Diamonds in the Apple Formation?
Claude Dion and Jean Goutier
Direction de Géologie Québec
The Apple Formation (Goutier et al.,
1998, 1999, 2000; Paquette and Gauthier, 1997) in the Lac Yasinski
area (NTS sheet 33F), Baie James region, is a quartz-rich sedimentary
unit composed of quartz arenite and pyritic and uraniferous conglomerate.
This unit (PDF Format,
411 Kb) unconformably overlies the Archean basement,
which consists of tonalitic gneiss of the Langelier Complex (2.78
to 3.6 Ga). The Apple deposit (map sheet 33F/02) is a
uraniferous conglomerate-type deposit (Goutier et al.,
1999) with a geological resource of 8.5 Mt at 0.052% U3O8 (Robertson et al., 1986). This deposit, discovered by Canico
in the early 1970s, bears some resemblance to paleoplacer-type
gold or uranium deposits found in the Witwatersrand Basin in South
Africa and at Elliot Lake in Ontario (Gauthier et al.,
1997). However, gold grades at Apple are low (below 100 ppb Au;
Paquette and Gauthier, 1997).
Click for enlargement
Heavy mineral accumulations encountered in placer-type
deposits constitute important resources for several mineral substances
such as precious metals (gold, platinum group elements), oxides
(cassiterite, rutile, magnetite, ilmenite), industrial and high-technology
minerals (garnet, zircon, monazite), and gemstones (diamond, ruby,
sapphire). In Québec, these types of deposits are known to
occur in the Beauce region (gold placers) and in the Côte-Nord
region (heavy mineral deposit at the mouth of the Rivière
Natashquan). Paleoplacers are similar deposits that were subsequently
modified to various degrees by metamorphism and hydrothermal fluid
circulation, and that have been preserved through geological time.
The Apple deposit is a rare example of this type of mineralization