Geochemical Characteristics of 

Mineralized Breccia Pipes in 

the Red Mountain District, 

San Juan Mountains, Colorado 

By FREDERICK S. FISHER and WILLARD P. LEEDY 

GEOLOGICAL SURVEY BULLETIN 1381 

A study of the distribution of oxides and 

elements in altered volcanic rocks around 

and within breccia pipes in the northwest 

San Juan Mountains 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1973 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress catalog-card No. 73-600089 

For sale by the Superintendent of Documents, u_s_ Government Printing Office 

Washington, D.C. 20402- Price 45c domestic postpaid or 30c GPO Bookstore 

Stock Number 2401.00320 
CONTENTS 

Page 

Abstract ................................................................ . 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Geologic setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Stratigraphy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

Geological features of breccia pipes in the Red Mountain district............. 8 

Physical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

Ore bodies and altered rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

Areas of detailed study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

National Belle pipe................................................... 9 

Red Mountain No. 3 pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

Sampling methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Methods of statistical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Distribution of oxides and elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

Rock type distributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

Areal distributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 

Suggestions for prospecting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

References cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . 43 

FIGURE 

ILLUSTRATIONS 

1. Map showing the location of National Belle and Red Mountain 

No. 3 areas and principal structural features in the vicinity 

of the Silverton caldera .................................. . 

2. Geologic map of the National Belle and Red Mountain 

Page 

3 

No. 3 areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

3-6. Histograms showing concentrations of various oxides and 

elements in rocks from the National Belle and 

Red Mountain No. 3 areas: 

3. Si02, Al203, Fe203, and MgO ........................ . 

4. CaO, Na20, K20, Ag, As, and Au ................... . 

5. Bi, Cu, Mn, Ph, and Sb ............................ . 

6. Sr, Zn, Ga, La, and Ni ............................. . 

7-12. Maps showing concentrations of elements in the National Belle 

and Red Mountain No. 3 areas: 

7. Silver ............................................. . 

8. Arsenic ............................................ . 

9. Gold .............................................. . 

10. Bismuth ........................................... . 

11. Lead .............................................. . 

12. Antimony 

III 

20 

22 

24 

26 

30 

32 

34 

36 

38 

40 
IV CONTENTS 

TABLES 

TABLE 1. Geochemical data for selected elements from the 

National Belle and Red Mountain No. 3 areas 

2. Logarithmic variance components for each element and 

oxide divided among the two levels of the analysisof-variance design within different altered-rock 

Page 

12 

types and different areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

3. Elements and oxides whose content differences were 

determined by t-tests to be nonsignificant at the 

95-percent level of confidence in different pairs 

of altered-rock types or areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 
GEOCHEMICAL CHARACTERISTICS OF 

MINERALIZED BRECCIA PIPES IN THE 

RED MOUNTAIN DISTRICT, 

SAN JUAN MOUNTAINS, COLORADO 

By FREDERICKS. FISHER and WILLARD P. LEEDY' 

ABSTRACT 

Distinctive geochemical anomalies associated with upper Tertiary breccia pipes in the 

northwest San Juan Mountains, Colo., provide useful prospecting guides and help in 

characterizing and delineating types of altered rocks in the area. 

Highly altered silicified rocks in the central zones of the pipes have been extensively 

leached of aluminum, magnesium, calcium, sodium, and potassium and consist of porous 

masses of quartz and sparse diaspore, barite, alunite, rutile, and leucoxene. Moderately 

altered rocks adjacent to and somewhat intermixed with the quartzose zones are composed of abundant clay minerals and lesser amounts of quartz, alunite, pyrophyllite, and 

rutile. These rocks have also been leached, but less completely than the highly altered 

rocks. The least altered rocks, in the outermost zones of the pipes, are characterized by 

fine-grained micaceous minerals, quartz, and pyrite; they are depleted of calcium and 

magnesium but are relatively unchanged in their content of aluminum, potassium, and 

sodium. 

Sulfide minerals associated with the pipes have high ratios of sulfur to metal and comprise silver-bearing copper and lead sulfosalts of arsenic and antimony and common basemetal sulfides. The concentrations of ore metals are generally greatest in the most intensely altered rocks and decrease progressively in less altered rock types. Silver, arsenic, 

gold, bismuth, lead, and antimony are probably the most useful elements in the prospecting for new breccia pipes. 

INTRODUCTION 

Pods, lenses, and vertical chimneys of ore in breccia pipes of the 

northwest San Juan Mountains, Colo., were intensively mined during 

the late 1800's. Even though much favorable ground still remains, subsequent mining and production of breccia-pipe ore have been minor and 

sporadic. Total production from the pipes is unknown; however, it 

probably exceeded $10 million (Burbank, 1947, p. 430). Prospecting for 

new pipes is difficult because of the small size of the structures, the 

complex geology, and the widespread hydrothermal alteration of the 

country rocks. Burbank (1947, p. 430-431) suggested that geochemical 

methods of prospecting might be useful in searching for new brecciapipe targets. Fischer, Luedke, Sheridan, and Raabe (1968) noted that 

'Kalium Chemicals Ltd., Prescott, Ariz. 
2 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

silver, copper, antimony, bismuth, mercury, and tin were more abundant in samples of pipe ore and gangue than in country rock; Burbank, 

Luedke, and Ward (1972) discussed the occurrence of arsenic and 

several other trace elements in samples from five localities in the Red 

Mountain district. 

The objectives of our study were to (1) determine the geochemical 

characteristics of altered rock types associated with the mineralized 

breccia pipe, (2) statistically examine the variability in the geochemical 

data as an aid to its interpretation, and (3) determine what elements 

are most useful in searching for new breccia pipes. 

GEOLOGIC SETTING 

The breccia pipes of the Red Mountain district are in or near the ringfault zone along the northwestern side of the Silverton caldera (fig. 1), a 

collapse structure that subsided as a result of the eruption of large 

volumes of rhyolitic and latitic ash flows during mid-Tertiary time. 

Mter subsidence, the collapsed block and surrounding area were 

faulted and resurgently domed, and numerous intrusive bodies were 

emplaced in the ring-fault zone and elsewhere in and near the caldera 

(Luedke and Burbank, 1968). 

Widespread propylitic alteration, characterized mainly by the addition of water and carbon dioxide (Burbank and Luedke, 1969; Burbank, 

1960), occurred during and after the late igneous activity. Later, 

hydrogen ion metasomatism and the resultant base cation leaching occurred in local areas within the caldera, especially in the Red Mountain 

district within and near breccia pipes and along numerous faults and 

fractures. This later alteration, called solfataric by Burbank and 

Luedke (1969) and Burbank (1950), resulted from hydrogen ion 

metasomatism as described by Remley and Jones (1964). The term 

"solfataric" implies, by definition, a surface or near-surface 

phenomenon associated with volcanism, whereas the altered rocks now 

exposed in the Red Mountain area were metasomatized at depths from 

several thousand feet to as much as a mile below the ground surface 

(Burbank and Luedke, 1969, p. 31; Burbank, 1950, p. 310, fig. 4). 

STRATIGRAPHY 

Layered volcanic rocks in the Red Mountain district are part of the 

middle Tertiary (Oligocene) Silverton Volcanic Group and are composed of several thousand feet of rhyodacitic, andesitic, and rhyolitic 

lava flows, breccias, and tuffs. Numerous small stocks, dikes, and breccia bodies ranging in composition from rhyolite to quartz latite and 

andesite cut all the layered rocks (Burbank and Luedke, 1964). 

In the Red Mountain district layered volcanic rocks have been 

divided into the Burns and Henson Formations (Burbank and Luedke, 

1964). The Bums Formation is composed of several thousand feet of 
107"45' 

38" 

-oo· 

37" 

50' 

STRATIGRAPHY 

35' 

_,,_Storm Peak -,, .... 

EXPLANATION 

Contact 

Tertiary intrusive rocks 

D 

Tertiary volcanic rocks Major faults 

~ + 

+ 

COLORAOO 

San 

•Juan 

Mts 

Mesozoic and Paleozoic 

sedimentary rocks Principal fissures, dikes, 

and veins, and minor faults 

Precambrian rocks 

3 

107"30' 

FIGURE 1.- The National Belle and Red Mountain No.3 areas, the area shown in figure 

2 (hachures), and principal structural features in the vicinity of the Silverton 

caldera. (Modified from Burbank, 1947, pl. 28.) 
4 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

thin to thick lava flows, breccias, and tuffs that are mainly rhyodacitic 

in composition. The formation has been divided into lower and upper 

members, each consisting of several units (Burbank and Luedke, 1969, 

p. 10). 

The overlying Henson Formation is defined as andesitic to 

rhyodacitic tuffs, lava flows, and breccias and scattered rhyolitic and 

quartz latitic lava flows and tuffs. Its maximum thickness is generally 

800-1,000 feet, possibly more in a few areas (Burbank and Luedke, 1969, 

p. 12). 

In the western part of the Red Mountain district (fig. 2) where the 

rocks are somewhat less altered, the flow-layered unit of the lower 

member of the Burns Formation has been recognized. This unit comprises most of the country rocks surrounding the National Belle and 

Hero pipes. The remainder of the mapped area (fig. 2) is probably CQmposed of the flow unit of the upper member of the Burns and possibly 

the lower part of the Henson Formation. 

Because of the extensively altered character of the country rocks, the 

relatively sparse outcrops, and the limited extent of the mapped area 

(fig. 2), we believe that identification of the rocks as specific formations 

for the purposes of this study would be impractical and possibly misleading. Therefore the rocks are distinguished on the map according to 

lithology. 

Four rock types were mapped: quartz latite intrusives, propylitized 

flows and breccias, intensely silicified rocks, and illitic rocks. 

Small irregular stocks of quartz latite are commonly associated with 

the breccia pipes. Their emplacement was undoubtedly controlled in 

large part by the same structures that controlled the emplacement of 

the pipes. In hand specimens the quartz latite is dark to light gray and 

contains large (1-4 em) phenocrysts of potassic feldspar and smaller 

phenocrysts of ferromagnesian minerals and quartz all set in an 

aphanitic groundmass. The groundmass makes up 50-60 percent of the 

rock, and as seen in thin section it has a felted to pilotaxitic texture and 

consists of microlites of potassic feldspar, plagioclase, quartz, and some 

magnetite. Where altered, these rocks are bleached light gray to white. 

Feldspars are altered to sericite and clay; augite, to chlorite and calcite; 

and biotite, to sericite. Pyrite is common in the groundmass. 

