FEBRUARY,1909
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continued the exploration of the hole, 5-foot samples beingtaken as before. Recently it has been the policy of the Oliver Iron Mining Co. to drill from the surface down, because of the convenience and rapidity, and the dangers attending numerous open test pits.
When drilling in surface and are, the churn is used. When drilling in rock, diamonds are used. If are is encountered below rock, the casing is blasted down and churning continued as before. In the are the casing is driven down with a 200-pound drop hammer. Prices for drilling range from $4 per foot 1D surface and ore, to $6 or more per foot in rock, depending on the locality.
Drill Outfit.-An ordinary drill outfit consists of a 36/1X84/1 boiler of 12-horsepower capacity, a No.3 Cameron pump, and a "Bravo" Sullivan diamond-drill rig, using a 200-pound drop hammer and 12-inch diameter bull wheel for churning. The tripods are 30 feet to 32 feet high. Such an outfit requires 7 to 9 barrels of water and a half ton of coal, running steadily
-m a lO-hour shift. These drills make from 15 feet to 40' feet .. shift through glacial drift unless boulders are encountered,
as high as 75 feet to 95 feet have been reported.
open-pit style. If the deposit is small and the"overburden not too great, the milling system may be used. In either of the latter two cases, the logical method of mining may be interfered with by natural location, inaccessibility, difficulty of approach, impossibility of obtaining suitable dumping grounds, drainage, or a combination of these factors. Adjoining lands, which would be desirable for dumping ground and necessary for approaches, may contain are bodies or be in possession of other parties. The expense of acquiring such properties might be prohibitive. These and similar factors, rather than the best engineering practice, often determine the method of mining to be followed. The depth of surface "wash" is a very important factor. The depth which it is economical to remove depends largely upon the extent of the ore body. At present, depths of wash as great as 2 to 1 in proportion to thickness of ore are being removed.
Equipment tor Pit Operations.-The equipment used by the Oliver Iron Mining Co., consists either of Marion or Bucyrus 90-ton steam shovels 'With 2~-cubic-yard dipper, both in strip-ping and mining operations. In stripping operations, either Baldwin or American locomotives, weighing 50 tons, hauling
HULL-I{UST MINES
Sampling and Analyses.- The method of getting a sample s as follows: The hole is cased and a stream of water is sent lawn the core barreL This water, rising up in the casing pipe, carries the chumings with it. This overflow is allowed to run .ut into barrels and settle. The water is poured off and the settlings dried and sent into the laboratory as a sample. Sam-ples are taken in this way every 5 feet in the are.
The samples taken are crushed finely, dried at 2120F. and
analyses made for iron, phosphorus, silica, and manganese, each analysis being checked. Reports are made to the engi-neering department and duplicates are kept in the laboratory records. Portions: of the samples are kept, since occasionally it is necessary to rerun a sample. Every laboratory has a special sample storehouse.
Detailed System of Exploration.- Whenever a property on which no ore body is expected to be found is drilled, a system of five holes to the 40-acre lot is usedJ making the holes about
500 feet apart. This practice, used in the Hibbing office of the Oliver Iron Mining Co., is followed when the land is expected to be used as a dump ground. If an are body is found, these holes are interspaced with others, placed in nearly straight lines, so that sections of the ore body can be made. Drilling is con-tinued in each hole until rock (taconite) is struck. It was formerly the policy to stop at taconite even when it was just below surface, but lately a few are bodies have been found partly beneath this rock. At present. drilling is continued on through the taconite if at the top or at a moderate depth in the ore body. The depth to drill in taconite in the bottom of an ore body is a matter of the engineer's judgment, which he bases on surrounding holes and neighboring are bodies. The practice of the Oliver Iron Mining Co. is to drill at least one hole on: each "~orty" through the iron formation, to quartzite. If taconite is encountered high up in the ore body and continues for some 50 feet or 60 feet in depth in the hole, it is termed a "horse," or ledge, of taconite, and drilling in the hole is dis-continued. The outlines of the ledge are determined by inter-' spaced holes if those already drilled do not determ ine it
Determination of Method at Mining.-After a property has been drilled, it is a question of judgment and circumstances as . to how it shall be mined. If capped by taconite, underground mining is the logical method. If capped by paint rock or mixed ore and the deposit is large enough, it may be stripped, the lean ore stock piled and the good ore mined in the common
six to fourteen 7-yard Peteler cars are used. In all operations 60-pound steel rails are used and the more permanent tracks, as approach tracks, consist of 80-pound steel, laid on standard ties. Stripping contractors use 12- to 20-ton, saddle-back, tank type, dinky locomotives, hauling 3- to d-cubic-yard Peteler and Western cars on Btl-inchgauge, using 40-pound to 60~poundrails. They use a 65-ton Marion or Bucyrus shovel.
Future Development at Pits.-The question of future develop-ment of pits has, no doubt, called forth considerable thought among engineers, but as no pit has so far been worked out by steam shovel, the problem of mining the ore remaining in the bottom has not been actually attacked. Many suggestions of a return to the old shaft-and-skip system have been made.
