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Introduction
Published in Sukumar Laik, Offshore Petroleum Drilling and Production, 2018
In the case of compaction, the overburden load plays a major role. Owing to the high overburden pressure, compaction in porous medium takes place and thus vertical subsidence of beds form folded structures. In the case of tensional folds, the rock layers are pulled away from each other by tensional forces. When this tensional force exceeds the threshold values, the gradual crustal thinning and finally faulting takes place in the form of horst and graben. Horsts are the elevated faulted blocks whereas graben are the subsided faulted blocks. Then continuous sedimentation on horst and graben gradually give birth to the folded strata as described in Figure 1.11.
Petroleum Geological Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
Horst and graben are the elevated (hill) and depressed (valley) blocks of crust that lie between normal faults. A graben is also known as a ‘rift valley’. Both occur side by side. Horst and graben structure is formed by tensional stress and are dip-slip faults. A horst is rock up thrown by faulting and a graben is a block dropped down between faulting lines. A horst is the hillock between two grabens. Both horst and graben vary greatly in size and area. A graben may form a petroleum basin supported by horst-associated trap rocks.
Ground control monitoring at the Nanisivik Mine
Published in Hans Kristian Olsen, Lida Lorentzen, Ole Rendal, Mining in the Arctic, 2020
Extensive faulting has resulted in a horst and graben structural setting. The mineralization formed by the replacement of the host rock in two main sulphide events, an early barren massive pyrite-dolomite event (uneconomic) and a later event, pyrite- sphalerite-minor galena-dolomite, that produced the economic mineralization. The Nanisivik deposit is a major sulphide deposit with an estimated 50–100 million tonnes of massive pyrite of which about 15 million tonnes being economic due to zinc enrichment.
Gravity and magnetic data processing further constrained inversion for 3D modelling and tonnage calculation
Published in Applied Earth Science, 2020
Saâd Soulaimani, Saïd Chakiri, Ahmed Manar, Ayoub Soulaimani, Abdelhalim Miftah, Mustapha Boujamaoui
As far as mining is concerned, the Hercynian basement of the Marrakech region hosts a large number of sulphide massifs. They are found as stratabound polymetallic mineralised bodies and often associated with volcanic rocks which crop up as submarine effusions of rhyolite and rhyodacite. These are volcano-clastic type mineralisations presenting a relatively distal character regarding the emplacement of the contemporaneous volcanic expressions (Bernard et al. 1988). Such mineralisations are often associated with underlying stockworks zones. Their mineralogical and chemical characteristics indicate a strongly reducing environment leading to the paragenesis formation of syngenetic pyrrhotite of highly dominant primary origin of Variscan age. In the Guemassa-Jebilets metallogenic province, pyrrhotite ore deposits outcrop as limonitic products forming gossans. They are roughly organised along sub-meridian lineaments (Jaffal et al. 2010; Admou et al. 2018). They are formed of mineral occurrences or ore bodies within the Visean volcano-clastic deposit of Sarhlef (Bernard et al. 1988). Felenc et al. (1986) proposed a genetic model in which such massive sulphide deposits are supposed to be emplaced during an extensional phase, during which sandy clay deposits infill in a sedimentary basin (Felenc et al. 1986). The development of this basin is favoured by the action of normal faults leading to horst and graben structures. Such an extensional regime, dated to ca. 330.5 Ma (U-Pb on zircons) by Essaifi et al. (2003), is followed by important magmatic activity characterised mainly by a bimodal plutonism emplacement. This led to high thermal perturbations generating a hydrothermalism which could appear as convection cells affecting magmatic bodies as well as their host rocks (Essaifi and Hibti 2008). However, the proximity of sulphide ore enriched in base metals and the acid plutonism (depleted in base metals) may indicate that this kind of plutonism is the main source zone for this hydrothermal system (Essaifi and Hibti 2008). The sulphide ore deposits of the Visean metallogenic province of Guemassa-Jebilets (Figure 1) may have been emplaced in an epicontinental rift environment of the external zone of the Hercynian chain (Lescuyer et al. 1997).