Otworowe badania spektrometryczne mineralizacji torowej w Sudetach

Abstract

Przedstawiono wyniki zastosowań otworowych pomiarów spektrometrycznych naturalnego promieniowania gamma w badaniach mineralizacji torowej na obszarze metamorfiku izerskiego (Sudety Zachodnie). Rezultaty mają zarówno charakter metodyczny, gdyż dotyczą zagadnień pomiarowo-interpretacyjnych, jak również dokumentacyjny, ponieważ związane są rozpoznaniem mineralizacji torowej. Przeważają one pod wieloma względami wyniki laboratoryjnych oznaczeń tego pierwiastka. Badania radiometryczne, nie tylko otworowe, wskazują na kontynuację strefy zmineralizowanej poza obszar objęty dotychczasowym szczegółowym rozpoznaniem wiertniczym, a ponadto nie wykluczają możliwości występowania w głębszych strefach omawianego obszaru innych nie rozpoznanych dotychczas stref zmineralizowanych.BOREHOLE SPECTROMETRIC GAMMA RAY MEASUREMENTS IN SEARCH FOR THORIUM MINERALIZATION IN THE SUDETY MTSThe paper presents results of use of spectrometric gamma ray method of measurement of natural gamma radiation in search for hydrothermal thorium mineralization. The studies covered an area situated in western part of the Izera metamorphic massif (NW part of the Sudety Mts). Measurements were taken with the use of four-channel borehole spectrometer adjusted to cover depth interval down to 100 m, made at the Academy of Mining and Metallurgy. The field works were preceded by methodological studies on questions connected with both taking measurements and their interpretation. The tests covered several hundreds shallow drillings, in which over 23,000 measurements have been taken. The paper presents results of comparisons of spectrometric measurements of eTh and analytical laboratory determinations of Th content. Isotopes Th-232, Ra-220, and TI-208 have been found to occur in an equillibrium state. Spectrometic logs revealed very slight mobility of both Th and products of its decay in this geological environment in the vertical. It is shown that results of quantitative determinations of eTh, based on interpretation of spectrometric logs, are more reliable from the point of view of natural sciences than laboratory determinations of Th. It should be noted that a high variability in concentration of eTh (from 2 to 20,000 ppm) significantly reduced accuracy of spectrometric determinations of eU, and practically precluded any quantitative estimations of K.Immobile character of products of decay of Th-232 in the studied geological environment suggests that results of emanational and spectrometric measurements should be comparable.Results of quantitative determinations of eTh for individual drillings were subsequently used to compile maps of distribution of this element in the studied area. The results of independently made surface spectrometric measurements showed congruity of the obtained information on distribution of thorium.Because of limited coring and losses of core material, the obtained spectrometric data were often the only available information on content of eTh and eU in the studied borehole columns. The data were also used to evaluate thorium resources in the thorium mineralization zone, discovered and explored in detail by drillings. Analysis of all the results of radiometric surveys (including those from unpublished older reports) indicates possibilities of continuation of the zone of mineralization further to north-east.