MLA 23-94 - State of Arizona Department of Mines and Mineral ...

IIIIIIIIIII!iIIIA fourth copper-porphyry of the Helvetia group, Peach-Elgin, is 1 mi west of the ManagementUnit(pl. 1, site 55). The copper porphyries have been known since the 1950's but have notbeen mined. They would probably be mined asagroup, viaopen-pit mining, with both heapleachingand conventional flotation methods, depending on the various ore types. TheRosemont copper-porphyry deposit alone contains 410 million st of sulfide ore and 90 millionst of oxide ore, at grades of approximately 0.6% Cu, 0.019% Mo, and substantial Ag.Broadtop Butte deposit contains a 9 million st resource comprised of oxides and sulfides;Peach-Elgin deposit contains a 24 million st oxide-and-sulfide resource. Copper andmolybdenum grades of those two deposits are comparable to the Rosemont deposit. No dataare known about the Copper World deposit.USBM mine modeling and economic analysis, using CES s and other cost data, estimatea 20-year mine life for an open-pit opera[ion, centered on the Rosemont copper-porphyrysulfide ore, supplemented by concurrent production from the other three copper-porphyrydeposits. Collectively, 20.5 million st would be mined per year with an average stripping ratioof three tons of waste to one ton of ore. A conventional sulfide flotation plant with amolybdenum recovery circuit would be utilized. Copper oxide ore would be recovered by heapleaching and SX-EW 6. Infrastructure development would include construction of a 4.5-milongaccess road from the mine to State Highway 83 and utility lines to the mine and millsites. Traffic on Highway 83 would increase as 1,060 st/d of copper concentrates would beshipped north via truck to a rail line. About 30 truck loads per day would be shipped (35 stper load). Estimated capital costs for the mine and mill would be about $490 million (all costsin 1994 dollars). Ore could be mined and milled for an estimated $6.43/st or $0.61 per Ib Cu.Cathode copper from SX-EW could be produced for about $0.27/Ib. At this level of capitaland operating cost, and a copper price of $0.92/Ib, a 15% ROR 7 could be realized over thelife of the property. An 11% ROR could be realized with copper selling for $0.81/Ib. Wastedisposal would require about 2,000 ac over the mine life for the settling of 20.4 million st peryear of flotation mill tailings. No plan was developed by USBM to determine how much of thismaterial would be ultimately stored on the National Forest surface. (See USBM, 1994b, p.8-12.)Undiscovered copper-porphyry deposits may exist in an area delineated by Ludington(1984) (pl. 1, site 56). However, the coincident location of the Madera Canyon recreational5 U.S. Bureau of Mines Cost Estimating System (version 2.0), an economic modeling software package for mineral deposits.e Solvent extraction-electrowinning.1 ROR is "rate of return".