Economic Geology and the Bulletin of the Society of Economic Geologists April-May 1921: Vol 16 Iss 3

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Economic Geology and the Bulletin of the Society of Economic Geologists April-May 1921: Volume 16 , Issue 3. Digitized from IA1518511-02 . Previous issue:…

Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.

Economic Geology

With Which Is Incorporated

The American Geologist

Vou. XVI APRIL-MAY, 1921

THE ORIGIN OF GRAPHITE. THomas H. Crark.

Contents.

Classification of Deposits Bedded Deposits Disseminated Deposits Vein and Vein-like Deposits Ceylon Siberia Montana Canada Adirondacks Pegmatite Deposits Deposits with Native Iron and in Meteorites ae, PESTEMONY OF ABTIFICIAL GRAPHITE <..05 os 6. sido se seesivecicscwc Den ORIGIN OF THE VEIN: LYPE OF GRAPHITE <..6.6 6 ss0ccsdsieccewacwcces

Introduction.

During 1919 and 1920 the writer devoted much time to the study of the literature concerning the occurrence and origin of graphite, and at that time had reason to believe that he had recog- nized the possibility of a previously unrecognized mode of origin of that mineral. Upon reading Alling’s recent treatise, to which he did not at first have access, it was seen that this mode of origin was to some extent recognized in that paper in what was probably

168 Thomas H. Clark.

a random remark, no attempt being made to support it by observa- tions or reasoning. I quote from Alling, italicizing the sentence in question:

This [a series of chemical equations] goes to show that the oxides of carbon (gases) in the presence of gaseous water react to form graphite. Much of this water is probably magmatic, while some of it may be derived from the sediments. Available analyses of such rocks give from I to 2 per cent. of water. This may partly explain the occurrence of graphite at the margins of pegmatites; the heat of the intrusives releas- ing it from the sediments and acting as one of the reagents. In a similar manner the CO, from limestones (CaCO,) may have been liber- ated and thus there is furnished another reagent for the process.

On account of the many excellent articles on the subject, this paper is devoted almost exclusively to a consideration of the evidence for, and an elaboration of, the idea suggested above.

An earlier reference to this idea is to be found in a paper by H. P. H. Brumell.? In the discussion, Brumell answered a ques- tion in the following words:

I would therefore suggest that these masses [intrusive bodies], in con- junction with siliceous or other waters, acted upon the original rocks

and freeing the carbon which forming sulphates and silicates rede- posited the carbon as graphite in the rock.

Here again this was a chance remark containing an idea which Brumell did not consider of sufficient weight to include in the body of his paper.

The Occurrence Of Graphite.

Classification of Deposits. Ina consideration of the occurrence of graphite, some classification of the many types of deposits is desirable. There are already nearly as many classifications as there are writers on the subject. Stutzer,® for instance, divides

1 Alling, H. L., N. Y. State Mus. Bull. 199, “The Adirondack Graphite De- posits,” 1918, p. 147.

2 Jour. Can. Min. Inst., 1908, vol. XI., pp. 236-50.

3 Stutzer, O., “Die Wichtigsten Lagerstatten der ‘ Nicht-Erze,’” Berlin, IQII, p. 77.

nn wm

The Origin Of Graphite, 169

all graphite deposits into first, those of organic origin, and second, those of inorganic origin. This system leads to confusion because of the difference of opinion as to the organic or inorganic nature of some deposits. Miller* adopts the same scheme, while Bastin® discusses the subject from the point of view of the occurrence of graphite in either igneous, sedimentary or metamorphic rocks. De Launay® used a more detailed classification than the last, recognizing four types of deposits, those in basic rocks, in acidic rocks, in gneisses and schists, and lastly bedded deposits. Most writers divide the occurrences of graphite into three types, bedded, disseminated, and vein deposits. Alling suggests that, owing to the confusion attending the indiscriminate use of the term vein, we substitute, whenever possible, the term contact deposit, a suggestion which is well supported by the evidence. A simple classification, complete enough to include every de-

posit of the mineral known to the writer, is given below: . Bedded Deposits. . Disseminated Deposits. 3. Vein, or Vein-like, Deposits.

Fissure Veins.

Contact Deposits.

Pegmatite Deposits. 4. Deposits with Native Iron and in Meteorites.

eS

iS)

Bedded Deposits.

This group includes all massive deposits in sedimentary rocks, concordant with the bedding, and usually of wide extent. A few typical examples of deposits of this class are, Sonora, Mexico ;? Raton, New Mexico;§ Newport, Rhode Island,? and Mount Bopple, Queensland.?° All writers agree that this type of graphite

4 Miller, B. L., Penn. Top. and Geol. Surv. Comm., Rept. 6, 1912, p. 23.

5 Bastin, E. S., Min. Res. U. S. for 1913, Part 2, U. S. G. S., 1914, p. 183,

6 De Launay, L., “ Traité de Métallogénie, Gites Minéraux et Meétalliféres,” pt. 1, Paris, 1913, p. 379.

7 Newberry, J. S., Sch. of Mines Quart., VIII., 1887, p. 334.

8 Lee, W. T., U. S. Geol. Surv. Bull. 530, 1913, pp. 371-374.

® Brown, C. W., U. S. Geol. Surv. Min. Resour. for 1908, Pt. 2, p. 731, 1900.

10 Min. Ind., 1904. Queensland Geol. Surv. 204, 1906.

170 Thomas H. Clark.

is the result of the metamorphism of carbonaceous sediments, and, in fact, in most cases, of coal beds. Either contact or dynamic metamorphism may be responsible for the change, but static metamorphism does not seem to have been active in trans- forming coal beds into graphite. Of the agents of metamorphism, heat seems to have been the most important factor, since all of the volatile constituents of the original coal must be dispersed in order to allow the formation of graphite. Even in the contact metamorphism of sediments, pneumatolytic processes seem to play no part in the production of this type of graphite. There is no apparent reason why static metamorphism should not produce graphite from coal, but it is rare that a series of sediments is affected by this type of metamorphism without other factors complicating the process.

Disseminated Deposits.

Under this head are described those occurrences in which the mineral is more or less evenly distributed throughout the rock, in most cases either a gneiss or a schist. Genetically, this type of deposit is not far removed from the preceding. In most cases, it is the result of the metamorphism of carbonaceous sediments, but not of sediments which would have ranked as coal beds in their original state. Thus a schist derived from a black shale would probably contain some graphite. In fact, wherever organic matter has been trapped in strata undergoing metamorphism graphite is likely to result. This transformation of organic mat- ter to graphite affects alike siliceous, argillaceous and calcareous sediments.

Here, too, are included the “bedded veins and masses” of Cirkel,1? which do not seem to be anything but local concentra- tions of disseminated graphite. Cirkel says:

The principal feature of bedded veins is that their general outline and main direction conforms with the stratification of the country rock;

they form in the majority of cases disconnected layers, lenticular masses or chain-like accumulations.

11 Cirkel, F., Dept. of Mines, Canada, “ Graphite,” 1907, p. 23.

The Origin Of Graphite. 172

This type is the most widely distributed and the most abundant form of graphite. Of the many well known regions where it is found, a few typical ones are: Passau, Bavaria;!2 Saazer Mts., Bohemia Madagascar ;1* Buckingham, Que.,” Grenville Dis- trict, Ont.,° and the southern part of the Adirondack region, New York.'*

With one exception, every investigator of this type of graphite deposit has come to the conclusion that the enclosing rocks are metamorphosed sediments, and that the present graphite repre- sents all or part of the original carbonaceous organic matter con- tained in them. Weinschenk concluded that the graphite of the Passau gneisses was an impregnation from the nearby intrusive granite, but there seems to be little or no evidence in support of this supposition. The difference between this type and the pre- ceding type, the Bedded Deposits, is chiefly that in the latter the original sediment was much richer in carbon; as a rule, too, the metamorphism of the beds containing the Bedded Deposits was not as intense as in the case of the rocks carrying disseminated graphite.

Vein and Vein-like Deposits.

As will be seen below, this class of deposits is genetically dis- tinct from the two preceding ones, and it is with the origin of some of these deposits that this paper is chiefly concerned. It is unfortunate that some writers on this subject either do not describe accurately what they see, or else are lax in the use of the term vein, since a good many so-called vein deposits are not deposits in veins, but merely segregations of the disseminated type. Moreover, as Alling has pointed out, many of the so-called vein deposits occur not in fissure veins but in contact zones be- tween sedimentary and igneous rocks.

12 Stutzer, O., op. cit., p. 65.

13 Stutzer, O., idem, p. 17.

14 Shelley, J. W., Min. Mag., vol. 14, June, 1916, p. 324.

15 Cirkel, F., Dept. of Mines, Canada, “ Graphite,” 1907.

16 Jdem. 17 Alling, H. L., op. cit.

172 Thomas H. Clark.

A few of the more important deposits of this type are: Ceylon, Siberia, Montana, Canada, Adirondacks.

Ceylon.—The deposits of Ceylon are of unusual interest in that they yield a fine grade of graphite in amount exceeding any other locality excepting Austria, and they also present problems for which no entirely satisfactory solution has yet been offered.

The island of Ceylon may be divided into two natural divisions —a lowland area, comprising four-fifths of the extent of the island, of Tertiary and Recent sediments on the northeast, and a mountainous region of crystalline rocks in the southwest. It is in the latter region that the graphite occurs. The crystalline rocks are gneisses of varying composition, interbedded with bands of crystalline limestones from a few inches up to several hundred yards in width. It is the presence of these beds of lime- stone which leads most geologists to believe that the crystalline rocks are of sedimentary origin. Locally they have been intruded by several types of igneous rocks, chiefly granite pegmatites.

Although graphite does occur disseminated through both gneisses and limestones, scientific as well as commercial interest is focussed upon the vein and vein-like deposits. All observers agree that in most cases these deposits occur in fissure veins, with two sharply defined boundaries, and occasionally there is an alteration of minerals in the vein. In small veins the graphite usually forms an aggregate of platy needles set at right angles to the wall. In the larger veins most of the graphite shows a coarse platy structure, with perhaps the needle structure next the walls for two or three centimeters. Usually the veins consist almost entirely of graphite. Pyrite is almost always present in varying amounts, either disseminated between the flakes of graphite, or forming a definite band in the central part of the vein. Quartz is also invariably present and sometimes forms a central band. Both these minerals often show intergrowths of graphite in them. Other minerals which are occasionally met with are biotite, ortho- clase, pyroxene, apatite, allanite, and rutile, the last often being developed along the cleavage planes of the graphite crystals.

The Origin Of Graphite. 173

In most districts the veins run parallel to the foliation of the gneiss; they cannot, however, on that evidence alone be supposed to represent carbonaceous beds. In the Kurunegale district the veins run parallel to a system of joint-fractures at right angles to the strike of the foliation. In most cases, minor veins or stringers are sent off from the main ones. One fact is granted by all, that the veins are distinctly younger than the rocks which they traverse.

In width, the veins may be from a few millimeters in diameter up to a meter or more. The walls are sharply defined, and the bordering rock is not impregnated with graphite to a distance of more than a centimeter or two from the veins.

A statement of the various theories'® that have been advanced to explain the origin of the Ceylon graphite has been so well put by Bastin that I quote it below:

Many and varied theories have been proposed to account for the origin of the Ceylon and similar deposits, but none have proven wholly satisfactory. Our knowledge of them is however sufficiently definite to permit us to rule out certain of these theories. The deposits are not metamorphosed interbedded coal, since they form irregular vein sys- tems often cutting across the foliation of the enclosing rocks; on the other hand it is perfectly clear that the graphite was deposited along irregular fracture-planes. Any theory of origin through lateral secre- tion from the wall rocks is untenable because of the extreme sharpness of the vein walls and the scarcity or absence of graphite in the wall rocks. The suggestion that they represent fissures filled with asphalt or other carbonaceous material which was later metamorphosed into graphite, is untenable because in Ceylon and in a number of other locali- ties where such veins occur they are themselves younger than any regional metamorphism or igneous intrusion capable of affecting such a change. ...

It seems necessary to accept the only remaining hypothesis, that of deposition from some sort of a solution penetrating along fracture planes in the rocks. In short, they are true fissure veins.

In conclusion, no theory of the origin of graphite veins can be satis- factory unless it takes into account not only the graphite but the acces- sory minerals, quartz, pyrite, and numerous silicates which are com-

18 Bastin, E. S., “The Graphite Deposit of Ceylon,” Econ. Grot., vol. 7, IQI2, pp. 430-432.

174 Thomas H. Clark.

monly present in these veins. Their presence imposes certain limita- tions which must be reckoned with.

It is precisely this mineral association which has led the writer to the conclusion that graphite of this type, almost invariably found in the contact zones between intrusives and carbonaceous or more frequently calcareous rocks, has been formed by the interaction of these two rocks, or more correctly by the inter- action of magmatic gases and the calcareous sediments. It is believed that there is abundant evidence to sustain the view that the magmatic gases, if they be predominantly siliceous, will combine with such calcite as is available, forming lime-bearing silicates and freeing oxides of carbon, which under favorable conditions may be trapped and reduced to graphite. This must be the result of unusual conditions, for no graphite occurs in the majority of contacts between limestones and intrusives. A fuller treatment of this idea is given in later pages.

Siberia—A deposit which offers problems similar to that of the Ceylon graphite is at the Alibert mines, near Irkutsk, Siberia. The graphite, according to Weinschenk, occurs in a nepheline syenite, which otherwise is quite normal in composition. This syenite with its lateral dikes cuts a series of gneisses, schists, and metamorphic limestones, though the interrelationship between the igneous and metamorphic rocks is not very well described in any work on the region; Weinschenk’s’® description of the field relations is none too clear; De Launay’s” is better; I have not had access to Jaczewski’s*! description.

The graphite occurs as veins and pockets in the syenite, and to some extent in disseminated form through the metamorphics. In thin sections of the syenite Weinschenk notes that there is an intergrowth of graphite with the normal primary minerals. He concludes that the graphite crystallized contemporaneously with

19 Weinschenk, E., Compte Rendu, VIII. Geol. Cong. Internat., vol. I., 1900, Pp. 447. 20 De Launay, L., op. cit., p. 382.

21 Jaczewski, L., “ Explorations géol. et miniéres le long du chemin de fer de Sibérie,” Livre XI., 1899, pp. 19-56.

THE ORIGIN OF GRAPHITE. 175 the other minerals, and therefore must be considered as a primary igneous mineral. Weinschenk says,??

Calcite is partly crystallized out as the first differentiate, and is sur- rounded by a ring of pure biotite. . . . The biotite is for the most part surrounded by feldspar. Graphite is to be found with the calcite.

This seems to indicate that the graphite was obtained from the calcite, and did not originate from the magma. In one sentence Weinschenk mentions “ great xenoliths of limestone in the nephe- line syenite . . . and further the primary calcite observed by ourselves in thin sections.”

De Launay** describes the huge blocks of crystalline limestone enclosed within the syenite. But he draws most of his conclusions from the “ kuge blocks of graphite in the syenite 30 or 40 cm. across and 97 per cent. pure, with no equivalent in the schist.” He continues,

No known reaction will explain such a concentration. Thus the Siberian graphite seems to be of a new kind, of deep-seated inorganic origin, probably of like origin with that of Ceylon.

