Active Stream Sediments Research Articles

Stream Sediments Geochemistry of the Nyambaka Drainage System Northern Cameroon (Central Africa): A Target for Mining Exploration

Mining exploration in the Nyambaka area Northern Cameroon still at reconnaissance stage. In this study, ten active stream sediments samples were collected for geochemical survey. These stream sediments were analyzed by inductively coupled Plasma/ Mass Spectometry (ICP/MS), the data set obtained was transformed into a standard formation an excel database, and was subject to statistical treatment using IBM SPSS statistics 21 for 33 chemical elements to highlight the relationship between the stream sediments geochemistry, the region lithology, the geological processes and eventual primary mineralization. The data were analyzed using multivariate statistics. R-mode analysis produced a five-factor model behind multi-elements associations which account for 93.40% of the total variance in the data with the following metals associations: Sc-Mo-V-In-Ga-Cu-Cr, Ba-Sr-Ag-Cr-Cu-Co-Be-Ni-Y-Zn-V, Ga-Hf-Zr, Sn-Au, As-Cd. Sn-Au association indicates that Au mineralization is link to Sn mineralization. As-Cd, Cu Ga, In, Mo suggested that the paragenesis represent others sulphidation events that is barren with respect to Au. The spatial distribution of Sn-Au and As-Cd factors show that these factors are mores express in the centre part of the study area; they can be link to granitic rocks, defining a primary gold target. A detail mining investigation have to me carry out in that area to highlight the primary mineralizations.

Granulometry, heavy mineral and geochemical studies of stream sediments around Bula, Dass District, Northeast Nigeria

Active stream sediments generally consist of broken-down fragments of pre-existing rocks by the action of river (stream) flow. This makes them target materials for routine geochemical surveys and provenance analysis. Fifteen (15) stream sediment samples were collected in some parts of Bula and its environs, northeastern Nigeria, in order to determine their textural characteristics, heavy mineral and elemental composition. The sediments were subjected to granulometric, heavy mineral and elemental analyses. The result of granulometric analysis show that the streamsediments are poorly to moderately well sorted, very platykurtic to leptokurtic, fine to medium grained and positively skewed. Zircon, rutile and tourmaline are the dominant heavy mineral species occurring in the sediments. The computed Zircon-Tourmaline-Rutile (ZTR) index values for the samples range from 59.18 - 83.53, indicating mineralogical maturity. The geochemical data of the stream sediment samples show that the mean contents of the trace elements [Ti (0.73 ± 0.74%), Fe (0.39±0.19%), Cr (816±639ppm), Ni (258±108ppm), Pb (48±12.37ppm) and Zn (502±126ppm)] were higher than their respective average crustal values except for Fe. Computed threshold values indicate possible mineralization containing Fe and Ti. The elements have variable spatial distribution. The study shows that the trace elements composition of the stream sediments is majorly lithogenic. Because mineralization in rocks and sediments are often characterized by considerable variation in their trace elements contents, the metal concentrations in these sediments are large enough for Ilmenite and Rutile mineralization to be suspected within the study area.

ANALISIS UNIVARIAT DAN MULTIVARIAT CONTO SEDIMEN SUNGAI DALAM PENENTUAN POTENSI MINERALISASI LOGAM DI HALMAHERA BAGIAN TIMUR, PROVINSI MALUKU UTARA

Penelitian geokimia dengan mengunakan metode analisis kandungan unsur dari conto endapan sungai aktif -80 mesh merupakan salah satu fase awal eksplorasi terutama untuk menemukan cebakan mineral logam. Halmahera bagian timur dengan tataan geologi yang kompleks dan berada dalam jalur metalogenik yang berpotensi membentuk cebakan logam, menghasilkan rona geokimia yang sangat bervariasi dan menarik. Data geokimia sedimen sungai aktif yang tertuang dalam bentuk peta sebaran unsur menyajikan informasi awal yang penting tentang indikasi mineralisasi untuk ditindaklanjuti ke tahap penelitian lebih rinci, khususnya mineralisasi nikel yang berasosiasi dengan litologi Komplek Ultrabasa.
 
