Gold definitions - "Alluvial", "Eluvial", "Colluvial" etc.

[user 4386]

I have indeed seen those granite boulders you speak of Goldie near Queenstown Tas and was wondering why/how they got there. It never occurred to me glacial movement is the likely cause.

If you stop and look where they occur on both the east (uphill) and west (downhill) side of the road, you will find that someone has put a plaque on one of them explaining their source.

There is fantastic evidence for glacial action farther east - I think it might be towards the northern end of the loop that goes past the Henty gold mine (Anthony road). Mt Townsend. It has a beautiful cirque and cirque lake, a bowl-shaped area carved by ice of a glacier (in m,myn n opinion).

This is all young - the last interglacial period of our presennt ice age.

https://www.bing.com/images/search?...F300B&selectedIndex=123&ajaxhist=0&ajaxserp=0

 

[user 4386]

https://www.bing.com/images/search?...D5F5CD&selectedIndex=13&ajaxhist=0&ajaxserp=0

 

[user 4386]

The granodiorite erratic in Victoria is known as the Crosbie erratic north of Heathcote and is the only example in Victoria of that form of granodiorite. The nearest form is in northern Tasmania.

A couple of minor points of correction - if you will excuse (but I have photographed the erratic myself and have studied the granodiorite (including cutting microscope sections of it and published on it) - starting in the 1960s, the last time in the 1990s.

1. It is the Stranger erratic and is west of Heathcote near the resorvoir at Derrinal/Knowsley East
2, I think the place is called Cosbie, not Crosbie that contains the granodiorite that PROBABLY supplied the erratic at Derrinal
3. The Cosbie granodiorite is not unique but one of many similar granodiorites of Late Devonian age in central Victoria.

This is from an earlier (Permian - 200 million years) ice age to the one I discussed above in Tasmania (the Tasmanian one being from a glacial interval in the present ice age that started less than 2 million years ago, the glacial interval only being around 50,000 years ago. The aborigines would have seen the glaciers there.


https://www.bing.com/images/search?...r+erratic+knowsley+east&ajaxhist=0&ajaxserp=0

 

[user 4386]

Some very good informative discussion happening on this thread and great work to all who are contributing.. Keep it up as we all benefit from such input...Cheers Wal.

Could be just water also ? Never underestimate the power of water ie forces of nature. Interesting stuff indeed and when ages of 1.5 billion years are mentioned, explains well why I struggle many times trying to imagine what the landscape was were I'm standing ..





Wonder the size this was originally before weather and time had it's way View attachment 2711

No, there is no way that water can transport boulders of that size (some so big that it is difficult to climb on top of them). However there are other features that tell us they are glacial. If you go to the reservoir at Knowsley East in dry years (low water) you will see "glacial pavements" of highly polished rock formed by the ice moving across the rock surface. And "chatter marks" and "glacial striations" formed by rocks embedded in the base of the ice scratching the polished rock surface - and of course the marks are linear and all parallel because the ice was moving in a constant direction.

This article has good photos of these features at Knowsley East.

https://weekendgeology.com/2018/04/26/lake-eppalock/

 

[user 4386]

A couple of minor points of correction - if you will excuse (but I have photographed the erratic myself and have studied the granodiorite (including cutting microscope sections of it and published on it) - starting in the 1960s, the last time in the 1990s.

1. It is the Stranger erratic and is west of Heathcote near the resorvoir at Derrinal/Knowsley East
2, I think the place is called Cosbie, not Crosbie that contains the granodiorite that PROBABLY supplied the erratic at Derrinal
3. The Cosbie granodiorite is not unique but one of many similar granodiorites of Late Devonian age in central Victoria.

This is from an earlier (Permian - 200 million years) ice age to the one I discussed above in Tasmania (the Tasmanian one being from a glacial interval in the present ice age that started less than 2 million years ago, the glacial interval only being around 50,000 years ago. The aborigines would have seen the glaciers there.


https://www.bing.com/images/search?...r+erratic+knowsley+east&ajaxhist=0&ajaxserp=0

Correction - you are correct that it is Crosbie, not Cosbie

 

[Bora68]

Just to stir the pot.
How about Diluvial gold.
Gold that is transported into place by flood waters.
Otherwise known as “flood gold”

Have got another one for you, Emuvial. Gold that has been picked up by an Emu and dropped in its dung. Have been told by old bushies that they pick up shiny nuggets after big rains. Am not sure if this is true. I recently had dry cattle dung give a strong signal, upon investigation turned up a small piece of ali

 

[Skip]

The granodiorite erratic in Victoria is known as the Crosbie erratic north of Heathcote and is the only example in Victoria of that form of granodiorite. The nearest form is in northern Tasmania.

