Processing techniques used at Glebe Mines

Currently the Company extract and process some 350-400,000 tonnes per annum to produce around 50,000 tonnes per annum of "Acid Grade" fluorspar. By-products from this process include approximately 10,000 tonnes of barytes, 1,000 tonnes of lead concentrate, 120,000 tonnes of limestone aggregate, sand and clay products.

The mill operates on a continuous shift basis for approximately 180 days a year in scheduled in campaigns.

The central blending and reserve stockpile receives ore deliveries by road during the week.

Close manual sampling of individual loads together with rapid determination of grade is necessary to maintain control of ore quality. The standard method of ore analysis is by neutron activation, which determines fluorspar, barytes and silica contents separately. A typical mill feed would contain 27-32% fluorspar (CaF2), 10-12% Barytes (BaSO4) and up to 1% galena (PbS); the remainder being "waste" limestone, some clay and other minerals.


These minerals are finely intergrown within the ore and the purpose of the Cavendish Mill process is to first liberate the constituents and then to separate out concentrates of fluorspar, barytes and galena in a high quality saleable form.

The crushing and grinding process releases from the ore the discrete particles of single minerals before separation.  The different hardnessand densities of the various minerals assist the process.

Ore processing involves five main operations comprising:

• Crushing and washing to reduce the maximum size of the ore to 18mm and remove the very fine clay-like material.
  
• Heavy Media Separation (a pre-concentration stage) exploits the differences in relative density between the minerals in order to discard as much of the clean limestone as possible.
  
• Grinding which “liberates” valuable mineral from unwanted “gangue”. The aim is a particle size where each individual is either mineral or gangue and is also a suitable size for flotation.
  
• Froth flotation is the process where reagents are added to the pulp and the mineral particles selectively become water repellent. In this way they attach to the surface of bubbles produced in the cell and float to the top. Unwanted gangue remains in the water and therefore the minerals become separated and concentrated. Further material treatment removes the barytes from the fluorspar circuit.  The flotation circuit produces waste which is pumped pumped into the tailings lagoon as a suspension of between 5-6% solids. 
  
• The thickening and filtering processes produce filtercake. Most of the acid grade fluorspar filtercake is supplied to INEOS Fluor as a dried powder and therefore requires a further drying stage.    A small amount of material is also dried and sold in bags.