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The preservation of biosignatures on Mars is largely associated with extensive deposits of clays formed under mild early Noachian conditions (> 3.9 Ga). They were followed by widespread precipitation of acidic sulfates considered adverse for biomolecule preservation. In this paper, an exhaustive mass spectrometry investigation of ferric subsurface materials in the Rio Tinto gossan deposit (~ 25 Ma) provides evidence of well-preserved molecular biosignatures under oxidative and acidic conditions. Time of flight secondary ion mass spectrometry (ToF-SIMS) analysis shows a direct association between physical-templating biological structures and molecular biosignatures. This relation implies that the quality of molecular preservation is exceptional and provides information on microbial life formerly operating in the shallow regions of the Rio Tinto subsurface. Consequently, low-pH oxidative environments on Mars could also record molecular information about ancient life in the same way as the Noachian clay-rich deposits, (Grant No. ANR-15-IDEX-02), European Regional Development Fund (Grant No. RYC2018-023943-I), Horizon 2020 Framework Programme (Grant No. RYC-2014-19446)

The article describes Reza gold deposit of Ugur exploration area located in Geda- bek Ore District of the Lesser Caucasus in NW of Azerbaijan. It is established that main mineralization in the Reza gold deposit consists of hematite-barite-quartz-kaoline veins- veinlets and breccia, pyrite stock-stockverk and quartz-sulfide veins. On the main orebody surface center secondary quartzites with vein-veinlets barite-hematite mineralization have occured over which remain accumulations of hydrous ferric oxides cementing breccias of quartz and secondary quartzites. “Reddish mass” is also observed in erosion parts, being an oxidation product of stock and stockverk limonite-hematite ores. Representing typical gossans, these accumulations by the data of trenches for thickness about 5-10 m contain gold 0.3-3.5 ppm and silver 1.0-45.0 ppm. There are three zones of gold mineralization within the Reza gold deposit: oxide mineralization; transition zone mineralization; sulfide mineralization. The oxide gold mineraliza- tion consists of clay-gravel weathering crust of kaolinite type. The gold-bearing mineralization has been oxidized to a depth of ap- proximately 50-100 meters. Typically, the gold mineralization is coarser and a minor increase in gold grade occurs within the oxides compared to the original rocks. The nugget effect increase in the gold grade of the oxides does not exceed approximately 10%. Deposit alteration signature has characteristics which suggest the current outcrop level may be near the top of a mineralized, gold-bearing high sulfidation epithermal (HSE) system. The gold mineralization at the deposit is interpreted as forming in shallow high sulfidation epith- ermal systems. The mineralization has been noted in well-confined hydrothermal breccia and associated with pyrite stock-stockwork. The majority of the deposit material and current estimates are formed within the barite-hematite-quartz-kaoline mineralization in the secondary quartzite rocks. The main brecciation and stockwork are hosted within secondary quartzite, sometime massive silicified andesite porphyritic rocks.

Phytomining is suggested as a technology to obtain platinum group metals (PGMs) nanoparticles from plants grown on the mineralized soils or tailings. Samples from North American Palladium (Canada) and gossans from Broken Hill (BH) (Australia) were studied to assess the possibility of using these PGM-rich samples as substrates for phytomining. The bioavailability of PGMs was indirectly assessed using geochemical procedures. The selective extractions showed that the highest available concentration of Pd is 5.38 ppm in BH gossan 1. The extraction of PGMs by ammonium acetate, fulvic acid or citrate-dithionite indicates natural availability to plants. The BH gossan 1 was the best of the five studied samples for phytomining of Pd due to available Pd concentration (> 2 mg/kg), low Electric Conductivity (< 2dS/m), high CEC (Cation Exchange Capacity) (38.8 meq/100g), and proper pH (6.5). Cu-tolerant plant species should be chosen to grow on BH gossan 1. A criterium for choosing substrates for phytomining of Pd was developed comprising various classical soil parameters plus selective extraction procedures.

The Voisey’s Bay nickel-copper-cobalt (Ni-Cu-Co) sulphide deposits constitute a significant resource of orthomagmatic mineralization. The deposits are not exposed at the surface except for in a small ferruginous gossan (Discovery Hill). The subsequent geophysical surveys and diamond drilling led to the discovery of the Ovoid ore body, buried beneath 20 m of till, and other deeper deposits in the bedrock. This study was initiated to characterize the sulphide mineralogy of these deposits through various stages of weathering, erosion, and transport. Because the samples ranged from bedrock through to a variety of surficial sediment types, the automated SEM-based identification provided by the MLA-SEM system was the ideal technique to quantitatively evaluate mineral distributions in the different media. The derived MLA-SEM data indicate that, aside from the Discovery Hill gossan, the surface sulphide mineralization at Voisey’s Bay was weathered in a pre-glaciation regolith at the Mini-Ovoid deposit and, on the surface of the Ovoid deposit, the massive sulphide was unoxidized due to a thin calcite-cemented clay cover. Pentlandite is very preferentially oxidized compared to other sulphides in the Voisey’s Bay ore, to depths of up to 10 m in bedrock. Conversely, within the coarse reject samples of crushed drill cores stored in sealed plastic bags, pyrrhotite was altered, whereas pentlandite and chalcopyrite are stable, presumably due to anaerobic reactions. The MLA-SEM detected trace amounts of minute sulphide grains in surficial sediments, but their contents abruptly decreased with distance from the sulphide mineralization. Microtextures such as troilite and pentlandite exsolution or twinning in pyrrhotite, however, could be observed in the fine sulphide grains from till, suggesting a derivation from orthomagmatic sulphide material, such as the Voisey’s Bay mineralization.