Before any such methods are employed, however, the present steam-shovel and locomotive system will be worked to its limit, that is, using the steepest grades possible. By using Lima, or some equally good grade-climbing locomotives, the bottom of almost every are body of any size can be reached. Grades as steep as 8 per cent. or 10 per cent. can be used and the entire pit" cleaned up." Already plans along such lines have been drawn up for some of the pits. In one case of the writer's knowledge, the bottom of an are body, which is 500 feet from the surface can be reached by a series of switchbacks on 7-per-cent. grades.
It is evident that the extensive track systems in open pits "tie up" a great deal of ore in the benches on which the tracks are laid. When the ultimate limit of stearn-shovel and loco-motive operations has been reached, some sort of shaft, or incline-and-skip system will be resorted to, to clean up the are left. Many variations embodying this fundamental principle could be suggested. Each pit will present features of its owri; and to outline any definite method of operating the "worked-out" pits would be wild speculation. Whatever systems may. be devised will certainly aim to continue the present cheap and rapid mining, which is the dominant feature of the great open
pits of the Mesabi Range. '
The method of developing an open-pit mine 'Willbe described in detail in the next issue of MINESANDMINER,ALS.
There were 2,214! hundre~w~ight of jade and jadeite taken out in the Myitkyina district mines, ·Burma, in 1906, which was,' valued at $39,309, and 2,685 hundredweight in 1905, valued' at $90,342, which shows a decrease for 1906. .
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FEBRUARY, 1909THE
ALICE
MINE
C/&dY ';;'
j(C",
Colorado's Largest Ore Body- Situated in the Fall River Dis-trict, Colorado
Writtem for "Mines and Minerals." by R. L. Herrick
Can a great body of porphyry carrying an average of $3 to $4 in gold and silver per ton, disseminated through it, be profitably exploited in the Fall River District of Colorado? Upon the answer rests the immediate future of the largest ore body in Colorado known to the writer. The existence of this are body has been well known for more than a score of years. In this time, dozens of prospectors, operators, and leasers have attempted to make their fortunes from it, but thus far without success'. Many of Colorado's well-known mining men have personally visited the property and several of the state's best mining engineers have carefully examined and reported on it. In Denver the property is well known to the mining fraternity. Few prospects have been the subject of greater investigation and correspondence. It therefore goes without saying that the property has been most alluring to many, chiefly because of its magnitude.
The little camp of Alice is situated at an elevation of about 10,300 feet upon the property of the old Alice Mining Co.
FIG. 1. ALICE MINE
Good roads connect it with Central City lying nearly due east, and Idaho Springs southeasterly, distant 8 and 12 miles, respec-tively. The Colorado & Southern Railroad connects both of these towns with Denver.
The first operations of the Alice Mining Co. date back to the early eighties. Having acquired seven adjacent patented placer claims embracinga total area.of ~70.3acres, the overlying gravels were attacked With hydraulic giants the water for which was furnished by Silver Creek. The depth of wash gravels overlying bed rock on the G. B. Harris placer was found to average but 5 or 6 feet and thus the bed rock was quickly laid bare to view. While the placer clean-up is said to have been about $60,000, hydraulicking operations were apparently abandoned shortly after the discovery of the great ore body laid bare by them.
Near the head of the little basin seen in Fig. 1, the removal of the surface gravels exposed an area roughly 300 feet square beneath which the ore body was everywhere apparent. While this area probably by no means includes the full extent of the ore body, it must remain for future exploration to demonstrate its limits.
Abandoning hydraulicking, the early operators erected an old-fashioned slow-drop stamp mill in which was profitably milled the oxidized surface are for three seasons. Profitable operations ceased, however, when, at a slight increase of depth, the ore changed to sulphides and the mill which saved only the metallic gold proved unadapted to treat it profitably.
The following history is quoted from the recent report of Mr. Edwin E. Chase, the well-known mining engineer of Denver: "In 1894 the newly organized Alice Mining and Milling Co. erected a LOu-ton concentrator, seen at the left in Fig. 1 and in detail in Fig. 2, equipped with second-hand machinery. Some 4,200 tons of ore were milled obtaining, I understand, 236 tons of concentrates averaging $31 per ton. As the ratio of concen-tration was 17.78 tons to one, this gave a recovery value of
$1.75 per ton of crude ore. '
"In 1898 Mr. George Crocker, of New York, operated the property through John W. Taylor, manager. After repairing and installing new machinery in the mill, the tunnel star-ted by the previous lessees was continued 250 feet into the ore body, other adits driven and the glory hole sunk to the tunnel as shown by the map Fig. 3, and Fig. 4. With the breasts of all the tun-nels still in ore, these developments proved the ore body at least 350 feet in east to west extent by 220 feet north and south and no limits yet found except on-the eastern side.
"During the Crocker lease, 1,542 tons of are were mille in 25 days' actual working time, yielding 131tons of concentra" after a 12:1 reduction. The records of the Argo smelter' the shipment of 84 tons of this product to it, but no trace, be found of the remainder. These records show that the aVE value of the concentrates before treatment was $21.60 per gold being paid for at $19 per ounce, silver at 56 cents copper at $1 per unit. As the concentration ratio was 1~ this gives $1.80 as the recovery per ton of crude are althou no data are obtainable concerning its assay value and millir, losses."
