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Characterization and identification of Au pathfinder minerals from an artisanal mine site using X-ray diffraction

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Gold-associated pathfinder minerals have been investigated by identifying host minerals of Au for samples collected from an artisanal mining site near a potential gold mine (Kubi Gold Project) in Dunkwa-On-Offin in the central region of Ghana. We find that for each composition of Au powder (impure) and the residual black hematite/magnetite sand that remains after gold panning, there is a unique set of associated diverse indicator minerals. These indicator minerals are identified as SiO 2 (quartz), Fe 3 O 4 (magnetite) and Fe 2 O 3 (hematite), while contributions from pyrite, arsenopyrites, iridosmine, scheelite, tetra-dymite, garnet, gypsum and other sulfate materials are insignificant. This constitutes a confirmative identification of Au pathfinding minerals in this particular mineralogical area. The findings suggest that X-ray diffraction could also be applied in other mineralogical sites to aid in identifying indicator minerals of Au and the location of ore bodies at reduced environmental and exploration costs.
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METALS & CORROSION
Characterization and identification of Au pathfinder
minerals from an artisanal mine site using X-ray
diffraction
Gabriel Nzulu
1
, Per Eklund
1
, and Martin Magnuson
1,
*
1
Department of Physics, Chemistry and Biology, IFM, Thin Film Physics Division, Linköping University, Linköping, Sweden
Received: 20 November 2020
Accepted: 11 December 2020
Published online:
11 January 2021
ÓThe Author(s) 2021
ABSTRACT
Gold-associated pathfinder minerals have been investigated by identifying host
minerals of Au for samples collected from an artisanal mining site near a
potential gold mine (Kubi Gold Project) in Dunkwa-On-Offin in the central
region of Ghana. We find that for each composition of Au powder (impure) and
the residual black hematite/magnetite sand that remains after gold panning,
there is a unique set of associated diverse indicator minerals. These indicator
minerals are identified as SiO
2
(quartz), Fe
3
O
4
(magnetite) and Fe
2
O
3
(hematite),
while contributions from pyrite, arsenopyrites, iridosmine, scheelite, tetra-
dymite, garnet, gypsum and other sulfate materials are insignificant. This con-
stitutes a confirmative identification of Au pathfinding minerals in this
particular mineralogical area. The findings suggest that X-ray diffraction could
also be applied in other mineralogical sites to aid in identifying indicator min-
erals of Au and the location of ore bodies at reduced environmental and
exploration costs.
Introduction
At mineralogical mining sites, the fast location of ore
bodies is paramounted in order to reduce exploration
costs. For this purpose, pathfinding minerals are
important. These minerals act as an aid in the original
ore body discovery. Au that can be traced from the
presence of pathfinding minerals mostly originates as
anhedral crystal assemblies (i.e., without well-de-
fined crystal facets) that naturally exist as single or
polycrystalline mineral aggregates that are usually
found in situ in hydrothermal quartz veins and other
kinds of key deposits in metamorphic and igneous
rocks [1,2].
The most common mineral at most Au mining sites
is pyrite (FeS
2
) that can also be found in oil shales and
coal [3]. Other common minerals at Au mining sites
are arsenopyrite, different forms of silicate minerals
(garnet) and magnetite (Fe
3
O
4
). Both mineralogical
and geochemical information are indispensable to
Handling Editor: M. Grant Norton.
Address correspondence to E-mail: martin.magnuson@liu.se
https://doi.org/10.1007/s10853-020-05681-5
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Metals & corrosion
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provide an initial valuation of the potential ore zone
of an exploration area.
Quantitative interpretation of X-ray diffraction
(XRD) data [4] has long been applied to distinguish
between mineral assemblages, and to define chemical
and mineralogical compositions [5]. Previous XRD
studies of Au and associated minerals have mostly
been performed to determine the grain size mor-
phology and crystallinity [6]. XRD has been used to
conclude that highly hydrated and water-saturated
environments contribute to the migration of Au
within alluvial regimes and on hydrothermal mineral
assemblages [79]. Multivariate statistical analysis
and geostatistical methods have been applied to
identify pathfinding elements [10,11]. Bayari et al. [4]
found that mineralized regolith profiles and mobility
of elements (minerals) in the soil at the Bole–Nangoli
gold belt in the north-eastern Ghana could mainly be
attributed to amorphous mineral phases. Further-
more, Zhao and Pring (2019) [12] studied the mineral
transformation in Au and silver (Ag) in fluids using
the telluride group of minerals associated with Au
and focused on the texture, reaction mechanism and
the kinetics of the oxidation leaching of the tellurides.
Cairns et al. [13] identified topsoil minerals and
pathfinders of Au by considering the fine grain size
and amorphous nature of the minerals. Furthermore,
XRD studies on the influence of thermal stability of
magnetite investigate the effect of temperature on the
phase transitions [1421]. This information is of
importance for the investigation of magnetite as a
pathfinder mineral of Au. As follows from this
background, there is still a need for the characteri-
zation of pathfinding Au-associated minerals by XRD
on residual samples to establish their relationship
and to preserve information about the physiochemi-
cal situations of their origin.
