Sulphide ore minerals:surface chemical properties

The surfaces of iron-containing sulphide minerals were oxidised by a range of inorganic oxidants, and the resultant surface alteration products studied using various spectroscopic techniques. The characterisation of surface oxidation is relevant to the alteration of ores in nature and their behaviour during flotation and leaching, of importance to the metallurgical industry. The sulphides investigated included pyrite (FeS2), hexagonal pyrrhotine (Fe9S10), monoclinic pyrrhotine (Fe7Se), violarite (FeNi2S4), pentlandite ((FeiNi)9Se), chalcopyrite (CuFeS2) and arsenopyrite (FeAsS). The surfaces were oxidised by various methods including acid (sulphuric), alkali (ammonium hydroxide), hydrogen peroxide, steam, electrochemical and air/oxygen (in a low-temperature (150ºC) furnace), The surfaces were examined using surface sensitive chemical spectroscopic methods including x-ray photoelectron spectroscopy (ms), Auger electron spectroscopy (LES) and conversion electron Mössbauer spectroscopy (CEKS). Physical characterisation of the surfaces was undertaken using scanning electron microscopy (SM), spectral reflectance measurements and optical microscopy. Bulk characterisation of the sulphide minerals was undertaken using x-ray diffraction and electron microprobe techniques. Observed phases suggested to form in most of the sulphide surfaces include Fe204, Fe1-x0, Fe202, Fe00H, Fe(OH)3, with iron II & III oxy-sulphates. The iron sulphides show variable extents of oxidation, indicating pyrite to be the most stable. Violarite shows stability to oxidation, suggested to result from both its stable spinel crystal structure, and from the rapid formation of sulphur at the surface protecting the sub-surface from further oxidation. The phenomenon of sub-surface enrichment (in metals), forming secondary sulphides, is exhibited by pentlandite and chalcopyrite, forming violarite and copper sulphides respectively. The consequences of this enrichment with regard to processing and leaching are discussed. Arsenopyrite, often a hindrance in ore processing, exhibits the formation of arsenic compounds at the surface, the dissolution of which is discussed in view of the possible environmental hazard caused by the local pollution of water systems. The results obtained allow a characterisation of the sulphides in terms of their relative stability to oxidation, and an order of stability of the sulphide surfaces is proposed. Models were constructed to explain the chemical compositions of the surfaces, and the inter-relationships between the phases determined at the surface and in the sub-surface. These were compared to the thermo-chemically predicted phases shown in Eh/pH and partial pressure diagrams! The results are discussed, both in terms of the mineralogy and geochemistry of natural ores, and the implications for extraction and processing of these ore minerals.

Diagenetic processes in ore formation with special reference to the Zambian copperbelt and permian marl slate.

This thesis is concerned with the role of diagenesis in forming ore deposits. Two sedimentary 'ore-types' have been examined; the Proterozoic copper-cobalt orebodies of the Konkola Basin on the Zambian Copperbelt, and the Permian Marl Slate of North East England. Facies analysis of the Konkola Basin shows the Ore-Shale to have formed in a subtidal to intertidal environment. A sequence of diagenetic events is outlined from which it is concluded that the sulphide ores are an integral part of the diagenetic process. Sulphur isotope data establish that the sulphides formed as a consequence of the bacterial reduction of sulphate, while the isotopic and geochemical composition of carbonates is shown to reflect changes in the compositions of diagenetic pore fluids. Geochemical studies indicate that the copper and cobalt bearing mineralising fluids probably had different sources. Veins which crosscut the orebodies contain hydrocarbon inclusions, and are shown to be of late diagenetic lateral secretion origin. RbiSr dating indicates that the Ore-Shale was subject to metamorphism at 529 A- 20 myrs. The sedimentology and petrology of the Marl Slate are described. Textural and geochemical studies suggest that much of the pyrite (framboidal) in the Marl Slate formed in an anoxic water column, while euhedral pyrite and base metal sulphides formed within the sediment during early diagenesis. Sulphur isotope data confirm that conditions were almost "ideal" for sulphide formation during Marl Slate deposition, the limiting factors in ore formation being the restricted supply of chalcophile elements. Carbon and oxygen isotope data, along with petrographic observations, indicate that much of the calcite and dolomite occurring in the Marl Slate is primary, and probably formed in isotopic equilibrium. A depositional model is proposed which explains all of the data presented and links the lithological variations with fluctuations in the anoxicioxic boundary layer of the water column.

