Date of Award

8-2021

Document Type

Thesis

Degree Name

Master of Science in Earth and Environmental Sciences

Department

Geological Sciences

First Reader/Committee Chair

Melchiorre, Erik

Abstract

The discovery of the SS Central America 1857 shipwreck site provides a time capsule that can be used to address questions about the spatial and temporal patterns of placer mining in California during the peak of the gold rush. Samples of placer gold in the collections of museums and private individuals can have uncertain pedigree due to labeling issues and alterations by cleaning and curatorial processes. However, placer gold from the 1857 shipwreck could only have come from the Mother Lode Country of California, as no other gold districts had yet been found in western North America. I compared the chemistry and mineralogy of well-characterized mid-19th century Mother Lode placer gold to the properties of the placer gold recovered within a safe from the shipwreck, which contained a vest with four pokes sewn into pockets. My analysis of gold from three of the pokes indicates that each was collected from a different area. Poke 1 has crystalline gold fragments that were found close to a gold source and rounded pieces that originated farther upstream. Platinum-group metal grains indicate this gold was sourced from the Yuba River. Poke 2 gold has inclusions of anglesite, a common secondary lead mineral that forms from the oxidation of galena. Anglesite inclusions in gold are rare in the Sierras, only found along the Feather River. Gold from Poke 3 has many inclusions of quartz and feldspar, which suggest close proximity to a lode gold source.

The ubiquitous traces of mercury (Hg) on the surface of the gold suggests that all the placer gold came from sites of significant mining operations as established mines used mercury at the time. The shape, geochemistry, and context of the placer gold imply that this gold was collected from active mining centers along the upper Yuba and upper Feather Rivers. Morphology and chemistry of the gold indicate all was collected within 15 km of the bedrock lode sources. Furthermore, almost all other gold on the shipwreck was found in passenger rooms and cargo areas. Gold from this study was found in the ship pursers’ safe in secret compartments in a vest, implying an owner with connections and discretion beyond those of a simple miner. Given this evidence, it is suggested that the placer gold was collected at several major mining camps by a professional gold buyer or mining engineer.

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