GEOLOGICAL AND GEOCHEMICAL EXPLORATION

1. GEOLOGICAL AND GEOCHEMICAL EXPLORATION Dr. Ahmed Ali Madani Associate Professor Tel. (off.): 64324 E-mail:aamadani18@hotmail.com cairogers2005@yahoo.com

2. Overview of Exploration Geology • Exploration geology is the process and science of locating valuable mineral or petroleum deposits, ie, those which have commercial value.  • The term “prospecting” is almost synonymous with the term “exploration”. • Mineral deposits of commercial value are called “ore bodies” (compared to commercially viable deposits of oil which are called “oil fields”).  • This course will be focused largely on mineral exploration, although many of the same techniques are used in petroleum exploration. 

3. The initial signs of potentially significant mineralization are called “prospects”.  • Through the exploration process, the prospect is investigated to acquire more and more detailed information.  • The goal is to prove the existence of an ore body (or oil field in the case of petroleum exploration) which can be mined (or “developed”).  • The exploration process typically occurs in stages, with early stages focusing on gathering surface data (which is easier to acquire), and later stages focusing on gathering subsurface data, including drilling data and detailed geophysical survey data.

4. Determining the value of an ore body (or “deposit”) requires determining two main features:  1) “tonnage” (or volume), and 2)  “grade” (or concentration). • The volume is determined by using drill data to outline the deposit in the subsurface, and by using a geometric models to calculate the volume.  If the ore body is exposed at the surface, then the dimensions of length and width can be gathered at the surface, possibly with the aid of some trenching or blasting methods.  However, most of the volume which must be defined is typically located at depth and requires the use of extensive drilling or underground excavation methods to define.  The volume is difficult to delineate because ore deposits often have irregular shapes.  • The “grade” is the average concentration determined from numerous assays of drill samples.  The grade can vary considerably within different parts of the same ore body. 

5. Development usually consists of extensive, close-spaced drilling which outlines the geometry of the deposit in great detail.  The development stage will also conduct extensive testing, with some preliminary metallurgical testing, to precisely determine grade of the deposit and the “recovery” (the amount of metal possible to extract, compared to the total amount of metal present in the ore body).  The final stage before actual mining or extraction is called “feasibility”.  During this stage, the actual mining or extraction method is proposed, taking into consideration all of the economic variables which effect the bottom-line profit (commodity price, milling cost, transportation cost, labor cost, etc...).  At this stage, a decision is made whether to mine the deposit from the surface (called “open-pit mining”), or to mine the deposit by tunneling (called “underground mining”).

6. Mineral seldom occur at the surface and are seldom obvious.  • Most often they are buried, sometimes at considerable depth.  • Since they are not visible we must detect their presence indirectly and extrapolate between points where data is known.  • Many different techniques can be used to detect an ore body.  This class will discuss the more important techniques in some detail; others are only briefly mentioned.  • The most important techniques used in exploration geology include geological field methods, geochemical sampling methods, and geophysical methods. Exploration conducted from the surface is far less expensive than drilling or underground excavation, so thorough surface exploration usually precedes either of these activities.

7. The Exploration Process • Exploration for a mineral deposit is usually conducted in a step-wise fashion which progresses through stages, each of which moves closer to making a valuation of the ore body.  Geological reconnaissance and surface geochemical sampling prevail in the earliest stage.  Simultaneously or afterwards, geophysical surveys are typically conducted.   Following surface exploration, the project moves into the drilling stage.  Drilling may begin with a small number of exploratory drill holes on select targets.  After this drilling stage, extensive, close-spaced drilling (called  “development drilling”) is conducted.  Finally, pending good results, “reserve drilling” is conducted, which is the type of drilling which makes the final assessment of the deposit before actual mining begins.  Generally, some amount of drilling will continue throughout the life of the mine, as further definition is required and new information is obtained and used to refine the deposit model.

8. Exploration Methods • If bedrock is exposed anywhere at or around a prospect, then surface bedrock mapping is an essential beginning step for an exploration program.  This would include mapping and sampling (field geologic methods).  This work focuses on identifying and mapping outcrops, describing mineralization and alteration, measuring structural features (geometry), and making geologic cross sections. • Geochemical methods involve the collection and geochemical analysis of geological materials, including rocks, soils and stream sediments.  The results mapping and sampling may suggest patterns indicating the direction where an ore deposit could be present underground or at the surface.  Geophysical methods focus on measuring physical characteristics (such as magnetism, density or conductivity) of rocks at or near the earth’s surface.  The measured values are then used to compare with the values and models of known ore deposits. 

