Orogenic gold deposits are a type of hydrothermal mineral deposit. More than 75\% of the gold recovered by humans through history belongs to the class of orogenic gold deposits. Rock structure is the primary control of orogenic gold mineralization at all scales, as it controls both the transport and deposition processes of the mineralized fluids, creating structural pathways of high permeability and focussing deposition to structurally controlled locations. General Overview Orogenic gold deposits are hosted by shear zones in orogenic belts, specifically in metamorphosed fore-arc and back-arc regions and were formed during syn- to late metamorphic stages of orogeny. Formation of orogenic gold deposits is related to structural evolution and structural geometry of lithospheric crust, as hydrothermal fluids migrate through pre-existing and active discontinuities (faults, shear zones, lithological boundaries) generated by tectonic processes. These discontinuities provide pathways and channel fluid flow, not only of ore-bearing fluids, but also of fluids transporting metallic elements such as silver, arsenic, mercury and antimony and gases, as well as melts. Gold-bearing fluids precipitate at an upper-crustal level between 3 and 15 km depth (possibly up to 20 km depth), forming vertically extensive quartz veins, typically below the transition of greenschist- to amphibolite metamorphic facies. Fluid Source In magmatic systems, ores and host rocks are derived from the same fluid. In the case of hydrothermal fluids, host rocks are younger than the predominantly aqueous fluids that carry and deposit metals and thus complicate defining a host rock associated with gold fluid formation. A number of rock types have been suggested as the source of orogenic gold, but due to the variability of host rocks in Earth’s history and deposit-scale, their relation to Earth-scale gold formation processes is unclear. Furthermore, age dating of the deposits and their host rocks shows that there are large time gaps in their formation. Age dating indicates that mineralization took place 10 to 100 Ma after the formation of the host rocks. These temporal gaps suggest an overall genetic independence of the fluid formation and that of local lithologies. Mineralogy and Geochemistry Geochemical studies on quartz veins are important to determine temperature, pressure, at which the veins were generated, and the chemical signature of fluids. Obviously, quartz is the dominant mineral in the veins. Ore bodies of orogenic gold deposits are generally defined by ≤ 3–5\% sulfide minerals, most commonly arsonopyrite in metasedimentary hostrocks and pyrite/pyrrothite in meta-igneous rocks, and ≤ 5–15\% carbonate minerals, such as ankerite, dolomite and calcite. A common characteristic of almost all orogenic gold lodes is the presence of widespread carbonate alteration zones, notably ankerite, ferroan dolomite, siderite and calcite. The tendency of gold to be preferentially transported as a sulfide complex also explain the near absence of base metals (Cu, Pb, Zn) in the same mineral systems, because these metals form complexes with chlor rather than sulfur. Genetic Models Orogenic gold deposits formed in metamorphosed terranes of all ages that have little in common except for being sites of complexity and low mean stress. For this reason, a discussion of the gold deposit formation in a universal genetic model is most difficult and several models have been considered. The fundamental control of the chemical signature of orogenic gold fluids can most likely be found in the processes that take place in the source region. Therefore, the discussion about genetic models of orogenic gold deposits concentrates on the possible source of gold-bearing fluids. Tectonics and Gold Formation Although efforts have been made to define a specific deformation structure associated with the formation of orogenic gold deposits, no specific structure could be identified. Rather, there are various types of faults hosting gold deposits. Nevertheless, orogenic gold deposits have a number of repetitive structural geometries that control ore-fluid formation, transport, and precipitation. Geodynamik Setting and Architecture Large-scale lithospheric deformation structures correlate with gold endowment, and active structural permeability in the crust is controlled by the prevailing tectonic stress field. There is an increasing body of evidence that the formation of orogenic gold deposits is tied to specific geodynamic settings, primary orogenic belts. Orogenic gold deposits show a spatial relationship to structural discontinuities, including faults, fractures, dilatation zones and shear zones. The ore- hosting structures are subsidiary faults or shear zones (mostly D3–D4 in a D1 to D4 structural sequence), which are always related to a major regional-scale deformation structures, such as lithospheric boundaries and suture zones. The deformation structures hosting the gold deposits are typically discordant with respect to the stratigraphic layering of the host rocks. The mineralised structures indicate syn- to post-mineralisation displacements, such as slicken-sides formed under hydrothermal conditions. The geometry of vein systems is primarily influenced by a combination of dynamic stress changes and fluid pressure variations. Examples Australia Mother Lode Homestak Ores Category:Mining templates
