Ree patterns for ore pyrite and host rocks of the orogenic gold deposit Mindyak (Souhern Urals)

Abstract

The aim of the research is to study the factors that controlled the fractionation of rare-earth elements in ore pyrite and to assess, on this basis, possible sources of matter in gold-sulfide ores of the Mindyak deposit (Southern Urals), the genesis of which is a controversial problem. The mineralization of the orogenic type deposit is localized in a polymictic olistostrome with carbonaceous clayey-siliceous cement Determination of REE contents was carried out in ore pyrite and in the host rocks using inductively coupled plasma mass spectrometry (ICP-MS) on an ELAN 9000 mass spectrometer (Perkin Elmer) at the Institute of Geology and Geochemistry UB RAS. In the early pyrite and late polysulfide-carbonate-quartz ore associations of the deposit, two types of pyrite were found. The REE patterns in one of them inherit the peculiarities of the composition of lanthanides in the carbonaceous shales of the olistostrome cement, and in the other, in their varieties enriched in syngenetic globular pyrite mineralization. The behavior of REE in pyrite and the fluid coexisting with it was also influenced by temperature, oxidation-reduction conditions and alkalinity of the mineral formation environment. Pyrite of the early ore association, crystallized under high-temperature reducing conditions from a fluid of increased alkalinity, has higher concentrations of lanthanides compared to the low-temperature pyrite of late polysulfide-carbonate-quartz ores. It was found that in the low-temperature environment of the late ore stage there was a slight oxidation and a decrease in the alkalinity of the fluid. Fractionation of REE in ore pyrite from the Mindyak deposit is mainly associated with the processes of mobilization of components from the olistostrome cement by the mineral-forming fluid, which can be considered as one of the sources of ore matter.