Notes Mine Exploration.doc
- 1. MINERAL PROSPECTING AND EXPLORATION Mining begins with prospecting and exploration stages with long periods of investments and high risks of failure. Extracting of minerals with a profit. Prospecting & Exploration discovers evidence of mineral occurrence and outline its size and character. It’s Program should be designed to find and acquire a maximum number of acceptable mineral deposits at a minimum cost and within a minimum period of time. Defining a mineral deposits is a collective efforts of geologists, geophysicist, geochemists, metallurgists, mining engineers, chemists, lawyers and even politicians. • Prospect – surface indication of mineralization that requires investigation. • Prospecting - is just part of exploration – it is the direct search for surface indication of ore mineralization. • Mineral – are naturally occurring substance that have a corresponding chemical composition and distinct physical properties. • Ore – any rock that contains enough mineral that can be mined at a profit. • Mineral Deposit – any known mineral occurrence with a potential to become an orebody worthwhile of mining. To find and acquire new deposits: - the explorer must have access to land; - it must undergoes rigorous government approval and monitoring process; - it must be capable of discovering deeply concealed (hidden) deposits which have eluded previous explorers; - the deposits must be amenable to economic extractive operations now or in the future. Each exploration entity shall defines its own objectives in terms of acceptable minimum rate of return on investments (ROI) for any deposit found and retained, and in terms of which commodities, and markets are to be involved. Who are Qualified Mineral Prospector/ Explorer - Geologist/Mining Engineer - Any engineer or professional with background in mineral exploration - Physically-fit and Good health - Risk-taker and Adventurous - Broad-minded and Patience - Knowledgeable on Use of Exploration - equipment/Apparatus
- 2. Factors to Consider in Prospecting - Valid Existing Geologic Information - Location and Accessibility - Climatic Condition - Terrain and Vegetations - Local Permits & Clearances; - Maps (topographic & geologic map); - Peace and Order; - Existing infrastructures and utilities at the prospect areas; - Budget Basic Geologic Instruments/Equipments in Prospecting 1. Brunton Compass, geologist pick, hand lens, pocket tape, cloth/chain tapes; 2. Geological knife, protractor, dilute HCl, magnet, nail, survey pads, cement nails, sample tags, sample bags, marking pen, aluminum sheet folder; 3. Sample ring for holding sample bags during chip sampling, pencils, pens, mapping sheets, log forms, field vest with large pockets, clipboard. 4. Portable Global Positioning System (GPS), camera, Laptop, etc. • COMMON EXPLORATION TERMS: • Rock – are aggregate of mineral • Waste Rock – are barren rock in the mine. • Host/Country Rock – are considered mother rock where the mineral is enclosed/deposited/confined. • Gossans – are ferruginous deposit filling the upper part of some mineral veins forming superficial cover over masses of pyrite. It consist mainly of hydrated iron oxides and has resulted from removal of sulfur as well as copper and other sulfides originally present. • Floats – are mineral exposures consisting of loose or traces of mineral remnants found downslope of a mineral deposit. • Bedrock – any solid rock in place underlying a soil, clay or other overburden. • Gangue Mineral – valueless minerals associated in the ore. • Talus – are transported broken rocks by surface water flowing downslope. • Geologic Map- is a record of geological facts in their correct space relations facts, be it noted, not theories.. PROSPECTING & EXPLORATION METHODS & TECHNIQUES A. STAGES OF EXPLORATION Stage 1 :Initial Prospecting Stage - Field and Library Researches - Reconnaissance Geologic Survey - Rock Sampling & Laboratory Testing - Plotting of Geologic Data & Map Interpretation
