Contrasting fluid types involved in the genesis of ca. 1.89 Ga, syngenetic polymetallic sulfide deposits, Falun and Zinkgruvan, Bergslagen, Sweden

• Metamorphosed polymetallic sulfide deposits in Bergslagen, Sweden, are currently divided into 1: Stratabound volcanic-associated limestone-skarn Zn-Pb-Ag-Cu-Au sulfide deposits (SVALS) and 2: Stratiform ash-siltstone hostedZn-Pb-Ag sulfide deposits (SAS). It has not been completely resolved if these deposit types formed from similar hydrothermal fluids. Recent investigations at the Falun SVALS deposit and the Zinkgruvan SAS deposit suggest that fluids of contrasting pH, ƒO2, salinity and Twere involved in their origin. Whereas Falun formed by cooling and neutralization of acidic (pH<4), hot (300-400ºC) and reducing fluids carrying metals and sulfur together, Zinkgruvan formed by reduction of oxidized brines at a near-neutral pH. Falun is a vent-proximal, synvolcanic carbonate-replacement deposit with similarities to VMS and skarn deposits, whereas Zinkgruvan is a post-volcanic, exhalative deposit with similarities to some SEDEX deposits. Our results suggest that the different character of SVALS and SAS deposits in part are functions of fundamental differences in fluid chemistry, controls on sulfide precipitation and relationship to volcanism.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

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Malmgeologi

Ore Geology

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