Table T2. Lithology and alteration of Units 1 to 26, Hole 1188A.

 
Unit Core, section (Piece) Curated depth (mbsf) Curated length (m) Lithology Alteration
Top
Base

193-1188A-




1 2R-1 (All) 9.60 9.85 0.25 Moderately vesicular rhyodacite with scattered acicular plagioclase phenocrysts (as long as 10 mm) and clinopyroxene (as long as 0.1 mm). Fresh unit. Patchy sulfate clay and Fe oxide films coat fracture surfaces and vesicles. Rare hairline sulfate veinlets. Trace pyrite is present as fine euhedra on films in vesicles and on fractures.

3R-1 (All) 19.20 19.38 0.18

4R-1 (All) 28.90 29.03 0.13

5R-1 (1-6) 33.60 33.95 0.35

6R-1 (2) 38.67 38.73 0.06


7R-1 (1-3) 48.20 48.35 0.15

2 5R-1 (7-8) 33.95 34.08 0.13 Completely altered aphyric volcanic unit with remnant perlitic texture, cut by fine silica veinlets (pseudoclastic texture). Strongly bleached, silicified (hard) gray unit. Silica veinlets give pseudoclastic texture. Trace disseminated pyrite. XRD mineralogy: opaline silica dominant, minor smectite, illite, plagioclase, and pyrite.
3 6R-1 (1, 3) 38.60 38.80 0.20 Moderately to highly altered, moderately vesicular aphyric dacite(?). Weak bleaching. Pervasive, moderate intensity alteration. Anhydrite (+ pyrite) lines vesicles. Mineralogy otherwise unknown, but volcanic glass is pervasively replaced.

7R-1 (4-5) 48.35 48.43 0.08
4 7R-1 (6-16A) 48.43 49.26 0.83 Completely altered aphyric, sparsely vesicular dacite with intervals of flow banding (Pieces 6 and 14) and an interval of hydrofractured breccia (Piece 8). Intense bleaching (silica-sulfate-clay alteration) with weakly developed patchy silicification. Medium- to coarse-grained irregular anhydrite-pyrite veins, which form the matrix in the fractured breccia. Anhydrite-pyrite vesicle fill, trace honey gold sphalerite noted in Pieces 11 and 15. XRD mineralogy: cristobalite and anhydrite dominant, minor pyrite and chlorite, trace kaolinite and hematite. Remnant igneous plagioclase also detected.
5 7R-1 (16B-20) 49.26 49.70 0.44 Completely altered hydrofractured volcanic rock with a pseudoclastic texture. Fragments show remnant perlitic texture, which is pseudomorphed by the alteration assemblage. Greenish gray alteration (silica-sulfate-chloritic clay), grading to gray-blue silica-sulfate-clay bleaching at the base of the unit (Sections 193-1188A-7R-1 [Pieces 19 and 20] and 7R-2 [Piece 1]). Remnant volcanic texture (perlitic?) replaced by silica and rimmed by chloritic clay. Fragments hosted in a stockwork matrix of anhydrite-(silica-pyrite) with white sulfate alteration halos bleaching the clayey rims of many fragments. In the gray-blue portion of the unit, fragments are dominantly sulfate-bluish clay and are again hosted in an anhydrite-pyrite stockwork. Silica is present as late drusy vug fills, with trace pyrite. XRD mineralogy: anhydrite and cristobalite dominant, minor pyrite and chlorite (upper green-gray portion); anhydrite dominant, minor cristobalite, pyrophyllite, and pyrite, and trace quartz (lower bluish portion).

7R-2 (1) 49.70 49.96 0.26
6 7R-2 (2-6) 49.96 50.56 0.60 Completely altered fractured volcanic rock with a pseudoclastic texture. Core 193-1188A-8R-1 (Piece 1) is moderately bleached and unaltered dacite and Core 193-1188A-8R-1 (Pieces 2 and 3) (which match the lower portion of the overlying unit) are interpreted to be fragments that have fallen down the hole. Greenish gray (silica-sulfate-chloritic clay) to gray-blue (silica-sulfate-clay) altered fragments hosted in a stockwork matrix of anhydrite-(silica-pyrite) veins with white sulfate alteration halos bleaching the clayey rims of many fragments. Fine-grained pyrite appears to be disseminated in many of the fragments, but on close examination seems more likely to be associated with fine silica veinlets as well as siliceous replaced flow bands. Scattered, 1- to 5-cm-wide, slightly nebulous, late anhydrite-silica veins cut and bleach sections of the stockwork and host minor pyrite and trace honey gold sphalerite. XRD mineralogy: anhydrite and cristobalite dominant, minor quartz, illite, pyrite, and traces of barite.

