Minelab GP Extreme User Manual

1. Introduction

About this manual

This manual is designed to introduce the detector's features. It gives you step-by-step directions for everything from assembling and adjusting your detector, to basic and advanced detector use.

1. INTRODUCTION: Basic overview of the 'GP extreme' and this User's Manual.

5. DETECTOR OPERATION: However experienced you are at using a metal detector, it is important that you read this.

2. ASSEMBLY: This chapter provides details and instructions on assembling and adjusting the 'GP extreme'.

6. DETECTOR TECHNIQUES: Once you are comfortable with the basic detector use, there are a few techniques you should be aware of.

3. BATTERY: The 'GP extreme' is powered by a rechargeable battery pack. This chapter provides details on battery installation, use and performance.

7. USER INFORMATION: This chapter provides a glossary of terminology, user guides, technical specifications, warranty and repair details and troubleshooting tips.

4. CONTROLS: This chapter is designed to familiarize you with the various features of the 'GP extreme' control panel. A few minutes spent reading this chapter will be a worthwhile preliminary to basic or advanced detecting.

Introducing the Minelab 'GP extreme'

Minelab 'GP extreme' is the first detector to use 'Dual Voltage Technology' (DVT). Minelab have developed this new Dual Voltage Technology (DVT) based on the Bi-Polar technology used in our military detector range.

The New Features:

• New DVT technology giving greater depth than ever before
• Selectable Tx (transmit) modes for different Soil conditions
• Selectable Rx (receive) modes for increased sensitivity and less susceptibility to interference
• Adjustable Signal response for target tone variation
• Volume limiting for users own preference
• New 'GP extreme' 1100 and 'GP extreme' 1800 coils which have been specially designed to take advantage of the new DVT.

Minelab are confident that you will find the 'GP extreme' to be the ultimate detector for finding metallic objects in highly mineralised and/or salty environments. Simple operation means that both the beginner and professional will find this detector very easy to use. Old gold fields, where mineralised ground and too much rubbish have shielded many nuggets from the 'prying eyes' of other detector operators, will likely yield new finds.

Minelab thanks you for purchasing this 'GP extreme' detector and wish you every success in your quest for gold and treasure.

2. Assembly

This chapter provides details and instructions on assembling and adjusting the 'GP extreme'.

Unpacking Your 'GP extreme' [easy reference]

The 'GP extreme' is shipped with the following components:

• A: 'GP extreme' 1100 Coil with Skid Plate and Fibreglass Lower Shaft attached.
• B: Intermediate Shaft.
• C: 'GP extreme' Control Box with Upper Shaft, Handle, Arm Rest, Arm Straps and Neoprene Armrest Cover attached.
• D: Headphones.
• E: Battery and Battery Pack.
• F: Velcro Straps, Knuckle and Bungy Cord.
• G: Battery Cable.
• H: Vehicle Charger.
• I: Mains Charger.
• J: Backpack Strap.
• K: Instruction Manual, Field Guide and Rubbish Bag.
• L: Hard Carry Case.
• M: 'GP extreme' 1800 coil with skidplate (in separate carton).

List of Pre-assembled Sections and Parts

The detector consists of the following pre-assembled sections and parts:

• A. Lower Shaft Assembly: 1. Extreme 1100 Coil, 2. Coil Cable, 3. Skid Plate, 4. Fibreglass Lower Shaft, 5. Nylon Nut & Bolt, 6. Teardrop Washers.
• B. Intermediate Shaft Assembly: 7. Intermediate Shaft.
• C. Upper Shaft Assembly: 8. Upper Shaft, 9. Handle with Wrist Strap, 10. Control Box, 11. Armrest Parts (2), 12. Nylon Bolt (2), 13. Nylon Nut (2), 14. Arm Straps (2), 15. Armrest Cover.
• D. Headphones: 16. Headphones.
• E. Battery and Battery Pack: 17. Battery, 18. Battery Pack, 19. Battery Power Cable.
• F. Extras: 20. Velcro Cable Straps (3), 21. Bungy Cord, 22. Bungy Knuckle.

Complete Assembly Instructions

Assembling and fitting the armrest

STEP 1: Place the two armrest halves (11) on either side of the upper shaft (8) and ensure that the bolt holes are aligned.

STEP 2: Slide the two nylon bolts (12) through the bolt holes and screw the nylon wing nuts (13) onto the bolts by a couple of turns.

STEP 3: Slide the 'T' section on top of the control box (10) into the armrest with the battery plug at the rear. Tighten the nylon wing nuts by hand.

STEP 4: Attach the arm rest straps (14) using the press studs on both sides of the arm rest.

STEP 5: Push the arm rest straps (14) through the slots in the neoprene arm rest cover (15) and then push the cover over the arm rest (11).

