Bauxite Deposits Research Articles

Petrographical and Mineralogical Characteristics of Bauxite Deposit of Darai-Daldali Plateau, Kabirdham district, Chhattisgarh

Petrographical and Mineralogical Characteristics of Bauxite Deposit of Darai-Daldali Plateau, Kabirdham district, Chhattisgarh

Sustainable development and environmental challenges in Cameroon’s mining sector: A review

Cameroon has a strong geological potential for a number of mineral resources that, if well managed, could support economic growth. The country contains potentially large deposits of iron ore, gold, bauxite, diamond, limestone, nickel, and gemstones, and indices of other numerous minerals and precious metals. Despite its geological wealth, mining has never played a major role in Cameroon’s economic development. A study on the state of sustainable development and environmental challenges in the Cameroon mining sector permits the identification of key points for improvement in order to position the country towards achieving a sustainable mining industry in the future. This paper reviews the mining potential, stakeholder participation, legislation, and mining policy in Cameroon mining industry. The methodology involves a single case study focused on the review of sustainable development in the Cameroon mining industry up to date. It includes scientific studies, and reports of ministries and support organizations, national laws, and regulations related to the area of study. Also the corporate sustainability reports of mining companies and mining stakeholders are analyzed. This research work covers the latest developments in terms of the institutional and regulatory frameworks for mining and the environment in the country, history of mining in Cameroon, and evolution and issues of the Environmental and Social Impact Assessment (ESIA) system in the mining sector until 2016. The work concludes with an identification of the current challenges of implementing sustainable development in mining as well as future directions that research works on this area should take.

Geology and geochemistry of the Xiaoshanba bauxite deposit, Central Guizhou Province, SW China: Implications for the behavior of trace and rare earth elements

In China, bauxite is mainly of the karst type. Karst bauxite deposits in Central Guizhou are widely distributed in the Qingzhen, Xiuwen, and Zunyi districts. The Xiaoshanba deposit is located in the Xiuwen district and is hosted in the Lower Carboniferous Jiujialu Formation. It shows parallel unconformity with the overlying and underlying strata. The main chemical contents of the bauxite ore in the Xiuwen district is Al2O3 (55.7 to 73.5 wt%), followed by SiO2, Fe2O3, TiO2, CaO, MgO, S, P, etc. There are obvious enrichments in rare earth elements (REEs) and immobile trace elements (such as Ti, Nb, Zr, Hf, Ta, and Th) in the Al-bearing rocks.The mass change calculation (MC) is an effective means of investigating the relative mobility of elements. Here we present the multiples of mass change calculation (MMC), which represents an improvement over the MC, and is effective for element mobile investigations. The MMC results for REEs of the Xiaohsanba Al-bearing rocks showed grouping phenomenon, in which REEs were divided into four groups (Group A: La–Ce–Pr–Nd; Group B: Pm–Sm–Eu–Gd; Group C: Gd–Tb–Dy–Ho, and Group D: Er–Tm–Yb–Lu) and showed different fractionation trends in the MMC curves. The tetrad characteristic of the REEs (tetrad effects) most likely induced the special grouping phenomenon. During bauxite mineralization, REE fractionations caused by mineral control, especially the widespread distribution of accessory minerals that are rich in REEs such as Ti-dioxide minerals (i.e., TiO2 such as rutile and anatase) and zircon, and water–rock interactions resulted in the REE grouping phenomenon in the Xiaoshanba profile.The majority of these immobile elements tend to concentrate in the accessory minerals of bauxite, and barely any elements (except Li and Ga) seem associated with the ore-forming minerals. For instance, Ti-dioxide minerals played an important role in the accumulation of some elements, such as Ti, V, Nb, and Ta. Another important mineral was zircon, which is rich in Zr, Hf, and Th, etc. In general, there were two main factors that influence the content of immobile elements in the karst bauxite profile: (a) the chemical composition of the precursor rock (the higher the content of immobile elements in the parent rock, the higher the content of accessory minerals and immobile elements in bauxite), and (b) the weathering degree of the precursor rock (the stronger the degree of weathering, the higher the content of accessory minerals and immobile elements in bauxite).

