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Kalassay GroupPerth - Kalgoorlie - Leonora

a member of the Inspectorate group of companies

Kalassay Fire Assay

Traditional

and

Fully Robotic!


• The particular fire assay method we are

discussing here is aimed only at

measuring

Gold and Precious Metals

• Variations of Fire Assay can be used for

other metals, however, in most

instances other analytical methods are

favoured

Fire Assay


Many methods have been developed and refined over the years,

but “Fire Assay” remains a favoured method for determining the total gold

content of a sample.

In this method, a pulverised mineral sample is dissolved using heat and fluxing

agents

Precious metals are extracted from the melted material using molten Lead.

The precious metals are then separated from the Lead in a secondary process

called “cupellation”.

The gold content of the precious metals collected is then determined, using a

variety of analytical techniques.

Fire Assay- Background


The beginnings of Fire Assay can be traced to finds in Troy II (2600B.C.) where

very pure silver was being produced by cupellation

Biblical references to the use of fire assay techniques can be traced back to the

prophet Moses 31:22,23 (approx 1300B.C.)

2000 years ago, the Romans used an amalgamation and heat process for Gold

recovery

In the middle ages, Agricola wrote “De Re Metallica”(1550) - the first and foremost

textbook on fire assaying

From that time, fire assay has been used and further refined as an analytical

methodSource: US Geological Survey Bulletin 1445

Fire Assay

- History


• Fire Assay is essentially used as a technique for extracting the gold from a geological sample

• The gold is then put into solution, using chemical and heat digestion methods

• Very sensitive, high-tech analytical equipment, is then used to determine the level of gold in the solution

• The amount of gold in the solution is then back-calculated, to indicate the amount present in the original sample

Fire Assay Today

So ancient technology, centuries of refinement and modern instrumentation combine to give us a very

powerful analytical tool


• Soil Samples

• Exploration Drill Samples

- RAB

- RC

- Diamond Core

• Grade Control

• Mill Solutions

• Tailings

Fire Assay- Applications

Pictures courtesy Barra Resources


• Sub-sampling & Catch-weigh

• Fluxing

• Firing

• Cooling & Separation

• Cupellation

• Parting & Dissolution

• Analysis

Traditional Fire Assay Method

(After Sample Preparation)


• A measured sub-sample (the sample charge) is taken from the pulverised sample

• The charge is mixed with a measured amount of specialised flux, which contains many components including Lead and Silver.

• The flux components are varied to suit the composition of the sample being treated. This is done to ensure that a successful fusion is achieved.

• The charge and the flux are thoroughly combined by mechanical agitation

• Blanks, repeat samples and standards are introduced into the batch at this stage

Fire Assay- Fluxing


• The flux/charge mixture is loaded into a fire assay crucible (referred to as a “pot”), ready for “firing”

• The pots are loaded into a reducing furnace and are subjected to a temperature of1100 C for approximately 50 minutes

• This allows the flux and mineral sample to fuse and form a “melt”

• During this process, the Lead, Silver and Gold present in the melt combine

If a fusion fails in some way, the assayer must diagnose the problem

and vary the method to overcome the problem

– this demands great skill

Fire Assay- Firing


• The melt is poured out of the pot into a mould

• The Lead / Gold alloy settles to the bottom of the mould and solidifies as a metal “button” as the mass cools

• The lighter fractions (i.e. Silica) solidify on top of this button as a glassy layer

• The solidified mass is removed from the mould, exposing the button

• The button is recovered and the glassy slag is sent to waste

Fire Assay- Cooling


• The Lead/Gold alloy button is placed on a small cup-shaped

receptacle called a “Cupel”

• The Cupel is loaded into a small oxidising furnace and subjected to

1000 C for approximately 50 minutes

• During this time the Lead is absorbed into the cupel, leaving behind a

small ball-shaped particle called a “Dore Bead”

• This bead is made up of Silver and precious metals including Gold

Fire Assay- Cupellation

Lead Button in

fresh Cupel

awaiting firing

Hot Cupels

removed

from

furnace

Cupel after

firing

showing

Dore Bead


Fire Assay Digestion

• The Dore Bead is put into a test tube and the

Silver is “parted” from the bead using Nitric

Acid. The Silver is then held in solution.

