Abstract

From 3.5 Ga the overall uniformity of the composition and character of sedimentary and mantle- and crustal-derived igneous rocks, and the persistence of ore types related to convergent continental margins (e.g. volcanic-hosted massive sulphide, porphyry Cu-Mo, Sn-W and lode Au), indicates continuity of tectonic processes broadly similar to the present. Secular variations in abundance of these ores reflect tectonic cycles having periods of perhaps several hundred million years, but other ores reflect long-term changes in tectonic style and the composition of the ocean and atmosphere. Thus the development of extensive continental margins and depositional basins from about 3.0 Ga heralded development of giant Au-U conglomerate and banded iron formation deposits, with at least the former suppressed in the Palaeoproterozoic as a result of increased atmospheric PO2. Aggregation of large continents and the development of extensive basins allowed formation of giant Cu-Co, Pb-Zn and U-platinum group elements-Au ores from about 2.0 Ga. There is no firm evidence that mantle heterogeneity has contributed to ore distribution, nor that Archaean crust or mantle was anomalously enriched in Au or platinum group elements. Mineralogical and isotopic data from volcanic-hosted massive sulphide deposits support the hypothesis that there was abundant sulphate in deep oceans from 3.5 Ga, and the lack of Pb and barite in Late Archaean ores may be related to the mafic-rich composition of the local shallow crust, steep thermal gradients, anoxic, sulphate basin waters or the compositions of particular magma types. Both the ocean margin (Holland 1973) and the hydrothermal plume/gravity current models for the origin of banded iron formations are broadly compatible with their composition, secular distribution and timing with respect to glaciation, ocean anoxia and tectonic activity. In the gravity current model the possible impact of the hydrothermal activity on climate warrants further investigation.
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Product Type/Sub Type

nonGeographicDataset

Constraints

Creative Commons Attribution 4.0 International Licence

IP Owner

Commonwealth of Australia (Geoscience Australia)

Author(s)

Date (publication)

1997-01-01T00:00:00

Product Type

nonGeographicDataset

Topic Category

geoscientificInformation

GA Catalogue Number

81476 Product http://www.ga.gov.au/metadata-gateway/metadata/record/81476/

Keywords

GA Publication
Journal
Earth Sciences

Resource Language

English

Resource Character Set

utf8

Resource Security Classification

unclassified

Lineage

Unknown

Digital Transfer Options

onLine

Distributor

Role
distributor
Organisation Name
Commonwealth of Australia (Geoscience Australia)
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address

Source Description

Source data not available.

Metadata File Identifier

fae9173a-71a1-71e4-e044-00144fdd4fa6

Metadata Standard Name

ANZLIC Metadata Profile: An Australian/New Zealand Profile of AS/NZS ISO 19115:2005, Geographic information - Metadata

Metadata Standard Version

1.1

METADATA SECURITY CLASSIFICATION

unclassified

Metadata Contact

Role
pointOfContact
Organisation Name
Commonwealth of Australia (Geoscience Australia)
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address
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