Emplacement of sharp-walled sulfide veins during the formation and reactivation of impact-related structures at the Broken Hammer Mine, Sudbury, Ontario

2020 ◽  
Vol 57 (10) ◽  
pp. 1149-1166 ◽  
Author(s):  
M.F. Hall ◽  
B. Lafrance ◽  
H.L. Gibson
Keyword(s):  
Massive Sulfide ◽  
Hydrothermal Fluids ◽  
Crater Floor ◽  
Sudbury Igneous Complex ◽  
Tectonic Events ◽  
Brittle Ductile Transition ◽  
Basement Rocks ◽  
Post Impact ◽  
Platinum Group ◽  
The Impact

Broken Hammer is a hybrid Cu–Ni–Platinum Group Element (PGE) footwall deposit located in Archean basement rocks below the impact-induced Sudbury Igneous Complex (SIC), Canada. The deposit consists of massive chalcopyrite veins surrounded by thin epidote, actinolite, and quartz selvedges and low-sulfide, high-PGE mineralization consisting of disseminated chalcopyrite (<5%) and platinum group minerals, associated with Ni-bearing chlorite overprinting alteration patches of epidote, actinolite, and quartz. The veins are grouped into five steeply-dipping sets, striking northeast-, southwest-, southeast-, south-, and east–west, which were emplaced along impact-related fractures that were reactivated multiple times during stabilization of the crater floor. Early reactivation of the fractures created pathways for the migration of hydrothermal fluids from which quartz and chlorite precipitated sealing the fractures. Renewed slip shattered the quartz–chlorite veins into fragments that were incorporated in massive sulfide veins that crystallized from fractionated sulfide melts or from high temperature (400–500 °C) hydrothermal fluids, which migrated outward into the basement rocks from a cooling and crystallizing SIC melt sheet. Hydrothermal fluids syn-genetic with the epidote–actinolite–quartz alteration distributed the PGE into the footwall rocks, or late hydrothermal fluids associated with the Ni-bearing chlorite leached Ni and PGMs from the sulfide veins and redistributed them to form low-sulfide, high-PGE zones in the footwall rocks. During post-impact tectonic events, slip at temperatures below the brittle–ductile transition for chalcopyrite (<200 °C to 250 °C) produced striations along the vein margins. The Broken Hammer deposit exemplifies how Cu–Ni–PGE footwall deposits formed by the reactivation of impact-related fractures that provided conduits for the migration of melts and hydrothermal fluids.

scholarly journals Post-Impact Faulting of the Holfontein Granophyre Dike of the Vredefort Impact Structure, South Africa, Inferred from Remote Sensing, Geophysics, and Geochemistry

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 96
Author(s):  
Martin D. Clark ◽  
Elizaveta Kovaleva ◽  
Matthew S. Huber ◽  
Francois Fourie ◽  
Chris Harris
Keyword(s):  
South Africa ◽  
Remote Sensing ◽  
Crater Floor ◽  
Impact Structure ◽  
Impact Melt ◽  
Geophysical Modeling ◽  
Tectonic Events ◽  
Post Impact ◽  
The Impact

Better characterization features borne from long-term crustal modification processes is essential for understanding the dynamics of large basin-forming impact structures on Earth. Within the deeply eroded 2.02 Ga Vredefort Impact Structure in South Africa, impact melt dikes are exposed at the surface. In this study, we utilized a combination of field, remote sensing, electrical resistivity, magnetic, petrographical, and geochemical techniques to characterize one such impact melt dike, namely, the Holfontein Granophyre Dike (HGD), along with the host granites. The HGD is split into two seemingly disconnected segments. Geophysical modeling of both segments suggests that the melt rock does not penetrate below the modern surface deeper than 5 m, which was confirmed by a later transecting construction trench. Even though the textures and clast content are different in two segments, the major element, trace element, and O isotope compositions of each segment are indistinguishable. Structural measurements of the tectonic foliations in the granites, as well as the spatial expression of the dike, suggest that the dike was segmented by an ENE–WSW trending sinistral strike-slip fault zone. Such an offset must have occurred after the dike solidified. However, the Vredefort structure has not been affected by any major tectonic events after the impact occurred. Therefore, the inferred segmentation of the HGD is consistent with long-term crustal processes occurring in the post-impact environment. These crustal processes may have involved progressive uplift of the crater floor, which is consistent with post-impact long-term crustal adjustment that has been inferred for craters on the Moon.

