Heavy Mineral Placer Deposits Research Articles

Distribution and Characterization of Heavy Mineral Placer Deposits along the Central Tamil Nadu Coast, India

Distribution and Characterization of Heavy Mineral Placer Deposits along the Central Tamil Nadu Coast, India

Cassiterite trace element discrimination diagrams to facilitate critical mineral exploration

Cassiterite is a weathering-resistant mineral, which can incorporate a variety of trace elements. Trace elements in cassiterite samples collected from twelve deposits in the Herberton Mineral Field, Australia, were measured with the use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The results were combined with published data from other tin fields, including the Andean Sn belt in South America; the Karagwe Ankole belt in Rwanda; and, from China, the Kangxiwa-Dahongliutan pegmatite field, the Youjiang basin, the Nanling belt and the Da Hinggan Range belt. Tin deposits in the dataset can be subdivided into four deposit types: 1) greisen and veins; 2) skarns; 3) Li-Cs-Ta pegmatites; and 4) polymetallic veins. The cassiterite dataset was analyzed using basic descriptive statistics, principal component analysis (PCA), and cluster analysis. Cassiterite grains from greisen and vein deposits are characterized by high concentrations of Ti (avg. 1751 ppm) and moderate concentrations of Al (avg. 97 ppm), whereas cassiterite grains from skarn deposits generally contain lower concentrations of Ti and Al. Chemical compositional boundaries in cassiterite from different deposits were recognized with cluster analysis. The relative enrichment of Al and Ti in cassiterite grains from greisen and vein deposits is likely due to greisenization reactions. The Ti vs. Al diagram can be used to differentiate between cassiterite grains derived from greisen and vein deposits, as compared to cassiterite grains derived from skarn deposits, whereas Sb vs. V diagram can be used to differentiate between cassiterite grains from polymetallic vein deposits. Zirconium and Nb concentrations are useful in identifying cassiterite grains sourced from LCT pegmatite deposits. The discrimination diagrams developed in this study through cluster analysis indicate that cassiterite grains sourced from different deposit types can be differentiated based on their trace element geochemistry and this can be a useful tool in critical mineral exploration. Therefore, these diagrams can be used effectively to understand metal association and deposit types in a region with detrital cassiterite from stream sediments, till and heavy mineral placer deposits.

Reappraisal of 75 Years of Exploration for Atomic Minerals in India and the Way Forward

Abstract In India, Atomic Minerals Directorate for Exploration and Research (AMD), the oldest unit under the Department of Atomic Energy (DAE) is mandated with the exploration and augmentation of atomic mineral(s) resources of the country to support the Nuclear Power Programme (NPP) of India. AMD, till date have established four (04) generations of uranium metallogeny in India, distributed in 46 deposits and several other occurrences, major share of which are contributed by the globally unique, stratabound carbonate hosted, syn-diagenetic Tummalapalle Group of deposit (~59%), metamorphite type deposits along the Singhbhum Shear Zone (~21%), unconformity related deposits in northern part of Cuddapah Basin (~5%) and sandstone type deposits in Cretaceous Mahadek Basin (~6%). Besides these, metasomatite type deposits along the North Delhi Fold Belt (4%) and granite related-structurally controlled, high grade deposits in Bhima Basin (2%) along with some small hydrothermal/metamorphite/migmatite type deposits in Aravalli, Kotri-Dongargarh, Higher Himalaya belts and Chhotanagpur Granite Gneiss Complex contribute to the national inventory which stands at 3,76,000 tonne uranium oxide. AMD have stockpiled substantial quantities of Nb-Ta, Be and Li minerals needed for the NPP of India from prospective pegmatite belts in the country. AMD have established immense potential for REE mineralization in carbonatite complexes of Ambadungar in Gujarat and per-alkaline granite-rhyolite of Siwana Ring Complex, Barmer district, Rajasthan. Exploration along the coastal and riverine placers of the country has established 130 heavy mineral placer deposits with substantial thorium and REE resources. The progressive advancements by AMD through adaptation of integrated multidisciplinary exploration techniques coupled with major thrust in airborne/ground geophysics and expansion of state-of-the-art analytical facilities have facilitated systematic planning for future augmentation of atomic mineral(s) resources. Exploration inputs are envisaged to be intensified in the brownfield target areas for resource augmentation while R&D and phase-wise exploration inputs will be focused for developing the identified greenfield areas following a planned roadmap to ensure selfsufficiency in atomic mineral resources for sustained growth of the NPP to reach the target of net zero carbon emissions by 2070.

