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Scraper Property
The Scraper Property is located 72 km (45 miles) north of Battle Mountain, Nevada, and is located directly on the northern extension of the prolific Carlin Trend of gold deposits. Subject to net smelter returns royalties Columbus controls a 100% interest in the property.
Geology
The property covers a volcanic center cored by a diorite intrusive cutting Upper Plate Vinini Formation cherts and siltstones. Highly altered volcanic rocks, coeval with the intrusive, lie marginal to the central core, with Vinini Formation exposed in erosional windows below the volcanic package.
The intrusive body is dated at 38.9 mybp, which is the age of igneous rocks associated with gold deposits elsewhere on the Carlin Trend. A detailed ground magnetic survey indicates that the intrusive body is approximately 1,676 metres (m) (5,500 feet (ft)) long, and 671 m (2,200 ft) in diameter.
Three types of targets exist at Scraper: 1) disseminated zones in the altered volcanic package, 2) Carlin-type gold deposits distal to the intrusive body, both in Vinini Formation and in the Lower Plate package at depth, and 3) either porphyry-hosted base-metals or polymetallic, gold-bearing skarns associated with the intrusive itself.
Past Work
Detailed geologic mapping, grid soil sampling, and rock sampling has yielded numerous gold anomalies at Scraper, including rock values to 0.02 opt along altered structures.
The area was first drilled by Western States Minerals, which drilled 13 holes to a maximum vertical depth of 198 m (650 ft). Western States drill hole SS-1 encountered a strongly anomalous gold zone from 93 to 143 m (305 to 470 ft), including 26 m (85 ft) of 0.025 opt gold from 98 to 123 m (320 to 405 ft). High assays over 1.5 m (5 ft) intervals were as high as 0.05 opt gold. The gold is hosted by cherts and siltstones of the Upper Plate Vinini Formation alongside the diorite intrusive rock. The gold mineralization has a Carlin-type geochemical signature.
Twelve widely-spaced rotary holes were later drilled by Cordex, mostly to a maximum dept of less than 183 m (600 ft). One hole was drilled to 579 m (1,900 ft), and encountered altered carbonate rocks of the Lower Plate of the Roberts Mountain Thrust at a vertical depth of 503 m (1,650 ft). The Lower Plate rocks were mostly silicified, and contained anomalous gold, copper to 0.2% over 15 m (50 ft), and zinc to greater than 1% over 1.5 m (5 ft) intervals. Many of the other shallow holes had anomalous gold, zinc, and arsenic.
Exploration programs were carried out in 2007 and 2008 by Newmont Mining and included a soil geochemical survey consisting of 797 samples, the collection of 202 rock samples, the completion of 24 km (15 miles) of IP survey, an airborne hyperspectral survey to identify alteration minerals, a helicopter magnetometer survey, collection of gravity data from 246 stations, the collection of 84 hand samples for petrographic work, and the drilling of three holes totaling 1,062 m (3,505 ft).
The three reverse circulation drill holes were located on what Newmont called the Diatreme Vent target. The holes were generally located 758 m (2,500 ft) from the area of gold mineralization in intrusive and Lower Paleozoic sedimentary rocks known from surface sampling and older drill holes. All three of the new holes cut surficial advanced argillic alteration for the first 61 m (200 ft) and then entered variably altered diorite intrusive. Alteration of the intrusive for the most part consisted of quartz-sericite-pyrite (QSP) superimposed on an earlier potassic alteration, marked by secondary biotite replacement. Pyrite content of the QSP was variable but high, ranging up to 35% of the sample in select drill intervals.
Planned Program
Newmont's geophysical surveys will be of value in targeting future drilling at Scraper. In particular, the IP survey yielded targets of interest, including six untested chargeability anomalies, likely related to high sulfides in the subsurface. Columbus Gold is seeking a new joint venture partner with a view to advance drilling on the numerous untested targets at Scraper.
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