Setting of a Magmatic Sulfide 

Occurrence in a Dismembered Ophiolite, 

Southwestern Oregon

U.S. GEOLOGICAL SURVEY BULLETIN 1626-A

Chapter A

Setting of a Magmatic Sulfide 

Occurrence in a Dismembered Ophiolite, 

Southwestern Oregon

By MICHAEL P. FOOSE

A reporting of an unusual occurrence of 

magmatic sulfides in part of an ophiolite

U.S. GEOLOGICAL SURVEY BULLETIN 1626 

CONTRIBUTIONS TO THE GEOLOGY OF MINERAL DEPOSITS
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE: 1986

For sale by the Distribution Branch, U.S. Geological Survey, 

604 South Pickett Street, Alexandria, VA22304-4658

Library of Congress Cataloging-in-Publication Data

Foose, M. P.

Setting of a magmatic sulfide occurrence in a dismembered 

ophiolite, southwestern Oregon.

(Contributions to the geology of mineral deposits) (U.S.

Geological Survey bulletin ; 1626-A)

Bibliography: p. 21

Supt. of Docs, no.: I 19.3L1626-A)

1. Sulphides. 2. Rocks. Igneous Oregon.

3. Ophiolites Oregon. 4. Pyroxenite Oregon. 

I. Title. II. Series. III. Series: U.S. Geological Survey bulletin ; 1626-A.

QE75.B9 no. 1626-A 557.3 s [553.6'68] 85-600137 

[QE389.2]
CONTENTS

Abstract Al 

Introduction Al 

Regional geology Al 

Previous work A3 

Sulfide occurrence A3 

Lithology A4

Pyroxene cumulates A4

Metagabbroic sequence A6 

Mineral and rock analyses A8 

Geothermometry and metamorphism A15 

Summary and discussion A16 

References cited A21

FIGURES

1. Index map and generalized geologic setting of the Illinois River sulfide occurrence A2

2. Geology of the Illinois River sulfide occurrence A4

3. Photomicrographs of sulfides in pyroxenite A7

4. Plot of pyroxene compositions in the Ca-Mg-Fe ternary All

5. Chondrite-normalized plot of PGM and Au contents after recalculation to 100 

percent sulfides A20

6. Composition of sulfides from cumulus pyroxenite plotted on the Fe-Ni-S diagram A21

TABLES

1. Modal compositions of rock units A6 

2 11. Electron microprobe analyses of:

2. Clinopyroxene A9

3. Orthopyroxene A10

4. Olivine A12

5. Plagioclase A13

6. Amphibole A14

7. Cordierite A15

8. Pentlandite A15

9. Pyrrhotite A16

10. Chalcopyrite A17

11. Pyrite A18 

12-13. Compositions of five sulfide-bearing samples:

12. Whole-rock analyses A19

13. Analyses recalculated to 100 percent sulfide A19

14. Metal-metal and metal-sulfur ratios from recalculated 100 percent sulfide compositions A20

Contents iii

Setting of a Magmatic Sulfide Occurrence in a 

Dismembered Ophiolite, Southwestern Oregon

By Michael P. Foose

Abstract

Cumulus pyroxenites are in fault contact with a sequence 

of predominantly metagabbroic rocks in southwestern Oregon. 

The cumulates are a relatively undeformed and unmetamorphosed series of rocks that are part of a dismembered ophiolite, 

and they host small amounts of sulfide minerals that are predominantly pyrrhotite and lesser amounts of chalcopyrite and 

pentlandite. Inclusions of sulfide globules in cumulus silicate 

grains show that an immiscible sulfide liquid was present while 

cumulus grains were precipitating. This sulfide liquid is estimated to have a Ni/Cu ratio of 0.2 and a chondrite normalized 

precious-metal pattern that is characteristic of sulfide deposits 

formed from gabbroic melts. The immiscible sulfide liquid 

formed a solid solution of (Fe, Ni^-xS (Mss) and Fe-Cu-S (Iss); 

pentlandites crystallized from the Mss contain about 6 weight 

percent cobalt. In contrast, the metagabbroic rocks form a 

highly deformed, granulite-grade metamorphic complex and 

host a distinctly different sulfide assemblage composed of 

stringers of pyrite and lesser amounts of chalcopyrite.

Both types of su If ides have locally been mobilized along 

the faults that separate the two rock types. Mobilized 

pyrrhotite-rich sulfides from the pyroxenite form stringers in the 

fault and have been injected into metagabbro. In addition, 

these mobilized sulfides show lower contents of Ni, Co, Cu, 

and precious metals than do the sulfides that appear not to 

have moved, and they also contain pentlandite, which has 

between 16 to 28 weight percent Co.

Sulfides precipitated from crystallizing mafic and ultramafic magmas are not commonly reported in ophiolites, so 

these sulfides are a rare occurrence. Other concentrations of 

similar sulfides are present in this ophiolite, and thus there is a 

slight chance that larger and more economically attractive sulfide concentrations may be present. This occurrence is also of 

interest as it may represent the type of primary metal concentration which elsewhere in the world has been mobilized during shearing and serpentinization to form the Co-Ni-Cu vein 

deposits found in many altered ophiolites.

INTRODUCTION

A thrust slice of ultramafic and mafic igneous rocks, 

20 km long by 6 km wide, is located near the Illinois River 

in southwestern Oregon (fig. 1). It is composed principally 

of harzburgite-dunite tectonite, cumulus pyroxenite, and 

sheared and metamorphosed gabbro. The ultramafic part of 

this complex is similar in petrology, structural fabric, and

regional setting to several adjacent ultramafic bodies that 

have been identified as parts of Mesozoic ophiolites (Harper, 

1980; Loney and Himmelberg, 1976, 1977; Himmelberg and 

Loney, 1973; Irwin, 1977). Although lacking the complete 

ophiolite sequence, probably these ultramafic rocks also represent part of a Mesozoic ophiolite complex and are a fragment 

of oceanic crust emplaced during the Nevadan orogeny (Coleman, 1972; Page, Gray, and others, 1981).

The cumulus pyroxenites and wehrlite in this thrust slice 

are similar to the cumulus sequences described from many 

other ophiolites (for example, Coleman, 1977; George, 1978; 

Jackson and others, 1975; Harper, 1979, 1980; Laurent, 1977; 

Morgan, 1977; Evarts, 1977; Hopson and Frano, 1977). They 

are therefore considered to represent rocks that accumulated on 

tectonized harzburgite and dunite, which may be either the 

depleted residuum left after partial melting (Dick, 1977; Coleman, 1977) or an earlier sequence of cumulates that were 

deformed during syncrystallization and subsolidus deformation 

(Thayer, 1980). The local occurrence of magmatic sulfides 

within cumulus pyroxenites in this thrust, however, represents 

an additional feature that either is not commonly found in other 

ophiolites or has not been reported.

This study concerns one small occurrence of coppernickel-cobalt-bearing sulfides. Other similar occurrences of 

sulfides are found elsewhere within this thrust slice (Page, 

Gray, and others, 1981) and appear to be a common feature 

of this fragment of oceanic crust.

REGIONAL GEOLOGY

The mafic and ultramafic rocks associated with the 

Illinois River sulfide occurrence lie near the western 

boundary of the Klamath Mountains (fig. 1). Rocks immediately to the east of this boundary are part of the western 

Jurassic belt, the westernmost, structurally lowest, and 

youngest of four major thrust slices that make up the Klamath Mountains in this part of Oregon (Irwin, 1964, 1966). 

This package of rocks has been thrust westward over the 

younger coastal belt, which contains the Coast Range ophiolites and related eugeoclinal assemblages of the Dothan 

Formation and the correlative Franciscan assemblage 

(Bailey and others, 1970; Irwin, 1977). Although entirely

Magmatic Sulfide Occurrence in Dismembered Ophiolite, Oregon A1
124 15' 123 45'

42 30'

0 5 MILES

I .'. .'i \ ,'. I

0 8 KILOMETERS

EXPLANATION

Tertiary Umpqua Formation

Cretaceous and Jurassic 

Myrtle Group

Cretaceous and Jurassic 

Dothan Formation

Jurassic Colebrook Schist

Jurassic volcanic rocks

Josephine Ophiolite of 

Harper (1980)

Jurassic cumulus pyroxenites 

that host sulfides

Jurassic peridotite associated 

with sulfide-bearing cumulates

Jurassic ophiolite of 

Pearsol Peak

Jurassic (?) to Paleozoic (?) 

metagabbro and Chetco River 

Complex of Hotz (1971)

/ '"Steep fault

Figure 1. Index map and generalized geologic setting of the Illinois River sulfide occurrence. Geology modified from Coleman 

(1972), Ramp and others (1977), Garcia (1979), and Page, Gray, and others (1981). SC, Snow Camp Mountain; CB, Collier Butte; 

SM, Saddle Mountain; and GL, Game Lake.

A2 Contributions to the Geology of Mineral Deposits
surrounded by coastal-belt rocks, the thrust slice containing 

the Illinois River sulfide occurrence is made up of rocks that 

have both lithologic characteristics and isotopic ages similar 

to those found in parts of the adjacent western Jurassic belt. 

For these reasons, Irwin (1977) interpreted this thrust slice 

to be an outlier of the older Klamath Mountains.

Thrusts and steeply dipping faults divide the region 

around the sulfide occurrence into several structurally and 

lithologically distinct areas (fig. 1). The structurally lowest 

unit is the Dothan Formation, which is a flysch sequence 

composed predominantly of graywackes and mudstones 

(Diller, 1907; Ramp, 1969, 1975; Coleman, 1972; Page, 

Gray, and others, 1981) and which is overridden by four 

slices of mafic and ultramafic rocks and by several sheets of 

predominantly volcanic and sedimentary rocks. To the west 

are the peridotites, pyroxenites, and metagabbroic rocks 

with which the sulfides are associated. These, in turn, have 

been covered by thrust slices of Upper Jurassic deep-ocean 

sediments, the Colebrooke Schist, and conglomerates and 

rhythmically layered sandstones and mudstones of the 

Myrtle Group (Coleman, 1972); parts are also overlain by 

the Tertiary conglomerate deposits of the Umpqua Formation. To the east, the Dothan is overridden by the predominantly gabbroic rocks that make up the Chetco River complex of Hotz, 1971 (see also Ramp, 1975; Page, Gray, and 

others, 1981). The Chetco River complex is in turn covered 

by the steeply dipping harzburgites and dunites that have 

become known informally as the ophiolite of Pearsol Peak 

(Page, Gray, and others, 1981). Both the Chetco River 

complex and the ophiolite of Pearsol Peak are bounded on 

the east by steep faults, across which is a melange of volcanic rocks that probably correlate with Jurassic volcanicarc deposits of the Galice and Rogue Formations (Garcia, 

1979; Page, Gray, and others, 1981). Finally, the Chetco 

River complex, ophiolite of Pearsol Peak, and the volcanic 

rocks are overridden along the Madstone Cabin thrust by the 

Josephine Peridotite, which is part of the Josephine ophiolite of Harper (1980) and which is at least 157 m.y. old 

(Harper and Saleeby, 1980).

Ultramafic rocks in the area were emplaced along the 

western edge of the Jurassic continental margin during the 

Nevadan orogeny (Burchfiel and Davis, 1975). Westdirected thrusting moved these sheets over the Chetco River 

complex, which includes rocks that may be part of a Late 

Jurassic subvolcanic island-arc complex (Nicholson, 1981) 

and volcanic rocks that are interpreted to be upper level 

volcanic-arc deposits (Garcia, 1979). Because the peridotites are also cut by numerous Late Jurassic intrusive 

bodies, it is possible that they either formed near an active 

arc complex (Harper, 1980) or were thrust onto an active arc 

system (Dick, 1977). Thrusting continued into the Cretaceous (Irwin, 1964) and later moved these rocks over the 

younger coastal-belt sequences. Much of the region was 

affected by normal faults formed during later Tertiary uplifts.

