Tuesday, May 26, 2009

Field Trip Day 2: Getchell Pit

Continuing with some recent posts showing photos of a field trip to the Humboldt Range and Osgood Mountains of northwestern to north-central Nevada, here's a stitched together photo of the Getchell pit, a scenic place that we stopped for lunch.

The pit follows the Getchell Fault zone, which overall strikes north-south to NNW and dips about 50 degrees to the northeast in the mine area. Timing of motion on the Getchell Fault is complex to unknown, with sub-horizontal slickensides overprinted by steeply dipping slicks. Gold has been mined primarily from sedimentary rocks of the Cambrian Preble and Ordovician Comus Formations in both the hangingwall and footwall of the fault.
Dark-colored rocks are mostly unoxidized, strongly carbonaceous sedimentary rocks in the footwall of the Getchell Fault; the light-colored gooey-looking mass in the hangingwall of the fault is oxidized granodiorite that is flowing slowly into the pit.
This relatively smooth surface in the southern part of the pit shows the fault relatively well. The rocks are probably granodiorite in the footwall of the fault, but I won't swear to it, because we didn't get to check it out. I can imagine that I see sub-horizontal lines in this photo (slickensides?), but again, I don't really know for sure; the sub-vertical lines are probably drip lines from runoff but could conceivably include slickensides.

Marlowe, K. E., Wood, K. Y., Loranger, R., Martin, D., Pinguely, R., and Reynolds, M., 2009, Geology, mineralization and exploration of the Getchell and Pinson deposits, Humboldt County, Nevada in Ressel, M. W. (ed.), 2009 Spring Field Trip Guidebook: Diverse Gold Deposits of the Osgood Mountains and Humboldt Range, North-Central Nevada: Geol. Soc. Nevada Special Pub. 49, p.51-61.

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