The 428 North copper occurrence is centred near the common corner of claims 39 to 42 in the 428-claim group, 9.5 kilometres north of the Gataga River and 5 kilometres southwest of Churchill Peak in the mountainous Muskwa Ranges of the Northern Rocky Mountains (Assessment Reports 2644, Geology Map).
The occurrence is in a region known as the Muskwa Anticlinorium, a major north-northwest–trending structure characterized by southwest-dipping thrust faults and moderate folding. This region is dominated by Middle Proterozoic (Helikian) clastic and carbonate rocks, unconformably overlain by Paleozoic rocks (Geological Survey of Canada Map 1343A; Geological Society of America, Geology of North America, Volume G-2, page 639). 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). Structurally controlled, Proterozoic diabase or gabbroic dikes are common in the region.
The 428-claim group is underlain mainly by the Aida Formation of the Muskwa Assemblage, comprising argillaceous limestone, black slaty argillite, and dolostone (Geological Survey of Canada Memoir 373, Paper 67-68; Assessment Reports 2644, 3318, 10960). The strata strike northwest and dip gently to moderately southwest. They are intruded by diabase dikes that strike north or north-northwest and dip steeply west.
A major fault zone passes through the centre of the claim group, striking north to northwest and dipping west approximately 70 degrees. It can be traced for greater than 3 kilometres and is generally 15 to 60 metres wide. The fault zone is important because it contains numerous mineralized quartz-carbonate veins and vein systems. The mineralization is intermittent but can be assigned to three main areas (Geology, Exploration and Mining in British Columbia 1971). This occurrence, the 428 North, is in the north part of the belt; the areas to the south are covered by the 428 Central (MINFILE 094K 030) and 428 South (MINFILE 094K 055) occurrences. The 428 North occurrence is much smaller than 428 Central and 428 South, but is otherwise typical. The veins generally strike approximately north and dip steeply west to vertically. Most veins are discontinuous and lenticular, and 1 metre or less in width. Some veins follow the margins of dikes in the fault zone, which may be sheared; others may be concordant with the prominent slaty cleavage in the sedimentary country rocks. The quartz-carbonate (ankerite) veins are mineralized with irregular masses, lenses or disseminations of chalcopyrite.
High assay values have been obtained from highly mineralized sections, such as 2.68 per cent copper over 0.9 metre (Assessment Report 2644, Geology Map), but this is not representative of the grade of the whole belt, which is lower and quite erratic (Assessment Report 3318).
Work History
In 1970 and 1971, Windermere Exploration Ltd. completed programs of geological mapping, hand trenching and rock sampling on the area as the Bronson and 428 claim groups. In 1979 and 1980, Halferdahl & Associates Ltd. completed a regional program of soil sampling on the area as the Tuchodi property.
In 1981 and 1982, Coppex Syndicate completed a program of geological mapping and geochemical (rock and soil) sampling on the area as the BE and MO claim groups.
In 2005, Twenty-Seven Capital Corp. completed a regionally extensive program of geochemical (rock, silt and soil) sampling and a 9002.0 line-kilometre airborne magnetic survey on the area as the Muskwa property.
In 2012, a remote sensing and geophysical data interpretation program was completed on the area as part of the regionally extensive Northern IOCG property.
In 2020, Fabled Copper Corp. completed a minor program of rock sampling and historical data review on the area as the Bronson property. The following year, a program of photogeological interpretation, rock sampling and 1.6 line-kilometres of combined airborne magnetic and ground electromagnetic (VLF) surveys were completed on the property.
