JOURNAL GEOLOGICAL SOCIETYOF INDJA Vol.49. May 1997. pp. 559-565 Geochemistry of Rajapur and Puttur Thermal Springs of the West Coast, India A. RAMANATHAN' AND D. CHANDRASEKfIARAM2 I School of Earth Sciences. KajamalaiCampus. Bharathidasan Unive~ity. Tiruchirapalli -620 023 2. Department of Earth Sciences. Indian Instituteof Technology. Powai. Bombay -400 076 Abstract: Thennal springs of Rajapur and Puttur (Irde and Banduru) areof low-temperature andlow- flow type. Though they are locatedat two different geological setup. they fall in Na-HCO) facies. The imprints of basalt-thenna! water interaction atRajapur and local equilibration of doleritic dyke with the thennal water of Irde is deduced. The reservoir of the Rajapurthenna!spring is likely to be locatedin the Precambrian fonnations,as thatof Puttur thermal springsand hence the chemical processes undergoing in these systems are similar. The reservoir temperatures estimatedusing chemica!geothermomete~ are about 200.C and >120.C for the Pullur and Rajapur thennalsprings respectively. Illite, K-mica, chlorite, kaolinite. Ca-montmorillonite and philipsite are the expected secondary minerals in the system. Keywo~: Hydrogeochemistry, Geothennics. ThennalSprings, DeccanBasalis, West Coast. INTRODUCTION n' Twenty thennal springs are located along the west coast of India in two different geological setups. Eighteen of them are located in the Deccan flood basalt Province (Konkan thennal springs), The remaining two are lo- cated south of Konkan but in Precambrian crystallines, near Puttur in Karnataka (Puttur thennal springs). The present stu9Y..deaIs with '. the Rajapur thermal spring (16°38'N; 73°34'E), the southernmost of Konkan and the Puttur thermal springs, namely Irde (12°48'N; 7S0l3'E) and Banduru (12°S4'OS"N; 7so17'Q4"E), Lo- cation of Rajapur and Puttur thennal springs L/' among the other thermal .springs of the west i coast is shown in Fig.l. ; The existing literature deals either with i Konkan (Krishnaswamy (1976), Pitale et al. (1987) or with Irde thermal spring of Puttur (Radhakrishna,1971 and Seshadri, 1974). The occurrence of the Banduru thennal spring is Tr oa reported only recently (Selvakumar, 1991). No Fig 1. Location of the Rajapur andPultur thennal springs detailed work has been carried out on Puttur among the other west coast thennal springs isr thennal springs and only partial chemical In~ia: Solid dot -thermal springs; Dash-.dotlines .., -.lineaments; a -Quarternary; c -TertIary; d - analysIs of the thermal waters IS available. Deccan Traps; f -Archean-Proterozoic; N -North This paper discusses the possible chemical Konkan;C -Central Konkan; 5 -South Konkan. 0016-7622/97-49-5-559/$ 1.00@ GEOL. SOC. INDIA