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Reno Chris
09-27-2012, 09:56 PM
Many prospectors will notice a relationship between faults and mineralization. Not all hard rock mineralization is associated with faults of course, but it's no accident that a good number are.
Geologists define a fault as a break in the earth's crust along which movement has occurred. The most common faults fall into three types: strike slip, dip slip and oblique. Strike slip faults move side to side along the break, dip slip have their principal movement down along the dip, and oblique are a combination of movement in both strike and dip directions.
A large percentage of precious metal mineral deposits (not all) are formed by the circulation of heated water. Solid rock does not generally form a good conduit for water flow, but faults, because they are breaks in the crust, do sometimes form a good conduit. That's why many veins are long and deep but narrow, just like faults - because they formed in a fault fracture. Sometimes porous rock can conduct these fluids and that's where large disseminated deposits like those in Nevada form. Sometimes wide broken shear zones where there is no clean break, but a wide zone of broken rock can also form a good water conduit.
Igneous dikes and sills that are intruded along a fault can open up a fault and lead to later flows of mineralizing fluids as nearby bodies of igneous rocks become the heat source for the fluid flow.
In general, mineralized faults do not have huge movement along them. Certainly there are exceptions to this, but generally big regional faults with lots of movement along them are less favorable sites than smaller faults with less movement. In Alaska, many sources of placer gold are associated with bodies of intruded igneous rocks like monzonite. Fractures associated with the intrusion of the body or fractures in the exterior shell which cools and solidifies before the interior allow flow and become mineralized but have very little movement along them. In Nevada, many mineralized veins are associated with ring fractures from a cauldera - they are the sites of long lived near surface volcanic heat and ring fractures don't move a lot - they form from the intrusion and explosion of a cauldera type volcano.

For prospectors who want to learn about the formation of hard rock gold, faults are an interesting subject to study. I thought it might make for a good discussion to talk about faults and mineralization.

geowizard
09-28-2012, 06:46 AM
Chris,

Great idea for a thread.

Earlier in my life, I started out as a technician for Schlumberger offshore in Kenai. Schlumberger was involved in logging oil wells there in the Cook Inlet. I kept learning about geology and how oil is trapped in the earth by folds and faults. Although Schlumberger wasn't involved in seismic surveys, I learned a lot about resistivity and other methods measuring the physical properties of the earth. I moved to Houston and became a training engineer for Halliburton at their headquarters for logging and Dresser Industries at their headquarters office, teaching new logging engineers about geology. The importance of understanding geology cannot be overstated.

I got out of the oil industry in the 1980's and became active in exploration for gold. Although I mainly stayed employed in electronics, I was compelled to find Gold. I realized that electronics was applied to finding oil and that electronics could be used to find gold too! That's how I got involved in geophysics.

Measurements of the earth's magnetic field can reveal changes in the structure of the earth. So, it's well known that a magnetometer can be used to find faults.

When the State of Alaska pays a company to do the geophysical surveys that I have mentioned here in the past, part of the contract involves interpretation of the survey. The interpretation includes geological information. Information about rock types and structural anomalies is a significant take-away from every one of these surveys. The faults are drafted onto the interpretation map. The Fairbanks survey for example shows all of the new found and combined with the old faults. This provides exploration companies with a view of the fault related deformation of the area around Fairbanks.

Knowing where faults are is part of the equation. The second part of the equation is mineralization. Mineralization can take two forms. Quartz and quartz monzonite are non-conductive minerals. Gold, Silver, Copper, Tungsten, and allof the other metals are conductive minerals. So, when they do the surveys and measure structure to find faults and intrusive structures, they also measure the conductivity of the earth. In areas that have both structure and mineralization, the best opportunity is present.

- Geowizard

geowizard
09-28-2012, 07:06 AM
Another consideration when considering the operation of a fault as a conduit for the flow of mineralizing solutions is the third dimension - Compession and expansion of the fault.

