Beach Placer Research Articles

Crustal evolution of peri-Gondwana crust into present day Europe: The Serbo-Macedonian and Rhodope massifs as a case study

The continental crust of Europe west of the Trans-European Suture Zone (TESZ), is mostly a collage of Peri-Gondwana Cadomian and Avalonian terranes that were formed on the late Neoproterozoic active margins of the supercontinent, rifted from it during consecutive opening of oceanic basins, and variably involved in Ordovician, Carboniferous (Variscan), and Cretaceous-Eocene (Alpine) orogenies. While in many localities it is possible to study isolated portions of the European geologic history, few sites can hold evidence for the entire record in a relatively small area. The Balkan terranes of the Serbo-Macedonian (SMM) and the Rhodope massifs, which contain Neoproterozoic Cadomian remnant basement, and were involved in multiple Phanerozoic phases of magmatism and metamorphism, provide an ideal locality in which we can study the entire crustal evolutionary history of Europe (west of the TESZ). Here we present new zircon U-Pb-Hf and rutile UPb data from basement rocks of the SMM and Rhodope as well as of beach placers from mouths of the large rivers draining the Balkan towards the Aegean Sea (Strymon, Nestos and Evros Rivers). Basement igneous rocks of the SMM and Circum-Rhodope were dated to the late Neoproterozoic (588 Ma), middle Ordovician (ca. 460 Ma), Carboniferous (300 Ma), Permo-Triassic (254 Ma), Paleocene (65 Ma) and Miocene (ca. 23 Ma), demonstrating the episodic nature of crustal evolution in this terrane assemblage. Hf-in zircon shows these intrusions evolve from negative εHf(t) values in the Ordovician towards positive values in the Paleocene. Zircons in beach placer samples also show distinct age peaks that follow the pulses of igneous activity in the source terranes, with the addition of Jurassic (ca. 150 Ma) zircons. The UPb system in rutiles from the beach placer samples was mostly reset, and records the final metamorphic phase during Alpine orogeny (35 Ma), with some rutiles preserving Eo-Alpine (80 Ma) ages. In contrast to the igneous samples, detrital zircons from the beach placer samples follow a trend bound by evolution lines leading to Hf-TDM model ages between 0.6 and 1.6 Ga. As a whole since the late Neoproterozoic the Balkan crust was the subject of repeated reworking in a series of magmatic/orogenic events. Some extent of juvenile igneous addition on this evolving Cadomian substrate brings about the shallow rise in εHf(t) values we observe in the igneous basement rocks. The end result observed in the Balkan is of a continental crust comprising a Neoproterozoic peri-Gondwana Cadomian core, reworked in multiple episodes of Phanerozoic orogenies, and augmented to some extent by variable mantle derived input. We argue that this mode of crustal origin and evolution is also applicable to many peri-Gondwana terranes of Western Europe.

Mass exhalation rates, emanation coefficients and enrichment pattern of radon, thoron in various grain size fractions of monazite rich beach placers

A study on exhalation rates of 222Rn and 220Rn and their enrichment pattern in different grain size fractions was carried out. Four different size fractions of the sand samples (1000-500 μm, 500-250 μm, 250-125 μm, and <125 μm) collected from the beach placers of south west coast of India were analysed for 226Ra and 232Th activity concentrations (Bq kg−1) by gamma spectrometry. Automated continuous measurement technique using scintillation cell based monitors were used to measure the 222Rn and 220Rn concentrations. These measured values were then fitted to appropriate model to extract the mass exhalation and emanation coefficients. The 222Rn mass exhalation rate varied from 0.7 ± 0.2 mBq kg−1 h−1 to 11.0 ± 0.9 mBq kg−1 h−1 while that of 220Rn varied from 88.5 ± 4.8 Bq kg−1 h−1 to 3066 ± 14 Bq kg−1 h−1. Higher mass exhalation rates, for both radioactive gases, were observed in finer grain size fractions. However, this was in contrast to the emanation coefficient values. Interestingly, higher radioactive monazite rich beach samples exhibited low emanation coefficient values compared to the low radioactive soil and sand samples reported in the literature. Statistical analysis showed a positive correlation, with correlation coefficient R = 0.84 and R = 0.79, respectively, between mass exhalation rates of 222Rn, 220Rn with their respective radioactive predecessors for different grain size fractions.

