GrayStone Exploration Labs, Inc.
15400 W 44th Ave. Suite 21
Golden CO, 80403
15400 W 44th Ave. Suite 21
Golden CO, 80403
Contact: Chuck Goudge chuck@graystonelabs.com
If you are sending samples from out of the United States you will need
special shipping instructions. Call to set up your shipment, 303-278-3252
special shipping instructions. Call to set up your shipment, 303-278-3252
General Lab Data
I currently have a data base containing more than 300,000 soil samples analyzed for iodine and other
components. Most are for oil and gas geochemical exploration surveys but also included surveys for
uranium, gold and other precious metals. These samples have come from all over the world including
Europe, Asia, Australia, North and South America, even a number of islands. Much of the data base is
from North America and the United States. The average for all of the current 300,000 samples is 2.4 ppm
I2, this includes all background and anomalous samples from all areas.
components. Most are for oil and gas geochemical exploration surveys but also included surveys for
uranium, gold and other precious metals. These samples have come from all over the world including
Europe, Asia, Australia, North and South America, even a number of islands. Much of the data base is
from North America and the United States. The average for all of the current 300,000 samples is 2.4 ppm
I2, this includes all background and anomalous samples from all areas.
Repeatability and Precision
As an analytical chemist I have followed a consistent regiment of quality assurance. I repeat nearly 10% of
all samples and include a known soil standard on each set (31 samples/set). Currently on just more than
30,000 repeats the average error has been plus/minus 5.4%. For comparison, contract labs working for
the EPA are only required to meet a plus or minus 20% error for EPA analysis. Some geochemical
exploration labs fail to meet even this standard. Below is the error chart for all of the repeats run by my lab.
Thirty seven percent of all samples repeated exactly, 71% are within 5%, 92% within 10% and 98% are
within 20%.
all samples and include a known soil standard on each set (31 samples/set). Currently on just more than
30,000 repeats the average error has been plus/minus 5.4%. For comparison, contract labs working for
the EPA are only required to meet a plus or minus 20% error for EPA analysis. Some geochemical
exploration labs fail to meet even this standard. Below is the error chart for all of the repeats run by my lab.
Thirty seven percent of all samples repeated exactly, 71% are within 5%, 92% within 10% and 98% are
within 20%.
Repeatability and precision are the most critical aspects of a geochemical exploration laboratory. If a lab
cannot repeat their results then their data is useless. Repeating a sample does not mean achieving exactly
the same result, although that would be great, but achieving a result within the limits of analytical precision
for the specific technique. Different analytical techniques and procedures will yield different ranges and
precision. As I have already mentioned the best laboratories regularly use a precision of plus/minus 20%
as their goal and the EPA has adopted this as the standard accepted precision for EPA approved labs.
Some techniques exceed this standard but few are much better than plus/minus 10%.
cannot repeat their results then their data is useless. Repeating a sample does not mean achieving exactly
the same result, although that would be great, but achieving a result within the limits of analytical precision
for the specific technique. Different analytical techniques and procedures will yield different ranges and
precision. As I have already mentioned the best laboratories regularly use a precision of plus/minus 20%
as their goal and the EPA has adopted this as the standard accepted precision for EPA approved labs.
Some techniques exceed this standard but few are much better than plus/minus 10%.
Over the long term the iodine procedure that I use has yielded an average of plus/minus 5.4%. This is
based on the regular repeats I run, but occasionally I will repeat a series of samples. The following example
is to illustrate the repeatability of the technique and to illuminate the nature of any analytical technique.
based on the regular repeats I run, but occasionally I will repeat a series of samples. The following example
is to illustrate the repeatability of the technique and to illuminate the nature of any analytical technique.
The analytical results of the following group of samples was in doubt because there was a consistent
increase in iodine in the first 49 samples, which were submitted as a batch, and the next group of samples,
from the same project, submitted and analyzed later. As there is always a chance of a systematic error I
reran the 49 samples and continued through the transition. The following is a list of that data.
increase in iodine in the first 49 samples, which were submitted as a batch, and the next group of samples,
from the same project, submitted and analyzed later. As there is always a chance of a systematic error I
reran the 49 samples and continued through the transition. The following is a list of that data.
