*. I

POMONA

Please do not destroy or throw away titia publication. If you hav* fto

for it, write to the Geological Survey at Washington and ask for afr*nkfe*e**rait

DEPARTMENT OF THE INTEBIOB

Ray Lrnaa Wilbar, Searetarr

. 8. GEOLOGICAL SURVEY 

Goorge Otts Smith, XMfeMtw

Professional Paper 158—F

CONTACT METAMORPHISM OF THE : ROGKS IN 

PEND OREIIXE DISTRICT,

JQSEPH-L.

Shorter contributions to geaeral

111-121)

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{ nnt- "s,: frqM .?] 

JH'.*-il u'SJc/iir; .11

UI^ITED STATES

GOVER3STMENT PRINTING OFFICE 

WASHINGTON: 1929

For sale by the Superintendent of Documents, Washington, D. C. Price 10 cents.
CONTENTS

Abstract......—._—._.__._._,__._..__...._______________________________....._._....._....

.Location,and general geology.——,—,———.———„__.___..._..._______—„_„.«,-,..,.___-_,,.

_. _. -, _,,__ _____*.._._»._».._*.._,__«t|_»*_-.^..4fc__..__.fc_»_- _#_-._»..,_-_,__,^_-._ ___»_» *. «p -v-» _.4k_._-*._*,_.A.-.- — — 4* _.-»-»-» — _, ^ .. ^ -» «* * ..i. .-i _*•*. -/._. •. _J<w i_jlni 4^M-.» *r _•!» «* f

«M metamorphism. '""'!_

ats. 

:>his_B(-

General features. 

Metamorphism of noncalcareous rocks.._________i____________________________.__ 113

General features--——————______________________________________________———._._—„ 113

Un<K£jt)a_x^i$_ibpment of the stages of nj6titi_iorphii-tt_._.____-__i___J___-____-___-_--____-___.______«._»_.;. 114

DtstribtrtSi.rof' microscopic metamorphism-.__________________________________.._.,..,:,-! 114

Biamples of intense metamorphism of noncalcareous rocks_____________________...__;,,_,__.» 116

Contact of Prichard argillite with Granite Creek granodiorite-________——_———...——....——.»_.._, 115

Contacts of Granite Creek granodiorite with Blacktail quartzite____________________________.___---.' 115

Intensely metamorphosed Striped Peak formation at Cape Horn.___________—___——__—_,_-- 115

Contact of Cambrian quartzite with Bayview granodiorite——____———— ——————— ———:_,—————.. , 116

Metamorphiam of calcareous rocks———________———— ——————— — ___-_ ————————— ———...——————— 116

General features.__________________________________________________________________«.____..__._.,^.. 116

Examples of metamorphism of calcareous rocks.---._-.-—.—_.-.____*_i,ii,k* — ___________ —————_,_».,, 116

Metamorphosed Wallace formation——_——_________ ——————— _______———_—___————.———_ 1.0

Metamorphosed Cambrian limestone.____________________——— — —— _———:__ ——— __———>,...__— 117

Endomorphism of the igneous rocks——_______ ——— ___ —— ——— ————————— — __ ———— __——————•——_—.__ 117

Tabular view of the metamorphiam—_—______________________________—_________—__„—„_——_<:___„-..—.....— 118

Summary of the evidence that the metamorphism ^went on in stages___ ——————_—/_._.„..,—._._,,**:.._..__.,*..*,.—— 118 

Mineralogy————————————___ ———— __ —— ——————————-———.--_.. ^^«>w|viw».^r-L>—_-.*->i r,?i,._.:_«,*~; ;. 118 

Conclusions-__,_.....__,___.___-,____.-_.___..._.._.._..____.-._-,.^«_.:»*_,_: _;»_,i^*J^-.^_._Ci_,W p.-^._.«_<-«.,>; -/-JUil

,. 

PLATE 15. A block of the Wallace formation found on the beach of Pend Oreille I-ake near Talaohe, Idaho.__—_~_.__._. 112'

FiatfKE 16. Map of the Pend Oreffle area, Bonner County, Idaho..__———_».*_-——,.---*..**:*,**:•,——_>»^,*.-;-_>( ,^g., ;.^ Ml 

17. Sketch from photographs taken from hill north of Lakeview, |di^..v.,-^.,-.^i«^-._-..»w^^
.-: f

CONTACT METAMORfcHISM OF THE ROCKS IN TR®

NORTHERN IDAHO

,OREWXE

By L. GILLSOW

In the Fend Oreille district, Idaho, a section of sediment*, 

part belonging to the Belt series, of Algonkian Age* And part 

t6 the Cambrian system, was intruded and Intensely metamorphosed by granodiotites of late Mesozoic or early Tertiary 

age. This metamorpnism proceeded in three overlapping 

stages. During the intrusion of the igneous rocks a general 

recrystalUzation of the sediments took place, the siliceous 

rooks changing to adinoles near the contacts and to pla$ioclaae-bearing rocks at greater distances and the limestones 

turning to marbles. Later, during the crystallization of the 

granodiorftes, emanations carrying the so-called mineraliaers 

were; given off in quantity and formed high-temperature 

silicates in the sediments. Still later, tilter the igneous rocks 

had solidified and the temperature ef the masses had becbme 

lower, sericite, chlorite, serpentine, magnetite, and sulphides 

wqre formed by replacement of the earlier minerals. Although 

n<9 fcs«« aaiwerals were found in the contact gonfes, more than 

ISO mia^fi^s common to such gone* ware ld*ntifi«di,

LOCATION AND GENERAL GEOLOGY

The Fend Oreille silver-mining district lies in 

Bonner County, in the panhandle of Idaho, and is 

adjacent to the south arm of Pend OfreiJte Lake, ft 

large body of water lying in a tremendous glacier-cut 

trough. (See fig. 16.) An area about 15 miles wide 

and 20 miles long was studied by a party of the 

United States Geological Survey under Edward 

Sampson in the summers of 1921, 1922, and 1924, 

and in the support of this study the Idaho State 

Bureau of Mines and Geology kindly cooperated.1

The district is underlain by sediments of Algonkian 

age (the Belt series) and Cambrian age intruded by 

igneous rocks, the largest masses of which, at least, 

are of late Mesozoic or early Tertiary age. These 

igneous rocks, which crop out over about one-fifth, of 

the land area, have already been described by the 

writer.2

The surface character of a part of the district and 

some of the geologic features are shown in Figure 17.

i Sampson, Edwftrd, Geology «a& aBvemafc deposits of the Pend OjMQte district, Idaho: Idaho Bur. Miaes and Geology Pampfa. 31, M88.

* Qfflson, JT. L., Granodiorites in the Pend Oreille district of northern Idaho: 

JoOr. Geology, Tot. 38, pp. 1-81, 1617. 

48862*— 2»

pauied by mftt-ftTTtftrpHfom t>o mfepw thatJinfesr j^ 

are the sediments free from its effects. 1%ft stiHy of

the rocks of the district has shown that

of igneous rnetaiaorphism Was long^ c^ntinuM

ift.-Map erf tlw^ndOt^e area, BonmrOotuiiy.iaaSo. 3 '»• 

pilug lu<fl«rtes tt^ 6* t^^^aoitaW nsetatmotiAism

that conditions progressively changed duiing1 th« 

crystallization of the magma. Thres periods «PI **#* 

in the metamorphism c&n be recognized^ Aud the chief

purposes of tldsp*p«r ATS improve 

occ-urred and to desarib* -thena. Th« c»alcw»ous rockd 

were changed m a diffei-ent manner from the HOB*

til ,
112 SHOETEE CONTRIBUTIONS TO GENERAL GEOLOGY, 1929

calcareous rocks, and the difference indicates that the 

primary character of the sediments was an important 

factor in the metamorphism. Furthermore, considerable material was introduced during all three stages 

of the metamorphism.

