LETTERS TO THE EDITOR — Non-destructive evaluations can

Further to the letter by Christopher Jennings on the problems inherent in acquiring diamond counts from samples (T.N.M., Aug. 8/94), I would like to suggest that there is indeed a way to quantify the amount of breakage in the crushing and milling samples: through the use of non-destructive evaluations.

By using a non-destructive method of characterizing the diamonds in situ, accurate estimates of macrodiamonds and microdiamonds can be made. The methodology I refer to utilizes CT X-ray scans and 3-dimensional visualizations. The data are acquired in a non-destructive and non-invasive way through the use of industrial X-ray scanners.

It is a technique that measures density distributions in materials by the attenuation of X-rays through matter. This is a well-established technique which is similar to conventional medical scanning but which utilizes higher energy levels and produces images of finer resolution. CT scanning can provide information about the internal structure and characteristics of virtually any material at resolutions in millimetres or even tens of microns. The data can be obtained as either a single “slice” through the sample or as a series of contiguous slices that can generate a volume data set. In this case, 3-dimensional volume visualization techniques can be used to quantify and describe the sample as it exists in its natural state without physically disturbing it.

What this means is that diamonds can be observed and measured in situ. They can be located and examined in the context of their size, morphology, relationship to other diamonds and minerals and their spatial distribution in a sample. In effect, this type of investigation can be used for a variety of purposes. It can provide valuable geological information about diamond emplacement, as well as accurate size distributions for the purposes of assessing grade. It can also be used in the evaluation of crushing and milling techniques.

Non-destructive evaluation has been successfully performed on diamond-bearing rocks. It is a viable, useful methodology that, given the inherent problems in diamond assessment, should be given serious consideration. Diana Wiese, President

MDC Geological Consultants, Toronto