S\W^ : .^\ •liF «/\. W ♦* ** '-W* : / % °°«y *** X •- % '•SH^' 7% '$Ws y'^+'-W&S r ^\,'Ww'\^ % ■*JS& "W :J§^ v* °4lK- **<>* :tf»: «*»* JOT" ?S :««*• ■a? »<* » ^ / V' %> **?vi»* ^ % V ''.T^ ,** 0* - • • _ y*V /v : .l K **%> o . . - . *o ;* < ^ T.T*\ A iV-* w <£%> r.i*- ,o* *o » *, *W A" ."•♦ '**+* ' .n* .-•. *~ J* A "oV * ^ c- W i*\*l^/% G°*.i&>>o vv ' o ^°^ °^ -^ r-.^\o° by 1 iL'AJ-* ^ *<'»<' , .* 4 o is*,* ^ v ^ - " • , **b ^/^^^ \/ --^fe't %/ -'^Kfe \/ •**•& **-** .-isSfei'- ^-^ *' ^v^ .0* .."■ ^ ,^ T4 , iP-n,. v „■> ^. y » o » o 4 o *^* v - V*'* A° "by * ^ y. ^ a VA. 4 v^ V • -5- A v • Jf^K .0 % • -p. ?a AT ^^W^' ^ «, »/v$.^a' "Pa a* *^* v - rAcr *bl^ o v "bv* A ^ £ -- V %.""' J • A* ve % . "Vo?" oV^ *bV" / .K ^ v^ - <» AT ^b* • u, -*% ^ 4** «• -" P^ a? ^°A - ^o* '^SiB- "ov* :^SIf^'- "^ ^ <^sm*» ^o ./V-^/V o^.^.:,."^ v* v *bv ^^ .vaSfcfc. V^ /dfeTL v.** .^¥a\ v>* yd^\ -^ .^ 4 o A v '^i^^: **\* •'■ % A* ^ IC 9133 Bureau of Mines Information Circular/1987 Estimation of Remaining Lode Gold Endowment in Selected Mining Districts of Alaska By Gary E. Sherman UNITED STATES DEPARTMENT OF THE INTERIOR Information Circular 9133 Estimation of Remaining Lode Gold Endowment in Selected Mining Districts of Alaska By Gary E. Sherman UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary BUREAU OF MINES Robert C. Horton, Director Library of Congress Cataloging in Publication Data: Sherman, G. E. (Gary E.) Estimation of remaining lode gold endowment in selected mining districts of Alaska. (Information circular/United States Department of the Interior, Bureau of Mines; 9133) Bibliography: p. 16. Supt. of Does, no.: I 28.27: 9133. 1. Gold ores-Alaska. I. Title. II. Series: Information circular (United States. Bureau of Mines); 9133. TN295.U4 [TN423.A7] 622 s [553.4T09798] 86-607928 CONTENTS Page Abstract 1 Introduction 2 Past and present gold production 4 Methodology 5 Estimation of remaining endowment 6 Chichagof District 7 Fairbanks District 8 Homer District 9 Hope-Seward District 10 Juneau District 11 Ketchikan District 12 Prince William Sound District 13 Willow Creek District 14 Discussion 15 References 16 Appendix A. — Raw production data for districts analyzed 17 Appendix B. — Regression analysis results, by district 23 ILLUSTRATIONS 1. Location of Alaska mining districts 3 2. Alaska lode gold production (1891-1965) 4 Grade-tonnage curve: 3. Chichagof District 7 4. Fairbanks District 8 5. Homer District 9 6. Hope-Seward District 10 7. Juneau District 11 8. Ketchikan District 12 9. Prince William Sound District 13 10. Willow Creek District 14 TABLES 1. Lode gold production, by district . 4 2. Summary of districts analyzed 6 Remaining endowment estimates: 3. Chichagof District 7 4. Fairbanks District 8 5. Homer District 9 6. Hope-Seward District 10 7. Juneau District 11 8. Ketchikan District 12 9. Prince William Sound District 13 10. Willow Creek District 14 11. Summary of remaining endowment 15 ii TABLES — Continued Page Raw production data: A-l. Chichagof District 17 A-2. Fairbanks District 18 A-3. Homer District 18 A-4. Hope-Seward District 19 A-5. Juneau District 20 A-6. Ketchikan District 21 A-7. Prince William Sound District 22 A-8. Willow Creek District 22 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT pet percent tr oz troy ounce St short ton tr oz/st troy ounce per short ton st/d short ton per day yr year ESTIMATION OF REMAINING LODE GOLD ENDOWMENT IN SELECTED MINING DISTRICTS OF ALASKA By Gary E. Sherman 1 ABSTRACT The Bureau of Mines estimated the remaining lode gold endowment of eight mining districts in Alaska using historic production data. A log- arithmic model of cumulative tonnage of ore processed versus cumulative grade was applied to the following districts: Chichagof, Fairbanks, Homer, Hope-Seward, Juneau, Ketchikan, Prince William Sound, and Willow Creek. To assess the remaining endowment, a computerized production data base was compiled from Bureau records. These data were aggregated in 5-yr intervals for each district. Data were sorted in order of declining grade, and log cumulative grade was plotted against log cumulative ton- nage. Linear regression was performed on the data for each district. The linear equation for each curve was used to predict remaining endow- ment at a limiting mining grade. Based on conservative extrapolation of the grade-tonnage curves, a substantial total endowment of 8,415,100 tr oz of gold remains in the eight districts. The districts with the greatest remaining endowment are the Juneau, Chichagof, Fairbanks, and Willow Creek Districts. 1 Physical scientist, Alaska Field Operations Center, Bureau of Mines, Juneau, AK. INTRODUCTION The Bureau of Mines Minerals Availabil- ity Program (MAP) was established in 1974 to systematically assess mineral supplies from domestic and foreign sources. In the context of MAP goals, an assessment of the remaining lode gold endowment for eight mining districts in Alaska was undertaken. Exploration activity in Alaska has de- clined dramatically in recent years, ow- ing primarily to metal price declines; however, there has been a renewed inter- est in the potential of past lode gold producers. Many past producing lode gold mines in Alaska were unable to resume production owing to economic conditions following World War II. Others discon- tinued production owing to declining grade or the lack of adequate reserves. Many of the past producers in Alaska may contain significant remaining resources of gold. Several studies have used grade- tonnage relationships in examining the characteristics of ore deposit types and metal contents (J_"_3)« 2 Lasky (4) estab- lished what has become known as Lasky 's law, in which cumulative log tonnage plotted against cumulative grade exhibits a linear relationship for many deposit types. This is a negative exponential relationship of the form g = C1-C2 log t, where g is average grade, t is tons, and C] and