What a fun job to look at maps for your entire 49 year old career, wow!. This was a very good explanation of these magnetic maps. It would be neat to see the one step further on how you then take this information and make any kind of guess as to where oil or minerals might be, I'm assuming it's the color/presence of magnetite and maybe the shape? Another good explanation Richard thank you.
Hi Josh, thanks for the nice words. It’s complicated 😊 which of course is why they paid me. The approaches are different for different goals. For oil and gas exploration, magnetic data provide information about the variations and distribution of mostly igneous and metamorphic rocks, which we wish to avoid for seeking oil and gas which are usually in sedimentary rocks. But for the information to be useful, ideally you need to integrate that with information from gravity data (which provide info about the densities of all the rocks in the subsurface, including sedimentary rocks), surface geology (so you know the ages and types of rocks that you may expect in the subsurface), and seismic data (for details of geometry in the bedded sedimentary rocks).
For minerals, unless you were exploring simply for iron, the distribution of magnetite is a start at thinking about ore deposits, and if you can identify tectonic features that might be conducive to producing ore deposits that can help too, but boots-on-the-ground (seeking surface geology evidence for ores, and drilling cores) and other techniques like radiometrics (identifying presence of radioactive elements like potassium and uranium, which point to some rock types) and electrical methods (which can help recognize the conductivity of things like metallic minerals) would be the subsequent methods.
For both kinds of exploration, and for more theoretical things like tectonics, fault distribution, earth history – which can be used for strategic concepts, identifying not specific locations but broader things like “this should be a good region to explore in more detail” – smaller-scale data can be useful especially in relatively unknown regions. I did that kind of work interpreting the magnetic map of the entire former Soviet Union, and the gravity maps of Africa and South America. Those were not really arm-waving projects, but detailed strategic efforts to narrow the focus for companies new to the regions.
I hope that helps – it really is complicated; I used to teach a 5-day course for geophysicists on using gravity and magnetic data in exploration.
You might find some things of interest on my web site, though I haven’t updated much there in years (it still says I’m available for consulting, which with few exceptions I’m not). http://www.gravmag.com/gmprimer.shtml
Fascinating explanation Richard, thanks for sharing that really helps me understand better how scientists use this data for exploration of oil and minerals! Hopefully you were able to travel to some of those other continents for some boots on the ground truthing! Thanks for the link to your consulting I will look it over, have a good day sir!
"Unexpectedly linear magnetic anomaly" okay maybe won't tempt everyone but it certainly made me read on. If your hypothesis is Rader Creek Pluton edge carved away by faulting - could you now see that also in the gravity measurements?
Yes, and there is no doubt that there is a thick pile (on the order of 2500 meters) of low-density, young (Cenozoic) sediments in the Jefferson Valley. The existing gravity data are not really adequate to define the edge (the fault, the edge of the igneous rock) with much accuracy, in my opinion, but they clearly show it in general terms. In fact I had privately said to someone "I sure wish there were good gravity data in there!"
Consider that this unexpected linear magnetic anomaly might be related to the Beaverhead impact structure 600ma to the southwest. I have found similar near other impact sites.
I'd have to say that's really pretty unlikely because of the timing; the igneous material that is the primary source of the anomaly is about 76 million years old, and the fault that follows its edge is about 15-35 million years old. At 900 million years old, even if the Beaverhead impact had far-flung effects in the rocks it impacted, I'd really be surprised if there was enough to affect these much later features, and there is no evidence for that. The present occurrence of shatter cones etc. in the Beaverhead Mountains have been tectonically transported tens of miles from the impact site in Idaho.
What a fun job to look at maps for your entire 49 year old career, wow!. This was a very good explanation of these magnetic maps. It would be neat to see the one step further on how you then take this information and make any kind of guess as to where oil or minerals might be, I'm assuming it's the color/presence of magnetite and maybe the shape? Another good explanation Richard thank you.
Hi Josh, thanks for the nice words. It’s complicated 😊 which of course is why they paid me. The approaches are different for different goals. For oil and gas exploration, magnetic data provide information about the variations and distribution of mostly igneous and metamorphic rocks, which we wish to avoid for seeking oil and gas which are usually in sedimentary rocks. But for the information to be useful, ideally you need to integrate that with information from gravity data (which provide info about the densities of all the rocks in the subsurface, including sedimentary rocks), surface geology (so you know the ages and types of rocks that you may expect in the subsurface), and seismic data (for details of geometry in the bedded sedimentary rocks).
For minerals, unless you were exploring simply for iron, the distribution of magnetite is a start at thinking about ore deposits, and if you can identify tectonic features that might be conducive to producing ore deposits that can help too, but boots-on-the-ground (seeking surface geology evidence for ores, and drilling cores) and other techniques like radiometrics (identifying presence of radioactive elements like potassium and uranium, which point to some rock types) and electrical methods (which can help recognize the conductivity of things like metallic minerals) would be the subsequent methods.
For both kinds of exploration, and for more theoretical things like tectonics, fault distribution, earth history – which can be used for strategic concepts, identifying not specific locations but broader things like “this should be a good region to explore in more detail” – smaller-scale data can be useful especially in relatively unknown regions. I did that kind of work interpreting the magnetic map of the entire former Soviet Union, and the gravity maps of Africa and South America. Those were not really arm-waving projects, but detailed strategic efforts to narrow the focus for companies new to the regions.
I hope that helps – it really is complicated; I used to teach a 5-day course for geophysicists on using gravity and magnetic data in exploration.
You might find some things of interest on my web site, though I haven’t updated much there in years (it still says I’m available for consulting, which with few exceptions I’m not). http://www.gravmag.com/gmprimer.shtml
Fascinating explanation Richard, thanks for sharing that really helps me understand better how scientists use this data for exploration of oil and minerals! Hopefully you were able to travel to some of those other continents for some boots on the ground truthing! Thanks for the link to your consulting I will look it over, have a good day sir!
"Unexpectedly linear magnetic anomaly" okay maybe won't tempt everyone but it certainly made me read on. If your hypothesis is Rader Creek Pluton edge carved away by faulting - could you now see that also in the gravity measurements?
Yes, and there is no doubt that there is a thick pile (on the order of 2500 meters) of low-density, young (Cenozoic) sediments in the Jefferson Valley. The existing gravity data are not really adequate to define the edge (the fault, the edge of the igneous rock) with much accuracy, in my opinion, but they clearly show it in general terms. In fact I had privately said to someone "I sure wish there were good gravity data in there!"
A little over my "pay grade", however I did learn some new things! Thanks, Dick!
I used to get paid to do things like this :)
Consider that this unexpected linear magnetic anomaly might be related to the Beaverhead impact structure 600ma to the southwest. I have found similar near other impact sites.
I'd have to say that's really pretty unlikely because of the timing; the igneous material that is the primary source of the anomaly is about 76 million years old, and the fault that follows its edge is about 15-35 million years old. At 900 million years old, even if the Beaverhead impact had far-flung effects in the rocks it impacted, I'd really be surprised if there was enough to affect these much later features, and there is no evidence for that. The present occurrence of shatter cones etc. in the Beaverhead Mountains have been tectonically transported tens of miles from the impact site in Idaho.