Drilling Update

25 September 2012

Sirius Minerals Plc

Drilling Update

§ Preliminary results from the SM7A deflection indicate continuity of the thick shelf seam with an estimated 54m of high grade 92.4% polyhalite, correlating with the shelf seam previously encountered at SM7 and also at SM2, 3, 4 and 6

§ Early interpretation of the SM7B deflection indicates the possible presence of the basin seam in addition to the shelf seam found in SM7 and SM7A, supporting the geological model which predicts overlapping seams in parts of the transition zone

§ SM6 assay results confirm the preliminary interpretation of high grade potassium mineralistion over 4km south west from SM3

§ Nearing completion of resource definition drilling programme to underpin financing and development of the York Potash Project

The Directors of Sirius Minerals Plc (AIM: SXX, OTCQX: SRUXY) ("Sirius" or the "Company"), the globally diversified potash development group, are pleased to provide an update of the drilling programme at the York Potash Project.

Chris Fraser, Managing Director and CEO of Sirius commented:

"The latest results from our drilling programme continue to build confidence and provide further evidence of the extent and quality of the world class polyhalite resource at the York Potash Project. We are hopeful that with these results we are now close to the conclusion of the resource definition drilling programme. Our consultants continue to progress modelling and analysis of the drilling and seismic results, and we are working to provide an upgraded resource statement in the near future."

SM7A (Mortar Hall deflection) preliminary results

SM7 was drilled 1.7km east of SM2 to probe the eastern limit of the shelf polyhalite seam and overlap of the shelf and basin seams originally discovered at SM2. SM7 intersected high grade shelf seam polyhalite from 1,435.6 to 1,521.1 mbRTE (metres below Rotary Table Elevation). The borehole was continuously cored with 100% recovery through the entire Fordon sequence and terminated in the Kirkham Abbey Limestone.

Legacy seismic data had suggested a small risk of structural disturbance at SM7 and results indicate that the polyhalite seam is cut by a minor fault zone, is locally brecciated and veined by halite and also contains some inherent bands of anhydrite and halite. Another minor fault zone is present above the polyhalite and below the Brotherton Limestone. The polyhalite seam itself shows some disturbance and drag-folding adjacent to the fault, but otherwise is massive and regularly bedded. Borehole imaging and an offset seismic survey indicated that both fault structures dip to the south.

SM7A, the first deflection from SM7, was drilled northwards to core the footwall of the structure and intersected the top of the seam approximately 45m northwest of SM7 at 1,446.6 mbRTE. Core recovery was 100% with massive polyhalite cored to 1,507.1 mbRTE, again with minor bands of anhydrite and halite. The borehole terminated in sulphatic halite at 1,536.8 mbRTE. Inspection of the SM7A core shows faulting above the polyhalite seam, which is considered to be part of the same system that affected SM7. There is also minor thrust faulting within the polyhalite seam, but on a relatively small scale.

Overall there was a very good match of the fabric and mineralogy of the SM7 and SM7A cores and after careful comparison, it is considered that the polyhalite in SM7A is nearer to representing the undisturbed seam and that the greater thickness cored in SM7 results from a partial overlap and a 20m repeat due to thrust faulting. Interpretation of Schlumberger's wireline spectral gamma logs for the entire cored intersections (disregarding overlaps, but including all bands of gangue) for the two cored boreholes is as follows:

Notes: 1) TVD - True Vertical Depth 2) No corrections made for dip or for repeated sections cross thrust faults. 3) Estimated from wireline log data, to be confirmed by mineralogical or chemical assay.

After allowance for the minor over-thrust in SM7A and for an average dip of 10 degrees, the true thickness of the polyhalite seam is considered to be in the order of 54m. The position of this single seam of high grade polyhalite in the Fordon sequence, in both SM7 and SM7A, correlates well with the shelf seam previously encountered in SM2, 3, 4 and 6, and nearby legacy boreholes.

SM7B (Mortar Hall deflection) preliminary results

A second deflection SM7B was drilled open hole to provide a further observation point on the seam, deflecting to the northeast of SM7. SM7B was wireline logged, but not cored. Polyhalite was intersected at 1,450m true vertical depth ("TVD"), approximately 57m northeast of SM7 and continued in a sequence of polyhalite, halite and anhydrite, to 1,605m TVD.

Two prominent beds of relatively massive polyhalite can be distinguished, separated by halite, and underlain by inter-bedded halite and lower grade polyhalite. In the absence of core, it is not possible to identify the presence of faulting, nor to estimate seam dip and thereby obtain indication of the true seam thicknesses. Conversion of core depths to TVD using wireline gyro data provides a better indication of likely seam thicknesses and the key parts of the borehole can be described as follows:

Notes: 1) TVD - True Vertical Depth 2) No corrections made for dip or faulting (if any). 3) Estimated from wireline log data, to be confirmed by mineralogical or chemical assay.

The wireline signature of the basal section of the uppermost polyhalite in SM7B resembles very closely the single polyhalite seam intersected in SM7 and SM7A. The occurrence in SM7B of two polyhalite seams resembles the results at SM2 and it appears that both types of occurrence previously seen in parts of the Transition Zone - the massive single shelf seam (SM7 and SM7A) and the overlapping, upper, 'shelf' and lower, 'basinal', seams (SM7B) - may exist within the area investigated at SM7.

These are provisional comments, based on field versions of wireline logs of the three boreholes and initial inspection of the cores of SM7 and SM7A. Further studies including Quantitative X-Ray Diffraction ("QXRD"), chemical analysis, and detailed inspection of final wireline logs, will follow and the interpretations may be refined, particularly with respect to SM7B.

SM6 (Newton House Plantation) assay results

SM6 was cored between 1,369.0 and 1,671.5 mbRTE and intersected the shelf polyhalite between 1,585.7m and 1,594.6m. Independent mineralogical analysis of the drill core was 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 4.5g portion of the milled sample was micronized, and analysed by QXRD.

SM6 was drilled as a step-out borehole to probe the westward limit of the shelf polyhalite seam, and consistent with preliminary results released on 24 August 2012, assay results confirm a true seam thickness of 8.8 m after correction for 10 degree bedding dip. In addition to the high grade polyhalite of 2.17m at 85.6%, the seam contains a thick band of anhydrite (the extent of which is unknown) and has also proved a band of kalistrontite.

Kalistrontite is a rare potassium-strontium sulphate mineral that contains 21.85% potassium and 24.48% strontium. It is therefore, a richer potential source of potassium sulphate than polyhalite. Strontium in its natural state, as found in kalistrontite, is stable and its compounds are used in optical, ceramic, alloying and medical applications. Kalistrontite has not been seen in any of the other borehole results and this occurrence is currently believed to be a localised feature at SM6. The ability to extract and use strontium will be considered as part of the long-term planning of the mine.

SM6 has been successful proving continuity of high grade polyhalite for a further 4km south west of SM3 and provides useful data from which to predict the westward extent of the seam.

Further drilling

The Company believes that the resource definition drilling phase of the York Potash Project is now nearing conclusion. Drilling has commenced at SM9 and is currently at a depth of 126m below surface. Subject to this borehole (and its planned deflections) achieving a successful coring of the polyhalite deposit, the Company and its consultants believe that the combination of the results of the completed boreholes, the legacy boreholes, new 2D seismic and legacy seismic data should be sufficient for an updated resource statement to underpin the financing and development of the mine. Further drilling will be dependent on the results of SM9. The shaft pilot borehole is currently in advanced stages of design and tender.

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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). 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, 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.

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.