The Yogo Gulch sapphire deposit is located on the northeastern
side of the Little Belt Mountains in Judith Basin County, about
74 miles east-northeast of Helena.
Commercial mining for sapphires at Yogo began in 1896.
Charles T. Gadsden, an English mining engineer, originally
oversaw the operation at Yogo. By the time the mine was
closed in 1929, Yogo had produced 2.5 million carats of gemquality
sapphires, reportedly worth as much as US$25 million.
For further information, the reader is referred to Voynick
(1987); Mychaluk (1995); and Hughes (1997).
The original Yogo mine, which has been owned by
Roncor Inc. since 1972, was most recently mined during 2000
and 2001 by a publicly traded Canadian company named
Pacific Sapphire. They have since ceased operations and
divested themselves of their sapphire interests. At the present
time, Roncor has no plans to resume mining. For almost 100
years, miners have worked material relatively near the surface.
Today, however, most of this area has been depleted, so
any future large-scale operations must go deep underground,
which is more difficult and much more expensive.
In 1984 a group of local prospectors formed the Vortex
Mining Company and discovered several new sapphire-bearing
dykes on the west end of the Yogo deposit. They began mining
in 1987 and are the only company mining at Yogo today; now
under the name Yogo Creek Mining. They are mining underground,
via a 260 feet deep shaft. They told the author recently
that production is very good, with demand much higher than
they are able to meet, especially in 1-carat-plus round brilliants.
Although the color of Yogo sapphires is often among the
very best in the world, the crystals typically are small less
than 10% weigh more than one carat and have a characteristic
flat, tabular shape that makes it difficult to retain a high
percentage of weight during cutting.
Yogo sapphires are unique in that they have a very uniform,
intense color and thus never require heat treatment.
The vast majority of Yogos are blue (historically referred to
as "cornflower"), although medium-toned purple stones are
Rock Creek, or Gem Mountain as it is popularly known, is
located near the town of Philipsburg in Granite County, about
80 miles west-southwest of Helena. The deposit runs principally
along two tributaries of the west fork of Rock Creek: Anaconda
Gulch and Sapphire Gulch.
Rock Creek is unique in that it is the only placer deposit
in Montana that was mined before World War II solely for sapphires
(the other areas were mined for their considerable gold
content). Mining commenced at Rock Creek around 1906 and
was fairly steady until 1943, when synthetic corundum replaced
natural sapphire for many commercial applications. Mining
records indicate that 190 million carats of sapphire were shipped
from Rock Creek between 1906 and 1923. Rock Creek has been
mined more extensively and produced more faceted gems during
its 110 year history than any of the other sapphire deposits
in Montana (including Yogo).
In this author’s opinion, Rock Creek is the most important
of the Montana secondary deposits. The mountain is covered
with sapphire that is easy to mine (there is a reason that the
entire mountain range is named the "Sapphire Mountains");
it heat treats extremely well, producing a full range of colors;
and cutters get high weight retention from the crystals (figure
4). Some blue and fancy-color sapphires found there are
attractive without heat treatment.
AGC owned the majority of the sapphire bearing ground at
Rock Creek from 1994-2001. AGC divested themselves of their
sapphire interests in 2001, selling the mine to one concern and
all of the other sapphire-related assets, including large inventories
of rough and cut sapphires, to Fine Gems International (a
wholesale company specializing in fine gemstones from around
Currently, the largest property owner (of nearly 500 acres
of mining claims) is operating a successful tourist operation,
selling buckets of sapphire-bearing gravels. He plans to begin
small-scale mining in 2003, with three people. In between and
adjacent to this property are several other individuals or small
companies that own mineral rights and sporadically mine in
groups of two or three. The severe winters restrict mining to the
period between mid-May and mid-October. Another company
offers tourists and sapphire enthusiasts the opportunity to enjoy
the spectacular area by taking a sapphire mining pack trip on
Robert Kane is the former Director of the Gübelin Gem Lab in Lucerne,
Switzerland and the former Manager of Gem Identification at GIA’s West
Coast Gem Trade Laboratory. He is currently President & CEO of Fine
Gems Inter-national, and can be contacted at firstname.lastname@example.org.
© 2002 Robert E. Kane