Big Gossan (BG) mine is an open stope mine operated by PT Freeport Indonesia(PTFI). This mine started its development in 2006. Currently, the mine consists of 9 active levels, each level is designed with about 1 km footwall drift East-West. The production initiated in 2009, but the mine was temporarily shut down due to a company decision. Lately the mine has been re-activated since 2017 and will be pushed into its peak production in 2019, with 7000 tpd production rate. In order to meet with the production goal, 5 levels consisting of 34 at least production stopes are required on a yearly basis. The other strategy to meet the production goal is an improvement of stopes sequencing. Big Gossan Mine is ventilated by two parallel 1600kW exhaust Mixed-Flow fans.This paper presents the ventilation plan and design to support the improved stope sequence until peak production, include the analysis of ventilation design criteria, ventilation network modeling, infrastructure required, possibility of main fans upgrade and other ventilation open stope mine challenges.

The drilling of the Rio Tinto basement has provided evidence of an underground microbial community primarily sustained by the Fe and S metabolism through the biooxidation of pyrite orebodies. Although the gossan is the microbial activity product, which dates back to the Oligocene (25 Ma), no molecular evidence of such activity in the past has been reported yet. A Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) molecular analysis of a subsurface sample in the Peña de Hierro basement has provided novel data of the ancient underground microbial community. It shows that the microbial remains are preserved in a mineral matrix composed of laminated Fe-oxysulfates and K-and Na-bearing sulfates alternating with secondary silica. In such a mineral substrate, the biomolecule traces are found in five different microstructure associations, (1) 200-micron thick layer with N-bearing adducts, and sphingolipid and/or peptide traces. It suggests the mineralization of at least five microbial preserved entities with different metabolic ca-pabilities, including: (1) Acidiphilium/Tessaracoccus-like phosphate mineralizers, (2) microbial patches preserving phosphate-free acylglycerides bacteria, (3) nitrogen oxidizing bacteria (e.g., Acidovorax sp.), (4) traces of heterotrophic ammonifying bacteria, and (5) sphingolipid bearing bacteria (e.g., Sphin-gomonadales, and δ-Proteobacteria) and/or mineralized biofilms. The primary biooxidation process acted as a preservation mechanism to release the inorganic ions that ultimately mineralized the microbial structures., Science and Technology Development Fund (FDCT) of Macao (Nos. 0005/2020/A1 and 0005/2019/A1), and the project on Civil Aerospace Technologies No. D020303 funded by China National Space Administration

Gossan ore of sulfide zinc deposit contains abundant zinc, iron, and other metal elements, which is a significant resource with complex components and can be utilized. In this study, a new technology of preparing zinc ferrite from zinc sulfide deposit gossan was proposed. The effects of Al2O3, CaO, and SiO2 in gossan on the formation of zinc ferrite were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and specific surface area and pore size analysis (BET). The results show that the presence of Al2O3 and CaO could hinder the formation of zinc ferrite, while silica had no effect on the formation of zinc ferrite. Under the conditions of the molar ratio of ZnO and Fe2O3 to Al2O3, CaO, and SiO2 of 1:1:1, an activation time of 60 min, and a roasting temperature of 750 °C for 120 min, the products, which had good crystallinity, smooth particle surface, and uniform particle size could be obtained. In addition, compared to the roasted products with Al2O3 and CaO, the specific surface area, pore volume, and pore size of the products with SiO2 were the largest.

Identification and delineation of alteration minerals and regolith play an important role in the discrimination of metallic and non-metallic minerals and are also significant for metallic and non-metallic mineralization zone identification. In this work, altered minerals and gossans have been identified in and around the Askot area in eastern Kumaon Himalaya using hyperspectral data. Analysis of the Hyperion data indicates alteration minerals in the alteration zones surrounding the Askot sulfide orebody. These minerals include alunite, axinite, illite, and pyrite. Besides, iron bearing minerals such as goethite and hematite are found in the gossans. These gossans are formed by surface weathering of sulfide orebodies and found in a northeast direction along the strike of the Askot orebody. Field surveys in two target prospective mineralized zones confirm the presence of gossan and altered minerals identified via the Hyperion hyperspectral data. This study demonstrates the ability of hyperspectral data and field investigations to identify hydrothermal alteration minerals, gossans, and potential mineralized zones in the Himalaya.

Trace elements in high concentrations are a huge problem worldwide. Monitoring of natural areas with a high concentration of these elements, such as soils under the influence of gossans, is important since there is little information available. This study aimed to evaluate the pseudo total and available concentrations of Fe, Mn, Pb, and Zn in the soil and its accumulation in native and cultivated plants in the area under the influence of gossan in the Semiarid region in Brazil. Soil samples (0-20 cm) were collected in the North, South, and center areas of the gossan and five transections separated by 1000 m. The pseudo total (EPA3050A) and available concentration (DTPA, Mehlich) of Fe, Mn, Pb, and Zn were determined. In the same points, plant samples were collected and processed to determine the concentration and bioconcentration factor of Fe, Mn, Pb, and Zn. Soils under the influence of the gossan had high Pb and Zn concentration (exceeding soil reference values), indicating that care should be taken in these areas to prevent any risk for the local community. Plants showed different accumulation patterns, with a higher accumulation of trace elements in the shoot (Fe, Mn, Zn), while Pb was primarily accumulated in the roots. Even though soil concentrations were high, plants showed in general, low bioconcentration factor of the potentially toxic elements, except for Zn, indicating that soil conditions limit their availability. RESUMO Elementos-traços em altas concentrações são um grande problema a nível mundial. O monitoramento de áreas naturais com alta concentração destes elementos, como solos sob influência de gossans, é importante, por existir pouca informação disponível. Objetivou-se neste trabalho avaliar as concentrações pseudototais e disponíveis de Fe, Mn, Pb e Zn no solo e seu acúmulo em plantas nativas e cultivadas na área sob influência de gossan no semiárido no Brasil. Amostras de solo (0-20 cm) foram coletadas no norte, sul e área central do gossan e em cinco transecções separadas em 1000 m. Determinou-se a concentração pseudototal (EPA3050A) e disponível (DTPA, Mehlich) de Fe, Mn, Pb e Zn. Nos mesmos pontos, amostras de plantas foram coletadas e processadas para determinação da concentração e fator de bioconcentração de Fe, Mn, Pb e Zn. Os solos sob influência do gossan apresentaram alta concentração de Pb e Zn (excedendo os valores de referência de qualidade), indicando que cuidados devem ser tomados nessas áreas para evitar qualquer risco para a comunidade local. As plantas apresentaram diferentes padrões de acumulação, com maior acúmulo de elementos-traço na parte aérea (Fe, Mn, Zn), enquanto o Pb foi acumulado principalmente nas raízes. Embora as concentrações no solo fossem altas, as plantas apresentaram, em geral, baixo fator de bioconcentração dos potenciais elementos tóxicos, com exceção do Zn, indicando que as condições do solo limitam sua disponibilidade.

