Jensen Technologies, LLC
Laboratory Services
Au-Ag-PGM
Fire Assay
Effective Date: January 1, 2012
15985 South Golden Road, Unit H
Golden, CO 80401
Phone: (303) 478-3929
E-mail:admin@jensentechnologiesllc.com
Website: www.jensentechnologiesllc.com
1
FIRE ASSAYING
J-Tech and others highly recommends analysis of samples by the fire assay method to determine
precious metal content
Fire assaying, in use for thousands of years, still stands the test of time. Jim Steinberg in Mining Artifact
Collector principally takes the following summary of the process from “Assaying,” The article was written
from a historical viewpoint, but the process is the same as the fire assaying of today except for the use of
electronic balances, mechanical pulverizers, and so forth.
In Webster’s dictionary assay is defined as follows: in metallurgy, the determination of the quantity of any
particular metal in an ore or alloy; especially, the determination of the quantity of gold or silver in coin or
bullion.
While the most common definitions of the word assay do revolve around the determination of gold or
silver in ore or alloys, assay is itself a much broader subject that involves the quantitative analysis of
chemical substances both organic and inorganic. The primary interest of this article is the assay of
metalliferous ores. Because even this is a broad subject that has filled a large number of books, the
highlights of fire assay by the scorification process in gold bearing samples are going to be summarized
here.
Initially, the sample must be reduced to a powder so that it can be tested. This powder is often called
“pulp” and the scales to weigh it are called “pulp scales.’ The assayer begins by running the sample
through a crusher. With many crushers, the fineness of the output is adjustable. The sample is still not
sufficiently fine after initial crushing, so the assayer then puts it onto a “buck board” for further
pulverization under a muller that rubs the material into a finer state with a sliding motion. Harder samples
are made finer using a device called a “rocker” that uses a heavier weight upon the sample being
pulverized. Assayers doing a smaller volume of work might use an iron mortar and pestle, although it
requires considerably more effort.
As the pulverization of the ore sample proceeds, the assayer mixes and then divides the sample into
smaller and smaller portions until he has reduced the amount of the sample to the size that he will
actually process (Splitting). This can be done manually or by using devices designed to assist in the
sampling process. This is done to assure uniformity within the sample and to increase the accuracy of the
assay to be performed.
When the sample has been sufficiently pulverized it must be run through sieves of the appropriate size.
Material that does not pass through must be further ground until the entire sample will pass through the
sieve (Sieving). What has passed through the sieves must then be carefully mixed and then stored in a
marked container. The contents of these containers should not be shaken or agitated as this can cause
the materials to begin stratifying according to their masses and upset the accuracy of the process.
From various parts of the container (Cone & Quartering), selected portions of the sample are taken and
weighed. The weighed sample is then placed in a scorifier, a dish that can sustain the heat of the
assayers oven. Along with the sample litharge (a form of lead), various chemicals that will assist in
allowing the metals in the sample to separate from the slag are included.
This mixture is roasted in the assayer’s oven (Assay Furnace) until the melted slag completely covers the
lead bead that forms in the scorifier.
The sample in the scorifier is next poured into the cup of the scorification mold. Here it is allowed to
remain until it is cold. Once cold, the sample is removed from the mold. It is cone-shaped, with the metal
at the apex of the cone and the slag forming the bottom. The metal part, or lead button, is detached from
the slag. This button may then be hammered into a cube with no sharp corners. The button is placed into
a cupel of appropriate size that is then placed in the furnace. Cupels are comprised of a material called
bone ash. When it has come up to heat, the button is placed in the cupel. In this process lead and other
impurities within the button are both oxidized and driven into the material of the cupel itself a good cupel
is capable of absorbing its own weight in litharge (the lead in the sample). The metal in the cupel melts
and will be observed to become smaller as the process proceeds.
2
Towards the end of the process, the surface tension of the metal will draw it into the shape of a bead.
The bead will appear to be in rapid motion and at the moment the process is complete, an optical energy
release will sometimes be visible as a “flash” or “blick.” At this point, the cupellation is complete and the
cupel with its bead may be removed from the oven.
