The Topley Richfield occurrence is located on the southwest slope of Tachek Mountain about 10 kilometres north of the community of Topley and 35 kilometres northeast of Houston.
The Topley Richfield property is underlain by Lower-Middle Jurassic Saddle Hill Formation rocks (Hazelton Group) in the eastern part of the Skeena Arch. Overburden in the area can be in excess of 50 metres thick. Mineralization is hosted primarily in pyroclastic rocks comprised of feldspar crystal tuff with lesser lithic tuffs, greywackes and thin beds of argillite. Pyroxene-bearing andesitic flows of the Early Jurassic Nilkitkwa Formation (Hazelton Group) are located on the western portion of the property.
Mineralization is structurally controlled and occurs in two alteration zones which strike north-northwest (350 degrees) and dip 45 degrees to the southwest. The zones range from 10 to 40 metres in width and are about 25 metres apart. They are characterized by pervasive silicification, brecciation, sideritic alteration and quartz and calcite veining. Bladed ankerite occurs commonly in calcite vugs. Pyrite is the most abundant sulphide with minor native gold, native silver, tetrahedrite, arsenopyrite, galena, sphalerite and chalcopyrite occurring as stringers, disseminations and blebs.
Lenses containing stronger sulphide mineralization occur within the alteration zones and are called the B/C and D zones. These lenses vary in width from 1 to 5 metres apart and rake to the southwest. The mineralization occurs in several narrow bands separated by unmineralized zones and makes up about 10 to 15 per cent of the lenses. Two intersections in the B/C lens in 1980 assayed 5486 grams per tonne silver over 20 centimetres, and 4.8 grams per tonne gold with 202 grams per tonne silver over 7.6 metres, respectively (Assessment Report 9294).
Faulting in the area has offset the main workings and displaced the main alteration zones by about 100 metres along a right-lateral fault.
Significant development from two levels occurred from 1927 to 1929 with significant recent evaluation occurring from 1979 to 1987.
Drill indicated reserves at Topley Richfield are 181,420 tonnes grading 4.25 grams per tonne gold and 191.96 grams per tonne silver (Canadian Mines Handbook 1989-90, page 327).
Work History
In 1926, the Topley-Richfield mineralization was discovered. The property contains a precious and base metal mineral prospect with underground workings on two levels that were constructed in 1927. Some 1500 metres of adits and inclined shafts were excavated. However, the underground workings were not accessible as of 2008.
The Topley-Richfield Mining Company constructed 240 metres of underground workings on two levels. In 1937, a 1.5-metre-wide shear zone in andesitic breccia located about 300 metres east of the underground workings was discovered. Within this shear zone, a 0.6 metre wide, well mineralized, lenticular quartz vein was found. The activities of the Topley-Richfield Mining Company are summarized in the Minister of Mines Annual Reports 1924 (page 98), 1926 (pages 138-143), 1927 (pages 140-147), 1928 (pages 173-174), 1929 (pages 179-180) and 1937 (pages 26-27).
In 1952, Topley Mining Syndicate conducted a program of mapping, rock sampling and trenching. From 1955-58, Silver Standard Mines conducted dewatering and underground sampling and drilled 291 metres on the surface.
In 1967, Seemar Mines Ltd. conducted ground magnetics/electromagnetic surveys and 1100 metres of surface drilling.
In 1975, Canadian Superior Exploration Ltd. conducted a program of mapping, silt sampling, induced polarization (IP) surveying and the drilling of 405 metres in 4 diamond-drill holes.
From 1979 to 1981, Canadian Superior Exploration Ltd conducted various exploration programs. The first IP and resistivity survey at Topley-Richfield were conducted (Assessment Report 5553). No IP anomalies were generated, and this was attributed to either the small size of the sulphide bodies or to the possibility that sulphides were shielded by quartz. In 1979, Cobre Exploration Ltd. conducted a very low frequency electromagnetic (VLF-EM) and vector pulse electro-magnetometer (EM) survey at Topley-Richfield. The VLF-EM survey detected a north-striking anomaly around the old mine workings interpreted to be the surface expression of the previously detected shear zone/fault. In addition, a southeast striking anomaly was interpreted to be a previously unknown fault. Smaller features were interpreted to be veinlets of “Topleyite”, the local term for highly altered rocks.
