Main Mineral Phases Research Articles

Uncommon mafic rocks (MgO >10 wt.%) in the northernmost Andean volcanic chain (4° 25″ N): Implications for magma source and evolution

Mafic volcanic rocks are typically formed by primitive magmas (MgO >8 wt.%) and are evidence of both a rapid magma ascent from the source and a negligible differentiation en route to the surface. Thus, mafic rocks on Earth are relatively close in composition to the primary magma. These rocks are common in intraplate and extensional tectonic environments, but not in subduction settings. At subduction zones, where magma differentiation is virtually inevitable, most magmas, if not all, evolve before reaching the surface. Hence it is difficult to approach primary compositions to understand, for instance, the percentage of partial melting in the mantle. This is the case in the northernmost Andean volcanic chain (~140 km) in Colombia. There, however, mafic rocks have been recently recognised, providing an opportunity to approach the composition of primitive magmas. The rocks are located at the south of the volcanic chain and are associated with the Quaternary Pijaos monogenetic volcanic field. The rocks are porphyritic, phenocryst-poor, and host two main mineral phases: olivine (Fo71-90) and clinopyroxene (Wo38-45, En45-54, Fs7-12), with plagioclase, pyroxene and Fe–Ti oxides as microlites. The products are basaltic to basaltic andesite, and have the typical sub-alkaline/high-K calc-alkaline chemical signature of subduction settings. Applied geothermobarometers indicate that olivine crystallised between 1325 and 1266 °C, while clinopyroxene between 1273 and 1117 °C. These values somehow constrain the partial melting temperatures not only below the field but also below the region. High-forsterite and high-CaO clinopyroxene evidenced in the rocks, also contribute to the comprehension of the magma evolution through deep fractional crystallisation in the complex magmatic plumbing system that dominates this region of the Andean volcanic chain.

A new integrated geophysical-petrological global 3-D model of upper-mantle electrical conductivity validated by the Swarm M2 tidal magnetic field

SUMMARY A new global model of the present-day thermochemical state of the lithosphere and upper mantle based on global waveform inversion, satellite gravity and gradiometry measurements, surface elevation and heat flow data has been recently presented: WINTERC-G (Fullea et al. 2021). WINTERC-G is built within an integrated geophysical-petrological framework where the mantle seismic velocity and density fields are computed in a thermodynamically self-consistent framework, allowing for a direct parametrization in terms of the temperature, pressure and composition of the subsurface rocks. In this paper, we combine WINTERC-G thermal and compositional fields along with laboratory experiments constraining the electrical conductivity of mantle minerals, melt and water, and derive a set of new global three dimensional electrical conductivity models of the upper mantle. The new conductivity models, WINTERC-e, consist of two end-members corresponding to minimum and maximum conductivity of the in situ rock aggregate accounting for mantle melting, mineral water content and the individual conductivities of the main stable mantle mineral phases. The end-member models are validated over oceans by simulating the magnetic field induced by the ocean M2 tidal currents and comparing the predicted fields with the M2 tidal magnetic field estimated from 6-yr Swarm satellite observations. Our new conductivity model, derived independently from any surface or satellite magnetic data sets, is however able to predict tidal magnetic fields that are in good agreement with the Swarm M2 tidal magnetic field models estimated by Sabaka et al. and Grayver & Olsen. Our predicted M2 tidal magnetic fields differ in amplitudes by about 5–20 per cent from the Swarm M2 tidal magnetic field, with the high conductivity WINTERC-e end-member model accounting for mantle melt and water content capturing the structure of Swarm data better than the low conductivity end-member model. Spherically symmetric conductivity models derived by averaging new WINTERC-e conductivities over oceanic areas are slightly more conductive than the recent global conductivity models AA17 by Grayver et al. derived from Swarm and CHAMP satellite data in the 60–140 km depth range, while they are less conductive deeper in the mantle. The conductivities in WINTERC-e are about three to four times smaller than the AA17 conductivities at a depth of 400 km. Despite the differences in electrical conductivity, our spherically symmetric high conductivity end-member model WINTERC-e captures the structure of Swarm M2 tidal magnetic field almost the same as a state of the art 1-D conductivity models derived entirely from magnetic data (AA17, Grayver et al.). Moreover, we show that realistic lateral electrical conductivity inhomogeneities of the oceanic upper mantle derived from the temperature, melt and water distributions in WINTERC-e contribute to the M2 tidal magnetic field up to ±0.3 nT at 430 km altitude.

