-

. Fluid-Inclusion Petrology 

Data from PorpHyry Copper Deposits 

and Applications to Exploration 
COVER PHOTOGRAPHS 

I 2 3 4 

5 6 

7 8 

9 10 

II 12 13 14 

1. Asbestos ore 

2. Lead ore, Balmat mine, N.Y. 

3. Chromite, chromium ore, Washington 

4. Zinc ore, Friedensville, Pa. 

5. Banded iron-formation, Palmer, 

Mich. 

6. Ribbon asbestos ore, Quebec, Canada 

7. Manganese ore, banded 

rhodochrosite 

8. Aluminum ore, bauxite, Georgia 

9. Native copper ore, Keweenawan 

Peninsula, Mich. 

10. Porphyry molybdenum ore, Colorado 

11. Zinc ore, Edwards, N.Y. 

12. Manganese nodules, ocean floor 

13. Botryoidal fluorite ore, 

Poncha Springs, Colo. 

14. Tungsten ore, North Carolina 
Fluid-Inclusion PetrologyData from Porphyry Copper 

Deposits and Applications 

to Exploration 

By]. THOMAS NASH 

GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 907-D 

A summary of new and published descriptions of fluid inclusions 

from 3 6 porphyry copper deposits and discussion of possible 

applica'tions to exploration for copper deposits 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1976 
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Nash, John Thomas, 1941-

Fluid-inclusion petrology-data from porphyry copper deposits and applications to exploration. 

(Geology and Resources of Copper Deposits) 

(Geological Survey Professional Paper 907-D) 

Bibliography: p. 

Supt. of Docs. no.: I 19.16:907-D 

1. Porphyry-Inclusions. 2. Porphyry-Southwestern States. 3. Copper ores-Southwestern States. 

I. Title. II. Series. III. Series: United States Geological Survey Professional Paper 907-D. 

QE462.P6N37 549'.23 76-608145 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

'Vashington, D.C. 20402 

Stock Number 024-001-02878-6 
APPRAISAL OF MINERAL RESOURCES 

Continuing appraisal of the mineral resources of the United States is conducted by the U.S. Geological Survey in accordance with the provisions of the 

Mining and Minerals Policy Act of 1970 (Public Law 91-631, Dec. 31, 1970). 

Total resources for purposes of these appraisal estimates include currently 

minable resources (reserves) as well as those resources not yet discovered or not 

currently profitable to mine. 

The mining of mineral deposits, once discovered, depends on geologic, 

economic, and technologic factors; however, identification of many deposits yet 

to be discovered, owing to incomplete knowledge of their distribution in the 

Earth's crust, depends greatly on geologic availability and man's ingenuity. 

Consequently, appraisal of mineral resources results in approximations, subject 

to constant change as known deposits are depleted, new deposits are found, new 

extractive technology and uses are developed, and new geologic knowledge and 

theories indicate new areas favorable for exploration. 

This Professional Paper discusses aspects of the geology of copper as a 

framework for appraising resources of this commodity in the light of today's 

technology, economics, and geologic knowledge. 

Other Geological Survey publications relating to the appraisal of resources of 

specific mineral commodities include the following: 

Professional Paper 820---"United States Mineral Resources" 

Professional Paper 926-"Geology and Resources of Vanadium Deposits" 

Professional Paper 933-"Geology and Resources of Fluorine in the United States" 

Professional Paper 959-"Geology and Resources of Titanium in the United States" 

CONTENTS 

Page 

System of measurement units ................................................................. VI 

Abstract. ....................................................................................................... D 1 

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

Acknowledgments.............................................................................. 2 

Types of fluid inclusions............................................................................ 2 

Type L Moderate salinity .......................................................... 3 

Type II. Gas-rich.......................................................................... 3 

Type III. Halite-bearing................................................................ 4 

Type IV. C02-rich.......................................................................... 4 

General physical and chemical character of the ore fluids .................. 5 

Temperature ...... ............................................................................... 5 

Pressure............................................................................................... 6 

Density.................................................................................................. 6 

Composition ........................................................................................ 6 

Page 

Distribution of fluid inclusions in space and time ................................ D7 

Fluids in intrusive rocks .................................................................... 7 

Fluids in intruded wallrocks.............................................................. 8 

Vertical distribution............................................................................ 10 

Distribution of fluids in time _______ ................................................... 10 

Correlation with geochemical features.................................................... 11 

Applications to exploration ...................................................................... 13 

Sampling and petrographic techniques .......................................... 13 

Identification of favorable intrusive bodies .................................... 14 

Char.acterizing hydrothermal systems ---------·-································· 14 

Gossans and leached outcrops .......................................................... 14 

Laterite and soil .............................. .................................................... 15 

References cited .......................................................................................... 15 

ILLUSTRATIONS 

Page 

FIGURE 1. Map of Southwestern United States showing locations of 

porphyry copper deposits described ............................................................................................................................................................ D2 

2. Sketches oftypical fluid inclusions observed in 

porphyry copper des posits .............................................................................................................................................................................. 3 

3-5. Photomicrographs: 

3. Type I fluid inclusion ................................................................................................................................................................................ 3 

4. Type II fluid inclusions ............................................................................................................................................................................ 4 

5. Type III fluid inclusion ··············································-·······--·--·--··········································-·······················---·································-------- 4 

6. Diagram of ranges of homogenization temperatures and salinities for 

moderate-salinity and halite-bearing fluid inclusions ................................................................................................................................ 5 

7. Map of distribution of high-salinity fluids in intrusive and 

sedimentary rocks at Copper Canyon, Nevada............................................................................................................................................ 9 

8. Generalized map ofthe Bingham Canyon area, Utah, showing distribution of very saline fluids 

and their spatial relationship to the copper ore zone, alteration zones, and the Bingham stock ........................................................ 12 

9. Photomicrograph of criss-crossing planes of fluid 

inclusions in vein quartz, Bingham Canyon, Utah ...................................................................................................................................... 14 

TABLE 

Page 

TABLE 1. Fluid-inclusion data for porphyry copper deposits .................................... , ................................................................................................... D2 

v 
VI CONTENTS 

SYSTEM OF MEASUREMENT UNITS 

In this report both the English and the metric systems of units are used. English units are given 

first and the equivalent measurement in metric unit is given in parentheses. Abbreviations are•noted 

below. The English units are converted to metric units by multiplying by the factors in the following 

list. 

English unit 

To convert Muliiply by 

Miles (mi) ··------------------------------------------------1.609 

Feet (ft) ----------------------------------------------------0.3048 

Inches (in.) ----------------------------------------------2.54 x 104 

25.4 

Pounds per square 0.608947 

inch (lb/in2). 

Metric unit 

To obtain 

Kilometres (km). 

Metre (m). 

Micrometres (J.~.m). 

Millimetres (mm). 

Bar. 

The conversion from temperature in degrees Fahrenheit (°F) to temperature in degrees Celsius 

(

0

C) is expressed by: °C =(5 /g) (°F-32). The conversion from temperature in degrees Celsius to 

temperature in degrees Fahrenheit is expressed by: °F = [(1.8 X 0C) +32]. 
GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

FLUID-INCLUSION PETROLOGY-DATA FROM 

PORPHYRY COPPER DEPOSITS AND APPLICATIONS 

TO EXPLORATION 

Bvj. THOMASNASH 

ABSTRACT 

Fluid-inclusion studies of 37 porphyry copper deposits, mainly in 

the United States, demonstrate that all but 3 evolved through a hydrothermal stage characterized by very high salinities, generally in 

excess of about 35 weight percent NaCl equivalent. Temperatures of 

these fluids ranged from about 250° to 700°C for various stages and 

deposits. Most systems boiled. High salinities, shown by halite-bearing 

inclusions, and boiling, suggested by coexisting gas and liquid-rich 

inclusions, are considered to be diagnostic of epizonal intrusions which 

are the most favorable parents for porphyry copper mineralization. 

Depth of emplacement of many copper-bearing stocks is deduced 

from fluid inclusions to have been about 6,000 to 10,000 feet (1,800 to 

3,000 metres); fluid pressures during mineralization are interpreted 

generally to be less than 500 bars. 

Moderate-salinity (less than about 12 percent) and moderatetemperature ( <350°C) fluids are noted in all porphyry copper deposits and were responsible for the deposition of most copper and 

molybdenum in deposits, such as Bagdad, Esperanza, Mineral Park, 

Morenci, Ray, Sierrita, in the Southwestern United States and several 

in southern British Columbia. However, with only three exceptions, 

highly saline fluids apparently were present at an early stage and also 

deposited metals. The relative amounts and economic importance of 

copper and molybdenum deposited from high- and moderate-salinity 

fluids varies within the porphyry deposit class. 

