THE INVERSIONAL PLUTONOGENIC GOLD-QUARTZ ASSOCIATION OF THE NORTHERN KAZAKHSTAN CALEDONIDES

The main Au deposits of Northern Kazakhstan are associated with the St epnyak-type minor intrusives distinguished by Yu. A. Bilibin as the St epnyak complex - a postbatholith association of Au-bearing minor diori te intrusives that are younger than the tonalite-granodiorite associat ion (TGA). Now, it is evident that all the TGA intrusives are Au-heari ng to various extents, and the Stepnyak-type intrusives, along with th e main Au deposits, belong to the TGA derivatives. Minor Au-bearing pl utons are composed of early (prebatholith intrusive phase) bodies cons isting of quartz biotite-hornblende leucogabbro-norites (stepnyakites) ; these intrusive bodies mark deep-penetrating faults that subsequentl y serve as ore-conducting structures. The gold-quartz association (GQA ) is due to beresitization and listvenitization processes that represe nt the youngest episodes of the postintrusive hydrothermal activity. T he ores had deep-seated sources of Au, Hg, Sb, and Te; the Au concentr ation was promoted by hydrocarbons and bitumoids. The ores were genera ted in a brittle deformation zone above the 400 degrees C isotherm at the depth interval of similar to 1 - 12 km. The ore deposition was cha racterized by the following maximum parameters: T370 degrees C, P 3.6 kbar, solution salinity 17%, C-CO2 7, C-CH4 2.5 mol/kg, P-H2S 2.5 kbar . The deposits formed in relatively ordered closed systems that stipul ated a stable composition of ores and ore minerals along the vertical section of particular deposits and the differentiation of ore material at various levels with specific facies and corresponding mineral type s of deposits:gold-Ag-sulfosalt-antimonite (with alpha-amalgam of Au) and gold-galena-sulfoantimonide types (P 0.3 - 1 kbar) in the hypabyss al zone; gold-galena-sulfoantimonide and gold-galena (with tellurides) types (P 1 - 1.8 kbar) in the mesoabyssal zone; and gold-galena-tellu ride and gold-telluride types (P 2 - 3.6 kbar) in the abyssal zone. Th e mineral facies of ores are strongly governed by the composition of h ost rock and the concentration of S. The TGA-GQA inversional series or iginated as a result of the strongest thermal influence upon the Earth 's crust, and probably, they correspond to the maximum metamorphism an d strong fluid H2O-CO2 flux.