 Penafsiran data geokimia di wilayah penelitian dengan pendekatan analisis statistik univariat dan multivariat yang terdiri dari unsur Cu, Pb, Zn, Co, Ni, Mn, Ag, Fe, Cr, dan Au, proses pengayaan unsur geokimia di lingkungan permukaan diperlihatkan oleh asosiasi spasial Co, Ni, Fe dan Mn, yaitu pengayaan unsur disebabkan pengikatan kimiawi (scavenging) oleh oksida Fe dan Mn. Berdasarkan kekerabatan unsur atau hubungan antar unsur diperoleh dua kelompok unsur yaitu ikatan unsur Cu-Pb-Zn-Ag-Cr dan Co-Ni-Mn-Fe-Au, akan tetapi tidak semua kelompok asosiasi unsur dapat dihubungkan dengan litologi di daerah penelitian.

Geochemical mapping based on regularly spaced composite stream sediment samples produced from stored aliquots - State of Paraná Pre-Cambrian shield, Brazil

A collection of 6,587 active stream sediment samples covering about 4,800 km² in the Parana Shield, southern Brazil was used to produce 75 composite samples each representing a 5’ x 5’ cell. The original samples were retrieved from the archives of the Geological Service of Parana - MINEROPAR and the Geological Service of Brazil - SGB / CPRM. The composite samples were submitted to four analytical methods with the determination of 66 elements. Geochemical maps of the isolated elements along with bivariate correlation analysis showed six associations between elements, each representing specific lithologies and at least one area with high exploratory potential, which was previously unknown given the small amount of elements analyzed in the original samples. The geochemical maps were produced either by cell classification (pixel maps) or by the application of the minimum curvature interpolation method, considered as the best interpolator for the generation of the isograd maps (vector maps). The comparison between composite and original samples showed that, even with different analytical techniques, the element contents of the composite samples are similar to the average of the contents in the original samples on each cell. The results obtained allow us to recommend the adoption of this set of procedures in stream sediment sample collections covering large areas, with at least three advantages of: (a) eliminating field costs by retrieving already collected and archived samples, (b) reducing the amount of samples to be analyzed and (c) minimize any positioning errors of sampling sites collected before the advent of GPS equipment. The verification and detailing of the areas of interest evidenced by this procedure can be done easily with the analysis of the original samples still stored in the collections.

Geochemical mapping and background concentrations of iron and potentially toxic elements in active stream sediments from Carajás, Brazil – implication for risk assessment

The Companhia de Pesquisa de Recursos Minerais (CPRM - Geological Survey of Brazil) has conducted geochemical surveys in the south-central region of the Itacaiúnas River watershed (IRW) in the Carajás region. The surveyed area covers 9,650 km2 and the data obtained by CPRM is the basis for the present study. A total of 833 active stream sediment samples, including 144 duplicates were collected. The <0.177 mm fraction of all samples was digested by aqua regia and 53 elements were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). From the results made available by CPRM, 14 elements, including Fe and some potentially toxic elements (PTEs, namely Ba, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sn, V, and Zn) are used in our study to define the geochemical signature of stream sediments in the area. A multivariate statistics was employed to evaluate major associations among elements and GIS techniques to derive interpolated geochemical distribution maps. Geochemical background values were calculated by multiple statistical methods, and based on that a preliminary environmental risk assessment was undertaken. Strong evidence of natural control in the spatial distribution of studied elements were observed. Large differences in the spatial distribution of many elements are observed between the central and southern region of the IRW and are related to contrasts in local geological settings. Background values were established in three different sets of geochemical sample locations, one for the whole study area, a second and third for the Central and Southern regions of the IRW, respectively. These background values were compared to existing stream sediment guideline values for (eco)toxicological effects of the same elements. Each applied statistical method to derive background values yielded different results. This difference is mainly influenced by the central criterion of the statistical method (median, mean, 75th, 95th, 98th percentiles). The Median ±2*(Median Absolute Deviation) furnished the most consistent and realistic results. Six environmental indicators were calculated to evaluate potential areas of risk. The results indicated that active stream sediments of the study area are generally uncontaminated. Occasionally local natural contamination sources were identified in the area of the recently created Ferruginous Fields National Park (FFNP). Moreover, there is no a clear impact of the changes in land use and land cover, as well as mining activities (e.g. Sossego copper mine), on the geochemistry of stream sediments. At the sampling scale, the variation in the background concentrations of all investigated elements in the stream sediment samples is apparently much larger than any anthropogenic impact.