I have been involved with the Hilltop mine in Cochise county, here in Arizona for the past 20 years. It is a Lead-Zinc-Silver mine with over five miles of underground workings. The mine is situated on the Apache Fault zone which is a 60 mile long fault zone trending north-west to south-east. Within the Hilltop mine is a perpendicular fault zone known as the blacksmith fault zone. The Blacksmith fault zone has five strands. All of the strands are identifyable because of difference of mineralization in each strand. The srands are found on each level of the mine at approximate 400 ft vertical levels over 1600 feet vertically and are visible on the surface.

In the mine, you can see the slicken sides of the fault strands. Certain areas are mineralized and others are not... Why?

Well, mineralization is controlled by the efficiency of the "conduit" to allow flow of mineralizing solutions. Where the fault was compressed, mineralization could not flow. In areas where expansion occurred, tremendous, massive mineralization is present!

We often hear terms like "The ore pinched out". Compression slowed or stopped the mineralization.

Many stopes can be seen in the mine where hundreds and thousands of tons of ore were mined.

Faulting is responsible for the mineralization in this famous mine. Faulting also caused its demise. Miners, drilling ahead in the ore face encountered pure, unmineralizad limestone. A fault had sheared off the mineralization and displaced it in an unknown direction.

- Geowizard

overtheedge
09-28-2012, 09:08 AM
Don't forget the accompanying fracture zones associated with faults.

I'm not knowledgeable enough to expound on them. Though I have noticed fracture zones associated with intrusions also. This leads me to think that intrusions form along fault-lines that might be long inactive to the point of suturing.

I'm a bit curious about any correlation between mineralization and dip angle relative to bedding. Logic seems to make me think that steeper dips would mean shorter path to lower pressure regions. Of course all bets are off if some of the strata has high porosity and permeability.

Which brings up a big question, given that quartz seams follow fault-lines and fractures and given Chris's contention in his book about "big quartz veins, little gold particles and little quartz veins, big gold particles", and given that any intrusion will create fractures radiating away from the main fracture zone, would it be logical to hypothesize that these radiating fractures could hold larger gold particles?
eric

Lady
09-28-2012, 09:53 AM
This is really interesting. On our Yellow Ribbon discovery for many years we used a trail head that all of us thought was dug by the old timers to divert water to there mill shed. Its about 7 miles long running the side of the mountain and runs into a small stream creek. I will post photos of our Aqua Fur out crop of quartz. And more of the red dirt we discovered. Where the Yellow Ribbon is situated and with Mike filling ore sacks I decided to take a closer look at what we have called our walking trail. All along this trail above is particles of quartz and red dirt that is visible. I believe it is a shear zone. Not a trail. Do I wish I had taken photos of this to study. I did not get time to collect samples. When your on that side of the mountain and its starts to rain, its straight down hill and its like walking on ice. With our back packs full we headed for the barn.What I`am wondering is all the discoveries we have made do they some how meet together? The ore were digging up is the same material.

Bill Bohan
10-01-2012, 08:52 AM
http://img.photobucket.com/albums/v351/Bilbo907/Figure88.jpg



link to non-complex models:

http://www.iris.edu/hq/programs/education_and_outreach/animations/2



There are 1st order , 2nd order and 3rd order faults that occur Across interior Alaska.
The map above shows most of the 1st order faults (which are actually fault zones)
2nd order faults are of North Easterly direction across the Tanana uplands.
Both 1st order and 2nd order faulting are "transpressional" in force offset although the 1st order faults ie Tintina and Denalit are more transcurrent and offset at greater distances than the Nor Easterly 2nd orders
Link to transpression:
http://en.wikipedia.org/wiki/Transpression

Now within the region of transpression are resulting " Rotational wrench zones". These Wrench zones are Trans-tensional and are of faulting and space filling mineralization.
With in the wrench is located 3rd order faults or Reverse faults

Both 2nd and 3rd order faults have reverse faults, but the 3rd order is distinct with mineralization.

geowizard
10-01-2012, 10:11 AM
Faults mapped around the Ryan Lode gold mine near Fairbanks:

http://www.alaska-gold.com/ryan_lode_faults.jpg
Image courtesy DNR DGGS pdf1995_012_sh001.pdf

- Geowizard

geowizard
10-01-2012, 10:38 AM
True North Gold Mine Faults:

http://www.alaska-gold.com/true_north_faults.jpg
Image courtesy DNR DGGS pdf1995_012_sh002.pdf

- Geowizard

geowizard
10-01-2012, 10:42 AM
Fort Knox Gold Mine faults:

http://www.alaska-gold.com/fort_knox_faults.jpg
Image courtesy DNR DGGS pdf1995_012_sh002.pdf

- Geowizard

shaftsinkerawc
10-01-2012, 01:00 PM
Thanks geowizard, is the Fort Knox Map part of a larger map? Does it show south of the Hot Springs Road?

geowizard
10-01-2012, 01:21 PM
If you give a township and range, I will check.

