Constraints on the source and evolution of mineralising fluids in the Norrbotten Fe oxide-Cu-Au province, Sweden

Martin Smith, Sarah A. Gleeson

Research output: Chapter in Book/Conference proceeding with ISSN or ISBNConference contribution with ISSN or ISBN

Abstract

Norbotten County, Sweden, is well known for the iron oxide-apatite deposits of the Kiruna and Malmberget areas. These are spatially associated with iron oxide Cu (+-Au) deposits and a genetic link between the two has been suggested as a part of the IOCG spectrum of deposits. Here we report the results of a fluid inclusion microthermometry and bulk crush leach halogen and chlorine stable isotope study, carried out to test that hypothesis. Quartz veins from late stage veins from Fe-oxide-apatite deposits and Cu-(Au) deposits contain hypersaline brine inclusions, with a salinity range of 32 to 38wt.% NaCl eq. in Fe-oxide bodies, and of 38 to 47wt.% NaCl eq. in Cu-Au deposits. In Cu-(Au) deposits these are sometimes accompanied by CO2-rich inclusions. The Cl/Br ratio of the fluid inclusion leachates is consistent with magmatic fluid compositions, and ranges between 859 and 9597, with no distinction between the Fe-oxide samples and the Cu-mineralizing brines. d[delta]37Cl(SMOW) values range from -0.99 to -5.63 0/00. The data are far removed from both mantle (d[delta]37Cl=+4.7 0/00) and crustal (d[delta]37Cl=0 0/00) values and must represent fractionation of the isotopes during the mineralizing process. We suggest that this fractionation occurred during the formation of Cl-rich mineral phases commonly found associated with the deposits e.g. scapolite, biotite and amphibole.
Original languageEnglish
Title of host publication8th biennial conference of the Society for geology applied to mineral deposits
Publication statusPublished - 2005
Event8th biennial conference of the society for geology applied to mineral deposits - Beijing, China
Duration: 1 Jan 2005 → …

Conference

Conference8th biennial conference of the society for geology applied to mineral deposits
Period1/01/05 → …

Keywords

  • Fluid inclusions
  • halogens, IOCG, chlorine isotopes.

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