Europium (Eu)-rich dark monazite has been found in 64 alluvial concentrates from 14 areas across Alaska between the Canadian border and the west end of the Seward Peninsula. This monazite is characterized by gray to black color, pelletlike form, high-Eu and low-thorium (Th) contents, turbidity caused by microscopic clouds of amorphous carbon and sagenitic rutile rods, and many inclusions of siltsized detrital minerals. Density (D) of Alaskan dark monazite ranges from 4.25 to 4.70, mainly due to the presence of inclusions. Otherwise, physical properties are similar to those of yellow mona zite. Refractive indices, a and 7, are similar to those of yellow mona zite, but interference figures are generally diffuse and show small (0°-5°) positive 2V. X-ray diffraction patterns and cell parameters are similar to those of yellow monazites. The average composition of 11 dark monazites from Alaska is (in percent): La-jOs 13.54,

Rock type m Ia_ ____________ • ___________ _ 16 Quartz monzonite adjacent to quartz veins_ Rock type md _________________________ _ 17 Mineralogical changes ______________ _ Rock type mda ________________________ _ 17 Chemical changes __________________ _ Rock type fl __________________________ _ 17 Alaskite adjacent to quartz veins ________ _ Rock type fla _________________________ _ 17 Granodiorite adjacent to chalcedony veins_ Rock type fib _________________________ _ 18 Elkhorn Mountains volcanics adjacent to Rock type fie _________________________ _ 18 quartz veins _________________________ _ Rock type fd ____. . : _____________________ _ 19 Comparison with Butte.district __________ _ Rock type fda _________________________ _

Minerals of the monazite structural group include arsenates, phosphates, and silicates with the general formula AB04 where A = Bi, Ca, Ce, La, Nd, Th, U, and/or Y; and B = P+5 s As+^, and/or Si+5. Monazite-family minerals contain essential REE and P04, and may have minor amounts of other elements. Monazite-(Ce) is the predominant species, constituting 763 analyses (Tables 1 to 3). Another 18 analyses are for other species of monazite and gasparite-(Ce) (Table 4), cheralites (Table 5), and huttonites (Table 6). Two additional tables list average compositions of monazite-(Ce) from various rock types, and a final table indexes the analyses of monazite-(Ce) according to the localities.

Table 1.Average size analysis of silica sand 92. Heavy mineral abundances 3.

A systematic study of heavy detrital minerals was begun in Liberia in June 1966 and by July 1972 more than 2,500 stream and beach panned concentrates were examnined. The heavy minerals in the concentrates were separated in the mineralogical laboratory by gravity and magnetic methods, and 47 different minerals were recognized. Diagnostic and distinguishing features of the typical minerals are described. The area of investigation covers much of western Liberia. Within the area, five mineral provinces were recognized by unusual, distinctive, or predominant mineral assemblages. These assemblages are: (1) sillimanite-kyanite-staurolite-corundum-monazite-gold; (2) almandite-monazite-rutile-xenotime-corundum-gold; (3) monazite; (4) magnetitemonazite-criromite-hypersthene-xenotime-gold; and 5) cassiterite-columbite-tourmalinealmandite-staurolite-andalusite.