineralizing fluids. We find that even if the fO2 levels are constant, simple cooling can alter mineralizing fluids to be more oxidized (e.g., from QFM to HM) and cause cassiterite precipitation, indicating that oxidizing agents are not necessary as previously thought. This explains why cassiterite can precipitate in host rocks (e.g., sandstone or quartzite) that do not provide oxidizing agents. A simple rise in fO2 levels and pH neutralization (e.g., greisenization) also cause cassiterite precipitation. Cassiterite solubility in oxidized acidic hydrothermal fluids (NNO < fO2≤HM) is high enough to account for the tin contents of fluid inclusions from typical tin deposits, but the mineralization potential of oxdized fluids is inferior to reduced fluids (fO2≤ NNO) under the same conditions.

Tectonic evolution of the Aggeneys-Gamsberg Ore District, South Africa, and implications for the geodynamic setting of the Namaqua Sector

Understanding the deformation history of the structurally complex Aggeneys-Gamsberg Ore District (A-GOD), in the Namaqua Sector of the Mesoproterozoic Namaqua-Natal Metamorphic Province of South Africa, is key to discovering additional metasediment-hosted base metal sulphide mineralization. Although several studies have examined the structure of the main ore deposits and outcrops in the district, and others have investigated the timing of sedimentation, magmatism, and metamorphism, no previous studies have focused on integrating these two datasets. We therefore combine structural observations and the resulting relative timeline of events with new and existing zircon U-Pb geochronology, to yield a temporally constrained tectonic history for the district.The regionally recognized Paleoproterozoic D1 deformation is not recorded in the A-GOD, which preserves only Mesoproterozoic rocks. The largely stratiform base metal deposits occur near the top of a sequence of metamorphosed siliciclastic sediments (Wortel and Hotson Formations), deposited after 1261 ± 5 Ma (youngest reliable detrital zircons). These metasediments are tectonically interleaved with the intrusive ∼ 1190 Ma Little Namaqualand Suite (Aroams Gneiss) and younger ∼ 1175–1145 Ma metagranitoids (Achab Gneiss, Hoogoor Gneiss, aplite sills). Magmatism occurred early during D2a deformation, which created kilometre-scale isoclinal folds and thrusts during S/SW-directed contraction, as recorded at the Swartberg and Broken Hill-Deeps deposits. Associated M2a metamorphism is dated at ∼ 1200 Ma (metamorphic zircon rims), but this was not the peak metamorphic episode as previously thought. The sequence was then exhumed, and the unconformably overlying clastics and bimodal volcanics of the Koeris Formation were deposited in local transtensional pull-apart basins at ∼ 1130 Ma. Thrust stacking in the Aggeneys Mountains may have occurred during subsequent D2c contraction, associated with ∼ 1075 Ma M2c metamorphism, but evidence remains cryptic. The entire sequence is affected by kilometre-scale sheath folds that close downwards to the ∼ ENE (as at Gamsberg and the Quarry Fold Nappe), associated with ∼ ENE-trending open, upright folds. These developed during D3a ∼ ENE-directed extensional to constrictional shearing at peak M3 amphibolite-facies conditions, which re-used the gently dipping D2 regional fabric and overprinted it with new ∼ E-W trending D3 linear features. Abundant metamorphic zircon dates suggest an age of ∼ 1025 Ma for D3a and M3. Ongoing extension at retrograde conditions reactivated earlier structures, such as the Swartberg Thrust, as D3b low-angle, ductile–brittle detachment faults. Finally, dextral transform motion created local D4 monoclines and dextral strike-slip faults, possibly associated with ∼ 1000 Ma M4 metamorphic zircon growth and emplacement of a regional pegmatite swarm.The A-GOD has traditionally been fitted into a regional tectonic model involving accretion of distinct terranes onto the Kaapvaal Craton, during the polyphase ∼ 1.2–1.0 Ga Namaquan Orogeny. In contrast, recent studies propose that the entire Namaqua Sector instead occupied a back-arc setting between ∼ 1.35 and < 1.1 Ga. Our results support a hybrid model, involving accretion and translation of previously extended crustal fragments against the craton, with initially the entire Namaqua Sector - but later only the western portion - located in a hot back-arc setting influenced by subducting slab dynamics.