First-principles calculation of iron and silicon isotope fractionation between Fe-bearing minerals at magmatic temperatures: The importance of second atomic neighbors

In order to elucidate the processes involved in iron and silicon isotopes partitioning during magmatic differentiation, it is essential to know the precise value of equilibrium fractionation factors between the main minerals present in the evolving silicic melts. In this study, we performed first-principles calculations based on the density functional theory to determine the equilibrium iron and silicon isotopes fractionation factors between eleven relevant silicate or oxide minerals in the context of magmatic differentiation, namely: aegirine, hedenbergite, augite, diopside, enstatite, fayalite, hortonolite, Fe-rich and Fe-free forsterites, magnetite and ulvospinel. Results show that Fe2+-bearing silicate minerals display significant differences in iron isotope fractionation factors that cannot be neglected, even at high temperature (1000 °C). Various physical and chemical parameters control the iron isotopic fractionation of silicate minerals. However, the main parameter, after temperature and the iron oxidation state, is the nature and number of iron second neighbors (i.e. the local chemical composition around Fe atoms). This conclusion is also valid for silicon isotopes. In the investigated nesosilicates and inosilicates, silicon isotope reduced partition function ratios (also called β-factors) show no correlation with the average Si-O bond length, which remains almost constant, but Si β-factors are correlated with the local chemical composition of the minerals. Fractional crystallization is one of the mechanisms, which could explain the evolution of iron isotopic compositions during magmatic differentiation. Using the present theoretical set of equilibrium fractionation factors allows us to assess the impact of inter-mineral isotopic fractionations, and shows that pyroxene appears to be the main mineral phase driving the isotopic evolution to a heavier signature in the most evolved lavas.

How to build a bone? - Hydroxyapatite or Posner’s clusters as bone minerals

For decades, hydroxyapatite has been considered the main mineral phase of mammalian tooth enamel and bone that crystallizes from a precursor phase, amorphous calcium phosphate. Amorphous calcium phosphate, in turn, is proposed to be made from small clusters of ions known as Posner’s clusters, with a size of 0.95 ​nm and chemical formula of Ca9(PO4)6. In isolation, Posner’s clusters are extremely unstable and spontaneously aggregate and nucleate to the thermodynamically stable phase of hydroxyapatite within a few seconds. In this critical review, we will discuss the progress made in identifying the role of Posner’s clusters in the bone mineralization process, visualization of the clusters and associated challenges, and potential pathways to utilize them in bone tissue engineering strategies. We hypothesize, based on collective data in the literature and our recent experimental data, that Posner’s cluster agglomerates and amorphous calcium phosphate particles are in fact the main mineral component of bone, and hydroxyapatite crystals are, in part, artefacts of sample processing.

Selective retention of extracellular polymeric substances induced by adsorption to and coprecipitation with ferrihydrite

Recent work shows that microbially-derived compounds constitute a significant fraction of the soil organic matter (OM) pool. These compounds include extracellular polymeric substances (EPS) whose mass can far exceed total microbial cell biomass. Sorption of EPS to soil minerals occurs via adsorption and coprecipitation and contributes to the preservation of OM in the soil environment. Little is known, however, about the sorption mechanisms of EPS and selective retention of different EPS constituents on iron (oxyhydr)oxides, especially during EPS adsorption versus coprecipitation with these reactive soil phases. This study examines how EPS interacts with the ubiquitous soil iron (oxyhydr)oxide ferrihydrite during EPS adsorption and coprecipitation and whether these different EPS-mineral association pathways affect EPS sorption and selective retention, and thus the mobility and fate of microbially-derived OM in the soil environment. We use several complimentary techniques to i) examine EPS-carbon, EPS-nitrogen and EPS-phosphorus sorption and fractionation, ii) visualize spatial relationships between EPS biomolecular classes and ferrihydrite using confocal laser scanning microscopy (CLSM), iii) determine EPS-C speciation and chemical fractionation with ferrihydrite using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and iv) determine functional group interactions with ferrihydrite using Fourier transform infrared spectroscopy (FTIR) combined with two-dimensional correlation spectroscopy (2D-COS) analysis. Results show that the coprecipitation of EPS does not change the ferrihydrite mineralogy, as the main mineral phase for EPS association, but it substantially increases the particle size of EPS-ferrihydrite. A substantial difference in the EPS mass fraction associated with the ferrihydrite is observed between the adsorption and coprecipitation experiments at an initial molar C/Fe ratio >1. The EPS-N is relatively enriched during the adsorption process, while more EPS-C and near-complete EPS-P are fixed in the coprecipitation process. XPS results show that the surface of the ferrihydrite formed through EPS adsorption is preferentially enriched with protein-like components, whereas, the surface of the ferrihydrite formed through EPS coprecipitation is enriched with polysaccharide-like components, which is visually confirmed with CLSM images. NEXAFS results reveal that the carboxylic/amide C-containing components are selectively retained during adsorption, with the aliphatic and O-alkyl C-containing components relatively enriched during coprecipitation. 2D-FTIR-COS results indicate that during EPS adsorption on ferrihydrite the PO functional groups are adsorbed faster than the amide and carboxylate functional groups, while during EPS coprecipitation with ferrihydrite the opposite trend is observed. The findings from this study indicate that the formation pathway of EPS-ferrihydrite associations substantially effects the sorption mechanisms and selective retention of EPS and may thus affect the mobility and fate of microbially-derived carbon (C), nitrogen (N) and phosphorus (P) in soils. These new insights on EPS behaviour at the mineral–water interface might be used to evaluate how microbially-derived compounds like EPS are stabilized by iron (oxyhydr)oxides and how EPS-iron (oxyhydr)oxide couplings might affect the reactivity and cycling of OM in natural environments.