PREVIOUS WORK

Several studies have described the geology and mineral resources of the area near the Illinois River sulfide 

occurrence (Wells and others, 1949; Coleman, 1972; Ramp, 

1975; Ramp and others, 1977; Page, Moring, and others, 

1981; Page, Gray, and others, 1981). K-Ar ages from associated dioritic or gabbroic rocks near Saddle Mountain 

(Dott, 1965) indicate that peridotites near the sulfides probably formed about 285 m.y. ago. Diorites that crosscut 

peridotites near Game Lake and Collier Butte yield K-Ar 

ages of 139-145 m.y. (Dott, 1965; Coleman, 1972). 

Medaris (1972) and Henry and Medaris (1980) used pyroxene and pyroxene-spinel geothermometers to show that peridotites near Snow Camp Mountain have undergone recrystallization in the range of 1,200° to 900°C.

The diverse gabbroic rocks associated with the Illinois 

River sulfide occurrence and the adjacent and presumably 

related Chetco River complex include sheared and metamorphosed gneisses, rocks with well-developed cumulus textures, and hornblende-rich crosscutting intrusions (Hotz, 

1971; Coleman, 1972; Ramp and others, 1977; Nicholson, 

1981). K-Ar ages range from 285 to 215 m.y. (Hotz, 1971; 

Floyd Gray, oral commun., 1981) to between 140 and 151 

m.y. (Hotz, 1971; Coleman, 1972; R.W. Tabor, in Himmelberg and Loney, 1973; Page, oral commun., 1981) and 

indicate a complex history of deformation and magmatism. 

Cumulus pyroxenites that have magmatic sulfides similar to 

those studies in this report occur as inclusions within 

younger gabbroic intrusions in part of the Chetco River 

complex (Loney and Himmelberg, 1977; Gray, 1980, and 

oral commun., 1980; Page, Gray, and others, 1981).

The sulfide occurrence studied here was previously 

identified as the "Cobalt Group" by Parks and Swartley 

(1916). Ramp (1964) reported that ore samples contained 

0.2 weight percent Cu and traces of Ni, Au, and Co.

SULFIDE OCCURRENCE

Pods and stringers of sulfide are exposed in the cliffs 

along the Illinois River in an area where late, steeply dipping faults have juxtaposed medium-grained, massive, and 

relatively undeformed pyroxene cumulates against a sequence of deformed and mineralogically and texturally diverse rocks that are predominantly gabbroic (fig. 2).

Both rock types contain distinctive sulfide assemblages. Most abundant are pyrrhotite-rich massive pods or 

disseminated sulfides that occur primarily in the pyroxene 

cumulates. The largest of the massive pods measures approximately 10 m by 5 m and has been explored to a tunneled depth of 15 m. Locally, these sulfides have been 

remobilized during faulting and are now stringers in the fault 

that separates the pyroxenite from metagabbroic rocks (fig. 

2). Where injected along this fault, the sulfides are found 

within both rock types.

Magmatic Sulfide Occurrence in Dismembered Ophiolite, Oregon A3
>-?

li;^?^

,i

. . .-.-.-.-. . . . .M ,» , ,»

\ ' ' » 

* ' »

V^V^

EPKfcSQy//;' 

! 256-2"

EXPLANATION

Pyroxene cumulate

Metagabbroic sequence

Massive sulfide

 245-1 Sample site

^s' Fault

^S* Contact

j-85 Strike and dip of layering

85

\fl Strike, dip, bearing, and

rgr - * 

?H::252: 1I

IX-X-I-r-XvX^iJi'oCO *3 fc::::::::::;:v:*!?^ 253-3

K;i!g;;253-1

90 plunge of minor fold

Dissemination and 

stringers of sulfide

200 400 600 800 1000 FEET

100 200

0 1 

KILOMETER

Horse Sign 

Butte

300 METERS

Silver x 

Peak

Hurt 

cabin S 

<r"

ENLARGED 

.AREA

Colliers 

^Bar

}

'. .Josephine Co..

Curry'co"" " " "

Figure 2. Geology of the Illinois River sulfide occurrence. Sample locations shown by dots.

The second class of sulfides are rare pyrite-rich 

stringers that occur only in the metagabbroic rocks. These 

are thin (less than 0.3 m) and discontinuous (less than 3 m 

in length) layers that conform to the layering of the surrounding rocks. Their sporadic distribution apparently was 

not controlled either by proximity to pyroxenite or by the 

presence of faults and shears.

LITHOLOGY

Pyroxene Cumulates

The pyroxene cumulates are massive, unlayered, and 

medium grained. Except where gossans are present, 

exposures are dark gray to black. Blocky clinopyroxene 

is the most abundant and in the field is usually the only

A4 Contributions to the Geology of Mineral Deposits
recognizable mineral; good cumulus textures are observed 

where small amounts of interstitial plagioclase or disseminated sulfides are present. The pyroxenites do not have a 

recognizable igneous lamination or a secondary foliation. 

Representative modes are given in table 1.

In rocks that are almost monomineralic, clinopyroxene forms 3-6-mm grains that have a xenomorphic granular 

texture. Most grains have a subhedral core, 1 to 2 mm wide, 

that contains orthopyroxene exsolution and is surrounded by 

an anhedral, exsolution-free rim. In rocks less rich in 

clinopyroxene, grains are more typically subhedral, 1 to 

3 mm in size, and contain uniformly distributed orthopyroxene inclusions. In many places, clinopyroxenes have growth 

twins; although some show slight undulatory extinction, 

kink bands and deformation lamellae are uncommon.

Olivine, orthopyroxene, and plagioclase are relatively 

rare and are the only other primary silicates. Olivine occurs 

both as a cumulus phase and as adcumulus interstitial 

masses. Cumulus euhedral olivine, 0.5 to 1 mm in size, is 

enclosed in plagioclase and orthopyroxene. Rarely, euhedral olivine is found within large euhedral clinopyroxene. 

Interstitial olivine occurs as anhedral masses and as stringers 

connected to euhedral olivine grains. Orthopyroxene occurs 

principally as anhedral reaction rims around euhedral 

olivine, but, in some samples, orthopyroxene (1-3 mm) has 

a euhedral form and may be enclosed by interstitial plagioclase or clinopyroxene. Plagioclase is always an interstitial 

phase between euhedral cumulus pyroxenes or olivine. 

Minor sericitic alteration is present in most places.

Serpentine and hornblende are alteration phases. 

Hornblende occurs mostly as isolated patches that have replaced clinopyroxene Serpentine replaces olivine and pyroxene and forms bastite and mesh-textured masses, which 

X-ray examination shows to be lizardite. Serpentine is most 

pervasive where sulfides are abundant.

Disseminated to massive sulfide occurs within the 

pyroxenite. Most sulfides are disseminated cuspate masses 

found along the grain boundaries of euhedral pyroxene and 

olivine. Where more abundant, these sulfides have net textures that enclose euhedral silicate grains. Where massive, 

sulfides typically include isolated grains of euhedral 

clinopyroxene or olivine (fig. 3A). Less common are sulfide 

blebs which have a maximum diameter of 1 mm and which 

have been found in clinopyroxene and orthopyroxene, but 

not in olivine (fig. 3B, C).

Primary sulfide mineralogy is simple and uniform. 

Most sulfides (60 80 percent) are pyrrhotite, which X-ray 

diffraction, treatment with a magnetic colloid solution, and 

electron microprobe analysis show to be almost entirely 

hexagonal with very minor intergrowths of the monoclinic 

phase. Pyrrhotite occurs as small (<0.5 mm) blebs enclosed 

in silicates, as anhedral grains molded around silicates, or as 

masses that enclose euhedral silicates. Isolated grains commonly also contain cnalcopyrite and pentlandite. Large

masses of pyrrhotite, however, generally do not have other 

sulfide phases. Chalcopyrite makes up most of the remaining (15 30 percent) sulfides, either as blocky or lamellaeshaped exsolutions in pyrrhotite blebs or as stringers and 

anhedral masses within massive pyrrhotite. It is rarely found 

as isolated grains. Cubanite is present in trace amounts as 

exsolution lamellae in chalcopyrite. Pentlandite (less than 5 

percent of the sulfide) always occurs in pyrrhotite. It is most 

abundant in small pyrrhotite blebs where it typically forms 

small (<0.3 mm) blocky grains near pyrrhotite-silicate 

boundaries. In massive pyrrhotite, pentlandite may form 

thin stringers or small disseminated grains that are entirely 

within pyrrhotite.

In pyroxenites, pyrite is found only in massive sulfide 

(samples 253-3 and 250-3) where it forms isolated 1-3- 

mm subhedral grains, birds-eye alterations on pyrrhotite, 

and less common stringers and lamellae enclosed in 

pyrrhotite.

Secondary magnetite and hematite are found in trace 

amounts in disseminated sulfides and are abundant in massive sulfides.

Silicate textures clearly show the rocks to be clinopyroxene, clinopyroxene-olivine, clinopyroxene-orthopyroxene, and clinopyroxene-orthopyroxene-olivine cumulates. 

Nearly monomineralic clinopyroxenites are good adcumulates. They show anhedral rims around subhedral clinopyroxene cores that contain abundant orthopyroxene exsolution lamellae. Most other rocks are mesocumulates showing 

both adcumulus growth and crystallization of trapped interstitial liquid. Although the layered sequence of diverse rock 

types needed to establish a crystallization trend is not 

present, cumulus parts of ophiolites typically start with the 

precipitation of olivine followed by olivine+clinopyroxene 

(Coleman, 1977). Plagioclase crystallization usually follows crystallization of olivine+clinopyroxene, although, in 

some places, minor amounts of orthopyroxene appear before plagioclase (Himmelberg and Loney, 1980). In these 

rocks, the inclusion of some euhedral olivine in cumulate 

clinopyroxenes suggests that olivine was locally the first 

phase to crystallize and that it was followed by clinopyroxene and minor amounts of orthopyroxene.

The mineralogy and textures of the sulfides in the 

pyroxenite are characteristic of magmatic sulfide deposits. 

The primary mineralogy of magmatic sulfides is usually 

very simple and consists dominantly of pyrrhotite with minor chalcopyrite and pentlandite. In this occurrence, these 

three phases are present in sulfide blebs that are enclosed 

within cumulus silicate grains; the textural relationship 

shows that an immiscible sulfide liquid existed while cumulus silicate minerals were crystallizing. This intergrowth of 

pyrrhotite, chalcopyrite, and pentlandite constitutes the expected exsolution product formed upon crystallization from 

typical magmatic Cu-Ni-Fe-S liquids (Kullerud and others, 

1969; Craig and Scott, 1974). Additional textural evidence

Magmatic Sulfide Occurrence in Dismembered Ophiolite, Oregon A5
Table 1. Modal compositions of rock units

[Sample locations given on figure 2; modes based on a minimum of 1,000 points per thin section]

Pyroxene cumulate Metagabbroic sequence

Sample number--- -

ClinopyroxeneOrthopyroxene ---

Hornblende -----

Biotite ---------

Chlorite --------

Sulfides --------

250-2

56.14 

24.07 

1.62

6.62 

6.65

4.90 

tr

250-3

40.30

1.61

39.14

18.95 

tr

251-3 253-3

61.70 19.53

20 95

3 02 -----

----- 46.99

9 57

4.76 21.56 

tr 11.92

245-1

15.81 

36.58 

5.77

25.77

6.09

3.00 

6.98

246-1

16.95 

39.74 

8.66

33.12

-----

1.53 

tr

251-4

4.30 

28.71

.59

38.62

3.03

24.75 

tr

252-1

21.49

56.31 

14.20

6.68 

1.32

253-1

-----

48.59 

29.34

17.05 

5.02 

tr

253-2

39.33 

30.83

7.32

4.64

14.36

3.52

of magmatic sulfide accumulation consists of the euhedral 

silicates disseminated within massive sulfide and the interconnected, cuspate sulfides in net-textured sulfides (Naldrett, 1973, 1979).

