Greisen


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greisen

[′grīz·ən]
(petrology)
A pneumatolytically altered granite consisting of mainly quartz and a light-green mica.

Greisen

 

a rock of metasomatic origin, composed basically of quartz and light-colored micas—lepidolite and muscovite. It not infrequently contains an impregnation of valuable ore minerals (such as cassiterite. wolframite, and tantalite) in industrial quantities. In such cases they are regarded as ore bodies. Deposits usually occur in the form of irregularly shaped sections in granite masses, mainly in their outer sections and sometimes in the rocks surrounding the granite Greisen is formed as a result of the greisening of rocks, often along the periphery of ore veins, and serves as an indication for prospecting.

References in periodicals archive ?
Greisen alteration is not only restricted to the selvages but also affects some parts of the granitic body (Fig.
The sample set for the study of the clay mineral assemblage represents typical examples of hydrothermally altered granites occurring immediately beneath the contact between greisen and granite bodies of the Hub stock (Fig.
Cabe senalar en este documento tecnico, que para la determinacion de concentraciones economicas de Ta-Nb-Sn-Ti, REES (Ce, La, Y, Nd) y asociaciones de PB-Th, se debe emplear al gu nos metodos/tecnicas tales como imagen satelital hyperespectral ASTER, para la discriminacion litologica, mapeo de estructuras geologicas y la identificacion de areas de alteracion hidrotermal y greisen, geofisicas (magnetismo, por presencia del hierro asociado), espectrometria de radiacion gamma, que diferencie presencia de radon-torio, K40, para aquellos casos asociados a radiactividad leve, y en general, refraccion sismica/equipo portatil, para medir espesores de los aluviones con potencial de coltan y otros minerales asociados.
Kelly Gregg (knee), Adam Terry (ankle), Nick Greisen (thigh) and Yamon Fugurs (hamstring) are listed as questionable.
A greisen is defined as a pneumatolytically altered granitic rock composed largely of quartz, mica and topaz.
Tony Greisen, head of the Special Olympics Asia Pacific region, said that's why it was important that such athletes as Pereira competed in Shanghai, as well as in future Special Olympics competitions.
Greisen. Living Liturgy for Extraordinary Ministers of Holy Communion: Year C 2007.
In Pemali, tin deposits exist as a stockwork and greisen in granite and turmaline casiterite veins which run parallel.
(2002) and Grundmann (2002) divided emerald deposits into the following categories: pegmatites without schist, pegmatite and greisen with schist, schists without pegmatites, and black shales with veins and breccias.
Take 'Mandatory' Out of Arbitration Agreements, by Paula Greisen and Alison Butler Daniels [Aug.
Within the literature, other studies showed a relationship between hypocarbia and PVL in this population (Calvert, Hoskins, Fong, & Forsyth, 1987; Fujimoto et al., 1994; Graziani et al., 1992; Greisen, Munck, & Lou, 1987; Okumura et al., 2001; Trounce, Shaw, Levene, & Rutter, 1988).
Because ultrasound studies (Greisen 1992) have shown that preterm infants weigh less than infants who remain in utero at the same gestational age, a fetus with restricted growth may exhibit a greater susceptibility to events that trigger premature labor.