In this work, we investigate the crystal structure of
Au in relation to the corresponding pathfinding
minerals, such as quartz (SiO
2
), Fe
3
O
4
,Fe
2
O
3
, FeS
2
and Fe
1-x
S, collected from an artisanal mining site, i.e.,
a small-scale hand-mining site, in the central region
of Ghana. XRD was used for phase identification and
to obtain structural information including Rietveld
refinement. In addition to the known minerals, we
also identified hematite (Fe
2
O
3
) as an important
pathfinding mineral. The present study can be used
to enable future identification of pathfinding miner-
als for Au exploration.
Experimental details
Description of the field site
The sample collection site is located close to the Kubi
Gold (Adansi Gold) on the outskirt of Dunkwa-On-
Offin, (5°580011.3200 N, 1°46059.1500 W) as shown in
Fig. 1. Dunkwa is the capital of the Upper Denkyira
East Municipal District located in the central region
of Ghana and is drained by several rivers and
streams with the Offin river serving as the main river
source. The location follows the geology of Ghana
which is associated with the antiquity of crystalline
basement rock, volcanic belts and sedimentary
basins. Most Au is found in steeply dipping quartz
veins in shear zones within the Birimian basins with
sulfur-rich minerals, such as arsenopyrites and FeS
2
.
Other sources of Au found are alluvial placer Au in
the Offin river deposits in gravels as well as some
mineralized placer Au reconstituted with minerals,
such as Fe
3
O
4
and Fe
2
O
3
in quartz-pebble conglom-
erates of the Tarkwaian deposits [22]. Extremely
oxidized, weathered or putrefied rock commonly
located at the upper and exposed part of the ore
deposit or mineralized vein known as ‘‘gossan’’ or
iron cap serves as a guide to trace buried Au ore
deposits in this area [23]. The surface oxides of the
minerals at this site are usually red, orange to yel-
lowish-brown color serving as an alteration to the
parent rock or soil.
Sample preparation
Sediment samples that contain Au were extracted
from a depth of 10 m of an artisanal mining site in
Dunkwa-On-Offin. Figure 2shows the depth pro-
file at the mining site. Each sample was divided into
two parts where one portion was refined into pure
solid Au, while the other part of the powder sample
was subjected to Au panning, that is, washing and
magnetic extraction of Fe-based minerals as shown in
Fig. 2. The final three samples (Fig. 3) containing a
solid Au nugget, untreated (impure) Au powder and
the separated black sand-like minerals were exam-
ined by X-ray diffraction. The size of the two powder
crystal samples ranges from 0.05 cm to about 0.2 cm
in the maximum dimension of which most were
hoppered single crystals with an octahedral crystal
structure with a few being of non-octahedral forms.
7660 J Mater Sci (2021) 56:7659–7669
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Figure 1 aGeographical and geological maps of the mining areas
in and around Dunkwa-On-Offin, in the Ashanti Gold Belt of
central Ghana, CC-BY license [24]. The right map indicates
different rock types in four pronounced mining
zones. bPhotograph of sampling collection area of the artisanal
mining site. On-site photographs by G. Nzulu in Nov. 2019.
J Mater Sci (2021) 56:7659–7669 7661
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Magnetizing process
During the panning process, the black sand that
consists of Fe
3
O
4
(magnetite) and Fe
2
O
3
(hematite)
sink to the bottom of the pan. While the black sand
remained in the pan, a strong permanent magnet was
swept over (to and fro) in a circular motion, a couple
of centimeters above the material to maximize the
magnetic susceptibility (induced ferromagnetics in
the Fe
2
O
3
) for easy capture of the magnetite and
Figure 2 aWet residual
sample from the Dunkwa-On-
Offin artisanal mine site.
bRefined part of a sample
into a Au nugget of 22 carats
as measured with a digital
electronic Au purity Analyzer
DH 300 K from VTSYIQI.
cDried sample after coarse
rinsing before fine panning.
Note that the sample contains
white quartz as well as black
magnetite and hematite.
dFinal impure Au after fine
panning. Photographs by G.
Nzulu.
Figure 3 aFinal residual
sample containing Au, sand,
and other magnetic materials
to undergo magnetic
separation. bImpure Fe
2
O
3
/
Fe
3
O
4
minerals. Photographs
by G. Nzulu.
7662 J Mater Sci (2021) 56:7659–7669
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hematite. The process was repeated until there was
no more added material on the surface of the per-
manent magnet. The magnetically captured material
was dominated by magnetite that is a pathfinding
mineral (Fig. 3b) in addition to minority minerals that
can be identified using XRD.
X-ray diffraction measurement
The samples (both solid and powder forms) were
irradiated using a PANAnalyical X’pert [25] powder
diffractometer with a theta–2 theta configuration. The
operating conditions and equipment settings were
Cu-Karadiation wavelength of 1.5406 A
˚(&
8.04 keV); Cu long fine focus tube set to 45 kV and
40 mA; scan step size of 0.033; counting time of
10.16 s per step and scan range between 30 and 100°
in 2 theta scans. The size of the solid bulk Au nugget
was 2 91.6 90.5 cm. The powder samples of
impure Au, Fe
2
O
3
and Fe
3
O
4
had varying grain sizes
(0.05–0.2 cm) and were put on a sample holder
mounted on the diffractometer’s sample mounting
stage such that the crystal face was properly oriented
and closely aligned with the diffractometer circle of
Figure 4 X-ray diffractogram
of the bulk solid Au sample
showing distinct peaks.
