Australian Museum Journal Occurrences and origins of gem zircons in eastern Australia

Shortform:
Hollis and Sutherland, 1985, Rec. Aust. Mus. 36(6): 299–311
Author(s):
Hollis, J. D.; Sutherland, F. L.
Year published:
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 package:
EndNote file
Title page:
Title page (134kb PDF)
Complete work:
Complete work (2324kb PDF)

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.