Simpson's Veins EarthCache
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In geology, a vein is a distinct sheet like body of crystallized minerals with in a rock. Veins are classically thought of as being the result of growth of crystals on the walls of a planar fracture in rocks, with the crystal growth occurring normal to the walls of the cavities, and the crystal showing in an open space. Veins are important to mineral deposits because they are a source of mineralization either in or proximal to the veins.
There are three different ways veins can be formed; 1) Open Space Filling, 2) Crack Seal Veins and 3) Hydraulic Fracturing.
For an open space filling to occur you need confining pressure below 0.5 GPa or less than 3-5 km. Veins formed this way can contain colloform texture and the minerals radiate out from nucleation points (budding points).
Figure 1 Example of Colloform Texture
A crack seal vein happens when a confining pressure is too great. They are thought to form quickly during deformation by precipitation of minerals within incipient fractures. Generally the space is in order of millimeters or micrometers. Veins can grow in thickness by reopening the vein fracture and progressive deposition of minerals on the growth surface.
Figure 2 Example of a crack seal vein
Hydraulic Fracturing may create a breccia which is filled with vein mineral. Such vein systems are quite extensive and can form the shape of a tabular dipping sheets, diatremes or laterally extensive mantos controlled by boundaries such as thrust faults, competent sedimentary layers or cap rocks.
Figure 3 Example of a thrust fault
Figure 4 Sedimentary Rock
Quartz is often found in veins that cut through rocks. Usually the term “vein” suggests that the veins of the quartz and other minerals are usually in thin tubes, but in this case they are in thin sheets. Quartz veins can become very large and doesn’t always have to be white and milky and can also contain other minerals with in the vein.
In this area if you are lucky enough you may also be able to find a piece of pyrite and quartz.
Figure 5 Example or Pryte and Quartz
TO SUCCESSFULLY LOG YOUR FIND YOU MUST:
1) Post a picture of yourself/team and or your GPS unit with the veins (optional)
Email me the answers to the following questions through my account …. DO NOT POST THEM HERE
2) What is the approximate length and width of the vein?
3) With your GPS give me the reading of the north end of the vein.
4) Based on the description above describe the type of vein and describe the texture of the quartz (what colour is it, what other minerals can you see if there is any)?
Additional Hints
(Decrypt)
Abgr: LBH QB ABG UNIR GB TB VA GUR ZVAR FUNSG ZHFRHZ SBE GUVF BAR.
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