The Alexis occurrence comprises copper-mercury mineralization in a broad alteration zone on a ridge 4 kilometres west of the centre of Chilko Lake. The mineralization was discovered in 1980, and was worked on intermittently in the 1980's, including 287 metres of diamond drilling over 3 holes.
The area lies within the Tchaikazan fault zone, a regional northwest-striking strike-slip fault (Geological Survey of Canada Map 5-1968, Paper 68-33, Open File 1163). It is located in a Cretaceous overlap assemblage, 25 kilometres northeast of the main margin of the Jurassic to Tertiary Coast Plutonic Complex (Geological Survey of Canada Open File 1163, Map 1713A). The fault zone is a series of subparallel faults, several kilometres wide, and was probably active in the early Tertiary (Geological Survey of Canada Open File 1163). The Alexis occurrence is hosted in a narrow, fault-bounded belt of Upper Cretaceous rocks of the Kingsvale Group within the zone, beyond which are Lower Cretaceous sedimentary and volcanic rocks. There are numerous smaller transverse, northeast-striking faults.
Locally the Kingsvale Group comprises dacitic, andesitic and basaltic volcanic breccia and tuffs, and sandstone, grit, greywacke, siltstone, mudstone, argillite and chert-pebble conglomerate (Assessment Reports 9535, 11661; Geological Survey of Canada Open File 1163). The rocks are intruded by hornblende-plagioclase porphyritic dykes and sills, and by small dioritic stocks, probably related to the Coast Plutonic Complex. Bedding strikes northwest and generally dips moderately northeast. Shear fractures are widespread.
The Alexis occurrence is marked by strong and pervasive alteration, brecciation, veining and mineralization; chalcedonic silica and vuggy vein textures are present in the vein breccias. These characteristics have been interpreted to fit the upper zone of the British Columbia epithermal model, related to fracturing and metal-rich hydrothermal activity in the Tchaikazan fault system (Bulletin 81; Assessment Reports 9535, 13892).
The alteration zone is discontinuous over an area about 1000 by 300 metres, centred on the Knob showing. Carbonate alteration is the most widespread and pervasive, and is associated with intense brecciation and veining of the host rocks, the disruption of which is so strong that they are described as "heterolithic breccias" (Assessment Report 9535). White calcite is dominant, although iron-bearing carbonate is common, giving rise to prominent limonitic or ankeritic areas of oxidation. At its most intense, carbonate has replaced the original mineralogy of the volcanic or sedimentary protoliths. Individual carbonate veins have a variety of orientations, but most strike northwest and dip steeply. Barite veins are also reported (Assessment Report 13892).
Silicification and quartz-calcite veins and stockworks are less common but are intensely developed in a 10 by 10 metre zone at the Knob showing, which contains most of the mineralization. Argillic alteration or "bleaching" of volcanic rocks is also present in the vicinity, with the production of kaolinite and calcite (Assessment Report 11661). Minor epidote and sericite alteration has been recorded in drill core (Assessment Report 13892).
Visible mineralization occurs mainly at the Knob showing and consists of cinnabar associated with calcite veins, malachite and azurite, and locally tennantite, tetrahedrite, realgar, hematite, aragonite, dickite and rarely stibnite (Bulletin 81; Assessment Reports 9535, 11661). Pyrite, pyrrhotite and arsenopyrite have been recorded in drill core (Assessment Report 13892). Samples of the mineralization have yielded assay values of up to 1.47 per cent copper, 0.39 per cent antimony and 16.5 grams per tonne silver (Assessment Report 9535). Lithogeochemical analyses include 27 grams per tonne silver and 0.8 per cent copper from a single sample (Bulletin 81).
Another showing, the Ridge showing, occurs 500 metres west of the Knob showing and is defined mainly by an arsenic anomaly (Bulletin 81; Assessment Report 11661). It is similarly brecciated and carbonate-altered, and contains arsenopyrite and alunite, as well as malachite and cinnabar (Assessment Reports 10608, 11661).
Assay values and rock and soil geochemical analyses are anomalously high but erratic in the area of the Alexis occurrence, particularly in mercury, arsenic, antimony, copper and zinc (Bulletin 81; Assessment Report 9535). Gold is anomalous but not high. There is a positive correlation between mercury lithogeochemical values (up to 0.45 per cent) and the degree of mineralization (Bulletin 81); mercury is considered an important pathfinder element (Assessment Report 9535). The erratic values are not inconsistent with this type of high-level, highly permeable environment in which leaching processes have redistributed metals, resulting in secondary enrichment or dilution of values (Assessment Report 9535).
Past work has generally concluded that more exploration of the extent and vertical zonation of mineralization in this system, particularly by deeper diamond drilling, is warranted to properly ascertain its economic potential, especially in terms of gold and silver (Bulletin 81; Assessment Report 18162). Other, similar showings of mineralization are known along the strike of the Tchaikazan fault zone which have not been explored to date. For example, the copper-mercury Stowe showing (092N 043) is 3 kilometres southeast of the Alexis, and traces of mercury mineralization exist 1.5 kilometres to the northwest (Bulletin 81).