Attaching the handle and bungy cord

STEP 1: Slide the handle (9) onto the other end of the upper shaft (8) and set it to a comfortable position. Tighten the two screws in the base of the handle with a small flat tipped screwdriver to hold the handle in position.

STEP 2: Slide the bungy cord knuckle (22) of the bungy cord onto the upper shaft (8).

Assembling the Intermediate and Upper shaft sections

STEP 1: Slide the intermediate shaft (7) into the end of the upper shaft (8) and snap into place.

STEP 2: Check that the coil (1) has a skid plate (3) attached.

STEP 3: Check that the coil pivot end of the lower fibreglass shaft (4) has two teardrop washers (5) installed.

NOTE: The washers should always be full thickness and should be replaced regularly as they wear out and allow the coil to become loose.

STEP 4: Push the lower fibreglass shaft (4) into the mounting brackets on the coil and ensure that the spring clip at the rear of the fibreglass shaft faces the rear of the coil.

Attaching the coil

STEP 1: Line up the holes in the coil with the pivot end of the fibreglass shaft (4).

STEP 2: Push the nylon bolt through the holes and fit the nylon wing nut then tighten by hand.

NOTE: Do not over tighten the nut as the coil housing may be crushed or damaged.

Attaching the lower fibreglass shaft

STEP 1: Slide the lower fibreglass shaft (4) into the intermediate shaft (7).

STEP 2: Adjust shaft length and coil angle for a comfortable position. Minelab recommends that the shaft length be set to give a comfortable sweep length of approximately 2 meters. The lower fibreglass shaft can be set into position by locating the spring clip into the holes provided in the intermediate shaft and hand tightening the locking nut at the end of the intermediate shaft.

Securing and connecting the coil cable

NOTE: Always ensure that the control box is turned off completely before connecting or disconnecting the coil.

STEP 1: Wind the coil cable around the shaft and plug the coil connector into the coil socket on the control box. Check that the cable is wound firmly around the shaft without strain, leave enough slack at the bottom of the cable near the coil to allow for adjusting the angle of the coil without placing strain on the coil cable.

STEP 2: Fasten the cable into position using the Velcro straps provided (20).

Fitting and connecting the battery pack

STEP 1: Fit the battery (17) into the back pack pouch (18).

STEP 2: Connect the headphones (16) and the power cable (19) to the appropriate sockets in the cap of the battery.

STEP 3: Put on the back pack (18).

STEP 4: Ensure that the power switch on the control box is switched off and plug the connector on the power cable (19) into the battery connector plug on the control box. This cable connects the battery and headphones to the detector.

Adjust for your own comfort

STEP 1: Adjust the bungy cord (21) from the knuckle (22) on the shaft to correct length to take some of the weight when prospecting.

STEP 2: Adjust the hand strap on the handle (9) for your own comfort.

3. Battery

The 'GP extreme' is supplied with a 6v DC rechargeable battery pack plus both mains and vehicle chargers. This chapter provides details on battery installation, use and performance.

The Battery

The 6v DC rechargeable battery should provide enough power to operate the detector for 10-12 hrs, when fully charged. The battery may be recharged at any time during the discharge cycle. It is very important to fully charge the battery before storage. Do not leave a battery fully discharged for longer than one day.

CAUTION: Never use a 12v DC battery because this would damage the detector. This damage is not covered by warranty.

Low Battery Indication

If battery level drops below the desired power to give full function, a series of signal pulses are given at 0.5 second intervals.

Charging the battery

STEP 1: Turn the detector Off before disconnecting the battery.

STEP 2: Disconnect the battery cable from the detector and connect to the appropriate charger.

Battery Chargers

Two types of battery chargers (Mains and 12v Vehicle Charger) are supplied.

Mains Battery Charger

The mains battery charger will charge the battery from local mains (AC) power outlets.

STEP 1: Connect the mains charger to a mains outlet.

STEP 2: Switch the mains outlet on.

Check the charger nameplate; it should be rated at 500mA or 1000mA. The 500mA charger will recharge a completely flat battery in approximately 20 hours. The 1000mA charger will recharge a completely flat battery in approximately 10 hours. Partially discharged batteries require a shorter period to recharge. Allow approximately 1.5 to 2 hours charging for each hour the battery was in use if using a 500mA charger and about 0.5 to 0.75 hours for each hour usage on a 1000mA charger.

Vehicle Battery Charger

The vehicle battery charger will charge the battery from the cigarette lighter socket of most motor vehicles.

CAUTION: The Vehicle Battery Charger is designed for use with vehicles which have a negative earth electrical system. Most cars manufactured after 1970 should have negative earth electrical system. Connecting the charger to a vehicle with a positive earth system will cause the fuse in the cigarette lighter plug to blow and the LED indicator will not light.

