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By Steve Herschbach
Gold in Meteorites and in the Earth's Crust, U.S.G.S Circular 603 by Robert Sprague Jones, 1968
Original pdf https://pubs.usgs.gov/circ/1968/0603/report.pdf
The reported gold contents of meteorites range from 0.0003 to 8.74 parts per million. Gold is siderophilic, and the greatest amounts in meteorites are in the iron phases. Estimates of the gold content of the earth's crust are in the range of 0.001 to 0.006 parts per million.
This report is one of several that summarize available data on the occurrence of gold. They have been prepared as background material for the Heavy Metals program of the U.S. Geological Survey, an intensified program of search for new sources of heavy metals, including gold. Data on the occurrence of gold in meteorites and tektites are summarized, and recent estimates of the abundance of gold in the earth's crust are compiled.
GOLD IN METEORITES
Table 1 shows reported gold contents of tektites, aerolites, siderolites, and siderites. The table is arranged so that the data on tektites, which have the lowest iron contents, are at the top of the table and the data on siderites, which have the highest iron contents, are at the bottom. The other meteorite groups are intermediate in iron contents except for the siderolites. Gold is most abundant in the siderites and least abundant in the tektites; therefore, meteorites supply good evidence of the siderophilic character of gold. The tektites and the achondrites are relatively low in gold contents and are distinct from the other groups of meteorites in this respect. The gold contents of tektites and achondrites are of the same order of magnitude as those of terrestrial rocks. The other meteorites, on the average, contain appreciably more gold.
Although the iron contents of meteorites are similar in many respects to those of mafic and ultramafic rocks, the meteorites tend to contain much more gold. In chondrites, the gold seems to be almost entirely in the dispersed metallic phase (Vincent and Crocket, 1960), and this is probably true of the other meteorite. The gold content of the metallic phase of the chondrites is about 1.4 ppm (parts per million), which is similar to the gold contents of siderolites, octahedrites, and ataxites (Vincent and Crocket, 1960; Goldberg and others, 1951).
The carbonaceous chondrites are primitive, relatively undifferentiated matter from which the other meteoritic types have evolved (Mason, 1962; Baedecker and Ehmann, 1965). The occurrence of gold in such primitive types may be of special interest. The average gold content for 13 carbonaceous chondrites is 0.16 ppm, an amount greater than that in the average terrestrial rock by a ratio of about 40 to 1.
It has been suggested (Aller, 1961) that the best approximation to the average composition of the earth's mantle or even the entire earth is provided by the composition of the chondrites. They are similar in chemical composition to the ultramafic rocks, and their isotopic constitution for several elements is basically the same as that for the rocks of the mantle.
Baedecker and Ehmann (1965) shew the abundances of gold, iridium, and platinum in four groups of chondrites. In the olivine-bronzite (H group), the olivine-hypersthene ( L group), and the carbonaceous chondrites, the abundance ratio of Pt :Ir :Au is approximately 7-9:2:1; but for the enstatite chondrites, gold is more abundant and the Pt :Ir :Au ratio is 3.5:0.2 :1. The iridium shows a relatively large decrease with respect to gold. These values, however, represent only analysis of the Abee enstatite chondrite made by Baedecker and Ehmann (1965) by neutron-activation methods. Analysis of this same meteorite by Crocket and others (1967), who also used neutron-activation methods, gives a somewhat different relationship. Their ratio for Pt :Ir :Au is 5.9 :1.5:1. The amount of platinum, iridium, and gold reported by Baedecker and Ehmann is 1.3, 0.083, and 0.37 ppm, respectively; Crocket and others reported 1.3, 0.32, and 0.22 ppm, :respectively. The iridium-gold ratio of terrestrial rocks is more like that of tektites than it is like the ratios of the other meteorites (Baedeckler and Ehmann, 1965).
The gold contents of the octahedrites do nott seem to vary with the coarseness of the octahedrites. Cobb (1967) noted that most of his valules for gold in meteorites were in the range of 0.2 to 2.5 ppm. Cobb (1967) and Goldberg, Uchiyama, and Brown ( 1951) analyzed parts (three in all) of the same meteorite, and Cobb obtained lower values. The average values of gold in hexahedrites were also low compared with those of Goldberg, Uchiyama, and Brown (1951). For the same 11 meteorites analyzed by neutron-activation methods by Goldberg, Uchiyama, and Brown (1951) and Fouche and Smales (1966), the average contents were 1.1 ppm gold and 0.9 ppm gold, respectively.
The various types of siderites have differing amounts of gold. Ataxites and octahedrites have an average gold content of ab1ut 1.3 ppm, which is about twice that for hexahedrites (0.64 ppm). The hexahedrites usually have less nickel than either the ataxites or the octahedrites. The Santa Catharina ataxite contained the most nickel ( 38.5 percent) and r.lso the most gold (4.0 ppm), but the Deep Springs ataxite (13.4 percent nickel) contained the least amount of gold (less than 0.1 ppm, but considered as 0.05 ppm for table 1).
Fouche and Smales (1966) analyzed 70 siderites and found gold contents that ranged from 0.055 to 3.61 ppm. The correlation coefficients between gold and rhenium and between gold and chromium were low and negative, giving values of -0.41 and - 0.31, respectively, but the correlation between gold and arsenic was +0.82 and between gold and palladium +0.68.
