01 12.05.27 iaea conf princep compress
•
0 likes•278 views
This document discusses techniques for processing radiometric logging data to distinguish uranium mineralization from background readings. It describes modifying factors like casing, radon, and disequilibrium that must be accounted for. Deconvolution is used to determine true thickness of mineralized intervals. Calibration against known mineralization is important for converting readings to equivalent uranium grades. Comparing composite mineralized intervals to assay results allows evaluating accuracy and disequilibrium factors. Proper data processing, calibration checks, and quality control are essential for reliable interpretation of uranium grades from radiometric logs.
Recommended
More Related Content
More from Monatom Mgl
More from Monatom Mgl (20)
01 12.05.27 iaea conf princep compress
- 1. Dave Princep, Matthew Owers How to sort the mineralisation from the background – Processing of radiometric logging data IAEA Sandstone Conference May 2012
- 2. • Introduction • Modification factors • Deconvolution • Disequilibrium • Comparison to Assays • Calibration • Data processing 1
- 3. Paladin • Top 10 Uranium producer, currently 8th • 2 producing mines, Namibia and Malawi • Significant investment in exploration on 3 continents • Approximately 566Mlb U3O8 attributable mineral resources • Logging in excess of 1,000,000m per year 2
- 4. Background • The background is considered to be the counts per second read in the absence of uranium mineralisation • Instrument will register counts as a result of small but widespread concentrations of various radioelements, cosmic rays and radon in the atmosphere • The local background is dependent on the local geology (soil, basalt, granite etc.) and may vary down the hole • Background effects need to be removed prior to the conversion of counts per second to an equivalent uranium grade
- 5. Background 200 180 160 140 120 100 80 Hole 1 60 40 20 Hole 2 0 0 10 20 30 40 50 60 70 80 90 Hole 3100 4
- 6. Casing • The effect of drill casing on logged counts per second, the blue trace has been logged open hole, the red trace has been logged in rods. •Casing factors need to be determined at the start of every drilling programme and when the rod string is changed.
- 7. Radon • The effect of either gaseous or dissolved Radon within a drill hole can be both variable down the hole and arbitrary in value. • The red trace shows the drill hole as originally logged showing highly variable apparent background (both locally and along the length of the hole), the blue trace shows the hole logged at a later date. •Some drill holes are known to exhibit a diurnal variation in apparent Radon effect
- 8. Radon • Detailed view of the previous trace showing background shift due to Radon, in the red trace, at the interface with the water table. • In this case the contribution to counts per second due to Radon is between 60 and 250 additional cps.
- 9. Deconvolution • The downhole radiometric log is deconvolved prior to use in order to confine the mineralised intervals to the correct spatial position in regards to thickness . • Whilst in normal practice, radiometric logs output information in small down hole increments (usually 5 or 10cm) the gamma rays being counted come from a significantly larger area. • The result of this is that the apparent peak of mineralisation will be wider than occurs in reality. This can be seen most easily in the slope in the sides of the calibration logs – in this instance there is a very sharp, perpendicular boundary between mineralised and barren material which is not accurately honoured. •Deconvolution is a mathematical process performed on the down hole logs in order to ensure that the transitions from mineralised to un-mineralised material (and vice-versa) results in the true thickness of the mineralisation being determined.
- 10. Disequilibrium • The difference between the radiometrically derived grade and the assay grade. • Due to separation of uranium and it’s daughter products, normally due to removal of either uranium or daughters in solution. • Is considered positive when there is a higher concentration of uranium present compared to daughters. • Is considered negative when there is a lower concentration of uranium present compared to daughters. • Is spatially variable within deposits that exhibit disequilibrium. • Is normally only present where there is active re-distribution of uranium or daughter products and effect diminishes over geological time once re-distribution ceases. • Not all secondary uranium deposits exhibit disequilibrium as mineralisation may be geologically old and have reached equilibrium. 9
- 11. Disequilibrium URANIUM DECAY SERIES Soluble and transportable 240 238 U238 primary element 4.5 x 109 y URANIUM GROUP 236 1.2 m (Relatively Soluble) Pa234 234 Th 234 U234 24 d 250,000 y 232 230 Th230 80,000 y 228 226 Gaseous and easily RADIUM GROUP Ra226 MASS NUMBER 224 (98% of Gamma 1602 y removable daughter Radiation) Gas ROAC, Track Etch, Alpha Card, 222 Rn222 Alpha Tube and Emanometers 3.8 d 220 218 Po218 As218 LEGEND Stable majority gamma 3m 2s Type of Decay emitters detected by m 20 216 2 14 Bi Scintillometers, scintillometers 214 Pb214 Po214 Spectrometers, 27 m 160 s Borehole Probes y 21 212 21 0 21 0 Pb Bi Principal Gamma d 5 Emitters 210 Tl210 Po210 1m 138 d 24 d - Half lives 208 Scintillometers 206 Pb206 Instruments used Tl 206 for Detection stable 4m 204 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 ATOMIC NUMBER 10
- 12. Comparison to Assays • In order to both confirm the validity of the downhole radiometrically derived grades as well as determine if any disequilibrium is present within the mineralised body a comparison to conventionally derived assay grades is normally undertaken. • During the drilling programme a statistically representative number of samples are taken from drill cuttings (these may be RC chips, cut drill core or similar). • The samples are processed through a laboratory with all appropriate QAQC procedures maintained (duplicates, blanks, certified standards etc) in order to maintain the accuracy and precision of the results for the final comparison. • During this process material is sampled from the mineralised zones as well as the non mineralised areas either side of mineralisation (at least 2-3m). • Whilst comparisons to radiometric grades (following application of all correction factors) can be undertaken on a metre by metre basis, variations in sampled down hole position normally means this method is unreliable. • Radiometric grades and sampled intervals should be composited to the entire mineralised interval plus 2-3m either side to allow for any variation in actual down hole position.
