The Riga 15 showing is located immediately northwest of Drybrough Peak, some 280 kilometres north of Smithers. The Riga 15 showing lies within the Omineca-Cassiar Mountains at the southern end of the Toodoggone gold camp. The showing is situated within a Mesozoic volcanic arc assemblage which lies along the eastern margin of the Intermontane Belt, a northwest-trending belt of Paleozoic to Tertiary sediments, volcanics and intrusions bounded to the east by the Omineca Belt and to the west and southwest by the Sustut and Bowser basins.
Permian Asitka Group crystalline limestones are the oldest rocks exposed in the region. They are commonly in thrust contact with Upper Triassic Takla Group andesite flows and pyroclastic rocks. Takla volcanics have been intruded by the granodiorite to quartz monzonite Black Lake Suite of Early Jurassic age and are in turn unconformably overlain by or faulted against Lower Jurassic calcalkaline volcanics of the Toodoggone Formation, Hazelton Group.
The dominant structures in the area are steeply dipping faults which define a prominent regional northwest structural fabric trending 140 to 170 degrees. In turn, high angle northeast-striking faults (approximately 060 degrees) appear to truncate and displace northwest-striking faults. Collectively these faults form a boundary for variably rotated and tilted blocks underlain by monoclinal strata.
The Riga 15 showing is underlain by Takla Group flows and pyroclastics consisting of purple and green andesite and andesite porphyry and tuff. Fracturing and chloritization is widespread. Magnetite is strong except in areas of strong pyrite alteration. Hornblende and biotite hornblende syenite to monzonite of the Early Jurassic Black Lake stock comprise intrusive rocks underlying the showing. Small dikes of the intrusive cut the Takla Group volcanics. The intrusion and the volcanics are rich in magnetite and locally pyrite. The formation of gossans by weathering is common. Chlorite-sericite is associated with mineralized fractures. Minor outcrops of Asitka Group limestone are exposed along the banks of Drybrough Creek to the north.
Mineralization at the showing consists of disseminations and fracture fillings of chalcopyrite and pyrite and blebs of molybdenite in the intrusion, over an area 76.2 metres long by 45.72 metres wide, and is associated with fractures in the volcanics. Chlorite, sericite and hematite alteration are associated with mineralization near fracture zones.
In 1973, chip samples (31-1 and 31-2) assayed 0.13 and 0.10 per cent copper with 0.010 and 0.154 per cent molybdenum over 2.7 and 7.5 metres, respectively (Assessment Report 4870).
A pit, approximately 6.1 metres in diameter, was dug at the showing in 1968. A chip sample was taken over 1.2 metres width in the eastern part of the pit. Assay results were 1.3 per cent copper and 0.01 per cent molybdenum (Assessment Report 1802). A random bulk sample from the west side of the pit assayed 0.18 per cent copper and 0.01 per cent molybdenum (Assessment Report 1802).
In 2003, a grab sample (121511) assayed 3.72 grams per tonne gold and 152 grams per tonne silver (Assessment Report 27230).
Work History
The Riga Group was owned in 1966-67 by Cordilleran Engineering Limited. Work during this period, carried out by Quebec Cartier Mining Company, included geological and geophysical surveys. The Riga 15 (094E 004) and 19 (094E 003) showings near the areas of Drybrough Peak and to the immediate northwest were reported to have resulted from this work in 1968.
The Riga showings were subsequently restaked as the RN 1-36 claims for Minas de Cerro Dorada Ltd to cover the copper-molybdenum showings. The company reported in their 1976 assessment report (5854) that previous surveys had consisted of modest programs of geochemical, geological and geophysical testing, very minor trenching and a single diamond drill hole of unknown depth. Except for a 1968 induced polarization survey (Assessment Report 2307) and geological survey (Assessment Report 1802) the results of the previous surveys were unknown. Work by Minas de Cerro Dorada during 1973 included geological mapping, a magnetometer survey over 7.2 kilometres, and a geochemical soil survey comprising 205 samples. During September 1975, a program consisting of soil sampling and detailed prospecting was conducted on the property. In 1976, Mineras de Cerro Dorado conducted soil sampling and IP geophysical surveying. This resulted in the discovery of 3 large soil anomalies on the north slope of Drybrough Peak.
In 1977 Cominco located four units covering parts of the later Star and Sun claims southwest of the Riga and RN claims and work. In 1978, Cominco Ltd (Assessment Report 6762) conducted a reconnaissance soil geochemical survey on the 4-unit Amigo Group. Mineralization exposed consisted of skarn type zinc-copper-lead-silver showings occurring at a quartz-monzonite-limestone contact.