Gossans are surficial deposits that form in host bedrock by the alteration of sulphides by acidic and oxidizing fluids. These deposits are typically a few meters to kilometers in size and they constitute important vectors to buried ore deposits. Hundreds of gossans have been mapped by field geologists in sparsely vegetated areas of the Canadian Arctic. However, due to Canada’s vast northern landmass, it is highly probable that many existing occurrences have been missed. In contrast, a variety of remote sensing data has been acquired in recent years, allowing for a broader survey of gossans from orbit. These include band ratioing or methods based on principal component analysis. Spectrally, the 809 gossans used in this study show no significant difference from randomly placed points on the Landsat 8 imageries. To overcome this major issue, we propose a deep learning method based on convolutional neural networks and relying on geo big data (Landsat-8, Arctic digital elevation model lithological maps) that can be used for the detection of gossans. Its application in different regions in the Canadian Arctic shows great promise, with precisions reaching 77%. This first order approach could provide a useful precursor tool to identify gossans prior to more detailed surveys using hyperspectral imaging.

The success of the DHEM method in detecting the Gossan Valley mineralisation, south of Gossan Hill mine, in 2008/2009 led to the systematic application of the DHEM method across the Golden Grove lease from 2011 to 2014. The method proved successful in identifying several new zones, including the Grassi resource. During these surveys it was noted that the EM method failed to elicit either in-hole or off-hole responses in a number of holes with economic intersections of lead, zinc and precious metal ore. It became clear that not all economic ore zones contained sufficient conductive sulphide to ensure detection using DHEM. This triggered an assessment of available methods to determine if other down-hole technologies could be used to complement the DHEM method. A program of core petrophysic measurements and petro-physical borehole logging led to the realisation that because the host rocks were very resistive there existed sufficient contrast for high frequency EM imaging to be viable. This led to a trial of the Radio Imaging Method at the Xantho resource of the Gossan Hill Mine in December 2016. The results of the trial suggested direct detection of the massive sphalerite ore is possible. Further work is being undertaken to better understand the optimum survey methodology in the Golden Grove Mine environment with a view to providing specific recommendations that if approved will see the use of the method expanded on the mine leases, both at Gossan Hill and Scuddles mines, as well as on the surrounding mine leases

Discrimination of iron oxide and hydroxide mineral assemblages is a key factor in porphyry copper exploration. This paper investigates the ability of the Worldview-3 VNIR data in mapping iron oxide / hydroxide minerals associated with the porphyry copper mineralization. The study area is situated in the central part of the Urumieh–Dokhtar magmatic arc, northeastern Isfahan, Iran, which hosts a number of important porphyry copper deposits. The copper mineralization is related to the porphyry intrusive complex that ranges in composition from diorite to granodiorite. Bands 2,3,4,5, and 8 of this satellite were used to enhance the pixels containing target minerals and to mask the effects of vegetation on these pixels. The best results in terms of mapping and discriminating target materials were acquired by the band math and the matched filtering (MF) methods. The MF output results enhanced pixels with the highest fractions of the target minerals. The field investigations, X-ray diffraction (XRD) analysis, and microscopic studies showed that the distribution pattern of target minerals correspond well to ground criteria and gossan caps associated with the porphyry copper mineralization. It was concluded that Worldview-3 has the efficient spectral bands in VNIR region, which could be proposed for the iron oxide / hydroxide mineral mapping.

Regional scale demarcation of alterations is an important preliminary step in mineral exploration. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imageries here have been used for alteration mapping and iron-rich (e.g., Gossans) area demarcation in a highly vegetated and relatively unexplored part of Eastern India, namely, South Purulia Shear Zone (SPSZ). The area is surrounded by mineral-rich Singhbhum Shear Zone (SSZ), but the mineral potentiality of SPSZ has not yet been proven. Alteration mineral assemblages are comprise of iron-rich alteration (gossan), clay alteration with varying amounts of iron content, sericitization, ferruginization and chloritization. In this paper, we discuss a few advantages and limitations of commonly used satellite image processing techniques for mineral mapping. We integrate the outputs of band ratio, Principal Component Analysis (PCA), PCA-loading, and thresholding; termed as Directed PCA (DPCA) for delineating mineral potential areas. Our approach mapped the alteration zones with overall 74% accuracy. Our study leads to demarcation of 28% alteration area within a 10 km wide and 60 km long stretch of SPSZ. Two areas, namely, Lawa (23° 1′ 39.31″ N, 86° 4′ 2.55″ E) and Sindurpur (23° 4′ 38.30″ N, 86° 5′ 3.99″ E) were identified as mineral potential zone. Samples from those areas were studied using XRF, microscope and SEM with the conclusive presence of mineralization. Lawa is potential for hydrothermal polymetallic sulfides along with gold mineralization. Sindurpur is potential for secondary iron and manganese mineralization. The study shows that DPCA is a useful tool for ASTER data processing for narrowing target area in preliminary stages of exploration in vegetated zones.

