Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

S. Basumallick ¹, B. C. Sarkar ¹, S. Banerjee ²

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad - 826 004, IN
2 Department of Geology, University of Oklahoma, Norman, US

Abstract

The Upper Proterozoic Lower Bhander Sandstone, occupying a major part of the Tamasa valley at Maihar, has been thought to be deposited in a tidal flat-lagoon complex,in an intertidal to supratidal environment, dominated by ebb and flood tides. A tidal bundle (a medium grained thicker sandstone unit and a thinner siltstone bed) is thought to bear the imprint of velocity and discharge associated with each tidal current as reflected in the thickness of the layers. Thickness data pertaining to 155 tidal bundles recognized in the exposures have been analysed using techniques of Smoothing, Autocorrelation and Fourier filtering, to reveal whether or not any tidal cyclicity existed. The results amply support not only the presence of alternating high spring-neap-low spring semi-lunar cycles, but a dominant periodicity of 32 bundles corresponding to 16 semi-lunar days.

Keywords

Tidal Cyclicity, Sedimentology, Fourier Analysis, Vindhyans, Madhya Pradesh.

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B. C. Sarkar ¹, V. K. Nayak ¹, P. Srinivas Rao ²

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad-826 004, IN
2 Mineral Exploration Corporation Limited, Nagpur-440 006, IN

Abstract

The Phosphorite deposit (74°25' to 74°26'E : 22°58' to 23°00'N), Jhabua district, Madhya Pradesh, is one of the productive deposits in India, and has evoked great interest with regard to its phosphogenesis, stromatolite association and resource potential. It is a sedimentary-stromatolite type of deposit within the Precambrian metasediments of the Aravalli Supergroup and represents the southern extension of the well known Jhamarkotra phosphorite deposit of Rajasthan. The geological set-up shows that the phosphorite occurs in two separate host rocks of older carbonate and younger chert sediments. Geological Survey of India (Khan et al. 1979), using conventional cross-section method, estimated the weighted average grade of the Khatamba Blocks from the available 21 intersections in 12 trenches as 28.60% P₂O₅. In the present study, statistical modelling of exploration data of the Khatamba Blocks, using histogram plots, probability diagrams and skewness and kurtosis parameters for 20 intersections reveals a 3-parameter log-normal distribution for accumulation (grade-thickness) and thickness values. The graphical estimate of the average grade from the probability diagrams is 29.59% P₂O₅ and that estimated by computer is 29.40% P₂O₅.

A computer programme ONEPOP.FOR in interactive FORTRAN77 has been developed for statistical modelling of the exploration data. Using this approach the grade. estimated for phosphorite deposit of the Khatamba Blocks shows a marginal increase in the value of average grade of P₂O₅, content as compared to the estimate made by conventional method.

Keywords

Stromatolite, Phosphorite, Economic Geology, Statistical Geology.

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Shakeel Ahmed ¹, B. C. Sarkar ², Indranil Roy ²

Affiliations
1 National Geophysical, Research Institute, Hyderabad - 500 007, IN
2 Indian School of Mines, Dhanbad, IN

Abstract

No Abstract.

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B. C. Sarkar ¹, Indranil Roy ²

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad - 826 004, IN
2 Central Ground Water Board, Guwahati, IN

Abstract

The prime purpose of orebody modelling is to reliably estimate the distribution of in situ and recoverable tonnages and grades of a mineral deposit. Conventional methods of estimation, such as polygonal, triangular, crosssectional and distance weighting provide local estimates of an ore body. However, such estimates are not error associated. Classical statistical techniques provide error of estimation but ignore spatial relationships, A thorough geostatistical estimation with careful attention to geology of mineralization provides not only an adequate global reserve estimate but also a more reliable block-by-block mineral inventory with associated confidence in the block estimates. Such estimates are crucial for short- and long-term planning for exploration of mineral deposits to maximise net return on investment. Kalta iron ore deposit, located in the state of Orissa, has been studied for resource evaluation using geostatistical approach taking into account the geological parameters wherever necessary. Using exploratory drill hole information, a study starting from statistical distribution modelling through semi-variography to generation of ore inventory and gradetonnage relationships has been carried out to highlight the effectiveness of such modelling.

Keywords

Geostatistics, Resource evaluation, lron Ore, Grade-Tonnage, Kalta, Orissa.

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Kalyan Saikia ¹, B. C. Sarkar ²

Affiliations
1 Central Mining Research Institute, Dhanbad - 826 001, IN
2 Department of Applied Geology, Indian School of Mines, Dhanbad-826004, IN

Abstract

Gurahar Pahar gold prospect, located in Sidhi district of Madhya Pradesh, is one of the most promising gold prospects of Mahakoshal greenstone belt in Central India. Gold mineralization is generally associated with sheared quartz veins, proximally found tuffaceous phyllite, carbonate veins and primary sulphides. This paper attempts an integrated modelling for resource evaluation of Gurahar Pahar gold prospect. The integrated approach combines together: (i) a geological understanding of the nature of gold mineralization from field observable evidences on host lithology, mode of occurrence, structural elements, viz. schistosity and foliation, and drill hole intersections from published exploration data; (ii) classical statistical modelling; and (iii) geostatistical evaluation for development of mineral inventory of the central part of Gurahar Pahar gold prospect. The integrated geostatistical resource evaluation using block kriging technique and grade-Tonnage relations of the central part of the prospect, bounded between 1040 S to 1540 S and 140 E to 840 E of the local grids and between 291 mRL and 181 mRL, indicate 3,36,000 tonnes of gold ore at a cutoff of 0.5 g/t with an average Au of 0.74 g/t.