Austrian versus Hungarian bauxites in an Alpine tectonic context: a tribute to Prof. Andrea Mindszenty

The correlation between the Cretaceous bauxites of Austria and Hungary was first highlighted by the pioneering work of Andrea Mindszenty in the 1980s. The physical distance today between these bauxite occurrences, located in the Northern Calcareous Alps and the Transdanubian Central Range, is on the order of hundred of kilometers. However, a semi-quantitative palinspastic reconstruction of their relative positions at the time of bauxite deposition during the Late Cretaceous (Turonian to early Santonian) shows their much closer proximity. Still, the important differences between these Upper Cretaceous bauxites are due to their different paleogeographic settings during their deposition on a subaerially exposed Eo-Alpine nappe substratum. Some other differences, such as porosity, are attributed to the subsequent tectonic overprint in the Alpine edifice. The Austrian and Hungarian bauxites not only record important information about of the syn-depositional geologic landscape but also provide clues about the pre- and post-depositional regional tectonic context of the areas where they developed. The typical setting for many of the Cretaceous bauxites in the broader Alpine region was uplift and karstification associated with the formation of various flexural basin systems. Therefore bauxites, in general, may contain important geologic information about the regional geodynamic processes, as it was pointed by Andrea Mindszenty, in a pioneering manner, already in the early 1990s.

RESEARCH OF BAUXITE DEPOSITS FROM UNDERGROUND MINING WORKS

The paper presents a new approach to exploring bauxite deposits from underground mining works in the bauxites area of Bespelj near Jajce in Bosnia and Herzegovina. In the area considered, bauxite deposits are being investigated and exploited over 60 years. Despite the high degree of exploration in the geologically intricate structures of Bespelj there are numerous up to the unexplored reservoirs. Up to now, they have been mainly investigated by drilling from the surface into the wells net to dictate the legal regulations. Due to the increase in depths on which deposits are located and complex structural relationships, such research has become more and less effective. From the geological point of view, the bauxite deposits are in the horizontal position. But long-lasting geological evolution from the upper Cretaceous to the present, has led to deposits in very different structural positions. That is why we find them in a tilted position, in subvertical and vertical, and often in an inverse position. For further research to become rational and efficient, a new approach to exploring basement from underground mining works will be developed that will serve for exploration and then for the exploitation of bauxite deposits.

High-resolution 3D geological model of the bauxite-bearing area Crvene Stijene (Jajce, Bosnia and Herzegovina) and its application in ongoing research and mining

Three-dimensional (3D) geological models are useful tools in various geological, mining and other engineering activities. Geological model shows stratigraphic, structural and lithologic settings of the study area in 3D space, and serves as a 3D geodatabase for a variety of input data. The study area is one of the bauxite-bearing sites, Crvene Stijene, near Jajce (Bosnia and Herzegovina). During the last decades, a number of geological, geodetic, mining and other data were collected through intensive geological research and mining (exploration), with the aim of finding and exploiting bauxite deposits. Therefore, selected area is a great polygon for the implementing and testing of workflow for the construction of a 3D geological model of bauxite-bearing field and its application in current and future research and mining. Presented workflow includes collection, digitalization, organization and visualization for different types of existing and new data (600 boreholes, geological maps and cross-sections, DEM, structural measurements from the surface, as well as in tunnels and adits) in 3D geological database. For this study, different types of geological objects, fault planes and geological surfaces were modelled with different interpolation algorithms. The constructed model is interactive and it can be easily updated by new input data from current research and exploitation activities: boreholes, underground mining objects, etc. The 3D geological model represents a relevant foundation for planning new research and mining activities. Furthermore, newly found deposits and their volumes can be quickly modelled, contoured and calculated. Presented modelling workflow is applicable to other areas and other mineral resources

Ore-forming fluid system of bauxite in Zunyi area of northern Guizhou province, China

The ore-forming fluid system of Laowashan bauxite in Zunyi area of northern Guizhou Province was studied through field geological survey and observation of hand specimens. It was concluded that surface runoff, atmospheric precipitation and sea level changes played important roles in the formation of the aforementioned bauxite. Under the impacts of vertical leaching of ore-forming fluids, industrial bauxite deposit and pyrite deposit formed in the upper and lower parts of the ore-bearing rock series respectively.

