EXPLORATION GEOLOGY (EVAL TECHNIQUES) Flashcards
expectations for an exploration geologists
1) Familiar with Mineral Deposit Geology
2) Understand implications of extraction on the hydrology of the mineral deposit area
3) Recognize importance of collecting geotech data as a precaution to strata control problems
4) Propose suitable mining methods
5) Assess economic viability
The basis of all geological evaluation
Sample
A scientific, selective process applied to a large mass or group (population) to reduce its bulk for interpretation purposes
Sampling
The portion of mineralized rock which are analyzed for elements of interest
Assay Portion
Parameters: Population = ________________: Sample
Statistics
The property that defines a population whose constituent units are strictlty identical with one another
Homogeneity
Mineralisation is what type of population?
Heterogeneity
Sampling methods which ensures that all constituent units of the pupulation have a uniform probability of being slected to form the sample and the integrity of sample is respected
Random Sampling
Mean
Average
Median
Middle value of an ordered sample of numerical values
Mode
Value that occurs most frequently
Variance
The measure of the spread or dispersion of values about the mean (midpoint)
Small variance - concetrated about the mean
Large - Spread out about the mean central clustering is weak
Standard Deviation
Square root of the variance
Normal Distribution
?Curve is Symmetrical and bell shaped
?Variable has a continuous and symmetrical distribution about the mean
?All three measure of central tendencies coincide
?Standard Deviation is realted to the area under the curve
Asymmetrical Distribution
?Much of Geological data
?Assymetric Cuve (Proponderance of low values with a long tail of high values - Positive Skew - nasa kanan ang tail)
?Median lies in between mode and mean
Mathematical Transformation of Skewed data to normal distribution
1) Log Normal Transformation
2) Gaussian transformation - (simulation data)
Type of statistics which specify conditions regarding the nature of the population being sampled
Parametric Statistics
Independent of nature of population and is necessary in Mineral exploration
Non Parametric Statistics
Three main steps of Sampling
1) Extraction of the samples from in-situ Minerals - involves delimitation and collection
2) Preparation of the Assay Portion - involves reduction both mass and grain size to an assay portion for chemical analyses
3) Analysis of the Assay Portion
Includes all errors in all the three steps of sampling
Global Estimation Error (GE)
Includes all error in extraction and preparation
Total Sampling error (TE)
Part of TE which is inherent in both extraction and Preparation (error in the procedures and decisions)
Selection Errors (SE)
Errors are restriced to mechanical processes used in sample reduction such as crushing, weighing, drying, grinding
Preparation Errors (PE)
Minimizing Selection Errors (SE)
1) Correct definition Sample Spacing
2) Correct definition of the Sampling Area
?Long dimension of the sample must be perpendicular to the dip of mienralisation never parallel
?Cut in plan is ideally circular, square or rectangle
?Length should penetrate the full length of the sampled area
3) Correct extraction and collection - Ideal Diamond Core Drilling
4) Correct preparation of the assay portion from original sample
Type of SE which comprises the inherent heterogeneity of the sample which also represents the irreducible minimum of the TE
Fundamental Error (FE)
Possible sources of Preparation Errors (PE)
Mga errors due to careless treatment of samples and can be caused by inasequate crushing and grinding equipment
1) Alteration due to overheating during drying (coal, sulfides of Hg, As, Sb, Bi)
2) Alteration of the the sample’s physical condition due to mishandling
3) Losses due to assay portion preparation - can be checked by consistently weighing samples at each reduction stage)
4) Sample contamination (steel chips from hammers, crushing and grinding equipments)
5) Unintentional Sampling errors (Mislabeling and mixing of fractions of different samples)
correct sampling techniques
Random Sampling
Variance of a larger sample tends to be
Smaller
Variability is (directly, indirectly) Proportional to sample volume
Indirectly (the larger the volume the smaller the variance)
Largest scree size which retains 5% of the material
Maximum Particle Size
How much should the dimenstions of the collection device be when sampling?
