Heavy-mineral Concentrates Research Articles

Zr-Ti-Fe placers along the coast of NE Argentina: Provenance analysis and ore guide for the metallogenesis in the South Atlantic Ocean

The Zr-Ti-Fe placers along the coast of Rio Negro and Buenos Aires Provinces, Argentina, evolved within the reaches of the Malvinas Current (1st order hydrodynamic regime). Together with some regional 2nd order local currents it is of major influence on the mineral assemblage of these terrigenous linear shoreline deposits. The nearshore-marine placers came into being in a macro- to mesotidal (San Matias Gulf) and meso- to microtidal regime (Bahia Blanca Estuary).The modern-day placers under study result from a transgressive regime with only moderate detrital input by the contemporaneous river drainage systems. The proto-placers are hallmarked among the heavy minerals (HM) by changes in the redox system which affected predominantly the Fe-Ti oxides and lead to pseudobrookites and kleberite. Light minerals (LM) in the present-day placers played a different role which is mirrored by changes in the alkalinity of the intragranular fluid system. As far as the environment of deposition is concerned in these shoreline deposits, the dune belt and backshore are most prospective as to the concentration of magnetic and non-magnetic HM. The HM assemblage of the coastal placers is a mirror image of the Afro-American part of Gondwana and its break-up history during the Mesozoic and Cenozoic. The HM reflect the alternating orogenic and anorogenic geodynamic processes operative along the passive margin of both continents. While the orogenic regimes contributed to the accumulation of metallogenetically irrelevant HM (e.g. alumosilicates, spinel, garnet, amphibole) of the placers, the anorogenic geodynamic regime may be held accountable for the target elements in the placer deposits Zr, Ti and Fe. Fe-Ti oxides (rutile, ilmenite-titanohematites, titanomagnetites) and zircon form placer deposits in their own rights with zircon playing an additional minor role also as ore guide to rift-related deposits. Titanium dioxides (Nb-Ta rutile s.s.s., struverite) and Nb titanite take the most prominent role as ore guides to rare element-bearing pegmatites, alkali magmatic rocks and carbonatites. In conclusion, the HM suite encountered in the placer deposits denotes a hot-spot mineralization at a triple junction of the South Atlantic, the Antarctic and the Proto-Iapetus Oceans. The Zr-Ti-Fe placer deposits are part of the clastic halo or expressed metaphorical as remnants of this hot-spot metallogenesis encompassing anorogenic Nb-Ta deposits related to alkaline-magmatic rocks, Skaergaard-type Fe-concentration and anorthosite-hosted Fe-Ti deposits.

Gold in the hills: patterns of placer gold accumulation under dynamic tectonic and climatic conditions

Formation of placer accumulations in fluvial environments requires 103–106 or even greater times concentration of heavy minerals. For this to occur, regular sediment supply from erosion of adjacent topography is required, the river should remain within a single course for an extended period of time and the material must be reworked such that a high proportion of the sediment is removed while a high proportion of the heavy minerals remains. We use numerical modeling, constrained by observations of circum-Pacific placer gold deposits, to explore processes occurring in evolving river systems in dynamic tectonic environments. A fluvial erosion/transport model is used to determine the mobility of placer gold under variable uplift rate, storm intensity, and rock mass strength conditions. Gold concentration is calculated from hydraulic and bedload grain size conditions. Model results suggest that optimal gold concentration occurs in river channels that frequently approach a threshold between detachment-limited and transport-limited hydraulic conditions. Such a condition enables the accumulation of gold particles within the framework of a residual gravel lag. An increase in transport capacity, which can be triggered by faster uplift rates, more resistant bedrock, or higher intensity storm events, will strip all bedload from the channel. Conversely, a reduction in transport capacity, triggered by a reduction in uplift rate, bedrock resistance, or storm intensity, will lead to a greater accumulation of a majority of sediments and a net decrease in gold concentration. For our model parameter range, the optimal conditions for placer gold concentration are met by 103 times difference in strength between bedrock and fault, uplift rates between 1 and 5 mm a−1, and moderate storm intensities. Fault damage networks are shown to be a critical factor for high Au concentrations and should be a target for exploration.

