Geology and Geochemistry of 

Gold Deposits of the Big Canyon Area, 

El Dorado County, California 
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Geology and Geochemistry of 

Gold Deposits of the Big Canyon Area, 

El Dorado County, California 

By J. THOMAS NASH 

Description of geology and geochemistry 

of two types of lode gold deposits in 

metamorphic rocks and their similarities 

to nearby Mother Lode deposits 

U.S. GEOLOGICAL SURVEY BULLETIN 1854 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1988 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

Any use of trade names in this report is for descriptive purposes only and does 

not imply endorsement by the U.S. Geological Survey. 

Library of Congress Cataloging-in-Publication Data 

Nash, J. Thomas (John Thomas), ~94~-

Geology and geochemistry of gold deposits of the Big Canyon Area, El 

Dorado County, California. 

(U.S. Geological Survey bulletin ; ~854) 

Supt. of Docs. no.: I ~9.3:~854 

~. Gold ores-California-EI Dorado County. 2. Geology, 

Stratigraphic-Paleozoic. 3. Geology-California-EI Dorado 

County. 4. Geochemistry-California-EI Dorado County. I. Title. II. Series. 

QE75.B9 no. 1854 557.3 s [553.4'1'0979441] 88-600239 

[QE390.2. G65] 
CONTENTS 

Abstract 1 

Introduction 1 

Methods of study 2 

Acknowledgments 2 

Mining history 2 

Geologic setting 4 

Geology of the Big Canyon area 6 

Gold deposits 6 

Petrology and geochemistry of host rocks 8 

Big Canyon-type deposits 8 

Vandalia-type deposits 10 

Problematic alteration in the Vandalia sequence 14 

Ore petrology 14 

Minor-element geochemistry 17 

Discussion 19 

Big Canyon-type deposits 19 

Character of deposits 19 

Comparison with other gold deposits 19 

Exploration significance 20 

Vandalia-type deposits 20 

Character of deposits 20 

Comparison with other gold deposits 20 

Exploration significance 21 

Geochemical processes 21 

Conclusions 22 

References cited 23 

Appendix I. Description of chemically analyzed rock samples 26 

Appendix II. Methods and results of geochemical analyses 29 

FIGURES 

1. Map showing tectonic belts in the Sierra Nevada foothills and location of the 

Big Canyon mining area 3 

2. Map showing generalized geology and location of drill holes, Big Canyon 

area 5 

3-5. Photomicrographs of: 

3. Altered mafic rocks, Big Canyon area 10 

4. Metachert and alteration in metachert U 

5. Gold associated with pyrite 15 

Contents Ill 
TABLES 

1. Statistical summary of major-element chemistry of metamafic rocks and 

metachert, Big Canyon area 9 

2. Chemical changes in alteration of mafic rocks 12 

3. Statistical summary of minor-element chemistry of altered rocks, Big Canyon 

area 18 

4. Analytical results for samples from the Big Canyon area 30 

5. Lower limits of determination in geochemical analyses 40 

METRIC CONVERSION FACTORS 

For readers who wish to convert measurements from the metric system of units to U.S. customary 

units, the conversion factors are listed below. 

Metric unit 

micrometer (J.~.m) 

millimeter (mm) 

centimeter (em) 

meter (m) 

kilometer (km) 

degree Celsius ec) 

IV Contents 

Multiply by 

3.937x 10-5 

3.937X 10-2 

3.937 X 10-1 

3.281 

6.214 X 10-1 

[degree Fahrenheit eF)-32]/1.8 

To obtain U.S. customary unit 

inch 

inch 

inch 

foot 

mile 
Geology and Geochemistry of 

Gold Deposits of the Big Canyon Area, 

El Dorado County, California 

J. Thomas Nash 

Abstract 

Gold deposits in metamorphosed Phanerozoic rocks of 

the Big Canyon area, El Dorado County, California, yielded 

more than $3 million worth of ore prior to 1940. The deposits 

are in metamorphosed mafic extrusive and intrusive rocks, 

pyritic chert, and lean banded iron-formation of the Bear 

Mountains ophiolitic melange, just west of a major fault zone 

in Big Canyon that separates them from Upper Jurassic 

volcanic and clastic rocks that host the Mother Lode. The 

melange is a mostly chaotic assemblage of mafic volcanic 

rocks and mafic and ultramafic intrusive rocks, as well as 

metachert and banded iron-formation, of which the latter may 

have lateral continuity. These rocks were metamorphosed to 

greenschist grade in the Nevadan orogeny. Faults that 

influence the distribution of gold splay westward from the 

major fault, commonly with flat dips, and cut Upper Jurassic 

rocks. 

Gold deposits occur in two settings: (1) faulted and 

brecciated Paleozoic basaltic metatuff and metadiorite that 

have pyrite-carbonate-albite alteration and veining, as at the 

Big Canyon mine; and (2) weakly fractured, seemingly stratiform deposits in Paleozoic pyritic metachert and adjacent 

pyrite-carbonate-albite-altered balsaltic metatuff, as at the 

Vandalia mine. The Big Canyon mine was one of the largest 

lode gold mines in El Dorado County. Substantial marginal 

reserves of gold are indicated by drilling and workings at the 

Big Canyon mine and Live Oak prospect, and additional 

large inferred resources may occur in similar settings that 

display pyrite-carbonate-a! bite alteration along faults 

subsidiary to the Big Canyon fault. The Vandalia deposit may 

be unique in the Sierra Nevada foothills because comparable 

thicknesses of pyritic metachert have not been recognized 

elsewhere. 

The Big Canyon-type deposits contain multiple zones 

as much as 30 meters thick that are veined and flooded by 

pyrite-carbonate-albite, most of which contains more than 1 

gram per ton Au. These zones are enriched in Na, Ca, Mn, P, 

S, and C02 , as well as As, Sb, Se, Te, and rare-earth 

Manuscript approved for publication April 12, 1988. 

elements, but lack notable enrichment in Ag, Cu, Pb, or Zn. 

Gold-rich pyritic metachert at the Vandalia mine also is 

enriched in the same suite of major and minor elements 

found in the Big Canyon-type deposits; minor fractures in 

metachert appear to have allowed ingress of fluids that 

redistributed pyrite and caused carbonate and albite to form 

in thin bands along bedding. The gold in the Big Canyontype deposits is clearly related to structures that cut Upper 

Jurassic rocks, and the alteration cuts or overprints the 

prograde greenschist-facies (albite-epidote-actinolite) metamorphism. The pyritic metachert and associated lean 

banded iron-formation at the Vandalia mine probably originated as a volcanogenic exhalite; it could have contained 

gold as an original component, but more likely the gold was 

introduced along with other metals at the same time that the 

Big Canyon-type deposits formed. 

Gold deposits of both structural types in Big Canyon 

are interpreted to be of the same age and formed by similar 

processes; differences in form relate to physical properties of 

host rocks, behavior of the host rocks in postmetamorphic 

deformation, and different reactivity of the host rocks to 

hydrothermal fluids. In both settings, reactions of sulfur with 

iron silicate, carbonate, and oxide minerals seem to be a key 

to the deposition of gold. These sulfidation reactions may be 

indirect indicators of gold-depositing reactions or could be 

directly involved. The similarity of structural controls, alteration minerals, and geochemical signatures suggests that the 

Big Canyon deposits are similar to gold deposits of the 

Mother Lode and some deposits in Archean greenstone 

belts. By analogy to those well-studied world-class deposits, 

and from evidence at Big Canyon, the deposits are believed 

to have formed from alkaline, COz-rich fluids of moderate 

temperature (30Q-400 °C?) and pressure (1-2 kilobars?) of 

metamorphic origin. If the analogy to the Mother Lode 

deposits is apt, large volumes of mafic rocks in the melange 

zone along its bounding suture should be favorable for the 

development of gold deposits. 

INTRODUCTION 

The western foothills of the Sierra Nevada, particularly the Mother Lode zone, have been important 

Introduction 
producers of gold and other metals since the 1850's and 

are favorable for the occurrence of additional deposits 

and extensions of known deposits. The Big Canyon area 

(fig. 1 ), about 16 km southwest of Placerville and 7 km 

west of the Mother Lode belt, contains several gold 

deposits with substantial past production and indications 

of additional resources. This geochemical research was 

undertaken to contribute to the understanding of gold 

deposits in the area west of the famous Mother Lode belt 

and to determine possible similarities to the Mother 

Lode. Also, deposits of the two structural types in the Big 

Canyon area have similarities to world-class gold 

deposits in Archean greenstone belts elsewhere in the 

world, although those in El Dorado County are of 

Phanerozoic age and are not as highly metamorphosed or 

deformed. The gold deposits in metachert at the Vandalia mine resemble those recently discovered at Hemlo, 

Ontario, and seem to be one of the rare examples in the 

United States that might provide an analog for geochemical processes that may have formed the giant deposits at 

Hemlo. This report does not provide a complete 

explanation for the origin of these types of deposits, but 

the petrologic and geochemical descriptions, and possibly 

the interpretations, should be helpful to workers 

concerned with evaluation of gold deposits in metamorphic rocks. 

In 1983, Gold Fields Mining Corp.1 examined the 

Big Canyon area and recognized a potential for both 

high-grade vein deposits and bulk-minable near-surface 

deposits. Surface exploration and drilling in the period 

1983-1985 intersected many zones with gold grades in 

the range of 3-7 g/t (grams per ton, the same as parts per 

million), but the drilling was not sufficiently close spaced 

to define a mining reserve (R. Ridler, Gold Fields Mining 

Corp., oral commun., 1985). Environmental opposition 

to openpit mining was a factor that caused Gold Fields 

Mining Corp. to stop its exploration program in 1985 

after drilling about 40 holes, most of which intercepted 

zones that contain more than 1 g/t Au. In 1986, an El 

Dorado County company acquired the Big Canyon and 

Vandalia properties and continued feasibility studies. 

METHODS OF STUDY 

Geologic studies by Gold Fields Mining Corp. 

(Osterberg and others, 1984), and about 12,000 m of drill 

core, provided an excellent starting point for geochemical 

studies of host rocks and ores, which commenced in May 

1985. This study is chiefly based on observations made on 

1

The use of industry or firm names in this report is for location 

purposes only and does not impute responsibility for any present or 

potential effects on the natural resources. 

drill core and on about 120 samples collected while 

logging core. A magnetic susceptibility meter was used to 

test drill core for the presence of magnetic minerals such 

as pyrrhotite and magnetite. Brief studies were made of 

surface geology, but it was felt that the rocks were too 

weathered for petrologic and chemical studies of primary 

features. Samples selected for chemical study were sawn 

from drill core; samples of about a quarter of the core 

were 0.3 m in length and weighed about 1 kg. A slice of 

the sample was retained for petrographic study. A total of 

82 samples were submitted for chemical analyses. The 

samples are described in Appendix I. Thin section~, most 

with polished surfaces, were prepared from 98 samples. 

Chemists of the U.S. Geological Survey utilized X-ray 

fluorescence (XRF), induction-coupled plasma spectrometry (ICP), and wet chemical methods for the 

analysis of more than 40 major, minor, and trace 

elements. The methods and results of analyses and limits 

of detection are explained in Appendix II. Transmittedand reflected-light microscopic study of the thin sections 

utilized high-power oil-immersion objectives to identify 

fine mineral grains and their paragenetic relations to 

gold. 

ACKNOWLEDGMENTS 

This project was greatly helped by the careful 

geologic work of Mark Osterberg, Jerry Willis, and John 

Zimmerman of Gold Fields Mining Corp., whose maps, 

drill logs, and assays guided my studies and suggested 

good samples for study. Rolland Ridler and Paul 

Mogensen of Gold Fields Mining Corp. discussed the Big 

Canyon project and provided useful information. Gold 

Fields Mining Corp. allowed me to collect samples of 

drill core as well as rock samples from surface exposures. 

George Wheeldon rescued drill core from the Big 

Canyon project when it was about to be dumped. California Division of Mines and Geology provided 

temporary storage of drill core and provided facilities for 

me to examine core. James Saunders helped with petrographic studies. Discussions and field trips with Tom 

Anderson and Ralph Loyd, California Division of Mines 

and Geology, and Robert Earhart, U.S. Geological 

Survey, clarified aspects of the geologic setting of the Big 

Canyon deposits, and Earhart provided his preliminary 

manuscript on geology of the area. Earhart and Roger 

Ashley provided very helpful reviews of the manuscript. 

MINING HISTORY 

The Big Canyon (or Oro Fino) and Vandalia 

deposits (fig. 2) were discovered in the early 1880's, and 

underground workings were soon developed (Logan, 

1938; Clark and Carlson, 1956). The Big Canyon mine 

2 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 
10 15 KILOMETERS 

10 MILES LOCATION OF 

MAP AREA 

Figure 1. Tectonic belts in the Sierra Nevada foothills and location of the Big Canyon mining area. Tectonic belts are from 

Clark (1976), Duffield and Sharp (1975), Saleeby (1982), Loyd and others (1983), and Wagner and others (1981). 

Mining History 3 
was one of the most productive lode gold mines in El 

Dorado County; it produced more than $3 million in gold 

during 1893-1901 and 1934-1940. The Vandalia mine, 

which had substantial underground workings, produced 

only small amounts of gold in 1888, 1900, and 1926-1928 

(Logan, 1938). The mines, which have not operated since 

1940, are not accessible, but useful information is 

reported by Logan (1938) and Clark and Carlson (1956). 

The Big Canyon mine had a 20-stamp mill prior to 1888 

and was particularly productive between 1893 and 1901, 

during which time 180,000 tons of ore yielded $720,000 

(Logan, 1938, p. 220). During that period mining 

reached the 500-ft level. The flatly dipping ore shoot had 

a maximum length of 450ft (137m) and a thickness of 

about 60ft (18m). From 1934 to 1940 the workings were 

extended deeper and along strike; the average dip of 

veins was about 35° E. and the strike was S. 2SO W. 

(Logan, 1938). The ores from high levels were successfully treated by amalgamation, but that was not effective 

on the deeper pyritic ores which were treated by 

flotation. On February 26, 1937, water from Big Canyon 

Creek flooded the mine. Later in 1937 an openpit was 

developed to reach ore below the 100-ft level. The Big 

Canyon mine was forced to close in 1940 by the War 

Production Board Limitation Order. 

Logan (1938, p. 220-221) described the wall rocks 

in the Big Canyon deposit as altered meta-andesite 

breccia with a 

dike of serpentine between it and the Calaveras 

(Carboniferous) hanging-wall rocks. On the west it 

merges with amphibolite schist... The good ore has 

been found to consist of about equal parts of albite, 

ankerite, and quartz, of which albite appears to be 

necessary, or at least highly favorable, for gold 

deposition. Rock of very similar appearance superficially, and provisionally termed quartzite, but lacking 

the albite, does not make good ore. J.M. Basham, 

superintendent, reports three periods of sulphide 

mineralization. The first is of arsenopyrite, the second 

of barren pyrite, and the third of auriferous pyrite. 

The Vandalia mine produced about 14 tons per day 

in 1888, but there are no records of much production in 

later years despite several attempts (Logan, 1938, p. 

254 ). The ore mined in 1888 was described by miners as 

"partly honeycombed quartz and partly very sulphuretted 

rock" (Logan, 1938, p. 254). According to Logan (1938, 

p. 254) 

the geology in general is similar to that of numerous 

sulfide deposits in the county in which amphibolite 

schist and the rocks interbedded with it have been 

silicified and impregnated with pyrite which is more or 

less auriferous. The oxidized, upper parts of the bodies 

rich in sulfide yielded the ore of early days. Two ore 

shoots 20 ft (6 m) thick and 50 ft (15 m) and 100 ft (30 

m) long, respectively, were reported. The lowest of the 

old ad its reached the fresh sulfide at the bottom of the 

oxidized zone, and this has evidently not yielded 

enough gold, so far as opened, to pay a profit. 

Quoting observations made in 1900, Clark and Carlson 

(1956, p. 428) reported that dimensions for the Vandalia 

orebodies were somewhat larger and that ore commonly 

cuts the schistosity of enclosing wall rocks. 

Although some of the terms and concepts of the 

early miners are not accepted today, their observations 

are still a pertinent framework for economic geology and 

geochemistry. 

GEOLOGIC SETTING 

The Big Canyon area is in the west -central foothills 

of the Sierra Nevada (fig. 1) in a structurally complex 

zone called the melange belt by Duffield and Sharp 

(1975) and renamed the Bear Mountains ophiolitic 

melange by Saleeby (1982); the simpler term, melange 

belt, will be used here. The Mother Lode belt with its 

productive gold deposits is about 7 km to the east (Loyd 

and others, 1983). The Mother Lode fault system, which 

is about 190 km in length (Knopf, 1929), coincides with 

or is near the Melones fault zone, a major north-trending 

suture. The Melones fault juxtaposes Paleozoic rocks 

intruded by Mesozoic granitic rocks of the Sierra Nevada 

batholith on the eastern side with Mesozoic metavolcanic 

and metasedimentary rocks on the western side. It was 

probably active in the Late Jurassic (Duffield and Sharp, 

1975). Geochronologic studies of Mother Lode mineralization (Bohlke and Kistler, 1986) yield K/Ar ages of 

about 110-125 Ma, or about 30 m.y. after the peak of 

magmatism and metamorphism of the Nevadan orogeny. 

The Mother Lode belt is composed of Upper Jurassic 

clastic and volcanic rocks. The western limit of the 

Mother Lode belt of Jurassic rocks is a north-trending 

high-angle fault of regional extent; the segment in Big 

Canyon is here termed the Big Canyon fault zone for its 

importance in localizing gold deposits at the Big Canyon 

mine and other prospects to the south. The western 

boundary of the melange belt is the Bear Mountains fault 

zone (Clark, 1964; Duffield and Sharp, 1975) about 7 km 

to the west of the Big Canyon mine. 

The melange belt has been described as a chaotic 

assemblage of highly faulted and sheared clastic, volcaniclastic, and mafic intrusive rocks and serpentinite (Duffield and Sharp, 1975). There are differences of opinion 

regarding the degree of tectonic disruption in the belt 

with many workers favoring multiple stages of dismemberment and tectonic emplacement of mixed blocks 

of diverse rock types during subduction and accretion 

(Saleeby, 1982; Landefeld and others, 1986; Earhart, 

4 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 
Base from U.S. Geological Survey 

Latrobe, 1949 

Photorevision as of 1973 

0.5 1 MILE 

0 5 1 KILOMETER 

EXPlANATION 

Jl Logtown Ridge Formation (Jurassic) bm Basaltic metatuff (Paleozoic) 

me Metachert and banded iron-forma- bs Black slate (age uncertain) 

tion (Paleozoic) ----Contact-Approximately located 

sp Serpentinite (Paleozoic)-Aitered 

ultramafic rocks 

----Fault-Dashed where uncertain 

e30 Drill hole 

Figure 2. Generalized geology and location of drill holes, Big Canyon area. Geology is simplified from 

Osterberg (1984). Most of the area west of the Big Canyon fault has very poor outcrops and is underlain chiefly 

by Paleozoic basaltic metatuff and altered ultramafic rocks. 

Geologic Setting 5 
1988). However, regional mapping of distinctive lithologies by Gold Fields Mining Corp. personnel suggests 

some units that can be traced for as much as 25 km on 

strike are not totally chaotic (M. Osterberg, Gold Fields 

Mining Corp., written commun., 1987). Local areas are 

coherent and have conformable layering, which suggests 

they are kilometer-sized "clasts" in a megabreccia. One 

possible large "clast" (Earhart, 1988) is locally important 

at the Vandalia mine and Mt. Aigare (fig. 2) where a 

coherent unit of predominantly cherty rocks is exposed 

over an area about 3 km long by 0.5 km wide and is about 

150 m thick according to drilling. An alternative interpretation is that the cherty sequence can be traced on 

strike and thus is not composed of exotic blocks (M. 

Osterberg, Gold Fields Mining Corp., written commun., · 

1987) rafted into place by submarine slides or accretionary tectonics. Mafic volcanic and intrusive rocks, 

which are most characteristic of the melange belt, have 

been interpreted as dismembered parts of an ophiolite 

sequence (Saleeby, 1982). The belt includes some of the 

oldest known rocks west of the Sierra Nevada batholith 

according to lead isotopic ages of 200-300 Ma (Saleeby, 

1982). The Pine Hill intrusive complex (Springer, 1980) 

intruded and metamorphosed the Bear Mountains ophiolitic melange; this complex provides an important age 

reference of 162 Ma (Saleeby, 1982). The Big Canyon 

area is at the intersection of several major structures; the 

major questions about structure and stratigraphy of both 

the regional and local settings of the gold deposits remain 

unanswered. 

GEOLOGY OF THE BIG CANYON AREA 

The geology of the area (fig. 2) is more complex 

than shown on published regional maps. Recent mapping 

(Osterberg and others, 1984; R. Earhart, written commun., 1987) has clarified the structure, but ambiguities 

remain because of very poor outcrop in key areas. No 

stratigraphy can be established in Paleozoic rocks of the 

area, and tops of bedded units generally are not known. 

Metamorphism to greenschist facies obscures some 

lithologic features but is not so intense or variable as to 

cause problems in recognition of units or in the interpretation of protolith. At least five generalized lithologic 

units can be used in mapping and in logging of drill core. 

