EXPLORATION FOR SAND AND GRAVEL DEPOSITS IN GLACIAL TERRAIN

In glacial terrain, sand and gravel deposits are formed by glacial-fluvial action. Associated landforms include outwash plains, kames, eskers and valley trains consisting of river terraces, flood plains and channel deposits. Portions of end moraines also contain sand and gravel. Glacial landforms are identified using airphotos, topographic and geologic maps, and geologic literature including water well logs. On site exploration, accomplished by soil borings, provides details needed for economic evaluation. Oversize split spoon samples, taken continuously, provide needed detail and necessary volume for testing. Resource volumes are calculated based on areal extent and deposit thickness. Gravel percentages are determined from grain size analysis; aggregate quality is from standard highway engineering tests including those for deleterious materials. Unit weights are used to convert volumes to tonnages. Accuracy of sand/gravel estimates depends on boring density. For different exploration efforts, consider the following: preliminary study, 3 to 5 borings/site; possible or inferred reserves, double the previous number; probable reserves, one boring/4 acres; and proven reserves, one boring/acre. To illustrate the exploration procedure, studies from contrasting glacial geology settings are examined.