Understanding Soil Types and Mineral Deposits
Soil Types
There are various classifications of soils. Climatic or zonal soils are part of the principle that similar climates produce the same soil types, regardless of the parent rock, vegetation, and other factors. There are three categories of soils:
- Azonal: Independent of soil or climate, they may occur under any climate and latitude. They have a low degree of maturity and occur in floodplains, on mountain slopes, and in the sandy soils of deserts.
- Intrazonal: These soils are somewhat more developed. Among them, we can include:
- Calcimorphic soils: Developed on calcareous land, such as rendzinas.
- Siliceous soils: Developed on quartz fields.
- Saline soils and gypsum: Based on the bioclimatic conditions of the basin, they have accumulated salts.
- Saturated soils: Soils with excess water.
- Zonal: These soils are directly related to climate:
- High-latitude soils: Cold climates and tundra soils.
- Mid-latitude soils: Black or chernozem soils, rich in organic matter. Gray soils can be found in wet and cold regions (podzols). Brown clay and Mediterranean forest soils are rich in humus. The Mediterranean red soils (terra rosa) are clay soils.
- Low-latitude soils: Formed in warm, humid climates. Lateritic soils occur here.
Sedimentary Deposits and Mineral Formation
Major minerals that form sedimentary rocks are quartz, feldspars, micas, clays, calcite, iron oxides, bauxite, and gypsum. Some minerals originate in sedimentary basins themselves (indigenous minerals), while others come from outside the watershed (allochthonous minerals). Mineral deposits are accumulations that can be economically profitable.
Alteration Deposits
Alteration deposits form by infiltration of water and weathering of surface areas. These processes concentrate ore, also called bikers.
Mechanical Deposition
During transportation, mechanical selection occurs. Densities can concentrate valuable minerals scattered in the bedrock. Thus, placer deposits are formed. Oilfields in such placer deposits could be:
- Eluvial: Formed by rubble from the disintegration of the rock by weathering. More resistant materials can be found near the bedrock, such as gold.
- Alluvial: If river transport has weathered materials during transport, denser materials concentrate in certain locations on beaches or rivers.
Chemical Deposition
Chemical rainfall occurs by variation of salinity, temperature, and/or from the concentration of elements, for example, submarine volcanic emissions.
Biochemical Deposition
Biochemical sedimentation is caused by the metabolic action of organisms, such as bacteria that form sulfur beds at the bottom of lakes, the accumulation of skeletal remains that form phosphate deposits, or marine plankton that generate deposits of coal and oil, respectively.
Diagenesis
Diagenesis is the set of physical and biochemical changes that sediments undergo to become sedimentary rocks. These changes occur due to pressure, temperature, metabolic activity of living organisms, and changes in pH or oxidation-reduction potential.
Diagenetic Transformations
- Compaction: A decrease in volume due to pressure load and sediment burial.
- Cementation: The union between particles by a binder or cement, which may be carbonated, ferruginous, siliceous, etc.
- Other chemical changes modify the composition of the sediment:
- Dissolution processes.
- Ion exchange between the sedimentation and the solutions.
- Processes of oxidation and reduction.
- Recrystallization.
- Replacement of the first mineral by others.
Diagenesis can be distinguished by three constituents:
- Skeleton: A set of larger particles or grains that make up the frame of the rock.
- Matrix: Finer particles that partially or completely fill the pores between the skeleton.
- Cement: Material between the grains precipitated from chemical compounds dissolved in interstitial water.