White's TDI Pro in Silver Country [including Infinium Comparison]

[Jim Hemmingway]

The White’s TDI Pro in Ontario Silver Country

Introduction

The pulse induction TDI Pro, manufactured by White’s Electronics, is primarily designed as a gold detector but has proven effective for other pursuits such as relic, beach and even coin hunting. Searching for silver ores with the TDI Pro is a unique application of this detector. The mining areas searched are replete with conductive pyrrhotite hot rocks and iron junk of every type and size imaginable. This report looks closely at the TDI Pro’s ability to search these sites and separate iron from silver.

The TDI Pro has iron handling capabilities that merit discussion. Naturally some comparisons are made to the Garrett Infinium LS and these are included just for the heck of it. Many hobbyists will be interested to learn how these units compare with respect to iron ID / elimination and depth capabilities. Both these units are well suited for silver hunting. Their feature sets permit either to excel over the other in some situations. The TDI Pro is a versatile instrument that proved effective at finding some beautiful silver this past autumn.

The photo below depicts lovely autumn colors in rugged silver country that we’re sure electronic prospectors enjoy and appreciate. Those tailings may look like heck to some folks, but to us they’re an enticing snippet of heaven.

Quickview of the TDI Pro

TDI Pro is a solidly constructed unit with user-friendly analogue controls. It is lightweight, better balanced and less fatiguing to use compared to many PI units. Over the normal course of detecting where it is frequently set aside to dig targets, no undue arm fatigue was experienced. The TDI Pro can be hip / chest mounted to further reduce weight.

The TDI Pro comes with two lithium battery packs, a seven hour AC charger, and a “fast charge” three hour full charge auto cigarette lighter plug-in type charger. When the battery dies and needs recharging, the bright battery indicator light turns completely off in about a half-minute. With a full charge the TDI Pro is good for another full day of detecting, or approximately eight hours continuous use.

Gain determines the depth /sens that the detector sees a target at any given combination of ground balance and pulse delay settings. Optimal sensitivity is typically in the 6-8 range for our area. The gain setting affects the unit’s susceptibility to the effects of ground minerals and EMI. Excessive gain may increase instability resulting in excessive chatter and false signals. Set it for the prevailing conditions such that the threshold is reasonably smooth, permitting you to easily hear and identify target signals. The frequency control can mitigate external electromagnetic interference (EMI) to some extent, allowing operation near or under power lines.

Threshold control is best set above the “chatter” level to obtain a consistent “mosquito-like” hum. Reducing the threshold below the chatter zone to “silent” threshold reduces depth / sens especially to smaller or fringe depth targets. If the threshold volume level is excessive, adjust the volume control to reduce it. If using headphones, one may set the volume control to maximum and then adjust the headphones volume level to your preference.

Target Conductivity (Tone Mode) Toggle is activated when the GB Fine control is turned ON. It permits the user to choose whether signals are heard from low conductive targets only, high conductive targets only, or both high and low conductive targets. This feature offers a number of search options in concert with GB control adjustments. This subject is addressed in more detail further into this report.

Pulse Delay adjusts the sample pulse delay from 10-usec to 25-usec between the end of each transmitter pulse and the start of the receiver-sampling period. The 10-usec setting is the most sensitive to all targets including low conductive targets that comprise the vast majority of our silver nuggets and ores. Increasing the pulse delay towards 25-usec generally reduces overall target sensitivity, minimizes ground mineral signals and will suppress low conductive target signals that include signals from small iron bits and low conductive silver.

Ground Balance (Fine & Course) Controls are activated by turning the Fine GB control clockwise to the ON position. With ground balance activated, the target conductivity control and variable audio are also activated. The GB control’s chief function is to compensate for iron minerals in the ground. Most ground in prospecting country will balance between GB8 and GB9 on the coarse GB control.

 The TDI Pro has manual ground balance only. Pump the coil one to six inches above the ground and adjust the coarse control until there is no change in threshold. Over some soils the fine control may be adjusted to fine tune the ground balance, but this is not necessary here. Any adjustment to the pulse delay will require another ground balance procedure if you intend to operate the unit in a ground-balanced condition.

 If ground minerals are not excessive, the ground balance control may be adjusted to achieve some discrimination control. The GB control can be used in conjunction with the target conductivity tone mode toggle to selectively eliminate a GB scale range of signals from detection. Alternately, it may be used to select and hear all iron junk and natural silver signals but arbitrarily assign either a high or low conductive tone to a given portion of the GB scale target range depending on just where the GB control is set.

 If ground minerals are not excessive, the ground balance control may be adjusted to achieve improved depth on a given target GB range. The GB control setting impacts the depth / sens that can be achieved on a given target GB range. Where target GB range lies near or at the operating soil GB setting, reduced detection depths will result. Conversely, if we can search with a GB setting as far as possible from the expected target GB range, a significant depth improvement results for that target range. For example, a high conductive silver specimen has a GB point close to the soil’s ground balance setting, say at GB9. If ground minerals permit searching at GB1, improved detection depth on that target will result.

 Reducing the GB setting increases threshold stability. The GB1 setting is noticeably smoother and quieter to operate than GB9. Over some soils ground balance may not be required. In that case one may operate with fine ground balance control turned OFF, resulting in improved depth and threshold stability. However, operating with GB in the OFF position means that variable audio and target conductivity tone mode are inactivated such that all targets respond with the same tone.

