Mineralogical Information Research Articles

Modelling of soil solid thermal conductivity

Soil solid thermal conductivity (λs) is critical to model effective soil thermal conductivity (λeff) that is required for engineering design and estimate of soil surface energy flux and soil temperature. However, it is impossible to measure λs because soil is a porous medium and there is no way to compact the soil to a continuous solid state without any pore spaces. The indirect estimation of λs requires saturation of the soils or a complete soil mineralogical information or mineral component such as quartz that has much greater thermal conductivity. Therefore, many approximation approaches of various complexities to predict λs have been proposed. However, few studies have been conducted to assess these models. An extensive review were conducted and returned 20 models to calculate λs. These models were categorized and their performances were assessed with a compiled dataset consisting of 65 soils from five studies. The results showed that the Johansen approach can give satisfactory λs given that quartz content is available (RMSE = 0.60 W m−1 °C−1, NSE = 0.91) and the Tarnawski et al. model suitable for Canadian soils (RMSE = 0.55 W m−1 °C−1, NSE = 0.92). The Côté and Konrad approach that inversely model λs based on the geometric mean model and measured soil thermal conductivity at full saturation (λsat) give accurate λs (RMSE = 0.22 W m−1 °C−1, NSE = 0.99), but cannot be applied to soils without λsat measurement. The other approaches that take use of soil thermal conductivity at dryness (λdry) give unsatisfactory λs. Therefore, a new three-point method (three measurements between λdry and λsat) based on the He et al. model was proposed to predict λs. The results showed this approach provides a reliable method to estimate λs (RMSE = 0.17 W m−1 °C−1, NSE = 0.99) at various textures and water contents without knowledge on mineralogical information.

Diverse rock types detected in the lunar South Pole–Aitken Basin by the Chang’E-4 lunar mission

Abstract The South Pole–Aitken (SPA) basin, located between the South Pole and Aitken crater on the far side of the Moon, is the largest confirmed lunar impact structure. The pre-Nectarian SPA basin is a 2400 × 2050 km elliptical structure centered at 53°S, 191°E, which should have exposed lower crust and upper mantle due to the enormous excavation depth. Olivine, the dominant mineral in Earth’s mantle, has only been identified in small and localized exposures in the margins of the SPA basin, and the dominant mafic component is, instead, pyroxene. These mineralogical characteristics could be explained by the recent hypothesis that the lunar upper mantle is dominated by low-calcium pyroxene, not olivine. Here, we present observations from imaging and spectral data from China’s Chang’E-4 (CE-4) lunar mission in the first 4 synodic days, especially the first in situ visible/near-infrared spectrometer observations of an exposed boulder. We identified a variety of rock types, but not the recently reported olivine-rich materials in the landing region. The results are consistent with orbital observations. The obtained mineralogical information provides a better understanding of the nature and origin of SPA materials.

Drill-Core Mineral Abundance Estimation Using Hyperspectral and High-Resolution Mineralogical Data

Due to the extensive drilling performed every year in exploration campaigns for the discovery and evaluation of ore deposits, drill-core mapping is becoming an essential step. While valuable mineralogical information is extracted during core logging by on-site geologists, the process is time consuming and dependent on the observer and individual background. Hyperspectral short-wave infrared (SWIR) data is used in the mining industry as a tool to complement traditional logging techniques and to provide a rapid and non-invasive analytical method for mineralogical characterization. Additionally, Scanning Electron Microscopy-based image analyses using a Mineral Liberation Analyser (SEM-MLA) provide exhaustive high-resolution mineralogical maps, but can only be performed on small areas of the drill-cores. We propose to use machine learning algorithms to combine the two data types and upscale the quantitative SEM-MLA mineralogical data to drill-core scale. This way, quasi-quantitative maps over entire drill-core samples are obtained. Our upscaling approach increases result transparency and reproducibility by employing physical-based data acquisition (hyperspectral imaging) combined with mathematical models (machine learning). The procedure is tested on 5 drill-core samples with varying training data using random forests, support vector machines and neural network regression models. The obtained mineral abundance maps are further used for the extraction of mineralogical parameters such as mineral association.

