Bonanza Mine

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The Bonanza Mine is in the Hillsboro Mining District.  
It was first mined in 1877.  
The entrance to the Bonanza mine, photo above,
 is located at:32°56’43.76”N 107°33’31.01”W.

Bonanza Mine MapBonanza Mine

The Bonanza Mine is located northeast of Hillsboro, New Mexico at 5660 feet on the east side of Warm Springs Canyon.  It can be reached by a mining road and is roughly 1.7 miles from the Hillsboro Transfer Station (see The Bonanza Mine Trail).  Bulletin 10 describes the location of the Bonanza as “in the arroyo east of the Garfield-Butler and Bigelow groups and west of the arroyo in which the Rattlesnake vein is located” (p. 148).  An aerial view of the Bonanza (center of photograph) prior to 1934 is shown below.  Just over the ridge to the upper right (in the next wash) is the Rattlesnake.

Bulletin 10 describes the Bonanza as having three tunnels, one of which was caved in at the time of that report (1934).  The two remaining tunnels, as of that date, were 3,500’ in length (caved in at about 2,200’) and 2,000’ in length (caved in at 1,800’) and were about 500‘ underground at their deepest.  Subsequent to that date, additional cave ins have occurred.  At about 100’ the current tunnel has caved in, creating a hole which reaches the surface (see first large photo below).

The major mineral taken from the mine was Gold.  However, a variety of other minerals were found in the mine, including; Acanthite, Calcite, Chalcocite, Chalcopyrite, Galena, Limonite, Pyrite, Quartz, and Sphalerite.

The nature of the veins that the miners followed varied, sometimes significantly within the same tunnel.  In one of the Bonanza tunnels, the vein was a fracture zone 2-8’ wide in one spot and a shear zone 80’ wide in another.  

The nature of the mineralization varied within a tunnel as well.  The upper part of the veins tended to be oxidized.  Oxidization “enriches” the ore by a natural chemical process.  It was in the upper part of the veins that free-milling gold was found. “Free-milling gold” is that which has been effectively separated from other minerals, meaning that it could be recovered by concentrating methods without using chemical treatments. Such situations sometimes produce specimen gold.  Harley (Bulletin 10, p. 149) reports that at the time of his survey he found “numerous pieces in which broken pyrite crystals were prevented from falling apart by heavy wires of gold”.  It is safe to say, that all of that is gone now.  Now it is hard to find pyrite crystals period.  

Although the shape of the production between 1877 and is not known by me, we do know that “The deposits in Snake and Wicks Gulches were mined by hand methods, mostly during the years immediately following the placer discovery in 1877.” (p. 26, Placer Gold Deposits of New Mexico, by Maureen G. Johnson, Geological Survey Bulletin 1348, USGS 1972).  Tunneling through hard rock by hand is hard work, even when some blasting is possible.  In the middle of the photograph below, beneath the rope, a haul cart is possible.  Rock, all of the rock excavated to make the tunnel, was loaded into carts like that pictured and hauled out of the tunnel, sometimes donkeys or mules were used to do the hauling, sometimes it was human power.

Bonanza Mine 3

Mining is dangerous work, especially where the veins vary in size.  Sometimes the vein was higher than the tunnel.  In such cases, scaffolding was built inside the tunnel so the miners could stand on something higher than the tunnel floor and mine out the vein above.  The scaffolding also provided some protection from rock fall, a leading cause of injury and death.  The internal scaffolding shown to the right is at the point of the first cave-in in the Bonanza tunnel (the cave-in opened a hole to the surface).

A mill was constructed at the Bonanza in 1904, initially with 10 stamps - later increased to 20.  In 1932 the mill was remodeled, “consisting of a grizzley, small jaw crusher, automatic disc feeder, a small gyratory crusher, and 10 stamps.” (Harley, Bulletin 10, p. 151).  The cost of the remodeled mill was between $25,000 and $30,000 (1932 dollars).  

