Sirius Minerals Regulatory News (SXX)

1 May 2012

Sirius Minerals Plc

("Sirius" or the "Company")

Assay Results for SM3

§ Preliminary visual interpretation of intersected Shelf Seam confirmed

§ 25.2 metres of 87.5% polyhalite (25.3% K2SO4) including 16.2 metres of high grade 95.9% polyhalite (27.7% K2SO4)

§ SM3 deflection drilling completed showing a consistent overall seam thickness compared to the "mother" hole with approximately 50m total polyhalite mineralisation

§ SM6 drilling progressing well with new rig, preliminary results expected in the next few weeks

The Directors of Sirius Minerals Plc (AIM: SXX, OTCQX: SRUXY), the globally diversified potash development group, are pleased to announce the mineralogical assay results of the third new borehole ("SM3") drilled at the York Potash Project (the "Project").

Chris Fraser, Managing Director and CEO of Sirius said:

"These assay results of the third new hole of the York Potash drilling program have delivered yet another thick intersection of high-grade polyhalite in the Shelf Seam. These assays continue the strong results obtained from the drilling program, and combined with the results of the Detailed Scoping Study confirm the world-class nature of the York Potash Project."

Coring of SM3 was completed on 21 March 2012. The polyhalite-bearing Fordon Evaporite Formation was present from 1,416.6m to 1,649.7m below ground level ("bgl") - a total of 233.1 m - and was cored (85 mm diameter) with 100% recovery throughout almost its entire thickness. On 26 March 2012 preliminary results of the coring, based on visual inspection, were released. Results from the mineralogical analysis have now been received and are summarised in this announcement.

Polyhalite Analysis Process

Independent mineralogical analysis of the drill core has been carried out by the British Geological Survey ("BGS") at its Mineralogy, Petrology and Biostratigraphy Facility. Each sample was dried, crushed and milled and homogenised; then a 4.5 g portion of the milled sample was micronised, and analysed by Quantitative X-Ray Diffraction ("QXRD"). This is a non-destructive method developed by BGS to assess the mineralogical composition of rock and ore samples (with a typical accuracy of ±2.5% for mineral concentrations >60%; ±5% for concentrations between 60 and 30%; ±10% for concentrations between 30 and 10% and ±20% for concentrations between 10 and 3%).

Polyhalite Analysis Results

Borehole SM1 intersected approximately 49.3 m ("true" thickness) at 66% polyhalite, in which the three best sections aggregated 23m at 95% polyhalite; almost identical in mineral composition and vertical zonation to other historical drill holes in the area. Borehole SM2 intersected two seams, a lower seam that had basinal aspects and correlated with that intersected in SM1 (the "Basin Seam") containing 34.3m at 78% polyhalite; and an upper seam (the "Shelf Seam") containing 32.6m at 83% polyhalite. The Shelf Seam was similar to intersections in legacy boreholes drilled further north and west, and the polyhalite being developed underground at the Boulby Mine.

SM3 entered the Fordon Evaporites at 1,416.6m bgl and, as expected, the Upper Subcycle was chiefly halite and anhydrite. The Middle Subcycle was intersected at 1,493.4m bgl, at which point polyhalite was first encountered. As identified from visual examination of the core, polyhalite mineralisation extends mainly from 1,493.4m to 1,539.1m bgl with a cored thickness of 45.7m, with traces of polyhalite continuing down to 1,562.1m bgl. Dips measured within the unit as a whole vary from 0-10° from the horizontal. "True" thickness, corrected for an average dip of 5°, was estimated to be 45.5m. This section, with some overlying and underlying core material, has now been analysed.

The SM3 Shelf Seam polyhalite can be subdivided into an upper transitional section where anhydrite is present as the main gangue, a central massive high grade polyhalite section (dip 0 to 5°), and a lower transitional section where halite is the main gangue and where there is a gradual downwards decrease in polyhalite content.

The lower Basin Seam was not intersected in SM3. It is believed to have onlapped to the early Fordon carbonate ramp in accordance with the geological model. It is intended that the precise western limit of the Basin Seam will be determined by the ongoing drilling programme and seismic exploration.

From examination of the SM3 assay data detailed in the table below, the greatest thickness of potential value is 36.7m ("true" thickness) at 75% polyhalite. Within this we can define a section of 30.0m ("true" thickness) at 81% that includes 25.2m ("true" thickness) at 88% corresponding more or less with the section of massive polyhalite rock described in the core log. The highest grade section is 16.2m ("true" thickness) at 96% polyhalite.