Estimation of Mineral Abundance From Hyperspectral Data Using a New Supervised Neighbor-Band Ratio Unmixing Approach

This article compares the ability of nine unmixing models, including radiative transfer (RT) models as well as a new nonlinear unmixing approach called neighbor-band ratio unmixing (NBRU), to obtain mineralogical information from hyperspectral data. Their performance in estimating mineral abundances of 94 crafted mineral mixtures was first assessed. NBRU led to the best results among non-RT models with mean and median errors of 9.8% and 7.4%, respectively. Hapke’s and Shkuratov’s RT models obtained 6.5% and 5.6%, and 6.7% and 4.7%, respectively. In a second experiment, the mapping ability of six non-RT models and their robustness when facing endmember variability were evaluated. The assessment was performed on an AVIRIS hyperspectral image of the widely studied Cuprite area, NV, USA. Comparisons with validation maps showed that NBRU retrieved the best spatial distributions for seven of the nine minerals mapped.

Multimineral Modeling and Estimation of Brittleness Index of Shaly Sandstone in Upper Assam and Mizoram Areas, India

SummaryThe brittleness index (BI) has major implications for hydraulic fracture studies and production toward optimized recovery in unconventional reservoirs. The paucity of brittleness studies in Mizoram and Upper Assam, located in northeastern India, motivates us to take up multimineral modeling and estimation of BI. Two commonly used BI estimation approaches, mineralogical and geomechanical, have been implemented to characterize the shaly sandstone in the study area. Laboratory analyses of the available drill-cutting samples and crossplots from well log data along with previous literature confirm the types of minerals present in the study area. With this mineralogical information, a new approach of BI log estimation from multimineral modeling is suggested here using conventional log data in the absence of core/drill cutting samples. A multimineral model for Mizoram and Upper Assam is developed by using bulk density (ρ), compressional sonic velocity (Vp), shear sonic velocity (Vs), lithodensity, and acoustic impedance (AI) logs to calculate volumetric percentage of minerals. Estimated mineralogical BI from well log data using four established models are compared and calibrated with X-ray diffraction (XRD)-derived BI to validate the proposed procedure. Most brittle zones having a BI ≥ 66% are demarcated for high Young’s modulus (Y ≥ 60 GPa) and low Poisson’s ratio (ν ≤ 0.25) values in the Y vs. ν crossplot for the study area. The presence of brittle minerals estimated from both XRD and the multimineral model suffices the reason for the high brittleness of shaly sandstone in Mizoram compared with Upper Assam.

Early globalized industrial chain revealed by residual submicron pigment particles in Chinese imperial blue-and-white porcelains

The success of early Chinese blue-and-white porcelains relied heavily on imported cobalt pigment from the West. In contrast to art-historical concept, which contains both typological evidence and literature records, it is assumed that imported Sumali blue was completely superseded by domestic Chinese asbolane ore based on the analytical results of the Fe/Mn ratio in imperial productions from the Xuande reign (1426 to 1435 CE) onward. Using a focused ion beam transmission electron microscopy technique to reassess this hotly debated question, we have identified two classes of residual submicron pigment particles in the blue glaze with diagnostic differences in morphology, chemical composition, and distribution behavior. Compared with the microstructural features of the blue-and-white porcelains of the Yuan and Qing dynasties, we show that a mixture of imported and domestic cobalt pigments was used for aesthetic reasons, indicating that the overseas supply chain of imported pigment remained consistent and adequate even though the authorities had terminated official trade and tributary activities after the death of Admiral Zheng He. This discovery further suggests that the globalized trading network and cross-regional industrial chain had been extensively established in the 15th century. Moreover, we provide analytical evidence against the fundamental assumption of the current Fe/Mn provenancing criteria, implying that the failures of previous chemical analyses can be attributed to elemental differentiation between the silicate glaze and the arsenic pigment. We propose an innovative method for directly assessing original mineralogic information from submicron residual pigment particles that provides a more reliable way to trace cobalt circulation and holds great promise for provenance studies.