Jaczewski* considered that all of the graphite of the Alibert mines was of organic origin, a view which neither Weinschenk nor De Launay could accept. This view seems to me to be the most reasonable one, especially as the inference is that the graphite was derived from the sedimentary rocks. Although the presence of both blocks of limestone and of graphite in the svenite would induce the suspicion that the two materials were genetically related, it is not necessary to suppose that the carbon must have come from limestone. Associated with this rock are graphitic schists, whose carbon content might have yielded graphite after all other less stable minerals had been assimilated by the magma. The same processes might be appealed to to break up an inorganic limestone, (i.e., one in which there might have once been organic matter, all trace of which has long since disappeared), CaO being

22 Op. cit.

23 Op. cit., p. 382. 24 Op. cit.

176 Thomas H. Clark.

assimilated, and combinations of C, CO, O, or CO, being freed. So far as I have been able to find out, no one, with.the exception of Alling, has suggested that graphite might be the result of the calcium oxide being absorbed, and then some such reaction as Winchell** or Dixon*® suggested transformfhg the freed oxides of carbon irito graphite. Unfortunately, in this case, we are not told whether any xenoliths show alteration along these lines.

Montana.—A. N. Winchell** has described a deposit of graphite near Dillon, Montana, and in the same paper has devoted a great deal of space to a critical discussion of the chemical con- ditions surrounding its origin. It occurs here in many different forms. At one outcrop it occurs as seams in the bedding planes of the Paleozoic rocks. At another it is seen to be disseminated through nearby pre-Cambrian metamorphics. In some garnet schists, graphite sometimes completely surrounds the garnet crys- tals. All such occurrences might well be included in the Bedded or the Disseminated types. But two other well defined modes of occurrence are described. First, that in which the graphite is contained in a granite pegmatite; Winchell’s explanation of the field relations of this pegmatite is hazy, but he mentions the fact that it intrudes limestone as sills. Secondly, that in which graphite occurs as the filling of veins or fault fissures, not parallel to the bedding ; and also as irregular bunches, pockets and stringers, “having no relation to bedding, but similar to the mode of deposition of vein material in zones where rocks have yielded to stresses, not by clean fracturing, but by irregular shearing.”

This same author discusses the chemistry of graphite forma- tion and disposes of some views which he finds prevalent, as follows:

That the graphite did not exist in the silicate solution in the form of crystal flakes is indicated by the evidence that some of the constituents of the rock are enclosed by the graphite.

25 Winchell, A. N., Econ. GEot., vol. 6, pp. 218-230, I191T. 26 Dixon, H., Jour. Chem. Soc., 1886, 49, p. 94. 27 Op. cit.

The Origin Of Graphite. 177

Further, he cites the extremely refractory nature of the mineral as evidence that it did not exist in the form of liquid or gaseous carbon in the melt. The instability of hydrocarbons at moder- ately high temperatures leads him to reject these substances as a possible source of graphite; and, lastly, the fact that carbides of metals are exiremely unstable in the presence of oxygen (so com- mon in magmas) rules out—for Winchell at least—the carbide theory of the origin of graphite.

His own conclusions, arrived at after much discussion of the chemical reactions involved are best stated in his own words:

1. Graphite is probably formed in nature in several different ways. Graphite in sedimentary rocks may have an origin wholly different from graphite in veins and pegmatites.

2. Confining attention to pegmatites and veins, it is argued that the most probable mode of formation of graphite is by the deoxidation of the oxides of carbon.

3. The deoxidation of carbon dioxide may be caused by hydrogen, or other reducing agent.

4. The partial deoxidation of carbon monoxide occurs in the absence of any reducing agent at temperatures below 900° C, according to the reaction:

2Co=C-+ Co..

5. The oxidation of the carbon of bituminous shales by water (aque- ous gas) at high temperatures, its mobility as a consequence of the formation and the solution of the oxides, and its reprecipitation in places where the solutions reached lower temperatures may all be explained by appealing to the reversible reactions:

C+ 2H,O= Co, + 2H,,. C+ H,O=Co-+ H,.

Canada.—In writing of the Grenville deposits, Osann says,?*

The rocks are limestone, with bands of rusty gneiss, which are traversed by a white granite dike, and this in turn by a dike of light green diabase. The graphite occurs principally in two irregular veins, and also in the granite mass, and there is a small vein on the edge of the diabase.

At present the only graphite being mined at Grenville comes from a gneiss which is interrupted by bands of quartz and

28 Osann, Geol. Surv. Can. Rep. 1899, p. 780.

178 Thomas H. Clark.

granite, and contains beds of crystalline limestone. Between the granite and the graphite are localizations of the lime-contact minerals pyroxene and scapolite. Cirkel found that in most cases graphite was the sole vein-forming mineral, but in others pyroxene, green apatite, scapolite, titanite and wollastonite are associated with graphite. Here, as elsewhere, the presence of both graphite and lime silicates in a contact zone suggests that there may have been a common origin of both. At least, if a common origin can be found, it would considerably simplify matters.

Adirondack Deposits—Alling divides the graphite deposits of the Adirondacks into bedded and contact deposits,?® the first type being almost confined to the northern part of the Adiron- dacks, while the latter occur most frequently in the southern part. With regard to the contact deposits, he has given us a very good account of the geology of most of the known graphite workings

A study of the seventeen occurrences described in detail by Alling in the northern Adirondack region shows that all are in contact zones between igneous rocks (granites, granite pegmatite, syenite, and in a few cases basic rocks), and metamorphic sedi- mentary rocks. In twelve cases the sedimentary rock is lime- stone. In four cases it was probably a schist, and in only one case a quartzite. The most favorable conditions seem to be obtained at the contact between a granite or granite pegmatite and a crystalline limestone. It cannot be said that Alling has described the contact zones with the thoroughness of a petro- grapher,—that was not the purpose of the paper. However, I think we may assume that such minerals as he mentions having observed in connection with each deposit represent all that could be seen without making a careful microscopical examination. A tabulation of the minerals observed by Alling gives the following results.

29 Alling, H. L., of. cit., p. 38.

The Origin Of Graphite, 179

Number of Mineral. Localities. RBUEORONG 55s eae crs sce ah oeide edu wets aor spe eee radewesee 13 SET en Rene eR ee clin ray ei WRI snk Roe P BAR, ee 6 TREAT ANIIO 5 2s 2 ote hess clo halves aoa ecereie te Sele ee mews Mise 3 ROMER ee tan Gia OL ue ie tn ciel Ane comets ges ain Se 3 PER PARE Pees clo laa si divieiacin ob Vaiss ale Date eae eae eee ence we 2 Phlogopite

Thus it will be seen that with the exception of the last two minerals, all are lime-bearing silicates, especially the scapolite and the pyroxene. A casual inspection of the description of the graphite occurrences at Buckingham, Quebec,*® shows much the same kind of relations and contact minerals.

Pegmatite Deposits.

In many places, both in Canada and in Pennsylvania, where pegmatites have been in part at least the agents of metamorphism, they have been observed to carry graphite. Quite frequently this is more abundant towards the walls of the pegmatite bodies and rare or absent from the center. This suggests that the graphite was derived from the adjacent rocks, which are in most cases sediments.

Smith*? cites the case of the graphite-bearing pegmatite at Madrid, Maine, and Yarmouth, Maine. In the former case, he believed that the graphite was derived from the sediments, but of the latter he said “ there is no evidence of any source of the carbon of the graphite other than in the molten rock itself.” From a careful examination of the published field relations, how- ever, I am unable to see why the same explanation which he advanced for the second type of deposit at Madrid, would not equally well do duty for the occurrence at Yarmouth.

A more complicated case is that of a dike 26 miles northeast of Walcha, New South Wales.*? Here graphite occurs in a eurite (felsite) dike, generally micro-pegmatitic, and crowded with spheroidal segregations of graphitic material. The dike has a

30 Cirkel, F., op. cit.

81 Smith, G. O., U. S. Geol. Surv., Bull. 285, pp. 480-483, 1906. 32 Rothwell, Min. Ind., 1904, p. 234, 1905.

180 Thomas H. Clark.

proved depth of 400 feet, throughout which its content of graphite remains unchanged. The country rock is an acidic granite. The graphite of the spheritic kernels is exceedingly fine, and makes up one-quarter of their mass. The kernels are from one-half to one inch in diameter, and constitute one-half of the dike mass. The graphite is evenly distributed throughout the dike.

Greenland.—Steenstrup** has given an interesting account of the geoogical relations of the native iron bearing basalt of Ovifak, and other localities in Greenland. This author states that wherever native iron occurs in basalts, it is always accom- panied by graphite. As far as can be determined from the descriptions, the basalt with graphite (either in dikes or lava flows) is always in close proximity to a coal bed, in some cases cutting through one, as illustrated on page 13 of Steenstrup’s paper, and in others overlying the coal as shown on page 8. That there is a genetic connection between graphite and the native iron is hinted at in this paper; the coal having furnished carbon, part of which reduced the iron, the remainder becoming graphite.

Deposits with Native Iron, and in Meteorites.

The deposit of graphite with native iron near Ovifak, Green- land, discussed above, is mentioned here because there are still those who hold that the native iron of Greenland is of meteoric origin. This has long since been disproved. As for meteorites, no comparison can be drawn between the conditions under which meteoric graphite and the graphite of the earth’s crust were formed. Even if meteorites represent, as is supposed, sub-crustal material, that fact does not help us to understand crustal reac- tions.

The Testimony Of Artificial Graphite.

Graphite has long been recognized as one of the constituents of furnace slag, having been derived, presumably, from the fuel. In

88 Steenstrup, K. J. V., Mineral. Mag., vol. 6, No. 27, 1884, pp. 1-13.

'y

f

The Origin Of Graphite. 181

the laboratory many reactions (mostly at comparatively high temperature) have been recorded** which have yielded graphite For the most part, these have been considered accidents, and in many cases the production of graphite is objectionable. None of these “accidents” seems to throw any light upon the geological occurrence or origin of the mineral.

Clarke states*® Luzi “has shown that amorphous carbon can be converted into graphite by strong heating in melted potash glass containing calcium fluoride and water. In other words graphite can occur in a silicate magma either in consequence of its contact with carbonaceous matter, or as an original constituent brought up from below.” This statement it seems to me is open to ques- tion, since Acheson’s experiments indicate that the carbon of graphite is in the form of a carbide previous to its deposition as graphite. Hence Luzi’s carbon might, in the melt, become a carbide of potassium or calcium or some other allied compound, and crystallize as graphite from the carbide upon cooling. pet f this is a minor detail. %

Acheson was led to the commercial manufacture of graphite by one of the most curious paradoxes ever observed in the course of scientific experimentation. While attempting to obtain a hard crystalline form of carbon (graphite), he discovered the com- pound SiC which he named carborundum. He early recognized the value of the properties of this new substance, and devoted all of his time and energy for the time being to a systematic investigation of its formation. He soon devised a method by which it could be commercially produced. This was achieved by passing an electric current through a furnace filled with coke (C) and sand (Si). Strangely enough, in operating these furnaces, Acheson discovered a layer of brilliant graphite lving between the carbon core and the crystalline carborundum, and an exami- nation showed that this was formed from the decomposition of

34 Acheson, E. G., Journ. Franklin Inst., June, 1890, pp. 1-12.

Clarke, F. W., Bull. 695, U. S. G. S., 1920, pp. 222-323.

Fitzgerald, F. J., Journ. Franklin Inst., Nov., 1902, p. 16. 35 Clarke, F. W., op. cit.

182 Thomas H. Clark.

SiC. Thus, in searching for graphite, Acheson found carbo- rundum; and in experimenting with carborundum, he produced graphite.

Acheson found that by using pure petroleum coke practically no graphite could be made by this process. The larger the known percentage of impurities in the coke (quartz sand not being needed) the greater was the amount of graphite produced. By heating impure coke, first, carbides are formed, and if the tem- perature is held high enough the carbide will be broken down and graphite will result. It seems as if a small amount of ash might have to combine repeatedly with different and successive amounts of coke-carbon, thus allowing a progressive formation and disso- lution of carbides. Silica is not essential to this process, but oxides in general give the best results.

Acheson deduced, from his experiments, that “ graphite is the form that carbon assumes, when freed from chemical associa- tions, under conditions of low pressure and protection from chemical influence.”**

The conditions under which artificial graphite are produced are of very little assistance in helping to understand just how such a process as is implied in this paper might be satisfactorily carried out. Not only is all artificial graphite made from coke, but in the process of manufacture there is nothing which very closely simulates contact metamorphism, nor are there any lime- bearing silicates in the gross product. Acheson’s general con- clusion may be of help, for if the lime is absorbed in the process of contact metamorphism, anything which would deprive the oxides of carbon thus freed of their oxygen would render the carbon “ freed from chemical associations ” and graphite would be the form it would assume. Experimental evidence is needed to substantiate this.

THE ORIGIN OF THE VEIN TYPE OF GRAPHITE. A good summary of the various views concerning the origin of this type is given by Alling," one sentence from which is

86 Acheson, op. cit., p. 9. 37 Op. cit., pp. 144-148.

et

The Origin Of Graphite. 183

quoted previously in this paper. This idea I consider worthy of further elaboration.

Granting that the chemical processes upon which Dixon, Win- chell and others base their formulas are correct, the geological materials required are water and carbon monoxide or carbon dioxide. What evidence is there that these latter substances might come from the calcite of the limestones? This question has already been partly answered on page 176. Among the contact metamorphic minerals developed between igneous rocks and lime- stone the most abundant are lime-bearing minerals, two of which, scapolite and diopside, are almost exclusively confined to meta- limestones. Therefore, it seems probable that, if the limestone furnished the lime (CaO) for the silicates, the remaining carbon dioxide (CO,) furnished the material for the graphite. Of the two derivatives of the calcite, the carbon dioxide would be the more volatile, and therefore the less likely to be “caught” and crystallized. On account of this, it may be, the graphite is fre- quently not found actually at the contact, but separated from the igneous rock by lime silicates, which were less volatile. Just what the conditions are that result in the crystallization of the graphite remain to be established; the work and writings of Acheson offer the most satisfactory suggestion.

This method of deriving graphite renders the old classification of graphite into Organic and Inorganic types undesirable. Such a division must beg the question in many cases, and if the process suggested by this paper be substantiated, who shall say whether the graphite came from organic hydrocarbons, organic calcite, or aragonite, or from inorganic calcite? If this paper does no more than suggest that the best working classification at present is that which takes account only of present geological field relations of the graphite with the containing and surrounding rocks, the way will be cleared to some extent for a more nearly impartial investi- gation of the organic and inorganic origin of this mineral.

DEPARTMENT OF GEOLOGY, HarvarD UNIVERSITY, CAMBRIDGE, Mass.

The Graphite Rocks Of Sleaford Bay, South Australia.

C, &. Tuxey.

CONTENTS. MEDIR OCHO ceric Aci 2 woe MisN eee ae Ok Slee oes bw cab aie we SRE eee 184 SANS MEMACIRSIIEO TF SSETICS Sorc o.n 2 oars cw ose mine aise as wis 5 bree es aos weit SMe ioss 6x 184 TEP OSES Siccbe: She 2c 1 ee A ne een ey eee 185 MUMPUBGRERETROHEIGBES 2 chic sis aves a siete sos os sere a ores wlale k giteRice koa iec 186 MOO GM AISEEE UERISACE 554.5 8 ou olaln aise seo is akin ooib 5 wieierwione oss ov wesibib io we lernie 188 SSaeipt al EDERCTRISGM sc sic sos esc SG oes Wren ens Sic Sie a SSS is 6 she Ses Saw 188 ETT ores se ea resets Nad Ga s\cls Shea oie sine wiwiaisinlowta pices 189 SD CASPIAN MOT URANS GR GIEANIEIES: tors coscdere orc ios aes Sites eee oe wks oe wb wea ninasl Sere or 193 PRPORTADY OD. se SOs oo 5 conc lowes ts iS SE oe i os lee pie oes sued Cros ee ais als feiele eis 198

Introduction.

