Sirius Minerals CEO talks about tapping into high-grade polyhalite

Materials World magazine
,
1 Sep 2016

The beautiful North Yorkshire Moors will become home to the UK’s first deep mine in over 40 years. Ledetta Asfa-Wossen spoke to Chris Fraser, CEO of Sirius Minerals, about tapping into the world’s largest deposit of high-grade polyhalite.

Tell me more about the polyhalite deposit.

The deposit was formed in the late Permian period, around 260 million years ago, in the southern North Sea basin. Polyhalite is usually found at depths of 1,500m.

Is polyhalite a hard mineral to mine?

Not particularly – we will be using traditional mining methods but on a larger scale underground. The mineral itself is quite competent and is expected to be self-supporting. The polyhalite will be mined through a combination of continuous miners and drill and blast, using a traditional room and pillar mining approach. The continuous miners will be capable of producing 1.6Mtpa while the drill and blast production areas in the thicker parts of the orebody will produce 3.6Mtpa.

What will be the principal uses for potash from this mine?

Fertiliser. Polyhalite contains four of the six macro nutrients that are essential to plant growth – potassium, sulphur, magnesium and calcium. It can be used around the world as a direct fertiliser or part of a blended fertiliser.

Will you be mining or producing a by-product as a result?

There are no by-products in our process – because of the high grade nature of our deposit every tonne of ore mined will be a tonne of product. 

There is potential to develop other mineral seams within our area of interest in the future. For example, there are both salt and potash (muirate of potash) seams above the polyhalite which could potentially be accessed using the same infrastructure built to access the polyhalite in the future, subject to permissions.

What are some of the difficulties around extracting polyhalite deposits?

When you are mining around 1,500m below surface there is a five-year construction period to go through. But mining at those types of depths is relatively well understood, as the mineral itself is already being mined successfully in another nearby mine.

How is the new mine a broader opportunity for the UK?

It is a great opportunity for three reasons really. Firstly, it is a £2.7bln capital construction project that will generate jobs and stimulate growth in the North East for the next five years. Secondly, once in operation it can make a massive contribution to the UK’s balance of trade and create around 2,500 direct and indirect jobs. Thirdly, and most importantly, as a domestic source of these vital plant nutrients it will help make the UK self-sufficient for more than 100 years.

Do you think the UK is entering a mining renaissance? 

Ours will be the first deep mine in the UK in more than 40 years, and obviously the country has a strong mining history, but we are just one project – albeit a very significant one. The UK has interesting geology that has been exploited for generations for the benefit of the country. I am sure more opportunities will present themselves as exploration techniques improve.

Where else in the world does polyhalite occur?

Polyhalite can occur in evaporate sequences but evidence to date suggests it is usually in smaller thicknesses and much lower grades. There is currently only one other polyhalite development project, and that is located in New Mexico, USA.

There have been some concerns over environmental protection in the area. How has the mine been designed to protect the landscape?

At the mine site, surface buildings will be limited to a minimum and, where possible, sunk beneath the surface. In addition, topography, current and proposed tree planting and proposed landscaping will help shield the site from view. 

Mineral will be transported from the mine to the port in a 36km underground tunnel, meaning that there will be no surface impact of the day-to-day mineral transport.

Is it true that polyhalite deposits elsewhere do not have the mineral quality or material properties of the North Yorkshire resource? Why is that exactly? 

Sirius Minerals’ area of interest contains the largest and highest grade reported resource of polyhalite in the world. Polyhalite deposits can vary in grade depending on its location and how the deposit formed, affected by factors such as temperature and compression load during formation. 

For example, in New Mexico, the reserve has an average thickness of 1.8 metres compared with our average reserve thickness of 25 metres. And, in relation to grade, that deposit has a reserve grade of 78% polyhalite compared to ours, which is 88%.

When do you expect the mine to be built and working at full capacity?

We are currently raising finance in order to begin construction, which is expected to last for around five years. We hope to commence works this year, once financing has been raised. 

How much potash will the mine produce each year?

The initial output will be 10Mtpa, rising to 13Mtpa. Much of the key infrastructure is designed to accommodate a maximum of 20Mtpa.

Did you know?

Only 12 countries in the world produce potash. Canada, Russia, Belarus and Germany account for more than 75% of global supply. 

Potash has been used for thousands of years for making glass and soap and for bleaching textiles. In the past, it was made from leaching the ashes of land and sea plants. Most potash today comes from deep shaft mines which tap into vast underground beds of potash ore, created from sea water from ancient inland oceans that have evaporated, leaving cystallised potassium salts.

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