The Broken Hill deposit lies within the Broken Hill Group of the Palaeoproterozoic Willyama Supergroup and consists of nine separate but closely related orebodies that are stacked within a single stratigraphic package in the Hores Gneiss of the Broken Hill Group.

The impression that the Broken Hill orebodies are all massive sulphides with little else has long been dispelled.

Not only can different styles of mineralisation be identified but the information also gives valuable insights into the ways the deposit has responded to deformation and also to the predeformation characteristics of the deposit and therefore its genesis.

Massive sulphides form only a minor part of each orebody and are most common in deformed regions of the lenses. Sulphide-rich mineralisation is more often coarsely banded by variations in gangue mineral and sulphide abundance. Each orebody contains a high percentage of gangue minerals, including primary calcite, calcium or manganese pyroxenoids or pyroxenes, or quartz, that are distributed through the mineralisation as discrete bands, layers and stratigraphic horizons. Sphalerite (marrnatite) is the dominant sulphide constituent of all ore lenses and the percentage of galena diminishes in each orebody from 3L to BL.

Perilya has introduced significant changes and improvements in the operations at Broken Hill. An underground equipment replacement program has resulted in improved productivity, while the concentrator was simplified to improve recoveries and concentrate quality.

Mining is principally conducted using a longhole open stope method with variations developed for extraction of the secondary resource located in the previously worked pillars area.

Longhole stoping currently accounts for 70 per cent of underground production, with pillar extraction and development ore contributing approximately 30 per cent of the total. The ventilation system comprises ten ventilation shafts with three surface exhaust fans and one surface intake fan.

The Broken Hill silver-lead-zinc ores are probably the most famous in Australia, and have particular significance in mineral processing as it is these sulphide ores which provided the impetus (in the early part of last century) to develop an industrial flotation practice.

Perilya’s Broken Hill concentrator (known as NBHC in earlier times) is described elsewhere. All three parallel lines are identical, with the following configuration. Ore from the fine ore bin feeds a rod mill. The rod mill discharge flows in to a sump where it combines with the primary ball mill discharge, and is pumped to the primary cyclone bank. The primary cyclone underflow feeds the primary ball mill, and the overflow gravity feeds to the lead primary rougher flotation cells.