Propylitized flows and breccias are common in the western part of the 

mapped area and occur elsewhere as scattered isolated patches of rocks 

(fig. 2). Despite various degrees of alteration, the original character of 

the rock usually is still evident. In hand specimen these rocks are 

purplish to greenish to dark gray and commonly contain small (1-2 mm) 

phenocrysts of feldspar and ferromagnesian minerals. The groundmass 

of the flow rocks ranges in texture from cryptocrystalline to felted to 

pilotaxitic. Phenocrysts are mostly augite, plagioclase (An30_

45), 
STRATIGRAPHY 5 

hornblende, and biotite. Glomeroporphyritic clusters of these minerals 

are fairly common, as are lithic and crystal fragments. Accessory 

minerals are magnetite, rutile, and apatite. In some flows the groundmass contains abundant potassic feldspar and quartz. 

Interbedded locally with the flows are volcanic breccias. These rocks, 

in their overall mineralogical characteristics, are similar to the justdescribed flows. The fragments in the breccias are small (1-10 em) and 

in general are composed of the same type of materials as the flows. 

Commonly the breccias are highly altered, and therefore their original 

mineralogy cannot be definitely determined. 

Where altered, the propylitic rocks are characterized principally by 

epidote, carbonates, chlorite, and albite and subordinate amounts of 

fine-grained micaceous minerals (sericite(?) and illite). The degree of 

propylitization was rather variable in the area, and the propylites in 

hand specimen range from greenish-gray rocks having their original texture and mineralogy well preserved to highly bleached rocks consisting 

of fine-grained alteration products in which the original texture and 

mineralogy have been completely destroyed. 

Intensely silicified rocks are abundant in the mapped area and occur 

mainly in the upper parts of the breccia pipes and, to a lesser degree, 

adjacent to some fractures. The silicified rocks range from vuggy, caver-

·nous breccias to dense, massive rocks composed ·of very fine grained 

silica. Quartz, the predominant mineral, occurs in many forms. Within 

the breccias it ranges from cryptocrystalline to chalcedonic to anhedral 

grains in both the groundmass and fragments. Small (<2 mm) crystals 

of quartz commonly line cavities within the breccias. In more massive 

rocks the quartz occurs as very fine grains.( <I mm) within a siliceous 

cryptocrystalline groundmass. Rock fragments in the breccias are 

generally angular and range in size from< 1 em to approximately 10 

em. They are composed of the same material as the groundmass. 

Irregular veinlets of silica are common in both the breccias and the 

massive rocks. In many places the rocks are stained with iron oxides 

from the oxidation of pyrite. Sparse barite, leucoxene, alunite, rutile, 

and diaspore are also in the siliceous rocks. 

Irregular zones, pods, and lenses of argillic material occur within and 

adjacent to the intensely silicified rocks and, for mapping purposes, 

were included as part of the silicified rocks. They are also associated 

with some fractures. In hand specimen these rocks are grayish-white to 

yellow fine-grained to massive aggregates of clay and quartz. They contain kaolinite, dickite, quartz, and alunite; minor amounts of 

pyrophyllite, rutile, and diaspore; and sparse barite. 

The fourth mapped unit (fig. 2) consists of fine-grained light-gray to 

yellowish illitic rocks that are composed mainly of quartz, pyrite, and 

fine-grained micaceous minerals. In thin section these rocks are seen to 
6 

54' 

GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

Qs I 

Quaternary surficial deposits 

Tertiary quartz 

~ 

~ latite intrusives 

GJ 

Contact 

Approximately located 

u 

D 

Ring fault of Silverton caldera 

U, upthrown side; D, downthrown side 

Tertiary propylitized flows and breccias 

Fault or fissure 

>-

Ad it 

-

1 

Tertiary illitic rocks 

l!l 

Shaft 

X 

Prospect pit 

.2 

Sample locality 

be cryptocrystalline to microcrystalline and to be composed of quartz, 

illite, sericite(?), and minor amounts of clay, carbonates, chlorite, and 

rutile. Epidote is present as small irregular crystals in the ground mass 
/ 

/ 

"' 

7 

_) 

. ~ -· 

!_i~ _ _t_ _ _L_ 

0 

STRUCTURE 

500 1000 1500 

CONTOUR INTERVAL 200 FEET 

DATUM IS MEAN SEA LEVEL 

7 

2000 FEET 

FIGURE 2. -Geologic map of the National Belle and Red Mountain No.3 areas. Geology 

Mapped by Willard P. Leedy and F. S. Fisher, 1968-69. Base from U.S. Geol. Survey 

Ironton 7 V2 -minute topographic map, 1955. 

and as somewhat larger crystals occupying plagioclase voids. Commonly the original texture of these rocks has been obliterated by alteration productl3. These rocks are relatively common in the area and occur 

in the outermost zones of the breccia pipes and also near fractures. 

STRUCTURE 

Ring faults of the Silverton caldera are the major ~tructural features 

within the mapped area (fig. 2). These faults undoubtedly controlled 

the localization of many of the breccia pipes in the district by providing 
8 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

channelways for the altering and mineralizing solutions. Less obvious 

fissures and fractures in the mapped area also may have acted as 

channelways for solutions and thus may have localized breccia pipes. 

The linear nature of many of the breccia pipes, particularly at depth 

(Burbank, 1941, p. 187; Ransome, 1901, p. 106), indicates the importance of fracture control in their formation. Innumerable small fissures 

and fractures, not shown on the map, are probably related to the major 

fractures in the area. Many of these contain fillings of pyrite, but other 

sulfides are scarce. 

The layered volcanic rocks in the mapped area dip a few degrees to 

the west and northwest or are generally flat lying. Local variations in 

attitude occur, particularly near the major faults and in the vicinity of 

the breccia pipes. 

GEOLOGICAL FEATURES OF BRECCIA PIPES 

IN THE RED MOUNTAIN DISTRICT 

PHYSICAL CHARACTERISTICS 

Individual breccia pipes are irregular in plan view, and usually their 

horizontal dimensions are considerably smaller than their vertical 

dimensions which range from several hundred to at least a thousand 

feet. The axes of the pipes are steeply dipping to nearly vertical; 

changes in the axial pitch of individual pipes are common. Generally 

the pipes crop out as low mounds of silicified rock. Well-defined pipes 

commonly have a zone of vertical sheeting around the outer edge; in less 

well defined pipes the breccia grades continuously outward into 

relatively unbroken country rock. Many contain small intrusive bodies 

which range in composition from rhyolite to quartz latite. 

Rocks within the breccia pipes are highly shattered and altered. Apparently brecciation in some of the pipes caused almost no vertical 

movement of solid rock material. The brecciation may have resulted 

from one or more processes: explosive release of hot juvenile gases, a 

more passive release of gases and slow brecciation of the surrounding 

country rocks by chemical and volume changes (Burbank, 1941, p. 177), 

and brecciation due to the emplacement of the intrusive bodies. In 

some places the country rock is a volcanic breccia, and intense alteration of this breccia adjacent to fractures in local areas produced a 

pipelike structure in the rocks. 

ORE BODIES AND ALTERED ROCKS 

Individual ore bodies within the pipes have highly irregular shapes 

and range in form and size from small pods and lenses a few feet in the 

longest dimension 'to nearly vertical chimneys several hundred feet in 

height and several tens of feet in width (Ransome, 1901, p. 103). The ore 

chimneys are composed of massive sulfides and were formed by open-
GEOLOGICAL FEATURES OF BRECCIA PIPES 9 

space filling in the upper cavernous parts of the pipes and by replacement at depth. 

In general the ore minerals are vertically zoned within the pipes, 

changing with increasing depth from lead-rich ores to copper-silver ores 

to pyritic copper-arsenic ores (Burbank, 1941, p. 181). There is considerable overlap and telescoping of the different ore zones within individual pipes, and in some pipes the zoning is exceedingly complex. 

Principal sulfide minerals in the ore bodies are pyrite, enargite, 

chalcopyrite, chalcocite, covellite, bornite, sphalerite, and galena. 

Other minerals that are economically important in some of the ores are 

pyrargyrite, proustite, stromeyerite, tennantite, and free gold. 

Numerous other sulfides are locally present in trace amounts in the 

ores. With the exception of pyrite, quartz, and clay, the gangue 

minerals are sparse and consist of alunite, barite, fluorite, zunyite, 

diaspore, and pyrophyllite. 

The distribution patterns of the altered rocks within the pipes indicate that the intensity of base cation leaching decreased downward 

and outward from the center of the pipes (Burbank, 1950). Ideally, 

highly silicified breccias form caps or irregular massive bodies near the 

upper-central parts of the pipes or next to major channel ways. Adjacent 

to and intermixed within the silicified breccias are kaolin-rich clays of 

the argillic rock group. The argillic rocks commonly are poorly exposed 

in outcrop but appear to grade laterally into illitic rocks at the 

perimeter of the pipes. The pattern of alteration was thus one of 

decreasing hydrogen ion activity away from the center of the pipes or 

away from the major channelways. With increasing depth within the 

pipes, the silicified rocks give way to the argillic rocks, which pass into 

quartz-illitic rocks at still deeper levels, where base cation leaching was 

less intense. 

AREAS OF DETAILED STUDY 

Two areas in the Red Mountain district were selected for detailed 

study: the National Belle breccia pipe and the Red Mountain No. 3 

breccia pipe (fig. 2). The National Belle pipe is generally typical of the 

district's mineralized breccia pipes; rock exposures in and around the 

pipe are adequate for study, it is readily accessible, and silver, lead, 

copper, gold, and zinc ore have been mined from it in the past. The Red 

Mountain No.3 pipe is a large, conspicuously altered pipe that has not 

been adequately explored, and our reconnaissance samples from the 

pipe had shown anomalous amounts of metallic elements. 

NATIONAL BELLE PIPE 

The National Belle pipe, about 400 feet in diameter, crops out as a 

circular knob about 200 feet high. The core of the pipe is a silicified and 

kaolinized breccia and is encircled by a zone of highly silicified cavernous breccia which makes up the sides of the knob. The outermost 
10 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

envelope of the pipe is a poorly exposed zone of pyritized illitic rock 

which grades into propylitized country rock. Rocks of the core of the 

pipe and of the silicified rim have been extensively altered and leached. 

They are composed mostly of quartz and kaolinite, with lesser amounts 

of pyrite, alunite, and barite (Burbank, 1941, p. 185). 

The National Belle mine (fig. 2) was active during the late 1800's. 

