12. BORLHOlE lOGGING TECHNIQUES APPLIED TO BASE MLTAL ORE DEPOSITS
W.E. Glenn UURI-I arth Science laboratory, Salt lake City, Utah
P.H. Nelson lawrence Berkeley laboratory, Berkeley, California
Glenn, W.E. and Nelson, P.ll., Borehole logging techniques applied to base metal ore deposits; !!3: Geophysics and Geochemistry in the Search for Metallic Ores; Peter J. Hood, editor, Geological Survey of Canada, Economic Geology Report 31, p. 273-294, 1979. Abstract Interest in the application of borehole logging to metallic mineral exploration and deposit evaluation has grown substantially in recent years. However, borehole logging tools and techniques were developed primarily by the petroleum industry and neither the tools nor their application are directly suited to the needs of the metallic mineral industry. Lack of generally available commercial logging services for small diameter holes and for the measurement of quantities Kuch as magnetic susceptibility, induced polarization, and ore grade has inhibiLed the growth of borehole logging in metallic mineral mining. The need to study new mining technology and to search at greater depths for new ore deposits has created a demand for a slim-hole logging capability. The requirements range from elemental and mineralogical analyses, through properties used in geophysical exploration to bulk rock properties for either conventional or novel mining techniques. This paper reviews the presently available capabilities for downhole analyses for geological information, for geophysical properties and for fluid flow. Much of the review is based upon direct experience with a facility operated in-house by a major metals mining company. Resume n y a eu au cours des dernU~res annees un interet croissant pour l'application de la diagraphie par trou de sonde a l'exploration des mineraux metalliques et a l'evaluation des giKements. Toutefois, les outils et les techniques de diagraphie par trou de sonde ont ete mis au point principalement par l'industrie petroliere; ni les outils ni leur utilisation n'etaient directement adaptes aux besoins de l'industrie des mineraux metalliques. Le manque de services commerciaux de diagraphie accessibles en ce qui concerne les trous de petit diametre et la mesure de quantizes comme la susceptibilite magnetique, la polarisation provoquee et la teneur en minerai a empeche Ie developpement de la diagraphie par trou de sonde dans Ie secteur des mineraux metalliques. Le besoin d'etudier de nouvelles techniques d'exploitation et de creuser i:z des profondeurs plus grandes afin de trouver de nouveaux gisements de minerai a fait nai1:re une demande pour la diagraphie en diametre reduit. Les besoins vont des analyses elementaires et mineralogiques jusqu'aux proprietes utilisees en exploration geophysique et aux proprietes de la roche prise dans son ensemble, en ce qui a trait aux techniques d'exploitation classiques ou nouvelles. I.e present document etudie les methodes actuelles d'analyse, au fond du trou, de l'information geologique, des proprietes geophysiques et de l'ecoulement des fluides. La majeure partie de l'etude est basee sur des experiences pratiques a l'aide d'une installation exploitee par une importante societe d'exploitation de mineraux metalliques.
INTRODUCTION will be inexpensive, buL with the exception of techniques for mineralogiral and elemental analysis, many useful tools have Research on the Clpplication of well logs to porphyry already been developed and are avail
Table 12.1 Physical and chemical in-situ properties obtained by borehole logging with regard to mining applications
Porphyry Copper Dump Mine I Exploration Characterization Leaching Development Elemental and mineralogical analysis X X X X I Rock type identification and correlation X X X X Rock quality and fractures X X X Density X X Porosity X X Electrical and magnetic properties X X Temperature and thermal properties X X X Fuid flow X X X vVater sampling X X X X
--_.._-- Underlined entries indicate the categories for which examples are given in this paper. Borehole Logging 275
KENNECOTT COPPER CORPORAnON BOREHOLE ELEMENTAL AND MINERALOGICAL LOGGING SYSTEM ANALYSES IN BOREHOLES Kennecott Copper Corp. currently (1977) has three One of the most exciting and promising frontiers in logging trucks, of which only one is designed to measure a mineral logging is the development of tools to analyze for broad range of rock properties. The other two are devoted to specific elements in the borehole. In the specific case the hydrologic and environmental logging. A brief description of logging would be a borehole assay for particular ore minerals. the Kennecott Copper Corp. logging truck (Fig. 12.1 and 12.2) In the general case the type of logging would provide an in is given here. It is a four-wheel drive Ford F600 truck chassis si tu geochemical description of the mineral deposit. with a 14 feet (4.3 m) long, 6 feet (1.8 m) wide, 6 feet (1.8 m) Czubeck (1979) describes the current activity in high custom-built van on the bed. The van portion is divided borehole assaying, most of which is based upon radioactive into a forward operator/recorder cubicle and a rear and fluorescent techniques. A neutron activation method for mechanical/storage area. A boom is located over the rear the borehole assay of copper and nickel has been described by centre of the vehicle. The truck is equipped with 1830 m of Nargolwalla et al. (1974) and Seigel and Nargolwalla (1975). four-conductor 4.8 mm, steel armour cable with a Gearhart Their system, called Metalog, available as a routine service, Owen four-conductor cable head and an extensive set of was tested in Anaconda's porphyry copper mine near electronic and mechanical equipment. The electrical power Yerington, Nevada (Staff, Scintrex Limited, 1976). The test unit is a 6.5 kW gasoline generator. The truck typically results are very envouraging and are presented in Figure 12.5. carries fourteen different logging tools. The various tools Because of limited experience with this technology we will and their primary function(s) are shown in Table 12.2. All not attempt to describe progress in the field of nuclear tools are 2.25 inches (5.7 cm) or less in diameter. analysis, but will discuss a few examples obtained with more Many of the tools require only one conductor and the conventional methods. It is likely that the results from these armour for operation, but others such as the IP tool require other methods will supplement and constrain the nuclear all four plus the armour. Except for the resistivity and analytical methods when they become available. single-point resistance tools, all tools accomplish some The most readily available analytical technique in electronic signal processing and enhancement downhole boreholes is the measurement of the natural gamma before the signal is transmitted to the surface. Uphole radiation. In the mining environment the total count can modules are mounted in removable nuclear instrumentation often be directly correlated with the potassium content from modules and do various amounts of signal processing and the laboratory analysis of core material as shown in output the analog signals to one or more channels of a four Figure 12.6. In fact, based upon this kind of direct channel Texas Instruments chart recorder. A plug-in patch correlation, our logs are routinely scaled in K 0 content in panel (Fig. 12.2) and programmed patch boards (Fig. 12.3) 2 most environments. Where the uranium or thorium content is allow the operator to connect tool functions, module significant this straightforward procedure does not apply, and functions and auxiliary electronic equipment such as an oscilloscope in any fashion desired or to operate the system in spectral information is required to clistinquish the three some predetermined fashion by simply plugging in a board. elements. Indeed, spectral logging is applied to uranium The flexibility of the patch panel is essential for a research exploration and is discussed elsewhere in these proceedings (Killeen, 1979). and development logging system in that the electronic ~~ ~----- equipment can be quickly interconnected in a modified or new .... configuration and a new tool can quickly become operational. A block diagram of the system just described is given in Figure 12.4.
