The timing of high temperature metamorphism at the Snaefell magnetite deposit, South Australia

Abstract

Zircon and monazite geochronology and trace elemental analysis provide the first constraints on the timing of high temperature metamorphism at the Snaefell magnetite deposit in the northern Gawler Craton, South Australia. The granulite facies rocks which host mineralisation at the Snaefell magnetite deposit yield zircon ages of 1749 ± 15 Ma and 1673 ± 16 Ma, as well as monazite ages of 1670 – 1660 Ma, 1590 – 1580 Ma and 1559 ± 10 Ma. The data indicate that the host sediments have a protolithic age of ca. 1750 Ma, consistent with depositional ages in the adjacent Mount Woods Inlier. The metasediments were exposed to high temperature granulite facies metamorphic conditions during the period 1670 – 1660 Ma. These ages are previously unrecognised in the northern Gawler Craton may indicate that the ca. 1720 – 1690 Ma Kimban Orogeny had a prolonged effect on the region. A second metamorphic event recorded between 1590 and 1580 Ma saw the development of E-W-NE trending folds and is attributed to the 1570 – 1540 Ma Kararan Orogeny. Late deformation at 1559 ± 10 Ma caused north-dipping shear zones to cut across the granulites and is associated second generation garnet growth. Possible hydrothermal zircon may indicate that magnetite is also of a hydrothermal source.