Total production is unknown, but it was probably valued· at several 

hundred thousand dollars to $1 million. The mine was developed to a 

depth of about 450 feet, but most of the ore was produced from the upper 300 feet (Ransome, 1901, p. 231-236; Schwarz, 1890). The ore occurred as oxidized material in caverns in the upper parts of the mine 

and as sulfide minerals in the deeper parts. The oxidized ore was 

mainly carbonates of lead and iron, lead sulfates, iron oxides, 

sphalerite, and arsenates. Some residual galena and enargite were present as cores within the oxidized masses of ore contained in the caverns. 

The caverns, some of which were as large as 50 feet in diameter, 

decrease in size and number with depth (Schwarz, 1890, p. 141). 

The sulfide ore deeper in the mine occurred as irregular masses in the 

altered rock and consisted mainly of enargite with lesser amounts of 

chalcopyrite, galena, sphalerite, and tetrahedrite. The ore was 

generally argentiferous and also contained some free gold. 

RED MOUNTAIN NO. 3 PIPE 

The Red Mountain No. 3 breccia pipe is exposed as a crudely elliptical zone of silicified and kaolinized rock about 2,500 feet long that 

trends northeast (fig. 2). An elongate quartz latite intrusive body is exposed in the center of the pipe. The remainder of the central part of the 

pipe is mostly covered by soil and talus but appears to be composed of 

altered, kaolinized breccia. A zone of highly silicified rock surrounds 

the pipe and is conspicuous on the southwest side. Vugs and large 

caverns are common in the silicified rocks. Quartz and kaolin are the 

most abundant minerals, and alunite occurs in lesser amounts. 

Meteroic water has leached most of the original pyrite from the rock, 

and so only minor pyrite and some oxide boxworksremain. Rocks outside the silicified zone are either propylitized material similar to the 

country rocks near the National Belle pipe or fine-grained altered rock 

containing quartz, micaceous minerals, pyrite, and some clay. 

Some exploration beneath the Red Mountain No.3 pipe was undertaken in the late 1940's (Hillebrand and Kelley, 1957, p. 194). Two 

crosscuts at an elevation of about 10,800 feet were driven from the main 

drift of the Genessee-Vanderbilt mine beneath the areas of silicified 

rock on the eastern and western sides ofthe pipe (fig. 2). Diamond drilling was done from the crosscuts along the sides and toward the center of 

the pipe. Some mineralized rock was penetrated in the drilling and 

crosscuts; however, no production of ore is recorded. Pyrite, enargite, 
METHODS OF STATISTICAL ANALYSIS 11 

and minor chalcopyrite were found, mainly in northward-striking 

fissures, together with a gangue of kaolin and some alunite. The country 

rocks are highly altered and contain abundant fine-grained disseminated pyrite and clay. 

SAMPLING METHODS 

To determine the geochemical anomalies associated with the breccia 

pipes and to help characterize the nature of altered rocks in the area, 

126 rock samples collected from 63 sample sites were chemically 

analyzed. The sample sites (fig. 2) were randomly selected from 

available rock outcrops. Two samples, each consisting of about 3 

pounds of rock chips 1-2 em in size, were collected from each site. Each 

sample was ground to a powder before a split was taken for chemical 

analysis. The analytical results for selected elements are given in table 1. 

On the basis of X-ray and petrographic analyses the altered rocks 

were classified into four types: propylitic, silicified, argillic, and illitic. 

These types coincide only partly with the four mapped rock types. The 

propylitic rocks were formed by districtwide propylitization, whereas 

the other three types were formed locally by hydrogen ion 

metasomatism and represent an advanced argillic alteration 

assemblage. 

METHODS OF STATISTICAL ANALYSIS 

The geochemical data were statistically analyzed to determine and 

evaluate differences in the chemistry of the various rock alteration 

assemblages. Histograms and geometric means were used to summarize 

and characterize the data. Analysis of variance was used to examine 

variability and to estimate variance components. The statistical 

significance of the differences between geometric means for each element in the various groups of altered rock was determined by use of a 

two-tailed Student's t-test. 

Most of the frequency distributions of the original chemical data are 

positively skewed; accordingly a log transformation was used to normalize the data (Bennett and Franklin, 1954, p. 91; Miesch, 1967, p. 

B5). In general the transformation of the data to logs was effective in 

producing distributions that tend to be normal or at least roughly 

symmetrical. The transformed data were plotted as histograms, one for 

each element in each of the four main types of altered rocks in different 

areas (figs. 3-6). Geometric means for each distribution, also shown in 

figures 3-6, were estimated by use of the antilog of the arithmetic mean 

of the logs (Bennett and Franklin, 1954, p. 18). The geometric mean is 

an estimate of central tendency of a frequency distribution that is 

roughly symmetrical on a log scale, and it is therefore useful for describing and characterizing the abundance of a given element in an individual sample group (Miesch, 1967). 
12 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

TABLE 1.-Geochemical data for selected elements 

[Sample localities shown in figure 2. Silver, bismuth, copper, manganese, lead, antimony, strontium, zinc, gallium, Si02, Al,O,, Fe,O,, CaO, K,O, and arsenic analyses were made by X-ray fluorescence by J. S. Wahlberg and B. Breeden, J. A. Thomas, G. D. Shipley, W. D. Goss, E. J. Rowe, and Wayne Mountjoy. Symbols used: L, detected 

Sample Rock or alteration type No. 

lA 

1B 

2A 

2B 

3A 

3B 

4A 

4B 

5A 

5B 

6A 

6B 

7A 

7B 

SA 

BB 

9A 

9B 

lOA 

lOB 

11A 

11B 

12A 

12B 

13A 

13B 

14A 

14B 

15A 

15B 

16A 

16B 

17A 

17B 

18A 

18B 

19A 

19B 

20A 

20B 

21A 

21B 

22A 

22B 

23A 

23B 

24A 

24B 

25A 

25B 

26A 

26B 

27A 

27B 

28A 

28B 

28A 

29B 

30A 

30B 

31A 

31B 

32A 

32B 

33A 

33B 

34A 

34B 

Silicified 

........... do ......... . 

Illitic 

........... do ......... . 

Argillic 

........... do ......... . 

Silicified 

........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

Propylitic 

........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

Silicified 

........... do ......... . 

Propylitic 

........... do ......... . 

........... do ......... . ........... do 

........... do ........... do 

........... do ........... do 

Silicified 

........... do ......... . 

Propylitic 

........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

Argillic 

........... do 

Propylitic 

........... do 

........... do ........... do 

Argillic 

........... do 

Propylitic 

........... do ......... . 

........... do ......... . ........... do .. · ....... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