Figure 12.1. Kennecott Copper Company's logging truck. Figure 12.2. Interior view of operator section of Kennecott Copper Company's logging truck. 276 W.E. Glenn and P.H. Nelson
CHART r-;:;;~::;-I ~RECORDER
r-----.., '--";:--~---I I ICOMPUTER I l- .J
PROBE Figure 12.3. Program patch board,
Figure 12.4. Block diagram of logging system
% CU
o 0 o'I 1 020 o 4 o 5 o 6 20 o 6 8 Ot-----'---~cr_-'------L..----'
Core 1- -- I I 30 1 1 250 10 I Metalog 1000 ;; I 2 I E ,~ I .c 40 ii .c Q) 500 C. '0 Q) I '0 .~ I .~ L_- 2000 .c T C. I Q) '0 I 50 I 750 I -c I ~ Analytic Data --l
I 3000 __I 60 1000 --r I Figure 12.6. Comparison of analytic and well log analysis of [(20. 20 ~ I Examples of the dependence of the neutron log on both I pore water and water bound in hydrous minerals have been 70 IT presented before (Savre and Burke, 1971; Snyder, 1973; I Nelson and Glenn, 1975) and the example of Nelson and Glenn is reproduced in Figure 12.7. The chemically bound water can I be so high that it can be directly measured by the neutron I tool and hence mask the pore water contributions to the I neutron log. We will show in the section on porosity that when the two contributions are mixed, it is still possible to 80 I remove the bound water contribution. In any case the bound Figure 12.5. Borehole assaying. water can be quantitatively assessed, giving a measure of the hydrated mineral content of the rock, usually translatable as the altered, clay mineral fraction. Borehole Logging 277
Table 12.2 10 "" Response of drillhole logging tools to rock properties " );/. /," LOGGING TOOLS . . "'/to: W I ;::: "-/-" W . " Z CJ« . /~... ::. .. *" 1.0 Temperature I 4 .J .7 o ( Caliper I 4 4 > /' Neutron 2 2 3 4 VOL. % MAGNETITE = K/3000 Natural Gamma 2 4 / I Gamma-Gamma(density) 2 4 3 I 2 -- I 0,1 Veloci ty (ll T) 2 3 2 100 1000 10000 100000
Resistivity 3 4 4 3 2 MAGNETIC SUSCEPTIBILITY <,.u c. g. s. ) IP 4 2 Figure 12.8. Plot of magnetic susceptibility from logs versus volume per cent magnetite. Magnetic Susceptibility I
Fluid Flow I A third fairly direct measurement is the magnetite I Quantitative measure - high success content estimated from the magnetic susceptibility tool. 2 Quantitative measure - moderate success Figure 12.8, taken from Snyder (1973), demonstrates the Always responds qualitatively 3 correlation. Here again, as in the case of potassium, is one of 4 Often responds qualitatively the rare cases where a single element or mineral type possesses a distinctive physical property which can be readily measured and is unique to that mineral type in many cases of interest. o 1 2 4 wt , An obvious need in mining applications is a direct 2500J.-__.L-__1500-L__---l 1000i.-_----,counts/sec measure of the sulphide content. Our attempts at this measurement are detailed in subsequent sections on density 1200 and electrical properties.
ROCK TYPE IDENTIFICAnON AND CORRELAnON Identification of rock types is facili tated where there is 400 a direct correlation between an easily identified mineral species, such as magnetite, and the rock unit. A good example of this is evident at one of Kennecott's porphyry 1400 deposits. The copper mineralization is in an andesite pile neutron crosscut by numerous latite dykes. The dykes and andesites show contrasting expressions on both the natural gamma
...... - weight % (potassium) and magnetic susceptibility (magnetite) logs• Figure 12.9 illustrates this contrast. The latite between chemically bound water 163 and 186 m shows a high natural gamma response and a +' Q) near-zero magnetic susceptibility, whereas the andesite ...Q) exhibits a lower natural gamma response and magnetic .S ~ 1600 susceptibility averaging around 3000 ].l cgs. Note that the .... .c .c density of the latite is also lower than the density of the +' C. 0. 500 '" andesite. A short interval between 151 and 159 m has a very Q) "C '0 similar response on all logs as does the latite except that the magnetic susceptibility is not zero. We interpret this interval to be a near miss of the same dyke intersected at 163 m. The result suggests that the drillhole is parallel to a dyke over this interval. 1800 We have noted a striking correlation between resistivity variation and sulphide zoning at one of Kennecott's porphyry copper deposits. The highly variable, low to high, resistivity pattern evident in the upper part of the long and short normal log* for each hole shown on a cross-section in Figure 12.10 is coincident with the pyrite halo in this deposit. The lower cut-off of this variable resistivity is closely correlated with a 600 particular copper grade. Some detailed features of the resistivity logs can be correlated among the drillholes. These correlated features have been associated with both a Figure 12.7. Comparison of the neutron log with bound variation in sulphide veining and the degree of sulphide water analysis on pulps.
* Industry standard: 40 and 16 inches (1.22 and 0.488 m) respectively. 278 W.E. Glenn and P.H. Nelson
MAGNETIC H -, H-2 H- 3 H·4 H-5 DENSITY SUSCEPTIBILITY NATURAL GAMMA GEOLOGY gm/cc \.lc.g.s. % K20 3.10 2.60 2.30 o 5000 5 10 .O' Andesite ::'. ~: ~~ 200 .',. ....;1 Andesite breccia ~r "" Andesite 100 .,'. 400 ., ~-:'.
~ .' ~ :~ T ;; .~ .. Latite porphyry E 600 '" ~~ Andesite '" c 200 <:> ;'~ <:> -'= " c. · -, ~ hr---+--+-f--+-"-----l-----f-.l.,-+---I:2- -j---h~---I '" '" BOO :' " .~· ~ " :.~~ c'" ., · ./ 300 1000 Fault zone ~: Andesite
;It Andesite breccia
1200 .'~ ,~ ."If " Figure 12.9. Latite dyke correlation on natural gamma and Figure 12.11. Natural gamma logs. magnetic susceptibility logs.
