moises casusol
TRANSCRIPT
Ore sampling and sample preparation
techniques; how will they affect precision
in the laboratory?
Moisés Casusol
Anachemia Science
Introduction
Mining operations utilize specific sampling protocols to obtain representative
samples for the accurate estimation of ore mineralization and ore control
purposes. Usually blast-hole samples are homogenized in the field to the same
extent as the sample pulps are blended in the analytical laboratory.
The samples obtained are submitted and assayed by the primary laboratory.
Blind standard samples and Blanks are included in each sample set. Field
Duplicates are very useful.
This study discusses field sampling and sample preparation techniques as key
factor in achieving accurate and representative final assay results. The study
concludes with the feasibility of improvements in field sampling and sample
preparation techniques and ultimate laboratory precision.
Methodology
Copper, Zinc and Molybdenum assays were collected for this study. Remarkably,
the investigation was performed in every stage of the mining operation that has
a direct impact on the money makers elements for this mine.
The first component is the variance of the random variability that does not exist
in the field; it is artificially created and introduced by the selected observation
module mass, assaying mass, and sampling. This is the component that must be
minimized when sampling blast-hole.
The second component is the variance in the field that must be thoroughly
understood to perform effective grade control. The dependence between
measurements Xi and Xj must be measured with the best precision and
accuracy as possible.
n
i
n
j ji E x x
nn 1 12
2
2,cov
1
Methodology (2)
We can express the random variability (RV) as a function of every single stage as
follow:
Our project consists of sampling evaluation, sample preparation and analytical
laboratory assessment. In terms of variance, all of them were used to measure
an find out the biggest contributors for total measurements uncertainty.
2222222222
Le ExV B IL Is An sp s RV
Methodology (3)
Pulp samples, randomly selected and weighed twice in the same batch of
samples.
The material was from the mine, so the mineral matrix match with daily
samples. Concentration of copper, zinc and molybdenum were spread close to
the cut-off, medium and high grade for copper.
Laboratory Replicates
2222
ExV Is LR
Reference Materials
22222222
Le ExV B Il Is An RM
Methodology (4)
Since, we are focus on identifying proportion of each contributor of variance to
the total concentration measurement, the following formula has been used to
estimate the variance at the sampling stage.
Variance introduced at Sampling
222
LR fd sp
Then,
2
s
22
RM sp
=
=
Results
Variance introduced at sample preparation facility has been calculated, in this case 0.00940 represents
37.2% of the total variance. Reference material identified that error introduced in the analytical laboratory is
equal to 0.00255 (variance) which means 10.1% of the total variance. The variance introduced by sampling
is equal to 0.01331 (variance), it represents the biggest contribution (52.7%) to the total variance. This
demonstrates that blast-hole sampling is not working well enough in favour of this analysis.
Copper
Then,
Results
Variance introduced at sample preparation facility has been calculated, in this case 0.03330 represents
60.2% of the total variance. Reference material identified that error introduced in the analytical laboratory
is equal to 0.001187 (variance) which means 2.2% of the total variance. The error introduced by sampling, is
equal to 0.02079 which represents the second biggest contribution to the whole process. Sample
preparation facility, including the sample preparation protocol must be reviewed for its performance.
Zinc
Then,
Results
Variance introduced at sample preparation facility has been calculated, in this case 0.01878 represents
59.6% of the total variance. Reference material identified that error introduced in the analytical laboratory
is equal to 0.00191 (variance) which means 6.1% of the total variance. The error introduced by sampling, is
equal to 0.01081 (variance) which represents 34.3% of the total variance.
Molybdenum
Then,
Conclusions
The actual blast-hole sampling introduces 34% to 53% of the total variation of the Cu, Zn and Mo
measurements.
Blast-hole sampling cannot provide representative samples. The economic impact of such
shortcoming is vastly under-estimated. Reverse Circulation drilling alternative presents many
advantages that may far outweigh its additional, visible cost.
The sample preparation facility and protocols must be closely supervised by senior supervisor or the
accountable person for such important task. Sample preparation introduced, in this study, 30% to
60% of the total variance. It is mandatory to focus on this area to train and supervise operators well.
Analytical laboratories have many small tasks as well as error sources, keeping it under control will
give the best opportunity to evaluate grade control at the mine, mill and the final bulk concentrates.
ISO 17025 is strongly recommended. It is mandatory that external comparison must be done on a
regular basis with competent (accredited) laboratories.
Finally, this methodology provides a powerful tool to identify the biggest contributor of error.
Therefore, the improvement process will focus towards the best direction.
Muchas gracias
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