The Silver Dome Property is located 72 kilometres (45 miles) northwest of Delta, Utah along the western margin of the Fish Springs Mountains. Subject to net smelter royalties, Columbus controls a 100% interest in the property.
Geology
Silver mineralization at Silver Dome occurs with very fine-grained galena disseminated within flat-lying, Ordovician calcareous sandstones and cross-cutting, high angle structures. Due to the flat topography in the project area, and subdued outcrop exposure, size and geometry of the silver-bearing zones have not been determined.
Past Work
The Silver Dome Property is about 97% covered by thin alluvium, located near an area of intermittent bedrock measuring 3,280 ft x 328 ft (1000 m x 100 m) which contains a surface silver showing known as the Cactus Shaft. Surface sampling by Columbus near the Cactus Shaft and in float boulders on shallow pediment up to 492 ft (150 m) from the bedrock exposures yielded high grade silver assays (up to 85 opt silver), associated with lead, on high angle structures, and also indicated that low grade silver values were disseminating away from structures into an Ordovician sandstone layer (1-2 opt silver over widths of 70 ft (21 m)). The sandstone appears to dip gently west, and the larger target at Silver Dome likely lies west, south, and north of the Cactus Shaft area under thin alluvial cover, where Columbus Silver holds several square miles of potentially mineralized ground.
Columbus completed an initial drilling program in late 2008 consisting of 13 reverse circulation drill holes. The drilling results can be viewed here:
www.columbussilvercorp.com/i/pdf/nr/sd_drill_results_ph1.pdf
Five of the holes (SD-1, 2, 4, 5, and 6) were angle holes drilled to test below strongly mineralized outcrops near the Cactus Shaft. The drill holes all crossed under the target sandstone at shallower depths than expected, into relatively unmineralized carbonate rocks. As a consequence, only low-grade silver values were encountered, but subsurface information gained from the holes will allow future drilling to accurately intersect known mineralized structures where they cut the favorable sandstone layer.
The other 8 drill holes (SD-3, and SD 7 through 13) were vertical holes drilled on a grid, with 500 ft (152 m) spacing, stepping immediately north, west, and south of the Cactus Shaft into the area of alluvial cover. This drilling was surprising in that the favorable sandstone bed is thinner than expected, or even absent (none in SD-3, 10, and 13); likely due to erosion of the sandstone prior to deposition of the surficial alluvium. In general the alluvial cover averaged 140 ft (42 m) in thickness.
The target sandstone is commonly mineralized at depth, but is generally only anomalous in lead and silver, and at much lower grades than anticipated. SD-6 and 7 were the best holes in the Ordovician sandstone. SD-7 was the only hole to cut the maximum thickness of the sandstone which was 215 ft (65 m).
The last drill hole in the program, SD-13, cut 20 ft (6 m) of silver averaging 1.48 opt in the carbonate rocks well below the sandstone. The highest assay over 5 ft within this intercept was 3.8 opt silver. This hole was anomalous to the bottom (350 ft (106 m)) and also averaged 6215 ppm lead from 290-340 ft dept. This intercept indicates another horizon of potential to be tested with further drilling.
Planned Program
Columbus Silver's target at Silver Dome is bulk-mineable silver mineralization within the flat-lying calcareous sandstone host rocks amenable to open-pit development. Preliminary metallurgical test work on 16 samples of variable grade and location yielded recoveries ranging from 47%-91% (averaging 71%), suggesting the mineralization may be suitable for heap leaching or conventional milling with cyanide recovery.
Future plans at Silver Dome include shallow drilling at the Cactus Shaft, and more drilling further into the alluvial basin west, north, and south of the shaft where silver mineralization remains open, and focused on IP anomalies. In addition a line of 7-9 holes is planned across the magnetic high discovered by a ground magnetic survey about 1.5 miles (2.4 km) southwest of the Cactus Shaft. This high is interpreted to be a buried, but shallow, plug of intrusive rock about one half mile (0.8 km) in diameter with potential for mineralization particularly along its margin as at other nearby mining districts such as Tintic and Crypto, which is immediately north of the Silver Dome Project.