Post-impact deposits in Tvären, a marine Middle Ordovician crater south of Stockholm, Sweden

1994 ◽  
Vol 131 (1) ◽  
pp. 91-103 ◽  
Author(s):  
M. Lindström ◽  
T. Flodén ◽  
Y. Grahn ◽  
B. Kathol
Keyword(s):  
Sea Water ◽  
Time Interval ◽  
Early Date ◽  
Middle Cambrian ◽  
Middle Ordovician ◽  
Basement Rocks ◽  
Open Sea ◽  
Post Impact ◽  
The Impact ◽  
Stratigraphic Succession

AbstractThe well-preserved Tvären crater is noteworthy for being one of a small number of Early and Middle Ordovician impact structures formed in a marine environment. It is demonstrated to be an impact structure by the presence of a breccia lens, consisting of crystalline basement rocks, and shocked quartz. The breccia lens formed under dry-hot conditions after expulsion of sea-water by the impact. Resurging sea-water thereupon deposited a positively graded, 60 m thick turbidite-like unit. This graded resurge deposit is a previously unknown feature, to be expected in open-sea impacts. Breccia in the lower part of this graded deposit contains fragments of a remarkably complete orthoceratite limestone succession that existed at the site of impact, resting on non-lithified sand of probably Early to earliest Middle Cambrian age. A sedimentary succession was deposited inside the crater at depths decreasing from more than 200 m in the initial stages to some 100 m at the time of deposition of the youngest preserved beds. The environment within the crater thus favoured deposition of an essentially complete stratigraphic succession with depth-controlled palaeoecology for a significant time interval after the impact. Whereas planktonic members, like graptolites and chitinozoa, are present throughout the post-impact succession, and asaphids, almost as persistent, became established at an early date, burrowers were somewhat reluctant to enter and remopleuridids and small strophomenids came in at a late stage. We suggest as a result of this study that structures formed by impact may offer unique information about the palaeogeology and palaeoenvironment of the region hit by the impact.

The Unmetamorphosed Sedimentary Fill of the Brent Meteorite Crater, Southeastern Ontario

1975 ◽  
Vol 12 (4) ◽  
pp. 606-628 ◽  
Author(s):  
G. P. Lozej ◽  
F. W. Beales
Keyword(s):  
Sea Water ◽  
Sediment Accumulation ◽  
General Level ◽  
Crater Floor ◽  
Middle Ordovician ◽  
Basement Rocks ◽  
Shelf Sea ◽  
Precambrian Terrain ◽  
Sedimentary Fill ◽  
The Impact

