High pressure-temperature studies on an olivine tholeiite and a tholeiitic picrite from the pavagarh region,Gujarat, India

Experimental studies have been performed on an olivine tholeiite and tholeiitic picrite at pressure and temperature ranges of 20–40 kb and 1200–1300°C. The lower and upper limits of basalt-eclogite transition zone for tholeiitic picrite are 23 kb and 31·67 kb at 1200°C, and 24·67 kb and 33·67 kb at 1300°C, whereas for olivine tholeiite, these are 27 kb and 32·33 kb at 1200°C, and 28·70 kb and 33·70 kb at 1300°C. While the assemblages for both samples below the transition region are Pl+Px+Mt, they are Pl+Gt+Px+Mt within it. The eclogite field has Gt+Px+Mt. The ratio of garnet to plagioclase increases from the transition zone to the eclogite field and with the disappearance of plagioclase, the percentage of garnet increases to 30 in the eclogite field. Comparison of our results with previous studies on basalt-eclogite transition shows that the transition zone found by us occurs at higher pressure-temperature conditions. Seismic studies of the region below the Deccan Traps show an increase in velocity (1–4%) at depth. It is suggested that after partial melting, during ascent of the basaltic liquid, a significant portion of it crystallizes within the upper mantle as pockets of eclogite. As eclogite is more dense than peridotite, their presence should cause a similar increase in the seismic velocity below the Deccan area.     

Probabilistic Fuzzy Logic Modeling: Quantifying Uncertainty of Mineral Prospectivity Models Using Monte Carlo Simulations

Significant uncertainties are associated with the definition of both the exploration targeting criteria and computational algorithms used to generate mineral prospectivity maps. In prospectivity modeling, the input and computational uncertainties are generally made implicit, by making a series of best-guess or best-fit decisions, on the basis of incomplete and imprecise information. The individual uncertainties are then compounded and propagated into the final prospectivity map as an implicit combined uncertainty which is impossible to directly analyze and use for decision making. This paper proposes a new approach to explicitly define uncertainties of individual targeting criteria and propagate them through a computational algorithm to evaluate the combined uncertainty of a prospectivity map. Applied to fuzzy logic prospectivity models, this approach involves replacing point estimates of fuzzy membership values by statistical distributions deemed representative of likely variability of the corresponding fuzzy membership values. Uncertainty is then propagated through a fuzzy logic inference system by applying Monte Carlo simulations. A final prospectivity map is represented by a grid of statistical distributions of fuzzy prospectivity. Such modeling of uncertainty in prospectivity analyses allows better definition of exploration target quality, as understanding of uncertainty is consistently captured, propagated and visualized in a transparent manner. The explicit uncertainty information of prospectivity maps can support further risk analysis and decision making. The proposed probabilistic fuzzy logic approach can be used in any area of geosciences to model uncertainty of complex fuzzy systems.     

A new method for spatial centrographic analysis of mineral deposit clusters

A centrographic method for analysing mineral deposit clusters is illustrated using the komatiite-hosted Kambalda nickel sulphide deposit cluster, Yilgarn craton, Western Australia. In this method, the standard distance circle divides the cluster into a more endowed inner part and a less endowed peripheral part. The standard deviational ellipse, another centrographic object, depicts the preferred northwest–southeast trend of nickel orebodies at Kambalda. Weighted centrography shows that nickel endowment is greater in the eastern than western part of the cluster. The spatio-geometric interaction of the circle and ellipse splits the cluster into several partitions. The relative concentration of nickel orebodies or endowment within a partition in relation to their concentration within the entire cluster is termed ‘capture efficiency’. Komatiite areal trace exhibits higher nickel orebody capture efficiency than spatio-geometric partitions; however, some spatio-geometric partitions exhibit nickel endowment capture efficiencies comparable to that of komatiite. Furthermore, nickel orebody and endowment capture efficiencies of komatiite are elevated only within the standard distance circle. These results suggest that at Kambalda, (i) the standard distance circle is a prime window for understanding the komatiite-hosted nickel system, and (ii) spatio-geometric partitions are plausible locales for spatial analysis of nickel orebodies and endowment. The proposed centrographic method is potentially useful in mineral resource estimations and mineral exploration targeting.     

