Depending on the level of study being undertaken sampling design and requirements range from straightforward to more complex full geometallurgical style programs. opportunity assessments utilise current site domainGeological, statistical or spatial groupings used for modelling.s as a basis for generating a simple testing matrix. This then generates a first order result which is used to refine a second phase of testing. If separation potential is found, subsequent characterisation steps are designed to increase confidence and understanding of key response drivers. Alternatively, if no separation is found, then subsequent testing campaigns refocus efforts onto other options more likely to impact a given site.

The purpose of the grade by size testing is to define if specific assay elements (as a proxy for mineralogy) are preferentially deporting into specific size fractionClassified material based on specific size constraints (i.e. two specific sizes). s. This typically involves a systematic increase in finer fractions. assays from a series of size fractionClassified material based on specific size constraints (i.e. two specific sizes).s for each sample are used to generate Response CurveCurve generated by plotting response factors across sizes.s. A mathematical function is fitted to individual curves to generate a Response Ranking (RR) - a single number used to describe the magnitude of a Response CurveCurve generated by plotting response factors across sizes.. Response Rankings are used as inputs into Grade Engineering process simulation. Testing can be carried out at drill coreCylindrical "intact" rock taken for geological and metallurgical characterisation., blast holeCylindrical hole used to load explosives into unbroken material. chip or RC - though both these methods tend to provide less robust data most probably due to the impact or percussion impact nature of the breakage - or mill feedMaterial entering a predetermined system. production scaleTrials run at or near the size required for an operation. although there are obviously transforms required to compare different scales.

 

Drill Core Sampling

grade by size testing can be carried out using coarseSubjective term for the larger sized component of feed residues generated by crushing during routine laboratory assay preparation as a precursor to pulverisation. Many projects/sites routinely store coarseSubjective term for the larger sized component of feed residues specifically for future testing or check assaying. In this case stored coarseSubjective term for the larger sized component of feed residues can be used for cost effective grade by size testing. Stored pulps are not suitable for grade by size testing as the material is too fine.

Intrinsic rock characteristicsGeneric term for material properties. can be measured using a range of tools available (e.g. core scanning devices, visual logging etc…) pre breakage and then linked to subsequent separation characteristics to aid in model development.

Specific samples should be selected to ensure coverage of both relevant domainGeological, statistical or spatial groupings used for modelling.s and production years.  As a guide to commence a study, each domainGeological, statistical or spatial groupings used for modelling. as defined by the resource modelDigitised model of the deposit. is a good statrting point. Ideally each domainGeological, statistical or spatial groupings used for modelling. should have at least 10 samples included in the first round of testing.

In many cases drill coreCylindrical "intact" rock taken for geological and metallurgical characterisation. testing is the only method to evaluate future ores/domainGeological, statistical or spatial groupings used for modelling.s in the mine plan, unless they are exposed in the current mine workings.

 

crushing Protocols

crushing protocols for coarseSubjective term for the larger sized component of feed residues vary between sites and companies. The protocol is capable of being replicated in almost any onsite lab, and all commercial laboratories.  It requires no special or unique methodology or equipment.

The prime purpose of coarseSubjective term for the larger sized component of feed residues is to reduce the size of a drill coreCylindrical "intact" rock taken for geological and metallurgical characterisation. sample to a particle size distribution that is statistically suitable for splitting  off a fraction which can be used for fine pulverising prior to chemical assaying. A typical top size for coarseSubjective term for the larger sized component of feed residues is 99% passing -3.35mm or the equivalent #6 mesh. This is sometimes expressed as 80% passing 2mm.However, very little quality control on the particle size distribution of coarseSubjective term for the larger sized component of feed residues is generally carried out. particle size distributions are a function of the crusher gap setting, size of the initial drill coreCylindrical "intact" rock taken for geological and metallurgical characterisation. and hardness of the rock. Crusher gap settings in particular can vary between laboratories or drift over time.Within limits this variability does not affect use of coarseSubjective term for the larger sized component of feed residues for grade by size testing. However, it is necessary to establish actual particle size distributions for site specific coarseSubjective term for the larger sized component of feed residues as part of an initial evaluation program in order to select optimal sieve sizeSize based classification method for paticulate matter (e.g. 100mm, 10mm 1mm etc…).s for routine testing. Mass of specific sieve size fractionClassified material based on specific size constraints (i.e. two specific sizes).s is also monitored during routine testing before samples are sent off for grade by size assaying to provide a qa/qcQuality Assurance, Quality Control flag for samples that show unusual mass distribution that may not be suitable for grade  by size testing.The key overriding decision point on sieve sizeSize based classification method for paticulate matter (e.g. 100mm, 10mm 1mm etc…). selection is generation of the minimum number of data points to define a statistically meaningful Response CurveCurve generated by plotting response factors across sizes. and Ranking. This requires a minimum of three sieve sizeSize based classification method for paticulate matter (e.g. 100mm, 10mm 1mm etc…).s (generating four size fractionClassified material based on specific size constraints (i.e. two specific sizes).s) that cover the cumulative mass range as shown.
 
