Sedimentary Rocks: Sedimentary Processes And Ore Genesis
Sedimentary Rocks: Deposits associated with sedimentary processes or rocks include a number of metallic, non-metallic and industrial mineral deposits, types and commodities. Industrial minerals that formed due to sedimentary processes include various types of deposits like iron and manganese, bauxite, limestone, phosphates, evaporite etc. The most important metallic deposit is banded iron and sediment-hosted copper.
Sediment – hosted copper deposits are large and diverse group that includes some of the richest and largest copper deposit in the world formed by fluid mixing in permeable sedimentary and volcanic rocks, at observed in the Zambian copper belt, which have produce in excess of one billion metric tons of copper at an average grade of approximately 2.7 weight percent copper, as well as significant quantities of cobalt and silver.
Nevertheless, the formation of these ore deposits result from various sedimentary processes as consider later.
Sedimentary Rocks | SEDIMENTARY PROCESSES
Classically, sedimentary processes consist of the phases of weathering, erosion, transportation and deposition. These processes will be out line below and there are the major steps for the formation of most ore deposits.
Weathering is the processes which breakdown rock at the earth surface to form discrete particles. It is generally divided into biological, chemical and physical processes. Biological weathering is caused by chemical and physical effects of organic processes on rocks. Chemical weathering selectively oxidizes and dissolved the constituent minerals of a rock. Physical processes of weathering are those, which bring about its actual mechanical desegregations.
Erosion is the process, which removes newly formed sediment from bedrock. Erosion can be caused by four agents: gravity, glacial action, running water and wind. This is followed generally by transportation and finally, when energy is exhausted by deposition.
An ore is a type of rock that contains minerals with important elements including metals. The ores are extractable through mining: these are then refined to extract the valuable element(s). See table 1 below.
Ore bodies are formed by a variety of geological processes. The process of ore formation is called “ore genesis”. There are various theories of ore genesis that explain how the various types of mineral deposits were formed within the earth’s crust. Ore genesis theories are very dependent on the mineral or commodity. Ore genesis theories generally involve three components: Source, transport or conduit and trap.
- Source is required because metal first must come from somewhere and be liberated by some process.
- Transport is required first to move the metal bearing fluids or solid minerals into the right position and refers to the act of physical movement of the metal, as well as chemical or physical phenomenon, which encourage movement.
- Trapping is required to concentrate the metal via some physical, chemical or geological mechanism into a concentration, which forms minerable ore.
The biggest deposits are formed when the source is large, the transport mechanism is efficient and the trap is active and ready at the right time.