AA Assay

[Geowizard]

Guys and Gals,

The process of prospecting often gets down to the question of; WHAT is in this rock?

I often wonder how many prospectors have really found a major discovery and didn't know it.

Atomic Absorption Spectroscopy (AA) is the method often used by assayers to perform an assay. Most prospectors are probably aware of the advantage of getting an assay done on samples collected in the field. The problem is that assays cost money! A typical assay can be done for one element or many elements. The more elements, the higher the cost.

A solution;

I have found AA spectrometers available at auction! YOU can do this!

It's possible to bid on an AA spectrometer at auction and get your own personal AA spectrometer. The obvious advantage is that YOU can do your own assays at home. No, not in the kitchen.

So, this thread is dedicated to "HOW" the average prospector can overcome the cost of getting an AA assay done.

Ask me HOW...

- Geowizard

[Geowizard]

AES;

Atomic Emission Spectroscopy (AES) is similar to AA spectroscopy.

Atomic Absorption spectroscopy (AA or AAS) uses "cold cathode lamps" that are specific to individual elements. The lamps emit spectra - optical lines that represent a single element. When the lamps are used in an AA spectrometer, the lamp creates absorption spectra that result in a more sensitive assay - down to a few parts per million or less.

Atomic Emission Spectroscopy (AES) does NOT require a cold cathode lamp. In most cases, the sensitivity is less than AA. For prospecting purposes, AES provides "identification" of many elements and provides a measure of amount or quantity down to 100 parts per million or less.

When a sample is prepared for analysis (assay), it is usually dissolved into solution. That process is somewhat involved and requires patience and attention to detail. As with most things we do related to prospecting, there are additional skills that are learned. Being able to analyze samples of rock material is of great advantage to a prospector. As with panning or any other skill, patience and accuracy are important.

- Geowizard

[Micropedes1]

When I finally graduated from dredging in cold water to placer and hard rock mining, I quickly realized the need for an atomic absorption unit to perform my own analysis. After a bit of shopping, I finally found a barely-used unit with all the necessary hollow cathode lamps (HCL). It seems that the local farming cooperative had purchased one only to have their chemist leave unexpectedly. I purchased the unit at auction, with 30 HCL tubes for the outrageous price of $6.50. Stay on your toes; there is some very good, expensive equipment to be had out there!

[Geowizard]

Excellent!

I have a collection of AA Spectrometers, lamps, burners and autosamplers. I would blush to say how little all of that cost. Yep... Watch the auctions out there.

You need a "Lab" environment to set up an AA spectrometer. It needs to be a clean area with room to work. It needs to have clean air and a ventilated fume hood for the burner. It needs clean power without power line noise or glithches or brown outs. This is a piece of scientific instrumentation. Additional requirements are a SOLID bench with no vibration. You will need a tank of AA Grade Acetylene to run the burner. You will need an air pump and stable air tank for filtered air.

A AA Spectrometer requires calibration. "Standard" solutions are used for calibration. They can be made or they can be purchased from a supplier. Documentation in the form of "Analytical Methods" and procedures along with information about the spectral lines produced for each element is needed. The method of sample preparation is important in order to have a known amount of sample that enters the burner. Distilled wash water is used to clean the aspirator tube, nebulizer and burner as well as "zero" the instrument between samples.

Are we having fun yet?

- Geowizard

[Micropedes1]

AES will identify the elements that are present in your samples. Its quick and somewhat questionable in that it lacks accuracy when near the threshold limits of your machine.

AAS on the other hand requires much more work to mix a set of known concentrations, run your sample, and only then determine the concentration of your tested element as a comparison to known concentrations. Its very labor intensive to get those extra orders of accuracy. But before I sink my hard earned capital into a mining location, I want to know exactly what to expect.

[Micropedes1]

I didn't say that it was easy. It takes hard work to do it right. Once you get the standards mixed up in quantity, it gets way easier. The trick is to go back to your blank or a standard solution often enough to insure the accuracy of your results.

[Geowizard]

Exact amount of GOLD?

Yep... The AA spectrometer says precisely 3.2367927 parts per miliion. (+/- 10 percent)

Does "Exact" mean "accurate"? or does "Exact" mean "Precise"? Are you "certain"? How many samples were measured and what was the deviation of the samples? What is the "certainty" of the result?

All of these questions about the Exact result lead to an infinitely LARGE variable!

The GOLD deposit is neither consistent in grade nor consistent in composition. GOLD deposits are variable over an almost infinite range.

We will need another thread on "Sampling".

Suffice it to say, it's GOLD.

- Geowizard

[Jim_Alaska]

These posts that you two have been making are exactly what made the old forums so popular. This is the kind of information that most prospectors never get to see.

Thank you both for your time and expertise, it is truly appreciated and by more people than just me.

[Micropedes1]

I miss all the fiery discussions that we used to have on the old forum. Where is everybody?

[Jim_Alaska]

I miss all the fiery discussions that we used to have on the old forum. Where is everybody?

They have been slow registering for the new forums. I sent out notices to all I had contact information for when i switched over. Perhaps they will be back in time.

Meanwhile these sort of technical information posts can be the vehicle that makes this forum one of the best on the Internet. You just don't see this kind of information on other forums, once people start seeing the quality and volume of information we have the capacity to generate, they will come.