Layered pyroclastic rocks of basaltic composition are 

most abundant in and near the deposits; these are now 

epidote-amphibole-quartz-albite± calcite rocks with 

layered or schistose fabrics that I will term basaltic 

metatuff. Light-colored, finely laminated metasedimentary rocks are common on the ridge from Vandalia mine 

to Mt. Aigare; these are chiefly metachert with variable 

amounts of pyrite, hematite, and magnetite along bedded 

layers. In most places the metachert contains less than 5 

percent iron minerals, but a few outcrops found by 

Earhart (1988) contain more than 15 percent hematite 

and magnetite, and those beds can be called banded 

iron-formation (BIF). Outside of the ore deposits mafic 

and ultramafic intrusive rocks are common; these rocks, 

which were peridotite and diorite, have been metamorphosed to serpentinite and amphibolite. Metamorphosed debris flows have been recognized by R. Earhart 

(written commun., 1986); they contain coarse fragments 

(about 10-50 em in size) of basaltic rocks, chert, and 

exotic metamorphic rock fragments. Black slate and 

argillite occur in fault slices within the Big Canyon fault 

zone (fig. 2); the age of this unit is not known. The area 

east of the Big Canyon fault (fig. 2) is underlain by 

weakly metamorphosed volcanic rocks of the Jurassic 

Logtown Ridge Formation (Duffield and Sharp, 1975), 

which is chiefly basaltic tuff, breccia, and flows. The Big 

Canyon fault zone and many other faults in the area 

contain highly sheared serpentinite that may have been 

mechanically intruded as a ductile rock. 

Most structures in the area must be inferred 

because they occur in areas of low relief with very poor 

outcrop. Drill-core information helps define the position 

of faults but is not good for defining attitudes or offset. 

Structures that juxtapose rock types, some of which 

control the distribution of gold, could be the sites of 

either major dislocations or possibly only small 

displacements. 

GOLD DEPOSITS 

Two structurally distinct types of gold deposits 

occur in the Big Canyon area. The Big Canyon type, best 

illustrated by the Big Canyon mine, is structurally 

controlled by numerous closely spaced fractures in the 

Big Canyon fault zone. Gold is consistently associated 

with zones of PCA (pyrite-carbonate-albite) alteration of 

mafic rocks and vein filling. Relations observable in the 

glory hole of the Big Canyon mine and in drill core 

indicate that the alteration zones and gold mineralization 

are in basaltic metatuff and metadiorite that are in fault 

contact with serpentinite, slate, and black argillite. The 

serpentinite and argillite, which are locally altered and 

chemically modified, contain only traces of gold; these 

rocks evidently were chemically or physically unfavorable 

for significant gold mineralization. Another area of PCA 

alteration in fractured mafic rocks occurs 2 km south of 

the Big Canyon mine at the Live Oak prospect (fig. 2) in 

an area that was drilled by Gold Fields Mining Corp. and 

found to contain many intercepts with more than 1 g/t 

Au. Excellent examples of PCA alteration and gold were 

recovered from drill core for this study. 

The second type of deposit, known at the Vandalia 

mine, occurs in pyritic metachert and to a lesser extent in 

altered basaltic metatuff. These stratified rocks are 

6 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 
folded and faulted, and some pyrite occurs on fractures, 

but the gold-pyrite mineralization appears to be stratiform-although "beds" of ore have not been traced 

laterally in mine workings or drill holes, and the bedded 

nature of the minerals in hand specimen does not prove 

that they formed syngenetically with the enclosing 

sediment. Gold Fields Mining Corp. personnel interpreted the ore-bearing strata at Vandalia to have been 

originally a chemical sediment or exhalite. There is 

abundant evidence in support of the exhalite concept, but 

as will be discussed later, there also is substantial 

evidence for epigenetic metasomatism of the type that is 

well developed at the Big Canyon mine. The geometry 

and wall rocks of the Vandalia and Big Canyon types of 

gold deposits are clearly different, but new geochemical 

and petrographic data suggest that the two types of gold 

ores are geochemically similar and most likely formed at 

the same time. 

Structure at the Big Canyon mine and Live Oak 

prospect is too complex to be illustrated here. A series of 

vertical and angle core holes were collared east of the 

gold deposits to test for mineralization in the Big Canyon 

fault zone and beneath the surface exposures. Most of 

the rock recovered in core from those holes is extremely 

fractured and sheared. Although the general distribution 

of units in Big Canyon suggests a high-angle fault (fig. 2), 

the structure is much more complex in detail and no 

logical cross sections can be drawn from information 

from holes that were drilled 100 m apart. The Big 

Canyon structure is a series of subparallel high-angle 

faults in a zone more than 100 m wide with branching 

low-angle faults that cut off blocks between the highangle faults. My impression from drill core is a chaotic 

jumble of blocks, each about 10--20 m wide (E-W) and 

deep and of uncertain length (N-S), with abundant 

internal shear. Blocks of slate, argillite, and serpentinite 

are most common on the eastern side of the fault zone. 

The metasediments and serpentinite on the eastern side 

are only rarely cut by PCA alteration, and only a few 

assays show any detectable gold (more than 0.1 ppm). On 

the western edge of the fault zone blocks of relatively 

coherent mafic rocks are encountered, and in the 

mineralized areas the mafic rocks tend to be bleached 

from dark green to tan and highly altered to PCA from 

the fault contact westward. For 100-200 m westward the 

mafic rocks are cut by fractures with prominent tan 

alteration selvedges. One of the mineralized units at the 

Live Oak prospect is a brecciated metadiorite; the 

geometry of the intrusive contact is not known, but it is 

clear that the diorite was brecciated prior to alteration. I 

saw no metachert in drill holes from the Big Canyon-type 

deposits. 

All gold mineralization in the Big Canyon and Live 

Oak deposits is associated with fracture filling and wallrock alteration, which consists of tan carbonate and albite 

with 2-10 percent pyrite. Megascopically the pyrite, tan 

color, and hardness are obvious, as are late-stage lightcolored carbonate veinlets that effervesce violently in 

dilute acid. However, the albite and noneffervescing 

carbonate (ankerite) replacement are not easily distinguished megascopically from silicic alteration. The 

association of gold and pyrite with albite and ankerite 

rather than with quartz is clearly seen in thin sections. 

Structural style in the Vandalia gold deposit is 

much different from that of the Big Canyon-type 

deposits. The layered rocks are folded, probably twice, 

and fractured, but faults are not a major feature. Drilling 

density is not sufficient to document the likely continuity 

of pyritic layers at deposit scale, but outcrop features do 

suggest the continuity of some pyritic layers for hundreds 

of meters (Osterberg and others, 1984 ). There may be 

systematic facies variations in pyrite, hematite, and 

magnetite concentrations in the cherty sequence, as in 

iron formations elsewhere (James, 1954), but these have 

not been worked out. The major question about the 

structure and stratigraphy is the relationship of the cherty 

clastic rocks to basaltic metatuff. Earhart (1988) 

observed fault contacts between the two units in a few 

outcrops and inferred faults elsewhere as he reached the 

interpretation that the cherty sequence is a tectonic block 

in the melange. This may be correct, but some features 

revealed in drill core suggest other relations. All the drill 

holes in the northwestern part of the study area (fig. 2) 

intersect both metachert and basaltic metatuff, and in 11 

drill cores more than one cherty unit is intercepted. 

Layers of metachert 1-2 m thick appear to be conformable with enclosing basaltic metatuff in five drill 

holes; these layers occur 50--100 m below the thick 

metachert sequence. Bedding attitudes are consistent in 

both metachert and basaltic metatuff over distances of 

50-100m in many holes, and although basaltic metatuff 

is broken adjacent to metachert in some cores, a major 

fault is not indicated or required-the fractures seen in 

core could as well be explained by folding. Petrographic 

and chemical analyses, which are described in the next 

section, reveal that the metachert and enclosing rocks 

have both been subjected to PCA alteration, and variable 

contents of Si, AI, and Ti suggest the possibility of mixing 

of tuffaceous and exhalative components during sedimentation. Also, both metachert and basaltic metatuff 

sequences are cut by similar diabase dikes, which are in 

turn subjected to PCA alteration. The metachert and 

basaltic metatuff were clearly contiguous prior to folding, 

metamorphism, and PCA alteration, regardless of how 

the units came together. The gold and pyrite could be 

syngenetic with the cherty exhalite and thus of Paleozoic 

age and much older than the Big Canyon-type gold 

mineralization, but this is not required by available 

structural evidence. 

Gold Deposits 7 
PETROLOGY AND GEOCHEMISTRY OF 

HOST ROCKS 

Big Canyon-Type Deposits 

Host rocks for gold deposits of the Big Canyon type 

were metamorphosed prior to ore emplacement, thus the 

first step in this study was to determine the composition 

of the metamorphic rocks. Metatuffs that are located 

more than 100 m from gold mineralization and considered to be unaffected by ore processes are medium 

green with millimeter-scale compositional layering that 

probably reflects original bedding because most of the~e 

rocks are not foliated (fig. 3A). The chief metamorphic 

minerals are epidote and amphibole, about 20-40 

volume percent each, along with lesser amounts of plagioclase and calcite and minor quartz. Epidote is present 

as stubby grains 100-200 ) llm in size, and amphibole is 

highly prismatic (5:1 to 10:1, length to width), in grains as 

long as 100-500 /lm, with yellow to green or yellow to 

blue-green pleochroism of actinolite or sodic actinolite. 

Calcite occurs in thin beds ( < 5 mm thick) in much of the 

basaltic metatuff; the carbonate is so widespread that it 

does not appear to be ore associated. Fine plagioclase 

(albite), generally less than 100 llm in size and 

untwinned, occurs between the epidote and actinolite in 

amounts as great as about 20 percent. Metamorphic 

albite is of finer grain size and more disseminated than 

albite that formed during ore-associated hydrothermal 

alteration. Hematite, which occurs in plates or elongate 

grains as long as 200 /lm, is a common accessory (1-3 

percent) as is sphene, which occurs in both coarse (300 

llm) subhedral grains and fine grains or aggregat~s ~f 

fine grains about 20 llm in size. A few percent of pynte IS 

present in some little altered metatuffs that are located 

more than 100 m from mineralized structures. 

Metadiorite occurs in drill core from the Big 

Canyon and Live Oak deposits. Metadiorite, which is 

similar in color to basaltic metatuff but is not layered, has 

distinctive plagioclase phenocrysts set in an aphanitic 

matrix, a texture that is retained by metamorphic 

minerals. Most of the metadiorite that I saw has a breccia 

texture with subangular fragments that generally are less 

than 2 em in size. Sphene in metadiorite is like that in 

basaltic metatuff: aggregates of 20-40-!lm micro granules 

that have no textural similarity to possible igneous Fe-Ti 

oxide minerals. 

Alteration associated in time and space with gold is 

essentially one type with variations in texture and mineral 

proportions (fig. 3B-H). Pyrite, carbonate, and albite are 

abundant in this alteration, hence I will call it "PCA". 

These minerals formed by metasomatic processes by 

which S, C02 , and Na were added to the rocks during 

both vein-filling and replacement reactions. This is mineralogically similar to propylitic alteration ~Meyer and 

Hemley, 1967), but in these rocks there IS ab~~dant 

textural and chemical evidence for major compositiOnal 

changes rather than weak hydrogen a~d ~arbonate me.t~­

somatism that usually is charactenstic of propyhtic 

alteration. The end product of most intense alteration is 

a granular tan albite-carbonate-pyrite rock with little 

resemblance to the prior rock other than content of Fe, 

Mg, AI, and Ti that have been recons~ituted in newly 

formed minerals. A generalized sequential development 

of the alteration is apparent in adjacent samples collected 

at about 1-m intervals outward from the zones richest in 

gold or at centimeter scale in narrow mineralized zon~s 

in which the entire sequence from tan to green rock IS 

present in a hand specimen. A first stage. that is. eviden~ in 

thin section (fig. 3C), but not megascop1cally, IS floodmg 

by microgranular 10- to 30-!lm albite with pyrite, sphe~e, 

apatite, and minor ankerite. Scattered coarser albite 

crystals in the microgranular matrix can produce a 

texture that resembles an albite porphyry (fig. 3G), but 

this probably is a metasomati~ porphy:oblast.. A la~er 

stage, which is probably gradational 111 time or 111tens1ty, 

has much more carbonate that fills veinlets and replaces 

matrix albite; this stage is generally acco~panied by 

coarser (100-300 llm) tabular crystals of albtte that are 

twinned (fig. 3H). Crystals of apatite are prese~t wit.h the 

albite. A third, and possibly much later stage, IS vemlets 

of carbonate that are distinctively white in hand specimen 

and effervesce strongly with dilute acid; these veinlets 

typically contain only coarsely crystalline calcite with no 

pyrite or albite. 

Fe-Mg silicates show the effects of progress.ive 

PCA alteration. During early or weak PCA alteration 

actinolite tends to be modified to a variety with bluish 

pleochroism that is qualitatively indicat~ve . of sodic 

composition (riebeckite molecule). Hematite IS present 

in many of these weakly altered rocks or in residual 

patches in which green color and prismatic amphibole 

texture are preserved. In later or more advanced stag~s 

of PCA alteration, actinolite can be pre~ent but .Is 

seemingly bleached to a nearly colorless vanety, an? I.n 

most everely altered rocks, which are most charactenstic 

of large volumes of PCA-gold mineralization, there. i~ no 

trace of the amphibole or its texture: no trace of ongmal 

rock texture survives (fig. 3£-G). In these more 

advanced stages of alteration hematite is not present. 

Epidote occurs in some of the PCA alterati~n, b~t only as 

fine ( < 40 llm) inclusions in albite. ~~1lonte wtth. darkgreen color in transmitted light (Fe nch) forms 111 n;o 

stages: (1) early, in peripheral, weakly altered zones (f1g. 

3B), where it tends to be replaced by later ~arbonate 

minerals; and (2) late, with veinlets of calc~te. ~arly 

chlorite might be a replacement of metamorpluc eptdote 

but does not replace amphibole. 

8 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 
Table 1. Statistical summary of major-element chemistry of metamafic rocks and metachert, Big Canyon area 

[All values in percent, except Au,which is in parts per million. Normative minerals computed from chemical analyses: Q, quartz; Ab, albite, Carb, 

carbonate] 

Variable Meta mafic rocks ~N =57~ 

Minimum Maximum Mean Deviation 

Si02 ................... 33.70 73.20 46.24 6.75 

Al20s ................ 2.04 20.10 12.73 2.81 

Fe20s ................ 3.00 17.16 5.82 2.29 

FeO ................... 1.65 9.43 3.20 1.25 

MgO .................. .13 10.60 5.01 2.29 

CaO ................... .05 15.00 7.86 3.84 

Na20 ................. 1.07 7.96 5.24 1.42 

K20 ................... .04 3.43 .58 .60 

H2o+ ............... .11 6.00 2.13 1.47 

Ti02 .................. .38 2.68 1.20 .50 

P20s .................. .06 1.45 .20 20 

MnO ................. .03 1.55 .25 .27 

C02 ................... .01 19.80 7.59 5.05 

Stotal .................. .01 11.80 2.60 2.60 

0 ........................ 0.0 48.11 5.47 10.65 

Ab ..................... 9.67 68.65 46.10 12.40 

Carb .................. .02 42.97 16.58 11.42 

Au ..................... .10 70.00 3.51 11.01 

Major-element chemistry (tables 1, 4) reflects the 

mafic character of the metamorphic rocks just described. 

These rocks are relatively rich in Fe, Mg, Ca, and 

Ti-generally similar to the composition of unmetamorphosed basaltic rocks. The best estimate of starting 

compositions, taken from 12 samples judged to have 

undergone little ore-associated metasomatism, suggests 

45-55 percent Si02, 13-18 percent Ah03, and 0.8-2.1 

percent Ti02 (all recomputed on a C02-H20-free basis), 

generally comparable to basalts (Le Maitre, 1976). 

Samples thought to be metamorphosed diorite or diabase 

have approximately the same composition as layered 

basaltic metatuff samples, certainly within the compositional variation caused by metamorphic and hydrothermal alteration. Hydrothermally altered rocks contain 

large amounts of Na, C02, and S; the percentages of 

normative albite and carbonate (the sum of normative 

calcite, magnesite, and siderite) range as high as 68 and 

43 percent, respectively. 

Titanium is useful as an indicator of rock parentage 

in cases of severely altered rocks with no relict minerals 

or textures. Altered rocks with more than 10 percent 

C02 tend to contain less than about 1.2 percent Ti02, 

compared to about 1.8-2.1 percent Ti02 in least altered 

mafic rocks. Most Ti resides in sphene, and some highly 

altered rocks contain rutile. Titanium probably has been 

reconstituted several times in these rocks. During 

regional metamorphism Ti migrated from sites in oxide 

and silicate minerals of igneous rocks to relatively coarse 

sphene greater than 100 JLm with subhedral form. Microgranular aggregates of sphene formed during PCA 

Metachert ~N = 24) 

Valid Minimum Maximum Mean Deviation Valid 

57 46.20 95.39 83.38 13.04 24 

57 .69 19.30 3.61 3.66 24 

57 .32 12.01 3.65 3.42 24 

57 .17 6.60 2.00 1.88 24 

57 .11 2.79 .90 .74 18 

57 .03 5.20 1.28 1.55 16 

57 .23 4.37 1.18 .96 23 

57 .04 .56 .25 .19 12 

57 .11 10.00 1.17 2.02 24 

57 .02 .94 .26 .25 24 

49 .05 .61 .25 .18 8 

56 .04 1.85 .58 .57 17 

55 .01 7.77 1.77 2.66 16 

54 .02 8.61 1.70 2.61 22 

57 31.91 93.63 75.15 17.51 22 

57 1.29 34.43 9.6 7.94 24 

57 .02 17.71 2.65 4.59 24 

40 .02 8.61 1.70 2.61 22 

alteration are nearly opaque; the individual crystals are 

less than 40 JLm. In advanced stages of PCA alteration 

fine sphene is disseminated between grains of albite. 

There is nothing in the texture of sphene to indicate that 

it replaces igneous Fe-Ti oxides. Evidently Ti has 

migrated short distances (micrometers to millimeters) 

within the altered rocks but, on a bulk scale, has 

remained approximately constant except for zones of 

intense carbonate alteration that seem to have lost Ti. 

Gold (determined by assay) is always associated 

with tan PeA-alteration zones. These zones are fracture 

controlled, but megascopic and microscopic features 

suggest they are mainly replaced rock rather than vein 

filling. A myriad of millimeter-scale veinlets at centimeter intervals form a stockwork that consists of about 

90 percent altered wall rock and 10 percent vein. The tan 

PCA zones are thick (commonly 5-30 m ), and commonly 

several PCA zones occur in a 100- to 200-m interval. Tan 

PCA zones are not everywhere enriched in Au, but in 

many drill holes gold assays for 0.3- and 0.6-m intervals 

of PCA are consistently greater than 1 glt, with scattered 

intercepts that are much higher (10-70 glt). According to 

corrc lation analysis (Davis, 1986) of the chemical data, 

gold correlates strongly with P, Fe, and Mn, but is 

indepenJcnt of Na, C02, and S. The computed 

independence of Au with Na, C02, and S expresses the 

fact that albite, carbonate, and pyrite abundances are not 

proportional to Au content, despite the observation that 

Au is always associated with these minerals. 

Petrology and Geochemistry of Host Rocks 9 
A, Layered, weakly altered actinolite-epidote-albite basaltic 

metatuff with scattered pyrite (black euhedral grains). 

Sample BC32-374, plane light. 

8, Incipient alteration along carbonate veinlet (cb); form of 

metamorphic minerals survives, but mafic minerals are 

replaced by chlorite. Sample BC27-206, plane light. 

Qualitative estimates of changes in major-element 

composition during PCA alteration of mafic rocks are 

shown in table 2. Ideally, chemical changes are computed 

with knowledge of some constant parameter, such as 

volume or an immobile element like AI or Ti. For these 

highly altered mafic rocks I am not willing to assume that 

any element has been immobile, and it is very difficult to 

estimate the volume change during alteration. The 

computed values in table 2 are only rough estimates 

because changes in volume have not been included. 

These rough computations suggest that (1) Si is 

approximately constant; (2) AI, total Fe, Mg, K, Ti, and 

H20 + are lost; and (3) Ca, Na, P, Mn, S, and C02 are 

added. These trends are in general agreement with 

inferences from chemical changes and petrography. 

C, Moderately altered basaltic metatuff; acicular grains of 

actinolite survive in matrix of albite (ab) and pyrite (py). 

Sample BC27-226, plane light. 

D, Highly altered basaltic metatuff; most of rock is albite (a b), 

but original character of rock is indicated by relict patches 

with acicular actinolite (right side) or strings of the fine 

sphene (left side, fine opaque grains). Sample BC16-101, 

plane light. 

Vandalia-Type Deposits 

Host rocks for Vandalia-type gold deposits are 

chiefly metachert, but some gold also occurs in adjacent 

basaltic metatuff. These rocks have been metamorphosed, and there is uncertainty as to whether gold 

was introduced before or after regional metamorphism. 

Recent near-surface oxidation has affected many of these 

rocks, most obviously producing clay and limonitic iron 

oxides. In many places gold values are high in fractured, 

oxidized zones, which suggests that there m~y have been 

some supergene enrichment of gold. Supergene 

oxidation also unlocked gold and permitted much easier 

recovery than from pyritic ores, which were not economic 

(Logan, 1938). basis. 

10 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 
E, Albite-carbonate rock formed from basaltic metatuff; 

clusters of sphene (opaque) give a clue to protolith. Sample 

BC32-341, transmitted light. 

F, Albite-carbonate rock formed from basaltic metatuff; lightcolored fine-grained rocks like this can resemble metachert 

in Vandalia sequence, but presence of abundant albite and 

sphene indicate that protolith of this rock was a basaltic tuff. 

Sample BC16-1 01, crossed polarizers. 

G, Albite alteration of basaltic metatuff with coarse and fine 

albite (ab); Fe-Mg silicates are destroyed. Sample 27-183, 

crossed polarizers. 

H, Albite alteration of basaltic metatuff in which early 

pervasive albite (ab), with disseminated pyrite, is very fine 

grained and cut by later coarse albite. Sample L07-86, 

crossed polarizers. 