Environmental impact of potentially toxic elements on soils, sediments, waters, and air nearby an abandoned Hg-rich fahlore mine (Mt. Avanza, Carnic Alps, NE Italy)

The decommissioned fahlore Cu-Sb(-Ag) mine at Mt. Avanza (Carnic Alps, Italy) is a rare example of exploited ore deposits, as the tetrahedrite (Cu6[Cu4(Fe,Zn)2]Sb4S13) is the main ore mineral found. This multi-compartmental geochemical characterisation approach provides one of the first case studies regarding the geochemical behaviour and fate of Hg, Sb, As, Cu, and other elements in solid and water matrices and of Hg in the atmosphere in an environment affected by the mining activity of a fahlore ore deposit. Elevated concentrations of the elements (Cu, Sb, As, Pb, Zn, Hg) associated with both (Zn-Hg)-tetrahedrite and to other minor ore minerals in mine wastes, soils, and stream sediments were observed. Concentrations in waters and stream sediments greatly decreased with increasing distance from the mining area and the Igeo index values testify the highest levels of sediment contamination inside the mine area. Thallium and Ge were associated with the “lithogenic component” and not to sulfosalt/sulphide minerals. Although mine drainage water often slightly exceeded the national regulatory limits for Sb and As, with Sb being more mobile than As, the relatively low dissolved concentrations indicate a moderate stability of the tetrahedrite. The fate of Hg at the investigated fahlore mining district appeared similar to cinnabar mining sites around the world. Weak solubility but the potential evasion of gaseous elemental mercury (GEM) into the atmosphere also appear to be characteristics of Hg in fahlore ores. Although GEM concentrations are such that they do not present a pressing concern, real-time field surveys allowed for the easy identification of Hg sources, proving to be an effective, suitable high-resolution indirect approach for optimising soil sampling surveys and detecting mine wastes and mine adits.

Texture and iron‐oxygen isotope composition of magnetite in the Sanaga iron ore prospect, Nyong Series, southwestern Cameroon: Implications for the origin of the magnetite mineralization

The Sanaga iron ore prospect within the Palaeoproterozoic Nyong Series in Cameroon is a magnetite‐dominated iron ore deposit hosted within granodioritic gneisses with an estimated resource of 82.9 Mt @ 32.1% Fe. The main ore mineral being magnetite, provides an opportunity to study the magnetite texture and iron‐oxygen isotope composition of the mineralization, which has heretofore not been reported. These offer insights into the nature and condition of formation of the mineralization thereby paving the way for better understanding the genesis and evolution of the mineralization as well as classifying it. The mineralization is characterized by Type I and Type II magnetite varieties based on their textural features. Type I magnetite is the dominant magnetite and is characterized by ilmenite oxy‐exsolution features with triple junction contacts, while Type II magnetite lacks these features. The presence of ilmenite oxy‐exsolution features in the Type I magnetite indicates a primary magmatic formation of the magnetite followed by re‐equilibration of primary Ti‐rich magnetite in the presence of a high‐temperature fluid. Oxygen isotope (δ18O) values for the magnetite range from +2.89% to 9.30‰ indicating precipitation from evolved ore‐forming fluids through reaction with country rocks. The iron isotope (δ56Fe) of the magnetite shows little variation, with positive values ranging from +0.49–0.66‰. These values plot within the magmatic and magmatic‐hydrothermal magnetite fields when compared to the published global range of δ56Fe values for different deposit types. A similar result is obtained by plotting the coupled Fe–O isotope pair, further buttressing the magmatic‐hydrothermal origin of the mineralization. Based on these data, the Sanaga iron mineralization is best explained as a magmatic‐hydrothermal deposit.

