Point rousse listvenitas

Current Research (2009) Newfoundland and Labrador Department of Natural Resources Geological Survey, Report 09-1, pages 1-12

THE POINT ROUSSE LISTVENITES, BAIE VERTE, NEWFOUNDLAND: ALTERED ULTRAMAFIC ROCKS WITH POTENTIAL FOR GOLD MINERALIZATION?
M.P. Escayola, J.A. Proenza, C. van Staal, N. Rogers* and T. Skulski Geological Survey of Canada, 601 Booth Street, Ottawa, ON, K1A 0E8 Correspondingauthor: *nrogers@nrcan.gc.ca

ABSTRACT
The Point Rousse listvenites of the Baie Verte ophiolite belt, northern Newfoundland, are potential sites of gold mineralization. They are interpreted to have been formed during obduction-related deformation and the accompanying hydrothermal alteration of ultramafic rocks. These unusual rocks have much in common with those from other alteredserpentinite-associated gold deposits. Mineralized listvenites display widely varying morphologies and metallic mineral assemblages, but all examples are intimately related to fault zones that bound slices and blocks of carbonatized ophiolite. Several stages of hydrothermal alteration have been recognized in the Point Rousse listvenites. The hydrothermal mineral assemblages are controlled largely bytemperature, XCO2, and oxygen and sulphur fugacity. The transformation of the rocks to talc–carbonate schists (listvenites) by Ca-CO2-S and As-rich solutions liberated large quantities of silica that were subsequently mobilized and re-deposited to form silicified rocks and quartz-vein networks. High-magnesian chlorites found in the listvenites have estimated formation temperatures of circa 200°C, which areconsistent with the presence of pyrite and millerite in listvenites and birbirites (silicified ultramafic rocks). Gold that is present in trace amounts in some of the sulphides in the ultramafic–mafic rocks, appears to have been mobilized and deposited during hydrothermal alteration, during several deformational stages. The Point Rousse listvenites and their associated Au mineralization are asubject of interest for future research, and also for mineral exploration in the area.

INTRODUCTION
One of the most important aspects of mineral exploration is the recognition of distinct rock types that form markers for economically significant minerals. Amongst these, rocks recording hydrothermal alteration and metasomatism are perhaps the most valuable. Hydrothermal and metasomatic alterationproducts are a function both of the mineralogy of the original rocks and subsequent fluid-rock interactions. The influence of hydrothermal fluids in terranes composed of ultramafic rocks results in a wide spectrum of metasomatic rocks, including the distinctive association termed ‘listvenite’. Listvenite, sensu stricto, consists mostly of quartz, carbonate and chromium-rich mica that formed inresponse to the carbonatization of ultramafic and/or ophiolitic rocks. They are commonly associated with other metasomatic rocks, including quartz–carbonate rocks, talc–silica–carbonate-rich rocks and serpentine–talc–chlorite–carbonate rocks.

The term listvenite was first introduced by Rose (1837, 1842) to describe the silica–carbonate metasomatic rocks that host gold-bearing quartz lodes from theListvenaya Gora in the Ural goldfields (sequence is described in Halls et al., 1991). Transliteration from the original Russian has resulted in a number of different spellings for listvenite over the years, including 'listwanite' and 'listwaenite'. This matter was addressed by Halls and Zhao (1995), where they suggested that 'listvenite' should be used because it is the best translation from theRussian of the geographic feature the rocks were named after. Furthermore, as their description was about likely correlative rocks from Ireland, it seems appropriate to follow their nomenclature. Listvenites that are spatially associated with low-temperature Au, Hg, As, Co, and Ni mineralization are the most economically important set of metasomatic rocks derived from ultramafic precursors. The...