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Geochemical cycle and mobility of elements
The document discusses geochemical concepts relevant to mineral exploration, including the geochemical environment, cycle, dispersion, and mobility of elements. It describes the deep-seated and surfacial environments and how materials move between them in the geochemical cycle. Mobility depends on factors like viscosity and particle size. Hypogene mobility occurs under high pressure-temperature conditions, while supergene mobility is influenced by siliceous or sulfide environments at the surface. Indicator and pathfinder elements are discussed for detecting targeted ore deposits.
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Geochemical cycle and mobility of elements
- 2. CONTENTS INTRODUCTION GEOCHEMICALENVIRONMENT GEOCHEMICAL CYCLE GEOCHEMICAL DISPERSION GEOCHEMICAL MOBILITY HYPOGENE MOBILITY SUPERGENE MOBILITY ASSOCIATION OF ELEMENTS CONCLUSION REFERENCE
- 3. INTRODUCTION Geochemistry refersto the determination of the absolute abundant of elements in the earth. Geochemistry as applied in mineral exploration is mainly concerned with the preparation and interpretation of geochemical maps rater than the investigation of basic principles Geochemical prospecting can be realized only through a understanding of the principles that govern the distribution of element in the earth
- 4. Cntd Geochemically and geologicallythe earth is a is dynamic system in which materials move from one place to another and change in composition by a variety of geological process like melting , crystallization, erosion, dissolution, precipitation etc….
- 5. GEOCHEMICALENVIRONMENT Based onthe differential pressure temperature and chemistry the geochemical environment of the earth can be broadly classified into deep seated environment and surfacial environment . The deep seated environment extends downwards from the lower levels of circulating meteoric water to the deepest level at which normal rocks can be formed. It is an environment of high temperature and pressure, restricted circulation of fluids, and relatively low free oxygen content
- 6. Continued The surfacialenvironment is characterized by the process of weathering, erosion, and sedimentation at the surface of the earth. It is characterized by low temperatures, nearly constant low pressure, free movement of solutions, and abundant free oxygen, water, and CO2.
- 7. Geochemicalcycle The movementof earth materials from one environment to another can be conveniently visualized in terms of a closed cycle referred to as the geo chemical cycle
- 8.
- 9. continued In thegeochemical cycle starting on the right hand side of the diagram and moving clockwise direction Sedimentary rocks are progressively metamorphosed as they are subjected to increasing temperature, pressure, and increments of new materials from out side the system. The may eventually attain a state of fluidity such that on recrystallization they can differentiate into various kinds of igneous rocks and hydrothermal extracts. When erosion brings the resulting suite of rocks into the surficial environment again, the component elements are relative solubility in water. redistributed by weathering agencies primarily in accordance with their A new series of sedimentary rocks is then deposited ,and the cycle is closed The geochemical cycle therefore includes both deep seated process of metamorphism and igneous differentiation and the surficial process of weathering, erosion, transportation and sedimentation
- 10. GEOCHEMICAL DISPERSION Anymaterial on the earth is constantly subjected to transformation as process through different environment in the geochemical cycle. This process in which atoms and particals move to new locations and geochemical environment is referred to as geochemical dispersion. Geochemical dispersion may occur by mechanical process or even chemical and biological factors .
- 11. continued The response ofan elements to dispersion depends on its mobility that is how easily it can be dispersed relative to other associated material.
- 12. continued The distributionof elements of the constituents rocks and minerals in response to various geological process are referred to as geochemical mobility.
- 13. GEOCHEMICAL MOBILITY Fundamentally,the response of an element to dispersion process is governed by its mobility, that is the ease with which it may be move in any given environment Mobility depends an the mechanical properties of the mobile phase, and factors such as the viscosity of magmas and solutions and the size shape , and density of clastic grains in following scheme water. The relation between mobility and chemical differentiation, an other hand is rather more involved . Here the prime factors are the changes in relative stability of the various coexiting fluid (mobile) and crystalline (immobile) phases that result from changes in the environmental condition.
- 14. MOBILITY UNDER HIGHP-T CONDITIONS (HYPOGEN MOBILITY) In crystallization of magmas ,the constituents that can not be accommodated in the lattice structures of stable rock forming minerals are concentrated in mobile residual fluide. Water, which cannot be entirly accommodated in the minerals of igneous rock , is progressively enriched in the residual fluids . Hydrothermal vein deposits may be precipitated at this stage in the primary geochemical cycle . At high P-T the hydrous minerals of sedimentary rocks becomes unstable and water is released to become principal constituent of the mobile phase.
- 15. Continued The occurrence ofan element as a characteristic constituents of deposits formed from fluids of various kinds,either vapors,supercritical solutions,or normal aqueous solutions,may also be an indication of their hypogene mobility. In this group are the elements of complex pegmatites,hydrothermal vein deposits,juvenile water, and gaseous emanation.
- 16. Supergene mobility ofelements siliceous sulfide-free environment Relative mobility Very mobile Moderately mobile Moderately immobile Very immobile Major elements S,cl Ca,na,mg ,k Si,mn Fe,Al,Ti Minor elements Br,l,mo,b,se Zn,ba,u Ni,co,cu,as,pb Cr,Rare earths
- 17. ASSOCIATION OF ELEMENTS Ina geochemical survey an elements measured to detect and ore body is referred to as an “INDICATOR ELEMENTS”. In many situation the indicator elements is the same element as the ore deposits. Example-Element gold for gold deposits. If the ore element is difficult to analyze then another element associated with the ore will be useful which is referred to as a “PATHFINDER ELEMENT” Example- Arsenic for gold ,
- 18. PATHFINDERSTABLE Pathfinder Material Oretype elements sampled . As Wall rock , residual soil vein type Au ore Hg Wall rock & soil Complex Pb-Zn- Ag ores Se Gossan , residual soil Epigenetic sulfides Ag Residual soil Ag-bearing Au ore So4 Water sulfide deposits
- 19. CONCLUSION The movement ofearth material from one environment to another can be explained by this geochemical cycle. Geochemical exploration is mainly governed by mobililty of elements and the geochemical cycle and geochemical environments help understand the mobility of elements.
- 20. REFERENCE Geochemistry inmineral exploration H . E . HAWKES and J . S . WEBB, HARPER and ROW,PUBLISHERS. ( 1979). Pp. 10 - 23 WEB SITE -WWW.GOOGLE.COM http://en.wikipedia.org http://geochemical cycle.org
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