DIVERSITY AND CHARACTER OF APATITE IRON ORES AND THEIR RELATION TO EPIGENETIC CU-AU DEPOSITS IN THE NORRBOTTEN FE-CU-AU PROVINCE, NORTHERN SWEDEN

Norrbotten is an important mining province in northern Sweden, which is dominated by Fe- and Cu-Au deposits. Economically most important for the region are the apatite iron ores with an annual production of c. 31 M ton of Fe-ore and a total production of about 1600 M ton of ore the last 100 years. A Paleoproterozoic succession of greenstones, porphyries and clastic sediments that rests unconformably on a 2.7-2.8 Ga old Archean basement is geologically important in this area. Stratigraphically lowest are 2.5-2.0 Ga old rift-related greenstones. They are followed by c. 1.9 Ga Svecofennian volcanic and sedimentary rocks. Synorogenic 1.89-1.87 Ga plutons range in composition from gabbro to granite, while late orogenic intrusions are dominated by c. 1.79 Ga minimum melt granites and pegmatites. The apatite iron ores in Norrbotten shows a considerable variation in host rock relations, P-content, host rock lithology, associated minor components and host rock alterations. Most occurrences are dominated by either magnetite or hematite. Apatite, actinolite, carbonate and quartz are the main gangue minerals. Sulfides are mostly rare within the ores but may occur in the altered wall rocks. The content of Fe and P varies between 30-70 % and 0.05-5 %, respectively. A typical geochemical feature is the strong enrichment of REE. Epigenetic Cu-Au occurrences are common in Norrbotten. They are of at least two generations (c. 1.88 and 1.77 Ga) and have formed from highly saline fluids. Limited chronological data indicate a similar c. 1.88 Ga age for the older generation of Cu-Au occurrences and some of the apatite iron ores suggesting a possible genetic relation between Fe-oxide and Cu-Au mineralization. A combination of magmatic processes, deep crustal structures and evaporitic units in the lower part of the Paleoproterozoic succession might be genetically important for both types of occurrences.