Andesitic (SiO2: ~60 wt%) monogenetic volcanism in the northern Colombian Andes: Crystallisation history of three Quaternary volcanoes

The Quaternary Villamaría-Termales Monogenetic Volcanic Field (VTMVF) is one of the monogenetic fields located within the subduction related, volcanic chain in the northern Colombian Andes. The dominantly andesitic composition of the products from this field provides an opportunity to study the crystallisation history of monogenetic volcanic products, associated with long term crustal stagnation before eruption. This work focuses on the Victoria, Gallinazo and Tesorito monogenetic effusive volcanoes, using a combination of petrography, mineral chemistry and whole-rock chemical analysis, in addition to geothermobarometers, to estimate the crystallisation conditions of the main mineral phases and infer the depths at which such phases crystallised. We also present two K/Ar radiometric ages for Victoria and Gallinazo volcanoes in order to add to the known age (1.2 Ma) of the Tesorito volcano. This helps us to timeframe this volcanism within the ~140 km volcanic chain where it is located. The rocks are porphyritic with a glassy and microcrystalline groundmass, and display glomeroporphyritic and disequilibrium textures such as textures sieve in plagioclase and reaction rims in pyroxene. The main mineral phases forming the rocks are plagioclase (An22–67), orthopyroxene (Wo02 En65–80 Fs18–33), clinopyroxene (Wo39–45 En39–49 Fs07–17), amphibole (magnesiohastingsite, magnesihornblende, edenite and tschermakite), and Fe-Ti oxides Usp37–23 Mag63–77 and Ilm79–62 Hem21–39. Olivine (Fo71–87) only appears in the Victoria volcano. The volcanoes are subalkaline andesites with calc-alkaline affinity. Estimation of the crystallisation conditions (i.e. temperature and pressure) for in-equilibrium mineral phases, indicate the depths at which they crystallised. Olivine crystallised at 1198–1191 °C and ~1.4 GPa, orthopyroxene-clinopyroxene coexisted at 963–880 °C and 0.78–0.47 GPa, plagioclase formed at 928–908 °C and 0.76–0.17 GPa, amphibole crystallised at 998–877 °C and 0.79–0.16 GPa, and Fe-Ti oxides crystallised at 937–904 °C. This suggests that crystallisation starts at depths of ~53 km and it continues until the surface. The obtained radiometric ages for the Gallinazo (1.92 ± 0.06 Ma) and Victoria (1.97 ± 0.06 Ma) volcanoes indicate that they are ~0.7 Ma older than the nearby Tesorito volcano.

Introducing Semi-gem quality blue corundum from the Alvand complex, Hamedan, west Iran

Semi-gem quality corundum crystals are formed in a syenite pegmatite dyke in the Alvand igneous-metamorphic complex in west Iran. The dyke is intruded the igneous rocks and the surrounding hornfelses. Corundum is mainly associated with K-feldspar in the rocks and makes crystals 2 to 60 mm across. It shows gray, bluish-gray, pale blue, ink blue and dark blue colours. The crystals show colour zoning and trapiche-like zoning in hand specimens and under the microscope. The main mineral phase inclusions in corundum crystals are muscovite, phlogopite, hercynite and Nb-Ta oxides. LA-ICP-MS and electron microprobe analyzes indicate wide range of Fe/Mg, Fe/Ti, Ti/Mg and Ga/Mg ratios for the analyzed crystals while variation of Cr/Ga ratio is limited. The high Fe and Ga and low Mg and Cr contents suggest a magmatic origin for these corundums. Ti content was found as the main factor controlling the colour.

