FE-57 MOSSBAUER STUDY OF PUMPELLYITE-OKHOTSKITE-JULGOLDITE SERIES MINERALS

Fe and Mn distribution in the pumpellyite group minerals (W(8)X(4)Y(8) Z(12)O(56-n),,(OH).) has been studied by using Fe-57 Mossbauer spectro scopy. The studied Fe-pumpellyites, belonging to the pumpellyite-julgo ldite series, were collected from two localities; metabasites in the T okoro belt, Hokkaido, and gabbroic sills in the Shimane Peninsula, Jap an. Okhotskite, an Mn3+-dominant pumpellyite group mineral, was separa ted from the ores of metamorphosed manganiferous iron ore deposits in the Tokoro belt. Fe-57 Mossbauer spectrum of Tokoro Fe-pumpellyite is composed of two Fe2+- and two Fe3+-doublets. On the basis of the singl e crystal structure refinements of Al-pumpellyites published so far, d oublets were assigned to Fe-W(2+), (IS = 1.01 and QS = 2.,73 mm/s), Fe -X(2+) (IS = 0.97 and QS = 3.18 mm/s), Fe-X(3+):+ (IS = 0.29 and QS = 1.37 mm/s) and Fe-Y(3+); (IS = 0.36 and QS = 2.09 mm/s), where IS is i somer shift relative to a metallic iron absorber and QS is quadrupole splitting. The Mossbauer spectrum of the Mitsu Fe-pumpellyite is compo sed of three doublets assigned to Fe-X(2+) (IS = 1.14 and QS = 3.20mm/ s), Fe-X(3+) (IS = 0.36 and QS = 1.13mm/s) and Fe-Y(3+), (IS = 0.37 an d QS = 1.93mm/s). These assignments show strong preference of Fe3+ in the X-site. The Mossbauer spectrum of the okhotskite is composed of tw o doublets by Fe-X(3+) (IS = 0.37 and QS = 1.13 mm/s) and Fe-Y(3+) (IS = 0.42 and QS = 2.18 mm/s). The area ratio shows that Fe-X(3+):Fe-Y(3 +) ratio is 94:6. On the basis of chemical and Mossbauer analyses, Mn- X(3+):Mn-Y(3+) ratio is given as 19:81, indicating stronger Y-site pre ference of Mn3+ than Fe3+, what is consistent with Jahn-Teller theory. Al, Mn3+ and Fe3+ prefer the Y-site in this order.