Geostatistical Simulation of Structurally-Controlled Low Grade-High Tonnage Gold Ores: A Strategy for Targeting Genuine Enriched Zones

Abstract

This paper presents a geostatistical study of a classic, structurally-controlled, carbonaceous phyllite-hosted gold deposit with low grade/high tonnage characteristics. Gold in this mineralisation is hosted in boudinaged quartz veins that vary in size from 2 cm up to 60 cm. Larger quartz boudins are reported but only exceptionally. The boudins show maximum elongation along the regional mineral stretching lineation (N220) and an intermediate elongation perpendicular to the latter. Gold grades within zones rich in quartz boudins are known to be high, but are diluted as the phyllites comprising these mineralised veins contain little if any gold. Therefore, ore grades, though low, can vary considerably throughout the deposit.

Exploitation of such ore is done in large-scale open pit mines, allowing mining to be conducted even on fairly low grade ores. However, mining selectivity, for a number of reasons, is always a concern and there is considerable interest and debate as to whether enriched ore zones that necessarily coincide with a high incidence of quartz boudins, can be detected by geostatistical tools. Using stochastic simulation and a new technique for conditional integration of the mean of the simulated ore grades, the interquartile ranges and probabilities, this paper attempts to map high grade zones within the studied deposit.