ИССЛЕДОВАНИЕ ФОРМ МИГРАЦИИ МЕТАЛЛОВ В РЕКАХ, ПОДВЕРЖЕННЫХ ВЛИЯНИЮ ШАХТНЫХ ВОД КИЗЕЛОВСКОГО УГОЛЬНОГО БАССЕЙНА

Актуальность. Техногенному воздействию кислых шахтных вод подвержены поверхностные водотоки бассейна р. Чусовая – крупнейшего притока р. Кама на территории Пермского края (Россия). Изучение поведения металлов в реках-приемниках шахтных вод обусловлено необходимостью понимания особенностей миграции компонентов в природно-техногенных водах; определения геохимических процессов и механизмов, способствующих выведению токсичных элементов из растворов; и прогнозной оценки вторичного загрязнения за счет растворения образованных соединений при смене физико-химических условий. Результаты, полученные на исследуемом участке, могут отражать особенности геохимического поведения металлов в других загрязненных реках территории Кизеловского угольного бассейна при поступлении в них шахтного дренажа схожего состава. Цель: исследовать формы миграции металлов в водотоках, загрязненных шахтными водами, определить основные вторичные минеральные фазы, способствующие выведению токсичных элементов из раствора, и оценить устойчивость частиц образованных минералов при миграции в речной сети. Объекты: кислотный дренаж из штольни шахты «Таежная» Гремячинского месторождения Кизеловского угольного бассейна, содержащий высокие концентрации сульфатов и тяжелых металлов, и загрязненные шахтными водами реки: Большая Гремячая, Южная Вильва, Усьва и Чусовая. Методы. Физико-химическое моделирование химических форм нахождения металлов в растворе и расчеты степени насыщения выполнялись при помощи программного кода PHREEQC c базой термодинамических данных WATEQ4f. Результаты исследования показали, что в шахтных водах и загрязненных речных водах с рН 2,9–3,4 металлы (Al, Fe, Mn, Zn, Ni, Pb, Cd, Li) находятся как в форме свободных ионов, так и в виде сульфатных комплексов. В реке Юж. Вильва, ниже участка смешения с загрязненными водами р. Бол. Гремячая и далее по потоку, Fe и Al образуют исключительно гидроксокомплексы. Преобладающей формой миграции Ni и Pb являются карбонатные комплексы. Нахождение металлов Li, Cd, Mn и Zn в реках Юж. Вильва, Усьва и Чусовая преимущественно в виде свободных ионов позволяет предположить, что основным механизмом их осаждения является сорбция на гидроксидах и оксигидроксидах Fe и Al, а также на глинистых минералах. Отрицательные индексы насыщения по отношению к сульфатным минералам, характерным для шахтных вод, показали неустойчивость этих минеральных фаз в нейтральных и слабощелочных водах.

Engineering properties of dredged sediments as a raw resource for fired bricks

In the last decades, the amount of dredged sediments (DS) increased in France harbours. Dredged sediments consist of fine soil collected from the deepening, broadening and maintaining of public waterways. The present study reports the investigation of the beneficial reuse of dredged sediments collected from Le Havre (France) harbour as fired material for sustainability requirements. The main challenge is the use of untreated dredged sediments from land deposit of the Seine estuary and port areas as building material, especially for fired bricks manufacture. The chemical, mineralogical and particle size compositions of the raw material were assessed using X-ray fluorescence (XRF), X-ray diffraction (XRD) and laser particle sizer, respectively. The results indicate that the main oxide components are SiO2 and CaO3, while quartz and calcite are the main mineral phases. Lesser amounts of feldspar, chlorite, kaolinite, muscovite and halite were also determined. The physical properties of the raw clay material, including plasticity, organic content and salinity, were investigated in order to assess the product suitability as building material. Ceramic properties such as linear shrinkage, water absorption, bending strength and mineral neo-formations were also investigated in fired bricks at temperatures ranging from 700 to 1000 °C. A high mechanical strength has been obtained at a temperature of 900 °C. The use of ternary diagrams indicates that the raw material falls inside the industrial domain, and ceramic tests show that the raw material could be used in brick making because of its firing behaviour and mechanical resistance. As regards environment sustainability, chemical analysis reveals that the levels of metal traces from leaching tests remain low and within regulatory limits.

Mineral phases of metals in industrial sediments of St. Petersburg rivers with extreme pollution

The aim of the research was to determine the patterns of distribution of metals and their main mineral phases in technogenic bottom sediments of St. Petersburg watercourses in conditions of extreme pollution. The objects of research were the Yekaterinofka, Okhta, Krasnen'kaya, Smolenka, Karpovka and Chernaya Rechka Rivers. Bottom sediments of urbanized rivers are characterized by abnormally high concentrations of metals and metalloids (TMM). The maximum metal content established in river sediments corresponds to ore concentrations: Cu — 0.487 %, Pb — 5.54 %, Co — 0.129 %, Cd — 0.0439 % (0.01–5.0), Ba — 6.32 % and Zn — 0.818 %. According to the Geoaccumulation Index (Igeo), TMMs are characterized from moderate and severe pollution (Cr, Co, Ni, Zn, As) to extremely severe (Cu, Cd, Sb, Hg). The rivers have their own geochemical specialization of bottom sediments: the Okhta River is characterized by the highest concentrations of Ba, As, Sb, Zn and Hg; the Ekaterinofka River — Cr, Co, Mn, Pb, Cd; Smolenka River — Cu; Red — Fe, V, Sc; Chernaya Rechka River — Ni. Based on the method of the main components of factor analysis, paragenetic associations are identified that indicate the main sources of pollution: the production of batteries using Sb-Cd-Pb-Co-Mn (Yekaterinofka River) and Ni (Karpovka River), paints and varnishes using Ba-Hg-As-Zn (Okhta River) and metal processing Cu-Cr (Yekaterinofka, Smolenka and Chernaya Rechka Rivers). Scanning electron micrographs studies showed a variety of authigenic minerals, among which barite, hematite, magnetite, goethite are of primary importance. The amount of barite formed is proportional to the concentration of Ba in the sediments. There are metal sulfides, framboidal pyrite, sphalerite, chalcopyrite, galena. An important feature of early diagenetic changes in the composition of sediments under extreme pollution conditions of the studied rivers is shown — the formation of native metals (Fe, Pb) and aggregates of complex composition (Fe, Pb, Zn, Cu). This is probably one of the significant mechanisms of the flow of metals under conditions of sustainable technogenesis.

