Progressive hydrothermal alteration associated with gold mineralization of the Zone 1 intrusion of the Callahan property, Val-d'Or region, Quebec

1989 ◽  
Vol 26 (12) ◽  
pp. 2495-2506 ◽  
Author(s):  
Cecilia L. Jenkins ◽  
Pierre Trudel ◽  
Guy Perrault
Keyword(s):  
Hydrothermal Alteration ◽  
Gold Mineralization ◽  
Drill Core ◽  
Average Composition ◽  
Free Gold ◽  
Gold Enrichment ◽  
White Colour ◽  
Grey Colour ◽  
Ore Grade ◽  
Felsic Rocks

The Zone 1 intrusion of the Callahan property, Val-d'Or, Quebec, is a relatively small (0.045 km2), pretectonic to syntectonic trondhjemitic mass that has been altered to varying degrees by progressive hydrothermal alteration. The entire intrusion is gold enriched, and the degree of mineralization is proportional to the degree of alteration. Examination of drill core reveals that visible colour variations are related to mineralogic and chemical alteration. Three degrees of alteration are identified: least, medium, and most-altered. The least-altered facies has a green–grey colour, whereas the medium-altered facies has a pale grey colour and the most-altered facies has a cream–white colour. As the intensity of alteration increases, the amount of albite, carbonate, and pyrite increases and the amount of phengite decreases. These progressive, mineralogic changes are correlated chemically to increases in Na2O, CO2, and S and to a decrease in K2O. The median gold values for least-, medium-, and most-altered trondhjemite are 42, 148, and 158 ppb, respectively, and the average gold values (excluding highly anomalous values) are 85, 172, and 188 ppb, respectively, indicating that gold enrichment is already advanced at the medium intensity of alteration. Despite its weak enrichment, tungsten is the most anomalous trace element of the typically gold-associated elements in lode deposits and is, therefore, of special interest. Gold, found principally in the medium- and most-altered facies, is most commonly observed as free grains in the gangue. It may also be associated with pyrite and, to a much lesser extent, with tellurides. The majority of the free gold grains have an estimated diameter between 20 and 60 μm, and their average composition is 95 wt.% Au and 5 wt.% Ag. This study and comparisons of the Zone 1 trondhjemitic intrusion with other gold-enriched, felsic intrusions in the Abitibi greenstone belt suggest that elevated sodium (i.e., albitization) and anomalous gold values, relative to barren felsic rocks, should be used to target ore-grade zones within pretectonic to syntectonic felsic intrusions.

Hydrothermal Sr contamination of the Dippin sill, Isle of Arran, Western Scotland

1984 ◽  
Vol 48 (348) ◽  
pp. 311-322 ◽  
Author(s):  
A. P. Dickin ◽  
C. M. B. Henderson ◽  
F. G. F. Gibb
Keyword(s):  
Stable Isotope ◽  
Hydrothermal Alteration ◽  
Closed System ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Drill Core ◽  
Sr Isotope ◽  
Core Section ◽  
High Silica ◽  
Isotope Measurements

Abstract The Dippin sill, which is emplaced into the Triassic sediments of SE Arran, is an alkaline basic sheet which displays pronounced hydrothermal alteration. The 40-m-thick sill has suffered pervasive contamination with radiogenic Sr, introduced from the Triassic sediments by hydrothermal fluids. Stable isotope measurements suggest that fluids were of meteoric origin, but were restricted to a small closed-system circulation. Initial 87Sr/86Sr ratios in the sill were raised from an original value of 0.7032 to a maximum of 0.7091, contamination being especially pronounced near the contacts at Dippin Head itself (localities 12 and 14) and in a drill core section through the sill above Dippin. Hydrothermal Sr was incorporated into an early-formed high-CaO, high-Sr analcime, which replaced unstable high-silica nepheline in interstitial patches. However, this high-CaO analcime, along with plagioclase, was later replaced by a low-CaO, low-Sr analcime, allowing Sr leaching from the margins of the sill. Hydrothermal fluids are thought to have migrated up to 1 km laterally, up the dip of the sill, mainly via tension joints forming in the cooling intrusion. Pooling of hot fluids at the upper end of the sill probably raised water/rock ratios in this region and allowed greater Sr contamination during mineralogical alteration. The undersaturated mineralogy of the sill accounts for its pervasive hydrothermal Sr contamination, which contrasts markedly with the relatively undisturbed Sr isotope compositions of Hebridean granites involved in hydrothermal systems.