- 3. Stage 2 : Detailed Prospecting Stage - Further Library/Field Researches - Preliminary Geological Mapping * Field Traverse along Rivers/Creeks & Roadcuts * Aerial Photogeologic Study * Stream Sediment Sampling (rocks & minerals) - Laboratory Testing (petrographic/mineralographic) - Plotting of Geologic Data on Maps/Interpretation - Preparation of Prelim Report Stage 3 : Exploration Stage - Detailed Geologic Mapping of Indicative Areas - Geochemical Testing - Geophysical Investigation - Drilling Investigation - Laboratory Testing - Preparation of Geologic Report Stage 4: Ore Reserve Determination - Geologic Modelling & Interpretation - Ore Reserve Estimation - Mine Evaluation - Mine Pre-Feasibility Report Prospecting Activities 1. Library and Field Researches – Gathering of old/existing geologic reports, maps, etc. 2. Surface Geologic Mapping- Surface investigation as to color and textures at the surface of weathered ore mineralization or outcrops are primary consideration. The tracing of mineralized “float”, fragments of ore, gossans and ore-associated rock that have been eroded and transported. 3. Trenching and/or Test Pitting – This involves excavation trial pits and trenches to expose the surface outcrop. This is also to determine the possible thickness of overburden and character of the ore deposit. If a vein is exposed near the surface, remnants of the vein called “float” will frequently appear downhill in the overburden material. If the vein material is resistant to weathering, float usually starts appearing some distance downhill from the hidden vein outcrop). 4. Field Sampling – Rock and Ore samples are collected from or near outcrops for visual examination and laboratory 5. Laboratory Testing – Samples are subjected for petrographic & mineralographic analysis. 6. Preparation of Geologic Reports 7. Presentation to Client/Investor
- 4. • What to map: Any exposure of rock presents a wealth of detail: - Soil and rock types - Geological structures - Physical properties - Chemical properties -Other surficial features (weathering, alteration) * What to map first: It seems advisable to record all possible features foot by foot or meter by meter as the mapping progresses. • Where are Ore Minerals Found? Minerals can not be planted like flowers. They can be found in as gained after long and patient search. They are usually found in: - Local stone quarries or abandoned quarries - Heaps of Mine Refuse - Abandoned shafts and caves; - Road construction, dams and tunnels - Digging graves - Rocky banks of rivers & brooks - River beds or gravel pits Prospecting Techniques 1. Heavy Mineral Panning 2. Airborne & Satellite Techniques 3. Fluid Inclusion Studies 4. Isotope Studies 5. Portable X-ray Fluorescent Analyzer 6. Laser Techniques • Heavy Mineral Panning - applicable to resistant metal and minerals with high specific gravity like: gold, platinum, cassiterite, tungsten, barite. • Airborne and Satellite Techniques - done by aerial photography supplemented by a satellite-airborne electronic imaging system to map structural, lithologic and alteration features. An example of satellite-airborne imaging system is a Multispectral Scanner (MSS) • Fluid Inclusion Isotopes - Detect fluids during ore-forming processes. The fluids (hydrothermal solutions) are those that are: - entrapped during the growth of its host crystals - entrapped after the growth of host crystal occurring along microfractures Isotope – any of two or more species of atoms of a chemical element with same atomic number and nearly identical chemical behavior but w/ differing atomic mass and different physical properties.
- 5. • Isotope Studies - the study of the different properties of isotopes in a mineral. • Portable X-ray Flourescent Analyzer - detect radioisotope sources to irradiate the sampled material with gamma rays; - very limited penetration of less than 3mm - metals detected by portable analyzer are Cu, Sn, Mo, Pb, Zn, Ni, Fe, Ti, Tn, Ba, Zr, Ag. • Isotope Studies - the study of the different properties of isotopes in a mineral. • Portable X-ray Flourescent Analyzer - detect radioisotope sources to irradiate the sampled material with gamma rays; - very limited penetration of less than 3mm - metals detected by portable analyzer are Cu, Sn, Mo, Pb, Zn, Ni, Fe, Ti, Tn, Ba, Zr, Ag. • Laser Techniques - utilize laser beam (luminex system) to measure luminescent radiation coming from minerals. The luminex system can detect and quantify responsive minerals occurring in an outcrop; - used to detect metals like tungsten, zinc, molybdenum, and gold.