High-Potassium Volcanism Approximately 640 Ma in the Southwestern Siberian Platform (Biryusa Uplift, Sayan Region)

On the basis of petrographic and mineralogical studies, we have established the presence of clastic rocks with a strong predominance of K-feldspar among the rock-forming fragments within the Late Precambrian sedimentary sequence in the southwestern part of the Siberian Platform. Two types of mineralogical occurrence of K-feldspars are determined: (1) huge zonal crystal clasts with increased Ba concentrations in the central parts of the grains and (2) the main mineral phase in the form of a decrystallized glassy mass. In both cases, low concentrations of Na (lower than 0.1 wt %) are detected. K-feldspars of the second type contain intergrowths of idiomorphic rhombic dolomite with a high ankerite component. Dolomite grains contain inclusions of K-feldspar. The prevailing accessory minerals are F-apatite (with high concentrations of REEs), zircon (with high concentrations of Th), magnetite, rutile, monacite, and sinchizite. Encasement minerals with an idiomorphic shape are identified, with K-feldspar being located in the center, while the middle shell is formed by apatite with a high REE content, and the outer shell is formed by apatite without rare earth elements. These rocks are products of high-potassium volcanic activity. The age of this event has been established on the basis of U–Pb zircon dating to about 640 Ma. The Lu–Hf zircon systematics for these rocks indicates the connection of volcanism with igneous events of mantle genesis within its range. The products of explosive eruption, which are widespread within the Biryusa uplift of the Siberian Platform, were erroneously considered earlier as Riphean sedimentary rocks of the Karagas Series.

Adsorption of Triterpene Extracts of <i>Momordica charantia</i> (Cucurbitaceae) Leaves by Local Kaolin from Boboyo, Far North Region (Cameroon)

Plant extracts are nowadays cited as suitable tools for better protection of stored grains insect pest attacks. These chemical insecticides are less attractive to producers because of their low persistence and difficulty to use as pure product. The present work aimed to study the formulation through adsorption of tetracyclic triterpene of the leaves of Momordica charantia (Cucurbitaceae) on kaolin. tetracyclic triterpene was obtained by macerated in methanol solvent. In this study, we tested the technical properties of kaolin physically and chemically, which include XRF, XRD, and FTIR. Based on the XRF test, the main composition of kaolin, SiO2, Al2O3, and Fe2O3, CaO, MgO, K2O, Na2O, SO3, P2O5 were 45.41, 20.54, 8.10, 0.13, 0.79, 01.10, 01.09, 0.04, and 0.03% respectively, while the rest were impurities. The FTIR spectra showed the functional groups of Al-OH, Al-O and Si-O. While the XRD diffractogram identified kaolinite as the main mineral phase in the presence of quartz, muscovite, and grossite tested in small quantities in the sample. The experimental parameters such as contact time, adsorbent dose, initial concentration of extract of triterpene and temperature were studied. The study revealed that the maximum quantity of adsorption is reached after 10 minutes, it is believed that the quantities adsorbed with the increase in the concentration of the adsorbate and quantities adsorbed decreases with the increase of the mass of the clay and temperature. The adsorbent showed good potential for adsorption with a maximum take up of 0.34 mg/g. The equilibrium data were well fitted by the Langmuir isotherm. Thermodynamic parameters suggested that the adsorption involved a chemical process, spontaneous, and endothermic in nature. The kinetic study showed that the second-order model gives a better description of the kinetics of the adsorption reaction. The study of the adsorption of triterpene extract by kaolinite can be used for a powdery formulation of insecticide.

Studi Ekstraksi Bijih Emas Asal Pesawaran dengan Metode Pelindian Agitasi dalam Larutan Sianida

Research on the extraction of gold ore from Pesawaran, , Lampung, Indonesia, was carried out using the agitation leaching method in cyanide solution. This study aimed to obtain information on the use of conventional cyanidation methods for extracting gold from the Pesawaran gold ore. The ore preparation was carried out in the form of crushing, grinding and sieving to obtain samples with fraction sizes of -60 + 100 mesh, -100 +150 mesh, -150 + 200 mesh and -200 mesh. The ore characterization was performed using XRD, XRF, SEM-EDX, and wet chemical analysis. The XRD analysis showed that the main mineral phases were silica, hematite, aluminium hydroxide and orthoclase. The major constituents of the ore were Si (53,628%), Fe (15,996%), K (19,744%) and Al (8,045%). The Au content was determined by wet chemical analysis and was found to be 9.67 ppm. The experimental results show that the highest percentage of gold extraction of 83.33% was obtained using sodium cyanide at a concentration of 1000 ppm, a percent solids of 40% and a grain size of 200 mesh. Higher gold extraction was not achieved despite the use of a high cyanide concentration was probably because the remaining gold was not properly liberated. The results of SEM-EDX analysis showed that the gold grain size was <20 µm, while the grinding was performed only to a sieve size of -200 mesh (74 µm).

