Saskatchewan Geological Survey 1 Summary of Investigations 2013 Volume 1

Quantitative Evaluation of Potash Grade and Mineralogy Based on Geophysical Well-log Analysis Preliminary Study of the Prairie

Evaporite in Saskatchewan

Chao Yang and Guoxiang Chi 1

Yang C and Chi G (2013) Quantitative evaluation of potash grade and mineralogy based on geophysical well-log analysis preliminary study of the Prairie Evaporite in Saskatchewan in Summary of Investigations 2013 Volume 1 Saskatchewan Geological Survey Sask Ministry of the Economy Misc Rep 2013-41 Paper A-1 10p

Abstract The potash-bearing beds from the upper part of the Prairie Evaporite in Saskatchewan consist of primarily a mixture of halite (NaCl) sylvite (KCl) carnallite (KClMgCl26H2O) and small amount of insolubles including clay minerals anhydrite quartz dolomite and red-coloured iron oxides The grades of the potash ores (in K2O) are usually determined by chemical analysis In this paper we have developed a method to estimate the K2O values from geophysical well logs using various combinations of equations relating mineral composition to geophysical log response values This method is based on the unique characteristic of the relative simple mineral composition of potash ore in Saskatchewan

The mathematical method is based on two assumptions Firstly the sum of halite sylvite carnallite and insolubles is 100 (the first equation) Secondly the total log value of an interval is made up of each mineral fraction (halite sylvite carnallite and insolubles) multiplied by its respective logging response value Eight equations are established using geophysical logs including gamma ray density photoelectrical neutron and sonic Quantitative estimation of the fraction of sylvite halite carnallite and insolubles (four unknowns) are achieved by solving four linear equations the first equation plus a combination of three equations depending on the availability of well logs

The method is tested for two wells Potash One Findlater 2113-24-19-25W2M (08K302) and Athabasca et al Burr 1101-17-35-22W2M (07F215) where both chemical analysis data and geophysical well logs are available The two sets of data show generally good agreements for sylvite and halite contents but more discrepancy for insoluble content Carnallite content was not verified due to very small amounts of carnallite in the tested drill holes The correlation between K2O calculated from well logs and from chemical analysis is very good when sample intervals with insolubles gt10 are less than 10 of the potash-rich intervals

The results of this preliminary study suggest that it is possible to obtain quantitative estimation of potash ore grade (K2O) and mineralogy through geophysical log analysis when potash cores are not available This provides a quick method of evaluating the distribution of potash grades over a large area which is helpful for the industry in planning exploration wells

Keywords potash potash mineralogy halite sylvite carnallite insolubles potash grade chemical analysis log analysis Prairie Evaporite Saskatchewan

1 IntroductionPotash production in Saskatchewan began when the provincersquos first mine opened in 1958 Over the next 12 years nine more mines were built the last in 1970 (Fuzesy 1982) Currently Saskatchewan produces approximately one-third of the worldrsquos potash (US Geological Survey 2013) In recent years the increasing global demand for fertilizer in heavily populated countries has increased the demand for potash which in turn has re-stimulated drilling activity in the provincersquos potash industry

The potash-bearing beds are widely distributed over much of southern Saskatchewan (Figure 1) and therefore a regional map showing variation of potash grades would be very helpful for resource evaluation and exploration However the number of cored wells drilled by the potash industry for which chemical analyses are publicly available is very limited which makes basin-wide potash mineralogy research and potash resource assessment difficult On the other hand there are numerous wells drilled by the oil and gas industry that have penetrated the

1 Department of Geology University of Regina 3737 Wascana Parkway Regina SK S4S 0A2

Saskatchewan Geological Survey 2 Summary of Investigations 2013 Volume 1

Figure 1 ndash Distribution of potash in Saskatchewan (modified from Saskatchewan Geological Survey 2013)

potash-bearing beds These wells have very few cores of the potash intervals however most wells do have excellent geophysical well logs which are potentially useful for potash grade evaluation The main objective of this paper is to establish models to allow quantitative estimations of ore grade (K2O) and mineralogy using geophysical well log analysis for the areas where potash cores are not available The results may not be accurate enough for reserve calculation to meet the Canadian National Instrument 43-101 standards but provide valuable information for planning drilling programs in the early stage of potash exploration

2 Methodology Saskatchewan potash ore consists of a mixture of sylvite halite carnallite and insolubles that mainly include clay minerals dolomite and anhydrite (Holter 1969 Yang et al 2009) Therefore we have

Halite + Sylvite + Carnallite + Insolubles = 100 (1)

Bedded evaporite minerals are basically non-porous and therefore formation water is not added to the calculation The gamma-ray density photoelectrical neutron and sonic geophysical well logs can be used to identify these mineral compositions The gamma-ray log is the most important log used to identify sylvite and carnallite because it detects radiation from the naturally occurring radioactive isotope of potassium (K40) in the potash minerals In shales the gamma-ray response is a function of potassium thorium and uranium content whereas in potash minerals it is a function of potassium concentration In general the level of radiation is higher in potash beds than in shales (Rider 1996) Sylvite and carnallite have gamma-ray API values of 747 and 200 respectively while halite and anhydrite have zero gamma-ray values (Alger and Crain 1965 Crain and Anderson 1966 Tixier and Alger 1970 Rider 1996 Crain 2013)

Yorkton

Melville

North Battleford

Legend

Underground potash mine

Potash area

plusmn

0 30 60 90 120 kilometres15

Solution potash mine

1-17-35-22W2

13-24-19-25W2

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49deg

50deg

51deg

52deg

53deg

49deg

50deg

51deg

52deg

53deg

ReginaMoose Jaw

Swift Current

Weyburn

Estevan

Saskatoon

Prince Albert

Humboldt

Saskatchewan Geological Survey 3 Summary of Investigations 2013 Volume 1

Density and photoelectrical logs are also useful in identifying the mineral composition of salt deposits Halite sylvite and carnallite have true densities of 216 198 and 161 gcm3 respectively Halite has a log density of 203 gcm3 while sylvite and carnallite have lower log densities of 186 gcm3 and 157 gcm3 respectively (Alger and Crain 1965 Crain and Anderson 1966 Tixier and Alger 1970 Rider 1996 Crain 2013) Sylvite also has a distinctly higher photoelectrical value of 876 which helps to distinguish it from other minerals including halite carnallite anhydrite dolomite calcite and clay minerals which have photoelectrical values ranging from 164 to 509 (Crain 2013)

Since the response from a neutron log is primarily a function of the hydrogen concentration it indicates the amount of bonded and free water present and can be used to distinguish the hydrous mineral carnallite (KClMgCl26H2O) from halite and sylvite Carnallite has a high neutron porosity value of 60 which differentiates it from halite sylvite and anhydrite which contain no water and hence have a neutron log value of -3 (Alger and Crain 1965 Crain and Anderson 1966 Tixier and Alger 1970 Crain 2013) Compared to carnallite clay minerals contain less water in their crystal structure and thus have a lower average neutron-porosity value of 30 to 37 (Rider 1996)

Sonic logs are also useful for salt mineral identification because different minerals have different acoustic properties The acoustic interval transit time for halite sylvite and carnallite is 67 74 and 78 microseconds per foot (or 220 242 and 256 microseconds per metre) respectively (Alger and Crain 1965 Crain and Anderson 1966 Tixier and Alger 1970 Rider 1996 Crain 2013)

The logging responses of individual minerals comprising the potash-rich intervals in the Prairie Evaporite in Saskatchewan are summarised in Table 1

Quantitative relationships between geophysical well logs and the mineral compositions can be established based on the geophysical log response values of the various minerals For example the gamma-ray log reading of a potash interval is the sum of each mineral fraction multiplied by its respective logging response value in Table 1 because K2O obtained from core chemical analysis (Hardy et al 2010) is linearly related to logging gamma-ray values in API units (Figure 2)

(0 x Halite)+(747 x Sylvite)+(200 x Carnallite)+(150 x Insolubles) = GrGamma log (API) (2)

Similarly eight more equations can be established for different geophysical well logs using logging response values in Table 1

(67 x Halite)+(74 x Sylvite)+(78 x Carnallite)+(120 x Insolubles) = TSonic log (sft) (3)

(203 x Halite)+(186 x Sylvite)+(157 x Carnallite)+(265 x Insolubles) = DDensity log (gcm3) (4)

(0 x Halite)+(-002 x Sylvite)+(06 x Carnallite)+(04 x Insolubles) =HNeutron log (fraction) (5)

(472 x Halite)+(876 x Sylvite)+(429 x Carnallite)+(35 x Insolubles) = PElog (barcm3) (6)

(220 x Halite)+(242 x Sylvite)+(256 x Carnallite)+(212 x Insolubles) = TSonic log (sm) (7)

(2030 x Halite)+(1860 x Sylvite)+(1570 x Carnallite)+(2650 x Insolubles) = DDensity log (kgcm3) (8)

(-3 x Halite)+(-3 x Sylvite)+(60 x Carnallite)+(37 x Insolubles) = Neutron log (porosity) (9)

Table 1 ndash Geophysical log response values of major mineral components in potash ore in the Prairie Evaporite Saskatchewan (summarized from Rider 1996 Tixier and Alger 1970 Edmundson and Raymer 1979 Crain 2013)

Logs Measurement Halite Sylvite CarnalliteInsolubles (mostly

clays) EquationGamma ray API 0 747 200 120 to 150 (2)Sonic travel time sft 67 74 78 90 to 120 (3)Density log gcm3 203 186 157 235 to 265 (4)Neutron hydrogen index fraction 0 -002 06 03 to 04 (5)Photoelectric barcm3 472 876 429 145 to 35 (6)Sonic travel time sm 220 242 256 155 to 212 (7)Density log kgcm3 2030 1860 1570 2350 to 2650 (8)Neutron porosity -3 -3 60 30 to 37 (9)

Saskatchewan Geological Survey 4 Summary of Investigations 2013 Volume 1

Figure 2 ndash Plot of K2O from chemical analysis (Hardy et al 2010) versus gamma-ray values in API units from gamma-ray log for well 13-24-19-25W2 in the upper part of the Prairie Evaporite Saskatchewan

Where Halite Sylvite Carnallite and Insolubles are percentages of these minerals (unknowns) The ranges of log values for insolubles in Table 1 are tested and the upper values are used because they yielded the best results

Using equation (1) plus any three equations of different logs from (2) to (9) depending on log availability the four unknowns (ie percentage of halite sylvite carnallite and insolubles) are solved from four of these linear equations with Microsoftreg Excel spreadsheets Sylvite (KCl) content is then converted to K2O (K2O = 06317 x KCl)

Digital logs are used to obtain the log values to ensure accuracy and efficiency For a given potash bed digital log values were averaged every 0152 m K2O values were calculated for each of these consecutive intervals

3 Test of the Method for Potash Grade Calculation The method discussed above is tested for the Potash One Findlater 2113-24-19-25W2M (08K302) well drilled by Potash One Inc in 2008 where both geophysical logs and assay values are available The calculated results are compared to core assay data (Hardy et al 2010) Different combinations of geophysical logs produce different results and it is found that the combinations of gamma-density-neutron (equations 2 4 and 5) gamma-sonic-density (equations 2 3 and 4) and gamma-sonic-neutron (equations 2 3 and 5) yield the most comparable results with those of chemical analysis (Figures 3 to 5)

The plots show a very good agreement between the two sets of data for K2O and NaCl but more discrepancy for insolubles Carnallite is not included in the graph because of its small fraction

The average digital log values for every 0152 m and every 0025 m are plotted to see if the calculation accuracy can be improved by increasing points of count from logs (Figure 6) No significant improvement is observed

The method is also tested for the Athabasca et al Burr 1101-17-35-22W2M (07F215) drilled by Athabasca Potash Inc in 2007 The calculated K2O from three log combinations is also comparable to the chemical analysis data (Lomas 2008) Good agreements between the two sets of data are observed with slightly higher K2O from log calculations (Figure 7)

The correlations between K2O from chemical analysis and from well log calculation are illustrated in Figures 8 and 9 Very good correlations are shown when sample intervals with insolubles gt10 count for less than 10 of the total potash ore intervals Three different log combinations yield similar results (Figure 8) In contrast the correlations are poorer when sample intervals with insolubles gt10 count for about 40 of total potash ore intervals eg from 1524 m to 1537 m in well 2113-24-19-25W2M (Figure 9)

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0 100 200 300 400 500Gamma ray (API)

K2O

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Saskatchewan Geological Survey 5 Summary of Investigations 2013 Volume 1

Figure 3 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Den-Nue) (equations 2 4 and 5) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Figure 4 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Son-Den) (equations 2 3 and 4) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

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Calculated from Gr-Son-Den logs Chemical analysis

Saskatchewan Geological Survey 6 Summary of Investigations 2013 Volume 1

Figure 5 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Son-Nue) (equations 2 3 and 5) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Figure 6 ndash Comparison of K2O derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Den-Nue) (equations 2 4 and 5) for well 2113-24-19-25W2M (08K302) in upper part of the Prairie Evaporite Saskatchewan A) data point interval is 0152 m and B) data point interval is 0025 m

A) K2O B) NaCl C) Insoluble

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Calculated from Gr-Son-Neu logs Chemical analysis

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Calculated from Gr-Den-Neu logs Chemical analysis

Saskatchewan Geological Survey 7 Summary of Investigations 2013 Volume 1

Figure 7 ndash Comparison of K2O derived from chemical analysis (Lomas 2008) and log calculation for well 1101-17-35-22W2M (07F215) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue (equations 2 4 and 5) B) combination Gr-Son-Den (equations 2 3 and 4) and C) combination Gr-Son-Nue (equations 2 3 and 5)

4 Discussion There are numerous factors that can affect the calculation and can be the sources for errors for this mathematical method

a) Effect of Bit Size and Drilling Mud on Gamma-ray API Value

Equation (2) is established based on an assumption of a linear relationship between K2O and gamma value in API units This can be tested by a plot (Figure 2) when core analysis data is available and wells are logged by the same company in a project area However a linear relationship may not be observed when gamma value (API) is larger than 300 or 350 especially for older logs In such cases it has been found that the API values are not only related to K2O but also to the bit size and density of drilling mud A corrected relationship between K2O and gamma API values has been proposed by Crain and Anderson (1966) as follows

