The Thomas A. Edison Papers Digital Edition

Transcription

Dolores, N. M.
Sept. 13, 1900.
Mr. Thomas A. Edison,
Orange, N. J.
Dear Mr. Edison :-
Our work on the shafts since our last report of Aug. 16th has been considerably delayed on account of rains. This seems to have been the rainy season, about the first of September, tho' the general opinion is that it came somewhat late this year. It rained so frequently for a week or ten days that screening of the gravel at the shafts was impossible.
We inclose a report on Shaft No. 3, the first one that worked, and would like to know whether it is in a satisfactory form and if you wish any additional data or any changes made. Unless we hear from you soon we will conclude that it is satisfactory and have some blanks printed. We would also like to know whether you have any objection to our using the Metric System in giving the weights in our reports. We use it in our work here entirely and it would be very convenient to make our reports in that system.
The manner in which we are working the shafts now is as follows -
The shafts are sunk of bed of rock 4/12 X 6 ft. in size. This gives us one cubic yard of gravel per of depth. The gravel is raised and dumped on a platform where the stones over 4" are hand picked out. The remainder is then passed over a 2", 1", 1/2" square wire screen and a 1/8" slot screen successively. We use this order of screening so that the gravel will go over as many screens as possible to clean off the stones and break up the lumps. These screens are so arranged on platform as to reduce the loss and mixing with surface material to a minimum. The different sizes this obtained, namely, over 12", 12" to 4," 4" to 2", 2" to 1", 1" to 1/2", 1/2" to 1/8", and under 1/8", are weighed in loads of uniform weight, with the exception of the last size which is measured in boxes of known capacity. All sizes above 1/2" are thrown aside after being weighed. The size between 1/2" and 1/8" we find contains a large quantity of lumps which carry a considerable gold. On this account we save this size and treat it as explained below. The mill size after being measured is hauled to the dry horse in a specially made wagon box which is perfectly tight. After the shaft is finished we take its dimensions every three feet from surface to bed rock and its average depth. From this data its cubic contents is calculated.
(In working Shaft No. 3 instead of weighing the sizes larger than mill size we attempted to measure them by volume. This we found to be very inaccurate as it gave us a volume of material excavated a considerable in excess of the actual volume of the shaft, as you will see in the report.)
The mill size on reaching the dry house is stored in a bin until there is a sufficient quantity to run the rotary dryer. After going through the dryer it is weighed and spread on the floor of the dry house until the entire mill size of the shaft being worked is in the dry house and ready for sizing.
The dry house is situated far enough above and back of the mill to permit of the gravel being run by gravity down to the belt conveyor which delivers it into the hopper feeding the screening apparatus, or as we call them "sizers".
The gravel between 1/2" and 1/8" which contains quite a proportion of lumps as mentioned above is run over .119" screens until these lumps are broken up and the pebbles cleaned of adhering particles, the screenings of this are added to the mill size. The portion that docs does not break up comprises the 1/2" to 1/8" size.
The sizes of material are then screened out in the following order: .119 to 1/8", .094 to .119, .074 to .094, .059 to .074, .029 to .059, under .007, .007 to [.015?], .015 to .029.
The rate of feeding the sizers is at present about one ton of the mill size per hour per screen, with which is run about an equal amount of coarse gravel. We use two sizes of coarse gravel, the larger, between a 1/4" slot and 3/8" square screen is sizing the gravel above .029 and a smaller, between a 1/4" square and 1/4" slot screen, in sizing the remaindor.
The sized gravel is weighed and the weight per cubic foot is determined by measuring and weighing six cubic feet of each size. It is then stored in numbered and labeled bins ready for separation.
As the sized gravel is run through the separator a sample of the tailings, (about 4%) is taken by means of a 2" belt conveyor running through the center of the machine. The total concentrate is saved and the magnetite removed by means of a hand magnet.
In your original instructions, items 39 to 43 inclusive, you suggest triplicate assays by fire of portions of the concentrate and tailings sample. This we find to be impractical for the following reasons. The tailings contain so little gold that we could not assay enough to get a button that could be seen and handled. There are so few colors of gold in the entire sample of the tailings that a sample could not be taken that might be depended on for fairness, it might contain one of the colors and it might not. The concentrate contains so few particles of gold in comparison with the total that accurate samples can not be taken. We have tried dividing the concentrate into two parts but even these varied a considerably in the amount of gold contained. For these reasons we are having panned the entire concentrate and the entire tailings sample by Mr. Burn and a Mexican expert. This passing is done very carefully and the material is panned a second time to make sure that no gold is lost. If gold is found in the second panning it is panned again. The concentrate from those pannings are assayed. Thus we virtually assay the entire concentrate and about 4% of the total tailings.
This method prevents our saving any of the concentrate or tailings sample as you instructed us to do. If you want a part of the concentrate and tailings saved and sent to the laboratory we would like some suggestion as to the method of obtaining samples. We have understood from Mr. Burn that there is some question as to the number and location of the shafts that are to be sunk and we would like definite instructions from you in the matter.
In the meantime we are sinking a shaft near the N. W. corner of lot No. 50, which is about midway between the lines of old Mexican workings along Cunningham Arroyo and Arroyo Viejo. The gravel is in this vicinity has not been worked at all nor tested by Mr. Burn.
Accompanying each sheet of the shaft report is a sheet explaining the exact meaning of each item of the report.
Respectfully yours,
John V. Miller
Cloyd M. Chapman.