The former Stemwinder mine is located 1 kilometre west of Burnell Lake and 6 kilometres west-northwest of Oliver, BC.
Regionally, the area is underlain by a northwest- trending, narrow ,elongate belt of complexly deformed, regionally metamorphosed, Carboniferous to Permian Kobau Group metasedimentary and metavolcanic rocks, which separate two large intrusive bodies; the Jurassic Oliver Plutonic Complex granite to the northeast and the Jurassic to Cretaceous Fairview intrusion granodiorite to the southwest. Both plutons cut the lithologies and structures of the Kobau Group. The Kobau Group rocks comprise banded and foliated quartzitic lithologies with minor mafic schists, and thick, compositionally layered mafic schist units with intercalated quartzite bands. Minor meta-carbonates and mafic metavolcanic flows or sills occur within the quartzites and schists, which have undergone at least three phases of folding and later brittle faulting. The metasedimentary-volcanic package is cut by aplite dikes;, small granitic, dioritic and mafic stocks, and Tertiary northeast- trending mafic dikes. Dacite dikes occur in swarms and are parallel to the regional compositional layering within the Kobau Group rocks east of the Fairview intrusion. Auriferous quartz veins occur in all lithologies but are thickest and most continuous where they occur in the quartzites. Some significant veining also occurs in the intrusive bodies. Tertiary faults crosscut all lithologies including the quartz veins.
The Stemwinder mine area is underlain by a northwest- trending sequence of three distinct lithologic units: an upper 'green argillite' primarily composed of chlorite with variable amounts of biotite and narrow quartzite laminations; an underlying central grey quartzite that varies from cherty quartzite to banded quartzite, laminated with fine and coarse biotite and a lower, 'dark argillite' that is essentially a massive greenstone. A series of intermediate to felsic dikes parallel to foliation occur in this sequence.
The stratigraphy is tightly squeezed and strongly foliated at 100 to 130 degrees between Oliver Plutonic Complex granite to the north and Fairview intrusion granodiorite to the south. Dips are to the northeast at 50 to 65 degrees. Small-scale isoclinal folding can be seen in the sedimentary and volcanic units as well as the quartz veins. Regional foliation (S1), which trends 130 degrees, parallels both the quartz veins and the sericite-biotite-graphite-sulphide filled fractures commonly found within the veins. These vein fractures may represent axial planar cleavage related to the small scale isoclinal folding and regional foliation developed during emplacement of the Fairview granodiorite. A later fracture cleavage (S2), trends 000 to 020 degrees and dips 50 to 70 degrees west. It is especially evident in quartz veins and is possibly related to late faulting.
Faulting of at least two separate ages is common throughout the Stemwinder mine area. The oldest faults parallel the regional foliation and are best developed in the area of quartz veining, where they are located on both the top and bottom of the quartz veins. They are commonly graphitic, usually filled with clay and/or sand gouge and often have associated caving. Slickensides on fault planes within the quartz veins typically have a southeast plunge at 30 to 40 degrees. Direction of movement has not been determined. A large number of younger, possibly Tertiary, faults are common throughout the mine workings. Many of the larger faults are left-lateral reverse faults that offset the quartz veins approximately 18 metres horizontally. The vertical component of movement is unknown. The faults, like the quartz veins, have a considerable roll, often flattening substantially over short distances. Normal faults, which seem to be about the same age or slightly younger than the reverse faults, occur throughout the mine and may reflect a 'relaxing' of compressional forces.
Mineralization is confined to a quartz vein system that is generally conformable to penetrative fabrics developed in the Kobau Group host rocks and displays a variety of early ductile and later brittle deformation features. The vein system has been traced over 4 kilometres from the Morning Star mine (MINFILE 082ESW006) in the southeast through the Stemwinder to the Fairview mine (MINFILE 082ESW008) in the northwest. The veining consists of two dominant veins, often with a third or fourth present. The veins occur in the middle quartzite sequence, usually within 60 metres of the Fairview granodiorite contact. Veins intersected in drill holes usually occur within grey laminated quartzite. Individual veins range from 0.30 up to 9 metres in thickness and pinch and swell rapidly along short distances, both along strike and down dip. The quartz is white, either massive or fractured and ribbon-textured. The vein system is composed of the principal Main vein, the HW vein (Hanging wall or North vein) and the FW vein (Footwall or South vein). The vein system is evident at the Fairview mine and continues through to the Stemwinder mine in the southeast. Several high-grade shoots occur within these veins.
