According to many gold prospectors, geochemical exploration is the most effective and economical means of locating and defining the presence of disseminated gold deposits and gold vein deposits. Basically, the technique uses geological, geophysical and chemical methods to detect the presence of gold deposits. In some cases, the length of anomalous zones varies from several to more than 20 kilometers and depends on the type and tenor of mineralization. Despite generally marked relief and extreme physical and chemical weathering, some anomalies with gold content appear to reflect closely variations in the gold ore mineral content of immediately underlying rocks.
Threshold values vary with local geology conditions and type and grade of gold bearing minerals. In some circumstances significant threshold in stream sediments are about 3 g/t and 15 g/t for gold in disseminated and vein gold occurrences, respectively. It has been noted that these differences need to use a scale of threshold values at progressive stages in each exploration program. Disseminated gold occurrences are usually the major source of gold. During approximately four to eight weeks an orientation survey involving geological mapping, geophysical surveying and geochemical prospecting is conducted over a potential gold deposit. This study is oriented to demonstrate the economic and technical feasibility of geochemical prospecting for the location and delineation of a gold deposit.
Geochemical techniques are also applied in an orientation study of a vein occurrence. The results of these studies usually suggests that in reconnaissance work, stream sediment and samples analyses, combined with the determination of some ph values can be employed to indicate areas underlain by rock containing concentrations of gold, whether it occurs in the large tonnage, low grade, disseminated deposits or in the comparatively small tonnage, high grade, and gold vein occurrences. The orientation surveys demonstrate that soil sampling and analyses serve effectively to outline more closely the mineralized zones within the generally anomalous areas.
Sometimes, geographical conditions have influence in the design and execution of the mineral exploration programs. For example, access may be limited, topographic relief is marked, and slopes are steep, 35o - 45o. Physical and chemical weathering may be intense, particularly during the rainy season. Vegetation cover may vary from terraced, cultivated slopes to relatively virgin forest. Also, in some locations, the thickness of soil may range from 30 to 90 cm. Under these conditions, it is apparent that for any exploration technique to be useful, it must be simple, flexible, economical and rapid in order that results can be obtained, quickly evaluated and employed to form the basis of the continuous work in field. Geochemical exploration fulfill these requirements and more important, its application gives significant results that justify a more detailed and expensive exploration and development technique to confirm with more detail the potential of the gold deposit.