Grain size variation in sand column along Chhatrapur coast, Ganjam district, Odisha – A clue to the depositional environment

The concentration of heavy mineral placer deposits along the coastal tracts are function of various favourable factors i.e. hinterland geological formations, prevalence of favourable climatic condition, their transportation through intricate drainage systems and various coastal processes, which operated during the geological past. Textural analysis of the available unconsolidated sediments from the present deposits is of vital importance to decode the prevailing depositional environment while grain size analysis is the major parameter used. Present study highlights the grain size analysis of the identified sand column from Chhatrapur Mineral Sand Deposit along the coastal tract of Odisha to infer the environment of deposition of heavy mineral bearing sand and their heavy mineral content variation. Standard procedure of sampling, data analysis and interpretation techniques were adopted. Result shows that, sands from frontal and rear dune are characterized by distinct bi-modal distribution, medium to fine, moderately to well sorted with good positive skewness, whereas, sand from Inter-dunal region shows dominant unimodal, medium to coarse grain, moderately poorly sorted nature and slightly positive skewness. The better heavy mineral concentration (10 to 25 % grade) in frontal and rear dunes is attributed to prevalence of aeolian dune deposition accompanied by good sorting. In contrast, the low concentration of heavy mineral (3 to 6 %) in inter dune region is due to occasional fluvial regime and poor sorting of sediments. Thus, grain size analysis can be an effective tool to decipher local prevailing depositional environment, which has a bearing on heavy mineral concentration as well.

DISTRIBUTION OF SUBSURFACE QUATERNARY SEDIMENT IN SOUTH BINTAN ISLAND WATERS AS A POTENTIAL HEAVY MINERAL PLACER OR RARE EARTH ELEMENT DEPOSIT BASED ON SEISMIC INTERPRETATION

Bintan Island is one of the areas traversed by the Southeast Asian granitoid belt which is known to have the potential for heavy mineral placer deposits. Due to the dwindling presence of heavy mineral placer deposits in land areas, it is necessary to look for the potential presence of heavy mineral placer deposits in water areas. Searching for placer heavy mineral deposits accomodation in these waters requires subsurface mapping.The method used in this subsurface mapping is a single channel seismic method with a total of 179 lines in the direction of northeast – southwest and west – east. The results of this seismic recording are then interpreted the boundaries of the seismic facies unit and distributed using the kriging method. Furthermore, the thickness calculates by using the assumption velocity 1600 m/s.Based on the facies unit boundaries that have been interpreted, the quaternary sediments that formed in the study area are divided into 2 types of units, namely: Unit 2 which is estimated to be fluvial – transitional sediment, and Unit 1 which is estimated to be transitional sediment – shallow sea. There is also a difference in thickness patterns in these two units, where unit 2 shows a pattern of sediment thickening that resembles a paleochannel trending northeast – southwest, while unit 1 is relatively uniform.From the results of this study, it can be said that the area that has potential for heavy mineral placer deposits is in the west - center of the southern waters of Bintan Island. Where the potential for heavy mineral placer deposits should be in the paleochannel deposits that are part of Unit 2.