Metagabbroic Sequence

Metamorphosed and deformed rocks of predominantly gabbroic compositions are in fault contact with the 

pyroxenites and are referred to here as the metagabbroic 

sequence. Most are fine- to medium-grained dark-gray 

rocks that range from rare epidote-chlorite-quartz gneiss to 

more common interlayered sequences of clinopyroxeneorthopyroxene-plagioclase-hornblende ± quartz, cordieriteplagioclase-orthopyroxene±quartz, and quartz-plagioclasehornblende gneisses. The rocks are commonly finely 

layered to massive and are well foliated. The foliation parallels axial surfaces of tight to isoclinal minor folds and crosscuts compositional layering in fold noses. Rare concordant 

sulfide stringers are present within some gneisses and are 

also folded and cut by axial planar foliations.

With the exception of hornblende, most minerals are 

smaller than 1 mm and form anhedral masses that have 

strong undulatory extinctions. Textures are mostly blastomylonitic, although locally porphyroclasts of clinopyroxenes and pyrite occur. Mineral phases are described briefly 

below, and modes of metagabbroic rocks are given in 

table 1.

Blue-green and green-brown amphiboles occur as alteration around clinopyroxene and orthopyroxene and as 

subhedral laths as long as 3 mm. Laths lie in and, in many 

places, conspicuously define the foliation. Many large hornblendes are spongelike masses that enclose all other mineral

phases in the rock. Modal variation in hornblende forms the 

most recognizable compositional layering.

Small anhedral grains of both clinopyroxene (1.0 

mm) and orthopyroxene (0.5 mm) occur as untwinned, anhedral grains that show slight undulatory extinction and are 

aligned in the foliation. In blastomylonitic rocks (sample 

246 1), some clinopyroxene also makes twinned (3 mm) 

porphyroblasts. In contrast, orthopyroxene may occur as 

large (2 to 3 mm) unstrained spongelike masses that enclose 

all other minerals except hornblende.

Anhedral quartz that has strong undulatory extinction, 

cordierite that appears similar to quartz, and slightly sericitized anhedral and twinned plagioclase commonly occur as 

grains as large as 1 mm. Larger grains of quartz (to 3 mm) 

are formed in the epidote-chlorite-quartz gneiss (sample 

253 1) and are rimmed by masses of chlorite.

Minor secondary anhedral epidote (<1 mm), occurring with chlorite and biotite that alter both pyroxene and 

hornblende, is locally present.

Sulfides in the metagabbroic rocks are dominantly 

pyrite and also contain lesser amounts of chalcopyrite and 

scarce pyrrhotite. Anhedral grains (<0.5 mm) and rare 

granulated subhedral cubes (to 1 mm) of pyrite typically 

constitute between 50 to 90 percent of the sulfides. Chalcopyrite constitutes between 5 to 15 percent of the sulfides 

and occurs as rims around pyrite and as small replacements 

patches in pyrite. Pyrrhotite is rare except where faults have 

placed rocks near pyrrhotite-rich pods hosted in pyroxene 

cumulates (sample 251-4). In these pods, pyrrhotite, which 

appears to have been mobilized from the adjacent cumulates, may constitute more than 80 percent of the sulfide. 

More typically, pyrrhotite makes up less than 5 percent of 

the sulfides and occurs as small (<0.3 mm) grains and 

embaying alterations on pyrite. Locally, small pyrite cubes

A6 Contributions to the Geology of Mineral Deposits
Figure 3. Photomicrographs of sulfides in pyroxenite. A, Reflected light showing subhedral clinopyroxenes enclosed in massive 

sulfide. Note small sulfide bleb included in lower-right clinopyroxene. B, Cumulus orthopyroxene enclosing two sulfide blebs 

and enclosed by lighter gray intercumulus plagioclase in transmitted light. C, Upper sulfide bleb from B shown in reflected light. 

Po-pyrrhotite, Cp-chalcopyrite, Pt-pentlandite. Approximate long dimensions of photographs are 4 mm for A and B, 2 mm for 

C.

Magmatic Sulfide Occurrence in Dismembered Ophiolite, Oregon A7
have been completely replaced by pyrrhotite. Pentlandite 

has not been found in the metagabbroic units.

Patchy secondary magnetite and hematite are associated mostly with sulfides. However, compositional layering 

in some rocks (sample 245-1) is partly outlined by disseminated layers of subhedral magnetite grains that are smaller 

than 0.5 mm.

Megascopic and microscopic examinations show that 

the metagabbroic rocks have been highly deformed and 

metamorphosed. The tight to isoclinal folds and the penetrative mineral foliation are the result of at least one intense 

deformation. Also, the occurrence of orthopyroxene as both 

small strained grains and as large, unstrained and poikillitically enclosing masses indicates that granulite-grade metamorphism took place both during and after deformation 

(Winkler, 1967). Other evidence for granulite-grade metamorphism is from pyroxene geothermometry (discussed below) that indicates metamorphic temperatures of approximately 900°C. The pressure of metamorphism is less well 

defined. The presence of cordierite without garnet has traditionally been interpreted as a low-pressure assemblage that 

would place these rocks in the low-pressure subfacies of the 

granulite facies as defined by Miyashiro (1973). However, 

the reaction that produces garnet from cordierite as pressure 

increases also is dependent on Mg/(Mg+Fe). Studies by 

Henson and Green (1972) of systems without excess aluminum show that cordierite compositions with Mg/ 

(Mg+Fe)=0.9 (similar to those in this unit), which are in 

the assemblage cordierite-hypersthene-quartz, may be stable to a maximum of 8-9 kilobars. Metamorphism may 

therefore have taken place at depths as great as 30 km.

The metagabbroic sequence can be directly correlated 

with rocks of similar composition that make up the Big 

Craggies to the south. These rocks have also been deformed 

by at least one penetrative deformation and metamorphosed 

to granulite grade (Coleman, 1972; Ramp, 1975). Furthermore, these rocks are also similar to sheared gabbroic rocks 

which make up parts of the adjacent Chetco River complex 

and which have been interpreted as part of an island-arc 

complex (Nicholson, 1981). Regardless of environment of 

formation, the deformation, metamorphism, and type of 

mineralization shown by this unit are in sharp contrast to the 

pyrrhotite-rich mineralization found in the adjacent pyroxenite, and they lead to the conclusion that relatively recent 

and steeply dipping faults have juxtaposed part of a highly 

deformed and metamorphosed gabbroic complex with minor 

stringers of pyrite-chalcopyrite mineralization against a 

fragment of oceanic crust containing magmatic pyrrhotitechalcopyrite-pentlandite mineralization.

MINERAL AND ROCK ANALYSES

Mineral compositions were determined for all primary 

phases and for some secondary hornblendes in the pyroxenite. Compositions were obtained by means of an ARLEMX SM microprobe in which combined wave-length and 

energy-dispersive systems were used. Operating conditions 

were 15 kV and 0.1 microamp beam current. In analyses of 

silicates, natural and synthetic standards and matrix corrections were used, and the procedures of Bence and Albee 

(1968) and Albee and Ray (1970) were followed. In analyses of sulfides, synthetic standards and data were reduced by 

means of the ZAF computer program provided by Tracor 

Northern. 1 Analytical results and structural formulas are 

given in tables 2-8. All compositions are averages from at 

least three grains, on which at least two spots were analyzed.

Pyroxenes (table 2, 3; fig. 4) from the pyroxenite are 

richer in Mg and are more uniform in composition than 

those from the metagabbroic sequence. As previously described, some grains have exsolution-rich cores and 

exsolution-free rims. Analyses made between visible exsolution lamellae in grain centers are similar to analyses obtained on exsolution-free grain rims. No compositional differences were found between cumulate and intercumulate 

grains in the pyroxenite or between pre- and postdeformation grains in the metagabbroic rocks. Pyroxenes 

from the pyroxenite have uniform and low A12O3 (<2 

weight percent); orthopyroxenes from the metagabbro have 

somewhat higher A12O3 and MnO contents than those from 

the pyroxenite.

Olivines (table 4) are Fo79_87 . Nickel contents are less 

than 0.07 percent, which is lower than values typically 

found in magmatic olivines of this composition (Simkin and 

Smith, 1970). However, Duke and Naldrett (1978) and 

Duke (1979) showed that similar low-nickel contents can 

result when olivine is crystallized from a melt that is already 

saturated with, and is precipitating, immiscible sulfides.

Plagioclase (table 5) is rarely found in the pyroxenite 

as intercumulus grains of composition An87 . Within the 

metagabbro, plagioclase ranges from An^ to An88 , and no 

apparent correlation exists between rock mineralogy and 

plagioclase composition.

Amphiboles (table 6) were chemically characterized 

by means of the method of Papike and others (1974). Analyses of two amphiboles occurring as brown alteration patches 

of magnesiokaersutite in pyroxenite show widely variable 

amounts of other than quadrilateral components. In contrast, 

the primary amphiboles from the metagabbroic sequence are 

more compositionally uniform magnesiokaersutites, containing 62 to 65 percent other than quadrilateral components.

Cordierite (table 7) is Mg rich (Mg/(Mg+Fe)=86 to 

91). Totals of analyses are slightly less than 100, which 

suggest that some structural water might be present.

'Any trade names in this publication are used for descriptive purposes only 

and do not constitute endorsements by the U.S. Geological Survey.

