High Metal Values Research Articles

Soft bottom mollusc assemblages and pollution in a harbour with two opposing entrances

Conventional harbours, provided with only one entrance and devoid of channels, are enclosed areas with low water renewal, high sedimentation rate and high concentrations of pollutants in sediments; the soft bottom communities are characterised by low species richness and low values of the diversity and evenness indexes. The harbour of Ceuta, North Africa, presents an unusual structure since it is provided with two opposing entrances and a channel, which increase the water renewal across the middle of the harbour. These unusual characteristics turn the harbour of Ceuta into an adequate locality to test its environmental implications on macrofaunal assemblages. In the present study, the spatial distribution of mollusc community associated with soft bottoms was studied in relation to the influence of environmental factors on the harbour of Ceuta and nearby areas, North Africa. Twenty-one stations (15 inside and six outside the harbour) were sampled and 26 variables were measured in the sediment of each station: depth, %sand, organic matter, lipids, P, N, Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, S, Sr, Zn. The special configuration of Ceuta harbour created a great variability in sediment characteristics and environmental measures depending on the stations and, due to this heterogeneity, the mollusc species richness in the sediments inside the harbour (45 species) was higher than in conventional harbours. The multivariate approach based on MDS analysis was much more sensitive than univariate techniques to detect differences between internal and external stations of the harbour of Ceuta. The percentage of sand was the main factor to affect the distribution of the mollusc assemblages according to the BIO-ENV procedure and the CCA. SIMPER showed that the bivalves Parvicardium exiguum, Ervilia castanea, Spisula subtruncata and Digitaria digitata were the species that most contributed to the dissimilarity between internal and external stations; P. exiguum, S. subtruncata and D. digitata were more abundant in the internal stations whereas E. castanea was more abundant in the external stations. The bivalves P. exiguum, Abra alba and Corbula gibba and the opistobranch Retusa obtusa dominated in the most enclosed stations inside the harbour where sediments contained very high values of organic matter, lipids, and heavy metals. The data of the present study might assist in the building of new harbours in the future.

Heavy metal trends in the Calabar River, Nigeria

Heavy metal concentrations in sediments of the Calabar River: Pb (0.6–30 ppm); Ni (1.2–22.5 ppm); Cr (0.6–3.3 ppm); Cu (0.3–48 ppm); Zn (0.8–27 ppm); Fe (0.2–2,880 ppm) and V (0 ppm) are generally below levels that are known to be harmful to aquatic biota. Metal levels displayed marked seasonal, spatial and tidal variations, which are attributed to both anthropogenic influences and natural processes in the environment. Iron and Cr increased during the dry season (January), while Cu, Zn, Pb and Ni had their peak values in the wet season (September). High values of metals during the wet season indicate inputs through human activities mediated by rainfall. Relatively higher concentrations of metals are obtained during high tide compared to low tide regime. This is attributed to redox processes in the sediment and subsequent displacement of sediment pore water rich in metals by seawater intrusion during high tide. Higher values of Fe observed in the dry compared to the wet season may be attributed to oxidation and precipitation of soluble forms brought into the river during the wet season.

A Special Issue on Alteration Associated with Volcanic-Hosted Massive Sulfide Deposits, and Its Exploration Significance