THE ROCKS PRIOR TO METAMORPHISM

T4ie'section1 of Belt rocks in the Pe'rid 6reiUe district 

is similar to that in the near-by Coeur d'Alenei&Mriet/ 

described by Kansome and Calkins.3 The Pend 

Oreille section differs principally from that in the Coeur 

d'Alene district in that the rocks at the horizona.of the 

Revett and St. Regis formations—that is, the rocks 

underlying the Wallace formation and overlying the 

Burke formation—are nibr&sllieeMs, and a new name, 

il formation, has been given to them. The

to be of algal origin. The Striped Peak, the uppermost 

formation of the series, is also locally calear'MHis.

Belt sediments.—The beds of the lowest formation, 

the Prichard, consist of dark-colored argillit© and 

grayish quartzite. Some beds of the quartzite are 

fairly coarse grained. Many of the beds are cjosely 

laminated, owing to frequent alternations o* sand and 

'mud m deDd^iticm.^^^fe^lcloWaay^A^^^^

"black, and in many places very closely spac^.

The Burke formation, which overlies the Priehard, 

consists of thin layers of medium-gray fine-grain©d 

light-weathering quartzite interbedded with da^k-gray 

siliceous argillite, the bedding surfaces of which, are 

micaceous, are either green or nearly Fack, and 

exhibit conspicuous mud-wadis. Some of the quartzite has a distinctly bluish tint on fres]ti,fraefwrj|. Some

17.—Sketch from photographs taken from hill nprth-ofLffcevie^+.

Belt rocks are chiefly argillites .and quartzitea ot great 

thickness, and the strata differ only in color and in the 

proportions .of argillaceous and siliceous material. 

They are affected by load metamorphism, and where 

not contact-metamorphosed they consist almost entirely of quartz and white mica. Under the microscope the quartz grains appear detrital and each is 

surrounded by a film of finely divided mica. In the 

more argillaceous beds the mica flakes are very abundanfr-and tend toward a general orientation with their 

flat sides parallel to the bedding. The rocks are almost 

everywhere devoid of flow cleavage and preserve such 

sedimentary features as ripple marks, cross-bedding, 

mud cracks, clay galls, and Tarely casts of salt crystals. 

Tne Wallace formation, which overlies the Blacktail, 

differs from the rest of 'the series in that it contains 

almost throughout a considerable 'amount of calcite, 

which is present in very peculiar structures, considered

* Kansome, P. I*, and OalWns, F. O., Geology and ore deposits of the Coeor 

d'Alene district! Idaho: TJ. 8. Gteol. Survey Prof. Paper 62, pp. 29-44,1908.

iisr occur..

-f,, I" i •* 'i'»tf "> '"*"" . -J{Ji^ : -'i !*•«,% **< f1 • m"'j(*J' ""'Sii't 5 -U i W'»" The lo weir part of t^ Blaoklail formarn|i, whicli: ' i- J.-L "i '-S : i ' ;^j :'.- f3'/aV''' vT^ 1 - ; ? ...'«' - overlies the Burke^, is domiuaD.tly a .very massive, "'""'' " * «• -4,1 j' I *i* ' * * ~ i: * i • i

bluish-gray quartzite that weainers nearly' I^Jaclr i^iia. 

breaks into large rec|angiuar;V bloelcs; ; |34 e^oi^'

faces across the bedding oUscontniuous fcr^mlfiI^or

,.,;,, - , ,^; ;- y^7^":\' --, ; :i5^Tp, 'mi I purplish bands occur, apuadan^ in .some JN^%, *s|l"e.©r

absent in -others. The^ ^d^ii|j s^aec|Brj\aifc' til& 

shaly, partin^j purple p|' nuur^baa. lustriuis ]wSl eoiispicuously ifiud* cracke^^ a»4 .pjpj^tfT* 3EQ]BjrfeMr ^'l^a: 

uppejr pa^| pf tfef f<?rmAti4n .^niore ^^fa^^ and 

tne purple 'snaly spariiiip'*are 'closely spiwjea/Vl 

ojf..th.e/ upHer ^«rt M« green but do

. • ..-: 

The lithology of the succeecung "Wallade formation

is varied, but two features appear in so m^ny.of the 

beds that its identification was' usually fchnple. The 

argillaceous partings of thin-bedded quartriteJ#xpos& 

a bedding surface of lustrous black, on whici\ are con-
TJ. S. GEOLOGICAL SURVEY PEOPESSIONAL PAPER 158 PLATE 15

A BLOCK OF THE WALLACE FORMATION, 10 BY 18 BY 24 INCHES IN SIZE, FOUND ON THE BEACH OF PEND

OREILLE LAKE NEAR TALACHE, IDAHO

Shows the peculiar contorted cavities caused by the more rapid solution of the calcite bodies than of the rest of the rock. These

cavities are believed to be of algal origin.

CONTACT METAMORPHISM OF BOCKS IN PEND OREIUJI S6-BTHERN IDAHO 113

spicuous mud cracks. Also, the peculiar structures of 

calcite above mentioned are especially diagnostic. 

The calcite masses are fine grained, and most of them 

fire elongated in two directions at fight angles. The 

vertical cross section is the most striking. It shows a 

peculiar wavy band from 0.5 to 4 mfllimeters wide and 

from 0.5 to 6 centimeters high. Some cross sections 

Tesemble- a question mark* into which a few extra 

crooks, hav.e been put. .Owing to the more rapid solution of the calcite these,structures are represented on 

weathered surfaces by cavities, and by them the 

formation was generally distinguished. (See pL 15.) 

These calcite masses modified the metamorphism to a 

different type from that prevailing in the surrounding 

noncalcareous materials, and in intensely metamorphosed beds they were seen as pseudomorphs. Argillaceous beds of the Wallace are black on fresh fracture 

but weather buff. A flinty green argillite is found at 

the bottom of the formation, and at the top the beds 

are closely laminated, similarly to those in the Striped 

Peak formation.

The Striped Peak, the top formation in the Belt 

series in the Pend Oreille district, is a thin-bedded fissile 

dark-gray argillite with interbedded white quartzite. 

Brick-red is the predominant color on exposed surfaces. 

Mud cracks and ripple marks, few of which are more 

than a centimeter in width, are conspicuous on the 

beds. The intercalation of many thin argillite and 

quartzite layers;, 15 or 20 to the inch, is a characteristic 

feature of the formation. A considerable thickness of 

the Striped Peak differs, however, from the main type 

and is an unlaminated olive-drab graywacke. At 

least at one horizon the upper part of the formation 

contains irregu ar masses of calcite similar to those in 

the Wallace.

Cambrian sediments.—The Cambrian rocks comprise a massive conglomeratic quartzite, a thin-bedded

friable shale, lo ;aUy fossiMferous, and a thick limestone

with several fades, fossiliferous at some horizons. 