There is compelling geologic and geochemical evidence that 

chloride is important for transport of metals, but the porphyry coppers stand out as a class associated with fluids of especially high salinity 

during at least one stage of their formation. Halite cubes in fluid 

inclusions are an effective, although rough, indicator of those salinities 

and can be conveniently monitored during petrographic study of thin 

sections. Thus, fluid inclusions can be used to characterize favorable 

intrusions, metal anomalies, and caprocks as an additional method of 

detecting possible disseminated porphyry copper metallization. The 

presence of halite-bearing inclusions, especially coexisting with gasrich inclusions, is considered to be a favorable fluid anomaly in the 

search for porphyry ore. 

INTRODUCTION 

Fluid-inclusion studies have added important insight 

into the genesis of ore deposits, but little effort has been 

made to apply these techniques and data to mineral 

exploration. Compelling experimental and thermodynamic evidence shows that chloride in hydrothermal fluids is a potent solvent for metals through the 

formation of chloride-metal complex ions (Helgeson, 

1964; Holland, 1972); fluid-inclusion data (Roedder, 

1967, 1972) has been an important contribution to these 

geochemical advances. Because fluid inclusions yield the 

most direct evidence about the salinity of hydrothermal 

fluids responsible for metallization, and provide a link 

between the laboratory and the field, they have potential 

use in exploration. This paper will attempt to summarize the present knowledge of fluids in porphyry 

copper deposits and to outline some practical applications of fluid-inclusion technology to exploration. 

It should be emphasized at the outset that fluid inclusions are by no means rare or unusual in rocks and 

vein-forming minerals. The problem is knowing how to 

recognize them and interpret their significance. More 

than 50 years ago, petrographers commonly made reference to fluid inclusions and, in their early concepts of 

ore genesis, considered such inclusions to be evidence. 

One of the most astute observers was Lindgren, who 

devoted several pages to the description of fluid inclusions in the copper deposit at Morenci, Ariz. Part of his 

observations (Lindgren, 1905, pp. 213-214) are as follows: 

Fluid inclusions have been observed in the quartz grains of the 

granite, the quartzite, the porphyry, and the vein quartz occurring 

in this district. There is nothing uncommon in this; it is indeed the 

ordinary condition of affairs. As these fluid inclusions beyond 

doubt contain aqueous solutions, it may be regarded as certain that 

such fluids were present when the quartz grains in question were 

formed. 

At present I know of fluid-inclusion data for 37 porphyry copper deposits (table 1) and for a number of 

prospect areas. Observations have been made by many 

people, but, for consistency, reliance will be ·placed 

mainly on my own studies (many of which were reconnaissance in nature) of 25 economic deposits. Figure 1 

shows the location of 22 of the deposits in the SouthD1 
D2 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

western United States. Discussion will focus on the general composition (salinity) of inclusions, e~pecially where 

this may be estimated at room temperature from conventional thin sections. Although some geochemists 

have advocated the use of inclusion thermometry in ore 

exploration- (for example, Ermakov (1966) and Bradshaw and Stoyel (1968) - that parameter by itself does 

not appear reliable or discriminating as a guide to disseminated sulfide deposits of the porphyry copper type. 

TABLE I.-Fluid-inclusion data for porphyry copper deposits 

[Inclusion types: . I, Moderate salinity; II, gas-rich; III, halite-bearing; IV, C02-rich. H9st: PQ, pnmary quartz; SQ, secondary quartz, including veins; CS, calc-silicate mmerals] 

Deposit 

Arizona: 

Ajo 

Bagdad 

Bisbee 

Christmas 

Copper Basin 

Esperanza . Inspiration 

Mineral Park 

Mission 

Morenci .. Poston Butte 

(Florence) 

Ray .... 

Sacaton 

San Manuel 

Sierrita 

Silver Bell 

Twin Buttes 

Nevada: 

Copper Canyon 

Ely ..... 

Yerington 

Other areas: 

Chino, N. Mex. 

Bingham, Utah 

Butte, Mont. . . . Catheart Mountain, 

Maine ..... . 

.1, II, III 

.I, II, III, IV 

.1, III 

.1, III 

.I, II, III 

.1, III 

.I, II, III 

.1, II, III 

.1, III 

.I, II, III 

.1, II, III 

.I, III 

.1, III 

.1, II, III, IV 

.1, II, III 

.1,-11, III 

.1, III 

.1, II, III, IV 

.1, II, III 

.1, II, III, IV 

.1, II, III 

.1, II, III 

.1, II, III, IV 

.1, II, III 

El Salvador, Chile . .I, II, III 

Breccia pipes, Chile .I, II, III 

La Caridad, Mex. . .1, II, III 

Bethlehem, BC., 

Canada .I, III 

Victoria, B.C., 

Canada .I 

Valley Copper, B.C., 

Canada ...... I 

Helecho, Puerto Rico I, II, III 

Sapo Alegre, 

Puerto Rico 

Saindak, Pakistan 

Mt. Fubilan, 

New Guinea 

OK Tedi, 

.I, II, III 

.1, II, III 

.I, III 

Host of halite- bearing inclusions 

PQ,SQ 

PQ,SQ 

PQ,SQ 

PQ,SQ 

PQ,SQ 

PQ 

PQ,SQ 

PQ,SQ 

SQ,CS 

PQ,SQ 

PQ,SQ 

PQ, SQ (rare) 

SQ 

PQ,SQ 

PQ,SQ 

PQ,SQ 

SQ,CS 

PQ,SQ,CS 

PQ,SQ 

PQ,SQ 

PQ,SQ 

PQ,SQ,CS 

PQ,SQ 

PQ,SQ 

PQ,SQ 

SQ 

PQ,SQ 

PQ,SQ 

PQ,SQ 

PQ,SQ 

PQ,SQ 

PQ,SQ 

PQ,SQ 

SQ 

Reference1 

1 

2 

1 

3 

1 

1, 4 

3 

1, 5 

1, 4 

1, 6 

1 

1, 7 

3 

1,7,8 

1, 4 

1, 4 

3,4 

9 

1, 10 

1 

11 

4, 12 

4, 13, 14 

19 

15 

16 

17 

1 

18 

18 

19 

20 

New Guinea .. I, II, III PQ, SQ 21 

Koloula, Guadacanal I, II, III PQ, SQ 21 1 Reference: 1, Observed by J. T. Nash (this report); 2, Nash and Cunningham (1973); 3, D.P. Wheeler (written commun., 1973); 4, Roedder (1971); 5, Drake (1972); 6, Lindgren 

(1905); 7, Logsdon (1969); 8, J.D. Davis (written commun., 1973); 9, Nash and Theodore (1971); 10, Spencer (1917); u;b. Norton (oral commun., 1971); 12, Moore and Nash (1974); 

13, Meyer, Shea, Goddard, and others (1968); 14, Roberts (1973); 15, Gustafson nd Hunt (1975); 16, Sillitoe and Sawkins (1971); 17, T. G. Theodore (oral commun., 1974); 18, Observed by D.P. Cox and J. T. Nash; 19, Observed by R. G. Schmidt and J. T. Nash; 20, Bamford (1972); 21, A. R. Cfiivas and R. W. T. Wilkins (written commun., 1975). 

120° 

42or--------- 1140 

-r--- ----.--------~ 

I r l ~oppe' Canyo':, Sal( Lake City -----, I .o I 

I l Bingham Canyon l oReno NEVADA • i UTAH i '\. •Yerington Ely 1 

'"'', i I 

" I I 

' r------------i-

'"' ('"' ARIZONA 

', \ Mineral Park 

'\' . 

\ 

t" 

I 

( 

Bagdad 

PI 

• . 0 CoPP"' s-.;n .I 

1oen1x0 I nsptratJOn 

Ray • Morenci 1 

Poston Butte • • •I • / Sacaton.• Christmas~ Chino 

0 50 100 Ml LES l............_ Ajo Silver • 

I 1 -.......... • Bell_.... OTucson 

I -............ Sierrita~Mission I 

0 50100 KILOMETRES ~ranza_,- "Twin ~uttes '------------------'-------=---- • Bts~~ 

FIGURE I.-Map of the Southwestern United States, showing locations 

(squares) of porphyry copper deposits whose fluid inclusions are 

described. 

This paper presents a brief summary of fluidinclusion observations from porphyry copper deposits, 

makes some inferences from the data, and suggests ways 

in which fluid inclusions can be used as a tool in exploration. This is clearly a "state of the art" report and reflects 

my current ideas. Hopefully, new data, refined concepts, and better applications will emerge from additional studies of these copper deposits. Qualitative features rather than quantitative numbers will be emphasized. 

ACKNOWLEDGMENTS 

This reconnaissance study would not have been possible without the assistance of many geologists in the U.S. 

