Application of Lead Isotopes to Geochemical Exploration of Gold Deposits in Baoban , Hainan Province, China

Lead isotopes have been widely applied in geochemical exploration and evaluation of ore deposits, as well as in ascertaining the age of mineralization and the source of ore fluids.Long-term practice showed that the method of lead isotope targeting is somewhat efficient for macroscopic evaluation of forecasting areas, but not powerful enough for for ecasting concealed orebodies. As the contents of U and the variation of U/Pb ratio sharply decrease with depth in the lithosphere, U-Th-Pb isotopic differentiation must have occurred during the crust-mantle e-volution. Lead isotopic ratios show a wide variation range, varying in the front of mineralizationand shallow-derived ores, but maintaining very stable in the major orebody and being usuallyclose to the average isotopic composition of the crust and mantle of the continent block fromwhich the ores were derived. Therefore, the lead isotopic composition can serve as a measure for identifying the position of mineralization. The lead isotope geochemistry was applied to the ex-ploration and evaluation of the Baoban gold deposits of Hainan Province, China. The an alyticalresults of ore veins and adjacent rocks showed that there is a correlation between the lead isotopedata and the position of orebody. Based on the experience from the Baoban gold deposits and other ore deposits in Yunnan Province, an exploration principle has been established, that is,positive anomalies of lead isotope eigenvectors for prospecting deep-seated orebodies and nega-tive anomalies of eigenvectors for enlarging lateral exploration surrounding the known deposit.The ore beds in the Erjia and Beiniu mining districts should be as signed to the deep part of the orebody and those in the Tuwaishan mining district should be the shallow part, so ore beds cor-responding to those in the Erjia and Beiniu mining districts may be found in the Tuwaishan min-ing district.     

Forward Modeling of Gravity, Gravity Gradients, and Magnetic Anomalies due to Complex Bodies

On the basis of the results of improved analytical expression of computation of gravity anomalies due to a homogeneous polyhedral body composed of polygonal facets, and applying the forward theory with the coordinate transformation of vectors and tensors, we deduced both the analytical expressions for gravity gradient tensors and for magnetic anomalies of a polygon, and obtained new analytical expressions for computing vertical gradients of gravity anomalies and vertical component of magnetic anomalies caused by a polyhedral body. And also we developed explicitly the complete unified expressions for the calculation of gravity anomalies, gravity gradient, and magnetic anomalies due to the homogeneous polyhedron. Furthermore, we deduced new analytical expressions for computing vertical gradients of gravity anomalies due to a finite rectangular prism by applying the newly obtained expressions for gravity gradient tensors due to a polyhedral target body. Comparison with forward calculation of models shows the correctness of these new expressions. It will reduce forward calculation time of gravity-magnetic anomalies and improve computational efficiency by applying our unified expressions for joint forward modeling of gravity-magnetic anomalies due to homogeneous polyhedral bodies.     

Biogeochemical cycling of nutrients in karstic catchments, southwestern China: Linkages to changes of eco-environments

In southwestern China, karst rocky desertification, a process of land degradation, takes place widely due to human impacts on the fragile karstic ecological systems, which includes soil erosion, extensive exposure of basement rocks, and drastic decrease i…     

Application of Weights of Evidence to Mineral Potential Mapping of Yujiacun Ore Field in Northwest Yunnan Province, China

The multivariate information conprehensive processing technique is especially important at present to the digital mineral prospecting. However, the GIS-based weights of evidence have provided us with powerful tool for the quantitative assessment of mineral resource potential. In this paper, the mineralization model is established, based on the achievements made by previous researchers, to mend such deficiencies ad few references on ore fields in Yujiacun, Yunnan Province and the shortage of quantitative prediction and assessment of mineral resources. In addition, the weights of evidence are used to make a systematic quantitative prediction and assessment of mineral resources there, so that 2 mineral prospecting target areas of grade Ⅰ and 8 mineral prospecting target areas of grade Ⅱ are delineated, providing the further mineral resource exploration with the basis for the selection of mineral deposits.     

Erratum to: Results of 40Ar/39Ar Dating of Ores of the Ermakovo F–Be Deposit,West Transbaikalia,Russia

Doklady Earth Sciences - An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X22340013     

Contributions of boron isotopes to understanding the hydrogeochemistry of the coastal detritic aquifer of Castellón Plain,Spain

The Castellón Plain alluvial aquifer, Spain, is intensively exploited to meet the demand for agricultural irrigation and industrial water supply. The geochemistry of its groundwater shows complex salinization in the northern and southern parts of the aquifer, with significant pollution from human origin in the central portion. Boron content and B isotope geochemistry are useful for distinguishing between various sources of pollution and their relative importance in different parts of this aquifer. Boron concentrations in the groundwater vary between 0.01 and 0.85 mg/L. In the more saline groundwaters, found at the northern and southern ends of the study area, the presence of B is linked to inputs from seawater and water with a calcium-magnesium sulphate facies, which feed the aquifer and clearly influence the chemistry of its waters. Evidence of B adsorption processes in some samples is shown by the low B/Cl ratios and the high values of δ¹¹B. In the central portion of the aquifer, the high B/Cl ratios and the strongly negative δ¹¹B are related to pollution of human origin.     