As it is evident that the total cost of mining and milling for the methods used by the lessees thus far chronicled, must have exceeded $1.80 per ton, comment upon their failure is super-fluous. Before proceeding to outline the results achieved during the year 1908 by the present set of lessees, an outline geology of the ore body may prove. interesting.
Geological.-The Alice property lies in the belt of tl; strong gold-bearing veins running in a northeast to scuthwes direction from Gilpin County to the Empire and Georgetown districts of Clear Creek County. Many of these veins are thought to cross the Alice property, although none have been developed, and extend into the Yankee Hill district to the north, where a number of mines are being steadily operated.
As Mr. James Underhill has explained in his" Areal Geology of Lower Clear Creek," page 118, the area traversed by mineral-ized fissure veins is likewise extensively traversed by porphyr-dikes. This porphyry is classed as Iatite porphyry, after th. authority of F. L. Ransom, who coined the term to include those varieties of extrusives intermediate in compoeitior between trachyte and andesite. The Aliceare body is undoubt edly composed, at least in part, of what was originally this latite porphyry. Although many have guessed at its true nature, the Alice ore body still remains something of an unsolved conundrum owing to its lack of complete development. The United States Geological Survey has studied the region close up to the Alice property but it is to be regretted that its field men stopped just short of working out the geology of this ore body. This much is well known, however, the gneisses and granites characteristic of the region, surrounding the ore body, are interspersed with porphyry dikes running both with and across the general northeast to southwest strike of the veins. In the report already referred to, Mr. Chase says':
"The ore body in question has been ejected through the granite presumably in dike form, but at this particular spot has probably been spread out in lava-like condition over a con-siderable area. Scattered all through this rock are vug holes and cavities containing iron and copper pyrites which are associated with gold and silver, the ratio in value being about six of the former to one of the latter. In some of the upper workings were found occasional bunches of high-grade bismuth-silver (gray copper?) assaying over $1,000 per ton.
"Associated with the are is the porphyry dike, shown on map Fig. 4. This dike is about 7 feet wide on the surface and has a strike of about N 65°E. This, I believe, clearly indicates that both dike and ore deposit have the strike mentioned above as no other dike is exposed in the vicinity. As the dike has an altogether different appearance from the ore body, it may possibly date to later eruption than the former."
Until further development has determined the limits of the are body, particularly in a vertical direction, it appears idle to speculate whether the surface dimensions indicate a width of dike exceeding 300 feet, or whether the ore body is an over-flow as Mr. Chase intimates. It is of course possible that the intrusion of the dike has here so altered the original granite country rock by metamorphism, that no distinct boundary is now apparent between the porphyry and the altered granite. This probability has been pointed out by some engineers. It should be noted, however, that if this is the case, it establishes
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295 a new precedent in Clear Creek County where, Mr. Underhillhas pointed out, that in but one case has he found a sign of contact metamorphism.
In a report recently made on the property by N. H. Brown, United States Deputy Mineral Surveyor, of Idaho Springs, are recorded the measurements of the are body as shown by the map, Fig. 4. These measurements show it equivalent to a block 300 feet in north-south extent, by 350 east-west, by 132 feet thick down to the level of the main tunnel. Reckoning 12.5 cubic feet to the ton gives a total blocked out of, roughly, 1,100,000tons. To show the probabilities of this amount being eventually increased by considerable, it is only necessary to mention that every foot gained in depth below the main tunnel adds 6,200 tons and every foot of advance of the main tunnel into the hillside, allowing nothing for slope, adds 2,400 tons of are to the amount now plainly exposed.
This are body everywhere shows evidence of shrinkage in cooling, most plainly evidenced by the lines of fracture during e breaking of the rock. The whole mass is everywhere -rspersed by interlacing narrow seams of secondary quartz.
~ pyrite appears finely disseminated everywhere through re body, as indeed it is through the 7-foot porphyry dike . above, the bunches of bornite, chalcopyrite, and gray (er are invariably found in seams rarely exceeding an inch vidth. The evidence seems to indicate that these seams e primarily fanned by cooling and the bunches of copper e noted have been deposited in them by percolating waters cich deposited them at points in the seams where projecting ...-lyriteoffered a favorable nucleus. The gold values, however, are mainly free and found in a finely divided state disseminated throughout the mass of rock.
Thus while "secondary enrichment" is evidently respon-sible to some extent for concentrating the copper and silver -alues, all assays show that the average copper content varies elm .3 to .5 per cent. and thus indicate that the economic ffectof this is negligible. Hand sorting this are would undoubt-dly save the copper-silver ores for the smelter, but the problem of saving the gold values admits of but one solution-the mill-ing of the whole mass of rock.
