Detection of K-enrichment (Illite) Chimneys Using Ground Gamma Ray Spectrometry, McArthur River Area, Northern Saskatchewan

R.B.K. Shives 1, K. Wasyliuk 2

• and G. Zaluski 1

Shives. R.B.K., Wasyliuk. K. , and Zaluski. G. (2000): Dctt:ction ofK-cnrichment (illite) chimneys using ground gamma ray spectrometry. McArthur River area. northern Saskatchewan: in Summary of lnvcstigations 2000. Volume 2. Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 2000-4.2.

Abstract

In the Athabasca Basin, previous work has shown that hydrothermal alteration chimneys may extend hundreds of metres above uranium mineralization into overlying rocks, and redistributed in glacially derived surficial materials, including boulders. In 2000, a brief field study was conducted in the McArthur River uranium mine area, to determine ifgrvund gamma ray spectrometry can map radioactive element (K. eU, and eTh) variations associated with known illite enrichment in sandstone boulders.

Initial results show that, although the bedrock and overburden sampled contain very low concentrations of all three radioactive elements (K, eU, and eTh). potassium variations associated with illite enrichment in boulders can be measured using a portable gamma ray spectrometer. These subtle potassium patterns are enhanced through the use ofeTh!K ratios. No obvious relationship has been discerned between eU or eTh concentrations and the boulder clay-fraction geochemical data. Further study may pro1:ide additional correlation.

The potassium concentration of sand deposits exceeds that of sandstone outcrop and boulders where measured. The sands can be distinguished from outcrop or boulder-rich tills by very low eTh!K ratios. In the mature Athabasca sandstone basin, where the background concentrations of radioactive elements are typically the lowest of all regions in Canada, radioactivity associated with these materials may produce anomalies in modern, high-sensitivity airborne gamma ray spectrometric surveys, thereby assisting exploration and surjicial mapping.

1. Introduction

In 1990, Earle et al. described regional lithogeochemica l patterns established through analysis of glac ia l boulder geochem ical data at several uranium exploration properties in the eastern Athabasca Basin (Figure I) . They used major and trace e lement analyses to calculate proportions of ill ite, chlorite, and kaolinite follow ing a technique described by Earle and Sopuk ( 1989). They compared the patterns with shallow bedrock drilling results in severa l areas , including the

Read Lake and McArthur River propert ies , where hydrothermal alteration associated with uranium m inera lizat ion was known to subcrop. Despite extens ive, locally thick (up to 75 m) overburden, bedrock a lteration patterns were clearly reflected in the boulders as anomalies in the concentrat ions of illite, boron, chlorite, uranium, and lead.

In 1999, at the Saskatchewan Geological Survey ' s 30th Annual Open House in Saskatoon, Ken Wasyliuk delivered a ta lk entitled "C lay a lteration in the Manitou Falls Formation". He presented additiona l information from the Read Lake-McArthur River property, including co lour images of the boulder geochemistry. This presentation prompted the principal author to conduct a brief fie ld study in August 2000 to determine if ground gamma ray spectrometry can be used to map potass ium variation assoc iated w ith the illite. The work was done under the Geological Survey of Canada (GSC)-Saskatchewan Energy and Mines (SEM) EXTECH IV Athabasca Uranium Multidiscipl inary Study, sub- project 6 . This paper provides a brief summary of the results of this work to date.

2. Gamma Ray Spectrometry

Fue led by early successes, radiometric surveys have played an obvious and significant role in the explo rat ion history o f many uranium deposits worldwide. In the Athabasca Basin. in northern Saskatchewan, airborne and ground scinti llomete r surveys have outlined uran iferous boulder trains associated with mineralization at Rabbit Lake, Cluff Lake, Key Lake, Midwest Lake, and Read Lake. The surveys are successful because the sc int illometers are able to detect the re latively high radioactivi ty (relative to background) associated with uranium-enriched material e roded and transported from orebodies. The instruments typically use small detectors and measure only total radioactivity from all sources includ ing uran ium and thorium.

A modem , field-portable gamma ray spectro meter uses a much larger, more sensitive detector and is calibrated to provide accurate estimates o f the three most common, natura lly occurring radioactive e lements, potass ium , uran ium , and thorium. This extends the

I Radiation Geophysics Section. Geological Survey of Canada. 573 - 601 Booth Street, Ottawa. ON KIA OE8. I Cameco Corporation, 212 1 - I Ith Street West. Saska1oon. SK S7M IH.

