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Porphyroid

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porphyroid [′pȯr·fə‚rȯid]
(petrology)
A blastoporphyritic, or sometimes porphyroblastic, metamorphic rock of igneous origin.
A feldspathic metasedimentary rock having the appearance of a porphyry.
Porphyroid 

(also porphyritoid), a rock formed as a result of the metamorphism of rocks with similar composition, such as diabases, porphyrites, or gangues. Porphyroid is usually composed of feldspar, amphibole, pyroxene relicts, calcite, chlorite, talc, and clay; sometimes it contains quartz and zoisite. As a result of strong cataclasis, porphyroid sometimes takes on a slaty texture.
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Accordingly, the highest silver-copper-antimony grades are in those parts of the vein which are hosted by relatively ductile quartz-sericite phyllites on Levels 8 and 9 whilst lower grade mineralisation developed in parts of the vein hosted by competent porphyroids (mostly on Level 13).
Resource Estimate For Strieborna Vein Silver Project Completed, ... by PR Newswire
 
 
 
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