Figure 3 (above and facing page). Photomicrographs of altered mafic rocks, Big Canyon area. All photomicrographs taken 

in transmitted light. 

Four facies can be distinguished in the metachert 

sequence: (1) chert, (2) pyritic chert, (3) chert with iron 

silicate, and ( 4) chert with iron oxides. The terminology 

of banded iron-formations (BIF) (James, 1954; Gross, 

1980) can be used for some of these facies as long as the 

prefix "lean" is used because only rarely do the rocks 

contain more than 15 percent iron. Most of the metachert 

sequence is white or tan and contains less than 5 percent 

iron; it was derived from a "clean" chemical sediment 

with more than 90 percent silica. A small quantity is dark 

red to black, produces a red streak, and contains a few 

percent of fibrous riebeckite along with hematite; this 

could be termed lean silicate BIF (compare James, 1954) 

because total iron content is only 5-10 percent. The lean 

silicate BIF contains local "kicks" in gold but is not a host 

for large amounts of gold by either grade or volume. 

Finely layered metachert with laminae of iron oxides is 

interbedded with white metachert and in a few places 

contains more than about 20 percent total iron, thus this 

metachert could be called BIF. The majority of the BIF 

or lean BIF in the vicinity of gold mineralization is 

nonmagnetic by magnet or magnetic susceptibility test on 

core and outcrop. However, magnetic BIF forms a 

sequence more than 9 m thick about 1 km south of the 

Vandalia mine (R. Earhart, written commun., 1987). The 

part of the metachert unit of most interest for gold is the 

chert facies, which probably is a facies that was enriched 

in pyrite during chemical sedimentation or diagenesis as 

Petrology and Geochemistry of Host Rocks 11 
Table 2. Chemical changes in alteration of mafic rocks 

[Major elements are recalculated to a volatile-free basis, based on 

average compositions from 12 least altered and 20 highly altered 

samples] 

Variable least altered Highly altered Percent 

(in percent) (in percent) change 

Si02 ........................ 49.60 49.57 0 

AI20s ..................... 15.88 12.51 -21 1

Fe20s .................... 10.30 9.26 -10 

MgO ....................... 7.49 4.92 -34 

CaO ........................ 8.38 10.94 +31 

Na20 ...................... 4.87 6.24 +28 

K20 ........................ 0.93 0.43 -48 

Ti02 ........................ 1.41 1.14 -19 

P20s ....................... 0.16 0.18 +12 

MnO ....................... 0.22 0.27 +23 

Stotat ........................ 0.73 4.92 +573 

2H2o+ ................... 3.41 1.04 -70 

2co2······················· 3.89 10.77 + 177 2

Au (in ppm) ........ 0.15 2.16 +1340 

1

Total iron expressed as Fe20s. 2

Not recalculated to volatile-free basis. 

postulated for pyritic BIF (James, 1954; and others). All 

these cherty rocks are finely laminated, and chert and 

pyrite layers are locally tightly folded in intraformational 

folds that seem to be soft-sediment features as might be 

produced in a sea-floor slump. No replacement or partial 

replacement textures involving pyrite and possible 

precursor sedimentary iron oxides have been seen. Tight 

narrow fractures coated by pyrite (or limonite after 

pyrite) are abundant, commonly about two or three per 

meter of core, and probably indicate remobilization of 

pyrite from earlier syngenetic sites. 

Carbonate iron-formation is commonly interbedded with other facies of iron formation (James, 1954; 

Gross, 1980), and many large gold deposits elsewhere are 

associated with layered Fe-Mg carbonate that was 

interpreted to have formed as a volcanogenic exhalite 

(Ridler, 1971; Hutchinson and others, 1971; Boyle, 

1979). All the large areas ofFe-Mg-carbonate rock in the 

Big Canyon area formed by alteration of mafic rocks; I 

saw no rocks that could be called carbonate ironformation or carbonate exhalite. 

Texture of the metacherts in thin section is 

distinctive. Quartz is the chief constituent and occurs in a 

tightly interlocked mosaic of 50-75 p.m grains (fig. 4A). 

There is little or no evidence for clastic grains of quartz in 

these siliceous metasedimentary rocks. Fine laminae of 

white micas are evidence of former thin layers of clay, 

and small amounts of fine epidote indicate a calcareous 

component in the sediment. Hematite is present as fine 

plates about 20-50 p.m long; fine sprays of riebeckite 

often radiate from the hematite. Titanium minerals such 

as sphene are rare to absent. The residence of about 1 

percent NazO is not obvious in these fine-grained rocks; 

it might be partly in white mica, but most is probably 

A, Typical finely layered pyritic metachert. Most of the pyrite 

is very fine grained and occurs along certain layers; some 

pyrite that is coarse grained reflects later hydrothermal or 

metamorphic processes. Carbonate (granular, high-relief 

grains) occurs in some layers. Sample BC2-132, plane light. 

8, Carbonate vein (cb) cuts layers in metachert, and 

scattered fine rhombs of carbonate form in chert next to vein. 

Dark layers are fine pyrite, epidote, and actinolite. Sample 

BC1 0-111, plane light. 

present as small grains of untwinned albite that have 

escaped notice. 

Identification of alteration in metacherts that is 

associated with gold mineralization is not straightforward 

because of the fine grain size of most minerals. Some vein 

and replacement textures that include carbonate, albite, 

and pyrite (fig. 4B-E) suggest a postmetamorphic stage 

of superimposed alteration. It is difficult or impossible to 

distinguish between metamorphic redistribution and 

postmetamorphic introduction of components. If the 

gold (or other elements) was deposited with pyrite early 

in the history of the chemical sediments, then it would 

have been present during metamorphism and postmetamorphic alteration. In this scenario gold would logically 

be recrystallized and possibly mobilized a short distance 

12 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 
C, Pyrite-carbonate-albite alteration (right side) recrystallizes 

layered metachert in a zone of fractures. This alteration is 

thought to be postmetamorphic. Sample BC1 0-113, crossed 

polarizers. 

D, Pyrite-carbonate-albite replaces metachert; the pyrite (py) 

is in fractures that are obvious in core, but the carbonate (cb) 

and albite (ab) are most clearly shown by chemical analyses 

and thin sections. Sample BC1 D-73, crossed polarizers. 

during metamorphism; this seems to have happened to 

pyrite (fig. 4A). Sodium and carbonate enrichment in 

metacherts is probably postmetamorphic, as suggested 

by textures of some samples (fig. 4C-D), thus might be 

considered to have been overprinted on earlier(?) gold. 

This cannot be proven or disproven by textural relations 

among the fine-grained minerals or by bulk chemical 

analyses that cannot discriminate among minerals of 

different ages. However, in later sections of this report it 

will be argued that structural evidence and geochemical 

associations are most consistent with postmetamorphic 

introduction of gold and other elements at the same time 

as in the nearby Big Canyon deposit. 

The major-element composition of 24 samples of 

mctachert (tables 1, 4) is consistent with the predominance of quartz in these rocks. Concentrations of 

E, Albite-altered rock, the protolith of which probably was a 

chert. Rock is rich in gold and pyrite; most of the latter is 

discordant to bedding and seemingly added along with 

albite. Sample BC1D-60, crossed polarizers. 

F, Albite-rich rock, the protolith of which probably was a 

basaltic tuff. Although this interval of core is finely laminated 

and very light in color (originally thought to be metachert like 

the rocks above it in core), the abundant fine sphene and 

rutile (opaque, seemingly along beds) and albite suggest 

that its protolith probably was a mafic volcanic rock. 

Chemical analyses show its composition is much closer to 

basalt than to chert. Sample BC1 Q-63, plane light. 

Figure 4 (above and facing page). Photomicrographs of 

metachert and alteration in metachert. All photomicrographs 

taken in transmitted light. 

Mg, Ca, K, and Ti generally are very low, but total iron 

(expressed as Fe203) ranges to more than 20 percent. 

Contents of Na and AI are higher than expected of 

"clean" metacherts; computed normative albite ranges as 

high as 34 percent and averages 9.6 percent. In most 

samples the amount of Na is close to that in stoichiometric balance with AI to make albite; this is interpreted to 

mean that during sodium metasomatism Na was 

deposited only to the extent that it could combine with AI 

Petrology and Geochemistry of Host Rocks 13 
already present in the metasedimentary rocks to form 

albite. Content of Au in the metachert samples correlates 

most strongly with AI, strongly with FeO and Fe20 3, and 

moderately with Ti, P, and S. 

Problematic Alteration in the Vandalia Sequence 

There are at least four lithogeochemical problems 

for rocks of the Vandalia sequence that bear on the 

question of the age and character of the Vandalia gold 

mineralization. These problems are: (1) the composition 

of beds that seem to represent sedimentary mixing of tuff 

and siliceous chemical sediment, (2) the enrichment of 

Al-Na-Ti in metacherts, (3) the textural and chemical 

evidence for postmetamorphic addition of carbonate and 

albite to metacherts, and ( 4) the sodic and carbonate 

alteration of diabase dikes in metachcrt. These problems 

can be reduced to two fundamental questions regarding 

(1) the relative ages and structural relations of chert and 

basaltic tuff and (2) the relative age and influence of 

carbonate-albite alteration on the metachert sequence. 

The metachert sequence is in fault contact with 

basaltic metatuff according to the interpretations of 

Earhart (1988), and there is substantial evidence for this. 

This relationship is consistent with the vastly different 

compositions of the two units and with the presence of 

fractures at the lithologic contact. However, relations in 

most of the 16 drill holes in the northwestern part of the 

study area (fig. 2) are not entirely consistent with this 

interpretation. All16 drill holes intersect both metachert 

and basaltic metatuff sequences, and most of the holes 

display alternating 1-3-m-thick layers that seem to 

represent interbedding because there are no breccias or 

changes in bedding attitudes suggestive of faults. Basaltic 

metatuff adjacent to the thick section of metachert is 

commonly fractured, but this seems to reflect deformation next to a rigid body during folding rather than the 

presence of a fault. PCA alteration is developed in both 

metachert and basaltic metatuff in the vicinity of some of 

these contacts (fig. 4E-F) as seen in thin sections, but this 

is not evident megascopically. However, it must be noted 

that there is a general problem that some faults are not 

prominent in drill core. In addition, diagenesis or 

metamorphism might have healed or obscured the faults, 

which would make them especially difficult to recognize 

m core. 

Some bedded rocks that were sampled for chemical 

analysis (about 0.3-m-long sections of core) have 

chemical compositions intermediate between normal 

metachert and balsaltic metatuff: Si02 is 55-80 percent, 

Ah03 is 2-10 percent, Na20 is about 2-5 percent, and 

Ti02 is greater than about 0.3 percent. In thin section 

these rocks have unusual textures that seem to be similar 

to metatuff in parts of the thin section and more like 

metachert a few millimeters away. The presence of high 

concentrations of AI and Ti in samples with the texture of 

a chemical sediment is hard to explain by any mechanism 

other than mixing with a tuffaceous component because 

AI and Ti seem to be quite immobile in epigenetic 

processes in these rocks and elsewhere. 

Fine-grained diabase dikes that cut metachert have 

major-element compositions that are generally similar to 

the basaltic metatuff, which would be logical if the dikes 

are roughly contemporaneous with the basaltic metatuff. 

Also, the dikes provide another time reference for 

alteration. They are strongly enriched in Na and COz, 

which I interpret as indicating that the alteration of the 

dikes occurred at the same time as the PCA alteration 

along the Big Canyon fault zone. 

Carbonate minerals vein the metachert sequence 

and PCA alteration is developed at many locations in 11 

of the 16 northwestern drill holes. Many of these PCA 

alteration zones contain anomalous Au, and in some 

intercepts the Au exceeds 1 g!t. The formation of gold 

mineralization of both Vandalia type and Big Canyon 

type less than 100 m apart vertically, as seen in drill holes 

4, 10, and 32, is most easily explained as one event. 

ORE PETROLOGY 

Opaque minerals were examined in fair detail in 

reflected light at magnifications from 40 x to 1,000 x to 

gain information on their identity and paragenesis. In 

most cases the ore minerals are very fine grained (less 

than 100 p.m) and disseminated in the rock matrix, thus 

the time of their formation is not as easily determined as 

for vein-filling minerals. 

Arsenopyrite.-Arsenopyrite is reported to occur 

with gold in the Big Canyon mine (Clark and Carlson, 

1956). Such an occurrence would seem likely in these 

ores, but it has not been confirmed in these petrographic 

studies. The shape and optical properties of arsenopyrite 

are similar to those of pyrite, and consequently arsenopyrite could have been missed. Concentrations of about 

1,000 ppm As, which are found in many rocks in this 

study, could produce just a few grains of arsenopyrite per 

thin section. Alternatively, the As could be in the pyrite 

lattice as demonstrated by microprobe studies of pyrite 

from Carlin-type gold deposits in Nevada (Wells and 

Mullins, 1973), but this may not be an appropriate analog 

for these deposits. 

Go/d.-Native gold has been identified in 26 

polished sections using reflected-light optical methods. 

About 50 grains have been identified with confidence 

(fig. 5), and an equal number were located although their 

sma11 grain size ( < 1 p.m) did not permit positive 

identification. Most of the identified gold grains are in 

PCA-altered mafic rocks (24 samples). Only two samples 

of metachert contained gold grains large enough to 

14 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 
permit reliable identification, but grains smaller than 1 

p.m and suspected to be gold were observed in several 

other samples of metachert. Pyrite was present in all the 

gold-bearing samples, but gold occurred as inclusions in 

pyrite in only three samples (fig. 5). Most gold that I 

recognized in reflected light occurs in the matrix between 

grains of albite or albite and carbonate. Based on microscopic features and correlation of gold assays and 

alteration, it is evident that gold occurs chiefly with 

albite-pyrite or albite-carbonate-pyrite flooding and 

veining of mafic rocks that are tan or medium gray. The 

texturally late calcite-chlorite veins do not appear to have 

much gold. The native gold in the PCA-altered mafic 

rocks is relatively coarse grained; most grains are 2-8 

p.m, but some are as coarse as 30 p.m. Some gold grains 

A, Gold (Au) with pyrite (py) and chalcopyrite (cp), enclosed 

in albite-carbonate gangue (black). Sample L0?-59. 

probably are less than 1 p.m, but their identity requires 

confirmation. 

Gold is difficult to locate in samples of metachert. 

Only a few grains larger than 2 p.m could be spotted; 

about 25 grains smaller than 1 p.m had color that was 

more yellow than pyrite, but these could have been 

chalcopyrite. Samples of metachert that contain microscopic gold and most samples of metachert with assays 

> 1 ppm Au have textural or chemical indications of 

added albite ± carbonate as well as pyrite and are 

enriched in the same trace elements as the PCA-altered 

mafic rocks. 

Hematite.-In this study the term hematite is 

reserved for hard, crystalline iron oxide with red internal 

8, Gold (Au) on grain boundary of pyrite (py), enclosed in 

albite-carbonate gangue. Sample L0?-59. 

C, Gold (Au) in pyrite (py), within albite-carbonate alteration 

of basaltic metatuff. Sample BC2s-167. 

Figure 5. Photomicrographs of gold associated with pyrite. Photomicrographs taken in reflected light with oil-immersion 

lenses. 

Ore Petrology 15 
reflections, thereby eliminating iron oxides in the 

weathered zone. In both metachert and metabasaltic 

rocks of this area hematite is generally tabular or platey 

in form and less than 100 p.m in length. In metacherts 

hematite is generally oriented with plates parallel to 

bedding, and fine needles of riebeckite commonly radiate 

from the hematite. The texture of hematite in metacherts 

is consistent with its formation as part of a chemical 

sediment, with only minor textural change in metamorphism. Hematite also occurs in amounts as great as 

about 1 percent in some of the less altered mafic igneous 

rocks. It appears to form along with epidote (a ferric iron 

mineral) and actinolite in regional metamorphism. 

Hematite is not present in most hydrothermally altered 

mafic rocks but is present in some local parts of thin 

sections that have retained much of their metamorphic 

texture, mineralogy, and green color. There is no 

evidence for partial replacement of hematite by pyrite, 

and pyrite does not mimic the platey form of hematite. 

Thus, in the hydrothermal alteration of mafic rocks of 

this area it appears that if hematite was produced in the 

rock by metamorphism it subsequently was dissolved and 

the iron was redistributed into hydrothermal sulfide, 

carbonate, or silicate minerals. 

Magnetite.-Magnctite generally is absent from 

these rocks but locally is abundant in magnetic BIF 

sequences south of the Vandalia mine. According to 

magnetic susceptibility measurements and petrographic 

studies, magnetite is not present in most of the metachert 

sequence near the Vandalia mine. Magnetite is present in 

a few samples of slightly altered metacliorite or metabasalt from the Big Canyon and Live Oak deposits. In those 

metamorphic rocks the magnetite is present as subhedral 

equant grains 50-100 p.m in size. A few of the grains abut 

pyrite, which suggests possible replacement by the 

sulfide, but most pyrite in these mafic rocks is coarser 

than the magnetite and does not show direct evidence of 

having replaced former magnetite. 

Sphene and 1utile.--Although not always considered to be "ore" minerals, sphene and rutile will be 

described here because they have been studied in detail 

as indicators of probable mafic rock precursors. 

Titanium in these rocks resides predominantly in sphene 

and rutile rather than in Fe-Mg silicates. Sphene formed 

during metamorphism, and it probably was redistributed 

during hydrothermal alteration. Most sphene is anhedral 

and very fine grained (less than 50 p.m). It is translucent 

to nearly opaque and is generally brown in transmitted 

light. In reflected light with high-magnification oilimmersion objectives, sphene has bright white to 

brownish-red internal reflections because of its high 

dispersion. In reflected light this sphene, which often 

looks like sugar, is very distinctive while making highmagnification scans for gold. At high magnification with 

reflected light most sphene is observed to be an 

aggregate of many microgranular crystals in an anhedral 

mass about 100-200 p.m in size. In a few metadiorites the 

sphene aggregates take on a boxwork form that 

resembles ilmenite lamellae in Fe-Ti oxides, but in most 

samples sphene has no specific morphology to suggest 

formation by replacement of a former Ti-bearing 

mineral. In highly altered rocks that are characterized by 

albite and carbonate, sphene tends to occur as 20-40-J,.t.m 

microgranular single or multiple grains in albite (fig. 3F) 

and locally as closely spaced grains that appear to be in a 

veinlet. In foliated rocks, sphene tends to be in clots or 

aggregates that line up on foliation; mechanical shear 

may have caused the tiny grains to aggregate. At high 

magnification, in which the microscope focuses inside the 

thin section rather than on its surface, tiny (less than 5 

p.m long) needles of a honey-colored mineral can be seen 

to grow from some sphene surfaces-the needles are 

thought to be rutile or anatase (Ti02 polymorphs). 

Sphene is present in small amounts in metacherts. 

Rutile is present in some highly altered mafic rocks 

where it can exceed sphene in abundance (1-3 percent). 

Rutile is honey colored in convergent transmitted light 

and is gray with medium reflectivity in reflected light. 

Where crystals are 100-200 J..t.m in size they are prismatic, 

and striations can be seen on the prism faces when 

observed with high-power oil-immersion objectives and 

reflected light. As mentioned above, some rutile seems to 

form from corroded sphene, but most is isolated in a 

silicate matrix and shows no textural indications of 

parentage. Rutile is supposedly rare in metamorphic 

rocks and possibly is formed only under conditions of 

unusually high C02 partial pressures (Schuiling and 

Vink, 1967). The textures of both rutile and sphene 

suggest that titanium has been mobile locally in these 

rocks during metamorphism and hydrothermal alteration, but near constancy of Ti02 contents for most 

altered rocks suggests that the titanium has not moved 

more than a few mi11imeters. 

Chalcopy1ite .-A characteristic feature of these 

ores is the low content of base-metal sulfide minerals. 

The only one that is observed in many samples is chalcopyrite, but it is never more than a trace constituent. 

Chalcopyrite occurs chiefly in altered mafic rocks as 

5-20-J,.t.m grains that at first glance (at 400 x magnification) resemble gold. Some chalcopyrite occurs as 

inclusions in pyrite. 

Pyn·hotite.-A tan sulfide occurs as small inclusions 

in the cores of pyrite. This phase is not as anisotropic as 

most pyrrhotite that I have studied from other deposits, 

but this estimate may be caused by the very small size 

( < 20 J..t.m) of these grains. Pyrrhotite is reported to occur 

in the Big Canyon deposit (Clark and Carlson, 1956), but 

from my research it does not appear to be abundant. The 

lack of magnetism in the sulfidic ores as measured by a 

16 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 
sensitive magnetic susceptibility meter also indicates 

little or no pyrrhotite is present. 

Pyrite.-Pyrite is an important mineral in these 

gold deposits as it constitutes a visual guide to potential 

gold zones. Pyrite is present in all rocks that contain gold 

at concentrations greater than about 0.1 ppm, except in 

the weathered zone where gold is associated with limonitic iron oxides derived from pyrite. The formation of 

pyrite is probably directly or indirectly involved in gold 

precipitation. 

Pyrite is present in metachert in amounts as great 

as about 10 percent. Pyrite in the metachert occurs both 

on bedding planes, as indicated by layers rich in other 

minerals such as riebeckite, epidote, or hematite, and on 

fractures. Perhaps the best evidence for a syngenetic or 

diagenetic origin for some pyrite is its occurrence in 

layers that are folded or swirled in intraformational 

structures that almost certainly formed while the 

sediment was unconsolidated. There is no textural 

evidence for pyrite replacing a sedimentary iron oxide in 

these swirled beds. Also, there is some regularity and 

predictability in the stratigraphic occurrence of pyritic 

metachert as mapped by Gold Fields Mining Corp. 

personnel (Osterberg and others, 1984), although threedimensional information from outcrop and drilling is not 

sufficiently detailed to permit reconstruction of likely 

facies changes that include pyrite, hematite, and 

magnetite in the chemical sediment. Because of the tiny 

grain size of gold that has been observed in metacherts, 

no reliable paragenetic relation can be defined for gold 

relative to pyrite; ambiguous relations can easily be 

attributed to very local mobilization during metamorphism or possible postmetamorphic processes. I 

assume that much of the sulfide in the metachert 

sequence was a product of diagenesis, and that some 

probably was remobilized into fractures. 