Three cycles of paleoweathering and supergene activity have been identified within the Penokean Volcanic Belt (PVB) of northern Wisconsin, Michigan and east-central Minnesota, USA. These cycles are responsible for significant subaerial weathering, erosion, oxidation and most importantly local supergene Au, Ag and Cu enrichment that has a major economic impact upon volcanogenic massive sulfide (VMS)-style mineralization within the PVB. The paleoweathering profile (regolith-saprolite) that developed on the exposed PVB surface now marks an angular unconformity with stratigraphically overlying, late Paleoproterozoic Baraboo Interval quartzites and late Cambrian sandstones. Differential uplift of the PVB surface is a direct result of the ∼1850 Ma compressional tectonic event that occurred during the Penokean orogeny. The uplifted PVB paleosurface experienced its first weathering cycle in the mid to late Paleoproterozoic. VMS mineralization near the paleosurface was exhumed and affected during this protracted cycle which ceased upon deposition of Baraboo Interval quartzites (1788–1714 Ma). Further uplift and subsequent unroofing of the quartzites during the Mazatzal orogeny (∼1650–1630 Ma) initiated a second paleoweathering cycle that culminated within the Neoproterozoic – Cambrian transition. During this cycle of accelerated and uninterrupted paleoweathering, new and surviving supergene Au-Ag-Cu-enriched profiles geochemically matured over exhumed mineralized sections in terrains with favorable fault block movements. Supergene systems that developed during both cycles were highly acidic environments. Low protolith reactivity and high hypogene pyrite concentrations promoted acidity of supergene fluids thus facilitating enhanced Cu, Au and Ag mobility. In those systems that lacked sufficient carbonate, Zn and Pb were lost to surrounding aqueous regimes. The second paleoweathering cycle ended with the deposition of overlying late Cambrian sandstone (497–485.4 Ma). Erosional retreat of the overlying Paleozoic sequence exposed many of these supergene deposits to a third, possibly brief paleoweathering cycle before the onset of Quaternary continental glaciation. VMS profiles not protected by sandstone outliers or within down-dropped fault blocks were glacially eroded. Of the 14 or more known VMS deposits and occurrences in the belt, four have preserved or partially preserved paleoweathering profiles. The most significant are at the Flambeau and Back Forty deposits where Au-Ag-enriched indigenous gossans with extensive or local underlying supergene-enriched Cu sulfide zones have developed over hypogene massive sulfide horizons. These profiles demonstrate efficient cumulative or multicyclic Au, Ag and Cu-enrichment to ore grades. Although commonly small (≤2 million tonnes), such supergene-enriched deposits are generally shallow, allowing for development by low cost open pit methods and production of exceptionally high-grade, direct shipping copper and/or gold ores. As such, the buried PVB unconformity is considered a prime exploration target that is highly prospective for new discoveries of commercially viable, supergene-enriched VMS resources.

The Namib Lead and Zinc (Pb-Zn) Mine is hosted within the Karibib Formation of the Swakop Group, Damara Sequence. The host marble contains sulphide-rich beds and is locally Pb- and Zn-rich over a strike extent of >100 km. Mining took place in the upper portions of a remobilized MVT or SEDEX orebody, which may occur adjacent to a reactivated major structure. Pb and Zn show locally anomalous copper, tin, indium and fluorine concentrations. Based on the position of gossans, individual orebodies comprise discrete elongate shoots around an antiform and its meso-scale parasitic folds, within calcitic marble. Non-coaxial flattening of the fold-cleavage geometry reflects a series of non-coaxial deformation events, recorded in the Southern Central Zone of the Damara Belt which were superimposed on a NE-SW structural grain and pre-existing fold axial planes. Non-coaxial flattening resulted in further remobilization of sulphides into dilational rhombs which formed from shearing along overlapping axial planar cleavage, in concert with the dilation of banding in the host marble.

This study used the ability of remote sensing technology to identify alteration zones in porphyry copper mining and Iron oxides of area in south Nain district in Iran by using Lands at-8 data source. The band ratio of 3/2 derived from image spectra was used to indicate the distribution of iron oxides and 6/3 for identifying gossan. Hydrothermal alteration mineral zones associated with porphyry copper mineralization identified and discriminated based on two algorithms of target detection, MTTCIMF and OSP. Those techniques identified porphyry copper mineralization in study area and six points were diagnosed as the best location for ore exploration. For more accurate study and recognition between mineralization and tectonic structure of district, the lineament map of area was produced by applying Gaussian high-pass filter on IRS data. The Spatial distribution of hydrothermal alteration zones has been verified by inspection in field works and Fuzzy logic. Results showed that image processing techniques have a great ability to obtain comprehensive information for reconnaissance stage of porphyry copper exploration in the case study and assist researcher to explore porphyry copper and iron oxides regions before time-consuming and costly ground investigation.

The Eocene (ca. 55–38 Ma) Bear Lodge alkaline complex in the northern Black Hills region of northeastern Wyoming (USA) is host to stockwork-style carbonatite dikes and veins with high concentrations of rare earth elements (e.g., La: 4140–21000 ppm, Ce: 9220–35800 ppm, Nd: 4800–13900 ppm). The central carbonatite dike swarm is characterized by zones of variable REE content, with peripheral zones enriched in HREE including yttrium. The principle REE-bearing phases in unoxidized carbonatite are ancylite and carbocernaite, with subordinate monazite, fluorapatite, burbankite, and Ca-REE fluorocarbonates. In oxidized carbonatite, REE are hosted primarily by Ca-REE fluorocarbonates (bastnasite, parisite, synchysite, and mixed varieties), with lesser REE phosphates (rhabdophane and monazite), fluorapatite, and cerianite. REE abundances were substantially upgraded (e.g., La: 54500–66800 ppm, Ce: 11500–92100 ppm, Nd: 4740–31200 ppm) in carbonatite that was altered by oxidizing hydrothermal and supergene processes. Vertical, near surface increases in REE concentrations correlate with replacement of REE(±Sr,Ca,Na,Ba) carbonate minerals by Ca-REE fluorocarbonate minerals, dissolution of matrix calcite, development of Fe- and Mn-rich gossan, crystallization of cerianite and accompanying negative Ce anomalies in secondary fluorocarbonates and phosphates, and increasing δ18O values. These vertical changes demonstrate the importance of oxidizing meteoric water during the most recent modifications to the carbonatite stockwork. Scanning electron microscopy, energy dispersive spectroscopy, and electron probe microanalysis were used to investigate variations in mineral chemistry controlling the lateral complex-wide geochemical heterogeneity. HREE-enrichment in some peripheral zones can be attributed to an increase in the abundance of secondary REE phosphates (rhabdophane group, monazite, and fluorapatite), while HREE-enrichment in other zones is a result of HREE substitution in the otherwise LREE-selective fluorocarbonate minerals. Microprobe analyses show that HREE substitution is most pronounced in Ca-rich fluorocarbonates (parisite, synchysite, and mixed syntaxial varieties). Peripheral, late-stage HREE-enrichment is attributed to: 1) fractionation during early crystallization of LREE selective minerals, such as ancylite, carbocernaite, and Ca-REE fluorocarbonates in the central Bull Hill dike swarm, 2) REE liberated during breakdown of primary calcite and apatite with higher HREE/LREE ratios, and 3) differential transport of REE in fluids with higher PO43−/CO32− and F−/CO32− ratios, leading to phosphate and pseudomorphic fluorocarbonate mineralization. Supergene weathering processes were important at the stratigraphically highest peripheral REE occurrence, which consists of fine, acicular monazite, jarosite, rutile/pseudorutile, barite, and plumbopyrochlore, an assemblage mineralogically similar to carbonatite laterites in tropical regions.

