The characterization of aliettite-bearing rocks of the Olympus mine, Stanleyville, Ontario

Aliettite, a rare, regularly interstratified talc-smectite clay mineral, occurs at the Olympus mine, Stanleyville, Ontario. The mine was originally developed for its vermiculite, which formed by hydrothermal alteration of metapyroxenite associated with local thrust faulting. The metapyroxenite generally consists of tremolite and diopside that have been replaced by talc, aliettite, and serpentine. Three stages of hydrothermal alteration are recorded, 1) replacement of tremolite and diopside by talc and phlogopite, 2) minor oxidation resulting in Fe-oxide-staining of talc, and 3) serpentinization of the phlogopite. The results suggest that aliettite formed by surface weathering superimposed upon earlier, low-temperature hydrothermal alteration. 2001-D2 M. Sarfi et al. 1 CURRENT RESEARCH RECHERCHES EN COURS 2001 Article Article Titles Titres Purchase Information Information pour acheter 1 Carleton University, Earth Science Department, Ottawa, Ontario K1S 5B6 2 2283 Bowman Road, Ottawa, Ont. K1H 6V4 3 Canadian Museum of Nature, P.O. Box 3443, Station ‘D’, Ottawa, Ontario K1P 6P4 INTRODUCTION M clay minerals occur in a variety of geological environments and form by various processes including weathering and hydrothermal alteration. In Stanleyville, Ontario (Fig. 1), an occurrence of a rare, regularly interstratified, mixed-layer clay mineral, aliettite, has been reported (Percival et al., 1997). Aliettite, an interlayered talc-smectite (saponite variety) mineral, was originally discovered in ophiolite rocks in the Taro Valley, Italy (Alietti, 1958). Veniale and Van der Marel (1968) identified and characterized a similar mineral in serpentinite rocks of the Nure Valley, Africa, and named it ‘aliettite’. It is typically found as a white clay that coats other minerals. At the Olympus mine property, aliettite is associated with altered Precambrian metapyroxenite and highly serpentinized rocks. CURRENT RESEARCH RECHERCHES EN COURS 2001 Article Article Titles Titres Purchase Information Information pour acheter 2001-D2 M. Sarfi et al. 2 Résumé La mine Olympus, située à Stanleyville (Ontario), renferme de l’aliettite, minéral argileux rare composé d’interstratifications régulières de talc et de smectite. La mine a été mise en valeur à l’origine afin d’exploiter la vermiculite formée par l’altération hydrothermale de la métapyroxénite associée à la formation de failles de chevauchement à l’échelle locale. La métapyroxénite est généralement constituée de trémolite et de diopside qui ont été remplacés par du talc, de l’aliettite et de la serpentine. On a mis en évidence trois étapes d’altération hydrothermale, soit 1) le remplacement de la trémolite et du diopside par du talc et de la phlogopite, 2) l’oxydation peu importante entraînant la coloration du talc par l’oxyde de fer et 3) la serpentinisation de la phlogopite. Les résultats laissent supposer que l’aliettite s’est formée lors de processus d’altération superficielle superposés à une altération hydrothermale antérieure à faible température. Because of the apparent global paucity of aliettite-bearing rocks, we thought it prudent to characterize the genetic and textural relationship of aliettite-bearing assemblages in the altered metapyroxenite of the Olympus mine. The current study is part of a larger project examining the genesis and occurrence of rare interstratified clay minerals at various sites in eastern Ontario using scanning and transmission electron microscopy (SEM-TEM; e.g. Percival et al., 1995). GEOLOGICAL SETTING Regional geology T Olympus mine is located within the Frontenac terrane of the Central metasedimentary belt of the Grenville Province. It is cut by late Precambrian intrusive rocks and overlain by late Paleozoic rocks (Easton, 1992; Fig. 2). The emplacement of the Late Precambrian rocks was accompanied by regional metasomatism. In general, Grenville-series rocks include paragneiss, quartzite, calcitic, dolomitic marble, and metapyroxenite (MacKinnon et al., 1990). The Central metasedimentary belt consists mostly of supracrustal rocks of the classical Grenville series, and is largely underlain by basement gneiss of the Central gneiss belt. The maximum age of rocks of the Frontenac terrane has been estimated at 1415 Ma (Easton, 1992). Olympus mine site geology T study site is located on the northern half of lots 17 and 18, concession VIII, of North Burgess Township, Ontario, 0.8 km southwest of Stanleyville and 13 km southwest of Perth (Fig. 1). Vermiculite from the Olympus mine was used mainly in ultralightweight industrial aggregates and pet-waste 2001-D2 M. Sarfi et al. 3 CURRENT RESEARCH RECHERCHES EN COURS 2001 Article Article Titles Titres Purchase Information Information pour acheter