- Email: [email protected]
The use of bromine pentafluoride in the extraction of oxygen from oxides and silicates for isotopic analysis
Gr
Press Ltd.
Printed
in S0rtllernIrrlnnd
The use of bromine pentafluoride in the extraction of oxygen from oxides and silicates for isotopic analysis* ROBERTN.CLAYTON
and TOSHIKO K.MAYEDA
The Enrico Fermi Institute for 1\Tuclear Studies The University of Chicago, Chicago, Illinois (Received
30 January
1962; reviseri 13 April
1962)
Abstract-A technique has been developed in which bromine pentafluoride is used as a reagent for quantitative liberation of oxygen from oxides and silicates. For all of the rocks and minerals analysed, the oxygen yields are 100 + 2 per cent of the theoretical amount. The advantage over techniques involving reduction with carbon lies in the consistently better oxygen yields, with consequent decrease in systematic errors in isotopic composition. Bromine pentafluoridc has advantages over fluorine in being easier and safes to handle in the laboratory, in being readily purified, and in reacting with some minerals which do not react completely with fluorine. The results of isotopic analyses are compared with measurements made in other laboratories by other procedures.
SEVERAL analytical procedures have been described for the extraction of oxygen from silicates and other oxygen compounds for precise isotopic analysis [BAERTSCHI and SILVERMAN (1951), BAERTSCHI and SCHWANDER (1952), CLAYTON (1955), CLAYTON and EPSTEIN(~~~~),DONTSO~A(~~~~),SCHWANDER(~~~~),TA~LOR and EPSTEIN (1962),TUDGE (1960),VINOGRADOV et al. (1958)]. They are all based on one of the following two types of reaction: (1)reduction by carbon at high temperature (1600-2000°C) to yield carbon monoxide; (2) oxidation by fluorine or halogen fluorides to yield oxygen as 0,. Experience with both approaches has led us to prefer the oxidation reaction and the present paper describes a variation on the fluorine procedure used by SILVERMAN (1951) and BAERTSCHI and SILVERMAN (195O),differing in that bromine pentafluoride is used as t,he oxidizing agent. The reduction methods and the oxidation methods are approximately equivalent with respect to such considerations as cost and complexity of apparatus3, skill required for operation, time per sample, etc. For some minerals, both procedures are capable of giving isotopic reproducibility of $0.1 to 0*2x,. In cases where the carbon reduction method and the fluorine oxidation method have been compared by analysis of identical test samples, it has been shown t,hat t,he two procedures give identical differences in 01s/016 between quartz samples, but that the carbon dioxide sample produced by the carbon reduction method is about 0.5x,, richer in 0 18 than that produced in the fluorine method (CLAYTOX and EPSTEIN 1958, TAYLOR and EPSTEIN 1962). The syst’ematic discrepancy is probably due to low yields (95-97 per cent) in the carbon reduction analysis caused by some volatilization of SiO. The carbon reduction method as used by SCHW;ZNDER (1953):BAERTSCHI and SCHWANDER (1952),and CLAYTON and EPSTEIN (1958), * This work was support,ed by a grant from the National 43
Science Foundation
(NSF-G7292).
ROBERTI\. CLBYTONand TOSHIKOK. MAYEDA
44
gave oxygen yields of 50-80 per cent from mineral samples containing alkali metals, alkaline earths, or aluminum. These low yields were accompanied by large isotopic fractionaCons. More recent improvements in t’he carbon reduction technique have increased the oxygen yields on such minerals to 95-100 per cent (VINOGRADOV, DONTSOVA and CHUPAKHIN, 1958; and DONTSOVA, 1959), presumably decreasing the effects of fractionation. Oxygen yields in the fluorine method used by BAERTSCHI and SILVERMAN (195 1) were found to be quantitative for most rocks and minerals, but fell to about 80 per cent for basic and ultra-basic rocks. Similarly, TAYLOR and EPSTEIN (1962) report less than quantitative ext,ract’ion of oxygen from olivine, magnetite, epidote and garnet. The yields generally increase as the reaction temperat’ure is increased, but above 50073, the fluorine is consumed by reaction with the nickel container. Our experience with both the oxidation reactions and the reduction reactions has been that complete oxygen yield is of prime importance. Reactions yielding less t’han 98 or 99 per cent of the theoretical amount almost invariably produce an isotopic fractionation, which may be quite reproducible for a given mineral or sample! which introduces systematic errors into t’he isotopic analysis. As a result’. all published analyses showing low oxygen yields must be suspect until verified by other procedures. It is not clear whether all the techniques described in the literature give accurate results (in the sense that the 01*/016 ratio in the mass spectromet’er gas sample is identical with that in the rock or mineral specimen). Necessary criteria for accurate results are: (1) a b sence of contamination by extraneous oxygen; (2) absence of exchange between oxygen of the sample and oxygen of the apparatus or reagents; (3) either quantitative extractJion of oxygen from the mineral, or ext’raction by a chemical react’ion involving no isotopic fractionation. A disadvantage in the carbon reduction procedure arises in the case of hydroxylbearing minerals. The analytical procedures usually require a high-temperature vacuum outgassing of t’he carbon react,ion vessel containing t’he sample. In order to be efficient, this outgassing must be done at temperatures of 1000°C or more, which will drive off the bound water from the mineral sample, so that the oxygen ultimately analysed is not ident’ical with t’hat in the original mineral. The fluorine reaction does not require such a high outgassing temperature. and no appreciable loss of bound water occurs in this process. APPsRATUS
The high-vacuum
apparatus
used is similar to those described by BAERTSCHI and SILVERMAN (1951), by CLAYTON (1955), and by TAYLOR and EPSTEIN (1962). The metal section of the vacuum line is shown schematically in Fig. 1 and the glass section in Fig. 2. The metal line is monel, silver-soldered to copper fittings, and using monel valves. Gaskets are Teflon, and the reaction tubes are pure nickel with capacity of 60 cm3. The reaction tubes are made from 3/4 in. O.D. nickel tubing joined to the valve above by a Teflon-gasketed flanged connection. In order to keep the valve and gasket cool while the reaction tube is hot, cooling
water is applied to the upper end of each tube through one turn of copper tubing soldered to the tube just below the flange.
The use of bromine
pentafluoride
45
in the ext,ractjion of oxygen High Vacuum
High Vacuum
t Vent -
=!!a=-
=O=
Oxygen
Dry
Ned=0
Collection Line
Glass Gloss ---
Metal 1 ---
\ f--J
Metal
Reaction
Tubes
Br Fs Cylinder
Fig.
1. Apparatus
for reaction
of oxygen
compounds
with bromine
penMluoridc.
