Sirius Minerals Regulatory News (SXX)

28 November 2011

Sirius Minerals Plc

("Sirius" or the "Company")

Chemical Assay Results

§ 22.1 metres (true-thickness) of high grade polyhalite across three beds

§ 15.1 metres (true-thickness) of assays received to date across the three high grade beds with average polyhalite grade of 95.7% including 5.83 metres of continuous +99.5% polyhalite

§ Grade and thickness of polyhalite in SM1 significantly exceeds previous JORC Exploration Targets and Preliminary Results

The Directors of Sirius Minerals Plc (AIM: SXX, OTCQX: SRUXY), the globally diversified potash development group, are pleased to announce chemical assay results of the first bore hole drilled at the York Potash Project.

Coring of SM1, the first new borehole in the York Potash Project, was completed on 26 October 2011. On 27 October 2011 preliminary results of the coring based on visual inspection were released, which were followed by a summary of the gamma-log results on 31 October 2011. Results from the first batch of chemical and mineralogical analysis of the three key target seams have now been received and are summarised in this announcement. Analysis of a second batch of samples is expected in the second week of December 2011.

Chris Fraser, Managing Director and CEO of Sirius said:

"These results are outstanding. The thickness and grade of the polyhalite seams has exceeded all previous expectations and analysis. While we await the second batch of assay results, what has been received to date indicates much thicker and higher grade material than expected. There have never been grades or thicknesses like this in any polyhalite deposit anywhere in the world, confirming the York Potash Project as one of the world's most significant potash projects.

"The quality of these drill results, if repeated at our next holes, will result in a positive reassessment of a number of project concepts such as scale of production, bulk-mining methods, and processing routes. As a result we are looking for ways to accelerate development of the York Potash Project even faster to fulfil the Company's goal of becoming a major potash producer even sooner."

Background to SM1

SM1, the first borehole drilled by Sirius in the York Potash Project, was commenced on 31 July 2011 and coring was completed on 26 October 2011. The goal of this initial hole was to confirm the presence of the three target seams of potash mineralisation - the Fordon Polyhalite Seam plus the two potassium chloride (Muriate of Potash - MOP) seams, the Sneaton Seam and the Boulby Seam. Polyhalite is a primary source of the higher value Sulphate of Potash ("SOP") product and is the focus of the York Potash Project.

All three seams were intersected and cores successfully recovered. The preliminary results of the visual inspection of these cores were announced on 27 October 2011. This visual inspection identified two beds of massive polyhalite with a combined true thickness of 19 metres. The wireline logging of the hole was then undertaken and the results of the natural gamma ray spectrometry wireline logging were obtained, indicating an average polyhalite grade above 80% across the 19 metres of massive polyhalite. In addition, it was identified that there were areas within the massive polyhalite zones with grades significantly higher.

The cores for SM1 were sent for independent chemical and mineralogical analysis by the Analytical Geochemistry Laboratories of the British Geological Survey ("BGS"). Different procedures were used for the potassium chloride (sylvite) bearing seams and the potassium sulphate (polyhalite) seam.

§ Sylvite Bearing: Samples were dried to 30⁰C and analysed by combinations of ICP-OES, ion chromatograph, potentiometric titration, and gravimetry. The analytical and extraction uncertainty is +/- 10%.

§ Polyhalite Bearing: Samples were dried, crushed, homogenised and analysed by X-Ray Diffraction. 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%

Results have now been received on the first batch of samples submitted for analysis. These cover the Sneaton and Boulby sylvite bearing seams and partial coverage of the polyhalite zone. Due to the significant thickness of the intersection of the polyhalite, a second batch of samples is still being processed.

Assays are still ongoing on the second batch of samples and include the unanalysed remainder of the three high-grade polyhalite beds plus the lower grade polyhalite-bearing sections surrounding the high-grade beds. The results of these assays are due to be received in the second week of December. In addition, it is intended to carry out chemical tests on the high-grade polyhalite-bearing horizons to provide elemental analysis and to check trace element composition. The data received so far (albeit incomplete) are sufficient to establish the remarkable significance of the borehole.