- Geowizard

Agent_34
10-02-2012, 05:18 PM
This is an interesting topic. The area I have was mined previously. The previous miner believes that some of the gold he found was from local origins and some was not. His theory is that the local gold was coming from something he called "stringer veins"-gold producing veins that were too small to find and mine as a hardrock deposit. Does this make sense?

Do water springs have a known relationship to faults?

One of my claims has a contact between two different rock types. This is shown on the geological map. This area was also surveyed for resistivity and magnetism. Both of thoses surveys show a line that seems to corrolate very well with the rock contact shown in the geological map. Is this significant? A water spring is located in that same area.

Bill Bohan
10-04-2012, 09:40 AM
For sure does make sense Agent . The stringer vein model is what I use to discribe my deposit permo elluvial deposit on O'Connor creek and my Vixen Deposit on Fox Creek.
2-6 inch wide quartz with a decomposed sulfide and rust layer on both sides of the rust layer . The vein width incorporates the mineralized widths which are 2-4 inches on either side . Total vein width is 6- 8 inches .
I kin the stringer to throwing a dart at a car window. The safety glass breaks over a large surface area but with spider stringing like a web. Quartz , water, carbonic, and metal laden sulfides come in and space fill the latice of breaks.

Bill Bohan
10-04-2012, 09:50 AM
Springs can make it to the surface emmanating from faults. There are sulfur springs hot water springs, and rust laden springs, and degassing volitale springs. Hot springs are heated by near surface vulcanism or Isotopic half life- ing at depth (exothermic reations in volving heat). The ductile portion of a shear zone will be a source of heat....but this at depth, not at the surface.

A fresh water spring is usually meteoric or from mountain or hill run off collecting in the water table and then resurfacing at a lower elevation.

Epithermal gold deposits are hot springs generated.

Agent_34
10-04-2012, 12:00 PM
Bill,

I believe the spring is a fresh water spring and the water is transported from higher up along the contact structure that I mentioned. This particular structure is quite long and the river crosses it. I believe it could be a fault. The miner told me that he found a peice of gold and quartz down river from there that, in his words, didn't look like it had traveled 30 feet. From the aerial photo, there appears to be a continuation of this fault? that travels far beyond where my claims stop. And as I mentioned there is a clearly defined line in this area on the resistivity and first derivative magnetic surveys. The total magnetics survey also shows something similar.

The miner also talked about finding gold that had recently been transported out of the vein and, in his words, still had black oxide still on it. I am not sure what that means or if it makes sense geologically. However, I found a little peice of gold covered with what appears to be rock of some type and dark brownish/black stuff. I think I found this piece in the tailings of his clean up sluice. See the attached pictures.

Didn't you once post about finding gold in the schist (or places where gold used to be in the schist) that were essentially the size and shape of placer gold flakes?

geowizard
10-05-2012, 07:51 PM
Here's an example of mineralization in a fault and mineralization outside of a fault. This is a plot of what you would get if you took a magnetometer and two metal detectors and walked in a straight line for twenty miles writing down the readings and plotting them on a graph. The grey line is the magnetometer reading and the other two lines give a reading of mineralization.

http://www.alaska-gold.com/L20950.jpg

This plot is done using a software package called Oasis Montaj.

It is a line that was surveyed southwest of Moore Creek, (north to south) between Moore Creek and Flat.

- Geowizard

Bill Bohan
10-05-2012, 08:30 PM
Agent,

The majority of faults are probably not mineralized nor not fissure vein filled. Don't assume that every fault is vein filled. Fault congestion like at Pogo at times was one fault per 20 feet that intersected the heading. That is inclusive of faults that trend in the direction of the heading.