C2 are constants. Lasky suggested that the tonnage-grade distribution for porphyry copper deposits could be used to estimate unknown copper resources by ex- trapolating the curve to some limiting cutoff grade (_5). Cargill (JO used historic production data to predict remaining usable re- sources in a log grade-log tonnage model. Use of historic production data inher- ently includes geologic, economic, and political conditions that have influenced production. The preferred method would be to measure cumulative return per unit effort, where effort includes such 2 Underlined numbers in parentheses re- fer to items in the list of references preceding the appendixes at the end of this report. factors as exploration, extraction, pro- cessing, and transportation (_6)» Since data on effort are generally lacking in the mineral industry, cumulative average grade is used in its place. Cargill ex- plained the method as follows: The underlying premise of this pro- duction-grade method of estimating usable resources is that the sum of industry experiences is reflected in its production and discovery statis- tics. This premise is true because the mineral and petroleum industries continuously adjust to economic and technologic pressures (each industry is forced by free market economics toward the lowest cost product), as well as to increasing geologic knowledge. .. .The suggestion that the future course of a mining industry can be estimated from its production history dates back at least to 1929 (D.F. Hewett). Production data were grouped in 5-yr intervals by Cargill to minimize yearly variations in the data, and a least- squares fit to the line was made using the equation log y = bo + [bi log x], (1) where y = cumulative average grade, x = cumulative ore, bo = a constant, and bi = slope of the line. Regression was performed to minimize the expression n I (log y, - b - [b, log x,]) 2 > (2) i=l where n = number of data points, yj, = cumulative grade, ith period, and x | = cumulative ore, ith period. Cargill (_7) proved that, for any point on the curve, y = L /(l+b,), where Lq = limiting grade. (3) By selecting an average mining grade and using equation 3 to determine cumula- tive grade, the initial tonnage of ore at the mining grade can be estimated. Sub- traction of past production yields the usable resources available at the mining grade chosen. Harris (8) expressed concern about the method used by Cargill. He suggested that a reordering of the data by declin- ing grade may be appropriate in certain cases. Such a reordering can produce a curve that is more linear than one based on a time series. Harris argued that by equating cumulative grade with cumulative effort, bias can be introduced when, for example, economic conditions force high grading of an ore body. This upsets the orderly decline of cumulative grade with time. However, Harris stated that reor- dering of production data may not be strongly indicated when there has been a significant decrease in grades over the life of a mine and when a grade-tonnage relation is fitted only to the low-grade portion of the data. Under these circum- stances, the influence of grade varia- tions in early years at relatively high grades is of little consequence. This is true because the cumulative average for the low-grade portion of the data may be unaffected by reordering production data at the earlier high grades (8_). Historically, grade-tonnage relation- ships provide an estimate of the physical stock or endowment (8^). Use of the reordered production data results in modeling of the physical stock, not a quantity-effort relationship as used by Barrow, *■ y Ancho airbank s ,Kodi«k . ■•' Mining Districts 1 Chichagof 2 Fairbanks 3 Homer 4 Hope - Seward 5 Juneau 6 Ketchikan 7 Prince William Sound 8 Willow Creek 300 I Scale, miles FIGURE 1.— Location of Alaska mining districts. (Modified from Ransome and Kerns (9).) Cargill (6^, since production is ordered by declining grade and not by year. Based on Harris 1 arguments, it was de- cided that reordering of the data by de- clining grade was the best approach for this study. Cumulative log grade-log tonnage curves were constructed for each district to provide an estimate of the nonproduced portion of the lode gold endowment. Production data from the Chichagof , Fairbanks, Homer, Hope-Seward, Juneau, Ketchikan, Prince William Sound, and Willow Creek Districts were analyzed. Locations of the districts examined are shown in figure 1. Mining district names and boundaries follow the convention of Ransome (9). PAST AND PRESENT GOLD PRODUCTION TABLE 1. - Lode gold production, by district ' (Ranked in descending order) District Juneau Chichagof Willow Creek Fairbanks Prince William Sound. Chistochina Alaska Peninsula Ketchikan McGrath Unclassified 2 Homer Hope Kantishna Nome Petersburg Admiralty Anchorage Seward Iditarod Bonnifield Hyder Valdez Creek Nizina Innoko Chisana Kodiak Fairhaven Chandalar Aniak Yentna Redoubt Total Gold, tr oz 5,652,776.00 826,739.00 611,833.20 233,347.10 137,889.60 56,843.55 51,692.54 51,305.35 38,592.88 17,213.60 16,026.58 15,113.53 7,643.59 6,189.17 5,913.23 4,997.13 4,478.78 3,020.15 2,892.06 2,301.27 2,240.57 1,700.80 1,363.26 478.91 172.00 71.24 70.19 70.00 49.70 1.65 .24 7,753,026.87 Districts with Bureau production re- cords. Production for which no district could be assigned owing to lack of information. Total gold production from Alaska (1880-1984) has been estimated at 31 mil- lion tr oz-(lO). Available Bureau data for the period 1891 to 1965 indicate a total lode production of 7,753,027 tr oz. Table 1 summarizes actual lode gold pro- duction by district, sorted in descending order. The majority of lode gold produc- tion in Alaska came from the Alaska Ju- neau Mine and the Treadwell group (the Treadwell, Mexican, Ready Bullion, and 700 Foot Mines), both in the Juneau Dis- trict. As seen in figure 2, lode gold production dropped sharply after 1917 ow- ing to the cave-in and subsequent closure of the Treadwell group, and again in 1942 following the issuance of War Production Board order L-208, which declared gold mining a nonessential wartime industry. Economic conditions following World War II prevented the resurgence of major lode mining activity, even though attempts were made to open mines with known 320 1891 1901 1921 1931 1941 1951 1961 1971 FIGURE 2.