Epithermal mineralization of the Bonanza-Sandy vein system, Masara Gold District, Mindanao, Philippines

The Masara Gold District in southeastern Mindanao island is an area of prolific hydrothermal copper and gold mineralization. This study documents the mineralization characteristics of the NW-trending Bonanza-Sandy epithermal veins to constrain possible hydrothermal fluid sources and ore-forming mechanisms. Epithermal mineralization in the NW veins is divided into three main stages: Stage 1 - massive quartz-sulfide; Stage 2 - massive to amorphous quartz-carbonate (calcite); and Stage 3 - colloform-cockade quartz-carbonate (bladed rhodochrosite). Stage 1 is the main gold mineralization phase, with chalcopyrite, pyrite, sphalerite and galena occurring with native gold and tellurides. Stages 2 and 3 contain invisible gold in the sphalerite, galena, pyrite and chalcopyrite. The deposit exhibits mineralization characteristics typical of intermediate sulfidation epithermal deposits based on the dominant chalcopyrite-pyrite mineral assemblage; illite-muscovite-chlorite alteration mineralogy that point to neutral pH conditions; and sphalerite composition of 2.26 to 8.72 mol% FeS in Stage 1 and 0.55 to 1.13 mol% FeS in Stage 2. The K-Ar age date of illite separates from highly altered diorite porphyry of the Lamingag Intrusive Complex yielded an Early Pliocene age (5.12 ± 0.16 Ma). Hydrothermal fluid exsolved from the magma that formed the Lamingag Intrusive Complex probably formed the ore-forming Stage 1 veins. Stages 2 and 3 involved the deposition of quartz and carbonate veins possibly by boiling hydrothermal fluids. Precious and base metal deposition was controlled by the Masara Fault Zone. Exploration markers for gold mineralization in the Masara Gold District and vicinity include the presence of Lamingag Intrusive Complex and massive sulfide veins.

Lithological dependence of aragonite preservation in monospecific gastropod deposits of the Miocene Mainz Basin: Implications for the (dia-)genesis of limestone–marl alternations

ABSTRACTThe origin of limestone–marl alternations (LMA) and their diagenesis is still lively debated. The most disputed question is whether original variations in sediment input control the differentiation of the precursor sediment into limestone and marl, or if a LMA can form without compositional differences in the precursor sediment. The Miocene brackish-water deposits (Rüssingen Formation) from the Mainz–Weisenau quarry in central Germany offer the opportunity to tackle this question. They are developed as a monospecific alternation of planar beds of moderately and poorly lithified sands of aragonitic Hydrobia snails, corresponding to “limestones” and “marls” in LMA, respectively. XRD analyses and the monospecific composition reveal only minor to no changes in sedimentary input and allow comparison of the preservation of Hydrobia in both lithologies. The differential preservation of the aragonitic fossils in lithified and less lithified layers is documented in thin-sections. CaCO3 contents are high throughout the measured section. However, XRD analyses revealed high amounts of aragonite and low amounts of calcite in less lithified beds, and the opposite in lithified beds in which calcite is the main mineral phase. Mg-calcite is abundant in both lithologies. Although the less lithified beds have experienced significant loss of aragonite by dissolution, they still mainly contain aragonite since the precursor sediment contained only aragonitic shells and Mg-calcite crusts. The relative amount of aragonite is higher than in the more lithified beds because the lithified beds imported the dissolved aragonite, which precipitated as calcite cements. This shifted the aragonite–calcite ratio to higher values in the less lithified beds than in the more lithified beds, although it is counterintuitive at first sight. This is supported by thin-section analyses and point counting, revealing moderate to good preservation of Hydrobia or their replacement by calcite spar in lithified beds, but intense dissolution of aragonite in less lithified beds. The aragonite–calcite ratio and the differential preservation of Hydrobia fit the model of differential diagenesis in “classical” LMAs, which assumes early diagenetic aragonite dissolution in marls and reprecipitation as calcite cement in limestones. It is concluded that the studied succession—although an endmember of LMA—was differentiated into lithified and unlithified beds by incomplete differential diagenesis while minor primary differences are not reflected in the change in lithology. The results suggest that the differentiation of a homogeneous precursor sediment into a LMA is possible and caution should be exercised using lithological change or proxies which are potentially altered by CaCO3 redistribution for cyclostratigraphic analyses.