Goldschmidt and Peters (1932) analyzed the Coahuila, Mexico, meteorite and reported that it contained 1 to 5 ppm gold, whereas analysis by the neutron-activation method by Goldberg, Uchiyama, and Brown (1951) gave 0.743 ppm gold; by Fouche and Smales (1966), 0.70 ppm gold; and by Cobb (1967), 0.43 ppm gold. Goldschmidt and Peters (1932), analyzed the Mount Joy, Pa., meteorite and reported that it contained 5 to 10 ppm gold, whereas analysis by the neutron-activation method by Goldberg, Uchiyama, and Brown (1951) gave 0.994 ppm gold. These comparative values along with others in this report seem to indicate that lower values are obtained for gold when neutron-activation methods are used.
ESTIMATES OF GOLD IN THE EARTH'S CRUST
Parker (1967) has pointed out the difficulty in estimating the composition of the earth's crust, which forms less than 1 percent of the earth's mass (Aller, 1961). Differences among the estimates given by various authors since Clarke and Washington (1924) are due partly to different concepts of what constitutes the earth's crust, the depth to the Mohorovicic discontinuity, the composition of the oceanic crust compared with the continental crust, and the changes in crustal composition with depth. Also, with respect to gold specifically, the newer method of analysis, that of neutron activation, has resulted in a general downward revision of gold values.
Table 2 gives the various estimates for the abundance of the precious metals, gold, platinum, and silver, in the earth's crust. Precious metal contents of various parts of the earth's crust has been noted by Tung and Chi-Lung ( 1966). These data are given in table 3.
The estimates of gold and silver in the earth's crust have varied little since those of Clarke and Washington in 1924, although the estimates for platinum have varied substantially. The Ag :Pt :Au ratios, based on Tung and Chi-Lung's (1966) figures, are 21 :13:1.
Aller, L. H., 1961, The abundance of the elements: New York, Interscience Publishers, 283 p.
Anderson, J. S., 1945, Chemistry of the earth: Royal Soc. New South Wales Jour. and Proc., v. 76, p. 329-345 .
Baedecker, P. A., 1967, The distribution of gold and iridium in meteoritic and terrestrial materials: U.S. Atomic Energy Comm. [Pub.] OR0-2670-17, and Ph.D. thesis, Univ. Kentucky, 110 p .
Baedecker, P. A., and Ehmann, W. D., 1965, The distribution of some noble metals in meteorites and natural materials: Geochim. et Cosmochim. Acta, v. 29, p. 329-342.
Berg, Georg, 1929, Vorkommen und Geochemie der mineralischen Rohstoffe : Leipzig, 414 p.
Clarke, F. W., and Washington, H. S., 1924, The composition of the earth's crust: U.S. Geol. Survey Prof. Paper 127, 117 p.
Cobb, J. C., 1967, A trace-element study of iron meteorites: Jour. Geophys. Research, v. 72, no. 4, p. 1329-1341.
Crocket, J. H., Keays, R. R., and Hsieh, S., 1967, Precious metal abundances in some carbonaceous and enstatite chondrites: Geochim. et Cosmochim. Acta, v. 31, p. 1615-1623.
DeGrazia, A. R., and Haskin, Larry, 1964, On the gold content of rocks: Geochim. et Cosmochim. Acta, v. 28, p. 559-564.
Fersman, A. E., 1933, Geokhimiya, Tom 1: Leningrad, 328 p.
Fouche, K. F., and Smales, A. A., 1966, The distribution of gold and rhenium in iron meteorites: Chern. Geology, v. 1, no. 4, p. 329-339.
Goldberg, Edward, Uchiyama, Aiji, and Brown, Harris~n, 1951, The distribution of nickel, cobalt, gallium, palladium, and gold in iron meteorites: Geochim. et Cosmochim. Acta, v. 2, p. 1-25.
Goldschmidt, V. M., 1934, Drei Vortage uber Geochemie: Geol. Foren. Stockholm For h. v. 56 p. 385-427.
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Tung, Li, and Chi-Lung, Yio, 1966, The abundance of chemical elements in the earth's crust and its major tectonic units: Scientia Sinica, v. 15, no. 2, p. 258-272.
Vincent, E. A., and Crocket, J. H., 1960, Studies in the geochemistry of gold. II. The gold content of some basic and ultrabasic rocks and sto:-1e meteorites: Geochim. et Cosmochim. Acta, v. 18, p. 143-148.
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Salutation at this very informative website us below: (and yes, do click on those read this and this links too)
Prepared by: Randy L. Korotev
Department of Earth and Planetary Sciences
Washington University in St. Louis
Please don't contact me about the meteorite you think you've found until you read this and this.
Many meteorite hunters prefer to search for space rocks using only their eyes to spot them on the ground. But when the area is strewn with dark colored terrestrial rocks that can mimic the look of a meteorite, relying on visual clues becomes a tough go.
In the photo below, I had just found a stony meteorite exposed on the surface with my metal detector. Test your skills and see if you can spot the chondrite.