Plagioclase Research Articles

Provenance and weathering conditions of the Moloundou swamp sediments, southeast Cameroon: Evidence from mineralogy and geochemistry

This work reports the mineralogical and geochemical characterization of the Moloundou swamp sediments in order to deduce their tectonic setting, source rock composition, weathering conditions and maturity. These sediments show sandy to loamy sand in nature; they are pale olive to greenish and contain organic matter in the top. Their mineralogy consists of quartz and clay minerals with small amounts of mica, rutile, anatase and feldspars. Tectonic discrimination diagrams and plots of K2O/Na2O vs. SiO2, and TiO2 versus Zr, intermediate sedimentary provenance, within active continental margins in a collisional setting. The A–CN–K ternary diagram points to a high degree of chemical weathering of the source area. The increased plagioclase index of alteration (PIA) values point to a high leaching of plagioclase feldspars during source weathering and transport. The chemical index of alteration (CIA) and the chemical index of weathering (CIW) values for the studied samples suggest a highly intensive chemical weathering in a humid warm climate. The strong chemical weathering of the source rocks is revealed by the presence of kaolinite, goethite and gibbsite. The Moloundou swamp sediments are tectonically in an active setting, derived from mixed acid to intermediate magmatic and metamorphic source rocks.

Geochemistry of a lateritic mantle developed on basalt in the Cameroon Western Highlands (Cameroon Volcanic Line)

Although lateritic mantles have been strongly documented, there is need to continuously characterise and update information at site-scale so as to optimize exploration and exploitation operations in various industrial domains. In this paper, four soil profiles developed on basalt are described in detail to appreciate their morphology, mineralogy, geochemistry, pedogenesis and ore potential. The basalt is composed of olivine, plagioclase feldspars and pyroxenes and accessory magnetite, sphene and apatite. The basalt shows high levels of Ba, Cr, V, Sr, Ni, Zn and Zr; meanwhile total REEs range from 185.03 to 199.45 mg kg−1. The weathering indices reveal an extreme weathering intensity of the parent rock. Newly formed minerals are kaolinite (15–48%), haematite (13–40%), Goethite (10.5–19%) and gibbsite (10–12%), magnetite (4–9.56%), feldspars (4.67–6.10), apatite (2.8–3.9) and sphene (1.77–2.46%). The weathered materials show high levels of Cr (40–850 mg kg−1), V (145–582 mg kg−1), Zr (300–583 mg kg−1) and Ce (24.2–510 mg kg−1). The total REEs of the weathered materials range from 126.52 to 1267.69 mg kg−1, with the predominance of LREE. The REE basalt-normalized patterns revealed slight LREE depletion, more pronounced for the B horizons relative to the underlying C horizons as well as HREE enrichment that increase with depth and altitude. In these soils, mass balance calculations reveal depletion of Si, Ca, Mg, Ba, K, Na, Mn, P, Rb, Sr, La and Lu, enrichment of Al, Fe, Ti, Ga, U, Zr, Dy, Hf, U, Tm and Yb meanwhile Cr, Cs, Sn, Ta, Th, Tl, V, W, Y, Nb, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Ho are either depleted or enriched from one profile to the other. Apart from Cr, V, Zr and Ce whose concentrations respectively attain 850 mg kg−1, 582 mg kg−1, 487 and 510 mg kg−1, the mining potential of the studied lateritic mantle is low.

Rare earth elements geochemistry of groundwater from Shanmuganadhi, Tamilnadu, India: Chemical weathering implications using geochemical mass-balance calculations

Groundwater samples were collected from Shanmughanadhi in Dindigul district of Tamilnadu, India, to determine the concentration and fractionation of REEs during chemical weathering. Groundwater samples collected from aquifers hosted in weathered and fractured crystalline formations were analyzed by ICP-MS for Rare earth elements (REEs) after filtering by 0.45 μm membrane filters. ΣREEs in Charnockite accounts 8.49 × 10−4mgL−1 and 1.08 × 10−3mgL−1 in hornblende biotite gneiss signifying higher REEs in Gneiss than Charnockite, due to higher flushing rates in gneiss and relatively shorter water residence time in Charnockite aquifer. Higher LREEs were observed upstream in the study area, followed by enrichment of MREEs and HREEs in midstream and discharge areas, respectively. Irrespective of lithology, the groundwater samples mostly exhibited a positive europium anomaly, which might be due to higher dissolution and mobilization of europium from plagioclase group minerals through rock-water interaction. The plagioclase feldspar, orthopyroxene, and alkali feldspars mineral weathering rates were 124, 17.5, and 20.0 mol/hectare/year. The rare earth minerals enriched in the host rocks provided the referenced material for the REE enrichment in the groundwater. Variations in pH and redox conditions in groundwater environments have influenced the enrichment of REE aided by continuous aquifer residence time, chemical weathering, and groundwater flow path.