APIGamma corrected = APIGamma log[1+005 (Dhole size - 6)+320( Dhole size - 6)(APIGamma log +100)] [1+01(Mmud density-72)]

where APIGamma log is gamma-ray log reading (API) Dhole size is drill hole size (inches) and Mmud density is weight of drilling mud (lbgal)

b) Composition of Insolubles

The insolubles in each potash-rich interval are comprised of different mineral fractions and the mineral compositions of insolubles are not determined for this study As a result the values of log responses for insolubles used in calculation may not represent the true log response values for insolubles of the potash interval which may cause error in calculation When samples with insolubles gt10 count for less than 10 of the total potash intervals the effect of the insolubles on the calculation is not significant and the calculated K2O is very close to that of chemical analysis (Figure 8) In general the samples with insoluble content gt10 have higher calculated K2O than that of chemical analysis (Figure 8)

Plots of Insolubles of core analysis versus Insolubles calculated from log suite in potash members of the Prairie Evaporite show poor agreements (Figures 3C 4C and 5C) The discrepancy may attribute mainly to the reason discussed above and the fact that the most insoluble-rich layers (clay seams) are thinner than the detection limit of log tools

Dep

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m)

950

960

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1000

0 20 40 60 0 20 40 60A) K

2O C) K

2OB) K

2O

0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

Calculated from Gr-Son-Den logs Chemical analysis

Calculated from Gr-Son-Neu logs Chemical analysis

Saskatchewan Geological Survey 8 Summary of Investigations 2013 Volume 1

Figure 9 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for 40 of the total potash intervals (1524 to 1537 m) of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

Figure 8 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for less than 10 of the total potash intervals of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

y = 10484x - 17085

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y = 10613x - 23059

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Saskatchewan Geological Survey 9 Summary of Investigations 2013 Volume 1

When samples with insolubles gt10 count for about 40 of the total potash intervals plots show more scattered distributions and the values of K2O obtained from log calculation are generally higher than that of chemical analysis (Figure 9)

c) Other Factors

When bed thickness is small a logging tool will measure not only the radiation of the thin bed but also that of adjacent beds As a result the measured radiation will be the sum of radiation emitted by the thin bed plus the sum of the radiation from all adjacent beds resulting in a discrepancy between the core analysis and log calculation The bed thickness corrections are suggested where the potash bed is less than 1 m (Nelson 2007 Crain 2013)

When a minimum of three logs is not available fewer minerals must be included in the calculation A potash geologist should apply their knowledge of mineral composition in the project area to determine which mineral has minimum content that can be delimited in the calculation Insolubles may be easy to ignore and carnallite may be negligible in carnallite-free areas

Because of small carnallite content in the test drill holes it is difficult to evaluate the effect of carnallite on this mathematic method Further work is required to test the method in a drill hole containing more carnallite or dominantly carnallite

Other factors affecting the calculation method include excessive logging speed depth misalignment between logging depths and core depths gamma-ray attenuation caused by cement and casing weight and content of drilling mud presence of uranium and thorium and washouts of potash zone (Nelson 2007 Crain 2013) Care must be taken when using logs for quantitative potash ore grade calculation

5 Summary Quantitative estimation of the fraction of sylvite halite carnallite and insolubles can be achieved by mathematical calculations from geophysical well logs The accuracy and precision of estimation largely depends on the total amount of insolubles in individual intervals Intervals with the smallest amount of insolubles provide the best results The method could be a valuable tool at the early stage of project evaluation where potash cores are not available The digital logs have improved efficiency and accuracy significantly by avoiding manual log reading and data entry Further studies are required in the area where carnallite is more predominant

6 Acknowledgements The authors wish to express their appreciation to Ross Crain for helpful discussions during preparation of this paper Our special acknowledgments go to K+S Potash Canada and BHP Billiton to give us permission to use their data for this study We also thank Megan Love for Figure 1 and Fran Haidl and Arden Marsh for comments andsuggestions for improvement of this paper

7 References Alger RP and Crain ER (1965) Defining evaporite deposits with electrical well logs in Second Symposium on

Salt Trans Northern Ohio Geol Soc Vol 2 p116-130

Crain RC (2013) Crainrsquos petrophysical handbook URLlthttpwwwspec2000net17-specpotashhtmgt accessed 26 June 2013

Crain ER and Anderson WB (1966) Quantitative log evaluation of the Prairie Evaporite formation in Saskatchewan J Can Petrol Tech v5 p145-152

Edmundson H and Raymer LL (1979) Radioactive logging parameters for common mineral Log Analyst v20 no5 p38-47

Fuzesy A (1982) Potash in Saskatchewan Sask Energy Mines Rep 181 44p

Hardy M Halabura SP Shewfelt D and Hambley DF (2010) Technical report 2010 potash reserve assessment for subsurface mineral permit KP 289 Saskatchewan URLlthttpwwwsedarcomGetFile dolang=ENampdocClass=24ampissuerNo=00007718ampfileName=csfsproddata112filings0165919500000001o3A5CCPU5C20105CPotashOneInc5C101112TR_sjg5CTR_sjgpdfgt accessed 4 June 2013

Saskatchewan Geological Survey 10 Summary of Investigations 2013 Volume 1

Holter ME (1969) The Middle Devonian Prairie Evaporite of Saskatchewan Sask Dept Miner Resour Rep 123 134p

Nelson P H (2007) Evaluation of potash grade with gamma-ray logs US Geological Survey Open File Report 2007-1292 14p

Lomas S (2008) NI 43ndash101 Technical Report for a resource estimation on the Burr Project Athabasca Potash Inc Saskatchewan Canada URLlthttpwwwsedarcomGetFiledolang=ENampdocClass=24ampissuerNo= 00026182ampfileName=csfsproddata93filings0134320800000001i3A5C1SEDAR5C5546375CTechnicalReport5CTechnicalReportpdfgt accessed 4 June 2013

Rider M (1996) The Geological Interpretation of Well Logs 2nd Edition Whittles Publishing Caithness 280p

Saskatchewan Geological Survey (2013) Mineral Resources Map of Saskatchewan 2013 Edition Sask Ministry of the Economy Saskatchewan Geological Survey Misc Rep 2013-1 URLlthttpwwweconomygovskca mineralresourcemapgt accessed 26 July 2013

Tixier MP and Alger PR (1970) Log evaluation of nonmetallic mineral deposits Geophys v35 no1 p124-142

US Geological Survey (2013) Mineral Commodity Summaries 2013URLlthttpmineralsusgsgovminerals pubsmcs2013mcs2013pdfgt accessed 15 July 2013

Yang C Jensen G and Berenyi J (2009) The stratigraphic framework of the potash-rich members of the Middle Devonian upper Prairie Evaporite Formation Saskatchewan in Summary of Investigations 2009 Volume 1 Saskatchewan Geological Survey Sask Ministry of Energy and Resources Misc Rep 2009-41 Paper A-4 28p URL lthttpeconomygovskcaSOI2009V1_A4gt

Saskatchewan Geological Survey 2 Summary of Investigations 2013 Volume 1

Figure 1 ndash Distribution of potash in Saskatchewan (modified from Saskatchewan Geological Survey 2013)

potash-bearing beds These wells have very few cores of the potash intervals however most wells do have excellent geophysical well logs which are potentially useful for potash grade evaluation The main objective of this paper is to establish models to allow quantitative estimations of ore grade (K2O) and mineralogy using geophysical well log analysis for the areas where potash cores are not available The results may not be accurate enough for reserve calculation to meet the Canadian National Instrument 43-101 standards but provide valuable information for planning drilling programs in the early stage of potash exploration

2 Methodology Saskatchewan potash ore consists of a mixture of sylvite halite carnallite and insolubles that mainly include clay minerals dolomite and anhydrite (Holter 1969 Yang et al 2009) Therefore we have

Halite + Sylvite + Carnallite + Insolubles = 100 (1)

Bedded evaporite minerals are basically non-porous and therefore formation water is not added to the calculation The gamma-ray density photoelectrical neutron and sonic geophysical well logs can be used to identify these mineral compositions The gamma-ray log is the most important log used to identify sylvite and carnallite because it detects radiation from the naturally occurring radioactive isotope of potassium (K40) in the potash minerals In shales the gamma-ray response is a function of potassium thorium and uranium content whereas in potash minerals it is a function of potassium concentration In general the level of radiation is higher in potash beds than in shales (Rider 1996) Sylvite and carnallite have gamma-ray API values of 747 and 200 respectively while halite and anhydrite have zero gamma-ray values (Alger and Crain 1965 Crain and Anderson 1966 Tixier and Alger 1970 Rider 1996 Crain 2013)

Yorkton

Melville

North Battleford

Legend

Underground potash mine

Potash area

plusmn

0 30 60 90 120 kilometres15

Solution potash mine

1-17-35-22W2

13-24-19-25W2

Well location

1

5

10

15

20

25

30

35

40

45

1

5

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3034W1M151015202530W2M151015202530W3

Tow

nshi

p

Range

102deg103deg104deg105deg106deg107deg108deg109deg110deg

49deg

50deg

51deg

52deg

53deg

49deg

50deg

51deg

52deg

53deg

ReginaMoose Jaw

Swift Current

Weyburn

Estevan

Saskatoon

Prince Albert

Humboldt

Saskatchewan Geological Survey 3 Summary of Investigations 2013 Volume 1

Density and photoelectrical logs are also useful in identifying the mineral composition of salt deposits Halite sylvite and carnallite have true densities of 216 198 and 161 gcm3 respectively Halite has a log density of 203 gcm3 while sylvite and carnallite have lower log densities of 186 gcm3 and 157 gcm3 respectively (Alger and Crain 1965 Crain and Anderson 1966 Tixier and Alger 1970 Rider 1996 Crain 2013) Sylvite also has a distinctly higher photoelectrical value of 876 which helps to distinguish it from other minerals including halite carnallite anhydrite dolomite calcite and clay minerals which have photoelectrical values ranging from 164 to 509 (Crain 2013)

Since the response from a neutron log is primarily a function of the hydrogen concentration it indicates the amount of bonded and free water present and can be used to distinguish the hydrous mineral carnallite (KClMgCl26H2O) from halite and sylvite Carnallite has a high neutron porosity value of 60 which differentiates it from halite sylvite and anhydrite which contain no water and hence have a neutron log value of -3 (Alger and Crain 1965 Crain and Anderson 1966 Tixier and Alger 1970 Crain 2013) Compared to carnallite clay minerals contain less water in their crystal structure and thus have a lower average neutron-porosity value of 30 to 37 (Rider 1996)

Sonic logs are also useful for salt mineral identification because different minerals have different acoustic properties The acoustic interval transit time for halite sylvite and carnallite is 67 74 and 78 microseconds per foot (or 220 242 and 256 microseconds per metre) respectively (Alger and Crain 1965 Crain and Anderson 1966 Tixier and Alger 1970 Rider 1996 Crain 2013)

The logging responses of individual minerals comprising the potash-rich intervals in the Prairie Evaporite in Saskatchewan are summarised in Table 1

Quantitative relationships between geophysical well logs and the mineral compositions can be established based on the geophysical log response values of the various minerals For example the gamma-ray log reading of a potash interval is the sum of each mineral fraction multiplied by its respective logging response value in Table 1 because K2O obtained from core chemical analysis (Hardy et al 2010) is linearly related to logging gamma-ray values in API units (Figure 2)

(0 x Halite)+(747 x Sylvite)+(200 x Carnallite)+(150 x Insolubles) = GrGamma log (API) (2)

Similarly eight more equations can be established for different geophysical well logs using logging response values in Table 1

(67 x Halite)+(74 x Sylvite)+(78 x Carnallite)+(120 x Insolubles) = TSonic log (sft) (3)

(203 x Halite)+(186 x Sylvite)+(157 x Carnallite)+(265 x Insolubles) = DDensity log (gcm3) (4)

(0 x Halite)+(-002 x Sylvite)+(06 x Carnallite)+(04 x Insolubles) =HNeutron log (fraction) (5)

(472 x Halite)+(876 x Sylvite)+(429 x Carnallite)+(35 x Insolubles) = PElog (barcm3) (6)

(220 x Halite)+(242 x Sylvite)+(256 x Carnallite)+(212 x Insolubles) = TSonic log (sm) (7)

(2030 x Halite)+(1860 x Sylvite)+(1570 x Carnallite)+(2650 x Insolubles) = DDensity log (kgcm3) (8)

(-3 x Halite)+(-3 x Sylvite)+(60 x Carnallite)+(37 x Insolubles) = Neutron log (porosity) (9)

Table 1 ndash Geophysical log response values of major mineral components in potash ore in the Prairie Evaporite Saskatchewan (summarized from Rider 1996 Tixier and Alger 1970 Edmundson and Raymer 1979 Crain 2013)

Logs Measurement Halite Sylvite CarnalliteInsolubles (mostly

clays) EquationGamma ray API 0 747 200 120 to 150 (2)Sonic travel time sft 67 74 78 90 to 120 (3)Density log gcm3 203 186 157 235 to 265 (4)Neutron hydrogen index fraction 0 -002 06 03 to 04 (5)Photoelectric barcm3 472 876 429 145 to 35 (6)Sonic travel time sm 220 242 256 155 to 212 (7)Density log kgcm3 2030 1860 1570 2350 to 2650 (8)Neutron porosity -3 -3 60 30 to 37 (9)

Saskatchewan Geological Survey 4 Summary of Investigations 2013 Volume 1

Figure 2 ndash Plot of K2O from chemical analysis (Hardy et al 2010) versus gamma-ray values in API units from gamma-ray log for well 13-24-19-25W2 in the upper part of the Prairie Evaporite Saskatchewan

