Beach Placer Research Articles

Compositional variations and morphological evolution in platinum beach placers, southern New Zealand

Morphologies of placer platinum group minerals (PGM) are more variable and resistant to modification during transport than placer gold grains. This study documents morphological evolution of PGM placer grains during up to 120 km of transport in beach placers after river transport from inferred sources up to 200 km inland. PGM morphological changes are calibrated with changes in morphology of associated placer gold. Most of the PGM are Pt-Fe alloy and have been fed into the beach placer system from a large river at the western end of the beaches on the south coast of New Zealand. The incoming fluvial PGM suite includes Os, Ir and Ru alloys which may have been derived from distal ophiolitic sources. More proximal sources have Ural-Alaskan affinities and these contributed cooperite and braggite, or sperrylite, locally, as well as Pt-Fe alloy grains. Some PGM may have been recycled through Cretaceous-Quaternary fluvial sediments before entering the modern placer system. Recycled placer PGM grains have also been derived from elevated Quaternary beaches near the coastline. PGM grains entering beach placers have rough surfaces, with remnants of crystal faces, and these evolve to smooth flakes with progressive long-shore transport. PGM flakes have slightly thickened rims caused by impacts by saltating sand on windy beaches, and the most distal beach placers contain flakes with incipient toroidal shapes. These PGM incipient toroids are poorly developed compared to accompanying well-formed toroidal gold that has developed in nearly all beach placers, including those on elevated Quaternary beaches. Typical PGM and gold placer grain size decreases with increasing distance of transport, from fluvial grain size of 400–1,000 to ∼200 microns on the most distal beaches, accompanied by eastward loss of equant PGM grains and associated increase in proportion of flakes. Although net transport distance is ∼120 km in the beach placer complex, frequent aeolian transport of grains from beach to dunes and subsequent recycling by storm surges substantially increased total transport distance in a dynamic windy tectonic environment.

Heavy minerals and the characters of ilmenite in the beach placer sands of Chavakkad-Ponnani, Kerala Coast, India

Indian beach placer sand deposits are, in general, ilmenite-rich. However, some concentrations are dominated by pyriboles. The Chavakkad-Ponnani (CP) area along the northern Kerala coast is one such deposit. This paper deals with the general character of the heavy minerals of CP with special emphasis on the characters of ilmenite. Most Indian beach sand ilmenites are of good quality. However, our observations on the ilmenites of CP using Optical Microscope, SEM and EPMA reveals that these are mineralogically very complex. The CP ilmenite varies from pure ilmenite to highly impure variety having intergrowths and inclusions of other oxide and silicate minerals. Ilmenite occurs as mixcrystals and forms intergrowth structure with hematite and Ti-hematite/ulvospinel; contains inclusions of hematite, quartz, and monazite. On the other hand ilmenite also occurs as inclusions within hematite and garnet. The pyriboles are dominantly amphiboles with hornblende-composition. Interestingly an inclusion of gold has been recorded within amphibole of hornblende composition. Garnets are mostly of almandine and pyrope type. Subordinate heavy minerals are sillimanite, zircon and rutile. Characteristic morphology, mineralogy and chemistry of amphibole, garnet and ilmenite together indicate that the placer sands of CP area are derived from the amphibolites, granite gneisses and basic igneous rocks lying in the hinterland towards the eastern border of Kerala. Though the overall quality of ilmenite is poor, highgrade ilmenite concentrate can be generated (of course with lower yield), by adopting precise mineral processing techniques. The CP deposit can be considered as a second-grade deposit but it has potential for future exploitation.