Now the bead is removed from the cupel. The composition of the bead should now be gold and silver.
The bead is weighed in a type of scale made specifically for this task called a button scale. Button scales,
because they are measuring something so small, must also be very accurate and are thus always
enclosed, while analytical or pulp scales do not always require enclosure. Weighing the bead has shown
how much metal is there, but has not told how much is gold and how much is silver.
The next step of assaying is called “parting.” In this step the gold and silver are separated from each
other by solution. The weighed bead is flattened, placed in a porcelain capsule and treated with a solution
of water and nitric acid. Once reaction begins, the capsule is warmed. Silver in the bead forms a solution
of silver nitrate that is carefully washed away until only the gold, if any, remains. This is gently dried in the
porcelain capsule and then removed.
The final sample of gold is again weighed in the button balance, unless it is too small to be weighed, in
which case it is simply described as a “trace” or “color.” From the weight of this bead the assayer will then
calculate the gold and silver ore value per ton of ore. The assayer may use a special set of assay ton
weights when weighing the gold to more easily calculate the assay value of the ore.
In Summary, Fire Assaying is a three-step process:
Fusion - The sample is mixed with flux, and then heated to 1095 C. A slag containing the unwanted
elements and a lead button containing the gold and silver are formed.
Cupelling - The lead button is heated and oxidized in a bone ash cupel that adsorbs the lead oxide,
leaving a precious metal bead in the cupel.
Parting and Weighing - In this part of the process, the gold is separated from the silver. Two weighing
steps are involved.
Discussion of Fire Assaying’s Purported Problems
Fire assaying is a series of chemical steps that takes advantage of the precious metal’s chemical
behavior. Those who claim they have non-fire assayable gold are saying they have a substance that
chemically does not behave like gold. Arguments used to explain why fire assay is not applicable to their
“Colloidal” or “Micron” gold generally falls into one of the three categories discussed below.
“The particles are so small they vaporize and so are not in the button.” 1063° C is below the melting point
of gold. Even if the temperature goes above this, the vapor temperature of gold is 2808 C. So very little
is lost. H2O, for example, has vapor pressure 6 orders of magnitude higher.
“Small particles of gold float on the surface of water so they float on the slag.”
This ignores the process that goes on. It is not dependent on gravity. The Pb02, now Pb, dissolves the
gold. It is the Pb that collects at the bottom of the crucible. “Interfering elements mask the gold.”
The London Mint ran an assay of 1000 mg tellurium, I g Au, 25 g Pb and skipped the fusion step! Even so
the “worst” they could do was to lose about half the gold. These conditions are highly unlikely in a rock
sample. What about the platinum group metals? These, if present, report with the gold in the bead.
3
Conclusion
Fire assaying, in use for thousands of years, still stands the test of time.
Reprinted and edited from the Arizona Department of Mines and Minerals Resources website.
Fire Assay Procedure (General)
Classification of ores:
Using a 100 X shop Microscope, carefully examine and classify the ore according to the amount of
silicates, sulfides, and lead that it contains.
Class I: High in silicates and carbonates:
Has no oxidizing or reducing power. If an appreciable amount of silicate, such as quartz, is present giving
the ore a glassy or vitreous luster, do not add more silica or glass (borax glass) to the basic flux used.
Quartz (Si02) is the strongest acid in its molten state.
Class 2: High in sulfides, carbonates and lead:
If the ore is rich in sulfides (pyrite, galena, tellurides, sulfur, etc.), it should first be ground, then roasted.
Place it in a roasting dish and roast in an oven until all of the sulfide fumes are driven off. If the ore
contains only a small amount of sulfides, these can be removed by placing a 16d (penny) steel nail in the
crucible with the assay. If low in lead, add an additional 12g of litharge to the standard flux.
Class 3: Iron, manganese, etc.
Assay Procedure
• Examine ore and adjust flux as explained, then pulverize as finely as possible, at least 100 mesh
(finer the better).
