Amisk Group Research Articles

Short vs Standard-Length Femoral Stems Cemented According to the “French Paradox”: A Matched Paired Prospective Study Using Ein Bild Roentgen Analyze Femoral Component at Two-Year Follow-Up

BackgroundThe purpose of this prospective matched paired study is to compare the in vivo migration patterns using Ein Bild Roentgen Analyze femoral component of shortened vs standard-length stems cemented line-to-line in primary total hip arthroplasty (THA) at 2-year follow-up. MethodsWe prospectively included the first 50 consecutive primary cemented THAs in 50 patients using a 12% shortened stem (AmisK group) of which design was derived from the original Charnley-Kerboull (CK) femoral components. These 50 patients were matched paired to 50 patients from a historical series of patients who underwent primary THAs using standard-length CK stems (CK group) with available long-term results, including Ein Bild Roentgen Analyze femoral component data at 2-year follow-up. ResultsBody mass index was significantly higher (P = .007) in the AmisK vs the CK group. At the 2-year follow-up, the mean subsidence was 0.65 mm (0-1.40) in the AmisK group vs 0.68 mm (0.07-1.43) in the CK group (P = .73). When using a 1.5-mm threshold, none of the stems in either group was considered to have subsided. Femoral cortical thickening in zones 3 and 5 occurred in 6 of the 50 hips (12%) in the AmisK group vs 20 (40%) of the 50 hips in the CK group (P = .003). ConclusionOur study showed that a shortened highly polished double-tapered stem cemented line-to-line provided similar results including minimal subsidence as its standard-length counterpart, with significantly less distal femoral cortical thickening. However, longer term survival analysis still needs to be determined.

Geochemical constraints on the depositional environment of the 1.84 Ga Embury Lake Formation, Flin Flon Belt, Canada

AbstractThe Flin Flon Belt of Canada contains Paleoproterozoic volcanic–sedimentary sequences that are related to the Trans‐Hudson Orogeny. The sequences include island arc volcanic and volcaniclastic rocks (Amisk Group) that are unconformably overlain by subaerial sedimentary rocks (Missi Group), and younger deep facies sediments. In the Flin Flon area, several north–south trending faults divide the sequences into blocks and obscure the depositional environment of the deep facies sediments. Locally, within the Flin Flon area, the Embury Lake Formation is in fault contact with island arc volcanic–sedimentary sequences of the Amisk and Missi Groups. To identify the depositional environment of the Embury Lake Formation, we used lithologic and geochemical approaches. Here, we report carbon isotopic values in organic matter (δ13Corg) and sulfur isotopes (δ34S), as well as total organic carbon and total sulfur measurements for the black shale in the formation. Samples were taken from a drill core that contains alternating bands of sandstone and black shale. Pyrite in the black shale is divided into four textural types: euhedral, vein‐type, elliptical, and microcrystalline. Microcrystalline pyrite is typically generated by microbially mediated sulfate reduction. An extremely low S/C ratio (avg. = 0.04) is consistent with lacustrine deposition. The ranges of δ13Corg (−36 ‰ to −27 ‰) and δ34S (+3.0 ‰ to +7.7 ‰) values can be explained by bacterial photosynthesis that involved Calvin cycle and acetyl CoA pathways, and sulfate reduction in a low‐sulfate environment. Considering the depositional age reported in a previous study of < 1.84 Ga, the Embury Lake Formation was likely emplaced in a lacustrine setting during the Trans‐Hudson Orogeny.

Age and source of detrital zircons from the Missi Formation: a Proterozoic molasse deposit, Trans-Hudson Orogen, Canada

