Some Aspects of the Geochemistry of Fluorine
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SOME ASPECTS OF THE GEOCHEMISTRY OF FLUORINE by ROBERT HENRY SERAPHIM B.App.Sci., Univ. of British Columbia 1947 M.App.Sci., Univ. of British Columbia 1948 SUBMITTED IN PARTIAL FULFILLAMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY at the MASSACHUSETTS INSTITUTE OF TECHNIOLOGY 1951 Signature of Author. -. -. .*p7,- - .-. --.---.. ,Mepartment of Geology, May 11, 1951 Certified by. .. .. .. - - - - -- - -- -*--.. - - - -- A - Thesis Supervisor 0 0D C i o GS Chairman, Departmental Committee on Graduate Students I1 SOME ASPECTS OF THE GEOCHEMISTRY OF FLUORINE ROBERT HENRY SERAPHIM Submitted for the degree of Doctor of Philosophy in the Department of Geology on May 11, 1951 Abstract A spectrochemical method has been developed to determine fluorine in minerals, rocks, and soils containing .005 to 1 percent fluorine. Samples are mixed with calcium carbonate and carbon, and arced in helium atmosphere. The intensity of a Cao band which masks the very sensitive B2 group of CaF bands is thereby effectively reduced. A B2 group head at 6036 A can be used to determine as little as .005 percent fluorine, provided three identical samples are superimposed in one spectrum. A method modified after one developed previously by Ahrens (1942) has been used to determine fluorine in rocks and minerals containing more than .03 percent fluorine. Samples are arced in air, with one exposure per spectrum, so the method is more rapid and economical, though less sensitive, than the one described above. Fluorine has been determined in about three hundred specimens and samples. Averages have been calculated for the fluorine content of apatite, amphibole, biotite, muscovite, and titanite. Specimens of pyroxene, epidote, and chlorite were analysed but in these minerals fluorine was detected in only one specimen, a chlorite. Fluorine substitutes for oxygen, chlorine, and more commonly, hydroxyl in crystal structures. Hypotheses are presented to explain the dif- ference of fluorine content of the minerals biotite, muscovite, and chlorite. Average fluorine content has been calculated for diabase, basalt, diorite and quartz diorite, andesite, granite, rhyolite, syenite and nepheline syenite, phonolite. A progressive increase in fluorine content occurs in the series as listed, except for anomalous phonolite. The fluorine content of some common sedimentary rocks: shale; sandstone, quartzite, and greywacke; limestone; salinastone, has been determined. Fluorine is'concentrated in phosphatic shales. A few samples of metamorphic rock have been analysed. In the areas ex- amined, fluorine is not introduced in great quantity and distributed evenly through the rock during metamorphism or metasomatism. The content increases several fold within a few inches of intrusive rock or vein contacts. TABLE OF CONTENTS Page ABSTRACT ... ... .. ... .. ... ... .. ... .. ... ACKNOWLEDGEMENTS . .. .. .. .. ... ....... 1 INTRODUCTION -- - . -- - - . - - . .. .. .. .. .. 2 PART I METHOD OF ANALYSIS. .-.-.-.-.-.-.-.-... .. 3 Band Selection ' - - - - . 3 Matrix Selection .. .. .. .. .. 11 Preparation of Sample -.......... ...... 12 Electrode Size and Type .. ..... .......... 12 Arcing Conditions . - - - - - - - - - - - - - . 13 Region of Arc Exposed . *... .. ... 13 Spectrograph Type . ..- -.. - . 15 Plate Type . .e............ .. 15 Use of Internal Standard- . 15 Working Curve Construction .. .... .. ... .. 18 Accuracy . .. .. ... ... .. 19 PART II SOME ASPECTS OF THE GEDCHEMISTRY OF FLUORINE . .. 23 Background . .. ...... ........ .. .. 23 Fluorine in Minerals . .. .. 23 Apatite .. ...... ....... .. 24 Amphibole ..................... .. ... ..... 24 Pyroxene .. .... ... ... .. ...... a . .a. 28 B iotite- .--------- . .---- .. .. ............................... 30 Muscovite . ... .... ... ... .... ... ... 30 Titanite . .. .. .. .. ... ...... 33 Minerals from Metamorphic Rocks -. ....... 35 "o- Im TABLE OF CONTENTS (CONT) Page Fluorine in Volcanic and Plutonic Rocks - . - . - . - . 39 Diabase . * * ............. .. ... 39 Other Basic Intrusives - -. .. 0 . * . 42 Basic Extrusives - basalt - - *........ .. .. .. 42 Diorite and Quartz Diorite -...... ... ... .. ... 42 Andesite - - .-..0 0 0 0--..-..--..-.......... 46 Granite . .. -. ... .. 46 Syenite and Feldspathoidal Syenite . .. 56 Phonolite . - -a............- - - - - - - - -. .59 Pegmatite . ................................ .. 60 Summary of Fluorine in Volcanic and Plutenic-Rocks. .60 Inclusions in Eruptives . .. .. .. .. .. .. ... 62 Contacts of Eruptives . .. .. .. .. .. .. 64 Fluorine in Sedimentary Rocks . .. .. .. 69 Shale - *...... .*. .. .. .. .. 69 Ocean Bottom Samples ...-.....* ...... .a. .*. .. 69 Sandstone, Quartzite, and Greywacke . .. *. .. .73 Limestone . - - * * * - * - - - - - - - - - - - . 