Formation of sulphide deposits and its relation to sodic and potassic alteration of Proterozoic metabasites in the Saxa rift basin, Bergslagen, Sweden

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Authors:Hellingwerf, R. H.
Author Affiliations:Primary:
Geol. Inst., NL-1018 VZ Amsterdam, Netherlands
Volume Title:Mineralium Deposita
Source:Mineralium Deposita, 22(1), p.53-63. Publisher: Springer-Verlag, Berlin, Federal Republic of Germany. ISSN: 0026-4598
Publication Date:1987
Note:In English. 40 refs.; illus. incl. geol. sketch maps, sect.
Summary:A number of Cu-Zn-Fe-Pb-As sulphide mineralizations spatially associated with metabasic sills, dykes and flows of originally continental tholeiitic composition occur in the 1900-1800 m.y.-old metavolcanic-sedimentary sequence in the Saxa sedimentary rift basin. In higher stratigraphic levels, weak sulphide mineralizations occur just below Na-rich, albite-chlorite-calcite-quartz-actinolite-bearing metabasic flows; in the lower stratigraphic levels sulphide mineralizations occur: 1) spatially asssociated with potassium-rich, microcline-scapolite- or biotite/phlogopite-rich metabasic sills and dykes, and 2) below metabasic flows in which albite and calcite are replaced by microcline and scapolite. The Na- and K-rich metabasites are demonstrated to represent products of spilitization and potassic alteration, respectively. During spilitization Fe, Cu, Co and HREE are leached from the basic flows, whereas during potassic alteration Fe, Cu, Y and possibly Zn and Zr are leached from the basic rocks, indicating a genetic relationship between the metabasites and the Cu-Fe-sulphide mineralizations. Spilitization probably took place due to interaction of the flows with descending, sea-water- dominated fluids in a sub-sea-floor hydrothermal system with T approx 250-400°C. Potassic alteration probably took place by ascending fluids at higher T than for spilitization. [L.G.L.]
Subjects:Base metals; Economic geology; Metabasite; Metaigneous rocks; Metal ores; Metamorphic rocks; Metasomatism; Mineralization; Petrology; Precambrian; Processes; Proterozoic; Spilitization; Sulfides; Transformations; Upper Precambrian; Bergslagen; Europe; Scandinavia; Sweden; Western Europe; Saxa rift basin
Abstract Numbers:88M/0338
Record ID:1988004796
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe
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