Log in

View Full Version : Electronic Prospecting in Silver Country



Jim Hemmingway
02-14-2012, 10:47 PM
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 may challenge some 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 quite a number of such large pieces over the years. I was fortunate to locate a deposit that yielded not one, but 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.



1324


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 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 deeper 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 target ID 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.



1326


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…when ground-balanced they 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. Target ID depends on size and shape, 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.

The photo below depicts a good quality silver specimen found with the F75…all-metal motion mode, bare threshold, near max sensitivity, GB at 86, Fe3O4 at 0.3% EM. This piece is quite heavy for its size. The areas shaded slightly gray indicate massive silver immediately beneath the surface…this rock would benefit from an acid wash to expose more silver.



1320


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 and shape in addition to strong target ID shifts that result from iron’s conductive and magnetic properties.

Below is a handsome example of ruby silver combined with native silver in a calcite matrix. Ruby silver comes in several forms. These are silver sulfide [sulfosalt] minerals with variable silver content on occasion mixed with some minor copper replacement, sulfur, antimony and / or arsenic content. The silver content ranges from roughly 60% to nearly 70% by weight depending on the type of ruby silver. The ruby silver in the photo below is a fresh surface that extends completely through the rock, whereas the reader’s left-hand side of the rock is comprised of native silver in calcite…a rare and unique specimen.



1325


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 an instructive, eye-opening experience. Wherever possible stick with the all-metal motion mode and use the target ID to advantage by removing overburden until you are satisfied about a target’s identity.

The photo below depicts a quality silver ore found at good depth…an Infinium hi-lo zero discrimination signal. This specimen is very heavy for its size and the native silver is quite pure. Although the photo describes it as a ‘massive veinlets’ structure…that is based on surface appearance only. Veinlets do not account for the weight or a conductive readout in the zinc penny range.



1321


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 non-conductive 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 http://www.akmining.com/forums/showthread.php/1124-White-s-TDI-Pro-in-Silver-Country-including-Infinium-Comparison and more specifically about the Garrett Infinium at http://www.akmining.com/forums/showthread.php/1092-Garrett-Infinium-Rock-Hunting-in-the-Silverfields-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 disseminated silver signals. When doing pick and shovel work to move and scan material, a VLF unit in the all-metal motion mode is both preferable and lightweight on the arm…VLF depth is more than sufficient for this work. Below is the first notably large piece found this year searching with a PI unit…the 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.



1330


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.



1329


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 but tend to be overlooked by hobbyists using some form of discrimination. Over such ground you are unlikely to find anything 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. Again, remove some material 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 use a properly ground-balanced VLF unit operated in the all-metal motion mode. By and large 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 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.



1319


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 handsome silver ore below is another typical quality piece found at the above excavation site this past autumn. It is rich with native silver…but isn’t all that photogenic. Many such ores ranging between a few ounces and several pounds were recovered at that site…a very productive deposit and certainly worth the time and effort required to sample and excavate.



1323


The large 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 didn’t anticipate finding such a large piece and almost passed over the signal thinking it would be buried trash. Finding it gave me an exciting few moments, 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.



1332


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…by using the camera’s optical zoom feature. 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.



1328


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 is 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…



1327


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.



1322


The lovely sunset photo below is but one reflection of silver country’s alluring rugged beauty. Nothing is so companionable as the quiet and peaceful solitude that reigns over the now abandoned mining camps and overgrown tracks that once bustled with activity.

A lot of time was spent within rifle shot of the scene depicted here. At the day’s end I’d frequently go down to this small lake to clean my equipment and wash-up. Two playful, inquisitive otters live there. They would go for a last swim each day at dusk. Over time we got semi-acquainted and they became less afraid and more curious about me. One evening near the end of the trip one of them sneaked-up to within about 25 yards, coming out of the water to sit on some rocks to watch me…probably wondering what all the fuss was about. I didn’t see or hear the little prankster at first, but did notice that something was different about the shoreline. I saw this big “rock” and was only a bit surprised when it gracefully slipped into the water…



1331


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
February 2012

shaftsinkerawc
02-15-2012, 08:24 AM
Thank you Jim, Great photo's & very interesting read - greatly appreciated.

