1595
Process Mineralogical Investigation into the Distribution of
Silver at Gamsberg Zinc
A. Mulelu, K.C. Corin, M. Becker
Centre for Minerals Research, University of Cape Town, Rondebosch, Cape Town, 7700, South Africa
P. Spathelf
Gamsberg Operations, Black Mountain Mining, Vedanta Zinc International, Aggeneys, South Africa
ABSTRACT: The Gamsberg zinc deposit in South Africa is well-known for its mineralogical complexity,
although it is unknown to what extent this complexity extends to the distribution of Ag in the deposit. Ore
samples representing current ‘geometallurgical’ ore end members from the Gamsberg East pit were analysed
to determine their Ag grades, distribution of Ag to different flotation products, and the occurrence of Ag, as
liberated or locked discrete minerals, or in solid solution within selected minerals. Elemental assays, QEMSCAN
analysis, SEM-WDS, and controlled sequential batch flotation were conducted to investigate the distribution of
Ag in the samples. Initial mineralogy work indicates a possible relationship between Ag and Pb, since Ag and Pb
grades were highest in the fresh low-Mn sample investigated. Batch flotation test work revealed that the majority
of Ag was recovered by this sample. The majority of Ag in the low-Mn ore is recovered to the Pb concentrate
due to true flotation of native Ag-galena and argentite-galena composites. In contrast, the majority of Ag in
the high-Mn ore is recovered to the Zn concentrate which is mainly due to the recovery of argentite-sphalerite
composites. Optimal conditions for Ag recovery and Ag mineral characteristics are highlighted in this work.
Keywords: process mineralogy, flotation, Ag distribution
INTRODUCTION
The Gamsberg deposit is one of several economic sediment-
hosted Zn-Pb-Ba-(Ag) Broken Hill-type deposits within
the Aggeneys-Gamsberg Ore District (A-GOD), having a
total resource of 636.6 Mt with 4.0% Zn, 1.1% Pb and
14 g/t Ag. Large-scale mining of the Gamsberg deposit
only commenced in 2015 and the first flotation concen-
trate was produced in 2018 (Price et al. 2023). Sphalerite,
the primary host of Zn, is recovered from the sulfidic ore
and metalliferous rocks of the Gams/Aggeneys iron forma-
tion at Gamsberg Mine, where mineralization occurs in
various ore types such as calc-silicate and metapelite-hosted
ores (Stalder and Rozendaal, 2004 Hövhn et al. 2021).
Ag is mainly produced as a byproduct at mines process-
ing Broken Hill-type ore deposits such as the neighbouring
Black Mountain Complex ores. Although the Gamsberg
deposit has Ag enrichment, little is known about the Ag
mineralogy and its processing characteristics.
In generic Pb-Zn-Ag ores, Ag may occur within galena,
chalcopyrite, pyrite, and other sulphides hosted through
solid solution substitution of more commonly occurring
metals, as well as in discrete Ag minerals like argentite, frei-
bergite, native Ag and sternbergite (Quinteros et al. 2015
Knights and Johnson, 2016). Discrete Ag minerals can also
Process Mineralogical Investigation into the Distribution of
Silver at Gamsberg Zinc
A. Mulelu, K.C. Corin, M. Becker
Centre for Minerals Research, University of Cape Town, Rondebosch, Cape Town, 7700, South Africa
P. Spathelf
Gamsberg Operations, Black Mountain Mining, Vedanta Zinc International, Aggeneys, South Africa
ABSTRACT: The Gamsberg zinc deposit in South Africa is well-known for its mineralogical complexity,
although it is unknown to what extent this complexity extends to the distribution of Ag in the deposit. Ore
samples representing current ‘geometallurgical’ ore end members from the Gamsberg East pit were analysed
to determine their Ag grades, distribution of Ag to different flotation products, and the occurrence of Ag, as
liberated or locked discrete minerals, or in solid solution within selected minerals. Elemental assays, QEMSCAN
analysis, SEM-WDS, and controlled sequential batch flotation were conducted to investigate the distribution of
Ag in the samples. Initial mineralogy work indicates a possible relationship between Ag and Pb, since Ag and Pb
grades were highest in the fresh low-Mn sample investigated. Batch flotation test work revealed that the majority
of Ag was recovered by this sample. The majority of Ag in the low-Mn ore is recovered to the Pb concentrate
due to true flotation of native Ag-galena and argentite-galena composites. In contrast, the majority of Ag in
the high-Mn ore is recovered to the Zn concentrate which is mainly due to the recovery of argentite-sphalerite
composites. Optimal conditions for Ag recovery and Ag mineral characteristics are highlighted in this work.
Keywords: process mineralogy, flotation, Ag distribution
INTRODUCTION
The Gamsberg deposit is one of several economic sediment-
hosted Zn-Pb-Ba-(Ag) Broken Hill-type deposits within
the Aggeneys-Gamsberg Ore District (A-GOD), having a
total resource of 636.6 Mt with 4.0% Zn, 1.1% Pb and
14 g/t Ag. Large-scale mining of the Gamsberg deposit
only commenced in 2015 and the first flotation concen-
trate was produced in 2018 (Price et al. 2023). Sphalerite,
the primary host of Zn, is recovered from the sulfidic ore
and metalliferous rocks of the Gams/Aggeneys iron forma-
tion at Gamsberg Mine, where mineralization occurs in
various ore types such as calc-silicate and metapelite-hosted
ores (Stalder and Rozendaal, 2004 Hövhn et al. 2021).
Ag is mainly produced as a byproduct at mines process-
ing Broken Hill-type ore deposits such as the neighbouring
Black Mountain Complex ores. Although the Gamsberg
deposit has Ag enrichment, little is known about the Ag
mineralogy and its processing characteristics.
In generic Pb-Zn-Ag ores, Ag may occur within galena,
chalcopyrite, pyrite, and other sulphides hosted through
solid solution substitution of more commonly occurring
metals, as well as in discrete Ag minerals like argentite, frei-
bergite, native Ag and sternbergite (Quinteros et al. 2015
Knights and Johnson, 2016). Discrete Ag minerals can also