Where Halite Sylvite Carnallite and Insolubles are percentages of these minerals (unknowns) The ranges of log values for insolubles in Table 1 are tested and the upper values are used because they yielded the best results

Using equation (1) plus any three equations of different logs from (2) to (9) depending on log availability the four unknowns (ie percentage of halite sylvite carnallite and insolubles) are solved from four of these linear equations with Microsoftreg Excel spreadsheets Sylvite (KCl) content is then converted to K2O (K2O = 06317 x KCl)

Digital logs are used to obtain the log values to ensure accuracy and efficiency For a given potash bed digital log values were averaged every 0152 m K2O values were calculated for each of these consecutive intervals

3 Test of the Method for Potash Grade Calculation The method discussed above is tested for the Potash One Findlater 2113-24-19-25W2M (08K302) well drilled by Potash One Inc in 2008 where both geophysical logs and assay values are available The calculated results are compared to core assay data (Hardy et al 2010) Different combinations of geophysical logs produce different results and it is found that the combinations of gamma-density-neutron (equations 2 4 and 5) gamma-sonic-density (equations 2 3 and 4) and gamma-sonic-neutron (equations 2 3 and 5) yield the most comparable results with those of chemical analysis (Figures 3 to 5)

The plots show a very good agreement between the two sets of data for K2O and NaCl but more discrepancy for insolubles Carnallite is not included in the graph because of its small fraction

The average digital log values for every 0152 m and every 0025 m are plotted to see if the calculation accuracy can be improved by increasing points of count from logs (Figure 6) No significant improvement is observed

The method is also tested for the Athabasca et al Burr 1101-17-35-22W2M (07F215) drilled by Athabasca Potash Inc in 2007 The calculated K2O from three log combinations is also comparable to the chemical analysis data (Lomas 2008) Good agreements between the two sets of data are observed with slightly higher K2O from log calculations (Figure 7)

The correlations between K2O from chemical analysis and from well log calculation are illustrated in Figures 8 and 9 Very good correlations are shown when sample intervals with insolubles gt10 count for less than 10 of the total potash ore intervals Three different log combinations yield similar results (Figure 8) In contrast the correlations are poorer when sample intervals with insolubles gt10 count for about 40 of total potash ore intervals eg from 1524 m to 1537 m in well 2113-24-19-25W2M (Figure 9)

0

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0 100 200 300 400 500Gamma ray (API)

K2O

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ical

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Saskatchewan Geological Survey 5 Summary of Investigations 2013 Volume 1

Figure 3 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Den-Nue) (equations 2 4 and 5) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Figure 4 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Son-Den) (equations 2 3 and 4) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Dep

th (

m)

A) K2O B) NaCl C) Insoluble

1520

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0 20 40 60 0 20 40 60 80 0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

A) K2O B) NaCl C) Insoluble

Dep

th (

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1550

1560

1570

1580

0 20 40 60 0 20 40 60 80 0 20 40 60

Calculated from Gr-Son-Den logs Chemical analysis

Saskatchewan Geological Survey 6 Summary of Investigations 2013 Volume 1

Figure 5 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Son-Nue) (equations 2 3 and 5) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Figure 6 ndash Comparison of K2O derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Den-Nue) (equations 2 4 and 5) for well 2113-24-19-25W2M (08K302) in upper part of the Prairie Evaporite Saskatchewan A) data point interval is 0152 m and B) data point interval is 0025 m

A) K2O B) NaCl C) Insoluble

Dep

th (

m)

1520

1530

1540

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0 20 40 60 0 20 40 60 80 0 20 40 60

Calculated from Gr-Son-Neu logs Chemical analysis

A) K2O

Dep

th (m

)

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0 20 40 60B) K2O

Dep

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)

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Calculated from Gr-Den-Neu logs Chemical analysis

Saskatchewan Geological Survey 7 Summary of Investigations 2013 Volume 1

Figure 7 ndash Comparison of K2O derived from chemical analysis (Lomas 2008) and log calculation for well 1101-17-35-22W2M (07F215) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue (equations 2 4 and 5) B) combination Gr-Son-Den (equations 2 3 and 4) and C) combination Gr-Son-Nue (equations 2 3 and 5)

4 Discussion There are numerous factors that can affect the calculation and can be the sources for errors for this mathematical method

a) Effect of Bit Size and Drilling Mud on Gamma-ray API Value

Equation (2) is established based on an assumption of a linear relationship between K2O and gamma value in API units This can be tested by a plot (Figure 2) when core analysis data is available and wells are logged by the same company in a project area However a linear relationship may not be observed when gamma value (API) is larger than 300 or 350 especially for older logs In such cases it has been found that the API values are not only related to K2O but also to the bit size and density of drilling mud A corrected relationship between K2O and gamma API values has been proposed by Crain and Anderson (1966) as follows

APIGamma corrected = APIGamma log[1+005 (Dhole size - 6)+320( Dhole size - 6)(APIGamma log +100)] [1+01(Mmud density-72)]

where APIGamma log is gamma-ray log reading (API) Dhole size is drill hole size (inches) and Mmud density is weight of drilling mud (lbgal)

b) Composition of Insolubles

The insolubles in each potash-rich interval are comprised of different mineral fractions and the mineral compositions of insolubles are not determined for this study As a result the values of log responses for insolubles used in calculation may not represent the true log response values for insolubles of the potash interval which may cause error in calculation When samples with insolubles gt10 count for less than 10 of the total potash intervals the effect of the insolubles on the calculation is not significant and the calculated K2O is very close to that of chemical analysis (Figure 8) In general the samples with insoluble content gt10 have higher calculated K2O than that of chemical analysis (Figure 8)

Plots of Insolubles of core analysis versus Insolubles calculated from log suite in potash members of the Prairie Evaporite show poor agreements (Figures 3C 4C and 5C) The discrepancy may attribute mainly to the reason discussed above and the fact that the most insoluble-rich layers (clay seams) are thinner than the detection limit of log tools

Dep

th (

m)

950

960

970

980

990

1000

0 20 40 60 0 20 40 60A) K

2O C) K

2OB) K

2O

0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

Calculated from Gr-Son-Den logs Chemical analysis

Calculated from Gr-Son-Neu logs Chemical analysis

Saskatchewan Geological Survey 8 Summary of Investigations 2013 Volume 1

Figure 9 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for 40 of the total potash intervals (1524 to 1537 m) of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

Figure 8 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for less than 10 of the total potash intervals of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

y = 10484x - 17085

0

10

20

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0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

B)

K2O

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om c

hem

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K2O calculated from Gr-Son-Den logs

y = 10613x - 23059

0

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0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

A)

K2O calculated from Gr-Den-Nue logs

K2O

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om c

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y = 10591x - 21491

0

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Regression Trend

C)

K2O calculated from Gr-Son-Nue logs

K2O

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K2O calculated from Gr-Den-Nue logs

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Insolubles gt 10

K2O calculated from Gr-Son-Nue logs

C)

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B)

K2O calculated from Gr-Son-Den logs

K2O

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Saskatchewan Geological Survey 9 Summary of Investigations 2013 Volume 1

When samples with insolubles gt10 count for about 40 of the total potash intervals plots show more scattered distributions and the values of K2O obtained from log calculation are generally higher than that of chemical analysis (Figure 9)

c) Other Factors

When bed thickness is small a logging tool will measure not only the radiation of the thin bed but also that of adjacent beds As a result the measured radiation will be the sum of radiation emitted by the thin bed plus the sum of the radiation from all adjacent beds resulting in a discrepancy between the core analysis and log calculation The bed thickness corrections are suggested where the potash bed is less than 1 m (Nelson 2007 Crain 2013)

When a minimum of three logs is not available fewer minerals must be included in the calculation A potash geologist should apply their knowledge of mineral composition in the project area to determine which mineral has minimum content that can be delimited in the calculation Insolubles may be easy to ignore and carnallite may be negligible in carnallite-free areas

Because of small carnallite content in the test drill holes it is difficult to evaluate the effect of carnallite on this mathematic method Further work is required to test the method in a drill hole containing more carnallite or dominantly carnallite

Other factors affecting the calculation method include excessive logging speed depth misalignment between logging depths and core depths gamma-ray attenuation caused by cement and casing weight and content of drilling mud presence of uranium and thorium and washouts of potash zone (Nelson 2007 Crain 2013) Care must be taken when using logs for quantitative potash ore grade calculation

5 Summary Quantitative estimation of the fraction of sylvite halite carnallite and insolubles can be achieved by mathematical calculations from geophysical well logs The accuracy and precision of estimation largely depends on the total amount of insolubles in individual intervals Intervals with the smallest amount of insolubles provide the best results The method could be a valuable tool at the early stage of project evaluation where potash cores are not available The digital logs have improved efficiency and accuracy significantly by avoiding manual log reading and data entry Further studies are required in the area where carnallite is more predominant

6 Acknowledgements The authors wish to express their appreciation to Ross Crain for helpful discussions during preparation of this paper Our special acknowledgments go to K+S Potash Canada and BHP Billiton to give us permission to use their data for this study We also thank Megan Love for Figure 1 and Fran Haidl and Arden Marsh for comments andsuggestions for improvement of this paper

7 References Alger RP and Crain ER (1965) Defining evaporite deposits with electrical well logs in Second Symposium on

Salt Trans Northern Ohio Geol Soc Vol 2 p116-130

Crain RC (2013) Crainrsquos petrophysical handbook URLlthttpwwwspec2000net17-specpotashhtmgt accessed 26 June 2013

Crain ER and Anderson WB (1966) Quantitative log evaluation of the Prairie Evaporite formation in Saskatchewan J Can Petrol Tech v5 p145-152

Edmundson H and Raymer LL (1979) Radioactive logging parameters for common mineral Log Analyst v20 no5 p38-47

Fuzesy A (1982) Potash in Saskatchewan Sask Energy Mines Rep 181 44p

Hardy M Halabura SP Shewfelt D and Hambley DF (2010) Technical report 2010 potash reserve assessment for subsurface mineral permit KP 289 Saskatchewan URLlthttpwwwsedarcomGetFile dolang=ENampdocClass=24ampissuerNo=00007718ampfileName=csfsproddata112filings0165919500000001o3A5CCPU5C20105CPotashOneInc5C101112TR_sjg5CTR_sjgpdfgt accessed 4 June 2013

Saskatchewan Geological Survey 10 Summary of Investigations 2013 Volume 1

Holter ME (1969) The Middle Devonian Prairie Evaporite of Saskatchewan Sask Dept Miner Resour Rep 123 134p

Nelson P H (2007) Evaluation of potash grade with gamma-ray logs US Geological Survey Open File Report 2007-1292 14p

Lomas S (2008) NI 43ndash101 Technical Report for a resource estimation on the Burr Project Athabasca Potash Inc Saskatchewan Canada URLlthttpwwwsedarcomGetFiledolang=ENampdocClass=24ampissuerNo= 00026182ampfileName=csfsproddata93filings0134320800000001i3A5C1SEDAR5C5546375CTechnicalReport5CTechnicalReportpdfgt accessed 4 June 2013

Rider M (1996) The Geological Interpretation of Well Logs 2nd Edition Whittles Publishing Caithness 280p

Saskatchewan Geological Survey (2013) Mineral Resources Map of Saskatchewan 2013 Edition Sask Ministry of the Economy Saskatchewan Geological Survey Misc Rep 2013-1 URLlthttpwwweconomygovskca mineralresourcemapgt accessed 26 July 2013

Tixier MP and Alger PR (1970) Log evaluation of nonmetallic mineral deposits Geophys v35 no1 p124-142

US Geological Survey (2013) Mineral Commodity Summaries 2013URLlthttpmineralsusgsgovminerals pubsmcs2013mcs2013pdfgt accessed 15 July 2013

Yang C Jensen G and Berenyi J (2009) The stratigraphic framework of the potash-rich members of the Middle Devonian upper Prairie Evaporite Formation Saskatchewan in Summary of Investigations 2009 Volume 1 Saskatchewan Geological Survey Sask Ministry of Energy and Resources Misc Rep 2009-41 Paper A-4 28p URL lthttpeconomygovskcaSOI2009V1_A4gt

Saskatchewan Geological Survey 3 Summary of Investigations 2013 Volume 1

Density and photoelectrical logs are also useful in identifying the mineral composition of salt deposits Halite sylvite and carnallite have true densities of 216 198 and 161 gcm3 respectively Halite has a log density of 203 gcm3 while sylvite and carnallite have lower log densities of 186 gcm3 and 157 gcm3 respectively (Alger and Crain 1965 Crain and Anderson 1966 Tixier and Alger 1970 Rider 1996 Crain 2013) Sylvite also has a distinctly higher photoelectrical value of 876 which helps to distinguish it from other minerals including halite carnallite anhydrite dolomite calcite and clay minerals which have photoelectrical values ranging from 164 to 509 (Crain 2013)

Since the response from a neutron log is primarily a function of the hydrogen concentration it indicates the amount of bonded and free water present and can be used to distinguish the hydrous mineral carnallite (KClMgCl26H2O) from halite and sylvite Carnallite has a high neutron porosity value of 60 which differentiates it from halite sylvite and anhydrite which contain no water and hence have a neutron log value of -3 (Alger and Crain 1965 Crain and Anderson 1966 Tixier and Alger 1970 Crain 2013) Compared to carnallite clay minerals contain less water in their crystal structure and thus have a lower average neutron-porosity value of 30 to 37 (Rider 1996)

Sonic logs are also useful for salt mineral identification because different minerals have different acoustic properties The acoustic interval transit time for halite sylvite and carnallite is 67 74 and 78 microseconds per foot (or 220 242 and 256 microseconds per metre) respectively (Alger and Crain 1965 Crain and Anderson 1966 Tixier and Alger 1970 Rider 1996 Crain 2013)

The logging responses of individual minerals comprising the potash-rich intervals in the Prairie Evaporite in Saskatchewan are summarised in Table 1

Quantitative relationships between geophysical well logs and the mineral compositions can be established based on the geophysical log response values of the various minerals For example the gamma-ray log reading of a potash interval is the sum of each mineral fraction multiplied by its respective logging response value in Table 1 because K2O obtained from core chemical analysis (Hardy et al 2010) is linearly related to logging gamma-ray values in API units (Figure 2)

