Long time since I sat on a drill rig but many of the aspects are probably still the same. Some evening reading.
Q1
Vertical vs inclined? The latter potentially gives better coverage and has become near industry standard for early phase exploration.
- Drilling is one of the last stages of exploration. By the time it is done a lot of information has been gathered so that this expensive process can hopefully give the best bang for the budget. Among the key information are the strike and dip of various lithologies, and/or structures plus the nature of the target which will be used to
design a drill program.
Many types of drill rig are available depending on what is required and best for the budget. In terms of cost RAB is
generally < AC < RC < Diamond ($~10-100+ per metre RAB - DD) and the quality plus usefulness of the samples provided usually reflects that cost. Aircore sample quality and speed mean the slight cost differential benefit of RAB (rotary air blast) is overcome making AC a major choice for today's first pass drilling. (I've been out of the game too long to know if this is entirely accurate but does seem that RAB is seldom used).
For the large aircore programs such as DEG are doing drilling to "refusal" (point where the style of drilling slows/stops under cover and weathered rocks) at -60 degrees or so is a good way to get very good coverage along a fence of holes.
The target of the program was large "Towerana look-alike" intrusives (Kneeshaw) hence the spacing along the lines does not need to overlap.
There is an element of luck as to whether there is an interesting hit or not. What would holes BWAC 245 and 258 have hit if drilled vertically? Most mineralisation does have some form of halo which potentially can be recognised. The low grade intersections in the Crow area Section A may have been checked earlier if there weren't better targets.
Q2
Deviation is inherent in drilling so down hole surveying is required to locate the 3d path of the hole. These surveys give the "beckham" effect you observe.
Hole deviations - have (in my experience) two major causes [can be interactive]: Drilling practices and ground condition.
This is mostly noticed with deeper RC and Diamond holes that get surveyed. AC/RAB seldom go deep enough and are followed up by RC/DD anyway if anything significant is found.
Drillers often get paid by the metres drilled in a shift so they will try to get the most possible. Sometimes this is OK but it is surprising how much the drill rods can bend.
Even if the driller is trying to drill a straight hole the combination of machine and rock can thwart the best efforts of the team. After a few holes in an area holes are designed to allow for the nature of the geology. Somewhat like allowing for wind with archery or shooting.
With diamond drilling hitting a 10x10m target at say 1 or 2000m, directional control is possible with the right equipment but at a fairly high cost in $s and time.
There are yarns of drills coming out in stopes 100m above where they started.
Personally I saw core from a hole that started sub vertical (-85 degrees) that was sub horizontal for its last hundred metres from 600-707m! It also changed azimuth (direction) dramatically. When it was resurveyed and re plotted, some 15 years after drilling, the geology finally made some sense.
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The above is just on minor aspect of what explorers have to get the announcements out. It is great when discoveries like Hemi are the result.
(20min delay)