State-of-the-art and perspectives in the heavy mineral industry of Sri Lanka

Heavy minerals have become an essential commodity in modern-day technology. The objective of this study is to examine the current status of the heavy mineral industry of Sri Lanka. The present study also examines the economic viability of potential heavy mineral placer deposits, based on geochemical data. Field investigations suggested the occurrence of heavy minerals as beach-placers, and inland/raised beach deposits along the coastline of Sri Lanka. Geochemical results showed the enrichment of TiO2, Fe2O3, Al2O3, and trace elements, and depletion of other major oxides such as Na2O, K2O, MnO, MgO, CaO, and P2O5. Consequently, it suggests the abundance of ilmenite, leucoxene, rutile, sillimanite, garnet, and rare earth element (REE)-bearing heavy minerals in potential placer deposits. In contrast, this study illustrates the exported quantity (in the weight ratio of 35:3:1) of ilmenite, rutile, and zircon minerals during the last decade. Ilmenite is the dominant heavy mineral in Sri Lanka, and thus, its production and price volatilisations are essential to understand the current status and predict the future behaviour of the heavy mineral industry. Statistical observations suggest that the global production and unit price variations of ilmenite have increased gradually from 1950 to 2015. Besides, the forecasted variations in annual global production and unit price changes of ilmenite indicate healthy compound annual growth rates of 1.27% and 1.43%, respectively. However, Sri Lanka has less contribution (< 1%) to global ilmenite production. Consequently, the value addition of ilmenite must be highly encouraged with at least an immediate stage (e.g. synthetic rutile). The present study also highlights possible value addition stages of available heavy mineral resources (low-, intermediate-, or high-level value addition), and discusses action plans to improve the quality of the heavy mineral industry of Sri Lanka. In recommendations, imposing sustainable regulations and policies would uplift the heavy mineral industry of Sri Lanka. For example, value addition to local heavy minerals and terminating raw commodity export are highly recommended.

Influence of nearshore sediment dynamics on the distribution of heavy mineral placer deposits in Sri Lanka

Beach sediments in Sri Lanka contain industrial-grade heavy mineral occurrences. Samples of both offshore and onshore sediments were collected to examine the provenance, mineralogy and geochemical compositions of the heavy mineral occurrences. Coastal morphodynamic changes along the coastline of Sri Lanka were analyzed using the time-series satellite images. These coastal morphodynamic changes were used to identify the prominent directions of monsoon-influenced longshore currents, coastal sediment accretion and depositional trends and their relationships to the provenance of the heavy minerals. Results show the concentrations of detrital ilmenite, zircon, garnet, monazite, and rutile vary in the onshore and offshore sediments. The heavy mineral potential of the northeastern coast is high (average contents of about 45–50% in the Verugal deposit, 70–85% in the Pulmoddai deposit, and 3.5–5.0% in offshore samples stretching from Nilaveli to Kokkilai), compared to sediments in southwest (average content about 10% in onshore sediments and 2% in offshore sediments from the mouth of the Gin River). Therefore, no economic-grade heavy mineral placers were identified in the offshore environments. The high concentrations of heavy minerals in beach sediments and low concentrations in offshore sediments suggest operation of a panning system in the surf zone to form enriched placer deposits. Major and trace element compositions of beach sediments show marked enrichments of TiO2, Fe2O3, La, Ce, Zr, Cr, Nb, Th and V compared to average Upper Continental Crust (UCC) values. Analysis of prominent coastal longshore transport patterns identifies bidirectional sediment transport in the northeast coast of Sri Lanka. In the southwestern coast, two transport directions occur with anti-clockwise transport from Galle to Hambantota, and clockwise transport from Hikkaduwa to Wadduwa. The heavy minerals in the placers were mainly derived from Precambrian metamorphic rocks, and transported to the coast through the river systems of Sri Lanka.

Influence of Porosity in Quantitative Analysis of Heavy Mineral Placer Deposits

Influence of Porosity in Quantitative Analysis of Heavy Mineral Placer Deposits

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.

