History Snippet: Drake

I noticed that the Northern Star Newspaper has an interesting snippet about historical copper mineral exploration near Drake. I thought It would be worth directing readers to the article.


http://www.northernstar.com.au/news/history-copper-hidden-in-the-hills-at-drake/2998850/


I've been meaning to do a detailed post on the geology outlined by Grace Cumming who in 2011 did a very detailed survey of the region and put together an interesting model which illustrates that the mines and prospects just north of Drake are actually the remnant of a very large 400 square kilometre volcanic caldera. I will get to that soon! There is always a million interesting things in our region that I seem to never get the chance to cover them all. In the mean time I can only point you to one post I've done about the 'Drake mines'. http://nrgeology.blogspot.com.au/2012/12/drake-mining-managing-muddy-mess.html


If you are interested in the current explorer and operator of the mines just to the north of Drake here is the link to White Rock Minerals Mt Carrington project overview.
http://www.whiterockminerals.com.au/projects/mt-carrington/overview/

Most important movie of the year?!

An excellent song by the Ameoba People. I will be featuring some of their exceptional work all this month. Keep a look out for the Geology dance moves... and give them a go! 

A Brand New Month and a Brand New Eruption at Mount Warning

This morning started in a very interesting way. I wasn’t sure but there was some shaking of my house. I just thought it was a garbage truck going by so I thought little more of it. That was until I drove to work and looked out at Mount Warning. The clouds that hang around the peak in the morning (often to the dismay of tourists watching the sunrise from its peak) looked just a little odd shaped and darker. Again, I thought nothing of it.

What I didn’t know I had just experienced was one of the many small earthquakes that struck the region last night and continue today. You can see the latest seismic readings from geoscience Australia here. The clouds were actually not morning clouds but small amounts of ash and steam rising from the peak as a new vent opened up (the first in a very long time). Australia has not had a volcano erupt on the mainland since pre-colonial times and even those volcanoes erupted in Victoria and South Australia, no-where near our pretty part of the world.

The news websites are going very busy and I know that there are some interesting Instagram and facebook pictures going around already. I should have one of my own pictures up shortly. By all accounts there is little danger away from the mountain but people intending to visit the national park should be aware of the dangers present and not attempt to climb if they see any evidence of Holocene lava.

A Rock of Gibraltar Range National Park - Part 2

Dandahra Creek Leucogranite

This post is a follow-on from an earlier post which can be read here.

The Dandahra Creek Leucogranite is mainly composed of granite which is depleted in dark (mafic) minerals. The crystals are of very similar size and medium to coarse grained. The crystals are mainly quartz with feldspars and occasional biotite mica. The term Leuco- simply refers to the light colour and lack of mafic minerals. There are also small amounts of other minerals that are disseminated through the rock these include the mineral zircon which is used for dating.

The dating of the Dandahra Creek Leucogranite was only conducted in the last couple of years. It is an example of using multiple techniques together to get an answer. The mineral Zircon is formed in magma chambers of granite and granite-like composition. This is a very stable mineral. Zircon locks up uranium in small amounts and this uranium undergoes radioactive decay to lead. By measuring the proportions of uranium to lead it is possible to determine how long ago the zircon had formed. In the past in some cases the whole zircon crystal have been used to determine the ratio. However, this method has some complications.

Not all of the zircon crystals in rocks show the same age. In the case of the Dandahra Creek Leucogranite some seemingly having much older ages. These crystals are actually inherited from the parent rock. The stability of the zircons means that they have not fully melted in the magma chamber. Often a good way to determine if a zircon is older than the magma chamber is to look at the shape and determine whether there has been any melting of the edges of the crystal. However, sometimes it is very hard to tell because the zircon often builds itself up again with an old core and a new crystal face.

To overcome the problem of age zoning in zircon crystals an alternative method was developed measure the ratio of lead and uranium. A high accuracy ion beam is aimed at the different portions of crystal. The ion beam vaporises the elements in that tiny area. The vapour is then measured for the abundance of each element and then the ratio of elements can be calculated. This is called the Sensitive High Resolution Ion Micro Probe or SHRIMP.

