Dislocations and Bubbles in Vein Quartz

Abstract

TWO types of quartz veins occur in the former goldfield area at Ballarat, Victoria; one is potentially gold bearing and the other had always been barren. The former (type B1 veins) which go deep into the crust are hydrothermal veins or quartz dykes associated with local granites. The latter (type B2 veins) are typical of veins that have formed by pressure solution processes^1,2. It is not always possible to distinguish one type from the other with confidence because of limited outcrop. But it is likely that, because of their vastly different origins, these veins might contain diagnostically different lattice defects. Samples, all polycrystalline, were selected from type B1 and B2 veins. The study was extended to include quartz from metamorphic veins, from granitic quartz and from quartz deposited by solution processes in tension gases at Bude, North Cornwall. The origin of the defects in these quartzes was also considered. Foils were prepared for electron microscopy by ion thinning of selected areas of petrological thin sections. Some initial studies were performed with an AEI EM6 electron microscope operating at 100 kV but, because of rapid beam damage, especially at dislocations and the difficulty in obtaining large transparent areas, all subsequent foils were examined in an AEI EM7 microscope operating at 1,000 kV.