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Getting Aquainted With The GPX 6000


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Simon,

You do a stellar job in your write-ups, lots of useful information, and it's fun to tag along as you learn.

All the best,

Lanny

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Another great write up as usual from you Simon!

Glad that you were able to find some of that yellow stuff while checking out the new toy.

Glad to hear that your unit is working as it should for you and I like your new toys also.

Some day I may have to get the 6000, but I think I need to really learn the 800 better.

I need more experience at detecting before spending that kind of money for a new unit.

Good luck on your next outing.

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I was doing some research into why the gold is often found inside the schist and I spend my time smashing it out and came up with this document

Gold In Otago.

Gold occurs in two distinct geological settings in Otago: within quartz veins in the schist (hard-rock gold), and as detrital gold grains in gravels (alluvial gold). The quartz veins which contain the hard-rock gold were formed by hot water (200-400°C) passing through fractures in the schist up to 15 kilometres below surface. The passing hot water deposited the quartz and gold as it rose and cooled through the schist bedrock. Hard-rock gold forms the original source for the alluvial gold, but many alluvial deposits have been derived by erosion of older gravel deposits. Gold is 19 times denser than water, and does not move far in streams unless it is as small particles (less than half millimetre).

The history of gold in Otago goes back about 150 million years, when Otago was mountainous, similar to the Southern Alps of today. The mountain ranges extended from Chatham Islands westwards beyond Wanaka, into Marlborough which at that time was immediately west of Haast. These mountains were made up of schist and greywacke as in Otago and Southern Alps today. Beneath the mountains, gold-bearing quartz veins filled active faults formed by earthquakes which accompanied the rise of the mountains. Similar processes have occurred during many times of fault activity and mountain building over the past 150 million years, and are still occurring today beneath the Southern Alps. Marlborough moved along the Alpine Fault nearly 500 kilometres northeastwards from Otago, taking its gold with it, over the past 20 million years.

As the mountains rose, they were eroded and gold from the quartz veins was concentrated into layers of coarse gravels on the eroded bedrock. Further uplift meant that these gravels were in turn eroded and the gold was reconcentrated. At least 15 kilometres of rock have been removed from over Otago. All that remains of that rock is the widespread alluvial gold, for which Otago is famous, and small amounts of gravel.

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Nice writeup Simon, thanks! Say, when you mentioned avoiding pellets with the GPX, what were you doing and listening for? If possible, can you post an example video with the sound of doing that with your GPX? 

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23 minutes ago, GotAU? said:

Nice writeup Simon, thanks! Say, when you mentioned avoiding pellets with the GPX, what were you doing and listening for? If possible, can you post an example video with the sound of doing that with your GPX? 

Yea sure I'll film it next time, I avoid them with the GPZ too as with the 8" you get the double blip as you pass them, it's mostly an odds game, pellets are often on or near the surface, with the GPX it's pretty easy to avoid them in this scenario as it really ROARS on them when they're right next to the coil, so if I do a few scrapes with my pick and signal is no longer in the same place and moved into my dig pile then it's less likely to be gold, combine that with the GPX losing the roaring target signal as soon as the pellet has any depth by being buried in my dig pile under a few inches of soil and the GPX signal becoming much more faint or even disappearing on some smaller lead pellets then I write it off as a pellet. Gold tends to keep its signal strength better than lead pellets.  We don't have many surface type nuggets around here unless on bedrock so this only works when there is a decent amount of top soil on the bedrock.

As you can see by how many pellets I dug a lot of them are too deep for this trick to work.  These were all pellets that survived past the first few scrapes and could have possibly been gold.  I rejected just as many as I dug I would guess.

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11 minutes ago, phrunt said:

Yea sure I'll film it next time, I avoid them with the GPZ too as with the 8" you get the double blip as you pass them, it's mostly an odds game, pellets are often on or near the surface, with the GPX it's pretty easy to avoid them in this scenario as it really ROARS on them when they're right next to the coil, so if I do a few scrapes with my pick and signal is no longer in the same place and moved into my dig pile then it's less likely to be gold, combine that with the GPX losing the roaring target signal as soon as the pellet has any depth by being buried in my dig pile under a few inches of soil and the GPX signal becoming much more faint or even disappearing on some smaller lead pellets then I write it off as a pellet.  We don't have many surface type nuggets around here unless on bedrock so this only works when there is a decent amount of top soil on the bedrock.

As you can see by how many pellets I dug a lot of them are too deep for this trick to work.  These were all pellets that survived past the first few scrapes and could have possibly been gold.  I rejected just as many as I dug I would guess.

Thanks for the help, Gerry is going to have to put you on his payroll!

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7 hours ago, GotAU? said:

Thanks for the help, Gerry is going to have to put you on his payroll!

I use products he doesn't sell 😄 It'd be like me working at a Ford dealer wearing a Toyota T-shirt 🙂

I was just watching this video by abenson and I would not trust my pellet rejection method in his area, it seems there is a lot of small shallow near surface gold where he is hunting and my method would likely lose a lot of gold there as where we are these nuggets are not on the surface like he's finding them, it works here but certainly not there.  It was interesting to see he has a lot of the same troubles as I do with the 6000 like the speaker and even quite reasonable size small nuggets near disappearing in dig out piles if they end up on edge in the piles or towards the bottom of the pile.  This behaviour is so different on the GPZ.   I can see why people hunting in this area he is at would love the GPX over a stock GPZ, it's hyper sensitive to small surface targets so these nuggets would stand out.

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