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A Reply to the Discussion of Sherman-Type Deposits by Brian J. Skinner

By
Robert J. Johansing
Robert J. Johansing
517 West 3rd Street, Leadville, Colorado 80461
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Published:
January 01, 1990

1. Definition

The criteria for the identification of Sherman-type deposits are based on field studies by Behre (1953). The presence and paragenetic position of white barite (prior to base and precious metals) is probably the most important field criterion used in the recognition of the Sherman-type assemblage because early white barite has not been found in other ore deposit types in the Mosquito Range. Additional criteria such as host rock (carbonate), sphalerite color (olive green), silver content (moderate to high), and quartz-pyrite content (typically low) are important, but by themselves are not diagnostic. More specifically:

A. The Sherman-type assemblage has been ob served in both clastic rocks and intrusive porphyries.

B. Olive green sphalerite occurs in many ore de posit types in central Colorado.

C. Base metal ore with high silver content occurs within the Leadville, Gilman, and Aspen districts,

D. A low qnartz-pyrite content, like the silver content, is not unique to the Sherman assemblage.

In the presence of early white barite, these features serve to support the identification of the assemblage as the Sherman type. However, in the absence of early white barite, the supporting field criteria do not unequivocally identify the deposit as Sherman type.

Behre’s description is based upon macroscopic features which can be readily applied in the field. In the time since his studies, the ores have been partially characterized isotopically and thermometrically. The two studies summarized in this volume have agreed that Sherman-type deposits contain J-type lead in the galena, contain sulfur from a sedimentary source, and have measured fluid inclusion homogenization temperatures between 150° and 300°C. These should also be considered as characteristics of Sherman-type deposits.

Up to this point, we have limited the definition to physical characteristics of the ores. However, Behre’s definition of the Sherman-type ore presumed a genetic relation to the-Leadville district. We conclude, in light of the two conflicting genetic models proposed in this volume for the origin of the Sherman-type ore, that it is premature to include a genetic model in the definition of Sherman-type deposits. We propose that Behre’s definition be modified to accommodate these uncertainties until adequate studies have been conducted.

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Economic Geology Monograph Series

Carbonate-Hosted Sulfide Deposits of the Central Colorado Mineral Belt

David W. Beaty
David W. Beaty
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;
Gary P. Landis
Gary P. Landis
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;
Tommy B. Thompson
Tommy B. Thompson
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Society of Economic Geologists
Volume
7
ISBN electronic:
9781629490021
Publication date:
January 01, 1990

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