The basement platform which forms the foundation of south- ern Eyre Peninsula, and on which the much younger Tertiary and Recent sediments repose, consists of a complex of igneous and metamorphic rocks of Precambrian age. These rocks may be regarded as a southeasterly prolongation of the great Pre- cambrian Shield of Western Australia. The Upper Tertiary and Recent sediments superposed on this older complex, consist of sands and travertine, the former largely of zolian origin. These deposits combined with the products of long continued weather- ing of the older rocks, form a mantle over large areas of the country, and hinder the study of the Precambrian over large tracts of the peninsula.

The Hutchison Series.

Within the area of development of graphite-bearing rocks, the Precambrian rocks are divisible into two well-defined series, the Hutchison series and the Flinders series.

Hutchison Series. The members of this series of rocks con- sist of highly metamorphosed sediments, and are the oldest rocks

GRAPHITE ROCKS OF SLEAFORD BAY. 185 recognized throughout the southern portion of the peninsula. The beds now exposed in a highly metamorphosed condition comprise mica schists, garnet gneisses, graphite schists, graphite gneisses, quartzites, dolomites, and calc-magnesian silicate rocks. The beds strike in a north-south direction and dip westerly from 75-90 degrees. Only remnants of this terrain are now exposed, the series having been broken up by the great intrusions of igneous gneisses that succeeded.

Flinders Series. The greater part of the southwestern por- tion of the peninsula is underlain by members of this series, which have invaded and intensely metamorphosed the sedi- mentary terrain of the Hutchison series. This group of rocks is predominantly constituted of acid igneous rocks showing a primary gneissic banding, and a group of basic amphibolites of anterior origin.

The Sleaford Bay Section.

The graphite rocks which are briefly described in this paper* outcrop along the shore line of Sleaford Bay, hundred (town- ship) of Sleaford. The section of the Hutchison series developed in this place is an exposure along the shore line of approximately

500 yards.

a

Fic. 18. Section along the shore at Sleaford Bay. a, Flinders gneiss; p, pegmatite; gr, granite; f, ironstone band; fm, forsterite marble; gs, graphite schist; gn, garnet gneiss; x, no exposure; dm, diopside microcline rocks; d, diopside rock, quartz veins; id, impure diopside rocks with micaceous bands ; tra, transition beds, containing diopside, highly silicified with fault breccia; GGN, garnet graphite gneiss; ms, mica schists. Thickness of individual beds not to scale.

186 Ge RE PEE, ay Ak

half a mile. In the accompanying diagrammatic sections, the relations of the graphite-bearing beds with the associated sedi- ments is indicated in Figs. 18 and 19. The whole series has been penetrated by sills of granite and pegmatite, and by veins of pegmatite and quartz, and composite hybrid rocks have in some

oA °

gn

s wt Soot & a &&@ uo sd 0d ae) Ww wo &

&

Oo k& Se EO >wW wm

ger

so] wD 00 oh

saa ty llretliys Nl

VY Leahey

Plesal hl Ve ee [tt

350 yards

Fic. 19. ‘Section along the shore at Sleaford Bay (continued from Figure 18). gr, granite; agr, aplitic gneiss; di, diopside rock; ms, mica schist; gs. graphite schist; f, ironstone band; ggn, garnet graphite gneiss; hr, horn- blende schist; gn, garnet gneiss; y, ?kaolinised schist with pegmatite veins.

cases thus arisen. A detailed petrographic description of the dolomites and the metamorphism expressed in these rocks, has already been published, and reference may be made to this paper’ for further information.

A brief description of the associated garnet gneisses of the Hutchison series, may here be given before the graphite rocks of Sleaford Bay are dealt with, as these rocks are of consider- able importance in any discussion of the gneisses of the associated graphite rocks.

Garnet Gneisses. The stratigraphical relations of these rocks in the Sleaford Bay area, can be readily interpreted from the accompanying Figs. 18 and 19. These rocks are conformably bedded with the cale-magnesian sediments. The most marked feature of these gneisses is the parallel banded structure, which

1 Tilley, C. E., Geol. Mag., vol. LVII., 1920, pp. 449-62, 492-500.

Graphite Rocks Of Sleaford Bay. 187

is essentially a structure arising from initial differences of com- position in the original sediments. The constituents of these rocks in the Sleaford Bay area, are quartz orthoclase, garnet, biotite, sillimanite, spinel, plagioclase, graphite and zircon.

The garnet is a pink almandine type developed in porphyro- blasts up to 4 inch in diameter. The potash feldspar is a striated microperthitic orthoclase, and plagioclase is usually in quite sub- ordinate amount. Sillimanite, although not an abundant con- stituent, is an important member of some of these rocks. It is accompanied by a dark green spinel of hercynite composition.

Graphite is a constant feature, although generally present in quite minor amount. The orientation is parallel to the banding, and in sections cut perpendicular to the foliation the flakes appear as elongated rods. In reflected light the flakes appear with a steel gray luster like that of magnetite. These rods, however, have the characteristic frayed and serrated edges and a striated appearance on the ground surface, these features arising as a result of the softness of the mineral during grinding.

Similar garnet gneisses are developed northward in the hun- dred of Hutchison, and in a similar association with metamor- phosed dolomites. In these rocks sillimanite is an abundant con- stituent, and is again often accompanied by a dark green spinel.

All these garnet gneisses bear evidence of much metamorphism. Their pronounced banding must be interpreted as a result of initial differences in composition in the original sediments from which they are derived. All traces of original clastic structure have been destroyed by the complete recrystallization that has been involved. The mineralogical composition of the group is that which might be expected in the metamorphism of sediments of the composition of shales grading into more quartzose types and even merging into arkoses where the felspathic element is dominant. An analysis of a typical garnet gneiss from the Slea- ford Bay area, shows that the available criteria for a sedimentary origin are satisfied, and the analysis is close to that of well defined shales. The abundance of the minerals garnet and silli- manite serve as indexes of the origin of the dominant potash

188 CoB, ATELY.

felspar. The strong metamorphism of argillaceous material results usually in the formation of potassic felspar from the more aluminous constituents as the micas, either sericite or biotite. It is obvious that the formation of new felspar from these con- stituents involves the setting free of an excess of alumina to be disposed of. In these rocks this has appeared either as garnet or sillimanite or more rarely spinel.

Garnet gneisses of this type can be matched in Precambrian tracts in other parts of the world. The most striking analogues are the garnet gneisses of the Grenville series of North America. In this connection the garnet gneisses in the region north of Mon- treal, Quebec, those of the Haliburton-Bancroft, Ontario, and the Adirondack region of New York may be mentioned.

The mode of occurrence and associations of all these rocks indicate that they are the products of sediments subject to intense thermal alteration, or members of Grubenmann’s Kata-Zone.”

The Graphite Rocks.

General Description The available data on the occurrence of graphite on Eyre Peninsula are to be found in the Mining Re- views of the Geological Survey of South Australia for 1917 and 1918. R. L. Jack here shows that the graphite deposits extend over a large area of country from the hundred of Slea- ford in the south along the “graphite line” to the county of Jervois in the north. As far as is known the graphite is asso- ciated with metamorphosed sediments-schists, gneisses, and crystalline dolomites, which in the southern area form the Hutchi- son series.

Unfortunately in this southern area, there are few localities where the field associations of the graphite rocks can be adequately studied owing to the paucity of exposures. The best exposures of unweathered graphite rocks known to the writer in the southern area, are those developed along the shore line at

2 The detailed petrography of the garnet gneisses of the South Australian

area will be given in a forthcoming paper in the Geological Magazine. 3 Mining Reviews Nos. 26, 27, and 28.

Graphite Rocks Of Sleaford Bay. 189

Sleaford Bay, where they are developed interbanded with garnet gneisses and metamorphosed dolomites as already described. Elsewhere the graphite rocks are very generally much decom- posed and weathered. “Superficial solution and redeposition has resulted in the formation of magnesite, siliceous and iron oxide cappings to the lodes. The iron is generally present as limonite but specular iron ore is also a common associate.” In the Hutchison area, graphite is found in the schists of the

Hutchison series, but the visible developments are quite unim- portant as compared with the graphite rocks developed at Slea- ford. Traces of graphite occur in all the metamorphosed sedi- ments at Sleaford Bay, in the dolomites, the diopside and calc-magnesian silicate rocks, and the garnet gneisses.

, The concentration of graphite is however, limited to a number

: of horizons. Some of them are very considerably altered so that it is difficult to obtain any idea as to the nature of the original rock. The chief types will be described in detail hereunder. In the diopside rocks, the graphite is limited to flakes along joints or partings or is sparingly present in the quartz veins which separate these rocks. In the impurer varieties, the graphite flakes are

often seen in close association with zoisite when this is present.

The occurrences of the graphite rocks are marked with asterisks

in Figs. 18 and 19.

; Petrography—The graphite rocks can be divided into two

types:

l (1) Graphite schists,

(2) Graphite gneisses.

1. The Graphite Schists.

The chief constituents of the graphite schists are graphite, biotite, quartz and felspar. By an increase in the proportion of mica these schists pass into biotite schists, and on the other hand,

Vv we

oo

or

biotite may decrease and ultimately disappear, and the schistose 1 character be given entirely by a parallel orientation of graphite flakes. The best exposures of these rocks occur on the shore

4 Mining Review No. 26, 1917, p. 49.

190 C. E. Tilley.

west of the granite sill which bounds—with an intervening iron- stone band—the garnet graphite gneisses shown in the foregoing section. This schist is subdivided by the intervention of a second ironstone band. It has the appearance of a distinct stratigraphic unit in an originally sedimentary series. In places it is inter- sected by pegmatite veins and has been subject to considerable alteration at a later date under the influence of carbonate solu- tions, as evidenced by the vug-like masses of calcite developed. This schistose bed is referred to by Jack.® The rock was trenched at the base of the coastal cliff and according to Jack was sampled over a width of 15% feet. The western three feet were too micaceous to sample, and the samples of the remainder yielded carbon contents up to 3 per cent. Specimens collected near low water show a higher content and the flakes reach a diameter of one eighth of an inch. The schistose structure is given by the content of graphite, and biotite may be completely absent from much of the rock. Although there is a general dis- tribution of the graphite through the schist, yet in cross-frac- tured specimens the flakes are often seen to be more closely segregated at intervals. Under the microscope the sections examined were seen to contain no biotite. The constituents are graphite, orthoclase quartz and secondary calcite. The graphite with parallel orientation appears in laths and rods in cross sec- tion. Of the felspar and quartz orthoclase is the more abundant, and the content of quartz varies considerably in different slides. The carbonate mineral, usually calcite, is very abundant and forms approximately 50 per cent. of the rock. The secondary character of the calcite is indicated by the manner in which it veins the whole rock, penetrating individual grains of orthoclase often along dominant cleavages and forming an interlacing net- work. A brecciated appearance is given to the felspar and quartz grains by this disruption—the whole being set in a matrix of calcite (see Plate VIIIA).

The graphite flakes as seen in the rod or lath-like sections have a diameter averaging 1% to 34 mm., but flakes are observed with

5 Mining Review No. 26, p. 60.

Graphite Rocks Of Sleaford Bay. I9I

diameters of 1% to 3 millimeters. The laths may be totally sur- rounded by a rim of secondary calcite. Graphite is also present as inclusions in orthoclase, and then resembles a type of poikilo- blastic structure, or it may form a peripheral rim to the same felspar, which in some cases is completely replaced by carbonate. The orthoclase is in clear grains with well developed oor and o10 cleavages, and does not show any perthitic structure. Quartz appears in distinct grains associated with orthoclase and may be present included within that mineral. A sample selected for determination of the quantity of graphite gave the mineralogical analysis:

CI eee eve es Q per cent. Orthoclase Ouartz 43 per cent.

fo ee era 48 per cent.

The carbonate was completely soluble in dilute hydrochloric acid and gave no reaction for magnesium. In other cases magnesite appears to be the dominate carbonate associated with weathered outcrops of the graphite rocks. The source of these carbonates is the dolomites with which the graphite rocks are interbanded.

The Graphite Gneisses.—The most striking rocks of the Sleaford group are the coarse textured garnet gneisses exposed on the foreshore. Unweathered specimens in situ are to be obtained at low tide, but there are water-worn pebbles of the gneiss close by the outcrop, and obviously derived from it. The total width of the bed is twelve feet, and this is subdivided into bands ten and two feet wide, by a sill-like mass of granite three feet in width. On the east, the gneiss is bounded by thin bads of graphite schist.

As seen in hand specimens, the rock is a coarse-textured type in which a gneissic structure is often well marked. The con- spicuous minerals are garnet, graphite, quartz, felspar, and flakes of biotite. Garnet occurs in well-shaped dodecahedral crystals up to % an inch in diameter and flakes of graphite of similar size can be observed. The garnet cross sections are character-

192 C. E. Tilley.

istically hexagonal. They may be quite skeletal in type and the included minerals are quartz, felspar and graphite. A zonal structure is often present

a pink central zone may pass into a darker middle zone, giving place to a pink periphery. The weathering of the garnets gives rise to a brown limonitic product, and the rusty weathering is due to this development of the iron oxide. In the fresh specimens collected in situ, the proportions of quartz greatly exceed the felspar, and the rock has the appear- ance of a psammitic gneiss.

Under the microscope the additional mineral observed is apatite in rounded grains. In thin section the garnet still pre- serves its pink tint, and contains inclusions of biotite, quartz, graphite and orthoclase. The biotite is the same type that char-

praiety PPT, aoe oe

Fic. 20. g, garnet; gr, graphite; f, felspar; gq, quartz.

acterises the garnet gneisses, and is occasionally intergrown with the graphite. Quartz and orthoclase are very variable constitu- ents. The former is usually the predominant mineral, and felspar may be quite subordinate. The orthoclase is character- istically the fibrous perthitic type that dominates the sediment garnet gneisses. Graphite appears in cross sections as long laths with the serrated outline and steel gray surface as seen in reflected light. During the growth of the garnet crystals, a zonal structure has developed as a result of the inclusion of swarms of fine

PLATE VIil. Economic GEoLoGy. VoL. XVI.

A. Graphite schist, Sleaford Bay, Sleaford, containing graphite, ortho- clase, quartz and calcite. Note intimate penetration of rock by carbonate; enclosure of certain graphite laths by a shell of calcite, and presence of graphite included poikiloblastically within orthoclase. X 30.

8B, Garnet graphite gneiss Sleaford Bay, containing garnet, graphite, ortho- clase and quartz. Note characteristic perthitic and fibrous nature of felspar, serrated character of the rod like graphite, and presence of zonary banding in the garnet prophyroblast, due to the inclusion of swarms of fine graphite flakes during growth. X 30. (Cf. with Fig. 20.)

Graphite Rocks Of Sleaford Bay. 193

graphite flakes. These graphite zones follow the outline of the growing crystal and give the zonary banding that is observed in hand specimens (see Fig. 20 and Plate VIII B).

The order of abundance of minerals in the rock is quartz, garnet biotite and graphite, apatite. The position of orthoclase in this series is variable, and it may come before garnet or after graphite in this order. A number of specimens of this rock broken from the outcrop at low water mark, yielded according to Jack, 6.5 per cent. concentrates assaying 68 per cent. carbon.®

Origin Of The Graphite.

A study of the principal graphite fields of the world has shown that the occurrence of graphite cannot be explained by any one mode of origin. Even within the one field, there are assemblages of graphite which illustrate diverse methods of development. The association of the graphite in the Sleaford Bay exposures resemble very closely the well-known graphite rocks of the Gren- ville series of North America—more especially the Adirondack region of New York. In all the well-known graphite fields, such as Ceylon, the Adirondack region, and Montana, the type of sedi- ment now highly metamorphosed, is closely similar to that ex- posed in the Eyre peninsula region. The graphite in these cases is found associated with sediments of the shale-limestone-sand- stone type subject to intense contact metamorphism by the intrusion of contiguous belts of igneous rocks.

