Lachlan Fold Belt – New South Wales
The Bushranger Project occurs within Rockley-Gulgong Belt of the Macquarie Arc within the Lachlan Fold Belt (“LFB”), also known as the Lachlan Orogen, which developed at the edge of the palaeo Australian Plate between 450 Ma and 380 Ma years ago.
The Lachlan Fold Belt in New South Wales hosts world-class porphyry copper-gold deposits (e.g. Cadia-Ridgeway – 3.5Bt @ 0.26% Cu & 0.4g/t Au, North Parkes – 597Mt @ 0.58% Cu & 0.2g/t Au), epithermal gold deposits (e.g. McPhillamy’s – 69Mt @ 1.04g/t Au, Tomingley – 6.4Mt @ 2.0g/t Au) and Volcanogenic Hosted Massive Sulphide Deposits (e.g. Woodlawn – 7.2Mt @ 6.3% Zn, 1.9% Cu, 2.4% Pb and 0.5g/t Au). The Lachlan Fold Belt is a highly mineralised terrane hosting world-class deposits, in an area of excellent infrastructure, making it an ideal location to explore and develop copper-gold and gold deposits.
The Macquarie Arc of the Lachlan Fold Belt is now fragmented into four structural/volcanic belts. From west to east, these are the Junee – Narromine Volcanic Belt, passing through Parkes (host to the North Parkes mine), the Molong Volcanic Belt, through Orange (host to the Cadia-Ridgeway mine), the Rockley – Gulgong Volcanic Belt through Oberon (host to the Racecourse copper-gold deposit) and the Kiandra Volcanic Belt in the Snowy Mountains of New South Wales.
The Macquarie Arc formed during four separate phases of arc-type magmatism separated by either hiatuses in volcanism or periods of limestone deposition. Phases 1 and 2, and 2 and 4 are separated by two major hiatuses in magmatism. Phase 3, represented only by intrusions, overlaps in time with Phases 2 and 4 which produced both intrusive and extrusive rocks. Phase 4 magmatism is closely associated with much of the major porphyry copper-gold mineralisation in the Macquarie Arc and is dominated by shoshonitic intrusions which were intruded between 458 Ma to 437 Ma. Between 443 Ma and 437 Ma, Phase 4 magmatism was manifested by the emplacement of the Group 4 porphyry Cu–Au deposits, including the giant Cadia-Ridgeway world-class porphyry system. Cadia-Ridgeway comprises at least six different individual porphyry deposits hosted by shoshonitic intrusions of the Late Ordovician Molong Volcanic Belt. The mineralisation includes porphyry hosted, sheet vein copper-gold at Cadia Hill and Cadia Far East, distal skarn-type copper-gold magnetite mineralisation at Big Cadia and Little Cadia, volcanic wall-rock hosted disseminated vein mineralisation at Cadia Quarry and quartz vein gold stockwork mineralisation at Ridgeway.
The Rockley-Gulgong Belt of the Macquarie Arc in central New South Wales, host to the Racecourse mineral deposit (71Mt @ 0.44% Cu and 0.064g/t Au, at a 0.3% Cu cut-off) contained within the Bushranger Project, occurs as isolated, fault-bounded outcrops. The Bushranger Project contains volcanic and volcaniclastic rocks with andesitic to basaltic compositions of the Ordovician Rockley Volcanics and is intruded by multiple porphyry’s. Age dates of monzodiorites and monzonite intrusions from the Bushranger project range from 451 Ma through to 437 Ma (Late Ordivician – Early Silurian). These ages are the same as those from mineralised monzonitic intrusives from the Cadia-Ridgeway mine where variably mineralised porphyritic intrusions range in age from 456 Ma to 438Ma.
The four volcanic belts of the Lachlan Fold Belt have been intersected by three prominent northwest trending structural corridors termed the Nyngan Transverse Zone, the Hunter River Transverse Zone and the Lachlan Transverse Zone. The intersections of the four volcanic belts with the transverse structural zones appears to have provided a locus for the emplacement of the shoshonitic intrusions associated with the porphyry copper-gold mineralisation at many of the major deposits within the Lachlan Fold Belt. For example, the deposits at Cadia-Ridgeway and North Parkes, are associated with the west-northwest trending Lachlan Transverse Zone. The Racecourse copper-gold deposit also occurs within the Lachlan Transverse Zone, where this structural zone intersects the Rockley-Gulgong Volcanic Belt.
The Bushranger Project and the Racecourse copper-gold deposit is highly prospective for the definition of major porphyry copper-gold deposits due to the following reasons:
- At 71Mt @ 0.44% Cu and 0.064g/t Au, at a 0.3% Cu cut-off, the Racecourse deposit is one of the largest undeveloped porphyry copper-gold deposits in the Lachlan Fold Belt
- The Racecourse deposit is open down dip and along plunge to the northwest and hence has substantial potential for a significant increase in the size of the currently defined mineral resource
- The last drilling conducted on the project in 2014 and 2015, delivered the thickest and highest-grade intersections recorded to date on the project and these intersections have not yet been followed up
- The intrusion hosting the Racecourse deposit is the same age as the giant Cadia-Ridgeway deposit to the west
- The Racecourse deposit is hosted within the Lachlan Transverse Zone, an important structure known to have controlled the emplacement of the intrusions hosting both the Cadia-Ridgeway and North Parkes mines