The Rum 66 occurrence consists of copper and molybdenum mineralization in mountainous terrain immediately east of the Tredcroft Glacier, 23 kilometres southeast of the southern end of Tatlayoko Lake.

The occurrence lies within a granodiorite to quartz diorite stock of the Late Cretaceous to Paleocene Bendor suite about 3 kilometres southwest of an important northwest-striking fault, the Stikelan fault. The stock was emplaced into a complex belt of Upper Triassic and Lower Cretaceous sedimentary and volcanic rocks of Stikinia Terrane and Overlap assemblages (Geological Survey of Canada Map 1713A). Intruded country rocks are mainly Upper Triassic mafic and intermediate volcanics and minor sedimentary rocks of the Mount Moore Formation, and Lower Cretaceous to Upper Cretaceous sedimentary rocks of the Taylor Creek Group along its northwest contact. The granodiorite stock is about 4 kilometres long and about 2 kilometres wide, elongate in a northwest direction, in common with the dominant structural trends in the area. The intrusion of the stock caused doming of the country rocks and low-grade contact metamorphism. Lamprophyre dikes are common in the area.

The mineralization is virtually confined to the granodiorite near its northwestern end (Assessment Report 2671). An area of about 1500 by 200 metres contains a number of small mineral showings, each about 25 by 3 metres. Coarse chalcopyrite and minor molybdenite occur in closely-spaced fracture-fillings of quartz, or as disseminations in the granodiorite. Locally aplite dykes and pegmatite are present, as are veinlets of calcite and epidote. In one locality, chalcopyrite occurs in volcanics, probably Upper Triassic, 300 metres north of the stock.

Assay values of samples from the mineralized zone range from 0.04 to 0.86 per cent copper. The zone is estimated to contain 0.5 per cent copper overall (Assessment Report 2671). Gold and silver were also assayed but they are not significant.

Geological mapping by Pacific Petroleums Ltd. on their Rum 1-96 mineral claims has shown that a number of small, mineralized zones occur sporadically throughout an area 1525 metres long and 215 metres wide. The zones are approximately 3 metres wide and 23 metres long, having an estimated (unverified) grade of 0.50 per cent copper (Assessment Report 2671). Geological mapping was done on a scale of 1 inch to 1000 feet.

See Tred (092N 060) for information on similar showing occurring the same stock about 2.5 kilometres to the southeast.