Sharbot Lake Research Articles

Importance of growth rate on mercury and polychlorinated biphenyl bioaccumulation in fish.

To evaluate the effect of fish growth on mercury (Hg) and polychlorinated biphenyl (PCB) bioaccumulation, a non-steady-state toxicokinetic model, combined with a Wisconsin bioenergetics model, was developed to simulate Hg and PCB bioaccumulation in bluegill (Lepomis macrochirus). The model was validated by comparing observed with predicted Hg and PCB 180 concentrations across 5 age classes from 5 different waterbodies across North America. The non-steady-state model generated accurate predictions for Hg and PCB bioaccumulation in 3 of 5 waterbodies: Apsey Lake (ON, Canada), Sharbot Lake (ON, Canada), and Stonelick Lake (OH, USA). The poor performance of the model for the Detroit River (MI, USA/ON, Canada) and Lake Hartwell (GA/SC, USA), which are 2 well-known contaminated sites with possibly high heterogeneity in spatial contamination, was attributed to changes in feeding behavior and/or prey contamination. Model simulations indicate that growth dilution is a major component of contaminant bioaccumulation patterns in fish, especially during early life stages, and was predicted to be more important for hydrophobic PCBs than for Hg. Simulations that considered tissue-specific growth provided some improvement in model performance particularly for PCBs in fish populations that exhibited changes in their whole-body lipid content with age. Higher variation in lipid growth compared with that of lean dry protein was also observed between different bluegill populations, which partially explains the greater variation in PCB bioaccumulation slopes compared with Hg across sampling sites. Environ Toxicol Chem 2018;37:1655-1667. © 2018 SETAC.

Steady and non-steady state kinetics describe polychlorinated biphenyl bioaccumulation in natural populations of bluegill (Lepomis macrochirus) and cisco (Coregonus artedi)

This study investigated polychlorinated biphenyl (PCB) bioaccumulation patterns across age classes of bluegill ( Lepomis macrochirus ) and cisco ( Coregonus artedi ) collected from Sharbot Lake, Ontario. For bluegill, lipid normalized concentrations of PCB congeners of log Kow < 6.8 did not demonstrate any significant increases across individuals 2–5 years of age. In similarly aged cisco, however, significant age-related increases in lipid normalized PCB concentrations were observed for the majority of these congeners. For PCBs of log Kow > 6.8, these congeners demonstrated significant and similar age-related fugacity increases in both species. These patterns indicated that the bioaccumulation of less hydrophobic PCB congeners in bluegill suggest quicker growth kinetics and demonstrate the potential of this species to achieve steady state within their lifetime. In contrast, PCB bioaccumulation patterns in cisco demonstrated that biomagnification and non-steady state kinetics better reflect the capacity of this species to bioaccumulate PCBs. These results demonstrated that for pollutants of log Kow < 6.8, growth dilution and age-specific metabolic rates are critical for understanding their bioaccumulation by freshwater fish. However, for increasingly hydrophobic pollutants, their bioaccumulation reflects the biology and ecology of these species in their respective warm- and cold-water habitats.

Delineation of isograds in siliceous dolomitic marbles along the Sharbot Lake – Frontenac terrane boundary of the Grenville Province, southeastern Ontario

This study presents details of the mineralogy and petrology of siliceous, dolomitic marbles of the Sharbot Lake domain along the Frontenac terrane boundary in the Grenville Province of southeastern Ontario. The location of four mineral isograds in the marble and the related univariant reactions were identified in the Almonte – Carleton Place area. Delineation of the isograds is based on detailed mapping, petrographic analysis of coexisting mineral assemblages, and a polybaric T–XCO2diagram calculated using thermobarometric data from associated gneissic rocks, where T is temperature and X is fluid composition. The T–X section is based on a field gradient of 32 °C/km. The isograds correspond to the first appearance of tremolite (5 dolomite + 8 quartz + H2O = tremolite + 3 calcite + 7 CO2), diopside (tremolite + 3 calcite + 2 quartz = 5 diopside + 3 CO2 + H2O), diopside + dolomite (tremolite + 3 calcite = dolomite + 4 diopside + H2O + CO2), and forsterite (diopside + 3 dolomite = 2 forsterite + 4 calcite + 5 CO2). Mineral assemblages above and below each isograd are described and relevant examples are shown. Results of this study are consistent with a mixed volatile fluid of a uniform composition during mid- to upper amphibolite-facies metamorphism.

