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Abstract
Mineral Potential Mapping for Epithermal Gold Mineralisation using Fuzzy Logic Method in The Island of Flores, East Nusa Tenggara, Indonesia
Prima Muharam Hilman,
Directorate of Mineral Resources Inventory, Indonesia
Email: prima@dim.esdm.go.id
Abstract :
This study focuses on applying mineral potential mapping techniques to a Geographical Information Systems (GIS) database for the island of Flores, East Nusa Tenggara, Indonesia. Reconaissance exploration work indicates that Flores is prospective for epithermal gold deposits.
The conceptual methods were used to define the exploration criteria for epithermal gold deposits because the study area is relatively unexplored and contains few known mineral occurrences.
The primary datasets used to construct the GIS database are: 1) digital geological map, 2) Digital Elevation Model (DEM), 3) geochemical stream sediment analysis, and 4) Landsat 7 ETM+ imagery. Deposit and mineral systems models were used to derive the following GIS layers from the primary layers in order to represent exploration criteria for epithermal gold mineralisation: 1) favourable lithologies (Kiro Formation, Tanahau Formation, and Granodiorite), 2) NW- and NE-trending regional-scale faults of Middle Miocene to Pliocene age, 3) stream sediment geochemical anomalies, and 4) hydrothermal alteration zones. The favourable lithologies and regional-scale faults were derived from digital geological map. The stream sediment geochemical anomalies were extracted from geochemical stream sediment data using a catchment-basin-analysis approach. Hydrothermal alteration zones were identified from Landsat 7 ETM+ imagery using Crósta’s technique.
A fuzzy logic method was used to integrate GIS layers representing exploration criteria for epithermal gold mineralisation into a mineral potential map. Three fuzzy inference networks and twelve sets of gamma, spread, and midpoint values were tested in order to combine the GIS layers. These experiment produced 46 mineral potential maps.
Mineral potential maps were ranked according to the degree to which the most prospective areas capture the known epithermal gold occurrences. This degree is defined as the value of the ratio D/A, where D is the percentage of known gold occurrences and A is the area corresponding to the most favourable portion of the mineral potential map. The most favourable zone is defined as map cells which correspond to the top 25 percentile of fuzzy membership values.
A significant result of this study is the delineation of new, highly prospective areas for epithermal gold mineralisation in the western and eastern parts of the study area.
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