CJ - USGS · 2019. 6. 6. · Webb, 1962). The effectiveness lies in the fact that key indicator elements are dispersed in halos in bedrock, overlying soils, and in stream sediments
1
DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY 88°37'30" EXPLANATION Pennsylvanian, probable Abbott Formation. Sandstone, tan to reddish, medium to fine grained, minor siltstone and shale, cross- bedded or ripple-marked in places .-<75 $ BS22x Strike and dip of bedding Inclined 750sE Horizontal Strike and dip of joint Inclined 83°NE Vertical Axis of small anticline plunging 12°NE Areas where bedrock has intense iron enrichment Fault of unknown dL<;placements, dashed where uncertain Synclinal axis, exact location uncertain Dry hole Bedrock sample Soil sample Panned and unpanned stream sediment sample 88°37'30" I l I \ I I \ .._as1 Be anomalous ' ~:, ,(} }\, \ \ I X E XPLANATION Soil sample showing elements that have anomalous values Bedrock sample showing elements that have anomalous values Stream sediment sample, panned and unpanned Drainage basin boundary [;t51l Area not sampled Drainage basin in which gold and silver were detected in panned stream-sediment sample CJ Drainage basin in which high or anomalous concentrations of beryllium, barium, fluoride, or lead were detected in stream-sediment sample Drainage basin that have no anomalous values GEOCHEMICAL TECHNIQUES Along with standard geologic techniques, geochemical techniques are an effective tool in the exploration for mineral resources (Hawkes and Webb, 1962). The effectiveness lies in the fact that key indicator elements are dispersed in halos in bedrock, overlying soils, and in stream sediments about a mineral deposit. The location of 63 samples collected from the Burden Falls Roadless Area for geochemical analyses are shown on figure 1. They consist of 17 bedrock samples, 24 stream-sediment samples (both panned and unpanned), and 22 soil samples taken in the B or A 2 horizon below the dark, humic, A 1 soi1 zone. Soil samples BS10 and BS14 through BS22 are from loess-covered areas, the rest from soil developed on bedrock. All samples were analyzed for 31 elements by a semiquantitative, six-step, direc t-curr ent arc, optical- emission spectrographic method (Grimes and Marranzino, 1968). Uranium concentrations were determined by a fluorometric method and fluorine by wet chemical-ion detection method (see Levinson, 1974, p. 296-297 for brief discussions of these techniques). The results, shown in table 1, display only those elements that occured in detectable amounts. Arsenic, bismuth, cadmium, molybdenum, antimony, thorium, tungsten, and zinc were not detected spectrographically in any samples; gold and silver were detected spectrographically in a few soil and panned stream-sediment samples, and niobium in all but the bedrock samples. 37°32'30" 37°32'30" Locations of stream-sediment samples were selected so that most small drainage basins were sampled throughout the study area (fig. 2). Unpanned and panned samples were taken at most locations. Unpanned sediments consist of the finest-grained sediments available in th e stream 37032, 30'' bed. Samples were sieved to -80 mesh (0.007 in. or 0.177 mm.) for geochemical analysis. Sediments that had a large range in grain size were collected for panning. Panning partially separates the light (less dense) minerals from the heavy {more dense) mfoerals. Heavy minerals were further concentrllted by magnetic separation (removal of magnetite) and by bromoform dense-fluid separation. This threefold concentrating procedure resulted in a heavy-mineral concentrate that was saved for spectrographic analysis. The stream-sediment samples and heavy-mineral concentrates were microscopically examined. Sampl@ "' 8822 B834 B!l39 l'\R~, 8851 BB57 BB65 BB68 BB"75 BBBO 8892 BB97 66104 BBi 11 BB\2& 88129 S<1"11ple "" m 8S8 "" BS11 BS 12 BS13 BS 14 8~15 BS16 6517 6518 BS19 BS20 6521 sa .. pl" 6F1H BF2H Br-311 BF4H BF5H BF6H BF7H BFSH BF9H 6F10H BF' 1H I\F 12H Sampl" BF 1L BF2 l. BF3 L 6F4 L Bf5L B F6L ll.F7L BFBL BF9L (IF IOL BF11L BF 12L 37°32'30" Base from U.S. Geological Survey Stonefort and Eddyville, 1961 0 88°37'30" Geology mapped by J,S. Klasner, 1980 1 MILE Lacltud<> 37 32 14 37 3:3 47 37 33 7 31 