Review of tetrahedrites from Bulgarian deposits in the light of changes in nomenclature and classification of these minerals taken in 2019

The crystal-chemical peculiarities of the minerals in the tetrahedrite group are considered as a prerequisite for their role as indicators of the formation environment. Particular attention is paid to the silver-containing representatives because they comprise more than 60% of the Bulgarian tetrahedrites and because the recently adopted by the International Mineralogical Association changes in the nomenclature and classification within this group affect most sensitively them and their relation to a given series, mineral species or variety. The achievements of the Bulgarian mineralogical science in the study of tetrahedrites are briefly presented, and various aspects are considered, illustrating the efforts of the researchers to cover the diversity of these minerals as well as the opportunity to derive from this various crystal-chemical, geochemical and other mineralogical information. In the light of the adopted changes, already published data from 450 electron-probe microanalyses of samples from 45 localities distributed in three metallogenic zones in the country have been processed. The established crystal-chemical trends in the spatial distribution of tetrahedrites in Bulgaria generally confirm and extend the observations of previous researchers. It has been shown that, by their chemical composition, these minerals can be carriers of typomorphic characteristics, both for individual deposits and for metallogenic zones. The information and data provided may serve to: (i) correctly determine the mineral species of the newly investigated tetrahedrites and their affiliation to a given series; (ii) what compositions may be sought or expected according to the location of the investigated localities; (iii) comparing the new results to previous ones to confirm, correct or reject established models and trends.

Adsorptive removal of phenol using faujasite-type Y zeolite: Adsorption isotherms, kinetics and grand canonical Monte Carlo simulation studies

Phenol and its derivatives are hazardous pollutants commonly found in industrial wastewaters. Their removal is a high priority for avoiding adverse impacts on the environment. Herein, the removal of phenol from wastewater, used as a model organic contaminant, onto faujasite-type Y zeolite (NaY) was investigated using experimental and theoretical techniques. The surface morphology was studied by scanning electron microscope (SEM). Mineralogical information and the crystal structure of zeolite were determined by X-ray diffraction (XRD). Surface area measurements were obtained by employing the nitrogen adsorption method. The phenol adsorption at different adsorption temperatures and pH was studied through batch experiments. The isotherm analysis results showed that the Langmuir adsorption isotherm model was the most suitable to describe the adsorption of phenol on zeolite NaY. The results indicated that the adsorption kinetic data were followed more closely the Pseudo-second order and intra-particle diffusion models. Grand Canonical Monte Carlo (GCMC) simulations were used to simulate the adsorption isotherm of the phenol in the zeolite at different temperatures. From the simulation study, density distribution profiles, the isosteric heat of adsorption and the sorption energy distribution were investigated. The results are very promising and point to the need for further investigation.

New developments in field-portable geochemical techniques and on-site technologies and their place in mineral exploration

This paper focuses on handheld and top-of-hole techniques which have appeared since 2007 or have undergone major improvements, and discusses their benefits, challenges and pitfalls, why we use them and what to expect from them. There is an ongoing need to be innovative with the way we undertake mineral exploration. Recent technological advances that have been applied to successful mineral exploration include on-site or portable instruments, on-site laboratory technologies, various core scanners, and technologies for fluid analysis. Portable or field technologies such as pXRF, pXRD, pNIR-SWIR, µRaman and LIBS aid in obtaining chemical and mineralogical information. Spectral gamma tools, a well-known technology, recently took advantage of improved ground and airborne (drone) instruments, to complement hyperspectral imagery. At mine and exploration sites, top-of-hole sensing technologies, such as Lab-at-Rig® and various core scanners (both spectral- and XRF-based) have become useful tools to analyse metres of core as it is being drilled. Fluid analyses are not as common as analyses of solid materials, but there are advances in such technologies as anodic stripping voltammetry, polarography and ion-exchange electrodes aiming for analysis of commodity or environmentally important elements. Field-portable geochemical techniques and on-site technologies now offer instant response and flexibility for most exploration tasks. By providing relevant data within minutes, they allow safer field decisions and focus on the most promising finds, while saving valuable resources in sampling grids or drilling. More efficient laboratory analysis programs are supported by sample screening and homogeneity checking on-site. Field analyses are not always as accurate as laboratory ones, but most of the time can be correlated with them, enabling reliable decisions. The level of confidence in field-made decisions needs to be compared between later and less numerous laboratory analyses, and less precise but more abundant and immediate field analyses. It may be demonstrated that, in many cases, the fit–for-purpose nature of the latter allows a better confidence level. Quality compromises associated with field analyses can be reduced by the application of better sample preparation and quality assurance/quality control (QA/QC) procedures. Most of the further development of on-site chemical analysis is expected to be based on its integration with lab methods and on sound QA/QC practice, allowing a precise evaluation of its confidence level and uncertainties. Mineralogical analyses are constrained by our ability to interpret the data in near-real time but offer promising approaches in both surface and drilling exploration campaigns. Thematic collection: This article is part of the Exploration 17 collection available at: https://www.lyellcollection.org/cc/exploration-17