The Missi Formation in the Flin Flon Basin forms part of a discontinuous series of molasse-type sediments found throughout the Early Proterozoic Trans-Hudson Orogen in northern Saskatchewan and Manitoba. The Flin Flon Basin contains a sequence of proximal-fan to braided-stream fluvial conglomerates and sandstones, which unconformably overlie subaerially weathered Amisk Group volcanic rocks. Stratigraphic way-up indicators have been preserved, even though these rocks have undergone greenschist-facies metamorphism and polyphase deformation. The sedimentary rocks are crosscut by intrusive rocks, which provide a minimum age of sedimentation of 1840 ± 7 Ma.Detrital zircons from each of the six stratigraphic subdivisions of the Flin Flon Basin were analyzed using the single-zircon Pb-evaporation technique. Euhedral to slightly rounded zircons dominate each sample, and these zircons give ages of between about 1854 and 1950 Ma. The Missi sediments were thus deposited between 1840 and 1854 Ma. Possible sources for the detrital zircons are Amisk Group felsic volcanic rocks and post-Amisk granitoid rocks and orthogneisses in adjacent domains within the Trans-Hudson Orogen. However, the immature character of the sedimentary rocks, the composition of clasts, the euhedral character of many of the zircons, and the range in ages suggest that most were likely derived from Amisk Group and granitoid rocks in the western Flin Flon Domain. Rounded zircons are uncommon but provide evidence for the reworking of older Proterozoic sedimentary rocks, or a distant Archean or Early Proterozoic granitoid terrane.

Mesothermal gold mineralization in a Proterozoic greenstone belt; western Flin Flon Domain, Saskatchewan, Canada

The Flin Flon domain, Trans-Hudson orogen, Canada, is an example of a Proterozoic greenstone belt that hosts a large number of small mesothermal gold occurrences. The greenstone belt consists of tholeiitic to calc-alkaline volcanic rocks (Amisk Group; approximately 1900-1880 Ma) unconformably overlain by molasse-type sedimentary rocks (Missi Group; 1850-1840 Ma). The supracrustal rocks are intruded by gabbroic to granitic rocks ranging in age from synvolcanic to late tectonic (1890-1835 Ma). Metamorphic grade varies from prehnite-pumpellyite facies to amphibolite facies, and peak thermal conditions generally were attained locally during granitoid intrusion. Many of the shear zones and the dominant regional foliation developed during ductile deformation coeval with peak metamorphism. These shear zones were reactivated and mineralized under brittle-ductile conditions during postpeak metamorphic uplift.Mesothermal gold mineralization is hosted in quartz veins that developed at jogs or zones of competency contrasts along brittle-ductile shear zones, in all lithologies in the region. Alteration envelopes, which consist of quartz-carbonate-chlorite-albite-muscovite-pyrite, are usually less than a few meters wide and overprint regional metamorphic assemblages. The veins consist of milky-colored quartz and may also contain tourmaline, ankerite, chlorite, and muscovite. Pyrite and arsenopyrite are the dominant sulfides, and gold grade is proportional to the modal abundance of sulfides.The dominant fluids associated with gold mineralization were H 2 O-CO 2 -NaCl (0.6-14.7 wt % NaCl equiv) in composition, with generally uniform H 2 O/CO 2 phase ratios in a given plane or zone but variable phase ratios between zones. Oxygen isotope mineral pairs indicate temperature of mineralization of between 360 degrees and 420 degrees C, which, when combined with fluid inclusion density estimates, indicate that most of the gold mineralization occurred at a pressure of about 2 kbars. Rapid pressure release in dilatant zones with related phase separation and change in fluid composition and properties, and local fluid-wall rock interaction, are the likely gold-precipitation mechanisms.The O, H, S, C, and Sr isotope compositions of hydrothermal minerals in the shear zones indicate that the mineralizing fluids interacted extensively with Proterozoic metamorphic and igneous rocks similar in composition to those presently exposed at the surface, at high temperatures and at low water/rock ratios. The O and H isotope compositions are compatible with formation of the fluids from devolatilization reactions during prograde metamorphism at depth. The O isotope composition of barren quartz veins varies with the host rocks indicating that these fluids were either locally derived or interacted extensively with the immediate host rocks.An Rb-Sr isochron age of 1760 + or - 9 Ma on tourmaline and muscovite from the Rio deposit is similar to 40 Ar/ 39 Ar plateau ages for muscovites from the premetamorphic Laurel Lake deposit in the Flin Flon domain. This suggests that fluid advection through the Rio deposit was contemporaneous with the thermal event that affected Laurel Lake muscovites. These ages, along with an age from the Tartan Lake mesothermal deposit (1791 + or - 4 Ma) in the Flin Flon domain, indicate that fluid flow related to hydrothermal activity along the shear zones in the western Flin Flon domain occurred periodically over a period of about 30 Ma.These Proterozoic gold occurrences are similar to Archean mesothermal gold deposits in terms of geologic, structural, and tectonic setting, alteration and vein mineralogy, and fluid composition, pressure, and temperature. However, the limited extent of alteration, the low gold content, the isotopic systematics, and the lack of either S-type granites or mantle-derived lamprophyres suggest that the shear zones hosting the western Flin Flon domain occurrences sampled limited quantities of fluids and, thus, were not transcrustal features capable of hosting giant gold deposits.

