3094 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
governing its adsorption onto the mineral surface. A certain
amount of oxygen in the pulp is required to allow the for-
mation of di-xanthogen and addition of secondary promot-
ers such as dithiophosphates to provide a synergetic action
with xanthates is also practiced (Chanturia et al., 2012,
Dunne, 2005). Often the impact from the synergetic effect
is an increase in recovery, however sometimes at the expense
of grade.
Since the principal precious metals carrier in the ore
is electrum, it is necessary to likewise focus on the role of
the gold/silver ratio when discussing electrum floatability.
Therefore special attention in this study was devoted to the
Ag grade in the precious metal grains which report to the
concentrate and tailings under the action of the reagents
tested.
Deposit Geology
The Ada Tepe deposit is situated in the East Rhodope
region, a section of the Rhodope metallogenic province,
which hosts a series of volcanic epithermal and base metal
vein deposits. Ada Tepe is characterized by a mineralization
of low-sulfidation epithermal gold mainly composed of
layers of breccia, conglomerates, sandstone, and limestone
(Márton et al., 2010). The sediments are conformed above
a low angle detachment fault also referred as the Tokachka
fault, followed by a metamorphic unit (Marchev et al.,
2004). The sediments are the principal source of gold in
the deposit since they have undergone high tectonic defor-
mation, resulting in high silicification and enrichment in
gold and silver.
The ore mineralogy consists of electrum and subordi-
nate pyrite with some traces of galena, and gold-silver tel-
lurides (Hessite and Petzite). The gangue minerals comprise
silica polymorphs like microcrystalline, sugary quarts, opal-
ine silica, etc., carbonates like calcite, dolomite of siderite
and adularia, compared to adjacent deposits witnessing
high Au/Ag ratio and low base metals content (Marchev et
al., 2003, Marchev et al., 2004, Marinova, 2008, Martón,
2010).
Gold Mineralization
Gold mineralization occurs in two different structures,
the lower zone or ‘Wall’ and the upper zone (Tsintsov and
Ivanov, 2016). The “Wall” is a highly silicified zone with a
massive tabular body located above the detachment fault.
Silicification in this area began with the deposition of mas-
sive white to light grey silica destroying the original rock
except for some gneiss fragments. Average gold content is
7.3 g/t (Marinova, 2008).
The second type of mineralization in the Upper zone are
open space-filling ores which are deposited within east-west
oriented listric faults. They go through the whole sediments
from their detachment fault to the surface. Their thickness
varies between 0.10 to 0.80 m and can reach gold grades
of 638 g/t (Marchev et al., 2003 and Marchev et al.,2004).
Figure 1 presents samples corresponding to high-angle
faults where colloform textures of quartz and adularia alter-
nate with electrum layers bringing increased gold content.
Electrum Morphology and Size
Within the Wall zone the electrum is deposited normally
in interstices of massive microcrystalline quartz, the mor-
phology depending on the inherited geometry of these
interstices. This situation can bring electrum to morph
into complex dendritic forms when associated with quartz.
However, in open spaces when liberated it can show a more
globular shape (Marinova, 2008). The particles found are
moderately flattened and almost isometrical and spherical
(Marinova, 2007).
Electrum from the high-angle veins is deposited in
colloform bands consisting of microcrystalline quartz, adu-
laria, pyrite, and in some circumstances chalcedony. The
thickness of the bands varies from tens of millimeters to 1
cm, rarely being thicker. This vein gold grade normally can
span from 0.5 kg/t up to 7.899 kg/t commonly referred to
as Bonanza gold. Also in these veins, electrum can occupy
50% of the volume (Marchev et al., 2004, Marinova 2008).
The size of electrum varies from 8 to 50 µm at the sur-
face and from 1–4 to 25 µm in depth, 90% of the particles
falling into that range, although in some cases particles
between 100 up to 650 µm can also be observed (Marinova,
2007).
Additional studies have been done on placers from Ada
Tepe, revealing that 95% of the grains were concentrated in
fractions smaller than 100 μm. Some work on placer gold
indicates that the higher gold content (45.32%) is found
below 63 µm, and that the coarsest (100–125 µm) frac-
tion reaches merely a concentration of 5.24% (Tsintsov and
Popov, 2012).
Electrum Au/Ag ratio
Previous work reported that the electrum from the Ada
Tepe has a ratio of Au/Ag of 3/1 (73–76% Au) for sam-
ples with gold content above 1% (Marchev, 2004). From
a flotation recovery perspective one would assume that the
reagents have to be adapted to deal with the various Au/
Ag ratios of the electrum in the ore. This assumption is
based on the fact that gold-silver alloys react with xanthate
at different potentials, with ratios 80/20 Au/Ag reacting at
governing its adsorption onto the mineral surface. A certain
amount of oxygen in the pulp is required to allow the for-
mation of di-xanthogen and addition of secondary promot-
ers such as dithiophosphates to provide a synergetic action
with xanthates is also practiced (Chanturia et al., 2012,
Dunne, 2005). Often the impact from the synergetic effect
is an increase in recovery, however sometimes at the expense
of grade.
