Mineralogy, geochemistry and metamorphism of the early Proterozoic Vähäjoki iron ores, northern Finland

The Vähäjoki iron ores occupy the uppermost part of the Karelian (Early Proterozoic) quartzite-dolomite sequence deposited on the late Archaean basement in southern Lapland. The ores occur as magnetite veins brecciating dolomite and as magnetite disseminations in chlorite and mica schists. Their average iron content is 40%, and they contain up to 3.8% P2O5 features which together with the division of the ores into 14 small bodies make them uneconomic. The only main ore mineral is magnetite, with which there occur accessory ilmenite, haematite, pyrite, chalcopyrite, pyrrhotite, arsenopyrite and cobaltite with small gold inclusions. The main gangue minerals classified by microanalysis are dolomite or Fe-dolomite in the dolomites, ferri-tremolite, tremolite, ferri-actinolite and ferrian actinolite, cummingtonite, magnesio-hornblende and tschermakitic hornblende in amphibole-bearing hosts rocks, green Mg-rich biotite, brown Fe-rich biotite and Ba-bearing (BaO 0.18‒7.9%) biotite, and chlorite in chlorite and mica schists. Major and trace elements were analyzed in 18 samples. The dolomites contain 24‒53% CaO and 3‒20% MgO, while the amphibole rocks, amphibole schists, chlorite schists and mica schists are chemically rather similar, containing about 13‒27% Fetot and 7‒21% MgO, the amphibole-bearing varities being a little richer in these elements than the phyllosilicate-bearing ones. The ore samples from magnetite matrix of the breccia type contain 71‒85% Fe2O3 and 0.05‒0.2% P2O5. The garnet-biotite and calcite-dolomite geothermometers and the mineral chemistry of the Ca-amphiboles suggest that the Vähäjoki iron ores were metamorphosed under greenschist ‒ amphibolite facies conditions (T = 465 °C and P = 2‒4 Kbar). Flunctiation in metamorphic grade is reflected in the change in amphibole composition from tremolite-actinolite to tschermakitic hornblende. The Vähäjoki iron ores were remobilized and enriched during early Proterozoic regional metamorphism and deformation, forming an epigenetic iron ore

Validation of predictive flotation models in blended ores for concentrator process design

Abstract The use of geometallurgical modelling is becoming common in the design of a concentrator plant and during its operational phase. Predictive modelling aims to define optimized process parameters for the concentrator plant to accommodate the variability of the ore feed characteristics. The main objective of this study is to simulate the metallurgical response for distinct ore unit types and their blends using kinetic models derived from experimental flotation tests. Kinetic flotation tests, including both rougher and cleaner, were applied on four ore types containing different ratios of chalcopyrite, chalcocite and copper oxide minerals from Rich Metal Group’s Madneuli copper–gold mine, Georgia. The metallurgical performance of complex copper ores Madnueli XI and V differs from each other significatively due to the different mineralogical distribution of copper sulphides and oxides. The blend of ore units in various ratios affects the efficiency of the process by decrementing the recovery and mass pull due to copper oxide-sulphate in the ore Madnueli V. HSC Chemistry® software was used to simulate the metallurgical response of blended ores based on mineral compositions of the ores, Klimpel kinetic rectangular distribution model and flowsheet model. Simulated and experimental results of copper grade, copper recovery and concentrate mass pull correlated well with R² values of over 0.95. These results demonstrate that the metallurgical response of ore blends can be simulated based on the flotation kinetics of distinct ore types. The use of predictive simulation can create savings during the test work phase and increase the flexibility and certainty in the process design stage

The validation of predictive geometallurgical models in concentrator process design

Abstract The use of geometallurgical modelling is becoming more common in concentrator plant design and during the operational phase. Predictive modelling aims to define optimised process parameters for the concentrator plant to accommodate variability within the ore feed. The main objective of this study is to show how the metallurgical response of different types of ore blends can be simulated using kinetic models derived from experimental flotation tests with different geometallurgical end-member ore types and their blends. For these validation tests, four different end-member ore types containing different ratios of chalcopyrite, chalcocite and oxidised copper minerals from Rich Metal Group’s Madneuli copper-gold mine, Georgia, were tested. Kinetic flotation tests, including both rougher and cleaner flotation tests, were carried out. The simulations were performed using HSC Chemistry software based on mineral compositions of the ores and kinetic models using rectangular distribution equations and flowsheet model. Simulated and experimental results of copper grade, copper recovery and concentrate mass pull correlated well with R2 values of >0.95. Based on these results, the metallurgical response of different ore blends can be simulated based on the flotation kinetics of end-member ore types. The use of this kind of simulation will create savings during the test work phase and increase the flexibility and predictability in the processing stage

The Mantle Section of Neoproterozoic Ophiolites from the Pan-African Belt, Eastern Desert, Egypt: Tectonomagmatic Evolution, Metamorphism, and Mineralization

The Eastern Desert (ED) Neoproterozoic ophiolites are tectonically important elements of the Arabian–Nubian Shield. Although affected by various degrees of dismemberment, metamorphism, and alteration, almost all of the diagnostic Penrose-type ophiolite components can be found, namely, lower units of serpentinized peridotite tectonite and cumulate ultramafics and upper units of layered and isotropic gabbros, plagiogranites, sheeted dykes and pillow lavas. The contacts between the lower unit (mantle section) and the upper unit (crustal section) were originally magmatic, but in all cases are now disrupted by tectonism. The mantle sections of the ED ophiolites are exposed as folded thrust sheets bearing important and distinctive lithologies of serpentinized peridotites of harzburgite and dunite protoliths with occasional podiform chromitites. The ED ophiolites show a spatial and temporal association with suture zones that indicate fossil subduction zone locations. Multiple episodes of regional metamorphism mostly reached greenschist facies with less common amphibolite facies localities. CO₂-metasomatism resulted in the development of talc–carbonate, listvenite, magnesite, and other carbonate-bearing meta-ultramafic rocks. Geochemical data from the ED serpentinites, despite some confounding effects of hydration and alteration, resemble modern oceanic peridotites. The ED serpentinites show high LOI (≤20 wt%); Mg# mostly higher than 0.89; enrichment of Ni, Cr, and Co; depletion of Al₂O₃ and CaO; and nearly flat, depleted, and unfractionated chondrite-normalized REE patterns. The modal abundance of clinopyroxene is very low if it is present at all. Chromian spinel survived metamorphism and is widely used as the most reliable petrogenetic and geotectonic indicator in the ED ophiolite mantle sections. The high-Cr# (mostly ~0.7) and low-TiO₂ (mostly ≤ 0.1 wt%) characters of chromian spinel indicate a high degree of partial melt extraction (≥30%), which is commonly associated with fore-arc settings and equilibration with boninite-like or high-Mg tholeiite melts. Based on the general petrological characteristics, the ED ophiolitic chromitites are largely similar to Phanerozoic examples that have been attributed to melt–peridotite interaction and subsequent melt mixing in fore-arc settings. The comparison between the ED Neoproterozoic mantle peridotites and Phanerozoic equivalents indicates considerable similarity in tectonomagmatic processes and does not support any major changes in the geothermal regime of subduction zones on Earth since the Neoproterozoic era. The mantle sections of ED ophiolites are worthy targets for mining and exploration, hosting a variety of ores (chromite, gold, and iron/nickel laterites) and industrial minerals (talc, asbestos, and serpentine)