-
Scale ’
High Vacuum
Sample Tube
Manometer
Toepler Fig.
2.
Apparatus
for
Pumps collect’ion
of oxygen
and conversion
t,o carbon
dioxide.
ROBERTN. CLAYTON and TOSHIKO K. MAYEDA
46
REAGENT The oxidizing reagent used in the present work is bromine pentafluoride (BrF,) . It is a colorless liquid at room temperature (M.P. -61+3”C, B.P. 40.5”). It is available commercially in steel cylinders, and can be handled in the laboratory in metal vacuum systems using copper, monel and nickel. It reacts readily with glass at room temperature, but shows no evidence of reaction at liquid nitrogen temperature. Its reactivity toward oxides and silicates appears to be approximately equivalent to that of fluorine. At high temperatures, of the order of 500-6OO”C, nickel is the only material known to be suitable for containing bromine pentafluoride. We have conducted reactions at temperatures as high as 700°C; at this temperature there is no evidence for decomposition of BrF,, and the reaction with the nickel container is not, too great. ANALYTICALPROCEDURE
The following with a silicate:
equation
KAlSi,O,
illustrates
+ 8BrF, +
a typical
KF + AlF,
reaction
of bromine
+ SSiF, + 40,
pentafluoride
+ 8BrF,
The mineral samples used range from 5-30 mg, with an approximately five-fold excess of reagent over stoichiometric requirements. The react’ions are usually run at 450°C for 12 hr with some exceptions as described below. The following paragraphs give a detailed description of the analytical procedure. The 6 reaction tubes, after removal of the gaseous products of the previous reaction, are filled to one atm pressure with dry nitrogen. The valves are closed, and the tubes removed from the line at the gasketed connector above the valves. The tubes and weighed samples are put into a dry box containing air dried by P,O,. After 3 hr, each tube is opened inside the dry box, the solid products of the previous reaction are dumped out, a new sample is put into the bottom of the tube, and the tubes are closed again. Then the tubes are returned to the vacuum line, and evacuated. The reaction tubes are heated for one hour at 400°C while open to t’he high vacuum line. This removes adsorbed air and water, but is not hot enough t’o The outgassing is followed by a predecompose hydroxyl-bearing minerals. treatment of the reaction tubes with BrF,. The reagent is expanded into the tubes and the metal vacuum line to a pressure of 15 cm of mercury. The tubes are shut off from the line and heated to 100°C for one hour. This procedure removes the very small amount of oxygen compounds which may form on the nickel walls while the samples are being loaded. The pre-treatment is probably an unnecessary precaution, since the amount of oxygen thus liberated is very small. In fact, the pre-treatment must be avoided for some minerals which react extensively with BrF, at 100°C. These include the feldspars and hydrated forms of silica (also phosphates (TUDGE, 1960) and carbonates (CLAYTON, 1961)). ?Ilostof the other common minerals are unaffected by BrF, at 100°C: quartz, micas. pyroxenes, It has been found possible to get good oxygen isotope analyses olivine, magnetite. from feldspars in the presence of equal amounts of quart’z, by conducting t,he reaction at 100°C.
The use of bromine pentaflnoride in the extract,ion of oxygen
47
After pre-treatment the reaction tubes are evacuated, then each tube is charged with BrF,. A portion of the liquid reagent which has been distilled from the commercial cylinder, then redistilled once, is allowed to evaporate into an expansion volume of 600 cm3 to a pressure of 0.1 atm. This reagent, about l/400 mole of BrF,, is then condensed into one of the sample tubes by immersing the tube in liquid nitrogen. Reagent is measured into each Oube in the same way. The size of the mineral samples is chosen to give 100-400 pmol of oxygen, so that the amount of reagent is approximately 5 times the stoichiometric requirement. The same quantity of reagent has been used regardless of sample size or composit’ion. The reaction tubes are then closed off and heated by electrical resistance furnaces. Quartz, micas, and feldspars are reacted at 450°C for 12 hr; magnetite, hematite and ilmenite are react,ed at 6OO’C for 12 hr; garnet and olivine are react’ed at 690°C for 12 hr. After reaction, the furnaces are removed and the tubes allowed.to cool to room t,emperature. Then the oxygen sample is extracted from each tube as follows: The valve on the reaction tube is opened to allow the gas mixture to flow into the metal vacuum line as far as valves Vl and V2 (E’ig. 1). Then valve V2 is opened slightly to allow the gas to flow slowly through the glass trap, cooled by liquid nit’rogen. Of all the possible volatile reaction products: O,, BrF,, BrF,, Br,, SiF,, HP, only oxygen passes through the cold trap. It is pumped by an automatic Toepler pump into a calibrated volume where the quant’ity of oxygen is determined. Complet,e collect’ion of the oxygen sample takes about 20 min. After collection and measurement of the oxygen, the gas is passed over hot carbon t’o convert it quantitatively to carbon dioxide by Dhe reaction: c! $O,-+CO,.