Structural setting and fluid characteristics of the Proterozoic Tartan Lake gold deposit, Trans-Hudson Orogen, northern Manitoba

The late-kinematic structural architecture of the Flin Flon domain is dominated by a network of anastomosing shear zones formed by compressional deformation during the Proterozoic Trans-Hudson orogeny (ca. 1900-1800 Ma). A number of structurally controlled mesothermal gold deposits occur throughout the region, associated with this shear zone network. The Tartan Lake gold deposit occurs in the Tartan Lake shear zone, at the contact between a layered gabbroic intrusive complex and metavolcanic rocks of the Amisk group (ca. 1875 Ma).Five phases of deformation have been recognized in the Flin Flon region (P1-P5). Midgreenschist facies peak metamorphic conditions (phase 3) at Tartan Lake are recorded by a mineral assemblage of biotite-actinolite-albite-muscovite-epidote and carbonate in volcani-clastic rocks, along with a well-developed phase 3 schistosity. Early movement of the Tartan Lake shear zone was initiated with phase 3 deformation, during which oblique slip occurred. During phase 4, this shear zone was overprinted by a major regional fold and the shear zone was reactivated by strike-slip movement. Regional phase 3 schistosity is refolded in a series of steeply plunging mesoscopic phase 4 fold closures that were synchronous with the shear zones.A network of conjugate strike-slip shear zones that vary in width from 5 to 35 m comprise the 0.3-km-wide structure at Tartan Lake. Deformation within the shear zones is marked by (1) development of S and C schistosities in which C is dominant, (2) weakly developed sub-horizontal mineral lineations, and (3) folding and kink banding of these schistosities. Within shear zones, sericite, chlorite, quartz, carbonate, albite, tourmaline, and pyrite are the dominant minerals and biotite and actinolite are retrograded to chlorite, such that this deformation and Au mineralization are postpeak metamorphism. Five stages of veining occurred within the shear zones, and these are characterized by distinctive orientations and mineral parageneses. Gold mineralization occurred with two of these stages of veining, along with pyrite, chalcopyrite, tellurides, monazite, scheelite, and rutfie. The timing of this mineralizing event has been constrained by the 40 Ar/ 39 Ar method at 1791 + or - 4 Ma; this is 20 to 40 m.y. postpeak metamorphism.Fluids were of H 2 O-CO 2 -NaCl composition throughout the ore-forming vein events, with modal salinity = 6.9 wt percent equiv, CO 2 density = 0.64 g/cm 3 , and homogenization temperatures ranging from 250 degrees to 390 degrees C (with a median of 295 degrees C). Stable isotope compositions of quartz (delta 18 O = 10.8-13.8ppm), chlorite (delta 18 O = 3.0-4.8ppm), muscovite (delta 18 O = 7.5-9.0ppm), scheelite (delta 18 O = 4.0-5.0ppm), albite (delta 18 O = 9.0-9.6ppm), tourmaline (delta 18 O = 7.9-8.8ppm), pyrite (delta 34 S = 1.7-3.1ppm), and chalcopyrite (delta 34 S = 1.4-1.7ppm) establish the temperature of gold mineralization between 315 degrees and 472 degrees C, with an average at 372 degrees + or - 41 degrees C (1Sigma ). Ore-forming fluids had delta 18 O = 5.2 to 6.5 per mil and delta D = -50 to -86 per mil, and Fe dolomites from mineralized veins exhibit restricted ranges of delta 13 C (-7.0 to -5.2ppm and delta 18 O (9.3 to 10.9ppm),suggesting a uniform fluid composition. These veins formed at a pressure of 1.2 to 2.4 kbars, corresponding to 4.3 to 8.6 km, if lithostatic fluid pressure is assumed.Constraints on the depth at which these veins precipitated and the character of the fluids suggest that this gold deposit formed from advecting metamorphic fluids. A postmineralization stage of brittle fracturing is represented by barren veins that exhibit significant depletion in delta 34 S (-29 to -30ppm). This may be the result of an increase in fluid f (sub O 2 ) in the final stages of crustal deformation during the Trans-Hudson orogeny.

