Latitude -32.722739, Longitude 148.195969
Located in the Central West Region of NSW, nearest town Peak Hill
Source: Alkane Exploration rehabilitation panels on site.
The Peak Hill Gold Mine is located 50 kilometres north of Parkes adjacent to the township of Peak Hill in central New South Wales. Mining has ceased at this site but the open cut has been set up by former miners Alkane Resources as a tourist attraction with walking trails, lookouts, explanatory information boards and some old mining relics.
Gold was first discovered in the Peak Hill area in 1889, and from 1904 to 1917 the richest parts of the ore body were mined via underground methods - hoisting ore up a vertical shaft adjacent to the ore body. Over 500,000 tonnes of ore was mined to produce around 60,000oz of gold. Although the original shaft development exceeded 200m vertical depth, production was limited to roughly 150m using standard underground driving and stoping. During this time, the mine implemented the relatively new cyanidation-zinc precipitation process, which resulted in overall recoveries of around 65%.
The main gold-bearing ore body in the Proprietary Pit was approximately 400 metres long, up to 80 metres wide and extended from the surface to a depth of 100 metres. The ore body was near vertical and was surrounded by un-mineralised, waste rock.
In 1996 around 100 years after the original mining, Alkane Resources re-commenced work by modern open cut methods. This entailed drilling and blasting to initially break the ore and enclosing waste rock. The broken ore and waste rock were mass excavated, loaded into large trucks and hauled up and out of the open cut along the incline ramp still visible in the western wall. The richer ore was dumped in front of the crushing plant for pre-treatment prior to stacking, whereas the poorer ore was sent directly to the leach stack. The waste rock was discarded. During this period a total of 153,000oz of gold was recovered.
Open cut mining requires the removal of the waste rock surrounding the ore body to provide access to the ore. To ensure the pit remains stable over the long term, the batters (pit walls) were "laid back" at an angle of approximately 60 degrees. Also, at 10 metre vertical intervals, 5 metre wide horizontal benches (known as catch berms) were constructed. Any rocks dislodging from the pit walls would come to rest on the berms, ensuring the safety of mine workers during operations.
Most of the rock in the pit walls is oxidised: that is to say, weathering processes over millions of years have changed the original minerals in the rock to minerals which are stable in the presence of air and water. For example, fresh pyrite (fool's gold) has been changed to iron oxides and sulphuric acid. The reds, browns and yellows in the pit walls are mainly caused by the presence of iron oxides. The blue-green patches of rock are fresh (unweathered) and still contain pyrite.
The water in the base of the pit is natural groundwater. The colour is very dark due to the presence of iron leached out of the surrounding mineralised rock. The groundwater is also acidic and contains metal such as copper. In the 1950s Jim Dunn, a local Peak Hill identity, pumped the groundwater up through the old mine workings and precipitated the copper onto scrap iron to form a saleable copper product.
Under the ownership of Alkane Resources, Peak Hill was construed as being located within the Ordovician magmatic arc, (a curved linear belt of volcanoes above a subduction zone, where tectonic plates collide) which extends north-south over 200km. This arc also includes the Goonumbla Volcanic Complex, which hosts the nearby North Parkes copper-gold porphyry system.
The alteration and mineralisation at Peak Hill display all of the characteristics of an epithermal deposit. These deposits are generally formed at shallow depths (less than 2 km) as a result of hot mineral bearing fluids circulating and cooling within fracture networks.
To access the "Open Cut Experience", turn east off the Newell Highway at the post office in Peak Hill. Travel up the hill to the parking area, the open cuts are fenced off for safety but you can get good views from the vantage points.