Table 1 Structural refinement
parameters of solid bulk Au
from XRD
Symmetry: cubic Space group = Fm-3 m
Wavelength Cu Ka= 1.5406A
˙COD ID: 9008463 Ref. cell volume = 67.83 A
˚
3
Wavelength Cu Kb= 1.5444A
˙Refined cell volume = 67.82 A
˚
3
Observed Calculated Difference
2 theta d h k l 2 theta d 2 theta d
38.211 2.35344 1 1 1 38.185 2.35500 0.026 0.00156
44.394 2.03895 2 0 0 44.393 2.03900 0.001 -0.00005
64.615 1.40276 2 2 0 64.578 1.44200 0.037 -0.03924
77.616 1.22911 3 1 1 77.549 1.23000 0.067 -0.00089
81.761 1.17696 2 2 2 81.724 1.17740 0.037 -0.00044
98.238 1.01882 4 0 0 98.137 1.01960 0.101 -0.00078
Cell
Parameters Refinement Reference Error
a(A
˚) 4.07803 ±5.7603E-5 4.07825 -0.00022
b(A
˚) 4.07803 ±5.7603E-5 4.07825 -0.00022
c(A
˚) 4.07803 ±5.7603E-5 4.07825 -0.00022
Alpha (°) 90.0000 90.0000
Beta (°) 90.0000 90.0000
Gamma (°) 90.0000 90.0000
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the goniometer. The XRD data were quantitatively
analyzed by Rietveld refinement using the MAUD
software [26,27].
Results and discussion
Figure 4shows an X-ray diffractogram of the Au
nugget sample in Fig. 2b with the result of Rietveld
refinement assuming pure Au together with the
residual of the fit [28]. The six pronounced peaks in
the diffractogram are indexed as a cubic fcc Au
structure (Fm-3 m space group) with lattice parame-
ter of a= 4.079 A
˚. Table 1ists the full assigned
observed peak list as well as the resulting crystallo-
graphic parameters from the refinement. These are in
agreement with literature assignments for Au
[28,29].
Figure 5shows an X-ray diffractogram of the
impure powder Au sample shown in Fig. 3a. Table 2
lists the refined crystallographic parameters of Au
and the pathfinder minerals identified from powder
Au samples. These data are in agreement with ref-
erence data [2732]. The diffractogram from the
unrefined powder sample shows the presence of
other minerals, that is, pathfinder minerals for Au.
These are dominated by SiO
2
(quartz) with some
Fe
3
O
4
(magnetite).
The lattice parameter of the SiO
2
in the impure Au
were found to be a=4.91A
˚and c= 5.43 A
˚(space
group P3221), consistent with reference data [30].
This sample also contains Fe
3
O
4
(cubic, space group
Fd-3 m) with a lattice parameter of 8.36 A
˚, consistent
with literature data [27].
Figure 6shows an X-ray diffractogram from the
residual black sand after Au panning. The diffraction
peaks of this sample were identified as the crystalline
structure of Fe
2
O
3
(hematite). Table 3lists the
diffraction peaks and crystallographic parameters
determined from the Rietveld refinement of Fe
2
O
3
.
This is in accordance with literature and reference
data [32,33]. The crystal structure of Fe
2
O
3
is rhom-
bohedral with a space group R-3c and lattice constant
of 5.0991 A
˚[34,35].
Comparing Figs. 4and 5, it can be seen that the
latter sample contains Au together with pathfinder
minerals in the form of magnetite and quartz. The
most abundant mineral observed in the diffraction
pattern of the impure powder Au sample is SiO
2
(quartz) having three distinct peaks at 2h= 40.284°,
67.957°and 90.818°corresponding to {111}, {212} and
{312} crystalline planes of the SiO
2
phase, respec-
tively. The refined pattern of SiO
2
shown in Fig. 5is
in agreement with the literature data in refs [3639],
which also holds true for the moderate amount of
magnetite present [27]. This shows that impure Au or
final concentrate (non-pure Au) have a high quantity
(percentage) of pathfinder minerals as impurities.
Note that Au atoms easily substitute with Ag atoms
forming an alloy with the same fcc crystal structure
and that it is impossible to distinguish pure Au from
an Au–Ag alloy with XRD.
The diffractogram in Fig. 6contains major peaks at
2h= 32.609°, 34.915°, 38.658°, 40.196°, 48.618°,
Figure 5 X-ray diffractogram
of the impure powder Au with
other pathfinding Au minerals.
7664 J Mater Sci (2021) 56:7659–7669
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53.966°, 62.990°, 69.975°, 80.837°, 83.475°and 91.533°
identified as {101}, {110}, {006}, {113}, {024}, {116},
{214}, {208}, {128}, {134} and {042} crystalline planes of
Fe
2
O
3
(hematite), respectively. These refined peaks
are in good agreement with the rhombohedral
structure of Fe
2
O
3
[32,33].