Jim Hemmingway
02-15-2012, 01:31 PM
Hi Shaftsincerawc….thanks for your comments, I’m pleased you seemed to enjoy the read despite that it is directed primarily at the silver hunters across the Great Lakes and northeastern states.

I neglected to mention in the article that when using an F75…the 10” elliptical concentric coil was used exclusively for this application. It improves overall sensitivity and handles tower transmission EMI slightly better, is lightweight and more maneuverable in tight spots. More important, I much prefer it to evaluate questionable target signals using the “ground grab” feature. It is more discerning whereas the stock DD tends to reduce both signal strength and the positive portion of a signal.

The bottom line to this article is that hobbyists are passing on silver because of reliance on iron discrimination, iron audio tones, or placing implicit trust in a target ID meter. By using discrimination modes, they are also restricting their units’ deepseeking ability…an issue that is more apparent as magnetic susceptible ground mineral strength increases…and they’re restricting their ability to properly sample new ground. Silver hunters need to slow down, stick with the all-metal motion mode wherever possible, and investigate more “iron” target ID signals. Indicators can lead to bigger and better things, so why restrict your potential for the sake of minor convenience? Slow down and find much more over the longhaul.

Below is a silver specimen photo…nothing special…another small piece that constitutes the bulk of silver recoveries this past autumn…



1333

rattlesnake jim
02-15-2012, 07:07 PM
Jim
Thanks for this post. It brings back fond memories.
Back in the 1980's a friend and I located a hi grader's cache near some old famous silver mines. We were using an old garrett deep seeker and a garrett groundhog. We found about 300 pounds of high grade native silver ore. The largest rock weighed about 20 pounds and was loaded with native silver.

Jim Hemmingway
02-16-2012, 02:46 PM
Rattlesnake Jim…many thanks for taking a moment to comment…glad you enjoyed the read. I had a feeling that somehow I’d crossed your trail somewhere but can’t place you.

I’m not surprised in the least Jim about your silver finds. You didn’t mention the general area so I don’t know if your success occurred in northeastern Ontario. Many spectacular silver recoveries have been made over the years, I’ve seen several by photos sent to me and another firsthand about 20 to 23 years ago...I’ve lost track now.

I met an engaging fellow from Texas who was in the area for a week. He had two partners…another from Texas and one from Tennessee. I spent an afternoon hunting with him and then he went his way. Later on that evening I was sitting at the back of my truck having coffee when their car came swooping down the road in a great dusty plume. They spotted me and whipped-up the short mine entrance, jumped out with happy salutations, opened their trunk and withdrew the prettiest and largest chunk of glittering silver I have ever seen inside or outside the local museum. It took two men to lift it to a makeshift stand. I’ll never forget my feelings of awe when looking at something that existed only in my dreams to that point. Their piece was far superior to my large find this year and if memory serves…it was much larger.

Now I don’t recall what they were using for detectors, but if memory serves there were some Fisher coils in the backseat. Their piece was recovered from a well-known float producing area. Moreover they also discovered a silver “ledge” that two of them could not budge despite working at it all day. At that time…I also used an older model Garrett ADS Deepseeker with 7½” and 12” concentric coils…a unit that I gave away recently. A locally well-known older prospector used the venerable Garrett Groundhog and did extraordinarily well. There are some hunters in the area that still use the older units. In fact I’ve seen an authentic photo of a 146 lb chunk of silver found only a few years back, and it was found with a BFO unit.

There have been other notable caches of silver ores located in the area, not the least well-known was discovered by Charles Garrett near a minesite that produced very little silver compared to most other mines. Incidentally it was Charles and a locally renowned prospector that first interested me in this hobby. Now I intend to help newcomers that are faring as poorly as me in the early years.

