ins.: 2011-09-03 00:00; ( Age: 13 yrs )
After passing through almost 200m of ultramafic rock, drilling is ...
After passing through almost 200m of ultramafic rock, drilling is proceeding slowly through the tough cherts that make up the Buck Reef. We started with NQ core equipment. i.e. a hole size 75.6mm and core size 47.6mm, and with it our advance in the chert was a magnificent 3m in 24hrs. We subsequently changed to a TNW bit which has the same hole size of 75.6mm and a core size of 60.5mm, giving us the double advantage of larger core and a faster rate of drilling (the reason for starting with NQ is that it is a wireline technique which, when used in normal rocks, is a very much faster drilling technique than TNW which requires that the entire rod string is withdrawn after each run). The thin-walled bit allows three times the penetration in the chert. A picture of the different core sizes is attached for information). We are now drilling at about 8- 10m per day and have reached a depth of 250m, about 50 m into the chert.