Geochemical Mapping of Iron Quadrangle region by active stream sediments, State of Minas Gerais, Brazil

The geochemical survey of Iron Quadrangle was performed by the Geological Survey of Brazil - CPRM involving geochemical data from the area between 42o30´W and 45oWand 19o30´S and 21oS, totalling 45.000 km2. Active stream sediment was analyzed. Fine fractions (< 80# or 0.175 mm) were pulverized to –150# fraction (~ 0.100 mm), digested by hot acqua regia and analyzed for 53 elements by ICPMS. Maps of raw and manipulated data (element concentrations and multi-elemental scores) were made. Stream sediment (< 80# fraction) is an effective sampling medium for regional geochemical surveys. Geochemical structures, lithological units and mineralization processes were recognized with the sample density of 1 sample per 12 km2. Sample density has a key role in the quality of the geochemical maps produced. Caution must be taken when interpreting the results because of its nature; these data do not necessarily pinpoint specific geochemical anomalies or single ore deposits. The interpretation of stream sediment samples is not straightforward and must take into account secondary processes involved in the evolution of sampling media. These data may be used in mineral exploration to delineate favorable targets for more detailed studies. Mineral deposits often occur in geochemical provinces characterized by elevated concentration of elements of economic interest and pathfinder elements. Ore deposits tend to cluster along specific stratigraphic units and/or structural trends over large areas. These geochemical data can be used in environmental studies, support decision makers in the definition of public policies and in the management of sustainable land use.

Regional geochemical baseline concentration of potentially toxic trace metals in the mineralized Lom Basin, East Cameroon: a tool for contamination assessment

The distribution of trace metals in active stream sediments from the mineralized Lom Basin has been evaluated. Fifty-five bottom sediments were collected and the mineralogical composition of six pulverized samples determined by XRD. The fine fraction (< 150 µm) was subjected to total digestion (HClO4 + HF + HCl) and analyzed for trace metals using a combination of ICP-MS and AAS analytical methods. Results show that the mineralogy of stream sediments is dominated by quartz (39–86%), phyllosilicates (0–45%) and feldspars (0–27%). Mean concentrations of the analyzed metals are low (e.g. As = 99.40 µg/kg, Zn = 573.24 µg/kg, V = 963.14 µg/kg and Cr = 763.93 µg/kg). Iron and Mn have significant average concentrations of 28.325 and 442 mg/kg, respectively. Background and threshold values of the trace metals were computed statistically to determine geochemical anomalies of geologic or anthropogenic origin, particularly mining activity. Factor analysis, applied on normalized data, identified three associations: Ni–Cr–V–Co–As–Se–pH, Cu–Zn–Hg–Pb–Cd–Sc and Fe–Mn. The first association is controlled by source geology and the neutral pH, the second by sulphide mineralization and the last by chemical weathering of ferromagnesian minerals. Spatial analysis reveals similar distribution trends for Co–Cr–V–Ni and Cu–Zn–Pb–Sc reflecting the lithology and sulphide mineralization in the basin. Relatively high levels of As were concordant with reported gold occurrences in the area while Fe and Mn distribution are consistent with their source from the Fe-bearing metamorphic rocks. These findings provide baseline geochemical values for common and parallel geological domains in the eastern region of Cameroon. Although this study shows that the stream sediments are not polluted, the evaluation of metal composition in environmental samples from abandoned and active mine sites for comparison and environmental health risk assessment is highly recommended.

Comparative geochemistry of three urban streams in Athens: Kifissos-Podoniftis-Pikrodafni

The geochemistry of three urban streams in Athens was analysed and compared on the basis of major elements and heavy metals content in water and active sediment. The studied streams of Kifissos, Podoniftis and Pikrodafni run through the Athens basin of a total area of 540 km2 but differ with respect to the origin of their headwaters i.e., Parnitha, Penteli and Hymettus mountains. The main aim of the study was to determine the geochemical signature of water and sediment within the Athens hydrological basin and evaluate the effect of natural and anthropogenic environment on these water courses. A total of 56 stream water samples were obtained and analysed for major anions, cations and heavy metals (Mn, Cr, Cu, Zn, Pb) as well as nitrate and phosphate concentrations. Active stream sediments were collected at 22 locations along the streams and were analysed for heavy metals (Pb, Zn, Cu, Mn, Cr, Ni, Cd). Results indicated that rock weathering, rather than atmospheric or pollution influx is the dominant process affecting the major ion geochemistry of stream flow in the urban setting. However, Kifissos and Podoniftis waters had higher nitrate and phosphate concentrations indicating greater influence by anthropogenic activities. In general the quality characteristics of water and sediment in the study area were found to be in a good state regarding the studied parameters.

