The pattern of sulfur transformation in peat across the Everglades basin indicates that pyrite formation in organic-rich swamps depends on the use of organic oxysulfur compounds in dissimilatory respiration by sulfur-reducing bacteria. This paragenesis explains the primary distribution of sulfur compounds in low-sulfur coals and possibly in most coals and many organic-rich soils and sediments. It also accounts for the occurrence of framboidal pyrite bound in fossil tissue in coal and sediments.

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The relative merits of different plating methods are discussed and a new type of electrolyte for autocatalytic gold plating is described. The chemical system of this bath has an ideal combination of properties such as stability and high deposition speed, combined with long bath life and high metal rurnover.The barh's composition, maintenance and sensitivity to contaminants are discussed, and its operating characreristics and the properties of the gold coatings formed from it are presented. Areas suitable for its application are suggested.

Platinum, palladium and rhodium have been determined in 18 U.S. Geological Survey reference materials by graphite furnace atomic absorption spectrometry after preconcentration by the classical leadfree assay technique. A comparison with literature values shows clearly the need for additional data on these samples before “best” values can be assigned.

TWO RELIABLE TECHNlQUES for the determination Of gold in geologic materials are neutron activation analysis and classical fire assay. The high sensitivity of activation analysis has allowed the measurement of gold at the parts-per-billion concentration level in rocks (1-5). In conventional activation analysis, 0.1-to 1-gram samples and standards are irradiated with neutrons dissolved in the presence of gold carrier, and the carrier plus activated gold are separated from other radioactivity by radiochemical procedures. Counting of the lg8Au and measurement of the chemical yield of the carrier allows calculation of the amount of gold in the samples. Several factors contribute to the uncertainty in results obtained by this technique. The relatively small samples used may not be representative for gold (6, 7). In addition, the gold standards may not be exposed to exactly the same neutron flux as the samples, and the chemical exchange between lg8Au and the carrier may be incomplete. On the other hand, contamination of the carrier gold by gold from the reagents can be ignored, thus eliminating the necessity for a reagent gold blank.Bugbee (8) and Beamish (9) have discussed classical fire assay procedures. Variations of the classical technique have involved the estimation of the gold content of the silver bead by spectrography (IO) and atomic absorption (11), but the sensitivities are not sufficient to measure nanogram quantities of gold and therefore, gold cannot be determined in rocks a t the parts-per-billion concentration level. Although larger, more representative samples are used in fire assay, the possibility exists for incomplete recovery of gold in the fusion and cupellation steps. With low levels of gold, contamination by gold from the reagents necessitates carrying a blank through the procedure.It is a logical step to combine fire-assay preconcentration of gold with the measurement of gold by rapid instrumental neutron activation analysis. Washington and Holman (12) developed such a procedure in which they irradiated the final silver bead and determined lg8Au by gamma counting. Their detection limit, with a precision of 50%, was only 10 ppb gold because of the large amount of 253-day llomAg, generated during the neutron irradiation, and a sizable reagent gold blank.The technique we have developed involves irradiation of the lead button obtained by the fire-assay procedure prior t o the addition of silver. This approach provides a uniform, dilute, and reproducible matrix for the neutron irradiation of gold, reduces the counting background due to llornAg, and avoids the possibility of introducing gold contamination with the silver. After irradiation, silver is added, the lead button cupelled, and the 1g8Au counted instrumentally without further separations. The sources of error in this technique differ from those in conventional neutron activation analysis; therefore, if both methods give the same result for gold, confidence in the reliability of each is increased. EXPERIMENTAL