Resolving the source of environmental contamination is the critical first step in remediation and exposure prevention. Australia's oldest silver-zinc-lead mine at Broken Hill (>130 years old) has generated a legacy of contamination and is associated with persistent elevated childhood blood lead (Pb) levels. However, the source of environmental Pb remains in dispute: current mine emissions; remobilized mine-legacy lead in soils and dusts; and natural lead from geological weathering of the gossan ore body. Multiple lines of evidence used to resolve this conundrum at Broken Hill include spatial and temporal variations in dust Pb concentrations and bioaccessibility, Pb isotopic compositions, particle morphology and mineralogy. Total dust Pb loading (mean 255 μg/m2/day) and its bioaccessibility (mean 75% of total Pb) is greatest adjacent to the active mining operations. Unweathered galena (PbS) found in contemporary dust deposits contrast markedly to Pb-bearing particles from mine-tailings and weathered gossan samples. Contemporary dust particles were more angular, had higher sulfur content and had little or no iron and manganese. Dust adjacent to the mine has Pb isotopic compositions (208Pb/207Pb: 2.3197; 206Pb/207Pb: 1.0406) that are a close match (99%) to the ore body with values slightly lower (94%) at the edge of the city. The weight of evidence supports the conclusion that contemporary dust Pb contamination in Broken Hill is sourced primarily from current mining activities and not from weathering or legacy sources.

Development of clean mining processes is a topic of increasing interest. Biotechnology could be a cost-effective and environmentally friendly alternative to conventional methods. Jarosites can have important economic and environmental impacts because of their content of valuable metals. The anaerobic reductive dissolution of jarosites and gossan mineral by Shewanella putrefaciens strain CN2 and its secondary products have been investigated. In addition, the ability of S. putrefaciens to reduce insoluble Fe(III) in presence of chelators (citrate and EDTA) was examined. The main components in the biofilm extracted from the cultures were determined. In addition, it was observed the formation of extracellular polymeric substances (EPS) during the biological process.

In supergene Zn non-sulfide deposits, the Fe-oxy-hydroxides (FeO/OH) are mainly concentrated in the residual zones (gossan) on top of the oxidized ore bodies, although they can also be found throughout the whole weathering profile coexisting with the primary and secondary ore assemblages. Fe-oxy-hydroxides are rarely pure as they form in systems where a wide range of metals, most of them of economic importance (e.g., Zn, Pb, Co, REE, Sc, Ga, Ge, V, etc.), freely circulate and can be &ldquo, captured&rdquo, under specific conditions. Although their occurrence can be widespread, and they have a potential to scavenge and accumulate critical metals, FeO/OH are considered gangue phases during the existing processing routes of Zn non-sulfide ores. Moreover, very little is known about the role of the deposit type on the geochemistry of FeO/OH formed in a specific association. Therefore, this paper provides a comprehensive assessment of the trace element footprint of FeO/OH from a number of Zn non-sulfide deposits, in order to define parameters controlling the metals&rsquo, enrichment process in the mineral phase. To achieve this, we selected FeO/OH-bearing mineralized samples from four supergene Zn non-sulfide ores in diverse settings, namely Hakkari (Turkey), Jabali (Yemen), Cristal (Peru) and Kabwe (Zambia). The petrography of FeO/OH was investigated by means of scanning electron microscope energy dispersive analysis (SEM-EDS), while the trace element composition was assessed using laser ablation-ICP-MS (LA-ICP-MS). Statistical analyses performed on LA-ICP-MS data defined several interelement associations, which can be ascribed to the different nature of the studied deposits, the dominant ore-formation process and subsequent evolution of the deposits and the environmental conditions under which FeO/OH phases were formed. Based on our results, the main new inferences are: (A) Zinc, Si, Pb, Ga and Ge enrichment in FeO/OH is favored in ores where the direct replacement of sulfides is the dominant process and/or where the pyrite is abundant (e.g., Cristal and Hakkari). (B) When the dissolution of the host-rock is a key process during the supergene ore formation (i.e., Jabali), the buffering toward basic pH of the solutions favors the uptake in FeO/OH of elements leached from the host carbonate rock (i.e., Mn), whilst restricting the uptake of elements derived from the dissolution of sulfides (i.e., Zn, Pb, Ga and Ge), as well as silica. (C) The input of exotic phases can produce significant enrichment in &ldquo, unconventional&rdquo, metals in FeO/OH (i.e., Cr and Co at Kabwe, Y at Cristal) depending on whether the optimal pH-Eh conditions are attained. (D) In the Kabwe deposit, FeO/OH records heterogeneous geochemical conditions within the system: where locally basic conditions prevailed during the alteration process, the V and U concentration in FeO/OH is favored, yet conversely, more acidic weathering produced Zn- and Si-bearing FeO/OH.

