Inversion of geophysical data over a copper gold porphyry deposit: A case history for Mt. Milligan

Geophysics ◽  
1997 ◽  
Vol 62 (5) ◽  
pp. 1419-1431 ◽  
Author(s):  
Douglas W. Oldenburg ◽  
Yaoguo Li ◽  
Robert G. Ellis
Keyword(s):  
Magnetic Susceptibility ◽  
Physical Property ◽  
Earth Model ◽  
Gold Concentration ◽  
Porphyry Deposit ◽  
Copper Gold ◽  
Susceptibility Model ◽  
Airborne Electromagnetic ◽  
Rock Model ◽  
Drill Holes

In this paper, we invert magnetic, DC resistivity, induced polarization (IP), and airborne electromagnetic (EM) data from the Mt. Milligan copper‐gold porphyry deposit and jointly interpret the inversion results with available geological and mineralization data. The inversions are carried out over an area that encloses an intrusive stock, known as the MBX Stock, and the resulting mineralization zone surrounding it. The earth model is discretized into a large number of cells having constant physical properties, and distributions of magnetic susceptibility, conductivity, and chargeability are obtained by minimizing a model objective function subject to adequately fitting the corresponding data. A 3-D magnetic susceptibility model is obtained directly by inverting surface total field anomaly data. 3-D conductivity and chargeability models are formed by compositing 2-D sections recovered by inverting DC/IP pole‐dipole data. The airborne EM data are inverted with a 1-D algorithm and composited into a 3-D conductivity model. The physical property models are compared with a rock model constructed from geologic information from 600 drill holes and with a 3-D model of gold concentration. The physical property models have features that correlate with various geologic boundaries and rock units. More notably, the recovered chargeability and susceptibility seem to reflect the distribution of mineralization: chargeability highs coincide with the greatest gold concentration, while the susceptibility displays an anticorrelation with it. Overall, our inversion results are consistent with the geology and mineralization models for the Cu-Au porphyry deposit, while the anticorrelation between gold concentration and susceptibility provides an important constraint that helps define the distribution and geochemical control of the orebody.

Classifying Copper-Molybdenum-Gold Porphyry Deposit Alteration using Magnetic and Spectral data

2021 ◽  
Author(s):  
Oliver Dixon ◽  
William McCarthy ◽  
Nasser Madani ◽  
Michael Petronis ◽  
Steve McRobbie ◽  
...  
Keyword(s):  
Machine Learning ◽  
Magnetic Susceptibility ◽  
Spectral Data ◽  
Learning Algorithm ◽  
Copper Production ◽  
Magnetic Data ◽  
Machine Learning Algorithm ◽  
Porphyry Deposit ◽  
Remanent Magnetisation ◽  
Magnetic Remanence

<p>Copper is one of the most important critical metal resources needed to achieve carbon neutrality with a projected increase in demand of >300% over the next half century from electronics and renewables.  Porphyry deposits account for most of the global copper production, but the discovery of new reserves is ever more challenging. Machine learning presents an opportunity to cross reference new and traditionally under-utilised data sets with a view to developing quantitative predictive models of hydrothermal alteration zones to guide new, ambitious exploration programs.</p><p>The aim of this study is to demonstrate a new alteration classification scheme driven by quantitative magnetic and spectral data to feed a machine learning algorithm. The benefits of an alteration model based on quantitative data rather than subjective observations by geologists, are that there is no bias in the data collected, the arising model is quantifiable and therefore easy to model and the process be fully automated. Ultimately, this approach aids more detailed exploration and mine modelling, in turn, reducing the extraction process carbon footprint and more effectively identifying new deposits.</p><p>Presented here are magnetic susceptibility and shortwave infrared (SWIR) data collected from the KazMinerals plc. owned Aktogay Cu-Mo giant porphyry deposit, eastern Kazakhstan, which has a throughput of 30Mtpa of ore. These data are cross referenced using a newly developed machine learning algorithm. Generated autonomously, our results reveal twelve statistically and geologically significant clusters that define a new alteration classification for porphyry style mineralisation. Results are entirely non-subjective, reproducible, quantitative and modellable.</p><p>Importantly, magnetic susceptibility measurements improve the algorithm’s ability to identify clusters by between 29-36%; enhancing the sophistication of the included magnetic data promises to yield substantially better statistical results. Magnetic remanence data are therefore being complied on representative samples from each of the twelve identified clusters, including hysteresis, isothermal remanent magnetisation (IRM) acquisition, FORC measurements, natural remanent magnetisation (NRM) and anhysteretic remanent magnetisation (ARM). Through collaboration with industry partners, we aim to develop an automated means of collecting these magnetic remanence data to accompany the machine learning algorithm.</p>

