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A study of shallow reflection seismics for placer-tin-reserve estimation and mining — A discussion
Geoexploration, 23 (1984/85) 291-293 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
291
Discussion A STUDY OF SHALLOW RESERVE ESTIMATION
REFLECTION SEISMICS FOR PLACER-TINAND MINING - A DISCUSSION
DENNIS V. WOODS*’ Department (Canada)
of Geological
Sciences,
Queen’s University,
Kingston,
Ont. X7L 3N6
(Received 31 October, 1984; accepted December 12, 1984)
Singh (1983) presents results from a shallow seismic reflection survey in the vicinity of placer tin deposits in Kinta Valley, Malaysia. In the paper, he discusses the results of an experiment to determine the effectiveness of a sledgehammer source as compared to weight drops. However, he presents the results in terms of kinetic energy of the falling weight or the sledgehammer head, at the instant of impact with a striker plate (Singh, 1983; fig. 3). It is well known (Mereu et al., 1963; Mooney, 1976) that the amplitude of the primary seismic pulse resulting from the elastic impact of a mass with the surface of the ground is proportional to the momentum of the mass at the TABLE I Calculation of weight-drop and sledgehammer momentum from data presented in Singh (1983, Fig. 3). Seismic amplitude, A (mm) Weight drop 4.5 7.5 10.5 9.0 11.0 12.0 14.5 Sledgehammer 18.0 h = E/mg u = (2gh)% mu = m (2gh)%
Kinetic energy, E (joules)
Height h(m)
36 71 107 128 142 188 214
0.5 1.0 1.5 1.8 2.0 2.5 3.0
640
Terminal velocity, u (m/s) -.. 3.13 4.43 5.42 5.94 6.26 7.00 7.67 16.7
Momentum, ;nkug.mis)
22.7 32.1 39.4 43.1 45.5 50.8 55.7 76
m = 7.257kg g = 9.81 m/s*
*‘On temporary exchange to the Geological Survey of Canada, 601 Booth Street, Ottawa, Ont. KlA 0E8 (Canada).
292
instant of impact. Hence, if the amplitudes of the first seismic arrivals shown by Singh (1983, fig. 3) are replotted versus the momentum of the falling mass, a straight line is obtained which passes through the origin (calculations are shown in Table I and results are presented in Fig. I). This is a more satisfactory result than having a seismic pulse amplitude of 3 mm for zero impact energy, as indicated by Singh (1983, Fig. 3).
Momentum
kg
m/s
Fig 1. Amplitude of seismic first arrival replotted sledgehammer blow; after Singh (1983, fig. 3).
versus momentum
of weight
drop and
If the straight line which best fits the data shown in Fig. 1 is extrapolated to the amplitude of the seismic pulse obtained by a sledgehammer blow, then a momentum of approximately 76 kg.m/sec is obtained for the hammer blow. This means that the sledgehammer had a terminal velocity of 16.7 mfsec, slightfy more than twice the velocity of the falling mass from a height of 3.0 m. As indicated by Mooney (1976), experience has shown that terminal velocity, and hence seismic amplitude, is approximately doubled if a sledgeh~mer is forcefully swung versus letting it free-fall. Finally, the kinetic energy of such a hammer blow calculates to about 640 J, about twice that quoted by Singh (1983) and in a subsequent paper (Singh, 1984).
REFERENCES Mereu, R.F., Uffen, R.J. and Beck, AX., 1963. The use of a coupler in the conversion of impact energy into seismic energy. Geophysics, 28: 531-546. Mooney, H.&I., 1976. Types and characteristics of seismic sources for engineering seismology. In: Handbook of Engineering Geophysics, Bison Instruments Inc., Minneapalis, Minn., pp. 21.1-21,Tl2. Singh, S,, 1983. A study of shallow reflection seismics for placer-tin-reserve evaluation and mining. Geoxeploration, 21: 105-135. Singh, S., 1984. Shallow seismic reflections with a propane-oxygen detector. Geoexploration, 22: 89-106.