Fluid inclusion and stable isotope studies at the Stemwinder occurrence indicate mesothermal fluids were responsible for mineralization events. The fluids are characterized by a high carbon dioxide content, temperatures of 280 to 330 degrees Celsius, salinities of 4 to 6 weight per cent sodium chloride and oxygen del 18 values of 4 to 6 per mil (relative to standard mean ocean water). The mineralization occurs at depths of 3 to 4 kilometres.
Gold and silver values occur in portions of the vein that contain pyrite, sphalerite, galena and chalcopyrite, which occur along ribbon-textured fractures or as disseminations in quartz. Precious metal grades show little preference for the hangingwall or footwall of the veins. Strong fracturing parallel to foliation with graphite, sericite, chlorite and biotite fracture-fillings accompanies the mineralized zones. Faulting parallel to the quartz vein zone may account for the rapid thickening and thinning of the veins.
Gold and silver values are closely associated with the presence of galena with or without chalcopyrite, sphalerite or pyrite. Galena, chalcopyrite, sphalerite and rare pyrrhotite are fracture- controlled, with most occurring along S1 fractures in quartz veins. A very small percentage also occurs along S2 fractures. For the most part, the best galena-chalcopyrite-sphalerite mineralization and highest gold and silver values occur in the hangingwall parts of the veins, although significant values have been obtained throughout the vein. Gold values are higher where the vein has well-developed S1 fractures lined with sericite-biotite-chlorite-graphite and sulphides.
Three high-grade gold zones or shoots have been discovered within the complex vein system. The Fairview Extension zone is located at the common boundary between the Fairview and Stemwinder mines, namely on the Wynn M claim (Lot 554); the Stemwinder zone is located on the east edge of the Stemwinder workings, namely the Stemwinder claim (Lot 384); and the Brown Bear zone located in the north drift near the centre adit on the Brown Bear claim (Lot 385). These high-grade gold zones are thought to plunge 60 degrees to the east on the Stemwinder property.
Drilling on the Fairview Extension zone over a strike length of 427 metres suggests it is an eastward and downward extension of the Fairview ore zone. The zone appears to plunge eastward 20 to 30 degrees. Diamond drilling in 1982 on the Fairview Extension zone yielded 4.79 grams per tonne gold and 44.22 grams per tonne silver across 1.37 metres (Main vein) and 1.64 grams per tonne gold and 25.02 grams per tonne silver across 1.06 metres (HW vein) ( Property File - Cooke, D.L. (1987): Report on the Stemwinder Mine property).
The Stemwinder zone was intersected by drill holes to the east of the 200 level of the Stemwinder workings. The zone is poorly defined due to faulting but has a defined strike length of 152 to 183 metres. The average grade of seven drill intersections yielded 4.04 grams per tonne gold and 45.60 grams per tonne silver (Cooke D.L., 1987). A channel sample across 0.97 metre of quartz vein assayed 7.02 grams per tonne gold and 10.62 grams per tonne silver (Assessment Report 16779). Channel samples from Stemwinder zone assayed 5.89 grams per tonne gold and 114.15 grams per tonne silver across 1.0 metre (Main vein; true width) and 10.28 grams per tonne gold and 185.11 grams per tonne silver across 0.87 metre (HW vein; Assessment Report 16779).
The Brown Bear zone (Centre adit) differs somewhat from the other mineralized zones. There is a lack of dikes or sills and biotite is absent in hangingwall and footwall quartzites and along S1 fractures in quartz veins where sericite is more prevalent. Graphite is also less prevalent in S1 fractures and there is little folding evident in the quartz veining. The major left-lateral reverse fault has apparent horizontal strike-slip offset of 110 metres. In 1982, three intersections from two drill holes approximately 61 metres apart yielded an average of 3.33 grams per tonne gold and 29.48 grams per tonne silver (Cooke, D.L., 1987). The results of the 1991 drill program were as follows:
On the Main vein, the average of six intersections in six drill holes was 0.48 gram per tonne gold and 3.43 grams per tonne silver over an average true thickness of 3.07 metres (Assessment Report 21501). On the HW vein, the average of 14 intersections from 13 drill holes was 0.99 gram per tonne gold and 6.17 grams per tonne silver over a true thickness of 3.74 metres (Assessment Report 21501). The results of three drill holes in 1994 yielded an average of 2.67 grams per tonne gold and 10.97 grams per tonne silver over an average true thickness of 1.83 metres on the HW vein. Intersections on the Main vein yielded 1.37 grams per tonne gold and 4.11 grams per tonne over a true thickness of 0.91 metre (Assessment Report 23404).
