“If Hell is Below, It Wouldn’t Take Long to Go There”:
Drilling and Blasting at Bodie
Michael H. Piatt
only way to get ore out of the ground is to dig it out. The methods employed at Bodie had been
adapted from eastern coal mining, then perfected on the Comstock during the
1860s. They remained essentially the
same throughout the mining West. Miners
most often began by digging ore where it was most accessible—at the place where
a mineral formation, usually quartz, “outcropped” the surface. They followed it downward on a meandering
course, leaving an open trench.
From various levels miners stoped the ore, preferably by excavating upward and allowing rocks to fall into chutes that fed them by gravity into mine cars. Tracks leading through dimly-lit drifts and crosscuts guided the loaded cars as men pushed, or mules pulled, the heavy cargo to the shaft. Hoisting equipment then raised the rock out of the mine, requiring powerful steam-driven machinery in buildings on the surface known as “hoisting works.” Most Bodie mines sank vertical or incline shafts, but three major companies drove horizontal tunnels to reach their ore bodies. All three tunnels intersected vertical shafts whose hoisting equipment provided access to levels above and below.
Sinking shafts and driving tunnels required explosives, and miners advanced underground passageways by following a specific sequence for blasting: drill a pattern of holes in the rock, load the holes with explosives, detonate, remove the broken rock, trim the opening to size, install timber supports, then drill the next group of holes.
Before about 1875, miners drilled holes in rock with tools consisting of a hand-held hammer and a drill. The drill was made from a steel rod, heat treated with a slightly arced chisel-shaped tip, or “bit,” that flared so that the hole was slightly larger in diameter than the rod, allowing the drill to be withdrawn. The miner held the drill in one hand while pressing its bit against the rock, then repeatedly struck it with a four-pound hammer clutched in the other hand. After each blow he rotated the drill a fraction of a turn. Drills of progressively greater lengths allowed holes to reach depths of about three feet. The drills dulled quickly, requiring frequent changes and blacksmiths on the surface who kept busy forging, heat-treating, and re-sharpening them.
Since miners were keen to save labor, they directed and arranged holes to take advantage of natural flaws in the rock. Miners swung hammers against drills in all directions--upward, downward, horizontal, and every angle in between. Horizontal and downward holes were easiest to drill, but rock dust retarded progress and had to be removed periodically with a long thin spoon. Cuttings fell freely from holes directed upward, but swinging a hammer at an overhead drill required skill. Hand drilling could also be performed by two men working together, a tradition brought to this country by Cornish miners. One man held, turned, and changed the drill, while his teammate wielded an eight-pound sledgehammer. Although impressive for its human dynamics, the economy of this method is doubtful, and it was only employed where labor unions were strong enough to enforce its use.
Depending on the passageway’s measurements, the hardness of the rock, the size to which rock pieces were to be broken, and the strength and amount of explosives, miners drilled a group of six or more holes in the direction the passageway was to be advanced. The group was known as a “round of holes.” Major passageways, such as main shafts and tunnels, required 30 or more holes per round. Explosives, usually in the form of cartridges, filled each hole, pushed in with a long wooden stick called a “tamping rod.”
When the explosives detonated, the holes exploded in sequence, controlled by the lengths of fuses. Sinking shafts required the first explosion to relieve the ground in the center, followed by explosions that radiated outward to the corners, each forcing debris into the void created by the previous blast. Driving horizontal tunnels called for another sequence. Middle holes exploded first, relieving the ground in the center, then top holes forced debris into the void from the first explosion. The final blast at the bottom lifted the broken rocks and dumped them onto iron sheets placed in the work area to make shoveling, or “mucking,” easier. The timed explosions also allowed miners listening from a safe distance to discern when a charge did not detonate. These “missed holes” or “misses” were extremely dangerous and had to be discovered and detonated before work continued.
Given that Bodie’s gold and silver were encased in rock
and consisted mostly of particles invisible to the naked eye, it is a wonder
that anybody expected to gain from mining there. Anticipating large profits, however, was
something at which western mining men excelled.
Their penchant for optimism was nourished by an epic transformation
taking place in nineteenth-century
Dynamite. When the
West was still young and wild, underground mining called for “blasting powder,”
a cheap explosive manufactured on the West Coast since 1864 by the California
Powder Works.(1) But, the industrialized
world demanded more powerful explosives—called for by the builders of rail and
wagon roads, canals, and those who mined coal or quarried stone for big-city
edifices. Despite devastating
consequences, inventors and manufacturers persevered with a new form of “high
explosive” discovered by an obscure Italian chemist. While teaching at the
nitroglycerine reached its highest level of development in 1867, during
construction of a 4 ¾-mile railroad tunnel in
Not until a struggling nitroglycerine manufacturer in
Driven as much by a desire to circumvent Nobel’s patents as to improve upon Giant powder, numerous American companies sprang up to produce competing brands. Aside from altered proportions of the principal ingredients, the primary difference between products was the material used for the absorbent filler. By choosing fillers that either enhanced or hindered the blast, dynamite could be produced with varying explosive characteristics. By 1874 the product was available under the names of Giant, Judson (a second line manufactured by the Giant Powder Company, named for a company founder Egbert Judson), Hercules (manufactured by the California Powder Works until 1876, when it was purchased by DuPont of Delaware, the country’s largest blasting powder manufacturer, which was seeking to enter the dynamite trade), and Vulcan. Agents for the companies advertised conspicuously in Bodie newspapers: “GIANT POWDER,” proclaimed one ad. “The company manufactures three different grades--Nos. 1, 2 and 3--and sells the same as low [in price] as any of the infringing powders under the names of Vulcan or Hercules Powders.” (Bodie Weekly Standard 6 November 1878) Merchants selling competing brands also advertised vigorously: “Hercules--Nos. 1 & 2. The best mining powder in use. Prices as low as any in the market.” (Daily Bodie Standard 7 July 1879) Until mid-1879 Giant, Hercules, and Vulcan products were distributed to Bodie’s mining companies from a magazine centrally located near the Standard Mine. In July the magazine inexplicably blew up, killing seven men, injuring more than 40 other people, and demolishing one of the Standard Company’s hoisting works.
