The Synnyr alkaline massif is located within the North Baikal region of Buryatia and the Mamsko-Chuysky District of the Irkutsk Region, in the interfluve of the Levaya Mama river and Bol’shaya Chuya river, 100 km north of the Baikal-Amur Mainline (BAM). It is at a distance of 160 km from Novyi Uoyan along the year-round road (joint operation with the Sinind artel). A technological climb has been carried out – in the future transport connection will be available by means of the projected road with a total length of 110 km. Moreover, there is a 220 kV electric transmission line along the BAM.
The Synnyr massif with an area of 585 km2, as well as the Khibinskii and Lovozerskii massifs, is one of the largest-scale alkaline intrusions known on the planet. Inside the massif, several development sites of absolutely unique ultra-potassium rocks (synnyrites) were identified, the largest of which is the subsurface site Kalyumnoe. Also within the massif, two more areas of the synnyrites development were identified – the Trekhglavyi and Verkhneushmunskii sites, but they are significantly inferior to the Kalyumnoe.
Synnyrites have a constant and uniform chemical composition with the following content range: K20 (16-21%), Al203 (21-23%) Si02 (54-56%) and insignificant amount of impurities (rarely more than 3%). The mineral composition of synnyrites under the condition of their complex processing allows obtaining a wide range of industrial products, the main ones of which are potash fertilizers and alumina.
The Synnyr massif is located in the axial region of the Baikal-Vitim uplift in the conjunction zone of ancient deep faults in the Kholodninskii graben.
The massif lies at the contact of the Upper Proterozoic (sedimentary-terrigenous and sedimentary-volcanogenic) and Lower Cambrian (carbonate and terrigenous consertal) rocks. In the near-contact zone, the enclosing carbonate rocks are skarnified, and the aluminosilicate rocks are hornfelsed and fenitized.
Alkaline rocks composing the main body of the intrusion are divided into two successive phases. The first includes a variety of feldspathoid syenites – nepheline, nepheline-calsilite and calsilite – the actual synnyrites. For all feldspathoid syenites on different sites, the development of various metasomatically altered rocks is observed. In addition, elongated vein-like bodies of alkaline gabbroids (schonkinites) and associated syenites with varying degrees of melanocratic character are noted everywhere inside the rocks of the first phase. The rocks of the second phase form an ellipsoidal body in the central part of the intrusion and are represented by alkaline syenites – pulaskites.
The Kalyumnoe subsurface site is located in the southeastern part of the central zone of development of ultra-potassium rocks of the Synnyr massif. On an area of about 12 km2 there are several large bodies composed mainly of synnyrites. These bodies have a northeastern strike and a northwestern dip unstable in the corners. The width ranges from a few tens to the first hundreds of meters. In addition to the synnyrites, numerous bodies of nepheline and alkaline syenites, schonkinites, and also zones of the development of metasomatically altered rocks are noted on the site. Over the site area and in the surrounding parts of the intrusion, a network of multidirectional tectonic disturbances can be traced, which can be accompanied by crushing zones up to tens of meters thick. According to the results of prospecting and evaluation works performed in the period from 1980 to 1986, the resources on the site Kalumnoe were estimated at 2.5 billion tons of ore.
Kalyumnoe deposit, 1986, A.A. Ushakov, North Baikal expedition