Provenance of Bengal Shelf Sediments: 1. Mineralogy and Geochemistry of Silt

This article illustrates a multi-technique frontier approach for the provenance study of silt-size sediments. The mineralogical composition of low-density and heavy-mineral fractions of four samples of fine to very coarse silt deposited on the Bengal shelf was analyzed separately for six different grain-size classes by combining grain counting under an optical microscope, Raman spectroscopy, and X-ray diffraction. The geochemical composition was determined on both bulk-sediment samples and on their <5-μm classes. Such a “multiple-window” approach allowed capturing the full mineralogical information contained in each sample, as well as the size-dependent intra-sample variability of all compositional parameters. The comparison between grain-size distributions obtained by different methods highlighted a notable fallacy of laser granulometry, which markedly overestimated the size of the finest mode represented by fine silt and clay. As a test case, we chose to investigate sediments of the Bengal shelf, where detritus is fed from the Meghna estuary, formed by the joint Ganga and Brahmaputra Rivers and representing the largest single entry point of sediment in the world’s oceans. The studied samples show the typical fingerprint of orogenic detritus produced by focused erosion of collision orogens. Bengal shelf silt is characterized by a feldspatho-quartzose (F-Q) composition with a Q/F ratio decreasing from 3.0 to 1.7 with increasing grain size, plagioclase prevailing over K-feldspar, and rich transparent-heavy-mineral assemblages including mainly amphibole with epidote, and minor garnet and pyroxene. Such a detrital signature compares very closely with Brahmaputra suspended load, but mineralogical and geochemical parameters, including the anomalous decrease of the Q/F ratio with increasing grain size, consistently indicate more significant Ganga contribution for cohesive fine silt. The accurate quantitative characterization of different size fractions of Bengal shelf sediments represents an essential step to allow comparison of compositional signatures characterizing different segments of this huge source-to-sink system, from fluvial and deltaic sediments of the Himalayan foreland basin and Bengal shelf to the Bengal Fan.

Mineralogical Imaging for Characterization of the Per Geijer Apatite Iron Ores in the Kiruna District, Northern Sweden: A Comparative Study of Mineral Liberation Analysis and Raman Imaging

The Per Geijer iron oxide apatite deposits are important potential future resources for Luossavaara-Kiirunavaara Aktiebolag (LKAB) which has been continuously mining magnetite/hematite ores in northern Sweden for over 125 years. Reliable and quantitative characterization of the mineralization is required as these ores inherit complex mineralogical and textural features. Scanning electron microscopy-based analyses software, such as mineral liberation analyzer (MLA) provide significant, time-efficient analyses. Similar elemental compositions of Fe-oxides and, therefore, almost identical backscattered electron (BSE) intensities complicate their discrimination. In this study, MLA and Raman imaging are compared to acquire mineralogical data for better characterization of magnetite and hematite-bearing ores. The different approaches demonstrate advantages and disadvantages in classification, imaging, discrimination of iron oxides, and time consumption of measurement and processing. The obtained precise mineralogical information improves the characterization of ore types and will benefit future processing strategies for this complex mineralization.

