The SOURCES of OUR IRON ORES.'
I1
ERNEST F. BURCHARD? United States Geological Survey, Washington, D. C
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I n this instalment** the iron ore deposits of the Lake Superior States, which normally furnish about 80 per c a t . of the a n n u l output of the United States, are described togelher with historical notes on dixovery and transportation of ore. Deposits i n the Mississifipi Valley and Western States are likewise outlined and the sources of imported ore are given. Rmiewing the whole field, it i s indicated that the great producing deposits of the Lake Superior and
southern Appalachian regions are of hematite i n basin areas of sedimentary rocks, that hydrated iron oxides and iron carbonates are generally found i n undisturbed comparatively recent sediments, and that magnetite occurs in metamorphic and igneous rocks; also that numerical abundance of deposits & not a criterion as to their real importance as a source of supply. Statistics of production of iron ore and estimates of reserwes of present grade conclude the paper.
Lake Superior States.-The map of the iron ore areas of the United States is a t first glance apt to give a misleading impression of the relative importance of the ore areas in the vicinity of Lake Superior. Although these areas can he represented on a small-scale map only by short thin lines, in reality they represent the accumulation of larger quantities of ore than a t any other areas of equal size, and for many years they have yielded about four-fifths of the total annual ore output of the United States. In the Lake Superior States the iron ore deposits may be grouped into seven long narrow areas, or "ranges," oiz., the Marquette, Menominee, and Penokee-Gogehic in northern Michigan and Wisconsin and the Vermilion, Mesabi, and Cuyuna in northern Minnesota. Three other minor and unimportant ore-hearing areas occur in Wisconsin. The iron ores in all the northern areas are in pre-Cambrian formations, generally considered to be of Algonkian and Archean age. The iron ores are confined to iron formations, bedded deposits, consisting chiefly of a mixture of chert, or quartz, and ferric oxide segregated in bands. The original forms of the iron-bearing deposits are considered to have been cherty iron carbonate and hydrous ferrous silicate (greenalite). MARQUETTE RANGE.-The Marquette Range extends from Marquette, Michigan, on Lake Superior, westward to Lake Michigamme, a distance of about 30 miles, and is 1 to 6 miles in width. I t lies wholly in the State of Michigan. The more important mines are near Ishpeming, Negaunee, and Republic. The iron formations occur in the upper and middle Huronian rocks which have been folded into a synclinal basin comprising a number of minor synclines and anticlines. The ores occur on the limbs of the basin, more particularly that at the north, and may he localized as ores a t the base of the Negaunee formation (middle Huronian), . . ores within the Negaunee, and
detrital ores a t the base of the Goodrich quartzite (upper Huronian). Those of the first type are of soft hydrated hematite and occur where the rocks have been folded into pitching synclinal troughs, and in places these troughs have been cut by basic dikes forming pockets where the ore has developed between the dikes and slate. Ores within the Negaunee are chiefly soft hematite and are developed a t the contact of the iron formation with basic intrusions, and the detrital ores were formed by breaking up of ores of the first two types during the erosional period between the deposition of the middle and upper Huronian rocks. They are of hard, specular hematite with some magnetite." Iron ore was discovered by a United States surveying party in 1844 near the site of the present city of Negaunee. The presence of the ore was noted by accident by the surveyors who, in endeavoring to run a northsouth line, found that in certain localities the needle of the compass was much disturbed. When the sod was dug up masses of iron ore were revealed which strongly attracted the needle. Shortly after the discovery of iron ore a sample was taken to Jackson, Michigan, and in 1845 the first iron to he made from Lake Superior ore was produced in a blacksmith's forge near that place. In 1847 a Catalan forge was built on Carp River, 10 miles from Marquette and in February, 1848, this forge produced the first iron ever made in the Lake Superior region. In 1852 six barrels of ore were shipped by sailing vessels from Marquette down the lakes to Newcastle, Pennsylvania, the earliest recorded shipment of Lake Superior ore to the lower lakes. In 1853, 152 tons of ore were shipped from Marquette to Erie, Pennsylvania. It required four sailing vessels to move the ore from Marquette to Sault Ste. Marie, where it was portaged and loaded on boats below the falls. It soon became apparent that the only economical way to transport the ore would be by through boats, and that this
-
* Published by permission of the Director, United States Geological Survey. t Geologist. United States Geological Survey, Washington, D. C. ** Part I ameared in the A ~ r i issue l
" The geologic descriptions of the Lake Superior ranges are "Iron ores, pig iron, and largely according to E. C. HARDER, (1908). steel," U.S. Geol. Suruey, Min. Res., pt. 1, pp. 3-7
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would be feasible only by means of alock canal. Before the discovery of iron ore-as early as 1837-the building of a canal was advocated. Work was begun in 1839 on a canal by the State of Michigan hut was soon brought to a close on account of a conflict with federal authorities because the route of the proposed canal traversed a federal military reservation. Many unsuccessful efforts were made to have Congress further the enterprise. Henry Clay is reported to have ridiculed it, saying that it contemplated a work beyond the remotest settlement in the United States, if not in the moon. Governmental aid in the form of grants of state land was finally granted in 1852, and the year 1853 saw the beginning of the great work. The canal was completed in April, 1885, a t a cost of about one million dollars. The total length was 5700 feet, or a little more than one mile, but its depth and the capacity of the locks were small as compared with those of the present canal. The first through lake shipment of iron ore was made in August, 1855. It consisted of 132 tons, and was carried by the sailing brig Columbia from Marquette, Michigan, to Cleveland, Ohio. The total shipments in 1855 were less than 1500 tons, and in the year following were about 6300 tons. This is a great contrast with later records when nearly 59,000,000 tons of iron ore passed through the locks of the Sault Ste. Marie canal in 1929, a year of maximum production. A single ore freighter will now carry more than 14,000 gross tons of ore on a single trip. Although almost the fist iron to be made from Lake
RANGES
Superior iron ore was produced near Marquette, Michigan, iron-making did not soon become a large industry in the region, and only after an interval of more than seventy years after iron ore was first discovered near Lake Superior plans were consummated for its manufacture on a large scale a t Duluth. Minnesota. MENOMINEE RANGE.-The second of the Lake Superior ranges to begin production of iron ore is the Menominee, about 25 miles northwest of Green Bay in the northern peninsula of Michigan, where ore was discovered in commercial quantity about 1867. The range extends a few miles beyond the state line into Wisconsin, and its total length is about 56 miles in a northwest-southeast direction and the ore is found in several areas. Among the mining towns are Iron Mountain, Metropolitan, Crystal Falls, and Iron River, Michigan, and Florence, Wisconsin. The iron ores mined in this district consist principally of gray, banded hematite, with small quantities of hard red hematite. The ores are chiefly in the upper Huronian Vulcan formation. The rocks are folded into a complicated structure having two major anticlines with minor folds superimposed on them. The ore deposits are large and occur on relatively impervious formations which are folded into pitching troughs a t places where ores are found.12 THE PENOKEE-GOGEBIC RANGE.-T~~Penokee-Gogebic Range is in northern Wisconsin and northern Michigan about 20 miles south of Ashland, Wiscoula HARDER, E. C., IOC. cd., pp. 45-8.
sin, on Lake Superior. The range occupies a narrow area extending northeast-southwest about 75 miles. Mining towns are Hurley, Wisconsin, and Ironwood and Bessemer, Michigan. The productive iron formation is mostly of femginous chert of upper Huronian age overlain by slate and underlain by quartzite and slate. Heavy gabbro above the upper slate has metamorphosed the iron formation in places to jasper and amphibole-magnetite rock. The sedimentary rocks dip steeply northwest and are cut by basic igneous dikes. Where these dikes cut the footwall quartzite or lower slate impervious troughs are formed through which iron-bearing waters converged, became ponded, and deposited their load of ore. The ore is mostly soft, hydrated hematite, but hard, slaty ore is also abundant. Some of the ore is manganiferous. The deposits reach depths of 1000 feet or more, and mining is entirely underground. The f a d that iron ore occurred in the Penokee-Gogebic Range was pointed out by geologists long before any ore was mined, but it required many years to build railroads to the districts and to prepare mines for a steady production. VERMILION RANGE.-The first iron range to be opened in Minnesota was the Vermilion, situated in northeastern Minnesota near the Canadian border and about 60 miles northwest of Lake Superior. Its width varies from 5 to 15 miles and its extreme length from northeast to southwest is about 100 miles. The principal deposits of ore are in iron formation in the Keewatin series of greenstones in which jasper has been infolded into troughs. These rocks are of Archean age, and older than most of the other commercial ore-bearing rocks of the region. The iron ore ismostly hard, blue or red hematite, and the principal mines are near the towns of Tower and Ely. M s s A B I RANGE.-T~~most important iron ore producing district in the Lake region and, in fact in the United States, is the Mesabi Range in northeastern Minnesota about 50 miles northwest of Dnluth. It has a northeast-southwest length of about 90 miles, and a width of 2 to 10 miles. A broken range, or ridge,
known as the "Giant's Range," forms the axis of the district. (Mesabi is the Chippewa Indian name for "giant.") The iron ore deposits lie along the outcrop of the iron formation a t the southeast base of the range and are best developed a t the minor transverse folds where surface waters carrying oxygen and carbon dioxide have effected alteration and concentration. The rocks dip slightly to the southeast and there are minor transverse folds. The iron formation, of upper Huronian age, is banded ferruginous chert and iron oxide, locally known as "taconite." In the eastern part of the range an intrusion of gabbro has metamorphosed the iron formation to amphibole-magnetite rock. The ores consist chiefly of rich, soft porous brown, red, or blue hematite, and are of great horizontal extent as compared with their vertical depth, which usually is not more than 200 feet. Mining is therefore carried on principally in large, shallow, open pits, the ore being stripped of cover, dug and loaded directly on railway cars by large steam or electric shovels. The magnetite-bearing rocks of the eastern end of the Mesabi Range containing 20 to 30 per cent. of metallic iron attracted attention twelve to eighteen years ago in view of the possibility of saving the iron in the rock. Experimental work by the University of Minnesota demonstrated that by grinding the rock very fine the magnetic iron oxide could be recovered from the siliceous material by dry and wet magnetic separation. A plant for handling this ore on a small shipping basis was put in operation a t Babbitt, Minnesota, in 1922, which succeeded in producing a high-iron, low-phosphorus sintered concentrate, but which is not now in operation. Geologists first noted iron ore in the Mesabi district in the "sixties," but it was not until 1890 that large ore bodies were discovered through extensive prospecting by drilling through the cover of glacial drift. A shipment of about 30,000 tons of ore was made from the Mesabi Range in 1892, and from this small beginning the annual shipments grew by leaps and bounds until in 1929 they were more than 42 million tons. The
Mesabi Range ranks first in both annual and total output of iron ore in the Lake Superior region and produces abont half the iron ore mines in the United States each year. Most of the large iron mines of the United States are on the Mesabi Range. Many of these have produced more than 1,000,000 tons of ore in a year and the one having the record output yielded 8,823,879 tons of ore in 1923. CUYUNA RANGE.-T~~ latest iron range to be opened in the Lake Superior region is the Cuyuna near Mile Lacs Lake in central Minnesota. Its length is about 65 miles and it comprises several parallel belts of ironbearing rocks. This is one of the most interesting of all the iron ranges because the presence of ore was discovered in an unusual way. There are no rocks visible in this part of Minnesota, the surface being low. flat, and in part swampy, and is covered by clay, sand. and gravel ranging from 35 feet to 400 feet in thickness. The presence of iron ore was not suspected until 1895 when it was found that the dip needle was strongly affected in some localities, even in swampy places. Observations with the dip needle and the solar compass led geologists to believe that there were large deposits of iron-bearing rocks below the surface clay. Drilling operations begun in 1903 realized the expectations of the geologists, and several steeply dipping ore bodies were found, some as much as 400 feet thick. By 1911 several mines had been developed and shipments of ore were begun. The Cuyuna iron mines are mostly nnderground, and in tbis respect differ from those of the Mesabi district. The geology and structure of the Cuyuna Range are difficult to determine because the rocks are buried by glacial drift. Broadly the rocks appear to have been closely folded into a complex series of northeastwardtrending anticlines and synclines near the axis of the southwestern extension of the Lake Superior synclinorium. The rocks are principally metamorphosed preCambrian, probably upper Huronian, with isolated overlying patches of Keweenawan volcanic and intrusive rocks and of Cretaceous sediments in places. The iron formation consists of cherty and argillaceous iron carbonate that in places has been altered to amphibolemagnetite rock, ferruginous slate, and iron ore. The ores vary from hard, blue, banded hematite and siliceous magnetite through all degrees of hydration into soft ochreous limonite. There is also much manganiferous ore here. The iron-bearing rocks are inclosed between layers of schist and slate. The rocks are intruded by gabbro and diorite.13 OTHER IRON ORE AREAS I N THE LAKE SUPERIOR
STATES.-T~~ only areas worthy of note in this region not in the immediate vicinity of Lake Superior are in Wisconsin a t Iron Ridge, abont 40 miles northwest of Milwaukee, a t Baraboo, near Devils Lake, and a t Spring Valley in the western part of the State. The ore a t Iron Ridge is sedimentary red hematite, la HARDER, E. C. m~ JOHNSTON, A. W., ''Notes on the geology and iron ores of the Cuyuna District. Minnesota," U.S. Geol. Survey Bull.. No. 660, pp. 1-26 (1917).
not so rich in iron as the average ore near Lake Superior, but i t is so near large iron-consuming centers that it may be mined profitably and reduced in local blast furnaces. Geologists find the Iron Ridge ore interesting because of its similarity to the hematite that is found in beds near Clinton, New York, Birmingham, Alabama, and in Novia Scotia and Newfoundland. At Baraboo the rocks are folded into an elongated basin, around the rim of which the rocks come to the surface. Low-grade iron ore is found in ferruginous slate, chert, and dolomite rocks of Algonkian age, similar to those of the Lake Superior region. Mining was done here in 1915-25, but proved unprofitable because of the low grade of the ore and because large quantities of water had to be pumped out of the mines. Brown ore occurs a t Sprinx Valley in westem Wisconsin, but is not mined a t present. Mississifipi Valley and Gulf States.-The deposits of iron ore comwrised within tbis -geomawhic division are * widely scattered and with few exceptions are not of great importance. Beginning a t the east, the siderite ores of eastern Ohio, western West Virginia, and northeastern Kentucky make a showing on the map beyond all proportiob to their relative value. The original siderite in the form of thin beds of blackband and limestone ore in the "Coal Measures" has weathered to limonite on the outcrop. These ores were used in local blast furnaces up to about 1882 but can hardly be considered of present or probable future importance. The western Tennessee River Valley brown iron-ore area comprises a narrow belt extending from Russellville, Alabama, near Muscle Shoals, northward across west-middle Tennessee on the east side of Tennessee River into western Kentucky. In the Alabama part of the area the ore is largely in the Cretaceous Tuscaloosa gravel, sand, and clay overlying the late Mississippian Bangor limestone, but in Tennessee it is more particularly associated with clay and chert residual from earlier cherty Mississippian limestones. The region has long been a producer of iron ore and pig iron and is today a producer of special irons such as ferrophosphorus, highsilicon iron, and charcoal iron. Two large by-product charcoal plants were built in Tennessee during the World War, as large forests of hardwood trees are still available in this region. There is considerable unmined ore, particularly near Russellville, Alabama, and the district will continue to be a factor in the iron industry for many decades. In northeastern Iowa, near Waukon, there is an interesting deposit of brown ore forming a cap on an eminence called Iron Hill. The ore overlies Galena and Platteville limestones, of Ordovician age, and occupies an area of less than half a square mile. In the deposit there is much clay, chert, and limestone intimately mixed with the ore and which must be excavated with it in open-pit mining, and in the exploitation of this deposit which was active a t intervals from 1913 to the close of the World War a dry separation process was employed in which the ore was finally partially reduced
to magnetic iron oxide which was recovered by means of electromagnets. The ore concentrates have been shipped to blast furnaces a t Milwaukee, Chicago, and St. Louis, and were carried to the latter place during the War by barges on the Mississippi River. Deposits of hematite and brown ore are scattered through large areas in central and southern Missouri. There are various types of hematite that range in age from pre-Cambrian to Carboniferous. In the Ozark region there are many small deposits of hematite filled into sink holes in the Cambrian rocks. The area south of St. Louis which contains specular hematite in porphyry at Iron Mountain and in slate and conglomerate at Pilot Knob is the most important in the State. Ore was mined here on a large scale prior to 1890 and in small quantities subsequently, but was thought to be nearly exhausted'until a few years ago when prospecting disclosed a considerable body at Iron Mountain. Two areas underlain by Cambrian and Mississippian rocks within which brown ore deposits are scattered are known, one a little southwest of the center of the State, the other in the southeastern part of the State and extending into northern Arkansas. Both hematite and brown ore from the Missouri deposits have been consumed in blast furnaces in the St. Louis district. In northeastern Mississippi scattered deposits of siderite in local thin leuses are found in beds of Eocene lignitic clay and sand. About 1915 a small amount of this ore was mined and reduced to pig iron in a charcoal furnace at Winborn, but the operation was not successful. Promising deposits of brown iron ore occur in several counties of northeastern Texas. The brown ore is found to grade into siderite below the weathered zone. The ore deposits are associated with glauconite (greensand) from which they probably have been derived. The ore-bearing formations which contain the principal deposits of ore are of Eocene age, and consist chidy of sand, gravel, and clay, generally only slightly consolidated. The ferruginous portions of the formations are the most resistant. The iron ore deposits are often found on flat-topped ridges which have persisted because of the greater resistance to erosion offered by beds of ferruginous sandstone, conglomerate, and brown ore with which they are capped. The iron ores of northeastern Texas are not being mined at present although in earlier years iron was mined and manufactured there. Five blast furnaces were operated, one being the property of the State, which, with its associated ore mines was operated by convict labor. Much of the pig iron produced was remelted and cast into iron pipe in local foundries. In Llano and Mason Counties in central Texas small deposits of magnetite or of mixtures of magnetite and hematite have been observed at more than thirty places, associated with schists and gneisses of preCambrian age. The ores are of good quality but of uncertain quantity. In the Black Hills of South Dakota deposits of hematite and brown ore occur in Custer, Meade, and Pen-
nington Counties. One type of the hematite consists of thin alternating layers of specular hematite and quartz, resembling the banded siliceous hematite of the Lake Superior region. The brown ore is of recent and present-day deposition in bogs from water carrying iron from slates and schists bearing pyrite and pyrrhotite. It forms as an ochreous precipitate which has been used in making paint. Rocky Mo/lounfein States.-Maps showing iron ore deposits in the west are as misleading as those of the eastern states. For instance, the two states of the Rocky Mountain group that are the largest producers at present, Wyoming and Utah, do not make as large a showing on the map as do Colorado, Arizona, or Nevada. New Mexico, Idaho, and Montana also are credited with a number of scattered deposits but with no important production. The most important deposits of iron ore in Wyoming are at Hartville in the eastern part of the State near North Platte River. The ore is high-grade hematite in lenses replacing pre-Cambrian schist in contact with a limestone footwall. Ore has been shipped from the Hartville mines since 1868 and constitutes the principal source of supply for the iron and steel plant at Pueblo, Colorado. The ores are mined from open-cuts that at depth become "glory holes" through which the ore is milled downward and camed through tunnels to shafts where it is hoisted to the surface. Other deposits of hematite are in the Seminoe Mountains and near Rawlins. The Rawlins ore is a rich, soft powdery red hematite replacing limestone. This ore was first mined about 1870 and shipped to smelters at Salt Lake City, Omaha, and other places as a metallurgical flux; in 1883 it was used as a paint on the newly completed Brooklyn Bridge. The Seminoe deposits occur in a banded jaspery iron-bearing quartzite of probable Archean age, very similar to formations of this character in the Lake Superior region. The deposits are near the southern edge of a block of preCambrian rocks that have been thrust over Cretaceous sediments. The Seminoe ore has not been mined and, until railroad transportation is available, it is doubtful if any developments will take place. A deposit of magnetite in the form of an igneous dike a t Iron Mountain in southeastern Wyoming is of geological interest but not of present commercial value because it contains generally 20 per cent. or more of titanium. The tonnage is large and, if it becomes possible to so treat the ore as to remove the titanium or if it could be mixed with other ores so as to produce a high titanium iron, the deposit may at some future time become of importance. In Wyoming the iron ores are more generally associated with sedimentary and metamorphic rocks than with igneous rocks. In central Colorado a group of iron ore deposits consisting of magnetite, brown ore, and hematite, in the order named, is exhibited by the general map. The magnetite deposits are principally of the type known as
M A P S H O W I N G D I S T R I B U T I O N O F I R O N ORE D E P O S I T S I N T H E U N I T E D STATES Prepared byE.F.Burrh.rd 0
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contact deposits, formed by replacement of limestone by magnetite a t or near the contact of an intrusive igneous mass, but there are also veins of magnetite within the igneous masses. Certain of the deposits a t Taylor Peak, White Pine, and Cebolla have seemed of sufficientinterest to warrant study and description, but they have not yet developed into mines. Hematite occurs in thin veins in granite. Brown ore occurs usually as a gossan capping deposits of metallic sulfides, having been formed by the oxidation of iron pyrites, but some deposits may have resulted from alteration of ores formed by the replacement of limestone by ironbearing magmatic solutions that first formed siderite and ankerite, as a t Orient in the Sangre de Cristo Mountains; others originated in bogs. Brown ore has been mined a t Orient for the production of iron a t Pueblo and a t other places for flux in local copper and silver smelters. Some of the brown ore contains manganese, as for instance a t Leadville, where it has been used in the manufacture of spiegeleisen. In New Mexico there are nine iron-bearing localities, among which magnetite predominates. The deposits are mainly in the western two-thuds of the State in areas of igneous rocks. Magnetite has been mined for making iron, and brown ore from Glorieta for smelter flux.
According to recent records, Arizona possesses deposits of iron ore a t about seventeen localities, a t ten of which hematite predominates; five are of magnetite, and two are of limonite, although a t certain places there are mixtures of these ores. The deposits are mainly in the southern and western parts of the State, associated with igneous rocks. A large deposit of hematite is on the Fort Apache Indian Reservation about 65 miles southwest of the Atchison, Topeka, and Santa Fe Railroad a t Holbrook. This ore was formed by the replacement of banded chert by iron-bearing magmatic waters. Other large deposits of hematite are in Yavapai and Yuma Counties in limestone and metamorphic rocks. Utah is the only state west of Colorado in which pig iron is a t present made. Most of the required iron ore is produced within the State, and fortunately coke from local coal is also available. Magnetite, brown ore, and hematite are present in scattered deposits a t about thirteen localities. The brown ore is mostly in the northern part of the State and some of it is manganiferous. A deposit of high-grade hematite occurs in the Uinta Mountains, about 35 miles east of Park City. The ore occurs in limestone, probably as a replacement along fracture zones. Magnetite and hematite occur together in large deposits a t Iron Springs, Desert Mount, and Bull Valley in southwestern Utah. These
deposits generally occur in fissure veins, as replacement deposits, and as breccia cement. The associated rocks are Carboniferous limestone, Cretaceous quartzite, and Tertiary limestone, sandstone and lava flows, with the Carboniferous and Cretaceous rocks intruded by early Tertiary andesite laccoliths. The ores are uniformly associated with the andesite and appear to have been deposited by hot ore-bearing solutions that came up from magmas through fissures in the andesite. Within the last 10 years the ore deposits in Iron County have been furnished a railroad outlet and large tonnages of ore have been shipped to the blast furnace a t Provo, Utah. Deposits of iron ore are recorded a t about twenty localities in northern and western Nevada. Magnetite predominates with brown ore and hematite about equally constituting the remainder. Important deposits of magnetite occur in Humboldt County and others are in Eureka, Churchill, Elko, and Pershing Counties, and the brown and hematite ores follow a somewhat similar distribution. Certain of the magnetite deposits are of the replacement type. Nevada is not at present producing iron ore. Idaho has deposits of iron ore a t eight or nine localities within the areas of metamorphic and igneous rock between Pend Oreille Lake and the Snake River. The deposits are mostly of magnetite with a very few of brown ore and hematite. The magnetite deposits although most numerous are apparently small, scattered, and unimportant; the hematite is widespread in lode deposits and not in itself of value; and the brown ore is perhaps the most promising of all. The brown ore is common in association with veins of ores of other metals in many mining districts and has resulted from the oxidation of iron carbonate. Small quantities have been mined as smelter flux and because of its wide distribution consideration has geen given to development of a supply in the northern part of the State near the Coenr d'Alene district to supply a proposed iron iudustry in the vicinity of Spokane. Investigations have not, however, yielded encouraging results as to quantities of ore available. Deposits of iron ore are recorded a t twenty or more localities in Montana. Of these deposits ten are of magnetite, seven of brown ore, and two are of hematite. The brown ore deposits have been formed by the oxidation of pyrite and in bogs. Some of these ores are manganiferons. The magnetite deposits are chiefly in western Montana, and consist of magnetite-bearing sandstone of Upper Cretaceous age. These beds are of sedimentary origin and resemble the accumulations of "black sands" found on certain beaches of the Pacific Ocean and the Great Lakes. The sandstone contains 30 to 50 per cent. of iron but snffers the disadvantage of also containing 6 to 12 per cent. of titanium oxide. Hematite of high grade and of considerable tonnage is found in central Montana, replacing Carboniferous limestone a t its contact with intrusive porphyry. Montana is a t present produang no iron ore. Pacific Coast States.-In California and Washington
iron ore deposits are fairly numerous but Oregon possesses comparatively few deposits. Twenty-five to thirty iron ore deposits are known in Washington. They are predominantly of magnetite but several hematite and fewer brown ore localities are known. The ore localities are mostly in the northern two-thirds of the State in areas of intrusive, metamorphic, and sedimentary rocks. In the southern part of the State there are large areas of Tertiary effusive rocks which are not so favorable for the localization of iron ore 'deposits. The iron ores have been studied by the State and divided into sedimentary, residual, lateritic, replacement, contact metamorphic, and magmatic segregation types. The largest known iron ore body in Washington is in the Cle Elum district, Kittitas County, among eastern spurs of the Cascade Mountains. The ores are apparently mixtures of hematite and magnetite. The most interesting feature of this deposit is its geologic history. The ore lies in discontinuous bodies on the surface of an old serpentine formation a t and in the base of a later sandstone, and there is reason to suppose that the iron ore is a result of concentration by weathering of the serpentine, which, itself, is an alteration product of an igneous rock, peridotite, of pre-Tertiary age. After these weathered, or lateritic, ore bodies were formed on the surface of the serpentine, the sandstone, of Tertiary age, was deposited over them and the rocks of the region were subjected to structural deformations. The iron ore deposits were thus metamorphosed from a probably limonitic state to magnetite and hematite by deep burial and movements of the earth's crust. The ores thus constitute "fossil" deposits (not fossiliferous, however) such as would result if the lateritic iron ores of the north coast of Cuba, now lying a t the surface, were to be buried and metamorphosed, and subsequently exposed by erosion. The ore is of low grade, carrying 40 to 50 per cent. of iron and considerable alumina and silica, also generally some chromium and nickel, as do the Mayari ores of Cuba. The question of establishment of an iron and steel industry in Washington has been considered several times. A steel plant now is in operation a t Seattle but obtains its metal in the form of scrap and as pig iron shipped from Utah and from China. In the interest of this plant a very comprehensive survey was made a few years ago of the iron ore resources of the Pacific Coast but apparently the information obtained did not disclose a sufficient supply to warrant building a blast furnace. Similar inquiries have been made by parties at Spokane with the same result. In northeastern Washington, however, certain deposits of magnetite and hematite in Stevens County have been considered of promise, and a quantity of magnetite mined in 1929 was fused with magnesite of local derivation for the manufacture of ferromagnesite, a refractory. Shipments of brown ore and magnetite for use as flux have been made in the past to smelters. A large part of Oregon is covered by Tertiary effnsive igneous rocks or by Quaternary sediments where iron
ore deposits are not usually found and the only areas in which deposits have been examined are in the extreme northwest and southwest parts of the State. In the northwestern area the ores are of the brown variety. The principal deposits are near the Columbia River a few miles below Portland. The ores lie on and are interbedded with Tertiary basalt and are thought to have originated by weathering of the basaltic rocks and accumulated as hog deposits on land surfaces earlier than the present. These deposits resemble in character and geologic associations some deposits examined by the writer in Misiones Territory, Argentina. A considerable quantity of ore has been shown here by prospecting, hut Oregon is producing no ore a t present on account of lack of markets. The ore in the southwestern area is in Curry County. It is magnetite, in boulders, lenses, and impregnation deposits. The ore of the latter type may be concentrated magnetically and has possible value. Deposits of iron ore are distributed over much of
fortunately, unable to produce iron on a commercial basis, but during the World War made ferrochrome and ferromanganese. The largest deposits are said to be those in Madera County, southeast of Yosemite Valley, the Minaret and Mount Raymond groups. These deposits are of magnetite and specular hematite. Magnetite deposits occur a t Providence Mountains, Cave Canyon, Iron Mountain, Iron King, Iron Age, and other places in San Bernardino County, and a t Eagle Mountain, Riverside County. The hematite deposits are not so important but several are found in the Sierra Nevada and Coast Range, as are also deposits of brown ore derived from the oxidation of pyrite and the alteration of magnetite. Brown ore is, in fact, so common that it is present in every county in California.
California, especially in the Sierra Nevadas and in the isolated mountains of the Mojave Desert. A few deposits are in the areas of volcanic rocks a t the north and a few deposits are near the coast. Recent records show a total of sixty-four deposits, of which thirty-five are of magnetite, fourteen of brown ore, eight of hematite, and seven are unclassified, but there are probably many more deposits that have not been recorded. Many of the deposits are small, or little is known about them, and others are large, but difficult of access. The inaccessibility of the more important deposits, together with the lack of a market for iron ore on the Pacific Coast has retarded the exploration and development of these deposits. The iron ore deposits in California are so numerous that only a few can he mentioned here. In the northern part of the State, on Pitt River, magnetite occurs a t the contact between diabase and limestone. This ore was used for several years in an experimental electric furnace a t Heroult which was, un-
ores of the Lake Superior and the Southern Appalachian regions, are in basin areas of sedimentary rocks that make an inconspicuous showing on the map. The Lake Superior deposits have been concentrated into ores of greater richness through igneous intrusions and agencies of metamorphism and through long weathering than the less disturbed beds in the southeastern states. Magnetite deposits are generally found in areas of metamorphic and igneous rocks. Brown ore and siderite are generally found in areas of undisturbed, often comparatively recent sediments, except where the brown ore is an alteration product of veins containing iron sulfides or iron carbonates in areas of igneous and metamorphic rocks. The majority of the deposits of iron ore of all classes, aside from those in the Lake Superior, southern Appalachian, and Adirondack regions, are widely scattered and of limited extent although much study is still desirable in order to appraise accurately the majority of the deposits in the Western
GEOLOGIC DISTRIBUTION OF THE IRON O R E DEPOSITS
As a general review it might be of interest to glance again at the map of iron ore deposits and to recall that the larger deposits of bedded hematite, including the
IRONORBM ~ B IN D TEE& UNlTBD STATBS I N 1930 AND 1931. BY STATBS *NO Vdllls~IBSM . GROSS TONS
States, It is also noteworthy that few iron ore deposits have been encountered in the central plains region or in large portions of the region covered by glacial drift.
(Exclusive of ore containing 6 per cent. or mare of manganese)
m.,-. 6" ef
slolc
FOREIGN SUPPLIES OF IRON ORE
The United States is not a t present dependent to an important degree upon foreign sources of iron ore. Certain eastern seaboard blast furnaces can a t present, however, utilize foreign ore more advantageously than domestic ore. The quantities of ore imported into the United States are not large, as compared with domestic production, having ranged in the last two decades between 300,000 tons and 3,140,000 tons annually. The foreign ores come from practically every continent, but the bulk of the recent imports are from Chile, Algeria and Tunisia, Sweden, Norway, Cuba, Spain, Newfoundland, Soviet Russia in Europe, Australia, Brazil, and Egypt, although the quantities vary considerably from year to year. The foreign ores come principally into the ports of Baltimore, New York, Boston, and Philadelphia. Most of these foreign countries and others, also, possess large reserves of high-grade iron ore which may be drawn upon when the domestic ores become too lean for profitable exploitation. Especially is this true of Brazil, Venezuela, and Newfoundland. This will tend to retard the exploitation of domestic deposits which do not fuliil the conditions mentioned on page 199 that ,are essential to the development of an iron ore deposit. PRODUCTION AND RESERVES OF IRON ORE
The following statistical summary by H. W. Davis, published in "Mineral Resources of the United States for 1930 and 1931" by the U. S. Bureau of Mines, gives the quantities of each variety of ore mined in the several states during the nearly normal year, 1930, and a year of depression, 1931. The grand total production of iron ore recorded from 1810 to 1931, inclusive. is 2,017,035,339 gross tons.
namofila
A di"~
Miner
1930 Alabama.. ..... Arizona.. Colorado. ...... Georgia.. Michigan.. Minneota.. .... Mirsouri.. New Jersey.. New Merieo.. New York.. .... North Cnm1ina. Pennnglvaoia.. Tennessee.. Utah. Virginia.. ...... wiscantin Wyoming.
...... ......
..... ...
.....
..
.
....
......... ......
23 1 1 5 60 84 6 6 2 5
13,544,277 34,517,748 132,434
1 2 3 3 1 4 1
326 8277,774
..... -
6,161,089 923
...
...
... 1
... ... ...
1,321,360 320.023
208 'd55,265.954 1931
...... ..... ...... ..... ......
Alabama. Calorado.. Georgia.. Michigan.. Minnesota.. .... M'Lso"~~. New 1"rsey..... New Mexico.. New York.. Penmylvania.. . Tenneseee.. Ufah. Wsrhington.. wircoosin.. Wyoming.
..
....
....
......... .. ....
14 1 3 55 67 '16 5 10 5 2 1 2 1 3 1
..... . -
3.%9.481
...
7.&2,581 17,445,003 54,139
...
... z ... ...
183.668
...
879.832 180.771
----
Total, 1931.. '186 '29,665,475 359,960 '1,105,249 818 Total. 1930... 208 ','55,265.954 V20.496 22.421.211 1.003
31,131,502 68.408.664
1 In addition, an undetermined number of small pits were worked at 212 propertics in Missouri. The output from there *ts is ineluded in the fisures ~
~
?+"en.
'Some hematite ioeluded with magnetite. a Some hematite included with brown ore.
A rough estimate of the probable reserves of ore of present grade in the United States today ranges between 5,000,000,000 and 7,500,000,000 gross tons. The reserves of low-grade ore are enormously greater.
(Part III on Sources of Ores of the Fnroczlloy Metals will appcar in the J m e issue.)
