Story, photos and video by Emily Stifler
As Mike Roberts drives his low profile
loading truck into the dark mineshaft,
the spring green hills of Yogo Gulch
disappear with the circle of daylight at
the tunnel’s entrance. Roberts’ headlamp
ricochets of the walls, and the truck’s
engine noise fills the narrow tunnel. The
air temperature cools. At the 250’ level,
he stops and turns off the engine.
Drip… Drip. Water trickles in the
dank tunnel, echoing. The lamp casts
a dim glow across the 10’-tall, 15’-
wide tunnel.
“My daughters love the crystal cave,”
Roberts says and climbs out of the
truck. He walks up a muddy side tunnel,
ascends a 15’ ladder, and lights a
cave of clearish-brown quartz crystals.
“Isn’t it pretty?” he asks.
But Roberts, who spends many waking
hours here, isn’t looking for quartz.
He mines Yogo sapphires, the nearly
flawless gemstones found only in the
Little Belt Mountains outside the tiny
south-central Montana town of Utica,
an hour’s drive west of Lewistown. In
2005, he traded a gold mine he owned
outside of Fairbanks, Alaska, for this
Montana mineral deposit. He’d been in
Alaska 20 years, but now, he’s worked
this secondary-vein of the main Yogo
dike ever since.
Roberts climbs down the ladder and
continues up the tunnel, balancing
his strong, compact frame across a wet
plank spanning a ditch. Stopping, he
shines his headlamp at a 12” wide strip
of cream-colored rock in the ceiling,
sandwiched between Madison limestone.
The Yogos, he explains, are scattered
“indiscriminately throughout”
this lighter colored dike of rock, which
is called lamproite.
300 million years ago, an ancient sea
covered much of what is now Montana.
The seabed, put under geologic
pressure, formed the Madison limestone
layer. Then, 50 million years
ago, an uplift created the Little Belt
Mountains. Magma from the earth’s
mantel rose into a fracture in the
limestone and formed a five-mile long,
ten-foot wide dike of lamproite—the
Yogo’s host rock. Geologic surveys
show this dike is 7,000’ deep, making
it the world’s largest known sapphire
deposit. Mining efforts here have
never extended deeper than 400’.
To access the Yogos, Roberts blasts
the dike rock and sometimes uses a
high-pressure washer to flush it from
the vein. Eight feet up in this cleft,
he’s set up rafters, so he can
work “from the bottom up.”
A couple years ago, he fell
from a spot like this and hurt
himself so badly he couldn’t
work for several months.
Even so, Roberts enjoys
his work. He picks up a
piece of the fallen dike
rock, which looks like clay.
He smiles. “I love it down
here. It’s like a mansion,”
he says. His grin is lit by
his headlamp. “But my
wife wouldn’t live in a
hole in the ground.” He
laughs. Instead, they live
with their three children in
Great Falls.
After collecting the dike
rock, Roberts lets it soften
by weathering, either on
the floor of the tunnel, or
outside, exposed to the
sun. This technique is essentially
the same used by
all who have mined here
over the last century.

A lovely cornflower blue
color and natural clarity
have given Yogo sapphires
prestige. Queen Victoria,
Kaiser Wilhelm of
Germany, the Duchess of
York and Lady Diana have
all owned them. They
are in collections at the
Smithsonian Institution in
Washington, D.C., at the
Museum of Natural History
in New York, and part
of the Royal Crown jewels
in London.
In Montana,
Yogos have special allure,
and many local jewelers sell
fine, expensive stones.
Unlike most other sapphires,
which must undergo
heat treatment to be
rid of impurities, Yogos are
naturally almost flawless.
Although well-cut Yogos
larger than one carat are
rare, exceptional gems can
sell for up to $100,000.
Lower quality rough-cut
stones are available for
under $100.
The Yogo dike
has produced more than
$25 million of the world’s
most beautiful sapphires,
but its history has been riddled
with mistakes, bad luck
and bankruptcy. Unlike
sapphires from the alluvial
beds of Australia, Sri
Lanka, Thailand and other
parts of Montana, Yogos
are embedded in hard rock,
which makes mining them
difficult and expensive.
Human history with the
Yogo dike began in 1879,
when more than 1000
prospectors flocked to Yogo
City, one of the last major
gold booms in Montana.
The miners found little
gold, but they did notice
small, translucent blue
pebbles that sank to the
bottom of their sluice
boxes. Interested only in
gold, the men threw these
away. Two years later, the
boom was over, and Yogo
City emptied out.
Then in 1894, locals Jake
Hoover and S.S. Hobson
began looking for gold
again. Legend has it that
the next year, Hoover lent
a schoolteacher friend
gold dirt to show her class.
When she returned the
dirt, she thanked him for
the sapphires.

