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8/8/2019 Maps Navigation.

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Introduction

1. Overview of PhysicalGeology

2. Rock Identification MethodsGeologic Principles

3. Maps & NavigationGeologic Maps

4. Igneous RocksMagmatic Deposits

5. Plutonic-Related DepositsAir Photos

6. Volcanic RocksVolcanic-Related Deposits

7. Sedimentary RocksLow Temp. DepositsGPS Navigation

8. Hydrothermal Veins&Alteration

9. Metamorphic RocksMetamorphic Deposits

10. Structural GeologyStructural Controls onMineralization

** Mid Term

11. Mechanical ErosionPlacer Deposits

12.Geochemical SamplingMethods

13. Adit/Trench MappingGeochemical Methods

14. Geophysical Methods

15. Project PlanningClaim Staking

16. Exploration DrillingMethods

** Final Exam

Class 3 Maps, Navigation and Geologic Maps - Notes

Reading Assignment pp. 45-47

Introduction to Maps Navigation and GPS Geologic Maps

INTRODUCTION TO MAPS

Maps are one of the most important media used to communicate informationin exploration geology. Maps are a two dimensional representation of thesurface of the earth and its features. Maps are a kind of shorthand languagemedia with two main purposes: 1) to convey detailed information about aspecific area, and 2) to indicate the position of the specific area relative toother parts of the earth. The first objective is accomplished by recordinginformation in graphic form, either directly from field observation or indirectlyfrom air photographs or a wide variety of other sources. The secondobjective is accomplished by showing reference marks (or a coordinatesystem), or by showing a small scale location map with well knownlandmarks. A coordinate system is nothing more than a graphical means oflocating any point on the map, with two coordinates for each point giving

positions with respect to the X axis and Y axis.

Most maps have more than just a map area they often have lots of otherinformation that is given in the space around the main map area. Acomplete map generally has several main components. In addition to themain map area, a complete map will usually include the following informationin various positions adjacent to the main map area: 1) title, 2) author(s), 3)date, 4) scale, 5) indication of true and magnetic north, and 5) coordinates orreference points. Additionally, almost all geologic maps, as well asgeophysical and geochemical maps, contain an explanation. Theexplanation is where the code for reading the map is provided. This mayinclude the colors, symbols and all other abbreviations used on the map.

Many types of maps are used in exploration geology. Topographic mapsare the most widely used maps. These depict the surface morphology byshowing lines of equal elevation (or contour lines). The most basic andessential type of map used by geologists is the geologic map. A geologicmap shows rock types (or lithologies) and their geometry. Geologic mapsare very often constructed on a topographic base map.

Other types of maps which are used in conjunction with geologic mapsinclude geophysical maps and geochemical maps. Geophysical maps showreadings of magnetism, gravity, electrical conductivity, radioactivity, or otherphysical properties of rocks in an area. Geochemical maps, likewise, show

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geochemical values of samples collected in an area. These may besamples of soil, rock, stream sediments or water. There may be numerousvalues or readings from an area, so typically a derivative map will becreated from these maps which summarizes the information or otherwisedepicts the data in a fashion such that it can be more quickly evaluated.Typically this is done by designing a map which delineates or emphasizesthe anomalous (outside normal) readings or values. One way thesederivative maps can highlight anomalous values is by contouring the data

similar to the way elevations are used to create topographic contours. Thismethod clusters data points with similar high values and shows the gradienttowards lower values just in the way hills and valleys show up on atopographic map. The other method of creating a derivative map is to createa thematic map. A thematic map uses colors or symbols to code thevalues on the map.

COORDINATE SYSTEMS

There are many, many types of coordinate systems used for maps, butrelatively few are in common usage in exploration geology. These includelatitude-longitude, UTM, metes and bounds and local grids. As stated, the

map is a two dimensional representation of an irregular surface forming aportion of a sphere of the earth (also called a geoid). Problems arise whentrying to fit a flat piece of paper onto a rounded object. The result is a flatmap which contains distortion, particularly in the corner areas. Thisdistortion is accommodated by using a projection, which is a mathematicalor geometric means of minimizing the problem.

Latitude-longitude has historically been the most frequently used coordinatesystem for both navigation purposes as well as for conducting explorationgeology. In this system the coordinates consist of degrees, minutes andseconds. The latitude, which represents the Y value, is the angular distancenorth of the equator, which ranges from 0 degrees at the equator to 90degrees at the poles. The longitude, which represents the X value, is the

angular distance westward from the 0 degree meridian, also known as theprime meridian.

