The 428 South copper occurrence is centred in claim 24 in the 428-claim group, located 6.5 kilometres north of the Gataga River and 7 kilometres southwest of Churchill Peak in the mountainous Muskwa Ranges of the Northern Rocky Mountains (Assessment Reports 2644, Geology Map; 3318, Map 2).
The occurrence is in a region known as the Muskwa Anticlinorium, a major north-northwest–trending structure characterized by moderate folding and thrust faulting. The structure consists of Middle Proterozoic (Helikian) rocks of the Muskwa Assemblage, as well as Paleozoic rocks (Geological Survey of Canada Map 1343A; Geological Society of America, Geology of North America, Volume G-2, pages 111, 639). All belong to Ancestral North America (Geological Survey of Canada Map 1713A). Northeast- to northwest-trending, Proterozoic, diabase dikes are common in the region.
The 428-claim group is underlain mainly by the Aida Formation of the Muskwa Assemblage, comprising slaty argillite, argillaceous limestone and dolostone (Geological Survey of Canada Memoir 373, Paper 67-68; Assessment Reports 2644, 3318). The strata strike northwest and dip gently to moderately southwest. They are intruded by diabase dikes, some of them 20 metres thick, which 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 zone is important because it contains numerous mineralized quartz-carbonate veins and vein systems (Assessment Reports 2644, 3318). The veins strike around north and dip steeply to vertically. Many 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. Individual veins range in width from 1 centimetre to 3 metres, with an average of 1 metre, and some occur in swarms between 3 and 20 metres wide. The larger veins are more persistent, reaching greater than 200 metres in length, whereas smaller veins are discontinuous and lenticular. Some veins are slightly disrupted or offset by younger faults.
The mineralization in this belt is intermittent but can be assigned to three main areas (Geology, Exploration and Mining in British Columbia 1971). The 428 South occurrence is towards the southern end of the belt (the other areas are covered by the 428 North and 428 Central occurrences, MINFILE 094K 015 and 094K 030, respectively). Here, the mineralized belt has been traced along strike for approximately 1000 metres. The quartz-carbonate (ankerite) veins in the zone are generally sporadically and weakly mineralized with irregular masses, lenses or disseminations of chalcopyrite. Disseminated pyrite occurs in some veins, and a minor amount of galena in one locality. The strongest mineralization appears to be associated with the most abundant inclusions of wallrock, which is generally altered (silicified and sericitized) (Assessment Report 3318). Secondary malachite, azurite and limonite occur on some surfaces in the veins and sedimentary hostrocks.
A wide range of assay values has been obtained from chip samples. A representative or average grade would be approximately 0.5 per cent over 1 metre, although short, high-grade sections yield assays such as 3.51 per cent copper over 0.9 metre (Assessment Report 2644, Geology Map), and 2.2 per cent copper over 1.28 metres (Assessment Report 3318, Map 2).
The fault zone hosting the 428 mineral occurrences is probably the same as that hosting the Book 6 (MINFILE 094K 019) and Book 9-10 or PJ Pelletier (MINFILE 094K 052) occurrences several kilometres to the south (Geology, Exploration and Mining in British Columbia 1971).
More recent work, in 2021, describes a quartz-carbonate vein hosting trace to 1 per cent chalcopyrite being exposed along a strike of 024 degrees for approximately 20 metres with a dip of 85 degrees west. A chip sample (D723478) from the vein assayed 1.035 per cent copper over 0.3 metre (Assessment Report 39912).
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 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 photo-geological interpretation, rock sampling and 1.6 line-kilometres of combined airborne magnetic and ground electromagnetic (VLF) surveys were completed on the property.
