Evolution of the Western Flin Flon Domain with special reference to epigenetic gold mineralization
| dc.contributor.advisor | Kyser, Kurt | en_US |
| dc.creator | Ansdell, Kevin Michael | en_US |
| dc.date.accessioned | 2012-10-31T12:49:09Z | en_US |
| dc.date.accessioned | 2013-01-04T05:07:31Z | |
| dc.date.available | 2013-10-31T08:00:00Z | en_US |
| dc.date.available | 2013-01-04T05:07:31Z | |
| dc.date.created | 1992 | en_US |
| dc.date.issued | 1992 | en_US |
| dc.date.submitted | 1992 | en_US |
| dc.description.abstract | The Flin Flon Domain is a Proterozoic example of a greenstone belt, and is one of the lithotectonic elements of the Reindeer Zone in the Trans-Hudson Orogen. The oldest rocks are a sequence of tholeiitic to calc-alkaline island arc and back arc extrusive rocks, termed the Amisk Group (U-Pb ages - 1925-1885 Ma) that host volcanogenic massive sulphides. These rocks are unconformably overlain by molassetype sedimentary rocks and intruded by gabbroic to granitic rocks ranging in age from syn-volcanic to late-tectonic. Metamorphic grade varies from prehnitepumpellyite (ca. 300°C, 2 kbar) to amphibolite facies (ca. 550°C, 5 kbar), 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 post-peak metamorphic uplift. Granitoid rocks range from syn-volcanic to late-tectonic in age, and have been dated using the single-zircon Ph-evaporation technique. The plutons dated were intruded between 1860 and 1834 Ma, and provide further evidence of a major period of intrusive activity throughout the Trans-Hudson Orogen at that time. The older plutons (1860 to 1848 Ma) are synchronous with P2 deformation and the early stages of peak metamorphism, whereas the younger plutons are synchronous with or postdate the P3 deformation event. The zircons from specific plutons usually have distinct ²⁰⁸Pb/²⁰⁶Pb ratios as well as ²⁰⁷Pb/²⁰⁶Pb ages. The Annabel Lake, Reynard Lake and Boot Lake plutons are generally metaluminous and calc-alkaline, enriched in LILE and depleted in HFSE relative to ocean-ridge granites, exhibit Ta-Nb troughs, have Rb, Y, Nb and δ¹⁸O values typical of subduction-related granitoids, and εNd(t) values between +2.2 and +4.5 suggesting that the magmas were probably derived by partial melting of the lower portions of the developing island arc crust. The youngest pluton, the Phantom Lake granite, also has characteristics suggestive of subduction-zone processes, but high Ba and Sr concentrations (> 1500 ppm) and lower εNd(t) (+ 1.4 to -1.0) values, which are indicative of an older crustal component, possibly subducted sediment, in the source region. However, all the granitoids studied in detail have undergone varying degrees of sub-solidus alteration, deformation and metamorphism resulting in complex open-system exchange of 0, Rb, Sr, Sm and Nd. Missi Formation sedimentary rocks in the Flin Flon Basin consist of a sequence of fluvial conglomerates and sandstones that unconformably overlie Amisk Group rocks. The sedimentary rocks are crosscut by intrusive rocks, which provide a minimum age of sedimentation of 1840 ± 7 Ma. Euhedral to slightly rounded zircons dominate throughout the stratigraphic succession of the Missi Formation, and yield Pb-Pb ages between about 1854 and 1950 Ma. The Missi sediments were thus deposited between 1840 and 1854 Ma. Similar ages indicate that possible sources for these zircons are Amisk Group felsic volcanic rocks, post-Amisk granitoid rocks and orthogneisses in adjacent domains within the Trans-Hudson Orogen. However, the mature 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, which yield Pb-Pb ages of up to 2529 ± 20 Ma, are uncommon, but provide evidence for the reworking of older Proterozoic sedimentary rocks, or a distant Archean or Early Proterozoic granitoid terrane. Epigenetic gold mineralization in the western portion of the Flin Flon Domain occurred prior to peak metamorphism, but more commonly postdates peak metamorphism. The Laurel Lake Au-Ag deposit is an example of the earlier phase of gold mineralization, and is distinguished from the more common epigenetic mesothermal gold occurrences by lack of obvious relation to a major shear zone, and high base metal sulphide content and Ag/Au ratio (5:1). Fluid inclusion and stableisotope data indicate that the mineralizing fluids had a high temperature (>300°C), were saline (> 10.3 wt.% NaCl equiv.) and C02 bearing and had hydrogen and oxygen isotopic compositions similar to modified seawater. This fluid leached sulphur, base metals, and precious metals as it interacted with Amisk Group volcanic rocks. The Laurel Lake deposit has fluid, vein, and alteration characteristics that distinguish it from both epithermal and mesothermal deposits, especially the involvement of modified seawater in the formation of the Laurel Lake deposit. ⁴⁰Ar/³⁹Ar incremental step-heating of muscovites from the Laurel Lake deposit yield plateau ages of about 1750 Ma, which is probably representative of the time that the muscovites last closed to Ar diffusion. Mesothermal gold mineralization in the western portion of the Flin Flon Domain 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 metres wide and overprint regional metamorphic assemblages. The veins consist of milky-coloured quartz and may also contain tourmaline, ankerite, chlorite and muscovite. Pyrite and arsenopyrite are the dominant sulphides, and gold grade is proportional to the modal abundance of sulphides. The dominant fluids associated with gold mineralization were H₂O-CO₂-NaCl (0.6 to 14.7 wt.