Electronic Prospecting in Silver Country

[Jim Hemmingway]

Electronic Prospecting in Silver Country

Introduction…

A prospecting trip to silver country is an opportunity to enjoy the great outdoors while pursuing your mineralogical interests in lovely rugged settings as depicted in the photo below. I recently enjoyed a highly successful two-month autumn prospecting trip to the area. This particular site is one of my favorites because it is more remote…a great place to detect silver in a quiet, relaxed environment.

You will see some quality recoveries from this trip including a 100+ pound silver and calcite sample that understandably will challenge many readers’ sense of credibility… such finds possibly are outside their experience or awareness. Nonetheless, while we don’t see them everyday, electronic prospectors searching in this area have recovered a number of such large pieces over the years. I was fortunate to locate a deposit that yielded several large museum quality silver specimens.

Many individuals and one mineral club were encountered this year at various sites. A number of these people did not experience much success at finding silver. We will discuss some basic metal detecting techniques and search strategies that should help them to be more successful. Perhaps some of these ideas will interest gold prospectors…please enjoy the read.

Searching Mining Camps and Surrounding Terrain…

A determined electronic prospector can recover specimen grade silver even at the more accessible mining camps in silver country despite several decades of collecting pressure. There is very good potential for those that do their research, use equipment appropriate to site conditions, and are willing to do some pick and shovel work.

To be effective, prospecting-capable metal detectors are required that can help separate silver from iron trash, non-conductive iron-mineralized hotrocks, and conductive hotrocks such as pyrrhotite. My ground-balancing PI units…the Infinium and TDI Pro have limited but very real ability to separate nails and larger high conductive iron from silver, do not respond to any non-conductive hotrocks encountered in this area when properly ground-balanced, and achieve good depth in tough ground minerals. My VLF units…the F75 and MXT achieve respectable depth even in moderately tough ground, and offer the benefits of target ID, discrimination, improved sensitivity to small stuff and to disseminated or spongy ore structures. These units are used for specific tasks as described below, and in the unlikely event that a unit should malfunction there is a capable replacement in the truck.

Ensure your VLF unit can operate in an all-metal motion mode for best depth in tough ground minerals, and can be ground-balanced either manually or using a GROUND GRAB feature. The GROUND GRAB is accurate and convenient, and is an additional quick source of information when evaluating questionable signals. It makes searching hotrock areas properly ground-balanced in the all-metal motion mode more feasible because it takes only a moment to check out a suspect hotrock signal and then quickly rebalance to the ground and continue searching. The F75’s GROUND GRAB for example, does not permit ground-balancing below GB40 to prevent locking into metals at more conductive GB settings.

The diabase positive hotrocks encountered at one excavation site this year converted to slightly negative hotrock signals and lost their target ID when ground-balanced using the GROUND GRAB technique. Most silver ores retained a good positive signal, but in the event a signal is lost or there is otherwise any doubt about a target’s identity…revert to the rule of thumb and dig it. There is more to be said about this technique as to how concentric and DD coils respond to various minerals, for example conductive pyrrhotite, niccolite and other arsenides, rusty iron, and even variable responses from silver ores. But for now we’ll put this subject aside pending further evaluation in the field.

Hotrock-level discrimination can be used to eliminate such signals and in some areas it is convenient to do so despite that it is less sensitive and less deepseeking than the all-metal motion mode. But the price is eliminating good silver in elevated magnetic susceptible iron mineral ground. The photo below is a prime example of silver that was identified as iron in diabase hotrock environs. But it did not exhibit elongated iron’s typical signal fluctuations when scanned from different directions, and when ground-balanced it retained a good positive signal with virtually no reduction in the GB readout. It was no positive hotrock and certainly didn’t look to me to be rusty iron. Those who rely on hotrock discrimination, iron audio tones, or exclusively on target ID would and likely did overlook it.

Visual target ID and ground balance readouts using the GROUND GRAB feature on my F75 were good sources of information in this application, but we should use some judgement. For example, positive diabase hotrocks read consistently at target ID “14” but as noted…ground-balanced positive diabase hotrocks lose their positive signal, their target ID disappears, and there is always a small reduction in their ground balance readout. This is because diabase exists within a narrow GB range from GB86 to GB92 on an F75. As a rule diabase is primarily a source of negative hotrocks, but that changes when the substrate is mostly comprised of diabase rocks. Other types of iron oxide hotrocks occupy much wider GB ranges and that also applies to weak strength pyrrhotite rocks…hence ground-balancing to these may result in a dramatic GB reduction. The important point is that positive diabase hotrocks…non-conductive iron mineralized hotrocks…lose their positive signal when ground-balanced using the handy GROUND GRAB technique.