- 6. ORIGIN OF MINERALS 1. Magmatic Formation 2. Weathering Process 3. Chemico-Sedimentary 4. Biological Origin 5. Metamorphism Magmatic Formation The earth’s depth are composed of glowing, liquid, molten silicates called “Magma”. Due to earth’s continuous movement, part of this magma have been driven upwards to cooler layers, where they gradually solidify forming rocks and minerals. Its composition generally corresponds with chemical properties of rocks forming the earth’s crust. In the course of cooling process, the first mineral start to separate out, their number growing with the gradual cooling of the magma. The lighter mineral remains in the upper levels and the heavier ones sink slowly down again. This process is called “Magmatic Differentiation”. Example : Magnetite, chromite, mica, tourmaline, beryl, tin, tungsten By Weathering Formation Surface earth rocks/minerals are constantly subjected to the disturbing effects of various forces called “weathering”. The effects of weathering are gradual, irrevocable, and continuous. Rock surfaces are mechanically affected by changing temperature and by shattering effects of frost. Disintegrated materials are then subjected to chemical action by atmospheric oxygen, carbonic acid and water. As a result of weathering, pyrite sulfuric acid is liberated, which may affect neighboring calcite, changing to gypsum or sulfates. In this way, several secondary minerals can originate from one mineral to another. Ex. Malachite, azurite, or limonite from chalcopyrite, Dripstone caves are another product of weathering process. Feldspar to kaolin, olivine to serpentine, pyrite to limonite Surface Changes : The surface changes that affect ores are important. Most mineral will change when left to the action of weather, thus pyrite changes slowly to limonite; chalcopyrite changes to limonite and malachite. Sometimes the valuable minerals are entirely dissolved at the surface and the rock is left barren. Examples of some weathering changes: - Feldspar changes to clay - Olivine and hornblende change to serpertine or chlorite rocks; - Impure limestone may dissolve and leave clay - Pyrite changes to hematite and limonite - Copper-sulfide minerals changes to malachite, azurite,cuprite; - Silver minerals change to horn silver (cerargyrite) or dissolve - Calcite dissolves - Gold may dissolve if manganese is in the rock; - Rhodochrosite change to psilomelane or pyrolusite
- 7. Chemico-Sedimentary Formation Various minerals are deposited from the sea water as a result of evaporation, or of a change in its chemical composition. Ex. Rock salt, sylvine, gypsum, calcite and some iron ores such as chamosite originate in this process. Biological Origin New minerals can be formed from mineral substances dissolved in water. Coral island and limestone bodies are the product of living organisms. New mineral can also originate from decomposed remnants of dead organisms, such as phosphate, sulfur, pyrite and marcasite. Coal was formed from accumulation of plant material buried beneath the surface that has undergone incomplete oxidation. Metamorphism Molten magma affect the crust layer by its temperature, pressure, chemical reaction with various substances. This caused the sedimentary rocks to change to their appearance, physical, and chemical properties. This process during which new secondary metamorphic rocks and minerals originate is called “Contact Metamorphism”. Ex. Mica, Garnet, Kyanite How Different Ores are Formed 1. Depth in the earth are masses of molten rock, and because the pressure is great and these masses are so hot, they gradually “eat” their way toward the surface of the earth. Some of them reach the surface, such as the formation of volcanoes, but some of them cool and harden before they reach the surface. Because of the pressure and heat of the solid rocks around these molten masses, it forms cracks and these cracks are filled with some molten rock which resulted to the formation of dikes and sills. When these molten rock hardens lead to IGNEOUS ROCKS. 2. The molten rock masses usually contain large quantities of water and steam. These may soak out into the solid rock next to the cooling of melted rock and will then change the nature of solid rock. Sometimes the water and steam are barren of valuable ores while at other times the hot water, soaking in, brings ore of gold, silver, copper, tungsten, or other metals. 3. Fissure Vein are formed when a mass of molten rock started cooling, and large quantities of liquids and gases are given off. Some of them soak into the rock but more will follow cracks and crevices and deposit the mineral matter on these cracks, but sometimes there are thousands of small cracks, thud forming an uneven and irregular vein. The waters forming these veins are hot and are under pressure, so that when they soak into the walls of the cracks, the ore may be wider than the actual vein crack. Vein formed often have quartz, calcite, fluorite or pyrite in the gangue.