% NaCl equiv.) in composition, with generally uniform H₂O/CO₂ phase ratios in a given plane or zone, but variable phase ratios between zones. Oxygen isotope analyses of mineral pairs indicate temperatures of mineralization of between 360 and 420°C, which, when combined with fluid inclusion density estimates, indicate that most of the gold mineralization occurred at a pressure of about 2kb. Rapid pressure release in dilatant zones with related phase separation and change in fluid composition and physical properties, and local fluid-wall rock interaction, were likely the gold precipitation mechanisms. The O, H, S, C and Sr isptopic compositions of hydrothermal minerals indicate that the fluids interacted extensively with Proterozoic metamorphic and igneous rocks similar in composition to those presently exposed at surface, under conditions of relatively high temperatures and at low water/rock ratios. The O and H isotopic compositions are compatible with formation of the fluids from devolatilization reactions during prograde metamorphism at depth. The oxygen isotopic compositions of barren quartz veins vary with host rock indicating these fluids were either locally derived or interacted extensively with the immediate host rocks. A Rb-Sr tourmaline-muscovite isochron age of 1760 ± 9 Ma from the Rio deposit, along with a published ⁴⁰Ar/³⁹Ar age on muscovite from the Tartan Lake deposit (1791 ± 4 Ma) indicate that fluid flow related to hydrothermal activity along the shear zones occurred periodically over a period of about 30 Ma. These Proterozoic occurrences are similar to Archean mesothermal gold deposits in terms of geological, structural and tectonic setting, alteration and vein mineralogy, and fluid composition, pressure and temperature. However, the limited extent of alteration, low gold content, isotope systematics and the lack of either S-type granites or mantlederived 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. The tectonic evolution of the western Flin Flon Domain is complex. Volcanic rocks and associated volcanogenic massive sulphides were formed in island arc, and back-arc ocean floor environments, prior to juxtaposition during east-directed ductile thrusting as a result of early arc-arc collision (pre-1860 Ma). Partial melting at the base of the developing oceanic island arc system resulted in formation of calcalkaline granitic magmas. The main phase of regional metamorphism was initiated by advection of heat through the crust by way of this phase of plutonism. The Wathaman Batholith was intruded synchronously with this phase of plutonism and represents arc-continent collision along the northwestern margin of the Reindeer Zone, which initiated southward propagation of major thrust sheets. Fluvial molasse sedimentary rocks were deposited (1854-1840 Ma) after erosion of mountain chains, which developed during this period of thrust sheet development, crustal thickening, and plutonism. Slivers of late Archean crust were incorporated into the thrust sheets, and were exposed and eroded during Missi Formation sedimentation. Similar sediments may have been a component in the source regions of late-tectonic magmatic systems, such as the Phantom Lake pluton (1840 Ma). Peak metamorphic temperatures were attained after nappe emplacement at about 1815 Ma during thermal equilibration of the thickened crust. Later thrusting, related to collision between the Superior Province and the Reindeer Zone, included thrusting of the Flin Flon Domain over the Hanson Lake block along the Sturgeon Weir Shear Zone. A source for gold-bearing metamorphic fluids may be devolatilization reactions during thermal re-equilibration of Proterozoic rocks in the Hanson Lake block, and these fluids were then focussed into structural sites in reactivated brittle-ductile shear zones in the western Flin Flon Domain at about 1790-1760 Ma. During continued uplift and cooling to about 200°C at 1700 Ma, brittle, generally oblique slip movements occurred along fault zones like the Tabbernor and Ross Lake faults. At this time, the remnants of the Trans-Hudson Orogen mountains were being eroded and deposited in the developing intra-cratonic Athabasca Basin. | en_US |
| dc.identifier.uri | http://hdl.handle.net/10388/etd-10312012-124909 | en_US |
| dc.language.iso | en_US | en_US |
| dc.title | Evolution of the Western Flin Flon Domain with special reference to epigenetic gold mineralization | en_US |
| dc.type.genre | Thesis | en_US |
| dc.type.material | text | en_US |
| thesis.degree.department | Geological Sciences | en_US |
| thesis.degree.discipline | Geological Sciences | en_US |
| thesis.degree.grantor | University of Saskatchewan | en_US |
| thesis.degree.level | Doctoral | en_US |
| thesis.degree.name | Doctor of Philosophy (Ph.D.) | en_US |