Heavy-mineral Concentrates Research Articles

Valuable heavy minerals from the Brahmaputra River sands of Northern Bangladesh

The sands of Bangladesh's rivers are potentially economically important hosts for heavy mineral (HM) resources. Characterisation tests carried out by the authors on 50 sand samples collected from sand bars of the Brahmaputra River in northern Bangladesh revealed that the HM assemblage of the predominantly quartz-rich sands ranged from 4.5 to 17.0% (by weight) HM. The HM assemblage of the samples tested predominantly comprised amphibole, epidote, garnet, kyanite and feldspars along with minor amounts of the valuable heavy mineral (VHM) components of ilmenite, magnetite, rutile and zircon. The HMs were generally well liberated and had an angular to sub-round texture. A grain size analysis of a composite sample prepared from a subset of 7 of the 50 samples collected indicated that >75% of the total HM assemblage was within the +250 to −125 µm size fraction with VHMs enriched in the size fractions −250 to +125 µm and −125 to +63 µm. The total HM contents in the coarser −500 to +250 µm size fraction and the finer −63 µm size fractions were negligible. The potentially recoverable VHM components of the composite included magnetite (∼3%), ilmenite (∼4%), titanite (∼1%), titanomagnetite (∼1%), zircon (∼0.5%) and rutile (∼0.4%). Preliminary laboratory separation studies on a bulk sample indicated that magnetite-, ilmenite-, rutile- and zircon-rich concentrates could be prepared from the sands. Analyses of the ilmenite indicated that the ilmenite was primary in composition (∼34% Ti), low in detrimental impurities and would be suitable for pigment production via the sulphate processing route. The zircon and rutile components were also low in total impurities and as such, little or no further processing would be required to produce saleable concentrates of these VHMs. However, the magnetite concentrate was contaminated by composite magnetite/silicate particles and further work involving fine grinding would be required to liberate the magnetite particles and generate a magnetite-rich product.

Modelling heavy and gangue mineral size recovery curves using the spiral concentration of heavy minerals from kaolin residues

Spiral concentrators are one of the most common gravity processing methods extensively used for the concentration of mineral based on their density, particle size and shape. As for every gravity concentration technique, particle size plays a major role in the separation mechanisms within the spiral. Thus, in addition to classical performance indices, such as grade or recovery, partition curves are also a valuable criterion for quantifying the separation efficiency. In this paper, we study and model the influence of wash water additions and pulp density on heavy and gangue mineral partition curves using kaolin residue enriched in heavy minerals and via a design of experiment (DOE). The results show that coarse particle size recovery curves are affected by a systematic decrease, which is mainly impacted by wash water additions. Partition curve modelling through particle size distribution and DOE regression model fitting allow a better understanding of the effect of wash water on the aforementioned phenomenon for each mineral fraction. Gangue minerals are more affected by this phenomenon, which has been interpreted as a result of the Bagnold effect and secondary flows within the spiral. A decrease in the coarse particle recovery represents a significant source of losses, and a better understanding of this phenomenon is necessary to avoid these losses.

Discovery of the Madimba heavy mineral sand deposit, Mtwara Region, Tanzania

Discovery of the Madimba heavy mineral sand deposit, located in Mtwara Region of southern Tanzania, resulted from reconnaissance surface sampling and subsequent follow-up drilling of anomalies >3% total heavy mineral. Two discrete zones of mineralisation have been defined within a host of low to moderate slime sand, known as the Madimba and Madimba East zones, with a long axis up to 3 km and width up to 1.5 km. Limited drilling to date has identified mineralisation from surface to 8 m below surface with grades up 12.36% total heavy mineral. Within the total heavy mineral concentrate, the average valuable heavy mineral content has a range 72–88% for the two zones. Although ilmenite species dominate the valuable mineral assemblage, very high zircon plus rutile components, up to 16% in the total heavy mineral, have been identified. Semi-quantitative chemical analyses of ilmenite and altered ilmenite mineral grains show average TiO2 ranges 50–52% and about 59%, respectively, for both zones. Based on the significant valuable mineral component, good ilmenite composition and proximity to port infrastructure, the Madimba deposits have significant economic potential and could theoretically produce high quality pigment feedstock.