A 10 000-ft (~3050-m) diameter circular structure that exhibits rimmed crater form, shock-metamorphic features, and underlying unbrecciated basement rocks occurs near Brent, Ontario, close to the southern margin of the Canadian Shield. In its center 863 ft (263 m) of Middle Ordovician sediments are preserved. Shortly after impact a nearly level crater floor was established and the subsequent sequence appears to have been deposited close to mean sea level. Repeated sediment laminae probably reflected wind-tidal marine incursions onto the low relief margin of the contemporary Ordovician epicontinental sea. Throughout much of its period of sediment accumulation, the crater floor appears to have been nearly flat. A 380-ft (115.8 m) sequence of dolostones, arkosic siltstones, and evaporite layers and veins formed within a breccia-rimmed depression. Initially sea water carrying fine silt invaded the crater and refluxed through the porous and permeable crater rim. Subsequently some 100 ft (30.5 m) of silty arkose blanketed the area, probably resulting from further transgression of the Middle Ordovician seas and breaching of the crater walls. An upper 380 ft (115.8 m) of predominantly thin-bedded lagoonal and shallow shelf sea limestones are divided into upper and lower sequences by a middle regressive set of red beds.The implied near-flat crater floor, coupled with preservation of over 800 ft (>244 m) of crater sediments, suggests continued slow subsidence. Earlier on, this subsidence affected only the crater area, but later episodes of subsidence were regional, involving Ordovician, Silurian, and Devonian sedimentation. The superincumbent load further compacted the total crater sequence. Preservation of the rocks described here is due to final depression of the sequence into a position below the general level of the surrounding Precambrian terrain. If Brent can be considered to be a typical peri-marine meteoritic impact crater, all such craters should have in common an inward-dipping succession of open-circulation sediments overlying a crater-rim restricted sedimentary sequence, which in turn overlies a shock-metamorphosed series of breccias.Compaction of the impact-generated breccias and subsequent unmetamorphosed crater-filling sediments influenced both sediment accumulation and the ultimate crater structure.

Granular zircon from Vredefort granophyre (South Africa) confirms the deep injection model for impact melt in large impact structures

Geology ◽  
2019 ◽  
Vol 47 (8) ◽  
pp. 691-694 ◽  
Author(s):  
Elizaveta Kovaleva ◽  
Dmitry A. Zamyatin ◽  
Gerlinde Habler
Keyword(s):  
South Africa ◽  
Large Impact ◽  
Crater Floor ◽  
Pressure Shock ◽  
Impact Melt ◽  
Basement Rocks ◽  
High Shock ◽  
Injection Model ◽  
History Of ◽  
The Impact

Abstract The Vredefort impact structure, South Africa, is a 2.02 Ga deeply eroded meteorite scar that provides an opportunity to study large impact craters at their lower stratigraphic levels. A series of anomalous granophyre dikes in the core of the structure are believed to be composed of an impact melt, which intruded downwards from the crater floor, exploiting fractures in basement rocks. However, the melt emplacement mechanisms and timing are not constrained. The granophyre dikes contain supracrustal xenoliths captured at higher levels, presently eroded. By studying these clasts and shocked minerals within, we can better understand the nature of dikes, magnitude of impact melt movement, conditions that affected target rocks near the impacted surface, and erosional rates. We report “former reidite in granular neoblastic” (FRIGN) zircon within a granite clast enclosed in the granophyre. High-pressure zircon transformation to reidite (ZrSiO4) and reversion to zircon resulted in zircon grains composed of fine neoblasts (∼0.5–3 µm) with two or three orthogonal orientations. Our finding provides new independent constraints on the emplacement history of Vredefort granophyre dikes. Based on the environment, where other FRIGN zircons are found (impact glasses and melts), the clast was possibly captured near the top of the impact melt sheet and transported to the lowermost levels of the structure, traveling some 8–10 km. Our finding not only provides the highest-pressure shock estimates thus far discovered in the Vredefort structure (≥30 GPa), but also shows that microscopic evidence of high shock pressures can be found within large eroded craters at their lowest stratigraphic levels.

scholarly journals Sandwich panel with in-plane honeycombs in different Poisson's ratio under low to medium impact loads

2021 ◽  
Vol 60 (1) ◽  
pp. 145-157
Author(s):  
Yi Luo ◽  
Ke Yuan ◽  
Lumin Shen ◽  
Jiefu Liu
Keyword(s):  
Poisson’S Ratio ◽  
Sandwich Panel ◽  
Impact Force ◽  
Impact Resistance ◽  
Poisson's Ratio ◽  
Compression Performance ◽  
Post Impact ◽  
Local Impact ◽  
Collapse Behavior ◽  
The Impact