- 8. 4. Porphyry/Disseminated copper ores are formed by this process. Molten mass of rock matter forced its way up near the surface, when it started cooling. The top cooled first and formed a GRANITIC ROCK, sometimes called PORHYRY, but the deeper rocks were still hot containing some steam and water trying to escape. The continuous movement of the earth created pressure from beneath thus shattering the cooled upper rock layer thus creating countless tiny cracks, into which the water coming from the hot parts below cooled, where the tiny cracks are filled with small amounts of ore minerals. These ore bodies sometimes extend a mile or two in each direction and are usually low grade but do not exist to a greater depth below 1000 feet. 5. There are veins also formed by cold water, which soaks in from the surface and percolate into the layers of rock. The percolating water dissolves some minerals in one place, and when it comes to a different kind of rock or to large cracks, the minerals are deposited; 6. Placers are formed from other deposits. As water for centuries washes over a gold vein on a mountain side it is worn away, and the gold is carried down by some stream. As gold is heavier than ordinary sand it will be dropped in any little hollow parts in the stream bed, together with more or less sand and gravel; WHAT ARE REGIONAL ORE GUIDES • Igneous rocks • Zone of faulting • Sedimentary rocks • Major structural features such as joints, fractures, karst, folds, alteration, etc. What are some Ore Guides - rock alteration - oxidation - gangue minerals - stratigraphic and lithologic layers - fracture patterns - geologic contacts - folds in rock mass - faults in rock mass Physical Properties of Minerals 1. Sp. Gravity – the relative number indicating how many times heavier or lighter it is than the same amount of water. Most minerals have Sp. Gr. of 2 to 4. 2. Cohesion – the structure of the crystal and the direction in which the crystals are affected. 3. Color - the color of the mineral 4. Hardness – the 10 Moh’s Scale of Hardness 5. Cleavage - crystals break apart along surfaces when writing can be read
- 9. through it 6. Fractures – breaking of rocks irregularly. 7. Streak – rubbing on a piece of unglazed porcelain that leaves a colored scratch. 8. Luster - type of reflection and refraction of light 9. Transparency – when writing can be read through it 10. Refraction of Light – a piece of writing placed under a mineral is seen twice. 11. Luminescence - exposure in the dark to ultraviolet lights elicits colored luminescence; 12. Heat Conductivity- taking a piece of copper in one hand, and a piece of amber in the other, we can feel that copper is colder. 13. Magnetism - pieces or powdered fragments of some minerals are attracted by magnet. Chemical Properties of Minerals: - By using Hydrochloric Acid (HCL), carbonates minerals are easily distinguished. White calcites can be distinguished from white gypsum as HCL reacts and dissolves the calcites. How are Minerals Identified 1. Visual Examination of Hand Specimen aided w/ hand lenses 2. Laboratory Examination - Microscopic Method a) Petrographic microscope for gangue & transparent minerals. It employs transmitted polarized light for use in studying fresh and altered rocks. b) Reflecting microscope for sulfides & opaque minerals - Petrofabric Method - Heavy Mineral Separation - Mineralogic studies-techniques, sequence of deposition, criteria of supergene-enrichment in copper ores, etc. - X-ray and Spectroscopic Studies Steps in Mineral Identification At a starting point, use a piece of fresh mineral broken off from larger specimen. Testing should be thorough and all properties seen by the naked eye or lens are carefully recorded. 1.Collect fresh mineral samples broken-off from a large specimen; 2.Testing should be thorough and all properties recognizable by the naked eye or hand lenses are carefully recorded; 3. Note the external shape and appearance of crystals; 4.Take note on the color, streak, luster, transparency, hardness; and other associated features present in the minerals; 5. Observe the presence or absence of cleavage, brittleness, malleability, flexibility and elasticity; 6. Weigh the sample for its specific gravity; 7. With smaller fragment of the mineral, test it in water or HCL for its solubility test; 8. Check or compare the results once more, comparing the data to the Book Guide on Rocks and Minerals.
