Carlin Trend Gold Mine, NV, USA

Newmont Mining Corp. 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 optimising 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, totalling 16,000oz by the year-end), are located on the Carlin Trend west of Elko, exploiting the unique mineralisation 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.

GEOLOGY AND RESERVES

'Carlin type' deposits comprise strata-bound disseminated gold mineralisation, occurring in carbonate rocks of palaeozoic age that have been metamorphosed to varying extents. They are usually structurally controlled.

Mineralisation 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.

MINING

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 has reported reserves of 2.7Moz, with ore hoisting scheduled to start by mid-2006 and to reach 1900t/d by end-2006: full-rate gold output should be 500,000–l550,000oz/y for more than eight years. Newmont is using MineStar to help manage its Nevada operations.

ORE PROCESSING

The process plants available, some using Newmont proprietary technology, provide considerable flexibility: a linear programme helps to direct ore types to the plant offering the highest economic return. Newmont groups its Nevada process units as follows:

Oxide mills: Carlin Trend mill 5; Midas, Twin Creeks; Lone Tree

Refractory mills: Carlin bio-leach (mill 5), Carlin roaster (mill 6); Lone Tree flotation, Twin Creeks and Lone Tree autoclaves

Dump Leach operations: Carlin-oxide, Carlin-refractory; Twin Creeks and Lone Tree oxide

Although Newmont processes several ore types, the proportion of gold recovered from refractory ores rose from 30% in 1996 to 66% in 2002.

PRODUCTION

In 2005, Newmont's Nevada open pits mined 175Mt of material and the underground mines 1.42Mt. The oxide mills processed 4.20Mt averaging 4.3g/t gold, the refractory mills 8.15Mt averaging 6.8g/t, and leach dumps 17.5Mt averaging 0.9g/t to give a total output of 2.46Moz of gold. The company’s consolidated Nevada gold sales were down 3.7% to 2.44Moz, while applicable cash costs rose 18.1% to US$333/oz. As the electricity price is a key contributor to cost increases, Newmont is building a 203MW power station near Elko, which it expects will save up to US$20/oz in total cash costs when it is completed in 2008.

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The brightest stellar explosion ever recorded may be a long-sought new type of supernova, according to observations by NASA's Chandra X-ray Observatory and ground-based optical telescopes.

This discovery indicates that violent explosions of extremely massive stars were relatively common in the early universe, and that a similar explosion may be ready to go off in our own galaxy.

"This was a truly monstrous explosion, a hundred times more energetic than a typical supernova," said Nathan Smith of the University of California at Berkeley, who led a team of astronomers from California and the University of Texas in Austin. "That means the star that exploded might have been as massive as a star can get, about 150 times that of our sun. We've never seen that before."

Astronomers think many of the first generation of stars were this massive, and this new supernova may thus provide a rare glimpse of how the first stars died. It is unprecedented, however, to find such a massive star and witness its death. The discovery of the supernova, known as SN 2006gy, provides evidence that the death of such massive stars is fundamentally different from theoretical predictions.

"Of all exploding stars ever observed, this was the king," said Alex Filippenko, leader of the ground-based observations at the Lick Observatory at Mt. Hamilton, Calif., and the Keck Observatory in Mauna Kea, Hawaii. "We were astonished to see how bright it got, and how long it lasted."

The Chandra observation allowed the team to rule out the most likely alternative explanation for the supernova: that a white dwarf star with a mass only slightly higher than the sun exploded into a dense, hydrogen-rich environment. In that event, SN 2006gy should have been 1,000 times brighter in X-rays than what Chandra detected.

"This provides strong evidence that SN 2006gy was, in fact, the death of an extremely massive star," said Dave Pooley of the University of California at Berkeley, who led the Chandra observations.

The star that produced SN 2006gy apparently expelled a large amount of mass prior to exploding. This large mass loss is similar to that seen from Eta Carinae, a massive star in our galaxy, raising suspicion that Eta Carinae may be poised to explode as a supernova. Although SN 2006gy is intrinsically the brightest supernova ever, it is in the galaxy NGC 1260, some 240 million light years away. However, Eta Carinae is only about 7,500 light years away in our own Milky Way galaxy.

"We don't know for sure if Eta Carinae will explode soon, but we had better keep a close eye on it just in case," said Mario Livio of the Space Telescope Science Institute in Baltimore, who was not involved in the research. "Eta Carinae's explosion could be the best star-show in the history of modern civilization."

3-Panel of Chandra, Lick & Infrared Images of SN 2006gy

Illustration of Stellar Explosion of SN 2006gy

A New Line of Stellar Evolution

Supernovas usually occur when massive stars exhaust their fuel and collapse under their own gravity. In the case of SN 2006gy, astronomers think that a very different effect may have triggered the explosion. Under some conditions, the core of a massive star produces so much gamma ray radiation that some of the energy from the radiation converts into particle and anti-particle pairs. The resulting drop in energy causes the star to collapse under its own huge gravity.

After this violent collapse, runaway thermonuclear reactions ensue and the star explodes, spewing the remains into space. The SN 2006gy data suggest that spectacular supernovas from the first stars - rather than completely collapsing to a black hole as theorized - may be more common than previously believed.

"In terms of the effect on the early universe, there's a huge difference between these two possibilities," said Smith. "One pollutes the galaxy with large quantities of newly made elements and the other locks them up forever in a black hole."

The results from Smith and his colleagues will appear in The Astrophysical Journal. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center