A8 Contributions to the Geology of Mineral Deposits
Table 2. Electron microprobe analyses of clinopyroxene 

[Standard deviations in parentheses]

Sample number ---- 250-2 250-3

Pyroxene 

cumulate

251-3

Metagabbroic 

sequence

253-3 245-1 246-1

Weight percent

SiQ2 ------------

A1203 -----------

MnO ------------

MgO ------------

PaO

Na.O -----------

Cr203 -----------

NiO ------------

Total -------

53.6 

(.574) 

.48 

(.091) 

5.02 

(.108) 

.16 

(.028) 

16.9 

(.409) 

23.4 

(.633)

(.000) 

.20 

(.048) 

.27 

(.051) 

.05 

(.037)

100.08

52.9 

(.346) 

1.80 

(.092) 

3.96 

(.141) 

.31 

(.155) 

16.7 

(.601) 

23.6 

(.177) 

.32 

(.169) 

.17 

(.007) 

.26 

(.021) 

.02 

(.014)

100.04

52.6 

(.159) 

1.10 

(-019) 

5.30 

(.269) 

.19 

(.164) 

16.6 

(.343) 

22.9 

(.411) 

.21 

(.030) 

.03 

(.000) 

.17 

(.083) 

.01 

(.015)

99.11

53.5 

(.076) 

1.21 

(.063) 

4.33 

(.226)

(.130) 

16.8 

(.305) 

23.7 

(.209) 

.11 

(.168) 

.08 

(.047) 

.31 

(-127) 

.05 

(.023)

100.09

52.6 

(.923) 

1.50 

(.156) 

9.22 

(.256) 

.50 

(.098) 

14.2 

(.316) 

21.2 

(.348) 

.22 

(.035) 

.14 

(.080) 

.03 

(.011) 

.02 

(.021)

99.63

52.6 

(.784) 

.50 

(.191) 

7.21 

(1-02) 

.25 

(.042) 

15.3 

(.049) 

22.5 

(.530) 

.10 

(.141) 

.27 

(.261) 

.01 

(.021) 

.02 

(.028)

98.76

Cations per 6 oxygens

Si --------------

AlIV

Sum TET ------

A1 VI

Fe+2 ------------

Mn -------------

Mg -------------

Pa

Ti --------------

Cr --------------

Ni --------------

Sum OCT ------

100 x Mg

Mg+Fe+Mn 

Fn --------------

Fs --------------

Wo -------------

1.970 

.021

1.991

.000 

.154 

.005 

.923 

.922 

.000 

.006 

.008 

.001

2.019

85.3

46.2 

7.7 

46.1

1.940 

.060

2.000

.018 

.121 

.010 

.913 

.926 

.023 

.005 

.008 

.001

2.025

87.5

46.6 

6.2

47.2

1.954 

.046

2.000

.002 

.165 

.006 

.920 

.911 

.015 

.001 

.005 

.000

2.025

84.3

46.1 

8.3

45.6

1.960 

.040

2.000

.012 

.133 

.000 

.917 

.929 

.008 

.002 

.009 

.001

2.011

87.3

46.4 

6.7 

46.9

1.967 

.033

2.000

.033 

.288 

.016 

.793 

.851 

.016 

.004 

.001 

.001

2.003

72.30

41.1 

14.9 

44.0

1.976 

.022

1.998

.227 

.008 

.855 

.905 

.007 

.008 

.000 

.001

2.011

78.4

43.0 

11.5

45.5

lrTotal Fe as FeO.

Magmatic Sulfide Occurrence in Dismembered Ophiolite, Oregon A9
Table 3. Electron microprobe analyses of orthopyroxene 

[Standard deviations in parentheses]

Pyroxene cumulate

Sample number ----

SiQ2 ------------

A1203 -----------

lpen -----

MnO ------------

MgO ------------

faO

Na2O -----------

Tir\

Cr /~i /~\ 2O3 -----------

NiO ------------

Total -------

250-2

56.3 

(.396) 

.01 

(.042) 

12.5 

(.357) 

.33 

(.059) 

29.5 

(.259) 

1.26 

(.053)

(.000) 

.04 

(.053) 

.13 

(.051) 

.06 

(.020)

100.13

251-3

Weight

55.5 

(.260) 

.49 

(.002) 

12.0 

(.299) 

.34 

(.124) 

29.5 

(.054) 

1.40 

(.573)

(.000) 

.05 

(.058) 

.06 

(.054) 

.04 

(.030)

99.38

245-1

percent

51.6 

(.858) 

1.03 

(.023) 

24.9 

(.096) 

.76 

(.152) 

19.5 

(.286) 

.82 

(.023)

(.000) 

.02 

(.075)

(.000) 

.03 

(.001)

98.66

Metagabbroic sequence

246-1

55.00 

(.088)

(.000) 

15.7 

(.530) 

.55 

(.068) 

27.0 

(.325) 

.67 

(.187) 

.08 

(.090) 

.11 

(.055) 

.02 

(.026)

(.028)

99.13

251-4

53.5 

(.431) 

2.17 

(.148) 

14.1 

(.064) 

.40 

(.035) 

28.8 

(.092) 

.18 

(.099) 

.09 

(.001) 

.03 

(.035)

(.000) 

.01 

(.049)

99.28

253-2

53.0 

(.515) 

2.91 

(.149) 

20.4 

(.212) 

.94 

(.096) 

23.9 

(.631) 

.20 

(.030)

(.000) 

.08 

(.056) 

.08 

(.040) 

.06 

(.011)

101.57

Cations per 6 oxygens

Si --.-.-.---.-..

AlIV

Sum TET ------

AJV1 ---- --

Fe+2 ------------

Mn -------------

Mg -------------

Ca

Na--------------

Ti --------------

Cr --------------

Ni --------------

Sum OCT ------

100 x Mg

Mg+Fe+Mn 

Fn --

Fs ---- --- -- -

Wo -------------

1.999 

.000

1.999

.000 

.370 

.010 

1.565 

.048 

.000 

.001 

.004 

.002

2.000

80.5

78.9 

18.7

2.4

1.984 

.016

2.000

.005 

.360 

.010 

1.570 

.054 

.000 

.001 

.002 

.001

2.003

80.9

79.1 

18.2

2.7

1.979 

.021

2.000

.026 

.798 

.025 

1.113 

.034 

.000 

.001 

.000 

.001

1.998

57.5

57.2 

41.0 

1.8

2.002 

.000

2.002

.000 

.479 

.017 

1.465 

.026 

.006 

.003 

.001 

.000

1.997

74.7

74.4 

24.3 

1.3

1.930 

.070

2.000

.022 

.427 

.012 

1.550 

.007 

.006 

.001 

.000 

.000

2.025

77.9

78.1 

21.5 

0.4

1.926 

.074

2.000

.051 

.620 

.029 

1.294 

.008 

.000 

.002 

.002 

.002

2.008

66.6

67.3 

32.3 

0.4

lrTotal Fe as FeO.

A10 Contributions to the Geology of Mineral Deposits
250-2

Mg

251-4 50 Fe

Figure 4. Plot of pyroxene compositions in the Ca-Mg-Fe ternary (atomic percent). Dots cumulus pyroxenite; crosses 

metagabbroic sequence.

Compositions of cumulus pyroxenes and olivines as 

well as intercumulus plagioclase in the pyroxenite are similar to those reported from cumulus zones in other ophiolite 

complexes (for example, Coleman, 1977; Himmelberg and 

Loney, 1980; England and Davies, 1973; Jackson and others, 1975; Juteau and Whitechurch, 1980). They are also 

similar to Gray's (1980) description of ultramafic rocks near 

Tincup Peak in the Chetco River complex, southeast of this 

study area (fig. 1). Silicates from the metagabbroic sequence are chemically more diverse. Pyroxene, plagioclase, 

and amphibole in much of this sequence have compositions 

similar to those found in sheared gabbroic rocks of the 

adjacent Chetco River complex, which has been interpreted 

as part of a volcanic-arc sequence (Nicholson, 1981).

Sulfides (compositions in tables 8-11) may be divided into those within pyroxenite and those within the 

metagabbroic rocks.

The sulfides in pyroxenite are either disseminated 

blebs (samples 250-2 and 251-3) or massive and interconnected concentrations (samples 250-3 and 253-3). The 

blebs are interpreted to be frozen immiscible droplets, and 

their compositions probably most closely approximate unaltered values. The more massive concentrations appear to be 

sulfides remobilized adjacent to faults and to have altered 

compositions. Pentlandites (table 8) from the droplets contain nearly 6 weight percent cobalt. This is significantly 

higher than the 0 to 2 weight percent cobalt found in most 

magmatic pentlandites that are associated with pyrrhotite, 

but it is within the range recorded from some sulfide deposits (Harris and Nickel, 1972). Adjusting these pentlandite compositions by adding proportional amounts of the

metals present as cobalt to iron and nickel results in compositions that have "adjusted" nickel contents, which, with the 

exception of the most cobalt-rich pentlandite (sample 250- 

3), are similar to those observed in other low-cobalt or 

"adjusted" natural pentlandites that occur with pyrrhotite 

(Misra and Fleet, 1973). In contrast, pentlandites in samples 

containing interconnected sulfides (250-3 and 253-3) have 

widely different and remarkably high cobalt contents (21 to 

36 weight percent). Pentlandites containing similar amounts 

of cobalt have been reported from a few other environments, 

among which are the copper ores hosted in quartzites at 

Outokupu, Finland (Kouvo and others, 1959; Huhma, 

1970), ores at Cobalt, Ontario, Canada (Petruk and others, 

1969), and ores in serpentinized wehrlites in Japan (Matsuhara and Kato, 1979). Although the means by which these 

pentlandites formed are not always clear, a variety of nonmagmatic processes seem to have been involved. The high 

cobalt content of the pentlandites in samples 250-3 and 

253-3 thus indicates that compositions of these sulfides 

have been altered, a conclusion compatible with the field 

relationships, which show the sulfides to have been mobilized within faults and shears.

Pyrrhotites (table 9) in these interconnected sulfides 

have cobalt and nickel contents (0.3-0.4 weight percent Co 

and 0.2-0.4 weight percent Ni) that are respectively higher 

and lower than in the disseminated sulfides (0.0-0.07 

weight percent Co; 0.41-0.53 weight percent Ni). Chalcopyrites (table 10) in both types of sulfides are similar in 

composition. Pyrite (table 11) occurs in the massive sulfides; one sample contains almost 1 weight percent Ni.

Magmatic Sulfide Occurrence in Dismembered Ophiolite, Oregon A11
Table 4. Electron microprobe analyses of olivine 

[Standard deviations in parentheses]

Pyroxene 

cumulate

Sample number --- 250-3 251-3

Weight percent

SiQ2 ----------- 40.3

(.215) 

ipeO ----------- 12.9

(.281) 

MnO ----------- .18

(0.28) 

MgO ----------- 46.3

(.953) 

CaO ----------- .13

(.056) 

NiO ----------- .03

(.029) 

Cr2O3 ---------- .05

(.075)

Total--------- 99.89

Cations per 4 oxygens

Si ------------- 1.002

Fe ------------- .269

Mn ------------ .004

Mg ------------ 1.717

Ca ------------- .003

Ni ------------- .001

Cr ------------- .001

40.3 

(.336) 

18.6 

(-245)

.21

(.108) 

41.2 

(.669)

.16 

(.045)

.07 

(.041)

.00 

(.000)

100.54

1.021

.394

.005

1.553

.004

.001

.000

Sum cations 2.997 2.978

100 x Mg

Mg+Fe+Mn S.3 79.6

'Total Fe as FeO.

Sulfides within the metagabbro are mostly stringers 

and disseminations of compositionally similar pyrites and 

chalcopyrite. Near faults, pyrite is locally replaced by minor 

amounts of pyrrhotite that has nickel (0.13 percent) and 

cobalt (0.06 percent) contents similar to amounts found in 

the host pyrite. In faults, the metagabbro locally also has 

massive pods of pyrrhotite (sample 251-4) that is similar in 

composition to the pyrrhotite in the adjacent pyroxenite (0.3 

percent nickel; 0.1 percent cobalt).

Five whole-rock analyses of samples, which were 

either from disseminated sulfides in pyroxenite or from interconnected sulfides in faults or shears in pyroxenite or in 

the metagabbroic sequence, were obtained for Ni, Cu, Co, 

S, Pt, Pd, Rh, and Au. Metal values are given in table 12, 

and the analyses recalculated to 100 percent sulfides are

shown in table 13. Recalculation to 100 percent sulfide is 

necessary to minimize effects of differing proportions of 

sulfides to silicates and allows comparison of the sulfide 

composition from a wide variety of deposits. Mineral compositions (tables 8-11) were used in calculations for table 

13. Norms calculated from table 13 approximate observed 

abundances. In addition, the recalculated noble-metal data 

have been normalized with respect to average chondritic 

meteorites (fig. 5) in the manner presented by Naldrett and 

others (1979).

