Environmental Assessment
Volume B-3.2
Mine
Geology and Geochemistry
Ambatovy Project
22
January 2006
3.2
GEOLOGY AND GEOCHEMISTRY
3.2.1
Introduction
This section discusses impacts on geology and geochemistry for the mine
development of the Ambatovy Project (the project). Changes in geochemistry
are not assessed as direct residual impacts in themselves, but are rather used in
the water quality Environmental Assessment (EA) (Volume B, Section 3.9).
The study area for geology and geochemistry is the same as the terrestrial
biology study area shown in Volume A, Section 7, Figure 7.2-1.
3.2.2
Baseline Summary
3.2.2.1 Geology
The regional geology for the areas surrounding the mine includes Precambrian-
aged (4.5 billion years ago to 570 million years ago) metamorphic rocks and
Palaeozoic to Tertiary-aged (570 to 2 million years ago) intrusive rocks.
Intrusive rocks of the ore bodies are from the Cretaceous Period (136 to
65 million years ago). The dominant feature of the regional geological setting of
the project is a north-south striking belt of gneisses and migmatites. These rocks
form part of the high-grade metamorphic rocks that underlie the eastern two-
thirds of Madagascar. A large intrusive, known as the Amtampombato Complex,
believed to be of Cretaceous age, cuts the gneissic terrain, and dominates the
geological setting of the project.
The Amtampombato Complex intrusive is elliptical in shape and oriented
northwest-southeast with the main axis some 12 km in length and the shorter axis
about 7 km in length. The complex is composed mainly of gabbroic and syenitic
rocks, and two smaller ultrabasic bodies. This area of the proposed mine is an
outcrop of nickel-rich ultrabasics. The Ambatovy deposit lies towards the
southern margin of the complex, and the Analamay ultrabasic deposit is located
at the eastern margin of the complex. The ultrabasic rocks of this complex are
more concentrated in nickel relative to other rocks.
Since the ore bodies are exposed on an uplifted ridgeline, they have been
subjected to intense weathering from the tropical conditions present in
Madagascar. The resulting laterite layer averages about 50 m in thickness. The
laterite can be divided into three zones: ferricrete, ferralite and saprolite.