SHRIMP was a method developed right here in Australia. It is regarded as one of the most reliable ways to analyse microscopic crystals to determine when and how they formed. The need for the special machine came from dating the Rocks that make up the oldest parts of Western Australia which are the oldest in the world. It has no become a recognised tool around the world (Ireland et al 2008). There are 20 SHRIMP analysers around the world with four built in the last couple of years in Japan, China and Poland. Like Wi-Fi, the Hills-Hoist and Pavlova it is another example of Australian scientific ingenuity.

The age of the intrusion given for the Dandahra Creek Leucogranite using the SHRIMP method is 237.6 Ma (plus or minus 1.8Ma). This makes it the youngest example of the Stanthorpe Suite of Granites (Chisholm et al 2014) and nearly the youngest in the whole Standthorpe Supersuite (Thanks for the correction rockdoc!).

References.Bibliography:

*Chisholm, E.I., Blevin, P.L. and Simpson, C.J. 2014. New SHRIMP U–Pb zircon ages from the New England Orogen, New South Wales: July 2012–June 2014. Record 2014/52. Geoscience Australia

*Clarke, Peter J. & Myerscough, Peter J. 2006. Introduction to the Biology and Ecology of Gibraltar Range National Park and Adjacent areas: Patterns, Processes and Prospects. Proceedings of the Linnean Society of New South Wales

*New South Wales National Parks and Wildlife Service 2005. Gibraltar Range Group of National Parks (Incorporating Barool, Capoompeta, Gibraltar Range, Nymboida and Washpool National Parks and Nymboida and Washpool State Conservation Areas) Plan of Management. February 2005. ISBN 0 7313 6861 4

*Ireland, T.R., Clement, S., Compston, W., Foster, J. J., Holden, P., Jenkins, B., Lanc, P., Schram, N. & Williams, I. S. (2008), "Development of SHRIMP", Australian Journal of Earth Sciences V55 p937–954

ABC Radio Interview - The river that flows the wrong way!

I had the pleasure of being interviewed by Joanne Shoebridge of ABC North Coast Radio last week. The story was about the way the Clarence River flows backward!

This was my first ever live interview and boy did I um and err a lot! Hopefully the story is interesting though and the amazing story of our landscape comes out. Let me know what you think.
https://sites.google.com/site/nrgeologymediafiles/home/mp3/01%20Track%201.mp3?attredirects=0&d=1

It was exciting to be interviewed but I also was excited to be offered a position on the National Parks and Wildlife Service Regional Advisory Committee for the Northern Rivers. Exciting to be part of a statutory board or Quango (quasi-autonomous non-governmental organisation) in Yes, Minister bureaucratic speak.

Sediments of the Anthropocene

In my workplace I have recently had some fun improving my knowledge and application of erosion and sediment control methods. It reminds me that sometimes a little knowledge and the best intentions can actually lead to wasted time or even worse outcomes. I’d like to use this post to look at what erosion and sediment control means for sites that are to be disturbed. This is because of a construction site I visited in my town a couple of weeks ago that made me laugh (I had to see the funny side otherwise I’d always be crying!)

Is this working?

The first point to know is that erosion and sediment control is two things (erosion and… sediment control). They are not one and the same thing. In fact the most important part is the erosion control bit. If you have erosion control you don’t need sediment controls. This lack of distinction I think causes the biggest waste of resources.

Have a look at the picture here. This is a classic example of a waste of time. It is something that was never going to be the solution and inevitably failed and wasn’t even looked after anyway. In this example a small slope was disturbed. This small slope had water running on to it from a grass slope. The people responsible thought “hey, treatment: sediment fence!”… But thought nothing about fixing the problem in the first place. A better solution would have been to do one or a combination of erosion control measures. These could have included:

• Diverting clean storm water around the exposed slope with a mulch bund or similar (many trees were chipped and removed from the area).
• Spraying the surface with a synthetic soil stabiliser.
• Spraying the surface with a hydro mulch or similar with grass seed.
• Covering with a synthetic or biodegradable mesh framework which was then seeded

Is this working?

None of these things would cost much more in time or money than installing and re-installing failed silt fences. And they would have actually fixed the problem in the first place. Just to add a little icing to the cake here is another control measure that was located about 20 metres away. The good old sandbag near a stormwater inlet. At the best of times this can only be considered a supplementary technique that should never be used in isolation. In this case the sandbag has ruptured and the sand appears to have actually gone into the storm water system itself! The small amount of sediment retained seems to only be effective because of weeds growing in the gutter. No thought again, and no checking to make sure things work and no fixing of failed problems for an obviously long time.

