Mineralization of the stainmore depression and northern part of the askrigg block

Abstract

Abstract; Pb - %n - Gu - F - Ba mineralization occurs in Carboniferous Strata in veins and associated replacement flats. Veins are most productive when of small. displacement, and in thick limestones and charts. Mineralization is especially rich near to the horizon of the Main Limestone. Faulting and therefore vein formation is controlled by basement structure especially the Stockdale Hinge Line. Bedded cherts around the eastern part of the Stockdale Line have increased competant-reactive strata thicknesses and therefore the number of productive veins. Spatial variations of mineral occurrence have been elucidated and four zones set up to describe them;- Q Zone, quartz + chalcopyrite; F Zone, fluorite ± barite + galena ± chalcopyrite + sphalerite ± witherite; P Zone, galena ± sphalerite + barite ± calcite; C Zone, copper minerals ± galena ± barite ± calcite. Parageneses etc. suggest that the Q Zone is proximal and the C Zone distal to the source. This is supported by the spatial variations of yttrium in fluorite and antimony and silver in galena. Fluid inclusion homogenization temperatures are close to 100 C in the F Zone. Leachates of quartz, fluorite, sphalerite and barite show a systematic increase of Na/K ratio towards the north and east. Very low ratios are found suggesting an evaporitic source of solutions. Primary zonations are thought to be due to a proximity mechanism, although a small contribution is possible from mixing and heterogeneous source mechanisms. Recent oxidation has affected many deposits on the watersheds producing baritic gossans with lead ore, and secondary enrichment of copper mineralization in the C Zone is thought to be Permian. The zonal pattern, trace element studies etc, may prove useful in exploration and development when conditions are suitable for reopening the orefield.