The Triassic potash deposits in China:an example from the Sichuan Basin

The Triassic evaporites occupy an area of more than 1 million km² in southern China. They have found to be involved in potash salts and K-rich brines,including polyhalite, langbeinite,kalistrontite and geogeyit.The mineralization degrees of the K-rich brines range between 255 and 382 g/1,and K contents vary from 4 to 49 g/l.The evaporite basins are generally delimited by palaeotectonics and palaeogeography,and show a depositional evolution from open platform,through restricted platform,to barrier lagoon and finally to salt lake.The potash deposits thus have undergone several stages of evolution.The K in the K-rich brines is derived mainly from the leaching of potash sulphate,and subordinately from the concentrated brines through evaporation and volcanic ash.The K isotopic age determinations range between 156 and 210 Ma,and 150 and 264 Ma,respectively,indicat-ing a same source of solid-and liquid-phase potash salts.It is inferred from geological background and mineral-forming environments that the Triassic potash salts only comprise one type,i,e,potash sulphate.The target horizons consist dominantly of T₁j^5-2 and T₂l^4-2, and mineralization zones are confined to the eastern part of the Sichuan Basin.The storage of K-rich brines depends upon the K-bearing potentiality of the evaporitic strata,fissure development in the carbonate rocks and structural controls on the potash deposits.The proposed model for the prospecting and exploration of the potash deposits suggests that further work should be conducted on both the potsh deposits and oil-gas deposits.