New Zealand Gold Prospecting & Metal Detecting Forums Archive

Gidday ocarlier

Many moons ago, before I got a detector and I lived in Auckland, I was at Piha one windy day, and I mean windy, the wind was blowing sand away and there were coins aplenty sticking up out of the sand. Didn't need a detector that day. Great beach, so is Muriwai. I hope you had fun

Good luck! You have the machine for it and the west coast beaches shouldn't be anywhere near as junky (iron etc) as the east coast's more sheltered beaches .

Being black sand I doubt many would have detected it previously or if they did not to a great depth (VLF detectors being the most common detectors). I can see you coming back with gold within a couple of trips! All you need now is a long handled sand scoop to make life easier.

Hi Anton,

I too tried Murawai after not being completely put off searching Piha; went at low tide and found lots of hair pins - the surfers / locals appear to be a little bit smarter than I first anticipated?

Also tried my Fisher F75 (VLF) and that went nuts with the 'OVERLOAD' warning and noise, just as yours did - until getting right down to the waters edge.

Looks like only a good beach for Pulse Induction machines, and even then my Garrett Infinium LS was making a fair bit more noise than over on the eastern beaches, and Piha. One could argue you found metal, iron and lots of it! Might enrange the locals removing enough of it to equal the value of a Gold ring.

3 types of soil a VLF detector (like your 305) will struggle on are:

Mineralised
Auckland's west coast beaches are an example of this, they contain a very high quantity of titanomagnetite (1/2 iron and other minerals mixed in). Some of it is from the Waitakere's but the majority has travelled up the coast from the New Plymouth area. This sand is magnetic and will overload a VLF detector - even a multi frequency one. Only a PI can punch through it since it's technology ignores mineralisation (a VLF needs to be ground balanced to remove it, but even automatic ground balancing can't balance to the extent needed).

Ferrous
Any iron in the ground, this includes the rusty halo in the surrounding soil / sand left after a piece of iron has rusted out. A multi frequency detector can be adjusted to ground balance this out but a large solid piece (i.e. man hole cover) will still overload the detector.

Conductive
Any non-metallic electrically conductive element. Saltwater at the beach is the classic example but overseas some areas also have problems with high fertilised areas. Multi Frequency detectors work best here because the processor can compare the ground signal from the different frequencies and balance the conductivity out (of course PI's as well because of their different method). Some single frequency detectors can also still work (like the AT Pro) but depth will suffer.

Thus the sand on the east coast beaches is mineralised, ferrous and conductive! A VLF's nightmare.

But finding black sand can be handy in certain circumstances. This sand is heavier then the normal white stuff and if a patch is found on the wet sand area of a beach not generally known for it, it means that some erosion may have occurred and the area should contain heavy targets (Gold!). In these spots minor amounts of black sand (Grey sand?) can be detected by ensuring proper ground balance and reducing sensitivity etc.

Edited by user Thursday, 14 February 2013 6:33:45 PM(UTC)  | Reason: Not specified