Genesis of the earthy ores at Garpenberg, south central Sweden
Titel:
Genesis of the earthy ores at Garpenberg, south central Sweden
Auteur:
Vivallo, Waldo Broman, Curt
Verschenen in:
GFF
Paginering:
Jaargang 115 (1993) nr. 3 pagina's 209-214
Jaar:
1993
Inhoud:
The earthy ore at Garpenberg consists of a soft, unconsolidated material made up of montmorillonite, kaolinite, quartz, chlorite and talc as main gangue minerals with native silver, galena, carbonates and sulfates as ore minerals. This ore type occurs on the hanging wall side of the massive sulfide deposits, vertical to subvertical and mainly parallel to the schistosily and bedding. Field relationships, for example gradational contact with the Zn-Pb-Cu-Ag ore bodies, and geochemical evidences suggest that the earthy ore was formed in situ alteration of an originally strat-abound volcanogenic sulfide ore hosted in tremolite skarn and dolomitic marble. Fluid inclusions in cerussite suggest that the alteration process occurred as a near surface process at low pressure and temperature. Oxidation of the former sulfide ore and parts of the wallrocks was produced by fresh water circulating through the ore bodies, channelled by faults and fractures. The oxidation of the sulfide ore produced an initially acid solution which, by interaction with the wall and host rocks, evolved towards alkaline conditions as showed by the presence of the assemblage galena, cerussite and anglesite in the earthy ore. The isotopic composition of the ore-lead was not affected by the alteration process. The geological relationships and mineralogical evidences also suggest that the earthy ore was formed long after the primary (volcanogenic) ore deposition and clearly postdate the Svecokarelian orogeny.
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