Below is an indoor photo of the 101 lb piece recovered this year. A quarter is placed halfway back on the top left-side for perspective. It’s a truer depiction of the color / tone than the austere-looking outdoor shot. This piece is wider than tall. I stood back maybe five feet, used the optical zoom to frame it, and took a flash shot…obviously some detail is lost. It’s a lifetime recovery for me, and it is better-looking than any digital photo I can post. All the very best…

Jim.


1334

Steve Herschbach
02-16-2012, 06:37 PM
Hi Jim,

We are very fortunate to have you posting here. Your scientific mind and attention to detail are amazing.

As is the huge chunk of silver you found. What is something like that worth? I think I am getting "silver fever"!

kiwijw
02-17-2012, 01:05 AM
Hi there Jim, Thank you for another outstanding post. You deserve all the success you got. I bet it was hard work & you were justifiably rewarded. I agree totaly with Steve's comment. Your scientific approach & attention to detail is superb. Many thanks for the effort. I bet you had the time of your life.
All the very best to you.

Regards

John (JW) :)

Jim Hemmingway
02-21-2012, 02:59 AM
Hi Steve...thanks very much. I have a minimum figure in mind but I doubt it'll ever matter. I prefer to see it on my shelf...its far more valuable to me than deflating dollars over the longterm.

Jim.

Jim Hemmingway
02-21-2012, 03:18 AM
Thanks very much John...it was a great trip in every respect. But I did work hard...lost some unwanted weight and never felt better in body or spirit. As to the detecting portion of this write-up...well...we try to get all possible information from these wonderful machines. I wonder if any of the people encountered this year will ever see this information...not one of the guys I talked to seemed aware that metal detecting forums existed. Heck the same applied to me about four years ago. I gave several of them written directions to access this forum.

Trust all is well with you and that you're getting out regularly...haven't seen much by way of your posts lately. Hope you've had a chance to get down to the south island. :)

Jim.

Bob(AK)
02-27-2012, 12:15 PM
Hi Jim, you are the designated silver expert, and this is very enlightening. You mention negative hot rocks, but that confuses me a bit. I have a few pieces of ore from an old silver mine here in Ak. They give me a signal which I guess is a negative hot rock signal. This is both with a GMT and a little Falcon unit--signal as the coil moves away from the rock. Does this sound right?? I believe it is silver ore just from the weight and color, soft material also, thanks Bob

Jim Hemmingway
02-28-2012, 07:32 PM
Hi Bob… sorry about a delay getting back to you. I hurt my back two days ago and have been unable to get around much. Your question...

This is both with a GMT and a little Falcon unit--signal as the coil moves away from the rock. Does this sound right?? That is correct for a hotrock response.

Your detector results indicate that your ore samples contain sufficient iron minerals to dominate the signal produced. I can’t answer as to whether the Falcon responds to silver sulfides that may or not be present. You didn’t mention the actual GB readout for your ore samples. I presume that you turned on your GMT to test the samples without any adjustment to the GB control. If that is the case Bob, you were testing at the default GB77…and that does indicate sufficient magnetite present in the ore to yield the negative hotrock signal.

If you’re unsure about interpreting the signal, decrease the SAT control as you wave the sample back and forth across the coil. A negative “hotrock” signal will be more easily distinguished from a normal positive signal. So to the extent of the information provided, everything seems to be working right...but that does not imply the ore samples contain no silver values.

I suggest you contact either Geowizard or GeoJim about a simple test method to determine the presence or absence of silver. I don’t bother with blowpipe oxidation of sulfides and HNO3 / HCl silver chloride coagulation tests for my application…simply no need. You know the alternatives…an assay or get the opinion of a district geologist.

Jim.

chickenminer
02-29-2012, 09:50 AM
Jim...
Great thread. I never get tired of looking at those gorgeous silver specimens you post!

I noticed the host rock seems to always be calcite. Is that true for your area ? Silver formation in general there ?

