The Rock that cried Silver Tears - The Early Jurassic Springdale Sandstone and its unusual precious metal mineralization at Silver Reef, UT revisited

Abstract

The light-gray Early Jurassic Springdale Sandstone Member of the Moenave Formation at historic Silver Reef and Harrisburg, now Leeds, UT is a place of one of the most unusual precious metal deposits in the world. Void of any recognizable hydrothermal activity, this sheet like, 30 m thick, fluvial sandstone, exposed in a syncline at Leeds, contains the rare minerals cerargyrite (AgCl; Horn Silver), bromargyrite (AgBr), and iodargyrite (AgI) in mineable quantities. These minerals are finely disseminated and are usually invisible to the naked eye. Discovered in 1866, it was at first believed to be a hoax because of the purely sedimentary nature of the host rock. However, the Silver Reef mining district came to produce over 7 million ounces Ag at a value of close to $8,000,000 from 1875 to 1909. After the ore waned mining experienced a brief recurrence as uranium was extracted from the same lithology during the cold war period.

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AIPG 53rd National Conference September 10-13, 2016
Land of Geologic Confluences and Cultural Crossroads Santa Fe, NM
The Rock that cried Silver Tears - The Early Jurassic Springdale Sandstone and its unusual
precious metal mineralization at Silver Reef, UT revisited
Uwe Kackstaetter, Ph.D. (Presenter)1
The light-gray Early Jurassic Springdale Sandstone Member of the Moenave Formation at
historic Silver Reef and Harrisburg, now Leeds, UT is a place of one of the most unusual
precious metal deposits in the world. Void of any recognizable hydrothermal activity, this sheet
like, 30 m thick, fluvial sandstone, exposed in a syncline at Leeds, contains the rare minerals
cerargyrite (AgCl; Horn Silver), bromargyrite (AgBr), and iodargyrite (AgI) in mineable
quantities. These minerals are finely disseminated and are usually invisible to the naked eye.
Discovered in 1866, it was at first believed to be a hoax because of the purely sedimentary
nature of the host rock. However, the Silver Reef mining district came to produce over 7 million
ounces Ag at a value of close to $8,000,000 from 1875 to 1909. After the ore waned mining
experienced a brief recurrence as uranium was extracted from the same lithology during the cold
war period.
The first scientific landmark investigation of the area in order to understand this unusual
mineralization was completed in 1953 by the late Paul Dean Proctor. Later researchers have tried
to tackle the mystery. While multiple hypothesis abound, the process of the unusual ore
mineralization has never been completely answered and the last papers about the district’s
geochemistry were published in the 1990's.
However, modern sophisticated instrumentation, such as portable x-ray fluorescent (XRF)
spectroscopy and scanning electron microscopy (SEM) with advanced energy dispersive
spectroscopy (EDS) have opened novel possibilities in geochemical analysis. Therefore, the
mystery of the Springdale Sandstone has been revisited through a variety of undergraduate
research projects associated with the new geology degree at Metropolitan State University of
Denver.
This presentation will pay homage to Paul D. Proctor and will familiarize the audience with one
of the most unusual precious metal deposits in the world. The current status of the some exiting
undergraduate research projects associated with this prospect will be introduced to facilitate the
connection between the Silver Reef student presentations exhibited at this conference.
1Metropolitan State University of Denver, Department of Earth & Atmospheric Sciences