Samplin.g".-Perhaps the most noteworthy sampling of this immense are body was done by Mr. Edwin E. Chase in June, 1908. In his report he says: "The proper method of sampling an are body, if it can be done, is to distinguish between the high-grade and the low-grade streaks, then measure, sample, and assay each by itself, and exclude from the samples any carren waste rock in between. In the present case this method was found impossible, for what would appear barren rock on an exposed face would often disclose mineral if broken into for only a few inches. The are is scattered through the rock something like plums in a pudding. The values are not altogether with the clearly visible pyrite, but often scattered in invisible par-ticles through the rock. Accordingly, the workings were divided into sections, generally of lO-£ootlengths each. The whole face of each section was then gone over and broken down. The resulting large sample was then finely broken on canvas, mixed and cut down for assay samples in the usual way.
"Figuring gold at $19 per ounce, and silver at 57 cents per ounce, the following were the assay results:
"The total number of samples was 58 of which 4 per cent. ran less than $1; 21 per cent. between $1 and $2; 42 per cent. between $2 and $5; 15 per cent. between 85 and $10; 15 per cent. over $10. The average of the samples figured $4.27 in gold and 69 cents in silver, giving a total average value of $4.96.
"In order to ascertain what values were contained in dean, heavy, iron and copper pyrite, sample 59 of this sort of material was assayed. In addition, samples No. 60 to 63, inclusive, were made of clean jig concentrates, while samples Nos. 64
and 65 were fine slime concentrates from Wilfleytables. The following were the assays:
Sample No. Gold Value Silver Value Total
59 $14.06 .$ 1. 71 $15.77 60 16.34 12.54 28.88 61 20.14 2.39 22.53 62 24.70 1.14 25.84 63 20.90 1.25 22.15 64 12.54 1.14 13.68 65 16.34 1.14 17.48 Average. . 1320.90
"It will be noted that this average value of $20.90 is practi-cally the same as obtained by Mr. Crocker from his shipment of S4 tons of concentrates to the Argo smelter. His concentra-tion ratio was 12:1 while the writer's sampling $4.96 per ton crude are shows that a ratio of 5:1 (figuring 80 per cent. saving) should give about the same result. It therefore appears that the mill formerly made a very poor saving of the values in the are.
Mill Runs.-We now come to the recent experimental work of the Alice Development Co. under the management of W. L. Shaffer and Arthur H. Roller, of Idaho Springs. This company, like its predecessors, has the property under a lease and bond from the Silver Creek Mining Co., a recent reorganization of the old Alice Mining Co.
The immediate predecessors of Messrs. Shaffer and Roller had attempted concentrating of the are by first crushing with a jaw crusher and rolls, then jigging out the concentrates. The resulting poor saving of values has been made sufficiently obvious by the foregoing. Believing that the are had been misinterpreted, the first work of the new lessees, during the year 19.08,was to remodel a portion of the old concentrator. Installing a single battery of five S50-pound stamps, five holes were bored at the back of the mortar, each opposite the center of a stamp die and on a level with its top. The height of the 20-mesh screens was lowered to 2 inches above the die tops. During stamping, water streams under pressure were admitted to the interior of the mortar via the five holes mentioned. These washed the crushed are against the screen and gave the stamps a high duty and greatly reduced the sliming of the brittle copper-silver ores. In fact, the duty during the whole season exceeded 5 tons per 24 hours while at times it was as high as 5.8 tons. The pulp flowed across a series of three amalgama-tion plates, then through a series of three amalgam traps and on to a Gilpin County bumping table. The tails from this bumper flowed to aVbox classifier,feeding its product of coarse sands to a single Card table while the overflow went to a Callow tank. The fine thickened slime was thence fed to another Card table used as a slimer. The tails from this flowed to waste through an oblong settling tank containing a series of riffles made by burlap frames. These caught considerable of the fine floating brittle copper and silver slimes and materially increased the saving.
.During the summer large lots of are were mined from all parts of the mine and run through this mill. All are treated was weighed on a track scale and sampled automatically by a Vezin sampler.
As the results achieved by this experimental mill, crude as it was, indicate something of what may be expected with a thoroughly modern mill, they are given below, through the courtesy of Messrs. W. L. Shaffer and A. H. Roller.
At the time of makin&"a final clean-up of the mill, at the end of the summer, the quick traps returned the equivalent of 20 cents per ton of are milled, while the burlap riffles returned the net saving of 11 cents per ton from the gold, silver, and copper slimes so that the total net saving per ton averaged $2.65
+
$.20+
$.11= $2.96. While the middlings from the table concentrators were not reground and retreated, tests made SUMMARY M1LL RUN RESULTSI
I
,
I Actual Saving
Lot No. Net Weight Value Crude Value Net Per Cent. Ratio
Tons 0" Au Ag
I
Cu Sa-ving's Net Saving Concentration
I
Per Cent. Per Cent. Per Cent.I 1. ... ...
... . ...
...
88.00 $4.00 82.5 56.5 39.5 $2.38 59.5 13.5 into 1 2 .. ... . . ..
. ... 39.46 4.07 82.0 84.0 59.0 2.17 53.3 6.4 into 1 3 ... ... 240 .50 4.67 82.2 41.1 42.6 3.01 64.4 7.8 into 1 4, .... ... 133.10 4.07 85.0 35.0 37.0 2.49 60.0 7.0 into 1 5.......
