TY - JOUR

T1 - Geochemistry of Ca-(K)-(Na) silicates from charoitites in the Sirenevyi Kamen gemstone deposit, Murun Complex, Eastern Siberia

AU - Dokuchits, E. Yu

AU - Jiang, Shao Yong

AU - Stepanov, Aleksandr S.

AU - Zhukova, Irina A.

AU - Radomskaya, T. A.

AU - Marfin, A. E.

AU - Vishnevskiy, A. V.

N1 - Funding Information: The study is dedicated to and in memory of Prof. N. V. Vladykin who spent decades studying charoitites and rare minerals. The authors also would like to thank the Sidorov State Mineralogical Museum (Irkutsk, Russia) and the Central Siberian Geological Museum (Novosibirsk, Russia) for providing photos of samples of charoitites for this study. This study was supported by the National Natural Science Foundation of China Project (No. 42050410318), the Ministry of Science and Technology (MOST) National Key R&D Program of China (No. 2017YFC0602405), the MOST Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (No. MSFGPMR03-2) and the “Mega-Grant” program of the Russian Ministry of Science and Education № 075-15-2019-1883. Publisher Copyright: © 2022 The Authors

PY - 2022/4

Y1 - 2022/4

N2 - Charoitite is a unique rock in the alkaline-carbonatite Murun Complex, Eastern Siberia, Russia with an occurrence of many rare minerals. Here we report a comprehensive summary on mineralogy, major and trace element characteristics of the Ca-(K)-(Na) silicate minerals from charoitites, including charoite, tinaksite, tokkoite, pectolite, fedorite, miserite, agrellite, frankamenite, and hydroxyapophyllite-(K). All these minerals belong to Ca-(K)-(Na) silicates. The content of Al, Fe, and Mg in these silicates is insignificant, though the presence of pyroxene, amphibole, and K-feldspar shows that these elements were present in the system. The high and variable concentration of water, CO2 and F in the majority of the minerals indicates a hydrous- and volatile-rich environment of crystallization. The trace element data show that rare Ca-(K)-(Na) silicate minerals of charoitites are characterized by relatively low content (typically < 0.1 wt%) of trace elements such as Nb, Ta, Th, U, Zr and Rb. The majority of trace elements likely acted not as structural components defining mineral structures, but as trace impurities. The REE distribution patterns show that LREE enrichment and HREE depletion are characteristic for most of the Ca-(K)-(Na) silicates in charoitite, whereas tokkoite and coarse-grained tinaksite could show HREE enrichment. The REE patterns are characterized by the absence of any significant Eu anomaly, indicating the absence of Eu2+ and significant plagioclase fractionation. The initial purple/lilac color of charoite related to Mn can be changed to brown or white color, by weathering and oxidation processes that were associated with the loss of K and Na but retained the trace elements including Mn. The fractionation of trace elements between minerals of charoitites is consistent with their typical geochemical properties and the main reason for the mineralogical diversity of charoitites likely was the limited degree of solid solutions in Ca-(K)-(Na) minerals.

AB - Charoitite is a unique rock in the alkaline-carbonatite Murun Complex, Eastern Siberia, Russia with an occurrence of many rare minerals. Here we report a comprehensive summary on mineralogy, major and trace element characteristics of the Ca-(K)-(Na) silicate minerals from charoitites, including charoite, tinaksite, tokkoite, pectolite, fedorite, miserite, agrellite, frankamenite, and hydroxyapophyllite-(K). All these minerals belong to Ca-(K)-(Na) silicates. The content of Al, Fe, and Mg in these silicates is insignificant, though the presence of pyroxene, amphibole, and K-feldspar shows that these elements were present in the system. The high and variable concentration of water, CO2 and F in the majority of the minerals indicates a hydrous- and volatile-rich environment of crystallization. The trace element data show that rare Ca-(K)-(Na) silicate minerals of charoitites are characterized by relatively low content (typically < 0.1 wt%) of trace elements such as Nb, Ta, Th, U, Zr and Rb. The majority of trace elements likely acted not as structural components defining mineral structures, but as trace impurities. The REE distribution patterns show that LREE enrichment and HREE depletion are characteristic for most of the Ca-(K)-(Na) silicates in charoitite, whereas tokkoite and coarse-grained tinaksite could show HREE enrichment. The REE patterns are characterized by the absence of any significant Eu anomaly, indicating the absence of Eu2+ and significant plagioclase fractionation. The initial purple/lilac color of charoite related to Mn can be changed to brown or white color, by weathering and oxidation processes that were associated with the loss of K and Na but retained the trace elements including Mn. The fractionation of trace elements between minerals of charoitites is consistent with their typical geochemical properties and the main reason for the mineralogical diversity of charoitites likely was the limited degree of solid solutions in Ca-(K)-(Na) minerals.

KW - Ca-(K)-(Na) silicates

KW - Charoite

KW - Mineralogical characteristics

KW - Murun complex

UR - http://www.scopus.com/inward/record.url?scp=85125473067&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/5b37dbc0-fc1c-3850-8ab5-6312f5500cd1/

U2 - 10.1016/j.oregeorev.2022.104787

DO - 10.1016/j.oregeorev.2022.104787

M3 - Review article

AN - SCOPUS:85125473067

VL - 143

JO - Ore Geology Reviews

JF - Ore Geology Reviews

SN - 0169-1368

M1 - 104787

ER -