Air-Powered Machine Drills. Hand drilling holes for blasting represented
75% of mining costs, calling for a device that would drill rock more
cheaply. The demand led to machine
drills, the second technological development that revolutionized underground mining. Improving upon a string of failed inventions
since about 1838 (including one by Isaac Singer of later sewing machine fame)
Charles Burleigh, a Fitchburg, Massachusetts, steam engine and machine tool
manufacturer, developed the first successful air-powered rock drill in 1866-67
while striving to advance the nearby Hoosac railroad tunnel.(4) Burleigh introduced his drill to western
mining in 1870, when he drove a tunnel into Sherman Mountain at Georgetown, Colorado. At times the tunnel advanced through solid
rock at speeds six times the rate of drilling by hand. A later demonstration in
Competing manufacturers quickly challenged the Burleigh Rock-Drill Company by producing a multitude of drills. The four most practical, judged by one expert in 1874, were the Burleigh, Rand, Ingersoll, and Waring.(5) The superior power of high explosives allowed deeper holes than those drilled for blasting powder. Machine-drills easily met this demand, and also produced holes larger in diameter that held more explosives than hand-drilled holes. Spurred by dynamite’s destructive force, deeper and larger holes, and accelerated drilling speeds, passageways advanced at astonishing rates. Ingersoll and Burleigh drills at Bodie in 1879 permitted the Noonday Company to sink its vertical three-compartment shaft at an incredible rate of five feet per day.
Inside a mine, the cumbersome machine drills swiveled from columns, horizontal bars, tripods, or carriages that supported their weight and resisted the reciprocating drill rod’s recoil. Advances in alloying, forging, and heat treating steel during the 1890s allowed manufacturers to produce drills that were compact and durable, with stronger cutting bits. Refinements led to a separate class of fast-acting machine drills characterized by a small, unattached piston that moved rapidly within the drill body and struck the drill rod instead of moving it back and forth. By the first decade of the twentieth century, the two styles had been delegated to specific tasks. Successors of Burleigh’s drill, referred to as “piston drills” (a misnomer because both styles contained pistons), were used to sink shafts and drive tunnels. These heavy machines delivered 600 strokes per minute, but required a rigid support and two men to set up and operate. Piston drills held the advantage for downward and horizontal holes, because the reciprocating drill rod’s pumping action removed cuttings, wetted by water poured into the hole to prevent dust. “Hammer drills,” on the other hand, delivered 2,000 blows per minute and were often light enough for one man to handle, but the drill rod lacked a pumping motion that would have removed cuttings from the hole. Attached axially to columns, these drills were reserved for upward angled holes where rock fragments fell out by gravity. Primarily used to stope ore, they were often called “stopers.” Otherwise, a hollow drill rod allowed high-pressure air to blow rock dust from the hole. Airborne silica dust had long been recognized as a respiratory health hazard, but not until 1914 was water commonly injected through the hollow drill rods (an idea that had been around since 1899) to suppress dust and expel rock fragments.
Machine drills greatly improved the economics of mining at Bodie, but for several reasons they were not employed at every mine. Compressed air to power the drills required costly machinery on the surface and extensive piping underground. During the first 15 years of Bodie’s industrial development, steam ran the air compressing machinery, requiring additional boilers in the hoisting works. Expensive equipment and fuel limited air-powered drills to mines worthy of the investment. Even then, managers carefully considered their use and most often reserved the machines for opening major tunnels and shafts. Meanwhile, hand drilling prevailed in isolated areas, where air pipes did not extend.
Furthermore, Bodie’s ore deposits tended to be narrow, and machine setups were impossible in confined spaces. Whether by pick, pry bar, or hand drill and dynamite, the necessity to take ore selectively also meant that its extraction remained a hand process. Drilling by hand persisted in the Standard Mine until it closed in 1913. The practice continued into the 1930s, when small-time operators leased ground in old mines and worked beyond the reach of air hoses from their diesel-powered compressors on the surface.
1. Gunpowder consisted of potassium nitrate, sulfur, and charcoal. The product remained essentially unchanged until 1857, when DuPont patented “soda” or “blasting powder” which used cheaper, more readily available sodium nitrate instead of potassium nitrate. While widely used in mining, blasting powder proved unsuitable for firearms. Thereafter, traditional gunpowder became known as “black powder.”
2. Gunpowder had always been set off by a spark or flame, but neither would always ignite nitroglycerin. In 1863 Alfred Nobel used a small exploding device he called an “initiator” to shock the nitroglycerin into detonating. Later referred to as “detonators” or “blasting caps” the mercury-fulminate devices could be fitted to either fuses or electric wires.
3. Upon dynamite’s introduction to this country, the expression “Giant powder” distinguished the high explosive from blasting powder, then known simply as “powder.” After dynamite became popular, miners also called it “powder.”
4. The 4 ¾ mile Hoosac Tunnel, begun in 1851 in Massachusetts became something of a proving ground for inventions that were later adapted to western mining. Burleigh’s air-powered rock drill proved superior to every mechanical drilling contrivance tried at Hoosac, where competing machines broke down so frequently that the tunnel was said to be “crowded with people carrying spare parts and tools for repairs.” (Raymond 1870, 506)
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