[1][2] The Chara-Tokkinskaya group of deposits (Чара-Токкинская группа месторождений), the largest iron ore accumulation in Russia, is located in the Tokko basin.

Its source is in a glacial lake located on the southeastern slopes of a nameless 2,025 m (6,644 ft) high peak of the Udokan Range, a subrange of the Stanovoy Highlands, very near the border of Transbaikalia.

[4] In its upper course the Tokko flows northwards across the Olyokma-Chara Plateau in the Olyokminsky District through a U-shaped valley bound by smooth mountains.

At about 362 km (225 mi) from its mouth the Tokko enters a deep valley where it narrows to a maximum of 300 metres (980 ft) and forms rapids.

90 km (56 mi) further downstream, after the confluence of the Choruoda, one of its main tributaries, the Tokko enters a 1,500 metres (4,900 ft) wide floodplain where it slows down, divides into arms and forms meanders.