Gemstone Exploration & Mining

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[email protected] [email protected] Geologist Geologist & & Gemological Gemological Sciences Sciences By By S.G SURENDER S.G SURENDER SOMIKA S.P.R.L SOMIKA S.P.R.L

Transcript of Gemstone Exploration & Mining

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GeologistGeologist &&

Gemological Gemological SciencesSciences

ByBy S.G S.G SURENDERSURENDER

SOMIKA S.P.R.LSOMIKA S.P.R.L

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Resources are not; they become. --- E.S Zimmerman

“A proper appreciation of mineral resources may be the

greatest service we as geologist can perform for our

society and country”.---E.L Chile.

Resources are not; they become. --- E.S Zimmerman

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IntroductionIntroduction Nearly 4000+ varieties of minerals are identified in Nearly 4000+ varieties of minerals are identified in

nature; only a few are referred as nature; only a few are referred as gem mineralsgem minerals due to their exceptional qualities and properties. due to their exceptional qualities and properties.

Gems have been a part of human history for more Gems have been a part of human history for more than 5000 years. Throughout the ages gemstones than 5000 years. Throughout the ages gemstones have been seen as representations of wealth, have been seen as representations of wealth, power and symbols of supremacy. power and symbols of supremacy.

Gem minerals are usually hard and relatively free Gem minerals are usually hard and relatively free from cleavage and occur as transparent crystals, from cleavage and occur as transparent crystals, with few exception such as opal, fluorite etc.,with few exception such as opal, fluorite etc.,

Thus gemstones are artificially polished fragments Thus gemstones are artificially polished fragments (faceted or with smooth curved finish) that are (faceted or with smooth curved finish) that are used for decorative purposes and personal used for decorative purposes and personal adornment.adornment.

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The study of gemstones is an accepted part The study of gemstones is an accepted part of of Mineralogy .Mineralogy .

A gem is a naturally occurring material A gem is a naturally occurring material desirable for its beauty, valuable in its desirable for its beauty, valuable in its rarity, and sufficiently durable to give rarity, and sufficiently durable to give lasting pleasure. lasting pleasure.

Gemology- is the subject matter the Gemology- is the subject matter the scientific study of gemstones (from scientific study of gemstones (from its genesis to valuation). its genesis to valuation).

Lapidary – is the science of cutting and Lapidary – is the science of cutting and polishing a gem mineral.polishing a gem mineral.

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Over the centuries numerous magical and Over the centuries numerous magical and medicinal properties were attributed to medicinal properties were attributed to precious stones. precious stones.

In Ayurveda (Indian System of Medicine) In Ayurveda (Indian System of Medicine) Audbhida-Extract form Plants,Audbhida-Extract form Plants, Jangama-Extract from AnimalsJangama-Extract from Animals Parthiva-Extract from Metals and MineralsParthiva-Extract from Metals and Minerals

Different types of BHASMA such as Hirka Different types of BHASMA such as Hirka Bhasma (Diamond), Manikya Bhasma (Ruby), Bhasma (Diamond), Manikya Bhasma (Ruby), Swarna Bhasma (Gold), Abhraka Bhasma Swarna Bhasma (Gold), Abhraka Bhasma (Mica) etc. were prepared from metals and (Mica) etc. were prepared from metals and minerals to cure variety of diseases.minerals to cure variety of diseases.

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• Gemstones are classified based on certain Gemstones are classified based on certain assertive aspects /parameters. viz.,assertive aspects /parameters. viz.,

CLASSIFICATION OF GEMSTONESCLASSIFICATION OF GEMSTONES

TYPES

Imitation

Inorganic

Organic

Synthetic

1.

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2. Based on 2. Based on AvailabilityAvailability

Availability

Precious Semi-Precious

The precious and semi precious classification of gemstones is largely based on the Market (Demand and Supply); it is an arbitrary classification based on local availability.

