Geochemical Point Of View Research Articles

Geochemical and isotopic tracers to define the aquifer’s vulnerability: the case study of the alluvial multi-aquifer system of the Friulian plain

The Friuli-Venezia Giulia Region (north of Italy) is characterized by the presence of high-quality freshwater resources which benefit local citizens, animals, environmental habitats, and also agriculture and production activities. Waters from wells, canal, and wastewater selected in the Fiume Veneto area, through a detailed lithological modeling, were sampled and analyzed to characterize them from a geochemical point of view. The chemical and isotopic characterization made it possible to establish provenance, and the average age of water used, making available the estimation of the relationships between recharge capacity and water use in the Fiume Vento area. The focus of this study is to define the average age of the resources based on the time required for the recharge contributions to compensate the losses induced by exploitation. The results made it possible to support the plans for a water balance using the provenance and average age of water sources for the protection of water reserves formed by the multi-aquifer system of the high and medium Friuli plain. The methodology applied has followed the legislation of the water directive considering the overexploitation due to unauthorized withdrawals of the sampling area.

On the elemental contents of aspen (Populus tremula L.) leaves grown in the mineralization area

The aim of this study is to investigate the behavior of major and trace elements in aspen leaves grown in an intensely altered region from a geochemical point of view. In this context, major and trace element contents of aspen leaves (Pop-ulus tremula L.) grown on Gümüştuğ (Gümüşhane/Türkiye) antimony mineralization were investigated. For this purpose, 56 leaf samples were collected from the field by grid method and at intervals of approximately 50–60 m. After routine sample preparation processes, analyzes were carried out to determine the major and trace element concentrations. Subse-quently, elemental concentrations of aspen leaves were evaluated by different statistical methods. As a result, major ele-ments Ca, Mg, Na, K, Al and S concentrations were determined in the range of 2%–3%, 0.23%–0.85%, up to 0.02%, 0.79%–2.01%, 0.01%–0.03% and 0.13%–0.43%, respectively. The trace element concentrations were determined in the range of 127–339 ppm, 86.7–265.30 ppm, 0.1–1.21 ppm, 13.5–453.20 ppm, 6.0–12.0 ppm, 14.0–82.0 ppm and 0.1–0.60 ppm for Mn, Sr, La, Ba, Ti, B and Se, respectively. Considering that the samples were taken from aspen leaves grown on the antimony mineralization, the concentrations of the antimonite element were determined above the detection limit in only a few sampling points in the study. But the concentrations of B, Mn, Sr, La of aspen (Populus Tremula L.) leaves are remarkable.

Comparative Study of Microbial Diversity in Different Coastal Aquifers: Determining Factors

Coastal aquifers have been extensively studied from the hydrodynamic and geochemical points of view, but there is still a significant gap in the knowledge of their microbial diversity. The bacterial communities of four coastal aquifers at different depths and salinities were studied in order to infer the anthropogenic and physico-chemical influences on groundwater microbiota. At the physico-chemical level, samples from different aquifers, but with similar salinities, are more similar than those taken within the same aquifer. The microbial community at the phylum level shows the dominance of Proteobacteria, Firmicutes, and Actinobacteria. Samples from the same aquifer, although having very different salinities, are more similar than samples with similar physico-chemical characteristics. Therefore, the taxa present in these media are resilient to environmental variations. The aquifer preserving the most pristine conditions harbors the lowest values of biodiversity, compared to those affected by anthropic activities. The incorporation of pollutants into the aquifer favors the development of a so-called “rare biosphere”, consisting of a high number of taxa which represent a low percentage (<1%) of the total microbial community. The analysis of microbial biodiversity in a coastal aquifer could be used as an indicator of the degree of anthropic alteration.