n 43 J? 32 24 37 34 17 37 3:J ,n 37 33 55 31 33 '3 37 33 7 Long t tuc<e sa 37 s2 88 38 32 BB 37 S2 88 37 ss 88 37 47 BB 37 7 R~ 37 11 86 37 S4 36 37 8 aB 36 S8 37 33 37 88 36 54 373223 883731 37 3~ •J M 3, ,i 37 32 58 88 36 53 37 32 25 88 36 ·~ 37:3256 88J615 37 32 37 88 JS 9 latitude 37 33 38 37 33 38 37 33 39 31 33 :n 37 33 32 long I tu de 88 36 •4 88 36 ~g aa 36 57 88 37 88 37 g 3733 ,9 883715 373333 88371~ 373335 883725 37333' 883732 37 33 33 88 37 .3 373333 883749 373333 883755 3;33n aaJa o 37 33 34 88 38 7 373331 883811 373329 883814 37332J 883819 373318 883822 37 33 18 88 38 ;3 373311 883830 37 33 7 88 38 37 373~32 883739 Figure 1.--Location of geochemical samples in the Burden Falls Road.less Area. Tab le 1.--Anolyses of 17 rock, 22 sail, and 12 panned and 12 unpmmed st.ream SBdiment samples from Burden Falls Raadless Area, Pape County, Ill. All analyses by six- step, direct-current arc, optical emission spcctrograph ic methods (Grimes and Marranzino, 1968) by G. W. Day , except fo r fluorine which is by wet chemical-ion <Jetection method (Levinson, 1D74, p. 262, 2n) by B.F. Abrog11st and ur11nium which is by a fluoromet ric method (Levinson, 1974, p. 732-734). The scmiquuntitativc spcctrographie values are report ed as six steps per orCer of magnitude (1, 0.7, 0.5, 0.3, 0.2, 0.15, or multiples of 10 of these numbers) and are approximate geometric midpoints of the concentration ranges. The expected precision is within one adjoining reporting interval on each side of the reported value 83 percent of the time and within two adjoining intervals 9fl percent of the time (Motooka and Grimes, 1976). Symbols used: pct, [lercent; ppm, parts per millfon; S, semiquantitative spectrographic analysis;:-, greater than value shown,<, less than value shown; N, not detected. Elemen ts loo ked for spectrographically but not found and the lower limit of detection in ppm ar e: in rock samples - Ag (0.5), As (200), Au (10), Bi (10), Cd (20), 1\10 (5), Nb (20), Sb (100), Sn (10), Th (100), W (50), and Zn (200); in soil samples - As (200), Au (IO), Bi (10), Cd (20), :/lo (5), Sb (JOO), Sn (10), Th {100), W (50), and Zn (200); in panned concentrates - As (200), Bi (10), Cd (20), Mo (5), Sb (100), Sc (50), Sn (10), 'I'h (100), W (50), and Zn (200); in stream sediments - Ag (0.5), As (200), Au (10), Bi (10), Cd (20), Sb (100), Th (100), W (50), and Zn (200). Fe - pct ' '° . ' ' LO ,.c a C ' 0 ,.o ' LO ,., . , 3.0 ,.c . ' ,.c ' ' Fe-pct. ' ' ' ' ' ' ~g-pct. ' " w < °' <.02 °' Mg - pct ' ' ., ' ' ., ., ., ' ., ' ., ' ' ., . , ' .a ., ., ., C~·pct. ' " <. O~ <.05 <.05 <.05 <.05 <.OR <.05 OS os, < . OS < .os < OS < .OS < .OS Ca-pct. ' ·" ·" . " . " " " " .,o " . " . " ·" " .w . " ·" . " Tl - pd ' . 150 .200 o,s ,oo "" . 050 300 ,oo . 150 ,oo 050 . ,oo . ,oo we <OO <OO 500 Tl-pct ' ' ' ' ' ' . ' ' ., ., ' ., ' ' ' ' ' ., ' . ' ., ., ., Mr> · PP"' 8 - ppm Ba - ppm ' ' ' 100 30 ISO 100 :xJ 150 150 10 20 10 <10 <20 150 10 70 150 10 70 200 JO 200 700 20 70 JO 05 70 200 10 70 ,oo ,oo Mn-ppm ,oo ,00 WO 1 ,000 ,oo ··= ,oo '" 500 1,500 700 ,00 Ag - ppm 8-ppm ' ' ' ' ' ,.o ' ' ' ' ' ' Burden Fa1 l s b,.drock san,ples B&-ppn, Co -ppm Cr-ppm N S 70 N S 100 " ' ' N N 70 N N 30 N N 70 1 10 70 N S 300 N N 20 N N 70 ' ' ' ' ' ' ' ,0 ' " ' ' ' ,0 " ,oo Cu - ppm <S ' Burden Fa l ls soil samples soo soo 500 1 JOO N ,oo ' ,oo ,oo ,oo ,oo ,oo ,00 ,oo "' aco aoo "' ,oo ' ' " Co·ppm Cr - pom ' 15 50 10 70 10 50 10 70 10 70 La - ppm ' ' " ' ' ' ,0 ' " ' ' ,0 ' ' Cu-ppm Bure1en Fa l ls panned stream sediment samples N1 -ppm " ' w ' ,0 ' <S Pb - ppn, ' ' ' ' ' " ' ' " <W ' " " ' ' ,, " " <SO "' " Sc-pp"' Sr-- ppm ' " ' ' " N 10•) N 100 N 100 ' ' " " N 100 " " N1 -pp,,, " " Pb - PIJ m v-ppm Y· ppm <10 <,0 ' ' <W ' " ' ' ' Sn - pr,n, Sr-ppm ' ' ,oo ' ,oo ' ,oo N 100 N 100 ' ' " ' ' ' ' ' ' " ' ' " ,oo ,oo ,oo ,oo ,oo ' ,oo "' " ' ,oo ,co ' ' ' Zr · ppi:, ,so ,oo ,oo soo soo V-pprn " ,oo ,o so " " ,oo ,oo so so l ~lltudc long i tude fe-oct. M g- pct. Ca · pct Tl - pct .• Mn-ppm Ag ·ppm Au-ppm B- ppm B~·ppm Be-pp,n Cr - ppm Cu - po'" L~·PP'" Nb·ppm NI-ppm PO- ppm 5r - pp'" V· ppn, Y· pp11 ' 373226 883749 37 n ~5 BB 31 47 373226 883743 373249 883736 373246 883735 37 33 11 88 37 S 37331.c 8837 0• 37 33 17 BS 36 49 373311 B83647 37 33 14 BS 36 40 373314 883628 3·1 33 22 88 36 IS ' ' " " " " ·" " ·" <.02 '' " . 