Trace element partitioning between pyrochlore, microlite, fersmite and silicate melts.

Area of Science:

• Geochemistry
• Mineralogy
• Experimental Petrology

Background:

• Trace elements play a crucial role in magma evolution and ore deposit formation.
• Understanding mineral-melt partitioning is key to deciphering geochemical processes.
• Pyrochlore-group minerals and fersmite are important accessory minerals in various geological settings.

Purpose of the Study:

• To experimentally determine trace element partition coefficients (D) between pyrochlore-group minerals, Ca fersmite, and silicate melts.
• To investigate the fractionation capabilities of these minerals for key trace elements (Zr, Hf, Nb, Ta, U, Th, REE).
• To provide insights into the behavior of these elements during the evolution of SiO2-undersaturated magmas.

Main Methods:

• Experimental determination of trace element partition coefficients.
• Analysis of mineral-composition and coexisting silicate melt composition.
• Varying conditions to assess element fractionation, including oxidizing conditions for U-Th partitioning.

Main Results:

• Pyrochlore and fersmite strongly fractionate Zr/Hf from Nb/Ta, with D values indicating compatibility differences.
• D(Ta) > D(Nb) for pyrochlore-group minerals, consistent with other Ti-rich minerals.
• Under oxidizing conditions, D(Th) > D(U), suggesting U-Th fractionation by pyrochlore-group minerals.
• Rare earth element (REE) partition coefficients are near unity, with light REE being more compatible.

Conclusions:

• Pyrochlore-group minerals and fersmite are significant fractionating agents for trace elements in SiO2-undersaturated magmas.
• The observed partitioning behavior explains high REE concentrations in natural pyrochlores.
• Experimental data provide valuable constraints for geochemical modeling and understanding ore formation processes.