Sample Preparation

The range of geological samples includes soils, silts, lake and stream sediments, rock, rock chips, drill core, percussion drill samples, panning concentrates and vegetation. Many of these sample types may be large, wet and heterogeneous. The purpose of sample preparation is to produce a smaller, dry and manageable sample suitable for laboratory scale analysis while at the same time ensuring that the prepared sample is homogeneous and fully representative of the original field material. A reduction of particle size through crushing and pulverizing is required for rock and drill core materials whereas it is usually sufficient to sieve soil and sediment samples to obtain suitable material for analysis.

It is essential that a geological sample be properly prepared prior to analysis. At ALS we have always maintained that a poorly prepared sample is simply not worth analyzing.

The risk of sample contamination is greater in the sample preparation process than in any other section of the laboratory. It is essential that a clean work environment be maintained through the enforcement of good work practices. Routine cleaning of workstation surfaces and crushing and grinding machinery is essential as is the use of a comprehensive dust control collection system.

Over the years ALS has developed its exclusive, patented Dustbox technology to ensure efficient extraction of dust during the sample preparation process. This technology provides sufficient extraction to avoid cross contamination of samples, while at the same time avoiding over-extraction of fine material. You can see the Dustbox in operation at all of our sample prep laboratories around the globe.

One essential feature of ALS operations is our insistence on sample classification and sorting according to sample type and expected metal concentrations. In this way we can separate high grade and low grade samples and reduce chances for cross contamination. Separate process lines are also maintained for high and low grade samples to minimize the effects of carryover within the sample preparation machinery. You, the client can help this process further by making note of any expected high grade material in the relevant boxes on the Sample Submission Form

Introduction

Geological samples are highly variable and encompass a broad range of sample types that includes soils, silts, drill core, rocks and panning concentrates. The purpose of sample preparation is to produce a small, dry and manageable sample suitable for laboratory scale analysis while at the same time ensuring that the prepared sample is homogeneous and fully representative of the original field material. Experience has shown that the potential risk for contamination is greater in the sample preparation process than in any other part of laboratory operations. For this reason particular care and attention must be paid to sample handling and there must be strict adherence to standard operating procedures and good work practices. The physical plant facilities must be designed for an orderly workflow, possess sufficient crushing and grinding equipment to allow for specialized usage, and have a comprehensive dust control system.

Sample Tracking System

ALS has developed a unique sample tracking system that is an integral part of the company s new Laboratory Information Management System (LIMS). This system utilizes bar coding and scanning technology that provides, for the first time by any laboratory, complete chain of custody records for every stage in the sample preparation and analytical process.

Upon receipt of samples at any of the ALS worldwide locations, a bar code label is attached to the original sample bag. This label is then scanned and the weight of sample recorded together with information such as date, time, equipment used and operator name. The scanning process is repeated for each subsequent activity performed on the sample from sample preparation to analysis through to the storage or disposal of the pulp and reject material. Sample labels are also scanned at the shipping and destination locations whenever samples are transported locally or internationally between ALS facilities. The system has also been designed to accept client supplied bar coded labels that are attached to the sample bags in the field.

The benefits to our clients of this system are:

• Complete traceability of the sample through the entire laboratory process.
• Sample integrity is guaranteed by scanning the sample label at every stage.
• Record of every sample weight submitted to the laboratory from the field.

Contamination Control during Sample Preparation

We take many steps to minimize the risk of cross contamination between samples during the preparation process. One of the most important steps is to sort and classify samples according to matrix type and expected metal concentrations as soon as they enter the laboratory. The samples will then be routed through the laboratory in different batch streams. Physically separated areas are maintained as much as possible so that, for example, concentrates and vegetation samples would never be processed in the same area.

Once samples are classified, they are prepared using equipment that has been designated for certain matrix types and expected metal concentration ranges. Equipment is color-coded and numbered so that it is clear for which sample type it is intended to be used.

In addition, our routine operating procedures call for the use of barren wash material to clean out sample preparation equipment between batches of submitted samples, drill holes (if identified) and samples that appear to be of a substantially different type than those submitted in the same batch. However, if the client expects significant mineralisation, we recommend that they identify the samples and request a clean wash between samples. The wash material is tested for the elements of interest prior to use in the laboratory, and on a routine basis once in use.

Our Dustbox dust extraction system is a key component of our sample preparation laboratories. The Dustbox ensures that crushing and grinding equipment is virtually completely enclosed. Our experience has shown that the fine dust, which can otherwise collect, will invariably

contain trace amounts of gold and base metals. The end result is an improved dust control system which reduces the risk of sample contamination and provides a healthier workplace environment for our employees.

