We report on the application of the U-Th-He method for the direct dating of pyrite and provide an original methodological approach for measurement of U, Th and He in single grains without loss of parent nuclides during thermal extraction of He. The U-Th-He age of ten samples of high-crystalline stoichiometric pyrite from unoxidized massive ores of the Uzelga volcanogenic massive sulfide (VMS) deposit, South Urals, is 382 ± 12 Ma (2σ) (U concentrations ~1–5 ppm; 4He ~10−4 cm3 STP g−1). This age is consistent with independent (biostratigraphic) estimations of the age of ore formation (ca, 389–380 Ma) and is remarkably older than the probable age of the regional prehnite-pumpellyite facies metamorphism (~340–345 Ma). Our results indicate that the U-Th-He dating of ~1 mg weight pyrite sample is possible and open new perspectives for the dating of ore deposits. The relative simplicity of U-Th-He dating in comparison with other geochronological methods makes this approach interesting for further application.

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Dependence of the dimension of the associates of water-soluble tris-malonate of light fullerene -C 60 [= C(COOH) 2 ] 3 in water solutions at 25 • C Investigation of the concentration dependence of the size and type C 60 [=C(COOH) 2 ] 3 aggregation in aqueous solutions at 25 • C was accomplished with the help of a dynamic light scattering method. It was determined that three types of aggregates are realized in the solutions. The average number of C 60 [=C(COOH) 2 ] 3 molecules in smaller aggregates and all types of aggregates were calculated. One can see that over the whole concentration range, from 0.01 to 10 g/dm 3 , aqueous solutions of C 60 [=C(COOH) 2 ] 3 are characterized by sub-micro-heterogeneous behavior (because second-type aggregates with the linear dimensions -hundreds of nm are formed in all solutions). Additionally, the most concentrated solution (C = 10 g/dm 3 ) is characterized by micro-heterogeneous or colloid behavior (because third-type aggregates with the linear dimensions on the order of µm -are formed). In order to describe or explain such behavior, a stepwise aggregation model was invoked.Keywords: tris-malonate of light fullerene, method of the dynamic light scattering.