You're welcome. Good to note you also try to research aspects to try and clarify what can be (are) difficult concepts to explain succinctly. I will respond to questions as time and knowledge (research) permit.
[Below is excruciating detail about aircore drilling. Most aspects of the exploration process require a similar level of knowledge or way beyond this especially for geophysics.]
One aspect of my last post was the use of an aircore rig.
Why aircore?
- Faster than RC so covers an area quicker than RC. If the sentinel interp above is accurate then 2 weeks of drilling has covered large areas of Crean and Emily with holes, locally, some 40m apart. Probably more holes in that time than the entire 2023 RC/DD program.
- Cheaper than RC per meter although sample quality and depth penetration are more restricted.
- Less footprint vs RC. Narrower access, almost none needed in more sparsely vegetated areas and no pads with sumps. Just clear enough ground to set out up to say 120m of individual drill cuttings. The latter plus the access tracts are about all that are visible on sentinel satellite imagery.
What is Aircore?
- Another useful summary of Aircore from Victoria. Shows inner details of the drill bit/cross over area - another example.
- The geodrill rig above probably uses 3m rods. 6m rods - probable as well.
- Not shown above but there is also an aircore hammer drill that can penetrate into hard rock. More expensive than standard AC and not as efficient as RC. Good add on when using a standard AC rig and you want to go deeper but not on a regular basis?
Cost?
Don't know and a matter of considering many factors that only come out in contracts.
Overall program cost per meter requires these.
From memory and 30Yrs ago per meter: Rab $4-6, AC ??$10-20, RC $40 and DD a basic NQ hole $100. Do not rely on these figures and add inflation to these rough meter costs [though suspect not as much as might be expected for RC DD from some figures I have seen recently].
The non drilling costs will be roughly the same for different non DD rig types - assays/field staff/sample prep. DD core prep is time consuming and hence costly.
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Some practical examples.
Most of my field experience was with DD/RC/RAB and only limited AC. Most of the RAB goes back decades to what may now be pleasant memories. Appreciated the contract geos after some days. The effort is what puts announcements to the ASX to be dissected by armchair chat room denizens.
One rare day saw 1000+m of Rab - exhausting playing catch up with the rig after 600m the day before and probably similar the next. That day had a sequence of easily drilled, 50m spaced holes to 70+-m along a flat well prepared line. No drill problems for the 12-15 holes drilled in 10+- hours. 50,000+-m programs year after year until Golden Grove was totally covered along strike. Quick and dirty mostly pre AC days. Adequate to produce RC DD targets that proved elusive. I note that more recent work finally decoded some areas we could not.
AC hammer drilling produced some surprises that were not obvious at the time of drilling. One hole in particular did not fit the geology UNTIL it was downhole surveyed by another company a year later. Turns out the AC driller prioritised speed over accuracy. The nett result was a hole that deviated dramatically in both dip and azimuth over its 160m. The rods were 6m long by 5-6 inches in diameter but they can bend in ways that are unexpected. Using new surveys moved the hole location 10s of meters laterally and vertically.
Vertical AC such as that used by ENR will deviate but unlikely to be a factor in future targeting with RC.
AC 'sausages', to use a polite term, are sometimes produced from the transition zone to fresh rock where a solid irregular core of significant size, compared to chips, is produced. Chatting with some Bostech drillers at a conference about this, they said around 50cm was the longest they had produced. 2-5cm relatively common larger are rare but both good to get.
Practical AC:
- Create enough access for the rig to wiggle along without staking tires. GPS (nowadays) to set up/record location or use surveyed pickets/flagged lines (unlikely but with GPS accuracy would be easier than my day).
- Put rig on a site and while setting up clear enough space for the 1m drill piles.
- Drill 1m increments and take the 'spoil' away to the cleared site to lay out systematically.
- Repeat until the rig cannot penetrate any further (usually fresh rock; but can be cap rocks or hard layers near surface which might prevent a proper test, there are options available, sometimes, for this with a change to hammer drilling then back again to rotary after the obstacle is passed)
- Geo and fieldie processing the spoil piles trying to keep up. 2 or 3 kitchen sieves used to remove the fines and leave chips to geologize, onto a laptop, before putting into trays (RC chips below but the process is the same).
- Fieldie collects assay samples commonly using a 'spear' of poly pipe. Various combinations of sample length can be taken with 1m for areas where the geo or "Gun" find it may be best to do so. Samples are bagged and when a batch is ready from multiple holes sent to the lab. Imagine the logistics of transport from West Arunta!
- Chip trays, coarse rejects, pulps are archived by most companies these days.
- Basic process. Will be variations and some new technologies coming out to remove the potential inconsistency of logging manually. May not be complete (above summary) so feel free to add comments that may be more current or accurate.
Start at sunrise and go til dusk with flies noise and dust. Cue violins....Fun memories NOW
(20min delay)