Severo-Krasnoborsky polyhalite mine field is located in the territory of Polessky District of Kaliningrad Region within the boundaries of a large Central European salt-bearing basin composed of evaporitic sediments of Upper Permian age, known as salt-bearing Zechstein rock formation. Severo-Krasnoborsky polyhalite mine field of potassium salts and magnesium salts (together with Vostochno-Krasnoborsky area) is one of the few Central European objects that belong to purely sulphatic type.

Targeted studies of Kaliningrad Region in terms of potassium and magnesium salts were initiated in 2003, when the Natural Resources Ministry of the Russian Federation (Protocol No. 07-11/0856-pr dated 15.12.2003) took into account the undiscovered resources of potassium-magnesium categories Р12 in the amount of 900 million tons expressed as К2О, which for the most part were located within the borders of Nivenskay and Vostochno-Polesskaya areas. Within the borders of Vostochno-Polesskaya area (Vostochno-Krasnoborsky mine field is located there) the undiscovered resources of potassium-magnesium salts were tested in category of Р1 – 200 million tons of К2О, and in category Р2 – 300 million tons of К2О.

In 2003-2008, as part of the government contract SZGGP Sevzapgeologia conducted surveying and appraisal work pertaining to potassium and magnesium salts of Kaliningrad-Danzig salt basin, as part of which three wells had been drilled with the depths of 950-1250 meters, including one well No. 2VP with the depth of 954 meters – in Vostochno-Polesskaya area within the boundaries of Severo-Krasnoborsky mine field. 2VP well validated the presence of potassium-magnesium sulphate type banks in Upper Permian subsalt anhydrites with the capacity of 79.6 meters, represented by polyhalite (with polyhalite content in the upper part >75%), anhydrite-polyhalite (up to 50%-75% of polyhalite) and polyhalite-anhydrite (more or less 50%) solids, which had been previously focused based on GIS materials on two (well 2SK and well 3SK) oil prospecting wells drilled back in the 1970s. Four polyhalite-containing zones with the capacities of 26.5 meters, 14.6 meters, 7.4 meters and 12.1 meters were mounted in well 2VP with the average content of polyhalite (and correspondingly the content of К2О) 79.01% (12.35%), 42.03% (>6.6%), 38.55% (6.03%), 57.38% (8.97%). The uppermost zone turned out to be the richest one (854.1-880.6 meters) and the most productive (26.5 meters), the average content of К2О in which amounted to 12.76% (which on average corresponds to 81.7% of polyhalite, and at certain intervals (864.5-872.5 meters) the content of К2О was 14.60% (which corresponds to 95.5% of polyhalite).

Later on, 2013 – to date geological prospective works at Severo-Krasnoborsky mine field (License KLG 02398 TP with the area of 10.5 km2, KLG 02518 TE with the area of 7.2 km2) and Vostochno-Krasnoborsky area (License KLG 02478 TP with the area of 19.59 km2) were conducted JSC KGDI at its own expense. Most works have been performed at Severo-Krasnoborsky area.

In 2013-2018, in accordance with the approved project (opinion by the Federal State-Funded Institution Rosgeolekspeditsia No. 144-02-01/2013 dated 25.11.2013) JSC KGDI successfully conducted geological prospecting surveys at Severo-Krasnoborsky area of exploration and appraisal stages. As part of such works 7 well bores have been drilled with the total length of 5,048.42 meters (including core recovery of 1,302.52 linear meters), and all the necessary types of geological prospecting work accompanying the drilling has also been performed.

Based on the results of such geological prospecting works in 2013-2018 JSC KGDI conducted the following activities:

- As part of the appraisal stage geological structure of the object was researched, as well as the chemical and mineral composition of potassium and magnesium ores, the structure of production- and water-blocking formations, mining, technical, and hydrogeological conditions of mining, reserves growth potential and undiscovered resources at adjacent areas were studied. It was discovered that the object contained subhorizontal bedding plane deposits of anhydrite-polyhalite salts with the capacity of 40-80 meters with the average K2О content of around 9%-11%, which were confined to the range of depths of 850-950 meters.

- Preliminary production research was conducted with regard to treatment of crude polyhalite ore into marketable end products (potassium sulfate and potassium magnesia);

- Provisional exploratory standards were developed and approved by TCNR (Protocol of TCNR Sevzapnedra No. 14-18/KO dated 26.06.2018);

- Reserves of polyhalite ores were certified and entered in the national register in categories C12 in the amount of 605,766 thousand tons of raw salts with the average content of K2O=10.62% and MgO=4.81%. Besides, as part of License KGL 02398 TP undiscovered resources of category Р1 were also taken into account in the amount of 217.3 thousand tons with the content of K2O=10.4% (Protocol of TCNR Sevzapnedra No. 15-18/КО dated 26.06.2018);

- Severo-Krasnoborsky area was assigned the status of Severo-Krasnoborsky mine field (Protocol of TCNR Sevzapnedra No. 15-18/КО dated 26.06.2018);

- The fact of discovery of Severo-Krasnoborsky mine field by JSC KGDI was validated in the duly established order (Certificate of Sevzapnedra No. KLG 18НЕМ00001 dated 06.08.2018;

- License KLG 02518 TE was secured for the prospecting and production at Severo-Krasnoborsky mine field with the validity period of 18.11.2019 – 18.11.2044;

- Geological-structural and modular models of Severo-Krasnoborsky mine field were developed for polyhalite;

- By order of JSC KGDI K-UTEC AG Salt Technologies conducted its expert appraisal of geological, mining and technical, technological, and economic parameters of Severo-Krasnoborsky project (level of elaboration SS and, partially, PFS).

In 2020, at Severo-Krasnoborsky mine field JSC KGDI developed its project for geological prospecting of the mine field. This project was validated and approval by the geological expert review (positive expert judgement No. 228-02-01/2020 dated 20.08.2020). Besides, in 2020 the term of License KGL 02478 TP was extended until 31.03.2023 for Vostochno-Krasnoborsky area (with the resource potential for polyhalite ores in the amount of 1.07 billion tons with the content of K2O=10.0%). A project for geological prospecting at the exploration and appraisal stages was developed. The project successfully passed geological expert review (positive expert judgement No. 182-02-01/2020 dated 20.07.2020).

Currently works are in progress at Severo-Krasnoborsky mine field (License KLG 02518 TE) and Vostochno-Krasnoborsky area (License KLG 02478 TP).

Fig. 1. Blueprint of the estimates of K-Mg ore volumes in-place at Severo-Krasnoborsky mine field (TCNR 2018).

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