Keywords

Geostatistical Modelling, Semi-Variogram, Block Kriging, Grade-Tonnage Relations, Greenstone Belt, Sidhi District, Madhya Pradesh.

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B. C. Sarkar ¹

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad - 826 004, IN

Abstract

Geomathematica techniques are gaining importance for analysis of geological data. The aim of geomathematical modelling is to replicate the reality as closely as possible using available sample information. In the case of a mineral deposit, geomathematical modelling provides a closer representation of the geological reality in terms of distribution of various spatial parameters in order to assess its 3D spatial configuration. Geomathematical modelling involves fitting a mathematical function, f(x) to define adequately a mineral deposit with respect to the distribution of its size, shape, grade, density, thickness and other geological attributes viz petro-Mineralogical characteristics with an aim to provide a three dimensional representation of the deposit with maximum possible confidence. This paper discusses the developments in geomathematics and focuses on the recent trends along with the computer applications in mineral resources assessment.

Keywords

Geomathematical Modelling Computer Applications, Mineral Resources Assessment, Fractal Relations.

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Indranil Roy ¹, B. C. Sarkar ¹

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad - 826 004, Jharkhand, IN

Abstract

Geological knowledge of associations between field evidence and deposit types for a range of iron ore deposits have been consolidated and structured into a rule-based prototype system, MODELER that is able to assist exploration geologist for diagnosing iron ore deposit types. The system contains knowledge on eighteen deposit models represented by eighteen compound rules based on the concepts of type area and genetic type. This paper focuses on the design and development of the system and its application to five iron ore deposits from eastern India.

Keywords

Expert System, Prototype, Iron Ore Deposit Types, Eastern India.

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D. K. Sinha ¹, Sohail Fahmi ¹, B. C. Sarkar ¹, M. K. Roy ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, 521207 Pratap Nagar, Tonk Road, Sanganer-Jaipur -303 609, IN

Abstract

Uraniferous polymetallic veins are found in the Gyangarh Asind acidic igneous suite and Sandmata Complex near Chhota-Udaipur in Rajasthan. These veins occur in continuation of the well-known U-Co-Mo mineralised albitite zone in Rajasthan and represent a potential target.

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B. C. Sarkar ¹

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad - 826004, IN

Abstract

Search for mica deposits presents peculiar problems owing to great complexities associated with pegmatite bodies. All pegmatites do not develop mica and not all mica-bearing pegmatites carry commercially workable quantity of mica. Prospecting for mica has therefore been a highly speculative and risky venture. It is in this context that the use of characteristic analysis, a multivariate statistical technique, has been made for the development of a composite geological model of the most typical indices of pegmatites of Nellore mica belt around Gudur in Andhra Pradesh, in order to evolve prospecting guides for mica search.

Data pertaining to geological variables gathered through surface mapping, field observation and geological studies of pegmatite bodies of Gudur mica region have been statistically treated for characteristic analysis. The approach elucidates most typical characteristics of pegmatites favourable for hosting commercially workable mica deposits. The geological variables associated with mica mineralization have been selected through an extensive survey and analogy. The model is governed by choosing sample locations and geological variables that best reflect mica mineralization. Presence of albite, undeformed pegmatite and kaolinization have been determined to be the most characteristic indices for mica search in the pegmatites of Nellore mica belt around Gudur.

Keywords

Pegmatite, Mica Mineralization, Characteristic Analysis, Statistical Modelling, Nellore Mica Belt, Typicality, Gudur, Andhra Pradesh.

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B. C. Sarkar ¹, Archana M. Nair ¹

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad - 826 004, IN

Abstract

Hutti gold mine, located in the Archaean Hutti-Maski greenstone belt, is one of the major gold producing mines in India. Gold mineralisation is associated with parallel to sub-parallel, steeply dipping auriferous quartz veins localised in a major shear zone in the western segment of the greenstone belt. Coarse and fine grained vesicular metabasalts of Buddinne Formation are the host for auriferous lodes reflecting a litho-stratigraphic control.

The present study deals with geostatistical modelling for Hutti gold mineralisation, keeping in view the various controls of mineralisation and geological setting. The geostatistical modelling carried out for gold accumulation and width of mineralisation from underground drives and cross-cuts at 18^th, 19^th and 20^th levels of Strike Reef reveal a positively skewed 2-parameter lognormal distribution fit. Semi-variogram modelling for gold accumulation reveal a high nugget effect and a moderate continuity with a small range of influence and that for width, a moderate to high nugget effect and a moderate continuity with a small range of influence. These spatial parameters reflect the erratic nature of gold mineralisation.

Block value estimation has been carried out employing 3-D kriging technique. The results of block kriging have been used to compute an ore inventory for the three levels and to establish grade-tonnage relationships estimating the (i) quantity of ore, gold metal and waste; (ii) average grade of ore above a series of alternative cutoff grades; (iii) waste-to- ore ratio following a step-wise integration of the block grade frequency distribution over a range of grades. These estimates then form a sound foundation for mine decisions.

Keywords

Geostatistics, Modelling, Semi-Variogram, Kriging, Ore Inventory, Gold Mineralisation, Hutti, Raichur District, Karnataka.

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