Topic
Aphanite
About: Aphanite is a research topic. Over the lifetime, 2 publications have been published within this topic receiving 1 citations. The topic is also known as: aphanitic rocks.
Papers
1 Mar 2012
TL;DR: In this article, the effect of micro-fabrics on uniaxial strength of weathered volcanic rocks from Tawau, Sabah was analyzed using polarizing microscope and scanning electron microscopy (SEM) techniques.
Abstract: This paper discusses the effect of micro-fabrics on uniaxial strength of weathered volcanic rocks from Tawau, Sabah. Volcanic rocks consist of basalt and andesite, aged from Pliocene to Quaternary. Weathered rock samples with grade range from slightly weathered (II) to completely weathered (VI) were collected from the road-cut slopes. Micro-fabric analysis was performed using polarizing microscope and Scanning Electron Microscope (SEM) techniques. Uniaxial strength analysis involved Point Load Test index (PLT) and Unconfined Compression Strength (UCS) test. The petrography analysis of basalt showed the domination of plagioclase with existence of orthoclase and pyroxene in aphanite texture. Meanwhile andesite consists of plagioclase, feldspar and amphibole in porphyritic matrix. Basalt samples with weathering grade from II to V showed the alteration of primary minerals from 12% to 55% and Imp (micro-petrography index) value ranging from 8.8 to < 0.2. Meanwhile andesite showed alteration of primary minerals ranging from 15% to 60% with Imp value of 4.9 to < 0.4. Andesite contains 16.8% stable minerals of quartz and feldspar phenocrysts that remain intact throughout the weathering process. Uniaxial strength results indicated that andesite exhibited a higher strength with value from 181.2 to 87.7 MPa while basalt showed 127.2 to 35 MPa. The porosity of andesite with Grade II to V was 4.1% to 49.5% whereas basalt ranged from2.5% to 47.8%. The uniaxial strength of Grade V showed basalt is slightly higher than andesite with 0.3 MPa and 0.2 MPa respectively. This is due to the presence of more clay minerals in basaltic soil (75.1%) than in andesite soil (65.2%). This study showed that the weathering process is able to alter the microfabric characteristics of rocks which contributes to the decrement of the strength of volcanic rocks.
2 citations
TL;DR: In this article, the relationship among the orebody, volcanic rocks, and a rhyolite dike in the large epithermal Kupol deposit (Western Chukotka) is considered.
Abstract: The relationship among the orebody, volcanic rocks, and a rhyolite dike in the large epithermal Kupol deposit (Western Chukotka) is considered. Almost throughout its entire length (more than 3000 m), the orebody of the deposit is intersected by rhyolite dikes. In the studied profiles in the mine excavations at the horizons 425, 455, 470, 515 m, a rhyolite dike clearly intersects and bisects the orebody, which is a 20-m-thick dominantly quartz vein with some adularia. The rhyolite has a porphyritic structure. The groundmass is devitrified with the formation of an aphanite quartz-feldspar aggregate with a mosaic microstructure. Some patches are fluidized. The rhyolites contain from 72.96 to 74.97 wt % SiO2, and the composition corresponds to biotite granites of the low-alkaline series. The following criteria have been identified to indicate the post-mineralization age of the dike: a clear intersection of a thick ore vein by the dike; vitrification of the dyke material at the contact with the vein; rhyolite cementing the crushed quartz vein material; the emergence of some small tongues from the dike that penetrate the quartz vein; xenoliths of quartz vein material in the dike body; the orebody tongues do not penetrate the dike; increased concentration of vein and ore minerals on the contact surface of the dike or in cracks of the endocontact zone. The formation of obsidian (vitrophyre) in rhyolite at contact with the orebody indicates that the dike was emplaced in a cold system. Preservation of the productive vein thickness, its morphological features, and the Au and Ag contents at the cabs of the rhyolite dike; identical textures and repeated rhythms in the areas of rhythmic-banded layering in the vein on both sides of the dike shows that in the Kupol deposit, post-mineralization dikes do not replace or impoverish the productive vein system, which is probably due to their dilatation nature and the infilling of separation cracks.
1 citations
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Performance Metrics
| Year | Papers |
|---|---|
| 2021 | 1 |
| 2012 | 1 |