Reg I've recently moved to Tassie living on the east coast, and the geology here has opened up my eyes to a whole new level. Such a difference in landscape to the main land. One I'm enjoying very much. This info has helped me join the dots. Probs just saved me 10 years of reading
Thanks guys

 

[Hawkear]

Auriferous reefs are usually not exactly vertical and dip in one direction or another or are even flat reefs emanating from the main reef line.
Looking at the current location of a reef outcrop we have to imagine that any gold that shed from its former upward extension should have been dropped on the side opposite to the dip of the reef.
Given that possibly many hundreds or even thousands of feet of rock have been eroded over the eons, the exact place of drop could be offset by many hundreds of feet also.
This could put the gold derived from that reef into an altogether different drainage system to that which would be below the remains of the reef today.

 

[user 4386]

Auriferous reefs are usually not exactly vertical and dip in one direction or another or are even flat reefs emanating from the main reef line.
Looking at the current location of a reef outcrop we have to imagine that any gold that shed from its former upward extension should have been dropped on the side opposite to the dip of the reef.
Given that possibly many hundreds or even thousands of feet of rock have been eroded over the eons, the exact place of drop could be offset by many hundreds of feet also.
This could put the gold derived from that reef into an altogether different drainage system to that which would be below the remains of the reef today.

What you say is quite correct of course, but I don't know how much of a factor it is in practice. The reasons being that with Victorian quartz reefs they are hard and resistant to erosion and tend to control the position of north-south ridges over extended periods of time during erosion. More to the point, the areas suitable for detecting now are modern hillslopes below the current outcrop positions. And very few veins extended laterally for very far because they would commonly be confined to things like one limb of a fold structure, or within a dyke, or within an anticline, and the "package" of quartz veins present would often be close to vertical, with veins in the package repeating at depth vertically below, even though individual veins within the package might dip at a low angle. So even in mines more than a km deep, the effect of dip of the package would rarely be 200 m from top to bottom of the mone - and where you are detecting now is at surface on modern hills anyway. And keep in mind that the total depth of erosion since Cretaceous uplift is only of the order of 1000-2000 m, so the amount removed vertically is only equivalent to the depth still remaining in our deeper mines. All the streams worked for gold, even the deep leads, were only a quarter as old as that uplift.

 

[user 4386]

I have indeed seen those granite boulders you speak of Goldie near Queenstown Tas and was wondering why/how they got there. It never occurred to me glacial movement is the likely cause.

Here is a photo of the glacial erratics near the road north from Queenstown TAS

 

[WalnLiz]

Here is a photo of the glacial erratics near the road north from Queenstown TAS
View attachment 2732

Great pic...how on earth has that rock on top not fallen off after such a long time....

 

[Skip]

Here is a photo of the glacial erratics near the road north from Queenstown TAS
View attachment 2732

Quite large.

The sign in my pic of lake Burbury has a short read displaying the valley was glaciated during the last ice age.

 

[user 4386]

Great pic...how on earth has that rock on top not fallen off after such a long time....

It will

 

[user 4386]

Precarious? This is precarious (apologies to crocodile Dundee)! Mukurob (the finger of God), Namibia. Mukurob is a Khoisan (Bushman) word - the Afrikaaners call it Vingerklip (finger rock).

It will fall down - Mukurob did. I used to camp near it, and one day the wind blew it down. The sea does the same to the Twelve Apostles (I'm keeping it biblical).

 

[Simmo]

We have the same phenomenon up at the Palmer...
But I put it down to a bored and skillful excavator operator on the Road Crew!!

 

[Reg Wilson]

The area near Queenstown is littered with massive boulders over a very large area. Some are the size of a bus. This occurrence is quite visible from the road.

 

[user 4386]

The area near Queenstown is littered with massive boulders over a very large area. Some are the size of a bus. This occurrence is quite visible from the road.

Yes, I only had that photo to hand. Amazing to think that the aborigines saw (and recorded) the Yarra River flowing out through the heads across the dry plain that is now Port Phillip bay. The glaciers of Tasmania and the Kosciusko range. The meteorite impacts as they fell in southern NT (also recorded). Volcanos erupting in South Australia and Victoria. They used to walk across Bass Strait and Torres Strait without getting their feet wet, but got cut off from Victoria before the dingo crossed or the returning boomerang was invented. They painted the Tasmanian Devil on a rock face near Obiri rock at Kakadu, and megafauna bones with tool marks have been recorded in a cave in the North Flinders Ranges.

 

[Reg Wilson]

goldierocks I enjoy reading your posts on geology as you have a deeper understanding than I do. Getting my mind around the immense amount of time, space and erosion that has taken place in relation to the formation of gold and its distribution has taken up a large part of my life, with rewards for my effort. When I stop learning I will have stopped breathing.

 

[user 22230]

Always my biggest challenge ........................ is where to start . Both these pics taken from the exact same spot ......................... and they still don't do the vastness justice.

 

[user 4386]

Always my biggest challenge ........................ is where to start . Both these pics taken from the exact same spot ......................... and they still don't do the vastness justice.

View attachment 2740View attachment 2741

That is why we really do it of course - why I became a geologist so I could spend major time out there,