Crystal chemistry of the natrojarosite-jarosite and natrojarosite-hydronium jarosite solid-solution series: A synthetic study with full Fe site occupancy

Members of the natrojarosite-hydronium jarosite [(Na,H 3 O)Fe 3 (SO 4 ) 2 (OH) 6 ] and jarosite-natrojarosite [(K,Na)Fe 3 (SO 4 ) 2 (OH) 6 ] solid-solution series were synthesized and investigated by Rietveld analysis of X-ray powder diffraction data. The synthesized samples have full Fe occupancy, where in many previous studies there were significant vacancies in the B site. Well-defined trends can be seen in the unit-cell parameters across the solid-solution series in the synthetic samples. The majority of the samples in this study were directly synthesized under hydrothermal conditions at 140 °C. End-member natrojarosite was synthesized using a two-step method, where the initial sample was heated in a 1.0 m H 2 SO 4 −0.5Na 2 SO 4 solution at 200 °C for 3 days, yielding a sample with 100% Na occupancy. Many of the samples were initially zoned and required grinding and re-heating in the reactant solution for homogenization. Substitution of H 3 O and K into natrojarosite changes unit-cell parameters in a linear fashion. The unit-cell parameters presented here are significantly different than the majority of previous studies on synthetic samples, as samples in the current study have full Fe occupancy and the Na-K jarosite series has no H 3 O substitution in the A site. Substitution in the A site mainly affects unit-cell parameter c with little change in a . As Na occupancy increases there is a decrease in A-O2 and A-O3 distances and a consequent increase in Fe-O2 and Fe-O3 distance leading to an overall decrease in unit-cell parameter c in both the Na-H 3 O and Na-K jarosite series. The synthetic samples are compared to natural samples from mine waste deposits in Rio Tinto (Huelva, Spain), Ely Mine (Vermont), and a mineral collecting locality near Sharbot Lake (Ontario), as well as natural and synthetic samples documented in the literature. Based on unit-cell parameters many of the natural samples appear to have full Fe occupancy and correlate well with the synthetic samples from this study. The infrared spectra of the samples were analyzed, and there is a gradual change in the spectral features across the solid-solution series between end-members. The results from this study will aid in the interpretation of the possible chemical compositions of natural jarosite group minerals in mine waste and on Mars.

Paleomagnetism of the Central Metasedimentary Belt, Grenville Province, Ontario: Differential uplift or collision of terranes?