05 c, ·" < ' <. < ' < ' ' ' < ' <.' < ' < ' < ' ' ' < ' ,oo aoo soc soo ,oo ' " ' ' ' ,oo ' " ' ' ' 100 200 ' ,oo 20 200 ' ,oo N 150 t .ooo 300 ' ,oo ' ,oo ' " ' ,oo ,oo ,oo ,00 500 ,oo 700 ,oo ,oo '" ,so ,oo '" soo ,oo ,so ,oo "' '" <,0 "' ,o <,0 <,0 " w ,0 "' Burden falls unpanned stream seellmen~ samples ,oo ,oo ,oo aoo ,o, ,oo aoo ,oo soo aoo soo ,so " " " so ,oo "' ,o " ,oo ,so ,oo " ,oo ,so " '" " 2.000 200 1.500 200 1.000 200 1.500 200 1,500 200 1.500 200 2.000 200 1,000 200 2.000 200 1.000 200 2.000 300 500 300 ,oo ,oo ,oo ,oo = ,oo ,oo ,oo ,oo = ,oo ,oo u,titU<l<I Longitude Fe-pct "g · pct C" - pct T l- pct Mn-ppm B-pp,11 Ba-ppm B<'·ppm Co-ppfll Cr-ppn, Cu-ppot La-ppn, Mo·ppn, Nb·ppM N<·pp11 Po-ppm Sc -ppn, Sn-ppm Sr - ppn, s 5 S 37 32 26 37 32 25 37 32 28 37 32 49 37 32 46 37 33 11 37 33 12 37 33 17 37 33 11 37 33 14 88 J7 47 BB 37 43 BS J7 41 BB 37 34 BIi 37 ~0 1111 37 5 SB 37 4 88 36 49 88 36 47 88 36 40 37 33 14 8B 36 28 37 33 21 88 36 19 . ' ' ' ' ' " " ' " ' ' a ' " ' ··= ~00 2.000 3.000 1 .500 2 .000 3.000 :.ooo 5.000 '·= ,oo aoo soo ,oo "' soo ,oo ,oo soo ,oo ,oo soo ,., " ' 0 ,., ,., " " ,., ,., ,., ,., ,. ' " " " " " " " " ac " " " " so " so " so so WO ,o w " ' ' ' ' ' ' ' " ' ' ' " " so so " " " " " " ' " ' ' ' ' '" '" ' ' " "' «o ' ' <00 <OO ,oo WO <OO SJ-F U·INST ' " ' " ' ,0 ' ,0 <100 40 <100 40 <100 N ' ' ' " ' ' ' ,0 N .30 ' " 300 2.70 N • 10 ' " 000 .80 30 500 30 500 30 soo 20 500 50 700 30 700 so 700 30 300 30 300 30 700 30 500 30 700 30 700 30 500 30 500 30 700 30 500 20 500 30 soo 30 500 20 500 20 500 Zr-pp'" Sl-F >2,000 N >2.000 N >2,000 N >2.000 <100 >2.000 N >2.000 N >2.000 N >2.000 N >-2.000 <100 >2.000 N >2,000 N >1.000 N V· ppM Y-ppm 100 30 70 30 150 30 150 50 \00 30 100 20 100 JO 100 30 150 50 70 30 ,oo "' ,oo "' Sl·F U-INST <100 .9 ' " <100 1.0 " .. ' ' ' ., <100 .9 <100 .8 <100 1.0 <100 .9 <100 . 8 ' ' <100 1. 2 <100 1.0 ' " <100 .5 <100 1.0 ,100 .a ' . ' N I. 1 N 1.0 <100 U-INST ,., " '" ' ' '" ' ' ,., ,., " ,.o ,., Zr - pp,n Sl-F 1,000 <100 >l.000 N t,000 <100 1,000 <100 1,000 N >1,000 N 1.000 TOO 700 <100 1.000 <100 >1.000 N 700 <100 700 <TOO U-I NST ' , , ,. ,. ' ,. ,. ' ,. ROADLESS AREA BOUNDARY 88°37' 30'' UJ UJ "' a: a: 0 'I, 1 MILE Figure 2.-Drainage basi ~s sampled in Burden Falls Roadless Area and location of anomalous element values in bedrock, soil and stream sediment samples. Anomalous means greater than two standard deviations above the arithmetic mean. Table 2.--Description of rock samples selected for geochemical analysis [.4.11 are chip sample5 ranging fro m 2 to 4 cm in 5ize or hand samp les about 10 cm in size.] I BB2-- Quartz sandstone, medium to fine grained, grayish tan, limonitic- clayey cement 8822-Quartz sandstone, medium grained, yellowish, reddish brow n, minor clay cement BB34-- Quartz sandstone, mediu m grained, yellowish-reddish-brown, limonitic-hemat it ic cement, slightly micaceous, mi nor thin veins of fine-grained iron-rich rock DD 39-Conglomcritic quartz sandstone, med ium to coarse grained, reddish- yellow brown, abundant thin, distorted veins of fine-grained reddish iron-ri ch rock BB42--Qunrtz sandstone, medium to firie grained, reddisl1, yellowish hrown, limonitic 8851-Quartz sandstone, mediu m grained yellowish brown, limonitic, numerous thin veins bf fine-gra ined iron-rich rock BB57-Silty shale, yellowish red, carbonaceous in p laces BB65-Quartz sandstone, l medium to fine grained, reddish brown, numerous thin veins of fine - grained iron- rich rock BB68 -Q uartz sandstone, med ium to fine grained, wilite with zones of yellow to yellow-brown staining BH75--Sandstone, fine grained, some layers of siltstone, primarily quartz yellowish tan, limonitic cement, carbonAceous BB80--Quartz sandstone, fnedium grained, dark reddish brown, crossbedded BB92-Quartz sandstone, fine grained, fissile, light-reddbh tan BB: 97-Quurtz san dstone , lmedium to fine grained, shale pebbles, yellowish brown BB104--Shale, black, fissile BBl 11--Quartz sandstone, fine grained, white, conglomeratic in places with clayey clast's BB12fi--Quartz sandstone, medium to fine grained, yellowish tan BB129-Shale, dtwk gray to tan, some carbonaceous plant material Table 3.