The geochemistry and fluid history of the Proterozoic Laurel Lake Au–Ag deposit, Flin Flon greenstone belt

The Laurel Lake Au–Ag deposit is situated 25 km southwest of Flin Flon in the Proterozoic Flin Flon Domain and consists of branching quartz–muscovite–pyrite–tennantite–chalcopyrite–sphalerite–galena–electrum–carbonate veins (stage 1) surrounded by a widespread zone of sericitized and pyritized Amisk Group felsic volcanic rocks. The deposit has been deformed and metamorphosed during the Hudsonian orogeny and is crosscut by nonauriferous quartz–dolomite–tourmaline–pyrite veins (stage 2). The timing of mineralization, the lack of obvious relation to a major shear zone, and high base metal sulphide and Ag/Au ratio (5:1) distinguish this deposit from epigenetic mesothermal gold deposits in the Flin Flon Domain. Fluid inclusion and stable-isotope data indicate that the mineralizing fluids had a high temperature (>300 °C), were saline (>10.3 wt.% NaCl equivalent) and CO2 bearing and had an isotopic composition similar to modified seawater. This fluid leached sulphur, base metals, and precious metals as it interacted with Amisk Group volcanic rocks. The hydrogen isotopic compositions of fine-grained muscovites in the surrounding altered felsic volcanic rocks have been reset during later metamorphism, whereas the coarse stage 1 vein muscovites have partially preserved their primary hydrogen isotopic compositions and fluorine contents. Stage 2 veins were deposited from low-salinity (<6.4 wt.% NaCl equivalent), CO2-bearing fluids, which also have the hydrogen and oxygen isotopic compositions of modified seawater. The Laurel Lake deposit has fluid, vein, and alteration characteristics that distinguish it from both epithermal and mesothermal deposits, and they can be explained by the involvement of modified seawater.

The Flin Flon paleosol and the composition of the atmosphere 1.8 BYBP.

Within the 1800 to 1900 my old Flin Flon-Snow Lake greenstone belt, Amisk Group volcanics are overlain by Missi Group fluvial sediments. Several localities along the Missi-Amisk contact, the volcanics show evidence of subaerial weathering. Field relationships, mineralogical evidence, and chemical analyses confirm that this alteration zone is a paleosol. Pedogenic fabrics and mineralogy were somewhat obscured by greenschist-grade metamorphism associated with the Hudsonian orogeny (1750 my). This is especially true in the upper meter of the paleosol, where metamorphic paragonite and sericitic micas developed in a crenulated fabric. This metamorphism did not, however, obliterate the imprint of weathering on the Amisk volcanics. Features characteristic of well-drained modern soils are evident in the paleosol. Corestones of spheroidally weathered pillow lavas occur at depth within the paleosol (Cr horizon). The corestones decrease in size upward and eventually disappear into a hematite-rich horizon at the top of the paleosol. These macroscopic changes are accompanied by a decrease in CaO and MgO and by an increase in Al2O3, TiO2, and total iron toward the paleosol-Missi contact. Ferrous iron decreases upward toward the contact; FeO was apparently oxidized to ferric iron and retained within the paleosol during weathering. The oxidation and retention of iron within the Flin Flon paleosol indicates that PO2 was probably > or = 10(-2) P.A.L. at the time of weathering. The behavior of iron in the Flin Flon paleosol contrasts sharply with its behavior in the 2200 my Hekpoort paleosol, which is strongly depleted in iron. This difference suggests that a significant increase in the ratio of PO2/PCO2 in the atmosphere took place between 2200 and 1800 mybp.

