Fresh Ore Research Articles

Analysis of bioleaching characteristics and multi-element dissolution behavior of complex zinc ores

In order to recover low-grade complex zinc ore in a reasonable way, this study adopts bioleaching method to study it. The ore samples contain 1.52%, 2.03% and 14.4% zinc, respectively, which occurs in the form of sphalerite. Other major minerals include pyrite, galena, quartz and mica. The inoculation of the domesticated strain was basically free of adaptation period, and the cell concentration could be rapidly increased after a short decrease. The leaching extent of zinc increased continuously, while the leaching rate decreased gradually. After the bioleaching process, sliver, lead and iron were mainly present in the residue phase. X-ray diffraction spectroscopy analysis showed that sphalerite, galena and pyrite were dissolved, and the latter two further precipitated to produce PbSO4 and jarosite. In addition, the dissolution of calcium compounds can lead to the formation of gypsum precipitation. These precipitates covered the fresh ore surface may hinder the further bioleaching process. The Exponential model was used to simulate the bioleaching process, and it was found that the fit coefficients were all greater than 0.98, and a reasonable leaching cycle was further discussed. The results provide a good basis for the economic and environmentally friendly recovery of low-grade complex zinc ores.

Effect of Long-Term Stockpiling on Oxidation and Flotation Response of Low-Grade Copper Sulphide Ore

Since the start-up of the Sossego copper concentrator, located in the Carajás Mineral Province in the southeast of Para State, Brazil, the low-grade ore (~0.34% Cu) has been stockpiled, as defined in the long-term mine plan, to be reclaimed at the end of the mine life. Given this imminent need to process around 40 Mt of this low-grade ore, questions have been raised related to the extent of oxidation that might have occurred in this stockpiled ore. In this context, a study was designed to characterize the stockpiled ore and assess the effect of the ore oxidation on its flotation response. A sampling campaign of the stockpiled ore was carried out to analyze the main variables that could influence the level of oxidation, and, consequently, copper recovery, such as stockpiling time, depth, and particle size. The results showed that there are two main factors negatively impacting the copper recovery of the low-grade stockpiled ore: the surface oxidation and the level of liberation of the copper mineral. Depth and period of stockpiling were not found to influence the level of oxidation, nor the flotation response. An empirical model was proposed for the copper recovery in the rougher stage, which resulted in a predicted value of 90.7%, which was lower than that for the fresh (and higher copper content) ore fed to the plant (93%).

Control Structure Design Using Global Sensitivity Analysis for Mineral Processes under Uncertainties

Multiple-input and multiple-output (MIMO) systems can be found in many industrial processes, including mining processes. In practice, these systems are difficult to control due to the interactions of their input variables and the inherent uncertainty of industrial processes. Depending on the interactions in the MIMO process, different control strategies can be implemented to achieve the desired performance. Among these strategies is the use of a decentralized structure that considers several subsystems and for which a SISO controller can be designed. In this study, a methodology based on global sensitivity analysis (GSA) to design decentralized control structures for industrial processes under uncertainty is presented. GSA has not yet been applied for this purpose in process control; it allows us to understand the dynamic behavior of systems under uncertainty in a broad value range, unlike approaches proposed in the literature. The proposed GSA is based on the Sobol method, which provides sensitivity indices used as interaction measures to establish the input–output pairing for MIMO systems. Two case studies based on a semi-autogenous grinding (SAG) mill and a solvent extraction (SX) plant are presented to demonstrate the applicability of the proposed methodology. The results indicate that the methodology allows the design of 2 × 2 and 3 × 3 decentralized control structures for the SAG mill and SX plant, respectively, which exhibit good performance compared to MPC. For example, for the SAG mill, the determined pairings were fresh ore flux/fraction of mill filling and power consumption/percentage of critical speed.

