Volcanogenic Massive Sulfide Ore Research Articles

Analytic continuation: A tool for aeromagnetic data interpretation

Extending potential-field data to vertical complex-plane slices provides opportunities, unique to analytic functions, for subsurface imaging. We begin with an existing numerical method for differentiation by integration using Cauchy's integral formula. An example from data over northern Ontario, Canada, illustrates better conditioning compared to derivatives computed using finite differences. Next, these quantities are used for analytic continuation using rational complex-series expansion (Padé approximation). This method provides stable downward continuation to distances that are significantly greater than are achievable by Taylor series and spectral methods. A synthetic test confirms that the rational approximant faithfully reproduces the magnetic response of a thin sheet. A sign reversal of the total field, coincident with the origin of the sheet, features prominently on this example. We also provide synthetic results for sheets with finite depth extent, point sources, thin slabs, and contacts. These also exhibit polarity flips near the source location. Further, these provide a template for interpreting the source geometry using the shape of the approximating function. Additional synthetic tests illustrate an automatic method for locating closely spaced random assemblages of isolated poles. We apply our methods to a deposit-scale heliborne survey over a recently discovered volcanogenic massive sulphide ore deposit in a Canadian greenstone belt. The analytically continued profile over the deposit suggests the presence of a subvertical thin sheet of unknown depth extent. This interpretation coincides with a sulphide ore body that has been previously delimited by several drill holes. Some known prospects near this deposit are also imaged on maps and profiles of the Padé approximant.

Porphyry and Volcanogenic Massive Sulphide Ore Deposit in Canada

Canada is one of the leading countries in ore production that involves variety types of ore deposits. Among the significant ore deposits found in the country, porphyry and volcanogenic massive sulphide (VMS) deposits stand out as major contributors to the production of copper, gold, molybdenite, zinc, lead and many other essential minerals. Porphyry deposits are the major copper production in the country that are predominantly located in British Columbia, where subduction processes occur. While the overall mineral grade of porphyry deposits is relatively low, their immense tonnage makes them the largest reservoirs of copper in Canada. Notable porphyry mines such as Copper Mountain and Highland Valley Copper produce millions of tons of ore annually. On the other hand, VMS deposits, associated with volcanic activities, play a significant role in the production of zinc, copper, lead, gold, and silver. These deposits are distributed across Canada, with concentrations found in the Ontario and British Colombia. VMS deposits make up nearly a quarter of the country's copper production with significant mine sites including Kidd Mine and Windy Craggy. The future of the mining industry in Canada and the whole world should be focusing on sustainability. Sustainable mining recognizes the interconnectedness of environmental, social, and economic aspects and seeks to balance them for the benefit of present and future generations.

Deciphering the Evolution of Adjacent Volcanogenic Massive Sulfide (VMS) Systems Based on Radiogenic and Stable Isotopes, the Case of Ermioni, Argolis Peninsula, Ne Peloponnese, Greece

The study follows previous work on Ermioni VMS and addresses in detail the formation and evolution of two adjacent VMS systems, Karakasi and Roro. It is based on a stable and radiogenic isotopic composition of sulfides and ganguefrom stringer (Karakasi) and massive (Roro) VMS ore. The isotopic geochemistry of Pb and noble gases (Ar-He) of pyrite from both sites indicates the development of a deep and evolved heat and possibly metal source attributed to subduction of radiogenic material (Pindos oceanic crust). The differences in the stable (Fe, S) and radiogenic (Sr, Ar) isotopic compositions between the two sites depict variation in the geologic environment of VMS formation, and in particular the effect of seawater. The higher δ57Fe and δ34S values of Roro massive pyrite are attributed to direct interaction of hot, ascending metal-bearing hydrothermal fluids with cold seawater. Karakasi stringer oreis characterized by higher 87Sr/86Sr ratios and radiogenic Ar values (as 40Ar/36Ar), indicating interaction of ore-bearing, hydrothermal fluids with crustal material (hanging-wall turbidites). During the approximate 0.5 Ma period separating the two systems, the hydrothermal system migrated from east to west, and at the same time evolved from free discharge on the seafloor (Roro—easterly), resembling contemporary seafloor style and mound-shaped massive sulfides, to a sediment-confined, subseafloor system (Karakasi—westerly).

