IIOROKHAN COMPLEX OF MINOR INTRUSIONS IN THE EASTERN PART OF THE BUREYA MASSIF: GEOLOGY, AGE, GOLD MINERALISATION

In this paper we analyze and summarize some recently acquired data coupled with the findings of previous geological, geochronological and metallogenic studies on igneous rocks of the Iorokhan gold-bearing complex in the eastern part of the Bureya massif. Four phases, whose rocks are of hypabyssal and subvolcanic intrusive facies, are shown to define the structure of the Iorokhan complex of minor intrusions; characteristic features of their composition and structural and tectonic settings of localization are given; geological and geochronological data are reported on their age (103 ± 1.0–97.4 ± 6.5 Ma), i.e. late Albian–early Cenomanian. By the ratio of alumina, calcium and alkalis, most of their compositions correspond to I-type high-alumina magnesia and magnesia-ferruginous varieties (A/CNK < 1.1) with low concentrations of HFSE, including HREE. Melting of an amphibolitic source rock produced a melt that could be a deep source of the Iorokhan diorites. A brief description of the Noni deposit is given and the main factors contributing to the localization of gold mineralization are considered. The ranges of the Iorokhan magmatites in the East Bureya volcano-plutonic zone can be considered as one of the fragments of the boundary structure between the continental margin of the eastern part of the Bureya massif and the accretionary wedges of the Sikhote-Alin orogenic belt. The Iorokhan complex of minor intrusions is assumed to be a small fragment of the wide belt of Late Albian–Early Cenomanian magmatite occurrence in the southern Far East of Russia, which formed in a setting of transform continental margin and zones of compression associated with extension resulting in the development of pull-apart basins typical of such margins.

CHARACTERISTICS OF SELF‐SIMILARITY OF SEISMICITY AND THE FAULT NETWORK OF THE SIKHOTE ALIN OROGENIC BELT AND THE ADJACENT AREAS

We performed a comprehensive analysis of the characteristics of self‐similarity of seismicity and the fault network within the Sikhote Alin orogenic belt and the adjacent areas. It has been established that the main features of seismicity are controlled by the crustal earthquakes. Differentiation of the study area according to the density of earthquake epicenters and the fractal dimension of the epicentral field of earthquakes (De) shows that the most active crustal areas are linked to the Kharpi‐Kur‐Priamurye zone, the northern Bureya massif and the Mongol‐Okhotsk folded system. The analysis of the earthquake recurrence plot slope values reveals that the highest b‐values correlate with the areas of the highest seismic activity of the northern part of the Bureya massif and, to a less extent, of the Mongol‐Okhotsk folded system. The increased fractal dimension values for the fault network (Df) correlate with the folded systems (Sikhote Alin and Mongol‐Okhotsk), while the decreased values conform to the depressions and troughs (Middle Amur, Uda and Torom). A comparison of the fractal analysis results for the fault network with the recent stress‐strain data gives evidence of their general confineness to the contemporary areas of intense compression. The correspondence between the field of the parameter b‐value for the upper crustal earthquakes and the fractal dimension value for the fault network (Df) suggests a general consistency between the self‐similar earthquake magnitude (energy) distribution and the fractal distribution of the fault sizes. The analysis results demonstrate that the selfsimilarity parameters provide an important quantitative characteristic in seismotectonics and can be used for the neotectonic and geodynamic analyses.