PART I PROJECT DEVELOPMENT
5. CONCLUDING REMARKS
(Chryssoulis et al., 2003a). With vacuum ultra-violet (VUV)-TOF-LIMS there is even less fragmentation of the collector molecule, so it is by an order of magnitude more sensitive than TOF-SIMS for cationic collectors (Dimov and Chryssoulis, 2004).Table 7lists all microbeam techniques used for gold analysis depending on the target area: surface vs. bulk of the particle.
Partial (narrow scope) gold deportment studies of intermediate products have been used to understand the kinetics and efficiencies of the gold unit process (e.g., flotation, leaching, pressure oxidation and bioleaching). Gold deportment in final flotation concentrates is carried out in conjunction with Fig. 33. TOF-SIMS spectrum of gold particle loaded with DIBDTP and amyl xanthate.
The spectrum is dominated by the unfragmented collector molecular ions (AX–at 163 m/z and DIBDTP–at 261 m/z).
Table 7
Microbeam techniques for bulk and surface microanalysis of mineral grains
Bulk analysis Surface analysis
EPMA (EDX/WDX) TOF-LIMS
m-PIXE TOF-SIMS
SIMS VUV-TOF-LIMS
TOF-RIMS SALI
L-ICP-MS TOF-RIMS
Modal analysis (mineral abundance and association) AIA
EPMA, electron-probe microanalysis; EDX, energy-dispersive X-ray analysis; WDX, wavelength- dispersive X-ray analysis;m-PIXE, micro-particle-induced X-ray emission; SIMS, secondary-ion mass spectrometry; TOF-LIMS, time-of-flight laser-ionization mass spectrometry; TOF-RIMS, TOF resonant- ionization mass spectrometry; VUV-TOF-LIMS, vacuum ultraviolet TOF-LIMS; SALI, surface analysis by laser ionization; AIA, automated image-analysis.
S.L. Chryssoulis and J. McMullen 62
the study of cleaner (scavenger) tails to assess the potential for improving rejection of insolubles or pyrite, without sacrificing gold recovery.
ACKNOWLEDGMENTS
Companies that have contributed indirectly in building the database are thanked. Without the support of these companies in providing problems to solve and the necessary financial support this contribution would not have been possible.
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Dr Stephen L. Chryssoulisreceived his education from the National University of Athens and his DIC, D.Phil. from the Royal School of Mines (1983). He held teaching and research positions at the University of Athens, the Research & Productivity Council of New Brunswick and the University of Western Ontario. He is currently the director of Advanced Mineral Technology Laboratory, Ltd. (Amtel).
S.L. Chryssoulis and J. McMullen 66
Jacques McMullenis Corporate Head, Metallurgy and Process Development for Barrick Gold Corporation. Based at Barrick’s Corporate Head Office in Toronto, he leads a team of metallurgists whose roles are to perform due diligence reviews and evaluations on new projects, develop processing scenarios and assist in conducting feasibility studies.
Operation’s support and optimization and the management of R&D projects that will enhance the strategic positioning of the Corporation corporation in the medium-and long-term horizons are also part of the his mandate.
Mr. McMullen is a professional Metallurgical Engineer. After completing his Bachelor Degree in Metallurgical Engineering at Laval University, Quebec, Canada, he completed a Master’s Degree in Applied Sciences in Mineral Processing. He joined Barrick in 1994, as a result of Barrick’s take over of LAC Minerals where he was then assuming the role of Director, Technical Services and Environmental for the North American business unit.
Mineralogical investigation of gold ores 67
Plate 1. Coarse gold flake from flotation
final tails. Plate 2. Coarse gold flakes from column
cleaner tails.
Plate 3. Gold minerals (clockwise): native gold, electrum, auricupride [Cu3Au] (with native silver inclusions) and tetrauricupride [AuCu].
S.L. Chryssoulis and J. McMullen 68
Plate 4. Gold mineral associations (clockwise): native gold rimmed by electrum [Au,Ag], native gold attached to chalcopyrite [CuFeS2], enclosed in pyrite [FeS2] and quartz (the latter two are considered in most cases as unfavourable associations).
Plate 5. Silver arsenate coating on residual free gold particle; in most cases the coating is too thin to be seen under the microscope; however, it is readily detectable by laser-probe microanalysis (TOF-LIMS).
