This EarthCache was placed with permission from the City of Ranie and is on public property. No physical cache has been placed. Please stay on the road right-a-way and off the adjoining private property. In order to log a find on this EarthCache read the cache page and send me the answers to the question below.
Our story begins over one billion years ago during the Precambrian period when an enormous volcanic hotspot that produced an ocean of magma that flowed out of rifts. The massive Midcontinent Rift, centered in Lake Superior and specific the Rainy Lake – Seine River Fault is where some gold deposits are found in the upper Minnesota area. Gold can be in quartz veins found in the basalt lava flows, following factures in the lava caused by liquids and gasses under pressure. Other ore and native metal veins are found in other parts of the Midcontinent Rift, for example the copper found in the Keweenaw Peninsula (Rose, 2017).
After discovery of gold in the Lake Vermilion area in 1864, prospectors were panning for quartz containing gold on Little America Island in Rainy Lake and discovered gold in 1893. George Davis and Charles Moore staked their claim to the property and later sold it to a mining company in Duluth. This strike created a gold rush but it was short lived. During this time, at least 11 mines were opened along the 280K Seine River Fault line running east/west. The gold bearing quartz on Little America was mined until 1900 when it became uneconomical to continue (National Park Service, 2019). With the Little Island mine only 8 miles to the west of us, this basalt flowstone with quartz veins is in the right place!
* If interested in this mine, an EarthCache GC7V56M; Strike it Rich can be found on Little American Island.
The term vein generally doesn’t refer to a thin round shape tube filled with quartz but rather a crack or fracture in the rock that quartz forms a thin sheet following those cracks. In magma-lava flows these cracks can be created by venting of pressurized gasses. These dissolved gasses in hot brine and granite pluton will sometimes carry minerals up with them and deposit them in these fractured cracks. This quartz is sometimes called gangue quartz, having a milky white color and sometimes containing crystals (Akhavan, 2019).
Don’t get your rock hammer out just yet! Conditions have to be just right for gold and other valuable minerals to be present in these quartz veins. Under volcanic system conditions, these minerals can be in a dissolved solution of rising acidic hot water and as the pressure decreases, gases like hydrogen sulfide come out of solution and escape, precipitated out native metals (Oregon State University, 2019). On close examination of this quartz vein, there doesn’t seem be any native metals in this quartz. But keep your eyes open when you see quartz veins, they can contain gold!
In order to log this EarthCache, please complete the following and email your answer (try your best, this is not intended to test your compass skills!
1) Using a compass (most smart phones have one), look at the general direction the veins are running. Standing on the rock flow / bank, which direction does the vein(s) run?
Example: either degrees or compass direction 180 or South. Note: The road runs SSW (200 degrees).
2) Please include a picture of yourself at the location, we always like to see people enjoying this EarthCache!
Option: You can post some personal item at the GZ if you prefer not to include a picture of self.
Bibliography
Akhavan, A. (2019, June 27). Occurrence. Retrieved from The Quartz Page: http://www.quartzpage.de/gen_occ.html
National Park Service. (2019, June 27). Gold Mining. Retrieved from National Park Service - Voyaguers: https://www.nps.gov/mwac/voya/shapingvoya/Mining.html
Oregon State University. (2019, June 27). Gold. Retrieved from Volcanic Minerals: http://volcano.oregonstate.edu/oldroot/education/minerals/gold.html
Rose, W. I. (2017). How the Rock Connects Us: a Geoheritage Guide to Michigans Keweenaw Peninsula and Isle Royale. Houghton, Michigan, USA: Isle Royale & Keweenaw Parks Association,.