Recommendations for an orientation geochemical survey of the Avissawella quadrangle, Ceylon

In consultation with officers of the Geological Survey Department of Ceylon, Colombo, September 23 to October 6, 1970, recommendations have been drawn up for an orientation geochemical survey of the Avissawella quadrangle, Ceylon. The area of the quadrangle is particularly suited for this study because diverse geologic and geomorphic features are found within the quadrangle, and the three main agricultural crops of Ceylon (rice, rubber, and tea) are cultivated in the area of the quadrangle. The geology of the quadrangle is published. The recommendations propose the staged acquisition of basic data on field and laboratory techniques suitable for use in an area of heavy rainfall, deep weathering, varied topography, where the valleys are commonly planted in rice, and where geochemical methods have not been previously evaluated. Classic methods of semiquantitative colorimetric, spectrographic, and atomic absorption analysis are recommended to determine selected minor elements in the magnetic and non-magnetic fractions of concentrates from fluvial gravel and from silt and clay, and in the minus 80-meshfraction of silt and clay. It is recommended that the mineralcomposition of the non-magnetic fractions of the concentrates be estimated, and the presence of radioactive and flourescent mineral species be determined.

It is recommended that suitable maps be prepared to show these chemical and mineralogical data. These maps will be compared with the geologic map of the Avissawella quadrangle, and with each other, to permit interpretation of the effects of geologic units, contacts, structures, and geomorphology on the distribution of detrital minerals and of minor elements in various sample media. The main purpose of the orientation survey is to determine which samplemedia and which methods of analysis are most effectivefor geochemical reconnaissance in Ceylon. Unsuitable media andmethods will not be used in work in other quadrangles. The role ofagriculture contamination and its effect on the results of geochemicalexploration would be determined. The spacing of samples would beevaluated to determine the optimum interval for reconnaissance inCeylon.

Prospecting for gemstones could be conducted on a scientific basis if pathfinder minerals for precious gems can be identified in concentrates. Therefore, it is recommended that old records on gem-mining in the Avissawella area be plotted and compared with the distribution of minerals in concentrates from the Avissawella sample net. These data, in turn, would be interpreted with the geology and geomorphology of the quadrangle. Test pits would be sunk in unexplored areas indicated by the orientation survey, and the results evaluated for applicability to the exploration for gemstones.

It is recommended that the results of the Avissawella orientation geochemical survey be thoroughly evaluated before further similar work is undertaken. If the appraisal of results is favorable, further work should then be undertaken in selected quadrangles using as simplified a total procedure as is consistent with the achievement of desired results.