Heavy mineral assemblages of the Storegga tsunami deposit

This study applies heavy mineral analysis to the Storegga tsunami deposit across a range of locations (Whale Firth, Maggie's Kettle Loch and Scatsta Voe) in Shetland (Scotland). The usefulness of this proxy is tested in the identification and characterization of these palaeotsunami units. Furthermore, provenance relationships are established based on the mineralogical content of tsunami deposits and their potential source. Finally, the capability of identifying different phases of tsunami inundation in an 8200years old tsunami deposit is attempted.Our results show that, overall, tsunamigenic samples presented a clear dominance of garnets and amphiboles. While Whale Firth presented a more balanced distribution between these two mineral groups, in Maggie's Kettle Loch and Scatsta Voe the tsunamigenic samples are dominated by amphiboles (>90% of transparent heavy minerals).Focusing on the two dominant heavy minerals (garnets and amphiboles) and their vertical variation, one could observe that garnets mimic the heavy mineral concentration variability — higher values at the base and decreasing values to the top. This effect of concentration of the heaviest of the heavy minerals assemblage presents similarities with the formation of beach placer deposits. In fact, based on the heavy mineral vertical variation of the tsunami deposits in Maggie's Kettle Loch, Scatsta Voe and Whale Firth it is possible to conclude that hornblende (most likely amphibole of the assemblage) has the lowest concentration factor indicating that its transport process is more efficient and consequently most of its particles eventually may have moved offshore in the backwash phase of the tsunami. Furthermore, the more platy shape of amphiboles also favours a slower deposition. The opposite can be observed for garnets, which require more energy to be transported (i.e. they are more difficult to entrain by the tsunami waves) and tend to be more easily preserved in the formation of a tsunamigenic (placer) deposit.The work presented here is of particular relevance for future high resolution sedimentological studies aiming to distinguish different inundation phases of the Storegga tsunami, and assess the degree of preservation of these deposits, especially considering the specific geomorphological and stratigraphic depositional setting of Scotland.

Petrography and geochemistry of sands from the Chachalacas and Veracruz beach areas, western Gulf of Mexico, Mexico: Constraints on provenance and tectonic setting

Compositional and geochemical analyses of sands collected from the Chachalacas (CHA) and Veracruz (VER) beach areas along the western Gulf of Mexico were studied to determine the provenance and tectonic setting of the source region. The modal composition showed that the proportion of quartz (Q) is lower in CHA than in VER sands. The average quartz-feldspar-lithic fragment (QFL) ratios for the CHA and VER sands are Q75F8L17 and Q86F4L10, respectively. The X-ray diffractometer (XRD) and Scanning Electron Microscope equipped with EDAX spectrometer (SEM-EDS) data revealed that the CHA sands were abundant in heavy minerals like magnetite, ilmenite, and zircon. The rare earth element concentration (REE) is higher in CHA than in VER sands, which is due to the concentration of heavy minerals in CHA sands. The weathering indices such as chemical index of alteration (CIA), plagioclase index of alteration, and A–CN–K (A = Al2O3, CN=CaO∗ + Na2O, K=K2O) plot suggested that the intensity of weathering in the source area was low to moderate. The index of chemical variability (ICV) for the CHA (∼1.9–3.0) and VER (∼0.82–1.33) sands indicated that the compositional maturity was higher for the VER sands. The concentrations of Co, Cr, Ni, and V are lower in VER sands than in CHA sands, indicating that the CHA sands were derived from the intermediate source rocks. Provenance modelling revealed that the CHA sands were associated with the mixture of basalt, andesite, dacite, and trachyandesite in the ratio of 5:20:25:50. The VER sands were best matched with a mixture having 75–90% dacite and 25–10% andesite compositions. The provenance difference between the two beach areas suggested that longshore current play a less significant role in mixing and homogenization of sands. The multidimensional tectonic discrimination diagrams revealed rift and collision settings for the VER and CHA beach areas, respectively, which is consistent with the general geology of the study areas.