Rb–Sr study of metavolcanic rocks from the La Ronge and Flin Flon domains, northern Saskatchewan

Two whole-rock suites of metavolcanic rocks from separate volcanic belts of the Churchill Province in northern Saskatchewan have been dated by Rb–Sr. Samples from the Amisk Group of the Flin Flon – Snow Lake domain provide an isochron date of 1784 ± 44 Ma; suites from the Waddy Lake and Devil Lake areas of the La Ronge (–Lynn Lake) domain yield isochron dates of 1814 ± 26 and 1854 ± 100 Ma, respectively. All are regarded as minima for, but close approximations to, emplacement ages. The maximum crustal age of any suite cannot greatly exceed 1850 Ma.Previous Rb–Sr and U–Pb isotopic dates together with these new determinations confirm the contemporaneous existence of two volcanic arcs, active during the late Aphebian (1875–1784 Ma) in the Churchill Province.Low initial 87Sr/86Sr ratios (0.7017–0.7022) are consistent with a petrochemically inferred subduction-related origin for the volcanic rocks with no closed-system reworking of Archean crust, and a linear evolution of 87Sr/86Sr ratio in the magmatic-arc mantle source region from 4.55 Ga to the present.

Origin of early Proterozoic volcaniclastic turbidites, south margin of the Kisseynew sedimentary gneiss belt, File Lake, Manitoba

In the File Lake area, well preserved, weakly recrystallized pebbly greywacke, greywacke, siltstone and mudstone of the early Proterozoic Amisk Group of the Flin Flon volcanic-sedimentary belt have been traced across a steep metamorphic gradient directly into migmatitic paragneisses of the Kisseynew sedimentary gneiss belt. The sedimentary rocks consist of a heterolithic mixture of volcanic detritus, mainly felsic in composition, and overlie a thick accumulation of mafic subaqueous flows. They are 1000 m thick and comprise debris flow deposits that are restricted to the Flin Flon belt and widespread turbidites and fluidized sediment flow deposits that are part of a subaqueous fan system. The large volume of sediments in this sequence implies a tectonically active subaerial source. The heterolithic character of the sediments is the result of subaerial transport and attendant mixing of detritus. The detritus was derived from easily eroded pyroclastic deposits of contemporaneous Amisk volcanoes rather than by dissection of an older volcanic terrain. This is indicated by: (i) only slight rounding of clasts; (ii) local intercalation of volcanic and sedimentary rocks; and (iii) absence of plutonic or metamorphic clasts. The sedimentary rocks are the deposits of a sediment dispersal system that developed around major stratovolcanoes of the Flin Flon belt. A large portion of the detritus which entered the sediment dispersal system was channelled into subaqueous fans and was transported into the adjacent Kisseynew sedimentary basin.

The Amisk Group: An Aphebian(?) Island Arc Deposit

The Amisk Group (Aphebian?) near Flin Flon, Manitoba, consists dominantly of andesitic lava flows and pyroclastic rocks, with minor basalt, dacite, rhyolite, and epiclastic rocks. These have undergone regional metamorphism ranging from chlorite to garnet zone, and locally have been sheared intensely.Major element chemical analyses indicate that intensely sheared Amisk rocks near the Flin Flon and Schist Lake Cu–Zn ore bodies have undergone considerable metasomatism. The unsheared, regionally metamorphosed rocks have undergone significantly less metasomatism, and the compositions of the least-altered of these suggest an island arc tholeiite chemical affinity.The lithology, primary structures, and major-element compositions of lavas within the Amisk Group suggest deposition may have been in an island arc environment.

Paleomagnetism of the Flin Flon – Snow Lake Greenstone Belt, Manitoba and Saskatchewan