160 Summary of Investigations 2()()(), l'o/ume 1

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The use of gamma ray spectrometry to determine concentrations of e lemental potassium , regardless of the associated potassium mineral species (orthoc lase, microcline, biotite, illite, sericite, muscovite, etc.) enables al teration mapping in various geological settings. In the Sull ivan Basin, British Columbia, airborne gamma ray spectrometric patterns provide useful regional stratigraphic mapping guides, but they a lso distinguish potassium associated with hydrothermal muscov ite within the Sullivan Pb-Zn corridor, from the regional potassium distribution re lated to development of metamorphic biotite (Lowe et al.. [997).

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In general, mapping variations in the "normal" radioactive element content of detrital sedimentary rocks is made difficult by the typically low abundance of K, U, and Th, as shown in Table I. A lthough borehole total radioactivity logs commonly del ineate grit and quartz pebble

• 155· conglomerate beds throughout the basin (Mwenifumbo et al. , this volume), courtesy of preserved

FUN FLON·

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thor ium-bearing mine rals . the majority of Athabasca sandstone is at the lowest ends of the rad ioactive

54• element concentration ranges shown.

Figure I - Location of tire McArthur River mine property, northern S11skatclrewan; PW, Pelican Window; HW. Hunter Bay Window, and NW, Nistowiak Window.

i his presents a challenge to gamma my spectrometry in terms of st ratigraphic mapping. However, in the search for ore, the extremely low

practical applicat ion of radioactiv ity surveys well beyond the search for uranium on ly.

In Canada, many studies (Shives et al., 1995, 1997; Shives and Ford. in press) documented the application of gamma ray spectrometry to surficial mapping (glacio-fluvial deposits, tills, soi ls), bedrock mapping at regional to depos it scales. exp loration for a wide variety of commodities (rare , base, and precious metals, granophile e lements. and industrial minerals), and environmental studies. In Australia and e lsewhere. where the effects of tropical weathering and lan<lform development may significant ly modify bedrock radioelement distribution (Dickson and Scott. 1997), the a irborne patterns provided important information for soi l, rego li th. and geomorphology studies used for land management and mineral exploration strateg ics (Wi lford e1 ul. , 1997). The technique has been <1pplied successfu lly to basin-scale studies at Mount Isa (Jayawardhana and Sheard, 1997) and hydrocarbon exploration (Sikka and Shives. in press). The latter

Saskatchewan (,eological Sun:ey

background levels support detection of very small geochemical var iations related to mineraliz ing, hydrothermal processes. Thus, given sufficient sensitivity, even very subtle increases in radioactive element composition may prove mappable.

3. Methodology

A II ground spectrometric measurements were made us ing an Exploranium GR320 spectromete r with a 0.35 liter sodium iodide detector and 120 s counting time. The spectrometer weighs 4 kg and is carried in a backpack. Prior to fieldwork , the unit was calibrated on concrete pads conta in ing known concentrations of potassium, uranium, and thorium, at the GSC's calibration facility in Ottawa. The instrument uses an inte rna l cesium source to automatically mainta in system stability. providing improved precision compared to older units. The unit displays properly corrected assays o f K. equivalen t U, and equ iva lent Th, in real time (the term "equivalent" or its abbreviation "e" is used to indicate that equilibrium is assumed

I ti I

Table I - Radioeleme11t conce11tratiom in tlijferellt classes of rocks.

Potassium (%) Uranium (oom) T horium (ppm) Rock Tvoe Mean Acid Extrusivcs 3.1 Acid Intrusives 3.4 Intermediate Extrusives I. I Intermediate Intrusives 2.1 Basic Extrusivcs 0.7 Basic Intrusives 0.8 Ultrabasic 0. 3 Alkal i Feldspathoidal Intermediate Extrusives 6.5 Alkali Feldsoathoidal Intermediate Intrus ives 4.2 Alkali Fcldsoathoidal Basic Extrusives 1.9 Alkali Feldspathoidal Basic intrusives 1.8 Chemical Sedimentarv Rocks 0.6 Carbonates 0.3 Detrital Sedimentarv Rocks 1.5 Metamorphosed Igneous Rocks 2.5 Metamorphosed Sedimentarv Rocks 2. 1

between the rad ioactive daug hter isotope monitored by the spec~w':1eter_, and its respectiv~ par~nt isotope; uranium- 1s estimated by measuring b1smuth2 1 and thorium232 via tha llium208

) . Each reading is a lso stored internally as a 256-channel spectrum, for subsequent downloading and further analysis. An Exploranium G R IO I sc intillometer was used to continuously monitor changes in total radioactivity.

