The Role of Remobilisation in the Formation of Nickel Sulfide Orebodies

The current historically high price of nickel has generated much interest in nickel deposits throughout the world. Consequently, SRK geologists in Australia and Canada have received many requests for work from clients, such as BHP Billiton, Consolidated Minerals, Goldstream Mining, Jubilee Mines and LionOre.

The established genetic models for nickel sulfide orebodies are based on exsolution of iron and nickel sulfides from ultramafic magma with the role of structures confined to controlling channels that localised lava flows. This model is based largely on the sulfides located at the contact of ultramafic rocks with various underlying rock types. But there is more to the story.

We have found that remobilisation was a significant, if not the dominant, process in the formation of many nickel sulfide orebodies, and has typically imparted a strong structural signature to mineralisation. The importance of understanding remobilisation becomes clear when we consider that potential effects can range from in-situ recrystalization, to comprehensive external transfer to form new sulfide deposit at sites distal from the initial accumulation.

Remobilisation may affect:

  • Beneficiation, by changing the mineralogy and smelting characteristics of ores
  • Mining, by dislocating ores and changing the ground conditions
  • Exploration, by relocating deposits

We have identified features that indicate remobilisation at nearly all scales and found that nickel sulfide deposits commonly display a spatial relationship to folds and other ductile structures. Additionally, a pervasive feature of these deposits is tectonic foliations overprinted by sulfides. Many of the deposits we have studied are essentially breccias – rock that has been fractured and later had sulphides deposited along the fractures.

Ore components can travel from centimetres to hundreds of metres or more during remobilisation. Remobilisation over short distances will have very little effect on mining and exploration activities, but movement over hundreds of metres will certainly influence exploration and will require models with a strong structural component. Commonly observed features of many nickel sulfide deposits show that they are not simply magmatic deposits.

By gaining a better understanding of the remobilisation processes involved, we can develop more effective exploration programs.

Toby Davis: tdavis@srk.com.au


 

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