The HW occurrence covers a number of small showings comprising gold, silver and copper mineralization, spread over several square kilometres in the rugged terrain northwest of Ottarasko Mountain. It encroaches on similar showings covered by the Lori (092N 047), AT 3-4 (092N 057), and Champagne (092N 059) occurrences.
The area lies in the area of the Cadwallader terrane and Cretaceous overlap assemblages near the northeastern margin of the Jurassic to Tertiary Coast Plutonic Complex, within a complex belt of folds and imbricated, gently southwest-dipping thrust sheets (Geological Survey of Canada Open File 1163, Map 1713A). These Late Triassic to Cretaceous imbricates are called the Eastern Waddington thrust belt imbricate zone and area 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 MaPlace geology).
The northeast-directed thrusting placed Upper Triassic (Carnian) and Lower Cretaceous 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 Upper Triassic and Lower Cretaceous volcanic and sedimentary rocks. At least one thrust is present in the area of the showings, separating grey volcanic rocks from an underlying sequence of shale, limestone and limy shale, about 100 metres thick (Assessment Report 19355). Supplementing regional information, the volcanics are probably mainly andesitic tuff and breccia (Geological Survey of Canada Open File 1163). The specific ages of the units are not certain. The area is intruded by basaltic dikes and numerous felsic to intermediate porphyritic dikes and sills; the dykes are generally steep, and strike north-northwest or east.
It has been speculated that the deformation was accompanied by hydrothermal activity which led to structurally-controlled quartz-carbonate veining and mineralization (not all mineralization is associated with quartz, however) (Assessment Report 19355). Quartz or quartz-calcite veins, stockworks and fracture-fillings occur in several places in the volcanics and the sedimentary rocks, particularly adjacent to the thrust. The veins tend to be steep, and strike either north-northwest or roughly east. Minor unspecified sulphides, locally including arsenopyrite, are generally present in the veins (but not in every case), and may give rise to conspicuous gossans. The host rocks may be strongly folded and fractured, and locally they also have disseminated pyrite and rusty alteration (oxidation).
The HW occurrence is centred on a broad quartz stockwork zone in (metavolcanic) greenstone. Assay samples from the zone average 21 grams per tonne gold, including a peak value of 41.6 grams per tonne (Property File - Berniolles, L.M., 1991). A composite sample of quartz-rich material from an outcrop 2 kilometres to the southeast yielded 1 gram per tonne gold, 7.2 grams per tonne silver and 0.59 per cent copper (Assessment Report 19355).
Onwner/operator Louis Berniolles of the 850-hectare HW1, HW4 and HW5 claims were prospected systematically by a three-person team, for a total of 93 man/days, over the periods August 10 days in 1988 and 10 days 1989. Thirty-four rock samples were collected and sent for analysis. Two types of mineralization were reported. 1) Gold-copper mineralization occurs both in place and in float, often in association with quartz, on the southern half of the claim group; values over 34 grams per tonne have been obtained. 2) Gold in association with arsenopyrite; in the central- northern part of the claim group, low gold values, of the order of 1 gram/tonne, have been found in various quartz structures, generally as networks of sub-parallel veins and veinlets of white quartz with minor arsenopyrite. This type of mineralization was thought possibly to be related to a richer occurrence of gold with arsenic documented by Homestake in 1983 when a float sample taken 800 metres east of the northeast corner of the HW4 claim assayed 89.14 grams per tonne gold and 0.154 per cent ppm arsenic (Assessment Report 19355). Most occurrences of economic mineralization on the claims, and on claims AT3 and AT4 to the south, are located at or near thrust faults, which
Elsewhere in the area, high values of gold, silver and copper were obtained from float or talus samples, most of which are probably fairly locally derived. Four kilometres to the west, for example, a sample of quartz with fine pyrite, which assayed 6 grams per tonne gold probably comes from a 100-metre-long quartz vein in a cliff which could not be sampled in place (Property File - Berniolles, L.M., 1991). In 1990, the HW9 claim was staked by Louis Berniolles as a western extension of the HW1, HW4, HW5 and HW6 group of claims. In 1991, all accessible areas of the 500-hectare (20 units) property were prospected by a three-person team, for a total of 42 man/days in 1991. Eleven rock samples and 11 stream sediment samples were collected and sent for analysis.
Skeena Resources revisited the area in 2007 (as reported in 2011 (Assessment Report 32152). Assay results of float samples returned between 10 parts per billion and 226 grams per tonne gold and 156 grams per tonne silver; this high gold sample was taken in an area that Berniolles had previously sampled with positive results for low grade gold. All high-grade gold samples were from float in moraine deposits, or as Berniolles described outwash from foot of glacier.
See Blackhorn Mountain (092N 019) for related geological and work history details.
