The Cliff fluorite showing is situated 250 metres southeast of Teeter Creek and 12 kilometres north of the settlement of Liard River on the Alaska Highway (Assessment Report 3975, Maps 4, 16), in one of the most important areas of fluorite mineralization in British Columbia.
The region is underlain by Lower to Upper Paleozoic, platformal sedimentary rocks of Ancestral North America (Geological Survey of Canada Maps 46-1962, 1712A, 1713A). The Cliff showing is one of many similar and significant fluorite deposits in a 17-kilometre-long belt extending north from Liard Hot Springs Provincial Park. This belt is defined by an open anticline, with a gently south-plunging axis, in the Upper Devonian Besa River Formation, with the Middle Devonian Dunedin Formation exposed in a several-kilometre wide zone in the core of the fold. All the fluorite deposits in the belt are situated at or just above or below the unconformity between these units.
The Dunedin Formation consists of mid- to dark-grey, massive to thinly-bedded fossiliferous limestone. It is generally exposed in the Teeter and Mould creek valleys, which are characterized by karst and 'mesa and butte' topography. The overlying Besa River Formation is predominantly black shale or slate and argillite, with some calcareous shale and minor, buff-brown dolomitic layers. The unconformity between the units is commonly characterized by brecciation and is very irregular in detail, probably due to an erosional or disconformable relationship between them, or to later faulting along the contact (Assessment Report 3975). The mineral deposits in the Liard fluorite belt generally occur as lenticular replacement bodies or infillings in breccias in one or both of the units.
The Cliff occurrence is located on the west-dipping flank of the anticline referred to above, although bedding attitudes are variable because of the generally low dips. Most of the area consists of Dunedin limestone exposed in north-trending cliffs over a length of 150 metres and a width of up to 30 metres. A few outcrops of Besa River shale or shale breccia are present, possibly occupying narrow, north-striking, fault-controlled structures. A chip sample in the main shale breccia outcrop contained 70 per cent calcium fluoride over 3 metres (Assessment Report 3975, Map 16). Elsewhere, thin mineralization was found at the shale's contact with the limestone by diamond drilling (hole 72-38).
The main mineralization at the Cliff is in limestone breccia or limestone (Assessment Report 3975; Geology, Exploration and Mining in British Columbia, 1972). It is unusual for the Liard region, occurring as a horizontal band of fluorite, mostly colourless but locally purple, and as fluorite veins. It is quite siliceous, possibly a relict of siliceous zones in the limestone, or possibly a by-product of the fluorite replacement (Assessment Report 3975). Diamond drill hole 72-39 contained 39.6 per cent calcium fluoride over 15.25 metres (Assessment Report 3975, Map 16). The Cliff showing is a component of the original 1975 resource estimate for the Liard Fluorspar, which was calculated at 3.5 million tonnes of 32 per cent calcium fluoride (Assessment Report 33580).
Fission-track studies of fluorite from the Gem prospect 8.5 kilometres to the south-southeast suggest that the age of the mineralization is 332 ± 56 Ma (Open File 1992-16).
See the Tam (MINFILE 094M 005) and Gem (MINFILE 094M 002) occurrence for a complete work and exploration history of the area.
