Lapas attēli
PDF
ePub

characteristic of the oil shale would be very important if one of the caving systems were used.

Fifth. Standing qualities-ertent rock will stand without timber.-If the standing qualities of the rock are good, the cost of development is very much less as very little timber will be needed for support. After the mine is in operation, the cost of repairs will be low as there will be no retimbering which must be done where the ground is heavy.

Coal-mining methods not applicable.-There is a wide difference of opinion regarding the method of mining which is most suitable for this deposit. Some hold that the richest streak should be mined like a coal seam, and that all the lower-grade material above and below this rich seam should be omitted, as in coal mining, where the seams are only 3 to about 10 feet in thickness. In coal mines such a procedure is a necessity as there are sandstones or shales above and below which have absolutely no value. These beds are generally horizontal and the method of mining therefore is the usual high-cost method used in various coal mines throughout the country. The cost ranges from $1 to $2 per ton.

In considering the entire oil shale deposit as a whole, an entirely different condition from that of the coal seam presents itself. Instead of taking a thin section only 6 feet in thickness like the coal seams just mentioned, this shale bed contains more or less oil-bearing material about 2,600 feet in thickness. A glance at the log shows that 525 feet of this vertical section carries approximately 13 to 17 gallons of oil per ton. The oil which has been extracted in tests thus far, I am told, may be compared in value to the oil known as the Pennsylvania crude, which is worth about $3 per barrel. Therefore, taking the above figure (13 to 17 gallons per ton), oil shale would be worth about $1 per ton. Should the coal mining method be considered in mining oil shale where the gross value per ton is only $1, the cost would be excessive as coal mining costs are from one to two dollars per ton, to say nothing of treatment charges, transportation, et cetera. Such a high cost method could not be applied to this low grade shale deposit. Even if the high grade seam as noted in the log were mined out separately (about 10 feet in height) it is apparent that a very small percentage of the oil bearing shale would be extracted (approximately 6 per cent) and by far the larger amount (94 per cent) would he lost through surface subsidence and weathering of the broken shale. From the standpoint of conservation, therefore, the loss of oil by working only 10 feet would be many times greater than the amount recovered.

Similarity of mining conditions existing in low-grade copper and oil-shale deposits.—At the large low grade copper properties in the southwest where the ore is obtained underground by the caving methods, there were certain prominent outcrops or surface showings where the early day prospectors first made their locations. Parts of the surface over the ore bodies merely presented a red or green appearance, better know locally as only red or green paint. Except for a few tons here and there none of it was commercial and all the prospector could do was to perform the annual assessment work and wait for a buyer. A few operators with limited capital tried to mine the lowgrade material but failed on account of the operations being on too small a scale. Finally, as it happened, about 17 years ago, at Miami and Inspiration, Ariz., the mining engineers who represented capitalists studied these lowgrade deposits. These engineers took options and recommended that the titles be cleared and the ground drilled.

The results of the drilling indicated that extensive low grade copper deposits existed in blanket form, ranging from 50 to 300 feet in thickness. The drill hole records showed rich, medium, and low-grade material which averaged 30 to 50 pounds of copper per ton. This was known as low-grade material which was never commercial up to that time. As the margin of profit was very small, it was evident that a successfull enterprise could only be established by introducing very low-cost mining and treatment methods.

At the Miami Copper Co., it took about five years of mine development, experimentation, and mill construction, at a cost of approximately $5,000,000, to attain the production stage. Near this property the Inspiration Copper Co. developed its ore bodies, and after an expenditure of approximately $13,000,000 it began production at the rate of 20,000 tons of ore a day.

The method of mining as worked out by each of these companies in the beginning was quite different, although at the present time they have practically the same system. This method of mining had to be perfected on account of

46780-31-6

the decreasing value of the ore, which began at 40 pounds of copper per ton, then 20 pounds, and now they mine as low as 12 pounds per ton. The caving system, which is used, consists of numerous haulage tunnels beneath the ore body, inclined raises or passageways extending upward to smaller tunnels, or drifts, as they are called locally, and then a series of finger raises. Those finger raises project upward in various directions to the bottom of the ore body. It is at or near the junction of these finger raises and these small tunnels, which is also called the breaking level, that the miners draw the ore at a very rapid rate. After the ore is undercut immediately above the breaking level, drawing operations are started and one man frequently passes a hundred tons a day into the chutes beneath him. For the total tonnage of each man in the mine they frequently average anywhere from 17 tons per man to 30 tons. The mining cost, which formerly was as high as $1.50 a ton, had been reduced in places about five years ago to $1 a ton, then to 60 cents a ton. and finally at the present time, with this incline raise system, many thousands of tons are being produced for 40 cents a ton.