- 10. Sequence in Logging a Mineral Sample: 1. Mineral and Host Rock 2. Color 3. pH 4. Weathering/Alteration/Oxidation 5. Grain/Crystal Arrangement (Texture, sorting, etc) 6. Specific Gravity 7. Degree of Jointing/Fracturing 8. Hardness 9. Streak and Luster 10. Percent Core Recovery (% CR) 11. Other descriptive features in mineral sample (magnetic, transparency, associated secondary mineral components, etc.) EXPLORATION • Exploration - is to look and search for something valuable to man. It includes all activities involved the discovery and evaluation of ore deposit, its size, grade, initial flowsheet and annual output of the new extractive operation. • Mineral Exploration – is defined as the scientific investigation of the earth crust to determine if there are mineral deposit present that maybe commercially developed. MAIN OBJECTIVES OF EXPLORATION To Human Beings: - To discover more God’s given natural resources for man’s maximum use in a wise and sustainable manner; -To provide the basic necessities of man to survive where almost everything that we eat, drink, wear, drive, live-in, fly-in depends on the products of mineral industries for either its components, its production, and its source of energy; To Mining Companies: - To find an economic mineral deposit that will increase the value of the company’s stocks to the stockholders on a continuing basis; - To find and acquire a maximum number of mineral deposits at a minimum cost and within a minimum period of time. Factors to Consider in Exploration Work - Scope of work of exploration project; - Permits & Clearances; - Amount of existing information; - General geology of the prospect; - Type of sampling and data required; - Availability of exploration technology, equipment, manpower, etc. - Capability of equipment - Cost of exploration works; - Environment (terrain, access, vegetation, etc.) - Social Acceptability; - Right-of-way to the site; - Peace and Order
- 11. - Availability of infrastructures and utilities. Mineral Exploration Methods 1. Geological Exploration 2. Geochemical Exploration 3. Geophysical Exploration 4. Drilling Exploration 5. Mining Exploration I. GEOLOGICAL EXPLORATION : A prime tool in mineral exploration & includes the following: - derivation of target concepts; - collection of available geologic data (mapping, alteration & zoning studies, core logging, etc.); - interpretation of data collected; - integration of geologic data on maps Activities Involved: - Office/Library Researches/Compilation - Photo-geologic Study (Aerial/Ground) - Outcrop Examination - Geologic Mapping/Investigation - Geologic Logging - Boulder Tracking - Test Pitting & Trenching Types of Mapping • Surface Mapping- a field activity conducted by geologist or engineers to trace, locate and record surficial geological information and plotted in map. • Underground Mapping - a subsurface activity conducted by geologist or engineer in the mines to trace, locate and update geological records and plotted in map. • Air Photograph Mapping - a field activity through the use of an aircraft to trace, locate and other surficial geological features using high polarizing cameras. 2. GEOCHEMICAL EXPLORATION - Defines the analytical measurements & chemical interpretation of the abundance of an element in naturally-occurring materials such as soil, rocks, water, air/gases, gossans, plants, micro-organisms, animal tissues, particulate and stream sediments. - Includes molecular & isotropic concentration and composition or bacterial counts;