Field # Iodine Iodine Iodine Plus Minus
..............Original Repeat Average Percent
..............Original Repeat Average Percent
543 2.8 2.8 2.8 0.0
544 3.8 3.8 3.8 0.0
545 2.6 2.2 2.4 8.4
546 3.8 3.7 3.8 1.3
547 2.8 3.1 3.0 5.0
548 2.5 3.3 2.9 14.0
549 2.9 3.5 3.2 9.5
550 2.9 3.3 3.1 6.5
551 3.6 4.5 4.1 11.0
552 3.3 3.6 3.5 4.3
553 3.2 3.8 3.5 8.5
554 3.2 3.6 3.4 6.0
555 4.1 4.4 4.3 3.5
556 3.2 3.1 3.2 1.6
557 3.7 3.3 3.5 5.7
558 3.5 3.9 3.7 5.5
559 3.7 3.1 3.4 8.8
560 2.6 2.6 2.6 0.0
561 3.5 3.3 3.4 3.0
562 3.9 4.1 4.0 2.5
563 4.2 4.8 4.5 6.5
564 2.9 3.3 3.1 6.5
565 3.7 4.0 3.9 3.9
566 3.8 4.7 4.3 10.5
567 3.3 3.7 3.5 5.5
568 3.7 4.0 3.9 3.9
569 3.9 4.4 4.2 6.0
570 3.5 3.8 3.7 4.1
571 3.7 3.8 3.8 1.3
572 3.7 4.2 4.0 6.5
573 3.1 3.5 3.3 6.0
574 4.3 4.3 4.3 0.0
575 4.5 4.5 4.5 0.0
576 4.9 4.9 4.9 0.0
577 3.7 3.9 3.8 2.7
578 3.8 3.7 3.8 1.3
579 3.7 4.0 3.9 3.9
580 3.2 3.6 3.4 6.0
581 3.3 3.6 3.5 4.3
582 3.9 4.0 4.0 1.3
583 3.6 3.3 3.5 4.3
584 3.6 3.8 3.7 2.7
585 3.9 3.9 3.9 0.0
586 4.2 3.7 4.0 6.3
587 5.1 4.5 4.8 6.3
588 4.9 4.8 4.9 1.0
589 5.3 4.9 5.1 3.9
590 5.9 5.4 5.7 4.4
591 5.3 5.4 5.4 1.0
break between groups
592 2.7 3.2 3.0 8.5
593 2.7 2.8 2.8 1.8
594 2.2 2.5 2.4 6.5
595 2.2 2.2 2.2 0.0
596 2.8 2.6 2.7 3.7
597 3.0 3.4 3.2 6.5
598 2.8 3.6 3.2 12.5
599 3.4 3.6 3.5 2.9
600 2.5 2.6 2.6 1.9
601 2.6 2.1 2.4 10.4
602 2.7 2.7 2.7 0.0
603 3.7 3.6 3.7 1.4
604 3.2 2.7 3.0 8.4
544 3.8 3.8 3.8 0.0
545 2.6 2.2 2.4 8.4
546 3.8 3.7 3.8 1.3
547 2.8 3.1 3.0 5.0
548 2.5 3.3 2.9 14.0
549 2.9 3.5 3.2 9.5
550 2.9 3.3 3.1 6.5
551 3.6 4.5 4.1 11.0
552 3.3 3.6 3.5 4.3
553 3.2 3.8 3.5 8.5
554 3.2 3.6 3.4 6.0
555 4.1 4.4 4.3 3.5
556 3.2 3.1 3.2 1.6
557 3.7 3.3 3.5 5.7
558 3.5 3.9 3.7 5.5
559 3.7 3.1 3.4 8.8
560 2.6 2.6 2.6 0.0
561 3.5 3.3 3.4 3.0
562 3.9 4.1 4.0 2.5
563 4.2 4.8 4.5 6.5
564 2.9 3.3 3.1 6.5
565 3.7 4.0 3.9 3.9
566 3.8 4.7 4.3 10.5
567 3.3 3.7 3.5 5.5
568 3.7 4.0 3.9 3.9
569 3.9 4.4 4.2 6.0
570 3.5 3.8 3.7 4.1
571 3.7 3.8 3.8 1.3
572 3.7 4.2 4.0 6.5
573 3.1 3.5 3.3 6.0
574 4.3 4.3 4.3 0.0
575 4.5 4.5 4.5 0.0
576 4.9 4.9 4.9 0.0
577 3.7 3.9 3.8 2.7
578 3.8 3.7 3.8 1.3
579 3.7 4.0 3.9 3.9
580 3.2 3.6 3.4 6.0
581 3.3 3.6 3.5 4.3
582 3.9 4.0 4.0 1.3
583 3.6 3.3 3.5 4.3
584 3.6 3.8 3.7 2.7
585 3.9 3.9 3.9 0.0
586 4.2 3.7 4.0 6.3
587 5.1 4.5 4.8 6.3
588 4.9 4.8 4.9 1.0
589 5.3 4.9 5.1 3.9
590 5.9 5.4 5.7 4.4
591 5.3 5.4 5.4 1.0
break between groups
592 2.7 3.2 3.0 8.5
593 2.7 2.8 2.8 1.8
594 2.2 2.5 2.4 6.5
595 2.2 2.2 2.2 0.0
596 2.8 2.6 2.7 3.7
597 3.0 3.4 3.2 6.5
598 2.8 3.6 3.2 12.5
599 3.4 3.6 3.5 2.9
600 2.5 2.6 2.6 1.9
601 2.6 2.1 2.4 10.4
602 2.7 2.7 2.7 0.0
603 3.7 3.6 3.7 1.4
604 3.2 2.7 3.0 8.4
The standard method of reporting precision is the percent above and below the average of the two analysis.
The original analysis was correct and the drop in the iodine values between the two sets was real. Of the
total of 62 samples the average plus/minus percent is 4.5. 19 of the 62 or 31% were 2 percent or less. Five
of 62 or 8% were greater than 10 percent with the highest at 14%.
The original analysis was correct and the drop in the iodine values between the two sets was real. Of the
total of 62 samples the average plus/minus percent is 4.5. 19 of the 62 or 31% were 2 percent or less. Five
of 62 or 8% were greater than 10 percent with the highest at 14%.
Conclusion
The real lesson is that even the best analytical lab will report a small percentage of samples with a large
enough error that if they are near the transition from background to anomaly they can negatively effect the
interpretation of the survey. The only sure way to overcome this limitation is to have a sufficient number of
samples limiting the effect of any one or two samples on the final interpretation.
enough error that if they are near the transition from background to anomaly they can negatively effect the
interpretation of the survey. The only sure way to overcome this limitation is to have a sufficient number of
samples limiting the effect of any one or two samples on the final interpretation.
___
Average 4.5
Average 4.5
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