A paleomagnetic traverse across the Central Metasedimentary Belt of the Precambrian Grenville Province in southern Ontario, linked to an earlier study of the adjoining Central Gneiss Belt, sampled 54 sites in the Frontenac, Sharbot Lake, Mazinaw, Elsevir and Bancroft terranes. 40Ar/ 39Ar thermochronometry indicates differential unroofing of these terranes, with slow cooling (1.0–1.5 °C/Ma) along parallel temperature–time paths. Presently exposed rocks cooled through ≈ 500 °C around 1100 Ma (Frontenac), 1010 Ma (Elsevir), 960 Ma (Central Metasedimentary Belt boundary zone) and 930 Ma (Mazinaw) [Cosca, M.A., Sutter, J.F., Essene, E.J., 1991. Cooling and inferred uplift/erosion history of the Grenville orogen , Ontario: constraints from 40Ar/ 39Ar thermochronology, Tectonics 10 (1991) 959–977]. 1100–930 Ma was a time of rapid paleolatitude shift but the various terranes do not have distinct paleomagnetic signatures. Frontenac, Sharbot Lake and Mazinaw terranes have similar reverse-polarity paleopoles in the central part of the Grenville polar wander track. Frontenac and Sharbot Lake normal poles are typical ≈ 1000 Ma Grenville A poles, while Mazinaw normal poles seem to be somewhat older. Frontenac poles bear no resemblance to 1100 Ma Keweenawan poles. The Elsevir pole and some Frontenac poles resemble Grenville B poles (600–800 Ma). Although 40Ar/ 39Ar hornblende ages were reset thermally between 1100 and 930 Ma during differential uplift of terranes, the terranes were not remagnetized at these same times. Frontenac, Sharbot Lake and Mazinaw terranes (like much of the boundary zone and the Central Gneiss Belt) seemingly were all remagnetized between ≈ 1000 and ≈ 900 Ma, perhaps by a widespread thermochemical event. A 600–800 Ma event affected Elsevir and part of the Frontenac, at the western and eastern extremes of the traverse, but not areas between. The lack of correlation between 40Ar/ 39Ar ages and paleomagnetic results for the Frontenac, Sharbot Lake, Mazinaw and Elsevir casts doubt on the thermochronometric age calibration of the Grenville apparent polar wander path, which is based on the assumption that the magnetic and isotopic systems respond in similar ways to slow cooling during uplift so that their blocking temperatures can be directly compared. The most discordant results – those of the Frontenac – could be reconciled if the Frontenac terrane acquired its A magnetization around 1100 Ma before it docked with Laurentia. This is geologically plausible but the match between the Frontenac poles and 900–1000 Ma Grenvillian poles seems too close to be coincidental.

A comparative study of wollastonite skarn genesis in the Central Metasedimentary Belt, southeastern Ontario, Canada

Potentially economic wollastonite-rich skarns are widespread in the Central Metasedimentary Belt of southeastern Ontario, Canada. Their genesis is evaluated through a comparative study of: the Platinova skarn (ca. 4 Mt grading 35% wollastonite), hosted by greenschist facies marble in the Elzevir terrane; the Olden skarn (ca. 2.8 Mt; 35%) in amphibolite facies marble of the Sharbot Lake terrane; and the St. Lawrence skarn (ca. 9 Mt; 41%) in granulite facies strata of the Frontenac terrane. The protolith for all of the wollastonite skarns was calcitic marble, locally containing impurities, but dolomitic marble may have been present at the St. Lawrence skarn. Each skarn is contiguous with an intrusive complex ranging from gabbro to granite in composition, and displaying megascopic fabrics indicative of magma commingling and mixing. The plutons are, however, of different ages and exhibit different geochemical characteristics. In each skarn, wollastonite is associated with varying proportions of diopside–hedenbergite and grossular–andradite. Skarn development is ascribed to the incursion of magmatogene, silica-rich, CO 2-poor ( X CO 2 between 0.1 and 0.3) fluids, rather than to regional metamorphism, and pressures varying between 200 MPa at Platinova and 350 MPa at Olden, at temperatures ca. of 500 to 650 °C. The Mountain Grove pluton has an U–Pb (zircon) age of 1153 ± 2 Ma. Hornblende and biotite from the same sample gave 40Ar– 39Ar plateau dates of 1058 ± 14 and 1047 ± 4 Ma, respectively, and the Olden skarn has been dated at 1074 ± 5 Ma ( 40Ar– 39Ar, phlogopite). These 40Ar– 39Ar dates are interpreted to record resetting by the contiguous 1070 Ma McLean pluton. U–Pb on titanite and 40Ar– 39Ar on amphibole separates from the St. Lawrence skarn yield 1147 ± ca. 8 and 1159 ± 6 Ma dates, respectively, similar to the U–Pb badelleyite age of the adjacent 1167 ± 2 Ma Leo Lake pluton. The age similarities between the skarns and the adjacent plutonic rocks are permissive evidence for a genetic link. Evidence of magma mixing and commingling in all the plutons contiguous with the wollastonite skarns may indicate that the concentration and egress of magmatogene brines at pressures locally attending 400 MPa was facilitated by thermal and compositional perturbation in the parental magma chambers.

