Mineral Resources of the Jacumba (In-ko-pah) Wilderness Study Area, Imperial County, California
U.S. GEOLOGICAL SURVEY BULLETIN 1711-D
Chapter D Mineral Resources of the Jacumba (In-ko-pah) Wilderness Study Area, Imperial County, California
By VICTORIA R. TODD, JAMES E. KILBURN, DAVID E. DETRA, ANDREW GRISCOM, and FRED A. KRUSE U.S. Geological Survey
EDWARD L McHUGH U.S. Bureau of Mines
U.S. GEOLOGICAL SURVEY BULLETIN 1711
MINERAL RESOURCES OF WILDERNESS STUDY AREAS: SOUTHERN CALIFORNIA AND CALIFORNIA DESERT CONSERVATION AREA DEPARTMENT OF THE INTERIOR DONALD PAUL MODEL, Secretary
U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1987
For sale by the Books and Open-File Reports Section U.S. Geological Survey Federal Center, Box 25425 Denver, CO 80225
Library of Congress Cataioging-in-Publication Data
Mineral resources of the Jacumba (In-ko-pah) Wilderness Study Area, Imperial County, California.
U.S. Geological Survey Bulletin 1711-D Bibliography: Supt. of Docs. No.: I 19.3:1711-D 1. Mines and mineral resources California Jacumba (In- ko-pah) Wilderness. 2. Jacumba (In-ko-pah) Wilderness (Calif.) I. Todd, Victoria R. (Victoria Roy) II. U.S. Geological Survey. III. Series. QE75.B9 No. 1711-D 557.3 s 87-600129 [TN24.C2] [553'.09794'99] STUDIES RELATED TO WILDERNESS Bureau of Land Management Wilderness Study Areas The Federal Land Policy and Management Act (Public Law 94-579, October 21, 1976) requires the U.S. Geological Survey and the U.S. Bureau of Mines to conduct mineral surveys on certain areas to determine the mineral values, if any, that may be present. Results must be made available to the public and be submitted to the President and the Congress. This report presents the results of a mineral survey of part of the Jacumba (In-ko-pah) (CDCA-368) Wilderness Study Area, Imperial County, California.
CONTENTS Summary Dl Abstract 1 Character and setting 1 Identified mineral resources and resource potential 1 Introduction 3 Area description 3 Previous and present investigations 3 Acknowledgments 3 Appraisal of identified resources 5 History and production 5 Mineral deposits 5 Appraisal of mineral deposits 6 Assessment of mineral resource potential 7 Geology 7 Geochemical studies 8 Geophysical studies 8 Conclusions 9 References cited 9 Appendixes Definition of levels of mineral resource potential and certainty of assessment 13 Geologic time chart 14
FIGURES 1. Index map showing location of the Jacumba (In-ko-pah) Wilderness Study Area, Imperial County, California D2 2. Map showing mineral resource potential and simplified geology of the Jacumba (In-ko-pah) Wilderness Study Area 4
TABLE
1. Prospects in and adjacent to the Jacumba (In-ko-pah) Wilderness Study Area D15
MINERAL RESOURCES OF WILDERNESS STUDY AREAS: SOUTHERN CALIFORNIA AND CALIFORNIA DESERT CONSERVATION AREA Mineral Resources of the Jacumba (In-ko-pah) Wilderness Study Area, Imperial County, California
By Victoria R. Todd, James E. Kilburn, David E. Detra, Andrew Griscom, and Fred A. Kruse U.S. Geological Survey
Edward L. McHugh U.S. Bureau of Mines
SUMMARY The study area is underlain by Cretaceous (66 to 138 million years before present (Ma); see appendix for Abstract geologic time chart) plutonic rocks of the Peninsular This report presents the results of a mineral Ranges batholith (informal name). The batholith is survey of part of the Jacumba (In-ko-pah) Wilderness composed of a variety of plutons that intruded Study Area (CDCA-368) that was designated by the metamorphosed Paleozoic and Mesozoic sedimentary Bureau of Land Management as suitable for mineral and volcanic rocks. Neogene (24 to 1.7 Ma) marine and surveys. In this report, the area studied is referred to alluvial deposits unconformably overlie the uplifted as the "wilderness study area", or simply "the study and deeply eroded batholithic rocks in the study area, area." The study area encompasses approximately and faults of the Elsinore fault zone cut both the 28,443 acres in southwestern Imperial County, Calif. batholithic rocks and the sedimentary deposits. Field work for this report was carried out between Evidence of mining or prospecting activity was found 1983 and 1985. Numerous mines, prospects, and claims at 26 sites in, or just outside of, the Jacumba (In-ko- are present in the study area, but none are being pah) Wilderness Study Area. In 1983, 106 claims were actively mined or prospected. Three sites inside the held in 13 claim groups. At that tim£, none of the study area have identified limestone resources that claims or sites was being actively mined or total about 1.8 million tons. Four areas in the prospected. northwestern, northern, and eastern parts of the study area have high potential for undiscovered limestone resources. Two north-trending belts in the western Identified Mineral Resources and Resource Potential and eastern parts of the study area have low resource potential for tungsten. Geologic and geochemical studies, and an evaluation of known mineral occurrences indicate locally high potential for undiscovered limestone Character and Setting resources in three areas in the northern part of the study area and in one area in the eastern part. In The Jacumba (In-ko-pah) Wilderness Study Area addition, a northwest-trending belt in the western part is located between the Peninsular Ranges province on of the study area and four irregular areas that define a the west and the Yuha Desert on the east (fig. 1). The north-trending belt in the eastern part have low United States-Mexico border forms the south boundary potential for tungsten resources (fig. 2). of the study area. Much of the area is characterized Metasedimentary strata of Paleozoic and by rugged topography. Maximum relief in the study Mesozoie(?) age that are present as steeply dipping area is about 3,400 ft. A semiarid climate and tabular bodies, or screens, within granitic plutons in chapparal vegetation are found at the higher the study area locally contain abundant limestone elevations, whereas an arid climate and desert plant (metamorphosed to marble). Known deposits in the communities are characteristic of lower areas. study area contain identified resources of about 1.8
D1 RECOVERY PARACHUTE TEST RANGE
ANZA-BORREGO DESERT STATE PARK
IMPERIAL VALLEY
ar\d Arizona Eastern Railroad
MOUNTAINS
Ocotillo e Wells JACUMBA (IN-KO-PAH) WILDERNESS STUDY AREA(CDCA-368)
YUHA DESERT
5 MILES I I I I I j
Figure 1. Index map showing location of the Jacumba (In-ko-pah) Wilderness Study Area, Imperial County, California.