The UTM (Universal Transverse Mercator) coordinate system is rapidlybecoming the coordinate system of choice in creating maps for explorationgeology. The major advantage to this system is that it is based on themetric system, using meters (or kilometers) for distance units. This greatlysimplifies mathematical calculations concerning scale and distancemeasuring. The UTM system is based on a series of geographic zones,each containing a rectangular grid. The Y value of the grid system isreferred to as the Northing and increases towards the north. The X value ofthe grid system is referred to as the Easting and increases towards the east.

Another coordinate system used in exploration geology, more for legaldescriptions of land than for navigation purposes, is the system of metesand bounds. This system is referenced to a known meridians (north-southand east-west lines), which is stated on the USGS topographic map of thearea. The largest subdivision is the township, which consists of 36 squaremiles. The township is six miles in length per side. Each township isdefined by a township number, which refers to the Y coordinate, and byRange number, which refers to the X coordinate. For example, Township 3North, Range 4 E refers to the thirty six square mile area extending from 18to 24 miles in an easterly direction from the meridian, and from 12 to 18miles in a northerly direction from the specified meridian. The




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sections (one square mile each) are numbered in a standard pattern,starting in the upper right corner of the township with Section 1 andincreasing to the west to Section 6. The pattern begins with Section 7assigned below Section 6, and across to the east to Section 12. Sec. 13 isbelow Sec. 12, etc... The next level of subdivision is the the quartersection, which, as the name implies, is one fourth of the Section. Thequarter sections are labeled with the quadrant direction specified as NE,NW, SE, and SW. The last subdivision is the quarter of the quarter

section, again labeled as to the quadrant direction.

NAVIGATION AND GPS

Accurate navigation is essential to conducting many types of geologicalinvestigations. The primary activities often involve sampling or datacollecting on a specified grid or other location system. For detailedsampling, past work has relied on the compass, although handheld GPSinstruments have become standard surveying equipment since about 1995in Alaska.

Bearing means direction. Bearing can be noted in two main ways. The

quadrant method indicates the bearing in terms of the number of degreesfrom a cardinal direction (N, S, E or W). For example, N30E indicates abearing of 30 degrees east of north. The second system is calledazimuth. The azimuth system refers to the number of degrees around acomplete 360 degree circle. For example, an azimuth of 300 indicates abearing of 60 degrees west of due north. The azimuth system is becomingthe most common for navigation purposes during exploration activities.

Reconnaissance surveying is often employed during geochemical samplingon grids. This is accomplished using a compass in conjunction with sometype of distance measuring device. The ones most commonly used are thehipchain and the tape. The hipchain lets out a thread, which is woundaround a counting device and allows distance measurements to be viewed.

Tapes are made of a few different materials, but are manipulated the sameway, which is to lay the tape, which has marked distances, out along thelength of surface to be sampled. Hip chains are used mostly forreconnaissance work where the terrain is rough and less precision isrequired. Tapes are used for detailed sampling, for example, along a trenchfloor.

The two main types of compasses in use today are the Brunton and theSilva Rangefinder (or comparable). The Brunton compass is moreexpensive, but more accurate than the Silva. The Brunton is calibrated tothe nearest degree, while the Silva is to the nearest two degrees. TheBrunton compass uses a bubble level type inclinometer, which is morereliable than the pendelum type used in the Silva. The compass must be set

to the correct declination of the area being explored. This is given onstandard one inch equals one mile USGS topographic maps for the area.However, where magnetic anomalies exist, the declination must be adjustedfor local variations. This can be done by locating a survey line in the areawith a known bearing. For example, many section lines, especially nearpopulation centers are brushed when they are surveyed.

GPS (global positioning system) is currently an integral part of anynavigation purposes. Handheld units have become very portable and quitereliable in many instances. GPSs can be used in two main ways. First,




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location coordinates can be pre-entered into the unit, so the unit can beused to guide the explorationist to a pre-determined point, perhaps obtainedfrom a map. The second way GPSs are used in the field is to mark orautomatically record a waypoint while in the field, and then plot the locationon a map. GIS (geographic information system) software can then be usedto plot the point on a map. Two of the most popular GIS programs areMapInfo and Arcview.