Geochemical mapping of riverbank profiles in the basin area of the river Ibar: Role in establishing the geochemical basis for the assessment of anthropogenic influence on the environment

Geochemical mapping of riverbank profiles of the basin area of the river Ibar was performed in the purpose of making regional geochemical map of Serbia 1:1000000. In this area, deposits of lead and zinc are located, and they are characterized by very complex geological composition. Sampling net at chosen locations of riverbank profiles was adjusted to the morphological and hydrographic characteristics of the terrain. At every profile, samples were collected from A-horizon, Ob-overbank sediment and S-active stream sediment, while tracking the changes of lithological members, in accordance to the WEGS methodology (Western European Geological Surveys). The preserved geochemical track in the overbank sediment is of special significance for correlation the results of chemical elements in the surface part of (A-horizon) and active contemporary stream sediment. In the analytical process, beside determining contents of Pb, Zn, Cu, Co, Ni, Cr, Sb, V, Cd and other elements, the radiometric examinations of contents of U 238 , Th 232 and K 40 , were also conducted as well as the appropriate sedimentological analyses. On the basis of geochemical prospection results, a data base was formed which represents a foundation for estimation of anthropogenic influence on the living environment of rural settlements in the basin area of the river Ibar. In accordance to the geological-structural and morphological characteristics of the terrain, the results are applicable in the research of mineral raw materials, in agriculture, forestry, geomedicine, etc.

Geomorphic process rates in the central Atacama Desert, Chile: Insights from cosmogenic nuclides and implications for the onset of hyperaridity

Geomorphic process rates in the central Atacama Desert, Chile: Insights from cosmogenic nuclides and implications for the onset of hyperaridity

Storage and origin of metals in active stream sediments from mountainous rivers: A case study in the River Douro basin (North Portugal)

The study area is located in the transboundary River Douro basin (northern Portugal); it comprises the River Corgo fluvial network, which drains a meso-scale rural catchment with an area of 295km2, underlain by crystalline rocks, in a temperate climate. The results reported in this study derive from a geochemical survey of active fluvial sediments, with the aim of characterising the spatial and temporal distribution of the contents of As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn in a basin with mountainous features. To assess total contents of metals and their potential availability, as well as possible different origins of metals (natural vs. anthropogenic), a sequential chemical approach was used (modified BCR procedure). Multivariate data analysis (PCA) was used to assist the interpretation of datasets.The results show that, on the one hand, the metal contents distribute among all the geochemical phases studied. For the most relative labile fractions the reducible fraction is the most significant. The element-partitioning among geochemical phases indicates: (a) Co and Mn are transported in greater proportions in the most labile fraction, as exchangeable ions, as well as important proportions of Ni, Zn and Cu; (b) Cd and Pb associate preferentially with the hydroxides of Fe and Mn; (c) Cr and Cu are also transported by the organic phase; (d) the residual phase transport important proportions of Cr, Ni, Zn, Cu, Fe and Pb. The higher concentrations of Cu, Zn and, in particular, Pb, in the most labile fractions, which are higher where the total contents are also higher (and not concomitant with a correspondent increase in the residual fraction), suggest an important contribution of anthropogenic activities to the total contents of these elements in the sediments. Chromium and Ni are the main metals from a lithological source, with relatively higher contents in the residual fraction, and the lowest in the most mobile fractions. On the other hand, the spatial distribution pattern of metal contents in the mobile and semi-mobile fractions (available+reducible+oxidisable), shows that, in general, higher contents of metals in the most mobile fractions occur along the main courses of the major tributaries, in particular in the flatter reaches. The patterns of seasonal occurrence and distribution of metals show, in general, that the relative contents associated with the potentially available fraction increase during the period of low flow, which extends from April to September.

