The geology of the greater Arcadia area is dominated by greenstone lithologies of the Arcturus formation of the Harare Greenstone Belt (HGB). These greenstones are encircled and intruded by a variable suite of granitic rocks, the oldest of which may have been coeval with the youngest felsic volcanic rocks of the belt. There is also some evidence for a small remnant area of gneissic basement to the greenstone belt.
The HGB takes the form of a complex refolded synformal structure, which crops out in two major limbs. An E-W trending Arcturus Limb occupies a broad band across the centre of the area, and to the west of the city of Harare this passes via a fold closure into the N-S trending Passaford Limb which is contiguous northwards with the greenstones of the Bindura area.
The main HGB lithological units comprise mainly meta-basalts, banded iron formations, meta-andesites, serpentinites, dolerites and the lithium bearing pegmatites that also host beryl, tin and tantalite amongst others.
The Arcadia Lithium Project (Arcadia-Green Mamba Camp) which lies close to the eastern end of the HGB is dominated by Arcturus Formation Metabasalts. Large dolerite sills and associated dykes are widespread and intrude the greenstone belt and the granitic terrain. They are tholeiitic, petrographically fresh, and are ascribed to the Mashonaland Event.
Regional Geological Map of Arcadia Lithium Project
The old Main Pegmatite is exposed in a 175m long pit on a steep hill slope and is 3 to 10 metres wide. It has a SW- NE strike, and is flat dipping at 3° - 5 °NW.
Main Pegmatite outcrop in Arcadia Pit – looking North
A package of up to 14 significant (>1m thick) stacked, sub-parallel pegmatites has been identified during the current phases of drilling. From youngest to oldest these are the Upper Pegmatite (U3), U2, U1, Main Pegmatite (MP), Lower Pegmatite (L1), L2, L3, L4/ LMP (Lower Main Pegmatite), L5, L6, L7 and L8.
The most significant bodies both in terms of thickness, lithium grade and lateral consistency are the Main Pegmatite and Lower Main Pegmatite, whose maximum thicknesses are 7- 10m and 25 – 50m respectively. The other pegmatites are much thinner, bifurcate and coalesce along strike and down-dip, but are also mineralised.
The drilling programmes undertaken by Prospect Resources have proved that the package of stacked pegmatites extends for over 3 km of strike length, while surface mapping and trenching has shown the total strike length to be almost 4.5 km.