Geological Survey and in mining companies. I appreciate the loan of samples and helpful discussions 

provided by the following colleagues: R. P. Ashley, 

N. G. Banks, D.P. Cox, S.C. Creasey, G. K. 

Czamanske, F. S. Fisher, R. 0. Fournier, W. J. Moore, 

T. G. Theodore, R. G. Schmidt, and D. E. White. Discussions with C. W. Field, Oregon State Univ., and D. P. 

Wheeler, Umont Mining Co., were most helpful. Resident geologists at the deposits sampled are thanked for 

their interest and assistance. 

TYPES OF FLUID INCLUSIONS 

Fluid inclusions can be classified according to many 

schemes, from simple to complex. The classification 
FLUID-INCLUSION PETROLOGY D3 

employed here is based on phase relations observable at 

room temperature, as in normal petrographic investigations. Additional discussion of fluid-inclusion classification is given by Kelly and Turneaure ( 1970) and Roedder (1971, 1972). Four general types are recognized. 

TYPE I. MODERATE SALINITY 

A common type of inclusion contains two fluid phases 

-a liquid and a small vapor bubble amounting to 10 to 

40 percent of the volume of the inclusions (fig. 2-I, fig. 

3). One or more birefringent daughter minerals 1 may be 

present. The volume of vapor is roughly proportional to 

temperature; calculated filling curves may be helpful in 

estimating temperature (Kalyuzhnyi, 1965), although 

consideration should be made of salinity. Tests on a 

freezing stage indicate a wide range of salinities from 

about 23 to nearly 0 weight percent NaCl equivalent. 

Freezing tests and chemical analyses of extracted fluids 

indicate sodium, potassium, calcium, and chlorine to be 

the major constituents (Roedder, 1972) in the aqueous 

phase. The vapor is mainly HzO, but crushing tests 

indicate positive pressures attributable to COz in some 

inclusions from porphyry copper deposits. More rigorous tests of vapor pressures and compositions are reported by Drake (1972), and Drake and Ypma (1969). 

Identification of daughter salts is generally difficult; 

birefringent crystals that are probably dawsonite 

[NaAlCOs(OH)z), rhombohedral carbonate, and anhydrite are relatively common in these inclusions, and 

hematite is found in some. Also, there are several unidentified daughter salts. 

Type I inclusions are ubiquitous in intrusive rocks, 

wallrocks, and veins of porphyry copper districts. In 

these rocks the presence of type I inclusions of many 

different ages along crisscrossing planes reflect introduction during repeated fracturing. Commonly, these 

inclusions are associated with propylitic or sericitic alteration, or with relatively late-stage ore veins, such as gold 

and pyrite at Copper Canyon, Nev. (Nash and Theodore, 1971); galena and sphalerite at Mineral Park, Ariz. 

(Drake, 1972; Nash and Cunningham, 1974); or fluorite 

at Ajo, Ariz., as observed by]. T. Nash. More important, however, is the association of moderate-salinity 

type I inclusions with chalcopyrite and molybdenite 

veins in many deposits, such as those at Bagdad, Esperanza, Morenci, and Ray, Ariz. The amount of copper 

associated with these inclusions appears to be highly 

variable in the many porphyry deposits studied. 

TYPE II. GAS-RICH 

These inclusions generally contain two fluid phases, 

liquid plus more than 60 percent vapor (fig. 2-11, fig. 4); 

a reddish or opaque hematite daughter mineral is com1 Minerals precipitated from inclusion fluids during <.:ooling. 

Ill IV 

Anhydrite 

FIGURE 2.-Sketches of typical fluid inclusions obsderved in porphyry 

copper deposits. T ypes I to IV correspond to those described in 

text. L, liquid; V, vapor; Lc02, liquid C02. 

.. 

0 10 20 MICROMETRES 

FIGURE 3.-Photomicrograph of type I inclusion in quartz-chalcopyrite vein, Copper Canyon, Nev. L, liquid; V, vapor bubble. 

monly present. The liquid has salinities in the range 0.4 

to 7 weight percent; the higher salinities are believed to 

reflect trapping of some high-salinity liquid with vapor 

(Nash and T heodore, 1971; Roedder, 1971). Crushing 

tests made by Roedder (1971) and by]. T. Nash commonly indicated positive pressures attributable to COz. 

The amount of COz present probably ranges from 

traces in type II inclusions to more than 25 percent in 

type IV inclusions (COz-rich). The phase proportions 

and composition are as expected of trapped steam, and 

such an origin is consistent with their occurrence. 
D4 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

FIGURE 4.-Photomicrograph of type II inclusions in 

Copper Canyon, Nev. L, liquid; V, vapor. 

The abundance of type II inclusions varies from deposit to deposit and from sample to sample. Some gasrich inclusions are generally present in the igneous 

quartz of the porphyries and, in many samples, constitute 50 percent or more of the population. Quartz in 

some intrusives, notably the Mesozoic intrusives of 

British Columbia, does not contain gas-rich inclusions of 

any age. Many quartz veins contain moderate to large 

numbers of type II inclusions; others contain few or 

none. These observations will be considered further relative to evidence for boiling. 

TYPE III. HALITE-BEARING 

Inclusions that contain well-formed, cubic halite, and 

generally several other daughter minerals (fig. 2-III, 

fig. 5) are characteristically observed in igneous quartz 

of the porphyries and in many quartz-sulfide veins. A 

second isotropic daughter mineral, sylvite, commonly is 

present; it has rounded edges, lower relief, and a higher 

thermal coefficient of solubility than halite. Hematite 

generally is present in type III inclusions; some is translucent red, and some is opaque, depending upon thickness, and may be anhedral or euhedral hexagonal or 

trigonal plates. A number of birefringent daughter 

minerals occur in these inclusions. One is rectangular, 

has parallel extinction, moderate relief, and is length 

slow in the position of minimum birefringence - it may 

be anhydrite (Nash and Theodore, 1971; Roedder, 

1971). An equant, highly birefringent mineral probably 

is calcite. Others with vague optical properties cannot be 

identified at present. In heating tests halite and sylvite 

dissolve, yielding information on salinity (Roedder, 

1971, p. 113-114). From the volume of NaCl and KCl 

present and from their behavior in heating tests, it is 

deduced that salinities commonly were near 40 percent 

and, at Bingham Canyon, were more than 50 percent 

(Roedder, 1971; Moore and Nash, 1974). Filling ternperatures range from about 225° to 725°C. Other 

daughter salts generally do not dissolve in 3 hours at the 

temperature of filling, indicating either disequilibrium 

or the effects of post-trapping changes, such as hydrogen diffusion 

FIGURE 5.-Photomicrograph of type III inclusion in a quartzchalcopyrite-molybdenite vein, Bingham Canyon, Utah. L, liquid; V, 

vapor; H, halite crystal. 

Halite-bearing type III inclusions are noted in at least 

some samples from all but two porphyry copper districts. Halite-bearing inclusions have been noted in both 

mineralized and unmineralized stocks examined from 

the Basin and Range province; they occur in a high 

proportion of veins associated with them. Indeed, early 

petrographers noted that such inclusions were the "ordinary condition of affairs." However, not all plutonic 

rocks contain high-salinity inclusions, nor do all veins in 

porphyry copper deposits. Halite-bearing inclusions are 

characteristic of porphyry copper deposits (Nash, 1971; 

Roedder, 1971) but are not exclusive to that environment and not uniquely associated with copper mineralization. Hence, the significance of these diagnostic inclusions needs to be assessed, and this will be done in this 

report. 

1YPE IV. C02-RICH 

The presence of a third fluid phase, liquid C02, at 

reduced temperatures distinguishes these inclusions 

(fig. 2-IV). Some have salinities near 2 weight percent 

(Nash and Cunningham, 1973), whereas others contain 

halite cubes and salinities believed to be approximately 

30 weight percent (Nash and Theodore, 1971). The 

C02:H20 ratio varies greatly also from the limits of 

optical detection (approximately 3 mole percent C02) to 

more than 30 mole percent. These grade into type IV 

inclusions with no optically detectable liquid C02 but 

with somewhat large C02 pressures at room temperature. Many type IV inclusions, as commonly indicated 
FLUID-INCLUSION PETROLOGY D5 

by their phase proportions, were trapped as vapor, su_ch 

as in an effervescing hydrothermal system. Type IV Inclusions are not typical of most porphyry copper deposits, but they have been noted in some samples from 

Copper Canyon, Nev. (Nash and Theodore, 1971), 

from Butte, Mont. (Roedder, 1971), and from Bagdad, 

Ray, and Yerington, Nev., by the author. The liquid 

COz-bearing inclusions appear to have filling temperatures of about 300°C, and are associated with relatively 

low temperature porphyry-type deposits, or their low 

temperature stages. This probably reflects the miscibility gap in the system COz-HzO (Takenouchi and Kennedy, 1964) which develops below 350°C; at higher 

temperatures COz is readily dissolved in aqueous solutions. For the porphyry coppers the concentration of 

COz generally is insufficient to form discrete liquid C02 

at room temperature. Ore fluids in the porphyry coppers typically contain <3 mole percent COz. 

