THE KYANITE QUARTZITE AT BOSLAND (SURINAME): A METAMORPHOSED HYDROTHERMAL ALTERATION SYSTEM

This represents the first research on the petrogenesis of the kyanite quartzite at Bosland, Suriname, since its discovery in 1901. The rocks form a 2km long, 300m wide N-S trending hill within a Proterozoic Greenstone Belt of the Guiana Shield. The hill contains three quartzites and intercalated fine-grained, white mica schist, all striking 350^o and dipping 50^oE. Kyanite is present in foliation planes, massive lenses and foliation-crosscutting quartz veins. Petrographic analysis shows the quartzite consists of quartz, kyanite, andalusite, staurolite, chloritoid, rutile and sulphides with minor chlorite, apatite, zircon and muscovite.

Four quartzite samples were analyzed for major oxides via XRF using a Lithium Borate fusion. Trace element concentrations were determined by ICP-MS after Lithium Borate fusion. The rocks consist of primarily SiO₂ (72-78 wt%), Al₂O₃ (15-21 wt%) and Fe₂O₃T (3-6 wt%), with extremely low values for MgO, CaO, NaO₂ and K₂O (<1wt%). Trace element signatures indicated the average composition of a trachy-andesitic tuff of the nearby Rosebel area as best-fit for the protolith.

The low values for alkalis and alkaline earths are believed to be caused by either extreme weathering/bauxitization or hydrothermal alteration. Alteration is favored because of the modal variation between the quartzites, the presence of intercalated sericite schist, and the presence of sulphides and rutile. The observed mineralogy is indicative of advanced argillic alteration, for which andalusite may be a remnant. Mass-transfer calculations with the Isocon method, show high mobility of the HFSE, implying a F- and Cl-rich fluid.

Based on a pseudosection of the average quartzite, textural observations and regional scale structures, the kyanite quartzites are concluded to have formed by hydrothermal alteration of a trachy-andesitic rock (P<2 kbar, T>350^o), which underwent subsequent greenschist to lower-amphibolite metamorphism during the Transamazonian Event, with peak metamorphic conditions in the kyanite-staurolite stability field (P>4 kbar, T=500^o-650^oC). This has implications for exploration activities in Suriname and the Guiana shield, because of the possibility of paleo hydrothermal systems, such as VMS- or porphyry-type deposits, that remain undiscovered because of the metamorphic overprint.