Raman study of shock features in plagioclase feldspar from the Mistastin Lake impact structure, Canada

AbstractPlagioclase feldspar is one of the most abundant minerals on the surface of the Earth, the Moon, and Mars, and is also commonly found in meteorites. Studying shock effects in feldspar thus provides us with fundamental information about impact cratering processes on planetary bodies. In this study, plagioclase from monomict and polymict breccias, impact melt rocks, and shock‐metamorphosed target rocks, from throughout the Mistastin Lake impact structure, Canada, was examined using 514 nm laser Raman spectroscopy. As one of the very few impact structures with anorthosite in the target rocks, the Mistastin Lake impact structure provides a unique opportunity to study shocked plagioclase displaying progressive shock metamorphic features. A series of microscopic features was observed within plagioclase, including twins, needle‐like inclusions, planar features, and alteration. The lack of planar deformation features is notable. Raman spectra of these features suggest that this technique is capable of differentiating and classifying shock features in low to moderately shocked rocks. Caution should be exercised, however, as Raman spectra collected from unshocked plagioclase references with known compositions indicate that peak width and peak ratio of the Raman peaks in lower wave number region (<350 cm−1) and the main signature peaks around 500 cm−1 vary with chemical composition and crystal orientation. Data collected from diaplectic glass suggest that Raman features are efficient in distinguishing crystalline plagioclase and diaplectic glass. We also observed significant variations in the Raman intensities collected from diaplectic glass, which we ascribe to the localized disorder or inhomogeneity of shock pressure and temperature throughout the target.

Shock metamorphism in plagioclase and selective amorphization.

Plagioclase feldspar is one of the most common rock‐forming minerals on the surfaces of the Earth and other terrestrial planetary bodies, where it has been exposed to the ubiquitous process of hypervelocity impact. However, the response of plagioclase to shock metamorphism remains poorly understood. In particular, constraining the initiation and progression of shock‐induced amorphization in plagioclase (i.e., conversion to diaplectic glass) would improve our knowledge of how shock progressively deforms plagioclase. In turn, this information would enable plagioclase to be used to evaluate the shock stage of meteorites and terrestrial impactites, whenever they lack traditionally used shock indicator minerals, such as olivine and quartz. Here, we report on an electron backscatter diffraction (EBSD) study of shocked plagioclase grains in a metagranite shatter cone from the central uplift of the Manicouagan impact structure, Canada. Our study suggests that, in plagioclase, shock amorphization is initially localized either within pre‐existing twins or along lamellae, with similar characteristics to planar deformation features (PDFs) but that resemble twins in their periodicity. These lamellae likely represent specific crystallographic planes that undergo preferential structural failure under shock conditions. The orientation of preexisting twin sets that are preferentially amorphized and that of amorphous lamellae is likely favorable with respect to scattering of the local shock wave and corresponds to the “weakest” orientation for a specific shock pressure value. This observation supports a universal formation mechanism for PDFs in silicate minerals.

Evolution of Mount Cameroon volcanism: Geochemistry, mineral chemistry and radiogenic isotopes (Pb, Sr, Nd)

