Geology of the Jaakonlampi area in the Siilinjärvi carbonatite complex

Abstract

The objective of this work was to describe the lithology and structures of the Jaakonlampi area of the Siilinjärvi alkali complex, eastern Finland. The research area is located directly north of the currently mined Särkijärvi open pit of the Siilinjärvi apatite mine. A drilling project to increase the knowledge on the phosphorus-bearing mineralization in the Jaakonlampi area was commenced in 2014. The defined lithological units and structural model were based on field observations and Yara Siilinjärvi Mine’s geological database and employed in resource estimation on the Jaakonlampi area.

The Jaakonlampi area consists of carbonatite, silicocarbonatite, carbonate-glimmerite and glimmerite, with fenite xenolith-bearing margins in contact with metasomatically produced fenite halo. A regional NE-SW-trending shear zone affects the northern part of the Jaakonlampi area. The alkali complex is cut by Svecofennian mafic and intermediate dikes, with varying age and composition. A previously unknown felsic pegmatitic dike was identified from the northwest part of the Jaakonlampi area. Four deformation phases were identified in the study area. The use of structural geology gives the ore evaluation process a better control over the calculation parameters in different areas, as all the lithological domains are affected by regional and local faulting and shearing.