-- Comparison of elemental abundances in rocks from the Burden Falls Roadless Area wit 11 average crustal abundances of elements as given in Turek1an and Wedepoh1 (1961). ['\JI figure5 m parts per m1lhon (ppm)J Element B, Be F Pb T 580 3 740 20 SHALE 3 samples H/A 300/217 3/2 300/300* 50/25 T = Crustal abundances from Turekian and Wedepohl. T , o. O.x 270 7 H = Highest value measured in Burden Falls Roadless Area. A= Average value measur ed in Burden Falls Roadless Area • xO.=tens of ppm. o.x=tenths of ppm. N = Element not det~ted at limit of detection. SANDSTONE 14 sAmples II/ A 150/88 1/N I 100/N 50/N * Two samples had values of 300 and the other had a value 100; the exact value 1s not known. T,ble 4.--Compa,i,oo by somple type of ovemge coocentrotwns of mow wt,rotoc elements fa, J ,,,poc deposits from Burden Falls (BF) and Lusk Creek (LC) Rood!ess Areas [All values are in part5 per million. See tf.xt for discuss ion. N-not calculated, <-less than.] Sample type Bedrock Soil Panned Concentrll.tes Unpanned stream sed iments Bai·ium BF LC 117 82 400 304 642 GIO 483 142 Beryllium Fluori ne BP LC N N BF LC N 2300 1 <100 6.2 5.8 N 2.3 LO Lead Bl:' LC N N 15 273 112 67 35 1 The 2300 represents the average of 6 out of 14 samples. The remaining samples consisted of four ~alues at:<100 ppm and four N values. The average was not calculated. The va lue shown is the one that occurs most frequently. 3Eight of 28 samples have values of<lO ppm and are not included in the average. 4Two of 10 samples have values of <100 ppm and are not in~luded in the average. TRble 5.--Comparison by sample t·ype of the highest concentrations of major indicator elements for (luorspar deposits from the Burden Fa!!s (BF) and Lu.sk Creek (LC) Roadl ess Areas lb,ll values in parts per million. See text for 6 1 iscussion. <-less than .] Sample type Barium Ucryllium Fluorine Bedrock Soil Panned Concentrates Unpanncd stream sediments GF LC BF LC BF 300 200 3 15 300 500 700 2 (100 1000 1500 <100 700 300 ~-0 2.0 100 LC 13,000 200 200 100 BF 50 20 200 70 Lead LC '10 zoo 150 100 Studies Related to Wilderness The Wilderness Act (Public Law 88-577, September 3, 1964) and related acts require the U.S. Geological Survey and the U.S. Bureau of Mines to survey certain areas of Federal lands to determine their mineral resource potential. Results must be made available to the public and be submitted to the President and the Congress. This report represents the results of a geochemical survey of the Burden Falls Roadless Area (09-103) in the Shawnee National Forest, Pope County, Ill. The area was classified as a further planning area during the Second Roadless Area Review and Evaluation (RARE II) by the U.S. Forest Service, January 1979. INTRODUCTION The Burden Falls Roadless Area (Index Map) lies near the western edge of the Illinois-Kentucky fluorspar district, in which fluorite deposits occur as lenticular veins emplaced along fault zones or as stratiform bedding-replacement deposits that occur near fault zones (Grogan and Bradbury, 1967, 1968; Trace, 1974, 1976). Although mineralogy varies between deposits, the principal minerals consist of fluorite (CaF) and calcite (CaC0 3 ) with associated sphalerite (ZnS), galena (PbS} and barite (BaS0 4 ). Minor quantities of iron-rich dolomite (Ca, Mg(co 3 } 2 ), pyrite (FeS 2 ), marcasite (FeS 2 ), and alteration products of zinc, lead, and copper are also found. Pinckney (1976) noted that both silver and cadmium occur in sulfide minerals associated with the fluorspar. Several authors (Grogan and Bradbury, 1967, 1968; Trace, 197 4, 1976; Pinckney, 1976) have noted the association between fluorspar deposits and diatreme breccias at Hicks Dome, located about 15 mi ea.st of the study area. The breccias are enriched in beryllium, thorium, and the rare-earth elements. Most major deposits of fluorspar and associated minerals in the Illinois-Kentucky fluorspar district are in Mississippian rocks (Grogan and Bradbury, 1968). Mississippian strata in the area are buried from about 50 to 700 ft beneath Pennsylvanian rocks, surficial deposits, and soil, as determined from drill-core descriptions provided by the Illinois State Geological Survey. They are