Obuasi Mine – Ghana

BLA designs open stoping mine in Ghana

Obuasi Mine – Anglogold Ashanti

Bottom-up Stacks & Crowns Longitudinal Retreat Open Stoping - Conceptual Study of Likely Stress and Deformation Effects

Gold mineralisation within the Obuasi area has a proven continuous lateral extent of about 8 km along strike and continues to an explored depth of over 2000m below surface. The main shear dips steeply to the north-west at 70º and is deformed resulting in an anatomising structural pattern. Characteristic of this type of shear hosted deposit is the development of strong pinch and swell structures.

There are variations in thickness, continuity, dip and strike of mineralised lodes. The result is a complex geological structure with unpredictable geometry and grade distribution. High-grade zones within the ore shears are surrounded by barren or very low-grade shear or host rocks. There are two main mineralisation types. The main historical source of high grade ore is from quartz veins in shear zones associated with free gold. The second type is disseminated sulphides (arsenopyrite predominant) in metavolcanics and metasediments. The ore zones are defined by the presence of mineralised quartz or presence of sulphides.

The narrow secondary shears now becomes the focus of mining and will form the core mining of any future deeper level extraction, below 1500m.

Obuasi Mine is situated along a north easterly striking 300 km wrench fault system known as Ashanti volcanic belt. This belt is the most prominent of the five Birimian Supergroup gold belts found in Ghana and comprises sedimentary and mafic volcanic rocks. The Birimian was deformed, metamorphosed and intruded by syn and post-tectonic granitoids. Folding trends are dominantly north east.

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