A study of field emission from cadmium sulphide

It was decided to investigate field emission from cadmium sulphide because many workers have found that the agreement between theory and experiment for this material, and other semiconductors, is poor. An electron energy analyser, similar to those used in most of the previously reported experiments, was, therefore, built. The performance of the analyser was thoroughly investigated both theoretically and practically and the results of these investigations were used in conjunction with a tungsten emitter. Excellent agreement was obtained between the usually accepted total energy distribution for tungsten and the corresponding .distribution measured with the present analyser. A method of obtaining reliable cadmium sulphide emitter was developed. These emitters were then used in the analyser and it was found that the agreement between theory and experiment was poor. Previous explanations of the lack of agreement are considered and are found to be doubtful. The theory of field emission from semiconductors is reviewed and possible reasons for the discrepancy between theory and experiment are proposed. Finally, further experiments are described which should prove or disprove the conclusions arrived at in this work.

Palaeozoic volcanogenic mineral deposits at Parys Mountain, Avoca, and S.E. Canada: a comparative study. Available in 2 volumes.

The sulphide mineralisation at Avoca and Parys Mountain is intimately related to volcanism and is of volcanogenic sedimentary type. The associated volcanics are predominantly pyroclastics of rhyodacitic composition and of Upper Ordovician age. They were erupted from discrete small volcanic centres, products of single local volcanic events, whose spatial distribution was related to fractures in the sialic basement of the paratectonic Caledonides of the British Isles. These fractures resulted in linear controls on volcanic, plutonic and tectonic features; they are the result of predominantly strikeslip stresses generated in this part of the European plate during closure of the Iapetus ocean. The mineralisation, predominantly pyritic, consists of a siliceous footwall zone containing bedded and cross-cutting sulphides and an overlying non-siliceous zone of bedded sulphides which may show vertical zoning of metal ratios. The sulphides are associated with chert and iron formation and have been affected by slumping. Mineralisation developed near the vents during intense fumarolic activity accompanying strong volcanism; at Parys Mountain, fumarolic activity commenced prior to, and continued after, the rnain volcanic event. Comparison with similar deposits in Newfoundland and at Bathurst, in the Canadian Appalachians, shows that mineralisation can be associated with any discrete pulse of acid magmatism in shallow subaqueous conditions. Local features of the sulphides and associated sediments are similar, although in more distal deposits (with respect to a volcanic centre) footwall alteration and mineralisation are less well developed. The nature of the basement and the presence or absence of earlier volcanics are not critical, although establishment of a local tensional regime at the time of ore formation may be important. The volcanics hosting mineralisation are rhyodacitic pyroclastics, generally related to a small centre and representing a single episode of volcanism.

Remobilisation of uranium and thorium by ore-forming fluids: a mineralogical study. Available in 2 volumes.

Mineralogical investigations have determined the sites of u and Th associated with two radioelement-enriched granites from different geological settings. In the Ririwai ring complex, Nigeria, the u- and Th-bearing accessories have been greatly affected by post-magmatic alteration of the biotite granite. Primary thorite, zircon and monazite were altered to Zr(±Y)-rich thorite, partially metamict zircon (enriched in Th, U, Y, P, Fe, Mn, Ca) and an unidentified LREE-phase respectively, by pervasive fluids which later precipitated Zr-rich coffinite. More intense, localised alteration and albitisation completely remobilised primary accessories and gave rise to a distinctive generation of haematite- and uranothorite-enriched zircon with clear, Hi-enriched rims and xenotime overgrowths. In the Ririwai lode, microclinisation and later greisenisation locally remobilised or altered zircon and deposited Y-ricl1 coffinite and Y(±Zr)-rich thorite which was overgrown by traces of xenotime and LREE-phase(s) of complex and variable composition. Compositions indicating extensive solid-solution among thorite, coffinite, xenotime and altered zircon are probably metastable and formed at low temperatures. The widespread occurrence of REE-rich fluorite suggests that F-complexing aided the mobility of REE, Y, U, Th and Zr during late-magmatic to post-magmatic alteration, while uranyl-carbonate complexing may have occurred during albitisation. The Caledonian, Helmsdale granite in northern Scotland has undergone pervasive and localised hydrothermal alteration associated with U enrichment. Zircon xenocrysts, primary sphene and apatite contain a small.proportion of this U which is largely adsorbed on to secondary iron-oxide, TiOand phyllosilicates.Additional sites for U in the overlying, Lower Devonian Ousdale arkose include coffinite, secondary uranyl phosphates, hydrocarbon and traces of xenotime and unidentified LREE-phases. U may have been leached from the granite and deposited in the arkose, along channelways associated with the Helmsdale fault, by convecting, hydrothermal fluids

