Physical Volcanology, Hydrothermal Alteration and Massive ...

More documents

Recommendations

Info

ounded to the north by the English River Gneiss Belt and to the south by the QueticoGneiss Belt (Trowell and Johns, 1986). The volcanic and sedimentary rocks of the areahave been subjected to regional greenschist facies metamorphism with almandineamphiboliteassemblages found locally (Trowell, 1974).Detailed mapping of the volcanic rocks in the south Sturgeon Lake area coupledwith the relogging of 200,000 m of diamond drill core (with emphasis on the physicalvolcanology of the rocks) has led to the recognition and description of a well preservedArchean submarine caldera complex. This complex, which has been named the SturgeonLake Caldera (Morton et aI., 1988, 1989, 1990), is approximately 30 krn in strike lengthand contains up to 4500 m of caldera fill material. Five separate, major ash flow tuff unitshave been defined, and each can be traced for kilometers across the complex withindividual thicknesses ranging from 100 to more than 1200 m. Based on the stratigraphicdistribution and thickness of the five ash flow tuff units and associated debris flowdeposits, it is believed that the Sturgeon Lake Caldera consists of a series of smallernested or overlapping calderas and that each ash flow unit is associated with a collapseevent. This interpretation is supported by studies of more recent caldera complexes whichshow that major ash flow tuff units are related to individual collapse events and that nestedor overlapping calderas are common (Cas and Wright, 1987).Based on detailed stratigraphic mapping and core logging, numerous synvolcanicfaults have been defined. Synvolcanic faults with major stratigraphic displacement (>150m) may represent individual caldera boundaries. In general the eastern and westernmargin of the complex has been located and the back (northern) bounding wall has beenpartially defined. A series of late, north-south-trending dip-slip faults has broken thecomplex into a number of blocks that allow the caldera complex to be observed at differentstratigraphic levels. Individual volcanic and intrusive rock units are traceable across thefaults, but thicknesses change dramatically (Fig. 3). As well, late east-west- andnorthwest-trending faults coupled with an east-west folding event (part of the KenoranOrogeny?) have, along caldera margins, affected the upper part of the sequence causingminor displacement of the upper pyroclastic flow units and the Sturgeon Lake Mine, LyonLake and Creek Zone ore bodies. Although much of this deformation has been taken upby caldera fill sedimentary rocks, shear zones are common in the massive to amygdaloidallava flows located north and east of these ore bodies. Zircon ages of the ash flow tuff4
deposits and late caldera margin dome lavas yield a similar age of 2,735 m.y. ± 1.5 my(Davis et aI., 1985).A large, sill-like intrusion (Seidelman Say Complex) has a similar age to the felsicvolcanics and represents, in part, the magma chamber for the eruptive material. Thisintrusive body can be traced along strike for 20 km and has an average width of 2.5 km.Its composition varies from trondhjemite to quartz diorite with feldspar and quartz ±feldspar porphyry phases. The Seidelman Say intrusive complex also hosts minoroccurrences of porphyry copper-molybdenum type mineralization, and the upper portionslocally contain stringers of zinc-silver mineralization. A mafic (gabbroic-quartz dioritic)dyke- to sill-like intrusion occurs across the length of the caldera complex (Fig. 3) and mayrepresent a ring dyke complex.Hydrothermal alteration is widespread within the complex and in the upper part ofthe Seidelman Say intrusion. Discrete assemblages of alteration and metamorphosedalteration minerals form zones that are a) widespread and largely conformable to thevolcanic stratigraphy, b) locally lens- or pod-like beneath sulphide occurrences anddeposits and c) narrow and elongate, cross-cut stratigraphy and are associated withsynvolcanic faults (Groves, 1984; Hudak, 1989; Jongewaard, 1989; Morton et aI., 1988;Morton and Franklin, 1987).5
Page 2 and 3: Electronic Capture, 2008The PDF fil
Page 4 and 5: Figure 3.Figure 4.Figure 5.Figure 6
Page 6 and 7: 95°HudsonBaySioux~LOOkoutSturgeonL
Page 10: (J)i~"l::.,,",,("'Q""oro Km[TI Late
Page 13 and 14: Sturgeon Lake Caldera from an initi
Page 15 and 16: epresents one segment of the calder
Page 17 and 18: chert and iron carbonate) and graph
Page 19 and 20: moat sediments that were related to
Page 21 and 22: HYDROTHERMAL ALTERATIONHydrothermal
Page 23 and 24: semiconformable and locally pipe-li
Page 25 and 26: ::>"-2:2:§"-2:2:"-2:2:2:::>"-2:?2:
Page 27 and 28: Aoo'3 STOP F-2~ C? 0 0{//t7< 22LLPY
Page 29 and 30: of the tuffs; and b) as pale blue b
Page 31 and 32: eserves were depleted in 1988. The
Page 33 and 34: Stop M-1a: Mesobreccia (HLMBX). The
Page 35 and 36: The outcrop shows some alignment of
Page 37 and 38: 13LEGEND OF GEOLOGICAL UNITS SYMBOL
Page 39 and 40: REFERENCESBusby - Spera, C., 1984,
Page 41: associated with the Lyon Lake massi

Physical Volcanology, Hydrothermal Alteration and Massive ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?