and sedimentary rocks of the Purilactis Group deposited in the basin. During this time volcanism occurred chiefly west of the basin rather than east as in the present, thus it was back then a back-arc basin. After the Purilactis Group had deposited tectonic movements tilted the strata in the north to east and in the south a thrust fault pushed old Late Paleozoic rocks over the younger Purilactis Group. Hydrology Salar de Atacama basin is bordered on the north by the Salado River basin, which is a sub-basin of the Loa River basin. To the east, the drainage divide approximately coincides with the international border with Bolivia until the Portezuelo del Cajón. The dividing range includes the volcanoes Cerros de Tocorpuri, Sairecabur, Curiquinca, Licancabur and Juriques. Going southward, the water divide runs along a chain of volcanoes that lie entirely in Chilean territory. To the west, the Cordillera Domeyko separates the Salar de Atacama basin from arheic areas. Its main tributaries are the San Pedro and Vilama rivers, which originate to the north of the salt flat. The volcanoes east of Salar de Atacama may be responsible for contaminating the incoming streams with salts. Lithium production Located in the Lithium Triangle, Salar de Atacama is the world's largest and purest active source of lithium, containing 27% of the world's lithium reserve base, and as of 2017 provided about 36% of the world's lithium carbonate supply, followed by China with 23%. High lithium concentration in its brine (2,700 parts per million), a high rate of evaporation (3,500 mm per year), and extremely low annual rainfall (<30 mm average per year) make Atacama's finished lithium carbonate easier and cheaper to produce than from the neighboring Salar de Uyuni, which is estimated to have half of the lithium reserves in the world. Salar de Atacama's evaporation rate is the highest in the lithium industry, followed by Puna de Atacama, Argentina (2,600 mm per year), and the Salar de Uyuni (1,300–1,700 mm per year). Extraction of lithium-rich brines is causing conflict with water use by local communities and is damaging the ecosystem, including the Andean flamingo. In the Salar de Atacama, boron is also extracted from brines as boric acid (up to 0.85 g/L as B). The natural removal of boron and lithium from present-day brines possibly occurs as ulexite and lithium-sulfate, this latter as double and/or triple salts. Sociedad Química y Minera (SQM)