Bob(AK)
02-29-2012, 11:12 AM
Thanks Jim, sorry about your back. Hope that improves soon. I will check out these samples further. I have a bunch of blizzard stone (if you know what that is)that gives the same signal. It has magnatite in it and it is magnetic, Bob

PS. You are right Dick, those specimens are great

Jim Hemmingway
03-01-2012, 08:24 PM
Hi Dick…thanks for taking a moment to comment here, each post is very much appreciated. :)

Most silver is found predominately in association with carbonate veins, for example calcite and dolomite. The vast majority of my samples are silver in a calcite matrix but I suspect some are in dolomite as observed by a reluctance to react with cold hydrochloric acid to nearly the same extent as does calcite. Otherwise I don’t distinguish between these two similar materials. Quartz is a common gangue mineral according to my research, but I have no quartz and silver samples after 26 years at this pursuit. And I do check my samples closely each evening back at camp. I think if quartz had been present in any amount that I would have noticed it. At least that’s my observation Dick. We’re not discussing a handful of samples either… but rather many hundreds of specimens found and examined over the entire trip this past autumn.

Silver ores in this area are associated with variable amounts of antimony, bismuth, very minor mercury, cobalt, nickel, arsenic, iron and other common gangue minerals. These minerals present themselves in far too many forms to list here.

The two specimens depicted in the photos below were recovered in the outback as discussed in the article. While no beauties, they have one thing in common…both were found by eyesight and were located not more than maybe five feet apart. The smaller sample illustrates that not all silver ores are attractive…that’s precisely why I bothered to clean and photo it. The larger piece has the thick protruding native silver on the reader’s right-hand side but it’s a question as to how far it penetrates into the structure. In any case it may well account for the upper pulltab conductive readout...a surprisingly heavy sample that belies its surface appearance.


1364


1365

Jim Hemmingway
03-01-2012, 08:34 PM
Hi Bob…thanks for your reply. :)

I wish I could say more to be helpful but I see no point in idle speculation. If you have a chance would you mind putting up a photo of the blizzard stone, maybe include your ore sample. I realize that mineralogy is about having the sample in-hand, but possibly Geowizard or GeoJim might chance a comment. No pressure though...I'm sure you have other things to do.

Lets put up another specimen found this year...nothing special although the real thing is a nice looking piece. The other side actually shows far more native silver and character but I can't get it to take a decent photo. The side showing was worn smooth as a baby's bottom...


1366

chickenminer
03-02-2012, 08:18 PM
Jim,
Thanks for the information.
Yes, from my reading I see dolomite is less reactant to the acid test. I know calcite can
fluoresce, what about dolomite? Could that be another way to test?
Then again, calcite can fluoresce with such variety I'm not sure anything could be conclusive there.

Fun seeing those samples ... whatever the host rock is :)

Hope the back is better ! Sure can be miserable.

Jim Hemmingway
03-04-2012, 08:03 PM
Hi Dick…seems like each winter something has to happen…usually it’s a good cold …but this year its a pulled lower-back. It’s easing-up now so I can get around similar to a hobbled horse…but have now acquired a nasty cold…go figger…

The subject of fluorescence is one that I know very little about. What little I have learned has been acquired through reading and checking samples with SW, MW (midwave) and LW lights thanks to my brother. He is quite knowledgeable, does a number of mineral shows each year with a fluorescent display and is familiar with fluorescent substances in this area.

The literature indicates that dolomite is seldom fluorescent while calcite is frequently fluorescent. Calcite fluorescence varies at different sites here and is not as consistent as geo-literature might suggest. Moreover, fluorescent calcite samples from this area do not compare with fluorescent calcite samples from Franklin, New Jersey…the standard to which others are compared. My calcite samples either do not fluoresce or its very minor. It was recently described to me that (a) calcite/dolomite normally fluoresces with SW or MW and rarely with LW. (b) There are activator minerals found in calcite that can produce fluorescence. An example is manganese that produces a red fluorescence.