Positional data was gathered using a Trimble GeoExplorer II . Stat ion locations were plotted manually on property-scale base maps ( Figure 2). Traverses were positio ned using the company boulder geochemistry maps (Figure 3), w ith emphasis on measuring boulders within highs and lows on the illite/(i llite+kaolinite) x 100 map, to determ ine if spectrometry responds to the associated, very subtle changes in potassium concentration. Access was limited to areas accessible by truck or four-wheel drive a ll terrain vehicle.

For ground gamma ray spectrometry (GRS), large, angu lar sandstone boulders are the preferred sample med i~m as they are usually well exposed and provide a sufficiently large source to fi ll the sensitive volume of the sodium iodide detector, as required by the calibration procedure. Smaller boulders and less dense, unconso lidated materia ls depart from the ideal source geometry and density , yie lding less quantitative results. For example, a reading of I 16 5 ppm c U from a small (50 cm) subrounded sandsto ne boulder from the Read Lake U-bou lder tra in like ly represents an underestimation, as the instrument assumes the detected radiatio n emanated from a larger volume of average density rock. In th is study, the length and w idth o f boulders measured ranged from I m by I m to over 6 m by 6 m , w ith the majority falling in the 2 m by 3 m range. In each case. the gamma ray detector was placed centrally, to avo id ed ge effects.

162

Range Mean Ranl!.e Mean Range

1.0 - 6.2 4. 1 0.8 - 16.4 11.9 I. I - 41.0 0. 1 - 7.6 4.5 0.1 - 30.0 25.7 0.1 - 253. 1 1. 1 . - 2.5 I. I 0.2 - 2.6 2.4 0.4 - 6.4 0. 1 -6.2 3.2 0.1 -· 23.4 12.2 0.4 - I 06.0

0.06 - 2.4 0.8 O.o3 - 3.3 2.2 0.05 - 8.8 0.01 - 2.6 0.8 0.0 1 - 5.7 2.3 0.03 - 15.0

0 - 0.8 0.3 0 - 1.6 1.4 0 - 7.5 2.0 - 9.0 29.7 1.9 --· 62.0 133 .9 9.5 - 265.0 1.0- 9.9 55.8 0.3 -· 720.0 132.6 0.4 -- 880.0 0.2 - 6.9 2.4 0.5 - 12.0 8.2 2. 1 - 60.0 0.3 - 4.8 2.3 0.4 - 5.4 8.4 2.8 - 19.6

0.02 - 8.4 3.6 0.03 - 26.7 14.9 0.03 - 132.0 0.0 1 - 3.5 2 .0 0.03 - 18.0 1.3 0.03 .. 10.8 0.01 - 9.7 4.8 0.01 - 80.0 12.4 0.2 - 362.0 0. 1 -6. 1 4.0 0.1 - 148.5 14.8 0. I - 104 .2

0.01 - 5.3 3.0 0.1 - 53.4 12.0 0. 1 - 9 1.4

4. In itial Results

Evaluation of the results was not complete at the time of writing , however. several features arc apparent from the I 08 in situ GRS readings collected. Traverses and individual station locations are shown on a topographic base in Figu re 2 and are superposed on the boulder geochemical maps in Figure 3. The main transect (stations 18 to 45 and 96 to I 07) lies a long a series of southwest-elongated. high-relief drum linoid featu res, wh ich dom inate the area. The northernmost traverse (stat ions 6 l to 82) lies a long on a we ll-sorted outwash sand depos it, with local mixed-c last till.

Much of the co lour variat ion present on the original boulder geo chemical maps is lost in conversion to the greytone images (Figure 3) required for publicat ion. For this reason, legends for the colour maps are not shown and tones have been labelled as e ithe r highs or lows. The dashed lines indicate the approx imate surface trace of the P2 fault, which conta ins the P2 North (McArthur River) orebody and P2 Main uran ium deposit, and curves to the southwest. The most striking featu re illustrated by the maps is the strong zoning in calculated clay fract ion compositions: high chlorite and low illite abundance west of the P2 fault, high ii lite and low chlorite east of the fault, and h igh boron a long the fault .

