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Derek W
08-14-2011, 10:22 PM
I've been swinging my Lobo ST around a bit and have encountered some signals that really peaked my interest. Unfortunately they've been in solid rock. After finding the signal initially with the all metal mode I switch to discriminate and am getting 'very good' signals at 6 7 & 8. So with further investigation and a rock hammer and sore arm I spend a considerable amount of time seeing if I can get to whatever it is making the signal.

Not having the ability to identify correctly the type of rock I'm banging on I imagine I could be wasting precious time detecting elsewhere. In the end I walk away with nothing to show for it, confused and unsure about whether or not I found something valuable or was just dulling my rock hammer.

I have good reason to believe that there is gold where I'm looking, and isn't there always a chance that an un-weathered gold vein is just below the surface. Suggestions?

08-15-2011, 08:56 AM
I with you here... Found myself in the exact same situation except I could see the metallic mineralization on the rock surface... Would sure be interesting to send in the samples. The solid bedrock I was on was schist With minimal quartz. I will try and take a couple photos to see if it compares. As far as the metallic mineralization, I poured some acid over it and it did not change color, nor does it flake off like mica and my GMT loves it. Only found it in two spots all day like that. Took samples of both tagets. I dont know enough to tell you what it is though sorry...

Steve Herschbach
08-15-2011, 09:41 AM
"In the end I walk away with nothing to show for it, confused and unsure about whether or not I found something valuable or was just dulling my rock hammer."

If it truly is a real signal you should be able to at some point bust out the chunk of rock that is signalling to see what it is. A signal at high discrimination settings has to be a very conductive item. Usually something metallic or metallic looking. The only rock I have run into that gives a good high reading but that basically looks like a rock are rocks that have a lot of graphite in them. I have one right now I found recently that looks like a piece of schist but it gives a strong metallic signal. I have yet to bust it open but I am fairly sure it has a seam of graphite in it giving the signal.

The most common hot rock signal near Anchorage comes from rocks containing a lot of arsenopyrite, which is very conductive. But it gives a strong iron reading so is easily identified.

The bottom line is I would try to isolate one of your signals to see what it is. Then you will know whether to ignore them or not. Luckily signals in solid rock are a rare thing around here. Not so rare in desert country to get signals in what might as well be solid rock.

08-15-2011, 10:03 AM
Hello. New guy, 1st post. Perhaps a royary hammer. Drill series of holes and pound in steel wedgeds to break the rock. I have small honda generator and rotary hammer so the cost would be small to try.

08-15-2011, 11:33 AM
Steve youre very right, you should be able to chip out a chunk that will give some signal, the rocks in these pics are some of the the chunks I busted out. The signal seemed to be isolated to these rocks, the signal strength decreased dramatically after breaking away these and several larger chunks.
I did not get a strong iron reading with my GMT the same way I would with a hot rock. This read at about 40% iron probability.

Heavy mineralization evident on these rocks

What appears to be pyrite or in my dreams... Gold, it didn't stain after being in nitric acid... (next to my thumb)

Jim Hemmingway
08-16-2011, 01:45 PM
Hi Derek / Fedfire,

From what I see in the photos Fedfire, those look like worthless hotrocks in these parts. A lot of surface iron oxidation over what I suspect is conductive material...possibly iron sulfide or some intergrade with other materials ie arsenopyrite. You hit on a phenomenon I’ve noticed too with similar rocks. Break them up and the big signal that initially attracted your attention diminishes quite a bit. A sharp blow with a rock hammer often results in a garlic (arsenopyrite) or sulfur (iron sulfide) odor.

There are many possibilities but the ones most commonly found in my area are sulfarsenides that can include variable amounts of cobalt, nickel and / or iron in addition to arsenic and sulfur. They respond quite well to VLF units but normally yield low conductive readouts on detectors. Similar looking rocks to your photos are not the types associated with carrying native silver in these parts.