The Potential for REE and Associated Critical Metals in Coastal Sand (Placer) Deposits of Greece: A Review

The rare earth elements (REEs) are characterized by the European Union (EU) as critical raw materials with a significant risk of supply because of their broad utility in both traditional and emerging technological applications. The growing demand for REE has caused a flurry in the search for new REE deposits in Europe and elsewhere in the world, and is also linked to rising exploitation efforts in a variety of geological settings. To this end, Greece appears to be a promising candidate to become a leading EU country in terms of REE by virtue of its natural endowment in sedimentary heavy mineral deposits (placers) along its long coastline. The present review focuses on the distribution, abundance, and bulk geochemistry of REEs and other critical metals (Ta, Nb, Co) associated with placer deposits of Greece, and specifically with geologically young heavy mineral sand accumulations developed proximal to felsic plutonic source rocks. These deposits are also enriched in the actinides uranium (U) and thorium (Th), as both of these metals are typically associated with REE-rich minerals such as xenotime, monazite, thorite, allanite, and zircon. Previous studies have employed a variety of analytical techniques down to nano-meter scale with the aim to elucidate the mineralogy and distribution of REE and associated actinides in Greek beach placers. In view of this mineralogically-intensive background, the present review focuses chiefly on bulk geochemical characteristics of the same deposits and the variations thereof between two major geographical regions (northern Greece, southern Aegean) and across individual placer occurrences within them. In this framework, we present comprehensive compositional comparisons between the different deposits, highlighting the geological sub-environments wherein they occur, their distinctive sources and geochemical signatures, and their potential economic significance in terms of REE and other critical metal enrichments where applicable.

Radiological assessment, mineralogy and geochemistry of the heavy-mineral placers from the Calabrian coast (South Italy)

The presence of heavy minerals, including radionuclides such as 238U and 232Th, in the beach placers outcropping along the western Calabrian coast (South Italy) has been investigated in order to single out the contribution from natural sources to the total radiation level. Assessing the human health radiation risk for these areas is of great importance due to their main touristic destination. With the aim of characterizing the natural radionuclides contents of the Calabrian sands, the correlations existing between their mineralogical and geochemical features and those of the parent rocks have been studied by measuring the sand radionuclides concentrations and decay products and by calculating the outdoor effective dose rate. The radioactivity in the Calabrian beach sediments is for the most part attributed to monazite and, in turn, to the high amount of Th (in the 409–464 ppm range), and is a function of the rock types and of the formation processes. The outdoor dose and effective dose rates for an exposure period of three months are in the range 1045–1240 nGy/h and 0.32–0.37 mSv/y, respectively. Although these values are remarkably higher than the corresponding average world values, they fall within the limits fixed by the Italian legislation, assuming individuals that spend three summer months on the beach. The results obtained for this area of the Southern Italy coastlines can be used as a baseline for future investigations concerning radioactivity background levels, also in other regions. Moreover, the coupling of the present findings with those of epidemiological studies will allow gaining a better evaluation of possible health effects on the population.

Garnet Compositions Track Longshore Migration of Beach Placers in Western New Zealand

Garnet Compositions Track Longshore Migration of Beach Placers in Western New Zealand

NATURAL RADIOACTIVITY MEASUREMENT AND DOSE ASSESSMENT OF BEACH PLACER SANDS IN THE COASTAL REGION OF TAMIL NADU (INDIA).

A preliminary study was carried out to determine the radioactivity concentration of 232Th, 226Ra and 40K in beach placer sands from 13 locations along the coast line of Tamil Nadu state, India. The ambient dose rates varied from 9 to 467 nGy h-1. The activity concentrations of radionuclide 232Th, 226Ra and 40K ranged from 5.2 to 683 Bq kg-1, 13 to 198 Bq kg-1 and 107 to 421 Bq kg-1, respectively. The annual effective dose rate ranges from 27 to 620 μSv y-1 and was higher at seven beaches in comparison to the UNSCEAR annual worldwide average value.