Porphyry Copper Discovery Beneath the Valeriano Lithocap, Chile

SEG Discovery ◽  
2016 ◽  
pp. 1-20
Author(s):  
Richard H. Sillitoe ◽  
Claudio Burgoa ◽  
David R. Hopper
Keyword(s):  
Gold Mineralization ◽  
Porphyry Copper ◽  
Northern Chile ◽  
Porphyry Copper Deposits ◽  
Copper Deposits ◽  
Alteration Zones ◽  
Copper Gold ◽  
Drill Holes

ABSTRACT Exploration for porphyry copper deposits beneath barren or poorly mineralized, advanced argillic lithocaps is becoming common­place; however, there have been few discoveries except in cases where the copper ± gold ± molybdenum mineralization has been partly exposed, typically as a result of partial lithocap erosion. At Valeriano, in the high Andes of northern Chile, completely concealed Miocene porphyry copper-gold mineralization was recently discovered beneath a lithocap. Here, the results of the staged drilling program that led to the discovery are summarized, with emphasis on the key geologic, alteration, and mineralization features that provided guidance. The final deep drill holes of the 16-hole program cut well-defined advanced argillic and sericitic alteration zones before entering chalcopyrite ± bornite–bearing, potassic-altered porphyry, with grades of 0.7 to 1.2% Cu equiv, at depths of ~1,000 to >1,800 m.

scholarly journals PEMODELAN 3-D SUSEPTIBILITAS MAGNETIK BAWAH PERMUKAAN DASAR LAUT PERAIRAN LANGSA, SELAT MALAKA-SUMATERA UTARA

2016 ◽  
Vol 7 (3) ◽  
Author(s):  
Budi Nhirwana ◽  
Subarsyah Subarsyah
Keyword(s):  
Magnetic Susceptibility ◽  
Magnetic Anomaly ◽  
Inverse Modeling ◽  
Inversion Technique ◽  
Geomagnetic Survey ◽  
Intrusive Rocks ◽  
Susceptibility Model ◽  
North Sumatra ◽  
Basin Area

Penyelidikan geomagnet laut di perairan Langsa, Selat Malaka-Sumatera Utara memberikan informasi tentang anomali magnetik akibat distribusi suseptibilitas magnetik di bawahnya. Distribusi suseptibilitas magnetik dapat diperoleh dengan menggunakan teknik pemodelan magnetik 3 dimensi (3-D). Penerapan metode ini pada data anomali magnetik residual perairan Selat Malaka manghasilkan model 3-D suseptibilitas magnetik dengan kisaran nilai -0.15 SI hingga 0.15 SI pada kedalaman 0 hingga 3000 m. Model suseptibilitas magnetik memperlihatkan adanya kelurusan struktur berarah relatif baratdaya-timurlaut yang membagi 2 sumber anomaly yang berada di bawah daerah selidikan. Diperkirakan adanya batuan diamagnetik dan batuan intrusif yang menjadi sumber anomali bawah permukaan daerah selidikan yang secara geografis terletak pada daerah cekungan busur belakang Sumatera Utara. Kata kunci : anomali magnetik, suseptibilitas magnetik, model inversi, Selat Malaka. Marine geomagnetic survey in Langsa Waters, Malaka Strait-North Sumatra provides information on the magnetic anomaly caused by magnetic susceptibility distribution underneath. Magnetic susceptibility model can be derived using 3-D geomagnetic inversion technique. The application of this method for residual magnetic anomaly data obtained from North Sumatra waters resulting 3-D of magnetic susceptibility model ranging from -0.15 – 0.15 SI at depth between 0 - 3000 m. Magnetic susceptibility model shows the present of structure lineation directing relatively southwest-northeast dividing two anomaly sources beneath investigated area. It is suggested that there are diamagnetic substance and intrusive rocks as anomaly source beneath the surveyed area where geographically located at fore arc basin area of North Sumatra. Keywords: magnetic anomaly, magnetic susceptibility, inverse modeling, Malaka Strait

