Authors / CoAuthors
Blake, D.H.
Abstract
Geological mapping of the Mount Isa Inlier and environs by the Bureau of Mineral Resources and Geological Survey of Queensland from 1969 to 1980 resulted in the production of the 1:100 000 maps which form the basis for the accompanying 1:500 000 geological map. Three broad tectonic divisions are distinguished within the Mount Isa Inlier: the Western Fold Belt, Kalkadoon-Leichhardt Belt, and Eastern Fold Belt. These are formed of early and middle Proterozoic sedimentary and volcanic rocks many thousands of metres thick, which are assigned to four major sequences, and numerous igneous intrusions. Correlatives to the northwest are exposed within and around the younger Proterozoic South Nicholson Basin and along the Murphy Tectonic Ridge. The oldest sequence in the region, designated basement, was deformed and regionally metamorphosed, in places forming migmatite, before about 1875 Ma. The three younger sequences are cover sequence 1 (1875-1850 Ma), consisting mainly of subaerial felsic volcanics, and cover sequences 2 (mostly 1790 1760 Ma) and 3 (mostly 1680-1670 Ma), comprising felsic, and mafic volcanics and predominantly shallow-water sediments. These sequences are intruded by I-type granites isotopically dated (U-Pb zircon) at around 1860 Ma, 1840 Ma, 1820 Ma, 1800 Ma, 1720-1740 Ma, 1700 Ma, 1670 Ma, and 1500 Ma. Mafic intrusions, ranging in age from pre-1860 Ma to about 1100 Ma, form dykes, sills, and pod-like bodies, and also netveined complexes with granite. The cover sequences were mildly to strongly deformed and regionally metamorphosed up to upper amphibolite facies between about 1620 and 1550 Ma. The deformation included thrusting, faulting, and open to tight upright folding. Major displacements have taken place subsequently along faults trending between northwest and northeast. The igneous rocks are markedly bimodal in composition. Four major chemically distinctive suites of felsic volcanics are identified, the oldest of which (cover sequence 1) is cogenetic with extensive granites. Most of the mafic igneous rocks are similar in chemistry to continental tholeiites. The Mount Isa Inlier contains major deposits of copper, lead, zinc and silver, and significant deposits of gold, uranium and cobalt; it has also produced minor amounts of manganese, cadmium, bismuth, tungsten, beryl, and mica. Most copper occurs in brecciated sediment-hosted deposits within the Western Fold Belt, but there are also numerous small shear and fault-controlled vein copper deposits to the east; most of the gold production has come as a by-product from these veins. Large stratiform lead-zinc-silver ores are hosted in shales, such as at Mount Isa mine. Geochemical, geographical, sedimentological and geophysical evidence favours an intracratonic tectonic setting for the Mount Isa Inlier and environs during the early and middle Proterozoic. Since about 1500 Ma, the region has been part of an essentially stable tectonic unit.
Product Type
document
eCat Id
21
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
ACT
2601
Australia
Keywords
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- GA PublicationBulletin
- ( Theme )
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- geology
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- AU-NTAU-QLD
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_External
Publication Date
1987-01-01T00:00:00
Creation Date
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Purpose
Maintenance Information
unknown
Topic Category
geoscientificInformation
Series Information
Bulletin 225
Lineage
Unknown
Parent Information
Extents
[-23.0, -17.0, 130.5, 141.0]
Reference System
Spatial Resolution
Service Information
Associations
Source Information
Source data not available.