- 13. Comparison to Assays 5,000 Comparison of gamma data 4,500 against assay values on a 4,000 metre by metre y = 0.964x basis, deposit and rock 3,500 type are known to exhibit a level of disequilibrium. 3,000 Note the scatter of data Assay 2,500 points and the lack of 2,000 correlation. Based on 511 samples. 1,500 1,000 500 0 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 Gamma 12
- 14. Comparison to Assays 5,000 The same base data but now 4,500 composited to mineralised 4,000 intervals (as deposit is layered normal additional un- 3,500 mineralised areas cannot be included in this example). 3,000 Note the correlation of data Assay 2,500 points. Minimum thickness for 2,000 a composite is 3m, average is y = 1.137x 6.39m and is based on 71 1,500 drill holes. 1,000 Additional analysis of the data 500 points to an effective disequilibrium factor of 0 approximately 1.17 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 Gamma 13
- 15. Comparison to Assays • It is unlikely that the comparison between radiometrically derived grades will be exact, however, in the absence of significant disequilibrium the basic comparison should be within 5% between the two. • This basic discrepancy may be due to a number of factors (formation factor, drill hole size issues etc) but can be normally collected together as a residual factor. • It should be noted that the comparison is between two processes that derive their values from fundamentally different sources – the drilling derived sample and the radiometric value for everything else except the drilling sample. There is a significant volume difference (and therefore potential variability) between the sampling methods – drilling is usually in the region of 10cm diameter and radiometric logging is up to 1m diameter and specifically excludes the drilled portion. 14
- 16. Calibration Probe Calibration at Kayelekera 3500 Probes are calibrated 3150 Kayelekera Pit against known thicknesses Active Layer Thickness = 1.02 m Hole Diameter = 110 mm and grades of 2800 Hole Fluid = air mineralisation in order to 2450 Probe T360 determine a K-factor, a Run 1 constant value to convert 2100 Run 2 logged counts per second Run 3 Run 4 to an equivalent uranium 1750 grade. 1400 The log to the left shows 4 1050 logging runs at the newly commissioned primary 700 calibration facility at the 350 Kayelekera Minesite. 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 Depth (metres)
- 17. Calibration (Pelindaba, South Africa) Probe Calibration at Pelindaba 4500 Calibration pits are constructed Calibration Pit: Pelindaba 4000 as a layer of barren material at Grade = 1440 ppm Thickness = 0.86 m the base, a layer of mineralised Hole Diameter = 100 mm 3500 Hole Fluid = air material with a known grade and thickness, and another Probe A775 3000 layer of barren material at the Probe T244 Probe S093 top. 2500 Probe T362 2000 Probe 005 The diameter of the Probe T279 construction is such that an 1500 apparent ‘infinite’ width can be seen by the logging equipment. 1000 The recent transportation of the 500 test pits at Pelindaba has resulted in damage as indicated 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 by the accompanying log. Depth (metres)
- 18. Calibration Recently constructed full calibration facility at the Kayelekera mine, the photograph shows the top surface of the facility with cased holes of various diameter. The covered pipe at the rear of the pad is a temporary termination for the moisture monitoring equipment.
- 19. Calibration check facility, LHU Individual historic test pits at LHU refurbished to allow for more frequent calibration checks. A full calibration facility, similar to that at Kayelekera, is currently being constructed at LHU to replace the Gencor pits. 18
- 20. Sensitivity Checks Probes are checked for instrument drift using a standardised rig and radioactive source. All probes are checked before use for exploration, before each shift for mining and at least once a week when not in normal use. If excessive drift is identified the probe is sent for re-calibration or repair. Probe status is monitored by dedicated staff at all sites (mining and exploration), in addition a report is issued by the geophysical department in Perth each month detailing the calibration and standardisation status of all probes 19
- 21. Sensitivity checks Probe returned to service Probe re-calibrated Probe damaged and sent for following excessive repair and calibration drift 20
- 22. Logging equipment Logging equipment, standard Auslog winch and DLS with custom made boom and winch enclosure mounted on Yamaha Rhino 4x4 base. Electrics currently upgraded to Solar power for battery re- charge. Gamma probes, 33mm slimline, with primary calibration at Pelindaba.