scholarly journals MAGNETIC SUSCEPTIBILITY AND GAMMA-RAY SPECTROMETRY ON DRILL CORE: LITHOTYPE CHARACTERIZATION AND 3D ORE MODELING OF THE MORRO DO PADRE NIOBIUM DEPOSIT, GOIÁS, BRAZIL

2015 ◽  
Vol 33 (2) ◽  
Author(s):  
Marta Henriques Jácomo ◽  
Tereza Cristina Junqueira Brod ◽  
Augusto Cesar Bittencourt Pires ◽  
José Affonso Brod ◽  
Matheus Palmieri ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Late Cretaceous ◽  
Gamma Ray ◽  
Gamma Ray Spectrometry ◽  
Drill Core ◽  
Carbonatite Complex ◽  
Central Brazil ◽  
Rock Types ◽  
Drill Holes ◽  
Fresh Rock

ABSTRACT. The Morro do Padre niobium Deposit, in the Late-Cretaceous Catal˜ao 2 alkaline-carbonatite complex, central Brazil, consists of stockworks of nelsonite and carbonatite dykes intruded into Precambrian phyllites, quartzites, and amphibolites. A gamma-ray spectrometry and magnetic susceptibility petrophysical survey was conducted on the cores of 73 drill holes in fresh-rock, producing a total of 1295 geophysical samples. Nelsonite, the host rock of the niobium mineralization in the Morro do Padre Deposit, has a characteristic geophysical signature, with higher gamma-ray spectrometry counting rates and magnetic susceptibility values, compared to other rock types. The studied nelsonites may be divided into N1 and N2 types. N2 nelsonite is richer in K, U and Th than N1. Carbonatites are divided into magnetic (C1) and nonmagnetic (C2) varieties. The nonmagnetic carbonatites can be subdivided into C2a and C2b. The C2a carbonatite is richer in K, U and Th than C2b, which is consistent with the presence of apatite and/or monazite in the former. The geophysical 3Dmodeling has shown that the main mineralized body is elongated in the E-W direction. It is about 100 m wide and 300 m long with a maximum depth of approximately 850 m reached by drilling.Keywords: 3D ore modeling, niobium ore, applied geophysics, alkaline rocks, nelsonite. RESUMO. O depósito de nióbio do Morro do Padre no complexo carbonatítico alcalino de Catalão 2 do Cretáceo Superior, região central do Brasil, consiste em stockworks de nelsonito e diques de carbonatito intrudidos em filitos pré-cambrianos, quartzitos e anfibolitos. A pesquisa petrofísica de gamaespectrometria e de susceptibilidade magnética foi realizada em testemunhos de 73 furos de sondagem em rocha fresca, produzindo um total de 1.295 amostras. Nelsonito, a rocha hospedeira da mineralização de nióbio no depósito Morro do Padre, tem uma assinatura geofisica característica, com maiores taxas de radiação gamaespectrométrica e maiores valores de susceptibilidade magnética em comparação com outros tipos de rochas. Os nelsonitos estudados podem ser divididos em N1 e N2. O nelsonito N2 é mais rico em K, U e Th do que o N1. Carbonatitos são divididos em magnéticos (C1) e não magnéticos (C2). Os carbonatitos não magnéticos podem ser subdivididos em C2a e C2b. O carbonatito C2a é mais rico em K, U e Th do que o C2b, o que é consistente com a presença de apatita e/ou monazita na composição minerológica. O modelamento 3D revela um corpo principal de nelsonito mineralizado, alongado segundo a direção E-W. Este é cerca de 100 m de largura e 300 m de comprimento, com uma profundidade máxima de 850 m.Palavras-chave: modelamento 3D de minério, minério de nióbio, geofísica aplicada, rochas alcalinas, nelsonito.

