Carbonate petrology of the Čiprovci ore zone

Pages: 
pp. 69-98
Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Abstract: 

The Čiprovci ore zone is known for its polygenic and polychronous mineralizations formed in a siderite-calcite marble bed of Early Paleozoic age. Its general leatures as well as structures, textures and mineral composition record the following events.
   1. Deposition of chemogene calcite limestone with hydrothermal-sedimentary siderite interlayers associated with a basic volcanism. Presumable age: Cambrian.
   2. Greenschist regional dynamothermal metamorphism that transformed the carbonate rocks into finegrained marbles. Siderite contains 27 ± 5 mol% MnCO3, 6 ± 3 mol% MgCO3 and 1-2 mol% CaCO3. The two kinds of ma1ble are compositionally mosaic due to each grain growing with the composition of its seed carbonate during the metamorphic recrystallization.
   3. Formation of a hydrothermal low-temperature silver-lead sulphide mineralization (Pb-Pb model age of 320-340 Ma). It developed metasomatically in the siderite bodies mainly. The hydrothermal fluids were magnesium-rich and their first product was dolomite MgO0.8FeO0.1Mn0.1. They gradually became richer in Fe and Mn supplied during the metasomatic replacement of earlier material, and the dolomite crystals were overgrown by ankerite (up to Fe0.7Mg0.3) and manganian ankerite (up to Fe0.5Mn0.4Mg0.1). Siderite and calcite were redeposited during the later stages of the process. The main characteristics of these metasomatic·carbonate crystals is that they are idiomorphic and compositionally zoned.
   4. Formation of syn- and postmagmatic mineralizations associated with a granite intrusion (Pb-Pb model age of 255 ± 17 Ma). Carbonate minerals formed and were transformed during asuccession of processes involving: 1. Thermal metamorphism that converted the siderite marble partly or completely into magnetite ore; 2. Skarn formation in the calcite marbles; and 3. Deposition of a post-skarn oxide-sulphide-arsenide high to medium-temperature mineralization. During the magnetite fo rmation, the fluids were enriched in manganese and magnesium solutes: (Fe, Mn. Mg)CO3+H2O → Fe3O4+Mn2++Mg2++CO-. They deposited high-temperature zoned Ca-Mg-Fe-rhodochrosite, Fe-Mn-magnesite and Mg-Mn-sideritc with end members Mn0.6Fe0.2Ca0.1 Mg0.1 and Mg0.5,Fe0.3,Mn0.2. The rhodochrosite-magnesite solid-solution interval shows a solubility gap observable even on areas smaller than 1 mm2. The end of the process produced also ankerites part of which show high manganese contents (reaching kutnahorite compositions Mn0.5Fe0.3Mg0.2).
   Formation of a quartz-barite mineralisat ion (Late Cretaceous?). The earlier carbonates were partly redeposited or recrystallized.

VOLUME 21 (1)/February 1991

Geological Institute, Bulgarian Academy of Sciences, 1113, Sofia, Bulgaria

Institute of Regional Geology for Latin America (IGREPAL), National University of San Juan (UNSJ), Argentina
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Institute of Regional Geology for Latin America (IGREPAL), National University of San Juan (UNSJ), Argentina
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Institute of Regional Geology for Latin America (IGREPAL), National University of San Juan (UNSJ), Argentina
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Institute of Regional Geology for Latin America (IGREPAL), National University of San Juan (UNSJ), Argentina

Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia

Université Claude-Bernard- Lyon 1, Centre des Sciences de Ia Terre et Unité associée au C.N.R.S. no 11, 27-43 Boulevard du 11 Novembre, 69622 Villeurbanne Cedex (France)
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Ecole supérieure des Mines et de Géologie, 1156 Sofia

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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Geological Institute, Bulgarian Academy of Sciences, 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