Environmental radioactivity evaluation in the coastal stretch of Bay of Bengal from Pondycherry to Velanganni (South East coast of India)

Background: Since the Madras Atomic Power Station, Kalpakkam and Kudankulam Nuclear Power Plant, Kudankulam are sited in Bay of Bengal coast, radiological study of this coastal environment is imperative to assess the impact of operation of nuclear power plant, if any, on the radioactivity profile of the coast. Materials and Methods: In the present study the environmental radioactivity was evaluated by measuring activity concentrations of primordial radionuclides namely 238 U, 232 Th and 40 K. in the beach sand samples using high purity germanium gamma ray spectrometry. 10 sampling stations were fixed along a 290 km coastal stretch of Bay of Bengal from Pondycherry to Velangannni. Results: The activity concentration of 238 U is always much less than that of 232 Th and 40 K and it ranged from 9 Bq/kg (Pondicherry coast) to 93 Bq/kg (Karaikal coast). However, 232 Th concentration fluctuated from 12 Bq/kg (Pichavaram Mangrove) to 1075 Bq/kg (Karaikal coast). The activity concentration of 40 K varied within a narrow range from 162 Bq/kg to 474 Bq/kg. The distribution of primordial radioactivity was non-uniform along the entire stretch of Bay of Bengal. The elevated levels of 232 Th were recorded in Karaikal coast (S7) (1075 Bq/kg), Tirumullaivasal coast (S4) (215 Bq/kg), and Nagapattinam coast (S9) (146 Bq/kg) and attributed to the presence of thorium-rich monazite as beach placer in coastal sands. Conclusion: The total absorbed gamma dose contributed by the activity of 238 U, 232 Th, and 40 K varied between 29 nGy/h and 308 nGy/h with a GM value of 64.4 nGy/h. Similarly, the annual effective dose recorded for Bay of Bengal ranged from 0.04 mSv/year to 0.38 mSv/year, indicating that the Bay of Bengal, in general, falls under Normal Background Radiation Area.

Gold in the Beach Placer Sands of Chavakkad-Ponnani, Kerala Coast, India

Abstract Although sporadic mining of placer gold from river beds is not uncommon in India, there is no documented literature on the occurrence of gold in the beach placer sand deposits of the country. While characterizing the heavy minerals of the Chavakkad-Ponnani (CP) beach placer sands along the North Kerala coast, the association of gold with the pyriboles in these sands has been observed. A native gold grain of about 25 μm was seen to occur as an inclusion within an amphibole of hornblendic composition. The pyriboles of the CP deposit are angular to sub-angular indicating a nearby provenance that may be in the upstream reaches of the Ponnani River in the districts of Malappuram and Palakkad or further north in the auriferous tracts of the Wynad-Nilambur or Attapadi regions. It is argued that the occurrence of native gold in CP deposit is not a freak occurrence and that it warrants thorough investigation of all the pyribole-ilmenite-rich placers to examine the possible presence of gold and its abundance in the beach placers of northern Kerala coast.

Beach placer, a proxy for the average Nd and Hf isotopic composition of a continental area

Abstract Beach placer deposits concentrate detrital heavy minerals which are the erosion products of large areas of continental crust. Here, we report the first analyses of Nd–Hf isotopic ratios and trace element concentrations that we measured in a beach placer from Camargue, France and in its pure mineral separates. Both the bulk composition of the placer and those of its pure mineral separates were determined. We also report mineral proportions obtained using observations under a binocular microscope and micro X-ray fluorescence mapping. Our results indicate that monazite totally controls the placer's Nd isotopic composition ( e Nd = − 9.3) while zircon dominates its Hf isotopes ( e Hf = − 13.0) even though both mineral phases represent only a small proportion of the heavy mineral assemblage (3.5 and 10% respectively). We demonstrate that the Camargue placer provides a good estimate of the average Nd and Hf isotopic composition of the continental area drained by the Rhone River in Western Europe ( e Nd ≈ − 9 and e Hf ≈ − 13). Using these values, we calculate two stage model ages and show that almost all the placer minerals are derived from Proterozoic crustal protoliths. This provides valuable information on the history of the continental crust drained by the Rhone River. In particular, it suggests that little juvenile crust was created during the recent geological events that formed the Alps and the Massif Central, the two main massifs from which the placer minerals originate. More generally, we propose that similar measurements made on other worldwide beach placer deposits could provide estimates of the present-day Nd and Hf isotopic composition of large continental areas, values that are difficult to obtain due to the well-known heterogeneity of continental material but are essential to model the growth of continental crust through Earth history or to model the impact of crustal material when recycled into the mantle.