scholarly journals A Remote Sensing-Based Application of Bayesian Networks for Epithermal Gold Potential Mapping in Ahar-Arasbaran Area, NW Iran

2019 ◽  
Vol 12 (1) ◽  
pp. 105 ◽  
Author(s):  
Seyed Mohammad Bolouki ◽  
Hamid Reza Ramazi ◽  
Abbas Maghsoudi ◽  
Amin Beiranvand Pour ◽  
Ghahraman Sohrabi
Keyword(s):  
Remote Sensing ◽  
Bayesian Network ◽  
Hydrothermal Alteration ◽  
Gold Mineralization ◽  
Epithermal Gold ◽  
Alteration Zones ◽  
Mineral Potential ◽  
Potential Map ◽  
Bayesian Network Classifier ◽  
Hydrothermal Alteration Zones

Mapping hydrothermal alteration minerals using multispectral remote sensing satellite imagery provides vital information for the exploration of porphyry and epithermal ore mineralizations. The Ahar-Arasbaran region, NW Iran, contains a variety of porphyry, skarn and epithermal ore deposits. Gold mineralization occurs in the form of epithermal veins and veinlets, which is associated with hydrothermal alteration zones. Thus, the identification of hydrothermal alteration zones is one of the key indicators for targeting new prospective zones of epithermal gold mineralization in the Ahar-Arasbaran region. In this study, Landsat Enhanced Thematic Mapper+ (Landsat-7 ETM+), Landsat-8 and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) multispectral remote sensing datasets were processed to detect hydrothermal alteration zones associated with epithermal gold mineralization in the Ahar-Arasbaran region. Band ratio techniques and principal component analysis (PCA) were applied on Landsat-7 ETM+ and Landsat-8 data to map hydrothermal alteration zones. Advanced argillic, argillic-phyllic, propylitic and hydrous silica alteration zones were detected and discriminated by implementing band ratio, relative absorption band depth (RBD) and selective PCA to ASTER data. Subsequently, the Bayesian network classifier was used to synthesize the thematic layers of hydrothermal alteration zones. A mineral potential map was generated by the Bayesian network classifier, which shows several new prospective zones of epithermal gold mineralization in the Ahar-Arasbaran region. Besides, comprehensive field surveying and laboratory analysis were conducted to verify the remote sensing results and mineral potential map produced by the Bayesian network classifier. A good rate of agreement with field and laboratory data is achieved for remote sensing results and consequential mineral potential map. It is recommended that the Bayesian network classifier can be broadly used as a valuable model for fusing multi-sensor remote sensing results to generate mineral potential map for reconnaissance stages of epithermal gold exploration in the Ahar-Arasbaran region and other analogous metallogenic provinces around the world.

Research in exploration geoscience: The AMIRA model

1989 ◽  
Vol 20 (2) ◽  
pp. 5
Author(s):  
J.R. May ◽  
J.D. Bailey ◽  
J. Cucuzza
Keyword(s):  
Case Studies ◽  
Gold Mineralization ◽  
Structural Information ◽  
Rock Magnetism ◽  
Gold Deposits ◽  
Drill Core ◽  
Specific Research ◽  
James Cook ◽  
Research Themes ◽  
Csiro Division

The paper summarises the exploration related R&D that has been managed by AMIRA/APIRA and gives details of the complex, market oriented process used to develop new projects.The process is illustrated by three case studies taken from the more than 70 exploration projects completed.The Gold Deposits of North Queensland Project conducted by James Cook University studied the various styles of gold mineralization. The Rock Magnetism project undertaken at CSIRO Division of Exploration Geoscience allowed both general and specific research themes to be undertaken in parallel with confidential proprietary investigations on sponsors' drill core. The Palaeogeographic Mapping project undertaken at the BMR Division of Continental Geology provided sponsors with palaeogeographic maps including interpretation and structural information of 70 time slices.Some of the benefits of the AMIRA/APIRA approach are discussed as well as some of the difficulties which arise in ensuring companies obtain appropriate benefits from their sponsorship.

scholarly journals Mineralogical and Geochemical Control of Altered Andesitic Tuff upon Debris Slide Occurences at Pelangan Area, Southern Mountain of Lombok Island, Indonesia

