Dating quartz veins

22-Apr-2015 16:50

This was a joint project between Geoscience Australia and the Northern Territory Geological Survey from 2000 to 2004 to try and determine the extent of orogenic gold mineral systems in the Tanami and Arunta regions of central Australia.

Outcrop in the area is sparse (~5%) and most of gold mineralisation is covered by a blanket of regolith consisting predominantly of transported sand and laterite.

The yellow zones in the diagram below show regions where we also observed veins with crustiform or bladed pseudomorphs which might be interpreted as epithermal or epizonal textures.

There are 2 populations of inclusions, both homogenising between 120 and 180 C.

The veins are dominated by aqueous Type D fluid inclusions with a small vapour bubble.

Occasional vapour-rich inclusions are due to necking-down processes.

The regolith is usually 10-20 m deep, but at places may reach more than 100 m.

Our strategy has been to carefully characterise the composition of the ore-bearing fluids at the major gold deposits in this region and then to expand our studies further a field.

In a few of the pits we were able to observe primary fluid inclusions in growth bands in vuggy quartz.The largest gold mine in the area is the Callie mine, which is a world-class deposit with over 4.5 Moz Au.