Abstract:

Previous studies have determined that a variety of complex breccias in the Jinding Zn-Pb deposit are genetically related to the salt diapirism. In this paper, breccia fractal analysis is used to determine two fractal dimensions of these breccias: D_r (the morphology of clasts) and D_s (particle size distribution), in order to understand their formation process. D_r indicates the morphological complexity and migration distance of the breccias or the degree of modification of the chemical process. D_s indicates the degree of brecciation and amount of energy that forms the breccias. Small D_r and D_s values imply that some of the breccias in Jinding were formed by diapirs of evaporite and gypsum-sand and near-in-situ brecciation of the host limestone. Bedded limestone-clast-bearing sandstone that is spatially transitional with these breccias have smaller D_r and larger D_s values, suggesting that limestone clasts in the sandstone were transported by evaporite rather than water into detrial sediments in a depositional system on the surface. Other breccias were formed by evaporite-sand-mud diapirs in a process where the breccia clasts were transported a certain distance, but the distance is limited and the clasts were not transported to the surface to enter a depositional system. Some of the breccias mentioned above also experienced post-brecciation fluid alteration and dissolution, resulting in a large D_r value. This study shows that evaporite diapir-related Zn-Pb deposits may contain breccias formed by a variety of diapir processes.

Key words: breccia, fractal analysis, formation process, Jinding