Discovery and geological significance of REE deposit in southern Songxian County, East Qinling, China

East Qinling Orogenic Belt is an important metallogenic belt of China due to its production of an enormous amount of metal mineral resources. Herein, One rare earth element (REE) deposit occurrence is firstly discovered in southern Songxian County, East Qinling, and its geological and geochemical characteristics are reported. The REE ore body occurs as mineral veins in the marginal facies of the syenite porphyry complex, with matrix composed of orthoclase, aegirine and quartz. Zircon geochronological research shows that the emplacement age of the syenite porphyry is 236.3 ± 2.6 Ma (MSWD = 0.77, n = 9). The investigated syenite samples are high-K alkali-rich syenite series alkaline rocks. X-ray diffraction (XRD) analysis of bulk ores and electron probe micro-analysis (EPMA) of mineral reveal that the dark mineral is aegirine, with the chemical formula of (Na0.46K0.26Ca0.10)(Fe0.74Mg0.54)Si2.14O6, and the REE is mainly hosted in aegirine. The total content of REE is high with the rare earth element oxide (REE2O3) between 0.12% and 0.52%, and the REE2O3 content of fresh ores reaches the cut-off grade. The contact features of the REE ore bodies and ore veins with the wall rocks show that REE deposit is magmatic (or post-magmatic) hydrothermal genesis. This finding filled the gap of REE deposits in the East Qinling area, which provides guidance for future geological prospecting.

Effect of multistage solution–mineral contact in in-situ recovery for low-grade natural copper samples: Extraction, acid consumption, gangue-mineral changes and precipitation

Recent decreases in the grades of copper reserves have stimulated interest in alternative mining technologies, such as in-situ recovery (ISR), which may be an attractive mining approach for low-grade ores. In ISR operations, lixiviant contacts subsurface ore when it is pumped through the deposit. Continuous flow of lixiviant with suitable properties (such as pH and solution potential, Eh) is required from the wellfield injection point through the ore to the recovery point. Leach solution pH and Eh adjustment is not possible between boreholes and therefore, undesired precipitate formation may result, which could produce blockages and restrict solution flow. Our experiments aimed to simulate the chemical processes that may occur when leach solution travels through an ore deposit from the injection to the recovery well by contacting a pregnant leach solution with fresh ore over multiple stages. Low-grade natural ore that contained refractory copper sulfides mixed with gangue minerals was leached with iron (III) as an oxidant in sulfuric, hydrochloric or methanesulfonic acid at 90 °C. The leach solution was contacted for 72 h with fresh ore in five successive stages, without acid or oxidant replenishment. Although copper extraction continued for the duration of the five stages, the copper extraction dropped off after two contact stages. Precipitates formed in all solutions after three contact stages; akaganeite precipitated in the chloride systems and jarosite and gypsum formed in the sulfate systems after the second contact stage. The extent of precipitation is predicted to increase with an increase in temperature and pH. These findings provide insights into the behaviour that could be expected in ISR operations and factors that influence borehole spacing and ensure continuous lixiviant–ore contact subsurface.

Influence of heat treatment on manganese ores as oxygen carriers

Manganese ores have been identified as promising oxygen carriers for chemical-looping processes with solid fuels, including combustion and gasification systems. Such Mn-based minerals are readily available globally and could thus be a cheap alternative to other naturally occurring oxygen carriers, such as ilmenite. These ores are usually highly heterogeneous, with varying phase composition, both on the inter-particle as well as intra-particle level. Further, manganese ores contain Mn in many forms and states, including combined or mixed oxides. The content of Fe, Al, Si, Mg and Ca can be high, but also vary significantly. Thus, it can be expected that there will be transformations of the chemical and physical structures during heating from room temperature to operational conditions. In fact, natural materials are often calcined in air prior to use in CLC systems, to avoid agglomeration and defluidization. In this work the effect of heat treatment is investigated for four different manganese ores that have widely different compositions. The mass losses during heat-up in a batch, fluidized-bed reactor and a thermogravimetric analyzer (TGA) were measured. In addition, the change in reactivity over 21 redox cycles with both methane and a syngas (CO/H2) was investigated for both heat treated and fresh ores. During the batch experiments, the defluidization tendency of the ores was investigated as well. The ores were characterized with X-ray diffraction (XRD) and ICP-SFMS. It was found that there was a release of CO2 and O2 from the ores during heat up in the batch experiment, likely originating from carbonates and thermodynamic unstable manganese oxides respectively. Also, significant mass losses were observed for the untreated ores in the TGA, and in addition to the release of CO2 and O2, a release of H2O was observed at lower temperatures. Reactivity was similar between heat treated and untreated ores, especially when considering the mass loss during heat-up. Still, the reactivity varied significantly among the different ores tested. Defluidization was observed only for one of the ores, when a blend of manganese ore and quartz sand was used as bed material during testing with syngas. However, no defluidization was observed during heat-up. In summary, depending upon the ore used, significant mass losses can be expected, which may need to be accounted for during operation with solid fuels.

