Fluid inclusion anomalies as exploration guides for granite-hosted Sn-W mineralization: prospects for the future?

摘要

Studies of the distribution and abundance of fluid inclusions in granitic quartz associated with granite-hosted Sn-W mineralization of the British Isles reveal local and regional scale anomalies. At a sampling interval of c. 5 ～ 50m, inclusion abundances increase towards zones of vein and stockwork mineralization exemplified by case history examples from exploration prospects in the Mourne Mountains of Northern Ireland and the Carrock Fell mining district of northwestern England. These steam aureoles provide a greater exploration target than the zone of visible alteration and mineralization and the lithogeochemical halo. But it is important to link them to geochemical data on fluid inclusion compositions, such as the semi-quantitative data from decrepitation-linked, ICP-AES (D-ICP) analysis, to optimize their exploration potential. Regional scale fluid inclusion anomalies, based on sampling intervals of c. 2km from the Sn-W mineralized granites of southwest England also broadly correlate with zones of intense mineralization in some areas. Regional-scale D-ICP analyses of quartz from SW England granites did not provide any convincing regional scale anomalies linked to mineralization except for positive boron anomalies around the centrally-mineralized Birch Tor area of the Dartmoor granite. Follow-up D-ICP analysis of quartz from stream sediments from this area, however, could be used to discriminate between samples related to mineralization from those draining unmineralized areas, using multivariate statistical analysis. At the present stage of development, the main contribution of fluid inclusion studies to mineral exploration is mostly limited to the conceptual stage where they continue to contribute to ore genetic theory and models. Costs and lack of knowledge transfer between research scientists and mineral explorationists limit their direct use during regional and target selection stages of exploration. Analysis of steam sediment quartz, using the more sensitive ICP-MS technique as a variant of the D-ICP method, appears to offer the greatest potential for future development as an exploration tool.