Mineralogical Varieties Research Articles

In-Depth Characterization of Natural Clays from Southeast Albania

Clays have been exploited in the manufacture of diverse products from ceramics to paints, pharmaceuticals, plastics, cosmetics, and more. Thus, they can be used in many industrial applications, showing good adsorbent ability thanks to their lamellar structure, high cation exchange capacity, pore size distribution, and large surface area. For this reason, considerable attention has been paid to their in-depth characterization, for further integration in sectors such as biomedicine, construction, remediation, aerospace, and nanotechnology. For this aim, two samples of natural clays, ALO1 and PRE4, from the southeast part of Albania, were subject to a multi-methodological characterization, with the aim of addressing the use of such geomaterials in possible sensing applications. X-ray fluorescence analysis, morphological characterization of the samples, and energy-dispersive system spectroscopy pointed to an extreme mineralogical variety, with kaolinite in AL01 and montmorillonite in PRE4 as the most abundant phases. This fact was further confirmed by powder X-ray diffraction, showing a quartz content of 20%, a kaolinite content of 64%, and a muscovite content of 16% for ALO1; meanwhile, for PRE4, we found a content of quartz of 45%, a content of montmorillonite of 34.9%, and a content of clinochlore of 20%. Infrared spectroscopy and thermal analyses confirmed the presence of hydroxyl groups in both samples, suggesting a higher content in ALO1. Measurement of N2 adsorption isotherms on the clay samples yields specific surface areas of 87 m2/g for PRE4 and 32 m2/g for ALO1, pore volumes of 0.721 cm3/g for PRE4 and 0.637 cm3/g for ALO1, and similar pore sizes in the range of 6–12 nm. Electrochemical analysis highlighted a good conductivity of ALO1 and PRE4 when used for the modification of commercial carbon-based screen-printed electrodes. In detail, higher currents were registered by differential pulse voltammetry for the electrodes modified with the clays with respect to bare electrodes, as well as good repeatability of the measurements. In addition, a comparative study with nanomaterials, known for their good conductivity, was achieved, using carbon black and gold nanoparticles as a reference, showing that the conductivity of the clays was lower than but not so different from those of the reference materials.

Identification of mineralogical ore varieties using ultrasonic measurement results

Purpose. To improve the measurement and information base of ultrasonic measurements rock characteristics to assess their mineralogical varieties. It is proposed to use a combination of measurement results of the acoustic quality factor of the test sample in relation to longitudinal and transverse ultrasonic waves, as well as the characteristic coefficient based on the dispersion and the average amplitude value of the received signal, for fuzzy identification of mineralogical and technological varieties of iron ore. Methods. As elastic waves propagate through the rock mass, they undergo attenuation due to absorption and dissipation of ultrasonic signal energy. The degree of attenuation, as well as the wave propagation velocity, is dependent on the physical-mechanical and chemical-mineralogical properties of the medium through which they travel. In this paper, we analyze a rock characterized by a complex structure comprising ore inclusions and surrounding matrix, each of which differs in its physical-mechanical and chemical-mineralogical properties. In particular, in iron ore samples, the distribution of mineral grains and aggregates exhibits significant heterogeneity in terms of both amount and size. Findings. An iterative method of fuzzy identification of mineralogical-technological iron ore varieties, based on the analysis of their properties in vector space of features, allows, by minimizing the sums of weighted distances between the analyzed and reference values of ultrasonic measurement results, to attribute them with a certain degree of belonging to the main technological types of ores mined at the deposit, and define them as magnetite quartzite with a confidence probability of 0.93. Originality. As an information base for identification of mineralogical iron ore varieties, the results of measuring the velocity and attenuation of longitudinal and transverse ultrasonic waves of appropriate frequency are used, on the basis of which the acoustic quality factor of the rock sample is calculated, as well as the characteristic parameter S, which is determined by the dispersion and average values of the received ultrasonic signal intensity, which has traveled a certain distance in the studied environment. Practical implications. The results of tests and practical approbation of the method for identifying mineralogical iron ore varieties based on the data of ultrasonic well logging testify to its high efficiency, which allows recommending the developed scientific-technical solutions for wide industrial application at mining enterprises.

