The Rex East occurrence is located in the headwaters of Fosselli Creek, approximately 7 kilometres west of Dunsmuir Point, on the Alberni Canal.

The area is underlain by basaltic flows of the Upper Triassic Karmutsen Formation (Vancouver Group), intruded by swarms of quartz feldspar porphyry dikes. A few outcrops of hornblende diorite of the Jurassic Island Plutonic Suite were observed in the area.

Locally, a 0.25-metre-wide sulphide-chlorite-quartz vein, oriented 140 degrees and dipping 20 degrees, is hosted in an epidote altered basalt. Sulphides include chalcopyrite and pyrite.

In 1996 through 2006, SYMC resources prospected the area as part of the Macktush property along the west side of the Alberni Inlet, now called the Dauntless property. A select rock grab sample (343892) yielded 0.009 per cent molybdenum, 13.91 per cent copper, 0.15 per cent zinc, 29 grams per tonne silver and 2.713 grams per tonne gold (Assessment Report 32484).

In 2009 through 2011, G4G Resources completed programs of geological mapping and rock and soil sampling on the area as the Macktush Copper property. A sample (J047358) assayed 10.5 per cent copper and 23.8 grams per tonne silver (Assessment Report 32484).

During 2012 through 2014, Nahminto Resources Ltd. completed exploration programs including limited prospecting, rock sampling, geological mapping and a satellite remote sensing survey and analysis on the Macktush group. A similar prospecting, geological mapping and rock sampling program was conducted on areas of the Macktush property for World Organics Inc. in 2015.