Tuesday, February 1, 2011

Alpine Fault drilled through again!

The customised system of open-hole drilling devised by Alan Speight (our head driller) worked fantastically. We rapidly progressed from 45 m to 93 m in 18 hours, including one unsuccessful attempt to core. We  changed back to coring again at 93 m because we noticed an obvious change in cuttings and mud colour.
A sample of cemented cataclasite is carefully extracted from the core catcher

Coring progressed smoothly this time, even though one of our drillers walked out on us for no apparent reason. For the last two days I have been working as a drillers offsider, trying to keep us on track with the project, but it has been tough to balance every demand.A sample of cemented cataclasite is carefully extracted from the core catcher.

Drama continued again last night when a sudden storm passed through at 2-4 a.m., flattening our core processing and logging facility. Fortunately, nothing catastrophic was lost or damaged.We rebuilt better and were ready to drill again by 7 a.m.

Cores of the Alpine Fault footwall emerge for the first time
Skies cleared during the morning, lovely cores continued to emerge from the borehole, and life was looking good. At around 4 p.m. today we ran into a slight problem: we hit an obstacle, obtained no core, and could not advance any further. We tripped out all the drill rods and checked the bit. It confirmed the suspicion that I had after inspecting the core catcher from our previous run. Light grey clay gouge was blocking mud circulation. Was it just a gouge-rich zone within the thick (>30 m) cataclasite zone, or was it the main fault?

At about 7 p.m. we collected the first core from beneath the problem zone (thanks to the skill of our driller on the levers, “Egor”). This core and the subsequent two confirmed that we had just crossed the principal slip surface of the Alpine Fault at a depth of 128 m. Fantastic!

Both of our boreholes have obtained high-quality cores across the fault, including the precious fault gouge of the primary fault surface. There is a clear sense of excitement and achievement, and a big group has decided to work through the night to see what is going to appear.The rock cores currently emerging are really interesting, because the rock types immediately beneath the fault are not well known, in comparison to the well exposed and studied sequence above.
A beautiful core of the Alpine Fault from 128 m

It is premature for me to say what the rocks are that we cored, but brilliant white and green shades indicated that we had crossed the fault. We decided to keep going for another  shift, and over the next 24 hours a preliminary geological description will be constructed.

If all goes to plan, we will have finished our main phase of drilling tomorrow. We will move onto
wireline logging and geophysical observatory installation. I personally now need a few hours
sleep after the drama of the previous two nights.

John Townend, Richard Norris, Rupert Sutherland, and Virginia Toy consider achievement so far