GEOLOGICAL SURVEY CIRCULAR 566 Tertiary Gold-Bearing Channel Gravel in Northern Nevada County, California Tertiary Gold-Bearing Channel Gravel in· Northern Nevada County, California By Donald W. Peterson, Warren E. Yeend Howard W .. Oliver, and Robert E. Mattick G E 0 l 0 G I C A l 5 U R V E Y C I R C U l A R 566 Washington 1968 United States Department of the Interior WALTER J. HICKEL, Secretary Geological Survey William T. Pecora, Director first printing 1968 Second printing 1968 Third printing 1970 Free on application to the U.S. Geological Survey, Washington, D.C. 20242 CONTENTS Page Page Abstract --------------- 1 Geophysical investigations of the channel Geology of the channel gravel, by gravel--Continued Donald W. Peterson and Warren E. Instrumentation and field procedures- -- 12 Yeend -------------- 1 Determination of bedrock configura- Introduction - -. ---- 1 tion -------- 12 Previous work ---- 2 Seismic method - 12 Acknowledgments -- 3 Gravity method -- 13 General geology- --- 3 Magnetic method ----- 13 Bedrock ------------ 3 Resistivity method 13 Auriferous gravel- -- 3 Electromagnetic method 13 Volcanic rocks --- 8 Induced-polarization method - 16 Colluvium- ---- 8 Detection of Tertiary channels under Tertiary channel near North Columbia -- 8 volcanic cover ---------- 17 Configuration of the channel ------ 9 Recognition and delineation of the ·- Grade and distribution of gold ----- 9 blue gravel ------------- 17 Geophysical investigations of the channel Location of concentrations of magnetic gravel, by Howard W. Oliver and minerals ---- ------ ·· - 19 Robert E. Mattick -- 11 Conclusions --- 19 Introduction ----- 11 References cited- -- 22 Acknowledgments- 12 ILLUSTRATIONS Page Figure L. Index map showing location of area studied --------- - - ----- - 2 2. Geologic map of part of area between the South and Middle Yuba Rivers ------ 4 3. Diagram showing inferred path followed by the Tertiary Yuba River --- 6 4. Diagrammatic section across an idealized Tertiary channel ------- 7 5. Detailed geologic map showing location of hydraulic pits and drill holes in the Tertiary gravel in the vicinity of North Columbia and Badger Hill- ------ 9 6. Subsurface contour map of bottom of channel near North Columbia as indicated by drill holes ---------------------------------- 10 7. Cross section of channel near North Columbia as indicated by one line of drill holes --------------------------------- 10 8. Contour map of the foot-assay product as indicated by drilling information 11 9. Seismic, resistivity, gravity, magnetic, and electromagnetic data and the interpreted geologic section along A-A' (figs. 2 and 5) and gold values --- 15 10. Resistivity soundings and interpreted layers at R 1 and R1 1 near profile A-A' (fig. 9) --------------------------------------- 16 1L. Geologic section, resistivity data, and seismic traveltimes along B-li' (fig. 2) - 18 12. Electromagnetic survey of Badger Hill diggings --------------------- 20 13. Magnetic, electromagnetic, induced-polarization, and geologic data along ..C.-.k' (figs. 2, 5, and 12), Badger Hill diggings ----------------------- 21 Ill Tertiary Gold-Bearing Channel Gravel in Northern Nevada County California By Donald W. Peterson, Warren E: Yeend, Howard W. Oliver and Robert E. Mattick Abstract delineate concentrations of magnetic material. The us:-fulness of resistivity methods appears from this study to be quite restricted The remains of a huge Tertiary gravel-filled channel lie in the because of irregular topography and the variable conductivity of area between the South and i\tiddle Yuba Rivers m northern Nevada layers within the gravel. County, Calif. The deposits in this channel were the site of some of the most producnve hydraulic gold mines m Calif(!rnia between the GEOLOGY OF THE CHANNEL GRAVEL 1850's and 1884. By Donald W. Peterson and Warren E. Yeend The gravel occupies a major ·channel and parts of several tributaries that in Tertiary tlme cut into a surface of Paleozoic and Mesozoic 1gneous and metamorphic rocks. The gravel is partly INTRODUCTION covered by the remains of an extensive sheet of volcanic rocks, but it crops out along the broad crest of the r 1dge between the canyons Some of the largest and most productive mines in of the South and Middle Yuba Rivers. The lower parts of the gravel deposits generally carry the h1ghest values of placer gold. Tradi­ California operated in the Tertiary gold-bearing tionally. the richest deposits of all are found in the so-called blue gravels between the South and Middle Yuba Piver s, gravel, which, when present, lies just above the bedrock and con­ Nevada County, Calif. These mines were in coeration sists of a very coarse, poorly sorted mixture of cobbles, pebbles, from the late 1850's until 1884, when a court decision sand, and clay. It is unoxidized, and, at least locally. contains appreciable quantities of secondary sulfide minerals, chiefly halted the dumping of debris into streams tributary to pynte. the Sacramento and San Joaquin Rivers. Thereafter, Information in drill logs from