Structure: Poison Canyon Fault The Poison Canyon Fault and a series of smaller faults and fractures.

Tectonics: Chaco Slope

Deposit: The ore deposits of this district are chiefly filled fissure veins with or without some replacement of the wallrock. They are usually single fissures ranging in width from 2 ft. to 8 ft. and are filled with banded and crustified vein material. Vein systems trending north-south are valuable for gold and silver with copper occurring sparingly in places. Vein systems trending east-west or roughly radial trends are valuable chiefly for silver and copper. In the extreme southern end of the district are veins containing galena, sphalerite and some associated gold, silver and chalcopyrite. Crib sites and record numbers for this district are Alaska Group(d002800) ; info.src : 1 pub lit the deposit consists of two tabular, string-like deposits associated with fossil logs and organic debris. There is both trend and redistributed ore present.

Development: The Poison Canyon mine was the first sandstone uranium discovery in the Grants district. A Navajo sheepherder, Paddy Martinez, was drawn to this site thinking that radiation in the canyon might be responsible for the mysterious deaths of hundreds of sheep. Assays of the uraniferous ore showed appreciable quantities of selenium. Several years later Helen Cannon of the USGS geobotanical branch proposed that the deaths were due to the consumption of the noxious plant, astragalus, which grows selectively in the presence of selenium.

Geology: In this district the oldest rocks exposed are limestones, shaley sandstones and shales of the Pennsylvanian Magdalena Group which are overlain by red sandstones and conglomerates of the Permian Abo fm.. Outcrops of these sedimentary rocks appear along the lower portions of some fault blocks and in general the beds dip to the east. Tertiary to Late Cretaceous propylitic andesites are more characteristic of the region and form extensive flows, tuffs and breccias along the eastern portion of the Black Range. Rhyolite flows and tuffs overlie the andesites but are less extensive. Tectonic setting is continental platform disrupted by extensive Cenozoic vulcanism and basin and range deformation. The deposit occurs in the Poison Canyon sandstone of the Brushy Basin member of the Morrison formation.

Rock formation(s): Morrison


Ore(s): A Series Of Faults And Fractures

Other Databases

Link to USGS MRDS:	10072196

Other Regions, Features and Areas containing this locality

References