Kirkland Lake Research Articles

U–Pb geochronology of the eastern Abitibi Subprovince. Part 2: Noranda – Kirkland Lake area

U–Pb zircon ages for 15 volcanic and plutonic units in the Noranda and Kirkland Lake areas help constrain the history of volcanism, plutonism, sedimentation, and deformation in the south-central part of the Abitibi belt. Volcanism occurred over an interval of at least 50 Ma, beginning with the deposition of the volcanic and volcaniclastic units within the Pacaud Structural Complex at 2747 Ma. Following a period of apparent quiescence, magmatism resumed at 2730–2725 Ma with the eruption of volcanic rocks in the Normétal and Lac Abitibi area. From 2715 until about 2698 Ma, volcanism occurred sporadically throughout much of the area, culminating in the eruption of the Blake River Group from 2703 to 2698 Ma. Several large intrusive bodies yield ages that indicate that they are plutonic equivalents of the Blake River Group. Plutons that are considered to have been emplaced during the Kenoran orogeny give ages that are only slightly younger than the youngest volcanic units of the Blake River Group, emphasizing the very rapid onset of Kenoran deformation following the cessation of volcanic activity.The Cléricy syenite, dated at 2682 ± 3 Ma, postdates the main period of Kenoran deformation in this area and intrudes sedimentary rocks of the Kewagama Group which contain detrital zircons as young as 2687 Ma. These data suggest that the Kewagama Group is the same age as late sedimentary sequences such as the Timiskaming Group and may have been deposited in a similar tectonic setting.

40Ar/39Ar age constraints on the thermal history of the Archean Abitibi greenstone belt and the Pontiac Subprovince: implications for terrane collision, differential uplift, and overprinting of gold deposits

40Ar/39Ar mineral age spectra of granitic and metamorphic rocks, in conjunction with existing conventional zircon geochronology, indicate that at least two major late Archean thermal events affected tectonic blocks of the Abitibi Southern Volcanic Zone (SVZ) and the juxtaposed Pontiac Subprovince. The earlier thermal activity (2690–2670 Ma) was accompanied by the intrusion of voluminous syntectonic plutons and caused low-pressure, greenschist-facies metamorphism in the SVZ and intermediate-pressure metamorphism in the Pontiac Subprovince. The second thermal event (2660–2630 Ma) was coeval with the emplacement of syncollisional, S-type garnet–muscovite granites in the Pontiac Subprovince and the higher grade Lacorne block of the Abitibi SVZ, and reset the K–Ar systems in preexisting rocks.Magmatic amphibole from the syntectonic Round Lake batholith (~2695 Ma U–Pb zircon age) of the Abitibi SVZ has a slightly disturbed Ar release spectrum with an upper plateau age of 2669 ± 6 Ma, signifying that the low-grade Round Lake block cooled through 500 °C at a slow rate. Amphiboles in syntectonic batholiths from the higher grade Lacorne block and the Pontiac Subprovince have substantially disturbed Ar release spectra, with high-temperature steps giving apparent ages of 2681 ± 4 to 2679 ± 4 Ma; these overlap zircon ages of 2690–2670 Ma, indicating relatively rapid cooling through the amphibole blocking temperature.Metamorphic rocks (amphibolites) from the Lacorne block and the Pontiac Subprovince contain amphiboles with substantially disturbed 40Ar/39Ar release spectra and higher temperature step ages of 2677 ± 6 to 2670 ± 5 Ma, representing the minimum formation age. Fine-grained muscovite and biotite (180–250 μm) from mica schists also have disturbed Ar release patterns, but much younger apparent ages at high-temperature release steps (2581–2523 Ma for muscovite, 2562–2455 Ma for biotite) than the amphiboles.Coarse-grained muscovites from pegmatites associated with syncollision, S-type garnet–muscovite granites (2644 ± 13 Ma) in the Lacorne block and Pontiac Subprpvince show undisturbed or slightly disturbed Ar release spectra and magmatic δ18Oquartz–muscovite = 1.8–3.5‰, with total integrated ages of 2615 ± 10 to 2594 ± 7 Ma (Lacorne) and 2572 ± 6 Ma (Pontiac), respectively, indicating different uplift rates for the two terranes. Amphiboles (~2680 Ma) from metamorphic rocks in the Lacorne block and Pontiac Subprovince and from the Round Lake batholith are disturbed, whereas coarse-grained muscovites from the pegmatites (2644 ± 13 Ma) are relatively undisturbed. This indicates that the disturbance of the amphiboles may have been caused by a thermal event that preceded or was coeval with the emplacement of the garnet–muscovite granite suite, rather than being a grain-size effect.These results are consistent with a model whereby early subduction of oceanic lithosphere beneath the Abitibi SVZ (2740–2680 Ma), and separately under the Pontiac Subprovince, was responsible for syntectonic batholiths and the first thermal event. Collision with the Abitibi SVZ and local underthrusting of the Pontiac Subprovince at about 2670–2630 Ma caused the second major thermal event and partial melting of the underthrust Pontiac-type metasediments to form the garnet–muscovite granites. Later differential uplift exposed the entire Pontiac Subprovince and the Lacorne block as a tectonic window of underthrust Pontiac in the Abitibi SVZ. Resetting of several isotopic systems, including apparent younger ages of gold mineralization, is probably related to this late collisional, tectonothermal overprinting event. Fluid and (or) thermal events at ≥275 °C influenced the Kirkland Lake – Cadillac fault down to 2513 ± 10 Ma, as indicated by a plateau age of postkinematic biotite in the fault. The fault was intermittently reactivated over a period of 440 Ma, from ~2690 Ma to ≤2250 Ma.

