henry r. cornwall - southern oregon universitysoda.sou.edu/awdata/060113b1.pdf · by henry r....

Chromite Deposits in the Seiad Valleyand Scott Bar quadrangles,Siskiyou County, California

By HENRY R. CORNWALL

CONTRIBUTIONS TO ECONOMIC GE OLOGY

GEOLOGICAL SlTRVEY BULLETIN

A description and economic assessmentof several small chromite deposits I-i

13 8 2 - D

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1981

UNITED STATES DEPARTMENT OF THE INTERIOR

JAMES G. WATT, Secretary

GEOLOGICAL SURVEY

Doyle G. Frederick, Acting Director

Abstract . -- - - --- ...............Introduction . - ...... ...........Geologic settingSeiad Creek chromite deposits -.....

Local geology ..................Chromite deposits .............

Ladd-McGuffy Creek chromite depoaLocal geology .....................Chromite deposits .............

Ladd mine . ...................McGuffy Creek deposits .......

Chemical composition .................Economic significance...............References cited ..

I-LI

Library of Congress Cataloging in Publication Data

CornwaLL, Henry Rowland, 1913-Chromite deposits in the Seiad Valley and Scott Bar

quadrangLes, Siskiyou County, CaLifornia.

(Contributions to economic geoLogy) (GeoLogicaLSurvey buLLetin ; 1382-D)

BibLiography: p. D17Supt. of Docs. no.: I 19.3:1382-D1. Chromite--CaLifornia--Siskiyou County. I. TitLe.

II. Series: United States. GeoLogicaL Survey.Contributions to economic geoLogy. III. Series:United States. GeoLogicaL Survey. BuLLetin1382-D.

QE75.B9 no. 1382-D 557.3s 80-606881[TN490.C4] [553.4'643]

For sale by the Superintendent of Documents, U. S. Government Printing OfficeWashington, D. C. 20402

FIGURE 1-4. Maps showing:1. Generalized geol(

rangles showinghere -- ---.. -.-.--.--

2. Geology and chr(3. Geology and ch

vicinity -- -- .4. Geology and ch

area

TABLE 1. Chemical data for chr(Scott Bar quadrang

CON'FENTS

THE INTERIOR

AbstractIntroduction ----- -- -- -- ................Geologic settingSeiad Creek chromite deposits

Local geology ,...........................Chromite deposits - - --- --- .. ......

Ladd-McGuffy Creek chromite depositsLocal geology -- ---Chromite deposits -- -- .. -- --- -..

Ladd mine -- -- --- -- - --- --..... . ...McGuffy Creek deposits ,...............

Chemical compositionEconomic significance .. - --- ------ -....References cited,.............................

PageDI

11226889

911131617

Director

IlLLtTISTRA 'lIONS

Publication Data

FIGURE 1-4. Maps showing:1. Generalized geology of the Seiad Valley and adjacent quad-

rangles showing locations of chromite deposits describedhere - ...................................... .-------- -.-- - --

2. Geology and chromite deposits of the Seiad Creek area ,,3. Geology and chromite deposits of the Ladd mine and

vicinity -- -- --- - -------,, -,. --- ---- -- -- ,, ,, -- --- -- - ,,------ ...---....----4. Geology and chromite deposits of the McGuffy Creek

area ,. .. - ..

Page

D34

10

12

Ley and Scott BarCaLifornia.

) (GeoLogical

'IABLE

County. I. TitLe.GeoLogicaL Survey.Logy. III. Series:rvey. BuLLetin

Page

TABLE 1. Chemical data for chromite from deposits in the Seiad Valley andScott Bar quadrangles, Siskiyou County, Calif -------,---,-, - --------- D14

80-606881

III

. Government Printing Office

CONTRIBUTIONS TO ECONOMIC GEOLOGY

Chromite deposits in the Seiad Valley andScott Bar quadrangles, Siskiyou County,

California

By HENRY R. CORNWALL.

k B, I RA(. I

(:Chloliticpi sltl)t)hits InI the Se l(;Idrck aild M (Gutlh (:ttek tli.,t cits aitd tIn lcld n1111e.

'siskioul C.otimN, C.ilf , o((tii 1l III dulite-pcldt~ otltl h)Odicts 111,t .11c 1),1lt of .111 ophilOlitl(

atI(e'stiniared to(tl itaoiil 1treat1 \'300,0001 ('rtii( toitsof 1o tk(oilltiilltg airla(li.ag(eof .tllttt 8

pttl(rt( r2 )3 Ii(i(lidl l(hi epottttt mtuNge iii i (-i fts ontf 20(1ito lol35,000) Oettin tott'softo(k aild(ottsistofthlilipaidIllellayetsanidllinear lntes sof( i oniiiteitid ti iiiit' Ih o(ksart folhted

,uiditipait tightlI foltled, ithigetrl1N plun"ging tnirs itlit .tied it10(1 ds. 1 plw11 1

) ( il-sl11e)'(l sca.ns of (Illoillit(', .1aitd tods of (tltitite.

Rcptescriitie ( Iriotirite ojin .ilX (Sof the tltl)(Slti IItlit(,tt (',.1,1gt (t 0(l2(1(0otnirt flIoll

SI to 59 pci( tit and orI (Ci Fe raitio ftor 2 2 to 2 8. A12(l tlirges holir ) to' ( elgllt per t( cnlt.

NIg() II to l1itieglht pet(ltotalt ISe tsC1(2(3 17 to25 xeiglrt pt(tttt.,ttd Ni()( N 0 06 to0.15

wilght pet(clt tii llcoiltsof p).LtiMItitrr-giltil) Ilttt.l1S Ill thhilottitte sauirpleat.12( C t\t ept

for ole sIltItple tha't (olitrlills 0 13 ppml1 platitittirI .11t(i 0.09 pp.t it l 1 hr(tnIrIr.

TIre( outlookfn et t(onoim explolitatiris of tese deposits is trot gootl I liec i(- ttoo sriildI

ar1t(l loss glade to tlliet U S Inloniltite r(qltill(elitrts fol rioole tIlal a setx slsoht I 1( tlo

INTRODUICTION

The chromite deposits in the Seiad Valley and Scott Barquadrangles, Siskiyou County, Calif., constitute the largest reserveof chromite in northern California. They have been described byDiller (1921), Rynearson and Smith (1940), and Wells and others(1949). I studied these deposits during the period 1977-79 in order toreappraise their size, nature, and geologic setting in the frameworkof current geologic concepts of the area.