GENERAL PHYSICAL AND CHEMICAL 

CHARACTER OF THE ORE FLUIDS 

A broad range of fluid compositions and physical 

conditions are recorded in inclusions from porphyry 

deposits. Physical conditions, such as temperature, pressure, and fluid density, are effectively determined from 

fluid inclusions. However, only gross chemical characteristics may be determined from fluid inclusions unless 

the inclusions are crushed and subjected to chemical 

and isotopic analysis, methods which are too costly and 

time-consuming for routine application to exploration. 

Studies of alteration and ore mineral assemblages 

(Meyer and Hemley, 1967) yield important information 

on the chemistry of ore fluids and are a necessary prerequisite upon which to base fluid-inclusion studies, especially regarding the crucial matter of sulfur fugacity . 

TEMPERATURE 

Filling temperatures have been recorded in the range 

from as high as 725°C at Bingham Canyon (Roedder, 

1971) to less than 200°C in several deposits (fig. 6). 

Filling temperatures greater than 600°C have been determined for coexisting gas-rich and halite-bearing inclusions in samples from Bingham Canyon, from El 

Salvador, Chile (Gustafson and Hunt, 1975), and from 

San Manuel Q. D. Davis, written commun., 1972). Filling temperatures require a correction for pressure unless the pressure at trapping is the same as that at filling; 

this condition is met when inclusions are trapped on the 

liquid-vapor curve (that is, from a boiling fluid). Because these fluids were in a boiling condition, they do 

not require a pressure correction and, hence, are the 

same as the temperature of trapping. 

Filling temperatures determined from vein samples 

50 

u 

z "' 

1-

z 

w 

u 

a: 

w 

0.. 

1-

I 

g 

w 

$ 

~ 

>-' 

1-

z 

::::i 

<{ 

CJ) 

00 100 

Inclusions of 

· m~derate salinity 

(type I) 

200 300 400 500 

HOMOGEN IZATION TEMPERATURE IN ° C 

600 

FIGURE 6.- Generalized ranges of homogenization temperatures and 

salinities for type I and type III inclusions from porphyry copper 

deposits. 

from individual deposits show a considerable range: 

300°-400°C at Copper Canyon (Nash and Theodore, 

1971), 230°-450°C at Mineral Park (Drake, 1972; Nash 

and Cunningham, 1974), 233°- 373°C at Bagdad (Nash 

and Cunningham 1974), and 350°-440°C in copperbearing breccia pipes in Chile (Sillitoe and Sawkins, 

1971). In the Butte, Mont., district pre-main (Cu-Mo) 

stage veins contain type I inclusions with filling temperatures of 370°±20°C (Roberts, 1973); interpreted pressure corrections are large (180° - 330°C) and yield temperatures of formation of 550°-700°C. Main stage veins 

at Butte contain inclusions with a range of compositions 

(types I, II, and III), and filling temperatures range 

from 275° to 335°C (Roedder, 1971). Type I inclusions 

in garnet from the skarn orebody of Copper Canyon 

studied by T. G. Theodore (written commun., 1975) 

have filling temperatures as high as 540°C; the type I 

inclusions coexist with type II, and boiling conditions 

are inferred. 

Filling temperatures can be estimated from room 

temperature phase proportions, but such estimates are 

subject to large errors on high salinity fluid inclusions 

because of the likelihood of misjudging the compressibility of the saline liquid and deducing erroneously low 

homogenization temperatures. Estimates of filling temperatures for typical inclusions in quartz-sulfide veins in 

many porphyry deposits range from about 250° to 

500°C. On the basis of estimates of pressure corrections 

required (generally small), it is my interpretation that in 

most porphyry deposits temperatures were typically 

about 400°± 100°C. Higher temperature pulses, where 

present, probably were of brief duration during intrusive surges. 
D6 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

PRESSURE 

Pressure determinations based on fluid -inclusion 

properties are generally less than 2,000 bars and are 

commonly less than 500 bars. Gas-rich and liquid-rich 

inclusions commonly coexist in vein and wallrock 

quartz, a relationship that probably reflects trapping 

from a heterogeneous liquid plus gas or boiling system. 

In this situation filling temperatures are the same as 

trapping temperatures because no pressure correction is 

required for fluids trapped in the two-phase boundary 

(boiling point curve). (See Haas, 1971.) With a temperature determined from heating tests or estimated from 

phase proportions, and a composition determined from 

freezing tests or from daughter minerals, one may refer 

to data from the system NaCl-HzO (Sourirajan and 

Kennedy, 1962; Haas, 1971) for an estimate of pressure. 

Application of such relations suggested about 160 bars 

pressure at Copper Canyon (Nash and Theodore, 1971) 

and about 1, 100 bars at Bingham Canyon (Roedder, 

1971). 

Conversion of pressures to geologic depth is highly 

subjective. In many systems one must invoke fluctuating 

pressures, such as in a system changing from lithostatic 

to hydrostatic, to explain inclusion and geologic observations (Nash and Theodore, 1971; Roedder, 1971; 

Moore and Nash, 1974; Drake, 1972). Different reasoning was employed by Nash and Cunningham (1974) to 

explain conditions at Bagdad: although very little volcanic cover is preserved, the rarity of boiling requires 

that pressures were typically greater than those of the 

boiling point curve, and that the inferred depth of cover 

was somewhat more than 6,000 feet (1,800 m). Depths 

of formation, interpreted from fluid -inclusion data, 

range from 6,000 to 10,000 feet (1 ,800 to 3,000 m) for 

Bingham Canyon (Moore and Nash, 1974), Bagdad 

(Nash and Cunningham, 1974), Copper Canyon (Nash 

and Theodore, 1971), and Mineral Park (Drake, 1972), 

as well as for breccia pipes in Chile (Sillitoe and Sawkins, 

1971). Somewhat more shallow levels of intrusion and 

deposition have been deduced for El Salvador (Gustafson and Hunt, 1975), and at Jamestown, Colo. (Nash 

and Cunningham, 1973), for a Tertiary stock which 

contains no economic copper mineralization. As an indicator of depth of formation, fluid-inclusion barometry is 

consistent with estimates made from geologic data. 

When-the thickness of the overlying rocks at the time of 

metallization cannot be estimated geologicaly, fluidinclusion barometry is the only reliable method for estimating depth of formation. 

There is considerable evidence that many porphyry 

copper deposits form at depths greater than about 3 

miles (5 km) in batholithic settings (for example, Hylands, 1972; Roberts, 1973; Cheney and Trammell, 

1975). The copper deposits of the Guichon batholith, 

British Columbia, and at Butte, Mont., are the best 

known examples. The limited amount of fluid-inclusion 

data available for these localities (Nash, this report; 

Roberts, 1973) indicate that gas-rich and halite-bearing 

fluid inclusions are not characteristic of these deposits as 

is apparent for copper deposits in epizonal stocks. 

DENSITY 

Densities of hydrothermal fluids may be determined 

with fair precision from measurements of phase proportions in fluid inclusions (Roedder, 1967). Fluid inclusions are the only source of this information. The density of high-salinity type III fluid inclusions from porphyry copper deposits is commonly greater than 1.0 

g/cm3 (grams per cubic centimetre), and is as high as 1.3 

g/cm3 at Bingham Canyon (Roedder, 197 1). Commonly 

coexisting with these dense liquids are gas-rich type II 

inclusions representing trapped steam with densities 

that range from 0.1 to 0.3 g/cm3 . Temperature is the 

major determinant of densities in the low density region. Moderate-salinity type I fluid inclusions commonly have densities that range from 0.7 to 0.9 g/cm3 

(Nash and Theodore, 1971). Fluid densities, particularly 

the density contrasts between high- and moderatesalinity fluids, may be of importance in controlling the 

circulation of hydrothermal fluids and help explain, for 

example, why high salinity fluids are generally restricted 

to the vicinity of intrusives (Nash and Theodore, 1971). 

The influence of fluid density on such factors as mixing 

or nonmixing of hydrothermal fluids and mineral solubility may have real academic and practical importance. 