Abstract In this study, a series of in-plane hexagonal honeycombs with different Poisson's ratio induced by topological diversity are studied, considering re-entrant, semi-re-entrant and convex cells, respectively. The crushing strength of honeycomb in terms of Poisson's ratio is firstly presented. In the previous research, we have studied the compression performance of honeycomb with different negative Poisson's ratio. In this study, a comparative study on the local impact resistance of different sandwich panels is conducted by considering a spherical projectile with low to medium impact speed. Some critical criteria (i.e. local indentation profile, global deflection, impact force and energy absorption) are adopted to analyze the impact resistance. Finally, an influential mechanism of Poisson's ratio on the local impact resistance of sandwich panel is studied by considering the variation of core strength and post-impact collapse behavior.

Pb-Nd-Sr Isotope Geochemistry of Metapelites from the Iberian Pyrite Belt and Its Relevance to Provenance Analysis and Mineral Exploration Surveys

2021 ◽  
Author(s):  
Filipa Luz ◽  
António Mateus ◽  
Ezequiel Ferreira ◽  
Colombo G. Tassinari ◽  
Jorge Figueiras
Keyword(s):  
Isotope Geochemistry ◽  
Mineral Exploration ◽  
Hanging Wall ◽  
Massive Sulfide ◽  
Iberian Pyrite Belt ◽  
Isotopic Signature ◽  
Sr Isotope ◽  
Provenance Analysis ◽  
Basement Rocks ◽  
World Class

Abstract The boundary in the Iberian Pyrite Belt is a world-class metallogenic district developed at the Devonian-Carboniferous boundary the Iberian Variscides that currently has seven active mines: Neves Corvo (Cu-Zn-Sn) and Aljustrel (Cu-Zn) in Portugal, and Riotinto (Cu), Las Cruces (Cu), Aguas Teñidas (Cu-Zn-Pb), Sotiel-Coronada (Cu-Zn-Pb), and La Magdalena (Cu-Zn-Pb) in Spain. The Iberian Pyrite Belt massive sulfide ores are usually hosted in the lower sections of the volcano-sedimentary complex (late Famennian to late Visean), but they also occur in the uppermost levels of the phyllite-quartzite group at the Neves Corvo deposit, stratigraphically below the volcano-sedimentary complex. A Pb-Nd-Sr isotope dataset was obtained for 98 Iberian Pyrite Belt metapelite samples (from Givetian to upper Visean), representing several phyllite-quartzite group and volcano-sedimentary complex sections that include the footwall and hanging-wall domains of ore horizons at the Neves Corvo, Aljustrel, and Lousal mines. The combination of whole-rock Nd and Sr isotopes with Th/Sc ratios shows that the siliciclastic components of Iberian Pyrite Belt metapelites are derived from older quartz-feldspathic basement rocks (–11 ≤ εNdinitial(i) ≤ –8 and (87Sr/86Sr)i up to 0.727). The younger volcano-sedimentary complex metapelites (upper Tournaisian) often comprise volcanic-derived constituents with a juvenile isotopic signature, shifting the εNdi up to +0.2. The Pb isotope data confirm that the phyllite-quartzite group and volcano-sedimentary complex successions are crustal reservoirs for metals found in the deposits. In Neves Corvo, where there is more significant Sn- and Cu-rich mineralization, the higher (206Pb/204Pb)i and (207Pb/204Pb)i values displayed by phyllite-quartzite group and lower volcano-sedimentary complex metapelites (up to 15.66 and 18.33, respectively) suggest additional contributions to the metal budget from a deeper and more radiogenic source. The proximity to Iberian Pyrite Belt massive sulfide ore systems hosted in metapelite successions is observed when (207Pb/204Pb)i &gt;15.60 and Fe2O3/TiO2 or (Cu+Zn+Pb)/Sc &gt;10. These are important criteria that should be considered in geochemical exploration surveys designed for the Iberian Pyrite Belt.