This process has been described by CLAYTON (1955)and TAYLOR and EPSTEIN (1962). In the apparatus used in our laboratories, the hot carbon is a hollow cylinder made from a spectrographic electrode. The dimensions are: diameter l/2 in., length 1 in., wall thickness l/32 in. The carbon is suspended inside a waterjacketed glass tube, and is heated by radio-frequency induction. The temperature is about 550-6OO”C, low enough to prevent the formation of appreciable amounts of carbon monoxide. Oxygen is circulated over the hot carbon, and the carbon dioxide is frozen out in a liquid nitrogen-cooled U-tube. The conversion of an oxygen sample to carbon dioxide takes about 15 min, and is carried out while the oxygen from the next sample is being collected from the nickel reaction tube. The graphite cylinder is replaced after approximately 30 samples. The carbon dioxide is transferred to a manometer for measurement of reaction yield, and Ohen to a sample tube for transport to the mass spectrometer. The ent,ire extraction of a set of 5 oxygen samples and one blank takes 3-5 hr. By running the BrF, reactions overnight, and extracting oxygen in the morning, one can complete one set of samples each day. The oxygen blanks are usually less than 1 pmol. The source of this oxygen
ROBERTN. CLAYTONand. TOSHIKOK. MAYEDA
48
appears to be the walls of the reaction tubes (from reaction with air during loading of the samples); the amount of oxygen in the reagent itself is completely negligible. No blank corrections were made to any of the isotopic analyses. Mass spectrometric analyses are made on a 6-in. double-collecting isotope ratio spectrometer after the designs of NIER (1947) and MCKINNEY et al. (1950). Analytical data are reported in the B terminology, as deviations in permil (parts per thousand) of the 01A/016 ratio from that in standard SMOW (CRAIG 1961). The value for the ratio (Ola~O16)CO~ gas/(01*/016)~~0 liquid at 252°C is taken as 1*04070 (~OMPSTO~ and EPSTEIN 1957). The measured values were correct‘ed for spectrometer valve mixing, and for CP variations according to the equations given by CRAIG (1957). ISOTOPIC REPRODUCIBILITY Several mineral samples have been analysed repeatedly over a period of 15 months as a continued check on the analytical procedures These samples were often run after unusual events, such as a repair to the vacuum system, washing t$he reaction tubes, etc., so that the reproducibility shown here is somewhat< poorer t,han for samples run routinely. The mean isotopic analysis and average deviatiorls are shown in Table 1. BROMINE TRI~LUOXUDEAS OXIDIZING REAGENT Bromine trifluoride has been used to liberate oxygen from uranium oxides (HOEKSTRA and KATZ 1955), and phosphates (TUDGE 1960). Several hundred analyses of 01S/016 in silicates have been done in our laboratory using BrF, as reagent, following the same procedure as described above for BrF,. The results of these analyses agree with those using t.he BrF, reagent, (see Table 1). We have Table 1 Sample
c)W(BrF,)
hOl”(HrP3)
--. Potsdam sandstone St. Peter sandstone Randville pegmat,ite quartz Randville pegmatite orthoclase Plagioelase RC-1 l-60 JL-3 hydrothermal quartz KS-lOamagnetite
15.44 11.02 10.07 8.80 9.90 11.52 -0.15
& 0.26 + 0,15 + 0.20 * 0.10 & 0.11 6 0.12 -& 0.09
(9 analyses) (13 analyses) (9 analyses) (5 analyses) (4 analyses) (41 analyses} (5 analyses)
11.07 r; 0.14 (6 analyst~s) 10.08 * O-14 (14 analysrs) 9.85 * O-07 (3 ana.lyses) 11.46 & 0.05 (2 analyses) -0.28 5 0.01 (R nnal\scfi)
found bromine pentafluoride more convenient to use because of its higher pressure: 390 mm at room temperature against 6 mm for bromine trifluoride. The higher vapor pressure facilitates the measuremer~t of the quantity of reagent to be transferred to the reaction tubes. It also increases the alnount of reagent in the vapor phase in the reaction tubes, since BrF, will condense at the water-cooled upper end of the tubes. COMPARISONS WITH OTHEH,TECHNIQUES AND ANALYSTS
Several samples have been analysed which had previously been run in other Comparisons of the isotopic analyses, and of laboratories using other techniques. the oxygen yields, where known, are shown in Table 2.
The UF’Oof bromine pent,afluoride in the extraction of oxygen
49
50
ROBERTS. CLAYTONand TORHIKOK. MAYEDA
Although all the isotopic analyses are given with respect to an ocean water standard, this standard is not identically defined for all the sets of data. SILVERMAN (1951) defined the zero of his isotopic scale to be oxygen from a single sample of sea water “Hawaiian sea water No. RT-6”. In the published data of CnAvToN and EPSTEIN (1958) and of TAYLOR and EPSTEIN (1962), t,he standard was defined to be oxygen with 01*/016 ratio equal to 0.98473 R,, where R, is the 01*/Oi6 ratio in Silverman’s sample of Potsdam sandstone. By this means. the 3 sets of dat,a all give 6 = +15.5 for the Pot8sdam sandstone. If any of t’he analyt’ical procedures int8roduce systematic errors into the measured (s values, this procedure of normalizing to a quartz sample should make the results of different analytical methods agree on quartz samples, but not necessarily on other minerals or rocks. Such is found to he the case. The oxygen of mean ocean wat,er is a logical standard for reporting oxygen isotope variations in natural materials, including meteoric waters and rocks and minerals. (The analysis of carbonates for ocean paleotemperature is an exception, where a carbonate standard is still preferable.) Such a st,andard has been proposed by CRAIG (196 1) for natural wat’ers and by CLABTOK and CRAIG (I 962) for rocks and minerals. A “Standard Mean Ocean Water” (SMOW) was defined to have 018/016 (SMOW)
= 1.008 018/016 (NBS-l),
where NBS-l is a water sample distributed by the National Bureau of Standards. This defines an ocean water standard in terms of materials readily available to everyone, rather than in terms of the limited quantity of a particular sample of Yotsdam sandstone. However, a completely satisfactory procedure for quantitative extraction of oxygen from water for isotopic analysis has not yet been reported. Differences in 018/016 between water samples are conventionally measured to high accuracy by measuring 018/016 ratios of carbon dioxide equilibrated with water at 25°C. The equilibrium constant for this equilibration: K = (018/016)C02/(0’s/016)HZ0 has been reported by COMPSTON and EPSTEIN (1955) to be 1.0407 f eOOO3. This value has been adopted in the present work. In practice, our oxygen isotope ratios are measured relative to carbon dioxide from a carbonate working standard, then recalculated to the SMOW standard. Thus, any future measurements which alter t’he accepted value of the water-carbon dioxide equilibrium constant, will change all the 6 values by a fixed amount. It happens by coincidence that the two definitions of an ocean water standard: (a) (OlS/O16) ocean water = .98473(O18/Oi6) Potsdam (b) (018/016) SMOW
sandstone
#2039
= 1~008(018/016) NBS-I
give identical &values for samples analysed by TAYLOR and EPSTEIN (1962), and by the present workers, and for most of the samples analysed by SILVERMAN (1951), so that a redefinition of the standard does not require a change in &values reported according to definition (a).
The USC of bromine
The results raw data, and This technique techniques, as
pentafluoride
in the extract’ion
of oxygen
.‘I
of CLAYTON and EPSTEIN (1958) have been recalculated from the are reported according to definition (b) of the SMOW standard. gives results consistently about’ 6.574, heavier than the oxidat,ive has been reported by TAYLOR and EPSTEIN (1962). DISCUSSION OF RESULTS
In Table 2, theoretical oxygen contents are presented, where available, for comparison with the measured oxygen yields. Sields are given in units of pmol of CO, per mg of mineral or rock sample (pmol/mg). The agreement is always within l-2 per cent; t’he error may be due entirely to weighing of samples and measurement of the gas volume in a simple mercury manometer. Oxygen yields in the carbon reduct’ion procedure are several per cent low for quart’z, but appear quantitative for magnetite. This is reflected in the systematic differences in do18 for quartz, and in the agreement in 6018 for magnetite, between the two methods. The disagreement found by TAYLOR and EPSTEIN (1962) between fluorine analysis of magnetite samples. and carbon reduction analysis is probably due to incomplete yields (~80 per cent) in the fluorine reaction. The data reported here are in excellent agreement with the results of TAYLOK and EPSTEIN, with the exception of one biotite sample No. WH-3. Our dat’a agree well wit’h about half the values reported by SILVERMAN (1951), but are in serious disagreement with t(he others. The disagreement is always in the same direction, with SILVERMA~‘S results showing lower 018/016 ratios. For 5 samples t,he difference is consistently %.5x,> suggesting an error in calculation of standards rather than some chemical effect.