D2 million tons of limestone, although economic Previous and Present Investigations conditions are unfavorable for the development of these small deposits at the present time. Abundant This mineral resource study is a joint effort by deposits of high-quality limestone are present in the the U.S. Geological Survey and the U.S. Bureau of Coyote Mountains to the north. Mines. The history and philosophy of such joint Tungsten-bearing skarn deposits are present mineral surveys of U.S. Bureau of Land Management between marble-bearing metasedimentary screens and Wilderness Study Areas were discussed by Beikman and surrounding plutons. These small, irregular, and others (1983). Mineral assessment methodology and sporadically mineralized skarn deposits are probably terminology were discussed by Goudarzi (1984). See the source of widespread anomalous concentrations of appendix for the definition of levels of mineral tungsten, molybdenum, and tin, and localized gold, resource potential and certainty of assessment. silver, bismuth, and zinc anomalies in stream Studies by the U.S. Geological Survey are designed to sediments in the study area. Rock samples from provide a reasonable scientific basis for assessing the several skarn deposits contain significant amounts of potential for undiscovered mineral resources by tungsten. Although known tungsten occurrences inside determining geologic units and structures, possible the study area are too small or low grade to be environments of mineral deposition, presence of considered resources, undiscovered resources may geochemical and geophysical anomalies, and applicable exist. Thus, areas of skarn deposits and metasedi ore-deposit models. The U.S. Bureau of Mines mentary screens in the study area have low resource evaluates identified resources at individual mines and potential for tungsten. No potential for geothermal known mineralized areas by collecting data on current energy, uranium, or oil and gas resources was and past mining activities and through field identified in the study area. examination of mines, prospects, claims, and mineralized areas. Identified resources are classified according to the system described by U.S. Bureau of INTRODUCTION Mines and U.S. Geological Survey (1980). The Jacumba (In-ko-pah) Wilderness Study Area Area Description includes parts of the In-ko-pah Gorge and Coyote Wells 7.5-minute quadrangles. Published geologic maps by The Jacumba (In-ko-pah) Wilderness Study Area Brooks and Roberts (1954) and Morton (1977) describe (CDCA-368) occupies 28,443 acres in the southwest the geology of the region. Unpublished mapping by corner of Imperial County, Calif, (fig. 1). The study T.W. Dibblee, Jr. (written commun., 1943) covers part area is located in the southeastern part of the of the Jscumba Mountains. The U.S. Geological Jacumba Mountains, which forms the eastern faulted Survey carried out field investigations in the study escarpment of the Peninsular Ranges immediately area between 1984 and 1985. The work included north of the international border with Mexico. The geologic mapping and whole-rock and stream-sediment Jacumba Mountains rise above the Yuha Desert, which sampling for geochemical analyses and radiometric is the western part of the Imperial Valley, a broad dating. A total of 52 panned heavy-mineral alluvial valley that lies partly below sea level. The concentrates from stream sediment samples were study area is roughly bisected by north-northwest- analyzed; the analytical data are given in Detra and trending Davies Valley (fig. 1), which was eroded along Kilburn (1985). a major fault zone that separates high-standing The U.S. Bureau of Mines conducted a library batholithic rocks on the west from low hills that search for information on mines and prospects in and expose metasedimentary rocks and Neogene volcanic adjacent to the study area. Mines and prospects in and and sedimentary rocks on the east. Other north- near the study area were described by Sampson and trending faults cross the eastern and western parts of Tucker (1942) and Morton (1977). These data were the study area, and part of the Elsinore fault zone supplemented by information from U.S. Bureau of Land bounds the study area on the east (fig. 2). These faults Management mining claim and land status records. have produced a rough stair-step topography in which Claim owners were contacted when possible. Field fault-bounded blocks are progressively lower to the studies by U.S. Bureau of Mines personnel were carried east. Elevations range from about 4,000 ft in the out in the fall of 1983. Rock samples collected from western part of the area to about 600 ft near the outcrops, prospects, and mines were analyzed for a eastern front of the range. The climate of the region variety of elements by fire-assay, atomic absorption, is arid, with rainfall ranging between 3 and 4 in. per colorimetr c, X-ray fluorescence, plasma year (Morton, 1977) and summer temperatures often spectrographic, and semiquantitative spectrographic exceeding 100 to 110 °F at lower elevations. methods. Detailed sample data are presented in Access to the area is chiefly from California McHugh (1985). Highway 98, which extends south from Interstate 8 to Calexico. Several dirt roads maintained by the Bureau of Land Management lead southwest from California Acknowledgments Highway 98 into the eastern part of the area. On the west side of the study area, a jeep trail leads from The authors gratefully acknowledge Sean Jacumba Valley to the PK mine (fig. 2, No. 26). Hagerty and Steve Nelson of the Bureau of Land
D3 32° 116°05' 116°00' 115°55' 45 I
Ancient shoreline / of Lake Cahuilla f
APPROXIMATE BOUNDARY OF JACUMBA (IN-KO-PAH) WILDERNESS STUDY AREA (CDCA-368)
-' QTs
YUHA DESERT 32° 40' Gravel pit b x
H/D Ls
Qs
QTs___.
