There are several geologically distinct types of uranium deposits; these include unconformity related, sandstone hosted, paleoplacer, calcrete and pegmatite.  However, by far the most important type economically, because of high grade and large size, is the unconformity type.  Examples of unconformity deposits include:

Cigar Lake and McArthur River are the two highest grade, large uranium deposits ever discovered in the world.

Unconformity deposits are so named because they are spatially and genetically related to the geological hiatus, or unconformity, at the base of major sedimentary basins.  Specifically, the most prospective basins are accumulations of oxidized clastic sediments that were deposited during Middle Proterozoic time, 1.8-1.0 billion years ago.

Uranium, which was liberated by erosion that created the Proterozoic sediments, and from the sediments themselves after deposition, migrated through the sedimentary basin until the fluids encountered a suitable deposition site.  Deposition sites have two components; a favorable chemical environment, and an open space in which to accumulate uranium.  A reducing chemical environment allows hexavalent uranium, which is transported by oxidized fluids, to be reduced and precipitated in the tetravalent state.  The unconformity at the base of the Athabasca basin is in effect a basin-wide oxidation/reduction (redox) boundary, which can facilitate precipitation of uranium.  Open spaces are provided by faulting, fracturing, dissolution of the clastic sediments, and/or alteration of the host rocks.

Older rock units, Lower Proterozoic and Archean basement that underlie the sediments of the Athabasca and other Proterozoic basins, include granite, gneiss, schist and calcareous rocks.  Metamorphosed pelitic and semi-pelitic basement rocks are represented now as gneiss and schist.  Gneiss and schist, particularly those containing graphite and sulphides, provide ideal settings for accumulation of uranium for two reasons; graphite enhances zones of weakness in pelitic rocks that promotes faulting and development of open spaces, and graphite and sulphides help facilitate the chemical change necessary to reduce and precipitate uranium.  Some of the basement units may also have contributed uranium to the deposits.

The graphite and sulphides have an added bonus for exploration.  They are electrically conductive and can be detected with geophysical techniques, thereby providing an indirect method of searching for uranium deposits.

Proterozoic accumulations of clastic sediments, like the Athabasca Basin, are not significantly metamorphosed and, from the time they were deposited, have changed mainly through diagenetic alteration.  Accordingly, the porosity and permeability of the sediments has been maintained, which has allowed uranium to accumulate over hundreds of millions of years.

Unconformity uranium deposits may be hosted by the basement schists, gneisses, granites and carbonates, by the Athabasca clastic sediments, or more commonly, the deposits straddle the unconformity and are hosted by both.  Unconformity deposits are not only large, but they include the highest-grade uranium deposits in the world; and the Athabasca Basin deposits are by far the highest grade unconformity deposits in any Proterozoic basin.

Pitchstone's Saskatchewan properties are located within the main production area of the Athabasca Basin.  The high grade Athabasca deposits have catapulted Saskatchewan into the number one spot of world uranium producers; the relatively small region of the eastern Athabasca Basin produces 22% of the worlds uranium.