Trace-Element Minerals in Malignites From the Pokrovo-Kyriyivo Massif (Ukraine) and Their Petrogenesis
UDC 549.552.331 (477)
(1, 2) SHARYGIN V.V., (3) KRYVDIK S.G.
(1) Sobolev Institute of Geology and Mineralogy, Siberian Branch of RAS
3, Acad. Koptyug Av., Novosibirsk, Russia, 630090
(2) Novosibirsk State University
1, Pirogova Str., Novosibirsk-90, Russia, 630090
(3) M.P. Semenenko Institute Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine
34, Acad. Palladin Av., Kyiv-142, Ukraine, 03680
Mineralogical journal 2017, 39 (1): 19-35
Rock-forming, minor and accessory minerals from malignites of the Pokrovo-Kyriyivo alkaline massif were previously poorly studied due to their minute sizes and very complex intergrowths. Microprobe and scanning microscopic investigations allowed analyzing and identifying the minerals of trace-elements (Sr, Ba, REE , Nb and Zr) from these rocks. They are Sr-rich fluorapatite, Ca-rich strontianite, Sr-rich burbankite, bastnaesite-(La) and -(Ce), fluorbritholite-(Ce), REE -containing niobotitanates of the aeschynite group, pyrochlore and catapleiite. Most of them are late magmatic in the rocks and confined to small miarole-like isolations, which also contain zeolites, fluorite, Fe-rich micas (annite), K-feldspar and late nepheline. Such isolations (inclusions) commonly occur in götzenite and its alteration products. In contrast Sr-rich fluorapatite (maybe fluorcaphite, 14—21 wt. % SrO) is a primary mineral in malignites and usually occurs as crystal inclusions in main rock-forming minerals (nepheline, K-feldspar, clinopyroxene, amphibole, annite, götzenite, titanite). Sometimes it forms large euhedral crystals (up to 0.3 mm) and is observed in association with fluorapatite. In general, mineral assemblage in malignites indicates a tendency toward peralkaline compositions. The abundance of carbonates (REE -fluorcarbonates, strontianite, burbankite) is also evidenced about by a possible link with carbonatites. The mineralogy of malignites shows strong enrichment in Sr; this element is main or common constituent in such minerals as fluorapatite — Sr-rich fluorapatite, burbankite, strontianite and götzenite. Other trace elements are also incorporated into the main and accessory minerals: REE , Zr and Nb — into götzenite, titanite and niobotitanates; REE — into the apatite-supergroup minerals, fluorcarbonates, burbankite and niobotitanates.
Keywords: malignite, Sr-apatite, bastnaesite, burbankite, strontianite, REE -niobotitanates, pyrochlore, catapleiite.
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