Mount Cameroon volcano has erupted several times in the 20th Century with documented eruptions in 1909, 1922, 1954, 1959, 1982, 1999 and 2000. Evidence of historic volcanism is represented by several older lava flows and lahar deposits around the flanks of the volcano. This study aims to assess the evolution of Mount Cameroon volcanism through its eruptive history via interpretation of mineralogical, whole rock geochemical and Pb, Sr, Nd isotope data generated from historic and recent lava flows. In this study, samples were collected from the 1959, 1982, 1999 and 2000 eruptions and from several historic eruption sites with unknown eruption dates.Evaluation of major and trace element data demonstrates that Mount Cameroon is geotectonically associated with within-plate Ocean Island Basalt Settings. More than 90% of the studied historic lavas (n ​= ​29) classify as tephrites and basanites whereas the modern lavas (n ​= ​38) are predominantly trachybasalts, demonstrating evolution from primitive to evolved lavas over time typically in response to fractional crystallization. Petrographically, the lavas are porphyritic with main mineral phases being olivine, clinopyroxene, plagioclase feldspars and Fe–Ti–Cr oxides. The 1982 lavas are predominantly aphyric and dominated by lath-shaped flow-aligned plagioclase in the groundmass. Olivine chemistry shows variable forsterite compositions from Fo60–89. Clinopyroxenes vary from diopside through augite to titanaugite with chemical composition ranges from Wo45En32Fs7 to Wo51En47Fs17. Plagioclase feldspars vary from labradorite (An56–70) to bytownite (An80–87). For the Fe–Ti–Cr oxides, calculated ulvöspinel component shows a wide variation from ulv38–87. CIPW-normative classification on the Di-Ol-Hy-Qz-Ne system shows that all Mount Cameroon lavas are nepheline-normative (Ne ranges from 4.20 wt.% to 11.45 ​wt.%).Radiogenic isotope data demonstrate that Mount Cameroon lavas are HIMU (or high μ ​= ​238U/204Pb), characterized by 206Pb/204Pb ​= ​20.19–20.46, 207Pb/204Pb ​= ​15.63–15.69, 208Pb/204Pb ​= ​40.01–40.30, 87Sr/86Sr ​= ​0.70322–0.70339 (εSr ​= ​−21.37 to −18.96) and 143Nd/144Nd ​= ​0.51276–0.51285 (εNd ​= ​+2.29 to +4.05). The historic lavas show stronger HIMU signature relative to the modern lavas, suggesting evolution towards less HIMU signatures over time. This study has revealed that Mount Cameroon volcanism has evolved from primitive magmas characterized by stronger HIMU signatures with high 206/204Pb and 208/204Pb isotopes, low SiO2 and high Mg, Ni, Cr content towards lower HIMU signatures with relatively higher SiO2, lower Mg, Cr and Ni compositions. The geochemical and isotopic changes, which account for the evolution of magmatism on Mount Cameroon occur over long periods of time because all the modern lavas erupted within the last 100 years are isotopically homogeneous, with very limited variation in SiO2 compositions.

PETROGRAPHY AND MICROTEXTURAL CHARACTERISTICS OF GRANODIORITE FROM WASIMI, SOUTHWESTERN NIGERIA

Rock samples of granodiorite from Wasimi were studied in detail to determine the minerals, mineral associations and the different micro-texture present in order to unravel the processes that were involved during the cooling of the magma. The following minerals were observed; plagioclase feldspars, K-feldspars, biotite, pyroxene, amphiboles, with zircon and sphene as accessory minerals. The pyroxene are engulfed in amphiboles and have reaction rims. Pyroxene occur as inclusions in plagioclase feldspars. Amphiboles are poikilitic with inclusions of quartz. Symplectic texture exits between the following minerals; plagioclase and K-feldspar, biotite and quartz, plagioclase and amphibole. The plagioclase feldspars have fractured and bent twin lamellae. Crystals of plagioclase feldspars are zoned and also exhibit both Carlsbad and albite form of twinning. It can be said that there was an initial slow cooling of the magma which was responsible for the large crystals of feldspars which was later followed by rapid cooling as the magma rises close to the surface which gave rise to zoned plagioclase feldspars and indication of high level intrusive.

Mineralogical and geochemical changes due to hydrothermal alteration of the volcanic rocks at Acoculco geothermal system, Mexico