The liberation of oxygen by reaction with bromine pentafluoride has proved t,o be a reliable analytical procedure for a wide range of oxide and silicate minerals. giving oxygen isotope analyses in agreement with most of the previous analyses of test materials. The analytical procedures involving oxidation to liberate oxygen as 0, are generally more satisfactory than the reduction procedures liberating oxygen as CO. The former give oxygen yields which are quantitative within the error of measurement; the latter give yields which are typically 90-97 per cent on silicate minerals, introducing fractionation effects which are on the order of lx,, several times the experimental reproducibility. Bromine pentafluoride (and bromine trifluoride) have several advantages over fluorine in the oxidation reaction: (1) The reagent is a liquid at room temperature. and avoids the hazard of highpressure fluorine cylinders. (2) The reagent is readily distilled to make it. completely oxygen-free. Commercial fluorine usually contains about one per cent oxygen, for which blank correct’ions must be made. (3) Separation of excess BrF, reagent from the reaction products is accomplished simply by passing the gas mixture through a cold trap. After the fluorine reaction, the gases must pass through a heated trap filled with solid KBr, which
52
ROBERT S. CLAYTON and TOSHXO
K. MAYEDA
reacts with fluorine to give bromine which is then condensed in a cold trap. This process is time-consuming, and is a possible source of contamination. (4) Some minerals, such as magnetite, garnet, and olivine give quantitative oxygen yields with BrF,, but not with F,. It is expected that improvements in our techniques of gas measurement will make possible direct quantitative analysis of oxygen in rocks ad minerals with an accuracy comparable to t,hat obtainable for the ot’her major constituents. are grateful to Dr. 8. R. suml~lcs of rocks and minerals used in previous
.~ckrLo~Zeclgnlents-~~‘e
QILVERM.~N
isotopic
and .I>r. H. P. st)lltlies.
'I'_~YLoR
for
supplying
REFERENCES ~~~ERTSCHI PETER and SILVERMAN S. R. (1951) The Determination of t,be Relat.i\-e Abnndan~c of the Oxygen Isotopes in Silicate Rocks. Geochim. et Cosmochim. Acts 1, 317--32X. B~%ERTSCHIPETER and SCHUANDER H. (1952) Ein nencs lTerfahren zur Messung dcr Untcrschicd(x im 018-Gehalt, von Silikat,gestrinm. Rein. Chim. Acta 35, 1748-1751. B~-~~IXGTOX A. F., FAHEY J. and VLISIDIS A. (1955) Thermometric and l’ctrogenctic Significance of Titaniferous Magnetite. Amer. I. Sci. 253, 497-532. (‘LAYTON R. X. (1955) Variations in Oxygen Isotope Abundances in Rock Minerals. Ph. I). t.hcsis, California Institut,e of Technology. C'LAYTOS Ii. N. and EPSTEIN S. (1938) The Relat,ionship between 01*/01” Ratios in Co-existing Qnart,z, Carbonate and Iron Oxitles from Variolls Geological Deposits. J. Geol. 66, 352%3i3. CL.-~YTON R. N. (1961) Oxygen Isotope Fract,ionat,ion between Calcium Carbonatc: ant1 Water. .I. Chem. Phys. 34, 72&726. (‘LAYTON R,. N. and CRNc H. (1963) Standard for Reporting 0 l8 C’onccrrtrat’ions in Ttocks and Minerals. In preparat,ion. C’O~~PSTON 11’. and EPSTEIN S. (1958) A M&hod for the Preparation of C’arbon Dioxide from \Vater lTapor for Oxygen Isot,ope Analysis. Tsnns. ilrncr. Geophys. Un. 39, 31 l-512 (abstract). (‘n;\rc: 13. (1957) Isotopic Standards for Carbon and Oxygen and Correction Factors for ?rlassSpectrographic Analysis of Carbon Dioxide. Geock ini. et Cosmochirn. Acta 12, 13%149. Cn.~ra H. (1961) Standard for Reporting Concentrations of Douteri~lm and Oxygen-18 in Xat,ural \Vatcrs. Science 133, 1833-1834. DONTSO~.~ E. I. (1959) Method of Determination of Oxggcn Isotope Ratios in Tgncot~s Rocks ant1 Minerals. Geokhimiyn 8, 669-678. HOEKSTRA H. R. and KATZ J. J. (1955) [sot,opc Geology of Some cranillrn Minerals. I’roc. Ir~t. Cov~f. Peaceful Uses of Atomic Energy, Geneva, pp. 547-550. TJhas~~ E:. S., Jr. (1948) Batholith and Associated Rocks of Corona, Elsinorc and San Jduis Rcy Quadrangles, Southern California. Geol. Sot. Amer. ,VTern. 29. MCKINNEY C. R., M&REA J. M., EPSTEIN S., ALLEN H. il. and UREY H. c’. (1950) Improvements in Mass Spectromet,ers for the Measurement of Small Differences in Isotope Abandanco Ratios. RN!. Sci. In&r., 21, 724-730. NIER A. 0. C. (1947) A Mass Spectromet*er for Isotope and Gas Analysis. Rev. Sci. In&r., 18, 398-411. SCH~XTANDERH. (1953) Best,immung dos relativrn Sauerstoffisotopen-Verhaltnisscs in Silikat gesteinen und Mineralien. Geochim. et Cosmochim~. Acta 4, 261-291. Geochim. et Cosmochim. Acta 2, 26-42. SILVF,RILIAN S. R. (1951) The Isotope Geology of Oxygen. 'J'AYL~R H. P. and EPSTEIN S. (1962) The Relahionship bet,ween O1s/O16 Ratios in Coexisting Bull. Geol. Sot. Amer. 73, 461-480. Minerals of Igneous and Met,amorphic Rocks. T~JDGE A. P. (1960) A Method of Analysis of Oxygen Isotopes in Orthophosphate--Its Use in the Geochim. et Cosm.ochim. Acta 18, 81-93. Measurement of Paleotemperatures. VINOGRADOV A. P., DONTSOVA E. I. and CHUPAKHIN M. S. (1958) The Isotopic Composition of Oxygen in Igneous Rocks and Meteorites. Geokhimiya 3, 187-190.