Using zircon U–Pb ages to constrain the provenance and transport of heavy minerals within the northwestern shelf of the South China Sea

Numerous ore-grade heavy mineral placer deposits occur in the northern South China Sea region. Previous studies on these deposits have focused on the heavy-mineral ore resources themselves, but the provenance and transport pathways of these heavy minerals are poorly constrained. This paper presents U–Pb ages of detrital zircons from sediments within the northwestern shelf of the South China Sea, and uses this new dataset to determine the provenance and transport pathway of the sediments. Zircons in sediments from ten areas of the northwestern shelf exhibit distinct age populations, suggesting that they have multiple provenances. Zircons in sediments from the Pearl River Mouth, Shangchuan Island, and Moyang River Mouth areas all have an obvious peak of Mesozoic ages, indicating that they have similar sediment provenances; i.e., mainly from the Pearl River, and to a lesser degree from the Moyang River. Zircons in sediments from the areas around the Jian River Mouth and Leizhou Bay, and off Hainan Island have an early Paleozoic age, suggesting that the sediments predominantly originate from the Yunkai massif. Zircons of the sediments from the remaining four areas, the Leiqiong Strait, Wanquan River Mouth, Qiongdongnan, and the Outer Shelf, have Yanshannian and Indosinian age peaks in addition to an obvious early Paleozoic population, implying mixed provenances, including the Yunkai massif and Hainan Island. The sediment transport may have involved two hydrodynamic conditions in two distinct stages. First, the Guangdong Longshore Current carried the river sediments to where they dispersed in the inner shelf; subsequently, wave-induced strong currents further transported sandy sediments southeastward to the outer shelf. In addition to explaining the provenance and transport pathways of heavy minerals within the northwestern shelf of the South China Sea, these results provide new information relevant to exploration for heavy-mineral placer deposits.

Composition of ilmenite and provenance of zircon in northern Brazil

The mineral ilmenite (FeTiO3) is an important component of heavy-mineral placer deposits and constitutes the largest volume of valuable mineral in such deposits. The minerals zircon (ZrSiO4) and rutile (TiO2), which occur in lower concentrations than ilmenite in the deposits, have a greater value per ton – c. 1100 and 900 $/ton respectively – compared to ilmenite that ranges from 100 to 200 $/ton depending on its composition. Other minerals such as staurolite, sillimanite, amphibole and garnet are generally also present in placer deposits, but are of minor or no commercial value and, e.g. amphibole needs to be separated from the valuable heavy minerals which adds to the production cost.

Mapping of heavy mineral placers through marine GIS expert system: a case study in Kalaignanapuram coastal stretch, southeast coast of Tamil Nadu, India

The aim of the present study is to develop a knowledge-driven expert system for mapping the potential heavy mineral placer deposits along the coast using integrated Geographical Information System (GIS) and fuzzy logic techniques. The study has been carried out in Kalaigananpuram coastal stretch, southeast coast of India, where high-quality heavy mineral placers are deposited naturally. A total of six transects was laid perpendicular to the coastline, in which 36 samples per transect of 2 m interval per month was taken for analysis. Standard techniques were adopted for evaluating the beach profile, grain size, and heavy mineral weight percent. Moreover, the statistical results of these parameters were considered for mapping the heavy mineral placer potential zone in the study area. A fuzzy-based expert system model was developed through ArcGIS model builder to map the mineral potential zone. In this study, three evidential layers were fuzzified using the linear membership function. These evidential layers were further ranked based on expert knowledge from placer minerals exploration researchers. The analyzed results reveal that heavy mineral placer deposits are observed in the berm and high-tide region of the study area. The annual average weight percent of heavy mineral placer deposits in the study area range from 40 % to 60 %. The extracted heavy mineral placer potential maps can be used for sustainable mining and surveying purposes.

Source of zircon in world-class heavy mineral placer deposits of the Cenozoic Eucla Basin, southern Australia from LA-ICPMS U–Pb geochronology