Rusted iron may reside at various readings within the iron range, may jump in-and-out of the iron range, or may pretty much reside at various higher conductive readouts. It depends on size and configuration, coil sweep direction, state of oxidation and rust deposition into the surrounding soil, depth, and the ground mineral magnetic susceptible strength. That said, small iron normally occupies the iron range and larger iron tends to do otherwise in undisturbed field conditions. Deep large or compact iron is difficult to separate from large silver ore using VLF units until a good portion of the overburden is removed. Rusted iron produces a GB reduction but how much depends on conditions described above. For example, rusty drillrods in-situ can produce a dramatic GB reduction down into the low GB40s on the F75…an additional piece of information when evaluating target signals.

By comparison, silver ores can read anywhere from the iron range to silver dime conductivity. Whether silver ores target ID in the iron range depends on variables such as target size and depth, the proximity of iron junk, and ground mineral magnetic susceptible strength. When ground-balanced most silver retains a positive signal and target ID, but GB reductions tend to be a bit unpredictable. Small stuff changes very little but larger silver ores sometimes produce quite variable GB reductions. This may be due to minor iron, niccolite, or possibly cobalt mineral inclusions…that’s a guess…but niccolite ores normally produce dramatic GB reductions. If you know you’re searching in even moderately tough ground…remove some material to acquire a stronger signal where necessary…and further evaluate suspect signals by sweeping the coil from different directions. Silver doesn’t normally change, but larger or elongated iron target ID usually fluctuates…especially elongated iron. When evaluating suspect signals consider the target size, shape, and strong target ID shifts that result from iron’s conductive and magnetic properties.

Discrimination is sometimes essential to searching sites so replete with small bits and shards of metallic iron that searching in the all-metal motion mode is just not a viable option. It is better to find some silver in these conditions rather than spend a frustrating day dealing with countless blaring signals from bits of iron wire and small tacks and nails. After all…electronic prospecting is supposed to be rewarding and fun.

Setting discrimination levels in prospecting applications depends on the targets you want to eliminate, and the size and conductivity range of non-ferrous targets you want to find. The most likely procedure is to bury a few representative targets at reasonable depths and determine what control settings will get the job done to your satisfaction. Over some ground, target ID and discrimination will not work reliably and detection depth markedly suffers. Good silver can read as iron even at modest depths. In such environs if you want to get it all…you will have to dig it all…but it is very instructive.

Stick with the all-metal motion mode wherever possible and take whatever advantage you can from your target ID as you remove overburden until satisfied about a target’s identity. When in any doubt always dig the target. Below is silver ore found with the F75 in the all-metal motion mode, near maximum sensitivity, bare threshold, GB at 86, Fe3O4 at 0.3% EM. The lightly gray shaded areas represent massive silver just beneath the rock’s surface…a rock that would benefit from an acid wash to expose more silver.

For general field searching of specimen quality silver and ore pockets, I normally use a ground-balancing PI unit and reasonably large coil for maximum depth and coverage. Both my TDI Pro and Infinium are able to separate some iron trash from native silver…a real work and timesaver…but do it differently.

However, neither unit can separate low conductive iron signals from low conductive silver signals. But they do achieve better depth in tough ground than VLF units, and aside from conductive pyrrhotite they do not respond to most hotrocks in the area when ground-balanced to normally encountered ground mineral conditions. More information about these units for this application can be accessed on this forum at White's TDI Pro in Silver Country [including Infinium Comparison] and more specifically about the Garrett Infinium at Garret Infinium Silver Rock Hunting - Revised Edition February 2011.

Many areas are littered with iron and other trash such that “masking” of good silver occurs. I search these sites with smaller coils using a very slow PI sweep speed for reasonably good target separation while still achieving respectable depths. The TDI Pro excels at this task…particularly using the low conductive tone mode while properly ground-balanced at GB9ish in these parts. By and large with these settings, it will ignore nails and some other high conductive iron signals. If ground minerals are not excessive, a prospecting-capable VLF unit with iron target ID capability in the all-metal motion mode is a good alternative…especially since small nails and other iron tidbits target ID in the low conductive iron category on VLF units.

