Bulk Ore Research Articles

Mid-Silurian back-arc spreading at the northeastern margin of Gondwana: The Dapingzhang dacite-hosted massive sulfide deposit, Lancangjiang zone, southwestern Yunnan, China

The Dapingzhang dacite-hosted volcanogenic massive sulfide deposit is located in a late Paleozoic collisional zone, the Sanjiang fold-and-thrust belt, characterized by a collage of Gondwana-derived terranes at the southern margin of the South China (Yangtze) block. This area has experienced repeated Paleozoic and Mesozoic collisional and extensional events, and is overprinted by Himalayan strike-slip and thrust movements. The Dapingzhang orebody is strongly sheared into discontinuous ore lenses and blocks, and is hosted by a several-hundred-meter-thick volcanic rock sequence of dacite, with minor metabasalt (spilite), rhyolite, and chert. Bulk-rock Nd isotope data give εNd (429Ma) values of +2 to +5, and indicate a dominantly mantle source, or origin from young continental crust (TDM~800–1000Ma). The dacites have distinctly low abundances of Ti, Nb, Ta, Zr, Th, and REEs, which is typical of subduction-related volcanism.The base-metal mineralization occurs as polymetallic massive sulfide mineralization, mainly pyrite, sphalerite, galena, chalcopyrite, tetrahedrite–tennantite, and locally barite, and as pyrite–chalcopyrite stockworks. Pervasive hydrothermal alteration is dominantly quartz–sericite. Maximum enrichment in gold, bismuth, selenium, and tellurium is at the interface between the stockwork and massive sulfide mineralization styles. Deeper parts of the stockwork zone are characterized by elevated molybdenum and rhenium, whereas the distal parts to the massive sulfide mineralization have high mercury, antimony, zinc, cadmium, arsenic, lead and silver. The metal association and mineral assemblage are typical of volcanic rock-hosted massive sulfides in back-arc volcanic settings.Uranium–Pb dating on zircon by LA-ICP-MS defines an age of 429±3Ma (2σ) (n=19) for the dacite sequence. Rhenium–Os isotope data on Mo-rich bulk ore samples define an isochron of 429±10Ma (2σ) (n=9; MSWD 0.21; initial 187Os/188Os 3.1±1.9). Common Os is very low, and the absolute abundances of 187Re and 187Os define a model age of 429±4Ma (n=9; 95% confidence). The mid-Silurian dacite sequence and associated massive sulfide mineralization identify a hitherto unknown early rifting and back-arc seafloor spreading event at the northeastern Gondwana margin related to the early evolution of the Paleotethys Ocean.

Shake flask and column bioleaching of a pyritic porphyry copper sulphide ore

The purpose of this study was to test the feasibility of using bacterial leaching to solubilize copper from a porphyry sulphide ore, a part of the Sarcheshmeh Copper Complex. The bulk ore sample contained 18% pyrite and 0.8% Cu mostly as secondary chalcocite and Cu oxides. Mineral microscopy showed that pyrite grains in this porphyry ore were coated by chalcocite. Conventional flotation could not be used for ore beneficiation because Cu-sulphide could not be selectively separated from pyrite and consequently the flotation concentrate contained too much Fe and less Cu. Hence bioleaching was tested as an alternative process for this ore. The bioleaching was tested with a consortium of mesophilic acidophiles comprising Leptospirillum and Acidithiobacillus spp., originally enriched from the Sarcheshmeh site. Several mineral salt formulations were tested in shake flask bioleaching experiments. These experiments resulted in 89–92% Cu yields with no discernible differences between the different formulations. Sterile controls representing chemical acid leaching resulted in about 60% Cu solubilization. For column bioleaching experiments, ore samples (~40kg each; 75% −12mm) were agglomerated and treated with a schedule of 4days of irrigation and 4days of rest period. The column bioleaching tests yielded Cu recoveries of about 90%. The abiotic control had 50% Cu recovery. Thus the test results were favorable for using the bioleaching approach for this Cu-ore material.

Influence of Texture and Trace Element Composition on Hematite to Wüstite Reduction Rates of Fine Iron ore Fragments

Reduction of ore is the key process in its conversion to the metal form, and the reducibility of ore fragments is therefore a crucial parameter in smelting operations. At constant oxygen fugacity, reducibility is controlled by the texture of the ore fragments, which determines the transport length from reduction front to fragment interface, and the chemistry of the ore fragments, which impacts element mobility within the crystal lattice. Their relative contribution was studied here for iron-ore reduction by combining compositional analyses and thermo-gravitational reduction experiments on individual ore fragments. Results indicate that despite large, and ore-characteristic differences in chemistry, ore-fragment composition has a negligible impact on reducibility. The large variations among bulk ores; e.g. the start of hematite-tomagnetite reduction varies by over 300°C, is therefore attributable to ore-texture effects. Porous, goethitedominated ores show the highest reducibility, followed by fractured and layered fragments and finally dense ore fragments.

Modeling and Scheduling Optimization for Bulk Ore Blending Process

A new scheduling model for the bulk ore blending process in iron-making industry is presented, by converting the process into an assembly flow shop scheduling problem with sequence-depended setup time and limited intermediate buffer, and it facilitates the scheduling optimization for this process. To find out the optimal solution of the scheduling problem, an improved genetic algorithm hybridized with problem knowledge-based heuristics is also proposed, which provides high-quality initial solutions and fast searching speed. The efficiency of the algorithm is verified by the computational experiments.

