Publication Date

Fall 2021

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

Advisor

Emmanuel Gabet

Subject Areas

Geology

Abstract

Hydraulic gold mining in California, began not long after the discovery of gold in 1848. This type of mining dislodged large amounts of sediment, which were then deposited downstream. The Yolo Bypass, downstream from several northern California rivers, has received and continues to receive hydraulic mining sediment (HMS). The main goal of this study was to document the chemical and mineralogical characteristics of HMS in the bypass. Twelve borehole cores from the bypass and five in-situ auriferous gravel samples, which were used for background concentrations, were collected for this study. All twelve cores had higher Hg concentrations than the in-situ auriferous gravels. The Hg concentrations in the bypass range from 0.034 ppm to 1.32 ppm. Background concentrations from the five insitu auriferous gravel samples range from 0.010 ppm to 0.098 ppm. Using specific chemical and mineralogical indices such as Hg, Al/Ca, CaO, Ca/Sr, Ni/Zr, and quartz/plagioclase, fractions of sediment containing HMS were estimated. The fractions of sediment containing HMS, in the eastern bypass cores, range from 73% to 94%. Hydrologic banding, visually distinct threads of flow, with little lateral mixing due to shallow depths, occurs in the bypass. This study has identified distinct chemical and mineralogical differences between each band, primarily when considering Hg concentrations.

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