The tetrad-effect in rare earth elements distribution patterns of titanium-rich bauxites: Evidence from the Kanigorgeh deposit, NW Iran

The titanium-rich bauxite horizon of the Kanigorgeh bauxite (northeast of Bukan, NW Iran) is a part of the globally significant known Irano-Himalaya karst bauxite belt. This bauxite horizon was developed as discontinuous stratified layers and/or lenses within carbonate rocks of the Ruteh Formation of Upper Permian age. Studies of whole rock geochemistry along a selected profile across the horizon revealed that Ce anomaly values of the bauxite ore samples vary from 0.22 (negative) to 7.34 (strongly positive). The remarkable variations in ratios of some isovalent elements such as Y/Ho, Nb/Ta, and Zr/Hf along the profile illustrate non-CHARAC behavior which can be attributed to so-called tetrad-effect phenomenon in this residual horizon. The chondrite-normalized REE distribution patterns represent the irregular shapes known as M- and W-shape tetrad-effects. The illustration of diagrams of fourth tetrad-effects versus Ce anomaly values and ratios of Y/Ho, Nb/Ta, and Zr/Hf indicated that the studied residual horizon comprises two distinct zones with different geochemical behaviors. The upper zone, from top surface down to ~7.3m, was deposited under oxidizing conditions represented by the bauxitic composition. The lower zone, starting from ~7.3m down to the bottom of the horizon, was precipitated under reducing conditions manifested by the kaolinitic composition. The obtained results led us to deduce that the tetrad-effects can be used as a geochemical indicator to evaluate the depositional conditions of bauxite deposits. It has been further concluded that certain mechanisms such as mineral crystallization, REE-complexation, penetration of meteoric acidic surface waters, and lateritization intensity had striking influence upon occurrence of the tetrad-effects in the studied titanium-rich bauxite ores in the Kanigorgeh district.

Climate change during the Triassic and Jurassic

The transition from the Triassic to Jurassic is associated with dramatic changes in Earth's climate. Pangaea was breaking up as North America rifted away from Africa, the Central Atlantic Magmatic Province erupted, and the concentration of atmospheric carbon dioxide increased dramatically. This article summarises the changes in Earth's climate associated with this transition, including a discussion of the various impacts of the increased carbon dioxide on the Earth system, the question of whether the wet episode in the Carnian was a global or regional event, the formation of bauxite deposits, and how dinosaur distributions changed over time. Palaeoclimate model simulations reveal the spatial changes in climate between the Triassic and Jurassic, illustrating the subtropics becoming slightly cooler and wetter despite the warming trend for the Earth's average temperature.

Fully Mechanized Longwall Mining in an Underground Bauxite Deposit: A Case Study

Based on the boundary surfaces of bauxite deposit modelled by the two-dimensional biharmonic spline interpolation, it was ascertained that the fully mechanized longwall mining of bauxite is feasible in terms of lithological characteristics, orebed occurrence, physical–mechanical properties of ore–rock, faults, Karst caves, permeable fissures, etc. Furthermore, a comprehensive target function consisting of waste-rock interfused ratio and ore loss ratio was used to obtain the optimal cutting height of shearer by a virtual mining procedure that was proposed to numerically perform the fully mechanized longwall mining. For the 1102 longwall mining panel in Wachangping Bauxite Mine, the optimal cutting height of shearer ranges from 1.16 to 2.32 m supplied from two 1.16-m-diameter cutting drums, which meets the requirement of low-waste and high-recovery mining to achieve high-grade and low-loss exploitations of underground bauxite. These efforts can improve the application and popularization of fully mechanized longwall mining in non-coal underground mines.

