Daylesford, Victoria, Australia

Geological and mining history, including the age of volcanoes to the north and south, but not yet of Wombat Hill itself.

This is one of several pages concerning Daylesford and places nearby.  The index for those pages is here: ../.

2015-10-18 Robin Whittle rw@firstpr.com.au

Minor updates 2016-01-25, 2016-02-29, 2016-12-05 and 2017-07-13.




Daylesford with Wombat Hill Botanical Gardens, looking north-west from Wheelers Hill Road, 8th August 2014.  (Wheelers Hill is another volcano.)


Wombat Hill is a scoria cone volcano - one of the hundreds of volcanoes of various types in the Newer Volcanic Province, which stretches to Mt Gambier. (A map here of the whole province; DEPI maphighly informative poster.) 

My cell-phone's GPS function tells me that the elevation of Wombat Hill is 667 metres (2,182 feet).  By comparison, Mt Dandenong - the most prominent feature in the horizon around Melbourne - is 633 metres (2,077 feet).  The Wikipedia page for Daylesford https://en.wikipedia.org/wiki/Daylesford,_Victoria mentions an elevation of 616 metres (2,021 feet).  I guess this would be at the post office.  My GPS reports an elevation of
523 metres (1,716 feet) for the walking track close to the dam of Daylesford Lake.




There are numerous volcanoes in the region.  These can be seen as the orange circular areas in this map, which is freely available from http://dpistore.efirst.com.au/product.asp?pID=292&cID=30&c=125213 .  I count 16 volcanoes in this area, which is about 25km west to east.

To aid with printing the above section of the map, here it is as pages 1 and 2.

If it wasn't for the volcano, the Daylesford area would be undulating sedimentary ground, somewhat lower.  This rock is from the trilobite days of the Lower Ordovician - around 480 million years ago.  The volcanos are much more recent than this - the last few million years or so.  The July 2016 update of the Goldsfields Track Walking and Cycling Guide (http://www.goldfieldstrack.com.au page 15) states:

In this part of the world the youngest volcanoes are 0.5 to 1 million years old - so young that they still retain their volcanic shape.

Update July 2017:

I tried to find the age of the Wombat Hill volcano but have found any definitive research.  The closest I have come is this article:


Ismail-2013
Rafika Ismail, David Phillips & William D. Birch
40Ar/39Ar dating of alkali feldspar megacrysts from selected young volcanoes of the Newer Volcanic Province, Victoria.
Proceedings of the Royal Society of Victoria 125(1/2): 59–69.
http://www.publish.csiro.au/RS/RS13019   (Open access.)

Basalt from the Daylesford Ridge Road quarry: about 2.01 million years ago.

Mt Franklin 8.5km north of Daylesford, is much more recent: about 110,000 years ago.

The article refers to the date of a rock sample from a basaltic flow which (as far as I can see) is from the Leonards Hill volcano, about 9km to the south.  Here is a detail from the above map with the Ridge Road quarry location shown.  So we have very different dates for the two volcanos to the north and south and no date for Wombat Hill itself. 



Here is my understanding of the
argon-argon dating techniques (WP link)
technique used to estimate these ages:

The researchers find grains of feldspar, or some other suitable crystal which contains significant amounts or potassium.  In the case of the Daylesford sample, this was a 2cm long feldspar crystal embedded in basalt from the old quarry on Ridge Road at the corner of Stony Creek Road, 3km south-south-west of Daylesford (Google Maps).  From the above article [Ismail-2016]:

The quarry on Ridge Road . . . is  in  a  basaltic  lava  flow  along  the  former  valley
of  Stony  Creek,  which  is  now  entrenched  along one edge of the flow.  The feldspar sample selected for the present study consisted of a 2-cm long colourless,
compositionally zoned crystal fragment enclosed in the basalt.