Origin of the Neoarchean VMS-BIF Metallogenic Association in the Qingyuan Greenstone Belt, North China Craton: Constraints from Geology, Geochemistry, and Iron and Multiple Sulfur (δ33S, δ34S, and δ36S) Isotopes

Abstract The association of volcanogenic massive sulfide (VMS) deposits and Algoma-type banded iron formations (BIFs) in many Precambrian terranes indicates a link between submarine hydrothermal processes, seawater chemistry, and chemical sedimentation. The Neoarchean (~2.55 Ga) Qingyuan greenstone belt VMS-BIF metallogenic association, located on the north margin of the North China craton, is a typical example of such an association. The stratigraphy of the Qingyuan greenstone belt includes three units (from the oldest to youngest): (1) the Shipengzi Formation, composed of tholeiitic-transitional arc basalts with negative Nb anomalies, interlayered normal mid-ocean ridge basalts (N-MORBs) and FI-type dacites, and BIFs; (2) the Hongtoushan Formation, consisting of polycyclic bimodal suites of N-MORB-type basalts and FII-type dacites, as well as VMS mineralization and minor BIFs; and (3) the Nantianmen Formation, composed of schist, quartzite, and marble with minor basalts and BIFs. Positive Fe isotope compositions (δ56Fe of 0.48–0.69‰) for magnetite in the silicate BIF of the Shipengzi Formation indicate partial oxidation of aqueous Fe(II). Using a dispersion-reaction model, the relatively high δ56Fe values (0.72–1.04‰) estimated for primary ferric (oxyhydr)oxides in this BIF constrain local dissolved O2 contents of the Neoarchean surface ocean to 10–4 to 10–3 μmol/L. By comparison, negative δ56Fe values for magnetite (–0.83 to –0.65‰) in silicate BIFs of the Hongtoushan Formation and the Nantianmen Formation suggest deposition from a residual water column that was depleted in 56Fe. Following the formation of the bulk of the VMS deposits in the Hongtoushan Formation, a significant change to positive magnetite δ56Fe values (0.79–1.04‰) occurs in the youngest sulfide-bearing BIF in the Nantianmen Formation. This implies that the VMS-related hydrothermal vents injected a large mass of unfractionated ferrous iron into the ocean. Negative Δ33S anomalies in sedimentary pyrite of bedded VMS ores (avg of –0.08 ± 0.007‰, n = 6) and sulfide-bearing BIFs (avg of –0.06 ± 0.007‰, n = 3) of the Qingyuan greenstone belt, along with mass-independent fractionations (with an average Δ36S/Δ33S ratio of –1.1 ± 0.3), are best explained by incorporation of seawater sulfate of atmospheric photochemical origin during their formation. The systematic differences in whole-rock geochemistry and Δ33S values for different types of VMS ores imply variable seawater sulfate contributions to their mineralization. Our results are consistent with global anoxic conditions during the Neoarchean to Paleoproterozoic transition (i.e., at 2.5 Ga), and confirm that formation of the VMS-BIF metallogenic association took place in dominantly anoxic, ferruginous basins at different depths, with the VMS-related hydrothermal system contributing significant Fe to the deposition of BIFs.

Multispectral discrimination of spectrally similar hydrothermal minerals in mafic crust: A 5000 km2 ASTER alteration map of the Oman–UAE ophiolite

Multispectral remote sensing of hydrothermal alteration in volcanogenic massive sulfide (VMS) ore systems in mafic crust is relatively uncommon, in part due to the short-wave infrared spectral similarity of several key alteration minerals: epidote, chlorite, actinolite, and serpentine. In this study, we developed regional mosaic generation and classification workflows for Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery to discriminate these minerals over the entire crust of the Semail ophiolite (Oman–UAE). Spectral discrimination was achieved through adaptation of the ASTER (pre-)processing workflow to the specific mapping targets, available datasets, and location of this study. Necessary steps included the pre-selection of ASTER scenes without residual atmospheric water features, mosaic normalization based solely on overlapping target outcrops, correcting cross-mosaic ramp errors, and alteration map classification based on image-derived reference data. The resulting alteration map, validated through comparison with field mapping and sampling, is the most areally extensive continuous survey of hydrothermal alteration yet presented for oceanic crust, providing a renewed framework for research and mineral exploration of Earth's largest ophiolite. Our map confirms that the vast majority of the upper oceanic crust is regionally altered to a spilite type secondary mineral assemblage. Localized areas of epidosite alteration, marking focused hydrothermal flow paths, are confined to the upper oceanic crust, whereas areas of previously unrecognized but intense actinolite alteration are common in both the lower and upper oceanic crust. Our methodological developments expand the standard considerations necessary for regional geological mapping using infrared image mosaics. They further demonstrate the underappreciated capability of multispectral data for mapping spectrally similar rock types. Although the specifics of the method are necessarily optimized for the Oman–UAE ophiolite, re-optimization based on local reference data should allow similar results to be achieved in other well-exposed mafic-hosted VMS districts.