Bentonite Clays from Southeastern Spain as Sustainable Natural Materials for the Improvement of Cements, Mortars and Concretes

The effects of global climate change are becoming more evident and accelerating at an unprecedented pace. For this reason, human activities urgently need a paradigm shift to stop this entropic process before the consequences become irreversible. In this sense, the use of highly eco-efficient materials aimed at conveniently neutralizing CO2 greenhouse gas emissions entering into the atmosphere can contribute significantly to mitigating and reversing this process. This work aims to demonstrate the positive effects obtained when Portland cement is partially replaced by bentonite clays of volcano-sedimentary origin. The samples were initially characterized by various methods, such as Thin-Section Petrographic Study (TSP) and the analysis of mineral phases with XRD, chemical composition was determined via XRF, and morphological analysis was determined via scanning electron microscopy (SEM). To determine the technical properties of the samples, a qualitative chemical analysis (QCA) was performed, as well as a chemical analysis of pozzolanicity (CAP) at 8 and 15 days, respectively, and a study of the mechanical compressive strengths at 2, 7, 28 and 90 days. Characterization studies using TSP, DRX, FRX and SEM established that these bentonite clays have a complex mineralogical variety, composed mainly of smectite, mordenite, plagioclase and biotite, as well as altered volcanic glass and sericite. The results of the qualitative chemical analysis establish that more than 93% of the SiO2 present in the samples is reactive. Chemical analysis of pozzolanicity (CAP) showed significant pozzolanic behavior in all samples analyzed at both 8 and 15 days, while mechanical tests highlighted significant increases in mechanical strengths, with maximum values varying between 52.2 and 70.6 MPa at 90 days. These results show that the materials can be used as quality pozzolans for the manufacture of cements, mortars and concretes, which could be considered as a favorable factor and, therefore, relevant in the management and control of greenhouse gas emissions responsible for the deterioration of the environment.

ГЕОХИМИЧЕСКИЕ ПОСЛЕДСТВИЯ ЗАХОРОНЕНИЯ УГЛЕКИСЛОГО ГАЗА В ТЕРРИГЕННЫХ КОЛЛЕКТОРАХ

The paper is aimed at the research practice on identifying the features of interaction in the water-rockcarbon dioxide system in relation to terrigenous reservoirs, widely occurring in hydrogeological basins in the territory of the Russian Federation and potentially suitable for the placement of carbon dioxide. As the CO2 solution is saturated, along with an increase in total dissolved solids there is a naturally-determined increment in the volume of transition of ions into their complex forms. The main macro components (Ca2+, Mg2+, Na+, K+, (SO4)2–, Cl– ) migrate mainly in the form of their own ions, with a decrease in their fraction by an order of 1–3 % with an increase in mineralization. Ions such as Fe, Al3+, Mn3+, (NO3)–, (HCO3)–, SiO2, (NH4)+, (NO2)– are prone to transition into the form of complex compounds, the fraction of which in the total volume increases with the amount of saturation of solution with carbon dioxide. When CO2 is injected into the terrigenous reservoir, there is a natural decrease in the solution pH, absence of precipitation of carbonates and minimal changes in the rock porosity. The observed process of dissolution of primary aluminosilicate minerals (albite, anorthite, potassium feldspar) is characteristic of most of the considered mineralogical varieties of reservoirs, when they are saturated with CO2. This process is accompanied by deposition of secondary mineral phases in the form of montmorillonites, illites, chlorites, etc. Taking into account the low rates of these reactions, no significant changes in reservoir properties are noticed.