scholarly journals ANISOTROPY OF MAGNETIC SUSCEPTIBILITY (AMS) IN VOLCANIC FORMATIONS: THEORY AND PRELIMINARY RESULTS FROM RECENT VOLCANICS OF BROADER AEGEAN.

2004 ◽  
Vol 36 (3) ◽  
pp. 1308 ◽  
Author(s):  
I. Zananiri ◽  
D. Kondopoulou
Keyword(s):  
Magnetic Susceptibility ◽  
Flow Direction ◽  
Source Region ◽  
Physical Property ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Magnetic Fabric ◽  
Local Flow ◽  
Magma Flow ◽  
Preliminary Results ◽  
Scalar Properties

The anisotropy of magnetic susceptibility (AMS) is a physical property of rocks widely used in petrofabric studies and other applications. It is based on the measurement of low-field magnetic susceptibility in different directions along a sample. From this process several scalar properties arise, defining the magnitude and symmetry of the AMS ellipsoid, along with the magnetic foliation, namely the magnetic fabric. Imaging the sense of magma flow in dykes is an important task for volcanology; the magnetic fabric provides a fast and accurate way to infer this flow direction. Moreover, the AMS technique can be used in order to distinguish sills and dykes, a task that is almost impossible by using only field observations. Finally in the case of lava flows, the method can be applied to define the local flow conditions and to indicate the position of the "paleo" source region. However, this technique is quite new in Greece. Some preliminary results from volcanic formations of continental Greece and Southern Aegean are presented (Aegina, Almopia, Elatia, Gavra, Kos, Patmos, Samos, Samothraki and Santorini).

Spectral-element method with arbitrary hexahedron meshes for time-domain 3D airborne electromagnetic forward modeling

Geophysics ◽  
2019 ◽  
Vol 84 (1) ◽  
pp. E37-E46 ◽  
Author(s):  
Xin Huang ◽  
Changchun Yin ◽  
Colin G. Farquharson ◽  
Xiaoyue Cao ◽  
Bo Zhang ◽  
...  
Keyword(s):  
Time Domain ◽  
Forward Modeling ◽  
Spectral Element ◽  
Earth Model ◽  
System Of Equations ◽  
Primary Field ◽  
Secondary Field ◽  
Efficient Treatment ◽  
Mixed Order ◽  
Airborne Electromagnetic

Mainstream numerical methods for 3D time-domain airborne electromagnetic (AEM) modeling, such as the finite-difference (FDTD) or finite-element (FETD) methods, are quite mature. However, these methods have limitations in terms of their ability to handle complex geologic structures and their dependence on quality meshing of the earth model. We have developed a time-domain spectral-element (SETD) method based on the mixed-order spectral-element (SE) approach for space discretization and the backward Euler (BE) approach for time discretization. The mixed-order SE approach can contribute an accurate result by increasing the order of polynomials and suppress spurious solutions. The BE method is an unconditionally stable technique without limitations on time steps. To deal with the rapid variation of the fields close to the AEM transmitting loop, we separate a secondary field from the primary field and simulate the secondary field only, for which the primary field is calculated in advance. To obtain a block diagonal mass matrix and hence minimize the number of nonzero elements in the system of equations to be solved, we apply Gauss-Lobatto-Legendre integral techniques of reduced order. A direct solver is then adopted for the system of equations, which allows for efficient treatment of the multiple AEM sources. To check the accuracy of our SETD algorithm, we compare our results with the semianalytical solution for a layered earth model. Then, we analyze the modeling accuracy and efficiency for different 3D models using deformed physical meshes and compare them against results from 3D FETD codes, to further show the flexibility of SETD for AEM forward modeling.