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3. 3. OTHER TYPE OTHER TYPE CLASSIFICATIONSCLASSIFICATIONS

Optical Characters

Crystal Structure

Chemical Composition

Durability

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Physical and Optical properties are the Key elements to distinguish various types of gemstones

Optical Properties

• Refractive Index• Dispersion• Pleochroism• Interference Figures• Optic Axis• Optic Sign

Physical Properties

• Color *• Streak• Habit• Cleavage, Parting Plane,

Fractures.• Lustre (Reflectivity)• Diaphaneity (Transmisivity)• Hardness*• Specific Gravity• Tenacity & Toughness• Chatoyancy • Asterism

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COLOUR CAUSING TRANSITION METAL ELEMENTS IN IDOCHROMATICIDOCHROMATIC GEMS

Chromium Green UvaroviteIron Green

Redblue

PeridotAlmandinelazurite

Manganese Pinkorange

Rhodocrosite, RodoniteSpessartite

Copper BlueGreenRed

Azurite, Turquoise, ChrysocolkMalachite, DioptaseCuprite

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COLOUR CAUSING TRANSITION METAL COLOUR CAUSING TRANSITION METAL ELEMENTS IN ELEMENTS IN ALLOCHROMATICALLOCHROMATIC GEMS GEMSChromium Green

Red

Emerald, Gromularite, Cr-tourmaline, Cr-Chalcedony, AlexandriteRuby, Spinal, Topaz, Alexandrite

Chromium + Iron

RedGreen

Pyrope Jadeite, Diopside, Synthetic OPX

Cobalt Blue Syn. Spinel, Syn. Quartz & Glass.

Iron Green

Yellow

BlueViolet –

blueRed

Aquamarine, Tourmaline, Green Sapphire, Chrysoberyl, Epidote. Yellow sapphire, Citrine, Chrysoberyl, Orthoclase, Soundmen.Aquamarine, Spinal. Tanzanite, Iolite. Eudialyte

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Iron + Titanium

Blue Sapphire

Manganese PinkYellow - GreenViolet

Rhodonite, Rhodocrosite, Piedmmtite, Syn. OPX.AndalusiteTremolite

Nickel Green Syn. Olivine.

Vanadium GreenBlue – Green

to Purple – red

Blue

V- EmeraldV- GrossulariteV- SapphireSyn. CPX

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The main parameters of The main parameters of GEMSTONE GEMSTONE

•BEAUTY BEAUTY

•RARITYRARITY

•DURABILITYDURABILITY

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Gemstones are measured in terms Gemstones are measured in terms metric caratmetric carat, which is , which is equivalent to 200mg (1 carat is equivalent to 0.2 grams). A equivalent to 200mg (1 carat is equivalent to 0.2 grams). A CARAT CARAT is again sub divided into hundred is again sub divided into hundred POINTS (2mg). POINTS (2mg).

Gem Testing & Gemologist Certificate:Gem Testing & Gemologist Certificate: Gemstones are Gemstones are identified based on their properties (P & O) along with few identified based on their properties (P & O) along with few instruments (Chelsea filter, Refractrometer, Gemological instruments (Chelsea filter, Refractrometer, Gemological Microscopes, Hardness Pencils etc.). Microscopes, Hardness Pencils etc.). The efficiency of a The efficiency of a gemologist lies in identifying a stone without subjecting it gemologist lies in identifying a stone without subjecting it to any kind of destructive tests.to any kind of destructive tests.

A certificate from a certified GEMOLOGIST would certainly yield to A certificate from a certified GEMOLOGIST would certainly yield to its market, through proper identification and valuation.its market, through proper identification and valuation.

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Valuation of GemstonesValuation of Gemstonesvaluation of gemstones is done through valuation of gemstones is done through

thethe 4 C’s precept.4 C’s precept.

CColorolor

CClaritylarity

CCut &ut &

CCarat Weightarat Weight

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Exploration: Refers to geological, geochemical Exploration: Refers to geological, geochemical and geo-physical field work and complimentary and geo-physical field work and complimentary laboratory studies directed to the discovery of laboratory studies directed to the discovery of workable mineral concentration.workable mineral concentration.

Gemstone occurrence is a very rare and a Gemstone occurrence is a very rare and a transient geologic feature; once exhausted transient geologic feature; once exhausted cannot be replenished cannot be replenished with in a short time.with in a short time.