private sources indicates that a small hydraulic mines operated sporadically, and the 2 -mile stretch of the channel near North Columbia contains over high-grade deposits just above bedrock were mined half a ~illion ounces of gold dispersed through about 22 million locally by underground methods, but product:on from cubic yards of gravel at a grade averaging about 81 cents per the gravels never again reached the pre-18134 level. cubic yard. The deposit is buried. at depths ranging from 100 to 400 feet. The region is being studied to learn the extent of Several geophysical methods have been tested for their feasibility possible gold deposits remaining in plac~ and to in determming the configuration of the buried bedrock surface, in develop methods for establishing the location and size delineating channel gravel buried under volcanic rocks, and in of gravel deposits that may lie undiscovered beneath identifying concentrations of heavy minerals within the gravel. younger rocks. This report is preliminary an·i briefly Although the data have not yet been completely processed, pre­ liminary conclusions indicate that some methods may be quite use­ summarizes the results of current geological and geo­ ful. A combination of seismic-refraction and gravity methods was physical studies of the gravels in the area shown in used to determine the depth and configuration of the bottom of the figure 1. The work was done as part of tl·~ Heavy channel to an accuracy within 10 percent as checked by the drill Metals program of the U.S. Geological Survey. holes. Seismic-refraction methods have identified depressions which are in the bedrock surface, below volcanic rocks, and which One particularly attractive area, long recognized may be occupied by gravels. Seismic methods, however, cannot as representing a large, only partly exploited block of actually recognize the presence of low-velocity gravels beneath the higher v e 1o city volcanic rocks. Electromagnetic methods, ground, lies between North Columbia and Bacqer Hill supplemented in part by induced-polarization methods, show (Lindgren, 1911, p. 139; MacBoyle, 1919, p .. 48, 50, promise of being able to recognize and trace blue gravel buried 100; Haley, 1923, p. 118; Averill, 1946, p. 266-267). less than 200 feet deep. A broad vague magnetic anomaly across Drilling records in the files of the property owners the channel suggests that more prec1se magnetic studies might Figure 1.--Index map of part of northern California showing location of report area (shaded). indicate that a 2-mile stretch of channel within this reports draw heavily on Lindgren for much of their block· contains a placer deposit of over half a million basic in formation. The area covered b? this report is ounces of gold dispersed through about 22 million cubic inc 1 u de d in maps by Lindgren and Turner (1895), yards of gravel at a grade that averages about 81 cents Lindgren (1900), and Burnett and Jennin-;s (1962). Sum­ per cubic yard. This deposit is bur i e d at depths of maries of local information on the gravels and the from 100 to 400 feet by gravels containing gold values mines in Nevada County are given by Mac Boyle ( 1919) of just a few cents a yard.!/ and Logan (1941, p. 431-436). General information on the geology of the Tertiary gravels and their exploita­ Previous Work tion is given by Haley (1923), Averill (1946), and Jenkins ( 1946). Jarman ( 1927) reports on the feasibility The classic geologic studies of the Tertiary gravels of resuming hydraulic mining and citef' figures on re­ of the Sierra Nevada are those by Whitney (1880) and serves. An excellent brief summary of the Tertiary Lindgren (1911); most of the subsequent published channels is given by Clark ( 1965). A sum m a r y of the geology of the Sierra Nevada by Bat~man and :!./ \11 values cited in this report are based on a price of $35 Wahrhaftig (1966) provides a compreh.>nsive discus­ per ounce for gold. sion of the geologic framework of the Tertiary gravel.· 2 Acknowledgments morphic rocks and brings serpentine into contact with them. The volcanic rocks capping the ridge, however. The interest and cooperation of property owners are not offset by the fault (fig. 2). throughout the area are gratefully acknowledged. The San Juan Gold Co., D. R. Schiffner, Harold Helland, Auriferous Gravel M. J. Meredith, the Coughlan brothers, Herbert Jeffries, C. R. Echlin, and E. J. Colley have granted Gravel deposited by a major river system crops out access to their lands and operations and have offered on the divide between the Middle and South Yuba Rivers valuable suggestions and information. Special thanks and is p e r'c he d 500 to 1,000 feet above the present are extended to the San Juan Gold Co. for permission major streams. Although large sections of the old river to exam in e and use information in their files. The channel have been removed by erosion, the path of the California State Division of Beaches and Parks, the ancient river can be reconstructed with reasonable California State ivision of Forestry, and the U.S.