The fact is Dick there are so many shades…and I suspect intergrades observed from doing acid work…of calcite and other materials in this area that as a hobbyist I don’t try to distinguish between them. Research indicates that dolomite is far less common than calcite and is one of the first minerals deposited to the rock wall underlying other minerals such as calcite. I intend to check some raw or uncleaned samples found this past season with fluorescent meters in about a week. If I can find anything interesting I will post a photo with / without fluorescence. Below is another small silver in calcite sample representative of many modest finds made this trip.


1375

Bob(AK)
03-04-2012, 09:31 PM
Jim, I'll be working on some photos for you, but since you and Dick brought up fluorescence, wish I had a piece of dolomite.
With my limited studies most dolomite apparently does not fluoresce. I have a good quality short wave light but no long wave, seems most Alaskan minerals fluoresce best with short wave. I have also been experimenting with photographing fluorescent minerals. Here is a photo of an Alaskan thunderegg I cut recently that has a blast of bright orange calcite. Most calcite that I have is a light pink. Dick, I wish ultraviolet was more useful in identifying minerals, but so many minerals can be so many different colors--who knows.

http://img.photobucket.com/albums/v156/AKAUU/ak2010/0033.jpg

shaftsinkerawc
03-05-2012, 06:42 AM
Nice photo Bob, AMDS had a portable LW/SW Lamp in the past.

Bob(AK)
03-05-2012, 12:28 PM
I had one of those small lamps, OK at times but a bit weak. Here is a photo of the "silver ore" just looks gray, is quite soft and heavy. Blizzard stone is soft also with white feldspars which as you can see are much harder, Bob

http://img.photobucket.com/albums/v156/AKAUU/003.jpg

http://img.photobucket.com/albums/v156/AKAUU/002.jpg

Jim Hemmingway
03-06-2012, 10:49 PM
Hi Bob…

Your Alaska thunderegg fluorescence is gorgeous…I could stand some digital photography lessons from you…what a beautiful shot. :cool:

It's difficult to say what mineral(s) comprise your “silver ore” as it appears to be heavily tarnished or oxidized in the photo. If a silver ore I doubt it would yield a negative hotrock response on your GMT…obviously I’d prefer to have the sample in-hand to test myself for a result about which I could be more confident. However...lets put that result aside for now…

If soft and sectile, silver sulfides or cerargyrite (a silver chloride) are indicated and could be easily fused with a blowpipe or perhaps a good propane, butane, or other type of gas torch. Scrape off a small fragment, cut a small depression in a piece of charcoal, place the fragment into it… then heat it with the oxidizing portion (tip) of the flame. If sulfides are present sulfur fumes will result. Use HNO3 to dissolve any resultant possible silver bead, followed by HCl addition to check for silver chloride precipitation is the only surefire method I can suggest at the moment. BTW, cerargyrite has a silver content that varies between 60% and 75%. If this is cerargyrite it should fuse easily on charcoal to a layer of silver. This gray appearing silver mass can then be tested for its malleability and that will answer your question…I doubt there would be any need to further test with acids as described above…but of course you can do so for a more definitive result.

Below is a photo of mostly disseminated silver at least from its surface appearance. Aside from the larger bits of native silver and that it is framed with calcite and has been cleaned with a rotary tool…it wouldn’t look all that much different from your sample. If that piece is cerargyrite…hang on to it…such samples are increasingly difficult to find.

Jim.


1376

Jim Hemmingway
03-18-2012, 08:40 PM
Bob...had a chance to try short, mid, and long wave on my silver / calcite samples displayed on my shelves. It was a learning experience. Much of my research material describes calcite fluoresence more in reference to using a shortwave light...it may well be that the midwave light wasn't available at the time most of my reference books were published. The shortwave had little impact on most of my samples, while the longwave light had even less. However a few samples reacted sharply to the midwave light.

Two such samples stood out...the 101 lb and 2.7 lb pieces displayed in the article... responded with a solid glowing red fluorescence very similar in brilliance to your thunderegg calcite's orange-red result. Several others had partial fluorescence in red, while a few others produced a white or yellowy fluorescence. To produce a more brilliant fluorescence the light had to be held within a distance of about a foot to the rocks.