Geochemistry and clast lithology as an aid to till classification, Matheson, Ontario, Canada

The Matheson area of northeastern Ontario is of great interest for mineral exploration because of its geological similarities with the adjacent Timmins, Kirkland Lake and Larder Lake gold camps. Exploration in the area is hampered by an extensive and thick glacial cover. For this reason, till geochemistry has become an important exploration method. The use of till geochemistry, however, is made more difficult by a complex glacial stratigraphy consisting of multiple till sheets related to more than one ice advance and transport direction. A thick cover of glaciolacustrine sediments limits the examination and documentation of this complex stratigraphy. The objectives of this study were: (1) to determine the usefulness of the geochemical and lithological characteristics of till in defining overburden stratigraphy; (2) to determine the relative transport distances of till: and (3) to reconstruct ice flow patterns. These objectives were carried out through the examination of the characteristics of till samples from Ontario Geological Survey sonic overburden drill holes. Composition of the bedrock sources appears to be the major controlling factor on till composition such that tills can be divided into two distinct types: felsic and mafic. Felsic tills contain a greater proportion of felsic intrusive pebbles and are characterized by higher concentrations of SiO 2, Na 2O, K 2O and U. In contrast, mafic tills contain a greater proportion of metavolcanic pebbles and are characterized by higher concentrations of Cu, Zn, Ni, Co and As. Felsic tills were derived predominantly from the granitic and gneissic bedrock north of the study area whereas mafic tills were derived mainly from the more local, mafic volcanic greenstone bedrock. Thus, mafic tills more accurately reflect the composition of the local bedrock and thus, are a more desirable sampling medium. The uppermost (Matheson) till unit in the area generally has a more felsic composition while underlying till units commonly have a more mafic composition. The thickest and most complex sequences commonly contain older tills that are more likely to be mafic in composition. This information improves the present understanding of the Quaternary stratigraphy and can be used to increase the effectiveness of drift prospecting in the Matheson area.

Repetitive cyclical volcanism in the Late Archean Larder Lake Group near Kirkland Lake, Ontario: implications of geochemistry on magma genesis

The Larder Lake Group is the basal stratigraphic unit of the Upper Supergroup, the younger magmatic cycle of the Abitibi Greenstone Belt of the Superior Province. Three major suites of extrusive and hypabyssal rocks are recognized: (a) a high-magnesian suite of komatiite to Mg-basalt; (b) a tholeiitic series with Mg-rich and Fe-rich basaltic varieties, and (c) a low-magnesian series of basalt to rhyodacite. Fourteen such subcycles were recognized in the Boston Iron Range south of Kirkland Lake, and are grouped in four major stratigraphic intervals. The entire Larder Lake Group magma series evolved from a peridotitic mantle source through various stages of partial melting and fractional crystallization. LREE-enriched tholeiites are interpreted as the initial products of low degrees of melting of a chondritic mantle. Both magnesian suites show LREE-depleted patterns and identical Zr/Y and Zr/Ti ratios, suggesting that their parental magmas were generated by partial melting of the residual mantle from which the tholeiitic melts had been previously derived. The low-magnesian suite, which is genetically related to a komatiitic magma series, includes compositions as silicic as rhyodacite.