STEP 1: Connect the charger to the cigarette lighter socket and turn the ignition switch to Accessories. This supplies 12v DC power to the cigarette lighter socket. This voltage is converted by the charger to charge the detector battery. A red LED indicator will flash while the battery is charging. When the battery is flat the LED may flash fast enough so as to appear constantly on. As the battery charges, the LED will flash at a slower rate.

STEP 2: Leave the battery to charge for approx. 10 hours using this charger.

If the battery voltage of your vehicle drops below 11v, the charger will stop operating. Therefore the battery charger should not flatten the vehicle battery. Check that your vehicle battery is in good condition before camping in remote areas. Run your engine above idle speed for at least 30 minutes each day to keep your vehicle battery charged.

Important: When charging, the battery must be kept in an upright position.

Caution: Do not leave the mains charger on for extended periods because reduced battery life may result.

4. Controls

It is important to familiarise yourself with the features of the 'GP extreme' control panel. A few minutes spent reading this chapter will be a worthwhile preliminary to detecting.

Detector Sounds [easy reference]

Threshold and Tone: This is the background sound produced by the detector. The level is set using the Threshold control. The tone of the threshold is set using the Tone control.

Target Signal: This is the abrupt change of the tone and volume of the threshold sound when a target is detected.

• The maximum level is set by the Volume control.
• The amount of tone variation is set by the Signal control.
• If the tone falls first and then rises, as the coil is passed over a target, this generally indicates a small target.
• If the tone rises first and then falls, as the coil is passed over a target, this generally indicates a large target.

Ground Noise: These are irregular noises that are difficult, or impossible, to pinpoint when moving the coil over the ground. Ground noise is caused by the changing chemistry or 'mineralisation' of the ground. When the Balance switch is set to Tracking these effects are greatly reduced.

Tune Indication: An initial beep sounds then, while the detector is testing the range of frequencies for the most stable, the threshold may become more quiet or chattery. Once selection is complete three sharp 'beeps' are given.

Low Battery Indication: If the battery level drops below the desired power to give full function, a series of signal pulses are given at 0.5 second intervals.

CONTROL FUNCTIONS

There are two control panels: the rear panel and the front panel.

Rear Panel

The rear panel includes controls for Battery, Power, Boost, Threshold, Volume, Signal, Tone, and Audio.

Power (On/Off): This switch turns the power from the battery to the detector On and Off.

NOTE: Always switch the detector Off before connecting or disconnecting the coil or battery pack and when not in use.

Boost (Shallow/N/Deep)

Enhances the signals produced by different types of targets.

• Shallow: Amplifies target signals from small objects close to the surface, best suited for 'quiet' ground.
• N (Normal): Responds to all signals without boosting, for normal detecting conditions.
• Deep: Used for large targets at depth in 'noisy' ground. Smooths signals, making small changes easier to hear, but may mask very small targets near the surface.

Threshold

Adjusts the background audio signal or 'threshold' level. Set just above the point where the threshold is just audible and stable, ideally a smooth, gentle hum.

NOTE: Small surface objects, as well as large deep objects, will produce very small changes in the threshold. It is important to set the Threshold control correctly to ensure that these targets are heard. Experiment with known targets to assist in setting all controls to suit your hearing.

NOTE: Threshold should be reset after adjusting the Volume level.

Volume

Sets a maximum limit on the loudness of the target signal. Should be set so that target signals are clear and easy to hear but loud signals are not uncomfortable. Test by passing coil across a large target and setting volume at a comfortable level, then test very small targets.

Signal Pitch

Adjusts the pitch response of the target signal. At minimum position, pitch variance is reduced. At maximum position, pitch variance is increased.

Tone

Adjusts the tone of the threshold. Set to the preferred tone for your hearing. Turning clockwise increases the tone to a higher pitch.

Front Panel

The front panel includes controls for Tune, Iron Discriminate, Soil, Rx, Balance, Coil, and Level Adjust.

Tune

Reduces the effects of electromagnetic interference. Automatic tuning is started by pressing and releasing the Tune switch. The process takes approx. 60 seconds and is indicated by three sharp 'beeps'.

Iron Discriminate (All Metal/Disc)

Selects between discrimination or turning it off (All Metal). In 'Disc' mode, a strong response from a ferrous object causes the threshold to be 'blanked' or silenced. In 'All Metal' mode, all targets cause variations in tone and volume.

NOTE: If the target response is too weak for accurate discrimination, the detector will give a normal target signal.

Level Adjust

Allows the user to select sensitivity and likelihood of a target being ferrous or non-ferrous. It also affects how the detector recognises mineral effects in the ground. Important for ground balancing.

