Moving towards automated sampling and analysis with autonomous drilling in the mine.
Last week we asked ourselves the question “Why do we get biased samples in sample collection from the chips cones”. We discussed the challenges and the root causes of bias in a previous study. Now that we understand this challenge in more detail, the next is to discuss and propose a viable technical solution.
Figure1: Percussive Drill Sampler-Analyzer (PDSA) in two different applications, on the left in the Arctic on blast hole bench with standard cyclone, on the right with R/C and splitter setup in a tropical mine
When the research and engineering work was started the challenge was divided into two parts, which had to be practical and not too different from conventional mining practises in use (in sampling). First, the aim was to solve the two main big challenges:
a) how to get representative samples and how to verify them, and
b) how to analyse these samples on-line in a real mining environment
Testing the first on-line prototype in Gold and Nickel mines
The prototype was an on-line XRF conveyor analyser installed on a trailer. The idea and concept are clear and simple – take all drill cuttings as a sample from the hole and analyse it by continuous scanning method from the measuring conveyor belt while the hole is drilled. This method I called Analyse While Drilling (AWD).
Figure 2: “MOA” in FQML Kevitsa Ni-Cu and in AE Kittilä mine, R/C setup blows chips via a pipe into Cyclone, splitter and to on-line real-time XRF analysis
First, a riffle splitter was used to collect samples every meter from tens of holes for lab analysis to verify the performance of the analysis accuracy. Later when the concept performance was verified, samples for lab analysis were further taken at every 20 meters of drilled material for QC/QA purposes.
The first application was a new surface gold mine. Naturally being a gold application, the drill (Atlas Copco D65) was equipped for R/C drilling to enable the best possible sample representativeness.
Assays were calculated at every 15 sec. to 20 sec. time frames resulting in three to four analyses by meter drilled. To ensure the best possible lab samples after each meter a new sample bag was taken and the splitter rifle was cleaned by air.
When the test benches were ready, the prototype mobile on-line drill cuttings (“MOA”) XRF-analyzer performance was compared with collected samples, which were analyzed in the laboratory (As% and Au ppm). The gold ore in this mine is Arsenopyrite, and the gold is in this mineral lattice, so there is a strong correlation with Arsenic, which was used as the main proxy for gold.
Figure 3: Prototype MOA Sampler-Analyzer had a control unit, industrial computer and graphical user interface inside the steel enclosure. One set of samples was collected from holes (typically between 10m to 30m in length).
Table 1: Calibration comparison of MOA prototype on-line Sampler-Analyser with laboratory samples
Comparing strict acceptance criteria with collected laboratory samples (a total of about 2000pcs), 85% of the on-line analysis values from real testing met the criteria. The first ever on-line drill cuttings Sampler-Analyzer managed well on the first field test in arctic conditions.
The second test site was in a nickel-copper mine. The total number of collected meters and samples was about 200 pcs. Here, the on-line XRF data was compared with the laboratory analysis with excellent results too.
Table 2. Performance comparison with the prototype analyser with the laboratory gave excellent results.
This nickel mine application was done with a D65 drill rig and again with R/C equipment to get samples to the laboratory.
In our white paper, we answer in detail the questions below and give practical examples of how to integrate the IMA Sampler-Analyzer on big rotary drill rigs.
What happens with the major problems in sampling from chip cones?
- How to get samples from the first part of the hole when the chips are disappearing in the cracks of the rock? What about the sample from the sub-drill?
- What to do with the problem of drill chips volume varying from different levels? Some material may disappear in the cracks anywhere in the hole. Samples from different levels from the hole have different volumes, isn’t this making analysis weight averages different?
- Is it possible to avoid chips contamination from hole walls while chips travel up from the hole? During blast hole drilling, drill cuttings may collect contamination between the hole and the drill pipe. Can this be avoided?
- Why and how to collect MWD data?
Another topic covered in detail in our white paper is mine planning with 3D block models.
Figure 4: A final 2.5m*2.5m*2.5m block diagram of the same bench as in Figure 4. Here the analysis is from on-line frequent data collected and analysed by Sampler-Analyser.
Next week, we discuss the potential benefits of using the Sampler-Analyser technology including cost savings and value creation, environmental and sustainable matters.