- 12. Geochemical Exploration Methods a) Stream Sediment Sampling b) Water Sampling c) Rock Sampling d) Specialized Sampling e) Assaying Activities Involved: A. Field Survey – This involves the collection of closely spaced samples within the vicinity but preferably undisturbed mineralization; B. Sample Collection and Handling - This requires well-trained personnel capable of recognizing and describing the correct sample material and the sample site characteristics. The samplers should be able to recognize and if possible avoid situation where contamination from human activity or changes in the natural physiochemical conditions can produce spurious or unusual results. This must be under the supervision of a geochemist or geologist. Sampling Media : 1. Soil – are mixture of mineral & biologic matter. They are classified as residual and transported materials and vary in composition & appearance according to their genetic, climatic, & geographic environment. - Residual soils may contain detectable dispersion patterns developed during the weathering of mineralization of underlying bedrock. - Transported soil present more difficult sampling problems, but meaningful sampling is possible once the genetic origins of transported cover are understood; Soils are sampled along traverses or grids in the follow-up or detailed prospecting stage of a geochemical program. 2. Stream Sediments and Water : Stream sediment are natural composite sample of erosion materials from upstream derived from weathered mineralization. 3. Lake Sediments & Water : The sampling focuses in the collection of organic mud using especially-designed sampling device. 4. Rock Samples: The systematic sampling of outcrops, trenches, drill cores or cuttings within the zone of oxidation and weathering. Rock samples are grind and pulverized to grain size of less than 150-200 mesh. 5. Microorganisms : This organism is “Bacillus Cereus” which increases with the natural increase of precious metal content of soils in the vicinity of the known mineral deposits. 6. Gases and Air : Some mineral deposit produces gaseous emanations that can be detected by specialized measurements. Radon for example is produced during the radioactive decay of uranium and radium. Helium produced during radiogenic decay with deep-seated origin. Mercury produce by sphalerite and other sulfides.
- 13. How To Prepare Samples for Geochemical Test: 1.Drying : Exposure to sun or dried in an oven heating in excess of 1600F (700C) can lead to less volatile elements that may of value to exploration. 2. Sieving and Crushing: Using pestle and mortar or others (80-mesh) 3. Heavy Mineral Separation 4. Treatment of Chemical Reagents 5. Laboratory Analysis 3. GEOPHYSICAL EXPLORATION Geophysical-Airborne - Aeromagnetic Survey - Electromagnetic Survey - Radiometric Survey - Remote Sensing Geophysical – Ground - Gravity - Seismic - Magnetic - Electrical - Radiometric * Aeromagnetic Survey - conducted from an aircraft to detect the earth’s magnetic fields to at least an accuracy of a gamma. - a map shows the magnetic intensity over the area being surveyed as basis for interpreting the probable distribution of magnetic rocks in the earth’s crust. - susceptability of a mineral to magnetization depends on volume of magnetite content, field strength, grain size, presence of less common magnetic minerals, and the state of natural remanent magnetization. Ex.Magnetite-ilmenite series, magnetite associated w/ gold placers, phrrhotite, magnetite-chalcopyrite, magnetic nickel ores. • Electromagnetic Survey - conducted on fixed-wing aircraft used employing either continuous wave frequency domain, wave forms or pulse-time domain techniques; - applicable to electrically conductive minerals such as massive sulfide orebodies; • Radiometric Survey - set-up in an aircraft where gamma rays will penetrate into several hundred feet through the atmosphere but few inches into the earth to attenuate natural radiation; - gamma ray detectors consist of crystal that is activated to give off a minute flash of light upon being stuck by an ionizing gamma particles. Ex. Uranium, thorium, etc.