The Flin Flon – Snow Lake greenstone belt is of Archean or Aphebian age and has been metamorphosed to greenschist or low amphibolite facies during the Hudsonian orogeny. It contains four rock units — the Amisk Group, the Missi Group, metadiorite and metagabbro bodies, and the Boundary Intrusions. The rocks contain two main magnetizations, an early B magnetization and a later A magnetization. Both magnetizations contain reversals. The A magnetization (43 sites, direction 168°, +73°, k = 17, α95 = 5°, pole 24°N, 095°W) is found in all rock units. It can be divided into three parts (1, 2 and 3) which have the same general direction, but which are significantly different from one another. It is suggested that A1 is a viscous partial thermoremanence (vptrm), and A2 possibly a chemical remanence (crm). Both are considered to have been acquired during uplift (1600–1700 m.y.) following the Hudsonian orogeny. A3 is possibly a crm acquired during late fault movements and appears to be carried by hematite developed during retrograde metamorphism. A3 is considered to be about 1600 m.y. old. The B magnetization (7 sites, 129°, +04°, k = 12, α95 = 18°, pole 20°S, 046°W) occurs in all rock units except the Missi. It is particularly well developed in the Boundary Intrusions where it is considered to be a primary thermoremanent magnetization (trm). In other rock units B is considered to be a vptrm acquired during heating at the time of emplacement of the Boundary Intrusions. The B magnetization is considered to be about 1800 m.y. old. Some enigmatic magnetizations with very high blocking temperatures above 700 °C were observed. Formulas for calculating the coercivities in rocks with more than one magnetization are given.

Isotopic Studies of Ore-Leads in the Hanson Lake-Flin Flon-Snow Lake Mineral Belt Saskatchewan and Manitoba

Lead isotope abundances in 4 stratabound sulfide ores are presented and show characteristics of being single-stage lead deposits. Model ages based on these data range from 1780 ± 44 to 1900 ± 44 m.y. and are considered to be close approximations of the time of ore formation. Geological evidence in the massive sulfide deposits suggests they are coeval with their host rocks, which are predominantly volcanics of the Amisk Group. If this assumption is correct the average model lead age of the ores is essentially the age of the enclosing rocks. Within error limits the results are in good agreement with published Rb-Sr ages for Amisk rocks of the Flin Flon area, and with U-Pb ages in zircons of rhyolites, which also contain similar, massive sulfide ores in the Churchill Province of Arizona. This is considered to be good evidence that the Hanson Lake-Flin Flon-Snow Lake volcanic mineral belt, previously regarded as Archean, is Aphebian in part.A previously published Archean, Rb-Sr isochron for volcanic rocks in the Hanson Lake area may indicate that Amisk-type rocks are a folded complex of both Aphebian and Archean lithologies. The suggested Aphebian age of the Amisk-Missi Groups and their equivalents, indicates they are possibly eugeosynclinal equivalents of the miogeosynclinal Hurwitz sediments.

The Hudsonian Orogeny Near Flin Flon, Manitoba: A Tentative Interpretation of Rb/Sr and K/Ar Ages

Whole rock Rb/Sr age dating near Flin Flon, Manitoba, yields isochrons of 1775 ± 89 m.y. for the Amisk Group (mainly volcanic rocks), and 1805 ± 14 m.y. for the granodioritic Annabel Lake Pluton which intrudes the Amisk. These are considered to be emplacement ages (within their error–limits).A tentative interpretation of the Hudsonian Orogeny in this area is derived by fitting the Rb/Sr ages and previously published K/Ar ages to the sequence of events as determined from detailed structural studies. According to this interpretation, Amisk volcanism began approximately 1865 m.y. ago, and the Hudsonian Orogeny ended approximately 1800 m.y. ago.

Densities of Precambrian rocks of the Amisk Lake – Flin Flon area. A detailed study

Densities were determined for 1855 fresh bedrock samples taken from an area of about 110 sq. miles (285 km2) in east-central Saskatchewan. Average results for the region are as follows[Formula: see text]In this area, density depends primarily on the mineral composition of the rocks because their porosity is insignificant. However, the mineral composition varies widely for many reasons. Metamorphism has resulted in significant changes in rock densities because some low density minerals such as bytownite are altered to high density minerals such as zoisite. Conversely, olivine and some pyroxene are changed to low density serpentine. The density measurements are used to indicate possible subdivisions of the Amisk Group of meta-volcanic rocks. As a result, certain areas are recommended for mineral prospecting.Evidence is presented to show that some basic intrusions have increased the density of their wall rocks by metamorphism.The Bouguer gravity field in this area is closely correlated with the densities of outcropping rocks. The shape and depth of some rock units are estimated from the gravity. All the outcropping rock units extend less than 5 km in depth and some are very shallow.