Mineralization

Thread Content

During the evolution of the Earth, various geological processes that concentrate dispersed useful substances (chemical elements, minerals, compounds) to form mineral deposits. Mineralization is complex and diverse. Generally, it is classified into endogenic mineralization, exogenic mineralization, and metamorphic mineralization based on the mineralogical environment (see mineralogical background), the source of energy, and the nature of the processes involved. Accordingly, three major types of deposits are identified: endogenic deposits, exogenic deposits, and metamorphic deposits. Studying mineralization processes and the genetic types of deposits is of great significance for gaining a deeper understanding of the mechanisms behind deposit formation and their distribution patterns, as well as for guiding mineral exploration and mining development. Therefore, the study of mineralization is the core content of deposit geology. 　　Endogenic mineralization refers to the various geological processes that lead to the formation of mineral deposits, primarily driven by internal energy of the Earth, including thermal energy, kinetic energy, chemical energy, etc. Apart from volcanic mineralization that reaches the Earth’s surface and gives rise to volcanogenic deposits, all other types of endogenic mineralization take place within the crust, under conditions of higher temperature and greater pressure. 　　Endogenic mineralization can be classified into the following types based on the properties of the mineralizing fluids and the physicochemical conditions: magmatic mineralization. It refers to the process by which useful components become concentrated to form minerals during the crystallization and differentiation of magma; deposits formed through this process are known as magmatic deposits. Magma that contains minerals, and through relatively complete differentiation leads to a high concentration of metals such as iron, copper, nickel, chromium, and their compounds, is known as mineralized magma. This magma intrudes along fractures in the host rock, resulting in intrusive ore bodies (which are usually rich in minerals). Megacrystalline mineralization. It refers to magma rich in volatile components; through crystallization and gas-liquid metasomatism, useful components accumulate to form ores, and this process gives rise to pegmatite deposits. Contact metasomatism. At the contact zone between a magmatic intrusion and the surrounding rock, mineralization occurs primarily due to the alteration by gas-water solutions; the deposits formed in this way are known as contact alteration deposits. Since such deposits often occur between intrusive rocks and carbonate rocks and form a typical skarn mineral assemblage, they are also known as skarn deposits. Hydrothermal mineralization. During the process of mineralizing hydrothermal activity (including the interaction with the surrounding rock), the mechanism that causes useful components to concentrate and form minerals gives rise to hydrothermal deposits (see vaporized hydrothermal deposits). The formation conditions of hydrothermal deposits are complex and diverse, and there are many such deposits. 　　There are mainly two modes of mineralization for endogenic deposits, especially hydrothermal deposits: one is filling, whereby as the mineral-bearing solution moves through rock material that is not very chemically active, changes in temperature, pressure, and the composition of the solution cause minerals to precipitate in the cracks and pores of the surrounding rock. Another is the substitution process, whereby when a solution reacts chemically with the surrounding rock, there is an exchange of material components between them; components are transferred from one to the other, which leads to the enrichment of mineral-forming substances. Ore bodies formed by metasomatism commonly occur in chemically active rocks. 　　Epigenetic mineralization refers to various geological processes that occur in the upper layers of the Earth’s crust, primarily under the influence of solar energy, through the interaction between rocks, water, air, and organisms, resulting in the accumulation of mineralizing substances. Exogenetic mineralization generally occurs under the temperature and pressure at the Earth’s surface. In volcanic and hot spring areas, a large amount of internal geothermal energy and seismic forces are at work; as a result, the mineralization temperatures are higher than those at normal temperatures, and structural activities are more complex. 　　Exogenetic mineralization mainly includes 2 types: weathering mineralization. It refers to the process by which surface rocks are altered through weathering, causing useful substances to accumulate essentially in their original location to form minerals. Mineral deposits formed through this process are known as weathering deposits. When existing mineral deposits are subjected to weathering, the mineralizing components can become further enriched, thereby increasing the economic value of those deposits. Depositional mineralization. It is the process by which surface mineral-forming materials (such as products of rock weathering, volcanic ejecta, and biological organic matter) accumulate to form deposits through sedimentation and differentiation (mechanical, chemical, biological); the deposits resulting from this process are known as sedimentary deposits. 　　Metamorphic mineralization refers to the mineralization that occurs during contact metamorphism and regional metamorphism, or the process by which existing ore deposits are transformed through metamorphism; the ore deposits resulting from this are known as metamorphic ore deposits. Metamorphic mineralization occurs within the Earth’s crust, under high temperatures and pressures. 　　