The Northair mine is located in a Lower Cretaceous roof pendant of Gambier Group volcanic and sedimentary rocks within the southern Coast Plutonic Complex. This particular pendant, known as the Callaghan Creek pendant, is comprised of variably metamorphosed northwest trending volcanic and volcanically-derived sedimentary rocks, commonly characterized by a strong northwest foliation. The pendant rocks exhibit regional lower greenschist facies metamorphism, except near their contact with intrusive bodies, where they have locally undergone contact metamorphism.

The plutonic rocks in the area have a compositional range which varies from quartz monzonite to diorite. The plutonic rocks vary in age from Early Tertiary to Late Jurassic. Pendant contacts with adjacent plutonic rocks are often sharp and commonly marked by narrow shear zones which are parallel to the foliation within the pendant rocks.

Previous mapping in the Northair mine area has divided the geology of the 5000-metre thick Gambier Group into two major units. Unit 1 is a lower, volcanic-derived, sediment-rich unit characterized by well-sorted wacke with low fragment (clast) variation and minor volcanic tuffs, indicating a relatively long depositional history. Sedimentary features such as graded bedding and crossbedding are present with indicated tops to the northeast. Thin magnetite beds are locally present in wacke sediments. The stratigraphy appears to have a north to northwest strike and a steep dip to the northeast.

Unit 2 is comprised of a volcanic tuff of predominantly andesitic composition which stratigraphically overlies unit 1. Most of the southern contact between these two units is a fault which locally is occupied by a Tertiary felsic dyke. The upper 2500 metres of unit 2 is characterized by a high variability of clast size (ash tuff to block breccia) representing a rapid depositional environment. Depositional cycles are evident by the northeastward and southward fining of these fragmentals. Locally emergent conditions are indicated by features such as hematitic clasts which are well-rounded and similar in size. This is found particularly in the upper portion of the stratigraphy (northwest part of the property).

A proximal environment is indicated for the lower 1000 metres of unit 2, which is characterized by the absence of sediments, almost chaotic and locally clast-supported angular block and ash tuffs, volcanic breccias and lapilli tuffs which represent a brief, rapid depositional history. The significance of the lower unit lies in the fact that it hosts more of the ore.

Recent workers have interpreted the Gambier Group rocks on the property as a homoclinal succession (Assessment Report 18402). No minor fold structures have been observed. The bedding varies in strike from 160 to 200 degrees and dips from 45 to 89 degrees east. A pervasive cleavage is moderately well-developed and is common in the volcanic rocks; it has a strike of 160 to 180 degrees and is steeply inclined. Rock analyses show that the volcanics are calc-alkaline basalt to dacite in composition, with the majority of the samples falling into the andesite to dacite fields (Assessment Report 18402).

Host rocks to the ore deposits at the Northair mine are andesitic pyroclastic breccia and lapilli tuffs. The ore deposits are comprised of 3 or 4 steeply dipping, fault-dismembered tabular zones, 1 to 7 metres wide and approximately 1200 metres long. They dip steeply southwest and are known to extend downdip at least 300 metres. The four mineralized segments are separated by north trending faults and are named from south to north as: Manifold, Warman, C and Discovery.

The mineralized segments are generally small bodies. The sulphides comprise pyrite, galena, sphalerite and minor chalcopyrite disseminations, veins and locally discontinuous, banded segregations in quartz-calcite gangue. Anastomosing veins of pyrite, galena and sphalerite are common; often they are irregular sulphide pods and lenses, separated by barren, brecciated country rock (horses). Locally, spectacular ribbon-banded, quartz-chlorite-pyrite veins (with minor lead-zinc sulphides) are present in the ore zone. The vein zone which comprises most of the ore, as a whole has a steep southwest dip which is broadly discordant to the perceived northeast dip of the volcanic stratigraphy. A general pattern of sulphide mineralogy indicates silver-rich, base metal-poor mineralization in the Manifold zone, progressing to more base metals and less silver toward the northwest (through Warman, C and Discovery zones). The width of the mineralization increases from the south to the northwest. Local banded, massive sphalerite and galena were reported at the Discovery zone. Other minerals reported at the mine are tetrahedrite, argentite, bornite, pyrargyrite and electrum with trace amounts of gold and stromeyerite (Geology in British Columbia 1977-1981, page 100).

At the northwest end of the "Northair horizon" (C and Discovery zones), where highest base metal values are indicated, the tested extent of mineralization is essentially less than 150 metres below surface. This locality was considered to have the best chance for massive sulphides discovery because of reported local occurrences of banded sulphides and shallow testing by previous exploration (Assessment Report 18402).

A consistent black, biotite/chlorite hydrothermal alteration zone is closely associated with the mineralization. This alteration forms an envelope to the sulphide vein zone, and is in some cases asymmetrical; more often it appears to be broadest in the structural hanging wall. The biotite content increases toward the sulphide vein system; it is a pervasive, fine-grained overprint of dark green chlorite. A gradation exists from a dark green, pervasive chlorite-altered tuff to a black, biotite-dominant tuff, most strongly altered nearest the mineralization. The biotite forms 6 to 7-millimetre clumps or aggregates in the altered host rock very close to, and within the mineralized vein system. Pervasive sericite alteration is also evident, but it appears to be an earlier event, and much more extensive; it is not directly related to the mineralization. Near the sulphide vein system within the alteration is a quartz-calcite stockwork which contains weak base metal sulphides.

A long standing controversy has existed regarding the origin of the Northair mineralization. Two views are that the sulphides represent (1) volcanogenic massive sulphide mineralization or (2) that it is vein-type mineralization, related either to a synvolcanic hydrothermal system, or to nearby intrusions of the Coast Plutonic Complex; the latter genesis is proposed (Assessment Report 18402).

Production at the Northair mine began in 1974 and was suspended in mid-July 1982 due mainly to low grades and low gold prices.

Indicated reserves are 59,071 tonne grading 26.73 grams per tonne silver, 9.08 grams per tonne gold and 2 per cent combined lead-zinc (Canadian Mines Handbook 1986-87, page 285).