9. EXPLORATION  GEOLOGY  TERMS • Ore:  the rock material or minerals which are mined for a profit. • Ore Minerals:  the specific minerals within the ore which contain the metals to be recovered. • Gangue Minerals:  the minerals having no commercial value, they just happen to be mixed up with the ore minerals. • Prospect:  potential ore deposit, based on preliminary exploration. • Mine:   Excavation for the extraction of mineral deposits, either at the surface (open pit mine) or below (underground mine).   • Orebody or Ore Deposit:   naturally occurring materials from which a mineral or minerals of economic value can be recovered at a reasonable profit. • Mineral Deposit:   similar to an ore deposit, but is implied to be subeconomic or incompletely evaluated at present. • Mineral Occurrence:  anomalous concentration of minerals, but is uneconomic at present. • Grade:  this means the concentration of the substance of interest, usually stated in terms of weight per unit volume. • Cut-off Grade:  the lower limit of concentration acceptable for making a profit when mining.  • Host Rock:  the rock lithology (type) which contains the ore.  May or may not comprise ore. • Country Rocks:  the rocks of no commercial value surrounding the host rocks and/or the ore. • Anomalous:  above or below the range of values considered to be normal.

10. SAMPLING AND CALCULATION OF TONNAGE AND GRADE

11. Geochemical Sampling Methods • Geochemical sampling methodsare methods which involve collecting and analyzing various types of geological materials (such as soils, stream sediments and rocks) or certain biological materials (such as plants). Historically these methods have been some of the most productive in of any methods used in mineral exploration.  Sometimes mineralization can be extremely subtle, if not impossible to recognize, in hand specimen.  Without the use of geochemical sampling methods, many known ore deposits would probably not have been discovered.  • After discovery, geochemical sampling plays a key role in the delineation of mineralization.  For example, geochemical sampling of soils is often employed to outline the general distribution of mineralization at shallow depths where outcrops of bedrock are minimal or nonexistent.  The procedure involves collection of materials in the field, laboratory (or field) analysis of the geochemistry of the materials, plotting of the geochemical values on maps, and interpretation of the results.The materials may be analyzed for any number of elements.  Which elements are chosen for analysis depends on budget, the geology of the area, and the commodity which is being sought after.  Often there are specific elements or suites of elements which are known to be associated with specific types of mineralization.  Therefore it is possible to evaluate the potential for the existence of certain types of mineralization by evaluating which elements are associated in a given area.

12. Rock Sampling • Rock sampling reveals the true potential of an area for containing a mineral deposit.  An anomaly in a rock sample from bedrock has had no effects of secondary dispersion, so the location of the sample is the location of the source.  A rock sample anomaly will provide much more valuable information about the location of the mineral deposit because its source is within the mineralizing system, ie, it helps delineate the zone of primary dispersion.  However, this applies only to rock samples collected from bedrock.  Rock samples of float (rock material suspended in colluvium with no indication of proximity to the bedrock source), talus, glacial material, etc... give no indication of location of the source, so even if they are highly mineralized, they are of limited value.  Rubble (rock material suspended in colluvium and due to consistency or other information suggests proximity to the bedrock source) in some cases may be worthwhile to sample. • Several different types of rock samples are collected for mineral exploration.  Most importantly, rock samples are collected to determine the concentration of metals, including both the major and trace metals.  This type of sample is most commonly referred to as a “geochem” sample.  Trace metal values are often useful as “pathfinders”, which means they are closely associated with the metal of interest and may occur within a halo surrounding the mineralization of interest. 

13. Rock geochem samples are collected in different manners depending on the goal of the sampling.  The principle types include: • Grab Samples:   A grab sample is a sample of rock material from a confined area (< 1 foot across).  • It can be a single piece of rock.  • These are the most common types of samples collected.  If it is not specified otherwise, one usually assumes that is the sample type.  • The sample usually consists of a single piece of rock, or chunks (large piece), which are representative of a specific type of rock or mineralization.

14. Composite Samples:  A composite sample consists of small chips of uniform rock material collected over a large area (generally > 5 feet across).  • These are the ideal “representative” samples.  • The procedure is to collect small pieces of rock over a large area (usually at least 10 feet across) and to make the sample as homogenous as possible. • A composite sample might be collected to determine the background values of trace elements in a particular type of rock, or to determine if ore grade mineralization is present over a large area.

15. High Grade Samples:   A high grade sample consists of selective pieces of the most highly mineralized material, in which an effort is made to exclude less mineralized material.  • Consequently, a high grade sample is generally not representative of the overall mineralization type.  • A high grade sample might be collected to get an idea what the best possible values are, or to provide material for certain types of trace element analyses.  • If a such a selective sample does not return good results, then it is unlikely that valuable mineralization is present.  • When a high grade sample is collected it is important to note that it is a high grade sample so its values will not be misinterpreted as representing the “average” values.

16. Chip Channel Samples:  A chip channel sample consists of small chips of rock collected over a specified interval.  • The objective is to obtain the most representative sample possible for the specified sample interval. • Most of the time chip channel samples are collected in succession along a sample line which is laid out in advance using a tape.  • This provides a great deal of information about the width and other aspects of the geometry of a mineralized zone.  Often the chip channel samples are collected along the floors or walls of trenches or adits.  When chip channel sampling along walls, sometimes a piece of canvas or plastic is laid out for the material to fall on so as to avoid contamination and make the collection easier.  • The freshest material possible is sampled, preferably chipping directly from bedrock.  Sample intervals are set at a specified width, usually ranging from 1 to 20 feet.  For example, in a five foot interval, at the end of the first foot, 20 % of the sample bag should be filled, at the end of the second foot the bag should be filled to 40 %, etc...  Due to the method of sampling, chip channel samples tend to be rather large (up to 20 pounds for a five foot interval).