Polyhalite Assay Results

The Fordon Evaporite Formation, within which lies the polyhalite zones, was intersected at 1,390.1m below surface (1,255.4m below sea-level), with the first signs of polyhalite inter-beds at 1,580.1m below surface (1,445.4m below sea-level). The proportion of polyhalite increased gradually until, at 1,613.4m below surface (1,477.7m below sea-level) the first bed of massive polyhalite rock (the "Upper Bed") was encountered. This was dipping at approximately 35⁰ and so, although 9.42m was cored, the true seam thickness is approximately 7.72m. It was followed by 6.66m (5.1m true-thickness) of low-grade polyhalite and halite, then a second bed of massive polyhalite rock (the "Middle Bed") was encountered. This was cored for 14.99m (11.48m true-thickness @ 40⁰dip). Following a further 8.94m (7.3m true-thickness) of banded polyhalite, a further bed of massive polyhalite (the "Lower Bed") was cored for 3.39m (3.07m true-thickness), followed by interbedded halite and polyhalite.

The three massive polyhalite beds were sampled at approximately 0.5m intervals - taking care to isolate and analyse separately a 0.55m (0.4m true-thickness) parting of anhydritic material indicated on wireline logs as lying within the Middle Bed. The results from the first batch of results are as follows (quoted on a moisture free basis):

Upper Bed Overall 7.7m true-thickness. The first batch of results covers 6.8m true-thickness grading an average of 94.1% polyhalite. The upper part of the bed is the highest grade, and the proportion of polyhalite relative to halite reduces gradually downwards. The uppermost 5.8m of the section assayed so far has a polyhalite grade of 95.0% with halite being the main gangue element.

Middle Bed Overall 11.5m true-thickness. The first batch of results covers 8.36m true-thickness grading an average of 96.9% polyhalite. This includes 5.82m true-thickness of 99.5% polyhalite immediately above the anhydritic-rich band (0.4m true-thickness) that occurs approximately mid-seam. Other than this anhydritic band the gangue is halite.

Lower Bed Overall 3.1m true-thickness. Assay results are due to be received in the second week of December 2011.

SM1 FORDON POLYHALITE ZONE DETAILS (collar: 493587.28 E, 507066.01 N, 134.8m AOD)

Notes:

1) Assessments of "grade for the beds between the three main beds are based, at this stage, on visual observations of minerology, and are quantitative. Confirmatory tests are in progress.

2) Dip measurements on the core have been averaged, and then rounded off, for each unit. The borehole was 3.54⁰ to 4.0⁰ off vertical in this section.

3) Corrected for average inclination of the seam.

4) n/a - not available yet as assays still in progress.

5) All grades are quoted moisture free.

Interpretation of the SM1 Polyhalite Results

On 17 January 2011, Sirius released a JORC Exploration Target of between 3.3 and 6.0 Billion tonnes of 67% to 94% polyhalite (19% to 27% K2SO4)1 was established for the then contracted area of mineral rights within the York Potash Project. This estimate was prepared based on a 5 metre "extraction" section from a >10 metre very consistent seam of relatively high purity polyhalite.

1. See Competent Persons Note. These 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 reportable to an AIM standard.

The results so far for SM1 have significantly exceeded all parameters used in the JORC Exploration Target. The thickness of high-grade polyhalite of 22.1 metres is over four times greater than the assumed 5 metre thickness and the grade of the assayed sections of the high-grade beds average 95.7%, which is above the top end of the Exploration Target grade range.

In addition, the observations of the assay results and observations of the banded material above the high-grade beds reveal that the main gangue element in this hole is halite (common rock salt). The processing required to remove halite is relatively simple (crushing and washing) and low cost. This therefore introduces the potential to consider either a large extraction zone where the halite is removed to produce a high-grade beneficiated ore or a more focused high-grade extraction project. If the results from SM1 are repeated in the future boreholes Sirius believes it will have potentially significant positive implications for the project development concepts.

Potassium Chloride Assay Results

The two potassium chloride seams, the Sneaton Seam and Boulby Seam were both cored. Although polyhalite is the focus of the York Potash Project, coring the Sneaton and Boulby seams provides valuable data to be added to the historical data already obtained on them.

Sneaton Seam

The Sneaton Seam is expected to be present throughout the York Potash Project. Historical data suggests that it is typically banded and is usually relatively low grade sylvite (potassium chloride) and so it has not been included in the Company's previous JORC Exploration Targets.