To demonstrate Franklin, New Jersey fluorescence by comparison, my brother brought a chunk of pale green 'Willemite'...a zinc silicate... that reacts strongly even with the light held four or five feet away. This piece was also phosphorescent after the light was turned off.

There was no time to fool around with trying to get a decent photo... but I suggest that you get a midwave light...it may well give you some interesting surprises...:)

Jim.

Steve Herschbach
03-19-2012, 05:33 AM
Get up and learn something new - I never heard of midwave ultraviolet lights until I read this. Thanks Jim!

Jim Hemmingway
03-19-2012, 06:40 AM
Steve...here's a link to a site that gives a brief easily understood synopsis about such lights...I wondered if this would be useful as a resource for the forum...

http://www.google.com/url?sa=t&rct=j&q=midwave%20flurorescent%20lights&source=web&cd=1&ved=0CFMQFjAA&url=http%3A%2F%2Fwww.tigerowner.com%2FUVlamps.htm&ei=okJnT9KLI-fq0gHUrNixCA&usg=AFQjCNHvrBmA4-Mo-LrRIbvBP3UAysKnfA

Jim.

Bob(AK)
03-19-2012, 12:18 PM
I think you guys are right about midwave, not been around so long for some reason. Actually you may be able to make any wave length with different filters. The filters used are not cheap, and you can now buy lights with all three wave lengths in one unit--big bucks though. Perhaps someday when I get rich.

Jim I would think all your silver/calcite specimens from any given area would react the same with the ultraviolet light. Perhaps you do have some dolomite, Bob

chickenminer
03-19-2012, 05:54 PM
Geez... all my playing with ultraviolet light over the years, mostly shortwave, and I had never run across the mention of midwave ultraviolet !

It must be something realitively recent for mineral identification because of the fact I don't belive I have ever seen it mentioned in flouresence ID books.

I have never had any luck with getting a calcite sample to flourese. Now I'll have something else to play with.

Great photo Bob!

Jim Hemmingway
03-20-2012, 06:17 PM
Hi Bob….

I agree with you that the calcite in the area should react similarly / uniformly… and it pretty much does insofar as most silver-in-calcite samples react poorly to UV light at any length. I suspect the calcite we find in association with silver that reacts well to UV light contains activator constituents such as manganese, or highly mineralized silver at less than 1% by weight…or other activator substances. As well...there is some variability in calcite fluorescence between collection sites in the same area.

Steve…to answer your earlier question about pricing the large specimen. I’m reluctant to quote hard numbers here as it may attract criticism. But at today’s spot price X total specimen weight X 80% = a price that well exceeds the value that came to mind from the first moment I saw it... $25000 is the minimum that would interest me unless I receive expert advice that says otherwise. Such attractive large rich silver specimens are extremely rare. It would be necessary to give serious collectors a good opportunity to see it. To that end, it might prove interesting to contact a high profile mineral auctionhouse in New York.

The specimen below is another of many small pieces found this past autumn…

Jim.


1429

Jim Hemmingway
03-20-2012, 08:03 PM
Dick...PM sent tonight. :)

Jim.

Steve Herschbach
03-21-2012, 05:33 AM
Hi Jim,

Oh, we can all stand a little criticism, and I was just trying to get a ballpark idea. Looks like besides fun and adventure hunting silver can also pay off quite well. You did better on silver than I did on gold last summer.

Jim Hemmingway
03-22-2012, 09:10 PM
Steve…

Quote: “Oh, we can all stand a little criticism, and I was just trying to get a ballpark idea.”

Good heavens yes… after nearly 40 years of marriage I can attest to the truth behind that statement…but seriously I wasn’t thinking about you at all when I made that comment. :)

As to your other remark about gold vs silver…I doubt another such season here is possible. And despite a good showing of highgrade material, only about half the total weight are specimen quality…at least to my view. Possibly the remainder could be crushed and smelted, but I seriously doubt that is a viable option in a rural subdivision setting where we currently reside. There was very little by way of adventure last autumn for much of the trip, but recovering quality silver… even under mundane conditions requiring extensive physical labor…was surprisingly still lots of fun. That said, I think we both see electronic prospecting as an interesting and fun-filled adventure on its own merit… good finds are sauce for the goose.

