Gemstone Exploration & Mining


Published on

Published in: Education, Business, Technology
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Gemstone Exploration & Mining

  1. 1. Geologist &Gemological Sciences By S.G SURENDER SOMIKA S.P.R.L
  2. 2. Resources are not; they become. --- E.S Zimmerman “A proper appreciation of mineralresources may be the greatest service we as geologist can perform for our society and country”. ---E.L Chile.
  3. 3. Introduction Nearly 4000+ varieties of minerals are identified in nature; only a few are referred as gem minerals due to their exceptional qualities and properties. Gems have been a part of human history for more than 5000 years. Throughout the ages gemstones have been seen as representations of wealth, power and symbols of supremacy. Gem minerals are usually hard and relatively free from cleavage and occur as transparent crystals, with few exception such as opal, fluorite etc., Thus gemstones are artificially polished fragments (faceted or with smooth curved finish) that are used for decorative purposes and personal adornment.
  4. 4.  The study of gemstones is an accepted part of Mineralogy . A gem is a naturally occurring material desirable for its beauty, valuable in its rarity, and sufficiently durable to give lasting pleasure. Gemology- is the subject matter the scientific study of gemstones (from its genesis to valuation). Lapidary – is the science of cutting and polishing a gem mineral.
  5. 5.  Over the centuries numerous magical and medicinal properties were attributed to precious stones. In Ayurveda (Indian System of Medicine) Audbhida-Extract form Plants, Jangama-Extract from Animals Parthiva-Extract from Metals and MineralsDifferent types of BHASMA such as Hirka Bhasma (Diamond), Manikya Bhasma (Ruby), Swarna Bhasma (Gold), Abhraka Bhasma (Mica) etc. were prepared from metals and minerals to cure variety of diseases.
  6. 6.
  7. 7. CLASSIFICATION OF GEMSTONES• Gemstones are classified based on certain assertive aspects /parameters. viz., 1. TYPESOrganic Imitation Inorganic Synthetic
  8. 8. 2. Based on Availability AvailabilityPrecious Semi-PreciousThe precious and semi precious classification ofgemstones is largely based on the Market (Demandand Supply); it is an arbitrary classification based onlocal availability.
  9. 9. 3. OTHER TYPE CLASSIFICATIONSChemical OpticalComposition Characters Durability Crystal Structure
  10. 10. Physical and Optical properties are the Key elementsto distinguish various types of gemstones Physical Properties Optical Properties • Color * • Refractive Index • Streak • Habit • Dispersion • Cleavage, Parting Plane, • Pleochroism Fractures. • Interference Figures • Lustre (Reflectivity) • Optic Axis • Diaphaneity (Transmisivity) • Optic Sign • Hardness* • Specific Gravity • Tenacity & Toughness • Chatoyancy • Asterism
  11. 11. COLOUR CAUSING TRANSITION METALELEMENTS IN IDOCHROMATIC GEMSChromium Green Uvarovite Iron Green Peridot Red Almandine blue lazuriteManganese Pink Rhodocrosite, orange Rodonite Spessartite Copper Blue Azurite, Turquoise, Green Chrysocolk Red Malachite, Dioptase Cuprite
  12. 12. COLOUR CAUSING TRANSITION METAL ELEMENTSIN ALLOCHROMATIC GEMSChromium Green Emerald, Gromularite, Cr-tourmaline, Cr-Chalcedony, Alexandrite Red Ruby, Spinal, Topaz, AlexandriteChromium Red Pyrope + Iron Green Jadeite, Diopside, Synthetic OPX Cobalt Blue Syn. Spinel, Syn. Quartz & Glass. Iron Green Aquamarine, Tourmaline, Green Sapphire, Yellow Chrysoberyl, Epidote. Yellow sapphire, Citrine, Blue Chrysoberyl, Violet – Orthoclase, Soundmen. blue Aquamarine, Spinal. Tanzanite, Iolite. Red Eudialyte
  13. 13. Iron + Blue SapphireTitaniumManganese Pink Rhodonite, Yellow - Rhodocrosite, Green Piedmmtite, Syn. OPX. Violet Andalusite Tremolite Nickel Green Syn. Olivine.Vanadium Green V- Emerald Blue – Green V- Grossularite to V- Sapphire Purple – red Syn. CPX Blue
  14. 14. The main parameters of GEMSTONE • BEAUTY • RARITY • DURABILITY
  15. 15.  Gemstones are measured in terms metric carat, which is equivalent to 200mg (1 carat is equivalent to 0.2 grams). A CARAT is again sub divided into hundred POINTS (2mg). Gem Testing & Gemologist Certificate: Gemstones are identified based on their properties (P & O) along with few instruments (Chelsea filter, Refractrometer, Gemological Microscopes, Hardness Pencils etc.). The efficiency of a gemologist lies in identifying a stone without subjecting it to any kind of destructive tests. A certificate from a certified GEMOLOGIST would certainly yield to its market, through proper identification and valuation.