• Hydrochloric Acid is added to solution, forming

“Aqua Regia” This very powerful acid mixture

dissolves the Gold into solution


Fire AssayInstrumental Analysis - AAS

• Acid digest solution is subjected to AAS analysis

• Level of Gold determined by measurement of atomic absorption in the Gold wavelength

• Detection level Gold by Fire Assay / AAS method= 0.01ppm

• Results captured and collated on LIMS

• Results analysed by use of QA/QC controls:

Duplicates for Reproducibility

Blanks for Contamination

Standards for Bias

• Authorised data sent to client


Fire AssayInstrumental Analysis – ICP-OES

• Acid digest solution is diluted by computer-controlled dilutors and then subjected to analysis by ICP-OES instruments

• ICP-OES has the advantage of being able to analyseGold and other elements such as PGEs in one reading

• Results compared to known and verified standards

• Results captured and collated on LIMS

• Detection level Gold by Fire Assay / ICP-OES method = 0.01ppm

• Lower detection limits, down to sub-ppb available by other methods / instruments


Fire AssayLow - Level Gold

• Fire assay is also a very useful technique for ppb-level

analysis. Fire assay allows us to produce very good

values for Gold and PGEs

• The process followed is the same as standard fire assay,

but after the bead digest stage, the solution is subjected

to analysis by Inductively Coupled Plasma Mass

Spectometry (ICP-MS)

• ICP-MS is a very sensitive, very sophisticated instrument.

Three of the latest generation of these instruments are

located in the Perth Assay Laboratory.Agilent 7500 ICP-MS

at Kalassay’s

Perth Assay Laboratory


Robotic Fire AssayKalassay is investing heavily in automated systems

for Sample Preparation and Analysis.

The Fully Robotic Integrated Sample Preparation and Fire Assay System in

Kalgoorlie is a prime example.

Robotics offer superb consistency and maximum control over all aspects of the entire

process from sample preparation to final analytical result.

This system takes a

4kg sample and

through a series of

processes first

produces a pulped

sample and then a

fire assay result –

without human

physical

involvement!


Robotic Fire Assay 2

• This first of Kalassay’s robotic systems is a fully robotic

integrated Sample Preparation and Fire Assay Facility, at

the Kalgoorlie Assay Laboratory

• This system will be capable of taking a large, coarse

sample and taking it through all stages of preparation and

analysis to the production of final results without being

touched by human hands

• Robots are used to transport the sample from one

automated stage to another

• The whole process is controlled and monitored by highly

sophisticated computer systems under the control of highly

experienced, qualified analysts.

• All standard Kalassay Q.A./Q.C. protocols are incorporated

into the process


Results Reporting• Results captured and collated on LIMS

• Results analysed by routine utilisation of control samples:

Duplicates for Reproducibility

Blanks for Contamination

Standards for Bias

• Authorised data sent to client Results of analytical work are normally

reported by e-mail to a list of recipients authorised by the client

• Various report formats are available, but the overwhelming favourite is .csv

as this is readily imported into most databases

• Our Laboratory Information System (LIMS) is able to publish QA / QC data

at the same time as the job results, allowing real-time data verification.

• Results are also available in hard copy on request


Customer Focus

The Kalassay Group operates solely within the mining industry, offering

analytical services to mining exploration companies from all over the world

Our future is inextricably connected to the mining industry and we participate

in many industry organisations and initiatives

Our aim is to meet and exceed our client’s expectations at all times

We tailor our service to match client needs

We are always looking for ways to extend and improve our services

Got a challenge? – Come to us!

Got a problem? – Come to us!


• On-line Sample Submission

• Analytical Batch Information

• Useful Industry Links

• and The Latest Kalassay News !

www.assay.com.au

Visit us…….

on the web!


….at your service !

Perth Kalgoorlie Leonora

Assay Laboratory Assay Laboratory Assay Laboratory

Tony White Kevin Bride Wayne Turner

Ph: (08) 9250 6122 Ph: (08) 9091 7227 Ph: (08) 9037 6160

Fx: (08) 9250 6133 Fx: (08) 9091 7228 Fx: (08) 9037 6270

Em: [email protected] Em: [email protected] Em: [email protected]

www.assay.com.au

fire assay fundicion de oro

Documents

assay techniques

assay historya member

assay backgrounda member

sample charge

geological sample

pulverised sample

leonoraa member

measured subsample