Reconnaissance Study of District-Scale
Geochemical Trends in the Bayan Obo REE District, Inner Mongolia
Mason, Kelsey; Rock, Marlena;Friehauf,
Kurt, 2013, Reconnaissance
Study of District-Scale Geochemical Trends in the Bayan Obo REE
District, Inner Mongolia: Geological Society of America National
Meeting, Denver, Colorado (27–30 October, 2013).
This study examines district-scale REE
geochemical trends in the metamorphosed carbonate-hosted Bayan Obo
REE district in Inner Mongolia (China) by comparing the mineralogy
of samples from the East (EBO), West (WBO), and South (SBO) Bayan
Obo ore bodies. Uncoated polished thin sections of samples with
similar carbonate gangue material were examined using backscatter
electron imaging (BSE) with an environmental scanning electron
microscope (ESEM) in low vacuum, gas-phase mode. Automated feature
detection based on high Z BSE intensities enabled quantitative
analysis of a total of 6,126 REE mineral grains using energy
dispersive spectrometry (EDS).
The SBO specimens were rich in REE-Fe-Nb oxides (fergusonite – 84%,
aeschynite – 16%), and contained only trace monazite, bastnäsite and
barite. The REE minerals made up approximately 0.01% of the samples.
The carbonate and fluorite gangue occurred in subequal proportions,
along with pyrite and disseminated clinopyroxene. The REE-Fe-Nb
oxides occurred more commonly in fluorite-rich bands than carbonate
bands. Pyrite occurred both as segregated bands and intergrown with
the REE-Fe-Nb oxides. SBO samples had high Nb:Nd mole ratios (2.42,
2.13), lower Ce:Nd mole ratios (0.57, 0.81) and trace La.
Approximately 0.10% of the WBO samples consisted of REE minerals,
dominated by bastnäsite (68%) and monazite (32%), but containing
trace REE-Fe-Nb oxides. REE minerals were surrounded by quartz and
carbonate in subequal amounts, along with pyrite, clinopyroxene, and
barite. WBO samples had high Ce:Nd mole ratios (5.50, 13.49), lower
La:Ce mole ratios (0.27, 0.09), and trace Nb.
Approximately 0.15% of the EBO samples consisted of REE minerals,
containing abundant monazite (74%), bastnäsite (26%) and trace
REE-Fe-Nb oxides. The REE minerals occurred in quartz with
subordinate clinopyroxene, barite and trace pyrite and carbonate.
The REE minerals correlated with fluorite-rich bands. These samples
had a high Ce:Nd mole ratio (5.50), a lower La:Ce mole ratio (0.51),
and trace Nb.
Samples from the distal WBO deposit (5 km away) have a similar
geochemical signature with EBO samples, suggesting no lateral metal
zonation in the northern limb of the syncline. SBO, although more
proximal to the Main and East Ore Bodies (1 km away) is coarser
grained and geochemically distinct..
Reconnaissance Study of District-Scale
Geochemical Trends in the Bayan Obo REE District, Inner Mongolia
This study examines district-scale REE
geochemical trends in the metamorphosed carbonate-hosted Bayan Obo
REE district in Inner Mongolia (China) by comparing the mineralogy
of samples from the East (EBO), West (WBO), and South (SBO) Bayan
Obo ore bodies. Uncoated polished thin sections of samples with
similar carbonate gangue material were examined using backscatter
electron imaging (BSE) with an environmental scanning electron
microscope (ESEM) in low vacuum, gas-phase mode. Automated feature
detection based on high Z BSE intensities enabled quantitative
analysis of a total of 6,126 REE mineral grains using energy
dispersive spectrometry (EDS).