Press Ltd.
Printed
in S0rtllernIrrlnnd
The use of bromine pentafluoride in the extraction of oxygen from oxides and silicates for isotopic analysis* ROBERTN.CLAYTON
and TOSHIKO K.MAYEDA
The Enrico Fermi Institute for 1\Tuclear Studies The University of Chicago, Chicago, Illinois (Received
30 January
1962; reviseri 13 April
1962)
Abstract-A technique has been developed in which bromine pentafluoride is used as a reagent for quantitative liberation of oxygen from oxides and silicates. For all of the rocks and minerals analysed, the oxygen yields are 100 + 2 per cent of the theoretical amount. The advantage over techniques involving reduction with carbon lies in the consistently better oxygen yields, with consequent decrease in systematic errors in isotopic composition. Bromine pentafluoridc has advantages over fluorine in being easier and safes to handle in the laboratory, in being readily purified, and in reacting with some minerals which do not react completely with fluorine. The results of isotopic analyses are compared with measurements made in other laboratories by other procedures.
SEVERAL analytical procedures have been described for the extraction of oxygen from silicates and other oxygen compounds for precise isotopic analysis [BAERTSCHI and SILVERMAN (1951), BAERTSCHI and SCHWANDER (1952), CLAYTON (1955), CLAYTON and EPSTEIN(~~~~),DONTSO~A(~~~~),SCHWANDER(~~~~),TA~LOR and EPSTEIN (1962),TUDGE (1960),VINOGRADOV et al. (1958)]. They are all based on one of the following two types of reaction: (1)reduction by carbon at high temperature (1600-2000°C) to yield carbon monoxide; (2) oxidation by fluorine or halogen fluorides to yield oxygen as 0,. Experience with both approaches has led us to prefer the oxidation reaction and the present paper describes a variation on the fluorine procedure used by SILVERMAN (1951) and BAERTSCHI and SILVERMAN (195O),differing in that bromine pentafluoride is used as t,he oxidizing agent. The reduction methods and the oxidation methods are approximately equivalent with respect to such considerations as cost and complexity of apparatus3, skill required for operation, time per sample, etc. For some minerals, both procedures are capable of giving isotopic reproducibility of $0.1 to 0*2x,. In cases where the carbon reduction method and the fluorine oxidation method have been compared by analysis of identical test samples, it has been shown t,hat t,he two procedures give identical differences in 01s/016 between quartz samples, but that the carbon dioxide sample produced by the carbon reduction method is about 0.5x,, richer in 0 18 than that produced in the fluorine method (CLAYTOX and EPSTEIN 1958, TAYLOR and EPSTEIN 1962). The syst’ematic discrepancy is probably due to low yields (95-97 per cent) in the carbon reduction analysis caused by some volatilization of SiO. The carbon reduction method as used by SCHW;ZNDER (1953):BAERTSCHI and SCHWANDER (1952),and CLAYTON and EPSTEIN (1958), * This work was support,ed by a grant from the National 43
Science Foundation
(NSF-G7292).
ROBERTI\. CLBYTONand TOSHIKOK. MAYEDA
44
gave oxygen yields of 50-80 per cent from mineral samples containing alkali metals, alkaline earths, or aluminum. These low yields were accompanied by large isotopic fractionaCons. More recent improvements in t’he carbon reduction technique have increased the oxygen yields on such minerals to 95-100 per cent (VINOGRADOV, DONTSOVA and CHUPAKHIN, 1958; and DONTSOVA, 1959), presumably decreasing the effects of fractionation. Oxygen yields in the fluorine method used by BAERTSCHI and SILVERMAN (195 1) were found to be quantitative for most rocks and minerals, but fell to about 80 per cent for basic and ultra-basic rocks. Similarly, TAYLOR and EPSTEIN (1962) report less than quantitative ext,ract’ion of oxygen from olivine, magnetite, epidote and garnet. The yields generally increase as the reaction temperat’ure is increased, but above 50073, the fluorine is consumed by reaction with the nickel container. Our experience with both the oxidation reactions and the reduction reactions has been that complete oxygen yield is of prime importance. Reactions yielding less t’han 98 or 99 per cent of the theoretical amount almost invariably produce an isotopic fractionation, which may be quite reproducible for a given mineral or sample! which introduces systematic errors into t’he isotopic analysis. As a result’. all published analyses showing low oxygen yields must be suspect until verified by other procedures. It is not clear whether all the techniques described in the literature give accurate results (in the sense that the 01*/016 ratio in the mass spectromet’er gas sample is identical with that in the rock or mineral specimen). Necessary criteria for accurate results are: (1) a b sence of contamination by extraneous oxygen; (2) absence of exchange between oxygen of the sample and oxygen of the apparatus or reagents; (3) either quantitative extractJion of oxygen from the mineral, or ext’raction by a chemical react’ion involving no isotopic fractionation. A disadvantage in the carbon reduction procedure arises in the case of hydroxylbearing minerals. The analytical procedures usually require a high-temperature vacuum outgassing of t’he carbon react,ion vessel containing t’he sample. In order to be efficient, this outgassing must be done at temperatures of 1000°C or more, which will drive off the bound water from the mineral sample, so that the oxygen ultimately analysed is not ident’ical with t’hat in the original mineral. The fluorine reaction does not require such a high outgassing temperature. and no appreciable loss of bound water occurs in this process. APPsRATUS
The high-vacuum
apparatus
used is similar to those described by BAERTSCHI and SILVERMAN (1951), by CLAYTON (1955), and by TAYLOR and EPSTEIN (1962). The metal section of the vacuum line is shown schematically in Fig. 1 and the glass section in Fig. 2. The metal line is monel, silver-soldered to copper fittings, and using monel valves. Gaskets are Teflon, and the reaction tubes are pure nickel with capacity of 60 cm3. The reaction tubes are made from 3/4 in. O.D. nickel tubing joined to the valve above by a Teflon-gasketed flanged connection. In order to keep the valve and gasket cool while the reaction tube is hot, cooling
water is applied to the upper end of each tube through one turn of copper tubing soldered to the tube just below the flange.
The use of bromine
pentafluoride
45
in the ext,ractjion of oxygen High Vacuum
High Vacuum
t Vent -
=!!a=-
=O=
Oxygen
Dry
Ned=0
Collection Line
Glass Gloss ---
Metal 1 ---
\ f--J
Metal
Reaction
Tubes
Br Fs Cylinder
Fig.
1. Apparatus
for reaction
of oxygen
compounds
with bromine
penMluoridc.
-
Scale ’
High Vacuum
Sample Tube
Manometer
Toepler Fig.