COMPOSITION 

Some general inferences regarding fluid compositions can be made from fluid-inclusion data. The common presence of salt daughter minerals indicates 

salinities that range from about 30 to more than 50 

weight percent. Excellent data from halite and sylvite in 

inclusions from Bingham indicate compositions that 

range from 13 to 22 weight percent KCl, 28 to 39 weight 

percent NaCI, and 47 to 51 weight percent H20 (Roedder, 1971; Moore and Nash, 1974). K:Na molar ratios 

range from 0.26 to 0.59 (Moore and Nash, 1974). The 

concentration of CaS04 may be as much as 1.5 weight 

percent (Roedder, 1971) if the rectangular daughter 

mineral is anhydrite. Iron contents commonly ar e high, 

from approximately 1 ,000 ppm (parts per million) to as 

much as 1.2 weight percent (12,000 ppm; Roedder, 

1971). Similar but generally lower concentrations of Na, 

K, Fe, and S04 are deduced from relative volumes of 

daughter minerals in selected inclusions from other deposits. A nonmagnetic, often triangular, opaque mineral, occurring with hematite, is noted in inclusions 

from several deposits. It may be chalcopyrite, indicating 

relatively large copper concentrations (Roberts, 1973). 
FLUID-INCLUSION PETROLOGY D7 

The presence of hematite and anhydrite might appear 

to provide evidence of oxygen fugacity, but because 

hydrogen diffusion is likely and would cause selfoxidation, the daughter minerals are not valid indicators 

of oxygen fugacity. 

The composition of moderate-salinity type I inclusions is best determined on the freezing stage. Measurements of depression of freezing point indicate 

salinities generally less than about 12 weight percent 

N aCl equivalent (Nash and Theodore, 1971 ~ Roedder, 

1971; Nash and Cunningham, 1974). These inclusions 

occasionally contain hematite and anhydrite (?), indicative of appreciable Fe, Ca, and S. An elongate, birefringent mineral with the optical characteristics of dawsonite (Coveney and Kelly, 1971) is common. 

The most characteristic fluid-inclusion feature revealed by studies of porphyry copper deposits is the 

general occurrence of cubic crystals of halite. Halitebearing type III inclusions occur in primary quartz of 27 

intrusive bodies associated with the copper mineralization; only igneous bodies of the Guichon batholith, 

British Columbia (Victoria and Valley Copper deposits, 

Hylands, 1972), appear to be notably devoid of type III 

inclusions. Halite occurs as primary and secondary inclusions in some secondary quartz of hydrothermal 

mineralization in most deposits, and is notably sparse or 

absent only in the Esperanza, Ray, and British Columbia 

deposits. Therefore, very saline hydrothermal fluids 

were present during at least one stage of the porphyry 

copper mineralizing system. The fact that halite-bearing 

inclusions occur in more than 90 percent of the deposits 

so far studied, makes them a feature to be sought in any 

porphyry copper prospect. 

Halite-bearing inclusions are deemed to be a general 

attribute of porphyry copper systems and a guide to 

them; however, several cautions are in order. (1) Barren 

intrusive bodies are also known to contain halite-bearing 

inclusions. Probably these inclusions are typical of epizonal intrusives in general, not just the copper-bearing 

variety of great economic interest. (2) Favorable fluid 

composition in terms of salinity of course does not by 

itself create an orebody; hence, it is absolutely imperative that other evidence be considered in exploration 

(for example, presence of Cu minerals, structure, alteration, and geophysical data). (3) The abundance, in relative and absolute senses, of halite-bearing inclusions is 

highly variable within and among deposits. These inclusions are very abundant and obvious at Bingham Canyon, somewhat less abundant and smaller at Copper 

Canyon and Ely, and sparse at Ray. Their abundance 

per unit volume is low, but relative abundance to type I 

and II inclusions is high in the small Puerto Rico deposits. Presumably, the abundance of halite-bearing inclusions reflects many factors, including volume of 

hydrothermal fluid, tectonism, and pressuretemperature conditions. Clearly, most of the copper ore 

at Bagdad, Esperanza, Mineral Park, Ray, and Sierrita 

formed from moderate salinity fluids; hence, the viability and importance of these fluids should not be discounted. 

DISTRIBUTION OF FLUID INCLUSIONS 

IN SPACE AND TIME 

Zonal relations of alteration and metallization have 

been used for years in exploration for porphyry copper 

deposits. Because the population and general composition of fluid inclusions can be determined at relatively 

low cost during petrographic study of conventional thin 

sections, this information can be plotted on a map with 

other geochemical data. Available qualitative and quantitative data bearing on the distribution of fluid types 

and inferences which can be drawn from that data are 

presented in this section of the report. 

The complexity of the distribution of fluid inclusions 

in and adjacent to a porphyry copper deposit must be 

emphasized. The spatial occurr~nces of hydrothermal 

alteration are not easily mapped, and the ages of the 

inclusions relative to these occurrences is difficult to 

assess. Also, inclusions cannot be mapped in the field, 

and microscopic examination does not yield definitive 

ages. Even if the age of a vein can be determined, 

inclusions in quartz of that vein may be the same age as 

the vein (primary inclusions). More typically, however, 

inclusions are on microfractures through the quartz 

(secondary or pseudosecondary inclusions) and thus are 

younger than the vein. 

Determination of the ages of inclusions in igneous 

quartz of the intrusive bodies is particularly problematical, because recrystallization obscures original textures. Spatial distribution can be defined with good reliability, although possible errors may result from sample bias, destruction of certain inclusions, and comparison of inclusions of different ages; similar sampling 

problems pervade all geochemical studies. 

FLUIDS IN INTRUSIVE ROCKS 

All intrusive rocks contain fluid inclusions, but abundance and types present are variable and correlate with 

other factors of interest to geochemists. Particular attention should be paid to type II and III inclusions in 

intrusive rocks. Halite-bearing type II fluid inclusions 

are likely to form in chlorine-rich intrusive rocks crystallizing at low pressures (<1,000 bars) on the basis of 

experimental studies in the system N aAlSiaOs-N aCl -

H20 (Koster van Groos and Wyllie, 1969), and gas-rich 

type II inclusions will form from low to moderate density fluids that are boiling or in the three phase 

(NaCl-vapor-liquid) region. As previously discussed 

under "Fluid Inclusion Types," type III inclusions are 
D8 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

noted in intrusive rocks in most porphyry copper districts, and type II inclusions, probably cogenetic with 

type III, occur in many of these same rocks. Type II and 

III inclusions are rare in granitoid rocks, such as those 

of the Sierra Nevada batholith, which crystallized at 

greater depths than typical copper-bearing stocks. The 

abundance of inclusions appears to correlate with the 

amount of fracturing, especially where there are multiple intrusives. Post-ore intrusives at Ray, Ariz., Ely, 

Nev., and Park City, Utah, are characterized by the 

paucity of fluid inclusions, especially type III. Cox, 

Perez Gonzales, and Nash ( 197 5) observed this at the 

Sapo Alegre porphyry copper prospect in Puerto Rico. 

The composition and quantity of fluids present during emplacement of an intrusion is a major question of 

petrogenesis (Burnham, 1967; Fournier, 1967, 1972). 

Petrologists generally cite data from experiments and 

geologic features such as the presence of miarolitic 

cavities or the compositions of minerals to determine 

fluid pressures. Fluid-inclusion data could be useful for 

the determination of physical conditions if the specific 

time at which the inclusions were trapped can be established. Quartz phenocrysts commonly contain prominent fluid inclusions, but these inclusions are generally 

along microfractures indicative of secondary formation; 

isolated "primary-appearing" inclusions are likely toreflect recrystallization at high temperatures. A good description of probable primary inclusions in granitic intrusive rocks was presented by Roedder and Coombs 

( 1967). They noted the presence of glass in some inclusions, an important feature not reported from porphyry 

copper deposits. The hypothesis of immiscibility between silicate magma and salt-rich hydrothermal fluids 

(Roedder and Coo·mbs, 1967; Roedder, 1971) is an important model for fluid conditions at the magmatic stage 

in some intrusive rocks. However, immiscibility is determined by interpretation of relations between fluid 

inclusions and original features may be obscured by 

recrystallization. Some measured filling temperatures 

are in excess of 600°C for inclusions from copperbearing stocks (Roedder, 1971; Moore and Nash, 1974; 

Gustafson and Hunt, 1975). No pressure correction is 

required, but these temperatures still are 1 00°C or more 

below likely solidus temperatures. Samples of intramineral veins (veins formed betwe'en magmatic pulses, Kirkham, 1971), would seem excellent for study, but recrystallization and formation of secondary inclusions by 

later intrusions and by subsolidus hydrothermal 

mineralization creates a complex assemblage of inclusions that cannot be objectively related to one magma 

(Hall and others, 1974; Moore and Nash, 1974). 

FLUIDS IN INTRUDED WALLROCKS 

Pre-ore wallrocks contain from 0 to about 90 percent 

of the ore in various porphyry copper deposits (Lowell 

and Guilbert, 1970). The character of the ore and alteration of the wallrocks is highly variable and will not be 

considered here. Fluid-inclusion types and abundances 

also are highly variable and are an aid to understanding 

the physical-chemical environment of ore emplacement 

and distribution in wallrocks. 

