Mining District Research Articles

The Montecristo mining district, northern Chile: the relationship between vein-like magnetite-(apatite) and iron oxide-copper–gold deposits

The Montecristo district, northern Chile, is one of the few places worldwide where there is a direct relationship between magnetite-(apatite) (MtAp) mineralization and iron oxide-copper–gold (IOCG) mineralization. The MtAp mineralization includes Ti-poor magnetite, fluorapatite, and actinolite and is crosscut and partially replaced by a younger IOCG mineralization that includes a second generation of actinolite and magnetite with quartz, chalcopyrite, pyrite, and molybdenite. The MtAp stage at Montecristo is interpreted as the crystallized iron-rich melts that used the pre-existing structures of the Atacama Fault System as conduits. These rocks later acted as a trap for hydrothermal IOCG mineralization. Geochronology data at Montecristo indicate that the host diorite (U–Pb zircon 153.3 ± 1.8 Ma, 2-sigma), MtAp mineralization (40Ar-39Ar in actinolite, 154 ± 2 Ma and 153 ± 4 Ma, 2-sigma), and the IOCG event (Re-Os on molybdenite, 151.8 ± 0.6 Ma, 2-sigma) are coeval within error and took place in a time span of less than 3.4 Ma. The εHfi and εNdi values of the host diorite are + 8.0 to + 9.8 and + 4.3 to + 5.4, respectively. The whole-rock 87Sr/86Sri values of the IOCG mineralization (0.70425 to 0.70442) are in the lower end of those of the MtAp mineralization (0.70426–0.70629). In contrast, εNdi values for the IOCG mineralization (+ 5.4 and + 5.7) fall between those of the MtAp rocks (+ 6.6 to + 7.2) and the host diorite, which suggests that the IOCG event was related to fluids having a more crustal Nd (εNdi < + 5.7) composition than the MtAp mineralization. This likely reflects the mixing of Nd from the MtAp protolith and a deep magmatic-hydrothermal source, very likely an unexposed intrusion equivalent to the host diorite. Sulfur isotope compositions (δ34S, + 0.3 to + 3.4‰) are consistent with a magmatic source.

Alexander I. Pogrebetsky's Research Note on the State and Prospects of the Bodaybinsky District Amidst the Civil War

The research note published below is a fairly complete description of the economic status of the Bodaybinsky gold mining district. The note was prepared in the summer of 1919 in the conditions of political instability and economic crisis. Given the remoteness of the Bodaybinsky district and the lack of reliable information about its economic situation, this note was a valuable source for studying the affairs in this important for the economy of the Irkutsk Province area and the possible prospects for its restoration. Its task was to assess the economy and finances of the district in order to open a representative office of the Irkutsk branch of the Moscow People's Bank in it. This research note was not published and remained out of sight of researchers studying the history of the gold industry. Its author was Alexander I. Pogrebetsky, an active member of cooperative movement and an economist, later known as a researcher in the history of money circulation and finance in Siberia and the Far East.

Multiple metal exposure and metabolic syndrome in elderly individuals: A case-control study in an active mining district, Northwest China