.. 86.30 3.45 82.5 p5.0 31.0 2.28 66.0 10.7 into 1 I \I
I Total. ... .....
587.36Average per ton.
...
$4.22 $2.65 62.8 8.",1\\ C
Y C (I/,q
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FEBRUARY, 1909to demonstrate the value 'of this proposed treatment showed that by regrinding these middlings to 100 mesh or finer, then again amalgamating and concentrating, an additional saving (seemingly high) averaging 60 cents per ton could thus be recovered. Apparently then with crude ore averaging $4.22 per ton an average net saving of $3.56 can be made. This figure reckons only the cost of bullion refining, freight, and smelter charges on concentrates into account. Accepting $3 per ton as a conservative basis for estimate, however, we ~ave only to reckon. up the costs of mining and milling, which
include the usual Items of labor, fuel, interest, insurance, depreciation of plant, repairs, etc., subtract the total from $3 and we have the margin of profit.
Costs of Mining.-Thus far all development work has been done by hand mining and although the system of "glory hole" working partially developed by the first lessees was undoubtedly
FIG. 2. CONCENTRATOR AND TRESTLE, ALICE MINE
cheap, even their low mining costs can doubtless be reduced. To those familiar with the steam-shovel mining operations now practiced by the Boston Consolidated and the Utah Copper Cos., at Bingham, Utah, and by the Nevada Consolidated, at Ely, Nev., the similarity of conditions will suggest the use of steam shovels on the Alice property. After more than a year of work-ing, the Bingham companies have reduced their costs to about 18 cents per ton.
Under the circumstances, it seems reasonable to expect that steam-shovel mining costs at the Alice property should not much exceed the 30 cents per ton estimated by
Messrs.
Shaffer and Roller.The surrounding company property bears enough mine timber to supply the small amount of mine timber which will be required for years to corrie. The water supply is plentiful for both mill use and power, the latter being already developed to the extent of 100 horsepower by a Pelton wheel which ran the old concentrator. A minimum of 300 horsepower can be developed at any time during the year. .
Labor of a high grade-chiefly American-is obtainable at wages ranging from $2.50 to $4..50 per 8-hour shift for mine work, and 8 to 12 hours for mill work.
. Milling Costs.-With both water and power costing practi-cally nothing, the Alice mill will be situated to make a record low cost of milling. With a daily capacity ranging from 300 to 500 tons, it seems conservative to figure that the total milling 'costs will not exceed 60 cents per ton with the probability that 50 to 55 cents will prove nearer the actual cost.
At the present time the downhill haul of concentrates to the railroad costs $2.50 per ton. It is planned to eliminate this cost by laying a pipe from the mill to thG railroad at Fall River Junction over a grade averaging 53 feet fall per 1,000 feet for the entire distance of 8.2 miles. The concentrates will be flushed through this to settling tanks at Fall River Junction where they can be drained and loaded on the cars at a small cost. With a well-equipped modern mining and milling plant, it thus appears that the total costs should not much exceed $1 per ton, which figure does not reckon in the depreciation of the plant. The amount of depreciation cannot be figured until the capacity of the mill and its first costs are determined upon. As the mill site is distant about 10 miles from Idaho Springs, and the road grades heavy, the transportation of machinery
1 'rt-ials will enter heavily into the first cost. After the
. -centrates pipe line is built, however, transporta-- vreatly affect the cost of marketing the plant's
T' will be mainly bullion.
At the present time the Alice Development Co. is satis-fied that the showing made justifies the installation of a steam-shovel mining plant and a 300-ton mill to cost about $300;000. The next sea-
r---'.---..,
son's work of the company', however, will probably be the further ex-ploration of its immense are body to more definitely de-termine its limits. It goes without say-ing; that if the available ton-nage is proven by the contem-plated drilling operations as several times
the million tons now blocked out above the main tunnel Ie the erection of a concentrator of greater than 300 tons' capa\ will in the end prove the most economical.
FIG. 3. SECTION ON LINE B-B, FIG, 4
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/ »< I-"'....i..- ..-
---ir:
rr /V
"<y mnf? 0/f/ .
flQ,set -,1<-
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\ \ " -~L-;9 07m;;; ,,::~:
~s Q Plan &bcA-ed Od Tonna9¥' ,joof¥-.J)x.350~hjx/32'mtC,f- (100,000Tons ,.----",;-,;; ii' o " P,; "Ore " 0' Lo,,"" - f"nne \1\"
=g Lin'" -AI
'lINES AND MINERALS.
FIG. 4. PLAN AND SECTION OF ALICE MINE
Consul-General William H. Michael, of Calcutta, reports that the Secretary of State for India (Mr. Morley) has received a memorial from the Indian Mining Association which is averse to railway proprietorship of coal fields. The memorial will be submitted for the views of the government of India, which, when received, will largely determine his answer. It is under-stood that the secretary at this time does not see any objection to the principle of the railways owning coal properties solely for their own consumption.
IN "]
APRIL, Hl08
MINES
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409
In Group C it 'will be seen that the phosphorus is not exces-sively high in any particular section of the coal seam. So far as the phosphorus is concerned, the mining practice does not figure much in the problem. With little effort the phos-phorus will hover around .016 in t.he coke, which passes very 'Yell for Bessemer grade.