There are three naturally occurring isotopes of potassium
39K, 40K and 41K, with 20, 21 and 22 neutrons respectively in their nuclei.  All have 19 protons, which is what defines these nuclei as being of potassium atoms, since the 19 protons attract 19 electrons to form an electrically neutral atom.  The outermost electron of a neutral potassium atom is in its own "shell" (really a cloud of probability where the electron might be at any moment, if we think of it as a little ball, which is not quite the whole story . . .).  The shell below is full, with 8 electrons.  The lone outer electron is unstable and the total energy of the atom is significantly reduced if it can get rid of the electron.  So potassium in compounds does this, and becomes a positively charged ion.  In potassium chloride, the chlorine atoms have seven electrons in their outer "shell", which is also in a high-energy unstable state.  They accept the electrons from the potassium atoms and so too have full, low-energy, totally self-satisfied outer electron "shells".  The negatively charged chlorine ions are attracted to the positively charged potassium ions and form a neat cubic crystal.  Sodium chloride - table salt - is the same.

The number of neutrons in the nucleus of an atom does not affect how the atom forms compounds, so all three potassium isotopes are chemically indistinguishable.  All three had their nuclei formed by the extreme pressures and temperatures inside a supernova explosion of a star - one or more stars whose supernovae debris formed the cloud from which the Solar System formed about 4.6 billion years ago.  No-one knows how long ago these supernovae were, but these potassium nuclei have been unchanged since they were first formed by lighter nuclei being forced together in the supernova, so forcibly that their mutual repulsion was overcome and they stuck together as new, larger, nuclei.

39K and 41K are perfectly stable.  However, 40K is unstable AKA radioactive.  0.012% of potassium in and on the Earth is 40K.  (Wikipedia link) This has a half life of 1.251 billion years, so after this amount of time, half the atoms of 40K in a sample would be gone, since their nuclei will have broken down (decayed) into the nuclei of isotopes of the metal calcium and the noble gas argon.  10.72% of these decays involve an inner electron from the atom entering the nucleus and converting one of the protons into a neutron, with the release of electromagnetic energy as a gamma ray and a neutrino - an enigmatic particle which can usually pass right through the Earth without hitting anything!

So in any one year, there is a small, but precisely known, chance that a
40K
nucleus will transform itself from having 21 neutrons and 19 protons into having 22 neutrons and 18 protons, which means it is no longer a potassium nucleus, but the nucleus of the noble gas argon - specifically the stable (non-radioactive) isotope 40Ar

Since it now has one less positive charge, the nucleus only attracts 18 electrons to form an electrically neutral atom.  This is argon, and its outer electron shell is completely self-satisfied with 8 electrons - the whole atom is in a low energy state and there isn't any addition or subtraction of electrons which would cause it to be in a still lower energy state.

This means that argon does not bond covalently (electron sharing) or bionically (as with sodium and potassium, by giving up or gaining and electron) with any other atoms.  Argon, along with neon and krypton, are noble gasses which exist in the air we breath.  By mass 0.934% of air is argon, and 99.6% of this is
40Ar produced, as just described, by the decay of 40K in rocks, magma etc. within the whole Earth.  (There used to be a lot more 40K when the Earth was first formed.  It used to be the most important source of radioactive heating of the Earth's core and mantle, but it is now the third-most important after isotopes of uranium and thorium.)

If the feldspar crystal is hot enough, the argon atom behaves as a gas and can work its way through the crystal structure and so get out of the whole crystal.  However, this does not occur if the crystal is cool enough.

Long ago - I guess  millions  to a few billion years ago - a crystal of feldspar formed, incorporating potassium atoms whose nuclei were unchanged since being forged in one or more supernovae over 4.5 billion years ago.  This crystal somehow got mixed up in a flow of magma under the Australian continent, where this magma, later called lava as it erupts from what is now Leonards Hill, is hot enough to be molten, but not hot enough to melt the feldspar crystal.  This high temperature is, however, enough to allow all the
40Ar atoms which result from the radioactive decay of 40K to escape the crystal, go into the magma/lava, and, as the lava flows from the volcano, escape into the atmosphere.

