The Mun prospect is a stratabound barite deposit, situated at the headwaters of a tributary of Sulphur Creek in the Sentinel Range of the Northern Rocky Mountains (Assessment Report 7349, Plan 1). It is 5.5 kilometres northeast of the northern end of Muncho Lake, which is on the Alaska Highway.
The rocks in the area are predominantly Upper Silurian to Middle Devonian carbonates and shales belonging to Ancestral North America (Geological Survey of Canada Map 1713A). The regional trend is north-northwest, and the rocks have been deformed into broad folds, cut by thrusts and other faults.
The Mun claims are underlain by the Upper Silurian to Middle Devonian Wokkpash Formation and the Upper Silurian to Middle Devonian Stone and Dunedin formations (Geological Survey of Canada Open File 673, Assessment Report 7349). The Wokkpash Formation comprises distinctive, yellow-weathering dolomitic quartz sandstone and dolostone. The Stone Formation consists of pale grey, very fine grained dolostone, dolostone breccia and dolomitic quartz sandstone. The Dunedin Formation comprises grey, well-bedded limestone and argillaceous limestone, and minor calcarenite and dolostone. Also, the Upper Silurian to Lower Devonian Muncho-McConnell Formation may be present in the southeastern corner of the property.
The Mun deposit consists of two bands of bedded barite, possibly a single, discontinuous unit, within the Stone Formation (Assessment Report 7349). The setting is similar to the Mo occurrence (094N 008) 3 kilometres to the northeast, and the BV occurrence (094N 002) 2 kilometres to the southeast, although in those there is a zone of baritic breccia immediately overlying the bedded barite. The Mun occurrence differs in that the barite may be at a higher level in the Stone Formation, and there is no baritic breccia above it (Assessment Report 7349). The occurrence is situated in a broad, northerly-plunging syncline. The bedded barite and the host rocks generally strike northwest and dip gently to steeply southwest, although there is some variation due to faulting and folding in the area.
One of the two bands of bedded barite is in the north central part of the property. It dips 60 degrees southwest and can be traced along strike for about 500 metres; its exposed width is about 13 metres, but it may be wider. A continuous chip sample (sample section Mun 1) across the zone assayed 50.22 per cent barite (BaSO4) over 12.95 metres (Assessment Report 7349).
The other barite zone, near the northwest corner of the property, is larger and thicker, and extends for about 350 metres. Here, the barite beds dip north at 58 degrees. A continuous chip sample (sample section Mun 2) assayed 50.93 per cent BaSO4 over 17.4 metres (Assessment Report 7349). East of this locality, the strike of the host dolostone changes to southeast, and barite float can be traced downslope for 300 metres towards the first barite zone. Before it reaches it, however, there is an east-striking fault containing highly fractured dolostone and a 3-metre wide, near vertical vein of barite.
Similar deposits in the region, such as the BV occurrence (094N 002), have been interpreted as of replacement origin.
In 1978, Siscoe Metals of Ontario Ltd. staked the Mun claims conducted a geological investigation of the deposit in the same year. A total of 49 samples were collected (Assessment Report 7349). At that time snow cover in the shaded northerly facing cirque prevented other than sampling of the discovery outcrop of bedded barite in a creek on the valley floor. Initial prospecting had also uncovered abundant barite float at the southern end of the cirque and north of the MUN 1 sample section. Follow-up work continued in late 1978.