3X the LxWxH of the Max particle size
SAMPLING
PROCEDURE
Channel sampling
?A channel is cut in an outcrop w/ the same diameter as the core being collected
?Cut using a happer or a chisel or circular saw ACROSS the STRIKE of a mineralisation
?Cutting is allowed to fall to the floor covered a plastic sheet or sample tray from which it will be collected and bagged
?Best delimiting and extracting technique
?Provides samllest possible contribution to total error
Stratified Sampling
?Sampling relative to distinct and seaparate types of mienralisation
?Reduces Natiral Variation and variance
Chip Sampling
?Obtained by collecting rock particles “chipped” from a surface either linearly or over an area
?Rock chips from blastholes using scoops, channels or pipes pushed into heap
?Corellated with the core for corrections
?used as an ienxpensive reconnaissance tool prior to more expensive channel sampling
Grab Sampling
?Consist of already broken materials (floats)
?Handfuls or shovelfuls of Brocken rock picked at random in convenient location
?Low cost-rapid
?best used where mienralized rock as LOW VARIANCE(massive)
?Used as Quality control of mineralisation at strategic sampling points such as stope outlets and in an open pit
What is the ultimate purpose of sampling?
Estimate content by valuable constituents (mean and variance)
The few grams of material in subjected to chemical analysis
Assay Portion
After reduction of grain size by communition what happens next?
Splitting
Splitting
Step 1. Pile material into a Cone
Step 2. Flattened into a circular cake
Step 3. Repeat step 1 3x
Step 4: From the final cone, shovel material consecutively around its circumference alterantively into two separate piles
Step 5.Toss a coin to determine the new sample between the two smaller cones
Step 6: Repeat Steps 1 to 5 to further reduce weight
Cone and Quartering
A splitting technique wherein the cone is quartered and each quarter is further resuced in the same way
What should be the measure of the width of the hand or shovel
At least three times the coarsest particle sizze
How much should be the weight of the sample for assay portion?
100g
the most satisfactory of stationary instrument splitters which dive a dry sample into two equal parts
Jones Riffle
Splitters capable of separating laboratory to bulk samples and uses centrifugal force to split sample into four or six containers
Rotary Splitters
Splitter used at the drill site while having percussion or reverse cicrulation drilling
Sample Splitters
Splits samples into 70:30 or 80:20 basis
Asymmetrical Splitters
What should be done next is the observed total error in spliiting is smaller or of the same order of magnitude as the estimated total error?
Nothing should be changed in the reduction system
What should be done if the observed total error in splitting is larger?
1) Maintain the number of sampling stages but increase the mass of the sample at each separate stage
2) Increase the number of sampling stages but maintain the mass of the smaple
Densest of all common sulfide and six times that of quartz
Galena
How to control Analytical errors?
Submit Duplicate sampls and reference materials
When will pitting and trenching be expensive?
If it is below the water table
In what type of Deposit is Pitting ideal?
Lateritic Soils (Provided soil is dry)
Pitting Vs Trenching
Pitting - Square
Trenching - completed at RIGHT ANGLES to the general strike to sample over long lengths
Purpose
Quality
Reconnaissance and Exploration
Low
Resource or Reserve Estimation
High
Type of Drill
Characteristics
Auger
Light drills which can be hand held or truck mounted which have rods for spiral flights that bring soft material to the surface (Bailing)
Rotary
Non-coring method
Tungsten carbide rotatry bit
Flushes Rock Chips to the surface by drilling fluid / Mud
Not so mobile
Percussion
Hammer unit driven by compressed air imparts a series of short rapid blows to drill rods or bit w/rotary motion at the same time:
1) Down-the hole Hammer drills -
Tungsten Carbide tipped drill bit
Holes w/ diameter of up to 20 cm
Depths of up to 200 m
Drill cutting are flushed to the surface by compressed air
Truck mounted very mobile
2) Top Hammer -
Much lighter than down the hole
Diameter of up to 10cm
Depths of up to 100m
Reverse Circulation
?Air and water can be both used as the flushing medium
?Can produce both cuttings and or core
?double walled strings of drill rod
Sonic Core Drilling
?Retrieves core but without the contamination caused by drilling muds
?Uses principle harmonics to drill and case a borehole - uses a variable-frequency drill head to transmit vibration energy through the drill pipe and core barrel that allows continuous core sampling to take place
?up to 2.54 m diameter an 200 m vertical
Diamond Core Drilling
?Sample is cut by a diamon-aromored or impregnated bit
?Produces a cylinder of rock recovered from the inner tube of a core barel
Parts:
1. Drill bits -
a) Impreganted (Fine grained synthetic or industrial grade diamonds within metallic cement) - For though compact rocks such as chert
b) suface set (have individual diamonds sized by their number per carat) - for softer rocks such as limestone
2) Core barrels - as the core is cut by the circular motion of the drill it is forced up into the core barrel by the advancing drill rods.
