are the major mineral phases present, with pyrite dominant near 

 the inner core of the chimney (presumably in the highest 

 temperature regime) and sphalerite becoming the major phase in 

 the outer half of the chimney. Chalcopyrite is also present in 

 the inner sections of the core (Fig. 4). Consequently, 

 concentrations of Fe and Cu decrease steadily from core to outer 

 surface, and Zn increases. The gold content also increases 

 steadily toward the edge of the chimney, from 750 ppb to 

 2,800 ppb in the outer zone. Although high with respect to the 

 few parts per billion gold concentrations typical of other ridge 

 crest sulfides, the gold content of the Ashes chimney falls 

 within the range reported for samples from the CASM vent field, 

 at the northern end of the Axial Volcano caldera (_<6,700 ppb), 

 and a mature vent field on the Explorer Ridge, farther to the 

 north (<1, 500 ppb) . 



SEDIMENT Z0NATI0N 



A split from one sediment push core (Core 1141) and six 

 slurp gun samples were collected from the Ashes Vent Field with 

 Pisces IV in 1986. Despite the limited selection of samples 

 available, four sediment types are distinguishable, based on 

 results of x-ray diffraction; 1) anhydrite, 2) zinc, iron, and 

 copper sulfides, 3) iron smectite ( nontronite ) , and 4) x-ray 

 amorphous silica (+ iron oxide). The dominant sulfide phase 

 present is sphalerite, with pyrite, chalcopyrite, marcasite, and 

 wurtzite also present in lesser quantities. This combination of 

 mineral phases corresponds with the components found in the 

 chimney sample, suggesting that sediment in the immediate 

 vicinity of the high temperature vents is derived from the 

 hydrothermal plume. Mass wasting and redeposition can apparently 

 be ruled out, because no basal mound of sulfide debris has 

 developed around the two small chimneys, which are built directly 

 on top of lobate flows. 



This suite of near-vent sediments (<j300 m from the smoker 

 chimneys) is apparently distributed zonally, with near-source 

 anhydrite and/or sulfide-rich sediment grading to various 

 combinations of iron silicate, iron oxide, and amorphous silica 

 in the low temperature hydrothermal sediment zone. The sediment 

 suite collected at Ashes does not include the manganese oxide 

 component commonly associated with mid-ocean ridge hydrothermal 

 vent systems. It is likely that the relatively insoluble Mn is 

 transported farther than 300 m away from the vent exit site 

 before deposition and was, therefore, not sampled. Detailed 

 results of chemical analyses of the sediment samples are in 

 preparation. This distribution of sediment samples gives an 

 indication of the variable, yet extreme, chemical regimes 

 encountered within a typical composite (i.e., both high and low 

 temperature) vent field. Anhydrite and sulfide components are 

 indicative of the >350°C fluid regime encountered immediately 

 beneath the seafloor and within vent orifices; whereas in situ 



242 