deepest along the east edge of the study area and shallowest along the northwest edge. Van Alstine (1965) has shown that residual soil and alluvium in Colorado can contain significant concentrations of fluorine in the vicinity of fluorite deposits. He also notes that opinions differ concerning the applicability of using fluorine as a geochemical indicator element, especially from soil and stream sediments in the Illinois-Kentucky fluorspar district. Because we collected soil and stream-sediment samples for analysis for other elements, we also analyzed them for fluorine. Bedrock geology (fig. 1) of the study area has been mapped by Klasner (1983). Bedrock is primarily quartz sandstone with minor thin, intercalcated beds of siltstone and shale. Petrographic analysis of thin sections of the sandstone shows that although quartz is the predominant mineral, the sandstone also has grains of feldspar, lithic fragments of argillite and chert, interstitial mica, and rare grains of zircon and possibly monazite . Iron enrichment is abundant. The study area is transected by a northeast-trending syncline with a nearly fiat-lying axis. The axis appears to be offset left-laterally- by northerly trending faults. Strata in the study area are gently dipping, generally less than 10°. Acknowledgments The Illinois State Geological Survey helped considerably in this study. Jack A. Simon, Director, provided unpublished data where appropriate. James C. Bradbury and James W. Baxter, geologists who have worked in the southern Illinois region, spent several hours discussing the geology of the region with the author and provided well-log data and geologic reports. The U.S. Forest Service personnel at Harrisburg, Ill. provided trail maps for the study area. Daniel Shuart and Donald O'Brien assisted in the collection of field samples and Katherine Portner helped in preparation of illustrations for this report. Atomic absorption analyses were done by F.F. Abrogast, J.D. Sharkey and W.W. Vaughn of the U.S. Geological Survey Laboratories, Denver, Colo. J.T. Hanley and P.G. Schruben formatted the analytical data by computer methods for table 1. RES UL TS OF GEOCHEMICAL STUDIES Data in table 1 are discussed in the following paragraphs in terms of mineral resource potential for fluorspar deposits and deposits of gold and silver. Because barite, galena and sphalerite occur in close association with fluorspar in the Illinois-Kentucky district, we consider them collectively in the following discussion. Table 2 describes the rock samples selected for analysis. Fluorspar and Associated Minerals Major indicator elements for fluorspar and associated minerals are barium, beryllium, fluorine, and lead, all found in table 1. Zinc is also associated with fluorspar, but it was not detected spectrographically at the limit of detection (200 ppm). Beryllium reflects the association of fluorspar deposits with diatreme breccias, as do the rare-earth elements lanthanum and niobium. Other possible indicator elements that were included but not detected in the spectrographic analysis include cadmium and thorium. Silver, which is found in sphalerite in the Illinois-Kentucky fluorspar district, occurs only infrequently in table 1 and is discussed under the section on gold and silver. Significance of the elemental values in table 1, relative to deposits of fluorspar and associated barite, galena, and sphalerite, are evaluated in three ways: (I) (2) (3) The values for the major indicator elements in bedrock samples are compared to average crustal values for these elements in the same rock type as given in Turekian and Wedepohl (1961). Anomalous (greater than two standard deviations above the arithmetic mean) values of indicator elements relative to the sampling population are identified and compared to the geologic map of the area. Each type (bedrock, soil, panned concentrate, and unpanned stream sediment) is considered to be a single sample. Even though the number of samples is small, this evaluation enables us to determine whether or not indicator elements are concentrated along structural features such as faults. Average and highest values of the major indicator elements from the Burden Palls Roadless Area are compared with those