page_title: Siilinjärvi carbonatite
hierarchical_section_title: Siilinjärvi carbonatite
caption_attribution_description: A sample from which the thin section was made. English: Scanned image of thin section from Siilinjärvi apatite ore in cross polarised transmitted light. In the thin section apatite is mostly found as big inclusions in carbonate aggregates. The thin section has also a couple of narrow carbonate veins and a clear flow structure. Tetraferriphlogopite forms 70 area-% of the thin section. The grains are often quite broken and bent, but still, grains almost 5 mm wide are found. Small elongated chips form one third of the mica area, larger flakes two thirds. Flakes are usually 1-5 mm long, chips &lt; 1 mm and more elongated. Apatite appears as large rounded grains in companion with carbonates and forms 10 area-% of the thin section. The grains have carbonate inclusion trails. The diameter of the grains is 1-4 mm. Carbonates form large aggregates in the thin section and 10&#160;% of the area. Calcite is the dominating carbonate mineral. Grain boundaries are sometimes hard to distinguish because of the dustiness of the grain surfaces and small grain size. Usually the grains are &lt; 1.5 mm in diameter, at the aggregate margins smaller than that. Amphiboles form 10 area-% of the thin section, and are commonly found as small euhedral grains in the groundmass. The grains are altered into magnetite and &lt; 1 mm in diameter. A few elongated small grains and one large grain &gt; 1 cm long are also present.
context_page_description: The Siilinjärvi carbonatite complex is located in central Finland close to the city of Kuopio. It is named after the nearby village of Siilinjärvi, located approximately 5 km west of the southern extension of the complex. Siilinjärvi is the second largest carbonatite complex in Finland after the Sokli formation, and one of the oldest carbonatites on Earth at 2610±4 Ma. The carbonatite complex consists of a roughly 16 km long steeply dipping lenticular body surrounded by granite gneiss. The maximum width of the body is 1.5 km and the surface area is 14.7 km². The complex was discovered in 1950 by the Geological Survey of Finland with help of local mineral collectors. The exploration drilling began in 1958 by Lohjan Kalkkitehdas Oy. Typpi Oy continued drilling between years 1964 and 1967, and Apatiitti Oy drilled from 1967 to 1968. After the drillings, the laboratory and pilot plant work were made. The mine was opened by Kemira Oyj in 1979 as an open pit. The operation was sold to Yara in 2007.
  The Siilinjärvi apatite mine is the biggest open pit in Finland. Currently the mine comprises two pits; the larger southern Särkijärvi and the smaller northern Saarinen satellite pit.
context_section_description: The Siilinjärvi carbonatite complex is located in central Finland close to the city of Kuopio. It is named after the nearby village of Siilinjärvi, located approximately 5 km west of the southern extension of the complex. Siilinjärvi is the second largest carbonatite complex in Finland after the Sokli formation, and one of the oldest carbonatites on Earth at 2610±4 Ma. The carbonatite complex consists of a roughly 16 km long steeply dipping lenticular body surrounded by granite gneiss. The maximum width of the body is 1.5 km and the surface area is 14.7 km². The complex was discovered in 1950 by the Geological Survey of Finland with help of local mineral collectors. The exploration drilling began in 1958 by Lohjan Kalkkitehdas Oy. Typpi Oy continued drilling between years 1964 and 1967, and Apatiitti Oy drilled from 1967 to 1968. After the drillings, the laboratory and pilot plant work were made. The mine was opened by Kemira Oyj in 1979 as an open pit. The operation was sold to Yara in 2007.
  The Siilinjärvi apatite mine is the biggest open pit in Finland. Currently the mine comprises two pits; the larger southern Särkijärvi and the smaller northern Saarinen satellite pit. The Särkijärvi pit is approximately 250 m deep, with a bench height of 28 m. The Saarinen pit is located some 5 km north of the main Särkijärvi pit.
  The overall blast rate at the mine is 600 kt per week, 450 kt from the Särkijärvi pit and 150 kt from the Saarinen pit. Almost all of the glimmerite-carbonatite series rocks are ore-grade rocks; the fenites and crosscutting diabases are waste rocks. There are, however, some late apatite-poor carbonatite veins and certain blocks of carbonatite-glimmerite with < 0.5 wt-% P₂O₅. The reason why those are barren of apatite is unknown, but it could be related to metamorphism and fluid flow.
  The Siilinjärvi mine is the only operating phosphorus mine in the European Union. Since 1979, over 400 Mt of rock have been mined, about 65% being ore. By year 2016, the mine had produced 24.7 Mt of the main product, apatite. Ore reserves were 205 Mt in January 2016. The current production is roughly 11 Mt of ore per year, while the average in situ grade is 4.0 wt-% of P₂O₅. Roughly 85% of the apatite concentrate is processed on-site in Siilinjärvi to produce phosphoric acid and fertilisers, the rest of the concentrate is used in the company's other factories. The by-products are mica and calcite concentrates. Apatite concentrate is produced by flotation in the concentrator near the Särkijärvi pit. The concentrate can be then processed into phosphoric acid using sulphuric acid. The sulphuric acid is currently derived from Pyhäsalmi mine pyrite.
caption: Thin section of apatite-rich glimmerite in cross polarised transmitted light.
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