FAQ- 2. What is the nature of the Paroo/Basement fault in the Mine?
At issue is whether this fault is a late post-Cu ore structure or whether it is an earlier structure which is affected by deformation at the mine scale. A further issue is whether it formed as a normal or reverse fault. At many localities on the surface this fault contact between altered Eastern Creek Volcanics and the Mount Isa Group is not well exposed. Proffett (1990) recognised this fault along the northern margin of the Crystallena Block and showed it to be overprinted by the north-south cleavage. This contact had earlier been mapped as a younger fault. Folded exposures of the fault separating deformed Urquhart Shale from chlorite schists at deep levels in the Mine are shown in Perkins (1984). Figure 5 shows this shear zone strongly altered by rutile, which is folded and overprinted by a strong west-dipping foliation (S3). Figure 6 illustrates the same healed contact further south where it is cut and displaced by the Buck Quartz Fault.
Figure 5. Folded Paroo-Basement Fault beneath the 1100 orebody.
Exposure of the Paroo-Basement Fault beneath the northern part of the 1100 orebody. A 50mm yellow-green rutile-altered shear zone (eg at a) is within strongly altered basic volcanics and against carbonaceous slates of the Urquhart Shale. It has been folded and overprinted by the S3 cleavage. 17C sublevel 5400mN.
Figure 6. Paroo-Basement Fault cut by the Buck Quartz Fault.
Healed contact between chlorite schists of the Eastern Creek Volcanics and carbonaceous slates of the Breakaway Shale. There are blocks of schist extending upwards into the slate-rich shear zone. This early fault a is cut by the Buck Quartz Fault (b) consisting of quartz veins and carbonaceous mylonite. Photo courtesy D. Sims. 19C sublevel 4010N Looking North.
These illustrations show that the nature of the complex contact zone beneath the copper orebodies depend on whether it is observed further northwards where the contact is as shown in Figure 5 or southwards where it appears as the quartz-mylonite zone (referred to as the Buck Quartz Fault) Figure 6. Whether the folded contact is a normal or reverse fault remains equivocal. All criteria show the Buck Quartz Fault to be a reverse fault which cuts and displaces the Paroo-Basement Fault.