Pyrite also is widespread and abundant in mafic 

rocks other than serpentinite. Pyrite content is locally in 

excess of 10 percent in fractured and altered mafic rocks, 

but most commonly pyrite content is about 3-5 percent. 

Pyrite in the mafic rocks tends to be somewhat coarser 

than in the metacherts, with some grains in excess of 1 

mm, but grains finer than 100 J.Lm are not uncommon. 

Pyrite in these rocks is euhedral to subhedral. Pyrite 

grains coarser than about 200 J,Lm tend to have inclusions 

of silicate minerals, and the cores of some have tiny 

grains of a tan (in reflected light, oil immersion) mineral 

that resembles pyrrhotite. The grains of pyrite almost 

always are coarser than any magnetite or hematite seen 

in the mafic rocks, no pyrite has the form of the iron 

oxides, and no composite grains of pyrite plus iron oxide 

are seen-these features are evidence that pyrite does 

not form as a direct replacement of preexisting iron 

oxides in the mafic rocks. Pyrite is invariably accompanied by albite or carbonate in the mafic rocks, either 

flooding the rock or filling veinlets. Late calcite ± 

chlorite veinlets tend to have little pyrite. Some pyrite is 

weakly anisotropic, but the cause or significance of this 

for this occurrence is not known. 

MINOR-ELEMENT GEOCHEMISTRY 

Minor-element geochemistry of 82 samples is 

summarized in table 3. The most distinctive feature 

about the results of the minor-element geochemistry is 

the low content of base metals, such as Cu, Pb, and Zn, 

and the very low content of Ag, which was detected in 

only three samples (maximum concentration of34 ppm). 

Considering that most of the samples were picked as 

being mineralized with several percent of pyrite, a higher 

content of chalcophile elements might have been 

expected. The one very high concentration of Mo (14,000 

ppm) seems out of line and may reflect contamination by 

MoS2 in grease used on drilling equipment. Concentrations of the "mafic" suite of elements Co-Cr-Ni-Sc-V 

are quite high and seem to reflect the mafic character of 

the metamorphic host rocks, as will be described further 

in the next section. Arsenic is highly enriched in Aubearing samples. In general the minor-element composition of altered rocks from the Big Canyon and Vandalia 

deposits conforms to the pattern of enrichment in rare 

metals but not base metals that was described by Kerrich 

(1983) for Archean gold deposits of Canada. The rare 

elements and REE (rare-earth elements) emphasized by 

Kerrich are enriched with Au in these deposits as 

summarized in table 3. All results for Bi are < 10 ppm 

(lower limit of detection), and W could not be 

determined by the ICP method. Qualitative REE 

patterns (based on only five elements) for altered and 

Au-rich samples are flat with enrichments of about 

10-100 times chondrite values; similar patterns were 

reported by Kerrich (1983). 

Factor analysis (Davis, 1986) of the minor-element 

data for all 82 samples suggests some element 

associations: (1) rare-earth elements-Eu, Nd, Yb, Y, 

Ce, and La; (2) mafic group-Cr, Ti, Ni, Co, Sc, andY; 

(3) base-metal group 1-Mo, Pb, Hg, Sb, and Te; (4) 

base-metal group 2-Zn, V, Cu, Mn, Fe, S, and As; (5) 

P-Au with no other associated elements according to this 

analysis; (6) Ba-K, possibly asK-feldspar or white mica?; 

and (7) Se-As-S-of uncertain age and mineralogy. 

When major elements were included in a factor analysis, 

the group Ca-Sr-Na was indicated to be associated with 

C02, whereas Mg was indicated to be associated with the 

mafic group (2 above). There are many geologic, mineralogic, and age explanations of these statistical associations, but they are useful for directing attention to 

groups of elements in the large dataset. For instance, do 

the compositions of the two base-metal groups (3 and 4 

Minor-Element Geochemistry 17 
Table 3. Statistical summary of minor-element chemistry of altered rocks, Big Canyon 

area 

[All values in parts per million. ---, no data (none detected)] 

Variable Mafic rocks (n =57) 

Minimum Maximum Mean 

Ag ................ 2.0 34.0 12.4 

Au ................ .10 70.0 3.5 

As ................. .9 2700.0 409.5 

Ba ................. 8.0 6200.0 280.0 

Co ................ 2.0 100.0 40.2 

Cr ................. 8.0 800.0 251.3 

Cu ................ 5.0 630.0 77.5 

Ga ................ 10.0 37.0 20.0 

Hg ................ .02 6.3 .40 

Li .................. 2.0 59.0 18.6 

Mo ............... 2.0 14,000.0 988.6 

Ni ................. 14.0 390.0 157.3 

Pb ................. 4.0 570.0 56.6 

Sc ................. 9.0 50.0 28.6 

Sr .................. 10.0 680.0 235.7 

Sb ................. .1 69.0 3.8 

Se ................. .10 18.0 2.3 

Te ................. .02 22.0 .86 

v .................. 49.0 490.0 225.5 

Zn ................ 22.0 190.0 73.0 

Ce ................. 4.0 65.0 16.2 

Eu ................ 2.0 3.0 2.3 

Ho ................ 5.0 5.0 5.0 

La ................. 2.0 80.0 13.7 

Nd ................ 4.0 75.0 13.6 

Y .................. 4.0 50.0 16.3 

Yb ................ 1.0 4.0 2.0 

Th ................. 6.0 9.0 7.4 

above) indicate that there were two stages of sulfide 

deposition in time and space? This is not evident in the 

petrology of the deposits. 

The minor-element signatures of the two deposit 

types are different for elements that seem to reside in 

rock-forming minerals but similar for elements that are 

associated with Au. Keeping in mind the mafic character 

of the rocks in the Big Canyon-type deposits, it is not 

surprising that Ni, Co, Cr, V, and Sc have higher 

concentrations in those rocks, whereas La, Ce, Nd, and 

Eu have higher concentrations in the metachert suite of 

samples. The elements listed are statistically different 

between the two groups of samples and are reliable for 

distinguishing the two types of deposits when using a 

method termed "discriminant function analysis" (Davis, 

1986). The concentrations of Sr, Li, and Ga are 

significantly higher in the metamafic (Big Canyon) rocks 

and presumably reflect an association with aluminosilicates (albite). Concentrations of As, Hg, Sb, Se, and Te 

are not significantly different between the two groups of 

samples. Likewise chalcophile elements Cu, Pb, and Zn 

are not significantly different in the two groups. The fact 

that the content of probably ore associated "pathfinder" 

Metachert (n =25) 

Valid Minimum Maximum Mean Valid 

5 0 

40 0.1 9.0 1.8 7 

57 3.8 3300.0 469.9 25 

57 11.0 1200.0 262.7 25 

57 1.0 75.0 14.5 24 

57 4.0 210.0 28.6 25 

57 14.0 1000.0 135.9 25 

57 4.0 27.0 9.5 25 

54 .03 1.2 .29 23 

50 2.0 14.0 6.0 16 

18 2.0 480.0 70.8 9 

57 4.0 250.0 45.1 25 

13 4.0 43.0 12.8 16 

57 2.0 65.0 9.2 25 

57 3.0 140.0 39.0 22 

57 .2 11.0 2.5 25 

38 .3 11.0 2.8 10 

44 .04 2.6 .47 25 

57 10.0 870.0 125.6 25 

57 6.0 340.0 66.9 24 

49 8.0 96.0 22.0 25 

3 3.0 6.0 4.5 2 

1 0 

31 6.0 140.0 24.6 25 

48 5.0 150.0 22.6 25 

57 2.0 59.0 10.3 21 

50 1.0 8.0 2.8 6 

5 4.0 8.0 6.0 5 

elements, such as As and Se, and of chalcophile elements, 

is not systematically different in the two types of gold 

deposits may be an indication that the mineralization is 

more similar than dissimilar. 

Multivariate statistical tests of element associations 

with Au suggest that P, As, Ce, La, Nd, and Eu have 

significant positive associations, whereas some other 

elements that are suspected to be associated with Au, 

such as Hg, Sb, Se, Te, S, and N a, have only weak positive 

associations. The suite of elements associated with Au is 

the same for both deposit types as indicated by correlation analyses run on 25 Vandalia-type samples and 57 

Big Canyon-type samples. For both deposit types the 

association of Au with P and REE is significant. The 

unsuspected Au-P association is a reminder that apatite 

is a prominent accessory mineral in the albitic alteration 

zones. Two differences were indicated when comparing 

Au associations in the subgroups: in the Vandalia 

subgroup of samples Au has strong positive associations 

with S (r=0.64) and Na (r=0.22), whereas in the Big 

Canyon subgroup Au is independent of S and Na (r= 

0.05 and --0.02, respectively). The small correlation 

coefficients of Au-Na and Au-S do not seem consistent 

18 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, ElDorado County, California 
with petrographic observation but probably are correct as 

a reminder that many altered rocks in the Big Canyontype deposits have pyrite and albite but do not contain 

much Au. The computed positive associations of Au-Na 

and Au-S in the Vandalia subgroup of samples are 

consistent with petrographic features. 

Arsenic is enriched in these altered rocks and is 

associated with Au. The residence of As is not a simple 

problem. The highest concentrations of As (1,100-3,300 

ppm) are in near-surface, oxidized, limonitic samples 

that presumably contain an arsenate mineral such as 

scorodite. Many pyritic samples contain 500-1,000 ppm 

As, and six contain 1,100-2,700 ppm As; this amount of 

As would logically reside in arsenopyrite but might be in 

the pyrite lattice. If totalS and As results are recomputed 

in terms of pure pyrite, much "pyrite" would contain 

about 2 weight percent As, and a few samples suggest a 

"pyrite" with as much as 6 weight percent As. Microprobe analysis, which can detect less than 1 percent As in 

pyrite, should be undertaken to test the residence of As 

in the sulfidic rocks. 

DISCUSSION 

Big Canyon-Type Deposits 

Character of Deposits 

The Big Canyon deposit and other similar 

prospects in the study area, such as the Live Oak, are 

structurally controlled vein or stockwork deposits. These 

deposits formed after the peak of regional greenschistfacies metamorphism because those metamorphic 

minerals are altered along the gold-bearing structures. 

The maximum geologic age for the gold mineralization is 

Late Jurassic, which is the age of the Logtown Ridge 

Formation that is cut by the Big Canyon fault and that 

contains local alteration and minor gold. The Big 

Canyon-type deposits are characterized by intense 

alteration of mafic rocks that results in alteration and 

vein filling composed of albite, carbonate, and pyrite; this 

PCA alteration grades outward to chlorite-carbonatepyrite alteration. Gold is intimately associated with the 

PCA veining and flooding. Base metals such as Cu, Pb, 

and Zn are only slightly enriched in the gold zones, but 

As and REE, and to a lesser extent Hg, Sb, Se, and Te, 

are enriched along with Au. 

A different age and setting for the Big Canyon-type 

deposits are favored by the Gold Fields Mining Corp. 

exploration geologists (Osterberg and others, 1984; M. 

Osterberg, written commun., 1987). They interpreted the 

structure, especially at the Live Oak prospect where they 

drilled 15 core holes, as that of a pipe that formed during 

Paleozoic mafic volcanism in a manner similar to footwall feeder structures below massive sulfide deposits. 

The structure and associated carbonate alteration are 

thought to be low-pressure, synvolcanic processes. From 

my more limited knowledge of the Big Canyon zone of 

mineralization, I can see two major problems with this 

hypothesis: (1) The mineralized structures appear to be 

part of the Big Canyon fault zone; and (2) the PCA 

alteration is, in my opinion, superimposed on metamorphic assemblages rather than being synvolcanic (premetamorphic). Multistage genesis, including postmetamorphic remobilization, might reconcile the premetamorphic 

and postmetamorphic origins favored by Gold Fields 

Mining Corp. geologists and by me, respectively, but I do 

not have evidence in support of this and it will not be 

considered further. 

Comparison With Other Gold Deposits 

The Big Canyon-type deposits are generally similar 

to gold deposits of the famous Mother Lode and Allegheny districts of California (for example, Knopf, 1929; 

Ferguson and Gannett, 1932; Landefeld and others, 

1986). The carbonate alteration, and associated albite 

and pyrite, are very similar, although Cr-mica (mariposite) and muscovite are more abundant in the Mother 

Lode deposits. Albite is locally abundant in Mother Lode 

deposits (Knopf, 1929), but it does not seem to be as 

widespread or abundant there as it is in the Big Canyontype deposits. The structural style of the Big Canyon-type 

deposits may be similar to some Mother Lode deposits 

that tend to be localized on second-order structures 

associated with the Melones fault zone, rather than with 

the major structure (Knopf, 1929; Ferguson and Gannett, 1932). A big difference is the lack of abundant 

quartz vein filling at Big Canyon; the Mother Lode veins 

are dominated by quartz of many generations that fills 

veins tens of meters wide (Knopf, 1929). The Mother 

Lode deposits have low base-metal content but are 

enriched in As. 

The Big Canyon-type deposits are arguably similar 

to some Archean gold deposits of the world that have 

associated carbonate alteration and occur in mafic 

igneous rocks (Hutchinson and others, 1971; Boyle, 

1979; Hodgson and MacGeehan, 1982). In making this 

comparison it is important to exclude those deposits 

thought to be in or associated with carbonate exhalites, 

because there is no evidence for layered, exhalitive 

carbonate rocks in the Big Canyon area, regardless of the 

debate over the origin of Archean carbonate rocks in 

Canada, Australia, and other parts of the world. Very 

similar "gold-only" deposits in metamorphosed Archean 

mafic igneous rocks occur at Yellowknife, Northwest 

Territories (Boyle, 1979), Sigma mine, Abitibi Belt, 

Discussion 19 
Quebec (Robert and Brown, 1986), and Golden Mile, 

Kalgoorlie, Australia (Phillips, 1986). In addition to 

differences in age and structural setting, these examples 

have more potassic (muscovite) alteration (with minor 

albite or albite replaced by muscovite) than does the Big 

Canyon deposit. 

Exploration Significance 

Exploration and resource assessment of Big 

Canyon-type deposits can utilize several features that 

were previously described: structural control, PCA 

alteration, and minor-element signature. The most 

general feature is structural control by the suture that 

separates the Mother Lode belt from the Melange belt 

(locally the Big Canyon fault) and by secondary faults 

that splay from the Big Canyon fault. Mafic rocks cut by 

these faults should be examined for PCA alteration and 

enrichment in Na, As, or rare metals. Gold may be the 

best guide to gold deposits, but alone would not be 

diagnostic of the Big Canyon-type of deposit. There is a 

high potential for the existence of additional deposits like 

the Big Canyon, but discovery of such deposits may be 

extremely difficult because of poor exposure or cover by 

younger materials. 

Vandalia-Type Deposits 

Character of Deposits 

The Vandalia gold deposits are associated with 

pyritic and pyritic-hematitic metachert that formed as a 

chemical sediment (exhalite); some of the Vandalia gold 

also seems to occur in silicified basaltic metatuff. 

Questions remain about the formation of these ores. 

First, is the metachert sequence exotic relative to the 

adjacent basaltic metatuff, or did it form as part of the 

volcanic sequence? Second, did the gold form as part of 

the chemical sediment or was it introduced much later, 

following metamorphism, at the same time as the Big 

Canyon mineralization? These two problems are not 

necessarily related. There is little doubt that the chert 

formed as a chemical sediment, and the presence of 

several percent aluminum in nearly all samples suggests 

that there was a pelitic or volcanic component in the 

sediment. The origin of beds with compositions 

intermediate between chert and tuff (Si02, about 60-75 

percent; Ah03, 5-10 percent) is not clear-the most 

likely processes are (1) mixing and diagenetic alteration 

of tuff and siliceous exhalite, and (2) postmetamorphic 

hydrothermal alteration. Because some of these beds 

contain substantial amounts of titanium, which is thought 

to be relatively immobile in hydrothermal processes, and 

because silica does not seem to have been added in most 

of the hydrothermal alteration in the Big Canyon area, I 

prefer to explain the origin of these intermediate composition rocks by syndepositional processes. This mode 

of origin is at odds with the tectonic model (Earhart, 

1988) that explains the metachert unit as a series of 

megablocks that slid into the trench filled by mafic 

volcanic rocks. More work is needed to clarify the 

structure and geochemistry of the metachert-basaltic 

metatuff contacts to resolve this problem. Earhart (1988) 

believed that the gold was in the cherty rocks when they 

slid off the continental shelf to the east. This may be 

correct, but there are structural and geochemical 

arguments that the Vandalia gold did not form in this 

manner. The facts that basaltic metatuff located a few 

meters to 100 m from gold-bearing metachert contains 

gold and that the geochemical signature of deposits in 

metachert and basaltic metatuff, as well as the Big 

Canyon-type deposits, are the same, lead me to favor 

formation at the same time. According to this concept, 

gold and associated elements (Na, As, and so forth) were 

introduced into the metachert following its metamorphism; the metachert was in contact with basaltic 

metatuff, regardless of whether the metachert is autochthonous or allochthonous. The gold is localized by ferrugenous layers in the metachert sequence, chiefly those 

with pyrite, which explains the apparent stratiform 

character of the Vandalia gold. The stratiform appearance of Vandalia gold also would be enhanced if fractures associated with faulting and folding occurred along 

bedding planes in metachert and between the metachert 

(a rigid block) and basaltic metatuff. Much of the Vandalia gold is in metachert immediately adjacent to 

basaltic metatuff, and some gold is in basaltic metatuff 

just below metachert, a geometry that is possibly 

explained by fracturing in rocks of different competence 

across the contact. 

A chief ore control in this concept of epigenetic, 

postmetamorphic ore formation is the location of 

favorable pyritic beds in the metachert sequence. The 

pyritic beds are assumed to be synsedimentary because 

other iron minerals in the metachert formed with the 

chemical sediment, and there is no evidence for replacement of sedimentary iron oxides by sulfides. The lateral 

extent of potential Vandalia-type gold deposits is 

restricted to the occurrence of pyritic metachert. One 

goal of exploration is to define pyritic or formerly pyritic 

zones of metachert, some of which could lack surface 

exposure. 

Comparison With-Other Gold Deposits 

The Vandalia deposit seems to be unusual in the 

Sierra Nevada foothills, chiefly because the metachert 

sequence is rare in this region. Although Logan (1938, p. 

20 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 
254) expressed the opinion that Vandalia is similar to 

other gold deposits in El Dorado County that occur in 

silicified and pyritized amphibolite, he did not recognize 

the pyritic metachert and BIF at Vandalia. Pyritic 

metachert and BIF are not well described in the 

literature for the foothills but may be present south of the 

Cosumnes River in the Melange Belt as described by 

Duffield and Sharp (1975). Regional mapping by Gold 

Fields Mining Corp. geologists traced occurrences of 

metachert and BIF, similar to that at Vandalia, for about 

25 km from the Cosumnes River to the South Fork of the 

American River (M. Osterberg, written commun., 1987). 

Similar exhalative rocks may occur in other parts of the 

western foothills in volcanogenic settings that have 

produced Cu-Zn deposits that are now considered to be 

massive sulfide deposits (Albers, 1981). Some of the 

massive sulfide deposits contain significant amounts of 

gold, but these are polymetallic sulfide deposits that are 

geochemically different from the Vandalia deposit. 

The Vandalia deposit may be analogous to some 

gold deposits in Archean exhalite and BIF; this is a 

common association (Boyle, 1979), but there is heated 

debate as to whether the gold was deposited with the 

sediments or was introduced later. Some workers hold 

that the gold is synsedimentary with the enclosing exhalative rocks (Hutchinson and others, 1971; Fripp, 1976), 

but others argue that the gold was introduced at a later 

time (for example, Phillips and others, 1984). The 

pendulum of opinion swings regarding syngenesis and 

epigenesis of gold in exhalite host rocks, but several 

empirical associations (Ridler, 1971; Hodgson and MacGeehan, 1982; and others) for the Archean deposits may 

also apply to deposits in El Dorado County: (1) One 

variety of gold deposit tends to be "gold-only"; (2) the 

exhalites occur in volcanic settings, commonly at the top 

of a mafic volcanic sequence, and some exhibit lateral 

facies changes into volcanic rocks (neither of which can 

be established at Vandalia); (3) many deposits are 

associated with intrusions (not known at Vandalia); and 

( 4) many deposits are spatially associated with major 

faults that juxtapose mafic volcanic and sedimentaryexhalative rocks. The debate over the timing and 

significance of these associations is well illustrated by 

diverse opinions on the genesis of the recently discovered 

world-class gold deposits at Hemlo, Ontario. 

The Vandalia deposit has some similarities to the 

Hemlo deposits that might reflect similar geochemical 

processes despite the many differences. The Hemlo 

deposits (Cameron and Hattori, 1985; Patterson, 1986) 

occur at the top of a mafic volcanic section at a facies 

change to clastic rocks. Parts of these magnetite-rich 

clastic rocks may have similarities to BIF's. The gold 

zones are in siliceous, highly potassic (sericitic) rocks that 

are rich in barite and molybdenite and contain abundant 

As, Sb, Hg, Tl, and V. Metamorphism to kyanite grade 

obscures textural relations in the ore zone. The abundant 

Hg, As, Sb, and Tl and siliceous character have led some 

observers to propose a hot spring or epithermal genesis 

(Patterson, 1986), but others, who are impressed by the 

deformation and widespread structurally controlled 

potassic alteration of the deposits, disagree with this 

hypothesis (Walford and others, 1986). The Vandalia 

deposits lack the extreme enrichment of Mo, Sb, and Hg 

and the unusual abundance of barite found at Hemlo, as 

well as its size and grade, but the moderate enrichment in 

volatile elements and Na (rather than K) may have 

generally similar implications for chemistry of fluids and 

structural controls. 

