CARBONATITE MELTS AND GENESIS OF APATITE MINERALIZATION IN THE GULI PLUTON (northern East Siberia)
A.T. Isakova1,2, L.I. Panina1, E.Yu. Rokosova1,2
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Apatite, ijolites, carbonatites, silicate inclusions, alkaline carbonate-salt inclusions, carbonate inclusions
Abstract
Inclusions of mineral-forming enviroments in apatite-containing ijolites and magnetite-phlogopite-apatite ores in carbonatites were studied to elucidate the genesis of apatite mineralization in the Guli alkaline ultramafic carbonatite massif. Primary inclusions of carbonate-salt and carbonate melts have been discovered and studied. The carbonate-salt melt inclusions are of alkaline high-Ca composition and are enriched in P, Sr, SO3, and F (wt.%): CaO - 30-40, Na2O - 5-12, K2O - 2-4, P2O5 - 1-3, SO3 - 1.5-3, and SrO - 1-3. They also contain minor MgO, FeO, BaO, and SiO2 (tenths and hundredths of percent). The homogenization temperature of these inclusions is 850-970 ºC. The carbonate inclusions contain predominant CaO (54-67 wt.%) and minor MgO, FeO, SrO, Na2O, and P2O5 (tenths of percent). Their homogenization temperature is 840-860 ºC. Similar primary carbonate-salt and carbonate inclusions were found in garnet, and secondary inclusions were detected in silicate minerals (clinopyroxene and nepheline) of ijolites. Clinopyroxenes of ijolites also contain primary inclusions of alkaline ultramafic high-Ca melts similar in composition to melilitite-melanephelinites, highly enriched in P, SO3, and CO2 (wt.%): SiO2 - 41-46, Al2O3 - 8-16, FeO - 2-8, MgO - 3-6, CaO - 12-20, Na2O - 2-9, K2O - 1-6, P2O5 - 0.4-2.1, SO3 - 0.2-2.3, and Cl - 0.02-0.35. According to the obtained data, apatite of the magnetite-phlogopite-apatite ores and ijolites of the Guli pluton crystallized from phosphorus-rich alkaline carbonate-salt melts at 850-970 ºC. The generation of these melts was, most likely, due to the silicate-salt immiscibility in melilitite-melanephelinite melts highly enriched in salts, which occured either at the final stages of clinopyroxene crystallization or during the formation of melilite. The presence of alkalies, S, F, and CO2 in spatially separated carbonate-salt melts contributed to the concentration and preservation of phosphorus in them at low temperatures, which led to the formation of apatite mineralization in ijolites and ore deposit in carbonatites.
DOI: http://dx.doi.org/10.1016/j.rgg.2015.02.007
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