Talc indices from Boumnyebel (Central Cameroon), physico-chemical characteristics and geochemistry

Abstract

Two talc schist occurrences were discovered in the Boumnyebel area, embedded in the Pan-African mica schist, at the junction between Archean, Eburnean and Neoproterozoic formations in Cameroon. They have been analysed by different techniques such as chemical analyses, XRD, DRIFTS, DTA and TG. The talc schist of the northern deposit contains talc (up to 95 wt%) with chlorite, goethite and lepidocrocite as minor minerals. The talc schist of the southern deposit has up to 88% of talc and is speckled with dark green phenoblasts of amphiboles (coexisting prismatic tremolite and magnesio-riebeckite). Due to its high talc content, the amphibole-free talc schist is economically attractive. Chemical analyses show that most of the rocks consist of SiO 2 , MgO and Fe 2 O 3 , except the sample from the southern deposit that displays some amounts of Al 2 O 3 and CaO. Among trace elements, Ni, Co and Cr are as high as in serpentinized peridotites, and suggest a protolith of ultrabasic nature. Chromium concentration in tremolite reaches 6178 ppm; most of the trace elements (Cd, Cr, Dy, Er, Eu, Ga, Gd, Ho, Lu, Nd, Pr, Sm, Sn, Sr, Tb, Tm, Y, Yb, Zr) are compatible with a tremolite lattice. The regional metamorphism yielded garnet micaschist nappes and thus belongs to the upper greenschist facies. Based on the high talc contents of the rocks and occasional coexisting tremolite and magnesio-riebeckite, the origin of the talc deposits is assigned to a hydrothermal alteration of ultramafic rocks. During the hydrothermal event, the fluid composition changed from silica-rich to lime-rich, but very few trace element contents were affected. Thus the low Rb, Sr, Th, Nb, K, Ta, Y, Zr, Hf, MREE and HREE and high Ni, Cr, Co contents of the rocks point to depleted peridotites (harzburgite-lherzolite) and pyroxenite as protoliths. The hydrothermal alteration is expressed in the positive cerium anomaly accompanied by little LREE enrichment of talc-rich rocks and hornblendite. The studied talc schist deposits and the neighbouring gabbroic and ultramafic rocks may belong to a dismembered Pan-African ophiolite set.

More Value of Maroua Clay in the Formulation of Ceramic Products (Terracotta, Earthenware, Stoneware, Porcelain)

“…The idea is to split it into several categories of soil grains (or particles) of decreasing dimensions through a sieve stack manually finally get a better screening and have the best results when calculating different percentages. The apparatus consists of a column of standardised sieve opening, a vibrio-sieve trays, a precision balance sensitive to centigram, a thermostat oven, and a wire brush [5] [6] [21]- [24].…”

“…Sedimentometry involves measuring the density of a solid immersed in water suspension according to the sedimentation rate of the particles. The principle is based on the sedimentometry Stokes law which expresses, from equilibrium, the relationship between the settling speed and the diameter of a spherical particle supposed [5] [8].…”

“…Cooking is a cycle in three stages: the rise in temperature controlled, followed by maintaining the temperature to a certain value and finally, the gradual cooling to room temperature [5] [6]. The specimens were processed in the laboratory of Yaoundé MIPROMALO temperatures of 900˚C, 1000˚C, 1100˚C and 1200˚C according to the following program: temperature rise of 5˚C/min and held the bearing temperature and cook for two (02) hours [39]- [41].…”

“…The specimens were dipped in a water bath for six (06) hours of time; the amount of water absorbed is measured. The goal is to determine the amount of water absorbed by the sample as a function of the increase of the firing temperature [5] [6].…”

“…3) Loss on Ignition The loss on ignition (LOI), expressed as a percentage, is the weight loss of a sample after calcination, based on the initial weight (air drying) [5] By definition, the apparent density of a compact is defined as the quotient of the dry weight of the finished product, the volume occupied by the solid material, including voids contained in the grains. Measuring a density following the determination of the percentage of water absorbed in a balance beam, and immersed in a beaker of distilled water [5] [6] [13]- [15].…”