AbstractThe distribution of Au and associated trace elements in pyrite and
arsenopyrite from late Archean Hutti and Hira-Buddini orogenic gold
deposits, eastern Dharwar Craton, southern India was investigated by laser
ablation-inductively coupled plasma-mass spectrometry. X-ray element maps
acquired by electron probe microanalyser reveal oscillatory zoning of Co and
As indicating the crystallization of pyrite and arsenopyrite in an episodic
fluid flow regime in which fluid salinity fluctuated due to fault-valve
actions. The absence of any relationship between Au and As in pyrite obviate
the role of As in the incorporation of Au into pyrite, particularly here and
may be generally the case in orogenic gold deposits. On the other hand,
positive correlations of Au with Cu, Ag and Te suggest possible influence of
these chalcophile elements in the enhanced gold concentrationin sulfides.
Pb-Bi-Te-Au-Ag bearing micro-particles (<2 μm) are observed exclusively
in micro-fractures and pores in arsenopyrite. The absence of replacement
features and element gradient suggests direct precipitation of Pb, Bi, Te,
Au and Ag from a fluid that was unreactive towards arsenopyrite. An
intermittent fall in fluid pressure caused by the fault-valve action would
have resulted in the sporadic precipitation of Au, Pb, Ag, Bi and Te.
Nature and source of the ore-forming fluids associated with orogenic gold deposits in the Dharwar Craton