At jlsec/teet RDH-1 o ,.--,,-_8-l.0_..------L._...... -"4~O'--_ .I\-m 2 o 50 100 RQD
500 .... Figure 12.10. Long and short normal resistivity logs. 1500 Figure 12.12. Rock quality designation (RQ D) from core versus compressional wave transit time measured in a drillhole. Borehole Logging 279 oxidation. Also, at the same deposit, the natural gamma log TEMPERATURE CALIPER VELOCITY NEUTRON DENSITY hole dia. grn/cc shows a substantial increase in potassium as the causative OF inches jJsec/ft total water (vol. %) 75 95 1153 4 50 60 70 20 10 2 3.12.5 23 intrusive is approached. This feature is depicted in 24 35 10 14 Figure 12.11 where logs from five different drillholes are 'c shown. An interval of high potassium can be correlated on all logs as indicated by the dashed lines in Figure 12.11. The 200 increased potassium is seen in the core as an increase in sericite and orthoclase mineralization. 100 We have numerous examples of rock-type identification 400 and correlation that we have accomplished at several of ~. :i · Kennecott's porphyry copper deposits and prospects. c ~ · '00 E However, we feel the ones given here are sufficient to ·c :i 200 illustrate the ability to use well logs both to differentiate ~'" r. rock types and to correlate rock units across a deposit. This ~'" information is useful for structural geology studies and for 800 the understanding of the porphyry system geometry. 1000 300 ROCK QUALITY AND FRACTURE LaCA nON With logging techniques it is possible to determine the mechanical properties of rocks and to study the structural 1200 geology. In this section logging relevant to both topics will be described. Figure 12.13. Suite of logs showing rock fracture signature Rock Quali ty Designation (RQD) as used by mine on several well logs. geologists is the measure obtained by summing the length of core pieces greater than 10 cm and dividing the total length of sample, typically 1.5 m to 3 m of core. If all the pieces of core in a 1.5 m section, for example, were greater than 10 cm, the RQD would be 100%, if all pieces were smaller than 10 cm the RQD would be 0%. RQD is an empirical BOREHOLE SEISVIEWER LOG measure of rock competence. We have found that the CALIPER LOG At (TRANSIT TIME) LOG velocity (reciprocal of the compressional wave transit time) Hole Oiomeler lin.) psee/f!. log gives a fairly good measure of RQD where the rock is 8 920 50 moderately to well fractured and one example is shown in 20 22 em Figure 12.12. In this case, the velocity log responds primarily to the cracks or fractures in the rock. Fractures or fractured intervals of rock commonly give a characteristic response on several logs: caliper, velocity, 290 neutron and density. An example is shown in Figure 12.13. For illustration note the response of each log at 308 m where the geologist has noted a fault zone in the core. The caliper shows an increased hole diameter which indicates that NS material has fallen from the fracture or was plucked out by 961' 66° E the bit during drilling. The velocity log shows a low velocity, the neutron shows a high porosity and the densi ty log shows a ,N75W Q; 966 66 low density at this depth. Several fractures have been picked ~ from these logs and are indicated by an f beside the caliper log at the appropriate places. J: ~ The preceding analysis gives a location only for Ol fractures which appear open in the hole and does not provide "0 strike or dip information. "~1 We have used the seisviewer log offered as a service by N45 0 Birdwell to determine fracture orientation in drillholes. This 982' 37 N I 300 tool was first described by Zamanek et al. (1970). An example of this log along with the caliper and velocity logs is shown in Figure 12.14. The interpreted fractures and their orientation are noted beside the seisviewer log. The 992' 420 ~: seisviewer tool sends acoustic pulses toward the borehole " wall. The tool rotates and sends a signal to the surface when it passes through magnetic north. The acoustic energy reflected from the borehole wall is monitored and sent to the 1000 surface where it is presented on an oscilloscope and A B c photographed. The oscilloscope triggers on the north signal. IMagnetic North, Strike direction relative to MN. A smooth borehole wall will generate a strong reflection, the bright areas on the log, and a rough, caved borehole wall will generate a weak reflection, the dark areas on the log. Hence Figure 12.14. Fracture location and orientation obtained fractures are indicated by dark traces on the log. However, from an acoustic seisviewer log. if the tool is not centred in the hole or the hole deviates very much from L',P = 0.013 L',P = -0.012 L',P = -0.50 L', = 0.77% DENSITY LOGGING b g s Routine Den.sity Estimates Of the four unknowns, changes in the nonsulphide grrlin We routinely employ a single-detector, gamma-gamma densi ty will probrlbly produce the largest errors because there density probe in NX-size boreholes. The maximum tool is at present no way to assess grain density in the borehole. diameter is 5.5 cm. In operation the entire tool is held The bulk density measurement itself also can be a problem if against the borehole wall by ;] decentralizing arm which the count rate is insufficient. extends from the tool. Because only a single detector is used, The third variable, the sulphide grain density, is less the measurement is uncompensated, that is, no correction is critical because the sulphide estimate is less sensitive to its made for borehole rugosity. In cored holes in hard rock this fluctuations. The influence CRn be further reduced if an does not present as great a problem as in soft rock because estimate of the pyrite-to-chalcopyrite ratio is available and zones of severe rugosity are relatively infrequent and not no other sulphides a) Equal area net projection of poles Contoured equal area net projection to fractures observed on televiewer of poles to fractures observed on borehole log televiewer borehole log 10 IO,-----f..... Figure 12.15. 