Min imum. max imum, mean, and standard dev iation for K, eU, eTh, and eTh/K values at all spectrometry stations are provided in Table 2, grouped separate ly for boulders. sand/ti 11 , and outcrop. XY -plots for these groupings are shown in Figures 4A (eU vs. K) and 48 (eTh vs. K). Uranifcrous boulders at stations 2_ 19. and 20 (6.9, 7.2, and 1164 ppm eU , respective ly) arc not included in the stat ist ica l summaries .

Mean K values a re clearly higher in the outwash sand and till (0. 55% K) than in the unsorted sandstone boulders (0. 16% K) or outcrops (0.09% K). The ranges of cU and eTh values overlap considerably for a ll three med ia, and , as a result, elJ/eTh ratio values (not shown) are very similar. The best discriminator for the

Summary of /nvest1j!,alio 11s 2000. J 'u/11me 2

Field Spectrometry Station Locations McArthur River Mine Area

74 H/11, 14 (parts of)

Figure 2- Location ofgrou,u/ !,pectrometry station.5, July 27 to August I, 2000.

Saskalchewan GeoloRical Survey 163

Figure 3 - Ground .spectrometry travenes plotted on greytone maps of sandstone boulder geochemical data (Earle el al., 1990) as label/e,J. Shades of relative high and low concentration are indicated, but are best-viewed in original colour versions. For gridding purposes, an inver.se tli.~tance weighting algorithm (G. Zaluski) wm used to extent! each data puirit to JOOOm

/6-1 Summarv o/lnvestigations 2000, i·olume 2

Table 2 - Stati.rtical summary of in situ gamma ray 1pectrometry results for all stations reduces site-to-site variations and rnndslone, sand/till, and outcrop stations. which may better explain variation

All Sandstone Outwash Sandstone in the spectrometry data. Stations* Boulders Sand/till Outcron

K(%) min 0.01 0.04 0.23 max 1.00 0.34 1.00 mean 0.25 0.16 0.55 SD 0.20 0.06 0.18

eU (ppm) mm 0.17 0.35 0.42 max 2.83 2.83 1.44 mean 0.95 1.01 0.83 SD 0.38 0.39 0.29

eTh (ppm) llllll 0.74 0.74 0.88 max 10.53 10.53 5.95 mean 3.18 3.16 3.32 SD 1.16 1.10 1.39

eTh/K min 2.42 8.95 2.42 max 27105 167.89 11.62 mean 22.19 23.86 5.98 SD 31.08 20.76 1.65

Note: * excludes U-mincralized boulders at stations 2, 19, and 20.

different media appears to be the cTh/K ratio. The few outcrops sampled (n=5) were relatively siliceous and contai.ned less K (highest value of 0.15% K in outcrop at station 17) than the mean K content of boulders in the illite-areas. As a result, the eTh/K ratios on outcrops arc very high, with a mean value of 78. In strong contrast, the relatively potassium-rich sand/till sites produce very low cTh/K values, with a mean of six. These variations may be mappable using airborne gamma ray spectrometry.

Values obtained for K, eU, and eTh concentrations in bou1ders along t~e. m~in transect arc shown in Figure 5. Stat10n number 1s md1cated on the diagrams. The spatial relationship between the in situ GRS and boulder illite patterns in Figure 3A is clear. Stations 18 to 31 represent boulders occurring in the northwestern, low-illite area, and 96 to 107 are on boulders within the southeastern high-illite area. The intervening area contains spotty high and low patterns on the iliite geochemical map, such as a weak low in the vicinity of station 37, and a moderate high just south of stations 25 and 29.

In Table 3 and Figure 6, results for the sandstone boulders only, are presented, grouped simply according to occurrence in either the illite-rich or illite-poor areas shown in Figure 3A. Again, mean values for eU and eTh (and ratios eU/eTh and eU/K) offer little discrimination between the two groups. However, with minor exceptions, there is clearly more potassium in th~ high-illite area boulders than in the low-illite areas, with mean values of 0.18 and 0.11 respectively. Correspond mg eTh/K ratio values in the low-ii lite areas are twice those in the high-illite areas.