Mineralogical investigation of gold ores 69
Au atom
1.4 Å 1 nm 10 nm 100 nm 1 µm 10 µm
100 µm 1 Å
by HR-TEM detectable by SIMS
by microscopy
Plate 6. Continuum between solid solution, colloidal and micrometre-sized gold with method of detection. Gold inclusions are hosted in hematite [Fe2O3] and goethite [FeOOH].
Plate 7. Reaction rims showing the progression in the oxidation of pyrite in the roaster. The core is pyrite [FeS2], the inner rim is maghemite [Fe2O3with up to 8% Fe] and the outer rim is porous hematite [Fe2O3] (Goldstrike, NV, USA).
S.L. Chryssoulis and J. McMullen 70
Plate 8. Zoned roaster calcine particle, showing two well-defined maghemite [Fe2O3 with up to 8% Fe] zones interbed- ded with zones enriched in hematite [Fe2O3].
Arsenic is strongly enriched in the maghe- mite zones, and gold is confined the inner maghemite zone. Arsenic is in the form of ferrous pyroarsenite [FeAs2O5]. Inset: SIMS elemental maps for Fe, As and Au with con- centration scale (Goldstrike, NV, USA).
Plate 9. Porous calcine particle with discontinuous sintered rim made of maghemite-ferrous pyroarse- nite [FeAs2O5]. The sintered rim could be a relic of an original Au-rich arsenian pyrite layer coating an As/Au-poor pyrite or the reaction product of As2O3
with hematite [Fe2O3]. It should be noted that the areas with high arsenic content (yellow in SIMS maps) along the sintered rim are those where ma- ghemite is more obvious in the microscope photo- graph on the top. Gold is localized along the sintered rim (Goldstrike, NV, USA).
Mineralogical investigation of gold ores 71
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72
Developments in Mineral Processing, Vol. 15 Mike D. Adams (Editor)
r2005 Elsevier B.V. All rights reserved.
73
Chapter 3
Process flowsheet selection
D. Lunt and T. Weeks
GRD Minproc Limited, Perth, Australia
1. INTRODUCTION
The treatment of gold ores, in particular the competing technologies and their relative advantages and economics, has become a major focus within the in- dustry. A common issue is the increasingly refractory and complex nature of the ores being treated. This chapter gives an overview of the key process options.
While it does not purport to be complete, it will hopefully provide a starting point for the process engineer engaged in establishing the optimum flowsheet.
A variety of classifications and definitions of gold ores has been published.
Because of the many factors that can impact on the recovery of gold, it is difficult to develop a universal characterization applicable to all gold-bearing rocks. However,La Brooyet al. (1994)have provided a useful framework for characterization as shown inFig. 1.
In this categorization, free-milling ore is defined as yielding over 90%
recovery under conventional cyanidation conditions, while those ores that give acceptable economic gold recovery only with the use of sig- nificantly higher chemical additions (e.g. cyanide, oxygen, carbon) are de- fined as complex. Refractory ores are thus defined, by exception, as those that still give inadequate recovery. It is implicit in this definition that ad- ditional recovery requires some degree of pre-treatment prior to cyanidation.
Any further characterization of refractory ores, such as a definition of per- centage recovery, is somewhat arbitrary and ignores the impact of economics unique to each specific ore deposit. In terms of this discussion of alternative process routes, the above characterization is adopted.
DOI: 10.1016/S0167-4528(05)15003-0
Flowsheet selection for free-milling ores can be relatively straightforward, with the key issues revolving around comminution circuit selection, the use of heap leaching, treatment of high-silver ores and flotation options for free- milling sulfides.
Complex ores include those associated with base-metal mineralization, par- ticularly copper, that can consume cyanide and create issues in CIP and el- ution. The presence of preg-robbing carbon will demand flowsheet inclusions to achieve acceptable recovery without gross losses of gold to CIL tailings.
While refractory characteristics can be seen in a variety of ore types, in- cluding auriferous base metals and rocks with a high carbon content, the major focus in refractory gold processing has been on gold-bearing iron sulfides, such as pyrite, arsenopyrite, pyrrhotite, telluride and the stibnite family. It is the intention of this chapter to concentrate on the pre-treatment processes available for the latter ore types.
In summary, gold flowsheet options will be examined under the headings of:
Comminution processes;
Free-milling ore processes;
Complex ore processes;
Refractory ore processes.
2. COMMINUTION PROCESS OPTIONS