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QA/QC IN MINING REALITY OR FANTASY?
M. Sc. Samuel Canchaya
Exploration Senior Geologist
Cía. de Minas Buenaventura S. A. A. - PERU
Introduction
The importance of SAMPLING is well
understood
All aspire to get QUALITY
QA/QC procedures can help to achieve and control quality
It is good to know that today, QA/QC procedures are widely applied
However, currently these procedures are being applied inappropriately: focused mainly on secondary sampling and analytical procedures, neglecting the primary stage of sampling
Primary Sampling Stage is not only the most important stage, but the main source of errors.
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3
General structure of
sampling errors
GE = Global Error
PSE = Error in the Primary Sampling Stage
SSE = Error in the Secondary Sampling Stage
AE = Analytical Error
Errors aditivity:
PSE >> SSE > EA
GE = PSE + SSE + AE
General structure of sampling errors
Bias % Activity
1000Primary
sampling
50Secundary
sampling
0.1 a 1 Chemical
Analysis
After: Gy (1999:10)
Activity% Relative
error
Sampling 100 a 1,000
Transport and storage1 a 100
Volumen reduction
and comminution10 a 100
Chemical preparation:
digestion and acid
dissolution
5 a 20
Chemical Análisis 0.1 a 5
Compiled after Gy (1999:10); Gy & Francois-Bongarson
(1999) and Paski (2006)
QA/QC
QA/QC
The common practice
of QA/QC
Quality Assurance (QA) means the
set of systematic and preventive
actions to ensure the quality and
reliability in the sample, in order to satisfy optimal quality requirements
Quality Control (QC) is the set of regular activities whose purpose is to ensure that all quality requirements are being met
More widespread action of the QA/QC, is the properly insert of control samples within each sampling batch to be analyzed
Internationally accepted ratio of control samples is about 20 %
5
0
1
2
3
4
5
6
7
8
9
10
0 1 2 3 4 5 6 7 8 9 10
Ma
x
Min
Twin samples
Overall insertion rates of control
samples
6
Sample type %
Twin samples 2
Coarse duplicates 2
Pulp duplicates 2
Low value standards 2
Intermediate value standards 2
High value standards 2
Coarse blanks 2
Pulp blanks 2
Check samples in secondary lab 4
TOTAL: 20
Modified after Simon (2007)
Primary sampling: the most
neglected stage of mining industry
QA/QC procedures are mainly applied to the
stages of chemical analysis and the prior
mechanical preparation
Equipment and chemical analysis are becoming more and more sophisticated, with increasingly powerful processing and better performance. On the contrary, by the side of sampling, it is still difficult to convince managers to approve the purchase of sampling equipment, despite they are less sophisticated and cheaper
The number of publications related to chemical analysis is several times greater than those related to sampling
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…Primary sampling: the most
neglected stage of mining industry
In many countries sample-specific courses are almost non-existent in the universities, while courses in chemical analysis are regular
The staff responsible for chemical analysis are specialists with a high expertise while those in charge of sampling are considered of lower category and usually are not asked for exigent specific qualifications or experience
Labour force involved in sampling are generally frowned upon and belongs the lower scale of salary
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Conclusions:
QA/QC procedures mainly applied to the
phase of chemical analysis and the prior mechanical preparation
Primary stage of sampling is not only important, but it generates the largest proportion of bias and errors
However, primary sampling remains being the most neglected stage of the mining activity
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Recommendations:
Any company, unit of production, exploration
project or prospect should have Sampling Protocols
according to the nature of the targets
Spare no effort or money to achieve representative samples, preserved and unpolluted
Implementation of a Safety Sampling Chain, which distributes and transmits the responsibility for sampling and sample integrity, among all
those involved during the sampling process
Minimize errors in the primary sampling phase, especially: Choosing the most appropriate type of sampling for each case and
circumstance
Selecting optimal sampling grids or sampling distances, using geostatisticalprocedures
Monitoring deviation of holes during drilling
Defining sample weights, volume and particle size of the increments
Homogenising prior to any exercise of volume reduction
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…more Recommendations:
Avoid contamination during all stages of sampling
Control and minimize loss of fines (which often contain precious metals) especially during drilling, washing and cutting of witnesses.
Quantity, weight and grain size of increments of the samples should be determined with specialized procedures
Sampling equipment must meet TOS (Theory of Sampling) specifications
Always use the best equipment and sampling tools; and systematically verify that they are in good condition: “check lists”
Perform surface sampling of rocks and structures using portable diamond blade cutters
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…more Recommendations:
Appropriate scheduling of: Tests of repeatability and reproducibility (R&R)
Sampling annual audits, preferably made by outside companies
Tests of heterogeneity and bias, especially at the beginning of each sampling campaign
Recommended use of: Disposable gloves (specially when using spray paint)
Disposable wipes for cleaning hands and sampling tools
Water sprays instead of brushes to wet cores during logging
Rotary riffles (instead of splitters or quartering blankets)
Sampling stations at minerallurgical flows and belts, must meet TOS specifications and preferably should be installed at the end of the belts
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ERR %
50
30
10
20
40
0
60
…more Recommendations:
Conform Sampling Team with the best and most qualified human resources, with good pay, permanent training and qualification
Implement use of bar code, allowing direct recording of measurements and laboratory data with automated systems
Banish bad practices in the handling of cores, uncovered stacking boxes or walk on them, use a brush to moist them, bad transportation and poor storage, etc.
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Sampling procedures with
portable diamond blade cutters
Traditional way of sampling
Portable cutter
in operation
Portable cutter
Freshly cut slab
of rock
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Recommended tools:
Plattner Mortar
Homogenizer
Water spray
Disposable gloves
Clean hand towels
Not recommended:
Porous gloves
Quartering blanket
Paint brush Splitters
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Rotary riffles: OK
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Reduction of sample
volume:
Method DER Recomendation
Quartering
blankets10 Not recomendable
Splitter 1Only with proper
feed
Rifle 0.1 Good reduction
Relative standard deviation (RED) after Paski (2006)
Quartering blankets
Splitters with feed hopper
Riffle
Storage of cores
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Improper way
Proper way