Magnetite chemistry of the Sarkuh Porphyry Cu deposit, Urumieh–Dokhtar Magmatic Arc (UDMA), Iran: A record of deviation from the path sulfide mineralization in the porphyry copper systems

The Miocene Sarkuh porphyry Cu deposit is located in the southwestern part of Urumieh-Dokhtar Magmatic Arc (UDMA) in Iran. Compared with the neighboring giant Sarcheshmeh porphyry Cu deposit, this is a low-grade sub-economic porphyry Cu system (110 million tons @ 0.26 % Cu) characterized by an unusual abundance of magnetite. The present work tried to answer the question of whether or not there are differences in the hydrothermal system of Sarkuh, resulting in the lack of considerable mineralization. In this way, the mineral associations and EMPA data of magnetite were considered to distinguish the different stages of magnetite crystallization reflecting the magmatic-hydrothermal evolution of the Sarkuh deposit. They include (1) magmatic stage magnetite, including magnetite inclusions within primary silicate minerals (i.e., plagioclase and biotite), (2) pre-ore stage magnetite associated with potassic alteration assemblages, (3) main ore stage magnetite tightly associated with sulfide mineralization, and (4) late stage magnetite forming overgrowths on the sulfides. The results of EPMA analysis confirm that magnetite of these four stages differ in Mn, Fe, Ti, Mg, Al, Cr, and V concentrations. Higher V concentrations are found in the magmatic and pre-ore stages, whereas Al and Si reach the highest in the ore and late stages. Our data show that increasing fluid-rock interaction and changes in the oxygen fugacity, especially during the main ore stage extending to the late stage, are key factors controlling the trace element partitioning of magnetite. Most of ore stage magnetite formed at temperatures >500 °C and high temperatures prevailed during it. Magnetite crystallization after the main stage of sulfide mineralization accompanied by (partial) martitization indicate the increase of oxygen fugacity towards the late hydrothermal stage. This could explain why the ore and late stage magnetites show chemical similarities to those from sulfur-poor iron oxide copper‑gold (IOCG) deposits rather than porphyry deposits.

Assessing and Improving Biooxidation for Acid Generation and Rare Earth Element Extraction

Microorganisms (Acidithiobacillus ferrooxidanns) are effective in oxidizing ferrous ions that can be used to oxidize pyrite and produce sulfuric acid. Many coal waste resources contain significant concentrations of rare earth elements (REE) and critical materials (CM) that can be extracted using sulfuric acid. These coal waste resources often contain significant concentrations of pyrite, which if not utilized or removed present a future environmental liability for potential acid mine drainage. Thus, the combination of pyrite and REE/CM in coal waste provides a significant resource opportunity for sulfuric acid generation that can be utilized using biooxidation. In addition, the pyrite concentrate used for acid generation also contains REE/CM content that is released during biooxidation of the pyrite concentrate that augments the REE/CM release from the main ore being leached with the acid generated from the pyrite. Thus, this approach provides a very significant environmental advantage as well as augmented REE/CM recovery. Although there are many studies associated with biooxidation in relation to mineral oxidation, there is a lack of information regarding the effects of operating parameters on biooxidation performance and optimization for practical applications. In this study, findings from research in assessing and improving biooxidation for acid generation for REE/CM extraction are presented. Results show that bacteria can very effectively and efficiently oxidize ferrous ions to ferric ions, which oxidize pyrite to produce acid for REE/CM extraction. The factors that showed significant impact on biooxidation performance include air flow rate, stirring speed, residence time, solids concentration, and temperature. The dominance of Leptospirillum ferriphilum species was noted in the bioreactor after a prolonged period of operation, although Acidithiobacillus ferrooxidanns was used in the beginning.

