How does a mine work?

Six stages to unlocking Tyrone’s precious metals.

One of the most popular questions for our Community Relations team is ‘How does a mine work?’

Perhaps the best comparison is to think of Dalradian’s project as a hi-tech, highly regulated, precision-led quarry – only one that is below ground, with processing on the surface.

There are six stages to Dalradian’s environmentally responsible mining project: narrow-vein mining, processing, rock management, water treatment, shipping and final processing and rehabilitation.

Narrow-vein mining

Unlocking Tyrone’s Precious Metals

All of Dalradian’s mining activity will take place underground using a technique known as narrow-vein mining, so called because of the narrow seams of quartz rock – roughly 1m in width – which contain Curraghinalt’s gold, copper and silver.

The objective is to systematically extract just these seams (sometimes called ‘ore-bearing rock’) while leaving as much of the ordinary country rock in place as possible. This reduces the amount of mining and processing required, which minimises energy use.

Narrow-vein mining is a precision-led, largely mechanised process that uses computer modelling to help identify which seams to mine first and where best to drill and place small explosive charges. Mining usually takes place from tunnels underneath the seams to allow gravity to provide a helping hand.

The mined ore-bearing rock will then move onto the next stage, processing, which will further separate the metals from the rock. The majority of extracted rock will be returned underground to help backfill the spaces created by mining.

The hi-tech nature of modern mining has greatly increased the amount of machinery which can be controlled remotely from an underground safe area or from the surface, helping support a safe work environment. Wi-fi will track where people are working underground, further enhancing safety and ensuring energy is used more efficiently.

With an initial £15m training programme, it is expected that the mining aspect of operations will support around 250 jobs, providing roles for, among others, miners, haul truck operators, mechanics, welders and electricians.

Processing

Unlocking Tyrone’s Precious Metals

Once the narrow veins or seams which contain Curraghinalt’s gold, copper and silver have been mined underground, the next step is to separate the valuable minerals from the extracted rock.  This ‘processing’ begins underground before moving to the surface.

One of the project’s guiding principles is to retain or return as much mined barren rock underground as possible. This is environmental good practice, uses less energy, strengthens the mine development, and reduces the amount of rock that is stored above ground.

Using a ‘crusher’ underground, the mined rock is broken down into smaller pieces (tennis ball sized or smaller). These crushed rocks are separated from the minerals using a specialised ‘ore sorter’ with sensors to detect pieces containing gold, copper and silver.

To minimize carbon and dust emissions, a covered electric conveyor belt will transfer rock to the surface (this replaces the original proposal which used diesel-fuelled trucks and will, with other measures, reduce fuel consumption by 25%).

The ore goes to the processing building above ground, whilst the remaining rock, devoid of minerals, is either returned underground to backfill spaces created by mining or stored above ground in a ‘Dry Stack Facility’.

The ore enters a two-stage grinding circuit in the processing building. Using SAG and ball mills, the ore is rotated with steel balls and water in large “drums” to mill it into a finer size (similar to sand). It is then sent to a flotation tank.

Using just water and biodegradable substances, the flotation tanks help metallic elements attach to bubbles which float to the top where they are skimmed off to form a mineral concentrate. The concentrate will be shipped overseas to create gold and silver bars and copper sheets.

Thanks to changes which Dalradian introduced in 2019, no cyanide or smelting will be used on site, nor will a hazardous materials licence be needed.

Due to Tyrone’s leadership in designing and manufacturing mining and quarrying equipment, some processing equipment will be sourced locally.

Rock Management

A Best-in-Class Approach

Operations at Curraghinalt will mine two-types of rock – ‘ore’ which contains metals and ‘non-ore bearing rock’ which doesn’t.

The project is designed to retain as much non-ore bearing rock underground as possible. The remainder will be stored above ground in a Dry Stack Facility (DSF).

Rock is first processed underground through a crusher and an ore sorter. Ore is transported by an electric, covered conveyor to the surface for further processing. Non-ore bearing rock will be used to help backfill tunnels and leave mine workings in a stable condition. Some of this material will also help form the DSF’s outer shell. 

On the surface ore is further processed, creating a concentrate containing valuable metals to be shipped overseas. The left-over rock is known as ‘tailings’. Just over half of these tailings will be pumped underground and mixed with cement to backfill cavities. The remaining tailings will have most of their water removed before being sent to the DSF.

Traditionally, tailings would have been stored as a semi-liquid in ‘wet tailings dams’. By using the latest DSF technology (acknowledged by the EU as a best available technique) there will be no ‘wet tailings dams’ at Curraghinalt. Scotland’s new gold mine in the Trossachs National Park (similar climate and topography to the Sperrins) also uses DSF technology.

The DSF is an engineered, designed feature which is smoothed, shaped and compacted safely and securely. Over the c.25-year life of mine, it will have an average thickness of c.17m and won’t contain acid-generating rock.

