The Rocklands Group Copper Project
Cloncurry, Queensland, Australia
In 2017 UK Mining Ventures carried out a two-month long specimen recovery project at the Rocklands Group Copper Project in Queensland, Australia – in cooperation with mine owners CuDECO.
Copper was first discovered in the Cloncurry area of Queensland by Ernest Henry in 1867. The town sprang up to support the Great Australia Mine to the south.
In 1923 the Mount Isa outcrop was discovered by John Campbell Miles and became a highly successful Pb-Cu-Ag-Zn mine.
In 2006 Rocklands was discovered within the historical Cloncurry workings by Wayne McCree. It is located approximately 15km west of Cloncurry township. Native copper was first discovered during drilling.
The Rocklands Group Copper Project mine started operations in 2015. There are 11 main ore-bodies. The oxide zone was mined before specimens could be rescued, unfortunately, but UK Mining Ventures and CuDECO negotiated to implement a specimen recovery operation within the rich native copper zone in 2017. The specimens recovered from this operation first reached the collector market in 2018.
Geology and Mineralization
Las Minerale and Rocklands South contain a unique supergene-enriched zone with a pervasive high-grade coarse native copper and associated chalcocite ore from near-surface to depths of approximately 140 m and widths up to about 45 m. There is a combined native copper/supergene zone strike length of circa 1200 m.
The orebody type at Rocklands is confusing and there may be up to three different but related systems involved.
Intrusive Related Gold System (IRGS)?
Typically regional in scale, structurally controlled – repeats Iron Oxide Copper-gold System (IOCG)?
Iron Oxide Copper-gold System (IOCG)?
Tick-hill style (Mount Isa Mines) – structural controlled shear zone in the Corella Formation.
Gold Skarn System?
Potentially associated with the north – west intrusive system.
Minerals known from the deposit include:
Azurite – Cu3(CO3)2(OH)2
Calcite – CaCO3
Chalcocite – Cu2O
Chalcopyrite – CuFeS2
Copper (native) – Cu
Malachite – Cu2CO3(OH)2
Pyrite – FeS2
Rock types from the deposit include:
Dolerite (diabase), Gabbro, Jaspilite, Sandstone, Shale and Siltstone.
Between August and October 2017 during a two month collecting/recovery window two UK Mining Ventures/Crystal Classics professionals were on-site to aid with the recovery. The duration was constrained by the onset of Australian summer. With temperatures rising to 45 °C by mid afternoon collecting conditions are hard – native copper becomes very difficult to handle under this heat.
Removing Native Copper
Native Copper Concentrate
“The Butterfly”. Two coarsely crystallised branching plates of Native Copper, one approximately 16 x 16 cm and one 16 x 14 cm, diverge at 70°, forming the butterfly-like wings. The coarse branches are built from linked composite crystals which can attain 3 x 1 x 0.6 cm.
Crystals have developed as staggered overlain plates, many showing a crude triangular habit, possibly distorted spinel twins, modified to flattened triangular crystal faces.
17.3 x 16.0 x 16.4 cm
A 12 cm long x 1 mm wide stem of Native Copper with fine arborescent, chevron-branching along its length; one branch extending to 3 cm. This prime feature is densely surrounded by masses of open porous arborescent copper filaments, which form a repeating fractal structure across the display face. Underlying this is a nest of more coarsely crystallised native copper with crystals to 8 mm. Beneath the specimen is a 3 x 1 cm patch of pale olive-green dolerite.
Contact Twinning in Copper
Branching arborescent Native Copper fan with excellent spinel twins to 2.5 cm. Etched jaspilite and dolerite containing green-grey tinged quartz nodules form the 9 x 5 x 4.5 cm matrix. This specimen has a copper-red patina with patches of warm, iridescent reddish-bronze.