The Stemwinder claim group was discovered and staked in 1888. The claim group, owned by G. Sheehan and Associates, was composed of the Stemset Fr. (Lot 21s), Gunsite (Lot 25s), Stemwinder (Lot 384), and Brown Bear (Lot 385), and the Wynn M. (Lot 554) owned by E.D. Reynolds. Claims owned by Sheehan were Crown- granted in 1892, 1896 and 1906. The Wynn M. was Crown- granted in 1894. A small amount of ore was mined and milled in a small 5-stamp mill on Reed Creek owned by Strathyre Mining Co. Ltd. Mill operations were expanded in 1896 to a 10-stamp mill and the Brown Bear and Wynn M. claims were purchased. These claims were held until 1907. The Stemwinder claim was purchased by the Fairview Consolidated Gold Mines Co. in 1897. Underground development up to 1901 totalled approximately 1220 metres. The Tinhorn (MINFILE 082ESW005) and Joe Dandy (MINFILE 082ESW161) stamp mills were purchased and installed on the Stemwinder. The mill was expanded to 46 stamps in 1902. In 1903, a cyanide recovery plant was installed to increase gold recovery. Operations ceased in 1904. In 1906, the Stemwinder Gold and Coal Mining Co. Ltd. acquired the Stemwinder property and further development work was carried out. The Brown Bear and Wynn M. claims were also purchased from Strathyre Mining Co. Ltd. in 1906 and operations on these claims ceased in 1908. By 1930, the claims were owned by Federal Mining Co. Morning Star (Fairview) Gold Mines, Ltd. optioned the property in 1934. The old workings were dewatered to the 500 level and sampled. The option was subsequently dropped. Fairview Gold Mines Ltd. acquired the property.
In 1960, Cominco Ltd. acquired a 10 year lease with a potential 10 year extension on the Stemwinder. A total of 352 metres of diamond drilling was conducted in six holes. The lease was dropped in 1972. Cominco Ltd. obtained a second option on the Stemwinder property from Fairview Mining Co. Ltd., a subsidiary of Asarco Inc. Between 1982 to 1984, 27 diamond drill holes, totalling 4155 metres, were drilled, exploring the Stemwinder vein system over a strike length of 1341 metres. In 1985, Highland Valley Resources Ltd. optioned the Stemwinder claim group. Exploration included drifting from the Central adit and Brown Bear claim. Solomon Gold Corp. made an agreement with Highland Valley Resources Ltd. to acquire a 50 per cent interest in the property in 1988. In 1991 and 1994, Oliver Gold Corp. conducted exploration drilling on veins on the Brown Bear and Silver Crown claims. The 1991 drill program consisted of 1472 metres in 21 holes approximately 100 metres apart. Fifteen of these drill holes were on the Brown Bear zone, the remaining were on the Silver Crown and Morning Star claims (MINFILE 082ESW005). The 1994 program consisted of 13 drill holes totalling 1083 metres to test the HW and Main veins in the vicinity of the Brown Bear and Silver Crown adits. In 2007, EKG Minerals completed a program of rock sampling and a 2.2 line-kilometre self-potential survey on the area to the north east. In 2013 and 2014, Hi Ho Silver Resources completed programs of rock and soil sampling, geological mapping and 38.0 line- kilometres of ground electromagnetic surveys on the area.
Drilling by Cominco Ltd. and Asarco Exploration Company of Canada Ltd. between 1982 and 1984 outlined reserves of 640,000 tonnes of ore from the Main vein grading 3.8 grams per tonne gold and 51.4 grams per tonne silver (Mineral Exploration Review 1986, page 63). The North vein was estimated to contain reserves of 185,000 tonnes of ore grading 9.2 grams per tonne gold and 103 grams per tonne silver (Mineral Exploration Review 1986, page 63). In 1982, Cominco estimated 635,000 tonnes of reserves grading 3.43 grams per tonne gold in the Fairview Extension zone. The Stemwinder zone was estimated to contain 181,000 tonnes of ore grading 4.11 grams per tonne gold (Cooke, D.L., 1987).
Total recorded production between 1893 and 1956 from the former Stemwinder mine includes 27,947 tonnes mined and 27,666 tonnes milled, from which 100,310 grams of gold, 532,797 grams of silver, 3670 kilograms of lead and 249 kilograms of zinc were reported to have been recovered. The amount of gold recovered in 1893 and 1894 is calculated.