Prospecting Geology Maps?

[Nitric]

I'm looking at the Geology Maps for my state. And I'm wondering...... How accurate are the lines that separate each zone(?)? or even the fault lines? Is this different on map era, or is there a set distance of error? How does that work.

To give a quick example...I use Land matters, go to the state geology, blow up the map, down to where I see may street, and the line goes through the neighborhood according to the map. how much of a transition area is accounted for? Or is that line where it is? Or could that line be 100 yards off, half mile off, etc.....where that line is,is a ravine, or roll in the land which is really cool, if the map is that accurate.

Was just really curious how that worked...Again, Still kind of new to even a little understanding of how to read that. And sorry if this has already been asked or explained!


Also, What I'm trying to do is look at what the geology map says, then go to a local area and find an example, Just so I have something to see. This area is mixed with all kind of little things, a lot of white and clear quartz too. Your kicking the stuff out of the way at times so you don't hit it with the mower.I spend more time looking at rocks that work to the surface than actually mowing

 

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[Alex Burke]

Here's a good link about this subject, it probably won't answer the direct question lol as it depends quite a bit on: when the map was made, the scale, how the map maker was feeling that day, even the width of the pen tip used by the map maker could throw the map feet, yards or even miles off depending on the scale, plus the original survey could be wrong too!
http://www.igic.org/resources/standards/map-scale-accuracy/

Something I think about is the landmarks visible to the map maker, the further a map maker gets from a mountain or river the more inaccurate the map seems to be in the older maps in my experience.

I also find sometimes that what the early geologists and their map makers in Alaska considered to be 20 miles on the old Alaskan sketch maps is sometimes actually only about 17 or 18 miles. I assume this may be because the trekking was so tough it felt like twenty miles I am also assuming/guessing that they probably had to count their steps/paces and try to convert the steps into miles. How tall a person is and other factors like what they were carrying etc this could change the map accuracy at least for old maps if this was the case.

I'm sure the new maps are pretty accurate with gps and all the GIS info the new map makers use but it's an interesting topic and I'd like to hear what people with actual knowledge and not just wild theories like me have to add

 

[russau]

you may also want to check the soil survey for your State or area your looking at. My state (Misery) has completed it some years back for the entire state. I got a soil survey publication for a specific county that I want to check out to see what the soil make up is. theres lots of glacial till areas and for me that a good place to state for my state. these surveys are printed on a Topo map of that area and show the makeup of the soils in that particular location. mighty nice to know where to start your search and NOT be on someones land. I use this with the county Plat Book to show property lines and owners contact info. Need I say more?

 

[Hoser John]

Accuracy is stated usually on all maps in the bottom part. John

 

[KevinInColorado]

Accuracy is stated usually on all maps in the bottom part. John

But is not really dependable in the field away from well developed areas. I've seen county and federal maps off by 200 feet...and received an apology from a government official who told me off when I reported it and then he later realized I was right!

 

[Nitric]

There is one area around here that you can see the actual folded plate(?), I notice this is not even close to anything on maps. It is also the place of an old gold mine. I was trying to look at the maps, and follow that fault or plate, I can't find it on the maps. Maybe I just have no clue what I'm looking for ,or at! That is a good possibility too!

Just something interesting! Here's a picture of it in the link....It's really cool to see in person, the picture doesn't really show it well. When you are standing in the area, you can see where it was pushed and bent/folded. Or maybe it's and outward ripple from a fault miles and miles away?

https://tinycamper.wordpress.com/2014/05/03/pine-mountain-gold-mine/

 

[Alex Burke]

Here's a map Nitric, I think it might cover that area not sure though. You can download a digital copy at the link too. The map has a paper with it so the second link is the paper that goes with the map.

http://ngmdb.usgs.gov/Prodesc/proddesc_68373.htm

http://pubs.usgs.gov/imap/2602/report.pdf

 

[Nitric]

Here's a map Nitric, I think it might cover that area not sure though. You can download a digital copy at the link too. The map has a paper with it so the second link is the paper that goes with the map.

NGMDB Product Description Page

http://pubs.usgs.gov/imap/2602/report.pdf

Thanks!! I'll check it out!! I have a stack of books that explain all this stuff, but it's like reading some foreign language! So, What I have to do is pick an area I can go to and look at to put pictures or examples to something. Then maybe the books will start to make more sense. So,That's where I started looking at the maps and had to start there.

 

[Alex Burke]

I don't understand a lot of stuff I read in reports lol, when I started reading them I often just scanned for schist, slate, Au, garnets, rubies or other terms I thought would get me to the right section of the report. Then slowly I started to understand these certain sections of reports as they relate to gold but I still don't know much or understand a lot of the stuff in the reports.

It takes me a long time to actually read a full report as I often have to google terms or read the sentence several times for it to make any sense but I like learning about this stuff. So don't worry many people are confused by all this research and how to make sense of it I wish I could go back in time and have gone to college for geology!

 

[Clay Diggins]

Most Geology maps aren't very location accurate at all. They don't have the advantage of many visual reference points like roads or city maps. The various rock types are found by sampling and inference (educated guesses).

Often the rock sampling is on the order of every quarter mile or even a mile or more. From that simple point information the geologist draws a general line between the points to represent what he thinks the rock boundary looks like. Seldom are these lines representative of the facts on the ground. Those lines could easily be 1/4 mile off or even more.

The aerial survey, magnetic, sonic and bouguer maps are even more generalized. The simple fact is that the only way to really know what's in the ground is to dig. After you dig you only know what the rock was at the point you dig.