In the Adirondack region in a recent survey of the graphite deposits of this area, H. L. Alling,’ has classed the graphite deposits as exposed into the two types,

(a) The organic type of graphite,

(b) The inorganic type of graphite. An inorganic origin is ascribed to the graphite occurring in dis- tinct veins, and for the graphite in the contact zones between the sedimentary rock and the igneous intrusion, whilst the organic

6 Mining Review No. 27, p. 56. 7H. L. Alling, Bull. No. 199, New York State Museum, pp. 141-48, 1918.

194 Ce Pileey.

origin is ascribed to that graphite present in the metamorphosed sediment not of direct contact origin. Alling accepts Winchell’s views® that the inorganic type of graphite was derived from the reduction of the oxides of carbon by hydrogen. If such a re- action has occurred the silication of the limestones would supply enormous quantities of carbon dioxide which would be available for deoxidation. The occurrences of graphite in veins—asso- ciated usually with quartz and pyrite, and occasionally typical contact minerals—has been taken as showing that the graphite was deposited from solution and for the graphite itself, the reduction of oxides of carbon is most favored. The presence of graphite in pegmatites and granites is similarly explained.

The production of graphite by the reduction of oxides of carbon by hydrogen is based on theoretic reasoning and the

reversibility of the carbon-water reactions has first to be admitted. G7) C+ H,O CO+ Hg. (11) C-+-2H,O CO, + 2H.

The researches of Hahn’ have shown that the equilibrium in the reversible system

(iii) CO+H.O=CO,+H,

is such that at low temperature (700° C.), the equilibrium shifts towards the right, and at high temperature (1000° C.), equi- librium is established in the presence of a high content of carbon monoxide. The reversibility of the reaction shown in (i) and (11) above, at low temperatures is based on the endothermal character of the carbon-water reactions, an absorption of heat resulting in both cases. A further factor is the influence of pres- sure on the equilibrium. Under high pressures the reaction would tend to proceed in the direction of diminution of volume. Boudouard,’® and more recently Rhead and Wheeler™ have studied the reaction

8 Winchell, Econ. GEox., vol. 6, 1911, p. 218.

® Hahn, Zeit. physik. Chem., 1903, 44, 513, 1904, 48, 735.

10 Boudouard, Ann. Chim. Phys., 1901 vii, 24, 5. 11 Rhead and Wheeler, Trans. Chem. Soc., 1910, 2178, 1911, 1140.

a ee

Graphite Rocks Of Sleaford Bay. 195

(iv) 2CO@CO,+C. The disassociation of carbon monoxide in accordance with this equation is favored by low temperatures and high pressures, the system obeying Van’t Hoff’s principle of mobile equilibrium and LeChatelier’s theorem.

The reversibility of the carbon-water reactions has no experi- mental verification,’ but Weigert’* has discussed the question from the point of view of the heats of reaction, and their depend- ence on temperature. If this origin of graphite can be estab- lished, it would appear to afford an adequate explanation of certain types of vein graphite intersecting contact rocks, and the associated igneous intrusions, the source of the carbon being bituminous matter in the sediments oxidized at a higher tempera- ture or carbon dioxide released from carbonates on silication. On the same grounds graphite occurring along joint planes or partings in contact rocks (¢.g., the diopside rocks), may have the same origin.

It seems highly probable that whatever mechanisms are in- volved in the crystallization, in the cases under discussion, the sediments themselves must be considered as the ultimate source of the carbon whether as the carbon of bituminous material con- tained in these or the carbon chemically combined in calcite and dolomite, and released as carbon dioxide during the contact meta- morphism. The restriction of the vein type of graphite, and of the graphite in pegmatites—to the neighborhood of the meta- morphosed sediments finds a rational explanation therein.

For the extreme view of Winchell,’* that graphite is insoluble in silicate magmas, there seems little justification. The argument based on the refractory nature of graphite, does not necessarily

12 Cf., however, Gmelin-Kraut, “ Handbuch anorg. Chem.,” 1911, Bd. 1, Abt. 3, p. 658, where according to Dubrunfaut, the reduction of carbon dioxide to carbon, was accomplished by passing dry hydrogen over calcium carbonate heated to redness, and also by leading CO. and H: over red hot pumice, with the intermediate formation of carbon monoxide. (Compt. Rendu., 74, 125.)

13 Weigert, Abegg’s “ Handbuch anorg. Chem.,” 1909, 3, 2, pp. 196-108. 14 Op. cit., p. 222.

196 C. E. Tilley.

hold for the conditions prevailing in igneous magmas, nor sedi- ments undergoing a strong metamorphism, where the presence of volatile mineralisers is essential. As Bastin has remarked, it would be as reasonable to conclude that quartz was incapable of crystallizing out from melts at comparatively low temperatures. The controlling factors are the physical conditions and the nature of the solutions. For these reasons it is probable that graphite in certain pegmatites has been derived from contamination of carbon from the associated sediments, and has crystallized from solution as graphite.

In the case of certain contact metamorphic deposits of the Adirondack region, Bastin'® has shown that graphite and quartz have crystallized contemporaneously, and at a temperature below 575. C—the inversion point of alpha quartz. There would seem to be no valid reason to deny that the graphite is recrystal- lized carbon derived from the sediments without the intervention of oxides or_carbon.

As far as the graphite schists and graphite gneisses that are exposed at Sleaford Bay are concerned, a sedimentary origin is most in accord with the facts. As to the nature of the original sediments, all clastic structures have been destroyed by recrystal- lization. ‘The biotitic graphite schists were of the nature of bituminous shales and the schists without biotite, and with domi- nant orthoclase appear to have been arkoses. The felspar in this case cannot be considered to have been derived from mica, as there is no mineral present in which the excess alumina could have been absorbed in this conversion. The garnet graphite gneisses bear the stamp of strong metamorphism very similar to the associated garnet gneisses.

Normally the garnet arises as in the garnet gneisses by a biotite-quartz interaction :

r is de area 0) FESO + 380, “oe 4 4/3

— 2K AlSi,O, + 2Fe.MgAl,(SiO,), +2H,O

15 EF. S. Bastin, Econ. GEox., vol. 5, 1910, p. 134.

Per FP

- Fh OD fb

—Eee

Graphite Rocks Of Sleaford Bay. 197

Where, however, the necessary accompanying felspar of this reaction is absent, it is probable that an interaction of detrital iron oxide, kaolin and quartz is involved:

(vi) 3Fe(OH), +H,Al,Si,O, + SiO, — Fe,Al,Si,O,. + 5H.O.

In this metamorphism, the contact action of the granitic intrusion was operative. The graphite is considered as derived by a car- bonization of bituminous matter in the sediments, and a recrys- tallization of the carbon to graphite. The size of the individual crystals of graphite is related to the coarse grain size of the re- maining constituents of the rock, and the influence of the intrusive granite is to be discerned. The chemical composition of this gneiss indicates it as derived from quartzose shale. The quartz content in some parts is sufficiently high to class it as a psamitic gneiss.

For the graphite schist containing abundant orthoclase, the nearest analogue is the rock mined for graphite at the Rock Pond property in the Bear Pond mountain region, Ticonderoga. This rock is described under the name “arkosite”’ by Alling’® and the graphite is described as of sedimentary origin.

A rock of somewhat similar type to the garnet graphite gneiss described is the garnet quartz schist in the Dillon area, Montana, described by Winchell.‘ It differs in one particular in that graphite is not enclosed by garnet. The inclusion of graphite in the garnet porphyroblasts of the Sleaford gneiss is a character- istic and significant feature.

The foregoing remarks apply to the limited exposure of the graphite rocks on the shore at Sleaford Bay. There is, however, a wide and extended area over which these graphite rocks are known to be developed. In the adjacent hundred of Uley, the most extensive workings of these rocks occur, and the quality and the quantity of the graphite there revealed, is an index of the future prospects of the graphite industry in this area. The

16 Alling, op. cit., p. 60. 17 Winchell, op. cit., p. 221.

198 Ce; Tilley,

shafts excavated here have as yet only penetrated the upper weathered zone of the graphite beds. There is little doubt that when these deposits are further developed, much additional light will be shed on the origin of the graphite, and the vein type of graphite may then be found. In the exposure at sea level at Slea- ford Bay, no vein type of graphite has been observed.

Summary.

(a) The graphite rocks of Sleaford Bay are intimately asso- ciated and interbanded with crystalline dolomites, calc-magnesian silicate rocks, and para-garnet gneisses. Graphite is now known to extend over a large tract in southern Eyre Peninsula—the graphite belt following the strike of the oldest sedimentary series. This group of rocks has as yet been little investigated.

(b) In this paper the description of the graphite rocks is limited to those developed at Sleaford Bay. They comprise graphitic biotite schists, graphite schists with no biotite but con- taining orthoclase and quartz, and garnet graphite gneisses. Graphite is sparingly present in the contact diopside rocks—long joints and parting planes.

(c) For these rocks a sedimentary origin for the graphite is most in accord with the facts—the rocks being regarded as originally bituminous shales, arkoses and sandstones, in which a carbonization of the bituminous matter, and recrystallization of the carbon to graphite have accompanied strong metamorphism.

(d) The possible development of graphite by reduction of oxides of carbon by hydrogen, is discussed. This mode of origin may account for the development of graphite along joints and partings in the contact diopside rocks.

(e) The graphite rocks are compared with certain metamor- phosed graphite-bearing sediments of the Adirondack region, and of Montana.

SEDGWICK Museum,

Cambridge, England.

OIE oe

The Origin Of The Colemanite Deposits Of California.

WitiiaM F. FosHac.1

Introduction.

Since the discovery of the calcium borate, colemanite, in the Calico Mountains of California in 1882, it has become the most important source of boric acid and the borates of commerce. Over 50 per cent. of the world’s supply is obtained from this mineral, mined in California. So far it has been found in com- mercial amounts only in California, and, as far as the writer is aware, has not been reported even as specimens from any other locality. The mineral pandermite, formerly classed as a variety of colemanite, is now known to be distinct, and identical with the mineral priceite. The deposits of colemanite are restricted to the southwestern portion of the Great Basin and workable beds are found in Los Angeles, Ventura, San Bernardino and Inyo Counties in California. Borates in the form of borax and ulexite are found in the adjacent parts of Nevada. The waters of Borax and Hachinhama Lakes m Lake County, California, are rich in dissolved borax. The writer has had the opportunity of visiting some of the producing localities as well as a number of the playa lakes of this region, and of studying mineralogical specimens from other localities. The data thus gathered together with that already existing in the literature, have led to the interpretation given below.

The Minerals Of The Deposits.

Colemanite.—This mineral, now the only one used as a source of the borates in the United States, is a calcium borate, the com- position of which is expressed by the formula: Ca,B,O,,.5H.O. It is colorless or white, sometimes gray or brown from included

1 Published by permission of the Secretary of the Smithsonian Institution.

200 WILLIAM F. FOSHAG. mud. It crystallizes in clear glassy monoclinic crystals in a great variety of habits. It is easily distinguished from the other borate minerals by its eminent cleavage. When heated in a flame cole- manite loses water and falls toa powder. Since the other borates fuse easily but do not decrepitate this gives a simple test for the detection of colemanite.

Ulexite——At one time ulexite constituted one of the main sources of the borates of commerce. Today its production is restricted to a few localities in South America. It is the double borate of calcium and sodium, NaCaB,;O,.8H.O. It is abundani in many of the playas of North and South America. It occurs in aggregates of loosely coherent, acicular crystals. These aggre- gates are popularly called “ cotton-balls.” They are found in the surface salt crusts of the playa lakes as well as in the mud layers below. At the Lang deposits in California ulexite also occurs in lenticular masses with the colemanite at the foot wall of the beds. In the center of these masses the fibers are oriented in al! directions while at their peripheries the fibers are parallel and normal to the surfaces. These masses have the appearance of “cotton-balls ”’ that have been compacted by pressure. Ulexite fuses easily in a flame, coloring the flame intensely yellow.

Inyoite has been found in the Mount Blanco Deposits in Death Valley. Recently it has been found in the gypsum deposits of Nova Scotia. The fresh mineral is in clear glassy monoclinic crystals with eminent cleavage but the mineral at Mount Blanco is almost completely altered to a fibrous crystalline mass of meyer- hofferite. In composition inyoite is similar to colemanite but differs in its water content from that mineral. The inyoite con- tains thirteen molecules of water as shown by its formula, Ca,B,0,,.13H,O.

Mevyerhofferite is a third member of the colemanite series with seven molecules of water, Ca,B,O,,.7H.O. It has been found only in the Mount Blanco deposits as a dehydration product of the inyoite.

Howlite is a borosilicate of calcium, H;Ca,B,SiO,,. It occurs in all the important borate deposits of California in considerable

ee cote EA

Origin Of Colemanite Deposits. 201

abundance. It is found in friable masses of monoclinic crys- tals or in porcelain-like, nodular masses. It is white in color but rarely brown. It fuses in a flame coloring the flame green. Bakerite is a similar if not identical mineral.

Gypsum is present in all the deposits. It is always secondary with respect to the beds in which it is found. It occurs in clear glassy monoclinic crystals, as selenite, or as satin spar. No chemically precipitated gypsum appears in any of the deposits as far as the writer has been able to observe.

Calcite-aragonite.—Calcium carbonate appears in two forms in the deposits. As calcite it is present in the clays, perhaps as an original chemical precipitate. As aragonite it very rarely occurs as buff colored, acicular crystals perched upon and perhaps derived from colemanite.

Celestite—Strontium sulphate, SrSO,, is as far as known found only in the Calico beds. Here it occurs in colorless or

blue, long orthorhombie crystals in the geodes of colemanite.

The Playa Lakes.

In order to understand what has taken place in the Tertiary lakes it will be well to observe what is taking place in similar basins of today.

Borax Lake, in Lake County, California, was the first borax- producing locality in the United States. It is situated in a tri- angular valley surrounded by hills of basalt. A basalt ridge sepa- rates the lake from the larger, fresh water Clear Lake. Formerly Borax Lake shrunk to a small volume in the summer but it is now fed by an artesian well in the lake floor and is essentially a permanent body of water. The dissolved solids carried borax to the extent of 18 per cent., with about 62 per cent. of sodium car- bonate and 20 per cent. of sodium chloride. In the mud of this lake were numerous crystals of sodium borate, a rather peculiar feature, since the lake waters were not saturated with salts. About the edge of the lake were numerous small spires of cal- careous tufa ranging up to a foot in height. A small solfatara.

202 William F, Foshag.

known as the Little Sulphur Banks, is not far distant from the shores. cross the ridge that separates Borax Lake from Clear Lake is a solfatara of large dimensions, known as Sulphur Banks. The springs and waters emanating from this solfatara are highly boriferous. The boron in Borax Lake is without doubt derived from the adjacent solfataras.

Searles Lake in San Bernardino County offers a somewhat different type of playa lake. This is a concentration basin receiving its salines from the drainage of a considerable area. The area now drained is restricted to the Argus and Slate Ranges, but at some earlier period Owens Lake overflowed into the Searles Basin by way of Indian Wells and Salt Wells Valleys and it was these waters that contributed most of the salts now covering the floor of Searles Basin. In the winter a few inches of water covers the lake bed, but in summer the water level falls to a few inches below the salt crust. The crust is a mere efflorescence at the outer edge but acquires a thickness of about 50—75 feet in the center. Beneath this salt crust are beds of fine mud with em- bedded crystals of halite, hanksite, gay-lussite and others. These salts, especially the hanksite and pirssonite, are in sufficient abundance to form definite solid layers or strata. Many of these muds are rich in precipitated caleum carbonate, in the form of calcite. The minerals occurring here are chiefly sulphates and carbonates of calcium and sodium, chlorides of sodium and potassium, and borax. Ulexite, if present at all, is very rare, and no colemanite occurs.

