Nevada is now the leading gold-producing state in the nation, producing 82% of all gold mined in the United States. Almost all the gold in Nevada comes from large open pit mining and cyanide heap leaching recovery.
Prolific Gold Trends of North–Central Nevada;
Independence – Eureka Trend, Battle Mountain – Eureka Trend, Rabbit Creek Trend, Getchell Trend
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Carlin Trend Map
Carlin Trend Gold Mine, NV, USA
Carlin Trend Gold Mine, NV, USA
Carlin Trend Gold Mine, NV, USA
- In Nevada, approximately 300Moz of gold has been discovered and defined to date.
- Annual Gold production in Nevada exceeds 6Moz – 82% of US gold production
- Over $6 billion has been invested in regional infrastructure – including the development of processing facilities near Ironwood properties
- Premium valuations are achieved for new ounces of gold discovered
- The Carlin Trend is host to several of Newmont’s and Barrick’s largest gold mines;
- Regional Examples:
- Goldstrike, Leeville and Meikle mines: 80M oz Au to date. 2M oz annually*
- Gold Quarry and Tusk mines, 60M oz Au to date, 1M oz annually*
The Carlin Gold trend is one of the world's richest gold mining districts. It is a belt of gold deposits, primarily in Paleozoic limy sediments, that is about 5 miles wide and 40 miles long, extending in a north-northwest direction through the town of Carlin, Nevada. Gold was first discovered in the area in the 1870s, but there was very little production until 1909, and only about 22,000 ounces was produced through 1964. By 2002, mines in the Carlin Trend had produced over 50 million ounces of gold, worth around US$47 billion at 2009 prices. [1]
Gold was discovered in the vicinity of Carlin in Eureka County in the 1870s, but production was small. Placer deposits were discovered in 1907, but the deposits were too small to cause excitement. It was not until 1961 that the Newmont Mining Corporation found the large low-grade gold deposit at Carlin that the mining industry began to take notice. The Carlin mine began producing gold in 1965, but at the price then of $35 per troy ounce, the ore grade was still too low to cause a rush to northern Nevada. It was not until the gold price shot up in the late 1970s that mining companies rushed to look for similar deposits.[2]
The Carlin Trend, part of what is also known as the Carlin Unconformity by geologists, is 5 miles (8.0 km) wide and 40 miles (64 km) long running northwest-southeast, has since produced more gold than any other mining district in the United States. The trend surpassed 50 million troy ounces (1,555 tonnes) of gold in 2002. The Carlin and other mines along the trend pioneered the method of open-pit mining with cyanide heap leach recovery that is today used at large low-grade gold mines worldwide.
New ore deposits are still being opened along the trend. For example, the South Arturo deposit was discovered by Barrick Gold in 2005. The deposit contains an estimated 1.3 million ounces (40 tonnes) of gold.[3]
Newmont Mining Corp. [4] started mining gold at Carlin, Nevada, USA in 1965 and thereafter built up a strong land position in the state. Newmont Gold Company later became the company's only major asset, while the acquisition of Santa Fe Pacific Gold in 1997 increased Newmont's options for optimizing mining and processing. In early 2001, Newmont acquired Battle Mountain Gold Co. and in 2002 Normandy Mining, so further extending its gold mining and exploration base in Nevada. In 2002, Newmont owned or controlled 7,915km² of land along Interstate 80.
Mining started with open pits, some of which have been extended underground since 1994. Processing is by a number of methods, according to ore type. In 2005, the company operated 13 open pits, four underground mines and 14 active processing facilities in Nevada. Most, including Leeville (where development ore production started in Q3 2005, totaling 16,000oz by the year-end), are located on the Carlin Trend west of Elko, exploiting the unique mineralization identified by Newmont in 1964.
The Twin Creeks and Lone Tree Complex are in the Winnemucca region further west, while the Phoenix gold / copper project, where ore processing has started building up to a full rate output of 350,000–420,000oz/y of gold and around 21,000t/y of copper, is near Battle Mountain.
'Carlin type' deposits comprise strata-bound disseminated gold mineralization, occurring in carbonate rocks of palaeozoic age that have been metamorphosed to varying extents. They are usually structurally controlled.
"As the electricity price is a key contributor to cost increases, Newmont is building a 203MW power station near Elko."
Mineralization may be predominantly oxides, sulphides, refractory or carbonaceous sulphides and ore type determines the treatment route. High-grade oxide and sulphide ore can be treated by conventional milling and cyanidation, but for the lower-grade oxides Newmont developed heap-leaching technology. Similarly, for the large proportion of refractory ores that cannot be processed by conventional methods, the company completed a roasting unit for higher grades and a proprietary bio-oxidation system for lower grades, both in 1994. Refractory ore with a carbonaceous content is treated in the bio facility or by ammonium thiosulphate leaching. The Winnemucca operations use autoclaves to pre-treat refractory ores.
At end-2005, Newmont's total Nevada proven and probable gold reserves were calculated to be 33.3Moz (equity). At Phoenix, reserves have been increased by 3Moz gold and 408,150t copper since Newmont acquired the property.
Open-pit mines remain the major source of Carlin Trend ore. Carlin is the original pit but Gold Quarry, which opened in 1985 and has been supplemented by the Tusc satellite pit since 1994, is the largest. Other major pits have been Genesis and Post, while Bootstrap, Beast, Lantern and Sold were opened in 1995. Mining is conventional, using large shovels and haulers.
Underground mining, in higher-grade ore down-dip from existing open pits, started in 1994, with two extensions from Carlin. Rain, which works oxide ores by longhole stoping, is an extension of the depleted Rain pit, and Deep Star is an extension from Genesis. Deep Post, which started up in 2001 and produced 227,000oz in its first year, has its portal located within Barrick Goldstrike's Betze/Post open pit.
In 2002, development began on the 700m-deep Leeville deposit, which reported reserves of 2.7Moz. Full-rate gold output should be 500,000–550,000 oz/y for more than eight years.
The regional processing plants provide considerable flexibility: a linear program helps to direct ore types to the plant offering the highest economic return.
Sources:
- Remarks by Jonathan G. Price, Director and State Geologist, Nevada Bureau of Mines and Geology, 2002.
- Donald M. Hausen and Paul F. Kerr (1969) Fine gold Occurrence at Carlin, Nevada, in Ore Deposits of the United States, 1933-1968, New York: American Institute of Mining Engineers, p.908-940.
- Ed Cope and others, "South Arturo: a recent gold discovery on the Carlin Trend," Mining Engineering, Jan. 2008, p.19-25.
- http://www.mining-technology.com/projects/carlin/