2016 ◽  
Vol 1 (1) ◽  
pp. 19 ◽  
Author(s):  
Dwi Winarti ◽  
Dwikorita Karnawati ◽  
Hary Christady Hardiyatmo ◽  
Srijono Srijono
Keyword(s):  
Clay Minerals ◽  
Clay Mineral ◽  
Hydrothermal Alteration ◽  
Gold Mineralization ◽  
Slope Instability ◽  
Landslide Area ◽  
Debris Slide ◽  
Argillic Alteration ◽  
Wet Condition ◽  
Lombok Island

Debris slides were recently found in the Pelangan area at Southern Mountain of Lombok Island, Indonesia. Pelangan is well known as the gold mineralization and hydrothermal alteration area. This study is aimed to identify the mineralogy and geochemistry of altered andesitic tuff that controlled slope instability and induced debris slides. For this purpose, it is necessary to prepare the field observation and laboratory analyses. Landslide inventory reveals that the Pelangan debris slides mostly occur in altered andesitic tuff. Based on the outcrop observations in the field, andesitic tuff found around the Pelangan debris slides have been altered in general. The strong intensity of alteration developed by hydrothermal alteration in this study area produces large amount of clay minerals especially montmorillonite, kaolinite, and illite. The abundance of those clay minerals reflect the intermediate argillic alteration. Montmorillonite is a type of clay mineral that easily swells at wet condition and easily shrinkages at dry condition. Swelling of clay mineral destroys intersheet and interlayer bonds, and reduces shear strength. The presence of clay minerals in the altered andesitic tuff of intermediate argillic zone can be considered as one of the factors that induced to the Pelangan debris slides. Further studies on geotechnical and slope stability analysis of the landslide area are crucial to be done for better understanding of the characteristics of the altered rocks inducing hazardous landslides.

Hydrothermal Alteration Mineralogy and Geochemistry of the Archean World-Class Canadian Malartic Disseminated-Stockwork Gold Deposit, Southern Abitibi Greenstone Belt, Quebec, Canada

2019 ◽  
Vol 114 (6) ◽  
pp. 1057-1094 ◽  
Author(s):  
Stéphane De Souza ◽  
Benoît Dubé ◽  
Patrick Mercier-Langevin ◽  
Vicki McNicoll ◽  
Céline Dupuis ◽  
...  
Keyword(s):  
Gold Deposit ◽  
Fault Zone ◽  
Hydrothermal Alteration ◽  
Greenstone Belt ◽  
Gold Mineralization ◽  
Amphibolite Facies ◽  
Alteration Zone ◽  
Gold Deposition ◽  
Abitibi Greenstone Belt ◽  
World Class

Abstract The Canadian Malartic stockwork-disseminated gold deposit is an Archean world-class deposit located in the southern Abitibi greenstone belt. It contains over 332.8 tonnes (t; 10.7 Moz) of Au at a grade of 0.97 ppm, in addition to 160 t (5.14 Moz) of past production (1935–1981). Although the deposit is partly situated within the Larder Lake-Cadillac fault zone, most of the ore occurs up to ~1.5 km to the south of the fault zone. The main hosts of the mineralized zones are greenschist facies turbiditic graywacke and mudstone of the Pontiac Group (~2685–2682 Ma) and predominantly subalkaline ~2678 Ma porphyritic quartz monzodiorite and granodiorite. These intrusions were emplaced during an episode of clastic sedimentation and alkaline to subalkaline magmatism known as the Timiskaming assemblage (<2680–2670 Ma in the southern Abitibi). The orebodies define two main mineralized trends, which are oriented subparallel to the NW-striking S2 cleavage and the E-striking, S-dipping Sladen fault zone. This syn- to post-D2 ductile-brittle to brittle Sladen fault zone is mineralized for more than 3 km along strike. The ore mainly consists of disseminated pyrite in stockworks and replacement zones, with subordinate auriferous quartz veins and breccia. Gold is associated with pyrite and traces of tellurides defining an Au-Te-W ± Ag-Bi-Mo-Pb signature. The orebodies are zoned outward, and most of the higher-grade (>1 ppm Au) ore was deposited as a result of iron sulfidation from silicates and oxides and Na-K metasomatism in carbonatized rocks. The alteration footprint comprises a proximal alteration envelope (K- or Na-feldspar-dolomite-calcite-pyrite ± phlogopite). This proximal alteration zone transitions to an outer shell of altered rocks (biotite-calcite-phengitic white mica), which hosts sub-ppm gold grades and reflects decreasing carbonatization, sulfidation, and aNa+/aH+ or aK+/aH+ of the ore fluid. Gold mineralization, with an inferred age of ~2664 Ma (Re-Os molybdenite), was contemporaneous with syn- to late-D2 peak metamorphism in the Pontiac Group; it postdates sedimentation of the Timiskaming assemblage along the Larder Lake-Cadillac fault zone (~2680–2669 Ma) and crystallization of the quartz monzodiorite. These chronological relationships agree with a model of CO2-rich auriferous fluid generation in amphibolite facies rocks of the Pontiac Group and gold deposition in syn- to late-D2 structures in the upper greenschist to amphibolite facies. The variable geometry, rheology, and composition of the various intrusive and sedimentary rocks have provided strain heterogeneities and chemical gradients for the formation of structural and chemical traps that host the gold. The Canadian Malartic deposit corresponds to a mesozonal stockwork-disseminated replacement-type deposit formed within an orogenic setting. The predominance of disseminated replacement ore over fault-fill and extensional quartz-carbonate vein systems suggests that the mineralized fracture networks remained relatively permeable and that fluids circulated at a near-constant hydraulic gradient during the main phase of auriferous hydrothermal alteration.

