Activities SGA Siberian Chapter in 2018: Field trip to Sludyanka deposit, Baikal Lake.

A group picture of SGA students in a small town of Slyudinka, Irkutsk region, Russia.

The sample of Mg skarn with phlogopite (dark linen crystal), blue apatite and green diopside in calcite.

In June 2018 (18.06-22.06), six students of Siberian Student Chapter visited the Sludyanka deposit, which is located near the North-West coast of Lake Baikal in the Irkutsk region, Russia. The deposit is situated in 1800 km from our native city of Novosibirsk.

The Slyudyanska is a typical deposit of Mg skarns, REE granites and its pegmatites, which has been exploited in the open way. A small open-pit mine located 500 m from the bank of the Slyudyanska River has disclosed dolomite marbles composed of a 50 m thick stratum with calcite marbles in the bottom and biotite garnet and sillimanite gneisses in the roof. In the dolomite marbles consonant pegmatites and granites bodies occur. Moreover, rare relatively large pegmatite less often granite budins with lazurite can be found mainly in the central part of the dolomite marble formation. Many of them are crossed by substitution zones, which develop mainly in the contact zone of pegmatite with dolomite marble and along cracks in pegmatites (granites). Such lazuritic formations have a zonal structure: 1) pegmatite (core), 2) desilicificated pegmatite, 3) diopside-lazurite zone, 4) phlogopite zone with grains of colorless haüyne and diopside.

Our field trip started in a small town called Slyudinka that is located on the western shore of Lake Baikal. This place got its name from the deposit of mica (In Russian "slyuda" means mica). We visited three different old quarries of Mg skarns at a distance of 5-10 km from each other. For three days, we went to the hiking trails and as a result found interesting mineralogical samples of most common minerals of Slyudyanska deposit, such as mica (phlogopite), blue apatite and green diopside in calcite. This area was our main geological object to visit.

Further, we visited a place called in Russian Belaya Vyemka (White Extraction). This artificial outcrop occur on the shore of Baikal Lake caused by the construction of the Circum-Baikal Railway. This is one of the most powerful carbonate beds of the Sharyzhalgai series on the shores of the Baikal Lake. The most ancient rocks of the South-Western Baikal region are combined in this rock sequences. They form the Sharyzhalgay ledge, which is part of the Archean basement of the Siberian platform. Here, between stops of 107 and 102 km of the Circum-Baikal Railway, is the outcropsof the Sharalgai series of 1.5 km in length, which is very conspicious by its white color of the dolomite limestones.

Huge crystals of dark-green phlogopite from granite pegmatites.

For many years, this place has been attracting geologists with its mineral diversity. The collector can find excellent samples of a number of minerals in this area: spinel, apatite, lazurite, forsterite, phlogopite, diopside, scapolite, zircon etc. We spent all day exploring outcrops and taking samples. Here students of Siberian Student Chapter found specimens with blue and blood red spinel, forsterite, phlogopite and zircon.

In the very end of the field trip, we visited the museum of local lore. The main hall is dedicated to the history of the Slyudyanska deposit. We were told in detail how the history of the discovery of the deposit began and about the famous geologists who worked at the field.

In general, the trip gave new practical and theoretical knowledge. Moreover, everyone was able to replenish their collection with valuable specimens, some of which may take their place in the geological museum of Novosibirsk State University.

A small euhedral crystal of greenish-blue apatite in calcite.

A specimen of typical Mg skarn from Sludyanka with blue spinel crystals, orange phlogopite pseudo-hexagonal crystal and light-yellow grains of forsterite in calcite.