The Horsefly showing is 58.8 kilometres southwest of Kitimat and 86.6 kilometres southeast of Prince Rupert. It is high on the eastern slope above Ecstall Lake-Lower Lake. The showing crops out at 685 metres elevation in three adjacent creeks over 100 metres. The mineralized horizon is also exposed in a cliff face 300 metres further to the south.
The area is underlain by northwest trending metavolcanics and metasediments of the Central Gneiss Complex, intruded by granitic rocks of the Coast Plutonic Complex.
Massive and disseminated pyrite and minor sphalerite, chalcopyrite, and pyrrhotite occur along a shear zone within highly metamorphosed felsic volcanics, consisting of chloritic schists and weakly foliated andesite flows. These rocks lie adjacent to a pyritic quartz sericite schist horizon which contains anomalous copper-zinc values. The mineralized area measures intermittently over 1500 by 60 metres along a 150-degree trend.
Local stratigraphy is a complex succession of mafic to intermediate to felsic volcaniclastic rocks and flows, and minor intercalated sedimentary units. The showing consists of a one metre thick lens of massive pyrite with minor sphalerite, chalcopyrite and pyrrhotite hosted in a pyritic quartz-sericite schist unit that is 10 metres thick. Siliceous argillite units adjacent to the host quartz-sericite schist are weakly pyritic and anomalous in zinc and lead. A rock sample assayed 0.4 per cent copper, 3.8 per cent zinc, 0.08 per cent lead, 33.0 grams per tonne silver, and 0.5 gram per tonne gold (Assessment Report 15306). A sample 900 metres to the southeast, on the Steelhead grid (103H 036), assayed 1.08 per cent copper, 0.974 per cent zinc, 0.0018 per cent lead, 28 grams per tonne silver and 0.42 gram per tonne gold (Assessment Report 15306).
In 1995, with support from the Explore B.C. Program, Atna Resources Ltd. under joint venture with Ecstall Mining Corporation conducted an electromagnetic (EM) survey and diamond drilling (1075 metres in 8 holes) on the Horsefly and Steelhead (103H 036) showings. A 20-metre-wide zone of disseminated massive sulphides was located by two of the drillholes and traced for 90 metres. It is open in all directions. Three other targets located by EM survey remain to be drill tested (Explore B.C. Program 95/96 - M59). See also Packsack (103H 013).
In 1960, the sulphides in the creek bed were discovered by a Texas Gulf Sulphur Company Ltd. exploration team during a regional stream sediment sampling program following on from the discovery of the Packsack (103H 013) and Scotia (103I 007) deposits in 1957 and 1958. Subsequently, the property was explored by a joint-venture group in 1981, by Noranda Exploration in 1986, and by Atna Resources Ltd. in 1995. Five holes, totalling 652 metres, were drilled on the showing in October 1995. The claims are owned by Ecstall Mining Corporation Ltd. The drilling program outlined a 20-metre-thick zone of disseminated and semi-massive sulphides at depth, which is offset to the south from the outcropping Horsefly prospect sulphide showings. This zone is located 100 metres southeast of the Horsefly showing. It has been traced by drilling for 90 metres along strike and remains open in all directions. The best assay obtained from drill core was 2.75 metres of 1.69 per cent copper; however, grades up to 5.6 per cent copper, 1.6 per cent zinc, 900 parts per million lead, 30 parts per million silver and 860 parts per billion gold were obtained over narrower intervals of core.
In 2012, Winrock Resources Ltd. acquired the Packsack property, which includes the Horsefly showing, and in October conducted a rock sampling program and reconnaissance sampling program which targeted two main areas within the claim boundaries.
The Horsefly showing was part of Kingfisher Resources Ltd.'s 2019 airborne VTEM survey over its Ecstall property. The airborne survey was aimed at detection of structures and/or conductors related to potential Cu-Au-Zn-Ag VMS-style mineralization. 2019 work at the Horsefly consisted of prospecting and sampling (226 soils, 1 stream, 34 rocks). Work confirmed a significant zone of pyrite-chalcopyrite-sphalerite mineralization and hydrothermal alteration and focused on the southern portion of the zone where historically significant hydrothermal alteration and disseminated base metal mineralization had been identified (Assessment Report 39155).
