The area of the Dolly Varden occurrence, in the vicinity of Siwash Creek, is characterized by poorly to moderately bedded, dark coloured, pyritic, slaty argillite locally intercalated with thin beds of greywacke and siltstone, all assigned to the Ladner Group. These rocks have been intruded by locally altered, light coloured, felsic sills and dykes.
Gold is spatially associated with feldspar porphyry dykes and sills in the area of the three forks of Siwash Creek. Fine gold, occurring both in pyritic quartz veins and their intrusive host, is generally coated with a film of iron oxide (Bulletin 79, page 62). Refer to the Roddick occurrence (092HNW004) for details of regional geology and typical mineralization style in the Siwash Creek area.
Development work within the Dolly Varden/Jubilee claims consisted of a number of opencuts spread along one such dyke, striking northwest and dipping to the northeast. At one point, a quartz vein varying from 30 to 60 centimetres wide occurs along one wall of the dyke with Ladner Group slate along the other. Rocks on either side of the quartz vein are cut by a network of quartz stringers. Pyrite, chalcopyrite and galena occur in the quartz and the porphyry. Gold was reported to have been panned from surface samples.
An adit, started at an elevation of 1152 metres, was apparently driven to intersect the dyke, which is described as a highly altered (silicified) pyritic aplite. Samples across the dyke contained only trace amounts of gold and silver.