Conglomerate cliff curiosity for the GM

[Gregyem]

Just got back from my first week away in far too long. Great time away, despite the very few specs of panned flour gold in the vial and zero nugs or speccies.
After a bit of research I decided on trying a location, not hard to get to but not much visited by others I believe. First day was a scoping walk and a lot of old hand dug cliff-face excavating was found. There were no spoil heaps, only inches of powder and the odd pebble on the floor of the excavations. I assume the material was carried down to the creek for washing. Second day was about 4 hours of detecting around the cliff bases and into the safer excavated faces. The white powder floor and seams in the conglomerate were very quiet with only rare occurences of hot rock and mineralisation noise. Then things got very interesting. In a remnant column, left to hold up about 30m of overhead cliff, I got a very strong non-ferrous signal (and zero ferrous signal) along a white seam of fine grained material (like pipe clay but very hard). The target appeared to continue for about six inches horizontally and I could pick it up from either side of the column. Curiously, there was no "weeeepop" tone for the target that I hear when swinging over a small discreet gold target but there was a very strong loud tone. It was too risky to go chipping at this column so I walked on without finding any other targets bar a single small calibre lead slug and a boot nail. I am wondering whether this target may have been a deposit of flour gold concentrated in the fine matrix. What do you reckon?

 

[Moneybox]

I know nothing about geology but I've found the same sort of white or light grey fine grained bedrock. It looks like engineer's chalk, can be chipped away with the pointy end of the pick but the signal doesn't change as you dig in so no actual nugget down there.



I suspect it's Limonite, a form of Iron Ore.

 

[Hawkear]

You say that the signal although strong is much broader than a small gold signal. One immediately thinks of ground noise or a deep target which may also manifest as a broad signal at the surface (or side in this case). The fact that you can hear the signal from both sides of the column does not discount either possibility as the mineralised seam may run through the pillar.
How would you check the difference? If it were a seam of mineralised material or perhaps a concentration of flour gold, perhaps the signal should be broad along the seam but narrower across the seam ie at 90 degrees.
A single discrete gold nugget at some distance from the coil should produce the same signal width either way.
Another thing that may be useful, could be to try and replicate the signal at home using different sized gold or lead targets at different distances from the detector coil.
I have not used a GM but just some thoughts.
I would really want to be very certain before doing any work on that pillar supporting that large mass of conglomerate.

 

[Gregyem]

I know nothing about geology but I've found the same sort of white or light grey fine grained bedrock. It looks like engineer's chalk, can be chipped away with the pointy end of the pick but the signal doesn't change as you dig in so no actual nugget down there.

View attachment 11487

I suspect it's Limonite, a form of Iron Ore.

hmmm maybe but I wonder why the strong non ferrous signal?

 

[Gregyem]

You say that the signal although strong is much broader than a small gold signal. One immediately thinks of ground noise or a deep target which may also manifest as a broad signal at the surface (or side in this case). The fact that you can hear the signal from both sides of the column does not discount either possibility as the mineralised seam may run through the pillar.
How would you check the difference? If it were a seam of mineralised material or perhaps a concentration of flour gold, perhaps the signal should be broad along the seam but narrower across the seam ie at 90 degrees.
A single discrete gold nugget at some distance from the coil should produce the same signal width either way.
Another thing that may be useful, could be to try and replicate the signal at home using different sized gold or lead targets at different distances from the detector coil.
I have not used a GM but just some thoughts.
I would really want to be very certain before doing any work on that pillar supporting that large mass of conglomerate.

Yeah I did run the coil across the narrow inner zone. Not much signal and what was there was not reliable. I saw no sign of iron mineralisation in the faces that were excavated, only on the ground exposed to rain and run off. Also, no signs of quartz veins penetrating the conglomerate, which led me to believe the gold was fluvially deposited at the same time as the conglomerate matrix. I will go back to the area sometime (its lovely country) but certainly will not be doing any pick work on that column. There is a very good reason the old timers left it in place.

 

[grubstake]

hmmm maybe but I wonder why the strong non ferrous signal?

I think you'll find that any strong signal overwhelms the very basic discrimination circuitry of the Monster. It's meant for 'nail or nugget?' decisions (not that I'd ever trust it for that ), but if you go over something like a shallow horseshoe, I timagine that will also register as non-ferrous simply because of the large signal strength.

A patch of mineralisation that's uncharacteristicly stronger than that of the ground around it could likely do the same, which I believe is what is happening in the case of this column, as I doubt that a concentrated amount of flour gold would register.

 

[Gregyem]

I think you'll find that any strong signal overwhelms the very basic discrimination circuitry of the Monster. It's meant for 'nail or nugget?' decisions (not that I'd ever trust it for that ), but if you go over something like a shallow horseshoe, I timagine that will also register as non-ferrous simply because of the large signal strength.

A patch of mineralisation that's uncharacteristicly stronger than that of the ground around it could likely do the same, which I believe is what is happening in the case of this column, as I doubt that a concentrated amount of flour gold would register.

hmm, thanks for the input. I am yet to experience highly mineralised ground giving a strong clean non Ferrous signal. Horseshoes make my GM scream maniacly and iron rich ground makes it swing both ways erratically. As I think I mentioned initially, the fine white cement was dead quiet for the monster everywhereelse and I swung along a few hundred metres of it. I have only ever had this sort of signal with wet charcoal or wet salty ground but hey learning all the time.