17. Several other types of rock samples are sometimes collected to help interpret the history of mineralization in an area, to better understand the relationships between different ore minerals, or to determine more detailed geochemistry.  • These types of samples are often collected to evaluate the mineralization in a regional context, or to compare the mineralization with models which might apply to a given situation.  Although they can might be costly, the information they provide can be invaluable.  • Some of these sample types include:

18. Whole Rock Major Oxide Samples:Whole rock major oxide samples are most often collected to study the whole rock geochemistry of plutonic and volcanic rocks.  • The sample must be completely fresh, unweathered, and unoxidized.  • If necessary the weathered rind must be removed by chipping or by using a rock saw.  • Samples must also be unaltered by hydrothermal alteration (this adds new components and removes others, such that it will no longer represent the parent magma composition).  • The sample is analyzed for the principle oxides, including, SiO2, Al2O3, CaO, Fe2O3, FeO, K2O, MgO, MnO, Na2O, P2O5, TiO2.  Usually at least 98 % of the rock is made up of minerals comprised of some combination of these components.  Not uncommonly igneous rocks contain up to 1 % water.  This water is lost when the rock is oxidized in the furnace (referred to as LOI or “loss on ignition”).  • Major oxide analyses are used to classify igneous rocks based on their chemical composition.  These can be used to compare intrusions within a district or to use in regional studies by comparing the analyses with those for known models.

19. Age Date Samples:   Age date samples are used to determine the age of the rocks.  • There are several methods, including 40Ar/39Ar, U/Pb, K/Ar, Rb/Sr, and Carbon 14.  • They are all based on the half life theory, which states that certain isotopes of certain elements decay to radioactive daughter products at a specific rate, called a decay constant.  Knowing the constant, the amount of parent and daughter product material in the sample is measured and then used to calculate the age of the rock.  • The 40Ar/39Ar method can provide reliable age dates up to several hundred million years.  Argon gas forms by decay of potassium and gets locked in the crystal lattice.  • The U/Pb method is also quite reliable, and can be used to date rocks up to billions of years old.  Older rocks have longer histories, and during those longer histories more events can occur which cause problems.  For example, metamorphism and tectonic activity.  These can cause opening of the crystal lattice of the mineral being dated, and loss of the daughter product material, causing erroneous results.  Typically these effects cause the methods to yield ages which appear to be younger than the actual age of the rock.  Minerals can also obtain overgrowths during remelting events, causing excess parent material to be present, also making the rock appear younger.  Ar-Ar and U-Pb age dates can be obtained can be obtained from very small amounts of material.  The procedure involves separating the grains of one mineral type to be dated.  Ar-Ar age dates are usually obtained on minerals such as mica or hornblende.  U-Pb age dates are usually obtained on zircon or other accessory minerals which are known to contain small amounts of uranium.

20. Petrographic Samples:   Petrographic samples are collected to conduct thin section petrographic analysis of the rock, which is the identification and evaluation of the minerals comprising the rock by using a microscope equipped with both plane and polarized light.  • A thin section is made of the rock, which is a  paper thin slice of the rock mounted on a glass slide.  Different minerals have different optical properties when the plane light or polarized light is transmitted through the thin section.  Textural relationships also become apparent, which provides information about the order of crystallization (or paragenesis).  • The proceedure is to cut a flat side and use special epoxy to glue the piece of rock called a plug, to the glass slide.  Thin a special trim saw cuts off the part opposite the glass.  Then the rock wafer is polished with special grinders to achieve the desired thickness.  The thickness must be very precise to compare the optical properties with known standards. 

21. Fluid Inclusion:   Fluid inclusion samples are typically samples of quartz (others include fluorite, sphalerite or tourmaline).  The samples are prepared similar to a thin section, and examined using a special microscope equipped with a heating stage.  • The inclusions can contain solid, liquid or gas, or any combination of these.  The inclusions are formed when they are trapped on the surface as a new layer of the mineral crystallizes.  As the mineral cools down, the phases separate.   The sample is heated gradually while being examined under the special microscope to find the temperature at which the gas or solid crystal in the fluid inclusion will goes back into solution.  This provides valuable information about the temperature and pressure of formation of the ore forming fluids. • Polish Section:   to look at reflected light properties of ore minerals; ie, sulfide and oxide minerals. • Microprobe:    highly sophisticated method to determine mineral compositions and textures using electron beams.