ИЗУЧЕНИЕ ВЛИЯНИЯ ВИБРАЦИОННЫХ КОЛЕБАНИЙ НА ПРОЦЕСС КОНЦЕНТРАЦИИ ТЯЖЕЛЫХ МИНЕРАЛОВ ПОД ДЕЙСТВИЕМ ЦЕНТРОБЕЖНОЙ СИЛЫ

ИЗУЧЕНИЕ ВЛИЯНИЯ ВИБРАЦИОННЫХ КОЛЕБАНИЙ НА ПРОЦЕСС КОНЦЕНТРАЦИИ ТЯЖЕЛЫХ МИНЕРАЛОВ ПОД ДЕЙСТВИЕМ ЦЕНТРОБЕЖНОЙ СИЛЫ

Heavy Metals and Mineral Contents of Beef Sold at University Campus, Peshawar, Khyber Pakhtunkhwa, Pakistan

Heavy Metals and Mineral Contents of Beef Sold at University Campus, Peshawar, Khyber Pakhtunkhwa, Pakistan

Elevated concentrations of naturally occurring radionuclides in heavy mineral-rich beach sands of Langkawi Island, Malaysia

Study is made of the radioactivity in the beach sands of Langkawi island, a well-known tourist destination. Investigation is made of the relative presence of the naturally occurring radionuclide 40K and the natural-series indicator radionuclides 226Ra and 232Th, the gamma radiation exposure also being estimated. Sample quantities of black and white sand were collected for gamma ray spectrometry, yielding activity concentration in black sands of 226Ra, 232Th and 40K from 451±9 to 2411±65Bqkg−1 (mean of 1478Bqkg−1); 232±4 to 1272±35Bqkg−1 (mean of 718Bqkg−1) and 61±6 to 136±7Bqkg−1 (mean of 103Bqkg−1) respectively. Conversely, in white sands the respective values for 226Ra and 232Th were appreciably lower, at 8.3±0.5 to 13.7±1.4Bqkg−1 (mean of 9.8Bqkg−1) and 4.5±0.7 to 9.4±1.0Bqkg−1 (mean of 5.9Bqkg−1); 40K activities differed insubstantially from that in black sands, at 85±4 to 133±7Bqkg−1 with a mean of 102Bqkg−1. The mean activity concentrations of 226Ra and 232Th in black sands are comparable with that of high background areas elsewhere in the world. The heavy minerals content gives rise to elevated 226Ra and 232Th activity concentrations in all of black sand samples. Evaluation of the various radiological risk parameters points to values which in some cases could be in excess of recommendations providing for safe living and working. Statistical analysis examines correlations between the origins of the radionuclides, also identifying and classifying the radiological parameters. Present results may help to form an interest in rare-earth resources for the electronics industry, power generation and the viability of nuclear fuels cycle resources.

Reduced sediment supply in a fast eroding landscape? A multi-proxy sediment budget of the upper Rhône basin, Central Alps

