Collecting Field Data for a Bedrock Geologic Map

1
Collecting Field Data for aBedrock Geologic Map

• GEOL 3000

2
Preparation

• 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• Review published and unpublished maps (e.g.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 area

3
Gear for Northwoods Field Work
Im gonna find me some outcrop today!

• 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)

4
North Country Exposures
5
The Field Map

• Topographic Base
• page size
• scale greater than final map scale (e.g. for
  124,000 map, field map at 112,000 or
  110,000)
• 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

BE ACCURATE BE NEAT!
Field Map of part of Tofte 7.5 quadrangle
6
Finding Outcrop
Start here
M486
S80ºW or 260º 700 or 1120m 140 paces
massive gabbro
7
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

8
Finding More Outcrop
Start here
M486
No OC
25o
S60ºW or 250º 1100 or1750m 220 paces
M487
S75ºW or 255º 750 or1200m 150 paces
S5ºW or 185º 950 or1520m 190 paces
massive gabbro
M488
S--
layered gabbro
20o
9
Compiling Field Data In GIS