The CY 4 occurrence is located on Mount Weir, about 41 kilometres east of the community of Atlin.
Mount Weir lies within the Surprise Lake batholith (Surprise Lake Plutonic Suite), a Late Cretaceous lobe of the Coast Plutonic Complex. The batholith consists of several phases of alaskite, quartz monzonite and granite.
In Zone A, fractures filled with smoky quartz veins and hosting galena, sphalerite, magnetite and hematite occur in coarse-grained alaskite. In 1977, a grab sample from a 20 centimetre wide, 40 centimetre long quartz vein assayed 0.15 per cent uranium, 0.11 per cent lead and 4.0 per cent zinc (Assessment Report 6898). In 1977, the original discovery zone, Anomaly or Zone A, was found on the summit of Mount Weir, as a result of ground follow up of helicopter-borne radiometrics.
In Zone C, about 300 metres to the south, a yellow-orange coloured zone of supergene alteration, exposed over an area 10 by 40 metres, contains kasolite, wulfenite and vandendriesscheite. The mineralization likely leached from the highly fractured alaskite.
In 1977, an anomalously radioactive area had been delineated by Mattagami Lake Mines Ltd. during a reconnaissance helicopter-borne radiometric survey. As a result of the reconnaissance survey, Mattagami staked eleven claims in the area and during the 1977-78 field seasons carried out a detail geochemical sampling survey. In addition, a CEM survey was completed in one area of particular interest. Ground and helicopter-borne radiometric surveys, radon-in-soil survey and geological traverses were also completed.
In 2006, Aldershot Resources Ltd. conducted a spectral analysis program on their Atlin East property which covers the CX (104N 114), Mir 3 (104N 113), Mir 7 (104N 112), CX 2 (104N 111) and CY 4 occurrences. The program involved acquisition of satellite spectral data available from NASA, reconfiguring the data into a workable format, geo-referencing to TRIM map bases and extensive and rigorous classification of the data in search of indicators that might lead to the discovery of uranium mineralization.