2 MILES
Figure 2. Mineral resource potential and simplified geology of the Jacumba (In-ko-pah) Wilderness Study Area, Imperial County, California. EXPLANATION fcij: Area with high mineral resource potential 13 Jfi 13 Area with low mineral resource potential S3 Ci or C" g g>» = °O Co fD JB ^ O9 Mine with recorded past production See table 1 for Sf E o & * description 3 S See appendix for definitions of mineral resource potential and W TO 3- fp ET C O 05 o 3 " B- 51 05 CO 3 3 3 levels of certainty t_1 '^>!^COEo rp C/3 s 5. ** FB 3 ?i <-» Commodities ED O ^_i a ^ * g' §.8 5' fir0" 3 r* Ls Limestone SZ!^" - ^csgq1 W Tungsten 3 ® "^ a ^ i-b 3 05 2 0) rt> gj 3 a w S 3 fl) 3 fcT1 to 51 05 O5 1-1 w w 3 " Geologic map units -0 3 i' £? £ 5» m C>So CT S 3 B ^ § d Q< o TO^* OjP" Qs 1"^ 1^^ Q S3 ? w Q. 3 5'^ rO s? o 5> Ql Lacustrine deposits of Lake Cahuilla (Quaternary) C CL 3 OfQ S Q- l-h W £ ' w s TO 0? 3 "" g W 05 Qs Surficial deposits (Quaternary) 05 X
D6 the range. In the northern part of the area, fan calcite. Skarn minerals form irregular scattered deposits mantle bedrock both inside and outside the lenses as much as 300 ft across that commonly are study area. Development of sand and gravel deposits associated with isoclinally folded metasedimentary inside the study area is unlikely because similar rocks. Scheelite occurs locally in skarn as deposits are available closer to major population disseminated blebs, stringers, and pods locally as much centers. as 2 ft long but typically less than a few inches long. The eroded crystalline basement of the southern Jacumba Mountains is overlain on the north and east ASSESSMENT OF MINERAL RESOURCE POTENTIAL by Miocene through Pleistocene sedimentary and volcanic deposits; remnants of Miocene deposits By Victoria R. Todd, James E. Kilburn, David E. Detra, overlie the crystalline rocks on both sides of Davies Andrew Griscom and Fred A. Kruse Valley (fig. 2). These deposits are remnants of a thick U.S. Geological Survey (locally 20,000 ft) sequence of terrestrial and marine sediments and intercalated volcanic rocks deposited in, and marginal to, the Salton Trough. The Salton Trough Geology is a complex rift valley that has been tectonically active since Miocene time (Gibson and others, 1984). The southern part of the Jacumba Mountains is The Miocene Split Mountain Formation of underlain by relatively undeformed plutons that are Woodard (1974) crops out mainly east of Davies Valley considered to belong to a late-tectonic to posttectonic (fig. 2). Patches of this formation are also preserved intrusive sequence in the Peninsular Ranges batholith beneath the Jacumba Volcanics of Minch and Abbott (Todd and Shaw, 1979). Similar plutons to the west in (1973) in fault blocks west of Davies Valley. The Split San Diego County have uranium-lead zircon ages that Mountain Formation formed as a thickening wedge of range from 95 to 100 Ma (Silver and others, 1979; coalescing alluvial fans during the early phase of uplift Clinkenbeard and others, 1986). Thus, the plutons in of the Peninsular ranges (Gibson and others, 1984). the southern Jacumba Mountains are tentatively The formation underlies andesitic pyroclastic rocks in considered to be middle Cretaceous in age. Two the northeast part of the study area. These volcanic plutons of this intrusive sequence crop out in the rocks locally form a very thin, extensively faulted Jacumba (In-ko-pah) Wilderness Study Area. Strongly veneer over the Split Mountain Formation and possibly foliated late-tectonic tonalite forms most of the also over Quaternary sediments. The volcanic rocks crystalline bedrock east of Davies Valley, whereas may have been partly or wholly displaced by weakly foliated to massive posttectonic tonalite posteruptive gravitational gliding or large-scale underlies much of the block west of Davies Valley (fig. landsliding during uplift of the Peninsular Ranges. 2). Both plutons range in composition from The Salton Trough was flooded by marine waters hornblende-biotite tonalite to biotite granodiorite; the in early Pliocene time (Bell-Countryman, 1984). As western pluton also includes leucocratic muscovite- the basin continued to subside, a shoaling series of biotite granodiorite. Pegmatite dikes are abundant in alluvial fan, shoreline, and deep-water marine deposits both western and eastern tonalite plutons. was rapidly deposited conformably on the Split Screens and inclusions of wallrocks in the study Mountain Formation and volcanic rocks. Gradationally area consist of high-grade metasedimentary rocks of overlying these predominantly marine deposits is a unknown age including metaquartzite, semipelitic sequence of Pliocene and Pleistocene brackish-water schist, and marble, the last containing the limestone to lacustrine sediments with marine interbeds, the deposits mentioned in an earlier section of this Palm Spring Formation. The Imperial and Palm Spring report. These rocks may include two units deep- Formations crop out east of the study area in the water arkosic and graywacke sandstones and shale down-faulted Yuha Desert block, and in the badlands (turbidites) with scarce interbedded carbonate rocks that lie north of the study area between the Coyote that crop out in San Diego County to the west (the Mountains and the northern Jacumba Mountains. An Julian Schist) and a continental shelf sequence of undated sequence of alluvial fan sands and gravels quartz-rich sandstone, shale, and abundant carbonate overlies the Jacumba Volcanics in the northern part of that is present in the eastern part of the batholith. the study area; these sediments may correlate with the The Julian Schist is presumed to be Triassic and (or) Pliocene and younger Imperial and Palm Spring Jurassic in age (Donnelly, 1934), while the eastern Formations, or may consist of Miocene strata. prebatholithic rocks are at least in part Paleozoic The southern Jacumba Mountains probably began (Miller and Dockum, 1983). Therefore, the to rise as an uplifted fault block sometime during prebatholithic rocks in the study area are tentatively Pliocene time and then continued to be elevated during considered to be Paleozoic and Mesozoic(?) in age. Quaternary time by north- and north-northwest- The wallrock screens contain concordant fine- to trending high-angle faults in Davies Valley and along medium-grained granitic dikes that emanate from the the east flank of the range. A mosaic of north- and surrounding plutons. Pegmatite dikes commonly were east-trending dip-slip faults in the northeastern part of emplaced into contact zones between screens and the study area has produced a triangular graben tonalite plutons. Skarns developed locally where composed chiefly of Miocene rocks; this graben is limestone was intruded by tonalite and (or) by granitic bounded on the west by a fault, or faults, under the dikes. Retrograde alteration and oxidation of high- alluvium of Davies Valley (fig. 2). The Laguna Salada grade skarn minerals such as garnet and diopside led to fault, which lies about I mi east of the southern local concentrations of epidote, clinozoisite, Jacumba Mountains, cuts Quaternary alluvium tremolite-actinolite, chlorite, hematite, limonite, and suggesting that the range-bounding faults may still be