The freshly erupted lava, with this feldspar crystal in its mist, flowed down the edge of the volcano, and eventually comes to rest 3.3km away, where it cools and solidifies, forming the basalt at the quarry at the corner of Ridge  and Stony Creek Roads.  The lava would have cooled within days or months to the point where the continually produced
40Ar atoms remain trapped in the crystal.

Because enquiring minds want to know, Rafika Ismail and colleagues went looking for such a crystal, found it, and took it back to the lab for analysis.  By measuring how many
40Ar atoms are trapped in the crystal, and by determining (indirectly) how many 40K atoms are in the crystal now (or were in the past few million years, since their numbers are declining due to radioactive decay) it is possible to calculate how long ago the crystal and its surrounding lava cooled - so giving the age of the presumably single phase of eruptions which produced Leonards Hill.

This was done by sending the crystal to a Canadian nuclear reactor facility, where it was bombarded by neutrons, which converted some proportion of the stable 39K nuclei into radioactive 39Ar  nuclei.  (The high speed neutron boots out a proton and takes its place.)

The exact proportion of this conversion is measured by analysing another sample which is subject to the same neutron bombardment.

Then the crystal is crushed into small grains and placed in a mass spectrometer specifically designed for five of the isotopes of argon:
the Argus IV mass spectrometer at the University of Melbourne, School of Earth Sciences (link).

An infra-red laser heats the grains so that various gases, including all the argon atoms of various isotopes, escape the crystal.  (
The potassium atoms stay behind, ionically bound, since the temperature is not enough to free them from their ionic bonds with neighboring atoms.) The argon atoms are then ionised (an electron is added or removed).  These individual ions have the same electric charge, but different masses, according to the total number of protons and neutrons in their nuclei.  (The electrons are about 1/1,837 the mass of protons and neutrons, so they hardly contribute little to the total mass.)

The argon ions are accelerated electrically in a vacuum to form a narrow beam.  The beam is processed by a velocity selector (link) so that all the ions which emerge have the same velocity
.

The beam is bent about 90 degrees by a large electromagnet.  The bending force is the same for all the ions, since they have the same electrical charge.  However, they have different momenta in the original direction, since they are traveling at the same speed but have different masses.  The heavy ions are bent less than the light ion, so five separate beams emerge from the magnetic field, one for each of the five argon isotopes.  The number of ions in each of the five beams is measured simultaneously by the ions coming to a halt, with their electrical charges adding up to an electrical current, on five metal plates connected to five very sensitive amplifiers.

The 
39Ar  nuclei can only have come from the conversion of neutron beam conversion of  39K  nuclei.  Any such 39Ar which might have been present in the crystal from millions of years ago would by now have disappeared, since it has a half-life of 269 years.  The count of 39Ar can be used to calculate the crystal's 39K content, from which its much smaller present day and past (since it is slowly diminishing) 40K content can then be calculated.

With care, the number of
40Ar ions detected by the mass spectrometer reflects exactly what was in the crystal.  The crystal has been imbedded in solid, cool, basalt (through which argon atoms cannot move) since the lava flow cooled.  Ideally, the sample and the spectrometer will not contain any stray  40Ar atoms from the atmosphere.

With this simultaneous measurement of the crystal's
40Ar and 39Ar content, the amount of  40K (the original radioactive potassium isotope, created in a supernova) can be calculated for the exact same grains and laser heated gas release temperatures as are used for the  measurement of the amount of 40Ar in the crystal  (the decay product of this, collected in the years since the crystal and its surrounding lava cooled).  This overcomes various errors which would result from trying to measure the potassium and 40Ar content separately.  This reduction of error makes it possible to calculate dates when even when only a very small fraction of the 40K has decayed since the crystal cooled enough to trap all the 40Ar.  "Small fraction" in this case means a small fraction of a billion years or so.  So the technique is good for measuring the last melting time of rocks in the million to billion year range.  However, as far as I know, it is not the best method of measuring much shorter times, such as of a few thousand years since the Mt Gambier or Mt Napier eruptions.