Detrital record of the denudation of volcanic islands under sub-tropical climate (Cape Verde)

This research is focused on the composition of the sediments produced in volcanic islands when the climate does not favour weathering. The XRD mineralogy (bulk sample and fraction finer than 63 μm), petrography and geochemistry of a set of bedload stream and beach samples collected in the “old” Maio and the “young” Fogo islands of Cape Verde archipelago are used to investigate the compositional transformations promoted by exogenous processes during island denudation. The main factor responsible for the variability in sediment composition is the incorporation of biogenic material derived from the evolving shelves; it largely exceeds the effects of the exhumation of different volcanic and basement units. Given the arid climate (and steep land surface in Fogo), only the most labile components of basaltic rocks, such as volcanic glass, are decomposed. The incipient weathering and sorting processes are responsible for the depletion of Al in bedload deposits. The same happens with other elements usually regarded as non-mobile (namely, Nb, Th, REE, etc.), while Mg is concentrated. Thus, weathering indices grounded on the premise that “mobile” elements are lost and “non-mobile” elements are enriched via weathering are useless in Cape Verde bedload sediments. With time, weathering is able to promote Na leaching and the formation of secondary minerals, which tend to retain non-mobile elements released in the earlier stages of alteration (e.g., LREE, Th, Y, Nb, Ta etc.). Sorting processes are responsible for the selective removal of less-dense grains, explaining local differences between beach and stream deposits. Beach placers are enriched in augitic clinopyroxene (occasionally also in olivine in the Fogo island), and Sc, Cr and Co. Niobium and Ta must be hosted in fine-grained particles that are easily windblown and their abundances in dusts may reveal Cape Verde as a source of airborne material crossing the Atlantic Ocean.

Mineralogical Characterisation of Beach Placers at Kantiaghar in Ganjam District, Odisha

Abstract This paper details with the beach placer deposit of Kantiaghar area of Ganjam district, Odisha. In Odisha, Atomic Mineral Division (AMD) has explored a stretch of about 150 km from south of river Mahanadi to Orissa-Andhra Pradesh border. Here the potential deposits posses a grade range from 5 to 30%. The heavy minerals are present in the beach and dunes around Kantiaghar, which is in the NE of Rusikulya river mouth. The prospect extends in NE-SW direction having a width of about 1000m. Heavy minerals occur up to a depth of 10 m. A total of 12 samples were collected at an interval of half km along the shore of Bay of Bengal. The heavy minerals are mostly of 170 micron size. The average heavy mineral content of Kantiaghar beach is 67%. The heavy minerals constitute sillimanite, ilmenite, garnet, rutile, monazite and zircon. Along with these minerals trace amounts of magnetite and hornblende is also present. Leucoxene and anatase are reported from this beach. The average percentage of sillimanite is 50.15%, ilmenite is 19.47%, garnet is 13.5%, and rutile is 3.7%, monazite is 1.21% and zircon is 0.93%, the number percentage of the heavy minerals clearly shows that the concentration of sillimanite is high. Based on field relationships and mineralogy it can be interpreted that the river systems draining the Eastern Ghat, their metamorphic associates and basic intrusives account for these deposits.

РОССЫПИ ЖЕЛЕЗОСОДЕРЖАЩИХ МИНЕРАЛОВ В САХАЛИНСКОЙ ОБЛАСТИ

Ю.А. Билибин неоднократно подчеркивал, что для того, чтобы понять картину образования россыпей, необходимо учитывать полный цикл их превращений. Много внимания было уделено в последнее время проблемам поиска древних погребенных россыпей и россыпей сложного строения. Богатые резервы полезных ископаемых в россыпях объясняются множественностью их генетических типов, позволяющих вовлекать в промышленную эксплуатацию новые месторождения. Актуальность работы обусловлена необходимостью выявления новых источников получения железа, титана и ванадия в условиях сокращения ресурсов минерально-сырьевой базы. Поисковые работы, выполняемые с целью выявления россыпей, наиболее перспективных для разработки, могут проводиться на основании понимания генезиса их формирования. Цель работы: исследование закономерностей распространения россыпей железистых минералов в пределах Сахалинской области, выявление петрогенетических особенностей преобладающих минералов, определение перспектив освоения месторождений железосодержащего сырья, оценка экономической целесообразности его добычи. Методы. Исследованы железо-титан-оксидные минералы из различных по кремнекислотности горных пород островодужных вулканогенных комплексов Большой Курильской гряды. Для исследований были подготовлены шлифы горных пород, отобрана магнитная фракция из протолочек. Шлифы пород изучались под поляризационным микроскопом. Порошок протолочек горных пород и мономинеральных фракций исследовался посредством химических аналитических методов (гравиметрического, титрометрического, спектрофотометрического, рентгенофлуоресцентного, масс-спектрометрического с индуктивно-связанной плазмой). Результаты. Исследованы закономерности формировании железистых россыпей и определены их основные типы. На побережьях Дальнего Востока России встречаются два типа россыпей с различными условиями питания. Одна из них – Курило-Камчатская провинция собственно титаномагнетитовых россыпей – расположена на территории Сахалинской области. На островах Курильской дуги преобладают современные пляжевые россыпи и дюнные отложения низкой террасы. Главная роль в обеспечении минералами россыпей этого типа принадлежит туфопесчаникам, пемзам и пемзово-шлаковым пирокластическим толщам. Кристаллы железосодержащих минералов в горных породах вулканогенных комплексов имеют довольно разнообразные размеры: от мелких, пылеватых до крупных хорошо выраженных кристаллов, размерами более 1–2 мм. Химический состав титаномагнетитов различных вулканических комплексов изменяется в зависимости от кремнекислотности пород. Продуктивные породы характеризуются повышенным содержанием железа, титана и ванадия. Прибрежно-морские, а также древние погребенные россыпи содержат значительные объемы железосодержащих минералов. Изучение технологических схем переработки железосодержащего минерального сырья показало, что некоторые из них позволят провести его переработку с получением востребованных конечных продуктов. При определенных экономических условиях разработка россыпей может быть целесообразной.

