Collecting Field Data for a Bedrock Geologic Map GEOL 3000

Establish Objectives Why are you mapping? - previously unmapped or inadequately mapped area, adding additional level of detail to previously mapped area, trying to solve a specific geologic problem, evaluating economic potential of an area,... What are you mapping? - quadrangle, county, geological unit of interest, area of mineralization potential What scale will your final map be? -determines the scale of your field map (always map at more detail than the final map) and the coverage of outcrop you acquire Who will be mapping and where? - balance expertise, safety, coverage of field parties Research Previous Mapping and Useful Data Review published and unpublished maps (e.g. thesis maps, exploration company maps) and related reports or scientific articles Seek out original field maps and notes if available Investigate any handsamples and thin sections from previous studies Investigate any drill core or core logs in your field areaPreparation

Gear for Northwoods Field Work Clothing - long sleeve collared shirt - loose-fitting, light but rugged long pants - inexpensive rain pants and jacket - field hat - rugged water-proof boots - field vest &/or back pack Geologic Equipment - field map and map board - notebook (water-resistant) - Brunton AND orienteering compasses - hand lens, magnet, acid bottle - hammer (and chisel) - pencils (reg. & colored) - sample bags and permanent markers Other - insect repellent and more insect repellent - water (2 liters) - field lunch (gorp, fruit, jerky) I’m gonna find me some outcrop today!

North Country Exposures

The Field Map Topographic Base -~ page size - scale greater than final map scale (e.g. for 1:24,000 map, field map at 1:12,000 or 1:10,000) - add UTM grid for ease of locating - use waterproof paper or laminate - overlay with sheet of mylar Outcrops -label station ID that matches notebook and sample ID - discriminate rock type with colored pencil - note sample locations - draw strike and dip of measured structures Other Features - route taken - new roads or trails - possible geologic contacts or faults - other things of note Field Map of part of Tofte 7.5’ quadrangle BE ACCURATE BE NEAT!

Finding Outcrop Start here S80ºW or 260º ~700’ or 1120m ~140 paces M486 massive gabbro

Recording Outcrop Information Scout around the outcrop: Make careful observations of rock type(s), textures, structures; peel moss if necessary Measure orientation of structures/contacts Hammer off a piece of rock for a closer look Take a sample if necessary or important Take a picture if photogenic exposure Find a comfortable spot on the outcrop; Apply bugspray if necessary; pull out notebook and map; check GPS location On the field map, mark: Route to outcrop location Area of outcrop - ACCURATELY (in color?) Station ID# label Strike and dip symbols of structures Locations of samples taken In the notebook, record: Station ID#, UTM coordinates Extent, visibility, & type of outcrop Rock description- mineralogy, texture, structure Structure measurements Photographs taken Samples descriptions

Finding More Outcrop Start here S60ºW or 250º ~1100’ or1750m ~220 paces M486 S75ºW or 255º ~750’ or1200m ~150 paces M o S5ºW or 185º ~950’ or1520m ~190 paces M488S-- No OC massive gabbro layered gabbro 20 o

Compiling Field Data In GIS