Heavy Mineral Sands in the Eucla Basin, Southern Australia: Deposition and Province-Scale Prospectivity

The marine Eucla basin in southern Australia is emerging as a major new heavy minerals province in Australia. Beach placers are associated with a series of partially buried Cenozoic coastal barrier sands formed along an arcuate 2,000-km-long basin margin, the trace of which is up to 320 km inland of the present coastline. The presence of high-grade deposits with dominant zircon over ilmenite and lesser amounts of rutile and leucoxene was established with the discovery of the Jacinth and Ambrosia heavy mineral deposits in late 2004. An additional 10 heavy mineral prospects were subsequently identified and are at various stages of evaluation. The Eucla basin and its adjacent paleovalley system have a large areal extent that contains a complicated succession of marine and nonmarine strata spanning a wide range of depositional environments. Four distinct constructional phases for the development of shorelines can be recognized and correlated with major third-order sea-level events, established by others from the marine depositional record as occurring during the middle Eocene (~42.5 Ma), late middle Eocene (39–36 Ma), late Eocene (36–34 Ma), and Miocene-Pliocene (15–2.6 Ma). Prevailing westerly winds built extensive dune systems by longshore drift. Sediment movement was from west to east. Detrital zircon rocks from the Ooldea and Barton barriers show a distribution of zircon age that is consistent with the Proterozoic Musgrave province to the north of the basin as the dominant primary source area of the heavy minerals, with a contribution from the Albany Fraser orogen to the west. The likelihood is that these heavy minerals have been recycled via sedimentary basins that flank the Musgrave province and include the Neoproterozoic to Cambrian Officer basin and Permian to Mesozoic deposits of the Bight basin. Our current depositional model is summarized as follows: (1) initial rapid transgression and deposition of a shallow marine sand sheet subsequently overlain by shallow marine limestone during middle Eocene; (2) a major Eocene transgression and deposition of a shelf, barrier, and lagoonal shoreface marine complex during the late middle Eocene; ( 3) further transgression and highstand deposition during the late Eocene; (4) renewed transgression of barrier, lagoonal, and possibly flooding deltaic sand blanket in the southeastern coastal plain with neotectonic uplift tilting in the western Eucla margin during Mio-Pliocene time. Each stage of reworking increased the potential for heavy mineral concentration in placer deposits.

The SEM and EDS Energy Spectrum Analysis of a Beach Placer

In order to study the phase of Fe and Ti in a beach placer , different methods such as the X-ray diffraction analysis, chemical analysis, scanning electron microscopic , electron probe microanalysis are used to study the characteristics of the beach placer . The research results show the major metallic mineral in the beach placer is titanic magnetite, EDS and energy spectrum map features of which indicate that the vast majority of titanic magnetite contain a certain amount of Ti , the two elements of Fe and Ti take on closely symbiosis and distribute more evenly in titanic magnetite. The Ti exists in the Magnetite lattice in form of isomorphism. The theoretical highest grade of Fe and Ti in the separated Magnetic concentrate are 66.02per cent and 4.86 per cent respectively. In addition, the beach placer contains a small quantity of Ilmenite which is hysterogenic and exists in the form of fine solid solution separation structure in the titanic magnetite

Features Sustaining the Formation of Beach Placers along the Southern East Coast of India

Beaches between the Kallar and Vembar River mouths on the southeast coast of India are rich in placer mineral deposits. Beach sediments were sampled along this 25-km shoreline and were analyzed to determine the density sorting patterns in order to understand the process of beach placer formation. Determinations of individual placer minerals reveal that the density variations reflect the sorting process and were most effective in concentrating ilmenite, garnet and zircon, while the concentrations of quartz were reduced. This pattern of sorting reflects the density and grain size variations of the minerals present in the beach. Density sorting plays a very crucial role in the concentration of placer minerals in this region. The economically viable heavy mineral deposits are governed by the presence of the source rock being in close proximity, the existing drainage pattern, topography, climate, and coastal processes. These factors permit the identification of regions where the formation of placer deposits is favored.

