Previous Year Question
Consider the following statements.
Natural gas occurs in the Gondwana belts.
Mica occurs in abundance in Kodarma.
Dharwars are famous for petroleum.
Which of the statements given above is/are correct?
1 and 2
Only 2
2 and 3
None of these
Correct Answer: B
Detailed Solution
In this question, natural gas is used in the context of conventional natural-gas deposits. The Gondwana beds are principally known for India’s major coal deposits, whereas the major conventional natural-gas reserves are identified in Mumbai High and associated west-coast fields, the Cambay Basin and the Krishna-Godavari Basin.
An important modern qualification must be understood:
The Gondwana coal measures contain Coal Bed Methane—CBM.
CBM is an unconventional form of natural gas and is legally treated by the Government as natural gas.
According to the Directorate General of Hydrocarbons, the Gondwana sediments of eastern India host India’s existing CBM-producing blocks.
Nevertheless, under the conventional mineral-distribution classification used in this 2013 question, the association is “Gondwana beds—coal” and “younger sedimentary basins—petroleum and conventional natural gas.” Therefore, statement 1 was treated as incorrect.
Statement 2: Correct
Kodarma is a historical mica-producing region situated in the northern Chota Nagpur region of Jharkhand.
According to NCERT, mica deposits occur along the northern edge of the Chota Nagpur Plateau, and the Koderma–Gaya–Hazaribagh belt has been a leading producing region.
According to the Kodarma district administration, the region was once internationally renowned for mica production and was called India’s Mica Capital.
Mica is a mineral that splits into plates or thin sheets. Its dielectric strength, insulating properties and resistance to high voltage make it important for electrical and electronic industries.
Statement 3: Incorrect
Here, “Dharwars” refers not merely to the Dharwad district of Karnataka but to the Dharwar rock system.
The Dharwar Supergroup consists of very old Precambrian rocks, including metagreywacke, metabasalt, schist, quartzite and granitic gneiss.
Dharwar rock regions are associated with metallic minerals such as iron ore, manganese and gold; they are not famous for petroleum.
A commercial petroleum accumulation generally requires an organic-rich source rock, a porous reservoir rock, an impermeable cap rock and a suitable trap within a sedimentary basin. Ancient and intensely metamorphosed Dharwar rocks ordinarily do not constitute such a petroleum system.