The geological setting, geochemistry and geochronology of host rocks to high-and low-sulphidation style epithermal systems of the eastern Avalon high-alumina belt, eastern Avalon zone, Newfoundland

Sparkes, Gregory W. (2005) The geological setting, geochemistry and geochronology of host rocks to high-and low-sulphidation style epithermal systems of the eastern Avalon high-alumina belt, eastern Avalon zone, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The existence of well-preserved Late Neoproterozoic high- and low-sulphidation systems within the previously unseparated Manuels Volcanic Suite are hallmarks of the eastern Avalon high-alumina belt. These systems occur in a regionally extensive (15 x 1km) belt of hydrothermal alteration, located along the eastern margin of the Holyrood Horst, eastern Avalon Zone, Newfoundland. The contrasting formational environments of the pyrophyllite-diaspore-bearing high-sulphidation system and the auriferous colloform-crustiform chalcedonic silica + adularia ± calcite veins of the low-sulphidation system suggest a temporal or spatial break between the formation of the two systems. Both epithermal systems are hosted within a composite suite of predominantly felsic flows and ash-flow tuffs, which are locally intruded by rocks of the White Hills Intrusive Suite. The volcanic and plutonic rocks which host the epithermal systems are unconformably overlain by siliciclastic sedimentary rocks and associated mafic flows of the Wych Hazel Pond Complex. New U-Pb geochronology now permits the separation of older (625 to 614 Ma) and younger (ca. 585 Ma) intrusive units, older (pre-625 to 616 Ma) and younger (ca. 584 Ma) volcanic sequences, and provides time constraints on the development of the two epithermal systems. -- U-Pb dating carried out during this study has bracketed the intrusion of the White Hills Intrusive Suite between 625 and 614 Ma, which demonstrates that, in contrast to previous models, this magmatic event is not associated with the herein defined 580.5 to 585 Ma formation of the high-sulphidation system. The geochemistry from this intrusive suite, however, indicates that the White Hills Intrusive Suite is closely related to the regionally extensive Holyrood Intrusive Suite. Feldspar porphyry, which is intrusive into the Wych Hazel Pond Complex, represents the youngest magmatic event exposed within the field area and is defined at 585 ± 5 Ma. This intrusion may represent a late stage magmatic pulse associated with the development of the regional epithermal systems, and is chemically distinct from the older intrusions of the White Hills Intrusive Suite. -- The felsic volcanic succession hosting the high-sulphidation systems is now precisely defined at 584 ± 1 Ma. This sequence represents the younger Manuels Volcanic Suite, and can now be separated from the older (ca. 616 ± 2 Ma) White Mountain Volcanic Suite on the basis of new U-Pb geochronology and previously described intrusive relationships with the adjacent White Hills Intrusive Suite. Although these units represent a time span of ca. 40 Ma, both units display very similar arc-related trace-element geochemistry. -- The base of the Wych Hazel Pond Complex is now dated at 582 ± 1.5 Ma, which is the time of the overall cessation in felsic volcanism within the region, and the onset of arc-collapse. This age provides the maximum limit for the development of the high-sulphidation system and also supplies the minimum age for the base of the sedimentary sequence. -- New U-Pb zircon ages combined with previously known ages constrain the formation of the high-sulphidation system between 585 and 580.5 Ma. The maximum age limit for the low-sulphidation system is 586 Ma, combining this age with the fossil age of the unconformably overlying Cambrian succession restricts the formation of the low-sulphidation system between 586 and approximately 513 Ma.

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