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Petroleum Geological Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
An outcrop of rock is an uplifted part of the underground formation that is exposed and is visible at the earth’s surface. Two special features of the outcropped rock are worth noting, the ‘dip angle’ and the ‘strike’. The dip angle measures and indicates the angle in which the rock is dipping down into the earth (going down). Precisely the dip of a rock layer is the angle and direction in which the rock goes down into the subsurface. The strike represents the direction in which the rock is outcropping at the surface (going up). The movement of the outcropped rock is expressed as a vertical component. For example, a strike is indicated on the chart paper as north-east.
Geological Maps
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
Rocks are said to be exposed when they occur at ground level. An exposure should be distinguished from an outcrop which is the geographical position of a geological unit, regardless of whether or not it is exposed. Figure 12.1 illustrates the two terms and shows that every exposure is part of an outcrop. By studying the geographical distribution of outcrops at ground level, as is shown by a map of surface geology, it is often possible to determine the overall geological structure of the area represented.
The construction of a geotechnical model for a rock dredging contract
Published in Peter N.W. Verhoef, Wear of Rock Cutting Tools, 2017
The engineering geologist is occupied with the development of a geological model of the area. In order to understand the distribution of rocks and soils in the dredging area, it is commonly necessary and useful to pay attention to the coastal area on land as well. Observations of the landscape and inspection of rock outcrops can give valuable information, which can be compared with maps of underwater surface morphology.
Exploration for epithermal Au–Ag deposits in New Zealand: history and strategy
Published in New Zealand Journal of Geology and Geophysics, 2019
Anthony B. Christie, Mark P. Simpson, Richard G. Barker, Robert L. Brathwaite
Even where exploration uses remote techniques, field prospecting and mapping of outcrops are still important fundamental techniques to characterise the geological and structural setting, as well as style and footprint of hydrothermal alteration and mineralisation. Mapping the geological units can provide an indication of primary permeability and rheological properties of the rocks, which, in turn, may influence the potential to host veins. Important features noted during mapping include veins, hydrothermal breccias, silicified horizons and silica sinters (cf. Simmons 2017, 2019; Hamilton et al. 2018). Furthermore, documentation of vein textures may provide information on paleodepth (colloform-banded versus massive crystalline quartz) and boiling (e.g. bladed quartz or calcite; Simmons and Christenson 1994; Simmons 2019) that is a process conducive for the deposition of gold; breccia textures may indicate multiple hydrothermal events. The use of portable XRF (pXRF) and portable infrared spectrometers in the analysis of samples in the field, as well as for drill hole samples, has greatly assisted mapping of hydrothermal alteration by characterising the geochemical anomalies and mineralogy, respectively (e.g. Halley 2014; Halley et al. 2015). Portable XRD instruments are now also available and can be useful for determining and quantifying alteration mineralogy (e.g. Burkett et al. 2015).