OXYGEN ISOTOPE ZONING OF THE GREISEN ORE BODIES OF THE AKCHATAU DEPOSIT

Abstract

The authors describe the fractionation of oxygen isotopes during the generation of horizontal and vertical metasomatic zoning in the typical greisen-rare metal Akchatau deposit in Central Kazakhstan. The oxygen isotope distribution (δ18O) in quartz has been analyzed, the only mineral present in all types of greisens in this deposit and in ore veins in them. The authors ascribe the oxygen-isotope zoning of the greisen ore bodies to partitioning of 18O and 16O among coexisting phases of the flashing hydrothermal solutions, followed by vertical separation of those phases as they percolated upward. The frontal flows of the gas phase caused a decrease in the δ18Oqz values of the metasomatites and veins, while the lagging flows of the residual liquid phase tended to increase these values.