Abstract
AbstractThe assayers’ ingots recovered in 2014 from the SS Central America contain geochemical signatures and anomalies which convey information about the culture of miners and assayers in the late 1850s. A significant number of ingots (21%) contain elevated copper and zinc in the same ratio as a common brass alloy of the period, suggesting that adulteration of placer gold dust was a common issue. The ingots with the brass-like signature also have a gold fineness much lower than measured for typical California placer gold. Trace elements like palladium in uniform concentrations in all Kellogg & Humbert ingots suggest the use of quality high-temperature tools, while lead and tin in all ingots suggest specific contamination and industrial hygiene issues common to the whole industry. Other trace constituents such as arsenic, antimony and bismuth are likely to have originated from dense minerals associated with placer gold, or from the natural placer gold alloy itself. Comparison of modern analysis of ingots vs. assay values stamped on the ingots themselves suggests some firms like Kellogg & Humbert did superior assay work, while others like the San Francisco office of Justh & Hunter probably had issues with quality control. The variations in assay ingot alloy chemistry provide a window into this important period in American history.
Highlights
BackgroundThe first 10 years of the California Gold Rush (1848–1858) were one of the most important periods in US history
Gold was known to occur in California far earlier (e.g. Robinson, 1973; Hamann, 1985) than the official discovery on January 24, 1848 which is credited to James Marshall at the site of a sawmill he was building for John Sutter on the American River (Kinder, 1998)
The present study examines the purity of gold assayers’ ingots and compares these values to their historical stamped value, and was conceived as a project in March 2018 when Frank and Tina Reith visited with the lead author in southern California
Summary
The first 10 years of the California Gold Rush (1848–1858) were one of the most important periods in US history. About 87% of the face value of the gold in the commercial shipment consisted of assayers’ ingots. These ingots are essentially raw placer gold melted and poured into bar form and stamped with the precise weight and purity determined during the process. These gold bricks, as well as the placer gold found on the site, average ∼89% gold with the balance being silver. Some contemporary accounts estimate that the passengers may have carried a cumulative amount of gold equal to this 2000-plus kilogram commercial shipment
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