Geometric modeling of a Breccia pipe - comparing five approaches
Résumé
The El Teniente mine is famous not only as one of the largest known porphyry-copper ore bodies but also, among geologists, for its typical breccia pipe named "Braden", an almost vertical poorly mineralized cone, located at the center of the mine and surrounded by early-stage mineralizations. As the edge of the pipe constitutes the limit of the deposit and of the mining operation, estimating it accurately is important. For the ten thousand samples coded by a pipe indicator, four approaches are proposed: - Two-dimensional: among all the data, only the samples on the surface are used and the elevation of the pipe surface is estimated as a function of the northing and easting coordinates. - Binary: the samples are coded 0 or 1, and the probability of being in the pipe is estimated in three-dimensional space. - Intermediate: in the three-dimensional space, the points on the surface, initially coded 0 or 1, are replaced by 0.5 and the studied variable can then take three values: 0, 0.5 and 1. - Non-stationary: techniques of Intrinsic Random Functions of order k are applied on the previous variable. In this article, the four methods are described. The quality of the results is evaluated by cross validation and compared to the geologist approach. The article concludes with a discussion of the relevance of using stationary techniques in such a fundamentally non-stationary context.
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