Mineralogical Study of Manganese Bearing Skarn Minerals and Manganese Content in Magnetite in the Dannemora Skarn Iron Ore Deposit

Abstract: The Dannemora skarn iron ore deposit is located in the northeastern part of Bergslagen. The deposit has been mined from the 1400’s and stopped in 1992, the mine was reopen in 2012 and it will close in 2015. The Dannemora deposit is hosted by 1.9 Ga old sedimentary and volcanic rocks. The deposit consists of both manganese rich and manganese poor iron ore. The purpose of this study is to investigate the controlling factors for manganese content in both magnetite and surrounding silicate minerals, especially when garnets is present. Also the mineral assemblage and association with different host rocks lithologies shall be investigated. Petrographical and chemical studies indicate the occurrence of both calcic amphibole and Mg-Fe-Mn-Li type amphibole. The calcic amphibole is found in the majority of the samples and is dominant in manganese poor samples where as Mg-Fe-Mn-Li-type amphibole is more abundant in the manganese rich samples. Generally in the manganese rich samples garnet and epidote become more abundant, particularly if the sample is taken close to a volcanic section.