Comparison of Banded Ores in the Main/East, West, and South
Orebodies of the Giant Bayan Obo REE District, Inner Mongolia, China
Artz, Zachary J., Friehauf, Kurt C., and Xiao, Rongge*, Dept. of
Physical Sciences, Kutztown University, Kutztown, PA 19530, *Dept. of
Geology and Mineral Resources, China University of Geosciences -
Beijing, Mineral Deposit and Prospecting Section, 29 Xueyan Road, Hai
Dian District, Beijing, 100083, China
The Bayan Obo REE District in Inner Mongolia, China, consists of three
mineralized areas distributed over a 13 x 1.5 km region: the Main/East,
West, and South Orebodies. This is the first analysis of regional
spatial trends in mineralization in the world's largest known REE
deposit and the first study of the South Bayan Obo Orebodies.
The Middle Protereozoic Bayan Obo Group H8 dolomitic marble hosts
massive, disseminated, and banded ore types in all three areas. Banded
ore is characterized by mm to cm scale layers that vary both
mineralogically and texturally. We surveyed and sampled each ore body
and distinguished five broad varieties of banded ore: 1) equant,
medium-grained quartz-fluorite with bands of fluorite containing
disseminated monazite, highly variable magnetite, and trace pyroxene;
2) fine-grained aegerine augite bands with variable fluorite,
magnetite, and trace apatite; 3) weakly banded magnetite alternating
with blue amphibole-phlogopite-dolomite bands; 4) fine-grained
carbonate-fluorite-limonite with trace amounts of apatite, magnetite,
and pyrite; 5) evenly disseminated magnetite in weakly to moderately
banded coarse-grained dolomite-fluorite-magnetite with fine-grained
phlogopite and diopside. Samples from the Main/East Orebodies are
typified by varieties 1, 2, and 3, with much variation in the content
of REE minerals, whereas varieties 4 and 5 typify the West and South
Orebodies, respectively.
Limonite is much more common in the distant West Orebodies and sulfides
are sparse in the Main/East and South Orebodies, suggesting the West
Orebodies were initially richer in pyrite. If the South Orebodies are
continuous with the Main/East Orebodies beneath the H9 syncline, the
dominantly disseminated nature of the South Orebodies, the paucity of
fluorite and aegerine-augite, the lower REE grades, and greater calcite
content may indicate a more distal position of the South Orebodies
within the ore-forming system.
The presence of rhythmic pyroxene/fluorite-carbonate bands that wrap
around breccia fragments indicates some banding formed due to
metasomatic replacement. Boudinage in some banded ores and granoblastic
textures indicate post-banding deformation and a possible metamorphic
origin or modification for some banding.
2005 Salt Lake City Annual Meeting (October 16–19, 2005)
Session No. 227--Booth# 9
Economic Geology (Posters)
Salt Palace Convention Center: Hall C
8:00 AM-12:00 PM, Wednesday, 19 October 2005
Geological
Society
of America Abstracts with
Programs, Vol. 37, No. 7, p. 500