Through a continuous cycle of optimization, we are pushing our mines to achieve ever greater levels of efficiency and productivity, making Pro Asian Gold one of the lowest-cost gold producers in the industry.
The Mining Process
For many years, South Africa stood as the biggest source for gold in the world. From the 1880s to 2006, it was the top source for gold mining around the world. For instance, the production of gold from South Africa was roughly 79 percent of the entire gold being produced in the world in 1970. But South Africa was overtaken by China in 2007, and now it is not even in the top three countries. The three countries that produce the most gold in the world are China, United States and Australia, with South Africa, Russia and Peru being notable mentions as well. These figures are based on the number of kilograms of gold produced by each nation in 2009.
Today, China is the dominant mine producer with 494 tonnes in 2017, or 13 percent of total, followed by Australia with 289 tonnes and Russia with 272 tonnes.
The process begins with exploration companies. There are junior development companies, small gold mining producers, mid-tier producers, larger, multi-mine producers, and royalty companies. Each type of company has a role to play in the gold mining industry. Each one offers investors a distinct corporate profile and opportunity.
Searching for gold is a complex, scientific and time-intensive process. With odds of only one in 3,000 discoveries leading to mine development, and only 10 percent of the world’s gold deposits containing enough gold to mine, exploration can be wearisome and expensive. While gold is found throughout the world at concentrations of between two and four parts per billion, we need to discover areas that contain 2,000 to 3,000 parts per billion to be profitable.
So how do our exploration teams locate future large-scale projects?
The first step is prospecting. But with veins of gold typically spanning just a few feet in width, and curving along the Earth’s geography, it is extremely difficult to pinpoint an area of exploration among thousands of square miles of land.
Obviously, it makes sense to start in areas known to contain gold, but there are nearly 900 such locations in the world to choose from. Ideally, it is best to start looking in areas less explored first, but we also seek exploration partners and/or acquire junior mining companies to expedite the process.
Pro Asian Gold uses several methods to reduce the size of land to explore:
Once a target area has been identified, and geological, geophysical and geochemical data indicate a high probability of a deposit, drilling is conducted. Drilling helps us evaluate the type and grade of minerals in the ore.
Production geologists use information they obtain from sampling, testing, mapping and observation to determine the most efficient and effective mining techniques, as well as to identify the grade (amount of mineral) in the ore. In gold and silver mining, grade is reported as grams per ton. Copper grade is reported as a percentage. It is important to know the grade to determine which rock is sent to the plant for processing and which rock is sent to the waste rock storage area.
By using this data and complex computer programs to more accurately define the orebody, mine engineers can determine mining methods, design blast patterns, design dig patterns, and maximize the safety and efficiency of production – as well as determine how the ore should be processed.
Geologists also use drilling and sampling data to identify wet areas. Water can cause major problems in both open pit and underground mines. If areas of high water content can be avoided or planned for in advance, we can reduce safety risks, costs and production interruptions.
Gold demand worldwide from 2007 to 2017 (in metric tons)
World gold production by year in mines from 2005 to 2017 (in metric tons)
Designing and Constructing a Mine
There are two types of mine designs for mineral mining: surface (open pit) and underground.
Surface mines are generally preferred if the ore body is relatively shallow and uniform, and are made by digging into the Earth’s surface one layer at a time. The final mine is cone-shaped.
First, we drill holes in the ground and fill them with explosive. After the rock has been broken up by blasting, it is loaded into giant haul trucks using large shovels and front-end loaders. Rock containing gold, copper and other valuable minerals is hauled away for processing and waste rock is taken to a separate area for storage. Areas of waste rock are later rehabilitated.
As we dig farther down, it is necessary to dewater the mine to ensure that the water level remains below the pit floor. Each day, we pump thousands of gallons of water from the pit. Much of it is reused on-site (to control dust, etc.). Excess water is treated and discharged back into nearby rivers or lakes.
A significant amount of monitoring takes place in and around the open pit, to keep a watchful eye on:
Underground mines are used to extract minerals or metals from deep in the Earth. When building an underground mine, we dig a tunnel to get to the minerals. This can be a straight vertical tunnel called a shaft or a tunnel that spirals gradually downwards, called a decline. To access the ore from the shaft or decline, we dig other tunnels. We also mine out tunnels to provide proper ventilation and emergency exits.
We mine the tunnels and the ore bodies by drilling and blasting. The broken-up ore is then transported to the surface for processing. Waste rock may be transported to the surface or left in the mine and used to fill empty space.
Once we remove all material from inside the tunnels, we support them to make them safe. The type of ground support needed depends on how stable the ground is and how long the tunnel is going to be used for. These factors are identified in advance so that engineers can design the mine for maximum safety and value.
Ground support may be provided by rock bolts or split sets, which are forced into drilled holes to exert pressure on the surrounding rock, which keeps it intact. Chemicals or grouts are sometimes added with rock bolts to give them greater strength. We also install wire mesh to keep smaller rocks from falling down.