The Woxi W–Sb–Au deposit in Hunan, South China: An example of Late Proterozoic sedimentary exhalative (SEDEX) mineralization

The Woxi W–Sb–Au deposit in Hunan, South China is hosted by Proterozoic metasedimentary rocks, a turbiditic sequence of graywacke, siltstone, sandy slate and slate. The deposit has two principal styles of mineralization: stratiform and stockwork. The stratiform ores, which account for about 75% of the total proven ore reserves, are composed predominantly of interbedded, massive to laminated Au-bearing quartz, stibnite, scheelite, pyrite, and silty clays. Fine layering, at the macro- to microscale, is the most striking feature of the ores, with individual mm- to cm-scale bands traceable over distances of several meters to a few hundred meters along strike. Structures indicative of soft-sediment deformation due to slumping and synsedimentary sliding are commonly observed in the banded ores and the barren quartz–carbonate beds in the adjacent host rocks. The stockwork mineralization accounts for about 25% of the total ore reserves and is restricted to a 3–10m-thick zone immediately beneath the stratiform ores. It is characterized by numerous quartz+pyrite±scheelite stringer veins that are either subparallel or near perpendicular to the overlying stratiform ore layers. Alteration at Woxi occurs as semiconformable, tabular blankets asymmetrically enveloping the orebodies along their entire length, and, is dominated by a quartz+sericite+chlorite±carbonate assemblage. The footwall alteration is generally more intense and somewhat thicker than the hanging-wall alteration. Geochemical data show that, with distance above and below the mineralized horizons, contents of W, Au, As, and Sb systematically decrease, whereas concentrations of other trace elements such as Hf, Sc, Th, Ta, Y, Zr, Nb and REEs gradually increase. This may reflect a decreasing hydrothermal input in the sediments and an increasing dominance of detrital and seawater-derived components. The chondrite-normalized REE patterns of both bulk ores and individual minerals are comparable to those of many SEDEX-type deposits and associated exhalites, implying similar mineralizing fluids for these deposits. Sulfides from the ore have negative and variable δ34S values (from −12.3‰ to −1.2‰), suggesting a dominant sulfur contribution of bacterial sulfate reduction. A syngenetic (SEDEX) model is thus proposed for the formation of the Woxi deposit. Convective seawater circulated through the sediment pile and episodically vented metalliferous hydrothermal fluids onto the sea floor. Each exhalative episode was preceded by a period dominated by chemical and turbiditic sedimentation (footwall alteration blanket), followed by a peak release of hot metalliferous brines (stratiform ores and associated stringers), and terminated by a waning influx of hydrothermal fluids accompanying burial by later turbidites (hanging-wall alteration blanket).

Ore geochemistry, zircon mineralogy, and genesis of the Sakharjok Y-Zr deposit, Kola Peninsula, Russia

The Sakharjok Y-Zr deposit in Kola Peninsula is related to the fissure alkaline intrusion of the same name. The intrusion ∼7 km in extent and 4–5 km2 in area of its exposed part is composed of Neoarchean (2.68–2.61 Ma) alkali and nepheline syenites, which cut through the Archean alkali granite and gneissic granodiorite. Mineralization is localized in the nepheline syenite body as linear zones 200–1350 m in extent and 3–30 m in thickness, which strike conformably to primary magmatic banding and trachytoid texture of nepheline syenite. The ore is similar to the host rocks in petrography and chemistry and only differs from them in enrichment in zircon, britholite-(Y), and pyrochlore. Judging from geochemical attributes (high HSFE and some incompatible element contents (1000–5000 ppm Zr, 200–600 ppm Nb, 100–500 ppm Y, 0.1–0.3 wt % REE, 400–900 ppm Rb), REE pattern, Th/U, Y/Nb, and Yb/Ta ratios), nepheline syenite was derived from an enriched mantle source similar to that of contemporary OIB and was formed as an evolved product of long-term fractional crystallization of primary alkali basaltic melt. The ore concentrations are caused by unique composition of nepheline syenite magma (high Zr, Y, REE, Nb contents), which underwent subsequent intrachamber fractionation. Mineralogical features of zircon-the main ore mineral—demonstrate its long multistage crystallization. The inner zones of prismatic crystals with high ZrO2/HfO2 ratio (90, on average) grew during early magmatic stage at a temperature of 900–850°C. The inner zones of dipyramidal crystals with average ZrO2/HfO2 = 63 formed during late magmatic stage at a temperature of ∼500°C. The zircon pertaining to the postmagmatic hydrothermal stage is distinguished by the lowest ZrO2/HfO2 ratio (29, on average), porous fabric, abundant inclusions, and crystallization temperature below 500°C. The progressive decrease in ZrO2/HfO2 ratio was caused by evolution of melt and postmagmatic solution. The metamorphic zircon rims relics of earlier crystals and occurs as individual rhythmically zoned grains with an averaged ZrO2/HfO2 ratio (45, on average) similar to that of the bulk ore composition. The metamorphic zircon is depleted in uranium in comparison with magmatic zircon, owing to selective removal of U by aqueous metamorphic solutions. Zircon from the Sakharjok deposit is characterized by low concentrations of detrimental impurities, in particular, contains only 10–90 ppm U and 10–80 ppm Th, and thus can be used in various fields of application.

