Experimental modification of naturally deformed galena crystals and their grain boundaries

Summary

It is now well established that naturally—occurring sulphides—particularly galena—are frequently found in the deformed state and that at least part of this deformation can be eliminated by annealing in the laboratory.

The present contribution is concerned principally with galena, for which it is indicated: that tectonic deformation leads to natural work hardening, which may be reduced by simple heating in vacuo; that the rate of softening is related to the annealing temperature; that softening is related to recovery at low temperatures and to both recovery and recrystallization above 250–300 °C that single crystals of galena exhibiting minor slip and kinking recrystallize yielding new, unstrained grains elongated parallel to the old slips and kinks, i.e. a foliation involving unstrained grains may form under a regime devoid of compressive stress; and that where deformed galena and deformed sphalerite coexist, the galena may be made to recrystallize completely (e.g. at 325 °C in 50 days) while leaving the deformation in the sphalerite entirely intact; apparently the coexistence of a strained component A and an unstrained component B in a deformed ore or other metamorphic rock does not necessarily indicate differences in age or deformational history—it may simply indicate that post-deformational temperatures have exceeded the recrystallization temperature of one component but not of the other.