The Eucla Basin of southern Australia is a newly recognised zircon-rich mineral sands province with mining operations underway at the world-class Jacinth–Ambrosia deposits. Detrital zircon U–Pb dating via laser ablation inductively coupled plasma mass spectrometry from samples distributed along the length of the Eucla Basin paleoshore system reveals the majority of zircons (c. 55%) are from c. 1300 to 1000Ma source rocks. Many of the zircons of this age range have metamorphic textures indicating the source province(s) of these zircons underwent high-grade metamorphism during the Mesoproterozoic. A secondary provenance signature occurs at c. 1800–1600Ma, with significant amounts of c. 1680–1600Ma zircon. These two key age intervals, c. 1300–1000Ma and c. 1800–1600Ma match the major rock-forming intervals of the Albany Fraser Orogen and Musgrave Province, crystalline basement regions that crop out in the western and northern hinterland of the Eucla Basin and which are transected by extensive Early Cenozoic paleodrainage systems. The subordinant volume of Archean zircons in the paleoshoreline deposits are predominantly c. 2660Ma or older and are most likely derived from the Yilgarn Craton. The primary source regions for the zircons thus lie to the west and north of the main sites of heavy mineral sand accumulation, located in the central and eastern portions of the paleoshoreline complex of the Eucla Basin. This is indicative of the dominant process of westerly longshore drift as the primary control on sediment movement and redistribution along much of the Eucla Basin coastline. Zircons of these ages were also likely derived from recycling sediments of Neoproterozoic and Phanerozoic intracontinental basins, in particular the Officer Basin, which contains dominantly c. 1350–1000Ma zircons, and was widely incised by the Paleogene drainage network. Monazite U–Pb data from the Jacinth Mine records an abundance of c. 1350–1160Ma grains, supporting source areas to the north and west of the Eucla Basin. Heavy mineral input from the more proximal Gawler Craton was minor. The zircon-rich mineral sands province of the Eucla Basin is thus a result of large-scale zircon erosion, transport, recycling and eventual concentration on beach shorelines where sand movement was controlled by dominant westerly longshore drift.

Magnetic mineral transport and sorting in the swash‐zone: northern Lake Erie, Canada

AbstractA combined field and laboratory study in northern Lake Erie has provided new insights into the origin and dynamics of heavy mineral placer deposits on beaches consisting primarily of non‐magnetic sediment. Work was conducted on the cross‐shore and longshore transport of heavy magnetic minerals using magnetic susceptibility and fluorescent paints to trace the movement, in the field, of samples of magnetic (magnetite) and non‐magnetic (quartz and calcite) grains, respectively. Laboratory experiments examined how the burial of small, dense magnetic minerals is affected by the grain size of the non‐magnetic host material, and how grain burial affects magnetic susceptibility measurements at the surface. The field experiments demonstrated that the magnetic mineral tracers were buried rapidly beneath coarser, non‐magnetic grains under low to moderate wave conditions, and subsequently were unable to move in the longshore or cross‐shore directions. The laboratory experiments showed that the magnetic susceptibility rapidly decreased with the rate and depth of burial of the magnetic minerals, and that magnetic grain burial was most effective beneath coarser rather than finer non‐magnetic sand and, for the latter sediments, under less rather than more energetic conditions. The results imply that magnetic mineral concentrations develop in this area through magnetic grain burial under fairly mild conditions, and subsequent settling, exposure and concentration in the upper swash zone during more energetic periods, when the non‐magnetic grains are eroded. It is probably during these erosional periods, when the magnetic minerals are exposed in fairly homogeneous deposits, that longshore and cross‐shore transport takes place.

Ilmenite, Magnetite and Chromite Beach Placers from South Maharashtra, Central West Coast of India