Mineralogy of a Radioactive-Rare Earth Elements Occurrence in the Paleozoic Batholith, South-Central Chile

South-central Chile has some potential mineral resources including radioactive and rare earth elements (REE) minerals. This study reports some basic characteristics of the mineralogy of a radioactive-rare earth elements occurrence, related to a pegmatitic outcrop “Vertientes Pegmatite” hosted on Paleozoic granitic rocks of the South Coastal Batholith and discusses potential areas for REE deposits, particularly beach placers along the coastline of the BioBío region. In this pegmatite, X-ray diffraction analysis shows uranium-bearing minerals such as coffinite and metaschoepite, along with microcline, anorthoclase, albite, quartz and illite. Through optical microscopy and electron probe micro-analyzer (EPMA), rare earth minerals (monazite and xenotime) and radioactive minerals (thorite and thorium silicate ± uranium) were identified. Additionally, granitic rocks of the South Coastal Batholith around this pegmatite show rare earth minerals (monazite and allanite).

Studies on heavy mineral placers from eastern coast of Odisha, India by instrumental neutron activation analysis

The study shows geochemical characterization of placer deposit in parts of coastal Odisha, India using Instrumental Neutron Activation Analysis (INAA). Twenty seven elements were estimated in ten heavy mineral beach sand samples. The characterisation was mostly based on the trace element, radioactive element and Rare Earth Element (REE) content of the bulk sand samples. The results indicate elevated concentration of thorium and the REE’s. The concentration of Scandium has been reported for the first time along this area. Positive correlation between thorium and REE was observed in beach placer samples collected from study area.

FEG-EPMA mapping and Fe-Ti oxide mineral chemistry of Brahmaputra River sediments in Bangladesh: provenance and petrogenetic implications

The present research deals with the FEG-EPMA mapping and Fe-Ti oxide mineral chemistry of Brahmaputra River sediments in Bangladesh. Major heavy minerals in the sediments consist of garnet (8.5–21.3%), kyanite (5.35–11.9%), monazite (2.3–5.3%), sillimanite (1.8–4.7%), zircon (3.6–9.1%), and a considerable amount of opaques mainly Fe-Ti oxide minerals (23.1–35.4%). The detrital Fe-Ti oxide minerals carry significant clues to the parent rocks or sources. In these contexts, detrital opaques (Fe-Ti oxides) have been analyzed with an electron probe microanalyzer (EPMA). These opaques (Fe-Ti oxide) display six types of textural patterns, dominantly seriate with granular, emulsion, and acicular sandwich structures and trellis type of textural patterns. These textural patterns belong to five intergrowths of Fe-Ti oxide minerals such as (1) ilmenite-hematite, (2) magnetite-ilmenite, (3) hematite-rutile, (4) ilmenite-hematite-rutile, and (5) ilmenite-rutile, where ilmenite-hematite intergrowth is common. Alteration is seen in both exsolved and unexsolved ilmenites. Textural patterns and mineral chemistry of the studied ilmenite minerals provide lines of evidence of low-temperature magmatic inheritance, later modified by diffusional processes. The estimated temperature and oxygen fugacity from the magnetite-ilmenite exsolution range from 547.6 to 558.2 °C and from 10−21.4 to 10−21.7, respectively. The data are also consistent with hematite-ilmenite temperature (between 537 and 540 °C) and oxygen fugacity (10−21.7 to 10−21.9) measurements in Cox’s Bazar beach placers. These temperatures and oxygen fugacities specify Fe-Ti oxide assemblages equilibrated in a T-fO2 field very near to the FMQ buffer curve suggesting a crustal source (magmatic and/or metamorphic), which is modified significantly by metamorphic processes.

