Sampling technique for ore minerals
- 1. Sampling
- 2. Sampling
- 3. Physical and chemical data collection PHYSICAL CHEMICAL Sample location (Grid position, BH survey) Sample preparation and analysis Collection (Representativeness, Reliability) Repeatability, Bias Bulk, Drilling, Channel, Splits Bulk density (moisture, spatial variation)
- 4. Sampling • A sample is defined as a representative part or a single item from a larger whole, being drawn for purpose of inspection or shown as evidence of quality • If enough representative units of a larger over all population are selected without bias, the average value of the units will approximate that of the total population
- 5. BIAS • bias is systematic favoritism that is present in the data collection process resulting in misleading results. Reasons for BIAS: • Erroneous sampling equipment • Sampling technique • Analysis
- 6. Sampling Equipment • Rotary fluid circulation • Hand Auger • Rotary air blast • Air Core • Reverse Circulation • Diamond
- 10. Rotary fluid circulation • Rotation and hammering • Hammering action cuts material down the hole • Air drives the hammer and also work as coolant • Air is also the sample collection medium • Samples are collected at the collar
- 11. Rotary mud water circulation • Water or oil based polymer or clay suspension Advantage • Can hold unstable borehole Disadvantage • Liquid remove cuttings and heat at far lower volume and velocity then air
- 14. Augers
- 15. Types of Rotary Percussion Drill Advantages •No air loss • Clean sample • Efficient Disadvantages • No geological info Side wall contamination Insufficient air blast can cause loss of sample Mixing of two samples
- 17. Advantages Info about geological structures Logging information Info can be stored in form of cores Retains 95 % of information Disadvantages Core losses are mainly in mineralized area Expensive (120$/m)
- 22. Bulk density • Immersion method ------Weight in air------ Weight in air – Weight in Water
- 23. File design and data input • Data must be organized for ease in – Storage, retrieval and handling • Assay data must be accompanied by – appropriate geologic data e.g. – rock type, characteristic of mineralization, alteration etc – Location (3D co-ordinates) • Information can be stored in multiple files • Mandatory fields in data are: BHID, X,Y,Z,assay
- 25. Datafile types – Data is usually made available via a series of drillhole data files eg. • Header file specifying X,Y,Z of collar • Downhole survey information • Downhole grade information • Downhole geolgical information – This data is then converted into XYZ spatial data for use in resource estimation
- 26. Collar File – Structure & contents – Specifies information about the co-ordinates of each hole: • Hole ID • X, Y, Z co-ordinates of hole collar • Length of hole Hole ID X Y Z Depth 1 2674708 392931 3953.9 640 10 2657591 416910.5 3924.9 222 11 2655999 408777 4198.6 300 CX76 12 2660619 406345 4116 260 CX76 14 2664904 407109 4077.4 260 CX76 15C 2657160 413217 4182.8 240 CX76 02 2670888 396889 3964.9 240 CX76 20 2660564 399681 3770.7 360 CX76 21 2664876 395180 3694.6 337 CX76 23C 2664692 395477 3703.2 320 CX76 27C 2661528 392852 3751.7 337
- 27. Data Editing • For smaller datasets: – Check sample values and locations against original docs e.g. geologic maps, cross sections, etc • For larger datasets – Errors in location of drill holes – Geologic coding of samples – Recognize outlier values through histograms, prob plot, scatter plots
- 28. Collar File – What to check – Are the holes in the correct location? • Visual inspection by plotting hole positions on plan • Check Z co-ordinate against topography • Generate a top model using drillhole co-ords and compare with topography • Check co-ordinates with original survey sheets – Co-ordinate systems • UTM, local, other grid basis? • Has a rotation been used? Correctly? • Possibility of confusing X & Y co-ordinates
- 29. Datafile structure – Survey File – Provides information on the survey measurements taken at regular intervals down the hole – Usually supplied via a distance From – To basis • Hole ID • Distance down the hole from which and to the survey is taken • Azimuth and dip of each survey Hole ID From To Azimuth Dip 1 0 640 0 -90 10 0 222 0 -90 11 0 300 0 -90 CX76 12 0 260 0 -90 CX76 14 0 260 0 -90 CX76 15C 0 240 0 -90 CX76 02 0 240 0 -90 CX76 20 0 360 0 -90 CX76 21 0 337 0 -90 CX76 23C 0 320 0 -90 CX76 27C 0 337 0 -90
- 30. Survey File – What to check – Is each hole ID present in collar file? – Check for missing/overlapping from-to’s – Does last survey position exceed end of hole? – Confusion of dip & azimuth nomenclature (-90 down etc) – Have different types of surveying methods been used? Are they valid? – Spot check survey readings with drillers logs etc
- 31. Datafile Structure – Grade File – Provides information on the assay values taken at given intervals down the hole – Usually supplied via a distance From – To basis • Hole ID • Distance down the hole from which and to the assay is taken dh From To mst ash btu sul Na 0001C 84.5 86.5 20.68 3.13 10198 0.83 8.2 0001C 86.5 92.5 21.85 3.31 9917 0.32 7.26 0001C 92.5 98.5 23.51 2.37 9681 0.15 8.77 0001C 98.5 104.5 25.36 2.08 9549 0.1 9.72 0001C 104.5 110.5 26.02 2.39 9520 0.13 9.21 0001C 110.5 117.5 25.2 4.26 9457 0.54 9.67 0001C 117.5 123.5 24.44 4.5 9584 0.63 4.38 0001C 123.5 125.5 27.15 2.28 9406 0.2 6.9 0001C 125.5 127.5 26.46 2.42 9521 0.19 11.28 0001C 127.5 133.5 24.8 2.87 9717 0.2 8.38 0001C 133.5 141.5 22.6 3.77 10068 0.26 4.05
- 32. Grade File – What to check – Is each hole ID present in collar file? – Check for missing/overlapping from-to’s – From exceeds to distance? – Does last sample position exceed end of hole? – Zero values • Missing value?, Grade of 0.0?, What do they mean? – Blank characters • What do they represent?, Missing?, Value of 0.0? – Values out of range – Spot check values against assay certificates • 10% of total database • 5% of highest & lowest values
- 33. Datafile Structure – Geology File – Provides information on the down hole geological contacts – Usually supplied via a distance From – To basis • Hole ID • Distance down the hole from which and to each geological interval is noted dh From To Code 0001C 84.50 123.50 UAD 0001C 123.50 150.00 LAD 0001C 150.00 162.70 Waste 0002C 23.00 65.00 PAD 0002C 65.00 115.00 UAD 0002C 115.00 200.00 LAD 0001C 200.00 210.00 Waste
- 34. Geology File – What to check – Is each hole ID present in collar file? – Check for missing/overlapping from-to’s – From exceeds to distance? – Does last sample position exceed end of hole? – Blank or missing codes? Non-Printing characters? – Does interpretation make sense when drillhole sections are produced?
- 35. What Else? – Transcription errors • Hand written sheets often difficult to read • Electronic transfer preferred • What is the possibility that something has gone wrong? – Do drillhole contacts agree with geological model? • Snap to drillholes • Do proportions of geological units in drillholes match those in the geological model?
- 36. Summary – Database checking may seem laborious and time consuming, but done as data is collected and processed, it avoids potentially serious flaws in the resource estimate being uncovered later, when they are significantly more expensive to correct. – A ‘clean’ database is an essential part of the resource estimate and it should be given the highest priority. – Always check data back to original source and document any changes & assumptions