Once potentially productive ground is located that warrants further evaluation, I use a VLF unit in combination with a PI unit. VLF units offer the benefits described above, and give you a good “feel” for ground minerals and associated anomalies that sometimes result in picking-up weak sulfide or disseminated silver signals. When doing pick and shovel work to move and scan material, a VLF unit in the all-metal motion mode handles most of the close-up work. VLF depth is more than sufficient for this job. Below is the first really large piece found this year searching with a PI unit…the Garrett Infinium. I neglected to put in a quarter for perspective but the firewood at 16 inches length is a few inches longer than the specimen.

Suggestions for General Searching...

I increasingly tend towards a search strategy that might loosely be described as “pocket” hunting. Over tailings this might more aptly be described as locating spills or unintentional deposits of good material. This strategy accounts for much of my success searching mining camps in recent times.

Locate such deposits by searching sites most likely to have experienced unintentional dumping of good material. That means areas where valuable silver was handled and transported. Look for indications of surface veins, shafts, and storage areas where silver was graded, moved, and sometimes inadvertently misplaced. There is ample research information that can be accessed with modern computers, aside from local historical archives. Photos or drawings are sometimes available that show original building sites and other facilities at many of the now abandoned mining camps in this area. These are especially helpful to pinpoint areas where you may wish to focus your detecting efforts.

When a deposit is indicated, for example by multiple silver signals concentrated in a specific area…or visually as described below…do not be content to merely recover what are essentially surface signals and move on. You may well be standing over a good deposit that could extend down for several feet. Sample by removing some surface material and carefully recheck the excavation for signals. If there are no signals it doesn’t hurt to repeat this step…yes it is hard work but well worthwhile if paydirt is located. I can’t emphasize enough to take your time with this job and be thorough. Below is a fine example of typical quality silver ore recovered from the excavation site portrayed below.

Some potentially good sites have scattered concentrations of small calcite samples on the surface, some containing a tiny thin vein or two of silver. These may well indicate better pickings below. Most detectorists using some form of discrimination overlook them. Over such ground it is common to find nothing worthwhile for the first foot down. Good “detectable” pieces in the top foot likely have already been removed. If a site has potential you will tap into it below that layer. Dig down and scan with either a ground-balancing PI unit set to minimum pulse delay with a smaller coil more sensitive to disseminated or spongy ores…or a properly ground-balanced VLF unit operated in the all-metal motion mode are suitable for this task. I prefer the VLF for this work.

Admittedly this is not an easy task…particularly for the novice electronic prospector. Intensive detecting and collecting pressure for 40 years has removed most of the easily found surface indicator signals at most sites. But if you happen across such spots…make an effort to investigate. Sometimes we forget the lessons learned when searching for non-metallic minerals where two of our primary search tools are a pick and shovel. In concert with a metal detector these tools can do wonders in silver country. The photo below illustrates that I do exactly what I suggest you do at potentially good sites.

As a result of misgrading ores, good silver was occasionally dumped as waste rock on to the tailing piles as occurred at the site in the above photo. Tailings may occupy enormously large tracts that snake off into the bush. Some of these have been encroached upon by forest cover and are no longer visible from roadways or mining camps. These mine tailings were used to build local roads, storage beds, entrances into mine sites, loading ramps, and routes to facilitate waste rock transport from the mine to the tailings disposal areas. These are excellent prospects to investigate with a suitable metal detector.

The specimen below was recovered from a well-drained area not too far distant from a locally acknowledged source of silver floats. Glaciers stripped material from native silver veins and deposited that material in float trains. Some floats appear to be inexplicably distributed at random throughout the area like so much flotsam and jetsam. Scattered silver ores have been recovered over many decades dating back to the area’s pioneer days. Electronic prospectors have enjoyed good success at locating various floats…occasionally museum quality finds. All floats are not native silver but commonly are comprised of other minerals, for example cobalt and various arsenides. Searching the outback is all too often rewarded with digging abundant manmade junk, some now residing at good depth.

I never anticipated finding such a large piece and almost passed over the signal thinking it would be buried trash. Finding it gave me an exciting moment, but it was terribly frustrating trying to get this piece out of the bush and such a relief to finally get it safely into my truck. It was cleaned with a rotary tool and diamond bit that removes all surface silver flakes and horns except the most sturdy. For perspective a silver quarter is placed on the top left side about halfway back.

The ‘close-up’ photo below takes a better look at the silver detail unavailable in the above photo due to the sample to camera distance. The optical zoom feature on the digital camera was used to get a bit closer. The rock is inundated with thick coarse silver that protrudes almost an inch…on down to the tiniest veinlets and horns. The vein material travels completely through and around the rock. Other than one narrow section on the reverse side, there is nowhere to place your finger without it resting on silver. Checking it with a multimeter, there are no pair of silver contacts on this rock that are not electrically connected.