Generally, including possible microstrain in the
Rietveld refinement has a negligible effect on the
convergence of the fit (residual), indicating that the
samples are essentially strain-free. The results from
the impure Au powder sample indicate that SiO
2
(quartz) is the dominant impurity mineral serving as
the host rock containing all the pathfinder minerals at
Table 2 Structural refinement parameters of impure Au powder sample containing other pathfinder minerals
(a) Impure Au parameters [52.23%] COD ID: 9008463
Initial symmetry: cubic Space group = Fm-3 m Ref. cell volume = 67.830 A
˚
3
Refined cell volume = 67.832 A
˚
3
Observed Calculated Difference
2 theta d h k l 2 theta d 2 theta d
38.178 2.35539 1 1 1 38.185 2.35500 -0.007 0.00039
44.641 2.02824 2 0 0 44.393 2.03900 0.248 -0.01076
64.615 1.44126 2 2 0 64.578 1.44200 0.037 -0.00074
77.617 1.22910 3 1 1 77.549 1.23000 0.068 -0.00009
81.728 1.17735 2 2 2 81.724 1.17740 0.004 -0.00005
98.171 1.01934 4 0 0 98.137 1.01960 0.038 -0.00026
Cell
Parameters Refinement Reference Error
a(A
˚) 4.07830 ±4.7828E-4 4.07825 5.0 E-5
b(A
˚) 4.07830 ±4.7828E-4 4.07825 5.0 E-5
c(A
˚) 4.07830 ±4.7828E-4 4.07825 5.0 E-5
Alpha (°) 90.0000 90.0000
Beta (°) 90.0000 90.0000
Gamma (°) 90.0000 90.0000
(b) SiO
2
structural parameters [33.89%] COD ID: 1538064
Crystal system: hexagonal Space group = P3221 Ref. cell volume = 112.979 A
˚
3
Refined cell volume = 113.36 A
˚
3
Observed Calculated Difference
2 theta d h k l 2 theta d 2 theta d
40.284 2.23698 1 1 1 40.300 2.23613 0.026 0.00085
67.957 1.37829 2 1 2 67.744 1.38210 0.001 -0.00381
90.818 1.08167 3 1 2 90.831 1.08155 0.067 0.00012
Cell
Parameters Refinement Reference Error
a(A
˚) 4.90970 ±1.9E-3 4.91304 -0.00334
b(A
˚) 4.90970 ±1.9E-3 4.91304 -0.00334
c(A
˚) 5.43023 ±3.7E-3 5.40463 0.02557
Alpha (°) 90.00 ±0.00 90.0000 0.0000
Beta (°) 90.00 ±0.00 90.0000 0.0000
Gamma (°) 120.00 ±0.00 90.0000 0.0000
(c) Fe
3
O
4
structural parameters. [13.88%] COD ID: 9005813
Crystal system: cubic Space group = Fd-3 m Ref. cell volume = 583.816 A
˚
3
Refined cell volume = 584.277 A
˚
3
Observed Calculated Difference
2 theta d h k l 2 theta d 2 theta d
33.800 2.64979 1 0 4 33.153 2.70000 0.647 -0.05020
35.571 2.52190 1 1 0 35.612 2.51900 -0.041 0.00290
38.813 2.31830 0 0 6 39.277 2.29200 -0.464 0.02630
40.317 2.23523 1 1 3 40.855 2.20700 -0.538 0.02820
44.002 2.05620 2 0 2 43.519 2.07790 0.483 -0.02170
49.843 1.82806 0 2 4 49.480 1.84060 0.363 -0.01250
58.059 1.58740 0 1 8 57.590 1.59920 0.469 -0.01180
Cell
Parameters Refinement Reference Error
a(A
˚) 8.36 ±0.00 8.3578 0.0022
b(A
˚) 8.36 ±0.00 8.3578 0.0022
c(A
˚) 8.36 ±0.00 8.3958 0.0022
Alpha (°) 90.00 ±0.00 90.0000 0.0000
Beta (°) 90.00 ±0.00 90.0000 0.0000
Gamma (°) 90.00 ±0.00 90.0000 0.0000
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the mining site. It is known that SiO
2
is a so-called
gangue mineral (i.e., a commercially nonvaluable
mineral that surrounds or is mixed with a valuable
mineral) in hydrothermal ore veins [40], to preserve
information about the physiochemical situations of
the origin of the veins and to understand the forma-
tion of mineral deposits. These dominant SiO
2
species
contain structural defects that favor mineral infusion
due to underlying conditions and geological pro-
cesses, such as crystallization, metamorphism, alter-
ations, changes in crystallization temperatures and
precipitation [4143].
Au associated with Fe
3
O
4
is mostly formed in
skarns of granular magnetite usually found in contact
with metamorphosed areas with magma intrusion
into carbonate or silico-carbonate rocks that also
Figure 6 X-ray diffractogram
of the Fe
2
O
3
mineral.