The ore as it is mined is sent to the large concentrator, where a 20-to-1 ration is made. Then the one ton of ore is smelted and the pig copper is shipped to Galveston and from there to the refineries in New Jersey, where the copper is refined and then ready for manufacturing purposes.

Where two companies like the Miami Copper and the Inspiration have been developed by separate enterprises, there is a great deal of assistance rendered each company by the proximity of the two operations, as one may note something which the other has carefully developed, make improvements upon the idea, and thus use it to great advantage. This coincidence of proximity has a great bearing upon the mining costs.

At the Chili Copper Co., in Chile, that enterprise was started some years ago where one company had to build its town, branch railway, power plant, and develop an enormous tonnage. Before that plant was really producing on a large scale, a total investment of approximately $35,000,000 was made. Aside from opening in a new country, this shows the large expenditures that one company must be prepared to make if it goes into a district and must solve its own mining and metallurgical problems.

An iron mining company in Pennsylvania is at present developing its low grade iron mines with the hope of getting an increased tonnage from these deposits. As these mines are deep, incline shafts are being put down which must be concreted, and considerable underground work is necessary. The caving system has been decided upon as the most efficient method of mining. Before the larger deposits are producing their rated daily tonnage and the concentrator is moved and rebuilt, as well as all necessary surface improvements installed, this company will probably have spent about $4,000,000 to $5,000,000 on this project.

In the oil-shale deposits in Colorado, after making a general survey from the standpoint of mining methods, I feel that two systems of mining may be applied to advantage, one being the glory hole or quarrying system and the other the caving method.

The glory-hole method is applicable where there is no waste capping over the shale to be mined. There are a number of sides of canyons where the capping is eroded and glory holes might be located there to advantage. This is a simple method and used to a more or less extent in limestone quarries it most States of the Union.

The method which will have a wider field in mining oil shale is the caving system. Every caving system, when applied to an ore body in question, is generally modified to meet the local conditions. While many millions of tons of ore have already been mined by the caving system, it is possible that when it is applied to oil shale where there are many similar conditions slight modifications will be worked out. It is also reasonable to believe that similar costs per ton will be obtained when oil shale is mined on a large scale by caving to those of the low grade porphyry coppers.

Since the oil shale has different specific gravities according to the mineral content, as well as certain marked physical characteristics, one may expect that some method of concentration might be developed similar to those of the low grade coppers. When experiments are conducted along these lines as well as those in retorting which are now being performed in the field, it is reasonable to believe that the treatment problem will be solved.

In conclusion, I desire to say that in my opinion as a practical mining man the ordinary prudent man of to-day is justified in expending his time and his money in the preliminary exploratory and development work in connection with the oil shales with a reasonable expectation of developing his properties into a commercial enterprise.

CHAS. A. MITKE, Phoenix, Ariz.

(Thereupon the hearing recessed at 12.20 p. m. to reconvene at 2 p. m.)

AFTERNOON SESSION

Mr. ROBERT D. HAWLEY. Mr. Samuel G. McMullin, of Grand Junction, Colo., will be the first speaker.

Mr. MCMULLIN. Mr. Secretary, gentlemen of the department, it seems to me that possibly the issue which we have come here to meet might be more clearly stated. We understand that the department indicates, or has indicated, that a discovery of oil shale is legal only when a deposit of commercial shale is actually and physically exposed upon the surface and that in testing the case of commercial value the department will adopt the rule established by the Geological Survey that oil shale must contain 15 gallons to the ton.

We have always supposed that the proof of discovery would be such proof as the nature of the subject permitted. The nature of this subject does not in all cases permit such discoveries, although we are prepared to show that such shale exists in cases of land that has been classified as oil-shale land. I have prepared a printed argument-a legal argument by myself—and a paper by Mr. William O. Pray, a mining engineer of Denver, is included in this brief. Before reading Mr. Pray's papers I want to say that Mr. Pray is a California mining engineer who came to DeBeque, Colo., in 1920 and has had probably more actual, or as much actual experience in working in and with oil shale as any man living. He is not only a mining engineer but he is an expert chemist, having left the position of engineer for the Calaveras Copper Co., of Tuolumne, Calif., and became interested in oil shale. Pray's paper is as follows:

To the honorable the SECRETARY OF THE INTERIOR:

Mr.