Lets close this section with a few more suggestions that may improve our chances at successfully searching abandoned mine tailings or pursuing silver float deposits in the outback…

 Metal detectors are our main tools to locate precious metals. Ensure you know how to use your unit before arriving on site. If you are uncertain about your detector’s control settings over unfamiliar ground…take a few moments to bury some targets and adjust the detector controls to see what delivers the best results. These few moments checking your detector over unfamiliar ground are the best spent moments of your trip.

 Research information about whether vein materials were exposed to glacial action. With this information we can pinpoint areas that should offer realistic silver float hunting opportunities.

 Valuable silver ores were transported with wagons or carts and oxen. Occasional breakdowns resulted in spills and some silver doubtless remained right where it fell. Today’s roads are not necessarily the routes used by yesteryear’s carts loaded with highgrade silver ore. Compare topographical maps and historical documents…investigate some of those now overgrown and abandoned tracks…they are prime locations to search.

 Searching in the later autumn when the leaves are mostly down enhances our ability to
navigate the bush and normally there are no bugs. We can at least see natural features and those created by mining operations that otherwise may be cloaked by foliage. Also there are safety advantages in bear country.

 Exploration and sampling are essential to locating new potential sites. I put aside a week or two each season for this purpose alone. One result is that we always have alternate sites if our primary site disappoints.

Below is another of several large silver specimens recovered this trip. I consider this to be one of the better recoveries made over many prospecting seasons. The silver shows very well on all sides and on the bottom although the photo depicts the best-looking face. There is no doubt that many more such pieces are just waiting to be found in the outback by an enterprising electronic prospector, and you can bet dimes to doughnuts we are going to see about that next autumn…

Closing Remarks...

The silver specimen depicted in the photo below exemplifies the quality and typical size of silver ores comprising the bulk of the material recovered this past autumn. It won’t give you bragging rights but its good quality material. The success enjoyed this year was based on the 2010 season. Last year focused on exploration and sampling while evaluating the TDI Pro, whereas this season was largely spent exploiting the results of that work.

Far more time was spent laboring with a pick and shovel than operating a metal detector this season. It is not glamorous or adventurous, but is hard work that may not appeal to many electronic prospecting hobbyists. Yet if potentially good ground is to be evaluated or good silver to be recovered as described earlier, for individual hobbyists that means making generous use of a pick and shovel.

That’s it…other than to thank everyone for spending some time here. Comments are welcome. For newcomers to the hobby… no question is awkward or foolish… so don’t hesitate to ask it.

Jim Hemmingway
January 2012

[strickman]

wow !!!!!!!!!!!!!!! Go get-em Jim !!!!!!!!!! great post, very informative .Amazing specimens !

[Jim Hemmingway]

Thanks Jim...yes the big piece was a lifetime find for me but I'm hoping there will be more. Trust all is well with you folks down in Georgia...

Jim.

[strickman]

Doing well jim,hope you and yours are well . You must be froze in by now , hope you have a banner year this year . I believe this is a banner find ,with out a doubt!!!!!!!!!

[Jim Hemmingway]

Jim if you're still around...we've had a mild winter here. So far very little snow and most of that has melted within a few days. As I write now though...we've got several inches on the ground and cold temps over the past few days. If the pattern stays in place, it'll be gone shortly. But yah...I'm weary of winter...really looking forward to longer daylight and warm sunshine. Take care...

Jim.

[strickman]

We have had a very mild winter so far. More like spring temps. , should have been dredging . Had too much work lately , but that is a good thing.I have a [new to me ] 4" that I haven't even had a chance to use yet. Hopefully soon......

[Jim Hemmingway]

Jim...the weather pattern seems to be widespread across the continent. Nothing terribly new but if it repeats again next winter...we've got something to be concerned about. Good luck with your dredging this season...when you get it going it would be nice if you'd post some pictures here. Dredging is not something I do, but I own a small 2" backpacker Keene dredge, 25 years old but hardly used. Please say hello to your boys...I think it likely a little package could be sent their way later in the year...I have some to spare.

Jim.

[strickman]

You are too kind .The boy's said hello , Hope all is well with you and all the Ladies .We wish you luck ,you are definitely the silver warrior . That should be a banner find . I did nominate for banner. You should put up a pic in the recent finds section.

[Jim Hemmingway]

Thanks Jim but I doubt that silver prospecting or recoveries would hold much interest to the membership here...its too far removed from their "treasure hunting" reality. Could be wrong but thats my perception. Lets get in touch later next fall about getting a package down in time for Christmas.

