A trace element study of siderite–jasper banded iron formation in the 3.45 Ga Warrawoona Group, Pilbara Craton—Formation from hydrothermal fluids and shallow seawater

• Published in: Precambrian research Vol. 137; no. 1; pp. 93 - 114
• Main Authors: Bolhar, Robert, Van Kranendonk, Martin J., Kamber, Balz S.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 28.04.2005
• Subjects: Archaean; Banded iron formation; Caldera; Hydrothermal fluids; Marine; Panorama Formation; Pilbara Granite-Greenstone Terrain; Rare earth elements; Canada, Alberta, Jasper; Australia, Western Australia, Pilbara Craton; Australia, Western Australia, Warrawoona Group; Banded iron formation; Rare earth elements; Panorama Formation; Caldera; Hydrothermal fluids; Pilbara Granite-Greenstone Terrain; Archaean
• ISSN: 0301-9268; 1872-7433
• DOI: 10.1016/j.precamres.2005.02.001

Shale-normalised rare earth element and yttrium (REE + Y) patterns for siderite–jasper couples in a banded iron formation of the 3.45 Ga Panorama Formation, Warrawoona Group, eastern Pilbara Craton, display distinct positive Y and Eu anomalies and weak positive La and Gd anomalies, combined with depleted light REE relative to middle and heavy REE. Ambient seawater and hydrothermal fluids are identified as major sources of REE + Y for the BIF. In the case of siderites, strong correlations between incompatible trace elements and trace element ratios diagnostic of seawater indicate variable input from a terrigenous source (e.g. volcanic ash). We propose a volcanic caldera setting as a likely depositional environment where jasper and siderite precipitated as alternating bands in response to episodic changes in ambient water chemistry. The episodicity was either driven by fluctuations in the intensity of hydrothermal activity or changes in magma chamber activity, which in turn controlled relative sea level. In this context, precipitation of jasper probably reflects background conditions during which seawater was saturated in silica due to evaporative conditions, while siderites were deposited most likely during intermittent periods of enhanced volcanic activity when seawater was more acidic due to the release of exhalative phases (e.g. CO 2).