Petrophysical Facies and Inferences on Permeability at Brothers Volcano, Kermadec Arc, Using Downhole Images and Petrophysical Data

Abstract Downhole data and cores collected during International Ocean Discovery Program (IODP) Expedition 376 at Brothers volcano, Kermadec arc, provide unprecedented, in situ views of volcanic facies and fluid pathways in an actively forming volcanogenic massive sulfide (VMS) ore deposit. Brothers volcano is a submarine caldera with extensive sea-floor hydrothermal alteration. Downhole data were collected in two holes: Hole U1530A at the NW Caldera and Hole U1528D at the Upper Cone. Textural analysis of microresistivity images in Hole U1530A provides a continuous image facies record that greatly improves findings based upon sporadic and partial (18%) core recovery. Between 90 and 214 meters below sea floor (mbsf), the heterogeneous image facies with local pattern variations is consistent with the volcaniclastic facies interpreted from cores. Between 232 and 445 mbsf, a volcanic facies was not recognizable in cores because of overprinting alteration, apart from five intervals of coherent lava flows that were less altered. Based on the fairly constant petrophysical data, Vp-porosity relationship, and presence of five to six coherent image facies intervals on the microresistivity image, we propose that the apparent volcaniclastic textures observed on cores and microresistivity images beneath 232 mbsf are dominantly lava flows. The change from volcaniclastic to dominant lava flow facies occurs over a transition zone (214–232 mbsf) where all petrophysical properties gradually change. In Hole U1528D, cores and petrophysical data show a similar transition from deep coherent lava flows to shallower, largely volcaniclastic sequences at ~270 mbsf. Down to 232 mbsf in Hole U1530A and 360 mbsf in Hole U1528D, the overall first-order downward decrease in porosity is interpreted to be caused by compaction and increased alteration intensity. Volcanic facies and fractures exert a second-order local control on petrophysical properties. Beneath 232 mbsf in Hole U1530A, the prolonged hydrothermal activity is inferred to have diminished local petrophysical property variations within the proposed lava flow-dominated rock package. High downhole fluid temperatures in Hole U1528D contrast with the moderate temperatures in Hole U1530A. Permeable zones show a mix of structural (inferred fault in Hole U1530A) and lithological controls in both holes. Some low-permeability layers and/or lithological interfaces possibly focus fluids laterally in higher-permeability layers, which may act as a trap for metal-rich fluids to form stratabound massive sulfides and deposits. Matrix is likely too low in permeability to conduct fluids but provides perfect conditions for the storage of supersaline brines. In Hole U1530A, located near active vents at the sea floor, the relatively low fluid temperature and the alteration overprint of moderate temperature demonstrate the high spatial and temporal variations at Brothers volcano. The implications of the new stratigraphy and controls on permeability proposed here for Brothers volcano include a better understanding of the following: (1) submarine volcanic eruption sequences, (2) permeability in active submarine volcanoes, and (3) the formation of volcanogenic massive sulfide deposits on (and near) the sea floor.

Review of Late Cretaceous volcanogenic massive sulfide mineralization in the Eastern Pontides, NE Turkey

The production of Cu-Zn from volcanogenic massive sulfide (VMS) deposits in the eastern Pontides began in the early 1900s, with the exploitation of high-grade ores scattered across the district. The district still possesses economically important blind VMS and associated sulfide deposits. Careful descriptive documentation of the typical features of these VMS ores illustrated the geological characteristics that are important in identifying ore localities and can be used to define exploration targets. The eastern Pontide VMS deposits are examples of volcanic-hosted massive sulfide deposits that exhibit many of the characteristics typical of bimodal-felsic- type VMS mineralization. Nearly all known VMS deposits in the region are hosted by the Kızılkaya Formation, which is characterized by Late Cretaceous dacitic/rhyolitic volcanic rocks that are typically located at the top contact of the dacitic/rhyolitic pile or within the lower part of the overlying polymodal sequence containing various proportions of volcanic and sedimentary facies. Most VMS deposits are composed of a mound of high-grade massive sulfides formed above a zone of lower-grade stringer veins and disseminated mineralization. The dominant sulfide minerals in most deposits are pyrite, chalcopyrite, and sphalerite. Au also occurs in some deposits. The hydrothermal ore facies are diagnostic of subaqueous emplacement of the Pontide massive sulfide deposits that were deposited on the Cretaceous ocean floor. The immediate host lithologies associated with VMS mineralization have typically experienced intense and widespread alteration. The trace element geochemical signatures of the host rocks indicated that the Pontide VMS deposits likely formed in an extensional tectonic regime during subduction. Major lineaments and circular structures exerted fundamental controls on the locations of the VMS deposits in the eastern Pontide district. Age determinations indicated that almost all of the deposits in this region formed in a restricted time interval between ca. 91.1 and 82 Ma. The sulfur isotope compositions of the ore-forming fluids were consistent with those of fluids derived from modified seawater.

