Geoquimica

Certain geological conditions may require that all horizons of the soil be sampled.
Frecuently, Sampling of the organic horizon is effective in some areas, whereas in some regions other horizonsare more rewarding. In some places, deep sampling of a horizon by drilling is the only satisfactory method for soil and glacial till surveys. Heavy and resistate mineral surveys the of soil, till and,weathered debris have become increasingly useful. In yhese surveys the geological materials and panned, and the heavy and resistate minerals obtained. They are then examined microscopically for oreminerals or analyzed for ore and indicator elements; the results are poltted on maps. Heavy and resistate mineral maps, prepared on the same grid as those for soil surveys, provide valuable ancillarydata and often aid in the interpretation of de elemental dispersion patterns.
In soil analyses the fine fraction (minus 80 mesh) is generally analyzed for the chemically dispersed elements, whereas forheavy and resistate minerals a coarser fraction is used.
In glaciated terrains, as well as in certain other terrains, heavy and light clast (mineral fragments, stones, and boulders) tracing hs provedeffective in the discovery of certain types of minerals deposits. Examples are quartz boulders or fragments as indicators of gold-quarz veins, galena boulders or fragments as indicators of lead-zincdeposits. Surveys of this type are generally carried out on grids, the abundance of light or heavy clasts being visually noted and pltted at each sampling point or wherever they occur along the gridlines. In other surveys, lage samples of the till or overburden are obtained at each sampling point, and the light and heavy clast indicators are counted in the light and heavy concentrates obtainedfrom the samples. Well all data from clast surveys are plotted, fans or trains are commonly outlined whose apexes or starting points often mark the sites of underlyng mineralization.
Biogeochemical...