The prevalence of metabolic syndrome (MetS) is increasing at an alarming rate worldwide, particularly among elderly individuals. Exposure to various metals has been linked to the development of MetS. However, limited studies have focused attention on the elderly population living in active mining districts. Participants with MetS (N = 292) were matched for age (±2 years old) and sex with a healthy subject (N = 292). We measured the serum levels of 14 metals in older people aged 65–85 years. Conditional logistic regression, restricted cubic spline model, multiple linear regression, and Bayesian Kernel Machine Regression (BKMR) were applied to estimate potential associations between multiple metals and the risk of MetS. Serum levels of Sb and Fe were significantly higher than the controls (0.58 μg/L vs 0.46 μg/L, 2167 μg/L vs 2042 μg/L, p < 0.05), while Mg was significantly lower (20035 μg/L vs 20,394 μg/L, p < 0.05). An increased risk of MetS was associated with higher serum Sb levels (adjusted odds ratio (OR) = 1.61 for the highest tertile vs. the lowest tertile, 95% CI = 1.08–2.40, p-trend = 0.018) and serum Fe levels (adjusted OR = 1.55 for the highest tertile, 95% CI = 1.04–2.33, p-trend = 0.032). Higher Mg levels in serum may have potential protective effects on the development of MetS (adjusted OR = 0.61 for the highest tertile, 95% CI = 0.41–0.91, p-trend = 0.013). A joint exposure analysis by the BKMR model revealed that the mixture of 12 metals (except Tl and Cd) was associated with increased risk of MetS. Our results indicated that exposure to Sb and Fe might increase the risk of MetS in an elderly population living in mining-intensive areas. Further work is needed to confirm the protective effect of Mg on MetS.

The Charrarruca porphyry-type alteration zone: New evidence of mineralizing Late Cretaceous-Eocene magmatism in the Southern Central Andes of Argentina

The Charrarruca porphyry-type alteration zone is located in the northern part of the Andacollo Mining District (AMD), placed in the northern Neuquén Precordillera, (Argentina). Potassic, chloritic-carbonatic, sericitic, and propylitic alteration halo of ∼1.5 km2 affects an andesitic/dacitic subvolcanic body. These rocks, with arc affinity and Upper Cretaceous-Paleogene age (65 ± 2.5 Ma), derived from a magma evolved under normal crust thickness conditions, allowing the correlation with the intrusive facies of the Naunauco Group. The petrogenetic characteristics of these rocks attest to indications of the fertility of this magmatism, turning into a prospective guide for the unexplored Upper Cretaceous–Eocene Neuquén porphyry copper metallogenic belt.

Structural controls on the Co and Ni-bearing arsenides from the Bou Azzer mine (Case of Aït Ahmane F53 vein deposit): Implications for mineral exploration

The mining district of Bou Azzer is located in the central part of the Anti-Atlas, which is on the northern margin of the West African craton. Located about hundred kilometers southwest of the Ouarzazate city, the Bou Azzer inlier crops out along the major fault of the Anti-Atlas. In the eastern part of the Bou Azzer mining district, the "F53 vein deposit", in the Aït Ahmane area, represents one of the richest cobalt ore deposit; with production of more than 200 tons of cobalt per month. This study aims to define the different faults controlling the mineralization in the F53 vein deposit. In this work, we use the ArcPad mobile application to map faults, veins and geological formations and the digital collection of geological data (e.g., alterations, structural measurements, etc.) in the field. Then, we use the Win-Tensor software for structural analysis and reconstruction of paleostress. The results of this study indicate that the mineralization in the F53 vein deposit is structurally controlled by two main types of faults. The first one corresponds to overlapping faults with sinistral strike-slip component oriented N110° to N120° formed during the Pan-African orogenic event with a NNE-SSW to NE-SW of a maximum subhorizontal stress (σ1), and with N00 to N40° tension gashes. These faults control the mineralization located along the contact between the serpentinized peridotites and the quartz diorite. This type of mineralization named "Contact mineralization”, has massive to brecciated texture and are rich in Co–Ni–Fe arsenides. The second type correspond to a reactivation of tension gashes oriented N00° to N40° as reverse faults during a shortening phase, probably of Variscan age, with horizontal NW-SE trending maximum stress (σ1) and subvertical minimum stress (σ3). These faults oriented N00° to N40° control the vein-type mineralization, which has a banded texture and appears in the form of mineralized quartz-carbonate veins intersecting the quartz diorite. These mineralized faults N00° to N40° directions are transverse to the N120° fault contact between the serpentinized peridotites and the quartz diorite.

