Date of Award

9-2014

Document Type

Thesis

Degree Name

Master of Science in Earth and Environmental Sciences

Department

Geological Sciences

First Reader/Committee Chair

Dr. Erik Melchiorre

Abstract

The San Bernardino Mountains are well known for their rich mining history, especially, gold in the mid-1800s and the current mining of one of the world’s largest deposits of high purity limestone. The purpose of this study was to compile new, current, and historical data of the major economic resources that are present and mining that has gone on in the San Bernardino Mountains. It is estimated that historical mining of the Holcomb Valley recovered $457,660,000 of gold or about 350,000 troy ounces based on samples collected for this study and 2013 gold price. The current major geologic resource is the limestone deposits on the north slope of the San Bernardino Mountains. Presently, there are three operators: Omya, Specialty Minerals, and Mitsubishi Cement.

The San Bernardino Mountains are well known for skarn gold deposits. New work indicates that the placer gold from Holcomb Valley is often of very high purity. Placer gold samples were analyzed using the scanning electron microscope and energy dispersive x-ray spectra to determine the purity of the gold. Rim and core analysis of the placer gold was used to determine if the gold was transported from its source and to give an estimate of transportation distance. Results show some of the placer gold of Holcomb Valley has been rounded and flattened by weathering and transportation with increased gold purity in the rims while other gold grains still sustain their octahedral crystalline structure. Rims range in gold purity from 84.26% to 100%, with core gold purity ranging from 79.51% to 99.79%.

Gold samples were weighed, photographed, measured, and classified by shape, angularity and texture, to assess the effects of transportation. Gold weights where used to calculate an economic value of gold. Geographic Information System “GIS” was used to visually display geology, historical and current mine locations, locations of samples used in this study, and to help calculate the volume of the Holcomb Valley TsE rock unit, which is where the placer gold is deposited. Sediment sample 15 from TsE had the lowest gold value of .002 ounces per cubic yard. This value is inferred to represent the amount of gold remaining after mining. Based on this assumption and the estimated volume of TsE at 50,027,000 cubic yards, the estimated total weight of gold remaining in the deposit is about 100,000 troy ounces, with a dollar value of about $130,760,000, using gold values for 2013. Sample 17 had the highest gold value, with .014 ounces per cubic yard. This is inferred to represent the concentration of placer gold deposits within parts of Holcomb Valley that have never been mined. This yields a total weight of the deposit of roughly 700,000 troy ounces, with an estimated value of $915,320,000 using gold prices for 2013. The gold values were calculated using November 7, 2013 gold spot price of $1,307.60.

Additional Files
APPENDIX D Nicolette Grill.pdf (2734 kB)
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Additional Files

APPENDIX D Nicolette Grill.pdf (2734 kB)

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