Generation of reactive oxygen species on pyrite surfaces: A likely oxidation mechanism for near-vent, hydrothermal fluid-dominated BIFs

The key to understand the origin of banded iron-formations (BIFs) formed in 3.8–2.5 Ga is to identify the oxidation mechanism of Fe2+ in anoxic oceans. In this study, we proposed a likely pyrite-induced Fe2+ oxidation mechanism for near-vent, hydrothermal fluid-dominated BIFs. A series of important environmental conditions including light intensity, wavelength and pH were considered and monitored to check their effects on the production of reactive oxygen species (ROS) in anaerobic pyrite suspensions. By quantifying the concentration of OH and H2O2, we observed a stable ROS production as induced by pyrite in both dark and light under a wide pH range. Interestingly, light significantly promoted the producing rate of ROS, which increased with the light intensity, but was poorly correlated with the light wavelength. In addition, the producing rate of ROS remarkably increased as the pH decreased from 6.0 to 3.0, suggesting the acidic conditions were more beneficial for ROS generation. The production of ROS could be attributed to the semiconducting photocatalysis of pyrite, and the sulfur-deficient defect on its surface. Based on the sulfur content of volatiles in modern submarine basalts and black smokers, we assumed that the concentration of H2S in Archean hydrothermal fluids ranged from 0.5 to 55 mmol/kg. Combined with the experimental results of H2O2 producing rates under 150 mW/cm2 irradiation at pH 3.0 and under dark at pH 6.0, the H2O2 flux of 6.9 × 105–1.1 × 109 mol/yr could be estimated in a thermal flow. This value covered the amount of H2O2 required for Fe2+ oxidation in Archean oceans to form the near-vent, hydrothermal fluid-dominated BIFs (1.7 × 106–1.3 × 107 mol/yr). The reaction kinetics revealed that the conversion of amorphous FeS into pyrite under hydrothermal conditions was very quick, while the consumption of H2O2 during the back-reaction with pyrite was quite limited. This view can explain why this type of BIFs typically occurs as intercalated layers in volcanic rocks and is associated with volcanogenic massive sulfide ore (VMS)-type deposits.

Sphalerite and Pyrite on Kuroko-Type Ore Deposit: A Case Study of Phase Ambiguity and Its Prediction Technique by Means of X-Ray Diffraction Analysis

Kuroko-type VMS (volcanogenic massive sulfide) ore deposit is a deposit that has some abundant sulfide minerals such as pyrite, chalcopyrite, galena and sphalerite. Besides them, other common sulfide minerals also occur, such as bornite, acanthite (argentite) and some of tennantite-tetrahedrite series. In some cases, we can find sphalerite and pyrite on these deposits. These cases often make the difficulty of XRD analysis. It is caused by some overlapping diffraction peaks between pyrite and sphalerite, which are difficult to be distinguished. This problem can cause miscalculation of weight fraction between them. Therefore, this study was done in order to make sure the true phase between pyrite and sphalerite of the overlapping diffraction peaks. Cubic structure analysis and precise lattice parameter calculation were used as the method in this study in order to determine the true phase of sphalerite-pyrite overlapping peaks. An XRD analysis on the case study sample shows that there are five cubic planes, i.e. (111), (200), (220), (113), and (222) on some overlap diffraction peaks. By utilizing this method, these cubic planes can be distinguished where (111) and (113) are pyrite phases while (200), (220) and (222) are sphalerite phases.Keywords: Kuroko, sphalerite, pyrite, XRD, precise lattice parameter.

