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timboz

183 Posts.

6

09/08/15

21:09

Post #: 15776080
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Originally posted by timboz ↑

Ozblue,

I'll try and clarify it for you.

1.
The primary ore, containing the majority of the cobalt (some is in chalcocite ore) is
made up of two minerals; chalcopyrite which contains the copper, and pyrite which
contains the cobalt. Some of the cobalt is 'free' (outside the pyrite) in the associated rock.

2.
You are correct re the 467ppm globally but the 750 ppm is not as high as it first may seem. Imagine you had a lump of one tonne of 50% chalcopyrite/50% pyrite that graded our global average of 467ppm. Now we know there is no cobalt in the chalcopyrite so our 467ppm is contained in just 0.5 tonnes so our pyrite contains twice that per tonne = 934ppm. I won't do the maths but this effect holds true if our 'lump'
is 1% CHY and 1% PY also.

3.
The ore has been drilled very tightly, both the resource drilling and more importantly the grade control drilling. They assay those holes (5m deep) so know 'exactly' how much copper gold and cobalt is in each block of 5m cubed. You can of course computer log which ore goes where so you you know its grades before it is fed into the plant. Now we are only considering cobalt so our ore has been through all relevant processes except the very last - cobalt flotation. The pyrite is not collected in the copper flotation
as it is chemically suppressed . So at the end of copper flotation there is a slurry of ground pyrite and waste which can be assayed for cobalt. If the batch has enough cobalt they may know that it is valuable enough to make a profit on. (note that I'm not saying that it is profitable but just that it may be produced at a grade that could be)
Certainly it may be produced above 5600ppm (at the expense of 'losing' lower grade cobalt - we can't sell all (any?) of it profitably).

4.
So our high grade pyrite comes into the cobalt flotation circuit. Lets say what comes in
is 1000ppm and it produces a concentrate grade of 8000ppm. Clearly the pyrite containing the cobalt has been concentrated by 8 times but surprisingly we cant say that. Why? Because we need to consider how much of the available cobalt is captured (ie recovery). NAGROM testing showed recovery of 90% so our concentrate is missing 10% of the cobalt that passed through the float cells. There should have been 8000ppm/0.9recovery =8888ppm at 100% recovery(also 100% pyrite). This means our pyrite we fed in was 1000/8888 ppm = 11.25% pyrite mineral and 88.75% waste. It has been concentrated to 84%* (see lower down) pyrite in concentrate/11.25% pyrite in infeed = x 7.47 Now the tricky bit. We need to go through sulphur to get to cobalt. Cudeco have quoted 49% sulphur in concentrate (which will vary up or down a bit but we'll use it for a average). I'm not sure how good your chemistry is so I'll work through it. The sulphur is present in the pyrite, FeS2. That is there are 2 sulphur atoms for each iron (Fe) atom. Now iron in pyrite makes up 41.7% of one tonne and sulphur makes up 58.3% of the tonne of pure pyrite. As we are using a 49% sulphur content per tonne our collected cobalt concentrate so it can't be 100% pyrite otherwise it would be 58.3% pyrite. Therefore our cobalt concentrate is 49/58.3 = 84% pyrite. If we concentrated our infeed by x 7.47 then we should have a concentrate of 7.47 x 1000 = 7470ppm. We have 8000ppm so where is the missing 530ppm? It is found as free cobalt sulphide in some of the 16% of the concentrate that is 'waste' rock (remember back at point 1.)

In fact the maths is a whole lot more complicated and involves calculus but this will in in the +/- 10% accuracy range.

I hope this clarifies Oz.

Regards, Timboz

Expand

Hi All,

Just to add some weight to what I have been drawing attention to above - ie high grading cobalt. This is direct from page 3 of the 2013 JORC resource:

"The resources have been estimated within defined mineralisation wireframes domains based on geology and copper and cobalt grade envelopes."

I'm taking this to mean they have guidance to high-grade cobalt and they are (or were) intending to do this. (sorry about the font, it came through with the paste).
Spoiler, "copper and cobalt" may mean combined rather than separate.???

Food for thought!

Regards, Timboz

CDU Price at posting: $1.11 Sentiment: Hold Disclosure: Held
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