Exploration Significance 

The pyritic siliceous exhalite and associated lean 

BIF are distinctive rocks that should be good guides in 

exploration, especially because they are relatively well 

exposed in this area. Exploration can utilize either or 

both of two hypotheses: (1) Gold is syngenetic with the 

pyritic metachert, and (or) (2) gold is epigenetic and 

introduced along fractures and localized by the pyrite. If 

gold is indeed syngenetic, which I do not favor, there is 

evidence that gold is more abundant near postmetamorphic structures, thus structures seem to be 

important whether they acted to introduce or redistribute 

gold. Pyritic metachert units comparable in thickness to 

that at the Vandalia mine do not appear to be described 

in the literature, and if they are indeed rare or very thin 

in other parts of the foothills, then the potential for other 

Vandalia-type deposits would be low. 

Geochemical Processes 

Geochemical processes in the formation of Big 

Canyon- and Vandalia-type gold deposits seem to be 

generally similar despite differences in structure and host 

rock compositions. Both types of deposit exhibit enrichments in the same suite of elements (Na, P, S, C02, As, 

Sb, and REE) but negligible amounts of base metals, and 

in both types of deposits gold deposition favored rocks 

rich in iron. The PCA alteration and associated 

geochemical suite, which differs from that in most basemetal deposits, is a distinctive feature of "gold-only" ores 

in many parts of the world (for example, Boyle, 1979; 

Hodgson and MacGeehan, 1982; Kerrich, 1983). There 

probably are systematic differences in the origin and 

composition of the fluids responsible for transport and 

deposition of gold and associated metals relative to the 

fluids that produce base-metal deposits. 

Alteration mineralogy in these "gold-only" 

deposits is distinctive and testifies to the character of the 

ore fluids. The alteration assemblage carbonate-albiteDiscussion 21 
pyrite ± chlorite ± muscovite is unusual for ore deposits 

(Meyer and Hemley, 1967), yet it is consistently 

associated with gold deposits in metamorphosed mafic 

rocks around the world, including world-class deposits of 

the Yellowknife district, Canada (Boyle, 1979), Kalgoorlie, Australia (Phillips, 1986), and the Abitibi greenstone 

belt of eastern Canada (Fryer and others, 1979; Kerrich, 

1983; Robert and Brown, 1986). Although not much 

emphasized in the literature, many of these deposits 

show enrichment of phosphorous as apatite with gold. 

The chemistry and mineralogy of Na and K appear to be 

variable within this group of deposits-some deposits are 

characterized by Na loss and K enrichment in the form of 

muscovite, as emphasized by Kerrich (1983 ), whereas in 

other places such as Big Canyon, muscovite is minor but 

Na is fixed as abundant albite. This carbonate alteration 

reflects alkaline conditions with silicate mineralogy 

determined by ratios such as K/H+, Na/H+, and Na/K 

(Meyer and Hemley, 1967). 

Fluid geochemistry can be elucidated by studies of 

fluid inclusions and stable isotopes. Fluid-inclusion and 

stable-isotopic studies of samples from the Mother Lode 

suggest temperatures of about 200-350 °C, pressures of 

about 0.6-2.5 kilobars, and the presence of C02-rich 

fluids (Coveney, 1981; Rosenbaum and Taylor, 1984; 

Weir and Kerrick, 1984; Bohlke and Kistler, 1986). 

Stable isotopic ratios from Mother Lode vein and 

alteration minerals suggest a deep crustal origin from 

metamorphic rocks. Fluid inclusions from Canadian and 

Australian gold deposits in metamorphic rocks suggest 

depositional temperatures of 300-500 oc, about 5 to 

more than 50 percent C02, the presence of methane in 

some inclusions, salinities generally less than seawater 

(3.6 weight percent NaCl), and pressures of about 1-3 

kilobars (Kerrich, 1983; Phillips and Groves, 1983). 

Analyses of oxygen isotopes reveal enrichment in 18 0 

(Kerrich, 1983). This research has determined heavy 

oxygen isotopic ratios, high C02 contents, and presence 

of methane, which suggest the gold ore fluid is metamorphic in character. The ages determined for Mother Lode 

samples are not consistent with derivation during peak 

regional metamorphism as proposed by Kerrich and 

others but are consistent with deep crustal magmatism or 

metamorphism associated with subduction (Bohlke and 

Kistler, 1986). 

There has been considerable discussion and 

speculation on the reasons for the unusual "gold-only" 

geochemical associations and apparent nontransport of 

Cu-Pb-Zn (reviewed by Kerrich, 1983; Phillips and 

Groves, 1983). Integration of data for mineral equilibria 

and fluid inclusions from gold deposits and results of 

experimental studies of ore solubilities suggest that if the 

ore fluids were about 300-500 oc, COz-rich, reducing, 

and alkaline, the most likely mechanism for gold 

transport would be by bisulfide complexes (Seward, 

1984; Phillips and Groves, 1983). The practical application of this transport theory is that it predicts gold 

deposition in response to loss of aqueous sulfide, such as 

in the formation of pyrite or boiling; gold can also be 

precipitated from thio-complexes by oxidation and 

decrease in pH from alkaline to neutral. The mechanism 

of gold deposition in the Vandalia-type deposit is less 

clear than for the Big Canyon-type deposit if gold is 

indeed superimposed on earlier pyrite at Vandalia. 

However, the amount of feldspar and mica in the pyritic 

metachert might be too small to buffer pH in that rock; if 

the pH in the chert was lower than in enclosing rocks, this 

might have been sufficient to cause gold deposition. 

CONCLUSIONS 

Gold deposits in the Big Canyon area probably arc 

related in time and process despite their differences in 

host rocks and local structure. The Big Canyon and Live 

Oak deposits are clearly related to post-Jurassic, postmetamorphic structures that splay from the Big Canyon 

fault, which is a major discontinuity between contrasting 

terranes. The Big Canyon-type deposits are in highly 

fractured zones with numerous veins that result in wide 

zones (10-30 m) of PCA rock that carries gold in the 

range of about 1-10 g!t, as well as in locally richer 

streaks. The gold zones are a combination of veinlet 

filling and replacement of basaltic metatuff and metadiorite. The gold zones are enriched in Na, Ca, P, S, COz, 

and rare elements (As, Sb, Se, Te, and REE), but base 

metals (Cu, Pb, and Zn) and Ag are not notably enriched. 

Formation of the alteration and ore minerals is consistent 

with alkaline, COz-rich, hydrothermal (about 300-400 

°C) fluids of metamorphic origin as determined for 

Mother Lode deposits and other similar gold deposits. 

The Vandalia deposit occurs chiefly in pyritic 

metachert, which is part of a sequence that formed as a 

chemical sediment (volcanogenic exhalite). Gold favors 

strata rich in pyrite; the pyrite is probably synsedimentary, but the gold probably is epigenetic. The richest gold 

values are in fractured zones in which pyrite is largely on 

fractures, and the metachert contains more than 1 

percent N a as albite and several percent carbonate. The 

gold-rich samples from the Vandalia deposit contain 

elevated concentrations of the same major- and minorelement suites as found in the Big Canyon-type deposits. 

Although the timing and details of structures in the 

Vandalia deposit are not well understood, it is possible 

that second-order fractures related to the Big Canyon 

fault broke the metamorphic rocks at Vandalia at 

boundaries of metachert and balsaltic metatuff units and 

along bedding and allowed inflow of hydrothermal fluids 

similar to those that formed the Big Canyon deposit. By 

22 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 
this concept of postmetamorphic mineralization, gold 

was localized by reactions with iron minerals in zones of 

brittle fractures. 

The Big Canyon-type deposits display structural 

controls and alteration that are similar to deposits of the 

Mother Lode and other "gold-only" deposits in metamorphic rocks around the world which account for a 

major part of world gold production and many worldclass deposits. The suture between the Mother Lode belt 

and the melange belt, which is locally the Big Canyon 

fault, and especially s3cond-order faults related to that 

zone of deformation are favorable sites for development 

of these deposits. Useful guides to gold along these 

structures include PCA alteration and enrichment in rare 

elements. Iron-rich rocks are most favorable for 

reactions that localize gold. Pyritic and hematitic strata in 

siliceous exhalite were favored at the Vandalia deposit, 

but similar rocks do not seem to be present in significant 

amounts elsewhere in the Sierra Nevada foothills thus 

the potential for other deposits similar to the va:1dalia 

seems low. The known zones of major faults that cut 

mafic rocks outline large areas in the Sierra Nevada 

foothills that are highly favorable for the occurrence of 

Big Canyon-type deposits 

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References Cited 23 
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24 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 
DESCRIPTION OF CHEMICALLY ANALYZED 

ROCK SAMPLES 

and 

METHODS AND RESULTS OF GEOCHEMICAL ANALYSES 
APPENDIX I. DESCRIPTION OF CHEMICALLY 

ANALVZED ROCK SAMPLES 

(All samples are from drill core; drill sites are shown on figure 2. 

Sample numbers relate to drill-hole nomenclature-for example, 

BC2-135: BC =Big Canyon project (LO = Live Oak prospect); 2 = hole 2; 135 = depth 135 ft. Two types of information are given: M, 

macroscopic features; P, petrographic features observed in thin 

sections in transmitted and reflected light] 

Definitions: "carbonate" is nonspecific for calcite, ankerite, 

dolomite, and so forth, but where calcite is stated that is specific 

for the mineral that reacts strongly to dilute hydrochloric acid. 

Grade (generalized from gold assays): high, > 0.1 oz/t; medium, 

0.02-0.1 oz/t; low, 0.005-0.2 oz/t; barren, Au not detected 

( <0.005 oz/t); material sampled and analyzed by U.S. 

Geological Survey may not be the same as analyzed by Gold 

Fields Mining Corp. 

BC2-135. M: gray micaceous metachert with 2 percent pyrite; 

medium grade. P: mostly microgranular quartz (75 p.m) with 20 

percent intergrown carbonate rhombs and veinlets; 5 percent 

fine hematite; 2 percent pyrite (20-300 p.m); trace chlorite. 

BC2-147. M: gray micaceous metachert; sparse pyrite; low 

grade. 

BC2-169. M: tan and gray partly weathered dike with massive 

fabric and porphyritic texture; barren. P: porphyritic texture of 

plagioclase phenocrysts set in microgranular matrix of plagioclase plus Fe-Mg silicates that are altered to chlorite. This is 

probably an altered diabase dike. 

BC2-212. M: light-gray thinly laminated micaceous metachert 

with traces of pyrite on beds; barren. 

BC2-322. M: gray fractured and veined metachert; abundant 

(10 percent) pyrite on beds and in veinlets; high grade. 

BC4-92. M: tan metachert; originally 5 percent pyrite, most of 

which is oxidized to limonite; iron oxides in joints; low grade. 

BC4-103. M: white to cream-colored metachert; 1 percent 

pyrite that is partly oxidized; barren. 

BC4-605. M: green-gray laminated basaltic metatuff; swirled 

beds; weakly altered; scattered calcite veinlets; low grade. P: 

millimeter-scale layers of leucocratic (quartz plus albite) and 

layers of mafic minerals (chlorite plus epidote); disseminated 

carbonate and veinlets of carbonate. 

BC4-630. M: tan siliceous pyrite-carbonate-altered rock, 

probably basaltic metatuff; 8 percent pyrite; disseminated 

carbonate and veinlets of carbonate; low grade. P: original 

textured wiped out; granular PCA rock with no Fe-Mg silicates; 

swaths of coarse albite and carbonate as wide as 400 p.m; 

abundant coarse sphene with rutile overgrowths; 2 percent 

apatite in albite. 

BC4-656. M: tan silica-pyrite-carbonate alteration of basaltic 

metatuff; 20 percent pyrite in veinlets; medium grade. P: 

microgranular quartz-albite rock with no Fe-Mg silicates; veinlets of quartz, albite, carbonate, pyrite, and minor chlorite; 

disseminated apatite, sphene, and rutile. 

BC4-669. M: tan calcite-silica-pyrite-altered basaltic metatuff; traces of galena; medium grade. P: granular albitecarbonate rock with variable fine to coarse grains and no Fe-Mg 

silicates; albite and carbonate tend to be in separate swaths; 

minor late chlorite in veinlets with carbonate; 1 percent microgranular disseminated sphene. 

BC4-683. M: gray pervasively silicified and pyritized basaltic 

metatuff breccia; medium grade. 

BC4-701. M: tan pervasively PCA altered, basaltic metatuff; 

10 percent pyrite; high grade. P: swirled swaths of granular 

albite and carbonate with abundant disseminated pyrite and 

microgranular sphene; only Fe-Mg silicate is minor late chlorite; several 3-30-p.m gold grains. 

BC4-773. M: gray granular alteration zone; looks almost like 

unbedded quartzite; disseminated pyrite and carbonate; late 

calcite veinlets; high grade; protolith basaltic metatuff? P: 

coarse granular albite-carbonate rock; early albite with pyrite is 

cut and replaced by carbonate; 5 percent late pale-green 

chlorite is only Fe-Mg silicate; disseminated sphene and rutile 

in albite; one 4 p.m gold grain. 

BC4-781. M: slightly altered basaltic metatuff at lower 

boundary of gold zone; mostly green laminated basaltic 

metatuff with some tan PCA alteration along veinlets; barren. 

BC5-9S. M: tan and gray oxidized pyrite metachert with dark 

Fe-silicate layers; originally 5 percent pyrite, some pyrite is 

fresh; medium grade 

BCS-98. M: dark-gray hematitic metachert (lean BIF); some 

pyrite on beds; low grade. 

BC7-25. M: brown highly oxidized, laminated metachert rich 

in hematite and earthy iron oxides; probably had 10 percent 

pyrite to make iron oxides; medium grade. 

BC7-55. M: gray highly pyritic (20 percent) metachert; some 

pyrite in veinlets, most pyrite is fresh; this gold zone is more 

fractured and pyritic than adjacent metachert; high grade. High 

iron content caused interference problems in XRF analysis. 

BCS-84. M: ocher oxidized, laminated metachert; limonite 

after pyrite along beds and in joints; barren. 

BCS-135. M: gray laminated metachert; only slightly oxidized; 

dark layers of hematite; barren. 

BCS-218. M: zone of fractured and weathered metachert; soft 

ocher clay is abundant; medium grade. 

BCS-252. M: white and tan metachert with 1-cm-thick layers 

and veinlets filled with pyrite and earthy iron oxides; appears to 

be supergene altered fracture zone; medium grade. 

BCS-499. M: tan laminated basaltic metatuff with pyritecarbonate alteration; 3 percent pyrite; barren. 

BCS-501. M: tan pyrite-carbonate-altered basaltic metatuff 

breccia; early breccia is overprinted by alteration; 5 percent 

pyrite in veinlets and disseminated; barren. 

BC9-210. M: gray metachert with micaceous layers; trace 

hematite; barren. 

BC9-225. M: pale-gray dike; aphanitic texture; one of several 

massive rocks that crosscut the metachert sequence in this 

interval; I picked the hardest, least altered 1-ft interval; barren. 

P: porphyritic rock with plagioclase phenocrysts in aphanitic 

matrix. 

BC9-243. M: dark-gray laminated metachert with hematitic 

layers; 5 percent hematite overall?; nonmagnetic; low grade. 

BC9-348. M: dark-green laminated basaltic metatuff; more 

than 100 ft thick like this-composition uniform overall, 

millimeter-scale felsic and mafic layers; not foliated; barren. 

BCl0-63. M: gray chert with 3 percent pyrite; medium grade. 

P: microgranular texture of intergrown silicates which are 

mostly albite; some albite has radial texture; only Fe-Mg silicate 

is late pale-green chlorite; no carbonate; coarse pyrite randomly 

disseminated, not layered; abundant needles of honey-colored 

26 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 
rutile; 1 percent disseminated apatite and trace hematite. 

Highly altered basaltic metatuff? 

BCl0-74. M: gray bedded pyritic metachert; sample chosen 

for high pyritic content that seems to be on beds; medium 

grade. P: layers shown by variations in grain size and by pyrite 

and ricbeckite; swaths of albite and carbonate are coarser than 

microgranular quartz and have apatite; tiny (5 ,urn) inclusions of 

high-index silicate in quartz may be epidote; disseminated tiny 

hematite intergrown with quartz; no sphene or rutile seen. Odd 

rock! PCA-altered metachcrt? 

BCl0-101. M: green thinly laminated, basaltic metatuff; 2 

percent pyrite; barren. P: layers composed of quartz-albite and 

of chlorite-epidote; abundant chlorite (30 percent); 5 percent 

hematite; scattered trace pyrite; 4 percent sphene. 

BC10-111. M: gray and tan finely laminated hematite-pyrite 

metachert; medium grade. P: chiefly microcrystalline quartz; 

scattered rhombs and veinless carbonate; abundant lathes of 

hematite (20 percent in gray layers); iron oxides in place of 

cubic pyrite; trace sphene; one flake of 3-.um gold. 

BCl0-127. M: gray thinly laminated metachert; slump folds 

locally tight; low grade. P: chiefly microcrystalline quartz; 5 

percent micas (chlorite and muscovite) oriented along beds; 

rare opaques; trace sphene; no albite recognized. 

BCU-48. M: tan laminated lean iron metachert; weathered, 

argillized?; medium grade. P: > 90 percent microcrystalline 

quartz; 5 percent clay; sprays of fine ricbeckite; oxidized pyrite. 

DCll-145. M: tan, finely laminated limonitic (ex-pyrite) metachert; iron oxides in fractures; low grade. P: Chiefly microcrystalline quartz; scattered 2 percent pyrite altered to iron oxides. 

BCll-213. M: gray faintly laminated lean iron metachert; no 

oxidation; barren. 

BC16-46. M: tan weathered metachert; limonite in fractures; 

high grade. 

BC16-101. M: tan altered basaltic metatuff; layered; pyritic; 

veinlets of carbonate; low grade. P: thin layers marked by 

opaque minerals and rutile; abundant albite; needles of blue 

pleochroic sodic actinolite; golden nttile ( 4 percent); pock-y 

coarse pyrite; several specks of gold. PCA-altered mafic rock, 

possibly a dike. 

DC24-82. M: dark-gray pyritic argillite; bleached a bit in this 

area ncar fault and adjacent PCA alteration below 88ft; barren. 

Note high Na in chemical analysis. 

DC24-94. M: tan breccia, PCA-altered mctadiorite?; veinlets 

of pyrite and carbonate; medium grade. P: gash veins filled by 

coarse pyrite and carbonate cut very fine microcrystalline rock 

composed chiefly of untwinncd albite and fine carbonate with 

fine hematite; greener, less altered parts have chlorite. Proto lith 

might have been argillite rather than metadiorite, but original 

texture is obscure. 

DC24-120. M: tan and gray altered and brecciated aphanitic 

rock, metadiorite? Pyritic with late calcite veinlets; low grade. 

P: microgranular quartz and albite (can not tell abundances 

because albite not twinned); rare mafic silicates; disseminated 

pyrite and sphene; coarse calcite veinlcts. 

DC27-182. M: tan pyritic breccia; many late calcite veinlets; 

breccia was prealteration because fragments alter differently; 

medium grade. P: relicts of actinolitic magnetite texture largely 

wiped out by albite flooding; microgranular albite grades to 

coarser carbonate-albite rock with disseminated pyrite, cut by 

coarse calcite veinlcts; rutile (elongate, striated crystals, honey 

colored in transmitted light) abundant as 100 ,urn crystals in 

PCA-altered rock. 

BC27-204. M: green slightly altered basaltic metatuff breccia 

with sparse disseminated and vein calcite; low grade. P: 

fragmental texture; some clasts are layered; chiefly albite plus 

carbonate; disseminated hematite, pyrite, and rutile; late veinlets of carbonate and chlorite. 

BC29-168. M: tan pyritic metadiorite breccia; gray slightly 

altered metadiorite at 155 ft; stope of Big Canyon mine hit at 

193 ft; high grade. P: albite-carbonate microgranular rock; 

replaced earlier breccia. Earliest albite is microgranular with 

little carbonate; cut by vcinlcts of coarse-grained-chloritepyrite-minor albite; later cut by veinlets of coarse carbonatealbite-pyrite; microgranular sphene has boxwork texture. 

BC29-171. M: tan pyritic metadiorite breccia; high grade. P: 

micro granular albite rock cut by carbonate veinlets; early albite 

has elongate feathery morphology; grades to coarser twinned 

tabular crystals; apatite and sphene in albite; 6 percent 

disseminated pyrite. 

BC31-433. M: green slightly altered metadiorite breccia with 

only a few calcite veinlets; barren. 

BC31-436. M: tan and green moderately altered metadiorite 

breccia with about 10 percent pyrite and many calcite veinlets; 

high grade. P: centimeter-sized fragments replaced by intergrown albite with fine chlorite; cut by coarse carbonate vcinlcts 

with chlorite; abundant pyrite in albite and in carbonate 

veinlets. 

BC31-476. M: tan and gray pyritic basaltic metatuff; layered 

or sheared; high grade. P: shear foliation defined by aligned 

crystals of albite and actinolite; albite-actinolite-chlorite-pyritecarbonate rock cut by late coarse calcite veinlets; disseminated 

microgranular sphene. 

BC31-485. M: gray aphanitic rock; diffuse alteration; calcite 

veinlets have no selvages; high grade. P: original texture 

destroyed by albite flooding; no Fe-Mg silicates present; microgranular albite cut by quartz veinlets and carbonate veinlets; 

disseminated apatite and sphene in albite; a few flakes of 2-,u.m 

gold. 

