The occurrence of gold deposits is variable and some disseminated deposits may be associated spatially and probably genetically with large masses of rock. The description within or near the masses gives information about the economic mineralization and its concentration in zones of structural complexity developed along one or more of the major faults, especially those with a especial trend. By performing geochemical studies, the occurrence of gold is usually classified in disseminated and veins.
The mineralization in disseminated occurrences may be detected 10 to 20 km from its source by anomalous concentrations of gold in stream sediments and detailed follow up work on the anomalies clearly defined areas in which soil sample is warranted. It is important to mention that the distribution of gold in soils indicates gold bearing minerals. This area of mineralization may be detected readily in the course of routine, exploration stream sampling. For example, it is possible to detect a disseminated gold occurrence in diorite similar in topography and geology to the test performed in a close area. When a zone was sampled and apparently there is no mineralization, it will be important to have a geochemical response attributable to the partly defined mineralization and explore for similar deposits in other areas. In some cases, soil responses for the known mineralization could not be determined with reliability because the mass itself is exposed and devoid of cover.
It is important to perform a stream survey to evaluate rock masses over an area of about 30 sq km. By using a series of threshold values, areas of mineralization may be distinguished from other rocks and areas of probable mineralization within the area defined soil sampling, which were defined by results of the stream surveys. Basically a systematic soil survey within these areas delimits, on the basis of a significant threshold value, one or more zones of probable mineralization. The zone may be evaluated a simple underground work. The general area of interest could have been identified by stream reconnaissance without any prior knowledge. The effectiveness of combined detailed stream and soil surveys in locating and defining mineralization within the area of interest is supported by geochemical studies.
It is possible to detect disseminated gold occurrence in rocks whose mineralization appear to be almost entirely base metals oxide minerals at depths of 20 m below surface. In other zones, a further contrast with the area of pilot study may be identified. Stream sampling, defines the area of interest, while soil sampling within this area reveals a well defined anomalous zone. These results may be confirmed by drilling programs over an extensive area. For example, preliminary drilling at to a depth of 150 m may show an average of over 0.8 g/t of gold over this depth, the grade may improve with depth and is better than 1 g/t over the bottom 100 m of the hole.
A disseminated gold prospect may be located near an existing gold operation where gold is present in a large disseminated and fracture filling deposit. In this case, considerable exploration must be conducted in order to confirm the potentiality of the prospect. The geochemical work rapidly may gives an answer positive or negative, or also to indicate the restrictions to get acceptable results. In some cases, the contamination of the drainage from the gold operation could may difficult to determine whether the prospect was detected through routine stream reconnaissance.