ГЕОХІМІЧНІ ТРИГЕРИ ВИКИДІВ ВУГІЛЛЯ ТА ГАЗУ ЗА РЕЗУЛЬТАТАМИ ТЕРМОЛІТИЧНОГО АНАЛІЗУ ROCK-EVAL

Purpose. Investigation of the conditions for the occurrence of coal and gas outbursts from a geochemical point of view. Methodology. The paper examines and analyses the results of determining bituminous and hydrogen indices using the Rock-Eval thermolytic analysis method on safe and dangerous areas of coal seams in terms of coal and gas outbursts. Results. It was established that on safe mining seams, coal samples are within the oil window, where microcracks in the coal mass may still contain films of sorbed bituminous components (liquid hydrocarbons), which counteract the accumulation of energy of elastic deformations and the localization of gas accumulation. However, the transition from the area of liquid hydrocarbon generation to the gas window leads to a sharp increase in the volume of generated hydrocarbon gases, mainly due to the cracking of liquid hydrocarbons, that is, the emergence of geochemical triggers for the localization of coal and gas outbursts during coal mining. Scientific novelty. The new experimentally determined values of bituminous and hydrogen indices for coal seams of the Donetsk basin, and their comparison with the results within safe and dangerous mining seams, demonstrate the fact that all the studied coal samples from outburst-prone areas geometrically lie in the area of the gas window, starting from the moment of cracking of already formed liquid hydrocarbons and subsequent generation of dry hydrocarbon gases (mainly methane) due to the thermal degradation of higher carbon compounds first, and then low carbon compounds (wet hydrocarbon gases) and direct generation from the kerogen matrix. Practical significance. Established geochemical criteria that determine the conditions for the occurrence of gas-dynamic phenomena - outbursts of coal and gas during coal mining. Key words: coal and gas outbursts, bitumen index, hydrogen index, microcracks, hydrocarbon generation, gas window.

Recording the largest gabbro-anorthositic complex worldwide: The Kunene Complex (KC), SW Angola

The Kunene Complex (KC) represents a large Mesoproterozoic igneous body, mainly composed of anorthosites and gabbroic rocks that extends from SW Angola to NW Namibia (18000 km2, N-S trend, and ca. 350 km long and 25–50 km wide). Although the KC has been studied from a cartographic and geochemical point of view, little is known about its structure at depth below the sedimentary deposits of the Kalahari basin. Hence, we use available satellite gravity data to estimate its extent and to unravel its morphology at depth. The Bouguer anomaly map depicts a gravity gradient from the coast (+200 mGal) towards eastern Angola (-150 mGal), which is explained by the transition from a young, dense and thin basaltic oceanic crust, formed during the Mesozoic Atlantic rifting, to an old, light and thick Archaean to Proterozoic continental crust (Congo Craton), to the east. The outcropping KC interrupts the gravity trend, showing at the western, southwestern and northeastern sides, several positive and isolated gravity anomalies linked to gabbroic intrusions associated to KC (ca. 50 km wavelength and −90 mGal). In contrast, the anomalies found at the central part of the massif (50 km wavelength and < -110 mGal) correspond to the dominant anorthositic members, according to the spatial correlation of the mapping. Five 2.5D gravity profiles have been modelled to investigate the unexposed eastern boundary, reconstructing the surface crustal structure (between 0 and 15 km depth) overlaid by the thin sedimentary cover of the Kalahari basin. The gravity modelling helps us to show that the KC was emplaced in the Upper Crust and extends in depth up to ca. 6 km, showing a lobular geometry and following a large NE-SW to NNE-SSW linear trend, presumably inherited from older Palaeoproterozoic structures. The lateral continuation of the KC to the east (between 50 and 125 km) beneath the Kalahari sediments suggests an overall size of at least twice the outcropping dimension (about 42500 km2). This statement clearly influences in the economic potential of this massif, related to the prospecting of raw materials and certain types of economic mineralization (Fe-Ti oxides, metallic sulphides or platinum group minerals).