5. Discussion

To create the original colour grids, G. Zaluski used an mverse distance weighting algorithm to extend the influence of each data point to I 000 m. This facilitates interpretation of broad-scale features, but, by design,

Saskatchewan Geological Sur\'ey

0.01 0.15 0.09 0.04 0.17 1.00 0.61 0.30 2.71 323 2.94 0.20 21.02

271.05 78.09 96.61

In the composite boulder sampling program, small chips from IO boulders within a IO m radius were aggregated, at roughly I 00 m intervals along lines spaced 300 to 500 m apart or wider (Earle et al., 1990). Considering these factors, and the inherent 'nugget effect' in sampling boulders within glaciated terrain, correlation between the ii lite patterns defined by the geochemical data and the ground spectrometry results is surprisingly good.

Where information about variations in K, eU, or eTh is desirable, the relative ease and speed with which gamma ray

spectrometry data can be collected may compare very favorably with boulder sampling techniques.

During ground GRS, variability in source material types (bedrock, boulders, overburden) can be controlled by the operator and treated as separate populations. In airborne GRS surveys, however, each measurement represents the average radioactive clement composition of variable amounts of bedrock, overburden (highly variable in itself), surface water soil moisture, and vegetation. In this brief study, w~ observed, through the use of ground GRS, that K enrichment can be detected in individual illite-altered sandstone boulders, and that well-sorted outwash sands are consistently K-rich, eTh-poor, resulting in low eTh/K ratios. Where similar boulders are abundant or sand. deposi~s are sufficiently large, modem, high- ' sens1t1vlt)'. airborne gamma ray spectrometric surveys m~y prov1d~ e:'<ploration and surficial mapping g~1dance w1th11_1 the ~thabasca Basin. This potential will be further mvest1gated (Campbell and Shives, this volume).

6. Conclusions

Initial results show that although the bedrock and overburden sampled contain very low concentrations of all three radioactive elements (K, eU, and eTh), potassium variations associated with illite enrichment in boulders can be measured using a portable gamma ray spectrometer. These subtle potassium patterns are enhanced through the use of eTh/K ratios.

No obvious relationship has been discerned between eU or eT~ concentrations and the boulder clay-fraction geo~hem1cal data. Further study may provide add1t1onal correlation.

Potassium concentration of sand deposits exceeds that of sandstone outcrop and boulders, where measured.

/65

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B Figure 4 - Radioactive element plot.s for I 06 ground .spectrometry station.s illustrate the very low ab.rnlute concemmtiom of eU (A), eT/1 (B), a11d K i11 sandstone outcrop, sandstone boulders, anti unconsolidated .sand/till. Ranges for eTh and eU 11re narrow am/ overlapping for al/ three media, but K values (and, e1pecially eTh/K ratios, not i/Justrated) clet1rly distinguish !J·andlti/1 from the boulders and outcrop.

/ 66 Summary of lnvestigatio11s 2()()0, Volume 2

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station number B Figure 5 - Potassium concelllrations (A) along the main transecr corre"1te surprising(y well with relative illite enrichment shown in Figure 3A. U11</er.\·tandably, local variation between boulder.{ creates spikei·, but the general low- to high-il/ite (potanium) trend is apparent. Anomalou.{ elf (B) at stations /8 and 19 reflect known, lf-bearing sandstone boulders in a train extem/ing southwesterly from Read Lake. Neither elf nor eTh reflect the boulder geochemical palterns in any obvious way.

Saskatchewan Geological Survey /67

Table 3 - Statistical summary of in situ 1:amma ray spectrometry• re.Iults for suntlstone boulders occurring within low- am/ high-illite areas defined by boulder geochemical patterns.

K(°lo)

eU (ppm)

eTh (ppm)

eU/eTh

eU/K

eTh/ K

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0.04 OJ I 0. 11 0. 06 0.35 2.83 1.20 0.56 1.91

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167.89 38.74 33.68

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The sand can be distinguished from outcrop or boulder-rich tills by very low eTh/K ratios. In the mature Athabasca Basin, where the background concentrations of radioactive elements in the sandstones are typically the lowest of all regions in Canada, radioactivity associated with these materials may produce anomalies in modem, high sensitivity­airborne gamma ray spectrometric surveys, thereby assisting exploration and surficial mapping.

7. Acknowledgments

Cameco Corporation is thanked for approval to publish these preliminary results.