I think we all realize arsenopyrites can carry gold or silver values, but low level values would have little or no impact on target ID readouts. I sometimes wonder whether various combinations of these elements manifest a synergistic effect to the target ID circuitry / software on some brands of detectors. In my area there are large hotrocks that respond at a very high discriminate level on my Goldstinger yet that same signal disappears completely in iron discrimination on my Fisher unit. And they are worthless hotrocks.

You may want to check if and where on your ground balance scale these rock samples balance. Any electronic information you can glean from these experiences is knowledge to tuck away for future encounters with similar looking rocks. I keep good examples of every unusual rock I find and label their ground phase / magnetic readout / target ID in permanent ink taped right on the rock for future reference.

To settle the question definitively, assay a few samples on a one-time basis…then you’ll know for sure whether to disregard these rocks in the future. Possibly other forum members familiar with your area’s geology will offer you a better-informed appraisal.

In any case that my two cents worth from Ontariariariooooo...:)


08-16-2011, 03:14 PM
Jim I concur, I figured from the lack of quartz in the immediate area and the heavy amount of iron oxide present, that this was arsenopytrite. Also by the rich silver smell that accompanied the smashing. I am sure there is gold in some amount included in this stuff but I don't believe that it would be in high enough amounts to warrant an assay. At least not for me... I'm only gonna mess with hard rocks if there is visible gold.

Derek W
08-16-2011, 06:18 PM
Thanks everyone for commenting. Headed back to the area yesterday to continue poking around and reevaluate the same areas in question. Each positive signal I got on a high discriminate was very near a quartz vein, say within a foot or two feet. Also, within the rock there were almost micro sized white lines, perhaps quartz, perhaps something else. This time with the detector I did something a bit different. I would follow the quartz vein as far as I could, which on some places would easily be 100 to 150 feet at a time, and listen for similiar signals. I found in a few areas where the signal was a mineralized sound, and a few others that were a bit louder. Interesting, the mineralization heard in one area was within a foot and a half of a really big signal. Now narrowing the gap.

I eventually found a chunk of rock that would break of the mountain which contained no quartz at all but signaled at a solid 8 on discriminate. The area I'm working has almost no trash so you can imagine my excitement at such a good signal. The rock was a solid dark stone, no crystallization or cleavage pattern that I could define. Very heavy with a hint of redness on the broken side. Iron of some kind, has to be. I like your idea of keeping the rocks for future reference Jim, and would have had it not been as heavy as it was and so far from the car.

Steve Herschbach
08-16-2011, 10:41 PM
I am still confused by your description as a "solid 8" on discriminate. If you are saying on a Lobo with disc set at 8 you ate getting a signal it is almost impossible for this to be an iron type target.

Jim Hemmingway
08-18-2011, 11:11 PM
Hi Fedfire / Derek….

“but I don't believe that it would be in high enough amounts to warrant an assay. At least not for me... I'm only gonna mess with hard rocks if there is visible gold.”

Fedfire… I wouldn’t bother with it either based on similar looking rocks up here. They’re very plentiful, I could easily fill a bucket with them any given day just by what I see scattered around. So you did get a garlic odor when you smacked the rock? OK there you go. That aside, you can always put a mortar and pestle to work when things slow down in the winter if the notion strikes.

Derek… sounds like you are tracing a quartz vein that has intruded into highly mineralized basalt. If we readers could be on site with you, it would be so much easier to evaluate exactly what’s happening.

There would be a big difference in detector response between quartz and basalt. As you go from one to the other your autotune resets itself only to swing wildly in the other direction as you return the sweep. This may explain the signals as you follow along, but it is guesswork. It would be helpful if you could see where that big rock ground balances. I think you will have to turn down your sensitivity to do so.

Steve…lots of large high conductive iron can read right up into the high conductive silver target ID range or anywhere else for that matter, its well known among relic hunters as “falsing” or iron “wrap-around”. This is why I discussed the topic of high conductive large iron at length in the TDI report. Both the TDI and Infinium are easily able to identify much of this type of iron that gives VLF operators fits, and particularly when its deep large iron. In my post above I commented that I have encountered the very same phenomenon with large hotrocks on occasion… but not with what seems to be the basalt Derek is dealing with. My Goldstinger would produce similar high conductive signals over occasional conductive hotrocks but nary any silver. Rocks strictly barren of silver. I wasted a lot of time years ago breaking up such rocks. Over the same rocks my F75 purrs in iron discrimination…no signal is produced.