Recognition of mineralogical and technological varieties of iron ore on the basis of ultrasound backscatter spectrograms

The research is aimed to the analysis and modeling of the process of propagation of ultrasonic waves in iron ore samples to assess its mineralogical varieties. The paper analyzes domestic and foreign experience in modeling of ultrasonic waves propagation; methods of mathematical and computer modeling were used, as well as methods of mathematical statistics and probability theory for analysis of the results. Scientific novelty consists in developing and substantiating a method for recognizing the mineralogical and technological varieties of iron ore of a developed deposit based on spectrograms of a backscattered ultrasonic probing signal. Practical valueconsists in developing a methodology for non-contact non-destructive mineralogical analysis of iron ore to improve the efficiency and quality of its further processing and preparation for metallurgical processing. results. As measurable characteristic estimates of textural and structural features of iron ore varieties the results of spectral analysis of the reversed radiant ultrasonic signal were used. To implement the measurement results classification procedure, Adaptive Neuro-Fuzzy Inference System is used. At the vector of parameters of membership functions of terms of input variables and the vector of coefficients of linear functions in the conclusions of the rules was formed based on the characteristics of the processed ore and the spectrograms of the backscattered ultrasonic signal. The average accuracy of recognition of magnetite, chlorite-carbonate-magnetite, hematite-magnetite, magnetite-cummngtonite-chlorite-siderite mineral varieties of iron ore of the studied deposit was 93%.

Le Jade, plus qu’une pierre. Décoder la pierre précieuse emblématique de l’empire du milieu…

Jade is considered one of the most precious stones in the world. In Chinese, 玉 Yù is a word used to describe a very beautiful gem, it could also be simply translated by « precious ». It is the general name for “jade” and its different mineralogical varieties, such as jadeite and nephrite. Jade is this incredible material of various aspects, associated with numerous symbolics, much desired by collectors and jewelers all around the world. But to truly understand Jade, it is imperative to look further than just its gemological properties. One needs to understand its place and importance within Asian culture to understand its worth. As its rarity increases, so does the apparition of various treatments and imitation of jade within the market.

The effects of highly reduced magmatism revealed through aubrites

AbstractEnstatite‐rich meteorites, including the aubrites, formed under conditions of very low oxygen fugacity (ƒO2: iron‐wüstite buffer −2 to −6) and thus offer the ability to study reduced magmatism present on multiple bodies in our solar system. Elemental partitioning among metals, sulfides, and silicates is poorly constrained at low ƒO2; however, studies of enstatite‐rich meteorites may yield empirical evidence of the effects of low ƒO2 on elemental behavior. This work presents comprehensive petrologic and oxygen isotopic studies of 14 aubrites, including four meteorites that have not been previously investigated in detail. The aubrites exhibit a variety of textures and mineralogy, and their elemental zoning patterns point to slow cooling histories for all 14 samples. Oxygen isotope analyses suggest that the aubrite parent bodies may be more heterogeneous than originally reported or may have experienced incomplete magmatic differentiation. Contrary to the other classified aubrites and based on textural and mineralogical observations, we suggest that the Northwest Africa 8396 meteorite shows an affinity for an enstatite chondrite parentage. By measuring major elemental compositions of silicates, sulfides, and metals, we calculate new metal–silicate, sulfide–silicate, and sulfide–metal partition coefficients for aubrites that are applicable to igneous systems at low ƒO2. The geochemical behavior of elements in aubrites, as determined using partition coefficients, is similar to the geochemical behavior of elements determined experimentally for magmatic systems on Mercury. Enstatite‐rich meteorites, including aubrites, represent valuable natural petrologic analogues to Mercury and their study could further our understanding of reduced magmatism in our solar system.

Architectural Significance of Granite and Other Durable Rocks in the Context of India – An Analytical Study

Architectures created through the cutting of naturally occurred massive rocks include different structures, buildings, tombs, monuments, caves and sculptures. On account of hard and tough property, the granite is considered as strong construction stone in human history. Granite is very common in the continental crust of our mother earth. It is characterised as coarse grained plutonic intrusive igneous rock and is composed of quartz, alkali feldspar and plagioclase. Typical mineralogical character and textural varieties of granite facilitates to develop a wide range of colours, which include white, pink and grey etc. Granite rocks established itself as praiseworthy architecture stone since historical past because of its distinctive character like durability, appreciable finishing, fascinating polish nature and above all its magnificent colour diversities. As architectural stone, the granitic rocks demand attraction owing to the combination of style and elegance. The application of granitic rocks is witnessed in the ancient world through the mesmerising major architectures in India and around the world like Mount Rushmore, Washington Monument, Great Pyramid of Giza; Ajanta and Ellora caves, monolithic structure in the Zagwe-built Lalibela in Ethiopia along with in most of the long-lived old Indian temples, old forts and monuments etc. The monolithic free-standing architecture is generally rock-cut structures as depicted in the Ellora Kailasanathar Temple. The biggest monolithic statue in world, the Gommateshwara statue of Bahubali at Shravanabelagola present in the Indian state at Karnataka was carved in the 983 CE from a single block of granite rock. The radioactivity stuff in the granite is an important concern to the people in recent world. Even though the impact of radioactivity is proved mostly very less harmful to mankind, current research indicates that few granite products are showing radioactive substance index beyond permissible limit of the specified standard, which is responsible for environmental pollution during the use for long. Therefore, due attention is required towards the pertinent issue of radioactivity in the granite stones. Apart from granite, many of the architectures in India are created by the other rock types that include rocks like sedimentary, metamorphic and igneous rocks.

