Iron Oxide Systems and Base Metal Mineralisation in Northern Sweden
by
Christopher J. Carlon, Anglo American Plc.
in Porter, T.M. (Ed), 2000 - Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide, v. 1, pp 283-296.
ABSTRACT
The Lower Proterozoic succession in Northern Sweden, hosts a major iron oxide province with a widespread and diverse base metal sulphide mineralisation. A large amount of geological and exploration data exists, but fundamental questions remain regarding the distribution and relationship of the iron and predominantly copper rich sulphide mineralisation. Detailed field, isotopic, mineralogical, petrological, fluid inclusion and structural observations are now providing new data on this historically important and significant province. Genetic concepts can now be reassessed and specific deposits re-evaluated to investigate the inter-relationship of base metal mineralisation, iron oxide deposits, rock alteration, metamorphism, orogenic cycles, structural development and igneous activity.
Iron mineralisation predominantly occurs in four forms:
• Banded, stratiform, siliceous, "quartz-banded" iron oxide formations.
• Calc-silicate "skarn" and carbonate hosted, stratabound, iron formations.
• Concordant to discordant, massive, brecciated & vein, magnetite-actinolite, magnetite-apatite & magnetite-haematite-apatite ores.
• Disseminated, massive, vein and replacement iron oxides with silica and carbonate.
Base metal (Cu-Zn-Pb-Ag-Co) mineralisation, often with Au, occurs as:
• Disseminated sulphides within pelitic, siliceous, carbonate and calc-silicate metasediments.
• Hydrothermal veins in massive and brecciated magnetite (-haematite); and replacement in mixed siliclastics, metavolcanites and metacarbonates.
• Veinlet and disseminated sulphides in iron formations, iron-rich calc-silicates and chemical sediments; with magnetite in metavolcanites and intrusives.
Regional and locally developed rock alteration, spatially associated with mineralisation, occurs as scapolite, albite, K feldspar, sericite, biotite, chlorite, actinolite, epidote, carbonates, fluorite, tourmaline and silica.
Mineralisation is multistage, and apparently focussed and hosted by specific lithological hosts, lithostratigraphic units and brittle-ductile tectonic zones.
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