Mt Keith: a different recollection
12 November 2007
Letter to the editor
I HAVE just finished reading the most recent edition of HighGrade. Enjoyed it a lot, thanks.
In the cover story article “Tunnel Vision” you have quoted an unnamed source, presumably associated with WMC regarding Mt Keith and its early problems.
The source claims that Mt Keith was run at 50% recovery for the first 10 years (against target 75%), because idiot management made an assumption about the orebody being homogenous. They also say that geologists were excluded one way or another and that the alteration pattern that they knew all about was to blame for poor metallurgical recoveries.
I worked at Mt Keith as a geologist from 2000 – 2001 and was involved in the expansion drilling program as well as day to day grade control.
I suggest the postulation that Mt Keith was run at recoveries of 50% for the first 10 years is incorrect. Production of nickel concentrate began in 1994, which was six years before my time. Whilst I was there recoveries were reported in daily pre-shift instruction meetings routinely between high 60’s and low 70’s per cent – well above 50%, and had been for some time before I arrived. It is true that Mt Keith had a low recovery of nickel, but I’d say that whoever your source is was never as close to production as a graduate geologist from the comments they have made. The target was missed by 2-3%, not 25%.
As for complexity of the orebody and over printing alteration, it was very well understood at the time I was there. I have included a brief discussion of the relevant points below.
A PhD study was completed 1998 (By Leif Rodsjo at UWA) detailing the alteration patterns. The alteration (along with lithology, mineralisation, structure, etc) was logged in all exploratory holes, grade control holes and blast holes. I undertook a complete reinterpretation of the deposit – based on 14km of drilling I executed – including lithology, mineralisation, alteration and structure. My own Honours thesis was on the structural geology of the Mt Keith ultramafic complex and this relates very closely to the alteration pattern. The metallurgists were communicated with on a daily basis about the qualities of the ore packages they could expect to see at the mill, in fact the feeding regime was done by building blended stockpiles that were campaign fed to the mill, and each blended stockpile was described for it’s geological (and hence metallurgical properties). So I’m afraid the statement about “geologists were never consulted” is quite wrong. They were paraded in front of the metallurgy manager and mill superintendent every day, often in the company of the general manager.
The two aspects that caused problems at Mt Keith were the talc alteration that overprinted the deposit. Talc interferes with the flotation process so decreases nickel recovery at the concentrator. We were well aware of this and managed the amounts of talc rich ore going to the mill. It was only ever fed to the mill at elevated levels during times when severe weather events combined with long-term planning crises. In fact WMC spent vast amounts of money doing separate XRD analyses to accurately quantify the amount of talc in each and every sample, which was then block modelled.
The other aspect is the super fine grained nickel sulphide that was produced during the hydrothermal event. Significant nickel is tied up in the original rock (in sulphides). When fluids percolated through the rocks it contained sulphur, and liberated nickel from the rock. In effect there are three kinds of nickel now: primary sulphide, secondary sulphide and non-sulphide nickel. Recovery of nickel will be influenced by the proportions of each. Primary sulphide is course and most drops out in the concentrator. Secondary sulphides are fine and are hard to recover, but are generally taken out efficiently. Non-sulphide nickel is impossible to recover via flotation. Non-sulphide nickel was measured in every sample at the on-site lab, and was also modelled, and a rough inference could be made of the primary/secondary abundance. Between talc and non-sulphide nickel estimates in the block model, the recovery could be virtually modelled in 3D.
So it is ironic that the contact (who professes to understand the geology) alleges that head office was ignorant of the geological complexities. If geologists knew all about the alteration pattern (this much is true, as the source states) I’d like to know how they knew that so well without having logged the hundreds of kilometres of core. I’d say that person was ignorant of the way technical staff on site handled the problem, and sounds like they were from head office. I don’t think WMC would have persevered for so long (10 years) getting two-thirds of their planned revenue. The nickel price wasn’t that good.
It is true that the operation struggled to make the process come together, but that process took a very few years. In fact several initiatives took recovery of talc rich material above what they ought to have been through chemical additions and clever work with cyclones and gravity separation.
The article was about the inexperience of managers in some new companies and reasons for company failures. It concludes pointing out the benefits of risk being spread over several projects, which is most correct. The comment from the source regarding Mt Keith was intended to ram home this point and it did, but using totally inaccurate facts.
Maybe the point that needs to be made is that financially Mt Keith would possibly have been marginal (certainly not a failure). The main reason it could not succeed as a single operation in any company (and had always to be combined with another nickel mine) is the Fe-Mg ratio of the concentrate. The con on its own would need to be run through a very hot smelter, so to combat this it always needed to be combined with Perseverance ore.
I don’t mean to sound indignant or pernickety, but I feel you have been misled.
Name and address withheld.
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