Table 3 Structural refinement
parameters of Fe
2
O
3
powder
sample
Crystal system: rhombohedral Space group = R-3c
COD ID: 900139 Ref. cell volume = 302.722 A
˚3 Refined cell volume = 313.870 A
˚3
Observed Calculated Difference
2 theta d h k l 2 theta d 2 theta d
32.609 2.74380 1 0 1 33.158 2.70000 -0.549 0.04380
34.915 2.56768 1 1 0 35.612 2.51900 -0.697 -0.04868
38.658 2.32725 0 0 6 39.277 2.29200 -0.619 0.03525
40.196 2.24167 1 1 3 40.855 2.20700 -0.659 0.03467
48.618 1.87122 0 2 4 49.480 1.84060 -0.862 0.03062
53.966 1.69772 1 1 6 54.091 1.69410 -0.125 0.00362
62.990 1.47447 2 1 4 62.451 1.48590 0.539 -0.01143
69.975 1.34340 2 0 8 69.601 1.34970 0.374 -0.00630
80.837 1.18806 1 2 8 80.711 1.18960 0.126 -0.00154
83.475 1.15710 1 3 4 84.916 1.14110 -1.441 0.01600
91.533 1.07508 0 4 2 91.345 1.07680 0.188 -0.00172
Cell
Parameters Refinement Reference Error
a(A
˚) 5.0991 ±1.4E-3 5.0380 0.0611
b(A
˚) 5.0991 ±1.4E-3 5.0380 0.0611
c(A
˚) 14.0767 ±5.2E-3 13.7720 0.3047
Alpha (°) 90.00 ±0.00 90.0000 0.0000
Beta (°) 90.00 ±0.00 90.0000 0.0000
Gamma (°) 90.00 ±0.00 120.0000 0.0000
7666 J Mater Sci (2021) 56:7659–7669
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consist of garnet and silicate minerals, among others.
The residual black sand together with other dense
minerals is considered to be ore that is left over
during Au refinement and washing at riverbanks
when recovering its Au content [44]. This shows that
two of the three most common iron ore minerals;
Fe
3
O
4
and Fe
2
O
3
are widely spread within the mining
site and contribute to the Au host minerals alongside
SiO
2
. In a near-surface environment (oxide area)
Fe
2
O
3
act as the gangue mineral and can be trans-
formed to Fe
3
O
4
depending on the environmental
conditions such as high temperature, oxidation, and
pH [45]. The same color of Fe
2
O
3
in comparison with
black Fe
3
O
4
makes it difficult to distinguish between
the two in branded iron formations and standing
water [44,46]. It is likely that during the formation of
Fe-oxides in the alluvial regime at the Dunkwa–Kubi
geological site, Au is internally captured within
structures associated with Fe
2
O
3
(hematite) that acts
as crusts in saprolite and laterite environments. These
minerals reveal information about the physiochemi-
cal conditions of the origin of structures (structural
defects) useful for the understanding of mineral
deposit formations.
Conclusions
This study has revealed that sediments and black
sands containing Au are associated with pathfinding
minerals in impure compositions. This is indicative
that Au and pathfinding minerals are all deposited in
nature during hydrothermal activation. The XRD
analysis identified Au, SiO
2
(quartz), Fe
3
O
4
(mag-
netite) and Fe
2
O
3
(hematite). From the XRD patterns,
the impure Au and Fe
2
O
3
samples can be attributed
to the decomposition and transformation of these
indicator minerals. Also, the surface (oxide zones)
mineralization is altered by Fe
2
O
3
as one of the
indicator minerals apart from the garnet and the
gangue mineral SiO
2
to host Au with other pathfinder
minerals beneath the surface.
These results are of importance for the mining
industry to underscore the usefulness of XRD in
studying soil and sand sediments from mining sites
by identifying pathfinder minerals of Au in potential
geological sites.
Acknowledgements
We acknowledge support from the Swedish
Government Strategic Research Area in Materials
Science on Functional Materials at Linko
¨ping
University (Faculty Grant SFO-Mat-LiU No. 2009
00971). M.M. also acknowledges financial support
from the Swedish Energy Research (Grant No.
43606-1) and the Carl Tryggers Foundation
(CTS20:272, CTS16:303, CTS14:310). Asante Gold
Corporation is acknowledged for funding G. K. N.’s
industrial PhD studies at Linko
¨ping University,
Sweden.
Funding
Open Access funding provided by Linko
¨ping
University.
Compliance with ethical standards
Conflict of interest P. E. and M. M. declare no
competing financial interest. G. K. N.’s industry PhD
studies are funded by Asante Gold Corporation.
Asante Gold Corporation or G.K.N. have no potential
financial benefit from this study. The samples in this
study are from an artisanal mining site open to the
indigenous public.
Open Access This article is licensed under a Crea-
tive Commons Attribution 4.0 International License,
which permits use, sharing, adaptation, distribution
and reproduction in any medium or format, as long
as you give appropriate credit to the original
author(s) and the source, provide a link to the Crea-
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permitted use, you will need to obtain permission
directly from the copyright holder. To view a copy of
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References
[1] Cook RB, Coogan ER, Neumeier G, Staebler GA (eds)
(2003) Gold: The noble mineral. ExtraLapis English no. 5.
Lapis International, East Hampton CT
[2] Chapman R, Leake B, Styles M (2002) Microchemical
characterization of alluvial gold grains as an exploration tool.
Gold Bull 35(2):53–65
[3] Bhargava SK, Garg A, Subasinghe ND (2009) In situ high-
temperature phase transformation studies on pyrite, Elsevier.