D7 active. All of the above faults are part of the active included tungsten, tin, molybdenum, bismuth, gold, and Elsinore fault zone, which has undergone chiefly dip- silver. The sample contained a substantial amount of slip motion south of 33° N. lat (Todd and Hoggatt, scheelite (50 percent) and several gold flakes. The PK 1979). mine, initially a gold prospect but later mined for The most recent geologic feature adjacent to the tungsten, is situated within an irregular skarn body southern Jacumba Mountains is the high shoreline of near the contact between a metasedimentary roof ancient Lake Cahuilla, which lies less than 1 mi east of pendant and enclosing tonalite (Morton, 1977). the range. The lake originated by periodic flooding The tin anomalies appear to be a regional and overflow of the ancestral Colorado River into the geochemical signature of the late-tectonic to Salton Trough (Morton, 1977). Although it probably posttec tonic intrusive sequence. Although no existed as recently as several hundred years ago, the mineralogic or lithologic host was determined, it is lake has probably formed and dried up repeatedly since possible that much of the tin may be derived from an at least late Pleistocene time. Fine-grained lake accessory mineral or minerals disseminated throughout sediments in the northern part of the study area (the these granitic rocks. Additionally, skarns may have White Christmas diatomite deposit) (fig. 2, No. 6) and contributed in some measure to the tin anomalies. patchy lacustrine sediments east of the study area The source of the barium and barite anomalies is suggest that the earliest lakes may have extended uncertain. Although barite was identified as a minor westward into the valleys of the southern Jacumba component in most of the concentrates, the majority Mountains (Morton, 1977). of barium anomalies are restricted to the region east of Davies Valley. This may represent structural control by the numerous faults that bound the valley Geochemical Studies and the eastern range front and (or) lithological control by the Miocene sedimentary rocks that occur A reconnaissance geochemical survey of stream mainly east of Davies Valley. Anomalous sediments was conducted in the study area in 1984 by concentrations of strontium and barium are present the U.S. Geological Survey. Heavy-mineral jointly near the northeast boundary of the study area; concentrates were derived from fifty-two samples the strontium may be a constituent of barite, having collected from streams that drain areas ranging from a replaced barium in a solid solution series. fraction to several square miles within the study Most, and perhaps all, of the anomalous lead area. Each sample was sieved through a minus-80- concentrations can be attributed to contamination mesh screen to remove the coarsest material and rather than natural sources. Evidence includes lead divided into light and heavy fractions using a shot fragments found in over half the anomalous bromoform mineral separation technique. The heavy samples and the failure to identify a lead-related fraction was further separated using a magnetic mineral in any of the concentrates. separator. All samples were analyzed for 30 elements by a six-step semiquantitative emission spectrographic method (Grimes and Marranzino, 1968). A complete Geophysical Studies listing of the analytical results can be found in Detra and Kilburn (1985). In addition, concentrates were Three aeromagnetic and gamma-ray examined optically for mineral identification. spectrometer profiles (High Life Helicopters, Inc., and Spectrographic analysis of the concentrates QEB, Inc., 1980) cross the study area. The data were revealed widespread anomalous concentrations of collected along east-west and north-south traverses by tungsten and tin as well as numerous anomalous helicopter at a height of 400 ft above ground. The concentrations of barium, lead, and molybdenum. In magnetic data are nearly featureless because none of addition, isolated local anomalous concentrations of the rocks within the study area are particularly gold, silver, bismuth, zinc, and strontium were noted. magnetic, except for some weakly magnetic volcanic Mineralogically, the concentrates are characterized by rocks. The radioactivity data for these profiles show abundant barite and scheelite coupled with an apparent no anomalous amounts of uranium or thorium within, absence of ore-forming sulfide and oxide minerals. the study area. Optical studies also identified gold at one sample Gravity data available for the study area (Oliver site. Contaminating lead shot observed in the samples and others, 1980; Roberts and others, 1981) consist coincides with five of the nine anomalous lead only of about 15 stations and do not contribute concentrations. significantly to the mineral resource appraisal of the The ubiquitous scheelite and accompanying area. tungsten anomalies are undoubtedly mineralogical and The limonite mineral group has unique spectral chemical manifestations of the numerous skarn reflectance characteristics that can be detected on deposits that are present in the study area. Anomalous Landsat images using a color-ratio compositing concentrations of one or more of the elements technique described by Rowan and others (1974). This molybdenum, tin, gold, silver, bismuth, and zinc, often technique was used to map areas of limonite in the constituents of tungsten-bearing skarns, are associated Jacumba (In-ko-pah) Wilderness Study Area. Limonite with the tungsten anomalies throughout the eastern occurrences in exposed bedrock are considered part of the study area and in the western part near the anomalous and may indicate the presence of PK (Elliott) mine. A skarn-related multiple-element hydrothermal alteration. The largest limonite anomaly is found in a minor drainage below the PK occurrence is in the southeast corner of the study area mine (Elliott mine) in the southwest corner of the and covers roughly 1 mi . This and several other study area. The anomalous trace-element suite here limonite anomalies in the area seem to be associated
D8 with faulted parts of the tonalite of Granite Mountain Bureau of Land Management Wilderness Study (fig. 2). These areas are favorable for the occurrence Areas: U.S. Geological Survey Circular 901, 28 of hydrothermally altered rocks. Scattered limonite P- occurrences within the study area coincide closely Bell-Countryman, Pat, 1984, Environments of with the eastern of two zones of low tungsten resource deposition of the Pliocene Imperial Formation, potential (fig. 2) and, to a lesser extent, with the Coyote Mountains, southwest Salton trough, in western zone. However, these occurrences are small Rigsby, C.A., ed., The Imperial Basin tectonics, and their areal extent does not indicate a large sedimentation, and thermal aspects: Pacific hydrothermal system if indeed they are associated Section, Society of Economic Paleontologists and with hydrothermally altered rocks. Other limonite Mineralogists, v. 40, p. 45-70. occurrences are associated with volcanic rocks that Bowen, O.E., Gray, C.H., Jr., and Evans, J.R., 1973, also may be hydrothermally altered. The mineral economics of the carbonate rocks, in Bowen, O. E., ed., Limestone and dolomite Conclusions resources of California: California Division of Mines and Geology Bulletin 194, p. 13-60. Geologic studies, geochemical sampling, Brooks, Bay lor, and Roberts, Ellis, 1954, Geology of examination of prospects and mines, and a review of the Jacumba area, San Diego and Imperial the history of mine production in and near the Counties, in Jahns, R.H., ed., Geology of Jacumba (In-ko-pah) Wilderness Study Area indicate southern California: California Division of Mines that the study area contains two main types of mineral and Geology Bulletin 170, map sheet 23, scale occurrences, both associated with pre-Cenozoic 1:62,500. crystalline rocks. Metasedimentary strata of Clinkenbeard, J.P., Walawender, M.J., Parrish, K.E., Paleozoic(?) age that are present as screens within Wardlaw, M.S., and Smith, B., 1986, The tonalite plutons locally contain abundant limestone. geochemical and isotopic composition of the La Limestone resources were identified at three sites Posta granodiorite, San Diego County, California within the study area. The study area has a high [abs.]: Geological Society of America Abstracts potential, certainty level D, in four areas for with Programs, v. 18, no. 2, p. 95. additional low- to moderate-tonnage limestone Detra, D.E., and Kilburn, J.E., 1985, Analytical results resources in and near