Geology & GeoMetallurgy

Geology & GeoMetallurgy 2017-04-04T06:58:01+00:00
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Ore Blending (4 replies)

10 months ago
Charlie 10 months ago

Hello guys,

does anybody know what variables are needed/ taken into account to establish an optimum ratio for ore blending? I'm blending two different Pb-Zn ROM samples (low and high grade).

Alex Doll
10 months ago
Alex Doll 10 months ago

The unfortunate answer is to prepare blends that look like what the plant will see, which means doing at least some variability sampling.  If the plant could possibly see 100% of ore One, then 100% of ore Two the next week, then you need to test them separately and find a circuit that works for both.  If the mine promises that you always get a 45%/55% split of ore One/Two, then you can test that blend – if you believe them (hint - don't!).

I worked on a variability program for conceptual design of a Cu/Mo porphyry that involved 150 variability samples (batch-tests, 40% only rougher, 60% rougher & cleaners).  The variability samples were chosen so that the ore grade proportions in the 150 samples matched the histogram of the grade proportions of the orebody.  That means that if 10% of the orebody is 1%-2%Cu, then 15 samples (10%) where 1%-2%Cu, 23% of the orebody was 0.75%-1%Cu, then 35 samples (23%) had that grade range, and so on.

Once the variability suite was done, the results were analysed and the results were grouped into four or five domains – these samples had high Cu grade & recovery; these were medium-grade & poor recovery; and so on.  From these domains, composites were created by mixing the remaining sample of each domain, then the composites were subjected to locked cycle testing and reagent optimization.

Cost of the program was about $5M in drilling to get the proper samples (there was a separate comminution program collected from the same drill core) and about $3M in laboratory work.  This program intended to interpolate flotation recovery into the mine block model, thus the results of the150 samples got passed to the geostatistican.  We could have done the conceptual design with fewer, larger samples (the five domains), but we wouldn't have known what the domains were without the variability work.  You might be able to guess the correct number of domains and what controls the domains (e.g. alteration & lithology) and skip the variability program.

Lymon chibona
10 months ago
Lymon chibona 10 months ago

The best way to handle this is by using the weighted average. Given the grades and tonnage of the two samples, you can work out the ratio which will enable you get the grade you want.

10 months ago
Sudhirkumar 10 months ago

Hi Charlie,

somewhere there is a set of design parameters for the process plant, as to the maximum metal it can recover. As he says the liberation rate and capacity of the mill dictate the maximum mineral feed. Exceed this and you will lose precious metals to tailings. You should do some laboratory test-work to see what the natural extraction rate is, and then feed the ideal mix to the mill. However, life is not quite that easy, you also need to know the rock hardness across the ore types as this can also lead to overfeeding the mill. Ask for advice from the mill senior staff, they've probably already done these tests several times.

Ultimately it comes down to the lowest cost or highest value of product (operating profit) consistent with sustainable mine life. This is something you as the Metallurgist have to work out with the Mining Engineers and Geologists and accountants.

It pretty much has to be a joint effort as each group has their own areas of expertise that often don't overlap very much. The Geologists know what's there, the Mining Engineers know how to get it out of the ground and in what order it will be mined, and the Metallurgists hopefully know how it will process in the plant.

Current economics play a part too. Nobody will admit it but everyone high-grades the pit in poor economic times just to survive, possibly at the expense of long term sustainability.

Sugar Watkins
10 months ago
Sugar Watkins 10 months ago

Are you trying to process "average" quality for process stability, tonnage, etc or are you blending to a target metal throughput or recovery? Take into account tonnes available of each component, grade, mineralogy, process amenability, possibly even hardness - as you don't want different parts of the process working ineffectively. Blending may not be the answer if you have material present that is uneconomic to process, e.g. low grade due to dilution. Maybe upgrade the low grade material first separately using sorting, etc. Use real time on belt elemental and moisture analysis to control blend performance - it is done routinely in cement plants in raw mix applications, copper ore feed to a leach circuit with a metal throughput constraint, and for iron and manganese ores - all in real time.

Usually the blending is done of R.O.M. based on chemical properties. If the subsequent operation is mineral processing (based on physical properties/surface properties) I feel blending does not serve any purpose .When these particles enter the process, each particle is "on its own" and would respond according to its size/shape/specific gravity/surface property. It does not look for its partner with whom we did blending to get an average.

I think is the advise you should review carefully.

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