In this article, we report the discovery of a gossanite-type hematite and magnetite ore associated with sulfide mineralization in the Rayat area of NE Iraq. Detailed petrographic, mineralogical, and geochemical data define the features of the gossanite and the associated sulfide-rich rocks, providing an assessment of the mineralization and its relation to hydrothermal, microbial and alteration processes. The identified gossanite-like rocks are interpreted as part of a specific submarine gossan formed on the sulfide-rich serpentinite. In the uppermost part of the studied sequence, jasperite lithofacies occur, within which millimeter-thick layered iron oxide-silica alternations are also visible and comparable to the banded iron formation (BIF). Below the jasperite, an oxidized mineralized zone (OMZ) developed, representing gossanite that is exceptionally rich in iron oxides (up to 70%), chlorite, and quartz with some minor spinel content. The lowermost part of the studied sequence is the sulfide-rich reduced mineralized zone (RMZ) composed of silica, pyrite, chalcopyrite, pentlandite, Ni-chlorite, and siderite. The transition zone (TZ), approximately 1 m thick, between the OMZ and RMZ, contains chlorite, Fe-oxides, quartz, and partially altered sulfide minerals. The potential economic significance of the ore body in addition to Fe is the silver-nickel (Ag-Ni) and cobalt (Co) mineralization, with an average Ag concentration of 5.09 wt% per sulfide grain, which occurs as an exsolution phase within the sulfidic-cherts lithofacies. The Ni concentration ranged from 363 to 4,000 mg/kg, while that of Co ranged from 90 to 441 mg/kg, depending on the lithofacies. A thin lensoid coaly bed associated with the ore body, attributable to the Ophiolitic Melange, provides some initial clues for the epigenetic thermotectonic evolution of the studied strata. The overall data suggest that the Rayat gossanite, jasperite, and the underlying sulfide-rich zone were formed near the seafloor through a combination of initial hydrothermal alteration of serpentinites, which provided the sulfides, accompanied by the sedimentary deposition of Fe-Si-exhalatives along with the olistostromatic brecciated facies in the upper section, and the subsequent seafloor oxidation/weathering effects along microbial iron uptake. The discovery of gossanite and sulfides in the Rayat area, along with the already known chromitite deposits in the contiguous areas, highlights NE Iraq as a potential mineral-rich domain.

Oxide facies gold deposits are characterised by high Au-tenor free-milling gold nuggets and differ to their associated sulphide assemblages which have a lower Au-tenor. These changes point to an active gold geochemical cycle during the transitioning from sulphide- to oxide facies, which commonly also correlates with the formation of an iron oxide-rich gossan. Surficial gold occurrences in the Amani area of southwestern Tanzania are hosted by gossanous outcrops comprising weathered- to highly weathered quartz-carbonate veins and high Au-tenor gold, and thus represent an ideal natural laboratory in which to study supergene gold enrichment processes. The gossan mineralogy comprises goethite, hematite, malachite, azurite, siderite and quartz assemblages, with supergene gold particles up to 6 mm and with an average gold concentration of 95 wt%. The supergene gold particles have irregular and elongate morphologies, with elongate gold occurring exclusively along narrow ribs of neoformed goethite. The crystal habit of this gold shows a persistent orthogonal relationship between adjacent sub-micrometre-sized terraces, reflecting a possible crystallographic control on supergene gold precipitation. Novel results from 3-D X-ray computed tomography reveal that the micrometre- to millimetre scale distribution of gold follows a near-orthogonal pattern controlled by the textures and fluid flow pathways within the developing gossan. These elongate gold particles form interconnected 3-D skeletal gold networks which coalesce at discrete intersections to form larger nuggets (up to 6 mm in length) of high Au-tenor supergene gold. A detailed geochemical consideration of the mineralogy of the gossan, its precursor vein paragenesis and the surrounding host rocks suggest that the physicochemical conditions within the developing gossan favour supergene gold growth by dissolution-re-precipitation mechanisms involving an intermediate gold thiosulphate ligand complex.

The Las Cruces VMS deposit is located at the eastern corner of the Iberian Pyrite Belt (SW Spain) and is overlain by the Neogene–Quaternary sediments of the Guadalquivir foreland Basin. The deposit is currently exploited from an open pit by Cobre Las Cruces S.A., being the supergene Cu-enriched zone the present mined resource. The Las Cruces orebody is composed of a polymetallic massive sulfide orebody, a Cu-rich stockwork and an overlying supergene profile that includes a Cu-rich secondary ore (initial reserves of 17.6 Mt @ 6.2% Cu) and a gossan cap (initial reserves of 3.6 Mt @ 3.3% Pb, 2.5 g/t Au, and 56.3 g/t Ag). The mineralogy of the Las Cruces weathering profile has been studied in this work. Textural relationships, mineral chemistry, deposition order of the minerals and genesis of the Las Cruces gossan are described and discussed in detail. A complex mineral assemblage composed by the following minerals has been determined: carbonates such as siderite, calcite and cerussite; Fe-sulfides including pyrite, marcasite, greigite and pyrrhotite; Pb–Sb sulfides and sulfosalts like galena, stibnite, fuloppite, plagionite, boulangerite, plumosite, and the jordanite–geocronite series, Ag–Hg–Sb sulfides and sulfosalts including miargyrite, pyrargyrite, sternbergite, acanthite, freibergite, cinnabar, Ag–Au–Hg amalgams; and Bi–Pb–Bi sulfides and sulfosalts such as bismuthinite, galenobismutite, others unidentified Bi–Pb-sulfosalts, native Bi and unidentified Fe–Pb–Sb-sulfosalts. Remains of the former oxidized assemblage appear as relicts comprised of hematite and goethite. Combining paragenetic information, textures and mineral chemistry it has been possible to derive a sequence of events for the Las Cruces gossan generation and subsequent evolution. In that sense, the small amount of Fe-oxyhydroxides and their relict textures replaced by carbonates and sulfides suggest that the gossan was generated under changing physico-chemical conditions. It is proposed that the Las Cruces current gossan represents the modified residue of a former gossan mineralization where prolonged weathering led to dissolution and leaching out of highly mobile elements and oxidation of the primary sulfides. Later, the gossan was subject to seawater-gossan interaction and then buried beneath a carbonated-rich cover. The basinal fluids-gossan interaction and the equilibration of fluids with the carbonated sediments brought to the carbonatization and sulfidation of the gossan, and thus to the generation of Fe-carbonates and Pb–Sb-sulfides. The Las Cruces mineral system likely represents a new category within the weathering class of ore deposits.