from the recently studied Lusk Creek Roadless Area (Klasner and Day, 1984). Elemental values from the Lusk Creek study area include only those samples from the central and northwest part where flat-lying Pennsylvanian bedrock overlies Mississippian strata, similar to the Burden Falls area. Much of this part of the Lusk Creek study area has been assigned a moderate fluorspar resource potential on the basis of values of indicator elements that are significantly higher than crustal averages, values that are anomalous relative to sample population averages, and, in some cases, association of anomalous values with faults. Pennsylvanian sediments at Lusk Creek are 747 ft thick along the north edge of the area, similar to the 700 ft thickness of Pennsylvanian strata at Burden Falls. Results of these evaluations are given in the same order as above. 1) Table 3 compares the values of major indicator elements with crustal averages of Turekian and Wedepohl In nearly all cases the average elemental values at the Burden Falls study area are lower than the crustal averages. The average for lead is the only exception, and it is about the same as Turekian and Wedepohl's average for this element. Also, in most cases, the highest elemental values in the Burden Falls area are about the same as or lower than the crustal averages. Only the highest values of lead and barium in sandstone are significantly higher (one order of magnitude) than the values given in Turekian and Wedepohl Lanthanum, which is not shown on table 3, occurs at a level lower than the crustal average . Niobium was not detected in bedrock at the Burden Falls study area. 2) Figure 2 shows th e location of anomalous values of fluorspar indicator elements (gold and silver are discussed below). Comparison of figure 2 with the geology of the area (fig. 1) shows that several of the anomalous elemental values lie near the two north-trending faults. Beryllium in soil also lies near a fault. Bedrock samples BB57 and BB104 have anomalous fluorine, lead, or lanthanum and also lie along a fault. Also, the unpanned stream-sediment samples BF7 and BF9 have faults lying within their drainage basins and have anomalous indicator elements. 3) Tables 4 and 5 compare the average and highest values of indicator elements between the Burden Falls and Lusk Creek Roadless Areas. Table 4 shows that the average values of most indicator elements are about equal to or higher at Lusk Creek than at Burden Falls. Most notably, fluorine is anomalously high at Lusk Creek but is generally less than the limit of determination at the Burden Falls study area. The highest values of indicator elements at Lusk Creek (which were significant in determining the resource potential in that area) are about equal to or higher than they are at Burden Falls (table 5). The highest value for fluorine is 13,000 ppm at Lusk Creek versus 300 ppm at Burden Falls. It seems significant that seven of 14 samples of bedrock at Lusk Creek had significant fluorine whereas only two of 17 samples did at Burden Falls. Also, the two anomalous fluorine values at Burden Falls were in shale; none were found in sandstone, whereas all but one from Lusk Creek were in conglomerate, sandstone, or siltstone. Note on table 3 that average crustal values of indicator elements are much higher in shale than they are in sandstone. Table 5 shows that higher values of barium in unpanned stream sediments and lead in bedrock occur at Burden Falls relative to the Lusk Creek area. Based on data given above, we conclude that there is no compelling geochemical evidence to suggest the presence of significant deposits of fluorspar and associated barite, galena, and sphalerite. This conclusion is based mainly on the fact that the average, and even highest, values of major indicator elements for nuorspar and associated minerals are either about the same as or lower than the average crustal values given in Turekian and Wedepohl {1961) as shown in table 3. GEOCHEMICAL SURVEY OF THE BURDEN FALLS ROADLESS AREA, POPE COUNTY, ILLINOIS By Jehn S. Klasner, U.S. Geological Survey and Western Illinois University and Gordon W. Day, U.S. Geological Survey 1985 Mt="- Isl:,'.:> - B MISCELLANEOUS FIELD STUDIES MAP MF-1565-B Cam