Modelling heavy-tailed coarse gold deposits with a spatial point process

CIM Journal, Vol. 6, No. 2, 2015, pages 118-131

C. R. Mooney
Department of Civil & Environmental Engineering, Markin/CNRL Natural Resources Engineering Facility, University of Alberta, Edmonton, Alberta, Canada

W. Board
Pretium Resources Inc., Vancouver, British Columbia, Canada

J. B. Boisvert
Department of Civil & Environmental Engineering, Markin/CNRL Natural Resources Engineering Facility, University of Alberta, Edmonton, Alberta, Canada
http://dx.doi.org/10.15834/cimj.2015.14
Abstract Traditional geostatistical modelling methods are difficult to apply to heavy-tailed deposits because the extreme positive skew of the grade distribution leads to bias. The focus here is on an innovative method of modelling the high-grade population by conditionally simulating discrete volumes (nuggets) of gold with marked Poisson and Cox processes. Capping and other ad-hoc manipulation of the assay data is not required; however, an intensity map for the point processes is required. The method is demonstrated on a dataset from an epithermal deposit and demonstrates an improvement in reducing smearing and controlling the skew of the grade distribution.
Keywords: Capping, Cox, Epithermal, Estimation, Geostatistics, Gold, Kriging, Poisson, Resources, Simulation, Skewed distribution
Résumé Les méthodes traditionnelles de modélisation géostatistique sont difficiles à appliquer dans des gisements dont la distribution de la teneur est à queue lourde car l’extrême asymétrie positive de la distribution de la teneur génère des biais. Dans le présent article, l’accent est mis sur une méthode novatrice de modélisation de la population à haute teneur par la simulation conditionnelle des volumes discrets d’or (pépites) au moyen de procédés marqués de Poisson et de Cox. La limite d’utilisation et d’autres manipulations ad hoc des données ne sont pas requises; toutefois, il faut une carte des intensités pour le processus ponctuel. La méthode est démontrée sur un ensemble de données d’essais provenant d’un gisement épithermal et elle montre une amélioration dans le lissage du flou et dans le contrôle de l’asymétrie de la distribution de la teneur.
Mots-Clé Cox, distribution asymétrique, épithermal, estimation, géostatistique, krigeage, limite d’utilisation, or, Poisson, ressources, simulation
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