Source of metals in the Guocheng gold deposit, Jiaodong Peninsula, North China Craton: Link to early Cretaceous mafic magmatism originating from Paleoproterozoic metasomatized lithospheric mantle

Widespread Mesozoic Au and other hydrothermal polymetal (Zn–Pb–Cu–Mo–Ag–W–Fe–REE) deposits or smaller prospects occur in association with ancient mobile belts surrounding and cutting through the North China Carton (NCC). Among these, the gold ores of the Jiaodong Peninsula, Shandong Province, eastern NCC, represent the largest gold district in China. However, the genesis of these important gold mineralizations has remained controversial, notably their relationships to widespread mafic magmatism of alkaline affinity.The ore bodies of the Guocheng gold deposit on the Jiaodong Peninsula are fracture-controlled, sulfide-rich veins and disseminations, formed contemporaneously with abundant dolerite, lamprophyre and monzonite dikes at ca. 120Ma. Dolerite dikes possess mantle-like major element compositions and alkaline affinity, associated with prominent subduction-type trace element enrichments. The dikes show petrographic and chemical evidence of magma mixing that triggered exsolution of magmatic sulfide and anhydrite crystallization, preserved as primary inclusions in phenocrysts. LA-ICP-MS analysis of magmatic sulfide inclusions demonstrates that metal abundance ratios (Ag, As, Au, Bi, Co, Cu, Mo, Ni, Pb, Sb, Zn) largely correspond to those of both unaltered bulk rock and bulk ore. Together with identical Pb isotope ratios of dolerite and bulk ore, this demonstrates that gold mineralization and dolerite dikes share a common source.Lead isotope signatures of the ore sulfides are much less radiogenic (17.08<206Pb/204Pb<17.25, 15.41<207Pb/204Pb<15.45, 37.55<208Pb/204Pb<37.93) relative to the Pb signature of Phanerozoic convecting mantle and plot to the left of the Geochron and above the MORB-source mantle Pb evolution line. Forward Monte Carlo simulations indicate three events for the U–Th–Pb isotope evolution: (1) late Archean formation of juvenile crust is followed by (2) subduction of this aged crust at ca. 1.85Ga along with the assembly of Jiao–Liao–Ji mobile belt (suture within Columbia supercontinent). This late-Archean subducted crust released fluids with drastically reduced U/Pb that metasomatized the overlying depleted mantle, which formed cratonic lithospheric mantle. This metasomatized lithospheric mantle was (3) tapped in response to early Cretaceous extensional tectonics affecting notably the eastern margin of the NCC to generate mafic magmas and associated gold mineralization at Guocheng. Similarly non-radiogenic uranogenic Pb isotope data characterize the contemporaneous mafic dikes and gold deposits in the entire Jiaodong Peninsula, suggesting that our genetic model applies to the entire Jiaodong gold district.We propose that early Cretaceous melting of subcontinental lithospheric mantle metasomatized by subduction fluids during Paleoproterozoic amalgamation of terranes to the eastern NCC along with Columbia supercontinent assembly generated mafic magmatism and associated gold deposits. Given the conspicuous association of Phanerozoic hydrothermal ore deposits associated with reactivated Paleoproterozoic mobile belts, we envisage that our genetic model, which largely corresponds to that which is proposed for the Bingham porphyry-Cu–Au–Mo deposit, USA, may explain much of the magmatic-hydrothermal activity and associated ore formation all around the NCC.

Quantitative Measurements of Loss on Ignition in Iron Ore Using Laser-Induced Breakdown Spectroscopy and Partial Least Squares Regression Analysis

Laser-induced breakdown spectroscopy (LIBS) and partial least squares regression (PLSR) have been applied to perform quantitative measurements of a multiple-species parameter known as loss on ignition (LOI), in a combined set of run-of-mine (ROM) iron ore samples originating from five different iron ore deposits. Global calibration models based on 65 samples and their duplicates from all the deposits with LOI ranging from 0.5 to 10 wt% are shown to be successful for prediction of LOI content in pressed pellets as well as bulk ore samples. A global independent dataset comprising a further 60 samples was used to validate the model resulting in the best validation R(2) of 0.87 and root mean square error of prediction (RMSEP) of 1.1 wt% for bulk samples. A validation R(2) of 0.90 and an RMSEP of 1.0 wt% were demonstrated for pressed pellets. Data preprocessing is shown to improve the quality of the analysis. Spectra normalization options, automatic outlier removal and automatic continuum background correction, which were used to improve the performance of the PLSR method, are discussed in detail.