Ediacaran, Cambrian, Ordovician, Silurian and Permian shales of the Upper Yangtze Platform, South China: Deposition, thermal maturity and shale gas potential

For many years, the Yangtze Platform has been successfully explored and exploited for petroleum. The Lower Silurian Longmaxi Shale proved to contain commercial quantities of gas, but several other formations might also have a high potential for shale-hosted gas exploration. This paper comprises of geochemical, petrographical, petrophysical and mineralogical information on the major Proterozoic and Paleozoic gas shales in the Upper Yangtze area, which provides insights on the depositional environment, the thermal maturity of organic matter, shale gas storage capacity and the fracability of these rocks. The total organic carbon (TOC) content varies from 0.1 to 22.5% with an average value of 2.7% and most of these shales were deposited in an oxygen-depleted marine environment. Equivalent vitrinite reflectance (VRr) values range from 2.20 to 4.25%, indicating that all samples are in the gas generation window and lost a large amount of primary organic carbon. Porosity varies between 1.5 and 13.6% with an average value of 5.8%, while the excess sorption capacity ranges from 0.10 to 0.22 mmol/g rock. Minerology data show that quartz is the predominant mineral except for the Upper Permian Longtan Formation, in which clay minerals account for 29 to 84%. New data were combined with those from other publications and compared to information on other, well-studied shale-hosted gas systems.

Dispersed Geoheritage Points of the Lagonaki Highland, SW Russia: Contribution to Local Geoheritage Resource

Dispersed geoheritage points, which are small-sized and low-unique localities, manifest local geoheritage and, thus, may be useful for its comprehensive understanding. Field studies in the Lagonaki Highland (Western Caucasus, southwestern Russia) have permitted to find four geoheritage points that are described with argumentation of their importance to scientists, educators, and/or tourists. These points, none of which can be defined as a ‘traditional’ geosite, provide some precious sedimentary, palaeontological, and mineralogical information that improves perception of the local geoheritage landscape dominated by the Late Jurassic carbonate platform deposits. The studied localities are constituents of the local geoheritage resource because of their utility to three main categories of potential users. Scientists may be interested in these dispersed geoheritage points because of the need to collect massive geological data from big areas. Educators and tourists may appreciate these points because of their location along principal roads, i.e., their good accessibility.

Multimineral Fingerprinting of Transhimalayan and Himalayan Sources of Indus-Derived Thal Desert Sand (Central Pakistan)

As a Quaternary repository of wind-reworked Indus River sand at the entry point in the Himalayan foreland basin, the Thal Desert in northern Pakistan stores mineralogical information useful to trace erosion patterns across the western Himalayan syntaxis and the adjacent orogenic segments that fed detritus into the Indus delta and huge deep-sea fan throughout the Neogene. Provenance analysis of Thal Desert sand was carried out by applying optical and semi-automated Raman spectroscopy on heavy-mineral suites of four eolian and 11 fluvial sand samples collected in selected tributaries draining one specific tectonic domain each in the upper Indus catchment. In each sample, the different types of amphibole, garnet, epidote and pyroxene grains—the four dominant heavy-mineral species in orogenic sediment worldwide—were characterized by SEM-EDS spectroscopy. The chemical composition of 4249 grains was thus determined. Heavy-mineral concentration, the relative proportion of heavy-mineral species, and their minerochemical fingerprints indicate that the Kohistan arc has played the principal role as a source, especially of pyroxene and epidote. Within the western Himalayan syntaxis undergoing rapid exhumation, the Southern Karakorum belt drained by the Hispar River and the Nanga Parbat massif were revealed as important sources of garnet, amphibole, and possibly epidote. Sediment supply from the Greater Himalaya, Lesser Himalaya, and Subhimalaya is dominant only for Punjab tributaries that join the Indus River downstream and do not contribute sand to the Thal Desert. The detailed compositional fingerprint of Thal Desert sand, if contrasted with that of lower course tributaries exclusively draining the Himalaya, provides a semi-actualistic key to be used, in conjunction with complementary provenance datasets and geological information, to reconstruct changes in paleodrainage and unravel the relationship between climatic and tectonic forces that controlled the erosional evolution of the western Himalayan-Karakorum orogen in space and time.

Optimizing subsampling strategies for U/Th dating and geochemical proxies in carbonate speleothems

Since they provide the chronological frame on which paleoclimate and paleoenvironmental reconstructions are built, radiometric ages of carbonate speleothems, especially U/Th dating, are of fundamental importance to speleothem and paleoclimate sciences. Based on 17 aragonite-calcite speleothems from the Pont-de-Ratz Cave (S. France), we propose an integrated petrographical and geochemical approach for optimizing subsampling in speleothems. Portable energy-dispersive X-ray fluorescence was used as a fast and non-destructive in-situ trace-element screening of the speleothems. These geochemical results are combined with petrographical and mineralogical information to produce distribution maps showing the growth discontinuities and the identified primary and secondary (diagenetic) products on the speleothem slabs. Because they provide a clear and precise spatial distribution of primary and secondary carbonate phases at the sample scale, these maps constitute a valuable tool for selecting the position of subsamples for radiometric dating or environmental proxy analysis. The efficiency and reliability of our integrative approach is convincingly demonstrated by the remarkable coherence of U/Th ages both within and between speleothem samples.