— Alaska lode gold production (1891-1965). Miss- ing portions of the curve indicate lack of data. Based on Bureau of Mines production data. reserves. Lode gold production in recent years has been limited to small-scale (less than 200-st/d) operations such as the Little Squaw Mine in the Chandalar District, the Independence Mine in the Willow Creek District, and the Grant Mine in the Fairbanks District. Gold production in Alaska in 1984 ex- ceeded 175,000 tr oz , virtually all of it from placer deposits (10). METHODOLOGY Alaskan lode gold production records compiled by the Bureau from 1891 through 1965 were entered into a computerized data base to allow retrieval and manipu- lation. The production records are a combination of mint, smelter, and Bureau canvass records. These data are often lacking in terms of total production for a given mine, but were considered com- plete enough to attempt an estimation of remaining gold endowment. The eight districts for analysis were chosen based first on the quantity of in- formation available and secondly on the completeness of the historic production data. Many of the individual mine rec- ords lack key information such as tons of ore processed per year and mine name. In some cases only yearly district or re- gional totals were available. Where information allowed, missing an- nual tonnages were estimated. This was accomplished by using an average grade of production for a block of years surround- ing the year with no tonnage data. Only years with comparable production levels (troy ounces) were used to compute the average grade. The tonnage was then es- timated by dividing the troy ounces pro- duced in the missing year by the average grade for the block of surrounding years. When no annual tonnage figures were available for most of the district, the data could not be used in the model. Other districts are dominated by mines that produced gold from primary copper deposits. These deposits have lower gold grades than epithermal gold deposits and cannot be aggregated without changing the nature of the grade-tonnage relationship. Aggregating data across deposit types may introduce a high degree of variability in the grade-tonnage curve; therefore data were restricted to production from pri- mary lode gold (quartz vein) deposits. An exception to this is the treatment of the Juneau District, in which production was dominated by large low-grade deposits (Alaska Juneau and Treadwell Mines). Data for the quartz vein deposits were aggregated with those for the low-grade deposits. Since the "high-grade" quartz vein deposits accounted for less than 10 pet of the production from the dis- trict, these data exert little influence on the cumulative curve. Production records were cross refer- enced with the Bureau of Mines Minerals Availability System (MAS) sequence number for each deposit to verify that each mine was assigned to the proper district. Following elimination of duplicate and/or secondary records, the data were aggre- gated in 5-yr intervals for each dis- trict. Cumulating the data over a 5-yr period smooths the cumulative grade- tonnage curve by lessening the yearly variation. Curves were plotted, and a least-squares regression analysis was performed to fit a linear equation to each line. Extrapolation of the curve to a limiting grade provided an estimate of remaining gold endowment. Remaining en- dowment is defined for the purpose of this study as the nonproduced portion of the mineralized rock (at a limiting grade) associated with lode gold deposits that have produced in the past. Limiting grade is chosen to be less than the low- est production grade in the district, but greater than a technologic cutoff grade. Vein gold deposits in Alaska generally had a production grade greater than 0.2 tr oz/st. The Juneau District depos- its produced at grades of less than 0.15 tr oz/st. Based on these historical values, the limiting grade (grade at which remaining endowment was calculated) was taken to be 0.1 to 0.2 tr oz/st less than the historic production grades. Care should be taken not to extrapolate the curves beyond reasonable limit. Taking a very low limiting grade can result in estimates that are astronomi- cally high and probably invalid. Most of the cumulative grade-tonnage curves for the districts examined illus- trate an upper high-grade portion with a flatter slope than the rest of the curve. This is because many of the mines in Alaska were short-lived, high-grading op- erations. For a mine (and therefore ag- gregated district data) to exhibit an or- derly decline in grade over time, the mining operation must operate over a suf- ficient time span to allow a representa- tive sampling of the ore body. Because of this, the upper data points were dropped in the regression analyses for all of the districts except Chichagof, Juneau, and Willow Creek. The estimate of remaining endowment is based on an average limiting grade. Lim- iting grade is converted to a cumulative grade using equation 3. This cumulative grade is used in the equation = io(( lo g y b )/b,). (4) The tonnage x represents the total amount of ore originally present at cumulative grade y. Total gold present is equal to the product of x and y. Subtracting the previous production from the original amount of gold present yields an estimate of remaining endowment in troy ounces of gold. ESTIMATION OF REMAINING ENDOWMENT Table 2 shows the eight districts chosen for analysis along