Provenance Analysis of Sediments in ILU-TITUN and Environs, Eastern Dahomey Basin, Ondo State, Nigeria

Twenty eight sediment samples were obtained from road cuts and stream cuts in Ilu Titun area of Ondo State, Nigeria and were subjected to Grain Size Distribution (GSD) analysis, from which statistical parameters were calculated and used to determine the environment of deposition of the sediments. Six representative samples were selected for petrographic studies to determine the heavy mineral content of the sediments with a view to establishing the sediments source of Ilu Titun and environs which mark the eastern margin of the Dahomey basin. The Graphic Mean (Mz) ranges from 0.700F to 1.667&Phi while the Inclusive Graphic Standard Deviation (&sigma i ) range from 0.960 to 1.319. The Inclusive Graphic Skewness ( SK I ) of the samples ranges from -0.665 to 0.803 while Kurtosis range from 1.652 to 3.309. The bivariate plot of mean size against the Inclusive graphic standard deviation show that the sediments were deposited by river and beach processes. The plot of skewness against the Inclusive graphic standard deviation confirmed that the sediments were deposited by river processes. The results of the petrographic studies show that Slides EK 01 and EK 08 have Kyanite and Staurolite. Slides EK 13 and EK 24 have Staurolite, Tourmaline and Garnet. Slides EK 26 and 28 have Tourmaline and Zircon present in them. Bivariate plots using the statistical parameters show that the sediments were deposited by fluvial processes. The results from the petrographic studies indicate that the sediments were sourced from metamorphic rocks and pegmatites.

Mineralogy and Mineral Chemistry of Placer Deposit around Jhatipodar, Odisha

Abstract: The heavy mineral placer sands of Jhatipodar deposit, Odisha, India extends in NE-SW parallel to the coast over a width of 750-980m. A total of 195 samples were collected vertically in a grid pattern from 46 bore holes in 5 transects from beach and dunes covering an area of 75 hectares. The total heavy minerals (THM) content of the samples vary from 3.01% to 44.38%. The heavy minerals as observed from field and laboratory investigations are ilmenite, leucoxene, garnet, sillimanite, zircon, rutile, monazite, magnetite and corundum together with hornblende, diopside, tourmaline, sphene, apatite and epidote. The heavy minerals show similar pattern of grain size distribution from beach to dunes and are dominantly in the size of 90 - 350 μm with a peak distribution in -180, +125 μm. A bulk sample of dunal sands analysed 20.48% THM, contain 7.85% ilmenite, 7.65% garnet, 4.09% sillimanite, 0.20% zircon, 0.18% rutile and 0.13% monazite. The mineral grains are well liberated, rounded to sub-rounded and mostly free from surface coatings. The ilmenites contain 47.87-56.59% TiO2 with an average of 51.76% TiO2. The high TiO2 content (9.86-16.30%) in exsolved hematite is due to Fe2O3-FeTiO3 solid solution. Compared to ilmenite, leucoxene has higher amounts of Ti, Al, Si, Cr and lower amounts of Fe and Mn. The Ti/(Ti+Fe) in ilmenite varies between 0.46% and 0.55% while that in leucoxene has a range from 0.64% to 0.96%. The provenance rocks for this deposit are the khondalites, quartzites, calcsilicate granulites, granitic gneisses, charnockite, basic granulite, anorthosite and pegmatites of the Eastern Ghats Mobile Belt in the catchment areas of Rushikulya river. This paper deals with the distribution of heavy minerals in beaches and dunes, mineralogical association and chemistry of different minerals to evaluate the economic potentiality of Jhatipodar placer deposit and to decipher the amenability of different heavy minerals for mineral processing.

Recent vertebrate tracks in sandy substrates and their paleoenvironmental implications: examples from coastal Lithuania

A diverse suite of vertebrate footprints documented along the coast of Lithuania offers insight into the distribution and preservation potential of tracks in sandy substrates. Whereas ichnotaxonomy is not conventionally applied to modern tracks, a case is made for using footprint classification based on Vialov’s (1966) nomenclature to both observed and predicted track distribution based on extramorphological characteristics of the tracemaker. Along a barrier spit (Curonian Spit) and mainland shoreline (Būtingė) sites, two general types of avian footprints (Avipeda sp), as well as three carnivore (Bestiopeda), four ungulate (Pecoripeda, Suipeda, Hippipeda), and two rodent (Rodentipeda) track morphotypes are described. The habitat preferences result in a predictable distribution of track assemblages with a potential of differentiating vertebrate ichnofacies (lagoon shoreline, open sea beach, dunes). The moisture content, possibility of freezing and rapid aeolian burial, and lithological anomalies (e.g., heavy-mineral concentrations) enhance the preservation potential of tracks. Once preserved, the attitude of trackways in respect to bedding surfaces determines their integrity and here a model of potential regional track distribution is proposed. Track formation and preservation in modern settings provides a useful guide to locating and studying vertebrate footprints and other traces in sand-dominated coastal and aeolian sequences.

