Home – Home – Jornals – Russian Geology and Geophysics 2006 number 8

Based on microprobe data on the contents and distribution of Cl and F in halogen-containing minerals of enclosing intrusive rocks and their hydrothermally altered varieties, the role of metasomatic processes in the balance of volatiles of the ore-forming system is discussed by the example of porphyry Cu-Mo deposits of Siberia and Mongolia. Two groups of deposits are considered: essentially copper (Erdenetiyn-Ovoo, northern Mongolia, and Aksug, Tuva), with prevailing propylitization and quartz-sericite alteration, and essentially molybdenum (Sora, Kuznetsk Alatau), with prevailing K-metasomatism (orthoclase-biotite association). All types of hydrothermal transformations lead to a drastic decrease in Cl contents in metasomatic minerals as compared with halogen-containing magmatic minerals. In chlorites and sericites, which are the most widespread in metasomatites of essentially copper deposits, no Cl and Cl-containing minerals were detected by microprobe analysis, whereas F was found in large amounts in some metasomatic minerals: secondary biotite, actinolite, chlorite, and sericite. At the studied deposits, huge volumes of enclosing rocks (hundreds of mln tons) are involved in metasomatism. The large amounts of thus released halogens (particularly Cl) might have seriously influenced the regime of volatiles during the ore formation, including the increase in the salinity of hydrothermal solutions.