GEOLOGIC SETTING

The deposits occur in the so-called western Paleozoic andTriassic belt of the Klamath Mountains (Irwin, 1964). The rocksare part of an ophiolitic terrane described by W. P. Irwin (writtencommun., 1978) as follows:"The belt is 300 kilometers long from south to north and is generally between 40 and

80 kilometers wide. On the east the rocks of the belt are thrust beneath Devonian

metamorphic rocks of the central Klamath Mountains, and on the west are

Di

D2 CONTRIBUTIONS TO ECONOMIC GEOLOGY

underthrust by Upper Jurassic flysch and volcanic rocks (Galice Formation). Thebelt consists of both melange and coherent slabs of ophiolite and associated oceanicrocks as well as andesitic volcanic rocks.

In the Seiad Valley-Scott Bar area, the ophiolitic rocks of thewestern Paleozoic and Triassic belt consist of slablike bodies ofdunite and peridotite containing the chromite deposits describedhere enclosed in amphibolite and metasedimentary rocks. Theamphibolite was probably derived from basaltic and andesiticflows, tuffs, and tuffaceous sediments and possibly also gabbros.Intrusive diorite, quartz diorite, and granodiorite of presumableJurassic age also occur in the area.

The rocks of the western Paleozoic and Triassic belt are boundedon the east by a high-angle fault separating them from a largewindow of the Upper Jurassic Condrey Mountain Schist composedof quartz-muscovite schist, commonly graphitic, and actinolite-chlorite schist. Hotz states (1971, p. 13) that: "their lithologysuggests that they were derived from a sequence of pelitic sedi-mentary rocks with some interbedded mafic volcanic rocks." Theseschists are surrounded and overlain structurally along a thrustfault by rocks of the western Paleozoic and Triassic belt, includingthe ultramafic rocks of the Seiad Valley-Scott Bar area. Klein(1977) reports that at Happy Camp, 20 km west of the CondreyMountain area, the Upper Jurassic Galice Formation with lithol-ogy similar to the Condrey Mountain Schist is structurally overlainalong a thrust fault by amphibolite and other rocks of the westernPaleozoic and Triassic belt. He suggests that the Condrey Moun-tain Schist is correlative with the Galice Formation with a slightlyhigher metamorphic grade.

CHROMITE DEPOSII

42r00

41' 45'

e

ct;SEIAD CREEK CHROMITE DEPOSITS

LOC AL GEOLOGV

SDIMENTARY AND ME1ROC KS

Hornbrook Forma;Marlinne sedimentaryI

Albbe epidlte Quart

esenPalel,,l and Tr

Amphiyolite, siliceous Gr stphylltte and schict, argtll;quart.tte, and marble limes

Stuart i ork FormaPhyllitic quartzite, si

phs'llite, metabasalllimestone, and local

The Seiad Creek chromite deposits in the northwest quarter ofthe Seiad Valley quadrangle occur in two tabular ultramaficbodies, one a dunite, the other an harzburgite. The two bodies areseparated by a thin screen of metasedimentary rocks, marble,quartzite, and quartz-mica schist and are surrounded by a largearea of amphibolite (figs. 1 and 2).

The dunite body, called the West Fork dunite by Medaris (1966, p.106), extends north-northwest for 6.4 km; it has a maximumthickness of 3.2 km and tapers at both ends. The greatest concen-trations of chromite in the district occur in this body, one near itssouth end at the Seiad Creek mine and the other near the middle atthe Emma Bell mine (fig. 2). An ultramafic body of harzburgite, the

Central metamorph

Amphibolits, impurecalcareous and si-cs

FIGURE 1.-Generalized geololshowing locations of chro

NOMIC GEOLOGY CHROMITE DEPOSITS IN SISKIYOU COUNTY, CALIFORNIA D3

-anic rocks (Galice Formation). The,s of ophiolite and associated oceanic

l, the ophiolitic rocks of theconsist of slablike bodies ofchromite deposits describedretasedimentary rocks. TheFrom basaltic and andesitics and possibly also gabbros.granodiorite of presumable

nd Triassic belt are boundedparating them from a largey Mountain Schist composedly graphitic, and actinolite-. 13) that: "their lithology

n a sequence of pelitic sedi-mafic volcanic rocks." Thesestructurally along a thrust

c and Triassic belt, includingralley-Scott Bar area. Klein20 km west of the Condrey

Talice Formation with lithol-3chist is structurally overlainnd other rocks of the westernests that the Condrey Moun-ice Formation with a slightly

ITE DEPOSITS

)GV

in the northwest quarter ofin two tabular ultramafic

zburgite. The two bodies aresedimentary rocks, marble,d are surrounded by a large

rk dunite by Medaris (1966, p.L.4 km; it has a maximumh ends. The greatest concen-cur in this body, one near itsI the other near the middle atiafic body of harzburgite, the

42a00'

41-45'

SEDIMENTARY AND METAMORPHICROCKS Eastern Klamath belt

ELHorabrook Formation

Marine sedimetary rocks I

K

a0

K 3 Siltstooe, phylhte, chcrtj Iand limestone -

U-

2E I -

etX Albite-epidste Quarit -m-scoite and a -t;- amphibolite actinsist -chlorite schist 2

U Western Poleozoic and Triassi-belt

Ampbibolite, siliceoasphyllitr and schist,qart eite, and marble

IM

G--fi-, th,,,t,-gflht�, and in-I.-t-

2~

KI

0-zSt

00

IGNLOUS ROCKS

n k

Ultramafic rocksMays be Ordoc ican

near Yreka

'Jo

0:z 2n

a AtI -

St aatt Fork FormationPhyllitic q-aicest, siliceoas

phyllire, meeabasalt, minorlimestone, and locally, bl.enchiol

Central metamorphic belt

Amphibolite, impare marble,calcarnoas and siicesas schist

ContactDashed where inferred

FaualtDashed where inferred

Thrust faaltSareech on upper plate

Cheomite depositI W

FIGURE 1.-Generalized geology of the Seiad Valley and adjacent quadranglesshowing locations of chromite deposits described here (from Hotz, 1979).

CHROMITE DEPOSITSD4 CONTRIBUTIONS TO ECONOMIC GEOLOGY

1231 0'

Landslide deposits Alli

ECondrey M

Quartz-plagic

I

Amphibolite Metasedu

Chromite schhieren

Vertical

Strike and d

A

Base fron U S Geolog ca SurveySe ad Val ev NW 1955

0 5 1 2 K LOMETERI

i I I I0 1 1 MILE

CONTOUR NTERVAL 40 EET

FIGL'RE 2.-Geology and chromite deposits of the Seiad Creek area (modified fromMedaris, 1966).

