Mount Barney EarthCache

Approximately 24 million years ago, the Focal Peak Volcano to the west of the posted co-ordinates was formed. A number of roots formed under the surface, including a granophyre dome intrusion that would eventually become Mount Barney. Later the Tweed Valley eruptions buried much of the Focal Peak formations

Prior to the eruption, the landscape consisted of a series of south north valleys eroded into a sedimentary layers consisting of soft shales and sandstone of the Jurassic period. Below this were the Mt Barney beds consisting of carboniferous period sandstone.

Mount Barney was created when a granophyre dome intrusive mass, was pushed up more than 2000m through the Mt Barney sandstone beds. Erosion then stripped away the sandstone, though some still remain in places, to leave the Mt Barney formation we see today.

The diagram below shows the formation of Mt Barney as part of the Focal Peak volcano development (reproduced from Reference 1)

Granophyre is magna that crystallises, usually at shallow depths, to form a fine grained igneous intrusive rock, similar in appearance to Granite though it has a much fine grain size.

There are a number of other peaks that have formed in the area but they are predominantly of rhyolite. The nearby Mt Gillies, was the source of the rhyolite flows that formed Mt Lindsay and Mt Gennie.

Rhyolite is a fine grained extrusive rock, and like granophyre is similar to granite, but is formed from magna flow at the surface.

Reference 1. Neville Stevens and Warwick Willmott “MOUNT BARNEY - MOUNT BALLOW” Rocks and Landscape Notes, Geological Society of Australia No 5.

At the posted co-ordinates you will find an information board. To log this earthcache you need to do the following;

1. Visit GZ and send the owner (via the link below) with the following answers;
a) The basalt lava flow makes up the rich soils in which valleys?
b) The type of weakness that the massif formed?
c) What kind of volcanoes formed to create the extensive plains?

2.Take a photo of your GPSr(and if possible yourself) with Mt Barney in the background.(There some good and safe locations on the road leading to GZ)