The term “dispersion” describes how elements disseminated outwards from the place of its origin. A “dispersion halo” is defined as a region surrounding a mineral deposit, characterized by metal concentrations that are lower than the deposit itself but are comparatively higher than the background levels in the surrounding rocks. Dispersion halos can be classified as primary and secondary halos based on the dispersion processes involved.
Primary Dispersion Halo
The primary dispersion halo of an ore deposit is a zone where ore-forming and associated elements are enriched because of ore genesis processes and formed at the time of formation of deposit. Primary geochemical haloes of mineral deposits arise from the interaction between wall rocks and mineralizing fluids, are marked by either a decrease or increase in the metals or related trace elements. However, comprehensive multi-element geochemical data indicates that the primary halo is only part of a complexly differentiated geochemical system. This system includes both the primary haloes of enrichment (positive anomalies) and haloes of depletion (negative anomalies) of ore-forming and other elements.
These haloes are categorized into three types: axial, longitudinal, and transverse zonations. Among these, the axial zonation is crucial in the exploration of ore deposits because of its relationship with the direction of ore-forming fluid pathways. Studying the primary geochemical haloes of elements is a significant and effective technique for exploring hidden mineral deposits.
Secondary Dispersion Halo
Secondary dispersion pattern / halo is formed in the secondary environment for a long period of time after a mineral deposit form. This type of halo is usually the result of weathering of mineral deposit in place or of material dispersed from the ore deposit by gravity, moving water, or glacial ice and the reshuffling of primary halos. This halo can be identified in samples collected from various sources such as soil, rocks, sediments, plants, groundwater, and volatile substances, and can span distances from a few meters to several kilometers.
What is Geochemical prospecting or Survey?
Geochemical prospecting for minerals is a method of mineral exploration based on systematic measurement of the chemical parameters of a naturally occurring substance like rock, soil, water & plants etc. The objective of these assessments is to identify geochemical anomalies or regions where the chemical pattern suggests the presence of ore in the vicinity. These anomalies can be formed either deep within the earth through igneous and metamorphic activities, or on the earth’s surface by weathering, erosion, and surficial transportation.
Geochemical prospecting serves as a crucial instrument during the initial phases of mineral deposit exploration. It aids in identifying anomalous regions that might potentially lead to the uncovering of economically valuable mineral deposits.
The technique of primary halo prospecting has been proved by various studies and applications as an effective method for locating deep concealed ore bodies. It has been extensively used in the exploration of porphyry copper deposits and other hydrothermal ore deposits.
In the field of geochemical prospecting, elements like “pathfinders”, “indicators”, or “tracers” play a crucial role.
Definition of Pathfinders
Pathfinders element are relatively mobile element or gas that occurs in close association with an element or commodity being sought, but can be more easily found because it forms a broader halo or can be detected more readily by analytical methods. A pathfinder serves to lead exploration geologist to a deposit of a particular mineral or metal.
Examples of pathfinders in some types of mineral deposits.
Conclusion
Primary dispersion is linked to the initial formation of a mineral deposit and takes place inside the country rocks themselves, whereas secondary dispersion is a result of weathering and other processes that cause elements to get transported into the surrounding environment after they have already been formed. Halos caused by secondary dispersion are usually much more widespread than those caused by primary dispersion.