Hydrothermal alteration is defined as any alteration of rocks or minerals by the reaction of hydrothermal fluid with preexisting solid phases. Hydrothermal alteration can be isochemical, like meta-morphism, and dominated by mineralogical changes, or it can be metasomatic and result in significant addition or removal of elements.
Photographs of alteration styles in andesite, diorite, and …
Two superimposed alteration events control the regional distribution of five main alteration types in the Punta del Cobre belt, south of Copiap6, Chile. An early event of alkali metasomatism...
Andesite - Wikipedia
Andesite is an aphanitic (fine-grained) to porphyritic (coarse-grained) igneous rock that is intermediate in its content of silica and low in alkali metals. It has less than 20% quartz and 10% feldspathoid by volume, with at least 65% of the feldspar in the rock consisting of plagioclase.
Where present, biotite has altered to illite. Although alteration of the rhyolitic ignimbrite is slight it is of a more uniform intensity than the alteration of the andesitebelow.
Increasing the Permeability of Hydrothermally Altered Andesite …
2019年10月18日 · We investigate the impact of thermal treatment on the porosity and permeability of hydrothermally altered andesite using two different mineral assemblages from the Rotokawa hydrothermal system; an altered plagioclase-clinochlore-calcite-quartz andesite, which we label the “moderately altered” andesite herein, and an altered plagioclase ...
We observe theRotokawa Andesite to be a weakly porphyritic series of lavas, breccias and pseudo-breccias. We also observe both massive and flow-banded lava units with rare expressions of tuff that are almost 100% altered. Alteration in the andesite is pervasive and original mineral assemblages are typically replaced by secondary totally
Full article: The lithogeochemical signatures of hydrothermal ...
2019年8月26日 · Whole rock lithogeochemical data from the andesite rocks which host low-sulfidation epithermal gold veins in the Waihi district, New Zealand have been used to interpret hydrothermal alteration processes that variably altered the andesite rocks.
Silicification; hydrothermal alteration in an Archean …
Silicified andesitic flows, divided into two alteration facies; mottled (epidote-quartz altered) andesite and silicified andesite. Silicification was contemporaneous with volcanism.
Increasing the Permeability of Hydrothermally Altered Andesite …
2019年10月18日 · This study describes the results of thermal heating events lasting several hours on a “moderately altered” plagioclase-clinochlore-calcite-quartz andesite and a “highly altered” plagioclase-clinozoisite-quartz-clinochlore andesite from …
Compositional Variation of Hydrothermally Altered Volcanic …
2010年5月21日 · The hydrothermally altered andesite hosting the Hishikari gold-silver vein deposits in southern Kyushu, Japan, is analyzed with respect to the spatial variation in chemical composition. The (CaO + Na 2 O) content is found to be inversely correlated with the K 2 O content as it progresses away from the site of mineralization.