Based on the geological environment and mechanisms of mineralization, metamorphic mineralization can be classified as follows: contact metamorphic mineralization refers to the process in which, when an intrusive body comes into contact with the surrounding rock, the surrounding rock undergoes thermal metamorphism and recrystallization, resulting in the formation of mineral deposits; such deposits are known as contact metamorphic deposits. Regional metamorphic mineralization refers to the process in which useful minerals become concentrated as a result of regional metamorphic activities; the deposits formed in this way are called regional metamorphic deposits. Metamorphic migmatization mineralization refers to the process that occurs under deep metamorphic conditions, where alkaline siliceous magmas and metamorphic hydrothermal fluids cause migmatization, thereby activating and transferring useful elements from the surrounding rock so that they can accumulate to form minerals under favorable conditions; deposits formed through this process are known as metamorphic migmatization deposits. 　　Another way to classify metamorphic deposits is by distinguishing between metamorphosed deposits and transformed deposits, based on whether they were deposits or rocks prior to metamorphism. When an existing ore deposit is altered by metamorphism, a series of changes occur in its mineral composition and texture as well as in the orientation of the ore bodies; such deposits are known as metamorphosed ore deposits. Ore deposits formed from the metamorphism of original rocks are called metasomatic ore deposits. 　　These three major types of mineralization are interconnected; for example, some hydrothermal deposits are formed as a result of the combined action of magmatic hydrothermal fluids and groundwater hydrothermal fluids. Volcanic-sedimentary deposits, on the other hand, are the result of both volcanic activity and sedimentation. Some deposits are the result of the superposition of multiple metallogenic processes; for example, stratified deposits are often formed by a combination of endogenic and exogenic metallogenic processes. 　　Classification of deposit genesis: The classification of deposit genesis reflects the level of understanding people have regarding the origins of deposits, and it has always been an important topic of study in deposit geology. In 1911, the American scholar W. Ringgren proposed a classification based on the physicochemical processes involved in mineralization. H. Schneider of Germany emphasized the close connection between diagenesis and mineralization, classified deposits into three main categories—magmatic, sedimentary, and metamorphic—and laid the foundation for the classification of deposits. Since the 1950s, significant progress has been made in geophysical and isotopic geochemical research, making it possible to explore in greater depth the sources of mineralizing materials and to propose genetic classifications based on those sources (e.g., Xie Jiarong, 1961). Currently, the commonly used classification systems for deposit genesis are mostly based on three fundamental factors related to mineralization: the mineralizing substances and their sources, the mineralization environment, and the mineralization process itself. Among these, the mineralization process is the main criterion for classifying the types of deposit genesis. The genetic classification of deposits based on this principle is as follows:
Genetic Classification of Deposits
Endogenic Deposits
Magmatic Deposits
Porphyry Deposits
Vaporization-hydrothermal Deposits
Fumarolic Deposits (including volcanic-fumarolic deposits)
Contact metasomatic Deposits (skarn deposits)
Hydrothermal Deposits
Exogenic Deposits
Weathering Deposits
Residual Deposits (eluvial deposits)
Illuvial Deposits
Sedimentary Deposits
Mechanically deposited Deposits (sand deposits)
Evaporitic Sedimentary Deposits (salt deposits)
Colloidal-chemical sedimentary Deposits
Biо-chemical sedimentary Deposits (oil, coal, etc.)
Metamorphic Deposits
Metamorphosed Deposits
Transformed Deposits
Mixomicritic Deposits
The above genetic classifications represent the basic categories; further subdivisions are possible within each subcategory. For example, magmatic deposits can be divided into crystallization-differentiated deposits and melt-separated deposits; hydrothermal deposits can be classified as high-, medium-, and low-temperature hydrothermal deposits. In short, the classification of deposit genesis is constantly evolving; as exploration progresses, new types of deposits will be discovered, and the existing classifications need further supplementation and improvement. 　　Looking ahead, the study of mineralization is a systematic research effort that involves comprehensive analysis based on a large amount of information obtained from field observations of deposits, laboratory tests, mineralization experiment simulations, geophysical surveys, geochemical analyses, and engineering excavations. It involves various fields of earth sciences; therefore, the improvement of the overall level of geological science and technology will facilitate deeper research on mineralization processes. Currently, biogenic mineralization, hypothermic mineralization, tectonic mineralization, and planetary mineralization are prominent topics of interest. Quantitative studies on mineralization have also been put on the agenda. Strengthening the integrated study of the thermodynamics and dynamics of mineralization is of great significance for a deeper understanding of the mechanisms of mineral formation. From a systematic perspective, mineralization is a component of a complex and diverse system of geological processes. Mineral deposits are specific products of the evolutionary development of the lithosphere. Therefore, only by gaining a comprehensive understanding of the formation and evolution of the upper mantle, crust, hydrosphere, atmosphere, and biosphere, as well as their interactions and their influence on the formation and distribution of mineral deposits, can we truly comprehend the essence of mineralization and its changes over time and space. This post was last edited by The distance to happiness on 2009-4-7 18:49.]