China
Africa
Explore chapters and articles related to this topic
Rocks and civil engineering
Published in A.C. McLean, C. D. Gribble, Geology for Civil Engineers, 2017
The rate and cost of drilling into rock and the procedure adopted are controlled by the so-called hardness and abrasiveness of the rock. Hardness in this usage is not as defined for a mineral using Mohs’ scale (see Section 2.1.1) but is related to the compressive strength (qu) of the rock. The compressive strengths of the main rock types, and implicitly the probable ease with which they can be drilled, were given in Table 7.4. The abrasiveness of a rock is a measure of how rapidly drill bits are worn down, and it correlates fairly closely with the hardness (in the strict sense) of the minerals present in the rock, and with the grain size. In general, the most abrasive rocks are those with a high content of silica and a fine texture. The life expectancy of a normal 105 mm drill bit is only about 60 m of hole in fine-grained metamorphic quartzite, but may be up to 600 m in fresh quartz dolerite, a comparably strong rock. Table 7.7 gives a guide to abrasiveness of the common rock types.
Signature of precious metal mineralization in hydrocarbon fluids, Central Scotland
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
A comparable mineral assemblage occurs 25km to the south at Hilderston (Fig. 1), in Lower Carboniferous rocks. This deposit contains base metal sulphides and traces of silver/cobalt (Meikle 1994), and is similarly associated with a quartz dolerite intrusion. Consequently the Alva and Hilderston deposits are usually regarded as related (Jassim et al. 1983). They both contain bitumen, which can be attributed to Lower Carboniferous source rocks (Robinson et al. 1989). At Alva, the fault plane was probably important as the conduit for hydrocarbon migration. There are records of ‘petroleum jelly’ in the quartz dolerite dyke in the fault plane at Tillycoultry, 2 km east of Alva (Walker 1935), and black coloration in sandstones caught in the fault zone probably reflects thermally altered oil (Haldane 1927).
Mainland Europe, Turkey and Cyprus
Published in Ian Sims, Alan Poole, Alkali-Aggregate Reaction in Concrete: A World Review, 2017
Isabel Fernandes, Özge Andiç-Çakir, Colin Giebson, Katrin Seyfarth
Almost the entire ‘Sheeted Dyke Complex’ of the Troodos Ophiolite (Upper Cretaceous) is basaltic to doleritic in composition. The dolerite (diabase) occurs in the form of dykes that are parallel and contiguous, with thicknesses varying from 0.30 m to more than 3 m. After emplacement, the dykes have undergone hydrothermal alteration resulting in local modification of the original composition of the dolerite. The varieties that have been recognized are quartz-dolerite, epidote-dolerite (diabase), amphibole-dolerite and albite-dolerite. Therefore, the quality of the dolerite used for the production of concrete aggregate depends on the degree of alteration that the sheeted dykes have undergone.
Intraplate volcanism on the Zealandia Eocene-Early Oligocene continental shelf: the Waiareka-Deborah Volcanic Field, North Otago
Published in New Zealand Journal of Geology and Geophysics, 2020
James M. Scott, James D. L. White, Petrus J. le Roux
Doleritic sills, emplaced at very shallow levels, are a widespread feature of the volcanic field (Figures 1 and 3). The sills intrude Eocene sandstone at Tokarahi near Maerewhenua, limestone at Clarks Mill near Maheno, mudstone at Mt Charles, and siltstone and mudstone on the Moeraki Peninsula (Benson 1943, 1944) (Figure 1). Dolerite at Round Hill may also be a sill (Benson 1943), although this has not been confirmed. The most regionally extensive of these sills are the ∼20 m thick columnar-jointed intrusion at Tokarahi (Figure 4C), which may have been emplaced at the same time as Basalt Hill to the north (Figure 1), and the ∼ 50 m thick Mt Charles Sill (Figure 4D). Each of these sills is estimated to have an extent of over ∼25 km2 and volumes on the order of 1–2 km3 (Coombs et al. 1986). The Mt Charles Sill is underlain by flaggy concretion-bearing mudstone with the sill itself grading upwards from (weathered) olivine dolerite into quartz dolerite (Benson 1943; Coombs et al. 1986). The best studied sills, however, are those on the Moeraki Peninsula. Here, the Tawhiroko Sill is at least 50 m thick (the top having been lost to erosion) and has olivine dolerite at the base but a pegmatitic quartz dolerite core (Benson 1943, 1944). It also contains horizons remarkably rich in schist xenoliths, locally size-graded in bands within the sill (Figure 4E) despite Otago Schist being 10–100 m below the sill. Nakamura and Coombs (1973) interpreted chemical zoning in clinopyroxene grains in this sill to be due to progressive crystallisation of the magma. Benson (1943) attributed the chemical differentiation in the Waiareka-Deborah sills to gravitational settling, but the differentiation could also be due to emplacement of variably evolved magmas injected as different batches. This would better explain the occurrence of schist-rich horizons at Moeraki. Coombs and Roedder (1994) reported the occurrence of CO2 inclusions in plagioclase microphenocrysts from some Moeraki Peninsula sill rocks and inferred these to represent immiscible CO2 droplets in the melt at ∼ 10 km depth.