Diverse minerals are formed at different Diverse minerals are formed at different geological environments in different rock types, geological environments in different rock types, viz Igneous, Sedimentary and Metamorphic viz Igneous, Sedimentary and Metamorphic rocks, also few organically.rocks, also few organically.

EXPLORATIONEXPLORATION

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For Example:For Example: Diamonds in Kimberlites (Ultra-mafic HTHP)Diamonds in Kimberlites (Ultra-mafic HTHP)

Beryl in PegmatitesBeryl in Pegmatites

Quartz in Felsic rocks Quartz in Felsic rocks

Peridot in Ultra mafic rocksPeridot in Ultra mafic rocks

Garnets in Metamorphic RocksGarnets in Metamorphic Rocks

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The principle role of an The principle role of an Exploration GeologistExploration Geologist

Essential Mineral

Gem Quality Emerald Crystal in Quarts and

Dolomite.

Almandine Garnet embedded in Schist

Host Rock

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BERYL BERYL By the name Beryl is a Silicate of Beryllium and By the name Beryl is a Silicate of Beryllium and

Aluminum; is the principle store of beryllium in the Aluminum; is the principle store of beryllium in the earth's crust. In its rare gem form it is notable for a earth's crust. In its rare gem form it is notable for a variety of vivid allochromatic color with vivid variety of vivid allochromatic color with vivid names.names.

Chemical Composition: Chemical Composition: BeBe33AlAl22SiSi66OO1818 • Crystal System: Crystal System: HexagonalHexagonal • Habit: Usually well formed hexagonal prisms, either Habit: Usually well formed hexagonal prisms, either

flattened or elongate, with pinacoidal terminations. flattened or elongate, with pinacoidal terminations. • Hardness: Hardness: 7.5-87.5-8 • Specific Gravity: Specific Gravity: 2.67-2.782.67-2.78 • Refractive Index: Refractive Index: 1.57-1.591.57-1.59

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Distinguishing PropertiesDistinguishing Properties• Low R.ILow R.I• Low S.GLow S.G**• DichroismDichroism• Low BirefringenceLow Birefringence

Distribution:Distribution:Common rocks that hosts Beryl are Common rocks that hosts Beryl are GranitesGranites

and and PegmatitesPegmatites. . Vugs in these rocks may consists of fine Vugs in these rocks may consists of fine

crystals of Beryl, Tourmaline, Topaz, crystals of Beryl, Tourmaline, Topaz, Spodumene etc.Spodumene etc.

Mineralization occurs, where the Pegmatites Mineralization occurs, where the Pegmatites intruding the basis and ultra-basic rocks yield intruding the basis and ultra-basic rocks yield important gem deposits*. important gem deposits*.

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Varieties of BerylVarieties of BerylSl No. Variety Color Cause

1 Goshenite Uncolored No Specific Cause2 Heliodor Yellow UVCT (O2-- Fe3+)3 Aquamarine Blue IVCT (Fe2+ Fe3+)4 Green Beryl Green UVCT+IVCT5 Morganite Pink Mn2+

6 Bixbite Red Mn2+

7 Maxixe Blue Color Centre (No3)8 Maxixe -typed Blue Color Centre (Co3)9 Emerald Green

(Velvety)Cr3+/ V3+

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EmeraldEmerald

Velvety green variety of Velvety green variety of Beryl if known as Emerald.Beryl if known as Emerald.

CC: BeCC: Be33(Al,Cr)(Al,Cr)22 Si Si66OO1818

The typical velvety green The typical velvety green hue of emerald is distinctive. hue of emerald is distinctive.

The green shade of emerald The green shade of emerald caused on the account of caused on the account of chromium/vanadium chromium/vanadium impurity.impurity.

RI- 1.578-1.584;RI- 1.578-1.584; SG- 2.72SG- 2.72

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Aquamarine Aquamarine

• Palish blue, light blue green Palish blue, light blue green variety of beryl is known as variety of beryl is known as aquamarine. aquamarine.

• Sky blue color stone is the Sky blue color stone is the most valuable aquamarine.most valuable aquamarine.

• They exhibits a greenish They exhibits a greenish blue tinge due the blue tinge due the phenomenon of phenomenon of pleochroism.pleochroism.

