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.

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.

Mineral Prospectivity Modeling using AVIRIS-NG VNIR-SWIR data and Gravity data for Gold-Sulphide mineralization in parts of GADAG schist belt, Karnataka, India 

2021 ◽  
Author(s):  
Komal Rani
Keyword(s):  
Near Infrared ◽  
Gold Mineralization ◽  
Gravity Data ◽  
Mapping Method ◽  
Schist Belt ◽  
Sulphide Mineralization ◽  
Alteration Zones ◽  
Subsurface Structures ◽  
Present Study Area ◽  
Basement Depth

<p>Gadag schist belt, India is known for sulphide-gold mineralization. In the study area mineralization is controlled structurally and lithologically. In this context, Airborne Visible-Infrared Imaging Spectrometer - Next Generation (AVIRIS-NG) Visible Near InfraRed (VNIR) - Shortwave Infrared (SWIR) bands were utilized to derive alteration zones and structures present in the study area. Lithological boundaries have also been updated using AVIRIS-NG VNIR-SWIR bands derived images enhancement products i.e. Minimum Noise Fraction (MNF) and False Colour Composite (FCC). Further, image spectra of alteration zones (Hydrous mineral etc.) derived from AVIRIS-NG calibrated VNIR-SWIR bands were compared with the standard corresponding reference library spectra (USGS, JPL spectral library). These image spectra have been utilized to demarcate the alteration zones using the Matched Filtering spectral mapping method. Structures were demarcated using high pass (HP) filtered image and FCC images. Low pass (LP) filter image and along with MNF & FCC image composite were utilized to update the lithological boundaries in the study area.</p><p>Ground gravity data has also been processed to derive the subsurface evidences relevant to the deposit in the present study area. Subsurface structures which are responsible for the transportation of mineral rich fluid in the near subsurface are delineated using the gravity data derived products. Apart from this, basement depths are also derived from the gravity data which are being utilized for the validation as well as to further precise the locations of mineral deposits.  These subsurface structures (gravity data), lithology, lineament density and alteration zones are very important evidential layers which have been integrated using fuzzy logic integration techniques to identify potential zones of gold-sulphide mineralization in the present study area. The prospective zones are validated using the secondary data and basement depth derived from the gravity data.</p><p>For similar kind of gold-sulphide mineralization, AVIRIS-NG data and Gravity data can be used to derive the important evidential layers in any part of the world. There are only few studies where such integration approach has been utilized to explore new potential zones of gold sulphide mineralization. </p><p>Keywords: AVIRIS-NG, VNIR-SWIR, alteration, MNF, FCC, Gravity, Basement Depth</p>

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.

Some constraints on the form of the Welsh Basin from regional gravity and aeromagnetic data, with particular reference to Central Wales

1992 ◽  
Vol 129 (5) ◽  
pp. 515-522 ◽  
Author(s):  
R. M. Carruthers ◽  
C. J. N. Fletcher ◽  
A. J. W. McDonald ◽  
R. B. Evans
Keyword(s):  
Physical Property ◽  
Data Sets ◽  
Aeromagnetic Data ◽  
Near Surface ◽  
Magnetic Components ◽  
Major Fault ◽  
Magnetic Basement ◽  
Lower Palaeozoic ◽  
Regional Gravity ◽  
Geophysical Anomalies

AbstractGravity and aeromagnetic data sets provide systematic coverage over the whole of the Welsh Basin. Physical property information shows considerable overlap in densities within the Lower Palaeozoic and Precambrian formations, with relatively few units of the exposed succession being strongly magnetic. While the geophysical anomalies cannot be interpreted unambiguously in terms of these sources, the data can still be used to test different geological models and to indicate the range of possible solutions. The major fault zones are seen to influence the anomaly patterns in a variety of ways, reflecting a combination of differing near-surface contrasts and effects within the underlying basement. The general increase in gravity values towards Cardigan Bay may originate from the lower crust, and the large amplitude aeromagnetic low seen over Cardigan Bay indicates that a distinctive change in the character of the crust occurs here. Two-dimensional modelling in central Wales shows that a westward thickening of the Welsh Basin, to a maximum of about 10 km, may also be significant. It is necessary to postulate a separation of the base of denser, Lower Palaeozoic rocks from the underlying, more magnetic basement in order to account for offsets in anomaly source locations. This implies the presence of less dense Cambrian sediments and/or non-magnetic components of the Precambrian basement.

scholarly journals Structural model of the Northern Latium volcanic area constrained by MT, gravity and aeromagnetic data

1997 ◽  
Vol 40 (5) ◽  
Author(s):  
P. Capuano ◽  
G. Florio ◽  
P. Gasparini
Keyword(s):  
Structural Model ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Volcanic Area ◽  
Aeromagnetic Data ◽  
Geothermal Exploration ◽  
Magnetotelluric Soundings ◽  
Aeromagnetic Anomalies ◽  
Deep Boreholes

The results of about 120 magnetotelluric soundings carried out in the Vulsini, Vico and Sabatini volcanic areas were modeled along with Bouguer and aeromagnetic anomalies to reconstruct a model of the structure of the shallow (less than 5 km of depth) crust. The interpretations were constrained by the information gathered from the deep boreholes drilled for geothermal exploration. MT and aeromagnetic anomalies allow the depth to the top of the sedimentary basement and the thickness of the volcanic layer to be inferred. Gravity anomalies are strongly affected by the variations of morphology of the top of the sedimentary basement, consisting of a Tertiary flysch, and of the interface with the underlying Mesozoic carbonates. Gravity data have also been used to extrapolate the thickness of the neogenic unit indicated by some boreholes. There is no evidence for other important density and susceptibility heterogeneities and deeper sources of magnetic and/or gravity anomalies in all the surveyed area.

Depth to magnetic basement in the Anambra Basin, Benue Trough of Nigeria from aeromagnetic data: A prelude for hydrocarbon exploration

2021 ◽  
pp. 1-57
Author(s):  
Olatunbosun O. Olagundoye ◽  
Chiedu S. Okereke ◽  
Aniekan E. Edet ◽  
Dominic Obi ◽  
Aniediobong Ukpong
Keyword(s):  
Depth Estimation ◽  
Data Transformation ◽  
Hydrocarbon Exploration ◽  
Hydrocarbon Generation ◽  
Depth Range ◽  
Aeromagnetic Data ◽  
Benue Trough ◽  
Anambra Basin ◽  
Magnetic Basement ◽  
Fault Structures

Data transformation, regional-residual separation, trend analysis, and Analytic Signal (AS) depth estimation were applied to aeromagnetic data covering the Anambra Basin, which is a major depocentre in the Benue Trough, southeast Nigeria with the primary objectives of accentuating attributes of magnetic sources and determining if sufficient sediment thickness exists for hydrocarbon generation, maturation, and expulsion. The application of data transformation techniques (such as map projection, merging, and reduction-to-pole) and regional-residual ensured the computation of a crustal magnetic field that would be suitable for magnetic analyses. Results indicate that the magnetic basement in the basin forms an undulating surface overlain by sediments with average thickness ranging between 4 km and 7.5 km, while maximum thickness reaches 8 km in some areas. This depth range suggests promising prospect for source-facies maturation and expulsion. We expect that areas in the study area with these appreciable sediment thicknesses, good preservation of graben-fill, and suitable areal closures or fault structures would be favorable for hydrocarbon prospectivity.

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