rs Mill Mit chel l svill e : Equo111y T T T I 3' " 28 ~-"' MAP LOCATION Morion '===±= ==~ '°==d '~ " ===120 MILES Index map showing location of the Burden Falls Roadless Area and other roadless areas in southeastern lllinois. The association of anomalous elemental values with faults in the study areas suggest that some mineralizaHon may have taken place in the subsurface and migrated via groundwater along faults. Anomalous beryllium and lanthanum which occur along a fault may indicate the presence of a diatreme brec-cia in the subsurface. One might argue that Pennsylvanian rocks mask geochemical evidence of fluorspar and associated mineralization which may have occurred in underlying Mississippian strata. But data from the Lusk Creek Rondless Area, where up to 747 ft of Pennsylvanian rocks cover Mississippian strata, indicate that this is not the case. Both the average and highest values of several fluorspar indicator elemen ts at the Lusk Creek study area. are generally higher than at the Burden Falls Roadless Area (tables 4 and 5), Values of barium and lead in tables 3, 4, and 5 indicate enrichment in these elements at the Burden Falls study area relative to crustal averages and relative to values at Lusk Creek. We do not think, however, that these values are high enough to suggest significant subsurface mineralization. Also, they seem scattered throughout the region and are not generally concentrated along faults, which are important structural features that control the emplacement of fluorspar in the Illinois-Kentucky fluorspar district. Gold and Silver Spectrographic analysis showed gold and silver in three panned concentrate samples and two soil samples (table 1 and figure 2). Inasmuch as the panned concentrates underwent tertiary concentration for heavy minerals (panning, magnetic separation, and dense-fluid separation), the resulting samples were highly concentrated in mainly the most dense non- magnetic minerals. Because to the best of our knowledge gold has not been detected elsewhere in stream-sediment or bedrock samples in southern 1llinois, and because of the possibility of contamination, the following work was done to further test for the presence of gold and silver: 1) Unused portions of both the original panned concentrates and soil samples were reanalyzed by the semiquantitative spectrograph ic (SQS) technique. 2) Panned concentrate samples were examined under binocular microscope for visible gold and silver. 3) Panned concentrate and soil samples were recollected at tM original location for further analyses. Soil samples were analyzed by SQS, and panned concentrates were analyzed by SQS and atomic absorption (AA). 4) Bedrock samples BB42, BB75, BB92, BB104 and BB129 were analyzed by AA for gold. Samples BB42, 8875, and BB92 lie within the drainage basins that contained gold and silver in the initial SQS analysis. Samples B8104 and BB129 are from shale that lies upstream from the panned concentrate that had the highest gold value (BF6H). Results of this work are discussed below in the same order as above. 1) Reanalysis of unused portions of the original soil samples BS16 and BS! 7 by SQS did not reveal the presence of silver. Reanalysis of the unused portions of the panned concentrates (BFlH, BF3H, and BF6H) by SQS confirmed the presence of gold and silver (values were not recorded). 2) Microscopic examination of the panned concentrates did not reveal the presence of gold and silver. 3) In general analyses of recollected soil and stream sediment samples did not reveal the presence of gold or silver. SQS analysis of the soil samples did not show silver or gold at detection limits of 0.5 ppm and 10 ppm, respectively. Analysis of the three panned concentrates by SQS did not show silver or gold at the detection limits listed above. Analysis of panned concentrates BFlH and BF3H by AA did not show gold at a 0, 50 ppm detection limit; however, analysis of BF6H detected gold, but at a level below the level of determination--0.50 ppm. AA analysis of the recollected panned concentrates for silver was not done. 4) AA analysis of the bedrock samples, as well as microscopic examination, did not reveal the presence of gold or silver. There are two possible explanations