Ore-microscopic and geochemical characteristics of gold-tellurides-sulfide mineralization in the Macassa Gold Mine, Abitibi Belt, Canada

The Macassa Gold Mine is the only operational mine (Lac-Minerals Ltd., Macassa Division) of seven original gold producers in the Kirkland Lake camp of northern Ontario, Canada. The gold deposit is in Archaean volcanic and sedimentary rocks which have been intruded by a composite syenite stock. The mineralization has taken place in two stages. The first stage is not gold bearing but involves pyritization and concomitant development of titanium phase minerals (leucoxene, rutile) and hematite. It is mainly associated with carbonatization, silicification and hematitization marked by Ba, Sr and Rb enrichment. In contrast to this, the quartz vein-type mineralization is associated mainly with later silicification and enrichment with tellurium, lead, silver, gold and copper. It is relatively depleted in Sr, Ba and Rb. The ore mineralogical assemblages in the second stage include pyrite, chalcopyrite, petzite, altaite and native gold. Geochemical and petrographic evidence indicate that the reddened wall rocks (hematitized) and reddened fragments are neither related with nor contain any gold. Therefore, hematitization and the presence of barium, in this case in K-feldspars, could not be considered as the sole evidence to suggest a magmatic oxidizing fluid model for the genesis of Macassa gold deposit. Regarding the metals transport, tellurides and thiocomplexes are considered as the important carriers of gold and silver. Hence, fugacity of tellurium and sulphur controlled the precipitation of gold in the Macassa gold deposit.

The forest management decision support system project

The focus of a decision support system is much different from Management Information Systems (MIS) and data-based "decision support systems". Decision support systems, as defined by the authors, focus on decisions and decision makers, and on information. Technology is treated as a tool and data as the raw material. In many traditional systems the focus is on the technology, and the data is the "information", while decision makers are, to some extent, externalized.The purpose of the Forest Management Decision Support System (FMDSS) project is to develop a set of software tools for creating forest management decision support systems. This set of tools will be used to implement a prototype forest management decision support system for the Plonski forest, near Kirkland Lake, Ontario.There are three critical ingredients in building the FMDSS, these are: (1) knowledge of the decision making process, (2) knowledge of the forest, and (3) the functionality of underlying support technology. The growing maturity of the underlying technology provides a tremendous opportunity to develop decision support tools. However, a significant obstacle to building FMDSS has been the diffuse nature of knowledge about forest management decision making processes, and about the forest ecosystem itself. Often this knowledge is spread widely among foresters, technicians, policy makers, and scientists, or is in a form that is not easily amenable to the decision support process. This has created a heavy burden on the project team to gather and collate the knowledge so that it could be incorporated into the function and design of the system. It will be difficult to gauge the success of this exercise until users obtain the software and begin to experiment with its use.

Age and timing of igneous activity in the Temagami greenstone belt, Ontario: a preliminary report

The southernmost remnants of Archean supracrustal and intrusive rocks in eastern Ontario are exposed through a window in the Early Proterozoic Huronian Supergroup near the town of Temagami. U–Pb zircon ages from this area indicate the presence of some of the oldest felsic magmatism so far discovered in this portion of the Superior Province. The Iceland Lake pluton (2736 ± 2 Ma) and a nearby rhyolite flow ([Formula: see text]) are contemporaneous, which establishes that at least some of the intrusive rocks in the region are synvolcanic and coeval with the oldest volcanic cycle. The youngest plutonic activity is the emplacement of a late rhyolite porphyry dike at 2687 ± 2 Ma, an age that is bracketed by the 2675–2700 Ma emplacement ages of late internal plutons found throughout the Abitibi Subprovince. The 2736 Ma dates, however, are older than the nearest portion of the exposed Abitibi, some 120 km to the north near Kirkland Lake.

Magmatic Oxidation in the Syenitic Murdock Creek Intrusion, Kirkland Lake, Ontario: Evidence from the Ferromagnesian Silicates

The syenitic Murdock Creek intrusion, of late Archean age, lies within one of the major lode gold camps of the world, at Kirkland Lake, Ontario. There is a strong spatial association between syenitic intrusions, gold mineralization, and carbonatization. Hydrothermal fluids that carried the gold had an unusually high oxygen fugacity ($$f_{o_{2}}$$). Notwithstanding a wide range in rock compositions within the intrusion (from clino-pyroxenite to alkali-feldspar syenite), clinopyroxene and biotite have consistently low Fe/(Fe + Mg) and high $$Fe^{3+}/(Fe^{2+} + Fe^{3+})$$ ratios. These compositional features indicate a deficiency of $$Fe^{2+}$$ in the magma during crystallization. Together with the presence of abundant, early-formed magnetite and titanite, this is interpreted to result from an intrinsically high magmatic $$f_{o_{2}}$$ that remained constant during pluton evolution ($$f_{o_{2}} \approx 10^{-12} bars$$). Mineral compositions, proportions of crystallizing mineral phases, and textural features indicate that the pluton formed from a single pulse of already-evolved syenitic magma that fractionally crystallized in situ under low water pressure at mid-crustal depths. The intrinsically oxidized nature of the pluton implies an oxidized source region such as metasomatized upper mantle where partial melting occurred. $$CO_{2}$$-rich fluid or melt was the likely agent for metasomatism. Dissolution and transport of gold is favored by high $$f_{o_{2}}$$ in the fluid phase. The high $$f_{o_{2}}$$ of the syenitic magma suggests a common genetic link between magma generation, $$CO_{2}$$ represented by "carbonatization, and gold-bearing fluids.

