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Metamorphism
Published in Aurèle Parriaux, Geology, 2018
Quartzite is white, beige, or green in color due to the presence of phyllosilicates. In the Alps, the Permo-Triassic quartzites occur in thick (tens of meters) beds that often contain sericite (small muscovite crystals) and abundant pyrite. In outcrop, the oxidation of pyrite causes a brown patina (rock surface exposed to weathering) to form on the rock surface. These rocks resist erosion during detrital transport (Fig. 11.18) because of the hardness of quartz and their low degree of physico-chemical weathering. For this reason, alluvium is highly enriched in quartzite as compared to its proportion in the watershed. The hardness of quartz abrades drilling tools (boreholes, tunnel boring machines, etc.). In areas of tectonic crushing, quartzite beds can be weakened by intense micro-fracturing. Under these circumstances and in the presence of groundwater, quartzite can become a flowing rock that is very unstable in galleries.
Metamorphism
Published in Aurèle Parriaux, Geology, 2018
Quartzite is white, beige or green in color due to the presence of phyllosilicates. In the Alps, the Permo-Triassic quartzites occur in thick (tens of meters) beds that often contain sericite (small muscovite crystals) and abundant pyrite. In outcrop, the oxidation of pyrite causes a brown patina (rock surface exposed to weathering) to form on the rock surface. These rocks resist erosion during detrital transport (Fig. 11.18) because of the hardness of quartz and their low degree of physico-chemical weathering. For this reason, alluvium is highly enriched in quartzite as compared to its proportion in the watershed. The hardness of quartz causes the abrasion of drilling tools (boreholes, tunnel boring machines, etc.). In areas of tectonic crushing, quartzite beds can be weakened by intense micro-fracturing. Under these circumstances and in the presence of groundwater, quartzite can become a flowing rock that is very unstable in galleries.
Petroleum Geological Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
Clastic sedimentary rock is also called detrital sedimentary rock. Clastic and detritus refer to broken stone pieces of all kinds. Loose, broken and detached pieces of existing rock are known as fragments/particles/grains. The particles/grains are of various sizes and shapes. Size and shape are an important subject for the petroleum geologist and help in understanding the underground ‘petroleum system’.
Integration of SPOT-5 and ASTER satellite data for structural tracing and hydrothermal alteration mineral mapping: implications for Cu–Au prospecting
Published in International Journal of Image and Data Fusion, 2018
Reyhaneh Ahmadirouhani, Mohammad-Hassan Karimpour, Behnam Rahimi, Azadeh Malekzadeh-Shafaroudi, Amin Beiranvand Pour, Biswajeet Pradhan
In the band ratio of 6/7, 5/6 and 4/6 in RGB (Figure 6(b)), the areas in yellow to orange colour represent the high abundance of the mixture of Al-OH minerals (mostly phyllic and argillic zones) and Fe-OH minerals (jarosite). In this transformation, phyllic alteration zone is strongly enhanced in the resultant image map (Figure 6(b)) due to the effect of high Al-OH and Fe-OH absorption features in bands 6 and 7 of ASTER. In this image map, unaltered lithologies and limestone appear as blue to purple colour, which enhances due to the contribution of band ratio of 4/6. The green colour pixels (related pixels to band ratio of 5/6) are mostly alluvial deposits, sedimentary rocks (slate, conglomerate, phyllite and sandstone) and other igneous rocks with low content of Al-OH altered minerals. Sedimentary rocks, such as mudstone, shale, claystone and litharenite sandstones contain large amounts of detrital clays, such as montmorillonite, illite and kaolinite (Mars and Rowan 2006). Hence, they are manifested as the green tone in the image map (Figure 6(b)).
The effect of diagenetic environment on hydrocarbon generation based on diagenetic mineral assemblage in mudstone
Published in Petroleum Science and Technology, 2018
Jiazong Du, Jingong Cai, Guoli Wang, Xiang Zeng, Yujin Bao, Fei Liu
Mudstones contain various minerals, primarily detrital minerals, clay minerals and carbonate minerals. The minerals are formed either by deposition during the depositional period or by authigenesis/conversion during diagenesis. Therefore, the minerals can be divided into depositional and diagenetic minerals according to their source, both of which can reflect the environmental characteristics of their formation and are effectively distinguished according to their microscopic features and relative concentrations. The detrital minerals (e.g., quartz and feldspar), which are mainly formed by adventitious deposit, change slightly during diagenesis and transmit information about the depositional environment. However, clay minerals and carbonate minerals, whether they are adventitious deposits or authigenic, are converted or changed during diagenesis. Previous studies have shown that well-crystallized illite, chlorite, and kaolinite are formed by smectite illitization (Velde and Vasseur 1992), chloritization (Pelayo et al. 2016) and kaolinitization (Ryan and Huertas 2013), respectively, during diagenesis. Ankerite is formed by metasomatism of calcite during diagenesis (Krajewski and Wozny 2009). The abovementioned minerals are classified as diagenetic minerals and transmit information about the diagenetic environment. During burial diagenesis of mudstones, the temperature, pressure, pH, Eh, ion type and concentration change constantly with the increase in burial depth, leading to the changes in the diagenetic environment as well as changes in diagenetic minerals. Kaolinite is formed and stable in acidic environments (Ryan and Huertas 2013), while illite, chlorite and ankerite are formed under alkaline conditions (Lackner et al. 1995; Srodon 1999; Beaufort et al. 2015). Therefore, the variations of diagenetic environment of mudstones result in different diagenetic minerals and diagenetic mineral assemblages.