Geochemical perspective on large dams changing the downstream sediment sources

Human activities play an increasingly important role in shaping Earth surface and changing river geochemistry. This study presents elemental concentrations of suspended sediments collected from the water depth profiles in two hydrological years in the lower Changjiang (Yangtze) River, aiming to discern how intense dam constructions (e.g., Three Gorges Dam) homogenize the source signals of downstream sediments in a large river basin. Our results show that sediment sources indicated by elemental ratios of Cr/Th, Co/Th and europium anomaly (Eu/Eu*) displayed seasonal changes in 2010–2011, while the seasonal variability disappeared in 2014–2015. After excluding the effects of hydrodynamic sorting and weathering processes, the waning seasonal variation can be best explained by the shift of downstream sediment source and sink roles with dam constructions. Different from the traditional view that the middle basin became the dominant source of sediment into the sea after dam constructions, we suggest that the middle basin actually act as a transition or buffer zone for the upstream-derived sediments. From a geochemical point of view, the sediments from the Changjiang River still feature a source signal of its upper basin above the Three Gorges Dam. Our study sheds new light on great and comprehensive influences of human activities on river sediment geochemistry, and highlights the need to carry out integrated studies on physical and chemical processes during sediment transfer from land to sea in fasting changing world.

Interpretation of Mineralization in the Western Carpathians (Polish Segment)—A Tectonic Mélange Approach

Quartz, carbonates and other minerals as e.g., realgar are present in veins and caverns in sedimentary rocks in the Western Carpathians. In the Polish segment, they have been characterized from the mineralogical, petrologic, and geochemical points of view, as well as fluid inclusions. Their characters are discussed from perspective of a description of particular types of chaotic complexes—the tectonic mélange zones, distinguished in the Western Carpathian area over the last two decades. The mélange zones are considered to be geochemical systems open to fluid flow, a site for mineral crystallization and/or migration zones of hydrocarbons and mineralized waters. In this context the tectonic mélange in the Jabłonki/Rabe vicinity (SE Poland, the Bieszczady region) in comparison to that of the Mszana Dolna tectonic window area are proposed as the examples. The trapping conditions of fluids (brine and methane) in the minerals in the mélange zones appear to have been 180–205 °C and ~550–570 bars, and 220 °C and 500 bars for calcite and quartz, respectively. The general trend of the increase in temperatures and pressures from west towards east and south-east in the mélange zones points to an increase in the degree of exhumation of different parts of the Carpathians.

Geochemical and mineralogical composition of geophagic materials from Baringo town, Kenyan Rift Valley and their possible health effects on the consumers.

Consumption of geophagic materials can be detrimental to human health. These materials, which are harvested from the natural environment, can contain high concentrations of potentially harmful elements and minerals. In this study, mineralogical and geochemical investigation of geophagic rock materials consumed by the local population in Baringo town, in Kenya, was conducted to assess its possible health effects. Twelve representative samples were purchased from an open market in Baringo town for this investigation. Optical and scanning electron microscope as well as X-ray diffractometer was used to determine the mineralogy as well as the morphology of the minerals present in the studied samples. The material is composed of about 10 to 20% coarse to very coarse (0.38-3.00 mm) and semi-rounded to angular crystals of quartz, feldspars, and amphiboles, together with lithic fragments occurring in a fine-grained matrix. X-ray fluorescence and inductively coupled plasma mass spectrometry were used to determine the major and trace elements composition, respectively. The analyses show that elements such as Si, Fe, Mn, Al, Hg, Cr, Cd, and Pb are particularly above their recommended daily allowances. This study assumes 100% bioavailability of elements in the geophagic materials, in the absence of a bioaccessibility test. Therefore, the consumption of some of the revealed elements, based on this assumption, can be detrimental due to possible short- and/or long-term health effects. From a mineralogical point of view, the presence of feldspar and quartz with Moh's hardness of 6 and 7, respectively, and their coarse and angular morphology may cause damage to the dental enamel and the gastrointestinal tract. From a geochemical point of view, the high concentrations of the revealed chemical elements can have various health effects including, but not limited to neurotoxic effects, which are critical in prenatal exposure, neurodegenerative diseases, and cancer amongst other serious diseases.