It is unfortunate that all grinding surfaces impart some degree of metal content to samples during pulverisation. As a result, there will always be some degree of contamination when crushing and grinding procedures are used. However, at ALS we have a great variety of grinding surfaces that vary widely in their chemical composition. We offer equipment made of hardened manganese steel, chrome steel or carbon steel as well as non-ferrous materials such as zirconia and tungsten carbide. Hence an Explorer can choose one of these options in such a way as to eliminate the possibility of contaminating a sample with an element of potential exploration significance. In the following table is a typical chemical composition for a Chrome Free and Chrome Steel Pulveriser bowl. More information on this topic follow in the Contamination Introduced by Sample Preparation Equipment section.

Sample Preparation Equipment

The main equipment in use at ALS consists of:

• Drying ovens • Crushers (roll, traditional jaw and oscillating jaw)
• Pulverisers (small ring, large ring, flying saucer style puck)
• Ball mills • Screens
• Riffle splitters, and Rotary splitters

Drying Ovens

The sample drying process is more critical than may appear at first. Many samples arrive at the laboratory sopping wet. Drying time for these samples is invariably a major contributor to lengthened turnaround times. Hence it would be tempting to improve turnaround time by using blast furnace drying techniques. However there is a considerable risk to sample integrity by taking such an approach in that some samples will appreciably oxidize at higher temperatures (especially sulfides) and some potentially volatile elements (arsenic, antimony, mercury; all key pathfinder elements for gold exploration will be lost at elevated drying temperatures. Of course, even if these elements are not of immediate interest, the samples will be rendered useless for any future analysis.

At ALS we use two different drying temperatures and once again the choice of temperature depends on the sample classification. For rocks, rock chips, drill core and other "coarse" material with a relatively low surface area, we employ a drying temperature in the range of 110-120 C (230-250 F). Independent studies of these sample types have shown that the potentially volatile elements will not be lost at this temperature. However for soils, silts, sediments and other "fine" materials with a proportionately higher surface area, we limit the drying temperature to 60 C (140 F).

Our ovens are all large, gas-heated forced air furnaces; samples are pre-loaded onto moveable drying racks before being rolled into an oven. This avoids the potential contamination risk that is inherent in fixed shelving units. Large samples are placed into stainless steel trays to ensure efficient heat transfer and minimal drying times.

Crushers

In recent years improvements have been made to the traditional jaw crusher by the introduction of the oscillating jaw crusher. These new crushers, built specifically for laboratory usage, provide enhanced crushing by ensuring that the sample receives continuous grinding as it passes between the plates. The end result is a finer product in a single step, typically >50% is -1mm whereas only about 10% is -1mm in the traditional jaw crusher. These new crushers are also much easier to clean and therefore chances of cross contamination between samples are reduced.

Pulverisers

At ALS we use ring pulverisers. Ring pulverisers have become the industry standard in recent years. Basically they consist of a bowl that contains either a small puck and one or more rings, or a large saucer. Crushed samples are added to the bowl, the bowls are sealed and then subjected to centrifugal force by mechanical action. The puck and/or ring(s), being free to move inside the bowl, subject the sample to considerable grinding action, resulting in a very fine sample. Bowls are manufactured in different sizes ranging from 50 g capacity to 4 kg capacity. At ALS we use two sizes primarily, 250 g and 3 kg. The bowls themselves are made of different materials including manganese steel, chrome steel, zirconia and tungsten carbide so that it is easy to avoid contaminating a sample with an element of potential interest.

Screens

Screens are used to sieve soil samples in order that the fine fraction can be analyzed. At ALS we use stainless steel screens with stainless steel or nylon mesh depending on the application. Brass screens are a potential source of contamination for both copper and zinc, especially if the sample contains hard, abrasive particles.

Contamination Introduced by Sample Preparation Equipment

The intense grinding action produced by crushers and pulverisers results in wear metals being added to the samples being ground. The elements that are added will depend on the composition of the grinding surfaces. The concentration of the elements added is harder to determine as it will depend on a number of factors including the hardness of the grinding surface, the hardness of the sample and the length of grinding time.

Before putting any new sample preparation equipment into use we perform tests using ultra trace methods to ensure no significant amounts of elements are imparted to the samples being prepared.

The table below shows typical levels of elements that can be carried over for each type of grinding medium. It must be stressed that these are typical ranges that may not apply to exceptional samples.

