Metallogenic Geological Bodies

      Mineral exploration prediction falls under the category of spatial prediction. Its basic principle is to determine the spatial location of a reference object that has a definite relationship with the target object. In mineral exploration prediction, the reference object that has a definite relationship with the ore deposit (body) is the ore-forming geological body. The ore-forming geological body is the core carrier of various elements in mineral exploration prediction (including geology, mineral resources, geophysical exploration, and geochemical exploration), and it is the basis for constructing the geological model for mineral exploration prediction, thus playing a directional role in mineral exploration prediction.

1. Concept of Metallogenic Geological Bodies

      Metallogenic geological bodies refer to geological bodies closely related to the formation of ore deposits in terms of time, space, and genesis. They are the carriers of the metallogenic geological processes that form the main minerals (of industrial value) of ore deposits and determine the spatial location of the main metallogenic stages. The formation of ore deposits is simultaneous with or close to the formation of metallogenic geological bodies, and their spatial distribution is dependent on these bodies.

2. Types of Ore-forming Geological Bodies

      Geological processes refer to the continuous changes and developments in the material composition, internal structure and tectonics, and external morphology resulting from the interactions of different crustal layers caused by various Earth dynamics. Based on dynamic mechanisms, formation processes, and their products, geological processes are classified into six categories: sedimentary geological processes, volcanic eruptive geological processes, magmatic intrusive geological processes, regional metamorphic geological processes, large-scale deformation geological processes, and complex geological processes. The ore-forming geological bodies corresponding to each type of ore-forming geological process are as follows.

      (1) Sedimentary geological processes: The geological bodies are sedimentary basins and sedimentary strata formations, while the ore-forming geological bodies are ore-bearing strata and rock assemblages, mainly located at the basin margins or in areas with well-developed secondary structures. Basins are generally rift basins in their early stages and depression basins in their later stages. Therefore, mineralization is mainly concentrated at the basin margins and in areas with hidden fault complexes, and is primarily contemporaneous with the formation of the basin.

      (2) Volcanic eruption geological processes: The geological body consists of volcanic rock assemblages and volcanic structures. Mineralization is mainly concentrated in volcanic structures and eruption centers. Volcanic exhalative sedimentary deposits are located at the edge of basins adjacent to volcanic structures, while volcanic hydrothermal deposits are located at the top of subvolcanic rock bodies within volcanic structures, primarily after the volcanic eruption period.

      (3) Intrusive magmatic geological processes: The geological bodies are intrusive rock bodies, divided into two categories. One category is magmatic deposits, where mineralization is caused by the immiscibility of magma, and the ore bodies are formed by segregation, melting, or the crystallization of accessory minerals. The second category is magmatic hydrothermal deposits, where mineralization is mainly concentrated at the top of small rock bodies with high protrusions in the magma chamber and within and outside the contact zone. In terms of time, they are mostly intrusive bodies from the later stages of the same magmatic activity.

      (4) Regional metamorphic geological processes: The geological bodies are metamorphic formations and deformation structures. Mineralization is mainly concentrated at the turning points of folds, the axial parts, and certain special protolith formations. They can be divided into metamorphic deposits and transformed deposits.

      (5) Large-scale deformation structures: mineralization of ductile shear zones and metamorphic core complexes mainly occurs in the superimposed brittle structural parts of ductile shear zones and the central parts of metamorphic core complexes, mostly in the late stage of deformation structures.

      (6) Complex geological processes: typical examples include regional metamorphism and ductile shear zones, volcanic eruption and magmatic intrusion, and the combination of sedimentation and regional metamorphism.

      The study of geological processes includes formation and tectonics. Geologists generally understand formation as the material composition formed by geological processes, and tectonics as the structural features of geological bodies at different scales, or the formation process of material composition and the superimposed structures after formation. In the study of ore-forming geological bodies, formation refers to rock assemblages at different scales, while tectonics is the manifestation of the formation process and environment of rock assemblages, i.e., diagenetic structures, also known as "primary" structures and the modifications made to rock assemblages after formation. Those related to mineralization are included in the study of ore-forming structures.

3. Identify the mineralized geological bodies

      To identify ore-forming geological bodies, it is necessary to first accurately classify the types of ore deposits, determine the types of ore-forming geological processes and ore-forming geological bodies; secondly, the ore-forming geological bodies should be identified based on the formation age, spatial distance, and material composition comparison between the ore deposits (body) and the ore-forming geological bodies.

      The identification of ore-forming geological bodies can generally be roughly solved through thematic mapping in the field, and can directly guide mineral exploration work. However, final confirmation still requires the collection of thematic samples.

4. Determine the spatial location of the ore-forming geological body

      Determining the spatial location of ore-forming geological bodies requires identifying specific spatial elements such as their distribution range, three-dimensional morphology, and occurrence for the identified geological bodies.

      The identification of surface-exposed and prospecting-exposed ore-forming geological bodies is primarily achieved through geological mapping, prospecting projects, and three-dimensional mapping. Since mineralization mainly occurs at lithological, tectonic, and physicochemical interfaces, forming characteristic markers of mineralization, large-scale general geological maps, typically based on epochal or lithostratigraphic units, are insufficient for mineral exploration prediction. Therefore, various thematic maps reflecting ore-forming geological bodies, ore-forming structures and structural planes, and characteristic markers of mineralization are needed. These include the field measurements and compilation of thematic lithological and structural maps, alteration zoning maps, and ore-forming structures.

      The spatial location of concealed mineralized geological bodies is mainly determined by shallow geological identification markers, geophysical exploration, geochemical exploration, and other data, with geophysical exploration data playing a dominant role.

5. Study on the characteristics of ore-forming geological bodies

      The research content of sedimentary metallogenic geological bodies mainly includes sedimentary rock formation/sedimentation, tectonic lithofacies paleogeography, Quaternary fluvial and lacustrine systems, Quaternary sedimentary types and landforms, etc.; the research content of volcanic rock metallogenic geological bodies mainly includes volcanic rock formation/volcanic activity, volcanic lithofacies structures/volcanic structures, etc.; the research content of intrusive rock metallogenic geological bodies mainly includes igneous rock formation/magmatism, intrusive rock mass structures, etc.; the research content of regional metamorphic metallogenic geological bodies mainly includes metamorphic rock formation/metamorphism, metamorphic deformation structures, etc.; the research content of large-scale deformable tectonic metallogenic geological bodies mainly includes the type, scale, occurrence, combination form, formation age, deformation period, material composition, mineralization characteristics, mechanical properties, movement mode, and geotectonic environment, etc.