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·Materials Characterization and testing
Plutonic and Volcanic Basic Rocks Non-Destructive StudyValentin D. Vladimirov
Sofia University St. Kl. Ohridski, 15 Tzar Osvoboditel, Sofia, 1000, Bulgaria
Mitko M. Mihovski
Institute of Mechanics, Bulgarian Academy of Science, 24 G. Bonchev, Sofia 1113, Bulgaria
Increasing interest of the modern industry to cheaper row materials, which could be used directly without additional or with small transformation (just cutting, forming etc.) makes us to study physical properties of industrial minerals. An interesting object in this way are the plutonic and volcanic basic rocks from the Eastern Srednogorie, Bulgaria. Traditionally their investigation includes chemical and mineral composition determination. For the industry much more interesting are their physico-mechanical properties. In the rare cases when they are define, the destructive methods are used. Interpolation of these scare data to huge rock massifs leads to significant mistakes. The physical properties of the rocks from the same petrographic type vary a lot.
Non-destructive methods are cheaper and wide applicable. They have significant advantages compare to the destructive methods that are: the investigated object do not change its properties and whole? could be conducted directly on the field; and the measurements need (take) short time. They are used for the continues control and direct production characterization
Following the approach of Starostin (1979), the petrophysical analysis consisted of: (1) free water saturation method, which consisted of seven fixed in the time specimens weighting in the process of water saturation; and (2) determination of ultrasonic waves velocities (push - Vp and shear - Vs waves).
By computer processing, the following parameters were obtained: effective porosity (Pef, the percentage of the total volume of rock that consists of interconnecting voids); conditional momentary saturation (A, which reflects the saturation in the first few minutes i.e. 20 min) and in fact corresponds to liquid permeability; quantity of large (P1 > 10-2 mm), medium (P2 = 10-2 - 10-4 mm), small (P3 < 10-4 mm) pores, saturation constant (B, corresponds to exponential part of the saturation and it is independent of total porosity); density (r); Poisson's ratio (m, the ratio of the lateral strain to the longitudinal strain, in a body that has been stressed longitudinally within its elastic limit); Young's modulus (E, the ratio of applied stress of cross section to increase in rational length, N/m2 = Pa); Shear modulus (G, the ratio of applied tangential stress to angular deformation); Volume deformation coefficient (G, the ratio of applied stress and volume deformation in Pa); Acoustic impedance (Z, the ratio between the acoustic wave pressure and the velocity of the momentary velocity of the elementary particles in the material, ommom); Debye temperature (q, reflects substance structure stability, strength of connections between its separate elements, defects presence and their frequency, K) etc. (Starostin, 1979; Vladimirov, 1989, 1990, 1998, Mihovski, M., M. Lozev 1987).
For easier interpretation of so many physical characteristics, an integral complex petrophysical coefficient was involved (Starostin, 1979). The tape of calculation and set of properties used depended on which geologic process were to be discussed. In our study we use the following parameters: Pef, A, B, r, E, G. The complex petrophysical coefficient (Cpc) introduced in the authors interpretation, reflects the behavior of the investigated rocks in hydrothermal process. Its positive and large values define this rocks as a permeable medium and negative - as barriers for ore fluids.
For the Vickers hardness test (HV), ultrasonic impedance method was applied with SONOHARD SH 75, NAMIKON instrument.
Thermo electrical force (UT) determination (Dobrev P., M. Mihovski 1997)the special instrument UBK-TEC-3 was applied, innovation of Institute of Mechanics, Bulgarian Academy of Science.
Representative 26 samples of volcanic (latites - 3, latite breccia - 7 and andesitobasalts - 3) and plutonic (gabbro-porphyry - 6, monzogabbro - 7) rocks from the Eastern Srednogorie, Bulgaria are investigated.
Statistically computed results are presented in the Table 1, as for every petrographic rocks type as totally for the whole number of investigated rocks. They are shown in the 3 rows: in the first - mean value; in the second - minimal and in the third -maximal value for the given group of rocks.
|No||Rock type||Pef %||A%||P1%||P2%||P3%|
|Table 1:Petrophysical parameters|
|No||Rock type||B |
|Table 1: Continuation.|
|No||Rock type||m||E |
Pore-permeability parameters define investigated rocks as bad for filtration and fluids accumulation media. Generally more favorable in this case are latites and worst - gabbrtoporphyrites.
Plutonic rocks have significantly higher velocity and elastic values than the volcanic. This tendency results to the values of the complex petrophysical coefficient which is the lowest and negative for the plutonic rocks and especially for the monzogabbros.
The opposite trend we could see for the Vickers hardness which is highest for the latites. The lowest value is for the andesitobasalts but generally volcanic rocks show higher values than plutonic.
Thermo electrical force is lowest for the latites and highest for the andesitobasalts which reflects the presence and quantity of mineral magnetic fractions.
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