Sample Preparation Procedures

Crushing

Samples that require crushing are dried at 110-120 C and then crushed with either an oscillating jaw crusher or a roll crusher. Note that if the whole sample is required to be pulverized, then this condition becomes irrelevant. Crushing charges are based on the sample weight. The entire sample is crushed, but depending on the method only a portion of the crushed material may be carried through to the pulverizing stage. That amount, typically 250 g to 1 kg, is subdivided from the main sample by use of a riffle splitter. If splitting is required, a substantial part of the sample (the "reject" or spare ) remains.

Pulverising

A whole or split portion derived from the crushing process is pulverised using a ring mill. The size of the split is determined by the client based on the pulverising procedure that is selected. Split sizes for manganese or chrome steel rings are typically 250 g to 4 kg; however split sizes for zirconia rings are 100 g and those for tungsten carbide rings are only 75 g. Because of the relative lightness of these latter two materials, the size of the sample to be pulverized must necessarily be reduced to these weights in order to achieve the ALS QC specification for final pulverizing, namely that >85% of the sample be less than 75 microns (200 mesh) (see graph below ).

For those samples which require enhanced homogeneity, such as samples which are known to exhibit coarse gold behavior, intermediate pulverization of the entire sample (or a representative split) is also available.

Screening

Soil and sediment samples are typically sieved through a 180 micron ( -80 mesh) screen and the fine fraction is retained for analysis. This procedure is satisfactory for smaller (i.e. 500 g or less) samples where the exploration target is base metals. However, when gold is the exploration target, we recommend that the particle size of the minus fraction be further reduced using ring mill pulverization to > 85% - 75 microns (150 mesh) in order to obtain more reproducible gold data.

For gold exploration, many "soil" samples weigh in at several kilograms or more. In this latter case, the samples often contain larger components such as pebbles or agglomerations of clay and other material. For samples like this, we recommend that after disaggregation the sample is sieved through a -2 mm (10 mesh) screen to remove the coarse material. Following this intermediate screening, the -2 mm (10 mesh) material is then split to about 500g using a riffle screen and then sieved through a standard -180 micron (80 mesh) to obtain a minimum of 150 g of fine material. We still recommend further pulverization if gold is the exploration target, for the reasons outlined above.

Special Procedures

Vegetation and humus samples require special procedures because they are easily contaminated, difficult to reduce in particle size and awkward to homogenize. This type of sample tends to be highly variable, ranging from well-rotted humus to bits of tree trunk. Vegetation sample preparation is done in our Vancouver and Brisbane laboratories because we have special facilities available. Samples submitted to

regional offices will be shipped to the Vancouver or Brisbane laboratories and this may result in some extra shipping charges to the client if the weights or volumes are judged to be excessive.

Composites

Composite samples are normally prepared on a volumetric basis and the composite is homogenised either by: repulverisation, or; mixing the samples in vials which are mounted in dual orbiting mixers. Composites can be prepared on a weight basis if desired but the charges are greater because the labor costs are significantlyore higher.

Quality Control Procedures for Sample Preparation

QC Specifications for Crushing and Grinding

As mentioned in the Crushing and Pulverising sections, ALS does sizing test to ensure specifications for these procedures. A range of specifications are available for crushing and pulverising so that clients can select protocols that best meet their project needs. Statistics are maintained for each sample preparation workstation, permitting an assessment of all pieces of machinery. Not only does this data ensure sample preparation specifications are being met, but it also allows us to optimise the sample preparation process and helps us in the purchase of new equipment.

Sample Sequence Logs

For any sample preparation activities we maintain sample sequence logs at all workstations. These logs detail which samples have been prepared in what order and are very helpful for investigative purposes.

Pulp and Reject Policy

Materials that have been submitted for analysis are retained at our laboratories for a limited time only. The prepared master pulps are stored free of charge for 90 days from the time that we issue the final certificate of analysis. Coarse and fine reject fractions are stored free of charge for the first 90 days, except for large reject fractions (>3 Kg) which are stored for a nominal charge from day one. Monthly charges will be levied for storage of all sample types beyond the first 90 days. Instructions for pulp and reject handling can be placed in the relevant boxes of the Sample Submission Sheet as per the accompanying illustration:

We can provide reports about your pulps and rejects at any time upon request. These reports will include information about ALS workorder numbers, your project name or number, and numbers of samples. Please note that when local tipping fees are significant, we reserve the right to bill clients for the cost of disposing rejects to landfill.