H. S. Pandalai

Integration of Sparse Geologic Information in Gold Targeting Using Logistic Regression Analysis in the Hutti–Maski Schist Belt, Raichur, Karnataka, India—A Case Study

Logistic regression has been used in the study to integrate indicator patterns for estimation of the probability of occurrence of gold deposits in a part of the auriferous Archaean Hutti–Maski schist belt. Data used consist of categorical and continuous variables obtained from a coded lineament map and geochemical anomaly maps of the pathfinder elements of gold in soil and groundwater. Main effects and interactions of the variables studied were used in formulating the logistic regression model. Regression models using lineament-proximity data, combined with soil and groundwater geochemical anomalies were tested on parts of the schist belt with data not used in estimation of model parameters. Predicted probabilities greater than 0.9 identified known deposit locations in the area.

Noise-signal index threshold: a new noise-reduction technique for generation of reference spectra and efficient hyperspectral image classification

Reference spectra of terrestrial targets are usually collected using field spectro-radiometers for mineral abundance mapping and target detection. These spectra often have noise that masks characteristic absorption and reflection features and affects the efficiency of material mapping. This work aims at obtaining an empirical technique for reduction of high-frequency noise from field spectra. The proposed noise correction technique uses a ‘normalized’ measure Rn , where Rn = (Ln − Fn )/Ln for each band (n) calculated from field and laboratory spectra of test material, with Fn and Ln being the depth of the absorption feature in field and laboratory spectra, respectively. On the basis of the assumption of the constancy of this ratio in neighbouring bands, an empirical algorithm that approximates the ratio Rn of a noisy band to the corrected ratio of an adjacent band is used to obtain the noise-corrected field spectra. The classification accuracy increases significantly when noise reduced field spectra are used as reference spectra.

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.

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.

Evolution of Hutti-Maski greenstone belt of the Eastern Dharwar Craton: Evidence for metamorphic and hydrothermal phases from the Hira-Buddini deposit, Raichur district, Karnataka, India

The Hira-Buddini gold deposit is located along the steeply dipping ENE trending sheared contact of felsic and mafic rocks of strike length of about 600 m with mylonitic foliation parallel to the S1 schistosity in amphibolites. Second-generation open folds with axial planes (S2) marked by fractures that are often filled by later calcite veins are observed in surface and underground exposures. Garnetiferous amphibolites occur in patches on the footwall side of the shear in the western part of the deposit. This rock shows garnet porphyroblasts, coarse second-generation hornblende and large grains of biotite that grow over an early S1 fabric which is made up of early hornblende, plagioclase, ilmenite and retrograde first-generation chlorite. Second-generation hornblende and biotite grains make high angles to S1 schistosity and are sub-parallel to S2. Late hydrothermal alteration is marked by an albite-epidote-chlorite-zoisite assemblage. Geothermometric estimates based on garnet-biotite, and garnet-hornblende pairs, as well as Ti in biotite, show that temperatures during D2 deformation that led to the growth of the porphyroblasts were

Estimation of proportions of lithotypes using auxiliary information

530{\pm }20^{\circ }\hbox {C}

On the Equivalence of the Cokriging and Kriging Systems

530±20∘C. The fabric and mineralogy of the rock indicate that porphyroblastic growth of garnet, hornblende and biotite was preceded and succeeded by stages of hydrothermal alteration. Primary gold mineralization is inferred to be associated with the early stage of hydrothermal ingress.

Data Configurations and the Cokriging System: Simplification by Screen Effects

Mixing of metal-rich connate waters derived from evaporative seawater with local sulfide-rich water is postulated as the mechanism of ore deposition in many Phanerozoic carbonatehosted Pb-Zn deposits. The study of the Paleoproterozoic Balaria deposit of the Zawar belt of Rajasthan that hosts structurallycontrolled, stratabound Pb-Zn mineralization, provides insight into the nature of fluids in quartz that is closely associated with massive Pb-Zn ore.The present study is focused on the massive-type ore which forms one of the major ore-types at Balaria. Massive-type ore consists predominantly of galena and sphalerite (with minor pyrite and pyrrhotite) that occur in shear-induced dilatational fractures. The ore is associated with clear, rounded to semi-rounded bodies of quartz that are embedded within the ore. The quartz bodies are inferred to be fragments of vein-quartz that underwent shear deformation along with enclosing massive galena-rich ore. Primarybiphase fluid inclusions in quartz belong to H2O-NaCl±CO2, H2ONaCl- CH4-N2-CO2 and primary-monophase fluid inclusions to CH4-N2-CO2 types, while secondary fluid inclusions are biphase and belong to H2O-NaCl type. The salinity of primary-biphase H2O-NaCl type fluid inclusions range from 2 to 14 wt. percent NaCl equiv while that of secondary-biphase H2O-NaCl type fluid inclusions range from 3 to 5 wt. percent NaCl equiv. Homogenization temperatures for primary-biphase fluid inclusions range from 127o to 217oC while that of secondary-biphase fluid inclusions is 131o to 151oC. The molecular proportions of of CH4, N2 and CO2 in primary-biphase (H2O-NaCl-CH4-N2-CO2) and primary-monophase (CH4-N2-CO2) as measured from Raman spectra are widely variable. Variability in molecular proportions of CH4, N2 and CO2 is interpreted as an evidence for mixing of pulses of a regional fluid with a local fluid and reactions with graphitic and carbonate rocks at the site of deposition. The low salinity of fluid inclusions in the quartz and the lack of any sulfur species in the aqueous or gaseous phase of the entrapped fluids indicates that although quartz occurs as entrained bodies within the massive ore, the fluids in them may not represent ore-forming fluids of the main ore-stage of massive-type ore.