FLUORIDE-SULFATE AND CHLORIDE-SULFATE SALT MELTS OF THE CARBONATITE-BEARING COMPLEX MUSHUGAI-KHUDUK, SOUTHERN MONGOLIA

Inclusions of mineral-forming media were studied in fluorite from the celestite-fluorite rock of the alkaline carbonatite-bearing Mushugai-K huduk complex (Southern Mongolia). It was found that the late igneous stages of rock formation were characterized by the presence of salt me lts (density of 1.7-1.8 g/cm(3) and H2O contents of 4.7-6.0 wt %), sal t melt-solutions (density of 1.3-1.5 g/cm(3) and H2O contents of 30-40 wt %), and highly concentrated solutions (density of 0.7-1.0 g/cm3 an d H2O contents of 70-85 wt %). The calculated composition of the salt melts is the following (wt %): 26-35 CaO, 5.7-9.9 SrO, 1.2-1.9 BaO, 2. 7-11 Na2O, 3.7-3.9 K2O, 29-33 SO3, 0.1-10.9 Cl, 2.1-5.5 F, 4.7-6.0 H2O , and 2.13.5 CO2. The temperatures of the salt melts (670-600 degrees C), melt-solutions (550-370 degrees C), and concentrated solutions (43 0-265 degrees C) were determined. The cooling of the salt melts result ed in the crystallization of fluorite, calcite, barite, halite, and a series of unusual sulfate minerals with high contents of CaO, Na2O, K2 O, BaO, SrO, and F within the inclusions. The possibility of carbonati te melt segregation during the differentiation of alkaline magmas is n ow accepted by many petrologists. The data obtained from the study of salt melt inclusions together with experimental results suggest that t he same process may also produce sulfate-dominated melts with high con centrations of fluorine and chlorine.