14.8 x 11.5 x 5.2 cm
Large arborescent sprays of spinel-twinned Native Copper to 3 cm. These connect to form long chains of well crystallised copper, attaining 16 cm in length. Many have bent during crystallisation to form sinuous curved habits within the display face. Interspersed between spinel twins are equant dodecahedral copper crystals to 6 mm. Occasional areas retain grey-green dolerite.
37.1 x 22.9 x 5.9 cm
A large folded matt, 1 to 1.5 cm thick, of acicular native copper crystals and slender Copper spinel twins, with a little attached jaspilite matrix. The acicular crystals grow to 1.5 cm and have developed in apparent random alignment. 31.8 x 14.5 x 11.0 cm
A 3.0 x 3.0 x 2.5 cm block of biscuit-tan jaspilite, with included Quartz fragments, is attached to a 7 x 3 x 2 cm finger of well-crystallised dodecahedral Native Copper crystals. These are typically 2 mm across and form stubby, densely packed branches.
The patina varies from bright metallic copper through terracotta to iridescent peacock blue.
7.8 x 6.4 x 4.2 cm
“Australia”. A flat plate of Native Copper, somewhat resembling the shape of Australia from one side.
Primarily composed of dodecahedral Native Copper crystals, typically 4 to 8 mm across, which connect to form a granular crystalline assemblage. The specimen is dominated by five very fine spinel twins, the best of which measures 6.0 x 1.6 x 0.9 cm and forms a superb spear extending out from and above the display face.
All spinel twins are sharp and well crystallised and show well the various aspects of such twinning in the periodic table group 11 metals, copper, gold and silver.
8.8 x 8.1 x 3.8 cm
A 9.5 x 8.0 cm mass of very finely crystallised Native Copper protrudes vertically from a block of mottled green and cream dolerite. Densely packed dodecahedral Copper crystals, often modified to the more complex tetrahexahedral form, comprise the bulk of the specimen. A 5.5 x 1.0 x 1.0 cm repeated spinel copper twin showing a part skeletal habit adorns the apex of the specimen.
14.6 x 8.3 x 9.1 cm
An open group of long acicular Native Copper crystals form a delicate net-like structure. The acicular crystals, typically between 1 to 3 cm long, are elongated repeated spinel twins and branch in complex, herring bone structures and are often sprinkled with equant dodecahedral crystals to about 1 mm across.
The copper ranges from fresh copper-red, through patinas of bright silver, gunmetal and sooty-black. Two small patches of etched Calcite remain on the underside of the specimen.
11.1 x 6.8 x 2.8 cm
Coarse crystals of heavily oxidised Native Copper form a flat branching solid fern-like frond. The stem averages 8 mm thick, with branches tapering to around 3 mm. This flattened form of Native Copper is typical of the shale-hosted zone of the orebody, in which copper emplacement is constrained by bedding within the shale.
18.3 x 8.1 x 1.2 cm
A choice, single 6.8 cm long spinel twin of Native Copper, overgrown around its base by equant, 2 mm dodecahedral Copper crystals over a length of 1.5 cm.
A smaller, 1.5 cm spinel twin branches out from the main twin at around 70°. The entire specimen has an aesthetic patina of bronze-terracotta to a reddish sooty grey.
6.8 x 3.0 x 2.5 cm
A highly unusual and aesthetic form of crystallised Native Copper from the Las Minerale open pit at Rocklands. A 7 x 5 x 4 cm block of quartz-rich greenish dolerite is pervaded with almost spherical crystals of Native Copper to around 5 mm diameter. From this matrix, an 11 x 6 x 4 cm stacked mass of beautifully crystallized Copper rises vertically. All the crystals are large, blocky and curved, forming an elegant plumose column. Where examination allows, all the crystal appear to be forms of repeated spinel twinning, with pseudo hexagonal symmetry due to the stellate habit. Along the prism faces, herring bone striations are developed, in some cases very deep giving a near skeletal appearance. The patina is an overall deep rose-gold to brassy-copper-red.
15.4 x 8.0 x 5.7 cm
Becky Lindsay Clark