• Weigh out one assay ton, 29.2 g (1/2 AT or 14.58g) of ore, mix thoroughly with appropriate amount
of flux and place in a 20g or 30g crucible. This is your assay.
• If sulfides are present, roast ore or use niter with the charge.
•
Place the crucible in the furnace and turn to high heat. When the furnace reaches 1095°C. Note the
time or set a timer. The assay must remain in the oven at this temperature for 60 minutes.
• Remove the crucible from the oven. Pour the entire molten assay into a pouring mold and allow it to
cool.
• When the assay has cooled, remove the lead button from the bottom of the mold.
• Pound the button into a cube breaking away the slag. It is all right if a little slag adheres to the
button. Brush off the button with a button brush.
• Put the button in a cupel, and place it in the furnace at 950 °C until the cupel has absorbed all the
lead. The remaining bead contains all of the gold, silver, and PGM’s in the assay.
• Examine the bead carefully with a magnifier. Its color and surface appearance will tell you
4
something about the ratio of gold/silver/PGM’s present and whether these elements should be
parted as described below.
• Weigh the bead. Each milligram (mg) in weight represents I troy ounce of precious metals in each
ton of the original ore, or: I mg = I oz/T.
Parting
If your bead appears to be relatively pure gold, no parting is necessary. If the presence a significant
amount of silver and/or PGM’s is indicated, proceed as follows:
To part the silver from the gold, the button must contain at least 3 times as much silver as gold. If it
does not, add sufficient assay silver to make this ratio. This is called INQUARTATION. Then
proceed to ANNEAL the button as follows:
Annealing
Anneal by repeatedly hammering the bead flat and heating it in a
flame until it’s red-hot. Repeat heating after every couple of blows with the hammer.
The annealed strip is then rolled into a loose coil or Coronet, placed in a parting cup and covered with a
parting solution, a mixture of chemically pure nitric acid and distilled water, 6 parts water to I part acid, or
a 6/1 ratio.
Heat the flask gently. The coronet will blacken as the hydrogen bubbles off. Do not allow it to boil too fast.
If the coronet becomes immediately black, add a little more distilled water to slow the action.
Finish
Gravimetric
Instrumental:
Flame AAS, GA-AAS
Priority Service
Routine analyses are normally completed within 5 working days. Samples arriving after 3:00 pm are logged into
our system on the following business day.
When our analysis load permits, priority services are available for an additional charge. These services do not guarantee
Results within the number of days specified as some procedures or combinations of procedures require additional time.
Priority service does insure that your samples will be prioritized over standard service samples. Priority services require
prior arrangement to insure availability. Projects requiring exceptional levels of effort may be subject to additional
surcharges.
Priority Service ----------------------------------------------------------------------------------------------------------------------- $Quote
Results are delivered by mail or email, typically within 5 working days after sample receipt.
Quality Assurance / Quality Control
We maintain a QA/QC program to assure reliable results. We have certified standard reference materials for a variety of
matrices and analytes, allowing us to provide better matching between reference material and samples. In some cases,
we have alternate methods that can be used to confirm values obtained by our standard methods. We strive to make
5
results that are very reliable, but we encourage customers to contact us if data does not meet expectations.
Since quality is very important to us, we within reason, verify results at no additional charge.
Quality control (QC) data is available as a part of your results. The data includes blanks, laboratory control
samples (LCS), matrix spikes, and associated raw data. Contact Jensen Technologies for more information regarding your
quality assurance requirements.
Duplicate Analysis
Duplicate analysts are usually charged at the normal rate of a single analysis. Some services have special rates for duplicate
(or multiple) analyses.
Special Handling
Hazardous Material Handling requires special personal protective equipment or monitoring.
6
Sample Preparation
Routine
Rock and ore: $25 for first 2 pounds (0.9 kg) + $2.50/pound (0.45 kg) for each additional pound (0.45 kg).
Includes splitting and pulverization to –200 mesh (74 μm).
This is for material ¼ inch or less.