Automated interpretation of airborne electromagnetic data

Geophysics ◽  
1984 ◽  
Vol 49 (8) ◽  
pp. 1301-1312 ◽  
Author(s):  
G. T. DeMoully ◽  
A. Becker
Keyword(s):  
Data Interpretation ◽  
Earth Model ◽  
Computer Algorithms ◽  
Conductive Layer ◽  
Electromagnetic Data ◽  
Airborne Electromagnetic ◽  
Survey Results ◽  
Airborne Electromagnetic Data ◽  
Airborne Em ◽  
Interpretation Method

Recent improvements in equipment quality make it possible to increase the usefulness of airborne electromagnetic (EM) systems in areas of moderate electrical conductivity for the purpose of constructing simple electrical property maps which can be related to surficial geology. This application of airborne electromagnetics may be demonstrated and evaluated using Barringer/Questor Mark VI Input® survey results in places where independent verifications of the airborne data interpretation are available. For this purpose we have developed a set of computer algorithms which read digitally recorded Input data and interpret them automatically in terms of a simple electrical section that is defined by a single conductive layer whose thickness, conductivity, and subsurface depth are determined from the data. Because this technique is formally based on a one‐dimensional, three‐layer, three‐parameter, horizontally stratified earth model, it is only applicable in regions where the surficial formations are mildly dipping and the conductive layer is covered by, and rests on, highly resistive materials. The interpretation method is illustrated by three field examples. At the first field survey site, in Alberta, Canada, airborne EM survey data are used to map the depth of the interface between coarse and clayey sands. Data from a second survey site, this time in the Western USA, are interpreted to yield the section of a subsurface valley filled with conductive clay. The final example, taken from British Columbia, Canada, involves the mapping of all the three parameters for a weathered volcanic unit.

The Rock Physical Property Database of British Columbia, and the distinct petrophysical signature of the Chilcotin basalts,

2014 ◽  
Vol 51 (4) ◽  
pp. 327-338 ◽  
Author(s):  
Randolph J. Enkin
Keyword(s):  
British Columbia ◽  
Magnetic Susceptibility ◽  
Physical Properties ◽  
Mineral Exploration ◽  
Physical Property ◽  
Bimodal Distribution ◽  
Magnetic Survey ◽  
Survey Analysis ◽  
Magnetic Remanence ◽  
Geophysical Surveys

Rock physical properties provide the link between geophysical surveys and their geological interpretation. The British Columbia rock physical properties database, compiled by the Geological Survey of Canada, now comprises 3876 values of density, 930 values of electric resistivity, 12 356 values of magnetic susceptibility, and 2576 values of magnetic remanence and Koenigsberger ratio. The measurements are linked to sample locations, lithologies, and geological formation or unit. Maps, histograms, and biplots are used to demonstrate useful links between lithology and physical properties, and serve as a background for future rock physical properties studies. As expected, density and resistivity are controlled mostly by porosity and mineralogy. Magnetic susceptibility has a bimodal distribution (maxima at 4 × 10−4 and 2 × 10−2 SI) controlled by magnetite concentration. Magnetic remanence is shown to be more important than usually considered in magnetic survey analysis, with Koenigsberger ratios greater than unity in 42% of the samples. A case study of the Chilcotin Group basalts is highlighted, as they form a significant barrier to mineral exploration in central British Columbia. These rocks are magnetically distinct from other basalts in British Columbia, distinguished by magnetic susceptibilities having a range of values concentrated around 3 × 10−3 SI and falling in the valley between the two susceptibility modes. These basalts are also characterized by very high Koenigsberger ratios (96% above unity), probably caused by a preponderance of fine-grained single-domain magnetite. The database provides a wealth of petrophysical properties that can help constrain analysis of several types of geophysical surveys and, in particular, modelling of anomalies in the quest to determine the three-dimensional distribution of rock units.

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