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Plutonic Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
If late stage magmas lose their volatiles, they may cool quickly and form very fine-grained rocks called aplites that contain crystals that cannot be seen without a hand lens. The aplite dike shown in Figures 6.13a and 6.14, has intruded into a metamorphic rock near Sables d’Olonne in western France. Aplites are typically narrow, from a centimeter to perhaps a meter in width, white, gray, or pink dikes and veins, sometimes described as having a sugary texture. They intrude larger felsic or intermediate plutons or less commonly mafic plutons and are often associated with nearby larger granitic bodies. Often, aplites occur in swarms of roughly parallel veins traversing a much larger host rock.
Rock drilling methods
Published in Lopez Jimeno Carlos, Lopez Jimeno Emilio, Javier Ayala Carcedo Francisco, Ramiro Yvonne Visser de, Drilling and Blasting of Rocks, 2017
Lopez Jimeno Carlos, Lopez Jimeno Emilio, Javier Ayala Carcedo Francisco, Ramiro Yvonne Visser de
The rate of cooling of the magma gives the grain size of the crystallized minerals; large if it is slow, and small if it is rapid. In the first instance a rock called pegmatite is formed, and in the second it is called aplite. An intermediate case is denominated porpyhry, in which large crystals are observed within a fine grained mass or matrix. These three types are usually found in dike form with strengths that go from one to dozens of meters. The most normal is that of a moderate cooling time which produces a rock mass with a medium size grain, from 1 to 5 mm.
Geology and geochronology of the Two-Thirty prospect, Northparkes district, NSW
Published in Australian Journal of Earth Sciences, 2021
T. J. Wells, David R. Cooke, M. J. Baker, L. Zhang, S. Meffre, J. Steadman, M. D. Norman, J. L. Hoye
Pale, fine-grained aplite dykes with a saccharoidal to aphanitic groundmass of alkali-feldspar with minor biotite. Aplite dykes and dyklets were intersected in drill hole D245 where they crosscut QMP intrusions and sedimentary units. Alteration varies from weak potassic with hematite dusting to pervasive sericite. Most aplite dykes have minor disseminated pyrite and rare carbonate veinlets. However, one interval (552.5 m in D245) has abundant disseminated sulfides (pyrite–chalcopyrite) and carbonate base-metal veins (sphalerite, cassiterite and galena), which may be indicative of multiple generations of aplite dykes or a late epithermal mineralisation event.
Assessing the Lithium Potential of the Paleoproterozoic Rocks of the West African Craton; the Case so Far
Published in Geosystem Engineering, 2023
The pegmatites of Goulamina and Bougouni, located in Southwestern Mali are two of the more studied lithium deposits located in the Birimian of West Africa. These pegmatites present as spodumene dykes. The Goulamina deposit is estimated to be one of the world’s largest deposit of lithium and is found within a swarm of six individual dykes. Current data from drilling indicates that the Goulamina pegmatite field encompasses approximately 3 km2; however, this could be expanded with additional drilling. Several composite and steeply descending spodumene-bearing pegmatite dykes are wholly contained within the Goulamina Granite near its western contact. The average thickness of the pegmatite dykes is between 10 and 80 metres with a NW-SE orientation. A further 30% of the resource is confined within the cluster of the N-S Danaya dyke. Compared to the predominantly subparallel dykes of the main field, the dykes constituting the Danaya swarm are generally thinner and more difficult to correlate between drill sites, indicating that they may form an interconnected network of dykes (Wilde et al., 2021). At Goulamina, regional zoning has not been observed; however, three facies have been recognised within distinct pegmatite dykes. The random and indeterminate distribution of these facies within individual intrusions does not determine local zoning. Mineralogically uniform spodumene pegmatite dominates the limited outcrops in the area and constitutes approximately 90 percent of dykes. Individual spodumene crystals can reach 10–15 centimetres in length, but are typically much shorter. 10% of the dykes are composed of a fine-grained, often-layered rock known as aplite, which also contains morphologically similar, spodumene-free albitite. The monitoring of drill openings has failed to differentiate between aplite and albitite. The distribution of aplite and albite is unpredictable and irregular. The deformation of the spodumene pegmatite produced shearing along contacts and, on rare occasions, what appear to be isoclinal folds. Similarly, the Bougouni pegmatite field consist of mainly NE-SW and NW-SE trending dykes with steep to subvertical dips which swarm around the Madina, Sogola and Bougouni main areas (Sanogo et al., 2020).