22. SAMPLE TYPE When the Assay category is chosen, the sample type must be identified using one of the following: • BULK Bulk - a large volume sample collected from one or more sites for assay or metallurgical testing. It includes limited sampling or mining in initial production stages for plant site and operations testing. • CHIP Chip - a large number of small chips or specimens collected over a specific area. • CHNL Channel - a sample of all material collected from a channel of specific dimensions across a sample site. • DIAD Drill Core - a split or other type of drill core sample. • GRAB Grab - a single sample normally selected to represent either high or low grade material. • ROCK Rock - this may be a chip, channel or grab sample which has been analyzed by standard geochemical techniques rather than assay techniques. • TRNC Trench - a sample taken from a trench. • ****Unknown - This may only be used when the data is important and needs to be included but the sample type is not known.

23. Exploration Project Planning • The extensive effort, high costs, and short field season require a great deal of planning for an exploration project to be successful.  Details pertaining (relate) to the logistics of transportation, field camps, geological surveys, field equipment, communications, and emergency procedures are some of the more important aspects which must be considered.

24. Transportation • Many field projects in remote areas require the use of transportation by fixed-wing aircraft or helicopter, which are the most expensive forms of transportation.  Fortunately there are numerous short, but sometimes crude, airstrips around the state, particularly in the known mining districts.  There are also many airstrips on private land, which might be used if permission can be obtained.  Other areas may have airstrips built for hunting and fishing access, but if these are maintained by private individuals, permission should also be obtained, even if they are located on public land.  The right type of airplanes equipped with the right kind of landing gear (large tires) can utilize gravel bars along some of the major rivers.  Floatplanes can access the larger rivers as well as lakes in some areas.  Rates for air travel by small fixed-wing aircraft range up to a few hundred dollars per hour.  • Helicopters are the ultimate transportation method for remote areas, but are also much more expensive, typically ranging from $500 to $800 per hour depending on the type of helicopter used.  The most commonly used types are the Bell Jet Ranger and the Hughes 500, but several others are also available and suitable for remote work.  The Hughes 500 has a reputation for ability to land in very tight spots due to the greater height and shorter span of the rotors.  The big advantage to the use of a helicopter is the small landing area needed, which means they can be used to mobe gear and personnel to camps in very remote locations.  The helicopter can be used to drop off geologists at the beginning of the day at locations high on ridges, which would otherwise take many long hours of uphill hiking to access.  Then the geologist can design their daily reconnaissance traverses to cover a much larger area and obtain many more samples. • Various types of boats can also be used for transportation in remote settings.   Airboats are particularly advantageous in shallow, inland river settings because of the minimal water depth needed.  • If a project is fortunate enough to be on a road or trail system, 4-wheelers, or even 4-wheel drive vehicles, may be used.  The use of these vehicles can provide great cost savings when considering the larger area which is made accessible.

25. Field Equipment • Numerous equipment items are necessary to conduct geological field work.   Table 15 – 1 is a partial list of equipment items.  Obviously each different type of work activity requires a different selection of work-related equipment.  For example, claim staking requires different equipment than geologic mapping, and stream-sediment sampling requires different equipment than soil sampling.  It is the responsibility of the field geologist or assistant to make sure they depart for the field with everything they need to  conduct in an efficient manner the work they set out to do.  It is also their responsibility to make sure they have the items necessary to ensure their safety and comfort.  This means they need to carry an adequate food and water supply.  If the logistics call for a helicopter pick up, they should plan for the possibility that weather or mechanical problems may prevent the helicopter from picking them up when and where planned.  They may need to carry a tool such as a brush ax or saw to create a landing zone (or “LZ”) for the helicopter.  • Personal Comfort & SafetyWork-RelatedGood raingear (jacket & pants)Large pack w/ good support systemWarm hat & glovesRock hammerWork glovesSmall shovelWater supplySample bagsFood supplyWaterproof markerGood leather boots (rocky areas)PencilGood rubber boots (wet areas)Field notebookWarm jacketMineral I.D. kitFirst aid kitHand lensToilet paperBrunton compass &/or Silva Ranger compassGun & ammunitionHandheld GPSBear sprayHip chain and threadCowbell &/or whistleField maps & navigation mapsSun hatBrush ax or macheteBug dopeColored pencilsMosquito headnetPlastic garbage bag (for wet samples)Signal mirrorFluorescent spraySunglassesTapeWaterproof matches or lighterPick axRescue blanketHandheld radio w/ extra batteryPocket knifeExtra AA batteries for GPSParachute cordField vestWater filterGold pan  Sample tags

