The Eocene Babine Intrusive Suite of west-central British Columbia hosts a number of porphyry copper deposits, most significantly Bell, Granisle, and Morrison. All deposits feature central potassic zones containing the ore zones and peripheral propylitic zones. In addition, Granisle and Bell feature superimposed sericite-carbonate zones between the potassic and propylitic zones, and the Bell deposit also possesses a superimposed phyllic stockwork zone, which hosts most of the ore.Calculated fluid compositions from potassic zone biotites of all deposits yield a range from delta 18 O (sub H 2 O) = 6 to 8 per mil, whereas plagioclases yield delta 18 O (sub H 2 O) = 1 to 7 per mil. Since plagioclase samples yield more 18 O-depleted fluids than coexisting biotites and delta (sub plagioclase-biotite) values are very small, it appears that isotopically lighter fluids were present in later stages of potassic alteration. Oxygen isotope values from the sericite-carbonate and phyllic alteration zones yield fluid compositions more 18 O-depleted than magmatic fluids, requiring the incorporation of isotopically light ground waters.Calculated hydrogen isotope values of potassic, propylitic, and sericite-carbonate fluids fall in the range of -40 to -110 per mil. These results, in combination with the delta 18 O data, suggest that the alteration events were caused by mixtures of magmatic and meteoric waters. Phyllic and argillic alteration fluids (delta D (sub H 2 O) = -100 to -130 and -140ppm, respectively) indicate fluids dominantly of meteoric origin.The stable isotope data, in combination with the petrologic and field relations, suggest that early alteration fluids were derived from the magma, and in peripheral areas fluids evolved at very low water/rock ratios. Incorporation of external fluids in later alteration was responsible for the texturally destructive, cation-leaching alteration and remobilization of the ores.Differences in the stable isotope systematics and salinities of porphyry copper deposits compared to meteoric hydrothermal systems and epithermal ore deposits indicate that the systems are fundamentally distinct. The strong density contrast between the high-salinity magmatic fluids and low-salinity meteoric waters most likely inhibits mixing, resulting in separation of the hydrothermal systems.
Hydrothermal evolution of the deposit. Potential applications of isotopic analyses to exploration for stratabound, stratiform, Pb-Zn-Ag deposits. The deposit is hosted by the Proterozoic Aldridge Formation. The delta 18 O results for samples from the Aldridge range from 10.0 to 13.1 per mil with an average of 11.4 + or - 1.0 per mil. Oxygen isotope results from the tourmaline alteration zone, located in the footwall of the western, proximal ores, range from 10.7 to 13.1 per mil with an average of 11.9 + or - 0.8 per mil. The similarity between values for the tourmalinite and the Aldridge Formation suggests that the fluids which produced the tourmalinite alteration did not significantly alter the primary 18 O/ 16 O of the host sedimentary units. Isotopic values for samples from the albite-chlorite alteration zone, located in the hanging wall of the proximal ores, range from 6.1 to 7.7 per mil. Such values indicate that there is a distinct difference in the isotopic composition of the albite-chlorite zone relative to unaltered country rocks. The following sequence is proposed: the first hydrothermal stage consisted of the migration of low-temperature (<100 degrees C), boron-rich fluids up permeable zones, causing the development of the tourmalinite alteration zone. Subsequent to this event, hotter (approximately 150 degrees C) Pb-Zn-Fe-bearing fluids rose through the same zone at Sullivan and deposited sulfides on the sea floor. The final hydrothermal event was the alteration of the tourmalinite, ore, and hanging-wall sedimentary units to produce the albite-chlorite alteration assemblage. The fluids which produced the albite-chlorite assemblage were most likely more saline than normal seawater and had a temperature of 250 degrees C or more.--Modified journal abstract.
Volcanic glasses are rarely preserved in the rock record, and the quality of preservation generally declines with increasing age. Records preserved in ancient basaltic glasses therefore provide important links between processes operating in the distant past, and those that are active on the Earth today. Microbial colonization has been linked to the formation of characteristic structures in basaltic glass, including tubules and granule-filled tubules, which are thought to be produced by microbially-mediated glass dissolution. Structures of similar occurrence and morphology but filled almost entirely with fine-grained titanite have been documented in some ancient metabasalts. It has been suggested that the ancient titanite-mineralized structures are mineralized equivalents of hollow tubules in modern glassy basaltic rocks, but a direct link has not been firmly established. We report the discovery of tubular bioalteration structures in fresh and minimally-altered basaltic glasses of middle Jurassic (164 Ma) age from the Stonyford Volcanic Complex (SFVC), Coast Range Ophiolite, California. Tubular structures hosted in unaltered basaltic glass are typically hollow, whilst those in zones of zeolitic alteration are mineralized by titanite. Tubules are continuous across zeolite-glass interfaces, which mark an abrupt change from titanite-filled to hollow tubules, demonstrating that titanite growth occurs preferentially within pre-existing tubular structures. Titanite mineralization in the Stonyford Volcanic Complex represent a link between tubular structures in modern basaltic glass and titanite-mineralized features of similar morphology and spatial distribution in ancient metabasalts. Our observations support a link between textures in modern glassy basaltic rocks and some of the oldest-known putative ichnofossils.
Abstract We use isotopic analyses of authigenic siderite and calcite cements within Rosselia socialis burrows from shoreface deposits in the Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada, to reveal the early cementation history of the burrow and geochemical conditions of the initial sedimentary environment. Within the Horseshoe Canyon Formation, two forms of the Rosselia burrows are present: bulbous in situ burrows, and transported, spindlelike burrows, which display similar internal shaft diameters but smaller overall size compared to in situ forms. Transverse, incremental sampling of calcite and siderite cements in the Rosselia burrows reveals symmetrical isotopic deviation in δ13C and δ18O around the burrow core, representing accretionary records of evolving pore-water conditions. The number of isotopic deviations recorded in bulbous specimens is equal to those observed in spindle-shaped burrows, suggesting that in situ and transported burrows underwent similar periods of cementation. ...
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