Historical Information
The Fifield District was once Australia’s largest dedicated platinum producer. Platinum group metals and alloys, together with gold, were first discovered at Fifield in the 1880’s and are reported to have been produced from three alluvial leads (paleochannels), namely the Gillenbine, Fifield and Platina leads. The Platina lead is the largest of these at 3km strike length and 10m~25m deep.
The deposits were shallow and worked by surface mining with the ore material being first collected by horse drawn scoops. Deeper deposits were worked by underground selective hand mining. The usual method of treatment was to puddle the wash in puddling machines operated by horse or steam power, then to pass the de-slimed material through sluice boxes. The sluice box concentrates were further concentrated by hand panning and the gold was separated from the platinum by amalgamation with mercury.
The Fifield alluvial platinum deposits have recorded production of 650 kg (20,000 Oz) of platinum since the 1880’s and 6,200Oz of gold.
Historical mining techniques, a lack of water, and limited processing technology meant that a high grade was required for viability of historical operations. The reported historic head grade in the Platina Lead was around 15 g/t platinum grade.
Despite the early mining history drawing a significant population of prospectors and miners from the 1880’s, the Fifield district has seen very limited modern exploration.
Geological Setting
The underlying geological prospectivity of Rimfire’s tenement package is in part due to the presence and coalescence of major deep crustal scale structural trends; the Lachlan Transverse Zone and the Platina-Tresylva trend, which parallels the mineralised Gilmore Suture, within an interpreted Siluro-Devonian Rift Basin. The rift basin setting occurs in the back-arc to the world class Macquarie Arc which hosts Newcrest Mining’s giant Cadia Valley Operations, and the North Parkes porphyry systems, along with many other deposits, including Regis Resources’ McPhillamys deposit.
The Fifield rift basin overlies a terrain boundary between lower and upper Ordovician rocks and provides the backdrop for what appears to be carbonate base metal epithermal Au/Ag style mineralisation encountered to date at Sorpresa.
Rimfire has also revealed geological evidence for an additional target style at Fifield, possibly akin to the highgrade Tritton copper mine to the north. Similar stratigraphic and alteration assemblages have been observed at Fifield, particularly at the new Carlisle and Eclipse trend regional targets. The Tritton deposit is considered a Besshi style Volcanogenic Massive Sulphide (VMS) Cu-Au deposit, which remains a very attractive target style for Rimfire.
Modern day systematic exploration techniques applied by Rimfire quickly resulted in the greenfields discovery of the Sorpresa Au/Ag deposit. Given the lack of cover across the region, generally less than 10m, quick, simple and inexpensive exploration techniques such as rock chip, soil and auger geochemical sampling and shallow RAB and RC drilling are effective in generating targets. Broader application of these techniques on systematic grids, coupled with geophysical surveys such as aeromagnetics, gravity, and induced polarization has generated a significant pipeline of more than 30 exploration targets at various stages of assessment.