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.

Effect of Air Injector on the Performance of an Air-lift for Conveying River Sand

An air-lift has been more recently applied in the dredging, deep-seated beach placer mining and underground mining engineering. However, the influence and mechanism of various parameters on the air-lift performance are not quite clear, especially the influence of flow pattern on lifting efficiency. Focusing on the problems mentioned above, the key part of the air-lift (namely, the air injector) was proposed aimed to reduce friction loss in the inner pipe according to improving flow field performance, thus increase the lifting efficiency. The study of relative factors of the performance of an air-lift is performed and the river sand is used as simulation of underground ore bed. The total lifting height of the experimental system is 3 m, the water flux, mass flow of solid particles, concentration of particles and lifting efficiency are measured under the same submergence ratios by changing the air injector, which is divided into nine specifications of air injection in this research. The experimental results indicate that the optimal air flow rate corresponding to excellent performance of the air-lift can be obtained in the range of 35–40 m3/h. The air injection method has a great effect on the performance of the air-lift, the air injector with three nozzles is better than that in the case of one or two nozzles. Further more, the air injection angle and arrangement of air injection pipes also have great effect on the performance of an air-lift. The proposed research results have guiding significance for engineering application.

Effect of Tsunami in the Ilmenite Population: An Examination through X-Ray Diffraction, Scanning Electron Microscopy and Inductively Coupled Plasma Atomic Emission

Kerala state in the SW part of Indian subcontinent hosts one of the best beach placer deposits in the world. The near shore deposit is ~140Mt and is very rich in heavy minerals, often up to 70%, and ilmenite forms its chief constituent. The seasonal enrichment of this deposit takes place through monsoonal activity and the recent tsunami (24 December 2004) had significantly contributed its share. Mineralogical and chemical variation of the surface (pre- and posttsunamigenic) as well as subsurface ilmenites (4-5m depth) of this deposit has been investigated. SEM examination on ilmenites of pre-tsunamigenic period conveys that the micromorphology represents mostly of mechanical activities rather than chemical and solution activities. Both post-tsunamigenic and subsurface ilmenites were influenced dominantly by solution and chemical alteration. The pre-tsunamigenic (surficial) ilmenite grains consist only of rutile as an altered product with a small FeO – Fe2O3 ratio. However, the presence of considerable altered products such as rutile and pseudorutile in the post-tsunamigenic and subsurface ilmenite indicates that the ilmenite alteration is in an advanced state. Regarding trace element composition, it was found that Al, Mg, Na, Ca, Cd, Co, K, Sr and Pb have higher contents in both core and post-tsunamigenic ilmenite than the pre-tsunamigenic ilmenite. These elements play an important role in understanding the behavior of the minerals during beneficiation and further processing. The relative lesser content of such elements in the onshore pre-tsunamigenic ilmenite grains reveals that the chemical leaching has not been active compared to the ilmenite concentrates from the shallow sea that have been brought by the tsunami and also to that have been deposited earlier and now seen underneath up to a depth of ~5m.