scholarly journals Landsat-8, Advanced Spaceborne Thermal Emission and Reflection Radiometer, and WorldView-3 Multispectral Satellite Imagery for Prospecting Copper-Gold Mineralization in the Northeastern Inglefield Mobile Belt (IMB), Northwest Greenland

2019 ◽  
Vol 11 (20) ◽  
pp. 2430 ◽  
Author(s):  
Pour ◽  
Park ◽  
Park ◽  
Hong ◽  
Muslim ◽  
...  
Keyword(s):  
Hydrothermal Alteration ◽  
Satellite Imagery ◽  
Thermal Emission ◽  
Gold Mineralization ◽  
High Arctic ◽  
Mobile Belt ◽  
Landsat 8 ◽  
Free Region ◽  
Copper Gold ◽  
Ace Algorithm

Several regions in the High Arctic still lingered poorly explored for a variety of mineralization types because of harsh climate environments and remoteness. Inglefield Land is an ice-free region in northwest Greenland that contains copper-gold mineralization associated with hydrothermal alteration mineral assemblages. In this study, Landsat-8, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and WorldView-3 multispectral remote sensing data were used for hydrothermal alteration mapping and mineral prospecting in the Inglefield Land at regional, local, and district scales. Directed principal components analysis (DPCA) technique was applied to map iron oxide/hydroxide, Al/Fe-OH, Mg-Fe-OH minerals, silicification (Si-OH), and SiO2 mineral groups using specialized band ratios of the multispectral datasets. For extracting reference spectra directly from the Landsat-8, ASTER, and WorldView-3 (WV-3) images to generate fraction images of end-member minerals, the automated spectral hourglass (ASH) approach was implemented. Linear spectral unmixing (LSU) algorithm was thereafter used to produce a mineral map of fractional images. Furthermore, adaptive coherence estimator (ACE) algorithm was applied to visible and near-infrared and shortwave infrared (VINR + SWIR) bands of ASTER using laboratory reflectance spectra extracted from the USGS spectral library for verifying the presence of mineral spectral signatures. Results indicate that the boundaries between the Franklinian sedimentary successions and the Etah metamorphic and meta-igneous complex, the orthogneiss in the northeastern part of the Cu-Au mineralization belt adjacent to Dallas Bugt, and the southern part of the Cu-Au mineralization belt nearby Marshall Bugt show high content of iron oxides/hydroxides and Si-OH/SiO2 mineral groups, which warrant high potential for Cu-Au prospecting. A high spatial distribution of hematite/jarosite, chalcedony/opal, and chlorite/epidote/biotite were identified with the documented Cu-Au occurrences in central and southwestern sectors of the Cu-Au mineralization belt. The calculation of confusion matrix and Kappa Coefficient proved appropriate overall accuracy and good rate of agreement for alteration mineral mapping. This investigation accomplished the application of multispectral/multi-sensor satellite imagery as a valuable and economical tool for reconnaissance stages of systematic mineral exploration projects in remote and inaccessible metallogenic provinces around the world, particularly in the High Arctic regions.

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