Site 1189 is located at the Roman Ruins hydrothermal site, the largest development of active sulfide-sulfate chimneys at the PACMANUS hydrothermal field and one that has been surveyed and sampled in considerable detail by towed-camera video traverses and submersible dives. Chimneys as high as 20 m, but more commonly 3 m or less tall, include both simple and compound gray smokers and pillars, as well as cones that vent shimmering fluid through typically ribbed surfaces with a veneer of white material, presumed to be bacterial mat or surficial anhydrite coatings. At the fringes of the field, chimneys rise directly from the jagged surfaces of somewhat mafic dacite lavas (~65 wt% SiO2 on an anhydrous basis), whereas on the northeastern side there is a low mound, 10 to 15 m high, of chimney debris and Fe oxyhydroxide deposits topped by standing and fallen chimneys.
Two cored holes and one resistivity-at-the-bit (RAB) hole were drilled at Site 1189. Hole 1189A, tagged on the seafloor at 1690 m water depth, was sited near the center of the field in a shallow trough between chimneys, aimed at the mound crest but proving to be on its southwestern side. This was drilled to a depth of 125.8 meters below seafloor (mbsf), with modest core recovery, but was not logged because of the need to sever the pipe. Hole 1189B, placed ~35 m east-northeast from Hole 1189A, tagged bottom 6 m higher at 1684 m water depth, so it was evidently closer to the crest of the mound. This was drilled to 206.0 mbsf, having been cased to 31 mbsf using the new hard-rock reentry system (HRRS). With a free-fall funnel (FFF) installed, the hole was reentered and successfully logged, the remarkable imagery returned from the Formation MicroScanner (FMS) tool being one of the leg highlights. Recovery was very low to ~120 mbsf and then improved dramatically. Hole 1189C, the second logging-while-drilling (LWD) deployment of Leg 193, was drilled and logged to 166.0 mbsf at a site 30 m east-southeast of Hole 1189B. Placed at the foot of a 3- to 4-m-high active chimney encrusted by fauna near its crest, this tagged bottom at the deeper level of 1689 m water depth toward the eastern edge of the Roman Ruins hydrothermal site. The higher section of this hole was also logged by wireline tools, providing a valuable comparison of the two methods.
Despite their proximity, the sequences penetrated by Holes 1189A and 1189B differ significantly. After recovering samples of fresh black dacite in its first core at <10 mbsf, Hole 1189A passed rapidly into intensely altered rocks that continued to the end of hole. These contain disseminated pyrite, but apart from a 5-cm interval of semimassive sulfide in a volcaniclastic unit near 115 mbsf, there were no significant intersections of mineralization. By contrast, Hole 1189B appears to have intersected the mineralized stockwork that was expected from land-based orebody analogs to underlie the sulfide chimneys at Roman Ruins hydrothermal site. While casing the first 31 m, the rate of penetration (ROP) was initially fast, but then became difficult from 7 to 15 mbsf. Possibly the initial interval represented the hydrothermal mound, whereas the harder rocks were fresh lava corresponding to the near-seabed intersection in Hole 1189A. Below 15 mbsf, the ROP again became very rapid, a situation that continued when coring started at 31 mbsf and continued to ~120 mbsf with poor but exciting recoveries of the stockwork mineralized zone. Around 120 mbsf, there was a rapid change to more typical drilling conditions and better core recovery. This corresponds to a major lithologic break, passing into a darker, differently altered sequence of former felsic volcanic rocks containing only trace to minor amounts of sulfide minerals. The break also corresponds to a substantial change in FMS imagery, from conspicuous coarse-scale fracturing below to a more complex pattern above of resistive and conductive layers and pods presumed to denote and, indeed, amplify structure of the stockwork zone where core recovery was poor. Resistivity logging and FMS imagery delineated an interval from 65 to 70 mbsf, where significantly higher conductivity implies a marked increase in sulfide content. Unfortunately, this corresponds to an interval of no core recovery.
Resistivity logging and imagery in Hole 1189C delineated a similar break between coarsely fractured rocks below and a sequence with more complex, possibly veined structure above. Here the boundary is slightly deeper, at ~150 m. No particularly conductive layers were logged that might correspond to massive sulfide intersections.
