Cannington is a Broken Hill Type (BHT) silver-lead-zinc massive sulphide deposit hosted by Proterozoic age high-grade metamorphic lithologies of the Soldiers Cap Group, located in the Eastern Succession of the Mount Isa Block. Mineralisation is stratiform bound along the limbs of a tight isoclinal recumbent synform with an easterly dip and a southerly plunge. The core of the synform is composed of amphibolite with encompassing silver-lead-zinc sulphide mineralisation. The mineralisation has been divided into nine types based on textural, mineralogical and geochemical characteristics which assist in defining metallurgical performance.

The Cannington mineralisation is hosted within a 70 m to 90 m thick of interbedded garnetiferous psammite and basic volcanic units that enclose a fine to medium grained central amphibolite body up to 100 m thick. The psammite is itself intercalated with muscovite-sillimanite schist and enclosed by migmatitic quartzon feldspathic gneiss. Pegmatite horizons that are semi-conformable within the deposit sequence are thought to be predominantly the result of partial melts of clastic rocks within this package (Mark, 1993).

Structure
The psammite sequence is folded into a tight, northerly striking isoclinal recumbent fold that plunges to the south with limbs dipping between 40O and 70O to the east as the result of the second of four structural events (D1 to D4) described by Bailey (1998). Two major northwest trending D4 faults offset the sequence. The Trepell Fault divides the ‘Northern Zone from the ‘Southern Zone’ and the Hamilton Fault forms a southern limit of the Southern Zone’. This Proterozoic host sequence is truncated up-plunge in then Northern Zone at the sub-horizontal unconformity with the younger Cretaceous sediments that are between 10 m and 60 m thick in the Cannington Operations area.

The Southern Zone has a strike length of 600 m to 700 m and extends to approximately 650 m below surface. The metamorphosed sediment package has been folded into a synform structure and is displaced on a local scale by north northeast and northeast trending faults. The northeast trending faults are interpreted as conjugate sets to the Trepell and Hamilton Faults as a result of sub- horizontal sinistral movement.

The Northern Zone strike is approximately 500 m and extends to around 400 m below surface. It is less deformed than the Southern Zone and typically dips east, interpreted as being the eastern limb of an antiform.

Mineralisation
Silver, lead and zinc mineralisation is stratiform within the garnetiferous psammite and mafic host rocks and varies in textural, mineralogical and geochemical characteristics that have been classified as ‘mineralisation types’. These are divided into footwall (western limb), hangingwall (eastern limb) and fold hinge lead-rich and zinc-rich domains, with the mafic rocks more complex in mineralogy than the siliceous rocks as mineralisation grades from outer Pb-Ag to inner zinc zones. The sulphide mineralogy is dominated by coarse grained galena (PbS), sphalerite (ZnS), with silver mainly contained in freibergite (Cu6(Ag,Fe)6Sb4S13).

The underground mine is accessed via a single surface portal with a decline extending to a depth of 645m below surface. Stope production is conducted using the Long Hole Open Stoping (LHOS) with backfill mining method. The primary backfill method is paste fill with a supplementary use of ROM waste and ROM paste rock.

The stoping areas are accessed by sub-levels developed on a nominal 25 m vertical interval.

A number of ore passes, developed in ore, feed to a crusher loading level. Approximately two-thirds of the ore is crushed underground at the underground crushing station located at the base of the mining operation and hoisted to the surface. A 5.6 m diameter hoisting shaft extends to a depth of 650 m and is equipped with a tower mounted friction winder.

The balance of the ore is hauled directly to the surface via decline access, passes through a crushing plant and is stockpiled on the run-of-mine (“ROM”) ore stockpile.

Once stopes have been completely mined, they are backfilled with waste rock or paste. Paste fill is delivered from the paste plant to the underground workings for distribution via a conveyor system or a series of pipes, depending on the area to be backfilled. The paste backfill provides stability to the underground workings and allows ore beside the backfilled void to be extracted.

The Cannington Operation uses an underground production fleet of trucks and load haul dump (“LHD”) units, with all underground mining machinery and equipment serviced in an underground workshop.

Mining contractor's (Redpath Australia Pty Ltd) fleet consists of a Kleeman crusher, with CAT and Volvo machines operating on the surface, while underground equipment consists of Sandvik Jumbo’s and Cablebolter’s, and Normet Spraymec machines.

Ore is crushed in an underground double-toggle jaw crushing facility with the crushed ore hoisted to surface and trucked to an open, conical stockpile. In addition, some underground ore is trammed to surface using LHD units, where it is crushed and then placed on the same stockpile. The crushed ore is moved to the grinding feed stockpile using a front-end loader (“FEL”). The grinding circuit comprises a single 5.8 MW autogenous grinding (“AG”) mill at 8.53 m diameter and 3.96m effective grinding length. The AG mill operates in closed circuit with a pebble crushing circuit and primary hydrocyclones.

The hydrocyclone overflow product at a particle size distribution of 80 per cent passing around 110 microns (P80 = 110µm) is treated in two vertical ball mills (“Vertimills”) operating in closed circuit with a second bank of hydrocyclones. The overflow from this circuit is treated in a talc pre-flotation step to remove talc and a significant amount of fluorine. The concentrate from this pre-float step is disposed as a final tailing product.

The processes for extracting the silver, lead and zinc from the ore involve grinding, sequential flotation and leaching techniques that produce high-grade, marketable lead and zinc concentrates with a high silver content.

The ore treatment process at Cannington uses primary underground and surface crushing. Primary grinding and a preliminary talc pre-flotation step follow this.

The AG mill operates in closed circuit with a pebble crushing circuit and primary hydrocyclones. The hydrocyclone overflow product at a particle size distribution of 80 per cent passing around 110 microns (P80 = 110µm) is treated in two vertical ball mills (“Vertimills”) operating in closed circuit with a second bank of hydrocyclones. The overflow from this circuit is treated in a talc pre-flotation step to remove talc and a significant amount of fluorine. The concentrate from this pre-float step is disposed as a final tailing product. The floatation tailings is fed to another stage of hydr ........