Carbon isotope studies of auriferous quartz carbonate veins from two orogenic gold deposits from the Neoarchean Chitradurga schist belt, Dharwar craton, India: Evidence for mantle/magmatic source of auriferous fluid

Isotope (C and O) composition of auriferous quartz carbonate veins, central lode system, Gadag Gold Field, Dharwar Craton, India: Implications to source of ore fluids

“…The present study corroborates our previous reports from Ajjanahalli and G.R. Halli gold deposits (Sarangi et al, 2012) occurring in the vicinity of the southern extension of the same crustal scale shear zone on which all the GGF deposits are located. The age of gold mineralisation in this area has been reported to be 2522 ± 6 Ma by Sarma et al, 2011.…”

“…Ohmoto and Goldhaber (1997) have suggested that, in the case of hydrothermal ore deposits, the fluid δ 13 C ∑C obtained by calculations from the carbonate δ 13 C can be used directly to estimate the source of carbonate fluids. Such a procedure has been adopted in several studies (e.g., Shen et al, 2007;Sarangi et al, 2012) to determine the source of ore fluids. Hence these isotope data may reflect the primary isotope compositions of carbonates in the QCVs.…”

“…On the basis of such studies, in most cases, it has been found that there is involvement of mantle derived fluids or juvenile magmatism (see Table 1, Sarangi et al, 2012). For example, fluids for deposits in Jiadong Gold Province, China have been suggested to be of mantle origin, although the deposit is granite hosted (Qiu et al, 2002;Mao et al, 2008).…”

“…The Neoarchaean Dharwar Carton, southern India consists of a number of quartz-carbonate vein hosted, orogenic gold deposits/prospects in major shear zones such as at Kolar, Hutti, Jonnagiri, Ajjanahalli, and Gadag (Kolb et al, 2004;Pal and Mishra, 2004;Sarangi et al, 2012) (Fig. 1).…”

Metallogeny

“…Gold precipitated from such H 2 O-CO 2 -CH 4 -Au(HS) 2 -fluid as a result of phase separation and fluid-rock interaction. From δ 13 C PDB and δ 18 O SMOW values in carbonates Sarangi et al (2012) obtained average fluid δ 13 C and δ 18 O compositions of -5.81 ± 1.14 ‰, 13.78 ± 5.1 ‰ for the Ajjanahalli and -4.64 ± 0.7 ‰, -6.50 ± 0.6 ‰ for the Guddadarangavvana Halli gold prospects in the western Dharwar Craton. These isotopic compositions are interpreted as juvenile magmatic source of the ore fluid.…”