Site 1189, especially the lower part of Hole 1189B, provides a clear picture of the volcanic construction of Pual Ridge for 200 m below the Roman Ruins hydrothermal site at the PACMANUS hydrothermal field. The only fresh rocks recovered are aphyric dacite at the top of Hole 1189A. These contain 64 wt% SiO2 and are equivalent to dredged surface exposures in this vicinity. Although all other cores from this site show moderate to complete alteration, abundant preservation of textures (such as vesicles and, in less-altered intervals, phenocrysts and microlites) and of structures (such as perlite, spherulites, and flow banding) shows that the whole sequence penetrated is either volcanic or volcaniclastic in origin. Shipboard chemical determinations of the key immobile element indicator ratio Zr/TiO2 fall within the range from mafic dacite to rhyodacite throughout the entire sequence, with rhyodacites dominating the lower part of Hole 1189B.
The well-preserved lower part of Hole 1189B shows particularly well the same alternation of coherent and fragmental flows, with occasional volcaniclastic horizons, that we infer for the more altered parts where evidence is at times equivocal because of alteration. Many coherent volcanic units from Site 1189 are vesicular, with the degree of vesicularity ranging up to ~20 vol%. Fragmental flows tend to be conspicuously flow banded. Autoclastic textures and even contacts between coherent and fragmental sectors of the same flow have been observed. Confidently identified volcaniclastic units, including polymict breccias and volcaniclastic sandstone, define paleoseafloor horizons. Five such units were logged in Hole 1189B, but only one in 1189A. It is clear that Pual Ridge was not built in a single eruption. A maximum thickness of ~50 m is estimated for individual flow units, but a minimum figure cannot be set. One coherent unit in Hole 1189B shows consistent vertically oriented stretched vesicles over some 10 m of core. There is speculation that this might be a dike or alternatively a flow that has cascaded over a precipice. Some deeper coherent lavas contain a greater abundance of somewhat larger plagioclase microcrysts or pseudomorphs in their groundmass than those closer to the seabed, which might indicate slower cooling. However, as at Site 1188, there is no evidence for major intrusive bodies of hypabyssal or plutonic character.
Although very close together, Holes 1189A and 1189B show rather different alteration features. The assemblages and fabrics in Hole 1189A are similar to those at Site 1188, but the mineralogical profile is telescoped with cristobalite being restricted to the upper 25 mbsf. Below the cristobalite-bearing interval of this hole, quartz generally increases in abundance with depth. Quartz is patchily developed, overprinting early greenish silica-clay alteration and pale gray to white silica-clay bleaching that occasionally contains anhydrite. Illite and chlorite dominate the phyllosilicate mineral assemblages. Disseminated pyrite is present at the 1%-5% abundance range in all assemblages.
As expected, cristobalite was not found in the upper succession of Hole 1189B, which did not core the interval where it would be present based on the profile of Hole 1189A. The stockwork zone is characterized by quartz-bearing greenish silica-clay alteration of former volcanic wall rocks, with silicification increasing downhole. Illite and chlorite again dominate the phyllosilicate component, but smectite, chlorite-smectite, or illite-bearing mixed-layer clays, and possible kaolinite were also detected. Potassium feldspar was also identified by X-ray diffraction (XRD) in several samples. Although likely, it is uncertain whether this is a hydrothermal phase rather than an igneous relic.
The lower sequence of Hole 1189B, below ~120 mbsf, shows pervasive but rarely complete hydrothermal alteration, relict igneous plagioclase microlites and phenocrysts having commonly survived. Potassium feldspar of either hydrothermal or relict igneous origin is also present. The sequence is characterized by repeated alternations from cristobalite-bearing to quartz-bearing rocks and by a less abundant but very complex and variable clay mineral assemblage. Relative to the upper sequence in Hole 1189B and to Hole 1189A, as well as to the alteration profiles at Site 1188, the lower sequence is an interval subjected to less interaction between rock and hydrothermal fluids. Fragmental units tend to be more altered than their coherent associates.
Analyses were performed on board on altered rocks from Site 1189, and these generally reflect the alteration mineralogy. In Hole 1189A, green silica-clay altered rocks have high water and sulfur contents, and increases in Fe and Mg correspond to increases in reported chlorite, clay minerals, and pyrite. In Hole 1189B, SiO2, CaO, and Na2O increase in the lower sequence, in agreement with the observed increase in plagioclase content.
