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Anahi Ametrine Mine of Bolivia

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1 Anahi Ametrine Mine of Bolivia
Ametrine is a variety of quartz that contains both amethyst and citrine sectors in the same crystal. Both amethyst and citrine are colored by small amounts of iron (approx. 40 parts per million). Amethyst color develops when iron-containing quartz is exposed to ionizing radiation. In nature, gamma rays from the decay of potassium-40 are the most likely source of ionizing radiation. The model currently accepted is that radiation oxidizes Fe3+ to Fe4+. Citrine color is from Fe3+. The properties of the Fe3+ spectra suggest that the Fe3+ ions are aggregated and hydrated in clusters of unknown size. The only significant source of natural ametrine is the Anahí mine, in eastern Bolivia.

2 Anahí mine, in eastern Bolivia, iis operated by Minerales y Metales del Oriente, S.R.L., Santa Cruz, Bolivia, and employs about 70 workers at the mine site. The ametrine occurs in veins in a dolomitic limestone. It is the source of all the natural ametrine currently on the world's market.

3 MINING AND PROCESSING Actual mining the Anahí Mine is underground, tunnels follow the irregular veins and shafts are constructed for ventilation and transportation. Traditional mining methods are applied: drilling, blasting and removal of mine run and barren host rock, however no explosives are utilized when the mineralized structure has been reached, extraction of gem crystals is done by hand.

4 CAMP Mine Entrance

5 A 4 x 3 x 1 meter cavern of crystals was discovered in 1999
A 4 x 3 x 1 meter cavern of crystals was discovered in Note the miner for scale

6 Another view of the gem pocket.

7 The sorting hut where the production is washed and sorted
A stock of large crystals awaiting shipment at the mine.

8 The Anahí mine run production is bagged at the mine site and transported to M&M’s processing facility in Santa Cruz. The material is trucked from the mine site to Lake Mandioré, then by boat to Puerto Suarez and finally by train to Santa Cruz. A total distance of some 800 km. The processing of the mine run involves different operations, depending on the quality of raw materials and the areas from where they have been mined. These processes may include: high pressure water washing, hammering, sawing, performing, calibrating, faceting and polishing. Quality control in every stage of the processing is strictly practiced. All products are carefully graded according to color depth and size, thus the end product leaving M&M’s works is very uniform and quality can be repeated every time.

9 Many crystals are trimmed and quality controlled, only the gem quality interior portions are saved.

10 Here is a 5 cm clear interior portion of a crystal.
Stockpiled bags of trimmed crystals in Puerto Suarez, Bolivia, awaiting shipment to cutting centers.

11 The best quality production from the mine is used for faceted ametrine, amethyst, and citrine. Some specimen material and ametrine slabs are also produced. Mine run material is used for colorful carving.

12 AMETHYST Color due to small amounts of Fe distributed in layers parallel to rhombohedral faces Some strongly dichroic e.g. reddish violet to pale blue "Siberian" = dark purple; "Rose-of-France" = pale purple to pink. Principle sources are Brazil and Uruguay, as crystals lining cavities in lava flows. Also found in pegmatite veins. Fine U.S. material rare; from Maine, New Hampshire, N. Carolina, Colorado, Wyoming.

13 Amethyst Deposits of Four Peaks, Arizona. USA.
Approximately 60 miles northeast of Phoenix Arizona, high on a rugged mountain called Four Peaks, is located one of the United States premier amethyst locations. From a private claim located at the end of a steep and rocky jeep and foot trail come brilliantly colored amethyst crystals. Ugly hematite encrustations on fist-sized crystal points hide vibrant purple amethyst hearts. Like other gem locations, amethyst from this mine varies greatly in color and quality, but the best material displays the rich deep reddish-purple color characteristic of the highly prized Siberian gems.

14 Amethyst druse and individual crystal points from Four Peaks, Arizona
Amethyst druse and individual crystal points from Four Peaks, Arizona. The large crystals are often covered with layers of hematite and secondary growths of microscopic quartz crystals.

15 Amethyst Deposits of Petersen Peak, California, USA. Petersen Peak spans the California- Nevada border and is situated approximately 40 miles northwest of Reno, Nevada. The location is famous for large amethyst scepter crystals. There are many quartz crystal mining claims on Petersen Peak. Some are open to collecting on club-sponsored field trips, others are open on a fee basis.

16 The photo on the left was taken at the beginning of the dirt access road leading to the quartz crystal collecting area (The area within the blue box). The mountain is covered by a number of claims, some of which are open to collectors on a fee basis or by permission granted for club-sponsored field trips. The access road degrades into a 4WD track as it nears the mountain. The trail becomes slick and impassable after heavy rain so collecting is best attempted during the dry summer and fall months.

17 The photograph to the left was taken at the western base of Petersen Peak. Quartz crystals can be found loose in the lower talus slope or embedded in pockets in quartz veins in the weathered bedrock. A a portion of Petersen Peak being worked commercially for mineral specimens. The mountain consists of granite that has been heavily fractured. The fractures were later filled by infusion of hydrothermal solutions. In some areas the fractures were sufficiently large to permit quartz to form large, clear, terminated crystals. Subsequent periods of infusion and crystallization led to scepter crystals; some of which contain phantoms and smoky or amethyst coloration.

18 Spectacular scepter specimens, some over 16 inches in length, have come from this particular mine. The granite area being worked is close to the surface, has been heavily weathered, and the bedrock can be ripped and moved by backhoe to expose the abundant quartz veins and pockets.

19 These specimens were removed from a pocket in a quartz vein and have not suffered the abrasion typically seen on "floater" crystals found loose in the soil. Scepter crystals result from a second phase of crystal growth on a previously formed quartz crystal "stalk." The terminal quartz is often a beautiful amethyst color.

20 Commercial Oval cut: 5.98 ct., 14.5 x 11.1 x 8.0 mm, VVS, $30.00
NOTE: Too light in color to be called amethyst, but an exceptionally clean and bright gem. Minuet Cut: ct., VS, 20.2 x 20.2 x mm, $243.84

21 Amethyst Deposits of Crystal Park, Montana, USA. Crystal Park is located in the Pioneer Mountains at an elevation of 7,700 feet, approximately 70 miles by road from Butte, Montana. The site is under claim to the Butte Mineral and Gem Club and is jointly maintained and supervised by the club and the Beaverhead National Forrest. Because it yields exceptionally well formed quartz and amethyst scepter crystals, this site has been a favorite with amateur collectors for many years. This site is strictly reserved for amateurs; the length of stays are limited, and crystals can be collected using only hand tools.

22 Shown on the left are two scepter crystals: one is amethyst, the other shows a fine pattern of smoky color banding resulting in a scepter with "phantoms." End Cut: 6.78 ct., x 9.9 x mm, VS, $101.70

23 QUARTZ : var. rock crystal
Sometimes called "diamond" e.g. "Herkimer Diamonds", "Pecos Diamonds" Carved into objects, spheres (e.g. crystal balls) Major producer Brazil; U.S. near Hot Springs, AK, upstate, NY Recommended Reading: QUARTZ, and OTHER MINERALS ON THE OUACHITA NATIONAL FOREST: QUARTZ By: John C. Nichols, Forest Geologist

24 AGATE Blue Agate Nebraska State Gem Prairie Agate Nebraska State Rock
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