Mining Geology 405 Drilling and Sampling

1. Mining Geology 405Drilling and Sampling Joanna Hodge Centre for Exploration Targeting

2. Overview Drilling Techniques Drilling Equipment Downhole Surveying Sampling

3. Drilling and Sampling Important mineral exploration procedure Delineate subsurface conditions Expensive Number of techniques Tests ideas and theories developed during prospect and target generation LOCATES AND DEFINES ECONOMIC MINERALISATION

4. Drilling Techniques 3 main techniques used in Goldfields RAB (Rotary Air Blast) RC (Reverse Circulation) Diamond drilling

5. Rotary Air Blast (RAB) Cheapest Least penetrative (~100m) Geochemical sampling to base of regolith (ie only penetrates weathered cover over fresh rocks) Uses compressed air to break ground Air pumped down through drill rod Cuttings blown up hole between rod and hole wall Single barrel technique

6. Advantages Cheap Fast Large sample volume

7. Disadvantages No fresh rock samples Limited depth No structural data Contamination

8. RAB – single barrel technique, air blown down centre of rod tube, sample is blown to surface along narrow space between rod string and side of hole – Contamination! RC – dual tube system – air passes down hole between outer and inner tube, sample is returned to surface through inner tube – no contamination, determine exact location of samples Diamond – circular diamond bit rotating at v high speed cuts a cylinder of rock. Core enters core-barrel located behind bit and prevented from falling back into hole by core lifter. Core barrel holds three metres of core; when full device called overshot lowered down hole, attaches on to core barrel and it is returned to surfaceRAB – single barrel technique, air blown down centre of rod tube, sample is blown to surface along narrow space between rod string and side of hole – Contamination! RC – dual tube system – air passes down hole between outer and inner tube, sample is returned to surface through inner tube – no contamination, determine exact location of samples Diamond – circular diamond bit rotating at v high speed cuts a cylinder of rock. Core enters core-barrel located behind bit and prevented from falling back into hole by core lifter. Core barrel holds three metres of core; when full device called overshot lowered down hole, attaches on to core barrel and it is returned to surface

9. Reverse Circulation (RC) Moderately priced Good penetration (to ~350m) Samples fresh rock Dual barrel technique High pressure fluid forced down outer pipe and returns chips to surface up inner pipe

11. Advantages Relatively cheap Quick Large sample Uncontaminated

12. Disadvantages Limited access No structural data Sample contamination below water table

16. Diamond Drilling Expensive Greatest penetration Whole rock samples

17. RAB – single barrel technique, air blown down centre of rod tube, sample is blown to surface along narrow space between rod string and side of hole – Contamination! RC – dual tube system – air passes down hole between outer and inner tube, sample is returned to surface through inner tube – no contamination, determine exact location of samples Diamond – circular diamond bit rotating at v high speed cuts a cylinder of rock. Core enters core-barrel located behind bit and prevented from falling back into hole by core lifter. Core barrel holds three metres of core; when full device called overshot lowered down hole, attaches on to core barrel and it is returned to surfaceRAB – single barrel technique, air blown down centre of rod tube, sample is blown to surface along narrow space between rod string and side of hole – Contamination! RC – dual tube system – air passes down hole between outer and inner tube, sample is returned to surface through inner tube – no contamination, determine exact location of samples Diamond – circular diamond bit rotating at v high speed cuts a cylinder of rock. Core enters core-barrel located behind bit and prevented from falling back into hole by core lifter. Core barrel holds three metres of core; when full device called overshot lowered down hole, attaches on to core barrel and it is returned to surface

18. Advantages Maximum geological information Uncontaminated High quality sampling

19. Disadvantages Expensive Slow Small sample size Extensive site preparation and water supply required

20. Appropriate Drilling Methods RAB Early exploration First pass and infill drilling RC Intermediate exploration Delineate ore body Grade control Diamond Late stage Structural controls

