PRINCIPLES OF GEO CHEMICAL PROSPECTING.

By Robert E. Hawkes '34.Washington: U. S. Geological Survey, 1957.Bulletin 1000-F. 40¢.

Within the past half century the world has depleted more of its mineral wealth than in its previous four and a half billion years of existence. It is safe to say that in the inhabited parts of the globe virtually all of major ore deposits visible to the old-type prospector have been discovered. We have entered upon an era in which ail of the latest tools of the physical sciences must be applied in order to locate those ore bodies which are hidden under a cover of soil and vegetation or which exist several hundreds or thousands of feet below the earth's surface. When one reflects that here in New England, for example, only two percent of the land consists of bedrock outcrops, it is obvious that we have a vast future potential which must be examined by one means or another if the nation is to flourish.

Professor Herbert E. Hawkes '34, formerly of the M.I.T. geology staff and now head of the Department of Mineral Exploration at the University of California, has been active in the field of geochemical prospecting for twenty years and has been successful both as the first head of the Geochemical Prospecting Branch of the U. S. Geological Survey and as a consultant to the major mining companies.

Geochemical prospecting, to quote Dr. Hawkes, "includes any method of mineral exploration based on the chemical properties of a naturally occurring material." To introduce this topic the author first briefly summarizes the general principles of the geochemical distribution of the elements and then launches into the discussion of geochemical anomalies and their causes.

The geochemical prospector is concerned primarily with the dispersion pattern of the elements (i.e., their patterns of distribution). Primary dispersion (and concentration) of elements is due to deep-seated earth processes, such as igneous activity and metamorphism. Secondary dispersion of the primary pattern is due to surficial processes, such as weathering, erosion, and transportation. Where a mineral deposit is not present in a region, the abundances of most elements in the groundwaters or soils lie within welldefined statistical ranges. Deviations from these expected norms are indicative of higher primary patterns and may possibly outline areas in which ore deposits are situated.

Dr. Hawkes' primary concern is with the principles and causes for the distribution of elements in the earth's surficial materials, rather than with the specific field and laboratory techniques now successfully employed in analyzing for infinitesimally small amounts of certain metals. An excellent bibliography is supplied for this purpose, however, and, in addition, suggested procedures are set forth for layout of sampling programs and interpretation of results.

There is no doubt that this bulletin will be widely used in the geological and mining professions, and that its author has made a timely and authoritative summary of the principles of a new and vitally important geologic tool.