Water-Energy Nexus in the Antofagasta Mining District: Options for Municipal Wastewater Reuse from a Nearly Energy-Neutral WWTP

The region of Antofagasta is the mining hearth of Chile. The water requirement of the local mining sector is 65% of the total water uses, with a water consumption of approx. 9 m3/s in the year 2020. That determines an important pressure onto freshwater, which can only be alleviated by resorting to desalination or reuse of treated wastewater. At present, an amount equal to 90% of the wastewater generated in the city of Antofagasta is discharged into the ocean, after undergoing only preliminary treatments. The wastewater treatment plant (WWTP), which includes a conventional activated sludge (CAS) process, has a very low treatment capacity, insufficient to serve the whole population. A new WWTP will be built with the twofold aim of (i) purifying the totality of the wastewater generated from the city (approx. 320,000 equivalent inhabitants, e.i.), and (ii) allowing the reuse of 100% of the treated wastewater in the local mining sector, in agreement with the goals of the Chilean government. The new Antofagasta WWTP will include preliminary treatments and a conventional activated sludge (CAS) process with a higher treatment capacity. This study integrates a number of modeling tools, namely the Activated Sludge Model n.3 (ASM3), the Takacs model, and some stoichiometric and energy balances, to assess the impact that some changes, possibly introduced into the project of the new WWTP, could determine on its energy and environmental sustainability. Specifically, through an energy-economic-environmental (3-E) analysis, the original scheme of the planned WWTP was compared with three scenarios, of which Scenario 1 introduces anaerobic digestion (AD) of secondary sludge, Scenario 2 concerns primary sedimentation and AD of both primary and secondary sludge, and, finally, Scenario 3, other than primary sedimentation and AD, also includes a pre-denitrification process. The results of the study demonstrated that all the changes introduced by Scenario 3 were of capital importance to promote the transformation of the WWTP into a nearly energy-neutral water resource recovery facility (WRRF). Specifically, the processes/operations introduced with Scenario 3 can reduce the electric energy demand from external sources to only 20% of that of the original scheme, and consequently avoid the emission of 4390 tons CO2-equivalent/y.

Implication of the Triassic–Liassic rifting and Pangea breakup on the geodynamic, tectonic and mineralogical evolution of the Zeida Pb–Zn, Ba deposit (Upper Moulouya, Morocco)

The Zeida Pb–Zn, Ba stratiform deposit is part of the Upper Moulouya mining district at the junction of the Middle Atlas and the Central High Atlas. This paper aims to identify the geodynamic–tectonic setting of the emplacement of this ore deposit, using a multidisciplinary approach combining field and laboratory work associated with paleostress analysis. The lithostratigraphic and gitological studies enable descriptions of Pb–Zn, Ba mineralization impregnated in the Upper Triassic arkose beds unconformably overlying the Variscan biotite-bearing granites. The mineralogical study allowed determination of a primary paragenesis mainly composed of galena + barite with lesser copper and zinc sulfides (chalcopyrite, covellite and sphalerite). The supergene paragenesis is represented by galena oxidation products associated with iron and manganese oxides. The structural analysis revealed a complex fracture network controlling ore deposition with three main directional systems: (i) NNE–SSW to NE–SW system; (ii) ENE–WSW to E–W system, and (iii) WNW–ESE system. The reconstruction of the paleostress fields synchronous with the mineralization emplacement allowed to conclude that these fractures were developed under an extensional tectonic regime linked to the Atlasic rifting, and characterized by horizontal NW–SE-trending σ3 axis, and vertical σ1 axis. The relative age of the emplacement of the Zeida ore deposit is assigned to the Triassic–Liassic period during a regional metallogenic event related to the opening of the Central Atlantic and the Alpine Tethys in the framework of the breakup of the Pangea supercontinent.