Geochemical atlas of the Medvednica Mt.: natural distribution of geochemical elements in stream sediments

The sample catchment basin approach applying the active stream sediment as a sampling medium is a frequently used cartographic technique for mapping geochemical data. It is particularly useful in mountainous areas with developed drainage network where each individual catchment basin can be assumed to represent an elementary map unit. Stream sediments have been widely used during the last two decades as an alternative sampling medium (vs. soils and overbank sediments) for regional geochemical exploration, mineral exploration, and geochemical mapping as well as for fingerprinting purposes and provenance studies. In this study, uninhabited slopes of the Medvednica Mt. in the close vicinity of the Croatian capital Zagreb, including the whole Medvednica Nature Park, have been selected as an appropriate geochemical environment for evaluation of geochemical baselines at the local and regional scale. The single-element geochemical maps representing the spatial distribution of 21 elements (As, Ba, Ca, Co, Cu, K, La, Mg, Mn, Na, Nb, Ni, P, Pb, Sc, Sr, Th, Ti, V, Y, and Zn) reflect both natural and anthropogenic impact on the environment at the contact of urban and natural landscapes.

Metamorphic Rock-Hosted Orogenic Gold Deposit Type as a Source of Langkowala Placer Gold, Bombana, Southeast Sulawesi

DOI: 10.17014/ijog.v6i1.114In 2008, placer gold was discovered in Langkowala area (Bombana Regency), Southeast Sulawesi, Indonesia, and more than 60,000 traditional gold miners in the early 2009 have been operating by digging vertical pits and panning active stream sediments. The grade of placer gold ranges from 50 to 140 g/t. Local geological framework indicates that the placer gold is not related to volcanic rock-related hydrothermal gold deposit, e.g. epithermal, skarn or porphyry. This paper describes a preliminary study on possible primary deposit type as a source of the Langkowala (Bombana) secondary placer gold. A field study indicates that the Langkowala (Bombana) placer/paleoplacer gold is possibly related to gold-bearing quartz veins/veinlets hosted by metamorphic rocks particularly mica schist and metasediments in the area. These quartz veins/veinlets are currently recognized in metamorphic rocks at Wumbubangka Mountains, a northern flank of Rumbia Mountain Range. Sheared, segmented quartz veins/veinlets are of 2 cm to 2 m in width and contain gold in a grade varying between 2 and 61 g/t. At least, there are two generations of the quartz veins. The first generation of quartz vein is parallel to foliation of mica schist and metasediments with general orientation of N 300oE/60o; the second quartz vein generation crosscut the first quartz vein and the foliation of the wallrock. The first quartz veins are mostly sheared/deformed, brecciated, and occasionally sigmoidal, whereas the second quartz veins are relatively massive. The similar quartz veins/veinlets types are also probably present in Mendoke Mountain Range, in the northern side of Langkowala area. This primary gold deposit is called as ‘orogenic gold type’. The orogenic gold deposit could be a new target of gold exploration in Indonesia in the future.

Sedimentary petrological characteristics of lateral and frontal moraine and proglacial glaciofluvial sediments of Bertilbreen, Central Svalbard

Bertilbreen is a valley glacier located in the central part of the Spitsbergen Island, Svalbard. Glacier bedrock is composed of Devonian Old Red facies sedimentary rocks, Carboniferous clastic sedimentary rocks and Carboniferous to Permian limestones. Cobble clasts from the right-hand lateral moraine, frontal moraine and proglacial glaciofluvial sediments were studied. The upper part of the lateral moraine is composed mostly of passively transported supraglacial debris (originally unmodified scree, snow and scree/rock avalanche deposits) with a small proportion of actively transported clasts or reworked glaciofluvial sediments. Clasts in the middle part of the lateral moraine originate predominantly from the frontal moraine of a small glacier in the lateral valley. The lower part of the lateral moraine and frontal moraine of Bertilbreen are rich in subglacially transported material, which is supported by isometric clast shapes, roundness degree and common clast surface striations. Coarse gravel forms longitudinal bars in the glaciofluvial stream flowing from the glacier front. In the southern mouth of the valley, the proglacial stream grades into a braided outwash fan. Clast nature is affected by the source from the surrounding glacial deposits and bedrock outcrops, the impact of glaciofluvial transport on the clast nature increases in the braided outwash fan. Clast shapes are primarily influenced by bedding and fractures of source rocks, but are also significantly influenced by the type and proximity of material sources. Striation is cleared away the clast surface during the glaciofluvial transport. A morphostrati-graphically older glaciofluvial terrace formed by glaciofluvial sediments deposited during the glacier advance culminating during the Little Ice Age (LIA) is located at the southern end of the valley. The comparison of active proglacial stream sediments and those from older glaciofluvial terrace was done using the coarse pebble fraction.

