2096 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
a high magnetite/hematite or titano-magnetite/hematite
component, either in solid solution or as separate contami-
nant grains.
The mixed magnetic fraction was, as expected, iron-
rich (21.7 wt% Fe2O3) with considerable amounts of SiO2
(38.7 wt%), Al2O3 (15.5 wt%), CaO (7.5 wt%) and MgO
(3.6 wt%). The analyses are consistent with the bulk of the
mixed magnetic fraction comprising heavy mineral alumi-
nosilicates such as amphiboles, garnets, epidotes that are
typically present in Brahmaputra River sands (Rahman et
al., 2019). The minor amount of TiO2 (6.7 wt%) indi-
cates possible incorporation of ilmenite in the fraction that
could potentially be recovered with further refinement of
the process flowsheet. Both Na2O and K2O were low (
1 wt% each) indicating low amounts of feldspar in the frac-
tion. In comparison, the non-magnetic fraction was high in
SiO2 (47.6 wt%), CaO (12.2 wt%) and Al2O3 (13 wt%)
implying the presence of quartz, felspars and aluminosili-
cates, while high TiO2 (6.8 wt%) suggests possible rutile
incorporation. High P2O5 (3.3 wt%) implies the presence
of apatite and/or monazite and 3.8 wt %ZrO2 indicates
likely zircon grains.
The garnet fraction contained, on average 38 wt%
SiO2 and 18.6 wt% Al2O3 which is within the range of alu-
mina and silica values typically observed for garnets within
the four end members of the almandine(Fe)-pyrope(Mg)-
grossular(Ca)-spessartine(Mn) isomorphous series. A garnet
corresponding in composition with any one endmember is
rare, however, and the name is usually ascribed according
to the dominant ‘molecular’ type present. Average Fe2O3
(28.4 wt%), CaO (5.99 wt%), MgO (3.98 wt%) and
Mn3O4 (1.98 wt%) assays indicate that the garnets present
in the fraction are most likely almandine (i.e., Fe-rich) with
minor, in order of decreasing abundance, grossular, pyrope
and spessartine components. The levels of CaO and Fe2O3
may also include contributions from calcium and iron alu-
minosilicate heavy minerals such as amphibole and epidote.
Bulk Mineralogy of Fractions (XRD, SEM and EPMA)
The results of the phase identification and QPA
(Quantitative Phase Analysis or the relative wt% of crystal-
line phases) are given in Table 2 for the Fe-Ti oxide and
garnet fractions.
Ilmenite Fraction
The results of the QXRD phase identification indicated
a high proportion of ilmenite (59 wt%) and hematite
(21 wt%) and trace magnetite (1 wt%), consistent with the
high Fe2O3 and the low TiO2 assays reported in Table 1. All
these minerals are susceptible to recovery to the magnetic
fraction however it is unclear from the QXRD results as to
whether these phases are present as discrete phases or com-
posite particles. Minor rutile (2 wt%) was also present. It
is possible these represent mineral entrainment or minerals
occurring as composite phases or inclusions. Given rutile
and zircon inclusions are typically associated with ilmenite,
we suggest it is most likely the latter. Amphibole (8 wt%),
garnet (4 wt%), albite feldspar (2 wt%), quartz (2 wt%)
and mica (1 wt%) were the main gangue minerals. These
contribute to the elevated SiO2 and Al2O3 levels reported
for the bulk assay. The gangue mineral suite is also consis-
tent with the observed assays for the minor elements CaO
(amphibole, plagioclase feldspar, garnet), K2O (mica, feld-
spar), MgO (amphibole, garnet), and Na2O (plagioclase
feldspar).
Examination of the ilmenite fraction by BSE (Back
Scattered Electron) imaging confirmed the Fe-Ti oxide
and gangue mineralogy indicated by QXRD. Many of the
Fe-Ti oxide grains were angular to sub-angular in appear-
ance consistent with proximity to source. Further evidence
for little weathering/degradation includes the presence of
primary, unaltered inclusions (e.g., quartz) and sphene
(titanite) and garnet. Inclusions of other valuable minerals
typically associated with heavy mineral Fe-Ti oxides such as
rutile, zircon and monazite were also noted.
Table 2. Quantitative XRD (relative wt% of crystalline phases) results for the Fe-Ti oxide and garnet fractions
Sample
Phase Concentration (relative crystalline wt%)
Qtz Garnet Amph Mica Rutile Albite Pyr Hem Ilm Zircon Titanite Apatite Mag Epidote
Ilmenite 2 4 8 1 2 2 21 59 1
Mag. Mix 14 27 28 3 5 3 2 3 15
Non-Mags 22 12 14 1 3 6 3 5 8 7 16
Garnet 3 74 14 1 1 2 1 5
Qtz =quartz Amph =amphibole Pyr =pyroxene Hem =hematite Ilm =ilmenite Mag =magnetite.
a high magnetite/hematite or titano-magnetite/hematite
component, either in solid solution or as separate contami-
nant grains.
