Goldrush deposit is part of the Cortez deposits, which are Carlin-type sedimentary rock-hosted deposits.

Exploration currently reveals that the deposit has a maximum thickness of 76 m, a width of about 425 m, and extends along strike for approximately 5,275 m. The deepest significant intercept is currently at 1,435 masl. The Goldrush system remains open to the north into Fourmile, to the southeast, and in multiple directions in the Ken Balleweg (KB) Domain.

Exploration to date shows that mineralization at Goldrush is primarily stratigraphically controlled, occurring within subunit 5 of the middle Wenban Formation and to a lesser extent along the contact between the Horse Canyon and Wenban formations.

Mineralization is associated with low-angle thrust faults and their related hanging wall antiforms that typically concentrate gold along fold hinges and/or east-dipping limbs. Gold occurs within extensive zones of decarbonatization and silicification within the Devonian rocks.

The system is marked by a large stratiform silicified and sulfidized breccia horizon from 15– 70 m thick that extends more than 7,000 m on a north–northwesterly strike.

Mineralization
The main gold-bearing mineral is micrometre-sized arsenian pyrite that occurs as individual grains or as rims on pre-existing pyrite. Mineralization is primarily double-refractory and highly preg-robbing with both sulfides and active carbon present in the orebody. ........

The proposed method for mining the majority of the Goldrush deposit is small to moderate sized longhole stopes with cemented paste fill. The stopes will be extracted on a transverse primary/secondary system with (where possible), a continuous mining front. The mining direction is not fixed since the geotechnical and geometric conditions vary with each sub-area within the Goldrush complex.

Due to the mine access infrastructure being located on the western edge of the deposit, all cross cuts are mined from west to east. Considering this factor and the requirement to maintain a consistent mining front, the primary stopes will be extracted in a continuous sequence from east to west, top-down (where applicable) and from south to north. Once the second level of primary stopes are extracted and backfilled extraction of the secondary stopes can commence. The secondary stopes effectively follow the primary sequence.

Based on Mineral Reserves only, approximately 13% of the ore is produced from ore drive and drift-and-fill drive development, with the remaining 87% produced from longhole production stopes.

Each of the sub-areas within Goldrush were planned to be extracted in a regional sense from south to north. The five sub-areas were identified as:
• Red Hill;
• Crow’s Nest;
• 3½;
• Ranch;
• Meadow.

Mining is planned to commence in the Red Hill Zone as this will be the first area to be accessed from the twin decli ........

ROM ore is dumped into the crusher dump pocket at the mill and discharges onto a vibrating grizzly. Grizzly oversize material is crushed in a jaw crusher. Grizzly undersize material and the jaw crusher discharge are conveyed to the coarse ore stockpile. The coarse ore is conveyed to the SAG mill and lime is added to the belt based on ore requirements. The grinding circuit includes one SAG mill and one ball mill. Discharge from the SAG mill is screened on one of two vibrating screens.

Screen oversize is conveyed to a cone crusher where it is crushed prior to being recycled to the SAG mill feed. Screen undersize and ball mill discharge flow by gravity to the hydrocyclone feed pump box. The slurry is pumped from the pump box to the hydrocyclones. The ball mill is operated in closed circuit with the hydrocyclones to produce the target grind size for the CIL circuit, which is nominally 150 µm. The underflow from the hydrocyclones is recycled to the ball mill feed; the overflow from the hydrocyclones discharges into an agitated surge tank, which feeds the grind thickener. Cyanide is added to the surge tank to being the leaching process prior to the grind thickener. Milk of lime can also be added to the surge tank if the lime silo is down, and dry lime cannot be added to the belt.

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