Naica’s crystal cave captivates chemists

Deep below a mountain near Naica, Mexico, miners searching for fresh ore deposits in 2000 came across an unexpected and awesome sight. Massive, milky-white crystals towered around them, filling a horseshoe-shaped cave. Luminous beams of gypsum bigger than telephone poles, nearly 12 m long and 1 m wide, gleamed in the miners’ lights, jutting in all directions out of the brown limestone walls, floors, and ceiling. The Cave of Crystals, as it became named, is nestled 290 m underground, topped by a mountain rich in lead, zinc, and silver. Since its discovery by the mining company Industrias Penoles, the subterranean chamber has drawn researchers from around the world, enticing them with both rare beauty and scientific mystery. Juan Manuel Garcia-Ruiz, a crystallographer at the University of Granada, traveled all the way from Spain to see the crystals for himself. Garcia-Ruiz had grown crystals in laboratory flasks since age 15, so

Weathering of Bi-bearing tennantite

The tennantite-tetrahedrite solid-solution series [called fahlore; (Cu,Ag)6Cu4(Fe,Zn,Cu,Hg,Cd)2(Sb,As,Bi,Te)4(S,Se)13] is widespread in many geological environments. Since it incorporates heavy metals and toxic elements, a better understanding of its weathering behaviour and details of its weathering process is important to evaluate environmental risks (emerging mainly from the mobilization of As-Sb-Bi) and local and global metal fluxes in stream waters and oceans. In this study, weathering of Bi-rich members of this mineral group was investigated using microscopy, EMPA, SEM, TEM, LA-ICP-MS, Raman, μXRD, and MLA.Observations reveal a succession of four distinct stages of weathering: During stage 1, irregular tubes within fahlore show an assemblage of nm- to μm-sized roméite group minerals, tripuhyite, crystalline Cu-oxides and Cu-sulfides. Stage 1 textures and secondary sulfides indicate a low redox-potential and a low fluid/rock ratio, typical of cementation zones. Mass balance calculations show that during this stage all Zn and the majority of As and S are released to the weathering fluids. Bismuth is immobile in this stage and Sb and Fe are immobile, if Bi is sufficiently available from fahlore, but both are partly released, if the fahlore did not contain sufficient Bi. During stage 2, amorphous and nano-crystalline arsenates replace fahlore as weathering fronts. Such assemblages indicate a higher redox-potential than in stage 1, typical for oxidation zones. Mass balance calculations reveal that Zn, Sb, S and partially Cu are lost. Arsenic and Bi are immobile. Stage 3 occurs only locally, dissolving former weathering stages and/or precipitating amorphous Cu-arsenates/silicates reflecting processes in micro-compartments, not characteristic for the general weathering process. Stage 4 is characterized by the formation of crystalline Bi-, Cu-, Ba-, Ca- or Al-bearing arsenates and Cu-carbonates, spatially independent of the precursor fahlore. Copper and As originate from older weathering assemblages, whereas many other elements are derived externally (Ca, Ba, Al). This stage reflects the increasing importance of the local host rock and gangue mineralogy, as it is typical in near-surface environments of oxidation zones or on mine dumps, where elements are highly mobile and a high fluid/rock ratio prevails (gossan mineralization).The temporal evolution of fahlore weathering textures reflects the transition from fresh ore to cementation zone, oxidation zone and gossan assemblages in one hand specimen. Thus, one fahlore grain can record the uplift and erosion and the increasing fluid/rock interaction of a weathered ore deposit with time. Tube-like textures similar to the ones observed in stage 1 have been reported from other weathering environments and from a variety of element, oxide, arsenide, and sulfide phases. They also were produced during experimental work in ilmenite. This is clear evidence, that the diffusive process during the first contact with alteration fluids is a basic physical process and that it is not only valid for fahlore.The importance of Bi to stabilize Sb-bearing supergene phases (and thereby for the immobilization of toxic Sb) shown in the present work, may stimulate further investigations on the environmental immobilization of toxic elements by “companion metals” during weathering processes.