Marmora of the Traianeum of Italica (Santiponce, Seville, Spain): New data provided by archaeometric analysis

AbstractThis article aims to identify a series of stone materials used in the ornamentation of the Traianeum of Italica (Santiponce, prov. Seville, Spain), the imperial cult shrine commissioned by Hadrian in honour of his adoptive father, Trajan, from a petrographic, mineralogical, and geochemical point of view. The study highlights the simultaneous use of local and, above all, foreign marbles. Local marbles from Almadén de la Plata (prov. Seville) and Hill of Mijas (prov. Malaga) were used particularly for wall coverings and pavements, whereas Luni‐Carrara marble stands out as the preferred ornamental foreign marble used in column shafts, bases, capitals, balustrade finishes, and so forth. In addition, cipollino marble was mainly used for the column shafts of the hecatostylon portico, but the analysis has not been able to specify its exact provenance, whether it is from Euboea or local, possibly the area of Almadén de la Plata. However, given that this was a construction promoted by the emperor, it might be possible that it would have come from Greece.

Sedimentological, Geochemical and Hydrogeochemical Studies of Alluvial Fans for Mineral and Environmental Purposes (Case Study of Southwestern Iran)

The alluvial-fan sediments play a very important role in mineral reserves and underground water resources, though a comprehensive study on such sediments, especially from a geochemical point of view, is still lacking. In this research, a total of 22 particularly important alluvial fans across the Khuzestan Plain in the southwestern Iran were studied through field surveys, petrographic evaluations, and geochemical assessments. These investigations included particle size distribution studies, microscopic observation of 193 samples, subsurface study of 60 boreholes along 10 different sections, facies analysis on 46 different sections, and comprehensive geochemical studies through XRD, XRF, ICP Mass, and wet chemical analyses. Based on these studies, the sediments were found to be dominantly composed of gravel, muddy sand, silt, and clay. The sediments exhibited good roundness and good to fair sorting. The most abundant oxide in the study area being MgO followed by SiO2, Al2O3, and Fe2O3. According to the studies, most of the samples fell in the range of iron-bearing sandstones with rare cases of iron-bearing shales. Investigation of the geochemical indices showed the long sediment transport path from the source, humid climate, and moderate to extensive weathering of the deposit. The depositional setting was found to be dominantly an active continental margin and, to a lesser extent, a continental island arc. Investigating of the studied sediments provenance indicate a felsic to slightly basic source rock. The environmental studies were indicative of relatively low contamination of the region and abundance of rare earth elements including Y, Sc, Nd, La, and Ce, and the abundance of heavy elements including Cr, Zn, Pb, and Cd. Based on the mineralogical studies on the samples, the inter-grain cement in both gravel and conglomerate particles was found to be composed of calcite.

The Production and Marketing of Mineral Water in 21st Century Spain

Since the end of the last century, Spain has become a country of reference in the European Union due to its volume of bottled mineral water. This study aims to analyze the evolution of the key aspects of this sector over the last two decades. Through this research, it has been verified that (i) Spanish mineral water has been analyzed for a long time from a medicinal and geochemical point of view, and not so much in commercial analysis; (ii) water has great diversity due to the abundance of hydrogeological domains that this country offers; (iii) a very strict legal framework must be complied for its commercialization; (iv) its consumption has been growing; and (v) the business structure is characterized by the predominance of a small group of companies, with a very important role in multinational corporations. Three nature reserves: Montseny, Sierra Nevada, and Guadarrama Mountains, stand out from the rest of the Spanish territory in terms of catchment and packaging of natural mineral water, which is an increasingly strategic resource.

Palaeoweathering events recorded on siliciclastic continental deposits (Albian, Lower Cretaceous) in NE Spain

A set of materials from Teruel (NE Spain), which includes a karst bauxite deposit overlain by an Albian (Lower Cretaceous) kaolin-rich clay succession, has been characterized from a mineralogical, textural and geochemical point of view. The materials under study were examined by X-ray diffraction, optical and electron microscopy and by inductively coupled plasma (ICP) optical emission spectroscopy (OES) and mass spectroscopy (MS). The bauxite is pisolitic and predominantly red and the overlying clay succession is mainly made up of grey claystones. Upper-section of the clay succession is a layer with carbonate nodules and scarce pisolith-like particles that can be distinguished. The studied materials are mainly composed of kaolinite, coupled with gibbsite and accessory boehmite in the bauxite. Gibbsite is also identified in the layer with carbonate nodules. Mineralogical data, kaolinite crystallinity and the Chemical Index of Alteration indicate that the layer with carbonate nodules has recorded a weathering event that was not as intense as the one that led to the in-situ formation of the bauxite deposit. The geochemical behaviour of the analysed elements, especially the REEs, also supports the existence of a weathering event recorded in the layer with carbonate nodules, given the similar trends observed in this layer and in the bauxite. The weathering led to REE + Y leaching, with the HREEs being less mobile than the LREEs, and thus the Albian clay succession, except the layer with carbonate nodules, shows a greater potential as source of these strategic elements. The research has revealed that redox fluctuation made a significant contribution to the distribution of Fe and Ce during bauxitization concerning the precipitation of Fe oxides and accessory minerals such as those of the goyazite-crandallite series.

