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Nugget Mesh Size


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I've been trying to make a PI detector as a learning exercise in another forum(Geotech). Asked the question below but haven't got a reply. Maybe someone here could answer the question. 

Nugget sizing info:

We are often asked how many pieces per gram or ounce. It is very hard to predict how many pieces there are per gram or ounce as the # of nuggets by weight varies quite a bit per batch. But in general you can expect around 1-2 pieces of gold for 4 mesh, 2-4 pieces of 6 mesh per gram, 7-12 pieces of 8 mesh per gram and around 15-20 per gram for 10 mesh. You can expect many more pieces for smaller 12 (around 20-25), 14-16 (around 30-50 or more) pieces and hundreds for fine gold. Every batch is very different and each piece of gold is natural and of course therefore unique. Some may be flat and light or rounded and very dense (heavy).


How small a nugget can a good PI detect? What mesh size would make good test targets for smaller nuggets? 8 mesh, 10 mesh, both or other?

Any guess on typical TC for 8 or 10 mesh nuggets?
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Well, you are asking for a typical TC, which I am assuming is Time Constant. Most people here will be thinking in terms of target id numbers. Remember these are natural objects. A nugget can be 90% gold, 60% gold, or 10% gold. That alone will send conductivity all over the place, with pure gold being the best signal. Adding silver to gold does not raise conductivity as people assume because alloys do not conduct electricity as well as pure metal. Silver is a far better conductor than gold if both metal are pure, but adding silver to gold reduces the conductivity and therefore the time constant and target numbers are reduced.

The gold can be solid and round, or solid and flat as a pancake. The shape not only will change everything but also the orientation in the ground.

The gold can be solid or it can be porous. Porous gold is usually invisible to PI detectors. It can porous due to air spaces or porous due to enclosed minerals. If the enclosed minerals (iron sulphides for instance) have electrical or magnetic properties that will change everything.

Suffice it to say that gold is a mess when it comes to how it reacts with a detector.

Most of us do not use test nugget based on mesh size but on weight. I usually use a 1 grain nugget (480 grains per Troy ounce) to test VLF detectors. A PI will not normally detect that, so I am normally going to use a quarter gram or half gram nugget to test a PI. There are 15.43 grains per gram.

I just weighed a few 8 mesh nuggets, and they were from 1 grain to 4 grains in weight. That will definitely present a challenge to a PI, with some probably being detectable with a hot PI, and some not. Just depends on the above factors.

Here are a series of test nuggets and target numbers for them I did. The gold is larger but shows how the numbers vary with size and purity.

 

Size Equivalents
Two scales that are used to classify particle sizes are the US Sieve Series and Tyler Equivalent, sometimes called Tyler Mesh Size or Tyler Standard Sieve Series. The most common mesh opening sizes for these scales are given in the table below and provide an indication of particle sizes. The mesh number system is a measure of how many openings there are per linear inch in a screen. Sizes vary by a factor of √2. This can easily be determined as screens are made from wires of standard diameters, however, opening sizes can vary slightly due to wear and distortion. US sieve sizes differ from Tyler Screen sizes in that they are arbitrary numbers.

US Sieve
Size

Tyler Equivalent

Opening

mm

in

-

2½ Mesh

8.00

0.312

-

3 Mesh

6.73

0.265

No. 3½

3½ Mesh

5.66

0.233

No. 4

4 Mesh

4.76

0.187

No. 5

5 Mesh

4.00

0.157

No. 6

6 Mesh

3.36

0.132

No. 7

7 Mesh

2.83

0.111

No. 8

8 Mesh

2.38

0.0937

No.10

9 Mesh

2.00

0.0787

No. 12

10 Mesh

1.68

0.0661

No. 14

12 Mesh

1.41

0.0555

No. 16

14 Mesh

1.19

0.0469

No. 18

16 Mesh

1.00

0.0394

No. 20

20 Mesh

0.841

0.0331

No. 25

24 Mesh

0.707

0.0278

No. 30

28 Mesh

0.595

0.0234

No. 35

32 Mesh

0.500

0.0197

No. 40

35 Mesh

0.420

0.0165

No. 45

42 Mesh

0.354

0.0139

No. 50

48 Mesh

0.297

0.0117

No. 60

60 Mesh

0.250

0.0098

No. 70

65 Mesh

0.210

0.0083

No. 80

80 Mesh

0.177

0.0070

No.100

100 Mesh

0.149

0.0059

No. 120

115 Mesh

0.125

0.0049

No. 140

150 Mesh

0.105

0.0041

No. 170

170 Mesh

0.088

0.0035

No. 200

200 Mesh

0.074

0.0029

No. 230

250 Mesh

0.063

0.0025

No. 270

270 Mesh

0.053

0.0021

No. 325

325 Mesh

0.044

0.0017

No. 400

400 Mesh

0.037

0.0015

 

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31462256_goldnuggets_2.thumb.JPG.203bf30173caab9d7f116969a206e079.JPGI just weighed a few 8 mesh nuggets, and they were from 1 grain to 4 grains in weight. That will definitely present a challenge to a PI, with some probably being detectable with a hot PI, and some not. Just depends on the above factors.

