Newmont’s Carlin output could rival South Africa

Predictions that the Carlin gold belt of here could eventually rival South Africa as a gold producer can’t be discounted given the reserves found there by companies like Newmont Gold Company.

As The Northern Miner learned while visiting Newmont’s sprawling Carlin operations, the number of discoveries made there in recent years is truly remarkable. Newmont’s proven and probable reserves stand at 302.6 million tons averaging 0.049 oz gld per ton and the company has embarked upon a $450-million(US) capital program to develop its Carlin holdings.

Newmont’s annual gold output is expected to rise to 1.6 million oz in 1991. Sales were expected to reach 930,000 oz in 1988 but poor equipment deliveries and the destruction of a new crusher installation by fire will reduce that output to about 830,000 oz.

Newmont has been blocking out reserves at a break neck pace, so much so that it has run into a somewhat unusual problem — finding non-orebearing areas for plant sites, leach pads and tailings disposal. A large part of the company’s geologists’ time is spent trying “not to find” a gold deposit.

For example, when the company drilled a proposed mill site location for the Rain mine, it found the three million ton Gnome deposit. The Gnome is one of four established gold deposits at the Rain property which will be incorporated into the overall project.

Fending off a takeover bid by T. Boone Pickens’ Mesa Limited Partnership last year cost Newmont about $2 billion; and it’s been selling off assets to reduce that debt ever since. Shareholders in Newmont Mining, which owns 90% of Newmont Gold, were probably the biggest over-all winners. They received a dividend of $33 per share.

Newmont didn’t appear to have much choice in the matter and most analysts concluded that Pickens would have dismembered Newmont to cover all or part of its acquisition costs. According to one Newmont official, Vancouver-based Galactic Resources, which was part of the unsuccessful takeover bid, later approached Newmont about obtaining road access to one of its Nevada properties (Ivanhoe) through Newmont’s holdings. The answer was a very firm no.

Regarding the Deep Post discovery, which earlier this year returned a 470 ft intersection grading 0.93 oz gold per ton, Robert Zerga, executive vice president and general manager for Newmont Gold’s Carlin operations, confirmed the importance of the find. But he conceded it isn’t at the top of Newmont’s list of priorities at this time. Development of the Surface Post deposit is going forward and it will either be jointly mined by Newmont and American Barrick or on a contract basis.

About two-thirds of the Surface Post deposit lies on Newmont ground and the other third on American Barrick’s. To mine the deeper portions of its Surface Post deposit, American Barrick has actually had to step back onto Newmont’s property. Ore from Newmont’s portion of the deposit is being stockpiled by Barrick at their cost. The relationship between the two companies seems exceptionally good.

Zerga confirmed that Newmont was still drilling the Deep Post deposit which he conceded was really not that well defined by the company. Also, they don’t have a good handle on mining conditions or the metallurgy of the deposit. American Barrick has encountered heavy water flows on its portion of the deposit (rumored to be up to 20,000 gallons per minute, sometimes at 110 degrees F) but Zerga said they aren’t encountering anywhere near this on their side.

Final design and construction of the company’s No 4 mill at Post has been delayed so Newmont can study the implications of the Deep Post discovery. The sulphide material is definitely refractory and would probably require bioleaching or autoclaving.

Most of Newmont’s present pro- duction is coming from the Gold Quarry mine which is expected to yield about 60,000 oz of gold this month alone. There are 199.2 million tons of proven and probable reserves averaging 0.045 oz.at Gold Quarry which must rank as one of the great gold deposits of the world.

Work on the No 5 mill, which is adjacent to the No 2 mill at Gold Quarry, is well advanced. When completed, the combined plant will have a capacity of 25,000 tons-per- day, up from 9,000. The company is moving about 192,000 tons of material at the mine each day; 12,000 tons of this is milling ore (which grades about 0.1 oz) and about 50,000 tons (grading around 0.03 oz) is going to leach pads.

Carbonaceous material is now being encountered at Gold Quarry which will have to be treated separately by conventional milling techniques in the No 2 plant. None of this is loaded onto leach pads. Its affinity for gold would effectively negate the leaching process and render the pad useless.

The No 5 mill, which will treat oxide ore exclusively, is virtually the same at the No 2 plant but it has larger ball mills, one of which is presently being used to raise throughput from 9,000 to 12,300 tons per day. Throughput in the No 2 plant will actually drop to 6,000 tons when refractory ore is treated.

Gold Quarry is located in the South Area, a region that encompasses the Maggie Creek, Gold Quarry, Tusc, and Mac orebodies plus the No 2 mill and soon-to-be- completed No 5 plant.

Gold Quarry will rank as one of the largest heap leach operations in the world. Newmont is currently building a 7-million-sq-ft leach pad there that will have a capacity of 45 million tons. A new leaching area, known as the South Area leach, will be constructed over the next four years and have a total design capacity of 135 million tons. The combined area under leach will be over 20 million sq ft with leach pads piled 300-ft high in various lifts.

The Carlin pit, where Newmont began operations in 1965, has for practical reasons been mined out. Approximately four million oz has been extracted and the Carlin mill is presently handling 600 tons of refractory ore each day from Carlin stockpiles and about 3,400 tons from the Genesis and Blue Star orebodies. The former is about seven miles away but the economics are still favorable because Newmont has the Carlin mill in the area.

Current plans call for the mining of 50 million tons of leach material and nine million tons of milling ore from the Genesis and Blue Sky orebodies. These two deposits are located in the North area which also includes the Bootstrap/Capstone deposit, Post, North Star, Lantern, and Pete orebodies, plus the No 1 mill and crushing and leaching facilities. The No 4 mill, which will treat ores from the Post orebody and other deposits in the region will be completed in 1989.

The Rain mine, which was recently completed under budget at a cost of $45 million and is about 25 road miles from Gold Quarry, is now fully operational. It will produce approximately 110,000 oz gold this year from milling ores grading around 0.07 oz gold and leach material averaging approximately 0.029 oz. About one quarter of that production will be heap leach.

According to Jim Komadina, mill superintendent for Newmont’s No 3 mill at Rain, the economics of developing the property entirely as a heap leach operation were actually quite favorable, even with the lower recoveries from what would now be defined as milling ore. But the company ultimately decided to install a conventional mill for higher grade ore (which they have found more of since the decision) and a leaching operation for lower grade material.

About one million tons of low grade ore will be loaded onto leach pads each year and the plant will handle another 740,000 tons at a projected head grade of 0.13 oz. The mine has a single primary and secondary crusher and leach material is reduced to one inch, the same as conventionally milled ore.

A minimum recovery rate of 65% is expected for this leach material and 88% for milling ore which at times will contain a relatively high arsenic content. With prudent metallurgical controls, Komadina said they should know exactly when this refractory material will be encountered so adjustments can be made in the mill.

Portions of the Rain Deposit contain 30-40% barite and, indeed, it was originally a barite mine. Because of the barite, the ore body has a high specific gravity (3.6) which had to be taken into account in the design of the mill flow sheet. Almost everything in the plant runs by gravity and there are few pumps. Ore is ground to 80% minus 200 mesh, not the finest grind at Newmont’s Carlin properties, and the bond index is a modest 7.5, well below the industry average. As a result, the relatively small plant can handle about 2,100 tons per day.

The plant has been operating since July and the tune up phase involved a few days rather than weeks. A mining plan has been developed for the nearby Gnome deposit (which was discovered while searching for a mill site location) and the SMZ deposit. But the Rain orebody will be mined first.