TY - JOUR
T1 - Primary rare earth element enrichment in carbonatites
T2 - evidence from melt inclusions in Ulgii Khiid carbonatite, Mongolia
AU - Feng, Meng
AU - Wenlei, Song
AU - Kynicky, Jindrich
AU - Smith, Martin
AU - Cox, Clinton
AU - Kotlanova, Michaela
AU - Brtnicky, Martin
AU - Fu, Wei
AU - Chunwan, Wei
PY - 2019/12/20
Y1 - 2019/12/20
N2 - Carbonatites are abundant in the rare earth elements (REE), and they host the most important REE resources in the world. However, the mechanisms that concentrate these elements during carbonatitic magmatic processes are still poorly constrained. Here, we report the occurrence of apatite-hosted melt inclusions from the Ulgii Khiid carbonatites, Mongolia, and use these to reconstruct the evolution of REE concentrations and patterns in early, primary carbonatite magma. The melt inclusions consist of a varied polycrystalline assemblage of daughter minerals, including calcite, diopside, phlogopite, magnetite, pyrite, monazite, parisite, and a phosphate glass which is remarkably enriched in REE. Heating-quenching experiments show that the homogenization temperatures of the inclusions are above 1200 °C and produce three immiscible liquid phases (i.e., phosphate-, silicate-, and Fe-silicate-melt). The phosphate melt has much higher REE content than the silicate melts. We, therefore, suggest that the melt inclusions trapped a REE-, P- and silicate-enriched carbonate melt produced via carbonate-silicate liquid immiscibility. During this process, both REE and P preferentially incorporated into the carbonate melt. With subsequent crystal fractionation of REE- and P-poor carbonate and silicate minerals, the separated carbonatitic melt becomes P-REE-saturated, forming REE minerals and an immiscible REE-rich phosphate melt. The phosphate melt is highly efficient at concentrating REE during the immiscibility process and plays a crucial role in controlling the REE budget in the P-rich carbonatite magmas.
AB - Carbonatites are abundant in the rare earth elements (REE), and they host the most important REE resources in the world. However, the mechanisms that concentrate these elements during carbonatitic magmatic processes are still poorly constrained. Here, we report the occurrence of apatite-hosted melt inclusions from the Ulgii Khiid carbonatites, Mongolia, and use these to reconstruct the evolution of REE concentrations and patterns in early, primary carbonatite magma. The melt inclusions consist of a varied polycrystalline assemblage of daughter minerals, including calcite, diopside, phlogopite, magnetite, pyrite, monazite, parisite, and a phosphate glass which is remarkably enriched in REE. Heating-quenching experiments show that the homogenization temperatures of the inclusions are above 1200 °C and produce three immiscible liquid phases (i.e., phosphate-, silicate-, and Fe-silicate-melt). The phosphate melt has much higher REE content than the silicate melts. We, therefore, suggest that the melt inclusions trapped a REE-, P- and silicate-enriched carbonate melt produced via carbonate-silicate liquid immiscibility. During this process, both REE and P preferentially incorporated into the carbonate melt. With subsequent crystal fractionation of REE- and P-poor carbonate and silicate minerals, the separated carbonatitic melt becomes P-REE-saturated, forming REE minerals and an immiscible REE-rich phosphate melt. The phosphate melt is highly efficient at concentrating REE during the immiscibility process and plays a crucial role in controlling the REE budget in the P-rich carbonatite magmas.
KW - Carbonatite
KW - Immiscibility
KW - Melt inclusion
KW - Mineralization
KW - Phosphate
KW - REE
KW - Ulgii Khiid
UR - http://www.scopus.com/inward/record.url?scp=85077496309&partnerID=8YFLogxK
UR - https://authors.elsevier.com/c/1aWsccTGx~JLd
U2 - 10.1016/j.oregeorev.2019.103294
DO - 10.1016/j.oregeorev.2019.103294
M3 - Article
VL - 117
JO - Ore Geology Reviews
JF - Ore Geology Reviews
SN - 0169-1368
M1 - 103294
ER -