8R-1 (1-11) 57.90 59.30 1.40
7 8R-1 (12-13) 59.30 59.40 0.10 Completely bleached sparsely to moderately vesicular volcanic rock with patches of silicification. Bleached (silica-sulfate-clay altered) unit. Variation in color from pure white to medium gray may reflect silica abundance and is probably related to fluid-bearing fractures with zoned alteration halos. Vesicles are lined by anhydrite, with minor pyrite in the upper part of the unit, and silica filled farther down. XRD mineralogy: cristobalite and anhydrite dominant, minor quartz, illite, pyrophyllite, and pyrite, and traces of barite. Quartz is a major component at the base of the interval (= silica vesicle fill).

8R-2 (1-9) 59.40 60.13 0.73

9R-1 (1-6) 67.60 68.13 0.53

9R-1 (7-10) 68.13 69.10 0.97 Completely altered hydrofractured volcanic rock with a pseudoclastic texture. Fragments show remnant perlitic texture, which is pseudomorphed by the alteration assemblage. Strongly bleached (silica-sulfate-clay altered) fractured unit, cut by a fine anastomosing network of anhydrite and silica-pyrite veinlets. Appears to be a more pervasively bleached equivalent to Unit 5. Pyrite is present as late vesicle and vug fill and as fine disseminations, particularly in more siliceous portions of the unit. XRD mineralogy (from an intensely bleached portion of the unit): quartz and crystobalite dominant, minor pyrophyllite and anhydrite, and traces of pyrite and barite.
8 9R-2 (1-9) 69.10 70.51 1.41

9R-3 (1-2) 70.51 70.85 0.34

10R-1 (1-8) 77.30 78.15 0.85
9 10R-1 (9-14) 78.15 78.78 0.63 Completely bleached sparsely vesicular volcanic rock with patches of silicification. This unit is nearly indistinguishable in hand specimen from Unit 7. Bleached (silica-sulfate-clay altered) unit. Variation in color from pure white to medium gray seems to reflect silica abundance and is probably related to fluid-bearing fractures with zoned alteration halos. Vesicles are filled with silica and pyrite (dominantly) and less commonly by anhydrite. Pyrite is also associated with the zoned halos and is finely disseminated throughout the rock. XRD mineralogy: cristobalite, plagioclase (?? in a strongly leached rock), and quartz dominant, minor pyrite and anhydrite, and traces of barite.

10R-2 (1-13) 78.78 79.66 0.88

11R-1 (1-10) 86.90 88.28 1.38

11R-2 (1-7) 88.28 89.23 0.95

12R-1 (1-3) 96.60 96.99 0.39

13R-1 (1) 106.00 106.36 0.06
10 12R-1 (4-14) 96.99 98.08 1.09 Completely altered, fractured, frequently perlitic, and flow-banded volcanic rock. Flow banding defined in part by microspherulitic bands and entirely devitrified bands. Early pervasive gray-green silica-sulfate-chlorite alteration of the volcanic fabric, with later fracturing and pervasive flooding by silica with associated sulfide (pyrite-trace chalcopyrite). Late scattered simple to anastomosing anhydrite veins exhibit bleached and siliceous alteration halos. XRD mineralogy: cristobalite dominant throughout unit. Quartz and anhydrite, with minor pyrophyllite and pyrite, are the major components of a sampled sulfate vein. Quartz, anhydrite, and pyrite are minor to trace phases elsewhere in the unit, while illite, chlorite, and barite are present in trace concentrations. Plagioclase was detected as a major component in Sections 193-1188A-12R-1 (Piece 12) and 13R-1 (Piece 2). Subsequent careful binocular examination of these samples detected what may be remnant primary igneous plagioclase.

12R-2 (1-4) 98.08 98.62 0.54

13R-1 (2) 106.37 106.42 0.05
11 13R-1 (3-16) 106.42 107.69 1.27 Completely altered, pervasively bleached volcanic unit with sparsely vesicular patches. The unit is cut by a poorly to strongly developed silica-sulfate stockwork vein system. Pervasively bleached (silica-sulfate-clay altered) fractured unit. Two different styles of veining, which both appear to postdate the pervasive alteration, are present. Irregular, anastomosing vuggy sulfate veins contain up to 5% pyrite, primarily as open space fill in vugs, and postdate earlier narrow, sharply defined silica-trace pyrite stockwork veins. Pyrite also occurs as fine disseminations in the altered body of the rock. XRD mineralogy: cristobalite and plagioclase dominant, minor quartz and pyrite, traces of anhydrite, barite, and chlorite.

