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Relationships between microstructure and composition in enargite and luzonite

Mihaly Posfai and Peter R. Buseck
Relationships between microstructure and composition in enargite and luzonite
American Mineralogist (April 1998) 83 (3-4): 373-382

Abstract

Cu (sub 3) (As,Sb)S (sub 4) minerals commonly contain structurally disordered crystals of intergrown enargite and the luzonite-famatinite series (Posfai and Sundberg 1998). Here we discuss the relationships between the fine-scale structural variations and the Sb/As ratios of these minerals. Although luzonite typically contains more Sb than enargite, individual layers of luzonite within Sb-bearing enargite are not associated with higher Sb/As ratios. Defect-free enargite can also contain Sb. We develop a "structure-composition" diagram in which both the structural enargite-luzonite and the compositional luzonite-famatinite solid solutions can be represented. Compositions plotted in this diagram reveal that Sb-bearing enargite and luzonite contain only a relatively small number of defects, whereas Sb-free crystals can be heavily disordered. Coexisting enargite and famatinite and zoning in luzonite-famatinite indicate fluctuations in the Sb-content of the fluid during ore deposition. On the other hand, assemblages of Sb-free enargite and luzonite probably reflect thermal oscillations; heavily disordered, intermediate structures may have formed near the transition temperature of low-temperature luzonite to high-temperature enargite. Our results suggest that characteristic microstructures in enargite, luzonite, and famatinite can be useful for constraining fluid composition and temperature during ore deposition.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 83
Serial Issue: 3-4
Title: Relationships between microstructure and composition in enargite and luzonite
Affiliation: Arizona State University, Department of Geology and Chemistry, Tempe, AZ, United States
Pages: 373-382
Published: 199804
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 22
Accession Number: 1998-031625
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 199812
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