Evaluation of ability of Rock Check Dam to prevent the transportation of Pb-contaminated sediment in Khli Ti Creek, Thailand

Discharge of wastewater from the retaining pond of a Pb ore-flotation plant since 1967 and breaching of the retaining pond in April 1998 contaminated 17540 cbm of river bank sediment with 833 ton Pb, nearly 19 km along the Khli Ti Creek. High blood Pb concentration was detected in many inhabitants. Prohibition of water and aquatic biota consumption has caused difficulties for rural people to make their ends meet. The governmental agency closed the ore-floatation plant and built 2 rock check dams downstream. The dam was designed to slow down water velocity and precipitate particulate matter. Contaminated sediments that have been trapped in front of the dam were planned to be dredged and disposed in landfill. Until now, no dredging is performed because some experts claim that dredging will resuspend the contaminated sediment into the water column, and fresh sediment deposited during periods of high flow will cover the contaminated sediment. The aim of this study was to evaluate the ability of the rock check dam to prevent the transportation of Pb-contaminated sediment in the Khli Ti Creek. Sediment located before and after the rock check dam and 2 km downstream were collected in September 2003 and May 2005. During September 2003, Pb concentrations in sediment deposited before and after the rock check dam and 2 km downstream were 48840, 53741 and 36020 mg/kg, respectively. These results showed that Pb-contaminated sediment was transported over the first rock check dam but still remained after the rock check dam. Result of May 2005 sampling also showed the same trend, although with different ranges due to seasonal variation, types of collected sediment, sample preparation and analytical techniques. Pb concentrations in sediment were 209684, 306775 and 33760 mg/kg, respectively.     

Effects of hurricane floyd inland flooding,September–October 1999, on tributaries to Pamlico Sound,North Carolina

Hurricane Floyd in September 1999 caused disastrous flooding from South Carolina to Massachusetts in the United States, with particularly severe and prolonged flooding in eastern North Carolina resulting in record flood-flow loadings of freshwater and contaminants to Pamlico Sound, North Carolina. The inland flooding, water quality, and loadings to Pamlico Sound were determined as part of a multi-agency response to the floods and in an effort to understand the effects of the floods on the greater Pamlico Sound Basin. All major river basins draining to Pamlico Sound experienced floods at the 500-yr recurrence level. The volume of flood waters entering Pamlico Sound during September–October 1999 was estimated to be equivalent to about 95% of the volume of Pamlico Sound, meaning that flood waters could have essentially displaced most of the water present in Pamlico Sound. Nitrogen and phosphorus loads to the Pamlico River estuary and Neuse River estuary, the two principal estuaries draining to Pamlico Sound, in a 36-d period during the flooding were between 50–90% of the long term average annual loads. Pesticide concentrations in flood waters were surprisingly high, given the amount of dilution produced by the floodwaters.     

Anisotropy of magnetic susceptibility (AMS) studies of Campanian–Maastrichtian sediments of Ariyalur Group,Cauvery Basin,Tamil Nadu,India: An appraisal to Paleocurrent directions

Oriented samples of sediments from Ariyalur Group, Cauvery Basin, south India, were studied for low field anisotropy of magnetic susceptibility (AMS) measurements to unravel the magnetic fabrics and paleocurrent directions. The results of AMS parameters of the sediments indicate primary depositional fabrics for Sillakkudi, Ottakovil and Kallamedu sandstone formations and secondary fabric for Kallankurichchi limestone formation. The obtained low degree of anisotropy (P _j ), oblate shape AMS ellipsoid and distribution of maximum (K ₁) and minimum (K ₃) susceptibility axes on equal area projection confirm the primary sedimentary fabric for Sillakkudi, Ottakovil and Kallamedu Formations. In the case of ferruginous, lower arenaceous, Gryphaea limestone and upper arenaceous limestone beds of Kallankurichchi Formation have recorded more than one fabric. The observed AMS parameters like shape factor (T) (prolate to oblate), q value and random distribution of minimum (K ₃) and maximum (K ₁) susceptibility axes are supported for secondary fabrics in Kallankurichchi Formation as a result of post-depositional processes. Based on petrographic studies, it can be established that K ₁ AMS axis of biotite mineral could represent the flow direction. The established paleocurrent direction for Sillakkudi is NW–SE direction while Ottakovil and Kallamedu Formations recorded NE–SW direction. Overall the paleoflow directions observed for Ariyalur Group is NE–SW to NW–SE.     

