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Sources of head grade variation-difference (7 replies)

Alan Carter
10 months ago
Alan Carter 10 months ago

What could be the cause of getting different Head grades from two plants which receives the same Ore type from the same mine? The feed to the plants is only split by time or silo availability.The two plants uses FAG mills in close circuit with a classification screen. The one plant is consistently showing higher feed grades to the primary rougher float than the other. What affect the grade output from a mill?

Dizzy Flores
10 months ago
Dizzy Flores 10 months ago

1. Are there differences in sampling to determine ore grade between the two plants, i.e. is this a quality of measurement issue?

2. Is feed for the two plants pulled from different locations in a common silo/stockpile?

Carmen Ibanz
10 months ago
Carmen Ibanz 10 months ago

1. There is basically no difference in sampling since the samples are not taken manually unless the maybe the preparation which could be different however the consistence seems to be suggesting something else.

2. The feed is pulled from the same stockpile and the same bunker locations from the same mining shafts.

Although it will be difficult to determine if it is quality issue/people, other factors cannot be ruled out as well.

Helena Russell
10 months ago
Helena Russell 10 months ago

Perhaps there is a segregation issue in the stockpile? Is there a noticeable difference in feed size distribution to each train? Is there a grade-by-size relationship?

John Koenig
10 months ago
John Koenig 10 months ago

Some questions:

- Do you look at the difference daily?
- If you plot the difference Stockpile A - Stockpile B; is the difference sometimes positive and sometimes negative OR is it always positive or negative?
- What is size of difference as % of the average metal content?

Need some data to comment on your problem!

Jean Rasczak
10 months ago
Jean Rasczak 10 months ago

I would start by asking how different are they? Marginal or big difference? If its marginal its normal but if the difference is huge it might be one of the following

* haulage is split by time, it’s possible to receive Ore from different stopping areas which suffered different dilution factors

* analysis is done by separate labs for each plant, it’s possible that the equipment in use maybe different in accuracy or the skills of analyst.

Marshal Dienes
10 months ago
Marshal Dienes 10 months ago

We are having segregation issues I guess that is the main factor leading to the difference - there is consistently more coarse material going to the other plant than the other.The difference is similar throughout and positive.

Bill Fraser
10 months ago
Bill Fraser 10 months ago

Of course segregation in stockpile will cause the difference. The line with coarser feed size has less head grade and vice versa. But of course it depends on mineralogy of deposit. It refers to porphyry copper deposits.

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