Geology of the Molo
Madagascar’s geological setting comprises a fragment of the African Plate, which rifted from the vicinity of Tanzania at the time of the breakup of Gondwanaland, the name given to an ancient supercontinent, some 180 million years ago. At that time Madagascar remained joined with India, moving east-by- south until the Late Cretaceous (approximately 70 million years ago), whereupon the two landmasses split apart. On a regional scale Madagascar can be described as being formed by two geological entities, a Precambrian crystalline basin, and a much younger Phanerozoic sedimentary cover that hosts potentially economic coal deposits. The central and eastern two-thirds of the island are mainly composed of Neoproterozoic-aged, crystalline basement rocks, composed of a complex mélange of metamorphic schist and gneiss intruded by younger granitic and basic igneous rocks.
The geology of the basin of Madagascar is composed of intercontinental tectonic blocks made up of ancient poly-deformed, high-grade metamorphic rocks and later igneous intrusions. The tectonic and metallogenic basement framework was originally subdivided into four blocks (Besarie, 1967), these being the: northern Bemarivo Block; northeastern Antongil Block; central Antananarivo Block; and the southern Bekily Block.
The Molo Project lies entirely within the bounds of the Bekily Block.
The Molo Project occurs within the regional Ampanihy Shear Zone. The most striking feature of rocks found within this shear zone is their well-developed north-south foliation and vertical to sub-vertical nature. This was related to a transpressional regime during the horizontal shortening of the Earth’s crust when is was heating, which resulted in the exhumation of lower crustal material.
The Molo Project area is underlain by supracrustal and plutonic rocks of late Neoproterozoic age that were metamorphosed under upper amphibolite facies, and deformed with upright north-northeast-trending structures. The supracrustal rocks involve migmatitic (biotite, garnet) quartzo-feldspathic gneiss, marble, chert, quartzite, and amphibolite gneiss.
The Molo graphitic zone consists of multi-folded graphitic strata with a surficially exposed strike length of over two kilometres. Outcrop mapping and trenching on Molo has shown the surface geology to be dominated by resistant ridges of graphitic schist and graphitic gneiss, as well as abundant graphitic schist float.
Geological modeling has shown that the Molo deposit consists of various zones of mineralized graphitic gneiss, with a barren footwall composed of garnetiferous gneiss. The host rock of the mineralized zones on the Molo is graphitic gneiss.