Most of the volcanic rocks in the Acoculco geothermal system (AGS), near to the surface manifestations, are intensively altered. Thirty‐four surface volcanic rocks and five rocks from outcrop sections are considered in this work. Silica polymorphs (quartz, cristobalite and tridymite) are the dominant hydrothermal minerals in almost all the rock samples. The following other minerals are present in minor concentrations: alkali‐feldspars (sanidine potassic, anorthoclase and microcline), plagioclase feldspars (albite and anorthite), clay minerals (illite, kaolinite and montmorillonite), anhydrite, buddingtonite, titanoaugite, magnetite and anatase. This type of mineral assemblage of the rocks indicates an intensive silicic and argillic alteration. Comparison of the elemental concentrations of the surface acid rocks of the AGS with that of the precursor rock has indicated alteration‐induced changes in (a) chemical mobility in the concentrations of major element oxides, with an increase in the concentrations of SiO2, and TiO2, loss in those of Al2O3, Fe2O3, MnO, MgO, CaO, Na2O and K2O, and no statistically significant changes in those of P2O5, (b) no significant changes in the concentrations of LREE and MREE (except Dy and Ho), however, less but significant loss in the concentrations of Dy and Ho, and HREE, and (c) there is an enrichment in the concentrations of Nd, Sr, Sc, V, Nb, Ag, Sn, Pb, Tl, Ta, U and Th; and depletion in Be, Co, Zn, Ga, Ge, Rb, Y, Zr, Mo, Cs, Ba and Hf compared to those of the precursor rock. This type of distribution of the elements may indicate (a) an intense silicic alteration; and (b) REEs might have been leached from the original rocks because of hydrothermal alteration processes, but only LREEs, and MREEs (except Dy and Ho) can be redistributed and accommodated in the hydrothermal minerals, providing them with somewhat inert (immobile) behaviour. The mass change calculations have indicated that MnO and Sr have experienced the greatest and smallest mass changes, respectively. The identification of outliers in chemical data has revealed the presence of two distinctive groups of rocks. Ten out of the total 27 acid volcanic rocks with several elements as outlier data are negligibly to moderately altered (Group‐1), and the remaining 17 acid rocks without outlier data are intensively altered rocks (Group‐2).

Forsteritic olivine and magnesium-rich orthopyroxene materials measured by Chang'e-4 rover

China's Chang'e-4 probe achieved the first soft landing within the South Pole-Aitken (SPA) basin, which is the oldest, largest, and deepest basin on the lunar farside. The deployed Chang'e-4 rover made in situ spectral measurements along the rover traverse during a nominal three-month mission period. Spectral analyses imply that materials at the Chang'e-4 landing site have a forsteritic olivine (OL) and magnesium (Mg)-rich orthopyroxene (OPX) assemblage in almost equal fractions. The Chang'e-4 rover measured materials, which were essentially mixture of multiple sources, were primarily the weathering products of Finsen crater ejecta. Plagioclase (PLG), which has significant implication for the provenance, is often spectrally transparent or featureless in the wavelength range (450–2395 nm) of the in situ measured spectrum. Depending on the possible absence or presence of abundant PLG, the materials likely originated from a differentiated SPA impact melt pool or from an Mg-suite pluton in the lunar lower crust, and were less likely to originate from the lunar upper mantle.

Aqueous alteration mapping in Rishabdev ultramafic complex using imaging spectroscopy

Hyperspectral remote sensing/imaging spectroscopy has enabled precise identification and mapping of hydrothermal alteration mineral assemblages based on diagnostic absorption features of minerals. In the present study, we use Airborne Visible InfraRed Imaging Spectrometer-Next Generation (AVIRIS-NG) datasets acquired over Rishabdev ultramafic suite to derive surficial mineral map using least square based spectral shape matching in wavelength range of diagnostic absorption features of minerals. Resulting mineral map revealed presence of hydrothermally altered serpentine group of minerals and associated alteration products (talc and dolomite) along with clays and phyllosilicates. Mineral maps are validated using field spectral measurements and published geological map. Involvement of low temperature (<350 °C) hydrothermal fluid in serpentinization of ultramafic rocks in the region is inferred from analysis of deepest absorption features of muscovites at 2.20 μm, spectral abundance of lizardite and absence of prenhite-pumpyllite facies mineral assemblages. Talc was found to be the most common alteration product of serpentines followed by dolomites. Intense alteration of serpentines to talc along the fracture zone is attributed to the circulation of carbon dioxide rich hydrothermal fluids along these conduits. Kaolinite and halloysite are primarily associated with granites and are the result of hydrothermal alteration of plagioclase feldspar in granites while muscovite and illites are generally associated with phyllites and quartzites . The study demonstrates the potential of imaging spectroscopy for mapping hydrothermal alteration mineral assemblages in ultramafic complex.

