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Hyper- and multispectral image analysis methods for mineral identification: two cases of study

Gisela Barroso Guerrero

Lithica SCCL

This study briefly reviews geological applications of optical remote sensing and puts in practice some data analysis methods through two cases of study: ore assessment through the analysis of a hyperspectral image of a test panel of mine samples, and the recognition of mine waste materials through the analysis of a multi-spectral satellite image of a mining site (Sotiel, SW Spain). Principal Components and Linear Discriminant Analysis were applied, as well as classification methods (Random Forest, Support Vector and Spectral Angle Mapper). We also analysed and interpreted the spectral signatures. In the case of the panel of mine samples, Random Forest classification was able to discriminate ore with a 96% of accuracy, which puts in evidence the interest of developing “in situ” systems for the fast assessment of ore grade based on hyperspectral sensors. In the case of the mining area, our results show a high consistency of ASTER spectral signatures with the spectra of the endmember minerals previously derived by Spectral Mixture Analysis from aerial hyperspectral imagery by other authors, and a similar geographic distribution of major contaminated areas is found. Water polluted by mine waste at different intensities in the mine ponds is detected in the ASTER imagery. Combining the high analytical capabilities of aerial hyperspectral imagery with the extensive monitoring capabilities of satellite imagery can be effective for the control of mining environments.


Recovery of Tantalum from different resources

Natalia Generowicz and Joanna Kulczycka

Mineral and Energy Economy Research Institute of the Polish Academy of Science (MEERI PAS).

Tantalum is a chemical element with important properties. It is used in industry and its numerous branches for instance in jewelry and watchmaking products. As a result, it is not uncommon for this metal to become an object of interest for a variety of buyers. After it has been bought back from the customers, tantalum can be recycled and, as a result, its full content can be retrieved. In economy, tantalum has become a ‘technology-critical element’ which is increasingly used in new technologies. This has led to a need to evaluate potential environmental impacts, which, in turn, requires knowledge of its concentration in the natural and industrial environment. This paper will present secondary sources of tantalum extraction and recycling, which makes it possible to limit the use of this raw material from natural sources, which are in increasing exhaustion. The analysis also includes the case study of the old Penouta mine, and processing of tailings from waste-rock heaps and ponds on these area. It is located in the innermost part of the Iberian Variscan Belt in Galicia in northwest Spain where two main formations crop out: the Viana do Bolo Series (high-grade metamorphic rocks) and the Ollo de Sapo Formation.


Mineralogical study of sediments from water courses of the Motajica mountain, Bosnia and Herzegovina (Croatian)

Ana Anzulović and Lucia Hergotić

University of Zagreb, The Faculty of Mining, Geology and Petroleum Engineering.

The igneous-metamorphic complex of Motajica is located in northern BiH, along the Sava River, at border with Croatia. The massif is a part of the Sava – Vardar zone which belongs to the unit of the inner Dinarides and Helenida. The central part of the massif is a granite intrusion, surrounded by Cretaceous-Paleogene contact in regionally metamorphic formations.

Watercourse sediments of draining streams were investigated exclusively the igneous part of the complex and the watercourse sediments of the stream that drain the igneous and metamorphic part of the complex. Granulometric analysis by sieving, magnetic method, was performed separations and XRD analysis. All analyzed samples of watercourse sediments show dominance sand fractions (39–78% by weight), while samples of watercourse sediments draining granites show a higher proportion of silt (7–11% by weight) than those draining granites and metamophytes (3.8–8%).

The presence of the main minerals characteristic of granites (quartz, plagioclase, feldspars, mica) and the main minerals characteristic of the surrounding metamorphic formations (chlorite, amphibole). With described mineral composition, watercourse sediments from streams that drain granites also contain clay minerals, hematites and chlorite, which indicate subsequent hydrothemal changes of granite (chloritization, hematitization, sericitization), while the occurrence of tourmaline in watercourse sediments draining granites and metamorphites indicates the occurrence of Graisen mineralization upstream of the sampling site. Analyzes confirm that watercourse sediments reflect the geological structure of the investigated terrain and indicate later Grazian and hydrothermal alterations.


Fluid inclusions and geochemistry of Peña del Seo W-deposit, northwest Spain. Controlling mechanisms fot tungsten deposition

Sara Bergström

Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.

The Peña del Seo tungsten-greisen deposit in northwestern Spain is situated in the tin (Sn)-tungsten (W) metallogenic province of Europe - one of the richest tin-tungsten (tantalum-lithium) mineral provinces in the world. The Europe Union´s current goal is to become self-sufficient of these commodities in the near future and the iTarg3T project was launched in order to improve the understanding and provide innovative exploration methods of these types of deposits.