Soil (Normal/Sensitive/Salt)

Optimises the detector for different soil conditions and targets by changing signal processing.

• N (Normal): For all areas, including highly mineralised soil. Versatile for various nugget sizes.
• Sensitive: For small nuggets in highly mineralised soil. Allows coil to be used closer to the ground in areas of excessive ground noise. May not work well in salty ground.
• Salt: For areas with high salt content, or heavily mineralised areas without salt.

Rx (Receive) (Normal/E/Cancel)

Changes sensitivity and search pattern of the coil. Allows coils to be multi-versatile.

• Normal: For medium to very high mineralisation. Good for ground noise coping and pinpointing.
• E (Enhance): For low to medium mineralisation and small nuggets. Pinpointing may be off-centre.
• Cancel: For areas with very high electrical interference. Ideal near power lines, electric fences, or under poor atmospheric conditions.

NOTE: Coils not specifically designed for the 'GP extreme' may behave erratically or be ineffective in E or Cancel modes.

Balance (Fixed/Tracking)

Operates with fixed or automatic ground balance.

• Fixed: Ground balance remains at the current level.
• Tracking: Detector automatically ground balances through a two-stage process.

To obtain the best performance, know how different ground conditions affect detecting. See 'Ground Balancing' on page 33 for more information.

5. Operation

However experienced you are at using a metal detector, it is important that you read this chapter to understand how to use the 'GP extreme' to its full capacity.

Quick Start Instructions [easy reference]

STEP 1: Turn Power switch On.

STEP 2: Set Boost to N (Normal) for general detecting.

STEP 3: Set Volume to maximum, and Signal to midway.

STEP 4: Adjust the Threshold control so that a faint sound is heard through the headphones.

STEP 5: Adjust Tone for threshold level that suits your hearing.

STEP 6: To tune the detector, hold at waist height with the shaft horizontal. Keep the coil vertical.

STEP 7: Slowly move coil around your body through a half-circle until the noise from interference is loudest.

STEP 8: Hold this position, keep the coil motionless and push the Tune switch once to start the tuning function.

STEP 9: Tuning takes approximately 60 seconds. A series of three beeps will indicate that the optimum frequency has been selected.

STEP 10: For Discrimination, change the Iron Discriminate switch to Disc and set Level Adjust to the middle of its range.

STEP 11: Set Soil switch to N (normal).

STEP 12: Set Rx switch to Normal.

STEP 13: Set the Ground Balance by moving the coil up and down. While coil is in motion, change Balance switch from Fixed to Tracking.

STEP 14: The detector is now ready for operation.

Detailed Operating Instructions

HINT: Take time to read this manual thoroughly to obtain the best performance from your new 'GP extreme' detector.

Turn the 'GP extreme' On

Hold the coil away from the ground and metal objects and switch Power to On.

NOTE: When the 'GP extreme' is turned Off, important information (e.g. tuning frequency and ground balance) is saved in internal memory. If detection recommences in the same location, the user should not have to re-tune or re-ground balance the detector.

Set the Volume Control

Volume should be set so that target signals are clear and easy to hear but loud signals are not uncomfortable to your hearing. Set Volume by testing volume levels by passing coil across a large target and setting volume at comfortable level. Now test very small target at this level.

Set the Threshold control

Adjust the Threshold control until the threshold is just audible through the headphones.

NOTE: Small surface objects, as well as large deep objects, will produce very small changes in the threshold. It is important to set the Threshold control correctly to ensure that these targets are heard. Experiment with known targets to assist in setting all controls to suit your hearing.

Set the Tone control

Adjust the Tone control until the threshold is at a comfortable tone for your hearing. Interpretation of the target signals involves understanding the difference between the rising and falling tone and volume of the threshold in response to different targets.

HINT: Setting Tone to a high pitch may be more fatiguing, but is more suitable for identifying the faintest target signals.

Set the Signal control

The human hearing is sensitive to changes in tone, so the operator is more likely to hear a target signal when both the volume and the tone change rather than volume alone. The Signal control gives the operator, the ability to choose between a target signal that has a large variance of tone or one which has less variation. High variance can give the operator more signal definition to interpret, however in highly mineralised ground this high variance of signal may cause confusion and a lower setting preferred.

Soil switch

Use this switch to optimise the detector's ability to detect in different ground conditions (see page 24 for full description).

Rx switch

Selection of different positions of this switch, changes the electromagnetic field of the coil thus giving better performance in certain environments (see page 25 for more information). Normal has the coil operate in a conventional Double D search pattern with all the same advantages and disadvantages.

IMPORTANT: You will need to re-ground balance every time you select a new position for either the 'Soil' or 'RX' switches.