GEOLOGIC MAPS

Geologic maps are central to almost any geological exploration projects.First, all previous geologic maps and data for an area needs to be soughtafter. Once the previous geologic maps have been assessed, there may beneed for additional geologic mapping to be completed at a smaller scale toshow more detail. Geologic maps may be created at different scales toshow different levels of detail. For example, a reconnaissance geologic mapwill generally have less detail than an underground mine map. When trenchor underground mapping requires the illustration of great detail, so must bemade at a larger size.

Rocks can be exposed at the surface in three main ways. They can bepresent in outcrop, which is a direct observation of bedrock. They can bepresent in the form of rubble, which is loose rock having no obviousconnection with bedrock. Rubble is generally pretty consistent, and thusmay frequently be used to represent bedrock. Float is defined as looserock material which has no obvious origin. Float generally is less consistent,ie, there is more variability in composition. The type of rock exposureobserved in the field should be noted as outcrop, rubble or float. The mapshould eventually document what type of rock exposure is being used toprovide the basis for the interpretation of the geology shown on the map.Outcrop maps are more reliable to predict the subsurface geology.

There are several different types of outcrop geologic maps commonly made

at an early stage in the exploration of a prospect or area. The decision as towhich lithologies to show is a matter of mappers opinion. Each lithology canbe made into a separate map unit, or lithologies can be combined into onemap unit. The amount of detail needs to fit the map scale chosen, such thatit will fit within the map units and be legible. Within each outcrop, thevarious contacts between differing map units and structural features areshown.

GEOLOGIC MAPPING METHODS

The aim of geologic mapping is to create a map which summarizes thegeologic data gathered in the field. Every place that an observation is made,a sample is gathered, or any type of data collection takes place, it is

positioned on the map at the appropriate X Y coordinates. Conventionally,reconnaissance geologic maps are created with true north toward the topedge of the map. The map can be small scale and show much detail, or belarge scale and generalized. At each point, sometimes called a station,two essential pieces of information need to be recorded, including thelithology and the geometry (or structure), which are defined using color,shading, patterning, and symbology Generally the key to the graphics areshown in an explanation near one edge of the map. The informationshown graphically on the map is generally also recorded in writing in a fieldnotebook.




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As each contact between lithologies is traced on the map, the type ofcontact needs to be defined. The possible types of contacts includingdifferent types of sedimentary contacts, intrusive contacts, and faultcontacts. Sedimentary contacts may be either normal, which is called aconformable contact, or show an erosional surface as the contact, which iscalled an unconformable contact. Intrusive contacts are often sharp, butcan be gradational over a large zone. This could be illustrated graphicallyusing dashed or stipple lines.

The structure data which should be recorded include the geometry of thebedding in the case of sedimentary or volcanic rocks. It would include thefoliation in the case of a metamorphic rock. In some cases, layering withinplutonic igneous rocks can also be measured. Jointing in igneous rocks canalso be an important type of structural data to collect. Where faults arepresent, the surface must also be measured for its orientation. Fault traceson maps are often shown as heavy, dashed or squiqqly lines. There may belineations, such as streaks on fault surfaces or alignment of elongateminerals, which can be measured if they are present at the location. Theseare shown graphically as a small arrow in the direction of the lineation. Asmentioned, it is important to not only show the information graphically on themap.

The geometry of many types of planar features are shown using the strikeand dip symbol. The strike is the bearing of a horizontal line in the plane ofthe feature. It is measured with a compass and plotted on the map. Thedirection of inclination of the same plane is called the dip, and is measured,using an inclinometer, in a direction perpendicular to the strike. Theinclination direction is shown by the small mark on the side of the strike line,and the measurement is placed next to it.

The methodology of determining lithology and structure for map units is thesame for reconniassance, trench or underground mapping. However, thenormal convention of north at the top edge of the map is not always the case

for trench or underground maps, or any other type of geologic map where alot of detail is desired.

FIELD DATA COLLECTION

Field data collection, done in conjunction with field mapping, is frequentlydone in one of two ways. The first way is to record informationchronologically in a field notebook. The notebook represents a daily log ofthe field activities which were completed. Each day should begin with aheader consisting of the date. Then it is customary to summarize thegeneral location. Then a systematic list of stations, observations, samplenumbers, etc... should follow. The second method of collecting field data isto use a standard data collection form which is designed for the project.

This method requires a separate form for each station or sample location.


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