2.
Apparatus
for
Pumps collect’ion
of oxygen
and conversion
t,o carbon
dioxide.
ROBERTN. CLAYTON and TOSHIKO K. MAYEDA
46
REAGENT The oxidizing reagent used in the present work is bromine pentafluoride (BrF,) . It is a colorless liquid at room temperature (M.P. -61+3”C, B.P. 40.5”). It is available commercially in steel cylinders, and can be handled in the laboratory in metal vacuum systems using copper, monel and nickel. It reacts readily with glass at room temperature, but shows no evidence of reaction at liquid nitrogen temperature. Its reactivity toward oxides and silicates appears to be approximately equivalent to that of fluorine. At high temperatures, of the order of 500-6OO”C, nickel is the only material known to be suitable for containing bromine pentafluoride. We have conducted reactions at temperatures as high as 700°C; at this temperature there is no evidence for decomposition of BrF,, and the reaction with the nickel container is not, too great. ANALYTICALPROCEDURE
The following with a silicate:
equation
KAlSi,O,
illustrates
+ 8BrF, +
a typical
KF + AlF,
reaction
of bromine
+ SSiF, + 40,
pentafluoride
+ 8BrF,
The mineral samples used range from 5-30 mg, with an approximately five-fold excess of reagent over stoichiometric requirements. The react’ions are usually run at 450°C for 12 hr with some exceptions as described below. The following paragraphs give a detailed description of the analytical procedure. The 6 reaction tubes, after removal of the gaseous products of the previous reaction, are filled to one atm pressure with dry nitrogen. The valves are closed, and the tubes removed from the line at the gasketed connector above the valves. The tubes and weighed samples are put into a dry box containing air dried by P,O,. After 3 hr, each tube is opened inside the dry box, the solid products of the previous reaction are dumped out, a new sample is put into the bottom of the tube, and the tubes are closed again. Then the tubes are returned to the vacuum line, and evacuated. The reaction tubes are heated for one hour at 400°C while open to t’he high vacuum line. This removes adsorbed air and water, but is not hot enough t’o The outgassing is followed by a predecompose hydroxyl-bearing minerals. treatment of the reaction tubes with BrF,. The reagent is expanded into the tubes and the metal vacuum line to a pressure of 15 cm of mercury. The tubes are shut off from the line and heated to 100°C for one hour. This procedure removes the very small amount of oxygen compounds which may form on the nickel walls while the samples are being loaded. The pre-treatment is probably an unnecessary precaution, since the amount of oxygen thus liberated is very small. In fact, the pre-treatment must be avoided for some minerals which react extensively with BrF, at 100°C. These include the feldspars and hydrated forms of silica (also phosphates (TUDGE, 1960) and carbonates (CLAYTON, 1961)). ?Ilostof the other common minerals are unaffected by BrF, at 100°C: quartz, micas. pyroxenes, It has been found possible to get good oxygen isotope analyses olivine, magnetite. from feldspars in the presence of equal amounts of quart’z, by conducting t,he reaction at 100°C.
The use of bromine pentaflnoride in the extract,ion of oxygen
47
After pre-treatment the reaction tubes are evacuated, then each tube is charged with BrF,. A portion of the liquid reagent which has been distilled from the commercial cylinder, then redistilled once, is allowed to evaporate into an expansion volume of 600 cm3 to a pressure of 0.1 atm. This reagent, about l/400 mole of BrF,, is then condensed into one of the sample tubes by immersing the tube in liquid nitrogen. Reagent is measured into each Oube in the same way. The size of the mineral samples is chosen to give 100-400 pmol of oxygen, so that the amount of reagent is approximately 5 times the stoichiometric requirement. The same quantity of reagent has been used regardless of sample size or composit’ion. The reaction tubes are then closed off and heated by electrical resistance furnaces. Quartz, micas, and feldspars are reacted at 450°C for 12 hr; magnetite, hematite and ilmenite are react,ed at 6OO’C for 12 hr; garnet and olivine are react’ed at 690°C for 12 hr. After reaction, the furnaces are removed and the tubes allowed.to cool to room t,emperature. Then the oxygen sample is extracted from each tube as follows: The valve on the reaction tube is opened to allow the gas mixture to flow into the metal vacuum line as far as valves Vl and V2 (E’ig. 1). Then valve V2 is opened slightly to allow the gas to flow slowly through the glass trap, cooled by liquid nit’rogen. Of all the possible volatile reaction products: O,, BrF,, BrF,, Br,, SiF,, HP, only oxygen passes through the cold trap. It is pumped by an automatic Toepler pump into a calibrated volume where the quant’ity of oxygen is determined. Complet,e collect’ion of the oxygen sample takes about 20 min. After collection and measurement of the oxygen, the gas is passed over hot carbon t’o convert it quantitatively to carbon dioxide by Dhe reaction: c! $O,-+CO,.