U, Th and REE content of heavy minerals from beach sand samples of Sithonia Peninsula (northern Greece)

U, Th and REE content of heavy minerals from beach sand samples of Sithonia Peninsula (northern Greece)

Gold exploration using heavy minerals in till and weathered bedrock in Petäjäselkä, northern Finland

As a part of a gold exploration project in Petäjäselkä, northern Finland, carried out by the Geological Survey of Finland, heavy mineral studies and detailed till geochemical and stratigraphical studies were used for mineral exploration. These studies covered c . 22 km 2 in the Petäjäselkä area. The objective of this research was to find out how heavy minerals and till geochemistry can be used in gold exploration, and how they reflect the glacial dispersion in shallow till areas in Petäjäselkä. Furthermore, an automated mineralogical identification method (SEM-EDS) was tested in the indicator mineral research. Samples from till and underlying, pre-glacially weathered bedrock were collected from the test pits and trenches. A total of 381 heavy mineral and 713 geochemical samples were collected. The heavy mineral samples were concentrated with a spiral concentrator and a Knelson concentrator. The geochemical samples were analysed by ICP-AES and GF-AAS following aqua regia decomposition. The elevated gold contents and distinct anomalies found in till and weathered bedrock indicate the whole study area to have potential for gold mineralization. Based on microscopic and automated mineralogical studies, native gold was the only useful indicator mineral present in the heavy mineral samples for gold exploration in Petäjäselkä.The detailed till geochemical results show that the glacial transport distance in Petäjäselkä is short, only some tens of meters. Differences in the Au-Ag contents of the gold grains were noted between the three gold mineralized targets in Kerolaki, Selkä-Mäntypää and Ranta-Mäntypää. Arsenic, bismuth and tellurium proved to be pathfinder elements for gold mineralization both in till and weathered bedrock. The results of this study show that the heavy mineral studies, together with till geochemical studies, provide a useful method for identifying exploration targets in glaciated terrain. However, different methods of heavy mineral concentration affect the recovery of gold grains and thereby the final results of this study.

Heavy-mineral analysis as a tool to trace the source areas of sediments in an ice-marginal valley, with an example from the Pleistocene of northwest Poland

AbstractThe ice caps that covered large parts of the continents of the northern hemisphere during the Pleistocene glaciations drained huge quantities of meltwater. In several places the erosive power of the meltwater rivers has led to the formation of ice-marginal valleys (IMVs). A much-debated question is whether sediments deposited in IMVs by proglacial and extraglacial streams can be distinguished on the basis of their heavy-mineral content. This question was assessed by an inventory of the heavy-mineral assemblages from the middle part of the Toruń-Eberswalde IMV in northwest Poland, two sandurs that supplied sediment from the north and the pre-Wisła river system that supplied sediment from the south; all these streams fed the IMV. The largely similar heavy-mineral compositions and sediments concentrations of the middle part of the IMV and sandurs suggest that the sediment in the IMV was supplied almost entirely by the streams on the sandurs but also that some sediments were eroded from the Miocene subsoil of the IMV itself and for a small part from the south by the pre-Wisła river system. The only heavy mineral in the pre-Wisła sediments for which the percentage is significantly different from those in the sediments of the sandurs and the IMV terrace is epidote. The difference, however, is not seen in the sediments of the IMV so it can be concluded that the sediment supply to the middle part of this IMV by streams from the south was insignificant. This is in contrast with what was hitherto commonly assumed.

The Fluvial Concentration of Heavy Minerals in the Slieve Bloom Mountains, Central Ireland

The detrital mineralogies of both alluvial sediments and their glacigenic and bedrock sedimentary sources undergoing fluvial entrainment in the mountains are outlined. Relationships between patterns of heavy mineral concentration in the alluvial sediments and the controlling factors of source material distribution and provenance, the hydrodynamics of heavy minerals, the spatial variability in process environments of concentration and the interaction of these factors are deduced and the spatial distributions of correlated heavy mineral assemblages and concentrations are explained. Thus, a better understanding is gained of the processes and process interactions responsible for alluvial heavy mineral concentration in paraglacial environments.

