Summo sizes up Lisbon Valley

A feasibility study is under way on the Lisbon Valley copper project in southeastern Utah.

Summo Minerals (VSE) has enlisted Salt Lake City-based Roberts & Schaefer to determine the economics of an open-pit, heap-leach operation. Plans call for solvent extraction-electrowinning to produce more than 30 million lb. of cathode copper per year.

Minable reserves of three sandstone-hosted copper deposits — the Sentinel, GTO and Centennial — stand at 39.4 million tons grading 0.49% copper, with a stripping ratio of 2.1-to-1. If daily capacity were to be maintained at 10,000 tons, the mine life would be 12 to 15 years.

Last fall, in an effort to expand reserves, Summo drilled 68 stepout holes. Fifteen holes were drilled along the southern extension of the GTO deposit over a strike length of 1,500 ft. Ten of these returned an average grade of 0.85% copper over a thickness of 46 ft.; the other five penetrated above the area where the zone pinches out against a fault.

Situated a mile north of the GTO is the Centennial deposit, where 14 holes tested the eastern and northeastern extensions. A grade of 0.48% copper over 83 ft. was averaged for seven holes.

Northwest of holes 94R12 and 94R14 is the Sentinel deposit, which is hosted in the same sandstone. Hole 94R12 returned intervals of 15 ft. of 0.36% copper and 55 ft. of 0.99% copper, whereas hole 94R14 intersected 30 ft. of 0.21% copper, 10 ft. of 0.24% copper and 45 ft. of 0.45% copper. The area between the two orebodies remains to be drilled and is regarded as a high-priority target.

Eight holes, drilled in a Z-pattern across the Sentinel deposit in an effort to confirm historical drilling, returned 27% more copper than previously indicated. As a result, minable reserves for the deposit increased to 7.2 million tons grading 0.34% copper at a stripping ratio of 0.3-to-1. Reserves are being recalculated and will be incorporated into the feasibility study.