Mineral chemistry of hydrothermal alteration assemblage in hanging wall Shahapur granite associated with vein-type Gogi uranium deposit, Bhima Basin, Eastern Dharwar Craton, India: Implications for physico-chemical conditions of ore formation

Eastern Dharwar craton (EDC) is a major uranium province in India hosting number of unconformity related, vein-type and carbonate hosted strata-bound uranium deposits. Gogi uranium deposit (GUD) is a structurally controlled hydrothermal ore deposit (~1.35 Ga), hosted in a reverse fault zone between the foot-wall Mesoproterozoic Bhima Group carbonates and the hanging wall basement granites (~2.5 Ga) of the EDC. The hanging wall granites, locally known as Shahapur granite show extensive chloritisation and epidotisation, and constitute the propylitic outer zone of the main hydrothermal system of the GUD. We conducted systematic mineralogical and geochemical studies on hydrothermally altered assemblages to understand physico-chemical conditions of hydrothermal fluid. Quartz, epidote, chlorite, titanite, fluorite and hematite are the main hydrothermal mineral phases. Chlorites occur in two different forms, as pseudomorphic replacement of hornblende and as vein/cavity fillings. Epidotes occur as coarse prismatic grains in the main veins, or as replacement of albite in the wall rock. Mineralogical, textural data and geochemical mass balance calculation indicate that about 17.9% of total albites (Modal abundance = ~48%) and all the hornblendes (modal abundance = ~7.5%) of the parent rock were broken down and reacted to form quartz, chlorite, epidote, secondary titanite and hematite. The hydrothermal reaction resulted in creation of 13 vol% secondary porosity in the host rock and acidification of the evolved fluid. Thermodynamic calculation on chlorite compositions indicates ~ 250 °C temperature of formation and oxidising nature of ambient fluid, with log fO2 ranging between −37 and −31 (avg. −35). Available fluid inclusion data, in conjunction with chlorite geothermometric results, show fluid entrapment pressure between 625 bar and 792 bar, which is consistent with emplacement of hydrothermal fluid in low-pressure brittle deformation zone. We surmise that U6+ was liberated from basement granite by reaction with oxidised acidic fluid, transported as chloride, carbonate complexes and precipitated in high permeability fault-zone, possibly because of mixing with reduced- basin derived fluids.

Characteristics and nature of gold-bearing fluids in Fatira area, North Eastern Desert of Egypt: possible transition from intrusion-related to orogenic deposits

The gold lode in Fatira area is represented in three modes of occurrence: (1) altered felsite dykes, (2) massive quartz veins that are cutting through the hosting granitic rocks, and (3) siliceous-hybrid shear zone which is trending in NNW-SSE direction and separating between metavolcanic and granitic rocks. Metavolcanic rocks are described by meta-andesite and meta-dolerite varieties; they exhibit calc-alkaline magma type related to island arc system. However, granitic rocks are of I-type granodiorite composition with calc-alkaline affinity developed in convergent plate environment (island arc/active continental margins) during the late stage of orogeny. The wallrock alteration around the ore body includes propylitization, sericitization, and silicification facies. The ore minerals were observed as disseminated sulfides (pyrite, sphalerite, chalcopyrite, and covellite). Goethite, jarosite, and ilmenite are the main iron-rich mineral phase as well as malachite and rutile. Gold was detected by microprobe analysis within the internal composition of pyrite and/or jarosite. Two groups of fluid inclusions could be recognized in samples from different mineralized zones: (a) aqueous fluid inclusions (H2O–NaCl/KCl) and (b) aqueous-carbonic fluid inclusions (H2O–CO2–NaCl/KCl). Isochore construction from fluid inclusion data, combined with chlorite thermometry from alteration zone, revealed that Fatira gold deposits were formed at temperature range of 275–297 °C and pressure between 0.2 and 1.1 kb). The Fatira gold deposits exhibit similar features of both intrusion-related and orogenic deposits. Hence, the initial ore-bearing fluid was proposed to have originated from magmatic source at deeper levels related to the granitic emplacement (5–10 kb); moreover, the granitic batholith acted as an important vehicle for driving of the metamorphic hydrothermal currents and probably as a cause for the metamorphic process itself. Then, the migration of gold was taken place in form of bi-sulfide complexes and the final deposition occurred through fluid uplifting consequent with a possibility of mixing with meteoric water at shallow depths, pressure/temperature drop, and fluid/wallrock interactions.