1':1:ample of structure analyses from seisviewer log. scale could be attached to the resulting sulphide estimate. available. Given the present strlte-of-the-art, we recommend The density-derived sulphide estimate tracks the laboratory that the suite of logging tools employed in a given hole be as values well, and it is reasonable to expect that the agreement complete as possible. can be improved with a proper' calibration and judicious use of Other applications of the densi ty tool include 1) control equation fJ-4. At least for high sulphide contents (3 to 8 data for the interpretation of gravity surveys, 2) to establish weight per cent), useful estimates of sulphide content should the bulk modulus in combination with acoustic velocity data, result and the combination of electrically-derived (see next and 3) to obtain bulk tonnage estimates. section) and density-derived estimates should be useful. Figure 12.19 is a second field example which qualitatively illustrates both the sulphides and porosi ty POROSITY LOGGING effects on the density log. The cali per log shows fractures in Porosity is commonly estimated from one or more of several intervals but the reader should examine just two, one the following four logs: neutron, grlmma-gamma, resistivity between 348 to 360 m and the other between 245 to 280 m. and velocity logs. The methods used are well documented in rhe neutron log shows a high porosity for both intervals. The the literature (e.g. Pirson, 1963; Pickett, 1960; Savre and density log shows a lower density for the upper interval which Burke, 1971). However, each log responds to several rock reflects the increased porosity whereas only a part of the characteristics including porosity. There is an extensive lower interval has a lower density. In fact, between 259 m literature describing the response of these logs in various and 265 m the density is relatively high despite the higher sedimentary rock sequences but little information exists on porosity indicated by the neutron log. The higher density the response of these tools in igneous or metamorphic rocks reflects the galena and sphalerite veining over this interval. (e.f. Ritch, 1975; Nelson and Glenn, 1975; Merkel and Snyder, A second interval of sulphide veining where no high porosity 1977; Snyder, 1973). One problem is the calibration of tools. exists is evident in the density 10C] between 101 m and 131 m. No stand8rd facility such as that available for sedimentary We found that this mode of qualitative log inspection and rock environments with the API pits at the University of interpretation is enhanced greatly when several log types are Houston is available for the igneous and metamorphic rock 282 W.E. Glenn and P.H. Nelson 4.8 . :8'" JOf--~'---7L--+/-~'-- ,,L-+--7"---r'-- ..__,L.j-- ;': ;; 8ulphlde grain denali)' 1";,- 4,8 ,.vee 4.0 -/---,-,---,-,----.-,----,--r----,--r--,--+ 1.8 ; -260 ]' 4 8 12 ,'8 2~9 o i , , -265 !- pyrile/cho!copyrile rOfio R 1.5 18 -270 ~ 1 30-215 Figure Sulphide grain density 3~O 12.17. , 18,, 19, , -2.BO -0 17 ~ dependence on pyrite/chalcopyrite ratio R. 2 8 19 -2.85 ~ Bulk densily fa Igm/ee) Figure 12.16. Sulphide content versus bulk density, with porosity and grain density varying parameters. Graph is accurate for p = 2.70, most accurate for other p at for 6: =2.85, WEIGHT " SULPHIDES BY HEAVY LIQUIDS 2 4 6 8 10 12 14 r \ reduced den.lty log (no .c.le> ~ r I 1000 -==: r I \ sulphide. by heavy liquids (/) w ...a: w :I.. C GIl ...w W IL. ~ 1200 ...x: lL oW ,r-- -== ~ 1400 L..., I ~ , 1600 I I I I I I Figure 12.18. Comparison between sulphide estimates from reduced density log (unsealed due to lack of calibration) and total sulphide. accurate to ±0.1 degree, or about ±2 milliradians, at tem electrode on the surface, one current electrode downhole, and peratures up to 77°C. Resistivity is recorded on a two potential electrodes downhole. Most of Kennecott's logarithmic scale. A unique feature is the ability of the measurements are made with a one-metre pole-pole (normal) operator to change the downhole amplifier gain from the array. surface. This is necessary because the phase accuracy is limited to an amplitude range of 35 decibels. Operationally Correction Curves for Borehole IP Measurements this becomes a nuisance only if the resistivity varies by more than two orders of magnitude within a short vertical distance. Electrical data from boreholes must be corrected to With the gain change capability, the dynamic range of the eliminate the contribution of the borehole fluid. Such system is 100 decibels at a fixed transmitted current. The borehole correction charts (often called departure curves) for ability to control the current level gives another 30 decibels a variety of electrode arrays were computed years ago for of flexibility. We have made continuous logs in various rock resistivity logging (e.g. Schlumberger, 1955). The corre types with resistivities ranging from one ohm-metre to sponding chart for induced polarization corrections, which greater than 10 000 ohm-metre (40db). The system can amounts to a derivative of the resistivity chart, was published accommodate any electrode array which uses one current by Brant et a1. (1966). We have recomputed the resistivity 284 W.E. Glenn and P.H. Nelson CALIPER DENSITY NEUTRON hole dia. (in.) gm!cc vol. 'I; tote.:" water In practice, a fifth-order polynomial was fitted to the 4 5 3.11 2.59 2.25 2.16 1:) 20 curves and the logs were corrected to R t Flild 200 with a fluid conductivity apparatus. m m .0 Induced Polarization Logs f100 E c Figures 12.24 and 12.25 display IP and resistivity data ~ from two holes containing sulphide mineralization in the .Q " southwestern Uni ted States. Both logs were obtained in 8.3 em diameter, water-filled boreholes using the one-metre 300 1000 normal electrode array. DOH-SF1 penetrates andesite and andesite breccia. Sulphide mineralization is pyrite and chalcopyrite, with the pyrite to chalcopyrite ratio ranging from less than one to as high as ten. The borehole fluid 12 .J-_L- ....L_--"'----'==ce...:='--_.Ll.. --' resistivity was 14 ohm-metres. Sulphides occur predom 00 inantly along veins and also as disseminations. Figure 12.19. Correlation of density log with sulphide veining. In Figure 12.24, the erratic nature of the resistivity and phase logs is attributed to the veined character of the sulphirlcs. Estimates of