The photo below depicts a handsome half-pound acanthite / native silver specimen located with the TDI Pro. Acanthite is a silver sulfide comprising 87% silver and is often associated with wire silver here. It is quite soft and sectile, blackish and usually with a slight but distinctive deep bluish-black tint in these parts. The native silver you see poking out of the rock runs right through it in veins. This specimen is strictly a low conductive tone mode signal at any GB setting. It will not give a signal in the high conductive tone mode even at GB11…a technique we can use to arbitrarily differentiate high conductive targets from low conductive targets.

Target Signals and Ground Balance

(a) Target Signals

The ground balance scale runs from the GB1 position clockwise to the GB11 position. Target conductivity is highest at the GB1 position and decreases as the GB control is adjusted clockwise to the GB11 position. The lowest conductive targets fall into the GB11 category. The signal tone with which a target responds depends on its GB point in relation to where the GB control is set, in concert with the target conductivity tone mode toggle setting.

A low conductive tone mode signal is always strongest at the GB1 position. Depending on a target’s GB point, that low conductive tone signal may disappear or go quiet at some point as we adjust the GB control clockwise. Some targets will continue to give a low conductive tone signal at the maximum setting of GB11. A portion of these targets will only signal in the low conductive tone mode from GB1 up to and including GB11. They will not signal in the high conductive tone mode at GB11. They can only be searched for in either the low conductive or all-conductive tone modes. These are referred to as low conductives in this report.

Low conductive silver occupies a conductivity range up to and mostly including the mid-pulltab range. Low conductive targets, silver and iron junk alike, respond with a low conductive tone only, and must be searched for in either low conductor tone mode or in all-conductor tone mode. Examples of low conductive iron junk include rusty small iron tidbits, flat, thin sheet iron and tin, our plentiful twisted or braided iron wire, small nuts and small nut and bolt combos, small ¼ inch plate, rusted jar lids and so forth.

‘Low conductive’ silver does not imply the silver is somehow second rate. It means that factors such as purity, types of mineral inclusions, size, shape, or structure may be sufficiently dominant to affect where silver exists on the TDI Pro’s GB scale. The specimen illustrated in the photo below exemplifies high purity but very low conductive silver. The low conductivity is almost entirely due to the dominant spongy silver structure.

A high conductive tone mode signal is always strongest at the GB11 position. A target may continue to produce a high conductive tone signal as the GB control is adjusted counterclockwise, but in a prospecting context it normally loses its signal at some point along the scale. High conductive targets also signal in the low conductive tone mode anywhere from GB1 up to and including GB11. Any targets that signal in the high conductive tone mode at GB11 are referred to as high conductives in this report. To identify high conductive tone signals, only the high conductive or all-conductive tone modes can be used.

High conductive silver occupies a conductive range from roughly mid-pulltab up to and including copper penny level. Mid-pulltab range is where our silver ores separate into either high or low conductives in response to the TDI Pro. Most mid-pulltab silver here responds as low conductors, but some samples respond as high conductors. Examples of high conductive iron include all manner of nails, drill bits and drill rods, thicker plate iron, tools and implements, iron bar and pipe fragments, 3 ½ inch rail spikes so prevalent at our minesites, milling balls, and so forth.

Massive silver structure is not a prerequisite to attain high conductor status. The copper-colored niccolite in the sample photo below is insufficient to raise the conductivity above nickel level, thus the silver is responsible for increasing the sample’s conductivity. Yet this specimen may very well contain less silver than the low conductive sponge specimen above. As can be seen, both specimens are collectable regardless of conductive measurements on metal detectors.

(b) Ground Balance for a Metal Target

Ground balance points do not exist for low conductive metal targets as defined above because they only signal in the low conductive tone mode. For other targets, the ground balance point is the position on the GB control scale where a metal target will have its weakest signal. How do we locate a metal target’s ground balance?

 Using the all-conductor tone mode a silver nugget might signal with a low conductive tone from GB1 clockwise to GB3, and a high conductive tone from GB5 clockwise to GB11. Mixed high and low tones will be heard in a transition zone between GB3 and GB5. GB4 is the null or ground balance point for this nugget. High and low tones will be about equal in volume and duration at the ground balance point.

 Using the low conductor tone mode a good signal is heard from GB1 clockwise to GB3, then gradually weakens and is gone at GB5. In high conductor tone mode the nugget signals at GB11 counterclockwise to GB5, then gradually weakens and is gone at GB3. Again, the transition zone is from GB3 to GB5 and the null or ground balance point is GB4.

TDI Pro & Infinium Depth Comparison

The Infinium with elliptical 10”X 14” mono coil and the TDI Pro with stock 12” dual field coil were compared over a few targets buried in the ground, followed by some air tests presented below. TDI Pro gain was set to the maximum “10” setting. Infinium’s gain is preset, but increasing the threshold improves the depth at which target signals can be heard. The first target is a pre-1981 nickel that Infinium and TDI Pro at GB9 air test at seven and eight inches respectively. Interesting because both units air test a Jefferson nickel at twelve inches or more depending on settings.

Adjusting both units to proper ground balance and a bare threshold, TDI Pro at GB9 gives a modest, repeatable signal on a pre-1981 Canada nickel at ten (10) inches depth. Infinium signals one-way only, but increasing Infinium’s threshold to “6ish” yields a stronger, repeatable signal. If TDI Pro’s ground balance is reduced to GB1, then these units are very close on this target. If soil minerals permit, turning OFF the TDI Pro’s GB control further improves depth.

