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How do you identify FAULTS when out on a Goldfield ?
Faults ?
- Thread starter washgravel
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A fault line in a gold field is usually a quartz dyke that cuts through the country. From that dyke leads run off in the country rock which is made up of mainly slates, schist and shales.
Here is a picture of a dyke running through gold country. This was a fault line and the void was filled with quartz. This is the most popular types in gold areas, but there is other types of faults. I am not a geologist but this is my understanding of one common fault line.
Here is a picture of a dyke running through gold country. This was a fault line and the void was filled with quartz. This is the most popular types in gold areas, but there is other types of faults. I am not a geologist but this is my understanding of one common fault line.
http://earthquake.usgs.gov/learn/glossary/?term=blind thrust fault
here's a few more examples of different folding and faults
anticline fold http://www.geologycafe.com/nyc/images/fig40.jpg
http://www.geologycafe.com/class/chapter4.html
http://saturniancosmology.org/files/geology/sect2_1a.html check this one out very useful info
a fold is a band or several bands of sedimentary rock that has been folded like butter under immense pressure it is folded. a fault is two plates of rock kind of like tectonic plates that slide or slip past one another the picture above actually looks like a quartz blow rather than a fault to me
here's a few more examples of different folding and faults
anticline fold http://www.geologycafe.com/nyc/images/fig40.jpg
http://www.geologycafe.com/class/chapter4.html
http://saturniancosmology.org/files/geology/sect2_1a.html check this one out very useful info
a fold is a band or several bands of sedimentary rock that has been folded like butter under immense pressure it is folded. a fault is two plates of rock kind of like tectonic plates that slide or slip past one another the picture above actually looks like a quartz blow rather than a fault to me
I stand corrected, thanks HTY. After reading your links i agree its a quartz blow caused from cracks when the sedimentary rocks were folded. I have seen on my geological maps faults marked on the map. I will have to visit some of these areas or pick one that comes close to or crosses the road and have a good look. Currently mining companies are looking for diamonds in the area, they told me that they are looking at a particular fault which is not far from here. I will bail them up next time and ask them some questions about faults and folds.
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That top pic looks like the "China wall" in the Kimberley near Old Halls Creek.
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On on my travels while walking along Rocky Ridge many of the large rocks along that ridge had large cracks running through them which I assumed at that time to be a Fault Line.
Also a geologist once upon a time showed me a pile of "Rock Rubble" and he described to me as that being FAULT.
That vision from the time has long since faded from my mind and now when I come across a rise of ground containing "Rock Rubble" am I looking at a Fault and has that ground been pushed up to cause the amount of loose rocks?
Also a geologist once upon a time showed me a pile of "Rock Rubble" and he described to me as that being FAULT.
That vision from the time has long since faded from my mind and now when I come across a rise of ground containing "Rock Rubble" am I looking at a Fault and has that ground been pushed up to cause the amount of loose rocks?
Nice pick RoscoeRoscoe said:A fault line in a gold field is usually a quartz dyke that cuts through the country. From that dyke leads run off in the country rock which is made up of mainly slates, schist and shales.
https://www.prospectingaustralia.co.../1615/1408357045_10652875734_a980edd50e_c.jpg
Here is a picture of a dyke running through gold country. This was a fault line and the void was filled with quartz. This is the most popular types in gold areas, but there is other types of faults. I am not a geologist but this is my understanding of one common fault line.
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Thanks for your replies.
Oh well I will have to stick with my theories.
Oh well I will have to stick with my theories.
DWT, I didn't take that picture, i wished i did its a good picture. Goldtruck, it is the china wall near halls creek Washgravel, I have seen rocks that naturally have a cleavage cracks run through them. These are normally from what i have seen are sedimentary rocks or some metamorphosed rocks. If you are travelling out that way again, take some pictures i would like to see them to.
Washgravel, I have seen rocks that naturally have a cleavage cracks run through them. These are normally from what i have seen are sedimentary rocks or some metamorphosed rocks. If you are travelling out that way again, take some pictures i would like to see them to. 