The oil-shale deposits of northwestern Colorado occur in the Green River formation and form a large part of the great elevated plateau north of the town of DeBeque, Grand Valley, and Rifle, with particular reference to the area, covering the southern fringe of the plateau, where stream erosion has made deep incisions and exposed to view the entire stratigraphic column of the Green River formation and its basal contact with the top member of the underlying Wasatch formation.

In this general region, the Green River and Wasatch formations comprise the surface rocks exposed by erosion. The Green River formation is the younger and rests comfortably on the Wasatch. The Wasatch is confined to the lowlands of the major valleys while the Green River formation makes up the greater part of the elevated plateau, its topmost members forming the skyline of the plateau and its lower members bordering the troughs of the valleys.

There are no overlying formations with which the Green River formation might be confused. It consists of a great, flat-lying mass of sombre-colored sedimentary rock, resting comfortably on the highly colored rocks of the underlying Wasatch formation. The color change is usually sufficient to enable one to recognize the contact of the two formations, and the dominant position of the Green River formation in the topography of the region makes it comparatively easy to distinguish the one from the other.

The principal characteristic, however, that serves to distinguish the Green River formation from other geological horizons in northwestern Colorado is the unfailing presence, at various intervals throughout the entire stratigraphic column, of prominent and conspicuous zones of oil-yielding material, now recognized as oil shale.

These zones are so numerous and so closely interrelated with the rest of the formation that when one described the Green River formation he must necessarily include a description of the oil-shale deposits and, conversely, a description of the oil-shale deposits of Colorado must embrace a description of the Green River formation, for the two are as inseparable as the pages of a book.

It is an established fact that no large vertical section of this formation can be cut out of the stratigraphic column without eliminating zones of oil shale of a value well within the rule adopted by the United States Geological Survey for the classification of lands with respect to their oil shale character.

During the past six year. I have been actively engaged in the field in the details of the examination, sampling and testing of the major oil-yielding zones of this formation at many widely scattered localities. Also, I have had direct supervision of assessment work on tracts of oil-shale land covering many thousands of acres in extent. In the course of this work, I have had an opportunity to study the vertical and top exposure of the Green River formation over a broad expense of territory and to trace and correlate the lateral extension of the major oil-shale zones over many miles of outcrop.

The results of these observations have established such a remarkable lateral persistence and uniform stratigraphic distribution of the principal oil-shale zones as to permit of but one conclusion; that throughout the area under discussion, the major oil-shale zones persist with practically unbroken regularity and that wherever one establishes the presence of a certain oil-shale zone at the surface he is safe in assuming that he will find the other zones of the series occuping their respective horizons. The surface shale on top of these plateaus is necessarily low in oil content due to weathering and decomposition caused by the elements, but the existence of such shale on the surface is infallible evidence of the existence of the richer shales below. For instance, what is termed the Sandstone market is simply one series of the formation which infallibly lies above the red mahogany shale. This condition is not comparable to the ground beneath the surface of the earth where oil sands separated by hundreds of feet are penetrated but is comparable to coal, stone, marble quarries and great deposits of porphry copper where the rich zones are mingled with lean zones and all together form one great mass of valuable mineral bearing material.

For this reason there is in my opinion no reason for saying that the lean shale outcropping on the surface has no physical connection with the rich shales beneath the surface and are separate, distinct, and disconnected from them but on the contrary the lean shales are correlated with the richer shales in the Green River formation, all of which is extremely probable to be valuable for oil production without regard to rich and lean zones therein.

64

While certain horizons including the surface shale contain an abundance of characteristic fossils that serve to definitely establish their position in the stratigraphic column, it is seldom necessary to resort to such evidence in the identification of the various zones. The oil shale in each major zone is so different in physical characteristics from that of other zones that each zone weathers in characteristic forms at the outcrop and these peculiarities are generally sufficient for its identification and correlation. For instance, there exists near the top of the Green River formation, at a statigraphic elevation of 2,100 feet above the Wasatch or an altitude of 8,200 feet what is commonly referred to as the "curly shale" zone. This zone is approximately 45 feet thick and is made up of five distinct strata of characteristic curly" or "twisted" shale, ranging in thickness from 3 to 7 feet and yielding from 22 to 26 gallons of oil per ton. Between each seam occurs a thin bedded lean shale of entirely different characteristics than the "curly" shale. The curly shale has such distinct characteristics at the outcrop that even a novice could not fail in its identification. It is entirely unlike any other shale in the Green River formation. It can readily be identified by its warty and contorted outcrop. The warts represent inclusions of mud-balls which, because of their superior resistance to weathering, form wart-like projections on the weathered surface. Again, we have "geode" shale, the "bug-hole" shale of the miners; "paper" shale; "conchoidal" shale; "mahogany" shale; "streaked" or "ribbon" shale; and other varieties too numerous to mention. Space does not permit of detailed description of these many varieties but it may be said that all have their distinct characteristics which are known to the miners and are quickly recognized. It does not require expert knowledge to trace and correlate these various zones. In my opinion when one discloses shale on the surface of this area, he discovers all the shale from the Wasatch to the surface because they are physically connected in the same formation.