Genesis of the Olden wollastonite skarn, Sharbot Lake domain, Central Metasedimentary Belt, Grenville Province, southeastern Ontario, Canada

With a resource of ∼2.8 Mt at 30%–35% wollastonite occurring at a depth of about 75 m, the Olden (formerly Hawley) prospect is the largest of a swarm of skarns hosted by amphibolite facies, dominantly calcitic marble that occurs adjacent to and as inliers within the Mountain Grove pluton. The post-kinematic intrusion comprises units with a wide compositional range from anorthositic gabbro to alkali-feldspar granite and syenite and widely exhibits megascopic fabrics recording magma comingling and mixing. Isotope dilution – thermal ionization mass spectrometry (ID–TIMS) dating of zircon separates from a hornblende diorite unit yields a 207Pb–206Pb age of 1153 ± 2 Ma, significantly older than the contiguous 1070 ± 3 Ma McLean granite. Al-in-hornblende geobarometry on several Mountain Grove units indicates that the intrusion crystallized at pressures of 250–470 MPa, equivalent to mesozonal depths of 10–15 km. The main exoskarn body, ∼200 m long and up to 50 m wide, is dominated by wollastonite, clinopyroxene (Di73–94Hd2–19), and calcic garnet (Gr52–83And12–37) and ranges from massive to podiform. The eastern termination exhibits rhythmically alternating wollastonite- and calcite-rich layers, 10 cm wide and locally with chevron-shaped crenulations. These layers bear no relationship to bedding or metamorphic foliation and are interpreted as “wrigglitic,” i.e., they are a record of a metasomatic front that migrated. Veins of garnet–pyroxene–vesuvianite cut the main exoskarn. Retrograde phlogopite-rich skarns, with erratic serpentine and brucite, contain variable sphalerite and pyrite. Restricted pyroxene–garnet (–wollastonite–scapolite) endoskarn is developed in intrusive rocks contiguous with the exoskarn. Skarn development is ascribed to H2O-rich (XCO2 < 0.3) magmatogene brines and high temperatures (T = 500–650 °C), which caused intense Si, Al, and Fe metasomatism of the marbles, hydrothermal activity taking place at considerable depth. The occurrence of wollastonite around the periphery of the small Long Lake sphalerite deposit, restricted to a marble roof pendant in the Mountain Grove pluton 2.1 km east-northeast of the Olden prospect, indicates that this base-metal mineralization may be an exoskarn, rather than metamorphosed Mississippi Valley type. Incremental-heating 40Ar–39Ar dating of hornblende and biotite from the Mountain Grove diorite yields plateau ages of 1058 ± 14 and 1047 ± 4 Ma, respectively, and an exoskarn phlogopite age of 1074 ± 5 Ma. A genetic relationship between hydrothermal activity and the McLean pluton cannot be ruled out, but a parental role for the older Mountain Grove pluton is favoured on the basis of the close areal relationships of skarn bodies and that intrusion.

The geochemical nature of the igneous rocks of the Sharbot Lake domain, Central Metasedimentary Belt, Ontario

Two bimodal mafic-silicic suites of igneous rocks, the Sharbot Lake volcanic rocks and the Lavant Igneous Complex, are identified geochemically in the Sharbot Lake domain of the Central Metasedimentary Belt in Ontario, and their genesis and thermotectonic environment are evaluated. The Sharbot Lake volcanic rocks comprise a series of basalts characterized by light rare-earth element (LREE) depletion and relatively high concentrations of Σ Fe2O3, TiO2, MnO, V, and Y, together with rhyolites and silicic pyroclastic rocks. They are intruded by rocks of the Lavant Igneous Complex, which comprises tholeiitic gabbros characterized by LREE enrichment and low concentrations of Σ Fe2O3, TiO2, MnO, V, and Y, and granitoid rocks. The trace element signatures of the mafic rocks of the Sharbot Lake volcanic sequences are most like those of back-arc tholeiitic basalts, and those of the Lavant Igneous Complex are comparable to those of low-K tholeiitic basalt suites. The trace element signatures of the silicic rocks associated with both suites are typical of those formed by crustal melting. Volcanic sequences with trace-element signatures very similar to those of the Sharbot Lake suites have been previously described in the Belmont and Grimsthorpe domains of the Central Metasedimentary Belt, suggesting that the three domains all belong to the Bancroft – Elzevir – Mazinaw – Sharbot Lake superterrane. The lithological, structural, and igneous characteristics of this superterrane suggest that it represents part of a complex back-arc basin underlain by areas of rifted and attenuated continental crust and oceanic crust.

