The Callison is a showing of copper mineralization in the headwaters of Chischa River, 13 kilometres northeast of Mount Stalin in the mountainous Muskwa Ranges of the Northern Rocky Mountains (Vail, J.R. (1957) - Thesis, Geological Map).
The occurrence is in a region known as the Tuchodi Anticline, an open fold structure which formed on a ramp of a major northeast-verging thrust (Geological Society of America, Geology of North America, Volume G-2, pages 639, 642). Exposed in the anticline are rocks as old as Middle Proterozoic (Helikian), and these are flanked by Paleozoic rocks (Geological Survey of Canada Map 1343A). All belong to Ancestral North America (Geological Survey of Canada Map 1713A). The Middle Proterozoic rocks are pre-Windermere Supergroup, and are known as the Muskwa Assemblage (Geological Society of America, Geology of North America, Volume G-2, page 111). This assemblage of carbonate and clastic rocks has been divided into seven formations. From its location and limited descriptions, the Callison showing is probably in either the George or overlying Henry Creek Formation, or possibly both (Vail, J.R. (1957) - Thesis). The George Formation consists of fine-grained limestone and dolostone, and the Henry Creek Formation is mainly calcareous mudstone, with minor sandstone and limestone (Geological Survey of Canada Memoir 373, Paper 67-68).
The main Callison showing is in the Chischa River canyon (Vail, J.R. (1957) - Thesis). Mineralization is hosted in quartz-calcite-ankerite veins associated with faults, in shaly limestone, calcareous shale and argillite. The faults and veins are vertical, strike 320 degrees, and are concentrated in a 45-metres wide zone marked by shearing. The amount and sense of displacement are not known. Massive chalcopyrite occurs in zones up to 60 centimetres wide. Some limonite and malachite are present.
The fault zone and mineralization reappear above the talus on the slopes about 900 metres to the south of the main showing, where it is 15 to 30 metres wide and consists of quartz-calcite veins with some chalcopyrite. The fault zone can be traced even farther southeast, indicating an overall length of about 3 kilometres.
A reference has been made to disseminated chalcopyrite in a thick-bedded quartzite in the Tuchodi Formation (a younger unit of the Muskwa Assemblage) in this general area, that is, the headwaters of the Chischa River, 10 kilometres north of the Tuchodi Lakes (Geology, Exploration and Mining in British Columbia 1971). It is not clear if this has any relation to the Callison showing, the nearest MINFILE occurrence.
