Stratigraphy, age, and Sm-Nd isotope systematics of the country rocks to Zn-Pb sulfide deposits, Ammeberg District, Sweden

• DOI: 10.2113/gsecongeo.91.6.1009
• Publication Date: 2009-04-03T13:38:06Z
• Authors: R. A. Kumpulainen; J. Mansfeld; K. Sundblad; L. Neymark; T. Bergman
• Keywords: Felsic; Geochronology

The Aammeberg Zn-Pb ore district constitutes the southern margin of Bergslagen mining in south-central Sweden. It is hosted by a succession Paleoproterozoic supracrustal units belonging to Svecofennian domain and was considered as genetically distinct within already at beginning this century. most prominent deposit Zinkgruvan which has been major zinc producer for more than 100 years. In paper, results from an investigation stratigraphy, geochemistry, U-Pb Sm-Nd isotope systematics are reported ca. 10-km-thick volcanosedimentary forms country, rocks district, informally named Emme group.The group may be subdivided stratigraphically into eight lithological generally four parts. lowermost part (the Moesjoen Goekberget Igelfors formation) dominated felsic volcanic contains subeconomic Zn-Pb-(Cu) Marketorp. also intrusions subvolcanic rhyolitic porphyries (U/Pb age 190 + or - 18 Ma). volcanite-dominated grades upward homogeneous, medium-grained arkoses Nrkesberg continental derivation. Two selected single zircons these yielded 207 Pb/ 206 Pb ages 1959 52 2703 178 Ma, respectively, indicating derivation both Archean sources. This arkosic unit overlain upper containing (Mariedamm its lateral correlatives, Godegaard unit; U/Pb 1889 (super +35) (sub -24) Ma) locally display strong hydrothermal alteration associated with deposition Zn-Pb-Ag ores related carbonate Hoeksjoen limestone). Tholeiitic common group. uppermost composed sandy muddy turbidites Vintergoelen formation).The epsilon Nd (1.9 Ga) values volcanogenic range 0.1 1.1 comparable other elsewhere Bergslagen. -2.8 -1.9 -2.6 +0.9. demonstrates rapid dilution detritus material younger sources mafic 1.4 4.6 among highest These data indicate that primitive rift component introduced before formation completed. occurrences rift-related ore, partly providing separate metal source heat convecting cells.The interplay between voluminous, volcanism input large quantities continentally derived sediments. probable depositional site along active margin, where subsidence basin varied slow regular very fast.All sulfide were previously interpreted constitute characteristic type present least two different ore-bearing levels (Zinkgruvan Marketorp), constituting environments, can distinguished area. suggested level represent ore-forming environment Bergslagen, located deposited marine environment. particular characterizing appears extend all