This special issue on Alteration Associated with the Spectrum of Volcanic-Hosted Massive Sulfide Deposits and Its Exploration Significance largely reports the results of a three-year (1995–1998) collaborative research project (P439) between the Centre for Ore Deposit Research at the University of Tasmania and the Australian Mineral Industry Research Association (AMIRA). Volcanic-hosted massive sulfide deposits (VHMS) provide a significant contribution to world zinc, copper, lead, silver, and gold production. Some Australian deposits have been very profitably mined because of their particularly high polymetallic grades, high precious metal values, and large size. For example, Rosebery, Que River, and Hellyer were mainstays of the Tasmanian mining industry for several decades. Although VHMS targets have recently gone out of favor—fallen off the radar screens—for many large base metal exploration companies, they continue to be favorable targets for small- to medium-size mining companies. Due to the geological complexity of ancient submarine volcanic terranes, new VHMS deposits are extremely difficult to discover, especially those deposits buried more than a few tens of meters below the surface. The research team at the Centre for Ore Deposit Research and mineral explorers through AMIRA recognized that an improved understanding of alteration zonation was needed to enhance VHMS discovery rates in mature exploration districts. Extensive previous research in submarine volcanic terranes in Australia, North America, Japan, and Europe has documented the mineralogy and geochemistry of various styles of hydrothermal alteration, which are related spatially and genetically to VHMS deposits. Figure 1 illustrates the spatial relationships of seven major alteration styles in VHMS districts, as they were recognized at the beginning of this project. These are summarized below. 1. Footwall alteration pipes exist below most major mound-style VHMS deposits and result from focused upward flow of hydrothermal fluids to the sea floor. Previous studies (e.g., Shirozu, 1974; Riverin and Hodgson, …

Potential environmental hazard in the mining district of southern Iglesiente (SW Sardinia, Italy)

A stream sediment survey carried out in southern Iglesiente, southwestern Sardinia, comprised 249 samples which were analysed for 35 elements. The data from 83 samples derived from a previous survey by Ente Minerario Sardo were also used. Maps showing element distribution were created using the GIS program Arc View 3.1. For the compilation of potential risk maps, the regional distribution of the elements has been reclassified using as thresholds the Italian intervention criteria for residential/recreational and commercial/industrial land use. The main concentrations of heavy elements mainly follow the carbonate lithologies, hosting most of the ore deposits of Mississippi Valley and Sedimentary Exhalative types. Fairly high contents of Pb, Zn, Cd, and As are reflected in the stream sediments sampled along the carbonate ridges bordering the mining district along the Iglesias syncline. Treatment plants, tailings and dumps are also located in this area. Another area with high metal values is the swampy river mouth of Rio Sa Masa, near Gonnesa, draining not only the main mining sites of the Iglesias syncline, but also the small industrial areas around the town of Iglesias and a few villages. Potential risk maps have been compiled for four elements: Zn, Pb, Cd and As. Among those, the state of geochemical pollution is very serious for Cd, Pb, and Zn, which are the main elements contained in the stratabound orebodies, but less so for As. If even only partly transferred to the soils, the concentration in these elements should limit any further development in this area, unless remediation is carried out.

The use recent overbank sediments in geochemical mapping of Slovenia

Heavy inundations in 1990 left on flood plains much overbank sediment that was the object of our investigations. The overbank sediment is a homogenized sandy-silty material derived from numerous smaller and larger eroding areas upstream of the sampling point. Therefore it is considered a good sampling medium for geochemical mapping. On the ground of Chemical analyses of 134 overbank sediment samples of drainages in Slovenia two kinds of geochemical maps were made: for individual Chemical elements and for five elemental associations. In spite of low resolution, the geochemical characteristics of a number of Slovenia were established. Comparison of mean elemental contents in overbank sediments with mean contents in stream sediments showed similar values, and comparison with Clarke values for shale and soil showed lower means of Slovenia for most of the determined elements. A number of high values of certain metals (Cd, Cu, Cr, Hg, Mo, Pb, Sb, Zn) can be related to known mineral deposits and occurrences, and to industrial activities.

A study of the analytical variation of sampling and analysis of stream-sediments from areas contaminated by mining and milling

During an environmental study of stream-sediments, large variations in metal values were noticed in contaminated sediments taken from the same site at different times. The question arose as to whether these differences were due to variations in contaminate input or merely represented the heterogeneity of the contaminated sediments at the site. Large numbers of replicate samples and measurements could be utilized to help answer the questions, but this is time-consuming and costly. Random errors can be estimated by the use of a duplicate analyses scheme and much use has been made of duplicate analyses in geochemical surveys and prospecting. In the work reported here, use was made of duplicate analyses to study Cu, Pb, and Zn variation in environmental stream-sediment samples. Samples were collected from three areas: (1) adjacent to the La Bajada mine along the Santa Fe River, (2) adjacent to the Pecos mine along the Pecos River, and (3) downstream from the Alamitos mill located on a tributary of the Pecos River. Both rivers are located in northern New Mexico. The mines and the mill have been inactive for many years. ANOVA statistics were used to evaluate differences in Cu, Pb, and Zn values between contaminated sites that were immediately adjacent. The large variations in metal values noted on earlier trips at the sites on the Pecos River were not noted in this study. Analytical error was the greatest contributor to total variance. Differences in the adjacent site means were most apparent in the smallest size fraction (<63 μm). But even these differences were shown to be mostly due to random error. The smallest size fraction contained the highest metal values at all three sites. Stream-sediments at the La Bajada mine site did not appear to be contaminated.

