Breccia-pipe Uranium Mining in the Grand Canyon Region and Implications for Uranium Levels in Colorado River Water
Dataset Identification:
Resource Abstract:
The Grand Canyon region contains over 1300 known or suspected breccia pipes, which are vertical, pipe-shaped bodies of highly
fractured rock that collapsed into voids created by dissolution of underlying rock. Some breccia pipes were mineralized with
uranium oxide as well as sulfides of copper, zinc, silver, and other metals. Renewed exploration during and following a steep
rise in uranium prices during 2004-2007 led some to concerns about contamination of the Colorado River related to uranium
mining and ore transport. Total breccia-pipe uranium production as of Dec. 31, 2010 has been more than 10,700 metric tons
(23.5 million pounds) from nine underground mines, eight of which are north of Grand Canyon near Kanab Creek. Colorado River
water in the Grand Canyon region currently contains about 4 g/l (micrograms per liter) of uranium (equivalent to 4 ppb [parts
per billion by mass]), with approximately 15 cubic kilometers annual discharge. Thus, approximately 60 metric tons of dissolved
uranium are naturally carried by the Colorado River through the Grand Canyon in an average year. We consider a hypothetical,
worst-case accident in which a truck hauling thirty metric tons (66,000 pounds) of one-percent uranium ore is overturned by
a flash flood in Kanab Creek and its entire ore load is washed into the Colorado River where it is pulverized and dissolved
during a one-year period to become part of the dissolved uranium content of the river (such a scenario is extremely unlikely
if not impossible). This addition of 300 kilograms (660 pounds) of uranium over one year would increase uranium in river water
from 4.00 ppb to 4.02 ppb. Given that the EPA maximum contaminant level for uranium in drinking water is 30 ppb, this increase
would be trivial. Furthermore, it would be undetectable against much larger natural variation in river-water uranium content.
Citation
Title Breccia-pipe Uranium Mining in the Grand Canyon Region and Implications for Uranium Levels in Colorado River Water
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organisation Name
Arizona Geological Survey
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