Unconformities of the auriferous,neoarchæan central rand group of South Africa: application to stratigraphy

In addition to their importance as stratigraphical levels of enhanced Au concentration, the unconformities of the Central Rand Group of South Africa also form natural lithostratigraphical formation boundaries. With a view to stimulating research of these unconformities, two hypotheses on the origins of two types of unconformities are reviewed in this paper and criteria for their distinction are proposed. Progressive unconformities are syntectonic and diachronous in nature, and develop in response to source-area orogeny. The result of such tectonism is a basinward shift of the locus of erosion and a progradation, manifested by a conformable coarsening-upward succession in distal, downstream areas of net aggradation. However, in proximal areas net erosion prevails, and parts of such coarsening-upward successions are truncated. Progressive unconformities typically result from localised source-area tectonism and will therefore be restricted to the proximal regions of a particular sub-basin. Some unconformities develop due to eustatic changes and form during relative sea level falls. Because of differential subsidence within different parts of the composite Witwatersrand Basin, some such unconformities would be restricted to certain sub-basins. Both types of unconformities discussed form natural local lithostratigraphical boundaries. However, long-range correlation of formation boundaries is a practice alien to lithostratigraphy.     

Erratum to: Assessment of coastal communities’ vulnerability to floods using indicator-based approach: a case study of Greater Accra Metropolitan Area,Ghana

In this paper, the extent to which the potentially transit-dependent portion of the population is vulnerable to the effects of a hurricane is estimated. The vulnerability of an area is defined as a composite measure of the proportion of disadvantaged persons, distance to transit, and flooding potential of people within an area. Unlike past studies which have focused on the vulnerability of the population in relatively large geographic areas, this study estimates the vulnerability of the population in 30 m × 30 m areas as defined in the National Land Cover Database. Population estimates from the national census at block level are disaggregated to the 30 m × 30 m units using a modified dasymetric mapping method in ArcGIS. The modified mapping method assigns population to each small areal unit using weights estimated by regressing the area of each land use in a census block against the population in that block. The coefficients in the regression analysis are “weights” associating population with each land use, and are used to distribute the population in each census block to the small geographic units based on their land use. In a case study of New Orleans, the results show that some areas are not well served by the existing transit pickup locations, as evidenced by their high vulnerability scores. Reassignment of pickup point locations to cover higher vulnerability score areas was investigated using integer linear programming. The results show that the optimally located pickup points serve areas with a larger average vulnerability score than the current pickup points in the study area. The method appears to be helpful in identifying vulnerable areas that, subsequently, could receive improved hurricane evacuation service in the future.     

Groundwater’s significance to changing hydrology, water chemistry, and biological communities of a floodplain ecosystem, Everglades, South Florida, USA

The Everglades (Florida, USA) is one of the world’s larger subtropical peatlands with biological communities adapted to waters low in total dissolved solids and nutrients. Detecting how the pre-drainage hydrological system has been altered is crucial to preserving its functional attributes. However, reliable tools for hindcasting historic conditions in the Everglades are limited. A recent synthesis demonstrates that the proportion of surface-water inflows has increased relative to precipitation, accounting for 33% of total inputs compared with 18% historically. The largest new source of water is canal drainage from areas of former wetlands converted to agriculture. Interactions between groundwater and surface water have also increased, due to increasing vertical hydraulic gradients resulting from topographic and water-level alterations on the otherwise extremely flat landscape. Environmental solute tracer data were used to determine groundwater’s changing role, from a freshwater storage reservoir that sustained the Everglades ecosystem during dry periods to a reservoir of increasingly degraded water quality. Although some of this degradation is attributable to increased discharge of deep saline groundwater, other mineral sources such as fertilizer additives and peat oxidation have made a greater contribution to water-quality changes that are altering mineral-sensitive biological communities.     

Petrochemistry of Mesozoic mafic intrusions related to the Paraná Magmatic Province,Uruguay

The Cuaró Formation is part of the sequence of Mesozoic mafic intrusions related to the Early Cretaceous break-up of Gondwana and represents the southernmost occurrences within the Paraná Magmatic Province in Uruguay. We present field data, petrography and lithogeochemical results regarding these dike swarms and sills that crop out in the southern extreme of the Paraná Basin. Dolerites and sills mainly exhibit glomeroporphyritic textures; the phenocrysts consist of plagioclase, clinopyroxene, relicts of olivine and titaniferous magnetite. Bulk-rock geochemical analyses allowed their classification as low-Ti subalkaline tholeiitic basalts and andesitic basalts. Trace element data indicated that the protoliths of these intrusions include the subcontinental lithospheric mantle, as is generally recognized for other Gondwana-related continental flood basalt provinces.