Lead “nuggets” buried out in the patio were tested. The half-gram to one-pennyweight nuggets were made by hammering some small fishing sinkers together. They respond very poorly to PI units in air tests compared to similar size gold or silver nuggets. Neither Infinium using increased threshold nor the TDI Pro at GB9 will see the half-gram nugget at four (4) inches nor the one-gram nugget at five (5) inches. Infinium signals one-way over a one-pennyweight nugget at five (5) inches every two or three coil sweeps, while TDI Pro does not see this target at all. Now, adjusting the TDI Pro to GB1 results in a modest but repeatable signal over the pennyweight nugget. These units using the coils described are that close in performance on these targets. It would be interesting to see the results if Infinium used a dual field coil and TDI Pro used a 14” mono coil.

Air tests indicate the dual field coil improves sensitivity to small targets compared to a 14” mono elliptical coil. The chart below compares 5” diameter mono and 14” elliptical mono Razorback coils to the stock dual field coil on the TDI Pro. Check out the 0.4 gram nugget results in the chart below. BTW, within the 14” mono data the red-colored numbers highlight improved performance over the dual field coil.

The next chart presents air depths for both units tested under high residential EMI conditions. Again we see results that indicate improved sensitivity on small nuggets with the dual field coil. The 3 and 5.6 grainers are gold, the 4.5 grainer is solid lead, the half-gram and one-gram nuggets are native silver. Infinium has four sets of results whereby the first number indicates a “sound-off” while the second number indicates a repeatable signal.

Target depth on high conductive silver decreases as the target GB point approaches the TDI Pro’s operating GB setting. The closer the target GB is to the operating GB, the more significant is the depth loss. The chart below presents data that by design encompasses the full natural silver high conductive range. It does not take into account that high conductive silver ores in the pulltab to mid-screwcap range are more plentiful than those found at higher conductivity levels. The pulltab to mid-screwcap range is more susceptible to depth loss searching with a ground-balanced GB9 setting. BTW, the chart designations T = 4 or T = 6 refer to Infinium’s threshold settings.

The bar graph below illustrates an air test depth trend with a low pulltab range low conductive silver specimen. The depth loss at a pulse delay of 10-usec from GB1 to GB9 is 5 inches or 24% for this piece. On average the depth loss for samples tested in this specific range is closer to 15% at 10-usec. Regardless whether these air depths accurately reflect buried target depths, the data suggests using as low a GB setting as ground minerals permit to achieve best depth when searching low conductive silver ores and nuggets.

What About Iron?

High conductive iron and high conductive silver both yield high and low conductive tone signals. To see if anything can be done to separate them by using ground balance and tone mode controls, their respective GB scale signal ranges needed to be identified. Samples were tested in both high and low conductive tone modes by adjusting the GB control until a target signal was ignored while passing the target across the middle of the coil. High (HSEP) and low conductive signal end points (LSEP) were established for all samples tested. What exactly does that mean?

 Take a high conductive silver sample with a HSEP at GB5. This means in high conductive tone mode it will respond from GB11 all the way down to GB5 where the high conductive signal is finally ignored. It will not respond with a high conductive signal at a GB setting lower than GB5.

 That same high conductive silver sample may have a LSEP at GB7 for example. That means in low conductive tone mode it will respond from GB1 all the way up to GB7 where the low conductive signal is finally ignored. It will not respond with a low conductive signal at a GB setting higher than GB7.

The graphs do not represent relative proportions of various types of iron junk encountered in the field compared to silver finds. For example, if proportionate numbers of nails had been included, the HSEP graph iron numbers at GB4 and GB5 would exceed the graph upper limits by several orders of magnitude. This applies to the LSEP graph for those same nails residing within the GB6 to GB9 range. That said, the results indicate that high conductive iron and high conductive silver occupy a similar range on the TDI Pro ground balance scale.

(a) Some Observations

In the high conductive tone mode, there is no way to separate silver from iron based on any combination of tone mode and GB control. Moreover, searching strictly in high conductive tone mode eliminates all low conductive signals. The low conductive tone mode with a GB9 setting pretty much eliminates regular nail sizes from detection while capturing all low conductive silver signals. Much of the larger high conductive iron that signals at GB11 in low conductive tone mode can be separated from low conductives by checking signals at GB11 in the high conductive tone mode. Low conductives do not signal in the high conductive tone mode.

The other interesting aspect of the tests was to learn that high conductive iron generates much wider GB spans between HSEP and LSEP overall than does natural silver. Test measurements on 34 high conductive iron samples resulted in an average HSEP to LSEP span of five (5) GB units and that includes a number of smaller nails that pull that average down. The 30 high conductive silver pieces tested have an average GB span of two (2) GB units.

The difference in GB spans can be used as an indicator to distinguish high conductive silver from high conductive iron. It is not a definitive technique because a variety of very compact iron pieces such as drill bits, milling balls, and other nondescript chunky iron also exhibit “tight” GB spans similar to high conductive silver.

