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A study of the lead isotopic composition of galena at Manitouwadge, Ontario. Hayles, John Gordon 1973

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A STUDY OF THE LEAD ISOTOPIC COMPOSITION OF GALENA AT MANITOUWADGE, ONTARIO by JOHN GORDON HAYLES B.Sc, Queen's University, 1970 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in the Department of GEOPHYSICS We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA March, 1973 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia Vancouver 8, Canada (i) ABSTRACT Lead isotope compositions of galena from the Fox Creek Fault at Manitouwadge, Ontario form an anomalous linear array of values on a standard 2 0 7Pb/20''Pb vs. 2 0 6Pb/20-Pb plot and a 2 0 8Pb/20,tPb vs. 2 0 6Pb/20l4Pb plot. The last geologically reasonable time for galena mineralization along the Fox Creek Fault is during the Keweenawan age, 1100 million years ago. Using the slope of the anomalous lead line and this time of 1100 million years as the time of final galena mineralization along the fault gives an age of 2000 million years as the maximum. time of emplacement of uranium parent of the anomalous leads into the crust. The corresponding Th/U ratio for the source of the anomalous leads is 5.3. Lead isotope compositions of galena from the main ore zone at Manitouwadge are extremely homogeneous and do not show a lineation, other than along a 201*Pb error line, which would indicate them as anomalous leads. It is improbable for the ore zone deposits to be as young as 2700 million years as required by Tilton and Steiger (1969) . In order to relate ore zone leads to Fox Creek Fault leads at least a three stage lead growth model is required. Possibly no genetic relation exists between ore zone and Fox Creek Fault galenas analysed to date. Single galena crystal lead isotope variations should be studied in detail within the Fox Creek Fault (ii) itself. Sulphur isotope studies may help to determine the relation between ore zone and fault zone galena at Manitouwadge. 01 a ) TABLE OF CONTENTS ABSTRACT (i) LIST OF FIGURES (iiiLIST OF TABLES (iv) ACKNOWLEDGEMENTS (vCHAPTER I 1.1 Introduction 1 1.2 GeologyCHAPTER II 2el Analytical Procedures 7 2.2 Mass Spectrometry 8 CHAPTER III 3.1 Analytical Results and Interpretation 13 3.2 Summary 3REFERENCES 6 APPENDIXES A. Ion Exchange Column Preparation 40 B. Silica Gel - Lead Nitrate Loads 44 C. Precision and Double Spiking 46 (iii) LIST OF FIGURES FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 Location map and geologic map of Manitouwadge, Ontario. (a) Example of a typically stable lead isotopic ionization at 1230 C. (b) Example of a particularly unstable lead isotope ionization using the silica gel procedure. Results of this study, 2 0 7Pb/2("*Pb vs. 2 0 6Pb/20'*Pb compositions for galena from Manitouwadge, Ontario. Results of this study, 2 0 8Pb/20 **Pb vs. 2 0 6Pb/20 **Pb compositions for galena from Manitouwadge, Ontario. 2 0 7 Pb/ 2 0 <t Pb vs 2 0 6, Pb/201|Pb plot of lead isotope compositions of rocks and ores at Manitouwadge, Ontario and its environs. 20 S, 'Pb/^-Pb vs. 2 0 6Pb/zo,,Pb plot of lead isotope compositions of rocks and ores at Manitouwadge, Ontario and its environs. Page 2 11 15 16 26 27 (iv) LIST OF TABLES Page TABLE 1 The results of this study of lead 13 isotope compositions of galena at Manitouwadge, Ontario. TABLE 2 The normalized results of samples 24 analysed from in and around the Manitouwadge area by Ostic (1963), Doe, Tilton and Hopson (1965), Hart and Tilton (1966), and Tilton and Steiger (1969) . (v) ACKNOWLEDGEMENTS The writer wishes to thank all those who contributed to the preparation of this thesis. The assistance of Drs. T. J. Ulrych, J. M. Ozard and R. D. Russell is appreciated. Mrs. C. Curtis assisted the writer in the laboratory in many ways. Discussions with Mr. P. Le Couteur and Dr. J. Blenkinsop helped in almost all phases of the the work. The mine staff at the Geco mine, Mr. Unto Jarvi, Mr. Tim Bakker, Mr. Terry Williams, and Mr. Ross Weeks supplied samples and guided the author through much of the mine. Mr. Esko Autio, chief geologist at Willroy, donated the Willroy and Willecho samples analysed here. My wife typed this thesis. Lastly, I must thank Dr. W. F. Slawson who super vised this work. The study was supported financially by a National Research Council of Canada grant to Dr. Slawson. - 1 -CHAPTER I 1.1 INTRODUCTION Manitouwadge is about 165 miles east-northeast of Thunder Bay, Ontario and is about 60 miles north of Lake Superior. The townsite is about 40 miles by road north of Trans-Canada Highway #17 at Struthers, and is served by spur lines of both the Canadian National and Canadian Pacific Railways. Manitouwadge has been an important metal producing, area since 1957. The Geco mine, owned by Noranda Mines Ltd., is the largest deposit in the area, and in the 1957-1971 period produced 639,630 tons of zinc, 377,830 tons of copper, 29,013,600 oz. silver, and minor lead and gold from 19,544,170 tons of ore. Reserves are about 30 million tons of 4.4% Zn, 2% Cu, and 1.8 oz. Ag. The isotopic composition of lead in galena at Manitouwadge has been discussed in scientific literature since 1957. Frequently discussions on the age of the earth have centered around the lead isotopic composition at Manitouwadge. This thesis attempts to add insight into the origin of Manitouwadge leads. 1.2 GEOLOGY Geology of the Manitouwadge area is shown in Figure 1 and has been described by E. G. Pye (1957) , E. H. M. Chown (1957), Brown et. al. (1960) and Timms and I to I Figure 1 Geology of the iManitouwadge area modified after Pye (1957) and others. Locations of the Geco, Willroy, and Willecho mines are indicated by circled numerals 1, 2, and 3, respectively. _ 3 _ Marshall (1959) . Manitouwadge lies within the Superior Province of the Canadian Shield as a roof pendent of metasedimentary-metavolcanic rocks surrounded by granites, granodiorites and migmatites. The metasedimentary-metavolcanic sequence is of Keewatin age although its time relationship with other Keewatin rocks of the Shield is not known. The sequence forms a syncline with an axis trending 050° and plunging 15° to 20° to the northeast. Dips along the limbs of the syncline are steep. Relic bedding is noticeable in the metasediments and pillow structures can be found in the metavolcanics. Tops is not known due to high grade amphibolite facies metamorphism which occurred during the Kenoran Orogeny. This orogeny also obscured primary sedimentary structures and distorted the syncline. The strata are cut by pegmatite dikes and microgranodiorite dikes and sills which possibly were intruded during late phases of Kenoran Orogeny. The eight known orebodies in the Manitouwadge area are hosted by a grey gneiss sequence thought to be sedimentary in origin. This unit is located toward the top or concave side of the plunging syncline, as depicted in Figure 1. The major orogenic event in this area occurred 2700 million years ago as dated by Rb-Sr measurements according to Tilton and Steiger (1969) . Hanson et. al. - 4 -(1971) also report Rb-Sr ages of 2700 million years for rocks from northern Minnesota, which is within the same subprovince of the Canadian Shield as Manitouwadge. A swarm of northeast trending diabase dikes of probable Keweenawan age cut this older deformed terrain. A major Keweenawan intrusive complex is located about 50 miles south-southwest of Manitouwadge, along the structural boundary between the Superior Province and Southern Province. An enormous amount of basic volcanism and diabase intrusion occurred in the Southern Province during the Keweenawan, which has been dated by Goldich et. al. (1961) and the Geological Survey of Canada as occurring from 1200 to 900 million years ago. The intrusives were emplaced early in the evolution of the Southern Province, and are common in the surrounding Archean terrain, Halls (1966) . Ore deposits at Manitouwadge are conformable within the metasediments and have been classed as copper-zinc type not unlike other ore deposits which occur in an east-west belt across Ontario and part of Quebec. The Geco main zone and the Willroy #1 zone occur in a muscovite-quartz schist along with some bands of iron formation. Iron formation completely encloses the other Willroy and Willecho orebodies. The orebodies are classified as replacement deposits by Pye (1957), with three modes of occurrence: (1) massive ore (2) lode fissures and (3) disseminated ore. Pegmatite dikes have been replaced in places by ore, which has been taken by many geologists to indicate that mineralization is younger than pegmatite intrusion. However, minor remobilization of ore could have occurred during the waining stages of the Kenoran Orogeny, and may be the cause of this "replacement". Suffel et. al. (1971) suggest this latter view. Ore appears to be located in long low-amplitude drag folds which possibly were formed during regional folding. Galena samples were collected during September of 1970 by the author from the Geco, Willroy and Wilecho ore zones. At both the Willroy and Geco zones galena appears to have been emplaced later than other sulphides, which it often replaces. Galena constitutes less than one percent of the Geco ore, and occurs in the massive ore and along fractures in wallrock inclusions in the massive ore, along fractures in pegmatite dikes assiciated with disseminated ore, and associated with the Fox Creek Fault. Galena in the Fox Creek Fault is more abundant and occurs much larger crystals than in other parts of the mine. Fox Creek Fault galena is usually associated with calcite which is not common elsewhere at Geco. The Fox Creek Faul was inaccessible at the time of the author's visit, and so samples of galena from there were donated from the Geco office collection by Mr. T. Bakker and Mr. R. Weeks. Samples from the Willroy and Willecho mine were donated by Mr. E. Autio, the chief geologist. Suffel et. al. (1971) point out that many characteristics - 6 -of the Manitouwadge area are consistent with severe metamorphism. They note that the ore displays metamorphic granoblastic textures which indicates an origin prior to metamorphism, possibly of sedimentary or submarine volcanic origin. The conformable nature of ore supports this hypothesis. Since grade of metamorphism is high in this area it seems unlilcely that the genesis of these orebodies will ever be firmly resolved. The author favors a sedimentary origin. - 7 _ CHAPTER II 2.1 ANALYTICAL PROCEDURES The 13 galena-bearing samples analysed during this study were individually crushed and galena was separated by hand, as much as possible. Approximately four grams of galena from each sample were placed in 100 milliliters of 6 molar hydrochloric acid, and held at about 60° C for about 6 hours. The resulting hot solution containing lead chloride was then filtered, and cooled to precipitate lead chloride crystals. After about 2 hours, residual liquid was decanted, lead chloride crystals were washed in distilled water, dried in a warm oven overnight and stored in a clean bottle. A 30 cm. long ion exchange column with a 100-200 mesh Dowex lx8 chloride form exchange resin was used to purify the lead chloride since galena in the samples was always associated with sulphides of iron, zinc and copper. This ion exchange purification is based on a study by Kraus and Nelson (1955) with details given in Appendix A. After purification, lead chloride was converted to crystalline lead nitrate which was stored. A detailed flow chart of the analytical procedures is given in Appendix A. The silica gel-phosphoric acid method as des cribed by Cameron et. al. (1969) was used to make the lead analyses on a single outgassed filament of rhenium. - 8 -Essentially this method increases the ionization efficiency of lead on a hot filament and can be used for very small (nanogram) masses of lead. Details of the silica gel procedure are given in Appendix B. A double spike was used to correct for mass dependent fractionation which occurs in the source region of the mass spectrometer. The double spike used in this study was prepared by Mrs. C. Curtis, of this laboratory, from lead nitrate standards supplied by the Oak Ridge National laboratory U.S.A. The double spike has been calibrated by Dr. J. M. Ozard, and by the author against the N.B.S. equal atom standard, SRM 982. Calibration results are shown in Appendix C. 2.2 MASS SPECTROMETRY The mass spectrometer used in this study was a 12 inch, 90° sector, first order focusing, solid source mass spectrometer as described by Russell et. al. (1971) and Blenkinsop (1972). A digital computer is used on-line with the mass spectrometer as a standard feature at this lab to assist in data reduction. Voltages proportional to the ion current flow at the collector are measured digitally. This data is filtered giving peak heights above baseline heights which then is converted by the computer to isotopic ratios for each pair of spectra scanned and the results are recorded on a teletype. - 9 -The mass spectrometer chamber was reduced to a pressure of about 2><10 'millimeters of mercury, by an oil diffusion pump, a process requiring two hours after the sample had been inserted in the source region. Liquid nitrogen was placed into a cold finger near the source, which further reduced the pressure, to about 0.5x10" millimeters of mercury. The magnet current supply and the high voltage supply were usually turned on and allowed to warm up for ten minutes before the filament current was turned on. The filament current was increased gradually from zero to around 1.8 amperes over five minutes which brought the filament temperature to around 1000° C. as determined by an optical pyrometer. Lead beams were large enough to give good precision at about 1200° C. The ion current for the 20lfPb peak must be greater than 10"13 amperes to give sufficient precision of isotope measurement, and temperatures were adjusted to achieve at least this amount. Measurement of precise lead isotopic ratios also requires a stable rate of ionization in the source region, because only one ion beam can be measured at a time. If the ionization is unstable over the time the four beams of lead are scanned, meaningful isotopic ratios could only be obtained by averaging many measurements. Speed and precision of measurements of isotopic composition depend greatly on stability of the rate of ionization in - 10 the source region. At normal operation temperatures of 1050o c. to 1300° C silica gel is probably a liquid upon the filament. The ionization of lead atoms may take place as the atom evaporates from the filament or as the gaseous atom collides with the hot filament. No general theory exists to explain the sequence of events in the thermal ionization of an atom from a hot filament. The analyst must decide by trial and error the optimum values of filament temperature, filament position, and heating sequence which yield precise analyses. Usually ionization would be stable enough to begin measurement after 10 to 30 minutes of monitoring the beam at operation temperature. A typical group of eight scans of a stable beam of sample 791 are shown in Figure 2a. Even highly stable ion beams have some transients and an example can be seen at minute 62 on a 20"Pb peak. Measurements were continued for each sample until precision was estimated to be approximately 0.05 percent. Scan records were edited of scans with obvious transients, 2 0 k such as on the Pb peak near minute 62 xn Figure 2a, before final reduction of data to a mean, standard deviation, and standard error of the mean for the isotope ratios. A particularly unstable beam, from sample 802, - 11 u o O 1 5 -2 ° -208 Pb peak \ a £ UJ a. E u o o CM 204 206 D O) 208 u_ IONIZATION INTENSITY Pb xlO13 Pbi207Pb x3x10~13 Pb x 9 x 10 -13 ampere ampere ampere IONIZATION INTENSITY x27xl0 ampere - 12 -is shown in Figure 2b. After about one hour of ion ization at normal run temperatures the beam intensity was still highly irregular. Figure 2b not only shows this irregularity, it also shows a heating technique used to stabilize beams. Often if the ion beam is unstable, increasing the filament temperature 200°- 300°C. for 2-3 minutes and then bringing it back down increases the stability. This particular run was unsuccessful, for when the beam finally stabilized, the sample was too depleted to give a sufficient ionization beam. - 13 -CHAPTER III 3.1 ANALYTICAL RESULTS AND INTERPRETATION The results of this study of the isotopic com position of galena at Manitouwadge, Ontario, are shown in Table 1. Two samples from Manitouwadge were double spiked to correct for mass-dependent fractionation within the source region of the mass spectrometer. Fractionation corrections for the silica gel-phosphoric acid procedure used here were about 0.1 percent for the 2 0 6Pb/20,*Pb ratio; this was deemed insignificant to the results of this study and so fractionation corrections have ignored. Double spike calibration and corrections and replicate analyses of galena from Broken Hill, the U.B.C. standard lead, are given in Appendix C. Sample *06pb 2 o <.pb 20 7pb 2 0 ".Pb 2 0 8pb 2 0 >.Pb 782 Fox Creek Fault 750 level 29.815+.017* 17.481±.010* 46.72+.03* 783 Fox Creek Fault •p level 29.186+.007 17.389+.006 46.24 + .019 784 Fox Creek Fault 1000 level 31.72 +.013 17.817+.007 50.09+.016 785 Fox Creek Fault •p level 29.309+.009 17.403+.005 46.27+.016 786 Fox Creek Fault 250 level 32.10 +.002 17.868+.012 50.49+. 04 787 Geco Main Ore 1129 level 13.192+.005 14.370+.007 32.98+.023 789 Geco Main Ore 250 level 13.195+.006 14.377+.007 32.96+.017 790 Geco Main Ore 2250 level 13.206+.006 14.394+.009 33.02+.025 791 Geco Main Ore 2300 level 13.204+.004 14.384+.005 32.98+.019 800 Geco Main Ore 550 level 13.184+.003 14.340+.003 32.86+.007 802 Geco Main Ore ? level 13.223+.006 14.382+.005 33.01+.030 805 Willroy # 3 zone 13.182+.004 14 . 349+.004 32.91+.017 807 Willecho (Lunecho) mine 13.177+.005 14.359+.007 32.94+.018 * The ± figures are standard errors of the mean. Table 1 - 14 -The data of Table 1 has been presently graphically on Figure 3 and Figure 4, the 2 0 7Pb/2("*Pb vs 2 0 6Pb/2("*Pb plot and the 2 0 8Pb/201+Pb vs. 20ePb/20,>Pb plot respectively. A single stage growth curve for lead, after Cooper et. al. (1969) has been added to each Figure. In Figure 3, two distinct lead isotopic populations may be seen, one homogeneous cluster of values below the growth curve, which has been plotted at a more detailed scale in the Figure, and another group which forms an anomalous linear array to the right of the growth curve. Samples from the Fox Creek Fault all lie along this anom alous lead line while ore zone samples from the Geco, Willroy, and Willecho mines all have very closely the same composition. A 20I*Pb error line has been drawn through the ore zone lead composition in Figure 3 and any differences in the ore zone lead composition probably may. be ascribed to 201*Pb measurement error. A least square fit line, after York (1969)., has been fitted to the lead compositions from the Fox Creek Fault and is shown in Figure 3. This best fit line does not intersect within experimental error the ore zone lead composition. Figure 4 shows on the 2 0 8Pb/20,,Pb vs. 20 6Pb/2<"*Pb plot much the same relationships as that shown on the 2 0 7Pb/201*Pb vs. 2 0 6Pb/20,|Pb plot in Figure 3. The Fox Creek Fault leads form an anomalous linear array while the leads of the main ore zones of the Geco, Willroy, and 1 3.0 14.0 _l I I L. U 16 18 20 2"2 206 /204 Pb/ Pb 24 2 6 2 8 30 32 Figure 3 20 7Pb/20,,Pb - 2 0 6Pb/201,Pb compositions for galena from Manitouwadge, Ontario. Growth curve after Cooper et. al. (1969) labeled in units of billions of years before; present. 54 33.6 206 /204 Pb/ Pb Figure 4 2 08 Pb/201*Pb - 2 0 6Pb/2 0 4,Pb compositions for galena from Manitouwadge, Ontario. Growth curve after Cooper et. al. (1969) labeled in units of billions of years before present. - 17 -Willecho mines form a tight cluster of values above the growth curve. A section of Figure 4 containing the ore zone leads has been plotted at a more detailed scale and shows the isotopic compositions have a lineation along a 20l*Pb error line. A least square fit line, after York (1969) , through the Fox Creek Fault leads is well defined on this plot which seldom shows isotopic relations as well as the 2 0 7Pb/20l>Pb vs. 2 0 6Pb/2("*Pb plot. The anom alous line in this Figure 4 diverges even farther away from the ore zone lead composition than in Figure 3. Problems presented by the isotopic composition of lead at Manitouwadge to previous interpreters may assist in explaining the present results. At the University of Toronto, Russell and Farquhar (1957) made the first analyses of the lead isotopic com position of galena from Manitouwadge. They found that the lead composition of the main ore zone came from an environment of U-Th-Pb similar but not equal to that of many conformable ore deposits. Stanton and Russell (1959) suggested that conformable ore deposits usually have a simple lead isotopic evolution model while leads from vein type environments have a more complex evolution. Galena leads at Manitouwadge however presented a problem to this hypothesis because they were homogeneous and fit Stanton's classification for conformable ore deposit and yet plotted below the simple - 18 _ model growth curve determined by many younger conformable deposits. Ostic (1963) discovered a highly anomalous lead composition within the Fox Creek Fault at Manitouwadge. This led to the suggestion by Slav/son et. al. (1963) and Ostic et. al. (1967) that the Manitouwadge ore zone is part of an anomalous lead suite directly related to the anomalous leads along the Fox Creek Fault. Ostic regarded the ore zone lead composition to be contaminated slightly by anomalous leads similar to that found along the Fox Creek Fault. A different interpretation of the lead isotopic composition at Manitouwadge was made by Tilton and Steiger (1965) and Tilton and Steiger (1969). Their argument is straight forward. They postulated that the longer lead is mobile in the earth the better are its chances to com bine with leads from other U-Th-Pb systems and so become anomalous. They thought best to base calculations of the age of the earth on very ancient lead mineralizations which may have had less chance for contamination. Manitouwadge was chosen as a single example of an old mineralization and was combined in a single stage growth equation to calculate the age of the earth. Tilton and Steiger rely heavily on the observations by Pye (1957) that the ore zone mineralization must have been after emplacement of the Kenoran intrusives which date by Rb-Sr at about 2700 million years. The earths age is then - 19 -calculated as 4700 million years or about 200 million years older than previously calculated by Ostic et. al. (1963). It is interesting to note that Tilton and Steiger ignore the possible anomalous nature of the ore at Manitouwadge as postulated by Slawson et. al. (1963). (1963) and Tilton and Steiger (1965) and (1969) is a difference in views on the origin of the main ore zone deposits. The results of this study listed in Table 1 and shown on Figure 3 and Figure 4 have a definite bearing on the origin of the ore at Manitouwadge and may help to clear up the above mentioned differences of opinion. Fault form a linear array as can be seen in Figure 3 and Figure 4. The slope of the line determined by these anomalous compositions may be used to determine the latest times of mineralization along the Fault zone. The times obtained in this analysis are independent of the number of mixing stages that the lead has gone through, Kanasewich (1962) and Kanasewich (1968). If a three stage model is assumed to represent the lead along the Fox Creek Fault and the slope of the anomalous line is R then: This difference of opinion between Slawson et. al. The anomalous leads from within the Fox Creek R = 137.8 (e 1 (e X't2 Xt2 If t3 is allowed to be zero which would correspond - 20 -to a t3 mineralization yesterday, it is found that for a slope of 0.168±.003, on Figure 3, that tz must be 2580+50 million years. This age which coincides with the Kenoran Orogeny, would be the maximum time for emplacement of the uranium parent of the anomalous leads into the crust. Another time limit to mineralization may be obtained if t3 is allowed to equal t2 in the equation above. This gives 1580+40 million years for the t2 event. This time corres ponds to the minimum time for uranium emplacement into the crust and is also a maximum time for a final t3 mineralization. This interpretation suggests a final mineralization along the Fault somewhere in the time between the present and 1580 million years ago. A geologically reasonable time for this mineralization is 1100 million years ago during the Keweenawan age. During the Keweenawan a vast amount of volcanism occurred in the Southern Province of the Canadian Shield with a structural boundary about 50 miles south of Manitouwadge. Archean terrain surrounding the Southern Province was also riddled with dike swarms at this time. Certainly temperatures necessary to mobilize galena solutions existed then, and may have caused mineralization along the Fox Creek Fault. Possibly the Fox Creek Fault itself is a result of crustal cooling after the Keweenawan intrusive activity. A large diabase dike supposedly Keweenawan in age lies parallel to and 150 feet west of the Fox Creek Fault. - 21 -If t3 is placed at 1100 million years, t2 becomes 2000165 million years. The corresponding Th/U ratio for the source region of the anomalous leads is then calculated as 5.3, Kanasewich (1962) . Some event that we do not know about may have caused the Fox Creek Fault galena mineralization, in which case the above mentioned times are wrong. It is of little use to theorize with so many unknowns. The lead isotopic composition of galena from within the main ore zone at Manitouwadge is extremely homogeneous as may be seen on Figure 3 and Figure 4. The compositions show a spread along a 20''Pb error line. It is not possible to distinguish a pattern to these sample compositions which come from widely separated points along the ore zone. Galena lead from the main ore zone at the Geco mine is indistinguishable from Willecho mine galena lead 7 miles ' away. Homogeneity in lead isotopic composition is one of the characteristics of a primary lead as observed by Stanton, and Russell (1959) . Another characteristic of primary lead ores noticed by Stanton and Russell (1959) is a conformable relation to its host rock. The ore zone deposits are definitely conformable (see Figure 1) within the metasedimentary grey gneiss unit. The ore zone leads at Manitouwadge obey, as well as can be discerned, two of the criteria of Stanton and - 22 -Russell (1959) for distinguishing a primary lead and yet these same leads plot well below the primary lead growth curve determined by many younger deposits. Primary growth curves of Ostic et. al. (1967) and Cooper et. al. (1969) have 2 3 8U/20l*Pb ratios of 8.94 and 8.79 respectively while the primary model 2 3 8U/201*Pb ratio for Manitouwadge is well below these at 8.23. The ore zone isotopic composition at Manitouwadge if "primary" is certainly different from other primary lead systems. It is not surprising that Tilton and Steiger (1969) should postulate Manitouwadge ore zone lead as a true primary lead and use it in a single stage lead growth equation since the ore zone leads do have a gross simil arity to other primary leads. Tilton and Steigers evid ence for the ore to be 2700 million years old, post Kenoran intrusion, is not strong. Recent observations by Sangster .(1971) on sulphide stability during metamorphism and observations by Suffel et. al. (1971) of metamorphic textures within the Manitouwadge ore zone suggest a much older age to the ore zone than Kenoran. Therefore the calculation by Tilton and. Steiger placing the age of the earth at 4700 million years is based on an age which is much too young for the ore at Manitouwadge. Ore zone deposits at Manitouwadge are probably of sedimentary origin, abundant iron formation adjacent to the ore suggests a sedimentary environment as well. Possibly the ore deposits result from island arc, submarine - 23 -volcanic type sources which deposited the volcanic rocks at Manitouwadge. In Figure 3 and Figure 4 as stated previously no difference can be seen between any of the samples taken from along the ore zone except differences due to 201*Pb error. It is apparent also from these Figures that the anomalous Fox Creek Fault leads are not simply related to the lead isotope composition of the main ore zone. A two-stage mixing model would require ore zone lead com position to plot on the projection of the Fox Creek Fault anomalous lead line. In order to relate these two com positions genetically at least a three stage lead model must be employed. The ore zone lead composition must have existed within the fault zone prior to anomalous lead mineralization since the fault offsets the Geco orebody 200 feet north on the eastern side. High linearity of lead isotope compositions from the Fox Creek Fault suggests a mixture of two fairly homogeneous end members therefore, the ore zone lead would have had to be throughly mixed with some anomalous or primary lead and the final composition would then have to lie somewhere on the extension of the anomalous lead line. A 4 or 5 stage history of lead growth could be used to relate the ore zone isotopic composition to the fault zone but too many unknowns exist to do this. The normalized results of samples analysed from in and around the Manitouwadge area by Ostic (1963) Doe, - 24 -Tilton, and Hopson (1965), Hart and Tilton (1966) and Tilton and Steiger (1969) are presented in Table 2. Sample 2 0 6pb 2 0 7Pb 2 0 8Pb 20 wpb 2 0 tpb 20 '•Pb Ostic (1963)* 33 2 V7illroy mine, galena 13 .311 14. 423 33. 192 369 Willecho mine, galena 13 .316 14. 425 33. 257 370 Geco mine, galena 13 .319 14. 427 33. 233 372 Fox Creek Fault, galena 29 .785 17. 503 46. 883 Doe, Tilton and Hopson (1965)t KA 46 Echo Trail, Minnesota, feldspar 13 .572 14. 52 33. 06 KA 82 Birchdale, Minnesota, feldspar 13 .44 14. 48 33. 14 KA 249p Cusson, Minnesota, feldspar 13 .681 14. 58 33. 08 KA 356p Echo Trail, Minnesota, feldspar 13 .44 14. 53 KA 354 Ben Island, Ontario, feldspar 13 .51 14. 57 33. 10 Hart and Tilton (1966)§ Lake Superior sediment total sample 20 .53 15. 87 40. 34 acid leach 22 .84 16. 34 42. 86 water leach 22 .48 16. 20 42. 34 Tilton and Steiger (1969)t MG 4 8 Geco mine, galena 13 .26 14. 43 33. 39 MG 38 Willroy mine, galena 13 .26 14. 46 33. 38 MG 19 feldspar 13 .63 14. 57 33. 39 MG 20 feldspar 13 .82 14. 59 33. 35 MG 41 feldspar 13 .80 14. 57 33. 35 MG 45 feldspar 13 .55 14. 64 33. 34 * Normalized to absolute values of Broken Hill. Russell (unpublished) 16.009, 15.395, 35.70. t Normalized to absolute values of C.I.T. Russell (unpublished) 16.586, 15.425, 36.14. § Values not normalized. Table 2 The data from Table 2 above has been combined with the new data reported in Table 1 and has been plotted on conventional 2 0 7Pb/2(MtPb vs. 20SPb/20"pb and 208Pb/20*Pb vs. 2 0 6Pb/20l4Pb plots in Figure 5 and Figure 6 respectively. In each of these two Figures, only the new analyses for Fox Creek Fault leads reported in Table 1 were used in fitting the least square line shown. In this respect Figure 3 through Figure 6 are identical. A single stage growth curve after Cooper et. al. (1969) has been added to each plot. In Figure 5 the lead isotopic values fall in two distinct areas. One area is below the single stage growth curve and has been drawn at a more detailed scale within the figure. Lead compositions within this area are of two kinds, galena lead and feldspar lead. Galena lead com positions reported by this study . (see also Figure 3 ) show a definite lineation along a 20l*Pb error line-. Lead compositions for galena reported by Ostic (1963) and Tilton and Steiger (1969) do not fall significantly off this error line. Intralaboratory differences probably cause the spread of values shown here. The feldspar leads of Tilton and Steiger (1969) are from granitic rocks and pegmatites associated with the Kenoran Orogeny from around Manitouwadge and from other Kenoran areas of Ontario and Minnesota. The feldspar leads show more scatter than the ore zone leads due to the wide area from which samples were taken, these leads also lie beneath the growth curve. The second area of Figure 5 lies along a linear array Single Stage Growth Curve \ \ \ \ 1 4 ! 1 1 • 1 < r 1 * 1 — ~~ " I——" —1 — " ~~~ ~~ * / + CP / * A •/ 204Pb • error line s ...... • 1 1 3.0 1 4.0 Fox Creek Fault galena (This work) Ore Zone galena (This work) Ostic (196J) galena Ti Iton & Ste iger (1969) galen Ti Iton & Ste ige r (l 969) and Doe, Tilton & Hopson (1965) feldspar |ead Hart & Tilton (l 966) Lake Superior sediment 14 16 18 20 2 2  4 26 2 8 3 0 3 2 206Pb/204Pb Figure 5 2 0 7Pb/201,Pb - 2 0 6Pb/20,,Pb compositions of rocks and ores at Manitouwadg Ontario and its environs. This figure shows all pertinent data to date - 27 -33.6 | 1 1 • 1 1 1 ' 1 r 206Pb/204Pb Figure 6 208Pb/20*Pb - 2 0 6Pb/20,*Pb compositions of rocks and ores at Manitouwadge, Ontario and its environs. This figure shows all pertinent data to date. - 28 -of points to the right of the growth curve. The anomalous lead composition found by Ostic (1963) from the Fox Creek Fault lies close to the line defined in this study. Possibly intralaboratory differences if known, would bring this composition down to coincide with the line. Lake Superior sediment values of Hart and Tilton (1966) fall extremely close to the line determined by the Fox Creek Fault galenas. These values of Hart and Tilton (1966) have not been normalized to any absolute standard. Figure 6 is the 2 0 8Pb/2tMlPb vs. 2 0 6Pb/20,,Pb plot for the combined results to date on Manitouwadge and shows much the same relation as in Figure 5. Three areas of lead isotope compositions may be found in this figure, one adjacent to the growth curve and two others which form distinct linear arrays. The area adjacent to the growth curve shows the galena values of Ostic (1963), Tilton and Steiger (1969) and the new data of this report scat tered along a 201*Pb error line. Feldspar leads in this figure show similar variation to the feldspar leads plotted on the 2 0 7Pb/2CMtPb vs. 206Pb/20*Pb plot of Figure 5. Fox Creek Fault lead analysed by Ostic (1963) falls on the line determined by the new analyses although it was not used to determine the line shown here. In this figure the values of Hart and Tilton (1966) from Lake Superior sedi ment form their own linear array well away from the anom alous lead line of the Fox Creek Fault samples. The line determined by these sedimentary lead compositions passes - 29 -close to the general lead composition of Archean rocks and ores at Manitouwadge, Fox Creek Fault lead samples may not be at all related to the samples of the ore zone. The Geco ore is primarily copper-zinc, and grades less than one percent lead. It is probable therefore that very little of the ore zone lead exists in the Fox Creek Fault zone. The fault at the Geco mine consists of a breccia zone up to 80 feet wide and is extremely wet underground. Pye (1957) states that post fault pyrite, marcasite, and galena mineralization pos sibly related to hot solutions caused by Keweenawan dike intrusion has occurred within the fault zone. The author has noticed that large galena crystals seem to exist in the fault zone invariably associated'with calcite, while ore zone galena crystals are normally smaller, more dis seminated and associated with silicates or massive sulphides. No variation of isotopic composition with depth in the fault seems to exist. The author prefers a zero correlation model between the ore zone leads and the Fox Creek Fault leads analysed to date. The three or more stage mixing model required to relate the ore zone leads to the fault zone leads appears complex. A complete isotopic homogenization of lead within the fault zone, prior to a final anomalous mineral ization as required by a multistage model appears less likely than a simple mineralization completely unrelated to the ore zone lead isotopic composition. - 30 -The results of Russell and Farquhar (1957) are of interest here although their analyses are from an older technological era and cannot be directly compared with any of the newer data presented here. Russell and Farquhar analysed galena from certain faults cutting Keweenawan age rocks around Thunder Bay, Ontario, and found they were anomalous. The anomalous lead isotopic composition of galena from these faults formed a linear array very much the same as the Fox Creek Fault anomalous leads except the slope is steeper (.186) on a 2 0 7Pb/20l*Pb vs. 2 0 6Pb/20l,Pb plot. These anomalous leads were not simply related to Keewatin type leads analysed by Russell and Farquhar from Steeprock Lake, Ontario, Sioux Lookout, Ontario and from Manitouwadge. This result is similar to the new results reported here from within Manitouwadge1s Geco mine itself. This similarity strengthens the argument that the leads along the Fox Creek Fault are related to Keweenawan igneous activity. The relation of the Fox Creek Fault galenas to Keweenawan intrusives is supported further by the lead isotopic composition of a Lake Superior sediment analysed by Tilton and Hart (1966). This sediment lead, although not normalized to absolute, plots extremely close to the anomalous line determined by the Fox Creek Fault leads. Lake Superior is to a large extent underlain and surrounded by Keweenawan intrusive and volcanic rocks, Halls (1966 ).. - 31 -Estimates by White' (1966) place the total volcanic thickness in parts of Lake Superior at greater than 30,000 feet. The sediment within Lake Superior must be influenced by the huge amounts of Keweenawan rocks around the lakes drainage basin, the similarity of this sediment lead to the lead along the Fox Creek Fault then may hint that fault leads are of Keweenawan origin. It would be interesting to intensively sample the galenas of the fault zone to see if and where the ore zone galenas might be contaminated with these anomalous leads. A lead isotopic composition for the Keweenawan volcanics would be of great use, and in particular an isotopic analysis of lead from the large diabase dike 150 feet west of the Fox Creek Fault would also be interesting. A re-analysis of the Keweenawan galenas studied by Russell and Farquhar (1957) would also assist interpretation. Isotopic variations can possibly be found within single crystals of galena from within the Fox Creek Fault. It would be interesting to knew whether lead emplaced by mineralizing solutions along the fault have become more or less radiogenic with time; single crystal studies should answer this. Sulphur isotope studies may possibly show a difference in source between ore and fault zone galenas. Recent arguments by Richards (1971) and Le Couteur (1973) favour a source for primary lead of conformable ores within the crust itself. This requires a change of - 32 -view on .the words "primary lead", which in their hypothesis is a well-mixed lead from upper crustal sources. The simple explanation of a primary lead originating from a homogeneous U-Th-Pb environment in the mantle to being emplaced into the crust does not appear correct any more. They also suggest that connate brines within a sedimentary basin may act as the agent for both removal and precipitation of ore metals and that this brine solution can allow for the great mobility of lead necessary to produce a homogeneous isotopic composition. Perhaps the ore zone lead at Manitouwadge is actually a primary lead formed in a similar method to those advanced by Richards (1971) and Le Couteur (1973). Previous interpretations of lead isotopes at Manitouwadge have neglected to state that Manitouwadge is primarily a copper-zinc deposit with relatively minor amounts of lead. This small amount of lead makes the. deposit vulnerable to the additions of small amounts of anomalous, multistage lead, early in the sediments' history. This small smount of lead may also hint that the original crust from which these sedimentary metals were derived was at an early stage in its metallogenic evolution, with few lead minerals. - 33 -3.2 SUMMARY The lead isotopic composition of galena from Manitouwadge, Ontario forms two distinct populations. Galena leads from the main ore zone have a remarkably uniform lead isotope composition while galenas from within the Fox Creek Fault form an anomalous linear array of lead isotope compositions. Lead isotopic compositions of galena from the Fox Creek Fault form an anomalous lead line on a standard 20 7pb/20-pb vs> 2 0 6pb/20i*pb plQt and a 20 8pb/20Hpb V£, # 206Pb/20*Pb plot. Time limits obtained from the slope of the anomalous line place 2580+50 million years as the maximum age of emplacement for the uranium parent of the anomalous leads into the crust. The minimum time for uranium emplacement is 1580+40 million years which is also a maximum time for final lead mineralization along the Fox Creek Fault. The last geologically reasonable time for galena mineralization along the Fault is during the Keweenawan age, 1100 million years ago. Using this time for final galena mineralization requires an age of 2000 million years for the time of uranium emplacement into the crust. The corresponding Th/U ratio for the source of the anomalous component of leads along the Fox Creek Fault is 5.3. Possibly the Fox Creek Fault is itself a result of Keweenawan igneous intrusive activity. - 34 -The lead isotopic composition of lead in galena sampled from the main ore zone does not show any linear trend, other along a 20l*Pb error line, that might support an argument to classify them as anomalous leads. The lead isotopic composition from the main ore zone plots below the single stage lead growth curve of Cooper et. al. (1969) determined by many younger primary lead deposits. It is not yet resolved whether the ore zone leads are actually primary or anomalous. The ore deposits are probably much older than the 2700 million year age postulated by Pye (1957) and Tilton and Steiger (1969). Metamorphic textures in the ores as observed by Suffel et. al. (1971) support this idea. Ore only occurs within metasedimentary rocks which does not appear to support a Kenoran Orogenic age of the ore as required by Tilton and Steiger (1969) . Possibly the ores are the result of submarine volcanism and were deposited as a sediment in an ancient ocean. Possibly a crustal averaging process similar to those described by Richards (1971) and Le Couteur (1973) formed