Scholarly record

MULTIPLE GENERATIONS OF PYROCHLORES FROM THE OKA CARBONATITE COMPLEX, CANADA

Krzystof Foltyn

Abstract

The Oka carbonatite complex, one of the Cretaceous Monteregian Hills intrusions, consist of a wide range of silicate and carbonatite rocks (e.g. sovite, urtite, ijolite, jacupirangite, okaite). In the 60s, due to the abundance of pyrochlores and Nb-bearing perovskites, niobium mine (St. Lawrence Columbium mine) was developed and active until its closure in 1977, however significant amount of niobium minerals still remain at the deposit and surrounding dumps. Besides economic value as a niobium ore (and potentially, source of LREE as well), pyrochlore is an important tool in the attempts to decipher crystallization history of the Oka carbonatite complex. Pyrochlores observation in transmitted and reflected light microscope shows, that they occur as primary, non-altered crystals, commonly exhibiting internal zonation. Electron microprobe analyses reveal that there are at least two separate generations of this mineral: Ta-rich and Nb-rich. This distinction can be observed in the individual mineral grains, where Ta-rich core is often surrounded by Ta-depleted and Nb-enriched rim. In the second (Nb-rich) type of pyrochlores, trend toward increased content of F and decreased content of Ti, Zr, Ce with niobium enrichment is demonstrated. This changes in chemical composition of pyrochlores likely record the evolution of the source they crystallized from. Melt became progressively more Nb-rich and Ta-depleted and it may also indicate a new magma pulses emplaced into the complex.

Publication Impact Profile

• Captures
• Mendeley - Readers: 3

PLUMX see details

DOI resolver: doi.org/10.5593/sgem2018/1.1/s01.041

Publication details

Back to publication list