SiO, 

95 

89 

55 

59 

66 

66 

93 

93 

88 

91 

84 

91 

99 

94 

92 

91 

95 

99 

58 

60 

60 

65 

57 

64 

59 

59 

54 

54 

94 

92 

58 

56 

62 

62 

58 

61 

57 

57 

95 

95 

64 

59 

62 

61 

63 

c~ 

61 

64 

59 

63 

81 

82 

54 

52 

58 

56 

70 

71 

59 

59 

57 

55 

60 

58 

67 

65 

60 

56 

Oxide, in Percent 

AI,O, Fe,O, MgO CaO Na,O 

l.OL 0.3 l.OL .3 

17.0 .5 15.0 .7 

20.0 1.1 19.0 .,8 

3.0 1.6 1.0 1.3 

2.0 4.4 1.0 4.5 

3.0 1.7 1.0 1.7 

l.OL 1.0 l.OL .8 

2.0 2.2 2.0 2.0 

l.OL .5 l.OL .5 

15.0 8.3 19.0 8.6 

16.0 10.4 14.0 10.7 

15.0 8.0 23.0 8.1 

15.0 7.3 15.0 7.8 

14.0 9.2 16.0 9.5 

l.OL 2.7 1.0 1.7 

14.0 7.4 14.0 7.2 

16.0 8.8 14.0 8.6 

14.0 7.4 17.0 7.6 

14.0 7.1 16.0 7.8 

2.0 .9 l.OL .5 

16.0 7.8 15.0 8.2 

16.0 8.2 15.0 8.3 

14.0 11.5 13.0 11.2 

11.0 12.5 14.0 11.8 

15.0 9.6 15.0 9.0 

10.0 .4 9.0 .3 

17.0 9.6 17.0 9.7 

16.0 7.7 16.0 6.8 

16.0 2.9 15.0 2.6 

18.0 5.9 16.0 6.1 

16.0 6.7 15.0 6.6 

15.0 7.5 15.0 8.0 

12.0 10.3 12.0 11.0 

14.0 7.6 18.0 7.4 

0.02 0.1L .02 .lL 

.01 .3 .01 .3 

.02 .1L .02 .1L 

.01 .2 .01 .1L 

.01 .1L .02 .1L 

.02 .1L .01 .lL 

.02 .lL .02 .lL 

.02 .lL .01 .lL 

.01 .3 

.01 .1 

1.09 3.7 1.15 3.9 

1.09 .3 .94 .3 

.89 4.5 .87 4.9 

.92 5.4 .90 5.6 

1.04 4.9 1.11 5.4 

.02 .1L .02 .IL 

3.06 3.8 3.10 3.6 

3.37 .2 2.24 .3 

1.22 4.7 1.19 5.0 

2.28 6.0 1.57 6.0 

.01 .1L .10 .lL 

2.85 2.4 2.90 2.3 

.81 3.9 1.22 3.7 

1.82 1.5 1.75 .8 

2.21 2.1 2.06 1.3 

1.28 .4 2.25 .4 

.02 .2 .02 .2 

1.51 6.4 1.64 5.7 

1.34 3.6 1.24 4.0 

.01 .1L .OIL .1L 

1.42 5.4 1.39 5.9 

1.48 6.2 1.54 6.2 

1.70 4.0 1.74 3.8 

1.36 1.4 1.50 1.5 

1.75 4.6 1.05 5.0 

0.01 

.02 

1.47 

1.26 

.05 

.04 

.01 

.01 

.03 

.02 

.02 

.01 

.02 

.02 

.02 

.02 

.02 

.02 

1.87 

1.91 

.07 

.07 

1.00 

1.01 

1.02 

.90 

1.50 

1.04 

.02 

.02 

.03 

.03 

.02 

.02 

.05 

.06 

2.12 

2.04 

.01 

.01 

.03 

.03 

.70 

.69 

.06 

.07 

.03 

.04 

.09 

.03 

.01 

.01 

.71 

.17 

2.08 

2.28 

.02 

.01 

.10 

.11 

1.36 

1.30 

2.36 

2.60 

.06 

.07 

2.02 

1.92 

K,O 

0.1L 3.0N .1L 3.0N 

2.4 3.0N 2.4 3.0N 

1.1 15.0 .1L 23.0 

.lL 45.0 .1L 46.0 

.1 21.0 .1L 20.0 

.1L 9.0 0.1 7.0 

.1L 5.0 .lL 3.0N 

.1 35.0 .1L 51.0 

.1 3.0N .1 3.0N 

3.6 3.0N 3.7 3.0N 

3.3 3.0N 2.9 3.0N 

4.2 3.0N 4.1 3.0N 

4.1 3.0N 3.8 3.0N 

4.0 3.0N 3.9 3.0N 

.1L 15.0 .1L 13.0 

4.6 3.0 4.6 3.0N 

4.7 3.0N 4.3 3.0N 

4.3 3.0N 4.4 3.0N 

3.6 3.0N 3.6 3.0N 

.lL 17.0 .1 3.0N 

3.7 3.0N 3.4 3.0N 

4.7 3.0N 4.5 3.0N 

3.0 3.0N 2.7 3.0N 

2.0 3.0N 2.5 3.0N 

3.6 3.0N 3.4 3.0N 

.1 3.0N .1L 3.0N 

2.9 3.0N 3.0 3.0N 

2.9 3.0N 3.0 3.0N 

.1 3.0 .2 3.0N 

4.4 3.0N 4.0 3.0N 

3.0 3.0N 3.1 3.0N 

2.1 3.0N 2.0 3.0N 

2.1 3.0N 2.2 3.0N 

2.9 3.0N 3.2 3.0N 
METHODS OF STATISTICAL ANALYSIS 13 

from the National Belle and Red Mountain No. 3 areas 

lanthanum, and nickel analyses were made by direct-reader spectrometry by R. G. Havens, N. M. Conklin, and L. M Lee. 

M. W. Solt. MgO, Na20, and gold analyses were made by atomic-absorption spectrometry by J. M. Gardner, V. M. Merritt, L. 

but less than value shown; N, not detected at or below value shown] 

Au 

400 0.30 500 .20 

40L .05L 

40L .05L 

200 .20 40L .20 

70 

80 

130 

110 

70 

50 

210 

260 

4000 

3600 

130 

150 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

l90 

550 

40L 

40L 

40L 

40 

40L 

40L 

40L 

40L 

130 

250 

40 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40 

80 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

.40 

.40 

2.90 

3.00 

.40 

.40 

.30 

.20 

1.20 

1.10 

.10 

.20 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.40 

.30 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.07 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.50L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

.05L 

Bi 

lON 

12 

10 

14 

10 

14 

28 

20 

110 

80 

12 

11 

ION 

ION 

ION 

13 

ION 

lON 

lON 

lON 

lON 

ION 

ION 

ION 

ION 

lON 

lON 

lON 

16 

15 

lON 

ION 

lON 

ION 

ION 

ION 

ION 

ION 

15 

ION 

ION 

ION 

ION 

ION 

ION 

ION 

ION 

ION 

lON 

ION 

ION 

ION 

ION 

ION 

ION 

ION 

17 

17 

ION 

ION 

ION 

ION 

ION 

ION 

lON 

ION 

ION 

ION 

Cu 

11 

12 

6 

8 

62 

38 

24 

20 

59 

56 

72 

60 

119 

124 

1600 

4000 

20 

20 

60 

51 

66 

66 

84 

88 

54 

49 

27 

120 

1400 

1800 

60 

60 

49 

60 

52 

43 

42 

43 

37 

25 

70 

60 

53 

60 

84 

82 

84 

73 

51 

48 

19 

16 

110 

100 

120 

100 

31 

30 

61 

60 

46 

49 

51 

52 

60 

60 

49 

46 

Element, in parts per million 

Mn Ph Sb Sr Zn 

30 

24 

7N 

7N 

36 

7 

15 

7N 

IO 

14 

30 

18 

8 

11 

30 

11 

1700 

1800 

1200 

1200 

1100 

1300 

900 

1100 

2700 

3000 

14 

36 

1800 

1500 

1100 

690 

1300 

1200 

1650 

1700 

24 

7 

3400 

3000 

1300 

1600 

790 

890 

1450 

830 

2550 

2400 

22 

9 

2100 

1600 

1200 

1100 

7N 

7N 

1200 

1300 

1200 

1300 

1250 

1200 

1250 

1400 

2100 

2100 

110 

120 

560 

570 

1400 

1300 

190 

130 

210 

170 

290 

230 

20N 

20N 

60 

75 

35 

30 

20N 

20N 

20N 

20N 

20N 

20N 

20N 

20N 

20N 

20N 

47 

41 

20 

29 

31 

20N 

20N 

23 

21 

29 

95 

70 

880 

20 

20N 

20N 

30 

25 

35 

27 

56 

76 

37 

44 

20N 

20N 

20N 

20N 

470 

415 

20N 

20N 

20N 

20N 

27 

38 

20N 

20N 

20N 

20N 

300N 60 300N 60 

300N 420 300N 380 

300N 3500 330 2000 

350 

300N 

590 

575 

300N 

300N 

300N 

300N 

870 

1000 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

30N 

30N 

400 

255 

220 

150 

30N 

30N 

60 

90 

130 

90 

600 

440 

30N 

50 

360 

420 

330 

340 

260 

320 

30N 

30N 

60 

30N 

30N 

30N 

300 

270 

1550 

1900 

100 

30N 

30N 

30N 

225 

240 

70 

90 

100 

30 

60 

40 

300 

370 

160 

120 

490 

370 

1100 

690 

220 

300 

420 

510 

420 

380 

85 

160 

460 

600 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

500 

300N 

300N 

600 

300N 

300 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300 

1200 

630 

300N 

300N 

620 

550 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

485 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

Ga 

iON 

12 

23 

28 

46 

44 

10 

10 

lON 

lON 

lON 

lON 

lON 

lON 

ION 

lON 

lON 

ION 

25 

25 

26 

23 

24 

27 

23 

23 

30 

27 

ION 

ION 

27 

26 

30 

22 

28 

34 

25 

25 

lON 

ION 

30 

30 

26 

24 

26 

25 

23 

21 

28 

24 

ION 

15 

27 

27 

25 

24 

25 

22 

29 

25 

28 

26 

24 

22 

22 

24 

26 

24 

La 

50N 

50N 

60 

60 

100 

90 

50N 

50N 

50N 

50N 

50N 

50N 

50N 

50N 

50N 

50N 

50N 

50N 

90 

77 

60 

50N 

78 

94 

73 

78 

64 

80 

50N 

50N 

71 

54 

65 

60 

82 

83 

74 

78 

50N 

50N 

70 

61 

60 

63 

50N 

56 

56 

50N 

58 

50N 

50N 

56 

74 

60 

77 

60 

94 

95 

69 

80 

64 

60 

67 

60 

76 

60 

74 

72 

Ni 

10 

10 

9 

8 

7 

9 

10 

7N 

7N 

7N 

7N 

7N 

7N 

7N 

7N 

7N 

7N 

7N 

20 

18 

13 

14 

20 

20 

15 

18 

18 

20 

12 

11 

21 

13 

14 

10 

20 

18 

19 

20 

7N 

7N 

15 

15 

13 

15 

16 

21 

20 

15 

11 

10 

10 

7N 

8 

8 

15 

12 

7N 

7N 

15 

17 

12 

15 

14 

12 

16 

17 

17 

20 
14 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

Sample Rock or alteration type No. 

35A 

35B 

36A 

36B 

37A 

37B 

38A 

38B 

39A 

39B 

40A 

40B 

41A 

41B 

42A 

42B 

43A 

43B 

44A 

44B 

45A 

45B 

46A 

46B 

47A 

47B 

48A 

48B 

49A 

49B 

50 A 

50B 

51 A 

51B 

51 A 52B 

53 A 53B 

54 A 54B 

55 A 

55B 

56 A 56B 

57 A 

57B 

58 A 58 A 

59 A 59B 

60A 

60B 

61A 

61B 

62A 

62B 

63A 

63B 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

Argillic 

....... : ... do ......... . 

Intrusive quartz latite ........... do ......... . 

Propylitic 

........... do ......... . 

Intrusive quartz latite ........... do ......... . 

Silicified 

........... do ......... . 

........... do ......... . ........... do ......... . 

Intrusive quartz latite ........... do ......... . 

Silified 

........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

Intrusive quartz latite ........... do ......... . 

........... do ......... . ........... do ......... . 

Silicified 

........... do ......... . 

Illitic 

........... do ......... . 

........... do ......... . ........... do ......... . 

........... do ......... . ........... do ......... . 

Silicified 

........... do ......... . 

Argillic 

........... do ......... . 

Silified 

........... do ......... . 

Argillic 

........... do ......... . 

Illitic 

........... do ......... . 

Silified 

........... do ......... . 

