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GIS approach to statistical modelling for mineral deposits in the Singhbhum copper belt, Bihar, India, using geological and geophysical parameters
A.K . Ray & B. Mukherji
Geological Survey of India
Abstract
The Singhbhum Copper Belt (CBM), a curvilinear zone
of approximately 160 km length between Kharswan-Duarpuram in the west and
Baharagora-Kesharpur in the east, in Bihar state of India, is a well known
repository of copper, uranium and apatite-magnetite mineralisation, related to
extensive shear effect caused by structural phenomena involving rocks of the
lower Proterozoic age (C. 2400-2300 Ma). Drawing upon the geological and the
aero-geophysical data on the mineralised belt from extensive information base
generated over years of study by the Geological Survey of India and other
exploration agencies and the academia, the parameters for probable
mineralisation were identified from the known mineral occurrences in the Belt.
A dual approach was then made to prepare a probability model for
targeting mineralisation in the Central Sector of the Belt better known for the
known deposits. The first approach was to use a total of 122 geological
variables in a stretch of the area between Baharagora and Tamadungri.
Two types of statistical analysis was done, to select or identify
variables which were important for the analysis and to obtain an equation
connecting the metal accumulation with the other variables. A network of cells
each of 1km x 1km area was superimposed on the geological map and the variables
present in each cell were noted. The reserve figure of copper and their grade in
15 locations were collected and total metal accumulation in each was calculated.
The results were scaled, summed for larger unit cells and contoured to give a
probability index.
From the database, statistical techniques employed to
reduce the number of variables were done automatically with the help of programs
written in Dbase V and SPSS and interfacing them. The grids and the probability
contour map were also generated with the help of computer.
The result
indicate possibility of new mineral deposits in the unexplored areas lying
between known deposits in the Singhbhum Copper Belt. Six new areas were
identified by this approach.
The second approach was to generate a
spatial model by subjecting the (a) geological map, (b) the aeromagnetic total
intensity anomaly map and (c) the Bouguer gravity anomaly map over the shear
zone to digitization and integration in the ARC-INFO GIS environment. Using the
range of values for each parameter in the known deposit areas, the integrated
combination focused on areas with potential for mineral find, requiring
validation by ground exploration methods.
Introduction:
The
Singhbhum Copper Belt in Bihar is well known for its wealth of mineral
resources, mainly of copper and also of uranium, apatite-magnetite and kyanite.
The copper producing mines of this belt under Hindustan Copper Limited (HCL)
leasehold form the major contributors in the production of copper from Eastern
India. This belt with indications of copper mineralisation stretches for an
approximate strike length of 160 km from Duarpuram-Kharswan in the west to
Baharagora-Kesharpur in the southeast (Fig.1). The economic occurrences are
known only in parts of the central sector, which constitutes about 15% area of
the total stretch. To locate new targets, volumes of data on geological,
geophysical, geochemical and mineral investigations were generated over the last
few decades. These were compiled, collated and synthesized by GSI under 'Project
- Singhbhum', 1991 with special emphasis on identifying the gaps in information
and knowledge, and locate the areas which deserve follow up action.
The
present work attempts at analyzing the data of the known variables in copper
producing central sector drawn from the data bank, created by the 'Project -
Singhbhum', 1991, by digitizing the mapped data and subjecting them to (a)
statistical analysis and (b) GIS, to create probability models statistically and
spatially using for the first, the geological parameters only and for the
second, the geological and geophysical parameters in an interactive manner.
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