Huge gold find in Western Australia

Huge finds like this are being found using detectors modified by us. These modifications optimise the detector to cancel out the ground mineralisation when using large drag-coils. We manufacture custom drag coils from 25" to 72" in diameter.

Optimal GPX settings

Here is an explanation of these settings, plus why pros use the extreme settings they do. Higher adjustments are used primarily to consistently find both large and small gold in highly mineralized ground.

Coil/RX Setting: Mono with a Mono coil.

We use the Mono setting with an 18" NF Mono coil, Minelab recommend using the Mono position too, not the DD position. Coils larger than 18" used for general prospecting can increase EMI to an unacceptable level.

Ground balance: fixed, when using Enhance.

Fixed is recommended, after a careful ground balance. In Enhance timings, correct ground balance is mandatory. Even though the machine sounds ground balanced, get into the habit of ground balancing often. Using Tracking can ground balance out a faint small or deep target in 2 sweeps of the mono coil. Detect in fixed tracking.

Soil Timings: Enhance with a Mono on hot soils.

Enhance is the best thing the 4500 has going for it in hot ground conditions, this timing gets most of the missed gold, (Large & Small), plus its quiet running lets you hear the faintest of responses.

The 5000 is much the same as the 4500 with an important addition and that is the Fine Gold setting, Fine gold is much the same as enhance as the detector output to the coil is the same but some extra filtering and turning on the input receiver on a bit quicker than enhance, this allows better detection of fast decaying targets such as specimen gold in quartz or tiny gold nuggets. We discovered that with the additional upgraded front-end gain control and sub board installed that there is very substantial depth improvement when using Enhance and Fine gold modes. By adjusting the back panel Gain and stabilizer to setting 1 and adjusting the added gain to full that depth increases in the order of up to 20% have been observed in some ground. This has allowed much more gold to be found in previously worked ground. Special credit goes to B. White for his extensive testing on his upgraded GPX-5000 in old worked ground.

Search Mode (Front End Cap): Deep, in deep ground. (1–3'+)

We recommend this mode with the Digital settings below, as it has proven to us that the 4500 differs from what settings we had used on the GPX 4000.

Digital menu

• Backlight: Off (Unless detecting at night)
• Battery Test: 8.0+V (Recharge battery each night)
• Volume Limit:
  • 15—Headphones
  • 18—Speaker with adjustable amp. (Experiment with this, don't go below 12. It can also be run at 20)
• Ground balance type: General Specific is too much of a handful, its use is only recommended in highly magnetic soil conditions. Manual Tune find the best response over a known deep buried target, try in the range of between 80 to 110, all machines are different to get their ultimate frequency position (it does make a difference). Only tune out EMI up to 5 digits either side of your detectors best setting. Have the machine always set on Manual Tune while detecting, as the EMI interference waves come through, reach down and adjust the right hand knob a few digits up or down to get a quiet frequency. We don't use the auto tune button.

General menu

• Motion: Slow (or use "Very Slow" if there is bad EMI)
• RX Gain: 12 for the deep quiet ones, if EMI is nonexistent, try 13.

  Why would you not have your detector near to maximum gain? When it has been proven to produce large gold at depth. It also gets the fly shit down to ⅕ of a gram with this gain setting.

• Audio: Normal (Less EMI and spurious noises)

  Do not use Deep setting here when Deep is used on the F/E Cap, as the Signal to noise ratio is infringing on the faint responses. With the 4000 you could use Deep / Deep, but on the 4500 it's noisy.

• Audio Tone: 33

  A lower tone is more suitable for the low growly deep faint signals; it is also less annoying to the ear over many hours of detecting. The small gold signals still comes through with their rising pitch.

• Stabilizer: 11

  Factory pre set is 10, with what you are looking for, (better size gold), a tweak up is better than down.

• Signal Peak: 19

  This helps to determine target responses from ground signals, set high; it provides a sharp clear target response with a quicker diminishing fall away.