Danby Lake covers a large area near the town of Amboy in San Bernardino County. Although it presents some unusual features, it has never been studied in detail. Near the western edge of the lake a small cone of basalt arises aud some of the flows cover a portion of the lake bed. The surface is covered with gypsum and mud. The mud is rich in small crystals of elauberite and the brines carry a large amount of calcium chloride as well as sodium chloride. A stratum of salt underlies the mud but its extent and thickness are undetermined. No wlexite or colemanite have been reported from here.

at

Origin Of Colemanite Deposits. 203

Rhodes Marsh is one of the types of playa lake that formerly produced considerable quantities of borax before the discovery of the colemanite beds. It is situated in Esmeralda County, Nevada. According to the description of LeConte,? common salt occupies the center of the flat. Around this to the margin, the deposits differ from place to place. In some parts borates occur as borax or “ tincal,” in others the borate is ulexite. Com- mon salt is found nearly everywhere, more or less mingled with the other salts. Sodium carbonate and sulphate are present in considerable amounts. The well known ulexite “ balls ” occur in a semicircular area surrounding the central salt area on the north. They are embedded in a stiff, wet clay. If the loose earth is removed to the depth of a foot or more, until the stiff clay is reached, the “cotton balls” are found. In places the beds of ulexite reach a thickness of six to eight feet. This concentration of the ulexite into patches seems to be a common feature of both western deposits and the South American lakes. In some of the later deposits the ulexite occurs in considerable quantities and of great purity.

Geology Of The Deposits.

General Geology.—The colemanite deposits are found inter- stratified with lake bed deposits of Tertiary age. These lake bed deposits are for the most part volcanic ash or material derived from volcanic rocks laid down under shallow water conditions in closed basins. The beds in direct association with the colemanite are fine-grained, thin-bedded shales of various colors. Lavas of rhyolitic, andesitic or basaltic character are often present in the boron-bearing series. For the most part they appear to be sur- face flows.

The borate beds themselves follow the bedding of the series but are somewhat irregular in form. They do not form continu- ous, well-defined beds but rather represent shale beds in which the borates are more or less irregularly distributed. They are, how- ever, restricted to a definite member of the series.

2 Third Ann. Rept. Calif. State Min. Bur., p. 51, 1883.

204 William F. Foshag.

The borate-bearing beds have all undergone some movement. They range from beds almost perpendicular to beds but slightly tilted. There is also evidence of movement within the beds them- selves.

Lang.—The sedimentary rocks in the region about Lang are coarsely stratified sandstones of a light buff color. These sand- stones grade into conglomorates. In the immediate vicinity of the colemanite deposits they are fine, thin-bedded shales. The borate- bearing beds have an east-west trend and dip at an angle of about 70° to the south.

The commercial product is colemanite, in cleavage masses and very often in columnar bands. There is evidence of movement and pressure in the ore-bearing strata, but hardly sufficient to account for the large masses of cleavable colemanite. Much of the colemanite is of gray color, due to included mud, but second- ary colemanite is of a pure white color. Crystals are rare. How- lite is present in considerable abundance as botryoidal concretions which sometimes are several feet in diameter. The howlite nodules are imbedded in the colemanite and form “ augen” in the strata. Rarely howlite and colemanite are intergrown, and still more rarely the howlite is later than the colemanite.

The mineral of greatest significance is ulexite, which occurs in abundance in some of the workings. At the 250-foot level the footwall is composed largely of ulexite. It is not the ordinary “cotton-ball” type but is massive and fibrous. It has the appear- ance of cotton balls that have been consolidated by pressure. That it is typical ulexite is shown by the following analysis:

GND Soe h oe oe cke he se eeeS Ree eR eS 14.14

CO nas Sr Pees anne aA gate Gorter 35.68

ADS 4. occas bees ob aw ee eeeice ee bh emins 43.12

INDE} occbek sein cis oc eee RS ences (7.05) (by difference)

The ulexite occurs in irregular masses, more or less lens-like and surrounded by thin layers of clay. In structure these lenses are compact-fibrous, the fibers oriented in all directions fn the centers, and parallel at the peripheries.

Origin Of Colemanite Deposits. 205

Calcite is rare in the deposits and none was observed in direct association with the colemanite. Aragonite occurs sparingly and is always secondary.

Borate.—The borate deposits are situated in the Calico Moun- tains not far from the old silver camp of Calico. The nearest town is Yermo on the Salt Lake Railroad, eight miles distant by wagon road. At the time of the writer's visit (May, 1920) a small amount of work in the nature of “ gophering” was being done. Since the mines have been idle for a number of years the extensive old workings are no longer accessible, so that the only data obtainable was from the dumps and shallow workings.

The sediments here are sandstones and shales. The borate beds are in thin-bedded shales similar to those at Lang. The beds have an east-west trend and dip to the south. South of the deposits rises the main rhyolite mass that forms the core of the Calico Mountains. Storms* states that “the rocks have not suffered, in the region about the borax deposits, the slightest metamorphism.” The surface exposures are unaltered, loosely coherent, shales. The colemanite beds outcrop along the hill for a distance of about one-half mile and show, beside colemanite, occasional bands of howlite and numerous veins of satin spar gypsum. Storms describes the beds as being much mixed with sandy sediments and gypsum at their western end, giving the appearance of having formed “ near the shore line of a basin.”

A peculiarity of the colemanite occurring here is the large number of geodal nodules lined with excellent crystals of cole- manite with sometimes celestite and selenite. In some parts of the deposit they occur in great numbers imbedded in the shales, much after the fashion of the ulexite nodules described by LeConte at Rhodes Marsh.* The geodes often show two genera- tions of colemanite crystals. In certain other portions of the deposits colemanite gives way to cavities containing clear and brilliant selenite crystals. The shale containing these selenites has a decidedly honeycombed structure, and the cavities now con-

3 Calif. State Min. Bur., 11th Ann. Rep., p. 346. 4 See above, under Rhodes Marsh.

206 William F, Foshag.

taining the selenite crystals were undoubtedly formed by the removal of some previous mineral. Associated with both the colemanite and the selenite are small nodules of howlite. The colemanite crystals of many of the geodes, especially those near the surface, are partially or wholly altered to calcium carbonate, in many cases still retaining the external form of the colemanite crystals.

V entura.—The Ventura deposits have been described by Gale® and were not visited by the writer. They are situated on the south flank of Mt. Pinos, near the San Emigdio Range, in Ven- tura County. The general trend of the borate-bearing beds is northeast and southwest and they dip to the southeast. These beds have been extensively folded and faulted. The colemanite occurs in shales and limestones intercalcated with flows of basalt.

The colemanite is typical of the mineral as it occurs elsewhere. It is crystalline with excellent cleavage, white in color, but in places gray from included mud. The masses follow the bedding of the sedimentary strata with which they are associated but appear to be very irregular in form. The mineral is often radiated and in places crystallized in open cavities. The cole- manite appears to have been developed in immediate association with a bed of limestone included within the shales. The lime- stone is massive or of a roughly porous character. The outcrops rarely show any colemanite but are indicated by an abundance of gypsum. This gypsum is in the form of selenite and is of vein character.

Death Valicy.—The geology of the Death Valley deposits has been described by’ Keyes. He characterizes the borate-bearing beds as fine olive green clays that weather pale green or white. Numerous basalt sheets from ten to a hundred feet thick are inter- bedded. In the upper part of the sequence much selenite gypsum, beds of colemanite and thin layers of limestone of probable chem- ical origin, occur. Underneath these beds are strata of sand- stone and conglomerate. ;

5U. S. Geol. Survey Prof. Paper 85, p. 5. 6 Trans. Am. Inst. Min. Eng. Bul. 34, p. 870, 1910.

Origin Of Colemanite Deposits. 207

The richer borate beds are from a few inches to fifty feet thick. In the unweathered portions they consist of bluish clays interspersed with milk-white layers, nodular bands and nodules of colemanite. Through the strata carrying the coarsely crystal- lized colemanite the clays are more or less highly impregnated with fine particles of the borate mineral, and yield upon leaching ten to twenty-five per cent. of anhydrous boric acid. Mingled with the coarse colemanite are often found large amounts of crystallized gypsum. In some places the gypsum is so abundant that the borate minerals are all but completely obscured. Fre- quently there are present large amounts of pure limestone. How- lite, although not mentioned in any of the published descriptions, is abundant in many of the colemanite specimens examined from this locality by the writer. In appearance it is very similar to the Calico howlite.

Chemistry Of The Minerals.

Boric acid is one of the weakest of inorganic acids, dissociat- ing to a less extent than carbonic or hydrosulphuric acids. The dissociating constant for boric acid is 1.7 X 10° at 18° as compared with carbonic, (H,CO;), 3.04 X 10% and hydrosul- phuric (H,S), 0.91 X 107. Besides orthoboric acid there exist in the form of salts metaboric acid, HBO,, tetraboric acid, H,B,O,, and a number of poly acids. In respect to its formation of poly acids, boric acid is similar to silicic acid.

The dissociation of metaboric acid takes place as follows:

HBO, + BO... Theoretically orthoboric can give three hydrogen ions, but the dissociation

H,Bo, + Hbo’;

takes place to such a very slight extent that further ionization is not measurable. The orthoborates in nature are accordingly of the type R’H,BO,, e.g., pinnoite, Mg(H,BO3;),.H.O; and such salts as Mg,B.O, do not form from solution.

208 William F, Foshag.

Orthoboric acid upon heating loses water and passes over into metaboric acid. Further heating converts it to the oxide, B,O3. The oxide is volatile only at high temperatures. The orthoboric acid, however, is volatile in steam and this explains its presence in fumaroles and volcanic exhalations.

Although orthoboric acid is weaker than carbonic it may pos- sibly replace the latter to some extent in hot concentrated solu- tions. This would be due to the greater volatility of the carbonic acid. The reaction, however, has never been studied in any detail. The writer subjected sections of calcite to the action of boric acid for a period of several months without any change of the carbonate to the borate.

When boric acid dissolves it tends to form complex molecules with the formation of meta, ortho, tetra and poly acids, so that a solution of boric acid does not contain the orthoboric acid ion alone but the others in equilibrium with each other.

Borax solutions in the presence of sodium chloride attack cole- manite to form ulexite and calcium chloride. Ulexite is the com- mon occurring borate in the playa lakes where it is found with borax and salt. Ulexite has been synthesized by Van’t Hoff‘ by the action of a borax and sodium chloride solution on Ca,B,O,,, 9H.O, one of the members of the colemanite series.

At 83° ulexite splits into its component borates according to the equation

2NaCaB,O0,.8H,O Na.B,O; + Ca.B,0,,.7H,O + 9H.O. This splitting takes places at lower temperatures in the presence of sodium chloride. It will be noticed that one of the products of the above reaction is the mineral meyerhofferite, one of the colemanite series. Kraut® obtained another member of the cole- manite series, Ca.B,O,,.6H,O, by simple leaching of ulexite.

Van’t Hoff found further that the pentahydrate, colemanite, was less soluble in sodium chloride solutions than the hepta- hydrate, meyerhofferite. By treating the heptahydrate with a sodium chloride solution he obtained the pentahydrate, cole-

7 Sitsb. Acad. Wiss. Berlin, p. 566, 1906. 8 Arch. Pharm., 2, 112.

Origin Of Colemanite Deposits. 209

manite. By leaching ulexite with sodium chloride solutions in- stead of pure water he obtained colemanite in place of meyer- hofferite. The reaction

2NaCaB,O0,.8H,O Na.B,O,.10H,O + Ca,B,0,,.5H.O + H.0.

is completely reversible and by varying the amounts of borax the reaction can go in either direction—colemanite and borax may result from ulexite or ulexite from colemanite and borax. If an excess of borax is present any colemanite is converted into ulexite while if the borax is removed as fast as it is formed the ulexite will break down completely, leaving the mineral meyer- hofferite if no sodium chloride is present but giving colemanite if the solutions are salt-bearing ones.

Origin Of The Boron.

Three hypotheses have been put forward to explain the source of the boron in the various borate deposits: (1) origin from sea water, (2) from the decomposition of borosilicate minerals, and (3) volcanic exhalations.

1. In such deposits as those at Stassfurt the source of the boron is without doubt from sea waters. The amount of boric acid in the waters of the ocean is sufficient to account for the rela- tively small amounts of borates in these salt beds. For the Cali- fornia deposits, however, all evidence points to an origin other than the evaporation of sea water, so that this possible source may be dismissed.

2. The average boron trioxide content of igneous rocks is very small but may reach an appreciable amount in such rocks as tour- maline granites. These rocks, upon decomposition, may give up their boron, which may then be leached out and concentrated in suitable basins. But borosilicates such as tourmaline are resistant minerals and no accumulations of borates are known that can be definitely traced to this source.

3. The volcanic origin of the boron has much evidence to favor it. Boron has been detected in the vapors of many volcanoes. It

210 William F, Foshag.

is one of the important mineralizers of igneous rocks. But most important of all is the actual accumulation of boron in the craters of certain volcanoes and in the hot springs and solfataras of volcanic regions. Thus sassolite, B(OH), is sometimes found at Vesuvius: while at Volcano, borates were at one time present in such quantities that it became profitable to work them in the very crater.

At Steamboat Springs, Nevada, a hot spring connected with rhyolitic rocks, the boron content of the dissolved solids is as high as 9 per cent. B,O,.. At Sulphur Banks, in Lake County, California, there is a solfatara of large dimensions discharging highly boriferous waters and close by are borax deposits of actual commercial importance. The waters of the hot springs carry over 25 per cent. of B,O, (of the dissolved salts) while waters collected in the old Parrot Shaft contained solids with over 40 per cent. beric oxide. Thus in the case of Sulphur Banks a large quantity of borax is discharged yearly into the waters of Clear Lake. These springs are connected with fairly recent basalt flows and have a direct genetic connection with the sulphur and cinnabar deposits from which they isssue.

The Tuscany soffioni have long been cited as an example of the volcanic origin of the boron, although the evidence here is not conclusive, since the waters pass through strata of sandstone and other sedimentary rocks, and a possible source of the boron in these rocks is not entirely precluded.

It is significant that all deposits of borax and other borates are situated in regions of past or present volcanic activity. The Borax Lake in California is adjacent to the solfataras of the dis- trict, the deposits of the desert region are connected with numer- ous volcanic flows. The borate deposits of South America are, according to Chamberlain® largely confined to those lakes which lie close to the volcanoes of the western Cordillera. Away from these volcanoes the borates rapidly disappear. The original source of the boron in our Western deposits is most probably to be found in the hot springs and solfataras connected with the

9 Jour. Geol., 20, 763, 1912.

Origin Of Colemanite Deposits. 211

tremendous volcanic activity that characterized the Tertiary Period when these deposits first accumulated.

Previous Theories.

To account for these accumulations of calcium borate two theories have been proposed. The older, and the one accepted for many years, is that of the chemical precipitation of the cole- manite from the waters of inclosed basins during periods of great desiccation. This theory was first put forward by W. H. Storms’ and later supported by Campbell,’! Keyes,’* Baker,'* and others.

It fails, however, to explain the reaction by which such masses of colemanite might form. In order to produce beds of any thickness the amount of water would have to have been very great, because of the slight solubility of the colemanite. Since the borate-bearing beds have all the appearance of shallow-water deposits, it is difficult to conceive any means whereby such masses could be deposited by simple evaporation. In the playa lakes of today no precipitation of colemanite is evident. In fact, under ordinary playa conditions, where there are large amounts of borax present, the formation of colemanite seems impossible ; for under these conditions any simple calcium borates are pre- vented from forming, any calcium in solution separating as the double sodium calcium borate, ulexite. Colemanite forms only from solutions free of sodium borate, a condition which is appar- ently never reached in the playa lakes. These relations have been discussed under the separate minerals.