Transformation from Permian to Quaternary bauxite in southwestern South China Block driven by superimposed orogeny: A case study from Sanhe ore deposit

Permian karstic bauxite and its Quaternary derivative, in western Guangxi, southwestern, South China Block, possess a total tonnage greater than 0.5 billion tons. The primary late Permian karstic bauxite formed in reduced environment in the background of Tethyan accretionary orogenesis. And as one consequence of Cenozoic convergence of the Indian and Eurasia continents, the primary orebody was uplifted, eroded and re-sedimented within Quaternary laterite. The geochemical variation and its controls during the ore transformation from Permian to Quaternary remain poorly understood. Quaternary ore blocks comprise an inner zone of fresh ore, and then it gradually transited through a middle zone to a margin with extensive weathering. One such bauxite block was selected and further subdivided into twenty-three samples for geochemical and mineralogical analysis. The inner and middle zones contain similar mineralogical compositions, dominated by diaspore and amesite, with minor illite, anatase, goethite, pyrite, zircon, and rutile. The margin is composed of diaspore, with small amounts of amesite, boehmite, illite, goethite, anatase, kaolinite, zircon, rutile, and barite. Bauxite in all three zones is composed of mainly Al, Si, Fe, and Ti, and high contents of Zr, Cr, Li, F, S, Zn, V, Sr, Nb, Ba, and REE. Variations in Fe2+ and Fe3+ between the three zones were observed. The elements Si, Al, Fe2+, Mg, Ba, Cr, F, Li, Ni, Zn, and REE decrease from the core of the ore block outwards, corresponding to an increase in S and Fe3+. Depletions in Si, Al, Fe2+, Mg, Ba, and Cr were caused by the dissolution of amesite. Most of the Al and Si in amesite were lost during the weathering, and minor retained to form kaolinite. Depletions in Li, Ni, and Zn resulted from changes in the depositional environment between the late Permian and Quaternary. Dissolution of REE-bearing fluorocarbonates resulted in depletions of REE and F. The enrichment of Fe3+ and S was related to the precipitation of goethite, hematite, and barite in an oxidizing environment, while local enrichment of Ce resulted from the redox change of Ce3+→Ce4+ under the same condition. This shows that the chemical composition of laterite enwrapping the bauxite also took part in Quaternary bauxite transformation. This study shows that the elements migrations during bauxite transformation were influenced by multiple independent factors except for the elemental attributes.

Supergene Alteration of Platinum-Group Minerals and the Formation of Pd-Cu-O and Pd-I-O Compounds In the Limoeiro Ni-Cu-(PGE) Deposit, Brazil

Abstract The effects of weathering of platinum-group minerals (PGM) in the Limoeiro nickel-copper and platinum-group element [Ni-Cu-(PGE)] deposit reveal a progressive alteration of the abundant primary merenskyite, including neoformation of Pd-Cu±Bi rosettes and a rare I-rich PGM in the supergene reaction front of the deposit. Pyrrhotite with smaller equal proportions of chalcopyrite and pentlandite and minor PGM are typical of the fresh ore assemblage in the primary deposit. Weathering has produced a ∼3 m thick gossan cap over the base metal sulfide-rich parts of the Limoeiro primary ore. The mobility of Pt is very dependent on whether it is trapped in arsenide (sperrylite), which is very durable, or in bismuthotellurides ( i.e ., merenskyite–moncheite–melonite solid solution series), which break down more easily. The weathering over the Limoeiro deposit was not intense enough to overcome the pH- and redox-buffering capacity of the underling harzburgite and consequently Pd has not been leached, transported, or dispersed more than at a millimeter-scale. As a result, the Pt/Pd ratio of ∼0.4 remains roughly constant from the fresh ore at depth to the gossan on the surface. Weathering effects are apparent as deep as ∼50 m with the oxidation of pentlandite and pyrrhotite to produce violarite and pyrite, respectively. Chalcopyrite is more stable, beginning to alter at a depth of around 20 m. The PGM start to alter at a depth of ∼25 m where merenskyite becomes Pd-rich because much of the Te has been released into the adjacent goethite. With progressively more weathering towards the surface the merenskyite appears partially dissolved and pseudomorphed by goethite, which is often coated with newly formed Pd-Cu±Bi rosettes. A proportion of the remobilized Pd has precipitated as small (

An overview of rare-earth recovery by ion-exchange leaching from ion-adsorption clays of various origins

AbstractContinuous development of advanced technologies has created increasing demand for rare-earth elements (REE), with global emphasis on identifying new alternate sources to ensure adequate supply. Ore deposits containing physically adsorbed lanthanides are substantially lower grade than other REE deposit types; however, the low mining and processing costs make them economically attractive as sources of REE. To evaluate the commercial potential for the recovery of REEs from ion-adsorption deposits in a systematic manner, a standardized procedure for REE leaching was developed previously. Using this procudure it was found that, regardless of variations in ore origin and REE content, all REE consistently reached peak extraction levels under ambient conditions with fast kinetics. Various techniques to improve the REE extraction through process variations were also investigated: it was found that decreasing the L:S ratio, re-using leachate on fresh ores and counter-current leaching were all capable of increasing REE concentrations in the resultant leachate, albeit at the expense of REE extraction levels. In addition, the water content trapped in the leached material was found to contain significant amounts of REE and residual lixiviant requiring thorough washing of the solid residue.

