Friday, May 29, 2009

Field Trip Day 2: Pinson Pit Overview

After lunch, the two field trip buses took us from Getchell down to Pinson. All 79 of us (more or less) then stood near the edge of the Pinson CX pit and looked in, while a guy who acted like the safety guy went around trying to get us to back away from the edge. Prior to this pit overview, we viewed some posters and examined some nice-looking, high-grade drill core.

The stitched-together photo above looks mostly west: southwest to slightly north of west from left to right. Miscellaneous equipment and things in the pit are related to currently suspended underground development and exploration, and possibly to ongoing dewatering.
Above, a closer view looking at the north part of the CX pit. The mine dump in the upper right part of the photo is a dump from some old tungsten workings. The upper benches of the pit on the northwest side (right) are in unconsolidated alluvium.
And this is what it looks like on the next to bottom bench of the CX pit: a geology field trip invasion. Geologists on this kind of field trips do a lot of talking and, for some reason, seem to want to examine rocks when the buses are trying to leave!
And why did we go down there, besides the fact that it was there? To look at rocks and to argue over features like this one, above: was the feature caused by soft-sediment deformation or by post-lithification structural deformation? Keep in mind that these rocks are Cambrian or Ordovician, that they were around during two orogenies during the Palaeozoic, have been intruded and contact-metamorphosed during the Cretaceous, and were mineralized and subjected to Basin-and-Range extension during the Tertiary. The immediate pit area is cut by so many faults that developing and maintaining the underground workings has been difficult to say the least. Geologists on the trip did not reach an agreement about the origin of the deformation seen at Pinson. Some agreed that the answer might be both: soft-sed and structural.

Scale for that last photo is unclear, but the plants are probably very small ones (smaller than my hand).

No comments: