Emission spectrographic determination of volatile trace elements in geologic materials by a carrier distillation technique

Journal of Geochemical Exploration, 25 (1986) 367--378 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

367

EMISSION SPECTROGRAPHIC DETERMINATION OF VOLATILE T R A C E ELEMENTS IN G E O L O G I C M A T E R I A L S BY A C A R R I E R DISTILLATION TECHNIQUE

H.N. BARTON U.S. GeologicaI Survey, Federal Center, MS 973, Box 25046, Denver, CO 80225, U.S.A.

(Received June 14, 1985; revised and accepted November 19, 1985)

ABSTRACT

Barton, H.N., 1986. Emission spectrographic determination of volatile trace elements in geologic materials by a carrier distillation technique. J. Geochem. Explor., 25: 367-378. Trace levels of chalcophile elements that form volatile sulfide minerals are determined in stream sediments and in the nonmagnetic fraction of a heavy-mineral concentrate of stream sediments by a carrier distillation emission spectrographic method. Photographically recorded spectra of samples are visually compared with those of synthetic standards for the two sample types. Rock and soil samples may also be analyzed by comparison with the stream-sediment standards. A gallium oxide spectrochemical carrier/buffer enhances the early emission of the volatile elements. Detection limits in parts per million attained are: Sb 5, As 20, Bi 0.1, Cd 1, Cu 1, Pb 2, Ag 0.1, Zn 2, and Sn 0.1. A comparison with other methods of analysis, total-burn emission and atomic absorption spectroscopy, shows good correlation for standard reference for materials and samples from a variety of geologic terranes. INTRODUCTION C h a l c o p h i l e elements are i m p o r t a n t i n d i c a t o r s o f a variety o f d e p o s i t t y p e s : p o r p h y r y Cu massive sulfide, c o n t a c t m e t a s o m a t i c , and Mississippi V a l l e y - t y p e s t r a t a b o u n d deposits; e p i t h e r m a l veins, s t o c k w o r k s , a n d diss e m i n a t i o n s ; a n d s a n d s t o n e - h o s t e d Pb-Zn and Cu deposits (Boyle, 1 9 7 4 ; Erickson, 1982). These e l e m e n t s have been d e t e r m i n e d generally b y either emission s p e c t r o g r a p h y , w h i c h yields d e t e r m i n a t i o n s for m a n y metallic e l e m e n t s f r o m a single analysis a n d has m o d e s t t o g o o d limits o f d e t e c t i o n a n d precision, or b y a t o m i c a b s o r p t i o n s p e c t r o s c o p y , w h i c h d e t e r m i n e s each e l e m e n t s e p a r a t e l y a n d gives b e t t e r precision and d e t e c t i o n limits b u t requires a greater e x p e n d i t u r e o f e f f o r t in sample p r e p a r a t i o n and dissolution. The volatility o f t h e sulfides o f t h e c h a l c o p h i l e e l e m e n t s allows a separat i o n in t h e e l e c t r o d e d u r i n g arcing f r o m the great mass o f m o r e r e f r a c t o r y r o c k - f o r m i n g e l e m e n t s a n d is t h e basis o f t h e carrier distillation m e t h o d . T h e

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368 i n t e r f e r e n c e f r o m these r e f r a c t o r y e l e m e n t s , s o m e having e x t r e m e l y c o m plex spectra, is a v o i d e d because t h e y largely r e m a i n undistilled in the elect r o d e while the volatile e l e m e n t s are v a p o r i z e d i n t o t h e arc t o be dissociated a n d e x c i t e d to e m i t t h e i r characteristic spectra. S e p a r a t i o n o n t h e basis o f volatility d u r i n g arcing was first a c c o m p l i s h e d b y t h e d o u b l e - a r c t e c h n i q u e , in which o n e arc is used f o r h e a t i n g the s a m p l e in a f u r n a c e e l e c t r o d e a n d t h e o t h e r is used to excite t h e escaping vapor. Ahrens ( 1 9 5 0 , 1955) described the m e t h o d s used b y Shaw, J o e s u u , and Ahrens and also t h o s e used b y Wedepohl. S c r i b n e r a n d Mullin (1946), in t h e i r classic carrier distillation m e t h o d a c c o m p l i s h e d b o t h f u n c t i o n s with a single arc in d e t e r m i n i n g i m p u r i t i e s in u r a n i u m oxide. T h e s a m p l e was a r c e d in a d e e p c r a t e r e l e c t r o d e t o selectively volatilize i m p u r i t i e s f r o m the refract o r y u r a n i u m o x i d e a n d avoid e x c i t a t i o n o f t h e c o m p l e x u r a n i u m s p e c t r u m . E n h a n c e m e n t o f volatilities with r e f r a c t o r y b u f f e r s was the basis o f a m e t h o d b y T e n n a n t ( 1 9 6 7 ) f o r t h e d e t e r m i n a t i o n o f volatile trace e l e m e n t s in silicates. T h e m e t h o d d e s c r i b e d here was designed p r i m a r i l y f o r t h e analysis of s t r e a m s e d i m e n t s and t h e n o n m a g n e t i c f r a c t i o n o f a h e a v y - m i n e r a l conc e n t r a t e f r o m s t r e a m s e d i m e n t s , and s t a n d a r d s w e r e p r e p a r e d to a p p r o x i m a t e these t w o s a m p l e media. Gallium o x i d e is used as a s p e c t r o g r a p h i c b u f f e r and carrier.

Spectrograph and operating conditions T h e Bausch and L o m b ' 2-m dual grating stigmatic E b e r t s p e c t r o g r a p h used in this s t u d y utilizes t w o gratings, w h o s e characteristics are s h o w n in T a b l e 1. T h e e n t r a n c e slit d i m e n s i o n s were 10 p m b y 1 m m . S p e c t r a f r o m b o t h gratings were r e c o r d e d on a single 100 b y 2 5 0 m m (4 inch b y 10 inch) K o d a k SA1 p h o t o g r a p h i c plate. Plates were d e v e l o p e d in K o d a k D-19 TABLE 1 Grating characteristics and settings of the Bausch and Lomb 2-m dual grating stigmatic spectrograph used for determination of volatile trace elements Grating

Grooves (mm -~ )

Reciprocal linear dispersion, first order (nm/mm)

Wavelength Spectral region order recorded recorded (nm)

A B

1200 600

0.408 0.823

280--380 247--343

1 2

The use of brand names in this report is for descriptive purposes only and does not constitute endorsement by the U.S. Geological Survey.

369 for 3 minutes at 18.5°C. The anode was an Ultra Carbon Corporation type 7075 graphite crater electrode having a crater diameter of 3.66 m m and a depth of 6.00 mm, and the cathode was an American Society for Testing Materials (ASTM) t y p e C-3 electrode. Excitation was by a 12 ampere d.c. arc for 30 seconds. A 50% transmittance neutral filter was used with grating A. Table 2 presents the wavelength of the primary line for each element and the grating of preference. Grating preference takes into consideration line and background intensities, interferences, and the quality of the spectra. TABLE 2 Primary spectral lines and grating of preference for volatile elements Element

Wavelength Preferred (nm) grating

Ag As Bi Cd Cu Pb Sb Sn Zn

328.068 279.022 306.772 326.106 327.396 283.307 259.806 283.999 334.502

A B B B A A B B A

Sample preparation Stream-sediment samples were sieved to minus 30 mesh (~ 0.6 mm). Heavy-mineral-concentrate samples were hand-panned, dried, and sieved to minus 30 mesh. Low-density minerals were separated by flotation in bromoform (specific gravity 2 . 8 0 - 2 . 8 8 ) . Separation on the basis of magnetic susceptibility using a Frantz Separator 1 yielded a fraction that was nonmagnetic at 0.6 ampere, which consisted mainly o f sulfide minerals and their oxidation products, barite, cassiterite, monazite, rutile, garnet, spinel, and zircon (Lovering and McCarthy, 1978; Reiser et al., 1983; Cathrall et al., 1983). Both stream sediments and heavy-mineral concentrates were ground to approximately 200 mesh (75 pm). A 50-mg sample was mixed with 20 mg gallium oxide and transferred to the electrode. The sample charge was shaped and compressed in the electrode with a conical tipped tool similar to that described by Grimes and Marranzino (1968}. Sample spectra of stream sediments and heavy-mineral concentrates were visually compared with those of the appropriate standards prepared in concentration steps of 1, 2, 5, 10, etc., times various powers (expressed in parts

370 per million). Interpolation o f same readings yielded semiquantitative analysis values o f 1, 1.5, 2, 3, 5, 7, 10, etc.

Standard preparation Standards used for comparison with stream sediments were prepared as described in detail by Grimes and Marranzino (1968). The composition of the nonmagnetic fraction of a heavy-mineral concentrate of a stream sediment can vary widely. The typical mineralogical composition o f nonmagnetic heavy-mineral concentrates was estimated after consultation with T. Botinelly, W.R. Griffitts, and R.B. Tripp of the mineralogical laboratories o f the U.S. Geological Survey (pers. commun., 1980). It contained the following percentages of minerals: sphene (CaTiSiOs), 20%; zircon (ZrSiO4), 20%; rutile, anatase, and brookite (TiO2), 15%; apatite (CaF2" 3Ca3P20~), 10%; kyanite, sillimanite, and andalusite (A12OSiO4), 15%; d o l o m ite (CaMg(CO3)2), 5%; pyrite (FeS2), 5%; and biotite [(K, Na)(Fe, Mg)2(Si3AI)O10(OH)2], 10%. A mixture of oxides and carbonates, hereafter t e rm e d " m a t r i x material", was prepared to have the same metallic element composition as the above typical nonmagnetic heavy mineral concentrate. Ten grams of matrix material were prepared as follows: SiO2, 2.010 g; Al:O3, 0.956 g; Fe203, 0.463 g; CaCO3, 2.962 g; MgO, 0.180 g; ZrO2, 1.214 g; TiO2, 2.091 g; Na2CO3, 0.054 g; and K2CO3, 0.070 g. Matrix material was then used to dilute mixtures and standards containing chalcophile elements. The following three mixtures of elements were prepared: (1) Mixture A, containing 50,000 ppm each of Ag and Bi, was prepared by mixing 78.8 mg AgNO3, 55.8 mg Bi203, and 865.4 mg matrix material to give 1 g total. TABLE 3 Preparation of heavy-mineral concentrate standards Standard number

1 2 3 4 5 6 7 8 9 10

Cu, Pb, Zn (ppm)

5000 2000 1000 500 200 100 50 20 10 0

As, B, Cd, Ag, Bi Sb, Sn (ppm) (ppm)

500 200 100 50 20 10 5 2 1 0

*Use mixture C, described in text.

50 20 10 5 2 1 0.5 0.2 0.1 0

Prepare by mixing Preceding Matrix standard material (rag) (rag) 142" 621 752 704 608 720 640 480 400 0

1279 931 752 704 912 720 640 720 400 800

371 (2) Mixture B, containing 50,000 ppm each of As, Sb, B, Cd, and Sn and 5,000 ppm each of Ag and Bi, was prepared by mixing 63.5 mg SnO2, 286.0 mg H3BO3, 57.1 mg CdO, 66.0 mg As203, 60.0 mg Sb203, 100.0 mg mixture A, and 367.4 mg matrix material to give 1 g total. (3) Mixture C, containing 50,000 ppm each of Cu, Pb, and Zn; 5,000 ppm each of As, B, Cd, Sb, and Sn; and 500 ppm each of Ag and Bi, was prepared by mixing 62.6 mg CuO, 53.8 mg PbO, 62.2 mg ZnO, 100.0 mg mixture B, and 775.2 mg matrix material to give 1 g total. Standards were prepared as shown in Table 3. Standard #1, containing 5000 ppm each of Cu, Pb, and Zn; 500 ppm each of As, B, Cd, Sb, and Sn; and 50 ppm each of Ag and Bi, was prepared by mixing 142.1 mg of mixture C and 1278.7 mg matrix material. Each succeeding lower concentration standard was prepared by diluting the preceding standard with matrix material. The quantities shown in Table 3 provide 800 mg of each standard. RESULTS AND DISCUSSION

Selective volatilization Selective volatilization of the elements from the arc followed that observed by Ahrens (1950}. He described the order of appearance of the elements for free elements, sulfides, and oxides. Sulfates, carbonates, and phosphates decomposed to oxides and behaved similarly. The spectra of the chalcophile elements of interest all appeared prior to those of A1, Ca, Ce, Co, Cr, Fe, La, Mg, Mn, Ni, Sc, Si, Th, Ti, W, Y, and Zr and prior to the band structure of SiO and cyanogen in moving plate studies conducted on synthetic oxide standards, U.S. Geological Survey geochemical exploration standards (Allcott and Lakin, 1978), and heavy-mineral-concentrate samples.

Ejection of sample Ejection of the sample from the electrode during arcing was prevented by the use of a large amount of gallium oxide carrier/buffer {20 mg Ga203 with a 50-mg sample) and by tamping and venting the sample-carrier electrode charge with a conical-tipped tool similar to that described by Grimes and Marranzino {1968). Ejection was common with lesser amounts of gallium oxide or with sodium fluoride as a carrier and was not related to electrode type (UCP 7075 or ASTM S-2) or to sample size. Initiation of the arc at lower current or without high-voltage spark ignition did not prevent ejection, nor did prior heating of the sample in the electrode. High alumina content increased the probability of sample ejection.

Selection of spectroscopic carrier and buffer Tennant (1967) noted that the presence of large amounts of refractory oxides enhanced the intensity of spectral lines of volatile elements. This

372 effect was not found to be beneficial in the present study, though, because the refractory oxides caused sample ejection, spectral interference from line and SiO band spectra, and a high spectral background continuum. Varying amounts of the refractories A1203, MgO, SiO2, A1203 + CaCO3, and SiO2 + CaCO3 were added to the geochemical reference standards of Allcott and Lakin (1978) to study this effect. A relatively large amount (20 mg) of gallium oxide gave uniform excitation of the sample, suppressed Fe, A1, Si, SiO, Ti, Zr spectra, suppressed the background continuum, and prevented sample ejection. Gallium oxide gave slightly better sensitivity than sodium fluoride for elements of interest for both oxide standards and heavy-mineral-concentrate samples. The influence of alkali metal elements was not found to be significant, and the presence of 2% Na2CO3 plus 2% K2CO3 had no detectable effect.

Selection of electrode type Little difference was found in the results obtained with the Ultra Carbon Corporation type 7075 crater electrode and the ASTM type S-2, an anode cap electrode frequently used for carrier distillations. An Ultra Carbon type 101-L combination boiler cap gave superior sensitivity for Hg, approximately equal sensitivity for As and Cd, and less sensitivity for the remaining elements. The Ultra Carbon type 7075 was chosen simply because it was more readily available in this laboratory than the ASTM type S-2.

Detection limits and comparison with total burn method Detection limits for the volatile elements attained with this method are compared to those of a total burn spectrographic method of Grimes and Marranzino (1968) in Table 4. The total burn spectrographic method is a general purpose method used for the determination of 31 elements, both volatile and refractory, in geologic materials.

Analysis of geologic standard reference materials Geologic standard reference materials analyzed by this method were: (1) USGS sample G2 of granitic composition (Flanagan, 1969), (2) USGS synthetic glass reference samples, GSB, GSC, GSD, and GSE {Myers et al., 1976), and (3) USGS geochemical exploration reference samples GXR 1-6 (Allcott and Lakin, 1978). The accepted analytical values for the volatile elements in these standards are compared to those determined by a singlecarrier distillation analysis in Table 5. The set of four artificial glass reference standards, GSB, GSC, GSD, and GSE, prepared for the USGS by Coming Glass Works contained 49 trace elements at concentrations of approximately 0.5, 5, 50, and 500 parts per

373 TABLE 4 Detection limits of volatile elements attainable by this carrier distillation method and by the total burn method of Grimes and Marranzino (1968} Element

Detection limit in parts per million Carrier Total burn method distillation Heavy-mineral Stream concentrate sediments

Ag As Bi Cd Cu Pb Sb Sn Zn

0.1 20 0.1 1 1 2 5 0.1 2

1 500 2O 50 10 20 200 20 500

0.5 200 10 20 5 10 100 10 200

million. T h e a c c e p t e d values o f T a b l e 5 are m e d i a n values f r o m replicate d e t e r m i n a t i o n s b y a n a l y s t s in a n u m b e r o f s e p a r a t e l a b o r a t o r i e s b y a t o m i c a b s o r p t i o n , emission s p e c t r o s c o p y , a n d X - r a y f l u o r e s c e n c e , ranging f r o m 15 d e t e r m i n a t i o n s o n G S B t o 50 o n GSE. T h e G X R s a m p l e s are r o c k a n d soil s a m p l e s c o l l e c t e d f r o m a v a r i e t y o f geologic e n v i r o n m e n t s a n d likewise h a v e b e e n s u b j e c t e d to i n t e r l a b o r a t o r y analysis c o m p a r i s o n s . T h e s e s a m p l e s are b r i e f l y d e s c r i b e d as follows: G X R 1 J a s p e r o i d r e e f in C a m b r i a n l i m e s t o n e . Au, Cu, a n d Mn m i n e d in area. G X R 2 Soil, g r a y - b r o w n l o a m o v e r P e n n s y l v a n i a n q u a r t z i t e . Cu, Pb, Zn, and Ag m i n e d f r o m veins a n d r e p l a c e m e n t s in area. G X R 3 H o t spring d e p o s i t ; Fe- a n d Mn-rich e a r t h y m a t e r i a l c e m e n t i n g alluvium on phyllitic shale, c a p p e d w i t h c a l c a r e o u s tufa. T u n g s t e n m i n e d in area. G X R 4 U n o x i d i z e d p o r p h y r y Cu ore. G X R 5 P o d z o l soil o n glacial till; u n d e r l y i n g b e d r o c k is q u a r t z m o n zonite, n o r i t e , p e r i d o t i t e ; c o n t a i n s d i s s e m i n a t e d c h a l c o p y r i t e . G X R 6 Y e l l o w - r e d soil f r o m shear z o n e ; b e d r o c k is sericitized m u d s t o n e a n d p h y l l i t e , r h y o l i t e , a n d andesitic basalt. G o l d a n d base m e t a l s m i n e d in area. A c c e p t e d values p r e s e n t e d in T a b l e 5 f o r G X R s a m p l e s are m e a n values r e p o r t e d b y A l l c o t t a n d L a k i n ( 1 9 7 8 ) f r o m t h e analyses o f 50 r a n d o m samples o f each b y a t o m i c a b s o r p t i o n or c o l o r i m e t r i c m e t h o d s , w i t h t h e e x c e p tions o f Bi a n d Sn in all s a m p l e s a n d Zn in G X R - 3 , w h i c h w e r e r e p o r t e d o n l y by emission spectroscopy.

G2 GSB GSC GSD GSE GXR1 GXR2 GXR3 GXR4 GXR5 GXR6

Reference standard

0.04 0.5 4 37 380 29 15 1.7 3.6 1.3 1.1 4

<20 150 300 <20 1500 100 <20 150

40 480 540 <10 <10 14 <10 <10

<20

6

2

15 42 100 450 30 290 10 <10 0.5 5 9 0 0 2 62 0.5 16 0.2 270

A <0.5 --

D

Bi

<20 <20

1 0.3

0.7 0.3

A

A

D

As

Ag

2

<0.1 <0.1 15 150 1000 1 <0.1 10 <0.1 <0.1

D

2.5

0.01

30 420 2.1 3.4 1.7 0.9 <0.2 <0.2

A

Cd A

9

10 5

15 45 100 500 <1 1100 <1 66 <1 9.6 <1 6100 <1 360 <1 67

<1

<1 <1

D

Cu

5

20 5 50 500 1500 70 3 10000 300 100

D

15

30 13

D

7

20 7 --

--

A

Sb

0.05

52 30 37 500 300 470 750 700 110 600 500 44 100 20 35 78 50 6.3 53 10 1.8 140 70 4.9

A

Pb

<5 <5 <5 50 100 70 50 50 <5 <5 <5

D

D

A

Zn D

<10 3 80 100 0.6 < 0 . 1 8 <2 5 3 12 <2 43 15 43 50 440 500 500 200 57 70 670 1500 <10 2 490 700 <10 2 <200 200 <10 15 59 100 <10 2 42 50 <10 2 100 150

A

Sn

[ D a t a in p a r t s p e r m i l l i o n . A c c e p t e d v a l u e s are f r o m F l a n a g a n ( 1 9 6 9 ) f o r G2, M y e r s et al. ( 1 9 7 6 ) f o r G S B , C, D, a n d E, a n d A U c o t t a n d Lakin (1978) for GXR1-6.]

A c c e p t e d values ( A ) f o r v o l a t i l e - e l e m e n t c o n t e n t in g e o l o g i c s t a n d a r d r e f e r e n c e m a t e r i a l s a n d v a l u e s d e t e r m i n e d b y t h i s c a r r i e r distillation m e t h o d (D)

TABLE 5

oa

375

Application of method to geochemical exploration The ultimate test of an alaytical method for geochemical exploration is in the results produced; i.e., can it be used to locate a hidden mineral deposit? Stream-sediment samples from the Koiyaktot Mountain locality in the Brooks Range, Alaska (Howard Pass 1 ° × 3 ° quadrangle) provided such a test. An area of moderate to high mineral potential had been previously located from plots of Ag, Cd, Pb, and Zn distribution determined by total burn emission spectroscopy, X-ray fluorescence, and atomic absorption analyses of a variety of sample media, including stream sediments, heavymineral concentrates, oxalic acid leaches of iron-manganese oxide pebble coatings, and oxalic acid leaches of veined streambed rocks (Barton, 1980; Theobald and Barton, 1978; Theobald, pets. commun., 1980). This area of moderate to high mineralization is shown shaded in Figs. 1, 2, and 3, which 156015 ,

6 8 ° 15'

68" 15'

156°15" I

I

I

I

5 I

10 km I

Stream N Lake ~ Area of known mineral potential | Moderate potential BIB High potential

Cadmium c o n c e n t r a t i o n , parts per m i l l i o n o<1

•

7

• • • • •

• •

10 15

1 1.5 2 3 5

Fig. 1. D i s t r i b u t i o n a n d a b u n d a n c e o f c a d m i u m in s t r e a m s e d i m e n t s in t h e K o i y a k t o t M o u n t a i n area, Alaska, d e t e r m i n e d b y carrier distillation m e t h o d , c o m p a r e d t o previously l o c a t e d areas of m i n e r a l p o t e n t i a l .

376 156° 15 '

68 ° 15'

68 ° 15'

156 ° 15' 0

t

5

I

I

i

~

I

Stream <~E> Area : =lib

10 km

1 N

Lake 1~ of known mineral potential Moderate potential High potential

Lead concentration, parts per million o • • •

<10,10 15,20,30 50,70 100,150

• •

500 700

• 200 • 300

Fig. 2. Distribution and abundance of lead in stream sediments in the Koiyaktot Mountain area, Alaska, determined by carrier distillation method, compared to previously located areas of mineral potential. are, respectively, plots o f the distributions and a b u n d a n c e s o f Cd, Pb, and Zn in stream sediments d e t e r m i n e d by the carrier distillation m e t h o d . The close c o r r e s p o n d e n c e o f a n o m a l o u s l y high c o n c e n t r a t i o n s o f all three elements with the previously d e t e r m i n e d areas o f m o d e r a t e to high mineral p o t e n t i a l d e m o n s t r a t e s t h a t the a n o m a l o u s area can be d e t e c t e d and m a p p e d using analyses o f s t r e a m - s e d i m e n t samples b y this carrier distillation m e t h o d . CONCLUSIONS The usefulness o f the carrier distillation m e t h o d for the d e t e r m i n a t i o n o f volatile chalcophile elements in geologic materials has been d e m o n s t r a t e d for s t r e a m - s e d i m e n t samples and heavy-mineral c o n c e n t r a t e s o f s t r e a m - s e d i m e n t samples. Analyses o f large n u m b e r s o f samples o f b o t h t y p e s f r o m a variety o f geologic terranes show good c o r r e l a t i o n with analyses b y the t o t a l burn emission spectrographic and a t o m i c a b s o r p t i o n m e t h o d s . The low d e t e c t i o n

377 156°15 '

68 ° 15'

68°15 '

156° 15• 0

I

5

t

L

I

I

I

parts

I

Stream

N

Lake

T

A r e a of known mineral potential Moderate potential roll High potential

Zinc concentration, per million

10 km

o <100

•

t00 • 150 • 200 • 300

•

1000

•

1500

•

2000

500

•

3000

•

•

700

Fig. 3. Distribution and abundance of zinc in stream sediments in the Koiyaktot Mountain area, Alaska, determined by carrier distillation method, compared to previously located areas of mineral potential.

limits attained by this method yield significantly fewer qualified (less than) values for Ag, As, Bi, Cd, Sb, Sn, and Zn, than other arc-emission spectrographic methods. The application of this carrier distillation method is intermediate between that of general purpose emission spectrographic methods, which provide semiquantitative analyses for many elements from a single arcing, and that of atomic absorption methods, which provide a more quantitative determination of separate elements but require more sample preparation and dissolution. Nine chalcophile elements can be rapidly determined at low concentration levels from a single carrier distillation analysis without sample dissolution.

REFERENCES Ahrens, L.H., 1950. Spectrochemical Analysis. Addison-Wesley Press, Cambridge, Mass., pp. 68--75.

378 Ahrens, L.H., 1955. Quantitative Spectrochemical Analysis of Silicates. Addison-Wesley Publishing Co., Cambridge, Mass., pp. 81--84. AUcott, G.H. and Lakin, H.W., 1978. Tabulation of geochemical data furnished by 109 laboratories for six geochemical exploration reference samples. U.S. Geol. Surv., Open-File Rep. 78-163, 8 pp. Barton, H.N., 1980. Portable x-ray spectrograph in geochemical exploration. Society of Mining Engineers in AIME, Minneapolis, Minnesota, October 22--24, AIME preprint 80-311. Boyle, R.W., 1974. Elemental associations in mineral deposits and indicator elements of interest in geochemical prospecting (revised). Geol. Surv. Can., Paper 74-75, 40 pp. Cathrall, J.B., Day, G.W., Hoffman, J.D. and McDanal, S.K., 1983. A listing and statistical summary of analytical results for pebbles, stream sediments, and heavy-mineral concentrates from stream sediments, Petersburg area, southeast Alaska. U.S. Geol. Surv., Open-File Rep. 83-420-A. Erickson, R.L., 1982. Characteristics of mineral deposit occurrences. U.S. Geol. Surv., Open-File Rep. 82-795,227 pp. Flanagan, F.J., 1969. U.S. Geological Survey Standards-II. First compilation of data for the new USGS rocks. Geochim. Cosmochim. Acta, 33: 81--120. Grimes, D.J. and Marranzino, A.P., 1968. Direct current arc and alternation current spark emission spectrographic field methods for the semiquantitative analysis of geologic materials. U.S. Geol. Surv., Circ. 591, 6 pp. Lovering, T.G. and McCarthy, J.H., 1978. Appraisal of the application of different sample media to geochemical exploration in the Basin and Range province. In: Conceptual Models in Exploration Geochemistry -- The Basin and Range Province of the western U.S. and northern Mexico. J. Geochem. Explor., 9: 253--276. Myers, A.T., Havens, R.G., Connor, J.J., Conklin, N.M. and Rose, H.J., Jr., 1976. Glass reference standards for the trace-element analysis of geological materials -- compilation of interlaboratory data. U.S. Geol. Surv., Proj. Pap. 1013, 29 pp. Reiser, H.N., Brosg~, W.P., Hamilton, T.D., Singer, D.A., Menzie, W.D., II, Bird, K.J., Cady, J.W., LeCompte, J.R. and Cathrall, J.B., 1983. The Alaska Mineral Resource Assessment Program: Guide to information in folio of geologic and mineral resource maps of the Philip Smith Mountains quadrangles, Alaska. U.S. Geol. Surv., Circ. 759, 22 pp. Scribner, B.F. and Mullen, H.R., 1946. The carrier-distillation method for spectrographic analysis and its application to the analysis of uranium-base materials. J. Opt. Soc. Am., 36,357--369. Tennant, W.C., 1967. General spectrographic technique for the determination of volatile trace elements in silicates. Appl. Spectrosc., 21 : 282--285. Theobald, P.K. and Barton, H.N., 1978. Basic data for the geochemical evaluation of National Petroleum Reserve, Alaska. U.S. Geol. Surv., Open-File Rep. 78-70-D, 102 pp.