Oxidative pre-treatment in thiosulphate leaching of sulphide gold ores

Abstract A diagnostic leaching showed that partial oxidation of the sulphide minerals in a gold ore was beneficial for thiosulphate leaching of gold. A pre-treatment process with oxidative ammoniacal solution enhanced the thiosulphate leaching of the sulphide ore, while the thiosulphate consumption was substantially reduced. The sulphide minerals partially decomposed in the pre-treatment process, exposing gold to the leach solution. Oxygen input by air bubbling and a longer contact time enhanced the oxidative ammonia pre-treatment process and hence accelerated subsequent thiosulphate leaching of the sulphide ore. Gold extraction in 0.8 M ammonia and 0.1 M thiosulphate solution after 24 h increased from 69% without pre-treatment to 81%, 84%, 90% and 94% respectively after 1, 3, 7 and 22 h pre-treatment. The consumption of sodium thiosulphate was 2.37 kg/t after 24 h leaching without pre-treatment, but was negligible after over 1 h oxidative ammonia pre-treatment. A counter-current leaching process was conducted in the leaching of the sulphide ore. The fresh leachant still gave higher leaching rates in contact with the pre-leached ore, while the pre-used leachant had significantly lower leaching kinetics and overall gold extraction in contact with the fresh ore. This 2-step counter-current leaching process proved that the leachant, other than the passivation, was the determinant factor causing the gold leaching rates to decrease after a certain time of leaching. The findings enable the thiosulphate leaching of high sulphide containing gold ores to be more efficient at lower thiosulphate consumption following the oxidative ammoniacal pre-treatment.

Impact of oxidation on flotation of Ni–Cu sulphide ore with respect to grinding

Impact of oxidation on the flotation of a complex Ni–Cu sulphide has been investigated using two approaches. In the first approach, the samples to be floated were allowed to oxidise before grinding while in the second approach they were allowed to oxidise after grinding. Their flotation characteristics were examined with reference to behaviour of a fresh ore sample. Oxidation before or after grinding has produced an inferior nickel grade–recovery performance. However, the latter case has induced a much greater adverse effect associated with several times more nickel losses and poorer selectivity between pentlandite and pyrrhotite. This was due to over oxidation of part of pentlandite and more importantly enhanced flotation of pyrrhotite which is related to metal ion activation and elemental sulphur formation. Oxidation characteristics of samples in each category are discussed in terms of pH, redox and conductivity behaviour that are utilised for correlations with flotation performance.

Morphology and composition of gold in a lateritic profile, Fazenda Pison “Garimpo”, Amazon, Brazil

This study describes the morphological evolution of gold grains in a lateritic weathering profile in an equatorial rainforest climate. Primary sources of gold are quartz veins associated with shallow granophyric intrusion. Gold grains were found in fresh ore, saprolite, transition zones, ferruginous duricrust, red latosol, and yellow latosol. Irregularly shaped grains predominate, with smaller proportions of dendritic and prismatic forms. Gold grains are weathered in the uppermost 10 m of the regolith. Mean gold grain size is maximum in the duricrust (>125 μm) and decreases progressively upward into the yellow latosol (<90 μm). Voids and corrosion pits appear on grain surfaces, and progressive rounding is observed from the bottom of the profile to the top. Gold grains can be classified as either homogeneous or zoned with respect to their chemical composition. Homogeneous grains contain 2–15% Ag (mean 8.3%). Zoned grains have more variable Ag contents; grain cores have means of approximately 10% or 23% Ag, with Ag-poor zones of approximately 3.7% Ag along internal discontinuities and/or outer rims. Formation of Ag-poor rims is due to preferential depletion of silver. Processes responsible for duricrust formation may preserve some grains as large aggregates, but subsequent transformation into latosol further modifies them.