Alpine water and sediment supply influence the sediment budget of many important European fluvial systems such as the Rhine, Rhône and Po rivers. In the light of human induced climate change and landscape modification, it becomes increasingly important to understand the mechanisms of sediment production and supply in Alpine sediment systems. This study aims to investigate the modern sediment budget of the upper Rhône basin, one of the largest Alpine intramontane watersheds, located in the Central Alps of southwestern Switzerland. Major areas of sediment generation are fingerprinted by framework petrography, heavy mineral concentrations and bulk geochemistry. The relative contributions of the three major sources to the sediment of the trunk Rhône river are identified by compositional mixing modelling. Concentrations of the terrestrial cosmogenic nuclide 10Be measured in quartz separated from fluvial sediments provide spatially averaged denudation rates for selected tributary basins. Results from sediment fingerprinting and mixing modelling suggest that tributaries located in the North and the East of the catchment are generating most of the sediment transported by the Rhône river to its primary sedimentary sink in Lake Geneva. Despite having some of the highest denudation rates within the basin, tributaries located in the southern area of the Rhône basin are relatively underrepresented in the sediment budget of the Rhône river. These tributaries are severely affected by human activities, for example through sediment mining as well as water and sediment abstraction in large hydropower reservoirs. Together, these processes reduce the basin-wide sediment discharge by about 50%, thereby explaining most of the observed compositional pattern. In addition, there is evidence suggesting that large amounts of glaciogenic sediments are currently supplied by retreating glaciers. Glaciogenic material with its low 10Be concentrations can lead to a significant overestimation of denudation rates and thus limit the applicability of cosmogenic nuclide analysis in such glaciated settings.

Tellurium and selenium in Mesoproterozoic red beds

Samples of red bed sediments in several Mesoproterozoic successions contain enrichments of tellurium (Te), including discrete telluride minerals. The tellurides were neoformed during redox-controlled diagenesis, rather than representing mechanical concentrations of heavy minerals. Tellurium is enriched relative to selenium, which may reflect erosion of Archean and Palaeoproterozoic rocks with high Te contents. High continentality during the Mesoproterozoic would have limited the delivery of Te and other trace elements to the oceans, so accumulated Te on the continents.

Contribution of natural and anthropogenic effects in the Iznik Lake bottom sediment: Geochemical and microfauna assemblages evidence

The relationship between the distribution of benthic foraminifera with ostracoda and sediment type and geochemical environment in the Iznik Lake is discussed. The microfauna (benthic foraminifer and ostracod) were sampled in seven recent bottom sediment samples, and geochemical variables of the sediment of the same samples were measured. This study is aimed at investigating the geochemical properties of 7 bottom sediment samples analysed in 5 lines in Iznik Lake. The depths for the samples varies from 1 to 68 m. The microfauna individuals were found in very low quantity, a total of 5 species foraminifera and 11 species 10 genus ostracod were identified. The geochemical properties were found to correspond well to the sediment type and depositional environment and five different sediment/depositional environment types could be distinguished. The individuals of microfauna reveals specific faunal assemblages that are closely related to these sediment and geochemical environment types. According to the survey, sediments encountered in the formation of gypsum crystals feature when considered together with the magnetism of Iznik Lake and the surrounding area suggest that are affected by new tectonics. Again this geochemical study the magnetic properties of the heavy-mineral contents, the entire amount of magnetite and hematite and heavy-mineral content has appeared to be affected by changes in the process. The purpose of this work is to distinguish the natural (geogenic) component, originated by techtonical origin this lake, from anthropogenic contamination owing to human activity. There were relationship between microfauna assemblages and heavy metals, trace element pollutant in the bottom lake sediments. Additionally, less individuals are found in most of the sediment samples in observed (in this 7 samples), this coincidence suggests that the heavy metals within the environment can also be a cause. The reason that of heavy metals, trace element pollutants are a factor in the distribution of microfaunal assemblages of genera and species were observed.

Physicochemical and elemental studies of Hydrocotyle javanica Thunb. for standardization as herbal drug

