Using a Discrete Fracture Network and Spatial Point Processes to Populate Veins and Model Grade in a Coarse Gold Deposit

Abstract

Vein-hosted gold deposits are characterized by mineralization, which is spatially restricted to narrow vein structures. Drillholes intersecting a mineralized vein can lead to unreliable and biased assay values compared to selective mining unit scale block grades. In this work, a discrete fracture network is simulated and adapted to model gold mineralization within the veins. Veins are assumed planar and the required inputs are distributions of vein orientation, vein length, and vein intensity (i.e., density). These inputs are collected from drillhole data, geological mapping, and expert knowledge of the deposit. A spatial point process is then applied to model gold grade as discrete events or “nuggets,” which are spatially restricted to the simulated quartz veins for the case of incomplete mineralization of the veins; when the vein is completely mineralized, a vein thickness distribution is required. The methodology is applied to an epithermal gold deposit in northwestern British Columbia, Canada and shows improvement in restricting the influence of the high-grade gold samples without resorting to ad-hoc manipulation of input assays through capping or cutting. The final output of this methodology is a block model of gold grade, which better honors the spatial structure of the veins in the deposit and is suitable for use in mine planning or resource estimation.