the sulphides content is based upon and IP departure curves for the pole-pole array in a borehole laboratory analysis (heavy liquid separation) on 3 m composites of the cored samples. These analyses are plotterl of resistivity R surrounded by an infinite medium of m in the left-hand column on Figure 12.24 and also used to resistivity R (F ig. 12.21 and 12.22). The method of t establish the absciss8 in Figure 12.26. The data points in computing the resistivity was taken from Gianzero and Rau Figure 12.26 are 3 m averages of amplitude and phase over (1977). The factor B on Figure 12.21 is 2 the corresponding intervals. The [lhase values do not display any particular trend as the sulphide content increases. As a R ,l[{ t 'a result the ratio ¢/R (also in Fig. 12.26) increases with the B2 ~ aR - sulphide content, roughly following the trendline indicated by a t the square root of 10 "'::l~.... ",. >=~ "'0 ..,.N-Q o < o ::l .j:l. o Q.." JJ ::l 0 ~.., o '"<~-. ~(J) 0':; -i '"~(\) '<", .4 .-...... I. I 1 1 I-R ~Mud resistivity .-/ A '\ m I-R ~Formation resistivity l.-1/ .... 1:>< i'.. AI \ 1\ t 1.--..,. V I- AM =Po1e- 001 e seoarati on /' 1/ D< X /\ 1\ \ 15'.., d ~Hole diameter L V ...... ~i'.. "- en I.2 .- ./ ...... hi' / 1/ V f\ \ f\ ~ / \ g, v v~ / ~/ ~- IJi\. / '\. f\. en 1 r I..--"'" V j<.. "- '\ o ~ 7' r- )(.... " 1/ 1/ ~ '\ 8 1/ r-..V /'J "- X. "- I.C 2 1/ r--...... I.C ".,-v/' ""7r-- V v ...... / "r-... l/ ...... ~ ~ I...... S' k: Y-. t/<-- k" I.C V V """- 7---2t:--Lr---. "'" -J. r- t:::--:t:--~r-- -.:.-~ // /' -7 1-7"------" , 0l,.1f /' / - V / 1/ V V / / / / / / ~o' /' ./ / V // / // ./ / ~\o / /' / V V V / / --- 0/ V / o. ./ /' V .....,v / / ..... IV '" V ,/ / /' ...... V /' V /' / / .-&0/ / ,/ ,/ ./' ./ ./ '/ i/ ./ i/ V _,00"'" ___ ,.,./ i'" .....i'" ~ ~v I-' ~ ,...... / -~!Soo- i--- >- _f- o. S 2 -eooo - --10000 -- - I'( ------Values 01 of 'm AM •ilo.... d j II"""" I Q~ W 100 1000 RATIO OF POLE SEPARATION (AM) TO HOLE DIAMETER (d) Figure 12.21. IP departure curves. (Beds of infinite thickness.) Centred pole-pole array. N en V1 286 W.E. Glenn and P.H. Nelson I T 30000 1 I .1 1..11111 ~ R =Apparent resistivity ~I- a . V -...... I-Rm~Mud resistivity i,,;' ~ R =Resistivity of formation V I- t V ~ "'" d ~Drillhole diameter ~V i'-r--- ~AM ./ 1---1- =Spacing (normal device) V r--.... 10000 ~ ,...... / ./ ./ ..... "'" // 1./ ...... 1-1- "7 "7 .- '" ~ V V'/ 7 ...... ~ 1/ V / I.--" ...... V / );' V - ...... / / 1// ~ v ...... 1-- f- V v"" "'-."-...... -- ~ ~ / v~ to-. V r---. r-... ~ f- / v"" i'-.I-- r----- V / V V l/ r-...... ~~ /. / Vi;:t;; r...... ~V V r-... ,tl'/ I000 OO / ./ / Wo / / / -.- '- ...... / 1/ /' r---. ~7~o / // / v ...... o / V -- lL.-... ' / 1/ ~"J0°..../ V V vI.-- ...... 0 '/ / -- -- r-...... t---~ V V I- -- "PffP / 1/' , V/ V I.-- r-..... '- v ...... V V V r-...... ~,~~ V v~ r...... r-~ ./ / ./ i'-...... ~oo/ ..... V t- r...... r- V I- [/f!J _/V V ftoo 0/ V r----. /' fl,0./V V I'-l-t-. .- -- 100 ./ ./ ./ I--'"' ...... ~o" ./ ~ ,fj / /' I--- V 0/ V L--- -...... 17( /' ./ ...... I-- ,,0' / 0' /0 '/ r---. ~o/ 10- f- ~ t- -- >-.. v' ./ ./ k'.~/~ -I- --- V,6 r- 0- 10 ./ - -"~ V ~o- ~ Yolues 01 •R, AM III d »t- . 10 100 eDr RATIO OF SPACING (AM) TO HOLE DIAMETER (d) Figure 12.22. Resistivity departure curves. (Beds of infinite thickness.) Borehole Logging 287 Im no rma I In 3.12 ho Ie. of IP parameters upon sulphide content divides into two classes governed by the geometrical distribution of sulphides AMid 12.6 in rock: Lz-.------.-7\. A. Mineralization Predominantly Disseminated Electrical conduction is controlled by the pore fluids so the resistivity is independent of the sulphide content. Hence the resistivity obeys Archie's Law after the fluid resistivity is modified to account for surface conduction. The phase shift 1.1 is proportional to the sulphide surface area exposed to the / \.. pore fluid, usually manifested by a linear dependence of phase / . upon sulphide content. Such a dependence of phase upon sulphide content is substantiated by our experience with ./. laboratory measurements on artificial samples and also by 1.0 4.0 prediction from simple mathematical models. ./'1 B. Mineralization Predominantly Along Veinlets In this case, the sulphide mineralization is distributed 4 along intersecting planar features and is sufficiently ~0.9 3.0 continuous that electrical conduction is controlled by the sulphide content. Empirically, the resistivity decreases E inversely with the square of the sulphide content. The phase 0:: is relatively independent of sulphide content, because the ...... 0 abundance of sulphide-electrolyte interfaces does not change 0.8 / /\. 2.0 0:: much as the sulphide content increases. Empirically, the factor /10<1> /R or some modification of it provides an /. \ ~"" estimate of the sulphide content. These two categories are rather general and are ;I. . probably not distinct; that is, there will be many instances 0.7 1.0 where the mineralization is equally disseminated and controlled by veining. In fact, using a prototype version of ./ the equipment described herein, Snyder (1973) observed a cube root dependence of the <1> /R factor upon sulphide content, but suggested that the dependence will be a function of rock type and sulphide distribution. The eventual form of 0.6-+------r------.------.