“All works of history are interim reports,what people did in the past is notpreserved in amber……Each generationlooks back and drawing from its ownexperience and presumes to find patternstat illustrate past and present”. -- John Noble Wilfred
Introduction“A mineral is defined as a naturally occurring homogenous solid with a definite chemical composition and highly ordered atomic structure”. Minerals with their intricate properties, that marks its presence in the industry.Diamond the mineral form of element carbon, the mere mention of its word fills the mind with multitude of concepts and images. Peerless “King of Gems” that glitters, dazzles that symbolizes purity and strength.
Diamond is indomitable the hardest substance known;with exceptional qualities that collectively makes it animportant social, industrial and scientific material. Diamond is likely one of the oldest thing that a man would posses; 3 million years in age; (two thirds the age of
Classification Bruton (1978), have classified diamonds into three major groups DIAMOND GEM INDUSTRIAL DIAMONDDIAMONDS STONES BORT* Shaped Rough Diamonds Stones * bort- Minutely and randomly crystallized and shapeless diamond extremely hard and has high abrasive value.
Properties and Uses Category Native Nonmetal, Mineral Chemical formula: Carbon, C Identification Color Most often colorless to yellow or brown. Rarely pink, orange, green or blue. Crystal habit: Octahedral, spherical or massive; Crystal system: Isometric Cleavage: Octahedral; perfect and easy Fracture: Conchoidal Mohs Scale: hardness10 Luster :Adamantine to greasy Refractive index: 2.417 Pleochroism: None; Streak: None; Specific gravity: 3.516–3.525 Fusibility: Burns above 800°C, melting point 3550 °C Solubility: Resistant to acids, but melts in hot steel Diaphaneity Clear to not Major varieties Ballas Spherical, radial structure, cryptocrystalline, opaque black Bort Poorly-formed, cryptocrystalline, shapeless, translucent, Carbonado Massive, microcrystalline, opaque black.
Due to its exceptional properties diamond is used for a variety of purposes, namely: Due to its hardness; diamond is either used as single crystals or finely ground powder are used in cutting abrading, polishing tools. (it is imbedded in another material and used as a tool or abrasive). Industrial diamond are extensively used in drill bits & cutting devices. Other applications include their use in mining, electronic, optical, thermal, machining, dentistry and medicinal industries. Scientific applications include radiation, photo detection, etc.
MARKET Of the several billion dollars of annual transaction in gems, 90% of the value are accounted for by diamonds. 80% Eighty percent of the diamonds mined annually are used in industry; 4 times that production is grown synthetically for industry - thats a total of over 500 million carats or 100 metric tons. Compared to most other gem minerals the percentage of gem quality crystals recovered is quite high in diamond. 20% of the diamond is of gem quality.
Brief Geology of Angola THE GEOLOGY OF ANGOLA IS RELATIVELYCOMPLEX, IMPERFECTLY KNOWN IN SPITE OF A BIGRECENT PROGRESS, THE FORMATIONS BEINGDISTRIBUTED PARALLEL TO THE COAST, NNW TO THENORTH, NNE TO THE SOUTH. The CrysTalline BasemenT; a Big parT of TheCounTry is formed By The preCamBrianBasemenT of The "Basis Complex", wiTh Twivery Big BaTholiThs of graniTe To The n. andTo The s. of The Cuanza. The exTreme ne is aparT of The very old Kasaï shield (2,500 myor more); a zone TheoreTiCally favoraBle ToThe KimBerliTiC inTrusions.
SAMPLING METHODSThe sampling methods vary from simple grab samples onexisting exposures to sophisticated drilling methods. Thedisposition and density of sampling must be adapted to eachplacer. The rule is: "A minimum of samples for a maximumof information.Existing ExposuresHand-Dug Excavations ( Pits & Trenches)Backhoe TrenchesBulldozer TrenchesChurn Drills
Other Machine-Dug Excavations Machine-dug excavations are shafts or pits that are dug using powered equipment such as large augers, bucket drills, or clamshell-type excavators. Digging shafts with the aid of powered equipment requires experienced operators and suitable machine access. Dry, stable ground is also needed for successful sampling operations when digging shafts and pits.
Some of the Special Problems Associated with Placer SamplingLarge Rocks and Boulders: In sampling alluvial, there is a tendency to bypass areas containing many boulders or to sample the easily collected finer material around the boulders. In many cases, this is essentially salting the sample since the valuable material in a placer deposit usually occurs in the finer material.Uncased Holes: The use of uncased drill holes should be discouraged in placer sampling, especially in sampling ground with a high unit value mineral. If uncased holes are used, there is a tendency to unintentionally salt the sample and get overvalued sample results.
Data Processing and Record KeepingAccurate, systematic records must be kept for proper placerevaluation. As an example, data that must be recorded on alog sheet when churn drilling a placer gold depositincludes:1) Name of property2) Location3) Date4) Pits – trench hole line number5) Hole number6) Hole collar elevation7) Time (the time is given for each bailing. A summary oftime consumed in drilling, pulling, moving, repairs, etc. )8) Depth of the drive shoe for each sample interval9) Depth of pumping for each drive or sample interval
10) Total hole depth11) Core rise in the pipe for each drive14) Volume bucket measurement18) Depth and nature of overburden19) Labour used20) Depth of the pay gravel21) Depth to bedrock22) Nature of bedrock23) Thickness of pay zone24) Diameter of the drive shoe30) Value in milligrams, grams or cents per cubic meter (cubic yard)31) Price of gold used in calculations if cents per volume are used32) Signature of the driller, panner, and helper
RENDERING POINTS The detailed records can be efficiently used to determine the value of the deposit and its mineablity. Information obtained from the drill logs can be used in selecting its mining method. The value of the placer material is reported as bank cubic yards.
Reserve Estimation and ValuationAfter samples have been collected, washed, and assayed,reserves for a deposit can be estimated. There are manyplacer reserve estimation methods available. Some of theseare the block, triangle, polygonal, traverses, and diamondmethods.Methods that can be used for reserve estimation andplacer valuation are: (1) block method (2) triangle method (3) polygonal method (4) cross-section method (5) method of diamonds.
CONCLUSION It is important to remember to use care in sampling and to select the method that best suits the type of occurrence that is being sampled Placers formed in cold climates like Alaska or Yukon, are very different from tropical placers formed under laterization processes. Geological Province/Terrain characteristics must be kept in consent. Prospection for one mineral may lead to the discovery of many other essential minerals.