geology of the Northwest Quarter of the Anaconda .../67531/metadc958035/...Geology of the Northwest Quarter of the Anaconda Quadrangle Deer Lodge County, Montana By ALEXANDER A. WANEK

geology of theNorthwest Quarter of the

Anaconda QuadrangleDeer Lodge County, Montana

LOGI C AL SUR VEY BU L LET IN 1222-B

Geology of theNorthwest Quarter of theAnaconda QuadrangleDeer Lodge County, MontanaBy ALEXANDER A. WANEK and C. S. VENABLE BARCLAY

CONTRIBUTIONS TO ECONOMIC GEOLOGY

G E OL OGI C AL S U R VEY BU L LE

Geology and mineral resources of partof the Anaconda quadrangle nearButte, Montana

T I N 1222-B

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UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON :1966

UNITED STATES DEPARTMENT OF THE INTERIOR

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY

William T. Pecora, Director

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

CONTENTS

PageAbstract-_-_.-_-------------------_--________-----__-____________BLIntroduction_ -------------------------- _______- -_______ ----------- 2Stratigraphy------------------------------------ _____________ .- .. .. 4

Precambrian System-----------------------------------------5Newland Formation_------_------_------_-___-. ____- __________ 5Spokane Formation---. -------- ---- _ -__ -___ -_-_-------.._--6

Cambrian System-- - -- - - -- - -- - - -- - -- - - - --- ___.______..____ _______._____________ 7Flathead Quartzite-_---- _--..--_..--_ ----_------_-----_-- ______ ___ 7

Cambrian and Devonian rocks not exposed-_--------_----.-.-_----.--_--.-__ _ 7Mississippian System-- -------------------------------------- 8

Madison Limestone--------------------- ---------------- 8Mississippian and Pennsylvanian Systems..--_-----_ -- _-----..____. . 9

Amsden Formation---------------------------------_-_ _____ __-._ 9Pennsylvanian System----------------- -----------------..--- 10

Quadrant Formation-__-.--------_-_--...--_-_-.. --. ____.. _..__----10Permian, Jurassic, and Cretaceous rocks not exposed.... ------..- ___ 10Cretaceous System---..----------_--_---------.---_---_----.-__ . _ _.... -.----11

Colorado Shale...-.----------..---------..----__ _ . --- _-__-_-.-_-_--..-_11Tertiary System...-....-------------- -------------------- _ .. __ ....__ __ 12

Lowland Creek Volcanics.--..-------- ---..--.. -- _...____..__-.----12Conglomerate-.....----------------------------------.-- 15Gravel-------.--.----..-------- _--- _---_--------- ---- -- . 16

Quaternary System .... - - --.....- - ------.. _____._....... ..... ___- 17

Igneousrocks------------------------------------------------- 18Granite and diorite-..-..--....-------..---- ---------..-----..------ 18Andesite or trachyandesite plugs------- --- _. ___..-_- - -------..-..-- 20

Geologic structure----..---....-------..-------------.-..--........... ._ 22Late Cretaceous and early Tertiary deformation..--.-.....-...--------- _ 22Late Tertiary deformation.-----.. --------- ....-. _---------....--24

Economic geology _---- _-----.-...-.---_--_-----_--------_--------_ _ _ _------24Coal----.. --.-----..-.----.. --------- --..-.---------..--- _-_ - ____ _.. 24Giland gas-------------____________------.-----.--___-_----25Phosphate---_-----_ -- __----_--_----------_--______________--25Gold__-____-------__ ---- __-----------_---_------__-._._______ 26Limestone--_-_---.. ------_-_.--_-_--...------------------ ___. - ... _____ 26Fire clay-----_-----------__------------_--_--_..---..-.-----.._______ 26Gravel_-----.-..---..-----_----_--.--------------__-_--__--26

References cited--------- - ___-- ----------._ ----------... ---____...----27

ILLUSTRATIONS

[Plates are in pocket]

PLATE 1. Geologic map and section of the northwest quarter of the Anacondaquadrangle.

2. Generalized stratigraphic section of the northwest quarter of theAnaconda quadrangle.

PageFIGURE 1. Location map----_----------.- ------------------------- B3

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CONTRIBUTIONS TO ECONOMIC GEOLOGY

GEOLOGY OF THE NORTHWEST QUARTEROF THE ANACONDA QUADRANGLE,DEER LODGE COUNTY, MONTANA

By ALEXANDER A. WANEK and C. S. ENABLE BARCLAY

ABSTRACT

The northwest quarter of the Anaconda quadrangle covers about 52 squaremiles in Deer Lodge County in southwestern Montana. This quarter of thequadrangle includes the southeastern part of the Flint Creek Range, the extremenortheastern part of the Anaconda Range, and part of the west side of DeerLodge Valley.

Rocks of Precambrian, Cambrian, Mississippian, Pennsylvanian, Cretaceous,Tertiary, and Quaternary age are exposed in the quadrangle. Certain units ofCambrian, Devonian, Permian, Jurassic, and Cretaceous age are present in thesubsurface but are missing at the surface because of faulting. The stratigraphicunits are exposed in normal succession in the adjoining Philipsburg quadrangle.

The Eocene rocks are divided into a threefold volcanic sequence correlatedwith the Lowland Creek Volcanics exposed near Butte, Mont. These Eocenerocks are overlain by a conglomerate unit of probable Miocene age and beveledby gravel of middle Pliocene age. Coal beds are in the volcanic breccia and red-bed member, which is the youngest unit of the Lowland Creek Volcanics, andin the overlying conglomerate unit.

Glacial moraine deposits are along Lost Creek. Colluvium and landslide de-posits occur along steep slopes above the valleys, and alluvium and terracegravel are along stream channels.

In general, the Precambrian and Paleozoic rocks crop out in the northwest-ern part of the quadrangle, where they are thrust faulted against Mesozoicstrata and intruded by granite along zones of faulting. The major deforma-tion occurred in Late Cretaceous or early Tertiary time, and periods of minordeformation followed during the Eocene, Miocene (?), and the Pliocene Epochs.Tertiary strata consecutively bevel the older rocks and in many places are infault contact with them.

Granitic intrusions were concurrent with the thrusting and penetrated Pre-cambrian, Paleozoic, and Mesozoic strata. Later intrusions consisted of ande-site plugs emplaced in Eocene and Miocene (?) rocks in the valley of WarmSprings Crock.

Coal and other mineral resources in the area have not been exploited. Thecoal beds are thin and composed of lignite and are of no economic value.Phosphate occurs in the Phosphoria Formation at depths greater than 2,000feet below the surface. Gold mining has been abandoned. The gravel depositsare utilized in highway construction and in concrete aggregate,

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B2 CONTRIBUTIONS TO ECONOMIC GEOLOGY

INTRODUCTION

The northwest quarter of the Anaconda quadrangle covers an areaof about 52 square miles in Deer Lodge County in southwestern Mon-tana. The south and north boundaries are at lat 46*O7'30"~ N. and46*15' N., respectively, and the east and west boundaries are at long112*52'30"~ W. and 113* W., respectively (p1. 1). The town of Ana-conda, Mont., is in the southwestern part of the report area. U.S.Highway 1OA connects Anaconda, Philipsburg, and Butte, Mont.Deer Lodge, Mont., the county seat, lies about 10 miles north of thenortheast corner of the quadrangle in Deer Lodge Valley and can bereached via U.S. Highways 1OA and 10 from Anaconda. Jeep trailsand several good gravel roads serve the area. The Chicago, Milwau-kee, St. Paul, and Pacific Railroad and the Northern Pacific main linetraverse Deer Lodge Valley from Butte north to the cities of DeerLodge, Missoula, and Helena. The Butte, Anaconda, and Pacific Rail-road operates a spur track between Butte and Anaconda to haul oreconcentrates and processing materials for the Anaconda smelter.Several commercial airlines maintain airport facilities at Deer Lodgeand Butte.

Physiographically, the northwest quarter of the Anaconda quad-rangle is divisible into three areas: the east slope of the Flint CreekRange, part of the north slope of the Anaconda Range, and partof the west side of Deer Lodge Valley (fig. 1). The foothills of theFlint Creek Range are rounded and grass covered and rise abruptlyfrom the floor of the valley. They merge in the west with the rug-ged central peaks of the range. South of the valley of Warm SpringsCreek, the relief is great, and the land surface rises steeply to thecrest of the Anaconda Range. The floor of Deer Lodge Valley isflat and surfaced by dissected terraces that slope eastward to thealluvial plain of the Clark Fork of the Columbia River.

All drainage in the area is tributary to Clark Fork of the ColumbiaRiver, which flows northward through the Deer Lodge Valley. Peren-nial streams such as Lost Creek, Warm Springs Creek, AntelopeCreek, and other smaller streams drain the east slope of the FlintCreek Range and the north slope of the Anaconda Range.

Deer Lodge Valley lies in the rain shadow of the Flint Creek andthe Anaconda Ranges. Mean annual precipitation ranges from ap-proximately 10 inches at Deer Lodge to 13 inches at Anaconda. Partof the land in the valley is irrigated, and an abundant crop of potatoesis raised annually. Much of the foothills is used for grazing cattleand sheep. The higher slopes of the Flint Creek Range are cov-ered by heavy stands of lodgepole pine and some Engelmann spruce(Picea engelmanni). Logging operations began in 1961, and all thecut timber is processed at the sawmill in Deer Lodge.

