The autosem ore characterisation of conglomeratic and banded iron formations

Image processing is applied in the calculation of clast sizes for conglomeratic type ore and band width mineral distributions/compositions for banded iron formation (BIF) type ores. Hematite band widths are defined according to hematite mass percent thresholds and were developed to act as a bridging concept between microscopic hematite band widths and macroscopic hand specimen band widths. The difficulties of defining clasts against matrices through automated mineralogy include the occurrence of hematite clasts in a hematite matrix making clast boundaries indistinguishable in a QEMSCAN system. Defining clasts according to size is also problematic since hematite can either form matrix when associated with quartz granules or clasts when associated with clay. After mineralogical classification the ores are crushed to determine liberation and grind size characteristics. The correlations between hematite clast size/hematite band width with liberated grind sizes are compared for use in predictive models.     

The contributions of geometallurgy to the recovery of lithified heavy mineral resources at the Namakwa Sands mine, West Coast of South Africa

The Namakwa Sands heavy mineral deposit is located at Brand-se-Baai along the West Coast of South Africa and is a world class producer of premium quality zircon (ZrSiO₄), ilmenite (FeTiO₃) and rutile (TiO₂) concentrates from mainly aeolian sands. Superimposed on the coastal clastic Cainozoic ore-bearing sequence is a calcium-magnesium-rich pseudo-stratigraphy locally referred to as cemented hard layers that effectively lithify the mineralised sands to various degrees of hardness, rendering it unsuitable for routine treatment by wet spirals. Namakwa Sands has recently completed an expansion programme, inclusive of a SAG mill and screen installation, which allows the processing of the cemented hard layers, the first ever in the mineral sands industry. Operationally, the SAG mill and screen are performing well in tandem and are helping to improve mineral resource utilisation to levels not previously possible. Contained zircon output has increased, but at the cost of marginally lower recoveries as predicted from pilot studies. This paper reports on the systematic geometallurgical approach to improve mineral resource utilisation by successfully processing lithified ore.     

Process mineralogy studies of Corrego do Garimpo REE ore, catalao-I alkaline complex, Goias, Brazil

Corrego do Garimpo is described as a lateritic rare earths (REE) deposit related to hydrothermal alteration of dolomitic carbonatitic rocks. Although the deposit has been known since the sixties, all the previous mineral dressing attempts to concentrate the REE bearing minerals resulted in unsatisfactory outcomes. Process mineralogy studies of bulk and borehole samples were fundamental to understanding the ore's behavior and to the development of an unusual physical concentration process.The ore comprises a medium to very fine-grained soil material with large amounts of secondary (autigenous) minerals. Monazite, the essential REE bearing mineral, occurs as microcrystalline aggregates, sometimes presenting colloidal textures, which are frequently associated with iron oxide—hydroxides and quartz. Since these aggregates are extremely friable, the monazite crystallites are mainly associated with the −20 μm size fraction.These particular characteristics supported the development of an unconventional mineral processing method for monazite based on disaggregation, followed by scrubbing and hydrocyclone classification operations. Three volumetric samples and 27 borehole samples, comprising four ore types, have been studied. The attained final products, −10 μm, were further submitted to leaching tests, simulating chemical processing for the REE sulphuric extraction at low temperature.     

Detailed characterisation of antimony mineralogy in a geometallurgical context at the Rockliden ore deposit,North-Central Sweden

The antimony (Sb) content of the Rockliden complex Zn–Cu massive sulphide ore lowers the quality of the Cu–Pb concentrate. The purpose of this study is to characterise the Sb mineralogy of the deposit. The Sb-bearing minerals include tetrahedrite (Cu,Fe,Ag,Zn)₁₂Sb₄S₁₃, bournonite PbCuSbS₃, gudmundite FeSbS and other sulphosalts. On a microscopic scale these minerals are complexly intergrown with base-metal sulphides in the ore. Based on these observations mineralogical controls on the distribution of Sb-bearing minerals in a standard flotation test are illustrated. Deposit-scale and rock-related variation in the Sb-content and distribution of Sb-bearing minerals were found. This underlines the importance in understanding the geological background as a basis of a 3D geometallurgical model for Rockliden. Such a model is expected to predict the Sb content of the Cu–Pb concentrate, among other process-relevant factors, and helps to forecast when the Cu–Pb concentrate has to be treated by alternative processes, such as alkaline sulphide leaching, before it is sold to the smelter.     