U–Pb ages and tectonic significance of late Archean alkalic magmatism and nonmarine sedimentation: Timiskaming Group, southern Abitibi belt, Ontario

The paper presents U–Pb ages for zircons of the calc-alkalic to alkalic igneous suite and associated alluvial–fluvial sedimentary rocks of the Timiskaming Group in the late Archean Abitibi greenstone belt, Superior Province. The Timiskaming Group rests unconformably on pre-2700 Ma komatiitic to calc-alkalic volcanic sequences and is the expression of the latest stages of magmatism and tectonism that shaped the greenstone belt. An age of 2685 ± 3 Ma for the Bidgood quartz porphyry, an age of about 2685–2682 Ma for a quartz–feldspar porphyry clast in a conglomerate, and ages ranging from 2686 to 2680 Ma for detrital zircons in sandstones appear to reflect an early stage in the development of the Timiskaming Group. The youngest detrital zircons in each of three sandstones at Timmins, Kirkland Lake, and south of Larder Lake define maximum ages of sedimentation at about 2679 Ma; the latter sandstone is cut by a porphyry dyke dated by titanite at [Formula: see text], identical to the 2677 ± 2 Ma age for a volcanic agglomerate of the Bear Lake Formation north of Larder Lake. Similar ages have previously been reported for syenitic to granitic plutons of the region. The dominant period of Timiskaming sedimentation and magmatism was thus 2680–2677 Ma. Xenocrystic zircons found in a porphyry and a lamprophyre dyke have ages of 2750–2720 Ma, which correspond to the ages of the oldest units in the belt, predating the volumetrically dominant ca. 2700 Ma greenstone sequences. The presence of these xenocrysts and the onlapping of the Timiskaming Group on all earlier lithotectonic units of the southern Abitibi belt support the concept that the 2700 Ma ensimatic sequences were thrust onto older assemblages during a phase of compression that culminated with the generation of tonalite and granodiorite at about 2695–2688 Ma. Published geochemical data for the Timiskaming igneous suite, notably the enrichments in large-ion lithophile elements and light rare-earth elements and the relative depletion of Nb, Ta, and Ti compare with the characteristics of suites at modern convergent settings such as the Eolian and the Banda arcs and are consistent with generation of the melts from deep metasomatized mantle in the final stages of, or after cessation of, subduction. Late- and post-Timiskaming compression caused north-directed thrusting and folding. Turbiditic sedimentary units of the Larder Lake area which locally structurally overly the alluvial–fluvial sequence and were earlier thought to be part of the Timiskaming Group, appear to be older "flyschoid" sequences, possibly correlative with sedimentary rocks deposited in the Porcupine syncline at Timmins between 2700 and 2690 Ma.

Geochemistry and age of Timiskaming alkali volcanics and the Otto syenite stock, Abitibi, Ontario

Tephrites and trachytes of the Timiskaming volcanics from the Kirkland Lake area (Ontario) and syenites and a granite from the nearby Otto Stock are characterized by extreme enrichment of incompatible elements coupled with relative depletion of Nb, Ti, and to a lesser extent Zr and Y.The volcanic rocks have a whole-rock Sm–Nd isochron age of 2740 ± 117 Ma (2σ error), and minerals separated from the Otto Stock, a Sm–Nd age of 2544 ± 50 Ma. Conventional and ion probe U–Pb analyses of zircons from the Otto Stock yielded an upper intercept age of 2700 ± 19 Ma, whereas the more concordant ion probe analyses had a mean 207Pb/206Pb age of 2671 ± 8 Ma (2σ). The latter is interpreted as the age of emplacement of both the volcanics and the pluton, and the Sm–Nd mineral isochron age is thought to reflect a period of later disturbance, probably during regional metamorphism.A high initial εNd of 2.5 ± 1.5 for Kirkland Lake volcanics indicates long-term isotopic depletion of their source. This value is the same as that for volcanic rocks throughout the Abitibi belt and indicates that any chemically enriched material in the source cannot have been much older than the volcanics themselves. An environment remote from older continents is inferred.