TABLE 1.- Geochemical data for selected elements from 

SiO, 

60 

60 

58 

59 

54 

55 

74 

77 

56 

56 

55 

57 

75 

71 

96 

92 

95 

94 

55 

57 

95 

95 

94 

96 

97 

97 

98 

92 

92 

99 

99 

94 

93 

95 

64 

62 

65 

63 

94 

06 

55 

62 

76 

75 

42 

41 

91 

89 

87 

76 

95 

92 

71 

67 

46 

44 

98 

99 

Oxide, in Percent 

Al,O, Fe,O, MgO CaO Na,O 

20.0 

16.0 

16.0 

14.0 

14.0 

15.0 

12.0 

12.0 

14.0 

13.0 

17.0 

13.0 

16.0 

16.0 

1.0 

l.OL 

l.OL 

1.0 

13.0 

14.0 

2.0 

l.OL 

l.OL 

l.OL 

l.OL 

l.OL 

1.0 

1.0 

l.OL 

1.0 

2.0 

3.0 

l.OL 

l.OL 

12.0 

12.0 

16.0 

15.0 

l.OL 

l.OL 

18.0 

18.0 

16.0 

16.0 

21.0 

21.0 

2.0 

3.0 

5.0 

4.0 

l.OL 

1.0 

13.0 

15.0 

17.0 

17.0 

l.OL 

l.OL 

8.0 .93 3.0 8.1 1.00 3.4 

15.6 .12 .2 15.7 1.30 .2 

8.4 .86 5.5 8.3 .86 5.5 

.8 .01 .1L .8 .01 .1L 

6.2 6.10 4.2 5.9 5.99 4.2 

8.3 1.73 6.8 9.8 1.60 5.5 

1.5 .02 .1L 2.0 .01 .1L 

.4 .01 .1L .4 .02 .1L 

.8 .02 .1L .8 .01 .1L 

6.1 2.83 4.6 7.4 7.35 5.1 

.8 .02 .1L .9 .02 .1L 

.7 .02 .1L .6 .02 .1L 

.5 .02 .1L .3 .02 .1L 

.6 .12 .1L .6 .02 .1L 

.4 .01 .1L .3 .02 .1L 

.8 .02 .1L .2 .01 .1L 

.3 .02 .1L .3 .01 .1 

.1L .02 .3 

.2 .02 .2 

3.0 .42 .5 2.9 .40 .5 

.2 .02 .1L .2 .01 .1L 

2.4 .02 .2 2.5 .02 .3 

.9 .01 ·.2 

.7 1.74 .1 

.1 .01 .1L .2 .01L .2 

.8 .01 .1L 1.0 .01 .1L 

.5 .01 .2 .4 .03 .1 

1.0 .01 .1L 1.3 .02 .1L 

2.7 .02 .3 3.0 .01 .3 

.3 .01L .2 .3 .01L .1 

.6 .01 .1L .7 .01 .1L 

1.80 

1.80 

.18 

.06 

.73 

.77 

.04 

.01L 

.08 

.11 

.17 

.15 

.01 

.01 

.01L 

.01L 

.01 

.01 

1.96 

2.00 

.01L 

.01L 

.01 

.01 

.01L 

.Q1 

.01 

.02 

.01 

.01 

.10 

.01 

.02 

.01 

.57 

.70 

.o7 

.o7 

.02 

.Q1 

.17 

.14 

.04 

.05 

.83 

.83 

.04 

.02 

.13 

.16 

.02 

.02 

.03 

.04 

.24 

.21 

.01 

.01 

K,O 

3.2 3.0N 3.0 3.0N 

2.4 3.0N 2.3 3.0N 

3.5 3.0N 3.6 3.0N 

.1L 3.0N .1L 3.0N 

5.0 3.0N 5.4 3.0N 

3.4 3.0N 3.6 3.0N 

.1L 3.0N .1L 3.0 

.1L 3.0N .1L 3.0 

.1 110.0 .2 98.0 

7.2 3.0N 7.6 3.0N 

.1L 130.0 .1L 100.0 

.1L 11.0 .1 13.0 

.1L 3.0 .1L 3.0 

.1L 200.0 .1 200.0 

.1 30.0 .1L 36.0 

.1L 3.0 .1 3.0N 

.1L 6.0 .1L 4.0 

2.3 3.0N 2.6 3.0N 

3.7 3.0N '3.5 3.0N 

.1L 3.0N .1L 3.0N 

1.8 3.0N 1.8 3.0N 

.1 3.0N .2 3.0N 

4.3 3.0N 4.4 3.0N 

.1L 3.0N .1L 3.0N 

1.2 3.0N 1.1 3.0N 

.1L 3.0N .9 5.0 

.2 4.0 .1L 3.0N 

4.4 3.0N 4.9 3.0N 

.1L 3.0N .1L 3.0N 

In some samples from each rock type, not all the elements considered 

were detected. In such censored distributions each undetected element 

was assigned a value equal to one-half its limit of detection. In distributions whose censored part is small, the replacement of values is 

justified because estimates of the geometric means are nearly independent of any reasonable values that are substituted in the distributions. 

Analysis-of-variance techniques, following the general mathematical 
METHODS OF STATISTICAL ANALYSIS 

the Nation Belle and Red Mountain No. 3 areas- Continued 

Au Bi 

40L .05L ION 

40L .05L ION 

40L .05L IO 

40L .05L ION 

40L .05L ION 

60 .05L ION 

40 .05L 10N 40L .05L ION 

40L .05L ION 40L .05L ION 

40L .05L ION 

40L .05L 10N 

40 .05L 11 40 .05L 11 

40 .40 ION 

40 .05L ION 

600 .07 68 700 .Q7 110 

40L .05L 10N 

40L .05L ION 

590 .30 415 590 .30 300 

350 .40 10N 130 .50 10N 

110 .20 10N 

50 .20 ION 

910 .50 300 1200 .80 250 

40L 2.00 29 40L 1.90 74 

110 

60 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

40L 

80 

100 

200 

40L 

40L 

40L 

300 

600 

40L 

40L 

80 

40L 

40 

.10 

.20 

.80 

.60 

.06 

.06 

.05L 

.05L 

.07 

.05 

.05L 

.05L 

.05L 

.05L 

.05 

.05 

.60 

.50 

.20 

.20 

.90 

.90 

.40 

.50 

.IO 

.10 

.50 

.50 

ION 

10N 

13 

11 

ION 

ION 

10N 

10N 

ION 

10N 

10N 

10N 

10N 

10N 

17 

16 

17 

28 

ION 

lON 

10N 

10N 

46 

100 

10N 

10N 

ION 

ION 

Cu 

60 

55 

59 

60 

48 

42 

60 

55 

50 

39 

60 

70 

21 

24 

29 

29 

4I 

50 

71 

60 

35 

32 

28 

20 

44 

51 

25 

20 

17 

52 

8 

24 

1N 

2 

95 

91 

22 

93 

21 

20 

10 

9 

16 

19 

7 

10 

26 

36 

250 

360 

14 

12 

Element, in parts per million 

Mn Pb Sb Sr Zn 

2500 

2300 

770 

630 

2000 

1800 

7N 

7N 

1300 

800. 

2700 

2400 

7N 

9 

30 

14 

13 

60 

600 

900 

13 

32 

21 

10 

13 

24 

19 

7N 

14 

26 

20N 300N 340 20N 300N 300 

21 300N 120 

25 300N 80 

20N 300N 270 20N 300N 240 

550 300N 1300 510 300N 1200 

30 300N 340 23 300N 300 

20N 300N 270 20N 300N 190 

560 300N 690 490 300N 430 

89 300N 30N 84 300N 30N 

430 600 250 

410 810 290 

25 300N 4100 37 300N 2900 

190 890 30N 140 660 30N 

180 300N 60 100 300N 70 

98 300N 30N 

67 300N 30N 

420 590 110 480 370 180 

260 300N 200 220 330 130 

13 220 330N 

300N 

320 

1300 32 400 

25 65 

19 60 

22 660 

18 750 

36 46 33 45 

17 110 

14 210 

8 110 

8 140 

11 120 11 180 

7N 3500 

7N 3000 

18 160 13 200 

8 550 47 630 

12 190 

27 340 

12 6000 

7 8300 

7N 1600 8 2700 

21 41 17 66 

300N 

300N 

330N 

300N 

300N 

300N 

300N 

470 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

40 

30 

470 

300 

640 

670 

30N 

30N 

340 

360 

150 

145 

790 

930 

200 

180 

360 

380 

130 

150 

1300 

2900 

1300 

4100 

30N 

50 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

400 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

300N 

Ga 

30 

25 

29 

27 

25 

24 

20 

17 

30 

25 

24 

30 

36 

45 

ION 

10N 

10N 

10N 

25 

26 

10N 

ION 

ION 

ION 

10N 

ION 

10N 

ION 

10N 

10N 

10N 

30 

ION 

10N 

35 

29 

30 

32 

10N 

ION 

36 

32 

24 

24 

73 

68 

12 

17 

37 

40 

10 

16 

120 

160 

100 

150 

10N 

10N 

La 

89 

76 

84 

69 

84 

60 

90 

90 

180 

160 

61 

60 

100 

99 

50N 

50N 

50N 

50N 

180 

170 

50N 

50N 

50N 

50N 

50N 

50N 

50N 

50N 

50N 

50N 

50N 

140 

50N 

50N 

130 

120 

160 

150 

50N 

50N 

74 

72 

60 

60 

64 

60 

50N 

50N 

96 

100 

50N 

50N 

120 

140 

140 

210 

50N 

50N 

Ni 

18 

15 

21 

16 

25 

20 

7N 

7N 

160 

120 

20 

16 

12 

17 

7N 

7N 

7N 

7N 

160 

150 

7N 

7N 

7N 

7N 

7N 

7N 

7N 

7N 

7N 

7N 

7N 

13 

8 

11 

9 

8 

63 

60 

9 

8 

11 

10 

8 

8 

9 

8 

8 

9 

8 

9 

9 

9 

11 

10 

7 

7N 

9 

9 

15 

methods described by Anderson and Bancroft (1952, p. 325-330), were 

used to examine the variation in the concentrations of different 

elements and to estimate the variance components between samples 

from the same site and between sample sites. The variance components 

are given in table 2. 

Generally the variance components between sample sites are sufficiently large in comparison with the variance components between in-
16 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

TABLE 2.- Logarithmic variance components for each element and oxide divided among 

different 

[Numbers in parentheses express each variance component as a percentage ofthe total logarithmic variance. Asterisks of the data were censored and accordingly 

Type of rocks ............ Silicified 

National Belle National 

Area ................... and National Belle Red Mtn. No. 3 and 

Red Mtn. No.3 RedMtn. 

Number of samples ...... 44 18 26 12 

Variance between ........ Sam2les Sites Sameles Sites Samples Sites Samples 

Oxides (in percent) 

SiO, ................... 0.00013 0.0001 0.00013 0.00018 *0.00011 *0.000042 0.00036 (56) (44) (42) (58) (72) (28) (23) 

Al,O, .................. .0013 

(3) 

Fe,O, .................. .013 .1 .0078 .091 .017 .039 .004 (12) (88) (8) (92) (30) (70) (3) 

MgO ··················· *.057 *.0 *.079 *.0 *.047 *.0068 *.034 (100) (0) (100) (0) (87) (13) (68) 

CaO ................... 

Na,O ·················· .037 .029 .0075 .018 *.055 *.034 .078 (56) (44) (29) (71) (62) (38) (36) 

K,O ................... 

Elements (in parts per million) 

Ag ..................... 0.044 0.46 0.089 0.24 0.019 0.62 (9) (91) (27) (73) (3) (97) 

As ..................... .035 .28 .012 .31 .052 .25 (11) (89) (4) (96) (17) (83) 

Au ..................... .045 .3 .021 .29 .062 .17 (18) (82) (7) (93) (27) (73) 

Bi ..................... Cu ..................... .025 .36 .013 .66 .035 .051 0.0084 (6) (94) (2) (98) (41) (59) (3) 

Mn .................... *.16 *.0 "'.1 *.0 *.21 *.0 *.066 

(100) (0) (100) (0) (100) (0) (52) 

Ph ..................... .024 .13 .005 .21 .039 .07 .0028 

(16) (84) (2) (98) (36) (64) (.5) 

Sb ..................... 

