GEOCHEMICAL AND PETROLOGICAL STUDIES OF A CARBONATISED METALAMPROPHYRE AT KALAGALLA -

EVIDENCE FOR SHOSHONITIC CALC-ALKALINE MAGMATISM WITHIN AURIFEROUS RAMAGIRI-PENAKACHERLA SCHIST BELT (2.5 Ga), EASTERN DHARWAR CRATON, SOUTHERN INDIA

  • Rameshchandra Phani Pothuri
  • Raúl Lira CONICET-National University of Córdoba, Córdoba, Argentina
  • María José Espeche CONICET-National University of Córdoba, Córdoba, Argentina
  • Ananda Reddy Rokalla Geological Survey of India, Hyderabad

Abstract

Geochemical and petrological characteristics of a lamprophyre dyke at Kalagalla intruded into the auriferous schistose rocks of the Ramagiri-Penakacherla Schist Belt, Anantapur district, Andhra Pradesh, India are presented here. The Kalagalla lamprophyre (KGL) is a melanocratic rock exhibiting typical knobbly or pustular texture on the rock surface. The micro-textures and mineralogy typical of lamprophyres are obscured by metamorphism; however, it exhibits porphyritic, nemato-granoblastic texture representating greenschist facies metamorphism. The rock is sheared and carbonatised possessing several globules formed by polycrystalline aggregates of calcite rimmed by coronitic subhedral plagioclase and biotite-phlogopite, evidencing its magmatic origin. The mineral assemblages noticed in thin-sections include amphibole, plagioclase, biotite-phlogopite with calcite ocelli as essential while apatite, zircon, magnetite, ilmenite and several opaque minerals as accessory phases. The SEM-EDS investigation on the opaque minerals revealed accessory sulphide and silicate phases like As-free pyrite, haematitised Ni-bearing chalcopyrite and Ni-As-Co- minerals indicative of sulphidation associated with greenstonevauriferous lodes; along with oxide phases like LREE-bearing titanite partially transformed into leucoxene and goethite. Presence of amphibole and dominance of plagioclase, it is presumably a spessartite variety. Based on its geochemistry, the rock is classified as a shoshonitic calc-alkaline lamprophyre. The LREE-bearing titanite appears to be the contributor of LREE enrichment. The high Mg# (77-79), Ni (153-162 ppm) and Cr (380-470 ppm) support a mantle source. The trace and REE patterns (ƩREE:326-343 ppm, LREE>HREE) indicate ivolvement of residual garnet at the source enriched in phlogopite in a ‘subduction-related’ environment. The absence of Eu anomaly reflects lack of plagioclase fractionation. The high Zr/Hf ratio (163-202) indicates carbonatite metasomatism and lack of crustal contamination. Further investigations are in progress.

Author Biographies

Rameshchandra Phani Pothuri

I am an exploration geologist with a 20+ years of experience in commodities like diamonds, gold, base metals, iron ore and industrial minerals. I am recognised as a qualified person (RQP) by the Ministry of Mines, Government of India. I have 25 papers to my credit published on various aspects of geosciences and mineral exploration. I ahve presented more than 50  abstracts in various international and national level conferences.

Raúl Lira, CONICET-National University of Córdoba, Córdoba, Argentina

Dr Raul Lira

Universidad Nacional de Córdoba

Laboratorio de Microscopía Óptica y Microtermometría

Museo de Mineralogía y Geología "Dr. Alfred W. Stelzner"

Centro de Investigaciones de Geología Aplicada (CIGeA)

Av. Vélez Sarsfield 249

Córdoba (X5000JJC) - Argentina

 

María José Espeche, CONICET-National University of Córdoba, Córdoba, Argentina

María José Espeche

Researcher, 

Universidad Nacional de Córdoba

Laboratorio de Microscopía Óptica y Microtermometría

Museo de Mineralogía y Geología "Dr. Alfred W. Stelzner"

Centro de Investigaciones de Geología Aplicada (CIGeA)

Av. Vélez Sarsfield 249

Córdoba (X5000JJC) - Argentina

Ananda Reddy Rokalla, Geological Survey of India, Hyderabad

R. Ananda Reddy,

Superindent Geophysicist,

Geological Survey of India,

Bandlaguda,

Hyderabad, india.

Published
07-07-2020
Section
Articles