Magnetic curve fit for a thin dike: Calculator program (TI 59)

Geophysics ◽  
1980 ◽  
Vol 45 (3) ◽  
pp. 447-455 ◽  
Author(s):  
Edwin J. Ballantyne
Keyword(s):  
Massive Sulfide ◽  
Sulfide Deposits ◽  
Curve Fit ◽  
Magnetic Curve ◽  
Original Field ◽  
Susceptibility Contrast ◽  
Magnetic Profile ◽  
Depth Of Burial ◽  
Minimum Points ◽  
Interpretation Problem

In the exploration for massive sulfide deposits, many of the sources of magnetic anomalies are long tabular dike‐like bodies which are thin in relation to the depth of burial. That is, the width of the dike is less than the depth of burial. A program is presented to aid in the inverse solution of this interpretation problem. Demagnetization effects are ignored, and the program will not function for symmetrical anomalies. Given field‐observed amplitudes and coordinates of maximum and minimum points on a total‐ or vertical‐field magnetic profile, this program fits the corresponding theoretical profile for a thin dipping magnetic dike. Coordinate and depth of the top of dike, dip of dike, and width‐susceptibility contrast of the dike are calculated. A theoretical anomaly profile may also be calculated for comparison with the original field curve. Successive iterations may be used to refine estimates of the calculated parameters.

LIMITING PARAMETERS IN THE MAGNETIC INTERPRETATION OF A GEOLOGIC STRUCTURE

Geophysics ◽  
1962 ◽  
Vol 27 (6) ◽  
pp. 807-814 ◽  
Author(s):  
Gordon E. Andreasen ◽  
Isidore Zietz
Keyword(s):  
Goodness Of Fit ◽  
Drill Hole ◽  
Magnetic Interpretation ◽  
Basement Rocks ◽  
Randolph County ◽  
Susceptibility Contrast ◽  
Magnetic Profile ◽  
Limiting Parameters ◽  
Dip Angle ◽  
Depth Of Burial

A prominent aeromagnetic anomaly in Randolph County, Indiana, suggests the existence of a dikelike structure within the Precambrian basement rocks. Because of the ambiguity inherent in magnetic interpretation, a unique solution for the parameters involved (depth of burial, geometric configuration, and magnetic susceptibility of the mass producing the anomaly) is impossible. However, if one of the parameters is known it is sometimes possible to indicate a range of plausible values for each of the remaining parameters. The depth to the surface of the Precambrian rocks in Randolph County is known from drill‐hole data to be about 3,000 ft. As the depth of burial is known, limits need be set only on the thickness, angle of dip, and susceptibility contrast of the assumed dike. These limits are determined by a graphical method. Theoretical anomalies over the postulated dike are computed for different dike thicknesses, angles of dip, and susceptibility contrasts. The computed profiles are then fitted to an observed magnetic profile flown at right angles to the trend of the feature. Numerical values for the “goodness of fit” are calculated by using the statistical method of sums of squares. Two plots, one of the index of goodness of fit and the other of susceptibility as functions of dip angle and dike thickness, are made to show graphically the interdependence of the variables and the plausible range of each. The contoured plots of the goodness of fit and the susceptibility contrast show that the range of best fit is between dip angles of 30 and 60 degrees and dike thickness of 1,000 to over 4,000 ft. The contoured plot of the susceptibility contrast, translated into percentage of magnetite, shows this parameter to be independent of the dip angle, varying only with thickness.

Plumbotectonics IIA, Precambrian massive sulfide deposits

1976 ◽  
Author(s):  
J. S. Stacey ◽  
B.R. Doe ◽  
L.T. Silver ◽  
R.E. Zartman
Keyword(s):  
Massive Sulfide ◽  
Sulfide Deposits ◽  
Massive Sulfide Deposits

Possible excess 40 Ar in hornblende and biotite from the Appalachian massive sulfide deposits at Ore Knob, North Carolina, and Ducktown, Tennessee

1980 ◽  
Vol 75 (2) ◽  
pp. 329-334
Author(s):  
P. D. Fullagar ◽  
S. A. Kish ◽  
A. L. Odom ◽  
R. D. Dallmeyer ◽  
M. L. Bottino
Keyword(s):  
North Carolina ◽  
Massive Sulfide ◽  
Sulfide Deposits ◽  
Massive Sulfide Deposits
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