Trace and rare earth elements constraints on the sources of the Yunfeng paleo-karstic bauxite deposit in the Xiuwen-Qingzhen area, Guizhou, China

A number of Carboniferous paleo-karstic bauxite deposits occur in the Xiuwen-Qingzhen area, central Guizhou Province, which constitute an important part of the central Guizhou-Southern Chongqing bauxite belt in southwestern China. These deposits consist of lenticular and stratiform orebodies hosted in the Lower Carboniferous Jiujialu Formation, which lies unconformably above carbonate rocks (mainly dolomite) of the Middle and Upper Cambrian Loushanguan Group, Shilengshui Formation and Lower Cambrian Qingxudong Formation. Although it is generally agreed that the bauxite resulted from weathering of Cambrian rocks below the unconformity, it remains unclear whether the carbonates alone can provide sufficient material for the formation of the deposits. In this study, we examined the mineralogy and major, trace and rare earth elements geochemistry of bauxite and bauxitic clays from the Yunfeng deposit in the Xiuwen-Qingzhen area and compared them to previously published data of a paleo-weathering profile consisting of Loushanguan dolomite underlying the sub-Carboniferous unconformity and the “Black Rock Sequence” of the Lower Cambrian Niutitang Formation, in order to evaluate the sources of the bauxite. The bauxite ores are composed of diaspore as the main ore mineral, along with small amounts of pyrite, arsenopyrite, galena, stibnite, xenotime and uranium-bearing minerals, and are characterized by high contents of uranium and phosphorus. Chondrite-normalized REE patterns and various bivariant diagrams commonly used to study the provenance of bauxite including Eu/Eu∗ vs TiO2/Al2O3, Eu/Eu∗ vs Sm/Nd, TiO2 vs Al2O3, TiO2/Th, Th vs Ta, Th vs Nb and Nb vs Ta suggest that the Loushanguan dolomite and the Niutitang “Black Rock Sequence” are both potential source rocks. However, a comparison in U and Th contents between the paleo-weathering profile of the Loushanguan dolomite and the bauxite samples suggests that the dolomite alone cannot provide the materials for the bauxite ores. Instead, the “Black Rock Sequence” may have contributed most of the ore-forming materials, which are mainly transported from source regions where the Niutitang Formation was exposed, weathered and eroded. Therefore, the Yunfeng bauxite deposit is of mixed autochthonous and allochthonous origin.

Statistical analysis and source rock of the Minim-Martap plateau bauxite, Cameroon

The Minim-Martap plateau bauxite deposit, located between the Minim and the Martap villages, is one of the 11 plateaus within the Minim-Martap bauxite region. The plateau has an elevation of 1294 m above sea level, with three to more 30 m thickness of bauxite horizon. These plateaus were formed as result of supergene weathering of volcanic rocks occurring as dissected flow basalt landscapes that form relatively flat plateau rising steeply from the surrounding granites. The bauxite deposit of the plateau is lateritic, with the surface of the plateau been completely covered by indurated caps. Seventeen bauxite samples were collected from the plateau and prepared for geochemical analysis. Whole rock analysis was carried out using the X-ray Fluorescence technique and ICP-MS was used for trace elements investigation. Statistical analysis reveals that average values of Al2O3 (54.87%), Fe2O3 (7.17%), SiO2 (2.44%), and TiO2 (4.54%) indicate the plateau bauxite deposit is an of a world class standard with very little impurities compared to the standard major element contents of bauxite (> 40% A12O3, less than < 20% Fe2O3, and less than < 8% combined SiO2). Abundant trace elements include Zr, Ce, Sr, V, Ba, La, Nd, Ga, and Nb. Weathering due to chemical alteration indices using the Ruxton ratio and CIA approaches revealed the plateau have undergone intense weathering process that formed the bauxite deposit. Three different classification systems indicate it as a low iron-rich bauxite deposit. Precursor rock investigation indicates the origin of the bauxite is mafic, basaltic andesite igneous rocks with intermediate pH (basic–acidic characteristic).