Naturally Occurring Asbestos in Valmalenco (Central Alps, Northern Italy): From Quarries and Mines to Stream Sediments

ABSTRACT The Valmalenco area (central Alps, northern Italy) is an excellent case study for naturally occurring asbestos (NOA) because of the huge outcrops of serpentinites and widespread quarrying and mining activities. Extensive sampling of rocks, soils, stream sediments, and airborne asbestos has been in progress since 2004. The combined use of scanning electron microscopy and transmission electron microscopy has proven to be effective for the correct discrimination between asbestiform and non-asbestiform mineralogical varieties (but falling into the World Health Organization fiber definition), whereas phase contrast microscopy has not proven suitable because of the very small size of fibrils after strong mechanical fragmentation. The quantitative analysis of “massive” samples (rocks, soils, and sediments) requires accurate and representative sampling as well as specific counting and discrimination criteria to determine NOA. Over a decade of experience has allowed us to identify critical issues and adopt effective preventive measures.

Finding Deep Concentration Techniques for Rich Iron Ore of the Kursk Magnetic Anomaly

—The research results on deep concentration of basic mineralogical variety of natural rich ore to obtain high-quality iron ore product for metallization are presented. The main methods of mineral dressing (selective crushing, magnetic separation in weak and strong fields, gravity separation and flotation) are tested in the technological experiments. It is shown that high-quality iron ore product can be obtained from natural rich ore using a simple technology. The simple technology should be applied at the first stage of processing for maximum possible extraction of high-quality product. Wet separation processes should be used at the later stage as they unavoidably result in high loss of marketable product, as well as bring difficulties connected with dewatering and drying.

An Investigation into Different Correlation Methods between NMR T2 Distributions and Primary Drainage Capillary Pressure Curves Using an Extensive Sandstone Database

Many workers have recognised the link between Nuclear Magnetic Resonance (NMR) derived T2 distributions and pore size distributions in reservoir rocks. This property has been used to develop models to obtain primary drainage capillary pressure curves from T2 distributions. These models often assume that the rocks pore space resembles a simple bundle of capillary tubes. They do not consider the existence of multiple pore body connections and pore body restrictions/throats. The most successful models utilise variable scaling factors to convert T2 times to pore diameters and hence capillary pressure. The variable scaling factor approach recognises the existence of variable surface relaxivity throughout the pore space due to variations in mineralogy and pore topography. This investigation uses SCAL data from the ART NMR Sandstone Rock Catalogue to obtain core calibrated variable scaling factors for 174 reservoir sandstone samples. The depositional environments for these samples include; aeolian, fluvial, coastal and shallow and deep marine. The samples used have a wide variety of mineralogy, diagenetic overprints and cover six orders of magnitude in absolute permeability. Three different methods for obtaining the scaling factors are presented and the relative merits of each discussed. A global model to predict capillary pressure from NMR T2 distributions in reservoir sandstones has been developed using correlations between the variable scaling factors and permeability.