As at Site 1188, pyrite is the dominant sulfide at Site 1189. It is disseminated throughout the altered volcanic rocks, is present within quartz-anhydrite veins, and occurs as linings and cores to vesicle fill. Sphalerite and chalcopyrite are noticeably more abundant in Hole 1189B than in Hole 1189A, whereas chalcopyrite in the lower levels of Hole 1189A is more common than at Site 1188. Marcasite, galena, tennantite, and covellite are rare, and the latter three have only been identified in cores from Hole 1189B. The relationships between the accessory sulfides and pyrite provide evidence for at least two generations of pyrite-quartz precipitation at Site 1189. In addition, the oxides magnetite and hematite are present.
Semimassive sulfide mineralization comprising ~50% sulfides was recovered in Hole 1189B by the first core below casing. Besides pyrite, this contains substantial chalcopyrite and subordinate sphalerite. The gangue is mainly coarse anhydrite, in part replaced by gypsum. Ovoid features tentatively interpreted to be mineralized worm casings are present. This interpretation, if correct, would imply an exhalative seafloor origin and burial by the lava presumed to be present from drilling characteristics during the casing operation, but numerous small fragments of altered wallrock in this sample suggest the occurrence is basically related to the underlying stockwork. The stockwork grades into breccia, and extends to the discontinuity in Hole 1189B at ~120 mbsf, with sulfide veins becoming less abundant downward in the limited material recovered. Nevertheless, the overall sulfide content of this zone is low and should be considered as only a very weakly mineralized stockwork sequence.
The structures identified in Holes 1189A and 1189B were primary volcanic layering, brecciation of volcanic rocks, orientation of veins, and age relationship between veins. There are several interesting similarities and differences between the two holes with respect to vein structures.
The brecciated rocks in the two holes are very similar, consisting of variably altered volcanic fragments, crosscut by vein networks of quartz with pyrite and minor anhydrite. However, the volcanic rocks recovered from Hole 1189B are more brecciated than the rocks from Hole 1189A. Additionally, the vein intensity is higher and intervals of vein network (stockwork) are thicker in Hole 1189B. In contrast to Hole 1189A, in Hole 1189B magnetite and hematite are present in the networks as minor components, whereas sphalerite and chalcopyrite are trace minerals. In both holes, late coarse-grained anhydrite veins crosscut vein networks and brecciated rocks.
Bacteria were not detected by direct count below 50 mbsf in cores from Hole 1189A, or below 31 mbsf in Hole 1189B. Enrichment cultivations of samples from Hole 1189A showed growth of bacteria in aerobic conditions to 25°C, and as high as 90°C in anaerobic conditions. Samples from Hole 1189B exhibit growth of bacteria in anaerobic cultures from as deep as 130 mbsf, and at temperatures to 90°C.
Magnetic susceptibility decreases from top to bottom in the cored section from Hole 1189A. A similar pattern is expressed in data from the lower part of Hole 1189B, although the overall susceptibility is distinctly higher. Compressional wave velocity averages 4.4 km/s at ambient pressure. Thermal conductivity is relatively constant at ~2 W/(m·K), with the exception of one pyrite-rich sample that has a value of >5 W/(m·K). Solid-rock density varies little in all samples measured from both holes, averaging 2.7 g/cm3. As in samples from Site 1188, porosity is highly variable, from 15% to nearly 70%.
In terms of rock magnetic behavior, Site 1189 shares many common features with Site 1188. The uppermost part of the section at both sites is characterized by high susceptibility and high remanent intensity caused by abundant magnetite and titanomagnetite. At both sites, the upper few tens of meters are underlain by an interval of low remanent intensity. Below this is a zone of high susceptibility and high remanent intensity. Inasmuch as the maximum remanent intensity is in this lowermost interval, it is conceivable that this lower zone is equally important, if not more so, as the source of the magnetic anomalies measured from the sea surface. Some significant differences also exist between Sites 1188 and 1189 in terms of magnetic behavior. The highest measured magnetization intensity is deeper at Site 1189 than it is at Site 1188. However, susceptibility and remanent intensity are both generally lower at Site 1189. This may reflect more intense high-temperature alteration at Site 1189.
Site 1189 will likely turn out to be the highlight of downhole measurements for Leg 193. Continuous wireline logs were collected in Hole 1189B, with excellent tool response as a result of good borehole condition. FMS data are particularly striking, imaging different patterns of faulting and local dissemination of sulfide minerals. A second LWD/RAB hole, Hole 1189C, was drilled to 166 mbsf, past a distinct change in the fracturing pattern probably equivalent to the lithology change described in the cores of Hole 1189B and potentially imaged in Hole 1189B wireline logging data. Following completion of RAB drilling, we dropped a FFF and conducted wireline logging of Hole 1189C. This marks the first time in the history of the Ocean Drilling Program (ODP) that we have the opportunity to correlate directly between wireline logging and RAB data from the same drilled interval in hard rock.