Kangaroo peridotite of Medaris (1966, p. 106), extends southwestfrom near the middle of the dunite for 4.8 km with a width of 0.8-1.2km. It is separated from the dunite by a thin screen of metasedi-mentary rocks. The small Anniversary chromite deposit occurs inthis harzburgite body just west of the metasedimentary screen.The dunite and harzburgite locally contain scattered lenses andirregular dikes of lherzolite, pyroxenite, and amphibolite (parga-site), most 1-40 cm thick but a few as thick as 25 m. The pyroxeniteconsists of enstatite, augite, or both. These rocks are fresh exceptlocally near the margins of the body where serpentinization maybe pronounced.

The olivine of the dunite and harzburgite is xenoblastic, theindividual grains ranging from 0.15 to 1.4 mm in diameter andaveraging about 0.4 mm. The subhedral chromite grains range

from 0.07 to 0.34 mm in di;massive chromite schliereireach a maximum diametspecimens of the dunite r,density is due mainly to ir

Using the X-ray methodsition of the olivine was fothe samples tested fall in ipositive, 2VW 85°-90°. Sery(<1 mm) veins of chrysotgrains by lizardite. Olivreplaced by purple kaemigreen fuchsite (chrome-be,

The lherzolite and pyroeproportions of enstatite, atare mostly xenoblastic acommon than enstatite. TI

11C GEOLOGY CHROMITE DEPOSITS IN SISKIYOU COUNTY, CALIFORNIA D5

EXPLANATION

Landslide deposits Alluvium

Condrey Mountain Schist

peg

Quartz-plagioclase pegmatite

Metasedimentary rocks

1- QUATERiNARY

Glacial deposits i

I JURASSIC

JURASSIC} OR1 TRIASSIC

< l TRIASSICF-E t AND

PALEOZOICUltramafic rocks

ct FaultDotted where c-ncealed

- 20

Trend and plungeof lineaton

Amphibolite

Chromite schlieren Approximate conta

50-0- -~

Vertical Inclined

Strike and dip of foliation

2 KILOMETERS

' TLE

EET

- X i-i

Adit Pit Opencut

FIGURE 2.-Continued.

;eiad Creek area (modified from

). 106), extends southwestkm with a width of 0.8-1.2i thin screen of metasedi--hromite deposit occurs inmetasedimentary screen.tain scattered lenses andand amphibolite (parga-

k as 25 m. The pyroxeniteese rocks are fresh excepttere serpentinization may

urgite is xenoblastic, the1.4 mm in diameter and

al chromite grains range

from 0.07 to 0.34 mm in diameter and average 0.14 mm. In nearlymassive chromite schlieren, the individual crystals are larger andreach a maximum diameter of 3.5 mm. The specific gravity of 16specimens of the dunite ranges from 3.08 to 4.02; the increase indensity is due mainly to increased proportions of chromite.

Using the X-ray method of Hotz and Jackson (1963) the compo-sition of the olivine was found to range from fo91 0 to fo95 7. Most ofthe samples tested fall in the range fo9 19 4. The olivine is opticallypositive, 2V+ 85°-90°. Serpentinization consists mostly of narrow(<1 mm) veins of chrysotile plus a little replacement of olivinegrains by lizardite. Olivine interstitial to chromite is partlyreplaced by purple kaemmererite (chrome-bearing chlorite) andgreen fuchsite (chrome-bearing mica).

The lherzolite and pyroxenite lenses and dikes contain varyingproportions of enstatite, augite, and locally pargasite. The texturesare mostly xenoblastic and partly porphyritic. Augite is morecommon than enstatite. The grain size ranges from 0.05 to 0.3 mm,


averaging 0.2 mm with phenocrysts as much as 1.0 mm long. Verylittle, or no, chromite is found in these lenses and dikes.

The sparse amphibolite lenses in the dunite and harzburgite aremostly colorless pargasite. Layers and lenses of green hornblendeor pargasite occur near and parallel to the borders of the dunite andharzburgite bodies (Medaris, 1966, p. 120). A typical amphibolitelayer consists of pargasite that is hypidiomorphic porphyritic;crystals in the groundmass average 0.25 mm in length, andphenocrysts are as long as 2 mm, tending to cluster along themargins of the layers.

The dunite and harzburgite are foliated and lineated. In thedunite, foliation is visible only where schlieren and lenses ofchromite, harzburgite, or pyroxenite are present. The lineation,however, is commonly pronounced, even in the dunite. It consistsof pencils of chromite and rods of dunite several centimeters to 1 mthick. Locally, particularly at the Emma Bell mine, chromiteschlieren are tightly folded, and the fold axes are parallel to theother lineations.

Foliation in the dunite strikes northwest and dips 40°- 70°northeast. Lineation in the foliation plane dips from gentlysoutheast to gently northwest. In the harzburgite in the area of theAnniversary mine, the foliation strikes north-northeast and dips30°- 55° W. Lineation is nearly horizontal.

Foliation and lineation in the peridotite bodies are concordant tofoliation and lineation in the surrounding amphibolite, and thetabular peridotite bodies are themselves oriented parallel to thefoliation (Medaris, 1966, p. 41, 60-63). The foliation patterndescribes an antiform (fig. 2); foliation in the east body, the dunite,strikes northwest and dips northeast; that in the harzburgite to thewest strikes northeast and dips northwest. It is clear that thedeformation of the peridotite bodies, which probably were derivedfrom the mantle, must have occurred after their juxtaposition withthe amphibolites and metasedimentary rocks, which probablywere originally deposited in an island-arc environment at or nearthe margin of the North American continental plate.

CHROMITE DEPOSITS

The principal chromite deposits in the Seiad Creek district, inorder of relative size, are the Seiad Creek (Mountain View), EmmaBell, Anniversary (Kangaroo Mountain), and Black Eagle. Alldeposits except the Anniversary occur in the dunite; the Anniver-sary occurs in the harzburgite just west of the dunite.

The Seiad Creek mine, the largest of this group, was minedduring World War I and again during World War II. Production

CHROMITE DEPOSITS ]

amounted to 715 metric to1943-44. The U.S. Bureau (sampling and diamond diSurvey made detailed geooccurs as layers and line;parallel, pencil-shaped seEwest-southeast and dip ab100 SE. According to Webodies of chromite occurfoliation. Individual depoE15-60 m deep. Wells and otreserves of this deposit ator more of Cr203.

The Emma Bell deposchromite schlieren and dextending northwest-soutwide. The overall grade iindividual zones, 5-50 mchromite lenses containstrike northwest-southeasilayers are tightly foldedsoutheast or northwest E

diamond drill holes were (1978 to depths ranging frczones. Mineralization waksurface.

The amount of chromitsecond only to that in the 'individual concentrationseconomic exploitation isinferred tonnage of 10,00'Emma Bell deposit.

The Anniversary (Kanjharzburgite body on the w(fig. 2). The chromite occu55 x 13 x 13 m elongated r15° W. and dips 500 SW.peridotite is dunitic in theand others (1949, p. 45) e:metric tons of indicatedpercent Cr203.

The Black Eagle depositthe Emma Bell in the durpits and an opencut in an E

MIC GEOLOGY

nuch as 1.0 mm long. Veryenses and dikes.iunite and harzburgite are,enses of green hornblendeLe borders of the dunite and20). A typical amphibolitepidiomorphic porphyritic;0.25 mm in length, andLding to cluster along the

ated and lineated. In thez schlieren and lenses of.re present. The lineation,n in the dunite. It consistsseveral centimeters to 1 m

nma Bell mine, chromiteId axes are parallel to the

'thwest and dips 40°--70°plane dips from gently

Lrzburgite in the area of thenorth-northeast and dips

Lal.te bodies are concordant toling amphibolite, and thees oriented parallel to the3). The foliation patternn the east body, the dunite,Lat in the harzburgite to theiwest. It is clear that theiich probably were derivedHer their juxtaposition withry rocks, which probablyirc environment at or neartinental plate.

4TS

he Seiad Creek district, ink (Mountain View), Emmain), and Black Eagle. Allin the dunite; the Anniver-t of the dunite.of this group, was minedWorld War II. Production

CHROMITE DEPOSITS IN SISKIYOU COUNTY, CALIFORNIA D7

amounted to 715 metric tons in 1918 and 2,093 metric tons during1943-44. The U.S. Bureau of Mines explored the deposit by channelsampling and diamond drilling in 1941, and the U.S. GeologicalSurvey made detailed geologic studies at that time. The chromiteoccurs as layers and linear lenses of chromite within which areparallel, pencil-shaped seams of chromite. The layers strike north-west-southeast and dip about 50° NE. The lineations plunge about100 SE. According to Wells and others (1949, p. 51, p. 20), fivebodies of chromite occur in a zone 400 m long parallel to thefoliation. Individual deposits are 60-150 m long, 10-21 m wide, and15-60 m deep. Wells and others (1949) have estimated the indicatedreserves of this deposit at 241,000 metric tons averaging 6 percentor more of Cr2 03.

The Emma Bell deposit consists of discontinuous zones ofchromite schlieren and disseminated chromite grains in duniteextending northwest-southeast for 1,220 m and as much as 60 mwide. The overall grade is low, probably 1-3 percent Cr203, butindividual zones, 5-50 m long and 0.5-3 m wide, of concentratedchromite lenses contain 5-15 percent Cr203. Individual lensesstrike northwest-southeast and dip mostly 45°-85° E. The lensoidallayers are tightly folded locally. Fold axes plunge gently eithersoutheast or northwest as do linear seams of chromite. Threediamond drill holes were drilled by the U.S. Chrome Company in1978 to depths ranging from 96 to 132 m beneath well-mineralizedzones. Mineralization was found to be similar to that seen on thesurface.

The amount of chromite in the Emma Bell deposit is probablysecond only to that in the Seiad Creek deposit described above, butindividual concentrations of chromite are so widely scattered thateconomic exploitation is probably not possible. I estimate aninferred tonnage of 10,000 metric tons at 5 percent Cr203 in theEmma Bell deposit.

The Anniversary (Kangaroo Mountain) deposit occurs in theharzburgite body on the west wall of a northward-draining cirque(fig. 2). The chromite occurs as lenses and linear streaks in a zone55 x 13 x 13 m elongated parallel to the foliation which strikes N.150 W. and dips 500 SW. The lineations plunge 5°-15° NW. Theperidotite is dunitic in the area of chromite mineralization. Wellsand others (1949, p. 45) estimate that the deposit contains 4,760metric tons of indicated and inferred rock containing about 5percent Cr2 03.

The Black Eagle deposit, located about 600 m south-southwest ofthe Emma Bell in the dunite body, has been explored by severalpits and an opencut in an area 150 x 60 m elongated in a northwest-


southeast direction. The deposit consists of layers, lenses, anddisseminations of chromite elongated parallel to the foliationwhich is variable but in general strikes N. 450 W. and dips 70° SW.Linear streaks of chromite plunge about 10° NW. Purple kaem-mererite (Allen, 1941, p. 124) and green amphibole are associatedwith some of the high-grade chromite layers. I estimate that thedeposit may contain 2,700 metric tons of rock that averages 5percent Cr 2O3 .

A small pit containing layered chromite in fresh dunite is located1.3 km west of the Black Eagle deposit, at the west edge of thedunite; it is separated by a fault from amphibolite and metasedi-mentary rocks to the west. This is a small deposit containingpossibly 200-500 tons of chromite with a grade of 10 percent Cr2 O3 .

LADD-McGUFFY CREEK CHROMITE DEPOSITS

LOC(:AL (;EO LOG N'

The Ladd mine is located in the southeast quarter of the SeiadValley quadrangle (figs. 1,3), and the McGuffy Creek deposits are inthe northeast quarter of the Scott Bar quadrangle (figs. 1, 4). Thedeposits occur in an ultramafic complex called the Ladd and TomMartin ultramafic bodies, respectively, by Barrows (1969). Thecomplex extends southeast for 16 km, 3 km west of Hamburg. Itstraddles the Klamath River at its north end and is 2.4-4 km wide(figs. 1, 3, 4). The ultramafic complex is tabular and flat lying tomoderately westward dipping. The Ladd ultramafic body has anareal extent of 7.8 km2 , the Tom Martin 39 km2 (Barrows, 1969).

The Ladd ultramafic body (fig. 3) is distinguished from the TomMartin body (fig. 4) by an abundance of clinopyroxene. Except fora half square mile of dunite surrounding the Ladd chromitedeposit, the body is composed of clinopyroxenite, wehrlite, andlherzolite. The olivine of dunite in the vicinity of the Ladd chromitemine has a composition of fo93 as determined for this study usingthe X-ray method of Hotz and Jackson (1963). Barrows (1969)reports a composition of fo9,. The dunite is 50-100 percent serpen-tinized. According to Barrows (1969), the clinopyroxene in thepyroxene-bearing part of the body is diopside, which is partlyserpentinized. These rocks also contain some amphibole. Barrows(1969) states that, in contrast to the Tom Martin body, the rocks ofthe Ladd body are not foliated, but I observed moderate foliation ofthe dunite at the Ladd chromite deposit. Layers and tabularschlieren of chromite strike northwest and dip steeply northeastand southwest. Olivine crystals are elongated parallel to chromiteschlieren in the foliation plane. The dunite is xenoblastic with

CHROMITE l)EPOSITS

olivine grains 0.3-1.3 mmchromite grains 0.05-0.35

The Tom Martin ultram.a tabular body more thEhornblende-bearing harztthe top and bottom of the 1foliated hornblende har2blende orthopyroxenite, hlite, hornblendite, and gamphibole, is common ne.

The chromite deposits o:near the south end of thEolivine grains 0.05-1.0 mrrnated chromite grains 0.01chromite grains averageschlieren. The compositioimy X-ray determinations.using the same X-ray metdikes in the vicinity of thE

The hornblende harzbupart of the Tom Martin ulnear the center of the bo(hornblende harzburgitehornblende. Barrows (196(normally contains 25-34orthopyroxene and hornblharzburgite and in the boriented parallel owingAccording to Barrows (19(olivine in the harzburgit(Disseminated chromite ihornblende harzburgite. Npresent in parts of the bococcur locally.

At the south end of the Tithe McGuffy Creek chroTabular schlieren and lay40°-60° SW. Lineations, iiaxes and pencillike schl(fig. 4).

CH

The Ladd chromite mir

I

)MIC GEOLOGY

ists of layers, lenses, andI parallel to the foliationN. 450 W. and dips 70° SW.)ut 10° NW. Purple kaem-.amphibole are associatedlayers. I estimate that thes of rock that averages 5

ite in fresh dunite is locatedit, at the west edge of theimphibolite and metasedi-small deposit containing

a grade of 10 percent Cr20 3.

OMITE DEPOSITS

heast quarter of the Seiad!Guffy Creek deposits are inQuadrangle (figs. 1, 4). Thex called the Ladd and Tomi, by Barrows (1969). The3 km west of Hamburg. Ith end and is 2.4-4 km wides tabular and flat lying toid ultramafic body has ani 39 km2 (Barrows, 1969).istinguished from the Tomclinopyroxene. Except for

riding the Ladd chromite)pyroxenite, wehrlite, andcinity of the Ladd chromitemined for this study usingcn (1963). Barrows (1969)e is 50- 100 percent serpen-the clinopyroxene in thediopside, which is partlysome amphibole. Barrows

n Martin body, the rocks oferved moderate foliation of)osit. Layers and tabularand dip steeply northeastigated parallel to chromitelunite is xenoblastic with

l


olivine grains 0.3-1.3 mm across, averaging 0.6 mm, and subhedralchromite grains 0.05-0.35 mm, averaging 0.1 mm.

The Tom Martin ultramafic body is, according to Barrows (1969),a tabular body more than 1,500 m thick composed mainly ofhornblende-bearing harzburgite. The hornblende is pargasitic. Atthe top and bottom of the body are relatively thin complex zones offoliated hornblende harzburgite, hornblende websterite, horn-blende orthopyroxenite, hornblende wehrlite, hornblende lherzo-lite, hornblendite, and gabbro. Dunite, which rarely containsamphibole, is common near the margins of the Tom Martin body.

The chromite deposits of the McGuffy Creek area occur in dunitenear the south end of the body. This dunite is xenoblastic witholivine grains 0.05-1.0 mm across, averaging 0.6 mm, and dissemi-nated chromite grains 0.05-0.3 mm across, averaging 0.2 mm. Thechromite grains average 0.6 mm in diameter in the massiveschlieren. The compositional range of olivine is fo9196 according tomy X-ray determinations. Barrows (1969) reports a range of fo8893using the same X-ray method. I observed clinopyroxenite (augite)dikes in the vicinity of the chromite deposits.

The hornblende harzburgite zone makes up the major interiorpart of the Tom Martin ultramafic body. Some harzburgite existsnear the center of the body, but most of it has been modified tohornblende harzburgite with more than 5 percent pargasitichornblende. Barrows (1969) states that the hornblende harzburgitenormally contains 25-34 percent hornblende. Phenocrysts oforthopyroxene and hornblende, 1-5 mm long, occurring both in theharzburgite and in the hornblende harzburgite, are commonlyoriented parallel owing to a moderate foliation of the body.According to Barrows (1969), the range of forsterite content of theolivine in the harzburgite and hornblende harzburgite is fo89s 95.Disseminated chromite is ubiquitous in the harzburgite andhornblende harzburgite. Magnetite and aluminous spinel are alsopresent in parts of the body. Amphibole-clinopyroxene dikes alsooccur locally.

At the south end of the Tom Martin ultramafic body in the area ofthe McGuffy Creek chromite deposits, the dunite is foliated.Tabular schlieren and layers of chromite strike northwest and dip40°-60° SW. Lineations, indicated by mullions in dunite, and foldaxes and pencillike schlieren in chromite, plunge 5°-25° NW(fig. 4).

CHROMITE DEPOSITS

LADD MINE

The Ladd chromite mine (fig. 3) is in the Ladd ultramafic body


123°07'30 123°05

41 '50'

CHROMITE DEPOSITS

EAll

Includestenas,

Condrey Mountain ScQuartz-muscovite sc

EQuartz-plagi

Homblende-plagioclase Metavogneiss Greenstone, ,

......

Chromite schlieren

50

Strike and dipof foliation

Base from U S Geoogicai SurveySead Valley SE and SW 1955

5 1 2 KILOMETERS

S '1MILE

CONTOUR INTERVAL 40 FEET

FIGURE 3.-Geology and chromite deposits of the Ladd mine and vicinity (modifiedfrom Barrows, 1969).

north of the Tom Martin ultramafic body (Barrows, 1969). Thebody is mainly wehrlite and lherzolite, but the chromite depositoccurs in dunite in the southwestern part of the body.

The deposit, explored by a number of pits and several short adits,consists of four separate chromite zones (Wells and others, 1949, p.52-53). The largest zone is a flat lens 20 m long, 3-5 m wide, and ofunknown depth. This lens, which strikes northwest-southeast andis nearly vertical, is elongated parallel to foliation as chromitelayers indicate. The chromite lens consists of irregular stringers,indistinct bands, and high-grade disseminations of chromite.Several other similar but smaller chromite lenses occur 45-185 msouth and southwest of the largest lens.

Wells and others (1949, p. 52-53) estimate that the indicated and

FIGU

inferred reserves of the La(of which about 1,800 metr2,900 metric tons is dissconcentrated prior to ship1,915 metric tons of ore ha

McGLtI

The McGuffy Creek chmapped in detail by Wellssouth side of McGuffy Crdunite near the south end ideposits consist of conceniup to 20 cm thick of chrchromite in dunite. The laysouthwest (fig. 4) and are isprominent and is best iioriented rods and schlier

MIC GEOLOGY CHROMITE DEPOSITS IN SISKIYOU COUNTY, CALIFORNIA DlI

123°05 EXPLANATION

QUATERNARYAlluvium

Includes landslide andtenrace deposits

Condrey Mountain SchistQuartz-muscovite schist

W

Granitic rocks


Metavolcanic rocksGreenstone chert. and argillite

Hormblende-plagioclasegneiss

JURASSIC

JURASSIC} OR- TRIASSIC

< 1 TRIASSICL AND

Ultramafic rocks PALEOZOIC

Fault

Adit Pit

Chromite schlieren Approximate contact

50

Strike and dip Trend and plungeof foliation of lineation

KILOMETERS

1 MILE

I FEET


Ladd mine and vicinity (modified9).

)ody (Barrows, 1969). The, but the chromite depositIrt of the body.)its and several short adits,(Wells and others, 1949, p.m long, 3-5 m wide, and ofs northwest-southeast andI to foliation as chromite,ists of irregular stringers,seminations of chromite.nite lenses occur 45-185 m

late that the indicated and

inferred reserves of the Ladd deposit total about 4,700 metric tons,of which about 1,800 metric tons is high-grade shipping ore and2,900 metric tons is disseminated ore that would need to beconcentrated prior to shipping. They also state that, up to 1943,1,915 metric tons of ore had been shipped from the deposit.

McGl!FFY CREEK DEPOSI IS

The McGuffy Creek chromite deposits (fig. 4), studied andmapped in detail by Wells and others (1949, p. 55-62), occur on thesouth side of McGuffy Creek. The deposits occur in an area ofdunite near the south end of the Tom Martin complex (fig. 1). Thedeposits consist of concentrations of layers, lenses, and schlierenup to 20 cm thick of chromite with intervening disseminatedchromite in dunite. The layers strike northwest and dip moderatelysouthwest (fig. 4) and are isoclinally folded. Lineation is commonlyprominent and is best indicated by fold axes and parallellyoriented rods and schlieren of chromite. The lineation plunges


123°05' 123°02'30"41 45'

4,.42'30"

CHROMITE D)EPOSITS I!

AlluviuIncludes talulandslide de,

Condrey Mountain SchistJima. epidote amphiboliteJcms, quartz-muscovite schist

Quartz-plagiodas

Armphibolite Metasediment

Chromite schlieren Apr

- 20Trend and plunge

Base from U S Geological SurveyScott Bar NE, 1955

FIG

0 5 1 2

0 '/r I MILE

CONTOUR INTERVAL 40 FEET

KILOMFETRS

FIGURE 4.-Geology and chromite deposits of the McGuffy Creek area (modifiedfrom Barrows, 1969).

50-250 NW. Foliation and lineation are best displayed in the VetaChica deposit, but they are also present in the other deposits. Thequality of the chromite is good. Five samples analyzed for Wellsand others (1949, p. 41) ranged from 56.83 to 58.58 percent Cr20 3,and Cr:Fe ratio from 2.29 to 2.83.

Production from the McGuffy Creek deposits amounted to 517metric tons during World War I and 46 metric tons during WorldWar II. The deposits were intensively explored during World War IIby the owners with assistance by the U.S. Bureau of Mines and theU.S. Geological Survey. As a result of this exploration, Wells andothers (1949, p. 62) give the following statement of indicatedreserves: "It is indicated that approximately 22,860 metric tons of

ore that will average aboutlarge-scale selective methodEgiven for individual claims

ClaimVeta Chica .................Cerro Colorado..............Veta Grande ...................Grand Falls and GrandMary Lou .......................

Lady Gray - ..........Total ..........................

CHEMICG

Chemical data for 11 samin table 1. SiO2 contents raindicate that small amountsSix samples are from the 'mine, and four from McGu:

IIIC GEOLOGY CHROMITE DEPOSITS IN SISKIYOU COUNTY, CALIFORNIA D13

123°02'30" EXPLANATION

AlluviumIncludes talus andlandslide deposits

I Jcma I Jcnns I

Condrey Mountain SchistJcma, epidote amphiboliteJcms, quartz-muscovite schist

Homblende-quartzdiorite

I QUATERNARY

JURASSIC

JURASSIC} OR- TRIASSIC

TRIASSICAND

- PALEOZOIC


Metasedimentary rocks Ultramafic rocksAmphibolite

Chromite schlieren Approximate contact

- 20Trend and plunge of lineation

50

Strike and dip of foliation

x -

Pit Opencut


2 KILOMETERS

1 MILE

EET

ore that will average about 18 percent of Cr2O3 can be mined bylarge-scale selective methods from the claims in the area." Reservesgiven for individual claims are:

e McGuffy Creek area (modified9).

best displayed in the Vetain the other deposits. Theimples analyzed for Wells.83 to 58.58 percent Cr2O3,

deposits amounted to 517metric tons during World

plored during World War IIS. Bureau of Mines and thehis exploration, Wells andg statement of indicatedately 22,860 metric tons of

Claim

Veta Chica . .Cerro Colorado .. . .Veta Grande ... .Grand Falls and Grand CanyonMary Lou -- .Lady Gray . .

Total.

Metric tons

12,3608,165

907907340181

22,860

CHEMICAL COMPOSITION

Chemical data for 11 samples of nearly pure chromite are givenin table 1. SiO2 contents ranging from 1.4 to 2.6 weight percentindicate that small amounts of silicates are present in the samples.Six samples are from the Seiad Creek area, one from the Laddmine, and four from McGuffy Creek deposits. The Cr2O3 content

1

TABLE 1.-Chemical data for chromite from deposits in the Setad Valley and Scott Bar quadrangles, Siskiyou County, California z

[Weight percent determinations of oxides Cr2O, and NiO determined volumetrically and by atomic absorption, respectively, by A Neuville and P Aruscavage S02,, AIO,, total Fe asFezO,, and MgO determined by rapid-rock analysis by Z A Hamlin Platinum metals determined by Joseph Haffty and A W Haubert using method of Haffty and Riley (1968)Semiquantitive six-step spectrographic analyses determined by Leon A Bradley Values reported are midpoints ofarbitrary brackets G =greater than IC percent L detected but belowlimit of determination -- below limit of determination]

Sample No 'S-4 Sl-5 S1-7 Sl-8 S44 S46-1 L7-2 M2 M2-5 M7-1 M8-1

Oxide analyses (weight percent) O

Cr2,O -- --- 5 4 .6 5 5 .5 5 4 .4 5 5 .8 5 7 .1 5 8 .9 5 4 .3 4 9 .7 5 6 .8 5 5 .2 5 6 .8 -2

NiO .11 .11 .09 .10 .06 .08 .11 .15 .11 .09 .10SiO2 ---- - 2.6 1.4 2.1 1.9 1.8 2.3 2.4 1.5 1.6 2.1 1.7 CA120 3 -- - 6.9 7.0 5.4 6.5 8.8 5.0 6.7 16.3 6.6 5.5 6.4 3Fe2O3

2 21.9 21.2 24.6 22.4 21.4 23.0 21.1 17.4 20.5 23.3 20.6 °MgO. . 14.3 13.3 12.6 13.2 11.9 11.1 13.9 15.5 13.8 12.7 13.4 u

Platinum metals (ppm) °

Pd - <.004 <.004 <.004 <.004 .019 .004 .005 <.004 <.004 <.004 <.004 (Pt - - - <.010 <.010 <.010) <.010 .044 .13 <.010 .014 <.010 <.010 <.010 °Rh . .018 .019 .010 .022 .027 .069 .024 .020 .013 .013 .021 O

Semiquantitative spettrographik analyses

(weight percent) 0

Si ... ... ....... 3. 3. 10. 5. 3. 3. 3. 3. 1.5 3. 3. rAl ..... ......... 7. 7. 3. 3. 5. 5. 7. G 7. 3. 7. OFe 7. 10. 7. 7. 7. 10. 7. 7. 7. 7. 7.Mg 10. 10. G 10. 10. 7. G G 10. 10. 10.Ca .. .. ----- .15 .15 .07 .15 .07 .07 .07 .005 .005 .007 .03Ti .07 .1 .05 .07 .07 .03 .07 .07 .1 .07 .07

(ppm)

Mn 300 300 500 300Ba . . . ..Co - .. 200 200 150 200Cr ------ - G G G GCu. 3 7 5 5Ni . .. 1,500 1,000 1,500 1,500Pb - 15 ......Sc . . 10 10 7 10V - 500 500 200 500Ga 15 15 15 15

500 700 300 300 300 300 70015 .. .

200 500 300 200 300 150 150G G G G G G G7 L 50 2 7 15 7

700 700 1,500 1,500 1,000 1,500 1,500

0

0

cjn

rA7 10700 700

15 15

15700

15

7700

15

10

70015

7 10300 700

15 15

Rh .018 .019 .010 .022 .027 .069 .024 .020 .013 .013 .021 O

ii( analyses nSemiquantitative spectrograpl

(weight per(ent)

Si. .............. 3. 3. 10. 5. 3. 3. 3. 3. 1.5 3. 3.Al -- 7. 7. 3. 3. 5. 5. 7. G 7. 3. 7.Fe.. .... .. ..... 7. 10. 7. 7. 7. 10. 7. 7. 7. 7. 7.Mg --- 10. 10. G 10. 10. 7. G G 10. 10. 10.Ca .15 .15 .07 .15 .07 .07 .07 .005 .005 .007 .03Ti ........... .07 .1 .05 .07 .07 .03 .07 .07 .1 .07 .07

0

r,000

(ppm)

Mn ............. 300 300 500 300 500 700 300 300 300 300 700Ba --------------- ------ ...... .. ... .. ... 15 ------ ------ . . ........ .Co ............. 200 200 150 200 200 500 300 200 300 150 150Cr ............... G G G G G G G G G G GCu .....- 3 7 5 5 7 L 50 2 7 15 7Ni . . 1,500 1,000 1,500 1,500 700 700 1,500 1,500 1,000 1,500 1,500Pb 15 ...... ------ . . . . ...Sc ........... 10 10 7 10 7 10 15 7 10 7 10V ............ 500 500 200 500 700 700 700 700 700 300 700Ga . ........... 15 15 15 15 15 15 15 15 15 15 15

Ratio Cr:Fe

Cr ............. 37.4 38.0 37.2 38.2 39.1 40.3 37.1 34.0 38.9 37.8 38.9Fe ........ ..... 15.3 14.8 17.2 15.7 15.0 16.1 14.8 12.2 14.3 16.3 14.4Cr/Fe ........... 2.44 2.56 2.16 2.44 2.61 2.50 2.52 2.79 2.71 2.32 2.70

'Sample No: Sl-4, -5, -7, -8, Selad Creek mine, S44, Black Eagle deposit, S46-1, Anniversary deposit, L7-2, Ladd mine, M2, ,M2-5, M8-1, Veta Chica deposit, M7-1, Bluestone depositiTotal Fe calculated as FeOO.

F.


ranges from 54.4 to 58.9 weight percent except for one McGuffyCreek sample (M2) that contains only 49.7 weight percent. Thissample contains about twice as much Al2 03 (16.3 weight percent)as the other samples; the A1203 must be in the chromite rather thanfrom included silicates, because the SiO2 content is only 1.5 weightpercent. NiO ranges from 0.06 to 0.15 weight percent; MgO rangesfrom 11.1 to 15.5 weight percent. Total iron calculated as Fe2O3ranges 17.4 to 24.6 percent. The Cr/Fe ratio ranges from 2.16 to 2.79and is mostly greater than 2.4.

The assays for platinum-group metals are all low and notnoteworthy except for sample S46-1 from the Anniversary deposit,Seiad Creek area. This sample contains 0.13 ppm platinum and0.069 ppm rhodium; these high contents suggest that other chro-mite deposits in the Seiad district may have anomalous amounts ofplatinum-group metals.

ECONOMIC SIGNIFICANCE

The outlook for economically feasible exploitation of the chro-mite deposits discussed here in the Seiad Valley and Scott Barquadrangles is not good for the foreseeable future. The deposits aretoo small and low grade to meet the U.S. chromite requirements formore than a very short period (Thayer, 1973). The largest singledeposit, located at Seiad Creek, is 135,0U0 metric tons containingabout 6 percent Cr2 03. The McGuffy Creek and the Ladd depositsrange from 200 to 12,000 metric tons each; the grade is higher thanat Seiad Creek, probably 15-20 percent Cr2O3. The Cr/Fe ratio forall of the deposits would probably average close to 2.5.

The deposits described here are disseminated; the chromitewould have to be concentrated to be economically recovered. Adeposit consists of a number of layers and schlieren 1-5 cm thick, ofmassive or abundant chromite separated by similar or greaterthicknesses of dunite, which is barren or contains scatteredchromite grains. Although the largest disseminated deposit foundthus far by exploration contains about 135,000 metric tons ofmineralized rock, most are less than 15,000 metric tons. The totaltonnage is probably close to 300,000 metric tons averaging about 8percent Cr2 03.