Variations in Trace Metal Concentrations in American Oysters (Crassostrea virginica) Collected from Galveston Bay, Texas

Nearly one thousand oysters (Crassostrea virginica) were collected at 15 sites on four sampling trips to Galveston Bay during 1992–1993. Iron, silver, arsenic, cadmium, copper, lead, and zinc were determined in the whole soft part of the individual oysters. Trace metal concentrations were found to vary among individuals within a site on a given trip, and spatially and temporally around the Galveston Bay estuarine system. Differences in metal concentrations from site to site were a factor of 5 or more for some metals, and similar differences were found from time to time at a given site. Zinc was found in anomalously high concentrations at several sites, mainly along the west side of Galveston Bay. Isolated high values of other metals were found scattered throughout the bay; however, only one site (GBSL, near Swan Lake in lower Galveston Bay) was found to have significantly higher than average concentrations for several metals (Ag, Cu, Pb, and Zn). One obvious trend found in this study was that metal concentrations, except for As, were highest in the summer, followed by the fall, and lowest in the winter and spring. The temporal changes in metal concentrations in oysters cannot be explained by changes in body weight in different seasons, and are apparently caused by changes in environmental conditions (e.g., metal input, salinity) or biological activity (e.g., metabolism, depuration).

Mineralogy and geochemistry of the clay fraction of till in northern Finland

The mineralogy and geochemistry of the clay fraction of till in different moraine types and in different bedrock areas in northern Finland have been studied. Moraine types include ground moraine, Rogen moraine, Pulju moraine, Sevetti moraine and Kianta moraine. The bedrock is composed of granite, granite gneiss and mafic volcanite. X-ray diffraction, differential thermal and thermogravimetric analyses, transmission electron microscopy, X-ray fluorescence and atomic absorption spectrometry were used as analytical methods. Quartz, feldspars and amphibole are the primary rock-forming minerals occurring in nearly all the samples of each study area. The clay minerals proper include kaolinite, vermiculite, swelling-lattice vermiculite, chlorite, illite and mixed-layer minerals. Kaolinite occurs most abundantly only in till in the Kittiläarea, where a preglacial weathering crust has been the source rock. Poorly crystalline or amorphous Fe oxides also abound in till at Kittilä. Sodium, Ca and Si have been depleted and Al, Mg, Fe, K, Ti, P and trace elements have been enriched in the clay fraction compared with the fine fraction. The contents of Si, K and Na are higher in the granitic areas and the contents of Cu, Co, Ni and Zn are higher in the mafic volcanite areas. Preglacial weathering has led to the depletion of Si, Mg, Ca, K and Na and to the enrichment of Al, Fe, Ti, P and trace elements in the clay fraction of till in the Kittiläarea. High base metal values in the Inari area suggest the possibility of sulphide mineralizations there and high As values in the Kittiläarea indicate Au potential there. The most important factors controlling the mineralogical and geochemical composition of the clay fraction of the tills in northern Finland are the composition of the bedrock and the possible occurrence of an old weathering crust. The final grain size composition of the tills and consequently the quantitative proportions of the different minerals are often related to the last glacial quarrying and sorting processes; therefore the mineralogical composition of the tills is to a certain extent bound also to the respective moraine types.