The second theory is one put forth by H. S. Gale."* From his studies of the Ventura deposits he reached the conclusion that the colemanite was formed by metasomatic replacement of lime- stone beds intercalated with beds of shale between basalt flows.

10 Calif. State Min. Bureau, 11th Ann. Rep., p. 346, 1893.

11 U. S. Geol. Survey Bull. 200, p. 8, 1902.

12 Am. Inst. Min. Eng. Bull. 34, 1909.

13 Univ. Calif. Pub. Dept. Geol. Bull., vol. 6, No. 15, 1911. 14 Prof. Paper 85, U. S. Geol. Survey, p. 3, 1914.

212 William F, Foshag.

In support of this hypothesis he calls attention to the irregular character of the deposits and the vein character of the associated gypsum. Furthermore he states that “ certain specimens collected on the ore dumps and in the mines show that at least a part of the colemanite is a replacement deposit. Irregular portions of the limestone are surrounded by white crystalline colemanite and minute fractures which traverse the limestone throughout are also filled with this mineral. These veinlets are observed to have been enlarged irregularly within the limestone. Small rounded masses of limestone are also included within the solid portions of the colemanite, indicating that in places the same enlargement of the intersecting veinlets has been carried to a further stage and the separated portions of the limestone are residual within the deposited colemanite.” These reactions are possible, for, although boric acid is a much weaker acid than carbonic, the greater vola- tility of the latter may allow replacement to take place in concen- trated and hot solutions of boric acid. The reverse reaction takes place in nature, however, to a great extent and colemanite crys- tals altered to calcium carbonate are common in the borate de- posits. It is doubtful if the boric acid emanations from the neighboring basalts were of sufficient volume and of long enough duration to effect the replacement of such large amounts of lime- stones. Being surface flows, their period of activity must have been short. What replacement of limestone has taken place is more probably due to borate solutions of vadose origin.

Eakle’® arrived at a similar hypothesis to the above. He con- sidered the Lang deposits as probably derived from marls by the action of boric acid solutions.

Origin Of The Deposits.

Van’t Hoff’s work clearly demonstrates that, under the con- ditions existing in playa lakes, ulexite forms instead of cole- manite, and in order to accomplish the splitting of the ulexite into

15 Univ. Calif. Pub. Dept. Geol., vol. 6, No. 9, 1911.

ae eS

6 ee ee 0 0 oe

Origin Of Colemanite Deposits. 213

its component calcium borate and sodium borate the sodium borate must be removed as fast as it is formed. In the closed basins of the playa lakes with their clay floors this removal of the sodium borate cannot take place to any large extent either by surface or underground drainage, so that the borate accumu- lations consist wholly of ulexite and borax. When these deposits are later covered over and uplifted sufficiently to allow free drainage from the beds, the percolation of chloride solutions gradually converts the ulexite to colemanite and other members of the colemanite series.

The evidence to support this hypothesis is:

1. The total absence of colemanite or any member of the cole- manite series in any of the playa lake deposits.

2. The occurrence of ulexite in large quantities in the borate beds at Lang, where it lies for the most part near the foot wall.

3. The bedded character of the deposits.

4. The structural features of the deposits, especially the nodu- lar and geodal character of a large part of the coelmanite.

The first three points have already been treated. The fourth item will now be discussed briefly. It has been pointed out that nodular and geodal masses are common in the deposits, in fact at the Calico beds and presumably at those at Death Valley a large proportion of the ore consists of nodular geodes embedded in the clays. This suggests strongly LeConte’s description of the occurrence of the “ cotton-balls ” in the clays of Rhodes Marsh. If the theory of the derivation of colemanite from ulexite be accepted, there is a ready explanation of this type of ore. The ulexite embedded in the clays is acted upon by salt solutions. The light, fluffy “ cotton-balls ” are converted into the more compact colemanite, giving rise to the more or less spherical geodes and allowing the free crystallization of the colemanite in the center. It is inconceivable that the cavities were original in the shales and that they were later filled in with the colemanite. Where ulexite was aggregated in more compact masses the colemanite took a more massive form but the contraction of volume stiil allowed for a large number of drusy cavities such as are so

214 William F. Foshag.

abundant in the deposits. In some deposits, as at Lang, the pres- sure exerted was sufficient to close the cavities and compact the mass. The selenite gypsum and perhaps some of the limestone also, resulted from the action of sulphated and carbonated waters upon the colemanite.

Smithsonian Institution,

U. S. Nationa, Museum, WasHIncTon, D. C.

reser

Economic Geology And Highway Construction.

E. F. Brean.

One of the most important problems before this country today is the construction of highways. This condition will continue just as long as the 2,500,000 miles of highways continue to be the capillaries in the transportation system in which the railways are the arteries. These highways are essential to the economic and social development of the country, and it is the duty of tech- nical men to make every possible contribution to this work.

Geologists have always been more or less closely associated with the highway movement. Several state highway programs were started by state geologists, and reports on road material resources have been published by many state geological surveys. Geologists have in the past in numerous cases acted as special advisors in problems of highway construction. With the growth of the highway construction program new opportunities are open- ing to the geologist to extend the scope of his activity. Engi- neers are coming to recognize the fact that geological informa- tion is just as essential in the planning of highway construction as engineering data. In some states this more extensive coopera- tion is now in effect.

The civil engineer has done his share in planning roads de- signed to meet the needs of traffic. He has studied the problems of drainage, alignment, surfacing, and maintenance, and the design of bridges, culverts, and pavements. The geologist can be of much value to the public in questions relating to character of subgrade, excavation, and the planning of relocations, but neither he nor the engineer can effect large savings in these items of present cost. Some of the remaining large factors in the cost of highway construction are, first, labor, second, materials

216 E. F, BEAN. such as cement, steel, and sand, gravel and crushed rock from commercial plants, third, transportation by rail, truck, and wagon. The engineer can effect some saving in each of these factors either by increasing the efficiency of labor or by shrewd buying. This has been accomplished in most cases. However, out of a total annual expenditure for highways of $500,000,000, prob- ably over a half is spent for the materials and their transporta- tion to the construction projects, and it is in the cost of these materials that the largest savings can be effected. These ma- terials are sand, gravel, rock, and clay. The location and selec- tion of these come within the field of the geologist in cooperation with the engineer. Experience has shown for example that the geologist can in many cases effect considerable saving by locating deposits of material nearer the project, thus reducing the large item of transportation, or he may even locate a usable type of road material in a region thought to be absolutely dependent upon outside sources. He may locate equally good deposits which may be bought more cheaply than those previously used. This field of usefulness of the geologist is rapidly developing with the in- creasing efficiency and scope of road-building operations.

As an illustration of the use of geology in highway construc- tion, the general plan of field work as conducted in Wisconsin may be described. The road-building program here is so large, and properly trained men are so few in number that it has been necessary, in order to keep up with construction, to confine the investigations to the definite stretches of road where construction is planned in the near future. In general a survey is made on each side of the proposed highway for a distance as great as that from the nearest railroad station (a source of rail-hauled material). An area even larger is covered if the alternative rail haul for commercial materials is a great distance. The quantity and quality of materials suited to this construction which have been located by this survey are reported upon in considerable detail. For concrete pavements this involves screen analyses, as well as silt and colorimetric tests (for organic matter), of all

pre peer

ees

' E t f

Economic Geology And Highway Construction. 217

gravel and sand deposits both developed and undeveloped. Quarries and rock outcrops as potential sources for crushed rock are given detailed study. For surfacing, a search is made for all available material, whether this be gravel, shale, limestone, granite, clay, or sand.

Not only are all available exposures examined, but in the case of undeveloped deposits test pits are dug, just as in the explora- tion for iron ore or any other valuable mineral matter. After the geologist has eliminated all but a few of the more desirable deposits, the engineer carries on more extensive exploration of these before determining what deposit shall be developed.

In addition to qualitative information the geologist must fur- nish estimates of the yardage available and of the amount of stripping necessary for each deposit. Rock outcrops must be carefully examined not only to determine the utility of the rock, but also to determine the quantity available, the conditions of quarrying, and the transportation problems that affect their availability.

The geologist must have a good working knowledge of general and glacial geology, stratigraphy, petrology, and physiography. Mapping on a more detailed scale than is possible on published maps is necessary, as an area too small to appear on such a map may be underlain by sufficient material for a large project. This work requires geologists of considerable field experience, since it involves not merely the making of geological observations such as would be necessary in a glaciated region to distinguish terminal moraine, ground moraine and outwash. He must determine in what particular knoll of the terminal moraine or in what small tract of the outwash plain will be found the best and most cheaply developed source of the desired kind of road material. This might be accomplished by tedious and expensive test pitting over a whole outwash plain, for example, but a properly qualified geologist through his knowledge of the minute details of glacial geology should be able to eliminate large areas from considera- tion and concentrate his efforts upon the most favorable ones.

218 E. Fr BEAN. In the study of an esker, instead of having to make test pits throughout its length the geologist should be able to select at a glance the places most likely to yield the particular kind of ma- terial needed for the project under consideration. In the area of glacial lake Wisconsin, the soils are generally sandy. A search is made for places where the underlying lake clays are under but a thin sand covering. Such a search involves a careful study of topography and soils in order to locate small areas where the clay is readily accessible. In the non-glaciated areas of Cam- brian sandstone the detailed stratigraphic sections made by Dr. E. O. Ulrich have proved of great practical value, since in this area deposits of Cambrian shale are the only material available for surfacing the sand roads. With this stratigraphic knowledge as a basis, the geologist studying road materials must select the particular sites where the material needed can be secured and delivered on the road with the least possible expense. In drift- less southwestern Wisconsin, which lacks the wealth of readily accessible road material to be found in much of the glaciated area, search is made for limestone of suitable quality and availability. The sandstones are studied to find a formation suitable for fine aggregate. This requires more careful, quantitative field study than is usual for general geologic purposes. In the areas of thin drift overlying granitic rocks, the glacial material is not of much value for road material. Search must therefore be made for disintegrated granite suited for road surfacing, or for fresh granite which can be used in concrete. These illustrations show the detailed type of work required, and indicate the scientific training a geologist may acquire in this type of economic work. During the 1920 field season four parties, each consisting of a geologist and an engineer, were employed in the survey of 300 miles of 1921 construction projects. The Highway Commission found in some cases that the saving resulting from a few days’ investigation by the geologist paid his salary and expenses for a whole season. In one county a material survey of one four mile project resulted in a saving of $6,000. In another gravel

Economic Geology And Highway Construction. 219

was hauled a distance of six miles. Investigation showed that better gravel was available at a distance of but one-half mile. The Commission was so strongly impressed by the practical value of the work that they asked for the services of eight parties in 1921 and twelve in 1922. This number of parties was de- termined by the available number of adequately trained men. When more men become available, the work will be extended. “The surveys have been very helpful and have located materials where the local people and the county highway commissioner were sure none could be found; a large amount of road material was discovered in one county which had been shipping in material of the same type by rail for some distance; this discovery was important because it showed that if material surveys were made for every county in the state, the findings would determine the road-building program in each county. No successful/and busi- ness-like road-building program can be made in a cOunty until an exhaustive material survey has been made.”? MAY One of the incidental results of the geologist’s work was the discovery that many’ counties were paying land owner an, ex- cessive royalty for road materials purchased by the cubic yard. This royalty was in one case as much as 70 cents a yard, and 25 cents per yard, was a common figure. The payment of these

‘royalties resulted in costs of $4,000 to $28,000 per acre for land

worth from $50 to $400 per acre as agricultural land. Geologic information showed that road materials are so abundant that such prices are not justified, and that deposits of road material should be bought by the acre at practically the agricultural value of land. A table was prepared to contrast the relative costs under the two methods of purchase. The distribution of this table has helped to educate many of the county officials away from the royalty basis of purchase. This change alone will effect large savings each year.

In addition to the financial saving, the use of the local material has a direct bearing on the problem of rail transportation. The

1 Statement as to the utility of this work recently made by a Wisconsin Highway Commission division engineer.

220 E. F. Bean.

railroads have for some time been unable to move freight promptly—a serious problem which vitally affects the comfort and prosperity of every citizen. The movement of coal has been hampered by the shortage of gondola cars. Highway materials are moved almost exclusively in gondolas, and their movemem is confined largely to the season of maximum movement of coal. Car shortage has resulted in expensive delays in highway con- struction. The use of local road materials relieves the railroads of this additional load and liberates cars for the use of coal and other commodities, and in addition prevents expensive delays in the highway work. Also, private building operations have for some time been subnormal; when they resume normal propor- tions, highway construction should compete as little as possible with private concerns, either for aggregate or for cars. Such competition can be reduced very greatly by the use of local materials.

Even if the geologist can effect no saving in cost, if he can by his studies bring about a decreased use of railway cars, his work is more than justified.

From the standpoint of economic geology the development of road-material investigation is important in affording a wider field of service, which for some years will be limited only by the number of properly trained men available. This work will ab- sorb the entire output of such men in the geology department of the University of Wisconsin during the next field season.

Such work affords the young geologist an opportunity to gain a wide range of field experience. Though this is economic geology of a most practical sort, it must be remembered that, if the results are to be of value, the work must be done with the scientific viewpoint and with a willingness to observe facts with extreme care. Such work will add greatly to the store of avail- able scientific information, and should aid in the development of geologists of broad scientific training.

There is available as a background for this work all the pub- lished material relating to areal geology. Scientific reports, even

th

Economic Geology And Highway Construction. 221

though not made with the economic viewpoint, are an essential basis for the search for road materials. In southeastern Wis- consin constant use is made of W. C. Alden’s report? on the Pleistocene Geology. This was intended as a purely scientific report, but the use of his carefully prepared map and discussion makes it possible to conduct a survey more rapidly and in- telligently.

The geologist, therefore, has in this work new opportunity to increase his range of usefulness. His contribution may be in saving either in original cost of material or in transportation of material. He may develop supplies that will relieve the railroads of an extra burden. The state highway commissions have a strong interest in this matter, since it will be difficult to carry out their programs unless the railroads are employed for the trans- portation of road materials only to those projects where it is impossible to produce local material. The state geological sur- veys are always interested in opportunities to render service, and work of this nature has large possibilities.

Wisconsin GEOLOGICAL

AND NATURAL History SURVEY, Manpison, Wis.

2 Alden, W. C., “Quaternary Geology of Southeastern Wisconsin,” U. S.

Geol. Survey, Prof. Paper 106.

Editorial

International Mineral Problems.

During and since the war much has been said about the need of investigating world mineral problems; but it is still probably true that many persons concerned with mineral resources, both in business and professional ways, have only vague notions as to what these problems are, their bearings on the domestic resource situation, and their relations to pending political questions. It is not unusual to find a detached academic interest coupled with a subconscious assumption that this is some other person’s field. It has not yet come home to some economic geologists that they have a responsible part in the elucidation of these problems, and that they cannot personally avoid an active interest in this work if they expect to keep up with the economic developments in their pro- fession. A report by an economic geologist on a mineral resource, which does not take into acount the world situation, is likely to be misleading, even though accurate in its description of physical

facts.

A few of the questions involved in this general subject may be briefly touched upon.

With the increasing complexity of mineral industry and the rapidly multiplying per capita consumption of minerals, the time has long since passed when any one country is entirely self-sup- porting with reference to essential minerals. Neither does any one country have a broad enough market for all of its output. The United States is perhaps better favored than any other country, in regard to both supplies and markets, and yet this country can scarcely get along without drawing on foreign sup- plies for many essential minerals,—for instance, those of the ferro-alloy group. Likewise its great iron and copper mining

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Editorial.