Relative age of Otto stock and Matachewan dykes from paleomagnetism and implications for the Precambrian polar wander path

North-trending diabase dykes within and near the Otto syenite stock of the Kirkland Lake area of the Superior Province carry a stable paleomagnetic remanence identical to that of 2454 ± 2 Ma Matachewan dykes far from the stock. A positive baked contact test for the remanence of a dyke within the stock demonstrates that the remanence is primary. Thus, (1) these dykes belong to the Matachewan swarm, (2) the Otto stock has not magnetically overprinted Matachewan dykes in its contact aureole as previously reported, and (3) the stock must be older than 2454 Ma.The magnetic remanence associated with the Otto stock, previously thought to be primary, must now be considered of uncertain age. Nevertheless, the positive baked contact test for the remanence of the Matachewan dyke within the stock demonstrates that the remanence associated with the stock predates intrusion of the Matachewan swarm.The conventional polar wander path for Precambrian North America decreases in age from the Matachewan paleopole to the Otto stock paleopole. Since this study demonstrates that the Otto stock pole is older than the Matachewan pole, there is a serious problem with the conventional path.

Geochemistry of fine-grained clastic sediments in the Archean Abitibi greenstone belt, Canada: Implications for provenance and tectonic setting

Archean sandstone and shale samples from turbiditic (TF) and alluvial facies (AF) in the Southern Volcanic Zone of the Abitibi greenstone belt, Canada, have been analyzed for major and trace elements. The sandstones from TF are mainly greywackes, whereas those from AF are lithic arenite. SiO 2 ranges from 51 to 68%. Geochemically, the clastic sediments cluster into mafic element (MEP) and low mafic element (LMEP) populations. The MEP sediments, which include turbiditic facies sediment samples from the Larder Lake Group in the Kirkland Lake area, are characterized by elevated abundances of MgO (>5%), Ni (>200 ppm), Cr (>400 ppm), Sc (>22 ppm), and FeO (>7.5%) abundances; lower contents of incompatible elements, such as Th, U, Ta, Hf, Zr, and total REEs (<45 ppm); and lower contents of alkaline earth elements, Sr, Ba, and Cs, relative to the LMEP sediments. La/Yb N ratios are ≤4.5, with Eu/Eu* ≥ 1. The LMEP sediments (which include samples from the Beatty, Dome, and Three Nations Lake formations in Timmins, the Kewagama Group, Noranda area, and Timiskaming Group in the Kirkland Lake area), however, show reverse abundance distributions. The geochemical gaps shown by the major and trace elements define two populations of sediments, suggesting contrasting provenances for them: the MEP sediments require a dominantly mafic and ultramafic (90%) source with 10% felsic contribution, whereas the LMEP sediments require a mixture of felsic (75%) and mafic (25%) rocks. This compositional distribution of the sediments is closely related to their tectonic environments. The MEP was formed in basins proximal to or within an active oceanic rift, consequently having ultramafic and mafic rocks as the major source. For the LMEP, calc-alkaline volcanic sequences formed in an island arc-like setting were the major source. These two contrasting volcanic-plutonic terranes were tectonically juxtaposed during late Archean collisional tectonics.

Internal structure of the Cadillac tectonic zone southeast of Val d'Or, Abitibi greenstone belt, Quebec

The Kirkland Lake – Larder Lake – Cadillac Break is a major fault zone of the Abitibi greenstone belt, well known for its spatially associated gold camps. A detailed structural analysis of this fault zone in the Val d'Or area has shown the presence of a 200 – 750 m wide zone of high strain, defined here as the Cadillac tectonic zone (CTZ), which includes the narrower schist zone generally regarded as the Cadillac Break. The boundaries of the CTZ, which coincide with major lithologic contacts, strike approximately east–west and dip 80° to the north.The internal structure of the CTZ is best analysed in terms of two increments of the same progressive deformation. The D1 strain increment is characterized by an east–west-striking, subvertical S1 foliation, at low angle in strike to the bound aries of the CTZ and containing subvertical elongation lineation. Primary lithological contacts have been transposed into S1 and folded by F1a folds. F1b intrafolial folds of S1 ranging from noncylindrical, subhorizontal folds to subvertical sheath folds, indicate dip-slip movements within the CTZ. The D1 strain increment records synchronous dextral transcurrent shearing, as required by the obliquity of S1 to the CTZ boundaries, and subvertical elongation, as indicated by elongation lineations and F1b folds. The D2 strain increment is chiefly characterized by the development of moderately to steeply plunging asymmetric Z-shaped F2 folds with associated S2 cleavage, recording dextral transcurrent shearing.The studied segment of the CTZ is best interpreted as a zone of dextral transpression, evolving from a zone with a significant shortening component (D1) into a zone increasingly dominated by a transcurrent shearing component (D2).

