Sedimentary deposit

A deposit formed by sedimentation, including weathering, erosion, and transportation, followed by diagenesis. Along with igneous deposits and metamorphic deposits, it is one of the three major classifications of deposits based on their origin. They are often distributed widely in layers, forming large deposits. Because sedimentation and diagenesis are complex geological phenomena, the origins of sedimentary deposits are diverse, and a fully systematic classification has not yet been established. If elements and minerals are separated and concentrated during the processes of weathering, erosion, and transportation, weathering residual deposits, bauxite deposits (the main source of aluminum), alluvial deposits, etc. are formed. There are many examples of syngeneic deposits formed with sediments, including gold and uranium deposits associated with conglomerate (the gold-bearing conglomerate in the Witwatersrand region of South Africa is a world-famous example), copper deposits associated with coarse sandstone (the Copperbelt region of Zambia), lead and zinc deposits associated with fine sandstone (the Sullivan deposits in Canada), copper and lead and zinc deposits associated with mudstone (copper-bearing shale spread throughout Europe), and lead and zinc deposits associated with calcareous rocks (the Mississippi Valley-type deposits in North America). Banded iron deposits, which precipitated on a global scale at some point during the Precambrian era, are important as a high-quality iron resource distributed widely across continents. There are also many other examples of sedimentary deposits that are important as resources, such as sedimentary manganese deposits and rock salt deposits, which are important as a source of potash.

[Hidehiko Shimazaki]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

風化、侵食、運搬を含む堆積作用全般と、それに引き続く続成作用によって形成される鉱床。火成鉱床、変成鉱床とともに、鉱床を成因により三大別したうちの一つ。層状をなして広く分布し、大規模な鉱床をつくる例が多い。堆積作用、続成作用は複雑な地質現象であるため、堆積鉱床の成因も多岐にわたっており、まだ十分に体系的な分類はなされていない。風化、侵食、運搬の過程で元素や鉱物の選別、濃集がおこれば、風化残留鉱床、ボーキサイト鉱床（アルミニウムのもっとも主要な供給源）、漂砂鉱床などが形成される。堆積物とともに同生鉱床をつくる例は多種多様で、礫(れき)岩に伴う金・ウラン鉱床（例としては、南アフリカ共和国ウィトワーテルスランド地方の含金礫岩が世界的に有名）、粗い砂岩に伴う銅鉱床（ザンビアのカッパーベルト地方）、細かい砂岩に伴う鉛・亜鉛鉱床（カナダのサリバン鉱床）、泥質岩に伴う銅鉱床、鉛・亜鉛鉱床（ヨーロッパ全域に広がる含銅頁(けつ)岩）、石灰質岩石に伴う鉛・亜鉛鉱床（北アメリカのミシシッピバレー型鉱床）などが代表的なものである。先カンブリア時代のある時期に全世界的な規模で沈殿した縞(しま)状鉄鉱鉱床は、大陸地域に広く分布した良質な鉄資源として重要である。このほか、堆積性マンガン鉱床、カリの資源として重要な岩塩鉱床など、資源上重要な堆積鉱床の例は数多く分布している。

［島崎英彦］

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