Erosion control should always be the first focus and even when using sediment controls consideration needs to be given to whether they will even be effective. For example “silt fences” are actually not good at holding back silt. They only hold back sand! They should be called “sand fences”. Clays, silts and any dispersive soils will pass straight through a silt fence. It is important that people in the know to undertake erosion and sediment control works. This is important were ever significant disturbance is to occur or where sediment may easily enter waterways or other sensitive receptors.

A rock of Gibraltar Range National Park - Part 1.

A lookout on the Gwydir Highway

I was going to write a very long post on the Dandahra Creek Leucogranite but I think it lends itself to two posts. This post will focus on the amazing Gibraltar Range National Park and the second will focus on Australian ingenuity and dating of the Dandahra Creek Leucogranite.

A few months ago I travelled from Glen Innes to Grafton via the Gwydir Highway. The landscape in this area is wonderfully diverse and surprisingly contradictory. For example usually Sandy soils on the plateau give rise to swamps with peat. It is a special area because the link between the geology, vegetation and even bush fire patterns is quite obvious. I'd like to focus on one rock unit that makes up the balance of the Gibraltar Range National Park area, the Dandahra Creek Leucogranite.

The Dandahra Creek Leucogranite was often referred to as the Danhahra Granite (and still regularly called this in botanical circles). It is part of the New England Batholith and has recently been dated at at 237.6 Ma (Chisholm et al 2014). It is the youngest member of the Stanthorpe supersuite of granites. Outcrops are very frequent in the Mulligans Hut area and the Gwydir highway transverses the unit.

The spectacular tors which are major features of the landscape of Gibraltar Range National Park arise from weathering from the Dandahra Creek Leucogranite. These tors form through onion peel weathering (technically called exfoliation or spheroidal weathering). This weathering process is where water enters cracks in the rocks and then freezes over night. As water turns to ice it expands and sheets off rock just like an onion skin. This is usually a fairly slow process except with the last sloughing off of the onion peel occurring quite rapidly.

Tall open forest is a major feature of the landscape of the Dandahra Creek Leucogranite. These eucalyptus dominated forests can have an open, grassy understorey featuring grass-trees and/or tree-ferns. These landscapes are quite fire prone. Indeed their structure is dependent on multi-decadal scale fires.

There are also some more unusual vegetation communities on rock outcrops because the tor outcrops lend themselves to protecting some vegetation from fires. They are also very thin soils with low nutrient content so even carnivorous plants can be found.

Heathlands and grasslands occur around the rock outcrops and are particularly important as they contain the greatest concentration of rare, threatened or geographically restricted species, or species found at the limits of their distribution (NPWS 2005). The grass and heath land burns very frequently often with bush fires only every several years.

The shallow wide valleys that are formed on the sandy granitic derived soils result in common large peat swamps. The shape of the valleys slows down water and the underlying massive granite means that the water does not infiltrate. The swamps contain sedges and other water loving plants.

If you are interested in the bush or interested in rock the Gibraltar Range National Park is for you. If you are in to camping, bush walking, amazing views of rugged valleys the Gibraltar Range National Park is for you. If you are in to spectacular flowers, rainforests, exploring a rocky creek the Gibraltar Range National Park is for you. If you are in to staying in a lodge, want to see some snow, or bathe in a rock pool on a summers day the Gibraltar Range National Park is for you.

References/Bibliography:

*Chisholm, E.I., Blevin, P.L. and Simpson, C.J. 2014. New SHRIMP U–Pb zircon ages from the New England Orogen, New South Wales: July 2012–June 2014. Record 2014/52. Geoscience Australia

*Clarke, Peter J. & Myerscough, Peter J. 2006. Introduction to the Biology and Ecology of Gibraltar Range National Park and Adjacent areas: Patterns, Processes and Prospects. Proceedings of the Linnean Society of New South Wales

*New South Wales National Parks and Wildlife Service 2005. Gibraltar Range Group of National Parks (Incorporating Barool, Capoompeta, Gibraltar Range, Nymboida and Washpool National Parks and Nymboida and Washpool State Conservation Areas) Plan of Management. February 2005. ISBN 0 7313 6861 4