The highest nickel, copper, and noble-metal concentrations in 100 percent sulfides are in samples containing 

disseminated sulfides (250-2, 251-3) that probably most 

closely approximate magmatic sulfide liquid compositions. 

In comparison, interconnected sulfides in pyroxenite (250- 

3, 253-3) and in metagabbro (251-4) show much lower 

amounts of Cu, Ni, platinum group metals (PGM's), and 

Au, and slightly higher concentrations of Fe and S. These 

concentrations suggest three possibilities: iron and sulfur 

have been added, the other elements have been depleted 

during fault-related mobilization, or an initially irregular 

distribution of metals existed. The second possibility is considered unlikely because such large primary changes in 

metal content over such short distances are unlikely and also 

because the interconnected sulfides hosted in pyroxenite 

(250-3 and 253-3) are geochemically similar to those occurring along faults that are entirely within metagabbroic 

rocks (251-4). Furthermore, the variations in metal-metal 

and metal-sulfur ratios between disseminated and interconnected sulfides (table 14) are consistent with differential loss 

of metals due to differing geochemical behavior of elements 

during mobilization; this suggests that the interconnected 

sulfides did not form by dilution resulting from the addition 

of Fe and S. The nearly constant Fe/S, but slight decrease 

in (Fe+Ni+Cu+Co)/S, suggests that formation of interconnected sulfides involved removal of Cu, Ni, and Co; the 

relatively small decrease in Ni/Cu and larger decrease in 

Ni/Co shows Ni to be slightly more depleted than Cu and 

much more depleted than Co in the interconnected sulfides. 

This relative enrichment of Co relative to Ni and Cu is 

consistent with the extremely cobalt-rich pentlandites observed in the interconnected sulfides. Relative concentrations of precious metals appear unchanged between the interconnected and disseminated sulfides.

The compositions of 100 percent sulfides in pyroxenite have been plotted on the Fe-Ni-S ternary diagram (fig. 

6). In this diagram, the sulfide compositions were corrected 

by removing the metals and sulfur present in chalcopyrite 

and by adding proportional amounts of cobalt present to iron 

and nickel. With the exception of sample 253-3, all samples 

fall in the monosulfide solid-solution ((Fe,Ni)!_xS or Mss) 

field at 500°C (Naldrett and others, 1967); this indicates that 

exsolution occurred below this temperature to yield the observed sulfide phases. Samples 250-2 and 251-3, which

A12 Contributions to the Geology of Mineral Deposits
Table 5. Electron microprobe analyses of plagioclase 

[Standard deviations in parentheses]

Sample number ----

Pyroxene 

cumulate

250-2

Metagabbroic sequence

245-1 246-1 251-4 252-1 253-2

Weight percent

SiO2 ------------

A1203 -----------

IpeO

r^n

Na2O -----------

v r\

Total --------

47.0 

(.876) 

34.0 

(.532) 

.02 

(.074) 

17.7 

(.325) 

1.22 

(.224) 

.28 

(-014)

100.22

52.8 

(.956) 

30.9 

(.870) 

.24 

(.092) 

12.8 

(.436) 

4.20 

(.199) 

.00 

(.000)

100.94

46.7 

(.452) 

35.4 

(.337) 

.55 

(-126) 

17.7 

(.233) 

1.12 

(.556) 

.30 

(.263)

101.77

47.3 

(.812) 

34.5 

(.054) 

.24 

(.078) 

16.9 

(.389) 

1.39 

(.355) 

.25 

(.052)

100.58

56.4 

(.015) 

27.7 

(.753) 

.08 

(.001) 

9.6 

(.005) 

6.03 

(.152) 

.13 

(.151)

99.94

55.6 

(.505) 

28.4 

(.492) 

.25 

(.161) 

10.3 

(.304) 

5.88 

(.148) 

.17 

(.061)

100.60

Cations per 32 oxygens

Si ..............

Al

p~

fa

Ma

8.625 

7.352 

.003 

3.469 

.433 

.065

9.474 

6.548 

.036 

2.464 

1.462 

.000

8.460

7.554 

.083 

3.434 

.394 

.069

8.626 

7.417 

.037 

3.312 

.492 

.058

10.126 

5.876 

.012 

1.858 

2.101 

.030

9.971 

5.995 

.037 

1.987 

2.045 

.039

Sum cations 19.947 19.984 19.994 19.942 20.003 20.074

Or ------------.

Ah

An

1.6

10.9

87 *\

End member proportions

0.0 1.8

37 2 10 1

£T O CO 1

1.5

12.7

QC 0

0.7

52 7

46.6

1.0

50 2

AQ Q

'Total Fe as FeO.

may more closely reflect actual magmatic sulfide compositions, plot near the center of the Mss field and would probably not exsolve pentlandite until temperatures dropped 

below 300°C. The copper content of these disseminated 

sulfides is between 7 and 12 weight percent, which would 

exceed the solubility of chalcopyrite in Mss below 500°C 

(Kullerud and others, 1969) and which indicates that an 

intermediate solid solution (Cu-Fe-S solid solution or Iss) 

must have been present.

Although the sulfides were hosted in a clinopyroxenite cumulate, three chemical features suggest that the sulfides formed in equilibrium with gabbroic liquids. Naldrett 

and Cabri (1976) established relationships between Ni/Cu 

and magma composition showing that Ni/Cu of 0.19 to 

0.21, such as found in samples 250-2 and 251-3, would be

in equilibrium with gabbroic liquids that contain less than 10 

weight percent MgO. Naldrett and Cabri (1976) also determined that Pt/Pd in sulfides precipitating from nonkomatiitic liquids decrease as Ni/Cu decreases such that the Pt/Pd 

values of 0.30 and 0.49, observed in samples 250-2 and 

251-3, are also expected values from liquids containing 

about 10 weight percent MgO. Finally, the work of Naldrett 

and others (1979) and Naldrett (1981) established that chondrite normalized patterns for PGM's and Au in sulfides from 

gabbro-hosted nickel deposits have a sloping trend that is 

distinctly different from the flatter pattern made by sulfides 

precipitated from ultramafic (komatiitic) liquids. The steep 

increase from Rh to Au in the Illinois River sulfides (fig. 5) 

is comparable with the sloping pattern made by the gabbrohosted Sudbury ores.

Magmatic Sulfide Occurrence in Dismembered Ophiolite, Oregon A13
Table 6. Electron microprobe analyses of amphibole 

[Standard deviations in parentheses]

Pyroxene cumulate

250-2 251-3 245-1

Metagabbroic sequence

246-1 252-1

Weight percent

SiQ2 -..-------------..

A12O3 -----------------

ipeO ----------------

MnO ------------------

MgO ------------------

PaH

Na2O -----------------

v r\

TiO2 ------------------

Cr203 ----------------

Total ----------------

P<» re2C\ U3 ----------------- 

FeO ------------------

New Total ---____-_-.

52.0 

(.272) 

5.73 

(.171) 

6.54 

(.110) 

.21 

(.035) 

18.4 

(.119) 

13.1 

(.022) 

.66 

(.126) 

.52

(.111) 

1.08 

(.171) 

.64 

(.032)

98.88

.05 

6.50

98.89

48.3 

(.135) 

7.67 

(.197) 

7.72 

(.172) 

.11 

(.054) 

17.4 

(.253) 

12.4 

(.158) 

1.21 

(.029) 

.79 

(.077) 

1.49 

(.109) 

.32 

(.044)

97.41

1.61 

6.27

97.57

46.6 

(.406) 

9.15 

(.078) 

14.2 

(.127) 

.18 

(.002) 

12.7 

(.106) 

11.8 

(.290) 

1.33 

(.106) 

.17 

(.106) 

1.39 

(.148)

(.007)

97.52

2.28 

12.2

97.80

46.4 

(.487) 

11.7 

(1.03) 

10.93 

(.106) 

.10 

(.162) 

15.1 

(.339) 

12.6 

(.028) 

1.73 

(.021) 

.13 

(.110) 

.74 

(.028) 

.14 

(.077)

99.57

3.98

7.35

99.97

47.2 

(.856) 

11.6 

(.202) 

11.5 

(.628) 

.31 

(.215) 

14.0 

(.480) 

11.6 

(.550) 

1.10 

(.033) 

.13 

(.050) 

.92 

(.212) 

.00 

(.000)

98.36

3.66

8.23

98.75

Cations

Si --------------------

AlIV .

Cllw. '|*|_." 1'

Ti --------------------

AlVI

Fe+3 ------------------

Fe+2 ---- ----

Mn -------------------

Mg ------------------

Cst

Ma

Sum Cations ---------

Quadrilateral

components ----------

2Pa

2Mg ------------------

2pe+2 -----------------

2A ------ -----

2NAM4

2AT A

7.304 

.696

8.000

.114 

.252 

.005 

.762 

.025 

3.843 

1.967 

.180 

.093

15.241

65.21 

29.93 

58.47 

11.60 

24.93 

3.23 

71.84

6.925 

1.075

8.000

.161

.223 

.174 

.753 

.013 

3.720 

1.907 

.312 

.145

15.408

46.25 

29.89 

58.31 

11.80 

26.55 

3.25 

70.20

6.816 

1.184

8.000

.153 

.393 

.251 

1.488 

.022 

2.764 

1.842 

.377 

.032

15.322

40.81 

30.22 

45.36 

24.41 

20.20 

5.46 

74.34

6.533 

1.467

8.000

.078 

.486 

.422 

.867 

.012 

3.176 

1.912 

.473 

.023

15.449

26.66 

32.11 

53.34 

14.55 

22.88 

2.39 

74.72

6.697 

1.303

8.000

.098 

.637 

.391 

.977 

.037 

2.967 

1.768 

.303 

.023

15.201

34.85 

30.96 

51.94 

17.10 

12.40 

7.62 

79.98

lrTotal Fe as FeO.

Definition and method of calculation given by Papike and others (1974).

A14 Contributions to the Geology of Mineral Deposits
Table 7. Electron microprobe analyses of cordierite 

[Standard deviations in parentheses]

Metagabbroic sequence

Sample number --- 251-4 253-2

Weight percent

SiO, -----------

MnO -----------

MgO -----------

K

/^v

TiO2 -----------

Total ---------

48.9 

(.422) 

35.2 

(.381) 

2.24 

(.005) 

.05 

(.114) 

12.6 

(.085)

(.000) 

.12 

(.008)

(.000) 

(.000)

99.11

48.7 

(.621) 

34.4 

(.226) 

3.37 

(.080) 

.02 

(.020) 

11.6 

(.082) 

.06 

(.081) 

.18 

(.008)

(.000) 

.00 

(.000)

98.33

Cations per 18 oxygen

Si -------------

Al

Fe -------------

Mn ------------

Mg ------------

Na-------------

Ti -------------

Mg/Mg+Fe -----

4.866 

4.129 

.186 

.004 

1.872 

.000 

.023 

.000 

.000

11.080

.909

4.906 

4.090 

.284 

.002 

1.744 

.006 

.035 

.000 

.000

11.067

.860

1 Total Fe as FeO.

Table 8. Electron microprobe analyses of pentlandite 

[Wt, weight percent; At, atomic percent; SD, standard deviation. All analyses are averages of several points on several grains]

GEOTHERMOMETRY AND METAMORPHISM

Coexisting pyroxenes from four samples were used to 

estimate temperatures by means of the pyroxene geothermometer of Wells (1977). Samples 250-2 and 251-3 from 

cumulus pyroxenite respectively yield temperatures of 

919°C and 923°C. Temperatures calculated from samples 

245-1 and 246-1 from the metagabbroic sequence are 

951°C and 897°C.