The mixed magnetic fraction was, as expected, iron-
rich (21.7 wt% Fe2O3) with considerable amounts of SiO2
(38.7 wt%), Al2O3 (15.5 wt%), CaO (7.5 wt%) and MgO
(3.6 wt%). The analyses are consistent with the bulk of the
mixed magnetic fraction comprising heavy mineral alumi-
nosilicates such as amphiboles, garnets, epidotes that are
typically present in Brahmaputra River sands (Rahman et
al., 2019). The minor amount of TiO2 (6.7 wt%) indi-
cates possible incorporation of ilmenite in the fraction that
could potentially be recovered with further refinement of
the process flowsheet. Both Na2O and K2O were low (
1 wt% each) indicating low amounts of feldspar in the frac-
tion. In comparison, the non-magnetic fraction was high in
SiO2 (47.6 wt%), CaO (12.2 wt%) and Al2O3 (13 wt%)
implying the presence of quartz, felspars and aluminosili-
cates, while high TiO2 (6.8 wt%) suggests possible rutile
incorporation. High P2O5 (3.3 wt%) implies the presence
of apatite and/or monazite and 3.8 wt %ZrO2 indicates
likely zircon grains.
The garnet fraction contained, on average 38 wt%
SiO2 and 18.6 wt% Al2O3 which is within the range of alu-
mina and silica values typically observed for garnets within
the four end members of the almandine(Fe)-pyrope(Mg)-
grossular(Ca)-spessartine(Mn) isomorphous series. A garnet
corresponding in composition with any one endmember is
rare, however, and the name is usually ascribed according
to the dominant ‘molecular’ type present. Average Fe2O3
(28.4 wt%), CaO (5.99 wt%), MgO (3.98 wt%) and
Mn3O4 (1.98 wt%) assays indicate that the garnets present
in the fraction are most likely almandine (i.e., Fe-rich) with
minor, in order of decreasing abundance, grossular, pyrope
and spessartine components. The levels of CaO and Fe2O3
may also include contributions from calcium and iron alu-
minosilicate heavy minerals such as amphibole and epidote.
Bulk Mineralogy of Fractions (XRD, SEM and EPMA)
The results of the phase identification and QPA
(Quantitative Phase Analysis or the relative wt% of crystal-
line phases) are given in Table 2 for the Fe-Ti oxide and
garnet fractions.
Ilmenite Fraction
The results of the QXRD phase identification indicated
a high proportion of ilmenite (59 wt%) and hematite
(21 wt%) and trace magnetite (1 wt%), consistent with the
high Fe2O3 and the low TiO2 assays reported in Table 1. All
these minerals are susceptible to recovery to the magnetic
fraction however it is unclear from the QXRD results as to
whether these phases are present as discrete phases or com-
posite particles. Minor rutile (2 wt%) was also present. It
is possible these represent mineral entrainment or minerals
occurring as composite phases or inclusions. Given rutile
and zircon inclusions are typically associated with ilmenite,
we suggest it is most likely the latter. Amphibole (8 wt%),
garnet (4 wt%), albite feldspar (2 wt%), quartz (2 wt%)
and mica (1 wt%) were the main gangue minerals. These
contribute to the elevated SiO2 and Al2O3 levels reported
for the bulk assay. The gangue mineral suite is also consis-
tent with the observed assays for the minor elements CaO
(amphibole, plagioclase feldspar, garnet), K2O (mica, feld-
spar), MgO (amphibole, garnet), and Na2O (plagioclase
feldspar).
Examination of the ilmenite fraction by BSE (Back
Scattered Electron) imaging confirmed the Fe-Ti oxide
and gangue mineralogy indicated by QXRD. Many of the
Fe-Ti oxide grains were angular to sub-angular in appear-
ance consistent with proximity to source. Further evidence
for little weathering/degradation includes the presence of
primary, unaltered inclusions (e.g., quartz) and sphene
(titanite) and garnet. Inclusions of other valuable minerals
typically associated with heavy mineral Fe-Ti oxides such as
rutile, zircon and monazite were also noted.
Table 2. Quantitative XRD (relative wt% of crystalline phases) results for the Fe-Ti oxide and garnet fractions
Sample
Phase Concentration (relative crystalline wt%)
Qtz Garnet Amph Mica Rutile Albite Pyr Hem Ilm Zircon Titanite Apatite Mag Epidote
Ilmenite 2 4 8 1 2 2 21 59 1
Mag. Mix 14 27 28 3 5 3 2 3 15
Non-Mags 22 12 14 1 3 6 3 5 8 7 16
Garnet 3 74 14 1 1 2 1 5
Qtz =quartz Amph =amphibole Pyr =pyroxene Hem =hematite Ilm =ilmenite Mag =magnetite.