For an initial orientation program it is recommended that 5 sieves are used generating six size fractionClassified material based on specific size constraints (i.e. two specific sizes).s. An example is shown below.

 

Bulk Sampling Options

In Pit or Stockpile Meso Sample

This method can be used as a guide to determine the "real world" response of the RR from run of minePost blast material in the load/haul cycle. ore.  Note the sample is NOT fully representative of the rock mass to be sampled, and will contain a bias that is unquantified at this stage.

The actual method to be deployed will vary to the equipment and resources available, but may follow the below as a guide.  It is reccommended to sample minimum of 500-600kg with small loader, escavator or bobcat  (or 2 x 44 gallon drum equivalent) and upto 4-5 tonnes at the maximum.

Sample WILL be biased as the method will likely avoid rocks >200-300mm.  However it is relatively easy to collect and process and will provide initial guide to natural deportment response.  Second stage representative bulk sampling can be completed later, if initial test work warrants follow up

 

Laboratory Screening

Meso Sample

At either the onsite lab, or a commercial lab the sample needs to undergo preparation for screening, weighing and assay.  The method will vary from location to location.  As a guide the below method has been utilised several times, with the ability to process approximately 100 meso samples in 2 weeks on site.

• Transport sample to onsite/offsite lab
• Dump sample onto a large tarp for contamination purposes, and ease of retaining the finesSubjective term for the smaller sized component of feed
• Several technicians manually screen entire pile manually with sequentially reduced sized Gilson screens
• Finer fractions screened with RoTap in the lab
• Initial screen sizes need to be assessed but the sites prior knowledge of blasting particle size distribution should assist.  Otherwise a common starting point may be: +110mm, -110+60mm, -60+30mm and -30mm
• Weigh each fraction when entire sample has been processed
• Crush and split for assay (all material) each fraction for assay
• Multiple spliiting and reduction stages maybe required depending on starting mass
• assaying method, assay suite and repeats/duplicates etc should be determined by sites current knowledge, requirements and methods
• It may be important to assay not only for target elements, but delaterious elementsElements having a negative impact on final destinations. in case they are also upgraded (or downgraded) by metal deportment

 

Bulk Sample - Manual Preparation__

Preparation for a bulk sample is essentially the same for meso samples, but the starting sample is larger and is more represenataive of the entire PSD.

• Collect 3 to 4 tonne of run of minePost blast material in the load/haul cycle. sample collected by excavator or loader - expit or stockpile
• Dump sample onto a large tarp for contamination purposes, and ease of retaining the finesSubjective term for the smaller sized component of feed
• Several technicians manually screen entire pile manually with sequentially reduced sized Gilson screens
• Finer fractions screened with RoTap in the lab
• Initial screen sizes need to be assessed but the sites prior knowledge of blasting particle size distribution should assist.  Otherwise a common starting point may be: +110mm, -110+60mm, -60+30mm and -30mm
• Weigh each fraction when entire sample has been processed
• Crush and split for assay (all material) each fraction for assay
• Multiple spliiting and reduction stages maybe required depending on starting mass
• assaying method, assay suite and repeats/duplicates etc should be determined by sites current knowledge, requirements and methods
• It may be important to assay not only for target elements, but delaterious elementsElements having a negative impact on final destinations. in case they are also upgraded (or downgraded) by metal deportment

Commercial Gilson Screen (or equivalent)

This sample preparation is effectively the same as a meso sample however with some modifications.  They key difference is the use of a large Gilson Screen (or equivalent) to remove the manual labour.  Size is generally limited to several 100's kilograms.

 

• Top screen size is generally 100mm.  Visually remove oversizeMaterial above a specific size (generally used to define material that is retained on a screen deck). manually
• Sequentially fed balance through Gilson in smalerl batches
• Trays emptied and material stockpiled as required
• Repeat until entire sample processedInitial screen sizes need to be assessed but sites knowledge, but approximately +110mm, 110 - 60mm, 60 - 30mm and -30mm
• Weigh each fraction
• Crush and split for assay (all material) each fraction for assay
• Multiple spliting and reduction stages maybe required depending on starting mass
• assaying method, assay suite and repeats/duplicates etc should be determined by sites current knowledge, requirements and methods
• It may be important to assay not only for target elements, but delaterious elementsElements having a negative impact on final destinations. in case they are also upgraded (or downgraded) by metal deportment

Note: This process is readily available in commercial laboratories.   It is reccommended to closely supervise all sample preparation methods as the preparation is labourious.  CRC ORE has found "short cutting" has been an issue on several occassions where supervision is lacking.

 

Bulk Sample - Custom Jig

CRC ORE  has built and supervised a custom screening JIG that has proven to be effective and efficient.  All parts are generally available on most mine sites. It is particlarly effective when utilised for screening the sub-samples collected by either loaders or excavators from a mobile jaw crusher as discussed below.

