MINERALOGICAL AND GEOCHEMICAL INDICATORS OF MULTIPLE SOURCES OF NATIVE GOLD IN A GOLD DEPOSIT OF THE EASTERN SAYAN REGION

Abstract

We investigated a geologically complex deposit in the Eastern Sayan region. It is confined to a steeply dipping (80°) shale-carbonate member that is inferred to be of Riphaean age and is sandwiched between Paleozoic granite and Early Precambrian granite-gneiss. The sedimentary sequence and the surrounding granite and granite-gneiss have undergone strong metasomatic alteration of the listvenite-berezite type. The deposit contains three types of gold-bearing ore bodies. The spatial distribution of gold in the various ore types was determined by the autoradiographic activation method, using a computerized image analyzer for interpretation of the autoradiograms. This method eliminates the effect of interfering radiosotopes and makes it possible to derive a local distribution pattern for a single element, in the present case gold. To summarize, various types of rocks are likely sources of gold in the deposit, and in addition, ore generation took place in several stages. The granite not only functioned as a source of gold-quartz veins and as the extractant of gold from ultramafics, but also had a strong thermal and metasomatic effect on the clastic sedimentary deposits. This ultimately resulted in the redistribution of gold (and in some cases in a homogenization of its composition), and produced relationships between the elements that we have described above.