Magmatogenic manganese ores of the South Minusa Intermontane Trough

The first data on the mineral composition and formation conditions of manganese ore at the Chapsordag and Malosyrsky deposits in the Askiz ore district of Khakassia are integrated and systematized. The detailed mineralogical mapping of the deposits has been carried out. The identification of minerals and examination of the ore microstructure were performed with optical microscopy in transmitted and reflected light and using SEM/EDS, EMPA, XRD, IRS, and other methods. It was established that the ore mineralization is spatially and genetically related to the Early Devonian magmatism and accompanying hydrothermal activity and metasomatism. Syngenetic braunite was detected for the first time in elevated amounts reaching an economic level in the devitrified groundmass of volcanic rocks, in cement of lava breccia, and in fragments in pyroclastic rocks. By analogy with iron deposits, this magmatogenic type of manganese mineralization is regarded as ore lavas and tuffs combined with metasomatic and hydrothermal mineral assemblages into a strata-bound orebearing complex and as a source of hydrothermal metasomatic ore. The elevated Mn content in magmatic melts of the Early Devonian trachybasalt-trachyandesite-trachydacite association is caused by assimilation of Riphean and Lower Cambrian high-Mn carbonate sequences in crustal magma chambers. In contours of economic orebodies, the hydrothermal economic ore is recognized as sites of massive, patchy and impregnated, brecciated, stringer-disseminated, and disseminated varieties. High-grade massive ore occurs as stratiform and branching bodies up to 1.5 m thick and a few tens of meters long and as smaller pocketlike bodies. Braunite and pyrolusite (polianite) are major ore minerals varying in size, degree of crystallinity, and character of intergrowths with associating minerals. Gangue minerals include carbonates, sulfates, albite, quartz, chlorite, actinolite, piemontite, and okhotskite, a Mn-pumpellyite identified in Russia for the first time and studied in detail in this paper. The veined hydrothermal ore is classified as a calcite-barite-pyrolusite type. The crystallization temperature of hydrothermal metasomatic ore is estimated at 350–180°C; oxygen fugacity is above the hematite-magnetite buffer. The surface of high-grade ore is encrusted with supergene goethite-hydrogoethite, chalcedony-hematite, and pyrolusite-psilomelane crusts and veinlets (less than 1% of the bulk ore mass). The data obtained facilitate prospecting for high-quality manganese ore at walls of superimposed rifts in fold regions, including large economic manganese concentrations in the form of ore lavas and tuffs as products of solidification of metalliferous melt.

Electrochemical studies on interplay of mineralogical variation and particle size on bioleaching low grade complex sulphide ores

The interplay of mineralogical variation and mineral phase distribution within varying particle sizes on the dissolution behaviour of a low grade complex sulphide ore was investigated through bioleaching experiments and electrochemical technique. Investigations were carried out utilizing mineralogical data on the variations in mineral and phase distribution within particle sizes of <53 μm, 53–75 μm, 75–106 μm and 106–150 μm in mixed mesophilic cultures of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans. Electrochemical behaviour was studied using particulate electrodes from the four varying particle sizes and from massive electrodes prepared from the two major sulphide mineral rich phases (sphalerite-rich and galena-rich) and a complex mineralogical phase of the bulk ore. Bioleaching studies reveal the highest recoveries at a particle size of 75 μm, while electrochemical investigations reveal the highest dissolution at particle size of 106 μm. Electrochemical results show that sphalerite rich phase has the highest dissolution rate while galena-rich complex phase has the least. SEM studies confirm the highest bacterial attack at the sphalerite-rich phase. The discrepancies between the dissolutions within particle sizes obtained from bioleaching experiments and electrochemical studies are consistent with and attributed both to the physical and mineralogical influences. Electrochemical behaviour is influenced and controlled by galvanic interaction resulting from mineralogical variation, while bioleaching behaviour is influenced by mineralogical variation as well as physical effect of particle size.

Gold in the Brunswick No. 12 volcanogenic massive sulfide deposit, Bathurst Mining Camp, Canada: Evidence from bulk ore analysis and laser ablation ICP─MS data on sulfide phases

