Transcript No Slide Title

THAILAND’S RUBY AND SAPPHIRE DEPOSITS
• In lateritic soils atop Plio-Pliestocene basalt, or in gem gravels
derived from basalt. Deposits are about 6-20' below the surface.
• Source is thought to be basalt (corundum xenocrystic?).
• Mining restricted to Thai nationals since 1919.
• 85-90% from the Chanthaburi-Trat gem field (since 1850?),
• Once about 70% of world production.
• Darker red; brownish to purplish overtone ruby due to Fe
• More Fe-rich than Burma ruby, show a much weaker red than
Burmese stones in short and long u.v..
• Characteristic inclusion is pyrrhotite (iron sulfide).
Present situation !
Hughes, R.W. (1996) Ruby & Sapphire.
RWH Publishing, Boulder, CO, 512 pp.
Map of Corundum sites in Thailand and Cambodia. (Modified
by R.W. Hughes from Vichit & Vudhichativanich et al., 1978)
A miner works with traditional methods at Khao Ploi Waen, just outside of
Chanthaburi. Mechanized mining has resulted in rapid depletion of most mines
in Thailand, making miners such as this an endangered species.
A handful of rough
sapphires from Khao
P l o i W a e n.
A ruby mine near Tok Prom. Today it is operated
mainly for tourists, and will soon close.
( P h o t o : R . W . H u g h e s ; J a n., 1996)
Thai military sign outside Bo Rai
forbidding declaring that entry into
the area within five kilometers of
the Cambodian border is
restricted to those with military
permits. According to one villager
with whom the author spoke, this
zone contains a number of
Khmer Rouge camps, but this was
denied by military officials along
t h e
b o r d e r.
(Photo: R.W. Hughes; Jan.,
1996)
The early morning
rough ruby market at
Bo Rai, in Trat
province, Thailand.
Where once close to a
thousand people
gathered to trade
gems, today only a
few stragglers remain.
(Photo: R.W. Hughes;
J u l y , 1996)
VIETNAM
Vietnam produces rubies as good as anything from
Burma. But the machinations and intrigue surrounding
the gem business in that country have left this potential
l a r g e l y
u n e x p l o i t e d.
http://www.ruby-sapphire.com/vietnamese_rubies.htm
Map of northern Vietnam, showing the location of
the important ruby mines at Quy Chau and Luc Yen.
Like ruby mines in Thailand
and Cambodia, bulldozers or
backhoes are used to
excavate the land. The earth
is then forced into a
separation jig by the use of
water cannons. Once in the
jig, the “heavies” (higher
density minerals) are sorted
by hand to remove the rubies.
Nominally-illegal pit mining
is also carried out throughout
the district, mainly on the
fringes of the mechanized
m
i
n
e
s.
Corundum deposits of India
Sapphires from the famous Kashmir mine
http://www.ruby-sapphire.com/r-s-bk-india.htm
http://www.palagems.com/kashmir_sapphire.htm
Reprinted from Records of the Geological
Survey of India. Vol. 23, Pt. 2, May, 1890, pp.
59–69
The location and
geology of the famous
Kashmir sapphire
mines near Sumjam.
The sapphires of
Kashmir occur in
outcrops high on
the wall of the Kudi
Valley. Within an
actinolite-tremolite
rock, small
pegmatite lenses
occu r, an d it is
within these lenses
that the sapphires
a r e f o u n d.
View of the Kashmir sapphire mines taken in 1887-
This 4-ct. plus Kashmir sapphire exhibits the
velvety blue color that has made stones from
this source without peer in the world.
K a s h m i r
sapphires,
such as the
stone above,
are often cut as
sugarloaf
cabochons.
A 3.03-ct Kashmir sapphire
illustrates the color and velvety
texture which has made stones
from this locality so famous.
The sapphire washing apparatus constructed at the Kashmir mine taken in 1887-8.
The famous Kashmir sapphire
mines produce two different
types of rough. Some of the
crystals display heavily
corroded surfaces, while in
others the original crystal
surfaces are largely intact.
The color in Kashmir sapphires lies mainly along the crystal faces, with the core
of the crystal being colorless. Unfortunately, in the corroded crystals this vital
color layer is largely absent, making them poorly suited for cutting. Both
corroded and uncorroded crystals have proven satisfactory for heat treatment.
Mining methods at the Kashmir mines have always been
primitive, due to the altitude and remote location. Today,
the mines remain accessible only by foot or helicopter.
At first, huge quantities were obtained by simple digging.