This process has been described by CLAYTON (1955)and TAYLOR and EPSTEIN (1962). In the apparatus used in our laboratories, the hot carbon is a hollow cylinder made from a spectrographic electrode. The dimensions are: diameter l/2 in., length 1 in., wall thickness l/32 in. The carbon is suspended inside a waterjacketed glass tube, and is heated by radio-frequency induction. The temperature is about 550-6OO”C, low enough to prevent the formation of appreciable amounts of carbon monoxide. Oxygen is circulated over the hot carbon, and the carbon dioxide is frozen out in a liquid nitrogen-cooled U-tube. The conversion of an oxygen sample to carbon dioxide takes about 15 min, and is carried out while the oxygen from the next sample is being collected from the nickel reaction tube. The graphite cylinder is replaced after approximately 30 samples. The carbon dioxide is transferred to a manometer for measurement of reaction yield, and Ohen to a sample tube for transport to the mass spectrometer. The ent,ire extraction of a set of 5 oxygen samples and one blank takes 3-5 hr. By running the BrF, reactions overnight, and extracting oxygen in the morning, one can complete one set of samples each day. The oxygen blanks are usually less than 1 pmol. The source of this oxygen
ROBERTN. CLAYTONand. TOSHIKOK. MAYEDA
48
appears to be the walls of the reaction tubes (from reaction with air during loading of the samples); the amount of oxygen in the reagent itself is completely negligible. No blank corrections were made to any of the isotopic analyses. Mass spectrometric analyses are made on a 6-in. double-collecting isotope ratio spectrometer after the designs of NIER (1947) and MCKINNEY et al. (1950). Analytical data are reported in the B terminology, as deviations in permil (parts per thousand) of the 01A/016 ratio from that in standard SMOW (CRAIG 1961). The value for the ratio (Ola~O16)CO~ gas/(01*/016)~~0 liquid at 252°C is taken as 1*04070 (~OMPSTO~ and EPSTEIN 1957). The measured values were correct‘ed for spectrometer valve mixing, and for CP variations according to the equations given by CRAIG (1957). ISOTOPIC REPRODUCIBILITY Several mineral samples have been analysed repeatedly over a period of 15 months as a continued check on the analytical procedures These samples were often run after unusual events, such as a repair to the vacuum system, washing t$he reaction tubes, etc., so that the reproducibility shown here is somewhat< poorer t,han for samples run routinely. The mean isotopic analysis and average deviatiorls are shown in Table 1. BROMINE TRI~LUOXUDEAS OXIDIZING REAGENT Bromine trifluoride has been used to liberate oxygen from uranium oxides (HOEKSTRA and KATZ 1955), and phosphates (TUDGE 1960). Several hundred analyses of 01S/016 in silicates have been done in our laboratory using BrF, as reagent, following the same procedure as described above for BrF,. The results of these analyses agree with those using t.he BrF, reagent, (see Table 1). We have Table 1 Sample
c)W(BrF,)
hOl”(HrP3)
--. Potsdam sandstone St. Peter sandstone Randville pegmat,ite quartz Randville pegmatite orthoclase Plagioelase RC-1 l-60 JL-3 hydrothermal quartz KS-lOamagnetite
15.44 11.02 10.07 8.80 9.90 11.52 -0.15
& 0.26 + 0,15 + 0.20 * 0.10 & 0.11 6 0.12 -& 0.09
(9 analyses) (13 analyses) (9 analyses) (5 analyses) (4 analyses) (41 analyses} (5 analyses)
11.07 r; 0.14 (6 analyst~s) 10.08 * O-14 (14 analysrs) 9.85 * O-07 (3 ana.lyses) 11.46 & 0.05 (2 analyses) -0.28 5 0.01 (R nnal\scfi)
found bromine pentafluoride more convenient to use because of its higher pressure: 390 mm at room temperature against 6 mm for bromine trifluoride. The higher vapor pressure facilitates the measuremer~t of the quantity of reagent to be transferred to the reaction tubes. It also increases the alnount of reagent in the vapor phase in the reaction tubes, since BrF, will condense at the water-cooled upper end of the tubes. COMPARISONS WITH OTHEH,TECHNIQUES AND ANALYSTS
Several samples have been analysed which had previously been run in other Comparisons of the isotopic analyses, and of laboratories using other techniques. the oxygen yields, where known, are shown in Table 2.
The UF’Oof bromine pent,afluoride in the extraction of oxygen
49
50
ROBERTS. CLAYTONand TORHIKOK. MAYEDA
Although all the isotopic analyses are given with respect to an ocean water standard, this standard is not identically defined for all the sets of data. SILVERMAN (1951) defined the zero of his isotopic scale to be oxygen from a single sample of sea water “Hawaiian sea water No. RT-6”. In the published data of CnAvToN and EPSTEIN (1958) and of TAYLOR and EPSTEIN (1962), t,he standard was defined to be oxygen with 01*/016 ratio equal to 0.98473 R,, where R, is the 01*/Oi6 ratio in Silverman’s sample of Potsdam sandstone. By this means. the 3 sets of dat,a all give 6 = +15.5 for the Pot8sdam sandstone. If any of t’he analyt’ical procedures int8roduce systematic errors into the measured (s values, this procedure of normalizing to a quartz sample should make the results of different analytical methods agree on quartz samples, but not necessarily on other minerals or rocks. Such is found to he the case. The oxygen of mean ocean wat,er is a logical standard for reporting oxygen isotope variations in natural materials, including meteoric waters and rocks and minerals. (The analysis of carbonates for ocean paleotemperature is an exception, where a carbonate standard is still preferable.) Such a st,andard has been proposed by CRAIG (196 1) for natural wat’ers and by CLABTOK and CRAIG (I 962) for rocks and minerals. A “Standard Mean Ocean Water” (SMOW) was defined to have 018/016 (SMOW)
= 1.008 018/016 (NBS-l),
where NBS-l is a water sample distributed by the National Bureau of Standards. This defines an ocean water standard in terms of materials readily available to everyone, rather than in terms of the limited quantity of a particular sample of Yotsdam sandstone. However, a completely satisfactory procedure for quantitative extraction of oxygen from water for isotopic analysis has not yet been reported. Differences in 018/016 between water samples are conventionally measured to high accuracy by measuring 018/016 ratios of carbon dioxide equilibrated with water at 25°C. The equilibrium constant for this equilibration: K = (018/016)C02/(0’s/016)HZ0 has been reported by COMPSTON and EPSTEIN (1955) to be 1.0407 f eOOO3. This value has been adopted in the present work. In practice, our oxygen isotope ratios are measured relative to carbon dioxide from a carbonate working standard, then recalculated to the SMOW standard. Thus, any future measurements which alter t’he accepted value of the water-carbon dioxide equilibrium constant, will change all the 6 values by a fixed amount. It happens by coincidence that the two definitions of an ocean water standard: (a) (OlS/O16) ocean water = .98473(O18/Oi6) Potsdam (b) (018/016) SMOW
sandstone
#2039
= 1~008(018/016) NBS-I
give identical &values for samples analysed by TAYLOR and EPSTEIN (1962), and by the present workers, and for most of the samples analysed by SILVERMAN (1951), so that a redefinition of the standard does not require a change in &values reported according to definition (a).
The USC of bromine
The results raw data, and This technique techniques, as
pentafluoride
in the extract’ion
of oxygen
.‘I
of CLAYTON and EPSTEIN (1958) have been recalculated from the are reported according to definition (b) of the SMOW standard. gives results consistently about’ 6.574, heavier than the oxidat,ive has been reported by TAYLOR and EPSTEIN (1962). DISCUSSION OF RESULTS
In Table 2, theoretical oxygen contents are presented, where available, for comparison with the measured oxygen yields. Sields are given in units of pmol of CO, per mg of mineral or rock sample (pmol/mg). The agreement is always within l-2 per cent; t’he error may be due entirely to weighing of samples and measurement of the gas volume in a simple mercury manometer. Oxygen yields in the carbon reduct’ion procedure are several per cent low for quart’z, but appear quantitative for magnetite. This is reflected in the systematic differences in do18 for quartz, and in the agreement in 6018 for magnetite, between the two methods. The disagreement found by TAYLOR and EPSTEIN (1962) between fluorine analysis of magnetite samples. and carbon reduction analysis is probably due to incomplete yields (~80 per cent) in the fluorine reaction. The data reported here are in excellent agreement with the results of TAYLOK and EPSTEIN, with the exception of one biotite sample No. WH-3. Our dat’a agree well wit’h about half the values reported by SILVERMAN (1951), but are in serious disagreement with t(he others. The disagreement is always in the same direction, with SILVERMA~‘S results showing lower 018/016 ratios. For 5 samples t,he difference is consistently %.5x,> suggesting an error in calculation of standards rather than some chemical effect.