(b) Definitive High Conductive Iron Lo-Hi-Lo Tones

Iron lo-hi-lo tones can be used to separate high conductive iron from all silver. This procedure usually involves adjusting the GB control to determine whether a lo-hi-lo tone can be had as we sweep the loop over the target from different directions. The target conductivity tone mode toggle must be set to the “all-conductive” position. GB control adjustment may cause a target to lose considerable depth and go quieter. Try to rotate the GB control slightly off a “quiet” setting but not so far that we lose the ability to discern high and low conductive tones. If we can acquire a lo-hi-lo signal, we know it will be an iron target. The lo-hi-lo tone is a definitive technique to identify iron if it can be had. Perhaps there are other examples such as modern coins with magnetic content that may give a lo-hi-lo tone, but they will not include silver nuggets and ores.

The GB control adjustment technique does not always acquire a lo-hi-lo tone over some iron. Compact high conductive iron such as milling balls, drill bits, and other nondescript iron chunks have very “tight” GB spans. Lo-hi-lo tones are difficult to get without some delicate GB control adjustment, and sometimes they’re impossible to acquire. Elongated iron items like nails, bolts and rods normally present no difficulty obtaining the iron tone.

Part 2 of the report is posted immediately below...

[Jim Hemmingway]

Prospecting in Silver Country

(a) TDI Pro Field Use

The vast majority of our native silver is low conductive silver. It signals in the low conductive tone mode at GB11, and does not signal at GB11 in the high conductive tone mode. This is how we arbitrarily separate high conductives from low conductives. Searching in a ground-balanced condition at GB9 in the low conductive tone mode captures all low conductive silver and will occasionally snare higher conductive silver. This technique eliminates most nails and some larger high conductive iron junk from detection. As noted earlier, using GB9 whether in low conductive or all-conductive tone mode results in some depth loss on some targets when compared to using lower GB settings. It amounts to a trade-off whereby best overall available depth is sacrificed for the benefit of iron discrimination in nail-infested areas. In some areas ground minerals may dictate using the TDI Pro in a ground-balanced condition at GB9.

In areas reasonably free of iron junk and where ground minerals permit, searching in low conductive tone mode at GB1 offers best overall depth to the entire silver GB range. All target conductivities will signal. The options are to dig all signals, dig only low conductive tone mode signals and / or pursue high conductive target signals as described under Definitive High Conductive Iron Lo-Hi-Lo Tones. If the lo-hi-lo tone cannot be had, the only sure target ID technique is your pick and shovel. The handsome specimen below indicates that high conductive signals are worth investigating…

At GB1 in low conductive tone mode, increased magnetic susceptible iron minerals prompt a low conductive tone volume increase as the coil is lowered within an inch or two of the ground. This was no issue here since the coil needs to be held several inches above the ground to accommodate the uneven rocky terrain. Where possible try to maintain a reasonably level coil height and slow down your sweep speed to help attenuate ground noise. If these are insufficient to reduce the ground noise then adjust the ground balance clockwise until effective searching is possible.

An alternative ground-balanced search technique is GB9 in the all-conductive tone mode if you wish to hear all high and low conductive signals. More information is immediately available about whether a target signal is a high conductive at that setting or potentially a low conductive target. Some iron targets yield a lo-hi-lo tone without the necessity of ground balance control adjustments. This technique results in some depth loss on some targets when compared to using lower GB settings and it can be annoying in areas replete with iron junk.

Low conductive iron signals must be dug to ensure low conductive silver is not overlooked. Although the TDI Pro arguably can discern target size particularly when using the low conductive tone mode, it is very difficult to evaluate most low conductive signals with any confidence when target size and depth are highly variable factors. Raising the coil above a target signal to assess signal strength is not a viable technique since low conductive silver occurs in a wide size range and signal strength that could easily be mistaken for low conductive iron at various depths.

The specimen illustrated below resulted from trenching into a bank where good silver has been found in the past. The TDI Pro gave a modest low conductive tone signal on fairly deep silver, maybe 15 or 16 inches into the bank on a downward angle. The sample has lots of exposed silver that we don’t see often. The photo doesn’t show innumerable tiny veinlets. Usually an HCl bath is required to expose silver veins to this extent, but the sample came out of the ground as you see it other than minor surface staining. It had me dashing for the nearby water like winged Pegasus, but unfortunately I forgot to unplug or remove my Nugget Buster headphones. Good news though, the cable snapped off at the headset and my resourceful wife was able to fix it that night back at camp. I always carry spare headphones in my packsack as insurance against these events.

(b) Some Comparative Iron Field-Tests…

Early in the trip I decided to use the quiet out-of-the-way spot in the scene photo above for a few days to compare signals between the TDI Pro and the Infinium. Signals were located and flagged with the Infinium, and then rechecked with the TDI Pro.

This location had an abundance of 3 ½ ” by roughly 1/3” rail spikes with a solid 1” diameter cap. None were beyond 8 or 9 inches depth. Infinium identified these as lo-hi signals in zero discrimination and again in reverse discrimination clearly indicating iron targets. TDI Pro signaled nicely in GB1 and again at GB11 in the low conductive tone mode. The tone mode toggle was flipped to high conductive tone mode and all pieces gave a high conductive signal. The GB control was reduced until the signals disappeared, always in the GB2 to GB4 range. The slight GB variation likely resulted from how these targets were positioned in the ground. At roughly GB9 [there’s lots of GB forgiveness on elongated iron] all these targets easily responded with a lo-hi-lo tone in the all-conductive tone mode. A drill bit rod five (5) inches long by one-inch diameter was found at a half-foot depth. Both units correctly identified it as high conductive iron. It had an HSEP = GB4 and an LSEP = GB10 and easily gave a lo-hi-lo iron tone.