75 Salinastone . .. - -. - - - - - - - - - - - - - - - 75 Fluorine in Metamorphic Rocks . .. ..... ..... 78 Conclusion ..-.-.-.-.-.-.-.-.-... .. .. ...... .. 82 Bibliography . ......... .... .. Suggestions for Further Work . - - - - - - - - - - - . - - . 95 Biographical Note....... .. .. .. .. .. .. 96 OEM LIST OF TABLES 1 Calcium Sub-fluoride Bands . .. .... .. .. .. 4 2 Fluorine Content of Amphiboles -- 26 3 Fluorine Content of Pyroxenes . .. .. .. .. .. 29 4 Fluorine Content of Biotite - -- - - -- . .. .. 31 5 Fluorine Content of Muscovite - - - - - -- - - . .. 32 6 Fluorine Content of Titanite - - -- - - - -- - - . .. 34 7 Fluorine Content of some Iiinerals from Metamorphic Rocks . .. 36 8 Fluorine Content of Diabase . .. .. .. 40 9 Fluorine Content of Miscellaneous Basic Intrusives....... 43 10 Fluorine Content of Basalts . .. .. .. .. .. .. 44L 11 Fluorine Content of Diorite and Quartz Diorite . .45 12 Fluorine Content of New England Granite .. .. .. .. .. 47 13 Fluorine Content of Granite North America . 54 14 Fluorine Content of Granite - Analyses from Literature . 55 15 Fluorine Content of Rhyolite . .W. .. .. 57 16 Fluorine Content of Syenite and Feldspathoidal Syenite . 58 17 Fluorine Content of Shales . .. .. .. .. .. 70 18 Fluorine Content of Deep Sea Cores . .. .. ..* 71 19 Fluorine Content of Sandstone, Quartzite and Greywacke . 74 20 Fluorine Content of Limestone . .. .. .. .. .. .. .. 76 21 Fluorine Content of Salinastone . ... ... .. .. .... 77 22 Fluorine Content of Some Metamorphic Rocks ... &. .. .. .. 79 23 Fluorine Content of Volcanic and Plutonic Rocks . ... ... 85 24 Fluorine Content of Sedimentary Rocks . .. .. ... ... 86 25 Fluorine Content of Some Common Minerals .. .. ... .. .. 87 LIST OF FIGURES 1 Page 1 A and A Bands of Calcium Sub-fluoride . .. - 5 2 B2 Group of Calcium Sub-fluoride Bands . .. .. .. 8 3 Reproducibility of 'Glt in Air .. ... ... .... ... .. 21 4 Reproducibility of 'Wil' in Helium . .. ...... ... 22 5 Fluorine and Chlorine in Apatite from Eruptive Rocks . .. .. 25 6 Relation of Fluorine Content to Minerals in Palisade Diabase .. 41 7 Histogram - Fluorine Content of Granites .. .. .. .. .. 49 8 Biotite, Muscovite and Fluorine in New England Granite - - - - . 50 9 Mica and Fluorine in New England Granite .. .. - - . 52 10 Fluorine in 'Igneous' Rocks .. .. .. .. .. 61 11 Contact of Inclusion of Cambridge Siltstone in Quincy Granite .. 63 12 Contact of Shale intruded by Granite . ...... 65 13 Contact of Salem Gabbro-diorite Intruded by Granite . .. .. 66 14 Contact of Salem Gabbro-diorite Intruded by Granitic Dike .. 68 15 Contact of Beaverdell Quartz Diorite Intruded by Quartz-Sulfide Vein . 81 LIST OF PLATES Page 1 A and A Bands of Calcium Sub-fluoride .. .. ... .. .. 6 2 B2 Group of Calcium Sub-fluoride Bands . .. .. .. .. 6 3 B2 Groups of Calcium Sub-fluoride of 1Wl and 'Gli Compared with Calcium Oxide Masking Band, Arcing in Helium and Using Hartmann Diaphragm . .. .. .. .. .. .. .. .. 10 4 A Band from a Horizontal Cross Section of the Arc . .. .. 14 5 Pole to Pole Spectrum of A bands .... ......... .16 6 Contact of Inclusion of Cambridge Siltstone in Quincy Granite . .63 7 Contact of Shale Intruded by Granite . .. .. 65 8 Contact of Salem Gabbro-diorite intruded by Granitic Dike .. 68 Acknowledgements The author thanks Dr. L. H. Ahrens of the Massachusetts Institute of Technology for supervision of this work. His guidance in the development of the analysis method was invaluable, and he made many useful suggestions on the problems of geochemistry. Miss M. Kearns and Mr. F. Canney assisted in many ways in the labo- ratory. Their assistance is appreciated. Members of the faculty and students of the Department of Geology loaned and donated many samples and specimens. Thanks are given Dr. H. W. Fairbairn, Dr. L. H. Ahrens, Dr. P. M. Hurley, Dr. W. H. Dennen, Dr. F. B. Whiting, Mr. F. C. Canney, Mr. R. Edie, Mr. C. K. Bell, Mr. W. Pinson, Mr. T. Podolsky, and Mr. R. Tenney. Dr. Vallee of the Biology Department kindly permitted use of his appa- ratus for preliminary experiments in the helium atmosphere. INTRODUCTION Fluorine has long been neglected in analyses of minerals and rocks. Until Willard and Winter (1933) developed a reliable volumetric method for quantitative determination of fluorine, analyses for fluorine had been very inaccurate, particularly in the lower limits of analysis. The reported analyses were invariably low. Modifications of the Willard and Winter method may be used to determine as little as .001 percent fluorine (Koritnig 1950). Shepherd (1940) and Koritnig (1950) have used the Willard and Winter method, or modifications thereof, to analyse minerals and rocks, but have not analysed enough samples of suitable rock types to make a significant contribution