TY - JOUR

T1 - Bastnaesite and Fluorite Rocks of the Ulan-Ude Occurrence (Mineral Composition, Geochemical Characteristics, and Genesis Issues)

AU - Ripp, G. S.

AU - Prokopyev, I. R.

AU - Izbrodin, I. A.

AU - Lastochkin, E.

AU - Rampilov, M. O.

AU - Doroshkevich, A. G.

AU - Redina, A. A.

AU - Posokhov, V. F.

AU - Savchenko, A. A.

AU - Khromova, E. A.

N1 - Publisher Copyright: © 2019, V.S. Sobolev IGM, Siberian Branch of the RAS.

PY - 2019/12

Y1 - 2019/12

N2 - Within the city of Ulan-Ude, several sites of bastnaesite-fluorite rocks and calcite-containing rocks were found. They are confined to the exposures of Paleozoic schists and quartzites. The rocks have an age of 134.2 ± 2.6 Ma. They are brecciated lenticular and vein-like bodies cemented mainly with bastnaesite-fluorite aggregate. The content of fluorite in the rocks is several tens of percent, and the content of bastnaesite-(Ce) is 20-30%, often reaching 50%. Among the secondary minerals, there are monazite-(Ce), albite, and K-feldspar, and the accessory minerals are zircon, Nb-containing rutile, and manganilmenite. Light lanthanides are predominant among REE in the rocks. Bastnaesite and fluorite contain brine-melt fluid inclusions with homogenization temperatures of 490-520 ºC. The salts of these inclusions are composed of predominant Na and Ca sulphates and subordinate Ca and REE carbonates, and the gas phase contains CO2. Gas inclusions and part of water-salt inclusions homogenized at 150-200, 290-350, and 430-450 ºC. The salts of late fluids are composed of Ca and REE carbonates, K and/or Na chlorides, Ca, Mg, and Fe hydrosulphates, and Ca and Na hydrocarbonates, and the gas phase contains CO2 ± H2. The isotopic compositions of carbon (-5.9 to -8.3% d13CV-PDB) and oxygen (4.3 to 8.3% d18OV-SMOW) in bastnaesite and calcite fall in the PIC square specific to unaltered intrusive carbonatites. The primary strontium isotope ratios in fluorite and bastnaesite are equal to 0.70559-0.70568. The proximal location, close ages, and mineral and geochemical features indicate a genetic relationship of the studied rocks with the late Mesozoic carbonatites of southwestern Transbaikalia. The finding of this rock occurrence indicates a existence of one more carbonatite-bearing area and expands the distribution area of such rocks, which makes southwestern Transbaikalia promising for REE mineralization.

AB - Within the city of Ulan-Ude, several sites of bastnaesite-fluorite rocks and calcite-containing rocks were found. They are confined to the exposures of Paleozoic schists and quartzites. The rocks have an age of 134.2 ± 2.6 Ma. They are brecciated lenticular and vein-like bodies cemented mainly with bastnaesite-fluorite aggregate. The content of fluorite in the rocks is several tens of percent, and the content of bastnaesite-(Ce) is 20-30%, often reaching 50%. Among the secondary minerals, there are monazite-(Ce), albite, and K-feldspar, and the accessory minerals are zircon, Nb-containing rutile, and manganilmenite. Light lanthanides are predominant among REE in the rocks. Bastnaesite and fluorite contain brine-melt fluid inclusions with homogenization temperatures of 490-520 ºC. The salts of these inclusions are composed of predominant Na and Ca sulphates and subordinate Ca and REE carbonates, and the gas phase contains CO2. Gas inclusions and part of water-salt inclusions homogenized at 150-200, 290-350, and 430-450 ºC. The salts of late fluids are composed of Ca and REE carbonates, K and/or Na chlorides, Ca, Mg, and Fe hydrosulphates, and Ca and Na hydrocarbonates, and the gas phase contains CO2 ± H2. The isotopic compositions of carbon (-5.9 to -8.3% d13CV-PDB) and oxygen (4.3 to 8.3% d18OV-SMOW) in bastnaesite and calcite fall in the PIC square specific to unaltered intrusive carbonatites. The primary strontium isotope ratios in fluorite and bastnaesite are equal to 0.70559-0.70568. The proximal location, close ages, and mineral and geochemical features indicate a genetic relationship of the studied rocks with the late Mesozoic carbonatites of southwestern Transbaikalia. The finding of this rock occurrence indicates a existence of one more carbonatite-bearing area and expands the distribution area of such rocks, which makes southwestern Transbaikalia promising for REE mineralization.

KW - rare-earth elements

KW - bastnaesite

KW - fluorite

KW - fluid inclusions

KW - FLUID-INDUCED NUCLEATION

KW - RARE-EARTH-ELEMENTS

KW - (Y+REE)-PHOSPHATE MINERALS

KW - REE-CARBONATITES

KW - ISOTOPE

KW - APATITE

KW - DEPOSIT

KW - CONSTRAINTS

KW - FLUORAPATITE

KW - COMPLEXES

KW - Fluorite

KW - Bastnaesite

KW - Rare-earth elements

KW - Fluid inclusions

UR - http://www.scopus.com/inward/record.url?scp=85089034425&partnerID=8YFLogxK

U2 - 10.15372/RGG2019136

DO - 10.15372/RGG2019136

M3 - Article

VL - 60

SP - 1404

EP - 1424

JO - Russian Geology and Geophysics

JF - Russian Geology and Geophysics

SN - 1068-7971

IS - 12

ER -