Legacy Hg-Cu Contamination of Active Stream Sediments in the Gold Hill Mining District, North Carolina

El propósito de este estudio es evaluar la evolución longitudinal de mercurio (Hg) y cobre (Cu) en sedimentos de canales activos en la parte baja del distrito minero de Gold Hill, en el Piedmont de Carolina del Norte. La minería de oro (Au) y Cu desde 1844 a 1915 produjo Hg (asociados con el procesamiento de Au) y Cu en una cuenca de 254 km 2 . Regresión lineal múltiple se utiliza para cuantificar las tendencias espaciales y geoquímicas en 93 muestras de canales activos, recolectadas en cauces principales contaminados y en localidades en tributarios secundarios. Modelos de regresión simple de dos parámetros combinando los efectos de ambos procesos de dispersión a escala de las cuencas hidrográficas (distancia río abajo) y a escala del alcance del transporte de sedimentos (arena por ciento) explican el 85 por ciento de la variación de Hg y 90 por ciento de la variación de Cu en los sedimentos de canales activos. Las tendencias de contaminación en dos diferentes medios de sedimentos, barra baja y bancos de depósitos de mayor elevación, fueron efectivamente similares cuando la influencia del tamaño del grano local se contabilizó en los modelos de dos parámetros. Modelos geoquímicos de antecedentes explican el 84 por ciento de la variación de Hg y Cu en muestras no contaminadas de tributarios utilizando parámetros relacionados al tamaño de grano, sustratos geoquímicos secundarios, y fuentes de meteorización de minerales. Más del 45 por ciento de la variación de Hg y 20 por ciento de Cu en sedimentos contaminados puede ser explicada a través de parámetros de antecedentes. Firmas geoquímicas difieren entre Hg y Cu en los sedimentos de canales activos debido a variaciones en insumos mineros, trasfondo geoquímico, y las fuentes de contaminación actual.

Overbank sediments as appropriate geochemical sample media in regional stream sediment surveys for gold exploration in the savannah regions of northern Ghana

Conventional stream sediment sampling in which sediments are taken from the active channels during reconnaissance regional geochemical surveys in gold exploration has over the years failed to delineate prospective target zones in northern Ghana, where the relict is flat. Whereas the technique has been successful in the south western Ghana, which is characterised by moderate to high relief, generally the savannah north is associated with low relief, commonly with flat topographies and generally decoupled stream channels. Geochemical comparison of active stream and overbank sediments in this study demonstrate that active stream channels may contain contaminated materials of recent origin, but overbank sediments, except for the uppermost horizons, represent alluvial regolith of earlier depositional cycles over time. Based on gold value repeatability, composite samples taken from the overbank sediment layers were relatively less erratic and are considered to be an appropriate geochemical medium in delineating potential regional gold targets for follow up. The results show that overbank sediment sampling can be used as a cost-effective method to define broad anomalous zones; and the technique must be considered useful during reconnaissance geochemical surveys in the savannah regions.

Stream sediment geochemical survey of an area around Dass, N.E. Nigeria

Stream sediment geochemical survey was carried out in Dass area to determine possible dispersion train for Pb, Cu, Co, Ni and Zn. A total of 114 active stream sediment samples were collected over an area of 60km2. The samples were treated with hot HNO3 and analysed for Pb, Cu, Co, Ni, Zn, Mn, Mg, Ca, and Fe.The results indicated high concentration of Zn (81.3µg/g), Cu (10.8µg/g), Pb (50.0µg/g), Ni (20.0µg/g) and Co (51.6µg/g) in the area. Descriptive statistical method together with element distribution maps, employed in the presentation of the result, point to a dispersion train for anomalous Pb, Zn, Cu, Co, and Zn in the western flank of the study area. The underlying geology probably played a major role in the distribution of the anomalies. Keywords: Dass, Dispersion train, Stream sedimentGlobal Journal of Geological Sciences Vol. 6 (2) 2008: pp. 105-112

Overbank sediment sampling in Greece: a contribution to the evaluation of methods for the ‘Global Geochemical Baselines’ mapping project