There are some public geology maps of very limited areas that are accurate to within a few hundred feet. We use those when we can in our advanced commercial mapping. The size and information density of those maps pretty much rule out trying to present them on a simple internet map like Land Matters. The higher the density of the information on a map the more it's going to tax the users internet connection. We've spent months digitizing some of these maps for our business where we don't have to worry about internet speeds.

Mining companies sometimes make very detailed maps. These tend to be huge and very expensive. They are also privately owned and very well guarded. We see these on a pretty regular basis in our work but we can't reveal what we learn from them. One very popular gold field in Arizona has virtually no public geology mapping but we've seen geology mapping with a 6 foot resolution across the entire area. Yep the geologists that made the map took rock samples on a six foot grid!. That took several years and is probably their most valuable property.

Geology maps found on the internet should never be considered "accurate". If the line goes down the middle of your street it's a sure bet that it's just a coincidence. In the desert southwest we can often see the boundary between rock types on the ground. These boundaries are never nice smooth lines like you see on internet maps. Digging at the boundaries will teach you pretty quick that those boundaries overlap at a shallow angle more often that they do at a steep one so even surface evidence doesn't tell the real story of whats happening below. In areas with a lot of overburden, ground cover or commercial development you won't see any evidence of rock transitions except possibly through soil coloration or plant distribution changes.

The internet geology maps can be a good general indication of what rock type you have in your area. They don't and can't show you just where the rock boundaries are.

Heavy Pans

 

[Nitric]

I don't understand a lot of stuff I read in reports lol, when I started reading them I often just scanned for schist, slate, Au, garnets, rubies or other terms I thought would get me to the right section of the report. Then slowly I started to understand these certain sections of reports as they relate to gold but I still don't know much or understand a lot of the stuff in the reports.

It takes me a long time to actually read a full report as I often have to google terms or read the sentence several times for it to make any sense but I like learning about this stuff. So don't worry many people are confused by all this research and how to make sense of it I wish I could go back in time and have gone to college for geology!

Same here! There are so many subjects I want to understand. And geology has so many other things in it. Chemical, mechanical, etc....I can understand the mechanical part of it for the most part, The terms are what get me!

 

[Nitric]

Most Geology maps aren't very location accurate at all. They don't have the advantage of many visual reference points like roads or city maps. The various rock types are found by sampling and inference (educated guesses).

Often the rock sampling is on the order of every quarter mile or even a mile or more. From that simple point information the geologist draws a general line between the points to represent what he thinks the rock boundary looks like. Seldom are these lines representative of the facts on the ground. Those lines could easily be 1/4 mile off or even more.

The aerial survey, magnetic, sonic and bouguer maps are even more generalized. The simple fact is that the only way to really know what's in the ground is to dig. After you dig you only know what the rock was at the point you dig.

There are some public geology maps of very limited areas that are accurate to within a few hundred feet. We use those when we can in our advanced commercial mapping. The size and information density of those maps pretty much rule out trying to present them on a simple internet map like Land Matters. The higher the density of the information on a map the more it's going to tax the users internet connection. We've spent months digitizing some of these maps for our business where we don't have to worry about internet speeds.

Mining companies sometimes make very detailed maps. These tend to be huge and very expensive. They are also privately owned and very well guarded. We see these on a pretty regular basis in our work but we can't reveal what we learn from them. One very popular gold field in Arizona has virtually no public geology mapping but we've seen geology mapping with a 6 foot resolution across the entire area. Yep the geologists that made the map took rock samples on a six foot grid!. That took several years and is probably their most valuable property.

Geology maps found on the internet should never be considered "accurate". If the line goes down the middle of your street it's a sure bet that it's just a coincidence. In the desert southwest we can often see the boundary between rock types on the ground. These boundaries are never nice smooth lines like you see on internet maps. Digging at the boundaries will teach you pretty quick that those boundaries overlap at a shallow angle more often that they do at a steep one so even surface evidence doesn't tell the real story of whats happening below. In areas with a lot of overburden, ground cover or commercial development you won't see any evidence of rock transitions except possibly through soil coloration or plant distribution changes.

The internet geology maps can be a good general indication of what rock type you have in your area. They don't and can't show you just where the rock boundaries are.

Heavy Pans

Thank You!! That answers all my questions and what I was trying to understand. You read my mind!! Because I know my writing stinks!!

That also makes it more fun in trying to find new areas never mentioned before. I have some thoughts of an area, I pretty much know it was mined! By ground and pond, indicators(?) even a few old half buried dump piles of rock all the same aprox.size But I can not find anywhere where there were mines listed or mentioned. I'm not sure what kind of mines they may have been even. I have permission to be on one of the lands. We are finding, I'm guessing Gneis(?) with small dots of what looks like garnet or garnet color, reds and pinks, yellows, maybe corundum(?) in these small piles. The only way I can describe it is,.....It was hot and small bubbly through out the rock. Guessing Granite in there too. Anyhow, I don't know the terms and I'm just playing around trying to see what else is exposed in that area, different quartz veins too, of all colors, from clear to a dirty yellow. All kinds of neat stuff!

May be nothing at all! But it gives me something to walk and look at stuff and try to identify. That and it's great because that land borders my back yard, so whenever I get time I run back and look for something different to look at. Identifying it is a whole other game! For me at least!

There was also a copper mine a couple of miles from here. Just makes me wonder whats under the ground around here that we can't see!