Description
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AMIS0494 Au 6.42g/t Greenstone Geita Tanzania
Origin of Material: AMIS0494 is an Anglo Gold Ashanti commissioned CRM made from material supplied by Geita Gold Mine and Nyankanga. The Geita Gold Mine is situated 80km south-west of the town of Mwanza in the north-west of Tanzania. The Geita gold deposit is an Archaean mesothermal orebody, located in the Sukumaland Greenstones of the Geita Greenstone Belt. It is largely hosted in
a banded ironstone formation (BIF). Mineralisation is found where auriferous fluids, which are interpreted to have moved along shears often on BIF-diorite contacts, reacted with the BIF. Some lower-grade mineralisation can occur in the diorite as well (usually in association with BIF-hosted mineralisation). Approximately 20% of the gold is hosted in the diorite. The Nyankanga Deposit is hosted in a package of BIF, shales and greywackes forming a roof-pendant next to the top of Nyankanga Intrusive Complex. The Nyankanga Intrusive Complex is composed of several facies of diorite bodies. Sets of quartz-feldspar-porphyry and quartz-porphyry dykes strike northeast and dipping northwest, cross cutting both BIF and diorite.
Approximate Mineral and Chemical Composition: The Geita Mines major gangue mineral is magnetite with quartz, ankerite, and minor pyrrhotite and chalcopyrite. Gold occurs primarily as discrete grains. At mineral scale for Nyankanaga, gold mineralization is associated to chlorite-carbonate+hematite+albite-silica-pyrite/pyrrhotite-alteration in the damage zones. The latter comprise a variety of structural features, including veins and veinlets of variable composition, thickness and shapes; hydrothermal breccias; quartz+albite+carbonate veins forming local feeders spreading sulphides and gold outwards to replacing magnetite rich layers forming banded sulphide facies; and massive replacements and disseminations. Barren tourmaline-carbonate-quartz veins have been observed at places hosted in diorites
Recommended Concentrations and Limits
(at two Standard Deviations)
Certified Concentration
Au Pb Collection 6.42 ± 0.28 g/t
Cu 4A_MICP 66.2 ± 9.1 ppm
S Comb/LECO 2.84 ± 0.16 %
SG 3.04 ± 0.17