Since 1927, the mines have been worked intermittently,
but with no real success. Every few years the Kashmir
Government makes noises about leasing out the mines,
but so far these attempts have not come to fruition.
Blue velvet--inclusions
of Kashmir sapphires
Top left: Most distinctive of
the Kashmir sapphire
inclusions are the rounded
zircon crystals with tiny
accompanying black
u r a n i n i t e c r y s t a l s.
Top right: Healed fissure with flat, strongly recrystallized cavities (negative crystals) in
a Kashmir sapphire. Some of these cavities contain tiny opaque crystals of unknown
identity. 50x.
Below left: Pargasite crystal in Kashmir sapphire. Below right: Tiny hexagonal crystals
with thin-film satellite haloes in a Kashmir sapphire. These are similar to those found
in Thai/Cambodian rubies. (Photos: Henry Hänni/SSEF)
CORUNDUM
DEPOSITS
OF
SRI LANKA
Sri Lanka Corundum Deposits
• Sri Lanka and has supplied the world with fine Rubies and
Sapphires for over 2,000 years.
• All varieties of Corundum are found in Sri Lanka including the
"PADPARADSCHA" which is unique to the island.
• Main deposits (gem gravels) in the Ratnapura district, about
100 km S.E. of Colombo, and Elahera district (115 km NE of
Colombo).
• Rubies are typically more pinkish (could be referred to as pink
sapphire in some cases) than those of Burma or Thailand.
Characterized by 1.) sparse, long, rutile inclusions, and included
zircons with radiation halos. 2.) give off a strong orange-red in
long u.v. light. and 3.) exceptional star stones.
• The Sri Lankan gem gravels also produce zircon,
tourmaline, peridot, quartz, garnet, feldspar and a number
of other stones.
•Mining in Sri Lanka is mainly alluvial with gem deposits
found not only in present river systems but also below rice
paddies where ancient rivers once flowed.
• The depth of the gem gravel or "ILLAM" varies from 3m
to 20m to as much as 40m at Pelmadulla.
• The search for gems is a highly speculative operation and
is usually carried out by a group of native workmen on a
share basis. 1/5th goes to the owner of the land, 1/5th to
the financier and the rest goes to the workers.
Traditional gem mining in Sri Lanka
Mining areas
around Elahera
Open-pit mine in
the Elahera area
http://www.cigem.ca/srilanka/sri.html
The gem-bearing level
has been reached
Active open-pit mine
http://www.cigem.ca/srilanka/sri.html
The miners are extracting the
gem-bearing gravel (illam).
Washing off the illam to
filter out the gems.
http://www.cigem.ca/srilanka/sri.html
The washing area is often
separated from the mining
area.
Washing the gem gravel
in baskets
http://www.cigem.ca/srilanka/sri.html
Sapphire Deposits of Australia
Queensland (1870) : Anakie and Lava Plains districts;
New South Wales (1960) : Glenn Innes and Inverell districts
• Gem dirt (alluvium) at the surface, to 50 ft. thick atop
weathered basalt.
• Anakie noted for fine yellows, also some very fine blue but
most has been characterized as "inky" (too dark) or strongly
dichroic dark blue and green; some production of pink and
orange as well.
• Dark sapphires are bought by Thai dealers and others who
lighten the color by heat treatment.
• Currently a major producer (50-70% of world production in
1990).
Sapphire Deposits of USA
MONTANA : Missouri River, NE of Helena, also Yogo Gulch,
near Utica
• Mined (Missouri river gravels) intermittently from 1865-present.
• Sapphires usually quite small, well-rounded or flat, and of a pale
blue or blue-green color.
• Yogo Gulch blue sapphire are said to rival Kashmir for color
• Yogo Gulch mine is in 2-8' wide dike that cuts limestone.
• Hard rock mining techniques and American labor makes mining
relatively expensive, less economic than East Asian counterparts.
• Geological surveys indicate a minimum of 28 million carats are
still in the ground, making this one of the largest proven deposits
in the world.
Sapphire from the Missouri River in Montana
Sapphire Deposits of Tanzania
•Umba River Valley near Kenyan border; since 1962.
• Sapphire in a "corundum pipe" (dike?, basalt flow?)4
miles in diameter.
• According to one source, the market in "East African"
corundum was cornered in 1965 by a group of dealers;
most rough still uncut.
• Noted for past production of fine orange-pink, deep
purples, dark, untreated golden yellows, and color-change
( i . e . a l e x a n d r i t e - l i k e ) s a p p h i r e s.