Titanium-Rich Beach Placers in As-Sufal, Hadhramout Coast

The accumulations of beach placers along the shoreline of Hadhramout at As-Sufal area have been prospected and analyzed for their radiogenic and chemical characteristics for the first time. The activity concentrations of $$^{226}\hbox {Ra}$$ , $$^{232}\hbox {Th}$$ , and $$^{40}\hbox {K}$$ in the beach placers’ samples were measured by gamma-ray spectrometry using a 56% HPGe detector and found to be $$1270\pm 237$$ , $$2098\pm 380$$ , and $$208\pm 40\,\hbox {Bq kg}^{-1}$$ , respectively. The results established As-Sufal as a high natural background radiation area. The hazard indices predicted elevation of the external exposure of residents when sand soiled with beach placers from this area is used as a building material. Radium equivalents of beach placers were 8.6–14.3 times the maximum recommended for the safe use of materials in the construction of dwellings. The outdoor annual effective doses ranged from 1.68 up to $$\sim $$ 2.82 mSv considerably higher than the recommended 1-mSv dose limit for members of the general public. The beach placers at the study locations are dominated by $$\hbox {TiO}_{2}$$ , $$\hbox {Fe}_{2}\hbox {O}_{3}$$ , and $$\hbox {SiO}_{2}$$ . Ir and Hf were found to be incorporated in Zr and Al compounds, respectively, and the anti-correlation of Zr with either Al or Hf indicates that Zr replaces both elements in the beach placers’ grains. The radionuclides in beach placers seem to be attributed to Mg-, Ca-, Si-, and Zr-bearing minerals and not associated with Fe-bearing minerals. The heaviest fractions are mainly composed of $$\hbox {TiO}_{2}$$ , $$\hbox {Fe}_{2}\hbox {O}_{3}$$ , and $$\hbox {ZrO}_{2}$$ . The $$\hbox {TiO}_{2}$$ -bearing minerals in the heaviest fractions contain V-rich portions.

Heavy minerals distribution and provenance in modern beach sands of Campania, Italy

The Campania region (southern Italy) is an excellent area to determine the effects of multiple source lithology (volcanic+sedimentary), climate, weathering, transport anddepositional environment on heavy minerals enrichments in the sandy beaches of the coastline between Pozzuoli and Bacoli, and at the Volturno river-mouth. The heavy mineral (HM) assemblage should reflect the clastic supply from the potassic to ultrapotassic lavas and pyroclastic rocks of the Campania and of the Roman Magmatic provinces (Phlegrean Fields, Roccamonfina volcano), and from the recycling of sedimentary - both carbonate and siliciclastic - terranes of the Apennine thrust belt. Opaque oxides, pyroxene and amphibole assemblage dominates in the beach placers of the Campania shoreline - from Bacoli to Pozzuoli - as well as in the Volturno river mouth sands to the north. Modern heavy minerals assemblages reflect clastic contribution from magmatic source rocks whereas contributionfrom sedimentary terranes - exposed extensively in the Volturno river drainage - provide no recycled heavy minerals to the river-mouth sand. Thus, heavy minerals linked to a provenance from the Apennine thrust belt source rocks result diluted and/or unrecognizable using the only HM approach with respect to the minerals provenance sourced by the potassic volcanic fields of Latium and Campania. Thediverse detrital heavy minerals have been characterized describing major stages of progressive chemical weathering, from unweathered to corroded to etched morphologies, a process - in this case-history - playing a minor role in reducing HM diversity through dissolution of moderately stable mineral species.

Heavy mineral beach placers of the Ordovician Amdeh Formation (Member 4, Wadi Qahza, Saih Hatat, eastern Oman Mountains): Where is the main source area?

