Encontrei sites q mencionavam mafic/ultramafic [rocks and-or minerals].
Considerei o trecho “Igneous rock composition”, abaixo, mais detalhado; o fato de vc ter se esquecido de acrescentar algum contexto, e deduzi q a perfuração é terrestre.
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Igneous rock composition
Classification based on chemistry takes into account the amount of silica (SiO2) and the composition of feldspar minerals (K, Na, Ca). (…)
1. Felsic -- Rich in feldspars and silica. (…). Typical of continental crust.
2. Intermediate -- Between felsic and mafic. (..) Found in association with subduction zones.
3. Mafic -- Rich in magnesium and iron with less silica. Silica content is 45% to 50%. Ca-rich plagioclase is the dominant feldspar with little or no K- or Na-feldspars. Typical of oceanic crust.
4. Ultramafic -- Still more magnesium and iron and even less silica. Silica content is less than 45%, and little or no feldspar is present. Derived from the mantle.

http://academic.emporia.edu/aberjame/field/rocky_mt/igneous....
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Ultrabasic Rock: An igneous rock with a very low silica content and rich in minerals such as hypersthene, augite and olivine. These rocks are also known as ultramafic rocks.

Mafic: A term used to describe an igneous rock that has a large percentage of dark-colored minerals such as amphibole, pyroxene and olivine. Also used in reference to the magmas from which these rocks crystallize. Mafic rocks are generally rich in iron and magnesium. Basalt and gabbro are examples of mafic rocks. (See felsic to contrast.)

http://geology.com/dictionary/glossary-m.shtml
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Mafic or Basaltic Rock =The class of rock which crystallizes from silicate minerals at relatively high temperatures is sometimes referred to as "mafic" rock. It is also sometimes called basaltic since the class includes basalt and gabbro. It is in a high temperature range of the Bowen reaction series. The term "mafic" is a short form indicator of the presence of a relatively large concentration of iron and magnesium. The term "ferromagnesian" is also used.

[fonte: não anotei, lamento]
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Rochas Máficas = Rochas ricas em Mg e Fe, bem como em vários outros nutrientes. São geralmente de cor escura e muito duras.

http://www.dcs.ufla.br/Cerrados/Portugues/CGlossario.htm
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unweathered = not worn by exposure to the weather; "chemical weathering was beginning to attack the unweathered bedrock"

rocha sã = rocha que não foi atacada por processos intempéricos físicos ou químicos. Em geral são rochas com grande resistência, suportam teto de túneis ou peso de grandes estruturas.
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hth.
beatriz_souza