Natural sources of Sodium sulfate

Two thirds of the world’s production of the decahydrate (Glauber’s salt) is from the natural mineral form mirabilite, for example as found in lake beds in southern Saskatchewan. In 1990, Mexico and Spain were the world’s main producers of natural sodium sulfate (each around 500,000 tonnes), with Russia, USA and Canada around 350,000 tonnes each. Natural resources are estimated as over 1 billion tonnes. Major producers of 200,000–1,500,000 tonnes/a in 2006 include Searles Valley Minerals (California, USA), Airborne Industrial Minerals (Saskatchewan, Canada), Química del Rey (Coahuila, Mexico), Criaderos Minerales Y Derivados and Minera de Santa Marta, also known as Grupo Crimidesa (Burgos, Spain), FMC Foret (Toledo, Spain), Sulquisa (Madrid, Spain), and in China Chengdu Sanlian Tianquan Chemical (Sichuan), Hongze Yinzhu Chemical Group (Jiangsu), Nafine Chemical Industry Group (Shanxi), and Sichuan Province Chuanmei Mirabilite (Sichuan), and Kuchuksulphat JSC (Altai Krai, Siberia, Russia). Anhydrous sodium sulfate occurs in arid environments as the mineral thenardite. It slowly turns to mirabilite in damp air. Sodium sulfate is also found as glauberite, a calcium sodium sulfate mineral. Both minerals are less common than mirabilite.
http://www.lookchem.com/Sodium-Sulphate/