Certain zones, such as the curly, paper and mahogany, assume such conspicious features in the surface topography of the region that one can trace their outcrops with the naked eye over hundreds of miles of exposures, while riding in an automobile along the valleys and tributary canyons. This will convey an idea of the ease of identification and correlation.

In the early literature on the geology of the oil shales of Colorado we find a reference to the upper, middle and lower parts of the Green River formation, which has been construed by some as indicating three distinct divisions of this formation. Statements have been made that of the three divisions, only the middle division is of economic importance. In my six years' experience in the field, I have found no evidence that would support such a view. While it is true that the middle part contains the richest zone in the formation there are important zones in the lower portion of the formation and at many horizons up to the base of the mahogany zone and from there to the top of the series. In fact, the vertical section from the base of the mahogany zone to the top member of the curly zone, representing an interval of from 500 to 550 feet, may be assumed, from an economic standpoint, to be a single body of oil shale and in all probability, will be mined as such when large-scale operations begin. The fact that there may be a few thin beds of sandstone included within this zone, or that parts of it may be very lean in oil content, will be of no consequence to the miner. He will mine sandstone, lean shale, and all and depend upon the richer portions to raise the average of the whole to an economic grade.

The metal miner does not confine his operations to thin, high-grade streaks of ore, if, by including larger masses of lean ore, he can obtain a lower unit cost in the production of his end product; nor would a shale miner be justified in resorting to selective mining if, by mining thick sections of relatively lowgrade shale, he can reduce the unit cost of his crude oil. Again, even though his cost per barrel be the same or a little high, he might still be justified in mining the large masses of low-grade material, if by so doing he can greatly augment his reserves of raw material and increase many fold his recovery of oil per acre of land and thus prolong the life of his enterprise.

The great Alaska-Juneau enterprise, which involved an original investment of close to $10,000,000, was based on estimated profits of 75 cents per ton from gold ore of an estimated value of $1.50 per ton. The Nevada Consolidated Copper Co. is now utilizing material, formerly considered waste, containing around 10 pounds of copper per ton, and many of the large "porphry" copper mines have added to their reserves, millions of tons of material that formerly was regarded as of no economic value.

These facts are cited to illustrate the necessity of caution in appraising the prospective value of low-grade materials where they occur in enormous quantities and can be mined at a very low cost per ton, compared with the relatively high cost of mining thin deposits of rich material. It is a well known fact that the refined copped market is dominated by producers who have nothing but low-grade ore to draw upon and that this domination is the result of low-unit costs compared with relatively high costs of production from small bodies of ore of high value.

These facts, I believe, have an important bearing on the question as to what constitutes a sufficient discovery to support the claim of an oil-shale placer locator who is seeking or intends to seek patent under the general mining laws, and it is this idea that prompts me to submit them.

WILLIAM O. PRAY,

Mining Engineer, De Beque, Colo. Mr. McMULLIN (continuing). The top of these plateaus is necessarily low in oil content. I asked Mr. Pray before leaving if he would kindly also furnish his views as to the effect of weathering where the shale is exposed on the surface, and since arriving here I received the following affidavit from him. STATE OF COLORADO,

County of Mesa:

William O. Pray, being duly sworn, on his oath deposes and says that he is a resident of De Beque, Colo.; is 48 years of age and a mining engineer by profession. That he has been engaged in oil-shale engineering for the past six years and is familiar with the effects of weathering on the outcrops of the oil shale deposits of northwestern Colorado.

That the surface exposures of oil shale are susceptible to the same processes of alteration and decay by atmospheric agencies as are the outcrops of coal seams and metalliferous deposits, and are found in various stages of decomposition, depending on the time and conditions of exposure, topographic environment, and the difference of resistance offered by shales of different character. Physical structure is an important factor in the resistance to penetration. Shales of massive structure, whether lean or rich, are more resistant than are thin-bedded, platy, or papery shales. Thick-bedded "geode" shale, because of

« iepriekšējāTurpināt »