EXPERIMENTAL STUDIES ON THE SOLID-STATE DIFFUSION OF CU-INDUCED SEGREGATIONS), IN SPHALERITE AND THEIR GEOLOGICAL APPLICATIONS(IN IN ZNS AND ON DISEASE, DIS (DIFFUSION)

Isothermal solid state experiments on the diffusion of Cu, Fe, Zn and In and related effects have been carried out in sphalerite single crys tals. The driving force for the diffusion and corresponding reactions are chemical potential gradients which are established by differences in sulfur fugacity, oxygen fugacity and the chemical activity between sulfide powders as metal sources and receptor crystals. Studies in the system ZnS-CuInS2 show replacement rims in sphalerite produced by the formation of solid solutions between ZnS and CuInS2. These difference s reflect the extent of mutual solid solution. The composition profile s of these rims at different temperatures and sulfur fugacities are ca lculated to diffusion coefficients for the coupled substitution of Cu + In3+ versus 2 Zn2+. The interdiffusion coefficients of (Cu + In) in Fe-free sphalerite at the Fe/FeS sulfur fugacity of the sources obey to the relation: D [cm(2)/s] = 1 10(-3) * exp(5.53 * N) * exp((E + 2 N)/RT) (E = - 168.6 [kJ/mole]; N = mole fraction of Cu0.5In0.5S in ZnS). The interdiffusion coefficients increase with the sulfur fugacit y, the Fe-content of sphalerite and in the presence of water. If Fe-be aring sphalerite crystals are used, the diffusion experiments in the Z nS-CuInS2 system at higher fS(2) additionally show ''chalcopyrite dise ase''. Using different Cu- or (Cu + Fe)-bearing sources like CuS, Cu2S , CuFeS2, Cu5FeS4 Fe-free sphalerite and Fe-bearing sphalerites at all fS(2) show replacement rims. Fe-bearing sphalerites reveal ''disease' ' phenomena in addition to diffusion rims and replacements depending o n fS(2) at corresponding metal ratios in the source. Based on the expe rimental studies we propose the expression ''diffusion induced segrega tions (DIS)'' instead of ''disease''. The mineral phases and the textu re of the DIS depend on sulfur fugacity, Cu contents of the source, an nealing times and temperature. The grain sizes, forms and orientation of the DIS bodies depend on the annealing temperatures and times and t he defects of the sphalerite single crystals. The DIS phases chalcopyr ite and bornite are formed by reaction of the diffusing Cu with the Fe contained in sphalerite which is oxidized from 2(+) to 3(+) within th e chemical potential gradient. If the critical Fe-content of 2-3 at % is exceeded and a minimum fS(2) is reached, additionally to the occurr ence of DIS, Fe decreases in the primary sphalerites. If the critical Fe-content is not reached Fe can be introduced into the sphalerite. Th ese different phenomena can be directly correlated to natural occurren ces. Following our experimental studies and descriptions of natural pa rageneses the ''chalcopyrite disease'' has to be extended to correspon ding phenomena of bornite and digenite.