Of Mines and Men

 

Boroo Gold is located a 2 hour drive north from UB, straddling Bayangol and Mandal sums. Pastoral land surrounds the area, with farmers herding sheep and goats over the hillsides. It is owned by Centerra, a Canadian company. The mine itself is in it’s twilight years, milling and processing much lower grade material with closure scheduled for the end of December. In the meantime, production is ramping up at nearby Gatsuurt, 35 km from Boroo.

Boroo Gold

Boroo Gold

Rocky slurry after milling

Rocky slurry after milling

Rocky material from the mine is taken to the processing plant where it is crushed and milled down to 75 micron particles. Water is added at a 1:1 ratio to make a slurry. There’s a few gravity/thickening stages before the gold is leached from the rocky material using a cyanide solution. Recovery of the gold takes place via absorption to carbon, and elution using a cyanide/caustic mixture under high temperature and pressure. From the wastewater, arsenic is precipated out using iron sulphate, and the cyanide is also recovered and recycled.

 

 

The director of the mine chuckled as he showed me a figure that said that there is more cyanide in apple seeds and cherry stones than in the tailing water (1ppm). A reason to spit the pips?

However, at least there is some kind of biological route for cyanide degradation. Before the modern mining operation here, mercury was used to make an amalgam. In 1956 the storage area of the former Boroo Gold Recovery factory exploded, releasing substantial quantities of mercury into the Boroo river. In a rather cruel twist, this has now spawned a cottage industry of mercury scavengers who seek out the deposits for the illegal placer mining operations.

For the new mine at Gatsuurt, the gold is “refactory”, that is to say, it is embedded in a coat of sulphide which makes it difficult to recover. The company had to make a choice, either go with a roasting technology, or implement a process known as BIOX – biological oxidation. They have chosen the latter, and a $200m plant will be constructed if they get the go ahead from government. The technology was developed in South Africa in the 1970s, but is used globally from Brazil to Kazakhstan for the recovery of difficult deposits. Step up please Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans, Acidithiobacillus caldus, Leptospirillum ferriphilum and Ferroplasma acidiphilum. The bacteria operate at an astounding pH of 1.2-1.8. Little competition there then. The reaction is exothermic which provokes another hearty laugh from the director, “No problem in Mongolian winter!”

From my point of view it was fascinating to see the adoption of a biological process within such a hard industry. It isn’t to say the bacteria can’t be fickle – As(III) is toxic, as is a number of other compounds. Without good gas dispersion the process won’t work (sound familiar algae folks?) – in this case oxygen demand is high. Despite all of these characteristics that on paper make the process seem tricky, it seems like the BIOX bugs have a rather impressive track record.

Carbon used for gold capture

Carbon used for gold capture

Tailings pond

Tailings pond

Showing me around the site today is Oki, one of the environmental engineers. She is whip-smart, articulate and super knowledgeable about the reclamation activities. Dotted over the hillsides are signs indicating when the land was restored. Topsoil is added to the crushed rock and seeds from perennial grasses of the region are collected yearly to establish new parts. The vegetation is sparse, but no different to the surrounding areas. In one of the plots there is a plantation of sea buckthorn, laden with jolly orange berries. Acacias, elm and willow accompany them as neighbours. Being autumn the saplings look a little frail, but there seems to be a plan to take care of them until they become established.

IMG_0351

Watering twiggy

A school group are on site for a tree planting exercise, so we join in. While we’re fetching pails of water from a lorry, Oki tells me that the programme for the long term maintenance of the reclaimed land will stretch to 2020. I hope she is right.

 

 

 

 

 

 

 

 

 

 

 

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