AbstractThe heavy mineral placer deposits of the coastal sediments in south Maharashtra stretch for 12.5 km from Pirwadi in the north to Talashil in the south. The area is a sand bar represented by a narrow submergent coastal plain lying between the Achara and Gad Rivers. The sediments in the area are mainly sands which are moderately well sorted to well sorted. The heavy mineral concentration in the surficial sediments ranges between 0.69 and 98.32 wt % (28.73 wt % in average). The heavy mineral concentration shows an increasing trend from north to south. The heavy mineral suite consists predominantly of opaque minerals (ilmenite, magnetite and chromite), garnet, pyroxene, amphibole, zircon, tourmaline, rutile, staurolite, etc. Ilmenite grains are fresh whereas magnetite grains show the effect of weathering and alteration. The chromite grains are rounded to sub‐rounded with alteration at the margin of the grains. The surficial textures of the opaque minerals show mechanical breaking that indicates limited distance of transportation.Ilmenite has TiO2 in the range between 40.04 and 46.6 wt %. Based on ore microscopy studies, the magnetite grains appear to be of two types: pure magnetite and titano‐magnetite. Compositionally, the total magnetite fractions have Fe2O3 between 32 and 46 wt %, FeO between 19.0 and 25 wt % and TiO2 between 14.3 and 23.9 wt %. The chromite grains are an admixture of two varieties, ferro‐chromite and magnesio‐chromite. The chromite grains have 32.06–47.5 wt % of Cr2O3 with total iron between 23.86 wt % (4.73% Fe2O3 and 19.13% FeO) and 27.89 wt % (4.36% Fe2O3 and 23.53% FeO) and MgO between 12 and 40 wt %.The observed variations in the distribution of heavy minerals in the area are due to differences in the sediment supply, their specific gravity and oceanographic processes all of which result in a selective sorting of the sediments. The observed mineral assemblages of transparent heavy minerals (pyroxene, amphibole, tourmaline, kyanite, garnet, zircon and olivine) are suggestive of their derivation from a heterogeneous provenance comprising of igneous rocks, high grade metamorphic rocks and reworked Kaladgi sediments. The chromite grains appear to have been derived from ultrabasic rocks present in the upper reaches of the Gad River. The inferred reserves of ilmenite, magnetite and chromite are 0.175, 0.395 and 0.032 million tons, respectively.

Cenozoic Eucla Basin and associated palaeovalleys, southern Australia — Climatic and tectonic influences on landscape evolution, sedimentation and heavy mineral accumulation

The Eucla Basin including the vast Nullarbor Plain lies on the margins of the Yilgarn, Musgrave and Gawler cratons in southern Australia and owes its distinctive landscape to a unique set of interactions between eustatic, climatic and tectonic processes over the last ~ 50 Ma. Understanding of the history of the basin and the palaeovalleys that drained from the surrounding cratons are important because they contain major mineral deposits, and the sediments derived from them contain remobilised gold, uranium, and heavy minerals. In particular, a remarkably preserved palaeoshoreline sequence along the north-eastern margin of the Eucla Basin is highly prospective for heavy mineral placer deposits. The record of marine, marginal marine, estuarine, fluvial and lacustrine environments, as constrained mainly by an extensive borehole dataset, reflects major depositional events during the Palaeocene–Early Eocene, Middle–Late Eocene, Oligocene–Early Miocene, Middle Miocene–Early Pliocene and Pliocene–Quaternary. These events reflect the key role of eustatic sea-level variation which, during highstands, inundated the craton margins, flooding palaeovalleys to up to 400 km inboard of the present coastline. However, a systematic eastward migration of the depocentre across the Eucla Basin during the Neogene, together with apparent flow reversals in a number of palaeovalley systems draining the Gawler Craton, suggest that the Eucla Basin has also been subject to differential vertical movements, expressed as a west-side up, east-side down tilting of ~ 100–200 m. This differential movement forms part of a broader north-down–southwest-up dynamic topographic tilting of the Australian continent associated with relatively fast (6–7 cm/yr) northward plate motion since fast spreading commenced in the Southern Ocean at ~ 43 Ma. We suggest that the evolving dynamic topography field has played a key role in facilitating development of placer deposits, largely through multistage, eastward reworking of near-shore sequences during highstand transgressive cycles on a progressively tilting platform under the influence of persistent westerly weather systems.

Granulometry and mineralogy of some northeastern Florida placers: a consequence of heavy mineral concentration in nearshore bars

