GEOLOGICAL MAPPING PROCEDURES

Large scale and detailed geologic mapping is a part of the target investigation or follow up stage in exploration. Still, a certain amount of detailed geologic mapping will already have been done in areas of critical lithology, stratigraphy, structure and alterations.The need for information from detailed mapping in a part of the reconnaissance area may not become apparent until work has begun in one of the selected target areas.Detailed geologic mapping takes place in many locations and for many reasons. Nor is geologic mapping an isolated activity, it is one element in a group of investigations that includes trenching, drilling, geophysics, and geochemistry. A geologic map provides the context for all the other investigations.

Types of geological map

Geological maps fall into four main groups:1) Geological reconnaissance maps: Is made to find out as much as possible about

the geology of an unknown area as quickly as possible. It is usually made at a scale of 1:250,000 or less.

2) Regional geological maps: reconnaissance has given the outline of rock distribution and general structure, now the geology must be studied in more detail, most commonly at a scale of 1:25,000 or 1:50,000.

3) Detailed geological map: Here, scale is anything from 1:10,000 upwards and they are usually made to investigate a specific geological problem, perhaps resulting from discoveries made during regional mapping, or perhaps with economic objectives, such as a mineral investigation.

4) Specialized maps: are many and varied. They include large scale maps made in great detail of small areas to record specific geological features. Many are made for economic purposes, at scale from 1:1000 to 1:2500 and even 1:500. They are many other types of maps with geological affiliations too. They include geophysics, geochemical, structural, sampling plans with outline geology. Many are prepared as transparent overlay (Folio system), to be superimposed on a normal geologic map at the same scale.

Instruments and equipment- Hammers and chisels- GPS- Compasses and clinometers- Altimeters- Hand lenses (7 to 14 times)- Tapes- Map cases- Topographic maps- Field notebooks- Scales- Scale Protractors- Pen, pencils and erasers- Acid bottle- Sample bags- Pocket Stereoscopes- Pocket size electronic calculator

- Field bags and geological vest

Geologic mapping procedures

Field mapping is a process of analysis and communication. Geologist put a picture together for themselves and for their associates; this means that most of their observations, even their thoughts, belong on the map where someone can study them, not in book or side notes. But space on map sheets is too limited for some of the detail unless it can be presented in well understood symbols and abbreviations.

Most organizations have additional standards and modifications that relate to a particular kind of “home” terrain or to their special group of mineral commodities. Standardization is important.

Putting symbols, abbreviations, and ideas on paper follow nearly the same procedure whether the base map is an aerial photograph or a topographic map.

A ground location is determined on the base map, the map is oriented, additional map and ground features are matched, and the geological observations are plotted.

If the main control points are too far away or completely off the mapping sheet (we are using Total Station for control points), a traverse may have to be made from one of them to a convenient secondary control point or it may be necessary to establish the secondary control point by resection.

The control point and subsequent traverse point serves as hubs for plotting geology by estimation.

A widely used technique is to plot geologic data on overlays sheets (Folio System), of polyester drafting film. Pencil lines and colors may be used on the drafting film overlays and they will be relatively well protected in the aluminum sheet holder.

In most practice with overlays (Folio System), the topographic map is left unmarked and the geologic data are plotted on the overlays sheets, as follows:

Overlay 1: Topographic map, outcrop boundaries, lithologic identifications, geologic contacts, and notes on texture, color and weathering.Overlay 2: Structural data, including bedding, faults, joints, fracturing, cleavage, schistosity and rock fabric.Overlay 3: Mineralization and alteration, with notes on geochemical sampling and the location of explanatory field photographs or topo sheets of outcrops. Once the field data have been recorder and the type, intensity and distribution of mineralization carefully noted, they can be transferred to the computer with the intention of data base creation for each sector or area.