CANADIAN GOLD PROSPECTING FORUM - Gold Prospecting Forums

Gold Prospecting Forums - General => Geology and Earth Science => Topic started by: EMF on April 15, 2015, 09:49:57 AM

Title: Fault Finding
Post by: EMF on April 15, 2015, 09:49:57 AM
When I'm out prospecting I make waypoints on my GPS of any features of interest such as outcrops of certain kinds of rock, old pocket mines, prospect holes, contacts, springs, dikes, veins, float occurrences, or anything else of geological interest. Sometimes there are areas of enrichment where faults intersect veins or dikes, but faults are often obscured by erosion or by their tendency to "smear" into shear zones, making them tricky to find.

In an aerial view, they will show up as line shaped formations that cut through hills or make hills along their path. One of the features that faults create are springs, caused when faults bring impermeable rock into contact with water saturated rock, blocking underground flow and causing the water to flow to the surface.

Using Google Earth Pro, I plotted out my collected waypoints while mapping my area of prospecting. The springs I found aligned themselves right along with one of those line formations that can be seen with Google Earth, revealing a fault zone. The springs are marked as red dots, while the yellow lines enclose the fault/shear zone.

There are many faults, veins and dikes in that area running parallel with the springs fault, creating by the uplift of a nearby granitic pluton. There is a another series of much older fractures that intersect with these formations, and those intersections are some of the places I'm checking out for mineralization.   [ You are not allowed to view attachments ]

[Old attachment removed automatically]

[Old attachment removed automatically]
Title: Re: Fault Finding
Post by: spudnick on April 15, 2015, 02:42:55 PM
Mapping, plotting, good to know  and makes alot of sense  ..i just have to learn GPS.. lol ..  Thanks for sharing and posting EMF.
Title: Re: Fault Finding
Post by: sunshine on April 15, 2015, 07:47:14 PM
Other thing I have noticed is some streams follow the main fault.
Title: Re: Fault Finding
Post by: aumbre on April 16, 2015, 11:10:10 AM
Recognize alinements from aerial photos.
(http://gpex.ca/image-sharing/images/faults2acopybob.jpg)
(http://gpex.ca/image-sharing/images/faults3copy.jpg)
(http://gpex.ca/image-sharing/images/faults4.jpg)

(http://gpex.ca/image-sharing/images/faults4copy.jpg)



Title: Re: Fault Finding
Post by: EMF on April 16, 2015, 01:02:02 PM
That fact you pointed out, aumbre, is illustrated in the google image by the drainage systems which angle in from the top right. The stream channels that angle in from the top right follow the older fault system that predated the rise of the pluton that created the fault system that runs parallel with the fault indicated by the springs.

The sheared rock of the older system eroded as the land was pushed up with the rise of the pluton, several miles from the top part of the image. The older fractures contain listwanite alteration zones, stream channels, and a few dikes, while the newer set of faults made spaces for the many dikes and veins that formed as the pluton pushed its way upward. Closer to the pluton, the whole area was so intensively fractured that it eroded away to leave a valley between the uplifted area in the image and the mountain itself.

I used the same technique of plotting waypoints from the GPS, but without Google Earth Pro, to connect a series of quartz outcrops and and old pocket diggings to discover that they were all on the same vein. The waypoints were so far from each other, with intervening hills, that much like the springs, I could not see that they were linked until I mapped them. This technique only works easily with steeeply dipping formations, though.

A vein with a more lateral dip would outcrop on a hilly surface all curvy like a logging road and be harder to trace.
Title: Re: Fault Finding
Post by: UvicProspector on May 10, 2015, 10:07:16 PM
Looks like you know your stuff! One additional thing to consider is conjugate fractures planes. If a fault forms, another will make a 60 degree angle in the orientation of the principal stress field. Check the Dip angle of the fault plane to be sure, they will have very similar strike and dip if they are not conjugates faults. If they are conjugates then they will have a strike 180 degrees different or the dip angles difference will be about 60 degrees.

Cheers!

