Banded Iron Formations (BIFs) are archives of Precambrian seawater composition. Presence or absence of negative Ce anomaly (Ce/Ce*) in BIFs has been widely used to understand paleo-redox conditions on the Earth’s surface in the Precambrian. However, whether the extremely negative Ce anomaly associated with the BIFs reflects a primarily depositional signature or not has been questioned and it has been suggested that such signatures could also arise from secondary alterations.1 We report elemental and Nd isotopic data for BIFs and associated clastic rocks from the Sirsi region in southern India. Major and trace element compositions of these BIFs were measured using an Inductively Coupled Plasma Mass Spectrometer (ICP-MS, X series II) while Nd isotope ratio (143Nd/144Nd) measurements were performed using a Thermal Ionization Mass Spectrometer (TIMS, Triton Plus), both at the Centre for Earth Sciences (CEaS), Indian Institute of Science Bangalore, India. The BIF samples are sub-divided into two groups based on their REE+Y (REY) compositions. The group-1 BIFs show seawater-like REY pattern with HREE enrichment over LREEs and super-chondritic Y/Ho (41-52). These BIF samples also lack significant negative Ce anomalies. In contrast, group-2 BIFs show high LREE/HREE enrichment, negative Ce anomaly, and sub-chondritic Y/Ho. Very high values of La/Yb in the group-2 BIFs cannot be explained by simple two-component mixing of basement rock (Dharwar TTG) and pristine Sirsi BIFs. Instead, fluid-rock alteration by LREE enriched, and Ce depleted fluid could explain the observed REY variations. We further utilized Sm-Nd isotope systematics to calculate the timing of this alteration event. These BIFs show lowest RSD (%) in their initial 143Nd/144Nd composition around 0.6 Ga, which we consider as the time of alteration event which affected the Sm/Nd of these rocks. The timing of alteration event coincides with the Pan-African orogeny which had regionally affected the Greater Dharwar Craton. The associated red shales are also characterized by high LREE/HREE ratios and negative Ce anomalies. These shales also show very high Chemical Index of Alteration (CIA) values (83-99) suggesting high degree of chemical weathering. [1] Bonnand et al, (2020) Earth and Planetary Science Letters