Bohlen and Essene (1979) reviewed the use of the 

two-pyroxene thermometer in metamorphic granulites and 

showed that experimental, analytical, and theoretical uncertainties cause the geothermometer to yield only approximate

Pyroxene cumulate

Fe 

Wt -----------

At- --------

<sD

Ni 

Wt -----------

At --------

sn -- -

Cu 

Wt -----------

At

sn --------

Co 

Wt -----------

At

sn --------

S 

Wt -----------

At

sn

Total

(Wt) ------ 

Metal/S ----------

ORO o

98 <>

23 4

.- (.461)

33 2

oc 07

.- (.654)

31

93

 - (.465)

5.71

4.44

1 1 1Q\

32 2

 - 46.06

 - (.181)

QQ Q9

1.171

250 3

17.0 

13.84 

(.351)

13.9 

10.73 

(1.32)

36.0 

27.76 

(1.06)

33.7 

47.07 

(-747)

100.6

1.097

251-3

29.1 

23.92 

(.642)

31.5 

24.55 

(.502)

.50 

.36

(.283)

5.39 

4.19

(.421)

32.9 

46.99

(.536)

99.39

1.128

253-3

22.2 

17.83 

(.629)

24.0 

18.33 

(.431)

21.5 

16.37 

(.120)

34.0

47.47 

(.742)

101.70

1.107

temperature data. Henry and Medaris (1980) recently evaluated the use of pyroxene geothermometers in southwest 

Oregon peridotites. They determined that each method has 

inherent differences that result in different temperatures. 

However, for pyroxenes equilibrated at relatively low temperatures (<1,000°C) and containing little A12O3 (such as 

those studied here), the geothermometer proposed by Wells 

(1977) was believed to be the most reliable.

Temperatures obtained from peridotites adjacent to 

the Illinois River sulfide occurrence show that recrystallization took place over a temperature range of 1,200°C to 

800°C (Henry and Medaris, 1980). Pyroxene augens yield 

temperatures between 1,200°C and 1,000°C, whereas matrix pyroxenes give lower temperatures between 1,000°C 

and 800°C. Himmelberg and Loney (1980) obtained temperatures between 975°C and 880°C from harzburgite, metacumulates, and cumulates within the Canyon Mountain Complex, Oregon, using Wells' geothermometer. The pyroxene 

cumulates at the Illinois River sulfide occurrence thus yield

Magmatic Sulfide Occurrence in Dismembered Ophiolite, Oregon A15
Table 9. Electron microprobe analyses of pyrrhotite 

[Wt, weight percent; At, atomic percent; SD, standard deviation]

Pyroxene cumulate

Fe 

Wt ------------

At --

<5D

Ni 

Wt ------------

At

sn -

Cu 

Wt ------------

At -

<2D

Co 

Wt ------------

At -

<2F>

s 

Wt ------------

At

sn -

Total 

(Wt) -------

Metals/S ----------

250-2

60.0 

47.18 

(.228)

.53 

.39 

(.089)

.00 

.00 

(.000)

.00 

.00 

(.000)

38.3

52.43 

(.135)

98.83

.907

250-3

60.3 

46.84 

(.550)

.24 

.17 

(.180)

.12 

.09 

(.167)

.33 

.26

(.125)

38.9 

52.64 

(.338)

99.89

.899

251-3

60.9

47.52 

(.479)

.41 

.31

(.376)

.00 

.00 

(.044)

.07 

.04 

(-121)

38.4 

52.13 

(.930)

99.78

.918

253-3

59.6 

46.61

(.954)

.41 

.30 

(.180)

.24 

.17 

(.191)

.39 

.29 

(.379)

38.6 

52.63

(.272)

99.24

.900

Metagabbroic 

sequence

251-4

60.4 

47.00 

(.401)

.28 

.22 

(.440)

.00 

.00 

(.000)

.11 

.09 

(.259)

38.9 

52.69 

(.163)

99.69

.898

253 2

60.6 

47.08 

(.242)

.13 

.09 

(.100)

.05 

.04 

(.095)

.06 

.04 

(.130)

39.0 

52.57 

(.197)

99.84

.896

temperatures similar to those recorded in surrounding peridotites and in other ophiolites. The values obtained from 

these pyroxenes show temperatures of reequilibration, not 

the temperature of initial crystallization.

SUMMARY AND DISCUSSION

Rocks adjacent to the Illinois River host two distinctly 

different types of sulfides. Disseminated, net-textured, and 

massive sulfides composed principally of pyrrhotite, chalcopyrite, and cobalt-bearing pentlandite occur in relatively 

undeformed and unmetamorphosed pyroxene cumulates. 

The sulfides have textures and compositions typical of magmatic sulfide deposits. Ni/Cu and precious-metal patterns 

indicate that the sulfides equilibrated with gabbroic liquids. 

In contrast, metagabbroic rocks that show granulite-grade 

metamorphism and intense deformation contain stratabound 

stringers of pyrite-chalcopyrite mineralization.

Locally the sulfides have been remobilized during the 

faulting that juxtaposed the two rock types. This is most 

clearly shown by the pyrrhotite-rich sulfides that occur as 

massive pods near the fault, stringers in the fault, and injections into adjacent metagabbroic rocks. The chemical effect 

of remobilization has been to reduce the abundance of Ni, 

Cu, Co, and precious metals relative to Fe, to increase the 

amount of Co relative to Ni and Cu, and to form minor 

amounts of pentlandite that is very rich in cobalt. Although 

rocks adjacent to the fault appear unaltered, it is not known 

if this remobilization occurred solely as a result of deformation or if it also involved movement of fluids.

Whereas the pyroxenite appears to be relatively undeformed and unmetamorphosed, the adjacent metagabbroic 

rocks clearly have a complex history of granulite-grade 

metamorphism and intense deformation. Two environments 

for these events seem possible. High-temperature and lowto moderate-pressure metamorphic assemblages occur in dynamothermally metamorphosed rocks at the base of some

A16 Contributions to the Geology of Mineral Deposits
Table 10. Electron microprobe analyses of chalcopyrite 

[Wt, weight percent; At, atomic percent; SD, standard deviation]

Pyroxene cumulate

Fe 

Wt --------------

At ------ -_..__.

<»n

KiWi --------------

At - -

<»n

Cu 

Wt --------------

At

<»n

Co 

Wt --------------

At ---------------

<sn

S 

Wt --------------

At

<5D

Total 

(Wt) ---------

Metal/S -------------

250-2

30.8

25.22 

(.477)

.13 

.09 

(.115)

34.5 

24.80 

(.465)

.08 

.05 

(.138)

35.0 

49.84 

(.163)

100.51

1.006

250-3

30.2 

24.72 

(.530)

.08 

.05 

(.131)

34.7 

24.95 

(.457)

.21 

.14

(.244)

35.2 

50.14 

(.356)

100.39

.995

251-3

30.1 

24.75 

(.629)

.03 

.05 

(.072)

34.2 

24.70 

(.848)

.16 

.14 

(.100)

35.2 

50.37 

(.185)

99.69

.985

253-3

30.7 

25.06 

(.355)

.01 

.00 

(.026)

34.0 

24.41 

(.242)

.05 

.05 

(.126)

35.5 

50.48 

(.242)

100.26

.981

245-1

29.8 

24.47 

(.827)

.45 

.37 

(.636)

33.6 

24.25 

(.714)

.22 

.18 

(.317)

35.5 

50.73 

(.346)

99.57

.971

246-1

29.4 

24.25 

(.460)

.00 

.00 

(.304)

34.7 

25.17 

(.254)

.00 

.00 

(.000)

35.2 

50.57 

(.353)

99.30

.977

Metagabb

251-4

31.2 

25.3 

(.143)

.21 

.14 

(.189)

34.2 

24.47 

(.892)

.00 

.00 

(.000)

35.4 

50.09 

(.170)

101.01

.996
Table 11. Electron microprobe analyses of pyrite 

[Wt, weight percent; At, atomic percent; SD, standard deviation]

Pyroxene 

cumulate

Fe 

Wt ------------

At

SD -

Ni 

Wt ------------

At

<2F>

Cu 

Wt ------------

At

sn

Co 

Wt ------------

At -----

<5D

s 

Wt ------------

At

sn

Total 

(Wt) -----

Mptate/S ----------

250-3

47.06 

33.30 

(.200)

.19

.13 

(.115)

.18 

.12

(.028)

.20 

.13 

(.190)

53.81 

66.32

(.057)

101.44

.507

46.1

33.15 

(.602)

.95 

.64

(.545)

.05 

.04 

(.123)

.22 

.16 

(.404)

52.7 

66.01 

(.150)

100.02

.515

45.2 

32.24 

(1.13)

.15 

.08 

(.177)

.74 

.48 

(1.48)

.04 

.04 

(.090)

54.1 

67.16 

(.831)

100.23

.489

246 1

46.7 

32.99 

(.687)

.14

.08 

(.170)

.00 

.00 

(.000)

.01 

.00 

(.144)

54.4 

66.93

(.128)

101.25

.494

Metagabbroic sequence

46.0 

32.91 

(.689)

.29

.20 

(.480)

.14 

.08 

(.107)

.12 

.08

(.245)

53.51 

66.73

(.334)

100.06

.498

252 1

46.6

33.13 

(.145)

.05 

.04 

(.100)

.00 

.00 

(.000)

.08 

.04 

(.700)

53.9 

66.79 

(.198)

100.63

.497

253 1

45.7 

32.89 

(.484)

.27 

.20 

(.386)

.03 

.00 

(.065)

.03 

.00 

(.038)

53.3 

66.91 

(.426)

99.33

.495

253 2

46.80 

33.4 

(.501)

.02 

.00 

(.061)

.02 

.00 

(.061)

.11

.08 

(.133)

53.4 

66.57 

(.249)

100.35

.503

ophiolites. However, these sequences are generally less than 

1,000 m thick, are multiply deformed, and show closely 

spaced changes in metamorphic mineral assemblages that 

indicate presence of a steep thermal gradient in the past 

(Williams and Smyth, 1973; Malpas, 1979). These are features not apparent in the limited exposures of metagabbroic 

rock near this sulfide occurrence or in extensive exposures 

of similar rocks that make up the Big Craggies (fig. 1). 

Alternatively, these rocks may be part of a hightemperature, low-pressure metamorphic belt that formed 

near an island-arc complex (Miyashiro, 1973). Similarities 

in age and petrology between these rocks and those of the 

Chetco River complex, parts of which are considered to be 

part of an island arc (Nicholson, 1981), make this latter 

alternative attractive. Blueschist assemblages that are the 

same age as some of the younger metagabbroic rocks occur 

to the west (Coleman, 1912) and could represent the complimentary high-pressure low-temperature part of the paired 

metamorphic belt.