Sources of monazite sand in southern Orissa beach placer, eastern India

This paper intends to explore whether there is an important source for monazite beach placer of the Gopalpur-Chhatrapur-Rushikulya coast, Orissa, in the adjacent Eastern Ghat Mobile Belt (EGMB). Petrographic and mineralogical studies were conducted on all the rock types constituting the EGMB exposed over a stretch extended up to ∼20 km landward from the estuary of the River Rushikulya that is believed to transport the major bulk of sand to the Gopalpur-Chhatrapur-Rushikulya beach. Heavy mineral population was concentrated using bromoform and percentages of each heavy mineral constituting the population were estimated for all the potential source rock types. Isodynamic separation and XRD techniques were deployed for precision identification of every heavy mineral present. The study identified the granitoid (or migmatite) basement rock as by far the major contributor of monazite to the Chhatrapur beach sand. The study also reveals that charnockite is an important contributor of orthopyroxene as well as garnet, although the sillimanite-garnet-quartz schist (khondalites) is also an important source for the latter. On the other hand, garnet-quartz schist and garnet-biotite-quartz schist may also contribute substantial quantity of pyroxene and garnet. The high grade metasedimentary rocks, in general, could be the major sources for rutile, while ilmenite, magnetite and zircon in the beach sand have their sources perhaps in all the varieties of rocks constituting the EGMB.

Assessment of dispersive pressure as a beach placer mechanism

The concept of sediment sorting extending from the Bagnold constitutive relationship for sediment under shear is examined in the context of beach placer formation. The traditional interpretation of shear sorting is found to be inconsistent with data from new granular flow experiments. A binary mixture satisfying the shear equivalence relationship displayed pronounced segregation during shear. This observation is contrary to shear sorting as applied in the literature where no such segregation for this pairing of mineral species is expected. Further experiments minimizing the potential of grain percolation of smaller grains or kinetic sieving also demonstrated sorting patterns inconsistent with the existing shear sorting interpretation. Consequently, the shear sorting process, as currently formulated, may not be an appropriate means to describe beach placer formation. Kinetic sieving appears to be a more likely mechanism in this context, enhanced by the shearing and dilation of the granular-fluid flow.

Radon exhalation rate in Chhatrapur beach sand samples of high background radiation area and estimation of its radiological implications

Chhatrapur beach placer deposit, situated in a part of the eastern coast of Orissa, is a newly discovered high natural background radiation area (HBRA) in India. The sand samples containing heavy minerals, were collected from Chhatrapur region by the grab sampling method at an interval of ∼1 Km. Radon exhalation rates were measured by “Sealed Can Technique” using LR-115 type type II in the sand samples containing heavy minerals collected from the beach. Radon activity is found to vary from 1177.1 to 4551.4 Bq m-3 whereas the radon exhalation rate varies from 423.2 to 1636.3 mBq m−2h−1 with an average value of 763.9 mBq m−2h−1. Effective dose equivalent in sand samples estimated from exhalation rate varies from 49.9 to 193.0 μSv y−1 with an average value of 90.1 μSv y−1. From the activity concentration of 238U, 232Th and 40K computed radium equivalent is found to vary from 864.0 to 11471.5 Bq kg−1 with an average value of 3729.0 Bq kg−1. External hazard index, Hex range from 2.3 to 31.0 with a mean value of 10.1, which is quite high. This value supports the conclusion based on high mean absorbed gamma dose rate in air due to the naturally occurring radionuclides as 1627.5 nGy h−1. A positive correlation has been found between U concentration and radon exhalation rate in the sand samples. The use of sand as construction material may pose a radiation risk to ambient environment.

Natural radioactivity measurements in beach sand along southern coast of Orissa, eastern India

The beach placer deposits in the southern coastal Orissa, India may have significant levels of radiation due to the presence of Th and U bearing minerals such as monazite and zircon. In this study, Gopalpur and Rushikulya beach regions were selected to study the ambient radiation environment. The average activity concentrations of radioactive elements such as 232Th, 238U and 40K of beach sand samples were measured by γ-ray spectrometry using a HPGe detector, and found to be much higher than the internationally accepted values. The cross plots of eTh/eU and eTh/K inferred that the sand samples of Gopalpur and Rushikulya beach placer deposit were deposited in leached uranium and an oxidising environment. The absorbed γ dose rate levels of the study areas are similar to other monazite sand-bearing HBRAs of southern and southwestern coastal regions of India and of world. Different radiation hazard indices were estimated for the present study area and were found to be much higher than the internationally accepted values. Hence, Gopalpur and Rushikulya beach placer region can be considered as a high background radiation area and a potential zone for radiogenic heavy mineral exploration.