The “Stella Polare” Expedition (1899–1900): Study and Enhancement of the Rock Collection

The “Stella Polare Expedition” collection represents the rocks collected during the attempt to reach the North Pole in the winter of 1899–1900 by the Italian explorer Luigi Amedeo di Savoia, better known as “Duca degli Abruzzi”. The collection is currently kept on loan at the Regional Museum of Natural Sciences in Turin and belongs to the series of mineralogical-lithological collections owned by the University of Turin. It is unique from both the historical and the scientific points of view. It mainly consists of effusive magmatic rock samples, such as tholeiitic basalts, basaltic andesites and sub-intrusive rocks, such as dolerites. In the collection are also present sedimentary rocks (i.e. sandstone, siltite, jasper), high-grade metamorphic rocks (i.e. granulite) and a good number of mineralizations (i.e. quartz, opal, calcedony, calcite and zeolite), probably included within the effusive magmatic rocks in the form of veins or amygdales. From the geochemical point of view, it was possible to classify volcanic rocks as effusive products belonging to the sub-alkaline subduction-related tholeiitic series, which in turn can be distinguished into two main types, corresponding to basalts and basaltic andesites. Furthermore, the dolerites show geochemical features compatible with an oceanic environment analogous to Ocean Island Basalts, not or scarcely contaminated by the continental crust, in agreement with the geographic and geological position of the Franz Josef Land, located at the border of the Eurasian continental shelf and close to the Nansen depression ocean floor. The rediscovery and study of this collection have made it possible to enhance historically, and to deepen, with a scientific approach, the study of materials that would have been difficult to retrieve.

Geochemical and petrographic identification of stone quarries used for the construction of the Anahita Temple of Kangavar (West Iran)

The archaeological site of the Anahita Temple in Kangavar is one of the best-known stone monuments in western Iran and dates back to the Persian Empire period of Iranian history (about 550 BC to 650 AD). The Temple was constructed on a semi-artificial hill out of large stone blocks, many of which are cubic in shape, and short thick columns. In the Kangavar area (basin) there are various sites in which there is evidence of stone extraction. The aim of this paper is to characterize the stones used in the Anahita Temple of Kangavar and their correlations with the quarrying activities observed in the Kangavar regions. In fact, we tried to find out which of these quarries may have been the source of the stone blocks used in the construction of the Anahita Temple. To this end the stones used in the Temple have been characterized by conducting a multi-analytical study involving chemical, mineralogical and textural analyses including XRF, XRD and thin section petrography. The results show that although all the quarries could have provided the stone used in the construction of the Temple, the largest, most probable source was the Chel Maran quarry. It is due to the more similarity of stones used in the Anahita Temple and the samples from this quarry from geochemical point of view as well as the archaeological evidences present in this quarry. The results are also useful for conservators to select appropriate materials for reconstruction of the decayed parts of the Anahita Temple.