The study of the Illinois River sulfide occurrence was 

part of a larger program designed to evaluate the mineralresource potential of this part of southwestern Oregon (Page 

and others, 1982). Although this sulfide is not economically 

significant, similar sulfide occurrences in adjacent parts of 

this ultramafic complex indicate that more economically 

significant sulfide concentrations might be found. However, 

the sulfides described here are more likely to be of interest 

because they represent a rare documentation of immiscible 

magmatic sulfides within a fragment of oceanic crust. This 

type of mineralization may also represent the primary concentration of metals that are remobilized and reconcentrated 

to make the Co-Ni-Cu arsenide and sulfide vein deposits 

found in many altered ophiolite complexes. Although not a 

well-known part of ophiolite metallogeny, vein deposits of 

this type are found in the Mackinaw Mine, Washington 

(Milton and Milton, 1959), Mesozoic ophiolites in Italy 

(Zuffardi, 1977), the West Carpathians (Hovorka and Ivan, 

1980), the Proterozoic ophiolite at Bou Azzer, Morocco

A18 Contributions to the Geology of Mineral Deposits
Table 12. Compositions of five sulfide-bearing samples, whole-rock analyses

[Co, Cu, and Ni were determined by flame atomic absorption, and total sulfur was obtained by an infrared sulfur determinator (analyses made in USGS 

group metals (PGM's) and Au were determined by means of a fire assay-spectrographic method (USGS laboratory; R.R. Carlson and E.F. Cooley, an

Sample 

number

250 2 ---------

250 3 ---------

251 3 ---------

253 3 ---------

251 4 ---------

Ni 

(ppm)

740

420

11 n

7OO

99O

Cu 

(ppm)

3 400

1,600

1,600

4 900

9 4OO

Co

(ppm)

130

270

76

340

130

S 

(percent)

1 8

10.7

53

7

f

5.9

Pt

(ppm)

0.150

.150

.150

.150

.050

Pd 

(ppm)

0.500

soo

100

100

9OO

Rh

(ppm)

0.002

< no9

<.002

< 002

<.002

Au 

(ppm

0.70

.15

10

9O

9O

Table 13. Compositions of five sulfide-bearing samples, analyses recalculated to 100 percent sulfide

i

o

C/l

In

5*

g

1

i.

Sample 

number

250 9

29SO 1

251 3 ---------

2253 3 ---------

3251 4 ---------

Fe 

(weight 

percent) 1

53.2 

(41.8) 

59.1 

(45.6) 

48.6 

(38.6) 

56.9 

(44.2) 

58.1 

(44.9)

Ni 

(weight 

percent) 1

1.5

(1.1) 

.1

CD 

2.2 

(1.7) 

.4 

(.3) 

.1

CD

Cu 

(weight 

percent) 1

7.1 

(4.9) 

.6 

(-4) 

11.6 

(8.1) 

2.5 

(1.7) 

1.6 

(1.0)

Co

(weight 

percent) 1

0.3 

(.2) 

.1

CD 

.5 

(.4)

.2

(.1) 

.08 

(.0)

S 

(weight 

percent) 1

37.8 

(51.8) 

40.1 

(53.8) 

37.1 

(57.2) 

39.9 

(53.8) 

40.0 

(53.84)

Pt

(ppm)

3.15 

.568 

10.4 

.767 

.330

Atomic percent is in parentheses. 

2Based on pyrite/pyrrohotite = 1/15. 

3Based on pyrite/pyrrhotite = 1/10.

n 

O
Table 14. Metal-metal and metal-sulfur ratios from recalculated 100 percent sulfide compositions

Sample number

Disseminated sulfides

250-2 251-3

Interconnected sulfides

250-3 253-3 251-4

Ni/Cu ---------------------

Ni/Co ---------------------

Pt/Pd----------------------

Pt/Au ---------------------

(Fe+Ni+Cu+Co)/S ---------

TJ^/O

Fe/Ni+Cu+Co -------------

0.21

5.00

.30

.21

1.64

1.41

5.98

0.19

4.40

.49

1.49

1.69

1.31

3.40

0.18

1.10

.29

1.00

1.49

1.47

73.8

0.16

2.00

.50

7.50

1.50

1.43

18.3

0.06

1.25

.25

.25

1.50

1.45

32.6

100

CO 1.0

UJ

Q

0.1

.01

250-2

251-3

Rh Pt Pd 

ELEMENT

Au

Figure 5. Chondrite-normalized plot of PGM (platinum group 

metals) and Au contents after recalculation to 100 percent 

sulfides. Also shown are fields determined by Naldrett (1981) 

for komatiites, Sudbury ores, and average pattern of several gabbro-hosted sulfide deposits. Detection limits greater 

than the amount of Rh present are shown by dashed line and 

arrow.

(Leblanc, 1975, 1981), and in the Limmasol Forest Plutonic 

Complex, Cyprus (Panayiotou, 1980). Of these occurrences, the one at Bou Azzer, Morroco, is the most significant and, in fact, until recently was the only deposit where 

cobalt was mined as the principal product.

The well-documented arsenide mineralization in part 

of the Limmasol Forest Plutonic Complex, Cyprus, has 

particular bearing on this type of mineralization. This complex, which is part of the Trodoos ophiolite, contains two 

separate mineralized areas (Panayiotou, 1980). Both have 

sulfides and arsenides (mostly monoclinic pyrrhotite, chalcopyrite, cubanite, and loellingite in the first area, and 

troilite, valleriite, maucherite, chalcopyrite, and pentlandite 

in the second) that are concentrated in veins and fractures. 

Most of the mineralization is near the contact between 

wehrlite and harzburgite and is believed to result from 

arsenic-bearing fluids that remobilized magmatic sulfides 

during serpentinization (Panayiotou, 1980). Small amounts 

of disseminated sulfides occur above the ore zone and are 

described as drops of an immiscible sulfide liquid that 

formed the initial deposit and were subsequently remobilized and altered by the arsenic-bearing fluids.

The sulfides in the nearly unserpentinized cumulates 

along the Illinois River may, therefore, represent the protore 

from which the mineralization in the Limmasol Forest Plutonic Complex formed. Although the processes by which 

the secondary vein deposits form, and particularly the 

source of the arsenic-bearings fluids, are not well established, the metals in these deposits were probably moved by 

arsenic-bearing fluids, which were derived from outside 

sources and were introduced during serpentinization and 

shearing (Zuffardi, 1977; Leblanc, 1975; Panayiotou, 

1980). Regardless of the process, the chemical and mineralogical alteration observed in the cumulate-hosted sulfides 

along the Illinois River show that mobilization of Cu, Ni, 

Co, and precious metals occurred.

A20 Contributions to the Geology of Mineral Deposits
Fe Ni

70-

EXPLANATION

Mssat500°C

WT % Fe

~ ^T ~ ~ Mss boundary at 300°C

Figure 6. Composition of sulfides from cumulus pyroxenite plotted on the Fe-Ni-S diagram. For this diagram, proportional amounts 

of cobalt have been added to nickel and iron; the compositions of 100 percent sulfides from table 13 have been further modified 

by removing the metals and sulfur present as chalcopyrite. X, compositions of pentlandites; Po and Py, fields of pyrrhotite and 

pyrite compositions.

REFERENCES CITED

Albee, A.L., and Ray, Lily, 1970, Correction factors for electron 

probe microanalysis of silicates, oxides, carbonates, phosphates, and sulfates: Analytical Chemistry, v. 42, p. 1408- 

1414.

Bailey, E.H., Blake, M.C., Jr., Jones, D.L., 1970, On-land 

Mesozoic oceanic crust in California Coast Ranges, in Geological Survey Research 1970: U.S. Geological Survey Professional Paper 700-C, p. C70-C81.

Bence, A.E., and Albee, A.L., 1968, Empirical correction factors 

for electron microanalysis of silicate and oxides: Journal of 

Geology, v. 76, p. 382-403.

Bohlen, S.R., and Essene, E.J., 1979, A critical evaluation of 

two-pyroxene thermometry in Adirondack granulites: Lithos, 

v. 12, no. 4, p. 335-345.

Burchfiel, B.C., and Davis, G.A., 1975, Nature and controls of 

Cordilleran orogenesis, western United States; extension of

an earlier synthesis: American Journal of Science, v. 275-A, 

p. 363-396.

Coleman, R.G., 1972, The Colebrooke Schist of southwestern 

Oregon and its relation to the tectonic evolution of the region: 

U.S. Geological Survey Bulletin 1339, 61 p.

 1977, Ophiolites: Berlin, Springer-Verlag, 229 p.

Craig, J.R., and Scott, S.D., 1974, Sulfide phase equilibria, in 

Ribbe, P.H., ed., Sulfide mineralogy: Mineralogical Society 

of America, Short Course Notes, p. CS1-CS110.

Dick, H.J.B., 1977, Partial melting in the Josephine Perdotite I, 

the effect of mineral composition and its consequence for 

geobarometry and geothermometry: American Journal of Science, v. 277, no. 7, p. 801-832.

Diller, J.S., 1907, The Mesozoic sediments of southwestern Oregon: American Journal of Science, ser. 4, v. 23, p. 401-421.

Dott, R.H., 1965, Mesozoic-Cenozoic tectonic history of the 

southwest Oregon coast in relation to Cordilleran orogenesis: 

Journal of Geophysical Research, v. 70, p. 4687-4708.

Magmatic Sulfide Occurrence in Dismembered Ophtolite, Oregon A21
Duke, J.M., 1979, Computer similation of the fractionation of 

olivine and sulfide from mafic and ultramafic magmas: Canadian Mineralogist, v. 17, p. 507-514.

Duke, J.M., and Naldrett, A.J., 1978, A numerical model of the 

fractionation of olivine and molten sulfide from a komatiite 

magma: Earth and Planetary Science Letters, v. 39, no. 2, 

p. 255-266.

England, R.N., and Davies, H.L., 1973, Mineralogy of ultramafic 

cumulates and tectonites from eastern Papua: Earth and Planetary Science Letters, v. 17, no. 2, p. 416-425.

Evarts, R.C., 1977, The geology and petrology of the Del Puerto 

ophiolite, Diablo Range, central California Coast ranges, in 

Coleman, R.G., and Irwin, W.P., eds., North American 

Ophiolites: Oregon Department of Geology and Mineral Industries Bulletin 95, p. 121-139.

Garcia, M.O., 1979, Petrology of the Rogue and Galice Formations, Klamath Mountains, Oregon: Identification of a Jurassic island arc sequence: Journal of Geology, v. 87, p. 29-41.

George, R.P. Jr., 1978, Structural petrology of the Olympus ultramafic complex in the Troodos ophiolite, Cyprus: Geological 

Society of America Bulletin, v. 89, p. 845-865.

Gray, Floyd, 1980, Geology of the igneous complex at Tin Cup 

Peak, Kalmiopsis Wilderness Area, southwestern Oregon: 

U.S. Geological Survey Open File Report 80-1243, 72 p.

Harper, G.D., 1979, "Anomalous" ophiolite underlying late Jurassic metasedimentary rocks of the Galice Formation, western 

Jurassic belt, northwestern California [abs.]: Geological Society of America Abstracts with Programs, v. 11, no. 3, p. 82.

 1980, The Josephine Ophiolite; remains of Late Jurassic 

marginal basin in northwestern California: Geology, v. 8, 

no. 7, p. 333-337.

Harper, G.D., and Saleeby, J.B., 1980, Zircon ages of the 

Josephine Ophiolite and the Lower Coon Mountain Pluton, 

western Jurassic belt, northwestern California [abs.]: Geological Society of America Abstracts with Programs, v. 12, 

no. 3, p. 109-110.

Harris, D.C., and Nickel, E.H., 1972, Pentlandite compositions 

and associations in some mineral deposits: Canadian Mineralogist, v. 11, p. 861-878.

Henry, D.J., and Medaris, L.G., Jr., 1980, Application of pyroxene and olivine-spinel geothermometers to peridotites in 

southwestern Oregon: American Journal of Science, v. 280- 

A, p. 211-231.

Henson, B.J., and Green, D.H., 1972, Experimental study of the 

stability of cordierite and garnet in pelitic compositions at 

high pressure and temperatures. II, Compositions without 

excess alumino silicates: Contributions to Mineralogy and 

Petrology, v. 25, p. 331-354.