We studied an excellently exposed section of the slightly metamorphic siliciclastic Amdeh Formation. The section is near the base of the Amdeh Member 4 (Am4). Am4 is of Early to Mid-Ordovician age and 1677 m thick. Two lensoid placers were examined for their mineral composition (X-ray diffraction, transmitted and reflected light microscopy), geochemistry (X-ray fluorescence), in-situ gamma-ray emissions and the sedimentary structures of the host rocks. The placers were deposited in a beach environment as indicated by sedimentary structures in the associated quartzites, such as parallel lamination, parting lineations and sand volcanoes and as indicated by the compositional and textural maturity of the host rock and the placers. Placer deposition may have been favored by rising sea-levels. Overall, the dark placers contain the following heavy minerals: anatase (up to 35–40%) > ilmenite > zircon > hematite (a few %) > and apatite (<1%, may be present in trace amounts as indicated by low phosphorous contents in XRF analysis). The presence of monazite is indicated in our study by LREEs plus yttrium. Due to the high amounts of ilmenite and anatase, the placers' titanium contents are high (up to 20.5 wt%). In both placers, the concentrations of the light rare earth elements (LREEs) lanthanum, cerium, praseodymium and neodymium plus yttrium (geochemically affine to HREEs) are noteworthy (between ∼3000 and 7000 ppm). The source rocks can be expected in metamorphic and acidic plutonic rocks in the basement of Oman, which may have shed detritus from exposed basin flanks, but other potential source areas lay to the north and south of the basin. A source area with pre-enriched quartz in sandstone to explain the massive quartz influx would also be possible. The coastal/shallow shelf facies of Am4 shows very little bathymetric variability despite its thickness, which requires rapid and continuous subsidence. We attribute basin subsidence to rifting, withdrawal (and subrosion?) of salt in the subsurface (Ara Formation) due to sediment loading and possibly to gravity-driven subsidence due to the presence of dense ophiolite units below the Ara Salt. The absence of the Amdeh Formation in the west (Jabal Akhdar Dome) may be explained by rift shoulder uplift. While the Amdeh Formation accumulated in the rift basin, the Jabal Akhdar region occupied parts of the northwestern rift shoulder.

Provenance discrimination among foreshore, backshore, and dune environments in the black sand beaches along the Samandağ/Hatay coasts, SE Turkey (E Mediterranean)

The occurrence of beach placers, the chromite-rich black sand, and the factors controlling their distribution along the Samandag coasts, SE Turkey, was investigated. One hundred fifty-two surficial (upper 2 to 5 cm) samples of beach sediments from foreshore, backshore, and dune subenvironments; 24 river sediments; 25 samples from ophiolitic source rocks; and ore samples from 4 chromitite mines were collected between the years 2012 and 2015. In addition to hydrogeographic and geomorphological field observations, grain size analysis and total heavy mineral separation and conventional petrographic microscopy studies were carried out. Bimodal, well to moderately well sorted, fine to medium sands were predominant, and on the basis of grain size distribution, at least six sectors could be distinguished by their alongshore fining or coarsening tendencies. Obviously, spatial variations in drainage pattern of fluvial input, wave and current motions, and beach morphology played a crucial role in changing sediment texture. The total heavy mineral (THM) concentrations ranged from 1 to 92 wt% (avg. 40 wt%) in beach sediments and from 3 to 50 wt% in fluvial sediments whereby the bed load of the major and perennial Asi River contained lower THM (9–25 wt%) than its ephemeral tributaries (14–50 wt%) which are in much closer proximity to the source areas. Overall, the THM concentrations in foreshore, backshore, and dune subenvironments tend to decrease in southward direction, except for THM enrichment close to the Asi River mouth. This would reflect rather higher inputs from northerly ephemeral rivers draining the ophiolitic rocks with additionally net longshore sediment transport towards south. The coastal physical processes favoring heavy mineral enrichment such as spatial and temporal variations in swashzone wave dynamics with uprush, backwash, and infiltration effects on the beaches were also observed in the field. The opaque heavy mineral fractions are mostly found in grain size less than 0.25 mm and composed of chromite, magnetite, and ilmenite species with intergrowth textures. Non-opaque heavy mineral fractions were dominated by various species of pyroxenes and amphiboles with lesser amounts of serpentinized olivine. Formation of chromite-rich black sand placers along the Samandag beaches (SE Turkey) and also in river/stream beds resulted from the weathering of mafic-ultramafic rock complexes (“Hatay or Kizildag Ophiolites”) and chromite-rich ores of the Amanos Mountains to define the provenance of placers and no considerable input was detected from the Asi River downstream from the Bassaer ophiolites of Syria.