Study of mineralogical variability of ferruginous quartzites of productive strata of the eastern wing of the Petrovsky synclinal fold with using diagram Mm-Mo

Relevance of the problem. Petrovsky deposit is promising area for the extraction of magnetite ores. Detailed research on this deposit was carried out in the 80 years of the last century, but with the deepening and expansion of the pit data from previous studies have lost their relevance. In 2016-2018 years, in the north-eastern part of the deposit, an in-mine exploration in the direction of the eastern wing of the Petrovsky synclinal fold was carried out.Analysis of previous research. Petrovsky deposit of ferruginous quartzites is located in the remote southwestern part of the area of the Right Bank magnetic anomalies. Two groups of rocks were defined in the geological structure of the deposit: the crystalline rocks of the Precambrian base and the loose Cenozoic deposits that were on the top of them. Rocks of the Precambrian Age are highly metamorphosed and dislocated ones of the crystalline base and are represented by Archean and Lower Proterozoic formations. Lower Proterozoic formations are represented by the Ingul-Ingulets series which is divided by the (bottom up): zelenorichenska, artemivska, radionivska suites. The Artemivska suite is productive in the territory under investigation.In the structural plan, the Petrovskiy deposit is a compressed synclinal fold, the western wing of which is taper out, and the eastern wing extends in the northern direction. In connection with this, the object of research was the eastern wing.Purpose and tasks of research. The main purpose of the study was identification of the mineralogical variability of ferruginous quartzites, the allocation of mineralogical varieties of ores according to their chemical composition and to determine the regularities of expanding of these varieties within the productive strata of the eastern wing. These tasks were resolved using chemical analysis of rocks data, calculation of magnetic module MM and oxidation module MO, and the construction of a diagram in the coordinates of magnetization-oxidation of iron (MM-MO).Presentation of the main material of the article. Within the eastern wing of the Petrovsky synclinal fold, the eight mineralogical varieties of the ore were identified: silicate quartzites with magnetite, silicate-magnetite quartzites, magnetite-silicate quartzites, magnetite quartzites with hematite, hematite-magnetite quartzites, magnetite-hematite quartzites, hematite quartzites with magnetite. In the boundaries of the work area of a regular change of varieties of ores from hematite quartzites with magnetite in the central parts to silicate quartzites with magnetite on the periphery was established. In the same direction the regularities of changing the content of Fetot., Femagn. and sulfur (S) were elaborated. However, the authigenic-mineralogical zonality of the productive strata of the eastern wing of the syncline structure of the deposit was disturbed as a result of the overprint of metasomatic processes caused by the formation of bodies of aegirine and rebekitic metasomatites on the basis of ferruginous quartzites was established.

Combined vibrational, structural, elemental and Mössbauer spectroscopic analysis of natural phillipsite (zeolite) from historical eruptions in Tenerife, Canary Islands: Implication for Mars

The outcrop of “Las Arenas” volcano in Tenerife, Canary Islands (Spain) has been presented as Terrestrial volcanic analog for ancient Mars, showing a great variety of alteration processes and interesting mineralogy. The current analysis has been done by means of measurement techniques used or proposed on Martian studies. The new analysis of the zeolite has been carried out using Raman spectroscopy, Mössbauer spectroscopy, X-ray diffraction (XRD), Infrared spectroscopy, Laser induced breakdown spectroscopy and Scanning electron microscopy (SEM-EDX). The zeolite has been carefully analyzed using vibrational spectroscopy and it has been identified as Ca-phillipsite. The other techniques support and confirm the results. The measurements and results using the Raman Laser Spectrometer (RLS) simulator system show the capabilities RLS system in the ESA Exo-Mars mission. The chemometrical methods for the vibrational mineral detection show the advantages of Raman spectroscopy to understand the possible geological context. Furthermore, the proposed diagenesis and formation of the zeolites in southern part of Tenerife island have been confirmed by the twin space prototypes used. A new hypothesis about the origin for the special case of “Las Arenas” volcano Ca-phillipsite has been proposed. Finally, a multi-complementary comparison among the different techniques used on the current studie has been done and, also an analogy with the next space mission has been established. These analyses emphasize the strength of the different techniques and the working synergy of the different techniques together for planetary space missions.