Studies of normative mineralogy and rare earth elements geochemistry of the Gazanjeh bauxite deposit, southeast of Mahabad, NW Iran

Studies of normative mineralogy and rare earth elements geochemistry of the Gazanjeh bauxite deposit, southeast of Mahabad, NW Iran

EASILY LEACHABLE RARE EARTH ELEMENT PHASES IN THE PARNASSUS-GIONA BAUXITE DEPOSITS, GREECE

The Parnassus-Giona karst bauxite deposits contain significant concentrations of rare earth elements (400-500 ppm). Preliminary results from a pilot leaching study show that between 19 and 47% of rare earth elements in the bauxite are easily leachable using ion exchange agents such as ammonium sulphate.

Tracing multiple resedimentation on an isolated karstified plateau: The bauxite-bearing Miocene red clay of the Southern Bakony Mountains, Hungary

The Vöröstó (=Red Lake) Formation, located in the Southern Bakony Mountains and the Balaton Highlands (Hungary), is a red, clayey continental assemblage containing hard, up to fist-sized bauxite pebbles, occurring in a large apparent stratigraphic gap between underlying karstified Triassic carbonates and mid’ Miocene to Quaternary cover. The origin and the exact stratigraphic position of the assemblage have been controversial for a long time. In this study, petrographic observations on the bauxite pebbles revealed common features with Cretaceous bauxite deposits known in the region, whereas heavy mineral composition of the red clay matrix is similar to those known from the Eocene bauxite horizon of the region. Single grain zircon U–Pb ages obtained from the bauxite pebbles and their red clayey matrix show similar late Archean to Jurassic age components. Additionally, Cenozoic U–Pb ages are well represented in the mostly euhedral zircon crystals separated from the red clays, whereas this volcanogenic contribution completely missing from the bauxite pebbles. SEM morphology and related EDX chemical analysis of clay minerals indicate polygenetic, detrital origin for the red clays. The main source material of the bauxite bearing Vöröstó Formation is most probably local Cretaceous and Eocene bauxite deposits exposed during the middle-late Miocene. These tropical weathering products were partly decomposed and degraded, but dilution by siliciclastic contribution is negligible. We suggest a transport mechanism dominated by local redeposition of mostly pelitic and allitic material through seasonal muddy debris flows within a karstic landscape.

Metallogenic mechanism of Pingguo bauxite deposit, western Guangxi, China: Constraints from REE geochemistry and multi-fractal characteristics of major elements in bauxite ore

Major and REE geochemistry and multi-fractal analysis of two types of bauxite (primary bauxite and accumulated bauxite) ores were studied in Pingguo bauxite orefield in western Guangxi, China. The results of geochemical data show that the accumulated bauxite has a feature of high Al2O3 whereas relative low Fe2O3 and SiO2 contents compared to the primary bauxite. The similar chondrite-normalized rare earth element (REE) patterns illustrate that they have a cognate relationship. However, the negative Ce anomalies of primary bauxite and positive Ce anomalies of accumulated bauxite indicate that the ore-forming system changed from reducing environment to oxidation environment. The results of multi-fractal spectrum and parameters of Al2O3, Fe2O3 and SiO2 between primary bauxite and accumulated bauxite show that the distinct multi-fractal spectrum parameters reflect the different grade distribution between accumulated and primary bauxite ores. Metallogenic process from primary bauxite to accumulated bauxite is accompanied by the loss of diffluent elements (e.g., Si and S) and enrichment of stable elements (e.g., Al and Fe) in the surface environment. Among the rest, the migration mechanism of iron during the evolutionary process from primary ore to accumulated ore can be described as combined leaching and chemical weathering action with participation of sulfur.

