The CY 6 occurrence is located southwest of Caribou Creek in the southwest corner of the CY 6 claim (ca. 1979), about 41 kilometres east of the community of Atlin.
This showing is located near the southern margin of the Surprise Lake batholith (Surprise Lake Plutonic Suite) which covers about 1100 square kilometres east and northeast of Atlin. The batholith is dated at 70.6 plus or minus 3.8 million years or Late Cretaceous. It is composed primarily of medium grained, equigranular alaskite which is essentially a leucocratic granite with microcline and orthoclase with subordinate quartz and may or may not contain plagioclase and mafics. There are some coarse grained, quartz feldspar porphyritic varieties. The contacts between the various textural varieties are commonly gradational. Massive aplitic dikes crosscut the batholith. There are also some very coarse grained pegmatitic zones within the alaskite with large quartz and feldspar crystals and books of biotite. The width of these zones varies considerably, but the contacts are almost always sharp.
Two different zones of mineralization occur on a steep ridge composed of alaskite, just south of Caribou Creek. These were examined and described in 1979 (Assessment Report 7556). The first zone is a linear zone 4 to 5 metres wide containing abundant sphalerite. This zone is exposed over a strike length of 180 metres and a vertical height of about 120 metres.
Thirty metres south of this zone is a second zone of highly friable fine grained, green rock containing up to 15 per cent magnetite and 20 per cent sphalerite. This zone was interpreted as mafic dikes intruding alaskite but was later identified as "chloritized alaskite veins". These "veins" are characterized by very fine grained black cores of up to 90 per cent sphalerite locally. The intruded alaskite sometimes shows silicified contacts with the "veins", up to 1 metre wide. The "veins" strike at 048 degrees and dip 62 degrees northwest. In 1979, a sample of this rock analyzed 0.20 per cent lead, 0.18 per cent zinc and 0.55 per cent fluorine (Assessment Report 7556).
In 1980, several diamond-drill holes were drilled, some intersecting sections of "chloritized alaskite veins" over 20 metres wide. Locally these contained up to 50 per cent sphalerite, 25 per cent magnetite and a trace of galena (Assessment Report 8638).
In 1977, eleven CY and Eng claims were staked in the Weir Mountain area for Mattagami Lake Mines Ltd. to cover a radioactive area discovered by a regional helicopter-borne radiometric survey. Geochemical sampling, radon detection in water and soil, and radiometric surveys were carried out to cover most of the CY claims in 1977. Detailed geochemical and geophysical surveys (magnetometer, Radem, VLF-EM, induced polarization, radiometric) were completed during the summer of 1978, predominantly on the CY-3, CY-4 and CY-6 claims. During the first part of the 1979 program (June and July) work was concentrated on the CY-3, CY-6 to CY-9, and ENG 1-3 claims. This included geological mapping, prospecting, magnetometer and radiometric surveying, and radon in soil surveys. This work was conducted on four interconnected grids; magnetometer surveys were conducted over all grids although the survey is not complete in some areas. More than 640 soil samples were collected over three of the grids.
