TY - JOUR

T1 - Pyrochlore-group minerals in the granite-hosted katugin rare-metal deposit, Transbaikalia, Russia

AU - Starikova, Anastasia E.

AU - Bazarova, Ekaterina P.

AU - Savel’eva, Valentina B.

AU - Sklyarov, Eugene V.

AU - Khromova, Elena A.

AU - Kanakin, Sergei V.

PY - 2019/8/1

Y1 - 2019/8/1

N2 - Pyrochlore group minerals are the main raw phases in granitic rocks of the Katugin complex-ore deposit that stores Nb, Ta, Y, REE, U, Th, Zr, and cryolite. There are three main types: Primary magmatic, early postmagmatic (secondary-I), and late hydrothermal (secondary-II) pyrochlores. The primary magmatic phase is fluornatropyrochlore, which has high concentrations of Na2O (to 10.5 wt.%), F (to 5.4 wt.%), and REE2O3 (to 17.3 wt.%) but also low CaO (0.6–4.3 wt.%), UO2 (to 2.6 wt.%), ThO2 (to 1.8 wt.%), and PbO (to 1.4 wt.%). Pyrochlore of this type is very rare in nature and is limited to a few occurrences: Rare-metal deposits of Nechalacho in syenite and nepheline syenite (Canada) and Mariupol in nepheline syenite (Ukraine). It may have crystallized synchronously with or slightly later than melanocratic minerals (aegirine, biotite, and arfvedsonite) at the late magmatic stage when Fe from the melt became bound, which hindered the crystallization of columbite. Secondary-I pyrochlore follows cracks or replaces primary pyrochlore in grain rims and is compositionally similar to the early phase, except for lower Na2O concentrations (2.8 wt.%), relatively low F (4 wt.%), and less complete A-and Y-sites occupancy. Secondary-II pyrochlore is a product of late hydrothermal alteration, which postdated the formation of the Katugin deposit. It differs in large ranges of elements and contains minor K, Ba, Pb, Fe, and significant Si concentrations but also low Na and F. Its composition mostly falls within the field of hydro-and keno-pyrochlore.

AB - Pyrochlore group minerals are the main raw phases in granitic rocks of the Katugin complex-ore deposit that stores Nb, Ta, Y, REE, U, Th, Zr, and cryolite. There are three main types: Primary magmatic, early postmagmatic (secondary-I), and late hydrothermal (secondary-II) pyrochlores. The primary magmatic phase is fluornatropyrochlore, which has high concentrations of Na2O (to 10.5 wt.%), F (to 5.4 wt.%), and REE2O3 (to 17.3 wt.%) but also low CaO (0.6–4.3 wt.%), UO2 (to 2.6 wt.%), ThO2 (to 1.8 wt.%), and PbO (to 1.4 wt.%). Pyrochlore of this type is very rare in nature and is limited to a few occurrences: Rare-metal deposits of Nechalacho in syenite and nepheline syenite (Canada) and Mariupol in nepheline syenite (Ukraine). It may have crystallized synchronously with or slightly later than melanocratic minerals (aegirine, biotite, and arfvedsonite) at the late magmatic stage when Fe from the melt became bound, which hindered the crystallization of columbite. Secondary-I pyrochlore follows cracks or replaces primary pyrochlore in grain rims and is compositionally similar to the early phase, except for lower Na2O concentrations (2.8 wt.%), relatively low F (4 wt.%), and less complete A-and Y-sites occupancy. Secondary-II pyrochlore is a product of late hydrothermal alteration, which postdated the formation of the Katugin deposit. It differs in large ranges of elements and contains minor K, Ba, Pb, Fe, and significant Si concentrations but also low Na and F. Its composition mostly falls within the field of hydro-and keno-pyrochlore.

KW - Alkaline granites

KW - East Transbaikalia

KW - Fluornatropyrochlore

KW - Katugin rare-metal deposit

KW - Pyrochlore-group minerals

KW - PLUTON

KW - SILICIFIED PYROCHLORE

KW - CARBONATITE

KW - pyrochlore-group minerals

KW - NIOBIUM

KW - fluornatropyrochlore

KW - alkaline granites

KW - ROCKS

KW - ALKALINE COMPLEX

KW - REE

KW - MINERALIZATION

KW - RICH

KW - MAGMATIC EVOLUTION

UR - http://www.scopus.com/inward/record.url?scp=85073296073&partnerID=8YFLogxK

U2 - 10.3390/min9080490

DO - 10.3390/min9080490

M3 - Article

AN - SCOPUS:85073296073

VL - 9

JO - Minerals

JF - Minerals

SN - 2075-163X

IS - 8

M1 - 490

ER -