Arianne Ford

A Comparative Analysis of Weights of Evidence, Evidential Belief Functions, and Fuzzy Logic for Mineral Potential Mapping Using Incomplete Data at the Scale of Investigation

AbstractLarge amounts of digital data must be analyzed and integrated to generate mineral potential maps, which can be used for exploration targeting. The quality of the mineral potential maps is dependent on the quality of the data used as inputs, with higher quality inputs producing higher quality outputs. In mineral exploration, particularly in regions with little to no exploration history, datasets are often incomplete at the scale of investigation with data missing due to incomplete mapping or the unavailability of data over certain areas. It is not always clear that datasets are incomplete, and this study examines how mineral potential mapping results may differ in this context. Different methods of mineral potential mapping provide different ways of dealing with analyzing and integrating incomplete data. This study examines the weights of evidence (WofE), evidential belief function and fuzzy logic methods of mineral potential mapping using incomplete data from the Carajás mineral province, Brazil to target for orogenic gold mineralization. Results demonstrate that WofE is the best one able to predict the location of known mineralization within the study area when either complete or unacknowledged incomplete data are used. It is suggested that this is due to the use of Bayes’ rule, which can account for “missing data.” The results indicate the effectiveness of WofE for mineral potential mapping with incomplete data.

Evaluating geological complexity and complexity gradients as controls on copper mineralisation, Mt Isa Inlier

Faults and lithological boundaries are pathways for focusing the large volumes of fluid required to form hydrothermal orebodies. The distribution of faults and lithological boundaries as a function of scale can be measured by the geological complexity, quantified by a fractal dimension obtained by box counting, that increases with complexity. Copper mineralisation in the Mt Isa Inlier has well-documented structural and stratigraphic controls, and may therefore have a strong relationship with geological complexity. In this study, a two-dimensional approach is implemented for analysing the relationship between complexity, complexity gradients and copper mineralisation. There is a strong positive relationship between complexity and copper distribution and endowment in both the major lithostratigraphic subdivisions of the inlier, the Eastern and Western Successions. This relationship may suggest that abundant fluid pathways and physico-chemical contrasts are critical factors in copper mineralisation. A weak inverse relationship exists between complexity gradients and copper endowment. At small scales, there is a departure from the fractal relationship between number of boxes containing faults or lithological boundaries and box size, called roll-off. Roll-off is shown to be a function of the detail of mapping. This allows variation in mapping detail to be accounted for in measurements of geological complexity by due consideration of the scale at which roll-off occurs. The results imply that complexity could be used as an exploration tool.