Discrimination between volcanic associated massive sulphide and porphyry mineralisation using a combination of quantitative petrographic and rock geochemical data: A case study from the Yubileinoe Cu–Au deposit, western Kazakhstan

Abstract

Rock geochemical surveys have been widely used for mineral exploration in Russia and more generally, the former Soviet Union. Some conducted by VSEGEI have in addition to geochemistry, determined quantitative petrography on the survey samples.In the case described, a regional survey in the Yubileinoe area southern Urals of Kazakhstan has been undertaken to investigate a district which has both the characteristics of volcanic associated massive sulphide and porphyry style mineralisation. Samples were collected on a 500m or tighter grid over a 10×10km area and analysed by direct current arc spectrometry as well as quantitative mineral determination on thin sections. The combination of these techniques was used to determine elemental loss and gain relative to host rocks in addition to alteration facies. GIS techniques were also used to investigate the spatial variation of geochemical and mineral primary concentrations.Although the porphyry deposit at Yubileinoe gives a clear signature, software based discrimination of alteration into VMS and porphyry types allows better targeting for follow-up. The porphyry signature is detectable for approximately 350m into wallrock in mono-element data, notably Cu and Au. Multiplicative haloes are of similar magnitude although less noisy. This approach also allows the mapping of alteration facies and combination into loss and gain maps as well as a prognostic map of mineral deposit potential.The use of manual quantitative mineralogy is prohibitively expensive where labour is costly. However the advent of computer-based methods means that this approach may well be viable in the future.