Ground‐Water Problems in the Mesozoic Pax Mountain Fault Zone
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ABSTRACT More than 100 steeply dipping or vertical Mesozoic fault zones, which cut across Paleozoic igneous and metamorphic rocks, have been reported in the Piedmont and Appalachians of the Carolinas. The present investigation deals with the hydrological problems encountered in exploring for ground water in the Pax Mountain Fault zone. This is the largest known Mesozoic fault in the Carolinas, having a length of more than 75 km and attaining a width of 1 km in places. Subsurface studies of seven wells, which were drilled along the axis of Pax Mountain, South Carolina, show that the composition of the fault rocks is much more complicated than was known heretofore. These rocks consist of angular particles of quartz and feldspar fault breccia enclosed in a kaolinitic clay gouge. They vary greatly in degrees of consolidation and permeability, and these variations were the cause of some serious ground‐water problems. Two wells were dry holes because the intergranular spaces of the breccia were clogged with clay and also because most of the joints were filled with secondary minerals. Three wells, which were drilled in more permeable, but poorly consolidated fault rocks, caved in at a depth of about 80 m just when they had encountered large volumes of water. Two of the seven wells produce potable water, but chemical analyses of the ground water showed that their turbidity values were 6.0 t.u. and 2.0 t.u., which exceed the limit of 1.0 recommended by the South Carolina Department of Health and Environmental Control.Keywords:
Breccia
For several years past it has been known to us that fragmental igneous rocks exist in different parts of Ireland, which, though they resemble tuffs, and in certain cases have been described as volcanic rocks, cannot be regarded as ejectamenta, on account of their character and mode of occurrence in the field. Of those which have come more especially under our notice, we may at the outset briefly mention a few particulars, to introduce our subject, before describing in detail the sections exposed in the South-east of Ireland which afford the chief evidence upon which our views of such rocks are based. In the Explanatory Memoir (1888) accompanying Sheet 24 of the Geological Survey Map of Ireland, pp. 34 & 35, certain breccias occurring to the east of Lough Easke, in Donegal, are described as ‘agglomerates,’ though not in the sense of their having been at any time considered volcanic rocks. In parts, these masses might better be described as crush-breccias, as they, in such cases, follow lines of dislocation. In parts, however, they consist of partly-fused, broken-up, felspathic mica-schist or ‘gneiss,’ and they merge with felsite-dykes. Sometimes they occur dispersedly in sporadic masses in the mica-schist; and north-east of Lough Easke the breccia forms a wide band adjoining the granite, suggesting the conclusion that its formation may be attributed to the earth-stresses which immediately preceded, or in a sense accompanied, the intrusion of the Barnesmore granitic mass. Rocks similar to these occur in the district of Forkhill, in Armagh
Breccia
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Optically stimulated luminescence
Optical dating
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This article has summed up the current researches on separating quartz from feldspar through flotation with no-fluoride, and analyzed the mechanism that causes the differences of floatability between quartz and feldspar in these several processes. The results have indicated that the most widely used process without fluoride of separating quartz from feldspar is feldspar-flotation in acidic condition at present, while the most promising process is flotation in neutral or alkali condition.
Alkali feldspar
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Mass concentration (chemistry)
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Optically stimulated luminescence
Thermoluminescence dating
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ABSTRACT The in the quartz from 35 igneous rocks and 16 metamorphic rocks were studied in detail in thin sections. They were grouped into regular, acicular, globular, and irregular inclusions following a modified scheme proposed by Mackie in 1896. In this study, regular characterize the quartz of schists, irregular predominate in igneous quartz, and globular and acicular are most abundant in igneous quartz although they also occur in metamorphic quartz. Spectrographic analyses were rim on 35 samples of petrogenic quartz. Even clear colorless quartz is rich in elements other than silicon and oxygen. Probably ordinary rock-forming minerals in sub-microsopically fine particles are abundantly included in most petrogenic quartz.
Acicular
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The use of quartz is critical to the electron spin resonance (ESR) dating of sediments and fault gouges. The germanium center (Ge center) in quartz is a commonly used color center employed in ESR signal measurement. Although Ge center signals in quartz can be detected using an ESR spectrometer, they are weak and sometimes undetectable. Impurities in quartz grains can further aggravate these deficiencies and may even invalidate any attempt to repeat ESR ages due to the deficiencies evident in the processes used in sample preparation. Using sieving, carbonate-organic matter removal, water flotation, magnetic separation, heavy liquid separation, and HF solution etching, we separated quartz, feldspar (plagioclase), mica, and the heavy minerals and measured the ESR signal in each of them to examine the impact of impurities within mineral grains on the ESR signals. From the ESR spectra, we observed intense ESR signals in feldspar and the heavy minerals and weak signals in mica at the same positions as the Ge center in the quartz. The ESR signals in the feldspar proved to be the most intense and overrode the peaks exhibited by the Ge center in the quartz. Feldspar is commonly associated with quartz in sediments, but it is difficult to separate it from quartz as their colors, specific gravities, and magnetic properties are similar. Any ESR signal in quartz containing foreign minerals would therefore be likely to be heavily disturbed by the signals from these foreign minerals, particularly from the feldspar and heavy minerals. ESR signals in the feldspar decreased similarly to those in the quartz when exposed to sunlight, declining by 70%–80% after being exposed for 50 h. Such declination was more obvious in high-altitude areas than in low-altitude areas. Our results indicate that highly pure quartz is required when dating; we would therefore strongly suggest that the procedures for the purification of quartz grains should include floating, heavy liquid separation, and HF solution etching to remove the feldspar, heavy minerals, and any remnant magnetite. Such a procedure would guarantee that the signal that is measured comes from the quartz alone, allowing repeatable measurements using the same spectrometer as well as valid comparisons between the spectrometries derived from different spectrometers.
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