Fluoride contamination in Gharbar Village of Dhanbad District,Jharkhand, India: source identification and management

This paper reports occurrence of high fluoride concentration in groundwater of Gharbar Village, Dhanbad District, Jharkhand, India. The concentration of fluoride varied from 0.3 to 14.9 mg/L in 27 groundwater samples. The correlation studies demonstrate that fluoride has strong positive correlation with pH and sodium and negative correlation with calcium. It indicates dominance of ion exchange activity and rock water interaction. Thermodynamic consideration shows that all the samples were oversaturated with calcite and most of the samples were under saturated with fluorite. The results indicate that occurrence of high concentration of fluoride is leading by geochemical composition of rocks, alkaline environmental condition, weathering of rocks and ion exchange processes.     

Assessment of undiscovered nickel sulphide resources,Kalgoorlie Terrane,Western Australia: Part 1. Deposit and endowment density models

The use of mineral deposit density regression models to estimate the number of undiscovered deposits is gaining acceptance in mineral resources assessments. The deposit density regression models currently in use are based on well-established power law relationships between deposit density (deposits/km²) and the areal extent of the host rocks in well explored regions (control areas) worldwide. Although these generalized or global deposit density models can generate guideline estimates that are useful at the terrane scale, locally-derived terrane-based deposit density regression models may potentially yield more relevant estimates at the terrane scale. Using 12 selected komatiite-defined control areas in the Kalgoorlie Terrane, Western Australia, we found that the size (km²) of the control areas had power law relationships with (i) nickel sulphide deposit density, and (ii) nickel endowment density (nickel metal/km²). Regression analyses showed that both power law relationships are statistically significant at the 5% level. This suggests that nickel sulphide deposit and endowment density models could be used to estimate the number of undiscovered nickel sulphide deposits and amount of nickel metal endowment in less explored komatiites in the Kalgoorlie Terrane. This study shows that global geological relationships can be viably downscaled onto local geological terranes thereby supporting the hypothesis that the processes of mineral deposit formation and preservation are scale-independent and self-similar.     

Compressed History Matching: Exploiting Transform-Domain Sparsity for Regularization of Nonlinear Dynamic Data Integration Problems

In this paper, we present a new approach for estimating spatially-distributed reservoir properties from scattered nonlinear dynamic well measurements by promoting sparsity in an appropriate transform domain where the unknown properties are believed to have a sparse approximation. The method is inspired by recent advances in sparse signal reconstruction that is formalized under the celebrated compressed sensing paradigm. Here, we use a truncated low-frequency discrete cosine transform (DCT) is redundant to approximate the spatial parameters with a sparse set of coefficients that are identified and estimated using available observations while imposing sparsity on the solution. The intrinsic continuity in geological features lends itself to sparse representations using selected low frequency DCT basis elements. By recasting the inversion in the DCT domain, the problem is transformed into identification of significant basis elements and estimation of the values of their corresponding coefficients. To find these significant DCT coefficients, a relatively large number of DCT basis vectors (without any preferred orientation) are initially included in the approximation. Available measurements are combined with a sparsity-promoting penalty on the DCT coefficients to identify coefficients with significant contribution and eliminate the insignificant ones. Specifically, minimization of a least-squares objective function augmented by an l ₁-norm of DCT coefficients is used to implement this scheme. The sparsity regularization approach using the l ₁-norm minimization leads to a better-posed inverse problem that improves the non-uniqueness of the history matching solutions and promotes solutions that are, according to the prior belief, sparse in the transform domain. The approach is related to basis pursuit (BP) and least absolute selection and shrinkage operator (LASSO) methods, and it extends the application of compressed sensing to inverse modeling with nonlinear dynamic observations. While the method appears to be generally applicable for solving dynamic inverse problems involving spatially-distributed parameters with sparse representation in any linear complementary basis, in this paper its suitability is demonstrated using low frequency DCT basis and synthetic waterflooding experiments.     

