First finds of noble metal minerals in amphibolite and quartzite of the Ilikanskii terrain (Southeastern Frame of the North Asian Craton)

Abstract

766The Ilikan terrain (or structural zone) is one of the largest structural elements of the Dzhugdzhur-Stano voi superterrain ( Fig. 1) in the southeastern area of the North Asian Craton. According to the existing con cepts, it is composed of rock series of the same name related to the Stanovoi Complex, mainly biotitehornblende, biotite, two mica, sometimes garnet bearing gneisses, crystalline schists, amphibolites and pyroxene, amphibole schists, gneisses with garnet, biotite, sillimanite, corundum, hypersthenes, and amphibole (see [1,2] and others).By now estimations of the Nd model age (T Nd(DM) = 2.6-3.2 Ga) have been obtained for metamorphic rocks of the Ilikan series and the period of the forma tion of detrital zircons from metasedimentary rocks (2700-2900 Ma) has been established [3]. In addition there are data that the age of gabbroids intruding gneisses of the Ilikan series and synchronous structural metamorphic transformations under the conditions of the high temperature amphibolite series is 2635 ± 4 Ma [4]. The totality of the above mentioned materi als provides evidence for the fact that the time of the formation of the Ilikan series may be limited to the range of 2630-2700 Ma; as this took place, Precam brian formations underwent metamorphism and gran itization at the time of 1.85-1.92 Ga and 127-130 Ma [2,5].Within the Ilikan terrain, among the stratified for mations of the series of the same name (upper streams of the Mogot River, right tributary of the Gilyui River), the authors discovered thin bodies of magnetite quartzites, serpentinized dunites, pyroxenites, and amphibolites; the latter contain palladium tellurides, as well as native gold. In this study we present the first data on the mineral composition of noble metal min eralization in the mentioned formations, and the model of its formation is suggested.As is known, ultrabasic-basic intrusions being derivates of mantle or basaltic melts, as well as their metamorphosed varieties host numerous known deposits of various ranks and manifestations of noble metals; moreover, they are perspective formations in relation to platinum metal mineralization (see [6][7][8][9] and others). However, in spite of the established rela tionships of the high concentration of platinum group elements (PGEs) and gold with the mentioned forma tions, study of the forms of occurrence of these ele ments is often difficult because of their low concen trations and difficulties in diagnostics; thus, it is of high scientific interest.Until recently, the concentration of PGEs was related directly to the magmatic stage of intrusion for mation [7,10]. However, currently there is evidence for the multistage character of platinum metal miner alization and for the possibility of PGE accumulation at the stages of low temperature hydrothermal and metasomatic rock alterations [6,11,12]. These pro cesses are provided by the presence of minerals carry ing the background PGE concentrations, as well as minerals concentrating PGEs for various types and stages of the formation of platin...