Copper Hills, Rudall River District, East Pilbara Shire, Western Australia, Australiai

Regional Level Types
Copper Hills	Group of Hills
Rudall River District	Mining District
East Pilbara Shire	Shire
Western Australia	State
Australia	Country

Located in the western Great Sandy Desert, in tabletop terrane of the Rudall Complex, consisting of Proterozoic schist, amphibolite and metasedimentary rocks of lower amphibolite facies. After much searching, an exploration company map places the prospect south of the Rudall River National Park boundary, south east of Mt Cotton, and possibly in the Harbutt Range. Searching for the site on the ground is not recommended due to the remote nature of the region.

The site was explored by Prosilver Pty Ltd and later Australian Platinum Mines NL, but both considered it too small to mine. The reference studied five specimens given to the CSIRO which had not been destroyed in the analytical process. As such the reference is strong on species described but there is little information about the geological setting of the deposit.

It is a small vein polymetallic deposit dominated by malachite, and containing native silver and gold, palladium, platinum and copper selenides, mercury and palladium and platinum oxides. The co-existence of four precious metals is uncommon. It is thought to have resulted from low temperature (around 140 degrees) hydrothermal high acid solutions with high salinity and low Ph, containing Cu, Pd, Pt, Au, Ag, Hg and Se elements, reacting with carbonate (dolomite) resulting in the precipitation of malachite, and the co-precipitation of selenides of the various metals. The oxides of palladium and platinum is the result of decomposition of the primary selenides.

Malachite is the dominant species at the location and comes in three forms. Bright green fine grained un-mineralised malachite intergrown with quartz and occassionally chrysocolla. Ferruginous malachite of fine grained greyish green bands intergrown with quartz and goethite, hosting finely disseminated particles of copper selenides, and occassional gold grains. Finally mineralised malachite as nodules with abundant inclusions of opaque minerals described below. This malachite is black from the included particles. Malachite in general can occur at Copper Hills as nodules, nodular fragments, aborescent fronds, balloon like forms, and irregular grains.

Berzelianite occurs as locally concentric finely disseminated bluish white grains, while umangite is the same form but the grains are slightly larger and pink. Umangite at the deposit contains Pt, Ag, Hg, and Pd in large amounts.

Naumannite forms the core of the malachite nodules, is yellowish-grey in colour. It is also minor as inclusions in native silver, and core grains rimmed by tiemannite. Large grains of naumannite have a corroded appearance and are enclosed with chalcomenite as a product of oxidised naumannite.

Chrisstanleyite is a rare species occuring in the copper bearing lode rather than gold at its type locality, and closely associated with the naumannite.

Oosterboschite was confirmed via chemical analysis. It is found only within the malachite nodules as irregular grains and veinlets. The larger grains were rimmed by a darker phase being an alteration product of oosterboschite. The species was found as disseminated small particles, large irregular grains, veinlets, aborescent fronds, and layers in the malachite nodules. The species was yellow and the alteration product grey.

Luberoite was found in the mineralised malachite and a lesser degree quartz as diffuse clouds of dispersed particles, as aborescent fronds and concentrically zoned concentrations. Cu was dominant because of the malachite host. It is a very rare species.

Native silver occurs as veinlets and irregular masses sometimes visible to the naked eye, with the silver being partially replaced by copper. It contains appreciable amounts of bromine in the malachite nodules. It was formed late in the sequence and cuts all the other minerals.

Gold is described as being abundant in the mineralised and ferruginous malachite as disseminated particles, sometimes visible to the naked eye. Occurs also as veinlets and is closely associated with the silver mineralisation.

Potarite is a relatively rare element of the platinum group, occurring here as small dispersed grains in the coarse dolomite matrix. Tiemannite is grey in colour as small irregular grains in the mineralised malachite and as rims around some grains of naumannite. Chalcomenite is alteration rims around naumannite and chrisstanleyite.

There were three un-identified species. Palladium and platinum oxides occurring as spherical and sub-spherical grains as a mixture of several phases in the mineralised malachite. A Pt-Cu hydroxide mineral as tiny transparent anisotropic crystals within some of the quartz in the malachite nodules. A Pd-Hg-Cu selenide as tiny yellow anisotropic prismatic crystals closely associated with umangite in the ferruginous malachite.

The Mindat co-ordinates are very approximate and denote only the Harbutt Range.

Other Regions, Features and Areas containing this locality

References