Geologic descriptionThis prospect was discovered in 1992 by following up results of a soil geochemistry survey. Mineralization continues to the south and the prospect is also probably related to quartz and sulfide vein mineralization reported as the Dakota group of some 13 claims (NM174) on Boulder Creek below Twin Mountain Creek (Mertie, 1918 [B 662-I, p. 429]). A soil geochemistry survey was completed on the northeast bench of Boulder Creek downstream from its confluence with Twin Mountain Creek in 1991. Soil samples were collected on 50-foot intervals on northeast lines about 200 feet apart. Some samples contained more than 1 percent arsenic and more than 2,000 ppb gold. In general, a strong arsenic anomaly (values in hundreds of parts per million) extends northwesterly across the bench. A series of five trenches with a total length of 900 feet was excavated; four were parallel to the soil sample lines and one crossed them. All trenches found mineralized zones, although establishing continuity between individual zones was difficult. A trench excavated on the soil line with values greater than 1 percent arsenic and 2,000 ppb gold (Trench NEBLdr-T1, Kennecott Exploration Company, written communication, 1992) found a massive quartz-arsenopyrite vein below 10 feet of overburden. A 30-foot-long zone in bedrock centered on the vein averaged 6.4 ppm gold and greater than 1 percent arsenic. Trenches 80 feet west and 100 feet east found lower values; these consisted of as much as 10 feet of 1,020 ppb gold 100 feet to the east and 10 feet of 4,400 ppb gold 80 feet to the west. A trench excavated 400 feet to the west of Trench NEBLdr-T1 contained one 10-foot sample with greater than 10 ppm gold and a 30-foot sample with about 500 ppb gold. This mineralization probably extends northwesterly into Twin Mountain Creek and could include the occurrences described in two adits driven into the east side of Twin Mountain (Cathcart, 1922, p. 251). One of these adits reportedly contained scheelite in a quartz-feldspar vein. The northwesterly trending mineralization at this prospect may be cut off or displaced by the Rodine fault (Bundtzen and others, 1994). |