14R-1 (1) 116.00 116.03 0.03
12 14R-1 (2) 116.03 116.10 0.07 Completely altered volcaniclastic, granule to pebble breccia. Strongly bleached, sulfate-rich altered volcanic clasts are cemented in silica. Some clasts show silica. Trace pyrite occurs disseminated in the silica.
13 14R-1 (3-12) 116.10 117.04 0.94 Pervasively bleached and fractured volcanic rock. Possible remnant flow banding and vesicles in some pieces. The unit is cut by a very strongly developed silica-sulfate stockwork vein system. Pervasively bleached (silica-sulfate-clay altered) fractured unit, with obvious similarities to Unit 11. Well-developed fracturing hosts a stockwork of sharply defined silica-trace pyrite veins, some of which appear to predate anhydrite veins, while others seem to be synchronous. Anhydrite veins with very distinct narrow silica halos. Pyrite also is present as fine disseminations in the altered body of the rock. XRD mineralogy: quartz and anhydrite dominant, minor pyrite and cristobalite (upper sample only), and traces of talc.
14 14R-1 (13-18) 117.04 117.31 0.27 Completely altered volcaniclastic, granule to pebble breccia. Rock resembles Unit 12. Strongly bleached, sulfate-rich altered volcanic clasts are cemented in silica. Some clasts show silica. Trace pyrite is present disseminated in the silica.
15 15R-1 (1-5) 125.70 125.94 0.24 Crustiform anhydrite-pyrite vein. Bleached volcanic fragments attached to the vein margin.
16 15R-1 (6-22) 125.94 126.81 0.87 Completely bleached and silicified, sparsely vesicular volcanic rock with scattered sulfate veining and fine sulfide veinlets. Very strongly silicified unit. Anhydrite veins, 1 cm thick, are present in the rubble, which makes up the upper portion on the unit (related to Unit 15, above?). The basal part of the unit comprises hard, pervasively silicified vesicular volcanics, which are cut by <<1-mm-wide pyrite veinlets with 1-mm anhydrite selvages, surrounded by well defined 2- to 5-mm silica alteration halos. Pyrite is present throughout the rock as fine-grained vesicle fill, intergrown with anhydrite and/or quartz. Apparent extremely fine grained disseminated pyrite is probably material filling microscopic vesicles.
17 16R-1 (3-20) 135.47 136.86 1.39 Completely silicified, sparsely vesicular volcanic rock with pale green tinges and irregular silica-anhydrite veining. Some pieces show traces of primary volcanic layering. Very strongly silicified unit. The unit comprises hard, pervasively silicified vesicular volcanics, which are cut by <<1-mm-wide pyrite veinlets with 1-mm anhydrite selvages, surrounded by well defined 2- to 5-mm silica alteration halos (as seen in the above unit). Rare medium-grained anhydrite veins are also present. Pyrite is present throughout the rock as fine-grained vesicle fill, intergrown with anhydrite and/or quartz. Apparent extremely fine grained disseminated pyrite is probably material filling microscopic vesicles. XRD mineralogy: quartz dominant, minor plagioclase, traces of anhydrite, illite, chlorite, and pyrite.

16R-2 (1) 136.86 136.91 0.05
18 16R-2 (2-12) 136.91 137.79 0.88 Finely laminated, flow-banded, gray-green volcanic rock. Strongly silicified. Gray-green alteration, dominantly silicification, with minor chlorite. Chaotic structure at the top and base of the unit. Minor vuggy silica, laminated silica, and laminated sulfate veins. Trace very fine grained disseminated pyrite throughout rock. XRD mineralogy: quartz and plagioclase dominant, traces of chlorite, anhydrite, and pyrite.
19 16R-2 (13-15) 137.79 138.05 0.26 Silicified, bleached volcanic rock with rarely preserved perlitic texture and vesicles. Some intervals of hydrothermal brecciation with silica veinlets. Silicified, bleached volcanic rock with rarely preserved perlitic texture and vesicles. Cut by fine silica-trace pyrite veinlets and more abundant irregular, anastomosing to simple anhydrite-minor magnetite-trace pyrite veins, which have distinct bleached to siliceous alteration halos. There is evidence to suggest the silica veinlets and the anhydrite-magnetite veins are contiguous. Magnetite also is present as patches of very fine euhedra on fracture surfaces and, less commonly, as disseminations throughout the rock. Some intervals of hydrothermal brecciation with silica veinlets. XRD mineralogy: quartz dominant, minor anhydrite, traces of illite and magnetite.

