Niocorp Developments Ltd (NB)

[Blairman]

Continued:

ppm and Nd as much as 13,100 ppm; their chondritenormalized
REE patterns display typical carbonatite REE
patterns (Fig. 1). Similar to the apatite beforsite, samples
of barite beforsite with the highest LREE content contain
late-stage fluorocarbonates and phosphates. The magnetite
beforsite, the carbonatite unit that contains much of the Nb
mineralization, has an anomalous REE pattern displaying
enrichment of the more valued middle and heavy REEs
(Eu, Gd, Tb, and Dy) relative to lower mass La, Ce, and
Nd, and higher mass Tm, Yb, and Lu (Fig. 1). Studies are
underway to determine the hosts of these elements in the
magnetite beforsite.
In our study, the chemical compositions of 25 samples
of various carbonatite lithologies were determined to
characterize general features of the carbonatite. The
samples were integrated pulps from ten-foot core intervals.
The apatite beforsite has the highest P2O5 concentrations
(up to 3.7%), but La is not correlated with P2O5,
suggesting that apatite concentration does not control the
high REE abundance. This is consistent with the
observation of fluorocarbonates in high REE zones.
Fluorine concentrations are variable (up to 39,100 ppm),
and do not correlate with La or Ce. Fluorite likely controls
the fluorine budget and masks the presence of
fluorocarbonates. In the magnetite and barite beforsite,
barium concentrations are higher (24,800 to 83,400 ppm)
than in the apatite beforsite (500 to 34,200 ppm). From
our limited samples, the highest Nb concentration (12,400
ppm) was found in an apatite beforsite sample, and the
magnetite beforsite samples (n=5) had the highest median
Nb concentration (6800 ppm, compared to 470 ppm for
the apatite beforsite). Further work by utilizing
microanalytical methods is underway to better constrain
which minerals control the REE budget in each carbonatite
lithology.
Acknowledgements
This work was supported by the US Geological
Survey’s Mineral Resources Program, in part through the
MRP External Research Program. We greatly appreciate
the effort of Matt Joeckel, University of Nebraska-School
of Natural Resources, for providing access to the archived
core and to Tony Mariano for lively discussions of
carbonatite petrology.