Plugging these two measurements, together with a measurement from the reference sample from the neutron, provides the time since the cooling.  For the Daylesford sample, this was 2.01 million years, with +/- 110,000 years error margin.

I mention this because it indicates that it is in fact quite difficult to accurately determine the age of rocks!  (This explanation is for general interest: geology students should read the article regarding corrections for entrapped atmospheric argon, and the hypothesis that the feldspar crystals are xeoncrysts, rather than being formed as the lava cooled.)


The last eruptions were 5,000 years ago in Mt Gambier.
  Researchers estimate that the Newer Volcanics Province has averaged one eruption every 10,800 years, so it is still considered active.

One good source of information I found online about the New Volcanic Province volcanos of Victoria is in this 1993 field trip guide: 


Nicholls-1993
I. A. Nicholls, A.G. Greig, C.M. Gray and R.C. Price
Newer Volcanics Province - Basalts, Xenoliths and Megacrysts (IAVCEI  Canberra 1993 Pre-Conference Field Trip Guide)
Record 3 1993/58 Australian Geological Survey Organisation.
http://www.ga.gov.au/corporate_data/14654/Rec1993_058.pdf (Open access.)

This includes information about many other places of interest, including the Byaduk lava blisters (tumuli) formed in the lava which flowed from what is now Mt Napier.

We have ordered Bill Birch's book "Volcanoes of Victoria", from the Royal Society of Victoria (there's no web-ordering, so we called them by phone).

Maps and other material can be found for searching for "Newer Volcanic" at:

http://vrosearch.agriculture.vic.gov.au/results.php?q=newer%20volcanic

Dr Julie Ann Boyce has a number of articles which can be downloaded at:

https://www.researchgate.net/profile/Julie_Boyce

A compendium of some of her articles on Victorian volcanoes is in a long PDF:

http://about.elsevier.com/media/idra/011.pdf

This is a description of Julie Boyce's Google Maps project: "Victorian Volcanoes":

Julie Boyce's interactive Google Map of all the volcanoes in Victoria and South Australia

https://www.google.com/maps/d/viewer?mid=znL0MWNL51Mw.keepDtG_Zq1k

There's also a great article by Jeremy Bourke: "Forged by fire: Volcanoes in Victoria":

http://www.australiangeographic.com.au/topics/science-environment/2017/05/volcanic-victoria

and a list of Victorian volcanos to visit, including our illustrious Wombat Hill, which is the Daylesford Botanical Gardens, planted with conifers from all over the world:

http://www.piecesofvictoria.com/2016/10/six-must-visit-volcanoes-in-victoria/


Back to Daylesford . . .

Despite the numerous examples of "Wombat" in local place names, we are yet to see a wombat here.  Bullarto is the closest we have seen signs of wombats, and we are yet to see one alive.  This interactive map of wombat sightings:

https://womsat.org.au/womsat/map.aspx

indicates that this area is at about the western-most limit of wombat inhabitation in Victoria.


Gold mining was originally alluvial (gold washed from reefs into river beds) and then went underground chasing the (quartz) reefs themselves.  I don't yet know enough about the geological history, but it is my impression that the gold is not connected with this recent volcanic activity - the incursion of quartz reefs is probably much older than the last few million years.

I understand (from the abstract of http://researchonline.jcu.edu.au/1785/ "Stable isotope geochemistry of cold CO2-bearing mineral spring waters, Daylesford, Victoria, Australia: sources of gas and water and links with waning volcanism" I. Cartwright et al. 2002) that the mineral and carbon-dioxide content of the many local springs is due to the volcanism.  Although none of the springs are hot, (according to some other reference I can't recall) their mineral composition varies so much that the source of the mineralization and CO2 must be only a few hundred metres below the surface.