Set the Tune control

Tuning should be done initially with the RX switch in Normal or in E (Enhance). If the interference is still severe after completing the tuning operation, change the RX switch to Cancel and then re-tune detector again.

• Hold the detector at waist height and the coil vertical.
• Keeping the coil vertical, slowly move it through a half-circle around your body.
• Listen for an increase in interference as you move the coil.
• When the interference is loudest, stop moving the detector, hold it motionless in that position and momentarily press the Tune switch.
• The detector will then scan through the available range of transmission frequencies and automatically select the frequency that results in the greatest reduction of noise from electromagnetic interference.
• The end of tuning process (which takes approx. 60 sec.) is announced by three beeps.

NOTE: While the detector is selecting the preferred frequency, the coil must be kept motionless and clear of metal objects.

IMPORTANT: When tuning detector in close proximity to other detectors, each operator needs to take turns tuning. Do not try to tune two detectors at one time.

Ground Balancing

The ground contains not only sand, but also many different chemicals, minerals and salts. These extra materials are referred to as ground mineralisation. This ground mineralisation may often produce a sound from the detector, known as 'ground noise'.

The 'GP extreme' has the ability to cancel out the effects of ground mineralisation. This minimises ground noise and retains maximum sensitivity to metal targets. Cancelling the effects of ground mineralisation is referred to as 'ground balancing'. This ensures that target signals from objects, such as gold, are not confused with interfering ground noise.

The 'GP extreme' has automatic ground balancing. This continually adjusts to minimise the effects of ground mineralisation when Balance is set to Tracking.

The 'GP extreme' may be operated with fixed ground balance or automatic ground balance.

• When Balance is set to Fixed, the ground balance remains at the current level.
• When Balance is changed from Fixed to Tracking, the detector begins to automatically ground balance through a two stage process. The first stage is a very rapid adjustment to the ground mineralisation. This lasts for 5 sec. so coil movement should be at the same time as Balance is changed from Fixed to Tracking. The second stage continues to adjust to the ground mineralisation, but at a greatly reduced speed. This adjustment continues all the time that Balance is set to Tracking.

While in Tracking mode, the detector usually stops ground balancing when a target signal is detected. However, a weak target response may not be recognised as a target if the coil is repeatedly passed over an object, it may be 'balanced out'. For this reason Balance should be changed to Fixed when pinpointing a target.

HINTS:

• Use 'Tracking' in areas with high ground noise for best results.
• Change from 'Tracking' to 'Fixed' when pinpointing a potential target.

NOTE: The Level Adjust control also effects the Tracking mode by altering the detectors perception of what is ground noise and what is a weak target (see pages 37 and 38).

Ground Balancing Procedure

STEP 1: Move the coil up and down between 20mm and 100mm above the ground and, while moving the coil, change Balance from Fixed to Tracking.

The fast ground balance takes only 5 sec. after switching to Tracking. Therefore, it is important to be moving the coil as the switch is changed.

Keep moving the coil until all ground noise has stopped. A persistent signal may indicate a target in the ground.

If this occurs, then move the coil to a new location and repeat the procedure.

When there is no longer a change in the threshold, while the coil is being raised and lowered, the detector is 'ground balanced'.

When the detector has been ground balanced, the user may select either Fixed or Tracking for detecting.

If the ground is mineralised or variable, use Tracking. If the ground is very 'mild', use Fixed and switch back to Tracking temporarily if the threshold becomes noisy. Do not test a target by switching to Tracking when the coil is above it.

HINT: It may useful to repeat the ground balance procedure if ground conditions change rapidly.

Iron Discrimination

Discrimination is the ability of a detector to distinguish between different types of metal objects and to assist the user in identifying a target. Some goldfields are littered with 'rubbish', e.g. metal objects which are of little value and are an annoyance to detector users.

The 'GP extreme' is capable of rejecting many iron objects while still detecting non-ferrous metals. The ability of the detector to discriminate ferrous targets means that, while detecting in littered goldfields, much of the iron rubbish may be ignored, with a high probability that valuable targets will not be missed.

Iron Discriminate

Iron discrimination with the 'GP extreme' is the silencing or 'blanking' of the threshold which occurs when the detector determines a target is comprised of ferrous metal.

There is no discrimination when Iron Discrimination is set to All Metal. Targets will cause the tone and volume of the threshold to vary. These variations convey no consistent information about the type of metal detected.

Iron discrimination operates when Iron Discriminate is set to Disc. Objects must produce sufficiently strong target responses for the detector to successfully discriminate. Fortunately, most iron rubbish is located near the surface and should produce the required strong signal response.

NOTE: When Disc is used, small or deeper targets, whether ferrous or non-ferrous, will produce a normal target signal.