Heavy Mineral Potentiality and Alteration Studies for Ilmenite in Astaranga Beach Sands, District Puri, Odisha, India

Fifteen beach sand samples were collected from a depth of 1mt at different locations of the Astaranga beach, Puri with an interval of 300 mts. The beach sand samples were studied for heavy mineral concentration at different location points and were subjected to scanning electron microscope studies for the mineral ilmenite. The percentage of total heavy mineral in Astaranga beach varies from 16.42% to 24.47%. The important minerals are ilmenite, rutile, zircon, sillimanite, garnet, monazite, pyroxene and others. For all samples a set of sieves bearing ASTM nos. 30, 40, 60, 80, 100, 120, 140, 170 and 200 corresponding to 0.59 mm, 0.42 mm, 0.25 mm, 0.177 mm, 0.149 mm, 0.125 mm, 0.105 mm, 0.088 mm and 0.074 mm respectively were used to separate different size fractions. The sieve mesh sizes vary from 0.59 mm to 0.74 mm. It was observed that maximum concentration of heavies was confined to +200 ASTM sieve or 0.74 mm. The total average heavy mineral concentration and light mineral concentration was found to be 20.07% and 79.49% respectively. The concentration percentage of different heavy minerals varied from higher to lower in the order like ilmenite, zircon, sillimanite, garnet, rutile, pyroxene, monazite and others. The ilmenite mineral in this area is found to have altered to secondary phases like pseudorutile, leucoxene and rutile along the fractures, cavities and grain boundaries. The alteration condition was observed as streaks, irregular patches, bands, and rim like structures around the ilmenite grains. Detailed study of alteration in ilmenite was carried out by Energy Dispersive Spectrometer (EDS) attached to Scanning Electron Microscope. The potentialities of heavies found at different locations of the Astaranga beach suggested a good source for the exploration. The alteration of the mineral ilmenite and high concentration of heavy minerals clearly pointed to the sedimentary environment and mechanical concentration process due to repeated wave action.

Controls and Implications of Geo-Technical Variation in Quartzose Rocks from Peshawar Basin, North-Western Pakistan

Petrographic and geo-mechanical properties of samples representing quartzose rocks of Tanawal Formation (Baja Bamkhel area, Swabi) and Misri Banda quartzite (Nowshera) from Peshawar Basin, NW Pakistan, have been investigated. Although formerly referred to as quartzite, mineralogical composition and textural details support characterization of the studied quartzose samples of Tanawal Formation as blasto-psammite and those of Misri Banda as sub-arkose. The two rock types also show significant differences in terms of matrix and heavy mineral concentrations as well as the degree and frequency of intra-granular deformation. On the basis of unconfined compressive strength (UCS), both fall in the category of very strong rocks. Correspondingly, their specific gravity and water absorption values are high and low respectively and lie well within the range permissible for use as construction material. However, both contain high amounts of deleterious components, i.e. reactive forms of silica (chert and/or strained quartz) and clay minerals. Therefore, they cannot be used as coarse aggregate with Ordinary Portland Cement (OPC) and asphalt. The modal abundance of quartz is higher in the Misri Banda than the Tanawal samples, but the quartz to feldspar ratios are higher for the latter. Yet, the sub-arkosic Misri Banda rocks are stronger than the Tanawal blasto-psammites, most probably because they are i) almost totally devoid of matrix; ii) finer grained; iii) having a higher percentage of grains with irregular and sutured contacts and iv) lesser abundance of grains displaying intra-granular deformation.

Comparing levels of certain heavy metals and minerals and antioxidativemetabolism in cows raised near and away from highways*

The scope of this study was to investigate the concentrations of certain heavy metals, mineral levels, and antioxidative metabolism in cows raised near (300 m) and away from highways (2.5 km) in Çankırı Province. For this purpose, blood samples were collected from 100 cows (aged 3-5 years) raised near and away from highways in this province. Concentrations of certain heavy metals and minerals in the serum were analyzed on an ICP-MS device. Additionally, lipid peroxidation product malondialdehyde (MDA) in the plasma and antioxidative defense system indicators, erythrocyte superoxide dismutase (SOD) and catalase (CAT) activities, were measured with a spectrophotometer. As a result, levels of certain heavy metals and minerals and antioxidative status were determined in cows raised near and away from highways. Aluminum, iron, nickel, and zinc levels in the cows raised near highways were significantly different from those of the cows raised away from highways. Furthermore, MDA concentrations and SOD activities were significantly different between the two groups. It is concluded that monitoring the concentration of these heavy metals periodically may be useful to increase the productivity of cows.