AVERAGE
I
No. 1 No.2 No.3 No.4
NO.51
---I
A'i£a';;;n~;
65
,ampl~'.c,pc,,;nt'n
g.035 .035 .012 .016 .041
I
Average phosphorus in 65 samples, representing 22 mines and the full height of the coal seam, .016. By excluding 6 inches of coal next to the roof and 4 inches of coal next to the bottom, which may be considered a fair average mining practice, the phosphorus average for the 22 mines is .013.
The above general average will show in what sections of the coal seam the maximum phosphorus is to be found. This average may correct certain preconceived notions as to the location of phosphorus, due perhaps to imperfect data find lack of thorough examination of the seam in sections. By excluding 10 or 12 inches in the top and 4 inches in the bottom the average phosphorus for the coke will be .017 or .018, which will advance a point or two with less exclusion from the top and bottom.
It will always be of advantage to the operator to give his coal seam a thorough examination for all impurities at stated periods. Any outlay in this respect wilt yield profitable returns if by so doing he is enabled to better the quality of his product. Sulphur is easily detected but phosphorus is elusive. It is a veritable "'iVill-'o-the-wisp" which now leads the operator into the meshes of despair, now disappears for a time and again glimmers in the distance. He is constantly alternating between hope and fear. When he strikes a section of his mine that shows phosphorus like the example cited below, he begins to think he ought to go in for the manufacture of phosphorus instead of coke.
GROUP X
No. 1 No.2 No.3 No.4'
=1
--- ---.023 .029 .0]3 .705 24541 .HH .044 .020 .017 .623 .022 .009 .029 .118 1.451 .079 .024 .021 .240 1.509 Sample No.1. No.2 . No.3 . Average of 3 samples.The above samples were taken at a short distance from each other. This would appear to be an anomalous condition. The writer has never seen this except at this particular locality. Perhaps it may not come amiss to say something upon the origin of phosphorus in coal. The phosphorus of the coal is said to be foundinthe spores and potlen grains of the decomposed vegetable matter that entered into its composition. The burden of the Carboniferous flora may be said to be made up of giant cryptogamous plants, such as ferns, equisetae and lycopods. There were perhaps some conifers under phenogams or flowering plants. The size of all the plants of the coal age as compared with the existing species of the same plants, might be likened unto the following:
His spear to equal which the tallest pine Hewn on Norwegian hills, to be the mast On some great admiral, were but a wand, He walked with. to support uneasy steps Over the burning marl.
There were indeed giants in those days. As the poet has Beelzebub wading about in the "fiery lake," so .does science inform us that the lepidodendra waxed luxuriant in the carbon dioxide atmosphere of the coal age and attained the height of 7? feet or more, strikingly contrasting with the little Ground pme of today.
Thus it is in the spores and pollen of these immense plants we look to find the phosphorus of the coal measures, the cause of all our woe in the matter of this element at the present time.
Longiucdinai Variation of Phosphoru,s.-The preceding tables have shown the distribution of the phosphorus through a vertical section of the coal measure. Itmay be said that the longitudinal phosphorus content is variable also. In other words different parts of the same mine have different averages for the channel section in the matter of phosphorus. This variation is sudden, a distance of a few feet oftentimes causing a wide variation. On the whole, however, the run-of-mine coal
will yield a tolerably constant phosphorus content from day to day and from month to month; the average is very uniform in most mines. Some mines, in certain localities, however, are very erratic and the operator can never tell what the day or the week is going to bring forth for his phosphorus average. As has been noted elsewhere there is nothing to guide the operator so far as the physical appearance is concerned, being unlike sulphur in this respect. A chemical examination is the only course open to the coke producer. The research chemist perhaps will say that a microscopical examination .will reveal the outlines of the before-mentioned spores and pollen grains but this is too uncertain for the practical man. The best thing to do is to make a thorough chemical examination of the measure both vertically and longitudinally at regular periods, if the least trouble is experienced with high phosphorus.
THE GEOLOGY OF DIAMONDS
Alluvial Diamonds-Diamond Pipes-Theories in Regard to the Original Formation in Pipes
·Written for" -'Wines and Minerals"
The diamonds of the Transvaal are produced from two sources namely, alluvial gravels and "diamond pipes."
Alluvial Diamonds.-Alluvial deposits may be classified as those whose diamonds undoubtedly have their source in the svstem of "diamond pipes" now known or exploited, and those whose source is unknown. Thus the gravels of the streams in the Pretoria district leading from the vicinity of known "diamond pipes" contain diamonds whose marked similarity to those mined in the pipe fixes their origin beyond doubt.
The gravels along the Vaal River, however, which in the past produced, and still continue to produce the bulk of the alluvial diamonds, are undoubtedly the debris of an older series of rocks than those containing the present known pipes. The quality of these Vaal River diamonds is invariably better than that of the average produced from the pipes, and their character-istics are much different. While not generally known, the fact remains that diamonds from different localities possess such varying and distinctive characteristics of color, cleavage, and crystallization that the expert can usually readily state the locality which produced a given stone.