The principal au thor sincerely thanks several Cameco Corporation technical and support staff At the McArthur River minesite : Dan Brisbin atTanged logistical support; Larry Richardson provided office accommodation and well-presented summaries of the mine geology; Brian McGill freely shared valuable in formation about earlier boulder prospecting methods and results; Scott McHardy provided much appreciated logistical help and guidance concern ing Read Lake boulder geochemical anomalies; and Lawson Forand offered background infonnation on property exploration history. In the Saskatoon office, Ron Matthews ensured de livery of maps critical to field logistics and Wally Harildstad provided digita l base

• low-illite area

0

high-illite area

0 .0 0 0 .0 5 0 . 1 0 0.15 0 .20 0.25 0 .3 0 0 . 3 5

Potassium(%) Figure 6 - A thorium/potassium plot of sandstone boulders only, clearly show.{ the elevated range of K co11£"e11trations (roughly 0.15 to 0.35% K) ill boulders within high-illite areas, relative to those in low-iflite areas. Higher eTh at stations 19 and 94 re.m lts from the presence of thorium-bearing minemls preserved in purple, heavy mineral-rich grit beds.

168 Summary of Investigations 200(), 1 'olume 2

information. Excellent field assistance was provided by summer student Charley Murphy. Geological Survey of Canada Contribution Number 2000160.

8. References

Dickson, R.L. and Scott. K.M. ( 1997): Interpretation of aerial gamma ray surveys - adding the geochem ical factors; I\GSO 1. Australian Geol. Geophys., vl7, no2, pl87-200.

Earle, S.A.M. and Sopuk, Y .J. ( 1989): Regional lithogeochernistry of the eastern part of the Athabasca Basin uranium province, Saskatchewan, Canada; in Uranium Resources and Geology of North America, Proceedings ofan IA EA Technical Committee Meeting, Sept. I to 3, l 987, Saskatoon, II\ EA-TECDOC-500, p263-296.

Earle, S., McGill , B., and Murphy, J. ( 1990): Glacial boulder geochemistry: An effective new uranium exploration technique in the Athabasca Bas in, Saskatchewan; in Beck, L.S. and Harper, C.T. (eds. ), Modern Exploration Techniques, Sask. Geo I. Soc., Spec. Publ. No. I 0, p94- I l4.

Jayawardhana, P.M. and Sheard, S.N. ( 1997): The use of airborne gamma ray spectrometry by M.I.M. Exploration - a case study from the Mound Isa Inlier. North West Queensland, Austra lia; in Gu bins. A.G. (ed.), Proceedings of Exploration 97, Fourth Decennial International Conference on Mineral Exploration, p765-774.

Lowe, C .. Arown, D.A .. Best, M., and Sh ives, R.B.K. ( l 997 ): East Kootenay multi parameter geophys ical survey, southeastern British Columbia: Regional synthesis; in Current Research I 997-1\ , Gc~I. Surv. Can ., pl67-l76.

Shives, R.B.K., Charbonneau, B.W., and Ford, K.L. ( l 997): The detection of potassic alteration by gamma-ray spectrometry - recognition of alteration related to mineralization; in Gubins, A.G. (ed.), Proceedings of Exploration 97, Fourth Decennial In ternational Conference on Mineral Exploration, p74 l-752.

Shives, R.B.K., Ford, K. L. , and Charbonneau. B.W. ( l 995 ): Applications of gamma ray . spectrometric/magneti c/VLF-EM surveys -Workshop Manual; Gcol. Surv. Can., Open File 306 1, 82p.

Shi ves, R.B.K. and Ford, K.L. (in press): Mapping and exploration applications of gamma ray spectrometry in the Bathurst Mining Camp, northeastern New Brunswick ; in Goodfe llow, W.D., van Staal, C.R. , Mcc utcheon, S. R., and Thomas, M.D. (eds.), Massive Sulphide Deposits of the Bathurst Min ing Camp and Northern Maine, Econ. Geo!. Mono.

Sikka. D.B. and Shives, R.B.K. (in press): Radiometric surveys of the Redwater oil fi e ld, Alberta: An

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early surface exploration case history (and similar case histories) suggest mechanisms for the development of hydrocarbon-related geochemical anomalies; Amer. Assoc. Petro. Geochem.

Wilford, J.R., Bierwirth, P.N., and Cra ig, M.A. ( l 997): Appl ication of ai rborne gamma ray spectrometry in soil/regolith mapping and applied geomorphology: AGSO J. Australian Geol. Geophys., v l 7, no2, p20 1-2l6.

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