Abstract:
The dehydration, iron oxidation, and diffusion of radiogenic argon (40Arr) on heating in air at 373-1273 K were studied for sericites from sericite schists hosting the Katsdag and Filizchai deposits of the Belokan-Shekin metallogenic zone, Azerbaijan. It was established that ferrous iron oxidation, as well as water and 40Arr release, begin at 573 K, are most significant (up to -80%) within the range 573-1073 K, and are very slow at 1073-1273 K. Within 893-1080 K, the semilogarithmic dependences of 40Arr diffusion coefficients and dehydration rates display an inflection point. The "poles" of 40Arr diffusion and dehydration were calculated from experimental data, and the fulfillment of the compensation law of diffusion was established. The empirical equation E = 30.02 + 3.321n(D0/a2) was obtained, which satisfactorily describes the experimental results. Using experimental data on parameters of 40Arr diffusion, as well as mineral age (t) and the radioactive decay constant of potassium (λ , the disturbing parameters were obtained for decay-diffusion equation (F0/λt), where F0 = (D/a2) 273Kτ is the Fourier criterion. The criterion of 40Arr retention in the mineral is a low value of (F0/λt) ≪ 1. For the sericites studied, these respective parameters are 4 × 10-10, 6 × 10-13, and 2 × 10-15 ≪ 1, which are much lower than one. This indicates that sericite can serve as an important K-Ar geochronometer for dating ore occurrences and low-grade metamorphic rocks.