An orogenic gold deposit is a type of hydrothermal mineral deposit. More than 75\% of the gold recovered by humans through history belongs to the class of orogenic gold deposits. Rock structure is the primary control of orogenic gold mineralization at all scales, as it controls both the transport and deposition processes of the mineralized fluids, creating structural pathways of high permeability and focussing deposition to structurally controlled locations. Overview Orogenic gold deposits are hosted by shear zones in orogenic belts, specifically in metamorphosed fore-arc and back-arc regions and were formed during syn- to late metamorphic stages of orogeny. Formation of orogenic gold deposits is related to structural evolution and structural geometry of lithospheric crust, as hydrothermal fluids migrate through pre-existing and active discontinuities (faults, shear zones, lithological boundaries) generated by tectonic processes. These discontinuities provide pathways and channel fluid flow, not only of ore-bearing fluids, but also of fluids transporting metallic elements such as silver, arsenic, mercury and antimony and gases, as well as melts. Gold-bearing fluids precipitate at an upper-crustal level between 3 and 15 km depth (possibly up to 20 km depth), forming vertically extensive quartz veins, typically below the transition of greenschist- to amphibolite metamorphic facies. Fluid source In magmatic systems, ores and host rocks are derived from the same fluid. In the case of hydrothermal fluids, host rocks are younger than the predominantly aqueous fluids that carry and deposit metals and thus complicate defining a host rock associated with gold fluid formation. A number of rock types have been suggested as the source of orogenic gold, but due to the variability of host rocks in Earth’s history and deposit-scale, their relation to Earth-scale gold formation processes is unclear. Furthermore, age dating of the deposits and their host rocks shows that there are large time gaps in their formation. Age dating indicates that mineralization took place 10 to 100 Ma after the formation of the host rocks. These temporal gaps suggest an overall genetic independence of the fluid formation and that of local lithologies. Mineralogy and geochemistry Geochemical studies on quartz veins are important to determine temperature, pressure, at which the veins were generated, and the chemical signature of fluids. Obviously, quartz is the dominant mineral in the veins. Ore bodies of orogenic gold deposits are generally defined by ≤ 3–5\% sulfide minerals, most commonly arsonopyrite in metasedimentary hostrocks and pyrite/pyrrothite in meta-igneous rocks, and ≤ 5–15\% carbonate minerals, such as ankerite, dolomite and calcite. A common characteristic of almost all orogenic gold lodes is the presence of widespread carbonate alteration zones, notably ankerite, ferroan dolomite, siderite and calcite. The tendency of gold to be preferentially transported as a sulfide complex also explain the near absence of base metals (Cu, Pb, Zn) in the same mineral systems, because these metals form complexes with chlor rather than sulfur. Genetic models Orogenic gold deposits formed in metamorphosed terranes of all ages that have little in common except for being sites of complexity and low mean stress. For this reason, a discussion of the gold deposit formation in a universal genetic model is most difficult and several models have been considered. The fundamental control of the chemical signature of orogenic gold fluids can most likely be found in the processes that take place in the source region. Therefore, the discussion about genetic models of orogenic gold deposits concentrates on the possible source of gold-bearing fluids. Tectonics and gold formation Although efforts have been made to define a specific deformation structure associated with the formation of orogenic gold deposits, no specific structure could be identified. Rather, there are various types of faults hosting gold deposits. Nevertheless, orogenic gold deposits have a number of repetitive structural geometries that control ore-fluid formation, transport, and precipitation. Geodynamic setting and architecture Large-scale lithospheric deformation structures correlate with gold endowment, and active structural permeability in the crust is controlled by the prevailing tectonic stress field. There is an increasing body of evidence that the formation of orogenic gold deposits is tied to specific geodynamic settings, primary orogenic belts. Orogenic gold deposits show a spatial relationship to structural discontinuities, including faults, fractures, dilatation zones and shear zones. The ore- hosting structures are subsidiary faults or shear zones (mostly D3–D4 in a D1 to D4 structural sequence), which are always related to a major regional-scale deformation structures, such as lithospheric boundaries and suture zones. The deformation structures hosting the gold deposits are typically discordant with respect to the stratigraphic layering of the host rocks. The mineralised structures indicate syn- to post-mineralisation displacements, such as slickensides formed under hydrothermal conditions. The geometry of vein systems is primarily influenced by a combination of dynamic stress changes and fluid pressure variations. Examples Australia Mother Lode Homestak 
R
Orogenic gold deposits are
An orogenic gold deposit is
D
General
R
Source
source
R
Geochemistry
geochemistry
R
Models
models
R
Gold Formation
gold formation
R
Geodynamik Setting and Architecture
Geodynamic setting and architecture
R
slicken-sides
slickensides
D
Ores Category:Mining templates