China
Africa
Explore chapters and articles related to this topic
Plutonic Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Ultramafic rocks, because they are mostly made of mafic minerals, are commonly dark colored (if unaltered), but some peridotites are light green because they contain abundant olivine. The peridotite in Figure 6.29 contains large conspicuous green clinopyroxene crystals surrounded by finer-grained olivine weathered to a light brown color. Figure 6.13i shows a peridotite that contains garnet. Because ultramafic rocks are quite unstable at Earth’s surface and at shallow depths in Earth, they often alter to produce green serpentinites that are mostly made of serpentine, chlorite, and iron oxides (Fig. 6.10).
Genesis and properties of chromite deposits in Denizli region (Southwestern Anatolia), Turkey
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
Ultramafic rocks are composed of serpentinized harzburgite and dunite, which occur around chromite bodies as lenses or small stocks. In addition, orthopyroxenites are found as small veins which cut through hazrburgitic tectonites. In the ultramafic rocks, the following minerals were identified by optical microscope:
Composition and Miocene deformation of the lithospheric mantle adjacent to the Marlborough Fault System in North Canterbury
Published in New Zealand Journal of Geology and Geophysics, 2023
Sophie J. Bonnington, James M. Scott, Marshall C. Palmer, Nadine P. Cooper, Malcolm R. Reid, Claudine H. Stirling
Peridotite and pyroxenite are coarse-grained ultramafic rocks that dominate Earth’s upper mantle. Since mantle xenoliths lock in the mantle composition at the time of their entrainment, their investigation can provide direct insight into mineralogy, temperature, buoyancy, deformation and age of the middle to lower lithosphere (e.g. Griffin et al. 1988; Carlson et al. 2005; Pearson et al. 2014, 2021). New Zealand has over 70 known mantle xenolith locations (Scott (2020) and references therein) and these give a snapshot of the composition of the lithospheric mantle underpinning the continental crust portion of Zealandia. However, the Canterbury region is relatively unstudied, with the only known mantle xenolith locations being the little-studied Le Bons Bay basanite plug in Akaroa and in the Little Lottery Intrusives in NW Canterbury (Figure 1) (Coote 1987; Sewell et al. 1993; McCoy-West et al. 2013, 2015, 2016).
Integrated feed management of mineral processing plants with application to chromite processing
Published in Canadian Metallurgical Quarterly, 2021
F. A. Peña-Graf, T. Grammatikopoulos, A. Kabemba, A. Navarra
Mineable chromium occurs mainly as natural chromite, which is a chromium spinel that varies in composition according to the chemical formula (Fe,Mg)O⋅(Cr,Al,Fe)2O3. The majority of the World's commercially viable chromite is mined from mafic and ultramafic rocks. These ores can be subdivided into stratiform and podiform. Stratiform ores are associated with mafic/ultramafic layered intrusions, are Precambrian in age, and have an intracratonic setting. Podiform ores are mainly Phanerozoic in age, have a highly irregular geometry, and are associated with ophiolites [10]. Major associated gangue minerals are Fe-Mg silicates and their alteration products, such as talc, serpentine, amphibole, chlorites, and Fe-(Ti)-oxides.
Cathaysian slivers in the Philippine island arc: geochronologic and geochemical evidence from sedimentary formations of the west Central Philippines
Published in Australian Journal of Earth Sciences, 2018
C. B. Dimalanta, D. V. Faustino-Eslava, J. T. Padrones, K. L. Queaño, R. A. B. Concepcion, S. Suzuki, G. P. Yumul
Some elements such as V, Cr, Ni and Y are compatible during igneous fractionation. The elements Cr and Ni become incorporated in chromite, pyroxene or olivine in mafic and ultramafic rocks. Thus, the Y/Ni ratios are lower in mafic–ultramafic rocks compared with felsic rocks, while higher Cr/V ratios are noted with increasing inputs from ophiolitic or mafic/ultramafic rocks (e.g. Maravelis et al., 2016; McLennan et al., 1993). In the Y/Ni vs Cr/V diagram, the Palawan, northwest Mindoro and northwest Panay clastic rocks plot closer to the granite end-member (Figure 6c). The low Cr/V ratios displayed by the samples preclude inputs of mafic–ultramafic components into the clastic rocks.