The sample below was found in the same trench as the 1½ lb sample described above. In fact both these samples were found within about twenty minutes. After detecting up the left side of the trench, occasionally digging low conductive iron, I returned along the opposite side of the trench. Perhaps three or four feet in from where the first specimen was found on the left side, another target signaled low down on the bank. For readers unfamiliar with naturally occurring silver, this is a solid silver chunk wrapped in a thin veil of calcite. The light grey-colored calcite you see only in this photo represents native silver just below the surface.

(c) A Word about Searching with Infinium…

The Infinium identifies high and low conductives more conveniently without involved manipulation of the controls to identify high conductive iron. At zero discrimination high conductives give a lo-hi signal and low conductives give a hi-lo signal. Infinium automatically performs this task and does so to its detection depth limit.

 At zero discrimination, the Infinium gives a hi-lo low conductive signal on all ferrous and non-ferrous targets that dwell within a conductivity range roughly up to the lower fringe of zinc penny range. High conductive lo-hi signals represent all targets that roughly lie at and above the lower fringe of zinc penny range.

 In reverse discrimination, the Infinium gives a hi-lo low conductive signal on all ferrous and non-ferrous targets that dwell within an expanded conductivity range up to and including copper penny range. In a prospecting context, lo-hi signals represent iron targets that lie above the copper penny range. Naturally occurring silver that will respond with a lo-hi signal in reverse discrimination is so extremely rare as to be considered practically non-existent in this area.

In reverse discrimination, all zero discrimination lo-hi tone targets, ferrous and non-ferrous, within a range bordered by zinc penny up to and including copper penny will change tone to become hi-lo tone signals. High conductive iron is far more plentiful than high conductive silver in this limited range. To avoid digging this iron in trashy sites, you may prefer to stick with zero discrimination tones only. The trade-off is the rather remote odds of ignoring a very high conductive piece of silver. This strategy frees up a lot of time to cover a lot more ground. Reverse discrimination hi-lo signals should otherwise be dug, especially in gold country where high conductive gold is possible.

In summary, zero discrimination hi-lo signals remain hi-lo signals in reverse discrimination. Some signals lose much or all of their volume in reverse discrimination. Some zero discrimination lo-hi signals will change to hi-lo signals in reverse discrimination. All these signals must be dug if one intends to avoid overlooking any silver.

To ensure effective target ID, always sweep the coil over a target from different directions. Any target that gives both hi-lo and lo-hi signals in zero discrimination is definitely iron. Elongated iron will give a lo-hi or double lo-hi signal along its length and a usually a hi-lo signal across its width.

Low conductive iron is pretty much as described earlier for TDI Pro except Infinium's low conductive range extends to zinc penny range. Infinium’s reverse discrimination concept of reduced signal volume over non-ferrous targets is a useful indicator to distinguish larger iron from silver ores. However, smaller low conductive iron can lose signal volume in reverse discrimination similar to low conductive silver. By comparison, solidly structured high conductive silver tends to retain its volume in reverse discrimination. The reverse discrimination concept of reduced signal volume over non-ferrous targets is not a definitive technique and should be used as an indicator only.

The specimen below gave a modest signal while operating the TDI Pro in low conductive tone mode at GB1. I could tell you how the TDI Pro was put through the usual GB adjustments but that was not the case. It was a favorite area where many good silver specimens had been found before. Iron was almost absent at this spot and I had every intention of digging this signal. The signal seemed to indicate a small and fairly shallow target but some quick digging soon proved otherwise.

After digging what seemed like an awfully deep hole in rocky substrate, the target was found embedded in the bottom. I called the wife over to have a look and said to her “What d’ya think, maybe 18 inches?” Now I don’t carry a tape measure around when searching silver ores but my larger Estwing pick is 25+ inches long. It measured a 1.4 lb high grade specimen at about 20 inches depth. There’s no doubt the unit would have found that piece several inches deeper.

The photo doesn’t show that this rock is inundated with tiny veins of silver coursing throughout the grey / white calcite. Having returned home so late this year, there was not much time to fiddle with these samples to show them to best effect. In fact between the cold weather and property chores there was no chance to clean most of my finds. What you see is pretty much how it came out of the ground except for a quick buzz with the rotary tool to remove surface grunge. Later testing revealed it would have responded with a high conductive tone signal at GB11. It has no iron lo-hi-lo tone, good information in and of itself, nor does it have a GB span, so obviously this piece would have been dug had it been evaluated on site.

Summary

The TDI Pro has a number of attributes for this and other applications. It is an easy unit to use straight out of the box, but it’s somewhat more involved understanding all its potential. It feels good on one’s arm compared to many PI units. A control box cover is well worthwhile to protect against scratches, weather and dust.

The TDI Pro offers alternate operating techniques for prospecting applications. (a) Generally search reasonably low iron junk areas in the low conductive mode at GB1 if possible over your ground. All natural silver will signal, threshold stability is improved, and best overall depth is achieved on the entire silver conductive range. (b) If your terrain will not permit using the GB1 setting, you may try adjusting the GB clockwise until you can search without annoying ground noise from differences in coil elevation. If this is the case, you may wish to search in the all-conductive tone mode to ensure signals from the entire conductive range are heard. (c) Ground minerals may necessitate searching in the all-conductive tone mode in a ground-balanced condition at GB9 if you wish to hear all targets. The all-conductive tone mode is noisier and may require adjusting the gain and frequency control to reduce any ensuing “warble” in the threshold. Targets that fall near or at the soils ground balance point will suffer some measure of depth loss, but otherwise you’ll hear all targets. (d) A favorite setting is to search in the low conductive tone mode at GB9. This setting eliminates most typical size nails, but similar to (c) above, targets near GB9 suffer some depth loss.

