The McFadden float train is partially underneath a glacier east of the Johnny Mountain Mine, approximately 7 kilometres south of the Bronson Airstrip on Iskut River.
Three stratigraphic assemblages have been mapped in the area: (1) Upper Palaeozoic sediments and volcanics of the Stikine Assemblage, (2) clastic sediments of the Triassic Stuhini Group, and (3) Lower Jurassic sediments and volcanics of the Hazelton Group.
Four plutonic suites intrude the above; (1) Late Triassic calc-alkaline intrusions coeval with Stuhini Group stratigraphy, (2) Jurassic Copper Mountain, (3) Jurassic Texas Creek and (4) Tertiary Coast Plutonic suite. Metallogenically, Texas Creek potassium feldspar megacrystic porphyries are of primary interest as they are spatially associated with several gold deposits and showings in the area.
The McFadden zone consists of a sulphide "float zone" or moraine train that extends about 350 metres in length and 40 metres in width on Johnny Mountain. It was found in 1960 by Hudson’s Bay Mining and Smelting prospectors but not worked on again until the early 1980’s. Apparently, all of the altered, mineralized material, including jarositic fines, carries significant gold values. Indicated reserves at McFadden are 27,216 tonnes grading 96.0 grams per tonne gold; sulphide float; measurable reserve estimate to give an inventory of 2,381,400 grams gold (Property File - Skyline Explorations Ltd., Reg Project (1984).
A second resource outlined by surface exploration includes an extensive blanket of gold-bearing eluvial material extending downslope from the east end of the main Stonehouse (104B 107) gold zone. Preliminary work indicates this material has an area of at least 260,000 square metres with a minimum depth of one to two metres. At present, only the 80-fraction has been assayed in detail and averages 1.5 grams per tonne gold (Grove, E.W., 1987).
The float zone consists of a lateral moraine along the west side of Johnny Glacier containing a significant portion of highly altered and mineralized material which is noticeably limonite stained. Thrust planes at the toe of Johnny Glacier reportedly contain jarositic material that were also anomalous for gold. The un-mineralized portion of the moraine consists of volcanic material of the Hazelton Group like that exposed on adjacent hillsides. All the altered and mineralized material in the zone apparently carries gold mineralization in significant amounts. Massive sulphide mineralization makes up a significant portion of the altered mineralized portion.
Source of the gold-bearing float is a gold shear-vein system buried beneath Johnny Glacier and till. Such a vein system could project under adjacent hillsides where dacites, rhyolites, andesites and sediments of Hazelton Group have been mapped.
In 2013 SnipGold exploration program 21 rock samples were collected from the McFadden Float Zone, located 300 m beyond the most northerly workings in the Johnny Mountain Mine. It was found that the current extent of the Johnny Glacier has been significantly reduced due to ice retreat since the last significant phase of work at McFadden 20 to 25 years ago. A sample collected within the area of historic sampling returned the highest assay value of 155.50 grams per tonne Au, confirming the presence of high-grade float existing at the McFadden Zone. Several other float occurrences sampled up-ice of the historic zone returned high Au assays from similar looking gossanous and silicified boulders containing sulphide (pyrite) mineralization, suggesting the source of the boulders remains further up-ice (Assessment Report 34703).
All 2014 high-grade samples from McFadden display a consistent geological signature, with the host rock being a light- to medium-grey conglomerate with well-rounded matrix-supported clasts. The matrix displays hornfels alteration, is strongly sheared and has a moderately well-developed linear fabric. The matrix has also undergone considerable pyrite replacement.
The best result of 2014 boulder sampling yielded 380.00 grams per tonne gold, 59.4 grams per tonne silver and 1.455 per cent copper (SnipGold Corp., News Release, October 22, 2014).
SnipGold Corp. concluded from 2014 work that the McFadden mineralization was structurally controlled and indications were that they had a likely genesis similar to that of the Snip mine mineralization.
SnipGold's 2016 geophysical surveys showed conductors immediately up ice of the high-grade gold boulder train, in an orientation coincident with the Snip mine structural trend. SnipGold reported that geological mapping had placed McFadden within the lower Jurassic Hazelton group, located within a few hundred metres of the Triassic-Jurassic unconformity, a characteristic of other regionally significant deposits.
Recent Work History
In 2014, Snipgold conducted a boulder sampling program at McFadden. A total of 11 float samples were collected from McFadden for analysis.
In 2016, the Iskut Project held by SnipGold Corp was obtained with the closing of Seabridge’s acquisition of SnipGold Corp. in June 2016. The property was subsequently held as the KSP by Seabridge.
In 2016, Seabridge Gold Inc. completed a limited amount of drilling this summer at the old high-grade Johnny Mountain gold mine to test detailed ore control concepts on a known deposit while proceeding with the comprehensive program. Drilling results (with assays) are found in a 2016 news release (Seabridge Gold Inc., News Release October 26, 2016).
In 2016, Seabridge conducted a multipronged exploration program on its 100-per-cent-owned Iskut project. Drilling confirmed the key structures that control mineralization and the likely elevation where we should expect to find higher grades. Seabridge sees the Johnny Mountain mine as being on the edge of a larger system that lies near the bottom of the productive gold-bearing zone which was largely eroded away by glaciation. The nearby, higher elevation Quartz Rise (new to MINFILE 2018) resisted glaciation and remains largely intact in part due to its higher silica content.
Detailed magnetotelluric and airborne hyperspectral surveys were completed over Jurassic Hazelton group rocks on the west slopes of Johnny Mountain. The purpose of these surveys was to identify the alteration patterns in the underlying rock formations. Magnetotelluric (MT) technology acquires data over a large frequency band providing information on rocks to a potential depth of three kilometres. A hyperspectral survey was also flown with sensors collecting data in wave lengths between 390 to 2,450 nanometres with a two-metre spatial resolution.
See the nearby the Johnny Mountain past producing mine (104B 107) for further details.