Delineation of subsurface structures using self-potential, gravity, and resistivity surveys from South Purulia Shear Zone, India: Implication to uranium mineralization Arkoprovo Biswas 1 , Animesh Mandal 2 , S. P. Sharma 1 , and W. K. Mohanty 1 Abstract The unexplored South Purulia Shear Zone (SPSZ) at the north of Singhbhum Shear Zone (SSZ) in Eastern India is a prospective zone for structural-guided hydrothermal mineralization. We carried out an integrated geophysical study using self-potential (SP), gradient-resistivity profiling (GRP), and gravity study across the SPSZ to identify the near-surface structural features and probable correlation with the uranium mineralization of the region. We studied a broad low SP, anomaly zone correlated with corresponding low-gravity and low- resistive zone across the same part of the study area. This conductive and low-density zone was identified as the width of the brittle-to-ductile and highly altered SPSZ. The 2D modeling of SP and residual gravity data along a northeast–southwest profile across the shear zone between Raghunathpur and Barabazar localities revealed the northerly dipping shear zone with an average width of ∼4.5 km. However, the 2D modeling of the SP data sug- gested numerous thick, sheet-type vertical and/or inclined structures intervening the shear zone, which were well correlated with the vertical structures delineated by the 2D gravity inverse model. The vertical alteration zones (density and conductivity) at ∼40-, 200-, and 400-m depths have been identified over this region. These alteration zones are likely to be mineralized zone because a hydrouranium anomaly has also been reported from those locations earlier. We studied the efficacy of an integrated approach using GRP, SP, and gravity surveys for the investigation of near-surface vertical to dipping conducting structures associated with uranium minerali- zation in such shear zone regions. Introduction Natural radioactive mineral deposits normally occur in suitable geologic environment associated with shear zones, unconformity contacts, vein-type deposits, etc. (Bhattacharyya, 1992; Tuncer et al., 2006). Uranium is an important radioactive element and is used in many purposes. Scarcity of fossil fuels in future may make nu- clear energy a real solution for energy demand. Shear zones are the most important geologic structure for the occurrence of uranium mineralization (Kříbek et al., 2009; Turchenko et al., 2009). The mineralization may occur due to hydrothermal vein-type deposit; strata- bound deposit, disseminated type and brecciated com- plex type in the form of vertical, dipping as well as horizontal sheet-type structures. The unexplored South Purulia Shear Zone (SPSZ) at the north of Singhbhum Shear Zone (SSZ) in Eastern India is a prospective zone for structural guided hydro- thermal mineralization. The uranium mineralization has been reported from some discrete places like Beldih and Kutni (Katti et al., 2010) (Figure 1). Regional gravity and magnetic survey over the Eastern Indian Shield has been carried out earlier (Verma et al., 1984). The Bou- guer gravity anomaly map and magnetic data (Gupta and Basu, 2000) suggests that there is a contrasting change from the Singhbhum granite craton in the south to the Chota nagpur granite gneissic complex (CGGC) in the north. The recent gravity-magnetic study shows a broad low-gravity anomaly zone and high-magnetic anomaly (A. Mandal, personal communication, 2014) and low-resistive zone (Biswas et al., 2014). Again, there is a very good correlation with the nature of uranium deposit in Beldih mine with the uranium present in dif- ferent locations of the SSZ (Katti et al., 2010). However, detailed geophysical activities for delineating the asso- ciated near-surface structural features (such as fault, fractures, or alteration zones) have never been per- formed in this area. Chemical analysis of the water samples from deep tube well also shows signature of hydrouranium anomaly (∼40 ppb) within the study area 1 Indian Institute of Technology Kharagpur, Department of Geology and Geophysics, Kharagpur, West Bengal, India. E-mail: arkoprovo@gmail .com; arkoprovo@gmail.com; spsharma@gg.iitkgp.ernet.in; wkmohanty@gg.iitkgp.ernet.in. 2 Formerly Indian Institute of Technology Kharagpur, Department of Geology and Geophysics, Kharagpur; presently CSIR-National Geophysical Research Institute, Hyderabad, India. E-mail: animeshphys@gmail.com. Manuscript received by the Editor 21 October 2013; revised manuscript received 6 February 2014; published online 10 April 2014. This paper appears in Interpretation, Vol. 2, No. 2 (May 2014); p. T103–T110, 6 FIGS. http://dx.doi.org/10.1190/INT-2013-0170.1. © 2014 Society of Exploration Geophysicists and American Association of Petroleum Geologists. All rights reserved. t Technical paper Interpretation / May 2014 T103 Interpretation / May 2014 T103 Downloaded 04/14/14 to 14.139.95.131. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/