Page 59 - Introduction to Mineral Exploration

42 A.M. EVANS & C.J. MOON

TABLE 3.1 Summary of elements used in the models for unconformity-related uranium deposits by Grauch and
Moiser in Cox and Singer (1986) and Tremblay and Ruzicka in Eckstrand (1984).

Element Cox & Singer Eckstrand
Synonym: Vein-like type U U ( Ni, Co, As, Se, Ag, Au, Mo)
Commodities
(Eckstrand)
Description U mineralisation in fractures
and breccia fills in metapelites,
metapsammites, and quartz
arenites below, across, and above
an unconformity separating early
and middle Proterozoic rocks
Geological environment
Rock types Regionally metamorphosed Ores occur in clay sericite and chlorite
carbonaceous pelites, psammites, masses at the unconformity and along
and carbonates. Younger intersecting faults and in clay-altered
unmetamorphosed quartz arenites basement rocks and kaolinized cover rocks
Textures Metamorphic foliation and later
brecciation
Age range Early and middle Proterozoic Most basement rocks are Aphebian, some
affected by Proterozoic regional may be Archaean. Helikian cover rocks.
metamorphism Ore: Helikian (1.28 ± 0.11 Ga)
Depositional Host rocks are shelf deposits and Basement: graphitic schist and gneiss,
environment: overlying continental sandstone coarse-grained granitoids, calc silicate
Associated rocks metasediments. Cover rocks: sandstone
(Eckstrand) and shale
Tectonic setting Intracratonic sedimentary basins Relatively undeformed, intracratonic,
(Cox & Singer) on the flanks of Archaean domes. Helikian sedimentary basin resting
Geological setting Tectonically stable since the unconformably on intensely deformed
(Eckstrand) Proterozoic Archaean and Aphebian basement.
Deposits are associated with unconformity
where intersected by faults. Palaeoregolith
present in Saskatchewan
Associated deposit Gold- and nickel-rich deposits
types may occur
Form of deposit Flattened cigar shaped, high grade bodies
oriented and distributed along the
unconformity and faults, especially
localized at unconformity–fault
intersections. High grade bodies grade
outwards into lower grade
Deposit description
Mineralogy Pitchblende + uraninite ± coffinite Pitchblende coffinite, minor uranium
± pyrite ± galena ± sphalerite ± oxides. Ni and Co arsenides and sulfides,
arsenopyrite ± niccolite. Chlorite + native selenium and selenides, native
quartz + calcite + dolomite + hematite gold and gold tellurides, galena, minor
+ siderite + sericite. Late veins contain molybdenite, Cu and Fe sulfides, clay
native gold, uranium, and tellurides. minerals, chlorite, quartz, graphite,
Latest quartz–calcite veins contain carbonate
pyrite, chalcopyrite, and bituminous
matter