Petrographic and structural analysis of exposed rocks of Musawa Sheet 56, Northwestern Nigeria

This work is among the few studies conducted in Musawa sheet 56 NE, which is part of the basement complex rocks of TudunWulli - Kankia area. The study area lies between Latitude 12º 19ʹ 00ʹʹ to 12º 23ʹ 00ʹʹN and longitude 7º 42ʹ 00ʹʹ to 7º 46ʹ 00ʹʹN. Due to the continuous play of geologic processes on the earth, there is the need to continuously update the geology of the Nigeria basement complex as this has a very important economic implication especially in areas like mineral and groundwater exploration. Equally, less attention has been given to this sheet unlike other sheets within the zone. The study done in this area has revealed the various rock types and their geological characteristics: field relation, macroscopic and microscopic features as well as structural elements. Results from the study shows that the area consists of granite, migmatite- gneiss and quartzite which all display a variety of colors, textures and mineralogy. Careful analysis of the distinctive mineralogy, textures, optical and structural characteristics led to the nomenclature of the rocks. The migmatite-gneiss display two petrographic varieties base on their foliation: one with linear foliation of alternating light and dark color minerals, and the other with wave like foliation. While granite is generally fine to medium grained in texture. The dominant structural trend of joints and faults in the study area are NNE-SSW and NW-SE. All these trends are consistent with the general trends of the Nigeria basement rocks. A study of thin sections of the rocks under a petrological microscope reveals optical properties peculiar to each rock type. The type and nature of structural elements associated with the rocks together with their geometry reveal that the rocks have undergone more than one deformational event. The occurrence of numerous brittle and ductile structures shows that the area has a great potential for groundwater and mineralization. But the area still experience shortage of water for domestic purposes.Keywords: basement complex, brittle structures, foliation, petrographic varieties, thin sections

Hydrothermal processes in the Edmond deposits, slow- to intermediate-spreading Central Indian Ridge

Abstract The Edmond hydrothermal field, located on the Central Indian Ridge (CIR), has a distinct mineralization history owing to its unique magmatic, tectonic, and alteration processes. Here, we report the detailed mineralogical and geochemical characteristics of hydrothermal metal sulfides recovered from this area. Based on the mineralogical investigations, the Edmond hydrothermal deposits comprise of high-temperature Fe-rich massive sulfides, medium-temperature Zn-rich sulfide chimney and low-temperature Ca-rich sulfate mineral assemblages. According to these compositions, three distinctive mineralization stages have been identified: (1) low-temperature consisting largely of anhydrite and pyrite/marcasite; (2) medium-high temperature distinguished by the mineral assemblage of pyrite, sphalerite and chalcopyrite; and (3) low-temperature stage characterized by the mineral assemblage of colloidal pyrite/marcasite, barite, quartz, anglesite. Several lines of evidence suggest that the sulfides were influenced by pervasive low-temperature diffuse flows in this area. The hydrothermal deposits are relatively enriched in Fe (5.99–18.93 wt%), Zn (2.10–10.00 wt%) and Ca (0.02–19.15 wt%), but display low Cu (0.28–0.81 wt%). The mineralogical varieties and low metal content of sulfides in the Edmond hydrothermal field both indicate that extensive water circulation is prevalent below the Edmond hydrothermal field. With regard to trace elements, the contents of Pb, Ba, Sr, As, Au, Ag, and Cd are significantly higher than those in other sediment-starved mid-ocean ridges, which is indicative of contribution from felsic rock sources. Furthermore, the multiphase hydrothermal activity and the pervasive water circulation underneath are speculated to play important roles in element remobilization and enrichment. Our findings deepen our understanding about the complex mineralization process in slow- to intermediate-spreading ridges globally.

Methane and the origin of five-element veins: Mineralogy, age, fluid inclusion chemistry and ore forming processes in the Odenwald, SW Germany

