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Mineralisation

MineralisationThe Buena Vista magnetite deposits formed as the result of metasomatic processes associated with the intrusion of the large Humboldt Gabbro lopolith. As such, they have similarities to the large, high grade magnetite deposits of Kiruna in Sweden and Savage River in Tasmania and are very different to the typical Banded Iron Formation magnetite deposits of Western Australia.

 

There are two significant differences between Buena Vista and the West Australian ores that have a major impact on the downstream processing.

  • The magnetite ore at Buena Vista occurs as high grade pods, veins and disseminations within a heavily altered volcanic rock, now mostly represented by scapolite and hornblende. Grades can be very high, with assays recording iron contents of over 66% Fe. This is in contrast to the Western Australian BIF magnetite deposits which contain a near consistent iron content of around 30 to 35% Fe.
  • Much of the magnetite at Buena Vista is liberated at relatively coarse sizes. This allows for a considerable upgrading by the removal of near barren material during the early stages of processing, reducing costs and allowing lower grade material to be utilised. The BIF magnetite deposits are all fine grained and cannot be upgraded prior to the final fine grinding and magnetic separation.

MineralisationKiruna-type ores typically have high titanium and phosphorus contents. Historical and current metallurgical test work on Buena Vista ore has shown that both are reduced to acceptable levels in the final concentrate.

 

There can be little doubt the magnetite mineralisation is a product of the late stage alteration of the intrusive Humboldt gabbro that gave rise to the intensely scapolitised lithologies. The distribution and nature of the magnetite mineralisation is a function of ground preparation by faulting and fracturing forming a series of conditions varying from open fractures through breccia zones and anastomosing networks of fine fractures into virtually massive material. The relative abundance of these various ground conditions produces the variations in mineralisation types from massive pods through to light disseminations.

 

Hypothetical Sketch Plan – Relationship of Magnetite Mineralisation to Structural Pattern