Heavy minerals form south-west Fiordland

(Inc. GST)
(Ex. GST)
Write a Review

Smale, D. 1990 Heavy minerals form south-west Fiordland. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report SL 22 10 p.

Abstract: Heavy mineral suites from Cretaceous and Tertiary sediments in south-west Fiordland were examined and compared with those form some outcropping basement rocks and Recent sediments derived from them. Basement suites are mostly dominated by hornblende, some with large amounts of epidote, sphene or garnet; others contain mostly biotite; pyroxene, tournaline, sillimanite and staurolite occur sparsely. Hornblende is absent from all the Cretaceous-Tertiary sediments. The Cretaceous sediment suites contain only very resistant minerals, in spite of the variety present in their source rocks, but the Tertiary (particularly Oligocene) sediments contain more sphene and epidote and less apatite. The overall heavy mineral distribution is consistent with derivation from local basement rocks followed by intrastratal solution of the less stable species. The presence of much apatite in the Cretaceous sediments indicates that they were affected by burial rather than weathering. The virutal absence of apatite in the Macnamara Formation (Eocene) may have resulted from an acid environment associated with coal measures. The presence of the less stable minerals in suits of comparable age from the Te Anau and Waiau Basins on the other side of the Fiordland massif suggests that these were less deeply buried. The results emphasize that restricted heavy mineral suites do not necessarily indicate a similarly restricted provenance.