(0 x Halite)+(747 x Sylvite)+(200 x Carnallite)+(150 x Insolubles) = GrGamma log (API) (2)

Similarly eight more equations can be established for different geophysical well logs using logging response values in Table 1

(67 x Halite)+(74 x Sylvite)+(78 x Carnallite)+(120 x Insolubles) = TSonic log (sft) (3)

(203 x Halite)+(186 x Sylvite)+(157 x Carnallite)+(265 x Insolubles) = DDensity log (gcm3) (4)

(0 x Halite)+(-002 x Sylvite)+(06 x Carnallite)+(04 x Insolubles) =HNeutron log (fraction) (5)

(472 x Halite)+(876 x Sylvite)+(429 x Carnallite)+(35 x Insolubles) = PElog (barcm3) (6)

(220 x Halite)+(242 x Sylvite)+(256 x Carnallite)+(212 x Insolubles) = TSonic log (sm) (7)

(2030 x Halite)+(1860 x Sylvite)+(1570 x Carnallite)+(2650 x Insolubles) = DDensity log (kgcm3) (8)

(-3 x Halite)+(-3 x Sylvite)+(60 x Carnallite)+(37 x Insolubles) = Neutron log (porosity) (9)

Table 1 ndash Geophysical log response values of major mineral components in potash ore in the Prairie Evaporite Saskatchewan (summarized from Rider 1996 Tixier and Alger 1970 Edmundson and Raymer 1979 Crain 2013)

Logs Measurement Halite Sylvite CarnalliteInsolubles (mostly

clays) EquationGamma ray API 0 747 200 120 to 150 (2)Sonic travel time sft 67 74 78 90 to 120 (3)Density log gcm3 203 186 157 235 to 265 (4)Neutron hydrogen index fraction 0 -002 06 03 to 04 (5)Photoelectric barcm3 472 876 429 145 to 35 (6)Sonic travel time sm 220 242 256 155 to 212 (7)Density log kgcm3 2030 1860 1570 2350 to 2650 (8)Neutron porosity -3 -3 60 30 to 37 (9)

Saskatchewan Geological Survey 4 Summary of Investigations 2013 Volume 1

Figure 2 ndash Plot of K2O from chemical analysis (Hardy et al 2010) versus gamma-ray values in API units from gamma-ray log for well 13-24-19-25W2 in the upper part of the Prairie Evaporite Saskatchewan

Where Halite Sylvite Carnallite and Insolubles are percentages of these minerals (unknowns) The ranges of log values for insolubles in Table 1 are tested and the upper values are used because they yielded the best results

Using equation (1) plus any three equations of different logs from (2) to (9) depending on log availability the four unknowns (ie percentage of halite sylvite carnallite and insolubles) are solved from four of these linear equations with Microsoftreg Excel spreadsheets Sylvite (KCl) content is then converted to K2O (K2O = 06317 x KCl)

Digital logs are used to obtain the log values to ensure accuracy and efficiency For a given potash bed digital log values were averaged every 0152 m K2O values were calculated for each of these consecutive intervals

3 Test of the Method for Potash Grade Calculation The method discussed above is tested for the Potash One Findlater 2113-24-19-25W2M (08K302) well drilled by Potash One Inc in 2008 where both geophysical logs and assay values are available The calculated results are compared to core assay data (Hardy et al 2010) Different combinations of geophysical logs produce different results and it is found that the combinations of gamma-density-neutron (equations 2 4 and 5) gamma-sonic-density (equations 2 3 and 4) and gamma-sonic-neutron (equations 2 3 and 5) yield the most comparable results with those of chemical analysis (Figures 3 to 5)

The plots show a very good agreement between the two sets of data for K2O and NaCl but more discrepancy for insolubles Carnallite is not included in the graph because of its small fraction

The average digital log values for every 0152 m and every 0025 m are plotted to see if the calculation accuracy can be improved by increasing points of count from logs (Figure 6) No significant improvement is observed

The method is also tested for the Athabasca et al Burr 1101-17-35-22W2M (07F215) drilled by Athabasca Potash Inc in 2007 The calculated K2O from three log combinations is also comparable to the chemical analysis data (Lomas 2008) Good agreements between the two sets of data are observed with slightly higher K2O from log calculations (Figure 7)

The correlations between K2O from chemical analysis and from well log calculation are illustrated in Figures 8 and 9 Very good correlations are shown when sample intervals with insolubles gt10 count for less than 10 of the total potash ore intervals Three different log combinations yield similar results (Figure 8) In contrast the correlations are poorer when sample intervals with insolubles gt10 count for about 40 of total potash ore intervals eg from 1524 m to 1537 m in well 2113-24-19-25W2M (Figure 9)

0

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0 100 200 300 400 500Gamma ray (API)

K2O

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Saskatchewan Geological Survey 5 Summary of Investigations 2013 Volume 1

Figure 3 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Den-Nue) (equations 2 4 and 5) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Figure 4 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Son-Den) (equations 2 3 and 4) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Dep

th (

m)

A) K2O B) NaCl C) Insoluble

1520

1530

1540

1550

1560

1570

1580

0 20 40 60 0 20 40 60 80 0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

A) K2O B) NaCl C) Insoluble

Dep

th (

m)

1520

1530

1540

1550

1560

1570

1580

0 20 40 60 0 20 40 60 80 0 20 40 60

Calculated from Gr-Son-Den logs Chemical analysis

Saskatchewan Geological Survey 6 Summary of Investigations 2013 Volume 1

Figure 5 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Son-Nue) (equations 2 3 and 5) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Figure 6 ndash Comparison of K2O derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Den-Nue) (equations 2 4 and 5) for well 2113-24-19-25W2M (08K302) in upper part of the Prairie Evaporite Saskatchewan A) data point interval is 0152 m and B) data point interval is 0025 m

A) K2O B) NaCl C) Insoluble

Dep

th (

m)

1520

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Calculated from Gr-Son-Neu logs Chemical analysis

A) K2O

Dep

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)

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0 20 40 60B) K2O

Dep

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)

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Calculated from Gr-Den-Neu logs Chemical analysis

Saskatchewan Geological Survey 7 Summary of Investigations 2013 Volume 1

Figure 7 ndash Comparison of K2O derived from chemical analysis (Lomas 2008) and log calculation for well 1101-17-35-22W2M (07F215) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue (equations 2 4 and 5) B) combination Gr-Son-Den (equations 2 3 and 4) and C) combination Gr-Son-Nue (equations 2 3 and 5)

4 Discussion There are numerous factors that can affect the calculation and can be the sources for errors for this mathematical method

a) Effect of Bit Size and Drilling Mud on Gamma-ray API Value

Equation (2) is established based on an assumption of a linear relationship between K2O and gamma value in API units This can be tested by a plot (Figure 2) when core analysis data is available and wells are logged by the same company in a project area However a linear relationship may not be observed when gamma value (API) is larger than 300 or 350 especially for older logs In such cases it has been found that the API values are not only related to K2O but also to the bit size and density of drilling mud A corrected relationship between K2O and gamma API values has been proposed by Crain and Anderson (1966) as follows

APIGamma corrected = APIGamma log[1+005 (Dhole size - 6)+320( Dhole size - 6)(APIGamma log +100)] [1+01(Mmud density-72)]

where APIGamma log is gamma-ray log reading (API) Dhole size is drill hole size (inches) and Mmud density is weight of drilling mud (lbgal)

b) Composition of Insolubles

The insolubles in each potash-rich interval are comprised of different mineral fractions and the mineral compositions of insolubles are not determined for this study As a result the values of log responses for insolubles used in calculation may not represent the true log response values for insolubles of the potash interval which may cause error in calculation When samples with insolubles gt10 count for less than 10 of the total potash intervals the effect of the insolubles on the calculation is not significant and the calculated K2O is very close to that of chemical analysis (Figure 8) In general the samples with insoluble content gt10 have higher calculated K2O than that of chemical analysis (Figure 8)

Plots of Insolubles of core analysis versus Insolubles calculated from log suite in potash members of the Prairie Evaporite show poor agreements (Figures 3C 4C and 5C) The discrepancy may attribute mainly to the reason discussed above and the fact that the most insoluble-rich layers (clay seams) are thinner than the detection limit of log tools

Dep

th (

m)

950

960

970

980

990

1000

0 20 40 60 0 20 40 60A) K

2O C) K

2OB) K

2O

0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

Calculated from Gr-Son-Den logs Chemical analysis

Calculated from Gr-Son-Neu logs Chemical analysis

Saskatchewan Geological Survey 8 Summary of Investigations 2013 Volume 1

Figure 9 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for 40 of the total potash intervals (1524 to 1537 m) of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

Figure 8 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for less than 10 of the total potash intervals of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

y = 10484x - 17085

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

B)

K2O

fr

om c

hem

ical

ana

lysi

s

K2O calculated from Gr-Son-Den logs

y = 10613x - 23059

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

A)

K2O calculated from Gr-Den-Nue logs

K2O

fr

om c

hem

ical

ana

lysi

s

y = 10591x - 21491

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

C)

K2O calculated from Gr-Son-Nue logs

K2O

fr

om c

hem

ical

ana

lysi

s

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

A)

K2O

fr

om c

hem

ical

ana

lysi

s

K2O calculated from Gr-Den-Nue logs

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

K2O calculated from Gr-Son-Nue logs

C)

K2O

fr

om c

hem

ical

ana

lysi

s

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

B)

K2O calculated from Gr-Son-Den logs

K2O

fr

om c

hem

ical

ana

lysi

s

Saskatchewan Geological Survey 9 Summary of Investigations 2013 Volume 1

When samples with insolubles gt10 count for about 40 of the total potash intervals plots show more scattered distributions and the values of K2O obtained from log calculation are generally higher than that of chemical analysis (Figure 9)

c) Other Factors

When bed thickness is small a logging tool will measure not only the radiation of the thin bed but also that of adjacent beds As a result the measured radiation will be the sum of radiation emitted by the thin bed plus the sum of the radiation from all adjacent beds resulting in a discrepancy between the core analysis and log calculation The bed thickness corrections are suggested where the potash bed is less than 1 m (Nelson 2007 Crain 2013)

When a minimum of three logs is not available fewer minerals must be included in the calculation A potash geologist should apply their knowledge of mineral composition in the project area to determine which mineral has minimum content that can be delimited in the calculation Insolubles may be easy to ignore and carnallite may be negligible in carnallite-free areas

Because of small carnallite content in the test drill holes it is difficult to evaluate the effect of carnallite on this mathematic method Further work is required to test the method in a drill hole containing more carnallite or dominantly carnallite

Other factors affecting the calculation method include excessive logging speed depth misalignment between logging depths and core depths gamma-ray attenuation caused by cement and casing weight and content of drilling mud presence of uranium and thorium and washouts of potash zone (Nelson 2007 Crain 2013) Care must be taken when using logs for quantitative potash ore grade calculation

5 Summary Quantitative estimation of the fraction of sylvite halite carnallite and insolubles can be achieved by mathematical calculations from geophysical well logs The accuracy and precision of estimation largely depends on the total amount of insolubles in individual intervals Intervals with the smallest amount of insolubles provide the best results The method could be a valuable tool at the early stage of project evaluation where potash cores are not available The digital logs have improved efficiency and accuracy significantly by avoiding manual log reading and data entry Further studies are required in the area where carnallite is more predominant

6 Acknowledgements The authors wish to express their appreciation to Ross Crain for helpful discussions during preparation of this paper Our special acknowledgments go to K+S Potash Canada and BHP Billiton to give us permission to use their data for this study We also thank Megan Love for Figure 1 and Fran Haidl and Arden Marsh for comments andsuggestions for improvement of this paper

7 References Alger RP and Crain ER (1965) Defining evaporite deposits with electrical well logs in Second Symposium on

Salt Trans Northern Ohio Geol Soc Vol 2 p116-130

Crain RC (2013) Crainrsquos petrophysical handbook URLlthttpwwwspec2000net17-specpotashhtmgt accessed 26 June 2013

Crain ER and Anderson WB (1966) Quantitative log evaluation of the Prairie Evaporite formation in Saskatchewan J Can Petrol Tech v5 p145-152

Edmundson H and Raymer LL (1979) Radioactive logging parameters for common mineral Log Analyst v20 no5 p38-47

Fuzesy A (1982) Potash in Saskatchewan Sask Energy Mines Rep 181 44p

Hardy M Halabura SP Shewfelt D and Hambley DF (2010) Technical report 2010 potash reserve assessment for subsurface mineral permit KP 289 Saskatchewan URLlthttpwwwsedarcomGetFile dolang=ENampdocClass=24ampissuerNo=00007718ampfileName=csfsproddata112filings0165919500000001o3A5CCPU5C20105CPotashOneInc5C101112TR_sjg5CTR_sjgpdfgt accessed 4 June 2013

Saskatchewan Geological Survey 10 Summary of Investigations 2013 Volume 1

Holter ME (1969) The Middle Devonian Prairie Evaporite of Saskatchewan Sask Dept Miner Resour Rep 123 134p

Nelson P H (2007) Evaluation of potash grade with gamma-ray logs US Geological Survey Open File Report 2007-1292 14p

Lomas S (2008) NI 43ndash101 Technical Report for a resource estimation on the Burr Project Athabasca Potash Inc Saskatchewan Canada URLlthttpwwwsedarcomGetFiledolang=ENampdocClass=24ampissuerNo= 00026182ampfileName=csfsproddata93filings0134320800000001i3A5C1SEDAR5C5546375CTechnicalReport5CTechnicalReportpdfgt accessed 4 June 2013

Rider M (1996) The Geological Interpretation of Well Logs 2nd Edition Whittles Publishing Caithness 280p

Saskatchewan Geological Survey (2013) Mineral Resources Map of Saskatchewan 2013 Edition Sask Ministry of the Economy Saskatchewan Geological Survey Misc Rep 2013-1 URLlthttpwwweconomygovskca mineralresourcemapgt accessed 26 July 2013

