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Rock characterization
Published in Dean Brox, Practical Guide to Rock Tunneling, 2017
The evaluation of rock durability should be performed in relation to the results of petrographic analyses and the identification of adverse minerals. Adverse minerals that are susceptible to deterioration include anhydrite, gypsum, zeolites (laumontite and leonhardite), and smectite clays. Basalts commonly include smectite clays due to deuteric alteration of primary minerals as well as amygdales filled with zeolites. The deterioration of highly amygdaloidal basalts by “crazing” or extensive micro-fracturing and expansion of these swelling minerals was experienced to a maximum depth of 500 mm in response to moisture and stress changes during the construction of the 45 km transfer tunnel as part of the Lesotho Highlands Project in the 1990s and warranted the complete concrete lining of the tunnel as a major design change (Broch, 2010). Figure 5.4 presents a petrographic thin section of a zeolite filled with laumontite, one of the most common swelling minerals and Figure 5.5 presents the deterioration of amygdaloidal basalt containing montmorillonite caused by natural humidity exposed during construction at the Lesotho Highlands transfer tunnels. Based on an extensive testing program both prior to construction and during tunnel excavation through the use of water spray rings, a critical threshold of about 30% by volume of deleterious minerals including 6% by volume of zeolites, can be expected to give rise to significant deterioration upon exposure to moisture which should be considered as part tunnel design (MacKellar & Reid, 1994).
Formation mechanism and controlling factors ofsecondary pore in clastic rock
Published in Ai Sheng, Energy, Environment and Green Building Materials, 2015
Y.R. Li, X.Y. Fan, R.G. Jiang, M.T. Li, X. Xiao
Three main conclusions are made through the formation mechanism and control factors: Formation mechanisms of secondary porosity are summarized into feldspar and acidic solution, the acidic solution of carbonate minerals, quartz and alkaline solutions, laumontite, and acidic solution;The development of secondary porosity is controlled by temperature, PH value, pressure, sedimentary facies, structural factors, the clay mineral transformation, and biological effects of different research areas. Temperature, pressure, and PH directly affect the development of secondary porosity; pressure, sedimentary facies, structural factors; the clay mineral transformation indirectly controlled the formation of secondary porosity, and they can strengthen the degree of development of secondary porosity.Despite decades of research on the formation mechanism of secondary porosity gaining some achievements, it does not reach a mature quantitative stage. There are still many problems and challenges in the study of secondary porosity, such as the formation mechanism of alkaline fluid, how abnormal low pressure can affect the development of secondary porosity, and how deep thermal fluid affects secondary porosity development and preservation.
Character of ore fluids in the eastern part of the Dachang ore district, south China
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
J. Pašava, P. Dobeš, Fan Delian, Zhang Tao, M.C. Boiron
The Huile cassiterite-sulfide deposit is located at the eastern limb of the Longxianggai anticline, about 1 km SE of Dafulou (Fig. 1). The deposit has been classified as a large deposit with about 1 million tones of ore at 1.1 % Sn and 1% Zn. Similarly as at Dafulou, the mine exploits stockwork and stratabound bodies (#22 orebody). Four mineralization stages were distinguished at Huile. Stage I consists of pyrrhotite impregnations found in close association with apatite, tourmaline, allanite and titanite. Stage II (main sulfide stage) is represented by massive pyrrhotite, arsenopyrite, chalcopyrite, Fe-rich sphalerite, cassiterite, less abundant stannite and pyrite and very scarce malayaite and scheelite. Stage III is developed to a lesser extent and represented mainly by native Bi, bismuthite and very rare küstelite. No Bi-Pb-Sb-Ag sulfosalts have been identified at Huile. Stage IV - post-ore mineralization consists of calcite veinlets with zeolites (laumontite with admixtures of stilbite) and fluorite.
Correlation between the Warepan/Otapirian and the Norian/Rhaetian stage boundary: implications of a global negative δ13Corg perturbation
Published in New Zealand Journal of Geology and Geophysics, 2022
The Arawi Shellbeds and Ngutunui Formation are a succession of volcaniclastic sedimentary rocks dominated by thin sandstones, siltstones and shales, with minor but conspicuous conglomerates, tuffs and shellbeds (Figure 3). Limestones are not present, although the shellbeds approach coquina limestone composition in places within the Arawi Shellbeds (Grant-Mackie 1985), and there are no radiolarian cherts. Compositionally, the volcanic lithologies are broadly andesitic but range from basaltic andesite to dacite. The tuffs vary in vitric, crystal and lithic composition. In every respect, the sedimentary rocks in the Kiritehere section are typical of Murihiku Supergroup. They have been weakly metamorphosed to zeolite facies grade with conspicuous zeolite veining (laumontite, stilbite) and zeolite ‘cements’ (laumontite, heulandite, analcime). There are minor faults in places and also some ‘slumps’ (Grant-Mackie and Lowry 1964) but in general the stratigraphy is more or less ‘layer cake’, easy to recognise in the field, and the named formations and groups can be traced for many tens of kilometres. However, the sedimentary sequence as a whole has been folded, and a number of anticlines and synclines are recognised and named within a broader Kawhia Regional Syncline (e.g. Kear 1960; Edbrooke 2005). In the Kiritehere section, the sequence is dipping and younging to the east, and is part of a large homoclinal structure that may be interpreted as the west limb of a syncline (e.g. Kear 1960; Kear and Schofield 1964; Edbrooke 2005).
Murihiku rocks as potential petroleum reservoirs in Zealandia
Published in New Zealand Journal of Geology and Geophysics, 2018
Karen E. Higgs, Greg H. Browne, Angus D. Howden
Zeolite minerals have also been identified from thin section in all Murihiku-A samples, forming a common but fairly minor cement phase (1–7 vol%, Table 2). They often occur as a last-stage pore-fill, post-dating the grain-coating/pore-lining clay minerals (e.g. Figure 4C,D), and infilling amygdules. These cements also locally appear to replace some of the original framework grains/crystals (e.g. Figure 4D). Zeolite minerals identified from thin section include laumontite, clinoptilolite-heulandite and analcime. Traces of zeolite in the form of analcime have been positively identified by XRD in sample P85682 (Table 3A), while minor zeolite minerals, tentatively including clinoptilolite, were identified in sample P85675 (4 wt%, Table 3A). Stilbite and fibrous natrolite may also locally be present in minor amounts; locally both stilbite and laumonitite were confirmed in four Southland-A samples (1 Early Jurassic and 3 Middle Jurassic) from XRD (Table 3C).