Bedrock gorges in the central mainland Kachchh: Implications for landscape evolution

Kachchh possesses a fault-controlled first-order topography and several geomorphic features indicative of active tectonics. Though coseismic neotectonic activity is believed to be the major factor in the evolution of the landscape, detailed documentation and analysis of vital landscape features like drainage characteristics, bedrock gorges and terraces are lacking. The present study is a site-specific documentation of gorges developed in the central part of the mainland Kachchh. We analyzed and interpreted four gorges occurring on either side of Katrol Hill Fault (KHF). The Khari river gorge is endowed with six levels of bedrock terraces, some of which are studded with large potholes and flutings. Since no active development of potholes is observed along the rivers in the present day hyper-arid conditions, we infer an obvious linkage of gorges to the humid phases, which provided high energy runoff for the formation of gorges and distinct bedrock terraces and associated erosional features. Development of gorges within the miliolites and incision in the fluvial deposits to the south of the KHF indicates that the gorges were formed during Early Holocene. However, ubiquitous occurrence of gorges along the streams to the south of KHF, the uniformly N40‡ E trend of the gorges, their close association with transverse faults and the short length of the exceptionally well developed Khari river gorge in the low-relief rocky plain to the north of KHF suggests an important role of neotectonic movements     

Water logging and drainage Assessment in Ravi-Tawi irrigation command (J&K) using remote sensing approach

Water logging is one of the major land degradation processes that restricts the economic and efficient utilisation of soil and land resources in command areas. Since independence, various irrigation schemes, for providing water for agriculture and drinking have been taken up by Central and State agencies in India. In most of these schemes very little efforts have been made for proper drainage. Obstruction of natural drainage by way of construction of roads, railways, aerodrome, various structures, etc., causes the ponding of monsoon runoff on the upstream of the structures. Periodic monitoring of command areas helps in analysing the extent of water logging, and should help in taking suitable remedial measures. Remote sensing and GIS are powerful tools, which could be effectively used to study the dynamic behaviour of waterlogged areas. In this study, waterlogged and salt-affected areas have been estimated in the command area of Ravi-Tawi Irrigation Complex in Jammu region. About 14% of the total command area is water logged/ salt-affected. Being a new project, this area is likely to grow in future when the project runs with its installed capacity, and as the distributaries expand in the command area. Plausible causes of water logging have been discussed, and remedial measures suggested for reclaiming operations.     

Utilization of remotely sensed data for soil resource mapping and its interpretation for landuse planning of Bhiwani district,Haryana

Visual interpretation of IRS-1A LISS-II (October 1988 & Feb. 1989) FCC (spectral bands 2, 3 & 4) at 1:50,000 scale was carried out for soil resource mapping of Bhiwani district (Haryana State) covering on area of 5099 sq. kim. Based on image characteristics, element analysis (landform, vegetation & erosion) and field traverses, physiography-soil relationship was established. Major physiographic units identified in the area are: Aeolian plain, Fluvio-acolian plain, Transitional plain, Alluvial plain, Hills and Pediments. Area was divided into 34 subunits. Final physiography-soil map on 1:50,000 scale was prepared. Taxonomically, the soils of each unit were classified and are found as: In aeolian plain—Typic Torripsamments/coarse loamy, Typic Camborthios; Fluvio-aeolian plain-Aridic Ustipsamments/coarse loamy/fine loamy Typic/Udic Ustochrepts; Alluvial plain—Typic Ustipsamments/coarse loamy/fine loamy Typic/Udic Ustochrepts; Hills and Pediments—fregmental Lithic Torriorthents/Typic Torripsamments. Interpretation for each subunit was made regarding land suitability for various land utilisation types. It was found that hills and pediments, dunal ridges, dunal complexes and serub-lands are best suitable for forestry and horiculture plantations. Dunal plains and inter-dunal depressions are best suitable for gram/bajra/oilseeds/guar, very gently sloping dunal plain and low lying plain are suitable for wheat/arhar/cotton/sunflower.     

Application of remote sensing technique in the study of distribution of micronutrients in relation to landforms in the Sahibi river basin of Haryana

A study on the profile distribution of DTPA extractable iron, manganese, copper and zinc and physicochemical properties in ten delineated landforms of the Sahibi river basin of Haryana was underaken. Mean values for available Fe, Mn, Cu and Zn were 9.0, 11.6, 2.3 and 0.35 ppm, respectively. The soils of this area are potentially deficient in zinc. The soils of various landforms were adequately supplied with available Fe, Mn and Cu at present. In most of the soil pedons distribution of micronutrients did not follow any typical pattern neither with depth nor with landforms perhaps due to their weak pedogenic manifestation. Based on multiple regression analysis 68, 70, 71 and 16% of the variations in contents of available Fe, Mn, Cu and Zn, respectively were accountable to the simultaneous influence of various soil parameters studied.