Geology and geochemistry of metasomatite rocks associated with Kiruna iron oxide apatite and the evolution of fluids responsible for metasomatism in Choghart and Chadormalu deposits (Bafq mining district, Central Iran)

Geology and geochemistry of metasomatite rocks associated with Kiruna iron oxide apatite and the evolution of fluids responsible for metasomatism in Choghart and Chadormalu deposits (Bafq mining district, Central Iran)

Apatite records metamorphic and hydrothermal fluid evolution at the large Shuangqishan orogenic gold deposit, SE China

Orogenic gold deposits are currently the world’s major source of Au, but uncertainty exists in the timing of mineralization relative to the ages of host rocks, metamorphism, and magmatism. Consequently, the origin and detailed evolution of ore-forming fluids have long been elusive. Apatite occurs widespread in various types of mineral deposits and can provide valuable information on ore genesis. Here, we present textural, high-precision in situ U-Pb geochronological, trace elements, and Sr isotope data for metamorphic and hydrothermal apatite in the Shuangqishan gold deposit in southeastern China. These data, together with U-Pb dates of metavolcanic host rocks, granitic and mafic intrusive rocks, allow us to precisely constrain the timing of mineralization and reconstruct the history of the ore-forming fluids there. The apatite crystals within metamorphic and auriferous quartz veins can be grouped into three generations according to cathodoluminescence imaging and trace element concentrations: Ap1 precipitated in the pre-mineralization metamorphic stage, whereas Ap2 and Ap3 formed in the auriferous hydrothermal stage. Metamorphic Ap1 displays a negative Eu anomaly, indicating a predominance of Eu2+ and crystallization under relatively reduced conditions. On the other hand, syn-gold hydrothermal Ap2 and Ap3 have marked positive Eu anomalies. Radiometric ages for metamorphic Ap1 are at ca. 461 Ma, whereas hydrothermal Ap2 and xenotime from auriferous quartz gave U-Pb ages of 425 ± 15 Ma and 416 ± 15 Ma, interpreted as the time of gold mineralization. Emplacement ages determined by U-Pb zircon data are 439 ± 2 Ma for granitic intrusion and 427 ± 2 Ma for a mafic dike in the mining district. Mineralization, therefore, postdates the metamorphism of local host rocks and granitic magmatism by ∼35 ± 24 m.y. and ∼14 ± 17 m.y., respectively. The synchronism of gold genesis and mafic magmatism provides additional evidence for a mantle derivation of the ore-forming fluids. The highly radiogenic 87Sr/86Sr ratios obtained for Ap1 (0.7178−0.7302) are consistent with its precipitation from a metamorphic fluid. Higher Sr concentrations (Ap2 = 1228−2884 ppm, Ap3 = 2325−3169 ppm) and positive Eu anomalies (Eu/Eu*: Ap2 = 1.03−2.84, Ap3 = 2.00−4.30) but lower and variable 87Sr/86Sr ratios in hydrothermal Ap2 (0.7100−0.7165) and Ap3 (0.7086−0.7116) are mainly ascribed to extensive fluid-wall rock exchange of Sr during mineralization. It is therefore suggested that fluid-rock reaction played a vital role in the observed positive Eu anomalies of hydrothermal apatite. Our study highlights the usefulness of apatite as a novel and robust geochronological, geochemical, and isotopic indicator of complex mineralization processes in hydrothermal gold deposits.

Efficiency of large-scale aided phytostabilization in a mining pond

Mining activities accumulate large quantities of waste in tailing ponds, which results in several environmental impacts. In Cartagena–La Unión mining district (SE Spain), a field experiment was carried out in a tailing pond to evaluate the effect of aided phytostabilization on reducing the bioavailability of zinc (Zn), lead (Pb), copper (Cu) and cadmium (Cd) and enhancing soil quality. Nine native plant species were planted, and pig manure and slurry along with marble waste were used as amendments. After 3 years, the vegetation developed heterogeneously on the pond surface. In order to evaluate the factors affecting this inequality, four areas with different VC and an area without treatment (control area) were sampled. Soil physicochemical properties, total, bioavailable and soluble metals, and metal sequential extraction were determined. Results revealed that pH, organic carbon, calcium carbonate equivalent and total nitrogen increased after the aided phytostabilization, while electrical conductivity, total sulfur and bioavailable metals significantly decreased. In addition, results indicated that differences in VC among sampled areas were mainly owing to differences in pH, EC and concentration of soluble metals, which in turn were modified by the effect of non-restored areas on close restored areas after heavy rains due to a lower elevation of the restored areas compared to the unrestored ones. Therefore, to achieve the most favorable and sustainable long-term results of aided phytostabilization, along with plant species and amendments, micro-topography should be also taken into consideration, which causes different soil characteristics and thus different plant growth and survival.