Five-element veins (Ag, Bi, Co, Ni, As) have been valuable mineral deposits since medieval times. The characteristic occurrence of large aggregates of native metals (up to several dm) surrounded by a succession of arsenides makes this vein-type attractive for mining industry, natural history museums and private mineral collectors. Nevertheless, the exact formation process of these specific vein types has not been fully understood. This is the first case study applying a new model, which includes methane as a reducing agent to two typical examples of such mineralisations from the Odenwald, SW Germany. We analysed all mineralogical varieties (Ag-, As- and Bi-dominated) of the five-element veins in the Odenwald (SW Germany) in terms of ore textures, mineral chemistry, fluid inclusion compositions (microthermometry and Raman spectroscopy), stable isotopes (C, O and S) and in-situ U-Pb age dating of calcite and prehnite.A variety of Ag-, Bi- and As-dominated native metal-arsenide-calcite veins, sulphide-calcite veins and arsenide-free Ag-Hg-barite veins occurs in the Odenwald and has been examined in this study. All arsenide veins have in common that up to dm-sized, often dendritic native metals are overgrown by a succession of arsenides, followed by carbonate and finally sulphides. The succession of arsenides shows a distinct spatial and temporal chemical trend in their composition. This trend evolves from Ni- to Co and finally Fe-dominated compositions from the core to the rim. In contrast, spatially closely related Ag-Hg-barite veins consist of almost mono-mineralic amalgam inter-grown with barite.In-situ U-Pb age dating of low-U calcite and prehnite was applied to constrain the age of hydrothermal mineralisation. The results imply that the five-element veins formed at 170–180Ma from Na-Ca-Cl fluids at 290°C, salinities of ~27wt.% and Ca/(Ca+Na) of 0.30 to 0.35 in the presence of methane. The age data clearly relate the relevant fluid migration to extension and crustal thinning caused by the opening of the North Atlantic. Ternary mixing of a deep-seated metal-rich basement brine (fluid A), a sulphide-bearing (H2S and HS−) basinal/sedimentary brine (fluid B) and methane-dominated fluid/gas (fluid C) induce ore formation. Mixing of such chemically contrasting fluids results in a strong chemical disequilibrium of the mixed fluid, which potentially leads to rapid precipitation of native metals and arsenides with these specific ore textures. In contrast, sulphide-bearing calcite veins formed under similar P-T-conditions due to mixing of fluid A and B, while fluid C was absent. Additionally, U-Pb analyses of post-ore calcite yields ages of ~60Ma, which indicates that a second calcite formation event is associated with the onset of the Upper Rhine Graben rifting.Veins with amalgam and barite form as a consequence of post-ore oxidation of Ag2S at ~135°C. Conspicuously, this secondary silver II has Hg contents of up to ~30wt.%, in contrast to Hg contents below 1wt.% of primary silver I and Ag2S. The formation of amalgam was most likely related to decrease of the S2−/SO42− ratio due to cooling of the late hydrothermal fluid resulting in the destabilisation of Hg-bisulphide complexes in this fluid.

Occurrence, Origin and Transformation Processes of Geogenic Chromium in Soils and Sediments

Weathering of ultramafic rocks has been linked to the occurrence of elevated concentrations of hexavalent chromium (Cr(VI)) in soils, sediments, and groundwater. Ultramafic rocks and the derived serpentine soils and sediments are encountered in populated areas around the world and present high Cr concentrations, with an average of 2200 and 2650 mg/kg for rocks and soils, respectively. Groundwater concentrations between 0.2 and 180 μg/L have been reported for Cr(VI) in ultramafic areas, exceeding occasionally the most prevalent drinking water limit of 50 μg/L Crtot, the 5 μg/L Cr(VI) limit established in Italy, and the 10 μg/L Cr(VI) limit proposed in California. Cr release in groundwater occurs through the dissolution of trivalent chromium (Cr(III)) from its mineral hosts, followed by sorption of Cr(III) onto high-valence Mn oxides and oxidation to Cr(VI), which desorbs and is mobile at alkaline pH. Recent findings indicate that hydrogen peroxide and birnessite produced on the surface of Cr(OH)3 by heterogeneous oxidation are two additional potential mechanisms. Thus, groundwater concentrations are controlled by a variety of geoenvironmental factors, including climate, soil mineralogy, pH, organic matter, and others. To provide a basis for the evaluation of Cr mobility in ultramafic environments, this paper presents an overview of the mineralogy and geochemistry of Cr-rich rocks, sediments, and soils, along with the weathering and geochemical processes that control the fate and transport in the subsurface.