26. Field Communications • For many field work projects, the ability to communicate in the field dramatically affects the efficiency of the operation and the safety of the workers.   Communications which are important include person-to-person (or person-to-base camp), person-to-aircraft, and camp-to-town.  Equipment includes the handheld radio, cell phones, Irridium satellite phones, regular satellite phones, and single sideband radios. • The handheld radio is the most common equipment used for person-to-person, person-to-base camp, and person-to-aircraft communication.  Some handhelds transmit for up to tens of miles, but the limiting factor is that they only transmit and receive line-of-sight.  This means one cannot communicate through obstructions (usually topographic features) in the line-of-sight path.  Better line-of-sight is often gained by climbing to higher elevations.  A handheld radio can only communicate with other handheld radios if they are all on the same frequency.  The handheld radio uses a rechargeable battery which usually only lasts a couple days.  It is important to always carry an extra radio battery.  • Cell phones, due to their small size, low cost, and extended range, are becoming increasingly popular for camp-to-town communications.   Areas covered by cell phone networks are constantly becoming more widespread as more and more repeater stations are constructed and antennae systems become more powerful.  Cell phones still require line-of-sight to the antennae or repeater, so this is a limitation in many instances.  • Satellite phones are the most desirable means of camp-to-town communications because of the dependability, size, and the fact that they can be used in extremely remote areas.  Two factors prevent their widespread use, including 1) cost (usually $3 to $5 per minute), and 2) reception is only as good as the satellite view (or the clearness of the path between the satellite phone and the satellites).  Due to the fact that the satellites are constantly moving, and never rise much more than about 10 degrees above the horizon, the reception at a given location will vary greatly over the course of the day.  There is also a safety consideration, because satellite phones transmit using microwave radiation, which is harmful to anyone in the path of the radiation.  Caution is imperative !!  There are several different satellite networks orbiting the earth, including both public and military networks.  The Irridium network is owned by the U.S. military, but is also used for public communications.  A Canadian company called Global Star owns another network used by the public.   • Single sideband (or SBX) radios were the standard means of camp-to-town communications prior to the age of cell and satellite phones.  SBX radios transmit low frequency radio waves (1.5 – 6.0 Mhz) which can travel extremely long distances.  This is because the radio waves bounce back and forth between the ionosphere and the earth.  However, this only applies to fair weather conditions.  The advantage of using the SBX radio is the low cost, long range, and the fact they can be used in valleys and at lower elevations successfully.  Disadvantages of the SBX are that they wave transmission is drastically affected by solar activity, and in some situations by the presence of high power electrical transmission lines.  They also require setting up a fairly elaborate antennae system.

27. Classes of Ore Reserves: • Paradoxically enough, no one can be sure how much ore there is in a mine until it has been mined out; therefore, at best, ore reserve figures are estimates rather than certainties. The tonnage of ore that is exposed on all sides by workings can be calculated with reasonable accuracy, but the tonnage that exists beyond or below any workings can be estimated only by making certain assumptions. It is, therefore, conventional to divide the ore reserve into categories based on the degree of assurance of its existence. Of several lassifications that have been proposed, all based on the same principle, the oldest and probably the most widely used divides the ore reserve into three classes as follows:

28. 1. Positive Ore or Ore Blocked Out. Ore exposed and sampled on four sides, i.e., by levels above and below and by raises or winzes at the ends of the block. This definition applies to veins; for wide ore bodies the workings must be supplemented by crosscuts. • 2. Probable Ore : Ore exposed and sampled either on two or no three sides. • 3. Possible Ore (geologist’s ore) : Ore exposed on only one side, its other dimensions being a matter of reasonable projection. Some engineers use an arbitrary extension of 50 to 100 feet. Others assume extension for half the exposed dimension.

29. Although these definitions are relatively rigid, they fail to specify one important factor - the distance between the workings that expose the ore. This factor is pertinent because there is always a chance that somewhere within the block there may be a barren patch, and this chance is greater as the distance between exposures is greater. Therefore, in order that ore may be considered Proved or Blocked Out, the workings in which sampling has been done should not be more than some specified distance apart; yet no arbitrary standard can be set up, because different types of ore vary in their regularity and dependability. In a spotty erratic ore body the spacing must be closer than would be permissible in a large uniform ore body. Recognizing this, Hoover says, “In a general way a fair rule in gold quartz veins below influence of alteration is that no point in the block shall be over fifty feet from the points sampled. In limestone or andesite replacements, as by gold or lead or copper, the radius must be less. In defined lead and copper lodes, or in large lenticular bodies such as the Tennessee copper mines, the radius may often be considerably greater, - say one hundred feet. In gold deposits of such extraordinary regularity of values as the Witwatersrand Bankets, it can well be two hundred or two hundred and fifty feet.”

31. Although ore of an erratic nature needs to be blocked out on four sides, as called for in the conventional definition of positive ore, a uniform ore body whose structure is well understood might be counted on with reasonable confidence if it were exposed on only two sides. Hoover, therefore, proposed categories based on more flexible definitions which allow some leeway to the judgment of the individual: • Proved ore : Ore where there is practical no risk of failure of continuity. • Probable Ore : Ore where there is some risk yet warrantable justification for assumption of continuity • Prospective Ore : Ore which cannot be included as “Proved” or “Possible”, nor definitely known or stated in any terms of tonnage.