Biostratigraphy and facies analysis of the Upper Cretaceous–Danian? platform carbonate succession in the Kuyucak area, western Central Taurides, S Turkey

The Upper Cretaceous succession outcropping in the Anamas–Akseki Autochton, consists of approximately 500 m thick purely platform carbonate sediments. It begins with Cenomanian limestones intercalated with limestone breccias (Unit-1) containing mainly Pseudorhapydionina dubia, Pseudonummoloculina heimi, Spiroloculina cretacea (Assemblage I) and unconformably overlies the Lower Cretaceous (Barremian–Aptian) limestones with Vercorsella laurentii, Praechrysalidina infracretacea and Salpingoporella hasi. The Cenomanian limestones include foraminiferal packstone–wackestone, peloidal packstone–wackestone and mudstone microfacies deposited in restricted platform conditions. The Cenomanian succession is truncated by an unconformity characterised by locale bauxite deposits. Immediately above the unconformable surface, dolomitic limestones and rudistid limestones (Unit-2) are assigned to the upper Campanian based on the benthic foraminiferal assemblage (Assemblage II) comprising mainly Murciella gr. cuvillieri, Pseudocyclammina sphaeroidea, Accordiella conica, Scandonea samnitica and Fleuryana adriatica (smaller-sized populations). The upper Campanian limestones composed of dominantly foraminiferal-microbial packstone–wackestone microfacies deposited in shallow water environment with low energy, restricted circulation. The following limestones of the Unit-2 is characterised by sporadic intercalation of “open shelf” Orbitoides, Omphalocyclus, Siderolites assemblage (Assemblage III), assigned to the Maastrichtian, in addition to pre-existing “restricted platform” species. In the upper part of this biozone, the Rhapydionina liburnica/Fleuryana adriatica concurrent range subzone (Assemblage IIIb) is distinguished by the presence of Valvulina aff. triangularis, Loftusia minor as well as the nominal species. The Maastrichtian limestones with sporadically open marine influence consist of bioclastic (rudist-bearing) packstone–floatstone, foraminiferal packstone–wackestone with rudist fragments and peloidal/intraclastic packstone–wackestone microfacies deposited in shallow subtidal–subtidal (lagoonal) environments. The Upper Cretaceous succession passes upwardly into 70 m thick limestones and clayey limestones (Unit-3) which do not contain rudists and pre-existing foraminiferal assemblage with one exception Valvulina aff. triangularis. Variable amounts of ostracoda, discorbids, miliolids, dasycladacean algae and Stomatorbina sp. (Assemblage IV) occur into mud-rich microfacies suggesting restricted conditions with low water energy. A probable Danian age is proposed for the Unit-3 based on the occurrence of Valvulina aff. triangularis and Stomatorbina sp. which were previously recorded from Danian of peri-Tethyan platforms.

Phase transformation processes in karst-type bauxite deposit from Yunnan area, China

Bauxite is the only resource of aluminum metal and forms through weathering, leaching, and deposition (i.e., bauxitization processes). Here we characterize the bauxite deposit in Yunnan area, China, through mineralogical and textural characteristics using XRD, SEM-EDX, and micro-Raman analyses. The Al-oxyhydroxide polymorphs (AlO(OH)) such as diaspore and boehmite are the dominant phases in most of the samples. Gibbsite (Al(OH)3) is the main mineral in two samples from Quaternary bauxite, and these three Al-rich minerals mixed with goethite, hematite, kaolinite, and small amounts of TiO2 polymorphs (anatase and rutile). Considering the textural characteristics and the stratigraphy of the bauxite deposit, some of the Al-oxyhydroxides and Ti-oxides are inferred to be products of the bauxitization in the lateritic soil during late Permian weathering. In the subsequent transgression stage, the earlier formed (Al-rich minerals and anatase) phases were transformed to diaspore or boehmite as spherulitic form and to rutile, respectively, with the processes of diagenesis, burial metamorphism, tectonic movements and magmatic activity. Following crustal uplift in the Yunnan Province after the late Triassic, diaspore was transformed into boehmite and the bauxite deposit formed earlier was exposed again to weathering resulting in the formation of gibbsite, hematite, goethite, kaolinite, and anatase, with diaspore, boehmite, and rutile remaining as relics. Our study provides insights into phase transformation during bauxitization and subsequent processes.

