Dehydration and Diffusion of Radiogenic Argon in Sericites from Massif Sulfide Deposits fo the Belokan-Shekin Metallogenic Zone, Southern Slope of the Greater Caucasus, Azerbaijan

摘要

The dehydration, iron oxidation, and diffusion of radiogenic argon (~40Ar_r) on heating in air at 373-1273 K were studied for sericites from sericite schists hosting the Katsdag and Filizchai deposits of the Belo-kan-Shekin metallogenic zone, Azerbaijan. It was established that ferrous iron oxidation, as well as water and ~40Ar_r release, begin at 573 K, are most significant (up to approx 80%) within the range 573-1073 K, and are very slow at 1073-1273 K. Within 893-1080 K, the semilogarithmic dependences of ~40Ar_r diffusion coefficients and dehydration rates display an inflection point. The "poles" of ~40Ar_r 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 + 3.32 ln (D_0/a~2) was obtained, which satisfactorily describes the experimental results. Using experimental data on parameters of ~40Ar_r diffusion, as well as mineral age (t) and the radioactive decay constant of potassium (lambda), the disturbing parameters were obtained for decay-diffusion equation (F_0/lambdat), where F+0=(D/a~2)_273 K~tau is the Fourier criterion. The criterion of ~40Ar_r retention in the mineral is a low value of (F_0/lambdat) 1. For the sericites studied, these respective parameters are 4 X 10~(-10), 6 X 10~(-13), and 2 X 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.