From arc evolution to arc-continent collision: Late Cretaceous–middle Eocene geology of the Eastern Pontides, northeastern Turkey

AbstractThe Eastern Pontide Arc, a major fossil submarine arc of the world, was formed by northward subduction of the northern Neo-Tethys lithosphere under the Eurasian margin. The arc’s volcano-sedimentary sequence and its cover contain abundant fossils. Our new systematical paleontological and structural data suggest the Late Cretaceous arc volcanism was initiated at early-middle Turonian and continued uninterruptedly until the end of the early Maastrichtian, in the northern part of the Eastern Pontides. We measured ∼5500-m-thick arc deposits, suggesting a deposition rate of ∼220 m Ma–1 in ∼25 m.y. We have also defined four different chemical volcanic episodes: (1) an early-middle Turonian–Santonian mafic-intermediate episode, (2) a Santonian acidic episode; when the main volcanic centers were formed as huge acidic domes-calderas comprising the volcanogenic massive sulfide ores, (3) a late Santonian–late Campanian mafic-intermediate episode, and (4) a late Campanian–early Maastrichtian acidic episode. The volcaniclastic rocks were deposited in a deepwater extensional basin until the late Campanian. Between late Campanian and early Maastrichtian, intra-arc extension resulted in opening of back-arc in the north, while the southern part of the arc remained active and uplifted. The back-arc basin was most probably connected to the Eastern Black Sea Basin. In the back-arc basin, early Maastrichtian volcano-sedimentary arc sequence was transitionally overlain by pelagic sediments until late Danian suggesting continuous deep-marine conditions. However, the subsidence of the uplifted-arc-region did not occur until late Maastrichtian. We have documented a Selandian–early Thanetian (57–60 Ma) regional hiatus defining the closure age of the İzmir-Ankara-Erzincan Ocean along the Eastern Pontides. Between late Thanetian and late Lutetian synorogenic turbidites and postcollisional volcanics were deposited. The Eastern Pontide fold-and-thrust belt started to form at early Eocene (ca. 55 Ma) and thrusting continued in the post-Lutetian times.

Hydrochemistry of pit lakes in the Portuguese sector of the Iberian Pyrite Belt

The Iberian Pyrite Belt (IPB) is a world-class metallogenic province with volcanogenic massive sulphide ore deposits. Most ore exploitation occurred since pre-Roman time, creating extensive galleries, wells, waste-dumps and pit lakes. These last structures are a concern for their potential environmental impact because they accumulate large volumes of mine water affected acid mine drainage. The present work classifies the pit lakes based on the surface water hydrochemistry. Using the Ficklin diagram for classification, pit lake waters vary from acid, high-metal to high-acid, extreme-metal and exhibit similarities with other pit lakes from the Spanish sector of the IPB.

Selenium in Volcanogenic Massive Sulfide Ores

This paper describes the Se proper minerals first identified in the primary ores in Uralian volcanogenic massive sulfide (VMS) deposits. The investigation was carried out by instrumental neutron activation analysis of bulk ore samples and the mineral monofractions and also by local analysis methods: LA-ICP-MS, electron microprobe analysis, and analytical electron microscopy. СSe reaches 977 ppm in the Uralian VMS ores. A significant positive correlation is characteristic for Se with Te, S, Fe, Co, Mo, Hg, and Bi. Se is concentrated in major sulfides, mainly in pyrite (73 ppm), chalcopyrite (49 ppm), and pyrrhotite (48 ppm). Sphalerite commonly contains <10 ppm Se. The Se content is high (up to 1–3 wt %) in secondary and rare minerals of the massive sulfide ores (mainly Pb, Te, and Bi compounds): tetradymite, galena, tellurobismuthite, altaite, and wittichenite. In the ores, the Se proper minerals occur as kawazulite, clausthalite, and galena–clausthalite Pb(Se,S), and also as micron inclusions with (Ag,Cu)2(Se,S); (Ag,Pb)3(Te,Se)S; and (Ag,Pb)2(S,Se) compositions.