Biooxidation of arsenopyrite concentrate using BIOX® process: Industrial experience in Tamboraque, Peru

The Tamboraque Plant is located in the mining district of Viso-Aruri, approximately 90 km east of Lima, Peru, at an altitude of 3000 m above sea level. In 1980 the previous owners of the mine and processing plant, Minera Lizandro Proaño S.A. (MLPSA), initiated an investigation into the available technologies for the recovery of refractory gold from old tailings. The Coricancha mine is a polymetallic ore deposit and lead and zinc concentrates can be produced by flotation. The zinc flotation tailings can be treated further by differential flotation to produce an arsenopyrite concentrate containing the bulk of the gold. The “TAMBORAQUE” project involved the expansion of the ore treatment capacity of the plant from 200 to 600 ton/day. The expansion also involved the installation of a separate flotation section for the zinc tailings and a BIOX® and CIL plant for the treatment of the arsenopyrite concentrate. The first phase of the project involved the installation of a flotation and BIOX® plant for the treatment of an existing zinc flotation tailings dump accumulated over the years. The second phase involved the expansion of the capacity of the existing plant to treat fresh ore from the mine. Initial batch tests indicated that the arsenopyrite concentrate could be treated successfully using biooxidation. A 50 kg/day biooxidation pilot plant was commissioned in Lima, using a native bacterial culture isolated from acid mine drainage from the Coricancha mine. MLPSA operated the pilot plant successfully for 20 months. At this stage MLPSA contacted Gencor (now Gold Fields Limited) for assistance in the optimization of the process. The continuous testwork indicated that 90% gold recovery can be achieved after only 80% sulfide oxidation. A licence agreement was concluded between MLPSA and Gencor in 1995 for the use of the BIOX® technology at the Tamboraque plant. As part of the agreement, Gencor carried out the process design of the biooxidation plant. Continuous plant operation commenced at the end of August 1998 after successful commissioning of the plant. The feed rate through the plant was, however, below the design due to concentrate shortages. The plant reached the design capacity during 2002, achieving 85% gold recovery on a bulk pyrite and arsenopyrite concentrate produced from fresh ore from the mine. The mining and metallurgical activities were, however, shut down in October 2002 due to financial and mining related problems.

Dispersion of gold and base metals in the Mborguéné lateritic profile, east Cameroun

Abstract In lateritic profiles, the behavior of trace elements is difficult to predict and may vary significantly from one element to another. As this behavior directly controls the formation of the secondary dispersion halo around mineralization, it has a dramatic influence on the effectiveness of geochemical techniques in such environments. In the Betare Oya region, in east Cameroun, gold mineralization was indicated by contents of As, Bi, Ag, Mo, W, Pb, and Au. The dispersion of Au and associated trace elements was studied in detail from the fresh ore in deep drill hole samples to soils in surface materials. The local geology consists of Proterozoic (Birrimian) volcanosediments dipping northwest at 35 degrees. Bedrock is covered by a deep (25 m) weathered mantle with ferruginous induration at the top. The mineralization is related to silicified structures and is completely oxidized and weathered at the surface. Trace elements have been dispersed in the lateritic profile. Four main chemical dispersion modes have been defined here for base metals: Bi is residual and is little dispersed; W, Mo, Pb, and Au are progressively remobilized and well dispersed; As is strongly associated with Fe and widely distributed, while Ag is completely leached. An attempt is made to evaluate and compare the size of the geochemical dispersion haloes in the different horizons of a laterite profile and to define an order for halo size at the top of the profile: Ag Little dependent on the hydromorphic processes, a new model for the formation of secondary haloes in laterites is proposed. Haloes could also be produced during lateritization by downward progress of the weathering front. Mineralized veins are dissolved in the top horizons, and trace elements are dispersed and concentrated in the surrounding ferruginous horizons.

Tropical weathering control of Ni, Cu, Co, and platinum group element distributions at the O'Toole Ni-Cu sulphide deposit, Minas Gerais, Brazil

Abstract The O'Toole nickel sulphide deposit is located in the Southern Plateau morphological and structural province of Minas Gerais, which has a humid tropical climate characterized by a mean temperature of 19°C and rainfall of 1600 mm. The primary ore reserve is 5.44 million tonnes at 2.72% Ni, 0.45% Cu, 0.06% Co, and 1.3 ppm combined platinum-group elements. Tropical weathering of the vertically dipping orebody has created gossans at the surface, an oxidized zone to a depth of about 20 m, and a zone of transition above fresh ore to a depth of up to 70 m. The weathering profile is similar mineralogically to the profiles at the Kambalda, Mt. Windarra, and Agnew Ni sulphide deposits in Western Australia, but differs in the depth extents of its mineralogically distinctive zones. These zones exhibit geochemically distinctive enrichments and depletions of various elements in this environment based on mass balance calculations and on the relative immobility of iridium. The work presented characterizes the geochemical behavior of Ni, Cu, Co, and platinum-group elements in the weathering of the O'Toole deposit.