The geochemical nature of the igneous rocks of the Sharbot Lake domain, Central Metasedimentary Belt, Ontario

The geochemical nature of the igneous rocks of the Sharbot Lake domain, Central Metasedimentary Belt, Ontario

Sharbot Lake terrane and its relationships to Frontenac terrane, Central Metasedimentary Belt, Grenville Province: new insights from U–Pb geochronology

The Sharbot Lake terrane of the Central Metasedimentary Belt in Ontario comprises marbles, minor tholeiitic basalts and siliciclastic rocks, metamorphosed at low to moderate degrees, and is intruded by several suites of mafic to felsic plutons. Gabbroic and associated monzogranitic phases of the Lavant complex in northwestern parts of the terrane yield ages of 1224 ± 2 Ma for zircon and monazite, and 1221–1211 Ma for titanite. The Wolf Grove structure, a gneissic domain in the northeastern part of the area, was migmatized and intruded by granites at 1168 Ma prior to its tectonic juxtaposition on amphibolites and marbles of the Sharbot Lake terrane. Correlative events recorded by gneiss, quartzite, and marble from Carleton Place farther east stress the strong affinity of the Wolf Grove structure with rocks of the Frontenac terrane. The 1156 ± 2 Ma posttectonic Maberly stock intrudes rocks near the boundary zone between the Frontenac and Sharbot Lake terranes, suggesting that the two terranes were linked by 1156 Ma. The distribution of U–Pb ages for titanite, monazite, and rutile throughout the area emphasizes the distinctive metamorphic evolution characterizing different domains of the region, documents the lack of 1168 Ma metamorphic overprint in western domains, records the main 1168 Ma high-grade event and slightly younger subsidiary events in eastern domains, and indicates local resetting events. The combined data underline the geological complexity of the eastern Central Metasedimentary Belt, confirming the existence of significant compressional and metamorphic events in the period 1170–1160 Ma.

Suturing and extensional reactivation in the Grenville orogen, Canada

Sutures are zones of weakness within orogenic belts that have the potential to become reactivated during orogenic evolution. The Robertson Lake shear zone marks a major tectonic boundary in the southeastern Grenville orogen of Canada that has been intermittently active for at least 130 m.y. The shear zone played a major role in the compressional stage of the orogenic cycle as well as during postorogenic collapse. The zone separates the Elzevir terrane to the west and the Frontenac terrane to the east. Sphene ages (U-Pb) indicate that these two terranes have distinct tectonothermal histories and that the shear zone represents a “cryptic suture.” In its current state, the shear zone is a low angle (30°ESE dip) plastic to brittle extensional shear zone that separates the Mazinaw (footwall) and Sharbot Lake (hanging wall) domains. Integration of structural, metamorphic, and chronologic data leads to a model that describes the complete evolution of this fundamental tectonic boundary that evolved from an early compressional zone (ca. 1030 Ma) to a late extensional zone (until at least 900 Ma).

