Biogeochemistry over the sulfidic​/auriferous zone near Ajjanahalli, Chitradurga Schist belt, Dharwar craton, souther India


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Prabhakar, B.C. and Rashmi, B.N. and Gireesh, R.V. (2013) Biogeochemistry over the sulfidic​/auriferous zone near Ajjanahalli, Chitradurga Schist belt, Dharwar craton, souther India. Journal of Applied Geochemistry, 15 (3). pp. 271-288. ISSN 0972-1967

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The sulfidic​/auriferous ridge near Ajjanahalli in Chitradurga schist belt is chiefly constituted by BIF and flanked on either side by a closely knit assembly of phyllitic schists and carbonaceous shales. The mineralization is confined to the shear zone and the ore minerals are disseminated in the fracture filling quartz​/carbonate veins of epigenetic nature. Pyrite, chalcopyrite, arsenopyrite and pyrrhotite are the chief sulfide minerals within which gold is hosted. The mineralized ridge is covered by fairly thick natural vegetation including herbs, shrubs and tree species. About half meter to meter thick well drained, coarse textured silty to gravelly soil form a crust over this mineralized ridge. The area is a semi-​arid tract with moderate annual rainfall of ∼500mm. In the present study, this auriferous zone has been chosen for geobotanical and biogeochem. study to appraise the morphol. characteristics of plant species and the metal dispersion pattern in them in relation to metal content in the ground. Soil geochem. suggests a poor to moderate accumulation of Cu (139-​627 ppm)​, most in the range of 250-​600 ppm. Many other metals show normal dispersion. Arsenic is in high concn. ranging from 695-​5470 ppm. Similarly, Se also shows anomalous content (1304-​2136 ppm)​. Plants show inhomogeneous accumulation of metals. Cu is in poor concn., probably owing to its poor content in soil. Slightly alk. nature of soil could have also hindered its dissoln. and the consequent mobility. Arsenic is significantly accumulated in a Fern species (Pteris vittata) which is confined only to the mine-​sections in mineralized ridge. Interestingly, a clear higher uptake pattern of Au by this Fern is also noticed, whereas other species do not show such comparable patterns of As and Au. Gold in soil also shows moderate concn. (40-​320 ppb)​. Thus, Fern species hint at the possibility of considering it as a local indicator for gold in sulfidic zones. But, detailed sampling of this species is necessary before ascertaining its value as an index plant. Other metals like Co, Zn and Mn, though present in variable concns. in plants, they do not reflect much significance. Se, though toxic to plants at higher concns., was found to be enriched in plants, aptly reflecting the sulfidic nature of the substratum.

Item Type: Article
Uncontrolled Keywords: Ajjanahalli, Auriferous zones, Sulfides, Geobotany, Biogeochemistry.
Subjects: Faculty of Science > Earth Sciences > Geology
Divisions: Jnana Bharathi / Central College Campus > Department of Geology
Depositing User: Mr. Lokeshareddy Y C
Date Deposited: 24 Nov 2016 09:09
Last Modified: 24 Nov 2016 09:09

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