DC31-498. M: gray metadiorite; slightly altered, but a few 

quartz(?) and pyrite veinlets; low grade. P: microgranular albite 

abundant with 10 percent interstitial fine chlorite, traces of 

sericite, and scattered rhombs of carbonate; cut by quartzalbite-pyrite veinlets; disseminated pyrite (5 percent) and 

microgranular sphene. 

BC32-339. M: tan stock"Work veined and brecciated basaltic 

metatuff; alteration pervasive here in gold zone; medium grade. 

P: abundant fine and coarse albite and carbonate; prismatic 

actinolite (5 percent); later chlorite and sericite (5 percent); 

coarse disseminated pyrite (7 percent); disseminated coarse 

sphene and trace of fine needles of rutile; a few flakes of 2-3-

,u.m gold. 

BC32-356. M: green slightly altered basaltic metatuff; minor 

disseminated carbonate; medium grade. P: textures of tuff 

layers survive; some layers are 50 percent pale-green chlorite; 

abundant albite in light layers; cut by albite-carbonate veinlets; 

disseminated apatite in albite, 3 percent pyrite, rutile, and 

microgranular sphene; several specks of 2-,u.rn gold. 

BC32-373. M: tan altered basaltic metatuff; 3 percent pyrite; 

low grade. P: weakly layered rock with 30 percent albite, 25 

Appendix 27 
percent carbonate, 20 percent chlorite, 10 percent actinolite, 

plus fine disseminated epidote (2 percent) and pyrite (5 

percent); cut by carbonate veinlets with no alteration selvage; 

disseminated microgranular sphene that forms aggregates; 

several 2-5-~m gold flakes. 

BC32-393. M: green slightly altered basaltic metatuff; 

disseminated carbonate and about 2 percent pyrite; barren. P: 

thin layers of albite plus actinolite veinlets. Chlorite; cut by 

swaths of carbonate that replace(?) chlorite; fine hematite in 

chlorite; disseminated microgranular sphene and euhedral 

pyrite. 

BC32-672. M: light-gray metachert with faint layers marked 

by 1 percent pyrite and cut by thin pyrite veinlets; barren. P: 

chiefly microgranular quartz of 20-200-,um size; scattered fine 

rhombs of carbonate (5 percent); albite (5 percent, some 

twinned); chlorite plus actinolite (5 percent) intergrown with 

quartz; disseminated euhedral pyrite (2 percent); trace 

hematite; rare microgranular sphene. 

BC32-705. M: medium-gray metachert with 5 percent pyrite 

that defines swirled beds; medium grade. P: chiefly microgranular quartz with swaths or layers of albite (10 percent), 

carbonate (5 percent), and chlorite plus actinolite (10 percent); 

disseminated lathes of hematite (2 percent), pyrite ( 4 percent), 

and microgranular sphene (3 percent); a few grains of gold(?). 

BC32-718. M: medium-gray pyritic metachert with fine layers 

of dark minerals; medium grade. P: fine layers suggested by 

differences in quartz grain size and thin layers of fine actinolite 

or pyrite; swaths of carbonate (5 percent) and albite (10 

percent); disseminated fine hematite (1 percent) and sparse 

sphene; a few 2-~m grains of gold. 

BC32-742. M: dark-reddish-gray hematitic metachert; barren. 

P: fine lamination shown by layers rich in pyrite, hematite, or 

fine Na-actinolite (riebeckite?); cut by late veinlcts of 

carbonate (5 percent); seems to be mostly microgranular 

quartz; no twins in 30-~m grains to indicate albite as is likely by 

high Na content; abundant (20 percent) 5-20-~m hematite in 

some layers exceeds pyrite. 

BC32-765. M: gray pyritic metachert; faint laminae of mafic 

silicates and pyrite are swirled; medium grade. P: layers marked 

by different quartz grain size and fine hematite, pyrite, or 

actinolite-epidote-sphene; some albite is shown by twins in 

coarser grains, but most is not evident; two flakes of gold. 

BC32-776. M: green layered basaltic metatuff with scattered 

calcite veinlets and 1 percent pyrite; barren. P: vague layering 

produced by shear? Approximately equal amounts of albite, 

epidote, and actinolite, plus splotches of carbonate (10 

percent); abundant microgranular sphene in 100-~m aggregates; sparse pyrite. 

BC34-777. M: dark-green massive amphibolite or metadiorite; sparse carbonate and pyrite; barren. 

BC34-794. M: similar to 777-ft sample; dark-green amphibolite; low carbonate and pyrite, 2 ft from Au-alteration zone; 

barren. P: granular texture of intergrown albite-actinoliteepidote in equal amounts; gash fractures filled by carbonate 

and albite; disseminated magnetite and microgranular sphene. 

BC34-796. M: tan alteration zone 0.3 m wide centered on 

pyrite-carbonate veinlets; cuts amphibolite as at 777 ft; low 

grade. P: granular albite-actinolite rock, replaced by carbonate, 

chlorite, and pyrite (5 percent); abundant microgranular 

sphene; one 4-,um gold grain. 

BC34-800. M: tan altered amphibolite; more pyrite and 

carbonate than at 796 ft; medium grade. P: granular intergrown 

albite, pale-green amphibole, and pyrite (10 percent); cut by 

veinlets of coarser albite and carbonate and late stringers of 

chlorite; abundant disseminated sphene, much intergrown with 

pyrite; one 2-~m speck of gold. 

BC34-802. M: tan altered amphibolite; abundant carbonate 

but low pyrite; barren. P: vague mineral layering indicates 

shear?; rock is microgranular albite-chlorite-actinolite, cut by 

veinlets of coarse carbonate with chlorite selvage; disseminated 

cubic magnetite and pyrite; granular sphene. 

L04-116 Live Oak prospect. M: green mafic breccia (metadiorite?); sample chosen to be little altered for background; 

barren. 

L04-124. M: dark-gray amphibolite or metadiorite(?) breccia; 5 percent pyrite; medium grade. P: layers of albite (50 

percent), carbonate (25 percent), and actinolite (20 percent); 

disseminated pyrite and 20-~m sphene. 

L04-157. M: dark-gray less altered amphibolite adjacent to 

0.6 m of tan PCA alteration; barren. 

LOS-42. M: tan pyritic metabasalt breccia; hardness suggests 

silicification; medium grade. P: PCA-altered rock in which early 

feathery albite grades to swaths of coarse albite and carbonate, 

cut by veinlets of coarse carbonate; disseminated pyrite (2 

percent), sphene, and rutile in albite; one flake of gold. 

LOS-46. M: tan siliceous-pyritic breccia, medium grade. P: 

albite of different grain sizes mimics breccia fragments; early 

albite is microgranular, later swaths of albite are coarser and 

twinned; erratic swaths of 10-~m and 100-~m pyrite; trails of 

20-50-~m sphene; one flake of gold in pyrite. 

LOS-125. M: dark-green metabasalt breccia adjacent to Au 

zone; 2 percent pyrite; scattered carbonate veinlets; barren. 

L07-59. M: tan pyritic metabasalt breccia; disseminated 

carbonate; this is a thin Au zone; low grade. P: abundant albite 

(microgranular to coarser with twins) intergrown with fine 

rhombs of coarse carbonate (30 percent); traces of fibrous 

amphibole bleached to pale green; abundant 20-40-~m pyrite; 

disseminated sphene and hematite; several grains 3-~m gold. 

L07-75. M: dark-green weakly altered metabasalt breccia; 

background sample; barren. 

L07-86. M: tan siliceous pyritic breccia; high grade. P: PCAaltered rock; traces of bleached fibrous amphibole. Grains of 

albite and carbonate variable 20-400 ~m in size, coarse grains 

probably filled veins; scattered coarse pyrite, apatite, and 

microgranular sphene aggregates in albite with traces of fine 

hematite. 

L07-102. M: tan siliceous pyritic breccia; medium grade. P: 

original texture wiped out; microgranular albite cut by veinlets 

of coarse albite and carbonate; small amount of chlorite but no 

other Fe-Mg silicates; disseminated 20-~m sphene and 50-~m 

rutile needles and sparse pyrite; a few 2-.um gold grains. 

L07-109. M: tan siliceous pyritic breccia; medium grade. P: 

original texture gone; no Fe-Mg silicates; abundant albiteearly feathery albite crystals grade to coarser ones with twinning 

in swaths with carbonate; 30-.um microgranular sphene, rutile, 

and hematite in albite; 3 percent pyrite is coarse (100-200 .urn), 

one 3-.um gold grain. 

L07-125. M: dark-green-gray weakly altered metabasalt or 

metadiorite; barren. P: mineral layers produced by shear? 

28 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 
Overall, albite> sodic actinolite> carbonate; inclusions of 20-

.um hematite, sphene, and epidote in albite. 

L07-142. M: light-gray siliceous breccia; twice fractured and 

cut by pyrite-carbonate veinlets; low grade. P: multiple veins cut 

fragments; rock is chiefly albite-carbonate-pyrite as replacement and vein filling; only outlines of fragments survive; 

abundant < 30-.um pyrite and hematite; streaks of micro granular sphene. 

APPENDIX II. METHODS AND RESULTS OF 

GEOCHEMICAL ANALYSES 

[Rock samples were analyzed by chemists of the U.S. Geological 

Survey using standard methods described below. For more information 

consult the references cited] 

X-Ray Fluorescence (XRF): Sample (0.8 g) is fused in lithium 

tetraborate, and the glass disk is analyzed for major elements by 

wavelength-dispersive X-ray spectrometry (Taggart and others, 

1988). Limits of detection shown in table 5. J.E. Taggart and 

A.J. Bartel, analysts. 

Induction Coupled-Plasma Atomic Emission Spectroscopy 

(ICP): Sample (0.2 g) is digested with mixed acids (HF, 

HCl-HNOs, HC104) to dryness, then redissolved in HClHNOs, then analyzed by induction-coupled plasma atomic 

emission spectroscopy with lutetium as an internal standard 

(Crock and others, 1983); Lower limits of detection in table 5. 

A few refractory minerals are not dissolved by this acid attack; 

specifically, for B in tourmaline and Zr in zircon, the sample is 

fused in Na202 prior to ICP analysis forB and Zr. Paul Briggs, 

analyst. 

Special Element Analysis: Six additional elements and H20 

and Co2 were analyzed on request as shown below. L.L. 

Jackson, E.E. Engleman, D.B. Hatfield, and E. Brandt, 

analysts. Methods are described by Wilson and others (1988) 

and by Jackson and others (1988). 

Fe as FeO: Sample (0.5 g) is decomposed with HF 

and H2S04, and the digestate is treated with solution of 

HsBOs, H2S04, and HsP04. Fe(II) is determined by 

potentiometric titration. 

H20: Sample (1.0 g) is heated at 110 oc for one hour, 

and H2o- is determined by weight loss. H20+ is 

determined on 0.05-g sample heated with lead oxide 

and lead chromate, and evolved water is analyzed by 

coulometric Karl Fischer titration. 

C02: Sample (0.05 g) is decomposed in 2 M perchloric acid, and evolved C02 is determined as an acid by 

coulometric titration. 

Stotal: Sample (0.25 g) is mixed with vanadium pentoxide and combusted at 1370 oc in oxygenated 

atmosphere; Stotal is determined at so2 by infrared 

absorption spectroscopy. 

Au: Sample (10 g) is digested with HBr-Br2, and Au is 

extracted with methyl-isobutyl ketone. After washing 

the organic phase with 0.1 M HBr to remove iron, Au 

is determined by flame atomic absorption spectroscopy 

(Hubert and Chao, 1985). 

Hg: Sample (0.1 g) is decomposed in closed vessel 

with HN03 and sodium dichromate, then Hg(II) is 

reduced by hydroxylamine hydrochloride-sodium 

chloride and stannous chloride; Hg vapor is transported 

to and measured in an absorption cell using atomic 

absorption spectroscopy. 

Se: Sample (0.3 g) is digested with K2S20s, HF, 

HN03, and HCl04 plus a second treatment by HNOs 

and HC104 plus H2S04. Solution is mixed with sodium 

borohydride, and resultant metal hydride is carried in 

an argon stream into a heated quartz glass tube and 

determined by atomic absorption spectroscopy. 

Te: Sample is treated as for Au analysis; Te is 

extracted into methyl-isobutyl ketone, HBr is added to 

remove iron, and Te is determined by flame atomic 

absorption spectroscopy. 

Appendix 29 
Table 4. Analytical results for rock samples from the Big Canyon area 

[N, not detected; H, not determined because of interference usually caused by high iron content; <, 

detected but below the limit of determination shown; >,determined to be greater than the value shown; 

S (as in Fe%-S), determined by ICP-AES. Type sample explained in footnote No. 2 at end of table] 

Sample 

BC10-101 

BC10-111 

13C10-127 

BClU-145 

BC10-63 

BCl0-74 

BC11-213 

BC11-48 

BC16-l01 

BC16-46 

BCZ-135 

BC2-14 7 

BC2-16<J 

BC2-212 

BCZ-322 

BC24-l20 

BC24-82 

BC24-94 

BC27-182 

BC27-204 

BC29-168 

llC29-171 

BC31-433 

BC31-436 

BC31-476 

BC31-485 

BC3l-498 

BC32-339 

BC32-356 

BC32-37 3 

BC32-393 

BC32-672 

BC32-7U5 

BC32-718 

BC32-742 

BC32-765 

BC32-776 

BC34-777 

BC34-794 

BC34-796 

BC34-8UO 

BC34-802 

BC4-103 

BC4-605 

BC4-630 

49.1 

56.2 

93.6 

95. l 

57. 3 

84.8 

95.4 

9 3. 6 

53.3 

4 3. 8 

7 3. 7 

71.0 

49.8 

90.9 

48.7 

36.6 

55.8 

40.4 

43.4 

4 3. 5 

44.6 

45.0 

44.9 

44.2 

42.5 

55.4 

52. 1 

44.7 

46.4 

42.6 

44.5 

91.8 

7 2. 6 

70.5 

66.8 

67.0 

45.3 

42.9 

45.4 

39.5 

44.0 

4 3.2 

95.4 

4 7. 7 

58.3 

Al ;~ 3FeTo 37( FeO% MgO% 

·------

17.20 13.50 7.90 

:2.04 13.00 .OH 

2.20 l.OO .56 

1.92 1.26 .1)4 

14.60 10.60 JlH 

1 • 00 7. 7 3 • OH 

2.23 • 77 .05 

3.93 .63 .05 

14.40 11.60 .I)H 

9.30 29.30 .OH 

3.02 9.00 JIH 

2.45 8.71 .OH 

17.60 10.60 8.21 

3.63 l. 76 1.09 

10.60 24.20 .OH 

9.11 9.24 .OH 

15.10 6.83 .OH 

11.00 9.22 .OH 

12.00 7.21 .OH 

14.20 12.00 53.26 

13.30 9.42 .OH 

12.90 8.55 .OH 

13.50 10.00 6.99 

11.90 8.82 .OH 

13.50 7.64 5.61 

12.60 5.96 .OH 

16.20 6.50 .OH 

10.60 9.32 .OH 

11.70 9.91 .OH 

13.40 11.70 7.81 

14.10 1l.21J .OH 

2. 77 1 • 30 • 6 3 

3.66 9.70 .OH 

3. 9 6 9. 3 2 • OH 

6.99 11.00 3.54 

1+.90 11.80 .OH 

15.30 10.60 6.00 

1 2. 1 0 7. 12 • OH 

16.20 11.30 5.44 

10.60 9.33 .OH 

12.10 9. 38 .OH 

13.80 10.50 6.59 

2.44 .51 .06 

14.70 10.90 6.05 

10.30 6.64 .OH 

4. 90 

3.19 

.45 

<.10 

2. 34 

• 21 

<. 10 

(.10 

4. 24 

.1 3 

l. 30 

l. 8 5 

6. 50 

• 97 

• 1 7 

9. 37 

3. 01 

') .17 

3. 91 

6.06 

4.87 

3.61 

9. 74 

3.85 

5. 6 7 

2. 7l 

2.44 

5.41 

5.08 

6. 90 

7. 09 

• 7 2 

l. fj 1 

l. 70 

2. 79 

1.48 

7. 45 

'i .13 

5. 20 

3. 80 

3. 14 

4. 77 

.!1 

6. 65 

l. 98 

CaO% Na:2o% 

4.03 5.07 

7.27 1.07 

• 68 .46 

(.02 .89 

.29 7.38 

• 54 • 55 

(.1)2 • 9 5 

(.02 (.15 

1.56 5.98 

.17 '). 22 

3.fi9 1.69 

5.20 1.39 

1.03 4.31 

.09 • 92 

.06 4.42 

12.40 2.44 

3.12 7.40 

10.20 5.89 

!0.30 6.75 

7.52 4.9! 

7.10 6.64 

7.31 7.43 

9.99 3.28 

11.70 5.29 

9.14 5.60 

5.1•4 6.66 

5.05 7.14 

8.63 5.58 

7.87 5.63 

9.63 4.52 

9.09 4.51 

.43 1.16 

2.!4 1.91 

2. 23 2. 11 

2.13 4.37 

2.61 2. 7l 

11.60 3.29 

9.35 6.60 

11.30 4.09 

15.00 4.93 

!0.60 6.07 

10.30 'i. 21 

<. 1)2 • 89 

10.70 3.97 

6.09 5.48 

0.61 

• 11 

• 55 

.11 

(.()2 

.09 

< .oz 

.66 

• 10 

<.02 

(.02 

l. 79 

• 56 

.04 

.97 

.6 5 

• 31 

.1 3 

1. 11 

• 4 7 

.10 

• 43 

.11 

.94 

• 34 

• 95 

.07 

• 11! 

• 29 

.77 

.11 

.06 

(.()2 

• 32 

.04 

.11 

.16 

• 24 

• 22 

.24 

1. Jfi 

• 12 

.10 

.26 

2. 42 

• 38 

.09 

.n8 

2. 2 5 

.02 

.:!9 

• 15 

2. fi8 

l. 62 

• 3 3 

.36 

1. rn 

.1'5 

• 51 

1. 30 

• 7 3 

• 58 

.94 

2. !3 

• 97 

.81 

1.10 

.8'5 

.86 

.63 

.77 

1.05 

l. 12 

l. 89 

l. 36 

.11 

.40 

• 'i2 

.94 

.48 

l. 58 

.77 

l. 4 7 

1.02 

l. 09 

l. 30 

.10 

1. 56 

.94 

30 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 

0.12 

.. 24 

(.05 

<.OS 

.1'5 

.1 3 

<. r15 

<.OS 

.40 

1.4 5 

• 39 

<.05 

• 10 

.05 

• 21 

.o8 

.24 

(.05 

• 15 

. 24 

• 21 

.48 

.10 

.11 

.08 

• 27 

.39 

(.05 

.o6 

• 21 

• 12 

(.0'5 

<.os 

(.05 

• 27 

.]8 

• l 7 

(.05 

• 14 

• !3 

.o8 

• 14 

(.05 

• 1 5 

.4 5 
Table 4. Analytical results for rock samples from the Big Canyon area-Continued 

Sample 

BC1Ll-10 1 

BCl0-111 

llC10-127 

BC10-145 

l:lC1U-63 

llClU-74 

BC11-213 

BC11-48 

BC1b-1U1 

BC16-46 

BC2-l35 

BC2-147 

BC2-lb'J 

llC2-212 

l:lC2-322 

llC24-120 

BC24-82 

tlC24-94 

llC27-182 

llC27_:204 

llC29-168 

tlC:29-17l 

llCH-43 3 

BC31-It36 

BC31-476 

KC31-4Cl5 

llC3 1-49Cl 

llC32-33:J 

HC32-35b 

llC32-373 

BC32-3'J3 

KCJ2-672 

HC3 2-7US 

llC32-7 Pl 

tlC32-742 

llC32-765 

IICJ2-776 

tlCJ4-777 

tlCJ4-7<J4 

BC34-796 

l:lG34-81JO 

tlC34-8U2 

BC4-103 

llC4-61J5 

tlC4-b 30 

NnO% H2o-z Ct1 2 ~~ 

-----

!1.15 

1. 37 

.14 

(,fJ2 

<. f)2 

.63 

<. iJ2 

<.02 

.44 

.65 

.82 

.')7 

1. 55 

.09 

.b2 

• 26 

.18 

.84 

• I b 

.17 

.17 

.13 

.21 

• IS 

• 14 

.12 

• I 5 

• 20 

.22 

.17 

.lb 

.ll 

1. 33 

!. So 

1. 85 

.')8 

• 22 

.14 

• 1 7 

.21 

• 16 

.19 

<.1)2 

• 19 

• 32 

3. 90 

• 23 

.4 7 

1. 56 

.11 

.42 

1.85 

3.16 

6.0[) 