Gold mineralisation in the Caledonides of the British Isles with special reference to the Dolgellau Gold-belt, North Wales and the Southern Uplands, Scotland. Available in 2 volumes.

Two aspects of gold mineralisation in the Caledonides of the British Isles have been investigated: gold-telluride mineralisation at Clogau Mine, North Wales; and placer gold mineralisation in the Southern Uplands, Scotland. The primary ore assemblage at Clogau Mine is pyrite, arsenopyrite, cobaltite, pyrrhotine, chalcopyrite, galena, tellurbismuth, tetradymite, altaite, hessite, native gold, wehrlite, hedleyite, native bismuth, bismuthunite and various sulphosalts. The generalised paragenesis is early Fe, Co, Cu, As and S species, and later minerals of Pb, Bi, Ag, Au, Te, Sb. Electron probe micro-analysis (EPMA) of complex telluride-sulphide intergrowths suggests that these intergrowths formed by co-crystallisation/replacement processes and not exsolution. Minor element chemical variation, in the sulphides and tellurides, indicates that antimony and cadmium are preferentially partitioned into telluride minerals. Mineral stability diagrams suggest that during gold deposition log bf aTe2 was between -7.9 and -9.7 and log bf aS2 between -12.4 and -13.8. Co-existing mineral assemblages indicate that the final stages of telluride mineralisation were between c. 250 - 275oC. It is suggested that the high-grade telluride ore shoot was the result of remobilisation of Au, Bi, Ag and Te from low grade mineralisation elsewhere within the vein system, and that gold deposition was brought about by destabilisation of gold chloride complexes by interaction with graphite, sulphides and tellurbismuth. Scanning electron microscopy of planer gold grains from the Southern Uplands, Scotland, indicates that detailed studies on the morphology of placer gold can be used to elucidate the history of gold in the placer environment. In total 18 different morphological characteristics were identified. These were divided on an empirical basis, using the relative degree of mechanical attrition, into proximal and distal characteristics. One morphological characteristic (a porous/spongy surface at high magnification) is considered to be chemical in origin and represent the growth of `new' gold in the placer environment. The geographical distribution of morphological characteristics has been examined and suggests that proximal placer gold is spatially associated with the Loch Doon, Cairsphairn and Fleet granitoids. Quantitative EPMA of the placer gold reveals two compositional populations of placer gold. Examination of the geographical distribution of fineness suggests a loose spatial association between granitoids and low fineness placer gold. Also identified was chemically heterogeneous placer gold. EPMA studies of these heterogeneities allowed estimation of annealing history limits, which suggest that the heterogeneities formed between 150 and 235oC. It is concluded, on the basis of relationships between morphology and composition, that there are two types of placer gold in the Southern Uplands: (i) placer gold which is directly inherited from a hypogene source probably spatially associated with granitoids; and (ii) placer gold that has formed during supergene processes.

Genetic studies of Cu-Pb-Zn mineralisation in Triassic red beds of Western Europe

