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GEOREF RECORD

Pb-Zn-(As) enrichments in amphibolites from broken hill-type ore systems, NW Queensland; products of retrograde hydrothermal dispersion

Patrick J. Williams and Michael J. Smith
Pb-Zn-(As) enrichments in amphibolites from broken hill-type ore systems, NW Queensland; products of retrograde hydrothermal dispersion
Geochemistry - Exploration, Environment, Analysis (August 2003) 3 (3): 245-261

Abstract

Amphibolites typically lacking visual signs of Pb-Zn mineralization are associated with pelitic gneisses at the Cannington and Maramungee "broken hill-type" Pb-Zn-Ag deposits in the eastern Mount Isa Inlier. Within 150 m of the sulfide-rich lodes these have consistently anomalously high chalcophile metal contents. The enrichments broadly mimic the primary distinctions between the two deposits in respect to the relative abundances of Zn, As and Pb. At Maramungee, metal concentrations of thin amphibolites broadly increase toward the mineralized rock body and comparison with data from gneisses illustrates the general superiority of basic rocks as a sample medium due to their inherently low Pb-content and comparatively homogenous primary chemistry. Most amphibolite at Cannington occurs in a single metamorphosed sill that is consistently anomalous, though with irregular chalcophile element distributions. Petrographic and SEM studies show that the metal enrichments are related to sulfides in complex retrograde parageneses which have selectively replaced metamorphic (calcic) plagioclase. Most galena occurs as sub-10 mu m grains. Chalcophile elements were dispersed in a hydrous fluid and selectively enriched in the amphibolites during retrograde metamorphism under greenschist to sub-greenschist facies conditions. Routine analysis of basic rocks for Pb (and Zn) might therefore provide a simple proximity indicator for broken hill-type deposits, especially in poorly exposed terrains where amphibolites are the most common cause of magnetic anomalies tested by exploration drilling.


ISSN: 1467-7873
EISSN: 2041-4943
Serial Title: Geochemistry - Exploration, Environment, Analysis
Serial Volume: 3
Serial Issue: 3
Title: Pb-Zn-(As) enrichments in amphibolites from broken hill-type ore systems, NW Queensland; products of retrograde hydrothermal dispersion
Affiliation: James Cook University, Economic Geology Research Unit, Townsville, Queensl., Australia
Pages: 245-261
Published: 200308
Text Language: English
Publisher: Geological Society Publishing House, London, United Kingdom
References: 37
Accession Number: 2004-026124
Categories: Economic geology, geology of ore depositsGeochemistry of rocks, soils, and sediments
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 1 table, geol. sketch map
S22°10'00" - S21°10'00", E140°19'60" - E141°00'00"
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from The Geological Society, London, London, United Kingdom
Update Code: 200408
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