SM3 POLYHALITE ZONE DETAILS (Borehole collar: 490315 E, 504861 N; 195.7m above sea level.)

1) The various zones identified as 'A' to 'H' are used for convenience of description, no correlation is implied with similarly identified zones in other drill hole results.

2) Depths are shown as metres below Rotary Table (mbRT), which was 4.4 m above ground level.

3) Analyses are reported on 'dry basis', and are subject to analytical uncertainty as described in the text.

Polyhalite Exploration Model

A significant amount of historical data provided the foundation for the geological model for York Potash. The western edge of the Zechstein Basin in the Fordon Evaporites is believed to have been a shallow-water depositional "Shelf", in which a condensed sequence of evaporites was deposited. Numerous holes have been drilled through the shelf for gas exploration and these repeatedly demonstrated the existence of a thick, relatively high grade (based on gamma logs), polyhalite seam.

The main part of the Fordon Basin, as explored by SM1 and by historical boreholes, is believed to have been a deeper "Basinal" environment. It also contains a thick high grade deposit of massive polyhalite, towards the bottom of the sequence. This was confirmed by SM1 where Sirius intersected the seam and proved an aggregated thickness of 23.3m (corrected for dip) of 95% polyhalite (27.5% K2SO4).

The geological model was refined after SM2 to include a transitional zone (with a width that is still to be determined) in the vicinity of the early Fordon carbonate ramp, where both the Shelf and Basin Seams appear to be present, separated by approximately 80m of mainly halite. SM3 lies close to the early Fordon ramp, providing a second intersection of the upper Shelf Seam polyhalite. As predicted by the model and confirmed by SM3, the lower Basin Seam does not appear to be present in the near vicinity of the ramp. Continuity between boreholes will be tested in detail by future drilling and seismic surveys.

The results to date continue to support the geological model; and the thickness and grades continue to be significantly higher than those used to define the Exploration targets.

SM3 Deflection

The SM3 deflection drilled from 1,213m has now been completed and shows a consistent overall seam thickness as compared to the "mother" hole with approximately 50m total polyhalite mineralisation. The deflection has an increased thickness of massive polyhalite, with approximately 19.5m of high grade mineral - directly comparable with mineral zone 'E' in SM3 (16.2m); and the lower, halite-polyhalite mineral zones ('A,B,C and D') appear significantly higher grade in the deflection than in SM3. The new core is currently in process of detailed logging, to be followed by assay.

Drilling Programme

Rig 5 is in the process of moving from SM3 to SM4 where drilling should resume by the end of this week. SM4 is already drilled to a depth of 747m. The new coring rig (Rig 16) commenced drilling at SM6 (Newton House) on 11 April and is performing well with preliminary results expected in the next few weeks.

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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), the United States (North Dakota), and Australia (Queensland and Western Australia). 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.

Competent Person's Statement and Risk Statement

The information in this Stock Exchange Announcement that relates to Mineral Exploration results and Exploration Targets, together with any related assessments and interpretations, have been verified by and approved for release by Dr Frederick W. Smith FIMMM., CEng, CSci., a qualified geologist and full-time employee of FWS Consultants Limited ("FWS"), Environmental and Geological Consultants. Dr Smith, who is a Fellow of the Institute of Materials, Minerals and Mining (IMMM), has sufficient experience which is relevant to the style of mineralisation and type of deposit under consideration and to the activity which he is undertaking to qualify as a Competent Person for the purposes of the AIM Rules. Dr Smith and FWS consent to the inclusion of the information contained in this announcement and the respective references to them in the form and context in which they appear. The JORC Exploration Target estimates of quantity and grade are conceptual in nature and there has been insufficient exploration to define a Mineral Resource on the property and it is uncertain if further exploration will result in discovery of a Mineral Resource on the Property. The estimates are not a Reserve or Resource statement in accordance with an AIM recognised Standard and should not therefore be relied upon as such. It should be noted that the Pan European Code of Reporting or PERC (that IMMM co-wrote) released in December 2008 and JORC are essentially identical on all key aspects relating to compilation and quoting Exploration Targets.

Qualified Person

Graham Clarke, Operations Director for Sirius Minerals Plc, who has reviewed this update, has over 26 years' experience in the potash mining industry. He has a Degree in Mining Engineering from the University of Nottingham and extensive operational experience gained at Cleveland Potash Limited in the mining of the Boulby Potash seam and the exploration and development of the upper Fordon Polyhalite seam.