ALBERT

Description: From 23 October 2007 to 1 August 2008, we made continuous measurements of sea surface partial pressure of CO2 (pCO2sw) in three regions of the southeastern Beaufort Sea (Canada): the Amundsen Gulf, the Banks Island Shelf, and the Mackenzie Shelf. All three regions are seasonally ice covered, with mobile winter ice and an early spring opening that defines them as polynya regions. Amundsen Gulf was characterized by undersaturated pCO2sw (with respect to the atmosphere) in the late fall, followed by an under-ice increase to near saturation in winter, a return to undersaturation during the spring, and an increase to near saturation in summer. The Banks Island Shelf acted similarly, while the Mackenzie Shelf experienced high supersaturation in the fall, followed by a spring undersaturation and a complex, spatially heterogeneous summer season. None of these patterns are similar to the annual cycle described or proposed for other Arctic polynya regions. We hypothesize that the discrepancy reflects the influence of several previously unconsidered processes including fall phytoplankton blooms, upwelling, winter air-sea gas exchange, the continental shelf pump, spring nutrient limitation, summer surface warming, horizontal advection, and riverine input. In order to properly predict current and future rates of air-sea CO2 exchange in such regions, these processes must be considered on a location-by-location basis.

Description: The Paleoproterozoic Flin Flon mining district is one of the world’s most prolific volcanogenic massive sulfide (VMS) camps and includes a single stratigraphic interval that hosts the 85.5 million tonne (Mt) Flin Flon, 777, and Callinan Zn-Cu-(Au) deposits. Rapid seafloor burial of the VMS hydrothermal system by a thick succession of pillowed basalt resulted in the hanging-wall strata being affected to varying degrees by the still upward migrating fluids. This hanging-wall alteration hydrothermal fingerprint allows delineation of the regionally metamorphosed paleohydrothermal system, and its characterization has the potential to lead to discovery of buried, stacked, or structurally displaced mineralization. Evidence for the presence of continued seafloor hydrothermal activity above the Flin Flon-Callinan VMS horizon is observed in the pillowed flows, interlayered hyaloclastite-rich flow tops, and also within finely bedded interflow volcaniclastic sediment. A 30% to 60% metalliferous exhalative component was detected through geochemical and mineral analysis in interpillow volcaniclastic rocks, chert, and epidosite in the hanging-wall sequence. The regional distribution of Fe- and Mg-rich chlorite, epidote-clinozoisite, biotite-annite, actinolite-hornblende-ferrotschermakite, and stilpnomelane and albite-oligoclase modifies metamorphic isograds and defines discrete vertical fluid pathways controlled by synvolcanic growth faults and associated sill-dike swarms. Silica-enriched hanging-wall alteration zones are proximal to Fe-Ti basalt sills and occur as discrete hanging-wall zones parallel to the plunge of the 62 Mt Flin Flon deposit. Anomalous concentrations of Hg, Sb, Ag, Pb, Te, As, Au, and Bi form within these hanging-wall halo alteration zones, indicating migration of the more volatile metals present in the underlying VMS deposits. Synvolcanic depressions, dike swarms, and hydrothermal-metamorphic fluid corridors are detectable through trace element anomalies, trace mineral chemistry, and 18 O isotope geochemistry. Oxygen isotope analysis of the Flin Flon-777-Callinan VMS hanging-wall strata defines a number of high O 18 anomalies extending 1,200 m above that indicate that 〈300°C subseafloor hydrothermal activity continued after burial of the massive sulfide deposits. Coupled with the geochemical and mineral chemical anomalies, this is indicative of the presence of continued, relatively low temperature hydrothermal fluid "leakage" from a robust seafloor hydrothermal event that generated the VMS deposits. A combination of techniques, including mineral chemistry, isotope, and trace element data, is demonstrated to be successful in identifying and delineating zones of hanging-wall hydrothermal alteration in greenschist- to amphibolite-grade metamorphic rocks of the Flin Flon mining camp. Use of these, coupled with mapping to define periods of quiescence as marked by horizons of sedimentary rocks in the hanging-wall basalts of the Hidden Formation, has the potential to lead to discovery of deeply buried deposits on the Flin Flon horizon or deposits at higher stratigraphic levels. Our findings indicate that the basaltic hanging wall on the Flin Flon-777-Callinan hydrothermal system was an efficient cap on the system, with vestiges of continued hydrothermal fluid flow detected in the interpillow and interflow components. These volumetrically minor components are critical sampling media and are pertinent to global exploration for detection of VMS mineralization buried beneath thick mafic volcanic sequences.