Sr ····················· .015 .27 .019 (5) (95) (14) 

Zn ..................... 

Ga ..................... .0061 

(4) 

La····················. .0013 

(7) 

Ni ····················· 

dividual samples from the same site to allow the recognition of 

differences in the concentration of a given element between sample 

sites. 

An asterisk in table 2 indicates that the variance between two 

samples of the same site is significant at the 95-percent level of confidence. In those instances the variance components between sample 

sites are small in comparison with the components between individual 

samples from the same site, making it impossible to statistically distinguish differences between sample sites and also complicating the interpretation of geochemical anomalies. Using elements whose concentrations are highly variable in a given type of altered rock would require 

collecting more than two samples from each site. The number of 
METHODS OF STATISTICAL ANALYSIS 17 

the two levels of the analysis-of-variance design within different altered rock types and 

areas 

indicate significance at the 95-percent level of confidence; leaders ( ........ ) indicate that more than 30 percent 

analysis of variance was not attempted] 

Arg:illic Illitic Pyropylitic 

Belle 

National Belle Red Mtn. No.3 Red Mtn. No.3 National Belle No.3 

8 4 10 50 

Sites Samples Sites Samples Sites Samples Sites Samples Sites 

Oxides (in percent) - Continued 

0.0012 0.000041 0.0015 *0.001 *0.002 0.00041 0.01 0.00018 0.00042 

(77) (3) (97) (33) (67) (4) (96) (30) (70) 

.049 .00042 .018 .0033 .12 .00029 .0022 *.0024 *.0006 

(97 (2) (98) (3) (97) (12) (88) (80) (20) 

.14 .0046 .13 .0028 .32 .012 .2 .0003 .0079 

(97) (3) (97) (.8) (99.2) (6) (94) (4) (96) 

*.016 .011 .045 *.079 *.0 *.51 *.062 .025 .024 (32) (20) (80) (100) (0) (89) (11) (51) (49) 

*.022 *.042 *.057 *.0092 .0035 .22 

(.34) (66) (86) (14) (2) (98) 

.14 *.11 *.023 .0059 .18 .0024 .35 .018 .53 

(64) (83) (17) (3) (97) (.7) (99.3) (3) (97) 

*.09 *.51 .0092 .38 .00054 .01 

(15} (85) (2} (98) (5) (95) 

Elements (in parts per million) - Continued 

0.0023 0.059 (4) (96) 

0.27 0.0065 0.05 .012 1.2 *0.034 *0.064 0.0094 0.0069 (97) (12) (88) (.9) (99.1) (35) (65) (58) (42) 

*.061 *.16 *.0 .0033 .028 (48) (100) (0) (11) (89) 

.53 .0013 .42 .0058 .57 .0098 .41 (99.5) (.3) (99.7) (1) (99) (2) (98) 

.12 .013 .13 *.03 *.24 .025 .18 .023 .26 (86) (9) (91) (11) (89) (12) (88) (8) (92) 

.13 .0072 .056 .0041 .15 .0041 .092 *.0013 *.0006 (96) (11) (89) (3) (97) (4) (96) (68) (32) 

.017 .0013 .017 *.0011 *.0067 .0031 .036 .0031 .0032 (93) (7) (93) (14) (86) (8) (92) (49) (51) 

*.001 *.0036 .0011 .005 .0036 .0081 

(22) (78) (18) (82) (31) (69) 

samples needed could be estimated according to procedures suggested 

by Shacklette, Sauer, and Miesch (1970, p. C12). 

A two-tailed t-test, as described by Guenther (1964, p. 23), was used 

to compare geometric means of the content of 20 elements and oxides in 

·the different types of altered rocks and in different areas. The 

hypothesis tested in each case was that no difference existed between 

the geometric means for a given element or oxide in the two altered-rock 

types or areas being considered. In table 3, shown in the boxes for the 

various pairs of altered rock types or areas, are the elements and oxides 

which were 9,etermined by the t-tests to be nonsignificant (that is, having no statistical difference between means) at the 95-percent level of 

confidence. For example, when differences in geometric means were 
18 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

compared for all 20 elements and oxides between silicified rocks and 

propylitized rocks, only two, copper and zinc, were nonsignificant at the 

95-percent level of confidence. For the remaining 18 oxides and 

elements that were tested, the hypothesis - that there is no difference 

between geometric means for a given element or oxide between the 

silicified group of samples and the propylitized group of sa~ples- was 

rejected; therefore, the differences in geometric means were significant 

for the remaining, unlisted oxides and elements. 

DISTRIBUTION OF OXIDES AND ELEMENTS 

ROCK TYPE DISTRIBUTIONS 

The distribution and relative depletion or enrichment of the various 

oxides and elements are shown in figures 3-6. The statistical 

significance of the differences between geometric means of the oxides 

and elements for comparisons between the various altered-rock types is 

shown in table 3. The concentration of the oxides and elements in the 

propylitized rocks provides a reasonable estimate of the background 

content of these oxides and elements in the National Belle and Red 

Mountain No. 3 areas and is also useful for describing the chemical 

changes in the rocks affected by advanced argillic alteration. 

Si0 2, Al20 2, Fe 20 3, MgO, CaO, Na 20, K20, Mn, Sr, Ga, La, and Ni 

(figs. 3-6) were constituents of the propylitized country rock in the area 

and were, in general, leached by the later hydrogen ion metasomatism. 

Some of these constituents (Si02, Sr, Ga, La; figs. 3, 6) are enriched in 

certain rocks; this enrichment is due not to their being added from the 

altering solutions but to depletion of other elements. 

The abundance of Si02 (fig. 3) is about the same in the propylitic and 

illitic rocks but increases progressively from the illitic to the argillic and 

to the silicified rocks. The numerous quartz veinlets, abundant cryptocrystalline silica, and common quartz crystals in vugs in the silicified 

rocks all suggest that the silica was rather mobile. Most of this silica 

was probably derived from the original rock material and was not introduced by the altering fluids. This is evident from the content of 

titanium (not shown in tables and histograms), which is progressively 

greater in progressively more altered rocks. Vein silica in the area contains little or no titanium; pipe silica contains about 0.5 percent or 

slightly more titanium, or approximately the same amount as the country rocks; and the silicified rocks contain the greatest amount, with a 

mean value of 3.5 percent. 

Strontium, gallium, and lanthanum (fig. 6) all show a slight increase 

in abundance in the illitic rocks as compared with the propylitized 

rocks, although for lanthanum the increase is not statistically significant (table 3). The concentrations of these three elements remain about 

the same in the argillic rocks as in the illitic rocks. In the silicified rocks 
DISTRIBUTION OF OXIDES AND ELEMENTS 19 

all three elements have been leached; gallium and lanthanum have 

been almost totally removed. 

Alumina (fig. 3) was rather resistant to leaching, being only slightly 

depleted in the argillic rocks as compared with the illitic and 

propylitized rocks. However, in the silicified rocks, it has been extensively leached. Some of the aluminum was reprecipitated in alunite and 

diaspore in both the argillic and silicified rocks. 

Magnesium, calcium, manganese, and nickel (figs. 3-6) were readily 

leached by hydrogen ion metasomatism even in the illitic rocks, and 

calcium has been almost totally removed from the argillic and silicified 

rocks. Potassium (fig. 4) decreases continuously in abundance in 

progressively more altered rocks, whereas sodium concentrations (fig. 4) 

remain about the same from the propylitic to the illitic rocks and then 

decrease sharply from the illitic rocks to the argillic and silicified rocks. 

Alunite and natroalunite(?), or sodic alunite, contain most of the 

potassium and sodium that remains in the silicified rocks. Chemical 

analyses by Hurlbu~t (1894) indicate a K20 content of 4.26 percent and 

a Na20 content of 4.41 percent for "alunite" from the National Belle 

breccia pipe. 

Silver, arsenic, gold, bismuth, copper, lead, antimony, and zinc (figs. 

4-6) were all added to the rocks during hydrothermal alteration and 

mineralization of the breccia pipes; generally, the more intensely 

altered rocks contain higher amounts of metallic elements, the greatest 

concentrations occurring in the silicified rocks. However, the degree of 

enrichment among the different types of altered rocks is rather variable. 

In the illitic rocks, lead (fig. 5) is significantly enriched (table 3), and 

arsenic, gold, and bismuth (figs. 4, 5) occur in more "'amples of these 

rocks, but their concentrations are not statistically different from their 

concentrations in the propylitic rocks. 

Gold (fig. 4) is enriched in the argillic rocks as compared with the illitic and propylitic rocks; silver, arsenic, bismuth, lead, and antimony 

(figs. 4, 5) are more common in the argillic rocks but are not enriched to 

statistically significant amounts. 

In the silicified rocks all the introduced elements except lead, zinc, 

and copper (figs. 5, 6) are enriched significantly. The content of lead 

decreases as compared with the argillic and illitic rocks. Zinc occurs 

more commonly in samples of the silicified rocks, but not in statistically 

significant amounts. 

Copper (fig. 5) is depleted in the illitic rocks, and its concentration is 

about the same in the argillic, silicified, and propylitized rocks. It was 

undoubtedly added to the rocks along with the other metals during 

mineralization, but its mobility in the highly acid supergene environment of the breccia pipes makes interpretation of its concentration 

patterns exceedingly difficult. 
20 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

INTRUSIVE 

QUARTZ 

LATITE 

(10) 

Nat;•::~Belle Red Mountain ~ ~ (10) _..__.__._...L.....L.__.I_ J....--L __ ,_ 

PROPYLITIC { National Belle 

{50) {50) 

SILICIFIED 

{44) 

ROCK OR 

ALTERATION 

TYPE 

Red Mountain 

{26) 

National Belle 

(18) 

Total 

(44) 

AREA 

(NUMBER OF 

SAMPLES) 

:~ ~~~~~~~~~8~~ ~'-''''''''' o~a~~~~~$~i88~ ooooo~~N~~~~ 000000000~~~~~ 

FeTOs MgO 

LOG CONCENTRATION, IN PERCEN'P 

FIGURE 3.- Histograms showing concentrations of Si02, Al 20 3 , Fe 20 3,and MgO in rocks 

mean; figure at right indicates percentage of samples that contained less than 
DISTRIBUTION OF OXIDES AND ELEMENTS 

+ 

II 

Al20a 

LOG CONCENTRATION, IN PERCENT 

• 

37 

I I 

52 

from the National Belle and Red Mountain No.3 areas. Arrow indicates geometric 

lowest amount of oxide shown. Vertical scale is frequency, in percent. 