Tixier MP and Alger PR (1970) Log evaluation of nonmetallic mineral deposits Geophys v35 no1 p124-142

US Geological Survey (2013) Mineral Commodity Summaries 2013URLlthttpmineralsusgsgovminerals pubsmcs2013mcs2013pdfgt accessed 15 July 2013

Yang C Jensen G and Berenyi J (2009) The stratigraphic framework of the potash-rich members of the Middle Devonian upper Prairie Evaporite Formation Saskatchewan in Summary of Investigations 2009 Volume 1 Saskatchewan Geological Survey Sask Ministry of Energy and Resources Misc Rep 2009-41 Paper A-4 28p URL lthttpeconomygovskcaSOI2009V1_A4gt

Saskatchewan Geological Survey 4 Summary of Investigations 2013 Volume 1

Figure 2 ndash Plot of K2O from chemical analysis (Hardy et al 2010) versus gamma-ray values in API units from gamma-ray log for well 13-24-19-25W2 in the upper part of the Prairie Evaporite Saskatchewan

Where Halite Sylvite Carnallite and Insolubles are percentages of these minerals (unknowns) The ranges of log values for insolubles in Table 1 are tested and the upper values are used because they yielded the best results

Using equation (1) plus any three equations of different logs from (2) to (9) depending on log availability the four unknowns (ie percentage of halite sylvite carnallite and insolubles) are solved from four of these linear equations with Microsoftreg Excel spreadsheets Sylvite (KCl) content is then converted to K2O (K2O = 06317 x KCl)

Digital logs are used to obtain the log values to ensure accuracy and efficiency For a given potash bed digital log values were averaged every 0152 m K2O values were calculated for each of these consecutive intervals

3 Test of the Method for Potash Grade Calculation The method discussed above is tested for the Potash One Findlater 2113-24-19-25W2M (08K302) well drilled by Potash One Inc in 2008 where both geophysical logs and assay values are available The calculated results are compared to core assay data (Hardy et al 2010) Different combinations of geophysical logs produce different results and it is found that the combinations of gamma-density-neutron (equations 2 4 and 5) gamma-sonic-density (equations 2 3 and 4) and gamma-sonic-neutron (equations 2 3 and 5) yield the most comparable results with those of chemical analysis (Figures 3 to 5)

The plots show a very good agreement between the two sets of data for K2O and NaCl but more discrepancy for insolubles Carnallite is not included in the graph because of its small fraction

The average digital log values for every 0152 m and every 0025 m are plotted to see if the calculation accuracy can be improved by increasing points of count from logs (Figure 6) No significant improvement is observed

The method is also tested for the Athabasca et al Burr 1101-17-35-22W2M (07F215) drilled by Athabasca Potash Inc in 2007 The calculated K2O from three log combinations is also comparable to the chemical analysis data (Lomas 2008) Good agreements between the two sets of data are observed with slightly higher K2O from log calculations (Figure 7)

The correlations between K2O from chemical analysis and from well log calculation are illustrated in Figures 8 and 9 Very good correlations are shown when sample intervals with insolubles gt10 count for less than 10 of the total potash ore intervals Three different log combinations yield similar results (Figure 8) In contrast the correlations are poorer when sample intervals with insolubles gt10 count for about 40 of total potash ore intervals eg from 1524 m to 1537 m in well 2113-24-19-25W2M (Figure 9)

0

10

20

30

40

50

0 100 200 300 400 500Gamma ray (API)

K2O

fr

om c

hem

ical

ana

lysi

s

Saskatchewan Geological Survey 5 Summary of Investigations 2013 Volume 1

Figure 3 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Den-Nue) (equations 2 4 and 5) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Figure 4 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Son-Den) (equations 2 3 and 4) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Dep

th (

m)

A) K2O B) NaCl C) Insoluble

1520

1530

1540

1550

1560

1570

1580

0 20 40 60 0 20 40 60 80 0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

A) K2O B) NaCl C) Insoluble

Dep

th (

m)

1520

1530

1540

1550

1560

1570

1580

0 20 40 60 0 20 40 60 80 0 20 40 60

Calculated from Gr-Son-Den logs Chemical analysis

Saskatchewan Geological Survey 6 Summary of Investigations 2013 Volume 1

Figure 5 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Son-Nue) (equations 2 3 and 5) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Figure 6 ndash Comparison of K2O derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Den-Nue) (equations 2 4 and 5) for well 2113-24-19-25W2M (08K302) in upper part of the Prairie Evaporite Saskatchewan A) data point interval is 0152 m and B) data point interval is 0025 m

A) K2O B) NaCl C) Insoluble

Dep

th (

m)

1520

1530

1540

1550

1560

1570

1580

0 20 40 60 0 20 40 60 80 0 20 40 60

Calculated from Gr-Son-Neu logs Chemical analysis

A) K2O

Dep

th (m

)

1520

1530

1540

1550

1560

1570

1580

0 20 40 60B) K2O

Dep

th (m

)

1520

1530

1540

1550

1560

1570

1580

0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

Saskatchewan Geological Survey 7 Summary of Investigations 2013 Volume 1

Figure 7 ndash Comparison of K2O derived from chemical analysis (Lomas 2008) and log calculation for well 1101-17-35-22W2M (07F215) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue (equations 2 4 and 5) B) combination Gr-Son-Den (equations 2 3 and 4) and C) combination Gr-Son-Nue (equations 2 3 and 5)

4 Discussion There are numerous factors that can affect the calculation and can be the sources for errors for this mathematical method

a) Effect of Bit Size and Drilling Mud on Gamma-ray API Value

Equation (2) is established based on an assumption of a linear relationship between K2O and gamma value in API units This can be tested by a plot (Figure 2) when core analysis data is available and wells are logged by the same company in a project area However a linear relationship may not be observed when gamma value (API) is larger than 300 or 350 especially for older logs In such cases it has been found that the API values are not only related to K2O but also to the bit size and density of drilling mud A corrected relationship between K2O and gamma API values has been proposed by Crain and Anderson (1966) as follows

APIGamma corrected = APIGamma log[1+005 (Dhole size - 6)+320( Dhole size - 6)(APIGamma log +100)] [1+01(Mmud density-72)]

where APIGamma log is gamma-ray log reading (API) Dhole size is drill hole size (inches) and Mmud density is weight of drilling mud (lbgal)

b) Composition of Insolubles

The insolubles in each potash-rich interval are comprised of different mineral fractions and the mineral compositions of insolubles are not determined for this study As a result the values of log responses for insolubles used in calculation may not represent the true log response values for insolubles of the potash interval which may cause error in calculation When samples with insolubles gt10 count for less than 10 of the total potash intervals the effect of the insolubles on the calculation is not significant and the calculated K2O is very close to that of chemical analysis (Figure 8) In general the samples with insoluble content gt10 have higher calculated K2O than that of chemical analysis (Figure 8)

Plots of Insolubles of core analysis versus Insolubles calculated from log suite in potash members of the Prairie Evaporite show poor agreements (Figures 3C 4C and 5C) The discrepancy may attribute mainly to the reason discussed above and the fact that the most insoluble-rich layers (clay seams) are thinner than the detection limit of log tools

Dep

th (

m)

950

960

970

980

990

1000

0 20 40 60 0 20 40 60A) K

2O C) K

2OB) K

2O

0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

Calculated from Gr-Son-Den logs Chemical analysis

Calculated from Gr-Son-Neu logs Chemical analysis

Saskatchewan Geological Survey 8 Summary of Investigations 2013 Volume 1

Figure 9 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for 40 of the total potash intervals (1524 to 1537 m) of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

Figure 8 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for less than 10 of the total potash intervals of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

y = 10484x - 17085

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

B)

K2O

fr

om c

hem

ical

ana

lysi

s

K2O calculated from Gr-Son-Den logs

y = 10613x - 23059

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

A)

K2O calculated from Gr-Den-Nue logs

K2O

fr

om c

hem

ical

ana

lysi

s

y = 10591x - 21491

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

C)

K2O calculated from Gr-Son-Nue logs

K2O

fr

om c

hem

ical

ana

lysi

s

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

A)

K2O

fr

om c

hem

ical

ana

lysi

s

K2O calculated from Gr-Den-Nue logs

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

K2O calculated from Gr-Son-Nue logs

C)

K2O

fr

om c

hem

ical

ana

lysi

s

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

B)

K2O calculated from Gr-Son-Den logs

K2O

fr

om c

hem

ical

ana

lysi

s

Saskatchewan Geological Survey 9 Summary of Investigations 2013 Volume 1

When samples with insolubles gt10 count for about 40 of the total potash intervals plots show more scattered distributions and the values of K2O obtained from log calculation are generally higher than that of chemical analysis (Figure 9)

c) Other Factors

When bed thickness is small a logging tool will measure not only the radiation of the thin bed but also that of adjacent beds As a result the measured radiation will be the sum of radiation emitted by the thin bed plus the sum of the radiation from all adjacent beds resulting in a discrepancy between the core analysis and log calculation The bed thickness corrections are suggested where the potash bed is less than 1 m (Nelson 2007 Crain 2013)

When a minimum of three logs is not available fewer minerals must be included in the calculation A potash geologist should apply their knowledge of mineral composition in the project area to determine which mineral has minimum content that can be delimited in the calculation Insolubles may be easy to ignore and carnallite may be negligible in carnallite-free areas

Because of small carnallite content in the test drill holes it is difficult to evaluate the effect of carnallite on this mathematic method Further work is required to test the method in a drill hole containing more carnallite or dominantly carnallite

Other factors affecting the calculation method include excessive logging speed depth misalignment between logging depths and core depths gamma-ray attenuation caused by cement and casing weight and content of drilling mud presence of uranium and thorium and washouts of potash zone (Nelson 2007 Crain 2013) Care must be taken when using logs for quantitative potash ore grade calculation

5 Summary Quantitative estimation of the fraction of sylvite halite carnallite and insolubles can be achieved by mathematical calculations from geophysical well logs The accuracy and precision of estimation largely depends on the total amount of insolubles in individual intervals Intervals with the smallest amount of insolubles provide the best results The method could be a valuable tool at the early stage of project evaluation where potash cores are not available The digital logs have improved efficiency and accuracy significantly by avoiding manual log reading and data entry Further studies are required in the area where carnallite is more predominant

6 Acknowledgements The authors wish to express their appreciation to Ross Crain for helpful discussions during preparation of this paper Our special acknowledgments go to K+S Potash Canada and BHP Billiton to give us permission to use their data for this study We also thank Megan Love for Figure 1 and Fran Haidl and Arden Marsh for comments andsuggestions for improvement of this paper

7 References Alger RP and Crain ER (1965) Defining evaporite deposits with electrical well logs in Second Symposium on

Salt Trans Northern Ohio Geol Soc Vol 2 p116-130

Crain RC (2013) Crainrsquos petrophysical handbook URLlthttpwwwspec2000net17-specpotashhtmgt accessed 26 June 2013

Crain ER and Anderson WB (1966) Quantitative log evaluation of the Prairie Evaporite formation in Saskatchewan J Can Petrol Tech v5 p145-152

Edmundson H and Raymer LL (1979) Radioactive logging parameters for common mineral Log Analyst v20 no5 p38-47

Fuzesy A (1982) Potash in Saskatchewan Sask Energy Mines Rep 181 44p

Hardy M Halabura SP Shewfelt D and Hambley DF (2010) Technical report 2010 potash reserve assessment for subsurface mineral permit KP 289 Saskatchewan URLlthttpwwwsedarcomGetFile dolang=ENampdocClass=24ampissuerNo=00007718ampfileName=csfsproddata112filings0165919500000001o3A5CCPU5C20105CPotashOneInc5C101112TR_sjg5CTR_sjgpdfgt accessed 4 June 2013

Saskatchewan Geological Survey 10 Summary of Investigations 2013 Volume 1

Holter ME (1969) The Middle Devonian Prairie Evaporite of Saskatchewan Sask Dept Miner Resour Rep 123 134p

Nelson P H (2007) Evaluation of potash grade with gamma-ray logs US Geological Survey Open File Report 2007-1292 14p

Lomas S (2008) NI 43ndash101 Technical Report for a resource estimation on the Burr Project Athabasca Potash Inc Saskatchewan Canada URLlthttpwwwsedarcomGetFiledolang=ENampdocClass=24ampissuerNo= 00026182ampfileName=csfsproddata93filings0134320800000001i3A5C1SEDAR5C5546375CTechnicalReport5CTechnicalReportpdfgt accessed 4 June 2013

Rider M (1996) The Geological Interpretation of Well Logs 2nd Edition Whittles Publishing Caithness 280p

Saskatchewan Geological Survey (2013) Mineral Resources Map of Saskatchewan 2013 Edition Sask Ministry of the Economy Saskatchewan Geological Survey Misc Rep 2013-1 URLlthttpwwweconomygovskca mineralresourcemapgt accessed 26 July 2013

Tixier MP and Alger PR (1970) Log evaluation of nonmetallic mineral deposits Geophys v35 no1 p124-142

US Geological Survey (2013) Mineral Commodity Summaries 2013URLlthttpmineralsusgsgovminerals pubsmcs2013mcs2013pdfgt accessed 15 July 2013

Yang C Jensen G and Berenyi J (2009) The stratigraphic framework of the potash-rich members of the Middle Devonian upper Prairie Evaporite Formation Saskatchewan in Summary of Investigations 2009 Volume 1 Saskatchewan Geological Survey Sask Ministry of Energy and Resources Misc Rep 2009-41 Paper A-4 28p URL lthttpeconomygovskcaSOI2009V1_A4gt

Saskatchewan Geological Survey 5 Summary of Investigations 2013 Volume 1

Figure 3 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Den-Nue) (equations 2 4 and 5) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Figure 4 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Son-Den) (equations 2 3 and 4) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Dep

th (

m)