If a target response is too weak for the detector to discriminate, it will internally change to the all metal mode. As soon as the target response becomes strong enough, the detector will resume discrimination.

Pinpointing is best performed using All Metal.

HINT: When a target has been located using Disc, the coil should be rapidly passed back and forth over the target centre several times. Remember to set Balance to Fixed for this.

The coil should always be passed smoothly over the surface of the ground, while maintaining the coil height above the ground. This is especially important when attempting to discriminate a target.

NOTE: Discrimination will give the best results when used in combination with the specially designed 'GP extreme' coils.

When detecting a piece of iron, a normal target signal should be heard until the detector determines that the object is ferrous. At this point, the signal will 'blank'.

The strength of the target response required for discrimination to occur may be altered by using Level Adjust.

Level Adjust Control

Level Adjust gives the user the ability to select the sensitivity and likelihood of a target being discriminated as ferrous when used in the Disc mode. This may also affect how the detector responds to ground mineralisation compared to metal targets when used in Disc. Mode.

There is usually some overlap between signals from useful targets and some types of iron rubbish. The user may set Level Adjust to select the amount of discrimination between two extremes:

• (Fully anti-clockwise): All targets detected, but some iron will give a normal signal.
• (Fully clockwise): Little iron detected, but some small non-ferrous targets potentially mistaken as ferrous.

Turning the control anti-clockwise increases the strength of a signal required for iron discrimination to be activated.

The Level Adjust also affects the Tracking mode.

• When set fully clockwise, it is unlikely the detector will 'balance out' genuine targets, but some ground noise may still give false signals.
• When set fully anti-clockwise, the detector will 'balance out' ground noise effectively, but some faint, weak target signals may be missed after repeated sweeps of the coil.

HINT: It is usually best to dig out all targets and only use the discrimination function in areas where a large amount of rubbish makes the digging of everything impractical.

NOTE: Discrimination functions will only work with strong, positive target responses. Weak responses will give normal 'all metal' type signals.

6. Detecting Techniques

Hints and techniques for better detecting and happy prospecting that will help you to utilise the power of your 'GP extreme' with DVT.

Check your footwear

Note: When detecting, do not wear steel cap boots or shoes with metal eyelets!

Some user tips:

• The battery should be worn in the backpack supplied. This places the battery at the furthest practical distance from the coil.
• Ensure that you do not set the shaft length too short.
• If the coil is too close to your body it might detect your pick, the battery or any other metal which you are carrying. If false signals are occurring as you sweep the coil, check that they are not produced by any metal that you are carrying.
• Move the coil closer, and then further away from your body, in order to check if the signals are coming from items such as your pick or battery. If they are, you must increase the distance between the coil and these items.

Motion detection

The 'GP extreme' is a 'motion' detector. Therefore the detector must be moving over a target to detect it.

Parallel Sweeping Procedure

• The coil should be swept over the ground in a side-to-side sweeping motion.
• While sweeping the coil, it is important to keep it parallel to, and at the same height from, the ground at all times. Lightly skidding the coil across the ground can sometimes help in this, depending on mineralisation.
• Do not raise the coil at the ends of each sweep as this will reduce the detection depth and may cause false signals.

Covering the search area

As the user moves forward slowly, the search pattern should resemble a snaking path. To ensure that the ground is thoroughly searched, approach the area from 3 different directions.

Overlap each sweep

Each sweep of the coil should overlap the area covered by the previous sweep to ensure a full coverage of the area being searched. Be aware of the search pattern of the coil being used and overlap sweeps to take this pattern into account. See also Pinpointing Technique, pages 43 and 44.

Prospecting Techniques

The 'GP extreme' has superior ground balancing and it is possible to find quite large objects near the surface in well-worked areas where other detectors have been unable to cope with the high degree of mineralisation and / or salt. Therefore the user should dig all target signals, even in previously detected areas.

For Maximum Gold Recovery

• Keep the coil as close to the ground as possible.
• Listen very carefully - this is more important than looking.
• SLOW DOWN! Do not rush, take your time.

Very sudden or large changes in the mineralisation of an area may produce a signal from the detector. In the Victorian goldfields, a response may be received from a concentration of orange/reddish dyke material or clay. In the loamy conditions of Western Australia, a pocket of dark orange/reddish colouration may produce a sudden signal change. If detecting areas of extremely variable mineralisation, detecting with the contours rather than across the changes will often stabilise the effect. In some ground (particularly heavily mineralised areas) the operator may need to sweep the coil 1 or 2 cm above the ground. This should give a more stable threshold and less ground noise.

Charcoal may sometimes produce signals, similar to a metallic object, when close to the surface. Charcoal is usually created by farmers burning off tree stumps or by bushfires. When the charcoal under the surface is disturbed, the signal will vanish.

