Sampling Challenges in Highly Dispersed Types of Mineralisation

摘要

Mineralisation in alluvial diamond or vein gold deposits is often hosted inrntrapping mechanisms. For instance, diamonds are nested in bedrockrndepressions such as gullies and potholes which were carved out by thernsea long before the diamond deposition took place. Similarly, goldrnmineralisation can precipitate in the necks of a boudinage structure.rnIn such deposits, the spatial distribution of the mineralisation isrngoverned by the mutual arrangement of the trapsites and by the gradernvariations within each trapsite. Reliable estimates can be obtained only ifrnthey rest on a proper knowledge of both degrees of variability. Thisrncreates a challenging sampling problem, as during the exploration phasernit is important to have a good global mean estimate to enable decisionrnmaking towards the future. A similar problem occurs for local estimatesrnat a later stage of development.rnTo understand and manage the sampling for global means, specificrnsampling procedures are required based on an appropriate choice ofrnsample support size and spacing. Estimates from such samplingrncampaigns should be unbiased, and the less variability they display, thernbetter the sampling parameters. The performance and impact of samplingrnparameters are tested and compared on different simulated deposits.