• Target Volume:
  • 10—Headphones
  • 12—Speaker with adjustable amp.
• Response: Normal

  This gives the best chance on the smaller bread and butter gold, usually with a sharp high rising response. Yet Normal response still responds well to the large deep gold, with that unmistakable dipping growl. In fact the majority of nuggets, say from 5" or 6"inches deep, will give this reverse pitch dipping signal when using Enhance. Most ground noises give a wide rising pitch signal, this is usually not consistent from all angles of the coil sweep, and with practice many can be eliminated. When in doubt have a dig, also after rain with the dry & wet patches, or wet charcoal under the surface, you do get some dipping ground noise responses, these tend to make you dig more, but better to be safe than miss one.

• Tracking: Slow

  The reason: When in fix and your ground balancing, the switch holds it in tracking for a short time. Using Slow Tracking restricts the EMI noise at this time and helps the ground balance process.

• Iron Reject: Off (It will not work with a Mono coil)

Remember the ground conditions have to be of a highly mineralised and variable nature to use the Enhance timing, so if the conditions are mild, you should be using Normal timings for better depth.

To get the perfect ground balance

Note: Keep the coil parallel with the ground during the pumping procedure. Keep your coil stationary 30mm above the ground. Hold in the green button on the handle, now pump the coil using small even movements of about 30mm to 40mm up & down, (at this height above ground). Bring the coil down slowly to the lowest point of the pump, (30mm from the ground), be sure to hold it really steady when you release the button. Never release the Quick-track Button whilst the coil is moving or twisted, as this can affect the accuracy of the Ground Balance. Be prepared to go through this same procedure 2 or 3 times to get it just right, as sometimes conditions make it hard to get it to ground balance the first time.

Modifications and upgrades

What are the advantages of a Modified Minelab Detector? Many people would ask this question and i will explain some of the rational behind the science. Ever since the first Minelab detectors, such as the SD2000 came onto the prospecting scene many people complain about noise and false signals. All these detectors have a very wide bandwidth receiver preamplifier and this is in order to make the detectors better at finding very small Gold. This wide bandwidth approach also makes the detector susceptible to man made interference and natural interference such as lightning strikes from storms many hundreds of miles away. Minelab have used a filter that can be classed as a high impedance in an attempt to stop this type of interference, we found a better approach in using low Q low impedance filters that start operating just above the pass band of wanted signals. Instead of trying to stop these signals our technique absorbs these interfering signals and has a negligible effect in the range of 1hz to 15Khz. We use material that can operate correctly with unipolar pulses and need no reset mechanism when compared to the standard ferrite inside the metal detectors.

Most users have noted that these pulse induction detectors are relatively noisy in mineralized soil, the jitter, groans and growls easily mask the signals from Gold Nuggets. It is imperative that we reduce or eliminate this type of noise from the system. I noticed that the filter band pass response was not sharp enough to reduce this type of noise so we remodeled the filter response to that with a greater low frequency cut off to reduce the noise. On the older detectors we replace input stage Fet devices with new state of the art devices that allow for increased sensitivity and depth.

The newest upgrade is the installation of variable front end gain, this differs greatly from the existing gain control on the GPX series detectors. The front end input stage is the most important stage to have low loss and low noise, any resistance in the circuitry leading to the first input stage drastically effects the depth and sensitivity of the detector, most detectors have input resistance of around 10 ohms, it may not seem like much but even this low figure reduces target signals to some degree. The other limiting factor is front end capacitance, using devices that add to the input capacitance has a negative effect on performance. It is our aim to improve all aspects of the detector as far as we can when upgrading the components.

Check your detector before you go

Before traveling thousands of miles to far and remote places please test your detector and it is a good idea to have a spare detector in case one fails.Even a cheap VLF will help to avoid a disappointing trip away. Take a screwdriver and a 12 volt soldering iron as a lot of simple faults can be fixed on site. Common ones are the internal wires falling off the circuit board due to vibration, dry or bad solder connection due to vibration. On the GPX-4500and GPX5000 the Mylar connections to the switches can break away and become bad connections. If this happens just trace the connection to where it goes and solder a jumper wire from the switch to the board. The white paint can be removed by scraping with a small flat jewelers screwdriver.When going over very bad roads it pays to wrap your detector in some foam rubber to reduce any damage caused by vibration.