Metallogenic Borate Provinces in the World

ALONSO, R.N.

Izmir

Congreso; International Earth Science Colloquium on the Aegean Region, IESCA-2012; 2012

Dokuz Eylül University

ABSTRACT Four main metallogenic borate provinces, with exogenous deposits of continental environments, were recognized in global scale. They are Anatolia (Turkey), California (USA), Central Andes (South America) and Tibet (Central Asia). These provinces have several common characteristics and some differences. Generally, the origin of borate deposits is related with Cenozoic volcanism, thermal spring activity, closed basins and arid climate. With the exception of Tibet, a collisional plateau, the other provinces were generated in a tectonic framework of non-collisional continental plateaus by plate subduction. Anatolia, Tibet and California are located in the northern hemisphere and the Andes in the southern hemisphere. The age of the borates is Cenozoic, principally, Miocene and Quaternary. Miocene borate deposits are present in Anatolia (ca. 18 Ma), California (ca. 22-6 Ma) and the Andes (ca. 7-5 Ma). Tibet has only Quaternary borate deposits and Anatolia only Miocene borate deposits. Four main tincal deposits are present in the world: one in Anatolia (Kirka), another one in California (Boron), and two in the Andes (Tincalayu and Loma Blanca). Kirka, Boron and Loma Blanca have similarities in order to the chemical and mineralogical composition of the borate minerals with sequences Ca/CaNa/Na/CaNa/Ca (colemanite and/or inyoite//ulexite //tincal//ulexite //colemanite and/or inyoite). Borate minerals are included in greenish volcaniclastic lacustrine evaporatic sequences, with scarce tectonic deformation. On the other side, Tincalayu looks different, with evaporites included in red beds, with disharmonic deformation, and a lithologic sequence composed from base to top of halite/gypsum/tincal/ulexite. Tincal textures are different in the four main deposits: chemical fine varves (mm) in Kirka, chemical thick varves (cm) in Boron, massive (m) in Tincalayu, and disseminated evapocrystals (mm to cm) in Loma Blanca. Colemanite deposits with or without probertite and hydroboracite are present in Anatolia (e.g., Emet), Death Valley, Ca. (Furnace Creek Fm.), and Sijes (Argentina). Quaternary borates are present in salars (Andes) and playa-lakes and salt pans (USA-Tibet). California and Andes have calcium and calcium sodium borates (ulexite, tincal, inyoite), and Tibet (ulexite and Mg-borates). Thermal springs and geysers, with related borate deposits, are common in the Central Andes. The four metallogenic provinces here described contain the most important borate reserves in the world.