It is this peculiarity that enables the geologist to author-itatively state that the source of the Vaal River diamonds is as yet unknown. The occurrence of green diamonds in the gold-bearing banket rock worked by the Klerksdorp Gold and Dia-mond Co., Ltd., throws some light on the problem.
This banket rock, or conglomerate, belonging to an older age than the diamond pipes, must have been formed from the detritus of still more ancient strata, possibly that igneous complex known as the Ventersdorp series. The Vaal River diamonds, so it is thought, possibly have the same origin as the Klerksdorp stones.
Diamond Pipes.-The reader will get a clear conception of a diamond pipe by regarding it as the solidified neck of an extinct mud volcano, or geyser. These pipes are fairly plentiful not only in South Africa but for some distance to the north. The majority of these pipes, however, are not only innocent of diamonds, but also of the minerals usually associated with them. A large number there contain the associated minerals without the diamonds, and still others contain diamonds but in too small quantities for profitable working.
Other pipes carry a sufficient quantity of stones, but of too poor a quality for profit.
These pipes are usual1y circular or oval in cross-section, usually from 90 to 300 feet in diameter and of indeterminate vertical extent. Two pipes of unusual size are those of the Premier Mine, oval in section, with its major diameter one-half mile, and its minor one-third mile long, \'lhile the No.3 pipe of the Montrose Mine, likewise oval, is 1,200 ft. X 400 ft. on its major and minor axes, respectively.
The pipes ','.'ere the vents for the several members of the great series of volcanics known as the Karroo system, success-ively deposited till the series had attained a maximum thickness of 14,000 feet. The filling of the diamond pipes, today known as Kimberlite, bluish green in color, is a breccia of serpentine rock and associated ultra basic minerals, for the most part silicates of calcium, magnesium, iron, aluminum, and manganese, such as augite, enstatite, olivine, biotite, chlorite, garnet, and the oxides ilmenite, magnetite, and chromite. In addition to these are found smaller quantities of quartz, calcite, magnesite, barite, and corundum. In prospecting the surface for pipes, garnets and ilmenite are searched for as indicator minerals which best resist the disintegrating action of the atmosphere.
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MINES
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MINERALS
APRIL, 1908The outcrop of a pipe is usually slightly depressed below the level of the surrounding surface, and in it the Kimberlite is altered by the atmospheric agencies to a soft reddish or yellow-ish earth with the so-called "blue ground" or unaltered Kimber-lite immediately beneath, usually at a depth not exceeding 40 to 50 feet.
Kimberlite weathers readily to a soft earth on exposure to the atmosphere enabling it to be washed for the contained diamonds, only that variety of Kimberlite known as "hardi-bank" resisting such action and being thus unworkable.
Imbedded in the Kimberlite are often found fragments of the inclosing, or a lower strata of rocks, varying in size from those known as "floating reef" which weigh many tons to the smaller ones known as boulders.
Daubree's theory concerning the format.ion of the pipes, now generally accepted by geologists, is as follows: The accumulation of gases under high pressure eventually resulted in violent explosions which burst through the overlying strata blowing out the passages for the extrusion of volcanic material which are today known as diamond pipes. As con-tributary evidence to this theory, Daubree produced a violent explosion on a piece of glass which resulted in blowing a . round hole through it without further shattering. Until recently the commonly accepted theory concerning the forma-tion of the diamonds themselves was that they were formed at a great depth below the earth's surface, forced into the diamond pipes by volcanic action and thus interspersed through the Kimberlite.
The finding of quantities of imperfect diamonds, thought to be the fragments of stones smashed in their upward journey along the pipes lent circumstantial evidence to this theory. The strongest evidence of all, however, was the finding of diamonds in garnet and eclogite masses of rock thought to be boulders, broken from the masses originally formed at depth and still further brecciated in their upward passages along the pipes. The upholders of this theory were thus content to class the formation of diamonds with the other mysteries of the
earth's great depths. .
Recently, however, some geologists have been breaking away from these time-honored theories. Among the foremost of these may be mentioned Dr. T. IV. Voit who forcibly presented his views before the Geological Society of South Africa.
Attacking the idea that the quantities of imperfect stones found were fragments smashed by attrition in the pipes, he claimed that the examination of a large parcel of stones from anyone pipe would show in the majority of cases finely crystal- . Iized stones whose sharp edges showed not the slightest trace of rounding due to attrition.
If diamonds all come from a certain depth one would expect to find the diamonds from certain groups of pipes to have certain distinguishing characteristics in common. On the contrary each pipe has its own characteristics shown in its dia-monds, indicating that each had its own physical and chemical conditions under which the stones were formed. Again, had the diamonds come [rom a depth one would naturally expect the quantity of stones to increase with depth whereas the contrary seems to be the case.
Dr. Corstorphine in a previous paper had cited the evidence observed at the Roberts Victor Mine where diamonds were found in masses of eclogite and pyroxenite surrounded by soft Kimberlite weathered yellow by atmospheric agencies. These masses, he maintained, were not boulders at all, but nodules or segregations, formed in place in the Kimberlite magma.