3) Circulating Medium - Usually water is circulated down the inside of the drill rods to lubricate and cool the bit and to remove crushed and ground rock fragments from the bit surface
4) Casing - cylindical casing used to seal the rock face of the hole and provides a steel tube in which the drill string can operate in safety and prevents loss of drill strings caused by rock collapse
5) Speed and Cost of Drilling -
Capacity 2000-6000 m may be inclined from horizonal to vertical
Rate of advance is slower as the diameter increases, as the the hole becomes deeper.
What should be specified in the Drilling contract between a mining company and a specialist drilling company or contractor?
1) Conditions of Drilling
2) Amount of Work Required (Work Program)
3) Cost of Drilling
The choice of Drilling method or equipment depend upon
The experience of the project manager
If the Project Manager is unsure and the drilling conditions are not well known what should be done first?
Test Work - to compare efficiency of different drilling methods
Costs in a Drilling Contract
1) Mobilization and Transport of Equipment to the Drilling site
2) Setting up at each site and movement between successive borehole locations
3) Basic cost per meter of hole drilled
4) Optional or miscellanoue costs such as cementing holes, casing holes and surveing
5) Demobilization and Return of Equipment
What are the duties of a geologist during drilling?
1) Monitor if the drilling proceeds according to the company’s plan and contract
2) Ensure adequate core recovery and that the hole is hitting the desired target
3) Signs documents at the completion of ech shift where progress and problems are described
4) Must be familiar with teh contract and the problems that may arise at the drill site
Conducted as a matter of routine in all holes (To examine)
Borehole surveys
Used in Borehole surveys to indicate direction (azimuth) and inclination of the hole at selected intervals commonly at 100 m
Small Magnetic Gyroscopic Compass
Reconnaissance
Isolated Holes
Exploration Proper
Up to 10 km apart
Detailed Exploration
“Fenses” - lines of holes
Hole are 100-200m apart
Fenses are 200-400m apart
What should be the inclination of indidivudal holes?
Right Angles to the expected average dip of the mineralisation
Methods of Assigning zones of Influence
Mean Square successive Difference test
Correlation Coefficients
Semivariogram
During exploration and initial evaluation, primary concern is
Geological Characteristic
Estimatio of Qualiity and Quantity of the Resource Present
JORC stands for?
Australoasian Joint Ore Reserves Committee
Whats the purpose of JORC
Adopt a rigorous procedures for companies to report their resources
Increasing resource quality depends on
Increasing Degree of Geological Confidence and Knowledge
For resource to be reserve what must be met
Modifying Factors which represent Feasibility
What are the modifying factors?
1) Mining
2) Metallurgical
3) Economic
4) Marketing
5) Legal
6) Environmental
7) Social
8) Governmental 9)Infrastructure 10) Governmental
JORC Code sets what?
Standard or system for classifying tonnage and grade estimates for the purpose of public reporting
What is beyond the scope of the JORC code?
How the estimate should be done or how much data is needed to qualify in certain categories
Who makes the decision based on direct knowledge of the deposit in question?
Competent persons
In the JORC Code, what is the definition of Mineral Resouce?
?Concentration or Occurrence of Material of Intrinsic economic interest IN OR ON Earth’s crust in SUCH FORM and QUANTITY that there are REASONABLE PROSPECTS for EVENTUAL ECONOMIC EXTRACTION
What are the information needed to define/estimate/interpret a mienral resouce?
Location
Quantity
Grade
Geological characteristics and Continuity
What is a mineral resource relative to mineralsation?
Realistic Inventory of mineralisation, which, under assumed and justifiable technical and economic conditions might, in whole or in part, become economically extractable
Economically minerable part of a mineral resource hich includes diluting materials and allowance for mining losses
Reserve
When is reserve usually assessed?
Feasibility Studies (in consideratio of and modification by realistically assumed modifying factors)
Economically mineable part of an indicated resource and in some circumstances measure mineral resource
Proabable Ore Reserve
Econmonically mineable part of a measure mineral resource
Proved Ore Reserve
Readily identifiable geologic boundaries of a mineralisation which needs to be defined before resource calculations
mineralisation Envelope