High-pressure spraying of Shotcrete (a mortar/concrete mix) onto the tunnels’ walls and backs provides more support. As we complete mining in each stope, we backfill it with a cement mixture as well.
Underground mines pose a greater safety risk and limit the size of equipment that can be used; however, they cause less environmental disturbance.
Operating a Mine
When operating a mine, we use stringent controls to prevent or mitigate any environmental impacts. Our environmental management systems are designed to ensure all environmental considerations – including management, monitoring, maintenance, training and action plans – are incorporated within an overall framework as an integral part of mining operations.
At all times, Pro Asian Gold will operate in compliance with applicable laws, regulations and other legal requirements. In addition to this mandate, we use an internal management system that includes a global set of performance standards to provide a set of acceptable performance criteria within a framework of continuous improvement.
Haul trucks transport the ore from open pits or underground operations to processing operations. Some ores may be stockpiled for later processing. Rock that is not economical to mine is stored in waste rock storage areas. The grade and type of ore determine the processing method used. Additionally, the geochemical makeup of the ore, including its hardness, sulfur content, carbon content and other minerals found within, impact the cost and methods used to extract gold.
Alternative Ore Processing
We use alternative gold recovery methods in some processing plants to accommodate different ore characteristics or other requirements. For example, ore that has a high level of sulfide minerals or carbon (or both) is called refractory ore. Refractory ore resists normal processing methods as the high sulfide minerals trap gold particles, making it difficult for the cyanide to reach the gold and leach it.
Heating – To leach gold from refractory ore, it must be subjected to high temperature, high pressure and/or oxygen. Pro Asian Gold treats refractory ore in two ways: by using an autoclave or a roaster.
An autoclave is used before leaching occurs. First, the slurry is heated and fed into an autoclave, where high-pressure steam, water and oxygen are applied to oxidize the sulfide material by a chemical reaction. The slurry is then cooled and sent back into the process to be leached.
An alternative to an autoclave is a roaster, a very high temperature oven that is often used instead of an autoclave if the ore to process contains a large amount of organic carbon. Roasting uses heat and air to burn the organic carbon into fuel and to burn the sulfur off ore, which we heat to high degrees.
Heap leaching – In heap leaching, we dump crushed ore into piles called heaps, to which we apply a weak cyanide solution, using drip feeders. The gold dissolves into the cyanide solution. The entire heap leach area is lined with heavy duty liners to ensure no solution leaks into the environment. Next, we collect the gold-cyanide solution in ditches and ponds, and then transport it to a recovery plant.
Flotation – Flotation is a method of separating minerals depending on their ability to attach to air bubbles.
Flotation can be used for a number of materials by adjusting the chemicals. At Pro Asian Gold, it is used for copper recovery and, in a very limited number of cases, for gold processing.
We introduce air bubbles to the slurry while it is in small tanks, called flotation cells. We add some chemicals to the slurry to assist the process. The desired minerals stick to the bubbles and rise to the top, resulting in froth. The froth overflows from the tank, and is removed and sent to the next step in processing.
Gravity circuit – A gravity circuit recovers coarse gold before it is leached. Gravity circuits use the same principles as gold panning: coarse gold is heavier than other material and will settle to the bottom so that it can be removed (gold is 19.3 times heavier than an equal volume of water).
Closing and Reclaiming a Mine
Pro Asian Gold is committed to leaving a positive legacy for the communities and the environment where we operate. In part, this commitment means developing an integrated approach to closure that takes into account community and environmental issues, and reclaiming disturbed land for beneficial use after our mines close.
Planning for closure and reclamation begins during the earliest stages of project development, before operations start at a new site, and continues during the development of the mine. Our goal is to minimize the disturbance of land in our exploration activities. We reclaim all disturbed ground, with the exception of roads if the local community or government wants them left intact.
Disturbed land is reclaimed progressively during the mine’s life. Our Closure and Reclamation Technical Team develops and applies a system that ensures the approach to site closure and reclamation, including the costs, are consistently evaluated and reported at every stage of the mine lifecycle.
In developing and implementing reclamation plans, Pro Asian Gold seeks to apply a new scientific approach to address mineral waste generated from the extraction of precious metals. At several of our sites, we have pioneered techniques that have been shared in the industry as scientifically proven approaches to mine site closure and reclamation worldwide. All operations look to balance environmental solutions with post-mining beneficial land use.
Our rehabilitation and closure plans are designed to ensure:
To restore the landscape for future uses such as ranching, recreation or wildlife habitat protection, we progressively rehabilitate areas of disturbed land in the mining area, which offers a number of advantages:
Closing a mine can have a significant impact on local communities. As such, in the earliest stages of project development, we engage with our stakeholders to ensure the value that is created during the mine operation is translated into lasting programs within the communities. Sites are required to set up a process for reviewing and updating closure plans regularly with external stakeholders over the life of the mine.