Neobvyklá žilná Cu-Zn-Ag-Pb-As-Sb-Se-Sn-Bi mineralizace z Jedové jámy u Vejprt v Krušných horách (Česká republika)

An extraordinary rich mineral assemblage consisting of 27 minerals has been newly discovered in quartz veins of the abandoned ore deposit, once exploited by the Drei König Mine, called also Giftschacht (Jedová jáma - Toxic shaft), situated approximately 2 km SE of Vejprty town. It includes 16 sulphides (plus one unnamed) with far prevailing arsenopyrite. In addition to common sulphides (chalcopyrite, sphalerite, galena and minerals of the tetrahedrite group), a wide suite of sulphosalts with substantial Bi-content was identified. Besides common bismuthinite and emplectite, also relatively rare Bi minerals (matildite, aikinite, hammarite, wittichenite), in the Czech Republic known from few localities only, have been found here. Bi is bound also in a rather exotic selenide bohdanowitzite and native bismuth. Bi is substantially present in some domains of tetrahedrites [tetrahedrite-(Zn), tennantite-(Zn) and tennantite-(Fe)]. In addition to local Bi enrichment, also Sn-minerals occur in the ore, represented by cassiterite and rare sulphides (kësterite and stannoidite). The presence of phosphates of the plumbogummite group [plumbogummite, goyazite and florencite-(Ce)] contributes to the remarkable mineral assemblage. From geochemical point of view, very interesting is the presence of florencite-(Ce), in which REE with dominating Ce are fixed. In addition, grains of fluorite, fluorapatite, rutile, topaz and aggregates of illite and a phase from kaolinite group are present. Supergene mineralization is represented besides limonite by abundant scorodite and rare strengite.

Опыт изучения перфорированной слюды из комплекса начального верхнего палеолита Монголии: трасологический анализ и датирование 40Ar/39Ar методом

Иногда в археологическом контексте могут быть обнаружены удивительные находки, которые не поддаются изучению классическими методами в силу своей уникальности. Небольшая тонкая пластина слюды со сверлением была обнаружена в 2015 г. на памятнике Харганын-Гол-5 в Северной Монголии. Комплекс горизонта 5, в контексте которого она найдена, определен нами как начальный верхний палеолит, датируемый временем около 38 тыс. лет назад (некалиброванных). Поскольку ни в один типологический ряд по украшениям эта пластина слюды не попадает, ее определили как предмет неутилитарного назначения. Использование слюды человеком фиксируется только с неолита, когда ее стали добавлять в тесто для керамики, а позднее, в Средневековье, она стала предметом торговли, поскольку использовалась в качестве оконных «стекол». Ее появление в комплексе начального верхнего палеолита поставило задачу доказать ее антропогенную модификацию, а поскольку слюда этого типа -мусковит — является довольно редкой, представилась возможность определить, откуда она была привнесена в бассейн Средней Селенги. Однако простого определения ее химического состава оказалось недостаточно. В статье мы приводим пример изучения этого предмета с позиций трасологии и геохимии. Впервые для территории Центральной Азии с помощью датирования 40Ar/39Ar методом стало возможным определить источник происхождения каменного сырья. Экспериментальное перфорирование мусковита также осуществляется впервые в мировой практике и выявляет специфику модификации этого типа сырья.

Mine Waste: Consolidation Behaviour of Precious Metal Tailings

All mine processing plants generate waste. These byproducts include waste rock and a fine-grained slurry referred to as ‘tailings’ (Beier, 2015). The primary objective of treating tailings is to remove water, to enhance strength and stiffness (Sobkowicz and Morgenstern, 2009). Studying the geotechnical properties of tailings is essential to understand consolidation behaviour and facilitate land reclamation. Moreover, the geochemical characteristics of tailings should be examined to examine the potential onset of acid rock drainage (ARD). Acid rock drainage occurs when pH falls below 4, which can cause metal heavy leaching as they become present in solution. This study investigates both the geotechnical and geochemical behaviour of precious metal tailings in atmospheric conditions. The geochemical parameters of interest are pH, redox potential (Eh) and electric conductivity (Ec). The Large Strain Consolidation test (LSC) was implemented to characterize the compressibility behaviour of the sample. Accordingly, the amount of deformation that the tailings underwent was measured as they were loaded to different effective stresses. In addition, the hydraulic conductivity or the velocity of water flow was measured at the end of each consolidation step. Furthermore, the chemical parameters were evaluated using standardized probes. The tailings exhibit high compressibility during self-weight consolidation due to a combination of high initial void ratio and a high initial saturated hydraulic conductivity. In addition, hydraulic conductivity decreases nonlinearly as the samples are loaded because loading reduces the pore volume. The permeability decreased two orders of magnitude during loading, from 2.14E-05 m/s to 1.60E-7 m/s. From the geochemical point of view, there is no significant change in pH as the tailings consolidate. In this scenario, the presence of calcium carbonate has an acid-neutralizing capacity. Moreover, there is a slight increase in both redox potential and electric conductivity due to exposure to the atmosphere. The increasing trend of redox potential had a slope of 10 mV per day. While the slope of electric conductivity was 9 mS/cm per day.