From 1980 to 1987 SEREM Ltd (who later changed their name to Cheni Gold Mines) conducted soil, stream and rock sampling and drilled their Acapulco property which consisted of the Acapulco, Sun, Star, Aca, Pul and Co claims. These claims covered the Riga and Amigo ground previously worked. The Riga 24 showing (094E 005) was discovered by Serem in this time frame, just east of Drybrough Peak. Serem undertook silt, soil and rock sampling, geological mapping and ground magnetiics/VLF-EM. surveying in 1980, 1982 and 1985 before drilling occurred in 1987 in the Amigo area at the Star 1 prospect (094E 134).
In 1980, work performed by Serem included the collection of 35 silt samples, 190 soils samples and 25 rock samples as well as preliminary geological mapping and prospecting. In 1981, Serem Ltd carried out a soil geochemical survey on the Star claim of the Acapulco group consisting of the collection of 204 samples. In 1982, mapping, trenching (5 metres) and the collection of 12 soils and 23 rock samples occurred on Acapulco, Sun, Star, Aca, Co and Pul (Assessment Report 11106). Work was done on all these claims except Co and Aca. The Aca covered the Riga showing area. Hand trenching and chip channel sampling in 1982 was carried out over the central Star claim area in response to favourable gold and silver values obtained from an earlier outcrop grab sample. All 12 soils were taken from the Sun claim south of Drybrough Peak. No work was reported for 1983 and 1984. In 1985, a program was completed in order to delineate skarn zones (Star claim) with VLF-EM surveys (12.5 kilometres completed) and detailed geological mapping (Assessment Report 14025). No work was reported for 1986. Drilling in 1987 intersected skarn zones on Star claim (094E 058) south of the Riga area (Drybrough Creek). Significant intersections of massive magnetite and chalcopyrite with associated gold value were obtained (Assessment Report 16463). The 1987 diamond drill program tested only a very small section of the anomalous limestone intrusive contact area, approximately 100 metres in length. Very positive results were obtained in this program. No work was done on the Riga showings.
In 1997, Tanuta Ventures Corp conducted soil and rock sampling and magnetic and electromagnetic geophysical surveying on their Acapulco claims, consisting of Star, Pul, Sun and Skarn claim. These claims appear to be many of the same claims as the Acapulco claims previously held by SEREM, except for the Aca claims that Serem/Cheni held adjacent, northwest of Drybrough Peak and which covered the Riga 15 showing area (094E 004). The focus of the Tanuta work was to the southeast of Drybrough Creek. Soil geochemical anomalies for gold, silver, lead, zinc, copper and molybdenum form an oval halo around the height of land defined by the Asitka limestone unit. A total 864 soil samples were collected, and 30 kilometres of ground magnetometer and 13 kilometres of VLF surveying were completed. Thirty-two grab type rock samples were collected from mineralized outcrops over the property. The extensive grid and work covered MINFILE showings 094E 134 (STAR 1), 094E 135 (STAR 2), 094E 136 (SUN 1), 094E 137 (PUL 1), 094E 138 (PUL 7).
In 2003, Northgate Exploration collected a total of 25 talus fine and 59 rock samples on their IXL claims that covered The Riga 15 (094E 004), Riga 19 (094E 003) and Riga 24 (094E 005). Maps show sampling completed in the Riga 15 and 19 (Assessment Report 27230). Attempts to locate the Riga 24 showing were unsuccessful, possibly due to recent talus slough in the cirque. Mapping and sampling by Northgate personnel confirmed the presence of high-grade copper mineralization in high angle east - west structures across the north face of Drybrough Peak.
In 2006, John Mirko and crew conducted a focused program the Acapulco claims, consisting of Star, Pul, Sun and Skarn claims which were the same claims worked by Tanuta in 1997. Mirko targeted the potential for new occurrences or indications of platinum group elements (PGE), and low-grade copper and precious metals. Prospecting, geological mapping and the collection of 16 rock samples were completed. Several samples were collected near Drybrough Creek on the west side of the Skarn claim. One high lead-zinc-silver value was obtained from a float boulder in the creek draining the old Amigo showing area (Sample 198134). This sample is located southwest of MINFILE showing Sun 1(094E 136). Tanuta and Mirko called this the Amigo showing as opposed to the MINFILE plot of Amigo (094E 058) just less than 2 kilometres to the east-southeast.
Refer to the Pine (MINFILE 094E 016) for details of the Pine property which contained the VIP (MINFILE 094E 047, 048, 049 and 129), Grace (MINFILE 094E 129) and Concha occurrences from the late 1990s to 2014. Exploration work included programs of rock and soil sampling, geological mapping and airborne geophysical surveys.
During 2016 through 2018, Amarc Resources Ltd. completed programs of soil and rock sampling, geological mapping, 115.0 line-kilometres of ground induced polarization surveys and 1940.0 line-kilometres of airborne magnetic surveys on the area as the Joy property.