Geochemical Exploration for Gold and the Association of As-Cu-Pb-Sn-Zn-Li in the Upper Proterozoic Granitoids of the Wadi Rumman Area, Southwest Jordan

The geochemical studies were conducted in an area covering about 15 km2 of the south side of the Wadi Rumman area, SW Jordan. The study area included a part of a basement of complex exposed rocks in southwestern Jordan. The complexes comprised igneous and metamorphic suites, mostly from the late Proterozoic age. A systematic geochemical sampling was conducted using rock and heavy mineral-panned concentrate of geochemical samples. Fifty rock samples were collected from the granitic rocks, simple pegmatite dyke, quartz veins and alteration zone, which covered the area. Next, 45 heavy mineral-panned concentrate samples were collected from the alluvium in the stream sediment within the catchment area, and the dray was sieved to less than 1 mm grain size. The geochemical samples were analyzed for their trace elements and gold by using Ione Conductive Coupled Plasma Emission Spectroscopy (ICP-AES) and the Atomic Absorption Spectrometer (AAS) at Natural Resources Authority (NRA) Labs. The results of the geochemical analysis indicated the presence of gold and heavy minerals in the study area, a result considered abnormal in the rock samples. A strong positive correlation was recorded of Au with As, Cu and W (r = 0.82, 0.7 and 1.0), as with Mo (r = 0.83), Cu with Pb (r = 0.83), Sn with Mo (r = 0.73), Mo with W (r = 0.97), Zn with W (r = 0.71), and Li with Bi (r = 0.7). These correlations revealed gold associated within the hydrothermal alteration, quartz veins and pegmatite dyke. Abnormal metals such as As and Bi were good path-finders to find Au. The HM samples showed low positive linear correlations among the concentrations of Au with As, Zn and Li, and negative linear correlations of Au with Pb, Sn, Bi and W. The combination of both rock and heavy mineral concentrate samples shows four geochemical anomalous areas of gold and heavy minerals. The geochemical signatures of Au and As in the Wadi Rumman appear to be in the hydrothermal alteration, quartz veins and pegmatite dyke, respectively. Heavy mineral concentration sampling delineated the Au geochemical anomaly in area 1 specificities with the rock geochemical anomaly of area 1.

Geochemistry of Tertiary Sequence in Shahbajpur-1 Well, Hatia Trough, Bengal Basin, Bangladesh: Provenance, Source Weathering and Province Affinity

Major and trace element compositions of Neogene sandstones and mudrocks from the Shahbajpur-1 (SB-1) well, Hatia trough, Bengal basin, Bangladesh were determined to examine their geochemical characteristics and provenance, in relation to Himalayan uplift, sediment dispersal, and correlation of coeval successions in a basinal context. Major and trace element abundances in the SB-1 succession vary vertically, with SiO2 content decreasing and Al2O3 increasing from the older (Surma and Tipam Groups) to younger (Dupi Tila Group) sediments. Marked geochemical fractionation between sandstones and mudrocks reflects advanced hydrodynamic sorting, and relative enrichment of several elements (e.g., TiO2, Zr, Ce, Th, Cr) suggests sporadic heavy mineral concentration in some sandstones. Major and trace element provenance discriminants indicate a uniform felsic source (Himalayan detritus and recycled sediments) for the entire succession. Values for the Chemical Index of Alteration (CIA) record moderate weathering in the source, and non-steady state conditions produced by Himalayan uplift. Comparison between the Hatia trough samples and coeval Sylhet trough (P2) sediments shows that the more distal SB-1 succession is compositionally more uniform. Strong similarity in geochemical composition between SB-1 and P2 support the hypothesis that the Hatia trough is an extension of P2, fed by the same dispersal system. DOI: http://dx.doi.org/10.3329/jles.v7i0.20115 J. Life Earth Sci., Vol. 7: 1-13, 2012

What drives nearshore sediment transport controls on the depletion of beach placers at Manavalakurichi, Southwest Coast of India?

