2630 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
development of new tungsten mining projects worldwide,
including in the EU (Suárez Sánchez et al., 2015). The Los
Santos mine in Spain started operations in 2008, produc-
ing 750 tons of tungsten in 2018, with estimated reserves
of 3.58 million tons averaging 0.23% WO3 (Wheeler,
2015). Additionally, the Hemerdon mine in the UK started
operations in 2015, with estimated reserves of 35.7 million
tons of ore at 0.18% WO3 (Yang, 2018). However, despite
producing 900 tons of tungsten in 2018, the Hemerdon
mine ceased trading operations in October 2018, primarily
due to a decrease in tungsten prices and poor processing
performances.
Securing tungsten supply is therefore of paramount
interest for the EU and the USA since tungsten consump-
tion is set to increase over the next few years for strategic
applications such as defense. Apart from recycling, tungsten
is exclusively extracted from wolframite and scheelite, the
two main tungsten-bearing minerals encountered in rocks
(Audion and Labbé, 2012 Pitfield et al., 2011 Schmidt,
2012a, 2012b Yang, 2018). While wolframite is generally
encountered in quartz-veins deposits, scheelite is tradition-
ally found in skarn deposits, which are generated through
the alteration of calcite or dolomite marble into calcic and/
or magnesium silicates (Kwak, 1987). Skarn deposits are
found across a diverse range of geological settings, rang-
ing from Precambrian to Cenozoic eras. However, most
economically significant skarn deposits are relatively young
and linked to magmatic hydrothermal activity associated
with plutonism in orogenic belts (Einaudi and Burt, 1982).
Conventionally, skarns originate during contact metamor-
phism, involving various metasomatic processes driven by
fluids of magmatic, metamorphic, meteoric, and/or marine
origin (Meinert et al., 2005). Tungsten skarns commonly
exhibit average WO3 grades ranging from 0.3% to 1.5%,
significantly surpassing other major types of tungsten
deposits (Yang, 2018). Despite lower tonnages compared
to other tungsten deposit types, many tungsten skarns
hold economic significance (Foucaud et al., 2020). They
have been continuously mined for decades, contributing to
the majority of the world’s tungsten production (70%)
during certain periods, such as the 1980s (Kwak, 1987).
The Xianglushan and Shizhuyuan deposits, considered
as tungsten skarns, contribute over 11,000 tons (14%)
to the annual global tungsten production (Cheng, 2016
Dai et al., 2018 Lu et al., 2003). Additionally, the Nui
Phao and Vostok 2 mines, together representing 10% of
world tungsten production, also exploit tungsten skarns
(Masan Resources, 2012 Soloviev and Krivoshchekov,
2011). Consequently, tungsten skarns play a significant role
in the current tungsten production, with some estimates
suggesting they account for over 40% of global tungsten
reserves (Pitfield et al., 2011 Schubert et al., 2006 Werner
et al., 1998). In skarns, scheelite presents a fine liberation
size and tends to form slime during comminution stages
since it is a brittle mineral. Due to these constraints, schee-
lite is traditionally beneficiated by froth flotation, which
provides very satisfactory recovery and grade (Kupka and
Rudolph, 2018). However, gangue calcium-bearing miner-
als such as calcite, dolomite, fluorite, and apatite are very
common in skarn deposits and can represent more than
15% of the total ore, raising significant selectivity issues.
These difficulties are due to common surface properties gen-
erated by Ca2+, WO42–, CO32– and PO43– on the surface.
Although good WO3 grades and recoveries were obtained
using fatty acids as collectors and a combination of sodium
silicate and sodium carbonate as depressants (Foucaud et
al., 2019b), the low selectivity of fatty acids caused by the
chemisorption of sodium oleate onto Ca2+ of the calcium
minerals surface generally results in a non-selective flota-
tion (Atademir et al., 1981 Marinakis and Kelsall, 1987
Marinakis and Shergold, 1985 Rao and Forssberg, 1991).
Hence, considering that a contrast exists in terms of zeta
potential between scheelite and the problematic calcium
minerals, this study aims at testing an amine-based room
temperature flotation for tungsten skarn ores. The sample
considered here, coming from the Tabuaço northern-Por-
tuguese deposit, is a fine-grained tungsten skarn composed
of silicates, fluorite, apatite, and scheelite, and represents
a typical archetype of world tungsten skarns in terms of
textural, chemical, and mineralogical features. To demon-
strate the feasibility of this new process, we used a combi-
nation of flotation tests and surface studies. Different pH,
collector concentrations, and depressant concentrations are
tested. The different recoveries are compared to find the
best conditions for maximizing it and reject calcium-bear-
ing minerals.
MATERIAL AND METHODS
Sampling
A sampling campaign allowed acquiring 1 ton of rocks to
conduct the mineral processing tests. The samples were as
representative as possible of the orebody and were used to
conduct a deep mineralogical and textural characterization
stage prior to the tests. Besides, at each stage of the process,
representative samples were selected using a riffle splitter.
