The formation and evolution of the Bitincke nickel laterite deposit, Albania

Abstract

The Bitincke nickel laterite deposit, located in the south east of Albania, contains an estimated ore resource of 35.6 Mt of nickel ore with a grade of 1.2 % Ni. The deposit developed on peridotites within Late Jurassic ophiolites which were obducted in the Early Cretaceous and which form part of the Albanian Mirdita ophiolite zone. Limestones and conglomerates overlying the deposit delimit the minimum age of lateritization to the mid-Eocene. The laterite is composed of two distinct ore zones characterized by silicate nickel and iron oxide phases. Within the silicate zone, Ni concentrations reach a maximum of 1.5 wt% and although laterally and vertically variable this zone is typically characterized by olivine and serpentine at the base of the horizon which are gradually replaced by secondary silicates and iron oxides up section. The boundary between the silicate and the oxide zone above is normally sharp and characterized by an increase in Fe₂O₃ (from ~10 to 80 wt%), decreases in SiO₂ (from ~30 to 5 wt%) and a dramatic reduction in MgO content (from ~10 to 0.1 wt%). The oxide horizon is dominated by goethite and displays relatively little variation in textural morphology or geochemistry. Nickel concentrations are greatest near the base of this zone, reaching a maximum of 2.3 wt%. Weathering profile formation and variation in the thickness of the deposit was controlled by the interaction between topography, faulting and protolith fracture density. The oxide zone formed on topographic highs was subject to increased rates of erosion, whereas the laterite profile within topographic lows, and in areas of relatively high fracture density, tends to be thicker due to increased permeability. The most substantive sections of the Ni laterite weathering profile developed in small fault controlled basins and were preserved by the deposition of a sequence of limestones and mudstones.