Resolving the Unique Invariant Slip-Direction in Rigid Three-Dimensional Multi-Point Impacts at Stick-Slip Transitions

2018 ◽  
Author(s):  
Abhishek Chatterjee ◽  
Alan Bowling
Keyword(s):  
Single Point ◽  
Three Dimensional ◽  
Impact Behavior ◽  
Slip Direction ◽  
Stick Slip ◽  
Impact Forces ◽  
Post Impact ◽  
Impact Problems ◽  
Slip Transition ◽  
The Impact

This work presents a new approach for resolving the unique invariant slip direction at Stick-Slip Transition during impact. The solution method presented in this work is applicable to both single-point and multi-point impact problems. The proposed method utilizes rigid body constraints to resolve the impact forces at all collision points in terms of a single independent impact forces parameter. This work also uses an energetic coefficient of restitution to terminate impact events, thereby yielding energetically consistent post-impact behavior.

Ni-Cu sulfide mineralization and PGM from the Samapleu mafic-ultramafic intrusion, Yacouba complex, western Ivory Coast

2021 ◽  
Vol 59 (4) ◽  
pp. 631-665
Author(s):  
Franck Gouedji ◽  
Christian Picard ◽  
Marc Antoine Audet ◽  
Thierry Augé ◽  
Jorge Spangenberg
Keyword(s):  
Ivory Coast ◽  
Massive Sulfide ◽  
Sulfide Mineralization ◽  
Platinum Group Minerals ◽  
Thermo Fisher Scientific ◽  
Mass Spectrometer System ◽  
Ultramafic Intrusion ◽  
Platinum Group ◽  
Mineralizing Process ◽  
Spectrometer System

ABSTRACT The mafic-ultramafic Samapleu deposits of the Yacouba complex, which host nickel, copper sulfides, and platinum-group minerals, are located in the Biankouma-Silipou region, western Ivory Coast. These intrusions originate from the mantle and would have been established during the Proterozoic (2.09 Ga) around 22 km deep within the Archean granulites (3.6–2.7 Ga) which at least partially contaminated them. Platinum-group and sulfide minerals from the Samapleu deposits were studied using optical microscopy, scanning electron microscopy, the electronic microprobe, X-ray fluorescence, fire assay, and a Thermo Fisher Scientific Delta S isotope ratio mass spectrometer system. The sulfide mineralization (mainly pyrrhotite, pentlandite, chalcopyrite ± pyrite) is mainly disseminated with, in places, semi-massive to massive sulfide veins. It is especially abundant in pyroxenite horizons with net or breccia textures. The isotopic ratios of sulfur measured from the sulfides (an average of 0.1‰), the R factor (between 1500 and 10,000), and the Cu/Pd ratios indicate a mantle source. Thus, the sulfides would have formed from sulfide liquids produced by immiscibility from the silicate mantle magma under mafic-ultramafic intrusion emplacement conditions and with possible geochemical modification of the magmas by assimilation of the surrounding continental crust. The platinum-group minerals (michenerite, merenskyite, moncheite, Co-rich gersdorffite, irarsite, and hollingworthite) are mainly associated with the sulfide phases. The nature of the platinum-group minerals is indicative of the probable role of late-magmatic hydrothermal fluids during the mineralizing process.

scholarly journals Mineralization and Alteration of a Modern Seafloor Massive Sulfide Deposit Hosted in Mafic Volcaniclastic Rocks

2019 ◽  
Vol 114 (5) ◽  
pp. 857-896 ◽  
Author(s):  
Melissa O. Anderson ◽  
Mark D. Hannington ◽  
Timothy F. McConachy ◽  
John W. Jamieson ◽  
Maria Anders ◽  
...  
Keyword(s):  
Low Temperature ◽  
Massive Sulfide ◽  
Hydrothermal Fluids ◽  
Sulfide Deposit ◽  
Massive Sulfide Deposit ◽  
Remotely Operated Vehicle ◽  
Eruptive Fissure ◽  
Seawater Sulfate ◽  
Volcaniclastic Rocks ◽  
Seafloor Massive Sulfide

