The Brandywine Number 1 Adit (Quartz Tunnel) is situated along the south side of Brandywine Creek, approximately three kilometres northwest of Brandywine Falls in the Pacific Ranges.

The prospect is underlain by diorite of the Jurassic to Tertiary Coast Plutonic Complex, outcropping along the western contact with the Callaghan Creek roof pendant of Lower Cretaceous Gambier Group volcanic and sedimentary rocks.

A one-metre wide mineralized fissure cuts the diorite body, striking 177 degrees and dipping 80 degrees west. The fissure contains narrow bands and stringers of quartz which are mineralized with streaks and disseminations of pyrite, sphalerite, galena and occasional chalcopyrite. Diorite wallrock enclosing the quartz stringers is pyritic and contains local streaks of sphalerite. The fissure walls are locally coated with pyrolusite.

A grab sample from 10 tonnes of sorted material assayed 1.37 grams per tonne gold, 96 grams per tonne silver, 12 per cent zinc, 0.3 per cent copper and 1 per cent lead (Property File - O'Grady, 1936). The best drill hole intersection (DDH QTX1, 1974) assayed 0.69 grams per tonne gold, 27.4 grams per tonne silver, 2.08 per cent zinc, 0.33 per cent lead and 0.11 per cent copper over 0.62 metres of (Assessment Report 5404).