An in-depth analysis has been made to simulate hydrodynamic scenarios for understanding the nearshore sediment transport controls of placer mineral depletion at Manavalakurichi, India. From the analyses of topographic configuration (extracted from Hydrographic Nautical Chart No. 2048 and data generated during year 2010), we inferred that the 5-m isobaths had broadened and exhibited shallowness. Distances between the coastline and the isobaths were found to have increased significantly over the past five decades. Along with this, the 10 and 20-m contours were found to have shifted about 35–100 m horizontally landward. These changes led to severe sediment deposition in these regions due to the changed wave energy levels and refraction patterns. Numerical simulations linking bathymetry, hydrodynamics, sediment load, and significant wave heights revealed that changes in bathymetry would amplify the wave heights and convergence of wave energy. Associated removal of sand from the high-energy zones will eventually lead to sediment starvation situations and depletion of placers in the adjacent beaches. As the observed trends of depletion generate great concern, detailed oceanographic investigations should be taken up immediately in the region. Fine-resolution hydrodynamic data-sets should prove useful for further evaluating the physical responses of the system to the altered geometry and for exploring remedial measures for restoring the heavy mineral content of the beach sand.

Recycling of Coastal Dredged Sediments from the Northern Nile Delta, Egypt, for Heavy Minerals Exploitation

Mineralogical and textural analyses of 45 undisturbed short cores and 80 grab sediment samples, collected from five frequently dredged navigational areas within harbors and water pathways of the Nile delta littoral system, were utilized for evaluation of these sediments as potential source of economic heavy minerals (EHMs). Results of mineralogical characterization indicate that the average total heavy mineral (HM) concentrations are as follows: Abu Qir Bay (1.7%), Rosetta estuary (3.1%), Burullus fishing port (4.5%), Damietta Harbor (2.9%), and El Gamil lagoon inlet (1.9%). Assessment of HM grades indicates predominance of magnetite, ilmenite, hematite, leucoxene, garnet, zircon, and rutile. Results of the feasibility analysis indicate that dredged sediments at these study areas are considered as a potential source of EHMs and economically promising to be mined for HMs. The present study suggests a practical operative plan of two successive phases for HMs recycling: (1) in-situ initial separation of HMs on the dredger deck using wet-gravity spirals, then (2) transportation of the recovered HM concentrates to an onshore processing plant to selectively separate individual HMs via wet and dry magnetic and electrostatic separators. Alternatively, dredged sediments can be directly pumped to a nearby onshore area as stockpile to be recycled afterward in inland processing plant.

Climate forcing of fine-grained deep-marine systems in an active tectonic setting: Middle Eocene, Ainsa Basin, Spanish Pyrenees

A multi-proxy approach to understand environmental change in deep time was undertaken on about 150m of core from a 230m-long Middle Eocene core from the Ainsa basin, Spanish Pyrenees, representing deep-marine siliciclastic sediments, using detailed sedimentary logging, high-resolution multi-element XRF geochemistry, total organic carbon, and stable carbon isotopes. The Well A6 was drilled, as part of an industry–university consortium, through siltstones, fine-/very fine-grained sandstone turbidites, and hemipelagic structureless mudstones, that were deposited as overbank and off-axis deposits from a sandy submarine fan, and interfan deposits. For comparative mineralogy between the sandstone turbidites and siltstones, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were undertaken on selected samples. The sandstone turbidites show enrichment of detrital elements such as Si, Zr and Ti, that can be linked to greater quartz and heavy-mineral content compared with adjacent siltstones. Structureless hemipelagic mudstones comprise mainly clay minerals and carbonate. We interpret the sandstone turbidites as from hyperpycnal flows during high river sediment discharge, whilst hemipelagic mudstones resulted from the suspension fall-out of hypopycnal flows. Cyclostratigraphic analysis of the core reveals Milankovitch cyclicity at frequencies of ~0.03cycles/m (short eccentricity), ~0.09cycles/m (obliquity), ~0.15cycles/m (precession couplet) and ~0.19cycles/m (precession couplet). Orbital parameters appear to have controlled the cyclic delivery of coarser-grained sediment by turbidity currents. Two equally plausible depositional models, both as Milankovitch-driven, can explain the cyclical changes in the deep-marine sediments: (1) climatic cycles, with humid periods of enhanced chemical weathering, increased storminess and greater riverine run-off, leading to high sediment flux to the deep basin as sandstone turbidites; (2) climatic cycles, with cooler conditions linked to high-frequency small-scale eustatic sea-level fluctuations, with lowstand shelf-edge delta progradation, resulting in greater volumes of coarse detrital sediment to the seafloor by hyperpycnal flows. This study provides an insight into the likely depositional effects of orbitally-induced climate change on the nature and delivery of terrigenous sediment into deep-marine environments.