<p>I'm holding a Geiger counter next to a piece of radioactive rock talus enriched in secondary uranium minerals.  This is an outcrop in the town of Elliot Lake, Ontario.  The radiation reading reached between 1 and 3 milliroentgens per hour.
</p><p>The rocks are uraniferous, pyritic, K-feldspar-bearing, quartz-pebble conglomerates of the Matinenda Formation.  The unit dates to about 2.3 to 2.48 billion years old.  Detrital zircons in the Matinenda Formation range in age from &gt;2.6 Ga to &gt;2.8 Ga.
</p><p>The rocks here range from quartz-pebble conglomerates to pebbly sandstones to apparent granulestones.  K-feldspar granules are visible, as are detrital pyrite sand grains and black specks of apparently detrital uraninite (UO2 - uranium dioxide sand grains).  The sediments were deposited in an ancient braided river system.
</p><p>Geiger counter-wise, these rocks are "hot" (= radioactive).  Iron oxide-coated joint surfaces are hotter - they have concentrations of remobilized uranium minerals.  Some chunks of yellowish-colored, secondary uranium minerals are present at the site.
</p><p>Stratigraphy: Matinenda Formation, Elliot Lake Group, Huronian Supergroup, Paleoproterozoic, ~2.3 to 2.48 Ga
</p><p>Locality: Spine Road Outcrop - roadcut on the northern side of the western end of Spine Road, due east of Hector Lake, western side of town of Elliot Lake, Ontario, southeastern Canada (46° 22’ 59.60” North latitude, 82° 41’ 02.99” West longitude)
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<hr><p>Some info. from: 
</p>
Easton (2011) - Detrital zircon geochronology of the uraniferous Paleoproterozoic Matinenda Formation (Huronian Supergroup), Elliot Lake, Ontario.  Geological Society of America Abstracts with Programs 43(5): 41.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/47445767@N05">James St. John</a>
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<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/jsjgeology/47722571651/">Radiation reading of rock talus enriched in secondary uranium minerals (Spine Road outcrop, Elliot Lake, Ontario, Canada) 1</a>