Since the principal precious metals carrier in the ore
is electrum, it is necessary to likewise focus on the role of
the gold/silver ratio when discussing electrum floatability.
Therefore special attention in this study was devoted to the
Ag grade in the precious metal grains which report to the
concentrate and tailings under the action of the reagents
tested.
Deposit Geology
The Ada Tepe deposit is situated in the East Rhodope
region, a section of the Rhodope metallogenic province,
which hosts a series of volcanic epithermal and base metal
vein deposits. Ada Tepe is characterized by a mineralization
of low-sulfidation epithermal gold mainly composed of
layers of breccia, conglomerates, sandstone, and limestone
(Márton et al., 2010). The sediments are conformed above
a low angle detachment fault also referred as the Tokachka
fault, followed by a metamorphic unit (Marchev et al.,
2004). The sediments are the principal source of gold in
the deposit since they have undergone high tectonic defor-
mation, resulting in high silicification and enrichment in
gold and silver.
The ore mineralogy consists of electrum and subordi-
nate pyrite with some traces of galena, and gold-silver tel-
lurides (Hessite and Petzite). The gangue minerals comprise
silica polymorphs like microcrystalline, sugary quarts, opal-
ine silica, etc., carbonates like calcite, dolomite of siderite
and adularia, compared to adjacent deposits witnessing
high Au/Ag ratio and low base metals content (Marchev et
al., 2003, Marchev et al., 2004, Marinova, 2008, Martón,
2010).
Gold Mineralization
Gold mineralization occurs in two different structures,
the lower zone or ‘Wall’ and the upper zone (Tsintsov and
Ivanov, 2016). The “Wall” is a highly silicified zone with a
massive tabular body located above the detachment fault.
Silicification in this area began with the deposition of mas-
sive white to light grey silica destroying the original rock
except for some gneiss fragments. Average gold content is
7.3 g/t (Marinova, 2008).
The second type of mineralization in the Upper zone are
open space-filling ores which are deposited within east-west
oriented listric faults. They go through the whole sediments
from their detachment fault to the surface. Their thickness
varies between 0.10 to 0.80 m and can reach gold grades
of 638 g/t (Marchev et al., 2003 and Marchev et al.,2004).
Figure 1 presents samples corresponding to high-angle
faults where colloform textures of quartz and adularia alter-
nate with electrum layers bringing increased gold content.
Electrum Morphology and Size
Within the Wall zone the electrum is deposited normally
in interstices of massive microcrystalline quartz, the mor-
phology depending on the inherited geometry of these
interstices. This situation can bring electrum to morph
into complex dendritic forms when associated with quartz.
However, in open spaces when liberated it can show a more
globular shape (Marinova, 2008). The particles found are
moderately flattened and almost isometrical and spherical
(Marinova, 2007).
Electrum from the high-angle veins is deposited in
colloform bands consisting of microcrystalline quartz, adu-
laria, pyrite, and in some circumstances chalcedony. The
thickness of the bands varies from tens of millimeters to 1
cm, rarely being thicker. This vein gold grade normally can
span from 0.5 kg/t up to 7.899 kg/t commonly referred to
as Bonanza gold. Also in these veins, electrum can occupy
50% of the volume (Marchev et al., 2004, Marinova 2008).
The size of electrum varies from 8 to 50 µm at the sur-
face and from 1–4 to 25 µm in depth, 90% of the particles
falling into that range, although in some cases particles
between 100 up to 650 µm can also be observed (Marinova,
2007).
Additional studies have been done on placers from Ada
Tepe, revealing that 95% of the grains were concentrated in
fractions smaller than 100 μm. Some work on placer gold
indicates that the higher gold content (45.32%) is found
below 63 µm, and that the coarsest (100–125 µm) frac-
tion reaches merely a concentration of 5.24% (Tsintsov and
Popov, 2012).
Electrum Au/Ag ratio
Previous work reported that the electrum from the Ada
Tepe has a ratio of Au/Ag of 3/1 (73–76% Au) for sam-
ples with gold content above 1% (Marchev, 2004). From
a flotation recovery perspective one would assume that the
reagents have to be adapted to deal with the various Au/
Ag ratios of the electrum in the ore. This assumption is
based on the fact that gold-silver alloys react with xanthate
at different potentials, with ratios 80/20 Au/Ag reacting at