-----+-0.0 a quantitative relation and the determination of its usefulness 0.0 1.0 2.0 3.0 4.0 must await further collection and correlation of empirical log R, IR m data. Because of sampling problems this must be done in the Figure 12.23. Borehole correction factors for the pole-pole field rather than in the laboratory. Although it is possible to array in a borehole penetrating a uniform medium. perform surface studies in mines, we believe that borehole methods provide the most expedient means of pursuing this goal. content, a correlation which did not occur in DOH-SF1. The MAGNETIC SUSCEPTIBILITY LOGGING same data, replotted on a linear graph show a fairly linear The magnetic susceptibility tool, like the induced correlation between the phase and sulphide content polarization tool, is more useful in mining applications than in (Fig. 12.28) with about 15 milliradians of phase shift produced other geotechnical applications. A quali tative use, for rock by 1.0 weight per cent sulphides. To emphasize the type identification and correlation, has been demonstrated independence of resistivity from sulphide content, above (Fig. 12.9). The system used by Kennecott for logging Figure 12.29 displays the porosity computations based upon is similar to that described by Broding et al. (1952) and the neutron log, <1>N' and upon the resistivity log, <1>. The Zablocki (1966). <1>R trace is based 'upon Archie's Law using a "cerrfentation exponent" of 2.0 and a pore fluid resistivity of 1.75 ohm The magnetic susceptibility tool is also used for metres. The 2.0 value of the cementation exponent is in quantitative studies in exploration. Figure 12.30 is one accord with the values found by Brace and Orange (1968) for example where the magnetic susceptibility measurement in laboratory samples of igneous rocks. The 1.75 value is one several drillholes yielded the thickness and magnetic fourth the 7.1 ohm-metres value of the borehole fluid, a fact susceptibility of the Gila conglomerate (southwestern United which can be attributed at least in part to the effects of States). The volume susceptibility is relatively uniform surface conduction in the rock, as also observed by Brace and around 1000 \l cgs. These data enabled the exploration Orange. The main point, however, is that the resistivity geophysicist to improve his aeromagnetic interpretation for determined porosity values are reasonably close to the this prospect. neutron-porosity, which is not the case when conduction is A second quantitative use, the direct measurement of controlled by the sulphide content. the magnetite content has been demonstrated by Snyder (1973) and also in Figure 12.8, but we have not pursued this Dependence of IP Parameters upon SUlphide Content application any further. Although the data base is Ii mited (only three other rock types were examined in the same detail as the two cases discussed above), we propose that the functional dependence 288 W.E. Glenn and P.H. Nelson GEOLOGY TOTAL SULPHIDES O~/R PHASE RESISTIVITY R /1 t weight .. mllilradians ohm-melres • • 15 so 75 100 31 l()() 316 100;) ,JJ ~ """=- ~ -..~. andesite 400 ~ ~ ~ -=- ~ ~ 1..., ;- r=--:> = "'---- II ?, eulphldes ~ ~ _.:J- sulphIdes ::;; ; magn lite ~ • .1 ~ e t.,~ /iOi7R ~ ~ .: 5 p; ::::> D ~ Ol --- , -5 -- t> " '1'« ~ fraclure zone 600 .~ 1<::::" '":,' ~- t:> r ' c:::::z"" ., ~ r',;' C ~p ~ ~ , :: IBOO :-,<," Figure 12.24. Sulphide data and IP log results corrected for borehole et't'ects in DDH-SFl. GEOLOGY PHASE RESISTIVITY (millirodions) (ohm - melers) 0 25 50 75 100 125 1000 600' 1300 ..r0- t... :;;s:: , ~ tesisljyjtJ L.., <:: 800 f ...... > ~ ~ L-- rrJl \Sulphide P ~ ...Q) Q) .5 -E t:2' ... co -mnrr- r---I ~ /hose h { 1000 1 ~ ~- l ~ o 2 4 6 8 10 12 (weight %) SULPHIDE ESTIMATES Figure 12.25. IP logs and sulphide estimates in DDII-SF2. . . 1000+ II + 1+. I..;. I + 1000+ I. ..1: + I+ I/I + .. . .. L"O,/R : ". '.~ / 500- 05- /. '. • 500- "• O~ '. " .... /. / " ••• " ,~, ,,/. , E :'.. '.... .: / '200- ' ~ .02-'-' '/' 200- ~ 02- / '' . . ~ " ~ '00; .. I'.:.' .I + Li:'·:-· + '00+ II + I 0,1 .'...... :. + I 2 5 10 - I 2 5 10- • s' (wg~%) ~ 5' (wgIO!o) ~ •• - ~ - CD 0.05- 0.05- ::r o ;' r o . .. .c .c 5' 100+. • II + 002- 100+ II '.' ;",+ 002- .c . . . -. - .. . ..e:, '.' .". . .. ',: .50-;- : .:.' • - 001+ II + 50- • - 0.01+ II + "" ·r 1 2 5 10 1 2 5 10 ~'. S'(w91 %) ~ S'(w91%) ~ I • . D , . i, 20- - 20-- II I II 10+I 2 5 +10 10+1 2 5 +10 S'lwgl%1 (w91%1 L- s' ---.J Figure 12.26. IP parameters and sulphide content, DDH-SFI. Figure 12.27. IP parameters and sulphide content, DDH-SF2. N D:l '" 290 W.E. Glenn and P.H. Nelson 140+-----,-----,------,-----,-----,---,------,- and a number of the contacts show the greatest cooling effects on the temperature logs, The direction of any "j groundwater flow in these rocks should be strongly influenced by intrusive and volcanic rock contacts. 120 I FLUID FLOW DETERMINAnON .j In the previous section on temperature logging we noted 100 how the temperature log could indicate points of fluid flow or fluid exit in a drillhole. Some attempt can be mude to u; / c: quantify this flow from the temperature anomalies but the '0'" ./" method is very imprecise. The rocks will often show ~ 80 temperature variation beyond the zone of flow and ! mathematical modelling is not simple (Smith und Steffenson, .. j 197U), UJ (/) « ph••• : 15.0xS"'phl•• A more direct quantitative measure can be made with a I ..r Q. 60 spinner log (c.f. Schlumberger Production Log Interpretation, 1974). However, a spinner tool at best measures flow .; accurately only above 0.75 mimin. Figure 12.33 shows two flow profiles made in holes used for dump leaching at one of 40 Kennecott's operating properties. The logs show that fluid / exit is nonuniform and is exiting primarily out the top portion j of the completed hole interval. 20 / CALIBRAnON OF LOGGING EQUIPMENT The American Petroleum Institute has established / certain recommended standards for calibration and format of o+---,------,----,---,------,---_+_ borehole logs; lor example, nuclear logs (API, 1974) and o 4 6 8 10 12 SULPHIDE (weight %) electrical logs (API, 1967). API has also estnblished a calibration facility on the Univ8rsity of Houston campus, Figure 12.28. Phase values averaged over 10 foot interval available to anyone for a set fee. The c8libration facili ty is versus sulphide content, DDH-SF2. designed for oil field envirownents and for nuclear logs. The Uni ted States Bureau of Mmes hrls established a calibration facility for the mining arld engineering logging applications. The tool has been calibrated using magnetic This facility provides standards for density, magnetic susceptibility measurements on core samples and the susceptibility, sonic velo::::ity, resistivity and caliper logs calibration is routinely checked with spot core measurements. (Sn:Jdgrass, 1976) and the facility is available to industry. I"igure 12.31 shows an example of this ckeck in an exploration hole in southern Arizona. Kenrlecott has calibrated nuclear tools at the API pits and the rp,st of thp,ir tools with