The quartzite probably corresponds to the Flathead 

quartzite of Montana; the shale contains a small fauna 

of Middle Cam brian age. The fossiM.of one stratum 

of the limestone correspond with those,-©f the Lang^ton 

limestone of tha Blacksmith Fork section ia Utah, and

a shale in the limestone may be correlated with the

Spence shale member of tjie Ute limestone of Utah.4

Each sedimi 

foundly meta] 

and each was 

phosed. The 

which complete 

an almost total

THE METAMORPHISM

GENERAL FEATURES

ejitary formation was found to be promorphosed somewhere in the district, 

nearly everywhere slightly metamortzones of intense metamorphlsm, in 

recrystallization had taken place with 

elimination of sedimentary characters,

«Walcott, O. D., Smlthsonlaa Misc. Coll., vol. 63, pp. 191,197,1908.

are reiatively small/ 4ewohfiing more than 

wide on the surf ac^O

however, was "more widespread, and at some; 

marbles oeeur-withoH^neWtby^g^o^Bresol igiieo«*r^ck/

The metainorpjiisni of the Priclmrd, the JBurke, fcb* 

Blacktail, the noncalcareous part of the StripeA JF^^fc, 

and the€&mbriaa! ^uatt*faa1i^ ?sdf ^mllar as 

no separate descrijft&ft^Tbe :metamorphos*il 

careous .roch^ con tain many r Matures jn ^• 

although, the Wallaf^ and tfce eal|Cai|eous 

Striped Peak, >©B|g

from the metame^hie, WP^ttct of ,£he, .purer 

limestone. ,-; ,/; n . , ; -, 1FJIJ?

The igneous rocks t&At caused the exomorpl^is]^ qf 

the sediments are 1

In a narrow zone, close; to the 

diorite contains niuseoyite and ha« .been Kathei intensely affected by sericitimtion an4 <jW|srjj;isa*ion 

accompanied by the fojrmatwa of considerable nagnetite. Locally molybdenite and pother 

formed in the endomorphic zone. ••-•*'" ?=/!•»

METAMOEPHISM OF NONCAICABKOUS EOCE6

The more intense ittetamoi^nism of the 

careous rocks has visibly changed them. They are 

commonly spotted, and crystals of bibtite; stnd 

vite a milHmeter in diameter can be 

The more argillaceous beds have bewme inore'i^is^ 

to erosion and makg bold outcrops. ^ 

shows that the old fabrib of texture ahdt structure nas 

been very largely preserved, but the quartz anil finely 

divided white mica Have been replaced by dH^ocJas©-* 

albite. with or without quiertz. The feldspar eTryHmls 

are of the same size as tiie formei' quartz grains and 

make a mosaic of iinterldckmg anhedral grrtris. 

Irregularly distributed in tMs fabric a^ crystal" of 

biotite, andalusite, tourmalme, apatite, ' ztH;ont ind 

iron-rich chlorite and muscoyite, most of which ar* of 

anhedral form and 5 in general inuch'Iar^^thrfn th« 

quartz and feldspar. AH were formed wflfiout 

to the boundaries of the feldspar aittl qUartss 

clearly replacements' of those minerals, 

divided sericite and chlorite were depodtedt'by 

ment of all these other naaerils, and last of al mag*te*i^ 

ite, pyrite, and pyrrhotite werfe formecl la the J gfefcife 

and chlorite. i ( n^ !i

There were thus three rather well-defin^ ipeilocfi OTmineral formation—^first a period .of rex^ys^lUzation 

and substitutioa of a sodic plagioclase, for the r^icsa 

and some of the quartz, later a ^i^j3rbf'f6islnltMbvilof 

hign-temperature .silicates, and finally•':&^ period of 

sericitization with fine formation'^ of magnetite and 

sulphides. ~'\ '"[

Farther from the contact the cha^ge¥ tih^Sreiif 

on in the rocks differ only in degree fronv ttese justi
114 SHORTER CONTRIBUTIONS TO GENERAL GEOLG&Y,

described. The sodic plagioclase is present in subordinate amounts, and most of the interstitial mica 

of the load metamorphism remains. The biotite and 

iron-rich chlorite are present in small quantities, but 

magnetite and sulphides are more rare.

UNEQUAL DEVELOPMENT OF THE STAGES OF

METAMORPHISM

The moderately metamorphosed rocks were not in 

general affected equally by the three stages of metamorphism. For example, a bed of white quartzite in 

the Wallace formation exposed on the shoulder of the 

spur on the north side of Dry Fork, near the mouth 

of Fleming Fork, was entirely recrystallized to an 

allotriomorphic aggregate of quartz and albite-oligoclase, the average grain size of which is about 0.05 

millimeter. A few minute tourmaline prisms are seen 

in thin section, but there is no biotite, chlorite, serieite, 

or magnetite. Thus the rock was strongly affected 

by the first stage of metamorphism but hardly at all 

by the later stages.

Many other examples of this unequal development 

of the metamorphism could be given. The beds in 

Maiden Rock belong to the Blacktail formation and 

were recrystallized during the first stage, with the 

formation of much feldspar, but only a few rhombs 

of a late carbonate resulted at a later stage. The 

Blacktail beds at the summit of Chilco Mountain were 

not at all affected by the first stage, but biotite and 

tourmaline are abundant in them as replacement 

minerals. The Burke quartzite in the tunnel of the 

Phil Sheridan mine, on the north side of Granite 

Creek near its mouth, and in contact with the Granite 

Creek granodiorite at the lake shore, a short distance 

north of the mouth of the creek, was intensively 

metamorphosed only during the third stage of meta- 

.morphism. It contains pea-sized aggregates of late 

serieite, with chlorite, magnetite, pyrite, pyrrhotite, 

and some calcite. Only a little feldspar, biotite, 

apatite, and zircon were formed in earlier stages. At 

iiTWjint on the west side of the Chilco Mountain, ridge 

the Blacktail quartzite was found to hare been in-» 

tensively metamorphosed during the tMr4 Stage* so 

that the earlier metamorphio minerals^ once rather 

abundant, were almost completely eliminated. This 

lack of relation of the stages of metamorphism affords 

one of the best proofs that the metamorphism took 

place in stages.

DISTRIBUTION OF MICROSCOPIC METAMORPHISM

Examples of beds that had not been metamorphosed 

were sought with care, in order to compare the entirely 

unmetamorphosed phases of each formation with the 

metamorphosed phases. During the early part of the 

field work it was not realized how widespread $he 

metamorphism is, for except near the contacts of the 

igneous rocks the sediments are not visibly;contact

metamorphosed; When thin sections of rr^ks supposed to be unmetamorphosed wetfe^xamiaf *l, it Was 

found that the sodio pkgioolase, bidtitej «h^4ter *&£ 

minute prisms of towrmalia* Irere »f aJnw«fc ttaiWiftl 

occurrence. Study showed, feoW«Ter, tshattl ^^mfaierals

by regional lowl ^

the clastic texture of the Foek has 

obliterated, whereas in the *0ck»«f tfe« nttoi^ typieal 

clastic character these minerals are abaettt. Detrital 

feldspar occurs in some beds, but the grainr are surrounded by a film of serieitio material. The sodie 

plagioclase occurs as fresh glassy crystals that interlock 

with one another or with the quartz. Foils if * detrital 

biotite were found interstitially feetween eta*f% ^qvanffa 

grains; the metamorphio biotite has replaced the 

quartz grains, and a great many are larger than the 

average grain size of the rock. The tourmalin prisms 

have Hkewise replaced adjacent quartz grams, ffee 

tourmaline is remarkably widespread, being present at 

almost every point where specimens were collected. 

Calkins 6 found this universal distribution/in the locks 

of the Coeur d'Alene district, and he also «iH4ideriMi 

it to be of metasomatic origin. Tourmalins was not 

found in rocks showing no other effects of meteteta^ 

phism but was invariably accompanied by feldspar 

and biotite.

Proof that these minerals were aofc formed by 

recrystallization in the course of Hi« toad metamof*- 

phism that turned the old sediments into argillites 

and quartzites is afforded by the fact tMJI' (iit0li 

sericitic quartzites or siliceous argillites we*e t^hoitit 

by analysis to be low in soda, iron, »ad magnesia. 