The 329-Mt Brunswick No. 12 volcanogenic massive sulfide deposit (total resource of 163 Mt at 10.4% Zn, 4.2% Pb, 0.34% Cu, and 115 g/t Ag) is hosted within a Middle Ordovician bimodal volcanic and sedimentary sequence. Massive sulfides are for the most part syngenetic, and the bulk of the sulfide ore occurs as a Zn–Pb-rich banded sulfide facies that forms an intimate relationship with a laterally extensive Algoma-type iron formation and defines the Brunswick Horizon. Zone refining of stratiform sulfides is considered to have resulted in the development of a large replacement-style Cu-rich basal sulfide facies, which is generally confined between the banded sulfide facies and an underlying stringer sulfide zone. Complex polyphase deformation and associated lower- to upper-greenschist facies regional metamorphism is responsible for the present geometry of the deposit. Textural modification has resulted in a general increase in grain size through the development of pyrite and arsenopyrite porphyroblasts, which tend to overprint primary mineral assemblages. Despite the heterogeneous ductile deformation, primary features have locally been preserved, such as fine-grained colloform pyrite and base and precious metal zonation within the Main Zone. Base metal and trace element abundances in massive sulfides from the Brunswick No. 12 deposit indicate two distinct geochemical associations. The basal sulfide facies, characterized by a proximal high-temperature hydrothermal signature (Cu–Co–Bi–Se), contains generally low Au contents averaging 0.39 ppm (n = 34). Conversely, Au is enriched in the banded sulfide facies, averaging 1.1 ppm Au (n = 21), and is associated with an exhalative suite of elements (Zn–Pb–As–Sb–Ag–Sn). Finely laminated sulfide lenses hosted by iron formation at the north end of the Main Zone are further enriched in Au, averaging 1.7 ppm (n = 41) and ranging up to 8.2 ppm. Laser ablation inductively coupled plasma-mass spectrometry (ICP-MS) analyses of pyrite (n = 97) from the north end of the Main Zone average 2.6 ppm Au and range from the detection limit (0.015 ppm) to 21 ppm. Overall, these analyses reveal a distinct Au–Sb–As–Ag–Hg–Mn association within pyrite grains. Gold is strongly enriched in large pseudo-primary masses of pyrite that exhibit relict banding and fine-grained cores; smaller euhedral pyrite porphyroblasts, and euhedral rims of metamorphic origin surrounding the pyrite masses, contain much less Au, Sb, Ag, As, and Sn. Arsenopyrite, occurring chiefly as late porphyroblasts, contains less Au, averaging 1.0 ppm and ranging from the detection limit (0.027 ppm) to 6.9 ppm. Depth profiles for single-spot laser ablation ICP-MS analyses of pyrite and arsenopyrite display uniform values of Au and an absence of discrete microscopic inclusions of Au-bearing minerals, which is consistent with chemically bonded Au in the sulfide structure. The pervasive correlation of Au with Sn in the Zn–Pb-rich banded sulfide facies suggests similar hydrothermal behavior during the waxing stages of deposition on the seafloor. Under high temperature (>350oC) and moderate- to low-pH conditions, Au and Sn in hydrothermal fluids would be transported as chlorocomplexes. An abrupt decrease in temperature and aH2S, accompanied by an increase in fO2 and pH during mixing with seawater, would lead to the simultaneous destabilization of both Au and Sn chlorocomplexes. The enrichment of Au in fine-grained laminated sulfides on the periphery of the deposit, accompanied by sporadic occurrences of barite and Fe-poor sphalerite, supports lower hydrothermal fluid temperatures analogous to white smoker activity on the flanks of a large volcanogenic massive sulfide system. In lower temperature (<350oC) and mildly acidic hydrothermal fluids, Au would be transported by thiocomplexes, which exhibit multifunctional (retrograde–prograde) solubility and a capacity to mobilize Au to the outer parts of the sulfide mound. The sluggish nature of this low-temperature venting together with larger variations in ambient fO2 could lead to a sharp enrichment of Au towards the stratigraphic hanging wall of massive sulfide deposits.

Impact of the Treasure oil spill on African penguins Spheniscus demersus at Dassen Island: case study of a rescue operation

The bulk ore carrier MV Treasure sank between Robben and Dassen islands off western South Africa in June 2000. Although releasing less oil than the Apollo Sea spill six years earlier, the number of African penguins Spheniscus demersus oiled (approximately 19 000) in the Treasure spill was almost double the number oiled in the Apollo Sea incident. The majority of oiled penguins was collected from Robben Island. The capture, stabilisation and transport of oiled penguins following the Treasure spill were substantially more successful than during the Apollo Sea rescue operation and resulted in an increase in the percentage of oiled penguins that were released back to the wild. In addition to the 19 000 oiled penguins that were caught, 19 500 un-oiled birds (12 345 from Dassen Island) were evacuated to Cape Recife, 800 km to the east, to prevent them from becoming contaminated. The evacuated birds returned rapidly to Dassen Island and many resumed breeding soon after their return. The restoration success (proportion of birds observed at Dassen Island that were recorded breeding) was substantially greater for evacuated birds than for de-oiled birds. Lightly oiled birds that were released without being cleaned had lower survival rates and were less successfully restored into the breeding population than de-oiled birds, especially if more than 5% of their body was covered in oil. Reproduction exerted a greater cost to de-oiled birds than to evacuated birds. A total of 1 787 orphaned chicks was hand-reared at two separate facilities on the mainland and were released at Robben and Dassen islands. The chicks did not necessarily return to the colony at which they were released. The survival rates and restoration success of chicks reared at the two facilities differed, probably as a result of one group being overfed. Despite the death of about 2 000 African penguins in the Treasure spill, and the substantial disturbance that resulted from the rescue operation, the penguin colonies at Robben and Dassen islands increased by 18% and 26% respectively in the year following the spill. This increase was attributed to a significant increase in the biomass of anchovy Engraulis encrasicolus and sardine Sardinops sagax in 2001. These findings highlight the importance of preventing oil spills in the first place, and in the event of a large oil spill, the conservation value of evacuating un-oiled penguins to minimise their risk of becoming contaminated.