  16. 16. Valuation of Gemstonesvaluation of gemstones is done through the 4 C’s precept. Color Clarity Cut & Carat Weight
  17. 17. EXPLORATION Exploration: Refers to geological, geochemical and geo-physical field work and complimentary laboratory studies directed to the discovery of workable mineral concentration. Gemstone occurrence is a very rare and a transient geologic feature; once exhausted cannot be replenished with in a short time. Diverse minerals are formed at different geological environments in different rock types, viz Igneous, Sedimentary and Metamorphic rocks, also few organically.
  18. 18. For Example: Diamonds in Kimberlites (Ultra-mafic HTHP) Beryl in Pegmatites Quartz in Felsic rocks Peridot in Ultra mafic rocks Garnets in Metamorphic Rocks
  19. 19.
  20. 20. T h e p r in c ip le r o le o f a n E x p lo r a t io n G e o lo g is t Hos t Roc k E s s e n t ia l M in e r a lG e m Q u a lit y E m e r a ld A lm a n d in e G a r n e tC r y s t a l in Q u a r t s a n d e m b e d d e d in
  21. 21. BERYL By the name Beryl is a Silicate of Beryllium and Aluminum; is the principle store of beryllium in the earths crust. In its rare gem form it is notable for a variety of vivid allochromatic color with vivid names. Chemical Composition: Be3Al2Si6O18• Crystal System: Hexagonal• Habit: Usually well formed hexagonal prisms, either flattened or elongate, with pinacoidal terminations.• Hardness: 7.5-8• Specific Gravity: 2.67-2.78• Refractive Index: 1.57-1.59
  22. 22. Distinguishing Properties • Low R.I • Low S.G* • Dichroism • Low BirefringenceDistribution:Common rocks that hosts Beryl are Granites and Pegmatites.Vugs in these rocks may consists of fine crystals of Beryl, Tourmaline, Topaz, Spodumene etc.Mineralization occurs, where the Pegmatites intruding the basis and ultra-basic rocks yield important gem deposits*.
  23. 23. Varieties of BerylSl No. Variety Color Cause 1 Goshenite Uncolored No Specific Cause 2 Heliodor Yellow UVCT (O2-- Fe3+) 3 Aquamarine Blue IVCT (Fe2+  Fe3+) 4 Green Beryl Green UVCT+IVCT 5 Morganite Pink Mn2+ 6 Bixbite Red Mn2+ 7 Maxixe Blue Color Centre (No3) 8 Maxixe -typed Blue Color Centre (Co3) 9 Emerald Green Cr3+/ V3+ (Velvety)
  24. 24. EmeraldVelvety green variety of Beryl if known as Emerald.CC: Be3(Al,Cr)2 Si6O18The typical velvety green hue of emerald is distinctive.The green shade of emerald caused on the account of chromium/vanadium impurity.RI- 1.578-1.584; SG- 2.72
  25. 25. Aquamarine• Palish blue, light blue green variety of beryl is known as aquamarine.• Sky blue color stone is the most valuable aquamarine.• They exhibits a greenish blue tinge due the phenomenon of
  26. 26. • Golden colored variety of beryl is known as Golden beryl.• The yellow color is due to the presence of Fe3+ in a concentration of over 1%.• Yellow green variety of beryl is known as Heliodor.• Yellow green olive color is the typical character of Heliodor.