with the number of mines in the data set, documented pro- duction, total tons of ore produced, and average grade. Documented production is defined as gold production for which an- nual tons of ore produced are known. Tonnage of ore per year is essential in forming the cumulative grade-tonnage curve; mines lacking this information are not included in the analysis. For this reason, the production figures for each district in table 2 are less than those in table 1. Individual estimates by district are discussed in the following sections. For each district a table lists the remaining gold endowment estimates for a range of limiting grades. The range of estimates is given for each district to illustrate the dependency of the estimate on the limiting grade chosen. As stated pre- viously, at some point the limiting grade becomes meaningless in terms of mining, and the endowment estimate can approach astronomical proportions. A total remaining gold endowment of 8,415,100 tr oz was estimated for the eight districts. Appendix A presents raw production data for the eight districts, and appendix B gives regression analysis results by district. TABLE 2. - Summary of districts analyzed District Number of mines Documented production, tr oz gold Total ore, st Average grade tr oz/st Chichagof Fairbanks Homer Hope-Seward Juneau Ketchikan Prince William Sound. Willow Creek 56 8 20 28 37 27 28 787,347 230,499 10,391 17,587 5,583,121 16,042 82,777 607,726 827,313 195,071 9,020 18,271 116,089,758 38,175 74,818 539,624 0.95 1.18 1.15 .96 .05 .42 1.11 1.13 dumber of mines included in the analysis. TABLE 3. - Remaining endowment estimates, Chichagof District Limiting grade, tr oz/st Cumulative grade, tr oz/st Original ore available, st Remaining gold endowment , tr oz 0.1 0.183 .366 .549 .732 .915 1.097 1.280 1.463 32,386,600 7,019,100 2,869,600 1,521,200 929,800 623,200 443,400 330,200 5,139,400 .2 .3 .4 1,781,600 788,100 1 326,200 .5 .6 63,400 .7 Estimate of remaining endowment based on historic grades. CHICHAGOF DISTRICT Production from the Chichagof District (table 3) came primarily from the Hirst- Chichagof and the Chichagoff Mines. These two mines accounted for over 98 pet of the gold produced in the district. Figure 3 is a plot of the cumulative grade-tonnage data. Linear regression of the data in figure 3 yields values of 2.67 for bo and -0.453 for bi. The low- est grade material produced in the Chichagof District was ore with a grade of 0.49 oz/ton. Using 0.4 oz/ton as a limiting grade in equation 4, the esti- mated remaining endowment of gold in the district is 326,200 tr oz. Since the majority of the production data came from two mines and continued over a signifi- cant time span, the grade-tonnage curve fits the model well. Table 3 shows estimates of remaining endowment for the Chichagof District over a range of limit- ing grades. LOG 5\4 CUMULAT FIGURE 3.— Grade-tonnage curve, Chichagof District. TABLE 4. - Remaining endowment estimates, Fairbanks District Limiting grade, tr oz/st Cumulative grade, tr oz/st Original ore available, st Remaining gold endowment , tr oz 0.1. .2. .3. .4. .5. .6. .7. 0.123 .246 .369 .491 .614 .737 .860 .983 42,718,665,800 1,028,435,000 116,265,200 25,031,500 7,525,100 2,819,500 1,229,700 599,300 5,254,165,400 252,764,500 42,671,400 12,060,000 4,389,900 1,847,500 1 827, 000 358,600 Estimate of remaining endowment based on historic grades. FAIRBANKS DISTRICT Gold production in the Fairbanks Dis- trict came from a number of mines, many with a short production span. The Clearly Hill, Free Gold, Hi Yu , and McCarty Mines accounted for 65 pet of the district production. Figure 4 shows the cumulative grade- tonnage curve for the district. The upper data point was eliminated from the data set for the purposes of the regres- sion since it represents a small high- grade portion of the total district pro- duction. Regression yielded an equation with values of 1.07 for bo and -0.186 for b]. Based on the aggregated data, a grade of 0.895 tr oz/st was the lowest average grade mined in the district. Using a limiting grade of 0.7 tr oz/st, a total remaining endowment of 827,000 tr oz gold was estimated for the Fairbanks District. Table 4 shows the estimates for the district over a range of limiting grades. 45 4.7 LOG CUMULATIVE A3 5.1 TONNAGE, FIGURE 4.— Grade-tonnage curve, Fairbanks District. TABLE 5. - Remaining endowment estimates, Homer District Limiting grade, tr oz/st Cumulative grade, tr oz/st Original ore available, st Remaining gold endowment, tr oz 0.1 0.127 .255 .382 .509 .637 .764 .892 1.019 246,486,300 9,617,500 1,466,500 385,700 135,800 58,300 28,300 15,300 31,293,400 .2 2,442,100 .3 .4 .5 .6 549,800 185,900 76,100 34,200 .7 14,900 .8 '5,200 Estimate of remaining endowment based on historic grades. HOMER DISTRICT Gold production in the Homer District came primarily from the Nuka Bay region and is based on data from eight mines which produced high-grade ore over a 20-yr period. Figure 5 is the cumulative grade-tonnage curve for the district. The upper data point was eliminated from the data set in the regression analysis. Regression of the curve yielded coeffi- cients of 0.91 for b and -0.215 for b,. Past mining reached a lower grade of 0.94 tr oz/st. Using a limiting grade of 0.8 tr oz/st yields an endowment estimate of 5,200 tr oz of gold. Table 5 shows the remaining endowment estimates for the district over a range of limiting grades. .07 - 3.2 3.4 LOG CUMULAT 3.6 3.8 TONNAGE, FIGURE 5.— Grade-tonnage curve, Homer District. 