The liberation of oxygen by reaction with bromine pentafluoride has proved t,o be a reliable analytical procedure for a wide range of oxide and silicate minerals. giving oxygen isotope analyses in agreement with most of the previous analyses of test materials. The analytical procedures involving oxidation to liberate oxygen as 0, are generally more satisfactory than the reduction procedures liberating oxygen as CO. The former give oxygen yields which are quantitative within the error of measurement; the latter give yields which are typically 90-97 per cent on silicate minerals, introducing fractionation effects which are on the order of lx,, several times the experimental reproducibility. Bromine pentafluoride (and bromine trifluoride) have several advantages over fluorine in the oxidation reaction: (1) The reagent is a liquid at room temperature. and avoids the hazard of highpressure fluorine cylinders. (2) The reagent is readily distilled to make it. completely oxygen-free. Commercial fluorine usually contains about one per cent oxygen, for which blank correct’ions must be made. (3) Separation of excess BrF, reagent from the reaction products is accomplished simply by passing the gas mixture through a cold trap. After the fluorine reaction, the gases must pass through a heated trap filled with solid KBr, which
52
ROBERT S. CLAYTON and TOSHXO
K. MAYEDA
reacts with fluorine to give bromine which is then condensed in a cold trap. This process is time-consuming, and is a possible source of contamination. (4) Some minerals, such as magnetite, garnet, and olivine give quantitative oxygen yields with BrF,, but not with F,. It is expected that improvements in our techniques of gas measurement will make possible direct quantitative analysis of oxygen in rocks ad minerals with an accuracy comparable to t,hat obtainable for the ot’her major constituents. are grateful to Dr. 8. R. suml~lcs of rocks and minerals used in previous
.~ckrLo~Zeclgnlents-~~‘e
QILVERM.~N
isotopic
and .I>r. H. P. st)lltlies.
'I'_~YLoR
for
supplying
REFERENCES ~~~ERTSCHI PETER and SILVERMAN S. R. (1951) The Determination of t,be Relat.i\-e Abnndan~c of the Oxygen Isotopes in Silicate Rocks. Geochim. et Cosmochim. Acts 1, 317--32X. B~%ERTSCHIPETER and SCHUANDER H. (1952) Ein nencs lTerfahren zur Messung dcr Untcrschicd(x im 018-Gehalt, von Silikat,gestrinm. Rein. Chim. Acta 35, 1748-1751. B~-~~IXGTOX A. F., FAHEY J. and VLISIDIS A. (1955) Thermometric and l’ctrogenctic Significance of Titaniferous Magnetite. Amer. I. Sci. 253, 497-532. (‘LAYTON R. X. (1955) Variations in Oxygen Isotope Abundances in Rock Minerals. Ph. I). t.hcsis, California Institut,e of Technology. C'LAYTOS Ii. N. and EPSTEIN S. (1938) The Relat,ionship between 01*/01” Ratios in Co-existing Qnart,z, Carbonate and Iron Oxitles from Variolls Geological Deposits. J. Geol. 66, 352%3i3. CL.-~YTON R. N. (1961) Oxygen Isotope Fract,ionat,ion between Calcium Carbonatc: ant1 Water. .I. Chem. Phys. 34, 72&726. (‘LAYTON R,. N. and CRNc H. (1963) Standard for Reporting 0 l8 C’onccrrtrat’ions in Ttocks and Minerals. In preparat,ion. C’O~~PSTON 11’. and EPSTEIN S. (1958) A M&hod for the Preparation of C’arbon Dioxide from \Vater lTapor for Oxygen Isot,ope Analysis. Tsnns. ilrncr. Geophys. Un. 39, 31 l-512 (abstract). (‘n;\rc: 13. (1957) Isotopic Standards for Carbon and Oxygen and Correction Factors for ?rlassSpectrographic Analysis of Carbon Dioxide. Geock ini. et Cosmochirn. Acta 12, 13%149. Cn.~ra H. (1961) Standard for Reporting Concentrations of Douteri~lm and Oxygen-18 in Xat,ural \Vatcrs. Science 133, 1833-1834. DONTSO~.~ E. I. (1959) Method of Determination of Oxggcn Isotope Ratios in Tgncot~s Rocks ant1 Minerals. Geokhimiyn 8, 669-678. HOEKSTRA H. R. and KATZ J. J. (1955) [sot,opc Geology of Some cranillrn Minerals. I’roc. Ir~t. Cov~f. Peaceful Uses of Atomic Energy, Geneva, pp. 547-550. TJhas~~ E:. S., Jr. (1948) Batholith and Associated Rocks of Corona, Elsinorc and San Jduis Rcy Quadrangles, Southern California. Geol. Sot. Amer. ,VTern. 29. MCKINNEY C. R., M&REA J. M., EPSTEIN S., ALLEN H. il. and UREY H. c’. (1950) Improvements in Mass Spectromet,ers for the Measurement of Small Differences in Isotope Abandanco Ratios. RN!. Sci. In&r., 21, 724-730. NIER A. 0. C. (1947) A Mass Spectromet*er for Isotope and Gas Analysis. Rev. Sci. In&r., 18, 398-411. SCH~XTANDERH. (1953) Best,immung dos relativrn Sauerstoffisotopen-Verhaltnisscs in Silikat gesteinen und Mineralien. Geochim. et Cosmochim~. Acta 4, 261-291. Geochim. et Cosmochim. Acta 2, 26-42. SILVF,RILIAN S. R. (1951) The Isotope Geology of Oxygen. 'J'AYL~R H. P. and EPSTEIN S. (1962) The Relahionship bet,ween O1s/O16 Ratios in Coexisting Bull. Geol. Sot. Amer. 73, 461-480. Minerals of Igneous and Met,amorphic Rocks. T~JDGE A. P. (1960) A Method of Analysis of Oxygen Isotopes in Orthophosphate--Its Use in the Geochim. et Cosm.ochim. Acta 18, 81-93. Measurement of Paleotemperatures. VINOGRADOV A. P., DONTSOVA E. I. and CHUPAKHIN M. S. (1958) The Isotopic Composition of Oxygen in Igneous Rocks and Meteorites. Geokhimiya 3, 187-190.