Photogeology is a very important of gold deposit exploration. It gives complete information of high altitude photography and satellite photography. Images are recorded either on films or by recording the image digitally. Films used include black & white, true color, and Infra-red. In color photos, the red areas indicate live vegetation. This makes them useful for locating outcrops in highly vegetated areas. Also least affected by fog, and is effective in cloudy environment. It is also good for determining moisture content of soils. The typical aerial photos are those which are taken with the camera lens vertical due to oblique photos could exaggerate the relief.
In general, photogeology involves the interpretation of an area’s geology from analysis of landforms, drainage and vegetation. Basically, there are four types of information, fracture and trace analysis, fracture identification, seep detection and channel change study. When a fracture is observed in cross section, it seems to be vertical or near vertical breaks in the bedrock. Gold particles can be deposited into fractures. Other important information is the called lithological mapping, which involves the interpretation of surface features so that can be obtained a more exact map.
Identifying areas to be prospected
The map scale towards the center of the photo is different from the map scale toward the edges of the photo. Orthophotos are images which have the distortion rectified, and can be used directly for mapping purposes. There are many applications of photogeological methods in mineral exploration work as well as in the studies of environmental geology and geologic hazards. Most importantly, they are used to make accurate topographic base maps. In mineral exploration work, accurate topographic base maps are essential for recording geological observations. Rock and soil color changes, or color anomalies, can be delineated and possibly investigated with ground traverses.
Photogeologic analysis provides data on local geology conditions which help to detect possible gold zones. Even, it is possible to get information on ground water movement, and this is influenced by fracture traces, karst features and aquifer recharge and discharge points such as springs. It is possible to get information on lithology, alteration and structures. When the work was performed properly, there will be possible to know the structural features in a specific area, such as the direction and dip of the beds, fold direction, and fault plane dip. Color contrasts in exposed bedrock due to changes in rock type, or lithology, and can be traced on the photograph, to map out the contact. The information can be gathered more efficiently and safely than a ground traverse, although there is no substitute for direct observations.
Photographic surveys follow specified flight routes and take the photographs at regular spacing along the path. The overlap between adjoining photos in a sequence along the line is about 55-60 %. The overlapped area is detected by the camera from two different views in two different photos. The two adjoining photos used together make what are called a stereo pair. The two photos can be placed side by side and observed with a stereoscope.
Once the need for Photogeologic support is identified, the place is screened for suitability. A preliminary determination is made to insure that the site is located within the appropriate geologic terrene for the requested Photogeologic work. Government and private sources of overhead imagery are searched for available coverage and information on geology, hydrology and soils is compiled. Close contact with prospectors and gold companies assures that the results of the study will provide the information required. The results of the Photogeologic study are compiled into a bound report that includes figures, maps, and interpretation.