Integrated 3D Geological Modeling to Gain Insight in the Effects of Hydrothermal Alteration on Post-Ore Deformation Style and Strain Localization in the Flin Flon Volcanogenic Massive Sulfide Ore System

3D geological modeling of lithogeochemical and geological data provides insight into the role of the sulfide ore horizon and associated footwall hydrothermal alteration in localizing shear strain in the Flin Flon volcanogenic massive sulfide deposits, Canada, as deformation evolved from brittle-ductile to ductile regimes during collisional stages of the 1.9–1.8 Ga Trans-Hudson orogeny. 3D spatial characterization of hydrothermal alteration based on the Ishikawa index (AI) and normative corundum percentages outline sericite + chlorite-rich high strain zones, consisting of Al-enriched and Na-depleted felsic and mafic volcanic rocks in the footwall of the sulfide ore horizon. The hydrothermal vent complex, from which these sheared alteration zones originated, was stacked together with the ore horizon by W-vergent thrust faults during an early collisional deformation regime, imbricating molasse-type clastic sediments with the ore-hosting volcanic and volcaniclastic rocks of the Flin Flon arc assemblage. Chlorite-rich planar zones marked by high values of the Carbonate–chlorite–pyrite index (CCPI) are laterally more extensive and outline a later system of ductile shear zones, in which phyllosilicates, quartz and chalcopyrite in stringer zones localized shear strain and enhanced transposition of the hydrothermal vent stockwork. The contrasting deformation styles of these two thrusting events and their localization within the ore horizon and hydrothermal vent stockwork have important implications for vectoring towards undiscovered ore in this mature mining camp that are possibly also relevant to other strongly deformed VMS ore systems.

Cistus monspeliensis L. as a potential species for rehabilitation of soils with multielemental contamination under Mediterranean conditions

The Iberian Pyrite Belt (IPB; SW of the Iberian Peninsula) is one of the most important volcanogenic massive sulphide ore deposits in the world. Cistus monspeliensis L. is a native woody shrub that grows spontaneously in non-contaminated soils as well as in soils with multielemental contamination from the IPB. In this study, different ecophysiological parameters of C. monspeliensis growing in soils with different levels of metal(loid)s were evaluated to assess the potential of this species for revegetation of degraded areas. Composite samples of plants and rhizosphere soils were sampled in São Domingos and Lousal mines and in a reference area without soil contamination (Pomarão, Portugal) (Portuguese sector of IPB). Classical characterisation of the soils and quantification of their total and available metal(loid) concentrations were done. Multielemental concentration was determined in plants (shoots and roots). Ecophysiological parameters were also determined in shoots: concentrations of pigments (chlorophylls, anthocyanins and carotenoids), antioxidants (glutathione and ascorbate) and hydrogen peroxide as well as activities of several antioxidative enzymes. Although mining soils present high total concentrations of potentially hazardous elements, their available fractions were low and similar among studied areas. Soil pH as well as concentrations of extractable P, total concentrations of As, Cd and Ni and concentrations of Cu, Cr, Ni, Pb and Sb in the soil available fraction differentiate the studied areas. Only concentrations of Cd, Pb and Sb in roots and shoots were explained by the concentrations of the same elements in the soil available fraction. Although the majority of elements were translocated from roots to shoots, the shoots concentrations were below the toxic values for domestic animals and only As, Mn and Zn reached phytotoxic concentrations. Ecophysiological parameters were similar independently of the studied area. Due to its adaptability, tolerance and standard plant features, C. monspeliensis is a good choice for rehabilitation of soils with multielemental contamination under similar climatic characteristics.

THE 3D TRANSIENT ELECTROMAGNETIC FORWARD MODELING OF VOLCANOGENIC MASSIVE SULFIDE ORE DEPOSITS

AbstractThe transient electromagnetic forward modeling of volcanogenic massive sulfide (VMS) ore deposits is to calculate the eddy currents electromagnetic response of a three dimensional body in the full space of deep‐sea environment. We simulated the three dimensional transient electromagnetic response of the VMS deposits using full‐domain vector finite element method. The ore body was discretized with brick rectangular elements. The finite element equation was deduced in frequency domain by employing Galerkin procedure, and the conversion to time domain was by inverse Fourier transform. We confirmed the validity of the full‐domain vector finite element algorithm by comparing simulated results with analytical solutions of double half‐space model. The results have a good agreement with each other, which indicates that the vector finite element method is capable of solving whole space problem. In order to demonstrate the ability of the numerical method in calculating the response of VMS deposits containing complex boundary conditions, we compared vector finite element solution of a three dimensional electrical model with physical experiment results according to electromagnetic physical scale modeling rules. The comparison suggests that for the complex electromagnetic boundary of seawater, ore body and country rocks, the transient electromagnetic response of VMS deposits calculated by full‐domain vector finite element method has same features with the physical scale modeling result. The vector finite element method is simple and its results are precise with obvious and clear anomaly response.

