The Iva Fern occurrence is located near the top of the ridge between Cultus and Laib creeks; the veins strike northerly up the slope from Cultus Creek, with the main discovery located at approximately 1905 metres elevation on the Fern (Lot 12656) Crown grant.
The area is underlain by the upper Proterozoic Horsethief Creek Group, which has been intruded just to the west by a small stock of middle Eocene Coryell biotite monzonite-syenite. Rocks underlying the area have been mapped as belonging to the Irene volcanics (greenstone); however, descriptions in old reports mention only slates and shales. The Horsethief Creek Group is known to be composed of phyllites, quartzites and grits; regional strike is 010 degrees, dipping 60 degrees west. A basic lamprophyre dike accompanying the vein in places is also described as "hornblendic dike rock", which might be part of the Coryell Intrusions.
Locally, two main fissure veins, containing quartz, siderite, calcite and tourmaline, occur in variably silicified phyllite and slate. Mineralization is in two forms: either coarse galena with pyrite, chalcopyrite and sphalerite, or streaks and bunches of galena and sphalerite. There is significant development of limonite due to oxidation at the surface; outcrops are few, with abundant overburden approximately 1 to 2 metres deep covering most of the property. The main (No. 2) vein has been traced for greater than 600 metres along strike; the No. 1 vein lies 100 metres to the east of the No. 2 vein, is sub-parallel in strike and has been traced for greater than 50 metres. Vein widths vary between 0.6 and 2 metres.
In 1985, mapping for Agincourt Explorations Ltd. discovered three additional mineralized zones over a total width of 200 metres, concordant with and near the top of the Irene volcanics; the possibility exists that syngenetic sulphides deposited within siliceous sinter zones have been remobilized during metamorphism and nearby intrusion, but this is speculative (Assessment Report 14053). A geochemical survey described in Assessment Report 14053 suggests further mineralization may be buried below overburden to the north, although magnetic and electromagnetic surveys of this area failed to show any significant anomalies/conductors.
In 1917, a sample from the lowest elevation showing yielded 120 grams per tonne silver and 5 per cent lead over 1.8 metres, while another sample taken further up the hill assayed 0.7 gram per tonne gold, 116 grams per tonne silver and 22 per cent lead over 0.75 metre (Property File - E. Denny [1981-05-01]: Claims Map and Summary Reports - Iva Fern).
In 1919, a sample from a shaft on the No.1 vein yielded 4 per cent zinc, 35 per cent lead, 0.7 gram per tonne gold and 178 grams per tonne silver (Minister of Mines Annual Report 1919). Also, at this time, a 2.7- tonne test shipment was made that averaged 1.4 grams per tonne gold, 143 grams per tonne silver, 3.5 per cent copper, 9 per cent zinc and 26 per cent lead (Property File - R.P. Jordan [1951-12-11]: Preliminary Report on the Iva Fern Property).
In 1928, a grab sample from the dump on the No.1 vein assayed 65 per cent lead and 513 grams per tonne silver, while sampling of the No.2 vein from the main cross-cut yielded up to 99.2 grams per tonne silver, 8.2 per cent zinc and 11.5 per cent lead over 1.2 metres (Property File - E. Denny [1981-05-01]: Claims Map and Summary Reports - Iva Fern).
In 1929 or 1930, underground sampling (1502B) yielding up to 15.7 per cent lead, 2.4 per cent copper and 226 grams per tonne silver over 0.66 metre, while a select sample (1515B) from an approximately 454- tonne ore dump assayed 116 grams per tonne silver, 9.6 per cent lead and 4.4 per cent zinc (Property File - Miners Western Ltd. [1952-01-28]: Map - Sampling and Geology - Iva Fern Mine)
In 1981, a sample from the main shaft assayed 24.4 per cent lead, 0.88 per cent zinc, 1.38 per cent copper and 112 grams per tonne silver, while a sample from open-cuts on the No.1 vein yielded 244 grams per tonne silver, 38.9 per cent lead and 0.35 per cent zinc (Property File - E. Denny [1981-05-01]: Claims Map and Summary Reports - Iva Fern). Also, at this time, two dump samples (7199 and 7200) yielded up to 0.93 per cent copper, 6.71 per cent lead, 5.54 per cent zinc and 69 grams per tonne silver (Property File - MineQuest Exploration Associate Ltd. [1981-07-01]: Report on Cultus Creek Project Including Preliminary Exploration of Don and Next Claims).
In 1994, sampling of old trenches yielded up to 1.52 per cent copper, 24 grams per tonne silver and 2 grams per tonne gold across a width of 7.3 metres (George Cross News Letter No. 47, 1994).
During the 1915 through 1930, extensive surface and underground development was completed. This included a 180-metre long main drift, a 76-metre cross-cut tunnel, another 36-metre drift and two short shafts. A short tunnel was also developed, down slope, on the Iva (L.12655) Crown grant. The property was bonded to the Consolidated Mining and Smelting Company in 1918 and developed through the next year. In 1922, Standard Silver Lead Mining Company bonded the property and continued underground development during the following year. In 1928, the Consolidated Mining and Smelting Company bonded the property again. In 1929 and 1930, a further 425 metres of underground development was completed, including 137 metres of tunnelling and a 37.5- metre deep winze. In 1952, the area was examined by Miners Western Limited.
In 1981, the area was prospected and sampled by E. Denny. In 1985 and 1986, Agincourt Explorations completed programs of prospecting, geological mapping, sampling and an induced polarization survey. In 1993 and 1994, Yukon Revenue Mines examined the property with programs of road work, trenching and diamond drilling.