Gold-bearing quartz veins related to the orogenic gold type are typically ribboned as known from my research area northern California. The ribbons there are formed by vein-parallel shear planes, dividing the quartz in decimeter to micrometer thick bands. Ore-bearing fluids intruded the shear planes several times. This multi-stage mineralization is verified by microscopic investigation of gold ore. In most cases gold and galena are the last species deposited in the veins. The veins occur dominantly at intensely sheared lithological contacts.
A result of these observations is that the deposits developed in an active tectonic environment with multiple stages of fluctuating fluid influx in depths characterized by brittle deformation.
To improve my own understanding of fluid migration processes in hydrothermal systems I will try to summarize some general thoughts I worked off for myself from Cox et al. (2001) and, in part, from Yardley (1983). This is certainly not a complete overview of the topic. So donâ€™t hesitate to post critical questions, remarks or further arguments and ideas. (more…)