Impact of Mining and Ore Processing on Soil, Drainage and Vegetation in the Zambian Copperbelt Mining Districts: A Review

The regional environmental–geochemical surveying of the long-term impacts of mining and ore processing on a large part of the Zambian Copperbelt mining district was carried out by the Czech Research Group with cooperation of the Geology Department, University of Zambia, and the Geological Survey of Zambia in the period 2002–2018. This included the characterization of various sources of contamination, the extent of contamination of soils and crops, and the degree of contamination of river water and sediments. Solid speciation studies of potentially harmful chemical elements (PHEs), plant and human bioaccessibility studies, and a range of mineralogical techniques were used to assess the pathways of PHE cycling in terrestrial and aqueous systems and their impacts on human health. Ores of the Zambian Copperbelt mining district are mined for Cu and Co, but a number of other trace elements (Pb, As, Cd, Hg, Pb, Zn) gradually accumulated in soils and stream sediments. It was concluded that the most important problems related to ore mining and processing are the contamination of soil and crops due to dust fall out from tailing facilities and emissions from smelters. Moreover, leakages of solutions from tailing dams, insufficient technological control of their stability and breakdowns on pipelines transporting slurry from treatment plants to tailing impoundments cause contamination of water courses and deposition of metal(loids) in stream sediments. However, the contamination of the Kafue River water is relatively limited due to its high neutralization capacity. In contrast, in some Kafue River tributaries, especially those close to big mining centers, the concentrations of dissolved Cu and Co are high (up to 14,752 μg/L and 1917 μg/L) and exceed Zambian effluent limits. We also recommend measures that could contribute to minimizing the impact of ore mining and processing on the environment and the health of the local population.

Variscan magmatism of the Tighza Mining District (Moroccan Central Massif): mapping, petro-structural analysis, and geochemical characterization of the depositional mode

Variscan magmatism of the Tighza Mining District (Moroccan Central Massif): mapping, petro-structural analysis, and geochemical characterization of the depositional mode

Quantification of Pollutants in Mining Ponds Using a Combination of LiDAR and Geochemical Methods—Mining District of Hiendelaencina, Guadalajara (Spain)

More than twenty years after the last mining operations were completed in the Hiendelaencina Mining District, it is necessary to carry out a geochemical characterisation of the tailings stored in two contiguous mine ponds. Both have significant amounts of quartz, siderite, barite and muscovite and show significant contents of As, Ba, Pb, Sb and Zn. The tailings show alkaline pH and low electrical conductivity values, which support the visual observation that rules out acid drainage into the environment. The comparison of the National Topographic Map of 1954 with LiDAR data from 2014 has allowed estimating the volume of abandoned waste. Based on the volume of slurry and its average density, the total tonnage of pollutants has been estimated at 279 ± 9 t stored in Pond North and 466 ± 11 t stored in Pond South. Although these are significant quantities that pose a risk to the environment and nearby populations, they are lower than those present in other Spanish districts, such as the Iberian Pyrite Belt or Cartagena-La Unión. The combined use of LiDAR data, aerial imagery and geochemical methods has proven to be very useful for the estimation of the volume of pollutants stored in mine ponds.

