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Core Samples Preparation (13 replies)

Bill Rico
8 months ago
Bill Rico 8 months ago

Is that correct using two types sampling method in core preparation samples (half core & Coning/quartering)

8 months ago
Oberfuhrer 8 months ago

I think both methods are ok but that depends on what type of drilling method you opted viz. core or non-core. I think in core drilling for metal, half core would solve the purpose where as in case of non- core you can go for coning/quartering. Reason being doing this to have a duplicate of the same for preservation and would solve the problem if raises tomorrow. However i also have seen to send the quarter core to the lab for analysis. But in case of core drilling in coal, in India we are practicing to send the full core to the lab.

Maya Rothman
8 months ago
Maya Rothman 8 months ago

Coning quartering is to be avoided completely; it is an outdated technique for splitting the samples. You can use a simple splitter which is available in the market; an example can be seen at the following link http://is.gd/O5mcDm. Always preferable to crush the entire core and then divide using splitter, however the usual practice is that they split the core and then crush only one portion of it.

8 months ago
Sudhirkumar 8 months ago

Though I agree by crushing the whole core the sample will be more representative, crushing the whole core should be avoided for the purposes of transparency. By keeping a half core as it came from the core barrel any consultant or QA/QC representative will understand the style and structure of the mineralization being sampled. Photographs will not do, as these could have been taken of any core! To resolve the issue where the whole core does have to be crushed an independent report should be produced verifying the photographs and sampling sites.

Marshal Dienes
8 months ago
Marshal Dienes 8 months ago

Avoid coning/quartering, this is an obsolete technique. The coning/quartering can produce large errors, in a test with 30 cones, the differences between opposite quarters is 35% approximately, Copper mineralization in a porphyry. It is best to use a riffle or better yet, a rotary splitter.

8 months ago
Standartenfurer 8 months ago

I agreed. Core photos cannot be authentic as far as QA/QC is concerned. Half core or quarter core gives the true picture of the geology of the area. Half core is sent to the lab for the appropriate analysis and then quarter core can be used as the Duplicate, though there is always biasness.

David Kano
8 months ago
David Kano 8 months ago

Besides photography, there are other advantages to keeping a half core. The flat surface allows instant measurements such as portable XRF analyses - we are doing this right now - and no doubt that the fast progress of automated imagery will soon provide geologists with new data.

XRF data, even if it is difficult to obtain absolute precision results, provide fine details on the variations of many elements of interest: ore elements, indicator traces and major elements for facies identification.

Sugar Watkins
8 months ago
Sugar Watkins 8 months ago

Today we use a half core for sample prep to chemical analysis. Sample prep procedure: Primary crusher, the whole sample (half core) to -1/4". Secondary crusher, the whole sample -1/4" to -2mm. Rotary Sample Divider, 1Kg to pulverize -150# Tyler. This the standard procedure for porphyry copper.

Sachin Prakash
8 months ago
Sachin Prakash 8 months ago

It is a good practise to keep the remaining half core since it will be very useful for future reference.

8 months ago
Obersturmbann 8 months ago

I tend to come across core plugs quite often, drilled perpendicular to the core length. One or more can be taken from around the circumference and along the length. Crush rotary riffle and analyze separately for a "map" of heterogeneity in the whole core, or combine, crush, and rotary riffle for a representative sample of the whole. I've even seen four eighths taken (three perpendicular cuts, take opposites and combine) instead of a straight half.

Marshal Meru
8 months ago
Marshal Meru 8 months ago

All we are trying to do is to reduce the error margin. If were to put ourselves in a scenario where there will be no qa/qc team or auditors (not realistic though), crushing whole core or a quarter or half would be determined by applying the sampling formulas and chronograph to determine the minimum weight of the sample to be taken for crushing. Rule of thumb would be to take more sample for precious metals with high variance, thus whole core in this scenario and even down to a quarter for iron deposits, but deleterious elements in these high percentage ores is also a drawback to reducing the sample simply because of the element of interest.

In my opinion, quartering should never be mentioned for any project; 35% difference and this can even be much more. Riffle splitters currently exist anywhere.

Bob Mathias
8 months ago
Bob Mathias 8 months ago

One question from a novice in this area - why are the 2 halves of a core likely to be similar given the nugget effect?

8 months ago
Sturmbann 8 months ago

There is a chalk and cheese element here. Cone & quartering would be used to winow down a large sample to a manageable size. Say down to the size for a 'Jone' splitter. Coning and piling must be done a lot to get anything approaching an acceptable 'mix'. In general I would avoid cone & quarter if any alternative is available. Core typically isn’t nearly as large. Cutting cut is preferable to splitting as no preference in volume results from cutting. I have always thought people who consumed the whole core were hiding something.

Dizzy Flores
8 months ago
Dizzy Flores 8 months ago

The first question I ask myself is what is the purpose for the task you want to undertake and assess the risks of performing the task? Your major constraint will be money and resources available.

For resource estimation to comply with resource/reserve codes and feasibility studies the first requirement is that the sample & all sub-samples in the sampling chain are representative of the population of the commodity of interest in the ground. If it is highly variable like gold (especially presence coarse gold) larger diameter cores will give a more representative sample than smaller diameter core. For less variable commodities such as coal or iron ore, smaller diameter core maybe adequate unless trace elements are of interest.

A hole may be "twinned" by drilling an adjacent hole nearby to demonstrate how representative. A different, more expensive drilling technique (diamond core) maybe used to "twin" less expensive RC which may be biased by lower sample recovery or contamination or to determine close range structures for variographic modelling.

Preparing sub-samples of full core will give a more representative sample than a half core. I recommend cutting core that bisects the mineralised structure if half core is to be sampled. If the distribution of mineralisation is erratic best to sample full core rather than half core. High resolution digital cameras can take high quality core photographs that can be enlarged and geo-referenced to core traces. I do not see essential to keep all half core provided it is photographed and logged carefully in detail. Hand held XRF analysis of prepared pulps will give a more representative estimate than half core as suggested by Bruno, unless niche sampling or quick preliminary result is required.

It is common for quarter core be taken as a "duplicate" of half core. I do not normally recommend this practice as the samples are not of the same "support" (shape and volume); the quarter core will have a higher variance. Duplicate samples should be submitted to a laboratory as paired samples so that both samples are treated identically to minimise time based errors. Technically twinned holes and duplicates of half core are not regarded as true duplicate samples as there is a spatial separation. At best submitting duplicate half cores, is a proxy for duplicate samples to estimate the precision so you can tick a box in your QA list.

Sampling of particulate samples Gy sampling rules should apply to minimise sampling bias. Riffle & rotary dividors should be considered and cone and quartering a last resort.

Sample preparation of "Nuggety" samples: dispelling some myths about sample size and sampling error. Smee, B.W &Stanely, C.R Explore No 126 p21-26 &

USEB Guidance for obtaining representative laboratory analytical subsamples from particulate laboratory samples by Gerlachetc for some readable details on Gy's method of sampling.