Experimental studies of leaching and albitization in intermediate-basic rocks

Abstract

Experimental studies combined with geological evidence indicate that gaseous thermal fluids enriched in NaCl (or other chlorides) leach and metasomatize intermediate-basic and intermediate-acidic rocks. In this process, part or all of the rock- and ore-forming materials are mobilized and enriched to form skarns and Fe deposits. When gaseous thermal fluids enriched in NaCl (or other chlorides) act on intermediate-basic rocks, the mobilities of the main components in the rocks are, in decreasing order K (or Na), Fe, Ca, Si, Mg and Al. The mobility of Al is extremely small and the mobility of Mg is not large either. The leaching capacities of high-temperature fluids for rock- and ore-forming elements, depend mainly on the kinds and numbers of negative and positive ions, pH and Eh, temperature and pressure, etc. Acidic solution and high temperature favor the leaching of Fe whereas alkaline solution and high pressure favor the leaching of SiO 2. At 550°C and 750–1000 bar, weak alkaline solution enriched in NaCl favors the formation of albite. Acidic solution favors the formation of minerals such as amphiboles and chlorites while wollastonite can form in wider ranges of pH. The mobility of Fe and albitization represent the change in pH-values of the solutions at different mineralized stages.