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• Golden colored variety of Golden colored variety of beryl is known as Golden beryl is known as Golden beryl. beryl.

• The yellow color is due to the The yellow color is due to the presence of Fepresence of Fe3+ 3+ in a in a concentration of over 1%. concentration of over 1%.

• Yellow green variety of beryl Yellow green variety of beryl is known as Heliodor. is known as Heliodor.

• Yellow green olive color is the Yellow green olive color is the typical character of Heliodor. typical character of Heliodor.

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• Bixbite is an extremely rare Bixbite is an extremely rare variety of beryl. variety of beryl.

• Bixbite is strong ruby red or Bixbite is strong ruby red or violet red in color. violet red in color.

• Very rarely found, have an Very rarely found, have an different genesis to that of different genesis to that of found in pegmatite. In found in pegmatite. In extrusive magmatic rocks. extrusive magmatic rocks.

• The red color is due to the The red color is due to the presence of presence of Mn2+ is as an is as an impurity in their crystal impurity in their crystal structure. structure.

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Case Study:Case Study: Ndola Rural Emerald Ndola Rural Emerald Fields, ZambiaFields, Zambia

• Nolda –Rural Emerald field of the Zambian Republic Nolda –Rural Emerald field of the Zambian Republic represents a good source of easily mined emeralds. represents a good source of easily mined emeralds.

• To this day, many areas are a preserve of artisinal To this day, many areas are a preserve of artisinal miners. Lack of capital has lead to inefficient miners. Lack of capital has lead to inefficient exploration and exploitationexploration and exploitation. .

GEOLOGICAL SETUPGEOLOGICAL SETUP::• Zambia lies in between Zaire and the Zambian Zambia lies in between Zaire and the Zambian

cratons characterized geologically as being ancient cratons characterized geologically as being ancient mobile belt; comprising of Igneous, Sedimentary mobile belt; comprising of Igneous, Sedimentary and metamorphic formations of the Precambrian and metamorphic formations of the Precambrian age.age.

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• Mineralization in the Ndola Rural Emerald Fields Mineralization in the Ndola Rural Emerald Fields occurs where the occurs where the quartz-tourmaline-pegmatitequartz-tourmaline-pegmatite veins intrude the talc-chlorite-tremolite-magnetite veins intrude the talc-chlorite-tremolite-magnetite schist and alter the contact zone as biotite-schist and alter the contact zone as biotite-phaloghite rock, this alteration zone forms the phaloghite rock, this alteration zone forms the chief ore body.chief ore body.

Three distinct varieties of pegmatite are known in Three distinct varieties of pegmatite are known in the study area: the study area:

• 11stst Generation: Generation: initial feeder phase rich in quartz initial feeder phase rich in quartz and feldspar and contain minor fine grained and feldspar and contain minor fine grained tourmaline and not related to mineralization.tourmaline and not related to mineralization.

• 22ndnd Generation Generation: veins composed largely of : veins composed largely of tourmaline commonly associated with emerald tourmaline commonly associated with emerald mineralization.mineralization.

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• 33rdrd Generation Generation: composed of coarse quartz : composed of coarse quartz tourmaline (5-10 mm) always found in tourmaline (5-10 mm) always found in association with mineralization of emerald.association with mineralization of emerald.

• The distribution of emerald is very erratic; The distribution of emerald is very erratic; major emerald mineralization, rich in volume & major emerald mineralization, rich in volume & grade are associated with flat lying undulating grade are associated with flat lying undulating veins and number of vein intersects. veins and number of vein intersects.

• Granitic emplacement characterized by Granitic emplacement characterized by

intensive pulses of pegmatite activity rich in intensive pulses of pegmatite activity rich in minerals B, Be, F etc intruding through the well minerals B, Be, F etc intruding through the well developed shear system appears to be the developed shear system appears to be the cause. cause.

• Crystallization of beryl appears to have taken Crystallization of beryl appears to have taken place during metasomatic reaction between place during metasomatic reaction between the slow cooling pegmatite (3the slow cooling pegmatite (3rdrd Generation) Generation) and the surrounding schist.and the surrounding schist.