Mineralogy, mineral chemistry and thermobarometry of post-mineralization dykes of the Sungun Cu–Mo porphyry deposit (Northwest Iran)

Abstract The Sungun copper–molybdenum porphyry deposit is located in the north of Varzaghan, northwestern Iran. The Sungun quartz-monzonite is the oldest mineralized intrusive body in the region and was emplaced during the Early Miocene. Eight categories of the late and unmineralized dykes, which include quartz diorite, gabbrodiorite, diorite, dacite, microdiorite and lamprophyre (LAM), intrude the ore deposit. The main mineral phases in the dykes include plagioclase, amphibole and biotite, with minor quartz and apatite and secondary chlorite, epidote, muscovite and sericite. The composition of plagioclase in the quartz diorite dykes (DK1a, DK1b and DK1c) varies from albite-oligoclase to andesine and oligoclase to andesine; in the diorite, it varies from andesine to labradorite; in the LAM, from albite to oligoclase; and in the microdiorite (MDI), it occurs as albite. Amphibole compositions are consistent with classification as hornblende or calcic amphibole. Based on their AlIV value (less than 1.5), amphibole compositions are consistent with an active continental margin affinity. The average percentage of pistacite (P s) in epidotes formed from alteration of plagioclase and ferromagnesian minerals is 27–23% and 25–30%, respectively. Thermobarometric studies based on amphibole and biotite indicate approximate dyke crystallization temperature of 850–750℃, pressure of 231–336 MPa and high fO2 (>nickel-nickel-oxide buffer). The range of mineral compositions in the postmineralization dyke suite is consistent with a genetic relationship with the subduction of the Neotethys oceanic crust beneath the continental crust of the northwest part of the Central Iranian Structural Zone. Despite the change from calc-alkaline to alkaline magmatism, the dykes are likely related to the late stages of magmatic activity in the subduction system that also generated the porphyry deposit.

Nickel and cobalt losses from laterite ore after the sulfation-roasting-leaching processing

The sulfation-roasting-leaching process has successfully been used to extract nickel and cobalt from laterites due to its flexibility for application to ores with different chemical and mineralogical characteristics. One of the main characteristics of this process is to leave elements such as iron, aluminum, and chromium in the residues as insoluble oxides. In this work, a sample of nickel laterite ore from the northern region of Brazil was processed by the sulfation-roasting-leaching route. The samples after each step of the process were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), and chemical analysis by atomic absorption spectrometry. The phases quantification was carried out by the Rietveld method. Under favorable conditions, nickel and cobalt recoveries were higher than 80 (wt.%) while the iron recovery was only 5.5 (wt.%). Despite the higher nickel and cobalt extraction, it was verified after calculation of the metals distribution throughout the main mineral phases present in the solid leaching residue that hematite was responsible for 29.5 (wt.%) and 60.8 (wt.%) of nickel and cobalt losses in the solid leaching residue, respectively. The sulfation-roasting-leaching process efficiency is influenced by many variables, then, depending on the ore characteristics, furnace choice, and processing conditions. The possibility of reprocessing the hematite in the solid leaching residue to increase the recovery of valuable metals can be a key factor for the route viability.

U–Pb zircon geochronology and petrology of the early Miocene Göloba and Şaroluk plutons in the Biga Peninsula, NW Turkey: Implications for post-collisional magmatism and geodynamic evolution

The Biga Peninsula (NW Turkey) is an area where magmatic and tectonic events are observed together, and post-collisional plutons are extensively seen. Two plutons in this peninsula were studied; the Göloba Pluton is composed of quartz monzonite, granite and granodiorite, and the Şaroluk Pluton is composed of quartz monzonite, monzonite and granodiorite. U–Pb zircon dating yielded 20.87 ± 0.31 Ma for the Göloba pluton, 19.69 ± 0.25 Ma for a quartzmonzonite porphyry vein cutting this pluton, and 22.18 ± 0.40 to 21.51 ± 0.37 Ma for the Şaroluk pluton, revealing an Early Miocene emplacement age for these pluton magmatism. These plutons are geochemically similar to each other with high-K calc-alkaline compositions. Their A/CNK values range between 0.84 and 1.48, suggesting I-type and metaluminous to slightly peraluminous characteristics. The rock samples show linear-like correlations in major oxide and trace element variation diagrams, which indicate main mineral phase’ fractionation. The Göloba and Şaroluk plutons also exhibit enrichment in large ion lithophile elements (K, Sr, Rb and Ba), Ce and Th, with decreases in high field strength elements (Ti and Y), Ta and Nb. Chondrite normalised REE diagrams of the plutonic rocks show concave upward patterns (LaN/LuN = 11–34), and slight negative Eu anomalies (EuN/Eu* = 0.51–1.03). In the Göloba pluton samples, 87Sr/86Sr(i), 143Nd/144Nd(i) and ƐNd(i) values vary from 0.706792 to 0.707250, from 0.512435 to 0.512489, and from −2.36 to −3.41, respectively. In the Şaroluk pluton samples, 87Sr/86Sr(i) and 143Nd/144Nd(i) isotopic values range within 0.706978–0.707669 and 0.512456–0.512520 respectively, and ƐNd(i) values are between −1.75 and −2.99. Fractional crystallisation, rather than assimilation and mixing, seems to have been important in the evolution of the studied plutons. All geochemical data suggest that the parental magma(s) of the studied plutons were hybrid magma that originated from enriched lithospheric mantle and lower/middle crust end-members. According to the regional geology and petrological data, Neogene magmatism in the Biga Peninsula has post-collisional feature, and was closely related to slab break-off.