Hydrothermal Pb–Zn ore formation in the Central Rhodopian Dome, south Bulgaria: Review and new time constraints from Ar–Ar geochronology

Authors: Kaiser-Rohrmeier, Majka; Handler, Robert; Quadt, Albrecht V.; Heinrich, Christoph

Source: Swiss Bulletin of Mineralogy and Petrology, Volume 84, Number 1, April 2004 , pp. 37-58(22)

Publisher: Swiss Society of Mineralogy and Petrology

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Abstract:

Large lead-zinc mineralised metasomatic replacement bodies and vein swarms are associated with the Central Rhodopian Dome, south Bulgaria, which is interpreted as an Oligocene extensional core complex. Four ore fields occur in the vicinity of a low-angle detachment fault system, which is crosscut by rhyolitic dykes and ore veins. ⁴⁰Ar/³⁹Ar dating of white mica from veins and altered wall rocks is used to date the hydrothermal evolution and to relate the mineralisation to metamorphic uplift and silicic magmatism in the region.

⁴⁰Ar/³⁹ Ar plateau ages in coarse-grained muscovite separated from Mn-skarns and vugs in gneisses vary between 36 and 35 Ma and are interpreted as late-metamorphic crystallisation or early cooling ages. The age of 35.25±0.36 Ma of pre-ore muscovite from Davidkovo ore field is also interpreted as a cooling age following metamorphism and subsequent updoming of the footwall of the complex at around 36–35 Ma. Sericitic alteration in gneisses adjacent to the ore veins yields ages of 31.21 ± 0.38 Ma and 31.55 ± 0.46 Ma placing an upper bracket on ore formation in the Madan ore field. Ages of hydrothermal muscovite connected to sulphide precipitation cluster around 30 Ma, placing a lower bracket on the age of Pb–Zn mineralisation. Another hydrothermal sericite age ranges down to sim

26 Ma but it probably indicates local resetting by persisting geothermal activity. Rhyolitic dykes crosscut by the ore veins may be about 1–2 Ma older than these according to published U–Pb data on single zircons and similar in age to the Borovitsa caldera east of the Laki ore field. The close correspondence of hydrothermal and magmatic ages near 30 Ma and the small time difference of only sim

5 Ma to the amphibolite facies metamorphism in the footwall of the dome indicate that hydrothermal and magmatic activity are both related to rapid tectonic and erosional denudation during late-orogenic collapse.

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Keywords: HYDROTHERMAL PB&NDASHZN VEIN MINERALISATION; METAMORPHIC CORE COMPLEX; 40AR/39AR DATING; MADAN; RHODOPES; BULGARIA

Document Type: Research article

Publication date: 2004-04-01

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