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Title: Compositions and petrogenetic significance of the eudialyte group minerals from sushina, purulia, West Bengal
Authors: Chakrabarty A.
Pruseth K.L.
Sen A.K.
Published in: Journal of the Geological Society of India
Abstract: The eudialyte-group of minerals (EGM) is one of the most important index minerals of the peralkaline (agpaitic) nepheline syenites. They crystallize in varied physico-chemical conditions ranging from the early-magmatic (orthomagmatic) to late-magmatic and even in the post-magmatic (hydrothermal) stage. In India, the only agpaitic nepheline syenite gneisses of the Sushina Hill region contain both late-magmatic as well as hydrothermal eudialytes. Compositionally these are Mn-Nb-Ca rich eudialytes and are comparable to the other EGM occurrences such as Ilímaussaq (Greenland), Tamazeght (Morocco), Mont-Saint Hilaire (Canada) and Pilansberg (South Africa). High Mn content (>6.5 wt.%) for both varieties of the Sushina EGM indicates that they are highly evolved in nature. In terms of the calculated site occupancy, particularly the [M(3)] and [M(2)], the Sushina eudialytes mimic some Pilansberg eudialytes. In addition to the eudialyte, the host nepheline syenite gneiss also contains an unknown Na-Zr-silicate (NZS) which is often found to be replacing both types of eudialytes. Compositionally these NZS can be tentatively represented as Na2Zr2S6O17. These NZS are characterized by much higher Zr, but lower Mn and Nb concentrations compared to the associated eudialytes. Two distinct varieties of eudialyte and NZS indicate subtle changes in the alkalinity during their formations. The formation of the late-magmatic as well as hydrothermal eudialyte essentially took place at somewhat elevated pH conditions. The replacement or alteration of eudialytes by NZS indicates a decreasing pH condition. In terms of the chemical composition the late-magmatic eudialytes can be represented as a solid-solution series between the kentbrooksite-taseqite-aqualite while the hydrothermal eudialyte represents solid-solution between kentbrooksitetaseqite-Ce-zirsilite. © GEOL. SOC. INDIA.
Citation: Journal of the Geological Society of India (2012), 79(5): 449-459
Issue Date: 2012
Publisher: Geological Society of India
Keywords: Agpaitic systems
Eudialyte-group of minerals (EGM)
Na-Zr silicates (NZS)
Sushina hill
ISSN: 167622
Author Scopus IDs: 25121521500
Author Affiliations: Chakrabarty, A., Department of Geology, Durgapur Government College, Durgapur, 713 214, India
Pruseth, K.L., Department of Geology and Geophysics, IIT Kharagpur, Kharagpur, 721 302, India
Sen, A.K., Department of Earth Sciences, IIT Roorkee, Roorkee, 247 667, India
Corresponding Author: Chakrabarty, A.; Department of Geology, Durgapur Government CollegeIndia; email:
Appears in Collections:Journal Publications [ES]

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