A) K2O B) NaCl C) Insoluble

1520

1530

1540

1550

1560

1570

1580

0 20 40 60 0 20 40 60 80 0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

A) K2O B) NaCl C) Insoluble

Dep

th (

m)

1520

1530

1540

1550

1560

1570

1580

0 20 40 60 0 20 40 60 80 0 20 40 60

Calculated from Gr-Son-Den logs Chemical analysis

Saskatchewan Geological Survey 6 Summary of Investigations 2013 Volume 1

Figure 5 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Son-Nue) (equations 2 3 and 5) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Figure 6 ndash Comparison of K2O derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Den-Nue) (equations 2 4 and 5) for well 2113-24-19-25W2M (08K302) in upper part of the Prairie Evaporite Saskatchewan A) data point interval is 0152 m and B) data point interval is 0025 m

A) K2O B) NaCl C) Insoluble

Dep

th (

m)

1520

1530

1540

1550

1560

1570

1580

0 20 40 60 0 20 40 60 80 0 20 40 60

Calculated from Gr-Son-Neu logs Chemical analysis

A) K2O

Dep

th (m

)

1520

1530

1540

1550

1560

1570

1580

0 20 40 60B) K2O

Dep

th (m

)

1520

1530

1540

1550

1560

1570

1580

0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

Saskatchewan Geological Survey 7 Summary of Investigations 2013 Volume 1

Figure 7 ndash Comparison of K2O derived from chemical analysis (Lomas 2008) and log calculation for well 1101-17-35-22W2M (07F215) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue (equations 2 4 and 5) B) combination Gr-Son-Den (equations 2 3 and 4) and C) combination Gr-Son-Nue (equations 2 3 and 5)

4 Discussion There are numerous factors that can affect the calculation and can be the sources for errors for this mathematical method

a) Effect of Bit Size and Drilling Mud on Gamma-ray API Value

Equation (2) is established based on an assumption of a linear relationship between K2O and gamma value in API units This can be tested by a plot (Figure 2) when core analysis data is available and wells are logged by the same company in a project area However a linear relationship may not be observed when gamma value (API) is larger than 300 or 350 especially for older logs In such cases it has been found that the API values are not only related to K2O but also to the bit size and density of drilling mud A corrected relationship between K2O and gamma API values has been proposed by Crain and Anderson (1966) as follows

APIGamma corrected = APIGamma log[1+005 (Dhole size - 6)+320( Dhole size - 6)(APIGamma log +100)] [1+01(Mmud density-72)]

where APIGamma log is gamma-ray log reading (API) Dhole size is drill hole size (inches) and Mmud density is weight of drilling mud (lbgal)

b) Composition of Insolubles

The insolubles in each potash-rich interval are comprised of different mineral fractions and the mineral compositions of insolubles are not determined for this study As a result the values of log responses for insolubles used in calculation may not represent the true log response values for insolubles of the potash interval which may cause error in calculation When samples with insolubles gt10 count for less than 10 of the total potash intervals the effect of the insolubles on the calculation is not significant and the calculated K2O is very close to that of chemical analysis (Figure 8) In general the samples with insoluble content gt10 have higher calculated K2O than that of chemical analysis (Figure 8)

Plots of Insolubles of core analysis versus Insolubles calculated from log suite in potash members of the Prairie Evaporite show poor agreements (Figures 3C 4C and 5C) The discrepancy may attribute mainly to the reason discussed above and the fact that the most insoluble-rich layers (clay seams) are thinner than the detection limit of log tools

Dep

th (

m)

950

960

970

980

990

1000

0 20 40 60 0 20 40 60A) K

2O C) K

2OB) K

2O

0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

Calculated from Gr-Son-Den logs Chemical analysis

Calculated from Gr-Son-Neu logs Chemical analysis

Saskatchewan Geological Survey 8 Summary of Investigations 2013 Volume 1

Figure 9 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for 40 of the total potash intervals (1524 to 1537 m) of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

Figure 8 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for less than 10 of the total potash intervals of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

y = 10484x - 17085

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

B)

K2O

fr

om c

hem

ical

ana

lysi

s

K2O calculated from Gr-Son-Den logs

y = 10613x - 23059

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

A)

K2O calculated from Gr-Den-Nue logs

K2O

fr

om c

hem

ical

ana

lysi

s

y = 10591x - 21491

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

C)

K2O calculated from Gr-Son-Nue logs

K2O

fr

om c

hem

ical

ana

lysi

s

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

A)

K2O

fr

om c

hem

ical

ana

lysi

s

K2O calculated from Gr-Den-Nue logs

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

K2O calculated from Gr-Son-Nue logs

C)

K2O

fr

om c

hem

ical

ana

lysi

s

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

B)

K2O calculated from Gr-Son-Den logs

K2O

fr

om c

hem

ical

ana

lysi

s

Saskatchewan Geological Survey 9 Summary of Investigations 2013 Volume 1

When samples with insolubles gt10 count for about 40 of the total potash intervals plots show more scattered distributions and the values of K2O obtained from log calculation are generally higher than that of chemical analysis (Figure 9)

c) Other Factors

When bed thickness is small a logging tool will measure not only the radiation of the thin bed but also that of adjacent beds As a result the measured radiation will be the sum of radiation emitted by the thin bed plus the sum of the radiation from all adjacent beds resulting in a discrepancy between the core analysis and log calculation The bed thickness corrections are suggested where the potash bed is less than 1 m (Nelson 2007 Crain 2013)

When a minimum of three logs is not available fewer minerals must be included in the calculation A potash geologist should apply their knowledge of mineral composition in the project area to determine which mineral has minimum content that can be delimited in the calculation Insolubles may be easy to ignore and carnallite may be negligible in carnallite-free areas

Because of small carnallite content in the test drill holes it is difficult to evaluate the effect of carnallite on this mathematic method Further work is required to test the method in a drill hole containing more carnallite or dominantly carnallite

Other factors affecting the calculation method include excessive logging speed depth misalignment between logging depths and core depths gamma-ray attenuation caused by cement and casing weight and content of drilling mud presence of uranium and thorium and washouts of potash zone (Nelson 2007 Crain 2013) Care must be taken when using logs for quantitative potash ore grade calculation

5 Summary Quantitative estimation of the fraction of sylvite halite carnallite and insolubles can be achieved by mathematical calculations from geophysical well logs The accuracy and precision of estimation largely depends on the total amount of insolubles in individual intervals Intervals with the smallest amount of insolubles provide the best results The method could be a valuable tool at the early stage of project evaluation where potash cores are not available The digital logs have improved efficiency and accuracy significantly by avoiding manual log reading and data entry Further studies are required in the area where carnallite is more predominant

6 Acknowledgements The authors wish to express their appreciation to Ross Crain for helpful discussions during preparation of this paper Our special acknowledgments go to K+S Potash Canada and BHP Billiton to give us permission to use their data for this study We also thank Megan Love for Figure 1 and Fran Haidl and Arden Marsh for comments andsuggestions for improvement of this paper

7 References Alger RP and Crain ER (1965) Defining evaporite deposits with electrical well logs in Second Symposium on

Salt Trans Northern Ohio Geol Soc Vol 2 p116-130

Crain RC (2013) Crainrsquos petrophysical handbook URLlthttpwwwspec2000net17-specpotashhtmgt accessed 26 June 2013

Crain ER and Anderson WB (1966) Quantitative log evaluation of the Prairie Evaporite formation in Saskatchewan J Can Petrol Tech v5 p145-152

Edmundson H and Raymer LL (1979) Radioactive logging parameters for common mineral Log Analyst v20 no5 p38-47

Fuzesy A (1982) Potash in Saskatchewan Sask Energy Mines Rep 181 44p

Hardy M Halabura SP Shewfelt D and Hambley DF (2010) Technical report 2010 potash reserve assessment for subsurface mineral permit KP 289 Saskatchewan URLlthttpwwwsedarcomGetFile dolang=ENampdocClass=24ampissuerNo=00007718ampfileName=csfsproddata112filings0165919500000001o3A5CCPU5C20105CPotashOneInc5C101112TR_sjg5CTR_sjgpdfgt accessed 4 June 2013

Saskatchewan Geological Survey 10 Summary of Investigations 2013 Volume 1

Holter ME (1969) The Middle Devonian Prairie Evaporite of Saskatchewan Sask Dept Miner Resour Rep 123 134p

Nelson P H (2007) Evaluation of potash grade with gamma-ray logs US Geological Survey Open File Report 2007-1292 14p

Lomas S (2008) NI 43ndash101 Technical Report for a resource estimation on the Burr Project Athabasca Potash Inc Saskatchewan Canada URLlthttpwwwsedarcomGetFiledolang=ENampdocClass=24ampissuerNo= 00026182ampfileName=csfsproddata93filings0134320800000001i3A5C1SEDAR5C5546375CTechnicalReport5CTechnicalReportpdfgt accessed 4 June 2013

Rider M (1996) The Geological Interpretation of Well Logs 2nd Edition Whittles Publishing Caithness 280p

Saskatchewan Geological Survey (2013) Mineral Resources Map of Saskatchewan 2013 Edition Sask Ministry of the Economy Saskatchewan Geological Survey Misc Rep 2013-1 URLlthttpwwweconomygovskca mineralresourcemapgt accessed 26 July 2013

Tixier MP and Alger PR (1970) Log evaluation of nonmetallic mineral deposits Geophys v35 no1 p124-142

US Geological Survey (2013) Mineral Commodity Summaries 2013URLlthttpmineralsusgsgovminerals pubsmcs2013mcs2013pdfgt accessed 15 July 2013

Yang C Jensen G and Berenyi J (2009) The stratigraphic framework of the potash-rich members of the Middle Devonian upper Prairie Evaporite Formation Saskatchewan in Summary of Investigations 2009 Volume 1 Saskatchewan Geological Survey Sask Ministry of Energy and Resources Misc Rep 2009-41 Paper A-4 28p URL lthttpeconomygovskcaSOI2009V1_A4gt

Saskatchewan Geological Survey 6 Summary of Investigations 2013 Volume 1

Figure 5 ndash Comparison of A) K2O B) NaCl and C) insolubles derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Son-Nue) (equations 2 3 and 5) for well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan

Figure 6 ndash Comparison of K2O derived from chemical analysis (Hardy et al 2010) and log calculation (combination Gr-Den-Nue) (equations 2 4 and 5) for well 2113-24-19-25W2M (08K302) in upper part of the Prairie Evaporite Saskatchewan A) data point interval is 0152 m and B) data point interval is 0025 m

A) K2O B) NaCl C) Insoluble

Dep

th (

m)

1520

1530

1540

1550

1560

1570

1580

0 20 40 60 0 20 40 60 80 0 20 40 60

Calculated from Gr-Son-Neu logs Chemical analysis

A) K2O

Dep

th (m

)

1520

1530

1540

1550

1560

1570

1580

0 20 40 60B) K2O

Dep

th (m

)

1520

1530

1540

1550

1560

1570

1580

0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

Saskatchewan Geological Survey 7 Summary of Investigations 2013 Volume 1

Figure 7 ndash Comparison of K2O derived from chemical analysis (Lomas 2008) and log calculation for well 1101-17-35-22W2M (07F215) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue (equations 2 4 and 5) B) combination Gr-Son-Den (equations 2 3 and 4) and C) combination Gr-Son-Nue (equations 2 3 and 5)

4 Discussion There are numerous factors that can affect the calculation and can be the sources for errors for this mathematical method

a) Effect of Bit Size and Drilling Mud on Gamma-ray API Value

Equation (2) is established based on an assumption of a linear relationship between K2O and gamma value in API units This can be tested by a plot (Figure 2) when core analysis data is available and wells are logged by the same company in a project area However a linear relationship may not be observed when gamma value (API) is larger than 300 or 350 especially for older logs In such cases it has been found that the API values are not only related to K2O but also to the bit size and density of drilling mud A corrected relationship between K2O and gamma API values has been proposed by Crain and Anderson (1966) as follows

APIGamma corrected = APIGamma log[1+005 (Dhole size - 6)+320( Dhole size - 6)(APIGamma log +100)] [1+01(Mmud density-72)]

where APIGamma log is gamma-ray log reading (API) Dhole size is drill hole size (inches) and Mmud density is weight of drilling mud (lbgal)

b) Composition of Insolubles

The insolubles in each potash-rich interval are comprised of different mineral fractions and the mineral compositions of insolubles are not determined for this study As a result the values of log responses for insolubles used in calculation may not represent the true log response values for insolubles of the potash interval which may cause error in calculation When samples with insolubles gt10 count for less than 10 of the total potash intervals the effect of the insolubles on the calculation is not significant and the calculated K2O is very close to that of chemical analysis (Figure 8) In general the samples with insoluble content gt10 have higher calculated K2O than that of chemical analysis (Figure 8)

Plots of Insolubles of core analysis versus Insolubles calculated from log suite in potash members of the Prairie Evaporite show poor agreements (Figures 3C 4C and 5C) The discrepancy may attribute mainly to the reason discussed above and the fact that the most insoluble-rich layers (clay seams) are thinner than the detection limit of log tools

Dep

th (

m)

950

960

970

980

990

1000

0 20 40 60 0 20 40 60A) K

2O C) K

2OB) K

2O

0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

Calculated from Gr-Son-Den logs Chemical analysis

Calculated from Gr-Son-Neu logs Chemical analysis

Saskatchewan Geological Survey 8 Summary of Investigations 2013 Volume 1

Figure 9 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for 40 of the total potash intervals (1524 to 1537 m) of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

Figure 8 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for less than 10 of the total potash intervals of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

y = 10484x - 17085

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

B)

K2O

fr

om c

hem

ical

ana

lysi

s

K2O calculated from Gr-Son-Den logs

y = 10613x - 23059

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

A)

K2O calculated from Gr-Den-Nue logs

K2O

fr

om c

hem

ical

ana

lysi

s

y = 10591x - 21491

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

C)

K2O calculated from Gr-Son-Nue logs

K2O

fr

om c

hem

ical

ana

lysi

s

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

A)

