| Abstract: | Three periods in the development of geochemical methods for ore prospecting in Bulgaria may be distinguished — initial (1954–1960), middle (1961–1969) and contemporary (since 1970) — which are characterized by successively increasing numbers of samples and improving methods of geochemical data evaluation. Geochemical methods have been recognized as effective, rapid and relatively cheap methods for prospecting for ore deposits (Cu, Pb, Zn, Au, W, Mo, etc.), some nonmetalliferrous raw materials (fluorite, barite, phosphorites) and hydrocarbons. They are used in all stages of exploration at scales from 1:200,000 to 1:200. They have contributed to the elucidation of the ore perspectives in many regions, and a number of new ore bodies and deposits have been discovered.Basic geochemical methods applied to ore prospecting in the country utilize soil and rock to detect secondary and primary aureoles. Stream-sediment surveys, hydrochemical and atmochemical methods are of more restricted use. Samples are analyzed by emission spectrometry, atomic absorption and other methods. A united system of computerized processing of geochemical data has been developed, including automatic drawing of geochemical maps.Interpretation of the data consists in selection of prospective geochemical anomalies and prognostication of the composition, morphology, depth and industrial significance of hidden ore bodies. The main problem in the mathematical processing of data is the presentation of polydimensional results from analyses in the form of generalized quantities — multiplicative or additive geochemical indicator ratios for the type of mineralization, coefficients of zoning, intensity, etc. The geochemical indices for evaluation of the newly found anomalies are derived through studies of the primary geochemical aureoles of typical standard ore deposits.Residual secondary soil aureoles in most cases are well correlated in composition and structure with the ore bodies and primary aureoles which have generated them. Their successful use is related to the landscape-geochemical conditions in the ore regions. Micro- and macro-chemical zoning of ground waters and different concentration of soluble components in different elevation belts are used for evaluation of hydrochemical anomalies. |
