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Author Topic: Fault Finding  (Read 26502 times)

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Offline sunshine

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Re: Fault Finding
« Reply #10 on: May 14, 2015, 08:46:58 AM »
While I understand the theory, I have great trouble putting it into practice once erosion and overburden come into play.  I guess I should spend some more time learning and thinking about it.  ;-)
See my YouTube channel for fun amateur video:
https://www.youtube.com/channel/UCnz8kX6AZOeZbRt0F9XqVJA

Offline XT18000

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Re: Fault Finding
« Reply #11 on: May 14, 2015, 09:31:33 AM »
 
  Is your reply to me or EMF ?

Offline EMF

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Re: Fault Finding
« Reply #12 on: May 17, 2015, 10:24:47 AM »
An additional technique you can use with Google Earth that is good for seeing past erosion, vegetation and overburden is elevation exaggeration. If you click on the box that says "tools," then click on "options," you'll see the box for elevation exaggration, where 1 is normal. It can be exaggerated up to 3.

When this is used otherwise unnoticeable terrain features become easy to see, and subtle elevations from protruding dikes and veins, or drops in elevation from their weathering become apparent. Also apparent are uplifted portions of faults, and the old beds of some streams left high and dry by changes in the drainage patterns over the ages. 



Offline Rick62

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Re: Fault Finding
« Reply #13 on: September 29, 2015, 03:21:31 AM »
Recognize alinements from aerial photos.






 <-laugh->Streams do follow a fault nice to know !!


[/quote]

Offline Rick62

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Re: Fault Finding
« Reply #14 on: September 29, 2015, 03:23:47 AM »
Steams do follow faults good to know! [-1st-]

Offline East2west

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Re: Fault Finding
« Reply #15 on: February 08, 2016, 07:06:30 PM »
God I love you guys, I have been studying faults and mineral deposition and this was very interesting. Now have you found certain elements to to have an affinity for certain strikes in your area?

For example here in Southern New Brunswick faults with a N/E strike or trend are more often than not mineralized with Gold where as our N/W faults are proving to be more enriched with Antimony, Tungsten and Molybdnem .


Offline beav

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Re: Fault Finding
« Reply #16 on: February 09, 2016, 07:39:50 AM »
And if you guys want that entire paper, the excerpts of which were posted above, you can find it here:
http://pubs.usgs.gov/pp/0373/report.pdf

Beav

Offline EMF

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Re: Fault Finding
« Reply #17 on: February 09, 2016, 01:15:17 PM »
East2west, if you are finding different sets of elements depending on strike direction, it would most likely mean that the strikes going off in different directions represent separate periods of mineralization, from different geological events.

In my area, the older rocks were already faulted and mineralized, and then they were intruded by granitic plutons which shattered everything and deposited yet more minerals. The ultramafic rocks host different sets of minerals than the felsic rocks. The differences are seen in the rock types and not in the fault strikes. I haven't done any element assays yet, but gold is in the rocks both from before and after the intrusions.

Offline EMF

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Re: Fault Finding
« Reply #18 on: February 09, 2016, 09:51:59 PM »
Ore Hunter, intrusions happen when a slab of tectonic plate, like the edge of a seafloor, gets subducted under the edge of another plate, such as the edge of a continent. The friction between the two generates a tremendous amount of heat, and a lot of seawater gets pulled down into the subduction zone in the process. That water lowers the melting point of the heated rock, and this creates reservoirs of magma under the continental slab.

The magma has a lower density than the surrounding rock, which is highly compressed and very dense at depth, so it tends to rise, and it fractures and melts its way through the overhanging rock until it reaches a zone of rock that is of about equal density. At this point it will cool and become a pluton, unless the surface is too weak, allowing for volcanism.

Either way, it sits there cooking away its minerals in that chamber, with gases and water vapor under unimaginably high pressures, driving distilled fractions into the fractures of the surrounding rock, creating dikes and mineral veins. That surrounding, older rock can be of igneous, metamorphic or sedimentary character.

It is not hard to work out what happened in any particular place with some basic knowledge of geology, some geological maps, and some time spent walking around. The general story has been worked out and wriiten up by geologists in most areas, and it is unique to each place, with similarities to others.

Erosion will eventually expose the bodies of rock that were once bodies of magma, and the most commonly recognized type is granite, but there are many variations in composition of the old magma bodies, creating rocks of many types.

From the same magma chamber different kinds of molten rock can flow out into the surrounding fractures, creating dikes of different kinds of rock ranging from very light colored felsic types to very dark looking rocks like diabase. This happens over time as the heat in the magma chamber distills and separates the minerals inside and releases them into the country rock as conditions allow.

So the signs of intrusions are going to be dikes of igneous rock, mountains made of igneous rock, veins and fractures. Fractures that allowed for movement are faults. There could be extrusive rocks in the mix also, known as lavas, but they will be fine grained, full of bubbles, or glassy. Intrusive rocks cooled slowly deep underground and this allowed them to grow larger crystal grains, such as seen in granites or porphyries. But some intrusive rocks are also fine grained.

In my area, before the intrusions occurred, ancient seafloor was being subducted under continental plate, but a large mass broke free from the process and was obducted instead. That means it was pushed up onto and over the continental plate, and left there. It had already been been fractured and gone through chemical alteration from exposure to CO2 in its bottom of the ocean days, which created the peculiar minerals seen with that kind of alteration, and particles of gold that were spread pretty thinly in the rock before alteration became concentrated into coarser masses.

Then it sat on the surface exposed to a tropical climate for a few million years, altering sections of the old seafloor slab yet more, and concentrating some the gold in yet another way. Then the intrusions began, cooking more minerals into the mix, making for some complicated but fun prospecting.

I am somewhat familiar with lidar, but never found access to it. I like how it can be used to determine landforms concealed by vegetation. It would be good for locating areas of slumps and slides and their relationships to nearby faults. Those types of landform have disrupted more than a few gold traces I tried to follow.

I suspect though that the labor of soil sampling is going to be what it takes for you to zero in on the actual mineral location. It is good to check out your ideas of where the gold might be originating, because it could save a lot of time and labor, but on the other hand, if you let the gold tell you where it comes from, even if it is very labor intensive, you will find it.

If you can direct me to a source of lidar imaging, I'd like to look into it.

Offline EMF

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Re: Fault Finding
« Reply #19 on: February 10, 2016, 05:15:50 PM »
I looked over your lidar thread and then found out that the USGS has a lidar imagery project going that is publicly available, but the areas I'm interested in have not yet been covered. So that's for the future.

If you go to google images and search magma formation, you'll get a lot of very informative illustrations of the process along with explanatory links. It'll bring a lot more clarity to the subject.