Sapphire Deposits
of
Madagascar
The discovery of
sapphires in
Madagascar is
relatively recent.
The first report of the
existence of this
beautiful gem was in
1952 when a French
geologist noted the
presence of small
sapphire crystals.
In 1982 local traders
offered the first
commercial packages
and a disorganized
rush ensued.
There are three distinct types of layers:
•Layers found in metamorphic rock. These being
primarily found in the northern parts of Madagascar
(Anivorano), in the central part (Antanifotsy,
Faratsiho and Moramanga).
•Layers of alluvial deposits, which are located in
the regions of Ranohira, Ilakaka, Bezaha and
Sakaraha (the southwastern part).
•And the layers in marble, which are located mostly
in the south (Andranodambo). The marble being of
a limestone derivative rich in aluminum oxide.
• Sapphire district in northern Madagascar has significant
quantities of sapphires, many of which were produced by
artisanal miners in the most primitive of methods. Some
stones are of large sizes, 5 gram to 20 gram (25 to 100 carat
sic), being common.
• In the early nineties, deposits were discovered in the
southern part of Madagascar (Andranodambo).
Sapphires from Antsiranana
Province, Northern Madagascar
Dietmar Schwarz, Jan Kanis, and
Karl Schmetzer
Gem& Gemology,Fall 2000,
Volume 36 Issue 3
Since 1996, large quantities of yellow to
blue sapphires have been recovered from
alluvial deposits derived from basaltic
rocks in northern Madagascar. The crystal
morphology, internal growth patterns,
mineral inclusions, absorption spectra, and
trace-element contents of these northern
Madagascar sapphires are typical of
“basaltic-magmatic” sapphires.
Comparison of the properties of these
sapphires to those of sapphires from
different basaltic sources reveals no
significant differences. The northern
Madagascar sapphires are distinct from
those from Andranondambo, a skarnrelated deposit in southeastern
M a d a g a s c a r.
http://www.gmrcorp.com/
The biggest rush on
the island however,
was caused by the
discovery in 1995 of
blue sapphires in the
northern part of the
island (Anivorano)
of medium
"Ceylon" quality.
Then very fine blue, pink, blue-violet, violet, purple,
orange and yellow sapphires were discovered from a new
alluvial deposit in the south-west, in Ilakaka, at 80 Km
from Sakaraha or 210 Km from Tulear, 3 hours drive.
The Ilakaka booming city.
Natives coming from all over
the island set up very
precarious shelters, hoping to
rapidly discover the magic
stone and therefore, move to
another way of life
Ilakaka area: flat, vast and basically free of trees
There are an estimated 300,000 hand-miners in the
Ilakaka area working in the field at present day.
The booming community in Ilakaka has sprung up
within 3-6 months around the sapphire mining.
They use shovels and buckets to excavate their
digging-holes. The gravel is loaded into bags and
carried long distances to the nearest water-source for
processing.
They are digging on the surface deposits, which are
extremely rich. Some adventurers dig up to 15 meters
below the surface, risking their lives every second.
• The mineralization of the sapphire (blue, violet, pink
and translucent) and the accompanying minerals
(zircon, spinel, garnet, topaz and chrysoberyl) are
found in the upper and lower terraces.
• The layer commonly known as "lalambato" in the
region, is a layer of stones of many different sizes
mixed in with other blocks of rock of various types and
medium-grain sand.
• The useful minerals are mostly concentrated below
the layers consisting of blocks of rock.
Hand-miners digging-holes, up to 15 meters below the
surface, tremendous risk to try to get rich quick.
http://www.gmrcorp.com/page/ilakaka.html#
Sapphire Deposits
of
North Madagascar
http://www.royalgemscorp.com/
Test digging showed
sapphire formation with
limestone and basalts.
Magnificent rough sapphire from Northern Madagascar.
38 grams, 190 carats, field cost $3,000 U.S., estimated
value when cut $50,000
http://www.royalgemscorp.com/
Larger sizes of rough sapphire before heat treatment
http://www.royalgemscorp.com/
Heat treated opaque grade, cuts into cabochon star.
http://www.royalgemscorp.com/
Average grade melee of heat treated and cut sapphires.