ObjectiveTo explore the leaves of Hydrocotyle javanica Thunb. as a source of safe and effective antibacterial herbal medicine. MethodsThe standardization was validated by stepwise physicochemical studies, element analysis, determination of ash values, fluorescence analysis, assessment of moisture content, extractive values in different solvent systems and extraction methods. Heavy metal contents, mineral and element contents were analysed by atomic absorption spectrophotometry, inductively coupled plasma-mass spectrometer and CHNS/O analyser, respectively. ResultsThe methanol extract of the folklore medicinal plant having antibacterial efficacy contained flavonoids and phenolic OH groups. The ICP multi standard indicated the presence of three major compounds with molecular mass of 161190 and 221 Da. Heavy metals viz. lead, mercury and copper content were 4.38 ppm, < 0.05 ppm and 24.70 ppm, respectively. Minerals content of calcium, phosphorus, potassium and iron were 1190.94 mg/100 g, 375.57 mg/100 g, 2820 mg/100 g and 340.20 mg/100 g of plant sample, respectively. Elements like carbon, hydrogen, nitrogen and sulphur contents were 38.18%, 5.67%, 2.23% and 0.51%, respectively. Heavy metal profile of the tested plant was within the permissible limits of the regulatory authorities. ConclusionsHence the present physicochemical and elements studies reveals that the plant Hydrocotyle javanica Thunb. could be a potent source of herbal preparation as well as a safe and novel synthetic antibacterial drug.

Understanding heavy mineral enrichment using a three‐dimensional numerical model

AbstractLayered deposits of relatively light and heavy minerals can be found in many aquatic environments. Quantification of the physical processes which lead to the fine‐scale layering of these deposits is often limited with flumes or in situ field experiments. Therefore, the following research questions were addressed: (i) how can selective grain entrainment be numerically simulated and quantified; (ii) how does a mixed bed turn into a fully layered bed; and (iii) is there any relation between heavy mineral content and bed stability? Herein, a three‐dimensional numerical model was used as an alternative measure to study the fine‐scale process of density segregation during transport. The three‐dimensional model simulates particle transport in water by combining a turbulence‐resolving large eddy simulation with a discrete element model prescribing the motion of individual grains. The granular bed of 0·004 m in height consisted of 200 000 spherical particles (D50 = 500 μm). Five suites of experiments were designed in which the concentration ratio of heavy (5000 kg m−3) to light particles (i.e. 2560 kg m−3) was increased from 6%, 15%, 35%, 60% to 80%. All beds were tested for 10 sec at a predefined flow speed of 0·3 m sec−1. Analysis of the particle behaviour in the interior of the beds showed that the lighter particles segregated from the heavy particles with increasing time. The latter accumulated at the bottom of the domain, forming a layer, whereas the lighter particles were transported over the layer forming sweeps. Particles below the heavy particle layer indicated that the layer was able to armour the particles below. Consequentially, enrichment of heavy minerals in a layer is controlled by the segregation of a heavy mineral fraction from the light counterpart, which enhances current understanding of heavy mineral placer formation.

Geochemical characteristics of modern river sediments in Myanmar and Thailand: Implications for provenance and weathering

The elemental composition of organic matter and the major and trace element compositions of stream sediments from Myanmar (Ayeyarwady and Sittaung rivers) and Thailand (Mekong and Chao Phraya rivers, and their tributaries) were determined to examine their distributions, provenance, and chemical weathering processes. Higher total organic carbon (TOC) and total nitrogen (TN) contents in the finer grained sediments indicate hydrodynamic energy may control their distributions. TOC/TN ratios indicate inputs of both aquatic macrophyte and higher vascular plant material to the river sediments. The major element abundances of the sediments are characterized by predominance of SiO2 in coarser fractions and a marked negative correlation with Al2O3, representing primary grain size primarily control on SiO2 content. Marked depletion of most labile elements (Na2O, CaO, K2O, Ba and Sr) relative to UCC (upper continental crust), indicate destruction of feldspar during chemical weathering in the source area or during transport. However, enrichment of some high field strength elements (Zr, Th, Ce and Y) relative to UCC and higher Zr/Sc ratios indicate moderate concentration of resistant heavy minerals in finer-grained samples. Discriminant diagrams and immobile trace element characteristics indicate that the Mekong, and Chao Phraya river sediments were largely derived from felsic sources with compositions close to typical rhyolite, dacite/granodiorite, UCC, I- and S-type granites. Relative enrichment of ferromagnesian elements (e.g. MgO, Cr, Ni) and high Cr/V and low Y/Ni ratios in Ayeyarwady and Sittaung sediments indicate the presence of a mafic or ultramafic component in their sources. The ICV (Index of Compositional Variability), CIA (Chemical Index of Alteration), PIA (Plagioclase Index of Alteration), αAl, Rb/Sr and K2O/Rb ratios indicate that the Ayeyarwady and Sittaung sediments record low to moderate degrees of chemical weathering in their source, compared to moderate to intense chemical weathering in the Mekong and Chao Phraya river basins. These results are compatible with existing major ion data for river waters collected at the same locations.