Time‐gated Raman and laser‐induced breakdown spectroscopy in mapping of eudialyte and catapleiite

AbstractRaman analysis of rock samples containing rare earth elements (REEs) is challenging due to the strong fluorescence, which may mask the weaker Raman signal. In this research, time‐gated (TG) Raman has been applied to the construction of the mineral distribution map from REE‐bearing rock. With TG Raman, material is excited with a short subnanosecond laser pulse, and the Raman signal is collected within a picosecond‐scale time window prior to the formation of a strong fluorescent signal by means of single‐photon avalanche diode array. This allows signal readout with a significantly reduced fluorescence background. TG Raman maps are used to reveal the location of valuable minerals and are compared with the elemental distribution given by laser‐induced breakdown spectroscopy. The analysis was carried out from a REE‐bearing rock, nepheline syenite sample from the Norra Kärr deposit, where REEs are mainly hosted in eudialyte and catapleiite. The combination of these two complimentary laser spectroscopic methods offers valuable elemental and mineralogical information about rocks.

X-ray Microcomputed Tomography (µCT) for Mineral Characterization: A Review of Data Analysis Methods

The main advantage of X-ray microcomputed tomography (µCT) as a non-destructive imaging tool lies in its ability to analyze the three-dimensional (3D) interior of a sample, therefore eliminating the stereological error exhibited in conventional two-dimensional (2D) image analysis. Coupled with the correct data analysis methods, µCT allows extraction of textural and mineralogical information from ore samples. This study provides a comprehensive overview on the available and potentially useful data analysis methods for processing 3D datasets acquired with laboratory µCT systems. Our study indicates that there is a rapid development of new techniques and algorithms capable of processing µCT datasets, but application of such techniques is often sample-specific. Several methods that have been successfully implemented for other similar materials (soils, aggregates, rocks) were also found to have the potential to be applied in mineral characterization. The main challenge in establishing a µCT system as a mineral characterization tool lies in the computational expenses of processing the large 3D dataset. Additionally, since most of the µCT dataset is based on the attenuation of the minerals, the presence of minerals with similar attenuations limits the capability of µCT in mineral segmentation. Further development on the data processing workflow is needed to accelerate the breakthrough of µCT as an analytical tool in mineral characterization.

Soil Clay Mineralogical Phase Analysis of Ganges Floodplain Soils by XRD and XRF

Soil minerals study is vital in terms of investigating the major soil forming compounds and to find out the fate of minor and trace elements in soils. It is also essential for the soil-plant interaction purpose. To identify soil mineral phases especially clay minerals, X-ray diffraction (XRD) has been a popular technique. The clay mineralogical information of soils in Bangladesh is limited, especially in Ganges flood plain region (Agro Ecological Zone (AEZ) 12 and 13). Therefore, to overcome this limitation, in this study, we performed XRD analysis of <2 mm fractions soil samples of AEX 12 and 13. However, identifying mineralogical phases by XRD in <2 mm fractions soils is not so straight-forward due to many practical problems. We fully matched only two mineralogical phases in all the soil samples which is quartz and potassium-Aluminum-Silicate. However, the full XRD peaks indicate that more minerals are also present, but due to heterogeneity of soils samples, it is difficult to find other minerals phases by only XRD peak of <2 mm fractions. Therefore, to find more information about mineralogical phases, we performed XRF analysis that provides the elemental composition of minerals phase as oxide. XRF analysis indicated the presence of secondary minerals like illite and chlorite. The presence of high percentage Fe oxide not only indicated the iron mineral phase (goethite and ferrihydrite) but also indicated iron rich high charge smectite minerals (beidellite). The presence of iron rich smectite minerals in the Ganges sediments reported in several previous studies. Thus, we concluded that only XRD in <2 mm fractions of soils is not adequate to identify the mineralogical phases of soil samples. Others analyses like XRF, XRD in <2 μm fractions will be necessary to locate an entire image of soil mineralogical phases.