The present paper reports the first detailed petrological and geochemical study of non-sulfide Zn–(Fe Pb) deposits in the Riopar area (Prebetic Zone of the Mesozoic Betic Basin, SE Spain), constraining the origin and evolution of ore-forming fluids. In Riopar both sulfide and non-sulfide Zn–(Fe Pb) (“calamine”) ores are hosted in hydrothermally dolomitized Lower Cretaceous limestones. The hypogene sulfides comprise sphalerite, marcasite and minor galena. Calamine ores consist of Zn-carbonates (smithsonite and scarce hydrozincite), associated with abundant Fe-(hydr)oxides (goethite and hematite) and minor Pb-carbonates (cerussite). Three smithsonite types have been recognized: i) Sm-I consists of brown anhedral microcrystalline aggregates as encrustations replacing sphalerite; ii) Sm-II refers to brownish subhedral aggregates of rugged appearance related with Fe oxi-hydroxides in the surface crystals, which replace extensively sphalerite; and iii) Sm-III smithsonite appears as coarse grayish botryoidal aggregates in microkarstic cavities and porosity. Hydrozincite is scarce and appears as milky white botryoidal encrustations in cavities replacing smithsonite. Also, two types of cerussite have been identified: i) Cer-I cerussite consists of fine crystals replacing galena along cleavage planes and crystal surfaces; and ii) Cer-II conforms fine botryoidal crystals found infill porosity. Calcite and thin gypsum encrustations were also recognized. The field and petrographic observations of the Riopar non-sulfide Zn–(Fe Pb) revealed two successive stages of supergene ore formation under meteoric fluid processes: i) “gossan” and “red calamine” formation in the uppermost parts of the ore with deposition of Fe-(hydr)oxides and Zn- and Pb-carbonates (Sm-I, Sm-II and Cer-I), occurring as direct replacements of Zn Pb sulfides; and ii) “gray calamine” ore formation with deposition of Sm-III, Cer-II and hydrozincite infilling microkarst cavities and porosity. The stable isotope variation of Riopar smithsonite is very similar to those obtained in other calamine-ore deposits around the world. Their C O isotope data (δ 18 O: + 27.8 to + 29.6‰ V-SMOW; δ 13 C: − 6.3 to + 0.4‰ V-PDB), puts constrains on: i) the oxidizing fluid type, which was of meteoric origin with temperatures of 12 to 19 °C, suggesting a supergene weathering process for the calamine-ore formation under a temperate climate; and ii) the carbon source, that resulted from mixing between two CO 2 components derived from: the dissolution of host-dolomite ( 13 C-enriched source) and vegetation decomposition ( 13 C-depleted component).

The Ortaklar VMS deposit is hosted in the Kocali Complex consisting of basalts and deep sea pelagic sediments, which formed by rifting and continental break-up of the southern Neotethyan in Late Triassic. The basalts are of NMORB-type without notable crustal contamination. From the surface to depth, the Ortaklar deposit consists of a gossan zone, a thick massive ore zone and a poorly developed stockwork zone. Primary mineralisation is characterised by distinctive facies including sulphide breccias (proximal), graded beds (distal), stockworks and chimney fragments. Ore mineral abundances decrease in the order of pyrite, magnetite, chalcopyrite, and sphalerite. Two distinct phases of mineralisation, massive magnetite and massive sulphide, are present in the Ortaklar deposit. Textural evidence (e.g., magnetite replacing sulphides) and the spatial relationships with the host rocks indicate that magnetite and sulphide minerals were generated in different stages. The transition from sulphide to magnetite mineralisation is interpreted to relate to variation in H2S content of ore fluids. The 1st stage massive sulphide ore might have formed by early hydrothermal fluids rich in Fe and H2S. The 2nd stage massive magnetite might have formed by later neutral hydrothermal fluids rich in Fe but poor in H2S, replacing the pre-existing sulphide ore. The alteration patterns, mineral paragenesis, lithological features (massive ore-stockwork ore-gossan) of the Ortaklar deposit together with its trace elements, Cu-Pb-Zn-Au-Ag and REE signatures are all consistent with a Cyprus-type VMS system. The δ34S values in pyrite and chalcopyrite samples range from 2.6 to 5.7‰, indicating that the hydrothermal fluids were associated with sub-seafloor igneous activity, typical of Cyprus-type VMS deposits. However, magnetite formed later than sulphide minerals in the Ortaklar deposit, contrasting with typical Cyprus-type VMS deposits where magnetite generally occurs in lower sections. Consequently, although the Ortaklar deposit generally conforms to Cyprus-type deposits, it is distinguished from them by its late stage and high magnetite concentration. Thus, the Ortaklar deposit is thought to be an exceptional and perhaps unique Cyprus-type VMS deposit.