Years ago using my Fisher Aquanaut at a local rocky shoreline, occasional rocks would react similarly. Some were obvious abbreviated signals… often just one way. But others would give a perfectly good but comparatively broad signal despite jacking-up the discrimination. We long since became accustomed to these types of hotrock signals at Lake Simcoe. Unfortunately neither the Goldstinger nor Aquanaut has a visual meter, so where such rocks would have target ID’d is an open question.

The software / circuitry of my old White’s Spectrum XLT dedicated the highest conductive category [ +95 ] for hotrock ID. So perhaps how a unit is designed plays an important role.

Electronic prospectors would benefit if they learned the appropriate GB settings for their detector to eliminate positive responses from all non-conductive iron minerals and thus be able to differentiate them from conductive materials. It is an excellent technique to initially evaluate rock responses, and can save a lot of unnecessary time spent with a rock hammer. This topic is covered in the Phase Measurement & Magnetic Susceptibility article I posted to this forum. The next step… if needed in the case of an unfamiliar conductive rock… is to put a rock hammer and possibly a mortar and pestle to good use. Magnetic ground phase information cannot be determined by discrimination settings or target ID because iron mineral phase exists on a separate portion of a phase chart from conductive non-ferrous targets. For your F75 the GB45 setting captures all iron oxide as a negative response. If for example Derek’s rock does not give a positive signal at that GB setting on an F75, it’s a non-conductive iron mineralized hotrock, and no mistake.


Steve Herschbach
08-19-2011, 06:55 AM
Hi Jim,

Good point indeed. I commonly encounter man made ferrous items that read high conductive. I have not had that experience with iron hot rocks, probably due to the detectors I tend to use, but I see how it could occur.

Derek W
08-19-2011, 02:01 PM
Feeling confident overall with about 150 hrs on the super trac, (a single nugget to show for it I might add) I will admit to knowing very little about the ground balance and sensitivity of the unit. I know how to reset the ground balance when it's been interrupted or is out of whack by using the pumping motion and letting it reset itself in a neutral area. As far as the sensitivity I keep it mainly set on 8 as recommended by Bob at AMDS when I purchased the unit. I do periodically turn it down when I feel I need a more even threshold sound but mainly run at 8. "It would be nice to know where that big rock ground balances at"...What does that mean. I feel like I'm missing some key element here to understanding my detector..

...and it's worth it to me to go back to the rock in question and haul it out. if to only for learn from.

Jim Hemmingway
08-19-2011, 11:13 PM
Derek...after looking at the controls on your unit, I don't believe it has ore evaluation capability utilizing the ground balance. Aside from a discrimination feature, it is designed strictly as a nugget hunter and for that purpose it does very well. It has automatic ground balancing that eliminates the need for constant manual ground balancing adjustments...but the tradeoff is that it cannot be set and "locked" to evaluate ore samples. I did not appreciate that until reviewing its features tonight.

When you get repeatable signals over unfamiliar suspect rocks you will have to break them open and examine the rock with a jeweler's loupe to identify any minerals that may be present / visible. If you suspect the presence of gold, the next step is take a few small samples of the rock and grind them down with a mortar and pestle. This material can be checked by panning the concentrates. A definitive test is to to do an assay but only if you feel the cost is warranted.


Jim Hemmingway
09-04-2011, 11:51 PM
Hi everyone...

I've been a bit dissatisfied with the way this thread was left. Doing some reading in the Lobo ST's manual I see that in discrimination mode the autotracking is disabled. That implies that in disc mode, similar to my two units...the 1280X Aquanaut and Garrett Goldstinger...the ground balance is preset. Each of these units may have occasional difficulty with some hotrocks in discrimination mode. Is this a coincidence or is the issue tied directly to preset GB in disc mode... something to ponder...