If in doubt, scrape away some soil above the suspect signal; if the signal gets stronger, it is likely to be a target. Dig it!

Identifying Target Signals

Metallic targets will usually give a 'solid' sounding signal when the coil is swept across the object from any direction. Ground noises usually give a broad uneven signal when the coil is swept from different directions. A metallic target generally produces a short, sharp and mostly symmetrical signal.

If you are not sure if the sound is ground noise or a target signal, you need to investigate. Scrape a shallow hole about 70-100mm deep over the suspected target. Sweep the coil over the hole at the original ground level. Do not dip the coil into the hole. If the signal has decreased in volume or is less defined, it is probably ground noise. If the signal remains the same or becomes louder, it is likely a metallic target. If you are still not sure, make the hole deeper and repeat the process. You may also notice that mineral noises are often experienced from one direction only, on the return swing it is no longer there.

A 'halo effect', which may be built up around a buried metal object, makes the object appear to be larger to the detector than it actually is. This will be reduced once the target is disturbed from its position in the ground (e.g. a small object, detected at a substantial depth, may be more difficult to detect once recovered from the ground. If the object is reburied, the 'halo effect' will disappear)

HINT: Do not try to eliminate what might appear to be a faint, isolated ground noise by balancing the detector because you may be 'balancing out' the target response from a deeply buried metallic target.

Pinpointing

To find an object, and reduce the size of the hole required to remove it from the ground, it is necessary to pinpoint the exact location of the object.

If a target is heard, first confirm it by setting an accurate ground balance and then pinpointing. To ground balance, the coil should be passed around the area of the target, making sure that the target is not detected (keep the coil away from where the target is).

While the coil is moving around the area of the target, change Balance to Fixed. This will give a very accurate 'ground balance' on this area. One of the pinpointing techniques may then be used.

When a target is detected, sweep the general area with the coil, taking note of where the strongest signal is received. By shortening the length of the sweep it should be possible to draw an imaginary line in the ground where the strongest signal is located. Line up the target at 90° from the initial direction and repeat the process. The object is located where the two imaginary lines cross.

NOTE: Pinpointing will not locate a target in the centre of the coil if operating with the RX switch set to Enhance or Cancel.

Recovering the Target

When you are sure of the location of the target, it is necessary to dig a small hole to recover it. In order to preserve the environment, the hole should be as small as possible. Always replace the soil and grass which is removed.

It is essential to carry at least one of the following digging tools with you when searching:

• small, strong digging spade
• pick
• shovel
• and crowbar (for very deep objects in hard ground).

STEP 1: Before digging, clear the area of loose surface material and check that the target signal is still there. If it is not, the target should be amongst the surface material.

STEP 2: If the target signal is still present, dig to a depth of approx. 50mm.

STEP 3: If the target cannot be seen, sweep the coil over the hole.

STEP 4: If the target signal is not heard, then the target should be in the pile just dug.

STEP 5: Check that there are no objects buried in the soil under the pile.

STEP 6: Take care when you dig, as damaging a nugget may reduce its value. Start digging approx. 100mm in front of the target to reduce the chance of damage.

STEP 7: Pile the diggings carefully as it may be necessary to search them.

STEP 8: If the target is located in the soil which was removed, sweep the coil over the pile and pinpoint its exact position.

STEP 9: Keep halving the pile which has the target.

STEP 10: If it is still difficult to find the target, place the detector on the ground with the coil horizontal.

STEP 11: Take a handful of the diggings and pass over the coil.

• Your hands and wrists must be free of any metallic jewellery and watches.

STEP 12: If there is no signal, place the handful carefully in a new pile and repeat with another handful.

NOTE: Always refill any holes before leaving, and scatter leaves, etc. to restore the area to its original condition. Any rubbish you recover should be taken away with you and disposed of properly.

Recovering Deep Targets

The 'GP extreme' has depth capabilities that will surprise both new and experienced prospectors. If the target appears to be buried deeply, it should help to use the following technique:

• STEP 1: Use the cross sweeping method to locate the target accurately.
• STEP 2: Dig a hole large enough to insert the coil, approx. 100mm deep.
• STEP 3: Keep testing the target location as you dig deeper.
• STEP 4: Take care that the target is not in the wall of the hole. You may dig past it. Try pinpointing again to check your hole is in the correct position.

REMEMBER: Removing rubbish and refilling holes will help metal detector users maintain a good reputation. This should lead to more areas being readily accessible for prospecting.

Salty Environments

The 'GP extreme' will find objects at greater depth in salty environments. However, the interfering signals caused by highly concentrated salt may not be able to be completely 'balanced out' if using automatic ground balance alone.