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GEOLOGY, ANACONDA QUADRANGLE, MONTANA B3

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Several geologists have worked in the Anaconda quadrangle or ad-jacent areas. Douglass (1909) made a reconnaissance in which hestudied the Tertiary history of Montana and the occurrences of Terti-ary rocks just east of the Philipsburg quadrangle. Emmons andCalkins (1913) and Calkins and Emmons (1915) studied the geologyand the ore deposits in the Philipsburg quadrangle and reported onthe western part of the Anaconda quadrangle. Pardee (1913) in-cluded the quadrangle in his coal investigations of the Tertiary lakebeds of southwestern Montana. Pardee (1917), in connection withstudies of the Garrison and Philipsburg phosphate fields, describedbriefly the stratigraphy and structure of the Flint Creek Range. Areconnaissance of the quadrangle was made for the geologic mapof Montana (Ross and others, 1955). Alden (1954) correlated theglacial geology of the Flint Creek Range with adjacent areas in west-ern Montana. McGill (1959), Mutch (1960), and Gwinn (1961)mapped the geology of parts of the Flint Creek Range and the Drum-mond quadrangle. Ruppel (1961) made a reconnaissance study of thegeology and mineral deposits of the Deer Lodge quadrangle. Koni-zeski, McMurtrey, and Brietkrietz (1961) made a preliminary reporton the ground water resources of the northern part of the Deer LodgeValley. Smedes (1962) correlated the Tertiary volcanics of the Buttearea with the volcanic rocks near Anaconda.

The present investigation was done in 1961 and 1962 as part ofthe geologic quadrangle mapping and land classification program ofthe U.S. Geological Survey. A. F. Bateman, Jr., contributed val-uable geologic information and criticism during this investigation.

Geologic mapping was done on aerial photographs at a scale of1: 20,000. All geologic and cultural data were plotted on the photo-graphs and later transferred to a topographic base at scale 1: 24,000by inspection or by means of a reflecting projector. Spot altitudes oncontacts, obtained by aneroid barometer surveys, aided in accuratelytransferring the geology to the topographic maps.

STRATIGRAPHY

The sedimentary rocks in the northwest quarter of the Anacondaquadrangle range from late Precambrian to Tertiary in age (p1. 2).In general, Precambrian and Paleozoic rocks crop out in the north-western part of the quadrangle; they are intruded by granite andfaulted against Mesozoic strata. Mesozoic and Cenozoic rocks are inthe foothills of the Flint Creek and the Anaconda Ranges. Glacialmoraine deposits are along Lost Creek; colluvium and landslide de-posits occur along steep slopes above the valleys, and alluvium andterrace gravel are along stream channels.

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GEOLOGY, ANACONDA QUADRANGLE, MONTANA B

The Silver Hill, H-asmark, and Red Lion Formations of Middle andLate Cambrian age, the Maywood and Jefferson Formations of LateDevonian age, the Phosphoria Formation of Permian age, sedimentaryrocks of Jurassic age, and the Kootenai Formation of Early Cretaceousage are present in the subsurface but are absent at the surface due tofaulting. These rocks are well exposed in the adjacent Philipsburgquadrangle to the west.

PRECAMBRIAN SYSTEM

The oldest rocks exposed are the Newland and Spokane Formationsof late Precambrian age; these two formations have been assignedto the Belt Series ('Walcott, 1899). The Belt rocks occupy about 4square miles in the northwestern part of the quadrangle but are moreextensively exposed in the upper canyon of Lost Creek within the ad-jacent Philipsburg quadrangle to the west. In general, the strata aresilty shale, sandstone, and thin limestone beds that were deposited inshallow seas. The sequence is unconformably overlain by the FlatheadQuartzite of Middle Cambrian age. In places the Belt Series is trun-cated by volcanic rocks of Tertiary age. The aggregate thickness ofthe Belt is about 14,000 feet (Emmons and Calkins, 1913).

Several periods of deformation occurred in the late Precambrian andin the Paleozoic. The most intense deformation, however, was muchlater during the Laramide orogeny in the Late Cretaceous and theearly Tertiary. Compressive folding and intrusion by granite locallyaltered the Precambrian and younger rocks into schist and low-grademetamorphic rock.

NEWLAND FORMATION

The Newland Formation, the older unit in the Belt Series, is wellexposed in the steep cliffs along Lost Creek. Emmons and Calkins(1913, p. 42) believed that the Newland Formation is about 4,500 feetthick in the Philipsburg quadrangle. In the northwest quarter of theAnaconda quadrangle, the calcareous argillaceous strata of the New-land Formation have been altered to hornfels in areas bordering largegranite intrusions. The low-grade metamorphic rocks are very finegrained, siliceous, and dark gray to grayish green. The weatheredstrata show bedding 1-6 feet thick. The "beds" have a banded appear-ance ranging from white to grayish green and are deeply groovedalong pseudobedding planes on the weathered surface. In places therocks are discolored by small masses of limonite and ferromagnesianminerals. The thick beds of purer limestone have been locally alteredto light-gray marble on the divide between Timber Gulch and ModestyCreek in secs. 27, 28, and 34, T. 6 N., R. 11 W.

796-518-6,6--2

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In thin section the limestone of the Newland Formation shows alter-ation to a diopside-quartz-calcite-hornfels which includes minoramounts of plagioclase. Chlorite is probably an alteration product ofdiopside. The accessory mineral is magnetite. The shale beds nearintrusions are altered to greenish-gray and brownish-black scapoliteand diopside-bearing schist.

Emmnons and Calkins (1913, p. 43) stated,The common alteration of the Newland rocks is to dense horufels containing

abundant diopside or amphibole, or both, accompanied by quartz and feldspar,with titanite as a constant accessory. Biotite is commonly present, but subordi-nate to the other magnesian silicates. Residuary calcite may occur in consid-erable or insignificant amount, the maximum proportion which is rarely ap-proached being approximately 50 percent.

Correlation of the Newland Formation with formations in the BeltSeries in other places in Montana and Idaho is tentative. IRoss (1949,1959) correlated the Newland Formation with the Wallace Formationof western Montana and Idaho and with the Siyeh Limestone ofGlacier National Park and adjoining areas. The Newland Formationis conformable and transitional to the overlying Spokane Formation.

SPOKANE FORMATION

The Spokane Formation, the uppermost unit in the Belt Series, isexposed in discontinous outcrops along faults north of Lost Creekand in more extensive outcrops at the head of Timber Gulch. Emmonsand Calkins (1913) estimated that the thickness of the Spokane For-mation ranged from 200 to more than 9,000 feet in the Flint CreekRange and recognized that the variation in thickness is caused by anunconformity at the top of the formation. The Spokane rocks in thearea are medium- to thick-bedded dark-gray impure quartzite inter-calated with dark-green, greenish-gray, and brownish-black cordieriteschist. The quartzites are banded light gray to light greeen, and thedark layers seem to be composed of hematite and biotite. Colorlessmica and amphibole are abundant.

The schistose rocks are brownish gray and contain abundant rounddark protuberances on weathered surfaces. Emmons and Calkins(1913) found that the protuberances are small masses of cordierite andandalusite. Some masses are distinctly crystalline and contain largeflakes of mica.

In the Philipsburg quadrangle, the Spokane Formation exposed inthe canyon of Flint Creek is unaltered medium- to thick-beddedreddish-brown to grayish-orange sandstone and siltstone; the rocksare cross laminated and ripple marked. The reddish color is a char-acteristic feature in distinguishing these strata. The Spokane rocks

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are not resistant to erosion and generally weather into low roundedhills.

Ross (1949) correlated the Spokane Formation with part of thestrata in the Missoula Group and also considered it to be equivalentin part to the "Red Band" of the Siyeh Limestone in Glacier NationalPark (Ross, 1959). The Spokane Formation is unconformably over-lain by the Flathead Quartzite.

CAMBRIAN SYSTEM

FLATHEAD QUARTZITE

The Flathead Quartzite (Peale, 1893) of Middle Cambrian ageforms several isolated outcrops in the northwestern part of the quad-rangle where blocks of the quartzite are preserved along the faults.The quartzite is very resistant to erosion, and west of the mapped areait forms steep cliffs. Emmons and Calkins (1913) estimated the Flat-head Quartzite to be 20--200 feet thick. This unit is cliff-formingmassive- to thick-bedded light-gray to white vitreous quartzite thatlocally is tinted rose by hematite and limonite impurities. The whitevitreous quartzite can be readily distinguished from the gray quartzitebeds in the Spokane Formation.

The base of the Flathead Quartzite was not observed in the north-west quarter of the Anaconda quadrangle. Emmons and Calkins(1913) described an angular discordance between the Flathead and theSpokane Formations near the Carp mine in the Philipsburg quad-rangle. At another locality south of Lost Creek, just west of theAnaconda mapped area, the contact between these formations seemeddiscordant. At that locality the Flathead Quartzite contains a basalconglomerate.

The Flathead is widespread in Montana and northwestern Wyoming,and has been generally recognized as the base of the Paleozic sectionin this region. At most places it rests unconformably on the BeltSeries or older Precambrian schist or gueiss. The rocks of the Spo-kane and the Flathead Formations are believed to have been depositedin shallow-water environments.

The Flathead Quartzite is conformably overlain by the Silver HillFormation, which is not exposed in the Anaconda quadrangle.

CAMBRIAN AND DEVONIAN ROCKS NOT EXPOSED

The rocks above the Flathead Quartzite and below the MadisonLimestone are not exposed at the surface in the northwest quarter ofthe Anaconda quadrangle because of faulting, but they are believedto occur in normal stratigraphic position at depth. The formations

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between the Flathead Quartzite and the Madison Limestone are brieflydescribed herein, but more detailed descriptions of these rocks in thePhilipsburg quadrangle are given by Emmons and Calkins (1913).

The Silver Hill Formation of Middle Cambrian age is 100-600feet thick and consists of light-gray, brown, and greenish-gray calcare-ous shale and intercalated limestone beds that contain thin siliceouslaminae. The Silver Hill Formation is conformably overlain by theHasmark Formation.

The Hlasmark Formation of Late Cambrian age is about 1,000 feetthick and is composed mainly of carbonate rocks. The upper 350 feetand the lower 550 feet consist of cliff-forming thick-bedded light-graydolomite separated by 150 feet of dark-brown shale and nodular lime-stone. The Hasmark Formation is conformably overlain by the RedLion Formation.

The Red Lion Formation of Late Cambrian age is about 280 feetthick and is composed of an upper part of thin-bedded light- to blue-gray limestone which has closely spaced wavy siliceous laminae and alower part of black shale which has some interbeds of olive-green shale,gray-green sandstone, and flaggy red magnesian limestone. The RedLion Formation is unconformably overlain by the MaywoodFormation.

The Maywood Formation of Late Devonian age is about 250feet thick and consists mainly of thin-bedded reddish- and light-graydolomitic limestone intercalated with gray and olive-green calcareousshale. The Maywood Formation is conformable with the overlyingJefferson Dolomite.

The Jefferson Dolomite of Late Devonian age is about 1,000 feetthick and consists mainly of cliff-forming massive light-gray dolomiteand intercalated limestone beds. The formation is conformably over-lain by the Madison Limestone, which crops out at the surface in thequadrangle.

MISSISSIPPIAN SYSTEM

MADISON LIMESTONE

The Madison Limestone (Peale, 1893) of Early and Late Missis-sippian age crops out in a wide belt that crosses Lost Creek near itsconfluence with Timber Gulch in secs. 9, 10, and 15, T. 5N., R. 11W.,and also crops out north of Warm Springs Creek in sec. 17. The unitis about 1,200 feet thick and consists of cliff-forming massive dark-gray fossiliferous limestone containing numerous thin chert layers.Rocks in the lower part of the formation are thin bedded and containsome intercalated shale beds. Beds of light-gray limestone are increas-ingly numerous in the upper part of the formation, and the limestonecomprising these beds is finely crystalline. The abundance of chert

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varies by locality. The chert layers are, in general, irregular massesroughly parallel to bedding and are most abundant in the uppermassive limestone.

Most of the Madison Limestone exposed in the quadrangle is in theupper part of the formation. The strata are fossiliferous, and crinoidstems are the most abundant fossil remains. In localities where therock is altered by contact metamorphism, the Madison Limestone iscoarsely crystalline or marbelized and varies from light gray to verydark gray. White or gray tremolite occurs in the contact zones inabundance.

The lower part of the Madison Limestone is not exposed in the quad-rangle but is well exposed along the highway in the vicinity of SilverLake near Georgetown. The lower part consists of an estimated 300feet of very dense flaggy limestone that is dark bluish gray to nearlyblack. Thin beds of black compact shale are intercalated with thelimestone beds.

G. H. Girty (in Emmons and Calkins, 1913) examined the fossil col-lection from the Madison Limestone in the Philipsburg quadrangleand referred these rocks to the Lower Mississippian. The lower andupper parts of the Madison in Montana and western Wyoming arebelieved by the authors to be correlative with the units mapped as theLodgepole Limestone and the Mission Canyon Limestone, respectively,if the usage of Collier and Cathcart (1922, p. 173) is followed.

The upper part of the Madison Limestone is conformable and grada-tional with the Amsden Formation.

MISSISSIPPIAN AND PENNSYLVANIAN SYSTEMSAMSDEN FORMATION

The Amsden Formation (Darton, 1904) of Mississippian and Penn-sylvanian age forms several isolated outcrops in secs. 4 and 16, T. 5N., R. 11 WV. This formation is about 300 feet thick and near LostCreek consists of slope-forming soft reddish-brown shale interbeddedwith thin grayish-red fossiliferous limestone and medium- to thick-bedded fine- to medium-grained sandstone. The Amsden Formationis overlain conformably by the Quadrant Formation. In sec. 16, southof Lost Creek, the top of the Amsden is concealed by soil cover andits contact with the Quadrant Formation is arbitrarily placed at thebreak in slope below the lowest massive sandstone bed in the Quadrant.Elsewhere in the quadrangle, the Amsden Formation is faulted againstPrecambrian, Paleozoic, and Mesozoic strata. The Amsden is poorlyexposed but the extent of the formation is usually indicated by redfloat.

Emmons and Calkins (1913) included the Amsden Formation asa unit of the Quadrant Formation.

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BlO CONTRIBUTIONS TO ECONOMIC GEOLOGY

PENNSYLVANIAN SYSTEM

QUADRANT FORMATION

Strata assigned to the Quadrant Formation (Peale, 1893) of Penn-sylvanian age crop out in the high ridge between Warm Springs Creekand Lost Creek in sees. 16 and 17, T. 5 N., R. 11 W., and in TimberGulch in sees. 9 and 10, T. 5 N., R. 11 W. The Quadrant is 150-200feet thick and consists of cliff-forming massive light-gray quartziticsandstone that is locally much fractured and cut by veinlets of calciumcarbonate. The massive beds show poorly defined cross-lamination.The sandstone is well sorted, medium grained, and cemented by quartzand some iron oxide. The weathered surface of the sandstone is gen-erally buff. In the quadrangle the base of the Quadrant Formationis usually covered, and the contact is mapped at the break in slope be-low the lowest massive sandstone. Along Timber Gulch the QuadrantFormation is faulted against the Madison Limestone and AmsdenFormation.

In the Philipsburg quadrangle the Quadrant Formation as mappedby Emmnons and Calkins (1913) included units which, in accordancewith present usage, are subdivided into the Amsden, Quadrant, andPhosphoria Formations. Pardee (1917), on the basis of the occur-rence of phosphate, separated the Phosphoria Formation from theQuadrant Formation in the Garrison and Philipsburg phosphatefields. The Quadrant Formation is overlain conformably by the Phos-phoria Formation, which was not found at the surface in the north-west quarter of the Anaconda quadrangle.

PERMIAN, JURASSIC, AND CRETACEOUS ROCKS NOT EXPOSED

The rocks above the Quadrant Formation and below the ColoradoShale are not exposed at the surface because of faulting but are be-lieved to occur in normal stratigraphic position at depth in the north-west quarter of the Anaconda quadrangle. The formations betweenthe Quadrant Formation and the Colorado Shale are briefly described.More detailed descriptions of these rocks in the Philipsburg quad-rangle are given by Emmons and Calkins (1913).

The Phosphoria Formation (Richards and Mansfield, 1912) ofPermian age ranges from 150 to 200 feet in thickness. The lowerpart consists of interbedded cherty limestone, black calcareous shale,and a thin dark-gray oolitic phosphate bed, and the upper part ismassive- to thick-bedded gray to grayish-orange quartzitic sandstoneand some thin beds of soft calcareous shale. The Phosphoria Forma-tion is unconformably overlain by sedimentary rocks of Jurassic age.

The sedimentary rocks of Jurassic age are about 400 feet thick;the lower part consists of black calcareous shale interbedded with

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GEOLOGY, ANACONDA QUADRANGLE, MONTANA Bl

limestone and is overlain by thin- to thick-bedded grayish-green todark-gray sandstone containing a few beds of chert conglomerate.The sedimentary rocks of Jurassic age are overlain unconformably bythe Kootenai Formation.

The Kootenai Formation (Fisher, 1909) of Early Cretaceous age isabout 1,500 feet thick and consists in the lower part of a basal cliff-forming reddish-brown to grayish-green conglomerate which is over-lain by 500 feet of reddish-brown and grayish-green shale and inter-calated thick-bedded dark-gray limestone. The upper part is chieflyreddish-brown and greenish-gray shale and gray limestone and con-tains abundant fresh-water gastropods.

The Kootenai Formation is conformable and gradational with theoverlying Colorado Shale, which is widely distributed at the surfacein the quadrangle.

CRETACEOUS SYSTEM

COLORADO SHALE

Strata of the Colorado Shale (Hayden, 1876, p. 45) of Early andLate Cretaceous age are exposed in a northward-trending outcropin the central part of T. 5 N., R. 11 W. The base of the ColoradoShale is not exposed in the mapped area, and the top of the forma-tion is beveled by erosion and overlain unconformably by Tertiaryvolcanic rocks. The Colorado Shale is about 1,500 feet thick in thePhilipsburg quadrangle (Emmons and Calkins, 1913)

The lower part of the Colorado Shale is predominantly dark-grayto grayish-brown calcareous shale interbedded with siltstone and thinlimestone beds. Overlying these strata are several massive cliff-form-ing dark-gray to grayish-brown quartzitic chert-pebble conglomeratebeds. The conglomerate beds crop out in the hogback immediatelywest of the quarry on Lost Creek in the NW1/NW1M sec. 25, T. 5 N.,R. 11 W. Here, these beds are truncated by basal Tertiary strata, andthe erosion channeling along the unconformity is well exposed in theoutcrops in the NW1/NW1A sec. 25 behind the ranchhouse.

The upper part of the Colorado shale consists of thick-bedded dark-gray coarse-grained sandstone intercalated with thin dark-gray toolive-green shale beds. Near the top the sequence grades into thickdark-greenish-gray siltstone, black calcareous shale, and some thinflaggy limestone A few thin pebbly quartzitic sandstone beds areexposed in a shallow pit in NE1/4 E1/ sec. 10, T. 5 N., R. 11 W. Thethick-bedded sandstone in the upper part is dark gray on a freshsurface and weathers brown. The sand grains are chiefly quartz,black chert, and feldspar. The shale zone in the formation weathersinto rounded hills and into sharp ridges where quartzitic sandstoneis present.

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In general, the strata of the Colorado Shale are folded, faulted,and locally altered to phyllites and quartzites. Collections of fossilsfrom this area are few, and the formation was not separated into units.Gwinn (1961) estimated the thickness of the Colorado Group of Earlyand Late Cretaceous age in the Drummond quadrangle to be 9,170-11,500 feet. He divided the Cretaceous rocks that are younger thanthe Kootenai Formation and correlated these units with the ColoradoGroup described by Cobban and others (1959) on the Sweetgrass archin western Montana and with the Colorado Formation described in thesouthern Elkhorn Mountains by Klepper, Weeks, and Ruppel (1957).

The Colorado Shale is overlain unconformably by strata of theLowland Creek Volcanics.

TERTIARY SYSTEM

LOWLAND CREEK VOLCANICS

The Lowland Creek Volcanics of early Eocene age (Smedes andThomas, 1965) crops out extensively in the mapped area (p1. 1).Smedes (1962) reported that these volcanic rocks are distributed over600 square miles in Jefferson, Silver Bow, Deer Lodge, and PowellCounties, Mont. The type locality is Lowland Creek in the Elk Parkquadrangle northeast of Butte, Mont., where the stratigraphic andstructural relations of the rocks were first determined.

The Lowland Creek strata are at the surface in the barren foot-hills of the Flint Creek and the Anaconda Ranges (fig. 1) and are wellexposed along the valleys of Warm Springs Creek, Lost Creek, andAntelope Creek in the northwest quarter of the Anaconda quad-rangle. The rocks have an aggregate thickness in excess of 4,000feet and consist predominantly of intercalated beds of volcanic breccia,quartz latite flows, ash-flow tuff, welded tuff, and sedimentary strata.

The Lowland Creek Volcanics in the mapped area has been dividedinto three members. In ascending order they are the basal member,the ash-flow tuff member, and the volcanic breccia and red-bed mem-ber. These members correlate generally with units described bySmedes (1962). The basal member, locally as much as 400 feet thick,consists of massive- to thick-bedded grayish-brown cross-laminatedarkose, lenticular conglomerate beds that contain abundant volcanicpebbles, and gray to buff tuffaceous siltstone and claystone beds. Abasal conglomerate is present locally.

The unconformity between the Colorado Shale and the basal mem-ber is well exposed in the cliff behind the ranchhouse in sec. 25, T. 5N., R. 11 W. Here, the basal conglomerate which consists of bouldersof decomposed granite, volcanic rocks, and quartzite cobbles, rests onan erosion surface that has more than 50 feet of relief. Blocks of

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quartzite in the basal member of the Lowland Creek Volcanics werederived from the underlying rocks and accumulated as talus along theslopes of an ancient valley.

Intercalated dark-grayish-brown to dark-brown coarse arkose bedsand cobble conglomerate beds overlie the basal conglomerate and gen-erally constitute the main body of the basal member. The beds arecross-laminated, friable, and weather into rounded benches. Thecobbles in the conglomerate beds are chiefly quartzite and are as muchas 4 inches in diameter; however, pebbles of volcanic rock are abund-ant, and some limestone pebbles are present. The matrix is coarsesand consisting of quartz, feldspar, and mafic minerals and in placessome tuft.

The arkose interbeds are thick, cross-laminated, coarse grained, andweather readily to gravel and soil. The arkose is chiefly quartz butincludes a high proportion of feldspar and hornblende cemented byiron oxide and clay.

The thickness of the basal member varies as a result of an erosionsurface which separates it from the overlying ash-flow tuft member.

The ash-flow tuft member is widely distributed along Lost Creekand Antelope Creek, and in secs. 20, 21, 29, 32, and 33, T. 5N., R. 11W., and secs. 4 and 5, T. 4 N., R. 11 W., in the valley of Warm SpringsCreek. It is from 0 to about 3,000 feet thick and is composed chieflyof massive light-gray ash-flow tuft and gray, buff, and grayish-redquartz latite flows that are interlayered with gray lapilli tuft, somewelded tuft, and a few beds of greenish-gray conglomerate. In someplaces near the base of the member, thin beds of coarse-grained arkoseare interbedded with the ash-flow tuft.

The ash-flow tufts and lapilli tufts are hundreds of feet thick andseem to lack any distinctive structures. They are, therefore, difficult toseparate. These volcanic rocks contain abundant crystals of quartz,feldspar, biotite, and hornblende in a fine-grained matrix. In someash beds, sanidine occurs in distinct euhedral crystals. Fragments ofquartz latite rock and pumice lapilli are also abundant in the ash beds.Some strata along Antelope Creek are partly welded and show a pseu-dovesicular structure where the pumice has weathered out (Smedes,1962). The main mass, however, seems to be nonwelded ash-flowtuft.

The quartz latite lavas form thick flows that are gray, brown, andgrayish red. A grayish-brown lava unit crops out in prominent spursalong the ridge in SE1ANE1/ sec. 22, T. 5 N., R. 11 W. The rockis coarse grained and has some phenocrysts of quartz with finergrained hornblende, plagioclase, and biotite; euhedral crystals ofsanidine are abundant. The groundmass is quartz, plagioclase, and

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dust or clay. Veinlets of silicifled material occur at places in theflow. The flows are interstratified with tuff beds and weather into asharp relief. In other localities the flows are from 5 to 10 feet thickand many contain flow structure. Some are brecciated at the base.Several flow units in SE1/SE1A sec. 26, T. 5 N., R. 11 W., have beenaltered and show a color change from grayish red to predominantlygreen. These flows are fine grained, but the larger crystals of plagio-clase, biotite, and hornblende are altered to epidote and chlorite.

The greenish-gray conglomerate beds are lenticular and were prob-ably deposited in water. Well-rounded cobbles and pebbles of vol-canic rock and some quartzite occur in a matrix of pumice, lapilli tuff,and sand. Alteration of the constituent minerals in the cobbles andcoarse-grained matrix has changed the conglomerate to dark green.The alteration products, as in the other units, are chlorite, epidote,and celadonite.

The ash-flow tuff member is truncated by erosion and overlain un-conformably by the volcanic breccia and red-bed member, and in someplaces it is unconformably overlain by a conglomerate of probableMiocene age.

The third and youngest unit of the Lowland Creek Volcanics is thevolcanic breccia and red-bed member that is exposed in secs. 25, 26, 34,35, and 36, T. 5 N., R. 11 W., and in a wide belt of outcrop north ofAntelope Creek. It is from 0 to about 600 feet thick.

In the southern part of the mapped area, the member consists ofmassive gray to reddish-brown quartz latite breccia and agglomerateinterstratified with quartz latite flows, thick-bedded buff conglomerate,sandstone, and thin coaly shale beds. To the north, this sequence inter-tongues with buff and grayish-orange conglomerate beds containingboulders and cobbles of limestone, gneiss, and some volcanics. Theconglomerate is interbedded with reddish-brown coarse-grained sand-stone and gray tuffaceous siltstone. Some thin lignitic coal beds 4-6inches thick crop out in a gulch in NE'/NWA sec. 35, T. 5 N., R. 11W., and in the drainage cuts in NE NWMA sec. 36, T. 5 N., R. 11 W.

The lower part of the volcanic breccia and red-bed member is wellexposed in the north-trending gully in the SEl/4 EM/ sec. 35, T. 5N.,R. 11 W., where the rocks crop out along the axis of a faulted anticline.Massive beds of breccia containing latite blocks as much as 3 feet longin a matrix of volcanic ejecta are exposed in the outcrop. Interstrati-fled with breccia are light-gray ash beds containing pumice bombs asmuch as 4 inches in diameter, latite flows, and, near the andesitic plugat the mouth of the gully, some welded tuff. In places, beds of light-gray to white ash-flow tuff are conspicuous in the outcrop. The tuffcontains abundant euhedral crystals of sanidine, smoky quartz, and

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biotite in a chalky matrix of ash. Thin veinlets of chalcedony arecommon in the tuff beds. Thin to thick lenticular beds of cobble con-glomerate are scattered through the sequence, usually associated withsome reddish-brown tuffaceous siltstone and thin coal beds. Nearthe head of the gully are massive units of ash-flow tuff containing somecoalified stumps and pieces of silicifled wood.

Near the top of the member, the volcanic rocks grade into sedimen-tary strata. In NW%/ sec. 36, T. 5 N., R. 11 W., the gully that drainsnorthward into Lost Creek cuts through intercalated beds of boulderand cobble conglomerate, coarse arkosic sandstone, reddish- to grayish-brown tuffaceous siltstone, tuffs, and thin coal beds. These beds aresteeply inclined along a northeastward-trending fault zone and abutagainst the ash-flow tuff member.

Along Antelope Creek, a thick sequence of red beds is present.These beds overlie the ash-flow tuff member and consist of a massiveconglomerate that contains large boulders of limestone and Precam-brian rocks, arkosic sandstone, siltstone, and gray tuff beds. The redbeds are correlated with the upper part of the Lowland Creek Vol-canics in the south on the basis of stratigraphic position and lithology.The red-bed sequence intertongues with the volcanic strata south ofLost Creek. The red beds rest unconformably on the Colorado Shalealong Antelope Creek and are overlain unconformably by the gravelof middle Pliocene age. In the southern part of the quadrangle thevolcanic breccia and red-bed member is overlain unconformably bythe conglomerate of Miocene (?) age.

CONGLOMERATE

A conglomerate of probable Miocene age is exposed in the southernpart of the quadrangle where it truncates rocks of Eocene and Cretace-ous age. It has a maximum thickness of about 400 feet and generallyweathers into boulder rubble. The best outcrops are along the oldtramway above the valley of Warm Springs Creek in the SE',' sec. 35,T. 5 N., R. 11 W. There the rocks exposed generally are typical of theformation. The conglomerate unit consists of moderately induratedthick-bedded gray to buff conglomerate containing cobbles of gneissicgranite, quartzite, and volcanic detritus intercalated with thick bedsof tuffaceous siltstone and thin lenses of carbonaceous material andlignitic coal beds. The coal beds are 4--6 inches thick and weatherrapidly. The carbonaceous material contains an abundance of plantimpressions.

The conglomerate rests unconformably on the volcanic breccia andred-bed member near an andesite plug at the tramway; the relief of

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the erosion surface is considerable. In secs. 27, 28, 33, and 34, T. 5 N.,iR. 11 W., the unit rests unconformably on the quartzite beds of theColorado Shale. In sec. 36 the conglomerate bevels the ash-flow tuffmember and the volcanic breccia and red-bed member of the LowlandCreek Volcanics.

On the basis of the fossil pollen content, E. B. Leopold and L. M.Weiler (written commun., 1963) suggested that these strata (USGSPaleobat. boc. 1976) are probably of Miocene age.

GRAVEL

Locally, the Lowland Creek Volcanics and older rocks are uncon-formably overlain by coarse gravel of middle Pliocene age (Konizeski,1957). These strata are here informally called "gravel." The gravelis widely distributed over Deer Lodge Valley and forms the highterraces along the east side of the valley. The gravel beds are poorlyindurated thick-bedded gray to buff cobble conglomerate intercalatedwith soft coarse-grained sandstone, tuffaceous siltstone, and thin len-ticular carbonaceous shale beds. In some places surficial glacial out-wash material was mapped in conjunction with the gravel. Severalconglomerate beds that crop out in the gravel pit in sec. 36, T. 6 N.,iR. 10 W., near Galen, Mont., are thickly coated with manganese min-erals. The individual pebbles are covered by black sooty pyrolusitewhich sharply defines the cross-lamination in the beds.

The upper 10 feet of strata in the gravel pit in sec. 36 are composed ofbeds of poorly sorted fluvioglacial outwash material of Pleistocene age.These beds have been mapped and combined with the middle Pliocenegravel, but in places they rest unconformably upon the gravel.

The highest gravel beds crop out at an altitude of about 6,500 feet inthe northeastern part of the quadrangle. This altitude correspondsgenerally to the high terrace levels on the east side of Deer LodgeValley. There are some exposures of the underlying conglomerate ofprobable Miocene age in the deeper gullies on the west side of the valley.Where this conglomerate is exposed, the strata dip steeply and prob-ably were brought up along the northwestward-trending faults thatseem to be reflected in the unconsolidated surficial deposits. The maxi-mum thickness of the gravel in the quadrangle is about 800 feet.

G. E. Lewis (written commun., 1963) identified a fossil tooth foundin the gravel pit in sec. 36, T. 6 N,. R. 10 W., as an upper cheek toothof Pliohippua sp., a fossil horse of probable middle Pliocene age.Konizeski (1957) collected a middle Pliocene faunal assemblage fromthis gravel unit at several other localities in Deer Lodge Valley.

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QUATERNARY SYSTEM

Surficial deposits include glacial moraine deposits, terrace gravel,landslide deposits, colluvium, and alluvium. Along Lost Creek andsome of its adjoining tributaries the bedrock is covered locally byglacial moraine deposits. Large blocks of granite and poorly sortedmaterials left by ice in the lateral and terminal moraines are along theslopes near the confluence of Timber Gulch and the canyon of LostCreek. They occur up to an altitude of 6,500 feet and probably repre-sent the highest occurrence of ice in this area. The ice advanced inLost Creek as far as sec. 23, T. 5 N., ZR. 11 W. Most of the glacialdeposits have been removed by erosion; coarse glacial debris remainsalong the slopes of the valley of Lost Creek, but much of the smallersized material has been reworked by stream action.

Emmons and Calkins (1913) identified at least two periods of glacia-tion in the Flint Creek Range west of the mapped area, but only oneperiod of glaciation is indicated by evidence along Lost Creek. Onemile north of the quadrangle, however, in Racetrack Creek, severalperiods of glaciation are indicated by the successive lapping of termi-nal and lateral moraines. Pardee (1951, p. 80) believed that therewere three periods of glaciation in the Flint Creek Range and classifiedthe glacial drift as early, intermediate, and late. The deposits of thelate glacial period can be recognized generally by the well-preservedmoraines and the unweathered granite boulders. The authors, whofollow the description of Pardee (1951), believe that the deposits inthe canyon of Lost Creek represent the late glacial period. The lateglacial period here and in other areas in the Flint Creek Range iscorrelated with the Pinedale Glaciation, which has been identified withcertainty in most areas of the northern Rocky Mountains.

In sec. 32, T. 5 N., R. 11 W., older terrace alluvium borders the pres-ent flood plain along the valley of Warm Springs Creek. This allu-vium is probably an older coalescing fan deposited by the severaltributaries to Warm Springs Creek.

The landslides that were mapped are deposits formed by massgravity movements of earth or bedrock. A large landslide is in theNWiANWsec. 21, T5N., R. 11 W., where strata of the QuadrantFormation, much fractured along a major fault, has slid down overthe Tertiary rocks to the level of the valley. Another landslide isin sec. 36, T. 6 N., ZR. 11 W., in the volcanic breccia and red-bed mem-ber of the Lowland Creek Volcanics where landsliding in the tuffa-ceous siltstone and conglomerate has left a noticeable scar in the upperpart of the valley. Other smaller areas of landsliding occur in thevicinity of faults where the strata are softened by water seepage.

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Colluvium, composed of unconsolidated cobbles and boulders em-bedded in clay, sand, and gravel, was mapped where it obscured theunderlying bedrock.

The deposits of alluvium consist of clay, sand, and gravel depositedalong the principal streams. These deposits locally include glacialoutwash in the lower parts of valleys and in some of the coalescingfans where they terminate at Deer Lodge Valley (fig. 1). Severalsilt deposits resulting from the formation of lakes in the glacial driftwere mapped as alluvium.

IGNEOUS ROCKS

Granite, diorite, andesite, and trachyandesite rocks of Tertiary ageoccur locally. They chiefly form stocks or smaller plugs and, to alesser extent, dikes and sills. The older intrusive rocks are graniteand diorite and seem to be genetically related to the Philipsburg bath-olith and the Royal batholith in the Flint Creek Range (fig. 1). Theyounger intrusive rocks are andesite and trachyandesite plugs whichintrude Tertiary sedimentary rocks.

GRANITE AND DIORITE

A pluton of granitic rock is intruded into Precambrian and Paleo-zoic rocks in the canyon of Lost Creek. It covers several square milesin the canyon and in an area to the south of the quadrangle just northof Warm Springs Creek. The best exposures are in the glaciatedwalls of the canyon of Lost Creek where the granite shows conspicuouscurved jointing or sheeting near the surface of the intrusion. Thegranite that is exposed on the slope north of the valley of WarmSprings Creek and just west of the mapped area weathers in barrenknobs that rise to about 50 feet above the ground surface.

The rock is a biotite granite that is light gray on the fresh surfaceand weathers buff to light orange. It is medium to coarse grainedand in places pegmnatitic. The megascopic constituents are feldspar,quartz, biotite, and abundant hematite.

Thin sections show a medium- to coarse-grained biotite granitecontaining quartz phenocrysts and perthitic intergrowths of albiteand crudely grid-twinned microcline, and lesser amounts of biotite.Accessory minerals are apatite, zircon, fluorite, and hematite. Themineral constituents are quartz, 20-28 percent; total feldspar, 30-57percent; biotite, 3-13 percent; and accessories, 2 percent. Fluoriteis present in all samples and is generally associated with biotite; italso occurs in fractures in albite. Hematite is generally present asgrains and small irregularly shaped masses occurring interstitiallyand as fracture fillings in albite. The fluorite is late magmatic andmuch of the hematite is probably derived from the alteration of

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biotite by the corrosive action of fluorine. The locally fractured andbent albite associated with hematite, and the fluorite filling in frac-tures may indicate minor adjustments within the intrusive body justprior to or during the late stage of crystallization.

A light-colored finer grained zone near the roof of the intrusionwas sampled and found to contain higher percentages of quartz, feld-spar, and mica than the average granite. The sample contained 30percent quartz and a larger percentage of albite, usually about 79 per-cent of the total feldspar if microcline and albite in perthite arecounted separately, and 11 percent mica. The mica is chiefly hydro-muscovite and muscovite rather than biotite.

Schlieren within the large granite mass is generally a schistosebiotite-rich rock. One sample of schlieren contains quartz, biotite,plagioclase, potassium feldspar, and perthite; hornblende (?), apa-tite, and zircon occur as accessory minerals. The plagioclase is sodicoligoclase.

The border zone of the granite intrusive at the east entrance to thecanyon of Lost Creek is sheared and altered cataclastic granite. Thegranite is in contact with locally marbleized, silicified, and mineral-ized Madison Limestone. The granite is medium to fine grained,kaolinized, silicified, and iron stained. It contains 21--29 percentquartz phenocrysts and perthitic intergrowths of sodic oligoclase(An 11--16) and crudely grid-twinned microcline. The accessoryminerals total 1 percent and include fluorite, zircon, apatite, andhematite. Alteration products are sericite, kaolinite, hydromusco-vite, and chlorite. Quartz and feldspar are commonly granulated,and the quartz is recrystallized. Plagioclase laths are commonly bentand broken and have hematite filling the fractures. The highercalcium content of this plagioclase in relation to the plagioclase inthe main body of granite is probably the result of reaction with theintruded Madison Limestone. Fluorite is interstitial. Hematite oc-curs disseminated or as fracture fillings in the plagioclase and as thinsubparallel veinlets in quartz and clay. Sericite and kaolinite arealteration products of plagioclase and microcline. Hydromuscoviteand chlorite, which are often associated with the hematite, may bealteration products of the original biotite.

Medium- to coarse-grained granite dikes cut the granite mass andalso the Newland Formation. In general, the dikes are more leuco-cratic than the normal granite of the quadrangle although some dikescontain megascopically visible biotite in small quantities; the dikesgenerally contain a higher percentage of quartz and albite than thenormal granite. They also contain partly chloritized epidote asso-cited with the hematite and in addition the accessory minerals zircon,

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apatite, and fluorite. One granite dike that cuts a basic dike intrud-ing the Newland Formation contains sparse allanite as well as epidoteand the usual accessories; hydromuscovite (?) and muscovite replacebiotite. Much of the quartz and feldspar is partly recrystallized;many phenocrysts are bent and broken and fluorite fills many brokenphenocrysts.

Hornblende-plagioclase-sphene-biotite quartz dikes and sills cut theNewland Formation. The dikes and sills are finely layered and con-sist of thin alternating hornblende-sphene layers and plagioclase-richlayers. The accessory minerals are magnetite, apatite, zircon, andhematite.

There are two plugs of granitic rock along Lost Creek in sec. 15,T. 5 N., R. 11 W. The granite is fluorite bearing and similar to thegranite in the canyon of Lost Creek. The intrusives are consideredapophyses of the granite exposed in Lost Creek. The apophyses aremedium-grained quartz-rich gneissoid granite that contains 34 per-cent quartz phenocrysts and perthitic intergrowths of albite and grid-twinned microcline and about 3 percent muscovite. Accessory min-erals constitute 1 percent and include fluorite, hematite, zircon, andapatite. The plagioclase laths are commonly bent or broken, andhematite fills the fractures. The muscovite is commonly bent. Fluo-rite is interstitial.

The dioritic intrusion near the northwest corner of the quadrangleprobably is related to the large diorite mass along Racetrack andThornton Creeks just north of the mapped area. The diorite in themapped area is faulted against Precambrian and Paleozoic rocks andshows some mineralization in fracture or shear zones near the faults.It is very coarse grained, and the main constituents in order of abun-dance are plagioclase, hornblende, biotite, and quartz. Microcline andaugite are present in small amounts. Accessory minerals are magne-tite, zircon, and sphene. The diorite is cut by aplite dikes and smallintrusions of muscovite-biotite granite. Several small plugs of thegranite are intruded into Precambrian strata along the canyon thatdrains northward into Modesty Creek in NE1, sec. 27, T. 6 N., R.11 W.

ANDESITE OR TRACHYANDESITE PLUGS

Small plugs of andesite or trachyandesite are intruded into theTertiary sedimentary rocks along the valley of Warm Springs Creekin sec. 2, T. 4N., R. 11 W., and secs. 35 and 36, T. 5 N., R. 11W. Theplugs are composed chiefly of volcanic breccia or vent agglomerateand weather into talus that accumulates downslope from the intrusiveoutcrop. The breccia is reddish brown on fresh surfaces but is brown-ish black to black on weathered surfaces.

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The small pluglike mass in SE14SEA sec. 35, T. 5 N., R. 11 W.,is best exposed in the abandoned tramway where its relation to a bedof ash-flow tuff in the Lowland Creek Volcanics is clearly defined. Athin vertical crush zone occurs along the periphery of the intrusivepluglike mass, and the rock fragments are oriented parallel to the wall.inward from the contact, a zone of breccia contains blocks of intrusivematerial as large as 1 foot in diameter. The core of the pluglike massis finely porphyritic locally brecciated and silicified trachyandesitewhich contains broken partially altered plagioclase (andesine), abun-dant biotite, potassium feldspar, and clay. Clumps of radiating fi-brous silica, magnetite grains, and sparse accessory zircon and apatiteare present.

The country rock surrounding this pluglike mass is a latite or quartzlatite (?) ash-flow tuff containing crystals of biotite, sanidine, plagio-clase (andesine), and lesser amounts of zircon, muscovite, and mag-netite grains. The strata are horizontal except near the contact withthe intrusive where the beds are vertical.

Several small coalescing andesitic masses form a dikelike body inS'W' sec. 36, T. 5 N., IR. 11 WN. The andesitic rock is brownish blackon weathered surfaces. In thin section the porphyritic rock containssmall crystals of oxyhornblende; augite and accessory apatite andzircon occur in a microcrystalline groundmass that consists of feld-spar needles, shreds of pyroxene and oxyhornblende, and very finegrains of magnetite, hematite, and felsic material. Plagioclase lathsare commonly broken and the fractures are filled with intergrowths ofcalcite, hematite, and zeolitic material. Oxyhornblende phenocrystsare generally broken, and skeletal oxyhornblende which has thickopacite rims is abundant. Partial to complete replacement of oxy-hornblende cores by magnetite, pyroxene (probably orthopyroxene),and plagioclase grains is fairly common. The pyroxene generally hasbeen altered to bastite. Augite commonly has opacite rims and is gen-erally skeletal; augite cores partially replaced by calcite, plagioclase,and chlorite are fairly abundant.

Phenocrysts comprise 16-33 percent of the rock, and of this fraction,hornblende ranges from 10 to 20 percent, augite from 4 to 5 percent,bastite from 7 to 22 percent, and plagioclase from 53 to 75 percent.Accessory apatite and zircon phenocrysts are less than 1 percent.

An andesitic plug crops out in Stucky Ridge in NWMASE1/ sec.36, T. 5N., R. 11 W., is intruded in the volcanic breccia and red-bedmember of the Lowland Creek Volcanics, and is possibly the source ofthe thin lava flow downslope. Another plug is exposed in the drain-age between secs. 25 and 36, T. 5 N., R. 11 W.; it crops out in the gully,and the intrusive relation to the surrounding country rock is evident.

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Other small intrusive bodies cut the Tertiary strata at localitiessouth and west of the northwest quaffer of the Anaconda quadrangle.These plugs are of similar andesitic composition and may representvolcanic pipes that were a source of lava flows now removed by erosion.

GEOLOGIC STRUCTURE

The major geologic structure in the region are folds and faults inthe Flint Creek Range; these features formed during the Late Cre-taceous and the early Tertiary. They are nearly contemporaneouswith the intrusions of the granite batholiths (Emmons and Calkins,1913). In the northwestern part of the quadrangle, Precambrian andPaleozoic rocks are thrust faulted against Mesozoic strata, and graniteis locally intruded along the thrust fault. Tertiary strata bevel theolder rocks and in many places are in fault contact with them. Minordeformation occurred during the Eocene, Miocene, and the PlioceneEpochs.

LATE CRETACEOUS AND EARLY TERTIARY DEFORMATION

Along the lower slopes of the canyon of Lost Creek, Precambrianrocks are thrust faulted against Carboniferous strata. Vertical tooverturned limestone beds of the Amsden Formation are against theSpokane Formation in S'M' sec. 4, T. 5 N., B. 11 W. The thrust planeis very steep and is obscured in most places by granite intrusion or byTertiary strata. In Lost Creek the Precambrian rocks are separatedfrom Paleozoic strata by the granite intruded along the thrust fault.The displacement, based on the relative position of the sedimentaryrocks, seems to be in excess of 3,000 feet. North of Lost Creek thethrust fault strikes northeastward beneath surficial deposits along thewest slope of Timber Gulch. Rocks assigned to the Belt Series are injuxtaposition with strata in the Colorado Shale. The thrust faultis concealed beneath Tertiary strata from the divide at the head ofTimber Gulch to Modesty Creek just north of the quadrangle. It ispossible that this thrust fault is a continuation of the overthrustdescribed by Emmons and Calkins (1913, p. 149) along ThorntonCreek several miles northwest of the mapped area where Precambrianrocks are thrust over Paleozoic strata.

Two major reverse faults younger than the overthrust in Lost Creekcut rocks near the border of the granite stock in sees. 15, 16, 20, and 21and in secs. 3, 4, and 10, T. 5 N., R. 11 W. They are high-angle reversefaults and seem to have several thousand feet of vertical displacementat places where Carboniferous rocks are against Colorado Shale. Thefaults probably join beneath Quaternary cover in sec. 15, T. 5 N., R. 11W. In sec. 4, T. 5 N., R. 11 W., the relation of the northwestward-trending reverse fault to the overthrust in Lost Creek could not be

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determined because of the predominance of surficial deposits. Em-mons and Calkins (1913) described the southwestward-trending re-verse fault in secs. 16, 20, and 21, T. 5 N., R. 11 W., as one of themore extensive faults in the Lost Creek and Warm Springs Creekarea. This fault, in secs. 20 and 21, is concealed by Tertiary strata.It is thought by the authors that the reverse faults formed nearlyconcurrently with the overthrusting and the emplacement of thegranite and that the faults consequently are related more to the intensediastrophism of the Laramide orogeny than to the period of normalfaulting that followed.

In the area underlain by Precambrian and Paleozoic rocks, normalfaulting occurred after the major thrusting but earlier than the periodof normal faulting that cut the Tertiary rocks. In the E1/ sec. 5, T. 5N., R. 11 W., a normal fault striking northwestward and downthrownto the east has placed Newland Formation against Spokane rocks. Itintersects a system of faults that strike northeastward and are down-thrown to the east or west. Just west of the fault, Precambrian rocksare folded in a northwestward-trending anticline.

A system of subparallel faults cuts the Precambrian rocks in sec. 33,T. 6N., R. 11. W., north of Lost Creek and west of Timber Gulch.The displacement on some of these faults is as much as several hundredfeet. Near the northwestern part of the quadrangle, several inter-secting faults and small folds occur in the Precambrian rocks near agranite intrusion and in the overthrust plate. In secs. 9 and 10, T. 5N., R. 11 W., two parallel westward-trending faults cut the Paleozoicrocks and place Quadrant Formation against the Madison Limestoneand the Amsden Formation. The faults are truncated by the majorreverse fault to the east and are lost in the granite to the west. In secs.9 and 10 the Madison Limestone is warped in a sinuous asymmetricanticline whose east flank is cut by the northwestward-trending reversefault. South of Lost Creek, the Madison strata are sharply foldedagainst the southwestward-trending reverse fault.

The Colorado Shale is exposed in a large broad faulted anticline thatseems parallel to the trace of the overthrust in the canyon of LostCreek. In secs. 10 and 15 T. 5 N., R. 11 W., strata in the west flankof the anticline are folded in a syncline trending parallel to the reversefault. The shale beds in the Colorado Shale are altered to slate andphyllite and have excellent cleavage. The sandstone and chert con-glomerate beds are altered locally to quartzite. The metamorphismand folding can be attributed to the early phases of the Laramideorogeny and the consequent granite intrusion. Minor folds in theColorado Shale in secs. 10, 21, and 25, T. 5 N., R. 11 W., seem relatedto the period of earlier normal faulting.

B23


LATE TERTIARY DEFORMATION

Some folding and the system of normal faults that cuts the Tertiarystrata are related to the latest deformation in the area. In general,the normal faults strike northward and northeastward and are down-thrown to the east; in places they are intersected by transverse faults.In the east half of T. 5 N., IR. 11 WV., the faults are along a broadanticline which has exposed the Colorado Shale, and the Tertiarystrata dip away from the axis of the anticline. The throw on thefaults seems to increase to the south where strata of Miocene (?) ageare in juxtaposition with Eocene rocks. North of Lost Creek thebasal Tertiary rocks are locally in fault contact with the ColoradoShale. In this area Tertiary rocks bevel steeply dipping older for-mations, and the unconformities can be easily mistaken for faults.

In sec. 35, T. 5 N., R. 11 W., the conglomerate of Miocene (?) ageis folded and cut by faults. The large anticlinal fold exposed in theabandoned tramway is cut on the north end by a northeastward-trending fault. Another anticline that is subparallel and lies to theeast is cut by two eastward-trending cross faults. The axis of thisanticline is offset to the east. Other faults occur in the vicinity ofsmall andesite intrusive bodies. At these localities the faults seemto have been emplaced concurrent with the intrusive bodies or shortlythereafter.

Southwest of Anaconda, Eocene rocks are folded in a northward-plunging syncline. On the east flank of this structure the dip is from30~ to 35O, and on the west flank about 33O. The overlying gravelbeds are too unconsolidated to determine any deformation.

In secs. 29, 30, and 32, T. 6 N., R. 10 W., along Deer Lodge Valley,two fault scarps are in the Pliocene gravel. In this area the under-lying Miocene (?) strata are sharply folded in a northwestward-trending anticline which seems to be on the upthrown side of the faultzone. On areal photographs the fault scarps appear as linearfeatures where they cut the Pliocene gravel. The gravel beds are notas tightly folded as the underlying Miocene (?) rocks, and the faultsthat cut the gravel beds probably are superimposed on an older faultsystem. This latest period of faulting is related to the most recentdeformation in the area.

ECONOMIC GEOLOGY

COAL

No coal has been mined in the northwest quarter of the Anacondaquadrangle although coal beds are in the volcanic breccia and red-bedmember of the Lowland Creek Volcanics of Eocene age and in the con-

B24


glomerate of Miocene (?) age. The coal in the Eocene beds is classi-fied as lignite; a sample tested 5,740 Btu (British thermal units) onan "air dried" basis and 4,780 Btu on an "as received" basis. Severalcoal beds crop out in a gulch in the E%/SE1A sec. 35 and in the drain-age in the NEi/NW1/ sec. 36, T. 5 N., iR. 11 W. The coal in these ex-posures is compact and dull and has an irregular fracture. The coalbeds are thin, from 5 to 12 inches thick, and discontinuous; they areinterbedded with beds of ash-flow tuff, conglomerate, and volcanicbreccia.

Coal beds in the conglomerate of Miocene (?) age are thin, lenticu-lar, and very impure. They contain much carbonaceous shale andweather quickly where exposed. The coal is brown to black ligniteand is intercalated with thick conglomerate beds and thin shale beds.In most localities the coal beds are 4-12 inches thick.

According to Pardee (1913), a coal bed about 3 feet thick was re-ported to occur along Lost Creek nearly 2 miles north of Anaconda.No coal beds of this thickness were found to crop out at this locality.In general, coal beds of commercial value are not present in the area.

OIL AND GAS

The oil and gas potential in the area seems poor. The thick car-bonate rocks of Paleozoic and Mesozoic age in the subsurface havebeen subjected to considerable compression, metamorphism, and fault-ing. It is likely that intrusions of granite and volcanic rocks prob-ably caused a migration of fluids away from possible source beds. TheColorado Shale is too altered to be geologically favorable for oil orgas accumulation.

PHOSPHATE

Phosphate deposits occur in the Phosphoria Formation of Permianage. The Phosphoria Formation is not present at the surface in thenorthwest quarter of the Anaconda quadrangle owing to faulting, butis present in the subsurface. The Phosphoria crops out to the west inthe Philipsburg quadrangle where a phosphate bed is exposed belowmassive sandstone in the quarry in sec. 25, T. 5 N., R. 12 W. This phos-phate bed is about 3 feet thick and is composed of a dark-gray oolitic

phosphate rock. This bed should be in the subsurface below 2,000 feetin the central and eastern part of T. 5 N., RI. 11 W., in the northwest

quarter of the Anaconda quadrangle. The phosphate bed was not

sampled, and whether the percentage of P2 0, and the thickness of thebed at depth would make phosphate mining economical is unknown,

B25


GOLD

Warm Springs Creek, Lost Creek, and Antelope Creek drain the eastslope of the Flint Creek Range (fig. 1) where lode deposits of goldoccur in igneous and sedimentary rocks. It is possible, therefore, thatthe gravel beds in low terraces and stream channels might containplacer deposits of economic value. Gold-bearing gravels were minedat one time in the upper part of Modesty Creek just north of themapped area. Much of the recent gravel is glacial outwash and verycoarse and consequently difficult and expensive to remove.

Many pits dug to prospect for gold can be seen along Timber Gulch.The prospects have all been abandoned. A mine was reopened in 1961near the confluence of Timber Gulch and Lost Creek. The float inthe dump showed some sulfide minerals.

The basal member of the Lowland Creek Volcanics may containplacer deposits of gold or other resistant metals. The sedimentarymaterials in these strata were derived from local sources, includinggranitic bodies that contain ore deposits. Gold or heavy mineralsmight have accumulated in the old stream channels. The basal bedsare thick friable conglomerate units that weather readily and could bestripped by bulldozers.

LIMESTONE

The Madison Limestone crops out extensively along Lost Creek insec. 10, T. 5 N., R. 11 W. It was quarried at this locality; the lime-stone was burned in a kiln near the quarry, and the lime was used as aflux in the Anaconda smelter. The Madison Limestone is quarried forthe manufacture of cement in the vicinity of Drumnmond where itaverages 98 percent calcium carbonate (Perry, 1949, p. 36).

FIRE CLAY

Several quarries were opened in the basal member of the LowlandCreek Volcanics, and at one time the tuffaceous beds were mined for usein ceramics and as fire clays. The Anaconda Copper Mining Co. usedclay from the Deniff quarry in the NW'A sec. 25, T. 5 N., R. 11 W., tomake fire brick and refractory furnace lining. The quarry is in athick-bedded light-gray to white tuffaceous clay unit that dips about350 E. The quarried material averages about 75 percent 5i0 2 and 16percent Al2O, and has a little lime and iron. These clay beds seemto be extensive in the volcanic sequence and were mined at severallocalities in and outside of the area.

GRAVEL

The gravel beds of Pliocene age and the more recent glacial outwashdeposits are used locally as road metal. If properly screened and

B26


washed, these deposits can be used as concrete aggregate in tlie prepara-tion of bridges, abutments, and culverts. The deposits of gravel coverextensive areas in Deer Lodge Valley (fig. 1).

REFERENCES CITED

Alden, W. C., 1954, Physiography and glacial geology of western Montana andadjacent areas : U.S. Geol. Survey Prof. Paper 231, 200 p.

Calkins, F. C., and Emmons, W. H., 1915, Description of the Philipsburg quad-rangle [Montana]: U.S. Geol. Survey Geol. Atlas, Folio 196.

Cobban, W. A., Erdmann, C. E., Lemke, R. W., and Maughan, E. K., 1959, Revisionof Colorado group on Sweetgrass arch, Montana : Am. Assoc. PetroleumGeologists Bull., v. 43, no. 12, p. 2786-2796.

Collier, A. J., and Cathcart, S. H., 1922, Possibility of finding oil in laccolithicdomes south of the Little Rocky Mountains, Montana : U.S. Geol. SurveyBull. 736-F, p. 171-178.

Darton, N. H., 1904, Comparison of the stratigraphy of the Black Hills, BighornMountains and Rocky Mountain Front Range: Geol. Soc. America Bull., v.15, p. 398-401.

Douglass, Earl, 1909, A geological reconnaissance in North Dakota, Montana, andIdaho, with notes on the Mesozoic and Cenozoic geology : Carnegie Mus.Annals 5, p. 211-288.

Eminons, W. H., and Calkins, F. C., 1913, Geology and ore deposits of the Philips-burg quadrangle, Montana: U.S. Geol. Survey Prof. Paper 78, 271 p.

Fisher, C. A., 1909, Geology of the Great Falls coal field, Montana : U.S. Geol.Survey Bull. 356, 85 p., 12 pls.

Gwinn, V. E., 1961, Geology of the Drummond area, central-western Montana:Montana Bur. Mines and Geology Spec. Pub. 21 (Geol. map 4).

Hayden, F. V., 1876, Annual report of the United States Geological and Geo-graphical Survey of the Territories, embracing Colorado and parts of adja-cent territories, being a report of progress of the exploration for the year1874: 515 p.

Kiepper, M. R., Weeks, R. A., and Ruppel, E. T., 1957, Geology of the southernEikhorn Mountains, Jefferson and Broadwater Counties, Montana : U.S.Geol. Survey Prof. Paper 292, 82 p.

Konizeski, R. L., 1957, Paleoecology of the Middle Pliocene Deer Lodge localfauna, western Montana : Geol. Soc. America Bull., v. 68, no. 2, p. 131-150.

Konizeski, R. L., McMurtrey, H. G., and Brietkrietz, Alex, 1961, Preliminaryreport on the geology and ground-water resources of the northern part ofthe Deer Lodge Valley, Montana : Montana Bur. Mines and Geology BulL. 21,24 p.

McGill, G. E., 1959, Geologic map of the northwest flank of the Flint Creek range,western Montana: Montana Bur. Mines and Geology Spec. Pub. 18 (Geol.map 3).

Mutch, T. A., 1960, Geologic map of the northeast flank of the Flint Creek range,western Montana : Montana Bur. Mines and Geology Spec. Pub. 22 (Geol.map 5).

Pardee, J. T., 1913, Coal in the Tertiary lake beds of southwestern Montana:U.S. Geol. Survey Bull. 531, p. 229-244.

1917, The Garrison and Philipsburg phosphate fields, Montana : U.S. Geol.Survey Bull. 640, p. 195-228.

1951, Gold placer deposits of the Pioneer district, Montana : U.S. Geol.Survey Bull. 978-C, p. 69-99.

B27


Peale, A. C., 1893, The Paleozoic section in the vicinity of Three Forks, Montana:U.S. Geol. Survey Bull. 110, 56 p.

Perry, E. 5., 1949, Gypsum, lime, and limestone in Montana: Montana Bur. Minesand Geology Mem. 29, 45 p.

Richards, R. W., and Mansfield, G. R., 1912, The Bannock overthrust, a majorfault in southeastern Idaho and northeastern Utah: Jour. Geology, v. 20,p. 681-709.

Ross, C. P., 1949, The Belt problem [Montana] [abs.]: Washington Acad. Sci.Jour., v. 39, no. 3, p. 111-113.

1959, Geology of Glacier National Park and the Flathead region, north-western Montana : U.S. Geol. Survey Prof. Paper 296, 125 p.

Ross, C. P., Andrews, D. A., and Witkind, I. J., 1955, Geologic map of Montana:U.S. Geol. Survey, 2 sheets.

