Tumut Explanatory Notes (1990)

Abstract

The Tumut 1:100 000 map sheet area (part of the Wagga Wagga 1:250 000 map sheet area) covers part of the southwestern slopes region. The rocks are in (from west to east) the Wagga Anticlinorial Zone, Tumut Synclinorial Zone and Young Anticlinorial Zone of the Lachlan Fold Belt. Oldest rocks are the ?Cambrian-Early Ordovician Jindalee Group, a sequence of metamorphosed sedimentary and igneous rocks (including the Gundagai Serpentinite). Middle Ordovician to Early Silurian rocks include sedimentary rocks of the Wagga Metamorphic Belt, the Nacka Nacka Metabasic Igneous Complex - and dioritic to granodioritic intrusions. During the Early to Late Silurian a complex sequence of igneous and sedimentary rocks were deposited or emplaced - including the Coolac Serpentinite, the Honeysuckle Metabasic Igneous Complex, Jackalass Slate, Blowering Formation, Goobarragandra Volcanics and the Young Granodiorite. Some of these units are extensive - in thickness and areal extent. Early Devonian volcanic units and granites (such as the Bogong Granite) were the last of the Palaeozoic rocks formed in the Tumut 1:100 000 map sheet area. The geological history discussed in the Notes is from the perspective of terrane analysis. Younger units include a Jurassic lamprophyre dyke and Cainozoic igneous and sedimentary units - including sands and gravels (with some high-level sediments worked for gold. Most of the 295 metallic mineral deposits shown on the map contain gold. Hard-rock gold occurrences are widespread: veins (in various units); reefs in the Nack Nacka Metabasic Igneous Complex; and veins and fissure fillings in a wide range of rocks. Many of the gold occurrences were found in the Adelong Creek Goldfield - and there are four other declared goldfields. Most of the (hard-rock) gold occurrences seem to be of metamorphic hydrothermal origin. Other metallic mineral deposits include copper (and lead and zinc), chromium, tin, molybdenum, manganese and iron.

Reference

Basden, H., 1990. Geology of Tumut 1:100000 Sheet 8527. 275 pp. New South Wales Geological Survey, Sydney.