At the Mountain showing, pits and trenches reported from the 1800's and drilling in 1976 intersected a quartz vein in black argillites of the Helikian Lower Aldridge Formation (Purcell Supergroup). Diamond-drill hole 76-4, drilled to a depth of 152.5 metres, intersected banded black argillites with bands and disseminated pyrite and pyrrhotite along bedding surfaces. Scattered quartz veins and fracture-fillings host chalcopyrite, galena and some siderite as well as pyrite and pyrrhotite. Similar results were obtained from diamond-drill hole C-1-83 drilled in 1983.

Like the Rex zone (082GSW095), the Dean zone is also a two-vein system containing copper, silver and gold mineralization. The Dean zone outcrops in the proximity of “the eastern Trench boundary", 1.5 kilometres south of the Rex Zone. Vein DZ1, dips variously from 85 degrees north to 85 degrees south as indicated in an adit driven 25 metres on a bearing 080 degrees. Vein DZ2, striking 120 degrees and dipping vertically, was sampled across a 1.5 metre width in a trench exposure and was found to assay 0.5 per cent copper with traces of gold and silver (Exploration Report for Gallowai Metal Mining Corporation, September 22, 1997, Property File Document (PFD 676699).

In 1976, vertical diamond-drill hole 76-4, was located about 1.5 kilometres east of the south end of Rosen Lake and drilled to a vertical depth of 152.2 metres for R.H. Stanfield (Assessment Reports 5905).

In 1983, a core hole (C-1-83), re-entered the 152.2 metre vertical 1976 hole (76-4) on the Cedar 3 claim and was deepened to 1059 metres an additional drill length of 907 metres (Assessment Report 12796).

In 1992 a helicopter borne DIGHEM survey over the Balsam, Cedar, and Dogwood claims of R. H. Stanfield (Bul River Mineral Corporation Ltd.) was completed (Assessment Report 23012). In 2017, an NI43-101 technical report for Purcell Basin Minerals Inc. defined exploration targets peripheral to the copper ore body on the Bull River Mine property (Assessment Report 37195). This work was facilitated by the processing of Dighem airborne EM (AEM) data acquired from 1991-1997 surveys. Processing and interpretation of the historic Dighem data identified several target areas of coincident EM and magnetic features. Figures 7, 8, and 9 show magnetic and resistivity coverage from the Bull River mine area southeast to the Elko community area (Assessment Report 37195).

Refer to Bull River (082GNW002) for details of the greater Bull River property which contained the Rex (082GSW095) and Mountain (Dean) occurrences and 24 other MINFILE documented mineral occurrences (as of October 2022).