Timing and genesis of Hamersley BIF-hosted iron deposits: a new palaeomagnetic interpretation

Summary

A systematic palaeomagnetic/rock magnetic investigation involving detailed palaeomagnetic and petrophysical analysis of 578 oriented samples was done in the late Archaean-Palaeoproterozoic rocks in situ iron deposits of the Hamersley Province. Five phases of magnetic remanence were identified.

These results in turn suggest there were two major phases of martite-microplaty hematite formation or recrystallisation, and therefore iron ore magnetisation, in the Hamersley Province.

The older event at about 2400 – 2200 Ma is thought to have been important for ore formation in the eastern and central parts of the province, whereas the second phase at about 1800 – 1650 Ma is said to be dominant in the western central part of the province.

The younger event has caused reworking of iron deposits in the central Hamersley Province but not in its east.

The palaeomagnetism results also suggest that the first phase of ore genesis occurred while the Pilbara was at a palaeolatitude of c.500, whereas the second -phase occurred at a tropical palaeolatitude.

The report further asserts that the results fail to support the supergene model of iron ore formation for several reasons.

Keywords: geochemical anomaly, mobile metal, soil geochemistry, geochemical prospecting