Sugars Quarry was purchased in 1883 by Thomas Sugars to add to his existing farm holdings. Contemporary newspaper reports indicate that the property was first used for quarrying by Colledge Brothers & Collin after acquiring a 10 year lease on the property. By November 1887 that business was in liquidation and it appears that the operations were taken over by the Sugars family. The quarry operated under various ownerships until 1963 when it closed. It opened again briefly in 1975 before permanently closing the same year. In 1995 the site was reserved as a park before being formally opened in 2006 as part of Anstead Bushland Reserve.
During its lifetime the quarry produced hundreds of thousands of tonnes of crushed blue metal used in various construction projects around Brisbane. The blue metal from this quarry was regarded by local experts of the time as exceptional quality and although a finer grained rock, was more durable than blue metal sourced from other quarries of the region.
The blue metal from Sugars Quarry is in fact basalt, or more correctly basaltic andesite. Basaltic andesite differs from normal basalt due to the increased levels of silica present in the rock. Basalt contains 45% to 52% silica while basaltic andesite contains 52% to 57% silica (refer Figure 1).
Figure 1
The deposits at Sugars Quarry are a unique geological stratigraphic unit called Sugars Basalt. This formation is part of the Kholo Subgroup which in turn forms part of the Ipswich Basin (Ipswich Area), a.k.a. Ipswich Coal Measures. The Sugars Basalt was formed during the Late Triassic (Carnian) age – some 229-232 million year ago – as a result of sub-aerial volcanic eruption. Accordingly, the rock is classed as an igneous rock. At the type section of the Sugars Basalt at least seven separate lava flows occur.
A close examination of samples of the rock reveals almost indistinguishable mineral grains, evidence of the rapid cooling of the extruded lava. You may note, however, different coloured deposits in the rock. This is because the Sugars Basalt is amygdaloidal. Dissolved gas in lava can form bubbles as the pressure is released on eruption, and are trapped in the rock as it cools. After some time, groundwater or hot solutions connected with the volcanic activity pass through the porous lava and deposit crystals in the open cavities, which gradually fill up with quartz, calcite (calcium carbonate) or other minerals. These filled cavities are called amygdales, and a rock full of them can be called amygdaloidal.
The Sugars Basalt can also be described as a mafic rock. This is a rock which is rich in magnesium and iron (the term mafic being an abbreviation of magnesium and ferric), and it is these minerals which give the rock its dark colouring.
The waypoints of this earthcache will lead you on an exploration of different parts of the quarry. Along your travels you will need to obtain information to answer the following questions:
WP1: S27 32.745 E152 51.273 (listed coordinates)
Information board you may wish to read about the quarry.
WP2: S27 32.790 E152 51.235
Question 1: At the coordinates for WP2, you will find a large sample of rock from the quarry (it is the last rock at the eastern end of a line of large rocks). Describe the western and eastern end of the rock (particularly surface texture, colour, grain size).
Question 2: Do either of these ends display evidence of gas bubbles or amygdales? If so, state which end/s and describe what you see.
Please send an email with your answers via my user profile.
References:
Geological Society of Australia Inc. G.W. Hofmann (ed.) 1981 1981 Field Conference Brisbane-Ipswich Area (www.qld.gsa.org.au/GSA%20Guidebooks_files/1981%20Guidebook_files/1981%20Brisbane%20Ipswich%20Area%20Text.pdf)
Andrew Ferguson Roach 1998. Late Triassic volcanism of the Ipswich Basin Chapter 1 and 4 (http://hdl.handle.net/1959.14/113998)
Andrew Ferguson Roach 1996. Late Triassic Volcanism of the Ipswich Basin, in, Mesozoic Geology of the Eastern Australia Plate Conference, Geological Society of Australia, Extended Abstracts No. 43, p 476-484 Available from (www.oocities.org/aroach.geo/geology/meso96/) [13 January, 2016]
Australian Stratigraphic Units Database - Sugars Basalt Available from (http://dbforms.ga.gov.au/pls/www/geodx.strat_units.sch_full?wher=stratno=17504)[13 January, 2016]
Basalt-Igneous rocks Available from (www.sandatlas.org/basalt/) [13 January, 2016]
Rocks In Hand Specimen - Basalt lava (amygdaloidal) Available from (www.earth.ox.ac.uk/~oesis/rocks/ign5.html) [13 January, 2016]