Ag-Au ore

The Skylark claim is centred 2.7 kilometres east of Greenwood and 0.8 kilometre southeast of Twin Creek, at the elevation of 1140 metres. Access is 1.8 kilometres easterly by winding dirt road from the main Greenwood to Phoenix road.

The Greenwood-Grand Forks area contains Late Paleozoic and Mesozoic volcanic and sedimentary rocks, mainly in the greenschist facies of regional metamorphism, which are intruded by Mesozoic plutons and unconformably overlain by Tertiary volcaniclastic and flow rocks. The pre-Tertiary stratiform rocks are contained in a series of five, north dipping thrust slices with bounding faults, which at many places are marked by layers and lenses of deformed serpentinite. These thrust slices lie above high grade metamorphic complexes.

The Late Paleozoic rocks in the Greenwood area are the Knob Hill Group of chert, greenstone and related diorite and serpentinite, and the Attwood Group of dark grey argillite, limestone and minor volcanic rocks. They are unconformably overlain by the Brooklyn Formation of clastic sedimentary rocks, limestone and largely submarine pyroclastic breccias and related dioritic intrusions. These rocks probably formed in an environment of growth faulting and explosive volcanism (Open File 1990-25).

The distribution of the Tertiary rocks is controlled by a complicated array of extension faults. Three sets are recognized. The oldest are gently east dipping, at or near the base of the Tertiary. Later, dominantly west dipping listric normal faults have caused rotation so that the Tertiary strata dip to the east at moderate angles. The apparent offset on each of the five of these faults is measured in kilometres. The third and latest faults are north to northeast trending, steeply dipping, strongly hinged and influenced by the earlier faults.

The Skylark property is underlain by a sequence of northwest trending volcanic and sedimentary rocks of the Carboniferous or Permian Attwood Group which are intruded to the west by granodiorite of the Cretaceous Greenwood stock (Nelson Intrusions). The predominant rock type is argillite which strikes northwest and dips 35 degrees northeast. A sequence of andesitic volcanic rocks is found to be overlain by the argillite which in turn is overlain by bedded chert. The Skylark mine is located on a quartz vein in argillite near the east boundary of the Greenwood stock. The Skylark vein strikes approximately 020 degrees and dips 52 degrees east. It has been traced for over 200 metres by surface and underground workings. In the old stopes, the maximum reported width of the vein was 0.76 metre.

The Skylark claim was staked in 1893 by S. Bloyer and mined in the early years with some good results. The Skylark (Lot 763) and Denver (Lot 764) claims were Crown granted to G. Lavagnino in 1898. The focus of interest on the Skylark claim is a mineralized quartz- carbonate vein in argillite and greenstone units of the Attwood Group. The vein, has been worked mainly from 2 inclined shafts, dips 52 degrees southeast, averages 15 to 20 centimetres wide, and has a strike length of about 200 metres. The deeper shaft, which was completed in 1906, is 60 metres deep, plunges about 55 degrees to the east, and follows the vein to a depth of 24 metres where it is displaced easterly about 9 metres by a flat-lying fault. The vein was picked up again by a crosscut, and a winze was sunk on it to a depth of about 10 metres. On the 24-metre level of the mine a drift was run on the vein for about 75 metres following a north- south structure. The ore readily breaks free from the wallrocks and is easily mined.

Mining on the Skylark claim in the period 1893 to 1940 was intermittent, with the greatest production attained from 1905 to 1907, and 1915 (Skylark Development Company Limited), and in 1935 (W. McArthur). Total ore shipped for this period amounted to 1866 tonnes having 5282 kilograms of silver, 22.5 kilograms of gold, 25.8 tonnes of lead, and 4.8 tonnes of zinc. Recent production in 1988 and 1989 (Skylark Resources Ltd.) added an additional 33,298 tonnes, with recoveries of 11,751 kilograms of silver, 90 kilograms of gold, 9536 kilograms of copper, 107,538 kilograms of lead and 43,608 kilograms of zinc.

The values commonly occur as 'pay streaks' near the hanging and footwalls. The pay streak near the hanging wall is generally larger. Widths on it average 15 to 20 centimetres but a width of 38 centimetres is reported at one point. The mineralization has been described variously as fine grained steel grey galena accompanied by tetrahedrite and ruby silver; solid arsenopyrite with fine grained galena and sphalerite; and pyrite, silver bearing stibnite and native silver. The ore is easily mined and readily breaks free from the wall rocks. The vein occurs in a zone of intense silicification and carbonatization.

In 1980, the mine was reactivated and the Skylark vein was worked along strike for 150 metres and stoped down dip for 60 metres.

The H zone (Billy Fraction, Lot 999), discovered in 1984, is hosted by an andesite dike system intrusive into granodiorite along north trending fractures. This is likely a segment of the vein faulted from the south end of the earlier mine workings. The orebody itself is contained in a fault within an andesite dike. The fracture/fault structure strikes 040 degrees and dips 50 degrees to the southeast. Mineralization consists of fine-grained, banded sulphides with a variable quartz content (10-40 per cent). The vein matter varies from 2.5 to 60 centimetres in width but averages 10 centimetres. Sulphide mineralization consists of pyrite, hematite, sphalerite, galena, chalcopyrite, pyrargyrite, proustite and native silver. Locally both hanging wall and footwalls display fault breccia and gouge. Many subparallel faults have caused the ore zone to pinch, swell and locally be sheared. Measured reserves in 1986 for the H zone were 77,103 tonnes grading 685.6 grams per tonne silver and 2.74 grams per tonne gold (Assessment Report 15731).

The Serp zone occurs below the southwest part of the H zone and cuts the main shear structure at an oblique angle. The Serp zone is identified by the presence of serpentine, chlorite, carbonate and talc. This serpentinite is an erratic non-planar zone of variable thickness and orientation, with an indicated trend of 330 degrees that dips approximately 35 degrees east. The Serp zone is found intercalated with andesitic volcanic rocks that are within the granodiorite. The Serp zone contains variable high gold and silver values associated for the most part with narrow (1-6 centimetre) pyrite veinlets; native gold is also observed.

In 1986, a decline ramp was driven to the H zone and drifting and raising carried out. The decline was extended to 458 metres in 1987 and a drift driven to the Serp zone. Production from the H zone began December 7, 1987 at 90 tonnes per day, the ore being shipped to the Robert Mines Ltd. mill some 4 kilometres south of Greenwood. Mining operations ceased in early 1989. During this period, total production was increased by 33,298 tonnes, with recoveries of 11,751 kilograms of silver, 90 kilograms of gold, 9536 kilograms of copper, 107,538 kilograms of lead, and 43,608 kilograms of zinc.