Fuel 88:988–993
[4] Chung FH (1974) Quantitative interpretation of X-ray
diffraction patterns of mixtures. I. Matrix-flushing method
for quantitative multicomponent analysis. J Appl Crystallogr
7:519–525
[5] Bayari EE, Foli G, Gawu SKY (2019) Geochemical and
pathfinder elements assessment in some mineralized regolith
profiles in Bole-Nangodi gold belt in north-eastern Ghana.
Environ Earth Sci 78:268
[6] Rakovan J, Gasbarro N, Nakotte H, Kothapalli K, Vogel SC
(2009) Characterization of gold crystallinity by diffraction.
Methods Rocks Miner 84:54–61
[7] Naletoa JLC, Perrottaa MM, da Costac FG, de Souza Filhob
CR (2019) Point and imaging spectroscopy investigations on
the Pedra Branca orogenic gold deposit, Troia Massif,
Northeast Brazil: Implications for mineral exploration in
amphibolite metamorphic-grade terrains, Elsevier. Ore Geol
Rev 107:283–309
[8] Hong H, Tie L (2005) Characteristics of the minerals asso-
ciated with gold in the shewushan supergene gold deposit,
China. Clays Clay Miner 53(2):162–170
[9] Mann AW (1984) Mobility of gold and silver in lateritic
weathering profiles: some observations from Western Aus-
tralia. Econ Geol 79(1):38–49
[10] Nude PM, Asigri JM, Yidana SM, Arhin E, Foli G, Kutu JM
(2012) Identifying pathfinder elements for gold in multi-
element soil geochemical data from the Wa-Lawra Belt
Northwest Ghana: a multivariate statistical approach. Int J
Geosci 3:62–70
[11] Lindagato P, Li Y, Yang G, Duan F, Wang Z (2018) Appli-
cation of geostatistical analyst methods in discovering con-
cealed gold and pathfinder elements as geochemical
anomalies related to ore mineralization. Geologos
24(2):95–109
[12] Zhao J, Pring A (2019) Mineral transformations in gold-
silver tellurides in the presence of fluids: nature and exper-
iment. Minerals 9(3):167
[13] Cairns CJ, McQueen KG, Leah PA (2001) Mineralogical
control on element dispersion in regolith over two
mineralized shear zones near the Peak, Cobar, New South
Wales. J Geochem Explore 72:1–21
[14] Roberts AP, Chang L, Heslop D, Florindo F, Larrasoan˜a JC
(2012) Searching for single domain magnetite in the
‘pseudo-single-domain’’ sedimentary haystack: implications
of biogenic magnetite preservation for sediment magnetism
and relative paleointensity determinations. J Geophys Res
117:B08104
[15] Pati SS, Philip J (2013) Effect of cation trapping on thermal
stability of magnetite nanoparticles. J Nanosci Nanotechnol
13:1–10
[16] Gilbert B, Katz JE, Denlinger JD, Yin Y, Falcone R, Way-
chunas GA (2010) Soft X-ray spectroscopy study of the
electronic structure of oxidized and partially oxidized mag-
netite nanoparticles. J Phys Chem C 114:21994–22001
[17] Pati SS, Gopinath S, Panneerselvam G, Antony MP, Philip J
(2012) High temperature phase transformation studies in
magnetite nanoparticles doped with CO
2
ion. J Appl Phys
112:054320
[18] Wang Z, Luan W, Huang J, Jiang C (2011) XRD investi-
gation of microstructure strengthening mechanism of shot
peening on laser hardened 17–4PH. Mater Sci Eng A
528:6417–6425
[19] Rosas-Casarez CA, Arredondo-Rea SP, Cruz-Enrı´quez A,
Corral-Higuera R, Go´ mez-Sobero´ n JM, Medina-Serna TDJ
(2018) Influence of size reduction of fly ash particles by
grinding on the chemical properties of geopolymers. Appl
Sci 8:365
[20] Zhang W, Qian H, Sun Q, Chen Y (2015) Experimental
study of the effect of high temperature on primary wave
velocity and microstructure of limestone. Environ Earth Sci
74:5739–5748
[21] Zhang Y, Sun Q, Geng J (2017) Microstructural characteri-
zation of limestone exposed to heat with XRD SEM and TG-
DSC. Mater Charact 134:285–295
[22] Kesse GO (1984) The occurrence of gold in Ghana. In:
Foster RP (ed) Gold ‘82: the geology, geochemistry and
genesis of gold deposits. Geological Society of Zimbabwe,
pp 648–650
[23] Kim BJ, Cho KH, Lee SG, Park C-Y, Choi NC, Lee S (2018)
Effective gold recovery from near-surface oxide zone using
reductive microwave roasting and magnetic separation.
