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Ambatovy, Analamay |
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Madagascar |
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Ni Co
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Ambatovy and Analamay lateritic deposits are located approximately 130 km east of Antananarivo in Madagascar.
These deposits are developed over two masses of serpentinised pyroxenite-peridotite within the 8 x 9 to 10 km ovoid shaped Cretaceous (86 Ma) Antamponbato igneous complex which is related to the Karoo Basalts of southern Africa. This complex comprises a syenite (calc-alkaline monzonite to syenite) core and ring dyke in the centre and western half of a larger gabbro body which encloses two masses of serpentinised peridotite in the eastern half.
Laterite sheets have formed over and almost completely covered the two serpentinised peridotite bodies, and contain the orebodies of Ambatovy in the south and Analamay in the north respectively. The complex is surrounded by migmatite gneisses of the Neoarchaean Antananarivo Block.
The ore grade laterites are formed over serpentinised peridotite, with lateritised gabbro only yielding 0.2% Ni grades. Surface geochemistry gave up to 5000 ppm Ni in laterite overlying peridotite, 3000 to 5000 ppm over pyroxenite and 500 to 3000 ppm over gabbro. A typical lateritic profile is recorded as follows, from the top (BRGM, 1985):
* Cuirasse around 2 to 5 m thick, averaging near 2 m,
* Pisolitic layer, locally developed,
* Red soil with preserved texture and structure from the serpentinised peridotite,
* Clay-soil with residual texture (as above) with layers & pockets of Fe-Mn-Cr oxides & sometimes Co,
* Clay-soil with residual textures and structures, and boulders of un-weathered serpentinised
peridotite containing thin veins of giobertite and garnierite,
* A locally developed magnesian layer
* Bedrock.
The saprolite below the cuirasse is 5 to 40 m thick with nickel throughout at a grade varying from 0.5 to 2.5%, locally as high as 3% and exceptionally to 3.5% Ni. The grade is characteristically homogeneous throughout the profile, with little variation with depth, although higher grades of around 3% accompany serpentinite boulder zones which are only a minor part of the orebody (BRGM, 1985).
The deposit has a resource of 210 Mt @ 1.1% Ni, 0.10% Co (Dynatec web site, 2004).
The most recent source geological information used to prepare this decription was dated: 2005.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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