Radon does not come out of solid rock ...
When looking for the source of a radon-in-soil-gas anomaly, a nearby glacial erratic boulder of radioactive granite pegmatite is not the answer. Radon does not come out of solid rock.

In the Bancroft area I measured radon in snow over a highly radioactive granite pegmatite which had been stripped and trenched. It gave off high gamma radiation, even through the snow. The snow over the stripped and trenched area had no radon, but as soon as I moved a little downhill into a tree-covered area (indicating soil under the snow) I found anomalous radon in the snow. This was no surprise. The radium (immediate precursor of radon) has been washed downhill from the outcrop, either in solution or in ground up uranium minerals and deposited in soil. Being fine grained this soil can release some radon.

We did a similar survey over the Faraday mine. In this case there was some soil over the radioactive pegmatite and we also collected soil samples and analysed for radium and uranium. As expected, the radium and uranium anomaly was shifted downhill, and the radon-in-snow anomaly followed the radium in the soil, not the radioactive pegmatite. See http://www.finderschoice.com/radon/faraday.php

The same applies to a lesser extent to gamma surveys. If you dig into the soil at a gamma hot spot and find a radioactive boulder or pebble of any kind and it's the only radioactive thing in the hole, then it's probably glacially transported.

but still finds subsurface uranium mineralization in areas of over 99% outcrop.
  • The Radiore deposit, near Rayrock, lies beneath a hilltop with almost 100% outcrop.
  • We were initially puzzled as to how to use radon in soil gas to explore through solid rock.
  • Making a hole in solid rock would be difficult, moreover, radon would not migrate from the rock into the sample hole, and would not migrate any distance from the target to the sample site.
  • Soils suitable for radon exploration are confined to gullies, which represent fractures in the rock which in turn are loci of uranium mineralization.
  • In all cases the soils are rocky and shallow and the survey was attended by some difficulty.
  • The maps are missing from the assessment files, but we can include a description here.
  • The strongest radon anomaly occurs in an area where where uranium mineralization was intersected in three adjacent diamond drill holes. At this point a radon value of 1004 counts per minute was observed along with several lower though still anomalous values.
  • A second anomaly, with two radon values over 100 cpm occurs over a different area of drill-intersected uranium.
  • These intersections detected by radon were 50 feet deep.
  • In surveys of this type it is important to separate out the thoron from the radon readings.
Robert H. Morse, Ph.D., P.Eng.
August 13, 2014

  • We measure: radon - radium - thoron - radon daughters - alpha radiation.
  • The Lucas cell is recognized as the most sensitive and reliable method for these elements.
  • Our instruments are used around the world in exploration for uranium, oil & gas, groundwater and hydrothermal, and in environmental protection, health physics, earthquake prediction, and evaluation of hydrocarbon and NAPL contamination.
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