Himmelberg, G.R., and Loney, R.A., 1973, Petrology of the Vulcan 

Peak alpine-type peridotite, soufliwestem Oregon: Geological Society of America Bulletin, v. 84, p. 1585-1600.

 1980, Petrology of ultramafic and gabbroic rocks of the 

Canyon Mountain ophiolite, Oregon: American Journal of 

Science, v. 280-A, p. 232-268.

Hopson, C. A., and Frano, C. J., 1977, Igneous history of the Point 

Sal ophiolite, southern California, in Coleman, R.G., and 

Irwin, W.P., eds., North American ophiolites: Oregon Department of Geology and Mineral Industries Bulletin 95, 

p. 161-183.

Hotz, P.P., 1971, Plutonic rocks of the Klamath Mountains, California and Oregon: U.S. Geological Survey Professional Paper 684-B, p. B1-B20.

Hovorka, Dusan, and Ivan, Peter, 1980, A hydrothermal leaching 

of an ultrabasic body a determinant phenomenon of the 

Co-Ni arsenide vein deposit genesis (Dobsina, the West 

Carpathians), in UNESCO, an International Symposium on 

Metallogeny of Mafic and Ultramafic Complexes; the eastern 

Mediterranean-western Asia area, and its comparison with 

similar metallogenic environments in the world [abs.]: 

Athens, Greece, p. 172-184.

Huhma, M., 1970, Nickel, cobalt, and copper in some rocks in the 

Outokumpu region: Bulletin of the Geological Society of Finland, v. 42, p. 67-88.

Irwin, W.P., 1964, Late Mesozoic orogenies in the ultramafic 

belts of northwestern California and southwestern Oregon, in 

Geological Survey Research 1964: U.S. Geological Survey 

Professional Paper 501-C, p. C1-C9.

 1966, Geology of the Klamath Mountain province, in 

Bailey, E.H., ed., Geology of northern California: California 

Divison of Mines and Geology Bulletin 190, p. 19-38. 

1977, Ophiolite terranes of California, Oregon, and Nevada, in Coleman, R.G., and Irwin, W.P., eds., North American ophiolites: Oregon Department of Geology and Mineral 

Industries Bulletin 95, p. 75-92.

Jackson, E.D., Green, H.W., II, Moores, E.M., 1975, The Vourinos Ophiolite, Greece: Cyclic units of lineated cumulates 

overlying harzburgite tectonite: Geological Society of America Bulletin, v. 86, no. 3, p. 390-398.

Juteau, T., and Whitechurch, H., 1980, The magmatic cumulates 

of Antalya (Turkey); evidence of multiple intrusions in an 

ophiolitic magma chamber, in Panayiotou, A., ed., Ophiolites: International Ophiolite Symposium, Cyprus, 1979, Proceedings, p. 377-391.

Kouvo, O., Huhma, M., and Vuorelainen, Y., 1959, A natural 

cobalt analogue of pentlandite: American Mineralogist, v. 44, 

p. 897-900.

Kullerud, G., Yund, R.A., and Moh, G.H., 1969, Phase relations 

in the Cu-Fe-S, Cu-Ni-S, and Fe-Ni-S systems, in Wilson, 

H.D.B., and Bateman, A.M., eds., Magmatic ore deposits, 

a symposium [Stanford Univ., 1966]: Economic Geology 

Monograph 4, p. 323-343.

Laurent, Roger, 1977, Ophiolities from the northern Appalachians 

of Quebec, in Coleman, R.G., and Irwin, W.P., eds., North 

American ophiolites: Oregon Department of Geology and 

Mineral Industries Bulletin 95, p. 25-40.

Leblanc, Marc, 1975, Ophiolites precambriennes et gites arsenics 

de cobalt (Bou Azzer-Maroc): Centre Geologique et 

Geophysique Montpellier, France, Memoire Mois-Series , 

329 p.

 1981, Ophiolites precambriennes et gites arsenics de 

cobalt (Bou Azzer-Maroc): Notes et Memoires du Service 

Geologique du Maroc, no. 280, 306 p.

Leblanc, Marc, and Billaud, P., 1982, Cobalt arsenide ore bodies 

related to an upper Proterozoic ophiolite, Bou Azzer (Morocco): Economic Geology, v. 77, p. 162-175.

Loney, R.A., and Himmelberg, G.R., 1976, Structure of the Vulcan Peak alpine-type peridotite, southwest Oregon: Geological Society of America Bulletin, v. 87, p. 259-274.

A22 Contributions to the Geology of Mineral Deposits
 1977, Geology of the gabbroic complex along the northern 

border of the Josephine peridotite, Vulcan Peak area, southwestern Oregon: U.S. Geological Survey Journal of Research, v. 5, no. 6, p. 761-781.

Malpas, J., 1979, The dynamothermal aureole of the Bay of Islands ophiolite suite: Canadian Journal of Earth Science, 

v. 16, p. 2086-2101.

Matsuhara, S. and Kato, A., 1979, The occurrence of heazlewoodite and cobalt pentlandite from the Nakauri mine, Aich; Pretecture, Japan: Tokyo, Memoir of the National Science Museum, no. 12, p. 3 11.

Medaris, L.G., Jr., 1972, High-pressure peridotites in southwestern Oregon: Geological Society of America Bulletin, v. 83, 

p. 41-58.

Milton, Charles, and Milton, D.J., 1959, Nickel-gold ore of the 

Mackinaw mine, Snohomish County, Washington: Economic 

Geology, v. 53, p. 426-447.

Misra, K.C., and Fleet, M.E., 1973, The chemical compositions 

of synthetic and natural pentlandite assemblages: Economic 

Geology, v. 68, p. 518-539.

Miyashiro, A., 1973, Metamorphism and metamorphic belts: New 

York, John Wiley and Sons, 492 p.

Morgan, B.A., 1977, The Baltimore Complex, Maryland, Pennsylvania, and Virginia, in Coleman, R.G., and Irwin, W.P., 

eds., North American ophiolites: Oregon Department of Geology and Mineral Industries Bulletin 95, p. 41-49.

Naldrett, A.J., 1973, Nickel sulfide deposits their classification 

and genesis, with special emphasis on deposits of volcanic 

association: CIM Bulletin, November 1973, p. 45-63.

 1979, Partitioning of Fe, Co, Ni, Cu between sulfide liquid 

and basaltic melts and the composition of Ni-Cu sulfide 

deposits A reply and further discussion: Economic Geology, v. 74, p. 1520-1528.

 1981, Nickel sulfide deposits: Classification, composition,

and genesis: Economic Geology 75th Anniversary Volume, 

p. 628-685.

Naldrett, A. J., and Cabri, L. J., 1976, Ultramafic and related mafic 

rocks: Their classification and genesis with special reference 

to the concentration of nickel sulfides and platinum-group 

elements: Economic Geology, v. 71, p. 1131-1158.

Naldrett, A.J., Craig, J.R., and Kullerud, G., 1967, The central 

portion of the Fe-Ni-S system and its bearing on pentlandite 

exsolution in iron-nickel sulfide ores: Economic Geology, 

v. 62, p. 826-847.

Naldrett, A.J., Hoffman, E.L., Green, A.H., Chou, G., and Naldrett, S.R., 1979, The composition of Ni-sulfide ores, with 

particular reference to their content of PGE and Au: Canadian 

Mineralogist, v. 17, p. 403-415.

Nicholson, S.W., 1981, Petrography and geochemistry of the Illinois River Gabbros, Kalmiopsis Wilderness Area, southwestern Oregon: University of Massachusetts unpublished M.S. 

thesis, 137 p.

Page, N.J, Gray, Floyd, Cannon, J.K., Foose, M.P., Lipin, B.R., 

Moring, B.C., Nicholson, S.W., Sawlin, M.G., Till, Alison, 

and Ziemianski, W.P., 1981, Geologic Map of the Kalmiopsis Wilderness Area, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-1240-A.

Page, N.J, Grimes, D.J., Leinz, R.W., Blakely, R.W., Lipin, 

B.R., Foose, M.P., Gray, Floyd, 1982, Mineral resource

potential map of the Kalmiopsis Wilderness, southwestern 

Oregon: U.S. Geological Survey Miscellaneous Field Studies 

Map MF-1240-E.

Page, N.J, Moring, Barry, Gray, Floyd, Cannon, Jerome, and 

Blair, W.N., 1981, Reconnaissance geologic map of the 

Selma quadrangle, Josephine County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map, MF-1349.

Panayiotou, A., 1980, Cu-Ni-Co-Fe sulfide mineralization, Limassol Forest, Cyprus, in Panayiotou, A., ed., Ophiolites: 

International Ophiolite Symposium, Cyprus, 1979, Proceedings, p. 102-116.

Papike, J.J., Cameron, K.L., and Baldwin, K., 1974, Amphiboles 

and pyroxenes: Characterization of other than quadrilateral 

components and estimates of ferric iron from microprobe data 

[abs.]: Geological Society of America Abstracts with Programs, v. 6, no. 7, p. 1053-1054.

Parks, H.M., and Swartley, A.M., 1916, The mineral resources of 

Oregon: Oregon Bureau of Mines and Geology, Resources of 

Oregon, v. 2, no. 4, p. 57.

Petruk, W., Harris, D.C., and Stewart, J.M., 1969, Langisite, a 

new mineral, and the rare minerals cobalt pentlandite, siegenite, parkerite, and bravoite from the Langis mine, CobaltGowganda area, Ontario: Canadian Mineralogist, v. 9, pt. 5, 

p. 597-616.

Ramp, Len, 1964, Geologic adventures on the lower Illinois River, 

southwestern Oregon: Ore Bin, v. 26, no. 6, p. 97-108.

 1969, Dothan(?) fossils discovered: Ore Bin, v. 31, no. 

12, p. 245-246.

 1975, Geology and mineral resources of the upper Chetco

drainage area, Oregon, including the Kalmiopsis Wilderness 

and Big Craggies Botanical areas: Oregon Department of 

Geology and Mineral Industries Bulletin 88, 47 p.

Ramp, Len, Schlicker, H.G., and Gray, J.J., 1977, Geology, 

mineral resources and rock material of Curry County, Oregon: Oregon Department of Geology and Mineral Industries 

Bulletin 93, 79 p.

Simkin, Tom, and Smith, J.V., 1970, Minor-element distribution 

in olivine: Journal of Geology, v. 78, p. 304-325.

Thayer, T.P., 1980, Syncrystallization and subsolidus deformation 

in ophiolitic peridotite and gabbro: American Journal of Science, v. 280-A, p. 269-283.

Wells, F.G., Hotz, P.E., and Cater, F. W., Jr., 1949, Preliminary 

description of the geology of the Kerby Quadrangle, Oregon: 

Oregon Department of Geology and Mineral Industries Bulletin 40, 23 p.

Wells, P.R.A., 1977, Pyroxene thermometry in simple and complex systems: Contributions to Mineralogy and Petrology, 

v. 62, p. 129-139.

Williams, H., and Smyth, W.R., 1973, Metamorphic aureoles 

beneath ophiolite suites and alpine peridotites; tectonic implications with west Newfoundland examples: American Journal 

of Science: v. 273, p. 594-621.

Winkler, Helmut G.F., 1967, Petrogenesis of metamorphic rocks: 

New York, Springer-Verlag, 237 p.

Zuffardi, P., 1977, Ore mineral deposits related to the Mesozoic 

ophiolites in Italy, in Klemm, D.D., and Schneider, H.J., 

eds., Time and strata-bound ore deposits: New York, 

Springer-Verlag, p. 314-323.

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