Listric normal faulting during postorogenic extension revealed by 40Ar/39Ar thermochronology near the Robertson Lake shear zone, Grenville orogen, Canada

The Robertson Lake shear zone is a major plastic to brittle extensional shear zone in the Grenville orogen that bounds the Mazinaw and Sharbot Lake domains and provides information on the style of late extension and the unroofing history of the orogen. Argon isotope data were collected from hornblende and micas to determine 40Ar/39Ar ages, constrain the temperature‐time histories of these two domains, and infer the unroofing history of the region. Hornblende cooling ages across the Mazinaw domain (footwall) show little variation, indicating uniform unroofing of the footwall since 950 Ma. Phlogopite, muscovite, and biotite cooling ages of the footwall are 924 to 890 Ma. The cooling history of the Mazinaw domain is characterized by slow cooling after peak metamorphism (circa 1000 Ma), accelerated cooling (4°–5°C/m.y.) from 950 Ma to 890 Ma, and an average cooling rate of ∼1°C/m.y. to circa 590 Ma, when these rocks were at or near the surface. The cooling history of Sharbot Lake (hanging wall) domain is drastically different than that of the Mazinaw domain. Hornblende and biotite cooling ages in the central portion of the domain are 1009 and 969 Ma, respectively, indicating a cooling rate of 5°C/m.y. after slow cooling from metamorphic temperatures. Biotite and phlogopite cooling ages determined from samples located at different distances from the shear zone do not lie along the same cooling curve, indicating that the cooling history varied across the domain. Cooling rates in the hanging wall adjacent to the shear zone are low (2°C/m.y.). A biotite cooling age (1029 Ma) and preservation of an amphibole growth age (1205 Ma) in the hanging wall adjacent to the shear zone reflect shallow crustal levels for this sample since 1205 Ma. These data indicate that the hanging wall away from the shear zone was unroofed from deeper crustal levels faster and much later than the hanging wall adjacent to the shear zone. The varied cooling histories across the region are resolved by listric normal faulting that lead to uniform unroofing of the footwall and differential unroofing across the hanging wall due to rotation during fault displacement.

Differential unroofing within the central metasedimentary Belt of the Grenville Orogen: constraints from 40Ar/39Ar thermochronology

An 40Ar/39Ar thermochronological investigation of upper greenschist to granulite facies gneiss, amphibolite and marble was conducted in the Central Metasedimentary Belt (CMB), Ontario, to constrain its cooling history. Incremental 40Ar/39Ar release spectra indicate that substantial differential unroofing occurred in the CMB between ∼ 1000 and ∼ 600 Ma. A consistent pattern of significantly older hornblende and phlogopite 40Ar/3Ar cooling ages on the southeast sides of major northeast striking shear zones is interpreted to reflect late displacement due to extensional deformation. Variations in hornblende 40Ar/39Ar age plateaus exceeding 200 Ma occur over distances less than 50 km with major age discontinuities occurring across the Robertson Lake shear zone and the Sharbot Lake mylonite zone which separate the Sharbot Lake terrane from the Elzevir and Frontenac terranes. Extensional displacements of up to 14 km are inferred between the Frontenac and Elzevir terranes of the CMB. No evidence for significant post argon-closure vertical displacement is indicated in the vicinity of the Perth Road mylonite within the Frontenac terrane. Variations of nearly 100 Ma in phlogopite 40Ar/39Ar plateau ages occur in undeformed marble on either side of the Bancroft Shear Zone. Phlogopites from sheared and mylonitized marble within the shear zone yield 40Ar/39Ar diffusional loss profiles, but have older geologically meaningless ages thought to reflect incorporation of excess argon. By ∼ 900 Ma, southeast directed extension was occurring throughout the CMB, possibly initiated along previous zones of compressional shearing. An easterly migration of active zones of extension is inferred, possibly related to an earlier, overall easterly migration of active zones of regional thrusting and easterly migration of an ancient subduction zone. The duration of extensional shearing is not well constrained, but must have ceased before ∼ 600 Ma as required by the deposition of overlying undeformed Cambrian and/or Ordovician sedimentary rocks.