Bonanza Mine 2
Bonanza Mine 4


Ore from the new mill was processed as follows: “pulp from the stamps was fed into a patented shaking amalgamator, where the free gold was saved, thence to concentrating tables, where the sulfides were recovered and a final tailing product made” (Harley, Bulletin 10, p. 151).

From December 1904 to September 1905 the net proceeds from the mine were $34,721.  That is  equivalent to roughly $825,000 dollars in 2015, using simple inflationary adjustments.  Using an equivalency model based on the price of gold the figure is close to $2.2 million (34,721/18.96 [1904 price of gold] = 1835 oz., 1835 x 1200 [current price of gold] = 2.2M).  W. H. Bucher, who was the vice-president of the Sierra County Bank in Hillsboro, which handled the ore shipments from the Bonanza, said the value of those shipments was in the range of $700,000 (700,000/ 18.96 = 36,920 oz.)  This data bit is not precise as to time or value but using it as a rough estimate of the production of the Bonanza, the gold produced by the Bonanza would fetch in the range of $44.3M in today’s market (36,920 x 1200 = 44.3M.).  (Note, however, that some sources report production of 21,900 oz., which would yield a value of $26M.)  Harley (Bulletin 10, p. 140) reported that “During 1931-1933, activity was more general and more persistent in the camp, and mining and development work was done in the Bonanza... but most of the richer runs had already been discovered and removed, and it was only occasionally that such small-scale operations netted the worker more than a bare subsistence.”

By the Second World War, mining had become so unprofitable in the mines of the Hillsboro Mining District that most of the rails, seen along the bottom left edge of the photograph to the right, were removed from the mines to aid the war effort.

Very little information is available about production costs (the mill costs referenced above are a rare bit of data).  Wages were very low, still lower if you were Mexican or Chinese, there were no “benefits”.  Environmental and worker protections were non-existent.  Even with greater mechanization, it is likely that production costs are (comparatively) significantly higher now than during the major mining periods of the late 1800’s and early 1900’s.  Increased production costs and lower quality ore, more than likely, overshadow the increases in the price of gold.

In “The Ore Deposits of New Mexico 1910” (p. 276)  Lindgren, Graton, and Gordon note that “The Bonanza Mine is operated by the Ameranza Mining Company... The Bonanza is the only mine which was producing ore in 1905. The ores are free milling, with sulphides of copper carrying gold and silver values. Smelter returns of gold, silver, and copper are made. The lower-grade ores are treated in the company's mill, located in the valley three-fourths of a mile north of Hillsboro, and the concentrates, together with the shipping ores, are sent to the smelter at El Paso . . The smelter returns on three car lots of rich shipping ore, as taken from the company's records, are as follows:

Bonanza production 1905


Quartz is the chief gangue mineral. In places the lode consists of a single vein from 2 to 8 feet in width; in others, of a branching system of thin seams occupying a shear zone from 2 to 7 feet wide. These lead out into the country rock on the foot-wall side. The dip is to the west at a high angle-nearly vertical. The ore bodies occur along the walls, here on one side and there on the other. Some distance in from the portal of the tunnel the vein branches, but the branches come together again farther on. At 2,000 feet from the portal of the lower tunnel the vein splits up into several small veins, branching out into the foot walls. At this point the main vein becomes barren, and at the time of visit (1905) crosscutting was in operation in the hope 'of locating the lode. Mining operations here consist chiefly in drifting on the lode. Some of the upper tunnels extend through the hill and the lowest is about 2,000 feet in length. In 1905 forty men were employed, of whom twenty-five were at work underground. The mill, which had 10 stamps, was found insufficient and has been recently increased to 20 stamps. It began operations December 1, 1904, and up to September, 1905, the net returns on ores from the Bonanza mine were as follows: Bullion, $23,801.51; concentrates, $4,821.02; shipping ore, $7,099.29; total, $35,721.82.”

The Bonanza Mine is featured in this video with Steve Elam.  




© Robert Barnes 2018