A comparative mineralogical and geochemical characterisation of iron ores from two Indian Precambrian deposits and Krivoy rog deposit, Ukraine: implications for the upgrading of lean grade ore

Iron ores from two important Precambrian belts in India are studied in detail. The first of these is the Jilling-Langalota deposit, hosted by banded iron formations along with generations of shales, tuffs belonging to Iron Ore Group of Eastern India and is hosted in the Singhbhum-North Orissa Craton. The second group of ores is from the Chitradurga basin in Eastern Dharwar Craton, Southern India. These form part of the Archaean greenstone belts and show a typical oxide–carbonate–sulphide association. The Jilling-Langalota deposit contains considerable amounts of blue dust that is absent in the Chitradurga deposit. Comparisons are made between the Indian iron ores and those of the Krivoy Rog province of the Central Ukrainian Shield. The Indian iron ores are relatively richer in Fe and contain higher amounts of alumina and phosphorous compared with those of the Krivoy Rog deposit. The Indian iron ore samples contain porous and friable oxides and hydroxides of iron with kaolinite, gibbsite and quartz. In contrast, the ores from Krivoy Rog are massive with negligible clay and a higher quartz content leading to very low alumina and very high silica contents in the ores and slime. The Indian ores and slimes are manganiferous in nature with high alumina, which is deleterious to processing and is due to the presence of intercalated tuffaceous shales and clay. The Eastern Indian iron ore deposits could have been formed due to enrichment of the primary ore by gradual removal of silica. It is believed that the massive ores result from direct precipitation while powdery blue dust is formed owing to circulating fluids, which leach away the silica from the protore. The host rock is exhalatic banded iron formation and the ubiquitous presence of intercalated tuffaceous shales point towards a genesis that could have involved Fe leaching from sea floor volcanogenic rocks. The nature of these ores along with the parting shale is responsible for production of large amounts of alumina rich slime during mining and handling. The detailed mineralogical characterisation studies aided by X-ray diffraction, scanning electron microscopy—energy dispersive spectroscopy, physical parameters and chemical characteristics have indicated the presence of various mineral phases and established the nature of iron-bearing and gangue assemblages of the bulk ores and slime samples from the three iron ore deposits. These in turn are useful in understanding the amenability of the ores and slimes for beneficiation and waste utilisation.

Restoration of oiled African penguins Spheniscus demersus a decade after the Apollo Sea spill

The bulk ore carrier Apollo Sea sank south-west of Dassen Island off western South Africa in June 1994, oiling approximately 10 000 African penguins Spheniscus demersus, most of which were collected from Dassen Island. A total of 4 076 de-oiled penguins was released with flipper bands. From 1994 to 2005, follow-up research using re-sighting and capture-mark-recapture methods indicated that about 73% of the de-oiled penguins observed back at Dassen Island attempted to breed, and were thus successfully restored into the breeding population. For de-oiled breeders, the median interval between their first recorded sighting and first recorded breeding attempt was 11 months, indicating a short-term delay in restoration. At least 45% of the de-oiled breeders were still being re-sighted five years after their release, and a minimum of 4% survived into their ninth year. These results represent the most successful restoration estimates anywhere in the world. The proportion of de-oiled juvenile penguins re-sighted back at Dassen Island and recorded breeding was lower than that of birds in adult plumage. De-oiled non-breeders spent significantly more time along the shore and less time within breeding colonies than de-oiled breeders. The mean proportion of de-oiled breeders that abstained from breeding each year during the study period was greater than expected. There was a negative relationship between breeding and subsequent survival and breeding, suggesting a cost of reproduction for de-oiled birds.

Archean Komatiitic Sill-hosted Chromite Deposits in the Zimbabwe Craton

Lenticular chromite deposits of widely varying age, metamorphic grade and strain rate, as well as size, shape, and ore quality, are widespread in greenschist to amphibolite grade greenstonegneiss terrain in the south-central part of the Zimbabwe craton and in granulite grade equivalents in the Northern Marginal zone of the Limpopo belt in the far south. In order of age and, very approximately, decreasing abundance, they form three groups: (1) early Archean (3.5–3.2 Ga) deposits associated with amphibolite grade greenstone remnants in the 3.6 to 3.35 Ga Tokwe gneisses (e.g., Hornet, Valley) and on the amphibolite grade eastern flank of the Shurugwi greenstone belt, and granulite grade greenstone remnants in the Northern Marginal zone (e.g., Inyala, Rhonda); (2) mid-Archean deposits within the ca. 3.0 Ga Shurugwi Group in the main greenschist part of the Shurugwi belt (e.g., Peak, Railway Block) and associated with the ca. 3.0 Ga Belingwean Supergroup in several other belts; and (3) late Archean (ca. 2.74 Ga) deposits mostly in the western segment of the Masvingo belt (e.g., Prince). With their host and country rocks, the deposits together preserve geologic and chromite compositional evidence of formation within poorly differentiated, komatiitic sills intruded into predominantly siliciclastic, BIF platformal sedimentary sequences associated with mafic and/or ultramafic lavas. Unlike the thin, laterally extensive chromitite layers associated with macrocyclic units of large, layered intrusions, the komatiitic sill-associated deposits are the remnants of laterally discontinuous (up to several tens of meters) thick chromitite layers or dunite-chromitite zones located at high stratigraphic levels of their host intrusions not far below the upper pyroxenite differentiates. In at least some deposits—for example, at Railway Block, where the chromitites form narrow, elongate bodies at least 1,000 m long—the lateral discontinuities are most likely primary; in many others, later deformation obscures the primary geometry. Chromitite formation may have been delayed by the late attainment of equilibrium crystallization and the reduced nature of the magma. The crystallization of thick, massive, cyclically layered, Cr-rich chromitites was most probably controlled by the stabilization of chromite relative to olivine by absorption of connate water derived from wet host sediments and by episodic, flow-through processes which, at Railway Block, may have been focused along narrow pathways across the magma chamber floor. The remarkable abundance of such chromitites and their formation in repeated episodes over 1,000 m.y. (cf. other cratons) can be attributed to generation of komatiitic magmas in a mantle source that was both Cr rich and strongly reduced. Archean komatiitic sill-hosted deposits constitute a third type of chromite deposit in addition to stratiform and podiform deposits in layered intrusions and ophiolites, respectively. The economically important variability of bulk ore compositions (especially Cr, Fe, Al, Mg) is due to several factors: magnetite introduction during serpentinization and talc-carbonate alteration at greenschist grade, subsolidus fluid-related and other metamorphic cation exchange processes (dependant on chromite body size), and, possibly, exsolution of Cr-Al and magnetite phase pairs, both at midamphibolite to granulite grade, as well as fluid-related retrogression and partial conversion of chromite to (mainly) chlorite during amphibolite metamorphism.