Cooling and inferred uplift/erosion history of the Grenville Orogen, Ontario: Constraints from 40Ar/39Ar thermochronology

Stepwise 40Ar/39Ar degassing experiments of 57 mineral separates of hornblende, muscovite, biotite, and perthitic microcline have been used in conjunction with petrologic observations to place regional constraints on the postmetamorphic cooling and the inferred uplift and erosion history of the Grenville Orogen in Ontario. The 40Ar/39Ar data support an interpretation of slow, nearly uniform cooling (1°–4°C/m.y.) from temperatures of ˜500°C to below ˜150°C. In the Central Gneiss Belt (CGB) hornblendes cooled through Ar closure between 930 and 1025 Ma, whereas in the Central Metasedimentary Belt (CMB) hornblendes record the following range in 40Ar/39Ar cooling ages: 1104 Ma in the Frontenac terrane, 1007–1067 Ma in the Sharbot Lake terrane, 919–1026 Ma in the Elzevir terrane, and 972 Ma in the Central Metasedimentary Belt Boundary Zone. Regional uplift/erosion rates of 0.03–0.14 km/m.y. have been estimated for the Grenville Orogen in Ontario based on the 40Ar/39Ar data, a model retrograde P‐T path for rocks of the CGB, and an upper time constraint provided by flat, overlying Cambrian and Ordovician sediments. These erosion rates are consistent with rates estimated for other Proterozoic or Archean granulite terranes but are an order of magnitude slower than active orogens such as the Alps and Himalayas. A regular variation in hornblende 40Ar/39Ar cooling ages is observed in rocks that traverse highly strained often mylonitic shear zones that separate the four major terranes of the CMB. The pattern of 40Ar/39Ar ages is interpreted to reflect late‐tectonic extension, consistent with field observations in the Central Metasedimentary Belt Boundary Zone and elsewhere in the CMB. Up to 13 km of vertical displacement is inferred for some rocks in the CMB between the time they cooled below closure to argon diffusion in hornblende (˜500°C) and their exposure at the surface (˜25°C).

Alteration of Phlogopite to Corrensite at Sharbot Lake, Ontario

AbstractA low-charge corrensite, i.e., a regular 1:1 interstratified smectite/chlorite was found in veins and fissures of an extensively fractured dolomite south of Perth, Ontario, Canada. Total chemical analysis indicated that the mineral was trioctahedral, having a structural formula corresponding to: (Ca0.17)(Mg7.36Al0.90Fe3+ 0.45Fe2+ 0.42)VI(Si6.06Al1.94)IVO20(OH)10.The coefficient of variation (CV) of the d(00l) spacings calculated for the mineral from X-ray powder diffraction data was 0.42, well below the maximum recommended value for corrensite, 0.75. The corrensite coexists with phlogopite, which is present as small (~0.5 mm) crystals throughout the rock and locally as large (~5 cm) crystals in pegmatitic veins. Microscopic observatiofls of large phlogopite crystals partially altered to corrensite suggest that corrensite formed at the expense of phlogopite by hydrothermal alteration.

Rhigonema infecta (Leidy, 1849) Christie & Cobb, 1927 and the systematic position of the Rhigonematidae sensu Th�odorid�s, 1965

Rhigonema infecta (Leidy, 1849) Christie & Cobb, 1927, a member of the family Rhigonematidae sensu Theodorides, 1965, is redescribed from the diplopod Narceus annularis from Sharbot Lake and Long Point, Ontario, Canada. R. infecta is most similar to R. subtruncatum Dollfus, 1952 but differs from this species in possessing four rather than three post-cloacal papillae in the male. Rhigonematids have been affiliated with members of the order Oxyurida by most authors but study of R. infecta suggests that rhigonematids should be placed in their own order, the Rhigonematida. Members of the order Rhigonematida are characterized by: two spicules in the male; H-shaped excretory system; are round to oval sperms; thick and smooth egg-shell; apparently lacking a uterine layer; and development in the egg involving no moults and resulting in a long, thin, coiled larva. In contrast, oxyuridans have a single spicule, the excretory system is X-shaped, the sperm is comet-shaped and the egg-shell has a prominent striated uterine layer. Development in the egg involves at least one and probably two moults and results in a short, robust, uncoiled larva. ac]19810310

Occurrence of the Ptarmigan near Sharbot Lake

Occurrence of the Ptarmigan near Sharbot Lake