The geological objectives at Site 1189 were to delineate the vertical profile of alteration and mineralization patterns, and their variation with depth, beneath an area of focused, high-temperature venting—the Roman Ruins hydrothermal site. The data obtained on cored samples and by logging will allow assessments of the chemical and hydrological processes at this "end-member" location, just as comparison of this site with Site 1188 at the low-temperature diffuse vent field at Snowcap hydrothermal site would provide an understanding of lateral variations.
In addition, Site 1189 was designed as a test of the nature and extent of microbial life, particularly hyperthermophilic bacteria, at such a high-temperature hydrothermal site, together with delineation of the conditions conducive to the presence of a deep biomass.
After severing the pipe at Hole 1188A, a new rotary core barrel (RCB) bottom-hole assembly (BHA) was assembled, and the drill string and vibration-isolated television (VIT)/subsea camera were run to bottom at Site 1189. The precision depth recorder depth reading for this site was 1693.4 meters below rig floor (mbrf) corrected to the dual elevator stool. As at the previous site, a positioning beacon was attached to the VIT frame rather than being deployed from the surface. This was to allow a more accurate placement of the beacon relative to the actual hole location. At 1310 hr on 22 November 2000, while positioning off of a Global Positioning System (GPS) signal, a load shed occurred in the ship's hotel structure. Power to lighting and air conditioning services was cut; however, the regulated power to all computer systems remained on. All services were restored within 5 min. The cause of the power outage was an abrupt 15-m shift in the GPS signal position. This caused all thrusters to rapidly ramp up to full power as the vessel appeared to be off location. The resultant abrupt call for electrical power from the main electrical service bus overloaded the three engines on line at the time. This failure was attributed to attempting to position on a GPS signal alone without a seafloor beacon as a fixed reference.
The seafloor TV survey at this site began at 1515 hr on 22 November 2000. The beacon was released from the VIT frame at 1516 hr, and the survey continued until 1545 hr. Tall sulfide chimneys were readily apparent in the video images, many of which were active black/gray smokers. Once a candidate site was identified, a 3.0-m jet-in test was conducted to determine the viability of deploying a FFF should it be required. Hole 1189A (Fig. F1; Table T1) was spudded at 1615 hr on 22 November 2000, and the VIT frame was recovered while the driller maintained weight on the bit. We initiated RCB coring and deployed a Whirl-Pak microbiology core contamination tracer on Core 193-1189A-4R and maximum reading thermometers in the drill string accelerator (DSA) pressure housing on Cores 193-1189A-8R and 12R. Recorded circulating temperatures were 37° and 39°C, respectively. Core 193-1189A-13R was cut to a depth of 1817.1 mbrf (125.8 mbsf), but while running in with the sinker bars to recover Core 193-1189A-13R, the pipe stuck in the borehole. Despite our attempts to wrest the pipe free, the pipe remained immobile. Core 193-1189A-13R was recovered and the shifting tool was deployed to release the bit; however, the pipe remained firmly planted at 120 mbsf. Since shooting off the pipe was inevitable, the DSA tool housing was deployed one last time with the maximum reading thermometers. Recorded temperature at the bottom of the hole was 34°C with the circulating pumps shut down for 10 min. The driller continued to work the pipe while the third severing charge of the leg was deployed. The drill string was severed at a depth of 1708.0 mbrf (7.0 mbsf) in the third joint of the 5.5-in transition drill pipe. The remaining drill string was recovered and the severed pipe cleared the rotary table at 2045 hr on 23 November 2000. This concluded operations in Hole 1189A.
Hole 1189B is unique in that it represents the first complete deployment of the HRRS. After the conclusion of coring and logging operations at Hole 1188F, 33.6 m of 13.375-in flush joint casing were assembled with the HRRS casing hanger and the fluid hammer with a spline drive ring bit welded to the bottom of the shoe joint. In design, this would result in >30 m of cased hole, with ±2 m of casing above the seafloor for deployment of a free-fall reentry cone.