the ores at Manitouwadge. The ore zone lead isotope composition is not related in a simple fashion to the lead isotope composition along the Fox Creek Fault. At least a three stage mixing model is required to relate ore zone leads to Fault zone leads. It is very possible that Fox Creek Fault leads sampled to date are not at all related to ore zone leads - 35 -since less than one percent of the ore is lead at the Geco mine. Detailed studies of lead isotopes in the Fox Creek Fault would be interesting. It should be possible to find ore zone leads contaminated by anomalous leads in or near the Fault. Single crystal lead isotopic variations can possibly be measured from Fox Creek Fault galenas. It would be interesting to know whether mineralizing solutions along the Fault have become more or less radiogenic with time. Lead isotope determinations of the large diabase dike 150 feet west of the Fox Creek Fault have not been done and are suspected by the author to be very similar to the Fox Creek Fault leads. Sulphur isotope studies may be able to distinguish between ore and fault zone leads. - 36 -REFERENCES Blenkinsop, J. (1972) . Computer-assisted mass spectrometry and its application to rubidium-strontium geo-chronology. Unpublished Ph, D. thesis, University of British Columbia. Brown, W. L. and Bray, R. C. E. and Mine Staff (1960) . The geology of the Geco mine. Can. Min. and Met. Bull., 63, 1. Catanzaro, E. J., and Gast, P. W. (1960). Isotopic com position of lead in pegmatite feldspars. Geochim. Cosmochim. Acta, 19, 113. Catanzaro, E. J., Murphy, R. J., Shields, W. R., and Garner, E. L. (1968). Absolute isotopic abund ance ratios of common, equal atom and radiogenic lead isotopes standards. J. Res. Nat. Bur. Stand., 72A, 261. Chown, E. H. M. (1957). Geology of the Willroy Property. Unpublished M. A. Sc. thesis, University of British Columbia. Composton, W., and Oversby, V. M. (1969). Lead isotopic analysis using a double spike. J. Geophys. Res., 74, 4 338. Cooper, J. A., Reynolds, P. H., and Richards, J. R. (1969) Double spike calibration of the Broken Hill standard lead. Earth Planetary Sci. Letters, 6, 46 7. Daliwitz, M. J. (1969). Fractionation corrections in lead isotopic analysis. Chemical Geology, 6, 311. Dodson, M. H. (196 3). A theoretical study of the use of internal standards for precise isotopic analysis by the surface ionization technique. J. Sci. Instrum., 40, 289. Doe, B. R., Tilton, G. R., and Hopson, C. A. (1965). Lead isotopes in feldspars from selected granitic rocks associated with regional meta morphism. J. Geophys. Res., 70, 1947. Goldich, W. W., Nier, A. D. , Baadsgaard, H., Hoffman, J. II., and Krueger, H. W. (1961). The Precambrian geology and geochronology of Minnesota. Minn. Geol. Survey Bull. 41, 193p. - 37 -Graham, R„ A. F. (1967). Metamorphism of Willroy sulphide ore minerals by diabase dikes . Unpublished M. Sc, thesis, Univ. of Western Ontario. Halls, H. C. (1966). A review of Keweenawan Geology of the Lake Superior region. In: The earth beneath the continents, Am. Geophys. Union Geophys. Mon. Ser., No 10, 3. Hamilton, E. I. (1965). Applied Geochronology Academic Press, London - New York, 267p. Hanson, G. M., Goldich, S. S., Arth, J. G., and Yardley, D. H. (1971). Age of early Precambrian rocks of the Saganaga Lake—Northern Light Lake Area, Ontario—Minnesota. Can J. Earth Sci., 8, 110. Hart, S. R., and Tilton, G. R. (1966). The isotope geo chemistry of strontium and lead in Lake Superior sediments and water. In: The earth beneath the continents, Am. Geophys. Union Geophys. Mon. Ser., 10 127. Kanasewich, E. R. (1962). Approximate age of tectonic activity using anomalous lead isotopes. Roy. Astron. Soc. Geophys. J., 7, 15 8. Kanasewich, E. R. (1968). The interpretation of lead isotopes and their geological significance. In: Radiometric Dating for Geologists., Hamilton, E. I. and Farquhar, R. M. (eds.). Kraus, K. A. and Nelson, F. (1955). Anion exchange studies of fission products. Proceedings International Conference on the Peaceful Uses of Atomic Energy. 7, United Nations, New York. Le Couteur, P. C. (1973). A study of lead isotopes from Min Mineral Deposits from Southeastern British Columbia and from the Anvil Range, Yukon Territory, Unpublished Ph. D. thesis, University of British Columbia. Mookherjee, A. (1970), Dykes, sulphide deposits and regional metamorphism: Criteria for determining their time relationship. Mineral Deposita 5 pp. 120 - 144. Mookherjee, A. and Dutta, N. K. (19 70). Evidence for • incipient melting of sulphides along a dike contact, Geco mine, Manitouwadge, Ontario. Economic Geol., 65, 706. - 38 -Ostic, R. G. (1963). Isotopic investigiation of conformable lead deposits. Ph. D. Thesis, University of British Columbia. Ostic, R. G., Russell, R. D., and Reynolds, P. H. (1963). A new calculation for the age of the earth from abundances of lead isotopes. Nature, 199, 1150. Ostic, R. G., Russell, R. D., and Stanton, R. L. (1967). Additional measurements of the isotopic composition of lead from strataform deposits. Can. J. Earth Sci., 4,245. Pye, E. G. (1957). Geology of the Manitouwadge area. Ontario Dept. Mines Report, 66, 8. Richards, J. R. (1971). Major lead orebodies—Mantle Origin? Economic Geol., 66, pp. 425 - 434. Russell, R. D. and Farquhar, R. M. (1960). Lead Isotopes in Geology, Interscience, New York. Russell, R. D. and Farquhar, R. M. (19 57). Anomalous leads from the upper Great Lakes region of Ontario. Transactions, Am. Geophys. Union 38, 552. Russell, R. D., Blenkinsop, J., Meldrum, R. D., and Mitchell, D. L. (1971). On-line computer assisted mass spectrometry for aeological research. Mass Spectroscopy, 19, 19. Russell, R. D. (1972). An evolutionary model for lead isotopes in conformable ores and in ocean volcanics. Rev. Geophys. and Space Phys. 10,529. Sangster, D. F. (1971). Metamorphism as an ore-forming process. Economic Geol., 66, 499. Slav/son, W. F., Kanaswich, E. R., Ostic, R. G., and Farquhar, R. M. (1963). Age of the North American crust. Nature, 200, 413. Stacey, J. S., Delevaux, M., and Ulrych, R. J. (1969). Some triple-filiment lead siotope ratio measure ments and an absolute growth curve for single stage leads. Earth Planetary Sci. Letters, 6, 15. - 39 -Suffel, G. G., Hutchinson, R. W., and Riddler, R. H. (1971). Metamorphism of massive sulphides at Manitouwadge, Ontario, Canada. In: Soc. Mining Geol. Japan Spec. Issue 3, 235. Tilton, G. R. and Steiger, R. H. (1965). Lead isotopes and the age of the earth. Science, 150, 1805. Tilton, G. R. and Steiger, R. H. (1969). Mineral ages and isotopic composition of primary lead at Manitouwadge, Ontario. J. Geophys. Res., 74, 2118. Timrcs, P. D. and Marshall, D. (1959). The geology of the Willroy mines base metal deposits. Proc. Geol. Assoc. Canada, 11, 55. Ulrych, T. J. (1967). Oceanic basalt leads: A new inter pretation and an independent age for the earth. Science, 158, 252. White, W. S. (1966). Geologic evidence for Crustal structure in the Western Lake Superior basin. In: The earth beneath the continents. Geophys. Mon. Ser., Am. Geophys. Union, 10, 28. Williamson, J. H. (1968). Least squares fitting of