The Copper Canyon deposit, which contains no 

economic mineralization in the associated intrusive, has 

been studied in detail (Nash and Theodore, 1971; 

Theodore and Nash, 1973; Theodore and Blake, 1975), 

and will serve as a model for copper deposits in pre-ore 

wallrocks. Siliceous sedimentary rocks, particularly conglomerate of the Pennsylvanian Battle Formation, contain abundant fluid inclusions. A zone that includes the 

intrusive and the copper deposits is characterized by 

halite-bearing inclusions (fig. 7). The halite-bearing 

fluid inclusions in this zone are similar to those observed 

in quartz-chalcopyrite veins in the pit. The zone of 

anomalous high-salinity inclusions is somewhat smaller 

than the pyrite halo but much larger than the orebodies. 

The zonation of fluid inclusions provides a more satisfactory target than do minor element or alteration halos, 

both of which are poorly developed in the siliceous rocks 

(Theodore and Nash, 1973; Theodore and Blake, 

1975). 

High-temperature halite-bearing fluid inclusions are 

abundant in zones of intruded metasedimentary rocks 

at Bingham Canyon, Ely, Mission, and Twin Buttes. 

Quartzites from the eastern part of the pit at Bingham 

Canyon, which carry minor amounts of ore, contain 

numerous gas-rich inclusions and sparse liquid-rich type 

I or III inclusions. Although high-salinity inclusions are 

abundant in the intrusive rocks, they are very rare in 

quartzites more than 100 feet (30 m) from the eastern 

contact (Moore and Nash, 1974). If the inclusion population is representative, the wallrocks in this eastern 

zone must have been bathed in vapors rather than 

liquids, a physical condition which may explain the 

paucity of ore in those rocks. In oxidized rocks of the 

Ely district, jasperized Ely Limestone (Mississippian, 

Pennsylvanian, and Permian) and silicified Rib Hill 

Sandstone (Lower Permian) contain numerous halitebearing inclusions. Halite-bearing inclusions similar to 

those in primary ore veinlets occur in jasper several 

hundred feet above the Tripp orebody in the Ely district 

indicating that high-salinity fluids circulated through 

wall rocks above the intrusions at Ely, but the limits of 

this circulation have not been determined. 

The Ray porphyry copper deposit deserves special 

comment because its geology (Metz and Rose, 1966) and 

its fluid inclusions (Nash, this report; Logsdon, 1969) 

are not typical. Most of the primary and secondary enriched mineralization occurs in Precambrian Pinal Schist 

and Precambrian diabase, with a very small percentage 

in the Paleocene Granite Mountain Porphyry, the "host 
FLUID-INCLUSION PETROLOGY 

~Mea ~ of 

th;,,tudy 

~ 

~ 

_,J-----...J---7.~< .... 

f WEST ORE / ·;YA '· BODY~~ --.J../ ·, . 

" , ... 

.... '<>" ~ : : : . 

~ Q -:· ::::;::: . / ·. ·\ 

0 4000 FEET 

0 1000 METRES 

\ . 

, 

• 

EXPLANATION 

m Tertiary volcanic rocks 

~ Tertiary altered granodiorite 

D Permian to Cambrian sedimentary rocks 

- Surface projection of copper ore bodies 

1.) YJ Area of very saline fluids 

t-- ·-· ---t Sample traverse-fluid-inclusion studies 

e Diamond drill hole sample locality 

L--__.J Outer limit of pyritized rocks- Hachures 

outside of zone 

• • • 

Contact 

Thrust fault - Dotted where concealed or 

inferred. Sawteeth on upper plate 

High-angle fault - Dashed where approximately located or inferred 

FIGURE 7.-Distribution of high salinity fluids in intrusive and sedimentary rocks at Copper Canyon, Nev., as 

deduced from occurrence of halite-bearing fluid inclusions. Modified from Theodore and Nash (1973). 

D9 
D10 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

porphyry" (Metz and Rose, 1966, p. 180). My observations were of 140 samples from the surface, pit, and drill 

core. Quartz-sulfide veins and wallrocks at Ray typically 

contain type I inclusions consisting of liquid, ~20 percent vapor, and commonly one or more daughter minerals: hematite, carbonate (?), and anhydrite (?). Gasrich inclusions are conspicuously absent at Ray. Halitebearing inclusions occur sparsely in some veins, wallrocks, and intrusive rocks including post-ore dikes, but 

such inclusions are not considered characteristic of the 

ore-depositing fluids. At Ray the fluid inclusions are 

monotonously similar. No differences were detected in 

the fluid-inclusion population in quartz-chalcopyrite, 

quartz-molybdenite, or barren quartz veins, or in quartz 

associated with anhydrite, biotite, chlorite, or sericite. 

Homogenization temperatures were estimated to be 

300°±25°C and recent determinations on the heating 

stage are about 300°C (T. G. Theodore, written commun., 1974). The pressure correction could be as much 

as + 7 5°C but probably is less. 

VERTICAL DISTRIBUTION 

The vertical distribution of fluid inclusions may be 

potentially informative, although at present little is 

known because of typical limitations on sampling. My 

sampling of several deposits, such as Bingham Canyon, 

Copper Canyon, Ely, and Ray, includes less than 500 

feet ( 150 m) vertically through the deposits; in these 

examples no systematic changes with depth are detected 

in fluid-inclusion populations. However, some noteworthy changes have been observed in other environments. 

Distinct zones have been recognized in the Park City 

district (Nash, 1973), where rocks and veins were 

examined over a 6,000-foot ( 1 ,800-m) interval. A transition from non-boiling to boiling moderate-salinity fluids 

occurs at the upper part of the presently exposed Mayflower vein system; base- and precious-metal ores are 

limited to the lower part of the system, which is characterized by liquids rather than vapor. Also, in the intrusive rocks a different type of vertical zonation of fluids is 

noted; these rocks were later cut by the veins previously 

described. A gradual shift in the ratio of gas-rich to 

halite-bearing inclusions (roughly contemporaneous) is 

noted over a 3,000-foot (900-m) vertical interval. In 

samples at elevations from 9,000 feet (2,700 m) down to 

about 7,000 feet (2,100 m) gas-rich inclusions predominate by about 100:1, whereas below an elevation of 

about 5,500 feet (1,700 m) the ratio is about 1:1. These 

inclusion ratios are as expected of a saltwater system 

above and on the boiling point curve respectively. The 

lower part of the system, which was pre-vein ore, contains anomalous amounts of disseminated chalcopyrite 

(about 0.1 to 0.2 percent Cu). 

Samples were studied from two base- and preciousmetal districts in which changes in fluid inclusion types 

suggest possible underlying disseminated mineralization. In the Goldfield district, Nevada, a drill hole penetrated welded tuff and an altered quartz monzonite 

body. The quartz monzonite contained prominent 

halite-bearing and gas-rich inclusions resembling those 

from Bingham Canyon, whereas the volcanic rocks contained only low-temperature low-salinity inclusions. The 

deeper zone in quartz monzonite has fluid inclusions 

and other geochemical features not recognized in historic precious-metal ore zones of the district. A similar 

transition was observed in samples of drill core from a 

base- and precious-metal mining district in Colorado. In 

these examples the transition to considerably hotter, 

much more saline, more dense fluids occurred over an 

interval about 300 feet (100m), near a lithologic contact, 

and was associated with a change in alteration and sulfide mineral assemblage. Changes such as these may be a 

guide to disseminated metallization below barren 

ground or below base- and precious-metal ores. Evidence for such a transition should be sought in deep 

drill holes. 

Both the vertical distribution of fluids and their physical condition are sensitive to pressure in the epizonal 

environment, although factors, such as heat flow, permeability, and quantity of water, are also important 

(White and others, 1971). Massive boiling is to be expected in the high-temperature low-pressure environment in or above epizonal intrusions (Burnham, 1967; 

Fournier, 1972; White and others, 1971). Such boiling 

should be detected by the occurrence of gas-rich or 

coexisting gas-rich and liquid-rich inclusions. In some 

copper deposits, such as Bingham Canyon, Copper 

Canyon, and Ely, boiling was pervasive, and in some 

deposits, such as Bagdad, Butte, and Mineral Park, boiling occurred during some vein stages. In still other 

deposits (Bisbee, Silver Bell, Bethlehem, and Valley 

Copper) boiling conditions have not been detected, possibly because of insufficient sampling. 

DISTRIBUTION OF FLUIDS IN TIME 

The ages of copper-bearing porphyries studied range 

from Ordovician to late Tertiary. The oldest studied is 

the Ordovician Attean Quartz Monzonite exposed at 

Catheart Mountain, Maine (Young, 1968). The Sacramento stock at Bisbee is pre-Cretaceous (Bryant and 

Metz, 1966), and the productive intrusives in the Ely 

district are Cretaceous (Bauer and others, 1966). The 

copper-bearing intrusive at Saindak, Pakistan, is about 4 

million years old (Ahmed and others, 1972), and many 

in the Southeastern United States are early Tertiary. 

