Diamond Sampling for Success

The heavy mineral fraction may be subject to magnetic separation prior to binocular microscope examination for the selection of the diamond indicator mineral suite.

Stage crushing to desegregate the sample is more desirable than crushing and attrition. Stage crushing tends to yield a higher proportion of intact mineral grains (rather than abundant grain fragments) and reduces the chance of producing clusters of grains of similar composition on interpretative plots.

Sediment/Till
Most companies exploring properties prefer to field screen their samples prior to sending them to SGS Minerals Services for final concentration and diamond indicator mineral selection. Minerals comprising the diamond indicator mineral suite rapidly decompose in arid or tropical environments. As a result, unprocessed field samples should be 50-100 kg in size. Field screening on a 2 mm screen will reduce the volume of the field sample and reduce transportation costs related to shipping the product for further processing. In temperate to northern climatic conditions, the maximum sample size generally is on the order of 20-25 kg for stream sediment or till samples.

In the SGS Minerals Services laboratories, a heavy mineral concentrate will be produced through a combination of wet screening (20, 35 and 60 or 80 mesh), Wilfley table jigging and heavy liquid concentration at a density of 3.1 g/cc. Diamond indicator mineral selection is performed using a binocular microscope in the manner prescribed for selecting indicator minerals from concentrates produced from rock. Indicator minerals can be pre-screened prior to electron microprobe analysis using a scanning electron microscope SEM fitted with an energy dispersive X-ray analyser

If possible, several samples should be collected on the targeted body with sample sites evenly distributed on a sampling grid. First pass sampling should involve the collection of at least two 24-kg samples. Dykes commonly are zoned with a fine-grained, macrocryst-poor marginal phase flanking a coarser grained macrocryst-rich core zone. Each zone should be sampled separately as diamond will be preferentially concentrated in the core zone.

Diamond descriptions are reported by “root-2’ sieve sizes (0.105, 0.212, 0.300,0.435, 0.600, 0.750, 0.850, 1.18, 1.70, 2.36, 3.35, 4.75 mm, etc.) according to new industry standards.

MICROPROBE ANALYSIS AND MINERAL CHEMISTRY INTERPRETATION
The diamond indicator mineral chemistry should be evaluated in conjunction with microdiamond evaluations. It is recommended that 50-100 grains each of chromite, pyrope and eclogitic garnet, ilmenite and Cr-diopside be sent for microprobe analysis per sampled lithology. This number of grains will ensure that a preliminary evaluation of the mineral chemistry has been performed with a reasonable degree of confidence.

SINGLE PYROXENE GEOTHERMOBAROMETRY
Further assessment of diamond potential can be made by calculating the local geotherm using the single clinopyroxene method of Nimis and Taylor (2000) and as few as 25-30 grains of Cr-diopside. The method can help to assess whether the host intrusive has erupted from within the diamond or graphite stability fields and therefore has potential to host diamond.

Petrographic Study
Petrographic study is an essential element in the evaluation of any suspected diamond-bearing intrusive. Petrography is used to determine whether the target body is a bona fide kimberlite, orangeite or lamproite or one of several look-a-likes, such as an alkaline lamprophyre. Two polished thin sections are recommended for study from each rock unit recognised in the field.

SGS Minerals Services provides secure chain-of-custody sample transfer to ensure the safe handling of all types of exploration samples.

Fee schedules are available upon request. Volume discounts are available. Customized proposals and quotations can be prepared on request.