Jim.

[strickman]

Treasure is treasure ,and 158 lbs worth is nothing to sneeze at !!!!!!! You are the silver warrior !!!!

[strickman]

Am I the only one who thinks this is a banner find ?

[jimmatt_43]

Congrats on a great trip.Nice to see someone's hard word and research pay off for them.

[EagleDown]

Am I the only one who thinks this is a banner find ?

Not as far as I'm concerned!! This is a fantastic find. There are many prospectors
that have spent years combing the hills and have never found as much as this in
all that time.

Definately BANNER!!!

Eagle

[Tuberale]

158 Lbs. of Ag?!?!?! Banner for SURE!

[manorman]

I realy like your post, so informative.
Great finds and resreach.
MIke

[tmanfromtexas]

Jim, wonderful post and very nice pictures. I am wondering, in those pictures, it seems as though the silver runs in veins through the rock itself. How much silver do you think is actually in the rock formation, is it mostly silver or is it mostly rock with veins? Thanks, TMAN...

[Jim Hemmingway]

Hello everyone....thanks ever so much for your enthusiastic comments. To think that I had serious misgivings about even posting these finds initially...well...you guys are the best.

TMAN...lets answer your question. Generally I'd guesstimate that on average most rocks I bring home contain a minimum of 20% silver. But it varies wildly, so lets look at some of the examples in the post, and evaluate them by weight. Keep in mind these are exceptional samples...thats why they are in the article.

The 5.2 troy oz is at least 90% silver; the 2.7 lb piece appears to be veins but thats only because those are exposed surfaces of massive silver beneath...my estimate is 70% by weight; the 1.7 lb ruby piece probably only contains 10% native silver and 40% ruby silver...but its neither here nor there. The combined types of silver make it a unique and highly valuable piece. The 8.3 lb piece contains approx. 65% silver by weight; the 22.6 lb piece...figure the silver accounts for 17 to 18 lbs, no less; the 4.3 lb piece despite all the calcite showing is somewhere in the neighborhood of 40% silver...what we see are only the tips of massive silver beneath...but there is significant calcite. The 2.6 lb piece ought to be in the 15 to 20% range but the real thing is quite a showpiece so that dramatically increases the value; the 101 lb piece looks extremely rich but I doubt there's more than 35 to 40% silver...this is longtime experience speaking here. Think of it in terms of reversing the view and imagine the silver is calcite and vice-versa...there is much more calcite than native silver but this evaluation is by weight. Regardless, at todays prices and because such specimens are extremely rare...I doubt I'd let it go for anything less than $25,000. But that too is only an estimate...in the final analysis it would come down to what a museum or collector is willing to pay. The 22.1 lb piece is veins running through the rock and I doubt the silver content exceeds 15%...but its a rugged looking "character" specimen and so much more valuable than the silver content might suggest. Finally the 12.3 troy oz specimen contains much more silver than the photo indicates. The photo was taken for looks only...the reverse side and middle is almost entirely silver...but it makes for an uninteresting "look"...70% or more silver by weight.

Many ores this year are good solid 'vein' material but if smelted I think what looks to be 60% silver would actually come in around 20% pure silver once all the impurities are removed. Or about two troy oz per troy lb of material. I hope that helps...and thankyou very much for posting your question...its a good one.

Jim.

[Tuberale]

Had initial problems with the designation of calcite, Jim. Calcite in my area not at all gray, and usually not an indication of silver, although it may be an indication of an ore-bearing body nearby. How did you make the initial identification of calcite? Streak? Hardness? Fracture? Chemical?

I'm not questioning your identification skills, just wondering about the methodology.

[strickman]

Hopefully this will make the banner soon.....

[Jim Hemmingway]

Hi Tuberale…your point is a good one. Calcite [CaCO3} ranges from white to creamy white but various impurities may result in almost any color…even black. For example, fluorescent pink calcite is very common in the area. Calcite is soft…a penknife will easily scratch it but for example won’t scratch quartz. Very weak acid will easily dissolve it…even vinegar at approximately 5% acetic acid…producing CO2 bubbles, a distinctive feature associated with calcite.

Calcite is a dominate gangue material that precipitates from hot silver vein solutions in the area, and that is why it is so closely associated with silver here. In other geological conditions calcite does not indicate the presence of silver because it can form by other means and does not necessarily have to be associated with magmas at all. You can do the usual field tests and these identify calcite. The geology literature about the area confirms this to be true. Hope that helps…

Jim.