The seam was intersected between 1,223m and 1,232m below surface (1,088m to 1,097m below sea-level). The core showed interbedded sylvite-halite mixture (sylvinite), halite, and mudstone-rich horizons. Sylvite is concentrated in three particular bands. The core was sampled in detail (generally 0.20m to 0.40m intervals) with the exception of a halite band of 2.94m thickness that was tested semi-quantitatively. Due to surface etching and selective loss of sylvite from the core a 5% uplift in potash grade has been applied.

The laboratory results show:

§ 8.98m true-thickness of 13.97% KCl within which there is a high grade zone of 2.07m @ 36.69% KCl;

§ Water soluble potassium chloride is present as sylvite. Carnallite is effectively absent with water soluble magnesium present only at extremely low levels (averaging 0.05%); and

§ Trace gypsum and anhydrite are present.

Boulby Seam

The Boulby Seam is expected to be present throughout the York Potash Project. On 17 January 2011, Sirius released a JORC Exploration Target of between 330 and 400 Million tonnes of 35% to 40% potassium chloride (KCl)1 was established for the then contracted area of mineral rights within the York Potash Project.

1. See Competent Persons Note. These 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 reportable to an AIM standard.

Historical data and Sirius's understanding of the experience at the nearby Boulby Mine (owned by Cleveland Potash Ltd, a subsidiary of Israel Chemical) have shown that the Boulby Seam is susceptible to lateral migration and marked lateral variability in thickness and sylvite content. A crude estimate of the variation suggests circa 40% of the area of the seam, where proved historically, is 'payable' and 60% is 'non-payable' as potash ore. This makes it difficult to prove JORC resources by surface drilling and the Boulby Mine relies upon underground development and underground horizontal drill holes with offsets to identify potential production zones.

The Boulby Seam was intersected in SM1 between 1,271.3m and 1,279.2m below surface (1,136.6m to 1,144.4m below sea-level). The core recovered showed that the seam at this location consists largely of mudstone, impregnated with halite and minor sylvite. This is typically referred to at the Boulby Mine as "secondary ore". It is interleaved with thin bands of gneissose-textured halite and some sylvite, that is more typical of the "primary ore" mined at the Boulby Mine.

The core was sampled in detail (generally over 0.2 to 0.4m intervals) with the exception of a 3.06m band of mudstone that was judged visually to be very low grade. This band was tested semi-quantitatively. Due to surface etching and selective loss of sylvite from the core a 5% uplift in potash grade has been applied.

The laboratory results show:

§ 7.9m true-thickness of 3.45% KCl within which there is a higher grade zone of 0.97m @ 11.56% KCl;

§ Magnesium was present only at low levels (averaging 0.5%), which may indicate the presence of carnallite, but until verified by mineralogical testing it has been assumed that the sole potassium mineral is sylvite; and

§ Some gypsum and anhydrite are present.

SM1 was located in the middle of the area that was drilled by Rio Tinto (via its then subsidiary Yorkshire Potash Ltd) between 1967 and 1971. That drilling (holes designated as the 'YP' series) defined a historical (non-JORC) resource of 380 Million tonnes @ 22.3% K2O (~36.5% KCl). This drilling was targeting the Boulby Seam and did not go to the depths required to intersect the Fordon Polyhalite Seam.

Sirius has reviewed a number of historical wireline logs for the Rio Tinto drilling campaign and the interpretations from this review has shown that SM1 has delivered results consistent with the Rio Tinto results in the Boulby Seam. SM1 was located midway between two historical boreholes YP4 and YP7, one of which appears to have intersected relatively high grade sylvite and the other appears to have intersected approximately 3.4m of low grade potassic mudstone. In another example, historical borehole YP10 appears to have intersected high grade sylvite ore, and a deflection from that hole (YP10 Diversion) appears to have intersected low-grade potassic mudstone. This variability is therefore a characteristic of the seam and must be borne in mind when interpreting the SM1 results.

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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).

The Company is additionally progressing ongoing innovation initiatives into the secondary uses of salt and potash beds for energy storage and carbon dioxide sequestration.

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 the use of 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.