Bog manganese ore, associated with the banded iron formation of the Iron Ore Group (IOG), occurs in large volume in northern Odisha, India. The ore is powdery, fine-grained and soft in nature with varying specific gravity (2.8–3.9 g/cm3) and high thermo-gravimetric loss, It consists of manganese (δ-MnO2, manganite, cryptomelane/romanechite with minor pyrolusite) and iron (goethite/limonite and hematite) minerals with sub-ordinate kaolinite and quartz. It shows oolitic/pisolitic to globular morphology nucleating small detritus of quartz, pyrolusite/romanechite and hematite. The ore contains around 23% Mn and 28% Fe with around 7% of combined alumina and silica. Such Mn ore has not found any use because of its sub-grade nature and high iron content, and is hence considered as waste. The ore does not respond to any physical beneficiation techniques because of the combined state of the manganese and iron phases. Attempts have been made to recover manganese and iron value from such ore through smelting. A sample along with an appropriate charge mix when processed through a plasma reactor, produced high-manganese steel alloy having 25% Mn within a very short time (

The Igarape Bahia, situated in the Carajas Mineral Province, is a world-class example of a lateritic gold deposit. It has developed under tropical weathering conditions since at least the Eocene and resulted in a regolith cover of at least 100 m thickness. The regolith is dominated by ~ 80 m thick ferruginous saprolite containing gossan bodies that constitute the main Au ore. Above saprolite the regolith stratigraphy has been established considering two distinct domains. One composed of residual materials and the other transported materials deposited over palaeochannels. In the residual domain the ferruginous saprolite grades upwards into a fragmental duricrust, interpreted as a collapsed zone, and then into different types of ferruginous duricrusts. Over palaeochannel the ferruginous saprolite is truncated by poorly sorted ferruginous sediment of variable composition that grades upwards into the ferruginous duricrusts formed over transported materials. Lateritization took place during a marked period that transformed the colluvium of the residual domain, and the transported materials accumulated in the channel depressions, into the ferruginous duricrust units. A later bauxitization event has overprinted all duricrust types but has mostly affected the duricrusts over the palaeochannel forming gibbsitic nodules. All duricrusts were finally covered by a transported layer of latosol which flattened the whole landscape in the Carajas region. Gold shows a depletion trend across the regolith but is enriched in the fragmental duricrust below the ferruginous duricrust from which gold is leached. Gold is also chemically dispersed laterally into the fragmental duricrust, but lateral Au dispersion in the ferruginous duricrusts of the residual domain is probably also influenced by colluvial transport. Metals associated with Au mineralization (Cu, U, Mo, Pb, Ag, LREE, Sn, W, Bi, Sb and P) are generally depleted in the saprolite but most of them are still anomalous. The fragmental and ferruginous duricrusts are more leached but the tests performed to estimate the dispersion potential of metals contained in the ferruginous duricrust show that some metals are still significantly anomalous especially Au, Ag and Cu. However, if ferruginous duricrusts are used as an exploration sample media their environment of formation must be considered. Metal depletion is generally more advanced in the ferruginous duricrusts developed in the vicinities of palaeochannels as oppose to those developed in residual domain. On the contrary, Au over palaeochannel areas is enriched in the upper bauxitized ferruginous duricrusts and in their gibbsitic nodules as a result of lateral chemical transport that is more widespread than in the colluvium over residual domain. The latosol is highly depleted in most metals due to its transported nature. However, the nodular fractions of the latosol show the greatest dispersion potential especially for Au, Ag, W, U, Bi and Sn. It can incorporate magnetic nodules that bring a rich suit of metals associated to the magnetic gossans, and non-magnetic nodules, classified as concretion and pisolites, which bring metals enriched or dispersed in the ferruginous duricrusts. This suggests that Lag constitutes a promising sample medium for geochemical exploration in the lateritic terrains of the Carajas region.

New tools and algorithms for geological remote sensing are developed and verified at test sites throughout the world in preparation of the German hyperspectral satellite Mission (EnMAP), which is an Environmental Mapping and Analysis Program. The Aggeneys Cu-Pb-Zn deposit, situated in the arid north western part of South Africa, represents a unique field laboratory for testing these new tools. Here spaceborne hyperspectral data covering the Swartberg, Big Syncline and Gamsberg area were collected by the Hyperion sensor. New synergies between multispectral and hyperspectral spaceborne data can be demonstrated, such as the Iron Feature Depth index (IFD), which has recently been proposed for mine waste mapping in the North West Province of South Africa and for gossan detection at Haib River in South Namibia. The work presented here explores the potential of the IFD for gossan mapping and characterization at Gamsberg and Big Syncline, from EO-1 ALI and Landsat-8 OLI data together with mineral maps from expert systems such as the United States Geological Survey (USGS) Material Identification and Characterization Algorithm (MICA), and first results from EnMAPs EnGeoMAP algorithm. Field spectroscopic measurements and field sampling were carried out to validate and calibrate the results from the expert systems and the IFD. This ground truthing is a necessary complementary step to link the results from the expert systems and the IFD to in-situ field spectroscopy. Future mineral exploration initiatives may benefit from the techniques described here, because they can significantly narrow the expensive, exploration activities such as hyperspectral airborne data, field activities and drilling, by identifying the most promising mineral anomalies in an area from the spaceborne data.

Zinc-enriched targets have been detected at the Kimberley formation, Gale crater, Mars, using the Chemistry Camera (ChemCam) instrument. The Zn content is analyzed with a univariate calibration based on the 481.2 nm emission line. The limit of quantification for ZnO is 3 wt % (at 95% confidence level) and 1 wt % (at 68% confidence level). The limit of detection is shown to be around 0.5 wt %. As of sol 950, 12 targets on Mars present high ZnO content ranging from 1.0 wt % to 8.4 wt % (Yarrada, sol 628). Those Zn-enriched targets are almost entirely located at the Dillinger member of the Kimberley formation, where high Mn and alkali contents were also detected, probably in different phases. Zn enrichment does not depend on the textures of the rocks (coarse-grained sandstones, pebbly conglomerates, and resistant fins). The lack of sulfur enhancement suggests that Zn is not present in the sphalerite phase. Zn appears somewhat correlated with Na2O and the ChemCam hydration index, suggesting that it could be in an amorphous clay phase (such as sauconite). On Earth, such an enrichment would be consistent with a supergene alteration of a sphalerite gossan cap in a primary siliciclastic bedrock or a possible hypogene nonsulfide zinc deposition where Zn, Fe, Mn would have been transported in a reduced sulfur-poor fluid and precipitated rapidly in the form of oxides.