9652058
Persistent Identifier: https://pid.geoscience.gov.au/sample/AU9652058
| Property | Value |
|---|---|
| id | 9652058 |
| igsn | 10.60494/qv04-2g26 |
| sample_id | 2023330039 |
| eno | 867079 |
| sampling_feature_name | NDILLK03 |
| sampling_feature_type | borehole |
| sample_type | half core |
| sampling_method | core drilling |
| material_class | rock |
| stratigraphic_unit | None |
| geological_province | Delamerian Orogen |
| sample_remark | Mole et al. (2024): Drillhole NDILLK03 intersects the N edge of a prominent zone of irregular, high-frequency magnetic lineaments that trends NE and extends along the length of the Loch Lilly-Kars Belt. The igneous rocks intersected are magnetic, and are probably representative of the other magnetic lineaments in this zone. This hole was drilled using the coiled-tube rotary drill-rig and hence only one tray of full diamond core is available. Most of the interval comprises dark grey, fine to medium-grained, intermediate to mafic igneous rock. Plagioclase is common, occurring as ~1 mm grains. In addition, ~5 mm sub-rounded grey blebs, which may be amygdales, are observed throughout but concentrated mostly in the upper half of the intersection. The pXRF analysis yielded ~200 ppm Zr immediately above the cored interval. Lower in the hole the rounded blebs are less common and the rock is increasingly medium-grained. Based on these features, this unit was interpreted to be an andesite flow. A small (~20 cm thick) plagioclase-phyric interval towards the top of the intersection has plagioclase grains ~10 mm in length (sampled here). There is no clear variation in "groundmass" between this interval and the more equigranular (aphanitic?) rock. These two units may be comagmatic. Sample 9652058/2023330039 is a thin intersection (~20 cm) of the plagioclase-phyric grey unit with plagioclase grains up to 10 mm long. In thin section, the sample is a composite, comprising a medium- to coarse-grained plagioclase-phyric gabbroic enclave surrounded by a fine-grained quartz-diorite. Plagioclase is the only phenocryst phase in the gabbroic phase, occurring as tabular phenocrysts mostly 3-5 mm in length. Most phenocrysts display simple and lesser polysynthetic twinning, with a maximum anorthite content of An40 (andesine). Grains are dusted with a fine Fe-oxide and can be partially replaced by decussate chlorite and granular epidote. The groundmass to the gabbro comprises finer-grained (0.2-0.5 mm) slender laths of plagioclase within a matrix of green decussate masses of chlorite (likely after interstitial ex-ferromagnesian minerals), rodded granular masses of leucoxene (potentially after primary Fe-Ti-oxide), and occasional ragged grains of actinolite. Quartz is also present as a very minor phase (1-2%), mostly occurring as anhedral grains 0.3-0.5 mm in size, but also as euhedral hexagonal grains. Fine needles of apatite are an accessory phase. The finer-grained quartz-diorite host is of a similar grain size to the groundmass of the gabbroic enclave. Plagioclase (andesine) is abundant as interlocking, slender lath-shaped grains mostly 0.3-0.5 mm that display both simple; and polysynthetic twinning. The groundmass interstitial to plagioclase comprises decussate masses of green chlorite with abundant fine-grained, granular leucoxene. Quartz is relatively abundant (5-10%) as anhedral interstitial grains 0.5 mm in size. Most grains are optically clear but may include abundant needles of apatite. The sample is crosscut by a quartz-carbonate-epidote-chlorite-rich vein and the host rock has experienced extensive epizonal alteration involving chlorite, leucoxene and minor epidote replacement of ferromagnesian phases. The combination of macro- and micro-scale observations suggest that (1) this unit is gradational, with an "upper" portion with volcanic features, and a more massive "lower" region; and (2) the clumped plagioclase laths (gabbro "enclave") occur within the lower portion. Based on this, we interpret the sequence as a thick flow, with the base insulated from degassing. The plagioclase laths are interpreted to represent plagioclase cumulate material, possibly deposited" out of the flow, which has been disturbed and is disaggregating in the magma. |
| earth_materials | Y |
| structural_measurements | None |
| inorganic_geochemistry | None |
| organic_geochemistry | None |
| geochronology | Y |
| isotope_groups | None |
| hydrochemistry | None |
| rock_properties | None |
| mineralogy | None |
| thin_sections | None |
| repository_samples | Y |
| mineral_deposit_samples | None |
| mineral_deposit_waste_samples | None |
| linked_files | None |
| other_geological_data | None |
| project_name | EFTF - Darling-Curnamona-Delamarian (DCD) |
| gda94_longitude | 141.00119 |
| gda94_latitude | -32.825529 |
| sample_originator | Clark, A. |
| date_acquired | 2023-11-26 00:00:00 |
| Links |
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