DISCUSSION OF “AN EVALUATION OF BASEMENT DEPTH DETERMINATION FROM AIRBORNE MAGNETOMETER DATA” BY PETER JACOBSEN, JR.

Geophysics ◽  
1962 ◽  
Vol 27 (1) ◽  
pp. 162-162
Author(s):  
G. Ramaswamy
Keyword(s):  
World War Ii ◽  
Gravity Data ◽  
Data Gathering ◽  
Magnetic Data ◽  
World War ◽  
Depth Determination ◽  
Magnetometer Data ◽  
Exploration Tool ◽  
Basement Depth ◽  
Ground Magnetic

Mr. Jacobsen’s article and the accompanying discussions on the scope and outlook for the current interpretational practices in aeromagnetic surveys are very timely and deserve the attention of all geophysicists as well as exploration management. Since World War II the aeromagnetic surveys have replaced the ground magnetic surveys as a reconnaissance exploration tool chiefly because of the former’s rapidity and cheapness in data‐gathering. In this process, however, the aerial technique has lost one advantage going with the ground surveys. In land surveys the practice has been to make simultaneous magnetic and gravity observations and the interpretations of basement features are made from these paired observations. I believe that the absence of concurrent information on gravity has been a real handicap with aeromagnetic interpretation in reliably locating basement features in the early stages of exploration. Perhaps the present aerial gravitymeter instrumentation can be soon improved to desired sensitivity for exploration so that simultaneous gravity‐magnetic observations from the air will be possible. In large unexplored sedimentary areas the gravity data are as valuable, sometimes more, to the interpretation of magnetic data as a knowledge of the magnetic properties of any out‐cropping rocks.

Systematic Government Access to Private-Sector Data in Japan

2017 ◽  
Author(s):  
Motohiro Tsuchiya
Keyword(s):  
World War Ii ◽  
Private Sector ◽  
Legal System ◽  
Personal Information ◽  
Data Gathering ◽  
Executive Branch ◽  
Information Protection ◽  
World War ◽  
Sector Data ◽  
Personal Information Protection

The Japanese legal system has been based on the German legal system since the mid-nineteenth century, but the American legal system was grafted onto it following Japan’s defeat in World War II in 1945. The postwar Constitution contained an article regarding the secrecy of communications and protected privacy in terms of respect of individuals. Now, as the Personal Information Protection Law in the Executive Branch, which was enacted in 1988, and the Personal Information Protection Law, which was enacted in 2003, strictly regulate privacy, there have been fewer problematic cases regarding governmental access to private-sector data. Data gathering for law enforcement or intelligence activities has also been weaker following World War II. Private-sector corporations/organizations might share data with government agencies, but based on voluntary arrangements, not by any mandatory system. More focus is being cast not on governmental access to private-sector data, but on citizen’s access to data.

Discussions of “An Evaluation of Basement Depth Determination from Airborne Magnetometer Data,” by Peter Jacobsen, Jr.

Geophysics ◽  
1961 ◽  
Vol 26 (3) ◽  
pp. 317-319 ◽  
Author(s):  
R. J. Bean ◽  
Walter R. Fillippone ◽  
Norman R. Paterson ◽  
Isidore Zietz
Keyword(s):  
Quantitative Analysis ◽  
Sedimentary Basins ◽  
Depth Determination ◽  
Magnetometer Data ◽  
Local Relief ◽  
Basement Depth ◽  
Basement Surface

In his discussion of the magnetic interpretations, Mr. Jacobsen rightly distinguishes between the determination of basement depth and configuration by analysis of anomalies originating from magnetization contrast within the basement and the delineation of local relief or faulting at the basement surface by analysis of smaller anomaly trends. It cannot be emphasized too strongly that the principal purpose of conducting aeromagnetic surveys is to outline the extent and depth of sedimentary basins, and the calculation of depth to basement by quantitative analysis of anomalies has progressed to the point where reliable results can be obtained by skilled interpreters.

Application of aeromagnetic data to mineral potential evaluation in Minnesota

Geophysics ◽  
1995 ◽  
Vol 60 (6) ◽  
pp. 1704-1714 ◽  
Author(s):  
Allan Spector ◽  
Thomas L. Lawler
Keyword(s):  
Land Use Planning ◽  
Gold Mineralization ◽  
Gravity Data ◽  
Physical Property ◽  
Aeromagnetic Data ◽  
Precambrian Geology ◽  
Magnetic Basement ◽  
Copper Zinc ◽  
Basement Depth ◽  
Ground Magnetic

Aeromagnetic, ground magnetic, and gravity data, together with all available drillhole data and physical property measurements, were used to map the Precambrian geology of an area in Minnesota that is virtually devoid of outcrop. The work was done for purposes of land use planning and to encourage minerals exploration and mostly consisted of the analysis of profiles of aeromagnetic data to map magnetic/lithologic contacts, to infer structure, and to determine thickness of overburden cover. Two greenstone belts were resolved. They comprise higher density rocks separated by nonmagnetic metasedimentary intervals. The belts are deformed into synclinal structures that, according to modeling, range from 1 km to as much as 5 km in depth. Lithologic predictions were confirmed in five out of six holes drilled on completion of the magnetic interpretation. In over 40% of the area, Precambrian rocks are apparently mantled by less than 50 m of overburden, and in 50% of the area there is between 50 and 100 m of overburden cover. In the remaining 10%, the magnetic basement is overlain by a thick blanket of nonmagnetic Precambrian sedimentary rocks, over 200 m thick. Basement depth determinations were subsequently tested at six holes. Depth determinations at all drill sites were found to lie within the 20% error expectation of the method of depth determination. Thirty‐seven sites were resolved from the aeromagnetic data as targets for basemetal sulfide (copper, zinc) as well as precious metal (gold) mineralization. Thirteen magnetic anomalies were identified as possible kimberlite pipes.