The photo below is typical of many small low conductive ores located this year using this method. It is not evident from the photo below, but this particular specimen is essentially a solid silver nugget wrapped in very minor calcite.

The TDI Pro’s chief performance attribute for silver hunting is an ability to ignore a good deal of the commonly encountered nails and other high conductive iron while searching for low conductives. This is a very convenient set of circumstances insofar as the vast majority of our nuggets and ores are low conductives. The second most attractive feature was TDI Pro’s ability to identify many high conductive iron targets via the lo-hi-lo tones. This capability saved much time and effort.

I would like to thank my friend, geologist Dr. Jim Eckert of northeastern Ontario, for his many contributions to this report. Jim and I worked together to determine how we might operate the TDI Pro to search for silver.

Eckert / Hemmingway
February 2011

[Lanny in AB]

Wow--what an incredibly technical post Jim--you really know your stuff. This post bears re-reading many times--lots and lots of information to digest. Well done, as usual. And, by the way, nice finds!

All the best,

Lanny

[extractor]

Jim ! WoW ! I had to read it Twice . Great Report

[Jim Hemmingway]

Extractor and Lanny...thanks fellas, yep this write-up was a real PITA. So much to mention to cover everything off properly. No worries, these posts will stay here for good. I'm mighty tempted to suggest that if anyone wants an original copy to stick in their files to PM their email addresses. Maybe we could try it and see how it goes...

Jim.

[63bkpkr]

Jim,
I've enjoyed reading some other posts you were involved in relating the use of the TDI machine to things other than gold and this is superb follow on post to the earlier ones. Your information truly indicates how versatile and useful the machine is with the understanding that no machine is perfect. Then throw in a few techniques to understand what is in the ground before one digs it and the machine really shines.

Thank you for your time and information...........63bkpkr

As a side not, I appreciate your inputs all the more as the old Whites 6000D coinmaster could be super tuned so that by the flipping of a few dials and switches one Knew what was in the ground (coin related not for mining) before digging and that is absolutely awesome information to have.

[therover]

Jim,

Since I have both a TDI and Infinium, your reports are invaluable. Thanks a TON !

I wish you continued success in your excursions out in gold and silver country.


JC

[Jim Hemmingway]

JC thanks for looking-in here. I’m familiar with your posts and appreciate your comments a good deal. Thankyou.

“Your information truly indicates how versatile and useful the machine is with the understanding that no machine is perfect. Then throw in a few techniques to understand what is in the ground before one digs it and the machine really shines.”

63bkpkr…I am glad you made the above comment because that is exactly how this report should be interpreted at least for the application described. I’ve yet to discover any detector that can handle all tasks perfectly. Certainly the TDI Pro is a capable, versatile unit suitable for many applications and served us well searching for natural silver.

It really shined in areas inundated with iron junk. In low conductive tone mode, GB adjusted to GB9 this unit was a real ‘scrounger’ at finding low conductive silver while eliminating most higher conductive iron signals either outright or by acquiring the lo-hi-lo iron tone. Using a 5” round mono coil in such conditions is a real benefit.

We did our best to identify this unit’s capabilities for this application and we feel the unit does an admirable job. The search conditions encountered in our camps are as challenging as any electronic prospector is ever likely to encounter. In bygone times it was hard to imagine using a PI unit over iron-ridden tailings or mining camps. That is now entirely possible with either of these units as described in the report.

Jim.

[PennyFinder]

Jim, superb post, it's definitely detectorist's brain candy, many thanks amigo! I've kept this one for my records, great post!.

HH

PennyFinder

[Jim Hemmingway]

Thanks PennyFinder...hey if you want a good copy I am quite willing to send you an original copy.

Jim.

[goldbrick]

Jim, That is an outstanding report! I know that it will take me many repeated readings to extract all the knowledge contained within. Owning both these machines this report will be an invaluable tool to help me better understand the capabilities of them. I will pm you my email address as I would like to have this for my permanent files.
Thank You,
Merton

[Jim Hemmingway]

Thanks Merton, an email with both reports has just been sent to you.

You can figure I'm always interested in hearing anything you might have to say from your gold hunting experiences with either of these units.

Jim.

[oldestjim]

Hello Jim Hemmingway... Jim Straight here.... I post as oldestjim on this forum and as i have one of the first Infiniums off the line (it has been modded for the monos) and an early White's TDI "hole" detector I'm most impresssed by this post!

While Googling I happened upon your AMDA posts regarding the electomagnetic properites of soils which is most intersting to me as I have both a Teknetics T2
and a Fisher Gold Bug Pro that has the abilty to measure the magnetic susceptibilty of the soil... to get to the point; the google post which referred me to your post on the AMDA was limited out (I'm not a forum member) and I found
what little I was able to access most valuable information I have ever read...

It would be great if you would post more information on undug soil magnetic proprties regarding a targert viz disturbed soil... The is a way could be another explaination regarding the halo effect..

[Jim Hemmingway]

Howdy Jim…thanks a million for those kindly comments. You can bet your bank balance I appreciate it. As I look back in time, it is hard to imagine that I very nearly did not post this article. I felt it was too technical and lengthy…but it seems to have worked out OK.

