Polyhalite: 260 million years in the making

Polyhalite, which we market as Polysulphate, was deposited around 260 million years ago. At that time, the Permian era, Europe was much further south. Boulby was situated on the edge of a broad, shallow ocean called the Zechstein Sea. The prevailing hot and dry conditions at the time meant it evaporated quicker than it could be re-filled, leaving behind polyhalite, halite and potash minerals that we mine today.

Polysulphate™ is the product derived from the polyhalite mineral that lies 150m to 170m beneath the Potash Horizon at Boulby Mine. It is available in its natural state and is approved for organic use by Soil Association and Organic Farmers & Growers.

The formation process is much more complex than it may first appear to be and does take hundreds of millions of years, however, we have simplified the process into four fundamental stages.

1. The sun heats the Zechstein Sea

Polyhalite is an evaporate mineral, meaning it was left behind when the sun heated the ancient Zechstein Sea to the point where it evaporated in its entirety. 

Polyhalite under the North Sea

2. Evaporites are left behind

After the Zechstein Sea evaporated, mineral deposits, or evaporites were left and became became entombed in rock and land matter.


3. We send in our exploration geologists 

There are two teams of geologists who work together, divided into exploration and production. The exploration geologists find new material and then map out where these minerals lie underground, kind of like an ordinance survey style map. The production geologists then use what is known as a ‘long hole driller’, which retrieves samples from the identified areas. This further informs the mapping of mineral deposits.

Mineral mapping under the North Sea

4. We mine it 

Our miners travel 1.1km below the surface of the earth in search of the mineral deposits. These are then extracted, sent to the surface and then on to Tees Dock, where they will be shipped worldwide. With up to 600 miles of underground tunnels, Boulby Mine is the second deepest mine in Europe!

Polysulphate fertilizer