09-06-2011, 01:42 PM
I never GB my Lobo ST altho the manual says you are sposed to in All Metal.Guess maybe I should? Its still my best ever gold jewelry finder in swim areas with the 9x8 coil,too bad its not in a watertight case as I water damaged it 3 times .Tesoro told me no more free repairs so I bought a Headhunter after that.Supposedly, the water damage was due to condensation inside the plastic bag I had over the detector box.

-Tom V., ps,that new Garrett AT Pro waterproof VLF gold prospecting detector with a coin disc mode looks awful appealing. Wonder how much it costs, how it compares to MXT and Lobo ST, and what dealer discount we can expect?

Derek W
09-08-2011, 10:16 PM
"that new Garrett AT Pro waterproof VLF gold prospecting detector with a coin disc mode looks awful appealing." I agree, very nice looking unit.

More information regarding my initial posting...

This may give you an idea of where I'm searching for gold. The rock in question I feel pretty confident to say is a semi-metamorphic grawacke with mineralized quartz intrusions. I saw on display a rock identified as grawacke, with iron type rust spots on it. However it had something else much more interesting to me. The rock had a 45 degree slab look to it, and the gentelman I asked to help me identify it told me there was a quartz vein that had been attached to it and that it was not there anymore..."someone must have taken it off" he said. Hmmmm I thought. On the surface of the slabbed graywacke where the quartz vein used to reside there was numerous specs of golden something, perhaps gold. Sorry to say I couldn't identify if it was gold or something else. Where some of the surface certainly looked like gold, clumped together specs and stuck to the grawacke, other parts seemed to shine a bit to much, with almost a smooth face to them. Perhaps a combination of gold and something else?? help. I believe that load gold does shine a bit more than placered.

The geologist type I was speaking to didn't mention or speak on the gold part of the rock at all, and I didn't press, but instead said it was semi-metamorphic grawacke with high iron content.

More information for those interested

09-09-2011, 07:27 AM
FedFire & Derek W, have either of you crushed up and panned a sample yet? Pan carefully as fine gold will float. Look at the concentrates with a hand lens if you don't have access to a microscope. Pyrites are brittle and mica's will break or seperate into plates under preassure.

10-28-2011, 04:10 PM
I don't know squat about prospecting......newbie......but the first two pictures resemble what is referred to as chalcopyrite/CuFeS2 or Bornite/Cu5FeS4. Very common in arizona/southwest. Looks more like a form of Bornite to me.

11-03-2011, 08:19 AM
Derek, in 1990 on my Compass Gold Scanner VLF after first finding a signal in All Metal in bedrock I also put it up to about~7 or 8 in Disc. that was a still good signal. I phoned someone for advice and he told me that it could be that someone dropped a detector battery in a crack.(Also one other time we found a beer can in a hole in the ground then we used a shaving mirror on a stick to see it.) So I borrowed some hand tools and chisled it out and it was hardrock gold! I put the pieces in my wash basin and stupidly(worth more in the natural state) I had a fellow crush and pour a ~12 oz bar for me, I received ~$5,080 for it. I do not know blasting and I hate to hang on to a unhealthy vibrating jack hammer. I have yet to go back and dig it deeper to see if the vein continues on. It was directly in a hard chalky type of Kaolin material with a non-white blue-gray quartz. But there was white quartz very close by and a type of basalt-greenstone on both sides of that ~10 foot wide but long intrusion where I found it.

Matt (CA)
11-29-2011, 10:28 PM
Here's an example of what I think Jim Hemmingway was talking about.


11-30-2011, 01:12 AM
Wow, great stuff. Thats the reason we do it right?

12-07-2011, 12:28 AM
Here's an example of what I think Jim Hemmingway was talking about.


Good god! I am so glad this forum is not as bad as that one, that forum is a mess, so much misinformation packed into one thread! Thank you Steve for the professional atmosphere on this forum.