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industries require an outlet to the world market to insure their prosperity. Nature has distributed its mineral resources irregu- larly around the globe, and has thereby determined certain lines of efficient distribution of these materials in the interests of their best use and conservation. These basic conditions cannot be changed by legal enactments, and in the long run artificial barriers set up across any of the natural channels are likely to be swept aside by commercial demand. This fundamental reality should not be lost sight of in formulating international policies and laws relating to the mineral industry. Tariff questions now pending, for instance, cannot be intelligently settled without recognition of this basic fact. There is room for a considerable variety of tariffs for purposes of revenue and for equalizing differences in cost conditions, without seriously obstructing movements of minerals under laws of supply and demand; but some of the pend- ing measures go far beyond this point. If enacted they wil! interfere with the maintenance of supplies adequate for national welfare, except at costs which will handicap the industries based on the commodities in question.

A clear perspective of the underlying geologic facts of distribu- tion should be helpful also in considering another class of meas- ures,—namely, the various national restrictions now in force or proposed, in regard to discovery, development, and exploitation of minerals by nationals of other countries. There is a good deal of vitality in this tendency, and it seems to be extending to nations which have heretofore imposed the minimum restrictions. National self-interest seems to favor laws which reserve to the local government or peopie the benefits of its natural resources, and as long as the inhabitants of the country are effective in find- ing and exploiting mineral resources needed by other countries, it is difficult to point out adequate reasons why they should not enjoy the advantages therefrom. It not infrequently -happens, however, that the local use and demand is small; that because of lack of capital, or lack of interest, or disturbed political condi- tions, development falls far behind the insistent demands from other parts of the world. Political and commercial pressure from

224 Editorial.

other countries begins to make itself felt in response to the material demands of civilization, and often such pressure is ap- plied in a ruthless and undesirable fashion. The ethics of a situa- tion like this are not clear. On the one hand is the natural and laudable desire for self-determination; on the other is the demand for the product, created by civilization. Whatever the ethical principles involved, the demand for the product is likely to pre- vail; it probably could not be eliminated, even if it were decided that it were morally wrong. The use of force of some kind almost inevitably follows the demand, and in the present stage of organization of human affairs, probably cannot be eliminated unless the demand is eliminated. About the only practical step to ameliorate the situation thus created is to see to it that the ex- ternal pressure is applied under such public supervision, national and international, as to prevent the excesses which sometimes develop in exploitation by strong commercial interests. When viewed in a broader way, also, the developments forced by ex- ternal demand may in the long run be to the self-interest of the country concerned.

By way of illustration, the United States has built up a vast range of activities based on the use of energy derived from oil. There is not enough domestic oil to supply this demand. The demand is therefore transmitted to the nearest outside oil terri- tory—Mexico. Argument about the right or wrong of the pres- sure thus created is almost futile. Unless we are able and willing to change over our activities based on the use of this energy resource, the mandate to secure oil will make itself powerfully felt on Mexican territory, and may override the inclinations of the ‘Mexican people, so far as these lag behind the standard created by the demand. On the other hand, the methods used in satisfying this demand will probably warrant the closest scrutiny and supervision.

The Paris conference recognized the abuses in the development of resources in weaker nations, and attempted partially to meet the issue by providing that the development of resources in manda- tory countries should be managed to the best interest of all nations in the League of Nations. With the United States outside of the

a erage oer

Editorial. 225

League, the implication is obvious that the management need not be for our interest; hence some of the recent difficulties, for in- stance, with reference to oil development in Mesopotamia.

Another phase of this problem may be touched on, partly by way of digression. There has recently been heated discussion of the methods used by certain strong nations in attempting to monopolize for themselves the advantages from mineral resources in their own countries and in those which they control,—as illus- trated by the attempt of England to secure oil supplies. Economic geologists have taken part in this discussion. Criticism may well be directed to the methods sometimes used, but along with this has gone what seems to me entirely unwarranted criticism of motives. It has been made to appear that England is morally reprehensible for doing what she can to secure future reserves of an essential energy resource like oil, which the United States has heretofore largely monopolized. England’s motive or purpose seems entirely understandable and defensible. It is only the methods employed that might be open to criticism. While we are justified in striving for the open door, we owe it to ourselves to be fair in our arguments.

We may pass over the many ways in which minerals figure internationally in relation to new political boundaries created by the war, reparation terms, new political alignments, etc.

although there is hardly one of these which does not directly or indirectly have its reaction upon our domestic industry.

In the solution of all of these problems the economic geologist has an opportunity to play a legitimate part without getting too far away from the physical background of his science. He can make it understood that no nation is independent of other nations in regard to mineral supplies and markets. The specific nature of this dependence with reference to each of the commodities, their sources and possibilities of discovery, their natural channels of flow, may be saliently indicated. When a public question comes up relating to tariffs, to activities of outsiders in backward coun- tries, to difficulties of all sorts imposed by foreign restrictions, it seems fundamental that the situation should be viewed in this

226 ; Editorial.

broad perspective,—with clear recognition of the fact that the most efficient and conservational use of the world’s resources requires freedom of commodity movements and exchange through international cooperation ; that this situation is imposed by nature and not by human enactments.

The most direct approach to international mineral problems is naturally determined by the self-interest of the industry of a given country, but professional men should not lose sight of the fact that there are broader issues involved. First of these is the best use of the world’s resources in the interests of conservation, both of materials and of human effort. It seems also to be pretty well agreed that friendly international relations and world peace are based in large part on economic considerations. Among these considerations raw materials figure largely. An intelligent plan worked out for the handling of raw materials, based on an under- standing of natural physical conditions, should be of great aid in the formulation of more general international understandings. There has been some tendency in recent times to attempt to formu- late these understandings on political and ethical principles, which have not been brought down to earth and effectively adjusted to the economic facts. The method might be called deductive. It would seem the scientist might aid in establishing what might be called the inductive method of approach, by first ascertaining and correlating the underlying physical facts, as a solid foundation for the political superstructure. Thus it may be possible to avoid the readjustments and perhaps disaster to well-meaning efforts, in the interest of world peace, which ignore basic economic necessities.

C. K. Lerra. Mapison, WISCONSIN.

Discussion

This department has been established by the editors in order to afford tc those interested in questions relating to economic geology an opportunity for informal discussion. Contributions are cordially invited either in the form of discussion of more formal papers appearing in earlier numbers or bearing upon matters not previously treated. Letters should be directed to the Editor, Sheffield Scientific School of Yale University, New Haven, Conn. The full name of the author should be attached to all communications.

Origin Of Adirondack Magnetite Deposits-~

Sir: In 1919 the writer published in your journal? a paper on the “Magnetic Iron Ores of Clinton County, New York” in which the general geology of the region, and the character, struc- ture, and origin of the ore bodies are set forth. A new theory of the origin of the ore deposits, particularly those being mined at Lyon Mountain, is elaborated in that paper. Certain criticisms of that theory have been published by Newland.* Since the pub- lication of the above mentioned paper, the writer has made detailed surveys of two more quadrangles, each with a number of magnetic deposits, in northern New York, bringing the total number covered by him up to eleven, with magnetic iron ores more or less present in nearly all of them. During the last two field seasons the writer has also visited or revisited a number of iron mining localities, especially Mineville and Hammondville, in Essex County, for the purpose of testing his theory of the origin of the ores.

It is the present purpose to reinforce the theory by additional evidence from field and laboratory; to apply the theory to the Adirondack nontitaniferous magnetic deposits in general; and to answer Newland’s criticisms. The interested reader should have at hand the two papers mentioned as well as Newland’s “ Geology

1 Published by permission of the State Geologist of New York.

2 Econ. GEOL., vol. 14, 1919, pp. 500-535. 3D. H. Newland, Econ. GEot., vol. 15, 1920, pp. 177-180.

228 Discussion.

of the Adirondack Magnetic Iron Ores,’’* because certain im- portant features of the geology there discussed will not here be repeated. It should be clearly understood that the extensive titaniferous magnetite deposits directly associated with the Ad- irondack anorthosite are not considered.

Theories Of Origin Of The Magnetite Deposits.

The problem of the origin of magnetic iron ore deposits has been a puzzling one much discussed for many years. Any light which may be thrown upon the problem by a study of the Adiron- dack magnetites is of exceptional interest because they comprise some of the most important deposits on the continent, especially those now being worked at Mineville and Lyon Mountain, and at the abandoned mine at Hammondville. At least four theories have been put forth to account for the Adirondack magnetite deposits.

An older theory, commonly held by those directly interested in the mining and also by certain geologists who have dealt with the deposits, implies that the ores and their enclosing rocks are of sedimentary origin. “The apparent conformity between the deposits and the foliation of the gneisses, their lineal develop- ment and persistence for long distances on the strike are sup- porting arguments for the sedimentary theory” (Newland). But neither Newland nor Kemp, who have given much atten- tion to the subject, hold to the sedimentary theory. As a result of their work® it has been shown beyond question that the ores and enclosing rocks are of igneous origin, the arguments by Kemp being especially convincing.

According to a second theory, set forth by Kemp,® after his abandonment of the sedimentary theory, the ore deposits at Mineville are explained as a result of the intrusion of bodies of

gabbro as a “contact effect of the intrusive gabbro,”’ the latter

4D. H. Newland, N. Y. State Mus. Bul. 119, 1908.

5D. H. Newland, N. Y. State Mus. Bul. 119, 1908, pp. 30-33. J. F. Kemp, N. Y. State Mus. Bul. 138, 1910, pp. 126-132. 6J. F. Kemp, 4m. Inst. Min. Eng. Trans., vol. 27, 1897.

Discussion. 229

being regarded as younger than the syenite-granite which is the prevailing country rock.

A third theory,’ announced by Kemp after his studies con- vinced him that the basic gneisses directly associated with the ores at Mineville are integral parts of the syenite-granite series rather than gabbro, explains the ores as magmatic differentiation or basic segregation masses in the syenite-granite series. Kemp says that “we may think of the ore (at Mineville) as being more or less akin to pegmatites in its formation,” and Newland thinks that the final result of ore concentration of the nontitaniferous magnetites of the Adirondack region in general probably took place under “the influence of highly heated vapors and waters arising from the igneous mass” and that “the ore bodies thus formed would be comparable in a way to pegmatite dikes.”

The fourth theory,’ recently elaborated by the writer, agrees in certain respects with the third theory above outlined, but differs from it fundamentally in other respects. According to this theory a gabbro or metagabbro, earlier than the syenite-granite, was the main or sole source of the magnetic deposits, and the derivation of the magnetite from the gabbro and its concentra- tion into ore deposits was accomplished by the intrusion of the syenite-granite magma, more especially its residual pegmatitic and silexitic portions rich in hot gases, vapors, and fluids (mostly water).

SIGNIFICANCE OF THE ASSOCIATION OF THE ORES WITH GRANITE, PEGMATITIC GRANITE, AND METAGABBRO.

The almost or quite constant direct association of the non- titaniferous magnetic ores throughout the Adirondacks with granite, especially where it is rich in pegmatite or silexite, and an older metagabbro (in many cases more or less thoroughly injected or possibly assimilated) is a fact which cannot be too strongly emphasized. One of Newland’s main criticisms is that “admix- ture (of the granite) with foreign material seems to have no

7J. F. Kemp, N. Y. State Mus. Bul. 138, 1910, pp. 1 8W. J. Miller, Econ. Geor., vol. 14, 1919, pp. 528-33

230 Discussion.

bearing on the distribution of the ores in general” except to some extent in the Lyon Mountain district. With this statement the writer disagrees, and this disagreement is based upon numerous observations made at magnetite localities throughout the Adiron- dack region during the last fourteen years. In fact the associa- tion of ore with metagabbro (often greatly affected by granite), granite and pegmatitic granite is so constant that if one hears of an old iron mine or prospect he can, with little chance of failure, predict just such a combination of rocks. The writer has done this scores of times during the last three field seasons. Even in the very few places where metagabbro or its injection facies does not appear at the surface, it is more than likely present in considerable amount below the surface as shown in some of the mines.

The geological maps of the mining districts seldom give an adequate idea of the quantity of old basic gneiss (metagabbro and injected gabbro) associated with the ore. Thus many masses too small to map and others concealed under drift, occur near the Lyon Mountain mines; much basic gneiss is directly associated with the ore in the rock mapped as syenite around Mineville; and at Hammondville very considerable amounts of dark gneiss occur in the ore bearing country rock which is itself really too rich in plagioclase to be a true granite. It is of almost equal importance to bear in mind that the wide stretches of granite free from admixed metagabbro, even where locally richly pegmatitic, are remarkably barren of ore deposits. Surely, then, both the meta- gabbro and pegmatitic granite have been involved in the ore development.

The above mentioned combination of rocks is described in the writer's first paper as clearly and extensively developed in and near the Lyon Mountain mines, and similar rocks also occur at Mineville and Hammondville. Most of the gabbro masses of all these and other mining districts is regarded by the writer as older than the main country rock which is the syenite-granite series. Reasons for this view are the same as those stated in the earlier paper. At Mineville, Kemp regards the basic gneisses directly

Discussion. 231

associated in large amounts with the ores in the syenite-granite to be differentiates of the syenite magma, but the alternative suggestion is here made that those basic gneisses really represent more or less highly injected or possibly somewhat assimilated old metagabbro in every way much like rocks demonstrably of such origin in the Lyon Mountain and other districts. Kemp® says: “When we come to the relations of the gabbros to the syenite series, especially in the vicinity of Mineville, there is much obscurity’ and between certain “exposures of undoubted and typical gabbro there is the stretch of dark basic rock, which we also associate with the syenites. . . . One cannot say where the one ends and the other begins.’’ This basic rock, which has been examined by the writer, and the basic bands or zones deep within the mines, are here considered to represent mostly or wholly old gabbro more or less altered by the granite or syenite magma.

Field facts, therefore, strongly oppose Newland’s statement that admixture with foreign material has little or no bearing upon the distribution of the ores, and his argument that sufficiently large bodies of metagabbro and injected (but not necessarily absorbed) gabbro are not present to form a main source of sup- ply of the ore deposits completely breaks down.

Derivation Of The Magnetite.

Having established the fact that ores seldom if ever occur except in direct association with granite rich in pegmatite and large quantites of an old dark gneiss (presumably always a meta- gabbro) commonly more or less intimately penetrated or injected, but not necessarily thoroughly assimilated, by granite and pegma- tite, we come to a consideration of the derivation of the ores. According to the writer’s theory the syenite-granite magma, more especially its residual highly pegmatitic and silexitic por- tions, extracted the magnetite from the old dark iron-rich gneiss (metagabbro). Newland is very skeptical in regard to this idea. and says that convincing quantitative evidence is lacking, and this in spite of the fact that detailed statements, including chemical

9J. F. Kemp, N. Y. State Mus. Bul. 138, 1910, p. 127.

232 Discussion,

analyses, are presented in the writer’s earlier paper. The gabbro (and metagabbro), where not closely involved with granite, very typically contains much iron-rich hornblende (20 to 30 per cent.), iron-rich hypersthene (10 to 25 per cent.), a moderate amount of magnetite (3 to 6 per cent.), and usually some diallage. In the abundantly developed metagabbro-granite mixed or injection gneisses the hornblende is typically less conspicuous, the hypers- thene rarely ever shows at all, the magnetite is more variable but generally runs a little higher, while an iron-poor pyroxene (dial- lage) becomes conspicuous, commonly making up I5 to 35 per cent. of the mixed rock which, therefore, becomes a diallage gneiss. During mining operations bodies of practically pure diallage rock of considerable size are encountered.