Deciphering the diagenetic evolution of the lower Carnian succession in the Gorno and Pian Resinelli sulphide mining districts (Southalpine Domain, N Italy)

The stratabound Mississippi Valley-type (MVT) sulphide deposits of the Gorno and Piani Resinelli mining districts are hosted in the lower Carnian carbonate succession, mainly peritidal limestones, of the Lombardian Basin (Southalpine Domain, Northern Italy). In addition to the formation of the well-known sulphide deposits, these carbonate sediments experienced a complex diagenetic evolution, including different stages of dolomitization, silicification, dissolution, brecciation, calcite cement precipitation. Stratigraphic and petrographic features suggest that, apart from an early calcite cementation and a first penecontemporaneous dolomitization affecting the supratidal beds, diagenetic processes and sulphide precipitation, are intimately and genetically associated. They document the occurrence of a Carnian hydrothermal system developed shortly after deposition at shallow burial depth, confirmed by fluid inclusion microthermometry and U-Pb radiometric datings.

Effect of Lead–Zinc Mining on Socio-Economic and Health Conditions of Enyigba and Ishiagu Lead–zinc Mining Districts of Southeastern Nigeria

Effect of Lead–Zinc Mining on Socio-Economic and Health Conditions of Enyigba and Ishiagu Lead–zinc Mining Districts of Southeastern Nigeria

Environmental and human health risks of potentially harmful elements in mining-impacted soils: A case study of the Angouran Zn–Pb Mine, Iran

The soil pollution status, levels of exposure, and potential ecological and health risks to workers and residents by potentially harmful elements (PHEs) in the Angouran mining area (Iran), the biggest Zn–Pb mine in the Middle East, were studied. To this aim, topsoil (0–5 cm) samples (n = 63) from different land-uses were analyzed for their total PHEs concentrations. Mine worker's blood analysis and in vitro digestion extractions were applied in conjunction with human health risk assessment (HHRA) to assess the potential health impacts by exposure to PHEs. The maximum PHEs total concentrations were found in the soils near the waste rock dumps. HHRA indicated that ingestion of soils may induce a non-carcinogenic risk due to As and Pb (for both age groups of children and adults), while dermal contact for children may induce the same type of risk due to Cd, and Pb. The carcinogenic risks (CRs) of As, Cd, Cr, and Ni through ingestion route were above the acceptable value of 1 × 10−4, and children may face greater health risks. The average blood Zn, Pb, and Cd levels in the mine workers largely exceeded the safe concentration for adults, while 30% of the workers were tested positive for As in blood. In vitro digestion extractions indicated that the highest bioaccessible contents of As, Cd, Pb, Ni and Zn were found for the industrial-residential and mine soils in the area, while those of Cr and Cu were observed in the agricultural use soils. This study illustrates that a combination of techniques, including geochemical analysis, in vitro bioaccessibility extractions, HHRA, and blood analysis, is a workable integrated approach for evaluating pollution and health risks in mining districts.

Orogenic magmatism along the transition Precordillera-Sierras Pampeanas, between 29° and 31° S, Argentina

