Geochemical Exploration: From Investigation of Sample Density

Chuck K. Goudge
GrayStone Exploration Labs, Inc., Golden, CO

Sample density is a key component of a successful surface geochemical program. Survey densities and the quality of the results yielded by differing survey designs can be determined by a systematic study of the subsets of a high density survey.

A high density survey, consisting of almost eleven hundred samples covering an area of less than a quarter mile, was recently completed yielding impressive results. This survey, collected in January of 2007, was designed to evaluate the ability of iodine surveys to map areas of fault breccia previously identified in this area. Not only did the survey map the known fault clusters but it also detected smaller previously unknown features. This survey is an important demonstration of the ability of surface geochemistry, given sufficient density, to identify small features like faults, but it also provides an opportunity to evaluate the importance of sample density.

By separating the high density survey into subsets, with lower sample densities, it is possible to evaluate how well lower density surveys locate the features identified by the original survey. Beginning with the 121, 500 foot spaced sub surveys, and proceeding though the two half density sub surveys, each group of surveys can be evaluated for the probabilities of correctly identifying the known features. Important conclusions will be drawn about the effects of sample density in correctly identifying prospects along with the probablities of failure for low density surveys.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas