THE OCCURRENCE OF RUTILE IN THE TITANIFEROUS MAGNETITES OF WESTERN NORTH CAROLINA AND EASTERN TENNESSEE.1

W. S. BAYLEY.

INTRODUCTION

In the Appalachian and Piedmont districts of North Carolina are numerous bodies of titaniferous magnetites that have been known for many years. They have generally been regarded as consisting of ilmenite or of mixtures of ilmenite and magnetite, though Genth2 as early as 1875 surmised that some of them might be mixtures of magnetic iron with titaniferous hematite, or menaccite, and probably also with rutile; but none of the constituents could be separated in a state of such purity that their true mineralogical character could be verified by analysis. 
   It has long been known that some of the ores richest in titanium exhibit no magnetism when subjected to the influence of an ordinary horseshoe magnetite. In these the titanium is probably present in ilmenite since if it were present in rutile, there would necessarily be present also considerable quantities of magnetite, and the mixture would be magnetic. 
   In 1913 Singewald3 concluded as the result of his metallographic studies that some of the ores in the United States are pure

   1 Presented before the Society of Economic Geologists, Ann Arbor Meeting, December, 1922. The observations on which the discussion is based were made during a study of the iron-ores of the district under the auspices of the North Carolina Geologic and Economic Survey and the United States Geological Survey. Publication is with the permission of the Directors of these Surveys. 
   2 Genth, F. A., Report of the Geological Survey of North Carolina, vol. i, p. 244, 1875. 
   3 Singewald, J. T., Jr., " The Titaniferous Iron Ores in the United States," U. S. Bureau of Mines Bull. 64, pp. 80-93, 1913.

382

RUTILE IN NORTH CAROLINA AND TENNESSEE.           383

ilmenite and others are intergrowths of magnetite and ilmenite. 
   However, an analysis4 of the insoluble portion of a specimen of titaniferous ore from the Dannemora mine in Rockingham County, N. C., gave 11.82 per cent, TiO₂ and no iron. Evidently in this ore the titanium is in rutile or some other oxide. It cannot be in any compound of titanium except the oxide since only very small quantities of other constituents than SiO₂ and A1₂O₃ were shown by the analysis. (See p. 387.) 
   Thin sections of the ores from openings on the properties of Wm. Smith, and of C. Pennington, in Ashe Co., N. C., and from a pit in Lost Cove, Carter Co., Tenn., all show the presence of a yellowish-red rutile intergrown with an opaque ore-mineral which is probably in greater part magnetite. 
   Singewald5 has called attention to the fact that Soligman, Cathfein and Mugge have described intergrowths of rutile and magnetite, and Warren6 has pointed out that some of the analyses of titaniferous iron-ores from well-known localities show an excess of TiO₂ over that required for ilmenite. This he surmises is in the form of rutile, though positive evidence of the fact is lacking. 
   In the case described by Cathrein and Warren the rutile was in lamellar intergrowths in which the lamellae were so narrow that it was difficult or impossible to identify the mineral with certainty. 
   On the other hand, intergrowths of rutile and ilmenite are shown by a few pebbles from placer concentrates on the Pacific Coast.  In one there appeared to be a replacement of the rutile by the ilmenite, as the outside of the pebble was almost entirely ilmenite.  Moreover, Mr. Hess has called the attention of the author to crystals from Shooting Creek, Clay County, N. C., that are intergrowths of a large proportion of rutile with a small proportion of ilmenite, and recently, Watson 7 has described and

   4 Tenth Census U. S., vol. 15, p. 311. 
   5 Op. cit., pp. 24, 27. 
   6 Warren, C. H., " On the Microstructure of Certain Titanic Iron Ores," econ. geology, vol. 13, pp. 419—446, 1918. 
   7 Watson, T. L., " Rutile-ilmenite Intergrowth," Amer. Miner., vol. 7, p. 185, 1922. 

given analyses of rutile crystals from a quartz vein in Franklin County, Va., that are intergrowths of ilmenite and rutile. The forms are those of rutile crystals, but their material consists partly of ilmenite, in one case described by the author, to the extent of about 40 per cent. 
   Further, in a rutile-sapphirine-ilmenite at St. Urbain, Quebec, Warren 8 finds the ilmenite to be thickly sprinkled with grains of an orange-red rutile, spinel and other minerals. The rutile is in the form of crystal grains or clusters, distributed nearly uniformly through a lamellar intergrowth of ilmenite and hematite. Again, in the rutile-nelsonite9 of Goochland and Hanover Counties in Virginia the rutile may be intergrown with ilmenite, but the material is so thoroughly crushed that the nature of the intergrowth was not determined. 
   These observations indicate that whereas intergrowths of magnetite and rutile may be rare those of ilmenite and rutile are not uncommon.

   In the few sections of the North Carolina ores that have been examined microscopically rutile has been found in abundance. It is not in minute needles, nor in definite grains uniformly distributed through magnetite or ilmenite, but is for the most part in broad yellowish-brown translucent masses which in some cases are wider than the opaque magnetite or ilmenite between them. (Plate XI, A. C.) In the Tuscarora ore, however, it appears to exist in part as crystals imbedded in magnetite. 
   The appearance in the first variety is as though the rutile had formed along definite planes and had gradually replaced the magnetite or ilmenite on both sides,10 until in some specimens

   8Warren, C. H., "The Ilmenite Rocks near St. Urbain, Quebec; a New Occurrence of Rutile and Sapphirine," Amer. Jour. Sci., 4th ser., vol. 33, pp. 263— 277, 1912. 
   9 Watson,. T. L., and Taber, Stephen, " Geology of the Titanium and Apatite Deposits of Virginia," Virginia Geol. Survey Bull. III.—A. 
   10 The appearance is very similar to that of the polished surface of the Tuscarora ore illustrated by Singewald (op. cit., p. 88) in PI. 7, A, where the light-colored bars are described as ilmenite. 

there is now left only a narrow layer of the opaque mineral between neighboring layers of the brownish rutile. That the opaque mineral is magnetite rather than ilmenite is indicated by the strong magnetism of the ore. Of course, it is possible that the material of the ore grains was once an intergrowth of magnetite and ilmenite and that the present interlayering of magnetite and rutile is the result of some sort of metamorphism of the ilmenite.11 
   In the ore of the Tuscarora mine the rutile is apparently original, as some of its particles that are completely imbedded in the ore minerals show crystal outlines. Moreover, a few similar crystals are imbedded in the amphibole that lies between the ore grains. In the case of the Tuscarora ore it seems necessary to conclude that the rutile was one of the first minerals to form, as it was in the St. Urbain rocks and may be in the rutile-nelsonite of Virginia, being preceded only by spinel which occupies the centers of many of its grains. 
   Four thin sections of the Tuscarora ore, made from two specimens kindly furnished by Dr. Singewald, show the presence of many grains of red-brown, pleochroic rutile, a small quantity of a green transparent isotropic mineral that is probably pleonaste or a spinel closely allied to this, much opaque material and a very little colorless or very light green amphibole that may be anthophyllite. The opaque material is mainly magnetite with perhaps some ilmenite, but the two cannot be discriminated. The rutile occurs imbedded in the ore mineral and also to a less extent in the interstitial anthophyllite. Its particles bear the same relation to the opaque mineral as do the light and dark minerals shown in Singewald's photograph12 of a polished specimen of ore (Plate XI D). The rutile in the ore occupies the positions corresponding to the light portions of the photograph. Most of it occurs in streaks about 1 millimeter long and about 0.12 millimeter wide, or in sharp-edged rhomboidal

   11 Compare Warren's comments on the intergrowths of ilmenite and hematite in the St. Urbain ilmenites: Amer. Jour. Sci., 4th ser., vol. 33, pp. 266-7, 1912.
   12 Op. cit., pi. II., C.

    26 

or wedge-shaped grains measuring about 0.7 by 0.3 millimeters in diameter, but it occurs also as very irregularly outlined pieces, as small crystals, as narrow rods and as little dust-like particles scattered irregularly through the magnetite. In the centers of some of its grains are little masses of a green spinel with very irregular shapes. 
   The Tuscarora ore is similar to the emery ore at Dobson Mountain in Macon County except in the proportion of the components present. It is true that no corundum was detected in thin sections of the Tuscarora ore, but the mineral is known to be present in the ore-mass. 
   The Dobson Mountain occurrence is on the northeast side of the divide between Cartoogajay and Skenah Creeks, about 4 miles west of Franklin. The ore is in a talcose amphibolite, which is thought by Pratt and Lewis13 to occur as dikes near the borders of intrusive peridotite masses. The ore forms a series of indefinite veins
"along a contact of a sort of talc or soapstone material."14 
   Thin sections of the ore show an aggregate of light green amphibole, colorless corundum splotched with blue, bright green spinel, reddish-brown rutile and opaque magnetite. The magnetite and rutile serve as the matrix by which the other minerals are surrounded. Magnetite and spinel are the most abundant components, followed by rutile, amphibole and corundum. The last named mineral, in the two slides studied, occurs in streaks through the aggregate and the rutile appears to crowd around the magnetite as though deposited upon it.15 The ore is plainly a separation from the amphibolite phase of the peridotite magma.

CHEMICAL COMPOSITION OF THE ORES.

Gross Composition.—Two complete analyses and many partial analyses show the presence of chromium in all the samples of titaniferous ore in which it was sought, of an excess of A12O3 in many and only a small quantity of manganese in any. 
   13 Pratt, J. H., and Lewis, J. V., "Corundum and the Peridotites of Western North Carolina," North Carolina Geol. Survey, vol. I, p. 251, 1905.
   14 From a letter of Mr. J. L. Stuckey.
   15 The Fixkörper-Absatz of Vogt. See Jour, of Geol., vol. 29, p. 319, 1921. 

Analyses of samples of the ore from other openings show the

388                                        W. S. BAYLEY.

presence of TiO₂ varying between about 4 per cent. Ti to 96 per cent. Fe and 47.5 per cent. Ti to 52.5 per cent. Fe. In some samples which have not been examined microscopically, there is more than enough titanium present to form ilmenite with all the iron, consequently, it may fairly be assumed that in these, as well as in those that have been seen in thin sections, the excess of titanium is in rutile. 
    Chromium.—Moreover, in every sample in which it has been sought chromium has been found to be present in proportions varying between 0.34 per cent, and 1.19 per cent. of Cr₂O₃ in the whole ore, or from .007 to 2.3 parts Cr₂O₃ to 100 parts iron.  It is evident that the chromium is associated with magnetite rather than with ilmenite, or rutile, since when an ore from the McCuiston place in the Tuscarora belt was subjected to the influence of a magnet, most of the chromium went with the magnetic portion.¹⁶ Whereas about 95 per cent. of the TiO₂ went into the nonmagnetic portion nearly 77 per cent. of the Cr₂O₃ went with the magnetite.

COMPOSITION OF MAGNETIC AND NONMAGNETIC PORTIONS OF  McCUISTON TlTANIFEROUS ORE. 
 

Nearly all titaniferous ores, wherever found, contain notable quantities of chromium. Watson¹⁷ reports it in both the ilmenite and rutile of the Nelsonite district in Virginia and states¹⁸ that Hasselberg found it in 10 of 12 rutiles examined by him.  Kemp¹⁹

   ¹⁶ Genth, F. A., Report of the Geological Survey of North Carolina, vol I., p. 245, 1875.

    17 Op. cit., pp. 107, 119, 194, 1913.

   18 Watson, T. L., " Vanadium and Chromium in Rutile and the Possible Effect of Vanadium on Color," Jour. Wash. Acad. Sci., vol. 2, p. 431, 1912. 

   19 Kemp, J. F., "The Titaniferous Iron Ores of the Adirondacks," U. S. Geol. Survey, 19th Ann. Rept., pt. 3, p. 390, 1899. 

declares that " at least traces of chromium are almost invariably present in titaniferous ores" and quotes²⁰ a number of analyses to substantiate his statement.  The North Carolina titaniferous magnetites furnish another instance of this association, but in these ores the chromium appears to be in the magnetite rather than in the titaniferous component. It was not found in the rutile of the Dannemora ore. (Compare analysis III.)
   On the other hand, titanium has not been reported in the chromite of North Carolina, nor is it known to be present generally in the chromite of other regions, though it has been found in the chromiferous iron ores of Mt. Poon, Greece, where an ore is mined containing 47.50-49.10 per cent. of iron, 2.19-2.45 per cent. of chromium, and 0.45-0.60 per cent. of titanium dioxide.²¹ 
   .Vanadium.—Vanadium also is declared to be a common component of titaniferous iron-ores. It is usually present in less than half of one per cent. of V₂O₅, but the titaniferous magnetites, Kemp states, are the only magnetites yielding more than traces of this oxide. Watson²² reports it in the rutile and ilmenite separated from Virginia nelsonite and remarks that in the three specimens analysed the V₂O₃ is in excess of the Cr₂O₃.  He reports²³ that Hasselberg²⁴ found vanadium in 12 rutiles and that in those rutiles studied by him in which vanadium was present in appreciable amounts chromium was also present, but in those in which vanadium was present in very small amounts chromium was absent or was present only in traces.  In the North Carolina titaniferous ores, which are known to contain rutile, the chromium content is comparatively large and vanadium is absent.  At least this is true of the two ores in which vanadium has been sought. 
   In view of Kemp's statement with reference to the association of vanadium and titanium it is interesting to note that the ore from

   ²⁰ Op. cit., p. 387-388.

   ²¹ Quoted from Cirkel's Report on the chrome iron ore deposits in the eastern townships, Prov. of Quebec., Dept. of Mines, Canada, Mines Branch No. 29, p. 9, 1909.

   ²² Virginia Geol. Survey Bull. III.-A, pp. 107, 119, 194, 1913.

   ²³ Op. cit., p. 228.

   ²⁴ Hasselberg, B., Chem. News, vol. 76, pp. 102-104, 1897. 

390                                            W. S. BAYLEY.

the Smith place, in North Carolina, though it contains 12.96 per cent. of TiO₂ contains no V₂O₅ and there is none in the titaniferous ore of Lost Cove, Tenn.  Moreover, none was reported by the chemists of the l0th Census in the ore of the Dannemora Mine, Guilford Co., N. C., though in this case the absence of this oxide from the record may be due to the fact that it was not looked for.  On the other hand, the magnetite²⁵ of the Hibernia Mine in New Jersey, with only 0.54 per cent. of TiO₂ contains 0.14 per cent. of V₂O₃ (about 0.17 per cent. of V₂O₅), and that of the Richard Mine with only 0.30 per cent. of TiO₂ contains 0.11 per cent. of V₂O₃ (about 0.13 per cent. of V₂O₅).  
   Singewald²⁶ has already referred to the presence of vanadium in the New Jersey ores as controverting Pope's view²⁷ that the titaniferous magnetites are characterized by the presence of V₂O₅ in the ratio of about 1:28 of their TiO₂ content and that the nontitaniferous magnetities contain none.  He shows that in the New Jersey ores the ratio of V₂O₅ to TiO₂ varies all the way between 1 to 3.2 and 1 to 11.9, instead of being always in the neighborhood of 1 to 28.  If the New Jersey ores are not to be regarded as titaniferous, since they contain less than 1.5 per cent. of TiO₂, their analyses "indicate that a vanadium content is not characteristic of the titaniferous ores alone." The analyses of the Smith and Lost Cove ores, in North Carolina and Tennessee, indicate, on the other hand, that this oxide is not characteristic of all titaniferous ores.  Moreover, analyses of the nontitaniferous ores of the Cranberry and Peg Leg mines show no V₂O₃.  Thus we may fairly infer that presence or absence of vanadium in iron ores is more characteristic of the province in which the ores occur than of the variety of ore occurring in it. 
   Alumina.—The high alumina in many of the southern ores may be due in some to corundum and in others to a spinel.  A green spinel has been noted in the ore of the Tuscarora Mine,

   ²⁵ Bayley, W. S., " Iron Mines and Mining in New Jersey," Geol. Survey of N. J. Final Report Series of the State Geologist, vol. 7, pp. 112—113, 1910. 
   ²⁶ Singewald, J. T., Jr., op. cit., p. 80. 
   ²⁷ Pope, F. J., " Investigation of Magnetic Iron Ores from Eastern Ontario," Trans. Am. Inst. Min. Eng., vol. 29, pp. 395—397, 1899. 

and both spinel and corundum in the titaniferous emery of Dobson Mountain. Moreover, corundum is known to occur in many of the titaniferous ore-bodies at various points on the Piedmont Plateau in North Carolina.  The analysis of the insoluble residue of the Dannemora ore indicates its presence in this ore.

OCCURRENCE AND ORIGIN OF THE ORES.²⁸

   All the titaniferous ores in North Carolina and Eastern Tennessee that have been studied occur as vein-like bodies associated with peridotites, olivine gabbros or talcose and serpentinous schists.  In this respect they are very different from the non-titaniferous magnetites in the same district, which are always associated with pegmatite.  At Senia P. O., which is at the mouth of Roaring Creek in Avery County, N C, the ore is in a series of small veins in websterite.  At the Smith place, in Ashe County, the ore particles are in a weakly polarizing material in elliptical areas outlined by magnetite dust (Pl.XI B). This material under high powers is found to be composed of a light green, fibrous, chloride mass containing minute spicules of a brightly doubly refracting mineral and particles of magnetite or tiny grains of rutile.  If the streaks of magnetite dust that surround the elliptical areas mark the boundaries of some mineral that has disappeared, it is probable that this mineral was olivine, as the boundaries are like those of cross-sections of olivine.  Other sections reveal a mass of fibrous minerals among which may be recognized actinolite, epidote and chlorite and a large quantity of a very finely fibrous material that is probably serpentine, forming a felt in which the other fibrous components and the ore grains are imbedded.  In some places are curved lines of magnetite particles surrounding portions of the felt in a way that may mark the outlines of what were originally olivine crystals.  The titaniferous ores of other deposits in Ashe Co. are of the same general character as at the Smith place.  They consist of ore particles in a fibrous aggregate that may have been derived from olivinitic rocks.  At the Tus-

   ²⁸ For a more detailed discussion of the origin of the titaniferous ores see: U. S. Geol. Survey Bull. 735-G, pp. 260—261, 1922.

carora Mine the rock immediately associated with the ore is an olivine gabbro. 
   Thus the titaniferous ores are associated with basic rocks, which elsewhere in the State are dunites, amphibolites and olivine gabbros,²⁹ containing corundum, spinel, chromite, and in some places rutile.³⁰  The ores always contain titanium, chromium and spinel and in some places corundum.  At several places the mixture of magnetite, rutile, spinel and corundum, because of the large quantities of the last two named minerals present in them, are more properly ores of "emery" than of iron. 
   It appears probable, therefore, that most of the titaniferous magnetites studied are apophyses of dunite and peridotite magmas that have intruded pre-cambrian schists along their foliation planes in the form of narrow veins or flat lenses.  In North Carolina, however, some of the ores are apparently free from gangue.  These may have been deposited by hydrothermal processes, or they may represent late intrusions into cooled portions of the magma from which they were differentiated.

UNIVERSITY OF ILLINOIS,
    URBANA, ILL.

   ²⁹ Pratt, J. H., and Lewis, J. V., North Carolina Geol. Survey, vol. i, pp. 369-384, 1905. 
   ³⁰ Pratt, J. H., and Lewis, J. V., op. cit., pp. 277, 279, 280.