Rocks and Rock Masses

Description is the initial step in an engineering assessment of rocks and rock masses. Therefore, it should be both uniform and consistent in order to gain acceptance. The data collected regarding rocks and rock masses should be recorded on data sheets for subsequent processing. A data sheet for the description of rock masses and another for discontinuity surveys are shown in Figures 5.15 and 2.17, respectively. 

Anon. 1981. Basic geotechnical description of rock masses. International Society of Rock Mechanics Commission on the Classification of Rocks and Rock Masses. International Journal of Rock Mechanics and Mining Sciences and Geomechanical Abstracts, 18, 85-110. 

Reese (1997) proposed a procedure to calculate p-y curves for rock using basic rock and rock mass properties such as compressive strength of intact rock q. Rock Quality Designation (RQD), and initial modulus of rock E-. A description of the procedure is presented in the following. 

In combination, carbon is found as carbon dioxide in the atmosphere of the earth and dissolved in all natural waters. It is a component of great rock masses in the form of carbonates of calcium (limestone), magnesium, and iron. Coal, petroleum, and natural gas are chiefly hydrocarbons. 

Deposits which are forming are frequentiy characterized by venting streams of hot (300°C) mineralized fluid known as smokers. These result in the local formation of metalliferous mud, rock chimneys, or mounds rich in sulfides. In the upper fractured zone or deep in the rock mass beneath the vents, vein or massive sulfide deposits may be formed by the ckculating fluids and preserved as the cmstal plates move across the oceans. These off-axis deposits are potentially the most significant resources of hydrothermal deposits, even though none has yet been located. 

Isotopes are also used to determine properties of the environment. Just as carbon-14 is used to date organic materials, geologists can determine the age of very old substances such as rocks by measuring the abundance in rocks of radioisotopes with longer half-lives. Uranium-238 (t1/2 = 4.5 Ga, 1 Ga = 10y years) and potassium-40 (t,/2 = 1.26 Ga) are used to date very old rocks. For example, potassium-40 decays by electron capture to form argon-40. The rock is placed under vacuum and crushed, and a mass spectrometer is used to measure the amount of argon gas that escapes. This technique was used to determine the age of rocks collected on the surface of the Moon they were found to be 3.5-4.0 billion years old, about the same age as the Earth. 

Fig. 2.47. Model predicting mineral assemblages and proportions produced when basalt reacts with seawater in different water/rock mass ratios. The model is based on experimental data but is close to actual observed assemblages in recovered greenschist facies metabasalts (Mottl, 1983).

With calceous rock types, the oxide mineralization extends beyond the veins forming concretion and small masses. The lead content of these mineralization types range from 1.5% to 2.5%, of which 50% is oxidized. The zinc content ranges from 5% to 12%, of which 70% is oxide zinc. 

The relative area of mine solid waste tails (per 100,000 M3 of rock mass) is 0.7-0.8 of the total area. On average, the disturbed areas of uranium ore exploration site are partitioned as follows 32.3% of disturbed land is occupied by dumps, 27.2%, by pits, 20.3%, by industrial areas, 13.3%, by tails, and about 10%, by other types of land disturbance. 

In order to establish which base metal sulfide minerals host the PGE at the Creighton Mine we calculated a mass balance following the method of Barnes et al. (2008). We used the whole rock PGE content, the concentration of PGE in each sulfide and the mass fraction of each sulfide phase in the ore to determine the proportion (wt. %) of each PGE hosted by the sulfides in solid solution. 

The most common, and certainly the most familiar, inorganic fibers are the mineral fibers known as asbestos. Several minerals have been mined as asbestos (Fig. 1.1 A, C see chapter 2 for a detailed discussion of the asbestos minerals). These minerals are widespread in nature, but mining is economical only when they occur as continuous fibrous aggregates (veins) crosscutting rock masses. The veins are made up of hairlike fibers in parallel array that, on close inspection, appear bent (Fig. I.IB). Not surprisingly, a mineralogical term, asbestiform, has been used to describe this subset of inorganic materials. 

As must be obvious, we have only touched on the natural occurrences of crystalline fibrous Si02- For example, Si02, usually quartz, often replaces fibrous minerals of another composition as rock masses are altered. Si02 also occurs in fibrous form within some plants (phytoliths) and in the soil. To summarize, in addition to the usual and common occurrences of the mineral quartz and its varieties, several silica polymorphs occur as fibers in a variety of biologic and geologic environments. 

Temperature was set at 35 °C. Brine-rock mass ratio was set to 0.4 10, which corresponds to a porosity of approximately 10%. The mineral content and brine compositions were set to measured values (Table 1). Debyc-Hiickel equations were used to correct activity coefficients for saline solutions. The brine was allowed to come to equilibrium with the C02, then the 10 kg of sandstone was added and equilibrium assemblages were computed a second time. 

An important property of high-T systems is the reservoir formation porosity and the mass fractions of water and steam occupying the pores. These mass fractions and the formation porosity determine how large a fraction of the heat of the system is stored in the fluid and how large a fraction in the rock. Usually the quantity of heat stored in the reservoir rock is considerably larger than that stored in the fluid. This is particularly the case for vapour-dominated systems. For a liquid-dominated system at 250 °C with 10% porosity and no steam, the quantity of heat stored in the fluid in 1 m3 of reservoir rock is about 87 MJ, but that stored in the rock is some 500 MJ. The corresponding number for the heat stored in steam in a vapour-dominated system is only 5.6 MJ. 

Tunnels are subsurface constructions to overcome topographic barriers to transportation. They can serve various purposes (highway, railway, pipelines). Depending on local geologic conditions the tunnels can serve, especially in mountainous terrain, as heat/fluid sources railway and road tunnels as well as major galleries drain water from their surrounding rock masses. 

The absence of such minerals as biotite, which could have formed at temperatures as low as 300°C., supports the assumption of a lower maximum temperature for the rock mass. Fresh chlorite, the low temperature analogue of biotite, is abundant in the slate and is unstable only at higher temperatures. In view of these things, it is proposed that the slate and the anthraxolite were heated together at great depth, to a maximum temperature between 300° and 600°C., but probably much closer to the lower value. 

When we assume that the first minerals crystallized from a magma, a liquid rock mass, then the movement of the crystals in the magma will mainly be determined by their densities. Light minerals will rise to the surface, whereas heavy ones will sink. A number of densities of elements are listed in table 7.3 which will give you some idea of the occurrence of the various elements in the different earth layers. Please bear in mind that compounds are and were formed during the transport in magma and that this can lead to drastic changes in density. 

The Soxhlet extractor (figure 8.4) is filled with fine grains of one of the two kinds of rock which are most common on the earth s surface, viz. basalt and granite. Next water is constantly passed through this rock mass and for a very long time. This results in a continuous extraction of materials from the rock in other words the rock is exposed to... 

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