Green River Veins EarthCache
Hidden : 10/13/2012
Difficulty:
2 out of 5
Terrain:
4.5 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

This Earthcache is along the Green River. The listed coords will take you to a place on the side of the Green River. This area is very unique as it has many examples of rock veins.

In geology, a vein is a distinct sheet like body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation. The hydraulic flow involved is usually due to hydrothermal circulation.

Veins are classically thought of as being the result of growth of crystals on the walls of planar fractures in rocks, with the crystal growth occurring normal to the walls of the cavity, and the crystal protruding into open space. This certainly is the method for the formation of some veins. However, it is rare in geology for significant open space to remain open in large volumes of rock, especially several kilometers below the surface. Thus, there are two mains considered likely for the formation of veins: open-space filling and crack-seal growth.

Open Space Filling - Open space filling is the hallmark of epithermal vein systems, such as a stockwork, in greisens or in certain skarn environments. For open space filling to take effect, the confining pressure is generally considered to be below 0.5 GPa. (measure of force per unit area) Veins formed in this way may exhibit a colloform, agate-like habit, of sequential selvedges of minerals which radiate out from nucleation points on the vein walls and appear to fill up the available open space.
(In layman's terms, think of this as a non-uniform hole in your backyard. You fill the hole with concrete. You have filled the open space.)
Crack-seal veins - When the confining pressure is too great vein formation occurs via crack-seal mechanisms. Crack-seal veins are thought to form quite quickly during deformation by precipitation of minerals within incipient fractures. This happens swiftly by geologic standards, because pressures and deformation mean that large open spaces cannot be maintained; generally the space is in the order of millimeters or micrometers. Veins grow in thickness by reopening of the vein fracture and progressive deposition of minerals on the growth surface.
(In layman's terms, think of this as a tile floor. The grout between the tiles would be the vein.)

It is extremely hard to get a good signal in this area. So instead of looking for 1 or 2 veins, use what you've read above to answer questions about what you see in the general area.

1. Find a Crack Seal Vein in the area and measure it's length and width. There should be some close to the coords listed.

2. Looking around this out cropping of rocks, which type of vein is more prevalent? (Open space or crack seal?)

Email your answers to my profile and please do not put any answers in your log.

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