Continental red bed sequences are host, on a worldwide scale, to a characteristic style of mineralisation which is dominated by copper, lead, zinc, uranium and vanadium. This study examines the features of sediment-hosted ore deposits in the Permo-Triassic basins of Western Europe, with particular reference to the Cu-Pb-Zn-Ba mineralisation in the Cheshire Basin, northwest England, the Pb-Ba-F deposits of the Inner Moray Firth Basin, northeast Scotland, and the Pb-rich deposits of the Eifel and Oberpfalz regions, West Germany. The deposits occur primarily but not exclusively in fluvial and aeolian sandstones on the margins of deep, avolcanic sedimentary basins containing red beds, evaporites and occasionally hydrocarbons. The host sediments range in age from Permian to Rhaetian and often contain (or can be inferred to have originally contained) organic matter. Textural studies have shown that early diagenetic quartz overgrowths precede the main episode of sulphide deposition. Fluid inclusion and sulphur isotope data have significantly constrained the genetic hypotheses for the mineralisation and a model involving the expulsion of diagenetic fluids and basinal brines up the faulted margins of sedimentary basins is favoured. Consideration of the development of these sedimentary basins suggests that ore emplacement occurred during the tectonic stage of basin evolution or during basin inversion in the Tertiary. ð34S values for barite in the Cheshire Basin range from 13.8% to 19.3% and support the theory that the Upper Triassic evaporites were the principal sulphur source for the mineralisation and provided the means by which mineralising fluids became saline. In contrast, δ34S values for barite in the Inner Moray Firth Basin (mean δ34S = + 29%) are not consistent with simple derivation of sulphur from the evaporite horizons in the basin and it is likely that sulphur-rich Jurassic shales supplied the sulphur for the mineralisation at Elgin. Possible sources of sulphur for the mineralisation in West Germany include hydrothermal vein sulphides in the underlying Devonian sediments and evaporites in the overlying Muschelkalk. Textural studies of the deeply buried sandstones in the Cheshire Basin reveal widespread dissolution and replacement of detrital phases and support the theory that red bed diagenetic processes are responsible for the release of metals into pore fluids. The ore solutions are envisaged as being warm (60-150%C), saline (9-22 wt % equiv NaCl) fluids in which metals were transported as chloride complexes. The distribution of δ34S values for sulphides in the Cheshire Basin (-1.8% to + 16%), the Moray Firth Basin (-4.8% to + 27%) and the German Permo-Triassic Basins (-22.2% to -12.2%) preclude a magmatic source for the sulphides and support the contention that sulphide precipitation is thought to result principally from sulphate reduction processes, although a decrease in temperature of the ore fluid or reaction with carbonates may also be important. Methane is invoked as the principal reducing agent in the Cheshire Basin, whilst terrestrial organic debris and bacterial reduction processes are thought to have played a major part in the genesis of the German ore deposits.

Effects of hydrogen sulphide on the isolated perfused rat heart

Objectives: Hydrogen sulphide has been identified as a gas signalling molecule in the body, and has previously been shown to have vasorelaxant properties. The aim of the study was to investigate the effects of sodium hydrosulphide (NaHS), a hydrogen sulphide donor, on heart rate (HR), left ventricular developed pressure (LVDP) and coronary flow (CF) in the isolated perfused rat heart. Methods: A Langendorff isolated heart preparation was used to investigate the effect of a dose range of sodium hydrosulphide, in the presence and absence of inhibitors, on heart rate, left ventricular developed pressure and coronary flow. Results: Sodium hydrosulphide caused a significant decrease in heart rate at a concentration of 10-3 M (P <0.001). This decrease was partially inhibited by glibenclamide, a K ATP channel blocker (P <0.05); L-NAME, a nitric oxide synthase inhibitor (P <0.001), and methylene blue (P <0.001), but not by H-89, a protein kinase A inhibitor. Sodium hydrosulphide significantly increased coronary flow at concentrations of 10-4 - 10-3M (P <0.05). This response was significantly increased in the presence of L-NAME (P <0.001) and methylene blue (P <0.001), whereas H-89 inhibited the increase in coronary flow due to sodium hydrosulphide (P <0.001). Sodium hydrosulphide significantly decreased LVDP at all concentrations (P <0.001). In the presence of glibenclamide and H-89, the time period of the decrease in LVDP due to sodium hydrosulphide was extended (P <0.001), whereas methylene blue and L-NAME caused a significant reduction in the response to sodium hydrosulphide (P <0.05, P <0.01 respectively). Conclusion: Sodium hydrosulphide reduced heart rate and LVDP, and increased coronary flow in the isolated perfused rat heart; however, the mechanisms of action could not be fully elucidated.

