EXPLORATION DATA, DOCUMENTATION AND THE SCIENTIFIC PROCESS
John Horton
AIG Friday Seminar Series, Brisbane, 21 August 2015
Mineral Resources: from Exploration Targets to Ore Reserves‘Critical methods and case studies to maximise your dollar spend’
Documentation
The long time frame to bring an exploration project through to development means that most projects have • old data and • may or may not have current or modern datasets
Documentation is the key element to providing confidence in the resource database and should• Describe the processes• Record changes in process• Record targets, assumptions, checks and analysis• Preserve documents and SOPs• Summarise each phase• Pictures
Exploration Data
Exploration Inputs• Surface sampling
‐ pits, trenches, rock chips etc
• Drilling• Trenching• Underground sampling• Mapping• Geophysical surveys• Structural data• Analysis• Conceptual models• Interpretations
Data types• Point data ‐ assays• Line data ‐mapping• Orientation data• Grid data – imagery, geophysical profiles
• Block data – reconciliation, bulk samples
• Reports, manuals, file notes
Exploration Data
Data styles• Quantitative
• Assays
• Semi‐quantitative • Geophysics
• Qualitative• Geology logging
What to use
Need to consider under JORC what data to • Use• Discard biased, not usable, irrelevant• Consider insufficient, not precise• Adjust not accurate (biased)• Calculate fill in missing values using correlations
Infer from limited data
Quanitative Data?
ICP vs ICP
0
125
0 125
ICP
Lab
2
ICP Lab 1
LRE
0
5
10
15
0 5 10 15IC
P La
b 2
ICP Lab 1
Al2O3
The word “science” comes from the Latin “scientia,” which translates as “knowledge.”
Scientific Method• Observe• Question• Hypothesize• Test• Predict or repeat
Scientific Principal
Question Assumptions
Can sample types be mixedCan sample orientations be biasedSuitability and robustness of sampling/measurement methods
Question:What is the maximum expected recovery for drill core?
Avoid Preconceptions
Most hard rock geologists have a preconception of the maximum possible diamond drill core recovery is 100%
Avoid Preconceptions
Wet laterites are wet and in places supersaturatedLimonite zones as comprised super fine goethite claysThese combine to create zones of solid plasticine to toothpaste consistency materialDry drilling to recover coreNow water circulationNot removal of cuttings
Avoid Preconceptions
When saturated the laterite is not compressible There is nowhere for cuttings to go but into the core barrelThe difference in the outer and inner core barrel diameters provides a new maximum recovery expectation
Avoid Preconceptions
HQ bitInner diameter = 52 mm area = 163 mm2
Outer diameter = 64 mm area = 201 mm2
Area of outer over inner 123%
Avoid Preconceptions
Pacific Example: Rock Type From To Recovered
Length Recovery Core Size
Limonite 0.0 0.5 0.33 66% 46
Limonite 0.5 1.0 0.53 106% 46
Limonite 1.0 1.5 0.47 94% 46
Limonite 1.5 2.0 0.70 140% 46
Limonite 2.0 2.5 0.47 94% 46
Limonite 2.5 3.0 0.64 128% 46
Limonite 3.0 3.5 0.67 134% 46
Limonite 3.5 4.0 0.67 134% 46
Transition 4.0 4.5 0.57 114% 46
Rock 4.5 5.0 0.40 80% 35
Rock 5.0 5.6 0.51 85% 35
Regular core recovery of 125% or greater can be achieved for HQ core drilling
QAQC
Generally well done for assaying and perhaps sampling and may be 25% of the assaying
Poorly done for • Survey & DTM resurveys• Down hole survey regular checks & resurveys• Density alternate methods
Surveys
Collars record locations for• Planned• GPS as drilled• Survey & survey method• If needed manually offset twins/redrills
General survey• Resurvey some locations regularly for QAQC• Compile all survey data including resurveys• Survey more than just collars, particularly man made disturbance
Down Hole Surveys
Record magnetic bearings• Store original magnetic bearings• Correct for magnetic declination later
Magnetic declination• Varies across the country right down to local scale• Local geology can alter local magnetic declination• Assumptions may vary between geologists/operators
Density
Basics• Specific Gravity (SG) is not Bulk Density (BD)• BD includes pore spaces in‐situ• Assayed grades pertain to dried samples• Hence resource estimates require dry bulk density (DBD) which
relate to the in‐situ volume interpretation• Moisture content (MC) is also important for mine planning• Most field density measurements are wet resulting in wet bulk
density (WBD)• Unless oven dried to also derive dry bulk density (DBD)• You can always derive the third component of MC, DBD, WBD if two
are available
DensityBD is derived from weight and volume or relative weights
Method classes
• Direct Measure the core volume with callipersMeasure the pit volume with sand
• Displacement Measure the displaced core/sample volume with water or sandEither directly or by the weight of the water/sand
• Archimedes Based on the relative weight of the sample in air and immersed in water
DensityProcesses• Ensure adjustments for any material used wax, plastic, wires, trays etc• SOP and take photos• Environment risks – wind, level, dry• Whole core• Record the method used• Record all measurements in the database
Issues• Sample selection bias• Bubbles• Cavities• Adjustments and variability of materials and conditions• Absorption• Contaminating the samples• Sample loss• Systematic and consistent
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