Sedimentary rhythms in coastal dunes as a record of intra-annual changes in wind climate (Łeba, Poland)

Abstract It is shown that coastal dunes bear a so far unread archive of annual wind intensity. Active dunes at the Polish coast near Łeba consist of two genetic units: primary dunes with up to 18 m high eastward-dipping foresets, temporarily superimposed by smaller secondary dunes. Ground-penetrating radar (GPR) data reveal that the foresets of the primary dunes are bundled into alternating packages imaged as either low- or high-amplitude reflections. High-amplitude packages are composed of quartz sand with intercalated heavy-minerals layers. Low-amplitude packages lack these heavy-mineral concentrations. Dune net-progradation is towards the east, reflecting the prevalence of westerly winds. Winds blowing parallel to the dune crest winnow the lee slope, leaving layers enriched in heavy minerals. Sediment transport to the slip face of the dunes is enhanced during the winter months, whereas winnowing predominantly takes place during the spring to autumn months, when the wind field is bi-directional. As a consequence of this seasonal shift, the sedimentary record of one year comprises one low- and one high-amplitude GPR reflection interval. This sedimentary pattern is a persistent feature of the Łeba dunes and recognized to resemble a sedimentary “bar code”. To overcome hiatuses in the bar code of individual dunes and dune-to-dune variations in bar-code quality, dendrochronological methods were adopted to compile a composite bar code from several dunes. The resulting data series shows annual variations in west-wind intensity at the southern Baltic coast for the time period 1987 to 2012. Proxy-based wind data are validated against instrumental based weather observations.

Discrimination between wave‐ravinement surfaces and bedset boundaries in Pliocene shallow‐marine deposits, Crotone Basin, southern Italy: An integrated sedimentological, micropalaeontological and mineralogical approach

AbstractThe lower Pliocene Belvedere Formation, cropping out in the Crotone Basin, southern Italy, exhibits a metre‐scale to decametre‐scale shallow‐marine cyclicity that shares features of both high‐frequency sequences linked to shoreline shifts and controlled by minor relative sea‐level and/or sediment supply changes, and sedimentological cycles unrelated to shoreline shifts. In order to better understand the high‐frequency sequence stratigraphic framework of this succession, an integration of sedimentological, micropalaeontological (micro‐foraminifera assemblages) and mineralogical (heavy mineral abundance) data is used. From a sedimentological/stratigraphic point of view, wave‐ravinement surfaces bounding high‐frequency sequences, and associated substrate‐controlled ichnofacies, are prominent in outcrop and document environmental and water‐depth changes, whereas bedset boundaries separating sedimentological cycles have a more subtle field appearance and are only associated with changes of environmental energy. Moreover, condensed deposits are present only above wave‐ravinement surfaces, and the high‐frequency sequences bounded by these surfaces have a thickness that is an order of magnitude greater than that of the bedsets. Micro‐foraminifera assemblages may change, and the content of heavy minerals usually increases, across wave‐ravinement surfaces, whereas both parameters do not change significantly across bedset boundaries. The abundance of heavy minerals is systematically higher, with respect to the underlying and overlying deposits, in the condensed shell beds that overlie wave‐ravinement surfaces. An integrated sedimentological, micropalaeontological and mineralogical approach represents a powerful tool to discriminate between wave‐ravinement surfaces bounding high‐frequency sequences and bedset boundaries, and in general to investigate at the intra high‐frequency sequence scale. This integrated approach is expected to be very useful in the study of potentially all shallow‐marine successions composed of small‐scale cycles, in order to delineate a detailed sequence stratigraphic framework and understand the factors that controlled the cyclicity.