Dogmatic
Matt
The opencut mine I work in has number of dykes. They look like anctient white stone walls running down the high wall and across the pit floor.
I will have to try and get a photo of one and post it. Some of them look quite striking in contrast to the geology around them. The first time I saw
one I wasn't sure what to make of it as it looked like it was a buired pillar.
I will have to try and get a photo of one and post it. Some of them look quite striking in contrast to the geology around them. The first time I saw
one I wasn't sure what to make of it as it looked like it was a buired pillar.
Road cuttings are a great place to study Folds & Faults as they are a cross sectional slice of the rock formations in the close local area.
Some of the Geological maps available in Victoria have points of interest marked on them so that anyone wanting to identify what on the ground what is maked on the map can navigate to these points & have a look at the formations or features. The 1 in 50,000 yackandandah geological map. is a good one for the area between Beechworth & Wodonga. The Beechworth fault, a medium low angle compression fault that has displaced both horizontally and vertically can be seen in a cutting on the beechworth wodonga rd.
Some of the Geological maps available in Victoria have points of interest marked on them so that anyone wanting to identify what on the ground what is maked on the map can navigate to these points & have a look at the formations or features. The 1 in 50,000 yackandandah geological map. is a good one for the area between Beechworth & Wodonga. The Beechworth fault, a medium low angle compression fault that has displaced both horizontally and vertically can be seen in a cutting on the beechworth wodonga rd.
Was it Black (Silver) Swan mine ? south east of Kal that got mined in the nineties (nickel). A mate showed me a pick of the orebody (have tried to get it again but to no avail) that was so clinical and clean it looked like the earth had parted and then been filled with nearly pure metallic composite, no ore halo just country rock - orebody - country rock (think quartz/dyke vein but metallic).
Have to differ a bit here and I'll keep it simple - a fault is simply a fracture along which there has been movement of the rocks on one side relative to those on the other. Sometimes the distance of movement is so great that completely different rock types, previously distant from each other, now occur on either side of the fault (image below), other times it is the same and the fault may be difficult to recognise. Quartz veins can precipitate in faults (because fluids can flow along fractures), igneous dykes like granite and basalt can intrude along faults (because they are pathways for molten rock to follow. So although dykes and quartz veins can occupy faults, they are not faults.
Here is a "disturbing" example of a near-horizontal fault placing a gness (a rock that resembles granite) that is hundreds of millions of years old on top of young gravel .
Here is a "disturbing" example of a near-horizontal fault placing a gness (a rock that resembles granite) that is hundreds of millions of years old on top of young gravel .
got message
"On on my travels while walking along Rocky Ridge many of the large rocks along that ridge had large cracks running through them which I assumed at that time to be a Fault Line".
Look like what we call joints - a bit like faults, but unlike faults they have no movement along them in the plane of the fracture (the two walls have simply moved apart a minute amount to form the "crack").
but do not understand so can't quote person above:
"On on my travels while walking along Rocky Ridge many of the large rocks along that ridge had large cracks running through them which I assumed at that time to be a Fault Line".
Look like what we call joints - a bit like faults, but unlike faults they have no movement along them in the plane of the fracture (the two walls have simply moved apart a minute amount to form the "crack").
goldierocks said:
I don't write much on here but was astounded by this statement and had to say something. Your intro says your a geologist, but you have made statements that even a first year student would know are not right.
Neither granite or basalt form in dykes. A correct example would be dolerite and pegmatite
I am studying geology at the moment and was my understanding that almost any igneous rocks can form a dike. I thought sills, dikes and laccoliths are formed as the magma is intruded into the preexisting/wall rock and faults. I am Wondering why neither granite or basalt would form a dike?