• 3 5 

.26 

4.67 

.63 

2.95 

2. 87 

1.13 

.72 

.54 

2.96 

l. 17 

.II 

4.1)3 

1.96 

l. 64 

.41 

1.14 

!.US 

1. 97 

3. 9(1 

3. 3 5 

.4o 

.69 

• 13 

l. ()2 

.45 

3. 31 

.46 

2. 6f:J 

1.72 

l. 54 

2.80 

.41 

2.85 

.67 

0.13 o.o 1 

.us 9.85 

• 02 • 97 

.[1) .02 

.10 .04 

.()3 .81 

• 05 (.I) 1 

.1)9 <.!11 

• 31 • 19 

1.71 <.01 

<. f)l 4. 96 

.04 7.77 

.[9 !.46 

.tl2 .04 

.65 .03 

• 13 16.00 

.23 4.01 

• 20 15.30 

• 19 12. 50 

.14 6. 37 

• 17 9. 76 

.09 10.10 

• 18 3. 61 

• 14 8. 54 

• 12 12.60 

.us 7.10 

.04 5.80 

.13 9. 66 

• 19 6. 7 3 

.09 5.59 

• 07 4. 15 

< .o 1 • 53 

.os 3.25 

.06 4.os 

.1)3 1.86 

<.01 2.96 

.oz 1.82 

.04 12.30 

• 03 2. 19 

.04 11.10 

.08 8.04 

.06 7.22 

.04 <.01 

<.01 1.58 

.12 5.81 

total ~ 

r] .40 

9. 32 

.07 

.07 

5. 98 

5.87 

.20 

<.01 

2. 11 

.64 

1.88 

1. 58 

.07 

• 22 

!1.80 

.98 

1. 73 

1.77 

2.69 

<.01 

2.63 

5.40 

.05 

4. 37 

.55 

2.63 

1. 4 7 

5. 82 

5. 17 

.45 

• 70 

.30 

4.63 

6.87 

.14 

8.61 

.05 

4.94 

.16 

4.14 

5. 20 

.35 

.02 

<.01 

4.28 

LOI 9rJO °C Al %-S Fe %-S Mg %-S Ca %-S Na %-S 

---------------------------------------- 3. 18 

6.8() 

.74 

.59 

4. 81 

4.10 

.56 

1. 73 

3. 7 5 

8. 79 

3.11 

5.42 

5. 34 

.so 

11.00 

16.20 

4. 20 

13.10 

7. 17 

7. 56 

7.46 

4.44 

5. 20 

s. 58 

12.10 

4.11 

4.58 

4. 78 

3. 89 

7.43 

5. 29 

.84 

4.63 

5.47 

2.00 

6.05 

3. 01 

6.87 

2. 89 

7. 7 5 

4.91 

9. 37 

• 56 

2.94 

3. 56 

8. 90 

1.10 

1. 40 

1.10 

7.90 

.51 

1. 20 

2. 20 

7.60 

4.90 

1. 20 

1. 30 

9.40 

1. 90 

5.60 

s. 60 

8.40 

6.40 

7 .oo 

8. 30 

7.60 

7.30 

7. 70 

6.80 

7.80 

7.10 

9.00 

5.10 

6. 70 

7.90 

8. 20 

1. so 

2.00 

2.20 

4.00 

2. 70 

9.00 

6.90 

11.00 

6.20 

6. 90 

8.00 

1.20 

8.30 

s. 50 

8. so 

8.9() 

.87 

.95 

7.10 

5.40 

• 57 

.47 

7. 50 

20.00 

4.80 

6.10 

7.00 

1.30 

17.00 

7.00 

4.90 

6. 70 

5. 30 

8.80 

6.80 

6.10 

7. 30 

6.30 

s. 60 

4.20 

4.60 

5.60 

7.00 

8.50 

8. 20 

1.00 

7 .oo 

6.80 

8.20 

8.80 

7. 70 

5.00 

9.40 

6. 70 

6.60 

7.60 

• 38 

7.40 

4. 70 

2. 70 

1.80 

.30 

.01 

I. 30 

.11 

.02 

.02 

2. 30 

.06 

.61 

1.10 

3.60 

.56 

.06 

s. 70 

1.80 

3.10 

2. 40 

3. 70 

2. 90 

2.10 

s. 90 

2. 30 

3.40 

1.60 

1.40 

2. 70 

3.00 

4.10 

4. 30 

.43 

.94 

1.00 

l. 70 

.90 

4.40 

3.00 

3.60 

2.30 

1. 90 

2.90 

.04 

3.90 

1.10 

2. 800 

5.300 

.630 

.020 

.240 

.420 

.007 

.010 

1.100 

.130 

2.100 

3.800 

.730 

.070 

.050 

9. 300 

2. 300 

7. 300 

7. 600 

5.600 

5.100 

S.300 

7. 300 

8.400 

6. 700 

3.900 

3.600 

5.300 

s. 700 

7.100 

6.800 

.340 

l. 600 

1. 700 

1.600 

2.000 

8.500 

6.800 

9.400 

11.000 

7.600 

7 .soo 

.010 

7.SOO 

4.100 

3. 60 

.79 

• 37 

.72 

5. 20 

• 39 

.7! 

.03 

4.'30 

3.80 

.99 

1.10 

3. 20 

.64 

3.10 

2.10 

s. so 

4.70 

5. 30 

4.00 

5.10 

5. 50 

2. 80 

4.10 

4. 50 

5.00 

s. 50 

3.60 

4.30 

3.80 

3. 80 

.89 

1.40 

1.60 

3. 50 

2.10 

2.70 

5.10 

3.80 

3.90 

4.60 

4.10 

.64 

3.10 

3. 90 

Appendix 31 
Table 4. Analytical results for rock samples from the Big Canyon area-Continued 

Sample 

llClrJ-lU 1 

BC!0-111 

JlClU-127 

!JC10-145 

llC1U-b3 

BClU-74 

HCll-213 

HC11-4CJ 

llClb-llll 

l:lC1b-46 

llC2-l35 

JlC2-14 7 

llC2-169 

tlC2-2!2 

llC2- 322 

BC24-120 

l:lC24-S2 

BC24-9l+ 

BC27-l82 

l:lC:U-2C14l 

BC29-lb8 

BC29-17l 

llC31-433 

l:lCJl-436 

BC3l-476 

BCJl-485 

BC3l-49S 

HC32-339 

BC32-35b 

l:lC32-373 

JlC3 2-393 

BC32-b 72 

llC32-705 

BC32-718 

BC32-742 

HC32-765 

llC32-776 

BC34-777 

BC34-794 

BC34-7'Jb 

l:lC34-8UU 

!JC34-8U2l 

llC4-l03 

BC4-6U5 

BC4-630 

K%-S Ti%-S 

u.sz 1.1n 

p .1)8 

• 52 .o 5 

<.us .02 

• ll • 32 

<.us • ill 

.us .04 

<.us .l)b 

.57 1.00 

.09 • 2 5 

(.1) 5 • 13 

~ .os . 16 

1.60 .57 

.44 ,1)8 

(.1)5 .09 

• 93 .16 

• 57 • 22 

• 30 .12 

• 13 .1 b 

.ou 4') 

.43 • 46 

.to .20 

.40 • btl 

• 28 • 26 

.88 .38 

• 30 • 30 

• 84 • 30 

.06 .11 

.10 .18 

.28 .96 

.74 .85 

.10 .06 

.05 .19 

<.OS .12 

• 27 • 59 

< .1)5 .14 

.12 1.00 

.16 .08 

• 27 • 48 

• 21 • 30 

.22 

.20 

.11 

.tt 

.22 

.zu 

• 4 7 

.04 

• 89 

• 10 

l' ;~-s Ag ppo-S 

(). l 30 <2 

.11)(1 <2 

.020 (2 

<.005 (2 

.1)6() <2 

.uso (2 

.008 <2 

< .ous <2 

.1oo <2 

.62U 

.130 <2 

.o 10 <2 

.040 (2 

.020 (2 

.080 

.030 <2 

.100 <2 

(.005 (2 

.060 <2 

.1)91) <2 

.080 <2 

.210 (2 

.040 <2 

.040 <2 

.030 <2 

.110 <2 

.160 <2 

.010 (2 

.021) <2 

.1)51) <2 

.050 (2 

.020 <2 

<.005 <2 

<.005 <2 

.tOO <2 

.1)70 (2 

.070 (2 

.020 <2 

.060 (2 

.1)50 <2 

.I) 31J 

.060 

<. 01)5 

.061) 

.t8U 

<2 

<2 

<2 

<2 

<2 

As ppm-S 

so 

940 

(ill 

170 

il80 

870 

91) 

30 

100 

l ,500 

371) 

30 

211 

tO 

2, 700 

so 

60 

130 

340 

<tO 

250 

660 

<til 

821) 

too 

340 

• 2 

l, 100 

780 

40 

60 

50 

700 

1,400 

40 

1,000 

<to 

l ,too 

20 

830 

860 

tOO 

ItO 

<10 

740 

Au ppm Ba ppm-S 

o. 1 170 

3 .t 48 

<. 1 790 

• 3 15 

2. 4 91 

.8 l 5 

• 8 290 

• 2 20 

• l 230 

70.0 120 

• 3 17 

• 2 tt 

<. l 1, 900 

< .t l ,200 

tJ. 0 17 

• 5 !50 

<.1 130 

.3 380 

.8 86 

<.t 240 

4. 9 110 

4 .t 170 

<.t 99 

2.8 70 

3. 9 500 

3. 3 170 

210 41 

1.4 16 

• 9 15 

< .t ISO 

<.1 72 

<. 1 380 

2. 3 74 

2. 7 22 

<. l 270 

t. 6 27 

<.I 30 

.4 39 

<.t 860 

t.t 190 

1.4 

<.t 

.t 

<.1 

• 7 

180 

450 

510 

13 

24 

Ce ppm-S 

23 

32 

17 

tO 

22 

17 

14 

19 

30 

65 

13 

14 

62 

tO 

59 

39 

17 

24 

20 

20 

2n 

16 

<4 

<4 

16 

13 

23 

21 

18 

23 

10 

10 

15 

to 

(4 

Co ppm-S 

57 

41 

45 

18 

40 

21 

11i 

20 

47 

57 

44 

~4 

48 

28 

51 

31 

29 

58 

32 

28 

16 

39 

41 

49 

57 

22 

23 

33 

25 

48 

31 

60 

42 

40 

48 

<t 

46 

36 

32 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 

Cr ppm-S 

280 

83 

13 

11 

190 

tO 

11 

21 

220 

ttl) 

17 

3fi0 

17 

46 

480 

160 

ISO 

120 

200 

30 

19 

680 

230 

97 

45 

too 

230 

210 

340 

10 

28 

19 

63 

27 

240 

23 

400 

200 

160 

200 

12 

330 

180 
Table 4. Analytical results for rock samples from the Big Canyon area-Continued 

Sample 

BC11J-1U1 

HClU-111 

HC1U-l27 

llC10-1-'15 

BC111-b3 

llC10-74 

HC11-211 

HC11--'18 

BC16-1rl1 

BC16-4b 

BC2-135 

BC2-147 

BC2-169 

HC2-2lL 

llC..!-322 

BC24-1211 

BC24-82 

BC24-94 

BC27-182 

llC27-2U4 

BC29-168 

llC29-17l 

BC31-433 

llC31-436 

llC3l-47b 

BC3l-485 

BC31-498 

BC32-339 

BC32-356 

BC32-373 

BC32-393 

BC32-6 7 2 

BC32-705 

BC32-718 

BC32-742 

BC32-765 

BC32-776 

BC34-777 

BC34-794 

BC34-796 

BC34-800 

BC34-802 

BC4-l03 

BC4-605 

BC4-630 

Cu ppm-S 

35 

43 

14 

20 

1f>U 

23 

30 

20 

140 

110 

58 

71) 

55 

b 10 

11U 

11JU 

280 

13 

33 

110 

28 

66 

42 

120 

120 

12 

62 

12 

57 

83 

63 

130 

170 

83 

24 

85 

44 

76 

53 

65 

87 

18 

82 

89 

l~u ppm-S Ga ppm-S llg ppm La ppm-S Li ppm-S 

22 1).03 11 3l 

<2 lfl 1.60 41 <2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

(2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

33 

17 

24 

23 

3 7 

15 

17 

20 

21 

23 

20 

23 

15 

14 

20 

20 

21 

15 

30 

22 

20 

15 

16 

23 

17 

22 

17 

25 

15 

17 

19 

20 

22 

.10 

• 57 

• su 

• 79 

.I) 3 

.Cl3 

.07 

• 58 

• 30 

• 13 

.02 

<.02 

l.OO 

.20 

.61) 

.69 

• 13 

.06 

.89 

.91 

.03 

• 78 

.64 

• 55 

.07 

.36 

.16 

.03 

.07 

.12 

.43 

.61 

.03 

.42 

.02 

.32 

.04 

• 29 

.36 

.08 

.05 

<.02 

.86 

30 

13 

80 

13 

15 

67 

33 

23 

11 

<2 

<2 

10 

12 

20 

<2 

<2 

30 

27 

17 

30 

<2 

<2 

<2 

<2 

<2 

<2 

(2 

17 

<2 

<2 

57 

13 

31 

25 

lll 

(2 

39 

19 

11 

15 

36 

34 

14 

20 

30 

13 

13 

25 

20 

~In ppm-S No ppm-S 

1 ,noo <2 

9 ,111)0 <2 

1,200 

6 7 

18() 

4,400 

sg 

23 

2, 900 

4, 500 

4,400 

F, ,800 

10,000 

720 

4,300 

2,100 

l ,400 

6 ,01)0 

l '300 

1 '3110 

1,300 

991l 

1, 700 

1,200 

l, 100 

900 

l' 100 

l ,3110 

1 ,fiOO 

1, 300 

1, 300 

880 

9,400 

11,000 

13,000 

7 '100 

1,800 

l ,100 

1,500 

1,600 

1,200 

l, 500 

30 

1,400 

2,100 

<2 

43 

10 

<2 

<2 

<2 

1611 

<2 

<2 

(2 

<2 

<2 

<2 

<2 

<2 

<2 

22 

<2 

<2 

<2 

<2 

<2 

(2 

<2 

<2 

(2 

<2 

<2 

<2 

690 

Nd ppm-S Ni ppr1-S 

zn 19rl 

41 lfil) 

10 

17 

26 

10 

21 

75 

14 

16 

53 

30 

2fi 

10 

l'3 

1 ~ 

14 

13 

16 

23 

<4 

1-'1 

31 

27 

18 

27 

10 

10 

11 

22 

14'l 

68 

10 

1 3n 

80 

42 

50 

140 

27 

201) 

300 

93 

180 

93 

160 

36 

41 

390 

110 

50 

20 

14 

170 

190 

150 

230 

16 

45 

41 

70 

lOll 

150 

37 

200 

89 

87 

94 

150 

140 

Appendix 33 
Table 4. Analytical results for rock samples from the Big Canyon area-Continued 

Sample Pb ppm-S Sb ppm-S Sc ppm-S Se ppm Sr ppm-S Te ppm V ppm-S Y ppm-S Yb ppm-S Zn ppm-S Type 

BC10-101 

BC10-111 

BC10-127 

BC10-145 

BC1 0-63 

BC10-74 

BC11-213 

BC11-48 

BC16-l01 

BC16-46 

BC2-135 

BC2-147 

BC2-169 

BC2-212 

BC2-322 

BC24-120 

BC24-82 

BC24-94 

BC27-182 

BC27-2ll4 

BC29-168 

BC29-171 

BC31-433 

BC31-436 

BC31-476 

BC31-485 

BC31-498 

BC32-339 

BC32-356 

BC32-373 

BC32-393 

BC32-672 

BC32-705 

BC32-71H 

BC32-742 

BC32-765 

BC32-776 

BC34-777 

BC34-794 

BC34-796 

BC34-8UU 

BC34-802 

BC4-103 

BC4-605 

BC4-630 

(4 

<4 

<4 

<4 

<4 

<4 

20 

11 

23 

(4 

13 

15 

<4 

(4 

(4 

<4 

<4 

<4 

<4 

(4 

<4 

(4 

(4 

(4 

14 

17 

l2 

(4 

(4 

<4 

<4 

<4 

<4 

<4 

<4 

37 

0.6 

6.2 

.6 

11.0 

3. 3 

4.2 

• 6 

.6 

1.1 

6.7 

2. 2 

1.4 

• 7 

• 5 

9. 4 

1. 7 

2. 5 

3.4 

1.1 

.8 

2. 2 

4.0 

.1 

3.4 

1.1 

1. 7 

.6 

2. 6 

1.6 

• 5 

.6 

.4 

2. 7 

3.4 

.9 

3.1 

.4 

2. 6 

.6 

2. 3 

2. 3 

• 8 

.4 

• 3 

1.0 

44 

13 

32 

34 

22 

10 

36 

22 

28 

15 

16 

18 

37 

26 

16 

35 

31 

21 

11 

22 

30 

34 

39 

10 

17 

37 

26 

50 

43 

38 

44 

40 

20 

<O. 1 

2. 3 

(.l 

.4 

1.6 

1.2 

<. 2 

< .1 

• 5 

(2 .0 

<2.0 

.6 

.4 

<.1 

18.0 

.6 

4.4 

6. 9 

1.9 

<2.11 

1.3 

3. 2 

(5.0 

2.1 

<LO 

1.1 

• 4 

<2.0 

<2.0 

(.5 

<. 2 

<.1 

(2. I) 

(5.0 

(. 2 

11.0 

• 5 

(2.0 

(. 2 

<2.0 

<2.0 

<. 2 

<. 5 

<2.0 

4.0 

69 

210 

16 

23 

19 

(2 

39 

120 

82 

140 

29 

30 

28 

410 

130 

470 

350 

190 

500 

40() 

130 

301) 

390 

220 

370 

290 

280 

220 

150 

29 

74 

110 

49 

100 

200 

400 

201) 

680 

520 

240 

150 

83 

0.130 

1.200 

.050 

.100 

.450 

.430 

.060 

.120 

.130 

.830 

• 300 

• 260 

.044 

.150 

2. 200 

.062 

.210 

.890 

.078 

<.020 

.082 

.290 

(.020 

.130 

.087 

.190 

.023 

.410 

• 580 

.042 

.045 

.300 

.550 

1.000 

.065 

.770 

(.020 

.170 

(.020 

1.200 

.440 

.060 

.048 

(.020 

2.400 

3 30 

83 

27 

25 

150 

40 

15 

40 

220 

84 

230 

360 

220 

20 

78 

27() 

110 

94 

230 

3 [() 

480 

49 

210 

180 

390 

110 

130 

200 

370 

280 

260 

94 

130 

41 

330 

96 

280 

63 

310 

430 

340 

310 

26 

260 

140 

36 

14 

30 

17 

28 

14 

14 

17 

13 

12 

21 

15 

18 

22 

12 

10 

13 

16 

14 

29 

30 

14 

10 

30 

36 

19 

12 

10 

<2 

30 

14 

(1 

(1 

<1 

(1 

<1 

(1 

3 

<1 

(1 

(1 

<1 

<1 

(1 

(1 

(l 

170 

190 

23 

89 

120 

11 

110 

110 

44 

52 

92 

41 

120 

80 

110 

72 

55 

97 

62 

45 

70 

28 

69 

52 

54 

60 

49 

86 

92 

34 

96 

120 

150 

140 

66 

29 

120 

69 

64 

92 

<4 

92 

53 

34 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, ElDorado County, California 

25 

24 

13 

12 

24 

12 

12 

12 

25 

24 

15 

15 

25 

12 

24 

24 

25 

25 

24 

25 

24 

24 

25 

24 

25 

24 

24 

24 

24 

25 

25 

15 

14 

14 

14 

14 

25 

24 

25 

24 

24 

25 

12 

25 

25 
Table 4. Analytical results for rock samples from the Big Canyon area-Continued 

Sample 

BC4-656 

BC4-669 

BC4-683 

BC4-701 

BC4-773 

BC4-781 

BC4-88 

BC4-9 2 

BCS-95 

BC5-98 

BC7-25 

BC7-55 

BC8-135 

BC8-218 

BC8-252 

BC8-499 

BC8-501 

BC8-84 

BC9-185 

BC9-210 

BC9-225 

BC9-243 

BC9-348 

104-116 

L04-124 

104-146 

104-157 

105-125 

105-42 

LOS-46 

107-102 

107-109 

L07-125 

107-142 

107-59 

107-75 

107-86 

SiOz% 

45.0 

44.9 

39.6 

41.5 

43.7 

42.4 

94.0 

92.0 

65.8 

83.1 

73.2 

.OH 

94.3 

46.2 

73.1 

49.0 

48.0 

88.3 

94.3 

94.5 

51.3 

79.2 

46.1 

43.3 

41.5 

37.9 

40.8 

41.7 

33.7 

43.5 

49.0 

43.8 

46.8 

42.7 

38.7 

46.1 

44.9 

5.69 

12.10 

11.10 

11.00 

12.00 

14.10 

.79 

.69 

14.20 

1.81 

8.34 

.OH 

2. 18 

19.30 

2.65 

12.50 

14.40 

5.67 

2.18 

1. 91 

20.10 

4.53 

14.40 

15.60 

12.70 

10.90 

13.60 

15.60 

9.30 

12.10 

14.00 

12.30 

12.40 

12.20 

11.10 

14.70 

13.60 

11.10 O.OH 

5.79 .OH 

8.19 .OH 

8.79 .OH 

6.93 .OH 

8.22 6.01 

3.57 .06 

4.60 .09 

6.63 .OH 

8.37 .OH 

9.99 .29 

.OH .OH 

• 95 • 52 

21.40 <.01 

18.70 .04 

8.62 .OH 

11.80 .OH 

1.65 .06 

1.21 .86 

1.38 .72 

6.96 5.02 

9.33 .OH 

11.20 7.74 

10.50 7.67 

8.49 .OH 

9.03 .OH 

10.30 7.84 

11.50 7.86 

8.04 .OH 

7. 70 .OH 

5.37 .OH 

5.74 .OH 

9.76 6.07 

6.25 .OH 

10.30 .OH 

1 1. 80 7. 81 

10.10 .OH 

MgO% 

2.25 

2.67 

5.38 

5.82 

4.87 

7.36 

<.10 

<.10 

.85 

.96 

.1 7 

.OH 

.47 

.11 

<.10 

4.67 

7.00 

.19 

.62 

.55 

7.05 

.18 

10.60 

6.71 

4.40 

6.12 

6.82 

8.89 

7.62 

4.04 

3.49 

4.80 

5.38 

5.02 

6.87 

6.83 

5.57 

CaO% 

10.50 

12.70 

12.60 

9.90 

8.85 

7.85 

<.02 

<.02 

.17 

.53 

.OS 

.OH 

.03 

<.02 

<.02 

8.14 

4.33 

.04 

.07 

.07 

.20 

.04 

10.10 

8.93 

11.30 

11.50 

10.20 

8.27 

14.30 

9.01 

7.13 

9.95 

6.46 

10.20 

9.87 

6.39 

5.69 

2.25 

6.04 

4.80 

5.73 

6.91 

5.28 

.33 

.28 

4.78 

1. 57 

4.57 

.OH 

.51 

.23 

.23 

6.32 

5.14 

1.34 

• 61 

.47 

2.90 

1.71 

2.59 

4.72 

5.59 

5.18 

4.49 

3.27 

5.06 

6.38 

7.96 

6.67 

6.28 

6.81 

5.22 

5.13 

5.84 

KzO% 

0.79 

.44 

.54 

.16 

.09 

.68 

<.02 

<.02 

.04 

<.02 

.10 

.OH 

.22 

<.02 

<.02 

.ss 

2.21 

.so 

• 17 

.27 

3.43 

<.02 

.12 

.73 

.99 

1.01 

.74 

1. 7 2 

.18 

.86 

.12 

.42 

.73 

.30 

.40 

.56 

1. 12 

TiOz% 

1.94 

.58 

1. 04 

.98 

.76 

.93 

.08 

.OS 

1.47 

.10 

1.29 

.OH 

.08 

.80 

.52 

.94 

1. 16 

.23 

.09 

.08 

.96 

.53 

1.07 

1.16 

.82 

1.27 

1. 48 

1.12 

.48 

1.73 

1.14 

.95 

2.07 

.67 

1.22 

1.96 

1.66 

0.16 

<.os 

<.OS 

<.OS 

• 1 R 

.09 

<.os 

<.OS 

• 11 

.10 

.08 

.OH 

<.OS 

.28 

• 61 

.07 

.08 

<.OS 

<.os 

<.OS 

<.os 

<.OS 

.07 

• 11 

.14 

.21 

.16 

• 12 

.12 

.35 

.10 

.11 

.27 

<.os 

.08 

.23 

.15 

Appendix 35 
Table 4. Analytical results for rock samples from the Big Canyon area-Continued 

