Mineral investigations at Tredaule, near Launceston, Cornwall

This report describes geochemical investigations commenced in the vicinity of Tredaule, about lkm to the east of Altarnun and north of the A30 road, but not comprehensively completed owing to logistical problems. Five sediment samples from the two small streams east of Tredaule yielded panned concentrates with anomalous contents of both tin and tungsten, suggestive of local mineralisation. A single soil sampling traverse was sited parallel to the main stream and in the analyses of 34 soils from this line a small group of coincident tin and tungsten anomalies were reported, as well as a marked pair of silver anomalies farther to the south. In an endeavour to determine the source of these anomalies a gridded pattern of soil samples was collected over ground near Newhay farm. A total of 379 samples were analysed for a range of ore metals and associated elements. For some elements the results were combined with those from the adjacent traverse line prior to statistical treatment. From these combined results it is possible to recognise several soils anomalous in tin, usually with associated elevated levels of tungsten, and a different set anomalous in silver. The latter are sometimes associated with anomalous levels of copper, but there is a separate grouping of copper anomalies which may have closer relationships either to the tin anomalies or to the volcanic rocks over which they are located. There remains an open question of whether the anomalies have been fully defined in this restricted geochemical programme or whether they continue to the east of the Tredaule stream through the fields where sampling was not carried out. Because of this uncertainty it is unwise to speculate too deeply upon the form of mineralisation giving rise to the observed anomaly pattern, although the correlation between tungsten and tin, and the location of their anomalies relative to those of copper and to the mapped geology, is suggestive of an eastwest hypothermal vein. A source for the silver anomalies is not obvious.