Continental Africa – Guinea – Siguiri
AngloGold Ashanti Mineral Resource and Ore Reserve Report 2009
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Guinea – Siguiri
Location
Société Ashanti Goldfields De Guinée
Siguiri gold mine is situated in the Siguiri district in the north-east of the Republic of Guinea, West Africa, about 850km from
the capital city of Conakry. The mining concession consists of four blocks totalling 1,494.58km
2
. It is a multi open-pit oxide
gold mining operation. The current LOM plan entails the mining of eleven individual pits, several of which are multi-stage. All
ore and waste is mined by a mining contractor in a conventional open-pit mining operation. Processing is done via a CIP plant.
Geology
This concession is dominated by Neoproterozoic Birimian rocks which consist of turbidite facies sequences and lesser
volcanoclastic sequences. The mineralisation is structurally controlled and occurs either as sheeted veins or within shear
zones. There are two main types of oxide mineralisation in the Siguiri basin: elluvial- or alluvial-hosted laterite mineralisation
and primary quartz-vein-related or shear hosted mineralisation. The laterite mineralisation occurs as aprons of colluvial or as
palaeo-channels of alluvial lateritic gravel adjacent to, and immediately above, the in situ vein-related or shear zone
mineralisation. The in-situ mineralisation can occur as either sheeted veins or associated with shear zones, with the best
mineralisation often occurring at the intersection of the two.
The shear hosted style appears to be a slightly older event related to the development of a number of north-south striking
shear zones that may cut different lithologies. This phase of mineralisation is usually associated with silicification, brecciation
and quartz-albite-pyrite veining, with magnetite being present at some localities. The vein-related mineralisation occurs as
north-east to south-east to east-west striking, discontinuous sheeted veins. The better mineralised areas are associated with
vein stockworks that occur preferentially in the coarser, brittle siltstones and sandstones. The sheeted veins appear to be
related to a younger folding event and appear to be developed on fold axial planes. Mineralisation is associated with white
quartz veins, with grey selvages and scattered large arsenopyrite crystals proximal to these veins. Mineralisation at Siguiri has
been deeply weathered to an average vertical depth of 100m, and the mineralised saprolite provides the primary oxide
feedstock for the CIP plant. Fresh hard mineralisation is not processed in the current plant. The practice at Siguiri was to blend
the laterite and saprolite ore types and to process these using the heap-leach method. With the percentage of available laterite
ore decreasing, however, a CIP plant was brought on stream during 2005 to treat predominantly saprolite oxide ore.
The Siguiri mineralisation is characterised by coarse gold with low average grade and highly skewed distributions. This is the
main geological feature taken into account during data collection and estimation.
Exploration
The primary objective of the exploration initiative at Siguiri is to discover or upgrade prospective areas, enhancing the value
of the concession. Exploration is focused on finding and upgrading oxide style mineralisation in the saprolite, using drillhole
sampling, geophysics, and soil geochemistry in the context of the regional and pit-scale geological models. Almost 190,000m
were drilled during the year, and consisted of 156,700m brownfield exploration, 21,195m sterilisation, 7,032m Sintroko test
work and 5,071m for metallurgical testing.
The areas around the current pits were the focus of this year’s drilling, investigating potential extensions to the current pits.
The principal targets that were explored include Sintroko South and West, Kosise South, Kami South, Kami Saddle, Kozan
Northwest, Toubani Extension, Eureka East and Komatiguia. Extension drilling was undertaken at Sintroko South and to the
north-west of Seguélén pits. The Seguélén north-west extension drilling (Komatiguia project) was done after completion of a
detailed gravity survey and the identification of a geochemical soil anomaly. The fresh rock potential below a number of pits