In this theory Dr. Voit agreed with Dr. Corstorphine, hut Mr. H. S. Harger while agreeing with the theory of formation in place called attention to the weakness of the evidence, The latter gentleman stated that the finding of marginal phenomena, or arrangement of minerals around a nucleus, or some other evidence of magmatic segregation found in hard blue ground was necessary to settle the problem beyond dispute.
Returning to Dr. Voir's argument for the theory of for-mation in place, however, we note that he cited recent experi-mental work at Leipaic. Here diamonds were actually dissolved in ordinary blue ground at a high heat and under pressure. This does much to support the theory that the diamonds, origin-ally dissolved in ascending molten magma of Kimberlite, crystal-lized out as the magma cooled, a view likewise expressed by Prof. A. Lacroix.
Turning then to the artificial production of diamonds for additional evidence Dr. Voit cited the the following experi-mental work:
(a) The early work of Moissan in demonstrating that carbon dissolved in molten iron which was allowed to solidify under great pressure crystallized out as diamond.
(b) The more recent work of J. Friedlander which proves that graphite dissolved in fused olivine crystallizes out as
diamond in more diminutive form than obtained by Moissan,
probably due to the lack of pressure.
I
(c) The latest work by Dr. A. Frank, of Charlottenburg, who heated lime and coal to a temperature of 1,600° centigrade producing calcium carbide and carbon monoxide and then by heating the carbide in the presence of chlorine, phosphorus, or arsenic in gaseous form, secured graphite. By increasing the temperature and pressure the production of diamond is hinted at as a possibility.
"All the ingredients for the artificial production of dia-monds," said Dr.Voit., "are found in Kimberlite rock." Carbon in the shape of graphite is found plentifully in the diamond pipes, and-especially important-is found associated in the eclogite masses carrying diamonds. Dr. Voit stated his belief that carbon as a metallic carbide was present in the Kimberlite magma when first forced into the pipes by volcanic action.
The magma in cooling under great pressure caused the diamonds to first crystallize out, as they can stand great heat, close followed by the crystallization of the garnets; pyroxenes, micas, etc.
Then according to whether the chemical conditions, the temperature, and the physical conditions, including the pressure, were perfect, or imperfect, perfect diamonds crystallized, imper-fect ones formed filled with graphitic matter or hydroxides of iron, or last in the scale merely graphite resulted.
Imperfect conditions for crystallization resulted in the imperfect crystals formerly regarded as chips and fragments broken fr-om well-shaped crystals, the missing parts of which were conjured away.
Dr. Voit's theories concerning the crystallization of diamonds seem to have met the views of the majority of his colleagues. Replying to his argument, however, Mr. J. P. Johnson dis-sented from the opinion that the eclogite masses containing the diamond are concretions from the magma and maintains in no uncertain terms that they are boulders pure and simple. Con-trary to Dr. Voit's statement that the pipes contain very few foreign fragments, he cited the Roberts Victor pipe as an example of one containing great quantities of granite, quartz-ite, and crystalline schist boulders, quantities in excess of the eclogite masses which he claimed were boulders likewise.
In concluding he said, "what is wanted at the present time is a collection of more exact data regarding the better exposed occurrences. Without that basis all attempts at gen-eralization are bound to be futile."
The writer ventures the opinion that perhaps both Dr. Voit and Mr. Johnson are correct, that is the eclogite masses are concretions primarily and were observed in place by Dr. Voit, wbile in the particular pipes known to Mr. .Johnson, volcanic action had torn the eclogites from their original place and mixed the fragments with those from the pipe vvalls shat-tered by the same disturbing force.
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Recent Improvements
in Tube Mill Practice
In the discussion of Mr. Graham's paper before the Chemical, Metallurgical, and Mining Society of South Africa, previously mentioned in the Digest, Mr. Berington gave some data on experiments he has been carrying out with several tube mills, the lining of which tapered down in thickness from the feed to the discharge end. The two mills were 22 feet long by 5 feet 6 inches in diameter, and they were lined with silex blocks 8 inches thick, about 9 feet from the feed-end, from which point the lining tapered gradually down to G inches in thickness. One mill ran for 198 and the other for 161 days. The lining of both mills wore through in about the same place, namely, about 12 to 13 feet from the feed-end, and from there to the discharge end, where the silex was not actually worn through, but was very thin. Toward the discharge end, however, the silex was still some
2t
to 3 inches thick. On the various occasions when the mill was opened for inspection, it was very noticeable that the large pebbles, or rather the pieces of banket ore used for crushing were found to be at the discharge end and the small pieces at the feed-end, a fact which is the opposite to what is usually found ir a mill lined with silex of the same thickness. Mr. Beringtor attributes this to the funnel shape of the mill, causing tbe larger pieces to roll down. In his reply to the discussion, Mr Graham states that for the size of the pieces of quartz fed into the mill he prefers lumps of 4 to fjinches in diameter and does not think much of the use of larger pieces. Itis also necessary to have the size of the aperture in the discharge plate sufficiently large.After several stoppages due to their becoming choked, he had them all bored out to t or