This master thesis will contribute to the iTarg3T project. The aim was to determine which physico-chemical conditions (temperature, pressure, salinity) that prevailed during the emplacement of Peña del Seo deposits.

A geochemical study was done consisting of a fluid inclusion study on the quartz veins from the deposits, and a whole-rock geochemistry analyse of the granitic rock. Homogenisation temperatures ranged bertween 97.6º to 325.6ºC and salinities (NaCl % equiv.) between 0.2% to 21.3%. The fluid was determined to consist of a two-component system of H2O and NaCl based on eutectic temperature. Based on its geochemical classification the granitic rock was considered to be an alkaline granite, strongly peraluminous with S-type characteristics. At least two different type of fluids were present during the emplacement of the Peña del Seo deposits, one that was hot and with a moderate salinity, and one that has a lower temperature that the other fluid and a lower salinity, possibly meteoric water.

The depositional mechanism of tungsten is thought to be caused by a combination between mixing bertween two fluids and cooling of the fluids, with the main depositional mechanism being cooling since the change in salinity was not of such magnitude that ir would change the fluid chemical composition, while the decrease in temperature was. It is uncertain whether the granitic rock found at Peña del Seo is part of the granitic cupola of the greisen system. The granitic rock has similar characteristics as the leucogranites of the West Asturian-Leonese Zone and based on quartz vein morphology, which cut the D2 foliation, time of emplacement of the deposit could be linked to the syntectonic event at 320-310 Ma. If the relation between the granitic rock and the greisen system can be determined the time of emplacement would be possible.


Structural control on the Peña del Seo tungsten-greisen vein deposit, northwest Spain

Ida Kronsell

Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.

Tungsten is listed on the European Commission list of critical raw materials that are crucial to Europe’s economy. By raising awareness of tungsten as a critical raw material the EU can prioritise to enhance exploration, mining and recycling of tungsten. In this thesis the structural relationship between wall rock and veins, in a greisen-tungsten vein deposit, were analysed with the intention to interpret how tectonic deformation events control the emplacement of tungsten-bearing veins. The objective of this thesis is to investigate if and how structures controlled hydrothermal fluid flow and ore formation in the Peña del Seo tungsten-greisen vein deposit.

Greisen systems are associated with tin and tungsten-bearing minerals and are related to intrusive magmatic bodies of granitic composition. Greisen-related granites (leucogranites), form at shallow depths in the crust (1.5-4 km) generally in intracontinental tectonic settings such as orogenic belts.

The study site is located in the West Asturian-Leonese Zone in northwest Spain. This zone marks the transition between the foreland and the hinterland and is recognized as being part of a continental margin, where Palaeozoic rocks were deposited unconformably. These rocks were subsequently subjected to folding during the Variscan orogeny (370-290 Ma). Three main types of structures were generated due to three deformational phases (D1, D2 and D3) during the Variscan orogeny. D1 resulted in east-verging recumbent folding and formation of a related axial-planar parallel cleavage (S1), D2 resulted in displacement along large thrust sheets and D3 produced upright folding and refolding of F1 folds.

Geological mapping with a focus on structural geology was carried out in March 2019, covering an area of approximately 0.25 km2. Structural measurements and oriented rock samples for microstructural study in thin sections were collected in the field. Additionally, photogrammetric mapping of structures was performed on a 3D photogrammetry model derived from a UAS survey.

The geometry of the Peña del Seo tungsten-greisen vein deposit is interpreted to result from two major deformation events. The axial planar foliation (S1) at Peña del Seo is correlated to the regional fabric that developed during D1 of the Variscan orogeny. The related F1 folds are caused by buckling accompanied by flexural slip folding mechanism during D1. Forceful intrusion of the granite underlying the Peña del Seo deposit caused bending of the overlying rocks layers during D2. Layer-parallel stretching is likely to have caused tension fractures perpendicular to bedding in the outer arc of the F2 fold hinge. The formation of local crenulation and related spaced cleavage can be explained by layer-parallel shortening in the inner arc of the F2-fold. Local transposition of S1-foliation occurred during emplacement of quartz veins and explains the different orientation of strike of foliation between the northern and southern parts of the area. Fractures forming during formation of F2-fold are likely to have worked as conduits for ascending hydrothermal, ore-bearing fluids forming the Peña del Seo tungsten-greisen vein deposit.

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