21 
22 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

INTRUSIVE 

QUARTZ 

LATITE 

(10) 

PROPYLITIC 

(50) 

ILLITIC 

(10) 

ARGILLIC 

(12) 

SILICIFIED 

(44) 

{ 

National Belle 

and 

Red Mountain 

(10) 

National Belle 

(50) 

{ Red Mou•ta;• 

(10) 

Red Mountain 

(4) 

National Belle 

(8) 

Total 

(12) 

Red Mountain 

(26) 

National Belle 

(18) 

Total 

(44) 

ROCK OR AREA 

AlTERATION 

TYPE 

(NUMBER 

OF SAMPLES) 

L 

0 

~~~~~ ~ 

I I I I 1111 - I I 

~-~ I I I I I I I 

1· {- 75 12 

I I I I I I I I I I 

1· 50 8 

I I. I Ill Ill 

i 96 L ~ 

I I 

CaO Na20 

LOG CONCENTRATION, IN PERCENT 

FIGURE 4. - Histograms showing concentrations of CaO, NatO, K10, Ag, As, and Au in 

metric mean; figure at right indicates percentage of samples that contained less than 
DISTRIBUTION OF OXIDES AND ELEMENTS 

K20 

LOG CONCENTRATION, 

IN PERCENT 

23 

100 

Au 

rocks from the National Belle and Red Mountain No. 3 areas. Arrow indicates geolowest amount of oxide or element shown. Vertical. scale is frequency, in percent. 
24 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

INTRUSIVE 

QUARTZ 

LATITE 

(10) 

PROPYLITIC 

(50) 

ILUTIC 

(10) 

ARGILLIC 

(12) 

SILICIFIED 

(44) 

{ 

National Belle 

60 80 

and 30 Red Mountain 

(10) 

0 

{ 

National Belle 

(50) 

{ Red ~~)ota;o ~~--L..-L.----'---'---'L-'--L-.L..J.I--'1 

•·• ~:~··,;· ~l ~.......~.l---l-~...I.......JI __ _,I __ .....J.._..__.

50

-.J 

National Belle 

(8) 

Tot. I 

(12) 

soo~t 

~~ 60L 53 

Red Mountain t 

(26) 30 

0 

National Belle 

(18) 

Total 

(44) 

ROCK OR AREA 

~ ,..._onQQQQQQOQOQ 

N&riai~~~~~~~pjc;:;ti _.N·"~le~ ALTERATION 

TYPE Bi Cu 

(NUMBER 

OF SAMPLES) 

LOG CONCENTRATION, IN PARTS PER MILLION 

FIGURE 5.- Histograms showing concentrations of Bi, Cu, Mn, Pb, and Sb in rocks 

mean; figure at right indicates percentage of samples that contained less 
I 

I. 

I • 

DISTRIBUTION OF OXIDES AND ELEMENTS 

Mn 

I l I 

I I I 

33 

I I 

~L 64 

[J~J 

[ I+ I 

l., ,·I. 

l 

L2 

L2 

L2 

'. 

I II·-~ I I ~ 

Ph Sb 

LOG CONCENTRATION, IN PARTS PER MILLION 

from. the National Belle and Red Mountain No.3 areas. Arrow indicates geometric 

than lowest amount of element shown. Vertical scale is frequency, in percent. 

25 
26 GEOCHEMICAL CHARACTERISTICS. BRECCIA PIPES 

INTRUSIVE 

QUARTZ 

LATITE 

(10) 

PROPYLITIC 

(50) 

ILLITIC 

(10) 

ARGILLIC 

(12) 

SILICIFIED 

(44) 

{

National Belle 

and 

Red Mountain 

(10) 

{

National Belle 

(50) 

{

Red Mountain 

(10) 

Red Mountain 

(4) 

National Belle 

(8) 

Total 

(12) 

Red Mountain 

(26) 

National Belle 

(18) 

Total 

(44) 

ROCK OR AREA 

ALTERATION 

TYPE 

(NUMBER OF 

SAMPLES) 

1 

I II 

12 

~lLJ -~~· ·"__L_L_..LII• 

i.~ I I I I 

~~ + 87 

I I I I 

·_ Ga 

L 

[ I I I 

La 

LOG CONCENTRATION, IN PARTS PER MILLION 

FIGURE 6. - Histograms showing concentrations of Sr, Zn, Ga, La, and Ni in rocks from 

figure at right indicates percentage of samples that contained- less than lowest 
DISTRIBUTION OF OXIDES AND ELEMENTS 27 

L t 

• • I • LL L 

t 12 l { t 

Ill I I I I 

L 10 

I I 

l, ~~~ .. L • 

• [,II ,I t 

I I I I I I I II L 

l 62 l + 

I I I I 

~ 41 I + 

I I I I I I I ,, ~ 

~ 57 

._. I I I I I I ~ ~ [, .. 81 ll. 43 

I I I I I I I I l.: 

t. 63 

[~. 36 

I I I I I I I I I I I I I I I I I I I I I I I L ~~~~~~~N~~~~:~~~~~~~~! COa>..,<QONC!)Il>COil>"" 

..,...,a> .... ..,<O<Qa>o .... co ~;!N~::: .,...NC")U')CI() .. NO!It Ct')lllllt'cDOO::: ,...N.., 

Ni Sr Zn 

LOG CONCENTRATION, IN PARTS PER MilliON 

the National Belle and Red Mountain No.3 areas. Arrow indicates geometric mean; 

amount of element shown. Vertical scale is frequency, in percent. 
28 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

AREAL DISTRIBUTIONS 

Histograms showing the distributions of oxides and elements in 

silicified and argillic rocks from the National Belle breccia pipe and the 

Red Mountain No. 3 breccia pipe are presented in figures 3-6. Rocks 

from the two areas generally are geochemically very similar. Concentrations of iron, copper, and lead (figs. 3, 5) in the silicified rocks were 

determined to differ significantly in the two areas, and concentrations 

of calcium, gold, lanthanum, and nickel (figs. 4-6) in the argillic rocks 

were significantly different (table 3). 

TABLE 3. -Elements and oxides determined by t·tests to be nonsignificant at the 95-

percent level of confidence between different pairs of altered rock types or areas 

Silicified rocks 

National Belle 

and 

Red Mountain No. 3 

(44 samples) 

Argillic rocks 

National Belle 

and 

Red Mountain No.3 

(12 samples) 

Fe2 0 3 Zn 

MgO Ni 

K2 0 

Bi 

Cu 

Argillic rocks 

National Belle 

and 

Red Mountain No. 3 

(12 samples) 

Silicified rocks 

Red Mountain No. 3 

(26 samples) 

Silicified rocks 

National Belle 

(18 samples) 

Si02 

Al,03 

MgO 

CaO 

Na2 0 

K2 0 Mn La 

Ag Sb Ni 

As Sr 

Au Zn 

Bi Ga 

/1/itic rocks 

Red Mountain No.3 

(10 samples) 

Fe 2 0 3 

MgO 

Zn 

Fe20 3 Au Sr 

MgO Bi Zn 

CaO Mn Ga 

Ag Pb La 

As Sb Ni 

Illitic rocks 

Red Mountain No. 3 

(10 samples) 

Propylitic rocks 

National Belle 

(SO samples) 

Cu 

Zn 

Fe20 3 Sb 

Ag Zn 

As Ga 

Bi 

Cu 

Si02 Au 

Na2 0 Bi 

K2 0 Sb 

Ag Zn 

As La 

Argillic rocks 

Red Mountain No.3 

(4 samples) 

Argillic rocks 

National Belle 

(8 samples) 

Si02 

A1203 

Fe2 0 3 

MgO 

Na,o 

K2 0 Mn Ga 

Ag Pb 

As Sb 

Bi Sr 

Cu Zn 

The difference in iron (fig. 3) and copper (fig. 5) concentrations may 

be due to different rates of supergene leaching in the two areas. 
SUGGESTIONS FOR PROSPECTING 29 

However, because mine workings were inaccessible, we could not collect 

below the zone of supergene leaching, and the extent and degree of 

supergene leaching are unknown. 

The Student's t-test, as applied to the data for calcium, gold, 

lanthanum, and nickel in the silicified and argillized rock types, is 

biased because of the high variability in the data due to sampling (table 

2) and censored distributions (figs. 3-6). Therefore, whether concentrations of these four elements actually differ in the two areas is uncertain. 

Lead (fig. 5) reaches its greatest concentrations in the illitic and 

argillic rock types and is only moderately enriched in the silicified 

rocks. Figure 11 indicates that the lead anomaly does not coincide 

areally to the anomalies in silver (fig. 7), arsenic (fig. 8), gold (fig. 9), 

bismuth (fig. 10), and antimony (fig. 12). The relative enrichment of 

lead in the argillic rocks and the location of the lead anomaly outside 

the area enriched in the other introduced metals indicate a lateral zonal 

pattern around the breccia pipes or around the highly silicified major 

channelways within the pipes. Burbank (1941, p. 181) suggested a 

similar pattern of lead enrichment in the Guston breccia pipe, which is 

about 1 mile northeast of the National Belle pipe. 

SUGGESTIONS FOR PROSPECTING 

Figures 7-11 show the sample localities and the concentrations of 

silver, arsenic, gold, bismuth, lead, and antimony in samples from the 

National Belle and Red Mountain No.3 areas. Obviously, samples with 

anomalous metal contents are associated with areas of silicified rock. It 

is also readily apparent that the highest metal anomalies in the Red 

Mountain No. 3 pipe are at the southern end of the structure. The 

southern end has not been explored in the subsurface, and thus it 

provides an interesting exploration target. 

One further line of evidence concerning the possible target at the 

southern end of the Red Mountain No. 3 pipe should be considered. 

Schwarz (1890, p. 143), Ransome (1901, p. 111), and Burbank (1941, p. 

156, 181) each called attention to the vertical zoning of ores and metals 

within the breccia pipes; they also pointed out that enargite and pyrite 

are characteristically the deepest ores within the pipes and that the 

richer silver, lead, copper, and gold ores occur higher in the structure. 

As previously mentioned (p.lO') the mineralized rocks penetrated in the 

crosscuts and diamond drilling under the northern part of the pipe contained mainly enargite and pyrite. This suggests that the southern end 

of the Red Mountain No.3 pipe should be explored above the level of 

the northerly crosscuts (10,800 ft). The geochemical anomaly underscores .Burbank's (1941, p. 205-208) suggestion, based on geologic 

evidence, that the ground under the south and west slopes of Red 

Mountain No. 3 presents a favorable exploration target. 
37" 

54' 

30 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

EXPLANATION 

Parts per million 

• <1 

• 1-10 

• 10-100 

• >100 
SUGGESTIONS FOR PROSPECTING 

0 500 1000 1500 

CONTOUR INTERVAL 200 FEET 

DATUM IS MEAN SEA LEVEL 

2000 FEET 

31 

37" 

54' 

FIGURE 7. - Map showing concentration of silver in the National Belle and Red 

Mountain No.3 areas. Silicified rocks indicated by shaded pattern. Base from figure 2. 