Differences in breeding success between African Penguins (Spheniscus demersus) that were and were not oiled in the MV Treasure oil-spill in 2000

About 19000 African Penguins (Spheniscus demersus) were oiled when the bulk ore carrier MV Treasure sank off the west coast of South Africa in June 2000. Of these, more than 17000 Penguins were cleaned, rehabilitated and released back to the wild. The breeding success of these birds was compared with unoiled birds and birds oiled during other oil-spills, by measuring fecundity, hatching success and fledging success from 2001 to 2005 on Robben Island. Fledging success averaged 61% in birds that were not oiled in the Treasure spill and 43% in birds oiled during the Treasure event, with a large proportion of the reduction attributable to higher mortality of older chicks. Factors that may have contributed to differential fledging success include long mean intervals between capture and cleaning (22 days) and between capture and release (48 days) for birds oiled in the Treasure spill. One implication of these results is, if a similar large spill should occur in the future, every effort should be made to treat the oiled birds as quickly as possible to reduce the risk of their suffering a similar reduction in breeding productivity. Further, the other interventions, such as relocation of unoiled birds and captive-rearing of orphaned chicks may need to receive higher priority than hitherto.

Effects of ore mineralogy on the microbial leaching of low grade complex sulphide ores

The effect of ore mineralogy on the microbial leaching of low grade complex sulphide ores was investigated by utilizing mineralogical data on the variations in mineral and phase distribution within particle sizes of − 53, 53, 75 and 106 μm of a Nigerian ore consisting of siderite, sphalerite, galena and quartz, with traces of pyrite and chalcopyrite. Bioleaching was conducted using mixed cultures of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans in mechanically stirred glass reactors. The highest bioleaching recoveries were obtained at a particle size of 75 μm, while particle sizes of 106 μm gave the least recoveries. Mineral phases and morphologies of the bulk ore and the leached residues respectfully examined with XRD and SEM analysis showed differences both in phase and morphological changes, with the 75 μm having the highest transformation and attack. Higher silica contents which reduced acidity, iron mobility and oxidation led to lower recoveries at particle sizes of 53 and − 53 μm.

Mineralogy and Geochemistry of the Nižná Boca Sb-Au Hydrothermal Ore Deposit (Western Carpathians, Slovakia)

Mineralogy and Geochemistry of the Nižná Boca Sb-Au Hydrothermal Ore Deposit (Western Carpathians, Slovakia)Samples from hydrothermal Sb-Au mineralization in the area SE of Nižná Boca village in the N&amp;iAzke Tatry Mountains were investigated using a variety of geochemical and mineralogical methods. Ore minerals typically occur in N-S striking quartz-carbonate veins hosted by an I-type biotite granodiorite to tonalite of Variscan Age (the Ďumbier Type). Paragenetic associations in the deposit are comparable to other mineralizations of the same type in the Ďumbierske Nízke Tatry Mountains. A quartz-arsenopyrite, pyrite stage of mineralization is the oldest with a calculated temperature of formation of about 445°C. It is followed by a quartz-carbonate-stibnite, zinkenite stage and, in turn, a quartz-carbonate-sphalerite-galena, boulangerite-gold stage. The gold typically contains between 9-18 wt.% Ag regardless of mineral association. No evidence for further generations of gold was found although it is possible that some gold was remobilized from the structure of the auriferous arsenopyrite. The Au and Ag content of the bulk ore ranges from 0.53 g.t-1to 20.2 g.t-1and from 0.9 g.t-1to 31.2 g.t-1, respectively. A tetrahedrite-chalcopyrite stage is followed by a barite-hematite stage - the youngest assemblage in the deposit. Fluid inclusions from the first mineralization stage are usually less than 3 μm in size and contain less than 3.6 wt.% CO2; salinity, density and homogenization temperature range from 2.7-16.3 wt.% NaCl(eq), 0.85-1.03 g.cm-1and 128-280°C, respectively.