core analyses. An example of core calibration of the maqnetic susceptibility tool was given TEMPERATURE LOGGING in Figure 12.31. Since it is neither practical to calibrate the A temperature log is a continuous record of borehole various tools frequently at the calibration facili ties in ei ther fluid temperature with depth which will bc the geothermal Houston or Denver nor to continuously check the calibration gradient only if the fluid is in equilibrium with the adjacent with c', e analyses, Kennecott spot check with core analyses rocks and if there is no vertical cireulatiorl of fluid in the and also verify the tool calibration before and after each log drillhole, wilh some fixed reference. For example, the density tool calibration is checked with two blocks of material of known Temperature logs are necessary for the correct densi ties before and after euch log is made. A geometric interpretation of resistivity logs because of temperature array of ferrite rods is used to check the calibration of the effect on electrical resistance (Alger, 1966; Schlumberger, magnetic susceptibility tool. The calibration of slim hole 1972). The fluid resistivity needs to be corrected for tools is not an easy matter and Merkel and Snyder (1977) have temperature before it is used for porosity analyses or for an disclJssed this problem in some detail. Waller et al. (1975) estimate of total dissolved solids. examined some basic errors inherent in 1001 calibration. Temperature logs can also be used to examine fluid flow in drillholes (Keys and MacCary, 1971; Wilterholt and Tixier, CONCLUSIONS 1972). One method is to inject cooler surface water into a drillhole for some period of time and obtain temperature> logs 1. 13orehole logging methods will gradually bp,come rnore during injection and at periodic intervals postinjcction. These common in the base metals mining industry for logs are then compared to the preinjection log. The injected exploration, property assessment and engineering fluid will cool the borehole fluid and the zones of fluid exit studies. The demand will be a direct function of the from the hole. The temperature in the drillhole will recover ability to obtain in-situ data which is not readily toward the preinjection temperature profile with zones of <1Vailable from core, and the abili ty to reduce the need fluid exit recovering most slowly. Figure 12.32 illustrates for core recovery. In other words, the ability to this logging method. quantify the elemr,nts and minerals which have prime irnportancp, to the mining geologist is the key factor in A preinjection and two postinjection temperature the widespread use of borehole techniques. profiles are shown in Figure 12.32a and the difference between the post- and pre-injection logs are shown in Figure 12.32b. Also shown are fracture locations picked from the caliper log. The rocks are volcanics intruded by dacite Borehole Logging 291 #5 2.5 5 o· /C•/ oo.n, ~ POROSITY / (volume %) / o 5 10 ~ 600-+-----+-----1 / v 200 200 .eOJ .5 .r: ;;; 0... '0 en ... 600 820 250 840 1200'-J------L------' ..c: en 880 270 900 -i. ...L.. o Bison measurements on core Susceptibility tool measurements Figure 12.31. Comparison of magnetic susceptibility mea surements made in drillhole BB-1 and on BB-1 core samples from southern Arizona. 292 W.E. Glenn and P.H. Nelson % Cumulative Flow Loss 20 40 60 80 100 of Perforations 200 220 (il) (b) 70 TEMPERATURE (OF) TEMPERATURE DIFFERENCE (oF) 70 90 110 20 240 UJ " t( 'J ...... 1 ~ ,1 ...... 1/ ~ ) \ 9//4/74 .. 't" ( .~ 1C ,. 't~ a) Drill hole DU-l ,,' k ::: " of. Q, ~~ % Cumulative Flow Loss ~ ,"~ \\ k 60 80 100 , 20 40 " •~ ,.. of. .. 120 .. ( I \\ , '"~ ·I... ~,,~. ~ ~OStart of Perforations ~\ "... E ... , 11 '> -/\ 0 I-; 0 14 ~ " A < N lJC ( ~ 2/20/76 a ~ t • 0 \\ 2:55 p.m. In •, ••t '1.. 'lII (I • ( \\ « •• '1-"• ( J(.• 1 b) Drill hole DU-2 Figure 12.33. Cumulative per cent fluid loss with depth in two mine dump holes. Borehole Logging 293 2. In general, the added information which can be gleaned Clavier, C., Heim, A., and Scala, C. from a combination of logs instead of just one or two is 1976: Effect of pyrite on resistivity and other logging well worth the added cost of acquisition. This is true measurements; SPWLA 17th Annual Logging whether the application is a qualitative one such as rock Symposium, June. type and correlation, or a quantitative goal such as estimation of sulphide content. Conaway, J.G. 1977: Deconvolution of temperature gradient logs; 3. With present technology, it is now possible in the base Geophysics, v. 42 (4), p. 823-837. metal environment to make quantitative estimates of Czubek, J.A. porosity, fracture intensity, bulk density, magnetite 1979: Modern trends in mining geophysics and nuclear content, potassium content, and mineralogically bound borehole-logging methods for mineral exploration; water. We feel that with some additional effort and in Geophysics and Geochemistry in the Search for care it will soon be possible to add sulphide content to metallic ores; Peter J. Hood, ed., Geol. Surv. Can., this list. Econ. Geol. Rep. 31, Paper 11. 4. As pointed out by Snyder (1973) these measurements have particular application in the porphyry copper Daniels, J.J. 1977: Interpretation of buried electrode resistivity data environment where drillholes are often deep and costly. using a layered earth model; submitted to We emphasize that the logs have enhanced value when Geophysics for publication. they are applied on a deposit-wide basis and are integrated into geological and geochemical studies. Dyck, A.V., Hood, P.J., Hunter, J.A., Killeen, P.G., Overton, A., Jessop, A.M., and Judge, A.S. 5. We agree with an observation made by Dyck et al. 1975: Borehole geophysics applied to metallic mineral (1975) that there is a need for more case history prospecting; A review; Geol. Surv. Can., documentation and published empirical relationships for Paper 75-31. the mining environment such as exists for a wide range of logging applications in the oil and gas industry. Fishel, K. 1976: Applications of electric logs in Appalachian coal exploration; paper presented at 1976 annual ACKNOWLEDGMENTS meeting of Geol. Soc. Am., Denver, Colorado. D.D. Snyder