Geochemical Tracers of Buried Estuary of Rushikulya River from Odisha, East Coast of India

The sediments of the inner to middle shelf region of the central part of the east coast of India immediately near the growing spit of the Rushikulya River mouth, are characterized by very hard, compact, dark gray clayey silt and clay with medium to coarse sand and wood piece layers at different levels. Maximum output of the Rushikulya River during monsoon season is marked by thin layers of coarse to medium sand at different subsurface levels below the sea floor within the inner to middle shelf areas. Geochemical analysis (major and trace elements) of seabed sediments shows significant correlation with aluminium. Variation in other elements, except calcium and barium confirm their association with aluminosilicate minerals. The higher concentration of Ti-rich heavy minerals near the coast in front of the Rushikulya River is inferred due to terrigenous supply by the river. The REE analysed in the carbonaceous clays indicates enrichment of REE in the sediments, which is interpreted as due to the absorption of REE into the lattices of clay from sea water. Intermittent layers of carbonaceous clay with abundant wood pieces along with the presence of H2S and the enrichment of REE in the clay provide indirect evidences for the presence of a buried estuary in front of the Rushikulya River at different subsurface levels. The growing spit towards the northeast direction at the river mouth further acts as a favourable geomorphologic feature for the formation of an estuary in the study area. Presence of a reworked palaeosand ridge located between 54 and 57 m water depth is characterized by selective elimination of elements from the sediments. Furthermore, this sand ridge acts as the boundary for the buried estuary identified in the study area.

Scenario of the 1996 volcanic tsunamis in Karymskoye Lake, Kamchatka, inferred from X-ray tomography of heavy minerals in tsunami deposits

The concentration and distribution of heavy minerals in tsunami deposits is not random and mostly source-dependent. Heavy minerals may thus be good indicators of sediment provenance and tsunami flow dynamics. The tsunamis generated by the 1996 phreato-magmatic eruption in Karymskoye Lake represent a relevant case-study because the provenance of the abundant heavy minerals found in the tsunami deposits is well constrained (the on-going basaltic eruption itself). X-ray computed tomography (X-CT) of cores of tsunami sediments is used to identify heavy minerals and characterise their source and spatial distribution in the tsunami deposit, and to propose a scenario of the coupled eruption and tsunamis. An original combination of methods including X-CT, SEM and XRF core scanner allows distinguishing subunits corresponding to pulses of sediments deposition and associated inputs of heavy minerals, together with erosive contacts, laminations, and rip-up clasts of the substratum. The structure of the tsunami deposits suggests that a major tsunami consisting of two main waves inundated the coastal terrace up to 100m inland on the eastern shore of the lake; a scenario that is consistent with waves generated by experimental explosions. This largest tsunami might have occurred when underwater explosions were at a critical water depth of 40m (corresponding to a two-third submerged explosion in the 60m deep lake). However, more investigations are needed to better understand the critical conditions leading to a tsunami during underwater eruptions.