U–Pb zircon geochronology in the southwestern Abitibi greenstone belt, Superior Province

The Abitibi Belt is the largest continuous greenstone belt in the Superior Province of the Canadian Shield. It comprises several composite komatiitic–tholeiitic–calc-alkalic and sedimentary sequences that are folded, transected by major faults, and intruded by various generations of plutonic rocks. Precise U–Pb geochronology has been carried out in the belt for the past decade to solve chronostratigraphic and metallogenetic problems. This paper presents new zircon ages and reassesses previously published ones, now refined by the addition of abraded and concordant zircon analyses.Volcanic and subvolcanic units of the Timmins area yield the following ages: 2727 ± 1.5 Ma for a tuff of the upper Deloro Formation; 2703 ± 1.5 Ma for a tuff of the upper Tisdale Formation; and 2698 ± 4 Ma for the Krist fragmental, assigned to the top of the Tisdale Formation. The age of a dunite intrusive into the upper Deloro Formation is revised at 2707 ± 3 Ma, whereas the Aquarius diorite east of Timmins yields a poorly defined age of 2705 ± 10 Ma. In the Lake Abitibi – Kirkland Lake region, the following dates were obtained: 2713 ± 2 Ma for a porphyritic unit of the Hunter Mine Group; 2714 ± 2 Ma for a rhyolite at the base of the mainly tholeiitic to komatiitic Stoughton–Roquemaure Group; 2701 ± 2 Ma for porphyritic rhyolite of the Blake River Group; 2701 ± 2 Ma for a tuff of the Skead Group; and [Formula: see text] for a pyroclastic unit at the base of the Larder Lake Group. These data are generally consistent with the earlier proposed stratigraphic subdivisions and correlations. However, there are apparent age reversals, for example between the Larder Lake and Skead groups, that could support the concept of thrusting and tectonic thickening to explain particular lithologic relationships and the considerable stratigraphic thickness of the supracrustal sequences in the Abitibi Belt.One part of the study was dedicated to the problem of gold mineralization in the Timmins area. The zircon age of 2690 ± 2 Ma for the Paymaster porphyry, a less well defined but probably identical age for the Preston porphyry, and dates of 2689 ± 1 Ma for the Pearl Lake porphyry, 2691 ± 3 Ma for the Millerton porphyry, and 2688 ± 2 Ma for the Crown porphyry show that these intrusions were formed during a well-defined, short-lived episode unrelated to volcanism; furthermore, a date of [Formula: see text] for an albitite, which predates Au mineralization, demonstrates that Au is spatially but not genetically related to the porphyries.Finally, two ages are reported for late tectonic potassic intrusions: a refined age of 2678 ± 2 Ma for the Garrison stock east of Matheson and a precise zircon (and titanite) age of 2680 ± 1 Ma for the Otto stock near Kirkland Lake.

Northern Ontario Magic Circus’s Hurried Hamlet

It’s a cold morning in Kirkland Lake. The Magic Circus Theatre Company, in town to perform a 90-minute version of Hamlet called Hamlet in a Hurry, straggles into the enormous, harshly lit gymnasium of the Kirkland Lake High School. The room has the wildly echoing acoustics of an airplane hangar. While the stage manager lays masking tape along the floor to form the outline of a stage, the actors try out some dialogue and their faces fall. Their voices bounce around thunderously. Shakespeare is hard enough to make captivating to high school students without obstacles like this.

Petrography and geochemistry of an unusual Fe-rich basaltic komatiite from Boston Township, northeastern Ontario

