MacArthur Mine, Yerington Mining District, Singatse Range, Lyon County, Nevada, USAi

Regional Level Types
MacArthur Mine	Mine
Yerington Mining District	Mining District
Singatse Range	Mountain Range
Lyon County	County
Nevada	State
USA	Country

The MacArthur mine occurs in a quartz monzonite intrusive of Jurassic age that has been intruded by a series of northwesterly-trending steeply dipping quartz monzonite porphyry, rhyolite and andesite dikes. The copper mineralization is zoned, with a chalcopyrite-rich (low iron to copper ratio) eastern area grading into a pyrite halo (high iron to copper ratio) to the north and west. Oxide mineralization overlies the chalcopyrite-rich area and consists of copper oxides and silicates (malachite, chrysocolla), copper wad and iron oxides

Small-scale high-grade copper production began in 1943. The major period of porphyry copper exploration in the Yerington area began in the 1950s. The area was again extensively explored in the 1960s and in the 1970s Anaconda mined the main Yerington deposit. Copper mining in the historically active Yerington district in Lyon county ceased in the late 1970s. In 1992 Arimetco International Inc. of Tucson, AZ. acquired a 50% interest (Holcorp Mines Ltd. owned 50%) in the Yerington property and began mining. Arimetco mined, stacked and leached ore at a rate of almost 2 million tons annually. In 1994 Arimetco International produced 10 million pounds of copper from the Yerington mine, equal to 1993 production. This figure was expected to increase when production from the nearby MacArthur property began. Permits for development of the MacArthur copper deposit were finally received by Arimetco International and development of the deposit started. MacArthur crops out at the surface and contains estimated proven and probable oxide copper reserves of 97 million tons containing 0.21% Cu. Yerington mine had an open-pit oxide reserve of about 15 million tons averaging 0.32% copper at that time. In 1994, Arimetco entered into an agreement with Billiton Metals Inc. for Billiton to finance an expansion of the Yerington-MacArthur solvent extraction-electrowinning plant for cathode copper from 50,000 pounds per day to 80,000 pounds per day. Arimetco planned to complete the expansion by the end of 1994. Copper production increased by 30% from 1994 to 1995 as Arimetco, Inc. opened its new MacArthur Mine near its Yerington facility. 1995 copper production by Arimetco International Inc. from the Yerington and MacArthur Mines in Lyon County totaled almost 13 million pounds, up from 10 million pounds in 1994. In 1995, Arimetco International Inc. began operations at its MacArthur deposit from a 12-million-ton starter pit with an average grade of 0.33% copper. Ore was being trucked to leach facilities at Arimetco's nearby Yerington Mine. At the Yerington Mine, Arimetco planned to begin a 2-year project for dewatering the pit, preparatory to mining sulfide ore left by Anaconda, and permitting was underway for a 20,000 ton-per-day mining, crushing, and concentrating operation. Arimetco reported that the Yerington pit contained provable and developed sulfide ore of 50 million tons grading 0.49% copper with a 0.70:1 tripping ratio. Meanwhile, Arimetco was processing 18.5 million tons of low-grade oxide dump material by heap-leaching, yielding about 5,000 pounds of copper per day. In 1996, Copper production by Arimetco International Inc. from the Yerington and MacArthur Mines in Lyon County totaled 15 million pounds. In 1997 low copper prices caused Arimetco, Inc. to curtail mining at its MacArthur project after producing slightly over 10.5 million pounds from the combined Yerington operations in 1997. Quaterra Resources Inc acquired the MacArthur property and in 2006 planned to drill it and develop it. Quaterra began a first phase program consisting of data review and compilation in late 2006. During the first half of 2007 Quaterra plansa limited confirmation drilling program to validate the historic resource, calculate an oxide resource and complete a technical report. Drilling will also be initiated to determine the size and grade of the porphyry system beyond the pit boundaries.

In 1994, MacArthur was reported to contain an estimated proven and probable oxide copper reserve of 97 million tons containing 0.21% Cu. In 1995, MacArthur was reported to contain an estimated 51 million tons of oxide copper ore with an average grade of 0.26% copper. In 2006, the MacArthur oxide deposit was reported to contain a remaining resource of 29 million tons grading 0.28% copper, including 13 million tons of +0.40% copper.