First Report of Cryptomelane in Altered Rhyolite from Tazrouk Volcanic District, Latea, Hoggar, Algeria

Abstract

X-ray diffraction, ore microscopy, and electron microprobe studies have been implemented on ore samples obtained from rhyolitic rock collected at the Tazrouk volcanic district, Hoggar. The identified manganese ore minerals include Alkali-felspar, Magnesio-arfevdsonite and cryptomelane. All these minerals are poorly crystalline. The minerals’ chemical compositions indicate little contamination with other elements. Modes of occurrence are principally taking place through replacements, cavity or fracture fills, leaching and precipitation. Mineral associations seem rather complex, which makes definite paragenetic relations impossible to establish. Supergene formation of the manganese oxide ore is highlighted by the abundance of manganese minerals in solution channels, such as fractures and cavities within silicate gangue. Much of the ore, however, appears to have been enriched by leaching of gangue minerals and the subsequent addition of manganese. Noteworthy, also, is that this large field occurrence of cryptomelane has initially been described with respect to the Hoggar shield.