these deposits (fig. 2). See and sample locality maps of heavy-mineral appendix for definition of levels of mineral resource concentrate samples from the Jacumba (In-ko- potential and certainty of assessment. pah) (CDCA-368) Wilderness Study Area, The second type of mineral occurrence in the Imperial County, California: U.S. Geological study area consists of relatively abundant skarn Survey Open-File Report 85-272. deposits. Rock samples from four localities in the Donnelly, Maurice, 1934, Geology and mineral deposits study area contain significant amounts of tungsten and of the Julian district, San Diego County, minor amounts of gold. Samples from the PK mine California: California Journal of Mines and (Elliott mine) outside the study area contain tungsten, Geology, v. 30, no. 4, p. 331-370. gold, and silver. Widespread occurrences of the Gibson, L.M., Malinconico, L.L., Downs, T., and tungsten mineral scheelite in stream-sediment Johnson, N.M., 1984, Structural implications of concentrates in the study area probably originated in gravity data from the Vallecito-Fish Creek skarn deposits. Local anomalous concentrations of Basin, western Imperial County, California, in molybdenum, tin, gold, silver, bismuth, and zinc also Rigsby, C.A., ed., The Imperial Basin tectonics, probably are derived from tungsten-bearing skarns. No sedimentation, and thermal aspects: Pacific deposits of ore minerals containing these elements Section, Society of Economic Paleontologists and were found in the study area. Mineralogists, v. 40, p. 15-29. The parts of the study area that are underlain by Goudarzi, G.H., 1984, Guide to preparation of mineral known skarn deposits and (or) metasedimentary screens survey reports on public lands: U.S. Geological have low resource potential, certainty level C, for Survey Open-File Report 84-787, 51 p. tungsten in skarns of metasomatic origin (fig. 2). Grimes, D.J., and Marranzino, A.P., 1968, Direct- Known tungsten occurrences inside the study area are current arc and alternating-current spark too small or low-grade to be considered resources, but emission spectrographic field methods for the the widespread development of skarns in the study semiquantitative analysis of geologic materials: area indicates that other skarn bodies may be present U.S. Geological Survey Circular 591, 6 p. at depth. Geologic evidence suggests that such High Life Helicopters, Inc., and QEB, Inc., 1980, occurrences will be small, irregular, and only Airborne gamma-ray spectrometer and sporadically mineralized. No potential for other magnetometer survey, San Diego quadrangle*, mineral resources or for geothermal energy, uranium, California [ 1° by 2 ] sheet; National Uranium" or oil and gas resources was determined in the study Resource Evaluation program, GJBX-214 (80) ; area. Grand Junction, Colo., U.S. Department of Energy, variously paged. Logan, C.A., 1947, Limestone in California: California REFERENCES CITED Journal of Mines and Geology, v. 43, p. 175-357. Loomis, T.H.W., 1965, Mineral patent application of Beikman, H.M., Hinkle, M.E., Frieders, Twila, Marcus, Andrada Desert Enterprises, Inc., for the White S.M., and Edward, J.R., 1983, Mineral surveys by Christmas, White Christmas No. 2, and Le the Geological Survey and the Bureau of Mines of Plateau placer mining claims: U.S. Bureau of
09 Land Management Mineral Report Ser. No. R resources of Imperial County: California Journal 02425, 5 p. of Mines and Geology, v. 38, p. 105-145. McHugh, E.L., 1985, Mineral resources of the Jacumba Silver, L.T., Taylor, H.P., Jr., and Chappell, B., 1979, Wilderness Study Area, Imperial County, Some petrological, geochemical and California: U.S. Bureau of Mines Open-File geochronological observations of the Peninsular Report MLA 55-85, 27 p. Ranges batholith near the international border of Miller, R.H., and Dockum, M.S., 1983, Ordovician the U.S.A. and Mexico, in Abbott, P.L., and conodonts from metamorphosed carbonates of Todd, V.R., eds., Mesozoic Crystalline Rocks: the Salton Trough, California: Geology, v. 11, p. Geological Society of America Annual Meeting, 410-412. San Diego, Calif., 1979, Guidebook, p. 83-110. Minch, J.A., and Abbott, P.L., 1973, Post batholithic Todd, V.R., and Hoggatt, W.C., 1979, Vertical geology of the Jacumba area, southeastern San tectonics in the Elsinore fault zone south of Diego County, California: San Diego Society of 33°7'30" [abs.]: Geological Society of America Natural History, Transactions, v. 17, no. 11, p. Abstracts with Programs, v. 11, p. 528. 129-135. Todd, V.R., and Shaw, S.E., 1979, Structural, Morton, P.K., 1977, Geology and mineral resources of metamorphic, and intrusive framework of the Imperial County, California: California Division Peninsular Ranges batholith in southern San of Mines and Geology County Report 7, 104 p. Diego County, California, in Abbott, P.L., and Oliver, H.W., Chapman, R.H., Biehler, S., Robbins, Todd, V.R., eds., Mesozoic Crystalline Rocks: S.L., Hanna, W.F., Griscom, A., Beyer, L.A., and Geological Society of America Annual Meeting, Silver, E.A., 1980, Gravity map of California and San Diego, Calif., 1979, Guidebook, p. 177-231. its continental margin: California Division of U.S. Bureau of Mines, 1986, Mineral Commodity Mines and Geology, scale 1:750,000, 2 sheets. Summaries 1986: U.S. Bureau of Mines, 185 p. Roberts, C.W., Jachens, R.C., and Oliver, H.W., 1981, U.S. Bureau of Mines and U.S. Geological Survey, 1980, Preliminary isostatic residual gravity map of Principles of a resource/reserve classification California: U.S. Geological Survey Open-File for minerals: U.S. Geological Survey Circular Report 81-573, scale 1:750,000, 5 sheets. 831, 5 p. Rowan, L.C., Wetlaufer, P.M., Goetz, A.F.H., Weber, F.H., Jr., 1963, Geology and mineral resources Billingsley, F.C., and Stewart, J.H., 1974, of San Diego County: California Division of Discrimination of rock types and detection of Mines and Geology County Report 3, 309 p. hydrothermally altered areas in south-central Woodard, G.D., 1974, Redefinition of Cenozoic Nevada by the use of computer-enhanced ERTS stratigraphic column in Split Mountain Gorge, images: U.S. Geological Survey Professional Imperial Valley, California: American Paper 883, 35 p. Association of Petroleum Geologists Bulletin, v. Sampson, R.J., and Tucker, W.B., 1942, Mineral 58, no. 3, p. 521-526.
D10 APPENDIXES
Definition of levels of mineral resource potential and certainty of assessment
Definitions of Mineral Resource Potential
LOW mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics define a geologic environment in which the existence of resources is permissive. This broad category embraces areas with dispersed but insignificantly mineralized rock as well as areas with few or no indications of having been mineralized. MODERATE mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics indicate a geologic environment favorable for resource occurrence, where interpretations of data indicate reasonable likelihood of resource accumulation, and (or) where an application of mineral-deposit models indicates favorable ground for the specified type(s) of deposits. HIGH mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics indicate a geologic environment favorable for resource occurence, where interpretations of data indicate a high degree of likelihood for resource accumulation, where data supports mineral-deposit models indicating presence of resources, and where evidence indicates that mineral concentration has taken place. Assignment of high resource potential to an area requires some positive knowledge that mineral-forming processes have been active in at least part of the area. UNKNOWN mineral resource potential is assigned to areas where information is inadequate to assign low, moderate, or high levels of resource potential. NO mineral resource potential is a category reserved for a specific type of resource in a well-defined area.
