Genesis of the Weipa Bauxite deposits, N. E. Australia

Grubb, P. L. C.

doi:10.1007/bf00201885

Cited by 9 publications

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References 2 publications

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“…4, and agree with weathering profiles in natural systems (e.g. Grubb, 1971;Lawrence and Taylor, 1972). The profiles usually show a decrease of feldspars and increase of clay minerals, and sometimes an ac cumulation of silica in lower horizon.…”

Section: "Solubility Product" Of a Mineralsupporting

confidence: 75%

Calculating the theoretical change in the mode of a rock by simple and ideal water-rock interaction.

Tsuzuki¹

1989

Geochem. J.

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Hydrothermal alteration is characterized by a change in the mineral composition (mode) of rocks in water-rock systems. The mode of rocks is changed by reaction between minerals and solution, with the composition of the solution also changing as a result of the reaction. The composition of the splution within a hydrothermal system under set conditions is given by simultaneous equations which are based on formulae of each mineral, and written in a matrix form. On the basis of mass balance between the minerals and the solution, the amounts of minerals dissolved and precipitated due to changing condi tions are given by simultaneous equations which are also written in a matrix form. The latter matrix is transposed from that of the former. The change in the mode due to changes in the physicochemical con dition is obtained by combining the two calculations given above.The calculations are applied to hydrothermal alteration in a system in which there is a geothermal gradient and circulation of hydrothermal fluid. For a system involving a solution and rock consisting of quartz, feldspars, muscovite and others, a decreasing temperature results in an increase of quartz and muscovite and a decrease in the amount of feldspars.In systems where the number of mineral phases is more than that of metal elements, stable mineral assemblages in the solution are examined in a model in which the solution interchanges among domains in a rock. One example is the Al-Si system involving solution, quartz, gibbsite and kaolinite. The results indicate that the stable mineral assemblages under set conditions depend on the original mode.Formation of veins accompanied by wall rock alteration is calculated in the system described above. The result indicates the formation of quartz veins with temperature decrease; the general feature of wall rock alteration can also be predicted.

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Section: "Solubility Product" Of a Mineralsupporting

confidence: 75%

Calculating the theoretical change in the mode of a rock by simple and ideal water-rock interaction.

Tsuzuki¹

1989

Geochem. J.

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Petrographic Studies of a Part of East Coast Bauxite Deposits, Odisha, Eastern India and Implication on their Genesis

Nayak

Sinha

Sahoo

et al. 2023

Journal of the Geological Society of India

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The East coast bauxite deposits of Odisha are well known in the mineral map of India. Some such deposits exposed at Nunapaimali, Sasubohumali and Baphlimali overlying khondalite of the Precambrian Eastern Ghats belt have been studied in respect of petrology, mineralogy and microstructure with a view to find out their genetic evolution. Bore hole samples from two former deposits and mine profile samples from Baphlimali revealed a good profile differentiation, in terms of three horizontal zones of variable thickness, which in descending order are: 1 to 29m laterite zone, 2 to 28m bauxite zone, 9 to 36m saprolite zone, comprising of lithomarge and partially lateritised khondalite [PLK] developed over host khondalite. Petrographic and mineralogical difference between these three zones, brought out through optical microscopy and XRD studies, further confirms the differentiation. Genetic evolution of bauxite is interpreted from the study of a large number of samples and results are collated from the photomicrographs appended in the paper. The authigenic bauxitisation was brought about by gradual dissociation of Al-silicate to Al-hydroxide minerals through different weathering cycles as indicated from their microstructural manifestations and mineral assemblages. Primary gibbsite is formed in the initial stage of weathering directly from Al-silicate minerals. Advanced stage of prolonged weathering converts the Al-silicate to kaolinite and then to secondary gibbsite. Grain size enlargement and recrystallisation showing mosaic habit, grain boundary migration and grain orientation are the outcome of digenesis. The weathering / lateritisation process continues, resulting in colloidal precipitation of gibbsite from pore water of lateritic residuum and is in progress even in recent period The Fe-oxide phases, represented by goethite and hematite are youngest in the paragenesis, and formed due to solution, precipitation and dehydration. Iron is mostly contributed by almandine garnet present in the host khohdalite. During chemical leaching, Fe gets released from garnet and occur either as FeOOH along its fractures or fill the weak planes / inter-granular space as secondary goethite. The goethite dehydrates to hematite during digenesis. Goethitisation and limonitisation particularly in the laterite zone are the results of supergene alteration.

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