Calc-alkaline intrusions of all ages generate very saline 

fluids; thus, geologic time does not appear to be a factor. 

The anomalously low salinities observed in the British 

Columbia deposits seem to be a function of their 

batholithic setting, not age (Jurassic). No Precambrian 
FLUID-INCLUSION PETROLOGY Dll 

porphyry coppers have been studied, but they are expected to have comparable salinity. 

Individual hydrothermal systems span several million 

years; within this time, the earliest fluids that can be 

recognized in most copper-bearing stocks are highly 

saline . Bagdad may be an exception because hot 

moderate-salinity fluids may have preceded cooler 

high-salinity f1uids (Nash and Cunningham, 1974). 

Likewise, at Butte the moderate-salinity fluids observed 

by Roberts (1973) probably preceded the high-salinity 

f1uids described by Roedder (1971); both f1uids deposited copper and molybdenum. In many places highly 

saline fluids have deposited quartz-chalcopyrite veins, 

with or without molybdenite, that have biotite, biotite 

plus potassium-feldspar, or no alteration envelopes. 

These features indicate that the solutions were not far 

from equilibrium with the granitic host rocks. In calcareous rocks the early high salinity fluids form 

calcium-iron-magnesium skarn minerals, as in the Pima, 

Ariz., district and the Copper Canyon, Nev. , west orebody. Although age relationships between halitebearing inclusions and disseminated sulfides are generally nonspecific, the fact that the two are coextensive 

and that both occur in microveinlets suggests that they 

are related. 

All porphyry copper deposits contain moderatesalinity inclusions which generally are younger than 

halite-bearing inclusions. Age relationships of veins and 

fluid inclusions have not been defined with sufficient 

certainty in any deposit to define fluctuations in salinity. 

Post-copper quartz veins with galena, sphalerite, gold, 

or fluorite contain primary moderate-salinity inclusions 

at Copper Canyon (Nash and Theodore, 1971), Mineral 

Park (Drake, 1972; Nash, this report), Ajo (Nash, this 

report), El Salvador (Gustafson and Hunt, 1975), and 

other unspecified deposits (Roedder, 1971). Of greater 

economic importance are the many quartz-chalcopyrite 

and quartz-molybdenite veins that contain only 

moderate-salinity inclusions. In some deposits, such as 

Bagdad (Nash and Cunningham, 1974), Mineral Park 

(Drake, 1972; Nash, this report), Morenci, and Ray, and 

in three deposits in British Columbia (Nash, this report), 

moderate-salinity fluids deposited most primary copper 

minerals. These moderate-salinity fluids also deposited 

important amounts of molybdenum. Determination of 

the ages of inclusions and metallization stages, and 

quantifying their economic contribution is a complex 

and subjective task, but there are suggestions at this date 

that the relative importance of high and moderate salinity fluids varied in the porphyry deposits as a class. 

CORRELATION WITH 

GEOCHEMICAL FEATURES 

Fluid-inclusion data are especially useful when integrated with other geochemical information, yet there 

have been few efforts to correlate geochemical expressions, such as alteration, metal zoning, or minor elements, with the fluids that produced them. Combined 

maps of these parameters have been instructive when 

attempted (Theodore and Nash, 1973; Moore and 

Nash, 1974). A study of this sort requires careful integration of many techniques, and samples must be carefully collected so that relations between all parts of the 

rock are understood. The attempt made at Copper 

Canyon (Theodore and Nash , 1973) illustrates some of 

the difficulties; for instance, experience ther~ indicated 

that relatively unfractured wallrocks served best for 

minor-element distribution studies, but fractured samples were necessary for fluid-inclusion studies. Despite 

the sampling problems, at Copper Canyon good correlation was noted between the distribution of halitebearing inclusions, a lteration, the pyrite halo, and 

anomalous copper, mercury, gold, and bismuth. (See 

fig. 7 .) 

The geologic setting in the southern and central parts 

of the Bingham Canyon deposit is more favorable for 

study because initial rock compositions were more uniform than at Copper Canyon. At Bingham, alteration 

and metallization are unusually uniform rather than 

highly localized in or along veins. Good spatial correlation is noted between the outer limit of predominant 

halite-bearing inclusions, the copper ore body, and the 

inner limit of amphibole and magnetite (Moore and 

Nash, 1974; fig. 8). There was no detectable difference 

in fluid-inclusion populations in the sericitic and biotitic 

alteration zones. Note that a ratio technique was used in 

the Bingham Canyon study (fig. 8). The relative abundance of inclusion types changes across zones of the 

metallization system and is shown by plotting relative 

abundance in parts per ten; plotting presence or absence of inclusion types would not show nearly as much. 

Another factor recognized in the Bingham study was 

that the absolute abundance (per unit volume) of inclusions was vastly greater in the ore zone than in the 

"unaltered" amphibole-magnetite-bearing quartz monzonite. Absolute abundances were not determined because of the great difficulty making counts of inclusion 

types in three dimensions. The experienced eye, however, can quickly judge approximate abundances and it 

is helpful to record these semiquantitative estimates. 

Several mineralogical associations have emerged from 

these fluid-inclusion studies. On the basis of many scattered observations, hydrothermal biotite (either disseminated or pseudomorphous after amphibole) and 

potassium-feldspar are associated generally with highsalinity fluids, although some exceptions are noted, as at 

Ray. These high-salinity fluids also sulfidized wallrock 

magnetite in many deposits. In the Cu-Mo deposits I 

have studied, fluid inclusions are not systematically different in quartz-chalcopyrite and quartz-molybdenite 
N 

, ~ . . ."' .· 

.. . . · 

.. >~ 

s 

0 

0 

w 

• 

0 

0 

0 0 

.. 

• 0 

..... ----....... _......---- 0'-

1 

~ ~:,:" .. :.~~ 

#~ ~ 

0 

• ..,-

-~ ... 

~ <~·: .~.( _: 

• 

0 

0 

0 

0 

.: .. ·.·.·:·. 

~ 

~ 

bd 

D 

: ·. ·~.:: . 

EXPLANATION 

Bingham stock 

Zone of predominantly 

very saline solutions 

Copper ore zone 

0 

0 

0 

N 00 

0 1000 FE ET 

0 ~0 METR ES 

0 

s 

FIGURE 8.-Generalized map of Bingham Canyon area, Utah, showing distribution of 

very saline fluids and their spatial relationships to the copper ore zone, alteration 

zones, and the Bingham stock. The boundary of the zone of predominantly highly 

saline fluids was arbitrarily chosen at a natural break in the inclusion population. Four 

or more parts in 10 of type III inclusions is represented by a dot; less than 4 parts per 

10 type III inclusions, by a circle. Modified from Moore and Nash (1974). 

I::j 

...... 

~ 

0 

M 

0 

t"" 

0 

0 

-<: 

~ 

z 

tl 

::<:! 

M 

(JJ 

0 

c 

::<:! 

(") 

M 

(JJ 

0 

"rl 

(") 

0 

"0 

"0 

M 

::<:! 

tl 

M 

"0 

0 

(JJ 

::J 

(JJ 
FLUID-INCLUSION PETROLOGY D13 

veins. Hydrothermal sericite forms from both high- and 

moderate-salinity fluids, although I suspect that the latter association is the most common. Chlorite and kaolinite typically form from moderate-salinity fluids. Available paragenetic and fluid-inclusion data suggest that 

lead, zinc, silver, and gold minerals in porphyry copper 

deposits may be deposited from later, cooler, less saline 

fluids than are the copper and molybdenum. Observations at Bingham Canyon (Roedder, 1971), Copper 

Canyon (Nash and Theodore, 1971), and Mineral Park 

(Drake, 1972; Nash, this report) support this generalization, but many more studies of such occurrences are 

needed. 

APPLICATIONS TO EXPLORATION 

Although there are many unifying similarities between the various disseminated copper deposits, there 

are also many differences in such aspects as geologic 

age, wall rock lithology, alteration, and degree of 

supergene enrichment, factors which complicate assessment of ore targets. In previous sections of this 

report attention has been drawn repeatedly to the widespread occurrence of high-salinity halite-bearing fluid 

inclusions in porphyry copper desposits. Further, there 

is considerable evidence for the importance of saline 

liquids in the transport of base metals (Helgeson, 1964, 

1969; White, 1968; Holland, 1972) as metal-chloride 

complex ions. 

The presence of chlorine in intrusive rocks has recently been suggested as a possible prospecting tool 

(Stollery and others, 1971; Kesler and others, 1973). 

Microprobe analyses of biotites and amphiboles in intrusive rocks with associated mineralization have shown 

enrichment in chlorine (Stollery and others, 1971; 

Parry, 1972). Alternately, whole rocks or minerals may 

be analyzed for chlorine (Stollery and others, 1971; 

Haynes and Clark, 1972a, b). Though the findings of 

these studies are in basic agreement with those presented in this report, the methods used are rather expensive, time consuming, or nonspecific. Fluid-inclusion 

petrography employing conventional thin sections 

(Nash and Theodore, 1971; Moore and Nash, 1974) is a 

preferable method because it yields more information at 

less cost and is readily combined with other desirable 

petrographic studies. 