The different steps in the development of the floodplain or overbank sediment sampling procedure for continental-scale geochemical mapping are described with examples from the Greek pilot project of the Western European Geological Surveys’ Working Group on ‘Regional Geochemical Mapping’. The Greek overbank and stream sediment results were compared statistically with those of the national regional stream sediment survey. The purpose was (1) to compare the geochemistry of overbank sediment, collected from a single site, with that of several tens or hundreds of regional stream sediment samples taken from the upstream drainage basin, and (2) to develop a cost-effective procedure to assess the geochemistry of a drainage basin. ‘ Composite’ samples taken over the whole thickness of the overbank sediment sequence showed that element contents were close to the median, or within the interquartile range, of the same elements in the regional stream sediment samples. Overbank sediment samples collected from pre-defined intervals were not considered satisfactory, for they were taken across overbank sediment layers. Therefore, the method was subsequently refined by collecting samples from different overbank sediment layers, with the recommendation to collect samples at 25-cm intervals when thick layers of over 1 m were encountered. In selected river basins, surficial overbank and active stream sediments reflect contamination, whereas overbank sediment layers at depth show natural element contents, or pristine conditions. Such data are required for a realistic assessment of the degree of contamination of individual drainage basins. After considering results from Greece and other countries, it is recommended to sample both the surface overbank sediment (0–10 cm), and the deepest possible layer in order to measure pristine or pre-industrial conditions. The Greek results demonstrate that overbank sediments are useful for mapping natural geochemical conditions and baseline concentrations, as well as assessing anthropogenic contamination. The cost-effectiveness of overbank sediment sampling for the ‘Global Geochemical Baselines’ project of the International Union of Geological Sciences (IUGS) and International Association of GeoChemistry (IAGC) is verified.

Johnstuart Webb (1920–2007)

In 1978, publication of The Wolfson Geochemical Atlas of England and Wales , which showed the spatial distribution of concentrations of nineteen elements in the fine-grained (<0.177 mm) sieved fraction of samples of ~50,000 active stream sediments, collected at a spatial density of ~1 sample per 2.5 km2 over the whole of England and Wales where surficial drainage was present, established proof-of-concept of the multi-element regional geochemical atlas as a tool capable of providing geochemical data reflecting changes in bedrock geology and overburden, as well as both natural and anthropogenic sources of pollution. It represented the culmination of a programme of systematic research begun in 1954, when Webb established the Geochemical Prospecting Research Centre at the Imperial College of Science and Technology (ICST), London. His farsighted vision of geochemical atlases as a strategic national requirement, capable of providing information of relevance to fundamental geology, mineral exploration, agriculture and animal/human health, eventually became fully realised in the UNESCO Division of Earth Sciences International Geochemical Mapping Project, inaugurated in 1988. Webb was born in Balham, London, on 28 August 1920, the eldest child of George Stewart Webb and his wife Caroline Rabjohns ( nee Pengelly). Educated at St. Mary’s School, Balham (1925–30) and Westminster City School, London (1930–38), he graduated BSc (First Class Honours) in Mining Geology from ICST in 1941, having been awarded the Murchison Medal (1939), the Brough Medal (1940), the Clement le Neve Foster Prize (1941) and the Cullis Testimonial Fund (1941). After a brief period as assistant mining geologist to the U.K. Government’s Non-Ferrous Metallic Ores Committee, he served as a sapper in the Royal Engineers (1941–43) and was commissioned Second Lieutenant before being transferred to the Geological Survey of Nigeria (1943–44) as an economic mineralogist to look for tantalite, as at the time tantalum …

Geokimia regional Sulawesi bagian Utara percontoh endapan sungai aktif -80 mesh

http://dx.doi.org/10.17014/ijog.vol1no2.20062Geochemical investigation using the analysis method of -80 mesh of active stream sediment samples is one of the early phase exploration especially in fi nding out metallic mineral deposits. These deposits either as outcrop or as being still in subsurface, can be revealed in geochemical output data. Despite for determination of the availability of mineral deposits, elements distribution of stream sediment samples, can be used to determine the initial and last appearance of geological and situated in environmental condition of an area. Northern part of Sulawesi with its complex geologic setting and a metallogenic region is being potential to form metallic deposits, which create some variation and interesting geochemical performances. The regional geochemistry data by means in the form of elements distribution maps represent the basic important information of mineralization indications, which enable for detail follow up investigation.