32. Another set of terms, which allow rather wide latitude to the individual, has been adopted by the U.S. Geological Survey and the U. S. Bureau of Mines. Instead of Proved, Probable, and Prospective, these Bureaus use Measured, Indicated, and Inferred, defined as follows: • Measured ore is ore for which tonnage of computed from dimensions revealed in outcrops, trenches, workings, and drill holes, and for which the grade is computed from the results of detailed sampling, and measurements are so closely spaced, and the geologic character is defined so well, that the size, shape, and mineral content are well established. The computed tonnage and grade are judged to be accurate within limits which are stated, and no such limit is judged to differ from the computed tonnage or grade by more than 20 per cent. • Indicated ore is ore for which tonnage and grade are computed partly from specific measurements, samples, or production data, and partly from projection for a reasonable distance on geologic evidence. The sites available for inspection, measurement, and sampling are too widely or otherwise inappropriately spaced to outline the ore completely or to establish its grade throughout. • Inferred ore is ore for which quantitative estimates are based largely on broad knowledge of the geologic character of the deposit and for which there are few, if any samples or measurements. The estimates are based on an assumed continuity or repetition for which there is geologic evidence; this evidence may include comparison with deposits of similar type. Bodies that are completely concealed may be included if there is specific geologic evidence of their presence. Estimates of inferred ore should include a statement of the special limits within which the inferred ore may lie.

33. Proven (PV): Ore reserves are stated in terms of mineable tonnes and grades in which the identified substance has been defined using sufficient metallurgical, mine method, geoscientific, infrastructure, operating and capital cost data. Other applicable reserve adjectives may include measured recoverable, diluted, mineable, ore, or in situ. • Probable (PB): Ore reserves are stated in terms of mineable tonnes and grades where sufficient information is available about the thickness, grade, grade distribution, mineable shape and extent of the deposit. Continuity of mineralization should be clearly established. Other applicable reserve adjectives may include measured geological, drill indicated, or indicated. • Possible (PS): Ore reserves are stated in terms of mineable tonnes and grades computed on the basis of limited geoscientific data, but with a reasonable understanding of the distribution and correlation of the substance in relation to this data. Other applicable reserve adjectives may include inferred, geological, mineral inventory, or potential.

34. Measured (MG):Sufficient information is available about the thickness, grade, distribution, mineable shape and extent of the deposit to give defined grade and tonnage figures. Continuity of mineralization should be clearly established. Other applicable resource adjectives may include proven, measured recoverable, diluted, mineable, or in situ. • Indicated (IN): Tonnage and grade are computed partly from detailed sampling procedures and partly from projection for a measurable distance, based on geoscientific data. Sampling procedures are too widely spaced to ensure continuity but close enough to give a reasonable indication of continuity. Other applicable resource adjectives may include probable, measured geological, or drill indicated. • Inferred (IF): An estimate of tonnage and grade computed from geoscientific data or other sampling procedures, but before testing and sampling information is sufficient to allow a more reliable and systematic estimation. Other applicable resource adjectives may include possible, geological, mineral inventory, or potentiaL

35. OTHER: These are to be used only if the data cannot be categorized as Reserves or Resources. • Combined (CB): This designation is used when an inventory figure is reported to be a combination of categories (e.g.) PV + PB (Proven and Probable) reserves or MG + IF (Measured and Inferred) resources. It can be applied to both the Reserve and Resource categories. • Unclassified (UN): This designation indicates that the criteria for qualifying the inventory figures are not available. The Unclassified category can be applied to both the Reserve and Resource categories. For example, a tonnage figure is given with grades of commodities, but the category is not stated. • Assay/Analysis (BA): Samples of one or more of the various sample types listed below have been collected and analyzed. This category is reserved for deposits which have no reported inventory figures. The value quoted should normally be representative of a group of samples and is not necessarily the assay containing the highest values. If available the sample size should be identified in the comment field. The 'SAMPLE TYPE' must be identified when using this category. • Unknown (**): This designation indicates that not enough information is available to determine the category

36. GUIDES OF ORE DEPOSITS • Geochemical Guides Proximity to an ore body is indicated in some instances by the presence of metallic ions in rocks, soil or groundwater. Even though the element in question may be present in traces so small as to be detectable only by delicate chemical tests, a map showing its distribution may disclose target rings surrounding an ore body.

37. Groundwater as a Guide Groundwater in a mineralized region, especially where sulphides are undergoing oxidation, contains metals and sulphates in amount ranging from traces to so much that the water is undrinkable. If metals are present in the water, they are likely to be absorbed by the limonite or by the manganese dioxide associated with it, and show up as traces on analysis. Such metals may include Cu, Zn, Pb, Ni, Co, Mo, W, Sb, and Bi.

38. Geobotanical and Biochemical Guides • The possibility of using vegetation as a guide to ore depends; firstly (and probably least in importance), on the suggestion that metals and other elements may modify the appearance of foliage; secondly, on the fact that certain elements play a role in determining what species of plants which are able or unable to grow in a given place; and then, on the well-established bservation that certain plants can take up and concentrate elements selectively from soil solutions. • Some species of plants are poisoned by certain elements in the soil, while others, if they do not actually thrive on the same substances, are at least able to tolerate them and thus grow more abundance where competition is lacking.