Located in a natural hollow, the DSF will be contoured and progressively planted during operations to help it further blend in with the surrounding area, much like a landscaped embankment. Dalradian’s Environmental Statement contains detailed plans for the DSF which are being reviewed by planners and their expert consultants.

Water draining from the DSF (typically rainwater) or any water which comes into contact with mine operations will be captured and treated in a state-of-the-art, reverse osmosis water treatment plant in line with strict regulatory standards.

Water Management

Prioritising Water Recycling

Dalradian has proposed a sustainable approach to water management that meets stringent environmental and regulatory standards.

The underground gold-copper-silver mine will prioritise water recycling (c.90% within the processing plant) and minimise the use of fresh water. All water which comes into contact with operations will be captured, treated and monitored to meet independent, strict criteria set by the Northern Ireland Environment Agency.

Two major pieces of infrastructure will be built to achieve this. First, a state-of-the art water treatment plant that will treat and discharge water to a standard that preserves naturally occurring water in local streams, and secondly, four ponds to capture rainfall and water from the site / operations.

The water treatment plant will use ultra-filtration and reverse osmosis water purification technology (including a semi-permeable membrane that removes ions, molecules and large particles). Apart from iron and manganese which are present naturally at elevated levels in local waterways, the water discharged will meet drinking water standards.

One of the ponds will collect rainwater, some of which will be used in operations. The other three ponds will capture water that comes into contact with mining operations, including water from the underground mine and the Dry Stack Facility.

The ponds will be excavated fully into the ground. They are not ‘dams’ and will not use water retaining embankments or dam walls.  The ‘mine contact’ ponds are designed to contain a 1-in-a-1000-year, 24-hour storm event without overtopping.

All water in these ponds which isn’t reused in operations will be treated at the water treatment plant before being discharged.

Based upon extensive modelling and independent testing of over 1,000 samples, the proposed mine is designed to operate in tandem with the local environment. Water management is integral to that approach.

Shipping & Refining

Completing the transformation

During the planning process Dalradian listened and changed its proposals with the aim of becoming Europe’s first carbon neutral mine. We also reduced the amount of processing required at Curraghinalt by removing the use of cyanide. This means that the mineral concentrate produced by processing on site needs to be transported overseas to finalise the transformation of microscopic ore from the Sperrins into recognisable gold and silver bars, and copper sheets.

Although the final destination of the concentrate is still to be decided, there are a number of well-established smelters in continental Europe and North America which already process concentrate from around the world. To get there, sealed bags of concentrate in containers will leave Curraghinalt by road in covered lorries (around three a day) to a port where it will be shipped overseas. A similar approach is used by Tara Mines in Meath which ships its concentrate to Scandinavia.

Separating the concentrate into gold, silver and copper is achieved through ‘refining’, a process which traces its origins back thousands of years. Refining at modern smelters is, of course, much more sophisticated and highly regulated, but it is based on the same principles of using heat and other agents to remove impurities from the concentrate. This helps separate the concentrate into its valuable end products, each of which might undergo further specialist refining.

Dalradian’s proposal for Curraghinalt will produce 15,000 tonnes of copper, 3.5m ounces of gold and 850,000 ounces of silver – metals which are highly sought after because of their versatility.

Gold, silver and copper are known for their usefulness in electrical circuits. Today they can be found in everything from mobile phones to laptops, electric vehicles and for medical purposes, as well as emerging renewables technology which will be crucial to reducing global CO2 emissions.

Rehabilitation

Responsible mine closure is an opportunity for a positive legacy

Although mine operations may last up to 25 years, Dalradian has already submitted proposals to return the site to its present-day use in a Rehabilitation and Closure Plan. The plan forms the basis for a legal agreement with the Department for Infrastructure and which regulators / stakeholders will feed into. It will be regularly updated to take account of new technology and community views.

Rehabilitation is integral to the mine’s design and will start during operations. The Dry Stack Facility, for instance, will be progressively replanted with hedgerows and native species, and re-contoured to blend into the local landscape.

Some rehabilitation, i.e., removing underground equipment, can only occur after operations finish, but the objective is to restore the site to productive use for farming and/or heathlands. Alternatively, the community may wish to retain and repurpose some buildings / infrastructure, create a nature reserve to enhance biodiversity and act as a carbon sink or support other sustainability projects. Most rehabilitation will be completed within one year after closure but monitoring to ensure that environmental requirements are met will continue.

Dalradian will provide a financial guarantee and set aside funds (in advance and agreed with Government) to cover all rehabilitation costs as is the case at our current exploration site.

We also want to leave a legacy that supports the wealth and health of our community. A good example of what can be achieved is Lisheen Mine, Co. Tipperary. When it closed in 2015 a carefully structured closure plan was initiated in consultation with local communities. €80m-worth of facilities were kept, helping establish a leading European bio-tech research hub.

Dalradian has committed a minimum of £4m to support community sustainability projects and a £15m training programme should operations proceed. With skills development and training, community investment, business start-ups and expansions, potential development of centres of excellence, and the option to repurpose above-ground infrastructure or create a nature reserve, who knows what opportunities the future will bring?