Hydrogen sulphide rescues preeclampsia-like phenotype aggravated by high sFlt-1 in placenta growth factor (PlGF) deficiency

Placenta growth factor (PlGF) deficient mice are fertile at a Mendelian ratio. Interestingly, low maternal plasma levels of PlGF are strongly associated with early onset of preeclampsia, a pregnancy hypertensive disorder characterised by high blood pressure, proteinuria and fetal growth restriction. PlGF is increasingly being recognised as an early diagnostic biomarker, but the physiological importance of PlGF in the pathogenesis of preeclampsia is unknown. We investigated whether the decreased levels of PlGF in pregnancy exacerbate the fetal growth restriction associated with preeclampsia in the presence of high sFlt-1 and the potential of hydrogen sulphide to ameliorate these effects. Pregnant PlGF−/− mice were injected with adenovirus encoding sFlt-1 (Ad-sFlt-1) at 1 × 109 pfu/ml at E10.5 and mean arterial blood pressure (MAP), biochemical and histological analysis of maternal kidney, placenta and embryos were assessed at the end of pregnancy. Ad-sFlt-1 significantly increased MAP and induced severe glomerular endotheliosis in PlGF−/− mice compared to wild-type animals. Soluble Flt-1 also significantly elevated albumin–creatinine ratio and increased levels of urinary kidney injury molecule-1, a marker for proximal tubule injury. Furthermore, sFlt-1 over expression increased fetal resorption rate in the PlGF−/− mice and promoted abnormal placental vascularisation. To determine whether placental PlGF is critical for preventing fetal growth restriction associated with preeclampsia, we generated haploinsufficient PlGF+/− placentas and embryos in dams and exposed to high sFlt-1 environment. These mothers showed reduced fetal resorption, gestational hypertension and proteinuria when compared to pregnant PlGF−/− mice. Furthermore, treatment with hydrogen sulphide-releasing agent, GYY4137, significantly reduced resorption, hypertension and proteinuria observed in Ad-sFlt-1 treated pregnant PlGF−/− mice. Our study shows that placental PlGF is a critical protective factor against the damaging effects of high sFlt-1 associated with preeclampsia and activation of the hydrogen sulphide pathway may rescue preeclampsia phenotypes even under low PlGF environment.

Hydrogen sulphide rescues preeclampsia-like phenotype aggravated by high sFlt-1 in Placenta Growth Factor (PlGF) deficiency

INTRODUCTION: Low circulating levels of placenta growth factor (PlGF) is strongly associated with the onset of preeclampsia, a maternal hypertensive disorder characterized by high blood pressure and proteinuria after 20 weeks of gestation. Although, PlGF-deficient mice are born healthy and fertile at a Mendelian ratio, the physiological importance of PlGF in the pathogenesis of preeclampsia is unclear. We hypothesised that decreased levels of PlGF in pregnancy exacerbates the fetal growth restriction associated with preeclampsia in the presence of high sFlt-1. METHODS: Pregnant PlGF-/- mice were injected with adenovirus encoding sFlt-1 (Ad-sFlt-1) at high (i) 1.5x109 pfu/ml and low (ii) 0.5x109 pfu/ml doses. Mean arterial blood pressure (MBP), biochemical and histological assessments of maternal kidney, placenta and embryos were performed. RESULTS: Ad-sFlt-1 significantly increased MBP and induced severe glomerular endotheliosis in PlGF-/- mice at E10.5 gestation compared to wild-type animals. High sFlt-1 also significantly elevated albumincreatinine ratio and increased levels of urinary kidney injury molecule-1, a marker for proximal tubule injury.At a high dose of sFlt-1, there was complete fetal resorption in the pregnant PlGF-/- mice, and even the lower dose of sFlt-1 induced severe fetal resorption and abnormal placental vascularization. Hydrogen sulphide-releasing agent, GYY4137, significantly reduced resorption, hypertension and proteinuria in Ad-sFlt-1 treated pregnant PlGF-/- mice. To determine if placental PlGF is critical for preventing fetal growth restriction associated with preeclampsia, we generated haploinsufficient PlGF+/- placentas and embryos were generated in wild-time dams and exposed to high sFlt-1 environment. This resulted in reduced fetal resorption, gestational hypertension and proteinuria when compared to pregnant PlGF-/- mice. CONCLUSIONS: Placental PlGF is a critical protective factor against the damaging effects of high sFlt-1 in preeclampsia and the hydrogen sulphide pathway may rescue preeclampsia phenotypes.