39. 2 Hypogene Zoning as a Guide • All of the foregoing mineralogical variations might be regarded as aspects of hypogene zoning, but zoning in the stricter sense – the progressive change in mineralization along channel ways from source to surface or outward from a central axis – is serviceable in a somewhat different way. It finds its chief usefulness in the epithermal and the shallower of the mesothermal deposits, where noticeable changes may take place either laterally within the limits of a single company’s holding or in depth within the limits accessible to mining. • “At horizons above the top of the ore zone the vein fracture is often a mere slip …. Sparse quartz starts to come in with depth, usually at a narrow stringer along the slip. The quartz increases rapidly with depth and the top of the ore zone lies not far below the top of the quartz. Base sulphides are sparse here ….. Base sulphides increase with depth and reach a maximum at the heart of zone. Fragments of wall rock cemented by vein matter become abundant at this horizon; many are completely replaced by silica and sulphides. Here the vein attains its maximum width and this width usually continues to the lowest explored horizon.”

40. STRATIGRAPHIC AND LITHOLOGIC GUIDESIf ore occurs exclusively in a given sedimentary bed, the bed constitutes an ideal stratigraphic guide. Less perfect, but still serviceable as a guide is a bed or group of beds which contains most of the ore bodies even though other stratigraphic horizons may not be entirely barren. If the containing rock is not a sedimentary formation but an intrusive body or a volcanic flow, the same principles are applicable so far as ore search is concerned, but since in such cases the guide cannot properly be called stratigraphic, the term lithologic is more appropriate. The ore may be syngenetic (an original part of the body of rock) or it may be epigenetic (introduced into the rock)

41. 1 In Syngenetic Deposits If the ore is an original part of a body of rock, the rock itself will serve as a guide; that is the ore will be found within the particular rock formation and will be absent outside it. The location is most precise in layered rocks especially sediments but it is definite enough to be useful even in homogeneous igneous rocks If the ore consists of a bed in a sedimentary formation one need only know the stratigraphic sequence and the structure of the beds in order to predict where the outcrop will be found or at what depth the ore will be at any given place. For this purpose astructure contour map is the most convenient device for depicting the shape of the ore bed and projecting its position. • Syngenetic deposits of igneous origin are usually less regular than sedimentary beds. However in some thick sills and lopoliths, the rock constituents have a very regularstratiform arrangement.

42. 2 In Epigenetic deposits • Ore that has been introduced into rocks may show strain partiality to certain formations whether the ore follows fractures or replaces formations bodily. Replacement ore bodies differ from most sedimentary (syngenetic) deposits in that not all of the favourable stratum is ore; replacement within the bed is often controlled by someadditional loci which may consist of fold axes. • The rocks most receptive to gold seem to be those which contain chloride or otherminerals of similar composition, although chlorite in the immediate vicinity of the ore is often altered to sericite. There are more gold deposits in chloritic slates and phyllites and in basic to intermediate igneous rocks than in quartzites, rhyolites or limestones.

43. Structural Controls on MineralizationNearly all hydrothermal deposits exhibit some degree of structural control on mineralization.  Structures (fractures, faults or folds) which form prior to a mineralizing event are referred to as “pre-mineral” (Figure 10 – 6).  Geologists are keenly interested in pre-mineral structures because these structures influence the localization of ore by hydrothermal fluids utilizing these pathways.  By mapping these structures and projecting the geometry in the subsurface, new ore deposits may be discovered.  Structures which form after a mineralizing event, and hence may be responsible for offset or removal of mineralized zones, are referred to as “post-mineral”.  In some cases the formation of structures and mineralization appear to be nearly synchronous (Figure 10 – 7).  In these situations, shearing was probably ongoing during the mineralization event.  This is evidenced by ore minerals localized along a fault plane which are deformed.Fractures and fault zones provide excellent pathways for hydrothermal fluids to circulate through.  Open-space filling has long been recognized as the primary method of vein formation.  The formation of breccia and gouge due to the grinding action of the rocks adjacent to the fault plane increases the ‘structural porosity’, which in turn increases the permeability.  Under certain conditions, breccia or gouge may itself provide the host for mineralization.  Intersections of structural features often are better locations to prospect for mineralization, especially where the structures are high angle.  It is thought that the intersection of high angle structures provides pathways for fluids from deep sources to move closer to the surface.

44. Figure 10 – 6.  Fracture systems in rocks overlying an igneous intrusion.   A & B:  radial fractures above a circular intrusion. C & D:  longitudinal fractures above an elliptical intrusion (from Emmons, 1937).