 

• Collect appropriate sized sub-samples in free fall from a mobile crusher
• Collected by either excavator (preferred - less sample bias) or loader (potential sample bias)
• Standard screens maybe sourced from a screening deck that are commonly used on site for roadbase and/or stemmingGravel used to pack the top of blast holes to confine explosive energy.
• A topsizeLargest size material in a feed stream. screen maybe welded up from re-bar if standard screens are not available
• Requires appropriate sized collection box for final finesSubjective term for the smaller sized component of feed at the bottom - or a heavy duty tarp for subsequent collection
• Spacers are required for each screen
• Material fed in 50-100kg batches onto screen jig
• Manually shake/roll screens
• As screens fill transfer topsizeLargest size material in a feed stream. material directly into a storage container, and smaller "middling" fractions into double bagged sample bags
• shovel finesSubjective term for the smaller sized component of feedt fraction into bags and clean up with dustpan & brush to ensure all material is collected
• Weighing, crushing and assay is as per above methods

 

 

 

Manual Belt Cuts

 meso scale belt cuts can also be obtained from production conveyors.  meta data relevant to the sample should try and be captured where possible, such as the source dig blockA predefined spatial zone designated as extracted within a particular shift., truck number or shovel.  This allows sample characterisation to be matched to ore types or domainGeological, statistical or spatial groupings used for modelling.s.

Consideratyions that need to be taken into account are;

1. Sample meta data - eg: Are samples from 1 source (trucks or shovel) or blended sources.  Single sources are preferable.

primary crusher – Normal operating mode should be maintained and close size setting confirmed

1. Sampling at the conveyor after primary crushing
2. If in a crushing line/system a grizzly screen is present before the crusher, the following considerations need to be considered before sampling:
   1. Sample truck should try to skip the grizzly screen, and try to dump straight into the crusher. Only if operational and safety protocols permit.
   2. If Grissly screen can not be skipped, sampling can go ahead with screen in place only if Grissley screen is not scalping or separating more than 2% of the total material. If the Grissly scalps less than 2% then the material not sampled is minimal and should not effect preliminary studies.
   3.  If Grissly screen scalps more than 2% of the material, then that specific crushing line can not be utilized for sampling, or consideration needs to be given to rock breaking the oversizeMaterial above a specific size (generally used to define material that is retained on a screen deck). for sampling purposes.  The need to sample the oversizeMaterial above a specific size (generally used to define material that is retained on a screen deck). is less critical for ortientation studies, but becomes increasingly relevant for operational deployment studies.

 

Identify the following meta data details before dumping at the primary crusher for testing:
     - What region and polygon is the truck load coming from.
     - Expected tonnage of truck
     - Expected rock typeGeological classification of material into discrete groups.
     - Expected average grades for elements of interest.
     - truck ID, time of dumping, and final destination of material.

If practical ensure conveyor belt has no material from other truck load before sample truck dumps on primary crusher, or feedMaterial entering a predetermined system. 3-4 trucks of same material to "flush" the system.
Once sample truck load dumps on primary crusher and material is visible on at least 10 meters of conveyor belt, stop conveyor belt.  Isollation and sampling practices should be developed and followed according to sites requirements.
Take upto 3 samples as in the figure (e.g. Sample A, Sample B, Sample C) from conveyor belt, with a spacing of at least 1.5m between samples. Sample mass should be calculated from sampling theory according to particle sizes, metal distribution and sampling constants if known.

After samples have been taken, the rest of the truck load passing through the crusher can continue to its original destination without further interruptions.

• Each sample should be of around 1m (or more) of conveyor length. Each sample will have a weight between 200 to 400 kg.
• Ensure that 100% of the sample is collected (finesSubjective term for the smaller sized component of feed and coarseSubjective term for the larger sized component of feed) of the conveyor belt cross section.  Use a broom and dustpan for final clean up.
• As significant effort is required to stop and sample on the main conveyor it is reccommended to take 3 x coarseSubjective term for the larger sized component of feed "duplicates" from the same sampling station.  This allowes for;
  • Primary sample for natural deportment testwork
  • Secondary duplicate (or "near duplicate" as a true duplicate is not acheivable) for repeatability if required
  • Tertiary sample kept in reserve for follow up testwork and/or geomet synergies
• Repeat this process for every truck sample

crushing, sub sampling and assaying should follw one of the sample preparation methods discussed above.

 

Bulk Sample - Screen Deck Option

Bulk or small pilot trial options can be completed using a Mobile jaw crusher and a Screen Deck.  The below image provides a pictorial guide.

While suited to larger trials, and 100% of the sample is screened thus reducing the potential for bias, this method can be difficult for orientation studies due to the large sample masses generated.  As 100% of the sample is seperated into size fractionClassified material based on specific size constraints (i.e. two specific sizes).s, subsequent sub sampling of each pile is then required.  The sub sampling method can then re-introduce substantial bias risk through partcile segregation on the stockpile cone, as well as biased sampling through mass reduction in the subsample.

 

 

Bulk Sample – Mobile Crusher Option

The below discusses a methodolgy to subsample directly post mobile crushing.  Sampling via an inverted excavator bucket is the prefrerred option as it reduces the bias potential due to the ability of the excavator to make a single direction radial pass through the stream in freefall.  Sub sampling by using a loader bucket to pass into the stream (either front on or side on) introduces bias potential as not all the rock stream is collected into the buccket for the same amount of time.

The below image provides a pictorial guide.