10 TABLE 6. - Remaining endowment estimates, Hope-Seward District Limiting grade, tr oz/st 0.1. .2. .3. .4. .5. .6. .7. Cumulative grade, tr oz/st 0.131 .263 .394 .525 .656 .788 .919 1.050 Original ore available, st 88,300,700 4,734,200 867,600 260,000 102,000 47,300 24,800 14,200 Remaining gold endowment, tr oz 11,549,800 1,227,500 324,200 1 118,900 49,300 19,700 5,200 Estimate of remaining endowment based on historic grades. HOPE-SEWARD DISTRICT Data for the Hope and Seward Districts were combined to produce the cumulative grade-tonnage curve in figure 6. All mines in the district occur in the Valdez Group of metasediments and are typically small, high-grade vein deposits (11). Many of the mines produced over a 10-yr period. The most sustained production came from the Lucky Strike Mine, which was active for 26 yrs. The upper data point on the grade- tonnage curve was eliminated from the data set in the regression analysis. Re- gression yielded coefficients of 1.01 for bo and -0.238 for bj. The lowest grade mined previously in the district was 0.54 tr oz/st; using a limiting grade of 0.4 tr oz/st, an estimated 118,900 tr oz of gold remain. Table 6 shows remaining endowment estimates limiting grades. over a range of FIGURE 6.— Grade-tonnage curve, Hope-Seward District. TABLE 7. - Remaining endowment estimates, Juneau District 11 Limiting grade, tr oz/st 0.01. .02. .03. .04. .05. .06. .07. .08. Cumulative grade, tr oz/st 0.016 .032 .047 .063 .0883 .1060 .1237 .1413 Original ore available, st 2,572,130,300 385,683,100 134,652,600 60,379,700 32,496,300 19,614,200 13,130,400 9,053,800 Remaining gold endowment, tr oz 35,571,000 '6, 758, 700 745,600 Estimate of remaining endowment based on historic grades. JUNEAU DISTRICT The Alaska Juneau and Treadwell group mines accounted for 91 pet of the gold production in the Juneau District. Fig- ure 7 is a cumulative grade-tonnage plot for the district. The more gently slop- ing upper part of the curve is due to the large influence of relatively higher grade material from the Treadwell group. According to Bureau records, the grades at the Treadwell and Alaska Juneau mines averaged 0.11 and 0.03 tr oz/st respec- tively. Based on Bureau data used in the grade-tonnage model, the Treadwell group processed over 19 million tons of ore, thus influencing the grade-tonnage curve to a large extent. To include the influence of the Tread- well group production in the endowment estimate, all data points were used in the regression analysis. The resulting least-squares fit is not as good as could be obtained by eliminating the upper two points; however, including the Treadwell data yields a more realistic estimate of the remaining gold endowment in the Ju- neau District. The resulting regression equation has coefficients of 2.14 for bo and -0.428 for b]. At a limiting mining grade of 0.02 tr oz/st, 6,758,700 tr oz of gold remain as predicted by the grade-tonnage model. Table 7 lists the remaining gold endowment estimates over a range of lim- iting grades. LOG CUMULATIVE TONNAGE, st FIGURE 7.— Grade-tonnage curve, Juneau District. 12 TABLE 8. - Remaining endowment estimates, Ketchikan District Limiting grade, tr oz/st Cumulative grade, tr oz/st Original ore available, st Remaining gold endowment, tr oz 0. 1 0.158 .317 .475 .634 .792 .950 1.109 1.267 527,900 79,800 26,600 12,200 6,700 4,100 2,700 1,900 67,400 .2 1 9,300 .3 .4 .5 .6 .7 .8 Estimate of remaining endowment based on historic grades. KETCHIKAN DISTRICT Gold produced from the Ketchikan Dis- trict came from deposits with markedly lower grades than the other districts, except for the Juneau District. Most of the gold in the district was produced as a byproduct from primary copper mines. Only production data from primary lode gold deposits are included in the estima- tion of remaining gold endowment. Aver- age grade of the deposits in the data set was 0.42 tr oz/st, compared with grades near or above 1.0 tr oz/st in the other districts (excluding Juneau). Figure 8 is the cumulative grade- tonnage curve on which the regression was performed. The upper two data points were eliminated from the data set in the regression. Regression yielded coeffi- cients of 1.31 for bo and -0.369 for bj. Based on the lowest mined grade of 0.28 tr oz/st, a limiting grade of 0.2 tr oz/st was used to estimate the remaining gold endowment. This yielded a total of 9,300 tr oz of gold. Table 8 shows the remaining endowment over a range of limiting grades. o -.4 O 2.8 3 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 LOG CUMULATIVE TONNAGE, st FIGURE 8.— Grade-tonnage curve, Ketchikan District. TABLE 9. - Remaining endowment estimates, Prince William Sound District 13 Limiting grade, tr oz/st Cumulative grade, tr oz/st Original ore available, st Remaining gold endowment , tr oz 0.1 0.183 .367 .550 .733 .917 1.100 1.283 1.467 3,926,000 849,200 348,700 185,300 113,200 75,900 54,100 40,300 635,700 .2 .3 228,900 109,000 .4 1 53,000 .5 21,000 .6 .7 700 Estimate of remaining endowment based on historic grades. PRINCE WILLIAM SOUND DISTRICT The Prince William Sound District pro- duced 82,777 tr oz of gold from rela- tively high-grade quartz vein deposits. The largest producers were the Cliff and Granite Mines. Figure 9 shows the cumu- lative grade-tonnage curve for the dis- trict. The upper data point was elim- inated from the data set for purposes of the regression. Regression yielded coef- ficients of 2.26 for bo and -0.455 for bi« Based on 0.44 tr oz/st as the lowest grade mined, a limiting grade of 0.4 was used in the regression equation to pre- dict remaining endowment. A total of 53,000 tr oz of gold are estimated to re- main in the district. Table 9 lists re- maining endowment estimates over a range of limiting grades. LOG CUMULATIVE TONNAGE, st FIGURE 9.— Grade-tonnage curve, Prince William Sound District. 