Levels of Certainty
U/A H/B H/C H/D
HIGH POTENTIAL HIGH POTENTIAL HIGH POTENTIAL
M/B M/C M/D Z LU MODERATE POTENTIAL MODERATE POTENTIAL MODERATE POTENTIAL
UNKNOWN LU CJ POTENTIAL L/B L/C L/D DC O tt> LOW POTENTIAL LU DC LOW LOW
O POTENTIAL POTENTIAL N/D
NO POTENTIAL
B C
LEVEL OF CERTAINTY
A. Available information is not adequate for determination of the level of mineral resource potential. B. Available information suggests the level of mineral resource potential. C. Available information gives a good indication of the level of mineral resource potential. D. Available information clearly defines the level of mineral resource potential.
Abstracted with minor modifications from:
Taylor, R. B., and Steven, T. A., 1983, Definition of mineral resource potential: Economic Geology, v. 78, no. 6, p. 1268-1270. Taylor, R. B., Stoneman, R. J., and Marsh, S. P., 1984, An assessment of the mineral resource potential of the San Isabel National Forest, south-central Colorado: U.S. Geological Survey Bulletin 1638, p. 40^2. Goudarzi, G. H., compiler, 1984, Guide to preparation of mineral survey reports on public lands: U.S. Geological Survey Open-File Report 84-0787, p. 7, 8.
D13 GEOLOGIC TIME CHART Terms and boundary ages used by the U.S. Geological Survey in this report
AGE ESTIMATES EON ERA PERIOD EPOCH OF BOUNDARIES (in Ma)
Holocene Quaternary - 0.010 Pleistocene - 1.7 Neogene Pliocene
Cenozoic Subperiod Miocene * » A Tertiary Oligocene Paleogene JO Eocene Subperiod *J\J Paleocene _ cc Late Cretaceous Early - 96 no Late 1 Mesozoic Jurassic Middle Early one Late Triassic Middle Early - ~240 Phanerozoic Late Permian Early 9QO Late Pennsylvanian Middle Carboniferous Early Periods oou Paleozoic Late Mississippian Early ocn Late Devonian Middle Early - 410 Late Silurian Middle Early d?Rtoo Late Ordovician Middle Early - 500 Late Cambrian Middle Early _ ^,~D/U C"7/"\1 Late Proterozoic . Qnn Proterozoic Middle Proterozoic - 1600 Early Proterozoic £*j\j\j Late Archean OUVJU Archean Middle Archean - 3400 Early Archean
-(3800?)- - _ pre -Arc;hean 2
'Rocks older than 570 Ma also called Precambrian, a time term without specific rank, informal time term without specific rank.
D14 TABLE 1. Mines, prospects, and deposits in and adjacent to theJacumba (In-ko-pah) Wilderness Study Area [*, outside study area] Map No. Workings and (fig. 2) Name Summary production ______Sample and resource data ______1* Mountain Spring Coarsely crystalline, white to gray lime- An open cut in limestone Two samples of limestone bed averaged limestone deposit stone in a 200-ft-wide, 2,500-ft-long about 70 ft across and 35 0.60 pet AljO^, 51.8 pet CaO, 0.14 pet steeply dipping tabular body, or screen ft high. Three small Fe2 02, 1-6 pet Mgo, less than 0.03 pet composed of metasedimentary rocks in tona- prospect pits in skarn ^25' atu' "*^ Pct ^ ' ^2" ^ne °^ two lite. Screen also contains biotite schist zones. A few hundred tons from skarn zones contained 0.08 pet W03 . and narrow pegmatite dikes along bedding. of limestone mined in Lens contains 210,000-ton indicated, Limestone forms 1,600-ft-long lens as 1940 and 1959 (Morton, 1977; subeconomic limestone resource, much as 30 ft thick that strikes p. 66). N. 65° W. and dips 45° SW. Limestone contains small inclusions of schist and some disseminated graphite. Irregular pods of garnet-epidote-quartz skarn along margins of limestone lens; pods are as much as 5 ft thick and 15 ft long.
2 Myer Valley Banded epidote-diopside-garnet skarn Three small prospect pits and Four samples of skarn contained no prospect along contacts between small marble and several bulldozer cuts. significant mineral values, schist screens and tonalite. Screens are as much as 240 ft long and 80 ft wide. Pegmatite dikes and sills common.
3 Unnamed prospect Irregular veins of coarsely crystalline One 4-ft-deep, 5-ft-square Veins are too impure and highly white calcite in deeply weathered pit along road. fractured to be calcite re- tonalite. Veins are as thick as 25 in. source; one sample contained no and strike N. 55° E., dipping steeply significant mineral values, northwest.
4 Chain prospect Quartz-garnet-diopside skarn is in biotite Four shallow pits in One of four samples of skarn contained schist and marble near contacts with skarn zones in area 0.01 pet WO^; remainder contained tonalite. Skarn in irregular, scat- 1,000 ft across. no significant mineral values, tered lenses as much as 300 ft across.
5 Unnamed prospect A garnet-quartz-diopside skarn zone lies A 37-ft-long inclined shaft Three samples from skarn zone along bedding in marble. Zone was driven S. 56° W. and contained no significant mineral exposed 40 ft downdip and as thick down at 37°. values. as 4 ft; parts heavily limonite- stained. Ultraviolet light disclosed no scheelite.
6* White Christmas Diatomite beds as much as 12 ft thick in The diatomite beds are ex- Samples of diatomite were collected by deposit (Bronko Quaternary (?) lake sediments. Diato- posed along stream-cut T. Loomis in 1965 for patent appli- claims) mite mixed with volcanic ash and with channels, and in several cation: 7 ft channel sample from sand- and silt-sized grains of quartz, pits and trenches. southern exposure contained 83.62 pet feldspar, and biotite. Diatomite beds rest Si02 - Clay in Quaternary alluvium on older alluvium, including fanglomerate also sampled by Loomis (1965, p. 5) and montmorillonite clay, and over- but found to be unsuitable for lain by unconsolidated sand. Beds drilling mud or sealing reservoirs flat-lying and exposed in two erosional because of poor gelling properties remnants. Northern exposure 150 ft and excessive sand content. Two long and as much as 60 ft wide; southern diatomite samples collected by exposure is 200 ft long and as much as 50 U.S. Bureau of Mines in 1983 revealed ft wide. high content of sand, silt, and broken tests, which limits use of material for most filter applications.
