Data configurations and the cokriging system: Simplification by screen effects

Large cokriging systems arise in many situations and are difficult to handle in practice. Simplifications such as simple kriging, strictly collocated and multicollocated cokriging are often used and models under which such simplifications are, in fact, equivalent to cokriging have recently received attention. In this paper, a two-dimensional second-order stationary random process with known mean is considered and the redundancy of certain components of the data at certain locations vis-a-vis the solution to the simple cokriging system is examined. Conditions for the simple cokriging weights of these components at these locations are set to zero. The conditions generalise the notion of the autokrigeability coefficient and can, in principle, be applied to any data configuration. In specific sampling situations such as the isotopic and certain heterotropic configurations, models under which simple kriging, strictly collocated, multicollocated and dislocated cokriging are equivalent to simple cokriging are readily identified and results already available in the literature are obtained. These are readily identified and the results are already available in the literature. The advantage of the approach presented here is that it can be applied to any data configuration for analysis of permissible simplifications in simple cokriging

Secondary geochemical dispersion in the Precambrian auriferous Hutti-Maski schist belt, Raichur district, Karnataka, India. Part I: anomalies of As, Sb, Hg and Bi in soil and groundwater

The nature of secondary geochemical dispersion of As, Sb, Hg and Bi in soil and ground water of the semi-arid, tropical, Archaean, auriferous, Hutti-Maski greenstone belt has been investigated for identification of appropriate geochemical techniques for Au exploration in similar terrains. Results indicate that the <180 μm size-fraction of C-horizon soil is an appropriate sampling medium for delineating pedogeochemical anomalies of As, Sb, Hg and Bi related to gold mineralisation. These pedogeochemical anomalies along with anomalous values of alkalinity, chloride, sulphate, As and Sb in groundwater are controlled significantly by primary mineralisation located along shear zones in the greenstone belt. Arsenic anomalies in soil are broad, whereas, those of Sb and Bi are restricted to narrow zones directly over mineralised areas. In contrast, Hg anomalies around known mineralised areas are irregular and do not clearly demarcate the mineralised areas. The study indicates that anomalies of As, Sb and Hg in soil are principally hydromorphic, whereas those of Bi are clastic. The study recommends use of groundwater sampling at 2–3 km spacing with routine analysis of chloride, sulphate and alkalinity along with As and Sb in the first phase. This may be followed up with sampling of C-horizon of soils on a 1 km square grid for As-anomalies. Arsenic-anomalous areas may be sampled for As, Sb, Hg and Bi on a 500 m square grid for detailed exploration.© Elsevie

Secondary geochemical dispersion in the Precambrian auriferous Hutti-Maski schist belt, Raichur district, Karnataka, India. Part II. Application of factorial design in the analysis of secondary dispersion of As

The study uses the technique of factorial design for analysis of factors governing secondary dispersion of As in an auriferous Archean greenstone belt. Details of the sampling procedure and analytical techniques used for As in groundwater and soil of the Hutti-Maski schist belt are discussed in Part I of the paper in this issue. The main effects and interactions of topographic slope, drainage texture, proximity to lineament, depth of water table and soil types have been considered. The study shows that secondary dispersion of As is governed by proximity to lineament and factors that govern drainage and ground water movement. The factors retained were used to predict As values using a response surface model obtained by least square fitting using orthogonal polynomials. The goodness of fit of the model shows that the factors identified explain the secondary dispersion of As adequately.© Elsevie

Fluid inclusion studies on barite from Hutti Gold Mines, Karnataka, India: inferences on late-stage hydrothermal fluid

Late-stage, post-gold mineralization, cavity-filling veins with barite are reported here from the Hutti gold deposit of Karnataka. Large (10-15 cm) to medium (2-5 cm) sized translucent crystals of barite studded with numerous pyrite grains commonly of 1-2 mm size occur in these veins. Monophase and biphase fluid inclusions occur in primary clusters and pseudo-secondary trails in the barite crystals. Microthermometric and laser-Raman studies show that the barite has formed from aqueous fluids of relatively high salinity (14-22 eq. wt% NaCl). Minor Raman-shift peaks of methane are observed in the vapour phase of a few biphase fluid inclusions. Assuming pressure of less than 1 kbar, trapping temperature would be less than 200 degrees C. These post-ore veins at Hutti point to a source of oxidized fluid subsequent to the phase of gold mineralization

