Drilling Technique and Times17 Oct 2019 11:26
for anyone wanting to know about the drilling technique, initial logging and security .. it is all detailed in the NC Quarterly report ( pages 10 and 11 ) ..
https://www.newcrest.com.au/media/quarterly_reports/Quarterly_Exploration_Report_-_June_2019.pdf
the core diameters are PQ @ 86mm dia, HQ @ 63mm dia and NQ @ 47mm dia
I would imagine that it could take as long as 8 hours to do a 6m core run at a depth of 1200m .. so perhaps only 18m of core sample a day ( at depth ) ..
that is ave 1 min each to run the 6m core barrel and 6m drill rods down the hole x 200 drill rods is 200 mins,
allow say 60 mins to core 6m,
then 200mins to remove the drill rods and core barrel is another 200 mins,
then the hole casing needs to be advanced 6m which is quite quick at say 30mins
and thats assuming there are no problems, which generally on a good day, there are not
looks like they are drilling 'open hole' ( they call it 'mud rotary drilling') to the base of the cover ( est 3 x 24 hr days to 400m deep ) .. then 'core drilling' the ore body
so envisage they are drilling 100mm dia open hole to base of cover, installing 100mm hole casing ( to keep the hole from collapsing ), then core drilling in PQ ( 86mm dia ) until that hole casing becomes difficult to advance, so reducing to HQ ( 63mm dia ) and core drilling until that casing becomes difficult to advance, and finally reducing to NQ ( 47mm dia ) and core drilling until that becomes difficult to advance, that is where the hole probably stops .. if they want to drill deeper then they would probably have to start in a bigger diameter which means the whole thing takes even longer
if the hole is stable ( not likely to collapse, or rock part fall in ) then the hole may be able to be progressed without advancing the casing
there is a quicker technique called 'wire line' core drilling where the drill barrel is lowered on a wire rather than on drill rods .. but this is not mentioned in the report .. and a 1200m wire line would be a nightmare to control .. and if the wire broke then the hole is lost ..
based on my 12 years UK Rotary Drilling ( observation ) experience ..
but never seen anything like these depths