The magnetics resulting from various iron minerals are interesting…and seriously impact what can be achieved. A result is that over the years I’ve paid particular attention to them. So, its gratifying to see that write-up attracted your interest as well. A few friends, Ty Brook and our good buddy DJ in El Paso have been quite helpful as mentors on this subject in recent years, and certainly deserve recognition here for their roles in helping me gain an understanding on the subject. These two fine individuals have given freely of their time and knowledge for which I’m very grateful.

As to undisturbed vs disturbed ground magnetic measurements Jim… frankly I have not looked further into the matter. I’ve been content to understand the differences between these soil conditions with respect to target depth and ID and apply the knowledge accordingly when in the field. I believe it has made the difference to digging good targets many times over.

I’d rather not enter the long-standing debate about what exactly is responsible for the improved depth and target ID / discrimination experienced over “undisturbed” natural ground. I don’t have a definitive answer and neither does anyone else, but I’ll make a few comments…

Many hobbyists suggest a “halo” effect as the primary reason for improved performance in undisturbed ground. Other than iron oxidation, which is essentially maghemite, I don’t subscribe to the halo theory with conductive metals. Yes, other than perhaps very pure gold, precious metals and/or alloyed constituents may very well react with chemical substances in the soil resulting in molecular leaching / deposition into the soil. However, my view is that the amount involved cannot possibly sustain electromagnetic energy in the form of eddy currents sufficient to return a measurable signal. Its tough enough for a sensitive metal detector to give a useful response to disseminated precious metals in small rocks, and certainly detectors will not respond to non-ferrous chemical residues at a molecular level IMO. But heck, I’m prepared to stand corrected by anyone at any time.

I am more inclined to a view that metal detector performance over disturbed ground struggles either from the loss of electrical alignment / continuity within the disturbed soil, perhaps further aggravated by the disruption of the magnetic fraction of a soil’s composition. That’s just guesswork. What does matter is that we can identify the effect of disturbed ground on metal detectors vs undisturbed natural ground and this phenomenon is readily acknowledged by the manufacturers as well.

Hope the weather down your way has allowed you to get out and about in the goldfields. All the very best…

Jim.

[arizonaames]

Excellent presentation, Jim. I experienced similar results on my TDI while hunting for sub gram gold nuggets 45 miles north of Imlay, NV around Placerites, Rabbit Hole, Rosebud, Scossa, etc. With the ground mineralization at 83, according to my MXT, I was unable to move the GB down enough to acceptable levels to find any sub gram nuggets but was able to disciminate out most nails and bits of iron. I did find some bullet fragments and even a 3 ring bullet with this high mineralization at Placerites, where the iron mineralization seemed to be very high.

[TerryC]

A truly GREAT post, Jim! Not only did it cover the machines well, but it also clearly shows you KNOW the machines. That is the base concept others should learn from this and other fine posts.... Know your machine! Tnx. TTC

[Jim Hemmingway]

Thanks Jim for adding your comments. Feedback from gold prospectors like yourself who use this unit are exactly what I want. Your comment highlighted below...

"With the ground mineralization at 83, according to my MXT, I was unable to move the GB down enough to acceptable levels to find any sub gram nuggets but was able to disciminate out most nails and bits of iron."

If you happen to look back in here Jim, do you mind my asking where the TDI ground balanced in that area? If I'm interpreting your remarks correctly, it sounds as if you set the GB fairly high to eliminate nails and so forth...while searching for higher conductive gold in the high conductive tone mode...

Jim.

[Jim Hemmingway]

Well howdy TC, geez your post caught me by surprise. I haven't been following most of the posts too much now that summer is in full swing here in the Great Lakes area, but I seem to recall a short while back you had left for the outback in your RV.

So, let me ask you how you have been progressing with either your Goldbug2 or the GMT....

I felt you did a great job of presentation in your video. You kept it straightforward, took your time to make sure viewers could understand what was happening. Please don't be hesitant to add a few comments here about your further experiences. Anything you might say will definitely help me Terry as I've got a goldhunting trip planned for the end of the summer over to the Quebec / Maine border country...and yep...I'm taking my Goldbug2 along with a few other units that should do OK.

Jim.

[Jim Hemmingway]

Hi Everyone,

On a different forum I’ve encountered two separate comments that I’d also like to address here. The first comment as I understand it, was about an interpretation on the part of a reader whereby the third chart in the article was interpreted as to somehow imply a direct relationship between VLF target ID VDI readouts and GB placements on the TDI Pro ground balance scale. The second comment was about the utility of evaluating target signals when targets could be just as quickly dug up. I think we all realize that is not necessarily the case in many instances.

It is not possible to draw direct correlation between VLF target ID readouts on high conductive silver ores to their GB point on the TDI’s GB scale. Sure, we can identify trends whereby high conductive ores will tend to locate in the left area / lower #’s of the GB scale… silver coins are another good example. Lower conductive ores generally locate in the right area / higher #’s of the scale… nickels are a good example. And the remainder of target conductivities generally fall somewhere in-between.

Unfortunately, some of our silver ores, despite having similar VLF target ID readings, have quite variable GB placements on the TDI ground balance scale. The TDI does not establish GB points based on a phase shift relationship. Moreover, other factors pertaining to the structure / character, purity and type of inclusions, size, shape, and perhaps even the profile presented to the coil very likely contribute to a silver ore’s GB placement on the scale. Possibly other factors enter into the equation as well.

