The Paleoproterozoic Dorlin gold deposit, French Guiana: genetic constraints of the stable isotope geochemistry

This paper reports on oxygen, hydrogen, carbon and sulphur isotopic composi tions of silicates, carbonates and sulphides from the Dorlin gold deposit i n the Paleoproterozoic greenstone belt of central French Guiana. The Dorlin orebodies result from the polydeformation of a large tourmalinite-bearing stratabound sulphide deposit hosted by volcanic and sedimentary rocks of th e Paramaca Series, metamorphosed in the greenschist facies. The mineralizin g envelope would initially have consisted of an inner zone of tourmaline-su lphide-bearing ores (M2) surrounded by a zone of chlorite-sulphide-bearing mineralization (M1). The stratabound sulphide deposit was locally cut by a muscovite-sulphide-quartz stockwork (M3). The delta(18)O values of quartz a nd chlorite from the chlorite-sulphide mineralization are +12.2 parts per t housand and about +5.5 parts per thousand (SMOW), respectively; those of qu artz and tourmaline from the tourmaline-sulphide mineralization are about 14 parts per thousand and +8.5 parts per thousand (SMOW), and those of quar tz and muscovite from the discordant stockwork are +12.4 parts per thousand and +6.9 parts per thousand (SMOW). delta D values of the chlorite, tourma line and muscovite are about -45 parts per thousand, -28 parts per thousand and -38 parts per thousand (SMOW), respectively. Carbonates (calcite, dolo mite/ankerite and siderite) in the mineralizations have delta(18)O values b etween +10.8 and + 15.7 parts per thousand relative to SMOW and delta(13)C values of -5.2 to -0.8 parts per thousand relative to PDB. delta(34)S value s of samples from the three mineralizations range between -0.5 to +2.6 part s per thousand (CDT) with two exceptions at -2.8 and -2.9 parts per thousan d. The data support the existence of a zoned hydrothermal system largely co ntrolled by a network of paleofractures and slightly reworked by a late mus covite-sulphide-quartz stockwork. The isotopic geothermometers record tempe ratures of ore deposition in the range of 200-300 degrees C. The delta D an d delta(18)O values of the chlorites, tourmalines and muscovites would indi cate a large input of seawater in the Dorlin hydrothermal fluids, whereas t he delta(18)O and delta(13)C of the carbonates and delta(34)S of pyrite pro vide evidence of a magmatic component, resulting probably for a large part from leaching of the volcanic host rocks. (C) 1999 Elsevier Science B.V. Al l rights reserved.