Sapphire from Helena,
Montana (El Dorado Bar)
UNITED STATES
Montana produces sapphires as fine as any in the world. Not far from Utica,
Montana, a sapphire-producing lamproite dike cuts through the country rock for
almost five miles. Discovered by a prospector, Jake Hoover, in 1895, the
Yogo Gulch mine went on to produce hundreds of thousands of carats of
exquisitely-clean blue gemstones. Most are alluvial deposits such as those along
the Missouri River near Helena, or Dry Cottonwood Creek near Butte. Currently,
the largest sapphire production is coming from the Gem Mountain area near
P
h
i
l
i
p
s
b
u
r
g.
Many of the Montana sapphire fields have been open to amateur
collectors on a fee basis. El Dorado Bar is an ancient gravel bar
lying above the Missouri River not far from Helena, Montana. To
find sapphires at this location the collector first screens the gravel to
remove over-sized and under-sized materials (Most sapphires at
this site are larger than one-sixteenth of an inch, and smaller than
one-quarter of an inch in diameter). The screened gravel is then
moved to a suitable water source where a heavy concentrate is
made by either mechanical or hand jigging. The jigged concentrate
is then hand sorted in the hope of finding gem sapphire.
Digging for Sapphires at El Dorado Bar, Montana
A
B
A.) Digging and screening the sapphire-bearing gravel to remove the over-sized
rock and under-sized sand: El Dorado Bar, Montana
B.) Jigging the size-classified gravel to concentrate the sapphire, garnet and other
heavy minerals toward the bottom center of the boxed screen.
After the sapphire-bearing gravel has been concentrated by
jigging in water, the gravel is flipped on a table and carefully
hand sorted to identify the waterworn sapphire crystals. Most
sapphires from this area are a pastel blue or blue-green color,
but vibrant purple, pink and even red stones have been found.
The rough sapphire crystals and fragments from El Dorado Bar
are generally less than 5 carats in weight, but the clarity of the
g e m m a t e r i a l i s v e r y g o o d.
A
B
A.) Picking through the concentrated gravel for gem sapphire: El Dorado Bar,
Montana
B.) Typical waterworn sapphire crystals (note the hexagonal cross-section of
some pieces) from El Dorado Bar, Montana
A 3.5 Carat Faceted Sapphire from El Dorado Bar, Montana
Sapphire from Gem Mountain
(Rock Creek Area), Montana
UNITED STATES
Sapphire was first discovered in Montana in the late 1800's by
gold miners working the alluvial gravels of the Missouri River
near Helena. In 1892 gold prospectors discovered the Gem
Mountain sapphire deposit; one of the largest sapphire deposits
in the world. The famous Sapphire and Anaconda Gulches at
Gem Mountain were so rich they were mined exclusively for
gemstones. Since 1893 this mine has produced a reported
180 m i l l i o n c a r a t s o f s a p p h i r e.
Sapphires were mined at Gem Mountain continuously from the turn
of the century until the second world war. It wasn't until modern heat
treatment processes evolved that Montana sapphire production
skyrocketed. In 1991 a young state senator from Minnesota, Greg
Dahl, began acquiring mineral rights in the Rock Creek area. In
1994 he purchased the Gem Mountain sapphire deposit. In
1994 Dahl's company, American Gem Corporation, went public.
Since then the corporation has done a great deal of discovery work
on their properties, they have completed construction of a new plant
and mine on the Anaconda Bench on Gem Mountain, and have
pursued an aggressive expansion plan for production, cutting, and
s a l e
o f
f i n e
s a p p h i r e s.
The gemstones from this location are relatively small, but their color
and clarity are extremely fine. Colors include red, orange, yellow,
pink, green, blue, and many combinations of those colors. Many
crystals that do not naturally possess good color or clarity are heat
treated under carefully controlled conditions to improve the
appearance of the finished gemstones. Precambrian and Tertiary
deposits around Gem Mountain have been eroded to release and
bury the sapphire crystals under layers of gravel. The gravels and
sands that contain the sapphire consist of quartz, sandstone, chert,
dolostone, mafic volcanics and intrusives, and andesite and rhyolitic
rock fragments. For many years portions of the Gem Mountain
sapphire deposit were open to amateur collectors on a fee basis (At
o n e t i m e i t c o s t $60 p e r p e r s o n p e r d a y ! ).
The Gem Mountain stones display a remarkable range of colors including blue,
green, pink, and gorgeous yellows and oranges. Further stimulating the sapphire
"boom" in Montana is the application of advanced heat-treating technology that can
remarkably improve the clarity and color of many Montana stones (Don't get upset:
heat treatment has long been a standard practice in Thailand to turn ugly Sri Lankan
g u e d a s a p p h i r e i n t o f i n e b l u e g e m m a t e r i a l. )