Pick and shovel work in good ground is nothing more or less than a different form of exploration…slow but with immediate gratification in terms of silver recovered. Another benefit of working good ground was that on some days when feeling disinterested, or just plain tired-out… whatever… it was encouraging to know exactly where you were going, what you intended to do, and that you would undoubtedly find good silver. This helped a lot with transitioning from the usual exploration and sampling to ‘mining’ a site. To mitigate the tedious aspects of constantly moving and scanning material, I started to view my digsites in an archeological context, and this mindset did help to salve a restless yearning to be ‘moving on’…

Times may be changing as reflected by renewed corporate interest in bulk sampling and processing silver ores at formerly abandoned camps. Two productive sites have been lost recently…vast areas… that are now inaccessible due to a change in corporate ownership or policy. Increased silver values portend an uncertain future for prospecting hobbyists here…particularly in regard to searching abandoned mine tailings. I see little choice but to continue on from last season…to recover silver as expediently as possible while the opportunity exists.

So… that’s my plan for this year Steve. No exploration other than a friend’s invitation to hunt float late in the season. I think that anyone contemplating a visit to the area should be aware of the prospects as described in the write-up. It gives an honest appraisal of what is required to recover silver in any real quantity…especially so where time on site is limited.

Jim.

PS: A sincere thankyou to the party responsible for giving this thread a five-star rating. That was a nice surprise… below is another small specimen recovered this past autumn…



1440

Reno Chris
04-07-2012, 11:04 AM
Jim -
This thread, plus some specimens I saw at the Tucson Gem and Mineral show have inspired me to have a whack at detecting for silver in Arizona next year when I am down there. A number of mines in AZ produced significant amounts of native silver, some even in well crystallized forms.

Jim Hemmingway
04-10-2012, 05:20 PM
That sounds like quite an adventure Chris… but with your wide range of mineralogical interests I’m not at all surprised that you intend to search for silver in Arizona. I’ve often thought that your recently published book entitled Fists Full of Gold contains a good deal of information that is applicable to hunting silver as well as gold and other minerals. I wish you every success and look forward to learning more about the results of your trip.

The photo below is native silver mixed with some ruby silver… in this instance I suspect stephanite but haven’t tested to confirm. It’s the bigger brother to the 4.3 lb piece displayed in the article. Both specimens were found within moments at the close of my very last day in the field, on a cold blustery windswept afternoon at maybe three feet apart near the four-foot depth level in my “diggings”. My wife was present the final week of the trip…maybe to ensure I did actually pack-up and return home before freeze-up. I had both signals located when she left to get coffee out of the truck nearby. When she returned a few moments later I had both pieces in hand… the trip ended on the same positive note that characterized it throughout the entire autumn season.

Thanks for your comments here Chris, I look forward to, and enjoy your posts very much. :cool:

Jim.


1473

geowizard
12-24-2012, 09:05 AM
I have four 40 acre placer claims on a silver nugget locality. This location, referred to as the potato patch produced 100,000 ounces of silver nuggets in 1862. Miners and their families dug the nuggets with potato spades. They were shipped to the SF mint by freight wagon. I personally observed two potato sized nuggets about 15 years ago from a prospector that had found them there in the 1950's.

The territorial geologist, W. P. Blake, wrote in 1895;

The silver is found as chloride mixed with huge masses of native silver., and carbonates, some embolite, and vanadinite mixed with it. The whole mass is usually associated with hematite, and is invariably free from gold.

In the same report there is illustrated a 31 pound nugget from the area that was found in august, 1895.


- Geowizard

geowizard
12-25-2012, 09:00 AM
Ok, So, I'm pitching the nugget claims. They are in the Richmond mining district, about 15 miles north of Globe, AZ. I don't plan on filing the aol for 2012. These claims are in the National Forest domain. They overlay lode claims. :)

- Geowizard