Title: Re: Fault Finding
Post by: aumbre on May 11, 2015, 08:02:16 AM
Dear Uvic,
Did you mix up the words "strike and dip" in the last sentence?
Title: Re: Fault Finding
Post by: NS Gold Seeker on May 12, 2015, 06:23:57 AM
In glaciated terrain, streams and brooks can follow faults and be of great significance.  Lakes sometimes line up.
In dessert terrain it is more easy to do interpretation of satelite imagery and aerial photography. Less vegetative cover.
The use of handheld GPS and plotting in the field is amazing and can be a great tool. 
Access to Google Maps, Earth and EarthPro is something that opens up previously unexplored areas.

Fault intersections are great indicators of depositis and the path of fluid movement, crucial to deposit formation.
Suggest looking at shear zones (areas of heavily cleaved outcrops - measure this cleavage direction/dip and try to get a direction of movement of the fault by looking at the dragging of strata or formations in one direction.  Note any indications of iron staining, maybe plot as a different colour point.
Title: Re: Fault Finding
Post by: aumbre on May 12, 2015, 12:59:40 PM
Theory of "fault order" Motherlode area California.
(http://gpex.ca/image-sharing/thumbs/faultorder.png) (http://gpex.ca/image-sharing/images/faultorder.png)
Ore deposit are found mostly within third order faults.



Possible intersections...
(http://gpex.ca/image-sharing/thumbs/veindrawing.jpg) (http://gpex.ca/image-sharing/images/veindrawing.jpg)
Title: Re: Fault Finding
Post by: XT18000 on May 14, 2015, 05:38:56 AM
 
  Good work there; now finish it by taking soil samples and rock samples, send to ALS minerals for a 32 element test to see what really there

  not what you hope or think is there. To short of time now to go into that now but if you want or need more information on the subject PM me

  and I'll help you out. There are things that must be done and not be done if the samples are to be of meaningful value.
Title: Re: Fault Finding
Post by: sunshine 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.  ;-)
Title: Re: Fault Finding
Post by: XT18000 on May 14, 2015, 09:31:33 AM
 
  Is your reply to me or EMF ?
Title: Re: Fault Finding
Post by: EMF 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. 


Title: Re: Fault Finding
Post by: Rick62 on September 29, 2015, 03:21:31 AM
Recognize alinements from aerial photos.
(http://gpex.ca/image-sharing/images/faults2acopybob.jpg)
(http://gpex.ca/image-sharing/images/faults3copy.jpg)
(http://gpex.ca/image-sharing/images/faults4.jpg)

(http://gpex.ca/image-sharing/images/faults4copy.jpg)

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


[/quote]
Title: Re: Fault Finding
Post by: Rick62 on September 29, 2015, 03:23:47 AM
Steams do follow faults good to know! [-1st-]
Title: Re: Fault Finding
Post by: East2west 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 .

Title: Re: Fault Finding
Post by: beav 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
Title: Re: Fault Finding
Post by: EMF 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.
Title: Re: Fault Finding
Post by: EMF 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.
Title: Re: Fault Finding
Post by: EMF 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.
Title: Re: Fault Finding
Post by: bruno on February 10, 2016, 06:25:18 PM
EMF  Thanks that is a great wealth of information in those images. seeing the pictures make much more sense than reading geological terms
https://www.google.com/search?site=&tbm=isch&source=hp&biw=1280&bih=899&q=magma+formation&oq=magma+formation&gs_l=img.12..0j0i8i30j0i24l4.3404.3404.0.5226.1.1.0.0.0.0.86.86.1.1.0....0...1ac.2.64.img..0.1.85.IvWcBqYg1vw
Title: Re: Fault Finding
Post by: EMF on February 11, 2016, 01:25:13 PM
Yeah, with geology, it is really hard to get deep and useful meaning from words alone. Way too many unfamiliar terms to look up  <-thinking-> and then to look up again before they can be remembered.  <-d'oh->  But if those words are illustrated with good pictures and some visits to interesting locations, it helps in getting enough understanding of the subject that we'll know which places to prospect are more likely to bring success.. And then... <-gold_>
Title: Re: Fault Finding
Post by: kcm on February 11, 2016, 01:56:08 PM
Boy, ain't that the truth!! I've been studying like crazy - so very much to learn. However, it will be Spring, maybe Summer before I can get out and really study an area that holds a lot of promise. Never been much of one for studying - prefer to learn by doing. But you're surely right, there is just SSOOO much!

kcm