Petrogenetic implications of ophiolitic chromite from Rutland Island, Andaman—a boninitic parentage in supra-subduction setting

Chromites occurring in different modes have been characterized from ophiolites of Rutland Island, a part of Burma-Andaman-Java subduction complex in the Bay of Bengal. Chromite mainly occurs as massive chromitite pods in mantle ultramafic tectonite and as thin massive chromitite bands together with minor disseminations in crustal ultramafic cumulate. Other than pods chromite also appears as: (a) anhedral restitic grains, (b) strings occurring as exsolved phases and as (c) symplectitic intergrowth with orthopyroxene in mantle tectonite. The chromites occurring as massive chromitite pods and bands contain high Cr (Cr#—73 to 80). Restitic chromite grains in mantle ultramafics are high-Mg (Mg#—58), high-Al (Al2O3—34 wt.%) and intermediate-Cr (Cr#—37) chromites. The bivariant plots of TiO2 wt.% vs 100Cr#, Mg# vs Cr# and Cr-Al-Fe3+ ternary discrimination diagram show that the massive and disseminated chromites fall in the boninitic field. The (Al2O3)melt and (FeO/MgO)melt values for the massive chromitites are estimated as 10 wt.% to 11 wt.% and 0.67–1.78 respectively, corroborating a boninitic parentage. Massive chromitite on Fe2+/Fe3+ vs Al2O3 wt.% and TiO2 wt.% vs Al2O3 wt.% plots occupy mainly the field of supra-subduction zone peridotites. High-Mg olivine (Fo91−93), high-Mg orthopyroxene (En∼90) and high-Cr chromites of Rutland ophiolite are all supportive of boninitic source at supra-subduction zone setting. 57Fe Mossbauer study of chromite of beach placer shows that chromites occur in partly inverse spinel structure with iron distribution as Fe3+(A)Fe2+(A)Fe2+(B) which might be a result of oxidation. The olivine-spinel geothermometry shows 650–700°C re-equilibration temperature which is much lower than near crystallization temperature (950–1,050°C) derived from orthopyroxene-clinopyroxene assemblage. At supra-subduction setting an oxidizing hydrous fluid derived from subducting slab might have a major influence during the formation of Rutland ophiolite in this part of Burma-Java subduction complex.

Radon exhalation rate from sand samples from the newly discovered high background radiation area at Erasama beach placer deposit of Orissa, India

Situated in a part of the eastern coast of the state of Orissa, India, newly discovered Erasama beach placer deposit is a high natural background radiation region which is due to the presence of radiogenic heavy minerals. The sand samples containing heavy minerals were collected from Erasama beach placer deposit by the grab sampling method from places at an interval of ∼ 1 km . Radon exhalation rates were measured by “Can” technique using LR-115 type II plastic track detector to estimate the radiation exposure in given atmosphere. Radon activity is found to vary from 1471 ± 46 to 4686 ± 87 Bq m - 3 with an average value of 3349 ± 68 Bq m - 3 whereas the radon exhalation rate varies from 529 ± 16 to 1685 ± 31 mBq m - 2 h - 1 with an average value of 1204 ± 25 mBq m - 2 h - 1 . Variation of radon exhalation rate with the uranium concentration in the sand samples was studied. Overall a positive correlation has been found between U concentration and radon exhalation rate. The values obtained are on higher side and may pose a radiation risk to ambient environment, if the sand is used as construction material for mixing with cement.

