V.O. Syomka. NEW DATA ABOUT THE COMPOSITION AND AGE OF ORE-BEARING SKARNS OF VOLYN MEGABLOCK OF UKRAINIAN SHIELD
UDC 552.161 + 550.93
NEW DATA ABOUT THE COMPOSITION AND AGE OF ORE-BEARING SKARNS OF VOLYN MEGABLOCK OF UKRAINIAN SHIELD
V.O. Syomka, https://orcid.org/0000-0001-5202-4045
L.M. Stepanyuk, https://orcid.org/0000-0001-5591-5169
T.I. Dovbush, https://orcid.org/0000-0002-3512-3313
O.B. Vysotsky, http://orcid.org/0000-0002-3542-4685
S.M. Bondarenko, https://orcid.org/0000-0001-7948-3583
L.V. Syomka, https://orcid.org/0000-0002-7059-2502
M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine
34, Acad. Palladin Ave., Kyiv, Ukraine, 03142
Mineralogical journal 2019, 41 (3): 36-47
This article presents new mineralogical-petrographic and radiogeochronological data about the calcic skarns of the Korvinivka area and overprinted magnesian skarns of the Kocheriv area located in the south-eastern part of the Volyn megablock of Ukrainian Shield (USh). In the Korvinivka area, skarns are observed as vein infiltrated bodies among biotite-plagioclase gneisses. The main minerals of the skarns are hornblende, pyroxene, garnet, basic plagioclase and epidote. Accessory minerals are represented by apatite, titanite and orthite, and chalcopyrite is found as ore minerals. In the Kocheriv area, the skarns form layers and vein-like bodies of at on the contact between carbonate and aluminum silicate rocks and occur as associated with the Kocheriv and Zabilotsk massifs of aplite-pegmatoid granites. Among the main minerals of the skarns are pyroxene, phlogopite, scapolite, microcline, tremolite, serpentine and calcite. Sheelite is found in phlogopite-tremolite exoskarns. For the first time, age dating of skarns of the Volyn megablock is made by classical U-Pb method on titanite. Two stages of skarn formation within the Volyn megablock are established: 1. Magmatic stage of formation of calcic skarn formation. The average weighted mean calculated on 207Pb/206Pb isotope ratio in titanite indicates 2042.8 ± 3.7 Ma of skarn age. Such dating actually reflects the age of formation of high-temperature mineral associations in skarns of magmatic stage. Moreover, the age of "Bystriiv" granite type of with which skarns of the Kocheriv structural and tectonic zone are genetically associated is determined on zircon and monazite as 2080 Ma (Stepanyuk et al., 2000). These of skarns are almost 40 Ma than granites, which possibly indicates prolonged period of their crystallization. 2. Postmagmatic formation stage of the overprinted magnesian skarns. The weighted average mean calculated on isotope ratio of 207Pb/206Pb in titanite indicates the age of skarn formation as 1988 ± 1.2 Ma. Such an age perfectly matches the results of our early dating (by potassium-argon method on phlogopite) of the overprinted magnesian skarns of USh which makes 1980 Ma (Nechaev et al., 1990). Moreover, the second stage is thought to be the more favorable for sheelite mineralization in the south-east part of Volyn megablock of Ukrainian Shield.
Keywords: Volyn megablock, calcic skarns, overprinted magnesian skarns, age, titanite, magmatic stage, postmagmatic stage.
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