The Boston Creek Flow is a thick, Archean layered basaltic komatiite lava flow located 16 km south of Kirkland Lake, Ontario, within the Abitibi greenstone belt. It is superficially similar to the layered flows of Munro Township in that it consists of a basal pyroxenite overlain sequentially by peridotite, pyroxenite, gabbro, and pyroxene spinifex-textured rock and exhibits the typical cumulate komatiite crystallization sequence: olivine–clinopyroxene–plagioclase. The spinifex-textured unit is, however, unusually thick (33 m), and in comparison with other Archean lavas of similar magnesium content, the flow is Fe and Ti enriched and Al and Y depleted. CaO/Al2O3 and Al2O3/TiO2 ratios of 2–3 and 5, respectively, also distinguish it from other Archean magnesium-rich volcanic rocks.The preservation of typical tholeiitic chemistry in lavas underlying the Boston Creek Flow precludes metamorphism and metasomatism as explanations of the flow's enigmatic geochemistry. This is supported further by relict igneous textures exhibited by Ti-bearing oxides in the pyroxenite, gabbro, and spinifex-textured units of the flow. The presence of trellis-textured ilmenite lamellae in titanomagnetite, the textural evidence for symplectic intergrowth of titanomagnetite and clinopyroxene during crystallization, and the failure of assimilation models to explain the coupling of Fe and Ti enrichment with Al depletion suggest rather that the unusual geochemistry of the flow is a primary igneous feature. The Boston Creek Flow is more Al depleted and Fe and Ti enriched than Barberton and Minnesota Al-depleted komatiites (ADK) of the same magnesium number. It is therefore an Fe-rich, layered ADK.

Crustal outgassing and LILE enrichment in major lithosphere structures, Archean Abitibi greenstone belt: evidence on the source reservoir from strontium and carbon isotope tracers

Major structural discontinuities in the Abitibi greenstone belt acted as conduits for outgassing of the Archean crust, as reflected in fixation of a select group of lithophile elements including Si, C, K, Rb, Ba, Li, Cs, B and Pb, in metasomatized faults. For two of the largest structures, the Destor-Porcupine (DP) and Kirkland Lake — Cadillac (KC) fault zones ∼6×1015 g Si, 3×1015 g CO2 and 1015 g K were introduced into the faults during expulsion of an estimated 6×1018 g aqueous fluids. Strontium isotope ratios of tourmaline, piemontite, actinolite and scheelite mineral separates, characterized by Rb/Sr≤0.02, are concordant with respect to 87Sr/86Sr initial ratios over local sectors of the faults. The Sr isotope data record geographic variations which, from east to west on the KC fault is 0.7031–0.7041 (Val d'Or), 0.7008–0.7022 (Bourlemaque), 0.7017–0.7019 (Bousquet), 0.7029–0.7031 (Noranda), and 0.7013 to 0.7015 (Kirkland Lake). At Timmins, on the PD fault, 87Sr/86Sr initial ratios cluster at 0.7010 to 0.7020. Metasomatised fault zones are systematically more radiogenic than contiguous host lithologies, and imply a source reservoir (0.7010 to 0.7041) generally more radiogenic than the upper mantle at 2690 Ma (0.700±0.001), or contemporaneous volcanic rocks of mafic to ultramafic composition (0.700 to 0.7012). Whereas certain minerals are concordant and retentive, Rb-Sr isochrons based on suites of rocks at progressive intensities of metasomatism, have been systematically reset over an elpased time of ∼200 Ma after termination of outgassing, due to disturbance accompanying incremental displacements on structures.

Hydrothermal alteration zoning and gold concentration at the Kerr-Addison Archean lode gold deposit, Kirkland Lake, Ontario