Ruppel, E. T., 1961, Reconnaissance geologic map of the Deer Lodge quadrangle,Powell, Deer Lodge, and Jefferson Counties, Montana: U.S. Geol. SurveyMineral Inv. Map MF-174.

Smedes, H. W., 1962, Lowland Creek Volcanics, an upper Oligocene formationnear Butte, Montana: Jour. Geology, v. 70, no. 3, p. 255-266.

Smedes, H. W., and Thomas, H. H., 1965, Reassignment of the Lowland CreekVolcanics to Eocene age : Jour. Geology, v. 73, no. 3, p. 508-510.

Walcott, C. D., 1899, Pre-Cambrian fossiliferous formations: Geol. Soc. AmericaBull., v. 10, p. 199-244.

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UNITED STATES DEPARTMENT OF THE INTERIORGEOLOGICAL SURVEY

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57'30"

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APPROXIMATE MEAN

DECLINATION, 1966

SCALE 1:24 000

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Geology by A. A. Wanek andC. S. V. Barclay, 1961-62

~6~'15'

UNCONFORMITY

To

Conglomerate

UNCONFORMITY

TIu

Tim

TiI

Lowland Creek VolcanicsMembers separated by unconformitiesTiu, volcanic breccia and red-bed memberTIm, ash-flow tuff memberTII, basal member

UNCONFORMITY

ko

Colorado Shale

Kk

Kootenai Formation

UNCONFORMITY

Js

Sedimentary rocks

UNCONFORMITY

Pp

Phosphoria Formation

iPq

Quadrant Formation

IRMa

Amsden Formation

Mm

Madison Limestone

*1f

Flathead Quartzite

UNCONFORMITY

p-Cs

Spokane Formation

p-On

Newland Formation

IGNEOUS ROCKS

Ta

Andesite or trachyandesite plugs

ContactDashed where approximately located; short dashed

where indefinite

0

U

Normal faultDashed where approximately located; dotted where

concealed. U, upthrown side; D, downthrown side(neither U nor D shown where direction of movementunknown)

Reverse faultDashed where approximately located; dotted where

concealed. R, upthrown side

H-

Thrust faultDotted where concealed. T, upper plate

AnticlineShowing crestline. Dashed w here approxirna tely

located; dotted where concealed

SynclineShowing troughline - Dashed where a-pp co/-rn ately

located; dotted where co3?cea-led

Strike and dip of beds

eHorizontal beds

N N

Mine dump or slag heap

CONTOUR INTERVAL 80 FEETDATUM S MEAN SEA LEVEL

- '- p-OnpOs

-- [Pr, c/i

112~52'3O"

BULLETIN 1222-BPLATB 1

F. 6 N.r. 5 N.

[2'30"

EXPLANATION NSURFICIAL DEPOSITS

Qal

Alluvium

Qo

Colluvium

'3 ~ NNANj1

Qis A~AA5

t'~

Landslide deposits

Qt

Terrace gravel

Qm

Glacial moraine deposits

UNCONFORMITY

SEDIMENTARY ROCKS

Tg

Gravel

04

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0

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0

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0

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A

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8000 -

7000~

FLINT CREEK RANGE

55,

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0

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1 MILE

1 KILOMETER

U)C

(-NCN"'

112"~46" 07'30"2'30"

Strike of vertical bedsNI

Strike and dip of foliation

Quarry

8000~

7000 N

z0UJI-

0

UNITED STATES DEPARTMENT OF THE INTERIORGEOLOGICAL SURVEY

BULLETIN 1222-B

PLATE 2

FORMATIONIii

Co

Co

I-wH

Colorado Shale

SU

-o a

= 0

-.2 a

-n---r -

- r r ~

-L-

Phosphoria Formation - --

Kootenai Formation

Sedimentary rocks

Quadrant Formation

THICKNESS(FEET)

600-800

0-400

LITHO0LOGY

6-'o*6~0.6 o'.

- O

~x-

-

-4 4- -

~- -

~~-

-- * - - -- -

----

- J

. ---

- ~ :5

E' E :,'.- - _-

0-3000

400

1500

1500

400

150-200150-200

Amsden Formation 300

Madison Limestone

Jefferson Dolomite

1200+

1000

Maywood Formation 250

Red Lion Formation28+

Hasmark Formation10

Silver Hill Formation

Flathead Quartzite I

Spokane Formation

Newland Formation

7 : - -

-~ -_-

/ -

- , ~

- W

--- -- -

jI~

100-600+si

20-200 Clifi

Med200-9000 Ia

4500+

DESCRIPTION OF ROCKS

0-600+

ium- to thick-bedded reddish-brown to grayish-orange cross-minated ripple-marked sandstone and siltstone; where meta-orphosed, altered to dark-gray impure quartzite and dark-greenish-ray to brownish-black cordierite schist.

i- to thick-bedded greenish- to dark-gray calcareousshale inter-alated with thin- to medium-bedded light-greenish-gray banded-npure limestone; where metamorphosed, altered to cliff-formingiliceous limestone and dark-greenish-gray to brownish-blackcapolite and diopside-bearing schist; locally limestone beds alteredMarble.

-race gravel, landslide deposits, colluvium, and alluvium: high-levelgravel; landslide deposits; unstratified slope wash, talus; clay, sand,mnd gravel deposited along principal streams.

cial moraine: deposits of large boulders, chiefly granite and poorlyorted materials left by ice in lateral and terminal moraines andlacial outwash in Lost Creek Valley.

vel: poorly indurated thick-bedded gray to buff cobble- and pebble-hannel conglomerate intercalated with coarse-grained sandstone,uffaceous siltstone, and some thin carbonaceous beds; locallyicludes surficial glacial outwash material.

glomerate: moderately indurated thick-bedded buff conglomeratecontaining Precambrian cobbles and some volcanic detritus inter-

alated with thick beds of gray tuffaceous siltstone and thinarbonaceous lentils; weathers in unconsolidated rubble.

canic breccia and red-bed member: indurated massive- to thick-edded gray to reddish-brown quartz latite breccia and agglomeratenterstratified with quartz latite flows, thick-bedded buff conglom-rate and sandstone, some tuff, and thin coaly shale beds; inter-ongues toward the north with buff and grayish-orange conglomerateeds containing cobbles of limestone, Precambrian rocks and someolcanic rocks intercalated with reddish-brown coarse-grained sand-tone and gray tuffaceous siltstone beds.

-flow tuff member: massive light-gray quartz latite ash flows anduff intercalated with minor lenticular beds of greenish-grayonglomerate, gray lapilli tuff, and welded tuff; locally includeseveral coarse-grained arkose beds near the base.

al member: massive- to thick-bedded grayish-brown cross-laminatedrkose, lenticular conglomerate beds containing abundant pebblesvolcanic rock, and gray to buff tuffaceous siltstone and tuff beds;rades near the top into thick-bedded light-gray arkose, tuffaceousltstone, and gray-green limestone; grades toward base into someark-gray shale and limestone beds; includes locally a basal brecciaonglomerate where deposits accumulated in areas of low relief.

ck-bedded dark-gray coarse-grained sandstone and shale gradingt top to siltstone and shale; lower part mainly dark-gray to grayish-rown calcareous shale interbedded with siltstone and thin-beddedmestone, and overlain by massive dark-gray to gray-brown quartz-:ic chert pebble conglomerate beds; base is not exposed in areand upper part is truncated by Tertiary sediments.

yer part chiefly red and grayish-green shale and limestone beds)ntaining abundant gastropods and grading at the top to blackIlcareous shale and some thin gray to buff sandstone beds; lowerart consists of a basal cliff-forming reddish-brown to grayish-greenuiartzite cobble conglomerate overlain by a thick sequence ofCddish-brown shale and thick-bedded limestone.

i- to thick-bedded grayish-green to dark-gray sandstone containinglinor chert pebble conglomerate beds grading near top into thick-edded olive-gray calcareous shale and locally some nodular lime-tone beds; lower part chiefly black calcareous and fossiliferoushale and limestone.'-forming massive-to thick-bedded gray to grayish-orange quartz-ic sandstone separated in several ledges by thin-bedded softalcareous shale; lower part chiefly interbedded cherty limestone,lack calcareous shale, and a thin dark-gray oolitic phosphate bed.

F-forming massive light-gray quartzitic sandstone; locally much-actured and cut by many veinlets of calcium carbonate.

e-fsorin seoftsredish-brown shale interbeded with thi grayish-

f-forming massive dark-gray fossiliferous limestone containingabundant thin chert layers; lower part thinner bedded and containsome intercalated black shale beds; where metamorphosed, lime-:one altered to marble.

f-forming thick-bedded light-gray to buff dolomite and some lime-:one; commonly fine-grained to sugary texture; where meta-iorphosed, beds have light- to dark-gray cast.

n-bedded reddish- and light-gray dolomitic limestone intercalated/ith gray and olive-green calcareous shale; lower part chiefly thick-edded calcareous sandstone.

'-bedded light- to blue-gray limestone containing closely spacedavy siliceous laminae; lower part mainly dark-gray to black shalend limestone.

er part chiefly cliff-forming thick-bedded light-gray dolomite thatverlies a thin middle sequence of dark-brown calcareous shale andodular limestone; lower part thick-bedded light-gray dolomite.

t-gray, brown, and greenish-gray calcareous shale and intercalatedmiestone beds grading downward into limestone containing thinliceous laminae; lower part mainly dark-grayish-green s-hale.

-forming massive- to thick-bedded light-gray to white vitreousuartzite; locally tinted rose owing to impurities.

Mcodifipd after Fmmons rind Calkins (1913)

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EXPLANATION

Conglomerate

Sandstone and crossbeddedsandstone

-. -

Quartzite

Siltstone

Shale

Calcareous shale

Coaly shale

Limestone

Limestone, crinklybedded

Limestone, cherty

Dolomite

Ash flow and tuff

---

Latite flows

04 _ -

Volcanic breccia

F-- -

Volcanic brecciaand tuff

Schist and marble

Rock, phosphate

Moraine, unstratifieddrift

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