Concept and present state of a coal‐based smelting reduction process for iron ore fines

The concept of a two‐stage smelting reduction process is presented. In the first stage highly metallized iron ore fines are produced in a circulating fluidized bed. In the second stage a hot metal is produced in a melter‐gasifier where – together with metallized ore – coal and oxygen are injected to generate the required heat and the CO‐rich reducing gas. The process was tested stepwise in pilot scale installations. Although only a reduction temperature of 830 °C instead of the required 880–900 °C could be realized in the pilot unit, test results make it very probable that a metallization of 90% can be reached with any fine ore without sticking problems, if the ore is covered with a carbon layer by CO decomposition in a pretreatment stage with the reduction offgas at 500–600 °C. The CO decomposition on the fresh ore leads to a high gas utilization which renders a CO2 washing stage and gas recycling unnecessary.To prove the technical and economic feasibility of the combined process, the next development step should be the design and operation of a larger pilot plant with a capacity of at least 5 t hot metal/h for continuous and joint operation of both the melter/gasifier and the reduction stage.

The seismic signature of the Elura orebody

A limited, experimental seismic refraction survey over the Elura massive lead?zinc sulphide orebody obtained travel time data and time?distance plots with distinctive features. These can be regarded as a seismic signature of a zone of low seismic velocity, limited in dimensions by the higher velocity weathered host rock, and the much higher velocity fresh host rock and ore at depth. At Elura, these are produced by the low velocity plug of gossan which extends down through the weathered bedrock to the level of the fresh host rock and ore at a depth of about 90 m. The signature shows low seismic apparent velocities across the area of limited surface gossan. These apparent velocities are only slightly greater than the velocity of the surface material. In addition, there occur marked negative apparent velocity segments on the travel time?distance plots. These only occur on the further edge of the low velocity (gossan) zone to that of the location of the shotpoints. It is considered that these features or seismic signatures are produced by diffraction effects around the low velocity zone.

The geology of the manganese ore deposits of talwara, district Banswara, Rajasthan

Talwara (23° 34′: 74° 22′) is a small Manganese-producing locality in the district of Banswara, Rajasthan. From the Banswara Town, Talwara can be reached by a motorable road. In the past, the Manganese ores of the locality have drawn very little attention of the geologists. The ores of Manganese, being associated exclusively with the Aravalli limestone of Rajasthan, occur in the form of scattered masses occupying solution cavities, fissures, etc., in limestone. Aravalli quartzites, conglomerates, phyllites and slates also occur in the vicinity of Talwara. The white limestone with a mosaic structure is of common occurrence and is composed of calcite and dolomite with some magnetite. The impurer varieties of limestone are characterised by the presence of tremolite, hornblende and quartz with a little of biotite. Schistosity is developed only in a calc-amphibole rock having alternating bands of hornblende and limestone. Crush-breccia is noticed occurring in association with manganiferous limestone at a distance of about 2 miles west of Talwara. This breccia might have originated due to severe local crushing of the country-rock. The limestones seemed to be a product of low-grade metamorphism of a calcareous sediment. Fresh ores are generally hard and cavernous but on weathering they become softer and soily. Fragments of unreplaced limestone are occasionally present in the ore-bodies. This limestone has also been replaced by the Manganese ores to a greater or lesser extent, depending on the structural characters of the host rock. The ores are composed largely of massive and colloform cryptomelane. Pyrolusite forms an insignificant part of the ores. There are two generations of cryptomelane, of which, the earlier colloform one is veined by the later generation of cryptomelane. There are also examples of pseudomorphous replacement of limestone by cryptomelane. Most of the pyrolusite was derived from the supergene alteration of cryptomelane. From their nature and mode of occurrence the Manganese ores are classified as outcrop secondary ores formed in cavities in crystalline limestones belonging to the less metamorphosed type of Dharwar.