Reckoning the deposits at one third of the total product of the mines, the total yield of gold for the territory to June 30, 1872, was more than $60,000,000. For the extraction of the gold, the common stamp-mill process, with amalgamation in battery and upon copper plates, is now almost exclusively employed, although it is generally admitted that only a portion of the precious metals is secured in this way. According to the best statistics attainable, which are somewhat imperfect, the number of stamp mills in Colorado in 1870 was 105, with more than 1,800 stamps. Of these mills, 94 for the reduction of gold, with 1,607 stamps, of which 857 were in operation, were in Gilpin county, and the remainder in Clear Creek, Boulder, Park, and Lake counties; and 4 for the reduction of silver, with 70 stamps, in Clear Creek county, and 2 for the reduction of gold and silver in the same county. Although the discovery of silver in Colorado dates as far back as that of gold, it is only within a few years that rich deposits of this metal have been known to exist in the lodes of the mining counties. The silver ores have been divided into surface and galena ores. The former generally contain, besides more or less zinc blende, a little decomposed galena and sulphuret of silver; and very often the zinc blende is also decomposed. With increasing depth the amount of galena and zinc blende gradually increases, until at a depth not exceeding 100 ft. they decidedly predominate. The principal silver-producing county is Clear Creek. The actual development of the prominent silver lodes was begun in 1867; the whole amount of ore mined up to April 1, 1869, is estimated at 1,100 tons, which yielded $250,000 in coin. The production of silver ore in Clear Creek county amounts to about 2,000 tons per annum. The estimated yield of silver, including shipments of ore, during 1870, was about $400,000. The deposits of silver from Colorado at the United States mint, branches, and assay offices, to June 30, 1872, have been:
| YEARS. | Value. |
| 1866 | $419 00 |
| 1867 | 543 78 |
| 1868 | 46,881 13 |
| 1869 | 197,678 54 |
| 1870 | 236,689 49 |
| 1871 | $367,510 31 |
| 1872 | 264,821 18 |
| Total | $1,114,543 43 |
The following statement made by E. E. Burlingame, Feb. 17, 1871, shows the coin value per ton of 2,000 lbs. of specimens of ore from different districts of Gilpin and Clear Creek counties:
| SAMPLES. | Gold. | Silver. | Total. | ||||||||||||||||
|
$138 92 | $30 32 | $169 24 | ||||||||||||||||
| 90 30 | 37 62 | 127 92 | |||||||||||||||||
| 50 28 | 61 90 | 112 18 | |||||||||||||||||
| 24 10 | 11 37 | 35 47 | |||||||||||||||||
| 22 51 | 12 85 | 85 26 | |||||||||||||||||
| 20 07 | 17 14 | 37 21 | |||||||||||||||||
| 18 44 | 228 90 | 247 34 | |||||||||||||||||
| ..... | 409 81 | 409 81 | |||||||||||||||||
| 7 82 | 35 97 | 43 79 | |||||||||||||||||
| ..... | 86 31 | 86 31 | |||||||||||||||||
Iron pyrites is universal in the mines, occurring in cubes from the size of a pin's head to an inch on the sides. Copper, almost always in the form of pyrites, occurs in the prominent lodes in considerable quantities; the first class ores of some of the mines contain from 10 to 15 per cent. of it. Besides copper and iron pyrites, almost every lode contains a little zinc blende and galena; in some districts these minerals form a considerable part of the ore. Large beds of lignite, pronounced superior to any other found in the west, occur on the E. declivity of the mountains, in Boulder and Jefferson counties. The coal obtained resembles anthracite in appearance, but burns with a strong yellowish white flame, gives little soot, and from 2 to 3 per cent. of ashes of a reddish yellow color. It has been found in veins 14 ft. thick, of which 13 ft. are workable coal. The value of these beds of lignite is greatly enhanced by the simultaneous occurrence of fire clay and iron ore. The former, found in layers from 3 to 5 ft. thick between the different strata of coal, is of a grayish blue color, burns almost white, and compares favorably with the standard clays of Europe. Lignite is also found in the vicinity of the Raton mountains near Trinidad, and in the Arkansas valley E. of Cañon City. The iron ore occurs, scattered over the surface, all the way from South Boulder to Coal creek. At a depth not exceeding 5 ft. masses of 1,000 lbs. have been found in the sand; and though no defined bed has yet been discovered, the great quantity of superficial bowlders indicates that such a deposit exists. The ore yields from 50 to 60 per cent. of iron. Salt springs occur in South park, where extensive works have been erected. Valuable soda springs exist near the base of Pike's peak, and in other portions of Colorado. Hot sulphur springs, possessing valuable medicinal qualities, occur on a tributary of the Grand, in Middle park, about 12 m. from its S. boundary.—The climate of Colorado is remarkably equable and healthy. The winters are mild, and the summers cool and bracing. Hot, sultry nights are unknown. On the plains the temperature averages from 50° to 55°. At Denver during 1870 the mean temperature for each month and the amount of rain and melted snow were as follows:
| MONTHS. | TEMPERATURE. | Rain and melted snow, inches. | ||
| Max. | Min. | Mean. | ||
| January | 60° | 5° | 29.4° | 1.15 |
| February | 64 | 1 | 35.5 | 1.70 |
| March | 67 | -8 | 32.7 | .70 |
| April | 80 | 16 | 48.1 | 2.80 |
| May | 86 | 40 | 56.1 | .35 |
| June | 94 | 48 | 68.2 | .52 |
| July | 98 | 53 | 74.2 | .51 |
| August | 97 | 45 | 64.8 | .12 |
| September | 89 | 40 | 60.1 | 2.85 |
| October | 83 | 27 | 47.8 | .68 |
| November | 68 | 20 | 41.8 | .54 |
| December | 60 | -18 | 23 | .78 |
| Year | 48.5 | 12.65 | ||