Automated sulfides quantification by multispectral optical microscopy

The mining industry needs effective techniques to meet the future challenges of resources extraction. As the deposits become more and more complex, a very good knowledge of an orebody is necessary. Mineralogical characterization is an essential contribution to improve the knowledge on the ore and wastes for a given mining project. It could bring major advances in ore extraction, mineral processing, and integrated waste management. However, mineralogical analyses can be very tedious, when done manually. Consequently, automated mineralogy was developed during the last three decades to improve the rapidity of mineralogical characterization, so that mineralogical information can be routinely obtained. Nowadays, the systems commonly used are based on expensive equipment including scanning electron microscopes (SEM) with energy dispersive X-ray analyzers (EDX). Optical Microscopy (OM) is neglected, although this route can provide reliable and quick results, yet cheaper. In this study, the possibility of using optical microscopy in reflected light mode to automatically characterize opaque minerals is explored. The identification and quantification of six common sulfides from polymetallic ores (arsenopyrite, chalcopyrite, galena, pyrite, pyrrhotite, and sphalerite) were automatically accomplished on a polished section by optical microscopy. Six spectral images were acquired for multispectral image analysis. Five of them were acquired under a white light source, equipped with four different excitation filters (436 nm, 480 nm, 605 nm, and 650 nm). The sixth image was acquired under an UV-light source at 365 nm, after modifying the optical pathway to detect the reflectance of the minerals in the UV-spectrum without changing the acquiring camera. Two image analysis software solutions were then tested to automatically classify and quantify the six sulfide minerals. The classification was systematically done on the acquired multispectral images by grey thresholding with the Clemex Vision PE® software. The GOCAD® software used principal component analysis (PCA) analysis and a supervised K-means clustering method to classify the minerals. Then, the obtained results were compared to the SEM-EDS quantification, considered here as the reference. The differences between the computed surface areas were mainly due to the artifacts of the polished sections preparation. The two software solutions present promising results and could be fully exploited to proceed to other mineralogical analyses, such as mineral liberation, mineral associations, textures identification, and particle size distribution. This study is an initial step towards differentiate and identify sulfides via an optical route arguably reliable and cheaper to characterize mine products.

The metallogenic environment of the Dounan manganese deposit, Southeast Yunnan, China: evidence from geochemistry and Mössbauer spectroscopic

The Dounan manganese deposit is a typical large-scale marine sedimentary manganese deposit of the Middle Triassic in China. The metallogenic environment and change process directly dictate the migration, enrichment, and precipitation of Mn. To better understand its metallogenetic environment, a detailed study was undertaken involving field observation, mineralogical and geochemical and Mossbauer spectroscopic analyses. The major findings are as follows: (1) Lithofacies paleogeography, sedimentary structural characteristics, and geochemical indexes indicate that the deposits were formed in an epicontinental marine sedimentary basin environment of normal salinity; (2) there were three ore phases including Mn oxides, Mn carbonates, and mixed Mn ores. The ore minerals found were braunite, manganite, Ca-rhodochrosite, manganocalcite, and kutnahorite. Petrographic and mineralogical information indicates that the metallogenic environment was a weakly alkaline and weakly oxidized to weakly reduced environment, and the mineralization occurred near the redox interface; (3) the V/(V + Ni) ratios, δCe and Fe2+/Fe3+ found in profiles of Baigu and Gake ore sections show that the redox conditions of the ore-forming environment were continuously changing; and (4) three Fe species, α-Fe2O3, para-Fe3+, and para-Fe2+, were found in hematite and clay mineral samples using Mossbauer spectrum analysis. The presence and distribution of these Fe species indicate that the deposit was formed in a typical sedimentary environment during the mineralization process. In summary, our study showed that redox was a key factor controlling the mineralization of the Dounan manganese deposit. Our results have led us to the conclusion that transgression and regression caused fluctuations in sea level, which in turn caused the change of the redox environment. Mossbauer spectroscopy is an effective tool for studying the redox conditions of the paleoenvironment in which sedimentary manganese deposits were formed.