17R-1 (1-25) 145.10 146.60 1.50

17R-2 (1-6) 146.60 146.96 0.36

18R-1 (1-17) 154.70 156.56 1.86
20 18R-1 (18-23) 156.56 156.85 0.29 Silicified and bleached moderately vesicular volcanic unit, with some remnant perlitic texture. Very fine grained disseminated magnetite present in Section 193-1188A-18R-1 (Pieces 18-23). Silicified unit with similar alteration to overlying material. The pieces from Section 193-1188A-18R-1 probably have more in common with the lower portion of Unit 19 than with Pieces 1-4 of Section 193-1188A-19R-1. The entire unit is moderately vesicular, with fine to very coarse grained anhydrite vesicle and vug fill (± trace pyrite). A hairline fracture in Section 193-1188A-19R-1 (Piece 4) contains very fine grained pyrite and displays a 1-cm-wide siliceous alteration halo.

19R-1 (1-4) 164.30 164.52 0.22
21 19R-1 (5-13) 164.52 164.95 0.43 Silicified volcanic with some pieces exhibiting remnant microperlitic texture. Very rare vesicles. Silicified, bleached volcanic rock with remnant perlitic texture and rare vesicles, which are silica filled. Piece 9 from Section 193-1188A-19R-1 exhibits green clay (chloritic) alteration. Very little pyrite throughout.
22 19R-1 (14-16) 164.95 165.23 0.28 Moderately altered, vesicular dacite. Some alignment of vesicles at the top of the unit—probable flow structure. Fine-grained vesicular volcanic unit with magnetite, pyroxene and plagioclase microcrystals in the groundmass, although the magnetite may be an alteration product. Cut by rare irregular microcrystalline silica-anhydrite veins, with slightly bleached halos. Microvesicles are silica- and anhydrite-filled. Traces of very fine grained disseminated pyrite also in vesicles.
23 19R-1 (17) 165.23 165.27 0.04 Completely silicified, weakly to moderately chloritic magnetite-bearing volcanic rock. Pervasively silicified unit with green chloritic clay-rich patches. Very fine, slightly vuggy anastomosing silica-anhydrite ± pyrite veining is faintly visible and appears to have been overprinted by the pervasive silicification event, which also appears to be related to the ~5% very fine magnetite, which is disseminated throughout the unit. Pyrite is also disseminated throughout, but tends to be more abundant in chloritic sections of the unit. Rare poorly defined silica-anhydrite-pyrite veins are also overprinted by the pervasive silicification. XRD mineralogy: quartz dominant, minor plagioclase, anhydrite (in a sample including silica-anhydrite-pyrite veining), chlorite-smectite mixed-layer, magnetite, and pyrite, and traces of illite.

20R-1 (3-11) 173.98 174.81 0.83
24 20R-1 (12-13) 174.81 175.01 0.20 Distinctive dark green silicified unit with hairline silica-filled fractures and ovoid sulfate spots (perhaps after vesicles?). Dark green, pervasively silicified unit with hairline silica filled fractures, rimmed by narrow bleached halos. Ovoid sulfate spots appear to be remnant vesicles. Very fine grained pyrite is disseminated throughout the rock, but more concentrated in vuggy, silica-lined cavities. Extremely fine grained dark spots are disseminated magnetite (2%-3%). XRD mineralogy: quartz and plagioclase dominant, minor magnetite, chlorite-smectite mixed-layer, and pyrite, and traces of anhydrite.
25 20R-1 (14-15) 175.01 175.11 0.10 Green-black unit with patches of remnant soft green clay-rich material in a zone of pervasive silica-pyrite stockworking. Very fine magnetite is disseminated throughout. Remnant soft green clay-rich patches, containing disseminated magnetite, are surrounded by pervasive fine grained silica-minor pyrite flooding, which is associated with a network of anastomosing hairline fractures. Vuggy cavities in the silica are lined by fine crystalline quartz. Very fine grained euhedral pyrite is noticeably more abundant in silicified zones, particularly in the vuggy cavities. Magnetite appears to be replaced by pyrite in the silicified zones, suggesting it predates the silica-pyrite flooding. XRD mineralogy: quartz dominant, minor plagioclase, magnetite, chlorite-smectite mixed-layer, and pyrite.

21R-1 (1-18) 183.10 184.60 1.50
26 22R-1 (1) 192.70 192.86 0.16 Vuggy massive sulfate-silica with traces of disseminated pyrite and Fe oxide spotting. Probable vein material, which may be rubble from farther up the hole.

23R-1 (1) 202.10 202.29 0.19

Note: XRD = X-ray diffraction.