Geology & GeoMetallurgy

Geology & GeoMetallurgy 2017-04-04T06:58:01+00:00
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Difference between delimitation and extraction (4 replies)

Paul Morrow
1 year ago
Paul Morrow 1 year ago

I would like to understand the differences between delimitation and extraction errors because many times i think the sample suffered from both. What circumstances do you have both or either error?

Bill Rico
1 year ago
Bill Rico 1 year ago

IF/WHEN your sampling system (sampling tool) does not delineate EXACTLY the same volume of the process stream (identical arguments for sampling a stationary lot), successive increments/samples will not represent a fully comparable volume/mass, and your sampling process is now suffering from an IDE.

Irrespective hereof, IF/WHEN your sampling tool is not able ALWAYS to extract from this volume (+/- IDE) ABSOLUTELY ALL of the delineated material; your sampling process is now under also influenced by an IEE.

As we all know: It is all about eliminating the incorrect sampling errors already in the design of the sampling system (or LIVE WITH THE FATAL SAMPLING BIAS). You are right, OFTEN (but not universally) IDE and IEE are coupled (really lousy systems, right?). The most exhaustive analysis of IDE/IEE is found in Francis Pitard's book which is strongly recommended (as is his upcoming CSM course) - ENJOY BOTH, or at the very least the former 😉

OberstGruppen
1 year ago
OberstGruppen 1 year ago

Theoretically correct profile of the sample cut from the sampling target is defined in Theory of Sampling (TOS). e.g., if the sample is cut from a process stream the correct shape of the sample is a slice with constant thickness through the process stream. If the profile of the intended sample cut deviates from the correct one a sample delimitation error (DE) results. Sample extraction error (SE) error results if the sample cutter cannot extract the intended profile from the target. e.g. if you are using a sample cutter with parallel cutter blades moving at constant speed across the process stream the intended profile is correct and, consequently, the DE is eliminated, but if the opening of the sample cutter is 10 mm but largest fragments in the material sample are 15 mm, the sample cutter cannot extract the large particles and a sample extraction error is made. TOS defines the minimum aperture vs. cutting speed of the sample cutter to eliminate the extraction error.

Paul Morrow
1 year ago
Paul Morrow 1 year ago

I am really thankful to you for your advice and i greatly appreciate your efforts. Please help me with papers dealing on firstly the above and secondly on bias, reproducibility and representativeness showing calculations of descriptive statistics of sampling error.

Bill Rico
1 year ago
Bill Rico 1 year ago

It is always nice if/when a procedure is available, which results in a valid estimate of the Total Sampling Error. Such a procedure is actually easy to set up, but one would likely have to know enough about the Theory of Sampling (TOS) in order to eliminate the Incorrect Sampling Errors (ISE) - since most of the time TSE will be too big. The following is the most compact answer to your queries, a new international standard on representative sampling: DS 3077 (2013) - a very good place to start. You'll find it here: http://is.gd/VyRGjc

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