Abstract

In eastern Australia, zircons are common in alluvial deposits derived from Tertiary volcanic rocks. They are typically accompanied by corundum, pleonaste spinel and ilmenite ('the zircospilic association'). Although most occur in or near granite areas, fieldwork and dating confirm alkali basalts and some trachytes as their hosts; some even being found in situ. Most crystals show corrosion effects from their transporting magmas. A wide range of zircon crystal habits suggests diverse but, as yet, unknown sources. Possibilities include: (a) accidental sources from syenitic intrusives, plutonic cumulates and pegmatites, and (b) cognate origins in fractionated basaltic magmas, particularly their felsic end members. Dry, peraluminous alkaline magmas may be responsible for most of the large zircons. Eight groups are described on their physical characteristics. Most are (101)-pyramid dominant forms with short prisms. Variations in the incidence of crystal types show trends that may record changes in magma composition as well as temperature profiles. Felsic intrusions associated with Mesozoic and Cainozoic 'hot spot' trails form potential reservoirs to provide zircon xenocrysts in later basalts. The relative contribution of these to older Palaeozoic granitoid zircon sources is uncertain, pending detailed isotopic work.

 
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Bibliographic Data

Short Form
Hollis and Sutherland, 1985, Rec. Aust. Mus. 36(6): 299–311
Author
J. D. Hollis; F. L. Sutherland
Year
1985
Title
Occurrences and origins of gem zircons in eastern Australia
Serial Title
Records of the Australian Museum
Volume
36
Issue
6
Start Page
299
End Page
311
DOI
10.3853/j.0067-1975.36.1985.349
Language
English
Date Published
11 June 1985
Cover Date
11 June 1985
ISSN
0067-1975
CODEN
RAUMAJ
Publisher
The Australian Museum
Place Published
Sydney, Australia
Subjects
MINERALOGY; MESOZOIC; CAINOZOIC
Digitized
10 November 2008
Available Online
19 December 2008
Reference Number
349
EndNote
/Uploads/Journals/17637/349.enw
Title Page
/Uploads/Journals/17637/349.pdf
File size: 134kB
Complete Work
/Uploads/Journals/17637/349_complete.pdf
File size: 2324kB