Emminating stringer veins can converge to develop a fissure vein or vice verse . And ribbon veins can converge to form stringers.

geowizard
10-05-2012, 08:47 PM
The plot above, is a good example. It shows one mineralized zone in the fault and five outside of the fault. There are as many examples as there are faults.

Do springs emanate from fault zones? Yes. Do all fault zones have a spring? No. Do springs emanate from fractures? Yes. Do springs emanate from all fractures? No. Is a fracture a fault? No.

Most of the world is mineralized. What is a mineral? Quartz is a mineral. Is quartz a common mineral? Yes. Quartz is made of silicon. Silicon is the most abundant mineral. Silicate minerals compose over 90 percent of the earth's crust.

Faults may or may not be mineralized. Veins generally are mineralized because they are formed from fractures - filled by mineral solutions!

Hope this helps.

- Geowizard

Lady
10-05-2012, 09:08 PM
In one of discoveries we have a shear zone extending out 7,000 feet. Some areas are very rich in gold and you can see where it is pinched off and widened out. The rich areas are in very tight spots.The best is about 5" wide. The widest is a foot with some gold.

Bill Bohan
10-06-2012, 11:34 AM
Michelle you are attacking with hand shovel the shear from a cross cutting (profile) approach as also the Mountain is weathering the shear zone by cross cutting it. Now could you visualise your gold bearing shear zone if it was not dipping into the mountain, but was instead horizontal in orintation and the mountain was being weathered down to this horizontal shear? Now the creek in summer and frost heaving in the extended winter is stripping this horizontal ductile shear zone. And gold bearing placer from upstream loads also covers the shear zone . This would be one way a shear zone could contribute to a placer- a horizontal bedrock shear containing gold beaing weathered with placer gold upon it.......colluvial bonus!

Bill Bohan
10-06-2012, 12:00 PM
Wiz the L2950 might make better sense if you have a distance scale on the x -axis
I assume this is a profile running across a topographic map? Could you scale it on an A-A' profile layer overlaying a top map?

geowizard
10-06-2012, 06:45 PM
Bill,

It shows no less than four lode deposits. You want me to publish a map too?

- Geowizard

Lady
10-06-2012, 07:31 PM
We are on a very steep grade, that would be very hard to visualize.That is a good thought but the distance in cut of the shear does carry gold bearing quartz and free gold. I mentioned the lowest grade and the richest. We do dredge to give us our areas to prospect. Also our Blueberry is an extension of the Wheeler. We are working on a cut now hoping to extend it more. Its leading to the Spains Vein. And we have recovered placer gold. That is a bonus.

geowizard
10-07-2012, 07:27 AM
The problem with most of Alaska is that the valuable minerals as well as the related rocks are buried! It doesn't take very many freeze-thaw cycles to reduce a mountain to a mole hill. So, even the mountains are reduced to gravel and broken rocks. Where vegetation can thrive, it does! Where sediments can flow, they flow and where rivers can move a zillion cubic yards of MUD they do!

Alaska is buried in sediments and MUD. :)

That is why we need x-ray vision glasses! The tools are available to SEE THROUGH the mud and tundra! The profile above is an example.

The area around Palmer to Talkeetna has not been surveyed using geophysical methods from what I can find. I believe there are plans to eventually cover that area. Then we can see all of the buried faults and metal deposits.

- Geowizard

Bill Bohan
10-07-2012, 08:14 AM
Four lode deposits in one straight line is highly doubtful....perhaps your 20 mile long lineation is a fault with an offset of a non suseptible lithology on one side of the fault and a psuedo suseptible lithology on the other?

Bill Bohan
10-07-2012, 08:50 AM
Understandable Michelle,

I do agree. I was kind of modeling lower Ottertail ck. with that reference. Grubstake is a tighter drainage. And the extreme gradients in elevations also suggest that the shears and faults are steeply dipping.

Agent_34
10-07-2012, 10:05 PM
I am unable to see geowiz's picture. I don't know if there is a setting I have to change or what the problem is.