7* Stone quarry Intrusive rock of tonalite composition One opencut, several vats Claimants proposed to screen and wash has mantle of decomposed rock from for treatment of decomposed micaceous, decomposed intrusive rock to 0 to 5 ft thick. material. Apparently only remove coarse particles and sell material sufficient for biotite-chlorite-silt fines for use in testing was removed. drywall and paint industries. Expense of treatment would greatly exceed value of product (Loomis, 1965, p. 4). No samples were taken.
o_JL O1 o o>_JL TABLE 1. Mines, prospects, and deposits in and adjacent to the Jacumba (In-ko-pah) Wilderness Study Area-Continued
Map No. Workings and (fig. 2) Summary production Sample and resource data Fracture zone in volcanic mudflow debris None (prospect shown on One chip sample contained no significant strikes N. 15° E. and dips 60° NW. In-ko-pah Gorge 1:24,000 mineral values. sheet not found. Fracture zone at location was sampled).
Unnamed prospect Fragments of chalcedony and common opal One pit and one 3-ft-wide, One chip sample contained no significant in andesite tuff breccia. 10-ft-long, 1.5-ft-deep mineral values. trench.
10 Easy Pickins Area of unconsolidated Quaternary allu One 15-ft-deep shaft, caved No minerals of economic value were found; prospect vium, mainly sandy gravel, listed as no samples were collected. gold prospect by Morton (1977, p. 51).
White Hope lime- Two parallel beds of coarse-grained white One small opencut Four samples collected from western expo stone deposit gray limestone strike N. 10°- 35° W. and sure averaged 0.30 pet A12 03 , 54.5 pet dip 35°-55° SW. along foliation in CaO, 0.10 pet Fe2 03 , 0.76 pet MgO, gneissic tonalite. One bed 8 to 21 less than 0.02 pet P2 05 , and 2 ' 8 pct ft thick, averaging about 14 ft, and SiO, Western bed contains 175,000- exposed along strike for about 1,500 ft. ton indicated limestone resource; Second bed 300 to 400 ft to the east, eastern bed inferred to contain 170,000- about 20 ft thick, and exposed for ton inferred limestone resource. 1,000 ft along strike. Limestone contains sparsely disseminated graphite. Granitic sills intrude limestone in places and follow segments of beds.
Red Schist Intensely sheared and folded biotite Seven chip samples of schist, prospect schist pervasively hematite-stained. pegmatite dikes, and quartz Schist bounded on south and west veins contained no minerals of by tonalite and overlain by andesitic economic significance. One volcanic rocks and alluvium on stream sediment sample contained north and east. Schist contains bands 0.00046 oz/yd3 gold in minus-20- of marble and veins of quartz. Pegmatite mesh flakes. dikes to 10 in. thick contain coarse garnet, apatite, and sphene crystals.
Weaver deposit Vesicular, deeply weathered, dark-gray A small production of roof Although possible source of decora basalt exposed at the mouth of a dry ing granules during the tive gravel, degree of weathering wash. 1950's (Morton, 1977, and proximity of more suitable mate p 84). Several bulldozer rial 8 mi north in the Coyote Mountains cuts, and opencut about (Morton, 1977, p. 83) make development 130 ft square and 12 ft of deposit unlikely. deep
14 Hematite prospect A 2-ft-thick, hematitic quartz vein ex Two prospect pits: one on Two chip samples of quartz and one of tends for 22 ft along shear zone in quartz vein, one on weathered pegmatite contained no signif chloritic schist; it strikes N. 58° W. weathered pegmatite dike. icant mineral values. A sample of clay and dips 14° SW. Isolated quartz lenses bed had 13.3 pct A12 03 , 4.8 pct CaO, contain blebs of chalcopyrite. An 8-ft- 4.3 pct Fe2 03 , 2.4 pct K2 0, 3.4 pct MgO, thick bed of montmorillonite-rich clay 1.1 pct Na2 0, 0.038 pct P 2 05 , and underlies fanglomerate in area. 60.5 pct Si02 .
15 Unnamed prospect Quartz-garnet-actinolite skarn zones fol Two small prospect pits One grab sample of actinolite-rich skarn low bedding in interlayered quartzite contained 0.19 pct WO,. A chip sample and biotite schist. Strike about of one skarn zone (2.6 ft thick) con N. 15° W., dip 30°-60° NE (Morton, tained 0.01 pct W03 . 1977, p. 97). TABLE 1. Mines, prospects, and deposits in and adjacent to the Jacumba (In-ko-pah) Wilderness Study Area-Continued
Map No. Workings and (fig. 2) Name Summary production Sample and resource data
16 Unnamed prospect An 18-in.-thick marble bed in biotite A 44-ft-long incline (25°) Two chip samples of skarn from incline schist contains weakly developed (20 ft underground) was and grab sample of limonitic schist quartz-diopside-garnet skarn zone. driven S. 61° W. A 10- from site of vertical shaft contained Ultraviolet light disclosed no scheelite. ft-deep vertical shaft 800 no significant mineral values. ft southwest of incline (Morton, 1977, p. 96) has apparently been filled.
17 Unnamed prospect A limonitic pegmatite dike in biotite- One caved adit about 15 ft One sample of pegmatite contained no muscovite schist strikes N. 20° W. and long. significant mineral values, dips 35° SW.
18 Unnamed prospect Fine- to medium-grained diopside-tremolite- Southern working con- Four chip samples of skarn and quartz-rich garnet skarn in zones along contacts sists of 61-ft-long, pegmatite contained less than 0.01 pet where tonalite intrudes thinly laminated curved trench as much as WO.,. Scheelite-bearing skarn in samples limestone and biotite schist. Irregular 8 ft deep, at crest of from north and south workings, selected by quartz-tourmaline pegmatite dikes transect isolated knob. Northern use of ultraviolet light, contained 0.43 schist and skarn. Scheelite disseminated working, about 1,100 ft and 1.46 pet WO.,, respectively. No in skarn zones and in blebs as much as N. 18° W. from trench is samples contained detectable gold or 0.5 in. across and in stringers as 25-ft-long incline driven silver, much as 0.25 in. thick and 3 in. long. S. 80° W. Scheelite-bearing skarn zone at southern working exposed for about 65 ft in northerly direction and averages about 4 ft wide. Scheelite found in one apparently isolated, 2-ft-long pod at northern working.
