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GEOREF RECORD

Textural evidence for extensive melting of the Broken Hill orebody

B. Ronald Frost, Susan M. Swapp and John Mavrogenes
Textural evidence for extensive melting of the Broken Hill orebody
Economic Geology and the Bulletin of the Society of Economic Geologists (August 2011) 106 (5): 869-882

Abstract

Galena, pyrrhotite, and chalcopyrite in samples of Zn-rich ore from the Broken Hill orebody show textures similar to those in partially melted metamorphic rocks, including strings of low melting phases separating lithons of minerals likely to be restite, low dihedral angles between low melting-temperature minerals and restitic minerals, and enlargement of these dihedral angles due to partial annealing. Analysis of existing experimental work from the system Fe-Pb-Zn-S indicates that at 1 bar, galena and sphalerite coexisting with pyrrhotite of the compositions found at Broken Hill would have been partially melted at temperatures of about 750 degrees C; at 5 kbars, this melting would occur at 780 degrees C. This temperature is well within the range of metamorphic temperatures reported from the area. From these data we conclude that the Broken Hill orebody was partially molten at peak metamorphism, with much of the Pb, Cu, Ag, Sb, and As in the melt and Fe and Zn residing mostly in the restite. Differentiation during cooling enriched the residual melt in Sb, As, Ag, and other low melting-temperature chalcophile elements. The main sulfide melt froze after the last penetrative deformation to affect the orebody, at temperatures below 720 degrees C and possibly as low as 650 degrees C. Sulfosalts crystallized out of the remaining melt at temperatures of 600 degrees to 450 degrees C, and the final melt crystallized native bismuth at ca. 250 degrees C.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 106
Serial Issue: 5
Title: Textural evidence for extensive melting of the Broken Hill orebody
Affiliation: University of Wyoming, Department of Geology and Geophysics, Laramie, WY, United States
Pages: 869-882
Published: 201108
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 74
Accession Number: 2011-087804
Categories: Economic geology, geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sect., 2 tables, sketch maps
S37°30'00" - S28°15'00", E141°00'00" - E153°30'00"
Secondary Affiliation: Australian National University, Research School of Earth Sciences, AUS, Australia
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Society of Economic Geologists. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201146
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