Did You Know?
The Did You Know? page of this website is intended as an educational tool for people within the drilling industry. It looks at various topics of interest and will be updated with new subject matter progressively. If you have any topics of interest that you would like to share or have any questions about issues you are facing in your drilling application, feel free to drop us a line at firstname.lastname@example.org and we’ll look into it for you. We may even post it on this page?
Fines Loss from Sample
Independent data is proving fines loss to a dust collector or to atmosphere in cases where dust collectors are still not being used can account for up to 10% mineral loss, including gold (see Results & Scientific Papers). This dilutes the sample to cause underestimation of mineral content with a devastating impact on decisions and ultimate profit through missed opportunity as a consequence. But equally, in cases where little mineral content is present in the fines, the losses cause concentration of the mineral content within the coarse material in the sample leading to assumptions of higher grades present than are actually there.
Patented Progradex technology offers the only sampling system in the world that provides 100% recovery for sampling.
Correct Terminology – Avoid The Confusion
“Dust Suppression” means to suppress dust with water. So, a “Dust Suppression System” would be to introduce a water spray arrangement to keep the dust down. The correct term when talking about a dry application to capture dust emission to atmosphere is dust collection using a Dust Collector. Progradex Dust Collectors are designed specifically for drilling applications with conservative “air to cloth” ratios that guarantee a dust free and trouble free drilling environment.
Cyclones – The Rights & Wrongs
Beware! – If a cyclone is designed properly and correctly sized for the application, an exhaust fan on the back end of a sampling system will have no effect whatsoever on dust carry over to a dust collector. In fact, a system operating without an exhaust fan will be unbalanced and unpredictable due the varying positive air pressures inherent to the RC drilling process.
Beware! – Cyclones with a square to round transition in place of a cylindrical base cone, intended to directly match a riffle splitter flange and save height, will interrupt the vortex path that is required for the cyclone to function properly (i.e. to collect cuttings and dust) and, therefore, cannot and will not work.
Beware! – Some sampling systems have a trap door fitted directly on the bottom of the cyclone. Sampling systems that use the base cone of the cyclone to store the collected cuttings, albeit temporarily, will simply cause those cuttings to be carried over to the dust collector because a cyclone’s internals (when correctly designed) is a totally active vortex where material cannot be stored.
Tiered Riffle Splitters – The Fundamental Flaws
Have you ever wondered why your sampling results from a tiered riffle splitter do not correlate with the block they represent? Have you assumed that this is simply due to the natural variability of the ground or orebody? Have you ever tested a tiered riffle splitter for variability and repeatability? If you get a chance, try it with a known, free flowing bulk sample such as dry rice. You might be quite shocked at what you find? The fact is, even when you pour that same bulk sample through it again and again, the bag(s) sample variability is considerable and repeatability is non-existent.
So, why is this?
Below is a series of diagrams that show what happens to a bulk sample as it passes through stacked, tiered riffle banks. With each additional tier, the error goes from bad to worse…
- Single tiered Riffle Splitters provide a reasonably representative sample but suffer from extraction bias due to the vertical nature of the slot cutting blades. They are however only capable of splitting the bulk sample in half.
- Beyond the first tier, Riffle Splitters provide an unrepresentative sample because the distribution of ore sampled is not a representative cross section of the parent interval. This gets progressively worse with every additional tier thereafter.
- Potential for cross contamination between intervals and blockage is high because of the large surface area of faces internally that come into contact with the ore.
- Riffle Splitters are designed assuming that sample cuttings will evenly distribute across the base of each slot as it slides down them so that the next riffle bank can split it evenly. In reality, cuttings tend to segregate (coarse from fines) and have a tendency to slide down one side of the slot and not cut evenly in half at the next splitting tier. This variation is inconsistent so even a known sample will give a vastly different result each time it is poured through the same splitter. This in itself makes the sample unrepresentative because the sample-to-waste splitting ratio is variable every time and is why, in practice, riffle duplicates suffer wildly from variation in weight and grade. Duplicate repeatability is extremely poor.
- Split percentages available with tiered Riffle Splitters are limited to 50%, 25%, 12.5%, 6.25%, …& so on. They cannot target a specific weight/volume outside these percentages and cannot therefore be tailored to suit the lab capability to process them. In addition, safety protocols for manual handling or sampling protocol for representivity can not be assured. Furthermore, this inflexibility means drill hole diameters and sampling interval depths cannot be varied in-process without proportionally affecting the resulting bag sample weight/volume.
- Labs charge premiums for samples that exceed set cut off weights for processing. The natural variation in weights that are seen from Riffle Splitter samples often create additional post drill sampling splitting in the lab and incur additional charges. This extra work results in delays in receiving geological planning data and decisions on mining are often made blind as a result.
- Tiered Riffle Splitters are not a modular construction so any adjustment required to percentage splits results in the need for a completely new riffle splitter with a greater or lesser number of tiers. This effects the operating height of a drill sampling system and requires the rest of the system to be height adjustable to compensate for the change in working height. Single Tier Riffle Splitters are approx 500mm high while 5 Tier Splitters are approx 1800mm high.
With all things considered, we must therefore conclude that there can be no justification for using multiple tiered Riffle Splitters in any application if the goal is to achieve a Representative Sample.
Blast Hole Sampling versus RC Grade Control
It has been a topic of debate for many years; blast hole sampling, in pit RC grade control and diamond core (underground ops) for resource evaluation. The link below will take you to a PowerPoint Presentation titled, “Effect of Poor Drill Sampling” that seeks to explain the issues, the perceived advantages of one method versus another and the facts that must be considered before any decision is made regarding grade control for resource evaluation. Don’t be fooled, just because it has always been done a certain way, doesn’t necessarily make it right!