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Fault Lines, How To Find Them?


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Yep, field observations is key for small scale prospecting, maps are good for generalization though.

There are secondary observations you can make to ID faults on the ground that are too small to see by air, hard to recognize, or just buried now. It's too complicated for a single post though, but it's one of the main "secrets" I (and many others) use in exploration.

You mentioned contact zones Andyy, that's a good one. Often you can observe contact metamorphism in these zones too, and these sorts of rocks and minerals can be observed in the float even if the original old fault is no longer exposed.

Also dikes can get refaulted and these are sure giveaways on aerial imagery - you follow the line and then BAM, a zig zag in the dike, probably worth investigating.

Anyone looking for faults should google image search "slickenside", it's also a good sign that can be hanging around in the float, or maybe one of the walls eroded away but you can see remnants of it on another wall and you know it was a fault and not just erosion.

Etc...

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Synclines & anticlines to name a couple more features, although have found synclines are more productive for eluvial sheds but that may be because there are bugger all alluvials in country I prospect. Minor fault junctions with either a major or other minors. Have found some older geo maps, usually hand sketched from 100+ years ago show a lot more minor faults then the newer ones.

The advantages I`ve found with dedicated mapping software, doesn`t need a cell signal, find waypoints & track saving after many years of doing such gives you a historic database that can be recalled, plus I`m a wee paranoid about being online with my valuable data. Google Earth is a powerful tool that with time will evolve even more, find it invaluable for terrain checking at home to get a vehicle in close via bush-bashing, just mark a potential "easy" track and import across to handheld mapping software that accepts kml, kmz etc. Such Geo & GPS data is almost as powerful a tool as the detector.

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Oh my! I think I need a crash course in geology again. I'm not at all confused just more intrigued every day. Thanks to all of you for bringing this up and explaining. It's been a while and I've lost many many books on this over the years. Thanks again guys. 

John 

 

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On 1/20/2017 at 11:22 PM, tvanwho said:

Where do I even get a geologic map of an area in USA? We don't have any mountains in Illinois and Indiana, only glacial moraines pretty much.

Of course there was the gigantic earthquake back in 1820 something that changed the course of the Illinois river, the New Madrid earthquake as it was called.

The only metals mines were for zinc/galena in extreme NW corner of Illinois, coal mines central parts of both states, sand dunes around Lake Michigan.

There is better geologic mapping available Tom.

The maps and kmz available on the mrdata site are very low resolution generalized maps. You will find on those maps that the accuracy is only so so and the precision is very dependent on the mapping system being used. They can only give you a general idea of where faults and other features are located.

We present that same mrdata mapping on the Land Matters State Geology Maps with the ability to see them in combination with aerial imagery or topos. A land status map layer is available as well as the PLSS grid to help you find your way around. The fault layers when available are displayed separately for ease of use.

Many of the Land Matters maps have additional features as well. For example the Arizona map has Arizona rock chemistry location sample data and a mineral potential map layer as well. Each State geology map will be added to as data, time and funds become available.

If you are looking for better geologic mapping you can get the best free geologic maps available for any given location with just a few clicks. Those State Geology Maps I mentioned above have the ability to direct you to more and better information than you will find in those google kmz or even the Land Matters map layers. Here's how:

1. Start up the appropriate State Geology map.

2. Zoom in to your area of interest.

3. Click on the identify_off.gifinformation tool.

4. Click on the map in your area of interest and a new information window will pop up on the upper left of your map.

5 Look for the item in the information list titled Layer: National Geologic Map Database Query and click on the link Click for Map List. A new window will open with a list of all the geology maps in the USGS National Geologic Map Database for that quadrant.

A quadrant is the same area as a 7.5 minute topo map - the quadrant name in the information window is virtually always the same name and area as the 7.5 minute topo . Many if not all of those maps are available for free download on that same web page. Typically anywhere from 15 to 30 maps are available for each quad area. The 1:24,000 scale is the most detailed map and as the 1: numbers get bigger the map covers a larger area and generally has less detail.

Most of those National Geologic Map Database maps aren't in a form that you could easily display on another map but they have much more detailed information than web maps like google or Land Matters. They can be very useful as is for studying a specific area.

At our MinerDiggins business we do digitize these higher detail maps but that is truly a major effort. Essentially each map is reproduced by hand and the map information is hand entered in a database for each feature. A 200 square mile area usually takes an experienced cartographer about four to six weeks full time to digitize a single map. That really does pay off in the ability to use the geology information in combination with other mapped features as FootPrints software users know. Unfortunately the time involved pretty much guarantees most of the more detailed geology maps won't be made available in modern mapping form anytime soon.

Faults can be found from aerial images, 3D models and inferred from local geology. Contact zones can be associated with faults and even more important with localized enrichment. As jasong pointed out the real facts will only be found on the ground. Maps and aerial views can help you focus your search for enriched areas but in the end only feet on the ground can bring you a real knowledge of where fault features are located.

Illinois is a tough nut to crack geologically speaking. As a good portion of the State is buried under hundreds (or thousands) of feet of glacial fill and loess much of the basement geology is inferred. Follow those links on the Illinois State Map and I think you will find more information is available about Illinois geology than you imagined.

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tvanwho- just adding my bitz about your Faults...enjoy!:rolleyes:

...http://www.pitt.edu/~cejones/GeoImages/7Structures/OtherFaultEvidence2.html

 Also ck out my post in gems forum "Giant Amethyst:"

Cheers, idahogold

 

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-Chris,no wife here, still single..wonder if I am faultless?

-Clay, great site at Land Matters and I can actually see local fault lines.

-IdahoGold, pitt edu has great color photos of actual faults in the field and tips as to what to look for.

As a side note, my IE keeps crashing for Steve's website but Google Chrome works perfect, dunno why and the Land Matters website runs soooo fast on Google Chrome, barely crawls on IE...

Glad I asked the questions...altho I am a bit slow on geologic terms like hanging walls.

Just took a class for beginners on doing  Rock and Mineral Id tests at the Lizzadro Lapidary Arts Museum in Elmhurst, Illinois

this past Sat and learnt a few things , spent $100 on rock and fossil books with tons of color photos too.

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Google earth is good for locating faults, mineralized zones, ect.... another neat trick I use is overlay Bing Aerial maps on google earth, you will see so much more, that google earth colors dont show...

Dave

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