The Daylesford area was originally settled by Europeans for farming, but it became one of many gold-mining areas in Victoria in the 1950s (https://en.wikipedia.org/wiki/Daylesford,_Victoria)
.

The gold was introduced into the area in quartz reefs, which intruded into the sedimentary rock.  Some of this was eroded and the gold tended to settle in the creek beds, due to its high density.  This alluvial gold was found first at Wombat Flat, at the south-east corner of what is now Daylesford Lake.(See note below.)
   
The only proper account of the mining history of Daylesford seems to be this book.  There's a copy of the first edition in the local library (http://www.centralhighlandslibraries.org.au) .


100 YEARS OF DAYLESFORD GOLD MINING HISTORY
By HENRY T. MADDICKS
Assisted by K. H. BUTLER

This was published by the Daylesford Historical Society - now the Daylesford & District Historical Society http://www.daylesfordhistory.com.au/

The second edition of the book is now available from The Society at the Daylesford Museum (this is not its proper title, but I guess people will search for this term) and was  launched there at 6:30PM on 9th December 2016.
  The Society's collection (museum) is located at 100 Vincent St, just south of the post office. 

I guess that this book was written and published in the early 1980s.   The first sentence of the author's biography is: "H. T. Maddicks, well known in Daylesford as a 1920's Radio and later TV Engineer, a business he ran in Daylesford for 40 years.

The last page mentions "Abco Print, Daylesford".  This indicates that it was printed and perhaps typeset (Linotype) here.  Linotype machines were still used in those days before computers enabled phototypesetting.  A few historical books printed (or perhaps published) by this company can be found with this Google search.  This library page refers to a 1981 book manufactured by "Daylesford Abco Printing Service".

Despite giving a good account of a hundred or more mines, there is no discussion of the techniques used (at least in the first edition).  Did they drill and blast (with what kind of explosives?) or did they simply hack away at the rock.  Some of the rock here is quite soft - the sedimentary rock can crumble easily, but the volcanic and some other rocks (I guess metamorphic) are much harder.

In another page here ../04-daylesford-not-winter/ is a picture of one of the water races which supplied the mining industry - 240 miles of water races in total in the Daylesford area.

The 1980s original edition of this book lacks a map - and a good companion to reading it would be this map, now freely available as a PDF:

http://earthresources.efirst.com.au/product.asp?pID=282&cID=9
Castlemaine Deep Leads 1:100,000 map, Geological Survey of Victoria, 1989.

This covers several gold fields, including the rich and quickly mined shallow alluvial deposits of Yandoit, to the north of Daylesford.  From the above, here is a smaller, more detailed, map of the Daylesford gold fields.  To aid with printing, here it is as pages 1, 2 and 3.

(More on maps and guides below.)

Map of the Daylesford Gold Fields, one of the smaller maps of Castlemaine Deep Leads 1:100,000 map, Geological Survey of Victoria, 1989. http://earthresources.efirst.com.au/product.asp?pID=282&cID=9

This book (chapter 3) mentions the exact location of the first gold found in the Daylesford area:

The area referred to in evidence to the Gold Rewards Board was in Wombat Creek behind the present day Wentworth Hotel - Old Bakery area, now covered by the head waters of Lake Daylesford.

A friend of ours is of the family who ran the bakery - they used to deliver bread around Daylesford with five draught horses in the early 1960s.  The main industry of Daylesford in those days saw milling, though the woolen mill in East St was also active.  Here is the location:



I understand that the first gold was won from alluvial deposits (the current lake area was heavily mined, and then used as a market garden, before being dammed to make the lake), with tunnels chasing gold reefs, or more frequently pursuing the creek-beds which were buried by the volcano a few million years (I guess) ago.

The Township Lead was such a creek bed, and mining took place all the way along it, with shafts and tunnels under the main street and under the area where the churches are located, such as where the mine "Union" was located.