Notes on the geochemical dispersion of elements in the beach sediments along the coast west of the Atlas Mines, Visayas, Philippines

The copper operations of the temporarily closed Atlas Mines in Cebu has released silt and tailings in the Tañon Strait during the past 40 years. The silt has caused stress to local coral communities but the toxic effects of high metal values continues to concern the coastal population north and south of the tailings outfall. Recent sampling of beach sediments along the western coast gave geochemical data which indicated higher Cu, Pb, Zn, Fe and Co values immediately around the outfall. The values, however, decreased markedly towards the north and south. Nickel appears to show some association with these elements. In the north, manganese seems to be influenced by dispersion from the Balamban river which drains a catchment containing manganiferous sediments upstream. Mercury and As show negative correlation with each other. They show no affinity with the other elements and do not appear to have any geological significance. The geochemical data, therefore, point to a zone immediately around the outfall as the only area affected by high metal values. Regular sampling and analysis should be done to ascertain the extent of dilution within the beach and near-shore environments and the influence of seasonal variation in ocean currents on the configuration of the affected area.

Notes on the geochemical dispersion of elements in the beach sediments along the coast west of the Atlas Mines, Visayas, Philippines

The copper operations of the temporarily closed Atlas Mines in Cebu has released silt and tailings in the Tañon Strait during the past 40 years. The silt has caused stress to local coral communities but the toxic effects of high metal values continues to concern the coastal population north and south of the tailings outfall. Recent sampling of beach sediments along the western coast gave geochemical data which indicated higher Cu, Pb, Zn, Fe and Co values immediately around the outfall. The values, however, decreased markedly towards the north and south. Nickel appears to show some association with these elements. In the north, manganese seems to be influenced by dispersion from the Balamban river which drains a catchment containing manganiferous sediments upstream. Mercury and As show negative correlation with each other. They show no affinity with the other elements and do not appear to have any geological significance. The geochemical data, therefore, point to a zone immediately around the outfall as the only area affected by high metal values. Regular sampling and analysis should be done to ascertain the extent of dilution within the beach and near-shore environments and the influence of seasonal variation in ocean currents on the configuration of the affected area.

A mangrove stand under sewage pollution stress: Red Sea

A mangrove stand of Avicennia marina located at the South Corniche of Jeddah city receives about 100 000 m3 of sewage per day. The sewage has high values of BOD, COD, nutrient concentrations, heavy metals and faecal coliform counts. The mangrove stand is very small and occupies an area of about 0.45 km2. The trees are stunted with low pneumatophore density. The pneumatophore distribution is restricted to the area of substrate underneath the plant crown covers and they do not look healthy. A high proportion of them was observed to be dead and/or aberrant. These abnormal induced features were attributed to the sewage discharge in the area. The death of pneumatophores decreases the aeration area which apparently affects the respiration rate of the root system, nutrient uptake and plant growth, consequently leading to a retarded growth of the mangroves.

The Ag-Mn-Pb-Zn vein, replacement, and skarn deposits of Uchucchacua, Peru; studies of structure, mineralogy, metal zoning, Sr isotopes, and fluid inclusions