A characterization of symmetric isofactorial models

The paper examines symmetric isofactorial models. A necessary and sufficient condition for a bivariate stationary random function to be isofactorial is given. Using this characterization, a procedure for checking whether an isofactorial model is appropriate is outlined. If data indicates that an isofactorial model is adequate, the procedure also provides a method for identifying the factors of the model. The paper concentrates on the case where Z(x) takes values 0, 1, 2,..., N and the general case is discussed briefly

On the equivalence of the cokriging and kriging systems

Simple cokriging of components of a p-dimensional second-order stationary random process is considered. Necessary and sufficient conditions under which simple cokriging is equivalent to simple kriging are given. Essentially this condition requires that it should be possible to express the cross-covariance at any lag h using the cross-covariance at \h\ = 0 and the auto-covariance at lag h. The mosaic model, multicolocated kriging and the linear model of coregionalization are examined in this context. A data analytic method to examine whether simple kriging of components of a multivariate random process is equivalent to its cokriging is given

Spectral pathways for effective delineation of high-grade bauxites: a case study from the Savitri River Basin, Maharashtra, India, using EO-1 Hyperion data

Bauxite, the only source of aluminium, is an aggregate of minerals, most of which are oxides and hydroxides of aluminium and iron such as gibbsite, bohemite, goethite and haematite. Bauxite is used in the chemical and refractory industries and its quality is controlled by the presence of impurities such as iron and silica. Bauxite commonly occurs together with iron-rich laterites as alteration products of parental igneous and metamorphic rocks. Aluminium-rich bauxites grade towards highly ferruginous laterites with a transitional Al-rich laterites or ferruginous bauxite, herein described as Al-laterites. In the Savitri River Basin, bauxite contains 58-75% gibbsite, 6-11% goethite and 19-26% haematite, whereas the mineralogy of Al-laterites and Fe-laterites are dominated by haematite (29-68%) and goethite (6-25%) with subordinate amounts of gibbsite. Conventional techniques to demarcate the high-grade pockets of bauxites rich in gibbsite are tedious, time consuming and involve detailed field sampling and geochemical analyses. Our work illustrates how spectral properties of these three litho-units can be effectively utilized in mapping of high-grade bauxites occurring over wide areas using hyperspectral remote sensing (HRS). The methodology adopted herein involves generation of noise-free field spectral database of target materials, linear unmixing of field spectra for constituent minerals, classification of preprocessed Hyperion images using field spectra and finally accuracy assessment for ore grade estimation. It is observed that bauxite mapping using Hyperion data and noise-free field spectra yielded results that correlate well with the chemistry and mineralogy of representative samples. By adopting the above procedure, we achieved classification accuracies of 100%, 71% and 89% for bauxite, Al-laterite and Fe-laterite classes, respectively

Fluid chemistry and depositional mechanism of the epigenetic, discordant ores of the Proterozoic, carbonate-hosted, Zawarmala Pb-Zn deposit, Udaipur district, India

The Proterozoic, carbonate-hosted, Zawarmala Pb-Zn deposit has stratiform, banded pyrite-sphalerite ore, as well as discordant, sphalerite-galena veins and rich massive galena ore shoots. The mechanisms of deposition of discordant vein and massive ores have been studied using speciation and solubility calculations based on ore fluid characteristics and physical parameters inferred from petrography, fluid inclusion studies, and leachate analysis. Massive galena ore, which is the economic ore type, cuts across the earlier, F-2-related, vein-type ore and is distinct from the vein-type ore in terms of mineralogy, texture, and fluid inclusion characteristics. Fluid inclusions in quartz associated with the ores show that fluids forming vein-type ore are low-salinity (4.3-14.7 wt % NaCl equiv) H2O-NaCl fluids. The trapping temperature of vein-type ore fluid was estimated to be in the range of 395 degrees to 290 degreesC at a pressure of about 1,450 bars. Fluids associated with massive galena ore are H2O-CO2-NaCl fluids of lower salinity (about 3-4 wt % NaCl equiv). The wide variation in X-CO2 of fluid inclusions that occur in close proximity to each other within the same sample of massive ore suggests heterogeneous entrapment of the low-salinity H2O-CO2-NaCl fluids. From the intersection of isochores of local, homogeneously entrapped CO2 and aqueous biphase fluids of unmixed CO2-H2O-NaCl fluid, trapping temperature fluid was estimated to be between 250 degrees and 150 degreesC at pressures of 2,000 to 750 bars. Despite the low salinity of the ore fluids, speciation studies show that chloride complexes are dominant over most of the temperature range of interest in both ore fluids. The only bisulfide complex of importance is Pb(HS)(2)(0) which is dominant below 175 degreesC in fluids associated with massive galena ore. Data from fluid inclusions and solubility calculations reveal that cooling is the important mechanism of vein-type ore deposition. In contrast, physicochemical data indicate that an increase in reduced sulfur, by mixing a regional, high metal content, low sulfur fluid with a local, high sulfur fluid at the site of deposition, was the mechanism for massive galena ore deposition. The difference in oxidation state (and therefore also in metal content) of the two fluids is inferred to be a significant factor that caused differences in the modes of deposition of the two ore types and the relatively high value of X-CO2 (0.2033) in fluids associated with massive galena ore

