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Mineralogy and Occurrence of Europium-Rich Dark Monazite

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Mineralogy and Occurrence of Europium-Rich Dark Monazite Mineralogy and Occurrence of Europium-Rich Dark Monazite GEOLOGICAL SURVEY PROFESSIONAL PAPER 1J8.1 Mineralogy and Occurrence of Europium-Rich Dark Monazite By SAM ROSENBLUM and ELWIN L. MOSIER GEOLOGICAL SURVEY PROFESSIONAL PAPER 1181 Mineral-exploration research on Alaskan panned concentrates, resulting in recognition of a new guide to contact aureoles UNITED STATES GOVERNMENT PRINTING OFFICE, W AS H INGTON : 1 983 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES G. WATT, Secretary GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging in Publication Data Rosenblum, Sam. Mineralogy and occurrence of europium-rich dark monazite. (Geological Survey Professional Paper 1181) Bibliography: 67 p. 1. Monazite. 2. Europium. 3. Monazite Alaska. I. Mosier, El win L. II. Title. III. Series. TN948.M7R67 1983 553.4'943 82-600301 For sale by the Distribution Branch, U.S. Geological Survey 604 South Pickett Street, Alexandria, VA 22304 CONTENTS Page Page ——— 1 35 ———— ! Analytical procedures — — •— ••*- 35 ——— 1 35 36 ———— 4 37 37 Geology ——————————————————————————— J_S.L£}\^lAOO.LVSl..l 37 37 39 ———— 7 vjeocliemistry — *" —— " 43 */ 43 */ Geochemical abundances of the rare-earth elements ——— 43 TT O O TJ ———— 11 Chondrites ———————————————————————— 43 ———— 17 kJ^oWolAJr dllU IUCJS.& 43 ———— 17 45 x */ 45 46 Bangladesh —————————————————— \_4CAl.Ck7J.k7 49 Other localities —————————————————— " Consistent properties of dark monazite ——————————— 49 49 OC 51 Color ———————————————————————— Conversion of authigenic rhabdophane ———————— 51 4U 53 4* / 55 QlTO Weathering product of detrital monazite of igneous oo 57 oo Metasomatic enrichment ———————————————— 57 on - 60 GO i. r cicrrcu iiiuut? ui ui igui 60 Optical properties —————————————————— O A - 62 ,,.. , _ QA fi3 ILLUSTRATIONS FIGURE 1. Index map of Alaska showing areas with alluvial deposits that contain dark monazite 2. Map indicating worldwide occurrences of dark monazite ————————————————— 3-16. Geologic sketch maps: 3. Southeastern part of the Tanana quadrangle, Alaska —————————————————————— 4. Livengood district in the central part of the Livengood quadrangle, Alaska ——————————— 10 5. Fairbanks district, northeastern Fairbanks and southeastern Livengood quadrangles, Alaska • 11 6. Ruby-Poorman area in western Ruby quadrangle, Alaska - 12 7. Ophir district, southeastern part of the Ophir quadrangle, Alaska • 13 8. Yentna district, east-central Talkeetna quadrangle, Alaska • 14 9. Mount Michelson area, eastern Mount Michelson and western Demarcation Point quadrangles, Alaska • 15 10. Circle Hot Springs area, Circle quadrangle, Alaska ————————————————————————————— 16 11. Southeastern part of the Eagle quadrangle, Alaska —————————————————————————————— 17 12. Western part of the Teller quadrangle, Alaska ————————————————————————————————— 18 13. Northeastern part of the Teller quadrangle, Alaska —————————————————————————————— 19 14. Northwestern part of the Bendeleben quadrangle, Alaska —————————————————————————— 19 15. Nome area, eastern Nome and western Solomon quadrangles, Alaska ———————————————————— 20 16. Northwestern part of the Tanacross quadrangle, Alaska ——————————————————————————— 21 IV MINERALOGY AND OCCURRENCE OF EUROPIUM-RICH DARK MONAZITE Page FIGURE 17. Index map showing location of the area of the principal monazite placers on Taiwan ————————————————————— 23 18-22. Photographs: 18. Eu-rich dark monazite from Alaska ———————————————————————————————————————————— 26 19. Dark monazite grains from Alaska, showing flanges and tapered forms of attached sericite and (or) chlorite ——— 28 20. Series of dark monazite grains from a single placer concentrate from western Alaska showing gradual release of grains from the phyllitic matrix ———————————————————————————————————————————— 28 21. Handpicked concentrate of Eu-rich dark monazite grains from Montana ——————————————————————— 28 22. Eu-rich dark monazite from Zaire —————————————————————————————————————————————— 29 23-25. Scanning electron micrographs: 23. Dark monazite from Alaska and Montana ————————————————————————————————————————— 30 24. Dark monazite from Zaire and Taiwan ——————————————————————————————————————————— 31 25. Dark monazite from France and Bangladesh ——————————————————————————————————————— 32 26. Photomicrograph of Eu-rich dark monazite showing turbidity due to numerous inclusions ————————————————— 33 27. Density of dark monazite versus percent SiO2 and percent Ln2O3 ———————————————————————————————— 33 28. Rare-earth element relations, in atomic percent, for Eu-rich dark monazite from several countries, and for averages of several rock types and chondrites ————————————————————————————————————————————————— 47 29. Data