14 TABLE 10. - Remaining endowment estimates, Willow Creek District Limiting grade, tr oz/st 0.1. .2. .3. .4. .5. .6. .7. Cumulative grade, tr oz/st 0.127 .254 .381 .508 .635 .763 .890 1.017 Original ore available, st 15,722,138,900 608,907,100 90,909,000 23,582,500 8,280,200 3,499,200 1,699,600 909,100 Remaining gold endowment , tr oz 1,996,103,900 154,054,700 34,028,600 11,372,200 4,650,200 2,062,200 904,900 '316,800 Estimate of remaining endowment based on historic grades. WILLOW CREEK DISTRICT The Willow Creek. District was the third largest producer of gold in Alaska. The majority of production came from the In- dependence, Fern, Lucky Shot, War Baby, and Gold Cord Mines. Exploration, devel- opment, and minor production have taken place in the district in the last 5 yr. Figure 10 shows the cumulative grade- tonnage curve for the district. Regres- sion of the data yielded coefficients of 1.28 for bo and -0.213 for by. Based on 0.87 tr oz/st as the lowest grade pro- duced in the district, an estimated 316,800 tr oz of gold remain at a limit- ing grade of 0.8 tr oz/st. Table 10 shows the remaining endowment estimates over a range of limiting grades. 5.1 53 CUMULATIVE 55 5.7 TONNAGE, st FIGURE 10.— Grade-tonnage curve, Willow Creek District. 15 DISCUSSION The remaining gold endowment tables presented for the eight districts in- dicate the dependence of the estimate on the limiting grade chosen. The conserva- tive approach based on past mining grades was used to determine a likely estimate of the nonproduced portion of the endow- ment. Based on past production history, the estimates listed in the tables can be considered to be a conservative estimate of remaining gold endowment. Table 11 presents a summary of the remaining en- dowment by district, ranked according to quantity remaining. The feasibility of mining a deposit in any of these districts is not addressed. Economic feasibility depends on metal prices, deposit characteristics, and re- serves and grade. The estimates pre- sented above are intended to show the possible amount of lode gold remaining. Clearly other districts with major past producers may have remaining gold re- sources and future production potential. Not all districts were examined owing to the nature of the production data avail- able. Exclusion of a district from this study does not mean it has limited or no potential remaining gold resource. The Juneau District has the largest re- maining lode gold endowment, at a grade of 0.02 tr oz/st. Recent interest has been shown in the Alaska Juneau Mine and the Treadwell group mines. Barrick Re- sources Corp. obtained a lease on certain properties in 1984 and has been examining mine records and maps. Some fieldwork has also been conducted, and exploration targets have been defined (10). The Fairbanks District has been the site of extensive reexamination of past producers In recent years. Underground work and drilling have taken place at a number of properties (10). Presently, Silverado Mines LTD, in a joint venture with two other participants, is preparing to return the Grant Mine to production. The Chichagof and Willow Creek Dis- tricts have also had recent exploration activity, with a focus on reopening past producing mines. Interest has also been expressed in the other districts that were examined. It is possible that some of the past producing gold mines in Alaska will come Into production within the decade. Based on the results of this study, more than 8.4 million tr oz of gold could be pro- duced from the eight districts examined, provided that the political and economic climate is favorable. Other districts such as the Alaska Peninsula, Kantishna, and Bonnifield also have potential for future lode gold production, but lacked sufficient production data to be analyzed in this study. TABLE 11. - Summary of remaining endowment District Limiting grade, tr oz/st Initial ore, st Past production, tr oz gold Remaining endowment , tr oz gold Juneau Fairbanks , Chicagof , Willow Creek , Hope-Seward , Prince William Sound. Ketchikan , Homer , Total , 0.02 .7 .4 .8 .4 .4 .2 .8 385,683,100 1,229,700 1,521,200 909,100 260,000 185,300 79,800 15,300 5,583,121 230,499 787,347 607,726 17,587 82,777 16,042 10,391 6,758,700 827,000 326,200 316,800 118,900 53,000 9,300 5,200 389,883,500 7,335,490 8,415,100 16 REFERENCES 1. Musgrove, P. A. Lead: Grade-Ton- nage Relation. Min. Mag., v. 112, No. 4, 1965, pp. 249-151. 2. Singer, D. A. , D. P. Cox, and L. J. Drew. Grade and Tonnage Re- lationships Among Copper Deposits. U.S. Geol. Surv. Prof. Paper 907-A, 1975, pp. Al-All. 3. Ellis, J. R., D. P. Harris, and N. H. Van Wie. A Subjective Probability Appraisal of Uranium Resources in the State of New Mexico. U.S. Energy Res. and Dev. Admin. (now part of Dep. En- ergy), Open File Rep. GJO-110(76), 1975, 103 pp. 4. Lasky, S. G. Grade Relations Help erves. Eng. and Min. 1950, pp. 81-85. 5. . Mineral Resource Appraisal by the US Geological Survey. Q. CO Sch. Mines, v. 45, No. 1A, 1950, pp. 1-27. 6. Cargill, S. M. , D. H. Root, and E. H. Bailey. Estimating Usable Re- sources From Historical Industry Data. How Tonnage and Predict Ore Res- J. , v. 151, No. 4, Econ. Geol. and Bull. Soc. Econ. Geol. , v. 76, No. 5, 1981, pp. 1081-1095. 7. . Resource Estimation from Mercury, a Test Case. Geol. , v. 12, No. 5, Mineral Resources Univ. Press, 1984, Historical Data: J. Int. Assoc. Math. 1980, pp. 489-522. 8. Harris, D. P. Appraisal. Oxford 445 pp. 9. Ransome, A. L. , and W. H. Kerns. Names and Definitions of Regions, Dis- tricts, and Subdistricts in Alaska. Bu- Mines IC 7679, 1954, 91 pp. 10. Eakins, G. R. , T. K. Bundtzen, L. L. Lueck, C. B. Green, J. L. Gal- lagher, and M. S. Robinson. Alaska's Mineral Industry 1984. AK Div. Geol. and Geophys. Surv. Spec. Rep 38, 1985, 57 pp. 11. Jansons, U. , R. B. Hoekzema, J. M. Kurtak, and S. A. Fechner. Mineral Oc- currences in the Chugach National Forest, Southcentral Alaska. BuMines MLA 5-84, 1984, 218 pp. APPENDIX A.— RAW PRODUCTION DATA FOR DISTRICTS ANALYZED 17 TABLE A-l. - Raw production data, Chichagof District Year Ore, st Gold, tr oz Grade, tr oz/st Year Ore, st Gold, tr oz Grade, tr oz/st 1906. 1907. 1908. 1909. 1910. 1911. 1912. 1913. 1915. 1916. 1917. 1918. 1919. 1920. 1921. 1922. 1923. 1924. 1925. 1926. 1927. 