The economically minable chromite deposits found elsewherecontain pods and layers of massive chromite thick enough so thatnearly pure chromite can be mined from them. Most of the high-grade, high Cr/Fe chromite reserves are in Rhodesia and SouthAfrica. An average deposit there contains at least 1,000,000 metrictons (Cotterill, 1969, p. 174) of ore with Cr/Fe of 3.0 or more

CHROMITE DEPOSIT'

(Cotterill, 1969, p. 171-1'reserves, 1-5 million meTurkey, the Phillippino(Thayer, 1973, p. 117-118

REAllen, J. E., 1941, Geological ir

California Journal of MineAnhaeusser, C R., 1974, Arci

Geology Research Unit, Umation Circular 91, 38 p.

Barrows, A. G, Jr., 1969, GeolCounty, California, and peAngeles, University of Cal

Cotterill, P., 1969, The chromiteed., Magmatic ore deposits

Diller, J. S., 1921, Chromite in t-Geological Survey Bulletin

Haffty, Joseph, and Riley, L. Brhodium in geologic mateTalanta, v. 15, p. 111-117.

Hotz, P. E , 1971, Geology olCalifornia and Oregon: U.'

1979, Regional metamoricentral Klamath MountainPaper 1086, 25 p.

Hotz, P. E., and Jackson, E. Icomposition Fos 0 95 from stSurvey research 1962: U-SE101- 102.

Irwin, W. P., 1964, Late MesozoCalifornia and southwest(Paper 501-C, p. C1-C9.

Klein, C. W., 1977, Thrust plalHappy Camp, California: S]Division of Mines and Geol

Medaris, L. G., Jr., 1966, GeoCalifornia, and petrologyUniversity of California, P

Rynearson, G A., and Smitlquadrangle, Siskiyou Cou922-J, p. J281-J306.

Thayer, T. P., 1973, Chromium,mineral resources: U S. Ge(

Wells, F. G., Smith, C. T., Rynedeposits near Seiad and MGeological Survey Bulletin

1IC GEOLOGY

except for one McGuffy9.7 weight percent. This

1203 (16.3 weight percent)the chromite rather than

content is only 1.5 weightght percent; MgO rangesiron calculated as Fe2 03io ranges from 2.16 to 2.79

ils are all low and notthe Anniversary deposit,0.13 ppm platinum andsuggest that other chro-

ve anomalous amounts of

ANCE

exploitation of the chro-id Valley and Scott Bare future. The deposits arehromite requirements for1973). The largest single0 metric tons containing?k and the Ladd deposits; the grade is higher than'r2 03. The Cr/Fe ratio forre close to 2.5.;eminated; the chromiteonomically recovered. Aschlieren 1-5 cm thick, ofed by similar or greateri or contains scattered;seminated deposit foundL 135,000 metric tons of100 metric tons. The totalic tons averaging about 8

leposits found elsewherenite thick enough so thati them. Most of the high-] in Rhodesia and Souths at least 1,000,000 metrich Cr/Fe of 3.0 or more


(Cotterill, 1969, p. 171--172; Anhaeusser, 1974, p. 18). Substantialreserves, 1-5 million metric tons of high-grade ore, also occur inTurkey, the Phillippines, Malagasy, India, Iran, and Brazil(Thayer, 1973, p. 117-118).

REFERENCES CITEDAllen, J. E., 1941, Geological investigation of the chromite deposits of California:

California Journal of Mines and Geology, v. 37, no. 1, p. 101- 167.Anhaeusser, C. R., 1974, Archean metallogeny in southern Africa: Economic

Geology Research Unit, University of Witwatersrand, Johannesburg, Infor-mation Circular 91, 38 p.

Barrows, A. G., Jr., 1969, Geology of the Hamburg-McGuffy Creek area, SiskiyouCounty, California, and petrology of the Tom Martin ultramafic complex: LosAngeles, University of California, Ph. l). thesis, 301 p.

Cotterill, P., 1969, The chromite deposits of Selukiwe, Rhodesia, in Wilson, H. D. B.,ed., Magmatic ore deposits. Economic Geology, Monograph 4, p. 154- 186.

Diller, J. S., 1921, Chromite in the Klamath Mountains, California and Oregon: U.S.Geological Survey Bulletin 725, p. 1-84.

Haffty, Joseph, and Riley, L. B., 1968, Determination of palladium, platinum, andrhodium in geologic materials by fire assay and emission spectrography:Talanta, v. 15, p. 111-117.

Hotz, P. E., 1971, Geology of lode gold districts in the Klamath Mountains,California and Oregon: U.S. Geological Survey Bulletin 1290, 91 p.

1979, Regional metamorphism in the Condrey Mountain quadrangle, north-central Klamath Mountains, California: U.S. Geological Survey ProfessionalPaper 1086, 25 p.

Hotz, P. E., and Jackson, E. D., 1963, X-ray determinative curve for olivines ofcomposition Fo8 0 9, from stratiform and alpine-type peridotites, in GeologicalSurvey research 1962: U.S. Geological Survey Professional Paper 450-E, p.E101- 102.

Irwin, W. P., 1964, Late Mesozoic orogenies in the ultramafic belts of northwesternCalifornia and southwestern Oregon: U.S. Geological Survey ProfessionalPaper 501-C, p. C1-C9.

Klein, C. W., 1977, Thrust plates of the north-central Klamath Mountains nearHappy Camp, California: Short contributions to California Geology, CaliforniaDivision of Mines and Geology Special Report 129, p. 23-26.

Medaris, L. G., Jr., 1966, Geology of the Seiad Valley area, Siskiyou County,California, and petrology of the Seiad ultramafic complex: Los Angeles,University of California, Ph. D. thesis, 333 p.

Rynearson, G. A., and Smith, C. T., 1940, Chromite deposits in the Seiadquadrangle, Siskiyou County, California U.S. Geological Survey Bulletin922-J, p. J281-J306.

Thayer, T. P., 1973, Chromium, in Brobst, D. A., and Pratt, W. P., eds., United Statesmineral resources: U.S. Geological Survey Professional Paper 820, p. 111- 121.

Wells, F. G., Smith, C. T., Rynearson, G. H., and Livermore, J. S., 1949, Chromitedeposits near Seiad and McGuffy Creeks, Siskiyou County, California: U.S.Geological Survey Bulletin 948- B, p. B19-B62.