Advanced Prospecting Techniques - Stream Surveys and Aeromagnetic Mapping.
Prospecting for any mineral poses it's challenges, however there are resources available that one can use to better select locations for on the ground prospecting. The first part of this article will focus on looking at sediment surveys and what they can indicate above an beyond metal values.
Stream and Lake sediment surveys.
The Geological survey of Canada has released large volumes of stream and lake sediment surveys, in looking at these prospectors can find out the age of the stream, flow pattern, rock types associated with the stream and also what concentrations of metals are in the stream. For someone looking for gold they would be looking to see a gold anomalies in the stream survey. Anywhere from a few PPB for hard rock deposits right up to a couple of PPM for placer gold deposits. What individuals don't realize is that these surveys don't always catch the gold in the stream. For example, a placer gold occurrence in New Brunswick just south of the Annindale belt was found a couple of years back. Gold in the stream has been panned regularly anywhere from micro size up to a cm or two, with this occurrence Till geochemistry and stream sediment surveys indicated gold was below detection. However what was indicated on the surveys were elevated levels of Arsenic, Magnesium, Copper and Iron. Now this isn't saying that every stream with these elevated levels may indicate gold but rather to implement an old saying of don't judge a book by it's cover.
Migrating away from gold itself one of the techniques I have used to find potential mineral deposits is looking at relatively unexplored areas, or areas that have been surveyed with low but consistent anomalies. To have one mineral elevated could be interested but to have low anomalies in groups of elements could be an indicator to look at.
Low Hydraulic force makes transport difficult for heavier minerals, therefor also slowing the erosional process. Low anomalies across a set of minerals in these environments could indicate a nearby deposit which has been minimally eroded.
This also may apply for finding intrusions or bedrock that has yet to be properly mapped. For example while looking for potential gold bearing targets in an area that is mapped for granite, I was finding relatively similar readings from the streams. After further examination I noticed one stream had a high Iron, Magnesium reading. 8000ppm MN and 6.2% FE, so I took into prospecting the area. After prospecting the area twice I found a vertically inclined mafic intrusion which was rusted. Now in saying this it never turned out to be anything of value, but the geochemistry told the story before it was mapped. To step a little further on, there is one more piece of information you can pair with the stream sediment surveys to hone in on a target location.
Aeromagnetic Mapping
Now I have very little education with Aeromagnetic mapping but I have however used it in my prospecting with some success. If you go to the Geo Gratis website you can actually search these maps out by your NTS map plate ie 21h/12, 21g/09 . Now I don't know if there is any sense behind this but I have had a bit of success using this method in conjunction with the method above. Essentially you find a stream anomaly in the geochemistry survey you are looking at, You reference your bedrock mapping and wonder if there could be an unmapped fault or intrusion. Well this is where the Aeromagnetic Mapping comes into play. Basically you are going to look for Aeromagnetic anomalies, an anomaly is hard to explain so Instead of pretending I know what Im talking about I've posted a proper article which teaches you about interpreting aeromagnetic Anomalies and mapping alike. What I try to do is pair the data between the Stream anomaly with an anomaly on the Aeromagnetic mapping. Some of these anomalies indicate faults or contact zones which are the areas that most of us ultimately find our mineral deposits in, especially Epithermal deposits or those associated with regional mesomatism.
To find the information on Aeromagnetic Interpretation Click here and you will see the PDF published on the right side of the page.
Cheers,
NB PROSPECTING
