Sirius Minerals Regulatory News (SXX)

4 November 2013

Sirius Minerals Plc

Polyhalite product "POLY4" characterisation tests

· Positive results received from a range of product characterisation tests on the York Potash Project's POLY4 polyhalite product

· POLY4 is a fully soluble multi-nutrient fertilizer suitable for soil application at all commercial application rates

· All nutrients in POLY4 are rapidly transferred to the soil's available nutrient pool soon after application

· POLY4 is pH neutral, has no effect on the soil pH levels and has no negative effect on soil conductivity at commercial application rates

The Directors of Sirius Minerals Plc (AIM: SXX, OTCQX: SRUXY) ("Sirius" or the "Company") are pleased to provide an update on the latest results from its recently completed product characterisation testing programme on its POLY4 polyhalite products.

POLY4 is the powder and granulated product that will be produced from the York Potash Project. Its physical properties are as a result of the transportation process to Teesside (finely ground powder) and the granulation process that will be undertaken in Teesside. The testing programme was carried out by various independent bodies including Société Générale de Surveillance ("SGS") Laboratories in France, NRM Laboratories and Durham University in the United Kingdom, University of Florida in the United States and Shandong Agricultural University in China. The programme was designed to measure and validate the following characteristics of the York Potash POLY4 product in laboratory conditions:

· Product solubility;

· Nutrient release rates and availability; and

· The effect on soil pH and soil conductivity.

The test results confirmed that POLY4 is a soluble fertilizer, which has excellent nutrient availability to the plant and does not affect the soil pH or soil conductivity in a negative way at commercial application rates. This work provides further validation of the effectiveness of polyhalite as a valuable multi-nutrient crop input.

Chris Fraser, Managing Director and CEO of Sirius, commented:

"These third party tests demonstrate that our polyhalite product, POLY4, is an effective direct multi-nutrient fertilizer and a valuable blending component for fertilizer production around the world. Independent confirmation of nutrient release, solubility, pH and conductivity are important components of the value of polyhalite for our wholesale customers and their end-user farmers."

Solubility

The solubility of a fertilizer is defined as the maximum amount of the fertilizer which can be completely dissolved in a given amount of distilled water at a given temperature. The standard test for solubility in water is to add a specific quantity of a fertilizer to a specific volume of water, stirring until the fertilizer dissolves and continuing to add fertilizer until the saturation point has obviously been reached and solids have settled. Different fertilizers have different levels of solubility and saturation points.

The testing undertaken by both the University of Florida and SGS in France confirmed that POLY4 is fully soluble but has a lower level of saturation than other potassium fertilizers such as sulphate of potash ("SOP") and muriate of potash ("MOP") but higher solubility and saturation levels compared to other sulphate, calcium and magnesium sources. The combination of the solubility and saturation levels makes POLY4 ideal for soil application at all commercial application rates.

Nutrient Release

The concept of nutrient release refers to nutrients dispersing into the soil solution efficiently as the fertilizer dissolves. Once POLY4's nutrients are in the soil solution they are immediately available for plant root uptake. Incubation tests, the technique used to measure nutrient release in laboratories, were conducted by the University of Florida and Shandong Agricultural University. Both studies clearly demonstrated that all the macro nutrients in the polyhalite were available in the soil solution for plant uptake a short time after application.

The goal of these studies was to scientifically test and update with modern testing methods, historical claims of the "slow release" nature of polyhalite and also to test the impact of the specific physical form of the POLY4 products from the York Potash Project. The results validated the fact that POLY4 rapidly and simultaneously releases all the macro-element nutritional components into the soil solution and is therefore supportive of rapid plant growth from application. The results of the studies show that potassium, sulphur, magnesium and calcium interact with the soil exchange complex making the nutrients continually available for plant uptake.

pH Effect and Soil Conductivity

Soil pH is important for optimal plant growth and is affected by the addition of some fertilizers known to acidify the soil, particularly nitrogen fertilizers. Polyhalite is composed of sulphates of potassium, calcium, and magnesium which alone are well known not to affect soil pH.

The impact of a fertilizer on soil conductivity is affected by the fertilizer properties, rate of application and soil properties. It also depends on whether the soil can absorb ions, in which case the roots experience a lower electrical conductivity. In general, high fertilizer rates in the vicinity of seed can affect seed germination and early growth. Polyhalite behaves similarly to SOP and SOP-M (sulphate of potash - magnesia) in this regard which have lower salt index than MOP.

Further testing confirmed that polyhalite as POLY4 does not raise soil salinity and has no negative effect on soil pH at commercial application rates. This validates that polyhalite is a valuable product for heavy feeding crops especially in semi-arid environments or where growers have to use semi-saline water sources, making polyhalite a valuable delivery system for its crop nutrients.

A polyhalite factsheet will soon be made available on the Company's website.

For further information, please contact:

About Sirius Minerals Plc

Sirius Minerals is a globally diversified potash development company. Its primary focus is to bring on stream major potash mining facilities through the acquisition and development of projects overlying recognised potash deposits. Today it holds properties in the United Kingdom (North Yorkshire) and the United States (North Dakota). Incorporated in 2003, Sirius Minerals' shares are traded on the London Stock Exchange's AIM market. Its shares are also traded in the United States on the OTCQX through a sponsored ADR facility. Further information on the Company can be found at www.siriusminerals.com.