60 1,353 2,071 744 4,282 10,577 22,915 22,000 33,850 36,822 38,794 33,978 42,187 33,243 33,855 39,307 11,639 44,283 66,470 33,725 8,827 351 3,172 2,792 992 7,784 7,062 11,447 11,367 44,517 39,453 39,554 60,200 89,097 83,080 71,339 48,707 26,135 18,489 22,609 25,779 11,773 5.85 2.34 1.35 1.33 1.82 .67 .50 .52 1.32 1.07 1.02 1.77 2.11 2.50 2.11 1.24 2.25 .42 .34 .76 1.33 1928. 1929. 1930. 1931. 1932. 1933. 1934. 1035. 1936. 1937. 1938. 1939. 1940. 1941. 1942. 1943. 1944. 1947. 1950, 1951. 3,539 4,071 1,760 12,584 34,333 15,216 28,370 24,500 21,475 21,855 25,588 23,484 38,070 45,919 4,184 534 200 12 537 100 4,290 3,818 490 6,249 17,897 10,912 9,583 14,744 11,866 15,172 21,811 15,267 12,945 10,167 5,081 776 22 11 397 151 1.21 .94 .28 .50 .52 .72 .34 .60 .55 .69 .85 .65 .34 .22 1.21 1.45 .11 .92 .74 1.51 10 TABLE A-2. - Raw production data, Fairbanks District Year Ore, st Gold, tr oz Grade, tr oz/st Year Ore, st Gold, tr oz Grade, tr oz/st 1910, 1911, 1912, 1913, 1914, 1915, 1916, 1917, 1918, 1919, 1920. 1921. 1922. 1923. 1924. 1925. 1926. 1927. 1928. 1929. 1930. 1931. 1932. 1933. 1934. 1935. 1936. 1937. 148 875 4,708 12,237 6,526 6,545 1,111 1,200 1,035 1,384 504 949 1,524 1,278 4,528 3,663 1,089 1,919 4,871 4,657 1,964 3,222 12,549 214 297 4,519 12,418 14,839 841 3,103 9,417 16,905 10,905 10,535 1,905 2,142 1,294 1,507 967 2,104 2,542 1,197 4,870 4,064 788 4,064 4,004 3,618 2,527 6,000 12,590 222 389 3,665 5,669 15,688 5.68 3.55 2.00 1.38 1.67 1.61 1.71 1.79 1.25 1.09 1.92 2.22 1.67 .94 1.08 1.11 .72 2.12 .82 .78 1.29 1.86 1.00 1.04 1.31 .81 .46 1.06 1938, 1939, 1940, 1941. 1942, 1943, 1944, 1945, 1946, 1947, 1948, 1949, 1950, 1952. 1953, 1954. 1955. 1956, 1957. 1958, 1959, 1960, 1961. 1962. 1963. 1964. 1965. 12,440 15,474 17,414 13,571 7,054 3,000 1,250 2,427 1,295 461 498 463 199 152 275 194 1 1 55 5 214 1,075 135 162 861 2,447 3,172 10,315 18,117 18,195 13,751 13,502 3,561 1,428 4,217 1,676 1,126 277 207 309 236 398 144 1 1 28 2 538 1,215 279 293 1,134 2,055 3,556 0.83 1.17 1.04 1.01 91 ,19 ,14 ,74 1.29 2.44 .56 .45 1.55 1.55 1.45 .74 1.00 1.00 .51 .40 2.51 1.13 2.07 1.81 1.32 .84 1.12 TABLE A-3. - Raw production data, Homer District Year Ore, st Gold, tr oz Grade, tr oz/st Year Ore, st Gold, tr oz Grade, tr oz/st 1917 5 1 40 637 764 1,602 165 200 325 847 1 43 949 1,121 2,100 279 311 451 803 0.12 .32 1.08 1.49 1.47 1.31 1.69 1.56 1.39 .95 1932 21 423 326 255 1,550 1,141 341 84 160 60 102 429 252 147 1,497 1,266 306 23 103 55 4.84 1918 1933 1.02 1924 1934 .77 1925 1935 .58 1926 1936 .97 1927 1937 1.11 1928 1938 .90 1929 1940 .27 1930 1941 .64 1942 .92 TABLE A-4. - Raw production data, Hope-Seward District 19 Year Ore, St Gold, tr oz Grade, tr oz/st Year Ore, St Gold, tr oz Grade, tr oz/st 1911 274 534 1,133 1,831 815 711 140 297 96 55 150 300 250 800 392 315 5 450 751 605 478 697 856 1,195 804 835 223 460 435 169 345 643 218 761 116 231 7 231 505 329 1.74 1.30 .76 .65 .99 1.17 1.59 1.55 4.53 3.08 2.30 2.14 .87 .95 .29 .73 1.40 .51 .67 .54 1931 937 212 208 125 922 542 1,598 722 387 40 450 399 655 224 120 55 520 47 194 10 415 29 295 183 1,208 707 1,718 634 438 41 228 191 308 143 127 34 209 318 815 9 0.44 1912 1935 .14 1913 1936 1.42 1914 1937 1.46 1915 1938 1.31 1916 1939 1.30 1917 1940 1.08 1918 1941 .88 1919 1942 1.13 1920 1944 1.03 1921 1945 .51 1922 1946 .48 1923 1947 .47 1924 1948 .64 1925 1949 1.06 1926 1950 .62 1927 1954 .40 1928 1955 6.77 1929 1956 4.20 .90 20 TABLE A-5. - Raw production data, Juneau District Year Ore, st Gold, tr oz Grade, tr oz/st Year Ore, st Gold, tr oz Grade, tr oz/st 1891... 1892. .. 1893... 1895... 1896... 1897... 1905... 1906... 1907... 1908... 1909... 1910... 1911. .. 1912. .. 1913... 1914... 1915... 1916. .. 1917... 1918... 1919... 1920... 1921... 1922... 1923... 1924... 330 291 336 440 401 562 4 1,406 1,210 1,473 1,480 1,429 1,564 1,714 1,567 1,685 2,955 3,481 3,360 2,054 3,211 3,375 2,854 2,463 2,476 3,068 ,471 ,865 ,560 ,342 ,765 ,342 ,125 ,746 ,486 ,345 ,871 ,072 ,741 ,336 ,746 ,696 ,339 ,259 ,614 ,676 ,261 ,704 ,076 ,231 ,242 ,217 37,043 32,715 37,725 50,554 47,868 57,774 3,553 159,557 129,953 159,099 196,234 173,116 180,868 202,293 190,485 185,047 214,035 221,177 165,313 92,172 112,706 127,382 104,232 76,088 69,035 92,500 0.11 .11 .11 .11 .12 .10 .86 .11 .11 .11 .13 .12 .12 .12 .12 .11 .07 .06 .05 .04 .04 .04 .04 .03 .03 .03 1925... 1926... 1927... 1928... 1929... 1930... 1931... 1932... 1933... 1934... 1935... 1936... 1937... 1938... 1939... 1940... 1941... 1942... 1943... 1944... 1945... 1947... 1948... 1949... 1950... 1951... 3,485,976 3,829,783 4,267,810 3,720,087 3,838,660 3,924,460 4,162,350 4,001,630 4,428,564 3,756,206 3,489,492 4,366,801 4,442,765 4,663,950 4,648,154 4,739,792 4,354,857 2,765,885 1,461,905 379,350 888 10 72 101 119 15 98,985 93,913 112,646 151,951 164,477 162,800 179,785 151,347 151,150 128,602 119,032 149,207 151,773 148,015 128,863 123,415 119,618 77,126 39,949 10,316 734 8 102 391 352 41 0.03 .02 .26 .04 .04 .04 .04 .04 .03 .03 .03 .03 .03 .03 .03 .03 .03 .03 .03 .03 .83 .80 1.42 3.87 2.96 2.73 21 TABLE A-6. - Raw production data, Kechikan District Year Ore, st Gold, tr oz Grade, tr oz/st Year Ore, st Gold, tr oz Grade, tr oz/st 1906 1907 1908 1909 1910 1913 1914, 1915, 1916, 1917, 1918, 1919, 1920, 1921, 1922, 1923. 1924. 1925. 1926. 1927. 1928. 1,650 200 100 2,700 400 4,401 2,250 626 800 716 1,147 400 250 1,800 4 1,350 7 90 15 2,064 359 994 97 83 155 77 1,501 932 412 278 272 393 130 74 576 1 176 46 98 40 1,406 544 0.60 .48 .83 .06 .19 .34 .41 .66 .35 .38 .34 .33 .29 .32 .13 .13 6.59 1.09 2.68 .68 1.52 1929. 1930. 1931. 1932. 1933. 1934. 1935. 1936. 1937. 1938. 1939. 1940. 1941. 1942. 1945. 1946. 1947. 1948. 1949. 1950. 1954. 35 250 40 100 2,648 3,012 3,203 561 961 1,374 1,415 1,569 346 188 7 72 148 153 632 130 2 128 55 45 82 431 278 337 517 1,403 1,414 914 1,001 213 133 16 57 84 235 338 75 2 3.66 .22 1.13 .82 .16 .09 .11 .92 1.46 1.03 .65 .64 .62 .71 2.29 .79 .57 1.54 .53 .58 1.00 22 TABLE A-7. - Raw production data, Prince William Sound District Year re, st Gold, tr oz Grade, tr oz/st Year Ore, st Gold, tr oz Grade, tr oz/st 1910, 1911, 1912, 1913, 1914, 1915, 1916, 1917, 1918, 1919, 1920, 1921. 