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CONCLUSIONCONCLUSION

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The role of a The role of a GEOLOGISTGEOLOGIST in the field of in the field of Gemological Science:Gemological Science:

• Prospecting of a gem deposit.Prospecting of a gem deposit.• Establishing the properties of gem minerals.Establishing the properties of gem minerals.• Identification of stone in cut and rough form.Identification of stone in cut and rough form.• Enhancement of stone (synthesis).Enhancement of stone (synthesis).• Minerals grow in a definite physico-chemical Minerals grow in a definite physico-chemical

environment, thus a environment, thus a geologistgeologist is better able is better able to understand and reason out the to understand and reason out the paragenesis of a mineral or gemstone. It is paragenesis of a mineral or gemstone. It is easy to distinguish a natural stone from its easy to distinguish a natural stone from its synthetic counterpart.synthetic counterpart.

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Among the natural green gemstones Among the natural green gemstones hydrogrossular, dematoid, chrome hydrogrossular, dematoid, chrome

diopside, chrome-tourmaline, diopside, chrome-tourmaline, peridot, peridot,

may be confused for emerald.may be confused for emerald.

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““Gems are the flowers of the Gems are the flowers of the mineral kingdom, exquisite mineral kingdom, exquisite products of Nature which have products of Nature which have given a great deal of given a great deal of satisfaction, to those who behold satisfaction, to those who behold them. They have fascinated them. They have fascinated mankind for thousands of years”.mankind for thousands of years”.

-Dr. B.P Radhakrishna-Dr. B.P Radhakrishna

GEOLOGY ILLUMINATES THE PAST , GEOLOGY ILLUMINATES THE PAST , SUSTAINS THE PRESENT AND PROMOTES SUSTAINS THE PRESENT AND PROMOTES

THE FUTURE.THE FUTURE.

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References:References:• Bateman A.M., Tensen M.L., (1982) Economic Bateman A.M., Tensen M.L., (1982) Economic

Mineral Deposits, Third Edition, John Willy & Sons Mineral Deposits, Third Edition, John Willy & Sons pp/pp/

• Curizio Cipriani., Alessandro Borelli., (1992) Gems Curizio Cipriani., Alessandro Borelli., (1992) Gems and Precious Stones, Simon & Schuster Inc, pp. 10-and Precious Stones, Simon & Schuster Inc, pp. 10-49, 138-149.49, 138-149.

• Emerald Deposit of Nolda, Zambia (1997), Emerald Deposit of Nolda, Zambia (1997), www. members.tripod.com/emerald/html.www. members.tripod.com/emerald/html.

• O. Von Knorring., (1970) Mineralogical and O. Von Knorring., (1970) Mineralogical and Geochemical Aspects of Pegmatites from Orogenic Geochemical Aspects of Pegmatites from Orogenic Belts of Equatorial and Southern Africa, African Belts of Equatorial and Southern Africa, African Magmatism and Tectonics, Oliver Boyd PublishersMagmatism and Tectonics, Oliver Boyd Publishers

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• Guilbert J.M., Park C.F., (1988) Ore Geology, W.H Guilbert J.M., Park C.F., (1988) Ore Geology, W.H Freeman Company, New York, pp. 487-511.Freeman Company, New York, pp. 487-511.

• Hall Cally., (1995) Gemstones, Dorling Kindersley Publ.Hall Cally., (1995) Gemstones, Dorling Kindersley Publ.

• Joel. E Arem., (1987) Color Encyclopedia of Gemstones, Joel. E Arem., (1987) Color Encyclopedia of Gemstones, Van Nostrand Reinhold Company, pp 1-20. Van Nostrand Reinhold Company, pp 1-20.

• Karanth R.V., (2000) Gems and Gemstone Industry in Karanth R.V., (2000) Gems and Gemstone Industry in India, Geological Society of India, pp. 1-56, 233-242.India, Geological Society of India, pp. 1-56, 233-242.

• Klein Cornelis., Hurlbut S Cornelis Jr., (1993) Manual of Klein Cornelis., Hurlbut S Cornelis Jr., (1993) Manual of Mineralogy, John Wiley & Sons, pp. 593-605.Mineralogy, John Wiley & Sons, pp. 593-605.

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??QUESTIONS QUESTIONS