Sirius Minerals Regulatory News (SXX)

19 November 2012

Sirius Minerals Plc

Inferred Mineral Resource Estimate increased to 2.2 billion tonnes

·; York Potash JORC compliant Inferred Mineral Resource Estimate increased to 2.2 billion tonnes of 82.4% Polyhalite (24% K2SO4) within an area representing 5% of the project area

·; High grade mineralisation within Inferred Mineral Resource Estimate of 950 million tonnes of 90% Polyhalite (26% K2SO4)

·; Additional Exploration Target of between 1 and 2 billion tonnes outlined with a projected grade of between 80% and 90% Polyhalite (23% and 26% K2SO4) in the vicinity of the resource area

The Directors of Sirius Minerals Plc (AIM: SXX, OTCQX: SRUXY) ("Sirius" or the "Company"), the globally diversified potash development group, are pleased to announce an updated Inferred Mineral Resource Estimate for the York Potash Project of 2.2 billion tonnes of 82.4% Polyhalite (24% K2SO4).

The JORC compliant Inferred Mineral Resource Estimate was prepared by independent consultants SRK Consulting (UK) Ltd ("SRK") and reflects additional drill-hole and assay data obtained since the Maiden Inferred Resource was released in June 2012. SRK has extensive experience in resource estimation and reporting and the preparation of technical reports on potash deposits around the world.

Chris Fraser, Managing Director and CEO of Sirius said:

"The updated Inferred Mineral Resource Estimate of 2.2 billion tonnes is a 70% increase to the previous estimated Resource and further demonstrates the scale and significance of the world-class York Potash deposit. The drilling programme at York Potash is now focussed on upgrading a significant percentage of this Resource during Q1 2013 to underpin financing of the Project."

Inferred Mineral Resource Estimate

The Inferred Mineral Resource Statement is detailed in the table below and has been reported using the guidelines and definitions set out in the 2004 edition of the JORC Code. The consideration that this mineralisation is potentially economic is supported by the results of the Detailed Scoping Study released on 30 April 2012.

The York Potash Project is contained within the Permian Zechstein evaporites, which have been mined extensively for potash and halite in both the UK and north-western Europe. SRK's Mineral Resource Estimate occurs as two main Polyhalite horizons, an upper shelf seam and a lower basin seam. The shelf seam occurs predominantly in the western part of the area explored to date whilst the basin seam occurs predominantly in the eastern part of the area. 

SRK created a geological model for the Polyhalite horizons based on the hangingwall and footwall contacts of these horizons as delineated in drilling supported by drillhole logging information, wireline gamma data and the results of Quantitative X-Ray Defraction (XRD) analysis from which the Polyhalite grades were derived. The analytical data was then composited into 1.5 metre composites and subjected to a statistical and geostatistical analysis following which Ordinary Kriging was selected as the main grade interpolation method. The resulting interpolated grades were validated through visual checks and a comparison of the mean input composite and output model grades. SRK is confident that the interpolated block grades are a reasonable reflection of the available sample data.

Since completing the drilling of SM1, 2 and 3, Sirius has drilled a further 10 holes for a combined total of approximately 14,950 meters of drilling. The aim of this drilling has been to further explore the lateral extent of the resource from the mine shaft area and also to obtain additional close spaced data from deflections from mother holes to provide information at a mining scale and increase confidence in the continuity of the mineralisation at this scale. Extending drilling away from the mine shaft area of focus and into lower grade areas has resulted in decrease in average grade from 88.7% to 82.4%. Notwithstanding this, SRK has outlined approximately 950 million tonnes with a mean grade of approximately 90% Polyhalite within this 2.2bn tonnes Resource area.

Exploration Target

In addition to producing the updated Mineral Resource Estimate, SRK also used the structural interpretation and increased geological understanding, which are in turn supported by a detailed seismic survey, to outline additional areas where there is likelihood that Polyhalite horizons will be present but have not yet been drilled. This analysis has resulted in the delineation of an Exploration Target of between 1 and 2 billion tonnes of 80% - 90% Polyhalite in the vicinity of the Inferred Mineral Resource and when combined with the current resource area still represents only 10% of the total project area.

This potential quantity and grade is conceptual in nature and there has been insufficient exploration conducted to date to define a Mineral Resource. It is uncertain if further exploration will result in the determination of a Mineral Resource.

Mineral Tenure

Mineral Rights in the United Kingdom generally belong to either the present freehold surface owner or a previous owner who may have reserved them. In order to extract the minerals, permission is required from the mineral owner usually under the terms of a lease. Sirius is in the process of entering into agreement with respective landowners and has already signed agreements for approximately 75% of the Mineral Resource and more than 90% of the Exploration Target outlined above, Sirius is in the process of finalising agreements with the remaining mineral owners and has no reason to expect that this process will not result in all the required agreements being made in due course.

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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.

Qualified Persons

The information in this press release that relates to Mineral Resources is based on information compiled under the direction of Dr Mike Armitage C Eng, who is a Member of the Institute of Materials, Minerals and Mining which is a 'Recognised Overseas Professional Organisation' (ROPO) included in a list promulgated by ASX from time to time.

Dr Armitage is a full time employee of SRK and has sufficient experience which is relevant to the style of mineralisation and type of deposit under consideration and to the activity which he has undertaken to qualify as a Competent Person as defined in the 2004 Edition of the 'Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves' (the JORC Code) and for the purposes of the AIM Rules. Dr Armitage has reviewed this press release and consents to the inclusion in the press release of the matters based on his information in the form and context in which this appears.

Graham Clarke, Operations Director for Sirius Minerals Plc, who has reviewed this Stock Exchange Announcement, has over 26 years' experience in the potash mining industry. He has a Degree in Mining Engineering from the University of Nottingham, is a Fellow of the Institute of Materials, Minerals and Mining (IMMM) 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.