HINT: Change Soil switch to Salt setting for salty environments. To use the salt setting, you will have to use the specially designed 'GP extreme' range of coils.

7. User Information

This chapter provides a glossary of terminology, user guides, technical specifications, warranty and repair details and troubleshooting tips.

Technical Specifications

Table 7.1 Technical specifications

Troubleshooting

Use the following table to check for suggested solutions to problems.

Table 7.2 Troubleshooting

If you need to return your detector to Minelab for service, please supply as many details as possible about the fault. This will enable our service engineers to rectify the fault quickly and efficiently. Return the detector in a cardboard box for protection along with the Service Repair Form supplied in this manual. Please supply your name, address and phone number along with purchase date and serial number when sending detector parts for repair.

Service Repair Form

The Service Repair Form is provided for detailing faults when returning the detector for service. Please fill out the form completely and enclose it with the detector.

Warranty

The 'GP extreme' control box has a 2 year warranty covering parts and labour. The 'GP extreme' 1100 and 1800 coils have a warranty for one year against malfunction. The warranty commencement is the date of purchase. The Minelab warranty does not cover damage caused by accident, misuse, neglect, alteration, modifications or unauthorised service. The owner is responsible for all transport costs for the detector to Minelab. The repaired detector will be returned freight free.

NOTE: This warranty is not transferable or valid unless the enclosed warranty registration card is returned to Minelab Electronics Pty. Ltd. or an authorised Minelab Electronics Pty. Ltd. regional distributor within 14 days of the original purchase.

Accessories

Search coils: The 'GP extreme' is supplied with 'GP extreme' 1100 and 1800 coils. Other sizes are available. Using coils not specifically designed for the 'GP extreme' may cause instability.

Batteries: Spare 10A/hr batteries offer extended operation. A smaller 4.5A/hr battery is also available for shorter runs.

Corporate clothing: Minelab offers branded clothing such as caps, shirts, and jackets.

Glossary of Common Terms

• Control Box: Encloses detector circuitry, originates TX signals, interprets RX signals.
• Discrimination: Ability to estimate if a target is ferrous or non-ferrous.
• Double D Coils: Coils with two overlapping windings, offering stability, depth, and sensitivity.
• Electromagnetic Field: The 'signal from the coil' pulsed into the ground.
• False Signal: Signals caused by factors other than targets, like ground noise or hot rocks.
• Ferrous Metals: Metals containing iron.
• Ground Balance: Ability to compensate for ground mineralisation. The 'GP extreme' has automatic ground balance.
• Halo Effect: Diffusion around a buried object making it appear larger.
• Hot Rocks: Rocks with high mineralisation causing false signals.
• Interference: Electrical or radio waves causing instability or chattering.
• Mineralised Ground: Ground with minerals causing false signals.
• Monoloop Coils: Coils with a single loop winding, often cone-shaped field.
• Non-Ferrous Metals: Metals without significant iron (e.g., Gold, Silver, Copper).
• Pinpoint: Method to locate the precise position of a target before digging.
• RX: The received electromagnetic field detected by the coil.
• Salt: High salt content in the ground affecting ground balance.
• Search Coil: The circular plate swept over the ground.
• Search Pattern: The area of ground scanned by the coil.
• Threshold: The continuous audible background sound emitted by the detector.
• Target Response: The electro-magnetic effect generated by a metal target.
• Target Signal: The audio signal caused by a metal target.
• Tracking: Automatic Ground Balance function that compensates for ground mineralisation changes.
• TX: Transmit signals or electromagnetic pulses sent into the ground by the coil.

Detector Care and Safety

The 'GP extreme' is a high quality electronic instrument designed for professional gold prospecting. Take care of your detector:

• Keep the detector clean and dry. Ensure electrical connectors are clean and dry.
• The control box is water-resistant but not waterproof; avoid immersion.
• The coil is water-resistant but not waterproof; do not immerse.
• Regularly replace items like teardrop washers and skidplates.
• Do not expose to high temperatures or prolonged sun exposure. Shading is recommended. Do not leave in a closed vehicle in the sun.
• Use of a replaceable skid plate protects the coil.
• To prevent dirt entry, silk tape (e.g., Leukosilk®) may be used on the coil/skidplate join.
• Avoid contact with petrol or oil-based liquids. If contact with corrosive substances (salt water) occurs, wash with fresh water.
• Clean with a damp cloth and mild soap detergent; do not use solvents.

An Important Message from Minelab

Minelab asks all detector operators to take due care regarding the environment. Be responsible when recovering targets and BACKFILL EVERY HOLE YOU DIG. This ensures continued access to prospecting areas and preserves the natural environment.

Minelab thanks you for your efforts towards protecting the environment.