Abstract Tinakula is the first seafloor massive sulfide deposit described in the Jean Charcot troughs and is the first such deposit described in the Solomon Islands—on land or the seabed. The deposit is hosted by mafic (basaltic-andesitic) volcaniclastic rocks within a series of cinder cones along a single eruptive fissure. Extensive mapping and sampling by remotely operated vehicle, together with shallow drilling, provide insights into deposit geology and especially hydrothermal processes operating in the shallow subsurface. On the seafloor, mostly inactive chimneys and mounds cover an area of ~77,000 m2 and are partially buried by volcaniclastic sand. Mineralization is characterized by abundant barite- and sulfide-rich chimneys that formed by low-temperature (<250°C) venting over ~5,600 years. Barite-rich samples have high SiO2, Pb, and Hg contents; the sulfide chimneys are dominated by low-Fe sphalerite and are high in Cd, Ge, Sb, and Ag. Few high-temperature chimneys, including zoned chalcopyrite-sphalerite samples and rare massive chalcopyrite, are rich in As, Mo, In, and Au (up to 9.26 ppm), locally as visible gold. Below the seafloor, the mineralization includes buried intervals of sulfide-rich talus with disseminated sulfides in volcaniclastic rocks consisting mainly of lapillistone with minor tuffaceous beds and autobreccias. The volcaniclastic rocks are intensely altered and variably cemented by anhydrite with crosscutting sulfate (± minor sulfide) veins. Fluid inclusions in anhydrite and sphalerite from the footwall (to 19.3 m below seafloor; m b.s.f.) have trapping temperatures of up to 298°C with salinities close to, but slightly higher than, that of seawater (2.8–4.5 wt % NaCl equiv). These temperatures are 10° to 20°C lower than the minimum temperature of boiling at this depth (1,070–1,204 m below sea level; m b.s.l.), suggesting that the highest-temperature fluids boiled below the seafloor. The alteration is distributed in broadly conformable zones, expressed in order of increasing depth and temperature as (1) montmorillonite/nontronite, (2) nontronite + corrensite, (3) illite/smectite + pyrite, (4) illite/smectite + chamosite, and (5) chamosite + corrensite. Zones of argillic alteration are distinguished from chloritic alteration by large positive mass changes in K2O (enriched in illite/smectite), MgO (enriched in chamosite and corrensite), and Fe2O3 (enriched in pyrite associated with illite/smectite alteration). The δ18O and δD values of clay minerals confirm increasing temperature with depth, from 124° to 256°C, and interaction with seawater-dominated hydrothermal fluids at high water/rock ratios. Leaching of the volcanic host rocks and thermochemical reduction of seawater sulfate are the primary sources of sulfur, with δ34S values of sulfides, from –0.8 to 3.4‰, and those of sulfate minerals close to seawater sulfate, from 19.3 to 22.5‰. The mineralization and alteration at Tinakula are typical of a class of ancient massive sulfide deposits hosted mainly by permeable volcaniclastic rocks with broad, semiconformable alteration zones. Processes by which these deposits form have never been documented in modern seafloor massive sulfide systems, because they mostly develop below the seafloor. Our study shows how hydrothermal fluids can become focused within permeable rocks by progressive, low-temperature fluid circulation, leading to a large area (>150,000 m2) of alteration with reduced permeability close to the seafloor. In our model, overpressuring and fracturing of the sulfate- and clay-cemented volcaniclastic rocks produced the pathways for higher-temperature fluids to reach the seafloor, present now as sulfate-sulfide veins within the footwall. In the geologic record, the sulfate (anhydrite) is not preserved, leaving a broad zone of intense alteration with disseminated and stringer sulfides typical of this class of deposits.

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