I could not see why granite could form a dike being intrusive (though normally form batholiths), and as for basalt i had heard of basalt dikes but on reading your post, i started wondering how, if the majority of basalt is extruded. I found this question asked on an earthscience page http://earthscience.stackexchange.com/questions/2342/is-there-such-a-thing-as-a-basalt-dike
"
I've always understood that basalt is an extrusive rock (formed by eruption), and dikes are intrusions (no eruption)
This is not entirely accurate. Assuming that we are talking about rocks of this specific composition, then every extrusive rock is a basalt but not every intrusive rock is a gabbro (or diabase). Fine grained rocks, and basalts in our case, can also form in hypabyssal settings (underground, for example dykes) if conditions are favourable for very quick nucleation. When a magma of 1100 C intrudes a 20 C surface or 100 C rocks several hundred metres deep, the cooling rate is not too different, causing similar fine grained textures in the rock.
The concept of "basaltic" may differ in context. For example, people commonly use basaltic when the rock is similar to the sensu stricto composition of basalt/gabbro, but not quite. It does not necessarily mean that we are talking about a gabbro with a composition similar to basalt. In a wider context, it may refer to "basaltic" vs "granitic" compositions, whereby their coarse and fine grained forms are called "gabbro" and "rhyolite", respectively. No idea why this terminology is rooted like that."
Another Australian geologist talks about basalt and "fine-grained granitic rocks" http://www.icr.org/article/dikes-cooling/
"Abstract
When molten (igneous) rock forces its way, or is squeezed up, into a vertical or near-vertical crack in other rocks, be they flat-lying sedimentary rocks such as sandstone or shale, or folded metamorphic rocks such as schist or gneiss, or other igneous rocks, the crack is usually forced apart and the molten rock cools in the space to form a tabular igneous intrusion cutting across the surrounding rocks that is known as a dike (or dyke, depending on which country you live in!). The molten rock (magma) crystallizes as it cools, the most common dike rocks being diabase (or dolerite), basalt, and fine-grained granitic rocks. Although dike formation and magma cooling in dikes have not been observed and timed, prolific studies have still been directed towards understanding the mechanism of magma intrusion to form dikes and the timing of magma cooling in them."
I could not see why granite could form a dike being intrusive (though normally form batholiths), and as for basalt i had heard of basalt dikes but on reading your post, i started wondering how, if the majority of basalt is extruded. I found this question asked on an earthscience page http://earthscience.stackexchange.com/questions/2342/is-there-such-a-thing-as-a-basalt-dike
"
I've always understood that basalt is an extrusive rock (formed by eruption), and dikes are intrusions (no eruption)
This is not entirely accurate. Assuming that we are talking about rocks of this specific composition, then every extrusive rock is a basalt but not every intrusive rock is a gabbro (or diabase). Fine grained rocks, and basalts in our case, can also form in hypabyssal settings (underground, for example dykes) if conditions are favourable for very quick nucleation. When a magma of 1100 C intrudes a 20 C surface or 100 C rocks several hundred metres deep, the cooling rate is not too different, causing similar fine grained textures in the rock.
The concept of "basaltic" may differ in context. For example, people commonly use basaltic when the rock is similar to the sensu stricto composition of basalt/gabbro, but not quite. It does not necessarily mean that we are talking about a gabbro with a composition similar to basalt. In a wider context, it may refer to "basaltic" vs "granitic" compositions, whereby their coarse and fine grained forms are called "gabbro" and "rhyolite", respectively. No idea why this terminology is rooted like that."
Another Australian geologist talks about basalt and "fine-grained granitic rocks" http://www.icr.org/article/dikes-cooling/
"Abstract
When molten (igneous) rock forces its way, or is squeezed up, into a vertical or near-vertical crack in other rocks, be they flat-lying sedimentary rocks such as sandstone or shale, or folded metamorphic rocks such as schist or gneiss, or other igneous rocks, the crack is usually forced apart and the molten rock cools in the space to form a tabular igneous intrusion cutting across the surrounding rocks that is known as a dike (or dyke, depending on which country you live in!). The molten rock (magma) crystallizes as it cools, the most common dike rocks being diabase (or dolerite), basalt, and fine-grained granitic rocks. Although dike formation and magma cooling in dikes have not been observed and timed, prolific studies have still been directed towards understanding the mechanism of magma intrusion to form dikes and the timing of magma cooling in them."