45. Zoned Vein Deposits • Zoned vein deposits are deposits which form along fractures and faults as open-space fillings or replacements.  They are generally polymetallic.  Many have been mined for copper, lead and zinc, although substantial gold and silver credits occur locally.  These deposits generally fall in the category of low tonnage, high grade types of deposits.  There are two broad categories: 1) vein deposits associated with porphyry base metal deposits, and 2) vein deposits not associated with porphyry base metal deposits.  • Zoned vein deposits which are associated with porphyry base metal deposits appear to form at lower temperatures during a later mineralization event.  These veins are characterized by a strong sense of zoning from high temperature minerals in proximal (closer to the pluton) portions of the veins, to low temperature minerals in distal (far away) portions of the veins.   Proximal portions of the veins are copper-rich and contain sulfide minerals with high metal:sulfur ratios.  Distal portions of the same veins are lead-zinc-rich and contain sulfide minerals with lower metal:sulfur ratios.  At Butte, Montana, alteration halos adjacent to the veins change dramatically along the length of the vein and with increasing distance from the central porphyry copper-molybdenum deposit (Figure 8 – 2).  Proximal portions of the veins are characterized by advanced argillic alteration adjacent to the vein which is superceded outwards by sericitic alteration.  Distal portions of the veins are characterized by propylitic alteration adjacent to the vein which gives rise to fresh unaltered rock further away from the vein.  Zoned vein deposits which are not associated with porphyry base metal deposits are characterized by having moderate, more uniform temperatures over a larger area.  Zoning in these types of vein deposits is usually a function changes in the fugacity of sulfur along the length of the vein.

46. Figure 8 – 2.  Example of proximal and distal zoning of base metal vein deposit of the type associated with porphyry copper/molybdenum deposits.

47. ROCK IDENTIFICATION To classify a rock, three things must be considered:   1) origin,  2) composition,  and 3) texture.  Rock OriginThe first step to identify a rock is to try to categorize the rock into one of the three main types or groups of rocks.  These include igneous, sedimentary or metamorphic types.  The only rocks which do not fall into one of these categories are meteorites.  Igneous, sedimentary and metamorphic rock types are distinguished by the processes which form them. Igneous rocks:  form by crystallization of a melt (molten rock material).Subcategories:  Plutonic:  formed at significant depth below the surface.Volcanic:  formed at or near the surface.Sedimentary rocks:  form by the compaction small or large grains or fragments of pre-existing rocks, or by the precipitation of mineral matter from a body of water, such as an ocean, lake or stream.Metamorphic rocks:  formed from pre-existing igneous, sedimentary or metamorphic rocks by subjecting them to heat and/or pressure and/or migrating fluids, causing the original mineral assemblage of the rock to change to a new assemblage of minerals.The origin is not always obvious, but sufficient training will enable recognition of certain features which point to the most likely origin.  Examples include the common presence of bedding or layering in sedimentary rocks, and the presence of mineral foliations or lineations in metamorphic rocks.  One must also consider the geologic environment where the rock is found.  For example, in a young volcanic terrane one is less likely to find sedimentary or metamorphic rocks.  When the origin is completely unobvious, the composition and texture must be relied upon to make the best guess. 

48. Rock CompositionThe rock composition is found by determining which minerals make up the rock.  By definition, a rock is a solid mass or compound consisting of at least two minerals (although there are some exceptions when a rock may consist entirely of one mineral).The minerals comprising the rock can be identified using common field testing methods for individual minerals, particularly where the texture is sufficiently coarse-grained enough to distinguish the individual minerals with the naked eye or a hand lens.  Where the grain size of the minerals comprising the rock are too fine-grained to recognize discrete minerals, “petrographic” methods (those using a microscope) can be used for reliable identification in many cases.Petrographic methods involve the use of a microscope to examine the optical properties of discrete minerals magnified through the microscope lens.  Properties include the behavior of refracted, reflected and transmitted light either through a thin wafer slice of the rock (called a thin section), or of a sample plug (for reflected light).  The light source is adjusted to provide light which polarized in one or two directions.  Different minerals have characteristic optical properties, which can be used with tables of optical mineral properties to identify the mineral. 

49. Rock TextureThe texture of a rock is defined by observing two criteria:  1) grain sizes,    2) grain shapes.Grain Size:  the average size of the mineral grains.  The size scale used for sedimentary, igneous and metamorphic rocks are different (Figure 1).Grain Shape: the general shape of the mineral grains (crystal faces evident, or crystals are rounded).Examples of the size classifications for each of the three major rock types include: FINE-GRAINED > > > > > > > > > > > > > > > >  COARSE-GRAINEDSedimentary:           Shale         Siltstone        Sandstone       Wacke          ConglomerateMetamorphic:          Slate               Phyllite                 Schist                GneissIgneous:                 Rhyolite                                                                 Granite

50. GEOLOGIC  PRINCIPLES One of the main goals of mineral exploration is to predict the geometry and relationships of different rock types under the surface where they can’t be seen either below the surface or beyond the immediate exposures.  This is essential to know in order to plan a mine.  Much effort and a variety of techniques are used to analyze the timing or “geologic history” of the area (see “Geologic Time” below).  There are three main principles, or “laws”, which are used in field geological studies to guide in determining the relative timing of events. Law of Cross-cutting Relationship;