Geology of the Okanogan Highlands 2012 - Stop 5

Stop 5: Bryozoan Fossils

The group did not stop here due to access issues, but information was provided by the presenters:

At the reclaimed portal of the Lamefoot gold mine (mined from 1994-2000), the rock is marble. Marble starts out as limestone, becomes buried deeper in the crust, and is heated to metamorphic temperatures, which causes it to recrystallize. The metamorphism of this marble occurred at a low enough temperature that, if you look very carefully and very closely at the rock, you may be able to see small fossils in it.

The fossils are the hard parts of marine organisms such as crinoids (stemmed echinoderms made of hexagon-shaped segments) and bryozoans (fine mesh structures, like tiny nets, that contained numerous tiny colonial organisms). The habitat of these creatures was a shallow ocean floor in a sunny climate.

The rock is part of Quesnellia and is of Permian age, between 250 and 300 million years old. The gold ore associated with these rocks, which we don't see much evidence of here at the reclaimed surface, may have originated from a combination of volcanic and biochemical processes on the ocean floor. The location and concentration of the gold atoms in the rocks may have been modified by the warm water that circulated in cracks in the rock during the Eocene epoch, about 50 million years ago, when the Republic graben was forming. At this time, rocks in the area were being faulted and shifted, and volcanoes were erupting nearby.

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