Long term reactivity of CO2 in a low salinity reservoir-seal complex

An understanding of the long-term reactivity of different rock types to injected CO2 is needed for sequestration site assessment. Relative to saline aquifer studies, the long term reactivity of CO2 in low salinity aquifers has received little attention. Currently in Australia, the Surat Basin is being appraised for its large-scale CO2 storage potential within low salinity aquifers. Sixteen core samples from the Precipice Sandstone and Evergreen Formation – the notional target reservoir and seal complex – were characterized for mineral content; helium, mercury-injection and micro CT porosities; air permeability; and, imaged with SEM-EDS. Samples consisted of quartz rich reservoir sandstones, feldspar and clay rich or calcite cemented sandstones (secondary reservoir), mudstones (sealing complex), and oolitic ironstones (sealing complex) derived from braided river, fluvial-deltaic, and restricted marine shoal depositional environments, respectively. The reservoir sandstone samples characterized here had measured total porosity that ranged from 11 to 23% with pore throats mainly between 90 and 100 μm, and core air permeability from 558 to 3397 mD. In the Precipice Sandstone reservoir sample μCT plugs, 98% of the pore space was connected with calculated vertical permeability 145–4611 mD and horizontal 4291–8200 mD. Feldspar and clay rich sandstone and mudstone samples from the overlying Evergreen Formation had porosity that ranged between 0.2 and 22.9%, with a wide range of pore throat sizes from ~0.005 to 30 μm, and permeability from 0.2 to 28.1 mD, respectively. Ironstone and mudstone samples from the Westgrove Ironstone Member (Evergreen Formation) had porosity from 0.7 to 9.7% and a low permeability of 0.04 mD.Kinetic geochemical CO2 reactivity models made predictions over two time-scales: 30 or 1000 years. Selected models also accounted for the potential presence of 10 ppm SO2 gas. The Precipice Sandstone quartz-rich reservoir sandstones had consistently small amounts of reactive minerals and mineral trapping or scaling of the reservoir was not predicted over 30 years, with the pH approximately 4.5 after 30 years. Samples from the Evergreen Formation included feldspar and clay rich sandstones and mudstones, several contained variable amounts of carbonate cement. Their response to CO2 was more influenced by mineral content than rock type. Plagioclase feldspars and Fe-rich chlorite were the main silicate minerals that reacted to produce siderite and ankerite mineral trapping up to 2.57 kg/m3 CO2. In the very unlikely event that CO2 rich fluids migrated upwards as far as the Westgrove Ironstone Member, chlorite is predicted to alter to siderite. This study indicates that the Precipice Sandstone reservoir in the study region has a low likelihood of mineral scaling which is favorable to avoid CO2 injectivity issues. Mineral trapping as ankerite and siderite could be expected to trap CO2 in the chlorite and plagioclase rich Evergreen Formation seal lithologies. Further work is suggested on validating long term predictions with observation data from natural analogue studies.

Quartz- Porphyry Dolerite in A Selected Part of Southern Benue Trough, Nigeria

The dolerites in some parts of southern Benue Trough were studied petrographically. The results show that most of the dolerites in the Anambra and Afikpo basins are olivine dolerites except Umuchieze LokpaUkwu that host mostly quartz porphyry dolerites. The thin section results show that the dolerite rocks in Umuchieze LokpaUkwu has mineral paragenesis of plagioclase feldspar+quartz +pyroxene + biotite + hornblende + and hematite. The pore spaces and fractures in the rocks are healed by the infilling of quartz. The porphyritic texture of the dolerite in the study area show variable temperatures of the crystallized magma that formed the dolerite. The sharp contacts of the dolerites and the host rocks could play roles in the alteration of the crystallizing magma. Hydrothermal interaction, contamination and assimilation played major roles in the evolutionary processes of the magma that formed the quartz-porphyry dolerite. Key word : Quartz, Dolerites, Benue Trough, Magma DOI: 10.7176/JEES/10-2-09 Publication date: February 29 th 2020