Success and development in discovering beach placers in the Eucla Basin, southern Australia

One of the most zircon-rich heavy mineral sand (HMS) deposits on Earth has been discovered in part due to interrogation of new geoscientific models. The minerals are associated with fossil beaches, which formed almost 40 million years ago, along a huge margin of the Eucla Basin, southern Australia. The exploration implications of the proposed new geoscientific models have been realised by exploration companies (eg. Iluka Resources & Adelaide Resources), resulting in the recent discoveries of new zircon-rich HMS deposits in the eastern basin. The new discoveries, namely Jacinth, Ambrosia and most recently Tripitaka in South Australia, are hailed as the most significant discoveries of their type in nearly 30 years. This exciting outcome highlights the innovative nature and quality of geoscientific research a nd demonstrates how the resources industry can translate this research into economic benefits. The research successfully addresses National Research Priority Three ? frontier technologies to transform industry. Our models of landscape evolution and revised interpretation of the dynamics of sediment accumulation in palaeorivers and associated shoreline deposits has been extensively utilised to develop a new understanding of Cainozoic marine transgressions and deposition in the region. GIS based palaeogeographic reconstructions were based on digital elevation models, remotely sensed imagery, geological and drillhole data, and sedimentological analysis. On a more detailed scale, preliminary heavy mineral analyses utlising the AutoGeoSEM suggests that the heavy mineral suite at Jacinth is dominated by zircon, pseudorutile, rutile/anatase and ilmenite. Less common minerals include a variety of aluminosilicates (tourmaline), aggregates of hematite, quartz and clay, monazite and chromite. Our recent work indicates that the zircon contribution to this heavy mineral suite was dominantly derived from the Precambrian rocks of the Musgrave Province vs Officer Basin with minor grains from the Gawler Craton. We conclude that the Eucla Basin has become a world-class HMS province.

Impact of tsunami on texture and mineralogy of a major placer deposit in southwest coast of India

The great Indonesian earth quake (26 December 2004) triggered a tsunami wave across the Bay of Bengal and Indian Ocean basins and has brought a major havoc in several countries including India. The coastal segment between Thotapalli and Valiazhikal in Kerala state of southwest India, where considerably rich beach placer deposit with ilmenite percentage of more than 70% is concentrated, has been investigated to understand the impact of tsunami on coastal sediments. The grain size analysis flashes out the significant differences between the pre- and post-tsunami littoral environments. While the mineral grains collected during pre-tsunami period show well-sorted nature, the post-tsunami samples represent moderately to poorly sorted nature. Similarly, unimodal and bimodal distributions of the sediments have been recorded for pre- and post-tsunami sediments, respectively. Further, mineral assemblages corresponding to before and after this major wave activity clearly indicate the large-scale redistribution of sediments. The post-tsunami sediments register increasing trends of garnet, sillimanite and rutile. The total heavy mineral percentage of the post-tsunami sediment also shows an improved concentration, perhaps due to the large-scale transport of lighter fraction. Magnetite percentage of post-tsunami samples reflects higher concentration compared to the pre-tsunami samples, indicating the intensity of reworking process. X-ray diffraction patterns of ilmenite grains have confirmed the increased presence of pseduorutile, and pseudobrookite in post-tsunami samples, which could be due to the mixing of more altered grains. SEM examination of grains also confirms the significant alteration patterns on the ubiquitous mineral of placer body, the ilmenite. The reason for these textural, mineralogical and micromorphological changes in heavy minerals particularly in ilmenite, could be due to the churning action on the deeper sediments of onshore region or on the sediments entrapped in the near shelf region of the area, by the ∼ 6 m high tsunami waves.

Differential Alteration of Ilmenite in a Tropical Beach Placer, Southern India: Microscopic and Electron Probe Evidences

Abstract. The study based on microscopic and microprobe techniques reveals that ilmenite of Manavalakurichi deposit has generally reached the alteration phase of ‘leached ilmenite’. The XRD and bulk chemical analysis confirm the limited alteration undergone by ilmenite grains. Ilmenite alteration has been found to be a process of continuous leaching of iron from the mineral lattice and hydroxylisation. The enrichment of trace elements with progressive alteration is discussed. Si and Al are enriched by more than 100 fold. The prevalence of reducing environment at present in the deposit indicates that the oxidation of ferrous iron leading to pseudorutile formation would have occurred during transportation of sediments.