The HRRS running tool and release assembly, as well as the hammer, were tested before deployment. At 0015 hr on 23 December 2000, we began a brief camera survey and jetted in 1 m once an acceptable location was selected in the middle of a chimney field. The ROP was variable at first, but after only ~1 hr, the casing had advanced 7 m. The next meter (7-8 mbsf) required 1 hr of hammering before the ROP sped up again to between 8 and 10 mbsf. The interval between 10 and 15 mbsf appeared to be very hard, as it took more than 6 hr to advance. Speculation regarding potential failure of some part of the system was proven groundless when the hammer broke through the hard layer and drilled the next 15 m in <30 min, including a pipe connection. General hammer-drilling parameters were 5-20 klb weight on bit, top drive 10-40 revolutions per min, one pump at 40 strokes per min (spm) to two pumps at 50 spm held pump pressures of ~750 psi to as high as ~2000 psi. Average ROP was 3.0 m/hr for the 10.0 hr of operation. The running tool released without complication and, after recovering the subsea camera and rigging the HRRS reentry cone, the cone was deployed through the moonpool. The entire operation, from rigging the tools to recovery of the hammer, was complete in only 33 hr.
An RCB BHA was assembled with all available drill collars to maximize our potential depth of penetration. RCB coring commenced at 0815 hr on 24 December 2000. Although recovery was again poor (~8%), coring continued without incident through Core 193-1189B-18R to a depth of 1899.0 mbrf (206.0 mbsf). Hole conditions began to deteriorate, and because we were within 2 m of the maximum depth we could achieve without placing the top of the drill collars below the bottom of the casing, we decided to terminate operations in this hole. Wireline logging commenced at 2015 hr on 25 December 2000, and was complete by early afternoon on 26 December 2000, ending operations in this hole.
Following the temperature measurement and water sample recovery at Hole 1188F, we embarked on our second LWD/RAB experiment. Because the core recovery in Hole 1189B indicated a lithologic change at ~120 mbsf coincident with an increase in resistivity noted in the wireline log from that hole, we planned to attempt a total depth of at least 160 m with this operation. After a quick camera survey, Hole 1189C was spudded at the base of a spectacular chimney at 1700 hr on 27 December 2000. The RAB experiment proceeded flawlessly, reaching 166 mbsf in <26 hr. Before pulling free of the seafloor, we decided to drop a FFF to allow us to reenter Hole 1189C, measure a temperature profile, and if conditions allowed, run wireline logs and collect a water sample. The successful completion of the logging (albeit only to a depth of 67 mbsf because of a blockage in the hole) will provide the first direct comparison between LWD/RAB and wireline logging data in the same borehole spudded in volcanic rock in the history of ODP. The planned water sample was abandoned because of the low temperature measured in the borehole (~30°C) and our desire to collect another water sample from Hole 1188F before we were required to leave our operations area.
The entire survey for Hole 1189A (1500 to 1617 hr on 20 November 2000) occurred on target within an area 25 m east of where the beacon was dropped, across a field of standing and fallen chimneys and fine debris covering the basal mound. Sonar indicated we were in a low, elongate trough between two walls of high-standing chimneys. During the survey, the VIT passed close by the base of two large chimneys ~5 m across, over a 2- to 3-m-long fallen chimney, and across finer chimney rubble with occasional small chimneys (including two parasitic examples on the pediment of one large chimney). Shimmering water was seen at several places, and on one side of the field there were clouds of gray smoke. The jet-in test (3 m achieved in 50 strokes) and the final spud site (achieved after raising to add pipe) were both at sites of fine chimney debris with minor sediment cover (metalliferous ooze?).
The survey for Hole 1189B commenced as the bit and VIT descended close to the Hole 1189A site through a billowing smoke plume to a field of chimneys with rubbly debris below. The pipe was then moved east-northeast for 30 m, passing fallen chimneys, small chimneys, and rubble. With the overall seafloor gently rising, we concluded we were near the crest of the Roman Ruins mound. We stayed at the new site while twice raising to add pipe, then spudded Hole 1189B in rubble, including chimney fragments, on a gentle slope at the foot of a tall, active (white tipped) multi-spired chimney, between this and a small simple conical-tipped white chimney. The rubble moved after pumping started, so was not coherent.
Prior to spudding Hole 1189C, the bit and VIT descended over a large, active chimney encrusted with fauna. With minimal maneuvering of the pipe required, drilling commenced on apparently coherent hydrothermal deposit at the foot of this chimney.
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