Rosemount Estate, Gulgong

SITE EVALUATION AND VARIETAL MATCHING IN THE GULGONG AREA, NEW SOUTH WALES

In late 1999, Rosemount Estate (now part of Southcorp Wines Limited) commissioned Terroir Australia to assess the viticultural suitability of a large area of land that it had recently acquired close to its existing vineyards at Cumbandry, to the southeast of Gulgong, 30 km north of Mudgee. The land, previously used for mixed grazing and crop production, appeared to have soils that were generally suitable for wine grapes, is at an average elevation of 480 metres AMSL, and its slopes face between north and east.

As found in the Piccadilly Valley and Keyneton area projects, existing geological and soils information was far too generalised to be of use. High-resolution airborne radiometric data (see explanation in Petaluma page), as shown in the image below, revealed a complex interplay between soils formed on various substrates, including granitic, volcanic and two contrasting types of sedimentary bedrock, colluvial material derived from these rocks, and broad areas of mixed alluvium.

FALSE-COLOUR RADIOMETRIC IMAGE OF THE
"WOOLOOMOOLOO" AREA, GULGONG, NSW

1 Solid bright red - 'granite' (monzodiorite) & thin soils on monzodiorite;

2 Solid dark red - basaltic to andesitic volcanic rocks; thin soils on volcanic rocks;

3 Bright greenish blue - shaly/slaty sedimentary rocks; thin soils on these rocks.
Mixed/mottled red-and-blue tones correspond to:

soils on mainly sedimentary rocks (2) adjacent to solid red (hilltop) areas;

soils on colluvium, alluvium derived from monzodiorite (centre) & mixed sources.
Mottled and/or dark blue/greenish-blue tones correspond to
soils on alluvium & colluvium derived mainly from sedimentary rocks.
Very dark, rounded areas in the lower right of the image are where the aircraft gained altitude to clear clumps of trees and the gamma-ray signal was attenuated.
Green lines - areas under consideration for vineyard establishment.
Black lines - roads.
Grey line - railway line.

These 'categories' of radiometric signature are much more objectively identified and easily visualised by means of supervised classification* of the primary data, as illustrated in the image below.

CLASSIFICATION OF RADIOMETRIC DATA,
"WOOLOOMOOLOO" AREA, GULGONG, NSW

EXPLANATION

Red = exposed 'granitic' rock (monzodiorite) and very thin soils on monzodiorite;

Orange = thin soils on monzodiorite & monzodioritic volcanic rocks (trachyandesite);

Yellow = soils formed mainly on monzodiorite;

Lime green = soils formed mainly on basaltic & (trachy)andesitic volcanic rocks;

Bluish green = soils formed on mainly colluvium and alluvial fans of mixed source;

Deep blue = clay-rich soils on alluvium derived mainly from sedimentary rocks;

Grey = damp/wet clays mainly on alluvium/colluvium derived from sedimentary rocks;

White = no data.

Information from the two images above was used to produce a preliminary soil interpretation which was then used as a guide for ground observations. These observations - mostly from hand-auger holes drilled to an average of 1 metre - were then used to compile the final soil map, reproduced below.

SOIL MAP SUPERIMPOSED ON AERIAL PHOTOGRAPH,
"WOOLOOMOOLOO" AREA, GULGONG, NSW

The fine white lines mark soil boundaries as mapped using the radiometric data and field observations. The colour aerial photograph shows clearly some of the areas of damp to wet (or waterlogged) soils, which appear dark red-brown to grey. Note in particular the two areas labelled "B" (lower right) which correspond to areas of black clay, in which a calcrete layer is forming, and a frequently very high water table.

The soil map and accompanying report (which describes the soils in detail and makes recommendations as to grape varieties suited to each soil 'type') were used by Rosemount Estate viticulturalists to design new vineyards, which are now producing successfully. The area has considerable viticultural potential.

Following the successful application of Terroir Australia techniques and philosophy to the "Wooloomooloo" area, Rosemount Estate commissioned Dr Mackenzie to investigate the geology and soils of another, larger, area to the south of their original Gulgong vineyards at "Cumbandry".

* Radiometric signatures from areas of known geology and/or soil type are used to construct a complex formula, or algorithm, which classifies each data pixel and assigns it a colour. [ back ]

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