A Geostatistical Study pf Alumina-Content in Ores of An Indian Iron-Ore Deposit

Mining and blending operations in the high grade iron ore deposit under study are performed to optimize recovery with minimal alumina content while maintaining required levels of other chemical component and a proper mix of ore types. In the present work the regionalisation of alumina in the ores has been studied independently and its effects on global and local recoverable tonnage as well as on alternatives of mining operations have been evaluated. The global tonnage recovery curves for blocks (20m x 20m x 12m) obtained by simulation closely approximated the curves obtained theoretically using a change of support under the discretised gaussian model. Variations in block size up to 80m x 20m x 12m did not affect the recovery as the horizontal dimensions of the blocks are small in relation to the range of the variogram. A comparison of the local tonnage recovery curves obtained through multiple conditional simulations made with that obtained by the method of uniform conditioning of block grades on an estimate of panel 100m x 100m x 12m panel grade reveals comparable results only in panels which have been well conditioned and possesing an ensemble simulation mean close to the ordinary kriged value for the panel. Study of simple alternative sequence of mining on the conditionally simulated deposit shows that concentration of mining operations simultaneously on a single bench enhances the fluctuation in alumina values of ore mined

THE RELATIONSHIP BETWEEN CARBON, SULFUR, AND PYRITIC IRON IN THE AMJHORE DEPOSIT, BIHAR, INDIA

Low C/S ratios have been generally observed in pyritiferous black shales of the lower Paleozoic and late Proterozoic (Berner and Raiswell, 1983). In addition to factors such as high rates of bacterial sulfate reduction which might have existed during these early periods due to the low oxygen content of ocean water, availability and quality of organic matter, or lack of bioturbation and availability of reactive iron, low C/S ratios may also reflect low sedimentation rates. Three distinct situations within a single vertical stratigraphic column in the mid-Proterozoic Amjhore pyrite deposit reflect the effect of anoxic levels and sedimentation rates on pyrite formation. In the first (lower shale with a mean C/S ratio of 2.03), pyrite formation was diagenetic, whereas in the second (massive pyrite ore with a negligible carbon content) and the third (upper shale with a low C/S ratio of 0.27), pyrite formation took place under euxinic conditions. In environments where anoxic levels are high and the sedimentation rate low, low mean C/S ratios may occur. In such environments variations in total sulfate reduction per unit column of sediment deposited (resulting from variation in sedimentation rates or anoxic levels) are reflected in the slope of the carbon-sulfur plot by a greater slope. This may also result in lower intercepts on the sulfur axis. For upper shale samples the carbon-sulfur regression line has a very high slope of 3.73 and a low intercept on the sulfur axis of 0.21. Consistency of anoxic levels during deposition of upper shales is, however, indicated by the low standard deviation (0.051) of C/S data and a dominant control of the sedimentation rate on the sulfur content of the sediments is inferred. Sulfur isotope data on pyrite samples indicate an environment closed to SO4(-2) which was initially open to H2S (or HS-) and later during deposition of upper shale became closed to it due to a limited supply of reactive iron. This confirms that the pyrite bed and upper shales were laid down in a restricted environment and substantiates the interpretation of the carbon-sulfur relationships observed in them