OXYGEN-ISOTOPE SYSTEMATICS IN A MULTIPHASE WEATHERING SYSTEM IN HAITI

Physical and chemical (partial dissolution) techniques have been applied to a suite of young karst bauxite and laterite samples from the southern peninsula of Haiti. The delta-O-18 values have been obtained for nine mineral species and range from +1.0 parts per thousand for anatase/rutile to +33.4 parts per thousand for authigenic quartz. On one hand, results for quartz, calcite, kaolinite, gibbsite, and boehmite compare favourably with delta-O-18 values predicted from accepted mineral-water fractionation factors, assuming modern temperatures (25 +/- 2-degrees-C) and water delta-O-18 values (-3.1 +/- 0.5 parts per thousand). On the other hand, the delta-O-18 values measured for anatase, illite/smectite, chlorite/smectite, and some iron oxide samples do not compare favourably with predicted values. Departures from expected values for these minerals may be related to crystallization from water with a different delta-O-18 value than modern water, an imprecise knowledge of some mineral-water fractionation factors under surficial conditions, or nonattainment of isotopic equilibrium between mineral and water during formation. Partial dissolution techniques hold considerable promise for obtaining quantitative delta-O-18 values of individual minerals in single samples of complex, fine-grained regolith material.