The AT 3-4 occurrence refers to several copper and silver-bearing quartz veins in the ridges west of Ottarasko Mountain (Assessment Report 18022). It is, in part, a continuation of mineralization at the AT 2 occurrence (092N 048), between 1 and 2 kilometres to the southeast.
The AT 3-4 area occurs in area of Overlap and Cadwallader terranes near the northeastern margin of the Jurassic to Paleogene Coast Plutonic Complex, within a complex stack of recumbent folds and imbricated, gently southwest-dipping thrust sheets (Geological Survey of Canada Open File 1163, Map 1713A). The northeast-directed thrusting placed an imbricated package of metamorphosed Lower Cretaceous and Upper Triassic (Carnian) volcanic and sedimentary rocks over Lower Cretaceous (Hauterivian) sedimentary rocks (Geological Survey of Canada Open File 1163, Papers 88-1E, 89-1E; Geology 1991). The thrusting took place in the Late Cretaceous because the thrusts are cut by a quartz diorite intrusion dated at 68 million years by the uranium-lead method on zircon (Geological Survey of Canada Papers 88-1E, 91-2). The area of economic interest lies within the imbricated Lower Cretaceous and Upper Triassic rocks. The local geology probably involves more than one thrust sheet, but as thrusts were not recognized as such in the pertinent data sources, a structural interpretation of the local stratigraphy is not attempted here.
The Late Triassic to Cretaceous Eastern Waddington thrust belt imbricate zone was formed from slices of 6 units, the most significant being the lower Cretaceous Cloud Drifter Formation (lKCD) consisting of sandstone, siltstone and minor conglomerate and the Lower Cretaceous Ottarasko Formation lKCD) consisting of basalts, andesites and rhyolite flows, tuffs and breccias. The other 4 units that occur include, uTrMo, uTrlm, uTrsv and uTrMM units (see MapPlace geology).
Most of the area of the occurrence is underlain by andesitic tuff and breccia, phyllite, sericitic schist, siltstone, and rarely limestone; all are metamorphosed to greenschist grade. The strata generally strike north to northeast and dip moderately to the west. The area is intruded by numerous felsic to intermediate porphyritic dykes; the dikes are generally steep, and strike northwest.
The mineralization found on the AT 3-4 group falls under 4 categories the first two of which represent western extensions of the mineralization found on claim AT 2:
1. copper-nickel-cobalt sulphides in zones of magmatic segregation within the batholith, 2. Copper bearing quartz and sulphide veins and stockworks in the andesitic upper strata on the main southwest ridge of Mount Ottarasko,
3. Auriferous quartz occurences within the volcamc series near the eastern boundary of the property. The precise source location of the float samples taken is still unclear as they have been transported by the glacier,
4. Auriferous quartz and chalcopyrite in stratabound fracture fillings within one of the volcanic flows identified near the northern boundary of the group.
Mineral showings are associated with quartz or quartz-carbonate veins, fracture-fillings and stockworks. The veins strike predominantly northwest (about 155 degrees) and are subvertical, similar to the orientations of dykes and fault zones. Typically, the veins are 10 to 20 centimetres thick, but some reach 1 metre in thickness, and may extend for over 5 metres in length. Disseminated pyrite is generally present in the veins, locally accompanied by minor amounts of chalcopyrite, malachite and galena. The quartz vein sample on which this occurrence is centred was analyzed at 24.3 grams per tonne silver, 0.1 per cent copper and 0.17 per cent lead (Assessment Report 18022). The host metavolcanics or metasediments may also contain disseminated sulphides and are commonly oxidized with limonite around the veins.
The Copper Ridge showing lies 1.6 kilometres to the southeast but is incorporated into this occurrence. It consists of quartz veins and sulphide bands in tuffaceous metavolcanics, bearing chalcopyrite, cuprite, malachite and azurite, with values up to 0.73 per cent copper (Property File - Berniolles, L.M., 1991; this source also reports significant gold and silver values in probably locally-derived float blocks).
WORK HISTORY
The HW1, HW4 and HW5 claims were staked in 1988 and 1989 by Louis Berniolles as a northern extension to his AT group (AT2, AT3, AT4 claims) that he had prospected in 1987 and 1988 seasons. Eighteen rocks were collected in 1987 and 46 in 1988.
During the summer of 1988 a prospecting program on the AT 3 claim (just south of HW1) led to the discovery of gold mineralization, in association with copper and quartz, near the northern boundary of that claim. The ground to the north was therefore staked and prospected briefly to see if there was any northward extension to the known mineralization. Good values in float samples warranted a much more intensive prospecting program during the summer of 1988.
In 1997, Blackhorn Gold Mines Ltd. carried out a small, detailed exploration program on their Nuit Range property whose purpose was to determine the significance of the main mineral prospects. Little mention is made of the AT 3-4 occurrence. The exploration program consisted of geological mapping, prospecting and rock sampling (Assessment Report 25551).
See HW (092N 058) for information on the HW/AT claim group. Also refer to Blackhorn Mountain (092N 019) for related geological and work history details in associated areas.
