(a) Give an account of geology, mode of occurrence, genesis and distribution of Pb-Zn deposits of Aravalli region. (15…

Aravalli Pb-Zn deposits The Aravalli Pb-Zn province of Rajasthan is a classic Proterozoic sediment-hosted metallogenic belt. The deposits are largely stratiform or semi-stratiform, developed in Precambrian metasediments of the Aravalli and Bhilwara supergroups, with mineralization controlled by carbonate-rich horizons, red beds and faulted contacts. Rampura-Agucha, hosted in the Bhilwara Supergroup, and the Rajpura-Dariba-Bethumni belt in the Zawar belt, generally hosted by the Aravalli Supergroup, are type examples. Genesis is debated between syngenetic-diagenetic models, where metals were deposited from basinal brines or seawater during sedimentation, and epigenetic models, where later hydrothermal fluids remobilized and concentrated metals along faults and bedding. In practice, most deposits show a mixed history: primary sedimentary mineralization followed by tectono-thermal reworking during Aravalli orogeny. Distribution is concentrated in the southern Aravalli, especially the Zawar belt and Bhilwara district, making Rajasthan India’s principal Zn-Pb province.

Petroliferous basins and Cambay Basin India’s petroliferous basins are distributed across onshore and offshore sedimentary provinces. Geographically, they span the northeast, western, central, southern and offshore margins. Onshore, the major producing basins include Assam-Arakan in the northeast, Kutch, Saurashtra, Cambay, Rajasthan (Barmer), Mahanadi, Krishna-Godavari and Cauvery; important exploration or potential basins include Ganga, Vindhyan, Bengal and Jaisalmer. Offshore, the Mumbai offshore (Mumbai High), Krishna-Godavari offshore and Cauvery offshore are the key hydrocarbon provinces. Category-wise, Assam, Kutch, Saurashtra, Cambay, Rajasthan, Mahanadi, Krishna-Godavari, Cauvery and Mumbai offshore are generally treated as producing Category-I basins, while Ganga, Vindhyan, Bengal and Jaisalmer remain important Category-II or exploration targets. The Cambay Basin is a Tertiary rift basin developed along the Narmada-Tapti lineament in Gujarat. Its geology is dominated by Eocene-Oligocene sediments, with Olpad Formation volcanics and volcaniclastics, the organic-rich Cambay Shale as the principal source rock, and Kalol and Ankleshwar sandstones as the main reservoirs. Hydrocarbons are trapped in fault-block, anticlinal and stratigraphic traps, and the basin illustrates a rift-related, thermogenic petroleum system.

VMS deposits Volcanogenic massive sulphide deposits are formed by seafloor hydrothermal systems in submarine volcanic settings. They are commonly associated with bimodal volcanics, where intermediate to felsic magmatism drives metal-rich fluids that precipitate sulphides on the seafloor. The classic Cyprus, Kuroko and Besshi types differ in tectonic setting, ore texture and metal endowment, but all share massive sulphide lenses, footwall alteration and mineralization linked to volcanic-hosted hydrothermal circulation. In India, VMS occurrences include the Ambaji-Deri belt in the Aravalli region, Sargipalli in the Singhbhum craton and the Betul belt in Madhya Pradesh. The Ambaji-Deri belt lies in the South Delhi Fold Belt and is Mesoproterozoic, thus younger than the Paleoproterozoic Aravalli SEDEX-type Zn-Pb deposits; Sargipalli is linked with Archaean greenstone-related volcanism, while Betul is another Indian volcanogenic province. These deposits are important for Cu-Zn, giving them critical-mineral relevance.

Comparative synthesis The three systems contrast genetically and temporally. Aravalli Pb-Zn is sediment-hosted, developed in Proterozoic metasediments and linked to basinal brines and diagenetic-epigenetic processes. VMS deposits are volcanogenic, formed by hydrothermal seafloor systems in Archaean to Proterozoic volcanic terrains, with India’s examples spanning Archaean Singhbhum and Mesoproterozoic Ambaji-Deri. Petroleum systems are biogenic/thermogenic, dependent on organic-rich source rocks, reservoirs and traps, and are largely Tertiary in the Cambay and other basins. Economically, Aravalli Zn-Pb contributes significantly to India’s Zn-Pb self-sufficiency, while petroleum remains import-dependent, making basin exploration and offshore development strategic. VMS deposits offer potential for critical Cu-Zn resources. A way forward is integrated exploration: re-evaluating Aravalli SEDEX and VMS belts with geophysics, geochemistry and deep drilling, expanding Cambay and other onshore basins, and linking metallogenic mapping with critical-mineral policy.