The Pen 1 occurrence is located about 11 kilometres northwest of Kedahda Lake on the Tanzilla Plateau, 139 kilometres north-northwest of the community of Dease Lake.

Chalcopyrite, bornite and minor galena and molybdenite occur as plates in quartz-orthoclase veins averaging 0.6 centimetre wide in hornblende diorite and quartz diorite of the Early Jurassic Christmas Creek batholith. The veins contain accessory tourmaline and epidote. Chalcopyrite also occurs in xenoliths and hornblende clots. One 0.3-metre-wide quartz vein in a cirque wall south of Loon Lake (Pen 1) contains abundant coarse molybdenite. Malachite and powellite are common. Propylitic alteration is pervasive and basaltic dikes, trending east and steeply dipping, cut the older intrusive rocks.

In 2020, Goldstrike Resources Ltd. conducted a prospecting and geochemical exploration program on its newly staked Willie Jack property, which covers the historic Irv 101 (104O 007), Irv 22 (104O 008) and Pen 1 (104O 009) showings. The prospecting and geochemical survey included the collection of 185 ridge and spur soil samples and 94 rock grab samples. The program was successful in discovering gold mineralization in bedrock with assays up to 13.9 grams per tonne gold and 25 grams per tonne silver. Copper values as high as 1.74 per cent were also obtained from bedrock samples (Press Release - Goldstrike Resources Ltd., October 19, 2020).

Significant gold assays were obtained from both granitic intrusive rocks and Mississippian-Triassic Kedahda Formation (Cache Creek Complex) sedimentary rocks. The higher-grade gold values were from narrow, steeply dipping quartz-sulphide veins hosted in a propylitic altered granite. Weakly anomalous gold values were also returned from gossanous fracture zones in granite that contain disseminated fine-grained pyrite. Auriferous samples from the sedimentary rocks near the granite contact consisted of quartz-arsenopyrite veins and resemble gold skarn mineralization. Several soil sample sites covering 4.5 kilometres of the granite-sedimentary rock contact display an anomalous gold-silver-arsenic plus/minus bismuth-antimony-tellurium signature, further suggesting gold skarn mineralization.

In 1970, the Irv and Pen claims were staked and in 1971, geological mapping was conducted by El Paso Mining and Milling Company.