a straight line. Can. J. Phys., 46, 1845. York, D. (1969). Least squares fitting of a straight line with correlated errors. Earth Planetary Sci. Letters, 5, 320. York, D. and Farquhar, R. M. (1972). The Earths Age and Geochronology. Pergamon Press, Toronto. - 40 -APPENDIXES A. Ion exchange column preparation This is a procedure suggested by Dr. Ulrych at this lab, which is modified from a procedure given in Catanzaro and Cast (1960) . Figure A-l shows this procedure. The materials necessary for this procedure are dowex (1x8, 100-200 mesh) resin in chloride form, an ion column, 1,5 molar reagent grade hydrochloric acid, and pure distilled water. The fine particles were removed from about 100 grams of the resin by mixing it with 100 milliliters of 1,5 molar hydrochloric acid and pouring off the fine slower settling particles. This was repeated about three times to remove most of the fine resin particles. A slurry of resin and 1.5 molar hydrochloric acid was then poured into a clean glass ion column and allowed to settle to form a 28 to 29 centimeter length of resin in the column. The excess resin was carefully poured out of the column. About 200 milliliters of distilled water was then allowed to pass through the column followed by about 100 milliliters of 1.5 molar hydrochloric acid. This prepares the resin before introduction of lead chloride into the column. Lead chloride was dissolved to saturation in 100 FIGURE A-l SAMPLE PREPARATION FLOW CHART discard silicates 8 other sulphides STORE CRYSTALS ROCK SAMPLE goiena precipitate PbCl crystals  decant liquid 4 wash crystals 1 R IN SE ALCONOX + H20 BATH 10% HN03 BATH RINSE prepare column for new sample ION EXCHANGE COLUMN OOWEX IX 8 DESORB with pure H,0 precipitate PbCl crystals DI RTY GLASSWARE STORE convert to Pb[N03]2 crystalline PD[N03]J in 20ml. IM. HNO, TAKE -003gm. Pb[N03]8 + |Oml. 2(%) HNOj— SAMPLE READY LOAD FILAMENT - 42 -milliliters of 1„5 molar hydrochloric acid, and was poured into the column. Lead ions would be split within the resin from chlorine and would adhere to the resin. After this adsorption phase the lead ions may be desorbed completely from the resin in either 0 molar or 8 molar hydrochloric acid. For this study 0 molar hydrochloric acid (distilled water) was used for desorption. The first 10 to 15 milliliters of solution from the ion column during desorption with distilled water does not contain an appreciable concentration of lead. The results of a short test for lead is given in Table A-l. Approx. Time (minutes) Volume (ml.) pH Potassium Iodide Test 10 10 3.5 negative 20 20 3.5 positive 30 30 4.5 slight positive 40 40 5.0 negative Table A-l The second 20 milliliters of solution usually contains a high concentration of lead as determined by the potassium iodide test. Only this concentrated lead solution was collected. The column after lead desorption is then eluted with 200 milliliters of pure distilled water followed by 100 milliliters of 1.5 molar hydrochloric acid and the column is ready for another sample. Care must be taken to wash the - 43 -sides of the column reservoir in the distilled water phase to avoid contamination between samples. A test was made for contamination between samples by passing a radiogenic Fox Creek sample through the ion column immediately prior to Broken Hill. The values for Broken Kill were not affected as shown in Table A-2. Column #1 Date Sample 2 0 6Pb "2 0 4pb 2 0 7Pb 2 0 8Pb 2 0 "»Pb Feb. 28, 1972 786 Fox Creek Fault 32.10 17.893 50.52 Mar. 1, 1972 001 Broken Kill 16.004 15.358 35.52 001 Broken Hill (Russell) 16.009 15.395 35.70 001 Ave. of 6 15.991 15.367 35.58 Table A-2 - 44 -B. Silica gel - Lead nitrate loads The materials necessary for a silica gel lead nitrate load are listed below: - outgassed rhenium filament - lead nitrate solution ^ 300 p.p.m. in 2% HN03 - clean pipettes - silica gel solution - phosphoric acid (reagent grade), 0.375 N. - filament block - a.c. current generator (1 watt peak power)" - a.c. voltmeter and ammeter The following procedure worked well it was found, but variants on this procedure may work as well. The silica gel solution-suspension was agitated briskly and then left to stand quietly for one to two minutes. A large drop was then removed with a clean pipette and placed on the filament. The filament was then heated slowly by passing an alternating current through it of less than 1.0 ampere keeping a voltage of about 0.2 volts. Best results occur at this point if the silica gel is not allowed to lose all its water; heating was stopped when a translucent gel was visible on the filament. One medium size drop of lead nitrate was then placed on the filament followed by a small drop of phosphoric acid, 0.375 N. The excess liquid was evaporated from the filament with further heating at 1.0 amp, 0.2 volts until the translucent gel mass appeared on the filament. If a fair amount of silica gel was present on the filament then further heating could proceed. Often a small "capping" drop of gel was placed on top at this stage to ensure enough gel. The filament was next brought rapidly to a glowing red heat (about 1,8 amperes and 0.6 volts) for about 20 seconds and then allowed to cool. The mixture of gelf lead nitrate and phosphoric acid should turn white with initial heating and may give off white smoke for a time. The sample is now ready to be placed into the source assembly of the mass spectrometer. C. Precision and Double Spiking Replicate analyses of galena lead from Broken Hill, the U.B.C. standard, are given in Table C-l and shows good precision. Differences between these values and absolute values for Broken Hill as reported by Cooper et. al. (1969) or Russell (unpublished data) are not significant to material presented in this thesis. Run 2 0 6Pb 2 0 7Pb 2 0 8Pb 2 0 X pb 20 <*Pb 2 0 i* pb 1 15.998 15.379 35.65 2 15.978 15.363 35.58 3 15.991 15.368 35.63 4 15.977 15.360 35.58 5 16.000 15.376 35.55 6 16.004 15.358 35.52 Mean 15.991 15.367 35.58 Standard Error .005 .004 .019 Cooper etc al. 1969 16.003 15.390 35.66 Russell (unpublished) 16.009 15.395 35.70 Table C-l Calibration of the U.B.C. 207Fb - 20"Pb double spike was done against the N.B.S. equal atom standard S.R.M. 982 and is shown in Table C-2 below. The small fractionation corrections shown in Table C-2 are normal for silica gel-phosphoric acid procedures. - 47 -2 0 6pb 2 0 4Pb 2 0 7Pb 2 0 wpb 20 8pb ToTpb Measured Ratio Spike Corrected Ratio .2765 .2766 9.512 9.520 .6049 .6065 Measured Ratio Spike Corrected Ratio .2782 .2785 9.505 9.521 .6061 .6075 Average Corrected Ratio .2775 9.520 .6070 Table C-2 The results from double spiking tvzo Manitouwadge samples are shown in Table C-3. Spike corrections seen here are not significant to the isotope differences studied in this thesis and so have been ignored. Sample 2 0 6Pb 2 0 <*pb 2 0 7Pb 2 0 i* Pb 2 0 8Pb 2 0 4Pb 789 Measured Ratio Spike Corrected Ratio % difference 13.195 13.205 .08 14.377 14.393 0.11 32.96 33.01 0.15 786 Measured Ratio Spike Corrected Ratio % difference 32.10 32.14 0.12 17.868 17.906 0.16 50.49 50.63 0.28 Table C-3 


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