Economic Viability of the Tista River Sand Deposits in Bangladesh An Overview

The Tista River originates from the Himalaya Mountain, flows through Bangladesh and makes itself as the largest tributary of the Brahmaputra-Jamuna River, having huge sand deposits with valuable minerals. The present work implies economic viability of the Tista River sand deposits measuring heavy mineral concentration and comparing with other established deposits and marking the cut-off grade and prices of these minerals. The study shows that the average content of heavy minerals is 8.26%, containing garnet, ilmenite, magnetite, rutile, zircon and micas. The selected valuable oxides in the form of minerals are SiO2, MgO, K2O and rare earth elements. The commendable amount of SiO2 71.72 wt% makes it feasible as raw material in the glass factory. Another valuable oxide is K2O amounted 2.53 wt% (price per ton in US$ 350-400) makes it praiseworthy. The valuable elements found in deserving quantities are Ba, Rb, Th, V, Cs, Cr, Ni and Co. The remarkable finding of this study is Thorium (Th) measured 28 gm/ton of bulk sand. According to Nobel laureate Carlo Rubbia, thorium (Th) can produce 200 times more electricity than uranium and more environment friendly. So it is economically feasible to take proper initiative to set up mining for sand processing.

Oligo-Miocene coal in a microtidal environment reworked under Quaternary periglacial conditions (Western Falkland Islands/Isla Gran Malvina) – Coal formation and natural sand processing

The Western Falkland Islands are characterized by landforms and sediments of Quaternary age originating from the interplay of periglacial and marine processes. These have left their imprints on siliciclastic sediments and subbituminous coal, peatland, and podzolic soil. Our depositional study focuses on interpreting a stratigraphic sequence which contains white quartz sand with an interbedded coal seam by using petrography (coal petrography, carbon isotope analysis, sedimentary petrography, clay mineralogy, granulometric, morphometric studies), and geochemistry. The study of the coal-sand couple sheds some light on two contrasting sedimentary geological settings. Firstly, it broadens the knowledge of the regional geology at the southern tip of South America by examining how coal seams may be emplaced in a periglacial-microtidal environment. Secondly, the study is also relevant for applied geology by investigating how sand is processed in a coal-bearing paralic regime. The coal-sand couple evolved during 6 discrete stages. Stage I: The detrital parent material was derived from the Siluro-Carboniferous Gran Malvina Group. Stage II: From the Oligocene through the late Miocene under a warm tropical climate organic matter was accumulated in a paralic environment giving rise to subbituminous coal. Stage III: During the Pleistocene alternating erosion and deposition in a wave-dominated coastal-marine regime gave rise to the build-up of coal interbedded with sand. The hydrodynamic regime reduced the grain size to the level of medium to fine sand and enhanced its sorting coefficient causing the separation of minerals according to their specific gravity (mechanical processing). Stage IV: The coal seam has been reworked by the last glacial progradation. Stage V: Weathering by wind and waterworn sand grains into semispherical to spherical forms and the content of heavy minerals increased along backshore and in dune belt environments. Stage VI: Organic acids derived from the coal promoted chemical leaching and significantly contributed to the decrease of the labile constituents of arenites (feldspar, carbonate minerals, and calcareous tests of faunal remains). Chemical alteration was grinded to a halt by another sea level rise, which gradually destroyed the coal layer. The depositional environment most effective for the processing of sand is located in the microtidal setting. In the meso- to macrotidal hydrodynamic regime the chemical leaching becomes the only efficacious tool to improve the quality of the footwall rocks. Due to the predominance of argillaceous sediments there, the quality of clay is enhanced and kaolin deposits may come into existence.