291
Discussion A STUDY OF SHALLOW RESERVE ESTIMATION
REFLECTION SEISMICS FOR PLACER-TINAND MINING - A DISCUSSION
DENNIS V. WOODS*’ Department (Canada)
of Geological
Sciences,
Queen’s University,
Kingston,
Ont. X7L 3N6
(Received 31 October, 1984; accepted December 12, 1984)
Singh (1983) presents results from a shallow seismic reflection survey in the vicinity of placer tin deposits in Kinta Valley, Malaysia. In the paper, he discusses the results of an experiment to determine the effectiveness of a sledgehammer source as compared to weight drops. However, he presents the results in terms of kinetic energy of the falling weight or the sledgehammer head, at the instant of impact with a striker plate (Singh, 1983; fig. 3). It is well known (Mereu et al., 1963; Mooney, 1976) that the amplitude of the primary seismic pulse resulting from the elastic impact of a mass with the surface of the ground is proportional to the momentum of the mass at the TABLE I Calculation of weight-drop and sledgehammer momentum from data presented in Singh (1983, Fig. 3). Seismic amplitude, A (mm) Weight drop 4.5 7.5 10.5 9.0 11.0 12.0 14.5 Sledgehammer 18.0 h = E/mg u = (2gh)% mu = m (2gh)%
Kinetic energy, E (joules)
Height h(m)
36 71 107 128 142 188 214
0.5 1.0 1.5 1.8 2.0 2.5 3.0
640
Terminal velocity, u (m/s) -.. 3.13 4.43 5.42 5.94 6.26 7.00 7.67 16.7
Momentum, ;nkug.mis)
22.7 32.1 39.4 43.1 45.5 50.8 55.7 76
m = 7.257kg g = 9.81 m/s*
*‘On temporary exchange to the Geological Survey of Canada, 601 Booth Street, Ottawa, Ont. KlA 0E8 (Canada).
292
instant of impact. Hence, if the amplitudes of the first seismic arrivals shown by Singh (1983, fig. 3) are replotted versus the momentum of the falling mass, a straight line is obtained which passes through the origin (calculations are shown in Table I and results are presented in Fig. I). This is a more satisfactory result than having a seismic pulse amplitude of 3 mm for zero impact energy, as indicated by Singh (1983, Fig. 3).
Momentum
kg
m/s
Fig 1. Amplitude of seismic first arrival replotted sledgehammer blow; after Singh (1983, fig. 3).
versus momentum
of weight
drop and
If the straight line which best fits the data shown in Fig. 1 is extrapolated to the amplitude of the seismic pulse obtained by a sledgehammer blow, then a momentum of approximately 76 kg.m/sec is obtained for the hammer blow. This means that the sledgehammer had a terminal velocity of 16.7 mfsec, slightfy more than twice the velocity of the falling mass from a height of 3.0 m. As indicated by Mooney (1976), experience has shown that terminal velocity, and hence seismic amplitude, is approximately doubled if a sledgeh~mer is forcefully swung versus letting it free-fall. Finally, the kinetic energy of such a hammer blow calculates to about 640 J, about twice that quoted by Singh (1983) and in a subsequent paper (Singh, 1984).
REFERENCES Mereu, R.F., Uffen, R.J. and Beck, AX., 1963. The use of a coupler in the conversion of impact energy into seismic energy. Geophysics, 28: 531-546. Mooney, H.&I., 1976. Types and characteristics of seismic sources for engineering seismology. In: Handbook of Engineering Geophysics, Bison Instruments Inc., Minneapalis, Minn., pp. 21.1-21,Tl2. Singh, S,, 1983. A study of shallow reflection seismics for placer-tin-reserve evaluation and mining. Geoxeploration, 21: 105-135. Singh, S., 1984. Shallow seismic reflections with a propane-oxygen detector. Geoexploration, 22: 89-106.