Sedimentary processes controlling ultralong cells of littoral transport: Placer formation and termination of the Orange sand highway in southern Angola

AbstractThis study focuses on the causes, modalities and obstacles of sediment transfer in the longest cell of littoral sand drift documented on Earth so far. Sand derived from the Orange River is dragged by swell waves and persistent southerly winds to accumulate in four successive dunefields in coastal Namibia to Angola. All four dunefields are terminated by river valleys, where aeolian sand is flushed back to the ocean; and yet sediment transport continues at sea, tracing an 1800 km long submarine sand highway. Sand drift would extend northward to beyond the Congo if the shelf did not become progressively narrower in southern Angola, where drifting sand is funnelled towards oceanic depths via canyon heads connected to river mouths. Garnet–magnetite placers are widespread along this coastal stretch, indicating systematic loss of the low‐density feldspatho‐quartzose fraction to the deep ocean. More than half of Moçamedes Desert sand is derived from the Orange River, and the rest in similar proportions from the Cunene River and from the Swakop and other rivers draining the Damara Orogen in Namibia. The Orange fingerprint, characterized by basaltic rock fragments, clinopyroxene grains and bimodal zircon‐age spectra with peaks at ca 0·5 Ga and ca 1·0 Ga, is lost abruptly at Namibe, and beach sands further north have abundant feldspar, amphibole‐epidote suites and unimodal zircon‐age spectra with a peak at ca 2·0 Ga, documenting local provenance from Palaeoproterozoic basement. Along with this oblique‐rifted continental margin, beach placers are dominated by Fe–Ti–Cr oxides with more monazite than garnet and thus have a geochemical signature sharply different from beach placers found all the way along the Orange littoral cell. High‐resolution mineralogical studies allow us to trace sediment dispersal over distances of thousands of kilometres, providing essential information for the correct reconstruction of ‘source to sink’ relationships in hydrocarbon exploration and to predict the long‐term impact of man‐made infrastructures on coastal sediment budgets.

Environmental Implications of Mining of Beach Placers for Heavy Minerals

Environmental Implications of Mining of Beach Placers for Heavy Minerals

Economically viable rare earth element deposits along beach placers of Andhra Pradesh, eastern coast of India

A comprehensive study was carried out in order to determine the radioelement and rare earth element (REE) concentrations in beach placer deposits at selected locations along the eastern coast of Andhra Pradesh in India. This was done to evaluate the economic value of these deposits. The findings of this study suggest that high Th and low K concentrations delineate the prospective regions having REE deposits. The beach placers, in general, can be characterized by high thorium and moderate uranium concentrations. The concentrations of REEs vary in the following order: Ce > La> Nd > Pr > Sm > Gd > Dy. Rapid in situ thorium prospectivity coupled with laboratory-based techniques like ICP-MS, as proposed in this study, would help in the identification of prospective REE sources along the coastal placers. The development of indigenous resources of light rare earth elements (LREEs), medium rare earth elements (MREEs), and heavy rare earth elements (HREEs) would decrease the dependence on imports, which have a strategic hold on the production and supply of the REEs, globally.

A baseline record of trace elements concentration along the beach placer mining areas of Kanyakumari coast, South India

Trace element concentration in the beach placer mining areas of Kanyakumari coast, South India was assessed. Sewage and contaminated sediments from mining sites has contaminated the surface sediments. Enrichment factor indicates moderately severe enrichment for Pb, minor enrichment for Mn, Zn, Ni, Fe and no enrichment for Cr and Cu. The Igeo values show higher concentration of Pb ranging in the scale of 3–4, which shows strong contamination due to high anthropogenic activity such as mining and terrestrial influences into the coastal regions. Correlation coefficient shows that most of the elements are associated with each other except Ni and Pb. Factor analysis reveals that Mn, Zn, Fe, Cr, Pb and Cu are having a significant loading and it indicates that these elements are mainly derived from similar origin. The cluster analysis clearly indicated that the mining areas are grouped under cluster 2 and non-mining areas are clustered under group 1.