Field work, and the study of many thin sections, shows that, in and around the ore deposits, tremendous quantities of iron- poor diallage have resulted from the transformation of the iron- rich minerals of the old gabbro by the action of the granite magma and pegmatite. Obviously, then, large quantities of iron oxide were set free. But what became of so much iron oxide? According to the writer’s theory it was taken up in the pegmatitic solutions, carried along usually not very far, and concentrated in the form of ore deposits as we see them teday in the more highly pegmatized portions of the granite where it is intimately associated with more or less highly altered old gabbro.

Finally, Newland thinks there is no difficulty in the way of explaining the ore deposits as magmatic segregation masses in the granite itself and says that the new theory “ fails to account for the iron content of the granite in its normal phases.’ Now, the normal granite is that which is free from contamination or close association with old gneiss. Examination of many thin sections of such normal granite of the Lyon Mountain and other areas shows that it is very ordinary as regards iron content, the magnetite rarely running over a few per cent, while ferro-mag- nesian minerals run very low. Nor is such granite especially soda-rich as Newland claims, certainly not more so than the ordinary syenite and granite of the Adirondacks in general

——— Ee

DISCUSSION. 233 Microperthite, microcline, and quartz constitute the great bulk of the rock, while plagioclase seldom rises to 20 per cent., and usually amounts to only a few per cent. Newland’s misconcep- tions in these regards have no doubt resulted from study of thin sections of the granite only near the ores, as at Hammondville, where the rock has been affected by the old gneiss. If the ores are segregation masses of the granite itself, why did not at least some deposits of considerable size develop well within portions of the widespread granite free from admixture with the old gneiss?

Wittiam J. Mitter. SMITH COLLEGE,

NorRTHAMPTON, MAss.

Reviews

Geology of the Non-Metallic Mineral Deposits other than Silicates. Vol. I, Principles of Salt Deposition. By AMmapeus W. Grapavu. First Ed. New York, McGraw-Hill Book Co., 1920.

The nature of this work is best indicated by a quotation from the preface: “This book is essentially a treatise on applied stratigraphy. As the title implies it deals with non-metallic deposits exclusive of sili- cates, but the hydrocarbons and some of the native elements are only incidentally considered. Their fuller treatment is reserved for a future work. The book might be designated a hand-book of salt geology, if we use the term salt in a sufficiently broad sense to include nitrates, phosphates, borates and similar deposits.

“The emphasis is laid upon the geological relationships of these de- posits, and the chief endeavor has been to set forth our present under- standin gof the conditions under which such deposits are formed. To this end the first volume is devoted to a study of deposits now forming or which have but recently been formed, and of the physical conditions which control such deposition. When these are understood it becomes possible to investigate the history of older deposits with some hope of success.”

The first three chapters may be considered as introductory. In the first chapter natural salts are defined and the chemistry of their forma- tion is briefly discussed. The whole of the second chapter is devoted to an alphabetical list of the non-metallic salts other than silicates giving the mineral characters and geographical occurrence of each salt.

As the sea is perhaps the source of the largest number of natural salts, the third chapter discusses the sea itself, its geographical relations, its subdivisions, and the conditions under which the salts of the sea may be abstracted. Analyses of sea water and its saline matter are given, followed by a detailed description of the method and results of Usiglio’s experiments on the evaporation of sea water to discover the order of deposition of the salts. Van’t Hoff’s experiments are also discussed with illustrations of his saturation and crystallization diagrams. The explanation accompanying the diagrams does not seem sufficiently ex- plicit for students who are not familiar with equilibrium diagrams,

Chapters IV., V., and VI. describe the means by which sea salts are

REVIEIS. 235 abstracted from ocean water and the characteristics of each type of deposit. Salts may be abstracted from ocean water in four important ways:

A. By organic agencies—Organic Salts (Bioliths).

B. By reaction with other salts or with liquids or gases introduced—Pre-

cipitation Salts (Precipitates).

C. By concentration of the water—Cencentration Salts (Evaporates). D. By atmospheric distribution—Cyclic Salts.

‘

In considering salts deposits by organic agencies the author has intro- duced an extended series of illustrations of extinct and living organisms chiefly active in the formation of such deposits and the text has been reduced to a mere commentary on the illustrations.

The section on precipitation salts occupies only a few pages, since deposits of such salts are not very common.

Salts deposited by concentration of the sea water are much more im- portant. To effect such concentration two conditions

the climate must be arid enough so that evaporation exceeds precipi-

are necessary;

tation, and portions of the sea must be wholly or partially cut off from the main body. Sea-margin deposits of salt are those which have a limited connection with the sea while forming. They are of three types: marginal salt-pans, marine salinas, and lagoonal deposits. Basins en- tirely cut off from the main body of sea water form another important type of salt deposit.

Cyclic salts (salts which have been lifted from the sea with the spray and have been blown inland) occasionally form deposits of considerable extent although they cannot be considered as important as the deposits formed by the concentration of sea water.

Under each type of deposit the author considers one or more modern examples, enumerates characteristics, quotes analyses, and discusses the peculiarities which indicate the mode of origin.

Salts of terrestrial origin “include all salts which are deposited by terrestrial waters, by volcanic emanations, and by chemical reactions between deposits of salt already in existence in the earth’s crust, as well as those due to complete or differential solution and redeposition of o!der salt deposits.” The author classifies such deposits both according to the source of the material and according to the cause of deposition. The classification according to the source of the material, which is given below, is followed closely in the text.

A. Original Salt Deposits. (a) From Solution. 1. Connate Salts——Salts included in the pore space of older marine sediments.

236 Reviews.

2. Re-solution Salts——Salts derived from the solution of older salt deposits.

3. Decomposition Salts.——Salts derived from the decomposi- tion of other rocks (chiefly) igneous) of the earth’s crust.

4. Magmatic Salts——Salts derived from magmatic or juve- nile waters.

(b) From Vapors.

5. Volcanic Salts—Materials derived from the vaporous emanations of volcanoes and

6. Atmospheric Salts——Salts derived from the material nor- mally in vaporous solution in the atmosphere, such as snow and carbon.

(c) From Fusion.

7. Igneous Salts.—These include all the mineral species due

to solidification from igneous magmas (chiefly silicates). B. Secondary Salt Deposits.

8. Meta Salts——Salts derived by the chemical reaction be- tween reagents (water, gases, etc.) and a salt deposit, or by the combination or inter-reaction of original salts in contact.

g. Residual Salts——Salts or other substances left behind on decomposition of other substances and removal of cer- tain constituents—Kaolin, Bauxite, etc.

One chapter is given to salt deposits of connate origin, another to salts leached from older rock-salt deposits, and another salts leached from decomposition products of older rocks.

A separate chapter is devoted to descriptions of playa deposits of complex salts like those of western Nevada and southeastern California. Although the origin of these deposits is not definitely known the author is inclined to believe that nearly all of them are derived from the leach- ings of older rocks and consequently this chapter follows the chapter discussing the deposits of such an origin.

Since there is so little agreement among students as to the origin of nitrate deposits and since the origin of all nitrate deposits is not the same, the chapter dealing with them does not follow the classification closely. The nitrate deposits of Chile are briefly described but the author does not express a definite opinion as to their origin. .

The chapter on phosphate of lime deposits includes sections dealing with the kinds of deposits, their origin, and occurrence.

Salt deposits of mineral springs, salts of igneous origin, and meta salts are dealt with in Chapters XV. and XVI.

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Reviews. 237

The concluding chapters of the first volume on deformation of the salt bodies and salt deposition in former geological periods could perhaps have been better put as introductory chapters to the second volume for they have to do chiefly with the interpretation of the older salt deposits.

The first volume is admirably put together. The text follows closely a well-planned and logical outline. The literature on each salt deposit described has evidently been carefully studied and the evidence for a particular origin (when an opinion as to origin is given) diligently pre- pared. Numerous analyses are included.

As stated in the preface the first volume is devoted to an examination of the characteristics and origin of modern salt deposits in order that the origin of ancient salt deposits may be understood. If the second volume is as carefully planned and as painstakingly prepared as the first the whole work will make a valuable contribution. As it is, the first volume alone fills a long-felt want, for no previous book in English has treated the principles of salt deposition in an adequate way.

The illustrations and diagrams, although not numerous, are pertinent. Almost every description of a salt deposit is accompanied by a sketch map. The printing is good and typographical errors are few.

Herbert Insley.

U. S. GronocicaL SuRVEY,

WasHIncTon, D. C.

Mineral Resources of Armenia and Anatolia. By H.A.Karajian. 211

pp. Armen Technical Book Co. New York, 1920.

The book is a compilation of data relating to the geology and geog- raphy of Asia Minor.

Part I. is a general account of the country which may be pictured as an elevated interior plateau between higher bordering coast ranges on the north and south. The lowest rocks are pre-Devonian schists, char- acterized by a series of northeasterly folds which may date from the Caledonian disturbance. Above these older schists, all of the geological systems, beginning with the Devonian, are represented. In Miocene time they were folded and the axes of the folds follow the trend of the ranges, in general E.-W. Volcanic rocks are widely distributed in the central plateau.

Parts II. and III. deal with the non-metallic and metallic mineral resources.

Coal has been mined on an extensive scale only near Heraclea on the Black Sea, where a good bituminous coal occurs in folded and faulted Carboniferous rocks. In I9II, 750,000 metric tons were produced. Lignites, generally of Tertiary age, are found at many places through Asia Minor.

to 5) oe

4 Reviews.

Petroleum is not being produced in Asia Minor proper, though seep- ages and other indications of oil are noted from scattered localities. Detailed mention is made of occurrences near Baku.

Salt occurs as rock salt and in the brine of lakes in the area of inte- rior drainage of the central plateau. Borate is obtained, mainly pan- dermite from rock sources, and since 1900 ranged between 10,000 and 15,000 tons annually. Emery deposits near Smyrna yielded in 1899 24,475 tons. Meerschaum, sulphur, alum, limestone, gypsum, nitrate, clay, agate and siliceous marl are mentioned.

Gold mining was of importance in pre-Christian times, but is now practically dead: the 1906 production was $29,000. Silver, in 1906, amounted to $367,351, most of the old mines being idle. Copper ores occur but are not being mined. The production of iron is negligible. The chrome deposits of western Asia Minor have been of importance for some time, and in I1go01 the production was 40,972 tons. A/anganese occurs, especially in extensive deposits in Russian Trans-Caucasia; the production (1911) was 18,000 tons, though in the preceding twenty-five years it had varied between 669 and 55,300 tons. Small resources and production of mercury, antimony, lead, zinc, tin, arsenic and cobalt are mentioned.

The impression one gets from the book is that Asia Minor has promise of good mineral production when peace and an orderly government is established which will favor geological investigation and modern mining methods.

Lewis G. WESTGATE.

Scientific Notes And News'

A. O. Hayes, of the Geological Survey of Canada, is at pres- ent lecturing on the minerals and ore deposits of the Maritime Provinces of Canada at Queen's University, Kingston, Ontario.

J. A. Bancrort, of the Department of Geology of McGill University, Montreal, has been given a year’s leave of absence to become assistant general-manager of the Granby Consolidated Mining, Smelting and Power Co., Ltd., at Anyox, B. C.

Davin Wuite has recently been in Madison, Wisconsin, giving lectures at the University of Wisconsin on fossil fuels.

FREDERICK G. CLAPP, during March, gave a course of twelve lectures in Petroleum Geology and Petroleum Engineering at Harvard University. He also delivered an illustrated lecture before the Geological Conference in Cambridge on “A Geolo- gist’s Trip through China.”

M. I. GotpMaN, of the U. S. Geological Survey, is now study- ing salt domes in the Gulf States.

RALPH ARNOLD, consulting geologist, was in London for a short time in March.

JAMEs F. Kemp, of Columbia University, has been delivering a series of lectures at McGill University.

FrepertcK H. Hatcu, London, England, has been appointed Official Adviser for Minerals other than Coal, to the recently created British Mines Department.

E. W. SHaw resigned from the U. S. Geological Survey on March 30, to take up consultation work in oil and gas.

Geologists, mining engineers and others interested in applied geology are invited to keep the editor informed of new investigations of mining districts or scientific studies undertaken by them, together with such other scientific and personal items as may come to their notice.

240 Notes And News.

WALTER Harvey WEED recently made an examination of the properties of the United Arizona Copper Mining and Smelting Co., near Mayer, Ariz.

M. G. GuLLEy, of the U. S. Geological Survey, is investigating the reported showings of petroleum in wells drilled in the Im- perial Valley, California.

V. DotMacE has been transferred from the provincial office of the Geological Survey of Canada, at Vancouver, to the Ot- tawa office.

Joseru E. PocGue has opened an office at 29 Fifth Ave., New Oro Mining and Railway Co. with headquarters in Mexico City.

JoserH E. PoGNE has opened an office at 29 Fifth Ave., New York, for work in industrial economic engineering with special reference to the mineral industries.

R. H. SarGent has been doing commercial work in Bolivia, and has now returned to the Alaska division of the U. S. Geo- logical Survey.

Stuart St. Crarr, Consulting Geologist of 20 E. Jackson Blvd., Chicago, Illinois, has changed his location to 55 Liberty St., New York City. He is spending the next year in oil work in the Orient.

GreorcE H. GarrREy, mining geologist, is at present engaged in geologic work in British Columbia.

WaLTER FE, Gapsy is at Pachuca, Hidalgo, Mexico, with the Santa Gertrudis Co.

Carv I. LAusEN, formerly with the Moctezuma Copper Co., Nacozari, Mexico, has accepted a position as geologist with the Arizona Bureau of Mines, at Tucson, Arizona.

ARTHUR CLARK TERRILL, formerly with the Kansas State Geological Survey, Baxter Springs, Kan., and head of the de- partment of mining engineering at the University of Kansas, is now professor of mining in Pei Yang University, Tientsin, China.

J. B. Merrre, Jr., has returned to the U. S. Geological Survey after ten months’ commercial geologic work in South America.

Notes And News. 241

E. H. Cunningham Craig

has made a report on the proper- ties of the oilfields of Egypt.

DorsEy HAGER is now living at Los Angeles.

Davip E. Day AND RoLanp B. Day announce the admission of A. H. Heller into partnership in the Day Company, and that they are now prepared to undertake consulting work on problems of petroleum geology and technology, at the Hobart Building, San Francisco, and 715 19th St., Washington, D. C.

Hersert N. Wirt, formerly geologist to the Goldfield Con- solidated Company, and at present geologist to the North End Mines, Comstock Lode, has resumed consulting practice in Min- ing Geology, with offices at the Con. Virginia and Ophir Office Building, Virginia City, Nevada.

L. P. ANpERSON, chief divisional geologist for the Montana- Wyoming division of the Carter Oil Co., has moved with the divisional headquarters to the Continental Building, Denver, Colorado.

O. B. Hopkins resigned from the U. S. Geological Survey on April Ist, to continue his work in the prospective oil fields of Canada.

Harvey BAsster, on leave from the U. S. Geological Survey, without pay, and engaged in commercial geologic work in South America, was imprisoned for a week at Coracora, Peru, early in January, as a Chilean spy.

GrorGE M. Bevier, geologist for the Atlantic Oil Producing Co., has moved his office to Houston, Texas, where the company has an office. re

. VYpa™ ss : / ‘4, Rurus MATHER Bacc, formerly with the Maryland and New York State Geological Surveys, is now with the Departmefit of : Geology at Lawrence College, Appleton, Wisconsin. yn’ & 3] QO. W. NEWBERRY, mining engineer, has returned to the United

° 7: - - - p aes States from Nicaragua, after an absence of four months. ad