Geological characteristics and Nickel mineralization of the Valozoro deposit, Central-Southern Madagascar

Abstract

The Valozoro deposit is located in the rural commune of Fiadanana, within the Ambohimasoa district in the Haute Matsiatra region, in the central-southern part of Madagascar. It lies within the extension of the Ambositra and Fianarantsoa geological series, specifically in the Faliandra sector. Dating back to the Mesoproterozoic era, this formation belongs to the Ambatolampy group, part of the Antananarivo tectono-metamorphic Domain.The deposit is defined by intrusions of harzburgites embedded in formations of pyroxene- and amphibole-bearing gneiss, micaschists, and migmatites. The nickel-rich harzburgites form a distinctive subcircular hill at Valozoro. These holomelanocratic rocks, with a granular texture, are primarily composed of olivine, orthopyroxene, and plagioclase. Due to prolonged meteoric weathering, the harzburgites have undergone supergene alteration, leading to the serpentinization of olivine and orthopyroxene.The alteration process occurs in two key stages: (1) Early hydrolysis of olivine, resulting in the accumulation of residual iron enriched with nickel. (2) Progressive epigenization of serpentine ribbons by iron hydroxides, leading to intensified nickel enrichment. Serpentine exhibits an average nickel content of 2.5% and further alters into residual lateritic clay with nickel content ranging from 0.2% to 2.5%, averaging 1.2%. The harzburgites are intersected by significant veins of graphic pegmatite containing schorlite and milky quartz. They also feature fissures filled with centimeter-scale veinlets of garnierite, recognized by its dark green color. The primary exploitable ores at Valozoro include nickel laterites, garnierite, and serpentines.