| Popis: |
Recent developments in Geographic Information Systems (GIS) technology enable complex modelling of geoscientific data which would not have been practical using manual methods. New techniques have been developed in this study for the statistical analysis of the distribution of topographic lineaments and for hydrologic modelling of stream sediment geochemical data. Topographic lineaments interpreted from artificial illumination of a digital elevation model of Tasmania have be categorised into four types according to persistence, orientation and temporal relationships. Type 1&2 lineaments are the most persistent forming major features that can be traced across Tasmania. Type 3 do not form persistent patterns and Type 4 trend north-south cross cutting other lineaments. The spatial association between Tasmanian mineral occurrences (points) and topographic lineaments (lines) has been analysed using a number of methodologies. Existing methods for testing point line spatial association were found to be unsuitable due to the deleterious effects of mineral occurrence clustering. A new method of Monte Carlo analysis has been developed which, in part, overcomes the effects of clustering. Monte Carlo analysis has been used to test the spatial association of primary copper, gold and tin occurrences across the Tasmanian mainland. Primary copper and tin occurrences have a spatial association with Type 1&2 and Type 3 topographic lineaments and gold occurrences are only associated with Type 1&2 topographic lineaments. A spatial association may also be inferred between tin occurrences and a composite of Type 1,2&3 topographic lineaments inside a zone defined by the interpreted 2 km granite depth contour in northwest Tasmania. The value of stream sediment geochemistry to mineral exploration is significantly increased by accurate determination of lithological and dispersion residuals. Lithological background levels of stream sediment trace elements were determined for each rock type from a point in polygon overlay of sample locations in lithology polygons. The lithological background at each sample site was calculated from a flow accumulation model and subtracted from observed values to produce a lithological residual. The dispersion residual was calculated by subtracting the average lithological residual of all samples upstream from a sample site, weighted by sample watershed area. The lithological residual enhances definition of anomalies by removing gross lithological variation. Dispersion residuals, calculated from the lithological residual, highlight local effects and emphasise subtle variation down stream from major anomalies. Hydrologic modelling has been applied to a stream sediment geochemistry survey from the Natone district in northwest Tasmania. Analysis of the Natone geochemical data using the methodologies developed in this study defines anomalies which are coincident with known mineralisation and geophysical anomalies. The lithological residual extends copper and zinc anomalies from the Upper Stowport Prospect southeast across the Precambrian siltstone-Devonian granite contact indicating an enlarged geochemical anomaly which has not been identified by convent10nal data analysis techniques. In the Chasm Creek catchment previously undetected copper, lend and zinc dispersion residual anomalies are coincident with electromagnetic and magnetic anomalies that are untested by drilling. |