for the presence of gold and silver in soils and panned concentrates from the Burden Falls study area. Either the soil and stream-sediment samples were contaminated during collection or during instrumental analyses, or natural gold and silver are present in the stream sediments and silver in the soil samples. Because reanalyses of unused parts of the soil sample as well as analysis of the resampled soil did not show silver, contamination seems a real possibility. But because gold, although in minute amounts, was detected in a second sample from location BF6H, it is probable that isolated particles of natural gold were present at this location, and possibly at locations BF! and BF3. Nevertheless, the data, in our judgement, do not suggest that gold and silver are present in the Burden Falls Roadless Area at concentrations that would have resource potential. They may be present as isolated particles in stream sediments. The fact that placer gold and silver were detected in a region that is not glaciated, however, suggests that the broader igneous-rock province of southern Illinois, which includes diatremes and mafic dikes (Bradbury, 1962; Glegg and Bradbury, 1956), warrant further study concerning the resource potential of these precious metals. REFERENCES CITED Bradbury, J.C., 1962, Trace elements, rare earths composition of southern Illinois igneous rocks: Geological Survey Circular 330, 12 p. and chemical Illinois State Clegg, K.E., and Bradbury, J.C., 1956, Igneous intrusive rocks in Illinois and their economic significance: Illinois State Geological Survey Report of Investigations 197, 19 p. Grimes, D.J., and Marranzino, A.P., 1968, Direct-current arc and alternating-current spark emission spectrographic field methods for the semiquantitative analysis of geologic materials: U.S. Geological Survey Circular 591, p. 6. Grogan, R.M., and Bradbury, J.C., 1967, Origin of the stratiform fluorite deposits, in Genesis of stratiform lead-zinc-barite-fluorite deposits (Mississippi Valley type deposits}-A symposium, New York, 1966: of southern Illinois, Economic Geology Mon. 3, p. 40-50. Fluorite-zinc-lead deposits of the Illinois Kentucky mining district in --Ore deposits of the United States, 1933-1967. {Graton-Sales Volume): J.D. Ridge (ed.), American Institute of Mining, Metallurgical and Petroleum Engineers, v. 1, p. 370-399. Hawkes, H.E., and Webb, J.S., 1962, Geochemistry in mineral exploration: New York, Harper and Row, 415 p. Klasner, J.S., 1983, Geologic map of the Burden Falls Roadless Area, Pope County, Illinois: U.S. Geological Survey Miscellaneous Field Studies Map MF-1565-A. Klasner, J,S., and Day, G.W., 1984, Geochemical survey of the Lusk Creek Roadless Area, Pope County, Illinois: U.S. Geological Survey Miscellaneous Field Studies Map MF-1405-B. Levinson, A.A., 1974, Introduction to exploration geochemistry, 2nd ed.: Willmette, Illinois, Applied Publishing Ltd., 924 p. Motooka, J.M., and Grimes, D.J., 1976, Analytical precision of one-sixth order semiquantitative spectrographic analysis: U.S. Geological Survey Circular 738, 25 p. Pinckney, D.M., 1976, Mineral resources of the Illinois-Kentucky mining district: U.S. Geological Survey Professional Paper 970, 15 p. Trace, R.D., 1974, Illinois-Kentucky fluorspar district, in A symposium on the geology of fluorspar: Forum on geology of industrial minerals, 9th Proceedings, Kentucky Geological Survey, special publication 22, 58-76. 1976, Chapter on the Illinois-Kentucky fluorspar district, in Geology ---and resources of fluorine in the United States: D.R. Shawe, ed., U.S. Geological Survey Professional Paper 933, p. 63-94. Turekian, K.K., and Wedepohl, K.H., 1961, Distribution of the elements in some major units of the earth 1 s crust: Geological Society of America Bulletin, v. 72, p. 175-192. Van Alstine, R.E., 1965, Geochemical prospecting in the Browns Canyon fluorspar district, Chaffee County, Colorado: U.S. Geological Survey Professional Paper 525-D, p. D59-D64. NOV 2 2 i985 . i2 l( M(200) MF-/ 5bY G c.>, I I NrERI O fl-G EOLOGI CAL SURVEY, RESro~. IJA - 19B.5 For sale by Branch of Distri b ut ion. U.S. Geol Dgical Survey, 1200 South Eads S tr eet, Arli~n. 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