Metals 8:957. https://doi.org/10.3390/met8110957
[24] https://commons.wikimedia.org/wiki/Category:Maps_of_Gh
ana#/media/File:Un-ghana.png
[25] https://rsc.aux.eng.ufl.edu/_files/documents/2714.pdf/
[26] Wechsler BA, Lindsley DH, Prewitt CT (1984) Crystal
structure and cation distribution in titanomagnetites (Fe3-
xTixo4). Am Mineral 69:754
7668 J Mater Sci (2021) 56:7659–7669
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
[27] Finger LW, Hazen RM, Hofmeister AM (1986) High-pres-
sure crystal chemistry of spinel (MgAl2O4) and magnetite
(Fe
3
O
4
): comparisons with silicate spinels Sample: P = 13
kbar. Phys Chem Miner 13:215–220
[28] Swanson HE, Tatge E (1953) Standard X-ray diffraction
powder patterns. Natl. Bur. Stand. (U.S.), Circ. 539, U.S.
Govt. Print. Off. Washington, D.C., vol I, p 23 and 33
[29] Wyckoff RWG (1963) Cubic closest packed, ccp, structure
database. In: Crystal structures, 2nd edn, vol 1. Interscience
Publishers, Wiley, New York, London, Sydney, pp 7–83
[30] Kern A, Eysel W (1993) Mneralogisch-Petrograph ICDD
Grant-in-Aid. Inst Univ, Heodelberg, Germany
[31] Hanic F, Sumichrast L (1974) Alpha-beta phase transition in
quartz. Silikaty 18:1–9
[32] Morris MC et al (1981) Standard X-ray diffraction powder
patterns. Nat. Bur. Stand. (U.S.), Monogr. 25 — Sec. 18,
p 37, CODEN:NBSMA6, Iron oxide (hematite), a-Fe
2
0
3
[33] Blake RL, Hessevick RE, Zoltai T, Finger LW (1966)
Refinement of the hematite structure. Am Miner 51:123–129
[34] Lutterotti L (2010) Total pattern fitting for the combined
size-strain-stress-texture determination in thin film diffrac-
tion. Nuclear Inst Methods Phys Res B 268:334–340
[35] Lutterotti L, Bortolotti M, Ischia G, Lonardelli I, Wenk H-R
(2007) Rietveld texture analysis from diffraction images.
Z Kristallogr Suppl 26:125–130
[36] Kihara K (1990) An X-ray study of the temperature depen-
dence of the quartz structure. Eur J Mineral 2:63–77
[37] Trostel LJ, Wynne DJ (1940) Determination of quartz (free
silica) in refractory clays. J Am Ceram Soc 23:18–22
[38] Calvert SE (1966) Accumulation of diatomaceous silica in
the sediments of the Gulf of California. Geol Soc Am Bull
77:569–596
[39] Adams FV, Peter A, Joseph IV, Sylvester OP, Mulaba-Ba-
fubiandi AF (2019) Purification of crude oil contaminated
water using fly ash/clay Elsevier. J Water Process Eng
30:100471
[40] Go¨tze J (2009) Chemistry, textures and physical properties
of quartz-Geological interpretation and technical application.
Mineral Mag 73:645–671
[41] Rusk B (2014) Quartz cathodoluminescence: textures, trace
elements, and geological applications. In: Coulson IM (ed)
Cathodoluminescence and its application to geoscience.
Mineralogical Association of Canada, Que´bec City, QC,
Canada, pp 127–141
[42] Go¨tte T, Ramseyer K (2012) Trace element characteristics,
luminescence properties and real structure of quartz. In:
Go¨tze J, Mo¨ ckel R (eds) Quartz: deposits, mineralogy and
analytics. Springer, Berlin/Heidelberg, Germany,
pp 256–285
[43] Weil JA (1993) A review of the EPR spectroscopy of the
point defects in a-quartz: the decade 1982–1992. In: Deal
BE, Helms CR (eds) Physics and chemistry of SiO2 and the
Si-SiO2 interface 2. Plenum Press, New York, NY, USA,
pp 131–144
[44] Yuan K, Lee SS, Cha W, Ulvestad A, Kim H, Abdilla B,
Sturchio NC, Fenter P (2019) Oxidation induced strain and
defects in magnetite crystals. Nat Commun 10:703
[45] Knudsen M, Madsen MB, Kakane V, Awadzi T, Hviid SF,
Breuning-Madsen H (2000) Comparison of magnetic parti-
cles in airborne dust on Mars and Harmattan dust from south
of Sahara, geografisk Tidsskrift. Dan J Geogr 100:1–6
[46] Cornell RM, Schwertmann U (1996) The iron oxides. Wiley,
Germany, pp 4–26
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... The binding energy (BE) scale was calibrated using the ISO-certified procedure, with the spectra referenced to the Fermi edge in order to circumvent discrepancies associated with employing the C 1s peak from adventitious carbon [55]. Prior to the XPS core and valence band measurements, the structural properties were investigated [56]. From the XRD analysis [56], Au, quartz (SiO2), magnetite (Fe3O4), and hematite (Fe2O3) were identified in these samples. ...
... Prior to the XPS core and valence band measurements, the structural properties were investigated [56]. From the XRD analysis [56], Au, quartz (SiO2), magnetite (Fe3O4), and hematite (Fe2O3) were identified in these samples. ...
... This higher BE (708.4 eV) and lower for marcasite FeS2 is in closed agreement with the peak at (706.9 eV) from the XPS spectra in Figure 7, which is consistent with reference data [70] for FeS2. It can be deduced that the deficient main Fe 2p3/2 peak in the samples from Kubi Gold project contain pure metal Fe and FeS2, since FeS2 is one of the main indicator minerals in the mining area [56]. As telluric iron is extremely rare, we anticipate that the pure metallic Fe observed by our XPS measurements originates from iron oxides are readily reduced in the argon monomer sputter cleaning process. ...
