Carlin Trend’s gold
Carlin Trend pit
The USA was the fourth  largest world producer of gold  in 2009 with the most prosperous mining region located in the state of Nevada. Millions of years ago, hot springs laden with flecks of gold boiled up through deep fractures in the earth’s crust. But the golden residue did not accumulate in rich veins, instead, it disseminated throughout the sedimentary rock laid down by an ancient ocean
The vast bulk of this production is from large mines where the deposits consist of microscopic particles principally hosted in this sedimentary (or sometimes volcanic) rock. Many of these deposits lie along a few well known geologic trends, and the two best known are the Carlin Trend, and the Eureka trend. Its tiny size also explains why the old timers never found these deposits as their principal means of exploration was the gold pan.
Carlin Trend’s largest mine is the Goldstrike Property. The two o clock siren indicates that it is time to leave the pits so that the daily explosions can begin in the mine. Before the dust has time to settle, routine work resumes in the pits, 24 hours a day, 7 days a week. The best way to achieve high productivity is to use the most advanced technology, and the bigger it is the better. These six storey high shovels can load a truck with four shovel loads. Each truck carries 190 tons of ore equalling about 107 kilos of gold but what differentiates Goldstrike from a conventional open pit is a computerised management system run from a tower located on the edge of the pits.
What we are trying to do here is to optimise the efficiency of all the equipment we have to run the mines. All operations are computerised; each transportation or loading vehicle is fitted with a computer which communicates with the system in the tower.
Cranes and giant trucks extract gold from Goldstrike mine. Around 100 kilos of gold per truck
This screen shows us which shovels are available and unloading areas to which we can send the trucks, we can see which trucks are leaving the shovels and those which are leaving the unloading areas to return to the shovels.
To extract gold from such low-grade deposits, miners must crush tons and tons of rock, which is piled into mammoth heaps and irrigated with cyanide. The cyanide percolates through the heap, extracting the gold. In the early days of the invisible-gold rush, a ton of ore might contain a few tenths of an ounce of gold. Today that minuscule amount would be considered high grade. Nevada mines are now digging up a ton of rock to get back as little as 0.025 oz. of gold which would have been considered waste rock back in 1961.”
After this process, the purified ore is melted and cast into ingots with a purity exceeding 92%. Carlin Trend has become the industrial mining centre of America and has enabled the country to become the second biggest producer of gold in the world.
Timothy S Green, author of The World of Gold: “The boom in gold mining in the USA has created thousands and thousands of jobs. Somehow it has enabled Nevada to be reborn as a State. There is a whole life surrounding this industry which didn’t exist when I started being interested in gold in the mid 60’s. In North America, you will find Homestake mine plus one or two small producers. In Canada this industry lived off state subsidies and in the North of the Country we really struggled to keep mining towns standing. Today, this industry has been totally transformed, it is alive and dynamic.
Tags: Environment, Gold, Mining