- 23. Rhino service facility All Rhino based equipment is serviced and maintained on site. Service facility also contains a low background area for shift based probe sensitivity checks. 22
- 24. Data Processing Data from the logging process is downloaded at the end of each shift or drill hole and processed to las files. Data is then combined in a custom Access database where all calibrations and corrections are applied 23
- 25. Questions? 24
Editor's Notes
- Paladin is amongst the worlds top ten uranium producers and is currently positioned at number 8, production is expected to increase over the coming year with the ramp up of stage 3 of Langer Heinrich and the optimisation of Kayelekera. Paladin has active exploration projects in Africa, primarily around the Kayelekera minesite and in Niger, in Australia at Mount Isa and the Manyingee ISR project, and in Canada at the Michelin project. Paladin currently has projects around the world containing about 608Mlb U3O8 of total resources of which approximately 566Mlb U3O8 are attributable to Paladin. All exploration drill holes are downhole logged along with production blast holes at both Langer Heinrich and Kayelekera, this amounts to in excess of a million metres of logging each year.
- The local background radiation, from whatever source, is extremely important in relation to down hole logging as it adds directly to the apparent counts per second used in the determination of equivalent grades. The background is always additive to total counts and so will lead to an overestimation of equivalent grade if not treated appropriately. The local background should always be determined on a hole by hole basis as the values are likely to be inconsistent between holes on any project and will be influenced by local conditions. No attempt should be made to account for down hole backgrounds after the determination of an equivalent grade, particularly on multiple drill holes.
- As can be seen in this slide, from a single project with the holes positioned approximately 200m from each other, there is considerable local variation in apparent background values. The green trace has a background of approximately 75 cps, the red trace a background of approximately 12 cps and the blue trace a background of approximately 7 cps. An overall subtraction of background on a project wide would most likely result in the under estimation of equivalent grades on the red and blue holes and an over estimation of the green hole. Using the minimum value for background would result in over estimations for the red and green holes. In this case the holes were logged in rods so cps is approximately equivalent to uranium grade. The risk is that non removal of background will result in the generation of apparent, significant, mineralisation, both in terms of thickness and grade. It should be noted that background radiation due to Radon can be extreme (examples from Kayelekera are in the order of 500-1000cps).
- A significant amount of down hole logging will take place within the drill rod string, whilst the optimum process is to log in the open hole ground conditions will frequently make this unwise. Whilst there are tables available to calculate the attenuation of gamma rays due to the presence of varying thicknesses of steel it is recommended to perform a calibration of the actual casing factor on the drill rod string in use. Paladin calculates casing factors for drill rod strings, in various combinations, at the start of each drilling programme, with the rod strings in use, and whenever a rod string is changed (ie on rod change out or commencement of a new drill rig). As the casing factor will vary with down hole depth (due to the combinations of rods used) noting of the down hole position of each casing is extremely important. As the factor is a direct multiplier of cps it is very important to get the correct value.
- Radon is a frequently ignored, variable, background additive component within down hole logs. The effect of Radon is likely to be hole specific, though may often be associated with faulting and water table on a more project wide basis.
- Close up of the refurbished test pit, the original holes were carefully reamed out and full length PVC tubing cemented in place. Following the work the upgraded pits were monitored for Radon loss and repeatedly logged to confirm stability. In the background can be seen one of the scintillometer check pads.
- The mine currently uses 6 Yamaha Rhino 4 wheel drive vehicles modified for mine use with radio, marker lights etc, and a specially manufactured boom enclosure for the winch and logging system. The Rhino is set up for single person operation with all electronics housed in dust and waterproof enclosures. Some of the Rhino’s have now been converted to have solar panels on the roof cover to allow for continuous charging of the batteries used to power the logging system, previous battery charging at shift changeover having proved inefficient. At present software used for logging is the Auslog program Alog with all binary and las output files downloaded to the main mine system at the end of each shift. The Rhino was chosen for its ease of operation, low maintenance requirements and small size as it is able to fit between rows of blast holes without damaging drill collars.
- The site has constructed an extensive service and storage facility for both Rhino’s and logging equipment with the majority of repairs to any equipment able to be completed on site. The service bay also has an area specifically designated as low background where shift based probe sensitivity checks are carried out. Should a probe need extensive repair the on site calibration pits can be used to re-certify the K-factor for the probe provided that it is close to the original primary calibration. Should this not be the case the probe is returned to Pelindaba for a full re-calibration. As the site will log over 400,000m this year the additional investment in these systems and facilities is fully justified.
- Al the end of each shift all the data logged during the shift is downloaded onto the minesite main computer system. To speed up data processing and allow for the generation of ore markouts the las files are batch processed though an in house Microsoft Access database. This processing incorporates a dead time correction, background removal, deconvolution and application of K and other factors. At Langer Heinrich, due to the low overall background values, the background for each hole is calculated automatically from a minimum 1m moving average value (up to a pre-set maximum). Included for comparison is the same Microsoft Access database in use at the Kayelekera Mine site where, due to variable elevated backgrounds caused by Radon, each log has to be individually assessed. Up to 1000 las files can be processed at any one time, however the usual processing batch is 200-500 holes.