Quantitative measurement of copper mineralogy using magnetic resonance

A prototype instrument using magnetic resonance has been constructed for quantitative measurement of selected copper minerals, in bulk samples obtained from a number of commercial ore deposits. The instrument has been developed to provide rapid on-line determination of phase concentration. The on-line measurement of copper mineral phase would be of considerable assistance to the mineralogist or process engineer for process optimisation. Ultimately, the underlying method may be applied in ore streams on conveyors or batch samples. This paper describes the development of the instrument and measurement methods, with particular emphasis on chalcopyrite, focusing on the design route for instrument deployment. Quantitative results regarding detection limits and accuracy for dilute ore concentrations are presented. In addition, effects due to crushing and grinding are discussed. Owing to the very high selectivity of the technique, it has been possible to demonstrate mineral phase resolution of 0.1 wt% in bulk samples.     

Leaching of copper from Kupferschiefer by glutamic acid and heterotrophic bacteria

Polymetallic Cu–Ag ores of the Central European Kupferschiefer deposits are one of the most important sources of copper in Europe. Because the ores are typically complex and often exceptionally fine-grained the development of efficient alternatives to conventional beneficiation strategies are an important target of current research. Biomining – the use of biological components for metal extraction – may offer solutions that are both efficient and environmentally benign. As conventional bioleaching with acidophilic microorganisms is impeded by the high carbonate content of the Kupferschiefer ores, heterotrophic microorganisms and glutamic acid are investigated as a possible alternative in the present study. The focus of this investigation is solely on the recovery of copper from the Kupferschiefer sensu strictu. Bioleaching experiments were carried out using such material from the Polkowice Mine in Poland. This material is marked by high grade (3.8 wt.% Cu), complex ore mineralogy (chalcocite, bornite, chalcopyrite and covellite in significant quantity) and a gangue mineralogy that is rich in carbonate, organic carbon and clay minerals that together form a very fine-grained matrix. (Bio)leaching experiments yield best results when glutamic acid alone is used – reaching copper recoveries up to 44%. Recoveries are consistently lower in experiments in which glutamic acid and microbiological metabolites are both present. The leaching of chalcocite renders the greatest contribution to the copper recovered to the leach solution in all experiments. It can be concluded that glutamic acid solubilises copper efficiently from Kupferschiefer, mainly from chalcocite.     

A process mineralogy approach to geometallurgical model refinement for the Namakwa Sands heavy minerals operations,west coast of South Africa

The original geometallurgical model for the Namakwa Sands deposit was modified to accommodate ore blends in addition to the various single ore types. A process mineralogy approach was followed in a structured and systematic manner to evaluate the integrity of the adjusted model, particularly for ilmenite and zircon, the minerals of highest intrinsic value. This study reproduced recovery relationships predicted by the geometallurgical model for each of the key process functions, and as a result the integrity of the geometallurgical model is validated. Overall, the recovery potential determined for ilmenite and zircon are well adjusted to model estimates. Poor mineral liberation, an anomalously high abundance of garnet and pyroxene and variation in particle chemistry are recognized as the key recovery penalties. The gangue content is the most significant constraint to ilmenite recovery, whereas zircon chemistry is the most important negative factor in the production of a premium quality zircon product. Results of this study contributed to the refinement of the current geometallurgical model and also identified opportunities to optimise mineral resource utilisation in the future.