Drones and ultraviolet radiation for the detection of scheelite mineral

Technological development and mineral extraction have always been close-knit. Devices have become dependent on dozens of elements with scant concentrations in the Earth's crust. In order to compensate for the scarcity, the search for reliable mineral survey techniques is crucial. It is possible to take advantage of the fact that many minerals are sensitive to the physical phenomena of electromagnetic radiation. The ultraviolet light shows dazzling results since it can excite some minerals to the point of causing them to fluoresce, as is the case of scheelite (main ore of tungsten), a critical mineral that is under a significant mining activity. The purpose of this article is to present a methodology both for collecting spectral data of scheelite, supported by airborne multispectral sensors, and for working with machine learning algorithms, in order to develop an accurate procedure for mineral mapping. The results show that scheelite is easily detectable with a characteristic spectral footprint by making it react with an ultraviolet light source, which could be used in further research to detect this mineral without a severe environmental impact.

Mineralogy, Geochemistry and Fluid Inclusion Study of the Stibnite Vein-Type Mineralization at Rizana, Northern Greece

The stibnite mineralization at Rizana (Kilkis ore district; Serbo-Macedonian metallogenic province; northern Greece) occurs along a NE–SW-trending brittle shear-zone, which transects a two-mica and an augen-gneiss of the Vertiskos Unit. Barren Triassic A-type granites and satellite pegmatites and aplites, as well as Oligocene-Miocene plutonic, subvolcanic and volcanic rocks that are variably hydrothermally altered and mineralized, outcrop in the broader region. The mineralization appears as veins, discordant lodes and disseminations. Veins and discordant lodes exhibit massive and brecciated textures. Historic underground mining (1930s–1950s) produced 9000 t of stibnite ore, grading 40% Sb on average. The main ore mineral assemblage includes stibnite + berthierite + sphalerite + pyrite + chalcopyrite + native antimony and traces of wolframite, galena, tetrahedrite, marcasite, pyrrhotite, arsenopyrite, realgar, native arsenic and native gold. Quartz, minor barite and ankerite are the gangue minerals. Sericitization and silicification developed along the shear-zone, forming hydrothermal halos of moderate intensity in the two-mica gneiss. Locally, valentinite, goethite and claudetite are present due to the supergene oxidation of the stibnite mineralization. Bulk ore geochemistry shows enrichments in specific elements including As, Au, Cd, Se, Tl and W. Fluid inclusion microthermometry showed that the mineralization was formed under a limited range of temperatures and salinities. The fluids had low to slightly moderate salinities (6.6–8.1 wt% equiv. NaCl) with low homogenization temperatures (217–254 °C, with a maximum at 220 °C).

Genetic mechanism of super-large karst bauxite in the northern North China Craton: Constrained by diaspore in-situ compositional analysis and pyrite sulfur isotopic compositions

>5 billion tons of karstic bauxites were formed during the Late Carboniferous in the North China Craton (NCC). However, the metallogenic mechanism of bauxite is still obscure due to the unclear formation process of the main ore mineral, diaspore. We conducted geological, mineralogical, δ34Spyrite, and in-situ diaspore trace element analyses on the Baode-Xingxian large bauxite deposit in the northern NCC, aiming to clarify the diaspore-forming mechanism and explore the genesis of bauxite. Generally, bauxites in northern NCC contains three layers from bottom to top: Fe-bearing claystone, bauxite ore, and claystone. The bauxite ore is mainly diaspore, kaolinite, and illite; the Fe-bearing claystone is illite and berthierine; and the claystone is primarily kaolinite. The broadly distributed high positive δ34Spyrite values (10‰–40‰) indicate that bauxites in the northern NCC formed in shallow-water environments. Total 216 diaspore grains have similar trace element compositions, and are obviously enriched in Cr, V, Re and U, but not in Mo, indicating that diaspore was formed in the subreduced facies. Diaspore with Fe/Al up to 4 mol% has slightly large cells, indicated that small-scale larger ions, Fe, entered the diaspore lattice to form Fe-diaspore. The favorable temperature and water activity of Fe-diaspore precipitation is similar to that of Al-hematite+ boehmite. We thus propose a probable diaspore formation mechanism: the small scale of Fe for Al substitution in the diaspore lattice and stabilize it to induce Fe-diaspore formation. Fe-diaspore is metastable with respect to diaspore and tends to convert into it during the diagenesis process.