3-D Geologic Modeling in the Flin Flon Mining District, Trans-Hudson Orogen, Canada: Evidence for Polyphase Imbrication of the Flin Flon-777-Callinan Volcanogenic Massive Sulfide Ore System

Three-dimensional geologic modeling by integrated analysis and interpretation of drill core, 2-D and 3-D seismic, mine survey, and geologic map data provides new insights into the structural setting of the 85.5 million tonne (Mt) Flin Flon-Callinan-777 volcanogenic massive sulfide (VMS) ore system hosted in the Paleoproterozoic Flin Flon belt of Manitoba and Saskatchewan, Canada. The resultant camp-scale 3-D geologic model was, in addition to the densely drill intersected VMS-hosting mine horizon, constrained by lithostratigraphic reference drill holes intersecting the footwall and hanging-wall rock successions of the ore system, which were established by relogging 52 drill holes and systematically reconciling the lithofacies classes in their log descriptions with the lithofacies units of the 1:10,000-scale Flin Flon mining district geologic map. The lateral persistence and large stratigraphic range of these drill hole markers supported seismic interpretation and allowed tracing lithostratigraphic horizons and structures in areas with low drill hole density, expanding 3-D subsurface insight from the local to the more regional structural setting of the ore system. The overall 3-D modeled geometry and topological relationships between lithostratigraphic surfaces and multiple generations of thrust faults suggest that the Flin Flon mining district is underlain by an E-dipping stack of W-vergent thrust imbricates that formed during precollisional and collisional stages of the 1.9 to 1.8 Ga Trans-Hudson orogeny. The imbricate stack was subsequently deformed by E-trending ductile thrust faults that internally imbricated the Flin Flon arc assemblage and the molasse cover rocks of the Missi Group and brought up rocks of the former over the latter in a northerly direction. The VMS-hosting Millrock Member has been stacked on at least four structural levels, enhancing the VMS potential in the footwall and hanging wall of the known ore deposits where both thrust systems intersect.

Structural Reconstruction of the Flin Flon Volcanogenic Massive Sulfide Mining District, Saskatchewan and Manitoba, Canada

The Flin Flon mining district is part of a greenstone belt, the Flin Flon-Glennie Complex, in the Paleoproterozoic Trans-Hudson orogen. Its tectonic history began prior to 1872 Ma with the development of regional folds—the faulted F1 Burley Lake syncline and F2 Hidden Lake syncline—during D1 and D2 intraoceanic accretion of the 1888 Ma Flin Flon arc to other volcanic terranes. Amalgamation of the Flin Flon to Glennie terrane, possibly during D3, produced a W-propagating thrust-fold belt and basins in which fluvial sedimentary rocks were deposited between 1847 Ma and 1842 Ma. As the fold-thrust belt migrated westward, these rocks were incorporated into a stack of E-dipping thrust sheets bounded by NNW-striking thrust faults (1920 fault) and internally folded by W-verging folds (Pipeline, Mud Lake, and Grant Lake synclines). Subsequent D4 collision of the Flin Flon-Glennie Complex with the Archean Sask microcontinent was broadly coeval with but outlasted the emplacement of 1840 Ma Phantom Lake dikes. D4 produced a second truncating fold-thrust system characterized by N-directed thrust faults (Club Lake and Railway faults) and E-trending folds (Flin Flon Creek syncline). These folds were overprinted by two regional cleavages, and the thrust faults were reactivated as oblique-slip shear zones, either late during the same collisional event (D5) or during terminal collision (D6) of the Sask craton and Flin Flon-Glennie Complex with the Superior craton at 1.83 to 1.79 Ga. The Flin Flon volcanogenic massive sulfide ore system was thrust-imbricated during D3 and D4, and ore lenses were stretched parallel to a regional, SE-plunging, stretching lineation that formed during D4 and was later modified during D5.

Geology, ore facies and sulfur isotopes geochemistry of the Nudeh Besshi-type volcanogenic massive sulfide deposit, southwest Sabzevar basin, Iran

