Skip to Main Content
Skip Nav Destination
GEOREF RECORD

Origin and significance of postore dissolution collapse breccias cemented with calcite and barite at the Meikle gold deposit, northern Carlin Trend, Nevada

Poul Emsbo and Albert H. Hofstra
Origin and significance of postore dissolution collapse breccias cemented with calcite and barite at the Meikle gold deposit, northern Carlin Trend, Nevada (in A special issue devoted to gold deposits in northern Nevada; Part 2, Carlin-type deposits, Albert H. Hofstra, David A. John and Ted G. Theodore)
Economic Geology and the Bulletin of the Society of Economic Geologists (October 2003) 98 (6): 1243-1252

Abstract

The final event in a complicated hydrothermal history at the Meikle gold deposit was gold deficient but caused extensive postore dissolution of carbonate, collapse brecciation, and precipitation of calcite and barite crystals in the resulting cavities. Although previously interpreted to be part of the Carlin-type hydrothermal system, crosscutting relationships and U-Th-Pb geochronology constrain this hydrothermal event to late Pliocene time (ca. 2 Ma), nearly 36 Ma after ore formation. Mineralogic, fluid inclusion, and stable isotope data indicate that postore hydrothermal fluids were reduced, H (sub 2) S-rich, unevolved meteoric waters (delta (super 18) O = -17 per mil) of low temperature (ca. 65 degrees C). The delta (super 18) O values of barite and calcite indicate that these minerals were in isotopic equilibrium, requiring that barite SO (sub 4) was derived from the oxidation of reduced sulfur; however, preexisting sulfides in breccia cavities were not oxidized. The delta (super 34) S (15 per mil) values of barite are higher than those of local bulk sulfide and supergene alunite indicating that SO (sub 4) was not derived from supergene oxidation of local sulfide minerals. The 15 per mil delta (super 34) S value suggests that the H (sub 2) S in the fluids may have been leached from sulfur-rich organic matter in the local carbonaceous sedimentary rocks. A reduced H (sub 2) S-rich fluid is also supported by the bright cathodoluminescence of calcite which indicates that it is Mn rich and Fe poor. Calcite has a narrow range of delta (super 13) C values (0.3-1.8 per mil) that are indistinguishable from those of the host Bootstrap limestone, indicating that CO (sub 2) in the fluid was from dissolution of the local limestone. These data suggest that dissolution and brecciation of the Bootstrap limestone occurred where H (sub 2) S-rich fluids encountered more oxidizing fluids and formed sulfuric acid (H (sub 2) SO (sub 4) ). Intense fracturing in the mine area by previous structural and hydrothermal events probably provided conduits for the descent of oxidized surface water which mixed with the underlying H (sub 2) S-rich waters to form the dissolving acid. The surface-derived fluid apparently contained sufficient oxygen to produce H (sub 2) SO (sub 4) from H (sub 2) S but not enough to alter pyrite to Fe oxide. Although H (sub 2) S is an important gold-transporting ligand, the temperature was too low to transport a significant amount of gold. The presence of analogous calcite- and barite-lined cavities in other Carlin-type deposits suggests that the generation (and oxidation) of H (sub 2) S-rich meteoric waters was a common phenomenon in north-central Nevada. Previous sulfur isotope studies have also show that the Paleozoic sedimentary rocks were the principal source of H (sub 2) S in Devonian sedimentary exhalative-type, Jurassic intrusion-related, Eocene Carlin-type, and Miocene low-sulfidation gold deposits in the region. The similar sulfur source in all of these systems suggests that basin brines, magmatic fluids, and meteoric waters all evolved to be H (sub 2) S-rich ore fluids by circulation through Paleozoic sedimentary rocks. Thus, although not directly related to gold mineralization, the recent hydrologic history of the deposit provides important clues to earlier ore-forming processes that were responsible for gold mineralization.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 98
Serial Issue: 6
Title: Origin and significance of postore dissolution collapse breccias cemented with calcite and barite at the Meikle gold deposit, northern Carlin Trend, Nevada
Title: A special issue devoted to gold deposits in northern Nevada; Part 2, Carlin-type deposits
Author(s): Emsbo, PoulHofstra, Albert H.
Author(s): Hofstra, Albert H.
Author(s): John, David A.
Author(s): Theodore, Ted G.
Affiliation: U. S. Geological Survey, Denver, CO, United States
Affiliation: U. S. Geological Survey, Denver, CO, United States
Pages: 1243-1252
Published: 200310
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 43
Accession Number: 2003-086405
Categories: Economic geology, geology of ore depositsIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sect., 1 table, sketch maps
N40°30'00" - N41°10'00", W116°30'00" - W115°49'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200324
Program Name: USGSOPNon-USGS publications with USGS authors
Close Modal

or Create an Account

Close Modal
Close Modal