EXPERIMENTAL STUDY OF GOLD REDISTRIBUTION IN A SHOCK-METAMORPHOSED PYRITE-QUARTZ MIXTURE WITH THE USE OF THE 195AU RADIONUCLIDE

Abstract

The behavior and distribution of gold in shock-metamorphosed rocks were studied experimentally. A gold-bearing pyrite-quartz (Py-Qtz) mixture was affected by shock waves by the method of impulse-shock loading of powdered materials (P > 10-15 GPa, T > 2000 K) with the use of the cylindrical shock load of a porous mixture to enable (due to Mach reflection of the shock waves) the unique neighboring development of a region of high dynamic pressure and temperature and a strongly deformed peripheral region of lower temperatures and densities with zones of localized shearing. This created favorable conditions for vapor formation in the central zone and the redistribution of this vapor in the surrounding material. The morphology of the strongly deformed peripheral region facilitated vapor diffusion. This process efficiently transported gold in the direction of Mach wave propagation and resulted in a significant increase in the gold concentration at the container bottom. A complex of methods, including β-autoradiography, was used to identify a heterogeneous, zonal vertical and horizontal distribution of gold in the compacted Py-Qtz mixture (compactite). The vertical section is marked by two maxima of gold concentration: at the level where melt appears and near the bottom of the container, where the amount of the silicate melt attains a maximum. In horizontal sections, above the level where melt appears the gold distribution is undulant. Below this level, the distribution is approximated by a parabolic function with a maximum at the center and minima near the container walls, During shock loading, much gold passed into the gas phase (perhaps in atomic and ionic modes or as compounds with sulfur) and precipitated in the form of "disseminated" gold (atomic, cluster, and nanoparticle modes of occurrence) on all minerals of the mixture (quartz and pyrite). The maximum gold concentrations in the compactite are restricted to the silicic melt. Gold evaporated throughout the process of impact loading with a Mach wave, which provides evidence that the kinetic energy was very heterogeneously transformed into internal energy at the shock wave front, mostly on the surfaces of particles. The mechanism of axial gold redistribution was related to gold evaporation at the front of the Mach shock wave and the radial propagation of vapor (or even jet-boiling) ahead of the front of the Mach shock wave.