THE GEOLOGY AND MINERAL RESOURCES OF MADAGASCAR PRESENTED IN THREE NEW MAPS (1:1M SCALE): BEDROCK GEOLOGY, METALLOGENIC SUBSTANCES AND INDUSTRIAL MINERAL DEPOSITS

Two recent projects, completed under the auspices of the Projet de Gouvernance des Ressources Minerales and funded by the World Bank, have resulted in the production of three new maps (1:1M scale) of the bedrock geology and mineral resources of Madagascar. The new bedrock geological map – the first such compilation in 50 years – describes the Precambrian shield in terms of six geodynamic domains: Bemarivo, Antongil-Masora, Antananarivo, Ikalamavony, Androyan-Anosyan, and Vohibory domains. Each domain is defined by distinctive suites of metaigneous rocks and metasedimentary groups, and a unique history of Archean (~2.5 Ga) and Proterozoic (~1.0 Ga, ~0.80 Ga, and ~0.55 Ga) reworking. Superimposed within and across these domains are scores of Neoproterozoic granitic stocks and batholiths as well as kilometer long zones of steeply dipping, highly strained rocks that record the effects of Gondwana’s amalgamation (0.56-0.52 Ga). The Archean shield, comprising the Antongil-Masora and Antananarivo domains, is part of the Greater Dharwar Craton (GDC) to which three exotic terranes were added in Proterozoic time. In its reconstructed position, the GDC consists of a central nucleus of Paleo- Mesoarchean age (Western Dharwar, > 3.1 Ga) flanked by mostly juvenile “granite-greenstone belts” of Neoarchean age (Eastern Dharwar plus Madagascar, ~2.70-2.56 Ga). The Androyan-Anosyan domain is a continental terrane of Paleoproterozoic age (~2.0-1.8 Ga) that was accreted to the southern margin (present-day direction) of the GDC in pre-Stratherian time (~1.8-1.75 Ga). The Vohibory Domain, an oceanic terrane of Neoproterozoic age, was accreted to the Androyan-Anosyan domain in Cryogenian time (~0.64-0.62 Ga). The Bemarivo domain is a terrane of Cryogenian igneous rocks, with a cryptic Paleoproterozoic basement, that was accreted to the GDC in latest Ediacaran time (0.55-0.52 Ga).

Our new perspective links the Archean shields of India and Madagascar as a contiguous landmass since their time of formation (> 3 Ga) until their time of continental separation (~ 0.10 Ga). This new perspective forces a reconsideration of the mineral wealth of Madagascar especially its potential for major deposits of Neoarchean low-sulfide gold, iron formation, and komatiite-hosted nickel, as well as Paleoproterozoic chromite and base metal sulfides.