|
CSIRO
Number |
Core, section,
piece, interval |
Curated
depth (mbsf) |
Description
|
|---|---|---|---|
| 142697 | 193-1189A-7R-1 (Piece 17, 99–102 cm) | 59.14 | Jasperoid matrix of a breccia with ragged fragments to 1 cm across of soft greenish white altered volcanic rock (Fig. F2). |
| Jasperoid consists mainly of closely packed, relatively fine grained quartz (~40? m) with distinct cores clouded by minute hematite flakes (diameter < 2? m) and outgrowth margins relatively free of inclusions (Figs. F3; F4). | |||
| Contains numerous tiny and some larger irregular cavities (Figs. F2; F3; F4) and a prominent fracture (Fig. F5) lined mostly by terminated quartz crystals with fewer or no central inclusions, locally by subhedral to euhedral pyrites, and rarely by late-stage euhedral anhydrite blades. | |||
| Relatively common pyrite euhedra and subhedra (0.1–0.2 mm) are also intergrown with quartz in the more compact jasperoid, where they are not so clearly related to drusy structures. Rarer ragged patches of chalcopyrite occur in similar positions. | |||
| Narrow selvages (100–200? m) of clear quartz surrounding wallrock fragments (Figs. F6; F7) appear contemporary with quartz in the smaller druses and also with thin quartz veinlets cutting some fragments (Fig. F7). | |||
| Tiny barite crystals occur in some selvages but are very rare overall (Fig. F6). | |||
| At the immediate contact, selvage quartz appears to have replaced the wallrock (Fig. F7). | |||
| The wallrock fragment sectioned has phenocrysts and microlites of unaltered plagioclase set in a chlorite-dominated clay matrix. | |||
| 142707 | 193-1189B-6R-1 (Piece 5, 45–55 cm) | 79.45 | Jasperoid matrix of a breccia with numerous cavities and fragments of white, altered wallrock surrounded by 0.5-mm-thick selvages of pale yellow quartz, which also extends as a vein across one fragment (Fig. F8). |
| Smoky quartz also surrounds some drusy cavities. | |||
| Pyrite is more scarcely disseminated through the jasperoid, favoring the proximity of wallrock fragments. | |||
| Nearby Piece 2 (Fig. F1), used for preparation of shipboard thin section 1189B#116, contains similar jasperoid, but lacks the conspicuous smoky selvages around wallrock fragments. Here the jasperoid consists of mostly close-packed, rather larger quartz grains (~0.5 mm), again with sharply-bounded cores densely clouded with tiny hematite flakes as much as 5 mm in diameter (Fig. F9). Commonly the cores themselves have the shapes of doubly-terminated prismatic quartz. Jasperoid quartz also forms veins cutting the wallrock fragments, mainly with fewer, but one with more abundant hematite inclusions (Figs. F10, F11). | |||
| Jasperoid quartz also forms veins cutting the wallrock fragments, mainly with fewer, but one with more abundant hematite inclusions (Figs. F10, F11). | |||
| Poikiloblastic quartz with epitaxial orientations to vein quartz locally replaces wallrock adjacent to such veins (Fig. F10, and also surrounds rare prismatic quartz euhedra (considered replacive rather than phenocrystal) in some wallrock fragments. Rare fresh plagioclase phenocrysts occur in the clay-altered wallrock fragments, some but not all of which display palimpsest perlite structure (Figs. F10, F11) or vesicular fabrics. | |||
| 142714 | 193-1189B-11R-1 (Piece 3, 14–16 cm) | 127.74 | Jasperoid fragment with sliver of pale green chloritic and pyrite-rich wallrock on one side, the entire shipboard sample having a more obvious breccia structure with numerous inclusions of clay-altered wallrock showing vague flow banding. Wallrock contacts are irregular. |
| Abundant irregular microdrusy cavities lined by euhedra of quartz, pyrite, and lesser chalcopyrite, some also with anhydrite tablets (more common than in Samples 142697 and 142707) and patches of soft khaki clay. | |||
| Quartz surrounding these cavities is coarser and relatively clearer than the red quartz forming areas between them, causing a more spotty appearance than in Samples 142607 and 142707. | |||
| Quartz grain size is highly variable (0.2–1 mm). Larger grains are strained and have seriate outlines; finer grains tend to be euhedral. | |||
| Strange frondlike planar aggregates of thin hematite flakes (diameter = 15–25?m) occur within larger quartz grains, commonly extending across grain boundaries in a manner suggesting they formed early and became overgrown by the quartz (Figs. F12; F13). | |||
| Oval growths and curved trails of hematite, possibly lining former cavities, also extend across several large quartz grains (Fig. F14). | |||
| The smaller quartz euhedra show marked growth zones and tend to have the more typical central cores (also with euhedral habit) clouded by tiny hematite inclusions (Fig. F15). | |||
| Tiny barite crystals are rare inclusions in the larger quartz grains (Fig. F13). | |||
| The sample lacks the selvages of clear quartz around wallrock fragments seen in Samples 142697 and 142707, but quartz veinlets cut the wallrock inclusion (Fig. F16). |
Note: CSIRO = Commonwealth Scientific and Industrial Research Organization (Australia).