Placer deposit Skytevarn
Geology of the license area
Metamorphic and metamorpho-metasomatic rocks of the Upper Archean - Lower Proterozoic, Early Proterozoic intrusions, Quaternary sediments take part in the geological structure of the area.
Structurally, the work area is located within the Lapland structural-formational zone. The bulk of the rocks composing the area belongs to the Lapland complex of granulites (metasomatic enderbits and granulites).
The rocks of the Lapland complex are formed under the conditions of the granulite facies metamorphism along the ancient gneisses of the Salno-Tundra complex.
Most of the rocks of the Lapland complex are characterized by high contents of pyrope-almandine garnet: gneisses (5-20%), enderbites (5-30%), granulites (10-30%), sillimanite (up to 5% ) and rutile (up to 2%) are present in the rocks as accessory minerals.
The area of the region is almost completely covered by Quaternary sediments. The most common are the Upper Pleistocene and Holocene sediments. The Neopleistocene formations are represented by glacial deposits of the Ostashkov glaciation — moraine and fluvioglacial deposits; the Neopleistocene-Holocene formations — alluvial, marine, peat-marsh deposits.
Moraine deposits cover the crystalline rocks of the basement with an almost continuous cover and are represented by sandy moraine (the amount of gravel-pebble material is 10-60%, boulders 10-30%, in some cases up to 50-70%, garnet content - 2-5%) .
Aqua-glacial deposits form ridges up to 1-2 km long and up to 15-20 m high, located in valleys of streams and low parts of the relief. Aqua-glacial deposits are represented by boulder-pebble-gravel-sandy sediments (the content of coarse material up to 20-60%, the content of garnet up to 10%).
Marine sediments are noted along the river bed. Lotta strip up to 1-2 km (rarely up to 3 km), blocking the moraine and, possibly, aqua-glacial deposits. The upper limit of the distribution of marine deposits within the site is estimated at about 120-130 m.
In terms of marine sediments take part from the bottom up:
- clay (loam) of bluish color with thin parallel horizontal stratification. The clay thickness ranges from 0-0.5 m to 5-6 m in depression. The sediments of this horizon belong to the formations of the periglacial basin.
- sandy loam of greenish-gray color with thin horizontal lamination and sand interlayers. Garnet is not observed in sandy loam, but it is probably present in sand interlayers. Horizon thickness is up to 3.5 m.
- the horizon of marine sediments is composed of sands of a yellowish-brown color with sandstone interlayers. In the sand there is wavy, parallel horizontal stratification. The content of garnet in marine sands can be estimated in the range of 10-30% by weight. The thickness of the sands horizon vary from the first meters to 10-15 meters in the beach ridges oriented along the Lotta river bed.
Alluvial sediments are mapped as a narrow strip along the Lotta riverbed and are represented by garnet-containing sand and boulder-pebble-gravel-sandy sediments, depending on what rocks were eroded.
Marsh deposits are represented by peatlands (approximately up to 1 m thick). Marked along the streams, in low relief areas. Lay on moraine and marine sediments.
Geological model of the deposit
Placer deposit of technical garnet formed due to the weathering of garnet-containing moraine deposits (sandy-sandy moraine) in the conditions of the inland sea formed after the Ostashkov glaciation at the area of the lake Notozero (now the Verkhnetulomskoe reservoir).
Placer formation (combination of bottom and beach placers) occurred under estuary conditions (in the present relief is represented by the Lotta river valley) which coastline, in low-relief conditions, was abundant in islands, shoals and inlets, which complicated the hydrodynamic situation in the placer formation zone and accordingly led to complication its geological structure.
The placers are stratiform sub-horizontal deposits with thickness from the first meters to 10-15 meters in the beach ridges and bars. The upper limit of the distribution of marine sediments ranges from 100 m in the east (lower reaches of the Lotta River) to 130 m within the license area. Such a change in elevation of the boundary is associated with neotectonic movements. The expected length of alluvial deposits along the strike is 1.5-4 km with a width of 500-1000 m. The beach ridges are up to 1.5 km long with a width of 100-250 m.