Mineralogy and geochemistry of indium-bearing polymetallic vein-type deposits: Implications for host minerals from the Freiberg district, Eastern Erzgebirge, Germany

Located at the northwestern border of the Bohemian Massif in the European Variscides, the Erzgebirge is one of the most important Sn–W–Mo, Ag, Cu–Zn–Pb–In, U, and Bi–Co–Ni metallogenetic provinces in Europe. The ca. 1100 silver-base metal veins in the Freiberg metamorphic core complex are characterized by two principal types of late-Variscan polymetallic vein-type mineralization: (1) Quartz-bearing As(–Au)–Zn–Cu(–In–Cd)–Sn–Pb–Ag–Bi–Sb polymetallic sulphide association (‘kb’ ore-type), and (2) Carbonate- or quartz-bearing Ag–Sb polymetallic sulphide association (‘eb’ and ‘eq’ ore-type). High indium concentrations in the Freiberg silver-base metal vein district and other base metal and tin-polymetallic deposits suggest that the Erzgebirge is among the largest In-enriched ore provinces known worldwide. The first modern geochemical bulk ore and microprobe analyses addressing In distribution in the Freiberg district are presented in this paper and are compared with published data. Polymetallic veins in the Freiberg district show a wide range of In concentrations up to 0.15 wt.% with an average of 176 ppm ( n = 82). The ‘kb’ ore-type veins in the ‘Freiberg’ (up to 1560 ppm In, mean 253 ppm, n = 36), ‘Muldenhütten’ (up to 785 ppm In, mean 284 ppm, n = 10), and ‘Brand’ ore fields (up to 638 ppm In, mean 156 ppm, n = 15) occur the highest In resources in the Freiberg district. Two types of In concentration can be distinguished, based on microanalytical study. The first type was found in sphalerites of the Zn–Sn–Cu sequence (as presented in one of the figures in this article) which show In contents up to 0.38 wt.%, significant Cd up to 1.11 wt.%, and Ga contents up to 0.17 wt.%. Iron-rich sphalerites (mean 12.9 wt.% Fe, n = 202) from a representative Ag-base metal vein are characterized by In contents between 0.03 and 0.38 wt.% (mean 0.16 wt.% In, n = 202). A negative correlation exists between (Zn + Fe) and Cd, and (Zn + Fe) with In, reflecting structural substitution of In and Cd in sphalerite. The second type of In enrichment was identified as microscopic Zn–Cu–Sn–In–S grains in pyrite of a Cu-rich ‘kb’ vein. Quantitative electron images of these grains (up to 6 μm) shows high levels of Zn (5.6 to 52.8 wt.%), Cu (4.1 to 19.6 wt.%), Sn (0.3 to 17.2 wt.%), and In (1.3 to 2.9 wt.%). In the ternary (Cu + Ag)–(Sn + In)–(Zn + Fe) diagram, compositions of the Zn–Cu–Sn–In–S phase in a representative Cu-rich ‘kb’ ore-type sample fall along a linear compositional trend between Fe–Cu–In-rich sphalerite (Zn 0.76Fe 0.11Cu 0.06In 0.01S) and the ideal fields of petrukite and sakuraiite (Cu 0.29Zn 0.08Fe 0.32In 0.02Sn 0.13S). Both types of In enrichment support that the In-mineralization is associated with the Zn–Sn–Cu sequence (‘indium stage’) of the ‘kb’ ore-type association. Based on mineralogical, geochemical, isotopic, fluid inclusion, age relationships and structural data, the high In concentrations in base metal veins in the Erzgebirge may indicate an influence of fluids expelled from magmas during emplacement of post-collisional lamprophyric and rhyolitic dikes. The high In concentration of Cd- and Fe-rich sphalerites from Ag-base metal and Sn-polymetallic deposits in the Erzgebirge is an additional argument for a genetic link between these mineralization stages. Such evidence is significant for exploration of magma-affiliated In deposits in post-collisional settings.

ROCKNES OILED WILDLIFE RESPONSE BERGEN, NORWAY

ABSTRACT On January 19, 2004, the bulk ore carrier, Rocknes, capsized after striking rocks near Bergen, Norway. Tragically eighteen crewmembers lost their lives. Approximately 450 tonnes of marine fuel was spilled. Oil quickly spread over 15 kilometers of the Norwegian coastline, threatening the pristine fjord environment and oiling hundreds of animals. In past oiling events in Norway, the government has utilized trained and certified sharpshooters to humanely euthanize oiled birds. Immediately following the Rocknes oil spill, a group of non-govemmental organizations (NGO's) working in Norway formed a coalition called “Action Clean Birds,” and asked the government for formal permission to mount an oiled wildlife response. Permission was granted on the stipulation that a professional oiled wildlife response team be brought in to oversee the animal capture, transport, rehabilitation and reconditioning of the animals. The International Fund for Animal Welfare (IFAW) Emergency Relief (ER) Team, co-managed by the International Bird Rescue Research Center (IBRRC) was called upon to mount an oiled wildlife response effort. As the first authorized response for oiled wildlife in Norway, the Rocknes spill provided a platform to work with local wildlife rehabilitators, veterinarians, ornithologists and others, increasing their capacity to respond locally to future events involving oiled animals. During the month-long response, 131 oiled seabirds were captured, 81 of those were rehabilitated, reconditioned and released, the others died or were humanely euthanized as they were deemed unviable for release. If pre-planning had been involved, a significantly larger number of oiled birds could have been captured, increasing the probability that a higher percentage of them would have been viable for release due to early capture and treatment. This case study of the wildlife portion of the Rocknes response reviews steps taken to mitigate the effects of oil on wildlife, as well as demonstrates the importance of planning and preparedness as it relates to the success of an oiled wildlife response.