Bauxite formation on Proterozoic bedrock of Suriname

Lateritic bauxite deposits in Suriname rest on a variety of metamorphic, igneous and sedimentary parent rocks. Remnants of multiple planation surfaces with duricrusts that mark the tropical landscape are associated with recurrent episodes of bauxite formation since Late Cretaceous times. Plateau-type bauxites at the highest topographic levels developed on a range of Proterozoic crystalline bedrocks on the northern edge of the Guiana Shield in the country's interior. Weathering profiles of the Bakhuis Mountains, Nassau Mountains, Lely Mountains and Brownsberg largely correspond to the classical sequence of an iron-rich cap on top of a bauxite layer that covers a clay-rich saprolite interval grading into weathered and fresh bedrock. All of the investigated profiles are consistent with in-situ formation of the bauxite and are marked by Si-Al-Fe relationships indicative of medium to strong lateritization, with fresh bedrock being poorly exposed. The bauxite deposits contain gibbsite as the dominant Al-bearing phase, whereas boehmite is locally present in subordinate quantities. Their ferruginous character is expressed by relatively abundant goethite and hematite in the top layers. Kaolinite is the main mineral in the saprolite. Anatase and zircon are the most detected minor phases. The investigated bauxite deposits are generally of a medium-grade (average Al2O3 contents 33–49wt%) but have variable chemical compositions according to exploration drilling results. Average Fe2O3 contents (13–34wt%) show inverse relationships with Al2O3. Despite this overall conformity of the deposits, their thicknesses, textures, mineralogy and geochemistry are distinct in detail, reflecting contrasts in the nature of the parent rock and weathering history. Inter-element relationships show conspicuous differences between SiO2-poor (<5wt%) upper parts and SiO2-richer (>5wt%) lower parts of profiles in the Bakhuis Mountains, which developed on high-grade metamorphic pyroxene amphibolites and gneissic granulites. The bauxites of the Nassau Mountains and the other areas in eastern Suriname are marked by higher TiO2 contents (average>3.9wt%) and dissimilar profiles that reflect their development on variety of a low-grade metamorphic volcanic parent rocks. Weathering-induced redistribution of rare-earth and other trace elements affected even the least mobile elements. Differences in distribution patterns between individual profiles can be attributed to a combination of primary compositional differences of parent rocks, the nature and content of accessory mineral phases, and unequal responses to multiple bauxitization cycles.

Geological, geochemical and mineralogical characteristics of REE-bearing Las Mercedes bauxite deposit, Dominican Republic

Bauxite deposits, traditionally the main source of aluminum, have been recently targeted for their remarkable contents in rare earth elements (REE). With ∑REE (lanthanoids+Sc+Y) concentrations systematically higher than ∼1400ppm (av.=1530 ppm), the Las Mercedes karstic bauxites in the Dominican Republic rank as one of the REE-richest deposits of its style.The bauxitic ore in the Las Mercedes deposit is mostly unlithified and has a homogeneous-massive lithostructure, with only local cross-stratification and graded bedding. The dominant arenaceous and round-grained texture is composed of bauxite particles and subordinate ooids, pisoids and carbonate clasts. Mineralogically, the bauxite ore is composed mostly of gibbsite and lesser amounts of kaolinite, hematite, boehmite, anatase, goethite, chromian spinel and zircon. Identified REE-minerals include cerianite and monazite-Ce, whose composition accounts for the steady enrichment in light- relative to medium- and heavy-REE of the studied bauxites.Considering the paleo-geomorphology of the study area, we propose that bauxites in the Las Mercedes deposit are the product of the erosion and deposition of lithified bauxites located at higher elevations in the Bahoruco ranges. Based on the available data, we suggest a mixed lithological source for the bauxite deposits at the district scale: bedrock carbonates and an igneous source of likely mafic composition.