AA Assay

[Geowizard]

Accuracy and precision;

Accuracy;

When we make a measurement, the accuracy of the measurement is controlled by the quality of the instrument used to make the measurement. An example is a ruler. A ruler is an instrument used to measure distance. A poorly ruled ruler from a low cost discount store is not as accurate as a machinist's ruler. A low cost, poorly designed AA spectrometer can be expected to have minimal accuracy. In comparison, a laboratory quality AA spectrometer will cost more and be more accurate because design details include close tolerance, accurately machined optics and electromechanical subassemblies. Accuracy is specified as "Tolerance" and is defined as plus or minus a certain value of emission or Absorbance. The end user may not require accuracy and therefore, a low cost AA spectrometer may be adequate. In a scientific research application, obviously the importance of accuracy becomes a priority. GOLD prospectors need reasonable accuracy in order to make decisions on GO or NO-GO with respect to developing a prospect into a GOLD mine. Whether investment comes from personal resources or an outside investor, the data that is used to support the process of making a good investment decision requires accuracy in the data.

Precision;

When we measure a quantity like voltage, we might use a hand-held voltmeter. A low cost Digital voltmeter might have a display that shows three digits. Most measurements are considered "good" if the precision is to three digits. An application where we are measuring the voltage on a car battery is a good example. We know the voltage should be 12 volts in general terms. If we measure 12.8 volts, the measurement has sufficient precision that we can make a judgement call on the condition. An expensive voltmeter may have five or more digits. In certain applications where very small differences in voltage make a big difference, an equally precise measurement is needed. Prospecting for GOLD can be as simple as "Lookie here... I found a Nugget" or it can involve measuring the weight of milligrams of GOLD on an analytical Digital scale with great precision.

- Geowizard

[Geowizard]

Where AA is useful;

If a GOLD prospector or miner has a sample that needs to be assayed, it's important to know what the preferred method of assay is!

Most importantly, AA is useful for identification of WHAT the different elements are in a given sample. If the prospecting objective is GOLD, then the AA system can be set up for GOLD and a routine process put in place to prepare samples for analysis.

How much?

The AA method of assay applies to very small amounts of GOLD or other metals in a sample. AA assays are useful for measuring from 1 part per billion (ppb) up to 30,000 ppb or 30 parts per million. Samples having higher parts per million can be diluted to concentrations that fall within the required range.

Note: 30 grams of GOLD in one Metric Tonne = 30 parts per million. That's roughly one troy ounce per Tonne.

-Geowizard

[Geowizard]

Silver Assays;

From my experience, silver is more abundant than GOLD and usually a prospector will be looking for large amounts of Silver compared to GOLD. The amount of Silver needed to be of economic value is subject to the same variables as prospecting for GOLD. The cost of mining and related expenses have to be offset by the value of the silver present in the deposit. For small scale silver mining, values of silver must be in the range of ten to thirty troy ounces per metric Tonne or more based on $16 per troy ounce prices.

A silver assay, by economic necessity must involve silver values greater than one troy ounce per Tonne.

Dilute samples can be assayed by AA methods for identification and to a limited extent for the amount of silver present.

Sulfide ore;

Most often silver is contained in rock types that include sulfides including Lead Sulfide (Galena). Other mineralization commonly seen is combinations of Copper Sulfides with silver in sulfide form.

Sulfide minerals require "roasting" to burn off the sulfur. Because a pyro-metalurgical process is involved, and considering that a pyro-metallurgical recovery will be required for recovery, a pyro-metallurgical method of assay will obtain a result that is consistent.

- Geowizard

[Jim_Alaska]

Silver Assays;

From my experience, silver is more abundant than GOLD and usually a prospector will be looking for large amounts of Silver compared to GOLD. The amount of Silver needed to be of economic value is subject to the same variables as prospecting for GOLD. The cost of mining and related expenses have to be offset by the value of the silver present in the deposit. For small scale silver mining, values of silver must be in the range of ten to thirty troy ounces per metric Tonne or more based on $16 per troy ounce prices.

A silver assay, by economic necessity must involve silver values greater than one troy ounce per Tonne.

Dilute samples can be assayed by AA methods for identification and to a limited extent for the amount of silver present.

Sulfide ore;

Most often silver is contained in rock types that include sulfides including Lead Sulfide (Galena). Other mineralization commonly seen is combinations of Copper Sulfides with silver in sulfide form.

Sulfide minerals require "roasting" to burn off the sulfur. Because a pyro-metalurgical process is involved, and considering that a pyro-metallurgical recovery will be required for recovery, a pyro-metallurgical method of assay will obtain a result that is consistent.

- Geowizard

Good post Chuck, I don't think that many weekend prospectors know much about Silver, or even bother to look for indicators.

[Micropedes1]

I have a confirmed gold placer located. It is a minor deposit. But my problem is the same as Geowizard; I cannot determine the lode source. It doesn't help that I am searching in the vicinity of a major fault zone. So, the lode may actually be displaced from the gold that I have found.

In the meantime, I am confirming many conductive zones with minor deposits of copper, lead, and zinc. These representative ores are fairly easy to spot and identify. Silver ore, on the other hand, is difficult for me to identify. If all looks like a common rock to me, hence the AA testing.

[Micropedes1]

Due to the extremely remote location that I am prospecting, a silver strike would need to be inordinately rich to be profitable. I do not know of ANY mine that processes silver ore on site. Instead it is usually shipped to a smelter in large quantity. This location would prevent that. So, this is just an exercise in futility. I was merely curious about the rock's composition.

I will, however, continue to sample and analyze.

[Geowizard]

Silver is easy to refine;

If it's native silver, hand sort and ship it. If necessary, crush and run it through a sluice to concentrate.

Silver sulfide; Roast it to burn off the sulfur, Leach the oxide with HCL and precipitate the silver chloride to pure silver metal using lye and sugar. Silver can also be cemented out to pure silver metal using iron or copper or... ran through an electrowinning cell. Electrowinning is also a separation process that yields byproduct GOLD as mud on the bottom of the tank.

Complex ore may need to be smelted in extreme cases.

Spanish Explorers smelted silver ore in primitive furnaces in Arizona. The ore was crushed, mixed with charcoal and made into mud patties.The patties were placed in a clay furnace and the furnace was sealed off to reduce the silver to metal. Tons of this silver was shipped back to Spain.

- Geowizard

[Micropedes1]

How about a flotation cell or standard leach process like we use for gold? I know that complexing agents can complicate this process, especially sulfides. There ought to be a reliable process (with a small footprint) that recovers both gold and silver at the same time. Or at least reduce the volume of ore to a more easily transportable quantity for off-site refining

[Micropedes1]

Sluice silver ore? Am already dealing with hematite and ilminite while dredging. When your sluice box loads up all the riffles with that stuff, the gold just skates on thru

[Geowizard]

Spectral lines;

The interesting feature of AA spectrometers is the fact that metals other than GOLD can be identified. Each atomic element has characteristic spectral lines that are unique the that element. There are online resources that show the spectral emission lines produced by each element.

GOLD:




A Heated Graphite Furnace can create a plasma arc. The sample preparation is simplified to crushing a sample and placing a small amount in a graphite sample holder.

- Geowizard