Furthermore, so ubiquitous & distrfl&ti<8« r 0f toidt* 

maline, if it was formed bj reerystaHi&atJ^ of mi 

earlier detrital generation of tourmaline, cbrrands the 

ultimate source to have been a metamorphio terrane, 

from which other met&morphic minerals should lurre 

been earned itt with the tourmaline. No s\iol minerals 

have been foiirtd as detrital or yeerystalKued grains ia 

the rocks of tae Belt series. Th& tourma/^ 

therefore indicate that igaeous isolations have ' "

, bktite,

spar, etc., wer& formed by fehe action of solutions 

migrating from the inti^siT« granodtorite k affordetl 

by the increasing abu»4wvc^ <3| ih«- i^nticaJ varieties

of these minerals found in the sam« beds' toward the 

igneous contacts. -- '^ iii'

tioaa fr«pa the %a«ft^v /«emir©e, St

yarie^r ol ftakejRtt wat found

species, and tile rhombic form the most

of the occurrences. The carbonate was found IQ tvery

Ransome, I . ^Wms, ,f. C., The n^Hm and <we <Jepwi

, l&ba: U. S. Qe«ft,§tervey Prof , Paper 8% p. 101,
CONTACT OP IN *ENB ORBlliLB

Belt formation except to* Btoke and te moat abundant 

fctt the Wallace and in the Cumbrian limestone. Because of the greater abundance in originally calcareous 

rocks it is probable that most of the carbon dioxide 

was derived from the sediment Itself. As there was 

no apparent change in volume, some introduction of 

OOa, Fe, and Mg must be supposed to make an&erite 

fromcalcite.

EXAMPLES OF INTENSE METAMORPHI8M OF NONCALCARKOXJS ROCKS

Contact of Prichard argittite with Qra,n;de Creek 

gwnadiorite.—The igneous contact m sharply exposed 

on the east shore of the lake north of Granite Point. 

The well-defined bedding of the sedimentary rock is 

obliterated for approximately 100 feet, and the hornfels is cut by many quartz veins. For 25 feet from the 

contact the xock is a dense aggregate of quartz and 

albite but contains also biotite, zircon, apatite, and 

ilmenite. The albite decreases in abundance away 

from the contact.

Chemical analyses of the adinole at the contact and 

of a sample of the argillite collected at some distance 

from it definitely prove that an increase in soda and a 

loss in potash took place during metamorphism. 

There was also an unmistakable increase in iron, 

phosphorus, and zirconia and probably, in lime, 

magnesia, and titanium.

r of metamorphosed Prichard argiRite 

[J. 0. FataJhiM, Analyst]

Silica . _ .. . __ ..„ __ . . . .,

AlnmfnR it . ti ^j i,,-- -,•-,-,„.„„„. -„„„..-. -,-„„

XJttCBHttgtfiL

Lime... ... _ ...... ..

goda ___________ ______ * _________

Potash

Water <total)- _ . __ . ___ ........ ________

CarboadtojEjde........ ...... —— ... — .................

Phosphorus pentoxide _____ . ____________

Fluorine __________ .... _____________ MftnBRnwHi* oxftte ... . ., . .. a i

Zlreonium oxide . . .„ _ ........... ....

Contact

rock

6&96

16,42

.68

4.19

2.01

.62

*.57

1.96

1.00

.30

AT

.67

99.77

Slightly 

metamorphosed 

rock a

69,06

15.91 1 21

3.17

t no

l.«2

3.96 i as

.75

None.

>.03

98.78

• Contains organic carbon, probably graphitic.

* Accuracy of the zirconium determination ssid by Mr. Fan-child to be 0.006.

Contacts of Granite Creek graibodioriU with Blacktail 

guartzite.—A contact of Blacktail quartzite with the 

Granite Creek granodiorite is well exposed on the 

east side of the lake near the mouth of Fall Creek. 

The sediment near the contact is spotted with black 

knots of biotite 1 to 2 millimeters in diameter or is 

streaked and mottled with biotite and muscovite 

aggregates. The igneous rock contains visible crystals 

of muscovite and w seen under the microscope to have 

been also serioitized and enriched in magnetite.

The eedmi^i^ h«S ¥ 

oligoclase grains and q 

0.09 to 0.075 imlMmet^ ill tfiaifieter, exce 

the contftct, where they are twice tibia 

placing this groundmaes «Pe larger quartz 

abundant irregulariy shaped; grain* of biotite, 

vite, and andfilusit*^:%iu&j'Jit >y$&.Gh are 

as large as those of the groundmaas. Much 

andalusite ia partly altered t<) a finely divided gtee^h 

mica. Minute eiibaphedcal graiBs of apatitet, rtJ^%, 

and zircon are widely seattewKt in the rock. Aii3 ^ 

rons of magnetite and iittieaite, about 0.05 

in diameter and dissemiaat«d in the most 

manner, were certainly the latest minerals

On the west elope of Cfailco Mountain tfa« 

formation Is In contact with tlie Bftyriew batiio^th, 

but exposures are poof. The roek wrnfi recrystali' 

to an aggregate of quartz, microclin«, and 

oligoclase-albite, with little incfea«e In size of 

Later larger erystdte of rtiitttovfte, 

andalusite formed, many of the graina of wtrich 

more than a millimeter fe diameter. Minute eryt^als 

of zircon and blebs of fcn unidentified mineral 

about the refractive' indices aad birefri^ 

pyroxene are abundant. Matty of; 

grains are poikilitic, rftsembling a graphic intefgtC'Hh 

with quartz. In the later stages of tlie naet*^orpl ;sni 

the biotite was altered to chlorite with the separation 

of rutile needles, making sagenitic structure®; the 

andalusite and feldspar were B6tricitize4. Ju m **ny 

of the large cry»teii ; of 

spherulitee of sericite formed, the 

of which are hairUke, and many aw as long aa 

milUnieter. » ., ,

Cape Bw®.~- ]V£et««iorpho«ed 

Peak formation occur 1,700 to 2,000 feet above 

lake on the south side of Cape Horn. Th» 

teristic banding of the formation (aft seen ia 

is preserved, and the rock splits fairly weU *k>ng 

bedding. The dark band* *re rusiy brown; tJi« T" at 

ones yellow-brown. Some of the lig^ii) bands '-te 

marked with dark spote. The microscope shows tii&t 

the three stages of metamorphiftia. are weU indica^d. 

The groundmass consists of interlocking graiai' of 

quartz, mkrocUne, and albite-oligoela&e, in 

larger and very uregujar shaped crystals of . muscovite, and tourittaliiie had develop^ at ft 

time. Small crystals of zircon and apatite aue 

sory constituents of the second stage of 

phism. .Magnetite, ftericitej «.nd chlorite formed l^«r, 

as is indicated by the cross -cutting of the graiu4 and 

the replacement by them of biotiie and feids^Hr, 

The amount of feldspar that had formed during tiws< 

early period was rdatively less tha-n in-other Binwl*rly 

severely metamorphosed rock^. The tourmaUn^ k
116 SHORTER CONTRIBUTIONS TO GENERAL, GEOI/W,!

more abundant and occurs in larger grains than were 

found elsewhere in the district.

oj Cambrian guart&tie with Bayview granoA contact of the Cambrian quartzite with the 

granodiorite is exposed in the field east of the summer 

residence known as Drompre, northeast of Bayview. 

The sediment at the contact is a gray rock flecked with 

minute biotite scales and having an average grain size 

of 0.5 millimeter. In places it is faintly banded. The 

same sequence of metamorphism is indicated as in 

other contact zones. There was an early crystallization 

of albite-oligoclase with the quartz, forming an interlocking groundmass, the grains ..of which average 

about 0.1 millimeter in diameter. The feldspar is not 

uniformly distributed, making solid masses in some 

parts of the thin sections, and being absent from other 

parts. Biotite, muscovite, andalusite, and tourmaline 

formed abundantly; the tourmaline is found in small 

grains, the others hi large ones. Many of the biotite 

foils contain zircon crystals surrounded by pleochroic 

halos, and many foils are also altered to thuringite, 

with the separation of rutile needles. Sericitization 

had been intense and widespread, attacking most successfully the feldspar and andalusite. Magnetite and 

ilmenite are also abundant; many of the grains of the 

ilmenite are partly altered to leucoxene.

METAMORPHISM OF CALCAREOUS BOOKS 

GENERAL FEATURES

The mineralogy of the metamorphosed Wallace formation and of the Cambrian limestone is so strikingly 

different from that of the rocks above described that it 

indicates the importance of the original character of 

the rock in determining the nature of the minerals 

formed by metamorphism. Albite, andalusite, a 

-biotite with very high index of refraction, tourmaline, 

and thuringite are characteristic of the metamorphism 

of the noncalcareous sediments, but in those in which 

calcite was originally present garnet, diopside, a 

inagnesian biotite, amphibole, epidote, and titanite are 

abundantly developed, and scapolite, veswiazftte, 

olivine, chofidrodite, topaz, and fluorite were^ fotoid 

in a few places. On the other hand, zircon, quartz, 

apatite, sericite, chlorite, magnetite, and sulphides 

occur in both kinds of rock.

There were two distinct processes in the metamorphism of the calcareous rocks, and like the stages of 

metamorphism in the noncalcareous sediments the 

degree of development of one is more or less independent of the other. There was first marmarization 

of the limestones on a large scale, which eliminated 

the bedding and the carbonaceous material. Later 

came the introduction of material from the igneous 

rock, which formed the contact silicates above mentioned. This second process is conveniently divided 

into two stages on a rough basis of temperature, with

sericite and cWorite marking the, beginning of: the 

later stage. There were thus tJar%stages { IBO in the 

metamorphism of the^akar^ous roeks. •. .&• + t ,>

EXAMPLES OF

Metamorphosed 

the west sh<H*e of the 

under the Three Sisters, is all 

through much of this distance |he exposures consist of 

the Blacktail formation, jfarther north are found 

greenish and white quartzite beds, characteristic of 

the metamorphosed Wallftefc, the identity o* Wateft is 

estabhshed by the presence of 

shown in section, which prior to 

sisted of calcite structures of organic OfHa/v Itite 

grains are very small, and the foek has «- subieonehoi&al 

fracture. The green bands consist ©f a( pale-*green 

amphibole; the white bands are either of q* 

feldspar, quartz and scapoHte, or diopsitte/ 

some beds makes nearly solid masses. Zieisi* 

grossularite, titanite, zircon, apatite, and muscovite 

are accessory minerals. !

The climb up the east side of Bernard FHaH front 

West Gold Creek, at the south end- of th(8 fake, gives 

another instructive section of metamorphosed Wallace 

beds, there present as a capping over the Bayvie^r 

granodiorite, which is exposed almost to the fcoj^of t&e 

tremendous cliff that rises abruptly from the^ Shore. 

The same rock is also seen in the gap betw;f€** Bernard 

Peak and Chilco Mountain. This j-ock is massive, 

is marked with white or white and green bantlr,"«ftd is 

notably heavy from the abundance of heav7 silicates. 

The grain, however, is so fine that no miner^Js can be 

recognized with the hand lens. The^ miBer«4 eoatea^ 

is about the same as that of the rock- alongr the ^ore 

under the Three Sistersj consisting 0f quart* 

(both microcline and albite), diopsiete, zsoisite, 

titanite, zircon, apatite, ealeite, and magnetite, 

pyroxene and amphiboles are distinctly lakr th^n the 

feldspar. Titanite is v«ry abundant in 

eec^ra aijsfj^g^^au^''-' A pale-brown bio4te

from others, 

Anothej* area of inteaaely metamorphosf-i roeks is

on the, slope; «jisit,4i4^i!i%^

separating Chloride Guleb from the tributfnes of the

North Ibrk

of the district.

minute seams o

quarts1, potash, f«l^p^ e^d|; ; m&

Bed^ «tjaA

Hewer muW'wetfii *i^^tl - ifA^J ibck

greenish hornfds, csdn^stM^ of il'lfetocflinfi^ of^uartz"

arid iMdrocline, tt wMcit ari niimep&iiff fcr1^ jMvided

prisms of the green amphibolej ietccompanied in isome

beds by a fibwtal-dmjphltole1 of lower refractivig inft^£!

*
CONTACT METAMOBFH«iKl OP 8OOSS IN M3N1> .<HUK13J^4MS»P»,> IDAHO

Zircon^ "ta^rite, apatite, arid ma^^t^1*^* scattered 

widely through the rock. ,

In the uaetamorphic area just described bmt beyond 

the divide, in the North Fork drainage basin near the 

Lone Hand prospect, the difference between the 

minerals formed during metamorphism of calcareous 

and noncalcareous beds is convincingly demonstrated. 

In some laminae within a single .thin section are quartz, 

sodic plagioclase, and andalusite, with serieite and 

chlorite—-the typical mineraUzation of the siliceous 

sediment; whereas in adjacent originally calcareous 

laminae are epidote, diopsida, ^mphibolej fluorite, 

titarrite, and calcite. In some plates the calcite forms 

pseudomorphs after the amphibole. During a meseparation of one unban.ded specimen in 

, three-fourths of the powder sank, and of 

thitlraction 95 per cent was amphibole.

jfiqiamorphosed Cambrian limestone.—The Cambrian ^limestone "is marmarized, or partly so, over large 

areas. At the lime quarries near Bayview, at the old 

quarries at the head of Cocolalla Creek and near 

Whiskey Rock, and in the headwaters of North Gold 

Creek the rock is marmarized but contains few silicate®. The most interesting examples of more intense 

metamorphfem were found in an included block of 

limestone on the south side of Cape Horn, in cliffs 

along the east shore between South Gold Creek an4 

Pojrt^Rock, and at Vulcan Hill, east of Lake view:. 

'jmese zones have a varied mineralogy an4 present thes 

mosV interest to the mineralogist of all the contact 

zone&in the district.

! j Artiumber of prospects for ore on Vulean Hill have 

m&jde(good exposures of the contact of the granodiorite 

aj^d .limestone. The sediment is a white marble ib^ 

whicn many silicates and some ore minerals were' 

Ideally developed so abundantly that the rock is 

entirely replaced by them. In some beds the rock is 

banded green and yellow and consists principally of 

* garnet and augite but also contains vesuvianitej 

ejjidote, phologopite, amphibole, fluorite, quartz, 

'sSralte, chlorite, zeolites, magnetite, sulphides, and 

aiikerite. In some closely banded shaly limestones the 

jeffeot of alternating composition is again clearly demon-* 

strayed. Sodic plagioclase formed in the shaly layers, 

bujj at that stage of mineralization no silicate formed 

in ^ne limestone beds, and the rock only recrystallized 

.'to'1!; marble. Later biotite formed in the shale, an4 

gin-net, diopside, and amphibole formed in the limesfcooe. The later sericite and chlorite formed in both 

without regard to the boundaries of the layers. In 

one bed a considerable quantity of corundum was 

foiihd, apparently produced from the recrys^allization 

of »h impure bed in the limestone.

The garnet and pyroxene differ in composition in 

adjacent beds of the limestone and.indeed in the same 

bed, as the garnets are zoned in some places. The 

difference in zoned garnets, however, is slight, but in

adjacent beds groefcuksite -fljada aawlradi^te are 

and diopside and aygit«; oeomr ta* different

In the garnet zones on <3ape Horn a 

minerals occur in subordinate quantity, topaz, 

townite, find allanite being identified mic 

Some marble cliffs on the east shore of th 

tween the mouth of South, GoM Creek and 

also yielded additional minerals. At.ti,e east end of 

a little beach 160 yards south of the mouth of the 

creek the rock ia a light-gray and green, partly recrf stallized but stiH'bedded limestone. Besides ankerte, 

scapolite, spinel,, muscovite, and ehlorite, cousiderrble 

chondrodite is presenfc in imall ptd©-y^kwr : crystals, 

a few of which can be seea with a hand: lens. Farther. 

southwest, beyond a fault, the rock is more thoroug*idy 

marmarized and contains diopside, phlogopite, and 

tremolite and in the more shal^ laye.rs"B<Kiity|)|agioc?aBe 

and quartz. : - i

The independence of mai-marization aaid. siMc^te 

formation was well shown at the last series of outcrops. 

Marble occurs \sathout silieatee, and silicates are found 

in bedded limestone tita| ,ia bwt Htdft jaarmarirgd, 

Where silicates occur in marble th^f indkate fey their 

boundary relations, so far as these eaa be interpreted, 

that they were formed lato1 than th« raarniajiaAt: 'm. 

From these facts it ia inferred thftt tiie Jnarmarizal^on 

took place principally . during the first effusion of 

solutions from the magma, mostly of water* wl ;*?h 

mixed with and h|Atf d \^ter of connate or of surface 

origin, whereas tie jsiueates formed 

advance of crystaliaation in the 

caused a concentration of till© emana 

more material in solution.

ENDOMORHBSM OF THE BOCEg

The writer ** has elsewhere briNftjf' described 

endomorphism of the igneous ro^& an<t'lias1(S>nia® 

it, at least in a general way, with the Action of tM 

solutions that slowljr soaked ItejtiL. ^Ee fcodfy of the 

igneous rock and made a number of 

changes. At few points^ are tfie roek$ i 

endomorphosed, arid except tor some bhanges viale 

only under the ialcWcope tEe rocfes appear fhe 

at the sedimentarif contac^ ap Usewnere. 

tion of large flakes'of muscotite; ati intense 

tion and chloritizaMozi, arid ttjeeniiehmto of magn 

were the endomolpMc «Hai||©8j F|tti© muscovite '* 

not pyrogenetic,'for it has:rrej>la0fd ekrfier iriinei"%. 

If its time of foralatfoni iii the igneoik rocfo c«oi be 

fixed as conteinj^oranedi^ .witti that ia tibe adjacent 

sediments, the tinw 6f tfce^ irietafiiorpnisni in 

to the crystallzatipa of tlte igneous rock is 

well established. It :seents to^ thft wifittrthafe the 'tint* 

of crystallization of fhd tttuacoVite Must hare b^eri

contemporaneous in rae 

'''

two sides of a sharp contact

I. L., 

Jour. Geology, vol. 36, p. 5», 1967.

the Paad Onslle district of northern .Idajio;
118 SHORTER CONTRIBUTIONS TO GENERAL GEGLG8Ty 1926

between igneous rock and sediment. This 'assumption 

furnishes a bads for the dating of the stages of 

metamorphism in the sediments.

VIEW OF THE

The metamorphism of the rockfi in<the JT-'nd Qreille 

area CBJi be shown ia tabukr form IBS foito'1^:

MetQmorphism of rocks in Pend OreiUe district,

Stage Igneons rock Noncalcareooe sediments

Magma molten. A general and uniform recrystallization, 

with obliteration of the undulatory extinction of the quartz, elimination of the 

serieite, and the formation of more or less 

feldspar.

Marmarteatlon,

iilt/:-

Magma crystallizing and margin probably solid.

Pneumatolytic emanations carrying the elements known as mineralizers. The minerals that formed are andalusite, biotite, 

eordierite, tourmalins, quartz, apatite, 

and zircon.

Pneumatolytic emanations 

mentt known

erals formed are phlogopite. t 

diopside, groesalaritc/lroft-ta 

epidote, 

'paz, zircon, apatite, * ' * ^ *

ohte.

Igneous rock solid and attacked 

by abyssal pneumatolytic 

and hydrothermal emanations. The pyrogenetic minerals replaced by the new 

minerals muscovite. serieite, 

ehlorite, magnetite (or ilmenite), pyrite, quartz, ore minerals, and ankerite.

Abyssal pneumatolytic and hydrothermal 

emanations formed muscovite, serieite, 

chlorite, magnetite (or ilmenite), pyrite, 

pyrrhotite, and quartz.

Abyssal pneumatolytic and 

emanations formed seriefte, 

netite, pyrite^,pFn*ott<»i! 

of metallic sulphides, dru 

lites, ankerite, and *' J "'

'S&erwVf

srfcMrft't .

; Iwm'ii 

"^T^pHTwfrr

SUMMARY OF THE EVIDENCE THAT THE METAMORPHISM WENT ON IN STAGES

1. The marmarization of the limestone and. recrystallization of the siliceous sediments, with the 

formation of a sodic plagioclase and an elimination of 

the original potash mica, preceded the formation of all 

the other minerals, as shown by the mutual boundary 

relations and by the uniformly widespread distribution of the minerals formed by the early processes. 

The rock had been recrystallized to an aJlotriomorphic 

aggregate of even grain, and except in zones of most 

intense metamorphism the grain size is about the same 

as it was originally.

2. The second stage is represented by minerals the 

grains of many of which are muqh larger than those of 

the first stage and clearly replace them. In the noncalcareous sediments no order erf crystallization of 

minerals of the second stage can be determined, and 

it is probable that they were in great part contemporaneous. In some of the garnet rocks, however, a 

definite sequence from pyroxene to amphibole was 

shown. Many of the minerals formed in the second 

stage are known to require a high temperature during 

their formation. The minerals are generally considered to be pneumatolytic, and many required the 

so-called mineralizers for their formation. The irregular distribution of these minerals in some beds and 

their grouping into spots and streaks imply that they 

resulted from solutions that passed through the solid 

rock with more difficulty than the first solutions.

3. The third stage is the only one whose results are 

to be found in both exomorphic and endomorphic

zones, and this fact suggests that during the 

stages either the igneous rock'was not y^t 's< 

it was in equilibrium with the solutions 

the metamorphism in the sediments. The la 

of the minerals characteristic of the iM"tt 

clearly proved by the botindar^ relations 

grains. The minerals of the third stage 

known to be late in most parageneti 

form at rather moderate temperatures^ Heft 

period of formation is generally spoken <$ as 

thermal. /

4. The points above given prove tlptt th« 

phism of the sediments was progressive; 

Stages were to some extent independent of one 

is proved by the finding of many places 

products of one of the stages hare

abundan%«^to

regard t^

periods must b?s cojosidea^J as overlapping. <*rf»*«

H»W«j^

iil "

No unusual species 

- were found - ;• '. _• 

during 

.' T1?-.^*- 

ia©i; 4>

represented incloir^ a

generally

However, ^e speces 

proportion of those 

fee commopil|'

23nxk)i?ift4ii*cipe

common contact jp^era^. tiut Jhe writer 1 

published the evidence for knowing it to be 

contact mineral and has cited several other oceurrsrjtMW 

reported from contact zones.

At no point were large and well-formed crystil 

o| t|i0 contact minerals found. In most ~^ @~ '- 'Jii
CONTACT IN PEND IDAHO

the grains are less than 1 millimeter in diameter, 

hence necessarily most of the study was made under 

the microscope. In addition to the examination of 

about 150 thin sections a considerable number of thp 

specimens were crushed, the grains separated into

liquids. Thus tile atttt&ttijr"flfmost of the 

were determined from several specimens, The 

lation that follows may be of interest.

» T

Minerals of the e»ntact~inttamorpkosedl reeks of $ district,

Mineral

Stibt»it§ _____

Molybdenite _

Sphalerite

Pyrrhotite_____

Pyrite. ___ ...

Hatoida

iluorite.......

Oztdes

Quartz.. ... _ ,

Rutile _ _. _

Spinel. . .

Magnetite. -_._

Ilmenite ______

4 Cwrfooiwtes

Calotte., __ ..

Dolomite. — ...

Ankerite ._ _

Apatite

Silteates 

Mieroeline. . . _ -

Albiteto oligo 

olase albite.

Book oocorrenee

Oambriaa limeetone _ .

Paeksaddle Mouutain 

granodiorite. 

Cambrian limestone __

All rocks

. _ do.. ... . .

Wallace formation, 

Cambrian limestone.

All WC$£S>. __ ...

Cambrian limestone. _ - 

All rocks. _ _____

do

Cambrian limestone. - . 

All rocks.. _ ________

__— .do ______ _____

Most of the rocks.. _

Wallace and Striped 

Peak formations and 

Cambrian limestone. 

Wallace and Striped 

Peak formations, 

Cambrian limestone, 

and igneous rocks.

All rock* ________

All rocks but rare in 

the purely calcareous 

beds of the Cambrian limestone. 

All rocks except the 

purely calcareous 

beds of the Cambrian limestone. 

CambriAn limestone. _ .

Locality

Bapti.* clajacos on VulcaaHill. 

McBonnah* No. 2 

claim, Vulcan Hill. 

Keuo claims, Vulcan 

Hill. 

General . .

___ do __ _ __ __

2ones of intense metamorphism.

General .

Keno. Claim, Vulcan 

HilL

General. __

Along southeast shore 

of lake and lower 

workings of Arcade 

group, Vulcan Hill. 

General. __________ _

__ .do. ___

Nun>woii8 places ^_.

__ do ....

Widespread ——— . ——

In zones .of intense 

metamorphism. 

Bare but does occur 

in weakly metamorphosed rocks.

Many places.. ____

General. ________

Overlying the granodiorite sill on Cape 

Horn.

PKW.*. '

;

>

Biaxial in some specimens with & large 

optic angle.

Symmetrical extinction 

angles range from 5° 

to 13°, 10* twin* 

average.

angles of 40°, £«* UftQL

^^ji^ ^

Itf esuloiftDisd&^sed izone.

quantity. 

D!e£eminAted in .small &nbe*rai 

grains throughout metamorphosed roeka. /H 

D£sserrdn&t*d in small eswfeQa

tbrc

Not 

. aeo]

FOUIM 

• ted: 

mlFOUJH 

spe» 

Direa 

moi 

In mi 

U& 

phc

Foum 

tMi

One o 

abi

__tooC

tine

Qew_r 

rool 

recr 

ordi 

ime 

Minul 

Wa 

lim< 

Parall 

but 

the 

moi

.... 

'

Dk_«

but 

the

Escee

the 

jbdl

FoiKa 

pia

>«ghout metamorphosed BO ^ka.

common. Sfen only mi-?rolicfttty ifflffH" §8yiJl qu&JJ^ ^i« »

m«at. wtd as a replacen^nt 

leral ta> taleoreous rocks.

jimen of an Impure limestone, 

t f carnation fc.v co0t-x;t »-W» 

rphism not proved. 

,nute quantifies where fornd. 

at *&undaat in the. metaac^wsed Blaekta41 beds at ^he 

.thai FaB Creek. ^I/rA 

L in minute green crystaatl' in. 

i sections of 0 specimens.

f the most widespread mir-eriue to contact metamorphf em. 

ated with magnetite and id «»n- 

»_i bjr eheoaicw test, x £ >; :r

1 1 laaostly In the ejyk»_ar^ttl 

cs and is thsre due to single 

V'gt«UJEa,tion. Aistt in r<^ 

nate quantities in a few specis of other rocks, 

e rhombs widespread in the 

taee f oraatffeif a and CwnferisHl

KSton*. , _ ' " -• ::'.-.; ' "s...

Us dolomite in occurrence. 

found al»o in vetnsi O&« of 

l«st minerals in the m^taphio sequence.

Binafeediii raieroaeople ;ftH«i

Is xeowhere so abundant as. 

ftlbite-ojifoelase.

dirtgly ' . wMwpr^lMl, l«rii^ny

principal coaetituent of some 

loles.

l-ia mic3t»«6opic oyyat-ute at o^aft

se. ; *
120 SHORTER CONTRIBUTIONS TO GENERAL

Minerals of the contact-metamorphosed rocks of the Pend Oreitte district, Jdaho?—Continued,

Mineral

Silicates— Continued

Diopside and 

augite.

Aotinolite _ _ _ _ _

TremoUte___ _

Pyrope, grossularite andradite.

OUvine ________

Scapolite.. _____

Vesuvianite_-__ 

Zircon __ _____

Topaz__ _______

Andalusite _____

JZoisite____ ___

Epidote__ __ .

AUanite__ _ ___

Chondrodite__ _

Muscovite _ _ _ _

Lepidomelane _ _

Biotite __ ___ _

Phlogopite_ ___

Sericite. _______

Cordierite._ _ _

Thurincite_____

Rock occurrence

Only in calcareous 

rocks.

Wallace formation.

ate vein in old fault 

zone in the Wallace 

formation. 

Cambrian limestone

Only in calcareous 

rocks.

Cambrian limestone

and Wallace formation. 

Cambrian limestone. __

All rocks__ _ _____ ___

Cambrian limestone. _ _

Calcareous rocks ______

ous rocks and in calcareous rocks. 

Cambrian limestone _

do. __ _ _

_ _ :_do______-_____ _

All rocks __

ments.

calcareous sedimeats, . do

Locality

In all strongly metamorphosed beds of 

Wallace formation 

and Cambrian limeatone.

morphosed beds. 

West side of NW. #

SW.^sec.3,T.54N.. 

R. 2 W.

At many places, most

conspicuously in the 

cliffs along the southeast shore. 

In most strongly metamorphosed beds.

south side of Cape 

Horn.

Hill; shore below 

Three Sisters. 

Keno claim, Vulcan 

Hill. 

General. _____ _____

Overlying sill on south

side of Cape Horn.

morphosed zones.

of intensely metamorphosed Wallace, 

west shore below 

Three Sisters.

of Cape Horn.

east shore south of 

South Gold Creek.

_ _ do __ _

on west shore below 

Three Sisters.

lake and at Vulcan 

Hill.

Horn. 

General. ______ _ ____

_ .do _____

_____do____.__________

Properties

( J "»

0= 1.690 to 1.710; color 

from w.hite to green.

0= 1.635 to 1.645, pleo-.

chroism weak, Z 

slate, X nearly colorless, c/\Z about 25°. 

Strongly pleochroic in

green tints. 

Clear white. 0= 1.620,

cAZ 15°.

Conspicuously zoned, 

alternately anisotropic at Vulcan Hill 

n= 1.700 to 1.82. 

Colorless, or yellow 

to deep red. 

