Cannington Mine (South32 Cannington), McKinlay, McKinlay Shire, Queensland, Australiai

Regional Level Types
Cannington Mine (South32 Cannington)	Mine
McKinlay	- not defined -
McKinlay Shire	Shire
Queensland	State
Australia	Country

The Cannington silver-rich lead-zinc Mine is an underground mine located in north-west Queensland, in the Shire of McKinlay, about 200 kilometres (124 miles) southeast of Mount Isa, near the township of McKinlay.

The Broken Hill-type deposit was discovered by BHP Minerals in 1990 and the mine was commissioned in 1997 at a cost of some AUS$450m. Full production was achieved in early 1999, since then capacity has been expanded from 1.5Mt/y of ore to over 3Mt/y.

The deposit was discovered by Broken Hill Proprietary Company (BHP) in 1990. Although sitework and underground mining began in 1997, full production was not achieved until early 1999, with 1.5 million tons of ore processed in 1999. Production since has reached 3 million tons of ore per year. As of 2010 it was the largest and lowest cost silver and lead mine in the world. The expected life of the Cannington mine is 25 years.

On August 19, 2014, the mine's owner BHP Billiton announced it was splitting the company in two. A newly formed entity called South32 now houses BHP Billiton's non-core businesses including the Cannington Mine.

Cannington is the world's largest single silver producer, representing about 6% of the world's primary silver production, while its lead production represents about 7% of the world's primary lead output. The lead concentrate contains 70% lead and over 3,000g/t silver with low levels of impurities. Cannington is an underground mine accessed via a 5,250m-long, 5.2m-high by 5.5m-wide decline. The main, thicker hanging-wall orebodies of the deposit are mined by transverse, longhole open sloping.

Cannington lies in the south-east corner of the proterozoic Mount Isa Block, within the metamorphics of the lower middle proterozoic eastern succession and overlain by 60m of younger sediments. It is divided by faulting into a shallow, low-grade Northern Zone and a deeper, higher grade Southern Zone. Cannington’s major economic sulphides are galena and sphalerite. The silver occurs mainly as freibergite but is also present in solid solution within galena.

At the end of 2005, the orebody contained proved sulphide ore reserves of 18.0Mt grading 477g/t silver, 10.7% lead and 3.9% zinc. Measured resources totalled 2.3Mt at 536g/t Ag, 11.94% Pb and 4.49% Zn. The metallurgical recovery rates for zinc, lead and silver were 66%, 88% and 84% respectively.

Synchronous deformation and metamorphism at the Cannington Ag–Pb–Zn deposit involved a phase of Ca and Mn mobilization that accounts for the distribution of pyroxene-bearing and garnet-bearing rocks, which were selectively overprinted by sulfide mineralization. Garnet composition and its textural association in relation to three generations of planar fabric (S1 to S3) show that skarn-related grossular-rich garnet formed in the last garnet-stable event, D3. The D3 Cl-rich biotite in the gneiss is intergrown with garnet in veins, and within skarn rocks is continuous along strike with veins of garnet ± pyroxmangite, hedenbergite or amphibole, which indicates a period of anhydrous through to hydrous metasomatism. Compositional maps show that infiltration extended from alteration fronts through fractures, which indicates the high permeability of S3; these maps and XGrt profiles across skarn–gneiss contacts show that there was large-scale transport of mass by infiltration and varying degrees of hydrodynamic dispersion. Precipitation of oscillatory Ca- and Mn-zoned grossular-rich garnet in veins parallel to veins filled with Cl-rich biotite, in conjunction with the distribution of biotite-filled veins across the deposit, suggest that the mass transfer during D3 may be responsible for deposit-scale Ca–Mn skarn-like zoning.

The deposit is in Paleoproterozoic to Mesoproterozoic (2500–1000 mya) metamorphosed sedimentary rocks, known as the "Soldier's Cap Group", and is overlain by approximately 60 metres (197 ft) of Cretaceous and more recent overburden. The deposit was discovered as result of an aeromagnetic survey of the Soldiers Cap Group in the eastern Mount Isa inlier. The area was selected for survey based upon extrapolations from known prospects and associated lithostratigraphy. In other words, the rocks were the same as other known prospects, only slightly more deeply buried. The aeromagnetic survey pinpointed Cannington as a potential site and subsequent drilling proved it out.

The theory of formation of the Cannington deposit, and the related deposits at McArthur River, Century, Mt Isa, Hilton, and George Fisher, is explored in a 2005 paper by Large, et al.

The major ore minerals are galena and sphalerite. The silver occurs mainly as freibergite but is also present in solid solution within the galena.

Other Regions, Features and Areas containing this locality

References