AN EVALUATION OF BASEMENT DEPTH DETERMINATIONS FROM AIRBORNE MAGNETOMETER DATA

Geophysics ◽  
1961 ◽  
Vol 26 (3) ◽  
pp. 309-317 ◽  
Author(s):  
Peter Jacobsen
Keyword(s):  
Magnetic Data ◽  
Depth Information ◽  
Poor Agreement ◽  
Well Control ◽  
Depth Maps ◽  
Magnetometer Data ◽  
Local Relief ◽  
Basement Depth ◽  
Well Data ◽  
Basement Surface

Four years ago Creole Petroleum Corporation submitted identical airborne magnetometer data for a portion of the Eastern Venezuela basin to two different geophysical contractors for independent, detailed analysis. These contractors offer the customary generalized basement depth maps; but they specialize in delineating areas of relatively local relief on the basement surface. Both kinds of interpretation were requested by Creole. The main purpose of the study was to evaluate the reliability of interpretations of local basement relief from magnetic data. Accordingly, the region for study was deliberately chosen to include, in part, areas for which Creole had considerable knowledge of basement depths and local basement configuration from other sources. Local basement relief shown by the two magnetic interpretations is in poor agreement with basement depth information from seismograph and well data. Moreover, the two magnetic pictures bear little resemblance one to the other. With respect to regional basement depth contours, one of the magnetic interpretations compares statisfactorily with the picture based on seismograph and well control. A tentative conclusion is that local basement relief cannot be reliably interpreted from magnetometer data alone.

scholarly journals Analysis of gravity and aeromagnetic data to determine structural trend and basement depth beneath the Ajdabiya Trough in northeastern Libya

2021 ◽  
Vol 3 (2) ◽  
Author(s):  
Abdelhakim S. Eshanibli ◽  
Abel Uyimwen Osagie ◽  
Nur Azwin Ismail ◽  
Hussin B. Ghanush
Keyword(s):  
Gravity Data ◽  
Depth Estimation ◽  
Magnetic Data ◽  
Aeromagnetic Data ◽  
Pass Filter ◽  
Magnetic Basement ◽  
Basement Depth ◽  
Well Data ◽  
High Pass ◽  
Modelling Process

AbstractIn this study, we analyse both ground gravity and aeromagnetic data in order to delineate structural trends, fault systems and deduce sedimentary thicknesses within the Ajdabiya Trough in Libya’s northeast. A high-pass filter and a reduced-to-the-pole (RTP) transformation are applied to the gravity and aeromagnetic data respectively. Different filters are used to enhance the structural signatures and fault trends within the study area. The Werner deconvolution and source parameter imaging (SPI) techniques are applied to the RTP magnetic data for source depth estimation. Four well-data within the area are used as constraints in the two-dimensional forward modelling process. The results show that the Ajdabiya Trough is characterised by gravity anomaly highs and magnetic anomaly lows. The analysis of gravity data shows predominant Northeast–Southwest structural trends, whereas the analysis of magnetic data shows predominant North–South magnetic lineaments within the Ajdabiya Trough. The Euler deconvolution depth estimates of faults depths range between 1500 and 9500 m. The SPI estimates of the magnetic basement range between 2500 and 11,500 m beneath the study area (deepest beneath the Ajdabiya Trough). Constrained by the well-data, six major layers characterize the four profiles that are taken within the area. One of the profiles shows a high-density intrusion (about 4 km from the surface) within the sedimentary sequence. The intrusion may be the result of the rifting Sirt Basin which caused a weakening of the crust to allow for mantle intrusion.

scholarly journals The geophysical signature of Oyut deposits, Oyu Tolgoi, Mongolia

2021 ◽  
Vol 26 (52) ◽  
pp. 80-96
Author(s):  
Erdene Batbaatar ◽  
Munkhjargal Todbileg ◽  
Otgonbayar Sansar ◽  
Baatar Bataa
Keyword(s):  
Gravity Data ◽  
Porphyry Copper ◽  
Mineral Deposits ◽  
Magnetic Data ◽  
The South ◽  
Porphyry Cu ◽  
Gravity And Magnetic ◽  
Integrated Interpretation ◽  
Ground Magnetic ◽  
Gravity And Magnetic Data

The well-known Oyu Tolgoi Cu-Au group deposits can be divided into three main deposits: Hugo Dummett deposit (Hugo North and Hugo South), Oyut deposits (South Oyu, Southwest Oyu and Central Oyu), and Heruga deposit in the south. These deposits sit along 26 km long, north-northeast trending belt termed as the Oyu Tolgoi trend. This paper reviews investigations on geophysical signatures of the South Oyu, Southwest Oyu and Central Oyu deposits and compares geophysical models of the mineral deposits with their lithology, alteration, mineralization, and structures. A variety of datasets including induced polarization, ground magnetic, gravity survey are used in the study and generated inversion products of ground magnetic and gravity data with integrated interpretation. Typical responses from the Oyut deposits are: up to 0.1 mGal positive gravity anomaly above background, 100–200 nT low or high magnetic anomaly compared to background depending on the geological situations, and from 12 mV/V to 30 mV/V chargeability anomalies and low resistivity signatures from 100 ohm.m to 400 ohm.m. The interpreted geological-geophysical models of porphyry Cu-Au deposits presents in this study have emphasis on integrated interpretation of geophysical techniques, and inversions of gravity and magnetic data in gold rich porphyry copper system.

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