PARAGENESIS AND CHEMISTRY OF MULTISTAGE TOURMALINE FORMATION IN THE SULLIVAN PB-ZN-AG DEPOSIT, BRITISH-COLUMBIA

Detailed petrographic study, scanning electron microscope imaging, and electron microprobe analyses of tourmalines from the Sullivan Pb-Zn-A g massive sulfide deposit (British Columbia, Canada) document multi pi e paragenetic stages and large compositional variations. The tourmalin es mainly belong to two common solid-solution series: dravite-schorl a nd dravite-uvite. Ca-and Fe-rich feruvite and alkali-deficient tourmal ines are present locally. Products of tourmaline-forming stages includ e (from oldest to youngest): (I) rare Fe-rich dravite-schorl within bl ack tourmalinite clasts in footwall fragmental rocks; (2) widespread M g-rich, very fine grained, felted dravite in the footwall (the main ty pe of tourmaline in the footwall tourmalinite pipe); (3) recrystallize d, Fe-rich dravite-schorl (locally Ca-Fe feruvite) in the tourmalinite pipe, which preferentially occurs near postore gabbroic intrusions; ( 4) Mg-rich dravite or uvite associated with chlorite-pyrrhotite and ch lorite-albite-pyrite-altered rocks in the shallow footwall and hanging wall; (5) discrete Mg-rich tourmaline grains associated with chlorite and discordant Mg-rich tourmaline rims which occur on disseminated Fe -rich schorl in the bedded Pb-Zn-Ag ores. The timing of rare Fe-rich s chorl in the bedded ores is uncertain, but it most likely occurred dur ing or between stages 2 and 3. The different paragenetic stages and th eir respective tourmaline compositions are interpreted in terms of a m ultistage evolution involving contributions from: (1) variable mixture s of synsedimentary, Fe-rich hydrothermal fluids and entrained seawate r; (2) postore, Fe-rich, gabbro-related hydrothermal fluids; and (3) p astore metamorphic reactions. Early synsedimentary, Fe-rich hydrotherm al fluids which contained little or no entrained seawater formed Fe ri ch black tourmalinite clasts locally in the footwall. The major type o f tourmaline in the footwall tourmalinite pipe is Mg rich, recording s eawater entrainment under high water/rock conditions, rather than cont rol by the chemical composition of that original host sediments. Rare Fe-rich schorl within the bedded Pb-Zn-Ag ores is believed to have for med on the sea floor by reaction of an Fe-rich brine pool with detrita l aluminous sediments. Postore emplacement of gabbro sills and local d ikes in the footwall produced Fe-rich hydrothermal. fluids, which were responsible for formation of minor Fe-rich dravite-schorl which overp rinted earlier dravite. Postore, but synsedimentary, hydrothermal alte ration involving entrained seawater was responsible for deposition of dravite and uvite in the hanging wall and for dravite in the brown tou rmalinites of the shallow footwall. Mg-rich dravite-uvite associated w ith chlorite and in discordant rims on schorl in the bedded ores forme d by sulfide-silicate reactions during greenschist facies regional met amorphism.