We released our new report yesterday “Partial database for breccia pipes and collapse features on the Colorado Plateau, northwestern Arizona” (http://www.azgs.az.gov/news_releases2015.shtml#jun24) that found concentrations of breccia pipes 10 to 100 times higher than previously known, in two test study areas. Breccia pipes are primary targets for uranium and other minerals. We believe that same density of pipes extends across the entire region, which would make the area one of the largest and richest uranium districts in the world.
I interviewed lead author Jon Spencer on our video magazine Arizona Mining Review which was webcast yesterday and is online at https://www.youtube.com/watch?v=PGhJT945Ksw.
We will be sharing this report with our congressional members to help them make informed decisions about the proposed Grand Canyon Watershed National Monument.
Mineralized breccia pipes—pipe-like masses of broken rock—may contain high-grade uranium ore and variable amounts of copper, gold, silver, vanadium and other mineral ore. More than 71 mineralized breccia pipes have been discovered in the region, and as of 2010, nine of these pipes yielded more than 10,500 metric tons of uranium.
Breccia pipes are vertical formations, typically a few tens to hundreds of feet across and hundreds to thousands of feet in vertical extent. The pipes formed more than 200 million years ago within Paleozoic and Triassic rocks over a broad area around Grand Canyon. The pipes formed as groundwater, flowing through Redwall Limestone dissolution breccias and along fracture zones, dissolved more limestone, causing collapse of overlying rocks and possibly creating sink holes.
This new map is accompanied by an Excel Workbook database with three datasets. The datasets are drawn from geologic maps produced by the U.S. Geological Survey and from mapping by geologic consultant and co-author Karen Wenrich. The datasets include point locations and comments on features identified as 1) breccia pipes, 2) collapse structures that might be breccia pipes, and 3) circular features that might be collapse features or breccia pipes.
Some features occur in more than one dataset, so the total number of features is less than the 3,286 features comprising the three datasets. GIS data as ArcGIS shapefiles built from the three datasets are included with this publication.
US Geological Survey geoscientists estimated that roughly 8% of breccia pipes contain some mineralization (Wenrich and Sutphin, 1988). A fraction of those are likely to host economic concentrations of minerals.
In 2012, the U.S. Department of the Interior withdrew from mining 1,006,545 acres of federal lands in northern Arizona for a 20-year period to prevent further exploration or development of uranium on those lands. Withdrawal curtails new exploration of breccia pipes and limits production to those pipes with valid existing mineral rights.
Spencer J.E., Wenrich, K. and Cole, T., 2015, Partial database for breccia pipes and collapse features on the Colorado Plateau, northwestern Arizona. Arizona Geological Survey Digital Information, DI-42, 5 p., 1 map plate, shapefiles, and Excel Workbook.
Wenrich, K.J. and Sutphin, H.B., 1988, Recognition of Breccia Pipes in Northern Arizona. Arizona Bureau of Geology and Mineral Technology, Fieldnotes, v18, #1, p1-5.