Raman and Infrared Microspectroscopy of Experimentally Shocked Basalts

AbstractPetrographic, micro‐Raman and micro‐Fourier transform infrared spectral analyses of experimentally shocked basalt and basaltic andesite samples (up to ~63 GPa) indicated that progressive amorphization of plagioclase feldspar with increasing pressure resulted in detectable spectral variations that mimic those of the experimentally shocked, plagioclase‐dominated rocks analyzed in earlier studies. However, variations in starting sample composition and/or shock propagation through the minerals and mesostasis within these basaltic rocks resulted in variable distribution of shock effects within the samples, as manifested in their infrared and Raman spectra. In particular, the presence of primary igneous glass within the starting samples subdued the observed effects because of the spectral similarity between the glass and shocked plagioclase (maskelynite and plagioclase glass). This caused ambiguity in distinguishing between amorphization resulting from shock effects and that associated with primary glass, particularly for the more hypocrystalline basaltic andesite (~30% glass) compared to the basalt sample (~10% glass). Nonetheless, the correlation between shock pressures and key spectral parameters (Raman peak ratios, infrared reflectance peak band heights) for plagioclase‐bearing sample areas terminated in the ~25–30 GPa pressure range. This was consistent with the amorphization onset pressures of andesine and reflected the increasing presence of maskelynite at these higher pressures. Higher spatial resolution mapping using these techniques could provide better insight regarding the influence of grain boundaries and mineralogical variations on shock propagation in fine‐grained, glassy, basaltic samples. This would help refine the nature and magnitude of shock propagation effects in naturally shocked basaltic samples analyzed during in situ investigations of planetary surfaces.

Unconventional high-pressure Raman spectroscopy study of kinetic and peak pressure effects in plagioclase feldspars

We present the results of a high-pressure semi-hydrostatic study of two plagioclase minerals, andesine and albite, using diamond anvil cells (DACs) to characterize in situ variations in Raman spectra under different static pressures. In this work, we also examined the kinetic effects on deformation at both long and short timescales through non-traditional experiments in which the DAC was either dropped or struck with a mallet. We examined the effects of strain rate, quench rate, and pressure duration on the Raman spectra of plagioclase. We observed that amorphization occurred in all the plagioclase samples we analyzed, and that amorphization onset and permanence differ depending on the composition, kinetics, energy input, and peak pressure. In andesine, samples pressurized above a peak pressure of 18 GPa, amorphization is permanent. Below this critical pressure, the phase has ‘memory’, and crystalline andesine reforms on decompression. Our findings suggest the presence of a thermodynamic energy well in andesine around 18 GPa, and we show that any additional energy input while close to 18 GPa results in amorphization becoming permanent. The effect of the energy well may be relevant for longer duration impacts. For such impacts, equilibrium state studies of deformation and phase formation were previously considered to be applicable. These experiments illuminating the presence of memory effects in plagioclase have implications for comparing static compression, in which samples are measured while under compression, with shock compression, for which samples are measured after decompression.

Melt-rock interaction between granitic pegmatites and hosting amphibolites from the Chiavenna Ophiolitic Unit (Tanno Pegmatitic Field, Central Alps, North Italy)

The Tanno pegmatitic field, placed southward of Chiavenna (Central Alps, Sondrio, Italy), develops a large number of subplanar dykes that crosscut the Chiavenna Unit, an ophiolitic complex mainly composed, in the study area, of amphibolite rocks. This study focuses on the contact between a pegmatitic dyke and the amphibolitic country rock. We distinguished four zones across the contact: I) inner amphibolite, II) contact amphibolite, III) contact pegmatite, IV) inner pegmatite. The inner amphibolite, not affected by melt-rock interaction, is composed of amphibole, phlogopite, ilmenite, titanite and rutile. Two amphibole generations occur, both of them showing a patchy compositional zoning. Amphibole I are Mg-hornblende, whereas Amphibole II have a pargasitic composition. The contact amphibolite shows an enrichment of mica belonging to the phlogopite-biotite series, titanite and the presence of fluorapatite and plagioclase (Ab45-60), that is absent in the inner amphibolite. Close to the contact, amphiboles display no zoning and gain an Mg-horneblenditic composition. The contact pegmatite has quartz, albitic plagioclase, garnet (almandine-spessartine series), muscovite, K-feldspar and fluorapatite. It shows a comb texture, with elongation of plagioclase crystals normal to the contact itself. Far from the contact, the inner pegmatite has an increasing grain-size and a less organized texture. In this zone several accessory phases occur, including gahnite, columbite-(Fe), monazite-(Ce), xenotime-(Y), uraninite and betafite. Whole rock analyses suggest that a chemical exchange, concerning both major elements and trace elements, occurred between the pegmatitic melt and the hosting amphibolite. A considerable increase of SiO2, Na2O and, to a lesser extent, of Al2O3 is observed from the amphibolite towards the pegmatite; K2O and CaO show a decrease at the same extent. The REE pattern in the pegmatite highlights an enrichment in HREE at the contact. Mineral chemistry confirms this trend with variations observable in plagioclase, gradually more albitic from the amphibolite to the pegmatite. Mineralogical characters and geochemical features allow to classify the Tanno pegmatite in the LCT (Lithium, Cesium, Tantalium) family. Based on the metamorphic peak conditions reported from the Lepontine Dome the ambient conditions during pegmatite intrusion were ca. 550°C and 5 kbar. The reduced thermal difference between pegmatite and wall rock explains the diffuse contact observed by X-ray micro-computed tomography. The collected data suggest a chemical interaction between melt and wall rock, according to the following reaction taking place in the amphibolite Amphibole I + Amphibole II + Ilmenite + Pegmatitic melt → Amphibole III + Plagioclase + Phlogopite + Titanite + Fluorapatite

Plagioclase-facies thermobarometric evolution of the External Liguride pyroxenite-bearing mantle (Suvero, Italy)

Plagioclase peridotites are an important marker of the shallow geodynamic evolution of the lithospheric mantle at extensional settings. Based on lowpressure experiments, a recent study by Fumagalli et al. (2017) defined and calibrated a geobarometer for peridotitic bulk compositions, based on the Forsterite-Anorthite-Ca-Tschermak-Enstatite (FACE) pressure-sensitive equilibrium. The Suvero plagioclase-bearing peridotites, on which the FACE geobarometer was calibrated, are primarily associated to plagioclase pyroxenites. Assuming that the pyroxenites record the same Pressure-Temperature evolution than the plagioclase peridotites, they represent ideal candidates to test the applicability of the FACE geobarometer on pyroxenitic compositions. As documented in the plagioclase peridotites, the pyroxenites are characterized by the development of fine-grained neoblastic assemblages, indicative of partial recrystallization under plagioclase-facies conditions. Chemical zonations in these neoblastic mineral aggregates suggest equilibration stages at variable pressure and temperature and allowed to document two re-equilibration stages corresponding to the onset of plagioclase-facies recrystallization (830-850°C, 6.9-8.1±0.5 kbar) and a shallower colder re-equilibration (770-790°C, 5.8-5.9±0.5 kbar), respectively. The decompressional evolution reported for pyroxenitic bulk compositions is consistent with the exhumation history documented in the associated Suvero peridotite, although at slightly higher equilibrium pressures (~ 1 kbar). Remarkably, the much lower XCr in pyroxenites reflects in lower Cr incorporation in pyroxenes and, consequently, in significantly higher Ca-Tschermak activity in clinopyroxene that might introduce the systematic pressure overestimation by FACE geobarometer.

Mapping geology and structural features of Kazaure SE, NW Nigeria: Justifying groundwater potential model

This research is focused on the evaluation of lithological units of the Kazaure area, north western Nigeria. The geological mapping was carried out using topographical sheet on a scale of 1:50,000. The methodology adopted for the study involved Field studies and petrographic analysis, which included close observation of outcrops and their exposures, their mineralogy and structures as well as recording of their geographical locations and strike/dips of foliations. The analysis revealed that, the area is underlain by three (3) major rock units: muscovite schist, porphyritic granite and sandstone (Chad Formation) with quartzite occurring as a minor lithology. The trend of lineaments shows a predominating NE-SW direction in the rocks. The cations and anions analyzed revealed that they are within the range of acceptable standard, except the higher concentration ofand which might have formed from acidic water of the area. The dominant water facies in the study area is -. These facies might have taken their sources from rock-water interaction of silicate minerals (Plagioclase feldspar). Wilcox plot of salinity hazard of the water samples indicated that, the water of the area is good for irrigation. It can be classified, the value of electrical conductivity of 0 - 250 excellent, 250 - 750 good, 750 - 2250 doubtful and > 2250 µS/cm unsuitable. It is strongly recommended that the stake holders and governments at all levels enforce further studies of adjacent sheets for sustainable groundwater exploration and exploitation for better human and other domestic use.

Geology and petrography of precambrian rocks of Katsina urban area, northwestern Nigeria

This present study, the mapped area is located between latitude E07°35'00'' to E07°39'0011" and longitude N13°00'00'' to N12°57'00" of sheet 34NW, Katsina State, Northern Nigeria. The area is underlain by Basement Complex rocks and syeno-granitic rocks which dominate in the area. The two sets of granitic rocks were observed and distinguished by texture. The northwest of the mapped area consists of very coarse to coarse grained syeno-granitic rocks, while in the southeast, the rocks are medium to coarse grained. These outcrops exhibit various systems of joints. The mineralogical compositions determine by thin section results displays: quartz, biotite, muscovite, plagio-clase feldspar, apatite, sericite, hornblende, augite and microcline. There are two generalizations of joints with primary WSW to ENW direction and NE-SW, MMW-SSE and WWW-ESE secondary direction of NE-SW, MME-SSE and WWW-ESE.