  27. 27. • Bixbite is an extremely rare variety of beryl.• Bixbite is strong ruby red or violet red in color.• Very rarely found, have an different genesis to that of found in pegmatite. In extrusive magmatic rocks.• The red color is due to the presence of Mn2+ is as an impurity in their crystal
  28. 28. Case Study: Ndola Rural Emerald Fields, Zambia• Nolda –Rural Emerald field of the Zambian Republic represents a good source of easily mined emeralds.• To this day, many areas are a preserve of artisinal miners. Lack of capital has lead to inefficient exploration and exploitation.GEOLOGICAL SETUP:• Zambia lies in between Zaire and the Zambian cratons characterized geologically as being ancient mobile belt; comprising of Igneous, Sedimentary and metamorphic formations of the Precambrian age.
  29. 29. • Mineralization in the Ndola Rural Emerald Fields occurs where the quartz-tourmaline-pegmatite veins intrude the talc-chlorite-tremolite-magnetite schist and alter the contact zone as biotite-phaloghite rock, this alteration zone forms the chief ore body.Three distinct varieties of pegmatite are known in the study area:• 1st Generation: initial feeder phase rich in quartz and feldspar and contain minor fine grained tourmaline and not related to mineralization.• 2nd Generation: veins composed largely of tourmaline commonly associated with emerald mineralization.
  30. 30. • 3rd Generation: composed of coarse quartz tourmaline (5-10 mm) always found in association with mineralization of emerald.• The distribution of emerald is very erratic; major emerald mineralization, rich in volume & grade are associated with flat lying undulating veins and number of vein intersects.• Granitic emplacement characterized by intensive pulses of pegmatite activity rich in minerals B, Be, F etc intruding through the well developed shear system appears to be the cause.• Crystallization of beryl appears to have taken place during metasomatic reaction between the slow cooling pegmatite (3rd Generation) and the surrounding schist.
  31. 31. CONCLUSION
  32. 32. The role of a GEOLOGIST in the field of Gemological Science:• Prospecting of a gem deposit.• Establishing the properties of gem minerals.• Identification of stone in cut and rough form.• Enhancement of stone (synthesis).• Minerals grow in a definite physico-chemical environment, thus a geologist is better able to understand and reason out the paragenesis of a mineral or gemstone. It is easy to distinguish a natural stone from its synthetic counterpart.
  33. 33. Among the natural green gemstones hydrogrossular, dematoid, chromediopside, chrome-tourmaline, peridot, may be confused for emerald.
  34. 34.
  35. 35.
  36. 36. “Gems are the flowers of the mineral kingdom, exquisite products of Nature which have given a great deal of satisfaction, to those who behold them. They have fascinated mankind for thousands of years”. -Dr. B.P RadhakrishnaGEOLOGY ILLUMINATES THE PAST , SUSTAINS THE PRESENT AND PROMOTES THE FUTURE.
  37. 37. Re f e r e n c e s :• Bateman A.M., Tensen M.L., (1982) Economic Mineral Deposits, Third Edition, John Willy & Sons pp/• Curizio Cipriani., Alessandro Borelli., (1992) Gems and Precious Stones, Simon & Schuster Inc, pp. 10-49, 138-149.• Emerald Deposit of Nolda, Zambia (1997), www.• O. Von Knorring., (1970) Mineralogical and Geochemical Aspects of Pegmatites from Orogenic Belts of Equatorial and Southern Africa, African Magmatism and Tectonics, Oliver Boyd Publishers
  38. 38. • Guilbert J.M., Park C.F., (1988) Ore Geology, W.H Freeman Company, New York, pp. 487-511.• Hall Cally., (1995) Gemstones, Dorling Kindersley Publ.• Joel. E Arem., (1987) Color Encyclopedia of Gemstones, Van Nostrand Reinhold Company, pp 1-20.• Karanth R.V., (2000) Gems and Gemstone Industry in India, Geological Society of India, pp. 1-56, 233-242.• Klein Cornelis., Hurlbut S Cornelis Jr., (1993) Manual of Mineralogy, John Wiley & Sons, pp. 593-605.
  39. 39. ?