The Thomas A. Edison Papers Digital Edition

Transcription

At the request of Mr. Edison we report as follows on the work at Dolores, New Mexico, the methods employed, the efficiency of the process and the results obtained by mill tests and samples assayed.
We arrived at Dolores, Feb. 9th 1900 and found the excavation of the Hill only partially completed. The first two months were consumed in erecting the building and another month in installing the machinery. A preliminary run of the entire Mill was made May 7th.
The gravel from the excavation which had been screened to one half inch and saved was used in making preliminary tests of the process
On Aug. 15th work was begun on the shafts sunk by Mr. Burn at the head of the mesa for the Mill tests.
The method used in conducting the Mill tests was as follows: At the shaft all the material was divided into seven sizes as follows Mill size or under 1/8", 1/8" to 1/2", 1/2" to 1", 1" to 2", 2" to 4", 4" to 12" and rocks over 12". Each size was weighed and the Mill size was also measured by volume.
The Mill size was then taken to the Mill, (dried when necessary) and screened into the following sizes, Under .007", .007" to .015", .015" to .029", .029" to .059", .059" to .074", .074" to .094", .094" to .119", .119" to .125". Each of these sizes was weighed then separated.
The concentrate obtained was weighed, the iron magnetically removed, the remaining concentrate weighed, carefully panned down and this final concentrate assayed by fire.
The weight of the tailings was taken as the difference between the total weight of material of each size run and the concentrate obtained.
A sample of those tailings amounting to about 70 lbs. per ton was automatically and continuously taken during the run, weighed carefully panned down and the concentrate of this assayed by fire. Thus values of each size of gravel were obtained and the weight of the total gold in the gravel as it lay in the ground was calculated.
Table No. 1 contains the general results of the shafts run through the Mill.
It is only necessary to look over the column showing the percentage of gold on Table No. 1 to get a clear idea of the high efficiency of the process.
About Nov. 1st according to instructions from Mr. Edison, the Mill was closed down and work was confined to prospecting Cunningham Mesa by sinking and sampling eleven new shafts, covering about one and a half square miles. These shafts were sunk to bed rock, samples taken by cutting a channel down one side of the shaft large enough to take out about fifty pounds of gravel per foot of depth. The total sample thus taken was weighed, carefully panned and the concentrate assayed by fire.
Samples were also taken from Ritchie Hill, the Thousand foot Tunnel and shafts A. and B. Although the Thousand foot Tunnel showed the high average of 55 1/2 cents, yet the average value from surface to bed rock of the gravel in that immediate vicinity as shown by shafts A. and B. Although the Thousand foot Tunnel showed the high average of 55 1/2 cents, yet the average value from surface to bed rock of the gravel in that immediate vicinity as shown by shaft A. which almost passes through the tunnel is only 11 cents.
This high value of the tunnel may be accounted for by the fact that it followed a rich streak. Shaft B. which is only a short distance away and which showed a very much lower value sustains this opinion. The results of these shafts are tabulated in Table No. 2.
From these results and the Mill test, it is computed that there is 2,800,000 cubic yards at the head of the Mesa which carries 15 cents per yard. However this is a very liberal estimate and gives the Mesa the benefit of the doubt in every direction. With a Mill of 24000 tons capacity per day this would furnish gravel for only six months.
About Dec. 18th work on Cunningham Mesa was discontinued and prospecting was commenced on the Carachie placer. Five new shafts were sunk and sampled, and one shaft which Mr. Burn had sunk was sampled. The values of these shafts were obtained by the method used in Cunningham Mesa. Table No. 3 gives the result of this section.
This placer is of a small area, probably thirty acres, and very shallow and the average value 2.2 cents shows it practically worthless.
Following the work in the Carachie placer the Golden Placer was prospected. Eight samples were taken in this section, only one of them being from a new shaft, the remainder were old workings. In these cases the face of the gravel was removed to a depth of six inches down one side of the working before cutting the channel for the sample. These samples were taken and treated as described above.
Table No. 4 contains these results. This placer though of considerable area, perhaps one square mile, lies principally outside the grant and the results which are from the portion within the grant show it to be of low grade for consideration. [FINANCIAL TABLE] Cunningham Mesa.
[TABLE LISTING VALUE PER TON OF GRAVEL FOR EACH SHAFT] Table No. 3.
Carachie Placer.
Assays of Samples of Shafts.
Shaft No.                          Value per ton of gravel.
K. 1                                                   1.55 cents
K. 2                                                   0.21                "
K. 3                                                   1.71                "
K. 4                                                   3.17                "
K. 5                                                   2.48                "
K. 6                                                   0.34 "
Total                                                 2.15                 "                 Average Value. Table #4.
Golden Placer.
Sample No.                                Value per ton of gravel.

G. 1
G. 2                                                            4.63 cents
G. 3                                                            1.      "
G. 4                                                           0.35   "
G. 5                                                           3.43   "
G. 6                                                           1.59                   "
G. 7                                                           6.41                   "
G. 8                                                           11.21  "
Total.                                                         3.22                    "            Average value.