Geochemistry of advanced argillic altered rocks in the area of Breznik, Western Srednogorie Unit (Bulgaria)

Pages: 
pp. 93-108
Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
BRGM, BP 6009, 45060 Orléans cédex 2, France
Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Abstract: 

The distribution and behaviour of major and trace elements in the main zones of hydrothermal alteration (propylite, sericite and advanced argillic) in the area of Breznik Town have been studied, coupled with the chemical composition of alunite group minerals and their isotope geochemistry. The content of Sr decreases in propylite and especially in sericite rocks, and increases significantly in advanced argillic altered (AAA) rocks, which is connected with the formation of aluminium phosphate-sulphate (APS) minerals. Rubidium has high content in sericitic rocks, whereas the element is almost depleted in AAA rocks. The Rb/Sr ratio increases in sericitic rocks and strongly decreases in AAA rocks. Zirconium, Ti, Cr, V, Ga, Hf, Nb, Ta, Th, U and partially Sn and Ba have comparatively inert behaviour during alteration. Manganese, Zn, Ni, Co, Cs and Y are mobile in different degree, with a trend toward complete extraction in the most altered rocks. Arsenium concentrates in AAA rocks, while Li is concentrated only in kaolinite AAA rocks. LREE are comparatively inert in AAA rocks, while MREE and HREE are very mobile, especially in alunite rocks. Alunite has Na-K composition, with permanent admixtures of Ca, Sr, Ba and LREE. APS minerals themselves are woodhouseite and svanbergite-woodhouseite solid solutions (s.s.). Stable isotopes of alunite are characteristic for magmatic-hydrothermal alunite, whereas δ34S of jarosite is intermediate between δ34S of alunite and sulphides, which confirms its supergene origin. All these features define a high-sulphidation epithermal environment, and a possible porphyry mineralization at deeper part of the system is suggested.

Keywords: 

geochemistry, trace elements, alunite, APS minerals, advanced argillic alteration, Western Srednogorie Unit

VOLUME 46 (1)/July 2017

Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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Babeş-Bolyai University, RO-400084, Cluj–Napoca, Romania
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Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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Babeş-Bolyai University, RO-400084, Cluj–Napoca, Romania

Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Comenius University, Faculty of Natural Sciences, Department of Geology and Palaeontology, Mlynská dolina G–229, Ilkovičova 6, SK–84215 Bratislava, Slovak Republic
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Slovak Academy of Sciences, Institute of Earth Sciences, Dúbravská 9, P.O. Box 106840 05, Bratislava, Slovak Republic
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria

Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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BRGM, BP 6009, 45060 Orléans cédex 2, France
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Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria

Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., 1113 Sofia, Bulgaria
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Faculty of Geology and Geography, Department of Geology, Palaeontology and Fossil Fuels, Sofia University “St Kliment Ohridski”, 15 Tsar Osvoboditel Blvd, 1504 Sofia, Bulgaria