The southwest Sabzevar basin is placed in the southwestern part of a crustal domain known as the Sabzevar zone, at the north of Central Iranian microcontinent. This basin hosts abundant mineral deposits; particularly of the Mn exhalative and Cu-Zn volcanogenic massive sulfide (VMS) types. The evolution of this basin is governed by the Neo-tethys oceanic crust subduction beneath the Central Iranian microcontinent and by the resulting continental arc (Sanandaj-Sirjan) and back-arc (Sabzevar-Naien). This evolution followed two major sequences: (I) Lower Late Cretaceous Volcano-Sedimentary Sequence (LLCVSS), which is indicated by fine-grained siliciclastic sediments, gray basic coarse-grained different pyroclastic rocks and bimodal volcanism. During this stage, tuff-hosted stratiform, exhalative Mn deposits (Nudeh, Benesbourd, Ferizy and Goft), oxide Cu deposits (Garab and Ferizy) and Cu-Zn VMS (Nudeh, Chun and Lala) deposits formed. (II) Upper Late Cretaceous Sedimentary Dominated Sequence (ULCSS), including pelagic limestone, marly tuff, silty limestone and marl with minor andesitic tuff rocks. The economically most important Mn (Zakeri and Cheshmeh-sefid) deposits of Sabzevar zone occur within the marly tuff of this sequence. The Nudeh Cu–Zn volcanogenic massive sulfide (VMS) deposit is situated in the LLCVSS. The host-rock of deposits consists of alkali olivine basalt flow and tuffaceous silty sandstone. Mineralization occurs as stratiform blanket-like and tabular orebodies. Based on ore body structure, mineralogy, and ore fabric, we recognize three different ore facies in the Nudeh deposit: (1) a stringer zone, consisting of a discordant mineralization of sulfides forming a stockwork of sulfide-bearing quartz veins cutting the footwall volcano-sedimentary rocks; (2) a massive ore, consisting of massive replacement pyrite, chalcopyrite, sphalerite and Friedrichite with magnetite; (3) bedded ore, with laminated to disseminated pyrite, and chalcopyrite. Chloritization, silicification, sericitization and epidotization are the main wall-rock alterations; alteration intensity increases towards the stringer zone. The δ34S composition of the sulfides ranges from −1.5‰ to +3.69‰ with a general increase of δ34S ratios of massive ore facies to stockwork zone. The heavier values indicate that some of the sulfur was derived from seawater sulfate that was ultimately thermochemically reduced in deep hydrothermal reaction zones. Sulfur isotopes, along with sedimentological, textural, petrological, mineralogical, and geochemical evidences, suggest that this deposit should be classified as a Besshi-type VMS ore deposit.

Cross-hole reflection seismic to delineate a relatively thin volcanogenic massive sulphide deposit in shale hosted environment

SUMMARY The seismic reflection method is a high resolution technique that can be used in many exploration environments including mineral exploration. However, mountainous terrain, depth of burial and the steepness of ore bearing structures pose a challenge to the application of surface seismic in mineral exploration. The cross-hole seismic method may present an alternative approach under such conditions. Presented here is a synthetic study examining the capability of the cross-hole seismic method to delineate a volcanogenic massive sulphide ore body in a shale hosted environment. A simple model typical for volcanogenic massive deposits in Tasmania has been considered. There, an elongated steeply dipping volcanogenic massive sulphide deposit with an average thickness of 10 m is seated within a shale rock. The primary aim of the modelling is to test the capability of the technique to delineate relatively medium sized, steeply dipping volcanogenic massive sulphide lens in shale hosted environment. A second objective is to use the technique to prospect for extensions to mineralization along steeply dipping reflectors. Synthetic cross-hole seismic records were generated using a 120 Hz energy source. Kirchhoff VSP migration was applied to wavefield separated shot records and Pre- stacked Depth Migrated images created. The resulting migrated images correlate well with the position and dip of the ore body demonstrating the potential of the cross- hole reflection technique to delineate steeply dipping ore structures in challenging environments.

Mode‐converted volcanogenic massive sulphide ore lens reflections in vertical seismic profiles from Flin Flon, Manitoba, Canada

ABSTRACTIn October 2006, three‐component zero‐offset vertical seismic profile data were acquired from a deviated well in the Flin Flon mining camp in Manitoba, Canada, using a dynamite source. These vertical seismic profile data were processed to reveal reflections originating from the 85.5 Mt Flin Flon‐Callinan‐777 volcanogenic massive sulphide ore system. From drill records, mine plans, surficial maps, and seismic data, 3D voxel models of the local geology and known ore zones were built, which were then used in 3D finite‐difference modelled simulations of the vertical seismic profile surveys. The number of geological units partitioning the model was incrementally increased to study the effects of the massive sulphide ore and the major rock units on the seismic response. The simulations and field data were jointly visualized, and reflections originating at some of the known ore zones were identified. These reflections were observed in each of the three components in both the real field and the forward modelled data and indicate a strong mode‐converted component of the reflected wavefield.