32 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

EXPLANATION 

Parts per million 

• <40 

• 40-200 

• 200-1000 

• >1000 
SUGGESTIONS FOR PROSPECTING 

0 500 1000 1500 

CONTOUR INTERVAL 200 FEET 

DATUM IS MEAN SEA LEVEL 

2000 FEET 

33 

3JO 

54' 

FIGURE 8. - Map showing concentration of arsenic in the National Belle and Red 

Mountain No. 3 areas. Silicified rocks indicated by shaded pattern. Base from figure 2. 
34 

I 

I 

I 

3rl 

54' I 

GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

107'42'30" 

r 

\ /,' 

{='='=~ / \I 

,, -~ 

~ 

~ 

1) / 

: J II 

\1 /' \\I 

\\\ %; 

\\ 

\\ 

ll 

\1 // 1: II 

II I! 

\i II '::...9 

EXPLANATION 

Parts per million 

• <O.l 

• 0.1-0.5 

• 0.5-1.0 

• >LO 

~-
/ 

\ 

SUGGESTIONS FOR PROSPECTING 

( 

//) 

I 

0 

I 

,!/,--,...___. ____ . __ 

i 

/ //1 

() 

/1/ 

500 1000 1500 

CONTOUR INTERVAL 200 FEET 

DATUM IS MEAN SEA LEVEL 

2000 FEET 

35 

FIGURE 9. -Map showing concentration of gold in the National Belle and Red Mountain 

No. 3 areas. Silicified rocks indicated by shaded pattern. Base from figure 2. 

37" 

54' 
36 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

EXPLANATION 

Parts per million 

• <5 

• 5-50 

• 50-100 

• >100 
SUGGESTIONS FOR PROSPECTING 

0 500 1000 1500 

CONTOUR INTERVAL 200 FEET 

DATUM IS MEAN SEA LEVEL 

2000 FEET 

37 

37" 

54 1 

FIGURE 10. - Map showing concentration of bismuth in the National Belle and Red 

Mountain No. 3 areas. Silicified rocks indicated by shaded pattern. Base from figure 2. 
37" 

54' 

38 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

107{J4)'30'' 

EXPLANATION 

Parts per million 

• < 50 

• 50-200 

• 200-1000 

• > 1000 
SUGGESTIONS FOR PROSPECTING 

0 500 1000 1500 

CONTOUR INTERVAL 200 FEET 

DATUM IS MEAN SEA LEVEL 

2000 FEET 

39 

FIGURE 11. - Map showing concentration of lead in the National Belle and Red 

Mountain No.3 areas. Silicified rocks indicated by shaded pattern. Base from figure 2. 
40 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

J I ~- -

5.1' I 

EXPLANATION 

Parts per million 

• < 1_00 

• 100-250 

• 250'-500 

• > 500 
SUGGESTIONS FOR PROSPECTING 

CONTOUR INTERVAL 200 FEET 

DATUM IS MEAN SEA LEVEL 

41 

54' 

FIGURE 12. - Map showing concentration of antimony in the National Belle and Red 

Mountain No.3 areas. Silicified rocks indicated by shaded pattern. Base from figure 2. 
42 GEOCHEMICAL CHARACTERISTICS, BRECCIA PIPES 

Silver, arsenic, gold, bismuth, lead, and antimony are probably the 

most useful elements for prospecting for new breccia-pipe targets in the 

Red Mountain district. Some precautions must be taken, however, in 

interpreting concentration patterns of these elements. The distributions for bismuth and antimony are severely censored in all four 

types of altered rocks (fig. 5); distributions are similarly censored for 

silver, arsenic, and gold (fig. 4) in all altered-rock types except the 

silicified rocks (fig. 3). Because of the censored distributions, the 

variance components for these elements in most of the altered-rock 

types (table 2) could not be reliably estimated from the available data . . 

Without first obtaining variance components, interpreting the data is 

exceedingly hazardous because there is no reliable way to distinguish 

variability in the data due to differences between sample sites from 

variability within an individual sample site. For example, 97 percent of 

the variability of silver in silicified rocks from Red Mountain No. 3 

(table 2) is due to differences between sample sites, and only 3 percent 

of the variability is due to differences within individual sample sites. In 

contrast, 13 percent of the variability of magnesia in the same rock type 

is due to differences between sample sites, and 87 percent of the 

variability is due to differences within the individual sample sites. The 

low variability makes it impossible to statistically distinguish significant differences in magnesia concentration between sample sites. 

Some elements which were not enriched in statistically significant 

amounts in progressively more altered rocks are nevertheless useful for 

prospecting on the basis of their presence. Silver (fig. 4), though 

significantly enriched only in the silicified rocks (table 3), is present in 

33 percent of the samples of argillized rocks, but it was not detected in 

any samples of illitic and propylitic rocks. Antimony was not detected 

in any samples of propylitic and illitic rocks but was present in 30 percent of the silicified rocks (fig. 5). Bismuth, present in only 2 percent of 

the propylitic rocks, was detected in 50 percent of the argillic rocks, and 

in 53 percent of the silicified rocks (fig. 5). 

Lead is a favorable element to use for prospecting: it is severely censored only in the propylitic rocks (fig. 5), and most of the variability in 

its concentrations is due to differences between sample sites (table 2). 

Remember, however, that lead is laterally zoned around the areas of 

highest concentrations of the other introduced metals and that its 

highest concentrations are in tlte illitic and argillic rocks (fig. 5). 

Gold and arsenic are probably the best elements to use for 

geochemical prospecting in the silicified rocks. In those pipes in the Red 

Mountain district where the silicified rocks are poorly developed or 

have been removed by erosion, the exposed rocks are argillic and illitic, 

and lead would be the best element to use for prospecting. 
REFERENCES CITED 43 

REFERENCES CITED 

Anderson, R. L., and Bancroft, T. A., 1952, Statistical theory in research: New York, 

McGraw-Hill Book Co., 399 p. 

Bennett, C. A., and Franklin, N. L., 1954, Statistical analysis in chemistry and the 

chemical industry: New York, John Wiley & Sons, 724 p. 

Burbank, W. S., 1941, Structural control of ore deposition in the Red Mountain, Sneffels, 

and Telluride districts of the San Juan Mountains, Ct>lorado: Colorado Sci. Soc. 

Proc., v. 14, no. 5, p. 141-261. 

__ 1947, The San Juan region- General features and Red Mountain district, in Summaries of mining districts and mineral deposits, pt. 2 of Vanderwilt, J. W., Mineral 

resources of Colorado: Denver, Colo., Colorado Mineral Resources Board, p. 396-408, 

428-431. 

-- 1950, Problems of wall-rock alteration in shallow volcanic environments, in Van 

Tuyl, F. M., and Kuhn, T. H., eds., Applied geology, a symposium: Colorado School 

Mines Quart., v. 45, no. 1B, p. 287-319; and discussion by W. S. Burbank, T. S. 

Lovering, R. H. Sales, and Harrison Schmitt, p. 320-327. 

__ 1960, Pre-ore propylitization, Silverton caldera, Colorado, in Short papers in the 

geological sciences: U.S. Geol. Survey Prof. Paper 400-B, p. B12-B13. 

Burbank, W. S., and Luedke, R. G., 1964, Geology of the Ironton quadrangle, Colorado: 

U.S. Geol. Survey Geol. Quad. Map G0-291. 

-- 1969, Geology and ore deposits of the Eureka and adjoining districts, San Juan 

Mountains, Colorado: U.S. Geol. Survey Prof. Paper 535, 73 p. 

Burbank, W. S., Luedke, R. G., and Ward, F. N., 1972, Arsenic- an indicator element 

for mineralized breccia pipes in the Red Mountains area, western San Juan Mountains, Colorado: U.S. Geol. Survey Bull. 1364, 31 p. 

Fischer, R. P., Luedke, R. G., Sheridan, M. J., and Raabe, R. G., 1968, Mineral resources 

of the Uncompahgre primitive area, Color~do: U.S. Geol. Survey Bull. 1261-C, 91 p. 

Guenther, W. C., 1964, Analysis of variance: Englewood Cliffs, N.J., Prentice-Hall, Inc., 

199 p .. 

Remley, J. J., and Jones, W. R., 1964, Chemical aspects of hydrothermal alteration with 

emphasis on hydrogen metasomatism: Econ. Geology, V. 5~, no. 4, 538-569. 

Hillebrand, J. R., and Kelley, V. C., 1957, Mines and ore deposits from Red Mountains 

Pass to Ouray, Ouray County, Colorado, in NPw Mexico Geol. Soc. Guidebook, 8th 

Field Conf., Southwestern San Juan Mountains, Colorado, 1957: p. 188-199. 

Hurlburt, E. B., 1894, On alunite, from Red Mountain, Ouray County, Colorado: Am. 

Jour. Sci., 3d ser., v. 48, no .. 284, p. 130-131. 

Luedke, R. G., and Burbank, W. S., 1968, Volcanism and cauldron development in the 

western San Juan Mountains, Colorado, in Cenozoic volcanism in the southern 

Rocky Mountains: Colorado School Mines Quart., v. 63, no. 3, p. 175-208. 

Miesch, A. T., 1967, Methods of computation for estimating geochemical abundance: 

U.S. Geol. Survey Prof. Paper 574-B, 15 p. 

Ransome, F. L., 1901, A report on the economic geology of the Silverton quadrangle, 

Colorado: U.S. Geol. Survey Bull. 182, 265 p. 

Schwarz, T. E., 1890, The ore-deposits of Red Mountain, Ouray County, Colorado: Am. 

Inst. Mining Engineers Trans., v. 18, p. 139-145. 

Shacklette, H. T., Sauer, H. 1., and Miesch, A. T., 1970, Geochemical environments and 

cardiovascular mortality rates in Georgia: U.S. Geol. Survey Prof. Paper 574-C, 39 p. 

*u.s. GOVERNMENT PRINTING OFFICE: 1973-5!5-658/35