I found a place close to the fault or fracture where the rock is eroded into mud. One side of this place has milky white quartz and the other side is a dark colored rock which I think is andesite.

Bill Bohan
10-09-2012, 08:02 AM
Agent,
Sketch your study and post it . Also post pictures of the rock. If you own the claims, you can consider posting a topo map and or we can look at the location on google earth.

Agent_34
10-09-2012, 09:04 AM
Bill,

Thanks for the offer. I do own claims where this structure crosses the river. Unfortunately, I don't think I have a close-up picture of the rock. I really should take more pictures when I am out there. For a number of reasons, I don't want to post a map of the location. At least for now.

Bill Bohan
10-09-2012, 01:13 PM
Understandable Agent,

Your mud in the vicinity of your fault may actually be clay or fault gouge. If you call the one lithology an andesite it would be be nice to know why you chose andesite as your description?

Agent_34
10-09-2012, 02:50 PM
The reason I think it is andesite is because that rock type is one of the rock types defined for that area by the geological map. It seems to fit what I know about the geology of the area. However, I am not a geologist. There is also schist in the immediate area, but I tend to think it is andesite. From what I recall, the rock is dark in color and does not have large grains in it as you would expect from granite. I am aware that the "mud" could be caused by this area being a fault. I have not really given this area much attention. This thread has gotten me thinking about it more.

The quartz I find very interesting. If this area is a fault and quartz is found deposited in it, does that mean that the quartz was deposited hydrothermally?

I wish I could be more forthcoming with the information, but at this point I don't think the "pros" outweight the "cons" of letting the whole world know what I know. If I were interested in selling the claims, it would probably be different. I don't want to cause this area to be any more scrutinized than it already is. Besides that, although it is interesting to try to figure out what could be there from surveys, maps, etc., it really comes down to groundtruthing. I hope to have an excavator on my claims next summer and do some more exploration.

Bill Bohan
10-10-2012, 09:39 AM
Your claims are in Alaska correct?

geowizard
10-11-2012, 07:40 AM
The Kuskokwim Gold Belt has many placer gold deposits that have been mined over the past 100 years. The internet is loaded with images of the outstanding nuggets that have been found at Ganes Creek and Moore Creek. Placer mining also occurred at Ophir Creek where 100,000 ounces of placer gold was recovered. Surrounding creeks like Anvil Creek and Spruce Creek produced Placer Gold. A doctor that mines Little Creek has a reputation for returning with a mayo jar full of gold. The Iditarod district centered at Flat has had continous mining of over 1,000,000 ounces of placer gold. Geologists have written about the geology for over one hundred years. Hundreds of geologists have studied the area. They include geologists from all of the leading gold exploration companies from all over the world.

They were looking for the lode.

This region is located along the Iditarod - Nixon Fork Fault zone. It is a minor fault located between two larger fault zones that define the Tintina Gold Province.

Speculation has been that Monzonite intrusions are resposible for the gold. I have never seen one. Nobody else has either.

Where's the lode?

- Geowizard

Bill Bohan
10-11-2012, 12:56 PM
Wiz,
For some reason , the Tintina gold "belt" has developed into a province? That wordage approaches error in that a province might be smaller than a region? I am suggesting that a province would not be related to faulting but more so to rock lithologies. I could be wrong but it would be kin to saying the San Andreas "province" in order to combine all regions that this Cali fault passes through.

Steve Herschbach
10-11-2012, 01:30 PM
"Speculation has been that Monzonite intrusions are resposible for the gold. I have never seen one. Nobody else has either."

I and a whole bunch of other people have.

geowizard
10-11-2012, 05:09 PM
Steve,

I have seen countless monzonite intrusions without gold. I'm talking monzonite intrusions with Gold. :) Yes, if the intrusives around Moore Creek were feasible to mine, then they would undoubtedly be getting mined. Ore grade samples are one matter. Having a mineable width and feasibility is the challenge.

- Geowizard

Steve Herschbach
10-11-2012, 05:29 PM
The Moore Creek monzonite has gold. Whether it can be mined or not is another issue and one not mentioned previously. The Flat monzonite has gold, and it has been mined as a residual deposit.