19 Unnamed prospect Hematitic biotite schist has narrow dikes of One 5-ft-diameter, 2-ft-deep One chip sample from zone contained biotite tonalite along foliation. pit. no significant mineral values.
20 Golden Alter Two quartz veins strike N. 30° to 65° W. Eight pits and two shafts, Five chip samples from quartz veins prospect in gneissic tonalite and biotite 14 and 15 ft deep, on contained no significnt mineral values, schist; dip 65° NE to vertical. One quartz veins. One A select sample from manganese-rich vein exposed intermittently for 1,800 pit in tonalite. pod had 11 pet manganese and 0.051 pet ft and averages 3.4 ft thick; other Jeep trails and bulldozer zinc 50 ft long and 1 .4 ft thick. Both cuts lead to most workings, stained in places by iron and manganese oxides.
21 Unnamed prospect Narrow stringers of siliceous hematite One 6-ft-deep, 3-ft-square One chip sample from hematitic along biotite schist-pegmatite pit. contact zone contained 0.026 ppm gold, contact. Strike is N. 80° E., dip is 45° NW.
22 Roark mine A limestone lens at main shaft poorly A 30-ft-deep vertical A chip sample of quartz-garnet skarn (Graphite claim) exposed but at least 25 ft thick; it shaft has 80 ft of hori- in prospect pit contained 0.07 pet WO^. strikes N. 60° W. and dips 55° SW; a zontal workings at Chip sample of pegmatite from other weakly silicated zone in lens contains 30-ft level (Morton, 1977, pit contained no significant mineral disseminated scheelite (Morton, 1977, p. 96). Two prospect pits values. A grab sample from near shaft, p. 96). A 5- to 10-ft-thick felsic dike southeast of shaft. of gray, medium-grained limestone with forms footwall of bed and schist forms some diopside-quartz skarn contained hanging wall. Tonalite crops out nearby, 0.29 pet WO^. and biotite-tourmaline pegmatite dikes transect both metasedimentary and intru sive rocks. Scheelite sparsely dissemi nated in quartz-garnet skarn zone in interlayered limestone and biotite schist 600 ft southeast of shaft. o 00 TABLE 1. Mines, prospects, and deposits in and adjacent to the Jacumba (In-ko-pah) Wilderness Study Area-Continued
Map No. Workings and (fig. 2) Summary production Sample and resource data North Star Interlayered limestone and biotite schist One 52-ft-long adit Twelve samples collected from workings prospect near contact with underlying tonalite mainly in biotite schist and outcrops. Four samples from adit have been altered to tremolite horn- and pegmatite dikes and nearby pits contained no signifi fels and, in places, to garnet-quartz- crosscuts manganese- cant mineral values. One chip sample diopside-calcite skarn. Subparallel bearing sheared zone. from 3.2-ft-thick skarn zone in pit foliation and banding in metasedi- Ten prospect pits are in above, and 600 ft north of, adit mentary rocks strike N. 20 to 55° W. and alluvium, marble, schist, contained 0.02 oz/ton gold and 1.66 pet dip 20 to 75° SW. Skarn zones are or tonalite. Skarn zones WOo. Two of three chip samples from irregular and controlled by host rock exposed in three pits. skarn zone in pits 1,300 ft west of adit composition and proximity to intrusive contained 0.01 pet W03 ; third had no rocks. Segments of six skarn zones no significant mineral values. No exposed in workings and outcrops are 0.7 mineral values were detected in four to 7 ft thick and as long as 60 ft. other samples from skarn zones, schist, Pegmatite dikes as thick as 6 ft transect and pegmatite northwest of adit. both metasedimentary and intrusive rocks. An 8-ft-thick sheared zone in schist is enriched in manganese oxides.
24 Cal-White lime Bedded, white to gray, medium to coarsely A 14-ft-high, 30-ft-wide Twelve samples taken across apparent stone deposit crystalline limestone intercalated opencut and two shallow bedding in three limestone exposures (Cal-White, Little with schistose metasedimentary rocks and trenches in limestone contained 0.12 to 1.7 pet A1 2 03 , 43.4 White, Kimberly, gneissic tonalite. Limestone occurs where road ends at to 55.9 pet CaO, 0.12 to 1.7 pet Fe2 03 , and Ray claims) in lenses of variable orientation, appar foot of range. 0.8 to 10.6 pet MgO, less than 0.02 to ently having been thinned in places by 0.27 pet P2 °5» and 1-0 to 14.6 pet folding. Graphite is disseminated in SiOo* Three exposures contain about 1.4 minor amounts through parts of lime million tons of indicated subeconomic stone. A distinct HnS odor is released limestone resources. from freshly broken rock. Chlorite and coarse hornblende hornfels bands sporadically included in limestone bodies near margins. One irregular body essentially continuous for 1,550 ft and ranges from 6 to 50 ft thick. Other lenses 100 to 300 ft long and 16 to 30 ft thick.
25 Unnamed prospect Chloritic, limonite-stained tonalite con Sloughed pit(?) One chip sample from across limonitic zone tains veinlets of calcite. contained no significant mineral values.
PK mine (Elliott An irregular, tungsten-bearing skarn body Scheelite-bearing skarn Of 23 chip samples from skarn zone, 15 con mine) in small roof pendant in tonalite. Roof exposed in four adits with tained 0.01 to 0.91 pet W03 , and 11 con pendant 350 ft long and 300 ft wide and 108, 164, 169, and 253 ft tained a trace to 0.22 oz/ton gold. Two exposed along the crest of ridge. Pendant of workings. Stopes in select samples of scheelite-bearing skarn consists of biotite schist with thin beds three adits open to contained 0.75 pet and 1.84 pet WO,. One of interlayered limestone. Pegmatite surface. A fifth adit of three samples of tonalite contained dikes as much as 20 ft thick transect is 79 ft long entirely in 0.02 oz/ton gold and 0.1 oz/ton silver. both tonalite and rocks of roof pendant. tonalite. At least four Scheelite-bearing zone contains 30,000 Skarn consists of pyroxene (diopside), opencuts in roof pendant; tons of indicated subeconomic resources garnet (mainly adradite), and scheelite. largest is 40 ft in diameter with average grade of 0.19 pet W03 , Retrograde alteration and oxidation of and 25 ft deep. During including 9,000 ton block that contains skarn resulted in formation of epidote, 1954 and 1955, 1,950 tons 0.06 oz/ton gold. clinozoisite, tremolite, and hematite. of ore yielded 11,920 Ib W03 Scheelite both finely disseminated (596 short ton units). and in blebs to 1 in. across, concen trated in zone 200 ft long and about 30 ft wide.
''*« -vV^-i'-iS'-^ "^^K&t- H^fSsil^i; .- -'^»»**H*^.'