The 428 Central Zone copper occurrence is centred near the common corner of claims 3 to 6 in the 428-claim group, 8 kilometres north of the Gataga River and 6 kilometres southwest of Churchill Peak in the mountainous Muskwa Ranges of the Northern Rocky Mountains (Assessment Reports 2644, Geology Map; 3318, Map 3).
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). Northeast– to (more commonly) north-northwest–trending, steeply dipping diabase or gabbroic dikes are common in the region. These Proterozoic intrusions were structurally controlled; their presence and orientation are closely related to regionally important fault and fracture zones in the Proterozoic sedimentary rocks.
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 that strike north or north-northwest and dip steeply west. The dikes, some of them branching, are up to 20 metres thick. There is commonly a narrow zone of chloritic and epidotitic alteration around them. In the extreme east of the property, a thrust places all these rocks on a panel of Lower Paleozoic rocks.
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, 10960). 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 Central occurrence is typical and is in the approximate centre of the belt (the other areas to the north and south are covered by the 428 North (MINFILE 094K 015) and 428 South (MINFILE 094K 055) occurrences, respectively). The vein system here is discontinuously exposed for approximately 750 metres. The quartz-carbonate (ankerite) veins are mineralized with irregular masses, lenses or disseminations of chalcopyrite; minor amounts of galena and disseminated pyrite occur sporadically in some veins. 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.
Assay values of chip samples range from 0.16 to 0.5 per cent copper over 1 metre and 6.4 metres, respectively (Assessment Report 3318, Map 3). Much higher values have been obtained from highly mineralized sections, such as 2.56 per cent copper over 9 metres (Assessment Report 2644, Geology Map).
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).
In 2021, a chip sample (D723508) from the 428 Central vein hosting semi-massive chalcopyrite (8 per cent) and bornite (1 per cent), as exposed in a ravine at an elevation of approximately 2080 metres, yielded 5.88 per cent copper over 1.5 metres (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 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.