Characterisation of Biooxidation Feed and Products for Improved Understanding of Biooxidation and Gold Extraction Performance

This paper presents a study on characterisation of refractory ore, biooxidation feed and product, and cyanidation tailings with the aim of understanding the causes of excessive continuous frothing, incomplete sulphide oxidation, high reagent consumption, high cyanidation residues and low overall recovery as encountered in biooxidation of refractory ores. Techniques involving carbon and sulphur speciation, Quantitative X-Ray Diffraction (QXRD), Scanning Electron Microscopy (SEM) and Optical Microscopy (OM) were used to characterise the ore samples, flotation concentrate (BIOX® feed), biooxidised product (BIOX® CIL Feed) and cyanidation tailings (BIOX® CIL Tails) from a biooxidation plant. The main minerals present in the ore were quartz (45%), chlorites (21%), plagioclase feldspar (13%), dolomite (5%), pyrite (2%) and mica group (2%). The flotation concentrate recorded 18% mica, and this was responsible for excessive frothing in the biooxidation circuit as confirmed by the QXRD analysis. The carry-over froth to the CIL circuit led to short-circuiting of poorly leached material into the cyanidation tailings, resulting in high cyanidation residues. Secondary refractory minerals; gypsum and jarosite, which were observed in the biooxidation product by the QXRD, have the potential to coat unreacted sulphide particles, leading to incomplete sulphide oxidation as observed here. Partially oxidised sulphides led to high consumption of reagents such as oxygen and cyanide during cyanidation. Gypsum and jarosite also encapsulated gold particles as observed in the BSED analysis. Coated gold particles had reduced access to lixiviants during the subsequent cyanidation process, leading to high leach residues. The biooxidised product (BIOX® CIL Feed) also recorded a high organic carbon content of 6.67, while analysis by BSED revealed the presence of graphitic carbon and coatings on gold surfaces; an indicator for high preg-robbing activities during cyanidation of the concentrate. Preg-robbing indices of 64.4% and 72.7% were recorded for the flotation concentrate (BIOX® feed) and BIOX® CIL feed respectively. The overarching effect of all the observations is a decrease in overall gold recovery.

Soil Minerals Serving as Source of Arsenic in Alluvial Aquifers of Holocene: A Case Study from Indus Delta, Sindh, Pakistan

Groundwater arsenic contamination is recently reported in the alluvial aquifers of Indus deltaic plain. Since the source of arsenic is believed to be natural as widely reported in other deltaic aquifers of same age (Holocene), it is imperative to evaluate the soil characteristics for identifying the sources of arsenic and its mobilization mechanism. For this purpose, 49 soil samples were collected from near aquifer sites in all three talukas of Tando Muhammad Khan district. Visual analysis revealed that soil is light grey in color with fine texture ranging from silt to silty-clay. The X-ray diffraction study reveals the occurrence of quartz, mica and clay minerals in all collected soil samples. Plagioclase feldspar is second dominant mineral group in the order of albite (calcian) &gt;albite&gt;albite (disordered) = anorthite &gt; anorthite (sodian) = anorthite (disordered). Calcite is major carbonate mineral which is detected in 40 out of total 49 soil samples. The occurrence of other occasional minerals includes amesite, nitro-calcite, rutile and zinnwaldite. The frequency of micaceous minerals in collected samples is in the order of clinochlore&gt; polylithionite&gt; Biotite &gt; phlogopite&gt; muscovite. Polylithionite is found in about half of the total soil samples, where most of the aquifers contain arsenic &gt;20 μg/L (Khan, 2014). Phlogopite is observed in seven soil samples which are also associated with clinochlore. On the other hand, biotite is found in 14 sediment samples collected from Tando Muhammad Khan and Bhulri Shah Karim talukas and muscovite occurs in three soil samples of Tando Muhammad Khan taluka. It can be concluded from present study that fine-grained Phyllosilicates have strong affinity for arsenic retention. These sediments are important source of arsenic Indus delta and other deltaic plains of the world.