Heavy mineral placer deposits of Pleistocene age in northeastern Florida were examined sedimentologically. Neither general setting, nor granulometric or mineralogic results are in agreement with a concentration of the heavy minerals in a beach, eolian or fluvial environment. Granulometric moment parameters of the ore sands seem to be distinctive. They include moderate sorting, high positive skewness, high kurtosis and a distinctive fine tail. Similarities of grain size curves of the placer sands with nearshore-offshore sands exist. Mineralogically the samples are more variable but always impoverished in epidote. This scarcity of epidote is atypical for eolian sediments in the study area, and the lack of garnet and the fineness of ore sands are uncommon for beach placers of northeast Florida. Underlain by dune ridges, which acted as obstacles on the shallow sea floor during the Penholoway transgression (1.3 ± 0.1 Ma B.P.), heavy minerals in the Boulogne and Green Cove Springs main ore body must have been concentrated in bars by the interplay of longshore and transverse bottom currents. Lighter heavy minerals were deposited in smaller nearshore bars closer to the former coast (Green Cove Springs small ore body) or in dunes of barrier islands (Green Cove Springs western ore body). As is true today, layers of noteworthy concentrations of economic minerals in the swash zone of Florida beaches were formed only rarely during storms, contrary to the coasts of Australia or India, where higher energetic conditions prevail. The proposed model of concentration of heavy minerals in certain outer nearshore bars has long been assumed but never been proven.

The geochemistry of monazite types from the Eastern Ghats granulite terrain, India

Monazite occurs as an accessory mineral in a variety of rock types in the granulite belt of the Eastern Ghats, India. Five types of monazite paragenesis are distinguished based on the mode of occurrence. They include: 1) tiny inclusions in cordierite and garnet occurring in khondalites and charnockites, 2) distinct grains in charnockite, 3) associated with other phosphates (apatite and xenotime) in magnetite-spinel-sillimanite-sapphirine granulites, 4) well-developed grains in charnockites affected by shearing and 5) clustered grains in metasomatised pyroxenites. Microprobe analyses of these monazites show that they have some distinct chemical characteristics, mainly in terms of ELREE (La + Ce + Pr + Nd + Sm)/Actinides (U + Th) and ELREE/Y ratios. The chemistry of monazites supports the interpretation that actinides substitute for LREE, and implies other concomitant substitutions such as Ca for REE and Si for P. Among the five types of monazites, type 2 monazite is concentrated in greater abundance in some of the heavy mineral placer deposits along the east coast of India.

Superficial deposits as resources for development — some implications for applied geomorphology

Abstract Superficial deposits (residual, colluvial, alluvial) are important as environmental resources in tropical environments. An understanding of their formation through varying time periods is essential to a correct interpretation of their economic and hazard potentials. This requires an integration of process studies with a reconstruction of longer term development. Saprolite formation is considered over 105‐107 yr, while colluvial and alluvial sediments are commonly Late Quaternary (103‐105 yr) in age. The importance of Quaternary environmental changes in the humid tropics to an understanding of heavy mineral placer deposits in West Africa and Indonesia is illustrated. It is concluded that geomorphologists can often make their most important contributions to developing areas by offering a sound interpretation of landsurfaces and their underlying deposits for engineers, geologists and pedologists, with whom a close working relationship is essential.

Distribution, Geometry, and Origin of Heavy Mineral Placer Deposits on Oregon Beaches

ABSTRACT Beach segments (0.5-3 km in length) enriched in heavy minerals (20-100% by weight abundance) are located south of six prominent headlands that interrupt the 175-km coastline between Cape Lookout and Cape Perpetua, Oregon. Beach-face retreat in the winter of 1982-83 exposed underlying placers containing the economic minerals garnet, zircon, ilmenite and chromite. In each case, the highest concentration of placer minerals occurs in an area of maximum shoreline curvature at a distance south of the north bounding headland that is proportional to seaward extent of the headland. Cross-sections and magnetic surveys of one 8-km coastal section, Otter Rock to Yaquina Head, define a small placer body (heavy minerals > 50%) some 0.75 km in length and 80 103 m3 in volume that comprises 10% of the total beach sand between the bounding headlands. Mineral grain-size analyses of winter beach samples along this coastal section confirm earlier models of mineral segregation by entrainment processes; the light minerals are more susceptible to fluid shear stress than the heavy minerals. Maximum segregation and heavy mineral enrichment occur in the backshore and at shoreline inflection points where decreasing flow velocities produce gradients of fl id shear stress, allowing light minerals to be winnowed from more stable, heavy minerals. Development of placer deposits is controlled by shoreline configuration as the first-order factor and seasonal variations of wave climate, and longshore currents as second-order factors that delineate shape and concentration of heavy minerals in placer bodies.