Geochemical Mineral Exploration

Geochemical Mineral Exploration

Geochemical mineral exploration is the search for economic deposits of minerals or petroleum by detection of abnormal concentrations of chemical elements or hydrocarbons in surficial materials such as soils, waters, and plants. For convenience, geochemical exploration is usually divided into two areas of specialization: (1) the search for metallic minerals deposits, and (2) the search for accumulations of crude oil and natural gas. The object of the search is the same in each case—the discovery of some dispersion of chemical elements or hydrocarbon compounds at levels sufficiently above normal to be called a geochemical anomaly. It is hoped that the anomaly might indicate the presence of mineralization or hydrocarbon accumulations at depth.

Prospecting for metallic ores

Geochemical prospecting for buried ore deposits is an ancient technique. For thousands of years prospectors have sought iron and copper stains on rocks as possible indicators of mineralization below; the stains are geochemical anomalies that arise as a result of the interaction of the atmosphere and rain-water with a sulphide mineral deposit, and the dispersion of the oxidized products so formed. Detectable amounts of gold in stream sediments are geochemical anomalies. Panning for gold in stream sediments is one of the most ancient and successful methods of prospecting.

Modern methods of geochemical exploration came into practice in the 1930s in Russia and in the 1940s in North America. What brought about the change from traditional methods such as the panning of stream sediments was the development of rapid and accurate means of making chemical analyses in the parts per million range so that anomalies below the visibly detectable could be located.

Kinds of geochemical surveys

Surveys may be either reconnaissance or detailed. The object of a reconnaissance survey is the evaluation of an area of hundreds or even thousands of square kilometres. Only small sample densities are feasible with large areas; a typical example would be one sample per square kilometre. Reconnaissance surveys are usually carried out by sampling stream sediments and their purpose is not so much to locate a specific mineral deposit as to assess the likelihood that mineralization might be present in the region sampled and that further, more detailed exploration might be warranted.

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