New geochemical data and petrological analysis of Neogene volcanic units from the Pampean Flat Slab Segment (29°-31°SL) are presented in this contribution. Rocks were collected along a cross-section from the Western Sierras Pampeanas to the Eastern Precordillera. The outcrops delimit areas with a sub-parallel disposition to the orogenic front and main Andean regional structures. The study involves several volcanic rocks of the Formación Cerro Morado, sampled from the Huachi eruptive center and the Helvecia and Portezuelo de Los Burros mine districts, with thick lava flows and pyroclastic rocks. Lavas and breccias from several medium size outcrops near Huaco are also analyzed. To the NE, near the town of Guandacol, the Unidad Volcánica El Corral crops out. These rocks constitute the easternmost outcrops of the Precordillera in San Juan. We also studied rocks from the La Ciénaga volcano of the Sierra del Pocho Volcanic Field within the Sierras Pampeanas of Cordoba, which are the easternmost magmatic expression of the volcanic arc in this shallow subduction zone of the Central Andes.The new geochemical and isotopic data obtained from Formación Cerro Morado and lava flows belonging to the Unidad Volcánica El Corral, and its comparison with new geochemical data of the La Ciénaga volcano of the Sierra de Pocho show that these rocks result from the melting of two sources coming from two different types of crustal basements (Precordillera and Sierras Pampeanas). We found a magmatic association with similar geochemical features within the Formación Cerro Morado in Huachi region and Helvecia mine and Agua de Los Burros. It shows abundant hydrothermal fluids, which are often related to mineralization of economic interest.On the other hand, the rocks of the Formación Cerro Morado from Huaco, of the Unidad Volcánica El Corral and El Pocho Volcanic Field have a similar isotopic signature that allows us to infer the participation of the underlying Sierras Pampeanas Crust in their development. This feature leads us to interpret the continuity of the Sierras Pampeanas Basement Crust below the Western Precordillera.

Geología, alteración hidrotermal y mineralogía del sistema de vetas Sofía-Julia-Valencia, distrito minero Andacollo, Neuquén, Argentina

The Sofía-Julia-Valencia vein system, located in the Andacollo mining district in central west Argentina, is hosted by ENE-WSW oriented strike-slip faults which are the result of reactivation of normal faults affecting Carboniferous to Jurassic rocks during Upper Cretaceous-Paleogene. These veins contain a total resource of 22,900 Oz of gold with 5.5-6.7 g/t AuEq. Geologic mapping and a U-Pb age of 71±1Ma in zircon, obtained in an altered and mineralized dacitic dyke of the district, allowed to associate the mineralizing event to the Naunauco Andesitic belt magmatism (Upper Cretaceous-Paleogene) and to the Cretaceous-Paleogene Metallogenic Belt of the Andes in southwestern Argentina. The ore bodies are made up of multiple veins and veinlets that, from oldest to youngest, correspond to: (1) scarce early quartz+pyrite+molybdenite+iron poor-sphalerite veinlets, (2) quartz+epidote+calcite±albite (apatite+rutile+titanite+light rare earth elements bearing phosphates) associated with quartz+biotite, epidote (actinolite)+chlorite+calcite, with pyrite+pyrrhotite±chalcopyrite±(iron rich-sphalerite), marcasite veins. These veins are cut and reopened by (3) polymetallic veins and veinlets formed by quartz+sericite±carbonates (chlorite), with iron-gold rich sphalerite+silver rich-galena+chalcopyrite+pyrite, native gold±arsenopyrite±(pyrrhotite, bornite, argentite). Pyrite (4) and (5) carbonate+framboidal pyrite veinlets cuts all the previous ones. Multistage carbonate generation brecciate and cut previous veins and veinlets. Quartz shows granular, comb textures and some calcites developed platy textures. Four hydrothermal alteration types affected the veins host rock: (1) patches of early potassic alteration; (2) widespread propylitic alteration with disseminated sulfides; (3) later phyllic alteration overlapped to the previous ones; and (4) late supergene alteration. The sphalerite and chlorite composition in the veins (1 and 2) along with their mineral assamblages indicates they were formed by initially alkaline fluids (e.g., feldspar stable) with intermediate sulfur and oxygen fugacity and mesothermal temperature conditions (~400-240 °C), that evolved to conditions of lower sulfur (e.g., pyrrhotite stable) and oxygen fugacity, temperature

Structures, deformation history and dynamic background of the Qianyingzi Coal Mine in the Huaibei Coalfield, eastern China

The Qianyingzi Coal Mine is located in the west of the Suxian Mining District of the Huaibei Coalfield, eastern China. The study on structural development patterns and genetic mechanisms in this mine lays an important foundation for safe and efficiently underground mining, and is also the key to understanding the regional tectonic evolution. In this study, based on the analysis of three-dimensional seismic, drilling and underground measured data and regional tectonic correlation, the structures, evolution history and dynamic background of the Qianyingzi Coal Mine are discussed. The Carboniferous-Permian coal measure strata in the mine are generally a gentle syncline with a NNE-trending axis, and cut by a series of faults. The faults developed in this mine are mainly medium- and small-sized with a throw of less than 20 m, and the number of reverse faults is significantly greater than that of normal faults. The strikes of reverse and normal faults are both mainly NE, followed by NNE and nearly N‒S. According to the characteristics of structural geometry, tectonic association, fault property and cross-cutting relation, the structural deformation of coal measure strata in the Qianyingzi Coal Mine can be divided into five stages, and the corresponding tectonic stress fields are NWW‒SEE compressive stress, nearly E‒W compressive stress, NW‒SE compressive stress, nearly E‒W and NW‒SE extensional stresses, respectively. It developed the Fengjia Syncline with a NNE-trending axis in the first stage and nearly N‒S-striking reverse faults in the second stage, which were the results of foreland deformation and subsequent continent-continent collision during the convergence of the North China Craton and South China Plate in the Indosinian period. The NNE-striking reverse sinistral faults and NE-striking reverse faults developed in the third stage is related to the rapid oblique subduction of the Izanagi Plate toward the East Asian continental margin at the beginning of the Early Cretaceous in the western Pacific region. Later, the fourth and fifth stages of the nearly N‒S- and NE-SW-striking normal faults were developed under the backarc extensional background in eastern China during the Early Cretaceous. These new results can be used to guide the rational arrangement for underground mining and also provide a new understanding for regional tectonic evolution of the Huaibei Coalfield.

A novel non-destructive workflow for examining germanium and co-substituents in ZnS

A suite of complementary techniques was used to examine germanium (Ge), a byproduct critical element, and co-substituent trace elements in ZnS and mine wastes from four mineral districts where germanium is, or has been, produced within the United States. This contribution establishes a comprehensive workflow for characterizing Ge and other trace elements, which captures the full heterogeneity of samples through extensive pre-characterization. This process proceeded from optical microscopy, to scanning electron microscopy and cathodoluminescence (CL) imaging, to electron microprobe analysis, prior to synchrotron-based investigations. Utilizing non-destructive techniques enabled reanalysis, which proved essential for verifying observations and validating unexpected results. In cases where the Fe content was &amp;lt;0.3 wt% in ZnS, cathodoluminescence imaging proved to be an efficient means to qualitatively identify trace element zonation that could then be further explored by other micro-focused techniques. Micro-focused X-ray diffraction was used to map the distribution of the non-cubic ZnS polymorph, whereas micro-focused X-ray fluorescence (μ-XRF) phase mapping distinguished between Ge4+ hosted in primary ZnS and a weathering product, hemimorphite [Zn4Si2O7(OH)2·H2O]. Microprobe data and μ-XRF maps identified spatial relationships among trace elements in ZnS and implied substitutional mechanisms, which were further explored using Ge and copper (Cu) X-ray absorption near-edge spectroscopy (XANES). Both oxidation states of Ge (4+ and 2+) were identified in ZnS along with, almost exclusively, monovalent Cu. However, the relative abundance of Ge oxidation states varied among mineral districts and, sometimes, within samples. Further, bulk XANES measurements typically agreed with micro-focused XANES (μ-XANES) spectra, but unique micro-environments were detected, highlighting the importance of complementary bulk and micro-focused measurements. Some Ge μ-XANES utilized a high energy resolution fluorescence detector, which improved spectral resolution and spectral signal-to-noise ratio. This detector opens new opportunities for exploring byproduct critical elements in complex matrices. Overall, the non-destructive workflow employed here can be extended to other byproduct critical elements to more fully understand fundamental ore enrichment processes, which have practical implications for critical element exploration, resource quantification, and extraction.