URANIUM
Uranium is a very heavy metal which has been used as an abundant source of concentrated energy. Uranium occurs in most rocks in concentrations of 2 to 4 parts per million and is as common in the Earth's crust as tin, tungsten and molybdenum. Uranium occurs in seawater and can be recovered from the oceans. Uranium was discovered in 1789 by Martin Klaproth, a German chemist, in the mineral called pitchblende. It was named after the planet Uranus, which had been discovered eight years earlier. Uranium was apparently formed in supernovas about 6.6 billion years ago. While it is not common in the solar system, today its slow radioactive decay provides the main source of heat inside the Earth, causing convection and continental drift. The high density of uranium means that it also finds uses in the keels of yachts and as counterweights for aircraft control surfaces, as well as for radiation shielding. Uranium has a melting point of 1132 deg C. The chemical symbol for uranium is U.
THE ORPHAN MINE
Uranium was discovered in the Ophan mine in 1951. With an average of 45 men working two daily shifts, the Orphan Mine soon proved to be sitting on the richest uranium lode in a country. The ore was mined from 1953 to 1972. Uranium content in the ore was as much as 4.9 percent and approached 80 percent in individual samples. The patented land was acquired by National Park Systems in 1963, but extraction rights were retained by the operator until August 1988. When the mine closed it had produced 495,107 tons of ore, including 4,257,571 pounds of uranium oxide, 6,680,000 pounds of copper, 107,000 pounds of silver, and 3,283 pounds of vanadium oxide.
URANIUM MINERALIZATION AND LOCAL GEOLOGY
The Orphan Mine uranium orebody occurs in a nearly circular, vertical pipe structure, which ranges from about 150 to 500 feet in diameter. The pipe extends downward from the lower part of the Coconino Sandstone into the Supai Formation and may continue down into the Redwall Limestone. The pipe fill consists of downward displaced massive Coconino Sandstone, angular siltstone, shale and limestone breccia from the Supai and Hermit Formations. There is no intrusive material within the pipe so a direct igneous origin is unlikely. the pipe probably formed by solution collapse initiated in the underlying Redwall Limestone.
Uranium ore is concentrated in places along the pipe border and is distributed in irregular masses within the pipe. Uraninite and pyrite at the center of the pipe grade into a complex mixture of chalcocite, tennantite, chalcopyrite, galena and uraninite at the margins.
The pipe structure and mineral distribution suggest a hydrothermal origin, but a direct unmixed magmatic source is improbably. The ore solutions may have originated in a distant hydrothermal source and in moving upward mingled with groundwater.
A minimum age of about 141 million years has been furnished by U/Pb dating.
LOGGING REQUIREMENTS
In order to log this EarthCache, send me your answers to the following questions either through email from my profile page or through messages on my profile page.
1: Look down the canyon to the structure at bottom of the mine. What layer of the Grand Canyon was the Uranium deposit discovered in? (Kaibab Formation, Toroweap Formation, Coconino Sandstone or Hermit Formation)
2: What type of rocks is the Orphan Mine found in?
3: Pictures are not required but are appreciated. Please post a pic of you or your GPS from the overlook with any part of the mine in the background.
NATIONAL PARK SERVICE POLICY
In accordance with National Park Service Policy review on "GPS-Based Recreational Activities in National Park areas" updated October 1, 2009, this EarthCache does NOT require or encourage participants to leave the marked trail, move, touch, or in any other manner disturb the natural environment. Please use caution and stay at least 6 feet away from the edge of the canyon at all times. EarthCaches are a type of geocache that may provide participants with a learning experience in the geosciences, and do not involve a physical cache.
This EarthCache was developed in cooperation with and with written permission from the Grand Canyon National Park.