Looks like 8 mesh answers my question. Thanks for all the other information.

Including a picture with test results for three nuggets I have. Charted decay amplitude after PI Tx off(zero time). 10grain nugget  has a higher TC than 18grain nugget.

 

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  • 1 month later...

Received 8mesh nuggets. For a quick test I charted all the nuggets at same time(side by side flat not touching)to see how much signal. Should give average time constant. Decay time constant 1.7usec, good signal, think I can test them one at a time flat. TC on edge might be to low. Anyone familiar with small nuggets, do they look like what you would expect?

nugget simulation_8mesh.jpg

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Hi Green

   Those are some nice chunky nuggets. They haven’t been beat up, flattened and worn smooth by traveling for millions of years in an ancient river.

    Their size and shape are very detectable by most pulse induction detectors. They are typical of nuggets that are found closer to the original source of the gold.

   The three you show with your chart are typical of what is found in Californian hydraulic pits which are ancient river gravels.   

Have a good day,
Chet
 

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94361213_nuggetsimulation_11.thumb.jpg.5efea3415e1485fb9a5e9f4e53790d26.jpgCharted the nuggets. Looks like most of the decay TC's between 1 and 2 usec. Nuggets look a little larger than I was expecting, probably couldn't chart much smaller nuggets with my tester. Receive signal getting in the noise. Thanks again for suggesting 8mesh

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2 hours ago, green said:

Looks like most of the decay TC's between 1 and 2 usec.

How do you determine these values?  (I can see the graphs, but please explain how the graphs lead you to these values.)

 

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What exactly are you trying to prove? If it is trying to categorize  your total amount of gold into a neat little pigeon hole governed by size =  common consistant weight, then that is not possible. Determining how much gold someone has or the size it can be detect, is not ruled by size. It is ruled by weight because gold is so malible. It can be expanded or condensed by forces of nature. You can take 4 different nuggets each weighing 1 gram  but all four are different screen sizes because of each nuggets shape. But they are each still 1 gram. This is common sense as gold  has always been  as long as man has used gold as a commodity that weight not size accurately determines its volume and value.

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4 hours ago, Goldseeker5000 said:

What exactly are you trying to prove?

Trying to learn something. Didn't have an idea how fast smaller nugget signal decayed. Have asked before in another forum and always got the answer, to much variation. Wanted to know how small a nugget a good PI detector could detect to get some for testing. 

 

18 hours ago, GB_Amateur said:

How do you determine these values?  (I can see the graphs, but please explain how the graphs lead you to these values.)

I made a PI circuit. Tx coil, Rx coil, control circuit, amplifier looking at Rx and log amplifier looking at amplifier out. Record log amplifier out vs time and chart. Most targets with a time constant<10usec decay straight line on a linear log chart. Loose 63% of signal every time constant, loose 90%(decade on chart)) every 2.3 time constants,  loose 50% every 3 small divisions on chart. A eight inch coil could loose 3 to 4 inch detection distance for every decade lose in signal. The shorter the time constant the sooner the need to sample. Probably need a smaller coil to get a good chart for the 8mesh nuggets, data below the 0 line(1% 0f full scale amplifier out)starts to be effected by noise when charting. Added a 1 and 2usec time constant decay line on chart to compare target decay with, most nuggets decay with a slope between the two lines.

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  • 1 year later...

Compared some nuggets and lead shot from shotgun shells. Used a PI circuit, 3.5us delay with a Rx coil about 5 1/2 inch diameter. Appears 4, 6 and 8 shot are similar to the 8mesh nuggets. If I were to try to find small gold nuggets what detection distance for the lead shot should I want?  Larger coil would improve detection distance for the larger nuggets. 

nuggets.jpg.bc69bfeea4e0d2cac14651bf21f6bfd7.jpgnuggets6.png.2ada1708049ccddd9df31c4438e4d9c7.png

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