Tuesday, January 25, 2011

Core Impressive!

Just as I finished my previous update there was a sudden improvement in core recovery. We were at around 70 m depth and suddenly the cores looked very different – green, hard, and perfect; instead of falling to pieces with lots of washed out clay and residual fragments. Had we just crossed the main fault?

Egor, the driller, and some of the DFDP-1A team happily show off a perfect core of the principal slip surface of the Alpine Fault.

After we cleaned those cores and carefully logged them, we came to realise that we had not crossed the Alpine Fault, we were just getting the most beautiful cores. Maybe it was just the effect of increased confining pressure that resulted in better cohesion and recovery of the cataclasite. Our lab work, wireline logs and the DFDP-1B results should help to provide a scientific explanation for this change.

After 20 m of near perfect core recovery, we definitely did hit the principal slip surface. We were at 90 m depth. It was obviously the fault because there was Quaternary gravel lying beneath the thick sequence of cataclasite. The driller, “Egor”, was more excited than anyone – a perfect core across the critical zone. Fantastic!

The precious fault gouge core is now in a very secure box in a secret location and is marked “Beware of Virginia”. After reaching a depth of 96 m, we were having difficulty advancing further and for various reasons we decided to halt

drilling and then withdraw the drill string.

A perfect core of the active slip surface of the Alpine Fault from the DFDP-1A drill site, Gaunt Creek.

The project so far has been frantic, but efficient and very successful. There we were holding the first core of the Alpine Fault on Sunday evening and we were not even scheduled to start coring until the following Monday morning. We were at least 3 days ahead of schedule and it dawned on me, as project manager, that none of the other contractors were even here yet and some instruments had not even arrived from the USA. Elation started to turn into a mild panic. There was a lot of work to do and plans to change.

The revised plan and workforce has now started to fall into place, and the TV, radio, and newspapers have been on the phone all day. We reached a consensus decision today on where to site the DFDP-1B borehole and the percussion air-hammer crew has now showed up to start installing a surface casing at the new site. The current intention is to knock a 6” casing down to nearly 70 m, to try and avoid the difficult materials found in shallow parts of the DFDP-1A borehole. We are hoping to reach a total depth of around 200 m in our next borehole, if we hit solid rock beneath the fault. We start tomorrow morning.

Dave Prior decides to dig 200 m at the agreed site of DFDP-1B.

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