CMKX: Excellent article on sampling results.
What follows is an excellent article regarding bulk sampling, which follows up on my post last night regarding the Kensington/Debeers find. The article begins stating that the initial test drilling and evaluating the kimerlite in a region are the key first steps in this scientific process. This is a step by step process. Test drilling IS NOT going to result in report of a treasure chest of diamonds. Microdiamonds such as we found will result, as well as a geologic study of the kimberlite being tested.
Based on the evaluation of our first drilling and the results of a very impressive survey, I am looking forward to Mark Hutchison speaking to the value of our claims. That along with knowing the O/S and tradable float, will allow the market to determine the appropriate pps based on these and other factors.
Again, note the tonnage sampled in the Debeers/Kensington find. Now look at Shore Gold's 2 latest press releases. In June, 4,913 tonnes of dry kimberlite were tested in their find of 344 carats. This month they report 111 carats from 1,605 tonnes of dry kimberlite. Ours was a test hole of 80 lbs. I look forward to the day a targeted test site based on our recent survey is a candidate for bulk mining. So in tempering the discussion so emotions don't flare up again and again, test sampling is just that. Moving forward to bulk sampling a promising area is one of many things in the near future that makes this company exciting.
The article I read is long. I am taking an excerpt from it to repost here. Keep in mind the tonnage sampled in the above mentioned finds as you read the information below. We're on the ground floor of something that has a lot of promise. Be well, Bo
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The only way to get a definitive answer is to collect a "bulk sample" of 10 to 100 tonnes, for example, and process the sample to recover macrodiamonds (>0.4 mm in size). Usually sample processing is done via a dense medium separation plant (DMS or HMS), jig or diamond pan.
An example of a mobile exploration HMS MkIII commonly used in exploration and prospect testing in Australia is shown in the photo on the left. The plant has a HMS cyclone capacity of about 7 tonnes per hour which gives the plant a feed capacity of about 20 tonnes per hour (depending on the type of feed to the plant). New technological developments by Gekko Systems using an In-Line Pressure Jig can substantially increase the capacity of these small plants to approach production scale capacities.
Grade Estimation
The estimation of diamond grade is the process of determining the average weight of diamonds per unit mass or volume of source rock. The diamond weight is a function of the number of the number of diamonds and the size of these diamonds. The average or mean stone size of recovered diamonds is obtained by dividing the total carats by the number of diamonds. Grade can be expressed as;
Grade = diamond weight (carats) / sample weight (tonnes) or volume (m3),
and diamond weight = number of diamonds x mean stone size.
The diamonds recovered from sampling are weighed and the weight used to calculate the grade in carats per unit volume or mass (carats per cubic metre, ct/m3, or carats per tonne, ct/t). One metric carat is equivalent to 0.2 grams. The problem involved with diamond grade estimation is due to the typically small number of (usually small) particles per unit volume (or mass). It is basically a sampling problem where the larger the sample, the better is the grade estimate - but the higher the cost. A balance must be struck between the cost of the sample collection and processing, and the accuracy of the resulting estimate.
The preferred size of the sample can be estimated by statistics. A sample size that returns about thirty diamonds (or "stones") will give a "statistically significant" result but this may be impractical at the early stages of an evaluation program. In a preliminary sampling program, where there is no past data on the grade of the deposit, a useful starting point could be to use the world average for commercial diamond mining operations (Bliss 1992) as follows;
- average grade of 50 carats per hundred tonnes (cpht),
- average diamond size of 0.1 carats per stone (ct/st) and
- average diamond value of 50 US$/ct.
With this first ‘guesstimate’ of the diamond grade and size, the number of stones per unit volume (or mass), the "stone density" in stones per cubic metre (st/m3) or stones per tonne (st/t), can be calculated. Using the relationship above and the worlds average data, then the following can be derived;
Stone Density = (Grade / Av Stone Size) per unit volume or mass,
therefore if the Grade = 50 cpht = 0.5 carats per tonne (ct/t),
and the Mean Stone Size = 0.1 ct/st,
then the Stone Density = 0.5 / 0.1 = 5 stones per tonne.
The results indicate that on average, in the above example, 5 diamonds should be recovered from each tonne of processed source rock. To recover 30 diamonds we would therefore have to process 6 tonnes of source rock.
Typically, a deposit with a high stone density will be easier to evaluate than a deposit with a low stone density because the sample size required to recover a significant number of stones will be smaller. At the very high grade Argyle Mine in Western Australia, where the mean stone size is small (» 0.08 ct/st) (Atkinson et al 1984) and the stone density is high (» 60 st/t), samples of only one tonne were more than adequate to obtain an initial grade estimate.
The number of diamonds recovered from a sample will also depend upon the smallest size of particle recovered. In pipe evaluation, the macrodiamond is usually considered to be of a commercial size, ie. greater than about 0.5 mm, and below this size the diamonds are considered microdiamonds and are not usually recovered during commercial mining operations, except in the Sakha (Yakutia - Russian Federation) diamond mining operations. However many exploration companies use different definitions of what is a macrodiamond or microdiamond and care should be exercised in using this term; unless it is clearly defined. Australian and North American exploration companies usually use the term microdiamonds for diamonds less than 0.4 or 0.5 mm in size and usually recovered during early stages of an exploration program.
In primary diamond deposits, the number of in-situ diamond particles will usually increase, as the diamond size gets smaller. Diamond size distributions tend to follow a lognormal distribution. This means that the stone density, i.e. the recovered number of diamonds, is also a function of the recovered size range. The remainder of this discussion will focus on grades using the macrodiamond (greater than 0.5 mm) population. The relationship between microdiamonds and macrodiamonds have been discussed by a number of authors; eg. Deakin and Boxer 1989, etc.
AI