Petrogenesis of Middle Triassic volcaniclastic rocks from Balochistan, Pakistan: Implications for the break-up of Gondwanaland

Basaltic volcanic conglomerates near the Wulgai village in Balochistan occur in the undivided sedimentary rock unit of the Bagh complex which is the melange zone beneath the Muslim Bagh ophiolite. The presence of Middle Triassic grey radiolarian chert within the upper and lower horizon of the conglomerates suggests that the lavas, from which these conglomerates were principally derived, were eroded and re-deposited in the Middle Triassic. The Wulgai conglomerate contains several textural and mineralogical varieties of volcanic rocks, such as porphyritic, glomerophyric, intersertal and vitrophyric basalts. The main minerals identified in these samples are augite, olivine, plagioclase (An35-78) leucite and nosean, with apatite ilmenite, magnetite and hematite occurring as accessory minerals. These rocks are mildly to strongly-alkaline with low Mg# and low Cr, Ni and Co contents suggesting that their parent magma had undergone considerable fractionation prior to eruption. Trace element-enriched mantle-normalized patterns with marked positive Nb anomalies are consistent with 10%-15% melting of an enriched mantle source in a within-plate tectonic setting. It is proposed that this Middle Triassic intra-plate volcanism may represent mantle plume-derived melts related to the Late Triassic rifting of micro-continental blocks (including Afghan, Iran, Karakorum and Lhasa) from the northern margin of Gondwana.

Petrogenesis of the Northwest Africa 4898 high‐Al mare basalt

AbstractNorthwest Africa (NWA) 4898 is the only low‐Ti, high‐Al basaltic lunar meteorite yet recognized. It predominantly consists of pyroxene (53.8 vol%) and plagioclase (38.6 vol%). Pyroxene has a wide range of compositions (En12–62Fs25–62Wo11–36), which display a continuous trend from Mg‐rich cores toward Ca‐rich mantles and then to Fe‐rich rims. Plagioclase has relatively restricted compositions (An87–96Or0–1Ab4–13), and was transformed to maskelynite. The REE zoning of all silicate minerals was not significantly modified by shock metamorphism and weathering. Relatively large (up to 1 mm) olivine phenocrysts have homogenous inner parts with Fo ~74 and sharply decrease to 64 within the thin out rims (~30 μm in width). Four types of inclusions with a variety of textures and modal mineralogy were identified in olivine phenocrysts. The contrasting morphologies of these inclusions and the chemical zoning of olivine phenocrysts suggest NWA 4898 underwent at least two stages of crystallization. The aluminous chromite in NWA 4898 reveals that its high alumina character was inherited from the parental magma, rather than by fractional crystallization. The mineral chemistry and major element compositions of NWA 4898 are different from those of 12038 and Luna 16 basalts, but resemble those of Apollo 14 high‐Al basalts. However, the trace element compositions demonstrate that NWA 4898 and Apollo 14 high‐Al basalts could not have been derived from the same mantle source. REE compositions of its parental magma indicate that NWA 4898 probably originated from a unique depleted mantle source that has not been sampled yet. Unlike Apollo 14 high‐Al basalts, which assimilated KREEPy materials during their formation, NWA 4898 could have formed by closed‐system fractional crystallization.

The extremely reduced silicate-bearing iron meteorite Northwest Africa 6583: Implications on the variety of the impact melt rocks of the IAB-complex parent body

Northwest Africa (NWA) 6583 is a silicate-bearing iron meteorite with Ni = 18 wt%. The oxygen isotope composition of the silicates (∆′17O = −0.439 ‰) indicates a genetic link with the IAB-complex. Other chemical, mineralogical, and textural features of NWA 6583 are consistent with classification as a new member of the IAB-complex. However, some unique features, e.g., the low Au content (1.13 μg g−1) and the extremely reducing conditions of formation (approximately −3.5 ∆IW), distinguish NWA 6583 from the known IAB-complex irons and extend the properties of this group of meteorites. The chemical and textural features of NWA 6583 can be ascribed to a genesis by impact melting on a parent body of chondritic composition. This model is also consistent with one of the most recent models for the genesis of the IAB-complex. Northwest Africa 6583 provides a further example of the wide lithological and mineralogical variety that impact melting could produce on the surface of a single asteroid, especially if characterized by an important compositional heterogeneity in space and time like a regolith.