宁芜和庐枞地区钠长石化的钠质来源新探

Na SOURCE OF ALBITIZATION IN NINGWU-TYPE IRON-SULFUR DEPOSITS OF NINGWU-LUZONG AREA

It is believed that Na source of albitization in Ningwu type iron-sulfur deposits is derived from middle Triassic marine anhydrite beds.This paper considers the point doubtful, because there is not only no halite (NaCl) beds, but also less other form sodium in the anhydrite-bering sequence.So it is impossible for anhydrite beds to be main Na source of albitization.Based on studies of many aspects of geology and geochemistry, authors believe that main sourceof albitization is from high-saline brines in contemporary volcanic depressions.Main evidences are asfollowings:1) Alteration (albitization) and mineralizations are mainly located in the depressions or attheir margins, and clearly controlled by water-bearing depressions; 2) Under aridevaporate conditions, the depressions concentrated many brines enriched in sodium, having material base of Nasource; 3) H-O isotope composition is near to the atmospheric water line, showing that ore-bearing solutions mainly derived from surface water and/or ground water-Na-rich brines in the depressions.Rb-Sr and S isotope data also support this viewpoint; 4) It has been proved that most ore deposits formed in hot-water circulating system.Similarly, in this area circulating systems caused by calderaand subvolcanic rocks make Narich brines permeate downwards and react with volcanic rocks, resulting in a series of alterations (such as albitization) and mineralizations.