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... The binding energy (BE) scale was calibrated using the ISO-certified procedure, with the spectra referenced to the Fermi edge in order to circumvent discrepancies associated with employing the C 1s peak from adventitious carbon [55]. Prior to the XPS core and valence band measurements, the structural properties were investigated [56]. After XRD analysis [56], Au, quartz (SiO 2 ), magnetite (Fe 3 O 4 ), and hematite (Fe 2 O 3 ) were identified in these samples. ...
... Prior to the XPS core and valence band measurements, the structural properties were investigated [56]. After XRD analysis [56], Au, quartz (SiO 2 ), magnetite (Fe 3 O 4 ), and hematite (Fe 2 O 3 ) were identified in these samples. ...
... This higher BE (708.4 eV) and the lower BE for marcasite FeS 2 is in close agreement with the peak at (706.9 eV) from the XPS spectra in Figure 7, which is consistent with reference data [70] for FeS 2 . It can be deduced that the deficient main Fe 2p 3/2 peak in the samples from the Kubi Gold project contains pure metal Fe and FeS 2 , since FeS 2 is one of the main indicator minerals in the mining area [56]. As telluric iron is extremely rare, we assume that the pure metallic Fe observed by our XPS measurements originates from iron oxides that are readily reduced in the argon monomer sputter cleaning process. ...
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The study area in the West Junggar Basin is known to be rich in hydrothermal gold deposits and occurrences, even though there has been minimum exploration in the area. It is here hypothesised that this area could host more gold deposits if mineral exploration methods were to be reinforced. This research is aimed at identifying geochemical anomalies of Au, and determining possible factors and conditions which facilitate the formation of anomalies by referring to As and Hg as gold pathfinders. Geostatistical analyst techniques have been applied to 9,852 stream sediments and bedrock data collected on a total surface of 1,280 km ² of West Junggar, Xinjiang (northwest China). The kriging interpolation and quantile-quantile plot methods, combined with statistical methods, successfully identified both Au and its pathfinders’ anomalies. In the present study, median was considered as background values (10.2 ppm for As, 9.13 ppb for Hg and 2.5 ppb for Au), whereas the 95 th percentile were threshold values (28.03 ppm for As, 16.71 ppb for Hg and 8.2 ppb for Au) and values greater than thresholds are geochemical anomalies. Moreover, the high concentrations of these three discovered elements are caused primarily by hydrothermal ore mineralisation and are found to be controlled mainly by the Hatu and Sartohay faults of a northeast-southwesterly direction as well as their related secondary faults of variable orientation, which facilitate the easy flow of hydrothermal fluids towards the surface resulting in the formation of geochemical anomalies. Most of anomalies concentration of Au are found near the mining sites, which indicates that the formation of new Au anomalies is influenced by current or previous mining sites through geological or weathering processes. In addition, the low concentration of gold and its pathfinders found far from active gold mine or faults indicates that those anomalies are formed due to primary dispersion of hosting rock.
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The Pedra Branca gold deposit is a recent discovery conducted by private exploration companies in the Troia Massif of the northern Borborema Province, Northeast Brazil. It comprises an orogenic gold deposit hosted by the amphibolite-facies Serra das Pipocas greenstone belt. Airborne hyperspectral images (ProSpecTIR-VNIR-SWIR system) covering the Pedra Branca deposit as well as spectroscopic data (ASD-Fieldspec and SisuCHEMA instruments) from representative rock samples in the area were used in this study to investigate the spectro-mineralogical patterns of alteration minerals at both district and deposit scales, respectively. The spectroscopic data were integrated with geological information from the deposit, and also with X-ray powder diffraction and petrographic analyses, in order to reveal alteration footprints that could guide gold exploration targeting in the region. The results indicate the occurrence of a main hydrothermal calc-silicate alteration in ferromagnesian host rocks, consistent with proximal alteration assemblages found in amphibolite-facies gold deposits. White mica compositional trends suggest a later hydrothermal alteration that overprinted the pre-existing mineral assemblages and crystallized Al-rich white mica in distal zones and Al-poor white mica in the ore zone. Reflectance spectroscopy analyses of outcrop samples indicate that well-ordered kaolinite occurs as a weathering product of Al-poor white mica-bearing samples, and therefore could be used as a proxy to mineralization at the deposit scale. Mineral maps produced by processing airborne hyperspectral images, combined with soil geochemical anomalies, further support the notion that well-ordered kaolinite can be used as a proxy to mineralization in weathered ferromagnesian host rocks. Target areas for gold exploration can be defined by airborne hyperspectral data based on the identification of spectral mixtures of nontronite and well-ordered kaolinite. The mineral and physicochemical trends identified in this study set an important baseline for mineral exploration of amphibolite-facies orogenic gold deposits in greenstone belt terranes. The mineral guides defined here can be sensed by VNIR-SWIR hyperspectral sensors at multiple scales using portable, core scanning, wall-imaging, airborne or satellite-borne instruments, respectively.
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