Bauxite formation on Tertiary sediments in the coastal plain of Suriname

Lateritic bauxites in the coastal lowlands of Suriname form part of a belt along the northern margin of the Guiana Shield that has long been one of the world's major bauxite producing regions. The Surinamese deposits, many of which with an extensive mining history, originated on Tertiary siliciclastic sediments and were mostly buried under a layer of young sediments. The bauxite-bearing sequences are generally topped with an iron-rich layer largely made up of hematite and goethite. It covers a gibbsite-rich bauxite horizon that passes downward into a kaolinitic bottom section containing anatase and zircon as main accessory minerals. Weathering profiles across formerly mined deposits were analyzed for geochemical and mineralogical properties aimed at exploring compositional diversity, underlying controls of bauxite-formation and the nature of precursor sediments. Studied profiles in different parts of the coastal plain reveal overall similarities between individual deposits in showing significant depletion of Si, K, Na, Mg and Ca and strong, primarily residual, relative enrichment of Al, Ti, Zr, Nb, Hf, Ta and Th. In detail, however, there are distinct differences in major and trace-element signatures, accessory mineral assemblages, facies distribution and provenance of the terrigenous precursor sediments. Enrichments in high field-strength elements and heavy rare earth elements are largely attributable to accumulation of heavy minerals like zircon in the precursor. Petrological and trace-element evidence does not support a direct genetic relationship between bauxite and the underlying saprolitic clays. The complex petrologic characteristics and compositional heterogeneity of the coastal-plain deposits can essentially be explained by element fractionation, primarily through selective leaching, in combination with relative and absolute enrichment processes, erosion and reworking during two-stage, polycyclic bauxitization of a heterogeneous precursor

Bauxite formation on Tertiary sediments in the coastal plain of Suriname

Lateritic bauxites in the coastal lowlands of Suriname form part of a belt along the northern margin of the Guiana Shield that has long been one of the world's major bauxite producing regions. The Surinamese deposits, many of which with an extensive mining history, originated on Tertiary siliciclastic sediments and were mostly buried under a layer of young sediments. The bauxite-bearing sequences are generally topped with an iron-rich layer largely made up of hematite and goethite. It covers a gibbsite-rich bauxite horizon that passes downward into a kaolinitic bottom section containing anatase and zircon as main accessory minerals. Weathering profiles across formerly mined deposits were analyzed for geochemical and mineralogical properties aimed at exploring compositional diversity, underlying controls of bauxite-formation and the nature of precursor sediments. Studied profiles in different parts of the coastal plain reveal overall similarities between individual deposits in showing significant depletion of Si, K, Na, Mg and Ca and strong, primarily residual, relative enrichment of Al, Ti, Zr, Nb, Hf, Ta and Th. In detail, however, there are distinct differences in major and trace-element signatures, accessory mineral assemblages, facies distribution and provenance of the terrigenous precursor sediments. Enrichments in high field-strength elements and heavy rare earth elements are largely attributable to accumulation of heavy minerals like zircon in the precursor. Petrological and trace-element evidence does not support a direct genetic relationship between bauxite and the underlying saprolitic clays. The complex petrologic characteristics and compositional heterogeneity of the coastal-plain deposits can essentially be explained by element fractionation, primarily through selective leaching, in combination with relative and absolute enrichment processes, erosion and reworking during two-stage, polycyclic bauxitization of a heterogeneous precursor

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 33–49 wt%) but have variable chemical compositions according to exploration drilling results. Average Fe2O3 contents (13–34 wt%) 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 ( 5 wt%) 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 > 3.9 wt%) 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

Determination of Trace Elements in Bauxite Using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry on Lithium Borate Glass Beads

Quantification of trace element contents in bauxite by solution ICP-MS and other analytical methods that rely on conventional dissolution techniques can be challenging, because the refractory nature of common host minerals complicates complete digestion. Fusion with lithium borate, frequently used as a sample preparation method for XRF analysis of solid materials, avoids these problems. This manuscript documents that subsequent analysis of the low-dilution glass beads by laser ablation ICP-MS is a fast, accurate and precise method for determining trace element mass fractions in samples of bauxite and similar natural materials. The method was validated by determining thirty trace elements, including thirteen rare earth elements, in international reference materials for bauxite (ANRT BX-N, NIST SRM 69b, NIST SRM 696, NIST SRM 698) and iron formations (CCRMP FeR-2). Trace elements were typically measured to within 20% of reference values with an 'external' precision of < 20% RSD. Measurement results from various deposits in Suriname illustrate the procedure's effectiveness for studies concerning chemical properties and origin of bauxite

Determination of Trace Elements in Bauxite Using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry on Lithium Borate Glass Beads

Quantification of trace element contents in bauxite by solution ICP-MS and other analytical methods that rely on conventional dissolution techniques can be challenging, because the refractory nature of common host minerals complicates complete digestion. Fusion with lithium borate, frequently used as a sample preparation method for XRF analysis of solid materials, avoids these problems. This manuscript documents that subsequent analysis of the low-dilution glass beads by laser ablation ICP-MS is a fast, accurate and precise method for determining trace element mass fractions in samples of bauxite and similar natural materials. The method was validated by determining thirty trace elements, including thirteen rare earth elements, in international reference materials for bauxite (ANRT BX-N, NIST SRM 69b, NIST SRM 696, NIST SRM 698) and iron formations (CCRMP FeR-2). Trace elements were typically measured to within 20% of reference values with an 'external' precision of < 20% RSD. Measurement results from various deposits in Suriname illustrate the procedure's effectiveness for studies concerning chemical properties and origin of bauxite