Site Geology - Baikal

Geological structure and material composition of rocks and ores of the Kalyumnoe site.

Subsurface site “Kalumnoe” – Current data

The stratified series of the Synnyr massif in the area of the licensed block consists of rhythmic layering of alkaline gabbroids, as well as melanocratic syenites (at the base) associated with them, and leucocratic feldspathoid (nepheline, nepheline-calsilite or calsilite) syenites in the upper part. The rocks of the stratified series (in the study area and beyond in the northeastern part of the Synnyr massif) have a low-angle bedding of both feldspathoid syenites and alkaline gabbroids. The full dip of the rocks do not exceed 10-15 degrees (west, northwest), and only in the center of the subsurface site Kalumnoe a northwest dip with angles up to 30-35 degrees is observed.

The formation of the intrusive complex took place in the conjunction zone of two regional diagonal fault structures of the north-eastern and north-western strike. The formation of these structures began in the Proterozoic; along them there are still tectonic activities. As a result, there is a dense network of multidirectional disturbances, which are accompanied by crushing zones, slickensides, metasomatic occurrences of a different nature and scale. A fault set forms a series of small blocks on the study area, and the eastern part and the central part of the productive zone, where the rocks of the stratified series have maximum angles of incidence to the northwest, are characterized by maximum fragmentation. On the eastern flank, the fall of the rocks becomes more gentle, tends to zero, and the size of the blocks is noticeably enlarged.

The central part of the Synnyr alkaline massif is built of feldspathoid (calsilite, nepheline-calsilite and nepheline) syenites, alkaline gabbroids (shonkinites) and associated alkaline syenites with varying degrees of melanocracy, alkaline and nepheline containing syenites, lamprophyre dykes, veined alkaline and nepheline syenites, and extremely rare alkaline granites. Intensive processes of metasomatism led to the appearance of microcline, microcline-zeolite, microcline-sericite, sodalite-cancrinite, albite and albite-scapolite metasomatites.

Calsilite syenites (synnyrite): currently depending on structural and textural features they are divided into pseudoleucitic with the presence of a variety of symplectic aggregates of potassium feldspar and feldspathoids (from thin dactylotypic to micrographic) and granular varieties. In the geological section of the deposit stratified series, rocks composed of symplectic aggregates occupy the upper parts, while granular ones form the basis of deeper horizons. At the same time, pseudoleucitic rocks contain minimal amounts of dark-colored and accessory minerals, while the role of biotite and clinopyroxene significantly increases in granular ones and the concentration of apatite sharply increases.

Alkaline gabbroids of various stratification depths also differ markedly in material composition. So in the upper parts of the section biotitized clinopyroxene-feldspar shonkinites are noted; amphibole and garnet containing variations, sometimes with a high content of nepheline or its alteration products, appear at hypsometrically low levels.

Near-fault feldspar and feldspar-zeolite metasomatites form coronas around linear zones of intense tectonic disintegration; fields with fuzzy borders are formed at the intersections. Intensive microclinization in the immediate vicinity of tectonic structures is replaced by a local process of complete or partial replacement of nepheline at a considerable distance from them.

Microcline-sericite metasomatites form vast fields, gravitating to the upper spinal parts of both the Kalyumnoe site and the Synnyr massif as a whole. They are distinguished by a stable mineral composition, which very weakly depends on the substrate composition.

Cancrinite-sodalite metasomatites outline the productive part of the site from the east and southeast. Рockety and vein sodalite and sodalite-cancrinite mineralization in calcite syenites is replaced by a zone of continuous sodalite, sodalite-cancrinite and cancrinite syenites development, gravitating to a zone of intense tectonic disturbances of northeastern strike.

Separate outcrops of sodium albite and sodium-calcium albite-scapolite rocks are noted on the right side of the Taborny river valley outside the main field of ultra-potassium rocks development. The parameters of these metasomatite outcrops are not clearly defined due to the intensive distribution of slope formations here.

Compositions of rock-forming minerals: feldspathoid syenites of the Kalyumnoe site are characterized by low variability of both the mineral composition and the main rock-forming oxides inside potassium feldspar, calsilite and nepheline. The first two do not even contain minor impurities of the sodium component, in the latter the content of the calsilite molecule is 27-28%. In alkaline gabbroids and associated mesocratic syenites, the microcline always contains about 20% of the albite component. The compositions of dark-colored minerals in feldspathoid syenites and schonkinites are almost identical.

Metasomatosis processes noticeably redistribute rock-forming elements. So, in significantly microclinitic near-fault metasomatites, the contents of silica increase, when alumina and alkali fall (sodium until complete disappearance). In microcline-sericitic the input of alumina and silica is noticed; also there is a very stable reduced content of potassium oxide and a complete absence of sodium. The appearance of sodalite, sodalite-cancrinitic, albite and scapolite metasomatites is accompanied by the removal of potassium and the introduction of sodium and calcium. Significant zircon mineralization and significant increases in zirconium, niobium, tantalum and other rare earth elements are associated with sodium-calcium metasomatites.

The Synnyr massif

Geological structure and material composition of rocks and ores of the Kalyumnoe site.