Optically +-_----- ——

«=about 1.720; pleochroic in yellow tints.

o=1.620, 7=1.628—-

Typical- __ ———————

i8=about 1.710.. ..__-_

Typical

a = 1.635jJ=1.648jT*s

1.665, X pale yefiow* 

Y, Z colorless.; 2V 

near 90° » optiea_ly*4vt 

2V about 2T-400 - ^__

In noncaicapeoas »edii-

. Built}-; jMiiiMft 'to 

1.655, W 0. :f!tOM 

chroism - to Seep 

brown. ! 

i8=about 1.690. Beochroism in pale tints 

of brown. 

a= 1.560, 7=1.600, X

yellow, Y, Z greenish 

to pate yellow, 2V 0.

I dentified ;by Gpfttc )»i4$p,:

pleochroism, a-K-Mbit. 

«- 1.660 to 1.670, «—

1.630 to 1.635, Pleochroism from colorless to blue, green, or 

brown. 

£=1.620. Optically -|-

.also — .,',L.' 

^l.MSurGiitMSilIy •*-

•MIL ^'ii'r -•'• * J rr •• ...''»-,' 

Remarks '.-;<; ; i HV HI. .s^frtr?*,*!',*/:'! . •'

: :«- . '; --nui/'j^?: nklt 0«". . .i',-= --(-•-•"• 

•\'. . >5 -ti*'-jJ'*'> O !,'»/• ft fl'J; it,'' t •'

Always found in sma11 anladrens.

, - -o'VVf , "•'' 

•,.".-« , t ., s>.' ' • /;--',;;•

In. roinute priswaatic grftins^ forming felted masses.

»<hh'*,jl- •

Long needle-like crystals in quartz. ;

- . ' .^J< : : r ',' f ' : '

, ;.':,. '.',:-

Composition diflfeis markedly in 

adjacent beds. • ,

In microscopic erystf %, altering to

serpentine. 

Wernerite, found only .in. Maall

crystals.

Disseminated in microscopic anhedrons. One large crystal found. 

In very minute crystals. See Am»

Mineralogist, vol. 10, pp, 187-194, 

1925. 

Microscopic crystals in one specimen of garnet rock. 

In microscopic crystals many of

whick were more or less, altered 

to finely divided m'^firiiw*

In microscopic crystals and »nhedrons. itii»^ ; ,.,,; ; 

/ ' 

Bare accessory in ban spaeiiaatk. ,

Common at the or <* lo^Ji^y in

microseopie cxyrta]^ ,

- ' "'-' - . , * 

- .Very wideepcead. : '

'"•',::i;DB»'- ?'.-" 1

!<J'..' : '/ 4 <i':*

Abundant locally. „„<•*-•- i?,-* •

. ,-. - - -. • - '[' •.iii».4i'1

Bare.

Distinguished from, nxuscovit© by

minute size of flakes* »j^ 'belongs to & later ger oration. 

.Bound ui &sity fltoe sf 'XJijnejiv

. A microscopic cdairtituent in &11

moderately metamorphosed b^d». 

Absent fr4jsa sever^ \aaMwiiorphosed beds except locally.

Widely distributed e/peciaJI^ in thu

moderately metamorphosed beds. 

Do.
CONTACT METAM0BPHISM OF BOCKS IN PEND OEEILLB

Minefals of the contact~metamorphwed rocks of the Pend OreMe d

IDAHO

Mineral

Silicates— Continued 

Antigorite. _ _ _ _ _

Chrysotile _ ___

Heulandite _ __

Unidentified zeolite. 

Titanite_.. __ _

Rock occurrence

Cambrian limestone. _ _

___ do ___

;

_ do ___ „_

All calcareous rocks. ___

Locality

Cliffs along southeast

shore.

view. 

Upper adit of Arcade

group Vulcan Hill. 

-____do--_. _ _ ___ _

General. __.._____ __ _

Properties

j8=l.S5§; birefringence

weak. 

a= 1.500, 7«1.520 __ .

a =1.495, 7= 1.503. Optically -f-j 2V small. 

n=low. Birefringence

0.015. 

Typical.. ________

Eemarks

IB veinlets or as minute mttptf* ia

the limestone. 

Asbestiform material along 8ear-«,

Crystals in open cavities with «nkerite. 

Found with h«ulandit©.

Microscopic crystals locally abundant.

CONCLUSIONS

The conception that contact metamorphism went 

on in stages is simply a division of the long-continued 

process into overlapping periods. The idea oi slages 

in contact metamorphism was* perhaps first suggested 

by Spurr, Garrey, and Fenner 6 and has subsequently 

been advanced by several others. Umpieby 7 used 

the word "stages" in describing the metamorphism at 

Mackay, Idaho, and the idea is also expressed in the 

paragenetic tables of Eckerman.8 The descriptions of 

the Edwards zinc mine by Smyth 9 and by Wade and 

Wandke w speak of stages in the metamorphism.

The knowledge that contact metamorphism was 

produced by a long procession of solutions that came 

out from the igneous rock has succeeded the old idea 

that it was a simple recrystallization of material already 

present, caused by the baking heat transmitted by 

conduction from an adjacent intrusive. This knowledge is of importance not only in itself but also because 

of the light that it throws upon the process of crystallization of the igneous rocks and the nature of the 

residual liquids given off during crystallization.

Although contact metamorphism was not a simple 

recrystallization, this study of the rocks in the Pend 

Oreille district shows that the nature of the original 

rock was a very important factor in determining the 

kind of product resulting from the metamorphism.

• Spurr, J. E., Garrey, G. H., and Fenner, C. N., A contact-metamorphie ore 

deposit; the Dolores mine, at Matehoala, San Luis Potosi, Mexico: Econ. Geology, 

vol. 7, pp. 471-474,1912.

i Umpieby, J. B., Geology and ore deposits of the Mackay region, Idaho: U. 8. 

Qeol. Survey Prof. Paper 97, p. 65,1917.

8 Eckerman, H. von, The rocks and contact minerals of the Mansjo Mountain: 

Geol. Foren. F8rh., 1922, p. 343.

»Smyth, C. H., jr., Genesis of the zinc ores of the Edwards district, St. Lawrence 

County, N. Y.: New York State Mus. Bull. 201, p. 28,1917.

1° Wade, W. E., and Wandke, Alfred, A big zinc mine in New York State: Eng. 

and Min. Jour. Press, vol. 116, p. 96,1923.

It shows further that, except rery locally, the amount 

of material introduced permanently was not grsat 

in proportion to the mass of the rock. The parr genetic sequence of the minerals due to contact m«tamorphism suggests that the progre*| of crystallization 

of the igneous rock and the resulting metamorph;sm 

was somewhat as follows:

1. During intrusion and early crystallization of the 

magma, which marked the first stage, steam carrying 

soda and some potash was given off in considerrhle 

quantity from the whole magma and caused the country rocks to be reerystallized. Limestones <r<*re 

turned to marbles, and sericitic quartzites and siliceous argillites became adinoles. Connate and surface 

water played a part in this recryst&llization.

2. With tiie progress of crystallization of the igneous 

rock, which marked the second stage, the emanations 

given off from the residual liquid became richer in the 

so-called mineralizers. In addition iron, phosphorus, 

zirconia, and silica, probably magnesia, rare earths, 

and titanium, and possibly alumina and potash w«sr© 

also carried. Before this stage was over the igneous 

rock was solid at its borders, endomorphic muscxrdte 

had formed, and throughout the body of the igneous 

rock deuteric titanite, allanite, and probably apatite 

and zircon had crystallized by replacement.

3. After final consolidation of the main masssof the 

intrusive which introduced tl^e third stage, when the 

temperature had become lower, hot waters rich in 

potash and iron and later in carbon dioxide, stilpHur 

and base and precious metals were given off from 

greater depths. Sericite, chlorite, and magneHt© 

formed both in the igneous rock and in the sediments 

and were followed by sulphides, carbonates, and 

zeolites.

O