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...
TTC