21. Drilling

22. Directional control Important to survey RC and Diamond holes to ascertain exact position of underground features Rod strings can deviate significantly and do not travel straight. Inaccurately surveyed holes can lead to large discrepancies in the actual location of an orebody Surveying is undertaken down the drillhole by a single-shot camera to record dip and azimuth every 30-50m during drilling, or after drilling is completed by a gyro If surveying indicates that a drillhole is deviating significantly off course, the driller can take remedial action. Draw diagram Orientation of drill hole wrt dip and azimuth v important. Rod string not rigid, therefore attitude can change with depth – deviation. Holes usually flatten (downward drilling pressure) and swing right (direction rods turn) but not always. Deviation often influenced by dominant foliation (bedding or cleavage)Draw diagram Orientation of drill hole wrt dip and azimuth v important. Rod string not rigid, therefore attitude can change with depth – deviation. Holes usually flatten (downward drilling pressure) and swing right (direction rods turn) but not always. Deviation often influenced by dominant foliation (bedding or cleavage)

23. Sampling & Sampling Theory “Good sampling is like religion – everyone believes in it, but few practice it.” Sampling results are estimates made within bounds of precision (repeatability) and accuracy (lack of bias)

24. A Sample Representative part or single item from larger whole Taken for purpose of inspection Evidence of quality Part of statistical population whose properties are studied to gain information about the whole By definition have two elements Typicality Smallness

25. Problems, Bias Variable geological environments Erratic metal distribution High unit value of precious metals exacerbates error Low cut-off grades requires greater care when sampling Sampling provides basic data for subsequent resource and reserve calculations Grade control errors can be costly Discuss Variable geological environments – what is the missing material? Soft, friable or soluble? How would the missing material impact on the analysis? Oxidation, surface leaching and secondary enrichment, contamination from external sources. Density contrasts ie in chip samplesDiscuss Variable geological environments – what is the missing material? Soft, friable or soluble? How would the missing material impact on the analysis? Oxidation, surface leaching and secondary enrichment, contamination from external sources. Density contrasts ie in chip samples

26. Objectives Determine, minimise source of error Determine optimum sample size and density/spacing for In situ mineralisation (core, channel samples) Broken ore (drill chips, ROM material, crushed material)

27. Errors Core sample split unevenly or divided improperly Density differences in chip samples Hardness differences

28. Where biased or unrepresentative sample data can be recognised, the source of the error can be eliminated Geological bias can be taken into account by separating out sub-populations eg. zoned ore bodies, leaching or secondary enrichment Contamination should be avoided by good sampling methodology Human factors? Different samplers or procedures Fraud

29. Errors

31. Overall Error Estimation OE = AE+S(FE+GSE+DE+EE+PE) OE = overall estimation error AE = analytical error (lab precision) FE = fundamental error (in situ variability) GSE = grouping & segregation error (broken ore, drill chips) DE = delimitation error (sample site selection) EE = extraction error (sample selection) PE = preparation error (lab prep) =S(contamination error + sample loss + chemical/physical alteration + human mistakes + fraud)

32. Coefficient of Variability The higher the CoV, the more difficult ore grade estimation is 1.0 – 1.5 good precision 1.5 – 2.0 fair precision > 2.5 high imprecision – treat with caution

33. Ore Deposit Classification Type A: Simple geometry, low CoV Simple geometry, simple grade distribution, eg coal, iron, bauxite, nickel laterite Simple geometry, complex grade distribution, eg, disseminated copper, gold stockworks, Witwatersrand gold

34. Ore Deposit Classification Type B: Complex geometry, simple grade distribution, low CoV Base metal deposits

35. Ore Deposit Classification Type C: Complex geometry, complex grade distribution, high CoV Lode gold deposits – Yilgarn! Sampling procedures must be tailored to the style of mineralisation

36. Sample size Required sample size depends on: In situ concentration of ore mineral In situ grain size of ore mineral Other factors that apply specifically to broken or crushed material

37. Rules of Thumb Sample size limited by physical and economic constraints Bigger is better If samples are poor, then get lots of samples

38. Why Grade Control How much ore is going to the waste dump? How much waste is going through the mill? Important to eliminate dilution Even more important not to throw away your ore!

39. Grade Control Carried out routinely at all mine sites to evaluate ore distribution in the pit, or underground Variety of methods used – in open pits commonly RC drilling. Blast holes also logged and assayed. Drilling carried out on fixed pattern to a set depth, unlike exploration drilling Depth determined by size of bench being mined; usually covers two benches at a time. Samples usually only analysed for limited element suite eg. Au only in gold mine, however this is a site-specific decision.

42. Next Week Geological logging Geotechnical logging Ore deposit models Summary and review