Gondwana coal deposits of India: Fueling growth

Indian Gondwana Coal Basins

Introduction

The Indian Gondwana coal deposits are primarily found in the eastern and central parts of India, dating back to the Permian and Triassic periods. They are spread across several states in central and eastern India, primarily in the Damodar Valley Basin (Jharkhand and West Bengal), Mahanadi Basin (Odisha), Son-Mahanadi Basin (Chhattisgarh), Godavari Valley Basin (Telangana and Maharashtra), and Wardha Valley Basin (Maharashtra). These coal deposits are stratigraphically classified into several formations, including the Talchir, Barakar, Raniganj, and Kamthi formations. The coal-bearing strata are typically interbedded with sandstones, shales, and conglomerates, representing fluvial and lacustrine environments. These formations hold significant economic importance as they contain vast reserves of coal, contributing significantly to India's energy and growth needs.

Geological Setting

The Gondwana coal basins in India originated during the Permian and Triassic periods, approximately 250 to 300 million years ago, when the supercontinent of Gondwana began to break apart. Past plants, vegetation, forests flourished in the warm and humid climate, were accumulated and buried under sedimentary layers, leading to the formation of coal deposits over millions of years. The Gondwana coal basins cover an extensive area of approximately 225,000 square kilometers, making them one of the largest coal-bearing regions in the world. They are spread across several states in central and eastern India, primarily in the Damodar Valley Basin (Jharkhand and West Bengal), Mahanadi Basin (Odisha), Son-Mahanadi Basin (Chhattisgarh), Godavari Valley Basin (Telangana and Maharashtra), and Wardha Valley Basin (Maharashtra). Each basin has its unique geological characteristics, coal quality, and mining history, contributing to the diversity of India's coal resources.

The Indian Gondwana coal deposited in a half graben type structural basins. A half-graben structure is a geological formation characterized by a series of normal faults that dip on one side, creating a basin-like depression.

The primary feature of a half-graben is a normal fault, where one side of the fault drops down relative to the other side. As the crust stretches and the fault(s) accommodate the extension, a basin-like depression forms on the down-dropped side of the fault. This basin is often filled with sedimentary deposits, such as sandstone, shale, plants & vegetations and conglomerates, which accumulate over time. In regions where multiple half-grabens form parallel to each other, they create a series of alternating basins (grabens) and uplifted blocks (horsts). This arrangement is known as a horst and graben system, with the half-grabens representing the basins between the uplifted blocks. Over time, the half-graben structure may undergo further deformation and modification due to ongoing tectonic activity. This can include additional faulting, tilting of strata, and erosion, shaping the basins and influencing the distribution of sedimentary deposits within the basin. Some of the prominent Gondwana coal basins in India include:

Damodar Valley Basin: Located in the states of Jharkhand and West Bengal, the Damodar Valley Basin is one of the oldest and most significant coal-bearing regions in India. It is characterized by the presence of thick coal seams interspersed with layers of shale, sandstone, and clay. The basin has a long history of coal mining dating back to the British colonial era and continues to be a major contributor to India's coal production.

Mahanadi Basin: Situated primarily in the state of Odisha, the Mahanadi Basin is another important coal-bearing region in India. It is known for its extensive reserves of bituminous coal and is home to several large coal mines operated by government and private entities. The coal extracted from this basin is primarily used for thermal power generation and industrial applications.

Son-Mahanadi Basin: Covering parts of Chhattisgarh and Odisha, the Son-Mahanadi Basin is characterized by its vast coal reserves and relatively underdeveloped mining infrastructure. It is a significant contributor to India's coal production and is poised for further development as new mining projects are initiated in the region.

Godavari Valley Basin: Spanning across Telangana and Maharashtra, the Godavari Valley Basin is known for its high-quality coal reserves, including both coking and thermal coal. The basin has witnessed significant mining activity in recent years, with several coal mining companies operating in the region to exploit its rich coal deposits.

Wardha Valley Basin: Located in Maharashtra, the Wardha Valley Basin is relatively smaller in size compared to other Gondwana coal basins but is notable for its unique geological characteristics. It is known for its reserves of non-coking coal, which are primarily used for thermal power generation and industrial processes.

The stratigraphy of Indian Gondwana coal deposits is characterized by several distinct formations, each representing different geological periods and depositional environments. These formations include the Talchir, Barakar, Raniganj, and Kamthi formations, among others.

Talchir Formation: The Talchir Formation is the oldest sedimentary unit associated with Gondwana coal deposits in India. It consists of coarse-grained sandstones, shales, and conglomerates deposited during the Early Permian period. While not directly associated with coal deposition, the Talchir Formation serves as the basal unit for overlying coal-bearing strata.

Barakar Formation: The Barakar Formation represents the main coal-bearing unit in the Gondwana sequence. Deposited during the Middle Permian period, it consists of alternating layers of coal seams, sandstones, shales, and mudstones. The Barakar Formation is characterized by fluvial and deltaic depositional environments, indicating the presence of ancient river systems and swamp forests where coal-forming vegetation thrived.

Raniganj Formation: Overlying the Barakar Formation is the Raniganj Formation, which was deposited during the Late Permian period. This formation is notable for its thick coal seams, which are commercially exploited for their high-quality coal. The Raniganj Formation also contains layers of sandstones, shales, and siltstones, suggesting a similar depositional environment to the Barakar Formation.

Kamthi Formation: The Kamthi Formation, dating to the Early Triassic period, overlies the Raniganj Formation. It consists of interbedded sandstones, shales, and coal seams, indicating a transition to more terrestrial depositional environments. While not as extensive as the underlying Permian formations, the Kamthi Formation still contains significant coal reserves.

Indian Gondwana coalfields

Coal Depositional Environments

The formation of coal deposits in the Gondwana sequence was influenced by various depositional environments, including:

Fluvial Systems: Ancient river systems transported organic material from swamp forests to depositional basins, where it accumulated and eventually formed coal seams.

Deltaic Environments: Deltas formed at the mouths of rivers provided favorable conditions for the accumulation of sediments and organic matter, leading to the formation of coal-bearing strata.

Swamp Forests: Dense forests and wetland environments covered much of the land during the Permian and Triassic periods, providing the organic material necessary for coal formation.

Lacustrine Settings: Shallow lakes and ponds within the depositional basins served as additional environments for the accumulation of organic material, contributing to coal formation.

Coal Reserves and Quality

The Gondwana coal basins in India are known for their significant reserves of bituminous and sub-bituminous coal, which are ideal for thermal power generation and various industrial applications. These coal reserves are estimated to be several billion metric tons, providing a substantial energy resource for the country's growing economy. The coal extracted from these basins varies in quality, with parameters such as calorific value, ash content, sulfur content, and volatile matter influencing its suitability for different purposes. While some regions produce high-quality coking coal used in steel manufacturing, others yield thermal coal primarily utilized for electricity generation.

General geochemical characteristics of Indian Gondwana coals:

Ø  Moisture < 2% to 6%

Ø  Volatile - <18 to 35%

Ø  Carbon - 85 to 90% (on dmf basis)

Ø  Ash - 15 to 30% (excluding dirt bands)

Ø  Coking properties (eastern Coal Fields of Damodar Valley basins and some other coal basins)

Ø  Coke type - D to G6 or better where coking coal are present.

Conclusions

The Gondwana coal deposits in India are of immense economic significance, serving as a vital energy resource for the country's industrial and economic development. India is one of the world's largest producers and consumers of coal, with Gondwana coal contributing significantly to its energy mix. The coal mining industry supports millions of jobs and plays a crucial role in various sectors, including power generation, steel making, and transportation.