Sirius Minerals Regulatory News (SXX)

13 December 2011

Sirius Minerals Plc

("Sirius" or the "Company")

Completed Chemical Assay Results for SM1

§ Final assay results confirm first assay results released on 28 November

§ 23.3 metres (true-thickness) of 95% polyhalite (27.5% K₂SO₄) aggregated across three beds

§ Main high grade bed is 11.0 metres (true-thickness) of 97.1% polyhalite (28% K₂SO₄), including two high grade zones totalling 9.6 metres of 99.5% polyhalite

§ Total polyhalite zone of 49.3 metres (true-thickness) of 66% polyhalite (19.1% K₂SO₄)

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

Results from the first batch of chemical and mineralogical analysis of the three key target seams were summarised in the announcement dated 28 November 2011. That release contained the full summary of the two potassium chloride seams. Analysis of the second and final batch of polyhalite bearing samples has now been received and is summarised in this release.

Chris Fraser, Managing Director and CEO of Sirius said:

"The final batch of polyhalite samples has confirmed and extended the polyhalite results released on 28 November. The thickness and grade of the polyhalite seams is world-class and has exceeded our expectations. We are confident that the future holes will confirm the quality of this deposit.

"We are continuing to consider and analyse potential improvements to the mining and development concept. The thickness of high grade polyhalite within a much wider zone of banded material presents multiple mining and process opportunities. A significant amount of work is ongoing in our engineering and development studies, which will help us maximise the value of this large deposit."

Polyhalite Assay Results

For the background and the analysis undertaken on the cores recovered from SM1 please refer to the announcement dated 28 November 2011.

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 35° and so, although 9.75m was cored, the true seam thickness is approximately 8.0m. It was followed by 6.38m (5.2m 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 15.62m (11.00m true-thickness @ 45° dip).  Following a further 8.31m (6.8m true-thickness) of banded polyhalite, a further bed of massive polyhalite (the "Lower Bed") was cored for 11.2m (10.4m true-thickness).

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 are summarised follows (quoted on a moisture free basis):

Upper Bed             8.0m true-thickness at 92.31% polyhalite. The upper part of the bed is the highest grade (97.5% polyhalite), tailing off gradually downwards. Halite is the gangue mineral.

Middle Bed           11.0m true-thickness at 97.06% polyhalite. This includes 9.6m true-thickness of 99.5% polyhalite separated by the anhydritic-rich band (0.4m true-thickness) that occurs approximately mid-seam. Other than this anhydritic band the gangue is halite.

Lower Bed             This bed can be divided into three sections. The upper, most massive, Section A resembles the other massive polyhalite seams and is approximately 4.32m true thickness at 94.77% polyhalite. Section B is 2.2m true thickness at 78.17% polyhalite and Section C is 3.9m true thickness at 52.89% polyhalite.

The three highest grade seams (Upper, Middle, and Section A of the Lower Seam) represent an aggregate true thickness of 23.3m at 95% polyhalite. The entire zone (roof, seams, bands, etc…) cored was assayed from 1,604.01m to 1,669.0m from Rotary Table Elevation ("RTE") (1,464.85m to 1,529.84m below sea-level).

SM1 FORDON POLYHALITE ZONE DETAILS (collar: 493587.28 E, 507066.01 N, 139.2m AOD)

Notes:

1)     Dip measurements on the core have been averaged, and then rounded off, for each unit.  The borehole was 3.54° to 4.0° off vertical in this section.

2)     Approximate true thickness based on adjusting for average inclination of the seam.

3)     All grades are quoted moisture free.

Drilling Progress Update

Drilling progress at SM2 (Howlett Hall) has been slowed by a series of fluid loss zones which have been encountered as the hole approached commencement of coring depth. Completion of coring is now expected early in January 2012. The top-hole rig has completed its work at both SM3 (Raikes Lane) down to 669m, and SM4 (Gough) down to 747m and is in the process of moving to SM5 (Waite Lane). Sirius remains in discussions with its drilling contractor about securing a second larger coring rig for the York Potash Project. It is currently expected that this rig could be commissioned and on site around the middle of February 2012. This would significantly increase the rate of drilling and core recovery.

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), 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.