Sampling
The samples were crushed in three successive jaw crushers
and a gyratory crusher to obtain a –4 mm size fraction. To
reach the liberation mesh, this product was wet sieved at
development of new tungsten mining projects worldwide,
including in the EU (Suárez Sánchez et al., 2015). The Los
Santos mine in Spain started operations in 2008, produc-
ing 750 tons of tungsten in 2018, with estimated reserves
of 3.58 million tons averaging 0.23% WO3 (Wheeler,
2015). Additionally, the Hemerdon mine in the UK started
operations in 2015, with estimated reserves of 35.7 million
tons of ore at 0.18% WO3 (Yang, 2018). However, despite
producing 900 tons of tungsten in 2018, the Hemerdon
mine ceased trading operations in October 2018, primarily
due to a decrease in tungsten prices and poor processing
performances.
Securing tungsten supply is therefore of paramount
interest for the EU and the USA since tungsten consump-
tion is set to increase over the next few years for strategic
applications such as defense. Apart from recycling, tungsten
is exclusively extracted from wolframite and scheelite, the
two main tungsten-bearing minerals encountered in rocks
(Audion and Labbé, 2012 Pitfield et al., 2011 Schmidt,
2012a, 2012b Yang, 2018). While wolframite is generally
encountered in quartz-veins deposits, scheelite is tradition-
ally found in skarn deposits, which are generated through
the alteration of calcite or dolomite marble into calcic and/
or magnesium silicates (Kwak, 1987). Skarn deposits are
found across a diverse range of geological settings, rang-
ing from Precambrian to Cenozoic eras. However, most
economically significant skarn deposits are relatively young
and linked to magmatic hydrothermal activity associated
with plutonism in orogenic belts (Einaudi and Burt, 1982).
Conventionally, skarns originate during contact metamor-
phism, involving various metasomatic processes driven by
fluids of magmatic, metamorphic, meteoric, and/or marine
origin (Meinert et al., 2005). Tungsten skarns commonly
exhibit average WO3 grades ranging from 0.3% to 1.5%,
significantly surpassing other major types of tungsten
deposits (Yang, 2018). Despite lower tonnages compared
to other tungsten deposit types, many tungsten skarns
hold economic significance (Foucaud et al., 2020). They
have been continuously mined for decades, contributing to
the majority of the world’s tungsten production (70%)
during certain periods, such as the 1980s (Kwak, 1987).
The Xianglushan and Shizhuyuan deposits, considered
as tungsten skarns, contribute over 11,000 tons (14%)
to the annual global tungsten production (Cheng, 2016
Dai et al., 2018 Lu et al., 2003). Additionally, the Nui
Phao and Vostok 2 mines, together representing 10% of
world tungsten production, also exploit tungsten skarns
(Masan Resources, 2012 Soloviev and Krivoshchekov,
2011). Consequently, tungsten skarns play a significant role
in the current tungsten production, with some estimates
suggesting they account for over 40% of global tungsten
reserves (Pitfield et al., 2011 Schubert et al., 2006 Werner
et al., 1998). In skarns, scheelite presents a fine liberation
size and tends to form slime during comminution stages
since it is a brittle mineral. Due to these constraints, schee-
lite is traditionally beneficiated by froth flotation, which
provides very satisfactory recovery and grade (Kupka and
Rudolph, 2018). However, gangue calcium-bearing miner-
als such as calcite, dolomite, fluorite, and apatite are very
common in skarn deposits and can represent more than
15% of the total ore, raising significant selectivity issues.
These difficulties are due to common surface properties gen-
erated by Ca2+, WO42–, CO32– and PO43– on the surface.
Although good WO3 grades and recoveries were obtained
using fatty acids as collectors and a combination of sodium
silicate and sodium carbonate as depressants (Foucaud et
al., 2019b), the low selectivity of fatty acids caused by the
chemisorption of sodium oleate onto Ca2+ of the calcium
minerals surface generally results in a non-selective flota-
tion (Atademir et al., 1981 Marinakis and Kelsall, 1987
Marinakis and Shergold, 1985 Rao and Forssberg, 1991).
Hence, considering that a contrast exists in terms of zeta
potential between scheelite and the problematic calcium
minerals, this study aims at testing an amine-based room
temperature flotation for tungsten skarn ores. The sample
considered here, coming from the Tabuaço northern-Por-
tuguese deposit, is a fine-grained tungsten skarn composed
of silicates, fluorite, apatite, and scheelite, and represents
a typical archetype of world tungsten skarns in terms of
textural, chemical, and mineralogical features. To demon-
strate the feasibility of this new process, we used a combi-
nation of flotation tests and surface studies. Different pH,
collector concentrations, and depressant concentrations are
tested. The different recoveries are compared to find the
best conditions for maximizing it and reject calcium-bear-
ing minerals.
MATERIAL AND METHODS
Sampling
A sampling campaign allowed acquiring 1 ton of rocks to
conduct the mineral processing tests. The samples were as
representative as possible of the orebody and were used to
conduct a deep mineralogical and textural characterization
stage prior to the tests. Besides, at each stage of the process,
representative samples were selected using a riffle splitter.
Sampling
The samples were crushed in three successive jaw crushers
and a gyratory crusher to obtain a –4 mm size fraction. To
reach the liberation mesh, this product was wet sieved at