Anomaly delineation of porphyry copper deposits of Hanza Region through geochemical data analyses and multispectral remote sensing

Hanza region is located in the southern part of Urumieh–Dokhtar Metallogenic belt in southeastern Iran. This region includes six known porphyry copper deposits and it is considered as an ore- bearing region from geochemical point of view. The aim of this research is to examine effective processing techniques in the analysis of stream sediment geochemical datasets and ASTER satellite images. The processing methods have led to identification of eight new prospective areas. These methods are aimed at providing univariate geochemical maps. The stream sediment geochemical mapping for Cu and Mo was performed by the sample catchment basin approach. The results derived from this approach have been mapped in four classes associated with the first quartile, third quartile and threshold values obtained from Median Absolute Deviation method. False-colour composite and band ratio techniques were adopted as two well-known methods for the processing of an ASTER scene spanning the study area. Eight new targets for possible mineralization have been resulted from geochemical data analyses. Image processing techniques on the ASTER multispectral data have also revealed widespread hydrothermal alterations associated with the known porphyry copper deposits and the new prospects.

An investigation into the 87Sr/86Sr radiogenic isotope geochemistry of the manganese ore of the Kalahari Manganese Field with a view on hydrothermal fluid flow and related rare earth element enrichments

Abstract The Paleoproterozoic Kalahari Manganese Field is the largest known land-based manganese (Mn) deposit on Earth and comprises five erosional relics of the iron- and manganese-rich Hotazel Formation. A total of 19 manganese ore samples from the lower manganese ore horizon of the Hotazel Formation were selected for analysis based on their relative metasomatic alteration states. These samples range from primary diagenetic, classic supergene enriched, hydrothermally enriched (Wessels-type ore) and thrusted manganese ore. When normalised to Post-Archaean Australian shale composites, rare earth elemental analyses on the selected samples indicate significant relative enrichments within the thrusted manganese ore, an ore type that hasn’t been studied from a geochemical point of view, so far. A comparison between these respective enrichments and 87Sr/86Sr ratios indicates a distinct link between REE enrichments and associated alteration events, and a progressive increase in 87Sr/86Sr isotope values. An isotopic relationship between fluid infiltration events and REE redistribution within the Hotazel Formation has been established, highlighting unique isotope signatures necessary in better defining and characterising metasomatism within the Paleoproterozoic Kalahari Manganese Field.

Occurrence of albitite from Capo Malfatano, SW Sardinia: first report, characterization from mineralogy and whole-rock geochemistry

Within the sedimentary-volcanoclastic succession known as Bithia Unit (SW Sardinia) a decameter-wide albitite lens has been found and is here characterized from a geological, petrographic and geochemical point of view. Albitite is a yellowish, fine-grained body elongated and foliated according to the main schistosity of the hosting rocks (N20-25° - 40° NW). The rock is made up by plagioclase porphyroclasts in a fine-grained matrix of plagioclase (up to 80%) and quartz; both porphyroclasts and small grains in matrix are almost pure albite (Ab 98 ). Accessory phases are ilmenite, rutile, monazite, apatite and zircon. Bulk-rock chemical analyses show that the relative proportions of SiO 2 , Al 2 O 3 and Na 2 O strongly resemble those of pure albite. Major, trace and rare earth element (REE) contents strongly suggest geochemical affinity with the nearby Ordovician metavolcanics and orthogneiss from Capo Malfatano area described in literature. Furthermore, REE, Rb/Sr, Y/Ho and Zr/Hf ratios seem to exclude the involvement of a significant Na-rich fluid metasomatism.