As far as I know, the gold (in quartz infusions) long predates, and is unrelated to, the volcanism.  The volcanic activity is associated with the rise of carbon dioxide into the water table in this area.  In some locations, such as where the pink > points in the above image from Google Maps,  gas - presumably carbon dioxide (C02) - can be seen continually bubbling to the surface of the water, here a small lake to the east of the main lake.  Continual bubbles can be seen in the main lake in a line leading approximately NNW from there, including on the other side of Bleakley St, though these are normally only visible if there is little wind. 



The other location we have seen continual bubbles is in the creek at Tipperary Springs.

It seems that the pressure of this gas varies.  Twice (between April 2014 and October 2015) we have seen Wombat Flat spring (a few tens of metres SW of the above location) gushing with a little water and a lot of gas.  Normally, the pump there only produces water if the lever is pushed.   This extra pressure seems to be correlated with a little more activity in these continually bubbling spots in the small lake:



 

Here is a 15 second video, with no sound: CO2-bubbles-at-Daylesford-Lake.mpg.  


Click the following image for a 15 second video (again without sound) of Wombat Flats Spring gushing carbon dioxide on 28 September 2015:




So while Daylesford is now, in part, a place where one can come to get one's chakras realigned, or luxuriate for a day in a spa, it was, a few decades ago, a town of sawmills.  In the century and a half past, it was an extremely busy gold mining town, with rough, cold, wet, living alongside multiple newspapers, breweries and entertainment establishments with ballrooms and dance halls.  The Daylesford Brass Band traces its history to the gold mining days of 1861.

Daylesford has not gone all boutique.  There is a speedway, a concrete plant and, a few km to the east, a sheep abattoir.

There are many remnants of gold mining, and some buildings date to those days.  There are excellent bookshops - new and second-and bookshop (Paradise Books), and a second-hand book and cafe at the lake (Book Barn).  Trentham's bookshops include the quiet, bright and beautifully curated Dr B's Bookstore at 40B High St, and a second-hand bookshop (I can't remember the name) at 19 Victoria St, between Quarry St and Station St, just east of the lake.

See
../09-daylesford-trentham-food-etc/ for further information on local cafes and other businesses Tina and I particularly like:  .

There are no Bureau of Meteorology predictions or observations for Daylesford specifically - Ballarat is the closest.  However the CFA, in Bridport St SW of Coles, has a weather station:

http://www.daylesfordcfa.org.au/weather/

The CFA lists warnings and planned burns at: http://warnings.cfa.vic.gov.au/ .  The 4 day forecast and current situation for fire danger for all of Victoria is at http://www.cfa.vic.gov.au/warnings-restrictions/total-fire-bans-and-ratings/ with Daylesford in the Central district.



Daylesford, looking north-west, from the Cornish Hill lookout at the south end of Orford St, May 2014.  The cream building with tower is the post office.





On the 26 June 2014, on a gloomier day, looking more to the north.  The Bunya Pine which was blown down in the mini-tornado of February 2015 (see ../01-mini-tornado-feb-2015/)  is visible just behind the spire on the left.

Here are some maps and guides which I think will be of interest to people visiting the Daylesford and Castlemaine areas with an interest in bushwalking and mining history (see above for the 100 Years of Daylesford Mining History book):

The Goldfields Track Walking and Cycling Guide.  This booklet has many map pages and has full details of the track which runs from Mt Bunninyong, south-east of Ballarat, through Creswick, Daylesford, Hepburn Springs, Vaughn,  Fryerstown and Castlemaine to Bendigo.  The book is available from The Book Barn on Lake Daylesford and from  http://www.goldfieldstrack.com.au .

Two maps we bought from http://www.melbmap.com.au:

Meridian Wombat State Forest 4WD Touring Map 4th edn (link)

Hayman's Daylesford-Castlemaine-Ballarat Forest Activities Map (link)




This is one of several pages concerning Daylesford and places nearby.  The index for those pages is here: ../.

~~~ooo000ooo~~~