The coastal heavy mineral sand deposits of Africa

The trailing margin of the stable African continent is the depositional environment of several heavy mineral placer deposits of which seven have developed into viable world class operations producing titanium feedstock (ilmenite, rutile, leucoxene) and zircon. At least 30 other deposits are marginal under the present global economic climate but have the potential to be turned into account in the medium term with an increase in demand and higher commodity prices. Combined, the seven operating mines are the biggest single producer of titanium feedstock in the world and the second largest producer of zircon after Australia. Mineral resources are vast and the extensive African coastline offers significant exploration potential and possibly is the largest depository of valuable heavy minerals (VHM) on the planet. Generally, Pliocene to Holocene unconsolidated, siliciclastic sands of predominantly marine-aeolian, but locally fluvial origin host the heavy mineral suite and deposits are large coast-parallel dune fields with or without minor strandlines. Tonnages of these deposits are large and in several instances exceed a billion tons with grades between 2 and 12 percent total heavy minerals (THM). Deposit characteristics are influenced by continental tectonics, coastal morphology, sea level changes, tides, climate and the altered, eroded nature and composition of the provenance. The formation of an economically viable deposit requires the juxtaposition of most, if not all of these conditions to favour heavy mineral concentration with a high VHM content. Mining is by open cast using either dry mechanized, hydraulic monitoring, or floating dredge and wet concentrator methodologies. Mineral separation uses physical properties such as density, magnetic susceptibility and electrical conductivity to produce high quality concentrates for the international market. Only three of the mines, all located in South Africa, have their own smelters that convert ilmenite into titanium slag and pig iron. Coastal environments are all eco-sensitive and mine site rehabilitation is employed throughout, including effective disposal of radiogenic tailings associated with high U+Th zircon and monazite. The most effective exploration methods for these deposits include identification of trailing continental margins with Neogene to Quaternary coastal strandlines and dune fields spatially related to geomorphological features such as headlands and significant fluvial systems. High-resolution ground and aeromagnetic surveys reflecting ilmenite and traces of magnetite, coupled with radiometric surveys related to monazite and high U+Th zircon content have been the most effective geophysical methods for these deposits. Reconnaissance followed by detailed infill drilling of anomalous areas by truck mounted rotary drill to collect samples for THM and VHM determinations is the industry standard.

The application of microtextural and heavy mineral analysis to discriminate between storm and tsunami deposits

Abstract Recent work has applied microtextural and heavy mineral analyses to sandy storm and tsunami deposits from Portugal, Scotland, Indonesia and the USA. We looked at the interpretation of microtextural imagery (scanning electron microscopy) of quartz grains and heavy mineral compositions. We consider inundation events of different chronologies and sources (the AD 1755 Lisbon and 2004 Indian Ocean tsunamis, the Great Storm of 11 January 2005 in Scotland, and Hurricane Sandy in 2012) that affected contrasting coastal and hinterland settings with different regional oceanographic conditions. Storm and tsunami deposits were examined along with potential source sediments (alluvial, beach, dune and nearshore sediments) to determine provenance. Results suggest that tsunami deposits typically exhibit a significant spatial variation in grain sizes, microtextures and heavy minerals. Storm deposits show less variability, especially in vertical profiles. Tsunami and storm quartz grains had more percussion marks and fresh surfaces compared to potential source material. Moreover, in the studied cases, tsunami samples had fewer fresh surfaces than storm deposits. Heavy mineral assemblages are typically site-specific. The concentration of heavy minerals decreases upwards in tsunamigenic units, whereas storm sediments show cyclic concentrations of heavy minerals, reflected in the laminations observed macroscopically in the deposits.

Geomorfología de la duna remontante ubicada en el acantilado sur del Castillo de Araya, estado Sucre (Venezuela)

El objetivo es caracterizar en lo físico-químico y morfodinámico la duna remontante ubicada en Araya, para ello se asumieron las siguientes fases de investigación: a) “Campo”, que permitió la colecta sedimentológica en el ápice y la base del depósito; b) “Laboratorio” a fin de determinar tamaño y forma de los granos, contenido de CaCo y minerales pesados, y c) “Oficina”, centrada en el análisis estadístico. Se trata de arenas finas, generalmente redondeadas, bien seleccionadas, mineralógicamente compuestas por: 63,68% de cuarzo + feldespatos, 33,75% CaCo3 y 2,56% de minerales pesados, las cuales experimentan un cabalgamiento promedio de 1,16 metros sobre el acantilado entre septiembre-abril, posiblemente vinculado al incremento de la velocidad de los vientos locales, los cuales registran en promedio hasta 81,04 m/s.