FIELD: chemistry.;SUBSTANCE: sample preparation is carried out by making polished specimens or attaching separate mineral grains extracted from rocks to a filler-holder with subsequent opening of the crystals, grinding and polishing their surfaces and sputtering with carbon; images of the samples are obtained and analysed in back scattered electrons (BSE) using a microprobe analyser at accelerating potential of 15 kV and electron beam current of 30 nA; energy-dispersion spectra are obtained and analysed at accelerating potential of 15 kV and electron beam current of 30 nA; distribution maps of U, Th, Pb, Y and basic elements of the mineral-geochronometer matrix are obtained and analysed at accelerating potential of 15 kV and electron beam current of 80-250 nA depending on the mineral; qualitative and quantitative analysis of the composition of the mineral-geochronometers is carried out at accelerating potential of 15 kV and electron beam current of 250 nA; analytical data are recorded and the age of the minerals is obtained.;EFFECT: high accuracy of the method for electron-microprobe chemical U-Th-Pb-dating of mineral-concentrators of uranium and thorium radioactive elements.;3 dwg
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