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3D Structural Mapping of Gold Continuity, Venezuela

Gold Fields Venezuela commissioned SRK Consulting to undertake a study to determine the structural controls of gold mineralisation at the Choco 10 deposit in Venezuela. Gold Fields acquired the project when they completed the takeover of Bolivar Gold Corp in early 2006. In February 2006, SRK determined that the VBK mineralisation was strongly controlled by distinct foliation domains. Specifically, mineralisation appeared to be localised in areas of low strain, defined by folds and spaced crenulation cleavages which lay immediately adjacent to zones of high strain, where very planar or closely spaced crenulated foliations dominated. SRK recommended that Gold Fields compile and collect structural data from mapping and oriented core, and apply the data in 3D to improve structural interpretations of the relationship between mineralised domains and structural domains.

In July 2006, the Gold Fields Technical Manager commissioned SRK to provide a detailed structural study of the VBK mineralisation on the Choco 10 exploration lease. An intensive drilling program, begun in early 2006, was ongoing during the site visit in July. SRK provided a more detailed understanding of the controls on VBK mineralisation and updated the structural models using data from the recent drilling program. Our role was primarily to assist in planning resource and grade control drilling, 3D modeling and domain definition for resource estimation, and generating targets for exploration. The structural study was also designed to develop a deformation history for the Choco 10 deposits, and to link it to the regional-scale structural framework.

SRK representatives visited the site to map out the ore domains using the newly acquired structural database. To use the structural data effectively, we captured horizontal slices of the structural data every 25 to 50 metres and processed the data in a stereonet program where form planes of the data were generated and exported. 3D discs, created from this dataset, were imported into the Leapfrog computer program to compare the geometry of the foliation data set with Leapfrog wireframes of gold grade. Form lines based on the continuity of the foliation on sections parallel to the drill fences showed a clear relationship between the continuity of grade with the geometry of the foliation.

These form lines were imported into Datamine and Gold Fields staff used these lines in modeling the ore domains, increasing their confidence in the continuity of gold mineralisation. Together with the Gold Fields geologists, SRK was able to reach an improved understanding of the deformation framework and the structures that have most influence on gold mineralisation.

An abstract co-authored by Gold Fields and SRK Consulting was submitted to the SGA on the structural controls of mineralisation at the Choco 10 deposits; the paper is to be presented at the conference in 2007.

Andrew Ham:


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