of figure 28 plotted on log-normal graph paper ———————————————————————————————————————— 48 30. Chondrite-normalized ratios for La to Gd in Eu-rich dark monazites, in yellow monazites from igneous and metamor­ phic rocks, in biotites from igneous rocks, and in sedimentary rocks ————————————————————————————— 50 31. Shale-normalized ratios for La to Gd in Eu-rich monazites, in yellow monazites from igneous and metamorphic rocks, in biotites from igneous rocks, and in sedimentary rocks ———————————————————————————————————- 52 32. Chondrite-normalized ratios for La to Gd in sedimentary rocks, seawater, and rhabdophanes ———————————————— 54 33. Shale-normalized ratios for La to Gd in sedimentary rocks, seawater, and rhabdophanes ——————————————————— 56 34. Rare-earth element relations for 16 rhabdophanes from U.S.S.R., U.S.A., and Greenland plotted on the data of fig­ ure 28 ——————————————————————————————————————————————————————————————————— 58 35. Data of figure 34 plotted on log-normal graph paper ———————————————————————————————————————— 59 TABLES Page TABLE 1. Alaskan dark monazite provenances, distance to igneous contacts, and associated mineral commodities ——————————— 22 2. Physical properties of dark monazite ——————————————————————————————————————————————————— 27 3. X-ray data for dark monazite and yellow monazite ——————————————————————————————————————————— 34 4. Cell parameters for dark monazite and yellow monazite ———————————————————————————————————————— 35 5. Wavelengths of elements and concentrations of standard compounds used for analysis —————————————————————— 35 6. Analyses of Eu-rich dark monazite from Alaska ————————————————————————————————————————————— 38 7. Analyses of Eu-rich dark monazite from Taiwan, Zaire, France, U.S.S.R., and Peru ———————————————————————— 38 8. Comparison of analyses of Eu-rich dark monazite ———————————————————————————————————————————— 40 9. Average compositions of dark and yellow monazites —————————————————————————————————————————— 41 10. Comparison of compositions of dark and yellow monazites from Alaska and Taiwan ———————————————————————— 42 11. Rare-earth elements in biotite from igneous rocks ——————————————————————————————————————————— 61 MINERALOGY AND OCCURRENCE OF EUROPIUM-RICH DARK MONAZITE By SAM ROSENBLUM and ELWIN L. MOSIER ABSTRACT to several processes including precipitation from seawater, metamorphism of diagenetic rhabdophane, and as an accessory Europium (Eu)-rich dark monazite has been found in 64 alluvial mineral in tin-bearing granites; but none of these concepts has concentrates from 14 areas across Alaska between the Canadian general application. border and the west end of the Seward Peninsula. This monazite is The origin of dark monazite by igneous, high-grade regional- characterized by gray to black color, pelletlike form, high-Eu and metamorphic, or diagenetic processes is rejected, because of the low-thorium (Th) contents, turbidity caused by microscopic clouds dissimilarity in the distributions of the REE in dark monazite and of amorphous carbon and sagenitic rutile rods, and many inclusions in yellow monazite of igneous, regional-metamorphic, or diagenetic of siltsized detrital minerals. Density (D) of Alaskan dark monazite origin. We presume that the REE distribution in dark monazite is ranges from 4.25 to 4.70, mainly due to the presence of inclusions. inherited from the REE distribution in a former mineral, rock, or en­ Otherwise, physical properties are similar to those of yellow mona­ vironment. Thus, rhabdophane cannot be the precursor mineral, nor zite. Refractive indices, a and 7, are similar to those of yellow mona­ can seawater be the source of the REE distribution found in dark zite, but interference figures are generally diffuse and show small monazite. (0°-5°) positive 2V. X-ray diffraction patterns and cell parameters Contact metamorphism is proposed as the mode of origin of dark are similar to those of yellow monazites. The average composition of monazite. Geologic relations of the Alaskan occurrences of dark 11 dark monazites from Alaska is (in percent): La-jOs 13.54, monazite show that the preferred source rock is weakly metamor­ Ce2O3 29.00, Pr2O3 3.34, Nd2O3 14.00, Sm2O3 1.92, Eu2O3 0.31, Gd2O3 phosed shale or phyllite intruded by biotite granite. Commonly the 0.98, Y2O3 0.47, P2O6 22.36, ThO2 0.88, SiO2 8.35, TiO2 0.66, A12O3 shale is black and phosphatic. Under low-grade regional metamor­ 1.98, Fe2O3 1.77, CaO 0.28, MgO 0.23, H2O 0.94=101.01. Amor­ phism, dark monazite should be widespread, but our limited data phous carbon ranged from 0.22 to 1.22 percent in four samples and, indicate mainly local associations of this mineral with granitic intru­ in seven samples, minor elements were (in ppm): Ba 100-500, sions. From these observations, the prediction was made that dark Cr 200-2,000, Cu 50, Pb 20-70, Sn 150,
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