Mineralogy, Petrography and Geochemistry of the Ina Syenite (Linté, Central Cameroon) as a Source of Industrial Feldspars

Abstract

The syenite from Ina (Central region of Cameroon) constitutes a 1000 km2 syntectonic batholith intruded in the Paleoproterozoic granitic basement. The aim of this work is to assess the potential of the Ina batholith syenite as a feldspar minerals resource for industrial use through petrographic and geochemical characterization. Most of the rocks are grey coloured and consist of shimmering feldspar phenocrysts in a fine-grained ferromagnesian matrix. Petrography reveals the presence of two major syenite facies: a widely distributed porphyritic syenite and a less-abundant massive syenite. These facies are dominated by phenocrysts of sub-automorphic perthitic orthoclase. Its malgachite face is due to the presence of numerous inclusions of opaque minerals observed by scanning electron microscopy (ESEM-EDX). Plagioclase phenocrysts have a zonal texture characterised microscopically by an oscillatory compositional zonation. Biotite, hornblende and augite, identified by X-ray powder diffraction, are finely disseminated in the feldspar matrix. Quartz appears as small automorphic crystals with maximum abundance of about 4 wt%. The XRF chemical composition reveals, alongside silica (59.29 wt% to 63.27 wt%), significant proportion of alumina (15.82 wt% to 19.80 wt%), potassium and sodium oxides considered as fluxing elements (K2O + Na2O ≥ 10 wt%). The K2O/Na2O ratio varies between 1.65 and 5.51 (average 2.58). Iron and titanium oxides (1 ≥ wt% Fe2O3 + TiO2 ≥ 5), harmful in ceramic industry, are high as in most other feldspathic sources. The characteristics of the Ina syenite are close to most of the syenite ores used worldwide for ceramics and glass raw materials and necessitates purification and beneficiation treatments. Others rock types have been identified at the study site (granite, monzonite, granodiorite) and are considered as inappropriate as a source of industrial feldspars.