Uchucchacua is an Ag-Mn-Pb-Zn vein, replacement, and skarn mineral district in the central Andes of Peru. Host rocks are massive Jumasha Formation shelf limestones of Turonian age that have been folded into an asymmetric northeast-verging anticline of Andean trend. Strata near the fold crest are cut by minor dacitic intrusions and have been displaced by a conjugate set of steep wrench faults that strike northwest-southeast and northeast-southwest. Most ore occurrences are restricted to host rocks that lie below marly limestone at the top of the middle Jumasha Formation. Vein ores located along the fracture system have formed by fissure infill and by replacement of limestone wall rocks. Larger sheetlike replacement orebodies are parallel and adjacent to a large fault. Replacement is in zones of brecciation adjacent to fault bends which were dilatent during sinistral slip of the master fracture. Such fracture belts may have been subject to paleokarst solution processes before mineralization.Four paragenetic stages have been identified. Fe, Mn, and Si were introduced at the exoskarn stage (I) as the anhydrous silicates ferroan tephroite, johannsenite, rhodonite, and bustamite. During the early main stage (II) ferroan tephroite was replaced by friedelite and magnetite under oxidizing conditions at a relatively low pH. Pb, Zn, Fe, Cu, and B were introduced; principal sulfides are pyrrhotite, Fe-rich sphalerite, Mn-rich wurtzite, alabandite, galena, chalcopyrite, and tetrahedrite. Pyrrhotite was replaced by other sulfides during later stage II. Main gangue minerals were calcite, kutnohorite, rhodochrosite, and quartz. Ag, As, and Sb were introduced during the late stage (III) in the form of sulfosalts, principally pyrargyrite. Redistribution of metals introduced at stage II resulted in the growth of Fe-poor sphalerite and alabandite accompanied by calcite gangue. Decreasing Fe contents of alabandite and sphalerite during late stage II and stage III, together with the appearance of pyrite, indicate an increase in sulfur fugacity and/or decrease in temperature over this period. The supergene stage (IV) affects the upper 30 to 150 m of most veins and involves the growth of Mn hydroxides, goethite, orpiment, marcasite, cerussite, and siderite.Distribution patterns of metal ratios and high metal values define ore bands, with a succession of antiforms and synforms. Ore-band locations are determined by vein width, itself a function of wall-rock reactivity, and fracture permeability. Metal ratio distributions in the Luz vein show symmetric dispersion of metals at right angles to the ore-band axis. Ag shows the least dispersion with progressively greater dispersion of Pb and Zn.Geologic considerations indicate mineralization at a minimum depth of 1,600 m. Most primary fluid inclusions in calcite of probable stage II origin were trapped over a temperature range of about 200 degrees to 337 degrees C (hydrostatic pressure) or about 225 degrees to 362 degrees C (lithostatic). Fluid inclusions from late stage II quartz were trapped at about 165 degrees to 205 degrees C (hydrostatic) or 190 degrees to 230 degrees C (lithostatic). Salinity ranged from 0.5 to 29.7 equiv wt percent NaCl-CaCl 2 with little relation to temperature. Calcite 87 Sr/ 86 Sr values of 0.70743 to 0.71122 extend well outside the range of values both determined for magmatic rocks of the region and estimated for the host limestones but are probably compatible with older sedimentary rocks of the mine district. Salinity levels and NaCl/CaCl 2 ratios are similar to basinal brines associated with Mississippi Valley-type deposits. It is concluded that basinal brine, expelled from the deforming Mesozoic sequence, was a significant component of the ore fluid. This fluid was probably heated by dacitic magmas or cooling dacitic intrusions; a polygenetic high-salinity magmatic-basinal fluid then rose along existing strike-slip fractures toward the mineralization site where it mixed with heated low-salinity ground water.

Geological and isotope studies of microtonalite-hosted W-Sn mineralization in SE Ireland

A swarm of Caledonian microtonalite sheets is host to W-Sn mineralization in SE Ireland. Many but not all mineralized sheets are within a regional shear zone which, however, does not appear to have been a major control on mineralization. Scheelite and arsenopyrite are the dominant minerals within and adjacent veins in greisened tonalite. No wolframite occurs. The intrusions are affected by two alterations, a pervasive one and another which is spatially associated with veins. Both are associated with high metal values. Veining is confined to microtonalite sheets and was initiated at least partly by hydraulic fracturing of the intrusions. Stable isotope analyses indicate that mineral deposition occurred over narrow time and temperature intervals from a hydrothermal fluid of magmatic origin. Methane is important in fluid inclusions in quartz veins and the low oxygen fugacity of the mineralizing fluid was probably critical in concentrating metals and in suppressing wolframite formation.

Comparison of the structure and composition of cokes from the thermal cracking of Athabasca Oil Sands bitumen

Three different cokes obtained from the thermal cracking of Athabasca Oil Sands bitumen by delayed coker, fluid coker and flexicoker processes have been compared in terms of their chemical composition (elemental analysis) and physical structure (scanning electron microscope). Flexicoker coke has been found to have the highest metal values and lowest heteroatom content of the three cokes, and has a unique porous structure. These features favour the lability of the metals in this coke and may account for its previously noted susceptibility to chemical leaching.