Studies of Saprolite and Its Relation to the Migration and Occurrence of Groundwater in Crystalline Rocks.

摘要

Geochemical,mineralogical,and textural studies of weathering mantles of crystalline rocks of the Georgia Piedmont show that a low-permeability horizon,which develops during the weathering of some rock types and which impedes infiltration of water from the surface,is formed by the accumulation of kaolinite and oxides of iron,aluminum,and silicon. Three types of hardpan were found,but only one is extensive in its impedance of water infiltration. This is a dense layer,which forms in the weathering mantle of granitic and gnessic rocks. It may be possible to disrupt this low-permeability layer by application of organic reducing agents,thus increasing water infiltration for recharge of the underlying water table. The geologic terrane is of greatest importance in the development of the low-permeability horizons,which develop on rocks of fairly uniform structure and texture: plutonic granites and granite gneisses. Low permeability zones do not develop on dense fine grained rocks or metamorphic rocks with inclined foliation. Favorable well sites can be selected on the basis of a knowledge of the areal geology,so that areas with likelihood of hardpan development,and thus low water infiltration,can be avoided.