At Bora, a number of vein reefs have been mined along the main Borah Fault over a strike length of up to 1km. These mines include the include the Mt Borah and Golden Gully Mines, as well as other smaller occurrences and the historic Borah Creek alluvials.
Figure 2: Plan view of central area Bora Prospect
The mines at Bora were active between 1907-40 and 1976-81, producing 443t of ore at 6.6g/t Au at Mt Bora and 106t of ore at Golden Gully at 23g/t Au for a combined total of 172.4oz Au. Production at Buffalo Ranche, a mine within the larger Bora Prospect, is recorded at 3.9t at 78g/t for 9.8 oz Au. The Borah Fault is expressed as a 100m wide silicified mylonite zone hosted wholly within weakly foliated adamellite. Assessment by Getty Oil Development Company of early drilling results indicated the mineralisation lay at a moderate angle of 35° to the main Bora Fault trend.
There have been thirty-one holes drilled over a concentrated zone of 100m at Bora (Figure 2) and over a strike of up 350m. Although the mineralisation is structurally controlled, no detailed structural interpretation has been conducted to clarify strike and plunge of quartz veins to define and better target a mineralised shoot. Apparent discontinuity in section view (Figure 3) could be a result of incorrect interpretation and nugget effect associated with high-grade mineralisation.
Figure 3: Bora Prospect – Cross Section 1 showing peak result from the Prospect in hole BSD5
Four of the drillholes at Bora have demonstrated strong potential to identify high-grade shoots on this structure, returning significant intercepts associated with quartz veins:
• 4m @ 20.6 g/t from 93m (BSD5)
• 7m @ 4.6 g/t from 15.5m (BA_L2)
• 4.8m @ 6.0g/t from 90.7m (GR-B8)
• 1m @ 9.3 g/t from 145.62m (GR-B1) (incompletely sampled)
Drilling has not adequately tested the Bora Prospect and mineralisation potential is considered open in all directions. Further review of this prospect will involve 3-Dimensional interpretation to identify potential plunge direction of mineralised shoots, and identification of repeat en-eschelon shoots.
The last explorer concluded that additional drilling was required to confirm plunge and strike extent of mineralisation, and that there is scope for strike extensions to the northeast and southwest given the current distribution of drillholes.