Sample 

BC4-656 

BC4-669 

BC4-683 

BC4-701 

BC4-773 

BC4-781 

BC4-88 

BC4-92 

BCS-95 

BCS-98 

BC7-25 

BC7-55 

BCS-135 

BC8-218 

BC8-252 

BC8-499 

BC8-501 

BC8-84 

BC9-185 

BC9-210 

BC9-225 

BC9-243 

BC9-348 

104-116 

104-124 

104-146 

104-157 

105-125 

105-42 

105-46 

107-102 

107-109 

107-125 

107-142 

107-59 

107-7 5 

107-86 

MnO% 

0.23 

.25 

.26 

.18 

.19 

.18 

<.02 

.04 

.03 

.60 

.04 

.OH 

.10 

.10 

<.02 

.12 

• 15 

<.02 

.23 

.24 

.43 

.14 

.17 

.15 

.16 

.20 

.23 

.16 

.28 

.16 

.11 

.IS 

.12 

.15 

.16 

.19 

.12 

1.00 

1.22 

l. 69 

1.11 

.31 

2.87 

.88 

1.00 

3.79 

.49 

1.96 

1.22 

.56 

10.00 

3.74 

1.60 

2. 77 

1.38 

• 51 

.54 

5.85 

1.14 

4.01 

4.07 

1.50 

.94 

3.83 

4.54 

.96 

.53 

.22 

.48 

1.80 

.29 

1.44 

3.53 

1. 86 

0.06 

.20 

<.01 

.03 

.04 

.06 

.06 

.04 

.71 

.04 

.12 

.41 

.10 

1.88 

.67 

.20 

.11 

.10 

.04 

.04 

.48 

.22 

.05 

.08 

.07 

.05 

.09 

.06 

.06 

.04 

<.01 

.01 

.08 

<.01 

.02 

.07 

.02 

C02% 

10.00 

10.70 

13.30 

13.10 

12.60 

10.50 

.03 

.02 

.02 

.94 

.02 

1.64 

<.01 

<.01 

<.01 

4. 77 

l. 92 

<.01 

<.Ol 

.01 

<.01 

.02 

.78 

5.51 

10.60 

14.10 

8.52 

4.20 

19.80 

11.40 

10.40 

14.10 

2.25 

15.40 

12.90 

3.48 

7.76 

9.67 

3.51 

3.48 

3.18 

4.38 

.35 

.13 

.28 

.84 

1. 79 

.02 

17.70 

.03 

.02 

.02 

4.00 

2.36 

<.01 

.05 

.11 

.09 

4.56 

.03 

.02 

3.12 

3.16 

.02 

<.01 

1. 52 

3.65 

2.10 

1.36 

.01 

1.36 

3.10 

.56 

3.09 

101 900 °C Al %-S 

4.57 3.10 

6.95 6.70 

10.10 6.30 

9.01 6.30 

6.52 6.70 

11.60 

1.11 

1.35 

4.65 

1.69 

2.21 

.OH 

.84 

11.40 

4.11 

3.10 

2.86 

1.55 

.41 

.54 

5.49 

3.98 

2.90 

8.32 

8.37 

10.10 

11.10 

7.98 

17.70 

6.85 

6.97 

11.50 

9.14 

12.40 

9.72 

5.41 

5.80 

8.00 

.37 

.32 

7.40 

.91 

4.50 

3.00 

1.10 

10.00 

1.40 

6.80 

7.80 

3.10 

1.10 

1.00 

11.00 

2.50 

8.20 

8.70 

7.00 

6.10 

7.70 

8.90 

5.30 

6.70 

7.50 

6.90 

7.10 

6.80 

6.40 

8.20 

7.50 

Fe %-S 

7.30 

3.80 

5.50 

5.90 

4.50 

5.50 

2.70 

3.50 

4.30 

6.00 

7.10 

24.00 

.65 

14.00 

13.00 

5.50 

7.60 

1.20 

.90 

1.00 

4.70 

6.60 

7.50 

7.10 

5.70 

6.10 

6.90 

7.50 

5.50 

5.10 

3.50 

3.90 

6.70 

4.20 

7.00 

7.90 

6.80 

Mg %-S 

1.30 

1.50 

3.10 

3.40 

2.80 

4.20 

.o 1 

.02 

.46 

.57 

.08 

.78 

.26 

.04 

.o 1 

2.60 

3.80 

.09 

.35 

.33 

3.90 

.09 

5.90 

3.80 

2.50 

3.50 

3.90 

4.70 

4.50 

2.30 

2.00 

2.80 

3.20 

3.00 

4.00 

3.90 

3.10 

Ca %-S 

7.700 

9.200 

9.200 

7.300 

6.400 

5.800 

.009 

.020 

.140 

.430 

.050 

.530 

.030 

.030 

.010 

5.900 

3.200 

.040 

.070 

.060 

.160 

.040 

7.500 

6.200 

7.500 

8.100 

7.200 

5.700 

10.000 

6.100 

5.000 

7.000 

4.600 

7.300 

6.900 

4.500 

4.000 

36 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 

Na %-S 

1.60 

4.50 

3.70 

4.40 

s.oo 

4.00 

.19 

.15 

3.30 

1.20 

3.40 

2.50 

.30 

.02 

.01 

4.50 

3.70 

.97 

.39 

.27 

2.10 

1. 30 

2.00 

3.60 

4.20 

4.00 

3.50 

2.80 

4.00 

4.70 

5.60 

5.10 

4.90 

5.10 

4.20 

4.00 

4.30 
Table 4. Analytical results for rock samples from the Big Canyon area-Continued 

Sample K %-S Ti %-S P %-S Ag ppm-S As ppm-S Au ppm Ba ppm-S Ce ppm-S Co ppm-S Cr ppm-S 

BC4-656 

BC4-669 

BC4-683 

BC4-701 

BC4-773 

BC4-781 

BC4-88 

BC4-92 

BCS-95 

BCS-98 

BC7-25 

BC7-55 

BC8-l35 

BC8-218 

BC8-252 

BC8-499 

BC8-501 

BC8-84 

BC9-185 

BC9-210 

BC9-225 

BC9-243 

BC9-348 

104-116 

L04-124 

104-146 

L04-157 

LOS-125 

LOS-42 

LOS-46 

L07-102 

L07-109 

L07-125 

107-142 

L07-59 

107-75 

L07-86 

0.67 

.40 

.51 

.16 

.09 

.63 

<.OS 

<.OS 

<.OS 

<.OS 

.10 

.09 

.17 

<.OS 

<.OS 

.so 

1.90 

.42 

.15 

.21 

3.00 

<.OS 

.12 

.67 

.88 

.92 

.68 

1.60 

.17 

.78 

• 11 

.40 

.68 

.27 

.36 

.53 

.98 

0.06 o.oso 

.09 .009 

.17 <.005 

.17 .006 

.07 .070 

.20 .030 

.03 <.005 

.02 .009 

.29 .040 

.06 .040 

.27 .030 

.16 .190 

.as <.oos 

.17 .130 

.19 .260 

.46 .030 

• 66 .030 

.14 <.005 

.06 .009 

.as .020 

.56 .020 

.33 .010 

.63 .030 

.48 .040 

.18 .060 

.34 .090 

.35 .060 

.43 .050 

.04 .050 

.21 .160 

.23 .040 

.20 .040 

.53 .110 

.12 (.005 

.19 .040 

.62 .100 

.40 .060 

34 

3 

<2 

<2 

<2 

<2 

<2 

<2 

15 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

<2 

700 

440 

270 

260 

670 

10 

610 

480 

160 

300 

600 

3,200 

<10 

730 

550 

870 

550 

30 

10 

<10 

<10 

530 

<10 

<10 

490 

720 

20 

20 

200 

560 

220 

170 

<10 

140 

210 

<10 

320 

2. 1 

.9 

4.2 

4.8 

.7 

.1 

.5 

.4 

.6 

.9 

1. 8 

9.0 

<.1 

8.0 

1.7 

1.1 

20 

20 

13 

11 

14 

87 

28 

13 

8 

20 

13 

11 

710 

89 

21 

12 

.1 140 

<.1 1,000 

<.1 680 

< .1 320 

<.1 6,200 

1.1 35 

<.1 18 

<.1 270 

1.1 320 

1.6 230 

<.1 42 

<.1 470 

.4 150 

1. 7 140 

.4 23 

• 5 100 

<.1 310 

.2 38 

1. 7 52 

<. 1 130 

1.2 200 

<4 

12 

5 

5 

8 

10 

10 

8 

5 

19 

24 

91 

15 

96 

18 

<4 

6 

21 

14 

16 

25 

17 

4 

5 

<4 

7 

7 

5 

7 

16 

5 

15 

<4 

<4 

11 

10 

100 

29 

38 

39 

29 

37 

2 

3 

6 

23 

2 

75 

5 

13 

3 

39 

55 

2 

12 

13 

40 

14 

58 

56 

47 

43 

50 

60 

26 

27 

25 

24 

44 

24 

54 

52 

40 

140 

150 

310 

250 

120 

58 

19 

11 

250 

4 

49 

32 

10 

210 

79 

360 

520 

28 

12 

10 

390 

34 

590 

470 

610 

330 

370 

800 

140 

130 

300 

330 

330 

130 

400 

340 

280 

Appendix 37 
Table 4. Analytical results fur rock samples from the Big Canyon area-Continued 

Sample 

BC4-656 

BC4-669 

BC4-683 

BC4-70 1 

BC4-773 

BC4-781 

BC4-88 

BC4-92 

BC5-95 

BC5-98 

BC7-25 

BC7-55 

BC8-135 

BC8-218 

BC8-252 

BC8-499 

BC8-50l 

BC8-84 

BC9-185 

BC9-210 

BC9-225 

BC9-243 

BC9-348 

104-116 

L04-124 

L04-146 

L04-157 

105-125 

L05-42 

105-46 

L07-l02 

107-109 

L07-125 

107-142 

L07-59 

107-75 

L07-86 

Cu ppm-S Eu ppm-S 

47 <2 

18 <2 

33 <2 

20 <2 

39 <2 

97 <2 

89 <2 

84 <2 

37 <2 

300 <2 

40 <2 

1 ,000 3 

18 <2 

480 6 

200 <2 

40 <2 

83 <2 

44 <2 

33 <2 

42 <2 

100 <2 

320 <2 

100 <2 

37 <2 

130 <2 

39 <2 

50 (2 

110 (2 

5 (2 

20 (2 

8 (2 

9 (2 

81 (2 

10 (2 

77 (2 

76 (2 

100 (2 

Ga ppm-S Hg ppm La ppm-S Li ppm-S Mn ppm-S Mo ppm-S Nd ppm-S 

37 6.30 <2 7 1,700 14,000 <4 

28 • 77 4 8 1,800 1,100 8 

24 .36 <2 15 1,900 31 <4 

23 .20 <2 10 1 ,300 32 <4 

20 • 25 <2 <2 1 '300 9 7 

18 .20 <2 27 1 ,300 2 6 

7 .20 9 <2 190 2 7 

4 .49 8 <2 380 <2 7 

34 • 74 2 5 270 1,700 5 

8 • 30 24 7 4,500 10 20 

17 .32 17 2 400 <2 21 

27 1.20 140 10 11 ,000 22 92 

4 .03 8 5 720 <2 8 

24 .30 140 5 750 480 150 

10 .38 20 <2 220 61 23 

14 .09 <2 14 890 17 <4 

18 .03 <2 35 1,000 <2 6 

7 .12 10 5 86 8 8 

5 <.02 9 8 1,700 <2 9 

4 .OS 11 7 1,700 <2 11 

17 .03 13 59 3,000 2 19 

7 .18 19 <2 1 '1 00 9 18 

17 (.02 <2 21 1,300 <2 6 

17 .02 <2 44 1,100 <2 5 

16 .13 <2 16 1,200 <2 <4 

17 .os <2 10 1 ,500 <2 5 

17 .02 2 37 l '700 <2 6 

18 (.02 <2 52 1,200 <2 5 

17 .03 <2 3 2' 100 (2 5 

17 • 08 6 <2 l • l 00 <2 1 3 

19 .06 <2 <2 800 <2 <4 

17 .09 <2 2 1,100 <2 4 

15 .02 6 13 940 (2 15 

17 .03 <2 (2 1,100 <2 <4 

13 .09 <2 12 l, 200 <2 <4 

21 .08 4 29 1,400 <2 11 

16 • 08 3 14 870 <2 7 

38 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, ElDorado County, California 

Ni ppm-S 

290 

110 

190 

200 

130 

53 

4 

5 

44 

89 

16 

250 

22 

73 

9 

220 

290 

5 

31 

67 

200 

67 

360 

250 

240 

180 

210 

350 

150 

110 

110 

130 

220 

90 

270 

210 

130 
Table 4. Analytical results for rock samples from the Big Canyon area-Continued 

Sample Pb ppm-S Sb ppm-S Sc ppm-S Se ppm Sr ppm-S Te ppm V ppm-S Y ppm-S Yb ppm-S Zn ppm-S Type 

BC4-656 

BC4-669 

BC4-683 

BC4-701 

BC4-773 

BC4-781 

BC4-88 

BC4-92 

BCS-95 

BCS-98 

BC7-25 

BC7-55 

BC8-135 

BC8-218 

BC8-252 

BC8-499 

BC8-501 

BC8-84 

BC9-185 

BC9-210 

BC9-225 

BC9-243 

BC9-348 

104-ll6 

L04-124 

104-146 

L04-157 

105-125 

LOS-42 

105-46 

L07-102 

107-109 

107-125 

107-142 

L07-59 

107-75 

107-86 

570 

15 

<4 

<4 

<4 

<4 

<4 

<4 

10 

<4 

11 

<4 

43 

20 

<4 

<4 

8 

<4 

<4 

<4 

32 

<4 

<4 

<4 

<4 

<4 

<4 

<4 

<4 

<4 

<4 

<4 

<4 

<4 

69.0 

4.3 

2.0 

1.3 

1.8 

2.6 

2.4 

.9 

1.7 

2.0 

3.6 

9.4 

.2 

5.1 

5.3 

2.8 

1.9 

.9 

• 3 

.5 

1.4 

3.8 

• 2 

.4 

3.0 

2.6 

.9 

.6 

1.3 

43.0 

1.0 

.8 

1.6 

.6 

1.1 

1.1 

1.8 

28 

22 

33 

31 

20 

33 

36 

10 

15 

65 

19 

28 

39 

8 

37 

12 

37 

36 

28 

34 

35 

36 

11 

11 

12 

20 

47 

17 

30 

38 

33 

10.0 

2.6 

1.0 

.6 

1.5 

.4 

(2.0 

2.5 

2.0 

.4 

1.1 

<S.O 

<.1 

4.6 

5.8 

1.1 

.5 

.3 

<.1 

<.1 

.1 

1.4 

.2 

<.5 

2.4 

3.0 

<.2 

<.2 

1.4 

3. 1 

1.2 

1.4 

<.2 

3.5 

1.6 

.4 

2.0 

70 

90 

170 

390 

310 

230 

<2 

<2 

10 

56 

11 

21 

14 

84 

52 

48 

19 

140 

16 

130 

99 

4IO 

410 

190 

160 

530 

330 

250 

340 

210 

360 

350 

110 

210 

22.000 

1.000 

.280 

.230 

.290 

<.020 

.470 

.440 

1.200 

.420 

.300 

2.000 

.130 

2.600 

1.000 

.090 

.020 

.150 

.068 

.110 

<.020 

.240 

<.020 

<.020 

.038 

.029 

<.020 

<.020 

.063 

.056 

.048 

.029 

<.020 

.038 

.062 

<.020 

.032 

220 

120 

230 

380 

70 

230 

95 

93 

370 

65 

300 

870 

26 

270 

160 

160 

200 

43 

17 

10 

220 

17 

220 

210 

3IO 

270 

230 

200 

80 

96 

150 

230 

490 

79 

290 

250 

280 

11 

8 

11 

<2 

<2 

29 

8 

59 

14 

21 

9 

50 

15 

24 

24 

12 

15 

11 

23 

13 

17 

16 

8 

16 

<1 

<1 

<1 

<1 

<1 

8 

<1 

<I 

<I 

<I 

35 

30 

53 

49 

24 

79 

R 

8 

23 

100 

41 

340 

27 

91 

26 

49 

90 

17 

34 

3R 

120 

71 

75 

88 

92 

59 

86 

97 

83 

46 

22 

31 

90 

26 

66 

95 

68 

24 

25 

24 

24 

25 

25 

12 

12 

25 

12 

24 

11 

13 

I1 

11 

24 

25 

I5 

12 

12 

25 

15 

25 

25 

24 

24 

25 

25 

25 

24 

25 

25 

26 

25 

24 

26 

24 

1Results are not included for some ICP-AES determinations in which detectable amounts were present 

in only a few samples. Au detected in 4 samples (8-92 ppm); Be detected in 7 samples (1-3 ppm); Cd 

detected in one sample (3 ppm); Th detected in 10 samples (4-9 ppm); U detected in no samples with limit 

of detection 10 ppm. 

2Type: Two characters describe character of sample analyzed, First character is protolith type: 

1, metachert; 2, mafic igneous rock. Second character is alteration and mineralization character: 1, 

pyritic metachert, gold assay> 1 ppm; 2, pyritic metachert, gold assay < 1 ppm; 3, barren metachert, PCA 

alteration, gold assay> 1 ppm; 4, PCA alteration, gold assay < 1 ppm; 5, PCA alteration, barren; 6, 

barren and slightly altered mafic rock. 

3Total iron reported as Fe203• 

Appendix 39 
Table 5. Lower limits of determination in geochemical analyses 

Major elements, in weight percent 

SiOz •••••••••••••••••• 

Al203 ••••••••••••••••• 

1FeT03 

FeO 

MgO 

CaO 

. . . . . . . . . . . . . . . . 

Na2 0 •••••••••••••••••• 

KzO ••••••••••••••••••• 

2 Al ( S) ••••••••••••••• 

Ca ( S) 

Fe (S) 

K (S) 

0.05 

0.10 

0.04 

0.01 

0.10 

0.05 

0.15 

0.02 

0.05 

0.05 

0.05 

0.05 

Minor elements, 

Ag ................... 2 

As ................... 10 

Au ................... 0.05 

Ba ................... Be ................... 1 

Bi ................... 10 

Cd ................... 2 

Ce ................... 4 

Co ................... 1 

Cr ................... 

Cu ................... Eu ................... 2 

Ga ................... 4 

Hg ................... 0.02 

Ho ................... 4 

La ................... 2 

Li ................... 2 

1rotal iron reported as Fe2o3• 

in parts 

TiO z ••.•••••••••••••• 

Pzo3 ••••••••••••••••• 

MnO •••••••••••••••••• 

COz •••••••••••••••••• 

8total ••••••••••••••• 

Mg (S) 

Na (S) 

p ( s) •••••••••••••••• 

Ti ( S) ••••••••••••••• 

per million 

Mn . ................. Mo . ................. Nb . ................. Nd . ................. Ni . ................. 

Pb . ................. Sc . ................. Se . ................. Sn . ................. Sr . ................. 

Ta . ................. Te . ................. Th . ................. v . .................. y . .................. Yb . ................. Zn . ................. 

2(s), determined by induction-coupled plasma atomic emission 

spectrometry. 

40 Geology and Geochemistry of Gold Deposits of the Big Canyon Area, El Dorado County, California 

0.02 

0.05 

0.02 

0.01 

0.01 

0.01 

0.01 

0.005 

0.005 

0.005 

0.005 

4 

2 

4 

4 

2 

4 

2 

0.01 

10 

2 

40 

0.05 

4 

2 

2 

2 

* U.S. GOVERNMENT PRINTING OFFICE: 1989-673-047/86,045 REGION NO. 8 
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