K2O

fr

om c

hem

ical

ana

lysi

s

K2O calculated from Gr-Den-Nue logs

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

K2O calculated from Gr-Son-Nue logs

C)

K2O

fr

om c

hem

ical

ana

lysi

s

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

B)

K2O calculated from Gr-Son-Den logs

K2O

fr

om c

hem

ical

ana

lysi

s

Saskatchewan Geological Survey 9 Summary of Investigations 2013 Volume 1

When samples with insolubles gt10 count for about 40 of the total potash intervals plots show more scattered distributions and the values of K2O obtained from log calculation are generally higher than that of chemical analysis (Figure 9)

c) Other Factors

When bed thickness is small a logging tool will measure not only the radiation of the thin bed but also that of adjacent beds As a result the measured radiation will be the sum of radiation emitted by the thin bed plus the sum of the radiation from all adjacent beds resulting in a discrepancy between the core analysis and log calculation The bed thickness corrections are suggested where the potash bed is less than 1 m (Nelson 2007 Crain 2013)

When a minimum of three logs is not available fewer minerals must be included in the calculation A potash geologist should apply their knowledge of mineral composition in the project area to determine which mineral has minimum content that can be delimited in the calculation Insolubles may be easy to ignore and carnallite may be negligible in carnallite-free areas

Because of small carnallite content in the test drill holes it is difficult to evaluate the effect of carnallite on this mathematic method Further work is required to test the method in a drill hole containing more carnallite or dominantly carnallite

Other factors affecting the calculation method include excessive logging speed depth misalignment between logging depths and core depths gamma-ray attenuation caused by cement and casing weight and content of drilling mud presence of uranium and thorium and washouts of potash zone (Nelson 2007 Crain 2013) Care must be taken when using logs for quantitative potash ore grade calculation

5 Summary Quantitative estimation of the fraction of sylvite halite carnallite and insolubles can be achieved by mathematical calculations from geophysical well logs The accuracy and precision of estimation largely depends on the total amount of insolubles in individual intervals Intervals with the smallest amount of insolubles provide the best results The method could be a valuable tool at the early stage of project evaluation where potash cores are not available The digital logs have improved efficiency and accuracy significantly by avoiding manual log reading and data entry Further studies are required in the area where carnallite is more predominant

6 Acknowledgements The authors wish to express their appreciation to Ross Crain for helpful discussions during preparation of this paper Our special acknowledgments go to K+S Potash Canada and BHP Billiton to give us permission to use their data for this study We also thank Megan Love for Figure 1 and Fran Haidl and Arden Marsh for comments andsuggestions for improvement of this paper

7 References Alger RP and Crain ER (1965) Defining evaporite deposits with electrical well logs in Second Symposium on

Salt Trans Northern Ohio Geol Soc Vol 2 p116-130

Crain RC (2013) Crainrsquos petrophysical handbook URLlthttpwwwspec2000net17-specpotashhtmgt accessed 26 June 2013

Crain ER and Anderson WB (1966) Quantitative log evaluation of the Prairie Evaporite formation in Saskatchewan J Can Petrol Tech v5 p145-152

Edmundson H and Raymer LL (1979) Radioactive logging parameters for common mineral Log Analyst v20 no5 p38-47

Fuzesy A (1982) Potash in Saskatchewan Sask Energy Mines Rep 181 44p

Hardy M Halabura SP Shewfelt D and Hambley DF (2010) Technical report 2010 potash reserve assessment for subsurface mineral permit KP 289 Saskatchewan URLlthttpwwwsedarcomGetFile dolang=ENampdocClass=24ampissuerNo=00007718ampfileName=csfsproddata112filings0165919500000001o3A5CCPU5C20105CPotashOneInc5C101112TR_sjg5CTR_sjgpdfgt accessed 4 June 2013

Saskatchewan Geological Survey 10 Summary of Investigations 2013 Volume 1

Holter ME (1969) The Middle Devonian Prairie Evaporite of Saskatchewan Sask Dept Miner Resour Rep 123 134p

Nelson P H (2007) Evaluation of potash grade with gamma-ray logs US Geological Survey Open File Report 2007-1292 14p

Lomas S (2008) NI 43ndash101 Technical Report for a resource estimation on the Burr Project Athabasca Potash Inc Saskatchewan Canada URLlthttpwwwsedarcomGetFiledolang=ENampdocClass=24ampissuerNo= 00026182ampfileName=csfsproddata93filings0134320800000001i3A5C1SEDAR5C5546375CTechnicalReport5CTechnicalReportpdfgt accessed 4 June 2013

Rider M (1996) The Geological Interpretation of Well Logs 2nd Edition Whittles Publishing Caithness 280p

Saskatchewan Geological Survey (2013) Mineral Resources Map of Saskatchewan 2013 Edition Sask Ministry of the Economy Saskatchewan Geological Survey Misc Rep 2013-1 URLlthttpwwweconomygovskca mineralresourcemapgt accessed 26 July 2013

Tixier MP and Alger PR (1970) Log evaluation of nonmetallic mineral deposits Geophys v35 no1 p124-142

US Geological Survey (2013) Mineral Commodity Summaries 2013URLlthttpmineralsusgsgovminerals pubsmcs2013mcs2013pdfgt accessed 15 July 2013

Yang C Jensen G and Berenyi J (2009) The stratigraphic framework of the potash-rich members of the Middle Devonian upper Prairie Evaporite Formation Saskatchewan in Summary of Investigations 2009 Volume 1 Saskatchewan Geological Survey Sask Ministry of Energy and Resources Misc Rep 2009-41 Paper A-4 28p URL lthttpeconomygovskcaSOI2009V1_A4gt

Saskatchewan Geological Survey 7 Summary of Investigations 2013 Volume 1

Figure 7 ndash Comparison of K2O derived from chemical analysis (Lomas 2008) and log calculation for well 1101-17-35-22W2M (07F215) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue (equations 2 4 and 5) B) combination Gr-Son-Den (equations 2 3 and 4) and C) combination Gr-Son-Nue (equations 2 3 and 5)

4 Discussion There are numerous factors that can affect the calculation and can be the sources for errors for this mathematical method

a) Effect of Bit Size and Drilling Mud on Gamma-ray API Value

Equation (2) is established based on an assumption of a linear relationship between K2O and gamma value in API units This can be tested by a plot (Figure 2) when core analysis data is available and wells are logged by the same company in a project area However a linear relationship may not be observed when gamma value (API) is larger than 300 or 350 especially for older logs In such cases it has been found that the API values are not only related to K2O but also to the bit size and density of drilling mud A corrected relationship between K2O and gamma API values has been proposed by Crain and Anderson (1966) as follows

APIGamma corrected = APIGamma log[1+005 (Dhole size - 6)+320( Dhole size - 6)(APIGamma log +100)] [1+01(Mmud density-72)]

where APIGamma log is gamma-ray log reading (API) Dhole size is drill hole size (inches) and Mmud density is weight of drilling mud (lbgal)

b) Composition of Insolubles

The insolubles in each potash-rich interval are comprised of different mineral fractions and the mineral compositions of insolubles are not determined for this study As a result the values of log responses for insolubles used in calculation may not represent the true log response values for insolubles of the potash interval which may cause error in calculation When samples with insolubles gt10 count for less than 10 of the total potash intervals the effect of the insolubles on the calculation is not significant and the calculated K2O is very close to that of chemical analysis (Figure 8) In general the samples with insoluble content gt10 have higher calculated K2O than that of chemical analysis (Figure 8)

Plots of Insolubles of core analysis versus Insolubles calculated from log suite in potash members of the Prairie Evaporite show poor agreements (Figures 3C 4C and 5C) The discrepancy may attribute mainly to the reason discussed above and the fact that the most insoluble-rich layers (clay seams) are thinner than the detection limit of log tools

Dep

th (

m)

950

960

970

980

990

1000

0 20 40 60 0 20 40 60A) K

2O C) K

2OB) K

2O

0 20 40 60

Calculated from Gr-Den-Neu logs Chemical analysis

Calculated from Gr-Son-Den logs Chemical analysis

Calculated from Gr-Son-Neu logs Chemical analysis

Saskatchewan Geological Survey 8 Summary of Investigations 2013 Volume 1

Figure 9 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for 40 of the total potash intervals (1524 to 1537 m) of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

Figure 8 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for less than 10 of the total potash intervals of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

y = 10484x - 17085

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

B)

K2O

fr

om c

hem

ical

ana

lysi

s

K2O calculated from Gr-Son-Den logs

y = 10613x - 23059

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

A)

K2O calculated from Gr-Den-Nue logs

K2O

fr

om c

hem

ical

ana

lysi

s

y = 10591x - 21491

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

C)

K2O calculated from Gr-Son-Nue logs

K2O

fr

om c

hem

ical

ana

lysi

s

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

A)

K2O

fr

om c

hem

ical

ana

lysi

s

K2O calculated from Gr-Den-Nue logs

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

K2O calculated from Gr-Son-Nue logs

C)

K2O

fr

om c

hem

ical

ana

lysi

s

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

B)

K2O calculated from Gr-Son-Den logs

K2O

fr

om c

hem

ical

ana

lysi

s

Saskatchewan Geological Survey 9 Summary of Investigations 2013 Volume 1

When samples with insolubles gt10 count for about 40 of the total potash intervals plots show more scattered distributions and the values of K2O obtained from log calculation are generally higher than that of chemical analysis (Figure 9)

c) Other Factors

When bed thickness is small a logging tool will measure not only the radiation of the thin bed but also that of adjacent beds As a result the measured radiation will be the sum of radiation emitted by the thin bed plus the sum of the radiation from all adjacent beds resulting in a discrepancy between the core analysis and log calculation The bed thickness corrections are suggested where the potash bed is less than 1 m (Nelson 2007 Crain 2013)

When a minimum of three logs is not available fewer minerals must be included in the calculation A potash geologist should apply their knowledge of mineral composition in the project area to determine which mineral has minimum content that can be delimited in the calculation Insolubles may be easy to ignore and carnallite may be negligible in carnallite-free areas

Because of small carnallite content in the test drill holes it is difficult to evaluate the effect of carnallite on this mathematic method Further work is required to test the method in a drill hole containing more carnallite or dominantly carnallite

Other factors affecting the calculation method include excessive logging speed depth misalignment between logging depths and core depths gamma-ray attenuation caused by cement and casing weight and content of drilling mud presence of uranium and thorium and washouts of potash zone (Nelson 2007 Crain 2013) Care must be taken when using logs for quantitative potash ore grade calculation

5 Summary Quantitative estimation of the fraction of sylvite halite carnallite and insolubles can be achieved by mathematical calculations from geophysical well logs The accuracy and precision of estimation largely depends on the total amount of insolubles in individual intervals Intervals with the smallest amount of insolubles provide the best results The method could be a valuable tool at the early stage of project evaluation where potash cores are not available The digital logs have improved efficiency and accuracy significantly by avoiding manual log reading and data entry Further studies are required in the area where carnallite is more predominant

6 Acknowledgements The authors wish to express their appreciation to Ross Crain for helpful discussions during preparation of this paper Our special acknowledgments go to K+S Potash Canada and BHP Billiton to give us permission to use their data for this study We also thank Megan Love for Figure 1 and Fran Haidl and Arden Marsh for comments andsuggestions for improvement of this paper

7 References Alger RP and Crain ER (1965) Defining evaporite deposits with electrical well logs in Second Symposium on

Salt Trans Northern Ohio Geol Soc Vol 2 p116-130

Crain RC (2013) Crainrsquos petrophysical handbook URLlthttpwwwspec2000net17-specpotashhtmgt accessed 26 June 2013

Crain ER and Anderson WB (1966) Quantitative log evaluation of the Prairie Evaporite formation in Saskatchewan J Can Petrol Tech v5 p145-152

Edmundson H and Raymer LL (1979) Radioactive logging parameters for common mineral Log Analyst v20 no5 p38-47

Fuzesy A (1982) Potash in Saskatchewan Sask Energy Mines Rep 181 44p

Hardy M Halabura SP Shewfelt D and Hambley DF (2010) Technical report 2010 potash reserve assessment for subsurface mineral permit KP 289 Saskatchewan URLlthttpwwwsedarcomGetFile dolang=ENampdocClass=24ampissuerNo=00007718ampfileName=csfsproddata112filings0165919500000001o3A5CCPU5C20105CPotashOneInc5C101112TR_sjg5CTR_sjgpdfgt accessed 4 June 2013

Saskatchewan Geological Survey 10 Summary of Investigations 2013 Volume 1

Holter ME (1969) The Middle Devonian Prairie Evaporite of Saskatchewan Sask Dept Miner Resour Rep 123 134p

Nelson P H (2007) Evaluation of potash grade with gamma-ray logs US Geological Survey Open File Report 2007-1292 14p

Lomas S (2008) NI 43ndash101 Technical Report for a resource estimation on the Burr Project Athabasca Potash Inc Saskatchewan Canada URLlthttpwwwsedarcomGetFiledolang=ENampdocClass=24ampissuerNo= 00026182ampfileName=csfsproddata93filings0134320800000001i3A5C1SEDAR5C5546375CTechnicalReport5CTechnicalReportpdfgt accessed 4 June 2013

Rider M (1996) The Geological Interpretation of Well Logs 2nd Edition Whittles Publishing Caithness 280p

Saskatchewan Geological Survey (2013) Mineral Resources Map of Saskatchewan 2013 Edition Sask Ministry of the Economy Saskatchewan Geological Survey Misc Rep 2013-1 URLlthttpwwweconomygovskca mineralresourcemapgt accessed 26 July 2013

Tixier MP and Alger PR (1970) Log evaluation of nonmetallic mineral deposits Geophys v35 no1 p124-142

US Geological Survey (2013) Mineral Commodity Summaries 2013URLlthttpmineralsusgsgovminerals pubsmcs2013mcs2013pdfgt accessed 15 July 2013

Yang C Jensen G and Berenyi J (2009) The stratigraphic framework of the potash-rich members of the Middle Devonian upper Prairie Evaporite Formation Saskatchewan in Summary of Investigations 2009 Volume 1 Saskatchewan Geological Survey Sask Ministry of Energy and Resources Misc Rep 2009-41 Paper A-4 28p URL lthttpeconomygovskcaSOI2009V1_A4gt

