Lacustrine iron ore.

Национальный музей Республики Карелия

Lacustrine iron ore is a kind of ironstone, which is deposited on the bottom of lakes in Olonetsk province. It occurs as spongy mass, clusters of small spherical concretions (its size differs from a few millimeters to 5-10 cm in diameter), or flat circles (monetary ore). The ore contains 20-60% of iron oxide, and various impurities. From ...

Type Material
Lacustrine iron ore is a kind of ironstone, which is deposited on the bottom of lakes in Olonetsk province. It occurs as spongy mass, clusters of small spherical concretions (its size differs from a few millimeters to 5-10 cm in diameter), or flat circles (monetary ore). The ore contains 20-60% of iron oxide, and various impurities. From ancient times Karelia has been a source of iron for Russia. The start of the iron ore industry in Karelia region refers to the 11th – 12th centuries. People used to collect iron ore in the deposits on the rafts with special scoops. The presence of ore was determined with a piece of birch bark. The birch was simply put into the water, and if the outer layer eroded until the soft, smooth inner skin, people started to collect ore. The typical depth of an ore deposit varies from 1 to 5, maximum 10 meters. In some deeper areas lake ore can not be found. Iron was smelted in dome-ovens. The metal had a high quality, and it cost much more expensive at the Tikhvin fair than iron from other regions of Russia.
With the beginning of the Northern War, iron was priceless and there was sent a special expedition by Peter I to Karelia. In 1703 in place of the estuary of the river Lososinka and on the shore of Lake Onega Peter I started the construction of the first plant with a blast furnace (The factory of Peter I). The northern part of Lake Onega is framed with Selga ridges and folded volcanic rocks with the basic composition containing up to 14% of iron. Deep groundwater is a natural agent that washes iron oxides from rocks, transporting them into the lakes, representing the traps, especially linearly extended lakes (for example, Munozero, Konchezero, Pergozero and Gabozero). In 1946, the ore anomaly was discovered near a lake in Kostomuksha. In 1977 there was built a mining specific plant. The iron formations of the deposits belong to the complex of Proterozoic rocks at the age of about 2.8 billion years. The Kostomuksha mining plant has been producing about 9 million tons of ore pellets per year for more than 20 years.