- 14. • Remote Sensing - uses a high-altitude-radar-equip aircraft that maps earth’s topography by using satellite images to detect buried pipes, bedrock and mineralized boulders. - an energy is emitted in the radio portion of the electromagnetic spectrum of which the source portion is reflected back to the radar equipment. The single pulse radar wave is applied directly to ground surface or U/G tunnel and boreholes. The wave is turned and registered a video pulse which appear similar to seismic refraction wave. Irregularities on the wave action indicate reflector such as clay-filled, fault zone in crystalline rocks, cavern or rock. Limitation: In development stage, does not provide depths or engineering properties, shallow penetration of about 10-15 meters only. Ground Geophysical Methods • Gravity Method - Uses new cryogenic & mechanical-optical gravimeters to measure gravity variations and proved successful to detect small masses & subsurface voids (caves or tunnels); - buried channels that may contain gold or uranium minerals can be located by gravity or seismic method because the channel fill is less dense that the rock in which the channel has been cut. Bouguer Anomaly - that part of the difference between measured gravity and theoretical gravity which is a result of purely of lateral variations in material density Other factors affecting gravity are altitude and topography. Old gravimeters consisting of spring pendulum same as seismograph (Eotvos Torsion Balance) where heavy masses attract the instruments & conversely, light masses allow the instruments to be deflected away from them. Applicability: Widely used in petroleum geology but until recently have found little use in ore search partly because of rough topographic characteristic. It is normally used for cavity detection in limestone for engineering studies. - ores detected are chromite, hematite, barite that have such high density compared with the material that surrounds them Limitations: Detect major subsurface structures such as faults, domes, intrusion or cavities; • Magnetic Survey - Many rocks contain small but significant quantities of ferro-magnetic minerals which vary with rock type. The weak magnetization modifies the earth’s magnetic field to an extent that can be detected by sensitive instrument called “Magnetometers”.
- 15. Application: -Mineral prospecting & location of large igneous masses; - Magnetic orebodies that are strongly magnetic; Limitation: Normally not used in engineering studies; Equipment: Magnetometers – provide the measurements and when place in aircraft. 2. Electrical Method -Various surface material have characteristic conductance for direct currents of electricity. Electrolytic action, usually made possible by the presence of moisture and dissolved salts w/in the soil/rock formation, permit the passage of current between electrodes placed in soil surface. In general, conductance is good in such material as moist clay and silts, and poor material such as dry loose sands, gravel and sound rock. Resistivity – refers to the resistance to current flow developed in geologic materials, and is expressed as OHM-CM2/CM or simply as OHM-CM or OHM-FT. Applicability: - Locate water boundaries, clean granular & clay strata, rock bedrock; - Massive sulfide bodies such as arsenopyrite, chalcopyrite; - Outlining the contour of bedrock surface in placer deposit; - Locating quartz veins, cavities in limestone, potential failure; - Thickness of organic deposit & depth of GWL. Limitation: Difficult to interpret and subject to wide variations. Does not provide engineering properties. Basic Equipment: Terrameter, battery (energy source), potential meter, electrodes • Seismic Method - consist of detonating a charge of dynamite or other explosives and measuring the reflection and refraction of artificial earthquake waves set- up by a shock. Elastic waves travel through geologic media at characteristic velocities. The waves passing the material finally arrives at the surface where they detected and recorded by an instruments. Types of Seismic Methods: a) Refraction Method b) Reflection Method a. Refraction Method - determine stratum depth & character velocities in land/water; - ideal for land exploration to depths of less than 300 meter because of direct and refracted waves arrive first and tend to mask the reflected waves; - locate faults or underground caverns. Limitations: Maybe unreliable unless velocities increase with and bedrock surface is regular. Data are indirect and represent average.
- 16. Basic Equipment: Energy source (hammer or explosive); elastic wave detonators (seismometers) which are geophones (electro-mechanical transducer); seismograph (power source); amplifiers; timing device; and recorder. b. Reflection Method: Application: Not used on land for engg studies but useful for offshore continuous profiling. Provide a pictorial record of sea-bottom profile showing changes of strata, salt domes, faults and marine slides. Limitation: Does not provide velocities computation of depths to stratum. Changes require velocity data obtained from other means. Basic Equipment: 1) Boomers-operate in water depth (3-200m) and provide high resolution (15-30cm) but moderate penetration(100m); 2) Sparkers-operate in water depth (10-600m), high resolution of about 15-25m w/ penetration depth of 1,200m or more 3) Vessel-carry personnel and equipment