That fall,
Hoover sent a cigar box full
of blue stones to jeweler
Tiffany & Co. in New
York for appraisal. There,
America’s most prominent
gem expert, Dr. George
F. Kuntz, identified them
as “the finest precious
gemstones ever found in the
United States.” In return,
Tiffany sent Hoover a check
for $3,750 and a letter explaining
the sapphires were
of “unusual quality.”
A mountain man with a
knack for gold discovery and
a taste for booze, women
and trouble, Hoover “could
empty a Winchester faster
than any other man I ever
knew…” said Hoover’s longtime
friend, the legendary
cowboy artist Charlie Russell.
In 1896, Hoover, Hobson
and two others bought
claims on the eastern end of
the dike and started digging.
They realized though, with
no American gem cutting
facilities rough stones were
hard to market. Hoover sold
his share, paid his debts and
joined the Alaska gold rush.
From 1898-1952, a
London-based jewelry
giant owned the land and
renamed it the English
Mine. Sapphires were en
vogue in early 20th century
Europe, and Yogos
resembled the stylish, blue
Sri Lankan stones. Many
London jewelers passed
Yogos off as stones from
Sri Lanka. Ironically, Yogos
were not easily available in
Montana (they had to be
shipped overseas to be cut),
so jewelers at home bought
Sri Lankan sapphires and
sold them as Yogos.
In 1923, an intense storm
flooded and destroyed the
English Mine’s infrastructure
and washed away
weathering piles. All new
mining ceased, and the
operation closed two years
later. The last production
was recorded in 1927.
In the latter half of the
20th century, the mine
changed hands numerous
times. Many attempted
mining this perfect stone,
but high operating costs,
no domestic cutting facilities,
and poor marketing
caused them all to fail.
Big business came to Yogo
in 1981, followed by controversy.
Intergem, backed
by Citibank, brought
attention to heat-treating.
A common process in the
gem industry, it heats
sapphires to 1800 degrees
C, altering their chemical
structure and creating clear
blue stones from previously
worthless discolored
ones. Intergem accused
other jewelers of nondisclosure
and touted Yogo’s
natural worth. Five years
after opening, Intergem
couldn’t afford payments,
and ownership returned to
Roncor, Inc.
Then in 1984, four locals
on a day hike made
a new discovery at Yogo
– the side vein that Mike
Roberts mines today.
They staked claims at the
‘Vortex Mine’, sunk a
280’ shaft, and operated
successfully for several
years before leasing to the
Idaho-based Small Mining
Development, who drove
the shaft to 400’. Unsatisfied
with production and
profit, SMD closed the
Vortex Mine in 2004.

Today, Mike Roberts runs the
only commercial Yogo operation.
Nearby, the Sapphire Village
subdivision allows property owners
lifetime digging rights on the
old English Mine. For them, rock
hounding is a hobby, and residents
spend summers collecting buckets
of old mine dirt, leaked from flumes
that sat atop the hill above Yogo
Gulch 90 years ago.
Above ground, Roberts uses a bucket
loader to scoop weathered ore into
a large processor. The ore feeds into
a trommel, an eight-foot diameter
tube made of steel screens that spins,
separating different size materials.
Rocks crash against metal. A conveyor
belt dumps larger rocks into a
pile. Diverted creek water flushes the
smaller pieces down a flume and into
a sluice box, where sapphires sink to
the bottom of the riffles.

Roberts running the trommel:

Roberts shuts off the processor,
walks to the sluice box, and shovels
excess stone and dirt out with the
muddy water. When it’s poured off,
he sifts his fingers through the gravel
that remains.
“This is the jig bit,” he says, picking
up small black steel shot that’s sunk
below the limestone. “Anything
lighter stays on top of this and keeps
floating down as the water pulses up,
anything heavier will go down and
settle in it. Sapphires are just a little
heavier than the steel shot.”
With tweezers, he picks out tiny blue
sapphires. Barely visible among the
limestone and hematite, the gems
glisten when he holds them up to the
sun. He smiles, and his mischievous
blue eyes almost resemble the precious
Roberts has offers from major national
jewelers like Tiffany. But the
market in Montana is good, he says,
and he’s unsure if the costs outweigh
the profits to expand to larger sellers.
So, after two decades of mining gold
in Alaska, why Yogos? Roberts says
there is something special about sapphires.
“Their color is eye pleasing.
Mining for them is fun, and it’s a