Following the geophysical surveys, Cobre initiated a drilling program in 1980, and completed 28 diamond-drill holes (Assessment Reports 8525, 9294, 9563, 9875). Several holes were drilled to test the conductivity anomaly found by the geophysical surveys, however, this zone consists of highly sheared (and highly conductive) andesitic and ultrabasic rocks (likely carbonate altered or chloritized andesitic rocks) without any mineralization. Five holes (80-4 to 80-8) tested the extension of the mineralized zone of the underground workings (supposed to lie underneath the sheared, conductive unit.). One hole (80-4) intersected a mineralized horizon, but the favourable beds appeared to pinch out towards the south. All other holes tested the extension of the mineralized zone intersected in hole 80-4 to the north, south and its downdip extension to the west. The mineralized horizon was intersected in eight holes, and it was concluded that the ore zone thins out towards the south but may thicken again toward the southwest. In the north, the favourable beds thicken, but they are only weakly mineralized. This drilling campaign resulted in the discovery of the “B/C” ore shoot which was determined to be 300 metres by 55 to 70 metres by 2.2 metres and open to depth. Because of the stratabound nature of the mineralization (sphalerite, galena, chalcopyrite, arsenopyrite) in mono-mineralic layers, Cobre concluded that the type of mineralization was of the “volcanogenic type” (i.e., volcanogenic massive sulphide or “VMS”).
In 1982-83, Cominco undertook geophysical surveys (ground magnetometer and IP) (Assessment Report 11454). Sulphide bodies were not identified as a result of the IP survey.
Esso Minerals Canada drilled the property in 1987, completing 1018 metres of reverse circulation drilling and found only minor alteration and mineralization north of the underground workings (MacLeod, 1988, Assessment Report 17374). Later, diamond drilling targeted possible extensions of the mineralization southwest of previously delineated ore zones and found that the upper mineralized horizon thins out in this direction and the lower horizon was less mineralized although it maintained its thickness of approximately 40 metres. The drilling north of the old shaft intersected a 0.5-metre-thick mineralized horizon (Assessment Report 17374).
MacLeod (1988, Assessment Report 17374) reported reserves of 170,000 tonnes grading 3.9 grams per tonne gold and 177.3 grams per tonne silver. Although some reports indicate that the property was never mined, the British Columbia Ministry of Energy, Mines and Petroleum Resources MINFILE Production Detail Report reports that 43 tonnes of ore were mined between 1938 and 1953.
In 2006, the NXA Inc. exploration program primarily focused in the vicinity of the old underground workings. Ground geophysical surveys consisting of 15 kilometres of IP and ground magnetics were conducted. Soil sampling resulted in 232 samples being collected as well as four rock samples. In 2007, NXA Inc. conducted an exploration program that included line cutting, soil sampling and prospecting. Soil sampling along the exploration grid resulted in 332 samples being collected as well as eight rock samples. The combined 2006 and 2007 geochemical soil surveys conducted on the Topley-Richfield property identified a suite of metals which are mobile in the soil and are indicative of bedrock mineralization at depth. NXA followed through on its 2008 exploration program and completed approximately 11 kilometres of grid soil sampling, 16 kilometres of line cutting, 21 kilometres of IP-magnetics geophysical surveying, historical core reclamation, and sampling, as well as 2706.5 metres of diamond drilling in 14 holes. The first six holes drilled were designed to confirm historical drilling by Esso Resources Canada and Cominco Ltd., which had defined a gold-silver-lead-zinc-copper mineralized lens plunging moderately southwest from the original workings on surface. The first four holes reached their intended depth and were successful in confirming the presence and location of the gold-silver mineralization. Drillholes TRE08-05 and 6 were abandoned due to poor ground condition, but still intercepted several zones of gold-silver mineralization. All of the exploration holes were successful and intersected either gold-silver-bearing veins or breccia zones. NXA only tested four of its ten high-priority targets, and neither the strike nor depth extents of the newly discovered gold-silver-bearing zones have been tested. Furthermore, the strike extents of the zones identified by the 2008 drill program appear to be open to the south beyond the limits of the current geochemical and geophysical data.