SAMPLING AND PETROGRAPHIC TECHNIQUES 

The approach I have used in reconnaissance studies 

of fluid inclusions is subjective, yet it seems to produce 

plausible results. An important part of these studies is 

the collection of representative samples; here, one must 

use guides, such as structure, alteration, and sulfide 

mineralogy. Grid sampling is not recommended. Many 

students of fluid inclusions tend to collect vuggy wellformed vein materials known to contain the largest, 

best-preserved inclusions. Such samples are commonly 

late-stage, however, and may not be representative of 

the most economically important stages of metallization 

and alteration. To avoid such sample bias, ah effective 

technique is to sample quartz-bearing pre-ore rocks and 

to study secondary inclusions on fractures through 

quartz clasts or quartz phenocrysts. Such samples provide a record of changes in fluids introduced during 

multiple periods of fracturing, an advantage for exploration that outweighs the disadvantage of not knowing 

exact age relations. The sequence of fluids can best be 

determined from vein samples whose relative ages are 

established by structural and parage netic criteria. 

Three types of sample preparation may be used-thin 

section, polished thin section, or grains in immersion oil. 

Although the latter is the cheapest, it has the great 

disadvantage of conveying little or no textural information, and for that reason I have rarely used it. Conventional thin sections are highly advantageous; minerals 

are identified readily, textural relations are preserved, 

optical quality of inclusions in most minerals is very 

good even for those of 1 J.Lm diameter, and the preparations are made at low cost. Thin sections may be prepared with or without coverglasses, but one must be able 

to focus into the thin rock slice with a X 100 immersion 

objective (focal distance generally 0.09 mm). Doubly 

polished sections cut to a thickness which allows 

adequate light transmission are required for heatingand freezing-stage study and are superior for petrography of larger inclusions and for minerals with high 

indices of refraction. Structural and textural relations 

should be determined in the field or with a binocular 

miCroscope. 

Individual fluid inclusions are generally visible at X 

100 to x 200, although at such magnification they 

commonly look like "foreign matter" (fig. 9). Depending 

upon size and morphology, the inclusions may be clear 

or dark from internal reflection. For study of typical 

rocks from porphyry copper deposits a good quality X 

100 oil immersion objective and substage condenser are 

virtually indispensable for proper resolution of vapor 

bubbles and daughter minerals. At magnifications of 

about x 1 ,000, one focuses inside crystals and can resolve thousands of inclusions. Proper use of focused 

condensed light is required to illuminate the interior of 

inclusions. During petrographic study observations 

should be made of types of inclusions present, their 

textural occurrence (on fractures, isolated, healed or 

recrystallized, necked down, and so forth), identity and 

. size of daughter minerals, phase proportions, and r~lative abundance of inclusion types; total abundance 

should be estimated. This estimate is best made by reference to type samples and is recorded in a relative 

sense (high, moderate, and low). 
D14 GEOLOGY AND RESO URCES OF COPPER DEPOSITS 

,. .. .__., ... ' . . 

> • ; :·· .. .... FIGURE 9.- Photomicrograph of crisscrossing planes of fluid inclusions in vein quartz, Bingham Canyon, Utah. The inclusions appear 

as dark specks from total reflection of transmitted light because no 

condenser was used . 

IDENTIFICATION OF 

FAVORABLE INTRUSIVE BODIES 

Many petrologic features have been considered in 

attempts to characterize intrusives favorable for porphyry copper deposits (Stringham, 1966; Lowell and 

Guilbert, 1970). I believe that fluid inclusion types and 

abundance should be considered also. Evidence given 

previously suggests that favorable intrusive rocks should 

contain halite-bearing and probably gas-rich inclusions. 

Such inclusions appear to characterize epizonal intrusions, many of which have generated ore deposits. 

Abundance of these inclusions correlates with intensity 

of fracturing, water and salt content, and other unspecified physical conditions, all of which are favorable 

for metallization. Post-ore intrusions commonly can be 

discerned by a low abundance of inclusions, but not by 

inclusion types alone. Likewise, feeder dikes and very 

shallow intrusives can often be discerned by their low 

fluid-inclusion content. 

The fluid-inclusion criteria obviously should not be 

the only criteria used to evaluate the mineral potential 

of intrusive bodies because uneconomic hydrothermal 

systems can leave a similar record. Other features, easily 

noted while making the fluid-inclusion examination, 

should also be present, such as recrystallization, added 

potassium-feldspar or biotite, secondary biotite replacing amphibole, and sulfide minerals replacing magnetite . 

CHARACTERIZING HYDROTHERMAL SYSTEMS 

An important application of fluid-inclusion petrography is to aid in establishing the character of metal 

anomalies. Knowledge of fluid character should help 

the explorationist discriminate between types of hydrothermal systems and thereby increase his confidence 

that he has found a system that has a potential for 

extensive disseminated mineralization, rather than a 

small epithermal system. Vein and replacement baseand precious-metal deposits of the "mesothermal" and 

"dpithermal" type tend to form from moderate-salinity 

fluids (Roedder, 1963; Nash, 1972, 1973). As outlined 

here, the porphyry copper deposits appear to stand out 

as a class associated with highly saline and, commonly, 

boiling fluids. Hence, efforts should be made to characterize the hydrothermal system which caused the metal 

anomaly by looking for signs of high salinity (halitebearing inclusions) and boiling (gas-rich inclusions). 

Studies of high-temperature halite-bearing and gasrich inclusions in altered porphyry bodies in four 

precious-metal mining districts demonstrate specific 

application of this technique. Pyritized, potassic altered 

zones of intrusive bodies in the northwest San Juan 

Mountains, Colo., San Miguel Mountains, Colo., Park 

City district, Utah, and Goldfield district, Nev., bear 

reevaluation for potential disseminated sulfide 

mineralization at depth on the basis of these fluidinclusion observations. Base- and precious-metal ores in 

these districts were deposited from moderate-salinity 

( < 10 weight pe rcent N aCl) moderate-tern perature 

(<320°C) fluids (Nash, 1973, 1975). In three of these 

districts the observed zone of high-salinity fluids underlies the known precious-metal ore; it formed earlier 

than the precious-metal ore but during the same period 

of metallization. Alteration features in the deeper zone 

are not obviously different in the field. 

GOSSANS AND LEACHED OUTCROPS 

Fluid inclusions in silicified leached capping and gossans provide an important record of depositional conditions that is of great value to explorationists. Evidence 

from many districts indicates that fluid inclusions in 

quartz survive in excellent condition the leaching which 

destroys other primary minerals. Fluid inclusions in 

these surface samples allow a good estimate of thermal 

and compositional history during primary mineralization, and there is no confusion with supergene processes 

because such low-temperature conditions leave only 

liquid-filled inclusions with no gas bubble. 

Silicified caprock above the Bagdad, Bisbee (Lavender pit), Copper Canyon, Ely, Mineral Park, and Ray 

deposits all contain distinctive inclusions identical to 

those in the underlying orebody. Samples of caprock 

from Bagdad and Mineral Park contain few halitebearing inclusions, just as do ore veins in those deposits 

(Nash and Cunningham, 1974), but the samples from 

Copper Canyon and Ely contain abundant halite-

, bearing and gas-rich inclusions indicating the former 
FLUID-INCLUSION PETROLOGY D15 

presence of hot, highly saline, boiling fluids. Silicified 

capping above the Ray deposit contains only moderatesalinity, moderate-temperature (about 300°C) inclusions 

like those in ore veins. Leached, oxidized capping derived from the "older porphyry" in the Lavender pit 

contains abundant halite-bearing inclusions but no gasrich inclusions. Caprock above the La Caridad deposit, 

Mexico, contains prominent halite-bearing inclusions 

indicative of potent hot solutions (T. G. Theodore, oral 

commun., 1974). 

LATERITE AND SOIL 

Fluid inclusions in quartz survive even severe weathering in the tropics as shown by studies of deposits in 

Puerto Rico (Cox and others, 1975). Hence, inclusions 

can be examined in quartz in residual soils or laterite to 

determine the presence of hydrothermal alteration. For 

these studies soil samples are washed and coarsely sieved 

to remove clays, and the residual grains cast in epoxy 

prior to making thin sections. By study of the residual 

quartz grains it is possible to distinguish quartz phenocrysts from hydrothermal and supergene quartz on the 

basis of fluid inclusion types and abundance. Hydrothermal activity is clearly indicated by appropriate 

fluid inclusions, even in samples in which weathering 

destroys all textural and mineralogical evidence of hydrothermal alteration. 

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