1922. 1923. 1924. 1925. 1929. 1930. 1931. ,440 ,325 ,692 ,650 ,120 ,790 ,513 ,350 444 15 20 39 170 7 78 53 24 268 60 10,745 7,981 11,369 8,229 7,809 11,252 7,739 4,503 638 52 6 65 423 14 405 129 20 250 60 2.42 2.40 2.42 1.08 1.10 .67 .62 .84 1.44 3.45 .30 1.67 2.49 1.93 5.20 2.43 .84 .93 .99 1932. 1933, 1934. 1935, 1936, 1937, 1938, 1939, 1940, 1941. 1942. 1944. 1946, 1948, 1949, 1955. 1963. 1964. 52 95 1,641 658 375 1,748 785 72 1,204 3,253 1,300 40 500 2 1 25 8 1 36 62 976 384 624 1,014 1,038 58 874 3,885 1,775 17 282 291 4 26 3 1 0.70 .65 .59 .58 1.66 .58 1.32 .81 .73 1.19 1.37 .43 .56 4.50 4.00 1.04 .38 1.00 TABLE A-8. - Raw production data, Willow Creek District Year Ore, st Gold, tr oz Grade, tr oz/st Year Ore, st Gold, tr oz Grade, tr oz/st 1909 1010, 1911, 1912, 1913, 1914, 1915, 1916, 1917, 1918, 1919, 1920, 1921, 1922, 1923, 1924, 1925, 1926, 1927, 1928, 1929, 1930, 1931, 1932, 1933. 1934, 912 144 1,048 3,000 3,028 10,110 6,717 12,182 7,883 7,886 6,730 2,850 3,591 7,242 9,132 8,075 15,834 2,537 7,866 3,443 39 13,975 7,951 13,618 16,578 17,833 665 1,046 2,596 4,838 4,884 14,376 11,962 14,473 9,466 12,874 7,882 3,067 5,722 11,513 8,622 9,766 21,990 2,082 7,084 4,623 363 1,725 21,282 34,371 36,867 38,141 0.73 7.27 2.48 1.61 1.61 1.42 1.78 1.19 1.20 1.63 1.17 1.08 1.59 1.59 .94 1.21 1.39 .82 .90 1.34 9.31 .12 2.68 2.52 2.22 2.14 1935, 1936, 1937, 1938, 1939, 1940, 1941, 1942, 1943, 1944, 1945, 1946. 1947, 1948, 1949, 1950, 1951. 1952. 1953. 1954. 1955. 1958. 1960. 1961. 1963. 18,332 27,550 50,399 22,965 45,302 62,740 50,240 32,389 16,280 600 1,967 2,698 562 355 5,416 10,270 410 205 200 240 56 31 136 72 5 16,501 17,815 37,467 31,804 38,958 51,490 48,194 37,549 13,079 3,839 1,838 1,275 358 476 5,071 8,806 335 70 46 156 39 46 132 97 3 0.90 .65 .74 1.38 .86 .82 .96 1.16 .80 6.40 .93 .47 .64 1.34 .94 .86 .82 .34 .23 .65 .70 1.48 .97 1.35 .60 23 APPENDIX B. --REGRESSION ANALYSIS RESULTS, BY DISTRICT CHICHAGOF DISTRICT Equation coefficients: bO = 2.6669 bl = -0.4533 Partitioned sum of squares Source of variation Degrees of Sum c~. squares freedom Due to regression 1 0. 1 101 Deviations from regression 7 0.0OO1 Total 3 0.1 102 F = 5,529.26 Coefficient of determination (r squared) = 0.9987 Correlation coefficient (r) = 0.9994 FAIRBANKS DISTRICT Equation coefficients: DO = 1.0672 bl = -0. i860 Partitioned sum of squares Source of variation Degrees of Sum of square; f r eedom Due to regression 1 0. 0200 Deviations from regression 8 0.0002 Total 9 0. 0203 F = 655.84 Coefficient of determination (r squared) = 0.9879 Correlation coefficient (r ) = 0.9940 25087 241 24 HOMER DISTRICT Equation coefficients: bO = 0.9072 bl = -0.2149 Partitioned sum of squares Source of variation Degrees of Sum of square? ♦ reedom Due to r egression 1 0. 00 19 Deviations from regression 1 0.0000 Tota 1 2 0. 00 19 F = 998. lt> Coefficient of determination '.r squarec) = 0.9990 Correlation coefficient ir ) = 0.9995 H0PE-SEWARD DISTRICT Equation coefficients: bO = 1.0100 bl = -0.23S2 Partitioned sum of squares Source of variation Degrees of Sum of square-; freedom Due to regression 1 0.0408 Deviations from regression 5 0.0003 Total 6 0.04H F = 600.84 Coefficient of determination (r squared) = 0.9917 Correlation coefficient (r) = 0.9959 25 JUNEAU DISTRICT Equation coefficients: bO = 2.1353 bl = -0.4282 Partitioned sum of squares Source of variation Degrees of Sum a* squares f reeaom DLis to regression 1 0. I2&& Deviations from regression 6 0.0OO2 Total 7 0.1270 F = 3,270.77 Coefficient of determination (r squared) = 0.99S2 Correlation coefficient (r) = 0.9991 KETCHIKAN DISTRICT Equation coefficients: bO = 1.30S0 bl = -0.3686 Partitioned sum of squares Source of variation Degrees of Sum of squares freedom Due to regression 1 0. 0640 Deviations from regression 4 0.0001 Total 5 0.0641 F = 5,042.70 Coefficient of determination (r squared) = 0.9992 Correlation coefficient (r) = 0.9996 26 PRINCE WILL I Mil SOUND DISTRICT Equation coefficients: bO = 2.2594 bl = -u.4545 Partitioned sum of squares Source of variation Degrees of Sum of square? f reedom Due to rsgressi on 1 0. 04 76 Deviations from regression 5 0.0001 Total 6 0.0478 f = 1,611.45 Coefficient of determination (r squared) = 0.9969 Correlation coefficient (r ) = 0.99S5 WILLOW CREEK DISTRICT Equation coefficients: bO = 1.2777 bl = -0.2132 Partitioned sum of squares Source of variation Degrees of Sum of square? freedom Due to regression 1 0.0609 Deviations from regression S 0.0004 Total 9 0.0613 F = 1, 144.77 Coefficient of determination (r squared) = 0.9931 Correlation coefficient (r) = 0.9965 U.S. GOVERNMENT PRINTING OFFICE: 1987 -605-017/60040 ! go INT.-BU.OF Ml NES,PGH. , PA . 28465 U.S. Department of the Interior Bureau of Mines— Prod, end Distr. Cochrans Mill Road P Box 18070 Pittsburgh. Pa. 15236 OFFICIAL BUSINESS PENAL rr FOP PRIVATE USE. S300 ] Do not wish to receive this material, please remove from your mailing list. ^ Address change. Please correct as indicated* AN EQUAL OPPORTUNITY EMPLOYER * ,. <,«<>- "•*; -4* .W^' ***. " v* .'iSH^. '*W • ft' If* /7 v » ^ > • ^ : . rey V**V ./v^-y v**v V»V V^PV j3 " ^rS %. *•"* ^ ♦ «k o_ *; •-V« e y .♦ ♦ o J* • » f **^ "VSWV^ V'^>' V™ % > v V*^- 1 .«* V J° k- v^ •'£& \S i'dd&i \> -A&> X*5fcS. '° «•> y.-afeX .S-tib.* /.-safe V"*' f° ,. 4 0. V^!v- .' aV-^. -^E^« .^^. o^^^» ,A V ^ : W^.° ^«V ''fW.' .A V- *. '< .• .* v '^ '. .•y % •?«?>*' v-'Swf'-y v-^ T -y *<.'' 5 wp- , x v- ft - v* <■/ /••i^,- °* A-&&S. ^^J&S jfs&kS °^. V **. ♦*VassX ^ -sa&> *<* .-sSfcX /*$&?* ss4&\ /$&* ^ T, \/ V^V \^^\/ V*^*/ \^^\/ %.- '• A.^"^ -^Si^° c.^^ «^^^" A V *A -^^Bw^^ e,''^ "iff: A V "V ' (** . 6 J^.t^ V C 0> ^^,% "°o J*" ,.», ^ . C- .'^^% -o .. r o^;^»"» ^ ft r »m^-. -»>„