Deciphering structural controls in a greenstone belt in Ghana

In March 2010, Xtra-Gold Resources Corp. commissioned SRK to conduct a structural geology analysis of their Kibi Project that aimed to provide insights to the geological and structural controls on the distribution of gold mineralisation and guide further exploration. Xtra-Gold also commissioned SRK to conduct a structural interpretation of regional airborne geophysical data, with the aim of developing a litho-tectonic framework for the region that could be used for defining conceptual structural targets.

Xtra-Gold’s Kibi Project is located in the underexplored Kibi-Winneba greenstone belt in Southeast Ghana. Although SRK has previously conducted numerous geological studies in other belts in Ghana, little is known about the tectono-metallogenic evolution of this belt. SRK investigated Xtra-Gold’s drill core and exploration trenches to unravel the geology and controls on gold mineralisation and developed a structural framework that is the first of its kind in this belt.

SRK was able to determine that gold mineralisation at the Kibi Project occurred in quartz-albite-ankerite stockwork veins within quartz diorite intrusions, and quartz-carbonate veins in narrow northeast-trending graphitic shear zones that occur in tightly folded metasedimentary rocks. Gold mineralisation in the quartz diorite intrusions appears to be more widespread and forms the focus of Xtra-Gold’s ongoing exploration campaign.

The recognition that gold mineralisation was primarily hosted in quartz diorite allowed Xtra-Gold to focus its exploration drilling, and better define the 3D geometry of these intrusions and the extent of auriferous zones within them. Following further structural analysis of subsequently acquired drill core, SRK identified several northeast-trending shear zones that bound auriferous stockworks in the diorite intrusions. In addition to controlling the development of stockwork veins in diorite, these shear zones host auriferous fault-fill and extensional veins. Structural analysis of shear zone and vein elements indicated that these developed during protracted SE over NW compression. Moreover, identification of the auriferous shear zones allows Xtra-Gold to better focus regional exploration drilling along this newly-defined prospective structural corridor.

Ivo Vos: ivos@srk.com
 

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