Multiphase deformation and occurrence of oxides and sulphides as evidenced from magnetic and IP/Resistivity surveys: A guide to U-exploration in Galudih-Sankadih-Kadamdih sector of SSZ, Seraikela-Kharsawan district, Jharkhand

Two generations of magnetite veins (Ml and M2) and basic dyices (BD-1 and BD-2), in Galudih-Sankadih-Kadamdih area, are inferred from magnetic and Induced Polarization (lP)/resistivity data. The trend of Ml defines southern boundary of Singhbhum Shear Zone (SSZ) and M2 is within the shear zone. The B D l intrusions confined to the shear zone are non-magnetic in nature whereas BD2 intruded in the north of the shear zone are magnetic in nature. The dislocations in M1, M2, BD1 and BD2 trends indicated three generations of brittle deformations, across SSZ, post dating the two deformations namely ductile (D l) and brittle (D2) parallel to SSZ. The magnetite (M l) and uraninite (in most cases) are localized along D l . The second stage brittle deformation (D3) took place after emplacement of the Arkasani Granophyre within SSZ followed by BD-1 intrusion which is post Dl and pre D2, subsequent metamorphism and again deformations (D4 and D5) followed by another intrusion BD-2 which is post D4. Another magnetite vein (M2) has been formed between D4 and D5. The high chargeability trends, along D l, indicate polarizable sources which are further interpreted as sulphides from Relaxation-Time-Distribution analyses of time-domain IP data. The long wavelength folding (D l) and fiirther dislocations in the chargeability trends, suggest that the sulphide mineralisation has suffered ductile (D l) and subsequent brittle deformations (D2, D3, D4 and D5). This indicates sulphides are syngenetic/prior to the last stage of folding (D l) in SSZ. These sulphides have positive correlation with uranium minerals as corroborated by the borehole log data. Further, uranium mineralisation is displaced along D3, D4 and D5 in vertical and horizontal directions. Thus the spatial deformations, recognized from geophysical data sets, of the shear zone rocks are linked to the temporal development of mineralisation within shear zone. It is also concluded that the shear controlled uranium mineralisation is affected by postdated brittle deformations useful for correlation of uraniferous bands with magnetite and sulphide mineralisation bands.