MINERALOGY AND GENESIS OF SERICITES IN THE SAMSUNG MINE, KOREA

Geology of the Samsung sericite mine, located in the Chungnam Province, consists of granitic gneiss and schist of Precambrian age and biotite granite of Cretaceous age. The sericite ore deposit was formed by hydrothermal alteration of the biotite granite. Sericite ores consist largely of sericite and contain very minor amounts of quartz, muscovite, biotite and feldspars.

Sericite deviates markedly from the ideal muscovite both by substitution of Fe3+ for Al4+. Interrelationship of chemistry and lattice spacing of mica minerals is summarized as follows: (1) For a given value of Na/(Na+K), decrease of Al causes the cell volume to increase, solely due to increase of the lateral dimensions, inasmuch as c actually decreases; (2) At essentially constant (Mg+Fe), increasing Na/(Na+K) causes cell volume to decrease, mainly because c decreases; (3) Increases of (Mg+Fe) causes the Na/(Na+K) ration and c cell parameter to decrease.Hence (Mg+Fe) exerts more effect on c cell parameter than the Na/(Na+K) ratio does.

Sericite was formed from most of the constituent minerals of the biotite granite. Sericite ores are the alteration products by the KCl-rich solution. With advancing alteration, K and Al markedly increases, whereas Fe, Ti and Mn decreased.