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MINE DEVELOPMENT Rodeo's Roadheader Experiment Pays Off Mechanical cutting provides a safe solution to a hot problem at this Nevada gold mine By Russell A. Carter, Managing Editor A Sandvik MR360 roadheader at work in a stope at Barrick's Rodeo gold mine. Mechanical mining allowed Barrick to extract ore from a section of the mine in which drill and blast methods weren't effective. (Photo courtesy of Sandvik) The world's folklore contains countless tales of heroes fighting fire-breathing drag- ons and other fearsome foes to a) rescue villages, b) save maidens in distress, or c) reap a rich reward. In today's high-tech world, the battles, tactics and rewards are quite different than their medieval prede- cessors, but every now and then a story line reverts to the classic formula. In a underground mining project cur- rently taking place in Nevada's famous Carlin Trend, for example, the quest involves a campaign to gain access to mil- lions of dollars worth of formerly untouch- able gold ore—but in this tale, traditional roles are jumbled: The hero is a large piece of tracked equipment that vaguely resem- bles a mechanical dragon, and the foe is an ore body that is literally too hot to handle. Two Mines, Nine Zones Barrick Gold Corp.'s Goldstrike complex near Elko in central Nevada, USA, com- prises both open-pit and underground min- ing operations: the Betze-Post surface mine, and the Meikle and Rodeo under- ground mines located just north of the Betze-Post pit. The Meikle mine began production in 1996 to exploit a high-grade 78 E&MJ; • JUNE 2012 ore body that was discovered in 1989. It is mined by both transverse longhole stop- ing and underhand drift-and-fill methods. The ore body incorporates five mineralized zones: the Main Meikle, Meikle Extension, South Meikle, Griffin and West Griffin. Rodeo, situated between Meikle and the pit, works a moderate-grade ore body that was discovered in 1988 and brought into production in 2002. It includes four mineralized zones: Upper Rodeo, Lower Rodeo, West Rodeo and Barrel, all of which are mined using the same methods used at Meikle. The Meikle and Rodeo ore bodies are interconnected by two haulage drifts and can be accessed from two shafts and by a decline at the bottom of the pit. The deposits are all hosted in sedimen- tary rocks of the Silurian to Devonian ages. The Post Oxide ore body occurs in the siliceous siltstones, mudstones, argillites and minor limestones of the Rodeo Creek Formation. The Betze and Rodeo deposits are found in the silty limestones and debris flows of the Popovich Formation. The Meikle deposit occurs in hydrothermal and solution collapse breccias in the Bootstrap Limestone of the Roberts Mountains Formation. The gold at Goldstrike was car- ried into the various ore bodies by hot hydrothermal fluids, and deposited with very fine pyrite and silica. Over time, the pyrite oxidized, freeing the gold and making its extraction relatively easy, as in the Post Oxide deposit. In the deeper deposits— Betze, Rodeo and Meikle—the gold is still locked up with the iron sulphide and an additional processing step (autoclaving or roasting) is required to free the gold. The Rodeo mine was developed follow- ing a 1999 land-swap agreement between Barrick and Newmont Mining Corp. that allowed both companies to benefit from syn- ergies created by the consolidation of their overall land positions in the area of Barrick's Goldstrike Property and Newmont's North Area and Deep Star operations. Essentially, each company transferred assets that they agreed would generate greater value when developed by the other company. Under the transaction, Barrick received the land corridor currently separating the Betze-Post and Meikle mines on the Goldstrike property; the Goldbug deposit, with a reserve of 1,140,000 oz, adjacent to Barrick's Rodeo deposit; Newmont reserves of 860,000 oz in the Betze-Post open-pit; and the Banshee property to the north of Meikle mine. Newmont, in return, got Barrick's portion of the underground Deep Post deposit, a reserve of approxi- mately 450,000 oz; Barrick's 40% interest (1.2 million oz) in the High Desert proper- ty; the land corridor between the Deep Post and Deep Star deposits; approximately 350,000 oz contained in stockpiled ore; and surface rights to certain lands to the south of Barrick's pit dumps. In 2011, the Goldstrike complex pro- duced 1.09 million oz of gold at total cash costs of $511/oz. Production in 2012 is expected to be 1.25-1.30 million oz as the open-pit moves back into a higher ore phase. Total cash costs during 2012 are expected to be $525-$575/oz. Goldstrike's proven and probable mineral reserves as of December 31, 2011, contained an esti- mated 12.4 million oz of gold. Although the two underground mines at the Goldstrike complex began as separate entities, Barrick has essentially merged them into a single operation, integrating www.e-mj.com