initiated the Kennecott logging program in 1972 and formulated many of the practices and designs, Gianzero, S.C. and Rau, R. 1977: The effect of sonde position in the hole on including the initial design of the continuous IP logger. responses of resistivity logging tools; Geophysics, D. Purvance performed the numerical computations for the IP v. 42 (3), p. 642-654. departure curves. E.P. Baumgartner acquired and interpreted several of the logs presented in this paper. Dale Green, Hohmann, G.W., Nelson, P.H., and Van Voorhis, G.D. Roy Lenk, Jim Simmons and Dave Ewing contributed 1977: Field applications of a vector EM system; significantly to the development and maintenance of the presented at 47th annual international meeting and logging systems. Jonathan Jackson assisted in the recording exposition of Society of Exploration Geophysicists, and analysis of the spinner logs. We thank Kennecott Copper Calgary. Corporation for permission to publish the material in this Keyes, W.S. and MacCary, L.M. paper. 1971: Application of borehole geophysics to water resources investigations; Techniques of Water REFERENCES Resources Investigations of the Uni ted States Geological Survey, Book 2, chapter E1. Aamodt, R.L. 1976: in LASL Hot Dry Rock Geothermal Project July 1, Killeen, P .G. 1975 to June 30, 1976, compiled by A.G. Blair, Jr., 1979: Gamma-ray spectrometric methods in uranium W. Tester and J.J. Mortensen; Los Alomas pub. exploration: application and interpretation; !!! LA-6525-PR. Geophysics and geochemistry in the Search for metallic ores; Peter J. Hood, ed., Geol. Surv. Can., Alger, R.P. Econ. Geol. Rep. 31, Paper 10C. 1966: Interpretation of electric logs in fresh water wells in unconsolidated formations; SPWLA 7th Ann. Lytle, R.J., Lager, D.L., Laine, E.F., and Salisbury, J.D. Logging Symp., Tulsa, Oklahoma, May. 1976: Monitoring fluid flow by using high frequency electromagnetic probing; Lawrence Livermore American Petroleum Institute Laboratory pub. UCRL-51979. 1967: Recommended practice and standard form for electric logs; API RP 31, 3rd edition. Madden, T.R. and Cantwell, T. 1967: Induced polarization, a review; Mining Geophysics, 1974: Recommended practice for standard calibration v. II, Society of Exploration Geophysicists, Tulsa, and form for nuclear logs; 3rd edition. Oklahoma. Brace, W.F. and Orange, A.F. Merkle, R.H. and Snyder, D.O. 1968: Further studies of the effects of pressure on 1977: Application of calibrated slim hole logging tools to electrical resistivity of rocks; J. Geophys. Res., quantitative formation evaluation; SPWLA 18th v. 74 (16). Annual Logging Symposium, June. Brant, A.T. and the Newmont Exploration Staff Nargolwalla, 5.5., Rehman, A., St. John-Smith, B., 1966: Examples of induced polarization field results in the time domain; Mining Geophysics, v. I, Soc. and Legrady, O. 1974: In situ borehole logging for lateritic nickel deposits Explor. Geophys., Tulsa, Oklahoma. by neutron capture-prompt gamma ray Broding, R.A., Zimmerman, C.W., Somers, E.V., measurements; Scintrex Limited, Concord, Ontario, Wilkelm, E.S., and Stripling, A.A. Canada. 1952: Magnetic well logging; Geophysics, v. 17 (1), p. 1-26. 294 W.E. Glenn and P.H. Nelson Nelson, P.H. and Glenn, W.E. Snodgrass, J.J. 1975: Influence of bound water on the neutron log in 1976: Calibration models for geophysical borehole minerali zed igneous rocks; SPWLA 16th Annual logging; U.S. Bureau of Mines, Report of Logging Symposium, June. Investigations 8148, p. 2I. Patchett, J. Snyder, D.O. 1975: An investigation of shale conductivity; SPWLA 16th 1973: Characterization of porphyry copper deposits using Annual Logging Symposium, June. well-logs; Geophysics, v. 38 (6), p. 1221-1222. Pickett, G.R. Snyder, D.O., Merkel, R.H., and Williams, J.T. 1960: The use of acoustic logs in the evaluation of 1977: Complex formation resistivity, the forgotten half sandstone reservoirs; Geophysics, v. 25 (1), p. 250 of the r8sistivity log; SPWLA 18th Annual Logging 274. Symposium, June. Pirson, S.J. Staff, Scintrex Limited 1963: Handbook of well log analysis; Prentice-Hall, Inc., 1976: Application of the Metalog System for the grade Englewood Cliffs, New Jersey. determination of copper in a porphyry deposit; Scintrex Ltd., Concord, Ontario, Canada, p. 36. Ritch, H.J. 1975: An open hole logging evaluation in metamorphic Van Schalkwyk, A.M. rocks; SPWLA 16th Annual Logging Symposium, 1976: Rock engineering testing in exploratory boreholes; June. v. I of Exploration for I~ock Engineering, edited by Z.T. Bieniawski, A.A. Balkema. Savre, W.C. and Burke, J.A. 1971: Determination of true porosity and mineral Waller, W.C., Cram, M.E., and Hall, J.E. composition in complex lithologies with the use of 1975: Mechanics of log calibration; SPWLA 16th Annual sonic, neutron and density surveys; SPE Reprint Logging Symposium, June. Series No.1, p. 306-34l. Wilterholt, E.J. and Tixier, M.P. Schlumberger 1972: Temperature logging in injection wells; AIME, 19'J5: Resistivity Departure Curves, Document Number 7, SPE-4022, p. I-II. Schlumberger Ltd., New York. Wylie, M.R.J., Gregory, A.R., and Gardner, L.W. 1972: Log interpretation; v. 1 - Principles; Schlumberger 1956: Elastic wave velocities in heterogeneous and porous Ltd., New York. media; Geophysics, v. 21 (ll, p. 41-70. 1974: Production log interpretation; Schlumberger Ltd., Zablocki, C.J. New York. 1966: Electrical properties of some iron formations and adjacent rocks in the Lake Superior wgion; Mining Scott, J.H. Geophysics, v. I, Society of Exploration 1977: Borehole compensation algorithms for a small Geophysicists, Tulsa, OklClhoma. diameter, dual-detector density well-logging probe; SPWLA Trans. 18th Annual Logging Symposium, Zamenek, J., Glenn, E.E., Norton, L.J., and Caldwell, R.L. June. 1970: Formation evaluation by inspection with borehole televiewer; Geophysics, v. 35 (2), p. 254-269. Seigel, H.O. and Nargolwalla, 5.5. 1975: Nuclear logging systems obtains bulk samples from small boreholes; Eng. Mining J., v. 176 (8), p. 101-103. Smith, R.C. and Steffensen, FZoJ. 1970: Computer study of factors affecting temperature profiles in water injection wells; J. Petrol. Tech., November.