Saskatchewan Geological Survey 8 Summary of Investigations 2013 Volume 1

Figure 9 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for 40 of the total potash intervals (1524 to 1537 m) of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

Figure 8 ndash Plot of K2O from chemical analysis versus K2O calculated from well logs when samples with insolubles gt10 count for less than 10 of the total potash intervals of well 2113-24-19-25W2M (08K302) in the upper part of the Prairie Evaporite Saskatchewan A) combination Gr-Den-Nue or equations 2 4 and 5 B) combination Gr-Son-Den or equations 2 3 and 4 and C) combination Gr-Son-Nue or equations 2 3 and 5

y = 10484x - 17085

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

B)

K2O

fr

om c

hem

ical

ana

lysi

s

K2O calculated from Gr-Son-Den logs

y = 10613x - 23059

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

A)

K2O calculated from Gr-Den-Nue logs

K2O

fr

om c

hem

ical

ana

lysi

s

y = 10591x - 21491

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt10

Insolubles gt10

Regression Trend

C)

K2O calculated from Gr-Son-Nue logs

K2O

fr

om c

hem

ical

ana

lysi

s

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

A)

K2O

fr

om c

hem

ical

ana

lysi

s

K2O calculated from Gr-Den-Nue logs

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

K2O calculated from Gr-Son-Nue logs

C)

K2O

fr

om c

hem

ical

ana

lysi

s

0

10

20

30

40

50

0 10 20 30 40 50

Insolubles lt 10

Insolubles gt 10

B)

K2O calculated from Gr-Son-Den logs

K2O

fr

om c

hem

ical

ana

lysi

s

Saskatchewan Geological Survey 9 Summary of Investigations 2013 Volume 1

When samples with insolubles gt10 count for about 40 of the total potash intervals plots show more scattered distributions and the values of K2O obtained from log calculation are generally higher than that of chemical analysis (Figure 9)

c) Other Factors

When bed thickness is small a logging tool will measure not only the radiation of the thin bed but also that of adjacent beds As a result the measured radiation will be the sum of radiation emitted by the thin bed plus the sum of the radiation from all adjacent beds resulting in a discrepancy between the core analysis and log calculation The bed thickness corrections are suggested where the potash bed is less than 1 m (Nelson 2007 Crain 2013)

When a minimum of three logs is not available fewer minerals must be included in the calculation A potash geologist should apply their knowledge of mineral composition in the project area to determine which mineral has minimum content that can be delimited in the calculation Insolubles may be easy to ignore and carnallite may be negligible in carnallite-free areas

Because of small carnallite content in the test drill holes it is difficult to evaluate the effect of carnallite on this mathematic method Further work is required to test the method in a drill hole containing more carnallite or dominantly carnallite

Other factors affecting the calculation method include excessive logging speed depth misalignment between logging depths and core depths gamma-ray attenuation caused by cement and casing weight and content of drilling mud presence of uranium and thorium and washouts of potash zone (Nelson 2007 Crain 2013) Care must be taken when using logs for quantitative potash ore grade calculation

5 Summary Quantitative estimation of the fraction of sylvite halite carnallite and insolubles can be achieved by mathematical calculations from geophysical well logs The accuracy and precision of estimation largely depends on the total amount of insolubles in individual intervals Intervals with the smallest amount of insolubles provide the best results The method could be a valuable tool at the early stage of project evaluation where potash cores are not available The digital logs have improved efficiency and accuracy significantly by avoiding manual log reading and data entry Further studies are required in the area where carnallite is more predominant

6 Acknowledgements The authors wish to express their appreciation to Ross Crain for helpful discussions during preparation of this paper Our special acknowledgments go to K+S Potash Canada and BHP Billiton to give us permission to use their data for this study We also thank Megan Love for Figure 1 and Fran Haidl and Arden Marsh for comments andsuggestions for improvement of this paper

7 References Alger RP and Crain ER (1965) Defining evaporite deposits with electrical well logs in Second Symposium on

Salt Trans Northern Ohio Geol Soc Vol 2 p116-130

Crain RC (2013) Crainrsquos petrophysical handbook URLlthttpwwwspec2000net17-specpotashhtmgt accessed 26 June 2013

Crain ER and Anderson WB (1966) Quantitative log evaluation of the Prairie Evaporite formation in Saskatchewan J Can Petrol Tech v5 p145-152

Edmundson H and Raymer LL (1979) Radioactive logging parameters for common mineral Log Analyst v20 no5 p38-47

Fuzesy A (1982) Potash in Saskatchewan Sask Energy Mines Rep 181 44p

Hardy M Halabura SP Shewfelt D and Hambley DF (2010) Technical report 2010 potash reserve assessment for subsurface mineral permit KP 289 Saskatchewan URLlthttpwwwsedarcomGetFile dolang=ENampdocClass=24ampissuerNo=00007718ampfileName=csfsproddata112filings0165919500000001o3A5CCPU5C20105CPotashOneInc5C101112TR_sjg5CTR_sjgpdfgt accessed 4 June 2013

Saskatchewan Geological Survey 10 Summary of Investigations 2013 Volume 1

Holter ME (1969) The Middle Devonian Prairie Evaporite of Saskatchewan Sask Dept Miner Resour Rep 123 134p

Nelson P H (2007) Evaluation of potash grade with gamma-ray logs US Geological Survey Open File Report 2007-1292 14p

Lomas S (2008) NI 43ndash101 Technical Report for a resource estimation on the Burr Project Athabasca Potash Inc Saskatchewan Canada URLlthttpwwwsedarcomGetFiledolang=ENampdocClass=24ampissuerNo= 00026182ampfileName=csfsproddata93filings0134320800000001i3A5C1SEDAR5C5546375CTechnicalReport5CTechnicalReportpdfgt accessed 4 June 2013

Rider M (1996) The Geological Interpretation of Well Logs 2nd Edition Whittles Publishing Caithness 280p

Saskatchewan Geological Survey (2013) Mineral Resources Map of Saskatchewan 2013 Edition Sask Ministry of the Economy Saskatchewan Geological Survey Misc Rep 2013-1 URLlthttpwwweconomygovskca mineralresourcemapgt accessed 26 July 2013

Tixier MP and Alger PR (1970) Log evaluation of nonmetallic mineral deposits Geophys v35 no1 p124-142

US Geological Survey (2013) Mineral Commodity Summaries 2013URLlthttpmineralsusgsgovminerals pubsmcs2013mcs2013pdfgt accessed 15 July 2013

Yang C Jensen G and Berenyi J (2009) The stratigraphic framework of the potash-rich members of the Middle Devonian upper Prairie Evaporite Formation Saskatchewan in Summary of Investigations 2009 Volume 1 Saskatchewan Geological Survey Sask Ministry of Energy and Resources Misc Rep 2009-41 Paper A-4 28p URL lthttpeconomygovskcaSOI2009V1_A4gt

Saskatchewan Geological Survey 9 Summary of Investigations 2013 Volume 1

When samples with insolubles gt10 count for about 40 of the total potash intervals plots show more scattered distributions and the values of K2O obtained from log calculation are generally higher than that of chemical analysis (Figure 9)

c) Other Factors

When bed thickness is small a logging tool will measure not only the radiation of the thin bed but also that of adjacent beds As a result the measured radiation will be the sum of radiation emitted by the thin bed plus the sum of the radiation from all adjacent beds resulting in a discrepancy between the core analysis and log calculation The bed thickness corrections are suggested where the potash bed is less than 1 m (Nelson 2007 Crain 2013)

When a minimum of three logs is not available fewer minerals must be included in the calculation A potash geologist should apply their knowledge of mineral composition in the project area to determine which mineral has minimum content that can be delimited in the calculation Insolubles may be easy to ignore and carnallite may be negligible in carnallite-free areas

Because of small carnallite content in the test drill holes it is difficult to evaluate the effect of carnallite on this mathematic method Further work is required to test the method in a drill hole containing more carnallite or dominantly carnallite

Other factors affecting the calculation method include excessive logging speed depth misalignment between logging depths and core depths gamma-ray attenuation caused by cement and casing weight and content of drilling mud presence of uranium and thorium and washouts of potash zone (Nelson 2007 Crain 2013) Care must be taken when using logs for quantitative potash ore grade calculation

5 Summary Quantitative estimation of the fraction of sylvite halite carnallite and insolubles can be achieved by mathematical calculations from geophysical well logs The accuracy and precision of estimation largely depends on the total amount of insolubles in individual intervals Intervals with the smallest amount of insolubles provide the best results The method could be a valuable tool at the early stage of project evaluation where potash cores are not available The digital logs have improved efficiency and accuracy significantly by avoiding manual log reading and data entry Further studies are required in the area where carnallite is more predominant

6 Acknowledgements The authors wish to express their appreciation to Ross Crain for helpful discussions during preparation of this paper Our special acknowledgments go to K+S Potash Canada and BHP Billiton to give us permission to use their data for this study We also thank Megan Love for Figure 1 and Fran Haidl and Arden Marsh for comments andsuggestions for improvement of this paper

7 References Alger RP and Crain ER (1965) Defining evaporite deposits with electrical well logs in Second Symposium on

Salt Trans Northern Ohio Geol Soc Vol 2 p116-130

Crain RC (2013) Crainrsquos petrophysical handbook URLlthttpwwwspec2000net17-specpotashhtmgt accessed 26 June 2013

Crain ER and Anderson WB (1966) Quantitative log evaluation of the Prairie Evaporite formation in Saskatchewan J Can Petrol Tech v5 p145-152

Edmundson H and Raymer LL (1979) Radioactive logging parameters for common mineral Log Analyst v20 no5 p38-47

Fuzesy A (1982) Potash in Saskatchewan Sask Energy Mines Rep 181 44p

Hardy M Halabura SP Shewfelt D and Hambley DF (2010) Technical report 2010 potash reserve assessment for subsurface mineral permit KP 289 Saskatchewan URLlthttpwwwsedarcomGetFile dolang=ENampdocClass=24ampissuerNo=00007718ampfileName=csfsproddata112filings0165919500000001o3A5CCPU5C20105CPotashOneInc5C101112TR_sjg5CTR_sjgpdfgt accessed 4 June 2013

Saskatchewan Geological Survey 10 Summary of Investigations 2013 Volume 1

Holter ME (1969) The Middle Devonian Prairie Evaporite of Saskatchewan Sask Dept Miner Resour Rep 123 134p

Nelson P H (2007) Evaluation of potash grade with gamma-ray logs US Geological Survey Open File Report 2007-1292 14p

Lomas S (2008) NI 43ndash101 Technical Report for a resource estimation on the Burr Project Athabasca Potash Inc Saskatchewan Canada URLlthttpwwwsedarcomGetFiledolang=ENampdocClass=24ampissuerNo= 00026182ampfileName=csfsproddata93filings0134320800000001i3A5C1SEDAR5C5546375CTechnicalReport5CTechnicalReportpdfgt accessed 4 June 2013

Rider M (1996) The Geological Interpretation of Well Logs 2nd Edition Whittles Publishing Caithness 280p

Saskatchewan Geological Survey (2013) Mineral Resources Map of Saskatchewan 2013 Edition Sask Ministry of the Economy Saskatchewan Geological Survey Misc Rep 2013-1 URLlthttpwwweconomygovskca mineralresourcemapgt accessed 26 July 2013

Tixier MP and Alger PR (1970) Log evaluation of nonmetallic mineral deposits Geophys v35 no1 p124-142

US Geological Survey (2013) Mineral Commodity Summaries 2013URLlthttpmineralsusgsgovminerals pubsmcs2013mcs2013pdfgt accessed 15 July 2013

Yang C Jensen G and Berenyi J (2009) The stratigraphic framework of the potash-rich members of the Middle Devonian upper Prairie Evaporite Formation Saskatchewan in Summary of Investigations 2009 Volume 1 Saskatchewan Geological Survey Sask Ministry of Energy and Resources Misc Rep 2009-41 Paper A-4 28p URL lthttpeconomygovskcaSOI2009V1_A4gt

Saskatchewan Geological Survey 10 Summary of Investigations 2013 Volume 1

Holter ME (1969) The Middle Devonian Prairie Evaporite of Saskatchewan Sask Dept Miner Resour Rep 123 134p

Nelson P H (2007) Evaluation of potash grade with gamma-ray logs US Geological Survey Open File Report 2007-1292 14p

Lomas S (2008) NI 43ndash101 Technical Report for a resource estimation on the Burr Project Athabasca Potash Inc Saskatchewan Canada URLlthttpwwwsedarcomGetFiledolang=ENampdocClass=24ampissuerNo= 00026182ampfileName=csfsproddata93filings0134320800000001i3A5C1SEDAR5C5546375CTechnicalReport5CTechnicalReportpdfgt accessed 4 June 2013

Rider M (1996) The Geological Interpretation of Well Logs 2nd Edition Whittles Publishing Caithness 280p

Saskatchewan Geological Survey (2013) Mineral Resources Map of Saskatchewan 2013 Edition Sask Ministry of the Economy Saskatchewan Geological Survey Misc Rep 2013-1 URLlthttpwwweconomygovskca mineralresourcemapgt accessed 26 July 2013

Tixier MP and Alger PR (1970) Log evaluation of nonmetallic mineral deposits Geophys v35 no1 p124-142

US Geological Survey (2013) Mineral Commodity Summaries 2013URLlthttpmineralsusgsgovminerals pubsmcs2013mcs2013pdfgt accessed 15 July 2013

Yang C Jensen G and Berenyi J (2009) The stratigraphic framework of the potash-rich members of the Middle Devonian upper Prairie Evaporite Formation Saskatchewan in Summary of Investigations 2009 Volume 1 Saskatchewan Geological Survey Sask Ministry of Energy and Resources Misc Rep 2009-41 Paper A-4 28p URL lthttpeconomygovskcaSOI2009V1_A4gt