Uranium ore-forming systems of the - Geoscience Australia

Uranium ore-forming systems of the Lake Frome regionIn the Moorowie sub-basin up to 2300 m of Cambrian strata occur in the north-south striking halfgraben. Based on seismic data a series of north-south and northeast trending faults appear tocontrol thickness variations in the Cambrian sequences, and hence these are interpreted to be syndepositionalCambrian structures. One of these north-south trending faults identified in theseismic data is an east dipping normal fault with a half-graben in the hangingwall. There alsoappears to be some later inversion on the fault surface (Fig. 3.3, seismic line 84-SPG) thatprobably occurred during the Delamerian Orogeny with minor reactivation during recent times.Previous mapping of surface geology in the study area (e.g., compiled in the 1:1m map ofRaymond, 2009) identified several exposed faults within the Mesozoic and Cenozoic sedimentaryunits (Sandiford, 2008, in Heathgate Resources, 2009). Seismic data show that the locations ofmound springs near the eastern shore of Lake Frome are controlled by deep-seated long-livedfaults that transect Cenozoic, Mesozoic and Paleozoic strata (Fig. 3.9). A surface expression ofthis fault system is evident in the SRTM 90m DEM where it controls the lake shore and adjacentplaya lakes as well as truncating a series of low ridges. Figure 3.8 and the 3D map (Fig. 3.3) showthe Benagerie Ridge forming a basement high draped by Mesozoic and Cenozoic sediments.Sandiford (2008, in Heathgate Resources, 2009) identified a series of faults in the vicinity of theBeverley and Four Mile uranium deposits which have been mapped in 3D (Figures 3.5, 3.6, 3.10,3.11). The Wooltana Range Front Fault is a west dipping thrust fault that outcrops along theWooltana Range. In the north the Wooltana Range Front Fault is concealed by the Paralanaalluvial fan where it has been mapped as the Wooltana Fault by Sandiford (2008, in HeathgateResources, 2009). The Wooltana Fault terminates against, or is offset from, the Poontana-Parabarana Fault system.The Poontana-Parabarana Fault system has largely been identified in drilling through variations inthickness of Cenozoic units on either side of the fault and from seismic data for two lines (84-SPJand 84-SPG) that image the fault. As with the Wooltana faults; the Poontana-Parabarana Faultsystem has been interpreted as a west-dipping thrust fault.The Paralana Fault is a shallow west-dipping thrust fault that has directly controlled the depositionof the Paralana alluvial fan and the position of the Paralana Hot Springs. The Paralana Faultsystem is a deep-seated, long-lived structural zone it has been active since the Neoproterozoicwhen it controlled the deposition of the Adelaidean sediments (Preiss, 1987).The Four Mile fault is a splay off the main Paralana Fault, located along the range front near theFour Mile West uranium deposit. Two other fault segments, the Adams Fault and Buxton Fault(Fig. 3.5), as well as the Four Mile Fault are all west-dipping thrusts. The kinematics are clearlyevident in several exposures along the range front, where Neoproterozoic sedimentary rocks havebeen thrust over Cainozoic sediments (see Localities 11 and 13, Appendix 1).Page 38 of 151