Crushing: Greater than 3/8 inch material $25 for first 2 pounds (0.9 kg) + $2.50/pound (0.45 kg)
for each additional pound (0.45 kg).
Wet Gravity Concentration
RP-4 Gravity Table
Tabling: $50 plus $2.00 / Kg ($1.00/lbs) 1 Kg. = 2.2 lbs.
200 lbs = $50 + $200 = $250
100 lbs = $50 + $100 = $150
Introduction
Global Mining Solutions is dedicated to producing the ultimate gravity concentrating
equipment on the world market. Combining the world’s most used and successful gravityconcentrating table, with a “unique” reverse polarity magnetic separator, achieved this.
"Designed for hard rock gold mines, placer gold deposits, or heavy mineral separations.
Spinning rare earth magnets are placed underneath the deck surface of concentrating
shaker table. Reversing the magnetic polarity of magnetite at about 800 cycles per minute
(Elliptical polarization of the magnetite) magnetite will rise to the surface of the feed
material and will be washed into the tails by the transverse flow of wash water. Magnetite
has the ability to create more magnetism than the applied magnetism and will align their
magnetic poles with each other in long chains. This basic concept was invented by Darvin P.
Wade and has revolutionized placer concentrating equipment and the minerals
concentrating equipment.
An ABS plastic (truck bed liner material) one piece molded riffled deck and launder tray is
incorporated into the RP-4 gold shaker table. RP-4 shaker concentrating tables will process
up to eight hundred pounds or more per hour (average 400 lbs. black sands) of sand sized
feed with little or no loss of gold. Four hundred pounds of river gravel with a maximum size
of 3/4" inch can be processed when using a submerged deck screen. With the factory
installed deck screen the RP-4 gold separating table will operate as a shaker screen, a
magnetite separator and gold gravity concentrator. The submerged deck screen is just one
of many new and innovative techniques incorporated into the new line of heavy mineral
concentrators.
gravity concentrators will recover 99% of microscopic gold from your magnetite
concentrates and is designed to run continuously ". We have users claiming the heavy
mineral concentrators are saving down to one micron. Competitive tests with drum
magnetic separators, spiral separators, concentrating bowls, gold centrifuges, vanners,
micron tables, static charges, etc., prove the RP Gravity Concentrating Tables to be superior
in speed, recovery and economics. (Reduce tons to pounds, without losses).
RP-4 mineral concentrating tables are factory designed with a raised riffle for maximum
recovery of micron sized gold and platinum metals.
7
RP-4 gravity concentration tables weigh 60 lbs. and require about 8 to 14 gallons of water
per minute. Table comes equipped with a 1/2 HP motor and uses 8.6 amps. "1/3 HP motor
is optional at 6.8 amps.
Precious Metals Au-Ag-PGM Fire Assay, Instrumental
Flame Atomic Absorption Spectrometry (AA)
Gold (Au) Flame AA-Aqua Regia
Palladium (Pd) Flame AA
Platinum (Pt) Flame AA
Silver (Ag) Flame AA-Aqua Regia
Silver (Ag) Flame AA-PPVD (HNO3-HCl-HF)
Rhodium (Rh) Flame AA
Cyanide, Ag Hot Cyanide AA
Cyanide, Au Hot Cyanide AA
$50
$50
$50
$25
$25
$50
$50
$50
Graphite Furnace Atomic Absorption Spectrometry (GF-AAS)
Ruthenium (Ru), GF-AAS
Gold (Au), GF-AAS
Silver (Ag), GF-AAS
Platinum (Pt), GF-AAS
Palladium (Pd), GF-AAS
Rhodium (Rh), GF-AAS
$50
$50
$50
$50
$50
$50
Fire Assay (FA)
8
Au, FA, Gravimetric, 15g
Ag + Ag, FA, Gravimetric, 15g (inquart)
Au, FA, GA-AAS, 15g
Ag, FA, GA-AAS, 15g
Au Pt Pd Rh, FA, GA-AAS, 15g*
Au Pt Pd, FA, GA-AAS, 15g*
*Au, Ag, Pt, Pd, Rh, Ru GA-AAS, Tellurium Coprecipitation Collection available
Microscope Digital Photos of FA Prills
$50
$50
$50
$50
$100
$75
$250
$25/Sample
The minimum charge is $50 for Fire Assaying
9
ORDERING INFORMATION
GENERAL
Please, complete either our Analysis Request Form, (photocopy the form on page 11.) or supply the
following information on your company's stationery:
1. Purchase Order Number.
2. Reporting and billing addresses.
3. Reporting phone number, FAX number and/or email address
4. Street address for sample return.
5. Sample I.D.
6. Analyses requested.
7. Information about the chemical structure and physical properties of all samples submitted for analysis
8. The expected levels and required detection limits of requested analytes
9. Any hazards associated with the samples
10. Sample disposal information (see below)
Samples arriving after 3:00 pm. will be logged into our system on the next business day. Jensen
Technologies reserves the right to refuse to receive or analyze samples that are deemed to be unsafe to
handle in our facilities or for any other reason.
SAMPLE QUANTITY REOUIRED
Except for some physical tests, 100 grams of sample are typically an adequate amount for most analyses.
Check with Jensen Technologies to verify the sample quantities and/or handling required for analysis.
.
ANALYSIS REPORTS
Analysis reports are normally sent by e-mail. Upon request, reports will be provided by telephone, hard
copy, or FAX at no additional charge. Inquire about other reporting formats.
All results are held in strict confidence. Results will be released to a third party only when authorized by
the original client.
QUOTATIONS
Written quotations are available to secure pricing for projects and special analyses. These quotations are
valid for 30 days unless otherwise noted.
.
SAMPLE STORAGE, RETURN and DISPOSAL All samples remain the property of the client
Any unused portion of a sample will be returned unless the client certifies that the sample can properly be
disposed of in the municipal waste system (landfill or sewer). A fee of $3.00 per sample (minimum $10.00
per order) will be billed for all returned samples.
A minimum $50.00 surcharge will be added to orders requiring special packaging and labeling as
hazardous materials.
Samples are normally held for 30 days after reporting. Perishable samples will be returned to the
customer or discarded after allowed holding times have elapsed.
10
PRICING POLICY
It is the policy of Jensen Technologies to set prices at a fair and equitable level for quality analytical
services.
While we attempt to maintain the listed rates, the prices are subject to change without notice. Specific test
methods and pricing may not be applicable to all sample types. In these cases the customer will be
notified and, if appropriate, a special price quotation will be provided.
DISCOUNTS
Discounts may be available for large quantities of samples.
Contact Jensen Technologies for more information.
TERMS
Payment for services must accompany order unless credit is arranged.
PAYMENT
We accept cash or check for payment of services.
11
Jensen Technologies, LLC Assay Lab
Website: jensentechnologiesllc.com
15985 South Golden Road, Unit H
Golden, CO 80401
Cell: 303-478-3929 E-mail: admin@jensentechnologiesllc.com
Sample Submission Form
Please include this form with samples (please print)
Today’s date:
Project No:
Purchase order number:
Date results are required:
Project Name:
Price:
Company information (or include business card)
Company name:
Contact for report:
Phone number:
Fax number:
Street address:
P.O. box:
City:
State:
ZIP Code:
Description of work requested
Sample #
Matrix
Sample/Reference description
(used in final report)
Analytes
1
Au
Au, FA, 15g Grav
2
Ag
Ag, AAS-PPVD
3
EDXRF
30
elements
Sample
Prep
4
Cost/Sample
$
50.00
25.00
75.00
25.00
5
Number of Samples:
Date Received:
reporting
(standard turnaround for results are 5 working days after receipt of sample)
 No report
X Standard turnaround
Disposition of samples after analysis
 Discard samples after 3 months
X Return samples after analysis
Forward samples on to:
Include Contact:
* Extra charge
Authorization Signature:
Received Payment of $
rendered on
___/___/___
for services
_______________________________
Carl M. Jensen
Payment for services must accompany order unless credit is arranged.
12