Neotectonic faults of the Paralana Escarpment and their influence on uranium-bearing fluid flow

Abstract

The Paralana Fault Zone is situated on the eastern flank of the northern Flinders Ranges and separates the Mesoproterozoic Mount Painter Domain to the west and the Mesozoic-Cenozoic Lake Frome Embayment to the east. West-over-east neotectonic faults within the fault zone have been identified previously; the main ones having been described in literature but to date there have been no regional structural studies focusing on the geometry and kinematics of the Paralana Fault Zone. The fault zone juxtaposes uraniferous granites of the Mount Painter Inlier and the sandstone-hosted uranium deposits of the Lake Frome Embayment. Due to their proximity to such prospective zones of economic mineralization, understanding the interplay between these faults and the groundwater of the area is of crucial importance for future mineral exploration strategies. We have identified three individual thrust fault sets from a total of 56 catalogued faults, within an area of 150km2. Fault Set 1 strikes approximately NW-SE with moderate dip in both directions and a NE-SW principal stress direction (σ1). Fault Set 2 strikes N-S and has a shallow dip and E-W σ1. Fault Set 3 has an overall NE-SW strike, moderate dip, and is representative of the current stress regime with a σ1of NW-SE. Fault Set 3 features spectacular examples of neotectonic faulting, with Mesoproterozoic marbles and granites of the Mount Painter Inlier overlying Quaternary sandstones and conglomerates of the Frome Embayment. Observed fault displacements since the end of the Miocene range from 10 cm up to an estimated maximum of 800 m. We have sampled fault rocks from 34 measured faults and characterized micro textures ranging from unconsolidated fault gouge and breccia to heavily silicified fault gouge, indicating a range of fluid-flow conditions. To understand the possible fluids to have flowed through the faults, a hydrogeochemical study was conducted with water samples taken from range-proximal natural springs. After careful consideration of the fault orientation and attitudes, fault rock textures and chemical composition of spring waters, I conclude that there is no evidence for direct interaction between surficial neotectonic faults and uranium-bearing fluids.