Kerr-Addison, a major Archcan lode gold deposit of the Abitibi belt, with a production of approximately 10 X 10 6 oz Au ( approximately 320 metric tons up to 1983), is localized in a zone of talc-carbonate and chlorite-carbonate rocks, immediately south of a regional structural break--the Kirkland Lake-Larder Lake fault zone. Relict volcanic textures taken in conjunction with the ratios of diag-nostic, relatively less mobile elements collectively indicate that most of the wall rocks of the mine were originally mafic and ultramafic rocks along with their clastic derivatives. Regional greenschist facies metamorphism is locally superposed by a distinct zonation of gold-associated hydrothermal alteration characterized by massive introduction of CO 2 coupled with variable enrichments of alkali metals and calcium, which produced systematic trends of alteration mineral assemblages. Alteration types of the initial stage contain chlorite which is replaced by muscovite or albite in the advanced stage of alteration, with a concomitant increase in the proportion of carbonate minerals. Numerous generations of crosscutting veins are enveloped by alteration borders in which the sequence of the Al-bearing minerals, namely albite, mus-covite, and chlorite, develop from the vein to the wall rocks, always in a systematic sequence. The same sequence is observed at a larger scale from the ore zone to the periphery of the mine area.The intensity of alteration can be monitored by saturation indices: CO 2 /(Ca + Fe + Mg) for carbonates; and (3K + Na)/Al, 3K/Al, and Na/Al for muscovite + albite, muscovite, and albite, respectively (molar ratios). Plots of the moving averages of these indices across the 3,850-ft level of the mine reveal a remarkable correspondence to variations of gold abundance, suggesting a genetic relationship of gold enrichment to hydrothermal alteration. On a broad scale, gold is concentrated to the south of the Kirkland Lake-Larder Lake fault zone and at a more detailed scale in the transition zone between carbonate-muscovite and carbonate-albite alteration types. During advanced alteration, fluid X (sub CO 2 ) was approximately 0.1 and Na/K [asymp], 10.Volcanics of the Kinojevis and Larder Lake groups are 18 O enriched relative to pristine tholeiites and possess distinct mineral delta 18 O values, probably due to different conditions of marine-water alteration during or shortly after extrusion. In domains of advanced alteration these are all shifted down to a common narrow bracket: here 18 O/ 16 O and D/H data indicate fairly constant temperatures (270 degrees -300 degrees C) and a common isotopic composition of hydro-thermal fluids (delta 18 O -- +5ppm; delta D = -30 to -50ppm) across the alteration zoning; these results are in common with many other Archcan lode gold deposits. Fe dolomite has a uniform delta 13 C value of -2.8 + or - 0.42 per mil (1Sigma ) throughout the footwall and ore zones, but it is enriched by approximately 1 per mil in the graphite-free hanging-wall rocks. Fluid delta 13 C value was -4 + or - 1 per mil, reflecting either a magmatic carbon reservoir or mixtures of marine carbonate, carbonaceous, and magmatic sources.The enrichment of gold at one side of the Kirkland Lake fault zone is interpreted to be the result of development of a metasomatic zoning induced by gradients in oxidation state, the precious metal being concentrated in the reducing side. Zonation of alteration types south of the Kirkland Lake-Larder Lake fault zone represents various steps of a continuous process of incremental changes of the rocks to adapt to the composition of an externally generated fluid. Successive generations of fracture arrays and veins have the same alteration patterns and thus the composition of the incoming hydrothermal fluid seems to have remained essentially unchanged through time.Gold mineralization at the Kerr-Addison mine and its contiguous alteration halo are interpreted to be the result of repeated cycles of hydraulic fracturing, fluid penetration, and local reaction with rocks. Fluid-rock interaction produced lateral variations of fluid composition which led to gold concentration, probably due to gradients in pH, preferentially at the interface between the carbonate-muscovite and carbonate-albite alteration types, which is also the site of pyrite concentration. The alteration assemblages and specific site of gold-pyrite concentration at Kerr-Addison are common to several other described Archcan lode gold deposits.

Double beta decay of tellurium-130

The isotopic composition of xenon is reported in four, neutron-irradiated tellurium minerals — tellurobismuthite from Boliden, Sweden, native tellurium from the Good Hope Mine of Gunnison County, Colorado, altaite from the Kirkland Lake area, Ontario, and altaite from the Mattagami Lake area, Quebec. From the amount of radiogenic 130Xe and pile-produced 131Xe in these samples, it is concluded that the half-life of 130Te for ββ-decay is ≲ 1 × 10 21 y based on measured values of (1.0 ± 0.3) × 10 21 y and higher. Our results demonstrate that there has been no significant partial leakage of radiogenic 130Xe from these minerals over geologic time. Larger values of T 1 2 as indicated from some of the analysis reported here and in other studies, are attributed to recrystallization of the soft telluride minerals and complete resetting of the TeXe system after mineralization. The value obtained here for the half-life of 130Te is substantiated by recent measurements on xenon in tellurides from Kalgoorlie, Western Australia.

Geochemistry of Archean alkalic volcanic rocks from the Crystal Lake area, east of Kirkland Lake, Ontario, Canada

Twelve samples of Timiskaming volcanics from the Crystal Lake area were analyzed for major and trace elements (Ta, Th, Zr, Hf, V, Cr, Sc, rare earth elements (REE), Y, etc.) by X-ray fluorescence and instrumental neutron activation analysis techniques. The samples, which include mafic trachytes, trachytes and leucite trachytes, represent several batches of Archean alkalic magmas differentiated at shallow depths. The Cr/Sc Cr systematics and REE, Zr Th and Zr Y characteristics show, however, that their primary magmas generated at great depths in the “enriched” mantle where garnet remained in the refractory residue of partial melt. The chemical similarity between the Timiskaming samples and modern alkalic rocks in mature volcanic arcs strongly implies that the Timiskaming volcanism represents the last stage of a late Archean island arc volcanism present in the southwestern Abitibi Belt, Superior Province. The occurrence of Timiskaming-type alkalic rocks is not rare in Archean greenstone belts, thereby suggesting that a tectonic setting similar to modern volcanic arc system might have been common in late Archean time.