Description: Juvenile 1.89 Ga oceanic arc volcanic rocks of the Flin Flon volcanic belt at Snow Lake are characterized by extensive zones with anomalous 1.82 Ga metamorphic mineral assemblages, including porphyroblasts of garnet, staurolite, amphibole, biotite, gahnite, and/or kyanite. They were produced from altered rocks created during premetamorphic, 1.89 Ga, synvolcanic, hydrothermal fluid-rock interaction. Three separate episodes of hydrothermal alteration are recognized that span evolution of the host volcanic rocks from a primitive (nascent arc?) to mature arc geotectonic setting. The geologic, geochemical, mineralogical, and isotopic attributes of the zones indicate that they include volcanogenic massive sulfide (VMS)-related alteration, and they were produced at high and low temperatures and formed in seafloor/near seafloor and subseafloor (intrastratal) environments. Large-scale alteration zones at Snow Lake are up to 20 km in strike length and 0.8 km wide. Their large exploration "footprint," which is 36 times greater in areal extent compared to associated "pipe-like" alteration zones, means that such zones provide a useful target to "vector-in" exploration to VMS depositional settings within volcanic belts. The VMS-related large-scale alteration zones at Snow Lake display diagnostic variations in intensity and style of alteration along strike toward VMS deposits, are stratigraphically underlain by altered portions of synvolcanic intrusions, are crossed by discordant zones of more intensely altered rocks, and can be demonstrated to have formed by interaction with high-temperature(〉350°C) hydrothermal fluids. Cu-Zn–rich VMS deposits at Snow Lake formed in flow-dominated sequences, are hosted by large rhyolite flow complexes, and comprise lensoid orebodies. In contrast, Zn-Cu–rich VMS deposits, although also rhyolite associated, formed in volcaniclastic-dominated sequences, are spatially related to a district aquifer, and comprise stratiform, laterally continuous orebodies. This suggests that exploration for Cu-Zn VMS deposits could selectively target flow-dominated sequences and focus on rhyolite flow complexes that display significant alteration. Similarly, exploration for Zn-Cu VMS deposits could focus on volcaniclastic-dominated sequences in which a potential aquifer has been identified.

Description: The synvolcanic Mooshla Intrusive Complex intrudes coeval ~2699 to 2696 Ma volcanic rocks of the Blake River Group within the southern margin of the Archean Abitibi greenstone belt. The upper Blake River Group is host to the Doyon-Bousquet-LaRonde mining camp that contains Au-rich volcanogenic massive sulfide (VMS) deposits, possible subsea-floor epithermal-style deposits, and orogenic Au deposits. In total, the camp contains to date in excess of 28 million ounces (Moz) Au, making it a world-class example of Au-rich paleosea-floor environments. The Mooshla Intrusive Complex is spatially, temporally, and most probably genetically associated with all of the above types of mineralization. It is host to parts of the Doyon (5.5 Moz Au), Mouska (0.8 Moz Au), and Mic Mac (0.11 Moz Au) Au deposits and host to the smaller Mooshla A and B Au occurrences. Host volcanic units to the Mooshla Intrusive Complex are intensely deformed, metamorphosed, altered, and mineralized, as is the intrusion itself. The Mooshla Intrusive Complex was formed by nine distinctive phases of subvolcanic dikes, sills, and stocks. These were emplaced in two stages to form a shallow, multiphase synvolcanic intrusion along the contact between the Hébécourt and Bousquet volcanic formations. The Mouska stage is represented by a preliminary swarm of thin diabase sills, intruded by a well-layered gabbroic sill, a more crudely layered quartz diorite, and tonalite. A period of devolatilization accompanied crystallization of the xenolith-rich top of the tonalite magma chamber, as evidenced by the presence of an aplite dike swarm and associated extensive alteration zones and miarolitic cavities. The younger Doyon stage comprises a series of fine-grained aphyric to porphyritic, tonalite and trondhjemite dikes and sills, which also contain evidence of in situ devolatilization. The geochemical signatures of the Mooshla Intrusive Complex indicate emplacement during formation of an evolved, extensional oceanic island arc-style succession. Primitive mantle-normalized spider plots suggest a common origin for this island-arc intrusive suite that is similar to that of the volcanic succession of the upper member of the Bousquet Formation. Various element ratio plots used to further define magma origin and emplacement history suggest that whereas the Mouska-stage magmatic phases have a relatively straightforward, coexisting fractionation history, the Doyon-stage tonalite-trondhjemite has a more complex interplay of assimilation-fractionation-contamination, suggesting midcrustal partitioning and interaction with both earlier formed, partially hydrated ~2720 Ma oceanic crust and upper Blake River host strata (~2699-2696 Ma). The protracted and mulitphased magmatic evolution of the Mooshla Intrusive Complex led to the generation of volatile-rich phases that contributed to the development of a submarine magmatic-hydrothermal system that is thought to be responsible for the formation of the Doyon Au-Cu deposit. Geologic and timing relationships suggest that this magmatic-hydrothermal system might also have contributed to the generation of Au-rich VMS deposits higher in the host volcanic succession as part of a large Archean magmatic and hydrothermal center.