Product catalogue
Alteration of mafic igneous rocks of the southern McArthur Basin: comparison with the Mount Isa region and implications for basin-hosted base metal deposits
Mafic igneous rocks are thought to be an important source of metals for the ca. 1640–1595 Ma sediment-hosted base metal deposits in the Paleo- to Mesoproterozoic Mount Isa – McArthur Basin system of northern Australia. Such rocks are widespread—the voluminous rift-related mafic magmatism at ca. 1790–1775 Ma and ca. 1730–1710 Ma—and show local evidence for intense hydrothermal alteration and metal leaching. To better constrain the nature, degree, and regional and temporal extent of alteration and metal leaching in these rocks, we have undertaken regional sampling of mafic igneous units from available drillcore, for geochemistry, stable isotopes and petrological examination. Sampling focused on magmatism of both ages in the southeastern MacArthur Basin, complementing the extensive pre-existing data for the Mount Isa region. Alteration in the mafic igneous rocks of the southeastern McArthur Basin ranges from mildly to strongly chloritic in the older units to strongly potassic (K-feldspar–chlorite–hematite) in the younger units. The latter alteration is ubiquitous, well developed and characterised by strong K2O enrichment and extreme depletion in CaO and Na2O. Geochemical data show that this intense and pervasive potassic alteration extends to similar-aged mafic rocks in the western Mount Isa region. Metal leaching is present in both alteration types, with strong Cu and Pb depletion in the most chlorite-altered rocks, and Zn and Cu depletion in the potassic alteration. Our oxygen isotope data for these mafic rocks (of both ages) in the southeastern McArthur Basin show a limited range of values (δ18O of 6–10‰) that are negatively correlated with K2O content. Our values are significantly lighter than published data for similar igneous rocks to the west, and indicate either a temperature zonation (ca. 250 °C in the east versus ca. 100 °C in the west; preferred) and/or different fluids. Results from our geochemical forward modelling indicate the requirement for exogenous K2O to produce the observed potassic alteration. The most likely source of this K was saline brines, consistent with the interpreted lacustrine and/or evaporitic environments for much of the McArthur Basin. Timing of alteration is uncertain, and the alteration may have included diagenetic low-temperature local K-rich brines and younger higher-temperature deep basinal brines. The temporal and geographically restricted nature of the potassic alteration, however, suggests restriction of K-rich, bittern evaporitic brine production in the younger and inboard parts of the Mount Isa – McArthur Basin system. Our results provide insights that directly relate to the genesis and exploration of basin-hosted Zn-Pb and Cu-Co mineral systems. They confirm that mafic igneous rocks in the region have lost significant amounts of both Zn and Cu, many times more than required for known deposits. The study also shows that metal leaching was accompanied by magnetite-destructive alteration. Hence, identifying zones of metal leaching may be possible using inversions of geophysical data, which may assist in targeting exploration.
<b>Citation:</b> Champion, D.C., Huston, D.L., Bastrakov, E., Siegel, C., Thorne, J., Gibson, G.M. and Hauser, J., 2020. Alteration of mafic igneous rocks of the southern McArthur Basin: comparison with the Mount Isa region and implications for basin-hosted base metal deposits. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.
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Identification info
- Date (Creation)
- 2020-02-06
- Date (Publication)
- 2020-06-26T07:21:55
- Citation identifier
- Geoscience Australia Persistent Identifier/https://pid.geoscience.gov.au/dataset/ga/134206
- Citation identifier
- Digital Object Identifier/http://dx.doi.org/10.11636/134206
- Cited responsible party
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Role Organisation / Individual Name Details Author Champion, D.C.
Author Huston, D.L.
Author Bastrakov, E.N.
Author Siegel, C.
Author Thorne, J.
Author Gibson, G.M.
Author Hauser, J.
- Name
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Record
- Purpose
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EFTF abstract
- Status
- Completed
- Point of contact
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Role Organisation / Individual Name Details Point of contact Commonwealth of Australia (Geoscience Australia)
Voice Point of contact Huston, D.
MEG Internal Contact Resource provider Minerals, Energy and Groundwater Division
- Spatial representation type
- Topic category
-
- Geoscientific information
Extent
Temporal extent
- Time period
- 2016-11-20 2020-06-20
Extent
))
- Maintenance and update frequency
- As needed
Resource format
- Title
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Product data repository: Various Formats
- Website
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Data Store directory containing the digital product files
Data Store directory containing one or more files, possibly in a variety of formats, accessible to Geoscience Australia staff only for internal purposes
- theme.ANZRC Fields of Research.rdf
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EARTH SCIENCES
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- Keywords
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EFTF
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- Keywords
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Alteration
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- Keywords
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Geochemistry
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- Project
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Exploring for the Future
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- Keywords
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Mineral Systems
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- Keywords
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Published_External
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Creative Commons Attribution 4.0 International Licence
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CC-BY
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4.0
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- License
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- License
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Australian Government Security ClassificationSystem
- Edition date
- 2018-11-01T00:00:00
- Classification
- Unclassified
- Language
- English
- Character encoding
- UTF8
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Role Organisation / Individual Name Details Distributor Commonwealth of Australia (Geoscience Australia)
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- OnLine resource
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Extended Abstract for download (pdf) [2 MB]
Extended Abstract for download (pdf) [2 MB]
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pdf
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Resource lineage
- Statement
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This work was undertaken under the EFTF program in collaboration with staff from CSIRO and ANU, It was based on geochemical, isotopic and geophysical data of samples collected in 2016-2020 from drill core samples held at the Northern Territory Geological Survey and Geological Survey of Queensland core libraries (Darwin, Alice Springs, Brisbane and Mount Isa). Geochemical analysis was undertaken in Canberra and Perth, selected geophysical data was measured at core libraries, and in Canberra and Perth. Stable isotope analysis was undertaken in New Zealand. Data from collected samples were supplemented with existing geochemical data held at Geoscience Australia undertaken over the last 50 years.
Metadata constraints
- Title
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Australian Government Security Classification System
- Edition date
- 2018-11-01T00:00:00
- Classification
- Unclassified
Metadata
- Metadata identifier
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urn:uuid/5c706135-4d75-4732-9317-1b030938d8c1
- Title
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GeoNetwork UUID
- Language
- English
- Character encoding
- UTF8
- Contact
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Role Organisation / Individual Name Details Point of contact Commonwealth of Australia (Geoscience Australia)
Voice Point of contact Huston, D.
MEG Internal Contact
Type of resource
- Resource scope
- Document
- Name
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GA publication: Extended Abstract
Alternative metadata reference
- Title
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Geoscience Australia - short identifier for metadata record with
uuid
- Citation identifier
- eCatId/134206
- Date info (Creation)
- 2019-04-08T01:55:29
- Date info (Revision)
- 2019-04-08T01:55:29
Metadata standard
- Title
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AU/NZS ISO 19115-1:2014
Metadata standard
- Title
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ISO 19115-1:2014
Metadata standard
- Title
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ISO 19115-3
- Title
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Geoscience Australia Community Metadata Profile of ISO 19115-1:2014
- Edition
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Version 2.0, September 2018
- Citation identifier
- https://pid.geoscience.gov.au/dataset/ga/122551