Look at the chart referred to above when you have a moment…it’s the third chart down. This chart is only intended to draw the reader’s attention to an observation that target depth on high conductive silver decreases as the target GB point approaches the TDI Pro’s operating GB setting. The closer the target GB point is to the operating GB, the more significant is the depth loss.

The MXT target ID numbers assigned to the ore samples are not intended to attempt to establish a fixed relationship with GB placements. The target ID numbers were simply used to further identify the individual samples, and to illustrate that the entire high conductive range for silver ores is represented in the chart. The MXT itself was selected only because many hobbyists are familiar with the unit.

Look at the corresponding GB numbers in the chart. There is no identifiable direct relationship… linear, logarithmic, exponential or otherwise. In fact you will see that there are a number of ores at widely scattered VLF target IDs that have similar TDI GB points. Conversely, you can readily see a number of silver ores very close in VLF target ID but with quite variable GB points on the TDI.

Note for example, that the four penny / dime silver ores have a GB span between GB3.5 and GB6. More, there are silver samples with VLF target ID in the upper pulltab range with TDI GB points of GB6.5. ..very close indeed.

Perhaps this subject should have been explained within the text, but we simply overlooked doing so in the much-reduced version that was posted. There are other interesting nuances associated with the unit that were also excluded from mention in the posted version. I anticipated that if readers noticed or commented…that would be a suitable time to address them.

Now as to the second comment about target retrieval, if an operator can dig a target in the moment it would take to evaluate a target signal…then by all means do so. But that is not the case over much of our area. By and large, our ‘ground’ is a rocky substrate cemented together from the effects of pressure and weather over as much as a century. A target buried at 18 inches may well require 10 to 20 minutes of hard work to expose. If one can acquire a lo-hi-lo iron tone (as is also briefly referred to on page 28 of the Pro’s manual) and avoid expending time and effort to dig an iron drill rod, then that too is time well spent. Digging deep holes in our concrete-like rock substrate is not a chore to undertake lightly…we understandably check the target for the iron tone prior to digging when searching for high conductive silver.

To summarize generally, the report touched on many features and nuances associated with the full potential of operating this unit… for the sake of completeness only. In a prospecting context the settings could be as simple as delay at 10-usec, tone control set to ALL, GB ON and balanced to the soil, barely audible threshold, gain set as high as possible with reasonably stable performance such that you can hear faint signals…and hunt away. Dig all signals if that is your preference. Or try to acquire the lo-hi-lo iron tone first to save yourself some digging. Or search low conductives only in high iron junk areas by either ignoring high conductive signals in the ALL position or flip the tone control over to LOW conductives…and simply not hear high conductive signals. But you can choose your preferences based on complete information presented in the report about how this unit can be operated. There is no law saying you can’t select how you want to run the machine. Keep it as simple as possible to get the job done in the field.

Jim.

[arizonaames]

Just the opposite, Jim. Reading back on my notes and posts it seems that I recently (now that I am not using the TDI) confused high tone with having the switch in high conductor mode. I was in Low conductor mode with the GB on 8 1/2 to 9 1/2. It seems that the sub gram nuggets above .3 gram can be picked up by the TDI but only 1 to 3 inches from the coil if one moves the coil at a slow pace over the ground. Less than .3 grams ........ good luck.

One loses depth incrementally by increasing the GB. Thus, a higher mineralization will cause one to increase GB and one will lose some depth. However, lacking the power of the ML4000s for sensitivity and depth, the TDI does have some compensation. It is light weight because one can hip or chest mount the unit and only have to swing the shaft and the coil. Also, once the GB is set for the conditions, it is a very smooth running detector in gold country with high mineralization. My only wish was that it had more power for greater depth and for increased sensitivity. I walked and worked next to 2 ML4000s for 4 to 5 days and each of them found about 15 sub gram nuggets apiece to my zip. I was, to say the least, dissapointed. They were able to detect sub gram nuggets a lot deeper than I was able to with the TDI.

I would say that Whites would have a winner if they were to increase depth and sensitivity with increased power. However, currently, to compare a ML4000 or 4500 to a TDI, at present, is no comparison and to say that the cost is much less at 1/2 the price is not a good trade off if one spends 2 or 3 times that amount on a trip to get to gold country to do any detecting. One wants a detector that is going to produce after one spends the money to get to a detectable area of the country or on a long trip to Austalia. $1,500 to $1,700 is not chicken feed and neither is a few thousand dollars in travel costs to get to an area to detect gold nuggets. Again,with increased power for greater depth and sensitivity, the TDI will come out on tops eventually.

Thanks Jim for adding your comments. Feedback from gold prospectors like yourself who use this unit are exactly what I want. Your comment highlighted below...

"With the ground mineralization at 83, according to my MXT, I was unable to move the GB down enough to acceptable levels to find any sub gram nuggets but was able to disciminate out most nails and bits of iron."

If you happen to look back in here Jim, do you mind my asking where the TDI ground balanced in that area? If I'm interpreting your remarks correctly, it sounds as if you set the GB fairly high to eliminate nails and so forth...while searching for higher conductive gold in the high conductive tone mode...

Jim.


Just the opposite, Jim. Reading back on my notes and posts it seems that I confused high tone with having the switch in high conductor mode. I was in Low conductor mode with the GB on 8 1/2 to 9.